Glossary of technical terms for the use of metallurgical engineers Terms starting with alphabet ‘G’
Glossary of technical terms for the use of metallurgical engineers
Terms starting with alphabet ‘G’
GaAs compound – GaAs stands for gallium arsenide. GaAs compound is a high-performance III-V direct bandgap compound semiconductor composed of gallium (Ga) and arsenic (As). Engineered for high-speed, high-frequency, and opto-electronic applications, it offers higher electron mobility and superior heat / radiation resistance compared to silicon. Common uses include ICs (integrated circuits), LEDs (light emitting diodes), laser diodes, and solar cells.
GaAs conduction band – It is the conduction band in gallium arsenide (GaAs). It is the lowest unoccupied energy band where electrons move freely, enabling high-speed electrical conduction and photon emission. As a direct bandgap material (1.42 electron volt to 1.43 electron volt), its conduction band minimum aligns with the valence band maximum, allowing efficient opto-electronic transitions.
GaAs-devices – These devices refer to semiconductor devices made from gallium arsenide, which are known for their radiation tolerance compared to silicon devices, particularly because of the absence of gate insulators which prevents charge buildup. These devices can experience degradation in trans-conductance and gain when exposed to substantial ionizing radiation levels.
GaAs heterostructures – These are layered semi-conductor materials combining gallium arsenide (GaAs) with compounds like AlGaAs (aluminum gallium arsenide) to create customized electronic band structures. These, typically grown through MBE (molecular-beam epitaxy) or MOVPE (metalorganic vapour phase epitaxy), enable precise control over electron mobility and quantum confinement, necessary for high-performance devices like HEMTs (high-electron-mobility transistors), lasers, and opto-electronics.
GaAs lattice – It refers to the crystal structure of gallium arsenide, characterized by a specific periodic arrangement of atoms and defined by its lattice constant, which influences the bonding properties and electronic behaviour of the material.
GaAs layers – These are gallium arsenide (GaAs) layers which are III-V compound semi-conductor films used in high-speed electronics and opto-electronics, typically grown through epitaxy (molecular-beam epitaxy, MBE / metal organic chemical vapour deposition, MOCVD) to form active layers, buffer layers (0.2 micro-meters to 2 micro-meters), or quantum wells. Key engineering focuses include optimizing lattice matching, reducing defects, and controlling doping (e.g., silicon for n-type) for high electron mobility, efficiency, and radiation tolerance.
GaAs substrate – It is a single-crystal wafer of gallium-arsenide, normally semi-insulating, acting as a foundational base for growing high-quality epitaxial films in opto-electronics and high-speed electronics. It is preferred for its high electron mobility, direct bandgap (1.43 electron-volts), and radiation resistance in applications like LEDs (light emitting diodes), laser diodes, and microwave integrated circuits.
Gabbro – It is a dark, coarse-grained igneous rock.
Gable – It is the normally triangular portion of a wall between the edges of intersecting roof pitches. The shape of the gable and how it is detailed depends on the structural system used, which reflects climate, material availability, and aesthetic concerns.
Gable wall, gable end – It normally refers to the entire wall, including the gable and the wall below it.
Gabor dictionary – It is an overcomplete collection of atoms created by multiplying sinusoidal functions with a Gaussian window, allowing for time-frequency representation of signals. Each frequency appears multiple times, providing a more detailed analysis of time-varying frequency content.
Gabor filter – It is a linear band-pass filter used in image processing for edge detection, feature extraction, and texture analysis. It is defined as a sinusoidal plane wave, at a specific frequency and orientation, modulated by a Gaussian envelope. The Gabor filter is particularly useful since it minimizes the joint uncertainty in both spatial and frequency domains, providing optimal localization for identifying local image features.
Gabor function – It is a linear filter used in image processing and computer vision, defined as a Gaussian kernel modulated by a complex sinusoidal plane wave. It acts as a bandpass filter, optimizing joint localization in both spatial and frequency domains, making it ideal for texture analysis, edge detection, and feature extraction.
Gabor wavelets – These are complex linear filters used in image processing and computer vision to analyze texture, edge detection, and feature extraction, mimicking human visual system receptive fields. They consist of a sinusoidal plane wave (Gaussian envelope) and are favoured for minimizing joint uncertainty in both the spatial and frequency domains.
Gadolinium (Gd) – It is a chemical element having atomic number 64. It is a silvery-white metal when oxidation is removed. Gadolinium is a malleable and ductile rare-earth element. It reacts with atmospheric oxygen or moisture slowly to form a black coating. Gadolinium below its Curie point of 20 deg C is ferromagnetic, with an attraction to a magnetic field higher than that of nickel. Above this temperature it is the most paramagnetic element. It is found in nature only in an oxidized form. When separated, it usually has impurities of the other rare earths because of their similar chemical properties.
Gadolinium gallium garnet (GGG) – Gadolinium gallium garnet (Gd3Ga5O12) is a synthetic crystalline material of the garnet group, with good mechanical, thermal, and optical properties. It is typically colourless. It has a cubic lattice, has a density of 7.08 grams per cubic centimeter and its Mohs hardness is variously noted as 6.5 and 7.5. Its crystals are produced with the Czochralski method. During production, different dopants can be added for colour modification. The material is also used in the fabrication of different optical components and as a substrate material for magneto–optical films (magnetic bubble memory). It also finds use in jewelry as a diamond simulant. It can also be used as a seed substrate for the growth of other garnets such as yttrium iron garnet.
Gadolinium-iron garnet (GdIG) – It belongs to the family ferro-magnetic rare–earth garnets which are assigned to cubic structure (space group Ia3d) with every cell containing eight R3Fe5O12 molecules. Rare–earth ion R3+ cannot occupy the octahedral and tetrahedral sites because of its large ion radius, so R3+ ion can only occupy dodecahedral sites which have larger space.
Gagger – It is an L-shaped or hooked metal rod or iron piece embedded in the sand of a foundry mould to reinforce it and keep the sand or a core in place during the casting process. It acts as a structural support to prevent the mould from collapsing under the pressure of molten metal.
Gain, amplifier – It is a parameter defining the ratio of an amplifier’s output signal magnitude (voltage, current, or power) to its input signal magnitude, representing the amplification factor. It indicates how much a device increases a signal’s amplitude, typically expressed as a unitless ratio or in decibels (dB).
Gain bandwidth – It refers to the frequency or wavelength spectrum over which gain occurs in a laser amplifier, determined by factors such as the widths of energy levels involved in the laser transition and influenced by interactions such as collisions and Doppler shifts.
Gain-bandwidth product – It is a key metric for operational amplifiers (op-amps) and systems, defined as the product of an amplifier’s open-loop gain and its bandwidth. It represents the constant trade-off, where higher gain results in lower bandwidth. The gain-bandwidth product indicates the frequency at which the gain drops to unity (1 or 0 decibels).
Gain coefficient (g) – It quantifies the amplification of a signal or energy per unit length or per unit density, typically expressed in units of per meter (inverse meters) or per watt. It represents the rate at which optical power increases in amplifiers (like lasers or fibres) or how a physical parameter, such as solar heat, is transmitted through a material.
Gain compression – It refers to a decrease in gain which occurs in devices because of the non-linearity, particularly at larger input swings where the output current cannot increase proportionally with the input voltage, leading to a drop in effective transconductance. This phenomenon is influenced by factors such as high-field effects and limited output swing.
Gain, controller – It is the controller gain. It is a crucial, adjustable parameter in engineering control systems, particularly PID (proportional-integral-derivative) controllers, which determines the strength of the control action relative to the error between setpoint and output. It directly influences system stability, responsiveness, overshooting, and tracking error.
Gain crossover – It refers to the frequency at which the open-loop gain of a system first reaches the value of 1.
Gain crossover frequency – It is the frequency at which the magnitude of the open-loop transfer function equals one, indicating a balance between the system’s gain and stability, typically expressed in radians per second.
Gain factor – It is a dimensionless ratio or value (frequently in decibels, dB) quantifying the increase in signal amplitude, power, or intensity between an output and input. It represents an amplifier’s, system’s, or component’s ability to boost a signal, calculated as voltage gain (Av = Vout / Vin), power gain (Ap = Pout /Pin), logarithmic gain [10 log10 (Pout / Pin)] decibels.
Gain fields – These are specialized, frequently biologically-inspired, neural populations which compute spatial transformations by multiplying input signals. They represent a coordinate system shift, such as transforming visual data from eye-centered (retinotopic) to head-centered frames, using rapid, population-level modulation.
Gain flattening filter – It is a specialized optical component used to flatten the uneven spectral gain of amplifiers (e.g., erbium-doped fibre amplifiers, EDFAs) in fibre-optic communications. By introducing a loss profile that is the inverse of the amplifier’s gain spectrum, gain flattening filters ensure uniform signal amplification across multiple wavelengths. They are important critical for WDM (wavelength-division multiplexing) systems to prevent signal-to-noise ratio imbalances, with quality measured by the ‘peak-to-peak error function’ (PPEF).
Gain frequency – It defines the frequency at which an amplifier’s gain drops to unity (0 decibel, or a ratio of 1). It serves as a critical metric for the maximum usable bandwidth of a transistor or circuit, representing the point where the device ceases to amplify and begins to attenuate the signal.
Gain function – It is a mathematical representation of how a system, component, or device increases the amplitude, power, or intensity of a signal from its input to its output. It is defined as the ratio of output to input, acting as a critical metric for amplification efficiency, signal control, and system stability.
Gain matrix – It is an array representing the relationship between multiple inputs (manipulated variables) and multiple outputs (controlled variables) in a system. It defines how much each output changes per unit change in each input, important for analyzing multivariable interactions, control loop effectiveness, and system dynamics.
Gain output ratio – In thermal desalination and humidification-dehumidification (HDH) systems, It is a dimensionless, non-dimensional parameter defining the ratio of the latent heat of evaporation of produced distillate water to the total external heat input. It measures energy efficiency, typically ranging from 1 to 18.
Gain path – It is also called forward path. It is normally the route a signal takes from the input to the output of a system, through which it is amplified, attenuated, or otherwise modified. The ‘gain’ along this path is the product of all individual stage gains, representing the total amplification or reduction of the signal.
Gain ripple – It is the unwanted variation in amplifier gain across a specific frequency spectrum or signal bandwidth, preventing a perfectly flat response. In optical amplifiers, e.g., erbium-doped fibre amplifier, (EDFA), Raman, it causes uneven amplification across channels, leading to power fluctuations. It is measured in decibels (dB).
Gain saturation – It is a nonlinear phenomenon where an amplifier’s gain decreases as the input signal power increases and approaches the saturation power, causing the output power to stabilize. It occurs when energy extraction by stimulated emission exceeds the pumping rate, reducing the excited-state population.
Gain scheduling – It is a control technique which adjusts controller parameters (gains) in real-time based on changing operating conditions or scheduling variables (e.g., speed, altitude). It maps out system behaviour across different points, allowing a nonlinear system to be managed by switching or blending between multiple linear controllers.
Gain sequence – It refers to an ordered set of amplification or attenuation factors (1, K2, K3, —–, Kl) applied sequentially or over time to a signal, system state, or control action. Unlike a fixed gain, a gain sequence is frequently time-varying or adaptive, changing to meet specific performance criteria, such as tracking a maneuvering target, minimizing estimation error, or optimizing control efforts.
Gain spectrum – It is the graphical representation of an amplifier’s amplification factor (gain) as a function of frequency or wavelength, indicating how efficiently it boosts signals across a specific range. Key in photonics and electronics, it shows the non-flat, wavelength-dependent amplification, frequently measured in decibel (dB).
Gain stage – It is a specific point in an audio or electronic signal path where the signal’s amplitude (volume / level) is boosted or attenuated. Proper gain staging involves managing these levels across multiple, consecutive points to optimize the signal-to-noise ratio, prevent clipping (distortion), and ensure sufficient headroom.
Gain variation – It refers to the unwanted fluctuation or intentional adjustment of an amplifier’s signal amplification level (gain) across frequencies, time, or operating conditions. It is frequently characterized as a ‘ripple’ in the gain spectrum, typically measured in decibels (dB). It frequently occurs because of the environmental changes (temperature), supply voltage changes, or frequency-dependent behaviour in circuits.
Galena – It is lead sulphide which is the main ore mineral of lead, consisting of 86.6 % lead and 13.4 % sulphur, frequently containing substantial silver, copper, and zinc impurities. It is a dense, metallic, lead-gray sulphide which forms cubic crystals, prized for its low melting point, which enables easy smelting into lead metal.
Galerkin formulation – It is a numerical method where the test functions are chosen to be the same as the shape functions, leading to a discretization that typically results in an algebraic matrix equation.
Galerkin method – It is a numerical technique based on the method of weighted residuals, used to find approximate solutions to complex differential equations (such as heat transfer, phase field, or deformation equations) which describe physical phenomena. It is mainly used in ‘finite element analysis’ (FEA) and ‘element-free Galerkin’ (EFG) methods to model manufacturing processes like casting, forming, and heat treatment.
Galerkin solution – It is a numerical technique in engineering used to approximate solutions to differential equations by transforming continuous operator problems into discrete systems. It involves representing the unknown solution as a linear combination of basis-functions, where the residual (error) is minimized by making it orthogonal to the same basis functions. This method is fundamental to the ‘finite element method’ (FEM).
Galerkin-type formulation – It is a fundamental mathematical technique used in computational metallurgy and materials science to solve complex partial differential equations (PDEs) governing physical phenomena, such as heat transfer during casting, phase transformation, or stress-strain behavior. It belongs to the class of weighted residual methods, where the governing differential equations are converted into a weak (variational) form, and the solution is approximated using a linear combination of basis functions.
Galfan – It is a galvanized product coated with 95 % free zinc, 5 % aluminum and traces of mish metal in the coating. It provides extra corrosion protection with lighter coating weight. It has improved formability over regular free zinc coatings (hot dipped galvanized regular products).
Galilean transformation – It refers to the mathematical relationships which relate the coordinates of two reference frames moving at a constant velocity relative to each other, allowing for the conversion of position and time measurements between these frames. It is characterized by the implication that the speed of light is not constant across different frames, which contradicts the principles of relativity.
Gall – It means damage to the surface of a powder metallurgy compact or die part, which is caused by adhesion of powder to the die cavity wall or a punch surface.
Galling – It is a condition whereby excessive friction between high spots results in localized welding with subsequent spalling and a further roughening of the rubbing surfaces of one or both of two mating parts. It is also a severe form of scuffing associated with gross damage to the surfaces or failure. Galling has been used in several ways in tribology, hence, each time it is encountered its meaning is to be ascertained from the specific context of the usage.
Galling stress – It refers to the threshold stress level above which two contacting surfaces begin to adhere and transfer material when sliding against each other, leading to a form of wear known as galling. This phenomenon is also known as adhesive wear or cold welding.
Gallium (Ga) – It is a chemical element which occurs in very low concentrations in the crust of the Earth and virtually all primary gallium is recovered as a by-product, principally from the processing of bauxite to alumina. Majority of the gallium applications need very high purity levels, and the metal is to be refined before use until it contains no more than 1 parts per million (ppm) total impurities. Elemental gallium is a relatively soft, silvery metal at standard temperature and pressure. In its liquid state, it becomes silvery white. If enough force is applied, solid gallium may fracture conchoidally. Gallium has limited commercial applications in its metallic form. Its principal use is in the manufacture of semi-conducting compounds, mainly gallium arsenides (GaAs) and gallium phosphide (GaP). Majority of the gallium consumed is used for optoelectronic devices and integrated circuits (ICs). Opto-electronic devices, light-emitting diodes (LEDs), laser diodes, photo-diodes, and solar (photovoltaic) cells, take advantage of the ability of GaAs to convert electrical energy into optical energy and vice versa.
Gallium arsenide (GaAs) – It is a brittle, gray, crystalline inorganic compound formed from gallium and arsenic, mainly used as a III-V direct bandgap semiconductor. It is prized in electronics for its superior high-speed electron mobility, high-frequency operation, and optoelectronic capabilities (light-emitting diodes, lasers) compared to silicon. It is mainly known for its high electron mobility and efficiency in opto-electronic and high-speed electronic devices. It is analyzed as a synthetic, brittle, greyish cubic crystal (zinc-blende structure) with a melting point of 1,238 deg C, frequently needing specialized production methods to maintain stoichiometry because of the arsenic volatility.
Gallium content – It refers to the quantity of gallium present in a catalyst, which is controlled by treatments such as HCl (hydro-chloric acid) treatment for removal and can be quantified using techniques like inductively coupled plasma (ICP) analysis.
Gallium phosphide (GaP) – It is a hard, brittle, pale-orange Type III-V compound semiconductor with an indirect band gap of 2.26 eV (electron-volt) , widely used in opto-electronics for red, orange, and green LEDs (light emitting diodes). It possesses a cubic (zinc blende) crystal structure and is often produced via Liquid Encapsulated Czochralski (LEC) methods.
Gallium vacancy – It is a type of native point defect in gallium-based semiconductor materials, most notably gallium nitride (GaN) and gallium oxide (beta-Ga2O3), where a gallium atom is missing from its normal lattice site in the crystal structure. It is characterized as a ‘deep acceptor’ defect, meaning it introduces electron energy levels deep within the bandgap that trap charge carriers.
Gallon – It is a US (United States) customary and Imperial unit of volume / capacity for liquids. Engineering standards define the US liquid gallon as exactly 231 cubic inches (3.785411784 litres). The Imperial (United Kingdom, UK) gallon, used in some Commonwealth countries, is defined as 4.54609 litres liters or around 277.42 cubic inches.
Gallons per minute – It is a US (United States) customary unit of volumetric flow rate defining the number of gallons of liquid passing a specific point in one minute. It is used in engineering to measure pump capacity, HVAC (heating, ventilating, and air conditioning) system efficiency, plumbing fixture performance, and industrial fluid transfer.
Galvalume steel – It is the steel sheet with a unique coating of 55 % aluminum and 45 % zinc which resists corrosion. The coating is applied in a continuous hot-dipped process, which improves the weather resistance of the steel.
Galvaneal coating – It consists of coating on hot-dipped galvanized steels which has been processed to convert the coating completely to zinc-iron alloys. It is dull gray in appearance, have no spangle, and after proper preparation, are well suited for painting.
Galvanic anode – It is a metal which, because of its relative position in the galvanic series, provides sacrificial protection to metals which are more noble in the series, when coupled in an electrolyte. Galvanic cell – It is a cell in which chemical change is the source of electrical energy. It normally consists of two dissimilar conductors which are in contact with each other and with an electrolyte, or of two similar conductors in contact with each other and with dissimilar electrolytes. It is also a cell or system in which a spontaneous oxidation-reduction reaction occurs, the resulting flow of electrons being conducted in an external part of the circuit.
Galvanic corrosion – It refers to corrosion damage where two dissimilar metals have an electrically conducting connection and are in contact with a common corrosive electrolyte. In the electro-chemical model of corrosion, one of the two partial reactions (anodic metal dissolution and cathodic oxygen reduction) takes place almost exclusively on one metal. Normally, the less noble metal is dissolved (anodic metal dissolution), whereas the more noble part is not attacked by corrosion (serves only as the cathode for oxygen reduction). Where galvanic corrosion takes place, the rate of corrosion of the less noble metal is higher than it would be in a free corroding environment without contact to another metal. Using thermodynamic data and taking common experience gained in typical applications into account, it is possible to predict which material combinations are affected by galvanic corrosion. A positive example of active utilization of the galvanic corrosion phenomenon described here is the way zinc protects carbon steels and low alloy steels. Zinc is the less noble metal which actively protects steel by being
Galvanic couple – It is a pair of dissimilar conductors, normally metals, in electrical contact.
Galvanic couple potential – it is the potential of a sample (or samples in a galvanic couple) when two or more electro-chemical reactions are occurring.
Galvanic current – It is the electric current which flows between metals or conductive non-metals in a galvanic couple.
Galvanic displacement – It is a spontaneous electro-chemical process where a more noble metal cation in solution is reduced to a solid, while a less noble metallic substrate is oxidized and dissolves. It is a cost-effective, electroless technique used to engineer functional coatings, nano-structures, and catalysts by depositing thin metal layers on substrate surfaces. It involves two simultaneous, spontaneous electrochemical reactions (redox) without external current.
Galvanic interaction – It is an electro-chemical process where two dissimilar metals or materials, in contact with an electrolyte, form a cell which drives accelerated corrosion of the more active (anodic) metal while protecting the more noble (cathodic) metal. It is an important factor in materials selection to prevent structural failure.
Galvanic isolation – It refers to the technique of preventing direct electrical contact (a conductive path) between two dissimilar metals that are immersed in a common electrolyte (such as water or moist soil). By creating this ‘break’ in the electrical circuit, the flow of electrons between the anode (corroding metal) and cathode (protected metal) is stopped, hence eliminating or considerably reducing galvanic corrosion.
Galvanic series – It consists of a list of metals and alloys arranged according to their relative corrosion potentials in a given environment.
Galvanize – It means coating a metal surface with zinc using any of various processes.
Galvanized coating – Galvanized coating on the steel sheet consists of the steel core, with an inter-metallic alloy layer and outer zinc layer on both surfaces. Besides the outer layer of zinc (eta layer), it contains gamma, delta and zeta layers. The hardness of gamma, delta and zeta layers of the zinc coating, as expressed in diamond pyramid number (DPN), is higher than the underlying steel. Because of this higher hardness, these layers provide excellent protection against coating damage through abrasion.
Galvanized iron (GI) sheets – These are basically steel sheets which have been coated with zinc. These sheets include a range of hot dip galvanized and electro-galvanized steel sheet. The zinc coating provides a continuous barrier which does not allow moisture and oxygen to reach the steel. It reacts with the atmosphere to provide the base steel a protection.
Galvanized steel reinforcement – It refers to steel reinforcement which has been coated with zinc to improve its corrosion resistance in concrete construction. This includes traditional hot-dip galvanizing and newer continuous coating methods, which improve the performance and durability of the reinforcement under alkaline environments.
Galvanized steel reinforcement bars – These are the normal reinforcement steel bars which are coated with a protective layer of zinc metal. Zinc coating is normally carried out by hot dip galvanizing process. The zinc coating serves as a barrier to the corrosive environment which the rebars are exposed to when embedded in concrete. In addition to the barrier protection, zinc also provides cathodic protection where zinc corrodes preferentially when in contact with unprotected steel. This means that in case of any gap in zinc coating the surface of bare steel, the reinforcement bar is protected by the surrounding zinc.
Galvanized steels – These are steels coated with a thin layer of zinc to provide corrosion resistance. These are normally used in under body auto parts, garbage cans, storage tanks, or fencing wire. Sheet steels are normally cold rolled prior to the galvanizing stage. Galvanized steels are produced either by hot dipping process or by electro-galvanizing process.
Galvanizing – It is the process of applying a protective zinc coating to steel.
Galvanizing alloy – Galvanizing baths are alloyed with small amounts of other metals such as aluminum, nickel, or lead to improve the fluidity and resistance to oxidation of the zinc.
Galvanizing temperature – It is the temperature at which the molten zinc bath is kept in order to react with the steel. Typically, this temperature is between 443 deg C and 454 deg C.
Galvanneal – It means to produce a zinc-iron alloy coating on iron or steel by keeping the coating molten after hot dip galvanizing until the zinc alloys completely with the basis metal.
Galvannealed steel – In this steel an extra tight coat of galvanizing metal (Zn) applied to a soft steel sheet, after which the sheet is passed through an oven at around 650 deg C. The resulting coat is dull gray without spangle especially suited for subsequent painting.
Galvanomagnetic effects – These effects refer to transport phenomena which occur in the presence of electric and magnetic fields, such as the Hall effect and magneto-resistivity. These effects show how the motion of charge carriers is influenced by magnetic fields in conductive materials.
Galvanometer – It is an instrument for detecting small electric currents.
Galvanopair – It is also known as galvanic pair / couple. It refers to two electro-chemically dissimilar metals or conductive materials in physical contact with each other while exposed to a common electrolyte (a conductive liquid or moist environment). These pairing initiates a galvanic cell, resulting in accelerated corrosion of the more chemically active metal (the anode) and protection of the less active metal (the cathode).
Galvanostatic – It is an experimental technique whereby an electrode is maintained at a constant current in an electrolyte.
Game model – It is a framework used to analyze strategic interactions between agents, predicting behaviours at equilibrium (e.g., Nash equilibrium) in competitive or cooperative scenarios, such as system design. It defines rules, mechanics, and agent objectives to evaluate optimal strategies.
Game theory model – It is a mathematical framework used to analyze and optimize strategic interactions between rational agents, such as systems, algorithms, or stakeholders, seeking to achieve, e.g., a Nash equilibrium. It defines competitive or cooperative scenarios (e.g., energy systems) by specifying players, actions, payoffs, and information sets.
Gamification – It is the application of game-design elements (points, badges, leader-boards) and principles to non-game contexts to improve user engagement, motivation, and behaviour, such as in software development or technical education. It transforms tasks to increase productivity, improve knowledge retention, and foster collaboration, addressing complex problems.
Gamma alloys – These are specifically known as gamma titanium aluminide (gamma-TiAl)-based alloys. These are a class of intermetallic compounds designed for high-temperature structural applications. They are mainly composed of titanium (Ti) and aluminum (Al) and are characterized by a lightweight, high-strength structure, frequently used as a substitute for heavier nickel-based super-alloys.
Gamma correction – It is a nonlinear, power-law operation used to encode and decode luminance (brightness) in image and video systems. It adjusts the relationship between a pixel’s numerical value (signal) and its actual output luminance to match human visual perception and the non-linear properties of display devices, such as cathode ray tubes (CRTs), liquid crystal displays (LCDs), or light emitting diode (LED) pixels.
Gamma density – It is a probability distribution characterized by its shape and scale parameters, frequently used in Bayesian statistics, where it can serve as a prior distribution for the precision parameter in models involving normal distributions. In the context provided, the gamma density is expressed with respect to the precision variable, demonstrating its application in deriving posterior distributions.
Gamma distribution– The gamma distribution includes as special cases the chi-square distribution and the exponential distribution. It has several important applications. In Bayesian inference, for example, it is sometimes used as the a priori distribution for the parameter (mean) of a Poisson distribution.
Gamma ferrite – It is normally known as austenite or gamma-iron (gamma-Fe). It is a non-magnetic, face-centered cubic (fcc) allotrope of iron which exists between 912 deg C and 1,394 deg C. It is highly ductile, can dissolve considerably more carbon (up to 2.04 %) than alpha ferrite, and is important for heat-treating steel.
Gamma iron – It is the face-centered cubic form of pure iron. It is stable from 910 deg C to 1,400 deg C.
Gamma layer – It is the zinc-iron alloy layer closest to the surface of the steel in the galvanized coating. It is the first layer of zinc iron alloy growth from the base steel formed during the galvanizing process. The chemical composition of this layer is around 75 % zinc and 25 % iron. Gamma layer is the hardest layer in the coating and has a diamond pyramid number (DPN) of 250 compared to the DPN of 159 for the base steel. In the context of the iron-carbon phase diagram, the “gamma layer” refers to gamma iron (also known as austenite).
Gamma phase – It typically refers to austenite in iron-carbon alloys, a high-temperature, non-magnetic solid solution of carbon in face-centred cubic (fcc) iron, stable above 727 deg C. It is characterized by high ductility, improved corrosion resistance in stainless steels, and serves as the precursor for forming martensite.
Gamma-phase iron – It is also known as austenite. It is a metallic, non-magnetic allotrope of iron or a solid solution of iron with an alloying element. In plain-carbon steel, it exists above the critical eutectoid temperature of 727 deg C. Other alloys of steel have different eutectoid temperatures.
Gamma phase titanium aluminides – These are advanced, lightweight intermetallic compounds (around 45 % to 48 % aluminum) with a face-centered tetragonal (fct) crystal structure. They offer low density (around 4 grams per cubic centimeter), high specific strength, and excellent creep / oxidation resistance up to 750 deg C.
Gamma photons – These are quanta of gamma radiation, which are a type of electro-magnetic radiation originating from the nucleus of an atom. They are characterized by having zero rest mass and charge, and their energy is equal to the product of the radiation’s frequency and the Planck constant.
Gamma power – It refers to the intensity or energy output of gamma radiation emitted during radio-active decay or nuclear reactions, used for monitoring reactor core activity.
Gamma prime (gamma’) – It is a strengthening phase in nickel-based superalloys, which can be depleted in specific regions, such as gamma’-denuded zones, because of the improper heat treatment, leading to decreased material performance and increased susceptibility to failure.
Gamma prime (gamma’) solvus – It is a critical temperature in the metallurgy of nickel-based (and some cobalt-based) superalloys, representing the specific temperature boundary above which the precipitate phase, gamma prime [gamma’- typically Ni3(Al, Ti)), completely dissolves into the solid-solution matrix (gamma phase). Below this temperature, the alloy exists as a two-phase mixture (gamma + gamma’), while above it, the alloy is a single-phase solid solution.
Gamma process – It is a stochastic (random) process with independent, non-negative, and monotonically increasing increments, specifically following a gamma distribution. It is used to model cumulative, irreversible degradation over time, such as wear, corrosion, crack growth, or fatigue. It is frequently used to model the degradation process of components and can be estimated using different methods for practical engineering applications. The gamma distribution has an identical scale parameter and a time-dependent shape parameter.
Gamma quanta – These are high-energy photons (gamma-rays) emitted from atomic nuclei during radioactive decay or particle annihilation, possessing zero rest mass / charge. They refer to high-energy photons emitted during the decay of radionuclides, which are measured in gamma radiation analysis using detectors such as solid-state germanium detectors for energy resolution and relative detection efficiency.
Gamma radiation – It consists of very high-energy electro-magnetic rays produced during radioactive decay. These are similar to visible light and X-rays but significantly more energetic than the latter.
Gamma ray – It is short wave-length electro-magnetic radiation, similar to x-rays but of nuclear origin, with a range of wave-length from around 0.0005 nanometers to 0.14 nanometers.
Gamma ray irradiation – It is a high-energy, penetrating industrial process (typically using cobalt-60) which treats materials to ionizing electro-magnetic radiation. It is a high-energy irradiation method which generates free radicals and ions by exposing polymeric materials to gamma rays, leading to changes in molecular arrangement and new bond formation.
Gamma-ray spectrometry – It is the most powerful tool in the field of radio-nuclide analysis. It is an instrument which measures the distribution of the intensity of gamma radiation against the energy of each photon. It is used for the qualitative and quantitative determination of radio-nuclides which emit gamma radiation. Majority of the radio-nuclides send out gamma radiation during their transformations to stable decay products.
Gamma-ray spectroscopy – It is the qualitative study of the energy spectra of gamma-ray sources, such as in the nuclear industry, geochemical investigation, and astrophysics. It is used for the determination of the energy distribution of gamma-rays emitted by a nucleus.
Gamma structure – It consists of structurally analogous phases or electron compounds which are having ratios of 21 valence electrons to 13 atoms. This is generally a large, complex cubic structure.
Gamma system – It is a configuration which utilizes dual-energy gamma beams from two sources, typically 137 Cs (caesium) and 241 Am (americium), which are mounted in a shield and simultaneously directed through a sample section to a common detector. It includes electronic components such as power supplies and analyzers, frequently improved by internal computer boards for advanced spectroscopy.
Gamma titanium aluminide (TiAl) alloys – These are advanced intermetallic materials based on the TiAl compound, characterized by low density (around 4 grams per cubic centimeter), high-temperature strength, and excellent oxidation resistance. These alloys serve in a variety of structural materials applications. These are two-phase alloys consisting mainly of gamma-TiAl and alpha2-Ti3Al, bridging the gap between conventional titanium alloys and nickel-based superalloys.
Gamut colours – These are the range of colours a device can produce, frequently visualized as a triangle on a CIE (International Commission on Illumination) diagram connecting the primary RGB (red, green, blue) points.
Gamut mapping – It refers to a function which maps colours from one 3D colour space to another, allowing for the transformation of colour images while optimizing for specific objectives and constraints. It can involve fixed mappings, global image dependencies, or local image dependencies based on the colour content of pixels and their neighborhoods.
GAN – It is abbreviation for ‘generative adversarial network. GANs are a class of machine learning frameworks designed to generate new, realistic data which mimics a training dataset. They operate by pitting two neural networks, the generator and the discriminator, against each other in a competitive, or adversarial, game.
Gang die – It is also known as a multiple die. It is a type of press tool which features a number of punches and die cavities arranged together in a single punching head. It is designed to produce two or more identical parts or perform multiple identical operations (such as cutting several holes) simultaneously with a single stroke of the press.
Gangman – A gangman is part of rail / cable maintenance / engineering crew (called ‘Gang’) who are responsible for the upkeep of the track / cable conditions.
Gang milling – It consists of milling with several cutters mounted on the same arbor or with work-pieces similarly positioned for cutting either simultaneously or consecutively during a single set-up.
Gang nail – It is also known as a truss plate, connector plate, or metal web connector. It is a structural fastener made from galvanized steel, designed with multiple, punched-out pointed teeth on one side. These plates are mechanically pressed into timber surfaces to form strong, rigid, and permanent joints for timber trusses and wall frames.
Gang plate – It is also known as a truss connector plate, nail plate, or gang-nail. It is a light-gauge, galvanized steel plate punched to create a series of teeth on one side. These plates are mechanically pressed into timber surfaces to join wooden members, mainly in pre-fabricated roof and floor trusses.
Gang slitter – It is a machine with a number of pairs of rotary cutters spaced on two parallel shafts. It is used for slitting metal into strips or for trimming the edges of sheets.
Gangue – It is non-profitable minerals in an ore deposit which are frequently associated with the host rock. Gangue is the worthless portion of an ore which is separated from the desired part before smelting is commenced.
Gangue minerals in iron ores – In iron ore, white gangue minerals include quartz, feldspar, and calcite. The magnetic susceptibilities of white gangue minerals are close to zero. It is hence relatively easy to separate them from iron ores by magnetic separation.
Ganister – It is also spelled as gannister. It is hard, fine-grained quartzose sandstone, or orthoquartzite,
is a highly siliceous, fine-grained, hard rock (typically quartzose sandstone or orthoquartzite). It is mainly composed of silica (above 90 % SiO2) and is used to manufacture refractory bricks and linings for its exceptional ability to withstand extreme heat. Ganisters are cemented with secondary silica and typically have a characteristic splintery fracture. Where a ganister underlies coal as a seat-earth, it typically is penetrated by numerous root traces. These root traces typically consist of carbonaceous material. Ganister which contains an abundance of fossil roots, which appear as fine carbonaceous, pencil-like streaks or markings, are called ‘pencil ganister’. In other cases, the root traces consist of fine, branching nodules, are called ‘rhizoliths’, which formed around the roots before they decayed.
Gantry cranes – These cranes are essentially the same as the regular overhead travelling cranes except that the bridge for carrying the trolley or trolleys is rigidly supported on two or more legs running on fixed rails or another runway. These ‘legs’ eliminate the supporting runway and column system and connect to end trucks which run on a rail either embedded in, or laid on top of, the floor. The crane frame is supported on a gantry system with equalized beams and wheels that run on the gantry rail, normally perpendicular to the trolley travel direction. This crane comes in all sizes, and some can move very heavy loads.
Gantt chart – It is a type of bar chart which shows a project schedule. This chart lists the tasks to be performed on the vertical axis, and time intervals on the horizontal axis. The width of the horizontal bars in the graph shows the duration of each activity. Gantt charts show the start and finish dates of the terminal elements and summary elements of a project. Terminal elements and summary elements constitute the work breakdown structure of the project. Modern Gantt charts also show the dependency (i.e., precedence network) relationships between activities. Gantt charts can be used to show current schedule status using percent-complete shadings and a vertical ‘TODAY’ line. Gantt charts are sometimes equated with bar charts.
Gap – It is a non-standard term for joint clearance and root opening. In rolling mills, it refers to the space between the rolls in a roll stand in which the forming of the rolled material depending on the roll gap force takes place. The setting of this gap is crucial for the roll gap force, determining the thickness of the rolled metal (e.g. rolled steel sheets, rolled flat bar or rolled steel tube). Controlling the height of the roll gap, frequently supported by precise measurements using laser technology, allows direct control over the material thickness and speed.
Gap analysis – It is a strategic planning tool used to compare an organization’s current performance or state with its desired, ideal future state. It identifies the ‘gap’ between the two, helping organizations pinpoint deficiencies, maximize resource allocation, and create actionable plans to improve performance, meet goals, or address market needs.
Gap cell – It normally refers to an electro-chemical cell configuration where two flat electrodes are separated by a small, controlled distance (micro-meter to millimeter range) in a liquid electrolyte, designed to minimize ohmic resistance. It is frequently used in electrolyzers to manage gas separation and improve efficiency at high current densities.
Gap control in the rolling mill – It consists of controlling the height of the roll gap, frequently supported by precise measurements using laser technology. It allows direct control over the rolled product thickness and speed.
Gap energy – It is the energy difference between the top of the valence band and bottom of the conduction band in a solid, where no electron states can exist. It defines the minimum energy needed to excite an electron to move from a bound state to a conductive state.
Gap-frame press – It is a general classification of press in which the uprights or housings are made in the form of a letter ‘C’, hence, making three sides of the die space accessible.
Gap function – It is a l tool used to define, measure, and manage the distance between two components, surfaces, or states. It is mainly applied to ensure functional needs, such as avoiding clashes, allowing thermal expansion, or managing electrical signals.
Gap measurement – It is needed for precise monitoring or quality control in order to satisfy technical or visual requirements. Single point sensors can be used to monitor the gap distance between rollers, and sheets etc. Laser scanners can be used to profile the gap of a seam, object, or weld.
Gap model – It is a framework which identifies the disparity between a current state (As-Is) and a desired target state (To-Be). It is used to analyze performance gaps in processes, systems, or service quality to identify necessary improvements. By mapping these differences, teams can develop targeted interventions to improve efficiency, quality, and performance.
Gap penalty – It is a scoring mechanism used in sequence alignment which penalizes the opening of gaps more than their extension, reflecting the rarity of indel events in evolutionary processes. This scoring scheme, known as affine gap penalty, quantifies the total gap penalty based on the opening and extension penalties as well as the total gap length.
Gap phenomenon – It refers to the series of events in electrical discharge machining (EDM) which include plasma formation in the dielectric, interactions of electrons and ions, heat transfer, and material removal through melting and vapourizing, leading to debris generation and its subsequent flushing with the dielectric liquid. This process is characterized by rapid bubble expansion and high-pressure development within the dielectric fluid, which plays an important role in cooling and debris removal.
Gap ratio – It is frequently denoted as G/D or s/d. It is a dimensionless parameter defined as the ratio of the spacing or gap width (G or s) between two bodies (such as tubes, cylinders, or bridge decks) to their characteristic dimension, typically diameter or depth (D or d). It is mainly used to analyze fluid flow, heat transfer, and aerodynamic interference, with values determining whether wake interaction or vortex shedding dominates. It is also the measure of the variance in carbon reduction efficiency between a group’s frontier and its meta-frontier, with values ranging from 0 to 1. A gap ratio closer to 1 indicates a smaller difference in efficiency, while a value closer to 0 indicates a higher difference.
Gap semi-conductor – It refers to a type of semi-conductor characterized by the presence of a band gap, which is the energy difference between the valence band and conduction band. There are two main types namely direct gap semiconductors, where the top of the valence band and the bottom of the conduction band occur at the same wave vector (Γ point), and indirect gap semiconductors, where these occur at different wave vectors, requiring phonon assistance for transitions.
Gap statistic – It is a standard method for determining the number of clusters in a set of data. The Gap statistic standardizes the graph of log(Wk), where ‘Wk’ is the within-cluster dispersion, by comparing it to its expectation under an appropriate null reference distribution of the data.
Gap tolerance – It is the allowed variation in the space between two mating parts, ensuring proper assembly, function, and inter-changeability. It defines the maximum and minimum acceptable limits for clearance or interference, preventing issues from manufacturing inaccuracies. It is important for controlling fit, such as in welding or assembly.
Gap velocity – It refers to the fluid velocity specifically within a restricted passage, such as between two tubes, between a rotor and casing, or in a valve. It is an important parameter for calculating flow characteristics, shear stress, and potential resonance in heat exchangers or hydraulic systems.
Gap voltage – It refers to the electrical potential difference between two distinct points separated by a physical space, such as electrodes in machining (EDM) or a probe and a target. It is critical for controlling spark energy, material removal rates, and measuring displacement in machinery.
Garden hose – It is a flexible, multi-layered conduit, typically constructed from extruded synthetic rubber or soft thermoplastic elastomers (PVC), designed for transporting pressurized water. It features an internal fabric reinforcing mesh (e.g., polyester) to handle pressure and prevent bursting, finished with threaded end-couplers for secure, leak-free connection to water sources.
Garland idlers – These idlers are also known as catenary idlers. These idlers are a type of conveyor idler which consists of a series of rollers suspended from a frame, forming a flexible, chain-like structure. Unlike rigid frame idlers, garland idlers offer higher flexibility and can adapt to uneven loads and complex conveyor routes. They are frequently used in applications where belt alignment and smooth material flow are critical, such as in mining, construction, and logistics. Garland idlers can be furnished with quick release suspensions which allow the unit to be lowered away from belt contact in case of roll failure. Garland design idlers can be utilized on rigid frame or wire rope supported conveyor systems. Garland idlers are available as two-roll, three-roll, or five-roll units. Normally, two-roll units are utilized as return idlers and serve to aid in belt training because of the trough which is formed. Three-roll and five-roll units are used as carrying or impact units. Rubber discs can be utilized on three-roll units to provide additional cushioning. Five-roll units do not use rubber discs. All garland idlers are suspended from the conveyor framework by means of various devices such as hooks or chains.
Garnet – It refers to a group of complex silicate minerals (typically iron-aluminum or magnesium-aluminum silicates) that are crushed, screened, and used as a high-performance, natural abrasive and filtering medium. It is a common heavy mineral group characterized by isometric crystal structures, predominantly found in metamorphic and igneous rocks, and typically occurring in pink, orange, or red colors. It can serve as an index mineral, particularly pyrope, in the search for diamond-bearing kimberlite pipes.
Garnierite – It is a general name for a green nickel ore which is found in pockets and veins within weathered and serpentinized ultramafic rocks. It forms through lateritic weathering of ultramafic rocks and occurs in several nickel laterite deposits. It is an important nickel ore, having a large percent of NiO. Since garnierite is not a valid mineral name asper the Commission on New Minerals, Nomenclature and Classification (CNMNC), no definite composition or formula has been universally adopted. Some of the proposed compositions are all hydrous nickel-magnesium silicates, a general name for the nickel-magnesium hydro-silicates which normally occur as an intimate mixture and normally includes two or more of the following minerals, such as serpentine, talc, sepiolite, smectite, or chlorite, and nickel-magnesium silicates, with or without alumina, which have X-ray diffraction patterns typical of serpentine talc, sepiolite, chlorite, vermiculite or some mixture of them all.
Garnet – It is a generic name for a related group of mineral silicates which have the general chemical formula A3B2(SiO4)3, where ‘A’ can be calcium, magnesium, manganese, or ferrous iron, and ‘B’ can be aluminum, ferric iron, chromium, or titanium. Garnet is used for coating abrasive paper or cloth, for bearing pivots in watches, for electronics, and the finer specimens for gemstones. The hardness of garnet varies from Mohs 6 to 8 (1,360 Knoop), the latter being used for abrasive applications.
Gas – It is one of the four fundamental states of matter. The others are solid, liquid, and plasma. A pure gas can be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g., oxygen), or compound molecules made from a variety of atoms (e.g., carbon di-oxide). A gas mixture, such as air, contains a variety of pure gases. What distinguishes gases from liquids and solids is the vast separation of the individual gas particles. This separation normally makes a colourless gas invisible to the human observer.
Gas adsorption method – It is an analytical technique used to characterize porous materials by measuring the volume of gas (adsorbate) which adheres to a solid surface (adsorbent) at controlled, low temperatures and varying pressures. It determines specific surface area, pore size distribution, and porosity through physisorption (van der Waals forces) or chemisorption (chemical bonding).
Gas analysis – It is the determination of the constituents of a gaseous mixture.
Gas and steam turbine combined cycle – It refers to a power generation system which integrates gas turbines and steam turbines to optimize thermal efficiency in power plants. This cycle utilizes the waste heat from gas turbines to produce steam, which drives steam turbines for additional electricity generation.
Gas and vapour separation – It is a process used to isolate specific components from a mixture (e.g., hydrogen / nitrogen, carbon di-oxide / methane) or remove contaminants. It uses technologies like pressure-driven membranes (sorption / diffusion), adsorption (pressure swing adsorption, PSA), or condensation to achieve, high-purity, low-energy separation.
Gas atom – It is a single, electrically neutral, and energetic particle existing in a dispersed, gaseous state. These atoms move independently with high kinetic energy, frequently colliding, and possess no fixed volume or shape. Key examples include noble gases (Ar, He) or atoms in plasma.
Gas atomization – It is an atomization process whereby molten metal is broken up into particles by a rapidly moving inert gas stream.
Gas barrier properties – These barriers define a material’s capacity to restrict the permeation of gases (e.g., oxygen, carbon di-oxide, water vapour) through its structure, mainly determined by its polymer permeability, crystallinity, and filler content. It involves a three-step process, dissolution, diffusion, and desorption, crucial for optimizing packaging, electronics, and tire longevity.
Gas bearing – It is a type of fluid-film bearing which uses a pressurized gas film, typically air, nitrogen, or helium, instead of oil or grease to separate moving surfaces, allowing for near-frictionless, oil-free operation. They are widely used in high-speed, precision, and high-temperature machinery, such as turbines and compressors, because of low power loss. Gas bearing is a journal or thrust bearing which is lubricated with gas.
Gas blending – It is the precise, controlled mixing of two or more gases (e.g., argon, carbon di-oxide, oxygen, and helium) to achieve specific, consistent compositions needed for industrial processes like welding, heat treatment, and refining. It ensures optimal atmosphere control for improved metal quality, shielding, or combustion efficiency.
Gas blowby – It is a, frequently critical, scenario where high-pressure gas escapes through a liquid outlet (in process vessels) or leaks past piston rings into the crankcase (in engines) because of the seal failure, low liquid levels, or control valve failure. It causes severe overpressure in downstream equipment or engine damage.
Gas boiler – It is a system (pressure vessel) which burns a fuel gas to generate thermal energy, heating water for space heating or industrial processing. It transfers combustion heat through a heat exchanger to water or steam, operating as either a fire-tube or water-tube system to efficiently meet heating demands.
Gas Brayton cycle – It is a thermodynamic cycle modeling the operation of constant-pressure heat engines, mainly gas turbines and jet engines. It uses air or gas as a working fluid, involving adiabatic compression, constant-pressure heat addition (combustion), adiabatic expansion (power production), and constant-pressure heat rejection.
Gas brazing – It is also called torch brazing. It is a metal-joining process which uses a high-temperature gas flame (e.g., oxy-acetylene) to heat base metals above 450 deg C, while remaining below their melting point. A filler metal is melted and flows into the joint through capillary action to create a strong, sealed bond without melting the parent material.
Gas bubble – It is a pocket of gas, vapour, or both, entrapped within a liquid or solid phase, frequently formed because of the pressure reduction, temperature increases, or chemical reactions. They represent a two-phase flow phenomenon, important in heat transfer, chemical processing, and material integrity, capable of deformation, oscillation, and coalescence.
Gas burner – It is a device which converts gaseous fuel (liquefied petroleum gas, natural gas, coke oven gas, converter gas, blast furnace gas, and mixed gas etc.) into heat energy by means of a chemical reaction called combustion, i.e., air and gaseous fuel are mixed in the right proportion through a premixing device to make it burn fully. Gas burners have the advantages of easy ignition, complete combustion, stable flame, good spreading, no tempering, no de-flaming, large adjustment range, low noise, long life, safety and reliability because of the reasonable structural design.
Gas bursts – These are sudden, violent releases of pressurized gas, frequently occurring in contexts like mining (coal and gas outbursts), nuclear fuel elements, or pressure vessel failures. These events are characterized by rapid expansion, high energy release, and potential for structural damage, frequently involving the ignition of flammable gases or catastrophic, pressure-induced fracturing.
Gas cap – It is a region of free, compressed natural gas which accumulates in the high-pressure, upper portion of an oil reservoir, sitting directly above the oil zone. It acts as a primary energy source, expanding to push oil toward production wells, and is important for reservoir pressure maintenance. It occurs when more gas exists in the reservoir than the oil can hold at current temperature and pressure, causing the excess gas to separate. It also refers specifically to a method of producing steel ingots where the rimming action is intentionally stopped shortly after pouring.
Gas capacity – It refers to the maximum volume of gas a system (pipe, vessel, or reservoir) can hold or transport under specified pressure, temperature, and operating conditions. It defines the flow rate (Q) in volumetric or mass terms, determining the operational limits of storage facilities.
Gas cap expansion – it is a petroleum drive mechanism where free gas, located at the top of a reservoir, expands as pressure drops during production. This expanding gas fills voided pore spaces, pushing oil downward towards production wells to aid recovery, frequently achieving 20 % to 40 % oil recovery efficiency.
Gas cap size – It is the volume of gas accumulated above the oil zone in a reservoir, which can influence the efficiency of reservoir operations and the quantity of oil recoverable during production. A shrinking gas cap indicates a reduction in this volume, potentially leading to substantial oil loss.
Gas carburizing – In gas carburizing, the parts are surrounded by a carbon bearing atmosphere that can be continuously replenished so that a high carbon potential can be maintained. While the rate of carburizing is substantially increased in the gaseous atmosphere, the method requires the use of a multi component atmosphere whose composition must be very closely controlled to avoid deleterious side effects, for example, surface and grain-boundary oxides. In addition, a separate piece of equipment is required to generate the atmosphere and control its composition. The gas carburizing process is theoretically similar to pack carburizing process aside from the supply of carbon mono-oxide gas to the heated furnace and the carbon decomposition. Several of the problems with pack carburizing are eliminated in this process. The carbon mono-oxide gas needs to be contained safely. Despite this increased complexity, gas carburizing has become the most effective and widely used method for carburizing steel parts in large quantities.
Gas channels – These are machined, or cast structures (typically in separator plates) designed to transport reactant gases (e.g., hydrogen, oxygen) and manage product water in electro-chemical devices like PEM (proton exchange membrane) fuel cells. Their geometry, width, depth, and rib / land size, critically influences performance including pressure drop and heat management.
Gas characteristics – These characteristics define the physical, thermal, and chemical behaviours of gaseous substances based on pressure (P), temperature (T), volume (V), and mass (m). Key properties include high compressibility, low density, indefinite shape / volume, rapid diffusion, and thermal expansion, frequently modeled using ideal or real gas laws.
Gas chromatograph – It is an analytical instrument which is designed to separate organic species for subsequent detection by an analyte specific detector.
Gas chromatography (GC) – It is a common type of chromatography used in analytical chemistry for separating and analyzing compounds which can be vapourized without decomposition. It is an analytical technique which applicable to gas, liquid, and solid samples (components which are vapourized by heat). If a mixture of compounds is analyzed using gas chromatography, each compound can be separated and quantified. Typical uses of gas chromatography include testing the purity of a particular substance, or separating the different components of a mixture.
Gas chromatography applications – These refer to the practical uses of gas chromatography (GC) techniques, which include the analysis and separation of complex mixtures using gas chromatography coupled with mass spectrometry (GC-MS).
Gas chromatography-infrared (GC-IR) spectroscopy – It combines the high-efficiency separation ability of gas chromatography and the molecular structure identification ability of infrared spectroscopy, and is an effective method for the analysis of complex mixtures.
Gas chromatography–mass spectrometry (GC-MS) – It is used to identify the molecular weight, elemental constitution, and molecular structure of the compounds present in the sample. It is an analytical method which combines the features of gas-chromatography and mass spectrometry to identify different substances within a test sample. It comprises two very distinct analytical instruments namely gas chromatography, and mass spectrometry.
Gas chromatography technique – It is a separation technique where the mobile phase is a gas, and the stationary phase can be either a solid or a liquid coated on the column walls. It separates compounds based on their relative solubility in the stationary phase.
Gas classification – It is the separation of a powder into its particle size fractions by means of a gas stream of controlled velocity flowing counter-stream to the gravity-induced fall of the particles. The method is used to classify sub-mesh-size particles.
Gas classifier – It is a device for gas classification. It can be of laboratory size for quality control testing or of industrial capacity for accommodating powder production requirement.
Gas cleaning – It is the process of removing contaminants, such as dust, tar, sulphur compounds (hydrogen sulphide, sulphur di-oxide), halides (hydrochloric acid) and trace metals, from gas streams (e.g., syngas, exhaust, or natural gas). This essential process protects downstream equipment from corrosion, reduces emissions, and ensures the gas meets quality standards. Techniques include scrubbing, filtering, and precipitating.
Gas cleaning plant – The main function of the gas cleaning plant is to remove particulate matter from the exhaust gas of a furnace The exhaust is cleaned in gas cleaning plant normally in two stages namely primary gas cleaning stage and secondary gas cleaning stage. The gas cleaning plant can be a wet type plant or a dry type plant.
Gas clean-up system – It is a process unit designed to remove contaminants, such as particulates, tars, sulphur (hydrogen sulphide, sulphur di-oxide), and halides (hydrochloric acid), from raw gas streams (e.g., syngas, exhaust) to meet safety, environmental, or downstream processing needs. It involves cooling, scrubbing, and filtration technologies to protect equipment and ensure product quality.
Gas composition – It defines the specific mixture of individual components (gases, vapours, trace elements) within a sample, quantified by molar, mass, or volume fractions. It is important for analyzing processes like combustion, gasification, and refining, typically measured through gas chromatography to determine concentrations of hydrocarbons, carbon di-oxide, and nitrogen.
Gas compressibility – It measures a gas’s ability to decrease in volume when pressure increases, fundamentally defined by the compressibility factor (Z), which quantifies deviation from ideal gas behaviour (Z = PV/nRT). It is critical for calculating storage / transport capacity, as real gases deviate from ideal behaviour under high pressure, making ‘Z’ a multiplier in equations of state (e.g., PV = ZnRT).
Gas compressor – It is a mechanical device which increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor. Several compressors can be staged, i.e., the gas is compressed several times in steps or stages, to increase discharge pressure. Frequently, the second stage is physically smaller than the first (main) stage, to accommodate the already compressed gas without reducing its pressure. Each stage further compresses the gas and increases its pressure and also its temperature (if inter cooling between stages is not used).
Gas condensate system – It is a multiphase fluid system, occurring in reservoirs or pipelines, where high-pressure raw gas containing heavy hydrocarbons undergoes retrograde condensation to form liquids because of the pressure and temperature changes. It involves the production, transportation, and stabilization of natural gas liquids (C3 to C8 plus) which condense from gas when it drops below its dew point.
Gas condensation, coke oven – As the coke oven gas is cooled, water, tar and naphthalene condense out. The condensate collects in the primary cooler system and is discharged to the tar and liquor plant. As the raw coke oven gas is cooled, tar vapour condenses and forms aerosols which are carried along with the gas flow.
Gas coning – It is a phenomenon where high production rates create a pressure drawdown which pulls overlying gas downward into the oil perforation zone of a well. This forms a cone-shaped, premature breakthrough of gas, reducing oil productivity and efficiency. It is a rate-sensitive issue driven by different forces exceeding gravity forces.
Gas constant – It is the constant of proportionality appearing in the equation of state of an ideal gas, equal to the pressure of the gas multiplied by its molar volume divided by its temperature. It is also known as universal gas constant.
Gas-cooled fast reactor -It is a generation IV reactor concept using a fast-neutron spectrum, helium coolant, and a closed fuel cycle for sustainability. It operates at high temperatures (above 1,000 deg C) for high efficiency, needing advanced metallurgical solutions like ceramic fuel (uranium carbide, UC) in SiC (silicon carbide) matrices, ceramic-clad fuel elements, and high-temperature alloys to withstand intense radiation.
Gas-cooled reactor – It is the broad / generic expression which describes a nuclear reactor where gas is used as the coolant.
Gas cooling – It is the process of reducing a gas’s temperature by removing thermal energy, necessary for process optimization, condensation of vapours, and equipment protection. Methods include indirect cooling through heat exchangers (e.g., shell-and-tube) or direct cooling through quenching (liquid injection) or adiabatic expansion.
Gas cutter – It is a thermal cutting device used to sever, bevel, or gouge ferrous metals (mainly steel). It operates by utilizing a preheat flame to bring the metal to its ignition temperature (around 700 deg C to 900 deg C) and then applying a high-pressure jet of 99.5 % plus pure oxygen, which causes the heated metal to rapidly oxidize and burn away, creating a narrow gap or kerf.
Gas cutting – It is also called oxy-fuel cutting. It is a thermal, chemical process used to sever ferrous metals by rapidly oxidizing the material. It involves preheating the metal to its ignition point (700 deg C to 900 deg C) using a fuel gas / oxygen flame, followed by a high-pressure oxygen jet which burns the metal and blows away the iron oxide slag.
Gas cutting process – It is a thermal process which slices ferrous metals by preheating to 700 deg C to 900 deg C, followed by a high-pressure oxygen stream which rapidly oxidizes (burns) the metal and blows away the resulting slag. It relies on an exothermic chemical reaction rather than pure melting, making it ideal for cutting steel.
Gas cyaniding – It is very frequently referred to as carbo-nitriding. It is a surface-hardening (case-hardening) heat treatment process where carbon and nitrogen are diffused into the surface of steel to create a hard, wear-resistant layer. It is performed in a gaseous atmosphere, normally involving a mixture of hydrocarbon gas (such as methane or propane) and ammonia (NH3), typically in the range of 800 deg C to 875 deg C.
Gas cylinder – It is a portable pressure vessel or container designed to store gases under pressure, typically above atmospheric pressure. These cylinders are used for several applications, including industrial and scientific uses. Gas cylinders serve as a safe and efficient way to transport and store compressed or liquefied gases.
Gas deliverability – It is the capacity of a well to produce gas against surface and wellbore pressures, defined as the relationship between flow rate and pressure drawdown (Pres – Pwf). It determines the maximum sustainable production rate (absolute open flow, AOF) and is analyzed using inflow performance relationships (IPR) to optimize system performance.
Gas density – It is the mass per unit volume (d = m/V) of a gas, heavily influenced by pressure and temperature, typically measured in kilogram per cubic meter. It is critical for calculating flow rates, designing storage containers, and analyzing gas behaviour, frequently calculated using the real gas law to account for compressibility.
Gas differential – It refers to the difference in pressure between two points in a gas system, which is controlled to ensure a minimum buffer gas flow across the compressor and maintain the integrity of the seal interface. This differential pressure control is necessary for reliable operation and is historically utilized in buffer gas systems. It is used to maintain proper buffer gas flow across compressors.
Gas diffusion layer – It is a thin, porous, electrically conductive material (normally carbon-based) in fuel cells, located between the flow field plate and the catalyst layer. It facilitates reactant gas distribution, removes produced water, transports electrons, and provides structural support.
Gas dispersion – It is the process of distributing gas within a medium (air or liquid) to control its concentration, typically for safety (atmospheric dispersion) or reaction improvement (gas-liquid mixing). It involves modeling the transport, diffusion, and dilution of gases, frequently to mitigate hazards from leaks or optimize mass transfer in reactors.
Gas dissolution in a metal melt – It is a fundamental process where gaseous elements (very frequently hydrogen, nitrogen, and oxygen) from the surrounding atmosphere, fluxes, or raw materials are absorbed into molten metal, forming a liquid solution. Since molten metals act as a ‘sponge’ for these gases, they readily dissolve at high temperatures, but as the metal cools and solidifies, the solubility drops drastically, causing the trapped gas to form defects like porosity or embrittlement.
Gas distributor – It is a device, frequently a perforated plate, pipe grid, or nozzle, designed to uniformly inject gas into a reactor, column, or pipeline system. In chemical processes, it ensures stable fluidization and mass transfer. In utility contexts, it regulates, measures, and transports pressurized gas to end-users.
Gas drilling operations – These are multi-stage processes used in the oil and gas industry to create, secure, and complete boreholes for resource extraction. Utilizing rotary methods, these operations involve drilling, casing, and cementing wells to tap into reservoirs, with a focus on optimizing parameters like ROP (rate of penetration), weight-on-bit (WOB), and torque.
Gas drilling system – It is an integrated mechanism used to create boreholes for hydrocarbon extraction, utilizing compressed air, nitrogen, or natural gas to facilitate drilling in hard, dry formations. It operates by circulating gas down the drill string to cool the bit, lift cuttings to the surface, and maintain hole stability.
Gas drive reservoir – It is a petroleum accumulation where expanding natural gas provides the main energy for hydrocarbon production. It normally refers to two types namely solution gas drive (gas liberated from oil, typically 5 % to 20 % recovery) or gas cap expansion (a separate gas zone, 20 % to 40 % recovery). These reservoirs are characterized by rapid pressure decline, rising gas-oil ratios (GOR), and no substantial water influx.
Gas dynamic equations – These are a set of non-linear governing equations, derived from mass, momentum, and energy conservation laws, which model the behaviour of compressible, high-speed gas flows (frequently with shock waves). These equations (e.g., Navier-Stokes for viscous flow, Euler for inviscid flow) are fundamental for designing turbines.
Gas engine – It is an internal combustion engine which operates using gaseous fuels, such as natural gas, methane, or biogas, rather than liquid gasoline or diesel. Typically, these are reciprocating, spark-ignited engines, frequently utilizing the Otto cycle to drive generators or industrial machinery with high efficiency.
Gas entrapment – It is the unintended trapping of gas bubbles (frequently air) within a liquid or solidifying material (like metal or plastic) during processes such as casting, moulding, or coating. Caused by surface viscosity, rapid velocity, or surface cavities, it creates voids, porosity, and defects that weaken structural integrity.
Gas environment – It is a controlled, static, or dynamic atmosphere within a chamber used to manage material interactions, such as catalysis or electro-chemistry, by introducing specific gases. It involves precisely manipulating the gaseous composition to study or facilitate processes like combustion, environmental testing, or chemical synthesis.
Gaseous coolant – It is a fluid in its gaseous phase, such as air, helium, nitrogen, or carbon di-oxide, used to transfer heat away from components to prevent overheating. Although typically poorer thermal conductors than liquids, they are necessary for specialized applications like dry machining, high-temperature nuclear reactors, and electrical equipment cooling. It is mainly used in dry cutting (air), nuclear reactors, and electronics where liquid contamination is to be avoided.
Gaseous corrosion – It is the corrosion with gas as the only corrosive agent and without any aqueous phase on the surface of the metal. It is also called dry corrosion.
Gaseous diffusion – It is an industrial separation technique which forces a gaseous mixture, such as uranium hexafluoride (UF6), through a micro-porous membrane to separate isotopes based on their molecular velocities. Lighter molecules pass through the barrier more frequently than heavier ones, resulting in enrichment.
Gaseous emissions – These refer to the release of inorganic and organic gases, such as carbon di-oxide (CO2), nitrogen oxides (NOx), sulphur di-oxide (SO2), and volatile organic compounds (VOCs), from industrial processes, combustion, or waste management into the atmosphere. These pollutants are quantified by concentration or mass to manage environmental impact and regulatory compliance.
Gaseous flow – It is the motion of a gas, frequently compressible, moving through conduits, pipes, or over surfaces because of the pressure differences. It is characterized by high velocities, potential for turbulence, and sensitivity to temperature and pressure, typically analyzed through mass or volumetric flow rates.
Gaseous fuel combustion – It is the rapid, high-temperature exothermic chemical reaction between gaseous fuels (e.g., methane, propane, hydrogen) and an oxidant (normally air). Engineered to release maximum thermal energy efficiently, it involves precise control of fuel-air mixing to produce carbon di-oxide, water vapour, and heat, while minimizing emissions.
Gaseous lubricants – These lubricants are low-viscosity gases (e.g., air, nitrogen, helium) used in specialized bearings (aerodynamic / aerostatic) to reduce friction between moving surfaces, operating efficiently at extreme temperatures where liquids fail. They provide high-precision, low-friction performance but are limited to low-load applications due to their compressibility.
Gaseous medium – It is a state of matter, typically air, steam, or process gas, characterized by low density, high compressibility, and no fixed shape or volume, allowing it to fill any container. It acts as a transport, reaction, or insulating agent in systems like thermodynamics, HVAC (heating, ventilation, and air conditioning, and plasma processing.
Gaseous mixture – It is a combination of two or more non-reacting, distinct gas species which coexist in a single, homogeneous phase, such as air. Gaseous mixtures are analyzed based on mass or mole fractions, where the total pressure equals the sum of individual component partial pressures (Dalton’s law).
Gaseous molecules – These are discrete particles (atoms or molecules) in constant, rapid, and random motion, possessing high kinetic energy with negligible intermolecular forces. They occupy minimal volume compared to the space between them, leading to high compressibility and the ability to expand to fill containers.
Gaseous nitro-carburizing -It is a low-temperature thermo-chemical surface hardening process (typically 490 deg C to 580 deg C) which introduces both nitrogen and carbon into the surface of ferrous materials to improve wear resistance, corrosion resistance, and fatigue strength. It is a variant of ferritic nitriding—frequently called soft nitriding, which utilizes a gaseous atmosphere, normally comprising ammonia and a carburizing gas (such as methane or propane), in a sealed retort furnace.
Gaseous phase – It is a state of matter characterized by particles that are far apart, possess high kinetic energy, and move freely, resulting in low density, high compressibility, and the ability to expand to fill any container. It represents a uniform phase in terms of chemical composition and physical state.
Gaseous pollutants – These are airborne substances which exist in a gaseous state and can negatively impact human health and the environment. They are released into the atmosphere through several natural and human-caused sources. Common examples include sulphur di-oxide (SO2), nitrogen oxides (NOx), carbon mono-oxide (CO), and ozone (O3).
Gaseous reduction – It is the reaction of a metal compound with a reducing gas to produce the metal. It is also the conversion of metal compounds to metallic particles by the use of a reducing gas.
Gaseous species – These are distinct, individual chemical substances, e.g., oxygen (O2), hydrogen (H2), carbon di-oxide (CO2), methane (CH4) in the gaseous state, involved in transport processes like the capacity to fill any container, often obeying gas laws.
Gaseous stream – It is a continuous, flowing mixture of gaseous material, frequently containing varying compositions of gases, vapours, and sometimes entrained liquids or solids. It is an important component in processes, needing conditioning, separation, or treatment for industrial, environmental, or energy applications.
Gaseous waste – It refers to the unwanted, hazardous, or non-recyclable fumes, gases, and vapours emitted into the atmosphere during the extraction, smelting, refining, and processing of metal ores. These by-products are generated through high-temperature processes (pyro-metallurgy), such as fuel combustion, roasting, or smelting, and constitute a major source of industrial air pollution.
Gas exchange process – It refers to the removal of burnt exhaust gases and the introduction of a fresh fuel-air charge into an internal combustion engine cylinder. Key objectives include maximizing mass airflow through valve / port design (volumetric efficiency), characterized by 4-stroke intake / exhaust and 2-stroke scavenging.
Gas explosion – It is a phenomenon defined as the rapid combustion of a premixed fuel-air cloud, resulting in a sudden, violent release of energy, intense heat, and a rapid, high-pressure shock wave. It occurs when flammable gases (e.g., methane, propane, hydrogen) ignite within confined or unconfined spaces.
Gas field – It is a specialized geological accumulation of hydrocarbon-rich gas trapped in porous, permeable rock (e.g., sandstone) beneath impermeable, sealing cap rocks. Engineering-wise, it represents a defined geographic area containing commercial-grade, non-associated gas or gas-cap gas, normally delineated by, and developed with, specific infrastructure.
Gas-filled tube – It is an electron tube device which relies on the presence of gas for operation, normally at less than atmospheric pressure.
Gas-fired furnace – It is an industrial, brick-lined chamber which utilizes the combustion of natural gas, propane, or other fuel gases to generate heat for processing metals. It is an important component of pyro-metallurgy used to raise the temperature of metal components, frequently exceeding 400 deg C, for purposes such as smelting, casting, forging, and heat treatment (e.g., annealing, tempering, or hardening).
Gas-fired heating – It refers to the process of burning natural gas, propane, or other industrial gases in a controlled manner to generate high temperatures (frequently exceeding 1,000 deg C) for treating, melting, or shaping metal components. It is a fundamental industrial method for heat treatment, such as annealing, tempering, and hardening, where consistent temperature control and atmosphere management are necessary to alter the physical and mechanical properties of metals.
Gas flare – It is a gas combustion device which is used in processing plants. It is mainly used for burning of flammable gas released by safety valves during unplanned over-pressuring of plant equipment. During plant or partial plant startups and shutdowns, it is also frequently used for the planned combustion of gases over relatively short periods. Gas flares are also used for a variety of startup, maintenance, testing, safety, and emergency purposes.
Gas flow – It is the movement of gas, typically measured in standard cubic centimeters per minute (sccm), which is important for processes such as sweeping contaminants from a processing chamber in applications like reactive sputter deposition. It can be quantified using flow meters which measure the thermal conductivity of the gas and can involve the introduction of vapours through a vapourization chamber for certain processes. It is the movement of a compressible fluid (gas) through conduits, driven by pressure differences. Key regimes include laminar, turbulent, and molecular flow, determined by molecular mean free path, viscosity, and density.
Gas flow rate (Q) – it is the volume (V) or mass (m) of gas passing through a specific cross-sectional area per unit time (t). It measures the speed of gas movement through a pipe or conduit, frequently defined as Q = A x V (Area x velocity velocity). Common units include Litres per minute or standard cubic centimeters per minute. It is heavily influenced by pressure, temperature, and viscosity.
Gas foaming – It is a technique which involves the formation of gas bubbles within a polymer solution, either through the use of gas-foaming agents or by inducing a chemical reaction which releases gas. This process results in a polymer with a porous structure, although it frequently leads to poorly interconnected pores and a non-porous outer surface.
Gas formation volume factor – It is the ratio of gas volume at reservoir pressure and temperature to its volume at standard conditions. It converts surface-measured gas volumes to reservoir conditions to calculate reserves and production.
Gas fuel manufacture – It refers to the production of combustible gaseous fuels, such as coal gas, syngas, or reformed LPG (liquefied petroleum gas), through chemical transformation (gasification, pyrolysis, or reformation) of solid, liquid, or gaseous feedstocks. It involves processing raw materials to create energy carriers with specific compositions, distinct from directly extracted natural gas.
Gas fuel purification – It is the process of removing contaminants, such as water, acid gases (hydrogen sulphide, carbon di-oxide), and heavy hydro-carbons from raw gas streams to create a clean, dry, and high-energy fuel suitable for transport and industrial use. It involves stages like separation, scrubbing, and dehydration.
Gas furnace – It is an industrial heating, melting, or processing unit which utilizes the combustion of gaseous fuels to generate high temperatures for the thermal treatment of metals. These furnaces are designed to provide controlled heating for processes such as forging, annealing, smelting, and tempering, with heat transferred to the material via convection, radiation, or conduction from the combustion products.
Gas generator – It is an industrial furnace which produces its own controlled, protective atmosphere (or ‘generator gas’) for use in heat treating or refining metals. Unlike simple fuel-fired furnaces, these units are specifically designed to create a consistent, specialized, or inert gas mixture (such as hydrogen, carbon mono-oxide, and nitrogen) which interacts with the metal to prevent oxidation or carburization during heating.
Gas gouging – It is frequently referred to as flame gouging or oxy-fuel gouging. It is a thermal metal removal process used to create grooves or remove unwanted metal, such as old welds or defects, by utilizing a high-temperature oxy-fuel gas flame combined with a specialized, high-volume oxygen jet. It is considered a variant of conventional oxy-fuel gas cutting / welding.
Gas gravity – It is the ratio of a gas’s density to dry air’s density at identical pressure and temperature (standard conditions). It is a dimensionless measure indicating if a gas is lighter or heavier than air, calculated by dividing the gas’s molecular weight by 28.96 grams per mol.
Gas hazards – These refer to the safety risks posed by the generation, release, or accumulation of hazardous gases during metal processing, such as smelting, welding, and heat treatment. These hazards include toxic, asphyxiating, flammable, and explosive gases, which can cause severe health effects (e.g., suffocation, poisoning) or physical damage (e.g., fires, explosions).
Gas heater – It is an industrial device used to raise the temperature of a process gas, typically inert or semi-inert gases like nitrogen or argon, to a precise, uniform temperature for applications such as cold spraying, or to heat gaseous fuels for furnace operations. It heats process gas to high temperatures (up to 800 deg C to 900 deg C) to accelerate particles in a high-pressure gas stream. Unlike combustion-based heating, these heaters provide a very precise and uniform temperature distribution, which is ideal for processing thermally sensitive materials.
Gas holder – It is a large container or structure, typically cylindrical or spherical, used for storing gas, e.g., natural gas or coke oven gas etc., at near atmospheric pressure. These structures are designed to hold large volumes of gas and are frequently associated with gasworks or industrial sites where gas is produced or distributed.
Gas holdup – It is the volume fraction (or percentage) of gas (nomally air) present within a multiphase mixture, such as the slurry in a flotation cell or bubble column. It represents the ratio of gas volume to the total dispersion volume, typically determined by measuring the rise in bed height (bed expansion) or through pressure differential measurements.
Gas holes -These are holes in welds which are formed by gas escaping from molten metal as it solidifies. Gas holes can occur individually, in clusters, or throughout the solidified metal. In foundry, gas holes frequently referred to as gas porosity, blowholes, or pinholes. These are a common casting defect characterized by smooth-walled, normally spherical, or elongated cavities trapped within the metal casting. These voids occur when gas is entrapped in the molten metal during the pouring process, which subsequently fails to escape before the metal solidifies.
Gas hydrate production – It is the extraction of methane from solid, ice-like water-methane crystal structures in deep-sea or permafrost sediments, converting them into gas and water through depressurization, heating, or chemical injection. It is a multiphase heat / mass transfer process involving dissociation, differing from conventional gas extraction.
Gas hydrate stability zone – It is the specific range of pressures and low temperatures in seafloor or permafrost sediments where gas hydrates, crystalline water-methane ice structures, remain thermodynamically stable. It acts as a, boundary, typically found at water depths exceeding around 300 meters to 500 meters, separating stable, solid hydrate from dissociated gas.
Gasification – It is a technological process which can convert any carbonaceous (carbon-based) raw material such as coal into fuel gas which is also known as synthesis gas (syngas for short). Gasification occurs in a gasifier, normally a high temperature / pressure vessel where oxygen (or air) and steam are directly contacted with the carbonaceous raw material causing a series of chemical reactions to occur which convert the carbonaceous raw material to syngas and ash / slag (mineral residues).
Gasification agent – It is a substance (typically air, oxygen, steam, or carbon di-oxide) used in the thermochemical conversion of carbonaceous feedstocks (biomass, coal, waste) to facilitate partial oxidation and reduction at high temperatures (800 deg C to 1,200 deg C), generating a combustible synthesis gas (syngas) composed mainly of carbon mono-oxide and hydrogen.
Gasification of char – It is the high-temperature (above 800 deg C) thermochemical conversion of solid, carbonaceous residue (char) into synthetic gas (syngas) through reactions with steam, carbon di-oxide, or oxygen. As a critical rate-controlling step in gasifiers, it converts residual carbon into hydrogen (H2) and carbon mono-oxide (CO).
Gasification of coal – It is a conversion technology which converts any carbon containing material, such as coal, into synthesis gas (syngas). It is a high temperature process with temperature reaching typically 1,225 deg C. The temperature is optimized to produce a fuel gas with a minimum of liquid and solids. This process consists of heating the feed material coal in a vessel with or without the addition of oxygen. Carbon reacts with water in the form of steam and oxygen at relatively high pressure typically higher that 3 MPa and produce raw syngas and some minor byproducts. Composed mainly of the colourless, odourless, highly flammable gases carbon mono-oxide (CO) and hydrogen (H2), syngas has a variety of uses. The syngas can be further converted (or shifted) to nothing but hydrogen and carbon di-oxide (CO2) by adding steam and reacting over a catalyst in a water-gas-shift reactor. The byproducts are removed to produce a clean syngas which can be used (i) as a fuel to generate power or steam, (ii) as a basic chemical building block for a large number of uses in the petrochemical and refining industries, and (ii) for the production of hydrogen.
Gasification performance – It defines the efficiency, effectiveness, and quality of converting carbonaceous feedstock into syngas (carbon mono-oxide, hydrogen) under high-temperature, sub-stoichiometric conditions. Key performance indicators (KPIs) include ‘cold gas efficiency’ (CGE), ‘carbon conversion efficiency’ (CCE), syngas yield / syngas composition, and lower heating value (LHV).
Gasification rate – It defines the speed at which solid feedstock (carbon / char) is converted into gaseous products (carbon mono-oxide, hydrogen, carbon di-oxide, and methane) through chemical reactions with agents like steam, carbon di-oxide, or oxygen at high temperatures (800 deg C to 1,200 deg C). It is normally measured as the rate of char mass decrease relative to time and conversion.
Gasification reactor – It is also called gasifier. It is a pressurized or atmospheric vessel which converts carbonaceous materials (coal, biomass, waste) into combustible syngas (carbon mono-oxide, and hydrogen) and ash / slag. It operates at high temperatures (600 deg C to 1,500 deg C) with a limited supply of oxygen, air, or steam to facilitate partial oxidation rather than complete combustion.
Gasification system – It is a thermo-chemical process which converts carbonaceous materials (coal, biomass, waste) into synthesis gas (syngas, mainly carbon mono-oxide, and hydrogen) using partial oxidation at high temperatures (600 deg C to 1,500 deg C). It uses agents like air, oxygen, or steam to break down feedstock, providing a flexible, efficient, and cleaner alternative to combustion.
Gasification technology – It consists of a high-temperature (above 700 deg C to 1,200 deg C) thermo-chemical process which converts carbonaceous materials (coal, biomass, waste) into a combustible syngas (carbon mono-oxide, hydrogen, methane, and carbon di-oxide) using controlled quantities of oxygen, air, or steam. Engineered as a partial oxidation process, it breaks down feedstocks into raw gas for power, fuel, or chemical production.
Gasification technology development – It refers to the advancement of processes designed to convert organic or fossil-based materials into synthesis gas, which is a mixture of hydrogen and carbon mono-oxide, mainly for the production of synthetic fuels. This development includes improvements in gasifier designs, feedstock preparation, and downstream gas processing.
Gasification temperature – It is the high-temperature range (600 deg C to 1,500 deg C) at which carbonaceous feedstocks undergo partial oxidation and thermochemical conversion into syngas (carbon mono-oxide, hydrogen, carbon di-oxide, and water vapour). This critical parameter determines reaction kinetics, product composition, tar reduction, and efficiency, normally needing above 700 deg C to avoid excessive tar formation.
Gasifiers – Gasifiers are the equipment in which the complete gasification reactions are carried out. Gasifiers are required to be operated at certain temperature in order to drive certain endothermic carbon – steam and carbon – carbon di-oxide reactions. The required temperature is maintained by heat evolved from exothermic reaction between oxygen and coal. Depending upon the medium of gasification, gasifiers are classified into two categories namely (i) air blown, and (ii)oxygen blown. In air blown gasifiers, air is used as gasification medium while in oxygen blown gasifiers pure oxygen is used as gasification medium. When air is used as gasification medium, the nitrogen is simultaneously brought into the process which results in the product gas dilution. As a result, product gas has a lower calorific value. Depending upon the contact between gas and fuel, there are four types of gasifiers. These are namely (i) moving or fixed bed gasifier, (ii) fluidized bed gasifier, (iii) entrained bed gasifier, and (iv) transport flow gasifier. All the four types of gasifiers are based on partial oxidation (gasification) of a carbonaceous (carbon containing) feed material (coal). While each of these can make an acceptable reducing gas, the fixed bed and fluidized bed gasifiers are the preferred choice for high ash coals.
Gasifier turbine – It is also called gas generator. It is a specific component in a two-shaft gas turbine engine which produces high-pressure, high-temperature gas to drive a separate power turbine. It consists of a compressor, combustion chamber, and turbine, operating on the Brayton cycle to create rotational mechanical energy.
Gasifying agents – These are substances, mainly air, oxygen, steam, or carbon di-oxide, introduced into a gasifier to convert carbonaceous feedstocks (coal, biomass, waste) into usable syngas (carbon mono-oxide and hydrogen) through partial oxidation and chemical reduction. They determine the product composition, calorific value, and process efficiency.
Gas injection – It refers to the technique of introducing gases, such as argon, nitrogen, oxygen, or inert gas mixtures, directly into molten metal (iron, steel, or non-ferrous metals) to refine, stir, or alloy the material. This process is important for removing impurities, controlling temperature, and homogenizing the composition of the liquid metal in ladles, furnaces, or casting moulds. It is also a technique used in oil and gas reservoirs to improve hydrocarbon recovery, maintain pressure, or sequester gas by injecting gases, such as natural gas, carbon di-oxide (CO2), or nitrogen, back into the geological formation. This process improves oil flow by reducing viscosity and increasing reservoir pressure.
Gas injection method – It is frequently called ladle injection or submerged gas injection. It is a technique for refining molten metal (typically steel or aluminum) by blowing gas, or a mixture of gas and powder reagents, directly into the molten bath. This process is mainly used for stirring, degasification, and homogenization of temperature and composition in the liquid metal.
Gas injection pressure – It is the force applied (typically 20 mega-pascals to 30 mega-pascals) to introduce gases like nitrogen or argon into molten metal. It is used to refine, stir, or degas the melt, or in casting to create hollow, lightweight, or complex parts, reducing defects like shrinkage.
Gas injection rate – It is the volume or mass of gas (typically argon, nitrogen, or oxygen) introduced into molten metal per unit of time and / or per ton of metal (e.g., normal cubic meters per hour, or kilo-grams per to). This process is important for stirring, refining, or alloying in furnaces and ladles.
Gas injection system – It refers to equipment which introduces gases (e.g., argon, nitrogen, or reactive gases) into molten metal or onto a sample surface to improve processing. It is used for refining, degassing, alloying, stirring, and controlling solidification, frequently involving techniques like porous plugs, lances, or specialized nozzles.
Gas jet – It is a high-velocity, directed stream of gas, such as air, nitrogen, argon, or helium, released from a nozzle or pressurized containment. It is mainly used to impart substantial kinetic energy, shape materials, or protect against atmospheric contamination.
Gas jet cooling – It is a specialized, high-intensity heat treatment process where non-oxidizing, high-velocity gas jets (normally hydrogen, nitrogen, or argon mixtures) are blown directly onto the surface of a metal component, such as a steel strip or rod, to achieve rapid, controlled quenching. This method is mainly utilized to achieve high cooling rates (e.g., 100 deg C per second to 150 deg C per second) in continuous annealing furnaces for high-tensile steel, providing a non-oxidizing, uniform cooling effect, and preventing distortion.
Gas jet cooling equipment – It is a specialized, high-velocity cooling system designed to rapidly and uniformly lower the temperature of metal products (typically steel strip, pipes, or die-cast parts) by directing high-pressure gas (such as nitrogen, hydrogen or air) onto their surfaces. Unlike liquid cooling, this method prevents thermal distortion and surface oxidation, making it necessary for high-quality, continuous annealing, hardening, and precision casting processes.
Gas jet nozzle – It is a device which controls the direction, shape, speed, and pressure of a high-velocity gas stream as it exits a pipe or chamber, mainly to interact with molten metal, solid particles, or surfaces. These nozzles are important components used for accelerating gases (like oxygen, nitrogen, or argon) to convert pressure energy into kinetic energy, enabling precise, high-energy impact.
Gasket – It is a compressible material, or a combination of materials, which when clamped between two stationary members, it prevents the passage of the media across those members. The gasket material selected is required to be capable of sealing mating surfaces, resistant to the medium being sealed, and able to withstand the application temperatures and pressures. Normally, gaskets are called upon to affect a seal across the faces of contact with the flanges. Permeation of the media through the body of the gasket is also a possibility depending on material, confined media, and acceptable leakage rate.
Gasket lip expansion – This is a phenomenon which occurs due to edge swelling when the gasket is affected by confined fluid. This causes the gasket material to swell and increase the interaction of the gasket against the flange faces.
Gas kick – It is an unexpected and unwanted influx of gas into the wellbore, occurring when the pressure inside the wellbore is less than the formation pressure, leading to the migration of gas upward because of the density differences with the drilling fluid. It poses substantial risks as the gas can retain high pressure while moving through the wellbore.
Gas lance – It is a long, typically water-cooled, steel pipe or tube used to inject gases (very frequently oxygen, but also argon or nitrogen) at high velocity into molten metal inside a furnace or ladle. These lances are important for refining steel by initiating exothermic reactions to remove impurities (like carbon, silicon, and phosphorus), controlling temperature, and providing stirring.
Gas laser – It is a laser in which the lasing medium is a gas.
Gas laws – These laws (e.g., PV = nRT) define how pressure, volume, and temperature affect gases during processes like smelting, refining, and heat treatment. They are critical for controlling reactions, such as the behavior of shielding gases or the removal of dissolved gases to prevent porosity in metal castings.
Gas leakage – It is the uncontrolled release of gases, which poses substantial risks such as suffocation, fire hazards, and long-term health effects because of exposure to harmful pollutants. Early detection of gas leakage is important for ensuring safety in environments and preventing damage to human life and the environment.
Gas lift – It is an artificial lift method which involves injecting external gas into the produced flow stream within a wellbore, which reduces bottom-hole pressure and improves the inflow of produced fluids. This technique is particularly useful for dewatering gas wells and can be adjusted for different liquid production rates.
Gas-lift reactor – It is a type of pneumatically agitated multiphase reactor which uses the difference in gas hold-up between a riser and a downcomer to induce liquid circulation. It is a specialized vessel which drives fluid motion without moving parts, making it efficient for mixing liquids, gases, and solids. It improves hydrogen mass transfer rates in poorly soluble aqueous solutions.
Gas lift valve – It is a specialized, pressure-sensitive mechanical device installed in a side-pocket mandrel (tubing) to control high-pressure gas injection from the casing annulus into the production stream. These valves regulate flow to reduce fluid density, decreasing hydrostatic pressure and lifting oil to the surface.
Gas liquefaction system – It is an assembly of technology, equipment, and processes designed to convert gases (such as oxygen, nitrogen, argon, or hydrogen) into a liquid state by reducing their temperature below their boiling point. This process is necessary for producing high-purity gases for metallurgical processing, such as smelting, refining, and heat treatment, as well as for compact, efficient storage and transport.
Gas-liquid absorption – It is a process in which gas scrubbing with a liquid solvent selectively removes acid gases, such as CO2 (carbon di-oxide) and H2S (hydrogen sulphide), from a gas mixture. This process typically involves an absorption column followed by a desorption column, where the captured gases are released and the solvent is regenerated for reuse.
Gas-liquid ratio – It is a crucial operating parameter defined as the ratio of the volume of gas (or vapour) to the volume of liquid, measured at the same temperature and pressure, or at defined standard conditions. It is a fundamental parameter in gas-liquid reactors, such as packed columns, bubble columns, and agitated tanks, where it is used to control mass transfer, reaction kinetics, and the overall efficiency of processes like leaching, absorption, or smelting.
Gas-liquid reactors – These are equipment which facilitates reactions between gases and liquids, typically operating in the liquid phase and involving mass transfer through gas and liquid films. These reactors are similar in design to those used for gas absorption and can also involve solids as reactants or catalysts.
Gas lubricated bearings – These are frequently referred to as air bearings. These are a type of plain (sliding) bearing which utilizes a gas (normally air) as the lubricating medium to completely separate a moving component from a stationary component, preventing metal-to-metal contact during operation. These are utilized in high-speed, high-precision, and clean-operating applications, such as micro-turbines, gyroscopes, and hard drives.
Gas lubrication – It is a system of lubrication in which the shape and relative motion of the sliding surfaces cause the formation of a gas film having sufficient pressure to separate the surfaces.
Gas masks – These consist of a full-mask face piece, which covers the eyes, nose and mouth, connected either directly or through a non-kink flexible hose to a canister containing a granular sorbent.
Gas mass spectrometry – It is an analytical technique which provides quantitative analysis of gas mixtures through the complete range of elemental and molecular gases.
Gas metal arc – It is a welding process which utilizes a continuous, consumable solid wire electrode and shielding gas to join metals, with energy provided to establish and maintain the arc and melt both the electrode and base metal.
Gas metal arc cutting (GMAC) – It is an arc cutting process which is used to cut metals by melting them with the heat of an arc between a continuous metal (consumable) electrode and the work. Shielding is achieved entirely from an externally supplied gas or gas mixture.
Gas metal arc welding (GMAW) – It is an arc welding in which coalescence of metals is produced by heating them with an arc between a continuous filler metal electrode and the work-pieces. Shielding is achieved entirely from an externally supplied gas.
Gas metal arc welding (GMAW) process – This process is an arc welding process which joins metals together by heating them with an electric arc which is established between a consumable electrode (wire) and the work piece. An externally supplied gas or gas mixture acts to shield the arc and molten weld pool. In the gas metal arc welding process, an arc is established between a continuously fed electrode of filler metal and the work piece. After proper settings are made by the operator, the arc length is maintained at the set value, despite the reasonable changes which are to be expected in the gun-to-work distance during normal operation. This automatic arc regulation is achieved in one of the two ways. The most common method is to utilize a constant-speed (but adjustable) electrode feed unit with a variable-current (constant-voltage) power source. As the gun-to-work relationship changes, which instantaneously alters the arc length, the power source delivers either more current (if the arc length is decreased) or less current (if the arc length is increased). This changes in current causes a corresponding change in the electrode melt-off rate, thus maintaining the desired arc length. The characteristics of the gas metal arc welding process are best described by reviewing the three basic means by which metal is transferred from the electrode to the work namely (i) short-circuiting transfer, (ii) globular transfer, or (iii) spray transfer. The type of transfer is determined by a number of factors. The gas metal arc welding process can be operated in semi-automatic and automatic modes. All commercially important metals, such as carbon steel, high-strength low-alloy steel, stainless steel, and aluminum, copper, and nickel alloys can be welded in all positions by this process if appropriate shielding gases, electrodes, and welding parameters are chosen. The advantages make the process particularly well suited to high production and automated welding applications.
Gas migration – It refers to the undesired movement or entrapment of gas bubbles / voids within a molten or solidifying material. It is a process driven by buoyancy and pressure gradients, frequently leading to porosity, defects, or failure in the final component.
Gas mixing – It is also called gas blending. It refers to the process of combining two or more pure gases in precise, controlled proportions to create a specific, homogeneous mixture tailored for a particular industrial application. It involves the, regulation of flow rates, pressure, and, at times, temperature, to ensure the resulting mixture meets exact, consistent, and required specifications.
Gas mixture – It is a homogeneous combination of two or more gases or vapours (such as nitrogen, argon, oxygen, carbon di-oxide, or hydrogen) which do not react with each other at the operating temperature. These mixtures are designed for specific industrial, metallurgical, or analytical processes to control the atmosphere, prevent oxidation, or facilitate reactions.
Gas model – It refers to a mathematical or physical simulation used to represent the behaviour of gases (inert shielding gases, process gases, or gas bubbles) in metallurgical reactors, such as furnaces, ladles, and casting systems. These models are important for understanding fluid flow, heat transfer / mass transfer, and chemical reactions (e.g., in steel refining, degassing, and gas atomization) where direct observation is impossible because of the high temperatures.
Gas molecules – These are individual particles (atoms or compounds) in constant, rapid, and random motion, possessing high kinetic energy and weak intermolecular forces. They occupy a tiny fraction of the total gas volume, allowing for high compressibility, and they expand to fill any container.
Gas nitriding – It is a thermo-chemical surface-hardening heat treatment process which increases the hardness, wear resistance, and fatigue life of ferrous alloys (typically steel and cast iron) by diffusing nitrogen into the surface at temperatures below the transformation temperature, normally between 500 deg C and 590 deg C. This process relies on an ammonia-rich atmosphere (NH) which dissociates upon contact with the heated metal surface, releasing atomic nitrogen which then diffuses into the metal to form hard nitrides.
Gas oil – It is a refined petroleum distillate with a boiling range typically between 200 deg C and 370 deg C, situated between kerosene and lubricating oil. It is a middle distillate used mainly as diesel fuel, heating oil, and a feedstock for catalytic cracking units.
Gas-oil ratio – It is a key parameter defined as the ratio of the volume of gas (Vg) produced at surface standard conditions to the volume of oil (Vo) produced at surface standard conditions. Measured in ‘standard cubic feet per stock tank barrel’ or standard cubic meters per cubic meter, it is crucial for monitoring reservoir pressure, optimizing production, and designing surface processing equipment.
Gasoline – It is also called petrol. It is a refined, volatile, flammable, and complex mixture of hydrocarbon compounds (C3 to C12), mainly used as fuel in spark-ignition internal combustion engines. Produced through refining processes like fractional distillation, cracking, and reforming, it is engineered for specific volatility, boiling ranges (38 deg C to 205 deg C), and high-octane ratings to prevent pre-ignition.
Gasoline direct injection engines – These are internal combustion engines which spray fuel directly into the combustion chamber rather than the intake manifold. By utilizing high-pressure injectors (up to 35 plus mega-pascals) during the compression or intake stroke, gasoline direct injection improves fuel atomization, increases volumetric efficiency, allows higher compression ratios, and enables cooler, more precise combustion for better performance and lower carbon di-oxide emissions.
Gasoline engine – It is an internal-combustion engine which converts chemical energy from gasoline into mechanical energy through spark-ignition. It draws in a fuel-air mixture, compresses it, and ignites it using a spark plug to drive pistons, operating on either a four-stroke or two-stroke cycle.
Gasoline particulate filter – It is an exhaust after-treatment device, typically made of ceramic (cordierite), which captures soot and fine particulate matter (PM2.5) from ‘gasoline direct injection’ (GDI) engines. It uses a honeycomb structure to trap particles, reducing emissions by over 90 %, and normally regenerates passively because of high exhaust temperatures.
Gasoline refining – It is a complex, multi-stage process which converts raw crude oil into usable, high-octane fuel. It utilizes physical separation (distillation) and chemical conversion (cracking, reforming) to break down heavy hydrocarbons, remove impurities like sulphur, and blend components to meet specific engine performance standards.
Gasoline substitution – It is the process of replacing conventional petroleum-based gasoline in spark-ignition engines with alternative fuels, such as ethanol, methanol, or bio-derived hydrocarbons. to reduce emissions and dependence on fossil fuels. It involves blending fuels or modifying engine components (e.g., fuel systems, compression ratios) to maintain performance.
Gas permeation – It is the process where gas molecules (such as hydrogen, oxygen, or nitrogen) dissolve into, diffuse through, and desorb from a solid metal lattice or porous structure, moving from a region of high concentration / pressure to low concentration. It is a critical factor in understanding hydrogen embrittlement, porosity formation in castings, and high-temperature oxidation.
Gas permeation process – It is a diffusive transport process where gas molecules (frequently hydrogen) move through a solid metal or alloy, driven by a concentration or partial pressure gradient, frequently from a high-pressure to a low-pressure region. This phenomenon is important, as it normally refers to the involuntary, slow, and frequently detrimental migration of gases through metallic barriers, which can lead to material degradation, such as hydrogen embrittlement, blistering, and internal cracking.
Gas permeation rate – it is also called gas permeation flux. It is the volume or molar quantity of gas which passes through a solid metal barrier per unit area per unit time, normally under a specific pressure and temperature gradient. It is a measure of how quickly a gas (normally hydrogen) moves through a metal, frequently leading to degradation, corrosion, or embrittlement.
Gas permeation unit – It is the ratio of the molar flux of a penetrant gas to the pressure difference between the feed and penetrant gas. It is a measure of a membrane’s ability to allow gas flow, defined as 0.000001 cubic centimeter (standard temperature and pressure, STP) / (square centimeter . second . centimeter mercury, Hg). It represents the pressure-normalized flux (permeance) of a gas, typically used to quantify how quickly gases pass through materials like polymers or thin metallic sheets.
Gas phase – It is a state of matter, typically a mixture of gases, characterized by low density, high mobility, and high compressibility. It is a critical component in processes like chemical vapour deposition (CVD), smelting, and gas-phase nano-particle synthesis, where it facilitates mass transfer and atomic-level reactions, such as coating or coating materials.
Gas pipelines – These are specialized, high-strength, steel-based infrastructure systems designed for the long-distance transport of natural gas from production sites (wells, offshore platforms) to distribution networks, industrial, or residential consumers. These systems operate under high pressure and consist of interconnected networks, including gathering, transmission, and distribution lines. Gas pipelines are manufactured to strictly controlled, high-strength specifications designed to handle internal pressure, environmental factors, and fatigue over long, efficient, and safe operation.
Gas pipeline steel – It is a specialized type of high-strength, low-alloy (HSLA) steel, or advanced carbon steel, designed specifically for the safe and efficient transport of natural gas, hydrogen, and other hydrocarbons. These steels are defined by their superior combination of high tensile strength, very good toughness, and high weldability, which are important for resisting high-pressure, environmental stressors, and ensuring long-term structural integrity.
Gas piping systems – These are engineered, interconnected networks of pipes, valves, fittings, and safety components designed to transport flammable gases (such as natural gas or coke oven gas) from a source to end-user equipment. The materials used for the gas piping system needs to possess the necessary strength, fracture toughness, and corrosion resistance to safely contain gases, frequently under high pressure.’
Gas plasma – It is frequently referred to as plasma gas or simply plasma. It is the fourth state of matter, a high-energy, ionized gas consisting of free electrons, positive ions, and neutral particles (atoms, molecules, and radicals). It is distinguished from ordinary gas by its ability to conduct electricity and its strong response to electromagnetic fields. Gas plasma is used for its high thermal performance, extreme chemical reactivity, and ability to operate in controlled atmospheres.
Gas pocket – It is a cavity caused by entrapped gas. It is a void or cavity formed inside a metal casting or weld when gas becomes trapped as the molten material solidifies. Frequently appearing as rounded, hollow cavities (porosity), these defects are caused by gas evolution, entrapment, or dissolved gases during cooling, which can weaken the structure and affect structural integrity.
Gas poisoning – It refers to the acute or chronic toxic effects, injury, or fatality resulting from the inhalation of harmful gases or fumes produced during metal smelting, refining, welding, or cutting processes. It occurs when toxic vapours exceed allowable exposure limits, causing damage to cells, tissues, and the nervous system. Key toxic gases include carbon mono-oxide (CO), hydrogen sulphide (H2S), sulphur di-oxide (SO2), nitrogen oxides (NOx), and ammonia (NH3).
Gas porosity – It consists of fine holes or pores within a metal which are caused by entrapped gas or by the evolution of dissolved gas during solidification.
Gas power cycle – It is a thermodynamic cycle using a gas (typically air) as the working fluid, which remains gaseous throughout a repeated series of operations (compression, heat addition, expansion, and heat rejection) to convert heat into mechanical work. These cycles model engines like gas turbines (Brayton cycle) and internal combustion engines (Otto / diesel cycles).
Gas pressure – It is the force per unit area exerted by gas molecules colliding with the interior surfaces of a furnace, vacuum chamber, or within molten metal, defined by P = F/A. It is important for controlling processes like degassing, atmosphere heat treating, and preventing defects. Gas pressure is the result of countless gas molecules in constant, random motion colliding with the walls of a container.
Gas pressure regulator – It is a spring loaded, dead weighted or pressure balanced device which maintains the gas pressure to the burner supply line.
Gas processing – It involves purifying industrial gases (oxygen, nitrogen, argon, hydrogen) for metal production using methods like cryogenic distillation, adsorption, or membrane separation. It also includes treating process gases (e.g., in steelmaking or heat treatment) to remove impurities and control furnace atmospheres for consistent, high-quality metal products.
Gas production – It refers to the generation, separation, and supply of industrial gases (mainly oxygen, nitrogen, argon, and hydrogen) used to facilitate the production, refining, and processing of steel and non-ferrous metals. These gases are necessry for oxidation, reduction, protection, and agitation during high-temperature metallurgical operations.
Gas quenching – In gas quenching, the quenching medium remains gaseous throughout, and there are no phase transitions as with liquid quenchants. The only cooling mechanism is convection.
Gas recirculation – It is frequently referred to as ‘flue gas recirculation’ (FGR). It is a technique which involves diverting a portion of the exhaust gas (flue gas) from the furnace or combustion chamber and reintroducing it into the combustion air or directly into the chamber. This process is mainly used to control combustion characteristics, reduce pollutant emissions, and improve energy efficiency.
Gas-recycle – It is the process of collecting, cleaning, and reintroducing process gases (such as carbon mono-oxide, hydrogen, or carbon di-oxide) back into a metallurgical reactor (like a blast furnace or smelter) to improve thermal efficiency, reduce agent consumption, and minimize environmental emissions. It is a key component of sustainable steelmaking, such as ‘top gas recycling blast furnace’ (TGR-BF) technology.
Gas regulator – It is a device for controlling the delivery of gas at some substantially constant pressure.
Gas reservoir – It is a subsurface area where natural gas is trapped and accumulated within porous and permeable rock formations, typically sandstone or carbonate rocks, and is sealed by impermeable rock. These reservoirs are formed over geological time as natural gas migrates from source rocks and is trapped by structural or stratigraphic features.
Gas reservoir simulation – It is a specialized area of petroleum engineering which utilizes computer models and numerical calculations to replicate, analyze, and predict the behaviour of natural gas within underground porous rock formations over time. It acts as a digital, dynamic representation of a reservoir, integrating geological data (structure, porosity, permeability) with fluid properties (pressure-volume-temperature data, gas-water-condensate phases) to forecast production performance and optimize development strategies.
Gas response – It is the measure of the change in a physical or electrical property of the sensing material (typically resistance or conductivity) upon exposure to a specific gas, compared to its state in a baseline gas (normally air).
Gas saturation – It refers to the concentration of dissolved gases (such as hydrogen, oxygen, or nitrogen) within a molten or solid metal, frequently reaching a maximum limit (saturation) at a specific temperature and pressure. This is a critical factor in physical metallurgy and casting, as it affects the solubility and removal of gases to prevent defects like porosity, brittleness, or internal cracking during solidification.
Gas seal – It is a non-contacting, dry-running mechanical face seal used on rotating machinery (like compressors) to prevent process gas leakage. It uses specialized, high-strength materials (frequently tungsten carbide or silicon carbide) on mating rings with machined grooves to create a gas-lubricated barrier, eliminating the need for oil lubrication.
Gas seal system – It is a non-contacting, dry-running mechanical face seal that uses filtered, high-pressure process gas or nitrogen to create a 3 micro-meter to 10 micro-meter fluid film barrier between rotating and stationary rings, preventing process leakage. Normally used in centrifugal compressors, it eliminates oil contamination and reduces maintenance compared to wet seals.
Gas sensor – It is a solid-state device that detects and quantifies specific hazardous or process gases (e.g., carbon mono-oxide, hydrogen, nitrogen di-oxide) in industrial environments by converting chemical reactions with a metal oxide (e.g., tin oxide, SnO2) sensing layer into electrical signals. They are important for safety in furnaces, mines, and refineries.
Gas separation unit – It is a system designed to isolate, purify, or recover specific gas components from a mixed gas stream, or to separate gas from liquid / solid mixtures in metallurgical processes. These units are necessary for improving combustion, protecting equipment from corrosion, and creating controlled atmospheres for smelting, refining, and heat-treating metals.
Gas separator – It is a pressure vessel which separates gas from gas-liquid mixed fluid.
Gas shielded arc welding – It is also an electric fusion welding process. In this process, the weld pool is produced by the effects of an electric arc. The arc is quite visible as it burns between the electrode and the work piece. The electrode, arc, and weld pool are protected against the atmosphere by an inert or active shield gas which is constantly fed into the weld area. The gas shield arc welding processes are classified according to the type of electrodes and the gas used. These are normally divided into two main categories. The categories are (i) gas tungsten arc welding (GTAW) namely TIG (tungsten inert gas), and THG (tungsten hydrogen gas) arc welding, and (ii) gas metal arc welding (GMAW) namely MIG (metal inert gas), and MAG (metal active gas) welding.
Gas shut off valve, blast furnace – This valve is used for separation of a gas burner from the hot blast stove under ‘on-blast’ operation of the stove. It facilitates fast and safe changing of stove from ‘gas’ to ‘blast’. It is normally a water-cooled valve. The valve opens or closes quite fast (in around 10 seconds) to complete the stove changing cycle, and incorporates electro-mechanical actuator. The valve has normally steel fabricated construction, is self-supporting, and needs small space.
Gas-solid reactor – It is a vessel (e.g., blast furnace, rotary kiln, fluidized bed) where gaseous reactants (like hydrogen, carbon mono-oxide, oxygen) interact with solid materials (ores, metals, pellets) to facilitate chemical reactions such as reduction, oxidation, or roasting. These reactors are designed to maximize contact surface area for efficient heat and mass transfer
Gassing – It is the absorption of gas by a metal. It is also evolution of gas from a metal during melting operations or upon solidification. Gassing is also evolution of gas from an electrode during electrolysis.
Gas species – These refer to individual gaseous components (e.g., oxygen, hydrogen, nitrogen, carbon mono-oxide, carbon di-oxide, hydrogen sulphide) involved in high-temperature chemical reactions, phase transformations, or transport processes within smelting, refining, or heating operations.
Gas spring – In this spring, the spring action is provided by a volume of gas which is compressed.
Gas storage – It refers to the methods, materials, and systems used to contain, hold, and manage gases (such as hydrogen, natural gas, or specialty industrial gases) under specific pressure, temperature, or adsorption conditions. It consists of the design of containment vessels, pressure tanks, and the study of how gases interact with metals, including absorption, adsorption, and embrittlement.
Gas streams – These refer to the continuous, controlled flow of gases, such as oxygen, nitrogen, argon, hydrogen, or combustion products, used in processing, shielding, or refining metals. These streams are important for maintaining specific atmospheres, removing impurities, or altering chemical composition at high temperatures.
Gas stripping – It is a physical separation process, or unit operation, used to remove dissolved gases or volatile impurities from a molten metal or liquid metallurgical solution by bubbling an inert or reactive gas through it. This technique relies on mass transfer principles, specifically designed to drive a solute from the liquid phase into the gas phase, often to refine the metal or regenerate a solvent.
Gas suction – It refers to the intentional removal of gases (such as hydrogen, oxygen, or nitrogen) from molten metal or the surrounding processing environment by reducing the pressure, frequently utilizing a vacuum or a vacuum-assisted process. This technique is used to prevent metallurgical defects like porosity, brittleness, and poor surface quality, which can reduce the strength and plasticity of the final metal component.
Gas supply – It refers to the systems, infrastructure, and management processes designed to store, transport, and deliver industrial gases, such as oxygen, nitrogen, argon, hydrogen, and acetylene, to different production units (furnaces, casting machines, welding stations) for heating, protective atmosphere creation, or process improvement. These systems ensure an uninterrupted, safe, and regulated flow of gas to meet high-temperature, chemical-process, or shielding needs.
Gas suspension calcination kilns – Gas suspension calcination (GSC) kilns are a technique for minerals processing, such as the calcination of limestone, dolomite and magnesite from pulverized raw materials to produce highly reactive and uniform products. Most of the processes in the gas suspension calcination kiln plant, such as drying, preheating, calcination and cooling, are performed in gas suspension. Hence, the plant consists of stationary equipment and a few moving components. The amount of material present in the system is negligible, which means that after a few minutes of operation, the product conforms to specifications. There is no loss of material or quality during start-up and shut-down so there is no sub-grade product. The gas suspension calcination process produces a product with high reactivity, even when calcined to a high degree. The material to be processed in the gas suspension is required to have a suitable fineness. The practical experience has shown that 2 millimeters particle size is not to be exceeded.
Gas temperature – It refers to the thermal state of gases (such as shielding, atmosphere, or flue gases) involved in processes like welding, smelting, or heat treatment. It is fundamentally defined as a measure of the average translational kinetic energy of the gas molecules.
Gas testing – It can be divided into 2 categories, namely high-pressure and low-pressure gas testing. Both these tests are considered supplementary test requirements within the API 6D specification. For the low-pressure gas test, nitrogen is very frequently used along with acceptance criteria based on ISO 5208.For the high-pressure gas test, the standard hydrostatics seat test required by API 6D is carried out using an inert gas (normally helium) as the test medium.
Gas thermal conductivity – It is the ability of gas molecules within a furnace or heat-treating atmosphere to transfer heat through collisions, proportional to the gas’s specific heat, density, and mean free path. It is a critical parameter in determining heat transfer efficiency in heat treatment, normally increasing with temperature and influencing how gas atmospheres heat or cool metals.
Gas thermometer – It is a thermometer which measures temperature by the variation in volume or pressure of a gas. This thermometer functions by Charles’s law which states that when the temperature of a gas increases, so does the volume.
Gas throughput – It is the quantity of gas (expressed as the product of pressure and volume) which passes through a specific plane or pipe cross-section per unit of time. It represents the rate of mass flow of gas and is an important parameter in vacuum-based metallurgical processes like vacuum induction melting (VIM), vacuum arc remelting (VAR), and physical vapour deposition (PVD).
Gas to liquids (GTL) conversion – It is a process to convert natural gas or other gaseous hydro-carbons into longer-chain hydrocarbons, such as gasoline or diesel fuel. Methane-rich gases are converted into liquid synthetic fuels. Two general strategies exist, which are (i) direct partial combustion of methane to methanol and (ii) Fischer–Tropsch-like processes which convert carbon mono-oxide and hydrogen into hydro-carbons. Strategy ii is followed by diverse methods to convert the hydrogen-carbon mono-oxide mixtures to liquids. Direct partial combustion has been demonstrated in nature but not replicated commercially. Technologies reliant on partial combustion have been commercialized mainly in regions where natural gas is inexpensive. The motivation for gas to liquid conversion is to produce liquid fuels, which are more readily transported than methane. Methane is to be cooled below its critical temperature of −82.3 deg C in order to be liquified under pressure.
Gas-to-liquid technology – It refers to a set of industrial processes which convert stranded or low-value gaseous hydrocarbons (mainly methane from natural gas) into higher-value, clean-burning, liquid synthetic fuels (like diesel, kerosene, or naphtha) and chemical feedstocks, often using Fischer-Tropsch (F-T) synthesis. Gas-to-liquid (GTL) technology is used to produce liquid hydrocarbon products which can be used as reducing agents or to improve the economics of mining operations, particularly in remote areas.
Gas-to-methanol process – It is a technique that converts natural gas (mainly methane) into methanol (CH3OH) through a multi-stage process involving syngas production and catalytic synthesis. It is a key technology for converting stranded or flared gas into a valuable, transportable liquid fuel.
Gas to power – It refers to the process of converting combustible gases, frequently by-products of metallurgical processes, into electrical or mechanical energy. It is an important component of energy recovery systems, enabling steel plants to reduce energy costs and environmental impact by utilizing waste gases to generate electricity rather than flaring them.
Gas torch – It is a torch used for cutting and welding of metals. It is also known as cutting torch (arc), cutting torch (oxy-fuel gas), welding torch (arc), and welding torch (oxy-fuel gas).
Gas tracer method (technique) – It is used for the precise measurement of volumetric flow rates through small ducts or pipes. The procedure entails spiking the effluent with a known quantity of a ‘tracer gas’ and measuring the concentration of the tracer compound downstream of the injection point after allowing for complete mixing. The tracer compound is selected based on knowledge of the process. The tracer compound is required to be a stable, non-reactive gas which is not otherwise found in the native effluent.
Gas transmission rate – It is a measure of the permeability of a packaging film to gases by measuring the movement of a gas through the film under specified conditions.
Gas treatment – It refers to the industrial processes used to remove contaminants, impurities, and particulate matter from gas streams (such as flue gas or process gas) produced during mining, smelting, and refining operations. These systems are important for ensuring environmental compliance by cleaning emissions before release, as well as protecting downstream equipment from corrosion, erosion, or clogging.
Gas tungsten arc cutting (GTAC) – It is an arc-cutting process in which metals are cut by melting them with an arc between a single tungsten (non-consumable) electrode and the work-piece. Shielding is achieved from a gas or gas mixture.
Gas tungsten arc welding (GTAW) – It is an arc welding coalescence of metals is produced by heating them with an arc between a tungsten (non-consumable) electrode and the work. Shielding is achieved from a gas or gas mixture. Pressure and filler metal may or may not be used.
Gas tungsten arc welding (GTAW) process – This process is also known as HeliArc, tungsten inert gas (TIG), and tungsten arc welding. The melting temperature necessary to weld materials in the gas tungsten arc welding process is achieved by maintaining an arc between a tungsten alloy electrode and the work-piece. Weld pool temperatures can approach 2,500 deg C. An inert gas sustains the arc and protects the molten metal from atmospheric contamination. The inert gas is normally argon, helium, or a mixture of helium and argon. This process is used extensively for welding stainless steel, aluminum, magnesium, copper, and reactive materials (e.g., titanium and tantalum). The process can also be used to join carbon and alloy steels. In carbon steels, it is mainly used for root-pass welding with the application of consumable inserts or open-root techniques on pipe. The materials welded range from 0.05 mm to several millimeters in thickness. The gas tungsten arc welding process is applicable when the highest weld quality is needed.
Gas turbine – It is a rotary, internal combustion engine which extracts energy from a flow of hot gas produced by the combustion of fuel. It operates on the Brayton cycle and consists of three main components: a compressor, a combustion chamber (or combustor), and a turbine.
Gas turbine combined cycle power plant – It integrates a high-temperature Brayton cycle (gas turbine) with a lower-temperature Rankine cycle (steam turbine) to maximize efficiency, frequently exceeding 58 % to 59 %. It uses exhaust heat from the gas turbine in a ‘heat recovery steam generator’ (HRSG) to produce steam, driving a second turbine. Advanced materials, such as nickel-based superalloys and thermal barrier coatings, are necessary for handling turbine inlet temperatures of 1,200 deg C to 1,400 deg C.
Gas turbine combustion – It is the continuous, high-pressure, constant-pressure oxidation of fuel (e.g., natural gas) in compressed air to produce high-temperature gas for turbine expansion. It operates on the Brayton cycle, typically using can, annular, or can-annular chambers, frequently with air staging. It needs high-temperature, corrosion-resistant alloys (e.g., superalloys) to withstand thermal oxidation, creeping, and chemical damage within the combustor and turbine, particularly when using catalysts like palladium.
Gas turbine combustor – It is called gas turbine burner. It is the component in a gas turbine engine where fuel is mixed with high-pressure air from the compressor and ignited to produce high-temperature gas. It acts as a flow duct designed to stabilize the flame and operates under extreme conditions, frequently using nickel-based or cobalt-based superalloys for high-temperature strength, corrosion resistance, and thermal barrier coatings.
Gas turbine cycle – It is a thermodynamic power cycle, mainly the Brayton cycle, which converts chemical energy from fuel into mechanical energy. It is a continuous-flow, internal combustion process normally used for electricity generation, aviation propulsion, and industrial drives. The cycle consists of four main phases: isentropic compression, constant pressure heat addition (combustion), isentropic expansion, and heat rejection.
Gas turbine engine – It is a type of continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas generator or core) and in the direction of flow are a rotating gas compressor, a combustor, and a compressor-driving turbine. Additional components have to be added to the gas generator to suit its application.
Gas turbine plant – It is a type of internal combustion, thermal power plant which converts chemical energy from fuels (such as natural gas or diesel) into mechanical energy using the Brayton cycle, a process of continuous compression, combustion, and expansion. These plants are widely used for electricity generation, particularly for peak-load demand because of their rapid start-up times.
Gas turbine system – It is an energy conversion system which operates on the Brayton thermodynamic cycle and is typically fueled by natural gas or other fuels, with applications ranging from a portion of a megawatt to hundreds of megawatts. The most common type is the open-cycle gas turbine, although closed-cycle variants also exist.
Gas turbine tests – These are important procedures conducted to evaluate the material integrity, structural soundness, and degradation of high-temperature components (blades, vanes, rotors) under operational stresses, thermal fatigue, and corrosion. These tests are necessary during manufacturing, after overhauls, or during maintenance to ensure compliance with design specifications and to prevent catastrophic failures.
Gas turbine unit – It is a rotary internal combustion engine that converts fuel (natural gas, oil, or synthetic fuel) into mechanical energy using the Brayton cycle. It consists of three main components namely a compressor (axial or centrifugal) to compress ambient air, a combustor to heat the air, and a turbine to expand the gas and produce shaft power, which drives the compressor and a load, such as an electric generator. The main parts include the rotor, compressor / turbine blades and vanes, journal / thrust bearings, combustion chamber, and exhaust diffuser.
Gas velocity – It refers to the speed at which process gases move through a reactor, vessel, or nozzle, typically defined as the superficial gas velocity. Superficial gas velocity is calculated as the volumetric flow rate of the gas divided by the cross-sectional area of the containment vessel or furnace.
Gas welding – Gas welding joins metals by heating the materials to be joined so they can melt and fuse. It is the process of joining two metal items together by melting and cooling parts of both. This is achieved by creating a very hot flame using oxygen and a fuel gas. There are a few main types of gas welding which use different gases such as acetylene, gasoline, natural gas, MAPP (methylacetylene-propadiene propane), butane, propane, or hydrogen. Gas welding equipment includes a welding torch, control valves for fuel and oxygen and cylinders for both gases.
Gas well – It is a borehole designed to extract natural gas from geological formations, typically producing minimal to no crude oil. These wells are characterized by high-pressure, high-temperature environments, frequently containing corrosive elements such as hydrogen sulphide (H2S) and carbon di-oxide (CO2), needing specialized, durable metal alloys for equipment.
Gas well deliverability – It is the calculated or measured ability of a well to produce gas at specific flow rates against varying backpressures (wellhead / bottomhole). It defines the relationship between reservoir pressure and flow rate, often determined by back-pressure or 4-point tests to evaluate reservoir performance and future capacity. It represents the maximum rate at which a well can produce, accounting for restrictions in the wellbore, tubing, and reservoir (e.g., formation damage).
Gas well performance – It defines a well’s ability to produce gas by analyzing deliverability, pressure drop, and flow rates using data from transient tests and production history. This involves selecting materials, e.g., corrosion resistant alloy (CRA), carbon steel, which withstand corrosion (carbon di-oxide, hydrogen sulphide), erosion, and high-pressure / temperature conditions to maintain structural integrity and flow efficiency over time.
Gate – It is the portion of the runner in a mould through which molten metal enters the mould cavity. The generic term is sometimes applied to the entire network of connecting channels which conduct metal into the mould cavity. Gate is also the closure element of a gate valve. It is also a moving piece which is used to control the flow of glass into a revolving pot of a suction fed machine. In case of a conveying system, a gate is a conveyor segment equipped with a hinge mechanism, creating an opening for walkway access, operated manually or with a spring-loaded mechanism. In digital electronics, gate means a circuit whose output is a 1 only for some specified combination of inputs. This type of circuit is sometimes referred to as a combinational circuit. Gates implement Boolean functions (AND, OR, NOT, NAND, NOR, XOR, XNOR) to process data and make logical decisions.
Gate area – It is the cross-sectional area of the channel through which molten metal finally enters the mould cavity. It is an important component of the gating system, designed to control the flow rate, velocity, and temperature distribution of the molten metal to ensure a sound casting.
Gate bias – It is the electrical potential difference applied between the gate and source terminals of a transistor. It is used to regulate the flow of current between the drain and source by establishing an electrical field in the dielectric layer, hence controlling the carrier density in the channel.
Gate capacitance – It refers to the total capacitance associated with the gate electrode of a semi-conductor device, such as a MOSFET (metal oxide semiconductor field effect transistor) or TFT (thin-film transistor), defined as the ratio of the change in gate charge to the change in gate voltage. it is an important parameter determined by the interaction between the gate metal / material, the insulating dielectric layer, and the semiconductor channel.
Gate charge – It is the total electrical charge (measured in nano-coulombs, nC) needed to switch a power MOSFET (metal oxide semiconductor field effect transistor) or IGBT (insulated gate bipolar transistor) from an OFF to ON state, important for determining switching speed, driver requirements, and power losses. It is not a single capacitance value, but rather the integral of current over time, covering the charging of gate-source and Miller capacitances.
Gate circuit – It is a basic component of logical circuits which performs simple logic actions such as AND, OR, and NOT, and can be analyzed using truth tables to determine the output for every possible combination of inputs.
Gate dielectric – It is an essential, ultra-thin insulating layer (frequently silicon oxide, SiO2 or high-k materials like HfO2) placed between the gate electrode and the channel in a transistor. It prevents gate leakage current while allowing the electric field to control the conductive channel’s charge density.
Gated pattern – In foundry practice, it is a pattern which includes not only the contours of the part to be cast but also the gates.
Gate drive circuit – It is a power amplifier / interface bridging low-power controllers, e.g., micro-controller unit (MCUs), digital signal processor (DSPs) and high-power switches, e.g., MOSFETs (metal oxide semiconductor field effect transistors) or IGBTs (insulated gate bipolar transistors). It converts low-level pulse-width modulation (PWM) signals into the high-current, precise voltage required to rapidly turn switches on / off, ensuring efficient power conversion, protection, and isolation.
Gate driver – It is a power amplifier which accepts a low-power input from a controller integrated circuit (IC) and produces a high-current drive input for the gate of a high-power transistor such as an insulated gate bi-polar transistor (IGBT) or metal-oxide-semiconductor field-effect transistor (MOSFET). Gate drivers can be provided either on-chip or as a discrete module.
Gate drive signal – It is a low-power, high-frequency voltage pulse, e.g., pulse-width modulation (PWM) generated by a controller and amplified to switch power devices like metal-oxide-semiconductor field-effect transistors (MOSFETs) or insulated gate bi-polar transistors (IGBTs) on and off. It acts as an interface to provide necessary voltage and current to charge / discharge input capacitance, reducing switching losses.
Gated system – It is the complete assembly of sprues, runners, and gates in a mould through which metal flows to enter the casting cavity. This term also applies to equivalent portions of the pattern.
Gate electrode – It is a conductive material (typically doped poly-silicon or metal) deposited over a thin insulator (dielectric) in a field-effect transistor (FET). It acts as a control terminal, using applied voltage to modulate the electric field and regulate current flow between the source and drain terminals.
Gate function – It is a logical operation performed by a gate circuit, which processes input signals as per specific rules, such as AND or OR, with the possibility of active high or active low configurations determined by the presence or absence of inversion circles in the circuit symbol.
Gate-induced drain leakage – It refers to the tunneling-based leakage currents which occur where the gate overlaps the drain, induced by strong vertical and longitudinal electric fields which can lead to deep depletion and trap-assisted carrier generation. Gate-induced drain leakage contributes to standby power loss and excessive heat dissipation in devices.
Gatekeeper – It is an entity which mediates or controls the flow of information or resources between different portions of a network.
Gate network – It is a collection of interconnected logic gates (AND, OR, NOT, etc.) which perform complex Boolean, arithmetic, or switching operations on digital inputs to produce a specific output. These networks are fundamental in digital design, forming circuits like multiplexers, adders, and flip-flops within VLSI (very large-scale integration) systems.
Gate opening – It is a section of the conveyor system which facilitates an access point for human operators to pass through.
Gate oxide – It is an important, extremely thin insulating layer of silicon di-oxide (SiO2), or increasingly, high-κ dielectric materials, situated between the gate electrode and the channel in a MOSFET (metal-oxide-semiconductor field-effect transistor). It acts as a capacitive dielectric which controls the drain-source current through applied voltage while preventing gate leakage.
Gate stack – It is the critical multi-layer structure in a MOSFET (metal-oxide-semiconductor field-effect transistor), consisting of the metal gate electrode, dielectric (insulator), and semiconductor channel, which controls current flow. It acts as a capacitor, where voltage applied to the gate modulates charge in the channel to manage transistor switching and leakage.
Gate thickness – It refers to the dimension of the restriction through which material (molten plastic in injection moulding or metal in casting) flows into a mould cavity. It is an important parameter which determines the quality of the filling, solidification, and packing behaviour of the part.
Gate-to-gate analysis – It is a partial ‘life cycle assessment’ (LCA) which evaluates environmental impacts solely within a manufacturing facility’s boundaries, from raw material entry to product exit. It focuses on production efficiency, energy use, and waste, excluding raw material extraction, transportation, and end-of-life disposal.
Gate turn-off thyristor – It is a four-layer power semi-conductor device which can be turned on and off by signals at a control (gate) terminal.
Gate valve – A gate valve is a linear motion valve used to start or stop fluid flow. However, it does not regulate or throttle flow. The name gate is derived from the appearance of the disk in the flow stream. The disk of a gate valve is completely removed from the flow stream when the valve is fully open. This characteristic offers virtually no resistance to flow when the valve is open. Hence, there is little pressure drop across an open gate valve. When the valve is fully closed, a disk-to-seal ring contact surface exists for 360-degree, and good sealing is provided. With the proper mating of a disk to the seal ring, very little or no leakage occurs across the disk when the gate valve is closed. Gate valve is a straight-through pattern valve whose closure element is a wedge or parallel-sided slab, situated between two fixed seating surfaces, with means to move it in or out of the flow stream in a direction perpendicular to the pipeline axis.
Gate voltage – It is the electrical potential difference applied between the gate and source terminals of a field-effect transistor (FET), acting as the main control signal to modulate the conductive channel between the drain and source. It controls current flow by creating or depleting a channel of charge carriers, enabling, stopping, or amplifying the current based on whether the voltage exceeds the threshold voltage.
Gate width – It is the dimension of a transistor’s gate electrode measured perpendicular to the direction of current flow, determining the channel’s width and directly affecting the transistor’s current-carrying capacity, transconductance, and, inversely, its gate resistance. A larger gate width allows for a higher drain current and trans-conductance, increasing the device’s switching speed and power handling.
Gathering – It is a forging operation which increases the cross section of part of the stock. It is normally a preliminary operation.
Gathering stock – It is an operation whereby the cross section of a portion of the forging stock is increased beyond its original size.
Gating – It is a system for casting metal involving a mould with a channel or opening into which the molten metal is poured. It is also the process of controlling the operation of an electronic device by means of a gate, a signal which makes an electronic circuit operative or inoperative either for a certain time interval or until another signal is received.
Gating design – It is the engineering of the network of channels (pouring basin, sprue, runners, gates) which delivers molten metal into a mould cavity. It aims to fill the mould quickly, smoothly, and without turbulence to prevent defects like sand erosion, dross, or gas entrapment. Key components, such as tapered sprues and risers, are optimized to control flow velocity, maintain thermal gradients, and ensure sound castings.
Gating system – Gating is the term used to describe all of the passages leading to the casting cavity. When molten metal is poured into a mould, it is poured into the pouring basin or cup. It travels down the sprue through the runner into the feeder or riser then through the gate into the casting cavity. The gate is the breaking point at the casting from which the gating system is separated from the casting.
Gatorizing – This method consists of (i) pre-conditioning the stock under controlled conditions to secure a temporary condition of low strength and high ductility, (ii) hot working to the desired shape while maintaining those attributes, and (iii) restoring normal properties to the work-piece through heat treatment. With gatorizing, hard-to-work nickel alloys have been forged for the first time, and the higher strength which can be got from these alloys resulted in higher strength-to-weight ratios in aircraft components such as jet engine disks. This process also led to development of techniques for isothermal forging of integrally bladed engine rotors (disks of super-alloys forged integrally with ceramic blades).
Gauge – It is the thickness of sheet or the diameter of wire. The different standards are arbitrary and differ with regard to ferrous and non-ferrous products as well as sheet and wire. It is also an aid for visual inspection which enables an inspector to determine more reliably whether the size or contour of a formed part meets dimensional requirements. Gauge is also an instrument which used to measure thickness or length.
Gauge cock – It is a valve attached to a water column or drum for checking water level.
Gauge control – It is a technique to control strip thickness in the cold rolling mills, enabling tighter control of thickness by providing faster and more accurate control of the roll gap. It is normally done through automatic gauge control (AGC).
Gauge factor (GF) – It is a dimensionless parameter measuring the sensitivity of a strain gauge (electrical resistance-based sensor). It is defined as the ratio of the fractional change in electrical resistance (dR/R) to the fractional change in length or mechanical strain (s = dL/L).
Gauge, feeler – Feeler gauge, also known as thickness gauge, is physical measurement instrument which is used to precisely measure the disparity which exists between the two equal spacing, like the clearance among two machine parts or elements. Feeler gauges typically available as a set, with each set consisting of a series of dimensionally accurate shim stock pieces joined together with a central shaft and nut or riveted connection.
Gauge, form – Form gauge is a measuring instrument which is specifically designed to assess the profile of objects. One common type of form gauge is the radius gauge, which consists of a set of blades with varying convex and concave circular profiles. Form gauges are used to measure both corners and groove radii.
Gauge glass – It is the transparent part of a water gauge assembly connected directly or through a water column to the boiler, below and above the water line, to indicate the water level in a boiler.
Gauge head – It is the sensor component of a measuring instrument exposed directly to the medium (fluid, gas, or vacuum) to detect physical parameters like pressure or vacuum levels. It converts physical quantities into measurable signals (e.g., ion current, electrical resistance) for a connected controller. Common types include ionization, thermal, and mechanical sensor heads.
Gauge length – It is the original length of that portion of the test sample over which strain, change of length and other characteristics are measured.
Gauge marks – These are lines or marks on a work-piece, created by a marking gauge, which indicate a specific measurement or a distance parallel to a reference edge or surface. These marks are used in metal-working to guide subsequent cutting, shaping, or other operations.
Gauge, plug – A plug gauge is a cylinder-shaped dumble gauge. On one side, there is a go section, and on the other, there is a no-go section. It is used to determine the inner diameter of a hole. It is a gauge with attributes. Attribute gauge implies that it is the only way to tell if a part is good or bad. It does not offer any varying value.
Gauge point – It is a specific, designated location on a component or in a numerical simulation used as a reference for taking precise measurements. It serves as a fixed, traceable datum for monitoring physical quantities like pressure, stress, strain, or dimensional accuracy.
Gauge pressure – It is the pressure measured with respect to the atmospheric pressure and is normally expressed, for example, in ‘kPa g’. Gauge pressure varies with atmospheric pressure, which in turn varies with the altitude above the mean sea level and the weather conditions. Gauge pressure is the commonly used unit.
Gauge pressure instrument – It is an instrument normally with a threaded connection for measuring and indicating the pressure in a piping system at the point at which it is connected. It indicates zero pressure when vented to the atmosphere.
Gauge pressure transducer – It is a device which converts gas or liquid pressure into an electrical signal, measured relative to the local atmospheric pressure. It utilizes a sensing element, such as a diaphragm with strain gauges, to produce a signal proportional to the pressure applied, commonly used for process control in industrial applications.
Gauge, rail – It is also called track gauge. It is the distance between the two rails of a railway track. All vehicles on a rail network need to have wheelsets which are compatible with the track gauge. The term derives from the metal bar, or gauge, which is used to ensure the distance between the rails is correct. Railways also deploy two other gauges to ensure compliance with a required standard. A loading gauge is a two-dimensional profile that encompasses a cross-section of the track, a rail vehicle and a maximum-sized load i.e., all rail vehicles and their loads are required to be contained in the corresponding envelope. A structure gauge specifies the outline into which structures (bridges, platforms, lineside equipment etc.) are not to encroach.
Gauge, ring – The ring gauge is used to measure the outer diameter. As the name implies, it resembles a ring. Ring gauge is of two types namely go ring gauge and no-go ring gauge. Ring gauge is another gauge attribute.
Gauge rosette – It is also called strain gauge rosette. It is a composite sensor consisting of two or more, normally three, individual strain gauges arranged at specific angles to measure normal strains in multiple directions at a single point. It is used to determine complete surface strain states, including principal strains and their directions, particularly when the loading orientation is unknown.
Gauge, screw – A screw gauge is a tool for measuring the dimensions of very small items up to 0.01 millimeter. It is made up of a U-shaped metal frame. One side of the frame has a hollow cylinder connected to it. On the inside surface of the cylinder, grooves are carved through which a screw travels. A millimeter scale called ‘pitch scale’ is graded on the cylinders parallel to the axes of the screw. An arm is attached to one of the screw’s ends. The ‘head scale’ divides the head of the arm into 100 segments. The screw’s opposite end has a flat surface. A stud is connected to the opposite end of the frame, exactly opposite the screw point. The screw head has a ratchet configuration to inhibit the user from applying excessive pressure.
Gauge, snap – Snap gauge is indeed metrology tool which is used to measure the diameter or thickness of a part or material. This versatile tool is intended to provide a quick yes / no judgment on coils, shafts, grooves, as well as other similar parts as well as features in conventional machining. Snap gauges perform assessments on the exterior parts. They can check measurements on both cylindrical and non-cylindrical parts, whereas ring gauges can only be used on cylindrical parts.
Gauge, taper – Taper gauge is a measuring instrument which is used to determine the width of gaps, grooves, hole diameters, and the inner diameter of pipes. It comes in both plug and ring styles and is frequently made with polycarbonate or brass cases or caps for easy portability.
Gauge, thread – Thread gauge is also known as screw pitch gauge. It is a measuring tool which is specifically designed to determine the pitch and diameter of threads. Plug thread gauges are used to assess the internal threads of nuts and brushes, while ring thread gauges are used to evaluate the external threads of bolts and screws.
Gauge volume – It is the specific 3D region within a sample or material from which measurements (e.g., diffraction, strain, scattering) are collected. It is defined by the intersection of incident and detected beams, frequently used in non-destructive testing to map lattice spacing and structural integrity. It is a localized, fixed region in space, typically used to measure strain or crystallographic information. It is used extensively in neutron and X-ray diffraction, where aperture slits define the volume from which signals are detected.
Gauging – It is the process of measuring, checking, or verifying the dimensions, tolerances, and physical properties of components using a reference gauge to ensure they meet specified standards. It involves comparing a part’s size to limits (e.g., go / no go), rather than measuring exact dimensions, to ensure production quality. In a foundry, gauging refers to the process of inspecting cast metal parts to ensure their dimensions, tolerances, and physical characteristics meet specified standards. Unlike high-precision measuring instruments that give an exact numerical value, gauges in a foundry frequently act as ‘go / no-go’ tools, quickly verifying if a casting is within acceptable dimensional limits.
Gauging points – These refer to the specific, designated locations on a work-piece or test sample where measurements are taken to determine if dimensions conform to needed tolerances. These points are important for ensuring dimensional accuracy, such as diameter, length, or wall thickness, after manufacturing processes like casting, machining, or heat treatment.
Gauss (G) – It is the CGS (centimeter-gram-second) unit of magnetic flux density, representing the number of magnetic field lines per square centimeter. One Gauss is defined as 1 maxwell per square centimeter, and it is equivalent to 0.0001 Tesla, SI (International System of Units) unit. It measures magnetic field strength, with 0.5 G approximating earth’s magnetic field.
Gauss approach – It normally refers to Gauss elimination, a systematic, row-reduction algorithm used to solve systems of linear equations by transforming the coefficient matrix into upper triangular form. It reduces computational complexity for solving multiple unknowns in structural analysis, circuit simulation, and data modeling.
Gauss elimination – It is a systematic, numerical method used to solve linear equation systems (Ax = b) by transforming the augmented matrix into row echelon (upper triangular) form using elementary row operations. It simplifies complex systems for easier back-substitution to find unknown variables, necessary for structural analysis, circuit simulation, and algorithm design.
Gaussian additive noise – It is frequently referred to as ‘additive white Gaussian noise’ (AWGN). It is a signal impairment model where unwanted, random, and normally distributed perturbations are added linearly to a desired signal. It acts as a mathematical, baseline model for naturally occurring noise sources, such as thermal noise, uniformly distributed across a wide spectrum.
Gaussian behaviour – It refers to systems or data which follow a normal (bell-shaped) distribution, characterized by symmetry around the mean, where most data points cluster centrally and extreme values are rare. It defines random errors in measurements, thermal noise, and signal processing, determined by mean and variance.
Gaussian blur – It is a widely used image processing technique which reduces image noise and detail by convolving an image with a Gaussian function. It functions as a non-uniform low-pass filter, creating a smooth, hazy, or ‘translucent’ effect that is often used in computer vision as a pre-processing step to improve feature extraction. Unlike a simple box blur, the Gaussian blur gives more weight to the centre pixel, resulting in a more natural, gradual smoothing.
Gaussian case – It defines systems modeled by normal distributions, characterized by mean and variance or covariance matrix. It applies to random variables, processes, or fields where data follows a bell-shaped curve, allowing for efficient modeling of noise, measurement errors, and system response.
Gaussian curve – It is also known as a normal distribution or bell-shaped distribution. It is a normalized frequency distribution which is symmetrical about the mean value and characterizes measurement sets containing random errors, where small deviations from the mean occur more frequently than large deviations.
Gaussian distribution – The gaussian distribution is another name for the normal distribution. It is a probability distribution characterized by a bell-shaped probability density function, which is widely utilized in statistics applications. It is defined by parameters including the arithmetic mean and variance, which describe the distribution’s center and spread, respectively.
Gaussian elimination – it is also known as row reduction. It, is a systematic algorithm used to solve systems of linear equations by transforming the system’s augmented matrix into upper triangular form (also called row-echelon form) using elementary row operations. This mathematical tool is frequently applied to solve complex, simultaneous linear equations which arise in thermodynamic modeling, phase equilibrium calculations, heat transfer, and compositional analysis of alloys.
Gaussian error function – It is a special, non-elementary sigmoid function defined as the integral of the Gaussian distribution. It describes probabilities in normal distributions, diffusion processes (e.g., mass transfer), and heat conduction.
Gaussian filter – It is a linear, space-invariant filter used in signal and image processing to reduce noise and detail by blurring, achieved through convolution with a Gaussian function. It is characterized by having no overshoot to a step function input, minimal rise / fall time, and acts as a low-pass filter which attenuates high-frequency signals.
Gaussian formula – It represents a, symmetric ‘bell curve’ probability density function (PDF) used to model random variables, measurement errors, and noise.
Gaussian frequency shift keying – It is a modulation technique which pre-filters binary data with a Gaussian filter before frequency modulation. By smoothing abrupt frequency changes, it reduces spectral sidelobes, minimizing adjacent channel interference while improving bandwidth efficiency. Gaussian frequency shift keying is normally used in Bluetooth and GSM (global system for mobile communications) for high-speed, low-power, and robust wireless communications.
Gaussian function – It models natural phenomena (errors, signal noise) where ‘a’ is the height, ‘b’ is the mean (centre), and ‘c’ is the standard deviation (width). It is foundational for statistics, signal processing, and heat diffusion. It represents the bell curve.
Gaussian input – It refers to a signal or noise source which follows a normal (Gaussian) distribution, defined by its mean and variance. It is used in modeling system noise, simulations, and signal processing to characterize data spread, frequently applied in filter design and control theory to represent random, natural phenomena.
Gaussianity – It refers to the assumption or characteristic that a signal, dataset, or random process follows a Gaussian (normal) distribution, characterized by a symmetric, bell-shaped probability density function (PDF) defined by its mean and variance. It is a foundational concept used to model natural phenomena, measurement errors, and noise, e.g., AWGN (additive white Gaussian noise) because of its mathematical tractability.
Gaussian kernel – It refers to a mathematical function which is used to model local deformation in computer science. It is defined by the Gaussian form of the kernel function, which controls the width of the kernel. The Gaussian Kernel has a more compact support when the parameter controlling its width is small, making it useful for modeling local deformation with fewer control points.
Gaussian mechanism – It is a fundamental algorithm in differential privacy (DP) used to release accurate, privacy-preserving results from statistical queries or machine learning models by adding calibrated, random Gaussian noise to the output. It is particularly favoured for high-dimensional data (e.g., gradients in deep learning) since it adds less noise compared to the Laplace mechanism for the same privacy level, leveraging L2-sensitivity rather than L1-sensitivity.
Gaussian model – It is a statistical framework which assumes data points are generated from a normal (Gaussian) distribution. It is characterized by a bell-shaped curve, defined by its mean and variance, and is widely used for modeling data, identifying outliers (low-probability points), and as a foundation for more complex methods.
Gaussian noise – It is statistical signal interference with amplitude values following a normal (Gaussian) distribution, producing a bell-shaped probability density function. It typically represents natural, random, and unpreventable noise, such as thermal noise in electronics, or sensor noise in imaging, and is normally modeled as additive and white.
Gaussian profile beam – It is an electromagnetic radiation beam (normally laser light) with an intensity profile, I(r.z), following a Gaussian function. It is the fundamental transverse electric and magnetic (TEM 00) mode, characterized by a maximum intensity at the centre which decreases symmetrically toward the edges.
Gaussian quadrature rule – It is a highly accurate numerical integration method used to approximate definite integrals by calculating a weighted sum of function values at specific, optimized points (roots of orthogonal polynomials, normally Legendre) rather than equally spaced intervals. It maximizes precision, achieving exact results for polynomials up to degree ‘2n -1’ using only ‘n’ points.
Gaussian random variable – It is a continuous random variable with a bell-shaped probability density function (PDF), fully defined by its mean and variance. It is foundational for modeling noise, measurement errors, and physical phenomena because of the central limit theorem.
Gaussian shape – It is normally referred to as a bell-shaped curve or normal distribution. It is a symmetrical probability distribution defined by a central peak (mean) and a width parameter (standard deviation). It represents data which clusters around a central value, with fewer points occurring as distance from the center increases.
Gaussian spectrum – It is an optics, or signal processing profile where power, intensity, or amplitude follows a normal (Gaussian) distribution curve. It represents a smooth, bell-shaped distribution, frequently used for modeling laser beams, broadband sources, or noise with a defined central frequency and width.
Gaussian surface – It is an imaginary closed 3D surface used in electro-magnetism to simplify the calculation of electric fields or flux using Gauss’s law. It acts as a boundary which encloses a charge distribution, allowing engineers to exploit symmetry (spherical, cylindrical, or planar) to make the field constant over the surface.
Gaussian wave – It is a localized, bell-shaped wave profile defined by a Gaussian function, normally used for signal processing, laser optics, and quantum mechanics. It represents a wave with a maximum amplitude at the centre which tapers towards the edges, frequently minimizing uncertainty between spatial location and spectral width.
Gaussian white noise – It is a type of noise which has a Gaussian distribution and is characterized by having a constant power spectral density across all frequencies, meaning its noise characteristics are uniform. This type of noise is frequently assumed in digital communication systems to simplify mathematical analysis.
Gaussian window – It is a smooth function with a concentrated frequency response, characterized by its ability to achieve the minimum time-bandwidth product, as dictated by the uncertainty principle. It is typically represented by a truncated Gaussian function.
Gauss integration scheme – It is a numerical method for evaluating integrals by summing the values of the integrand at specified Gauss points, each multiplied by corresponding weight coefficients. This technique improves accuracy in integration, particularly for polynomial functions, by appropriately selecting the number of Gauss points based on the complexity of the integrand.
Gauss-Newton method – it is an iterative optimization technique which starts from an initial parameter estimate and approximates a fitting function using a first-order Taylor series expansion, minimizing the residual sum of squares (RSS) until convergence is achieved.
Gauss points – These are also called integration points. These are specific, optimal coordinates within a finite element method (FEM) element where numerical integration, material calculations, and stress / strain evaluations are performed. These points, defined by Legendre polynomial roots, maximize accuracy for determining element stiffness matrices and represent the most precise locations for output data.
Gauss-Seidel method – It is an iterative numerical technique used to solve systems of linear equations (Ax = b) by repeatedly refining initial guesses. It improves upon the Jacobi method by using the most updated values of variables immediately within the same iteration, resulting in faster convergence.
Gauss’s law – It is a mathematical relation between the electric flux passing through a surface and the charge contained within that surface.
Gauss’s method – It is also called Gaussian elimination. It is a systematic, algorithmic procedure used to solve systems of linear equations by transforming the augmented matrix into an upper triangular (row echelon) form using elementary row operations. It simplifies complex linear systems to calculate unknowns through back-substitution, normally applied in circuit analysis and structural engineering
Gauss’s theorem – It is a fundamental principle stating that the total electric flux through a closed surface is directly proportional to the enclosed electric charge. It is used for modeling electric field interactions in electro-plating, electro-chemical corrosion, and powder metallurgy.
Gay-Lussac’s law – It is important in smelting and refining. It states that the pressure of a fixed quantity of gas at a constant volume is directly proportional to its absolute temperature (‘P’ is proportional to ‘T’). It dictates that as temperatures rise in furnaces, gas pressure increases, which is important for safety and controlling gaseous reactions.
Geiger counter – It is a detection instrument which is used to detect particles of ionizing radiation namely alpha particles, beta particles, or gamma radiation. This instrument is also used to measure the radio-activity which emanates from certain minerals by means of a Geiger-Mueller tube.
Gear – It is a rotating circular machine part having cut or inserted teeth which mesh with another compatible toothed part to transmit torque and speed. Each gear tooth essentially functions as a lever with its fulcrum at the centre of the gear. Gear is typically used to transmit rotational motion and / or torque by means of a series of teeth which engage with compatible teeth of another gear or other part. The teeth can be integral saliences or cavities machined on the part, or separate pegs inserted into it.
Gear accuracy – It defines how closely a gear’s manufactured dimensions (profile, helix, pitch, runout) adhere to its theoretical design specifications, normally measured by standardized quality grades. It ensures efficient power transmission, low noise, and precise positioning by controlling deviation.
Gear blank – It is an unfinished, pre-shaped piece of metal or material, frequently forged, cast, or machined, which serves as the starting point for manufacturing gears. It acts as the raw material foundation, providing the necessary material for subsequent machining operations like hobbing, shaping, or grinding to form precise gear teeth.
Gear box – It is frequently called a transmission. Gear boxes simply refer to a set of gears and their casing. Gear box is a mechanical device which uses a gear set, two or more gears working together, to change the speed, direction of rotation, or torque multiplication / reduction in a machine. Gear box allows the machinery to operate efficiently and even aid in slowing and shutting down machinery.
Gear change – It is the process of switching between different gear ratios within a transmission or gearbox, allowing for adjustments in torque, rotational speed, and direction of motion between an input source and an output load. It involves engaging different sets of toothed gears to match engine power to operational needs.
Gear coupling – It is a mechanical device which is used for transmitting torque between two shafts which are not collinear. It consists of a flexible joint fixed to each shaft. The two joints are connected by a third shaft, called the spindle.
Gear cutting – It consists of producing tooth profiles of equal spacing on the periphery, internal surface, or face of a work-piece by means of an alternate shear gear-form cutter or a gear generator.
Gear drive – It is a mechanical power transmission system which uses meshing, toothed wheels (gears) to transfer rotational motion and torque between shafts. Engineered for short distances, it ensures a positive, high-efficiency drive without slippage. It is mainly used to adjust speed (reduce or increase) and modify torque or direction.
Geared press – It is a press whose main crank or eccentric shaft is connected by gears to the driving source.
Gear finishing – It is the final, high-precision machining stage in gear manufacturing which improves surface quality, accuracy, and geometry after rough cutting and heat treatment. It improves fatigue life, reduces noise, and ensures tight tolerances. Key methods include grinding, lapping, honing, shaving, and burnishing.
Gear (form) grinding – It is the removal of material to get correct gear tooth form by grinding. This is one of the more exact methods of finishing gears.
Gear hobbing – It consists of gear cutting by use of a tool resembling a worm gear in appearance, and having helically spaced cutting teeth. In a single-thread hob, the rows of teeth advance exactly one pitch as the hob makes one revolution. With only one hob, it is possible to cut inter-changeable gears of a given pitch of any number of teeth within the range of the hobbing machine.
Gear housing – It is also called gear casing. It is a rigid, protective, and structural enclosure which houses, supports, and aligns internal components like gears, shafts, and bearings. It acts as a lubricant reservoir, provides heat dissipation, protects internal parts from environmental contaminants, and is normally made from cast iron, steel, or aluminum.
Gear manufacturing – It is the process of designing, creating, and finishing toothed components, such as spur, helical, or bevel gears, to transmit power, torque, and motion between machine parts. It involves producing precise, durable gears through methods like machining, casting, forging, and powder metallurgy, followed by heat treatment and finishing.
Gear mesh – It is the interaction, engagement, or interlocked state between the teeth of two or more rotating gears, allowing for the transmission of power, torque, and speed. It needs precise alignment, matching tooth profiles (normally involute), and proper spacing to ensure smooth, efficient motion and to prevent premature wear.
Gear milling – It consists of gear cutting with a milling cutter which has been formed to the shape of the tooth space to be cut. The tooth spaces are machined one at a time.
Gear module (m) – It is the unit of size indicating how big or small gear teeth are, defined as the ratio of the pitch circle diameter (d) to the number of teeth (z), (m = d/z). It is a fundamental metric standard (International Organization for Standardization, ISO) used to ensure proper gear meshing. Gears are required to have the same module to function together.
Gear motor device – It is a mechanism converting electrical energy to mechanical energy through the gearbox, operating at a reduced speed.
Gear motor unit – It is an integrated motor and gearbox unit providing power to the equipments. Regular inspections are essential to ensure proper functioning and alignment.
Gear operated (GO) – It is the actuation of a valve through a gear set which multiplies the torque applied to the valve stem.
Gear pump – It is the simplest form of rotary positive-displacement pumps. It consists of two meshed gears that rotate in a closely fitted casing. The tooth spaces trap fluid and force it around the outer periphery. The fluid does not travel back on the meshed part, because the teeth mesh closely in the center. Gear pumps see wide use in car engine oil pumps and in several hydraulic power packs.
Gear ratio – It is the ratio of the pitch circles of mating gears which defines the speed ratio and the mechanical advantage of the gear set.
Gear rattle – It is a high-frequency, impact-induced noise caused by the, collision of lightly loaded or unloaded mating gear teeth in a transmission or drivetrain. It is mainly caused by speed fluctuations from engine torsional vibrations, resulting in teeth impacting within the backlash, and is normal at idle or low-speed conditions.
Gear shaping – It consists of gear cutting with a reciprocating gear-shaped cutter rotating in mesh with the work blank.
Gear system – It is a mechanical arrangement of toothed wheels (gears) which mesh together to transmit power, torque, and motion between shafts, typically changing speed, direction, or rotational axis. These systems, including trains, epicyclical, or rack-and-pinion arrangements, prevent slippage to ensure precise mechanical advantage.
Gear teeth – These are the machined, protruding, and interlocking components on a gear’s circumference, designed to mesh with another gear or part to transmit torque and motion. They are characterized by their profile (frequently involute for smooth operation), number, pitch, and pressure angle, which define the speed ratio and power capacity.
Gear-teeth surface – It defines the geometry, roughness, and hardness of the active flanks (tooth face above the pitch circle, flank below) to ensure efficient power transmission and durability. It involves optimizing involute / spiral profiles through heat treatment (carburizing, nitriding) and finishing (grinding, lapping) to manage stress, friction, and wear.
Gear train – It is a mechanical system of two or more meshing gears (toothed wheels) mounted on a frame, used to transmit power, control speed, and alter torque between shafts. These assemblies are crucial in metallurgy for reducing speed in heavy machinery, or increasing it, through gear-boxes and drives.
Gear train, gear set – It is a machine element of a mechanical system formed by mounting two or more gears on a frame such that the teeth of the gears engage.
Gear train, planetary – It provides high gear reduction in a compact package. A planetary gear train is a gear reduction assembly consisting of two gears mounted so that the center of one gear (the ‘planet’) revolves around the centre of the other (the ‘sun’). A carrier connects the centre of the two gears and rotates, to carry the planet gear(s) around the sun gear. The planet and sun gears mesh so that their pitch circles roll without slip. If the sun gear is held fixed, then a point on the pitch circle of the planet gear traces an epicycloid curve.
Gear units – These are mechanical, frequently enclosed, assemblies of gears (toothed wheels) which transmit power between shafts to change torque, speed, or direction of rotation. They act as vital links between motors and driven machines, adjusting speed and multiplying torque to meet specific application needs.
Gear wheels – These are also called gears. These are toothed, cylindrical, or conical machine elements which mesh together to transmit torque, speed, and motion between rotating shafts. They prevent slipping, ensuring high efficiency and precise, controlled mechanical power transmission. Common types include spur, helical, bevel, and worm gears.
Gehlenite – It is a calcium aluminum silicate mineral with the chemical formula Ca2Al2(SiO7). It is a member of the melilite group and can be found in various geological settings, including contact metamorphic zones, volcanic rocks, and even some meteorites. Gehlenite also occurs in artificial settings like foundry and incinerator slags.
Gel – It is the initial jelly-like solid phase which develops during the formation of a resin from a liquid. It is a semi-solid system consisting of a network of solid aggregates in which liquid is held. Gels are defined as a substantially dilute cross-linked system, which shows no flow when in the steady state, although the liquid phase can still diffuse through this system.
Gelatinization – It is an irreversible, heat-induced, and water-dependent process where starch granules swell, lose their crystalline structure, and increase in viscosity, transitioning from an ordered to an amorphous state. This phenomenon involves the disruption of intermolecular bonds, allowing water to act as a plasticizer and forming a viscous, gel-like, paste-like mixture.
Gelatin aqueous solution – It is a temperature-sensitive, reversible liquid-to-gel mixture of water and gelatin. It acts as a bio-compatible, bio-degradable colloid that forms a gel upon cooling (below around 35 deg C to 40 deg C) or remains a sol (liquid) when heated.
Gelatin replica – It is a reproduction of a surface prepared in a film composed of gelatin.
Gelation – It is the point in a resin cure when the resin viscosity has increased to a point such that it barely moves when probed with a sharp instrument.
Gelation concentration – It is the minimum concentration of a polymer, monomer, or colloidal particles required to form a 3D, interconnected solid network that spans a liquid medium, transforming a ‘sol’ (liquid) into a ‘gel’ (solid-like). It represents a critical threshold for sol-gel transition, determining the material’s structural integrity, viscosity, and curing time, frequently analyzed through rheology.
Gelation temperature – It is the specific temperature at which a liquid sol, polymer solution, or suspension transitions into a solid-like, three-dimensional gel network. It marks the point of infinite molecular weight, high viscosity, and, typically, when the storage modulus surpasses the loss modulus. It is the critical point in polymerization or cross-linking (physical or chemical) where a continuous, interconnected network forms, causing the material to lose fluidity and gain structural integrity.
Gelation time – It is that interval of time, in connection with the use of synthetic thermosetting resins, which is extending from the introduction of a catalyst into a liquid adhesive system until the start of gel formation. It is also the time under application of load for a resin to reach a solid state.
Gel battery – It is a type of ‘valve regulated lead-acid’ (VRLA) battery which immobilizes liquid electrolyte by adding silica fumes, creating a thick, spill-proof, gel-like paste. It is designed for deep-cycle applications, offering high vibration resistance, maintenance-free operation, and the ability to be mounted in different orientations.
Gel bonding – It is a method of joining materials (adherends) by using a viscous sol-gel solution as an adhesive which cures into a solid, porous 3D network. It is a wet-chemical, frequently low-temperature, process where a liquid ‘sol’ (colloidal suspension) undergoes hydrolysis and poly-condensation to form a ‘gel’ (a 3D solid network containing trapped solvent) which bonds two surfaces together.
Gel chromatography – It is also called size exclusion chromatography. It is a separation technique which sorts molecules by size (hydrodynamic volume) as they pass through a porous, gel-based stationary phase. Larger molecules cannot enter the pores and elute first, while smaller molecules enter the beads, taking longer to pass through.
Gel coat – It is a quick-setting resin applied to the surface of a mould and gelled before lay-up. The gel coat becomes an integral part of the finished laminate, and is normally used to improve surface appearance and bonding.
Gel filtration – It is a separation technique which relies on the differing abilities of molecules to enter the pores of a gel medium based on their molecular size, allowing larger molecules to elute faster than smaller ones.
Gel filtration chromatography – It is a separation technique which separates molecules based on size (hydrodynamic volume) using porous, gel-based stationary phases. Larger molecules elute first, passing around beads, while smaller molecules enter pores and elute later.
Gelling agent – It is a solid material dispersed in a liquid lubricant to produce a grease. Silica, clays, and metallic soaps are widely used as gelling agents.
Gel-permeation chromatography – It is a liquid chromatography method which separates molecules on the basis of their physical size. The polymer molecules are separated by their ability or inability to penetrate the material in the separation column. This technique is very frequently used in the analysis of polymers.
Gel point – It is the stage at which a liquid begins to show pseudo-elastic properties. This stage can be conveniently observed from the inflection point on a viscosity time plot.
Gel polarization – It is a phenomenon occurring in membrane separation (e.g., ultra-filtration) where high-concentration solutes accumulate at the membrane surface, forming a viscous ‘gel’ layer. This layer acts as a secondary, frequently irreversible, resistance to fluid flow, causing the permeate flux to become independent of pressure.
Gel polymer electrolyte membranes – These are advanced, flexible, solid-like ion-conducting materials comprising a polymer matrix, e.g., Polyvinylidene fluoride (PVDF), Poly-acrylo-nitrile (PAN), Poly-methyl-methacrylate (PMMA) swollen with liquid electrolyte salts. They bridge the gap between solid-state safety and liquid-like performance, offering high ionic conductivity and improved interfacial contact in lithium-based batteries. These membranes are formed by blending ceramic particles with polymers, effectively improving wetting characteristics, conductivity, and thermal stability in separators used in harsh conditions.
Gel process – It is a method to produce solid materials from small molecules through the conversion of monomers into a colloidal solution (sol) which serves as a precursor for an integrated network (gel) of discrete particles or network polymers.
Gel reaction – It is a process where a colloidal liquid (sol) transforms into a solid-like, three-dimensional network (gel). It occurs through cross-linking polymer chains or aggregating nano-particles, causing a sharp, viscosity-driven transition from fluid to solid. This transformation is necessary for synthesizing advanced materials, ceramics, and thin films.
Gel sample – It is normally defined a non-fluid colloidal or polymer network which is expanded throughout its whole volume by a fluid, acting as a soft, solid-like material. It consists of a three-dimensional, cross-linked network which traps a liquid phase, providing structural integrity while allowing for high fluid retention.
Gel state – It is a material state showing a combination of liquid-like and solid-like properties, which contributes to its unique mechanical characteristics. Defining the gel state precisely can be complex because of the variability in its properties.
Gel strength – In drilling fluids, it is a measure of the shear stress exerted by a fluid at low shear rates after standing still, indicating its ability to form a structure and suspend solids at rest. It determines how much force is needed to restart circulation, normally measured as 10-second and 10-minute intervals.
Gel test – It normally refers to a procedure used to determine the structural integrity, degree of cross-linking, or physical properties of a gel or gelatinous substance. These tests are vital for ensuring the quality of materials, such as in polymers (e.g., cross-linked poly-ethylene).
Gel transition – It is the process where a liquid suspension of particles, or a monomer solution (sol), transforms into a cohesive solid-like material (gel). This occurs via the creation of a continuous, 3D network through chemical or physical cross-linking, causing a sharp increase in viscosity and the loss of macroscopic flow.
Gel treatment – It refers to the application of polymer gels (either in situ or preformed) to control fluid flow, mainly used to mitigate excessive water production during oil recovery processes. This conformance control technique improves sweep efficiency by plugging high-permeability zones.
Gel water – It frequently referred to as a hydrogel or aqueous gel. It is a non-fluid, colloidal, or polymer network which is expanded throughout its whole volume by water. It is a soft, solid-like material consisting of a three-dimensional (3D) cross-linked network which traps large quantities of water (sometimes over 99 % by weight) while maintaining its shape and structural integrity.
General algebraic modeling system – It is a high-level programming language and software environment specifically designed for formulating, solving, and analyzing large-scale, complex linear, nonlinear, and mixed-integer optimization problems. It enables engineers to define models using human-readable, algebraic notation which is portable across different computer platforms. It is widely used in energy and power system optimization, process engineering, logistics, and economic modeling.
General arrangement (GA) drawing – It depicts the physical relationship of significant items using appropriate projections or perspective views. Reference dimensions are to be included in this drawing. This drawing does not establish item identification. It is prepared to convey a general description of the configuration and location of significant items. It is not normally used to control design. This drawing normally includes (i) sufficient views so that a general understanding of the configuration and location of significant items is conveyed, (ii) overall, locating, and other general dimensions necessary to describe the configuration, (iii) identities of significant items, and (iv) reference to applicable documents for further details.
General conditions of contract – These are those commercial conditions which are mostly common to all the types of contracts. General conditions of the contract are normally annexed to the contract.
General contractor – General contractor (GC) is the main entity responsible for overseeing a construction project, managing daily operations, hiring sub-contractors, and handling vendor procurement. They act as the main liaison between the owner and the specialized trade contractors, ensuring the project meets specifications, budget, and safety standards.
General corrosion – It is a form of deterioration which is distributed more or less uniformly over a surface. It is also the corrosion dominated by uniform thinning which proceeds without appreciable localized attack.
General exploration – General exploration involves the initial delineation of an identified deposit. Methods used include surface mapping, widely spaced sampling, trenching, and drilling for preliminary evaluation of mineral quantity and quality (including mineralogical tests on laboratory scale if needed), and limited interpolation based on indirect methods of investigation. The objective is to establish the main geological features of a deposit, giving a reasonable indication of continuity and providing an initial estimate of size, shape, structure and grade. The degree of accuracy is to be sufficient for deciding whether a pre-feasibility study and detailed exploration are warranted.
General inflation rate – It refers to the percentage rate of increase in the general price level of goods and services over a specific period, reflecting a decline in purchasing power. It is used to adjust cost estimates for inflation, frequently measured by indices like the ‘consumer price index’ (CPI).
Generalized aerodynamic forces – These forces refer to the aerodynamic force influence coefficients which are got from the frequency-domain responses of an aeroelastic system, typically derived from computational fluid dynamics (CFD) analysis and used in linear aeroelastic analyses.
Generalized beam theory – It is a 1D structural analysis method used for thin-walled members which expresses the displacement field as a linear combination of predefined cross-section deformation modes (local, distortional, global). It transforms complex 3D behaviour into 1D, offering high accuracy and computational efficiency for buckling, vibration, and linear / non-linear analysis. It is a refined, one-dimensional theory which models thin-walled beams by considering both cross-sectional deformation and axial behaviour, extending classical beam theory (e.g., Euler-Bernoulli).
Generalized chart – It is a universal graphical tool which plots non-dimensional parameters (e.g., reduced pressure / temperature, flow parameters) to describe behaviour across different substances or systems. It enables quick, approximate analysis, such as calculating gas compressibility or predicting flooding, without needing specific, system-dependent data tables.
Generalized coordinates – These are a minimal set of independent parameters (angles, distances, or coordinates) which uniquely define the configuration of a mechanical system relative to a reference position. They equal the system’s degrees of freedom, allowing for easier formulation of equations of motion in constrained engineering systems.
Generalized delta – It refers to an extension of the delta rule used in neural networks for updating weights during training, specifically accommodating hidden layer problems through the back-propagation algorithm.
Generalized delta rule – It is also called back-propagation. It is an AI (artificial intelligence) algorithm used to update neural network weights by minimizing output error, extending basic delta rules to multi-layer networks. It enables learning complex, non-linear relationships, forming the foundation for deep learning in robotics and, more broadly, representing small, finite changes.
Generalized differential quadrature method – It is a numerical technique used to solve partial differential equations by approximating derivatives as weighted linear sums of function values at discrete grid points. It is an efficient alternative to finite element methods, offering high accuracy in structural mechanics, particularly for buckling, vibration, and bending analysis of structures like shells and panels.
Generalized displacement – Within Lagrangian mechanics, It represents a change in the generalized coordinates which at define a system’s configuration. Unlike linear displacement, it can represent translational distances, angular rotations, or other parameters, and is used to analyze systems with complex constraints.
Generalized displacement vector – It is a column vector comprising independent generalized coordinates which completely define the deformed configuration of a mechanical system. It maps complex, multi-degree-of-freedom, or continuum mechanics systems, including both translational and rotational displacements, into a unified set of variables for structural analysis. It acts as a concise representation of the change in position and orientation of structural elements (nodes, beams, plates).
Generalized eigenvalue – It refers to the values L which satisfy the generalized eigenvalue equation A x = L B x, where ‘A’ and ‘B’ are matrices, and ‘x’ is the corresponding eigenvector. This concept is fundamental in different engineering computations, encompassing matrix polynomial eigenvalue problems.
Generalized eigenvalue problem – It solves the equation A x = L B x, where A (e.g., stiffness) and B (e.g., mass) are ‘n x n’ matrices, ‘x’ is the non-zero eigenvector, and ‘L’ is the eigenvalue. Unlike standard problems, it finds resonance frequencies and mode shapes by relating two distinct physical, frequently symmetric and positive-definite, matrices.
Generalized equation – It is a foundational, broad formula representing a physical phenomenon, which can be simplified into specific models by applying constraints or assumptions. It extends ordinary equations to handle complex, multivalued, or non-linear behaviours, such as the generalized equation of motion. Examples include the generalized engineering Bernoulli equation and generalized coordinates in mechanics. These equations frequently describe systems using generalized coordinates and forces, representing the entire configuration of a system with degrees of freedom.
Generalized forces (Qi) – These are scalar components representing the net effect of external forces and torques acting on a mechanical system corresponding to a specific generalized coordinate (qi), derived using the principle of virtual work. They need not have units of force (e.g., torque if ‘qi’ is an angle) and are used to simplify equations of motion in Lagrangian mechanics.
Generalized Fourier transforms – These are advanced, frequently multi-dimensional, analytical tools which map signals or data structures into frequency-domain representations, expanding beyond standard time-to-frequency conversion. They analyze complex, non-periodic, or multi-variable signals (e.g., 2D image processing, 3D systems) using specialized kernels. Generalized Fourier transforms extend standard Fourier techniques to analyze functions not covered by classical methods, frequently involving non-linear operations, fractional operators, or specialized algebraic structures.
Generalized Gaussian distribution – It is also called exponential power distribution. It is a symmetric family of probability distributions which adds a shape parameter (p) to the standard Gaussian (normal) distribution. It is used to model data with heavier or lighter tails than a normal distribution, specifically for signal processing, image compression, and error modeling, with p = 1 being Laplacian and p = 2 being Gaussian.
Generalized gradient approximation – It is a ‘density functional theory’ (DFT) method which improves the ‘local density approximation’ (LDA) by calculating exchange-correlation energy using both the local electron density and its gradient. It improves accuracy for molecular bond lengths, binding energies, and lattice constants by accounting for nonuniform electron density. Generalized gradient approximation expands upon local density approximation (which only considers density at a single point) by incorporating the gradient of the density, making it a ‘second rung’ on Jacob’s ladder of density functional theory.
Generalized Hooke’s law – It is the 3D constitutive equation relating stress and strain tensors for linear elastic materials, generalizing F = k x to complex loading. It defines how all six independent stress components relate to all six strain components using stiffness / compliance matrices, as per anisotropy and Poisson’s effect (lateral contraction). It establishes a linear, proportional relationship between stress and strain tensors, assuming the material is within its elastic limit.
Generalized input – It refers to the systematic process of defining, classifying, and structuring the data, signals, or physical quantities fed into a system to maximize flexibility, reusability, and performance. It involves moving from specific, hard-coded inputs to abstract, configurable, or probabilistic models, such as generalized transfer functions in control systems or generalized nodes in network analysis.
Generalized interpolation – It normally refers to advanced numerical methods which estimate unknown data points between known values, frequently by matching both function values and their derivatives, or by using flexible, multi-dimensional techniques to improve accuracy over standard, linear methods. In numerical simulation, specifically the ‘generalized interpolation material point method’ (GIMP), it reduces grid-crossing errors by allowing material points to interact with a broader, more flexible mesh area.
Generalized inverse – It is a mathematical concept used to solve systems of equations, specifically those of the form Ax = b, where the matrix A is not square or nonsingular. It is a tool which allows for the calculation of a solution even when the matrix does not have a traditional inverse. It extends the concept of inversion to non-square, singular, or rectangular matrices. It is used in engineering, statistics, and control theory to find solutions to Ax = b when an ordinary inverse does not exist.
Generalized least squares – It is a statistical regression technique used to estimate parameters when residuals are correlated or have non-constant variance (heteroscedasticity). It extends ‘ordinary least squares’ (OLS) by incorporating a known covariance matrix to produce more efficient, unbiased, and accurate parameter estimates. It addresses cases where ordinary least squares fails, specifically when error terms are not independent and identically distributed (IID).
Generalized Leontief – It is a cost function (or production function) which determines the optimal, cost-minimizing input mix for a given output. It allows for flexible input substitution, unlike fixed-proportion (Leontief) models, making it essential in engineering for calculating input-output demand.
Generalized likelihood ratio test – It is a statistical method for binary hypothesis testing which compares two hypotheses (null Ho and alternative H1) when parameters are unknown. It maximizes the likelihood of the data under both hypotheses using ‘maximum likelihood estimates’ (MLE), forming a ratio to determine if the alternative model considerably improves fit.
Generalized Lloyd algorithm – It is an iterative optimization technique used to design optimal or near-optimal vector quantizers for data compression and for feature clustering in pattern recognition. It is a generalization of Lloyd’s original Algorithm I for scalar quantization and is also widely known as the k-means algorithm in the pattern recognition community. The main objective of the generalized Lloyd algorithm is to find a set of representative points (called a code-book or cluster centroids) which minimize the average distortion between the original data points (or a training set of vectors) and their nearest representative points. This process effectively partitions the input data space into a set of regions called Voronoi regions.
Generalized mass – It is a modal analysis concept representing the equivalent mass of a vibrating structure for a specific mode shape. It is calculated by integrating the product of mass density, mode shape, and the mode shape squared over the structure’s domain. This scalar quantity normalizes mode shapes. Generalized modal mass, frequently used interchangeably with ‘modal mass’, represents the effective mass for a particular mode of vibration.
Generalized method of moments – It is a robust statistical technique used to estimate model parameters by minimizing the distance between theoretical population moments and their empirical sample counterparts. It is particularly effective for complex models with over-identified, non-linear, or endogeneity issues, providing consistent and efficient estimators without needing strict assumptions about data distribution.
Generalized plane strain – It is a 2D modeling approach for long, prismatic structures (e.g., pipes, tunnels) where strain depends only on cross-sectional coordinates (x, y) but allows for constant, non-zero axial strain (ez) and bending. Unlike standard plane strain (where ez = 0), generalized plane strain accounts for axial expansion / contraction and bending.
Generalized programme – In software engineering, is a flexible, reusable code structure created by extracting common patterns or behaviours from specific instances, reducing redundancy, and improving maintainability. It uses parameterization to tailor functionality to immediate task demands without needing separate, distinct programmes for every sequence.
Generalized strain – It refers to a broad class of deformation measures, including Lagrangian, Eulerian, and Hencky tensors, used in continuum mechanics to describe material deformation under load. It extends beyond simple linear engineering strain to account for large deformations, finite elasticity, and plasticity.
Generalized thermodynamic forces – These are driving agents (gradients in temperature, pressure, or chemical potential) which initiate irreversible, non-equilibrium processes and are coupled to fluxes (heat flow, mass diffusion). They represent the rate of entropy production per unit flow.
Generalized transfer function – It is a mathematical representation, typically in the s-domain (Laplace) or z-domain (discrete), defining the input-output relationship of a linear time-invariant (LTI) system with zero initial conditions. It is defined as the ratio of the output transform to the input transform, representing system dynamics through poles and zeros.
General layout drawing – General layout drawing is normally prepared in plan-view. It describes (i) entry gates and plant boundary, (ii) plant approach roads, (iii) location of the plant, equipment and facilities, (iv) provides the linkages between the plant equipment and facilities, (v) road and rail movements, (iv) conveyors and pipeline routings, (vi) critical and regulatory clearances if needed, (vii) location of chimneys and stacks, and (viii) green belts. The drawing is normally prepared to the scale with building dimensions.
Generally accepted accounting principles – These are the standardized, rules-based framework of accounting guidelines, standards, and procedures established by the ‘financial accounting standards board (FASB). They ensure consistency, transparency, and comparability in financial reporting for organizations.
General machine learning – It is defined as a subset of artificial intelligence which utilizes computer algorithms to automatically perform specific tasks by learning patterns and making predictions from data. It encompasses approaches such as supervised learning, unsupervised learning, and reinforcement learning, and includes different algorithms tailored for different applications.
General mathematical framework – It is a structured, unified set of equations, laws, and logical concepts used to model, simulate, and control complex physical systems. It translates real-world phenomena into mathematical representations (e.g., differential equations, CAD) to predict behaviour, analyze performance, and optimize design, bridging fundamental physics with practical applications.
General packet radio service – It is a 2.5G packet-switched, ‘always-on’ data transmission technology for GSM (global system for mobile communications) networks, enabling speeds of up to 171.2 kilo-bits per second (typically 40 kilo-bits per second to 60 kilo-bits per second). It allows for efficient, simultaneous voice and data services, representing a critical, early mobile internet standard which acts as a bridge between 2G and 3G.
General precipitate – It is a precipitate which is dispersed throughout the matrix.
General purpose polystyrene – It is a clear polymer which shows high stiffness, good dimensional stability, low specific gravity and excellent electrical properties. It offers several advantages over other polymers because of its clarity and ease of processing, both of which are because of its amorphous nature.
General records – These are documents, data, or files created during an organization’s day-to-day administration and operations which are not personal or mission-specific. They provide evidence of organizational activities, supporting functions like budgeting, scheduling, and procedures, and are typically managed under retention schedules.
General soldering – It means soldering technology which is used in applications that range from the packaging of integrated circuit chips to the fabrication of industrial heat exchangers. Hence, soldering applications are informally categorized as being either structural or electronic in nature. Regardless of these categories, soldering technology depends on certain fundamental parameters namely (i) properties and selection of solder alloy, (ii) selection of the substrate base material, (iii) joining technique, (iv) coating of substrate base material for enhancing solderability, (v) selection of flux for promoting adequate wettability by the solder, (vi) cleaning procedure to address the corrosivity of the flux residues, (vii) combined substrate, solder, and flux properties, and (viii) joint design and manufacturing procedures.
General support system – It is an interconnected set of information resources, including hardware, software, data, applications, communications, and people, under the same direct management control which shares common functionality. These systems are designed to provide processing or communications support across a wide array of applications.
General ventilation system – It is an engineered, broad-approach method which mixes outdoor air with indoor air to dilute contaminants, control temperature, and manage humidity across an entire space. It uses natural or mechanical (fan-driven) methods to supply and exhaust air, focusing on overall air quality.
Generate code – It refers to the process of producing executable code from design models, particularly for domain classes, which handle the logical processing defined in system operation contracts. This process can be automated and is frequently represented in pseudocode which can be translated into different programming languages, especially object-oriented ones.
Generated contaminants – These refer to foreign, unwanted substances, gaseous, liquid, or solid (particulate), which are produced, released, or introduced during manufacturing, industrial, or, in advanced cases, semiconductor, processes. Unlike external pollutants, these contaminants originate directly from tools, personnel, materials, or the specific process itself, needing specific, quantified engineering controls to maintain product quality, equipment reliability, or, in the case of clean rooms, to keep contamination below regulatory limits.
Generated electrical power – It refers to the electrical energy produced by generation stations or distributed generation units within electrical power networks, which is subsequently transmitted to consumers.
Generated electron – It refers to the liberation of free electrons from a material’s surface or within a medium, typically induced by external energy sources such as heat, light, or electric fields. These generated electrons are important for creating currents in devices like electron microscopes, vacuum tubes, and accelerators.
Generated energy – It is the process of converting main energy sources, such as chemical (coal, gas), nuclear, kinetic (wind, water), or solar, into electrical energy using generators or transducers. It involves transforming mechanical or thermal energy into electricity through electromagnetic induction, typically using turbines.
Generated images – These refer to artificially created visual content that embodies specific desired characteristics, frequently produced using generative adversarial networks (GANs) to replicate the visual aspects of real images associated with particular labels or classes.
Generated plasma – It is a, frequently artificial, fourth state of matter created by subjecting gases to high energy, such as electric discharges such as DC (direct current), RF (radio frequency), microwave), intense heat, or lasers, causing substantial ionization. It consists of free electrons, ions, and neutrals, engineered for applications like surface etching, thin-film deposition, and cutting.
Generated sample – It refers to a, frequently computer-simulated, data point or, in production, an engineering sample (ES) (prototype) which mimics real-world characteristics for testing. These samples are used to evaluate, analyze, or validate design specifications, such as structural reliability, signal processing, or manufacturing feasibility, before full-scale production.
Generated shock wave – It is a thin, high-amplitude discontinuity in a fluid, gas, or plasma caused by a sudden, intense disturbance or an object moving faster than the local speed of sound. It is characterized by nearly instantaneous jumps in pressure, temperature, and density, propagating outwards as a cone-shaped disturbance.
Generated stress – It is the internal resistive force per unit area (S = F/A) developed within a material to counteract external loads, thermal expansion, or growth, opposing deformation. It acts as an internal reaction to maintain equilibrium.
Generated voltage – It is the electromotive force (EMF) produced within an electrical machine’s armature windings through electromagnetic induction, proportional to magnetic flux, rotor speed, and machine construction. It acts as the internal voltage source before accounting for internal resistance / reactance drops, frequently called ‘back EMF’ in motors or ‘induced voltage’.
Generating capacity – It is the maximum, instantaneous electrical power output a generator or power plant is capable of producing, normally measured in mega-watts (MW) or kilo-watts (kW). It represents the installed capability (nameplate capacity) and is a critical metric for power system planning, adequacy, and reliability.
Generating mechanism – It is a specialized kinematic linkage or device designed to produce a specific, frequently complex, path, motion, or function by converting an input motion (normally rotary) into a predetermined output movement. They are fundamentally used in kinematic synthesis to achieve precise motion profiles needed in manufacturing, robotics, and machine design.
Generating plant – It is an industrial facility designed to convert different primary energy sources into electrical energy for distribution to the grid. Engineering these facilities involves harnessing mechanical energy, typically through turbines driven by steam, water, or wind, to turn generators. Common types include fossil fuel, nuclear, hydro, and renewable (solar / wind) plants.
Generating unit – It is a system consisting of a prime mover (e.g., turbine, engine) and a generator which converts mechanical, thermal, or chemical energy into electricity. It is an individual, identifiable component in a power plant with specific capacity constraints, frequently measured in mega-watts or giga-watts.
Generation assets – These are tangible, physical resources used to convert different energy sources (fossil fuels, nuclear, renewables) into electricity. They encompass machinery, equipment, and facilities like turbines, generators, and solar panels. These assets are important for utilities and independent power producers to generate revenue.
Generation capacity – It is the maximum potential power output a power plant or system can produce at a given moment, typically measured in mega-watts (MW) or giga-watts (GW). It represents the rated, installed, or nameplate capability of equipment to meet peak electricity demand.
Generation component – It refers to a piece of equipment, system, or software module designed to produce, convert, or create a specific output, such as electrical energy, mechanical components, or software code. These components are necessary for converting raw resources (fuel, wind, solar) into useful energy or transforming inputs into structured outputs.
Generation computer – It refers to the classification of computer systems based on significant technological advancements, categorized from the first generation using vacuum tubes to the anticipated fifth generation aimed at creating intelligent machines through software breakthroughs.
Generation cost – It is the total expense of building, operating, and maintaining a power plant, typically expressed in money value per mega-watt hour or per kilo-watt hour. It covers capital investment (construction, financing) and operational expenses (fuel, Operation and maintenance). The standard metric is the ‘levelized cost of electricity’ (LCOE).
Generation device – It is an electro-mechanical machine which converts mechanical energy (rotational movement) into electrical energy (current) based on Faraday’s law of electromagnetic induction. It uses a rotor and stator to produce alternating current (AC) or direct current (DC). Key applications include power plants, backup generators, and transport vehicles.
Generation investment – It refers to the strategic, technical, and economic allocation of capital to build, upgrade, or maintain power generation assets (e.g., wind, solar, gas turbines). It involves analyzing risks, market uncertainties, and technology choices to maximize returns, frequently using models like Monte Carlo simulation and bilevel optimization. This involves allocating funds to power generation technologies to meet electricity demand, particularly focusing on balancing risks and returns in liberalized markets.
Generation IV nuclear reactors – These are advanced, high-efficiency, and inherently safe designs selected by the Generation IV international forum (GIF) for commercial development by 2030–2050. These reactors focus on sustainability through closed fuel cycles, high-temperature operations (up to 1,000 deg C) for industrial heat / hydrogen production, and superior proliferation resistance.
Generation pump – It very frequently refers to a regenerative pump (also known as a regenerative turbine pump or peripheral pump). It is a type of rotodynamic (kinetic) pump characterized by its ability to produce high-pressure lift at low flow rates. These pumps operate by having an impeller with multiple radial blades, which recirculate fluid repeatedly between the blades and an annular casing channel.
Generation resources – These are physical assets, technologies, and systems which convert primary energy (fuel, solar, wind, hydro) into electricity, encompassing centralized power plants, renewable energy sources, and distributed energy resources (DERs). These resources are categorized by dispatchability, capacity, and operational characteristics, acting as the foundation for grid reliability and power supply.
Generation source – It is a device or system which converts mechanical, chemical, or radiant energy into electrical energy, such as generators, solar photo-voltaic, or fuel cells. It defines the specific point of origin, boundary, and control system for electricity injected into a grid or distributed network. These are methods for producing electricity, including renewable sources (solar, wind) and non-renewable sources (diesel generators).
Generation systems – These refer to systems which convert energy from one form to another, such as photovoltaic (PV) power systems which convert sunlight directly into electricity. These systems can be configured as stand-alone or grid-connected and are designed to meet varying power requirements.
Generation technology – It refers to the methods, systems, and equipment used to convert main energy sources, such as fossil fuels, nuclear, solar, wind, and hydro, into electricity. It covers a range of scales, from large, centralized utility power plants to distributed, small-scale systems designed for local, efficient, and reliable energy production.
Generation unit – It is an individual, identifiable piece of equipment or machinery which converts a main energy source (such as fuel, wind, or sun) into electrical power. Key engineering characteristics include minimum / maximum capacity constraints, efficiency (heat rate), and operating costs. These units can range from large-scale power plant generators to small-scale distributed generation (DG) units.
Generative methods – These are computational, rule-based techniques, such as AI (artificial intelligence), algorithms, or shape grammars, which automatically produce, simulate, and optimize design alternatives based on specific parameters, constraints, and objectives. This approach allows engineers to explore vast, complex design spaces efficiently, frequently yielding innovative, lightweight structures which exceed traditional manual design capabilities.
Generative models – These are a class of machine learning models designed to learn the underlying probability distribution of a dataset, allowing them to create new, synthetic data instances which resemble the training data. Unlike discriminative models, which focus on distinguishing between classes, generative models model the joint probability or the data distribution.
Generative process – It is a methodology which leverages artificial intelligence (AI), algorithms, and simulation to automate and optimize the creation of product designs and manufacturing processes. Unlike traditional, manual CAD (computer aided design)-based design, this approach focuses on engineers defining functional goals, constraints (such as materials, manufacturing methods, and cost), and performance criteria, allowing the software to generate numerous optimized design solutions. The generative process involves several key phases, frequently described as an ‘iterative’ or ‘evolutionary’ approach.
Generator – It is a machine which converts mechanical energy (from turbines, engines) into electrical energy using electro-magnetic induction. Based on Faraday’s law, a conductor moves through a magnetic field to create voltage. It is necessary for power grids, backup power, and industrial applications. Multiple energy sources are used to turn the generator. Generator is also a convolutional neural network (or similar structure) which takes random noise as input and transforms it into synthetic data (e.g., images, text, audio) with the aim of creating samples indistinguishable from real data.
Generator blocks – These refer to two main concepts namely structural foundations for power generation equipment or functional modeling blocks in simulation / electrical design. They provide robust support for turbine-generator shafts (concrete / steel) or represent electrical / mechanical components (speed, torque) in dynamic power system models.
Generator efficiency (n) – It is the ratio of useful electrical power output (Pout) to mechanical power input (Pin), normally expressed as a percentage [n = Pout/Pin) x 100). It measures how effectively a generator converts rotational energy into electricity, with losses typically dissipated as heat because of friction, windage, and resistance. The measure of how well a generator transforms mechanical energy into electrical energy, where a higher percentage indicates less energy loss during conversion.
Generator line – It typically refers to the main power connection system (or main leads) which carries electricity from the generator’s stator terminals to the main transformer or switchgear. It is an important component of the generator voltage system, responsible for transferring large quantities of current at typical generator voltages (frequently in the 10 kilo-volts to 25 kilo-volts range).
Generator matrix (G) – It is a ‘k x n’ matrix used in coding theory to encode message bits into codewords for error detection and correction. It generates a linear block code by multiplying a k-length message vector ‘m’ by ‘G’, producing an n-length codeword c = m x G. The rows form a basis for the code.
Generator mode – It refers to the operational state where an electrical machine converts mechanical energy (rotational kinetic energy) into electrical energy, based on Faraday’s law of electromagnetic induction. It operates by rotating a conductor within a magnetic field to induce a voltage.
Generator node – It refers to a specific, modeled point within a system (such as a power grid or network) where energy or signals are produced, injected, or managed. In electrical systems, these nodes represent power plants or generators supplying electrical power. They are important for analyzing, simulating, and controlling network behaviour, frequently acting as boundary conditions.
Generator polynomial – It is the unique non-zero polynomial of minimal degree within a cyclic code which can generate all other codewords through multiplication with a polynomial. Generator polynomial is a unique, minimal-degree polynomial used in coding theory to generate cyclic codes for error detection and correction. It acts as a divisor for all valid code-words. It is necessary for constructing BCH (Bose-Chaudhuri-Hocquenghem) and other linear block codes.
Generator set points – These are the target, pre-defined operating parameters, such as voltage, frequency, active power (kilo-watt), and reactive power (kilo-volt-ampere reactive), programmed into a controller to ensure the unit operates safely, efficiently, and within desired limits. These values guide automatic adjustments, ensuring stability during varying electrical loads.
Generator sizing – It is the systematic process of selecting a generator set that matches the electrical demand of a load, considering factors like power capacity, duty cycle, site environmental conditions, and the, startup requirements of connected equipment. It is important to prevent under-sizing, which causes overload trips, and oversizing, which leads to inefficiencies and higher maintenance costs.
Generator torque – It is the rotational force applied by a prime mover (like a turbine or engine) to a generator’s rotor, resisting the electro-magnetic counter-torque created by the electrical load. It determines power output, higher load current increases this braking torque, needing more mechanical input to maintain speed.
Generator transformer – It is a specialized, heavy-duty step-up power transformer located in power plants which increases the low-voltage output of a generator to a higher voltage, facilitating efficient long-distance transmission while isolating the generator from the grid.
Generator unit – It is an electro-mechanical system which converts mechanical energy (from a turbine or engine) into electrical energy based on Faraday’s law of electro-magnetic induction. It typically includes a rotor, stator, and, in power plant applications, is associated with a specific turbine and boiler as a single operating unit.
Generatrix – It is a line, curve, or point which moves along a specified path (directrix) to generate a 3D surface or solid in geometry and engineering design. It is normally used to define shapes in machining. It acts as the ‘generator’ of a shape, such as a straight line rotating to form a cone.
Generic architecture – It is a foundational, high-level abstraction or template consisting of patterns and components which are applicable across different types of systems or enterprises. It promotes reusability, standardization, and simplified modification by providing a ‘tried and true’ structural framework without depending on specific implementation details.
Generic checklist – It is a standardized, adaptable tool used to ensure accuracy, safety, and completeness in repetitive tasks or reviews. It serves as a memory aid to prevent errors by covering universally applicable needs, such as safety, quality standards, and design specifications. It serves as a memory aid to ensure critical items or steps are not overlooked during reviews or briefings.
Generic class – It is a blueprint for creating classes which can work with different data types while maintaining type safety, using placeholders (type parameters) for types specified at instantiation. They enable code reusability and efficiency by allowing a single definition to handle different data types, reducing the need for type casting and runtime errors.
Generic data – It is the information typically used for initial design and evaluation in system development, contrasting with life testing which is more suitable for later stages where reliability growth and system substantiation are critical.
Generic layer – It is a foundational, abstracted, or standard component within a multi-layered system—such as in material science, software, or network design, which possesses predefined properties (e.g., thickness, material, or function) designed to be adaptable across various applications, frequently serving as a base model for more specific implementations.
Generic model – It is a reusable simulation framework which allows for the adaptation of software across several projects with minimal modifications, facilitating efficient development processes in fields such as automotive engineering. It enables the representation of systems at multiple levels of detail, ensuring that models are systematically calibrated and integrated.
Generic specifications – These are specifications which apply to the classification of products of a resource project using United Nations Framework Classification (UNFC).
Generic standards – These are widely applicable, international, or industry-wide, non-product-specific documents defining uniform requirements, test levels, or procedures for processes and safety. They provide necessary, foundational guidelines (e.g., risk assessment) which allow for consistent, efficient development across diverse technical applications rather than specific, one-off designs.
Generic task – It is the process of creating abstract, reusable blueprints for problem-solving which define goals, needed input information, and control strategies for a family of tasks. It facilitates knowledge acquisition by establishing standardized frameworks for analysis, design, and construction, such as classification or diagnosis.
Geochemical analysis – It is the precise determination of the chemical composition, elemental abundance, and mineralogy of ores, rocks, and soil to identify valuable metal concentrations. It involves examining the distribution of elements to assess the economic viability of deposits and guide mining, extraction, and processing strategies.
Geochemical prospecting – It is a technique, which measures the content of specific metals in soils and rocks. Geochemical sampling defines anomalies for further testing.
Geochemical reactions – These are the quantified, frequently time-dependent, chemical interactions between rock, soil, water, and gas within geological systems, utilized to solve environmental or industrial problems. These processes include mineral dissolution, precipitation, and ion exchange, frequently modeled using thermodynamics and kinetics to predict behaviour in reservoirs or to remediate contamination. These are chemical transformations occurring naturally or engineered within earth’s systems, involving the interaction of the lithosphere, hydrosphere, and atmosphere.
Geo-composites – These are engineered, factory-fabricated materials consisting of two or more geosynthetic components, such as geotextiles, geogrids, geonets, or geomembranes, combined into a single product. They are designed to provide multiple, simultaneous functions (e.g., drainage, filtration, reinforcement, barrier) to improve soil structure performance and lower construction costs.
Geochemistry – It means the study of the chemical properties of rocks.
Geodesic – It is the shortest distance between two points on a surface.
Geodesic active contours – These are a class of geometric deformable models used in image processing and computer vision to detect, segment, and track object boundaries by evolving a curve to minimize a specific energy functional. Unlike traditional parametric snakes, Geodesic active contour is based on the theory of curve evolution and the level set method, which allows the contour to naturally handle topological changes, such as splitting or merging.
Geodesic curvature – It is defined as the curvature of the projection of a curve onto the tangent plane of a surface at a point, indicating how much the curve deviates from being a geodesic. If the geodesic curvature is zero, the curve is a geodesic, representing the shortest distance between two points on the surface.
Geodesic dome – It is a spherical or hemispherical, thin-shell structure based on a polyhedron (normally an icosahedron), composed of a complex network of triangles, or geodesics. It is designed to maximize structural strength while using a minimum of materials. Geodesic domes are celebrated for their ability to span large areas without the need for internal columns.
Geodesic isotensoid – It is the constant stress level in any given filament at all points in its path.
Geodesic-isotensoid contour – In filament-wound reinforced plastic pressure vessels, it is a dome contour in which the filaments are placed on geodesic paths so that the filaments show uniform tensions throughout their length under pressure loading.
Geodesic ovaloid – It is a contour for end domes, the fibres forming a geodesic line. It is the shortest distance between two points on a surface of revolution. The forces exerted by the filaments are proportioned to meet hoop and meridional stresses at any point.
Geo-environmental engineering – It is a multi-disciplinary branch of engineering which integrates geotechnical engineering, environmental science, and hydrogeology to manage and remediate contaminated soil and groundwater. It focuses on waste containment (landfills), in-situ soil stabilization, and protecting public health by managing subsurface pollution.
Geo-engineering – It consists of efforts to stabilize the climate system by directly managing the energy balance of the earth thereby overcoming the enhanced greenhouse effect.
Geo-exchange – It is also called ground-source heat exchange. It is an engineering technology which uses the earth’s relatively constant shallow subsurface temperature (typically within the top 30m meters to 150 meters) as a heat source in winter and a heat sink in summer for building heating and cooling. It utilizes a heat pump and underground fluid-filled loops to move, rather than create, thermal energy, providing high efficiency (2 units to 5 units of energy for every 1 unit of electricity used).
Geographical boundary – It is a defined, mapped line or transition zone (natural or artificial) which delineates specific spatial limits for data analysis, engineering projects, or administrative governance. It separates distinct regions based on physical features (rivers, mountains) or, for engineering, arbitrary limits (e.g., project sites, pollution zones, utility service areas).
Geographical information system – It is a computer-based system which is designed to collect, store, manage and analyze spatially referenced information and associated attribute data. It captures, stores, analyzes, manages, and presents data which are linked to location.
Geographic information systems software – It is an engineering-driven platform that integrates, stores, edits, analyzes, and displays geographically referenced information. It acts as a decision-support system, utilizing spatial data (vector / raster) and relational databases (data-base management system, DBMS) to map, model, and solve complex, location-based problems for infrastructure, planning, and environmental management.
Geoid – It is the equi-potential surface of earth’s gravity field which best fits mean sea level (MSL) across both oceans and continents. It serves as the physical reference surface for determining orthometric heights (elevations). Unlike the smooth, mathematical ellipsoid used in GPS (global positioning system), the geoid is an irregular, physical shape representing the true ‘level’ surface where gravity is perpendicular.
Geolocation – It is the process of identifying, tracking, and recording the precise real-time physical location of a device, person, or asset using technologies like GPS (global positioning system), cellular networks, Wi-Fi, and IP (internet protocol) addresses. It combines sensor data, geospatial modeling, and algorithms to determine latitude, longitude, and altitude.
Geolocation database – It is a specialized, frequently cloud-based system which maps internet-connected devices (through internet protocol addresses, Wi-Fi signals, or cellular signals) to physical geographic locations, such as countries, regions, cities, or GPS (global positioning system) coordinates. It functions as a lookup repository, enabling applications to retrieve location data through APIs (application programming interfaces) or direct queries, ensuring efficient, real-time data access.
Geological disposal facility – It is a long-term nuclear waste management option involving the disposal of waste in an engineered underground facility, where the geology provides a barrier against the escape of radioactivity and where the depth protects the waste from disturbances rising at the surface. Depth in this context can refer to both horizontal as well as vertical depth, e.g., if the disposal facility is built into the side of a mountain.
Geological formation – It is a body of rock having a consistent set of physical characteristics (lithology) which distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exposed in a geographical region (the stratigraphic column). It is the fundamental unit of lithostratigraphy, the study of strata or rock layers. A formation is to be large enough that it can be mapped at the surface or traced in the subsurface. Formations are otherwise not defined by the thickness of their rock strata, which can vary widely. They are normally, but not universally, tabular in form. They can consist of a single lithology (rock type), or of alternating beds of two or more lithologies, or even a heterogeneous mixture of lithologies, so long as this distinguishes them from adjacent bodies of rock.
Geological hazards – These are volcanoes, earthquakes, and landslides. These are the natural geological processes which present a direct risk to people or an indirect risk by impacting development. They can be subdivided between earth hazards, such as earthquakes, volcanoes and tsunamis, and shallow geological hazards. Shallow geological hazards occur in the near-surface, typically including landslides, sinkholes and discontinuities which result from cambering or fault reactivation, as well as a range of hazards that occur as a consequence of karst and Quaternary processes. The term ‘shallow geological hazard’ has also been extended by engineering geologists to embrace properties of geological materials which are a potential risk to infrastructure and include clay shrink-swell, collapsible soils, compressible soils, soluble rocks, ground gases, soil piping, soil geochemistry, and running sand. The properties associated with each of these geological hazards are sensitive to changes in moisture content and hence to the consequences of climate change and hydro hazards, including the different types of flooding namely pluvial, fluvial and ground-water.
Geological hydrogen storage – It is the engineered process of injecting and storing large volumes of hydrogen gas (H2) into deep subsurface geological formations, such as salt caverns, depleted oil / gas fields, or saline aquifers, to balance seasonal energy supply and demand, support renewable energy integration, and achieve net-zero emissions.
Geological mapping – It is the systematic field-based process of observing, recording, and interpreting rock types (lithology), structures (faults, folds), alteration zones, and mineralization on the earth’s surface to produce maps which aid in the discovery and extraction of economic mineral deposits. It acts as the main tool in exploration, helping to define the spatial distribution of ore-bearing host rocks and guiding drilling programmes.
Geological repository – It is an engineered, underground facility designed for the permanent, passive disposal of high-level radioactive waste. Located hundreds of meters to kilometers deep in stable geological formations (e.g., clay, salt, granite), it utilizes a multi-barrier system, combining engineered containers / buffers with natural rock, to isolate waste for thousands to millions of years.
Geological reserve – It is the identified, economically and legally extractable portion of a mineral or petroleum resource, confirmed through, and feasibility studies. It represents the tonnage / volume and grade of a deposit that can be mined or produced at a profit using current technology. Unlike resources, reserves are ‘proven’ or ‘probable’ based on high-confidence geological data, mining, metallurgical, economic, marketing, legal, and environmental factors.
Geological sequestration – It is the process of capturing industrial carbon di-oxide (CO2) emissions, compressing them into a supercritical fluid, and injecting them into deep underground porous rock formations (normally) for long-term storage, typically in saline aquifers or depleted oil and gas reservoirs.
Geological storage of carbon di-oxide – It is a process which involves capturing anthropogenic carbon di-oxide (CO2) and injecting it into deep subsurface rock formations, typically above 800 meters down, for permanent isolation from the atmosphere. This method utilizes secure storage in saline aquifers, depleted oil / gas reservoirs, or unmineable coal seams to mitigate climate change. Carbon di-oxide is injected as a high-pressure, super-critical fluid to maximize density and storage efficiency. Long-term containment is ensured through structural (cap-rock), residual, solubility, and mineral trapping.
Geological study – A geological study is an initial evaluation of economic viability. This is got by applying meaningful cut-off values for grade, thickness, depth and costs, estimated from comparable mining operations. Economic viability categories, however, cannot in general be defined from the geological study because of the lack of detail necessary for an economic viability evaluation. The resource quantities estimated can indicate that the deposit is of intrinsic economic interest, i.e., in the range of economic to potentially economic. A geological study is normally carried out in the four main stages namely (i) reconnaissance, (ii) prospecting, (iii) general exploration, and (iv) detailed exploration. The purpose of the geological study is to identify mineralization, to establish continuity, quantity, and quality of a mineral deposit, and thereby define an investment opportunity.
Geologic convection – It is the slow, creeping motion of the earth’s solid silicate mantle caused by currents which carry heat from the interior to the surface. Driven by density differences resulting from temperature variations (hotter material rises, cooler material sinks), it is the main mechanism for heat transfer in the earth’s interior and the main driver of plate tectonics.
Geology – It is the science which is concerned with the study of the rocks which compose the earth.
Geo-mechanical model – It is also called mechanical earth model (MEM). It is a quantitative, numerical representation of the sub-surface, integrating rock mechanical properties, in-situ stresses, and pore pressure. It simulates stress-strain-failure behaviour for tasks like well-bore stability, hydraulic fracturing, and reservoir compaction, typically spanning 1D (well-scale) to 3D (field-scale) dimensions.
Geo-mechanics – It is the engineering discipline focused on the mechanical behaviour of soil and rock in response to stress, pressure, and temperature changes. It combines geological science with engineering mechanics to analyze deformation, stability, and failure, important for applications like oil / gas drilling, mining, tunnel construction, and slope stabilization.
Geo-membrane – It is a very low-permeability synthetic membrane liner or barrier, typically made from polymeric sheets, e.g., HDPE (high-density poly-ethylene), PVC (poly-vinyl chloride), LLDPE (linear low-density poly-ethylene), used to control fluid migration in man-made projects. These durable, flexible liners (frequently 0.8 milli-meters plus thick) are mainly used for containment in landfills, ponds, and mining, as well as for waterproofing tunnels and dams.
Geo-metallurgical mapping – It is a multidisciplinary approach which integrates geological, mineralogical, and metallurgical data to create a 3D spatial, quantitative predictive model of an orebody’s processing performance. It maps how rock properties (e.g., hardness, mineralogy) change across a deposit, allowing mine planners to predict how specific ore blocks is going to behave in a processing plant, hence optimizing recovery and minimizing risk.
Geo-metallurgy – It is an interdisciplinary field integrating geology, mining, mineralogy, and metallurgy to create a spatially based, predictive model of an orebody’s metallurgical performance. By mapping ore characteristics (e.g., texture, mineralogy) across a deposit, it optimizes mining, processing, and economic returns, reducing operational risks and increasing recovery rates.
Geometric accuracy – It is the degree to which a manufactured part, model, or structure conforms to its intended, nominal, or CAD (computer aided design) defined dimensions, shapes, and positions. It measures the closeness of these physical features to their theoretical design, ensuring functionality and quality.
Geometric adaptive control – It is a type of adaptive control, in which the process is controlled using on-line measurements to maintain desired product geometry (for example, dimensional accuracy or surface roughness).
Geometrical acoustics – It is a method for modeling sound propagation by treating sound waves as rays which travel in straight lines, reflect, and diffract, mainly used when sound wave-lengths are much smaller than room dimensions. It is necessary for high-frequency analysis, predicting early reflections, and designing, optimizing, and visualizing sound in architectural spaces.
Geometrical aspect ratio – It defines the proportional relationship between an object’s main dimensions, normally the ratio of its longest side to its shortest side (e.g., length to width, or height to diameter). It is a dimensionless number used to analyze shape, structural integrity, and performance, such as in airplane wings, particles, or structural elements.
Geometrical characteristics – These are measurable, physical attributes of a part’s shape, orientation, and location, frequently controlled through ‘geometric dimensioning and tolerancing’ (GD&T) to ensure functional, precise, and consistent manufacturing. These parameters define specific geometric tolerances (e.g., flatness, parallelism, position) which govern the allowable deviation from a perfect, ideal form
Geometrical characterization – It is the process of defining, measuring, and analyzing the physical shape, size, and surface characteristics of a component or material, such as nano-fibres, pores, or machined parts. It involves quantifying features like dimensions, orientation, and surface roughness to ensure they meet design requirements, often using GD&T (geometric dimensioning and tolerancing) to control form, profile, and position.
Geometrical configuration – It refers to the specific, intentional arrangement, shape, and spatial orientation of components within a system. It dictates performance metrics like heat transfer, structural strength, and imaging accuracy by defining the physical layout and relationships between elements. It involves the spatial setup of elements (e.g., tanks, antennas, structures). In engineering, this translates to the precise physical layout, including dimensions, angles, and distances.
Geometrical kinematics – It is the branch of mechanics (frequently called the ‘geometry of motion’) which analyzes the position, displacement, velocity, and acceleration of points, bodies, and mechanisms without considering the forces causing the motion. It focuses on the geometric, time-based, and spatial relationships of moving components.
Geometrically close-packed – In geometry, close-packing of equal spheres is a dense arrangement of congruent spheres in an infinite, regular arrangement (or lattice). Carl Friedrich Gauss proved that the highest average density. i.e., the highest fraction of space occupied by spheres, which can be achieved by a lattice packing is pi/3 x root 2 = around 0.74048π32≈0.74048. The same packing density can also be achieved by alternate stackings of the same close-packed planes of spheres, including structures that are aperiodic in the stacking direction.
Geometrically necessary dislocations – These are a set of dislocations which are to be present in a crystalline material to accommodate lattice curvatures or non-uniform plastic deformation (deformation gradients). Unlike statistically stored dislocations (SSDs), which form random tangles and contribute mainly to isotropic hardening, geometrically necessary dislocations are ‘like-signed’ (have the same sign) and are needed to maintain the continuity of the lattice during inhomogeneous deformation.
Geometrically non-linear analysis – It is a method which accounts for large displacements, rotations, or strains which considerably alter a structure’s stiffness, shape, and load-carrying behaviour. Unlike linear analysis, it updates the equilibrium equations to the deformed configuration. It is critical for buckling, cables, and thin-walled structures. This analysis is used when deformations are large enough that the small-deflection assumption (where geometry changes are ignored) is no longer valid.
Geometrical mapping – It is the spatial representation of both geological and metallurgical properties of an orebody into 3D models. It maps physical, chemical, and structural attributes to predict how different parts of a deposit is going to behave during mining and processing.
Geometrical optimization – It is the process of refining a component’s shape, size, or structural layout to maximize performance (e.g., stiffness, efficiency) while minimizing costs, weight, or stress, typically using computational tools. It involves manipulating design variables, such as boundary positions or dimensions, under specific constraints.
Geometrical parameters – These are specific, quantifiable dimensions (lengths, angles, diameters, radii) and spatial ratios (e.g., width-to-height) which define the shape, size, and orientation of a component. These variables are critical for modeling, simulating, and optimizing mechanical, structural, or fluid systems, such as in CAD (computer aided design) / FEA (finite element analysis), where they control the geometry.
Geometrical product specifications – These are a comprehensive, international set of ISO (International Organization for Standardization) standards (mainly ISO/TC 213) which define a uniform language for specifying and verifying the geometric characteristics of products. It ensures unambiguous communication of design intent, covering dimensions, tolerances, surface texture, form, orientation, and location of parts.
Geometrical representation – It is the visual and mathematical depiction of physical objects, components, or systems using precise shapes (lines, curves, surfaces, solids) and coordinate systems. It is used in CAD (computer aided design), CAM (computer aided manufacturing), and simulation to define, analyze, and modify engineering designs, spanning 2D sketches to 3D solid models.
Geometrical similarity – It defines a strict relationship where two objects have identical shapes and angular relationships, but differ only in size. Corresponding linear dimensions (length, width, height, radius) maintain a constant, uniform scaling ratio, ensuring proportional shapes for accurate modeling and analysis. All corresponding lengths are scaled by the same ratio (scale factor), frequently denoted as ‘k’. Corresponding angles between the two objects are equal. The ratio of corresponding areas is ‘k-square’, and the ratio of corresponding volumes is ‘k-cube’.
Geometrical spreading – It is the decrease in wave energy density (intensity / amplitude) as it propagates outward from a source, caused by the expansion of the wavefront over a larger area. It is a purely geometric phenomenon, distinct from material attenuation (absorption), and is normally modeled as 1/r (amplitude) or 1/r-square (intensity) for spherical waves in homogeneous media.
Geometrical tolerance – It defines the maximum allowable variation of a part feature’s form, orientation, location, or runout from its theoretically perfect geometry. It defines a 3D tolerance zone (e.g., cylinder, plane) within which the surface or axis must lie. It ensures functionality, interchangeability, and proper assembly. It controls the shape and position of features rather than just their size. These tolerances are used to convey in a brief and precise manner complete geometrical requirements on engineering drawings. These tolerances are applied over and above normal dimensional tolerances when it is necessary to control more precisely the form or shape of some feature of a manufactured part, because of the particular duty that the part has to perform.
Geometric boundary conditions – These are also known as essential boundary conditions or Dirichlet boundary conditions. These are constraints applied to the boundaries of a physical system or computational domain which directly specify the values of the solution variables, such as displacement or slope. These are defined by the displacements or slopes on the boundary of a physical body. These represent kinematic constraints which dictate how the structure or fluid interacts with its environment at its edges.
Geometric Brownian motion – It is a continuous-time stochastic process where the logarithm of the random variable follows a Brownian motion with drift. It is defined by the ‘stochastic differential equation’ (SDE) ‘dSt = mStdt + sStdWt’, representing a variable (St) whose percentage changes are independent and identically distributed, important for modeling proportional growth and non-negative, continuous asset prices.
Geometric buckling – It is a core parameter in nuclear engineering which quantifies the curvature of the neutron flux shape within a reactor, determined solely by the reactor’s physical dimensions and geometry. It represents neutron leakage, where higher buckling values indicate a smaller reactor with higher leakage.
Geometric configuration – It refers to the specific, intentional arrangement, shape, and spatial relationship of components within a system or structure. It defines the physical layout (e.g., distances, angles, surfaces) necessary to meet performance, efficiency, and optimization constraints, such as in heat exchangers or antenna design.
Geometric conservation law – It is a principle for numerical simulations (computational fluid dynamics, CFD) which ensures moving or deforming meshes do not introduce artificial mass, momentum, or energy errors. It requires that the discrete volume change (Jacobian) of a cell matches the volume swept by its moving boundaries.
Geometric constraints – These are explicit restrictions or logical relationships applied to geometric entities (points, lines, arcs, circles, surfaces) to maintain specific spatial, angular, or connectivity relationships. These constraints are important for capturing design intent, ensuring that as dimensions or parts of a model change, the overall geometry preserves necessary characteristics (e.g., parallelism, tangency, concentricity).
Geometric deviation – It refers to the dimensional and shape inaccuracies of a manufactured component relative to its nominal (ideal) CAD (computer aided design) model or design specifications. It quantifies how far the as-built part departs from its intended geometry, encompassing variations in form, orientation, location, and surface profile.
Geometric dimensions – These refer to measurements described in terms of length (L), area (L-square), and volume (L-cube), which are fundamental for quantifying physical quantities.
Geometric dimensioning and tolerancing (GD&T) – These are a symbolic language used on engineering drawings to communicate design intent and allowable variations for manufactured parts. It provides a precise and standardized way to define the geometry, size, and allowable deviations of features, ensuring parts fit together and function as intended. Geometric dimensioning and tolerancing helps manufacturers understand the needed accuracy and precision for each feature of a part. It acts as a universal language for conveying design requirements from the designer to the manufacturer. It relies on a set of symbols and rules defined by standards, ensuring consistency and clarity.
Geometric discontinuity – It is an abrupt change, interruption, or irregularity in the physical shape, cross-section, or boundary of a component, such as holes, fillets, or sharp corners. These features disrupt uniform stress flow, creating localized stress concentrations which frequently reduce fatigue life and accelerate structural failure.
Geometric distortion – It is the undesired alteration, warping, or deformation of spatial relationships, shapes, and positions in digital images or physical structures. It occurs when an imaging system fails to map object points to the correct corresponding image points, resulting in straight lines appearing curved or incorrect relative positioning. Common types include barrel and pin-cushion distortions.
Geometric dynamic recrystallization – Geometric dynamic recrystallization occurs in grains with local serrations. Upon deformation, grains undergoing geometric dynamic recrystallization elongate until the thickness of the grain falls below a threshold (below which the serration boundaries intersect and small grains pinch off into equiaxed grains). The serrations can predate stresses being exerted on the material, or can result from the material’s deformation. Geometric dynamic recrystallization has six main characteristics namely (i) it normally occurs with deformation at high temperatures, in materials with high stacking fault energy, (ii) stress increases and then declines to a steady state, (iii) sub-grain formation needs a critical deformation, (iv) sub-grain misorientation peaks at 2-degree, (v) there is little texture change, and (vi) pinning of grain boundaries causes an increase in the required strain.
Geometric entities – These are the fundamental, mathematically defined components of a geometric model, including points, lines, surfaces, and volumes, stored in databases to define the properties, relationships, and shape of physical parts. They serve as the foundational building blocks for CAD (computer-aided design), CAE (computer-aided engineering), and CAM (computer-aided manufacturing) systems.
Geometric factor – It is a dimensionless parameter or scaling value which quantifies how the shape, size, and spatial arrangement of components influence physical phenomena like stress, radiation, or flow. It acts as a correction factor in calculations to adjust theoretical models for real-world geometry.
Geometric features – These refer to the measurable, physical, and spatial characteristics of a metal part or component, including its shape, dimensions, surface profile, and, in advanced manufacturing, features like fillets, slots, and holes. These features define the ‘as-manufactured’ form and are important for determining the part’s performance, strength, and structural integrity, frequently analyzed alongside micro-structural (metallurgical) properties.
Geometric flow – It is the deformation of geometric structures (shapes, surfaces, or manifolds) over time, governed by partial differential equations which frequently minimize energy functionals like area or curvature. This process is used for image segmentation, material surface processing, and optimizing fluid flow paths.
Geometric frustration – It is the intentional design of structural, material, or magnetic components where-local, optimal packing or alignment rules cannot be satisfied globally. It acts as an ‘engineered defect’ used to programme, tune, or improve material properties (like stiffness or density) and control energy, such as in origami-based meta-materials or metamaterials. Geometric frustration also refers to the phenomenon in which magnetic sites experience competing exchange constraints because of the topology of the magnetic sublattice, preventing the establishment of simple co-linear orderings. This frustration frequently arises in sublattices formed by condensed geometries, such as triangles and tetrahedra.
Geometric mean – It is a mean or average which indicates a central tendency of a finite set of positive real numbers by using the product of their values (as opposed to the arithmetic mean which uses their sum).
Geometric model – It is a mathematical representation of real objects using computer graphics and computer-aided design (CAD), utilizing two-dimensional (2D) or three-dimensional (3D) geometric shapes such as curves, surfaces, and volumes.
Geometric modeling – It is the mathematical, computer-based representation of the 3D shape, volume, and topology of physical objects using points, lines, curves, and surfaces. It is a fundamental component of CAD (computer-aided design) and CAM (computer-aided manufacturing), enabling visualization, simulation, and analysis of parts before production.
Geometric modeling kernel – It is the core software engine in CAD (computer-aided design), and CAE (computer-aided engineering) systems which provides the mathematical algorithms to create, edit, and analyze 3D solid and surface models. It acts as the underlying engine for operations like Boolean additions, fillets, and boundary representation (B-rep), ensuring high-precision, persistent geometry.
Geometric non-linearity – It is a phenomenon where a structure’s stiffness changes substantially because of the large displacements, rotations, or deformations, making the load-displacement relationship non-proportional. It occurs when deformation is large enough to alter the structure’s shape (e.g., more than 1/20th of the largest dimension), rendering small-strain assumptions invalid.
Geometric optic analysis – It is a method which models light as straight-line rays to analyze the trajectory, reflection, and refraction of light through optical systems. It uses principles like Snell’s law and Fermat’s principle to calculate image formation, magnification, and aberrations in components like lenses and mirrors.
Geometric parameters – These are quantifiable, numerical, and relational descriptors which define the spatial arrangement, size, and shape of components (e.g., length-to-diameter ratios, curvature, or tolerance values). These, frequently parametric, variables are used in design, modeling, and simulation to control geometry, improve structural precision, and analyze physical behaviour like vibration or flow. These represent specific dimensions (radii, lengths, angles) and ratios which influence characteristics like, for instance, friction in micro-channels or structural strength.
Geometric primitives – These are the fundamental, irreducible, and atomic shapes (e.g., points, lines, curves, surfaces, volumes) used in engineering, CAD (computer aided design), and computer graphics to construct complex 3D models. They are mathematically defined through equations, enabling efficient, standardized rendering and manipulation of 2D / 3D geometry.
Geometric progression – It is a sequence of numbers where each term, after the first, is found by multiplying the previous term by a fixed, non-zero number called the common ratio (r). It represents exponential growth or decay, where terms change by a constant multiplicative factor rather than a linear additive one, and is used to model phenomena like signal attenuation or compound interest.
Geometric random variable (X) – It models the number of independent Bernoulli trials needed to achieve the ‘first’ success, where each trial has a constant probability of success ‘p’ and failure q =- p. It is a discrete distribution, with ‘X’ taking values 1, 2, 3, ——–.
Geometric reasoning – It is the computational or analytical process of defining, analyzing, and manipulating the geometric properties, shapes, and spatial relationships of physical objects to solve design, analysis, and manufacturing problems. It involves using geometric principles, algorithms, and symbolic AI (artificial intelligence) to understand and reason about shapes, such as identifying features, checking tolerances, and calculating intersections, frequently to automate tasks in CAD (computer aided design), robotics, and computer-aided engineering (CAE).
Geometric relations – These are constraints (e.g., coincident, tangent, parallel, symmetric) defining the spatial, logical, or dimensional dependencies between sketch entities, parts, or features, essential for maintaining design intent in CAD (computer aided design). These constraints ensure, for example, that a hole stay centered or two surfaces remain parallel.
Geometric shape – It is a precise, mathematically defined 2D or 3D form (curves, surfaces, volumes) used to model physical objects, frequently using splines in CAD (computer aided design). These shapes have clear boundaries, measurable attributes (lines, angles, perimeter), and are foundational for spatial, structural analysis.
Geometric similarity – It occurs when a model and its full-scale prototype have the same shape, with all corresponding linear dimensions scaled by a constant ratio. It ensures which angles are equal and the ratio of lengths, areas, and volumes between the model and prototype remains constant.
Geometric space – It defines a 3D, continuous, and frequently axiomatic region (x, y, z) used to locate, model, and analyze physical components. It acts as a container for geometric entities (points, lines, planes, solids) and relies on boundary representation (B-rep) or constructive solid geometry (CSG) to define form, position, and orientation for CAD (computer aided design) / CAM (computer aided manufacturing) and robotics applications.
Geometric standard deviation – It is a multiplicative factor which describes the spread of data following a log-normal distribution, normally used in particle size analysis, material strength, and reliability engineering. It is calculated as the exponent of the standard deviation of the natural logarithms of the data.
Geometric stiffness (Kg) – It is a, frequently non-linear, structural matrix component which accounts for the influence of in-plane axial loads (tension or compression) on a structure’s bending stiffness and stability. It measures how applied loads alter structural resistance to deflection, important for buckling analysis and ‘P – delta’ effects. It represents the stiffness associated with an element’s buckled or deformed state. Unlike material stiffness, which depends on material properties (E) and cross-section (I). Kg depends on the axial force (P) and geometry.
Geometric transformation – It is a mathematical operation, frequently using matrix algebra, which alters the position, orientation, or size of CAD (computer aided design) models, images, or data points. Key types include translation, rotation, scaling, and shearing, which are essential for rendering graphics, robotic path planning, and structural analysis.
Geometric unsharpness (Ug) – It is the loss of image edge definition in radiography (penumbra) caused by the finite size of the radiation source (focal spot) rather than a perfect point source. It appears as a blurry transition zone, calculated as ‘Ug = ft/d’, where ‘f’ is the focal spot size, ‘t’ is object-to-detector distance, and ‘d’ is source-to-object distance. Geometric unsharpness is the blurry, gray ‘penumbra’ region at the edges of features in a radiographic image, indicating a loss of spatial resolution.
Geometry – It is the branch of mathematics concerned with the properties, measurement, and relationships of points, lines, angles, surfaces, and solids. It also refers to the physical shape, dimensions, and spatial configuration of metal components, castings, or weld beads. It is important for determining structural integrity, stress distribution, and manufacturing quality, specifically focusing on parameters like bead width, reinforcement height, and cross-sectional profile to prevent cracking.
Geometry-alloy interactions – These refer to how the physical shape, atomic size, crystal structure (geometry), and spatial arrangement of different elements (alloying) influence the resulting micro-structure, phase distribution, and performance of a metal. These interactions are critical since they define how the material deforms, resists corrosion, or gains strength.
Geometry factor – It is also called geometric factor. It is a dimensionless parameter which adjusts formulas to account for the specific shape, size, and orientation of components within a system. It modifies calculations for stress intensity, heat transfer (view factors), or electrical resistivity based on physical, non-material constraints.
Geometry, mensuration, and coordinate geometry – These are foundational mathematical disciplines used to define, measure, and analyze physical structures, spatial relationships, and shapes. They bridge the gap between theoretical design and physical construction or manufacturing.
Geometry optimization – It is a computational, iterative process which systematically adjusts the shape, dimensions, or structural boundaries of a component or system to minimize or maximize a specific performance target (objective function), such as minimizing mass, stress, or drag, while adhering to predefined performance constraints. This process is a critical part of computer-aided design (CAD) and simulation, frequently utilizing ‘finite element analysis’ (FEA) or ‘computational fluid dynamics’ (CFD) to evaluate the performance of each geometric iteration until an optimal, stable, or most efficient configuration is found.
Geometry, passage – It defines the specific shape, configuration, and dimensions of flow channels (e.g., in heat exchangers or fuel cells). It determines flow characteristics, pressure drops, and thermal efficiency. Common configurations include rectangular, trapezoidal, or sinusoidal channels. It determines how fluids, gases, or heat transfer, directly impacting the performance of systems like reactors.
Geophone – It is an electro-mechanical transducer used in engineering and geophysics to convert ground velocity (vibrations / seismic waves) into measurable voltage. Consisting of a magnet and a coil, it detects movements in soil, rock, or structures. Geophones are essential for oil / gas exploration, structural health monitoring, and construction, typically operating in the 1 hertz to 250 hertz range
Geophysical exploration – Airborne geophysical surveys are normally used as the first step in geophysical exploration. Large areas can be effectively covered in a short period of time. The most common aero geophysical maps are magnetometer maps which record the variations in the earth’s magnetic field with high degree of accuracy. The optimal selection of altitude and spacing as well as choice of instrumentation are important in an airborne geophysical survey. On surface, different geophysical methods are used to explore subsurface formations, based on the physical properties of rock and iron bearing minerals such as magnetism, gravity, electrical conductivity, radioactivity, and sound velocity. Two or more methods are frequently combined in one survey for acquiring more reliable data. Results from the surveys are compiled, and matched with geological information from surface and chips or core samples from any previous core drilling, to decide if it is worthwhile to proceed with further exploration. In case the survey results points towards further exploration then the information form basis for the drilling activities. As geophysical survey is normally conducted from the air to begin with, information from the surface surveys is compared and added to the airborne mapping.
Geophysical logging – These are also known as borehole logging or wireline logging. It’ is a technique that involves lowering instruments (sondes) into a drilled hole to continuously measure the physical, chemical, or radioactive properties of the rock formations and fluids. These measurements are recorded as a function of depth to create a “log’, providing in-situ data which complements or replaces the physical inspection of rock cores.
Geophysical methods – These are non-invasive, physics-based techniques used to map subsurface geology and detect ore bodies by measuring physical property contrasts (density, magnetism, conductivity). Key methods include seismic, magnetic, gravity, and electrical surveys, which allow miners to locate resources and define geological structures without extensive drilling.
Geophysical prospecting – It is technique which measures the physical properties (chargeability, resistivity, magnetism etc.) of rocks and define anomalies for further testing. It is the non-destructive, surface-based measurement of physical properties (e.g., density, resistivity, seismic velocity) to map subsurface conditions, detect anomalies, and characterize geological materials. It allows engineers to assess site stability, locate groundwater, or identify voids / contaminants without extensive drilling.
Geophysical survey – It is a scientific method of prospecting which measures the physical properties of rock formations. Common properties which are investigated include magnetism, specific gravity, electrical conductivity and radioactivity.
Geophysical techniques – These are used in the search for iron ores as in most geophysical mapping. These are based upon the presence of measurable contrasts of physical properties between the ore minerals and the surrounding rocks. The physical properties used principally are magnetism (both permanent and induced) and density. Electrical methods (including polarization and electromagnetism) and seismic studies are used sometimes in conjunction with magnetic or gravity surveys to obtain better definition of the ore bodies.
Geophysics – It is the study of the physical properties of rocks and minerals. Geophysics, as applied to iron ore explorations, is mainly a reconnaissance tool which provides information that must subsequently be complemented by geological mapping, petrographic studies, drilling and the evaluation of ore analyses and treatment tests.
Geopolymer composite – It is an advanced, eco-friendly, inorganic material formed by activating alumino-silicate-rich raw materials (e.g., fly ash, slag, or metakaolin) with alkaline liquids to create a ceramic-like binder. These materials are reinforced with fibres, fillers, or nano-particles to improve mechanical, thermal, or chemical properties, providing high durability, fire resistance, and low-CO2 (carbon di-oxide) emissions. These composites are inorganic, amorphous-to-semi-amorphous polymer networks consisting of SiO4 (silicon tetra oxide) and AlO4 tetrahedra. They behave similarly to ceramics but do not need high-temperature firing. They consist of a binder phase (geopolymer gel) and reinforcement materials (fibres, particles).
Geopolymeric mortar – It is an eco-friendly, inorganic engineering construction material produced by activating alumino-silicate industrial by-products (e.g., fly ash, slag) with alkaline solutions to create a 3D cementitious binder. It offers superior durability, high early strength, and improved chemical / fire resistance compared to Portland cement.
Geopolymerization – It is a chemical reaction involving alumino-silicate materials in an alkaline medium which results in a hardened product at room temperature or high temperatures. This process produces alkali activated alumino-silicate binders, which show mechanical properties similar to Portland cement while offering higher resistance to corrosion and reduced carbon emissions during production.
Geopolymers – These are inorganic, alkali-activated aluminosilicate binders formed through the polymerization of materials like fly ash or metakaolin, acting as a sustainable, low-CO2 (carbon di-oxide) alternative to Portland cement. They create a 3D, amorphous-to-crystalline, ceramic-like structure with high mechanical strength, durability, and resistance to fire and chemical attack.
Geosynthetic reinforced soil – It is a composite material comprising alternating layers of compacted fill and geosynthetic reinforcement (geogrids or geotextiles). It improves soil shear strength and bearing capacity, allowing for flexible, cost-effective, and durable construction of retaining walls, steep slopes, embankments, and shallow foundations.
Geosynthetic reinforcement – It is a method which uses polymer-based materials (geo-grids, geo-textiles, geocells) to improve the mechanical properties of soil, specifically strength, stability, and load-bearing capacity, by introducing tensile resistance. It works by creating a composite structure which distributes loads over a wider area, reduces vertical settlement, and minimizes lateral movement, normally used in embankments, steep slopes, and retaining walls.
Geotechnical – It consists of diamond drilling which is targeted and utilized specifically for the collection of information used for mine stability purposes.
Geotechnical application – It is the practical implementation of soil mechanics, rock mechanics, and geology to design, construct, and maintain infrastructure. It involves analyzing subsurface conditions to ensure the stability of foundations, slopes, retaining walls, tunnels, and dams. Key applications include foundation design, slope stabilization, earthwork and earth structures, ground improvement, geo-environmental engineering, and retaining structures.
Geotechnical conditions – These are the physical, mechanical, and chemical properties of soil, rock, and groundwater at a construction site. These conditions determine ground stability, bearing capacity, and settlement potential, important for designing safe foundations, tunnels, and earth structures. These are identified through site investigations, including drilling, sampling, and laboratory testing.
Geotechnical considerations – These are the assessment and analysis of soil, rock, and groundwater properties to determine their impact on, and suitability for, construction projects. These factors, including soil strength, compressibility, and stability, guide the design of foundations, earthworks, and slope stabilization.
Geotechnical engineers – They are civil engineers specializing in the behaviour of earth materials (soil and rock) to design safe foundations, slopes, and underground structures. They analyze site conditions, groundwater, and soil mechanics to support construction projects, mitigate natural hazards, and ensure structural stability. They perform field investigations, soil sampling, and laboratory testing to understand subsurface conditions.
Geotechnical engineering – It is also known as geotechnics. It is concerned with the engineering behaviour of earth materials. It uses the principles of soil mechanics and rock mechanics to solve its engineering problems. It also relies on knowledge of geology, hydrology, geophysics, and other related sciences.
Geotechnical instrumentation – It refers to the use of specialized, on-site sensors and equipment to measure the behaviour, stability, and performance of soil, rock, and related engineered structures. It acts as a diagnostic tool, providing data on parameters like pore pressure, deformation, and strain to mitigate risk, validate design assumptions, and ensure safety during and after construction. Geotechnical instrumentation is used to monitor ground / structure interaction, provide early warnings of potential failures, and verify design models. Common Instruments are inclinometers, piezometers, extensometers, strain gauges and load cells and tilt-meters.
Geotechnical investigation – It is a systematic, technical procedure used in civil engineering to acquire, analyze, and interpret data on subsurface soil, rock, and groundwater conditions. It is conducted to determine the physical and mechanical properties of the earth materials to ensure the stability, safety, and economic feasibility of construction projects, such as foundations, roads, and earthworks. The main objective to determine soil stratification, density, permeability, and shear strength, as well as to identify potential geological hazards (e.g., sinkholes, landslides, liquefaction). It involves a combination of desk studies (reviewing historical data), site reconnaissance (visual inspection), and sub-surface exploration.
Geotechnical site investigation – It is the systematic process of assessing, sampling, and testing subsurface soil, rock, and groundwater conditions to determine their engineering properties. It aims to provide critical data for safe, economical design of foundations, earthworks, and infrastructure projects. The purpose is to evaluate the feasibility of construction, determine bearing capacity, analyze settlement, assess slope stability, and identify potential risks like landslides or groundwater issues. It involves desktop studies, site reconnaissance, and subsurface exploration techniques such as test pits, trenching, and drilling boreholes.
Geotechnics – These technics mean the application of geological, geophysical, and hydrological principles to solve engineering problems related to the ground, encompassing different applications such as foundation design, earthworks, and slope stabilization.
Geotextile reinforcement – It is is the use of permeable, polymeric, planar fabrics to enhance the structural integrity of weak or compressible soils. It works through interfacial friction between the soil and fabric to increase shear strength, distribute loads, reduce differential settlement, and improve stability.
Geothermal – It pertains to the heat of the interior of the earth. Geothermal energy is heat within the earth. The word geothermal comes from the Greek words, ‘geo’ (earth) and ‘therme’ (heat). Geothermal energy is a renewable energy source because heat is continuously produced inside the earth. Geothermal resources are reservoirs of hot water which exist or are human-made at varying temperatures and depths below the earth’s surface. Wells ranging from a few meters to several kilometers deep can be drilled into underground reservoirs to tap steam and very hot water which can be brought to the surface for use in a variety of applications. Geothermal heat is used for heating and cooling, and for generating electricity.
Geothermal brine – It is a hot, highly saline water-based solution extracted from underground reservoirs (frequently 150 deg C to 375 deg C) used for geothermal power generation and mineral extraction. It contains dissolved salts and, in some cases, high concentrations of lithium. These fluids are pumped to the surface to spin turbines via steam, then typically re-injected into the ground.
Geothermal electricity generation – It is the process of harnessing naturally occurring heat (thermal energy) from the earth’s crust, through hydrothermal reservoirs or deep wells, to produce steam or vapour, which drives turbines to generate electricity. It provides reliable, continuous base-load renewable power with minimal emissions, utilizing dry steam, flash, or binary cycle technologies.
Geothermal energy – It is the renewable thermal energy generated and stored in the earth’s crust, derived from radioactive decay and residual formation heat. Engineered systems harness this subsurface heat through wells (1 kilo-meter to 2 kilo-meters deep) to produce electricity through steam turbines or for direct-use heating, utilizing hydrothermal, dry steam, or binary cycle technologies.
Geothermal energy applications – These refer to the use of geothermal energy resources for electricity production and other purposes, including aquaculture and heating greenhouses, with systems such as binary power plants reinjecting used geothermal water back into geothermal wells.
Geothermal energy extraction – It is the process of harvesting heat from earth’s crust (typically 100 deg C to 400 deg C at depths below 5 kilo-meters) for electricity generation or direct heating. It involves circulating fluids through natural or fractured rock formations to transport thermal energy to the surface. Key engineering techniques include hydraulic fracturing in ‘enhanced geothermal systems’ (EGS) and utilizing binary cycles for low-temperature, around 175 deg C resources.
Geothermal environment – It is a subsurface geological setting characterized by higher temperatures (higher than average geothermal gradient), normally possessing hot rock and fluids (water or steam) in porous or fractured rock at manageable depths for energy extraction. Geothermal environments are intentionally tapped to produce electricity (through high-temperature resources) or direct heating / cooling (through lower-temperature resources).
Geothermal exploration – It is the systematic process of identifying, locating, and assessing subsurface geothermal resources (heat, water, or steam) for energy production. It involves interdisciplinary studies, including geological, geophysical, and geochemical surveys, to minimize the high financial risk of drilling by defining reservoir properties and productivity.
Geothermal field – It is an area where water from the earth’s surface seeps through faults and cracks to hot regions within the crust, rising back to the surface as hot springs, geysers, or steam. These fields can contain underground reservoirs of hot water and steam, which can be utilized for electricity generation or heating.
Geothermal fluids – These are hot, mineral-rich liquids or vapours (water, steam, or gas mixtures) which transport heat from underground reservoirs to the surface for energy production. They typically range from 100 deg C to over 300 deg C, frequently flashing into steam upon depressurization in production wells, and are managed for heat exchange or power generation.
Geothermal heating – It is a system which provides space heating and / or cooling to multiple consumers from a single geothermal well or multiple wells, representing a substantial application of geothermal energy resources.
Geothermal heating system – It is a network which provides thermal energy and domestic hot water to a group of buildings using geothermal resources, involving heat production, a piping system for distribution, and a heat centre with equipment to meet heating demands.
Geothermal investment – It involves allocating capital to projects which harness the earth’s subsurface heat for electricity generation or direct heating. It needs high initial capital for drilling and surface infrastructure (power plants, heat exchangers), with substantial upfront exploration risks compared to conventional energy.
Geothermal manifestations – These are surface expressions of heat and fluids originating from the earth’s interior, serving as natural indicators of subsurface geothermal systems. These features are necessary for locating geothermal reservoirs, assessing their potential, and managing sustainable energy extraction.
Geothermal power generation system – It is a method for producing sustainable electricity by tapping into high-temperature heat from the earth’s crust (typically 1 kilo-meter to 4 kilo-meters deep). It uses steam or hot water from hydrothermal reservoirs to spin turbines, or a binary fluid in cooler systems, to drive generators.
Geothermal power plant – It is an industrial facility which converts heat energy from the earth’s crust, accessible as high-pressure hot water or steam, into electrical energy. Using wells drilled into geothermal reservoirs, these plants drive turbines to generate electricity, typically operating with efficiencies of 7 % to 10 %.
Geothermal prospecting – It is the process of detecting, locating, and mapping subsurface heat, fluid, and permeability to identify viable, exploitable geothermal reservoirs. It uses integrated geological, geophysical (e.g., resistivity), and geochemical techniques to find, quantify, and model geothermal systems for power generation or direct-use applications, optimizing for successful well drilling. It involves geological mapping, geochemical surveys of surface fluids, and geophysical methods like resistivity, seismic, and magnetotelluric (MT) surveys.
Geothermal reservoir – It is a subsurface volume of porous, permeable rock containing trapped hot water or steam (above 150 deg C for electricity). Engineering focuses on managing this fractured, frequently dynamic, hydrothermal system to sustainably extract thermal energy, treating it as a ‘heat bank’.
Geothermal reservoir engineering – It is the science of managing and optimizing the extraction of heat and fluids (steam / water) from underground reservoirs for sustainable energy production. It involves analyzing, modeling, and forecasting the behaviour of these sub-surface systems to ensure efficient, long-term, and economical power generation. It focuses on studying fluid changes (pressure, temperature, saturation) and flow within fractured, porous rock to maximize heat recovery while maintaining resource sustainability.
Geothermal source temperature – It is the thermal energy level of underground hot water, steam, or rock, typically ranging from 50 deg C to over 350 deg C. Engineering defines it by its application namely low-temperature (below 150 deg C) for direct heating, and medium-temperature / high-temperature (above 150 deg C) for electricity generation. Temperature range varies from shallow, low-temperature geothermal heat pumps (around 10 deg c to 20 deg C) to high-temperature reservoirs (above 200 deg C) used for power generation.
Geothermal springs – These are natural, geothermally heated groundwater discharges emerging at the earth’s surface, with temperatures considerably higher than the local ambient air temperature. From an engineering perspective, they are low-to-moderate temperature resources (50 deg C to 150 deg C) utilized for direct heat applications or potential power generation. These springs are created when groundwater is heated by, or comes into contact with, hot rocks (frequently near volcanic areas or faults) and rises through crustal fractures.
Geothermal storage – It is a method which uses the subsurface, such as aquifers, deep rock formations, or abandoned wells, to act as a natural, large-scale battery which stores thermal energy for later use. Unlike conventional geothermal power plants which only extract heat, geothermal storage systems can both ‘charge’ the underground with heat / cold and ‘discharge’ it, facilitating seasonal storage and grid stability.
Geothermal system – It is a sustainable, and renewable energy technology which extracts heat stored beneath the earth’s surface, contained in rock and fluids, for direct heating, cooling, or electrical power generation. These systems utilize natural heat from the earth’s crust, frequently using closed-loop boreholes or open-loop aquifer, to transfer thermal energy, and they can be improved (engineered) to improve efficiency when natural permeability is low.
Geothermal technology – It comprises methods used to capture, extract, and utilize heat from beneath the earth’s crust for sustainable power generation, direct heating / cooling, and industrial processes. These systems harness renewable thermal energy through wells, heat exchangers, and pumps, providing consistent base-load electricity and efficient climate control.
Geothermal water – It is groundwater heated by the earth’s interior to temperatures typically 30 deg cand above, frequently acting as a carrier medium (liquid or steam) for extracting thermal energy. It is treated as a mineral-rich fluid, managed through wells for direct heating or power generation, then normally reinjected.
Geothermal well – It is a borehole drilled 3 kilo-meters to 10 kilo-meters into the earth’s crust to access subsurface heat, transporting high-temperature water or steam to the surface for electricity generation or direct heating. These wells, frequently leveraging oil and gas technology, function as either production conduits or reinjection points.
Gerber parabola – It is also called Gerber line / criterion. It is a non-linear failure criterion used in mechanical engineering to predict the fatigue life of ductile materials subjected to combined fluctuating loads (a combination of alternating stress and mean stress). It provides a parabolic boundary on a fatigue diagram (mean stress against alternating stress) which best fits experimental failure points.
Gerchberg-Saxton (GS) algorithm – It is an iterative phase retrieval algorithm widely used in optics to determine the missing phase information of a wavefront from two known intensity measurements in different planes (typically the image and far-field, or Fourier, planes).
Germanium (Ge) – It is a semiconducting metalloid element. Although it looks like a metal, it is fragile like glass. Its electrical resistivity is about midway between that of metallic conductors and that of good electrical insulators. It has interesting electrical properties. Its first significant use has been in solid-state electronics, and with it the transistor has been invented. Indeed, the entire modern field of semi-conductors owes its development to the early successful use of germanium. Germanium is still used in the field of electronics, but its use in the field of infrared optics has surpassed its electronic applications. Germanium has also found widespread use in the fields of gamma ray spectroscopy, catalysis, and fibre optics.
Germanium (Ge) bottom cell – In photovoltaic (PV) applications, it is the lowest layer in a multijunction solar cell (typically triple-junction or higher) which acts as both the active material for long-wavelength photon absorption and as the mechanical substrate for growing top-layer semiconductors. It is typically a germanium wafer, frequently p-type, which is optimized to absorb near-infrared radiation.
Germanium (Ge) concentration – It refers to the quantity of Germanium present within a silicon-germanium alloy or crystal, normally measured as an atomic percentage or atomic fraction. It is a critical parameter in semiconductor manufacturing used to induce strain in transistor channels to increase hole mobility.
Germanium (Ge) crystal – It focuses on the predictable design, growth, and manipulation of germanium’s atomic and lattice structure to optimize its electronic, optical, and thermal properties for high-performance applications. It bridges the gap between pure semiconductor science (6N-13N purity) and industrial engineering, utilizing techniques like zone refining and Czochralski (Cz) growth to produce single crystals with tailored properties, such as low dislocation density and specific impurity control for radiation detectors or infrared optics.
Germanium (Ge) devices – These refer to electronic components which utilize germanium as the semiconductor material, particularly focusing on metal-insulator-semiconductor (MIS) structures, including germanium-on-insulator (GOI) configurations. These devices are modeled to understand their performance characteristics, especially in comparison to silicon-based devices.
Germanium (Ge) indiffusion – It is the process of introducing germanium atoms into a solid substrate (normally silicon) to form a new material or modify its semiconductor properties. It is a specific type of diffusion where germanium atoms, acting as dopants or alloy components, migrate from a source into a material lattice.
Germanium (Ge) interface – It refers to the boundary between germanium (Ge) and high-k dielectric materials, where stabilization is critical to prevent issues such as germanium indiffusion, which can adversely affect electrical characteristics. The selection of appropriate interfacial layers is important for maintaining the performance of high-k materials on germanium substrates.
Germanium-on-insulator – It is a substrate technology featuring a thin, high-mobility single-crystal germanium layer atop an insulating layer (typically silicon di-oxide) on a silicon wafer. It combines Germanium’s superior charge carrier mobility with silicon-on-insulator (SOI) benefits, such as reduced parasitic capacitance. Key fabrication methods include ‘smart cut’ technology, wafer bonding, and epitaxial growth.
Germanium (Ge) substrates – These are high-mobility, CMOS (complementary metal-oxide-semi-conductor) compatible, single-crystal semiconductors mainly used in advanced electronic / optoelectronic devices, infrared optics, and as epitaxial templates for III-V solar cells. Engineered Ge substrates, including germanium-on-insulator, offer superior performance in high-speed, low-power applications by addressing native oxide issues.
Germanium (Ge) surface – It refers to the precise, atomic-level control of the surface morphology, composition, and physical properties of germanium substrates. This field is critical for improving performance in semiconductor devices, infrared optics, and epitaxial growth.
Germanium (Ge) system – It refers to a prototypical example of a material system which follows the Stransky–Krastanow growth modality, characterized by island formation and complex phenomena such as Si/Ge intermixing and island ordering.
Germanium (Ge) wafer – It is a thin, single-crystal substrate of high-purity, semiconducting germanium, mainly engineered for its high electron / hole mobility, narrow bandgap, and infrared transparency. It is engineered through crystal growth (Czochralski method), slicing, and polishing to serve as a substrate for epitaxy, optoelectronics, and high-frequency, high-speed integrated circuits.
Getter – It is a substance which is used in a sintering furnace for the purpose of absorbing or chemically binding elements or compounds from the sintering atmosphere which are damaging to the final product. Getters are reactive materials (frequently barium, zirconium, or titanium) placed inside vacuum systems to absorb residual gases, hence maintaining high vacuum pressure. They are typically applied as coatings which chemically bond with or adsorb gas molecules, acting as a ‘getter’ for contaminants which otherwise degrades vacuum integrity.
Gettering box – It is a container for the getter substance which is readily accessible to the atmosphere and prevents contamination of sintered product by direct contact
Ghost lines – These are lines running parallel to the rolling direction which appear in a sheet metal panel when it is stretched. These lines may not be evident unless the panel has been sanded or painted.
Giant magnetostrictive materials – These materials are a class of functional, ‘smart’ materials which show considerably large changes in their physical dimensions (strain) when subjected to an external magnetic field. These materials are capable of producing magnetostrictive strains higher than 30 ppm (parts per million) or 0.001 order of magnitude at room temperature. These materials are distinguished by their capability to convert magnetic energy into mechanical energy (actuation) and vice-versa (sensing) with high energy density, fast response speeds, and high magneto-mechanical coupling.
Giant molecules – These are massive, three-dimensional networks composed of several atoms (e.g., carbon, silicon) or subunits linked by covalent bonds, featuring high melting points and structural strength. Giant molecules precisely assemble ‘nano-atoms’ (nano-scale building blocks) to create custom architectures with controlled functionalities, bridging the gap between small molecules and traditional polymers. These molecules consist of a vast number of atoms (frequently non-metals) covalently bonded in regular repeating lattices (polymers) or continuous, non-discrete networks (diamond, graphite, silicon di-oxide).
Gib – It is a tapered or wedge-shaped strip of metal (or sometimes wood) used in machinery to provide a precise fit, maintain alignment, and adjust for wear between moving parts.
Gibbing – It refers to the process of installing, adjusting, or securing a gib. A gib is a tapered or wedge-shaped piece of metal (or wood) used to tighten the sliding surfaces of machine components, such as a milling machine table or lathe saddle, to eliminate clearance (looseness) and ensure precise.
Gibbs adsorption equation – It refers to the relationship which describes how an increase in the chemical potential of a species at an interface leads to a decrease in the surface tension, indicating that surface tension becomes less positive as the species becomes more enriched at the interface. It is a fundamental thermodynamic relation which links the change in surface tension to the surface excess concentration of a solute. It states that if a solute reduces surface tension, it accumulates at the surface.
Gibbs distribution – it is also called Boltzmann-Gibbs distribution. It is a probability distribution which defines the probability of a system being in a specific state. It acts as a normalization, where probability depends on the state’s energy relative to temperature, favouring lower energy states.
Gibbs effect – It is the peculiar 9 % overshoot and ringing artifacts which occur at the edges of a signal when reconstructed using a finite number of sinusoidal components (Fourier series), particularly around jump discontinuities. It acts as a persistent error where the amplitude of oscillations does not disappear even as more Fourier terms are added, representing a classic artifact of signal truncation.
Gibbs energy function (G) – It is a thermodynamic potential defined as G = H- TS, where as ‘H’ is enthalpy, ‘T’ is temperature in Kelvin, and ‘S is entropy. It represents the maximum reversible, non-expansion work obtainable from a system at constant pressure (P) and temperature (T). It determines reaction spontaneity, where a decrease (-delta G) indicates a spontaneous process.
Gibbs free energy – It is a thermodynamic potential which can be used to calculate the maximum amount of work, other than pressure-volume work, which can be performed by a thermodynamically closed system at constant temperature and pressure It is the thermodynamic function delta G = delta H – T delta S, where ‘H’ is enthalpy, ‘T’ is absolute temperature, and ‘S’ is entropy.
Gibbs free energy minimization – It is a computational, thermodynamic method used to determine the stable equilibrium composition of a chemical system at constant temperature (T) and pressure (P) by finding the species distribution which results in the lowest total Gibbs energy, ‘G’, without needing individual reaction calculations. It is fundamental to chemical and process engineering for optimizing reactors, predicting phase behaviour, and reducing waste.
Gibbs free energy of formation – It is the change in Gibbs energy when 1 mole of a compound is formed from its constituent elements in their standard states (typically 298 K, 0.1 mega-pascal). It measures a substance’s thermodynamic stability and spontaneity at constant temperature and pressure.
Gibbs function (G) – It is also called Gibbs free energy. It is a thermodynamic potential defined as G = H- TS (enthalpy minus the product of temperature and entropy). It represents the maximum quantity of non-expansion work obtainable from a system at constant temperature and pressure, and is used to determine reaction spontaneity.
Gibbs-Helmholtz equation – It is a fundamental thermodynamic relation used to calculate changes in Gibbs free energy as a function of temperature, specifically to determine reaction spontaneity and equilibrium constants.
Gibbs-Marangoni effect – It is the mass transfer along a liquid-gas or liquid-liquid interface (such as a molten metal weld pool) driven by surface tension gradients. It causes molten metal to flow from regions of low surface tension to high surface tension, directly influencing melt pool shape, impurity distribution, and solidification structure in processes like welding and casting.
Gibbs method – It is a geometrical and vector-based technique, mainly used in orbital mechanics to determine a satellite’s orbit using three sequential position vectors. It ensures the orbit satisfies the geometric constraint that all three vectors are coplanar. It is a fundamental approach for determining preliminary orbit elements from observations.
Gibbs phase rule – It is a general principle governing multi-component, multi-phase systems in thermodynamic equilibrium. For a system without chemical reactions, it relates the number of freely varying intensive properties (F) to the number of components (C), the number of phases (P), and number of ways of performing work on the system (N) i.e., F = N + C – P + 1. F=N+C−P+1Examples of intensive properties which count toward ‘F’ are the temperature and pressure. For simple liquids and gases, pressure-volume work is the only type of work, in which case N = 1. The number of degrees of freedom ‘F’ (also called the variance) is the number of independent intensive properties, i.e., the largest number of thermodynamic parameters such as temperature or pressure that can be varied simultaneously and independently of each other. An example of a one-component system (C = 1) is a pure chemical. A two-component system (C = 2) has two chemically independent components, like a mixture of water and ethanol. Examples of phases which count toward ‘P’ are solids, liquids and gases.
Gibbs phenomenon – It is a signal processing and mathematical artifact where Fourier series approximations of signals with sharp, discontinuous edges (e.g., square waves) show persistent, non-vanishing oscillations (around 9 % overshoot) near the edges. These ‘ringing’ artifacts do not disappear as more harmonics are added.
Gibbs sampler – It is a Markov Chain Monte Carlo (MCMC) algorithm used to estimate complex, high-dimensional joint probability distributions by iteratively sampling from the conditional distribution of each variable. It breaks down intractable joint distributions into simpler, sequential, one-dimensional conditional updates.
Gibbs surface free energy – It is the excess energy per unit area (joules per square meter) at the interface of a material compared to its bulk phase, representing the work needed to create that surface at constant temperature and pressure. It indicates the imbalance of inter-molecular forces at surfaces and determines wettability, adhesion, and coating feasibility.
Gibbs-Thomson effect – It refers to the phenomenon where the equilibrium temperature (melting point, freezing point, or solvus temperature) of a phase changes based on the curvature of its interface with another phase. Specifically, it describes how small precipitates or crystals (high curvature) are less stable and have a lower melting point or higher solubility than large, flat surfaces. This effect is fundamentally driven by the increased interfacial energy required to maintain a curved interface, increasing the overall free energy of smaller particles.
Gibbs–Thomson equation – It relates the chemical potential of the vapour in equilibrium with a spherical drop to the radius and isotropic surface free energy of the drop. It quantifies the depression of the melting point (Tm) for a small solid particle of radius ‘r’ in its own liquid. It is a mathematical formula which extends Kelvin’s capillary equation to the case of condensed phases along curved interfaces at constant pressure. It is widely used in materials science to estimate solid-melt interfacial tensions and can explain the phenomenon of lowering the melting temperature for nano-scale materials.
Gibbs triangle – It is an equilateral triangle which is used for plotting composition in a ternary system.
Gibibyte – It is a unit of digital information storage that uses a binary prefix, defined by the International Electrotechnical Commission (IEC) to provide an unambiguous, base-2 measurement. It is used in computer science, and operating systems to accurately represent storage based on powers of two.
Gibs – These are guides or shoes which ensure the proper parallelism, squareness, and sliding fit between metal-forming press components such as the slide and the frame. They are normally adjustable to compensate for wear and to establish operating clearance.
Gibson-Ashby model – It is a widely recognized framework used to predict the mechanical properties (such as elastic modulus and yield strength) of cellular solids and lattice structures based on their relative density. It establishes that the mechanical behaviour of cellular materials is determined mainly by the deformation mechanisms of their microstructure, specifically, whether the material bends or stretches under load.
Gieseler plastometer test – This test method covers a relative measure of the plastic behaviour of coal when heated under prescribed conditions. This test method can be used to get semi-quantitative values of the plastic properties of coals and blends used in carbonization. The plastometer measures the plastic properties of coals by the use of a constantly applied torque on a stirrer placed in a crucible into which the coal is charged. The crucible is immersed in a bath and the temperature increased uniformly. The rates of movement of the stirrer are recorded in relation to increase in temperature.
Gigabit ethernet – It is a networking technology based on the Institute of Electrical and Electronics Engineers (IEEE) 802.3z standard which enables data transmission speeds of 1 gigabit per second (1 Gbps or 1000 Mbps), roughly 10 times faster than Fast Ethernet. It uses CSMA (carrier sense multiple access) / CD (compact disk) or full-duplex switched connections over fibre-optic (1000 Base-X) or copper (1000 Base-T) cabling.
Gigabyte – It is a unit of digital information storage, defined through the International System of Units (SI) as 1,000,000,000 bytes. While normally used to measure storage capacities for hard drives and data, it is distinct from the binary-based “gibibyte” (GiB), which equals 1,073,742,824 bytes.
Giga calorie (Gcal) – It is a unit of energy normally used quantify large quantities of heat, such as in power plants, and industrial processes. It represents one billion calories.
Gigahertz – It is a unit of frequency representing one billion hertz (cycles per second). It is mainly used to measure the clock speed of computer processors (central processing units, CPUs), indicating how many billions of instructions a processor can execute per second. Higher gigahertz normally means faster processing power.
GigaJoule – It is a measure of energy. A GigaJoule equals 1,000,000,000 Joules. A 100-watt light bulb turned on for one second consumes 100 Joules.
Gilbert cell – It is a specialized electronic circuit used mainly in integrated circuits (ICs) as an active, double-balanced frequency mixer or a four-quadrant analog multiplier. It produces an output current which is accurately proportional to the product of two differential input voltages, making it fundamental in radio frequency (RF) design for frequency conversion, modulation, and variable-gain amplification.
Gilbert equation – It is part of the Landau–Lifshitz–Gilbert (LLG) equation. It is a fundamental physical and non-linear partial differential equation which describes the dynamics of magnetization in a ferromagnetic material, incorporating terms for spin precession and relaxation towards an effective magnetic field. It models how magnetic moments process around an effective magnetic field and eventually align with it because of the energy damping, necessary for designing spintronics and magnetic recording devices.
Gilman-Johnston relationship – It is a fundamental empirical model which defines the relationship between dislocation velocity and applied shear stress in crystals. It describes how fast dislocations move through a crystal lattice under an applied force, which directly relates to the plastic deformation rate of the material
Gilsonite – It is also known as uintaite, natural asphalt, or asphaltite. It is a natural, solid hydrocarbon bitumen that is mined from the earth and used extensively in engineering for its unique binding, sealing, and strengthening properties. It is a shiny, black, brittle substance that, when crushed, turns into a dark brown powder, acting as a versatile, non-toxic additive in oil-well drilling, road paving, and construction materials.
Gimbal – It is a pivoted support mechanism, typically consisting of rings or frames mounted on orthogonal axes, which allows an object to rotate freely or remain stable in a specific orientation despite the movement of its base.
Gimbal ring – It is a pivoted, frequently circular, mechanical component which forms part of a gimbal system, allowing an object mounted within it to rotate freely about a specific axis, or to remain stable / upright when its support base tilts. Gimbals are normally nested one within another, frequently orthogonally (90-degree), to provide multiple degrees of freedom (typically pitch, yaw, and roll).
Gimbal system of charging – Gimbal system of charging facilitates controlled distribution of charge material into the blast furnace through a Gimbal type oscillating chute.
Girder – It is a beam used in construction. It is the main horizontal support of a structure which supports smaller beams. Girders frequently have an I-beam cross section composed of two load-bearing flanges separated by a stabilizing web, but can also have a box shape, Z-shape, or other forms. Girders are normally used to build bridges.
Girt – It is a horizontal structural member in a framed wall, mainly used in metal buildings to provide lateral support, resist wind loads, and support wall cladding. Typically made of cold-formed steel (frequently Z-shaped or C-shaped) or timber, they connect vertical columns to stabilize the structure.
Girth – It is the perimeter, circumference, or total distance around the outside of an object, frequently referring to the cross-sectional measurement of columns, pipes, or building structures. It is important for calculating materials (like steel reinforcement or concrete), estimating excavation volumes, and determining structural dimensions.
Girth dimensions – It is the measurement around an object, representing its total perimeter or circumference, rather than its length or height. It is used for determining the cross-sectional size of structures (like columns), calculating material quantities, sizing machinery components, and determining packaging or shipping dimensions [2(width + height) + length].
Girth measurement – It refers to the process of determining the circumference of an object or item, typically for logistics, shipping, or sizing purposes, using standardized calculation methods.
Girth weld – It is a circumferential butt weld used to join two cylindrical components, such as pipes or pressure vessel sections, end-to-end. It is a critical, typically multi-pass, structural weld made around the circumference (or girth) to connect pipeline segments or tank shells, frequently involving a root pass, hot pass, and fill / cap passes.
Givens rotation – It is an orthogonal matrix transformation used in numerical engineering to introduce zeros into specific positions of a vector or matrix, typically to create an upper triangular form. It performs a rotation in a chosen 2D plane (i, j) to zero out a target entry, making it efficient for sparse matrix computations and QR decomposition.
Glacial drift – It is the sedimentary material which has been transported by glaciers.
Glacial striations – These are the lines or scratches on a smooth rock surface caused by glacial abrasion.
Glacial till – It is a heterogeneous, unsorted mixture of clay, silt, sand, gravel, and boulders deposited directly by glaciers. It is frequently a dense, over-consolidated, and competent foundation material, but its high variability, ranging from clay-rich to sandy-gravelly, can lead to unpredictable seepage and inconsistent structural support.
Glaessner – It refers to a phase diagram, also known as the Baur–Glaessner diagram or Chaudron diagram, which efficiently represents the stability regions of solid species in the Fe-O-H system as a function of temperature and hydrogen partial pressure.’
Glancing angle – It is the angle (normally small) between an incident x-ray beam and the surface of the sample. In thin-film deposition (glancing angle deposition, GLAD), it is the highly oblique angle (typically above 70-degree) between an incoming vapour flux and the normal to a substrate surface. This technique leverages self-shadowing and limited surface diffusion to create porous, engineered nano-structures (e.g., columns, helices).
Gland (or gland bushing) – It is that part of a valve which retains or compresses the stem packing in a stuffing box (where used) or retains a stem O-ring, lip seal, or stem O-ring bushing.
Gland nut – It is a specialized threaded fastener used to secure, seal, and adjust packing materials or seals around a moving shaft or cable. It ensures a tight seal against pressure to prevent leaks while reducing wear on rods, frequently used in hydraulic cylinders and electrical cable entries to maintain system integrity.
Gland plate – It is the plate in a valve which retains the gland, gland bushing, or stem seals, and sometimes guides the stem.
Glass – It is as an amorphous, inorganic, non-crystalline solid which lacks a long-range, ordered atomic structure, normally formed by rapidly cooling (quenching) a melt to a solid state without crystallization. It acts as a supercooled liquid with high viscosity, is isotropic, brittle, and typically transparent, with properties tailored through composition. It is an inorganic solid material which is normally transparent or translucent as well as hard, brittle, and impervious to the natural elements. It is made from natural and abundant raw materials (sand, soda ash and limestone) which are melted at high temperature to form a new material, i.e., glass. It is also a term which is sometimes used for porcelain enamel or frit.
Glass additives – These are substances intentionally added to raw materials (mainly silica sand) during production to alter, improve, or refine the properties of the final glass product or to improve the efficiency of the melting process. They are important for customizing glass for applications needing specific mechanical, thermal, or optical characteristics.
Glass aggregate – It is a sustainable construction material produced by crushing and processing waste glass into angular particles, used as a functional alternative to natural sand, gravel, or crushed stone. It is characterized by high permeability, low water absorption, light weight, and excellent compaction, frequently used in backfill, road construction, drainage, and concrete.
Glass batch – It is the precisely measured, mixed, and formulated mixture of raw materials, including silica sand, fluxes, stabilizers, and cullet (recycled glass), which is heated to create molten glass. It defines the final chemical composition, purity, and physical properties of the glass, with compositions converted from mole to weight percentages for batching.
Glass beads – These are frequently referred to as glass microbeads or glass bead abrasive media. These are small, spherical particles made from lead-free, soda-lime glass, typically used for surface treatment. They are considered a ‘soft’ or non-aggressive blasting medium, designed to clean, peen, or finish metal surfaces without removing substantial base material or changing the dimensions of the part
Glass binder – It is a material, frequently finely ground waste glass (glass powder) or a low-melting glass frit, used to hold particles together, acting as a cementing agent in construction or a bonding agent in ceramics / composites. It provides pozzolanic properties in concrete, improves compressive strength, or facilitates hermetic sealing at specific curing temperatures.
Glass bonding – It is the process of joining glass substrates to themselves, metals, or polymers using techniques like adhesive bonding, anodic bonding, or fusion welding to create strong, durable, and frequently transparent joints. It is critical for micro-electro-mechanical systems (MEMS), optics, and fluidic devices.
Glass capsule – It is a brittle, hermetic encapsulation material, frequently used as containers for self-healing agents in concrete, or for holding electronics, liquids, or pharmaceuticals. These capsules create an air-tight and water-tight barrier, protecting substances from environmental factors while being designed to break upon specific stresses, such as crack formation.
Glass-ceramics – These are a family of fine-grained crystalline materials. These are polycrystalline materials produced by the controlled nucleation and crystallization of glass, containing at least one functional crystalline phase and a residual glassy matrix. Glass-ceramics are produced by the controlled, partial-to-complete crystallization of base glass through specialized heat treatment. They combine the fabrication versatility and ease of glass with the improved mechanical strength, toughness, thermal stability, and low thermal expansion of ceramics, typically containing both amorphous and crystalline phases.
Glass cloth – It is the conventionally woven glass fibre material.
Glass coatings – It is frequently referred to as vitreous or porcelain enamels. These are thin, inorganic, amorphous layers, mainly composed of silica (SiO2), boron oxide (B2O3), and other metal oxides, fused onto a metallic substrate. These coatings are engineered to protect the underlying metal, very frequently sheet steel, cast iron, or aluminum, from high-temperature oxidation, corrosive environments, and mechanical wear. Glass coatings also refer to layers applied to glass surfaces, which can improve properties such as durability and optical clarity, and are relevant in contexts where glass interacts with materials like bullets, as they can affect the characteristics of damage and the presence of embedded particles.
Glass cullet – It is crushed, sorted, and cleaned recycled glass (post-consumer or industrial waste) used as a primary raw material feedstock for manufacturing new glass containers, fiberglass, and other products. It acts as a sustainable, energy-saving material which melts at lower temperatures than raw materials, considerably reducing manufacturing energy, emissions, and resource consumption.
Glass electrode – It is a half cell in which the potential measurements are made through a glass membrane.
Glass emissivity – It is the measure of a glass surface’s ability to emit long-wave infrared (thermal) radiation, defined as the ratio of energy radiated from the glass to that emitted by a perfect blackbody at the same temperature, ranging from 0 to 1. Low-emissivity (Low-E) coatings reduce this value to inhibit heat transfer.
Glass envelope – It is a hermetically sealed, evacuated, or gas-filled glass housing (typically borosilicate) used to enclose vacuum tubes, light bulbs, and X-ray components. It provides structural support, electrical insulation, and prevents oxidation of internal components while allowing transmission of light or radiation.
Glass fibre – It is a fibre spun from an inorganic product of fusion which has cooled to a rigid condition without crystallizing. It is a material consisting of several extremely fine fibre of glass. It is formed when thin strands of silica-based or other formulation glass are extruded into several fibres with small diameters suitable for textile processing. Glass fibre has roughly comparable mechanical properties to other fibres such as polymers and carbon fibre. Although not as rigid as carbon fibre, it is much cheaper and considerably less brittle when used in composites. Glass fibre reinforced composites are used in marine industry and piping industries because of good environmental resistance, better damage tolerance for impact loading, high specific strength and stiffness.
Glass fibre filter – It is a high-efficiency porous medium composed of fine, randomly oriented boro-silicate glass fibres, designed for filtering air, gases, or liquids in engineering and laboratory applications. These filters are chemically inert, non-hygroscopic, and heat-resistant (frequently up to 180 deg C or higher), providing high particle retention and high dirt-holding capacity.
Glass fibre reinforced concrete – It is a composite construction material consisting of high-strength, alkali-resistant (AR) glass fibres embedded in a cementitious matrix (cement, sand, polymer, water). It is used in engineering for its high tensile / flexural strength, low weight, and excellent crack resistance, frequently applied in cladding, panels, and thin-shell structures.
Glass fibre reinforced epoxy – It is a high-performance thermosetting composite material consisting of high-strength glass fibres (reinforcement) embedded in a cured epoxy resin matrix. Engineered for structural applications, it offers superior tensile strength, chemical resistance, low moisture absorption, and excellent electrical insulation compared to other polymer composites.
Glass fibre reinforced plastic – It is a high-performance composite material engineered by embedding glass fibres within a polymer matrix (normally epoxy, polyester, or vinylester resin). It combines high strength-to-weight ratio, corrosion resistance, and insulating properties, making it ideal for automotive, aerospace, marine, and construction industries. It is a composite material which consists of a polymer matrix and glass fibres. The polymer matrix is normally an epoxy, vinyl-ester, or polyester thermo-setting resin. The resin which brings the environmental and chemical resistance to the product, is the binder for the fibres in the structural laminate and defines the form of a glass fibre reinforced plastic part. The glass fibres add strength to the composite. They can be randomly arranged, or conveniently oriented. The most common type of glass fibre used for glass fibre reinforced plastic is E-glass (electric), which is alumino-boro-silicate glass. E-CR-glass (electrical / chemical resistance) is also normally used in applications which need particularly high protection against acidic corrosion.
Glass filament – It is a form of glass which has been drawn to a small diameter and extreme length. Majority of the filaments are less than 0.15 millimeters in diameter.
Glass filament bushing – It is the unit through which molten glass is drawn in making glass filaments.
Glass finish – It is a material applied to the surface of a glass reinforcement for improving the bond between the glass and the plastic resin matrix.
Glass flake – It is a thin, irregularly shaped flake of glass, which is typically made by shattering a thin- walled tube of glass.
Glass former – It is an oxide which forms a glass easily. It is also the one which contributes to the network of silica glass when added to it.
Glass forming ability – It is a material’s resistance to crystallization during solidification, enabling it to form an amorphous solid (glass) rather than an ordered crystal upon cooling. A high glass forming ability (GFA) means a material can form a glass at slower cooling rates, allowing for larger bulk metallic glass (BMG) components
Glass-forming region – It is the specific range of chemical compositions within a material system (metallic, oxide, or chalcogenide) where, upon cooling from a liquid state, the material solidifies into an amorphous, non-crystalline structure rather than a crystal. It defines the compositional boundaries which allow a liquid to vitrify. Glass-forming regions (GFRs) are identified on phase diagrams where melt-spinning or rapid cooling techniques (around 10,000 Kelvin per second t0 100,000 Kelvin per second for metallic glasses) successfully avoid nucleation and growth of crystalline phases.
Glass frit – it is a type of finely ground, pre-melted glass (frequently inorganic, low-melting-point boro-silicate or lead-based glass) that is used as a bonding agent, sealant, or coating. It acts as an inorganic, high-temperature ‘glue’ which melts and flows at lower temperatures than the substrates it joins, providing strong, hermetic, and chemically durable seals. Glass frit is a powdered, low-melting-point glass used as a bonding agent, sealant, or coating, created by quenching molten glass and grinding it. It enables high-strength, hermetic sealing of MEMS (micro-electro-mechanical system) / electronic devices at temperatures below 40 deg C and acts as a porous filtering material (fritted glass) in chemical applications.
Glass frit bonding – It is a technique which joins substrates, normally silicon wafers, by melting a low-temperature glass paste (frit) between them, typically below 450 deg C. This process provides strong, hermetic sealing and high-yield encapsulation for MEMS (micro-electro-mechanical system) devices, creating durable, insulating seals that can accommodate surface irregularities.
Glass furnace – It is a specialized, high-temperature industrial refractory unit (typically 1,350 deg C to 1,600 deg C plus) designed for melting raw materials and cullet into molten glass. Engineered for continuous, long-term operation (9 plus years), these furnaces melt, refine, and homogenize glass using fossil fuels with heat recovery (regenerators) or electric boosting.
Glass-glass photo-voltaic modules – These are advanced solar energy systems designed with solar cells encapsulated between two layers of tempered glass, replacing the traditional polymer back-sheet with a second glass pane. This configuration is increasingly used in utility-scale and bifacial solar installations because of its superior durability, long-term reliability (frequently 30 plus year lifespans), and higher resistance to environmental stressors like moisture and UV (ultra-violet) light compared to standard glass-back-sheet modules.
Glass infiltration – It is a process where molten glass penetrates the pores of a ceramic or solid structure (frequently zirconia, ZrO2) to fill void spaces, typically improving mechanical properties, reducing porosity, and improving material strength. It is frequently used to strengthen materials. The infiltration process utilizes pressure or capillary action to introduce liquid glass into a porous ‘preform’ matrix.
Glass insulator – It is a non-porous component made from thermally toughened (annealed) glass, used in high-voltage electrical systems to prevent leakage current between overhead conductors and grounded supports. They provide high dielectric strength, high mechanical strength, and superior resistance to electrical punctures, environmental pollution, and aging.
Glass laminate – It is a type of safety glass manufactured by bonding two or more glass panes together with a durable, transparent plastic interlayer (typically polyvinyl butyral (PVB)) using heat and pressure. Under impact, the interlayer holds fragments together, preventing shattering and providing structural integrity, UV (ultra-violet) protection, and noise reduction.
Glass layer – It is an amorphous, rigid, and transparent or translucent sheet (or film) of inorganic material, typically soda-lime-silica, used for structural, optical, or protective purposes. It serves as a single component in laminates, glazing units, or surface coatings to improve mechanical strength, thermal insulation, safety, and energy efficiency.
Glass lid – It is a cover composed of tempered safety glass (or borosilicate glass) and typically a stainless-steel rim. It is designed to withstand high thermal shock, up to 200 deg C to 250 deg C, offering superior heat resistance, durability, and transparent visibility, allowing for monitoring food without losing moisture or heat.
Glass lubrication – It is a specialized, high-temperature lubrication technique which uses glass, glass-forming materials, or inorganic materials (typically in the form of frit, powder, or paste) to act as a protective barrier and lubricant between a metal workpiece and a tool (die). It is specifically designed for hot metal working processes, such as hot forging, extrusion, and casting, where temperatures are too high for conventional oil or grease lubricants.
Glass manufacture – It is the process of transforming raw materials, mainly silica sand, soda ash, and limestone, into a solid, amorphous material through high-temperature melting (1,400 deg C to 1,600 deg C), followed by precise shaping, controlled cooling (annealing) to remove stresses, and finishing. Key engineering techniques include float glass casting, blowing, and pressing to create materials with specific optical, thermal, and chemical resistance.
Glass mat reinforced thermoplastic – It is a lightweight, high-strength composite material comprising thermo-plastic resin (normally poly-propylene) reinforced with continuous or random glass fibre mats. It is engineered for compression moulding into complex, structural automotive parts (bumpers, underbody shields) because of its excellent impact resistance, fast processing times, and recyclability.
Glass matrix – It is a rigid, non-crystalline (amorphous) solid phase, typically composed of silicates or boro-silicates, which acts as a continuous binder in composite materials. It encapsulates fillers or fibres to improve mechanical properties, such as high fracture toughness and thermal resistance, while allowing processing through viscous flow. It serves as the continuous structural component which holds reinforcing phases (fibres, particles) in place, transfers loads, and protects reinforcements from environmental damage. It is frequently made from boro-silicate glass powder, e.g., SiO2 (silicon di-oxide), B2O3 (boron tri-oxide), Al2O3 (aluminum oxide), which offers good heat resistance and thermal stability.
Glass mat thermo-plastic – It is a semi-finished resin-fibre combination supplied as blanks for compression moulding. It is high-strength, lightweight composite materials consisting of random-chopped or continuous glass fibre mats impregnated with thermoplastic resin (normally poly-propylene). It offers superior energy absorption, recyclability, and corrosion resistance.
Glass melt – It is a high-temperature, viscous liquid mixture formed by reacting raw materials (silica sand, soda ash, limestone, cullet) at around 1,400 deg C to 1,700 deg C in a furnace. It is an important state which undergoes chemical homogenization and refining, preparing the material for solidification into an amorphous structure.
Glass panel – It is a rigid, sheet-like structural or cladding component, normally made of tempered, laminated, or float glass, used for structural glazing, façades, partitions, and windows. Engineered for specific strength, safety, and acoustic performance, these panels are frequently held by frames or point-support systems.
Glass, percent by volume – It is the product of the specific gravity of a laminate and the percent glass by weight, divided by the specific gravity of the glass.
Glass phase extraction – It is a high-temperature, one-step separation technique used to extract and recover specific metal ions from solid waste (such as spent catalysts) by using a constructed molten glass phase as a solvent. It is an efficient, environmentally friendly pyro-metallurgical method which separates metals through ‘melt-melt’ immiscibility, where the desired metal ions are selectively dissolved into the glass phase, while other impurities are separated into a different phase.
Glass powder – It refers to finely ground particles of inorganic, amorphous glass (typically soda-lime, boro-silicate, or alumino-silicate) with a particle size normally ranging from sub-micro-meters to less than 75 micro-meters. It is also known as ‘glass frit’ or ‘glass flux’ and is characterized by its high silica content, chemical stability, and angular morphology.
Glass reinforced plastic (GRP) – It is made up of a combination of glass fibre and polymer or plastic. It has several desirable properties which include high strength to weight ratio, excellent durability, light weight, electrically non-conductive, radar / radio wave transparent, and non-corroding. Glass reinforced plastic products are made from glass fibre reinforced polymers, typically with a polyester or vinyl-ester thermo-set resin matrix. Thermo-set polymers are formed by a chemical reaction, initiated by adding a catalyst, which causes an irreversible hardening of the resin. This is coupled with reinforcement achieved by the incorporation of glass fibres during the production process. The fibres can be in the form of fine long strands, chopped stands or woven mats. The production techniques by which this is achieved are varied and can range from a simple manual process to one which is highly automated, utilizing robotic machinery.
Glass removal – It refers to the techniques used to eliminate glassy, amorphous, or slag phases from the surface or body of a work-piece, typically in the context of cleaning castings, refining metals, or precision finishing. Glass removal is the process of eliminating unwanted, brittle amorphous layers (frequently referred to as ‘glass’ in specific contexts like investment casting or specialized machining) from a metal work-piece surface.
Glass ribbon – It is a continuous, extremely thin, and flexible strip of glass, frequently produced by rapidly cooling (quenching) molten material, such as through melt spinning for metallic glass or float processes for silicate glass, resulting in high surface smoothness and, in some cases, high elasticity.
Glass slurry – It is a fluid, typically water-based, suspension containing fine particles of glass or glassy-type materials. These suspensions are used in specialized applications, including coating, joining, polishing, and manufacturing, acting as a medium to transport, deposit, or abrade materials. Glass slurries consist of solid glass particles (frequently amorphous silicon di-oxide, SiO2, borosilicate, or cullet) dispersed in a liquid, which can also contain additives to manage viscosity and stability.
Glass stress – In a filament-wound part, normally a pressure vessel, it is the stress calculated using the load and the cross-sectional area of the reinforcement only.
Glass structure – Glass is as an amorphous, non-crystalline solid (a supercooled liquid) featuring a random, three-dimensional network of atomic structures (e.g., SiO4, silicon oxygen tetrahedra). Structurally, it is isotropic, strong in compression but brittle in tension, typically comprising silica, soda ash, and limestone. Glass structure lacks long-range order, formed by the rapid cooling of molten material to prevent crystallization.
Glass substrate – It is a rigid, flat, transparent, or dielectric material used as a base in engineering for depositing thin films or mounting electronic components. Key in display (thin film transistor- liquid crystal display / organic light emitting diode), semiconductor packaging, and solar technologies, they offer superior dimensional stability, heat resistance, and high-frequency performance compared to organic materials.
Glass thermometer – It is a liquid-in-glass thermometer instrument which measures temperature based on the volumetric thermal expansion of a liquid (normally mercury or coloured alcohol) housed within a sealed, graduated glass tube. It uses a bulb filled with liquid connected to a capillary tube, where liquid rises or falls corresponding to temperature changes.
Glass-to-metal seal – It is a process which creates a permanent, hermetic (airtight) bond between glass and metal components, normally used for electrical insulation, vacuum containment, or structural integrity in harsh environments. It relies on matched thermal expansion or compression to prevent breakage.
Glass transition – It is the reversible change in an amorphous polymer or in amorphous regions of a partially crystalline polymer from, or to, a viscous or rubbery condition to, or from, a hard and relatively brittle one.
Glass transition region – It is the temperature range where amorphous or semi-crystalline polymers transform from a hard, brittle, ‘glassy’ solid into a soft, flexible, ‘rubbery’ state. It marks a substantial drop in storage modulus and increased molecular chain motion, defining the upper service temperature for rigid plastics.
Glass transition temperature (Tg) – It is the temperature range where amorphous or semi-crystalline polymers transition from a hard, rigid, and brittle ‘glassy’ state to a soft, flexible, and ‘rubber’ state. It is an important parameter for determining material operating temperatures, mechanical properties, and manufacturing conditions, distinct from the melting point (Tm). It is the temperature at which an amorphous polymer (or the amorphous regions in a partially crystalline polymer) changes from a hard and relatively brittle condition to a viscous or rubbery condition. In this temperature region, several physical properties, such as hardness, brittleness, thermal expansion, and specific heat, undergo considerable, rapid changes. It is also the approximate mid-point of the temperature range over which the glass transition takes place. Glass and silica fibre show a phase change at around 955 deg C and carbon / graphite fibres at 2,205 deg C to 2,760 deg C. It is also the temperature at which increased molecular mobility results in considerable changes in the properties of a cured resin system. Also, it is the inflection point on a plot of modulus against temperature. The measured value of Tg depends to some extent on the method of test.
Glassware – It consists of a variety of equipment traditionally made of glass which are used for chemical analysis. Glass can be blown, bent, cut, moulded, or formed into several sizes and shapes. It is normally used in analytical laboratories.
Glass wool – It is an insulating material made from glass fibre arranged using a binder into a texture similar to wool. The process traps many small pockets of air between the glass, and these small air pockets result in high thermal insulation properties.
Glassy alloys – These are frequently referred to as metallic glasses or amorphous metals. These are a class of engineering materials characterized by a non-crystalline, disordered atomic structure. Unlike conventional crystalline metals, which have a long-range orderly lattice, glassy alloys have an atomic arrangement similar to that of liquid or window glass. These are typically produced by cooling molten metal alloys at extremely high rates, frequently exceeding 1,000,000 deg C per second, a process known as rapid quenching, which ‘locks’ the atoms in a disordered state before they can form a crystal lattice.
Glass yarn – It is a high-performance material produced by drawing molten glass into fine, continuous filaments (4 micro-meters to 13 micro-meters) which are then twisted, bundled, and spun into strands. Known for high tensile strength, non-combustibility, and chemical resistance, it acts as a main reinforcement for composite plastics (Fibre reinforced plastics, FRP/ glass reinforced plastics, GRP) and specialized industrial textiles.
Glassy carbon – It is also called vitreous carbon. It is an advanced, non-graphitizing carbon material combining glassy, ceramic, and graphitic properties. It is an isotropic material formed by high-temperature pyrolysis of organic polymers, resulting in high chemical inertness, high strength, low gas permeability, and electrical conductivity, normally used in electro-chemical electrodes and high-temperature crucibles.
Glassy layer – It refers to a thin, amorphous, non-crystalline solid film, frequently formed by rapid quenching or specific processing techniques, which lacks long-range atomic order. Such layers are typically characterized by high viscosity, rigidity, brittleness, and a ‘glass transition temperature’ (Tg). These are frequently used for passivation, coating, or in specialized thin-film devices, serving functions which differ from their crystalline counterparts.
Glassy materials – These are non-crystalline, amorphous solids produced by rapid cooling (quenching) of molten alloys, which by-passes crystallization to freeze atoms in a disordered, liquid-like state. These materials, frequently called metallic glasses or amorphous metals, show high strength, elasticity, and corrosion resistance.
Glassy phase – It is a non-crystalline, amorphous solid state formed when a liquid is cooled rapidly enough to bypass crystallization, resulting in a disordered, kinetically trapped structure. Below the glass transition temperature (Tg), molecular movement is arrested, creating a hard, brittle, and rigid material. It lacks long-range order, similar to a liquid, but behaves mechanically like a solid due to locked molecular positions.
Glassy phase, blast furnace slag – It is an amorphous phase, i.e., there are no crystals. Since blast furnace granulated slag gets lesser time for crystallization. It contains around 90 % of amorphous glassy phase. Slags differ in their glass content, depending upon their cooling pattern.
Glassy state – It is a non-equilibrium, amorphous (non-crystalline) solid state formed by supercooling a liquid, where atomic / molecular motion is frozen because of the high viscosity. It is characterized by high rigidity, brittleness, and a disordered structure similar to a liquid, occurring below the glass transition temperature. These materials, known as metallic glasses or amorphous metals, possess a disordered, liquid-like structure with high viscosity, high strength, and no distinct melting point.
Glauber’s salt (Na2SO4.10H2O) – It is the decahydrate form of sodium sulphate, a white, water-soluble, crystalline inorganic compound. It is used as a phase change material (PCM) for thermal energy storage (TES) because of its high latent heat of fusion (around 32.4 deg C). It also serves as a dyeing agent and chemical intermediate.
Glaze – It is a ceramic coating matured to the glassy state on a formed ceramic article, or the material or mixture from which the coating is made. In tribology, It is a ceramic or other hard, smooth surface film produced by sliding.
Glazed flat-plate solar collector – It is a device which captures solar radiation to heat a working fluid (water or air) for low-temperature applications. It consists of a transparent glass or plastic cover (glazing) which traps heat through the greenhouse effect, an insulated metallic box, and a black, selectively coated absorber plate with flow channels.
Glazing – It consists of dulling of the abrasive grains in the cutting face of a wheel during grinding.
Glazing materials – These are transparent or translucent infill materials, mainly glass, poly-carbonate, or plastic, used in windows, doors, and facades to create a building’s skin. They control light, thermal transmittance, acoustic performance, and security. Key types include annealed, tempered, laminated, and smart glass.
Glazing system – It is an assembly of glass panes, frames (aluminum / steel), gaskets, and sealants designed to form building envelopes, such as windows, facades, or curtain walls. Engineered to control solar heat gain, manage daylight, and reduce heat loss, these systems utilize multi-pane, insulating glass units (IGUs) for energy efficiency and thermal comfort.
Gleeble system – It is a computer-controlled, closed-loop physical simulation tool used to study material behaviour under precise thermo-mechanical conditions. It simulates industrial processes like forging, hot rolling, and welding by rapidly heating and deforming samples, with rates up to 10,000 deg C per second. Key capabilities include hot ductility testing, continuous casting simulations, and HAZ (heat-affected zone) studies.
Gleeble testing – It is a thermo-mechanical simulation technique used to study the behaviour of materials, particularly steels and alloys, under precise, controlled, and rapid thermal and mechanical conditions. It involves using a ‘Gleeble’ machine to subject a sample to specific heating rates (up to 10,000 deg C per second), cooling rates, and mechanical deformation (tension, compression, or torsion) to simulate industrial processes like welding, hot rolling, or casting in a laboratory setting.
Gleeble test unit – It is a sophisticated thermo-mechanical simulation system used to reproduce industrial hot deformation processes (like rolling, forging, or casting) and welding thermal cycles on a small laboratory scale. It is widely considered an industry standard for materials research.
Glicksberg – It refers to a theorem, specifically the Debreu–Fan–Glicksberg existence theorem, which establishes conditions under which a pure Nash equilibrium exists in a game, particularly focusing on the compact and convex nature of action spaces and the continuity of utility functions.
Glide – It is same as slip. It is also a non-crystallographic shearing movement, such as of one grain over another.
Glide-climb creep – It is also called dislocation creep. It is a high-temperature deformation mechanism where dislocations move along slip planes (glide) until obstructed, then bypass obstacles by moving to parallel planes through atomic diffusion (climb). The steady-state creep rate is typically controlled by the rate of climb.
Glide force – It is the component of the Peach–Koehler force acting on a dislocation in the direction of the Burgers vector, which results from the effective stress on the dislocation due to mechanical stress.
Gliding – It is the main mechanism of plastic deformation in crystalline materials, where dislocations move along specific crystallographic planes. It is a conservative motion, meaning it occurs without needing atomic diffusion. Gliding occurs when dislocations (linear defects in the crystal lattice) move along their glide planes, breaking and reconfiguring bonds stepwise to allow atoms to shift positions.
Gliding metals – These are alpha brasses with 80 % to 90 % copper content and no other alloying constituents apart from zinc. They have good ductility and are easily brazed or enamelled. They are used for decorative purposes such as Jewellery and architectural hardware.
Glide velocity – It refers to the speed at which dislocations move within a crystal lattice along a specific slip plane in response to an applied shear stress. This conservative motion, known as dislocation glide, is the main mechanism for plastic deformation in metals and alloys.
Global aspect – It refers to the holistic, systemic, or worldwide dimensions of a project, system, or professional practice, rather than isolated, local components. It involves designing with an awareness of international standards, environmental impacts, and the social and economic contexts of a worldwide market.
Global assessment – It refers to measuring an engineer’s competency to work effectively across borders, cultures, and diverse teams, focusing on knowledge, skills, and perspectives rather than just technical ability. It typically uses situational judgment tests and scenario-based assessments to evaluate how engineers navigate international standards, ethical differences, and collaboration in a globalized work-force.
Global climate change – It is the natural or human induced change in the average global temperature of the atmosphere near the earth’s surface. This condition poses serious dangers around the world, potentially prompting such disasters as flooding, drought, and disease.
Global community – It comprises people or nations deeply connected by technology, economics, and shared issues (e.g., climate change). It represents a shift towards a collective identity which transcends, but does not replace, national affiliation.
Global coordinate frame – It is a fixed, absolute, and universal reference system (typically Cartesian x, y, z) used to define the overall position, orientation, and geometry of an entire model, structure, or simulation, regardless of its internal components. It acts as the anchor for all local measurements and boundary conditions, enabling assembly of sub-components.
Global coordinate system – It isa fixed, absolute 3D reference frame (normally Cartesian x, y, z) used to define the overall position, geometry, and orientation of an entire structure or model. It serves as the master frame for assembling components and defining boundary conditions in simulation, distinct from local work-piece or part systems.
Global database – It is a geographically distributed database system which functions as a single logical unit, allowing data to be stored and accessed across multiple physical locations while concealing this distribution from the application. It is engineered to provide high availability, low-latency data access for global users, and strict data sovereignty compliance.
Global ecosystem – It is the integrated, planetary-scale network of biotic (living) and abiotic (non-living) components, spanning the atmosphere, hydrosphere, and lithosphere, which functions as a single entity driven by energy flows and nutrient cycles. It represents the sum of all biomes, supporting life through interconnected ecological processes. It comprises all living organisms and their surroundings (air, water, rocks), frequently referred to as the biosphere.
Global energy – It is the understanding and addressing of energy issues from a worldwide perspective, encompassing the development, distribution, and security of energy resources on a large scale to meet the demands of modern society while considering environmental impacts.
Global energy demand – It is the total quantity of fuel and electricity needed to power human activities, industrial processes, transportation, and residential needs. It is the total energy input needed from supply systems, frequently measured in tons of oil equivalent (TOE) or exajoules (EJ), driven by population growth and industrialization.
Global energy engineering – It is the multidisciplinary field focused on the sustainable production, transmission, and optimization of energy resources on a global scale. It involves designing systems for generating, managing, and consuming energy, including renewables like solar / wind and fossil fuels, to meet worldwide demand while improving efficiency and reducing environmental impacts, such as carbon emissions.
Global equilibrium – It refers to the state where the total sum of external forces and moments acting on an entire system or structure is zero, resulting in no net translational or rotational acceleration. It ensures the stability of the system as a whole, rather than its individual components.
Global feedback – It is a control mechanism which returns a portion of a system’s total output signal back to the input, influencing behaviour across the entire system rather than locally. It stabilizes amplifiers, reduces distortion, extends bandwidth, and manages stability by correcting errors between actual and desired performance.
Global harmonization – It is the process of aligning international technical regulations, standards, and safety policies to create a unified framework. It facilitates global trade, improves safety, and increases efficiency by ensuring products, particularly chemical products, adhere to consistent, internationally recognized standards.
Global horizontal irradiance – It is the total quantity of shortwave radiation received from above by a surface horizontal to the ground. It represents the sum of solar radiation that arrives directly from the sun’s direction (direct normal irradiance) and the radiation scattered by the atmosphere (diffuse horizontal irradiance).
Global interoperability – It is the ability of diverse systems, devices, and applications to connect, communicate, and exchange data seamlessly across different platforms, organizations, and geographical locations. It relies on shared standards to ensure functional, semantic, and technical compatibility without special user effort.
Global irradiation – It is the total solar energy (direct and diffuse) received on a specific surface per unit area over a defined period (e.g., kilo-watt hour per square meter per day). It is important for assessing solar energy potential and is typically measured by a pyranometer. It represents the sum of direct-beam and scattered diffuse components, essential for solar photo-voltaic (PV) or thermal system design.
Globalization – It consists of the growing integration and interdependence of countries worldwide through the increasing volume and variety of cross border transactions in goods and services, free international capital flows and the more rapid and widespread diffusion of technology, information and culture.
Global load sharing – It refers to a system-level strategy where the total load, whether structural, mechanical, or electrical, is distributed equally among all surviving components, particularly after a failure. Unlike local load sharing, it assumes the load from a failed component is redistributed across the entire system, minimizing the impact of local stress concentrations.
Globally harmonized system (GHS) – It is an international, UN (United Nations)-adopted framework designed to standardize the classification, labeling, and hazard communication of chemicals. It defines physical, health, and environmental hazards through consistent safety data sheets (SDS) and pictograms to improve work-place safety and facilitate international trade.
Global market – It refers to the interconnected, worldwide trading environment where technical products, services, and components are designed, produced, and sold across international borders. It emphasizes standardized design, global supply chains, and adaptation to diverse regional regulations, quality standards, and customer needs.
Global momentum balance – It refers to the application of the principle of conservation of linear momentum to a total system (metallurgical reactor, ladle, furnace, or mould) comprising multiple, often interacting phases (e.g., molten steel, slag, gas bubbles). It states that the time rate of change of the total linear momentum of the system is equal to the sum of external forces acting on it, such as gravity, pressure, and surface tractions, plus the net influx of momentum across the boundaries.
Global negative feedback – It is a control mechanism where a portion of an amplifier or system’s total output is sampled and subtracted from the input, creating a closed-loop system. This process, typically applied across multiple stages, reduces gain to improve stability, linearity, bandwidth, and input / output impedance.
Global planarization – It is the process of achieving an ultra-flat surface across the entire wafer, eliminating irregularities and height variations over large areas. Mainly achieved through ‘chemical mechanical planarization’ (CMP), it enables precise photo-lithography for multi-layered integrated circuits by polishing away excess dielectric or metal materials.
Global positioning system – It is a global navigation satellite system which provides location, velocity and time synchronization. It is a navigation system using satellites, a receiver and algorithms to synchronize location, velocity and time data for air, sea and land travel. It is a satellite-based radio positioning systems which provide 24-hour three-dimensional position, velocity, and time information. It can pinpoint a three-dimensional position to meter-level accuracy and time to the 10-nanosecond level, world-wide.
Global production – It refers to a geographically dispersed network of manufacturing entities, research and development centres, and supply chains interlinked by material, information, and financial flows. It involves coordinating international manufacturing activities, sourcing, production, and distribution, to optimize costs, quality, and operational efficiency.
Global radiation – It is the total, sum of shortwave solar irradiance (watts per square meter) received on a surface, calculated as the sum of direct (beam) radiation and diffuse radiation. Normally measured on a horizontal plane through a pyranometer, it represents the total energy available for solar technologies, including PV (photo-voltaic) panels.
Global reference frame – It is a fixed, coordinate system (e.g., Euclidean, Cartesian) used to measure the position, orientation, and motion of objects across an entire system. It acts as a stationary anchor, frequently the ground or a laboratory, to unify measurements from multiple moving, local frames.
Global response – It refers to the overall behaviour, performance, or deformation of a complete system, such as a building, bridge, or machine, under applied loads, rather than the behaviour of individual components. It is evaluated using techniques like structural monitoring to assess stability, safety, and dynamic characteristics. It encompasses how a structure as a whole reacts to environmental loads (wind, seismic) and operational conditions, frequently distinguishing the total system response from local component behaviour.
Global standards – These are industry or private standards, which are designed and developed with the entire world in mind. Unlike international standards, these standards are not developed in international organizations or standards setting organizations (SSO) which follow a consensus process.
Global stiffness matrix (K) – It is a mathematical structure in finite element analysis (FEA) and structural engineering which defines the relationship between the total applied forces (F) and the resulting nodal displacements (d) for an entire system, expressed as ‘F = Kd’. It is created by assembling transformed individual element stiffness matrices into a single, comprehensive matrix representing the whole structure’s resistance to deformation.
Global strength – It refers to the overall capacity of a complete structure to withstand total applied loads (gravity, buoyancy, environmental forces) without experiencing catastrophic failure, collapse, or excessive permanent deformation. Unlike local strength, which focuses on individual components, global strength ensures the integrity of the entire system.
Global stress – It refers to the overall, macroscopic stress distribution across a structure, calculated using nominal loads (normal and tangential) and global dimensions. It represents the average behaviour of a structure, frequently computed independently of detailed, localized stress concentrations in FEA (finite element analysis), or as the sum of applied and internal loads.
Global surface temperature – It is the global mean surface air temperature. It is the average temperature of the surface of the earth. More precisely, it is the weighted average of the temperatures over the ocean and land. The former is also called sea surface temperature and the latter is called surface air temperature. Temperature data comes mainly from weather stations and satellites.
Global system for mobile communication – It is a widely utilized, international standard for digital, second-generation (2G) cellular telecommunications, designed to facilitate voice calls, SMS messaging, and data transmission. Originally developed to create a unified European standard, it became the dominant global standard for mobile communications. It utilizes ‘time division multiple access’ (TDMA) combined with ‘frequency division multiple access’ (FDMA) to allow multiple users to share the same radio frequency channel. Unlike its predecessor (1G analog), it digitizes and compresses data, providing improved voice quality, reduced background noise, and better security.
Global temperature – It is the area-weighted average of earth’s near-surface air temperature over land and sea surface temperatures, tracking the planet’s energy balance. It serves as a key indicator of climate change, with rising trends driven by greenhouse gas-induced imbalances, showing a warming of around 1 deg C since the pre-industrial era.
Global thresholding – It is a foundational image processing technique which converts grayscale images into binary (black and white) images by applying a single, uniform intensity threshold (T) across the entire image. Pixels are classified as foreground (object) or background based on whether their intensity is above or below ‘T’.
Global time – It refers to standardized systems for measuring and coordinating time across different regions, such as ‘universal time’ (UT), ‘international atomic time’ (TAI), and ‘universal time coordinated’ (UTC), which are used to maintain synchronization in different applications and embedded systems. It is used to synchronize, timestamp, and order events across distributed systems, computer networks, and navigation systems. It acts as a universal reference, enabling consistent temporal ordering of events and data across different locations and nodes.
Global warming – It is the gradual increase observed or projected in global surface temperature as one of the consequences of radioactive forcing caused by anthropogenic emissions is known as global warming.
Global warming potential – It is an index, describing the radiative characteristics of well-mixed green-house gases which represents the combined effect of the differing times these gases remain in the atmosphere and their relative effectiveness in absorbing outgoing infrared radiation is known as global warming potential. This index approximates the time-integrated warming effect of a unit mass of a given green-house gas in today’s atmosphere, relative to that of carbon di-oxide.
Globe temperature – It is the temperature measured by a sensor at the centre of a matte-black hollow copper sphere, representing the combined effects of radiation, air temperature, and air velocity. It is used to assess environmental heat load. It is a measure of the thermal environment that accounts for radiant heat, as opposed to just ambient air temperature (dry-bulb).
Globe valve – A globe valve is a type of valve used for regulating flow in a pipeline, consisting of a movable disk-type element and a stationary ring seat in a generally spherical body. The valve can have a stem or a cage, similar to ball valves, which moves the plug into and out of the globe. The fluid’s flow characteristics can be controlled by the design of the plug being used in the valve. A seal is used to stop leakage through the valve. Globe valves are designed for easy maintenance. They normally have a top which can be easily removed, exposing the plug and seal. Globe valves are good for on, off, and accurate throttling purposes but especially for situations when noise and cavitation are factors. It is a valve with a linear motion closure member, one or more ports, and a body distinguished by a globular shaped cavity around the port region. Globe valves can be further classified as two-way single-ported, two-way double-ported angle-style, or three-way.
Globularization kinetics – It refers to the quantitative study of the rate and mechanisms at which a lamellar (or acicular / needle-like) micro-structure transforms into an equi-axed (globular) micro-structure, typically in alpha / beta titanium alloys. It measures the progress of this transformation, frequently expressed as a ‘globularization fraction’ (or percentage), as a function of thermomechanical processing parameters, specifically time, temperature, and deformation (pre-strain).
Globular microstructure – It is a non-dendritic, spherical, or ‘rosette-like’ solid grain structure suspended within a liquid matrix, created during the solidification of molten alloys, particularly in semi-solid metal (SSM) processing. This morphology improves material fluidity during moulding and leads to reduced porosity and better mechanical properties compared to dendritic structures. This microstructure is characterized by its spherical particle shape, which can enhance material properties.
Globular shape – It is one that is round or spherical, like a ball or a globe. It is a descriptive term for objects or structures that have a roughly spherical form.
Globular shaped inclusions – These inclusions are the most desired morphology of inclusions as they cause the least effects on the surrounding environment (metal matrix). Elongated shaped inclusions, also known as platelet shaped inclusions, weaken the grain boundaries and the mechanical properties of the material.
Globular transfer – In consumable-electrode arc welding, it is a type of metal transfer in which molten filler metal passes across the arc as large droplets.
Glory hole – It is an open pit from which ore is extracted, especially where broken ore is passed to underground workings before being hoisted.
Gloss – It is the shine or luster of a porcelain enamel or a painted surface. It is an optical property which indicates how well a surface reflects light in a specular (mirror-like) direction. It is one of the important parameters which are used to describe the visual appearance of an object.
Glossary – It is an alphabetical list of terms in a particular domain of knowledge with the definitions for those terms. It clarifies terms, distinguishing between common usage and technical application to aid professionals and novices in understanding complex, domain-specific language.
Glove box – It is a sealed, engineered enclosure designed to isolate materials from the external environment or protect users from hazardous substances. It features attached, sealed gloves for manual handling of items, allowing work with air-sensitive (using inert gas) or toxic materials without contamination or exposure, typically featuring a specialized transfer airlock.
Gloves – Gloves are used for the safety of hands. They are normally made from a wide variety of materials and are designed for several types of workplace hazards. In general, gloves fall into four groups namely (i) gloves made of leather, synthetic fibers or metal meshes, (ii) gloves made of fabric and coated fabric, (iii) gloves for chemical protection, and (iv) gloves made of insulating rubber gloves. Leather, synthetic fibre or metal mesh gloves are sturdy and provide protection against cuts and burns. Leather or canvas gloves also protect against sustained heat. They protect against sparks, moderate heat, blows, chips and rough objects. These gloves can be used for tasks such as welding. Aluminized gloves provide radiant heat protection by reflection and insulate/reduce heat conduction with a liner or insert.
Glow discharge – It is a self-sustained continuous direct current (DC) discharge which produces non-thermal plasma, characterized by luminous emission because of the relaxation of metastable atoms and secondary electron emission from a cold cathode. It occurs when a high voltage is applied across two electrodes in a weakly ionized gas, resulting in ionization and excitation processes which maintain a steady state.
Glow discharge mass spectrometry – It is a powerful analytical method used for direct trace analysis of solids, liquids, and conducting or nonconducting materials. It involves ionizing neutral species in a glow discharge plasma and separating positive ions based on their mass-to-charge ratios for detection.
Glow-discharge optical emission spectroscopy – It is a spectroscopic method for the quantitative analysis of metals and other non-metallic solids. Ordinary atomic spectroscopy can be used to determine the surface of a material, but not its layered structure. In contrast, glow-discharge optical emission spectroscopy gradually ablates the layers of the sample, revealing the deeper structure. Glow-discharge optical emission spectroscopy can be used for the quantitative and qualitative determination of elements and is hence a method of analytical chemistry.
Glycerin – It is a colourless, viscous, hygroscopic liquid used mainly as a lubricant, specialized quenching agent, and in surface treatment, such as metal finishing and polishing. It acts as a protective coating agent, humectant, and vibration damping filler for pressure gauges.
Glyceregia – It is a specialized metallographic etchant used to reveal the microstructural features, such as grain boundaries, phases, and carbides, of highly corrosion-resistant alloys. It is mainly used for stainless steels, nickel-based superalloys, and cobalt-base alloys.
Glycerol (C3H8O3) – It is a viscous, colourless, and non-toxic polyhydric alcohol used mainly as a green solvent, cooling agent, and, notably, a reducer for creating metal nano-particles. It serves as a sustainable, bio-derived source for hydrogen in metal-catalyzed transfer hydrogenation and reduction reactions, aiding in nano-particle synthesis. It is a three-carbon alcohol which can be valorized through electro-oxidation processes, particularly in the context of converting crude glycerol into valuable chemical products.
Glycerol carbonate – It is a colorless, non-toxic, and bio-degradable high-boiling solvent. It is a versatile bio-based platform chemical produced by converting bio-diesel-derived glycerol and carbon di-oxide, used in applications such as polymerization, gas separation membranes, lubricants, and eco-friendly coatings.
Glycidyl ether – It is an organic compound characterized by the presence of a glycidyl group, an epoxide (oxirane) ring attached to an ether functional group. Glycidyl ethers are mainly used as reactive modifiers, diluents, and crosslinking agents in epoxy resin systems.
Glycol – It is an organic compound belonging to the alcohol family. It is more commonly referred to as antifreeze, and it is known to have a sweet taste. However, it can be toxic and is normally fluorescent dyed or clear and slightly oily in terms of consistency. in the molecule of a glycol, two hydroxyl (-OH) groups are attached to different carbon atoms. The term is frequently applied to the simplest member of the class, ethylene glycol.
Glycol dehydration – It is defined as a process which uses a glycol solution, typically diethylene glycol or tri-ethylene glycol, to absorb water vapour from a natural gas stream, effectively removing moisture and allowing for the transportation of drier gas. The glycol solution is then regenerated by vapourizing the absorbed water, enabling its reuse in the dehydration process.
Glycol dehydration process – It is defined as a method that utilizes a liquid desiccant, typically an aqueous solution of glycol derivatives like diethylene glycol or tri-ethylene glycol, to absorb water from a water-wet natural gas stream, hence dehydrating the gas before it is transported.
Glycol gas contactor – It is a vessel, in which wet gas flows upward through glycol, allowing water vapour to be absorbed by the glycol, hence progressively drying the gas. The process involves passing the gas through trays or packing that maintain a specific glycol level and includes a mist extractor to remove any glycol from the exiting dry gas.
Glycol injection – It is a process in natural gas production where ethylene or diethylene glycol is sprayed into a gas stream to inhibit the formation of solid hydrates and manage water removal. It protects pipelines and equipment from plugging and corrosion by absorbing moisture during cooling processes, such as refrigeration or J-T (Joule-Thomson) expansion.
G Model – It is also called geometric model. It refers to the computer-compatible mathematical description of an object’s geometry. It is the foundation of computer-aided design (CAD) and computer-aided manufacturing (CAM), representing physical objects in 2D or 3D using curves, surfaces, and volumes.
Gneiss – It is a layered or banded crystalline metamorphic rock, the grains of which are aligned or elongated into a roughly parallel arrangement.
Goaf – It is also called gob. It is the void or abandoned area left behind after a mineral seam, particularly coal, has been extracted. It is characterized by collapsed rock (roof strata), residual coal, and waste materials. Goaf management is important to control rock pressure, manage spontaneous combustion, and reduce safety hazards.
Goal approach – It is a method used in multi-objective optimization which involves setting specific objectives to be achieved, frequently utilizing techniques such as goal programming to balance competing criteria.
Goal, policy – It involves translating high-level organizational objectives into operational, testable, and actionable requirements. It aligns stakeholders’ needs with system design by defining clear goals, creating constraints, and structuring policy frameworks to guide behaviour and system functionality. Key stages include goal elicitation, refinement, and validation.
Goals – Goals are strategic objectives which the organizational management establishes to outline expected outcomes and guide employees’ efforts toward the achievement of those outcomes.
Goal setting – It is the process of creating specific, measurable, and attainable goals and of setting deadlines for these goals if desired.
Goal specifications – These define the desired, high-level objectives, outcomes, or performance targets a system, product, or process achieve, frequently prioritizing functionality over specific implementation methods. These requirements are crucial for guiding design, enabling verification, and, when properly structured, forming the basis for functional requirements, non-functional requirements (NFRs), and performance metrics.
Gob – It is the area from which the mineral (normally coal) has been removed, and the space has been allowed to fall in, or is filled with waste material. It is also a selected, precise quantity of molten glass delivered to a forming machine from the furnace, typically passing through a feeder and a forehearth.
Goertzel algorithm – It is defined as a digital filtering method for computing discrete Fourier transform (DFT) coefficients at specified frequency bins using a sequence of digital data. It allows for efficient spectrum analysis without the need for complex algebra, producing the discrete Fourier transform coefficient as the final output of the filter process.
Goethite – It is a mineral of the diaspore group, consisting of iron (III) oxide-hydroxide, specifically the alpha-polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite is an iron oxyhydroxide containing ferric iron. It is the main component of rust and bog iron ore. Goethite’s hardness ranges from 5.0 to 5.5 on the Mohs Scale, and its specific gravity varies from 3.3 to 4.3. The mineral forms prismatic needle-like crystals (needle ironstone) but is more typically massive.
Goggles – Goggles are safety equipment used for eye protection. They are tight-fitting eye protection which completely cover the eyes, eye sockets and the facial area immediately surrounding the eyes and provide protection from impact, dust, mists, vapours and splashes. Goggles with direct ventilation typically are used for impact hazards and dusts, not for protection against chemical splashes or vapours. Goggles with indirect ventilation are used for protection from dusts and splash hazards. Goggles with no ventilation provide protection from dusts, splashes, mists and vapours. Goggles with foam or cloth padding are not to be used for chemical splash protection. Some goggles fit over corrective lenses.
Goggle valve – It is a specialized, large-diameter isolation valve designed for 100 % positive, ‘man-safe’ shut-off in heavy industrial gas pipelines (e.g., steel / petrochemical). It uses a rotating plate resembling goggles, featuring a solid disc for total closure and an open ring for flow, ensuring secure maintenance.
Gold – It is a chemical element, has symbol Au, and atomic number 79. In its pure form, it is a bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal, a group 11 element, and one of the noble metals.
Gold cyanide [Au (CN)2-] – It is a water-soluble complex formed during the extractive metallurgy of gold, where dilute cyanide solutions (NaCN or KCN) dissolve gold from ore. Engineered in mining to separate metal from rock, this process allows gold (Au) to be recovered through activated carbon or zinc (Zn) precipitation, typically operating at a high pH (10–12) to prevent toxic HCN (hydrogen cyanide) gas formation.
Gold deposits – These are natural, localized concentrations of gold-bearing minerals within the earth’s crust which are economically viable to extract. Engineered definition involves classifying these deposits by geological formation (e.g., orogenic, epithermal, placer) based on structural, chemical, and mineralogical characteristics to determine optimal, cost-effective extraction methods.
Golden section method – It is a robust, iterative numerical technique used to find the minimum or maximum of a unimodal function (a function with only one extremum) within a specified interval. It is particularly valuable when the function’s derivatives are unknown, hard to compute, or the function is not smooth, making it a derivative-free optimization method.
Golden section search – It is a numerical optimization technique used to find the maximum or minimum of a unimodal function (a function with a single peak or valley) within a specified interval, often applied to determine optimal process parameters without needing derivatives. It works by systematically narrowing down an interval to locate an extremum (e.g., optimal cutting temperature, maximum yield, or minimum cost) by evaluating points spaced according to the golden ratio (phi = around 0.618).
Gold filled – It means covered on one or more surfaces with a layer of gold alloy to form a clad or composite material. Gold-filled dental restorations are an example of such materials.
Gold lacquer – It is a protective coating which has a yellow colour. It can be of lacquer or baked enamel.
Gold mine – It is a specialized engineering site designed for the extraction, processing, and refining of gold-bearing ore from the earth, using methods like surface mining (open-pit) or underground mining. It involves identifying deposits, blasting, transporting ore, and using chemical processes like cyanidation to isolate gold.
Gold nano-shells – These are spherical nano-particles composed of a dielectric core (typically silica) surrounded by an ultra-thin gold shell, engineered to show tunable localized surface plasmon resonance. By adjusting core / shell dimensions, their light absorption / scattering is optimized for near-infrared (NIR) applications, including sensor development.
Gold plating – It normally refers to the process of applying a thin layer of gold onto the surface of another metal.
Gold plating, project management – In time management, gold plating is the phenomenon of working on a project or task past the point of diminishing returns. For example, after having met a project’s requirements, the developer works on further enhancing the product, thinking that the customer is going to be delighted to see additional or more polished features, beyond that which what has been asked for or expected. If the customer is disappointed in the results, the extra effort put into it can be futile.
Gold wire – It refers to high-purity (frequently 99.99 %) ultra-fine gold filament, typically 15 micro-meter to 50 micro-meters in diameter, used as a conductive interconnect in wire bonding to connect semiconductor chips to packaging. Valued for superior electrical conductivity, ductility, and high corrosion resistance, it ensures long-term reliability in ICs (integrated circuits).
GOLF analysis – It is an inventory management method based on nature of suppliers which determine quality, lead time, terms of payment, continuity or otherwise of supply and administrative work involved. The analysis classifies the items into 4 groups. ‘G’ group covers those items which are to be procured from the government agencies. Transactions with this category of items involve long lead time and payments in advance or against delivery. ‘O’ group covers those items which are procured the open market normally from private agencies. Transactions with this category of items involve moderate delivery time and normally with the availability of credit. ‘L’ group contains those items which are bought from local suppliers. The items bought from these suppliers are normally cash purchased or purchased on blanket orders. ‘F’ group contains those items which are purchased from foreign suppliers. Purchase of these items involve a lot of administrative work, needs opening letter of credit, and needs making of arrangement for shipping and port clearance.
Golf ball mould – It refers to a specialized, high-precision tool, typically made of hardened steel (like tool steel or stainless steel), beryllium copper, or through electroforming, used to cast or mould the cover or core of a golf ball with a specific surface pattern (dimples). These moulds are defined by their ability to produce a spherical, frequently ‘seamless’ shape with consistent, engineered surface textures, normally using two-part or multi-part construction with complex internal geometries.
Golf ball mould cavity – It is a precisely engineered, spherical void within a mould, typically composed of two mated hemispherical halves, designed to define the final shape, size, and dimple pattern of a golf ball during manufacturing. These cavities are normally produced from durable, heat-resistant metal alloys, such as beryllium copper, steel, or nickel alloys, designed to withstand high injection pressures and maintain tight tolerances (within 3 micro-meters to 5 micro-meters) for thousands of cycles.
Golf ball mould modeling – It refers to the design, simulation, and manufacturing processes used to create high-precision metal tools (typically steel, zinc alloy, or beryllium copper) which define the final, dimpled shape of a golf ball. This involves CAD (computer-aided design) / CAE (computer-aided engineering) modeling to define the dimple pattern and non-planar parting lines, followed by manufacturing techniques like CNC (computer numerical control) machining or electro-forming to achieve high sphericity.
Goniometer – It is an instrument devised for measuring the angle through which a sample is rotated or for orienting a sample (e.g., a single crystal) in a specific way.
Go / no-go decision – It is a type of decision where an absolute lower (or upper) limit has been established as necessary for the functioning of the design. All materials or components which do not exceed the lower limit specification are rejected (no-go), while those which do are accepted and subjected to further screening.
Go / no-go gauge – It refers to an inspection tool used to check a workpiece against its allowed tolerances through a go / no-go test. Its name is derived from two tests namely the check involves the work-piece having to pass one test (go) and fail the other (no-go).
Good air retention property – In pneumatic conveying and bulk solids handling, it refers to the ability of fine-grained or cohesive powdered materials to trap air within their bulk and resist deaeration. Materials with this property remain fluidized and fluid-like, allowing for low-velocity, dense-phase transport.
Good corrosion resistance – It is the ability of a material to withstand deterioration and maintain structural integrity while exposed to harsh environments (moisture, chemicals, or heat) over time. It is achieved through protective oxide films, specialized alloy composition (e.g., stainless steel), or protective coatings.
Good design practice – It is the application of established standards, scientific principles, and expertize to create safe, reliable, and functional products or systems, ensuring compliance with regulations and user needs. It involves a systematic, iterative process of research, simulation, and evaluation to deliver high-quality, efficient, and cost-effective solutions.
Good dispersion – It refers to the uniform, stable distribution of particles, fillers, or fibres within a matrix, breaking up agglomerates to achieve improved material properties. It is an important processing step involving shear-driven breakup (rupture / erosion) to ensure homogeneous, high-performance composites or mixtures.
Good engineering practice – It refers to the combination of standards, methods, and prudent engineering judgment, including codes, safety regulations, and technical expertise, used to design, construct, operate, and maintain systems securely, efficiently, and compliantly. It bridges technical requirements with safety, economics, and environmental protection across the project lifecycle.
Good infiltration – It is the effective contact and mechanical anchoring between fibre and matrix, resulting in a void-free and robust interface necessary for strong interfacial interactions and excellent mechanical properties.
Good light fastness – It refers to the ability of a dye to resist photodegradation when exposed to light, ensuring that printed images retain their colour and stability over time, particularly in applications where the dye is located very close to the surface of the substrate.
Goodman approximation – It is also called Goodman relation / line. It is a formula to estimate the effect of mean stress on the fatigue life of a material. It defines a safe operating envelope for components subjected to combined alternating (cyclic) and steady (mean) stresses.
Goodman diagram – It is a graphical tool used to predict the fatigue life of a material subjected to fluctuating loading, a combination of alternating stress (Sa) and non-zero mean stress (Sm). It maps the interaction between these stress components against fundamental material properties to define a ‘safe’ operating region, indicating that fatigue life decreases as mean stress increases.
Goodman endurance diagram – it is also called modified Goodman diagram. It is a graphical tool used to predict the fatigue life of a material under combined mean and alternating stresses. It defines a “safe” operating zone, plotting alternating stress (Sa) against mean stress (Sm) to determine if a component is going to fail.
Goodman relation – It is also called Goodman diagram, Goodman-Haigh diagram, Haigh diagram or Haigh-Soderberg diagram. It is an equation used to quantify the interaction of mean and alternating stresses on the fatigue life of a material. The equation is typically presented as a linear curve of mean stress against alternating stress which provides the maximum number of alternating stress cycles a material withstands before failing from fatigue.
Good manufacturing practices – It means a system for ensuring that products are consistently produced and controlled as per the quality standards. These practices conform to the guidelines recommended by standards / regulatory agencies.
Good mechanical properties – These refer to a material’s ability to withstand different stresses and strains while maintaining performance, characterized by factors such as impact resistance, fatigue behaviour, and overall durability at ambient temperature.
Good morphology – It normally means the optimized phase separation, crystal structure, or surface structure which maximizes the material’s intended function (e.g., reactivity, mechanical integrity, or electrical conductivity).
Goodness of fit – Goodness of fit describes a class of statistics used to assess the fit of a model to observed data. There are several measures of goodness of fit which include the coefficient of determination, the F-test, the chi-square test for frequency data, and numerous other measures. It is to be noted that goodness can refer to the fit of a statistical model to data used for estimation, or data used for validation.
Good permeability – It refers to a material’s high capacity to allow fluids (liquids or gases) to flow through its interconnected pore spaces or fractures. It indicates low resistance to flow, necessary for efficient drainage, reservoir production, or filtration, frequently measured in darcies (d) or milli-darcies (md).
Goods receipt note (GRN) – It is also known as a goods received note or material receipt note. It is a document which acknowledges the receipt of goods from a supplier. It is used to record the details of the goods received, such as the description, quantity, and any discrepancies in the order, and to ensure that the received goods match the purchase order.
Good rock mass – It is defined as a competent, stable geological formation with high strength, minimal jointing, and favourable, dry discontinuity conditions, allowing for minimal support in tunnels or excavations. It is quantified by high ‘rock quality designation’ (RQD ) – above 75 %, high ‘rock mass rating’ (RMR) – above 60, or high Q-values (tunnel quality index) – above 10, indicating low deformability and high bearing capacity.
Good sizing system – It is a structured framework which translates technical data for system into a consistent, optimized range of sizes. It aims to maximize accommodation (65 % to 80 % cover factor) while minimizing variance between actual and assigned dimensions, optimizing cost.
Goods train – It is also known as freight train or cargo train. It is a railway train which is used to carry cargo. Goods trains are made up of one or more locomotives which provide propulsion, along with several goods wagons which carry freight. A wide variety of cargoes are carried on trains, but the low friction inherent to rail transport means that freight trains are especially suited to carrying bulk and heavy loads over longer distances.
Good surface finish – It is the precise, controlled texture of a manufactured part, characterized by minimal surface roughness (Ra), waviness, and, or lay. It is defined by its ability to meet specific performance requirements, like reduced friction, improved sealing, or corrosion resistance, and is frequently quantified by an average roughness value (e.g., Ra = below 0.8 micro-meters).
Goods wagon – It is also known as a freight wagon or freight car. It is a railway vehicle designed for transporting goods or cargo. These unpowered vehicles are typically coupled together to form a freight train. They come in different types to handle different types of cargo, such as box wagons for general freight, flat wagons for oversized items, tank cars for liquids, and hopper cars for bulk materials.
Good thermal stability – It is the ability of a material or component to resist degradation, decomposition, or substantial physical / chemical property changes (such as shape, strength, or conductivity) when exposed to high temperatures or thermal cycling. It ensures structural integrity and performance reliability over time.
Goose-neck – It is a curved, hook-shaped component, pipe, or flexible fixture resembling a goose’s neck, designed to facilitate fluid / gas flow, allow for flexibility, or provide structural connection. Common applications include 180-degree plumbing vents to prevent water ingress, ventilator piping or ducting for exhaust fans, land-fill methane vent pipes, or any other piping implementation exposed to the weather, where the ingress of water ls undesired, adjustable mounts for lamps / microphones, and heavy-duty trailer hitches. In a coke oven, a goose-neck is a curved pipe or duct that connects the top of the coke oven to the gas collection system. Its main functions are to collect and channel the volatile gases released during the coking process, regulate gas pressure, and prevent leaks. In a blast furnace, a gooseneck is a curved pipe or section of pipe which connects the bustle pipe (a large ring main which distributes hot air around the furnace) to the tuyeres (nozzles that inject the hot air into the furnace). It allows for flexibility in the system, accommodating movement and thermal expansion while directing the hot blast into the furnace. In die casting, gooseneck is a spout connecting a molten metal holding pot, or chamber, with a nozzle or sprue hole in the die and containing a passage through which molten metal is forced on its way to the die. It is the metal injection mechanism in a hot chamber machine.
Gooseneck punches – These are a type of specialized upper tooling used in press brake machines for sheet metal fabrication. They are designed with a distinctive, deeply recessed curve (shaped like a goose’s neck) which provides clearance, allowing for complex, deep, or multi-sided bends (such as U-channels or deep boxes) without colliding with the already-formed vertical walls of the work-piece.
Gore-select membranes – These are a type of polymer electrolyte membrane (PEM), specifically a reinforced composite membrane for use in fuel cells and water electrolyzers. These membranes are characterized by a composite structure, a porous, expanded PTFE (poly-tetra-fluoro-ethylene) matrix infused with a per-fluorinated ionomer, designed to offer high mechanical, chemical, and thermal stability in harsh operational environments.
Gossan – It is the rust-coloured capping or staining of a mineral deposit, normally formed by the oxidation or alteration of iron sulphides.
Goss component – It refers to a distinct, highly oriented crystalline texture, defined by the Miller indices {110} <001>. It is a key factor in producing grain-oriented (GO) electrical steel with excellent magnetic properties, such as low hysteresis loss and high permeability in the rolling direction.
Goss grains – It refer to a specific crystalline orientation in grain-oriented electrical steel where the crystal lattice is aligned in a {110} <001> orientation. This means the {110} plane is parallel to the rolling surface, and the <001> direction (the ‘easy magnetization axis’ of alpha-iron) is parallel to the rolling direction. This texture is important for manufacturing efficient transformer cores since it allows for exceptionally high magnetic permeability and low power losses in the rolling direction.
Goss orientation – It is denoted as {110} <001>. It is a specific crystal texture in electrical steel where the cube edge <001> direction is aligned with the rolling direction, and the {110} plane is parallel to the sheet surface. It is necessary for producing high-efficiency, magnetically permeable grain-oriented steel, mainly forming during secondary recrystallization at high temperatures.
Goss recrystallization – It is the secondary recrystallization of {110} <001> oriented grains in electrical steel. It involves the selective, abnormal growth of specific grains at high temperatures to produce a highly texture-oriented material with excellent magnetic properties.
Goss texture – It refers to a specific, highly oriented crystalline structure found in electrical steels (silicon iron) characterized by the Miller indices {110} <001>. This means that the {110} crystallographic planes are parallel to the rolling surface, and the <001> direction (the easy axis of magnetization in body-centered cubic iron) is aligned with the rolling direction. It is mainly used to minimize energy loss (hysteresis loss) in magnetic components such as power transformers.
Goswami cycle – It is a combined thermodynamic cycle which produces both mechanical power and refrigeration simultaneously, using an ammonia-water mixture as the working fluid. It integrates a Rankine cycle for power and an absorption refrigeration system for cooling.
Gouge – It is fine, putty-like material composed of ground-up rock found along a fault. It is also a gross scratch.
Gouge material – It is a finely pulverized or abraded rock material (silt, clay, or rock flour) found within the shear zones or faults of rock masses, formed by the grinding of joint walls. It acts as a filling material, frequently reducing rock mass strength, acting as a lubricant in shear zones, and influencing water permeability.
Gouge, rolled in – It is a more localized gross rolled-in scratch.
Gouging – It is a thermal or mechanical metal-removal process used to cut grooves, remove defects, or excise weld metal by melting it and blowing it away. It is necessary for preparing joints, repairing cracks, or back-gouging welds to ensure full penetration. Common methods include air carbon-arc, plasma, and oxy-fuel gouging. In welding practice, it consists of the forming of a bevel or groove by material removal. Gouging is also surface tearing found on the inner surface of seamless (extruded) pipes and it is caused by excessive friction between the mandrel and the inner surface of the pipe. In a conveyor, gouging is the effect of sharp heavy material falling onto a conveyor belt cover to loosen or tear out pieces of the cover
Gouging abrasion – It is a form of high-stress abrasion in which easily observable grooves or gouges are created on the surface.
Gouging torch – It is a specialized, heavy-duty tool used in metallurgy and welding for removing metal by melting it with a high-temperature electric arc and simultaneously blowing away the molten metal with a high-velocity stream of compressed air. This process, mainly known as ‘air carbon arc gouging, is normally used to remove old or defective welds, prepare bevel edges for welding, and remove excess metal.
Gouging wear – It is the most severe form of high-stress abrasive wear, characterized by the removal of large volumes of material, deep scratches (frequently millimeters deep), and substantial plastic deformation caused by coarse, hard particles or asperities scraping a softer surface. It is normal in mining and heavy earthmoving,
Gouy–Chapman theory – It is the theoretical framework that quantitatively describes the double layer at the interface between a metal electrode and an electrolyte solution, particularly at low electrolyte concentrations and small deviations from the potential of zero charge. It describes the diffuse layer of ions (electric double layer) at a charged surface, where ions are distributed as per the thermal motion rather than a fixed layer. It combines Poisson’s equation for electrostatics with Boltzmann statistics for ionic concentration, defining the diffuse layer thickness (Debye length)
Governance – It is the overall complex system or framework of processes, functions, structures, rules, laws, and norms born out of the relationships, interactions, power dynamics and communication within an organized group of individuals for an example, organization. It sets the boundaries of acceptable conduct and practices of different actors of the group and controls their decision-making processes through the creation and enforcement of rules and guidelines. Furthermore, it also manages, allocates and mobilizes relevant resources and capacities of different members and sets the overall direction of the group in order to effectively address its specific collective needs, problems and challenges.
Governing differential equation – It is a mathematical model based on physical laws (conservation of mass, momentum, and energy) that describes the behaviour of a physical system over time and space. These equations, which can be ODEs (ordinary differential equations) or PDEs (partial differential equations), define how system variables change, forming the basis for analysis and numerical simulation e.g., finite element method (FEM), and computational fluid dynamics (CFD).
Governor – It is a speed regulator for a machine such as a generator. It is an early important feedback control cybernetic system.
Governor-free operation – It is also known as ‘free governor mode of operation’ (FGMO). It is a power system operating mode where turbine governors automatically adjust fuel / steam input in response to grid frequency variations. It enables generators to instantly increase load when frequency drops or decrease it when it rises, providing main frequency control and stabilizing the grid.
GPS data – It is the structured information collected from the ‘global positioning system’ (GPS) satellite network, comprising a receiver’s precise location, latitude, longitude, and altitude, along with time-stamps. GPS data frequently includes velocity, bearing, and system accuracy metrics, enabling 3D navigation, surveying, and positioning.
G-P zone – It means a Guinier-Preston zone. A G-P zone is a fine-scale metallurgical phenomenon, involving early-stage precipitation. G-P zones are associated with the phenomenon of age hardening, whereby room-temperature reactions continue to occur within a material through time, resulting in changing physical properties.
Grab sample – It is a sample from a rock outcrop which is assayed to determine if valuable elements are contained in the rock. A grab sample is not intended to be representative of the deposit, and normally the best-looking material is selected.
Graben – It is a down-faulted block of rock.
Grade – It is a standardized classification, frequently alpha-numeric, which defines a metal’s chemical composition, mechanical properties (strength, hardness, ductility), and intended application. These standards, such as ISO (International Organization for Standardization), ensure consistency, quality control, and proper selection for industries like construction, automotive, and manufacturing. In case of ores, grade is the quantity of metal in each ton of ore, expressed as grams per ton for precious metals and as a percentage for the majority of other metals. It is also the product classification as per the quality, based on standard specifications. Grade is also the category or rank given to entities having the same functional use but different requirements for quality. Grade reflects a planned or recognized difference in requirement for quality. The emphasis is on the functional use and cost relationship. A high-grade entity can be of unsatisfactory quality and vice versa. Where grade is denoted numerically, the highest grade is normally designated as 1, with lower grades extending to 2, 3, 4, etc. Where grade is denoted by a point score, such as a number of star symbols, the lowest grade normally has the least points or stars.
Graded abrasive – It is an abrasive powder in which the sizes of the individual particles are confined to certain specified limits.
Graded coating – It is a thermal spray coating consisting of several successive layers of different materials, e.g., starting with 100 % metal, followed by one or more layers of metal-ceramic mixtures, and finishing with 100 % ceramic.
Graded core – It refers to a structural or material core, frequently within a sandwich panel, which shows a continuously or stepwise varying density, stiffness, or composition. It is designed to optimize load distribution, improve energy absorption, and reduce stress concentrations at material interfaces compared to traditional, uniform cores.
Graded gravel – It is an aggregate comprising a well-proportioned mix of particle sizes, from fine to coarse, designed to minimize voids. It is frequently classified as ‘well-graded’ in the Unified Soil Classification System (USCS), if it shows a uniform distribution of sizes, providing superior stability, density, and drainage for road bases, foundations, and structural fill.
Graded gust – It is a, typically exponential or linear-ramp, modeling of a gust velocity increase over a specific distance, rather than an instantaneous (sharp-edged) hit, used for more accurate load calculations. This approach ensures that structural flexibility effects are not underestimated.
Graded layer – It refers to a structure or material where properties, such as composition, microstructure, density, or strength, vary continuously or stepwise over a specific distance. These layers, frequently known as ‘functionally graded materials’ (FGMs), allow for tailored properties, such as high heat resistance on one surface and high strength on the other.
Graded mixture – It refers to a material (like aggregate or asphalt) containing a controlled distribution of varying particle sizes, analyzed through sieve analysis. It defines the proportions of fine, coarse, and filler materials, normally categorized as well-graded, gap-graded, or open-graded to achieve specific density, stability, and permeability requirements.
Graded response – It refers to a system or model where outputs are not binary (on / off) but occur in ordered, incremental stages based on input intensity. It models responses across multiple ordered categories, where higher input levels generally produce higher-level outcomes, frequently used in materials, systems, and reliability analysis.
Graded sand – It is a material consisting of a controlled distribution of particle sizes, ranging from fine to coarse, designed to fill voids effectively and provide high stability, density, and interlocking characteristics, often classified as well-graded (SW) or poorly graded (SP) as per geotechnical standards like USCS (Unified Soil Classification System).
Grades bitumen – These grades classify the hardness, viscosity, and temperature susceptibility of bituminous binders (mainly for roads) based on tests like penetration (stiffness) or performance grade (temperature resistance). Common grading systems include ‘penetration’ (e.g., 60/70), ‘viscosity’ (e.g., VG-30), and ‘performance grade’ (PG) to ensure optimal durability.
Grade silicon – It refers to the classification of silicon based on its purity levels and specific applications, mainly divided into metallurgical (98 % to 99 % pure), solar (6N-9N purity), and electronic / semi-conductor grade (above 9N or 99.9999999% pure). These grades are determined by refining processes which remove impurities to enable needed electronic or structural properties.
Grades, plutonium (Pu) – These grades are defined by their isotopic composition, mainly the percentage of 239Pu against 240Pu, which dictates their use in weapons or reactors. Weapons-grade plutonium contains above 93 % 239Pu (below 7 % 240Pu), while reactor-grade has lower 239Pu (below 76%) and higher 240 Pu (above 19 %), increasing heat and spontaneous neutron emissions.
Grades, steel – These grades refer to the standardized classifications defining steel based on chemical composition (carbon/alloy content), mechanical properties (strength, hardness), and intended application. These classifications of steel alloys include variations such as ferritic, austenitic, and duplex stainless steels, which are selected for specific applications based on factors like corrosion resistance, weldability, and strength. Engineering standards use these grades to ensure consistent performance, weldability, and corrosion resistance for specific construction, automotive, or industrial uses.
Gradient – It is related to the term inclination. Both refer to the steepness or slope of a line or surface. The gradient is a measure of how much a quantity (like elevation or temperature) changes with respect to distance. Inclination specifically refers to the angle a line makes with the horizontal (x-axis). They are closely related concepts, as the gradient can be calculated from the angle of inclination (using the tangent function) and vice versa.
Gradient approach – It is an iterative optimization technique which uses derivatives (gradients) of an objective function to determine the steepest direction toward finding local maximum or minimum values. It systematically updates design variables to improve performance in simulations, control systems, and design optimization.
Gradient-based algorithm – It is an optimization method used in machine learning which leverages the gradient (the first derivative) of an objective function to iteratively find the direction of steepest descent (or ascent) toward an optimal solution. This process is central to minimizing a cost or loss function or maximizing a performance metric.
Gradient calculation – It is the process of estimating the steepness, slope, or rate of change of a variable (such as elevation, pressure, or temperature) relative to distance or another variable. It is defined by the ratio of vertical rise to horizontal run, frequently expressed as a percentage, ratio (e.g., 1:50), or angle.
Gradient curve – It refers to a smooth, curved transition that connects two different straight-line gradients (slopes). It is used to eliminate abrupt changes in direction (kinks) in infrastructure design, allowing for smoother, safer, and more comfortable movement. These curves are necessary in highway design, railway engineering, and pipeline management to transition between uphill and downhill sections, or between flat and inclined sections.
Gradient descent – It is a first-order iterative optimization algorithm used to find the local minimum of a differentiable function. It works by adjusting model parameters (such as weights and biases) iteratively in the opposite direction of the gradient of the cost function, aiming to reduce the prediction error to its lowest possible value.
Gradient descent method – It is a first-order iterative optimization algorithm used in several fields (especially machine learning) to find a local minimum of a differentiable function. It works by iteratively adjusting model parameters in the direction of the steepest descent, as defined by the negative of the function’s gradient.
Gradient direction – It is the vector which points toward the maximum rate of increase of a scalar field (like temperature, pressure, or elevation). It is perpendicular to constant level curves or surfaces, indicating the path of steepest ascent, which is important for optimization and identifying maximum change.
Gradient elution – It is a technique for improving the efficiency of separations achieved by liquid chromatography. It refers to a step-wise or continuous change with time in the mobile phase composition.
Gradient field – It is a vector field generated by taking the gradient of a scalar potential function, representing the direction and rate of fastest increase. It describes spatial variations, such as pressure, temperature, or electro-magnetic potential, and is important for calculating energy dissipation or forces.
Gradient information – It represents the rate of change of a physical quantity (like pressure, temperature, or signal intensity) relative to a variable, frequently distance. It acts as a vector pointing toward the maximum increase of a function, crucial for optimizing designs, determining slopes, or analyzing image data. It is the vector derivative of a multivariate function indicating the steepness and direction of maximum increase of a surface.
Gradient magnetic separation – It is a technique which uses strong magnetic fields combined with high-gradient magnetic fields (generated by ferro-magnetic matrices) to separate weak, fine magnetic particles from suspensions. It is widely used for industrial mineral purification, water treatment, and steel recycling.
Gradient magnitude – In computer vision, image processing, and field theory, the gradient magnitude is a scalar quantity which measures the local rate of change of a scalar field, such as pixel intensity in an image, temperature, or pressure. It represents the steepness of the change (slope) at a given point, independent of direction, typically highlighting boundaries, edges, or transition zones.
Gradient of the liquidus line – It refers to the slope of the liquidus curve on a phase diagram, which indicates how the melting point of an alloy changes with composition. It defines the relationship between the equilibrium liquidus temperature (Tl) and the concentration of the solute (Cl) in the liquid phase.
Gradient of the solidus line – It refers to the slope of this boundary on a temperature-composition phase diagram, usually denoted as dT/dXs (change in temperature over change in solid composition). The gradient indicates how the melting temperature of a solid solution changes with varying composition.
Gradient spin – It is also called gradient echo. It refers to the spatial variation of nuclear spin phases induced by deliberately applied magnetic field gradients (Gx, Gy, Gz). These coils create linear variations in the main magnetic field (Bo), causing spins at different positions to precess at distinct frequencies, allowing for spatial localization.
Gradient step – In machine learning, it is a first-order iterative optimization method used to update model parameters by moving them in the opposite direction of the gradient of an objective function, scaled by a learning rate. This process is important for minimizing cost, such as reducing prediction error, or maximizing performance in complex systems.
Gradient vector – It is a vector composed of the partial derivatives of a scalar field, representing the direction and magnitude of the steepest increase of that function at a given point. It serves as a tool to determine maximum slope, optimize design parameters (steepest descent), and analyze vector fields in 3D.
Gradient zone – It is a specialized layer where a physical property, such as temperature, concentration, or material density, changes linearly or predictably over distance. It is important for controlling heat transfer, material transport, or chemical processes within a system.
Grading process – It is the systematic reshaping of land contours and slopes to prepare a site for construction, focusing on stability, drainage, and erosion control. It involves rough grading (moving soil for general shape) followed by finish grading (precise finishing for drainage), normally designed by civil engineers based on topographic surveys.
Grading requirements – These refer to the specifications for the size distribution of aggregates, which are outlined in standards such as European Norm standard EN 12620, particularly for all-in aggregates where coarse and fine aggregates are combined.
Gradual depletion – It refers to the progressive, time-dependent reduction in quantity, quality, or functional capacity of a system, material, or natural resource. Unlike sudden failures, it involves a sustained, incremental loss, such as the gradual exhaustion of a fossil fuel reservoir, the thinning of an ozone layer, or the loss of mobile charge carriers in a semiconductor.
Gradual material erosion -It means the progressive loss of material because of friction and abrasion, needing systematic inspections and maintenance to prevent equipment failure.
Graduated idler spacing – It is higher than normal spacing at high tension portions of the belt. As the tension along the belt increases, the idler spacing is increased. Normally this type of spacing occurs toward and near the discharge end. Graduated spacing is not normally used but if it is used, care is to be taken not to exceed idler load rating and sag limits during starting and stopping.
Graduations – These are marks on a container to show fluid levels of contents on a scale of full to empty.
Graetz number – It is a dimensionless quantity used to characterize laminar flow heat transfer (and sometimes mass transfer) in conduits. It represents the ratio of heat capacity of the fluid flow to the thermal conductivity of the fluid.
Graetz problem – It is a classic engineering heat transfer problem, modeling the development of a temperature profile in laminar flow through a closed conduit (normally a circular pipe). It analyzes heat transfer from the wall to the fluid, focusing on the thermal entrance region assuming fully developed velocity but not temperature.
Graft copolymer – It is a branched copolymer consisting of a main, continuous backbone chain (one monomer type) with side chains (different monomer type) covalently attached. Engineered to modify polymer properties, they combine components to create materials with unique mechanical strength, toughness, and thermal stability.
Graft copolymerization – It is defined as a process used to covalently bond natural fibres to the macro-molecular chains of polymeric matrices, improving interfacial contacts and stress transmission in composites. This technique involves the attachment of one or more monomers or polymers to natural fibres, improving their compatibility with different resin systems.
Grafting polymerization – It is a method to modify polymer surfaces by directly synthesizing other types of monomers onto the polymeric surface, improving properties such as wettability and adhesion without damaging the underlying polymer structure.
Grain – It is an individual crystal in a polycrystalline material. It may or may not contain twinned regions and sub-grains.
Grain boundary – It is a narrow zone in a metal or ceramic corresponding to the transition from one crystallographic orientation to another, hence separating one grain from another. The atoms in each grain are arranged in an orderly pattern.
Grain boundary carbides – These are secondary phase particles (compounds of carbon and metals like chromium, molybdenum, or titanium) which precipitate at the interfaces between crystal grains in alloys. Formed during heat treatment / welding, they can strengthen materials by pinning grain boundaries, but frequently lead to embrittlement, reduced ductility, and sensitized corrosion resistance.
Grain-boundary corrosion – It is the corrosion which occurring preferentially at grain boundaries, normally with slight or negligible attack on the adjacent grains.
Grain-boundary denudation – It is a non-equilibrium condition in which there is a solute composition gradient of a solute from the grain boundary to the grain interior. The condition is frequently created when a phase rich in the solute forms in the grain boundary.
Grain boundary diffusion – It is one of the diffusion mechanisms in sintering. It is characterized by a very high diffusion rate because of an abundance of imperfections in the grain boundaries.
Grain-boundary energy – It is the excess interfacial free energy per unit area associated with the disordered, high-energy region separating two crystalline grains of different orientations in a material. It acts as a 2D planar defect, typically measured in joules per square meter, influencing properties like strength, corrosion, and vacancy mobility.
Grain-boundary etching – In metallography, it consists of the development of intersections of grain faces with the polished surface. Because of severe, localized crystal deformation, grain boundaries have higher dissolution potential than grains themselves. Accumulation of impurities in grain boundaries increases this effect.
Grain-boundary fracture – It is also known as inter-granular fracture. It is a type of material failure where a crack propagates along the boundaries between individual crystal grains (crystallites) in a poly-crystalline material. It occurs when the cohesive strength of the grain boundaries is weaker than the strength of the grains themselves.
Grain-boundary free energy – It is the excess Gibbs free energy per unit area associated with the interface between two crystalline grains of different orientations, compared to a perfect crystal. Caused by atomic mismatch, this positive energy (frequently around 1/3 of surface energy) drives metallurgical processes like grain growth, recrystallization, and segregation.
Grain-boundary liquation – It is an advanced stage of overheating in which material in the region of austenitic grain boundaries melts. It is also termed as burning.
Grain-boundary migration – It is the movement of interfaces between crystals of different orientations, driven by the reduction of internal energy (curvature or strain) during processes like annealing, recrystallization, and grain growth. It involves the atomic-level rearrangement where atoms jump across boundaries, causing grain boundaries to move.
Grain-boundary mobility – It is a fundamental metallurgical parameter, defined as the ratio of the boundary velocity (v) to the driving force (F or delta G) causing it to move, typically expressed as ‘v- M x F’. It quantifies how easily a grain boundary moves under forces like curvature during recrystallization or grain growth, strongly depending on temperature (frequently through an Arrhenius relationship), mis-orientation, and solute concentrations
Grain-boundary nucleation – It is a form of heterogeneous nucleation where new phases (solid, liquid, or gas) or new crystal grains preferentially form at the grain boundaries of the parent material. It is a critical component of phase transformations (e.g., solid-state precipitation, recrystallization, solidification) since grain boundaries act as high-energy, disordered interfaces which facilitate nucleation by lowering the activation energy barrier compared to forming in the bulk grain interior.
Grain boundary oxidation – It is also called intergranular oxidation (IGO). It is a high-temperature failure mechanism where oxygen preferentially diffuses along disordered, high-energy atomic boundaries in metals, forming oxide precipitates. It causes severe brittleness, reduces cohesive strength, and creates surface cracks by depleting alloying elements like chromium, manganese, or silicon.
Grain boundary segregation – It is the localized enrichment or depletion of solute atoms or impurities at the boundaries between crystalline grains in a material. Driven by the need to minimize lattice strain energy, this phenomenon alters local composition and atomic structures, considerably affecting material properties like strength, corrosion resistance, and ductility.
Grain boundary segregation engineering – It is a modern materials design strategy which intentionally uses solute decoration to tailor interfacial properties, such as controlling grain boundary mobility during heat treatment, or improving cohesion to prevent fracture.
Grain-boundary sliding – It is the tangential, relative displacement of adjacent grains along their shared boundary under shear stress. A key, time-dependent deformation mechanism, it occurs mainly at high temperatures, above 0.4 Tm (melting temperature), and low strain rates, playing an important role in creep, super-plasticity, and crack formation.
Grain-boundary sulphide precipitation – It is an intermediate state of overheating of metals in which sulphide inclusions are redistributed to the austenitic grain boundaries by partial solution at the overheating temperature and reprecipitation during subsequent cooling.
Grain-boundary vertex models – These are computational, mesh-based, Lagrangian, front-tracking simulation techniques used to model the micro-structural evolution of poly-crystalline materials (such as grain growth and coarsening). These techniques represent grain boundaries as discrete, connected linear segments in 2D or surfaces in 3D, where the vertices (or nodes) are the main objects whose displacement over time drives the evolution of the network.
Grain-coarsened heat-affected zone – It is also called coarse grain heat affected zone (CGHAZ). It is a part of heat affected zone (HAZ) which is affected by heat during welding process. Application of different heat input dramatically varies the microstructures of the grain-coarsened heat-affected zone without a noticeable changing in prior austenite grain size.
Grain coarsening – It is the process where small crystalline grains in a metal or alloy are consumed by larger ones, increasing the average grain size to reduce total grain boundary surface energy. This heat-activated phenomenon frequently occurs at high temperatures or during sintering, causing increased softness and reduced hardness in materials. It is a heat treatment which produces excessively large austenitic grains in metals.
Grain-contrast etching – In metallography, it consists of the development of grain surfaces lying in the polished surface of the micro-section. These become visible through differences in reflectivity caused by reaction products on the surface or by differences in roughness.
Grain-core deformation – It refers to the permanent, plastic change in shape of individual metal grains (crystals) within a poly-crystalline material. It is caused by the movement of dislocations within the grain lattice rather than the sliding of grains past one another.
Grain diameter – It is a quantitative measure of the average size of individual crystals (grains) in a polycrystalline material, typically expressed in millimeters or micrometers. It is calculated using techniques like the equivalent circle diameter formula ‘D = (4A/pi) to the power 1/2’ or through linear intercept methods.
Grain direction callout – It defines the orientation of the elongated, microscopic crystalline structure (or ‘grain’) within a metal work-piece, which is induced by manufacturing processes such as rolling, extruding, or forging. This, frequently referred to as ‘grain flow’ or ‘fibre direction’, is critical since it creates anisotropic properties, meaning the metal has different mechanical strengths, ductilities, and bending behaviours depending on whether it is formed with or against the grain.
Grained region – It refers to a specific area within a polycrystalline material (such as metals, ceramics, or soils) characterized by a distinct microscopic grain size, the individual crystals or grains which make up the material’s bulk structure. Grained regions are defined by their grain size distribution, which directly influences mechanical properties like strength, hardness, and toughness, often governed by the Hall–Petch relationship, where smaller grains (fine-grained regions) increase strength by restricting dislocation movement.
Grained soil – It is classified by particle size and distribution. Coarse-grained soils (gravel and sand) have above 50 % of particles retained on a 0.075 milli-meters (No. 200) sieve, featuring high strength and permeability. Fine-grained soils (silt and clay) have above 5 0% passing the No. 200 sieve, characterized by plasticity and lower permeability,
Grained steel – It refers to the poly-crystalline micro-structure of steel, consisting of individual microscopic crystals (grains) formed during solidification and heat treatment. The size of these grains, fine or coarse, crucially dictates mechanical properties, such as strength, toughness, and ductility. Fine-grained steel is normally superior, offering higher strength and impact resistance.
Grain fineness number – It is a weighted average grain size of a granular material. It is an American Foundrymen’s Society (AFS)-developed, quantitative measurement of the average grain size of moulding sand, derived from sieve analysis. It approximates the number of meshes per inch of a sieve which just passes a sand sample, with higher numbers indicating finer grains (higher surface area) and lower numbers indicating coarser grains. The American Foundrymen’s Society grain fineness number is calculated with prescribed weighting factors from the standard screen analysis.
Grain flow – It is fibre-like lines on polished and etched sections of forgings which are caused by orientation of the constituents of the metal in the direction of working during forging. Grain flow produced by proper die design can improve the needed mechanical properties of forgings.
Grain flow pattern – It can be longitudinal pattern or transverse pattern. Longitudinal (parallel to flow) pattern maximizes strength and toughness. Transverse (perpendicular to flow) pattern decreases strength but increases resistance to shear.
Grain growth – It is an increase in the average size of the grains in poly-crystalline material, normally as a result of heating at high temperature. In poly-crystalline materials, it is a phenomenon which is occurring fairly close below the melting point in which the larger grains grow still larger while the smallest ones gradually diminish and disappear.
Grain growth hardening curves – These are also called grain growth hardening kinetics curves. These curves define the relationship between grain diameter and processing time / temperature, representing the reduction of total grain boundary energy.
Grain growth inhibitors – These are substances, typically transition metal carbides or rare-earth oxides, added to a metal powder mixture to restrict the movement of grain boundaries and limit the coarsening (growth) of grains during sintering or heat treatment. By keeping the grain size small, these inhibitors improve the hardness, wear resistance, and strength of the final material, which is especially critical for producing fine-grained or nano-structured components, such as tungsten carbide hard metals.
Grain growth retarders – These are agents, additives, or specific alloying elements introduced into a metal alloy to restrict the movement of grain boundaries during high-temperature processing. By limiting the migration of these boundaries, they prevent the increase in average grain size (coarsening) and suppress abnormal grain growth.
Graining – It is the process of vigorously stirring or agitating a partially solidified material to develop large grains having a thin oxide coating.
Grain interior – It refers to the bulk volume of a single crystal (grain) within a poly-crystalline metal, excluding the narrow region of mismatch at the boundary. It represents the ordered, periodic arrangement of atoms, known as the crystal lattice, where the orientation of the atomic planes is uniform throughout that specific grain.
Grain junction – It is frequently called a triple junction or triple line. It is the point or line where three or more grain boundaries meet within a poly-crystalline material. These junctions are important, high-energy structural elements where the regular crystal lattice is severely disrupted, playing a substantial role in material properties like cracking, deformation, and diffusion.
Grain magnesite – It is dead-burned magnesia in granular form of size suitable for refractory purposes.
Grain material – It refers to hard substances, such as oxides, carbides, or nitrides of metals, including diamonds, used in lapping processes to achieve an optimum finish on work-pieces. These materials are required to have high uniformity of size and sharp edges to effectively cut the workpiece material.
Grain orientation – It refers to the specific crystallographic alignment of microscopic crystal grains within a metal, frequently oriented during manufacturing processes like rolling or extrusion. This orientation creates an anisotropic, ‘directional’ microstructure, or grain flow, which considerably impacts mechanical properties such as strength, bending, and magnetic performance relative to the direction of force.
Grain refinement – It is the process of reducing the average grain size within a metallic material, transforming large, coarse grains into a fine, uniform, and equiaxed micro-structure. This technique, used during casting or thermal processing, increases the volume fraction of grain boundaries, considerably improving the material’s strength, toughness, and ductility. It is the manipulation of the solidification process to cause more (and hence smaller) grains to be formed and / or to cause the grains to form in specific shapes. The term refinement is normally used to denote a chemical addition to the metal but can refer to control of the cooling rate.
Grain refiner – It is a material added to a molten metal to induce a finer-than-normal grain size in the final structure in the subsequent casting.
Grain refining – It is heating from some temperature below the transformation range to a suitable temperature above that range followed by cooling at a suitable rate.
Grain rolls – These are ‘indefinite chill’ iron rolls, having hardness 40 HSc (hardness Scleroscope C) to 90 HSc, which have an outer chilled face on the body. There is finely divided graphite at the surface, which gradually increases in quantity and in flake size, with a corresponding decrease in hardness, as distance from the surface increases. These rolls have high resistance to wear and good finishing qualities, to considerable depths. The harder grades are used for hot and cold finishing of flat-rolled products, and the softer grades are for deep sections (even with small rolls). Alloying elements such as chromium, nickel, and molybdenum are normally added, either singly or in combination, to develop specific levels of hardness and toughness similar to those of chilled iron rolls.
Grain roughness – It is frequently termed equivalent sand-grain roughness. It is a measure of surface texture, quantifying microscopic, high-frequency irregularities and deviations from an ideal, smooth surface. It represents the average height or distribution of peaks and valleys produced during manufacturing processes, considerably influencing wear, friction, and fatigue strength.
Grains – These are individual, microscopic crystals (crystallites) with a uniform atomic lattice orientation which make up the structure of a polycrystalline metal or alloy. Formed during solidification, these randomly oriented crystals grow until they meet at boundaries, with their size and shape dictating the metal’s mechanical properties.
Grain size – It is a measure of the areas or volumes of grains in a poly-crystalline metal or alloy, normally expressed as an average when the individual sizes are fairly uniform. In metals containing two or more phases, the grain size refers to that of the matrix unless otherwise specified. Grain size is reported in terms of number of grains per unit area or volume, average diameter, or as a number derived from area measurements. For grinding wheels, it is the nominal size of abrasive particles in a grinding wheel, corresponding to the number of openings per linear unit length in a screen through which the particles can pass. In sintered metals, it is a measure of the areas or volume of the grains. It is not to be mistaken for the particles of the original powder which have not yet dissolved in the structure.
Grain size control – It is the deliberate management of the average diameter of metallic crystals (grains) during manufacturing to optimize mechanical properties. Smaller grains increase strength, hardness, and toughness by creating more boundaries which prevent dislocation movement (Hall-Petch effect). Key methods include controlling cooling rates, alloying additions, inoculation, and heat treatment.
Grain size distribution – It means measures of the characteristic grain or crystallite dimensions (normally, diameters) in a poly-crystalline solid, or of their populations by size increments from minimum to maximum. It is normally determined by microscopy.
Grain size effect – It refers to the principle that a material’s mechanical properties, particularly yield strength and hardness, are considerably altered by the average size of its crystal grains. Smaller grains increase strength / toughness through the Hall-Petch relation (more boundaries), while larger grains reduce strength but can increase ductility.
Grain size modeling – It is the numerical simulation and prediction of the average diameter, distribution, and evolution of crystalline grains in metals during processing (e.g., casting, welding, annealing). It uses thermodynamic and kinetic principles to predict how temperature, time, and deformation affect micro-structure, ultimately determining mechanical properties like strength.
Grain slip – It normally refers to intragranular slip, which is the mechanism of plastic deformation where layers of atoms move (slip) over each other along specific crystallographic planes within an individual crystal grain. It is a fundamental process in the deformation of metals, often resulting in the formation of visible slip bands on the surface of a polished metal sample.
Grain subdivision -it refers to the structural breakdown of metallic grains into smaller, misoriented regions (sub-grains or fragments) during plastic deformation. It is a fundamental mechanism of strain accommodation and microstructural refinement, where initial grains divide into cell blocks, cells, or bands separated by dislocation boundaries. It frequently occurs in stages during cold-working, such as rolling or severe plastic deformation (SPD).
Grain switching – It is a mechanism of microstructural rearrangement, typically occurring during high-temperature deformation or super-plastic forming, where adjacent grains slide past each other and change neighbours without altering the overall grain shape. This process is necessary for maintaining cohesion in fine-grained materials under strain.
Grain yield stress – It defines the specific stress needed to initiate plastic deformation within a poly crystalline metal, specifically accounting for the role of grain boundaries as barriers to dislocation motion.
Gram-equivalent weight – It is the mass in grams of a reactant which contains or reacts with Avogadro’s number of hydrogen atoms.
Gram-molecular weight – It is the mass of a compound in grams equal to its molecular weight.
Gram-Schmidt orthogonalization – It is a method to get an orthogonal set of vectors from a given set, where each vector is adjusted by subtracting the components in the direction of the previously orthogonalized vectors, ensuring the resulting vectors are orthogonal and span the same subspace.
Grand canonical ensemble – It is an ensemble of open systems which are connected to a particle and heat bath, allowing for fluctuations in the number of molecules within the system. It is particularly useful in nucleation studies and molecular simulations of nucleation processes.
Grand partition function – It is a statistical-mechanics tool used to describe open systems (e.g., alloying, defects) which exchange both energy and particles with a reservoir. The function enables the calculation of thermodynamic properties (e.g., Helmholtz free energy, entropy) for systems with variable particle numbers, such as atomic defects in a metal lattice.
Grangcold process – It is a cold-bonding agglomeration method to produce iron ore pellets without high-temperature induration (firing). It is a type of cold-bonded pelletizing process designed to convert iron ore concentrates, residues, or waste materials into durable pellets using a cement binder, typically followed by an ambient temperature curing process rather than thermal hardening.
Granite – It is a coarse-grained intrusive igneous rock consisting of quartz, feldspar and mica.
Granitic extrusives – These refers to volcanic rocks with a composition similar to granite (high silica, quartz, and alkali feldspar) which has cooled quickly on the earth’s surface. While granite itself is an intrusive (plutonic) rock which cools slowly underground, its extrusive equivalent is rhyolite. These rocks are important as source rocks for ore deposits, providing materials for refining, and through the study of their chemistry for exploration.
Granitic intrusives – are also called intrusive granitic rocks. These are coarse-grained igneous rocks which crystallized from silica-rich magma (molten rock) deep within the earth’s crust. These are defined by their slow cooling process, which allows for the formation of large, visible mineral crystals (phaneritic texture), primarily quartz, feldspar, and mica.
GRANSHOT metal granulation process – It is the process which converts excess liquid hot metal from blast furnace into granules by immediate solidification in water. The ready-to-use bulk material, granulated pig iron (GPI), is produced directly from liquid metal, producing little to no fume emissions or dust. The GRANSHOT plant decouples ironmaking and steelmaking operations when needed as to enable optimum operating conditions for the blast furnace. It can be designed to process the entire output of the blast furnace. The granulation process consists of four steps. Control of hot metal flow is achieved by tapping into a tundish, where the nozzle limits the volume output (first step). The hot metal exits the tundish and strikes a refractory spray-head as to form liquid metal droplets. These are evenly distributed over the granulation tank’s water surface, immediately quenched as they hit the cooling water surface (second step). The water cooling and handling system is carefully balanced in order to ensure that the large quantity of heat added by the liquid metal gets removed. At the bottom of the granulation tank, the granules are discharged out of the tank by the ejector, which is powered by water and compressed-air (third step); After dewatering, the granules are stocked in an intermediate or final storage area or silo. The granules have ideal properties for logistical handling, making them easy to transport by conveyor belts, front-loaders, and magnets etc. (step four). The GRANSHOT process has some inherent characteristics namely (i) short stand–by time, typically 20 minutes to 30 minutes, (ii) rapid processing time of 30 seconds from hot metal to a cooled granule, (iii) unaltered chemical analysis because of the rapid quenching, (iv) close to 100 % process yield, and (v) rugged process with high availability, low on staff and with a minimum of maintenance.
Granular activated carbon – It is a porous adsorption media with extremely high internal surface area. It is made of tiny clusters of carbon atoms stacked upon one another, and is produced by heating the carbon source (coal, lignite, wood, nutshells, or peat) in the absence of air which produces a high carbon content material. It has a random porous structure, containing a broad range of pore sizes ranging from visible cracks and crevices down to molecular dimensions. It uses this porous structure to remove dissolved contaminants from water in a process known as adsorption. This porous structure leads to an extremely large amount of adsorption surface area, normally around 650 square meter per gram to 1,000 square meter per gram. Granular activated carbon is a material used to filter harmful chemicals from contaminated water or air. It is widely used for removing synthetic organic contaminants from potable water supplies, contaminated ground-waters, and industrial waste-waters.
Granular bed – It is a densely packed collection of distinct solid particles (media) forming a bed through which a fluid, gas or liquid, flows. These beds act as filter media, catalyst beds, or heat transfer mediums, trapping solid particulates in the interstices (voids) between the granules rather than solely on the surface. Materials used for granular beds include sand, anthracite, ceramic spheres, coke, or processed pebbles / aggregates.
Granular form – It refers to an agglomerated state of powder materials, where fine, primary particles are bound together to form larger, multi-particle entities known as granules. This processed state maintains the chemical identity of the original substances while transforming them from a fine powder into larger, often spherical or isodiametric, shapes typically ranging from 0.2 millimeters to 4 millimeters.
Granular fracture – It is a type of irregular surface produced when metal is broken. It is characterized by a rough, grain-like appearance, rather than a smooth or fibrous one. It can be sub-classified as trans-granular fracture or inter-granular fracture. This type of fracture is frequently called crystalline fracture. However, the inference that the metal broke since it ‘crystallized’ is not justified, because all the metals are crystalline in the solid state.
Granular gas – It is a non-equilibrium state of matter composed of a large collection of macroscopic particles (e.g., powder, sand, metal granules) which are sufficiently agitated, normally by vibration or shear, to be in a dilute, fluid-like state. While they behave similarly to molecular gases in that particles move randomly and collide, granular gases are ‘athermal’ since the grains are too heavy for Brownian motion and they lose kinetic energy during each collision.
Granularity – It is also called graininess. It is the degree to which a material or system is composed of distinguishable pieces, ‘granules’ or ‘grains’ (metaphorically). It can either refer to the extent to which a larger entity is subdivided, or the extent to which groups of smaller indistinguishable entities have joined together to become larger distinguishable entities. It refers to the size, shape, and distribution of the individual crystals (grains) which constitute a metallic microstructure. It defines the degree of resolution of the material’s microstructural components.
Granular material – It is a conglomeration of discrete solid, macroscopic particles which are characterized by a loss of energy whenever the particles interact (the most common example is the friction when grains collide). The constituents which compose granular material are large enough such that they are not subject to thermal motion fluctuations.
Granular media filtration – It is a common technology used to filter seawater prior to reverse osmosis systems, utilizing materials such as sand and anthracite, where suspended particles are adsorbed onto the media grains. This process frequently involves layers of different materials to optimize filtration efficiency and is improved by coagulation to remove finer particles.
Granular noise – It refers to acoustic or mechanical energy generated by friction and collisions between individual particles, grains, or solid particles within a material, particularly during deformation or structural vibration, frequently used in vibration-damping particle dampers. This noise is associated with grain-level interactions such as shear-induced flow. Granular noise occurs when particles move and interact, commonly caused by external forces like shaking or vibrations.
Granular pearlite – It is frequently referred to interchangeably with spheroidized carbide, spheroidite, or globular pearlite in some contexts. It is a specific micro-structure in steel where cementite (Fe3C) exists as spherical particles or granules embedded in a matrix of ferrite (alpha-iron), rather than in the typical lamellar (plate-like) structure. It is normally formed by the prolonged heating (spheroidizing annealing) of lamellar pearlite, martensite, or bainite at temperatures just below the eutectoid temperature (around 700 deg C to 725 deg C).
Granular powder – It is a powder having equi-dimensional but non-spherical particles.
Granular sludge blanket reactor – It is also called ‘up-flow anaerobic sludge blanket (UASB) reactor. It is a high-rate, methanogenic anaerobic wastewater treatment system which uses a suspended, dense bed of microbial granules. Wastewater passes upward through this granular bed, allowing microorganisms to degrade organic pollutants, producing biogas and achieving efficient solid-liquid separation within a single, compact unit.
Granular soil – It is a non-cohesive, coarse-grained material composed of discrete particles like sand, gravel, or silt, characterized by high permeability, lack of plasticity, and minimal clay content. Its behaviour is governed by friction, size, and arrangement of grains, making it important for stability in geotechnical applications. It is composed of separate, hard solid particles (frequently oxides, carbides, or nitrides in manufacturing contexts).
Granulated blast furnace slag – Granulated blast furnace slag is produced by quickly quenching (chilling) the liquid slag to produce a glassy, granular product. The most common process is quenching with water, but air or a combination of air and water can be used. When the liquid slag is cooled and solidified by rapid water quenching to a glassy state, little or no crystallization takes place. This process results in the formation of sand size (or frit-like) fragments, normally with some friable clinker like material. Granulated blast furnace slag is a glassy granular material which normally varies in size from coarse popcorn like friable structure higher than 4.75 millimeters (No. 4 sieve) in diameter to dense sand size grains passing a 4.75 millimeters sieve.
Granulated iron, granulated pig iron – Granulated iron, also known as granulated pig iron, has good chemical and physical properties like pig iron and can be used as a prime raw material for the purpose of steelmaking. It has a chemical composition identical to the liquid iron which is being granulated. There is no oxidation or slag entrapment in the granulated iron and there is high metallic content. It is the main product of the granulation of hot metal.
Granulated metal – It consists of small pellets produced by pouring liquid metal through a screen or by dropping it onto a revolving disk, and, in both the cases, chilling with water.
Granulating – It is the production of coarse metal particles by pouring molten metal through a screen into water or by agitating the molten metal violently while it is solidifying.
Granulation – It is the process of quenching liquid slag which breaks up the material into small particles and then solidifies as granules like coarse sand aggregates. It is also the process of forming grains or granules from a powdery or solid substance, producing a granular material. It is applied in several technological processes in the chemical industry.
Granulation of liquid Iron (hot metal) – Granulation of liquid iron is a method of handling of excess production of hot metal in a blast furnace, which cannot be consumed by steelmaking in the steel melting shop of an integrated iron and steel plant. It is a cost-effective method of producing a solid product which is known as granulated iron. The four basic steps of the granulation process for liquid iron are (i) control of flow of liquid iron to the granulator, (ii) granulation by forming of droplets of liquid iron and their rapid quenching in water in a granulator, (iii) discharge of solidified and cooled granulated iron normally by air water ejector, and (iv) dewatering of granulated iron and transport to storage location.
Granulators – These are industrial machines used to convert molten metal or metallic alloys into small, solidified, and consistently sized granules (particles). These are basically specialized apparatus which facilitate rapid cooling, normally through a water bath or cooling gas, to turn liquid metal into a solid, granular form suitable for further processing, such as melting, refining, or alloying.
Granulometric class – It is the mesh width of the finest sieve through which 95 % by mass of an unshaped refractory material passes. The sieve referred to is as per ISO 565.
Granulometry – It refers to the analysis of the distribution, composition, and texture of particles in different sedimentary environments based on their size ranges.
Grapevine – It is the informal, unofficial, and rapid spread of information within an organization, operating outside formal, structured channels. It thrives on social relationships, gossip, and word-of-mouth, often moving horizontally across departments. While it can transmit rumors or half-truths, it also provides quick, honest feedback.
Grapevine communication – It is a term that refers to the indirect way in which information is passed from one person to another. This type of communication often relies on gossip and rumors as a means of spreading information. In other words, grapevine messages are more likely than not untrue and unreliable. Grapevine communication is considered to be bad for effective communication.
Graph – It is a non-linear data structure, defined in engineering as a set of vertices (nodes) and edges (links / connections) used to model pairwise relationships between objects. Graphs represent complex networks, such as circuits, road networks, or software dependencies, with nodes representing entities and edges representing relationships, enabling analysis of flow, connectivity, and optimization.
Graph cut – It is a technique in computer vision and graph theory which partitions a graph into disjoint sets by removing edges, typically to separate foreground from background or to cluster data. It finds an optimal segmentation by identifying a set of edges whose removal minimizes the total weight (cost) of broken connections, frequently using min-cut / max-flow algorithms to solve energy minimization problems.
Graph cut technique – It is a computer vision and graph theory method which partitions an image (or data) into segments by modeling it as a weighted graph, where pixels are nodes, and an algorithm finds the minimum cost cut to separate foreground from background. It efficiently optimizes energy functions to find the globally optimal segmentation.
Graphene – It is a carbon allotrope consisting of a single layer of atoms arranged in a honeycomb nano-structure. The name ‘graphene’ is derived from ‘graphite’ and the suffix ‘-ene’, indicating the presence of double bonds within the carbon structure. Graphene is known for its exceptionally high tensile strength, electrical conductivity, and transparency, and being the thinnest two-dimensional material in the world. Despite the nearly transparent nature of a single graphene sheet, graphite (formed from stacked layers of graphene) appears black because it absorbs all visible light wavelengths. On a microscopic scale, graphene is the strongest material ever measured.
Graphene layers – These layers refer to single layers of carbon atoms densely packed in a honeycomb crystal lattice, derived from the rapid separation of an atomic layer of graphite. These layers show high stability, flexibility, and conductivity, making them significant in electronic applications. Graphene layers are two-dimensional, one-atom-thick planar sheets of sp2-hybridized carbon atoms arranged in a hexagonal honeycomb lattice. These layers are considered the fundamental building block of all graphitic materials.
Graphene nano-platelets -These are 2D, platelet-shaped particles consisting of small stacks of multi-layer graphene (typically 10 to 100 plus layers), normally 5 nano-meters to 10 nano-meters thick, acting as conductive, high-strength fillers. These platelets are used to improve mechanical, thermal, and electrical properties of metal matrices. Graphene nano-platelets are planar, high-aspect-ratio particles (sometimes called exfoliated graphite). hey are considered hybrids between graphite and graphene.
Graphene oxide – It is a single-atomic-layer, two-dimensional nanomaterial derived from the intense chemical oxidation of graphite. It consists of a carbon hexagon lattice heavily decorated with oxygen-containing groups (epoxide, hydroxyl, carboxyl), making it highly hydrophilic, dispersible in water, and an electrical insulator.
Graphene quantum dots – These are zero-dimensional (0D) nano-materials, typically below 20 nano-meters in size, consisting of single or few-layer graphene sheets (less than 5 layers). They represent small fragments of graphene which show both high surface area, strong photoluminescence, low toxicity, and quantum confinement effects.
Graphene sheet – It is a two-dimensional (2D), single-atom-thick layer of carbon atoms arranged in a hexagonal, honeycomb crystal lattice. It is the fundamental building block of all graphitic materials, including graphite (3D), carbon nano-tubes (1D), and fullerenes (0D).
Graphical diagram – It is the short-hand system of the industry and is normally preferred for design and troubleshooting purpose in pneumatic and hydraulic systems. In these diagrams, Simple geometric symbols represent the components and their controls and connections.
Graphical evaluation and review technique – It is a network analysis technique which uses Monte Carlo simulation to bring a probabilistic approach to network logic and the formation of duration estimates. It is an alternative to the programme evolution review technique (PERT) technique but is not frequently used in complex systems.
Graphical form – It is also called graphical representation / graphical diagram. It is a visual tool used to display complex data sets, material properties, phase relationships, or thermodynamic data in a simplified, intuitive manner. These forms, such as graphs and diagrams, facilitate the analysis of metal behaviour, predict transformations, and guide industrial processes.
Graphical interpretation – It refers to the analysis and understanding of visual diagrams, charts, and plots to determine the phases, properties, and transformations of metals and alloys under varying conditions such as temperature, composition, or pressure. It involves converting complex, multivariable numerical data into intuitive visual formats to predict material behaviour, such as phase stability in phase diagrams or reduction feasibility in Ellingham diagrams.
Graphical methods – These are data analytic tools which utilize visual displays to represent and analyze data, including both standard static methods, like histograms and box plots, and newer dynamic methods which involve real-time interaction with computer graphics devices.
Graphical model – It is a visual and probabilistic representation which uses graph theory to map complex relationships between metallurgical variables (such as composition, temperature, processing parameters) and the resulting microstructure or mechanical properties. These models can be probabilistic (Bayesian networks / Markov networks) for handling uncertainty in material properties, or structural / graph-theoretic (directed graphs) for modeling material flows and production processes.
Graphical presentation – It is the visual display of complex data, such as stress-strain relationships, phase equilibria, or composition changes, using graphs, diagrams, and plots to simplify analysis, highlight trends, and interpret material behaviour. It converts raw experimental data from procedures like tensile testing, XRD (X-ray diffraction), or EDAX (energy dispersive analysis of X-rays) into actionable visual insights for designing, testing, and controlling metallic structures.
Graphical programming – It refers to a visual-based, data-driven approach to designing, modeling, and controlling metallurgical processes, such as casting, reheating, or welding. Instead of using text-based code, this method utilizes diagrams, node-based connections, and visual flowcharts to construct applications and simulate metal properties.
Graphical representation – It refers to the visual depiction of complex data, such as temperature, alloy composition, phase structures, and thermodynamic stability, using charts, diagrams, or plots. These representations, e.g., phase diagrams, time-temperature-transformation (TTT) diagrams, and Ellingham diagrams, are important tools used to understand material behaviour, predict phase transformations, and optimize manufacturing processes like heat treatment and alloy design.
Graphical result – It refers to the visual representation of data derived from experimental analysis, thermodynamic calculations, or microstructural observations. These graphs are important for understanding the behaviour, composition, and processing of metals and alloys.
Graphical technique – It refers to the use of visual displays, diagrams, and plots to represent, analyze, and interpret complex material properties, phase equilibria, and thermodynamic data. These methods convert numerical data from experiments or thermodynamic formulas into visual forms, making it easier to predict alloy behaviour, determine optimal processing temperatures, and understand material structure.
Graphical user interface – It is a, user-friendly system, which allows users to interact with electronic devices through visual components like icons, menus, and windows instead of text-based commands. Engineered for usability, graphical user interfaces frequently use WIMP (window, icon, menu, pointer) elements to make navigating software intuitive, efficient, and accessible for tasks on computers, smartphones, and embedded systems.
Graphic language – It is a specialized visual communication system, consisting of technical drawings, diagrams, graphs, and symbols, used to describe the precise shape, size, micro-structure, and composition of metal objects. It acts as a universal ‘language’ for engineers and metallurgists to convey complex technical information which words alone cannot accurately express.
Graphical method – It is a visual technique used to analyze, represent, and interpret complex data or relationships between physical, chemical, or thermodynamic variables in metal processing. These methods, which include plots such as phase diagrams, Ellingham diagrams, and ternary diagrams, allow researchers and engineers to predict phase changes, determine process conditions, and optimize thermal reactions without performing exhaustive calculations.
Graphics – It is the universal language of engineers, utilizing standardized technical drawings, sketches, and diagrams to visualize, design, and communicate complex 2D and 3D physical objects. It translates conceptual ideas into precise technical specifications, including measurements, materials, and manufacturing processes, ranging from traditional drafting to CAD (computer aided design).
Graphics card – It is a dedicated computer hardware component, an expansion card, designed to render images, animations, and video for display, featuring its own processor (graphics processing unit, GPU) and high-speed memory (video random access memory, VRAM). A modern graphics card is a complex assembly of silicon, copper, aluminum, and different metal alloys, designed to handle immense heat and manage high-speed electrical signals.
Graphics processing unit – It is a specialized electronic circuit designed to rapidly manipulate and alter memory to accelerate the creation of images for display. Unlike CPUs (central processing units), graphics processing unit use parallel processing architecture with thousands of cores to handle multiple tasks simultaneously, making them highly efficient for rendering, machine learning, and high-performance computing.
Graphics window – It is the primary, large display area within a ‘graphical user interface’ (GUI) which shows the 3D model, finite element mesh, or simulation results. It is a new display area created for graphical output, where each window can be assigned an index and customized in size, directing all subsequent graphics output until another window is designated as current. Multiple graphics windows can exist simultaneously on-screen.
Graphic symbol – It is a visually perceptible figure, sign, or character used to transmit information independently of language. These standardized symbols are used in technical drawings, process diagrams, and material specifications to represent specific components, surface treatments, material properties, or manufacturing processes.
Graphitization – It is a metallurgical process where unstable carbides (cementite) in steel or iron decompose into graphite and iron, typically because of the long-term exposure to high temperatures (425 Deg C to 550 deg C). This form of degradation causes severe embrittlement and loss of strength in alloys. During graphitization, pearlite (a mix of ferrite and cementite) decomposes, allowing free carbon to migrate and form graphite nodules. It mainly affects carbon and low-alloy steels (e.g., carbon-molybdenum steel) in high-temperature applications like steam pipes and boiler tubes.
Graphite – It is a crystalline, lubricating allotrope of carbon, valued for its high thermal / electrical conductivity, thermal shock resistance, and chemical inertness. It is a form of carbon which is used in nuclear fission reactors to slow down (moderate) neutrons. It is normally constructed in the form of blocks or sleeves. The term graphite, also called synthetic, artificial, or electro-graphite refers to a carbon product which has been additionally heat treated at a temperature between 2,400 deg C to 3,000 deg C. This process is called graphitization, which changes the crystallographic structure of carbon and also changes the physical and chemical properties. Graphite is also found in nature. This natural graphite is found in flake form and, if used in a refractory product, is normally part of a mixture with ceramic material or used for the binder. Graphite is a critical industrial material, mainly used as a refractory lining in furnaces, a carbon raiser in steelmaking, and in crucibles, with structures comprising stacked hexagonal layers.
Graphite-austenite eutectic transformation – It is frequently referred to in the context of gray or ductile cast iron solidification. It is an invariant reaction occurring at a specific eutectic temperature (around 1,147 deg C in the iron-carbon system) where liquid iron transforms into a solid mixture of austenite and graphite. This reaction is central to the formation of stable (graphitic) microstructures in cast irons.
Graphite-base carbon refractory – It is a manufactured refractory comprised substantially of graphite.
Graphite-based lubricant – It is a type of solid-film or dry lubricant composed of finely powdered graphite (a crystalline allotrope of carbon) or graphite particles suspended in a carrier medium (such as oil, water, or grease). It is designed to reduce friction and wear between metal surfaces, especially under high temperatures, extreme pressures, or where conventional oil / grease lubricants break downs.
Graphite block – It is a solid, high-purity form of synthetic or natural carbon, characterized by exceptional thermal stability, high electrical conductivity, and high-temperature resistance. Graphite blocks act as important consumables, such as refractory lining, crucibles for melting, or electrodes in industrial furnaces, able to withstand temperatures up to 3,000 deg C.
Graphite carbon block, partial – It is made of calcined anthracite under high temperature and graphite. Medium pitch acts as binder. Main processes are extruding, baking and processing. Typical properties are with good thermal conductivity and anti-alkaline. Partial graphite carbon block is used in bottom of the blast furnace.
Graphite carbon block, ultra-thermal conductivity – It is made of low ash petroleum-coke with pitch acting as a binder. It is made by extruding, baking, impregnation, graphitization and processing. The product is with higher thermal conductivity which is helpful in reducing the temperature, cooling and slowing the erosion of the blast furnace bottom. Ultra-thermal conductivity graphite block is used in the hearth and bottom of blast furnace.
Graphite carbon fibre – It is a high-performance material characterized by a higher specific modulus than glass, offering resistance to high temperatures and chemical exposure, making it suitable for demanding applications.
Graphite electrodes – These are high-conductivity, cylindrical refractory materials made from petroleum coke and pitch, used in electric arc furnaces (EAF) to melt scrap metal and produce steel. They transfer massive electrical energy to create intense heat, facilitating high-temperature refining in metallurgy, with main types including UHP (ultra-high power), HP (high power), and RP (regular power) grades.
Graphite fibre – It is a fibre made from a precursor by an oxidation, carbonization, and graphitization process, which provides a graphitic structure.
Graphite fuel elements – These are specialized nuclear components consisting of fissile or fertile material, typically in the form of tri-structural-isotropic (TRISO) coated particles, embedded within a high-purity, synthetic, or natural graphite matrix. These elements act as both a neutron moderator, which slows down neutrons to sustain the chain reaction, and a structural component, providing thermal conductivity, strength, and a fission product barrier, mainly in ‘high-temperature gas-cooled reactors’ (HTGRs).
Graphite furnace atomic absorption spectrometry – It is also known as electro-thermal atomic absorption spectrometry (ETAAS). It is a type of spectrometry which uses a graphite-coated furnace to vapourize the sample. Briefly, the technique is based on the fact that free atoms absorb light at frequencies or wave-lengths characteristic of the element of interest (hence the name atomic absorption spectrometry). Graphite furnace atomic absorption spectrometry is an established technology for quantifying elements at trace and ultra-trace levels (down to low micrograms per litre) while using only small sample volumes (normally less than 100 micro-litres).
Graphite heater – It is a high-temperature heating element fabricated from high-purity, synthetic graphite. It functions through electrical resistance (Joule heating), passing current through the graphite structure to generate extreme heat, frequently exceeding 2,000 deg C to 3,000 deg C, typically in vacuum or inert gas atmospheres to prevent oxidation.
Graphite lubricant – It is a type of solid or dry-film lubricant consisting of high-purity crystalline carbon (graphite) in the form of powder, flakes, or colloidal suspensions. It is used to reduce friction, wear, and heat in high-temperature, high-load, or corrosive environments where traditional oil or grease lubricants would degrade.
Graphite lubrication – it refers to the use of graphite, a crystalline, flaky allotrope of carbon, as a solid lubricant to reduce friction and wear between metal surfaces, particularly under extreme conditions where conventional oil or grease lubricants fail. Because of its unique layered molecular structure and high temperature resistance, it is extensively used in metal-working, forging, casting, and bearing applications.
Graphite material – The term, graphite, also called synthetic, artificial or electro-graphite, refers to a carbon product that has been further heat treated at a temperature between 2,400 deg C and 3,000 deg C. This process of graphitization changes the crystallographic structure of carbon and also changes the physical and chemical properties. Graphite is also found in nature in flake form, and, if used in a refractory product, usually forms part of a mixture of ceramic materials for the binder. This ceramic bonded, natural graphite containing refractory is considered a ceramic product.
Graphite nano-particles – These are polyhedral carbon structures (10 nano-meters to 100 nano-meters range) composed of stacked graphene sheets, offering high thermal conductivity, lubrication, and high surface area. These particles are used to produce advanced metal matrix composites (MMCs), acting as solid lubricant additives or reinforcement agents to improve mechanical properties, wear resistance, and microstructure.
Graphite nodules – These are spherical or near-spherical particles of carbon formed within the microstructure of ductile cast iron (also called nodular or spheroidal graphite iron). These nodules are created through metallurgical treatment with elements like magnesium or cerium. Unlike graphite flakes in gray iron, nodules improve ductility, strength, and toughness by preventing crack concentration.
Graphite oxide – It is a layered, non-stoichiometric material produced by the heavy oxidation of bulk graphite using strong oxidizing agents and acids, such as the Hummers, Brodie, or Staudenmaier methods. It is considered a key intermediate for the production of graphene, graphene oxide, and functionalized carbon-based nano-composites.
Graphite powder – It is a highly crystalline, finely ground form of carbon derived from natural flake / amorphous graphite or synthetic sources. It is widely used for its exceptional thermal stability (up to 3,000 deg C), self-lubricating properties, and high electrical conductivity. It serves as an important alloying element and sintering aid to increase the strength and density of sintered parts.
Graphite, primary – It is the carbon precipitated as graphite flakes while the iron cools through the freezing eutectic in which austenite, graphite, molten iron, and carbide exist together. It is normally with reference to white fracture cast iron.
Graphite rod – It is a cylindrical, high-purity carbon-based component manufactured through the baking and high-temperature graphitization of carbonaceous materials (such as petroleum coke and coal tar pitch). It is specifically designed to function as a durable, conductive, and heat-resistant electrode or structural element in high-temperature processes, such as electric arc furnaces (EAFs) for steel recycling, non-ferrous metal production (aluminum / copper smelting), and Electrical Discharge Machining (EDM).
Graphite, secondary – It is the graphite formed by decomposition of austenite during slow cooling of cast iron.
Graphite shapes, cast iron – There are four types of the graphite shapes in cast irons. These are (i) lamellar (flake) graphite (FG), (ii) spheroidal (nodular) graphite (SG), (iii) compacted (vermicular) graphite (CG), and (iv) temper graphite (TG). Temper graphite results from a solid-state reaction (malleabilization).
Graphite suspensions in water – These are frequently referred to as aqueous graphite dispersions or colloidal graphite in water. These are specialized liquid mixtures where fine particles of graphite are dispersed in a water base. These are used as high-performance, eco-friendly lubricants and release agents.
Graphitic carbon – It is the free carbon in steel or cast iron. It refers to solid carbon in its stable, crystalline allotropic form (graphite), rather than combined as iron carbide (Fe3C) or in an amorphous state. It is characterized by hexagonal, layered ordering that provides self-lubricating, electrically conductive, and soft, machinable properties to materials like grey cast iron.
Graphitic carbon nitride (g-C3N4) – It is a metal-free, 2D polymeric semi-conductor composed of carbon and nitrogen, featuring a layered graphite-like structure. It is characterized by high thermal / chemical stability, excellent visible-light photocatalytic activity, and high hardness, often used for catalysis, coating, and energy storage, synthesized through thermal condensation of nitrogen-rich precursors.
Graphitic cast irons – These are iron-carbon-silicon alloys (above 2 % carbon, 1 % to 3 % silicon) which solidify with carbon present as free graphite rather than iron carbide (cementite). This structure, formed through graphitization, provides excellent castability, machinability, and vibration damping. Main types include gray (flakes), ductile (spheres), and compacted graphite (worms) cast irons.
Graphitic corrosion – It is the corrosion of gray iron in which the iron matrix is selectively leached away, leaving a porous mass of graphite behind. It occurs in relatively mild aqueous solutions and on buried pipe and fittings.
Graphitic steel – It is an alloy steel made so that part of the carbon is present as graphite.
Graphitization – It is the process of heating amorphous carbon for a prolonged period of time, rearranging the atomic structure to achieve an ordered crystalline structure which is typical of solids. During graphitization, carbon atoms are rearranged to fill atom vacancies and improve atom layout. The graphitization process needs heating up to temperatures of 3,000 deg C. It is the process of transforming non-graphitic carbon into graphite through heat treatment, which can also involve converting metastable diamond into graphite or forming graphite from unstable carbides in metallurgy at high temperatures.
Graphitization, iron and steel – It is the formation of graphite in iron or steel. Where graphite is formed during solidification, the phenomenon is termed primary graphitization and where it is formed later by heat treatment, it is termed as secondary graphitization.
Graphitization process – It involves a restructuring of the molecular structure of the carbon material. In the initial state, these materials can have an amorphous structure or a crystalline structure different from graphite. Graphitization normally occurs at high temperatures (up to 3,000 deg C), and can be accelerated by catalysts such as iron or nickel. When carbonaceous material is exposed to high temperatures for an extended period of time, the carbon atoms begin to rearrange and form layered crystal planes. In the structure of graphite, carbon atoms are arranged in flat hexagonal sheets which are stacked on top of each other. These crystal planes give graphite its characteristic flake structure, giving it specific properties such as good electrical and thermal conductivity, low friction and excellent lubrication.
Graphitizing – It consists of annealing a ferrous alloy such that some or all the carbon precipitates as graphite.
Graphitizer – It is a substance, such as silicon, titanium, aluminum, etc., which promotes the formation of graphite in cast iron compositions. It is an inoculant or alloying element added to molten iron (cast iron) to promote the formation of graphite flakes or nodules during solidification, rather than white iron (iron carbide). It acts to break down iron carbide (Fe3C) and encourage the carbon to precipitate as free graphite.
Graph node – It is also called graph vertex. It is a fundamental unit, point, or object within a graph data structure that represents an entity, such as a person, city, or data point. Nodes are interconnected by edges (links) to define relationships. They can contain data, attributes, or properties, and are crucial for representing networks.
Graph theoretic approach – It is a mathematical modeling technique which represents complex systems as graphs, consisting of nodes (vertices) and connections (edges). It analyzes relationships, structures, and behaviours of systems by reducing data to networked structures, allowing for identification of critical paths, clusters, and patterns.
Graph theory – it is a branch of mathematics which utilizes graphs to represent theoretical or structural relations, providing a useful tool for forming, viewing, and analyzing different kinds of structural models in different fields.
Graph, tree – It is a connected, undirected graph in graph theory that contains no cycles or loops, meaning there is exactly one unique path between any two vertices (nodes). It is a minimally connected graph with ‘n’ vertices and ‘n-1’ edges, normally used to model hierarchical structures.
Grashof number (Gr) – In fluid mechanics, it is a dimensionless number which approximates the ratio of the buoyancy to viscous forces acting on a fluid. It frequently arises in the study of situations involving natural convection and is analogous to the Reynolds number.
Grate kiln process – In the grate kiln process, the traveling grate is used to dry and preheat the pellets. Material moves on straight travelling grate till it attains the temperature in the range of 800 deg C to 1,000 deg C. After that, the material is transferred to refractory lined rotary kiln for induration where the temperature is further raised in the range of 1,250 deg C to 1,300 deg C. At 800 deg C, the ferrous oxide (FeO) of the magnetite iron ore gets converted into ferric oxide (Fe2O3) in an exothermic reaction. The liberated heat hardens the green balls which is helpful to withstand the tumbling impact because of the rotation of the rotary kiln. A circular cooler is used for cooling of the fired pellets.
Grating – It is any regularly spaced collection of essentially identical, parallel, elongated elements. Gratings normally consist of a single set of elongated elements, but can consist of two sets, in which case the second set is normally perpendicular to the first. When the two sets are perpendicular, this is also known as a grid or a mesh.
Grating equation – It is ‘m lambda = d [Sin theta-i + sin phi-m). This equation defines the relationship between light wavelength (lambda), grating spacing (d), incident angle (theta-i), and diffraction angle (phi-m) for a given order (m). It is necessary for analyzing surface micro-structures, measuring stress / strain, and determining composition through spectroscopy by analyzing diffraction patterns from periodic surfaces.
Grating fabrication – It is the process of assembling metal components, mainly bearing bars and cross bars, into a rigid, open-grid structure through welding, swage-locking, or riveting. It is used to produce durable, high-strength, load-bearing panels for industrial flooring, drainage, and ventilation.
Grating inscription – It refers to the process of creating a periodic,, and frequently microscopic, pattern of lines or grooves (a grating) onto a substrate, typically for optical, reflective, or technical applications. In the context of fibre optics, high-performance sensors, and metallurgy, this is frequently achieved through high-energy laser techniques that modify the refractive index or structure of the material.
Grating length – It is the overall dimension of a metal grating panel measured parallel to the load-bearing bars, which typically represents the span of the grating. It is distinct from the width, which runs perpendicular to the bearing bars along the cross-bars. The length runs in the same direction as the bearing bars, which are the main load-carrying members. It is the total length of the bearing bars from end to end, frequently covering the distance between support points.
Grating period – It refers to the uniform distance between the centres of adjacent lines, grooves, or structural units in a periodic pattern, such as in a diffraction grating or a micro-etched surface. It is the uniform distance between adjacent lines or grooves on a diffraction grating, which determines the angles at which light is diffracted.
Grating reflectivity – It measures the efficiency of a diffraction grating to reflect incident light into specific diffraction orders, typically expressed as a ratio of reflected to incident intensity (R = tan h-square (k x L). This involves metallic surfaces with periodic microscopic grooves which diffract light, frequently using reflective coatings to optimize intensity and resolution for spectroscopy,
Grating spectrum – It refers to the spatially separated, rainbow-like pattern of wavelengths (colours) produced when polychromatic light is diffracted by a diffraction grating, an optical component with thousands of finely ruled, parallel lines on a reflective metallic or polished surface. This technique is necessary for spectroscopy to identify the elemental composition of metal samples.
Grating strength – It refers to the load-bearing capacity of a metal grating panel, defined as its ability to resist static loads, dynamic forces, or impact without experiencing permanent deformation or structural failure. It is a critical safety and performance parameter, particularly for heavy-duty industrial flooring, catwalks, trenches, and stair treads. It is also the product of the coupling coefficient (κ) and the length of the grating (L), which determines the reflectivity of the grating, with ‘κ L’ higher than one indicating a strong grating and ‘κ L’ less than one indicating a weak grating.
Grating vector (K) – It is a vector which defines the periodic structure of a material, with a magnitude of ‘K = 2 pi /L’ (where ‘L’ is the grating period) and a direction orthogonal (normal) to the grating lines or planes. It represents the spatial frequency of the lattice in diffraction studies.
G-ratio – It is also called grinding ratio. It is a measure of grinding efficiency, defined as the ratio of the volume of work-piece material removed (Vw) to the volume of grinding wheel worn away (Vs). A higher G-ratio indicates superior wheel life and efficiency, frequently influenced by parameters like wheel speed, coolant, and material type.
Gravel – It is a loose aggregation of rock fragments. Gravel occurs naturally on earth as a result of sedimentary and erosive geological processes. It is also produced in large quantities commercially as crushed stone. Gravel is classified by particle size range and includes size classes from granule- to boulder-sized fragments.
Gravel concrete – It is a type of concrete which uses gravel, a loose aggregation of rounded, natural rock fragments (pebbles / cobbles) or crushed stone ranging in size from 2 millimeters to 64 millimeters as the coarse aggregate component. It is defined by its high strength, durability, and cost-effectiveness, making it a main construction material for foundations, structural concrete, and road building. Gravel concrete consists of Portland cement (binder), water, fine aggregate (sand), and gravel (coarse aggregate). The gravel acts as the skeleton, increasing the volume and structural strength.
Gravel pack – It is a sand-control method used in oil, gas, and water wells to prevent the production of formation sand and stabilize weak, unconsolidated, or poorly cemented geological formations. It involves placing a specifically sized, processed granular material (siliceous sand or gravel) in the annular space between a well screen and the borehole wall or perforated casing. This acts as a filter to allow hydrocarbons or water to flow into the well while preventing finer formation sand from entering and damaging equipment or restricting flow.
Gravel road – It is a type of unpaved road featuring a wearing surface made of compacted, and graded aggregate (crushed stone, gravel, and fines like clay or silt). It is sometimes referred to as ‘metal road’, and it is normally designed for low-volume traffic in rural areas.
Gravel-water thermal energy storage – It is a buried, insulated, sensible-heat storage system utilizing a gravel / water mixture, typically operating below 95 deg C to store thermal energy for later use. It acts as a hybrid storage, with gravel providing structural integrity and water improving heat transfer and capacity. The storage needs around 50 % more volume than water-only storage to achieve the same capacity. Gravel-water thermal energy storage is a form of ‘underground thermal energy storage’ (UTES) where a pit is filled with a porous medium (normally gravel) and water. It is considered a sensible heat storage system, meaning the stored energy simply raises the temperature of the gravel-water mixture.
Gravimetric absorbency testing system – It is an automated, high-sensitivity instrument which measures the liquid absorption rate and capacity of porous materials by analyzing mass changes over time. It is specifically used to assess the wettability and liquid absorption of materials like AGM (absorbed glass mat) battery separators. It precisely measures the ‘demand wettability’ or how quickly and how much liquid is absorbed into a porous solid.
Gravimetric capacitance – It is the capacitance of an electrode material divided by its total mass (Csp = C/m), typically measured in farads per gram or coulombs per volt-gram. It represents the ability of a material to store electrical charge per unit mass, frequently used in supercapacitor research to evaluate performance. It is frequently synonymous with ‘specific capacitance’ in battery or supercapacitor science, referring to charge storage relative to the weight of the active material.
Gravimetric method – It is also called gravimetric analysis. It is a quantitative chemical analysis technique used to determine the exact quantity of a specific element (analyte), such as a metal or impurity, in a sample based on the precise measurement of mass. This method relies on the law of conservation of mass and stoichiometric relationships to calculate the analyte concentration, frequently following the separation of the element from an ore, alloy, or solution.
Gravimetric surveys – These surveys measure small variations in the gravitational field caused by the pull of underlying rock masses. The variation in gravity can be caused by faults, anticlines, and salt domes which are frequently associated with oil-bearing formations. Gravimetric survey is also used to detect high density minerals such as iron ore.
Gravitational acceleration (g) – It is defined as the rate at which materials accelerate in a vacuum, a principle applied to casting simulations. It is the acceleration applied to materials, typically 9.81 meters per second at the earth’s surface, affecting processes like casting, particle separation, and metal density measurements. It represents the force per unit mass acting toward earth, directly influencing how molten metals flow in moulds and how refined metals settle based on gravity. The value of ‘g’ influences the pressure of liquid metal in a mould, where higher gravity creates higher metallostatic pressure, influencing defects and filling speed. In smelting and refining, gravitational acceleration causes denser slag or impurities to settle at the bottom of the furnace, separating them from the lighter molten metal. While 9.81 meters per second is standard, local variations based on latitude and altitude, or the use of artificial gravity (centrifuges), can alter the rate of settling and casting efficiency. This fundamental acceleration is crucial to predicting solidification behavior and material quality during processing.
Gravitational constant (G) – It is a fundamental physical constant (around 6.674 x 10 t9 the power -11) in Newton’s law of universal gravitation, determining the strength of gravitational attraction between two objects. It defines the force interaction which influences material processing and density-related casting defects. Gravitational constant is an empirical physical constant involved in the calculation of gravitational effects in the Newton’s law of universal gravitation and in Einstein’s general theory of relativity. In Newton’s law, it is the proportionality constant connecting the gravitational force between two bodies with the product of their masses and the inverse square of their distance. In the Einstein field equations, it quantifies the relation between the geometry of spacetime and the energy–momentum tensor.
Gravitational energy – It is frequently referred to as gravitational potential energy. It is the stored energy an object or material possesses because of its elevated position in a gravitational field, typically relative to the earth’s surface. This form of energy is mainly concerned with the mechanical and potential energy of raw materials and molten metals during production and processing.
Gravitational force (Fg) – It is the downward force acting on molten metal or particulates based on their mass and density, frequently expressed as ‘Fg = m x g’. Here ‘m’ is mass and ‘g’ is the gravitational acceleration. It plays an important role in processing by inducing material separation, aiding gravity casting, and causing density-driven segregation during solidification.
Gravitational load – It is also called gravity load. It is the force exerted on a component, structure, or material because of its own mass (self-weight) acting in the direction of gravity, normally downward. It is a fundamental, constant, and deterministic load type representing the weight of materials, including molten metal in casting, structural elements, and permanent fixtures.
Gravitational parameter (P) – It is the product of the gravitational constant (G) and the mass (M) of a body, ‘P = G x M’, acting as a measure of gravitational influence. This concept relates to gravity casting, where molten metal fills a mold using gravity rather than high pressure. The parameter ‘P’ simplifies calculations by combining ‘G’ and ‘M’.
Gravitational potential energy (GPE) – It is the energy stored in materials (ores, molten metal, scrap) because of their vertical position (h) in a gravitational field (g) relative to a reference level, calculated as ‘GPE = m x g x h’. It represents potential to do work, such as powering molten metal flow, driving ore sorting, or releasing impact energy during crushing. Gravitational potential energy is the energy an object or molten material possesses because of its position within a gravitational field, typically defined by its height above a processing base level.
Gravitational pull – It refers to the force of gravity acting on molten metal during casting, influencing solidification, mould filling, and the segregation of phases based on density. It is critical for determining how heavy impurities (dross / slag) sink or float, and causes hydrostatic pressure in tall moulds.
Gravitational settling – It is a separation technique where solid particles are removed from liquids or gases by letting gravity cause denser particles to sink and collect at the bottom of a vessel. It relies on low velocity, allowing particles to separate from fluid streams, acting as a key method for sludge removal or gas cleaning. Particles settle since their density is higher than the surrounding fluid, allowing gravity to overcome fluid drag, resulting in a settling rate described by terminal velocity.
Gravity – It is a natural phenomenon by which all things with mass or energy are attracted to one another. On Earth, gravity gives weight to physical objects. Gravity has an infinite range, although its effects become weaker as objects get further away.
Gravity anchor – It is a heavy, seabed-mooring foundation (frequently precast concrete, steel, or cast iron) which relies solely on its massive weight and frictional resistance to secure floating structures, such as oil rigs or wind turbines. They are ideal for hard bottoms, simple to install, and cost-effective.
Gravity base – it is a heavy foundation structure, typically made of reinforced concrete, steel, or cast iron, which uses its immense weight to provide stability against overturning, sliding, and environmental loads for marine, offshore (wind / oil), and onshore structures. It relies on mass rather than piling, making it ideal for deep water or rocky, stable sea-beds.
Gravity-based filter – It is a separation device which uses natural gravitational force, rather than high pressure or vacuum, to pass a liquid (frequently a slurry or coolant) through a permeable filter medium (such as paper, cloth, or sand) to trap solid metallic or mineral contaminants. This process is important for cleaning metalworking fluids, removing precipitates in hydrometallurgy, and dewatering mineral concentrates.
Gravity-based filtration – It is a physical separation process used to remove suspended solid impurities or gangue from liquid metal slurries, leaching solutions, or aqueous suspensions by utilizing natural gravitational forces to pull the fluid through a porous medium. Unlike pressure or vacuum filtration, it operates without external pressure, relying solely on the weight of the fluid to separate liquids (filtrate) from solids (residue).
Gravity-based separation – It is also called gravity concentration. It is a process which separates mineral particles based on their differences in specific gravity (density) and size, causing heavier particles to sink or be separated from lighter ones. It is one of the oldest methods of mineral processing, used extensively for recovering heavy metals like gold, iron ore, and tungsten.
Gravity-based structure (GBS) – It is a support structure held in place by gravity. These structures are frequently constructed in fjords (a long narrow piece of sea between cliffs) because of their protected area and sufficient depth.
Gravity brackets – These are brackets which are designed for the attachment of gravity conveyors to the ends of powered conveyors.
Gravity casting – It is frequently known as gravity die casting. It is a process where molten metal is poured into a mould using only gravitational force, without external pressure, vacuum, or centrifugal force. It is mainly used for non-ferrous metals like aluminum, zinc, and brass, offering high-quality surface finish and structural integrity.
Gravity concentration – It is widely being used in the beneficiation of hematite iron ores. This technology is used to suspend and transport lighter gangue away from the heavier valuable mineral. This separation process is based mainly on differences in the specific gravities of the materials and the size of the particles being separated. Value fractions can be removed along with the gangue material (tailings) despite differences in density if the particle sizes vary. Because of this potential problem, particle sizes are to be kept uniform with the use of classifiers (such as screens and hydro cyclones).
Gravity condition – It typically refers to the operating environment regarding gravitational force (1 g or improved) used to separate, refine, or cast materials based on density differences. It describes the intensity of the gravitational field applied to a system (normal gravity, micro-gravity, or super-gravity) and the subsequent effect on particle settling, bubble movement, or phase separation.
Gravity conveyor system – It consists of a non-powered conveyor system relying on gravity for material movement, needing periodic checks for proper flow and alignment.
Gravity corer – It is a geotechnical sampling device utilized in marine geology and oceanography to collect vertical, undisturbed sediment samples from the seabed. It is characterized as a robust, typically, carbon steel or stainless-steel tube, weighted at the top, which uses the kinetic energy of its own weight to penetrate seafloor sediments.
Gravity dam – It is a solid structure, typically built from concrete or masonry, which relies solely on its immense weight and base width to resist horizontal water pressure and ensure stability against overturning and sliding. It is normally shaped like a triangle, with maximum width at the base. The structure’s weight is sufficient to resist external forces such as water pressure, uplift pressure (seepage under the dam), silt pressure, and earthquake forces. It is mainly constructed of reinforced concrete, roller-compacted concrete (RCC), or stone masonry. The gravity dam acts as a rigid, monolithic structure, frequently straight in plan, which transfers loads directly to the foundation, needing high-strength bedrock.
Gravity data – It refers to measurements of the local gravitational field taken at the earth’s surface, from aircraft, or in boreholes to determine variations in the density of subsurface rocks and materials. These measurements help identify geological structures, such as faults, or locate mineral and ore deposits which have higher density than the surrounding rock (positive anomaly) or lower density (negative anomaly). Gravity data is collected using instruments called gravimeters (e.g., LaCoste-Romberg or Worden), which are passive and non-invasive, measuring gravity differences between locations (relative gravity) or absolute values. The main unit used is the Gal (centimeter per square centimeter).
Gravity die-casting – In gravity die casting, there is a metal, graphite or ceramic mould (other than an ingot mould) which is repeatedly used for the production of several castings of the same form. Liquid metal is poured in by gravity.
Gravity drainage – It is a main recovery mechanism where density differences between fluids (oil and gas) allow gravity to pull oil down into the wellbore, frequently improved by high permeability or gas injection. It acts as a natural or improved mechanism to separate oil from reservoir rock, frequently recovering 30 % to 60 % of oil in place.
Gravity drainage reservoir – It is a petroleum reservoir where the main producing mechanism is the movement of oil downward relative to gas (or upward relative to water) because of the density differences. This process involves the segregation of fluids within the reservoir, where gravity forces push hydrocarbons out of the porous rock and into the wellbore. Gravity drainage occurs when the reservoir pressure drops below the bubble point, releasing free gas that migrates up-structure to form a secondary gas cap, allowing oil to drain downward.
Gravity drop-hammers – They are the oldest type of forging equipment available. The principle of operation is that the moving die block is raised by a lifting mechanism and then released, so that it falls onto the fixed die attached to the anvil. The quantity of deformation which can be carried out is determined by the potential energy of the moving die block at its maximum height. This potential energy is converted into kinetic energy as the die block falls and is then dissipated in deformation of the work piece. Different in lifting mechanisms are used, including frictional means with boards, band brakes or belts, or a lifting cylinder employing steam, compressed air, or hydraulic fluid. These machines are available a range of blow energies from 0.6 kilo newton metre to 400 kilo newton metre.
Gravity flow – It is a flow of a liquid fluid such as water from a higher elevation to a lower elevation because of the force of gravity, and not by the energy provided by a pump. Gravity flow also refers to the movement of materials such as landslides, pyroclastic flows, and aeolian sediment under water because of the force of gravity, even if they originated on land.
Gravity hammer – It is a class of forging hammer in which energy for forging is achieved by the mass and velocity of a freely falling ram and the attached upper die. Examples are the board hammer and air-lift hammer.
Gravity meter, gravimeter – It is an instrument for measuring the gravitational attraction of the earth. Gravitational attraction varies with the density of the rocks in the vicinity.
Gravity method – It is normally referred to as gravity concentration. It is a physical mineral processing technique which separates valuable minerals from gangue (waste) material based on their differences in specific gravity (density). It is one of the oldest and most widely used mineral processing methods, frequently using water or, less commonly, air as a medium to facilitate the separation. Gravity method is also a passive, non-destructive geophysical technique which detects subsurface geological structures by measuring minute variations in the earth’s gravitational field. It maps lateral density differences, where denser rocks produce positive anomalies and lower-density materials (like voids or salt domes) cause negative anomalies.
Gravity pumps – In a gravity pump the fluid is lifted by gravitational force. Gravity pumps include the syphon and Heron’s fountain. The hydraulic ram is also sometimes called a gravity pump.
Gravity rollers – These are the rollers in a gravity conveyor system which use gravity to move materials, requiring inspections for wear, alignment, and smooth operation.
Gravity segregation – It refers to the separation of phases or components within a molten metal or alloy because of the differences in their density and the force of gravity. It is a form of macro-segregation which occurs when solid particles, liquid droplets, or intermetallic compounds settle to the bottom or rise to the top of a melt (or liquid-solid ‘mushy’ zone) during solidification. It means variable composition of a casting or ingot caused by settling out of heavy constituents, or rising of light constituents, before or during solidification.
Gravity separation – It is an industrial method of separating two components, either a suspension, or dry granular mixture where separating the components with gravity is sufficiently practical: i.e. the components of the mixture have different specific weight. Every gravitational method uses gravity as the primary force for separation. One type of gravity separator lifts the material by vacuum over an inclined vibrating screen covered deck. This results in the material being suspended in air while the heavier impurities are left behind on the screen and are discharged from the stone outlet. Gravity separation is used in a wide variety of industries, and can be most simply differentiated by the characteristics of the mixture to be separated – principally that of ‘wet’ i.e., a suspension against ‘dry’, a mixture of granular product. Gravity separation technique is used in iron ore beneficiation, where iron bearing minerals are free from associated gangue materials. The specific gravity of iron bearing minerals is normally higher than the specific gravity of gangue materials. Effectiveness efficiency of the gravity separation depends largely on to proper crushing and sizing of the ore so as to ensure a proper size feed to the gravity separation equipment and also removal of slime from the equipment. A large variety of equipments / processes functioning on gravity separation principle are available. Three gravity separation methods have historically been used for iron ore namely (i) washing, (ii) jigging, and (iii) heavy-media separators. Spirals and Reichert cones are other two methods for gravity separation.
Gravity take-up – It is a mechanical system which adjusts for the stretch or shrinking of a conveyor belt automatically by a weighted pulley in the system.
Gravity wave – It is a type of wave which occurs in a fluid medium, where the restoring force is gravity. These waves can be influenced by several perturbations, including turbulence and density currents, and typically show complex structures with time-varying amplitudes and multiple frequencies present. It is a wave disturbance in which buoyancy (or reduced gravity) acts as the restoring force on parcels displaced from hydrostatic equilibrium. There is a direct oscillatory conversion between potential and kinetic energy in the wave motion. Pure gravity waves are stable for fluid systems which have static stability. This static stability can be (i) concentrated in an interface or (ii) continuously distributed along the axis of gravity.
Gravity work – It is the separation of minerals based on differences in their density (specific gravity). It is an ancient, cost-effective, and environmentally friendly method which relies on the differential settling rates of mineral particles within a fluid medium (normally water) to separate valuable dense ores from lighter gangue material.
Gravure printing – It is also known as rotogravure. It is an industrial intaglio printing process which uses a metal cylinder, engraved with millions of tiny cells, to transfer high-viscosity ink directly onto a substrate. It is mainly recognized for its high-speed, high-volume, and high-quality printing capabilities, making it ideal for long-run applications such as packaging, magazines, and decorative materials. The core component is a steel cylinder, normally plated with copper and then chromium for durability. The image to be printed is etched into this cylinder using lasers, diamond styli, or chemical etching.
Gray (Gy) – It is a unit of measurement for the absorbed dose. The absorbed dose has been formerly measured in rads and 1 gray = 100 rads. When it comes into contact with matter, ionizing radiation collides with the atoms comprising it. During these interactions, it releases a part or all of its energy. The absorbed dose (expressed in Gray) is defined by the ratio of this released energy over the mass of the matter. A Gray corresponds to one Joule of energy released in one kilogram of matter.
Gray-box modeling – It is a hybrid approach which combines fundamental physical principles (white-box models), such as thermodynamics, mass, and energy balances, with data-driven techniques (black-box models), typically artificial intelligence (AI) or machine learning, to model complex metallurgical processes. This methodology is used when a process is too complex or computationally expensive to model solely with physical equations, but purely empirical (data-only) models lack reliability or physical insight.
Gray cast iron – It is a cast iron which shows a gray fracture surface consisting of ferrite and dispersed graphite flakes. When the composition of the iron and the cooling rate at solidification are suitable, a substantial portion of the carbon content separates out of the liquid to form flakes of graphite. The fracture path of such iron follows the graphite flakes. The fracture surface of this iron appears gray because of the predominance of exposed graphite. Gray cast iron is the result of stable solidification produced at slow cooling. It has several unique properties which are derived from the existence of flake graphite in the micro-structure. It possesses high compressing strength, fatigue resistance, and wear resistance. It is relatively soft and can be machined and welded easily. It has hardness conducive to good wear resistance. It resists galling under boundary-lubrication conditions. It has very good properties for use in vibration damping or moderate thermal shock applications. It is used for engine cylinder blocks, gears, flywheels, water pipes, brake discs, and machine tool structures etc. Gray coatings – Some steels produce a matt gray galvanized coating. These coatings are 100 % alloy layer and contain no free zinc. They tend to be thicker than standard shinier galvanized coatings.
Gray code – it is an ordering of the binary numeral system such that two successive values differ in only one bit (binary digit). For example, the representation of the decimal value ‘1’ in binary normally be ‘001’, and ‘2’ be ‘010’. In gray code, these values are represented as ‘001’ and ‘011’. That way, incrementing a value from 1 to 2 needs only one bit to change, instead of two. Gray codes are widely used to prevent spurious output from electro-mechanical switches and to facilitate error correction in digital communications.
Gray iron – It is also called grey iron. It is a widely used type of cast iron characterized by its graphitic microstructure, where carbon exists as flakes, giving the fractured surface a gray colour. It is a versatile, cost-effective alloy (2.5 % to 4 % carbon, 1 % to 3 % silicon) known for excellent machinability, high thermal conductivity, and superior vibration damping.
Gray iron melting – It is the process of heating a charge, typically pig iron, steel scrap, and returns, to liquid form (around 1,150 deg C to 1,200 deg C) in furnaces like cupolas or induction furnaces to create a molten iron-carbon alloy (2.5 % to 4 % carbon, 1 % to 3 % silicon). This molten metal is then adjusted chemically, treated, and poured into moulds.
Gray iron quality control – It is the systematic process of ensuring cast products meet specified standards for chemical composition, micro-structure (flake graphite), and mechanical properties (tensile strength, hardness). It focuses on consistency, dimensional accuracy, and defect reduction through raw material testing, melt control, and inspection.
Gray-King coke test – The purpose of the Gray-King coke test, which is one of the parameters adopted for the International Classification of Hard Coal by Type is to assess the caking properties of a type of coal or a blend of coals by carbonizing under standard conditions. ISO 502 describes the procedure for this test.
Gray level distribution – It is also called gray-level histogram. It refers to the statistical representation of pixel intensity values within a digital micrograph of a metal or alloy. It defines the frequency of occurrence of each brightness level, typically ranging from 0 (black) to 255 (white) in 8-bit images, representing how microstructural features (phases, grains, inclusions, voids) are spread across the image.
Gray level image – it is a digital micrograph, e.g., from SEM (scanning electron microscopy) or optical microscopy, where each pixel represents a single intensity value, typically on an 8-bit scale from 0 (black) to 255 (white). It maps the varied brightness of microstructural features, such as phases, grains, or inclusions, to shades of gray.
Gray list – It is a list of discrete entities, such as IP (internet protocol) addresses, email senders, software components, or devices, which have not yet been definitively classified as benign (white-listed) or malicious / unwanted (black-listed). Items on a gray list are typically placed under temporary restriction or closer scrutiny while more information is gathered to determine their safety.
Gray mapping – It is defined as a mapping from Z4 to F22 that assigns binary representations to elements of Z4 in such a way that adjacent values differ by only one bit, facilitating error correction in modulation theory. It can be extended to a map from Z4n to F22n while preserving the isometric property between the Lee and Hamming distances.
Gray markets – These are defined as the trade of authentic, branded products through unauthorized, unofficial, or unintended distribution channels. Unlike black markets which deal in illegal, stolen, or counterfeit goods, gray market goods are genuine products made by the original manufacturer, but they are distributed outside the authorized, brand-sanctioned supply chain.
Grayscale – It normally refers to the representation of microstructural features, such as grain boundaries, inclusions, phases, or pores, using shades of gray ranging from black to white, normally in a digital image. This is a fundamental aspect of quantitative metallography and image analysis, where the intensity of each pixel correlates directly to the optical or electron density of the material being examined, allowing for automated measurement and identification of features.
Grayscale image – It is a digital representation of a material’s micro-structure, such as grains, phases, or inclusions, where each pixel value represents only the intensity of light (luminance) rather than colour. It is a single-channel image, normally using 8-bit depth to provide 256 shades ranging from absolute black (value 0) to pure white (value 255).
Grayscale levels – It refer to the range of intensity values (0 to 255 in 8-bit imaging) assigned to pixels in a digital micrograph to represent the luminance or brightness of different phases, structures, or features within a metal or alloy. These levels range from pure black (0) to pure white (255).
Grayscale range – It refers to the spectrum of pixel intensity values (shades of gray) within a digital image, such as a micrograph taken through scanning electron microscopy (SEM) or optical microscopy. It defines the brightness distribution of structural features, allowing for the segmentation and quantitative analysis of constituents like phases, inclusions, grain boundaries, or pores.
Grayscale values – These are numerical representations of light intensity (brightness) assigned to individual pixels in digital images, typically used to analyze microstructures. In 8-bit digital imaging, normally used in optical microscopy and scanning electron microscopy (SEM), each pixel is assigned a value from 0 to 255.
Gray water footprint – It is a volumetric measure of freshwater needed to dilute pollutants from mining, smelting, or refining, such as heavy metals (e.g., mercury, lead), acidic runoff, and sulfates, to meet ambient water quality standards. It quantifies the pollution load, rather than just waste-water volume.
Grazing angle – It is also known as a glancing angle. It is the angle between an incident beam of radiation (such as X-rays, neutrons, or electrons) and the tangent of the sample surface. Unlike the conventional angle of incidence, which is measured from the normal (perpendicular) to the surface, the grazing angle is measured relative to the surface plane.
Grazing incidence – It refers to an experimental technique where X-rays or neutrons are directed at a surface at a very shallow angle, allowing for the study of surface roughness, layers, and nano-scale objects through specular reflection and off-specular small-angle scattering. This method is necessary for developing X-ray and neutron mirrors and understanding phenomena such as agglomeration or pore formation at surfaces.
Grazing incidence diffraction – It is a technique for interrogating a material using small incidence angles for an incoming wave, frequently leading to the diffraction being surface sensitive.
Grease – It is a semi solid lubricant. It is a mixture consisting of natural or synthetic oil base combined with thickeners and additives. It generally consists of a soap emulsified with mineral or vegetable oil. The National Lubricating Grease Institute (NLGI) defines grease as ‘a solid to semi-solid product of dispersion of a thickening agent in a liquid lubricant. Additives imparting special properties may be included’.
Grease colouring – It is the practice of adding dye or pigments to lubricating grease to act as a visual identifier for its type, application, or performance characteristics. While grease colour provides a helpful visual cue, it is not an absolute, standardized indicator of performance. It is mainly used to prevent cross-contamination and aid in maintenance.
Grease gun – It is a common tool used for lubrication. The purpose of the grease gun is to apply lubricant through an aperture to a specific point, normally from a grease cartridge to a grease fitting or ‘nipple’. The channels behind the grease nipple leads to where the lubrication is needed. The aperture can be of a type which fits closely with a receiving aperture on any number of mechanical devices. The close fitting of the apertures ensures that lubricant is applied only where needed
Grease-less compounds – These are a variety of buffing compounds in which the abrasive is blended with water and gelatin glue rather than tallow, wax, or oil.
Grease lubrication – It is the process of using a semi-solid lubricant (grease) to reduce friction and wear between moving parts, preventing damage and ensuring smooth operation. Grease, unlike oil, is a more viscous substance which stays in place, making it suitable for applications where a liquid lubricant might leak or be difficult to contain.
Grease pencil – It is a wax-based marking tool used to write on hard, smooth, glossy, or non-porous surfaces like metal, glass, and plastic. Made of hardened, moisture-resistant coloured wax, these pencils leave a durable, opaque mark which can be removed with a cloth.
Grease streak – It is a narrow discontinuous streak caused by rolling over an area containing grossly excessive lubricant drippage.
Greater dynamic range – It refers to an analytical instrument’s capability (such as in X-ray diffraction, spectroscopy, or imaging) to simultaneously measure or detect the highest signal intensity (before saturation) and the lowest signal intensity (near noise level). This allows for detecting both trace elements and major alloy components in one test. It is the ratio of the largest measurable signal to the smallest, frequently expressed in decibels (dB), bits, or orders of magnitude.
Greatest common divisor – It is also called ‘highest common factor’ (HCF). It is the largest positive integer which divides two or more integers without leaving a remainder. It is important for simplifying fractions, optimizing resource allocation, algorithm design, and reducing complex systems to their lowest terms.
Greedy algorithm – It is a heuristic optimization method that rapidly identifies promising material compositions or structures by making the locally optimal choice at each step of a multi-stage process. Instead of searching the entire potential compositional space, which is frequently computationally infeasible, the greedy algorithm constructs a solution step-by-step, choosing the best available option (e.g., highest strength, lowest cost, or highest conductivity) at that instant, assuming this short-term gain leads to a near-optimal overall solution.
Greedy approach – It is a problem-solving strategy which makes the locally optimal choice, the best immediate decision, at each stage of a process, with the goal of achieving a globally optimal result. It is frequently used in complex, non-polynomial time hard (NP-hard) optimization problems to achieve reasonable solutions efficiently.
Greek letters – In statistics, Greek letters are used for the parameters of the population and for a few other things.
Green – It means unsintered (not sintered), e.g., green compact, green density, green strength. The prefix ‘green’ also signifies ‘renewable’ or environmentally sustainable.
Green belt – It is the development of green cover around on empty land inside the project / plant area or within the project / plant influence area. The main objectives of green belt development are to minimize the pollution load generated from different developmental activities. Green belts are intended to reduce pollution, improve air quality, and protect the environment.
Green body – It is an unfired, shaped object composed of ceramic or metal powders mixed with binders, used in manufacturing before sintering. It represents an intermediate, fragile state, strong enough for handling and machining, but porous and not fully densified. The quality of the green body determines the final material’s density and strength.
Green catalyst – It is a sustainable substance, such as enzymes, nano-catalysts, or benign metal compounds, designed to accelerate metallurgical reactions (like ore leaching, refining, or waste treatment) while improving selectivity, reducing toxic byproducts, and lowering energy consumption, hence improving eco-friendly production.
Green ceramic body – It is an unsintered, shaped component composed of ceramic powder, binders, and additives. It is porous, fragile, and formed through techniques like molding or casting, representing the crucial intermediate stage before firing / sintering, where it achieves final density, strength, and structural integrity.
Green cleaning – It refers to using cleaning methods and products with environmentally friendly ingredients and procedures which are designed to preserve human health and environmental quality. Green cleaning techniques and products avoid the use of products which contain toxic chemicals, some of which emit volatile organic compounds causing respiratory, dermatological and other conditions.
Green compact – it is an unsintered, shaped component produced in powder metallurgy by compressing metal powder in a die, normally at room temperature. Held together by mechanical interlocking and cold welding, it possesses sufficient green strength for handling but needs sintering to achieve final density and structural integrity.
Green compact formation – It is the initial, room-temperature process of compressing metal powders within a die under high pressure to create a cohesive, near-net-shape, and handleable part. The resulting ‘green’ part is unsintered, held together by mechanical interlocking and cold welding of particles.
Green computing – It refers to the sustainable, environmentally conscious design, manufacturing, use, and disposal of computing hardware specifically to minimize ecological impact, energy consumption, and electronic waste. This involves using energy-efficient components, sustainable raw materials, reducing hazardous waste, and enhancing recyclability.
Green density – Green density is the measure of mass per unit volume of a powder metallurgy part immediately after compaction and before sintering. It represents how tightly packed the particles are, typically expressed as a percentage of the material’s theoretical density, with higher values indicating better sintering response and fewer pores.
Green diesel – It is also known as renewable diesel or hydrogenated vegetable oil (HVO). It is a high-quality, second-generation biofuel produced through the catalytic hydro-processing of renewable feedstocks, such as vegetable oils, animal fats, and waste cooking oils. Unlike conventional biodiesel (fatty acid methyl ester, FAME), which is produced through trans-esterification, green diesel is chemically composed of straight-chain and branched paraffins, making it chemically identical or very similar to petro-diesel.
Green design – It is a design methodology in which environmental factors are considered of equal importance to performance factors.
Green electricity – It refers to electrical energy generated from renewable, non-fossil sources, such as wind, solar, hydropower, or green hydrogen, used to power smelting, refining, and processing operations with near-zero greenhouse gas emissions. In the context of the metals industry, green electricity is the key driver of ‘green metallurgy’, aiming to replace carbon-intensive fossil fuels (like coal and coke) to achieve a near-zero carbon footprint in metal production, particularly in steelmaking.
Green emission – It refers to the reduction or elimination of harmful greenhouse gases (mainly carbon di-oxide) and environmental pollutants during the extraction, refining, and production of metals. It is a core concept in sustainable metallurgy aimed at mitigating the high carbon footprint of conventional metal production (roughly 8 % of global emissions)
Green energy – It is an energy type which is generated from natural resources, such as sunlight, wind or water. It frequently comes from renewable energy sources although there are some differences between renewable and green energy. The key with these energy resources is that they do not harm the environment through factors such as releasing green-house gases into the atmosphere.
Greenfield facility – It is a new mew metal-making complex which is built ‘from scratch’, presumably on a green field.
Greenfield project – It is that project (e.g., steel plant) which lacks constraints imposed by prior work, i.e., the project is constructed on unused land where there is no need to remodel or demolish an existing structure. The analogy is to that of construction on greenfield land where there is no need to work within the constraints of existing buildings or infrastructure.
Greenfield site – It refers to a piece of undeveloped, untouched land, such as agricultural, forest, or vacant acreage, which is chosen for the construction of a new manufacturing plant, smelter, or refinery from scratch. Unlike brownfield sites, these locations have no previous industrial use needing all infrastructure, foundations, and utilities to be built from the beginning.
Green film – It refers to a fabricated, un-sintered layer of material, typically ceramic, metal powder, or composite, which has been formed (frequently by casting or coating) but not yet subjected to high-temperature sintering to achieve its final, dense, and rigid state.
Greenhouse effect – It is the process through which heat is trapped near earth’s surface by substances known as ‘greenhouse gases.’ These gases can be imagined as a cozy blanket enveloping earth, helping to maintain a warmer temperature than it would have otherwise. Greenhouse gases consist of carbon di-oxide, methane, ozone, nitrous oxide, chloro-fluoro-carbons, and water vapour. Water vapour, which reacts to temperature changes, is referred to as ‘feedback’, since it amplifies the effect of forces which initially caused the warming.
Greenhouse gas balance of biofuels – It is a ‘life cycle assessment’ (LCA) metric which measures the net emissions of carbon di-oxide (CO2), methane (ch4), and nitrous oxide (N2O) produced or sequestered throughout the entire life cycle of a biofuel, from feedstock production to final combustion, compared to a fossil fuel reference. It is expressed in carbon di-oxide-equivalents (CO2-equivalents) to determine the total climate change impact, with a lower or negative balance indicating a higher reduction in emissions compared to conventional fuels.
Greenhouse gases – Gases which trap heat in the atmosphere are called greenhouse gases. Several chemical compounds in the atmosphere act as greenhouse gases. These gases allow sunlight (shortwave radiation) to freely pass through the atmosphere and heat the land and oceans. Greenhouse gases consist of three or more atoms. This molecular structure makes it possible for these gases to trap heat in the atmosphere and then transfer it to the surface of the Earth which further warms the Earth. The main greenhouse gases are carbon di-oxide, methane, nitrous oxide, and industrial gases, including hydro-fluoro-carbons, per-fluoro-carbons, and sulphur hexa-fluoride. Carbon di-oxide, methane, nitrous oxide, and certain manufactured gases called halogenated gases (gases which contain chlorine, fluorine, or bromine). Greenhouse gases become well mixed throughout the global atmosphere because of their long lifetimes and because of transport by winds.
Greenhouse gases, regulated missions, and energy use in transportation (GREET) model – This model is used to analyze the life-cycle energy consumption, greenhouse gas (GHG) emissions, and air pollutants of vehicle technologies and fuels. It operates using two main modules, GREET1 (fuel-cycle) and GREET2 (vehicle-cycle), to evaluate over 100 fuel pathways and 80 vehicle technologies from well-to-wheels.
Greenhouse gas release – it refers to the emission of heat-trapping gases, mainly carbon di-oxide (CO2), methane (CH4), and nitrous oxide (N2O), into the atmosphere during the extraction, refining, processing, and manufacturing of metals. These emissions occur through both direct combustion of fossil fuels and chemical reactions within furnaces and reactors, with iron, steel, and aluminum production being among the highest contributors.
Green hydrogen – It is defined as hydrogen produced from water electrolysis with zero-carbon electric power, can have considerable potential in helping countries transition their economies to meet climate goals. It is produced by using renewable energy. It is the most suitable one for a fully sustainable energy transition. The most established technology option for producing green hydrogen is water electrolysis fuelled by renewable electricity. The electrolysis process splits water molecules into hydrogen and oxygen. Electrolysis needs energy. This energy comes from lower-cost renewable sources and this makes this form of hydrogen ‘green’.
Green index – It is a quantitative metric or composite score used to evaluate and benchmark the environmental performance, sustainability, and ecological impact of metallurgical processes, industrial facilities, or specific products (such as steel or aluminum). It acts as a decision-making tool for industrial stakeholders to minimize waste, lower carbon emissions, and increase resource efficiency.
Green-Lagrange strain tensor – It is a measure of deformation for moderately large displacements, calculated based on two reference configurations namely the initial and current configurations. It incorporates both linear and non-linear components of strain, making it suitable for geometrically nonlinear problems.
Green liquor – It is the liquor resulting from dissolving molten smelt from the kraft recovery furnace in water.
Green machining – It refers to the machining of powder metallurgy (P/M) components while they are in their ‘green’ (unsintered) state, compacted powder held together by a binder. This process allows for shaping complex geometries, such as gear teeth, at lower cutting forces and costs before the component is fully densified and hardened through sintering, typically resulting in higher dimensional accuracy and reduced tool wear.
Green pellets or balls – Green pellets with a size range of 8 millimeters to 16 millimeters are prepared in a balling drum or in a disc pelletizer. Disc pelletizer is preferred for the production of the quality green pellets since in the disc pelletizer it is easy to control the operation with minimum of foot space. The pre wetted mix is fed into the disc at a controlled rate. In the disc, the material is coagulated and because of the continuous rotary motion gets formed into nodules/ pellets. Ore fines are lifted upwards until the friction is overcome by gravity and the material rolls down to the bottom of the disc. This rolling action first forms small granules called seeds. Growth occurs in the subsequent revolutions of the disc by the addition of more fresh feeds and by collision between small pellets. Surface tension of water, capillary action of water, and the gravitational force in the balling disc are the forces which act on the ore particles. Hence, they get coalesce together and form nuclei which grow in size and into ball shape.
Green permeability – It is the ability of a compacted moist (green) sand mould to allow gases and steam to escape through its pores during metal pouring and solidification. High permeability prevents gas-related defects (e.g., blowholes) by ensuring rapid venting, influenced by sand grain size, shape, and moisture.
Green process – It is a comprehensive manufacturing approach focused on minimizing environmental impact, reducing resource depletion, and optimizing energy efficiency throughout the entire life cycle of metal production, from raw material extraction to final product management. It moves away from traditional, pollution-intensive metallurgical methods, replacing them with cleaner, more sustainable technologies, such as utilizing green hydrogen for iron reduction, increasing the use of recycled scrap, and applying renewable energy sources.
Green product design – It is a proactive approach integrating environmental considerations throughout a metal product’s lifecycle, from extraction to end-of-life, to minimize ecological impact. It focuses on reducing energy consumption, eliminating hazardous by-products, ensuring high resource efficiency, and designing for recyclability and durability.
Green rating system – It is a voluntary, third-party assessment framework used to classify and certify metal production processes and products based on their environmental performance, sustainability, and resource efficiency. In the context of the steel industry, specifically, such systems (e.g., ‘star rating for green steel’) are designed to help producers and consumers identify steel produced with significantly lower carbon emissions compared to conventional methods.
Green rot – It is a form of high-temperature attack on stainless steels, nickel-chromium alloys, and nickel-chromium-iron alloys which are subjected to simultaneous oxidation and carburization. Basically, attack occurs first by precipitation of chromium as chromium carbide, then by oxidation of the carbide particles.
Green sand -It is a naturally bonded sand, or a compounded moulding sand mixture, which has been ‘tempered’ with water and which is used while it is still moist.
Green sand core – It is a core made of green sand and used as-rammed. It is also a sand core which is used in the unbaked condition.
Green sand mould – It is a casting mould which is composed of moist prepared moulding sand.
Green sand moulding – The mould is composed of a prepared mixture of sand, clay, sea coal, and moisture for use while still in the damp condition. The mould is not cured or dried and hence is known as a green (uncured) sand mould.
Green’s function – It is a mathematical tool used to solve linear inhomogeneous differential equations, specifically to calculate the system’s response (such as stress, temperature, or strain) to a localized, point-source disturbance. It is defined as the solution to a differential equation where the forcing term is a Dirac delta function, representing a unit disturbance at a single point affecting a response at point ‘r’.
Green’s function model – It is a mathematical approach used to solve complex, linear partial differential equations (PDEs) by identifying the system’s response to an impulse or point source. It is highly regarded for its ability to provide exact analytical solutions to problems involving heat diffusion, stress distribution, and diffusion-based damage (like fracture) by converting differential equations into manageable integral equations.
Green shale – It is a fine-grained, fissile (easily split) sedimentary rock, characterized by its green colouration caused by the presence of reduced (ferrous) iron and micaceous minerals like chlorite, illite, or biotite. It is recognized as a rich source of iron compounds and, when subjected to high heat, a material that can act as a raw ingredient in ceramics and cement production.
Green silicon carbide (SiC) – It is a high-purity (above 99 % SiC), synthetic abrasive material produced by melting petroleum coke and silica sand in a resistance furnace. Known for its green, translucent crystals, high hardness (only behind diamond), and friability, it is necessary in applications for precision grinding, cutting, and as an additive to improve wear / heat resistance in refractories.
Green steel – It is steel produced with significantly lower carbon emissions than traditional methods, often aiming for near-zero greenhouse gas emissions. It is produced by substituting coal with green hydrogen in iron reduction or using electric arc furnaces (EAF) powered by renewable energy, resulting in significantly reduced or zero emissions.
Green steelmaking – It consists of the use of those processes which result into reduction in emissions of carbon di-oxide. Development work for the green steelmaking processes is being done in several countries. For the development of the technologies for the green steelmaking, five key directions are being explored. These directions are (i) technologies involving coal usage, (ii) technologies involving use of hydrogen, (iii) technologies involving electrons, (iv) technologies involving use of biomass, and (v) technologies involving carbon capture, use, and / or storage (CCUS). Theare several pathways which are being explored for the break-through technologies for cutting of the carbon di-oxide emissions from the ore-based steel production routes.
Green strength – It is the strength of a tempered foundry sand mixture at room temperature. It is also the ability of a green compact to maintain its size and shape during handling and storage prior to sintering. It is also the tensile or compressive strength of a green compact. In case of refractories, it is the mechanical strength of a shaped, but unfired refractory.
Greenstone belt – It is an area underlain by metamorphosed volcanic and sedimentary rocks, normally in a continental shield.
Green supply chain management – It integrates environmental thinking into every stage of the metal lifecycle, from sourcing, production, and distribution to disposal, to minimize ecological impact. It focuses on reducing emissions, energy-efficient manufacturing, using recycled scrap, and implementing reverse logistics to enable a circular economy.
Green supply chain management practices – These practices refer to the strategies and actions taken to manage the supply chain in a way which minimizes negative environmental impacts and promotes sustainability, including reducing energy and water usage and utilizing renewable or recyclable materials. These practices involve evaluating the environmental impacts of suppliers and customers to ensure overall sustainable operations.
Green sustainable development – It is the practice of reducing the environmental footprint of metal production by lowering carbon di-oxide (CO2) emissions, energy consumption, and waste generation. It emphasizes a circular economy approach, optimizing material efficiency through recycling, using cleaner energy sources like hydrogen, and developing impurity-tolerant, durable alloy designs to replace traditional carbon-intensive processes.
Green synthesis – It is an eco-friendly approach to producing metal and metal oxide nano-particles by using natural, non-toxic resources, such as plant extracts, bacteria, fungi, or agricultural waste, as reducing and capping agents. It replaces hazardous chemicals and high-energy processes with sustainable, low-energy methods to produce biocompatible materials.
Greenwashing – It is a form of advertising or marketing spin which deceptively uses green public relations and green marketing to persuade the public that the products, goals, of policies of the organization are environmentally friendly. Organizations which intentionally adopt greenwashing communication strategies frequently do so to distance themselves from their environmental lapses or those of their suppliers. Organizations engage in greenwashing for two primary reasons namely to appear legitimate and to project an image of environmental responsibility to the public.
Green water footprint – It refers to the total volume of rainwater or soil moisture, not surface or groundwater, evaporated or incorporated into products during raw material extraction, such as mining and forestry. It mainly accounts for water used by vegetation on-site and in the production chain, rather than process water.
Greenwich mean time – It is the mean solar time at the Royal Observatory in Greenwich, London, defined along the Prime Meridian (0-degree longitude). Used as a foundational time standard for global synchronization, it acts as the zero-offset reference for all worldwide time zones. It is based on the earth’s rotation from noon-to-noon.’
Greenwood – It refers to a statistical model which extends the elastic Hertzian solution for a single asperity to an ensemble of asperities on rough surfaces, treating their deformation as independent and modeled by a statistical distribution of asperity heights. This model facilitates the calculation of total contact load and real contact area in tribological applications.
Greenwood-Johnson transformation – It is also called Greenwood-Johnson mechanism. It is a metallurgical theory explaining transformation-induced plasticity (TRIP). It describes how a material, while undergoing a phase transformation (such as austenite to martensite or bainite), can show plastic deformation even under applied stresses which are much lower than the material’s yield stress.
Green zone – It refers to the target range or middle half of the tolerance band on a control chart (Cpk). This indicates that the process is operating within normal parameters. It is part of a 3-zone system (green / yellow / red) where the green zone means the product is within specification and safely managed.
Greige, gray goods – It is a fabric before finishing, as well as any yarn or fibre before bleaching or dyeing, hence, it is a fabric with no finish or size.
Grey hydrogen – The most common process for grey hydrogen is to use either natural gas or coal as feedstock which reacts with steam at high temperatures and pressures to produce synthesis gas, which consists primarily of hydrogen and carbon mono-oxide. The process is known as steam methane reforming (SMR). The synthesis gas is then reacted with additional water to produce pure hydrogen and carbon di-oxide. These are well-established processes, but they generate considerable carbon di-oxide emissions, which is why the resulting element is termed ‘grey hydrogen’. The use of grey hydrogen emits substantial carbon di-oxide emissions, which makes these hydrogen technologies unsuitable for a route towards net-zero emissions.
Greywacke – It is also spelled as graywacke. It is a variety of hard, dark-coloured, and immature sandstone normally characterized by its poorly sorted, angular grains of quartz, feldspar, and small rock fragments (lithic fragments) set in a compact, fine-grained clay matrix.
Grid – It refers to a structured, open framework of interconnected metal wires, bars, or perforated sheets, designed for conductivity, support, or filtration. It is also an interconnected network, typically distributing electricity (power grid), organizing structural elements (structural grid), or discretizing space for computational modeling (computational fluid dynamics, CFD grid). It normally refers to a systematic arrangement of intersecting lines, cables, or components used to manage flow, structure, or spatial coordinates.
Grid based method – It involves partitioning numbers as per their place value and then multiplying them together. It makes multiplying numbers easier by breaking them into their separate place values and multiplying them step-by-step.
Grid bias – It refers to a voltage applied to a wire mesh (grid) placed between a plasma source (such as a filament) and a substrate. This grid voltage is used to control the plasma environment and the energy of ions that bombard the surface of a metal or substrate, acting as a crucial process parameter for modifying film microstructure, density, and adhesion.
Grid code requirements – These are a set of technical rules and regulations established by system operators (transmission system operator, TSO / distribution system operator, DSO) which define the necessary performance standards for facilities connecting to the electric grid, ensuring safe, secure, and reliable operation. While mainly electrical in nature, these codes implicitly demand which equipment, including structural, mechanical, and metallurgical components, withstand operational stresses, voltage dips, and fault conditions.
Grid-connected converters – These are power electronic devices which serve as the important interface between renewable energy sources (such as solar photo-voltaic, wind), energy storage systems (batteries), or DC (direct current) micro-grids and the utility AC (alternating current) grid. They are responsible for converting direct current into alternating current and vice versa, controlling power flow, regulating voltage and frequency, and ensuring high-quality, synchronized power injection into the grid. Grid-connected converters are specialized power converters that not only perform energy conversion but also manage the active and reactive power exchange with the grid. They are increasingly necessary for the energy transition toward cleaner sources.
Grid-connected inverter system – It is a power electronics converter which transforms DC (direct current) power (from sources like solar photo-voltaic, PV or batteries) into AC (alternating current) power synchronized with the utility grid’s voltage and frequency. It enables bi-directional power flow, allowing users to supply excess energy to the grid or import it when needed.
Grid-connected photo-voltaic system – It is a solar power setup which works in parallel with the utility grid, converting sunlight into AC (alternating current) electricity using inverters to power homes and feed excess energy back to the utility. These systems do not need batteries, relying on the grid for power at night, typically featuring PV (photo-voltaic) arrays, inverters, and net meters.
Grid-connected plant – It is a power generation facility, such as a solar PV (photo-voltaic) system, which operates in parallel with the electric utility grid. It converts energy (e.g., direct current to alternating current, DC to AC) and supplies electricity directly to the grid through an inverter and bi-directional meter, with no reliance on on-site storage.
Grid convergence – Within computational modeling of solidification, casting, or microstructure evolution, it is the process of refining the computational grid or mesh in a numerical simulation to ensure that the results become independent of the grid size. It verifies that the simulation results (such as dendrite arm spacing, temperature profiles, or segregation patterns) stabilize, minimizing discretization error and increasing accuracy.
Grid, electrical – An electrical grid is an interconnected network for electricity delivery from producers to consumers. Electrical grids consist of power stations, electrical substations to step voltage up or down, electric power transmission to carry power over long distances, and finally electric power distribution to customers.
Grid energy storage – It refers to large-scale methods used by power grids to store electricity for later use, balancing supply and demand, and supporting renewable energy integration. It is a method to improve the reliability and functionality of power grids by providing a storage buffer which holds excess energy when supply exceeds demand and discharges it during peak demand periods. Technologies include mechanical (pumped hydro, compressed air), electrochemical (lithium-ion, flow batteries), thermal, and chemical (hydrogen).
Grid extension – It is the expansion of existing high, medium, or low-voltage transmission and distribution networks to connect new areas, communities, or customers to the national power grid. It involves constructing new infrastructure, such as lines and transformers, to provide centralized, reliable electricity to previously unserved, rural, or remote locations.
Grid-forming converters – These are power electronic devices which act as voltage sources to establish, regulate, and support grid frequency and voltage, mimicking synchronous generators in low-inertia, renewable-dominated systems. Unlike grid-following converters, they operate autonomously without needing a ‘phase-locked loop’ (PLL) for synchronization, allowing for black-start capability.
Grid generation – It is also known as mesh generation. It is the engineering process of dividing a physical domain into smaller, discrete sub-domains (cells or elements) to solve governing equations in ‘computational fluid dynamics’ (CFD) and structural analysis. It translates complex geometric models into a numerical grid, structured, unstructured, or hybrid, which allows solvers to calculate physics like fluid flow or stress distribution.
Grid impedance – It is the total opposition to current flow in an electrical power grid, defined as the ratio of voltage to current (Zgrid = P/V) at a specific frequency at the ‘point of common coupling’ (PCC). It represents the sum of resistive and inductive reactance from lines, transformers, and generators, crucial for calculating grid strength, power quality, and inverter stability.
Grid lines – These are a system of referenced horizontal and vertical lines, frequently labeled alpha-numerically, used to provide a precise framework for locating, aligning, and designing structural components or layouts. They ensure accuracy in blueprints, construction sites, and computer-aided design (CAD), reducing misalignment and costly rework.
Grid modeling – It is the process of creating mathematical or computer-based representations of power systems to simulate, analyze, and optimize their behaviour. It balances accuracy with computational speed to guide planning, enhance reliability, and integrate renewable energy. These models are necessary for studying steady-state power flow, dynamics, stability, and protection.
Grid nodal point – It is a discrete, specific location within a computational mesh or physical structure where physical quantities, such as displacement, stress, temperature, or electrical potential, are calculated, stored, or defined. Nodal points act as the ‘knots’ or junctions which connect individual elements in finite element analysis (FEA), numerical simulations, and grid-shell structures.
Grid node – It is a specific, actionable point of intersection, connection, or measurement within a network. It represents a junction where pathways meet (in power grids) or a coordinate point where values like pressure or velocity are calculated (in simulation grids). Nodes function as important monitoring, management, or supply points within these systems.
Grid number – It is also called grid reference. It is an alpha-numeric identifier, typically letters on one axis and numbers on the other, used to locate structural components, columns, or points on a technical drawing or site plan. It serves as a coordinate system to ensure accurate positioning, layout, and identification of elements.
Grid potential – It is also called ‘ground potential rise’ (GPR). It is the maximum voltage a station grounding grid attains relative to remote earth during a power system fault. It represents the potential rise of grounded equipment, calculated as the fault current multiplied by the grid impedance (GPR = Ig x Rg). This is important for safety to prevent injury from step and touch potentials.
Grid quality – It refers to the geometric and numerical suitability of a mesh (computational grid) to accurately and stably solve partial differential equations in ‘computational fluid dynamics’ (CFD) or ‘finite element analysis’ (FEA). Key metrics include low skewness, high orthogonality, appropriate aspect ratios, and smooth cell volume changes.
Grid search – It is a traditional, exhaustive hyper-parameter optimization method in machine learning which systematically works through a pre-defined set of parameter combinations for a given model. It works by creating a ‘grid’ of specified values for each hyper-parameter and evaluating the model’s performance on every possible combination, normally through cross-validation, to identify the optimal configuration.
Grid-side converter – It is a power electronic device, normally an inverter, which connects a power source (like a wind turbine generator) to the AC (alternating current) grid. It functions as the interface, stabilizing the DC (direct current) link voltage, managing active / reactive power flow, ensuring synchronization with the grid frequency and voltage, and maintaining power quality.
Grid support – It refers to technical functionalities, such as voltage regulation, frequency control, and fault ride-through, provided by generators, storage, or inverters to ensure the stability, reliability, and security of an electrical network. It involves active management to balance supply and demand, preventing outages during disturbances.
Grid system – It is a structured framework of intersecting horizontal and vertical lines or interconnected infrastructure used to organize spatial data, design layouts, or distribute resources. It ensures precision in drafting, structural layout, or power transmission. Common types include structural layout grids, computer design grids, and electrical utility grids.
Grid technology – It refers to modernizing electrical networks (smart grids) or distributed computing systems by integrating advanced, bi-directional communication, automation, and real-time data to improve efficiency, reliability, and sustainability. These systems enable intelligent energy management, renewable integration, and decentralized resource sharing.
Grid-tie inverter – It is a power inverter which allows synchronization with the electrical grid for export of energy surplus to the facility’s needs.
Grid topology – it refers to the physical or logical arrangement, connectivity, and organizational structure of nodes and links within a network. It defines how electrical components (generators, loads, lines) or computational resources (servers, processors) are interconnected, directly impacting system performance, reliability, and stability. Grid topologies are mainly classified by how nodes are arranged to transport energy, data, or compute loads.
Grid turbulence – It is a type of fluid flow, characterized as normally homogeneous and isotropic, generated by forcing flow through a mesh or grid. It is used to produce well-defined, decaying turbulence in wind or water tunnels to model turbulence intensity and integral scales, frequently following a power-law decay downstream.
Grid voltage – It is the root mean square (RMS) value of the alternating current (AC) potential, normally 230 volts (single-phase) or 400 volts / 11 kilo-volts plus (three-phase), supplied by the electrical network to consumers. It acts as the electrical pressure which drives power through a transmission / distribution system, typically stepped up for efficiency and down for safe consumption.
Grid voltage fluctuation – It is a term referring to irregular, rapid, or systematic variations in the voltage envelope amplitude, typically within +/- 5 % of the nominal value. It represents a substantial power quality problem caused by abrupt load changes, renewable energy intermittency, or switching operations, resulting in ‘flicker’.
Griffith crack – It is a microscopic preexisting flaw in a material which serves as a critical site for the initiation of a macrocrack under stress, based on the premise that cracks cannot nucleate without such preexisting defects.
Griffith criterion – It is a fundamental concept which determines the conditions under which a pre-existing flaw or microcrack in a material propagates, leading to catastrophic failure. It defines that a crack grows if the decrease in elastic strain energy, caused by the extending crack, is higher than or equal to the energy needed to create new crack surfaces (surface energy).
Griffith theory – It states that brittle materials fail at stress levels below their theoretical strength because of the presence of microscopic, pre-existing cracks, which act as stress concentrators. A crack propagates when the stored elastic strain energy released equals or exceeds the surface energy needed to create new crack surfaces.
Griffith theory of brittle fracture – It states that a crack propagates in a brittle material when the released elastic strain energy equals or exceeds the surface energy required to create new crack surfaces. It explains that low-stress failures in brittle materials result from high local stress concentration around inherent microscopic flaws.
Grillage – It is also called roasting. It refers to a pyro-metallurgical process involving the heating of ores or intermediate metallurgical products at high temperatures in an oxidizing atmosphere. It is an important process, designed to alter the physical and chemical properties of solid materials, typically by removing unwanted elements like sulphur, arsenic, or antimony. Grillage is also a foundation type consisting of two or more layers of intersecting beams (steel or timber) arranged in a grid pattern to distribute heavy structural loads onto weak or low-bearing capacity soil. It acts as a bridge between columns and the ground, preventing excessive settlement by increasing the load-bearing area.
Grindability – It is the relative ease of grinding. It is analogous to machinability. It is a value which represents the efficiency of the grinding process. Grindability = (G-ratio) / (specific energy), where G-ratio = (volume of material removed) / (volume of the grinding wheel used) and specific energy = (grinding power) / (material removal rate).
Grindability index – It is a measure of the grindability of a material under specified grinding conditions. It is expressed in terms of volume of material removed per unit volume of wheel wear.
Grinding – It is removing material from a work-piece with a grinding wheel or abrasive belt. In case of ores and minerals, grinding is done after initial crushing. It reduces the ore particles to the consistency of fine powder (325 mesh, 0.44 micrometers). The choice of grinding circuit is based on the density and hardness of the ore to be ground. Although use of the rod mill or ball mill grinding is quite common, a few facilities use autogenous or semi autogenous grinding systems. Autogenous grinding uses coarse pieces of the ore itself as the grinding media in the grinding mill. Semi autogenous operations use metallic balls and / or rods to supplement the grinding action of the ore pieces. Autogenous grinding is best suited to weakly cemented ores containing some hard material. The benefit of autogenous grinding is that it is less capital and labour intensive. Semi autogenous grinding (SAG) eliminates the need for a secondary crushing circuit. Rod and ball wear, the principal maintenance cost of traditional grinders, is also eliminated with this method.
Grinding burn – It consists of getting the work hot enough to cause discolouration or to change the micro-structure by tempering or hardening.
Grinding circuit – It focuses on designing and optimizing mineral comminution systems, typically using ball mills, SAG (semi-autogenous grinding) mills, and crushers to reduce ore size for liberation. Engineering design, often utilizing closed circuits with cyclones, optimizes energy consumption (kilo-watt hours per ton) and maximizes throughput. Key focus areas include circuit simulation, liner design, and controlling particle size distribution (PSD).
Grinding cracks – These are the cracks which are formed in the surfaces of relatively hard materials because of excessive grinding heat or the high sensitivity of the material. Grinding cracks develop at locations where there is a localized heating of the base metal and they are normally shallow and at right angle to the grinding direction. Such cracks can be caused by the use of glazed wheels, inadequate coolant, excessive feed, or grinding depth.
Grinding equipment – It refers to the machinery, such as mills (ball, rod, roller, or vertical) and grinding machines, used in the comminution process to break down ore particles or refine metal parts through abrasive action.
Grinding fluid – It is an oil-based or water-based fluid introduced into grinding operations to (i) reduce and transfer heat during grinding, (ii) lubricate during chip formation, (iii) wash loose chips or swarf from the grinding belt or wheel, and (iv) chemically aid the grinding action or machine maintenance.
Grinding force – It is the mechanical action, specifically the tangential and normal forces, applied by a rotating abrasive wheel to a work-piece, resulting in friction, shearing, and material removal. It dictates material removal rates, surface integrity, and energy consumption, largely impacting grinding temperature and wheel wear.
Grinding machine – It is a power-driven metal-working tool which uses a rotating abrasive wheel to cut, shape, or finish metal surfaces to high precision. It removes small quantities of material (fine finishing) from hard metallic bodies to achieve high dimensional accuracy and smooth surface textures.
Grinding, machining – It is defined as an abrasive machining process which utilizes high-speed abrasive wheels, pads, and belts to shape and finish materials. It is a key component of modern manufacturing and can overlap with related processes such as polishing, lapping, and honing.
Grinding media – These are sacrificial, dense, and durable bodies, such as steel balls, rods, or ceramic beads, used in industrial mills (e.g., ball or semi autogenous grinding mills) to reduce the particle size of ores and materials through impact and abrasion. These act as the main means of transferring kinetic energy to crush and grind feedstock.
Grinding mills – These are size reductions machines which frequently often follow crushers in the processes where finer products are desired after crushing. Different grinding machines are normally named as mills, for example rod mills, ball mills, and attrition mills. The grinding mills are categorized in three groups, namely (i) tumbling mills, (ii) roller mills, and (iii) very fine grinding mills which include (a) high speed pulverizing or hammer mill, (b) vibrating mill, (c) pin mill, (d) turbo mill, (e) fluid energy mill, (f) stirred media mill.
Grinding oil – It is an oil-type grinding fluid, it can contain additives, but not water.
Grinding operation – It is a precision machining process which uses a rotating abrasive wheel to remove material from a metal work-piece. It acts as a finishing method to achieve high dimensional accuracy, smooth surfaces, and tight tolerances. The abrasive particles on the wheel behave like tiny cutting tools, removing metal to create flat, cylindrical, or shaped surfaces.
Grinding relief – It is a groove or recess located at the boundary of a surface to permit the corner of the wheel to overhang during grinding.
Grinding sensitivity – It is the susceptibility of a material to surface damage such as grinding cracks. It can be affected by such factors as hardness, micro-structure, hydrogen content, and residual stress.
Grinding stress – It is the residual stress, generated by grinding, in the surface layer of the work. It can be tensile or compressive, or both.
Grinding wheel – It is a consumable rotating cutting tool composed of abrasive grains (such as aluminum oxide or silicon carbide) held together by a bonding agent. It acts as a multi-point tool used for grinding, cutting, and surfacing metal, removing material through high-speed shear.
Gringarten type curve – It is a widely used, modern well-test interpretation chart (typically plotted on log-log paper) to determine reservoir properties, specifically permeability (k) and skin factor (S), from pressure drawdown or buildup tests. It is a diagnostic tool which accounts for wellbore storage and skin effects by displaying the relationship between dimensionless pressure and dimensionless time.
Grip – It means to seize or hold firmly.
Grip control – It refers to the specialized mechanisms and techniques used to securely hold a metal sample, such as a sheet, wire, or rod, during testing (very frequently tension, fatigue, or hardness testing) to ensure that force is transferred properly without slippage, premature fracture, or uneven stress distribution.
Grip force – It is also called clamping force. It is the perpendicular, normal force applied by gripping jaws to a sample to securely hold it during tensile or compression tests, creating sufficient friction to prevent slippage. It ensures the sample is held securely while the machine applies tensile loads.
Grip length – It is the length of the unthreaded portion of the fastener (i.e. shank) measured axially from the underside of the bearing surface to the starting thread. It is also called clamped length and is the total thickness of all materials, including plates, shims, and gaskets, secured together by a bolt and nut assembly. It represents the length of the fastener subject to compressive force, measured from the underside of the bolt head to the beginning of the nut.
Gripper – It is something which grips things or makes it easier to grip things. It can refer to gripping tools for building hand strength.
Gripper dies -These are the lateral or clamping dies which are used in a forging machine or mechanical upsetter.
Gripper-die stroke – It refers to the linear distance the movable gripping die travels to clamp a work-piece (such as a metal rod or wire) against a stationary die, or to release it.
Gripping – It refers to the mechanism or process of securely holding a test sample (such as a metal sheet, rod, or wire) within a tensile testing machine to apply force without allowing slippage or causing premature failure at the grips.
Gripping lifters – They use either friction or indentation-causing pressure to hold a load. Tong grabs or clamps utilize a scissor-type action to grip a load. Coil grabs grasp the outer diameter of a coil via tongs or gripping mechanisms to lift or turn it.
Grit – It is the crushed ferrous or synthetic abrasive material in different mesh sizes which is used in abrasive blasting equipment to clean castings.
Grit blasting – It is the abrasive blasting with small irregular pieces of steel, malleable cast iron, or hard non-metallic materials.
Grit size – It is the nominal size of abrasive particles in a grinding wheel, corresponding to the number of openings per linear unit length in a screen through which the particles can pass. It is also the particle size of an abrasive powder, such as carborundum, corundum, silicon carbide, or diamond used in cutting and machining operation.
Grizzly – It is also called mantle. It is a grating, normally constructed of steel rails, placed over the top of a chute or ore pass for the purpose of stopping large pieces of rock or ore which can hang up in the pass.
Grizzly-bars – These are the bars at the loading point. These bars absorb the impact energy from the lumps and redirect the (big) lumps to the belt, fines fall on the belt before the lumps.
Grog – It is also known as firesand and chamotte. It is a raw material normally made from crushed and ground potsherds, reintroduced into crude clay to temper it before making ceramic ware. It has a high percentage of silica and alumina. It is normally available as a powder or chippings.
Grog fireclay mortar – It is the raw fireclay mixed with calcined fireclay, or with broken fireclay brick, or both, all ground to suitable fineness.
Gronwall-Bellman Inequality – It is a fundamental mathematical tool used to bound an unknown function that satisfies a differential or integral inequality by the solution of the corresponding differential or integral equation. It is important for establishing stability, boundedness, uniqueness, and continuous dependence on initial parameters in modeling physical processes.
Groove – It is a long and narrow indentation built into a material, normally for the purpose of allowing another material or part to move within the groove and be guided by it. Examples include (i) a canal cut in a hard material, normally metal. This canal can be round, oval or an arc in order to receive another component such as a boss, a tongue or a gasket. It can also be on the circumference of a dowel, a bolt, an axle or on the outside or inside of a tube or pipe etc. This canal can receive a circlip, an O-ring, or a gasket, (ii) a depression on the entire circumference of a cast or machined wheel, a pulley or sheave. This depression can receive a cable, a rope or a belt, and (iii) a longitudinal channel formed in a hot rolled rail profile such as a grooved rail. This groove is for the flange on a train wheel. In thermal spraying, it is a method of surface roughening in which grooves are made and the original surface roughened and spread.
Groove angle – It is the total included angle of the groove between the work-pieces.
Groove depth – It refers to the perpendicular distance from the surface of the base metal to the bottom (root) of a prepared groove. It represents the extent to which the metal is removed or prepared for welding, directly impacting the amount of filler metal needed and the strength of the final joint.
Grooved lagging – It is the lagging with round or angular grooves to minimize material buildup on the pulley.
Grooved rolls – These rolls are used in section rolling mills. They are for rolling of work-pieces and section material. Bodies of these rolls have so called grooves (passes). They track profile of section metal. These grooves have a definition, they are called passes. Passes of two rolls with distance between them are called a groove.
Groove face – It is that surface of a joint member which is included in the groove.
Groove radius – It is the radius which is used to form the shape of a J-groove or U-groove weld.
Groove weld – It is a weld which is made in a groove between the work-pieces.
Groove weld size – It is the joint penetration of a groove weld.
Groove weld throat – It is a non-standard term for groove weld size.
Grooving corrosion – It is a localized, severe form of accelerated metal loss occurring as a narrow, V-shaped groove or ditch, primarily along electrical resistance welded (ERW) or flash-welded seams. It is caused by electro-chemical differences between the weld zone and base metal, high water cut, and flow-induced abrasion, leading to premature pipeline failure.
Gross calorific value (GCV) – It is also known as higher heating value (HHV). It is the total heat released by the complete combustion of a unit quantity of fuel (mass or volume), including the latent heat of vapourization of water vapour produced during combustion. It assumes combustion products are cooled to room temperature (25 deg C), allowing water vapour to condense.
Gross cracking – It is sometimes called gross cracks or macroscopic cracking. It refers to large-scale, frequently deep, fissures or fractures in a material which are typically visible to the naked eye, as opposed to micro-cracks. These cracks are normally severe enough to compromise the structural integrity, functionality, or serviceability of a component, frequently leading to rapid, catastrophic failure.
Gross damage – It refers to severe, large-scale deterioration of a metal surface or component, typically resulting from mechanisms like heavy scuffing, erosion, or wear, leading to rapid failure. It is characterized by substantial material removal, deep cracks, or surface destruction, frequently exceeding 1 millimeter in size (e.g., in coating breaches).
Gross domestic product (GDP) – It is the standard measure of the value added created through the production of goods and services in a country during a certain period. It is frequently used to measure the economic performance of a country or region.
Grossmann – It refers to a method for measuring the hardenability of steel, which involves determining the critical diameter (Dcrit) of cylindrical steel bars based on the percentage of martensite present after quenching, alongside the introduction of the ideal critical diameter (Di) to assess hardenability independently of quenching conditions.
Grossmann chart – It is a chart describing the ability of a quenching medium to extract heat from a hot steel work-piece in comparison to still water.
Grossmann factor – It is also known as Grossmann H-value (H) / factor. It is a numerical value which represents the severity or intensity of a quenching medium. It quantifies how efficiently a liquid (oil, water, brine, etc.) extracts heat from the surface of a steel part during heat treatment, influencing the resulting hardenability. It is defined as the ratio of the heat transfer coefficient (h) at the surface of the part, divided by twice the thermal conductivity (k) of the steel, H = h / 2k, where ‘h’ is the heat transfer coefficient at the surface, and ‘k’ is the thermal conductivity of the steel.
Grossmann hardenability – It consists of Grossmann’s method of measuring hardenability, which uses a number of cylindrical steel bars of different diameters hardened in a given quenching medium. After sectioning each bar at mid-length and metallographic examination, the bar with 50 % martensite at its centre is selected and the diameter of this bar is designated as the critical diameter Dcrit. Other bars with diameters smaller than Dcrit possess more martensite and correspondingly higher hardness values and bars with diameters larger than Dcrit contain 50 % martensite only up to a certain depth. The Dcrit value is valid only for the quenching medium and conditions used to determine this value. For determining the hardenability of a steel independent of the quenching medium, Grossmann introduced the term ideal critical diameter, Di.
Grossmann number (H) – It is a ratio describing the ability of a quenching medium to extract heat from a hot steel-work-piece in comparison to still water defined by the equation H = h/2k, where ‘h’ is the heat transfer coefficient and ‘k’ is the conductivity of the metal.
Grossmann quench severity factor (H) – It is a numerical value used to quantify the ability of a quenching medium to extract heat from steel, calculated as H = h/2k. It relates the effective heat transfer coefficient (h) at the steel surface to the thermal conductivity (k) of the steel.
Gross porosity – In weld metal or in a casting, it consists of pores, gas holes, or globular voids which are larger and in much higher numbers than those achieved in good practice.
Gross primary production – It is the quantity of chemical energy, typically expressed as carbon biomass, which the primary producers create in a given length of time. It is the total quantity of carbon di-oxide ‘fixed’ by land plants per unit time through the photo-synthetic reduction of carbon di-oxide into organic compounds.
Gross primary productivity – It is the rate at which solar energy is captured by plants to create organic matter.
Gross production – It refers to the total volume or value of metal, alloys, or components produced by a facility, plant, or process within a specific period, before deducting any losses, waste, or returns. It represents the total output of the production line (e.g., total tons of crude steel or copper), not the net quantity of finished, sellable product.
Gross profit – It also known as sales profit, gross margin, or gross income. It is the organizational profit after deducting the costs associated with producing and selling its products or services. It is the quantity of money which an organization makes from selling its products or services, minus the costs associated with producing and selling those goods or services.
Gross return – It is the total profit or income generated by an investment, asset, or organization before deducting any fees, taxes, or expenses. It represents the raw performance and growth of an investment, normally used for comparing investment options, or internal analysis, distinct from net return which is after expenses.
Gross sample – It is one or more increments of material taken from a larger quantity (lot) of material for assay or record purposes. It is also termed as a bulk sample or a lot sample.
Gross tonnage – It is a dimensionless, volumetric measure representing a ship’s total internal enclosed volume, rather than its weight, as per the 1969 International Convention on Tonnage Measurement of ships. It includes all enclosed spaces, such as machinery, cargo holds, and crew accommodations, used for calculating regulatory compliance, fees, and safety rules. Gross tonnage is calculated based on the total moulded volume of all enclosed spaces (V in cubic meters) using a formula established by the International Maritime Organization (IMO).
Grotthuss mechanism – It is the process of proton diffusion in which protons hop between dissociated water molecules, facilitated by the rotation or reorientation of these molecules, and is prevalent in proton-conducting electrolytes.
Ground – It is a reference point for electrical potential, frequently connected to the earth.
Ground acceleration – It Is frequently measured as ‘peak ground acceleration’ (PGA). It is the maximum acceleration experienced by the ground surface during an earthquake, typically recorded in meters per square second or as a fraction of gravitational acceleration (g). It represents the amplitude of seismic waves and is a critical design parameter for quantifying inertial forces that act on structures.
Ground and neutral – It is protective and circuit return conductors in a wiring system.
Ground application – It is frequently referred to as ground engineering or geotechnical application. It is the application of soil mechanics, rock mechanics, and geology to solve engineering problems related to the ground, subsurface materials, and earthworks. It involves the analysis, design, and construction of structures which interact with the earth, such as foundations, retaining walls, tunnels, and earth embankments.
Ground attenuation – It refers to the reduction in signal strength, mainly sound or vibration, as it travels over or through the ground, caused by absorption, scattering, and interference from the surface. It is a critical factor in acoustic modeling (noise control) and structural engineering (vibration propagation), frequently measured in decibels (dB) and heavily influenced by ground porosity, density, and texture.
Ground-bed – It is a buried item, such as junk steel or graphite rods, which serves as the anode for the cathodic protection of pipelines or other buried structures.
Ground clearance – It is the minimum vertical distance between the lowest structural component of a vehicle’s undercarriage (or a structure) and the ground plane. Frequently referred to as ride height, it is a critical engineering parameter measuring the space from the road to the lowest part, such as a differential or chassis, which influences off-road capability, stability, and rollover risk. It is typically measured in an unladen condition (no cargo / passengers), meaning the actual clearance decreases when loaded. In case of wind turbine, ground clearance is the distance between the blade tip and the ground.
Ground clutter – It refers to echoes from the ground which occur when transmitted radar energy interacts with the ground, frequently appearing strongest at low elevation angles. These echoes can interfere with the recognition of desired signals, such as weather phenomena, and are considerably influenced by factors like temperature inversions and the radar’s range resolution.
Ground coat – It is a porcelain enamel which is applied directly to the base metal to function as an intermediate layer between the metal and the cover coat. It is also a porcelain enamel coating on sheet steel containing adherence-promoting agents which can be used either as an intermediate layer between the metal and the cover coat or as a single coat over the base metal.
Ground connection – It is a safety feature in electrical systems which provides a path for electrical currents resulting from large transient events, such as lightning or short circuits, to safely dissipate, thus protecting equipment and human operators. It also ensures that subsystem elements maintain a common reference potential to reduce noise and operational discrepancies over distances. In arc welding, ground connection is a device which is used for attaching the work lead (ground cable) to the work. It is an electrical connection of the welding machine frame to the earth for safety.
Ground-coupled heat pump system – It is a highly efficient, closed-loop HVAC (heating, ventilation, and air conditioning) technology which uses buried high-density polyethylene pipes to exchange thermal energy between a building and the earth, acting as a heat source in winter and a heat sink in summer. It provides heating, cooling, and water heating. It comprised of a ground heat exchanger (boreholes or horizontal trenches), a circulation pump, and a heat pump unit.
Ground fault circuit interrupter – It is an electrical safety device which interrupts an electrical circuit when the current passing through a conductor is not equal and opposite in both directions, hence indicating leakage current to ground or current flowing to another powered conductor. The purpose of the device is to reduce the severity of injury caused by an electric shock.
Ground fault interrupter – It is a safety device which detects unequal current flow in the hot and neutral wires of an electrical circuit and instantly disconnects the faulty appliance from the outlet to prevent electric shock.
Ground fireclay – It consists of fireclay or a mixture of fireclays which have been subjected to no treatment other than grinding or weathering, or both.
Ground fireclay mortar – It is a refractory mortar consisting of finely ground raw fireclay.
Ground granulated blast furnace slag – It is a cementitious, powdery by-product of iron ore smelting, produced by quenching molten slag in water and grinding it. It acts as a sustainable, partial replacement for Portland cement (typically 40 % to 80 % usage), improving concrete durability, reducing permeability, and lowering hydration heat.
Ground granulated slag – The ground granulated slag is used in composite cements and as a cementitious component of concrete. The use of ground granulated slag as a separately ground material added at the concrete mixer together with Portland cement has gained acceptance. In some countries the term ‘slag cement’ is used for pure ground granulated slag. Practically, there are no concrete, mortar or grout applications which preclude the use of an appropriate quantity of ground granulated slag.
Ground heat exchanger – It is a system of underground pipes, typically ‘high-density poly-ethylene (HDPE), which transfers thermal energy between a working fluid (water or antifreeze) and the earth to provide heating or cooling. It utilizes the constant, moderate subterranean ground temperature (5 deg C to 20 deg C) to improve HVAC (heating, ventilation, and air conditioning) efficiency, operating as either a vertical bore hole or horizontal trench loop.
Ground impedance – it is the total opposition (resistance and reactance) a grounding system presents to AC (alternating current) current flow, measured in ohms. It represents the efficiency of a connection between equipment and earth, encompassing inductive and capacitive effects, crucial for managing fault currents, lightning, and electrical stability.
Ground improvement methods – These are geotechnical techniques used to improve the physical properties of weak or unstable soil, such as increasing shear strength, bearing capacity, and density, or decreasing permeability and settlement. These methods alter soil characteristics to provide better performance under loading without full soil replacement.
Grounding resistance – It is the opposition a grounding system presents to the flow of electric current into the earth, measured in ohms. It is the ratio of the voltage of the grounding system to the ground, relative to the current flowing through it, and is critical for safely dissipating fault current, minimizing shock risk, and protecting equipment.
Ground lead – It is a non-standard term for workpiece lead.
Ground-level power supply – It is a system for providing powers for electric trams without overhead wires and without a permanently energized third rail.
Ground level pollution – It refers to the established limit for the concentration of certain air pollutants, like ozone or particulate matter (PM2.5), present near the earth’s surface, which is considered safe for human health and typically measured in units like micrograms per cubic meter or parts per billion. The standards for ground level pollution are normally set by environmental agencies and can vary depending on the pollutant and region.
Ground loop – It is an unwanted electrical condition occurring when two or more inter-connected electronic components have ground connections at different potential levels. This creates a closed loop, allowing stray, low-frequency current (typically 50 hertz / 60 hertz) to flow through signal cables or shields, introducing noise, interference, and hum in systems.
Ground mapping – It is the process of surveying, measuring, and plotting the earth’s surface and subsurface features to create detailed, to-scale representations (maps or models) for design, construction, and planning. It integrates topographical, geological, and utility data to identify site conditions, constraints, and material properties, mitigating project risks.
Ground model – It is a 3D, digital, or schematic representation of subsurface geological, hydrogeological, and geotechnical conditions. It synthesizes site investigation data to identify risks, define geotechnical parameters (e.g., layer thickness, soil strength), and guide design for foundations, tunnels, and infrastructure, ensuring optimized engineering performance.
Ground motion acceleration – It is the measure of the rate of change of velocity of the earth’s surface during an earthquake, representing the intensity of shaking. Normally quantified by ‘peak ground acceleration, (PGA) in horizontal or vertical directions, it defines the inertial forces imposed on structures and is important for designing earthquake-resistant buildings. It is the acceleration time history, or accelerogram, showing how ground motion changes over time, usually measured in ‘g’ (acceleration due to gravity).
Ground movement – It refers to the displacement, horizontal or vertical, of the soil, rock, or ground surface caused by environmental factors, construction activities (e.g., tunneling, excavation), or natural hazards like earthquakes. It includes subsidence, uplift, and shear strain, which can severely damage surface structures, foundations, and underground services.
Ground penetrating radar – It is a non-destructive, non-invasive geophysical method utilizing electromagnetic radiation (ultra-high frequency, UHF / very high frequency, VHF) to map subsurface structures and identify buried objects or materials in real-time. It works by emitting, reflecting, and detecting signals to identify anomalies in soil, concrete, rock, and ice.
Ground penetrating radar systems – These refer to ground penetrating radar technologies which are used to detect sub-surface features and structures, aiding in safety by preventing damage during construction and identifying hidden problems in different environments.
Ground plane – It is a large, flat, electrically conductive surface, normally copper on a printed circuit board (PCB) or metal in antennas, connected to a common ground potential. It acts as a zero-voltage reference point, providing low-impedance paths for return currents, reducing noise / crosstalk, and shielding sensitive components from electro-magnetic interference.
Ground reflected radiation – It is the portion of global solar radiation (beam and diffuse) reflected off the ground surface onto a tilted surface or structure, such as a solar collector or building, often termed as ‘albedo’. It is a critical component in solar energy modeling, particularly for PV (photo-voltaic) system energy yield, determined by the ground’s reflectivity and the view factor to the tilted surface.
Ground reaction curve – It is also called Fenner-Pacher curve. It is a graphical tool representing the relationship between the internal support pressure (Pi) acting on an excavated tunnel boundary and the resulting radial deformation / convergence (delta) of the surrounding ground. It shows how ground support needs decrease as the ground relaxes. It is a key component of the ‘convergence confinement method. (CCM), used to determine the optimal timing for installing support (like shotcrete or bolts) to ensure tunnel stability.
Ground refractory material, double-screened – It is a refractory material which contains its original gradation of particle sizes resulting from crushing, grinding, or both, and from which particles coarser and finer than two specified sizes have been removed by screening.
Ground refractory material, single-screened – It is a refractory material which contains its original gradation of particle sizes resulting from crushing, grinding, or both, and from which particles coarser than a specified size have been removed by screening.
Ground sample distance – It is the physical distance on the ground represented by the centre-to-centre distance between two consecutive pixels in an image, typically measured in centimeters per pixel or meters per pixel. It acts as a measure of spatial resolution. A lower ground sample distance value indicates higher resolution, more detail, and higher accuracy in aerial mapping.
Ground settlement – It is the vertical, downward movement of the ground surface caused by the compression, consolidation, or displacement of underlying soil layers. It occurs because of the applied structural loads, groundwater lowering, or soil disturbance, frequently leading to structural damage, cracks, or serviceability failures in buildings and infrastructure. Common triggers include structural loading, compaction of loose soil, consolidation of clay (squeezing out water), groundwater extraction, and tunneling.
Ground simulation – It is a testing technique which uses physical hardware or numerical models to replicate real-world environmental conditions or dynamics on the ground. It evaluates system performance by creating simulated environments (e.g., thermal, vacuum, motion) for qualification, analysis, and validation without actual field exposure.
Ground source heat pump – It is a high-efficiency HVAC (heating, ventilation, and air conditioning) system which transfers heat between a building and the ground using a vapour compression cycle, acting as a heat source in winter and a heat sink in summer. It utilizes the constant, moderate temperature of the subsurface, normally 4 meters to 6 meters deep or through deep boreholes, to provide heating, cooling, and hot water.
Ground source heat pump system – It is also called geothermal heat pump. It is a solution for heating and cooling buildings which utilizes the relatively stable temperature of the earth as a heat source in winter and a heat sink in summer. It offers high efficiency (coefficient of performance 3 to 6) by moving heat rather than producing it through combustion.
Ground state – It is the lowest possible energy state for a given quantum mechanical system, at which the Gibbs energy is actually or theoretically minimized. Whatever energy remains in the system in its Ground state is called the zero-point energy.
Ground state energy – It is the minimum possible energy a quantum system (atom, molecule, or device) can occupy at 0 K or its most stable configuration. It is the lowest energy level (n = 1) for electrons, important for predicting material properties, device stability, and quantum behaviour. The system is in its lowest, most stable state, holding ‘zero-point energy’ which cannot be lowered further.
Ground state total energy – It is the minimum possible energy configuration of a quantum mechanical system, such as an atom, molecule, or solid, where electrons occupy the lowest available energy levels. It defines the most stable state (zero-point energy), typically calculated as the sum of kinetic (T) and potential (V) energies (E = T + V). It defines the lowest energy stationary state of a system, representing its most stable form.
Ground state transition – in photonics and quantum devices, it refers to the change in energy level of a system (such as an electron in a quantum dot) between its lowest possible energy level (ground state) and a higher excited state. This process involves the absorption or emission of electro-magnetic radiation.
Ground-structure interaction – It is also known as soil-structure interaction (SSI), is the study of how the behaviour of a structure is influenced by the soil it is built on, and how the structure, in turn, affects the soil. It is a crucial concept in geotechnical and earthquake engineering, as it highlights the interconnectedness of the structure and the ground it supports.
Ground subsidence – It is the vertical, downward sinking or settling of the earth’s surface, frequently caused by the loss of sub-surface support, soil compaction, or extraction of fluids. It represents a significant geohazard, distinct from structural settlement, where shrinking clays, mining voids, or groundwater withdrawal cause foundation failure.
Ground temperature – It is the measurement of the soil’s inherent warmth at different depths, serving as a critical parameter for heat transfer, foundation design, and geothermal systems. It varies based on surface conditions (diurnal / seasonal) but becomes relatively constant at deeper depths.
Ground terminal – It is a designated connection point in an electrical or electronic system which serves as the zero-voltage reference point, a common return path for current, or a safety connection to the earth. It acts as a stable datum for voltage measurements, ensuring circuit stability and providing a path for fault currents.
Ground truth image – It refers to the definitive, accurately annotated dataset used as a reference standard to train, test, and validate AI (artificial intelligence) models. It acts as the ‘correct answer’ or ‘gold standard’ to which model predictions are compared to calculate performance metrics such as accuracy, precision, and intersection-over-union (IoU).
Ground vibration – It refers to the oscillatory movement of the earth’s surface, typically triggered by anthropogenic activities like blasting, construction, traffic, or machinery. It is the propagation of seismic energy through soil or rock, which can threaten the stability of buildings, infrastructure, and foundations, often quantified by ‘peak particle velocity’ (PPV).
Groundwater – It consists of all kind of water under the surface of the ground whether in liquid or solid state. It originates from rainfall or snowmelt which penetrates the layer of soil just below the surface. For ground-water to be a recoverable resource, it is to exist in an aquifer. Ground-water can be found in practically every area, but aquifer depths, yields, and water quality vary.
Groundwater inflow – It is the movement of sub-surface water into a constructed facility, such as a tunnel, foundation, or mine. It is frequently considered a geological hazard or construction challenge, representing unwanted seepage which necessitates pumping, diversion, or waterproofing. It is driven by hydraulic head differences and permeability.
Groundwater influence – It refers to the impact of subsurface water on the stability, safety, and construction of geotechnical and structural projects. It covers the pressure water exerts on underground structures, its flow characteristics through soil or rock, and its effect on soil shear strength and bearing capacity.
Groundwater level – It is also called water table. It is the upper surface elevation of the saturated zone (aquifer) where pore water pressure is equal to atmospheric pressure. It acts as the boundary separating unsaturated soil from completely saturated soil below. This level is important for determining soil bearing capacity, calculating uplift pressures on structures, and planning dewatering for construction projects.
Groundwater pollution – It is the degradation of natural water quality in underground aquifers caused by human-made, industrial, or natural contaminants (such as chemicals, heavy metals, or microbes) exceeding safe levels, making it hazardous for consumption or use. It involves the infiltration of pollutants through soil from surface sources.
Groundwater pressure – It is the pressure exerted by water within soil or rock pores (pore water pressure) or fractures, measured as force per unit area. It represents a critical hydrological force (hydrostatic pressure) which acts against geotechnical structures, reducing effective stress and shear strength while increasing uplift and water intrusion risks.
Groundwater regime – It refers to the dynamic, integrated system of subsurface water, encompassing its occurrence, quantity, movement, and quality, governed by geological, climatic, and hydrological factors. It defines the spatial and temporal distribution of water within saturated aquifers (pores / fractures) and unsaturated zones, important for analyzing pressure, seepage, and stability in geotechnical projects.
Groundwater resources – These are all freshwater stored in saturated underground geological formations called aquifers, found in the spaces between soil, sand, and rock fractures. These resources act as massive, renewable, yet slow-replenishing natural reservoirs replenished by precipitation through a process called recharge, supplying water to wells, springs, and streams.
Groundwater source – It is the water located beneath the land surface in the saturated zone, filling pores and fractures within soil and rock layers known as aquifers. It acts as a major freshwater reservoir, representing roughly 99 % of all liquid freshwater, and is accessed through wells, springs, and boreholes for domestic, agricultural, and industrial use.
Groundwater table – it is also called water table. It is the upper surface of the zone of saturation, where soil or rock pores are fully filled with water. It separates the unsaturated vadose zone above from the saturated groundwater zone below. This level represents the pressure boundary where pore water pressure equals atmospheric pressure.
Ground wire – It is an intentional, low-resistance electrical conductor which connects circuits or equipment to the earth (ground) to provide a safe path for fault current, preventing electrical shocks and fires. It operates by bypassing the human body to trip circuit breakers during a fault, typically coloured green, green / yellow, or bare copper.
Group – It consists of number of samples tested at one time, or consecutively, at one stress level. A group can comprise one or more samples.
Group contribution method – It is an approach used to predict physical and thermodynamic properties of molecules, such as boiling points, critical properties, and Gibbs energy, by summing the contributions of individual functional groups (-CH3, and -OH etc.) within that molecule. It treats properties as additive, making it ideal for estimating properties when experimental data is unavailable. The technique assumes that individual functional groups (e.g., -CH2, C=O, Cl) make specific, additive contributions to the overall property of a molecule.
Grouped sample – It is a dataset organized into classes or numerical intervals (class intervals) rather than raw, individual data points. It simplifies large data analysis by summarizing frequencies within ranges, frequently used to determine particle distributions, quality control, or to protect data privacy. It consists of intervals (e.g., 0 to 9, 10 to 19) and frequencies (number of observations in that range).
Group interaction parameters (Amn, Anm) – These are empirical coefficients, mainly within ‘UNIQUAC (universal quasi-chemical) functional-group activity coefficient’ (UNIFAC) / ‘activity specific operating guidelines’ (ASOG) models, which characterize energy interactions between functional groups (‘m’ and ‘n’) in liquid mixtures. They represent the residual activity coefficient, allowing prediction of phase equilibria (vapour–liquid equilibrium, VLE / liquid–liquid extraction, LLE) for complex, non-ideal mixtures where experimental data is missing. These parameters quantify the interaction energy between different functional groups (e.g., -CH2 and -OH) rather than whole molecules, allowing for broad predictive applications.
Group members – They typically refer to elements located in the same vertical column (group) of the periodic table, which show similar chemical reactivity and physical properties because of having the same number of valence electrons. These groupings are important for predicting how metals behave in alloys, their corrosion resistance, and their extraction methods. Group members can also refer to either human team members or structural components. Human group members are individuals collaborating on shared tasks, defined by interdependence, communication, and shared goals, frequently including 3 to 8 participants from diverse technical backgrounds. In structural analysis, group members refer to a collection of individual structural elements, such as beams, columns, or braces, defined to share the same sectional properties, material, and design parameters. Grouping facilitates efficiency in design, optimization, load application, and modeling by applying uniform design criteria across similar components.
Group membership – It refers to the inclusion of model elements in an element group based on specified criteria, allowing for the organization of elements associated with particular characteristics, while noting that membership is not transitive between groups. Group membership defines, manages, and automates how users or entities are added to, maintained in, or removed from specific groups based on attributes, roles, or rules, rather than manual assignment. It ensures consistent access control, automates lifecycle management, and maintains security across systems.
Group model building – It is a structured, participatory approach in system dynamics which involves stakeholders and domain experts in collaboratively building simulation models. It combines team insights to create causal loop or stock-and-flow diagrams, increasing consensus, understanding of complex, dynamic, or ambiguous problems.
Group node – It is a structural, networking, or software entity which aggregates multiple individual nodes to simplify management, visualize hierarchies, or define shared properties. It acts as a container, similar to a folder, used in circuit diagrams, scene graphs, or node-based visual programming to organize complex systems. Group nodes define sets of network devices (routers, switches) to apply unified policies or display specific topology maps.
Group technology – It is an approach to design and manufacturing which seeks to reduce manufacturing system information content by identifying and exploiting the sameness or similarity of parts based on their geometrical shape and / or similarities in their production process.
Group sparsity – It is a regularization technique which forces entire predefined groups of model coefficients (variables) to zero, rather than individual elements. It promotes ‘structured sparsity’, where entire features or network nodes are inactive, improving model interpretability and computational efficiency in high-dimensional signal processing, compressive sensing, and neural network pruning.
Group technology – It is a manufacturing philosophy which identifies and groups similar parts (part families) based on design or manufacturing attributes to capitalize on their similarities. It streamlines production by utilizing cellular manufacturing to reduce setup times, inventory, and material handling, frequently integrating design with production.
Group velocity (Vg) – It is the speed at which the envelope, energy, or information of a wave packet travels through a medium. It represents the velocity of modulation rather than individual wave crests (phase velocity), mathematically defined as the derivative of angular frequency (w) with respect to wavenumber (k), ‘Vg = dw/dk’.
Grout – It is a dense fluid which hardens upon application and is used to fill gaps or as reinforcement in existing structures. Grout is normally a mixture of water, cement, and sand, and is used in pressure grouting, embedding rebar in masonry walls, connecting sections of precast concrete, filling voids, and sealing joints such as those between tiles.
Grout bag – It refers to a heavy-duty, flexible container, normally made of synthetic fabric like nylon or canvas, designed to be filled with grout or concrete slurry. It is used in marine, subsea, and structural engineering to fill voids, support foundations, or stabilize structures, such as under pipelines, seabed platforms, and caissons. It is mainly used for underpinning, stabilizing, and providing structural support beneath pipelines or structures where traditional concrete pouring is not feasible, such as underwater.
Grouted joint – It is a connection in construction where a high-strength, flowable grout material is injected into the annulus (void) between two structural components, typically concentric steel tubes or precast concrete elements, to create a rigid, load-bearing, and durable bond. It acts as a liquid shim to transfer shear, axial, and compressive forces, normally used in offshore wind structures, jacket foundations, and precast concrete connections. Grouted joint consists of an outer sleeve (or socket), an inner tubular member, and the intervening grout.
Grouted pile – It is a deep foundation element constructed by placing high-strength cement grout into an augured hole, or by injecting grout around a steel pipe or pile base to increase load-bearing capacity. It offers high structural stability and is frequently used to improve side friction and end bearing in soil, normally applied in micro-piles or post-grouting.
Grout filling – It is also called grouting. It is a process which involves injecting or pouring a fluid-like, hydraulic cementitious mixture into voids, cracks, or structural spaces to improve stability and strength. It strengthens structures, aids soil stabilization, seals water leaks, and improves load-bearing capacity by filling structural gaps, such as around machinery base plates or within concrete sections.
Grouting – It is the process of sealing off a water flow in rocks by forcing a thin slurry of cement or other chemicals into the crevices. It is normally done through a diamond drill hole.
Grouting equipment – It is a specialized machinery system designed to mix, pump, and inject grout materials (cement, chemical, or bentonite) into subsurface soil, rock, or concrete structures under pressure. It is used to fill voids, seal fissures, improve soil strength, reduce permeability, and ensure structural stability.
Grouting pressure – It is the controlled positive force used to inject fluid materials (cement, resin, or chemicals) into soils, rock fractures, or concrete gaps. It is used for soil stabilization, waterproofing, and structural lifting by forcing grout through a pipe or hole to fill voids, typically ranging from low pressure to over 35 mega-pascals depending on the technique.
Grout interface – It is the boundary surface where injected, hardened cementitious or chemical material meets rock, concrete, soil, or steel, crucial for structural load transfer and water sealing. It is defined by shear strength, friction, and bonding, and it is analyzed through its behaviour under stress, such as pseudo-elasticity, failure development, and residual strength. It represents the critical junction where grout interacts with substrates. It is necessary for strengthening foundations, repairing concrete voids, sealing rock fractures, and ensuring structural stability in marine pile-sleeve connections.
Grout pipe – It is also called grouting pipe. It is a tube used to inject cementitious or chemical slurry into voids, soil, or concrete structures for sealing, strengthening, or stabilization. It serves as a conduit to introduce material into cracks, pile systems, or underground, often used for soil reinforcement or sealing construction joints, allowing for controlled, pressurized filling.
Growing crystals – It refers to the process of forming single crystals of a pure substance through the orderly arrangement of molecules in a lattice, typically involving the dissolution of the substance in a moderately soluble solvent and using methods which induce gradual changes in solute or solvent conditions.
Growing mode – It is the fastest developing pattern in a system, which dominates the growth process when influenced by weak noise, allowing it to emerge over other competing modes.
Growing seed – It is also called seed crystal. It is a pre-existing, small piece of solid material used as a template to initiate and facilitate the crystallization of a larger crystal from a supersaturated solution, melt, or vapour.
Growler – It is a test instrument that is used to diagnose some faults with alternating current motors.
Growth – It means an increase in some quantity over time. The quantity can be physical (e.g., growth in height, growth in an amount of money) or abstract (e.g., a system becoming more complex, an organism becoming more mature). It can also refer to the mode of growth, i.e. numeric models for describing how much a particular quantity grows over time. In case of compacts, It is an increase in compact or part size as a result of excessive pore formation during sintering.
Growth analysis – It typically refers to the quantitative study of how crystal structures, grains, or phases increase in size, shape, and distribution within a metal or alloy over time, usually under the influence of heat treatment. It is a critical component of physical metallurgy used to control microstructures to achieve desired mechanical properties, such as strength, toughness, or ductility.
Growth behaviour – It refers to the kinetics, mechanism, and morphological evolution of microstructural components, such as grains, dendrites, or precipitates, within a metal or alloy as they increase in size. It describes how the size and shape of these features change over time, typically at high temperatures or during solidification, and is fundamentally driven by the reduction of internal energy (e.g., reduction of grain boundary area).
Growth, cast iron – It is a permanent increase in the dimensions of cast iron resulting from repeated or prolonged heating at temperatures above 480 deg C because of either to graphitizing of carbides or oxidation.
Growth coefficient – It very frequently refers to the ‘coefficient of thermal expansion’ (CTE), which quantifies how much a metal or alloy changes in size (expands or contracts) in response to a change in temperature.
Growth competition – It is also called competitive growth. It refers to the phenomenon during the solidification of a material where different crystals (grains or dendrites) with varying crystallographic orientations grow simultaneously, with favourably oriented grains outgrowing or blocking misaligned ones. This process is important in controlling the microstructure of cast or welded metals, specifically in defining the grain texture, columnar structure, and the resulting mechanical properties.
Growth-controlled annealing textures – These refer to the crystallographic orientations which develop in a material during the grain growth stage (following primary recrystallization) as a result of selective grain boundary mobility, where certain grain orientations grow faster than others. Unlike recrystallization textures, which are mainly determined by the nucleation of strain-free grains, growth-controlled textures are driven by the reduction of total grain boundary energy, surface energy, or interface energy, leading to the preferential consumption of grains with higher energy by those with lower energy.
Growth curve – It is a graphical representation showing the change in a specific physical or structural parameter of a metal (such as grain size, precipitate volume, or void size) as a function of time, temperature, or other processing variables. These curves are necessary al for predicting microstructural evolution, such as grain growth, recrystallization, or aging behavior, often following sigmoid or exponential patterns.
Growth-curve modelling – It is also known as the linear mixed model. It is a regression analysis in which the response variable is the trajectory of change over time in a quantitative study end point. Interest centres on describing the average trajectory of change, as well as what subject characteristics lead to different trajectories of change for different types of subjects.
Growth equation – It typically refers to the mathematical models used to predict the increase in size of grains (grain growth), precipitates, or solid phases during processes like solidification, annealing, or heat treatment. These equations are normally driven by the reduction of interfacial energy and are temperature-dependent.
Growth function – It is a mathematical model or relationship that describes how a material’s microstructural features, such as grain size, precipitate size, or thickness of an epitaxial layer, change over time, typically under specific heat treatment or solidification conditions.
Growth interface – It is the boundary between a developing solid phase and its parent phase (melt, solution, or vapour) where phase transformation occurs and the new crystal structure is formed. It is the specific region where atomic transport and rearrangement take place, controlling the solidification morphology and microstructure of the material.
Growth kinetics – It refers to the rate at which new phases, grains, or particles (such as precipitates, crystals, or intermetallic layers) evolve and grow over time during processing (e.g., solidification, annealing, or heat treatment). It is determined by the speed of atomic diffusion and interface reaction rates, controlling how microstructure changes at specific temperatures.
Growth method – It is a technique used to produce single crystals or tailored crystalline structures by controlling the solidification or deposition of a material, frequently using a seed crystal to dictate the crystallographic orientation. These methods involve managing phase transitions, such as liquid-to-solid or gas-to-solid, under specific thermal gradients and chemical conditions to minimize defects. Common growth methods are broadly classified by the phase involved such as (i) melt growth techniques (liquid-to-solid) which are the most popular methods (such as Czochralski (CZ) method or pulling method, Bridgman-Stockbarger technique, floating zone (FZ) method, and Verneuil method (flame fusion) for producing large, high-purity single crystals, (ii) solution growth techniques, e.g., high-temperature solution (flux) growth and hydrothermal growth, which are used for materials which cannot be melted directly, as they can decompose, or have very high melting points, (iii) vapour phase growth techniques such as physical vapour transport (PVT) / sublimation and chemical vapour deposition (CVD). Key components of growth methods are seed crystals, interface control, thermal gradient, and annealing.
Growth model – It is a mathematical, computational, or visual representation describing how a system, material, or population increases in size or complexity over time. These models use differential equations or statistical data to predict future states, optimize resources, or analyze processes such as bacterial growth, material deposition, or product life cycles.
Growth of knowledge – It is the cumulative process of expanding, refining, and applying information, understanding, or skills through experience, education, or research. It involves the evolution of ideas, where existing knowledge is updated, specialized, or combined to generate new insights, frequently leading to exponential growth in fields. Knowledge grows by building upon previous information. It is driven by research, learning, and the integration of new data. Rather than just storing information, growth involves interpreting, analyzing, and synthesizing information to form new understandings.
Growth polymer – It refers to a classification of polymerization methods based on how monomers connect to form high molecular weight chains (macro-molecules). There are two main types namely chain-growth and step-growth polymerization.
Growth pressure – It is defined as the pressure within a reactor during the deposition of materials, which influences the grain size, film quality, and growth rate of the resulting films, particularly in processes such as MOVPE (metal-organic vapour-phase epitaxy) for GaN (gallium nitride) films. Optimal growth pressure improves film quality by promoting larger grain sizes while affecting the nucleation and decomposition rates of the materials.
Growth process – It refers to the stage of micro-structural development where new, stable, or refined particles, such as crystal grains, precipitates, or phases, increase in size following an initial nucleation event. Growth involves the accumulation of atoms or molecules onto the surface of a nucleus, propagating its crystalline structure outwards. Growth occurs to reduce the total free energy of a system, such as reducing grain boundary area (grain growth) or minimizing surface energy.
Growth rate – It refers to the percentage change in the quantity of goods or services produced within a specific time period, typically a year, quarter, or month. It indicates how quickly or slowly production is increasing or decreasing. This metric is crucial for assessing economic performance, tracking industry trends, and making future production forecasts.
Growth-rate determination – It refers to the quantitative measurement and analysis of the speed at which a new phase (such as a solid crystal, recrystallized grain, or precipitate) grows into a matrix phase (such as a melt or deformed solid) during processes like solidification, recrystallization, or phase transformation. It is an important aspect of kinetic studies, determining how quickly a material’s micro-structure, and consequently its mechanical properties, changes under specific conditions, particularly temperature and time.
Growth reaction – It refers to the phase transformation process where newly formed nuclei (solid crystals, precipitates, or phases) increase in size over time. It is a critical component of microstructure evolution, which dictates the mechanical properties of materials. Growth reactions are often categorized within ‘nucleation and growth’ processes, where a super-saturated solid solution, liquid, or amorphous phase transforms at a specific temperature.
Growth stages – It typically refer to the phases of grain development during heat treatment (annealing) or the formation of crystalline structures during solidification. Growth is the process where atoms, ions, or molecules add to a nucleus to form a crystalline solid, moving outward from a nucleation site. In case of annealing post deformation, when a cold-worked metal is heated, it undergoes three consecutive, overlapping, and thermally activated stages (recovery, recrystallization, and grain growth) to reduce internal energy and defects. In case of solidification (casting), during solidification, the transition from liquid to solid occurs in three distinct stages nucleation, growth, and competitive growth. Key concepts in growth are driving force, mechanism, interface structure, and solute drag.
Growth temperature – It refers to the temperature at which specific microstructural features, very frequently grains or precipitates, increase in size during thermal processing. It is an important parameter in heat treatment (such as annealing) and solidification, where it determines the kinetics of microstructural evolution, influencing the final grain size, density, and mechanical properties of the metal.
Growth-textures – It refer to the non-random, preferred crystallographic orientation of grains which develops during the growth phase of heat treatment, such as annealing after cold work. Unlike deformation textures, which are caused by the rotation of lattices during mechanical shaping, growth textures are driven by the competitive growth of nuclei where certain crystal orientations have a mobility or energy advantage.
Growth twin – It is a twin formed in a crystal or grain during recrystallization or, rarely, during solidification.
Growth velocity – It is the rate at which a solid-liquid interface (solidification) or a new crystal phase (solid-state transformation) propagates. It dictates the resulting microstructure, transitioning from planar to cellular or dendritic forms, and is heavily influenced by undercooling, solute diffusion, and heat flow.
Grubbs catalysts (1st and 2nd generation) – These are ruthenium-based carbene complexes prepared by reacting ruthenium precursors like RuCl2(PPh3)3 with phenyl-diazo-methane and tri-cyclo-hexyl-phosphine (PCy3)). Second-generation catalysts further involve replacing a PCy3 ligand with an N-hetero-cyclic carbene (NHC) ligand for higher activity. These are normally synthesized under inert atmospheres, though paraffin-supported versions provide air stability.
Grubb’s test – It is a statistical method for detecting outliers in data which follow a normal distribution, which operates iteratively to identify and remove one outlier at a time. The null hypothesis posits that there are no outliers, while the test statistic measures the largest absolute deviation from the sample mean, expressed in units of the sample standard deviation.
GSM – In the context of coating weight, it stands for grams per square meter. It is a unit of measurement used to express the weight or thickness of a coating, typically applied to materials like steel sheets or fabrics. A higher GSM value indicates a heavier coating or a thicker material. It also stands for ‘global system for mobile communication (or communications), which is a 2G digital cellular network standard for mobile devices. It has been developed to provide a standardized, secure, and globally roaming-capable network.
Guaranteed delivery – It refers to a contractual agreement where a supplier warrants that metal components or raw materials meet specific quality standards, performance characteristics, and chemical compositions upon arrival. This differs from mere logistics tracking by guaranteeing the integrity of the material itself. Products (such as rolled steel plates or cast irons) are delivered with guaranteed levels of strength, ductility, or hardness, rather than just estimated averages.
Guarantee period – It is also known the defects liability period or warranty period. It is a specific timeframe, commencing upon the issuance of a Completion Certificate or commissioning of equipment, during which the contractor or supplier warrants that the supplied materials, machinery, or structural work conform to specified standards and are free from defects. If defects are discovered within this period, the contractor is obligated to perform remedial work, repairs, or replacements at their own expense.
Guarantee test – It also known as a performance guarantee test. It is a process used to verify whether a product, service, or system meets the performance standards or specifications outlined in a contract or agreement. These tests are designed to demonstrate that the item in question achieves the promised functionality, capacity, efficiency, or other performance criteria.
Guarding – It is use of any device or combination of devices designed to keep any part of a worker’s body out of danger zone of a machine during its operating cycle.
Guard rail – It is a physical, stationary safety barrier designed to protect people, vehicles, or equipment from hazards by preventing falls, controlling traffic, or delineating dangerous edges. Typically constructed of steel, concrete, or aluminum, these structures are essential in structural, civil, and occupational engineering to prevent injury or damage. In case of conveyors, guard rail is the protective barriers or rails installed along the conveyor to prevent materials from straying, needing regular inspections for stability and effectiveness.
Guard rail barriers – These are the barriers which run along the conveyor’s length to prevent obstruction and impact, necessitating routine checks for stability and effectiveness.
Guards – These are used for preventing the bending of the rolling stock upwards or downwards during its exit from the rolls and / or collaring on the roll. The placing of the guards is important depending on whether the mill stand works with top or bottom pressure, i.e. whether the rolling stock shows a tendency towards collaring on the bottom or top roll.
Gudmundson’s theory – It refers to a prominent framework for ‘strain gradient plasticity’ (SGP) to model size-dependent plastic behavior in materials at small scales (micron and sub-micron).
Guerin process – It is also known as rubber-pad forming or Guerin stamping process. It is a sheet-metal shaping technique. It is a rubber-pad forming process for forming sheet metal. The principal tools are the rubber pad and form block, or punch.
Guest atom – It refers to an atom or molecule which is introduced into the interstitial spaces (voids) or internal structure of a pre-existing ‘hos’ crystal lattice, typically without causing a substantial overhaul of that host structure. Guest atoms are normally introduced through intercalation, where they occupy space between atomic layers or in vacancies within a solid lattice.
Guest molecule – It refers to a small molecule, ion, or atom which is physically trapped, adsorbed, or encapsulated within the internal cavities, pores, or channels of a larger, porous host material, such as a ‘metal-organic framework’ (MOF) or other crystalline lattice, through non-covalent interactions.
Guidance condition – It refers to the specific criteria, physical constraints, or necessary set of parameters which are to be met to achieve a desired, frequently optimal, state or trajectory. It is critical for controlling a system toward a target and ensuring its performance, particularly in aerospace, optical systems, and structural engineering.
Guide – It consists of the parts of a drop hammer or press which guide the up-and-down motion of the ram in a true vertical direction.
Guide bearing – It is a bearing which is used for positioning a slide, or for axial alignment of a long rotating shaft.
Guided bend – It is the bend got by use of a plunger to force the sample into a die in order to produce the desired contour of the outside and inside surfaces of the sample.
Guided bend test – It is a test in which the sample is bent to a definite shape by means of a punch (mandrel) and a bottom block.
Guided iteration – It is a general problem-solving methodology applicable to engineering design. The steps in this process are namely formulation of the problem, generation of alternative solutions, and evaluation of the alternatives. If none of the alternatives is acceptable, the process continues with redesign, guided by the results of the evaluation.
Guided mode – It is a stable, confined electro-magnetic field configuration propagating within a waveguide structure (such as an optical fibre), characterized by its ability to travel without losing energy to radiation, unlike evanescent modes. These modes are defined by specific solutions to Maxwell’s equations, with power concentrated in the core and exponentially decaying in the cladding.
Guided wave propagation – It is the transmission of elastic, acoustic, or electro-magnetic waves constrained within a specific structure (wave-guide) bounded by surfaces, such as pipes, plates, or rods. These waves propagate over long distances with low attenuation, dispersing into multiple, frequency-dependent modes (e.g., Lamb waves) ideal for NDT (non-destructive testing) / SHM (simple harmonic motion).
Guided waves – These are mechanical, acoustic, or electro-magnetic waves confined within a bounded medium (like pipes, plates, or fibres), propagating parallel to its boundaries. By using the structure itself as a waveguide, they allow long-distance propagation with minimal energy loss, important for NDT (non-destructive testing) inspection or signal transmission.
Guided wave ultrasonic testing – It is an advanced non-destructive testing (NDT) method which uses low-frequency ultrasonic waves, typically between 10 kilo-hertz to100 kilo-hertz, to inspect large volumes of materials, such as pipelines, from a single location. It sends guided, axial, or torsional waves along the pipe wall boundaries to detect corrosion and defects over long distances (tens of meters).
Guide hole – It is a precision-machined feature designed to align, locate, or support components, or to direct tools during manufacturing. These holes, frequently used for positioning pins or fastening, need high accuracy to ensure proper assembly, such as in jig-and-fixture, mould-making, and structural applications.
Guide mill – It is a small hand mill with several stands in a train and with guides for the work at the entrance to the rolls.
Guide pin bushings – These are the bushings, pressed into a die shoe, which allow the guide pins to enter in order to maintain punch-to-die alignment.
Guide pins – These are hardened, ground pins or posts which maintain alignment between punch and die during die fabrication, set-up, operation, and storage. If the press slide in out of alignment, the guide pins cannot make the necessary correction unless heel plates are engaged before the pins enter the bushings.
Guide rollers -These are the rollers which are designed to guide and support the conveyor belt, necessitating regular checks for wear, alignment, and smooth operation.
Guides – The purpose of the guides is to correctly guide the rolling stock into the groove of work rolls at the entry side of the roll stand and its safe exit to the run-out table of the roll stand. Guide equipments guide the rolling stock at the entry and the exit of the roll pass so as to have smooth rolling of the rolling stock. The guiding equipments are to be sturdy, accurate and stable. They play a major role in ensuring the surface quality of the rolled product. The guides are to be designed for the wide variety of sizes and shapes of rolling stock which are normally encountered in the long product rolling.
Guide shoe – Within drilling and oilfield operations, it is a short, heavy-walled, rounded-nose device attached to the bottom of the lowest casing string. It is designed to facilitate the smooth insertion of the casing into the borehole and to protect it from damage. It guides the casing toward the center of the hole, minimizing the risk of hitting rock ledges or washouts, and helps prevent damage to the casing string while it is being run into the well. It consists of a steel shell, typically with the same diameter and threads as the casing, often with a rounded or tapered nose.
Guide vanes – These are stationary airfoils or vanes designed to direct and control the flow of fluids (like air, gas, or water) into a turbine or around bends in ducts, minimizing energy loss. They are crucial for optimizing efficiency in various mechanical systems, including turbines, and compressors.
Guide-vane shroud – It is a structural, normally annular component which supports, connects, and seals a ring of stator guide vanes (or nozzles) at their radially inner or outer ends. It acts as a boundary wall for the working fluid, ensuring that gas, steam, or air is directed evenly into the turbine or compressor blades with maximum efficiency.
Guillotine shear – It has a moving blade which runs on straight slides. The moving blade is almost parallel to the fixed blade during the entire stroke. The guillotine design uses a drive system to power the moving blade down. The guillotine shear needs a gibbing system to keep the blade beams in the proper position as they pass each other.
Guinier-Preston (G-P) zone – It is a small precipitation domain in a super-saturated metallic solid solution. A G-P zone has no well-defined crystalline structure of its own and contains an abnormally high concentration of solute atoms. The formation of G-P zones constitutes the first stage of precipitation and is normally accompanied by a change in properties of the solid solution in which they occur.
Gum – In lubrication, it is a rubber-like, sticky deposit, black or dark brown in colour, which results from the oxidation and / or polymerization of fuels and lubricating oils. Harder deposit are described as lacquers or varnishes.
Gumbel distribution – It is a specialized probability distribution used in engineering to model the maximum or minimum of a large number of samples, making it essential for predicting extreme events like floods, earthquakes, and material failures. It is a Type-I ‘generalized extreme value’ (GEV) distribution defined by location and scale parameters.
Gun – It is a device used in cutting and welding, e.g., air cutting gun, arc welding gun, electron beam gun, resistance welding gun, soldering gun, and thermal spraying gun.
Gun drill – It is a drill, normally with one or more flutes and with coolant passages through the drill body, used for deep hole drilling.
Gunite – It is a dry-mix, pneumatically applied concrete (a type of shotcrete) consisting of cement and sand, mixed dry and transported through a hose, with water added only at the nozzle. It is sprayed at high velocity to create dense, durable structural layers, frequently used for tunnel linings, and repairing concrete without needing formwork.
Guniting – It is a process used for the hot repair of the refractory lining which get damaged during the operation of the furnace. It is an important process which is frequently used for enhancing the refractory lining life of the furnace. Sometimes it is also called shotcreting. It is a process or technique which involves pumping of refractory guniting refractory mixes under high pressure through a hose to a nozzle (spray-gun) and then spraying them at high velocity onto a surface either by dry-mix or by wet-mix process. Guniting makes it possible to repair refractory linings in horizontal, vertical, and overhead positions or of irregular shapes. It does not need any forms.
Guniting equipment – The main equipment for guniting of the refractory material is a guniting machine. The guniting machines are mounted on wheels for portability. A valve is provided at the nozzle for the regulated flow of water which ensures very efficient and controlled hydration of the guniting refractory mix. For avoiding manual work, one lever operation is generally provided for charging the guniting material into working chamber. This also makes the operation easy and safe. Auxiliary equipment upstream includes the necessary pumps and pressure regulators, pre-wetting equipment, and the solid feed regulating system where the solids flow rate is determined. Manifolds are provided in airline to ensure minimum air pressure loss for the optimum utilization of air. This results into saving in air consumption. The upper and bottom vessels in the guniting machine can be unbolted for inspection and cleaning. A check valve is normally provided before manifold to prevent back flow of material into valves and air motor. The guniting machines are simple and safe to operate and can be operated even by an inexperienced person.
Guniting refractories – These refractories are monolithic refractories which are installed by guniting process. Guniting refractories consist of graded refractory aggregate and a bonding compound, and can contain plasticizing agent to increase their stickiness when pneumatically placed onto a furnace wall. Typically, guniting refractories are supplied dry. To use, they are pre-damped in a batch mixer, then continuously fed into a guniting machine. Water is added to the guniting mix as required by the guniting process to reach the proper consistency. Guniting refractories include siliceous, fireclay, high alumina, and dead burned magnesite and chrome types. Guniting refractories are granular refractory mixtures designed for application with air placement guns. A variety of air guns are used to spray the mixes at high velocity and pressure to form homogeneous compact lining essentially free from lamination and cracks. These refractories are either air-setting or heat-setting and some allow repairs to furnace linings without greatly reducing the furnace temperature. Light weight guniting refractories are used for insulation, while the denser guniting refractories are used in the more severe applications. Some compositions combine relatively low heat losses with good strength. Although guniting refractories need more skills than pouring castables, it can place a higher volume of material in less time than any other method. The properties of guniting refractories vary considerably, and hence encompass a wide range of applications. The guniting refractory mixes perform very well in both original linings and maintenance applications within a service range of 850 deg C to 1,900 deg C.
Gun metal – It is a type of bronze, i.e., an alloy of copper, tin, and zinc. Proportions vary but 88 % copper, 8 % to 10 % tin, and 2 % to 4 % zinc is an approximation. Originally used mainly for making guns, it has largely been replaced by steel for that purpose. Gunmetal casts and machines well, and is resistant to corrosion from steam and salt water. It is used to make steam and hydraulic castings, valves, gears, statues, and different small objects, such as buttons.
Gunn diode – It is a two-terminal solid-state device which hat is used in micro-wave oscillators.
Gunnert method – It is a semi-destructive technique used in physical metallurgy and engineering to measure the magnitude, direction, and distribution of residual stresses in metal components, particularly in welded joints. It is a specialized, refined version of the hole-drilling method, frequently used to determine how residual stresses change through the thickness of a material.
Gunning – It is an application technique which uses a pneumatic means to transport a refractory material and place it onto a cold or hot surface.
Gunning materials, refractory – It consists of mixtures of refractory aggregate and bond(s) specially prepared for placing by pneumatic or mechanical projection. Gunning materials can be either (i) a refractory castable which is supplied dry and used after the addition of water during or before gunning, or (ii) a plastic refractory which is specially designed for gunning under high air pressure with special equipment, and normally delivered in a ready-to-use state.
Gunning mixes – Gunning mixes consist of graded refractory aggregate and a bonding compound, and can contain plasticizing agent to increase their stickiness when pneumatically placed onto a furnace wall. They are granular refractory materials sprayed on application area using a variety of air placement guns. These are heat setting and are used for patching and maintenance works for kilns and furnaces. Typically, gunning mixes are supplied dry. To use, they are pre-damped in a batch mixer, then continuously fed into a gun. Water is added to the mix at the nozzle to reach the proper consistency.
Gusset plate – It is a thick sheet of metal (normally steel) used in structural engineering to connect multiple structural members, such as beams, girders, or trusses, at a joint. They act as reinforcing gussets, distributing loads, improving stability, and transmitting shear or tensile forces between members.
Gust effect factor (G or Gf) – It is an engineering parameter representing the ratio of a structure’s maximum dynamic response to its mean response under wind loading. It accounts for the increased structural load caused by wind turbulence and gusts, rather than just sustained mean wind speed, and is necessary for designing flexible or tall structures. It is defined as G = maximum response / mean response. It is frequently calculated using statistical parameters, including turbulence intensity, gust duration, and peak factors.
Gust factor – It is the ratio of peak wind speed (typically a short-duration 3-second gust) to the mean wind speed over a longer reference period (e.g., 10 minutes or 60 minutes). It quantifies wind turbulence, used to design structures for peak loads rather than just average wind speeds.
Gust loads – These are abrupt, transient aerodynamic forces imposed on a structure because of sudden vertical or horizontal atmospheric wind variations.
Gust velocity – It is the maximum, transient speed of a sudden air disturbance, representing a sharp deviation from the mean wind speed. It is a critical design parameter for structural load calculation, typically modeling sudden vertical air drafts (e.g., 8 meters per second to 5 meters per second) which cause abrupt aerodynamic forces, structural shaking, and potential safety risks.
Gutter – It is a depression around the periphery of a forging die impression outside the flash pan which allows space for the excess metal. It surrounds the finishing impression and provides room for the excess metal used to ensure a sound forging. It is a shallow impression outside the parting line.
Gutter-way – In bearings, it is a special type of spreader in which the groove is adjacent to the joint. It also refers to a channel or trough designed to carry away rainwater or other fluids, frequently found at the edge of a roof or along a road.
Guyed tower – It is a tall, slender structure which relies on guy wires (also called guy ropes or stays) anchored to the ground to provide stability and support against forces like wind and gravity. These towers are characterized by their reliance on external tensioned cables rather than the tower’s own structural strength to remain upright.
gyaku-sori – It refers to a reverse curve or a backward curvature of the blade. Unlike the standard sori (curvature) of a katana where the edge curves away from the spine (convex), gyaku-sori indicates a blade which has a reverse, negative, or near-straight, or slightly ‘downward’ bend toward the edge, resulting in a subtle curve which looks like a reverse tachi / katana curvature.
Gypsum – It is a soft, sulphate mineral (calcium sulphate di-hydrate, CaSO4.2H2O) used extensively in construction as a binder, fire-resistant material, and main component in plaster and drywall. It is mined as sedimentary rock, frequently utilized as a set retarder in Portland cement and for producing plaster of Paris.
Gypsum addition – It is the process of incorporating 3 % to 5 % CaSO4.2H2O (calcium sulphate di-hydrate) into cement clinker during final grinding to retard the setting time and prevent flash set. This important step allows sufficient time for placing and finishing concrete by controlling the hydration of tri-calcium aluminate.
Gypsum binder – It is an air-hardening, inorganic hydraulic-free binder produced by calcining gypsum rock (calcium sulphate di-hydrate, CaSO4.2H2O) into hemihydrate or anhydrite forms. It is a powdered material which sets and hardens when mixed with water, valued in construction for its rapid setting, fire resistance, lightweight, and sound insulation properties.
Gypsum board – It is a non-combustible, prefabricated construction panel consisting of a calcined gypsum plaster core encased between paper or fibre-glass facings. Used for interior walls, ceilings, and partitions, it provides fire resistance, sound attenuation, and thermal insulation, featuring a lightweight, easily finished structure widely used in dry-wall construction.
Gypsum cement – It refers to a high-strength, dimensionally stable plaster material, specifically alpha-hemihydrate calcium sulphate (CaSO4.1/2H2O), used for producing durable moulds and patterns, rather than a standard Portland cement, which is used for construction. It is valued for its ability to set rapidly, reproduce intricate details, and provide high compressive strength with minimal shrinkage.
Gypsum concrete – It is frequently called gypcrete. It is a high-performance, non-structural floor underlayment made from a mixture of gypsum plaster, Portland cement, and sand. It provides superior sound reduction, fire resistance, and superior surface leveling over wood or concrete sub-floors. It is a mixture of calcined gypsum (calcium sulphate hemihydrate, CaSO4.1/2H2O), sand, and cement (typically below 10 % for improved water resistance. It is mainly used as a, sound-rated, fire-resistant, and radiant heating floor underlayment. It offers high crack resistance, good compressive strength (similar to standard floor screeds), and low shrinkage. It is strictly for interior use and is not suitable for high-moisture environments or structural, load-bearing applications.
Gypsum content – It refers to the proportion of hydrated calcium sulphate (CaSO4.2H2O) within soil, rock, or construction materials, considerably influencing stability and strength. In geotechnics, high gypsum (above 10 %) causes water-soluble, collapsible soil hazards. In construction, it acts as a binder or cement retarder.
Gypsum plaster – It is a lightweight building material manufactured from semi-dehydrated gypsum (CaSO4.1/2H2O) which hardens when mixed with water. Mainly used for interior walls and ceilings, it provides a smooth, durable, and fire-resistant finish. It acts as an alternative to cement plaster, needing no curing and reducing shrinkage cracks.
Gypsum products – These are materials derived from heating natural gypsum mineral (calcium sulphate di-hydrate, CaSO4.2H2O) to produce calcium sulfate hemi-hydrate (CaSO4.1/2H2O), which hardens when mixed with water. These products, including plaster and board, are prized in construction for fire resistance, acoustic insulation, and high-strength, and low-porosity properties.
Gyrator – It is a theoretical two-port electrical network element which behaves as a non-reciprocal device inverting current-voltage characteristics. It enables, for example, a capacitor to behave as an inductor. In practice, gyrators are frequently implemented using op-amps (operational amplifiers) to simulate compact, high-Q inductance in filters, eliminating the need for bulky physical inductors.
Gyratory compactor – It is a laboratory device used to compact asphalt or bituminous mixture samples by applying a combination of static vertical pressure and shearing action (gyration) on an inclined axis. Developed under the Superpave method, it simulates field compaction to produce density-representative sample for performance testing, such as permanent deformation.
Gyratory crusher – It is similar in basic concept to a jaw crusher, consisting of a concave surface and a conical head with both the surfaces are typically lined with manganese steel liners. The inner cone has a slight circular movement, but it does not rotate. The movement is generated by an eccentric arrangement. The crushing action is caused by the closing of the gap between the mantle line (movable) mounted on the central vertical spindle and the concave liners (fixed) mounted on the main frame of the crusher. The gap is opened and closed by an eccentric on the bottom of the spindle that causes the central vertical spindle to gyrate. The vertical spindle is free to rotate around its own axis. The material travels downward between the two surfaces being progressively crushed until it is small enough to fall out through the gap between the two surfaces. A gyratory crusher is used both for primary or secondary crushing. Typically, it has a higher capacity than a jaw crusher.
Gyrobus – It is an electric bus which uses a large, heavy, rapidly spinning flywheel (gyro) as its primary energy storage system, rather than batteries or overhead wires. This technology stores kinetic energy in the flywheel, which spins up to 3,000 revolutions per minute (rpm), releasing it to power a traction motor for distances of 5 kilo-meters to 6 kilo-meters before needing to recharge at stations.
Gyro compass – It is a non-magnetic, inertial navigational instrument which determines true north by utilizing a fast-spinning rotor and earth’s rotation (angular momentum). It aligns with the earth’s axis, offering highly accurate heading data necessary for surveying, largely unaffected by local magnetic anomalies.
Gyroscope – It is a device used to measure or maintain orientation and angular velocity based on the principles of angular momentum and inertia. It consists of a rapidly spinning rotor within gimbals which maintains a constant spin axis, resisting external torque. Modern, non-mechanical types include MEMS (micro-electro-mechanical systems) and optical sensors used in navigation and stability.
Gyroscopic couple – It is a reactive torque or turning moment which opposes any change in the orientation of the axis of a spinning body, defined mathematically as the rate of change of angular momentum. It arises when a rotating body’s axis is forced to turn (precess) and acts perpendicular to both the spin axis and precession axis.
Gyroscopic effect – It is the tendency of a rapidly spinning object to maintain the direction of its axis of rotation, resisting changes in orientation because of the angular momentum. When an external force attempts to change this axis, the object precesses, moving perpendicular to the applied force, generating reactive torques.
Gyroscopic inertia – It is frequently called gyroscopic stiffness or ‘rigidity in space’. It is the tendency of a rapidly spinning object (gyroscope) to resist changes in its axis of rotation. It is a property derived from angular momentum, keeping the axis pointed in a fixed direction relative to space despite external torques.
Gyroscopic load – It is an inertial torque (couple) generated when a rapidly spinning mass changes its axis of rotation. As a vector quantity, this moment acts perpendicular to both the spin axis and the precession axis (the direction of change), frequently leading to unexpected stabilization or twisting motions in engineering systems.
Gyroscopic torque – It is a reactive turning moment produced by a spinning object when its axis of rotation is forced to change direction. Based on the conservation of angular momentum, this torque resists changes in the axis’s orientation and acts perpendicularly to both the spin axis and the axis of precession.
Gyrotron – It is a high-power vacuum tube oscillator which can produce micro-wave frequencies up to hundreds of giga-hertz at power levels up to mega-watts.
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