Glossary of technical terms for the use of metallurgical engineers Terms starting with alphabet ‘A’
Glossary of technical terms for the use of metallurgical engineers
Terms starting with alphabet ‘A’
A15 superconductors – The term A15 refers to a cubic crystal type in the Strukturbericht System represented by the example Cr3Si. The intermetallic A3B compound is formed by a body-centered cubic (bcc) arrangement of B atoms with two A atoms centered in every face yielding orthogonal chain structures running through the crystal. Of 76 known A15 compounds, 46 are known to be superconducting. The A atoms are from the groups IVA, VA, and VIA transition metals, whereas the B atoms are from groups IIIB, IVB, and VB and some transition metals including osmium, iridium, platinum, gold, and technetium.
Accm – In hyper-eutectoid steel, it is the temperature at which the solution of cementite in austenite is complete during heating.
Ac1 – It is the temperature at which austenite begins to form during heating.
Ac3 – It is the temperature at which transformation of ferrite to austenite is complete during heating.
Ac4 – It is the temperature at which austenite transforms to delta-ferrite during heating.
Ae1, Ae3, Aecm, and Ae4 – These are the temperatures of phase changes at equilibrium.
Arcm – In hyper-eutectoid steel, it is the temperature at which precipitation of cementite begins during cooling.
Ar1 – It is the temperature at which transformation of austenite to ferrite or to ferrite plus cementite is complete during cooling.
Ar3 – It is the temperature at which austenite begins to transform to ferrite during cooling.
Ar4 – It is the temperature at which delta-ferrite transforms to austenite during cooling.
AARH -it means arithmetical average roughness height’.
A-basis – It is the mechanical property value above which at least 99 % of the population of values is expected to fall, with a confidence of 95 %. It is also called A-allowable.
Aberration – It is an error which causes image degradation. Such an error can be chromatic, spherical, astigmatic, or comatic and can result from design, execution, or both.
Abnormal operation – It is that operation which is not the normal operation.
Abnormal grain growth – Abnormal or discontinuous grain growth, also referred to as exaggerated or secondary recrystallization grain growth, is a grain growth phenomenon in which certain energetically favourable grains (crystallites) grow rapidly in a matrix of finer grains, resulting in a bimodal grain-size distribution. In ceramic mterials, this phenomenon can result in the formation of elongated prismatic, acicular (needle-like) grains in a densified matrix. This microstructure has the potential to improve fracture toughness by impeding the propagation of cracks. Abnormal grain growth is encountered in metallic or ceramic systems showing one or more of several characteristics such as (i) systems with secondary phase inclusions, precipitates or impurities above a certain threshold concentration, (ii) systems with a highly anisotropic surface energy, and (iii) systems far from chemical equilibrium. Abnormal grain growth occurs because of very high local rates of interface migration and is enhanced by the localized formation of liquid at grain boundaries.
Abrasion – It is (i) a process in which hard particles or protuberances are forced against and moved along a solid surface, (ii) a roughening or scratching of a surface because of abrasive wear, or (iii) the process of grinding or wearing away a surface through the use of abrasives.
Abrasion fluid – It means of flushing abrasion debris from the abrasion track.
Abrasion process – It is an abrasive machining procedure in which the surface of the work-piece is rubbed against a two-dimensional array of abrasive particles under approximately constant load.
Abrasion resistance – Abrasion resistance can be defined as the ability of a surface to resist being worn away by rubbing or friction. It is the strength which the materials have against external actions that cause cracks or damage. It is a complex function of tear strength, coefficient of friction, resilience, heat dissipation, and other properties, and comparative values depend on the type of test. In case of galvanized steels, it is the ability of the galvanized coating to resist damage caused by contact with hard, rough, or coarse media or objects.
Abrasion resistant steels – These are alloy steels suitable for applications where resistance to wear is a critical demand. Examples of such applications can include (i) resistance to hard particles grinding under a surface sliding over the top of the steel surface, (ii) resistance to impact from rocks and other hard and heavy materials, and (iii) resistance to high velocity abrasive dust and other particles. Boron, manganese, nickel, and chromium are the alloying elements used to make the steel it wear-resistant.
Abrasive – It is a hard substance used for grinding, honing, lapping, superfinishing, polishing, pressure blasting, or barrel finishing. Abrasives in common use are alumina, silicon carbide, boron carbide, diamond, cubic boron nitride, garnet, and quartz. Abrasives are also hard particles, such as rocks, sand, or fragments of certain hard metals, which wear away a surface when they move across it under pressure.
Abrasive blasting – It is a process for cleaning or finishing by means of an abrasive directed at high velocity against the work-piece. It removes residue and contaminants from the surface of the work-piece. Abrasive blasting methods include grit blasting, sand blasting, and shot blasting.
Abrasive disk – It is (i) a grinding wheel which is mounted on a steel plate, with the exposed flat side being used for grinding, or (ii) a disk-shaped, coated abrasive product.
Abrasive erosion – It is the erosive wear caused by the relative motion of solid particles which are entrained in a fluid, moving nearly parallel to a solid surface.
Abrasive flow machining -It is the removal of material by a viscous abrasive media flowing under pressure through or across a work-piece.
Abrasive jet machining – It is the material removal from a work-piece by impingement of fine abrasive particles which are entrained in a focused, high-velocity gas stream.
Abrasive machining – It is a machining process in which the points of abrasive particles are used as machining tools. Grinding is a typical abrasive machining process.
Abrasive waterjet cutting – This cutting process operates by the impingement of a high-velocity abrasive-laden fluid jet against the work-piece, yet it produces no heat (and hence no heat affected zone) to degrade metals or other materials. The finished edge got by the process frequently eliminates the need for post machining for improving the surface finish.
Abrasive wear – It is the removal of material from a surface when hard particles slide or roll across the surface under pressure. The particles can be loose or can be part of another surface in contact with the surface being abraded.
Abrasive wear testing – The general elements of all laboratory wear tests are simulation, acceleration, specimen preparation, test control, wear measurement, and data reporting. Simulation is the most important element of the wear test since it ensures that the behaviour experienced in the laboratory test is the same as in the application. The ideal wear test exactly duplicates the wear situation, but in majority of the cases only an actual field test of the component accomplishes that. It is important, at the very least, that the laboratory wear test generates the same wear mechanisms as the application and that the primary wear mechanism in the application is the primary one in the laboratory test. Other factors of attention include test geometry, load range, surface conformity, break-in, and so on. Acceleration of the wear test is important since it reduces the overall time and cost of the testing effort. Accelerating the wear test, however, can influence or change the material response. For example, if the load or the speed of the test is increased, one wear mechanism can be emphasized more than another or the wear regime can pass from mild to severe. Even so, all laboratory wear tests are accelerated to one degree or another, either through continuous operation, measurement of smaller quantities of wear, or by applying higher loads, speeds, or temperatures. Attention to sample preparation and test control are important in laboratory wear testing since they determine the degree of scatter in the data (i.e., they either improve or degrade precision and reproducibility). In any test method, it is important to reduce as much as possible the number of factors which can influence the result of that test. Ideally, the wear test is to reflect differences in the material and not differences in the operation of the test. Sample preparation is critical.
Abrasive wheel – It is a grinding wheel composed of an abrasive grit and a bonding agent.
Abrasivity – It is the extent to which a surface, particle, or collection of particles tend to cause abrasive wear when forced against a solid surface under relative motion and under prescribed conditions.
Absolute instruments – These instruments are also known as primary instruments. These instruments are those instruments which give the value of electrical quantity to be measured in terms of the constants of the instruments and their deflection only e.g. tangent galvanometer. These instruments are rarely used except in standard laboratories, especially for calibration of secondary instruments.
Absolute pressure – Absolute pressure is a pressure that is relative to the zero pressure in the empty, air-free space of the universe. This reference pressure is the ideal or absolute vacuum. Absolute pressure uses absolute zero as its zero point, while gauge pressure uses atmospheric pressure as its zero point. Because of the varying atmospheric pressure, gauge pressure measurement is not precise, while absolute pressure is always definite.
Absorbance – It is the logarithm to the base 10 of the reciprocal of the transmittance. The preferred term for photography is optical density.
Absorbency– In ceramics, it is the ability of a material to soak up water.
Absorption – It is a process in which fluid molecules are taken up by a liquid or solid and distributed throughout the body of that liquid or solid. In extractive metallurgy, absorption is the process leading to extraction where analytes are partitioned from their matrix into a liquid.
Absorbed dose – It is the quantity of energy imparted by ionizing radiation to unit mass of matter such as tissue. The unit gray with the symbol Gy. 1 Gy is equal to 1 joule per kilogram. In terms of an effective dose, the Sievert is used.
Absorption spectroscopy – It is the branch of spectroscopy treating the theory, interpretation, and application of spectra originating in the absorption of electro-magnetic radiation by atoms, ions, radicals, and molecules.
Absorptivity – It is a measure of radiant energy from an incident beam as it traverses an absorbing medium, equal to the absorbance of the medium divided by the product of the concentration of the substance and the sample path length.
Abutment – In furnace construction, the structural member which withstands the thrust of an arch. In general, an abutment consists of a brick skew-back and a steel supporting member.
Accelerated aging – It is a process by which the effects of aging are accelerated under extreme and / or cycling temperature and humidity conditions. The process is meant to duplicate long-time environmental conditions in a relatively short space of time.
Accelerated cooling – Accelerated cooling is a controlled-cooling cycle (water cooling to a temperature of around 540 deg C to 600 deg C, followed by air cooling) immediately after the final rolling operation in a plate rolling mill. Accelerated cooling after either controlled rolling or controlled-finishing temperature rolling leads to additional structural refinement and, hence, an improved combination of properties. Accelerated cooling can improve properties of plates in the approximate thickness range of 12 mm through 100 mm.
Accelerated corrosion test – It is a method designed to approximate, in a short time, the deteriorating effect under normal long-term service conditions.
Accelerating admixtures – The addition of these admixtures, such as calcium chloride, to concrete accelerates its early strength development. The results of such additions are reduced times required for curing and protection of the concrete and the earlier removal of forms. However, because of corrosion problems, calcium chloride may not be added to concretes with embedded aluminum, concretes cast against stay-in-place galvanized steel forms, or pre-stressed concretes. Other accelerating admixtures that may be used include various soluble salts as well as some other organic compounds.
Accepted reference value – It is a value which serves as an agreed-on reference for comparison and which is derived as (i) a theoretical or established value, based on scientific principles, (ii) an assigned value, based on experimental work of some national or international standards organization, or (iii) a consensus value, based on collaborative experimental work under the auspices of a scientific or engineering group. When the accepted reference value is the theoretical value, it is sometimes referred to as the ‘true’ value.
Access tower – It is the tower made of steel with platforms at various levels so that easy access can be made to various levels of the blast furnace. The tower is normally free standing.
Accident – Accident is an unplanned event which results in harm to the people, damage to the property or loss to the process. It is an unintended event which includes operating errors, equipment failures and other mishaps, the consequences or potential consequences of which are not negligible from the point of view of protection and safety.
Accident conditions – These conditions are deviations from normal operation which are less frequent and more severe than anticipated operational occurrences. Accident conditions comprise design basis accidents and design extension conditions.
Accident causation – It consists of several factors which act together to cause accidents. These include (i) personal factors, (ii) job factors, and (iii) factors related to lack of management control.
Accident investigation – It is the process of systematically gathering and analyzing information about an accident.
Accident management – It is taking of a set of actions during the evolution of a beyond design basis accident. It consists of (i) to prevent the escalation of the event into a severe accident, (ii) to mitigate the consequences of a severe accident, and (iii) to achieve a long term safe stable state. The second aspect of accident management (to mitigate the consequences of a severe accident) is also termed severe accident management.
Accident prevention – It is the systematic application of recognized principles to reduce incidents, accidents, or the accident potential of a system or organization.
ACOP – It is ‘Approved Code of Practice’.
Accreditation – Accreditation is the process by which a facility becomes officially certified as providing services of a specified good quality so that the public can trust the quality of its service.
Accreditation of testing laboratories – Laboratory accreditation is a formal recognition earned by organizations proving they are qualified, competent, and comply with international standards. Laboratories of all kinds can become accredited, including calibration laboratories, material testing laboratories, environmental testing laboratories, and much more.
Accumulator – Accumulators are like an electrical storage battery. A hydraulic accumulator stores potential power, in this case hydraulic fluid under pressure for future conversion into useful work. This work can include operating cylinders and fluid motors, maintaining the required system pressure in case of pump or power failure, and compensating for pressure loss due to leakage. Accumulators can be employed as fluid dispensers and fluid barriers and can provide a shock absorbing (cushioning) action. Accumulators can be spring loaded, bag type or piston type.
Accuracy – It is (i) the agreement or correspondence between an experimentally determined value and an accepted reference value for the material undergoing testing. The reference value can be established by an accepted standard, or, in some cases, the average value got by applying the test method to all the sampling units in a lot or batch of the material can be used, (ii) the extent to which the result of a calculation or the reading of an instrument approaches the true value of the calculated or measure quantity.
Accuracy and precision – Accuracy is the degree of uniformity of the observations around a desired value. Precision is the degree of variability of the observations.
Accuracy of measurement – The closeness of the agreement between the result of a measurement and a true value of the measurands. However, it is to be noted that the accuracy is a qualitative concept. The term precision is not to be used for accuracy. Precision only implies repeatability.
Acetic acid – Acetic acid, systematically named ethanoic acid, is an acidic, colourless liquid and organic compound with the chemical formula CH3COOH. It is the second simplest carboxylic acid (after formic acid). It is an important chemical reagent and industrial chemical across various fields.
Acetylene – Acetylene is the chemical compound with the formula C2H2. It is an unsaturated hydrocarbon and the simplest of alkynes. An acetylene molecule is composed of two carbon atoms and two hydrogen atoms. The two carbon atoms are held together by what is known as a triple carbon bond. Acetylene is a gas used for oxy-acetylene gas cutting and welding and also in flame cutting machines of continuous casting machines. It is sometimes used for carburization of steel, flame heating, flame gouging, flame hardening, flame cleaning, flame straightening, thermal spraying, spot-heating, brazing, texturing and profile-cutting, and carbon coating.
Achromatic – It means free of colour. A lens or objective is achromatic when corrected longitudinal chromatic aberration for two colours.
Acicular ferrite – It is a highly sub-structured non-equiaxed ferrite formed upon continuous cooling by a mixed diffusion and shear mode of transformation which begins at a temperature slightly higher than the transformation temperature range for upper bainite. It is distinguished from bainite in that it has a limited quantity of carbon available, hence, there is only a small quantity of carbide present.
Acicular ferrite steels – These are ultra-low carbon (less than 0.08 %) steels having a micro-structure consisting of either acicular ferrite or a mixture of acicular ferrite and equiaxed ferrite.
Acid – It is a chemical substance which yields hydrogen ions (H+) when dissolved in water. It is also a term applied to slags, refractories, and minerals containing a high percentage of silica.
Acidity – It is the degree to which a material is acid. Furnace refractories are ranked by their acidity.
Acid base reaction – It is the reaction involving the transfer of a hydrogen ion between reactant species. Base is a substance which at produces OH− when dissolved in water. When an acid combines with a base, it leads to the formation of the corresponding salt and water. This reaction is known as an acid-base reaction. In chemistry, an acid–base reaction is a chemical reaction which occurs between an acid and a base. It can be used to determine pH through titration. Several theoretical frameworks provide alternative conceptions of the reaction mechanisms and their application in solving related problems; these are called the acid–base theories.
Acid cleaning – It is a process in which a solution of mineral acid, organic acid, or acid salt, in combination with a wetting agent and detergent, is used to remove oxide, shop soil, oil, grease, and other contaminants from metal surfaces, with or without the use of heat.
Acid embrittlement – It is a form of hydrogen embrittlement which can be induced in some metals by acid.
Acid extraction – It is removal of phases by dissolution of the matrix metal in an acid.
Acidic environment – An acidic environment refers to an immediate area or enclosure with a pH reading which is below 7. The lower the pH, the more acidic a solution is, which also means a higher hydrogen ion concentration and corrosion rate.
Acidic rocks – These are igneous rock carrying a high (higher than 65 %) proportion of silica.
Acidic water – An acidic water is one which has a pH value of less than 7. The acidity of several raw waters is below 7 because of the natural constituents, such as dissolved carbon dioxide or organic acids derived from peat or soil humus.
Acid pickling – It is carried out with normally sulphuric acid, or hydrochloric acid for the removal of rust and mill scale from the steel surface.
Acid process – It is a steelmaking method using an acid refractory-lined furnace. In this process neither sulphur nor phosphorus is removed.
Acid rain – It is atmospheric precipitation with a pH below 5.6 to 5.7. Burning of fossil fuels for heat and power is the major factor in the generation of oxides of nitrogen and sulphur, which are converted into nitric and sulphuric acids washed down in the rain.
Acid refractory – It consists of siliceous ceramic materials of a high melting temperature, such as silica brick, used for metallurgical furnace linings.
Acid steel – It is the steel made by an acid process.
Acoustic emissions – These are stress waves produced by sudden movement in stressed materials. The classic sources of acoustic emissions are defect-related deformation processes such as crack growth and plastic deformation. Sudden movement at the source produces a stress wave, which radiates out into the structure and excites a sensitive piezoelectric transducer. As the stress in the material is raised, many of these emissions are generated. The signals from one or more sensors are amplified and measured to produce data for display and interpretation.
Acoustic emission inspection – An acoustic emission inspection is normally carried out during a controlled loading of the structure. This can be a proof load before service, a controlled variation of load while the structure is in service, a fatigue test, a creep test, or a complex loading programme. Frequently, a structure is going to be loaded anyway, and acoustic emission inspection is used since it gives valuable additional information about the performance of the structure under load. Other times, acoustic emission inspection is selected for reasons of economy or safety, and a special loading procedure is arranged to meet the needs of the acoustic emission test.
Acoustical holography – It is the extension of holography into the ultrasonic domain. The principles of acoustical holography are the same as those of optical holography since the laws of interference and diffraction apply to all forms of radiation obeying the wave equation. Differences arise only because the methods for recording and reconstructing the hologram must accommodate the form of radiation used. This need to accommodate the form of radiation restricts the practical range of sound wave frequency which can be used in acoustical holography. At present, only two types of basic systems for acoustical holography are available namely (i) the liquid-surface type, and (ii) the scanning type. These utilize two different detection methods, and these methods in turn dictate the application of the systems to non-destructive inspection. Neither of these two types of systems relies on the interferometric techniques of optical holographic inspection, in which information on flaws at or near the surface of a test object is obtained from the pattern formed by interference between two nearly identical holographic images that are created while the object is differentially stressed. Instead, systems for acoustical holography get information on internal flaws directly from the image of the interior of the object.
Acoustic microscopy – It is the general term applied to high-resolution, high-frequency ultrasonic inspection techniques which produce images of features beneath the surface of a sample. Since ultrasonic energy needs continuity of materials to propagate, internal defects such as voids, inclusions, delaminations, and cracks interfere with the transmission and / or reflection of ultrasound signals. Compared to conventional ultrasound imaging techniques, which operate in the 1 MHz to 10 MHz frequency range, acoustic microscopes operate up to and beyond 1 GHz, where the wavelength is very short and the resolution correspondingly high. Acoustic microscopy is recognized as a valuable tool for nondestructive inspection and materials characterization. Acoustic microscopy comprises three different methods namely (i) scanning laser acoustic microscopy, (ii) C-mode scanning acoustic microscopy, and (iii) scanning acoustic microscopy. Each of these methods has a specific range of utility, and most frequently the methods are noncompetitive with regard to applications. That is, only one method will be best suited to a particular inspection problem.
Actinides / Actinoids – These are a group of 15 elements with atomic number from that of actinium (89) to lawrencium (103) inclusive. All are radioactive. Group includes Uranium, Plutonium, Americium, and Curium. Actinides are elements with partial occupation of the 5f electron shell. Lawrencium is strictly a transition metal (d-block element) but conventionally included in the actinide grouping. Elements heavier than Uranium are collectively termed Trans-uranics.
Activated sludge process – The activated sludge process is a type of biological wastewater treatment process for treating sewage or industrial wastewaters using aeration and a biological floc composed of bacteria and protozoa. It is one of several biological wastewater treatment alternatives in secondary treatment, which deals with the removal of biodegradable organic matter and suspended solids. It uses air (or oxygen) and microorganisms to biologically oxidize organic pollutants, producing a waste sludge (or floc) containing the oxidized material. The activated sludge process is a multi-chamber reactor unit which uses highly concentrated micro-organisms to degrade organics and remove nutrients from wastewater, producing quality effluent.
Activation – It is (i) the changing of a passive surface of a metal to a chemically active state, or (ii) the (normally) chemical process of making a surface more receptive to bonding with a coating or an encapsulating material. This term also refers to the process of creating a radioisotope. This is achieved when a stable element is bombarded with either neutrons or protons.
Active metal – It is a metal ready to corrode or being corroded.
Active zone – In the blast furnace ironmaking, the active coke zone is bounded by the cohesive zone, raceway, and deadman. It consists of loosely packed coke feeding the raceway or moves towards the deadman zone.
Activation analysis – It is a method of chemical analysis based on the detection of characteristic radionuclides following nuclear bombardment.
Activation enthalpy – It is defined as the minimum amount of extra energy needed by a reacting molecule to get converted into product. It is the energy needed for the reaction.
Activation entropy – The standard entropy of activation equals the change in entropy when the reactants change from their initial state to the activated complex or transition state.
Actual contact area – In tribology, it is the total area of contact formed by summing the localized asperity contact areas within the apparent area of contact.
Actuator – An actuator is a part of a device or machine which helps it to achieve physical movements by converting energy, frequently electrical, air, or hydraulic, into mechanical force. It is a component of a machine which produces force, torque, or displacement, normally in a controlled way, when an electrical, pneumatic or hydraulic input is supplied to it in a system. An actuator converts such an input signal into the required form of mechanical energy. It is a type of transducer.
Actuator device – It is used to operate a valve using electric, pneumatic or hydraulic means. It is frequently used for remote control or sequencing of valve operations.
Actuator lever – It is the arm attached to rotary valve shaft to convert linear actuator stem motion to rotary force (torque) to position a disk or ball of a rotary valve. The lever normally is positively connected to the rotary by close tolerance splines or other means to minimize play and lost motion.
Actuator spring – It is a spring, or a group of springs, enclosed in the yoke or actuator casing or piston cylinder which moves the actuator stem in a direction opposite to that created by loading pressure. Actuator stem – It is that part which connects the actuator to the valve stem and transmits motion (force) from the actuator to the valve.Actuator stem extension – It is an extension of the piston actuator stem to provide a means of transmitting piston motion to the valve positioner.
Actuator stem force – It is the net force from an actuator which is available for actual positioning of the valve plug, referred to as valve travel.
Adamite – Adamite is a type of hypereutectoid steel, which means it has a high carbon content, typically ranging from 1.35 % to 2.5 %, along with alloying elements such as nickel, chromium, and molybdenum. These elements contribute to the material’s improved wear resistance, strength, and hardness, which normally falls between 40 degrees Shore to 55 degrees Shore. The microstructure of adamite steel is mainly pearlitic with uniformly distributed cementite precipitations, which can be optimized through proper heat treatment to improve tribological properties under varying loads.
Adamite rolls – The adamite rolls has better strength and toughness than cast iron roll. They are widely used for work rolls in hot rolling mills. The adamite rolls are statically cast and go through a multi-stage heat treatment process followed by Tempering phases in order to develop the combination of hardness, toughness and wear resistance. The adamite roll materials can be considered as composite materials of two phases of coarse carbides and matrix. As a consequence, the hardness of these roll materials can be markedly affected by the quantity and hardness of coarse carbides. The carbon content of the alloy adamite roll is usually between 1.2 % to 2.3 % and the rest alloy elements contain chromium, nickel, molybdenum, and vanadium etc. The free carbide mass fraction is normally around 6 % to 10 % with small hardness drop, good wear resistance, good toughness, significantly reduced consumption.
Additive – It is a material added in small quantities to a solution to modify its characteristics, such as, additives can be added to a plating solution for modifying the character of the deposit. In lubrication, it is a material added to a lubricant for the purpose of imparting new properties or of improving existing properties. Main classes of additives include anti-corrosive, anti-foam, anti-oxidant, anti-wear, detergent, dispersant, extreme-pressure lubricant, and viscosity index improver additives. In blast furnace ironmaking, additives are miscellaneous materials like manganese ore, quartzite, and titani-ferrous iron ore etc. which are charged in blast furnace for the adjustment of the chemical analyses of hot metal and slag.
Adherence – In tribology, it is the physical attachment of material to a surface (either by adhesion or by other means of attachment) which results from the contact of two solid surfaces undergoing relative motion. However, it is to be noted that the adhesive bonding is not a requirement for adherence since mechanisms such as mechanical interlocking of asperities can also provide a means for adherence.
Adhesion – It is the attractive force which exists between a deposit and its substrate that can be measured as the force needed to separate a deposit and its substrate.
Adhesion promoter – It is a coating applied to a substrate, before it is coated with an adhesive, to improve the adhesion of the substrate.
Adhesion testing – There are several different techniques and test methods which have been devised for measuring the adhesion between solids. There is little standardization in this field, although some investigators tend to favour one method over another. Majority of adhesion test methods are designed to assess the ability of two materials to remain connected to one another despite the application of external or internal body forces in different directions with respect to the interface. For example, different types of adhesion tests have been designed to measure resistance to peeling, shearing, and delamination. In a few instances, adhesion tests are used in the study of frictional phenomena which occur at a fine scale between protuberances on mating surfaces. Friction and wear tests are important. These tests are not basic properties of materials but rather represent the response of a material pair in a certain environment to imposed forces, which tend to produce relative motion between the paired materials. Friction and wear behaviour is, hence, subject to the considerations of testing geometry, the characteristics of the relative motion, the contact pressure between the surfaces, the temperature, the stiffness and vibrational properties of the supporting structures, the presence or absence of third bodies, the duration of contact, and the chemistry of the environment in and around the interface
Adhesive – It is a substance capable of holding materials together by surface attachment. Adhesive is a general term and includes, among others, cement, glue, mucilage, and paste. These terms are loosely used inter-changeably. Different descriptive adjectives are applied to the term adhesive for indicating certain physical characteristics such as hot-melt adhesives, pressure-sensitive adhesives, structural adhesives, ultraviolet / electron-beam cured adhesives, and water-based adhesives.
Adhesive bond – It is the attractive forces, normally physical in character, between an adhesive and the base materials. Two principal interactions which contribute to the adhesion are van der Waals bonds and dipole bonds.
Adhesive bonding – It is a materials joining process in which an adhesive is placed between the faying surfaces. The adhesive solidifies to produce an adhesive bond.
Adhesive film – It is a synthetic resin adhesive, with or without a film carrier fabric, normally of the thermo-setting type, in the form of a thin film of resin, used under heat and pressure as an interleaf in the production of bonded structures.
Adhesive strength – It is the strength of the bond between an adhesive and an adherend.
Adhesive wear – It is the wear by transference of material from one surface to another during relative motion because of a process of solid-phase welding. Particles which are removed from one surface are either permanently or temporarily attached to the other surface. It is also the wear because of the localized bonding between contacting solid surfaces leading to material transfer between the two surfaces or loss from either surface.
Adiabatic – It is the occurrence without loss or gain of heat in the system, which can result in a local temperature increase or decrease. Adiabatic conditions differ from isothermal conditions (under which the temperature remains constant).
Adiabatic flame temperature – It is the theoretical temperature which is attained by the products of combustion provided the entire chemical energy of the fuel, the sensible heat content of the fuel, and combustion above the datum temperature are transferred to the products of combustion. This assumes no heat loss to the surroundings and no dissociation.
Adjustable armour – It is adjustable throat armour system, used in connection with the bell type top charging equipment to control and vary the burden distribution so that optimum permeability in the BF stack can be achieved.
Admixtures – These are materials added to concrete during or before mixing are referred to as admixtures. They are used to improve the performance of concrete in certain situations as well as to lower its cost.
Adsorbent – It is a condensed phase at the surface of which adsorption can occur.
Adsorption – It is the adhesion of the molecules of gases, dissolved substances, or liquids to the surfaces of solids or liquids with which they are in contact. It is also increase in the concentration of a dissolved substance at the interface of a condensed phase because of the operation of surface forces. Adsorption can also occur at the interface of a condensed and a gaseous phase.
Adsorption chromatography – It is the chromatography based on differing degrees of adsorption of sample compounds onto a polar stationary phase.
Advanced high strength steels – These are basically steels for auto body with very high strength to weight ratio. Their mechanical properties evolve from their unique processing and structure. Advanced high strength steels have three generations. The first generation has more formability than high strength low alloy steels at the same strength level. These steels typically have a martensitic micro-structure, sometimes with one or more additional phases to improve formability. Dual phase steel, complex phase steels, transformation induced plasticity steels, and martensitic steels (both roll formed and press hardened) are the first-generation advanced high strength steels. The formability of second generation advanced high strength steels is significantly higher than first generation advanced high strength steels at a tensile strength of 980 MPa. The difference in second generation advanced high strength steels is its austenitic microstructure which is the key to the transformation induced plasticity effect. When austenite is deformed, it transforms into martensite and hence gets stronger. Austenitic stainless steels, and twinning induced plasticity steels are the second-generation advanced high strength steels. Current applications of second generation AHSS in the automotive industry is still limited though they have very high formability and strength. This can be attributed to two main factors namely (i) high alloying elements increase the cost of steel, and (ii) the steels have a tendency for delayed cracking fracture after the automobile part is formed and stored. Advanced high strength steels of first generation have very limited formability. Advanced high strength steels of second generation though have high strength but are expensive because of their high cost alloying elements. Hence there is a requirement of a new generation of steel at reasonable cost which has high strength and high formability. Several third-generation steels have been developed recently but only two types of these steels are under production currently. These are ‘quenching and partitioning steel and TRIP (transformation induced plasticity) aided bainitic ferrite steel. Another type of third generation AHSS which is still under development is Nano steel. This steel is not yet commercialized. This steel has a nano crystalline structure created by special chemistry and heat treatment.
Aerated bath nitriding – It is a type of liquid nitriding in which air is pumped through the molten bath creating agitation and increased chemical activity.
Aeration – It is (i) exposing to the action of air, (ii) causing air to bubble through, (iii) introducing air into a solution by spraying, stirring, or a similar method, or (iv) supplying or infusing with air, as in sand or soil.
Aerial crane – This crane is sometimes called sky crane. It is helicopter designed to lift large loads. Helicopter is able to travel to and lift in areas which are difficult to reach by conventional crane. Aerial crane is normally used to lift units / loads onto shopping centres and high rise structures. This crane can lift anything within their lifting capacity. It is being used for the erection of transmission towers in difficult terrains. It also performs disaster relief after natural disasters for clean up, and during wild-fires it is able to carry huge buckets of water to extinguish fires.
Aerobic process – Aerobic treatment of wastewater is a biological process that uses oxygen to break down organic contaminants and other pollutants like nitrogen and phosphorous. Oxygen is continuously mixed into the wastewater or sewage by a mechanical aeration device, such as an air blower or compressor.
After contraction/after expansion – The percentage permanent contraction or expansion, measured after cooling, which takes place when a refractory material is heated for a specified period and temperature. It is also known, when measure linearly, as the permanent linear change (PLC) on reheating.
After damp – These are gasses resulting from underground combustion, normally carbon monoxide. This is a loose term implying any fatal gas in a mine after an explosion or fire.
After heat – It is the heat produced by the decay of radioactive materials in a reactor which has been shut down.
Age hardening – It is the hardening by aging (heat treatment) normally after rapid cooling or cold working. In case of grease, it is the increasing consistency of a lubricating grease with time of storage.
Age hardening steel – It is a steel containing sufficient carbon and other alloying elements to harden fully during cooling in air or other gaseous mediums from a temperature above its transformation range. The term is to be restricted to steels which are capable of being hardened by cooling in air in fairly large
sections, around 50 millimeter (mm) or more in diameter.
Age softening – It is the spontaneous decrease of strength and hardness which takes place at room temperature in certain strain hardened alloys, especially those of aluminum or containing magnesium.
Ageing – In heat treatment, it is a change in the properties of certain metals and alloys which occurs at ambient or moderately high temperatures after hot working or a heat treatment (quench aging in ferrous alloys, natural or artificial aging in ferrous and non-ferrous alloys) or after cold working operation (strain aging). The change in properties is frequently, but not always, because of a phase change (precipitation), but never involves a change in chemical composition of the metal or alloy.
Agglomerate – It is the clustering together of a few or several particles, whiskers, or fibres, or a combination thereof, into a larger solid mass.
Aggregate – It is building and construction, material used for mixing with cement, bitumen, lime, gypsum, or other adhesive to form concrete or mortar. The aggregate gives volume, stability, resistance to wear or erosion, and other desired physical properties to the finished product. Commonly used aggregates include sand, crushed or broken stone, gravel (pebbles), broken blast-furnace slag, boiler ashes (clinkers), burned shale, and burned clay. Fine aggregate usually consists of sand, crushed stone, or crushed slag screenings; coarse aggregate consists of gravel (pebbles), fragments of broken stone, slag, and other coarse substances. Fine aggregate is used in making thin concrete slabs or other structural members and where a smooth surface is desired; coarse aggregate is used for more massive members.
Aggregate moulding materials – These materials consist of different materials used to produce moulds and cores for sand casting. These materials include sands, clays, additions to sand mixes, and plastics. Suitability of a moulding material depends upon the type of material being poured, number of castings being made, the type of casting, quality requirement by the customer and finally on the mould and core making equipment owned by the foundry.
Aggressive environment – It is an environment which is particularly corrosive.
Agitation – In hydrometallurgical plants, agitation is necessary for suspending solids, solid / liquid contacting, dispersing gaseous phases, creating interfacial area in solvent extraction systems, increasing heat transfer and achieving homogeneity. Agitation is vital in chemical reactions because of (i) improved contact between reactants for improved efficiency, (ii) increased collision frequency and decreased diffusion barriers to improve reaction kinetics, (iii) creating a homogenous combination to avoid adverse effects and guarantee reliable results,(iv) effective heat transfer, which promotes temperature regulation and avoids regional hot or cold regions, (v) for ensuring maximum participation, preventing settling and maintaining solid particles in suspension, and (vi) consistent reactant mixing is necessary for industrial processes and quality control. Chemical process efficiency, yield, and control are all improved by agitation.
Air – It is the mixture of oxygen, nitrogen, and other gases, which with varying quantities of water vapour, forms the atmosphere of the earth.
Air atomizing oil burner – It is a burner for firing oil in which the oil is atomized by compressed air, which is forced into and through one or more streams of oil which results in the breaking of the oil into a fine spray.
Air bend die – It is an angle-forming die in which the metal is formed without striking the bottom of the die. Metal contact is made at only three points in the cross section: the nose of the male die and the two edges of a V-shape die opening.
Air bending – It is the process of bending in an air bend die .
Air blast – It is the air which is blown in a blast furnace. For generating the blast air, blast furnaces are equipped with centrifugal turbo blowers or axial blower. Air blast is normally enriched with oxygen. Moisture is added in the cold air blast when it is needed for blast moisture control. Before the air blast is delivered to the blast furnace tuyeres, it is preheated by passing it through regenerative hot blast stoves which are normally heated by combustion of the blast furnace top gas.
Air blower – It is an electromechanical device which uses an electric motor, impeller, and airfoils to effectively and efficiently improve airflow through ducting, chassis, or processes in a work-space. It is designed to be a permanent addition to a work-space, increasing airflow for exhausting, ventilating, and cooling. It can also be used for aspirating, conveying, or removing pollutants, dust, dirt, and particle matter. It is meant to produce higher pressure than a fan, putting them midway between a fan and a compressor. It can be centrifugal, axial, or positive displacement. Centrifugal blower has a gear system and one or more stage construction. Axial blower comes with blades linked to the central shaft, whereas positive displacement blower has rotor geometry.
Air carbon arc cutting – It is an arc cutting process which melts base metals by the heat of a carbon arc and removes the molten metal by a blast of air.
Air classification – It is the separation of a powder into particle size ranges by means of an air stream of controlled velocity.
Air compressor – It takes ambient air from the surroundings and discharges it at a higher pressure. It is an application of a gas compressor and a pneumatic device which converts mechanical power into potential energy stored in compressed air, which has several uses. Compressors are (i) low-pressure air compressors, which have a discharge pressure of 1 MPa or less, (ii) medium-pressure compressors which have a discharge pressure of 1 MPa to 7 MPa, and (iii) high-pressure air compressors, which have a discharge pressure above 7 MPa.
Air cooled slag – Air cooled slag is that slag which is produced when the liquid slag is poured into beds and slowly cooled under ambient conditions. Air cooling produces a hard, lump slag, which is subsequently crushed and screened. Air cooled slag has a crystalline structure.
Air deficiency – It is the condition of insufficient air, in an air-fuel mixture, for supplying the oxygen needed for complete combustion (oxidation) of the fuel.
Air drying – It refers to the air drying of a core or mould without the application of heat.
Air-entraining admixtures – These are used primarily to increase concrete’s resistance to freezing and thawing and provide better resistance to the deteriorating action of chemicals and salts. The air-entraining agents cause the mixing water to foam, with the result that billions of closely spaced air bubbles are incorporated into the concrete.
Air feed – It is a thermal spraying process variation in which an air stream carries the powdered material to be sprayed through the gun and into the heat source.
Air-free – It is the descriptive characteristic of a substance from which air has been removed.
Air friction damping – In case of air friction damping, the piston is mechanically connected to a spindle through the connecting rod. The pointer which is fixed to the spindle moves over a calibrated dial. When the pointer oscillates in clockwise direction, the piston goes inside and the cylinder gets compressed. The air pushes the piston upwards and the pointer tends to move in anti-clockwise direction. If the pointer oscillates in anti-clockwise direction the piston moves away and the pressure of the air inside cylinder gets reduced. The external pressure is more than that of the internal pressure. Hence, the piston moves downwards. The pointer tends to move in clock wise direction.
Air-fuel ratio – It is the ratio of the weight, or volume, of air to fuel.
Air gap – In extrusion coating, it is the distance from the die opening to the nip formed by the pressure roll and the chill roll.
Air-infiltration – It is the leakage of air into a setting or duct.
Air hardening steel – It is a steel containing sufficient carbon and other alloying elements to harden fully during cooling in air or other gaseous mediums from a temperature above its transformation range. The term is to be restricted to steels which are capable of being hardened by cooling in air in fairly large sections, around 50 mm or more in diameter. Such steels attain their martensitic structure without going through the quenching process. Additions of chromium, nickel, manganese, and Mo are effective toward this end.
Air jet – An air jet refers to a stream of air that can be classified based on its characteristics and diffuser type, such as compact, linear, radial, conical, incomplete radial, or swirling.
Air lift hammer – It is a type of gravity-drop hammer in which the ram is raised for each stroke by an air cylinder. Since length of stroke can be controlled, ram velocity and hence the energy delivered to the Work-piece can be varied.
Air lock – In galvanizing, it is an area where air is trapped in a fabrication and prevents the molten zinc from contacting the surface of steel, causing an uncoated area on the work piece.
Air mist cooling – Air mist cooling is carried out with nozzles which utilize compressed air in combination with water pressure to atomize cooling water and also offer much larger internal free passage compared to single fluid nozzles of the same flow rate size. Air mist cooling works by forcing water through specially designed mist nozzles. This creates a mist (fog) of ultra fine water droplets with an average size of 25 micrometers (0.025 mm) or less. With high pressure mist cooling, one can get an even smaller droplet size which is as small as 5 micrometers (0.005 mm). This creates a surface area larger than a big field from just one litre of water. Higher surface area helps water to evaporate very quickly. These tiny water droplets (fog) quickly absorb the energy (heat) present in the environment and evaporate, becoming water vapour (gas). The energy (heat) used to change the water-to-water vapour is eliminated from the environment hence cooling the environment.
Air pollutants – Air pollutants are those substances which causes pollution of the atmospheric air. They are those chemical, biological and physical agents which modify the natural characteristics of the atmospheric air. Air pollutants arise both from natural processes (volcanic activities, oceans, and forests etc.) and human activities (fossil fuel combustion, transportation, power plant emissions, or emissions from other industrial processes).
Air pollution – Air pollution is the contamination of the indoor or outdoor air by a range of gasses and solid particles which modify its natural characteristics. It occurs when gases, dust particles, fumes (or smoke) or odour are introduced into the atmosphere in a way which makes it harmful to humans, animals and plants. Air pollution is frequently not visible to the naked eye as the size of the pollutants is smaller than the human eye can detect. They can become visible in some situations for example in the form of sooty smoke, and smog etc.
Air pollution control devices – These are a series of devices which are used to prevent a variety of different pollutants, both gaseous and solid, from entering the atmosphere mainly out of the industrial stacks. These control devices can be separated into two broad categories namely (i) devices which control the quantity of particulate matter escaping into the environment, and (ii) devices which controls the acidic gas emissions into the atmosphere.
Air quenching – Air quenching is accelerated cooling process which uses forced air or inert gas to lower the temperature of heated metal or alloy. It changes the basic structure of the metal or alloy, resulting in a stronger and harder material.
Air ramming – It is a method of forming refractory shapes, furnace hearths, or other furnace parts by means of pneumatic hammers.
Air saturated – It is the air which contains the maximum quantity of water vapour which it can hold at its temperature and pressure.
Air scale – It is the iron oxide scale left on ferrous metal in processing. It formed on steel during hot working processes, when the heated steel is cooled in the presence of air. In the rolling mills it is called mill scale.
Air separation process – It separates atmospheric air into its primary components, typically nitrogen and oxygen, and sometimes also argon and other rare inert gases. The most common method for air separation is fractional distillation. Cryogenic air separation units are built to provide nitrogen or oxygen and frequently co-produce argon. Other methods such as membrane, pressure swing adsorption and vacuum pressure swing adsorption are commercially used to separate a single component from ordinary air. Air separation is also a process for separation of particles into groups of a given size by means of a stream of air or gas (sedimentation and elutriation).
Air setting – It is the characteristic of some materials, such as refractory cements, core pastes, binders, and plastics, to take permanent set at normal air temperatures.
Air setting refractory mortar – It consists of a refractory composition of finely ground containing chemical agents which ensure hardening at room temperature. These are available either dry or wet condition, which however, can need tempering with water for attaining the desired consistency and which is suitable for laying refractory bricks and bonding them strongly upon drying and upon subsequent heating at furnace temperature.
Air slide – It is also called air-activated gravity conveyor. Dry powdered materials, when aerated acquires fluidity and can move along a plane having a slope of only 4 % to 5 %. This principle is adopted in an air slide for short distance movement of powdery materials at a fairly controlled rate. The air slide consists of an inclined covered metallic trough with a longitudinal porous partition in between. Over the partition the material moves. Low-pressure air is allowed to enter from the bottom of the porous partition. The air fluidizes the powdered / pulverized material and makes it flow along the inclined partition due to gravity. Air slides are normally used for controlled movement of materials i.e. as feeders. For their simple design, low costs, low power consumption, high handling capacity combined with small overall dimensions, simple erection and adjustment and absence of moving and wearing parts, they are, in many cases, preferred over screw or vibrating feeders. Materials such as cement, ash, coal dust etc. can be effectively conveyed by air slides.
Air shaft – It is a vertical opening into a mine for the passage of air.
Air vent – It is a small opening through which air can escape from an enclosed space. It is a valved opening in the top of the highest drum of a boiler or pressure vessel for venting air.
Air vent valves – These are also known as automatic air vent or auto vent or air release valves and even mistakenly referred as air relief valves. These valves are normally used in pressurized systems to bleed the air which gets trapped in it because of the emptying of pipes especially after downtime of the hydro-pneumatic / chiller pump.
Airway – It is a passage in a mine along which an air current moves. Some passages are driven solely for air. Other passages, such as a main level, are all purpose, to move air, men, coal, and materials.
ALARA – It means as low as reasonably achievable. It is a term used in radiation protection making every reasonable effort to keep exposure to ionizing radiation as far below the dose limits as practical, consistent with the purpose for which the licensed activity is undertaken, taking into account the state of technology, the economics of improvements in relation to state of technology, the economics of improvements in relation to benefits to the public health and safety, and other societal and socioeconomic considerations, and in relation to utilization of nuclear energy and licensed materials in the public interest. It is a concept from the ICRP (International Commission on Radiological Protection), reflected in the Basic Safety Standards Directive 96/29/Euratom.
Alarm – It is a suitable horn, bell, light, or other device which when operated indicates of the malfunctioning or off normal condition.
ALARP – It means as low as reasonably practicable (social and economic factors taken into consideration). ALARP is the process by which radiological impacts to workers and the public are kept as low as reasonably practicable. This is to ensure that risks are ALARP is a fundamental requirement of the health and safety legislation. The fundamental steps in the ALARP process are (i) define and characterize the problem (ii) generate the potential options to address the problem, (iii) assess the options and their merits, (iv) Identify and justify the best option or options, and (v)implement the selected option In the regulatory bodies including Environment Agency and nuclear regulator equate the concepts of ALARA and ALARP. Where design has an impact on safety and the environment, it can be possible to undertake one integrated assessment which includes the relevant aspects of BAT (best available technology) and ALARP as several of the objectives of BAT and ALARP are consistent.
Alclad – It is composite wrought product comprised of an aluminum alloy core having one or both surfaces a metallurgically bonded aluminum or aluminum alloy coating which is anodic to the core and hence electrochemically protects the core against corrosion.
Alignment – It is a mechanical or electrical adjustment of the components of an optical device so that the path of the radiating beam coincides with the optical axis or other pre-determined path in the system.
Aligned system – It is a classification system which has been aligned with UNFC as demonstrated by the existence of a ‘bridging document, which has been endorsed by the ‘Expert Group on Resource Management’.
Alkalis – Alkalis are the compounds of the metal potassium and metal sodium. Alkalis have negative influences on the blast furnace process.
Alkaline cleaning – It is the cleaning by a material blended from alkali hydroxides and such alkaline salts as borates, carbonates, phosphates, or silicates. The cleaning action can be improved by the addition of surface-active agents and special solvents.
Alkaline earth elements – The alkaline earth elements are six chemical elements. They are beryllium, magnesium, calcium, strontium, barium, and radium. The elements have very similar properties. They are all shiny, silvery-white, somewhat reactive metals at standard temperature and pressure.
Alkaline electrolysis process –Alkaline electrolysis is the most common electrolyzer process. It is the most basic and mature technology and has a market share of around 70 % of the very small green hydrogen present market. It benefits from low cost, and this process has a long operational life. The alkaline electrolyzers consist of an anode and cathode separated by a porous separator (such as Zirfon) immersed in an aqueous alkali hydroxide electrolyte (typically potassium hydroxide, KOH). They show 59 % to 70 % conversion efficiency, and their relatively low cost has led most industrial producers to favour them over other approaches. Alkaline electrolyzers perform poorly with intermittent and fluctuating power sources because of slow start-up and cross-diffusion of hydrogen and oxygen molecules under low system loads. This process applies a solution which needs recirculating of the electrolyte into and out the stack components to separate hydrogen from water molecules by applying electric power. This technology needs constant flow of electric power and hence it is less efficient with variable renewable energy sources. This process is required to run continuously or the production equipment can get damaged.
Alkaline environment – An alkaline environment refers to a soil or medium with a high pH level above 7, which can induce nutrient deficiencies in plants by making certain nutrients inaccessible. Some plants have adaptations to cope with alkaline environments by secreting organic acids to solubilize nutrients.
Alkaline water – It is the water which is slightly basic pH more than 7). It contains basic minerals such as calcium, magnesium bi-carbonate. These compound bind to hydrogen ions in solution, making the water basic.
Alkalinity – It represents the quantities of carbonates, bi-carbonates, hydroxides, and silicates, or phosphates in the water and is reported as ppm as calcium carbonate.
Alkali resistance – It is the resistance of a refractory to chemical deterioration following exposure to an alkali environment.
Alligatoring – It is (i) the pronounced wide cracking over the entire surface of a coating having the appearance of alligator hide, or (ii) the longitudinal splitting of flat slabs in a plane parallel to the rolled surface.
Alligator shear – An alligator shear, historically known as a lever shear and sometimes as a crocodile shear. Itis a metal-cutting shear with a hinged jaw, powered by a flywheel or hydraulic cylinder. Alligator shears are normally set up as stand-alone shears. However, there are types for excavators. The jaw size can range from 100 mm to 910 mm long. They are normally used to cut ferrous members, such as rebar, pipe, angle iron, or I-beams.
Allotropy – It is the property by which certain elements can exist in more than one crystal structure.
Allowable working pressure – It is the pressure used in the design of a boiler for the purpose of calculating the minimum permissible thickness or physical characteristics of the different parts of the boiler.
Allowance – It is the specified difference in limiting sizes (minimum clearance or maximum interference) between mating parts, as computed arithmetically from the specified dimensions and tolerances of each part. In case of a foundry, it is the specified clearance.
Alloy – It is a substance having metallic properties and composed of two or more elements of which at least one is an elemental metal.
Alloy cast iron – Alloy cast irons are the casting alloys which are based on the iron-carbon-silicon system. They contain one or more alloying elements intentionally added to improve one or more properties. In gray and ductile cast irons, small quantities of alloying elements such as chromium, molybdenum, or nickel are added primarily to achieve high strength or to ensure the attainment of a specified minimum strength in heavy sections. Otherwise, alloying elements are used almost exclusively to enhance resistance to abrasive wear or chemical corrosion or to extend service life at elevated temperatures.
Alloy layers – These are the interior layers of the galvanized coating formed when molten zinc reacts with iron in the steel. The hot dip galvanized coating consists of a series of zinc-iron alloy layers which make up typically 80 % of the coating thickness. These alloy layers are coated with a layer of zinc. The zinc-iron alloys are much harder than zinc with excellent abrasion resistance.
Alloy phase diagrams – Alloy phase diagrams are thermodynamic data in graphical form. These diagrams are one of the basic tools of the metallurgist, materials scientist, and materials engineer. They can be used for alloy design, selection of hot-working and fabricating parameters, prediction of performance, guidance in selection of hot-working and fabricating parameters, prediction of performance, guidance in selection of heat-treating process parameters, solving performance problems, including failure analysis, and for several other purposes.
Alloy plating – It is the co-deposition of two or more metallic elements.
Alloy powder, alloyed powder – It is a metal powder consisting of at least two constituents which are partially or completely alloyed with each other.
Alloy steels – The term ‘alloy steel’ is used for those steels which have got in addition to carbon other alloying elements in their composition. Alloy steels are made by combining steels with one or more other alloying elements. There are a large number of alloying elements which can be added to steel. These elements are normally metals like nickel, manganese, tungsten, aluminum, copper, and molybdenum etc. The elements are intentionally added in steel to incorporate certain properties such as mechanical, electrical, thermal, magnetic or corrosion resistance properties which are not found in the plain carbon steels. Total quantity of alloying elements in alloy steels (other than micro-alloyed steels) can vary between 1 % and 50 %. Alloy steels cover a broad range of steels. Alloy steels are normally of three types. They are (i) micro-alloyed steels, (ii) low alloy steels, and (iii) high alloyed steels. Alloy or alloyed steels are defined by the ISO (International Organization for Standardization) specification 4948/1.
Alloy system – It is a complete series of compositions produced by mixing in all proportions any group of two or more components, at least one of which is a metal.
Alloy tool steels – The principal function of the alloying elements in tool steels is (i) to increase the hardenability, (ii) to form hard, wear resistant alloy carbides, and (iii) to increase resistance to softening on tempering. The alloy tool steels can be roughly classified as (i) low alloy tool steels which are having higher hardenability than that of the plain carbon tool steels so that they can be hardened in heavier sections or with less drastic quenches and thereby have less distortion, (ii) intermediate alloy tool steels which normally contain elements such as tungsten, molybdenum, and vanadium which form hard and wear resistant carbides, and (iii) high speed tool steels which contain large quantities of the carbide forming elements which serve not only to furnish wear resisting carbides but also to promote secondary hardening and thereby to increase resistance to softening at elevated temperature.
Alloying element – Alloying elements are added to the steel to change the chemical composition of steel and improve its properties over carbon steel or adjust them to meet the requirements of a particular application. Different alloying elements each have their own effect on the properties of steel. Steels having alloying elements in the composition are called alloy steels. The advantages of adding alloying elements to steel include (i) increase of the maximum tensile strength, (ii) availability of thick sections of steels with high hardness throughout the section, (iii) more controllable quenching with minimum risk of shape distortion or cracking, (iv) improved impact resistance at high temperature range, (v) improved corrosion resistance, and (vi) improved high temperature performance.
Allotropy – It is a near synonym for polymorphism. Allotropy is normally restricted to describing polymorphic behaviour in elements, terminal phases, and alloys whose behaviour closely parallels that of the predominant constituent element.
Allotropic transformation – An allotropic transformation simply means the crystal structure changes when the material is heated above or cooled below a critical temperature called the transus temperature. In pure titanium, the beta-phase can only exist above the transus temperature, and the alpha-phase only occurs below the transus temperature.
All-welded construction – It pertains to a valve construction in which the valve body is completely welded and cannot be disassembled and repaired in the field.
All-weld-metal test sample – It is a test sample wherein the portion being tested is composed wholly of weld metal.
Alpha – It is the low-temperature allotrope of titanium with a hexagonal close-packed crystal structure which occurs below the beta transus.
Alpha-beta structure – It is a micro-structure containing alpha and beta as the principal phases at a specific temperature.
Alpha brass – It is a solid-solution phase of one or more alloying elements in copper having the same crystal lattice as copper.
Alpha bronze – It consists of the alpha solid solution of tin in copper. Alpha bronze alloys of 4 % to 5 % tin are used to make coins, springs, turbines and blades.
Alpha case – It is the oxygen-enriched, nitrogen- enriched, or carbon-enriched, alpha-stabilized surface resulting from elevated temperature exposure.
Alpha ferrite – It is body-centered cubic type of iron stable below 910 deg C. It is thermodynamically stable and a fairly soft metal. Alpha iron can be subjected to pressures up to around 15 GPa before transforming into a high-pressure form termed epsilon iron. Magnetically, alpha iron is paramagnetic at high temperatures. However, below its Curie temperature of 771 deg C, it becomes ferromagnetic. In the past, the paramagnetic form of alpha iron was known as beta iron. Even though the slight tetragonal distortion in the ferromagnetic state does constitute a true phase transition, the continuous nature of this transition results in only minor importance in steel heat treatment.
Alpha iron – It is solid phase of pure iron which is stable below 910 deg C, possesses the body-centered cubic lattice, and is ferro-magnetic below 771 deg C.
Alpha particle – It is an ionizing particle consisting of two protons and two neutrons. It is a Helium nucleus – i.e. a helium atom stripped of its two electrons.
Alpha prime (hexagonal martensite) – It is a supersaturated, non-equilibrium hexagonal alpha phase formed by a diffusion-less transformation of the beta phase. It is frequently difficult to distinguish from acicular alpha, although the latter is normally less well defined and frequently has curved, instead of straight, sides.
Alpha process – It is a shell molding and core making method in which a thin resin bonded shell is baked with a less expensive, highly permeable material.
Alpha stabilizer – It is an alloying element which dissolves preferentially in the alpha phase and raises the alpha-beta transformation temperature.
Alpha transus – It is the temperature which designates the phase boundary between the alpha and alpha + beta fields.
Alternate immersion test – It is a corrosion test in which the samples are intermittently exposed to a liquid medium at definite time intervals.
Alumina – Alumina is a chemical compound of aluminum and oxygen with the chemical formula aluminum oxide. It is the most commonly occurring of several aluminum oxides. It is significant in its use to produce aluminum metal. It is being used as an abrasive material because of its hardness. It is also being used as a refractory material owing to its high melting point. Alumina affects the processes of producing iron and steel. Besides alumina is a very important refractory material for the lining of furnaces and vessels in iron and steel plants. It is sometimes used as a moulding sand. Alumina occurs in several forms, the principal being gamma-alumina and alpha alumina (or corundum). So called beta alumina contains a small quantity of alkali metal oxide.
Alumina refractories – Alumina (Al2O3) refractories are the part of alumina- silica (SiO2) group of refractories and belongs to the SiO2-Al2O3 phase equilibrium system. They differ from fire clay refractories in term of alumina content and normally have alumina content of more than 50 %. These refractories are used for lining of the different furnaces. Alumina content of refractories varies depending on in which zone of the furnaces they are used for lining. Alumina refractories are divided into seven different classes by percent alumina. These classes are (i) 50 % alumina, (ii) 60 % alumina, (iii) 70 % alumina, (iv) 80 % alumina, (v) 85 % alumina, (vi) 90 % alumina, and (vii) 99 % alumina.
Aluminizing – It consists of forming of an aluminum or aluminum alloy coating on a metal by hot dipping, hot spraying, or diffusion.
Aluminosilicate – It refers to materials containing anionic Si-O-Al linkages. It is normally, the associate cations are sodium, potassium and protons. Such materials occur as minerals and as synthetic materials, frequently in the form of zeolites. Both synthetic and natural aluminosilicates are of technical significance as structural materials, catalysts, and reagents.
Aluminothermic (thermite) welding – Aluminothermic welding is a fusion welding process in which two metals become bonded after being heated by superheated metal which has experienced an alumino-thermic reaction. The liquid metal which results from the reaction between a metal oxide and aluminum acts as the filler metal. The exothermic reaction is extremely violent if only the metal oxide and aluminum reducing agent are used. Pellets of ferroalloy are added to cool this reaction from a typical temperature of 3,090 deg C to 2,480 deg C. These additions also are used to produce the desired chemistry. The quantity of added alloy is very critical, since larger quantities cool the reaction to temperatures below 2,040 deg C, at which point the slag / metal separation can be incomplete.
Aluminum – It is a chemical element. it has symbol Al and atomic number 13. Aluminum has a density lower than that of other common metals, about one-third that of steel. It has a great affinity towards oxygen, forming a protective layer of oxide on the surface when exposed to air. Aluminum is used for deoxidizing and grain refining in steels. It is a strong deoxidizer.
Aluminum alloy – It is an alloy in which aluminum is the predominant metal. The typical alloying elements are copper, magnesium, manganese, silicon, tin, nickel and zinc. There are two principal classifications, namely casting alloys and wrought alloys, both of which are further subdivided into the categories heat-treatable and non-heat-treatable. Around 85 % of aluminum is used for wrought products, for example rolled plate, foils and extrusions. Cast aluminum alloys yield cost-effective products due to the low melting point, although they normally have lower tensile strengths than wrought alloys. The most important cast aluminum alloy system is aluminum-silicon, where the high levels of silicon (4 % to 13 %) contribute to give good casting characteristics. Aluminum alloys are widely used in engineering structures and components where light weight or corrosion resistance is needed.
Aluminum casting alloys– These are the most versatile of all common foundry alloys and normally have the highest castability ratings. As casting materials, aluminum alloys have the several favourable characteristics such as (i) good fluidity for filling thin sections, (ii) low melting point relative to those needed for several other metals, (iii) rapid heat transfer from the molten aluminum to the mould, providing shorter casting cycles, (iv) hydrogen is the only gas with appreciable solubility in aluminum and its alloys, and hydrogen solubility in aluminum can be readily controlled by processing methods, (v) several aluminum alloys are relatively free from hot-short cracking and tearing tendencies, (vi) chemical stability, and (vii) good as-cast surface finish with lustrous surfaces and little or no blemishes. Aluminum alloy castings are routinely produced by pressure-die, permanent-mould, green-and dry-sand, investment, and plaster casting. Aluminum alloys are also readily cast with vacuum, low-pressure, centrifugal, and pattern-related processes such as lost foam.
Aluminum/aluminum-silicon alloy coated sheet and strip – This coated product is produced dipping in a molten bath of aluminum/aluminum-silicon alloy. The mass of the alloy varies in general between 80 grams/sq m and 300 grams/sq m total on both the sides, which corresponds to a coating thickness of 15 micro-meters to 55 micro-meters per side.
Aluminium killed steel – It is a type of steel which is produced when aluminium is used as a deoxidizing agent to remove oxygen from steel during its production.
Aluminum-lithium alloys– These have been developed primarily to reduce the weight of aircraft and aerospace structures. More recently, they have been investigated for use in cryogenic applications (for example, liquid oxygen and hydrogen fuel tanks for aerospace vehicles).
Aluminum mill products – These are those aluminum products that have been subjected to plastic deformation by hot-working and cold-working mill processes (such as rolling, extruding, and drawing, either singly or in combination), so as to transform cast aluminum ingot into the desired product form. The micro-structural changes associated with the working and with any accompanying thermal treatments are used to control certain properties and characteristics of the worked, or wrought, product or alloy. Typical examples of mill products include plate or sheet (which is subsequently formed or machined into products such as aircraft or building components), household foil, and extruded shape such as storm window frames. A vast difference in the mechanical and physical properties of aluminum mill products can be obtained through the control of the chemistry, processing, and thermal treatment.
Aluminum silicate – It is a name normally applied to chemical compounds which are derived from aluminum oxide, and silicon dioxide, which can be anhydrous or hydrated, naturally occurring as minerals or synthetic. Their chemical formulae are often expressed as xAl2O3·ySiO2·zH2O.
Aluminum-zinc alloy coated sheet and strip – This coated product is produced by coating with aluminum-zinc alloy by dipping in a bath of molten alloy. The mass of the alloy varies in general between 90 grams/square metre and 450 grams/square metre. As per the aluminum content a distinction is made between (i) aluminum-zinc alloys (aluminum 50 % minimum, and (ii) zinc-aluminum alloys (aluminum content varying from over 3 % to 50 %).
Amalgam – It is an alloy of mercury with another metal. It can be a liquid, a soft paste or a solid, depending upon the proportion of mercury. These alloys are formed through metallic bonding, with the electrostatic attractive force of the conduction electrons working to bind all the positively charged metal ions together into a crystal lattice structure. Almost all metals can form amalgams with mercury, the notable exceptions being iron, platinum, tungsten, and tantalum.
Ambient – It is something normally used in relation to temperature, as ‘ambient temperature’ surrounding a part or assembly. It is frequently taken to mean ‘comfortable indoor temperature’.
Ambient air – It is the air which surrounds the equipment. The standard ambient air for performance calculations is air at 25 deg C, 60 % relative humidity, and a barometric pressure of 101 kilo pascals, giving a specific humidity of 0.013 kg (kilogram) of water vapour per kg of dry air.
Ambient temperature – It is the temperature of the air surrounding the equipment. .
Ambient pressure – It is the barometric reading of pressure exerted by the atmosphere. It is the normal pressure of the atmosphere (101 kilo pascals) on the sea level at 0 deg C. The ambient pressure on the object is the pressure of the surrounding medium, such as a gas or liquid, in contact with the object. Within the atmosphere, the ambient pressure decreases as elevation increases. Near sea level, a change in ambient pressure of 100 pascals is taken to represent a change in height of 9 metres. The ambient pressure in water with a free surface is a combination of the hydrostatic pressure because of the weight of the water column and the atmospheric pressure on the free surface. This increases approximately linearly with depth. Since water is much denser than air, much greater changes in ambient pressure can be experienced under water. Each 10 metres of depth adds another 100 kilo-pascal to the ambient pressure.
Ambient temperature – It is the air temperature of any object or environment where equipment is stored. The adjective ambient means ‘relating to the immediate surroundings’. This value is also referred to as the ordinary temperature or the baseline temperature. It is important for system design and thermal analysis.
Ammonia – Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the formula NH3. A stable binary hydride and the simplest pnictogen (A pnictogen is any of the chemical elements in group 15 of the periodic table, also known as the nitrogen group or nitrogen family) hydride, ammonia is a colourless gas with a distinctive pungent smell.
Ammonium sulphate – It is an inorganic, white odourless solid and crystalline salt with a number of commercial uses. Its chemical formula is (NH4)2SO4. The most common use is as a soil fertilizer. It contains 21 % nitrogen and 24 % sulphur. It is produced as a by-product during removal of ammonia from the raw coke oven gas generated during the coking of the metallurgical coal in by-product coke ovens.
Amorphous – It means not having a crystal structure, i.e., non-crystalline.
Amorphous solid – It is a non-crystalline material which does not have a crystal structure. In other words, it is a rigid material whose structure lacks crystalline periodicity, i.e., the pattern of its constituent atoms or molecules does not repeat periodically in three dimensions, such as metallic glass.
Amphoteric – It is the term applied to oxides and hydroxides which can act basic toward strong acids and acidic toward strong alkalis. These are substances which can dissociate electrolytically to produce hydrogen or hydroxyl ions according to conditions.
Amphoterism – In chemistry, an amphoteric compound (from Greek amphoteros ‘both’) is a molecule or an ion which can react both as an acid and as a base.
Ampholytes – These are amphoteric molecules which contain both acidic and basic functional groups.
Amplifier – A negative lens used instead of an eye-piece to project under magnification the image formed by an objective. The amplifier is designed for flatness of field and is to be used with an apochromatic objective.
AMR schemes – Acronym AMR stands for additions, modifications and replacements. In a plant which is operating for a number of years, implementation of AMR schemes is a necessity if the efficiency and productivity of the plant is to be maintained over a large number of years. Expenditures on AMR schemes are capital in nature and usually these expenditures are not very large and they are small in nature.
Amsler wear machine – It is a wear and traction-testing machine consisting of two disk-shaped samples oriented such that their axes are parallel and whose circumferential, cylindrical surfaces are caused to roll or roll and slide against one another. The rotation rates of each disk can be varied so as to produce varying degrees of sliding and rolling motion.
Anaerobic – It means free of air or uncombined oxygen.
Anaerobic process – It is a sequence of processes by which micro-organisms break down bio-degradable material in the absence of oxygen. The process is used for industrial purposes to manage waste or to produce fuels. Anaerobic process occurs naturally in some soils and in lake and oceanic basin sediments, where it is normally referred to as ‘anaerobic activity’.
Analog instruments – The devices which produce these signals are called analog Instruments. Analog is normally thought of in an electrical context. However, mechanical, pneumatic, hydraulic, and other systems can also convey analog signals.
Analog signal – Analog signal is one which varies in a continuous fashion and takes on infinity of values in any given range. An analog signal uses some property of the medium to convey the signal’s information.
Analog to digital converter – It is a device which converts a continuously variable electrical signal into discrete signals suitable for analysis by a digital computer.
Analysis – It is the quantitative determination of the constituent parts. It is the ascertainment of the identity or concentration, or both, of the constituents or components of a sample.
Analysis of variance (ANOVA) – It is utilized to make a comparison between the calculated separate outcomes of different groups which are the predictor variable and also multi-category. This tool can be used in inferential analysis.
Analysis, ultimate – It is the chemical analysis of solid, liquid, or gaseous fuels. In the case of coal or coke, it is the determination of carbon, hydrogen, sulphur, nitrogen, oxygen, and ash.
Analytical electron microscopy – It is the technique of materials analysis in the transmission electron microscope equipped to detect and quantify many different signals from the sample. The technique normally involves a combination of imaging, chemical analysis, and crystallographic analysis by diffraction at high spatial resolution.
Analytical transmission electron microscopy – Analytical transmission electron microscopy is unique among materials characterization techniques in that it enables essentially simultaneous examination of micro-structural features through high-resolution imaging and the acquisition of chemical and crystallographic information from small (sub-micrometer) regions of the sample.
Analyzer – It is an optical device capable of producing plane-polarized light.
Anchor – It is a metal or refractory device for holding a refractory lining in place. It is also known as the refractory or metallic pieces fixed to the casting and designed for ensuring the stability of refractory lining.
Anchorite – It is a zinc-iron phosphate coating for iron and steel.
Anchor pin – It is a pin welded to the body of a ball valve. This pin aligns the adapter plate and keeps the plate and gear operator from moving while the valve is being operated.
Andalusite – It is a natural alumino-silicate mineral with composition Al2O3.SiO2. It normally contains 60 % alumina and transform into mullite when fired.
Anelastic deformation – It is any portion of the total deformation of a body which occurs as a function of time when load is applied and which disappears completely after a period of time when the load is removed.
Anelasticity – It is the property of solids by virtue of which strain is not a single-value function of stress in the low stress range where no permanent set occurs.
ANFO – Acronym for ammonium nitrate and fuel oil. It is an explosive mixture which is used as a blasting agent in the ore mines.
Angle of attack – In tribology, the angle between the direction of motion of an impinging liquid or solid particle and the tangent to the surface at the point of impact.
Angle of bite – In the rolling of metals, it is the location where all of the force is transmitted through the rolls. It is the maximum attainable angle between the roll radius at the first contact and the line of roll centres. Operating angles less than the angle of bite are termed contact angles or rolling angles.
Angle of incidence – In tribology, the angle between the direction of motion of an impinging liquid or solid particle stream and the plane of the surface.
Angle of nip – In rolling, it is the angle of bite. In roll, jaw, or gyratory crushing, it is the entrance angle formed by the tangents at the two points of contact between the working surfaces and the (assumed) spherical particles to be crushed.
Angle of reflection – In case of reflection, it is the angle between the reflected beam and the normal to the reflecting surfaces. In case of diffraction, it is the angle between the diffracted beam and the diffracting planes.
Angle of repose – The angle of repose, or critical angle of repose, of a granular material is the steepest angle of descent or dip relative to the horizontal plane on which the material can be piled without slumping. At this angle, the material on the slope face is on the verge of sliding. The angle of repose can range from 0-degree to 90-degree.
Angle seat valve – It is an angle seat piston valve which is a pneumatically-controlled valve with a piston actuator providing linear actuation to lift a seal off its seat. The seat is set at an angle to provide the maximum possible flow when unseated. Angle seat piston valves are particularly suited to applications where high temperatures and large flow rates are needed. When used in reverse, some models of angle seat piston valve eliminate water hammer when operated.
Angle valve – It is a variation of the globe valve in which the end connections are at right angles to each other, rather than being in-line. It is a valve design in which the inlet and outlet ports are perpendicular to each other.
Angstrom unit – It is a unit of linear measure equal to 0.1 nanometer (nm) or one billionth of a meter. Although not an accepted SI (Systeme International or The International System of Units) unit, it is occasionally used for small distances, such as interatomic distances, and some wave-lengths.
Angularity – It is conformity to, or deviation from specified angular dimensions in the cross section of a shape or bar.
Angular misalignment – In angular misalignment, axes of shafts intersect at the center point of the coupling, but not in the same straight line.
Angulation – It is the deliberate departure from a horizontal pass-line on the entry side of a rolling mill used for one-side bright rolling.
Anion – It is a negatively charged ion.
Aniline point – Aniline point is the minimum temperature at which oil is miscible with equal amount of aniline. Aniline point is a measure of aromatic content of the lubricating oil. Low aniline point oil has high aromatic content which attacks rubber seals. Higher aniline point means low percentage of hydro-carbons (desirable). Hence, aniline point is used as an indication of possible deterioration of rubber sealing etc.
Animal based lubricating oils – These biological oil (sperm, fish, and wool oils from sheep such as lanolin) have extreme pressure properties but they have issues related to their availability.
Anisotropy – It is the characteristic of showing different values of a property in different directions with respect to a fixed reference system in the material.
Annealing – It is a generic term denoting a treatment consisting of heating to and holding at a suitable temperature followed by cooling at a suitable rate. It is used primarily to soften metallic materials, but also to simultaneously produce desired changes in other properties or in micro-structure. The purpose of such changes may be, but is not confined to: improvement of machinability, facilitation of cold work, improvement of mechanical or electrical properties, and/or increase in stability of dimensions. When the term is used without qualification, full annealing is implied. When applied only for the relief of stress, the process is properly called stress relieving or stress-relief annealing. In ferrous alloys, annealing is carried out above the upper critical temperature, but the time-temperature cycles vary widely in maximum temperature attained and cooling rate used, depending on composition, material condition, and desired results. Types of annealing are black annealing, blue annealing, box annealing, bright annealing, cycle annealing, flame annealing, graphitizing, isothermal annealing, malleablizing, process annealing, quench annealing, spheroidizing, and sub-critical annealing. In non-ferrous alloys, annealing cycles are designed to remove part or all the effects of cold working (recrystallization can be involved), cause complete coalescence of precipitates from the solid solution in relatively coarse from, or both, depending on composition and material condition. In non-ferrous alloys, annealing cycles are designed to (i) remove part or all of the effects of cold working (recrystallization can or cannot not be involved), (ii) cause substantially complete coalescence of precipitates from solid solution in relatively coarse form, or (iii) both, depending on composition and material condition. Specific process names final annealing, full annealing, intermediate annealing, partial annealing, recrystallization annealing, stress relieving, and anneal to temper.
Annealing carbon – It is fine, apparently amorphous carbon particles formed in white cast iron and certain steels during prolonged annealing.
Anneal to temper – It is a final partial anneal which softens a cold-worked non-ferrous alloy to a specified level of hardness or tensile strength.
Annealing twin – It is a twin formed in a crystal or grain during recrystallization or, rarely, during solidification.
Annular bearing – Normally it is a rolling bearing of short cylindrical form supporting a shaft carrying a radial load. It can also be a flat disk-shaped bearing.
Annual dose – It is the total radiation dose received by an individual in a one-year period.
Annular dies – These are the dies with annular cross sections are used to extrude pipes, tubes, tubular films, and parisons for blow moulding. Centre-fed dies are normally used for extruding pipes, while side-fed dies are used for tubular films and parisons.
Annular space – It is the difference between the stock line radius and the large bell radius in blast furnace.
Anode – It is the electrode in electrolysis cell at which negative ions are discharged, positive ions are formed, or other oxidizing reactions occur. Electrons flow away from the anode in the external circuit. It is normally at the electrode that corrosion occurs and metal ions enter solution. It is also called the positive (electron-deficient) electrode in an electrochemical circuit.
Anodic cleaning – It is the electrolytic cleaning in which the work is the anode.
Anodic coating – It is a protective, decorative, or functional coating, formed by conversion of the surface of a metal in an electrolytic oxidation process.
Anode copper – It is special-shaped copper slabs, resulting from the refinement of blister copper in a reverberatory furnace, used as anodes in electrolytic refinement.
Anode effect – It is the effect produced by polarization of the anode in electrolysis. It is characterized by a sudden increase in voltage and a corresponding decrease in amperage due to the anode becoming virtually separated from the electrolyte by a gas film.
Anode efficiency – It is the current efficiency at the anode.
Anode film – It is the portion of solution in immediate contact with the anode, especially if the concentration gradient is steep. It is also the outer layer of the anode itself.
Anodic etching – It is a method of revealing micro-structure by selective dissolution of the polished surface under application of a direct current.
Anodic inhibitor – It is a chemical substance or mixture which prevents or reduces the rate of the anodic or oxidation reaction.
Anodic pickling – It is electrolytic pickling in which the work is the anode.
Anodic polarization – It is the change of the electrode potential in the noble (positive) direction because of the current flow.
Anodic protection – It is a technique to reduce the corrosion rate of a metal by polarizing it into its passive region, where dissolution rates are low. It is the imposing an external electrical potential to protect a metal from corrosive attack and is applicable only to metals which show active-passive behaviour.
Anodic reaction – It is the electrode reaction equivalent to a transfer of positive charge from the electronic to the ionic conductor. An anodic reaction is an oxidation process.
Anodizing – It is an electrolytic oxidation process in which the surface of a metal, when anodic, is converted to a coating having desirable protective, decorative, or functional properties.
Anolyte – It is the electrolyte adjacent to the anode in an electrolytic cell.
Anthracite coal – As per ISO 11760, anthracite coal is defined as the coal, synonymous with high-rank coal, having a mean random vitrinite reflectance, equal to or greater than 2 % but less than 6 %, or, preferably, a mean maximum reflectance, less than 8 % for geologically unaltered coal. It is frequently being referred as hard coal. Since anthracite coal had been subjected to the pressure and heat, it is the most compressed and hardest coal available. Being a hard coal, it intense contains greater potential to produce heat energy than softer, geologically ‘newer’ coal.
Anthropogenic material – An Anthropogenic material is physical matter without any attribution from an economic, legislative, social, or environmental perspective, and without a specification of the aggregate state (solid, liquid, gaseous). Anthropogenic materials include, for example, mineral materials, sewage sludge, biomass, and off-gas.
Anthropogenic resource – An Anthropogenic resource is a concentration or occurrence of Anthropogenic material of intrinsic economic interest, in such form, quality, and quantity that there are reasonable prospects for eventual economic exploitation. It is recognized that in traditional resource classification systems, the quantity is subdivided into resources and reserves with elaborate definitions of the two. UNFC does not use these terms but refers to ‘Classes’ instead. The term ‘Anthropogenic resource’ has been adapted from the term ‘Mineral resource’ as defined in CRIRSCO.
Anthropogenic material product – Anthropogenic material product is a quantity which is saleable in markets. The cumulative quantities are equivalent to ‘Sales production’ as per UNFC. It is to be noted that the term Anthropogenic material product does not necessarily correlate with legal product declarations.
Anthropogenic specifications – The Anthropogenic specifications provides supplementary specifications for UNFC to classify secondary resource Projects in line with the Sustainable Development Goal (SDG), notably objective.
Anthropogenic sources – Anthropogenic sources are material quantities from anthropogenic materials sources, such as mining tailings, buildings, infrastructure, consumer durable goods, and all material life cycle stages, including recovery, production, use and end-of-life.
Anticorrosive additive – It is a lubricant additive used to reduce corrosion.
Antiferromagnetic material – It is a material wherein interatomic forces hold the elementary atomic magnets (electron spins) of a solid in alignment, a state similar to that of a ferromagnetic material but with the difference that equals numbers of elementary magnets (spins) face in opposite directions and are antiparallel, causing the solid to be weakly magnetic, that is, paramagnetic, instead of ferromagnetic.
Antifoam additive – It is an additive used to reduce or prevent foaming’ It is also known as foam inhibitor.
Antifriction bearing – Anti friction bearings use rolling elements (balls or rollers) to reduce friction. The rolling elements are constrained between an inner race (ring) and an outer race (ring). Generally, a separator (cage) keeps the rolling elements spaced apart so they do not rub against each other which would result in skidding. It is a bearing containing a solid lubricant.
Antifriction material – It is a material which shows low-friction or self-lubricating properties.
Antimony – It is classified as a heavy metal with potential toxicity and hygiene implications, especially as associated with the possibility of stibine gas formation and the effects of human exposure to other antimony compounds. At concentration levels equal to or higher than 0.05 %, antimony refines eutectic aluminum-silicon phase to lamellar form in hypo-eutectic compositions. The effectiveness of antimony in altering the eutectic structure depends on an absence of phosphorus and on an adequately rapid rate of solidification. Antimony also reacts with either sodium or strontium to form coarse inter-metallics with adverse effects on castability and eutectic structure.
Anticipated operational occurrence – It is a deviation of an operational process from normal operation which is expected to occur at least once during the operating life-time of a facility but which, in view of appropriate design provisions, does not cause any significant damage to items important to safety or lead to accident conditions. Examples of anticipated operational occurrences are loss of normal electrical power and faults such as a turbine trip, malfunction of individual items of a normally running plant, failure to function of individual items of control equipment, and loss of power to the main coolant pump.
Antioxidant – It is an additive which is used for the purpose of reducing the rate of oxidation and subsequent deterioration of a material.
Anti-pitting agent – It is an additive for electroplating solutions to prevent the formation of pits or large pores in the electro-deposit.
Antiwear additives – These are additives for lubricants to prevent metal-to-metal contact between parts of gears. Some popular antiwear additives are zinc dithiophosphate, zinc dialkyl dithio phosphate, tricresyl phosphate, halocarbons (chlorinated paraffins), glycerol mono oleate, and stearic acid.
Anvil – It is a large, heavy metal block which supports the frame structure and holds the stationary die of a forging hammer. Also, it is the metal block on which blacksmith forgings are made.
Aperture size – An Aperture is the opening within a lens which controls how much light hits the imaging sensor. The size of the aperture dictates two things namely (i) the depth of field, and (ii) the shutter speed needed to expose the image correctly.
Apochromatic lens – It is a lens whose secondary chromatic aberrations have been substantially reduced.
Apparent area of contact – In tribology, it is the area of contact between two solid surfaces defined by the boundaries of their macroscopic interface.
Apparent density (of solids and liquids) – It is the mass in air of a unit of volume of a material at a specified temperature.
Apparent porosity – It is the ratio of the total volume of the open pores in a porous refractory to its bulk volume expressed as a percentage of the bulk volume.
Approach angle – The approach angle is the most important section of a wire drawing die. This section of the die is where the reduction of area and lubricant compacting of the incoming wire takes place.
Approved for Development – Approved for Development needs that all approvals / permits / contracts be in place, and capital funds have been committed.
Apron conveyor – This is the most common type of chain conveyor. It consists of one or more strands of endless chain, normally link plate roller type, running in steel guides. Rollers ensure minimum pulling effort in the chain, while roller guides supported on the super-structure of the conveyor, carry the entire load of the materials and chains. The carrying surface of the conveyor is composed of a series of plates or shapes called ‘apron’, which are attached to the links of the chains through cleats. The bed created by the aprons is used for carrying bulk materials as well as unit loads.
Apron feeders – These feeders are a mechanical type of feeders used for transferring material to a crusher or other piece of downstream equipment at a uniform rate. They are typically used to feed primary crushers, but they can be used in primary, secondary and tertiary applications as a primary feeder, primary crusher discharge feeder, stockpile feeder, rail unloading feeder, storage bin feeder. These types of feeders are ideal for handling very hard, abrasive and tough materials.
Aquastat – It is a water limit temperature control. It is a safety device frequently used for boilers.
Aqueous– It is relating to, similar to, containing, or dissolved in water, or watery. An aqueous solution is made by using water as a solvent.
Aqueous corrosion – It is the corrosion with water or a water-based solution as the corrosive environment.
Aqueous solution – An aqueous solution is a solution in which the solvent is water. The word aqueous, which comes from ‘aqua’, means pertaining to, related to, similar to, or dissolved in, water. Since water is an excellent solvent and is also naturally abundant, it is a ubiquitous solvent. Since water is frequently used as the solvent in experiments, the word solution refers to an aqueous solution, unless the solvent is specified. It is mostly shown in chemical equations by appending to the relevant chemical formula.
Aramid – Aramid has twice the strength of steel, with stretch characteristics roughly halfway between steel and polyester. It is considerably lower in weight than steel and does not rust. Presently cost and availability of materials limit the use of Aramid in belt carcass construction.
Arbor – In machine grinding, it is the spindle on which the wheel is mounted. In machine cutting, it is a shaft or bar for holding and driving the cutter. In foundry, it is a metal shape embedded in green sand or dry sand cores to support the sand or the applied load during casting.
Arbor press – It is a machine used for forcing arbors or mandrels into drilled or bored parts preparatory to turning or grinding. It is also used for forcing bushings, shafts, or pins into or out of holes.
Arbor-type cutter – It is a cutter having a hole for mounting on an arbor and normally having a keyway for a driving key.
Arc – An arc is a discharge of electric current across a gap in a circuit. It is sustained by the presence of a thermally ionized column of gas (called a plasma) through which current flows. In general, atmospheric air is a poor conductor of electric current.
Arc blow – It is the deflection of an electric arc from its normal path because of magnetic forces.
Arc brazing – It is a brazing process in which the heat required is obtained from an electric arc.
Arc cutting – It is a group of cutting processes which melt the base metal with the heat of an arc between an electrode and the base metal.
Arc deposition – The vacuum arc is a form of electrical discharge which is sustained mainly on the electrons and ions that originate from the electrodes used to produce the arc. The value of using vacuum arc deposition to produce coatings stems from the copious quantity of ions of electrode material composition which are generated during the discharge. Since the output of the vacuum arc is highly ionized, it is possible to control both the trajectory of the coating material during its transit from source to part and the energy with which ions impinge on that part. This level of control can be contrasted to competing vacuum coating technologies, such as electron-beam evaporation and magnetron sputtering, where the atoms of coating material travel from the source to the part to be coated in an electrically neutral state.
Arc furnace – It is a furnace in which metal is melted either directly by an electric arc between an electrode and the work or indirectly by an arc between two electrodes adjacent to the metal.
Arc gouging – It is an arc cutting process variation used to form a bevel or groove.
Arc melting – It is melting of metal in an electric arc furnace.
Arc seam weld – It is a seam weld made by an arc welding process.
Arc spot weld – It is a spot weld made by an arc welding process.
Arc spraying – It is a thermal spraying process using an arc between two consumable electrodes of surfacing materials as a heat source and a compressed gas to atomize and propel the surfacing material to the substrate.
Arc strike – It is a discontinuity consisting of any localized remelted metal, heat-affected metal, or change in the surface profile of any part of a weld or base metal resulting from an arc
Arc welding – It is a group of welding processes which produces coalescence of metals by heating.
Arc welding electrode – It is a component of the welding circuit through which current is conducted and which terminates at the arc.
Arch – It is part of a structure bridging a gap in a wall (e.g., a door arch) or spanning the space between two walls (e.g., a furnace roof).
Arch brick – It is a brick in which the two large faces are inclined towards each other in such a way that, with a certain number of these bricks, an arch can be constructed.
Architectural drawing – It is the technical representation of a building which is made prior to the beginning of the construction process. It is made with lines, projections and is based on a scale.
Architectural site plan – It is an aerial view of the construction site which includes the primary building and its adjoining constructions. Among its wide applications, one can include construction drawings for building improvement and understanding the scope of construction activities. Along with it, it helps to identify the topography of the building including roads, and pavements etc.
Argon – Argon is a chemical element. It has symbol Ar and atomic number 18. It is a noble gas. It is an inert gas. Argon gas is the most abundant of the noble gases. It is a non-reactive component of the atmosphere. It constitutes 0.934 % by volume and 1.288 % by mass of the earth’s atmosphere.
Argon oxygen decarburization (AOD) – It is a secondary refining process for the controlled oxidation of carbon in a steel melt. The key feature of the AOD process is that oxygen, argon, and nitrogen are injected into a molten metal bath through submerged, side-mounted tuyeres. This argon dilution minimizes unwanted oxidation of precious elements contained in specialty steels, such as chromium. The process mainly used in production of stainless steel and other high-grade alloys such as silicon steels, tool steels, nickel base alloys and cobalt base alloys with oxidizable elements such as chromium and aluminum.
Argon rinsing – It is a secondary steelmaking process. Gas rinsing process is a method where rinsing of liquid steel in the teeming ladle is carried out through injection of inert gas into the steel bath. Argon gas is preferred for rinsing since it is not only inert in nature but its solubility in steel is also very low. Rinsing results from the expansion of gas due to heating and decrease in pressure as the gas rises. The argon rinsing of liquid steel is carried out for getting homogenous temperature, composition, and promotion of slag metal refining reaction. The argon rinsing of liquid steel is reported to be an excellent process for floatation and separation of non-metallic inclusions.
Armour – These are the steel castings used for lining of the throat of the blast furnace.
Armouring – In refractories, it is the internal metal protection at the top of the stack.
Armour steel – It is the steel which is being used for the protection of armour. Steels of high tensile strength, hardness, and ductility are mostly used as a ballistic protection plate. Armour steels are not ordinary steels. These are high strength steels with combined hardness and fracture toughness. The main properties such as toughness, hardness, good fatigue strength, ease of fabrication and joining and having relative low cost make the steel a popular material for the hulls of the armoured vehicle. Steel is the best all round performing armour material in spite of its high density because of its properties like toughness, ready availability, low cost, castability, and weldability etc. Armour steel is required to have such properties as (i) high resistance to perforation and ballistic impacts, (ii) possible fabricability, and (iii) adequate fatigue and wear resistance under service conditions.
Aromatic – In organic chemistry, it is pertaining to or characterized by the presence of at least one benzene ring.
Aromatic compounds – Aromatic compounds are chemical compounds that consist of conjugated planar ring systems accompanied by delocalized pi-electron clouds in place of individual alternating double and single bonds. They are also called aromatics or arenes. The best examples are toluene and benzene.
Aromaticity – It is a chemical property describing the way in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals shows a stabilization stronger than is expected by the stabilization of conjugation alone.
Arrest marks – These are macroscopic progression marks on a fatigue fracture or stress-corrosion cracking surface which indicate successive positions of the advancing crack front. The classic appearance is of irregular elliptical or semielliptical rings, radiating outward from one or more origins. These marks (also known as clamshell marks or beach marks) are typically found on service fractures where the part is loaded randomly, intermittently, or with periodic variations in mean stress or alternating stress.
Arrestor – It is a device to impede the flow of large dust particles or sparks from a stack, normally by screening at the top.
Arsenic – It is a naturally occurring, semi-metallic element widely distributed in the earth’s crust. It is a notoriously toxic heavy metal. It occurs naturally in several minerals, normally in combination with sulphur and metals, but also as a pure elemental crystal. It has various allotropes. Arsenic levels in the environment can vary by locality, and it is found in water, air, and soil. There are two general forms of arsenic are (i) organic arsenic compounds contain carbon, and (ii) inorganic arsenic compounds do not contain carbon. Inorganic arsenic is more toxic and its associated health effects are more severe. All arsenic is toxic to humans and can affect people of any age or health status.
Artifact – It is a feature of artificial character, such as a scratch or a piece of dust on a metallographic sample, which can be erroneously interpreted as a real feature.
Artificial ageing – It is ageing above room temperature.
Artistic drawing – It is a form of free-hand representation which makes use of pictures to provide a general impression of the object being drawn. There are no hard rules or standards in the preparation of artistic drawings. These are simply drawn by the artists, based more or less on their talent and skills. Although these drawings are frequently very attractive, they find very limited use in the world of science.
A-segregation – A-segregates arise because of the flow of solute-rich inter-dendritic fluid through thermo-solutal convection. These segregates are characterized in the final solidified micro-structure as channels of enriched solid, frequently with near-eutectic composition.
Asbestos – It is a naturally occurring fibrous silicate mineral. There are six types, all of which are composed of long and thin fibrous crystals, each fibre (particulate with length substantially higher than width) being composed of many microscopic ‘fibrils’ which can be released into the atmosphere by abrasion and other processes. Inhalation of asbestos fibres can lead to various dangerous lung conditions, including mesothelioma, asbestosis, and lung cancer. As a result of these health effects, asbestos is considered a serious health and safety hazard.
As-built drawing – It is also known as record drawing. On construction projects, it is normal for changes to be made during construction because of circumstances which emerge on site. As a result, it is normal that as-built drawings is prepared, either during the construction process or when construction is complete, to reflect what has actually been built. The as-built drawings provide a comparison between what has been built and the original plan.
As cast condition – It refers to newly produced, unmachined castings which that have not been subjected to any form of finishing operations (beyond gate removal or shot-blast cleaning) or treatment of any kind, including heat treatment.
As-fired fuel – It is the fuel in the condition as fed to the fuel burning equipment.
Ash – It is the incombustible inorganic matter in the fuel. It is the mineral matter present in the coal. It is a waste which is left after coal is combusted (burned). It is the particulate material which remains after coal is burned. It includes fly ash (fine powdery particles which are carried up the smoke stack and captured by pollution control devices) as well as coarser materials which fall to the bottom of the furnace. It has different physical and chemical properties depending on the geochemical properties of the coal being used and how that coal is burned. It is also referred to as coal combustion residuals. It has very little organic fraction. Chemical constituents of coal ash can include nitrogen, sulphur, unburned carbon, heavy metals, radioactive elements, and polycyclic aromatic hydrocarbons. Coal ash also contains coarse particles and fine particles which can be inhaled and can contribute to public health and environmental problems. Coal ash contains several toxic contaminants. When coal ash spills, leaks or leaches into nearby ground water or waterways, the toxins contained within pose serious health risks to nearby communities.
Ash free basis – It is the method of reporting fuel analysis, whereby ash is deducted and other constituents are recalculated to total 100 %.
Ash fusion temperature – It is the temperature at which the ash present in the coal begins to soften or melt. In general, a high ash fusion temperature is preferred, to avoid deposition of sticky ash inside the furnace. It is normally measured at four different temperatures under oxidizing and reducing atmospheres namely (i) initial deformation, (ii) softening temperature, (iii) hemispherical temperature, and (iv) fluid temperature.
Ash fusion test – It is performed in a reducing atmosphere and helps assess the combined effect the ash forming minerals have on ash softening properties at different temperature levels. Higher levels of ash fusion temperatures prevent ash from depositing on coke oven floors and walls or freeing up fresh carbon surfaces to reactive gases. The ash fusion temperature value of the metallurgical coal is to be ideally higher than 1450 deg C.
Ash pit – It is a pit or hopper located below a furnace where refuse is accumulated and from which refuse is removed at regular intervals.
Aspect ratio – The aspect ratio of a geometric shape is the ratio of its sizes in different dimensions. For example, the aspect ratio of a rectangle is the ratio of its longer side to its shorter side, i.e., the ratio of width to height, when the rectangle is oriented as a ‘landscape’. The aspect ratio is most frequently expressed as two integer numbers separated by a colon such as ‘x:y’, less commonly as a simple or decimal fraction. The values x and y do not represent actual widths and heights but, rather, the proportion between width and height. In objects of more than two dimensions, such as hyperrectangles, the aspect ratio can still be defined as the ratio of the longest side to the shortest side.
Asperities – These are the small-scale irregularities on a surface. These are also minute imperfections on a seal face or surface of a mating ring which are the result of normal surface finishing processes. It is to be noted that asperities, their shapes, sizes, and mechanical properties are the basis for developing several theoretical models for friction, lubrication, and wear behaviour.
Asperity – In tribology, it is a protuberance in the small-scale topographical irregularities of a solid surface.
Asphalt – It is a black or brown petroleum like material which has a consistency varying from viscous liquid to glassy solid. It is obtained either as a residue from the distillation of petroleum or from natural deposits. Asphalt consists of compounds of hydrogen and carbon with minor proportions of nitrogen, sulphur, and oxygen.
Aspirating burner – It is a burner in which the fuel in a gaseous or finely divided form is burned in suspension, the air for combustion being supplied by bringing into contact with the fuel, air drawn through one or more openings by the lower static pressure created by the velocity of the fuel stream. As-received fuel – It is the fuel in the condition as received at the plant.
As-rolled pearlitic structural steels – These steels are a specific group of steels in which enhanced mechanical properties (and, in some cases, resistance to atmospheric corrosion) are achieved by the addition of moderate quantities of one or more alloying elements other than C. Some of these steels are C-Mn steels and differ from ordinary C steels only in having a higher Mn content. Other pearlitic structural steels contain small amounts of alloying elements, which are added to improve weldability, formability, toughness, and strength.
Assay – It is the determination of how much of a sample is the material indicated by the name. For example, for an assay of FeSO4 the analyst determines both iron and (SO4)2- in the sample.
Assembly drawing – It is a drawing which shows the different parts of an equipment in their correct working locations. Assembly drawings demonstrate how a number of separate sub-assemblies, parts, standard components, and specifications come together in a unified assembly. Normally speaking, an assembly drawing is used to show fit and function, and to verify how a product is put together. In order to fulfill its purpose, assembly drawing is to provide sufficient information to enable the assembly of a component.
Assemblies – It is the fitting together of manufactured parts into a complete structure, machine, or unit of a machine. Assemblies sometimes need specific design features.
Assignable cause – It is a cause which can be recognized as the one giving rise to the change in the output of a process beyond the normal variations caused by common causes.
Asymmetry – It is the absence of, or a violation of, symmetry (the property of an object being invariant to a transformation, such as reflection). Symmetry is an important property of both physical and abstract systems. In fire-resistance rated wall assemblies, used in passive fire protection, including, but not limited to, high-voltage transformer fire barriers, asymmetry is a crucial aspect of design. When designing a facility, it is not always certain, that in the event of fire, which side a fire can come from. Hence, several building codes and fire test standards outline, that a symmetrical assembly, need only be tested from one side, since both sides are the same. However, as soon as an assembly is asymmetrical, both sides are to be tested and the test report is required to state the results for each side.
Asymmetrical edge wave – It is a rolling defect in which one edge is ‘wavy’ because of the steel material at one side is longer than the other side.
Asymmetric rolling – It is a special and fairly new technique of metal rolling. The basic characteristic of the asymmetric rolling process is rolling with different circumferential velocities of the upper and the lower work rolls. It can be carried out using several approaches such as (i) different diameters of the work roll, (i) different work roll velocities, (iii) single roll drive, and (iv) different lubricated work roll surfaces. Asymmetric rolling process is a relatively new technique only with reference to the improvement of the materials’ formability. It is actually one of the oldest flat rolling techniques using three-high rolling mills, invented to enable better plate profiles in comparison with the two-high rolling mill.
As welded – It is the condition of weld metal, welded joints, and weldments after welding, but prior to any subsequent thermal, mechanical, or chemical treatments.
Athermal transformation – – It is a reaction which proceeds without benefit of thermal fluctuations. Hence, thermal activation is not needed. In contrast, a reaction which occurs at constant temperature is an isothermal transformation. Hence, thermal activation is necessary in this case and the reaction proceeds as a function of time.
Atmosphere – It is a surrounding influence or environment which affects the rate of corrosion, frequency and quantity of moisture, humidity, chlorides, sulphides, and wind are some of the atmospheric components affecting corrosion rates. In furnaces, it is the gaseous environment within the kiln during the firing process. It can be oxidizing (an excess of oxygen) or reducing (a deficiency of oxygen).
Atmosphere control – Control of furnace atmosphere is necessary for the product quality and product yield. Furnace atmosphere control functions are carried out by a series of probes and sensors. These components measure and control gas ratios and oxygen, water vapour and carbon dioxide levels during the entire furnace cycle.
Atmospheric air – It is the air under the prevailing atmospheric conditions.
Atmospheric corrosion – It is the gradual degradation or alteration of a material by contact with substances present in the atmosphere, such as oxygen, carbon dioxide, water vapour, and sulphur and chlorine compounds.
Atmospheric-corrosivity categories – As per ISO 9223, atmospheric environments are classified into six atmospheric-corrosivity categories (i) C1, very low corrosivity, (ii) C2, low corrosivity, (iii) C3, medium corrosivity, (iv) C4, high corrosivity, (v) C5, very high corrosivity, and (vi) CX, extreme corrosivity. It is to be noted that CX covers different extreme environments. One specific extreme environment is the offshore environment.
Atmospheric riser – It is a riser which uses atmospheric pressure to aid feeding. Essentially, a blind riser into which a small core or rod protrudes, the function of the core or rod is to provide an open passage so that the molten interior of the riser is not under a partial vacuum when metal is withdrawn to feed the casting but is always be under atmospheric pressure.
Atom – It is the smallest particle of an element which retains the characteristic properties and behaviour of the element. It consists of a central core, or nucleus, which is made up of protons and neutrons. The protons and neutrons are themselves made up of sub-atomic particles. Electrons revolve in orbits around the nucleus.
Atomic absorption spectrometer – It combines the two basic components found in most modern spectrometers namely (i) a simple flame atomizer to dissociate the sample solutions into free atoms, and (ii) sealed atomic line source spectral lamps. Atomic absorption spectrometry is normally used for measuring relatively low concentrations of around 70 metallic or semi-metallic elements in solution samples.
Atomic bond – All materials are made up of atoms. These atoms are held together by forces called interatomic bonds which are incredibly important in determining the materials properties. The atoms are held together by forces called interatomic bonds. The bonds act like springs, linking each atom to its neighbour. Primary bonds involve sharing or donating electrons between atoms to form a more stable electron configuration. All elements except inert gases have an unfilled valence shell. Secondary bonds are weak in comparison to primary bonds. They are found in majority of the materials, but their effects are frequently overshadowed by the strength of the primary bonding. Bond Force determines the elastic modulus (or Young’s modulus) of a material (how stiff a material is). Similarly, stronger bonds enable a material to withstand higher temperatures before the bonds break and the material melts or softens.
Atomic energy – This term refers to the energy which is released in nuclear reactions. There are two chief ways this can occur. The first in nuclear fission, whereby a neutron initiates the breaking up of an atom’s nucleus into smaller pieces. The second is nuclear fusion, whereby two nuclei are joined together under intense heat. It is more correctly called nuclear energy.
Atomic mass – It is the mass of an isotope of an element expressed in atomic mass units, which are defined as one-twelfth of the mass of an atom of carbon-12.
Atomic mass unit – It is an arbitrarily defined unit expressing the masses of individual atoms. One atomic mass unit is defined as exactly 1/12 of the mass of an atom of the nuclide 12C, the predominant isotope of carbon.
Atomic number – It is the number of elementary positive charges (protons) contained within the nucleus of an atom. For an electrically neutral atom, the number of planetary electrons is also given by the atomic number. Atoms with the same Z (isotopes) can contain different numbers of neutrons.
Atomic orbital – In quantum mechanics, an atomic orbital is a function describing location and wave-like behaviour of an electron in an atom. This function describes an electron’s charge distribution around atom’s nucleus, and can be used to calculate probability of finding an electron in a specific region around nucleus. Atomic Orbitals refer to the mathematical equations that describe the energy and probability of finding electrons within a specific region of space in an atom. These orbitals are categorized by letters such as ‘s’, ‘p’, ‘d’, and ‘f’, and each orbital can hold a maximum of two electrons.
Atomic percent – It is the number of atoms of an element in a total of 100 representative atoms of a substance.
Atomic structure – It is the arrangement of the parts of an atom, which consists of a positively charged nucleus surrounded by a cloud of electrons arranged in orbits which can be described in terms of quantum mechanics.
Atomic weight – It is a number assigned to each chemical element which specifies the average mass of its atoms. Since an element can consist of two or more isotopes, each having atoms with well-defined but differing masses, the atomic weight of each element is the average of the masses of its naturally occurring isotopes weighted by the relative proportions of those isotopes.
Atomization – It is the subdivision of a compound into individual atoms using heat or chemical reactions. This is a necessary step in atomic spectroscopy.
Atomizer – It is a device by means of which a liquid is reduced to a very fine spray.
Attribute – It is the characteristics of a material or product.
Attribute data – It is the qualitative information of a product such as good or bad, satisfactory or unsatisfactory.
Attrition – It is a term applied to the reduction of materials by scrubbing it between two hard surfaces. It is the removal of small fragments of surface material during sliding contact. Hammer mills operate with close clearances between the hammers and the screen bars and materials reduce by attrition combined with shear and impact reduction. Though attrition consumes more power and exacts heavier wear on hammers and screen bars, it is practical method for crushing the less abrasive materials such as limestone and coal. Attrition is a combination of a dragging action combined with compression such as in a spark plug gasket where the spark plug is turned down on a gasket that is both compressed and screwed into the flange.
Attrition mills – Attrition mills are the most common type of mill and are the traditional mills for grain milling. They are based on attrition grinding between two circular stones, one rotating and the other stationary. Plate mills use a similar principle but are constructed of steel or ceramic plates and used more commonly in the vertical plane. Output from such a mill is low and the mill in used only for small scale milling.
Attritious wear – It is the wear of abrasive grains in grinding such that the sharp edges gradually become rounded. A grinding wheel that has undergone such wear normally has a glazed appearance.
Attritor – It is a high-intensity ball mill whose drum is stationary and whose balls are agitated by rotating baffles, paddles, or rods at right angle to the drum axis.
Attritor grinding – It is the intensive grinding or alloying in an attritor. Examples are milling of carbides and binder metal powders and mechanical alloying.
Audit – It is a systematic and documented process for obtaining evidence from inspections, interviews, and document review and evaluating it objectively to determine the extent to which the relevant criteria are fulfilled.
Auger electron – It is an electron emitted from an atom with a vacancy in an inner shell. Auger electrons have a characteristic energy detected as peaks in the energy spectra of the secondary electrons generated.
Auger electron spectroscopy – It is a technique for chemical analysis of surface layers which identifies the atoms present in a layer by measuring the characteristic energies of their Auger electrons.
Auger electron yield – It is the probability that an atom with a vacancy in a particular inner shell relaxes by an Auger process.
Ausferrite – It is a special type of micro-structure which occurs when ductile iron is austempered, consisting of acicular ferrite in carbon-enriched austenite.
Ausforming – It is the thermomechanical treatment of steel in the metastable austenitic condition below the recrystallization temperature followed by quenching to get martensite and / or bainite.
Austempered ductile iron – It is a moderately alloyed ductile iron which is austempered for high strength with appreciable ductility. It undergoes an isothermal heat treatment. The optimal micro-structure of this ductile iron consists of graphite nodules surrounded by acicular ferrite and high carbon content austenite, which is called ausferrite.
Austempering – It is a heat treatment for ferrous alloys in which a part is quenched from the austenitizing temperature at a rate fast enough to avoid formation of ferrite or pearlite and then held at a temperature just above the Ms (martensite start) temperature, until transformation to bainite is complete. Although designated as bainite in both austempered steel and austempered ductile iron, austempered steel consists of two-phase mixtures containing ferrite and carbide, while austempered ductile iron consists of two-phase mixtures containing ferrite and austenite.
Austenite – It is a solid solution of one or more elements in face-centered cubic iron (gamma iron). Unless otherwise designated (such as nickel austenite), the solute is normally assumed to be carbon.
Austenitizing – It is the formation of austenite by heating a ferrous alloy into the transformation range (partial austenitizing) or above the transformation range (complete austenitizing). When used without qualification, the term implies complete austenitizing.
Austenitic grain size – It is the size attained by the grains of steel when heated to the austenitic region. It can be revealed by appropriate etching of cross sections after cooling to room temperature.
Austenitic manganese steel – It is an alloy steel which combines hardness and toughness. The original austenitic manganese steel has contained 1.2 % carbon and 12 % manganese. Austenitic manganese steel is unique since it combines high toughness and ductility with high work hardening capacity and with good resistance to combat wear at service temperatures up to 250 deg C. It offers the best combination of toughness and resistance to high stress and gouging abrasion. Several variations of the chemical composition of the original austenitic manganese steel are available. These normally involve variations of carbon and manganese, with or without additional alloys such as chromium, nickel, molybdenum, vanadium, titanium, and bismuth.
Austenitic stainless steels – These steels have a face-centered cubic (fcc) structure. This structure is attained through the liberal use of austenitizing elements such as nickel, manganese, and nitrogen. These steels are essentially non-magnetic in the annealed condition and can be hardened only by cold working. They normally possess good cryogenic properties and high temperature strength. Chromium content in these steels normally varies from 16 % to 26 %, nickel up to around 35 % and manganese up to 15 %. The 200 series steels contain high nitrogen, 4 % to 15.5% manganese, and up to 7 % nickel. The 300 series steels contain larger quantities of nickel and up to 2 % manganese. Molybdenum, copper, silicon, aluminum, titanium, and niobium can be added to confer certain characteristics such as halide pitting resistance or oxidation resistance. Sulphur and selenium can be added to certain grades to improve machinability.
Austenitic steels – These are steels which contain sufficient austenite stabilizing elements, such as manganese, nickel, chromium, nitrogen, so that the microstructure of these steels is austenitic at room temperature. The austenitic steels offer the most resistance to corrosion in the stainless group, owing to its substantial nickel content and higher levels of chromium. Such steels cannot be quenched or air hardened but can be work hardened rapidly. They are non-magnetic.
Austenitizing – It is forming austenite by heating a ferrous alloy into the transformation range (partial austenitizing) or above the transformation range (complete austenitizing). When used without qualification, the term implies complete austenitizing.
Authorized person – Authorized person is a person who is approved or assigned to perform a specific type of duty or duties or to be at a specific location or locations at the jobsite.
Autocatalytic plating – it is the deposition of a metal coating by a controlled chemical reduction, catalyzed by the metal or alloy being deposited.
Autoclave – It is an airtight chamber, normally of steel, used for heating articles under pressure, used for a crazing or moisture expansion test.
Autogenous grinding – It is the process of grinding ore in a rotating cylinder using large pieces of the ore instead of conventional steel balls or rods.
Autogenous weld – It is a fusion weld made without the addition of filler metal.
Automatic control – It is the technology used to control processes in order to achieve desired behaviours.
Automatic gauge control – The automatic gauge control system is provided in hot strip mill for the purpose of achieving the desired thickness of the hot strip. It is the system for the regulation of the thickness. For its applications in hot strip mill, the automatic gauge control needs strictly the acquisition of the stretch for each stand. The acquisition of the stand stretch is very important in the case of hot strip mill while in the case of cold rolling mill it is much less important. The stand stretch represents the elastic behaviour of the mechanical structure of the stand when a compressing force is generated by the main hydraulic cylinder (i.e., the hydraulic gap control cylinder). This characteristic is to be known in advance for implementing the automatic gauge control in hot strip mill.
Automatic lubrication system – It lubricates continuously while the machine is working. This increases efficiency as there is no need to stop machinery for lubrication. Lubricating while the bearings are rotating also improves the distribution of lubricant. A small quantity of grease remains flowing, keeping out contamination even when the machine is operating in a harsh environment. It is an effective way to increase machine availability. The system provides the appropriate lubrication quantity at the correct intervals, minimizing friction and wear and optimizing bearing and machinery service life. It provides proper, precise lubricant replenishment to all required points, enabling a range of benefits in the process.
Automatic mode – Automatic mode is when the controller generates an output signal based on the relationship of process variable to the set-point.
Automatic press – It is a press in which the work is fed mechanically through the press in synchronism with the press action. The automation in an automatic press is provided along with the built-in electrical and pneumatic control equipment.
Automatic welding – It is th/e welding with equipment where the welding operation is performed without adjustment of the controls by a welding operator. The equipment can or cannot load and unload the work-pieces.
Automation – Automation describes a wide range of technologies that reduce human intervention in processes, mainly by predetermining decision criteria, subprocess relationships, and related actions, as well as embodying those predeterminations in machines. Automation has been achieved by various means including mechanical, hydraulic, pneumatic, electrical, electronic devices, and computers, normally in combination.
Automotive steels – Automotive steels can be classified in several different ways. One is a metallurgical designation providing some process information. Common designations include (i) low-strength steels (interstitial free and mild steels), (ii) conventional high strength steel (carbon-manganese, bake hardening and high strength low alloy steels), and (iii) the new advanced high strength steels (dual phase, transformation-induced plasticity, twinning-induced plasticity, ferritic-bainitic, complex phase and martensitic steels). Additional higher strength steels for the automotive industry include hot formed steels, post forming heat-treated steels, and steels designed for unique applications that include improved edge stretch and stretch bending.
Auxiliary anode – In electroplating, a supplementary anode positioned so as to raise the current density on a certain area of the cathode and hence get better distribution of plating.
Auxiliary electrode – It is an electrode normally used in polarization studies to pass current to or from a test electrode. It is normally made from a noncorroding material.
Auxiliary feedwater – It is the backup water supply for a nuclear power plant. It is used to supply water to steam generators during reactor start up and shutdown, and during accident conditions to remove decay heat from the reactor.
Auxiliary fuels – Auxiliary fuels are those fuels which are injected in the blast furnace through the tuyeres. Examples are pulverized coal, natural gas, heavy oil, tar, and coke oven gas etc.
Auxiliary poles – These poles on the load lifting magnet which are engaged only when the angles or round bars are handled, and provide the needed spacing and the needed magnet face contact on the angles and bars to make the lift.
Auxiliary pole plates – Auxiliary pole plates are added to the ‘integral’ poles of a magnet on its working face when the integral magnet poles do not match a load shape closely enough for efficient handling. Auxiliary poles can be interchanged on a magnet at different times to match different loads.
Available draft – It is the draft which can be utilized to cause the flow of air for combustion or the flow of products of combustion.
Availability factor – It is the fraction of time during which the unit is in operable condition.
Averaging pitot tube – It is an insertion or fixed probe which spans the process pipe diameter. The outer pitot tube of the probe has a number of pressure sensing ports facing upstream which are positioned at equal annular points in accordance with a log-linear distribution.
Avogadro’s number – It is the number of molecules (6.02 × 10to the power 23) in a gram-molecular weight of any substance.
Axial – It is longitudinal, or parallel to the axis or centerline of a part. It normally refers to axial compression or axial tension or orientation of a metallographic or mechanical test sample.
Axial fans – It consists of a propeller or disc type of wheel within a cylinder which discharges air parallel to the axis of the wheel. Axial fans move an air stream along the axis of the fan. The air is pressurized by the aerodynamic lift generated by the fan blades. Axial fans are normally used in clean air, low-pressure, high-volume applications. Axial fans have less rotating mass and are more compact than centrifugal fans of comparable capacity. Additionally, axial fans tend to have higher rotational speeds and are somewhat noisier than in-line centrifugal fans of the same capacity.
Axial loading – Axial loading is defined as applying a force on a structure directly along an axis of the structure. Axial loads are those which can withstand a force in the same direction as the axis, also known as thrust loading.
Axial ratio – It is the ratio of the length of one axis to that of another, for example, ‘c/a’, or the continued ratio of three axes, such as ‘a:b:c’.
Axial rolls – In ring rolling, these are vertically displaceable, tapered rolls mounted in a horizontally displaceable frame opposite to, but on the same centre-line as, the main roll and rolling mandrel. The axial rolls control ring height during rolling.
Axial strain – It is the linear strain in a plane parallel to the longitudinal axis. Strain can be axial (tensile or compressive) or shear. For constant-volume materials, axial strain in a direction is equal in magnitude to the areal strain on a plane who’s normal is in the direction of axial strain. Axial strain is the integral of a change in length divided by a length.
Axial stress – It is the result of a force acting perpendicular to an area of a body, causing the extension or compression of the material. If extended longitudinally, a body it is considered to be subject to a tensile axial stress, whereas if compressed, it is subject to a compressive axial stress. Conventionally in structural design, a tensile stress is positive and a compressive stress is negative.
Axis control – It is the heart of the control system and controls the position of the shear blades to assure precision and repeatability of the cut length. For performing this function, it receives, as inputs, the encoder of the stand, the encoder of the shear, the hot metal detector and the proximity switch and generates as output the speed or torque request for the shear drive.
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