the art and science of extracting metals from their ores and modifying the metals for use. Customarily, metallurgy refers to commercial as opposed to laboratory methods. It also concerns the chemical, physical, and atomic properties and structures of metals and the principles whereby metals are combined to form alloys. Metallurgic practices date from approximately 4000 BC. Copper is believed to have been the first metal extracted from ore. Copper mines have been found in several places in the Middle East, and the mined metal was probably used for weapons and other utilitarian objects. Bronze was probably developed between 4000 and 1400 BC, when it was discovered that an alloy made of copper and tin formed a metal that was less brittle than copper alone. The use of iron, noted as early as 3000 BC in the Middle East, became common there and in southwestern Europe about 1200 BC, and its use gradually spread to Asia. Brass, an alloy of copper and zinc, was developed from 1600 to 600 BC. It was used by the Romans for jewelry, armour, and as currency. Silver was successfully mined starting around 500 BC, and lead was ultimately recovered from the silver ore. Gold, one of the first metals mined, was used in an alloy with silver to form electrum. The first important steel production was started in India some time between 500 BC and 500 AD. Although the Romans made few metallurgical innovations themselves, they contributed to existing techniques of mining and casting and devised a variety of new uses for the metals. Metallurgical principles were first widely disseminated in the 16th century when Vannoccio Biringuccio and Georgius Agricola composed books cataloging most of the available metallurgical knowledge. Extracting metals from crude ore is performed in two phases, mineral dressing and process metallurgy. In the first phase, the ore must be gradually broken down to isolate the desired metallic elements from the crude ore. The most common means of liberating minerals from the ore is by a process of crushing and grinding, after which the ore is sorted, either by hand (for which the ore must have at least one visually distinctive characteristic) or by more advanced methods which may involve gravity concentration, separation by flotation, electrostatic or magnetic separation, or other specialized processes. Process metallurgy, the second phase, is the procedure or series of procedures whereby the minerals which have been separated from ore are reduced to metal, alloyed, and made available for specialization. The three processes commonly applied are pyrometallurgy, electrometallurgy, and hydrometallurgy. The product may be further refined by adapting additional metallurgical techniques, such as distillation. In pyrometallurgy the ore is heated to extreme temperatures, usually in a furnace. In most cases, the fire has a chemical as well as a physical function. The fire burns away certain components of the ore, or it deoxidizes, and thereby reduces, the ore. In electrometallurgy the ore is subjected to an electrolytic process in the extraction and refinement of metals. Hydrometallurgy refers to processes in which the metal is extracted from the ore by an aqueous acid or salt solution. From this solution the metal is precipitated by some suitable reagent. Few methods of metal extraction yield a pure product. What is obtained, as a rule, is a more or less impure metal which must then be further refined to become fit for commercial, industrial, or research purposes. There are six principal methods of metal processing: mechanical working (both cold and hot), foundry processes, surface treatments, powder metallurgy, nuclear metallurgy, and heat treatment. In cold working the metal is hardened and undergoes structural rather than chemical change. In hot working, the metal is softened by heat. This process alters the crystallinity of the metal so that it may then be refined. The metal may be forged or shaped by the rolling or drawing process. Foundries cast metals in molds so that each object is a uniform size and shape. Iron, steel, and nonferrous metals are cast in molds. Surface treatment methods involve the application of an exterior layer to metals by such means as hot dipping, electroplating, and cementation. The purpose of this process is to produce a layer to protect the base substance, or to otherwise alter the surface character of the metal. Powder metallurgy consists of processing metal powder into a die to produce a compressed shape which then, under the process of sintering (diffusion bonding by heating), becomes consolidated and strengthened. Metal powder may be manufactured mechanically or chemically. Nuclear metallurgy involves the production of highly specialized metals for nuclear engineering, specifically, it involves the isolation of fissionable materials. In heat treatment, metals are subjected to heat to produce or improve certain desired qualitiese.g., hardness, ductility, etc. Of great importance to metallurgy is metallography, the science and study of the compositions and structures of metals, particularly by microscopes and X-ray devices. art and science of extracting metals from their ores and modifying the metals for use. Metallurgy customarily refers to commercial as opposed to laboratory methods. It also concerns the chemical, physical, and atomic properties and structures of metals and the principles whereby metals are combined to form alloys. Additional reading History of metallurgy Arthur Street and William Alexander, Metals in the Service of Man (1944), available also in many later editions, is an enduring introduction to metallurgy, with short comments on historical aspects. R.F. Tylecote, The Prehistory of Metallurgy in the British Isles (1986), The Early History of Metallurgy in Europe (1987), and A History of Metallurgy (1976), provide authoritative reference in a field that is becoming the modern science of archaeometallurgy. Colin Renfrew, Before Civilization: The Radiocarbon Revolution and Prehistoric Europe (1973), deals with archaeological evidence of the introduction of metals; and Theodore A. Wertime and James D. Muhly (eds.), The Coming of the Age of Iron (1980), consists of chapters by authorities on specific archaeometallurgical topics. R.J. Forbes, Metallurgy in Antiquity (1950), was for a long time the best comprehensive history; for a more focused study, see Arthur Raistrick, Dynasty of Iron Founders: The Darbys and Coalbrookdale, 2nd rev. ed. (1989), recounting the history of a great centre of iron making in the 18th century and the development of coal-based smelting. The development of the understanding of metallic structure and the significance of that understanding is studied in Cyril Stanley Smith, A History of Metallography: The Development of Ideas on the Structure of Metals Before 1890 (1960, reprinted 1988). K.C. Barraclough, Steelmaking Before Bessemer, 2 vol. (1984), is a history of steelmaking prior to 1850, focusing on blister steel and crucible steel, and Steelmaking: 18501900 (1990), is an account of the development of the Bessemer and open-hearth processes. James A. Charles Extractive metallurgy Chemical theory, fuel technology, process control, and types of extraction processes are presented in J.D. Gilchrist, Extraction Metallurgy, 3rd ed. (1989). Basic principles involved in pyrometallurgy, hydrometallurgy, and electrometallurgy are discussed in W.H. Dennis, Extractive Metallurgy: Principles and Applications (1965). C.B. Gill, Nonferrous Extractive Metallurgy (1980), offers a detailed treatment of current hydrometallurgical and pyrometallurgical extraction and refining processes for the major nonferrous metals, grouped into reactive and nonreactive categories. H.Y. Sohn, D.B. George, and A.D. Zunkel (eds.), Advances in Sulfide Smelting, 2 vol. (1983), covers new and emerging technologies in the smelting of nonferrous metals; and John C. Taylor and Heinrich R. Traulsen (eds.), World Survey of Nonferrous Smelters (1988), covers operations of copper, nickel, lead, and zinc smelters worldwide. A.T. Peters, Ferrous Production Metallurgy (1982), reviews the materials and processes involved in the production of iron and its conversion into steel. Charles Burroughs Gill Physical metallurgy An extended overview of the properties and fabrication of all engineering materials, including metals, can be found in these texts: William D. Callister, Jr., Materials Science and Engineering: An Introduction, 2nd ed. (1991); Richard A. Flinn and Paul K. Trojan, Engineering Materials and Their Applications, 4th ed. (1990); and James F. Shackelford, Introduction to Materials Science for Engineers, 3rd ed. (1992).I. Minkoff, Solidification and Cast Structure (1986), describes the changes that occur on solidification of metals. Sharr Choate, Creative Casting: Jewelry, Silverware, Sculpture (1986), is a better book for someone who wants to cast metal as a hobby. Paul G. Shewmon, Transformations in Metals (1969), explains the changes that occur in metals on alloying and heat treatment; it deals more with theory than with manufacturing equipment. George E. Dieter, Mechanical Metallurgy, 3rd ed. (1986), is a classic text that treats the analysis and methods of deforming metals. William T. Lankford, Jr., et al. (eds.), The Making, Shaping, and Treating of Steel, 10th ed. (1985), covers equipment, compositions, and processing of steel. Fritz V. Lenel, Powder Metallurgy (1980), deals with the theory and practice of this method. The Annual Book of ASTM Standards, section 3, Metals Text Methods and Analytical Procedures, gives a detailed description of approved methods of measuring the properties of metals. In addition, relevant volumes of the Metals Handbook, 9th ed., 17 vol. (197889), a massive and detailed source prepared under the direction of the American Society for Metals, with a 10th edition that began publication in 1990, describe industrial equipment and practice for many processese.g., heat treating, powder metallurgy, mechanical testing, metallography, forming and forging, and casting. Paul G. Shewmon Physical metallurgy Physical metallurgy is the science of making useful products out of metals. Metal parts can be made in a variety of ways, depending on the shape, properties, and cost desired in the finished product. The desired properties may be electrical, mechanical, magnetic, or chemical in nature; all of them can be enhanced by alloying and heat treatment. The cost of a finished part is often determined more by its ease of manufacture than by the cost of the material. This has led to a wide variety of ways to form metals and to an active competition among different forming methods, as well as among different materials. Large parts may be made by casting. Thin products such as automobile fenders are made by forming metal sheets, while small parts are often made by powder metallurgy (pressing powder into a die and sintering it). Usually a metal part has the same properties throughout. However, if only the surface needs to be hard or corrosion-resistant, the desired performance can be obtained through a treatment that changes only the composition and strength of the surface. Structures and properties of metals Metallic crystal structures The commonest metallic crystal structures. Metals are used in engineering structures (e.g., automobiles, bridges, pressure vessels) because, in contrast to glass or ceramic, they can undergo appreciable plastic deformation before breaking. This plasticity stems from the simplicity of the arrangement of atoms in the crystals making up a piece of metal and the nondirectional nature of the bond between the atoms. Atoms can be arranged in many different ways in crystalline solids, but in metals the packing is in one of three simple forms. In the most ductile metals, atoms are arranged in a close-packed manner. If atoms were visualized as identical spheres and if these spheres were packed into planes in the closest possible manner, there would be two ways to stack close-packed planes one above another (see figure). One would lead to a crystal with hexagonal symmetry (called hexagonal close-packed, or hcp); the other would lead to a crystal with cubic symmetry that could also be visualized as an assembly of cubes with atoms at the corners and at the centre of each face (known as face-centred cubic, or fcc). Examples of metals with the hcp type of structure are magnesium, cadmium, zinc, and alpha titanium. Metals with the fcc structure include aluminum, copper, nickel, gamma iron, gold, and silver. The third common crystal structure in metals can be visualized as an assembly of cubes with atoms at the corners and an atom in the centre of each cube; this is known as body-centred cubic, or bcc. Examples of metals with the bcc structure are alpha iron, tungsten, chromium, and beta titanium. Some metals, such as titanium and iron, exhibit different crystal structures at different temperatures. The lowest-temperature structure is labeled alpha (a), and higher-temperature structures beta (b), gamma (g), and delta (d). This allotropy, or transformation from one structure to another with changing temperature, leads to the marked changes in properties that can come from heat treatment (see below Heat treating). When a metal undergoes a phase change from liquid to solid or from one crystal structure to another, the transformation begins with the nucleation and growth of many small crystals of the new phase. All these crystals, or grains, have the same structure but different orientations, so that, when they finally grow together, boundaries form between the grains. These boundaries play an important role in determining the properties of a piece of metal. At room temperature they strengthen the metal without reducing its ductility, but at high temperatures they often weaken the structure and lead to early failure. They can be the site of localized corrosion, which also leads to failure.
Meaning of METALLURGY in English
Britannica English vocabulary. Английский словарь Британика. 2012