TIN PROCESSING

preparation of the ore for use in various products. Tin (Sn) is a relatively soft and ductile metal with a silvery white colour. It has a density of 7.29 grams per cubic centimetre, a low melting point of 231.88 C (449.38 F), and a high boiling point of 2,625 C (4,757 F). Tin is allotropic; that is, it takes on more than one form. The normal form is white tin, or beta tin, which has a body-centred tetragonal crystal structure. The second allotrope, gray or alpha tin, has a face-centred cubic structure. Gray tin is theoretically stable below 13 C (55 F), but in practice it is readily formed only at about -40 C (-40 F). This transformation is difficult to initiate and is severely retarded by the presence of alloying elements or trace impurities. Nonetheless, it has given rise to the extremely rare laboratory curiosity known as tin pest. Tin finds industrial application both as a metal and in chemical compounds. As a metal it is used in a very wide variety of industrial applicationsbut almost always in combination with other elements as an alloy or coating, since its intrinsic softness precludes its use as a structural material. Although tin is usually a minor constituent in alloys, it is an essential one on account of the way in which its special properties confer improvements to the matrix metal. The major commercial applications of tin are in tinplate, solder alloys, bearing metals, tin and alloy coatings (both plated and hot-coated), pewter, bronzes, and fusible alloys. In its chemical reactions, tin exists in two valence states (II and IV) and is amphoteric (able to react as both an acid and a base). In addition, it can link directly with carbon to form organometallic compounds. These properties have given rise to many important uses for tin chemicalsfor example, in electroplating, agricultural and pharmaceutical products, and plastics and ceramics. Additional reading Comprehensive and up-to-date information on many aspects of metallurgy, individual metals, and alloys can be found in convenient reference-form arrangement in the following works: 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; Herman F. Mark et al. (eds.), Encyclopedia of Chemical Technology, 3rd ed., 31 vol. (197884), formerly known as Kirk-Othmer Encyclopedia of Chemical Technology, with a 4th edition begun in 1991; and its European counterpart, the first English-language edition of a monumental German work, Ullmann's Encyclopedia of Industrial Chemistry, 5th, completely rev. ed., edited by Wolfgang Gerhartz et al. (1985 ). The Editors of the Encyclopdia BritannicaB.T.K. Barry and C.J. Thwaites, Tin and Its Alloys and Compounds (1983), is a detailed scientific monograph covering the physical and chemical properties of tin and all aspects of its applications, both as a metal and as a chemical. Focus on mining, smelting, and refining is provided in C.L. Mantell, Tin: Its Mining, Production, Technology, and Applications, 2nd ed. (1949, reissued 1970). Ernest S. Hedges (ed.), Tin and Its Alloys (1960), contains expert contributions on the major metallurgical uses of tin. S.J. Blunden, P.A. Cusack, and R. Hill, The Industrial Uses of Tin Chemicals (1985), is a detailed scientific monograph on production, properties, and applications of tin compounds. B.T.K. Barry