ZINC PROCESSING

preparation of the ore for use in various products. Zinc (Zn) is a metallic element of hexagonal close-packed (hcp) crystal structure and a density of 7.13 grams per cubic centimetre. It has only moderate hardness and can be made ductile and easily worked at temperatures slightly above the ambient. In solid form it is grayish white, owing to the formation of an oxide film on its surface, but when freshly cast or cut it has a bright, silvery appearance. Its most important use, as a protective coating for iron known as galvanizing, derives from two of its outstanding characteristics: it is highly resistant to corrosion, and, in contact with iron, it provides sacrificial protection by corroding in place of the iron. With its low melting point of 420 C (788 F), unalloyed zinc has poor engineering properties, but in alloyed form the metal is used extensively. The addition of up to 45 percent zinc to copper forms the series of brass alloys, while, with additions of aluminum, zinc forms commercially significant pressure die-casting and gravity-casting alloys. In sheet form, zinc is used to make the cans of dry-cell batteries, and, alloyed with small amounts of copper and titanium, an improved-strength sheet is formed that has applications in the roofing and cladding of many buildings. The chemical compounds of zinc, particularly zinc oxide, have important industrial and pharmaceutical uses. 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 BritannicaC.H. Mathewson (ed.), Zinc: The Science and Technology of the Metal, Its Alloys, and Compounds (1959, reissued 1970), remains a most comprehensive treatment of the subject; a more modern update is S.W.K. Morgan, Zinc and Its Alloys and Compounds (1985), covering history, manufacture, economics, and applications of the metal. More specialized analyses include Frank E. Goodwin and Adolph L. Ponikvar (eds.), Engineering Properties of Zinc Alloys, 3rd rev. ed. (1989); and C.J. Slunder and W.K. Boyd, Zinc: Its Corrosion Resistance, 2nd ed., rev. by T.K. Chrisman et al. (1983). Alan W. Richards