CHROMIUM PROCESSING

preparation of the ore for use in various products. Chromium (Cr) is a brilliant, hard, refractory metal that melts at 1,857 C (3,375 F) and boils at 2,672 C (4,842 F). In the pure state, it is resistant to ordinary corrosion, resulting in its application as an electroplated protective coating for other metals. It dissolves in nonoxidizing mineral acids but not in aqua regia or nitric acid, which passivate the metal. Because chromium and chromium-rich alloys are brittle at room temperature, they have limited application. By far the largest consumption is as an alloying addition to iron. In amounts varying from 10 to 26 percent, chromium imparts corrosion resistance to steel; it is also used to improve hardenability, wear-resistance, and high-temperature strength. As the mineral chromite, chromium is employed extensively as a refractory material. Other chromium chemicals are used as pigments and tanning agents. 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 Metals Handbook, 9th ed., 17 vol. (1978-89), a massive and detailed source prepared under the direction of the American Society for Metals, with a 10th edition that began publication in 1990. The Editors of the Encyclopdia Britannica Articles on the extractive metallurgy and commercial applications of chromium and manganese are found in Herman F. Mark et al. (eds.), Encyclopedia of Chemical Technology, 3rd ed., 31 vol. (1978-84), 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- ). See also F.P. Edneral, Electrometallurgy of Steel and Ferro-Alloys, 2 vol. (1979; originally published in Russian, 1955); A.G. Robiette, Electric Smelting Processes (1973); and A.H. Sully and E.A. Brandes, Chromium, 2nd ed. (1967). James H. Downing