MANGANESE PROCESSING

preparation of the ore for use in various products. Manganese (Mn) is a hard, silvery white metal with a melting point of 1,244 C (2,271 F). Ordinarily too brittle to be of structural value itself, it is an essential agent in steelmaking, in which it removes impurities such as sulfur and oxygen and adds important physical properties to the metal. For these purposes it is most often employed as a ferromanganese or silicomanganese alloy; as a pure metal it is added to certain nonferrous alloys. Manganese is an allotropic metalthat is, its crystal structure changes with temperature. While cooling from the molten state down to 1,138 C (2,080 F), it solidifies into a body-centred cubic structure called the delta (d) phase; from that point down to 1,100 C (2,000 F) it is in the face-centred cubic gamma (g) phase, and from this point down to room temperature it goes through the beta (b) and alpha (a) phases. These last two phases, characterized by complex cubic structures, are extremely hard and brittle, while the simpler gamma phase is more ductile. Manganese metal oxidizes superficially in air, rusts in moist air, and burns in air or oxygen at elevated temperatures. It decomposes water slowly when cool and rapidly when heated, forming hydrogen gas and manganous hydroxide, and it dissolves readily in dilute mineral acids, generating hydrogen and various manganous salts. The chemical reactivity of the metal accounts for its utility in metallurgy and in various chemical compounds. 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. The Editors of the Encyclopdia BritannicaArticles 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. (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 ). See also F.P. Edneral, Electrometallurgy of Steel and Ferro-Alloys, 2 vol. (1979; originally published in Russian, 1955). James H. Downing