MAGNESIUM PROCESSING

preparation of the ore for use in various products. Magnesium (Mg) is a silvery white metal that is similar in appearance to aluminum but weighs one-third less. With a density of only 1.738 grams per cubic centimetre, it is the lightest structural metal known. It has a hexagonal close-packed (hcp) crystalline structure, so that, like most metals of this structure, it lacks ductility when worked at lower temperatures. In addition, in its pure form, it lacks sufficient strength for most structural applications. However, the addition of alloying elements improves these properties to such an extent that both cast and wrought magnesium alloys are widely used, particularly where light weight and high strength are important. Magnesium is strongly reactive with oxygen at high temperatures; above 645 C (1,190 F) in dry air, it burns with a bright white light and intense heat. For this reason, magnesium powders are used in pyrotechnics. At room temperature, a stable film of water-insoluble magnesium hydroxide forms on the metal's surface, protecting it from corrosion in most atmospheres. Being a strong reactant that forms stable compounds with chlorine, oxygen, and sulfur, magnesium has several metallurgical applications, such as in the production of titanium from titanium tetrachloride and in the desulfurization of blast-furnace iron. Its chemical reactivity is also evident in the magnesium compounds that have wide application in industry, medicine, and agriculture. 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 BritannicaNils Hy-Petersen, From Past to Future, Light Metal Age, 48(78):12, 1416 (August 1990), is a review of magnesium history. A comprehensive book on magnesium properties, alloys, and uses, with a condensed chapter on extraction technologies, is E.F. Emley, Principles of Magnesium Technology (1966). The best overview of current extraction methods is Nils Hy-Petersen et al., Magnesium, in Ullmann's Encyclopedia of Industrial Chemistry, 5th ed., vol. A15 (1990), pp. 559580. Robert S. Busk, Magnesium Products Design (1987), is a thorough work on magnesium design criteria. Kh. L. Strelets, Electrolytic Production of Magnesium, trans. from Russian (1977), is a reference book on the subject. Nils Hy-Petersen