COBALT PROCESSING

preparation of the metal for use in various products. Below 417 C (783 F), cobalt (Co) has a stable hexagonal close-packed crystal structure. At higher temperatures up to the melting point of 1,495 C (2,723 F), the stable form is face-centred cubic. The metal has 12 radioactive isotopes, none of which occurs naturally. The best-known is cobalt-60, which has a half-life of 5.3 years and is used in medicine and industry. Of the three common ferromagnetic metals (iron, nickel, and cobalt), cobalt has the highest Curie point (that is, the temperature above which its magnetic properties are weakened). It is unique in that, added in moderate amounts to iron, it raises that metal's saturation magnetization (the limit to which its magnetic properties can be raised). Magnetic alloys form the most important use of cobalt. The second most important cobalt outlet is in the making of high-temperature alloys, in which it improves the high-temperature strength and corrosion resistance of alloys based on more common metals, especially nickel and chromium. 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 BritannicaCobalt Monograph (1960), prepared by the Centre d'Information du Cobalt in Brussels in collaboration with the Battelle Memorial Institute in Columbus, Ohio, remains a valuable comprehensive source dedicated specifically to cobalt, covering all aspects of cobalt processing as well as its chemistry and physical, mechanical, and thermodynamic properties. W. Betteridge, Cobalt and Its Alloys (1982), in summarizing the occurrence and extraction of cobalt and in providing data on the properties and applications of cobalt, cobalt alloys, and cobalt compounds, is an ideal update and supplement to the older Cobalt Monograph. Joseph R. Boldt, Jr., The Winning of Nickel: Its Geology, Mining, and Extractive Metallurgy (1967), covers geology, mining, mineral processing, and extractive metallurgy of nickel and associated metals such as copper and cobalt. Boldt's work can be updated, but not replaced, by G.P. Tyroler and C.A. Landolt (eds.), Extractive Metallurgy of Nickel & Cobalt (1988), which collects symposium papers on the latest developments in mineral processing, hydrometallurgy and pyrometallurgy, nickel-cobalt health effects, and particular plant operations. John Campbell Taylor