NIOBIUM PROCESSING

preparation of the ore for use in various products. Niobium (Nb) has a body-centred cubic (bcc) crystal structure and a melting point of 2,468 C (4,474 F). Of the refractory metals, it has the lowest density and best workability; for this reason, niobium-based alloys are often used in aerospace applications. Because of its strengthening effect at elevated temperatures, its principal commercial use is as an additive in steels and superalloys. Niobium-titanium and niobium-tin alloys are used as superconducting materials. 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 Britannica Harry Stuart (ed.), Niobium: Proceedings of the International Symposium (1984), includes articles covering the entire spectrum of niobium science, technology, engineering, and marketing, with some in-depth discussions. A convenient single source of reference information on all the refractory metals is Clifford A. Hampel, Rare Metals Handbook, 2nd ed. (1961, reprinted 1971). Chun Tsin Wang Alexander Sutulov