cerium

cerium (sēr`ēəm) [from the asteroid Ceres], metallic chemical element; symbol Ce; at. no. 58; at. wt. 140.12; m.p. 799°C;; b.p. 3,426°C;; sp. gr. 6.77 at 25°C;; valence +3 or +4. Cerium is a soft, malleable, ductile, iron-grey metal with hexagonal or cubic crystalline structure. It is slightly harder than lead. It is the most abundant of the rare-earth metals of Group 3 of the periodic table. It does not tarnish rapidly in dry air but quickly loses its luster in moist air. It oxidizes slowly in cold water and rapidly in hot water. It is attacked by solutions of alkalis and by concentrated or dilute acids. When heated it burns with a brilliant flame to form the oxide (ceria) that exhibits incandescence and is used in making lamp mantles (see Welsbach mantle). The metal is used as a core for the carbon electrodes of arc lamps. The element forms alloys with other metals. An alloy of cerium and iron is used as the flint in cigarette and gas lighters. Minute particles of this alloy ignite in the air when scratched from the surface of the larger mass. Cerium is prepared by electrolysis of the chloride or by reduction of the fused fluoride with calcium. Cerium was recognized in 1803 in the oxide (ceria) as a new metal by M. H. Klaproth and by J. J. Berzelius and Wilhelm Hisinger; it was named for the asteroid Ceres, which had been discovered only two years earlier. The metal was obtained in a very impure state by C. G. Mosander and by Friedrich Wöhler some thirty years later; the nearly pure metal was not obtained until 1875 by W. F. Hillebrand and T. H. Norton.

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cerium

Chemical element, a rare earth metal of the lanthanide series (hence having many properties of the transition elements), chemical symbol Ce, atomic number 58. It is iron-gray and fairly soft and ductile. Found in many ores, it is about as abundant as copper and three times as abundant as lead. The metal is used in alloys and other metallurgical applications and (because it oxidizes strongly and rapidly) in illumination, ignition, and signaling devices and in propellants. Misch metal, used in lighter flints, is 50% cerium. Cerium compounds (in which it has valence 3 or 4) are used in the mantles of lanterns, in the ceramic, photographic, and textile industries, and in analytical chemistry.

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cerium

a malleable ductile steel-grey element of the lanthanide series of metals, used in lighter flints and as a reducing agent in metallurgy. Symbol: Ce; atomic no.: 58; atomic wt.: 140.115; valency: 3 or 4; relative density: 6.770; melting pt.: 798°C; boiling pt.: 3443°C

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cerium [′sir·ē·əm]

(chemistry)

A chemical element, symbol Ce, atomic number 58, atomic weight 140.12; a rare-earth metal, used as a getter in the metal industry, as an opacifier and polisher in the glass industry, in Welsbach gas mantles, in cored carbon arcs, and as a liquid-liquid extraction agent to remove fission products from spent uranium fuel.