Cerium
Title: Cerium
CAS Registry Number: 7440-45-1
Literature References: Ce; at. wt 140.116; at. no. 58; valences 3, 4. A rare earth metal, most abundant member of the lanthanide series. Naturally occurring isotopes (mass numbers): 140 (88.48%); 142 (11.08%), radioactive, T½ >5 ´ 1016 years; 138 (0.25%); 136 (0.19%). Known artificial radioactive isotopes: 124-135; 137; 139; 141; 143-152. Estimated abundance in the earth's crust: 46-66 ppm. Commercially important sources are the rare earth minerals monazite and bastnaesite; also found in cerite. Discovered by Klaproth, Hisinger and Berzelius in 1803. Can be separated from other rare earths by selective precipitation of ceric (4+) salts from buffered solns (pH 3-4); also by ion exchange techniques. Prepn of metal: Spedding et al., Ind. Eng. Chem. 44, 553 (1952). Review of prepn, properties and compds: The Rare Earths, F. H. Spedding, A. H. Daane, Eds. (Krieger, Huntington, N.Y., 1971, reprint of 1961 ed.) 641 pp; Hulet, Bode, "Separation Chemistry of the Lanthanides and Transplutonium Actinides" in MTP Int. Rev. Sci.: Inorg. Chem., Ser. One vol. 7, K. W. Bagnall, Ed. (University Park Press, Baltimore, 1972) pp 1-45; Moeller, "The Lanthanides" in Comprehensive Inorganic Chemistry vol. 4, J. C. Bailar, Jr. et al., Eds. (Pergamon Press, Oxford, 1973) pp 1-101; B. T. Kilbourn in Kirk-Othmer Encyclopedia of Chemical Technology vol. 5 (John Wiley & Sons, New York, 4th ed., 1993) pp 728-749; Chemistry of the Elements, N. N. Greenwood, A. Earnshaw, Eds. (Pergamon Press, New York, 1984) pp 1423-1449. Brief review of properties: G. T. Seaborg, Radiochim. Acta 61, 115-122 (1993).
Properties: Iron-gray, ductile, malleable metal. Only material known to have a solid-solid critical point. Crystalline forms: face-centered cubic a-form, d 6.770, transforms to b-form at -150°; hexagonal b-form transforms to g-form at -10°; face-centered cubic g-form transforms to d-form at 730°; body-centered cubic d-form exists at >730°. mp 798°. bp 3433°. Heat of fusion: 5.179 kJ/mol. Heat of sublimation (25°): 422.6 kJ/mol. E0(aq) Ce3+/Ce -2.48 V (calc). Stable in dry air, but superficially oxidized in moist air; when finely divided may ignite spontaneously. Slowly dec by cold, rapidly by hot water; sol in dil mineral acids. Ceric salts usually are yellow to orange-red in color and liberate iodine from KI. Cerous salts are usually white and give a white ppt with alkali hydroxides or sulfides, insol in excess of reagent; they also are pptd by ammonium oxalate from cold dil acid sols.
Melting point: mp 798°
Boiling point: bp 3433°
Density: d 6.770
Use: In metallurgy as stabilizers in alloys and as an alternative to thorium oxide in welding electrodes. In glass as polishing agent, decolorizer to stabilize impurities, to render glass opaque to near uv radiation, to resist discoloration from strong light or high energy electron bombardment (as in television screens). In ceramics as an opacifying and strengthening agent. Catalysts to impart high cracking activity for crude oil processing, in automotive exhaust control devices, as combustion additive, polymerization initiator, paint drier, polymer stabilizer. As phosphor in fluorescent lamps, cathode ray tubes and thorium dioxide gas mantles.

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