Nomenclature
CAS number: 7440-45-1
Description and 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, T 1/2 >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 α-form, d 6.770, transforms to β-form at -150°; hexagonal β-form transforms to γ-form
at -10°; face-centered cubic γ-form transforms to δ-form at 730°;
body-centered cubic δ-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). Flammable as slabs, ingots or rods.
Turnings or gritty powder dangerous when wet. 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.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.