2427. Cobalt

Nomenclature

CAS number: 7440-48-4

Description and references

Co; at. wt 58.933195; at. no. 27; valences 1, 2, 3; rarely 4, 5. Group VIII (9). One naturally occurring isotope: 59Co; artificial, radioactive isotopes: 54-58; 60-64. Widely distributed in nature; abundance in earth's crust 0.001-0.002%. Principle ores include cobaltite (CoS2.CoAs2), linnaeite (Co3S4), smaltite (CoAs2) and erythrite (3CoO.As2O5.8H2O). Metal first isolated in 1735 by Brandt. Reviews of prepn: Whittemore in Rare Metals Handbook, C. A. Hampel, Ed. (Reinhold, New York, 1956) pp 105-146; Houot, Ann. Mines 1969 (April), 9-36. Prepn of high purity metal: Ware in Ultrapurification of Semiconductor Materials, M. S. Brooks, J. K. Kennedy, Eds. (Macmillan, New York, 1962) pp 192-204. Cobalt appears to be essential to life. Plays an important part in animal nutrition; the absence of cobalt-contg vitamin B12 causes pernicious anemia. The reactor-produced 60Co (T 1/2 5.263 years; β- 0.314 Mev; γ 1.173, 1.332 Mev) is a widely used source of radioactivity: Centre d'Information du Cobalt, Cobalt Monograph (Brussels, 1960) 515 pp. Comprehensive reviews of cobalt and its compds: ACS Monograph Series no. 149, entitled “Cobalt, Its Chemistry, Metallurgy and Uses,” R. S. Young, Ed. (Reinhold, New York, 1960) 424 pp; Nicholls in Comprehensive Inorganic Chemistry vol. 3, J. C. Bailar, Jr. et al, Eds. (Pergamon Press, Oxford, 1973) pp 1053-1107; F. Planinsek, J. B. Newkirk in Kirk-Othmer Encyclopedia of Chemical Technology vol. 6 (Wiley-Interscience, New York, 3rd ed., 1979) pp 481-494. Review of toxicology and human exposure: Toxicological Profile for Cobalt (PB2004-104398, 2004) 486 pp.

Properties

Gray, hard, magnetic, ductile, somewhat malleable metal. Exists in two allotropic forms. At room temp the hexagonal form is more stable than the cubic form; both forms can exist at room temperature. Stable in air or toward water at ordinary temp. d 8.92. mp 1493°. bp about 3100°. Brinell hardness: 125. Latent heat of fusion 62 cal/g, latent heat of vaporization 1500 cal/g. Specific heat (15-100°): 0.1056 cal/g/°C. Readily sol in dil HNO3; very slowly attacked by HCl or cold H2SO4. The hydrated salts of cobalt are red, and the sol salts form red solns which become blue on adding concd HCl.

Caution

Potential symptoms of overexposure to metal, dust or fumes are coughing, dyspnea; wheezing and decreased pulmonary function; weight loss; dermatitis; diffuse nodular fibrosis; respiratory hypersensitivity; asthma. See NIOSH Pocket Guide to Chemical Hazards (DHHS/NIOSH 97-140, 1997) p 74.

Use

For alloys; manuf cobalt salts; in nuclear technology. Since 60Co can be encapsulated compactly, it has replaced radium in exptl medicine and cancer research. Cobalt is also used in the cobalt bomb, a hydrogen bomb surrounded by a cobalt metal shell. When the nuclear explosion occurs 60Co is formed from 59Co by neutron capture. Considered a “dirty bomb” because of long half-life and intense β- and γ radiation. Max permissible concentration of 60Co in air: 10-7μCi/cc, Natl. Bur. Stand. Handb. 69, 31 (1959).

Therapeutic Category

Trace mineral; 60Co as antineoplastic (radiation source).

Keywords

Cobalt 60Co: Antineoplastic (Radiation Source)