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   Cd

CADMIUM

(L. cadmia; Gr. kaalmeia ancient name for calamine, zinc carbonate)

Cd  at. wt. 112.40
     at. no. 48
     m.p.   320.9°C 
     b.p. 765°C
     sp. gr. 8.65 (20°C)
     valence 2.

Cadmium was discovered by Stromeyer in 1817 from an impurity in zinc carbonate. Cadmium most often occurs in small quantities associated with zinc ores, such as sphalerite (ZnS). Greenockite (CdS) is the only mineral of any consequence bearing cadmium. Almost all cadmium is obtained as a by-product in the treatment of zinc, copper, anct lead ores. It is a soft, bluish-white metal which is easily cut with a knife. It is similar in many respects to zinc. It is a component of some of the lowest melting alloys; it is used in bearing alloys with low coefficients of friction and great resistance to fatigue; it is used extensively in electroplating, which accounts for about 69% of its use. It is also used in many types of solder, for standard E.M.F. cells, for batteries, and as a barrier to control atomic fission. Cadmium compounds are used in black and white television phosphors and in blue and green phosphors for color TV tubes. It forms a number of salts of which the sulfate is the most common; the sulfide is used as a yellow pigment. Cadmium and solutions of its compounds are toxic. Failure to appreciate the toxic properties of cadmium may cause workers to be unwittingly exposed to dangerous fumes. Silver solder, for example, which contains cadmium, should be handled with care. The recommended maximum allowable (8-hr.-day) concentration of cadmium vapor in air is 0.1 mg/cu. meter. The current price of cad- mium is about $2.50/lb. It is available in high-purity form.

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