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Chromium

Author: Robert Husted, Mollie Boorman

Atomic Number 24
Atomic Symbol Cr
CAS ID No. 7440-47-3
Atomic Weight 51.9960 amu
Electron Configuration [Ar] 3d5 4s1
Melting Point 1857.0 C
Boiling Point 2672 C
Density 7.190 g/cm3
History

(Gr. chroma: color) Discovered in 1797 by Vauquelin, who prepared the metal in the following year, chromium is a steel-gray, lustrous, hard metal that takes a high polish.

Sources

The principal ore is chromite, which is found in Zimbabwe, Russia, New Zealand, Turkey, Iran, Albania, Finland, Democratic Republic of Madagascar, and the Phillippines. The metal is usually produced by reducing the oxide with aluminum.

Uses

Chromium is used to harden steel, manufacture stainless steel, and form many useful alloys. It is mostly used in plating to produce a hard, beautiful surface and to prevent corrosion. Chromium gives glass an emerald green color and is widely used as a catalyst.

The refractory industry uses chromite  for forming bricks and shapes, as it has a high melting point, moderate thermal expansion, and stability of crystalline structure.

Compounds

All compounds of chromium are colored. The most important chromates are those of sodium and potassium, the dichromates, and the potassium and ammonium chrome alums. The dichromates are used as oxidizing agents in quantitative analysis, also in tanning leather.

Other compounds are of industrial value; lead chromate is chrome yellow, a valued pigment. Chromium compounds are used in the textile industry as mordants, and by the aircraft and other industries for anodizing aluminum.

Handling

Chromium compounds are toxic and should be handled with proper safeguards.




Last Update: 2011-02-16