Free Web Hosting Provider - Web Hosting - E-commerce - High Speed Internet - Free Web Page
Search the Web

   Cr

CHROMIUM

(Gr chroma, color)

Cr at. wt. 51.996
   at. no. 24
   m.p. 1890°C
   b.p.  2482°C 
   sp. gr. 7.18-7.20 (20°C)
   valence chiefly 2, 3, or 6. 

Chromium was discovered in 1797 by Vauquelin, who prepared the metal the next year. Chromium is a steel gray, lustrous, hard metal that takes a high polish. The principal ore is chromite (FeO Cr2O3), which is found in Southern Rhodesia, U.S.S.R., Transvaal, Turkey, Iran, Albania, Finland, Malagasy, and the Philippines. The metal is usually produced by reducing the oxide with aluminum. Chromium is used to harden steel, to manufacture stainless steel, and to form many very useful alloys. Much is used in plating to produce a hard, beautiful surface and to prevent corrosion. Chromium is used to give glass an emerald green color. It finds wide use as a catalyst. All compounds of chromium are colored; the most important are the chromates 4, V of sodium and potassium (K2CrO4) and the dichromates (K2Cr2O7) and the potassium and ammqnium chrome alums, as KCr(504)2.12H20. 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. The refractory industry has found chromite useful for forming bricks and shapes, as it has a high melfing point, moderate thermal expansion, and stability of crystal- line structure. Hexavalent chromium compounds are toxic. The recommended maximum-allowable concentration of dusts and mists in air, measured as CrO3, is 0.1 mg./cu.m for daily 8-hr. exposure. Chromium is available in high-purity form.

Return to periodic table

© 1999 F. Davies
Delphi O.E.M. Co.
All rights reserved