Characteristics: Hard brittle semi-gray metal. Compounds have strong and varied colors. Cr ion forms many coordination compounds. Exists in active and passive forms, the latter giving rise to its corrosion resistance, due to a thin surface oxide layer that passivates the metal when treated with oxidizing agents. Active form reacts readily with dilute acids to form chromous salts. Soluble in acids (except nitric) and strong alkalies; insoluble in water.
Derivation: From chromite by direct reduction (ferrochrome); by reducing the oxide with finely divided aluminum or carbon; and by electrolysis of chromium solutions.
Hazard: Hexavalent chromium (Cr VI) compounds have an irritating and corrosive effect on tissue. Exposure limits for chromium metal and Cr III compounds is 0.5 mg/m3, water-soluble CrVI compounds is 0.05 mg/m3, and insoluble Cr VI compounds is 0.01 mg/m3. Chromium VI compounds are listed as carcinogenic by NTP and IARC.