About Chromates

Chromate Ion

Chromate salts contain the anion CrO42-, while dichromate salts contain the dichromate anion, Cr2O72-. Both classes of compounds contain chromium in the oxidation state +6--hexavalent chromium--and act as strong oxidizing agents. Water soluble chromates are frequently used in chrome electroplating processes used to protect underlying metals from corrosion or improve paint adhesion. Chromate conversion coating, a process which uses oxidants to passivate certain metal alloy surfaces, may utilize chromate derived from chromic acid. Non-soluble chromates have strong colors and have been used as pigments. Because hexavalent chromium is now known to be toxic, chromate waste disposal is regulated and chromate usage is declining in areas where there are suitable substitutes. In particular, chromium pigments such as chrome yellow, widely recognized as the color of American school buses, have largely fallen out of use in favor of safer pigment compounds.