METAL COATINGS COMPRISING HEXAVALENT CHROMIUM,TRIVALENT CHROMIUM,SILICA OR A SILICATE AND AN ALKALI METAL CATION

摘要

A method of providing metals with electrical and/or corrosion resistance, which comprises coating the metal surface with an aqueous composition that has a pH of not more than 4.0 and that contains, uniformly dissolved or dispersed therein: (a) a hexavalent chromium compound; (b) a trivalent chromium compound; (c) silica and/or a silicate in a total ratio of at least 0.5 grams per 100 ml of the composition; and (d) an alkali metal cation, the weight ratio of hexavalent chromium to total chromium (both determined as CrO3) being between 0.5: 1 and 0.75: 1, the total chromium content being at least 0 .5 grams of chromium (calculated as CrO3) per 100 ml. of the composition, and the weight ratio of hexavalent chromium (calculated as CrO3) to alkali metal (calculated as the hydroxide) being between 5: 1 and 100: 1; and then curing the coating to make its hexavalent chromium content substantially insoluble in water. (Machine-translation by Google Translate, not legally binding)