Non-peroxide trivalent chromium passivate composition and process

Abstract

An aqueous acidic peroxide-free solution and process for treating receptive metal surfaces to impart a chromium passivate film thereon containing chromium ions substantially all of which are present in the trivalent state, hydrogen ions to provide a pH of about 1.2 to about 2.5, at least one additional metal ion selected from the group consisting of iron, cobalt, nickel, molybdenum, manganese, aluminum, lanthanum, cerium, lanthanide mixtures as well as mixtures thereof present in an amount effective to activate the formation of the chromate passivate film and nitrate ions as the essential oxidizing agent present in an amount to provide a mol ratio of nitrate ions to chromion ions and activating metal ions of at least about 4:1 and sufficient to activate the hydrated trivalent chromium to form a chromate film on the substrate. The aqueous acidic solution can optionally, and preferably further contain controlled amount of sulfate ions, halide ions, organic carboxylic acids, a bath soluble and compatible silicate compound, and one or a combination of wetting agents to further enhance the characteristics of the passivate film produced.

Dependencies are inferred from the claim text.