Patent ID: 6022425
Filing Date: 2000-02-08
Classification: C23C

Abstract:
A process for forming a chromate and phosphate free conversion coating on the surface of a metal, including the steps:(a) contacting the metal surface with a deoxidizing solution in order to remove smut from the metal surface;(b) contacting the metal with an acid solution containing an oxidant selected from the group consisting of: metal halate, metal persulphate, nitrate, H.sub.2 O.sub.2 or (NH.sub.4).sub.2 Ce(NO.sub.3).sub.6 and having a pH of less than 1, in order to initiate growth of a metal oxide cell structure on the metal surface, said acidic, oxidant-containing solution having a composition different to said deoxidizing solution;(c) contacting the metal surface with water having a temperature between 70.degree. C. and the boiling point, for a period of time sufficient to thicken the oxide structure and form a metal oxide containing layer of a desired thickness; and(d) contacting the metal surface with an aqueous, rare earth element containing solution in order to impregnate and substantially seal the metal oxide containing layer.