The Effect of Borate on Cerium Film Formation

Cerium cations were found to inhibit corrosion of Aluminun alloys by the formation of a tetravalent cerium oxide film. The film forms by the oxidation of cerium in solution followed by precipitation under alkaline conditions. The process can be accelerated or facilitated by catalyzing the oxidation reaction, e.g., by the addition of hydrogen peroxide in solution. In this work a trivalent film was found to precipitate under similar conditions by the addition of borate to the solution. The addition of borate appears to stifle the oxidation of cerium in solution. The result is most likely the precipitation of an insoluble cerium compound followed by physical deposition.