Anodizing of Aluminum in Aliphatic Monoamine Baths Containing Organic Acid Salts

Abstract

We studied the formation of anodic oxidation coating on aluminum in a mixture bath of aliphatic monoamine and organic acid salts without ammonium fluoride. Aluminum was anodized in aliphatic monoamine baths (methylamine, ethylamine, propylamine, and buthylamine) containing organic acid salts (formic, acetic, oxalic, tartaric, and citric acid salts), at a bath temperature of 20°C, and a current density of 1A·dm^-2. Anodized films formed in monoamine baths containing ammonium tartrate and triammonium citrate. Film was found to be thinner about 4-5μm when formed in monoamine baths containing ammonium tartrate and triammonium citrate than film when formed in baths containing ammonium fluoride about 7-8μm. SEM observation of film showed that film formed in mathylamine baths containing ammonium tartrate or triammonium citrate had a smoother surface than that formed in other amine baths containing ammonium tartrate or triammonium citrate. The smooth surface was apparently formed by dissolution of the film surface in an amine alkaline bath. (tartrate bath pH=11.4 or citrate bath pH=11.7). Pore diameters of film formed in amine baths containing tartrate and citrate were about 25-45nm.