Dissolution behavior of the barrier layer of porous anodic films formed on aluminum studied by pore-filling technique.

Abstract

Dissolution behavior of the barrier layer of porous anodic films formed on aluminum after immersion in sulfuric acid has been studied using re-anodizing (pore-filling) technique. The higher a forming voltage is, the higher the dissolution rate of a film. The barrier layer of films formed in phosphoric acid was divided into three layers according as dissolution rate and was dissolved most rapidly in a middle layer. The defects were detected after the dissolution of an outer layer as fine pores which passed through the barrier layer. The volume of the defects increased with increasing forming voltage. In films formed in oxalic acid, however, no such defects as above but thickness unevenness were detected in the middle of the barrier layer which was divided into two layers. The dissolution rates of inner layers of films formed in two electrolytes at different voltages were low and almost same. The dissolution rate is suggested to depend on both contents of incorporated anions and defects.