Studies on Formation of Anodic Oxide Films in Organic Acid-Sulfuric Acid Mixture

Abstract

Anodic oxidation of aluminum was examined in various solutions, such as maleic, tartaric and citric acids as well as the mixtures of sulfuric acid and any of the above-mentioned acid. In tartaric and citric acid solutions, the addition of sulfuric acid increased the specific conductances linearly and resulted in formation of locally thick grown films. Further addition caused the films discontinuous but no pittings. In maleic acid, of which specific conductance was higher than those of tartaric and citric acid, the addition of 0.6-5.0g/l sulfuric acid did not increase the specific conductance and resulted in continuous and colored films having uniform thickness. However, further addition caused pittings.