Abstract
Anodizing of 99.99% aluminum sheets was carried out in various mono-, di- and oxy-carboxylic acids at a current density of 10mA/cm2, and the surface states of the films and of the substrata stripped from the oxide were observed by SEM. In mono-carboxylic acids, in general, anodic corrosion easily took place on the barrier films formed at the initial stage of anodizing, while in formic, acetic, and sometimes butyric acids, aluminum compounds such as oxides and hydroxides were formed on the pits. In butyric and gluconic acids, features of the pits were influenced by the orientation of the substrata. In glycolic acid as a mono-oxy mono-carboxylic acid, porous films with some pittings were formed. In di-carboxylic acids, barrier or porous films were produced, and cell diameters of the porous films as observed on the substrata had a linear relationship with the final bath voltage. In maleic acid, the porous film structure was observed clearly only inside the pits. These results obtained from the observation of structures of the film surfaces and substrata have made it possible to elucidate the anodic oxidation processes.
