UNOXIDIZED ALUMINUM PARTICLES IN ANODIC ALUMINA FILMS

Alumina films which were anodized in a sulfuric acid solution were studied optically and chemically to verify the presence of unoxidized aluminum in the films. We extracted metallic aluminum from anodic alumina films by using bromine methanol and detected unoxidized aluminum successfully. The volume ratio of unoxidized aluminum increases with the electric current density of anodization and decreases by heating the film after anodization. These results show the close relationship between unoxidized aluminum and the prominent polarization function that is observed in the alumina films. From the present experiments and theoretical analysis, it seems certain that some amount of aluminum remains unoxidized when anodization is carried out at a large current density.