Formation of porous anodic alumina at high current efficiency

Porous anodic films on aluminium have attracted much recent attention with a view to the generation of templates with ordered nanoporosity. The present work addresses the mechanism of film formation and pore development, through examination of films formed in phosphoric acid, with focus on the influence of current density on anodizing efficiency. The findings are consistent with the development of porosity by flow of film material, rather than by film dissolution. Flow of the film material contributes to the film being much thicker than the oxidized aluminium. Notably, the thickness enhancement is promoted at higher rates of film growth, which lead to reduced losses of aluminium species to the electrolyte as the efficiency increases from similar to 0.67 to similar to 0.93 between current densities of 5 and 30 mA cm(-2). Accordingly, an increased amount of oxidized aluminium is available for film formation, such that the film thickness rises from similar to 1.38 to 1.86 times that of the oxidized aluminium.