Transformation of the overall strict kinetic model governing the growth of porous anodic Al2O3 films on aluminium to a form applicable to the non-stirred bath film growth

The strict and complex, overall kinetic model, governing the growth of porous anodic Al2O3 films, was transformed to a form easily and directly applicable to the galvanostatic anodization in a non-stirred bath at constant bath temperature. It was shown that the transformed model always acquires a form different from that of a stirred bath anodization. The transformed model was applied to the experimental results of film growth obtained at 25°C, 15 mA cm-2 and in a wide range of H2SO4 concentration, 5-85% w/v. The application of the transformed model provided, consistently with other experimental observations, the existence of a critical electrolyte concentration near 5% w/v above which the normal mechanism of oxide production and film growth is valid and below which a deficient growth of oxide is observed. The transformed model permitted some predictions for the real pore shapes.