Nanopore formation and growth in phosphoric acid Al anodization

This work describes the pore formation mechanism for anodizations of aluminum foils in phosphoric acid (pore diameters ～100 nm). A detailed study of the four major anodization regimes in phosphoric acid is presented comparing scanning electron microscopy (SEM) cross-sectional views with the respective current density transients. The comparison of the anodization process in phosphoric acid with that using sulfuric and oxalic acid electrolytes is accurately performed through the normalization of the current transients to the characteristic times and current densities of the process.