Formation process of porous anodic film in sulfuric/oxalic acid mixture electrolyte

Porous anodic alumina film (PAA film) was fabricated on pure aluminum in sulfuric/oxalic acid mixture electrolyte and was compared with the film prepared in single sulfuric acid electrolyte. Scanning electron microscopy (SEM) was employed to investigate the surface morphology, and the j-t curves were also recorded to analyze the formation process of porous anodic film. Uniform pores of high regularity were obtained in sulfuric/oxalic acid mixture electrolyte. With addition of oxalic acid in the electrolyte, PAA film with a diameter of 47 nm and thickness of 57 μm was obtained at 26 V. The film formation process includes three stages: formation of barrier layer, germination of micro-pores and stable increasing stage of porous anodic film.