Evolution process of orderly nanoporous alumina by constant high field anodization in oxalic acid electrolyte

Abstract

The formation process of porous anodic alumina (PAA) fabricated by direct high field anodization in oxalic acid electrolyte was investigated. The results indicate that the evolution process of high field anodization of aluminum is obviously different from that of traditional low field anodization. The rise of current density at a high field implies pore growth, while at a low electrical field it is pore initiation. The interpore distances (Dint) at the top of the PAA films were only half of those at the bottom when the current densities reached peak. But there was a small change when the currents decreased. The origination of the change of Dint was explained by internal stress. The nonuniform internal stress would also be responsible for the slight plastic deformation of the PAA films and the self-adjusting distribution of the pores.