ON THE CAPACITY OF POROUS ALUMINUM OXIDE LAYERS

Porous aluminum oxide layers may be obtained by anodic oxidation in sulphuric acid. The base of the pores is separated from the metal by a thin insulating barrier layer. The experiments show that the ultimate thickness of the barrier layer remains constant after a critical value has been reached. The dependence of the final thickness on current density, concentration, and temperature has been investigated. It is suggested that an electronic current is involved in the mechanism which limits the growth of the barrier layer.