Study of porous oxide film growth on aluminum in oxalic acid using a re-anodizing technique

Abstract

The effects of current density on the porous alumina films formed on Al foil in 4% oxalic acid have been studied using the film thickness measured with the help of a mechanical profiler with computer signal processing, and the barrier layer thickness determined by a re-anodizing technique. A digital voltmeter with a computer system was used to record the change in the anode potential with re-anodizing time. It was established that the dependence of the logarithm of the ionic current density on the electric field strength consists of two linear regions. At electric field strengths higher than 9.9MVcm−1 a decrease in the rate of ionic current density growth by 1.88 times is observed. This peculiarity of the dependence was explained by the decrease in the effective charge of mobile ions that are jumping over the energetic barrier in order to enter the oxide. At high field strengths the linear dependence of the electric field strength across the barrier layer on the inverse volume expansion factor of porous alumina films has been established.