Anodic oxidation of aluminium in sulphuric acid under potentiostatic conditions

Abstract

The behaviour of the current and impedance have been investigated at low potentials and temperatures by means of a potentiostatic technique for the initial anodic oxidation of aluminium in sulphuric acid. A linear relationship between the reciprocal capacitance and the oxide over potential was obtained and found to be independent of temperature. However, the resistance of the oxide films was temperature dependent. It increases with increasing electrical field. A deviation from an exponential relationship between the current and the potential was found at lower potentials. The experimental data obtained indicate that the initial growth of the pores of the oxide films depends on the applied electrical field strength. A deviation from the empirical exponential relationship between the ionic current and the electrical field strength for the barrier type film is a characteristic of the porous type film in the region of low oxide over potentials.