ELECTRONIC CONDUCTION OF ANODIZED ALUMINIUM ELECTRODES

Anodic leakage currents je through non-porous oxide films on aluminium at 20°C have been investigated. The films were obtained by anodizing Al in an aqueous ammonium borate solution of pH = 6, first galvanostatically to the required potential, then potentiostatically until the current density had reached 1 μA/cm2. je was measured as a function of time after applying a given potential U and the observed hysteresis effect investigated. The steady current is different when a given potential is obtained by increasing or decreasing the potential, the difference increasing with the thickness of the oxide layer D. The relationship between je and field strength E across the layer could be described by the equations je = αe exp (βeE 1 2), where βe is a constant, and αe increases with the increase of D. This increase of leakage current with thicker layers is interpreted as due to electron multiplication as a result of impact ionization by electrons, accelerated by the electrical field in the oxide layer. je does not depend on the composition of the experimental electrolyte after anodizing under standard conditions. Existing theories on anodic leakage conductivity through alumina layers are criticized. © 1969.