ACTIVATION OF ALUMINUM IN HALIDE SOLUTIONS CONTAINING ACTIVATOR IONS

The activation of 99-999% aluminium by the 'activator' elements-indium, mercury, gallium, zinc and tin- was studied using potentiostatic current-time techniques. These ions, dissolved in the test electrolyte, plate on to the aluminium surface giving rise to localized attack which was manifested by current fluctuations or surges. The induction period-tau, prior to the onset of attack, was shown to depend on (i) passivation potential; (ii) halide type and concentration; (iii) quality of the passive film; (iv) temperature. The data obtained with mercury ions support the oxide-detachment mechanism advanced by Reboul et al. An alternative mechanism based on the surface-charge characteristics of the new-formed oxide is proposed for activation by indium and gallium species.