THE ACTIVATION OF ALUMINUM BY ACTIVATOR ELEMENTS

In this communication, the results of an investigation into the activation of aluminium electrodes by metal salt solutions, using potentiostatic current-time measurements, are described and discussed. Activator salt was added to the aggressive test halide electrolyte after a given passivation period and the current flowing at the electrode was monitored as a continuous function of time. Prior to the detection of activation, as current fluctuations in the potentiostatic measurements, an induction period, found to be a measure of the rate of initiation of attack, was observed. This induction period appears to be a critical phenomenon associated with the build-up of a sufficient concentration of deposited activator complex on the test electrodes to facilitate the onset of attack. For a given applied passivation potential, it is proposed that the role of deposited activator is to 'bias' the surface charge in the direction of activation, and that activation occurs only when sufficient bias has been achieved. Since halide adsorption occurs more readily at the biased surface, attack of the electrode proceeds the more readily.