Corrosion and passive behaviour of aluminium in weakly alkaline solution

The title subject has been studied by stationary and transient polarization measurements on high-purity aluminium electrodes in acetate solutions of pH 7–10 at 25°C and by Auger electron spectroscopic investigations of oxide films formed. In such deoxygenated solutions, aluminium corrodes under hydrogen evolution and is in some state of active/passive transition, or close to it. Oxygen (when added) acts as a passivator and mostly lowers the corrosion rate. The stationary passive current is potential independent, but varies with pH. It goes through a minimum at a pH of about 8. Oxide films formed have a thin inner barrier layer and an outer non-barrier layer whose thickness increases with increasing pH. Transients yield information on the barrier layer and on charge transfer reactions occurring.