Abstract

The electrochemical behaviour of aluminium in chloride solutions has been studied. Open-circuit impedance measurements reveal that in both acidic and neutral media the dissolution of the oxide formed on aluminium is governed by an empirical relation of the form C m -1 = a − Bt 1 2 where a and B are constants. The rate of the oxide film dissolution in the chloride-containing solutions is found to be markedly lower than that in other halide media, especially in fluoride solutions. The behaviour of the oxide is determined by the pH of the dissolution medium rather than its chloride ion content. Complex plane analysis of the anodic oxide film formed on aluminium indicates that the corrosion resistance is very high in neutral chloride solutions in comparison with acid solutions containing the same amount of chloride ions. Both the charge transfer resistance θ and the Warburg impedance caused by diffusional mass transfer attain markedly higher values in the neutral media which reflect the high passivation properties of the oxide film. It is suggested that many constructions could be coated with aluminium oxide films to protect them from corrosion, especially in marine media.

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