THE PASSIVATION OF ALUMINUM IN LITHIUM-CARBONATE BICARBONATE SOLUTIONS

The anodic dissolution and passivation of pure aluminium in aqueous lithium carbonate/bicarbonate solutions has been researched using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Sweep rate studies revealed a wide anodic peak and the total absence of a reverse peak. Data comply with all criteria for diagnosis of totally irreversible systems. The number of electrons transferred and the transfer coefficient were estimated. The anodic process was shown to be under mixed control in the presence of oxygen, its removal causing a change to diffusion control with loss of passivation. Results were confirmed by EIS insofar as the diffusional and mixed character of reactions. Capacitance values of 20 and 1-mu-F cm-2 were found for the case of de-aerated and aerated solutions respectively. Protection is conferred only in the presence of oxygen with lithium incorporated into a thin film. As a result, the open circuit potential changed by about 1 V when compared to values obtained in the absence of lithium in the same experimental conditions. The film produced was found to be remarkably resistant to chloride ions attack.