Abstract
The electrochemical potential for the active dissolution of aluminium in sodium chloride solution is found to be linearly related to the logarithm of the chloride ion concentration. The value of E0 calculated on the basis of the postulated electrode reaction is approximately 0.3 V more negative than the experimental value and a similar inequality is observed for bromide and iodide electrolytes.The electrochemical etching of aluminium in chloride, bromide or iodide solutions is initiated at weak points in the surface oxide film. Subsequent stages in the dissolution process involve a random attack leading to the formation of cavities and a selective attack leading to tunnelling. The dominance of one or other of these dissolution modes is largely dependent upon the electrochemical parameters. It is suggested that the reason for this dependency is associated with an alteration in the electrode potential for dissolution resulting from changes in the halide ion concentration within the tunnel structure.