Influence of In on the corrosion of Zn-In alloys

The anodic dissolution of Zn and Zn-5% In alloy was investigated in acid chloride and perchlorate solutions by means of polarisation curves and electrochemical impedance spectroscopy. The composition and morphology of surface attack were analysed by SEM/EDX. The presence of In, as a diluted solid solution in a rich Zn phase and as rich In phases segregated at grain boundaries, brings about a decrease of the rate of hydrogen evolution reaction. On the other hand, the strong interaction of In with OH- and Cl- at potentials more positive than -1.10 V vs SCE leads to an increase of the anodic dissolution rate of Zn near the corrosion potential. In perchlorate solutions, this is explained in terms of a reaction path involving the formation of the adsorbate ZnOH as an intermediate species. In chloride solutions, the more negative value of the potential of a zero charge of In allows Cl- to be adsorbed on Zn at more negative potentials increasing its oxidation rate. (C) 2001 Elsevier Science Ltd. All rights reserved.