AC impedance study on the activation mechanism of aluminium by indium and zinc in 3.5% NaCl medium

Abstract

Activation of aluminium by In3+ and Zn2+ ions in chloride media has been investigated by using potentiodynamic polarisation, potential vs. time measurements, electrochemical impedance spectroscopy and scanning electron microscopy studies. It is suggested that indium exhibits In+ and In2+ intermediates during the dissolution and redeposition processes. Incorporation of any of these lower valent ions changes the defect structure of the passive film, leading to an increase in anionic vacancies and a decrease in the number of electrons, promoting active dissolution of aluminium. The role of zinc is to moderate localised attack by increasing the electron concentration and cation mobility, thereby lowering the corrosion rate at activated sites. (C) 1997 .