Corrosion behaviour of zinc in sodium perchlorate solutions

I investigate the corrosion behaviour of zinc in aerated neutral perchlorate solutions. Three different techniques, namely, potentiodynamic polarisation, potentiostatic current time transient, and electrochemical impedance spectroscopy (EIS), are used. The potentiodynamic anodic polarisation cyclic voltammetry curves exhibit an active/passive transition followed by pitting corrosion, confirmed by SEM, due to the diffusion-controlled formation of a ZnO film by the dissolution-precipitation mechanism. The cyclic voltammograms show an anodic peak AI and two cathodic peaks CI and CLI. The peaks AI and CII are correlated to the formation and reduction of ZnO film, respectively, and CI is attributed to the reduction of the pitting corrosion products. The potentiostatic current time transients at different electrolyte concentrations and applied potentials involve three stages: the first involving ZnO layer growth, and the second and third involving pit nucleation and growth, respectively. The nucleation rate (t(i)(-1)) increases with increasing electrolyte concentration and anodic applied potential. EIS shows an increase in the charge transfer resistance with applied potential near the anodic peak AI as a result of passive film formation. At higher anodic potentials, the charge transfer resistance decreases as the applied potential approaches the breakdown potential Eb A nearly ideal Warburg tail of a dihedral angle of 45 degrees is obtained, suggesting that the corrosion of Zn in NaClO4 solution is controlled by diffusion in the passive range. (C) 2001 Elsevier Science B.V. All rights reserved.