Corrosion behaviour of zinc in sodium perchlorate solutions

I investigate the corrosion behaviour of zinc in aerated neutral perchlorat e solutions. Three different techniques, namely, potentiodynamic polarisati on, potentiostatic current time transient, and electrochemical impedance sp ectroscopy (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 voltammog rams 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, respect ively, and CI is attributed to the reduction of the pitting corrosion produ cts. The potentiostatic current time transients at different electrolyte co ncentrations and applied potentials involve three stages: the first involvi ng ZnO layer growth, and the second and third involving pit nucleation and growth, respectively. The nucleation rate (t(i)(-1)) increases with increas ing electrolyte concentration and anodic applied potential. EIS shows an in crease in the charge transfer resistance with applied potential near the an odic peak AI as a result of passive film formation. At higher anodic potent ials, the charge transfer resistance decreases as the applied potential app roaches the breakdown potential Eb A nearly ideal Warburg tail of a dihedra l angle of 45 degrees is obtained, suggesting that the corrosion of Zn in N aClO4 solution is controlled by diffusion in the passive range. (C) 2001 El sevier Science B.V. All rights reserved.