Polarization studies on cadmium by galvanostatic and potentiostatic techniques

Abstract

The anodic polarization of cadmium in alkaline solutions has been studied under constant-current conditions. The potential may rise from about −0.9 V (vs. Hg |HgO| N KOH) to as much as + 1 V on passivation; there appears to be more than one arrest in the polarization curves. Preliminary study of the effect of stirring indicates that it may hasten the transition in dilute solutions and delay it in concentrated solutions. Potentiostatic studies in the range −1·2 to + 1·2 V (vs Hg |HgO| N KOH) have shown that hydrogen is cathodically evolved at −1.0 V; then, in the first truly active region (ca. −0·86 V), the main reaction is the formation of Cd 2+ aq; after passivation (ca. + 0·70 V) it changes to oxygen evolution. Potentiostatic techniques reveal intermediate stages, undisclosed by constant-current methods, of pseudo-passivation and current-plateau regions, in which the passivating layer thickens, controlled by high-field cation transport. The results are briefly considered with special reference to the techniques adopted and results recently obtained by others.