The inhibition of pit nucleation and growth on the passive surface of iron in a borate buffer solution containing Cl − by oxidizing inhibitors

Abstract

The inhibiting effects of oxidizing oxyanion inhibitors on pit nucleation and growth were investigated for a passivated iron electrode in an aerated borate buffer solution containing Cl − at pH 8.49 by polarization measurements. The pitting potential E pit and the repassivation potential E rep were shifted towards positive potentials by the addition of MoO 4 2−, WO 4 2− and NO 2 −, indicating suppression of pit nucleation and propagation. CrO 4 2− and VO 4 − suppressed pit nucleation but stimulated pit growth. The value of E rep was increased in the presence of NO 3 −, whereas little effect on Epit, was obtained. The inhibition of pit nucleation and propagation with the oxidizing inhibitors is understandable from consideration of a hard acid-hard base interaction based on the hard and soft acids and bases principle.