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

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 MoO42-, WO42- and NO2-, indicating suppression of pit nucleation and propagation. CrO42- and VO3- suppressed pit nucleation but stimulated pit growth. The value of E(rep) was increased in the presence of NO3-, whereas little effect on E(pit) 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. Copyright (C) 1996 Elsevier Science Ltd