An Assessment of the Processes Leading to Pit Nucleation on Iron

In this review the controversial issues of the processes leading to the chemical breakdown of passivity are discussed. The following problems are considered: ( i ) aggressive anion concentration buildup and the effect of potential; ( ii ) effect of defects and inhomogeneities within the metal phase and/or within the passivating film; ( iii ) the possibility of incorporation of aggressive ions into the film; ( iv ) effect of aggressive ions on film thickness and structure; ( v ) significance of the induction period, and ( vi ) relevance of the prevention of repassivation.