Passivity and Breakdown

It is now well established that a metal is considered passive if an increase in its potential to more noble values leads to a smaller anodic current than at some more active potential. It is this electrochemical behavior of some of the non-noble metals that represents the basis of their successful use, whilst the breakdown of passivity in such metals is the primary cause of their failures. This article is intended to present basics of the current understanding of the phenomenon of passivity; more specifically its electrochemical nature and processes which may lead to or control passivity breakdown.