Toward a More Fundermental Understanding of Corrosion Processes

Abstract

A review is given of some simplified concepts that will contribute to a better understanding of corrosion fundamentals. The corrosion process involves not only electrochemical reactions but also acid-base reactions, and it is the acid-base nature that diversifies the corrosion phenomena. Anions either catalyze or inhibit the anodic metal dissolution, and the passivation will result from the hydroxide-catalyzed mechanism of metal dissolution. Corrosion precipitates frequently control the selective mass transport in corrosion processes. Anion-selective precipitates accelerate and cation-selective precipitates decelerate corrosion propagation. A bipolar precipitate film, if anodically polarized, undergoes deprotonation and turns into a passive film. The electrochemical stability of passivated metals is determined by the electron energy band structure of the passive film. The passive film of n-type semiconducting oxides appears electrochemically more stable than the passive film of p-type semiconducting oxides.