Passivity and Passivity Breakdown

The breakdown of passivity and the resulting localized corrosion is the primary cause of failures in metals which are in the passive state. While a number of different models have already been proposed, based on the film mechanical breakdown, adsorption of aggressive anions, localized acidification, existence of voids at the metal–film interface and selective dissolution, and some of them have in fact found a practical use, for example, kinetic stability diagrams, more research is still needed before both scientific and engineering (practical) questions about localized corrosion get sufficiently addressed. A unified theory is yet to come.