repassivation

Repassivation is the process by which a damaged or removed protective oxide layer on a metal surface reforms, restoring its corrosion resistance. It is a key phenomenon in metals that rely on a passive film, such as stainless steels, aluminum alloys, titanium, and nickel-based alloys. Repassivation typically occurs in oxidizing or neutral aqueous environments where oxide formation is thermodynamically favorable; its rate and completeness depend on alloy composition, temperature, pH, and the presence of aggressive ions such as chlorides.

Mechanistically, repassivation involves the rapid re-oxidation of the exposed metal surface and the growth of a new protective oxide film at defects or damaged regions. In pits or crevices, the initial breakdown of the passive film may be followed by repassivation, preventing further dissolution if conditions allow. Chloride-containing media often retard repassivation by destabilizing the oxide film, while sufficient oxygen content and favorable temperature promote it. Mechanical damage or surface roughening can increase defect density and influence the kinetics of film restoration.

Repassivation behavior is central to evaluating pitting and crevice corrosion resistance. It is commonly studied using electrochemical methods such as cyclic potentiodynamic polarization, where the repassivation potential is identified as the potential at which the passive film reforms during a reversal of the applied potential. If repassivation is readily achieved, pits may arrest; if repassivation is slow or inhibited, pits may propagate and lead to localized corrosion.

Understanding repassivation supports materials selection, corrosion testing, and treatment strategies such as passivation processes, where the oxide film is thickened to improve resistance to chloride-induced corrosion.