What is passivation?

• A. The formation of a stable, protective oxide film on certain metals (e.g., stainless steel) that reduces corrosion.
• B. Rapid oxidation
• C. Mechanical polishing
• D. Conductive coating

Answer: (A)

Passivation is the formation of a thin, stable oxide layer on a metal surface that acts as a barrier to moisture and ions, greatly reducing the rate of corrosion. In stainless steels, chromium in the surface oxidizes to form a dense, adherent chromium oxide film (Cr2O3). This protective film slows or stops further oxidation by limiting access of water and aggressive species to the underlying metal, and it can repair itself if damaged, restoring protection quickly when the environment allows.

This is different from rapid oxidation, which is a uncontrolled, aggressive loss of material. It also isn’t about mechanical polishing, which can remove protective films rather than create them, and it isn’t about applying a conductive coating, which can alter surface properties in ways that don’t confer corrosion resistance. Passivation, then, specifically means that self-repairing oxide shield that reduces corrosion.