The passivation of stainless steel is a process that involves the formation of a thin, protective oxide layer on the surface of the metal. This oxide layer, primarily composed of chromium oxide Cr2O3 , acts as a barrier that protects the underlying metal from corrosion and environmental degradation.The mechanism of passivation can be explained through the following steps:1. Exposure to air: When stainless steel is exposed to air, the chromium present in the alloy reacts with oxygen to form a thin layer of chromium oxide on the surface.2. Formation of chromium oxide layer: The chromium oxide layer is only a few nanometers thick, but it is highly stable, adherent, and chemically inert. This layer acts as a barrier that prevents further oxidation of the underlying metal.3. Self-healing property: One of the key features of the passivation process is its self-healing property. If the chromium oxide layer is damaged or removed, the exposed chromium in the stainless steel will immediately react with oxygen to reform the protective layer. This ensures that the stainless steel remains protected against corrosion even if the surface is scratched or damaged.4. Enhanced corrosion resistance: The passivation process significantly enhances the corrosion resistance of stainless steel by preventing the formation of iron oxide rust on the surface. The chromium oxide layer not only acts as a barrier against oxygen and moisture but also prevents the migration of metal ions, which can lead to galvanic corrosion.In summary, the passivation of stainless steel is a natural process that occurs when the metal is exposed to air. The formation of a thin, protective chromium oxide layer on the surface of the stainless steel provides enhanced corrosion resistance and protection against environmental degradation. This self-healing property ensures that the metal remains protected even if the surface is damaged, making stainless steel an ideal material for various applications in harsh and corrosive environments.