Passivation is a method of converting a metal surface into a state that is not easily oxidized, and delaying the corrosion rate of the metal. In addition, an active metal or alloy, in which the chemical activity is greatly reduced, and becomes a noble metal state phenomenon, also called passivation.
Passivation, the corrosion product of the metal due to the role of the medium produced by the formation of a thin film (often invisible), if the resulting corrosion product, closely covers the surface of the metal, then change the surface state of the metal, so that the metal electrode The potential greatly changes in the positive direction and becomes a passive state of corrosion resistance. For example, when Fe→Fe2+, the standard potential is −0.44 V, and after passivation, it jumps to +0.5 to 1 V, and shows the performance of a noble metal that resists corrosion. This film is called a passivation film.