Passivity

Definition - What does Passivity mean?

Passivity refers to a corrosion preventative mechanism whereby an oxidation layer forms a continuous film on a metal's surface that prevents further corrosion. Passivity is the loss of electrochemical reactivity, thereby decreasing the corrosion rate of the metal.

Passivation results in a barrier of passive film between the metal and the electrolyte. The barrier film can be crystalline or amorphous, and can be made of either insulators, such as aluminum, titanium, or tantalum, or made of semiconductors, such as iron or nickel. Passivation is used on many different engineering alloys, such as stainless steel, nickel-based alloys, and aluminum-based alloys.

Corrosionpedia explains Passivity

Passivity is generated by the buildup of a layer of metal oxide on the surface of a metal. In order to provide passivity, this oxide layer must be stable. It is formed by corrosion insoluble components in the immediate environment of the metal. The metal oxide acts as a barrier by separating the metal's surface from its environment and prevents corrosion until the reactants are able to diffuse through the oxide film. This diffusion may take a significant time to occur.

Galvanization is a corrosion preventative measure that is based on the occurrence of passivity for steel or iron, in which the substrate is coated with zinc to prevent it from rusting. The process entails immersing clean, oxide-free iron or steel into molten zinc in order to form a zinc passivation coating that is metallurgically bonded to the metal's surface.

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