What Does Theories of Passivity Mean?
Theories of passivity are ideas developed to explain the usefulness certain active metals in the galvanic series towards having certain corrosive resistance when exposed to passivating environments or polarization. This means that, active metals can be made passive, so that they corrode less as compared to their original state, which corrodes rapidly. It is achieved by reducing the anodic reactions that occur at the surface of the metals. Theories of passivity explain how protection is achieved in certain structures by the development of passive films on the surface of the metallic material.
Corrosionpedia Explains Theories of Passivity
Theories of passivity are based on the formation of oxide films on the surface of the material that is in a passive state. By anodic polymerization, certain metals like iron can become passive, thus demonstrate some corrosion resistance. The oxide films can exist when certain metals have pronounced corrosion tenancies, but produced lesser reactions with the surrounding environment. As they undergo these passive states, their potential approaches those of noble metals which do not react easily, like platinum.
The theories of passivity also explain the essence of adsorption in the reduction of reaction activity of the metals which are termed as active. The oxygen adsorption on the surface of these metals prevents further anodic reactions, thus protecting the material from degradation.