Differential areation cell

When a metal is exposed to oxygen containing solution (electrolyte or pure water) so that the whole area is uniformly accessible, without the conditions for the formation of differential areation cells, the whole area may be covered with a corrosion resistant film of oxide, thus retarding the rate of the anodic reaction. This situation can also be obtained by treating the metal with oxidizing agents, such as concentrated nitric acid. The phenomenon, called passivity , will be discussed in greater detail after the description of corrosion by electric current. 

One way of reducing the rate of corrosion is by reducing the area of one of the electrodes, commonly the anode in a potential differential areation cell, or by eliminating it altogether. Thus, the anodic reaction is checked by ensuring a uniform accessibility of air to the metal surface. 

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