Metallic surfaces can be polarized by the application of an external voltage or by the spontaneous production of a voltage away from equilibrium. This deviation from equilibrium potential is called polarization. The magnitude of polarization is usually described as an overvoltage (h) which is a measure of polarization with respect to the equilibrium potential (Eeq) of an electrode.This polarization is said to be either anodic, when the anodic processes on the electrode are accelerated by changing the specimen potential in the positive (noble) direction or cathodic when the cathodic processes are accelerated by moving the potential in the negative (active) direction.