2. Understanding Corrosion

2.6 A Look at Polarization [1/3]

The phenomenon of polarization is best explained in terms of cathodic and anodic reactions when a metal system such as   Cu2+ + 2e Cu  is at equilibrium, the rate of forward anodic reaction is equal to the rate of reverse cathodic reactions

Cu2+ + 2e Cu 

This is not net reaction and therefore there is no net current flow. The potential across the metal/solution interface is the equilibrium potential (Eequilibrium). However, if the system is displaced from equilibrium and net anodic or cathodic current flows, and the potential varies with the current. The shift of potential from the equilibrium is called over potential or polarization, h.

h = Eapplied potential - Eequilibrium potential

At equilibrium potential, Eeq also called Ecorr (corrosion potential), h = 0. Any departure from Eeq gives a measure of polarization.