The degradation of metals and alloys is eventually inevitable and the “prevention” of corrosion mainly deals with slowing down the rate of corrosion. In this section we shall deal with some elementary aspects of corrosion kinetics. The concepts involved herein are overpotential, exchange current density, polarization, corrosion velocities and breakdown of passivity.
The electrode potentials of electrodes that were discussed in the earlier chapters/lectures were the potential differences between a point in the bulk metal of the electrode and a point in the bulk solution in contact with the electrode. When the cell is not in equilibrium and is producing a current (net flow of electrons into the solution or into the electrode), the dynamical processes at the electrode surface become important. Since the solvent surface immediately in contact with the metal is different from the bulk solvent, the charge transfer across a metal surface is an activated process. The rate (k) of charge transfer may be written as
k charge transfer = B exp [-G#m/ RT ]
(25.1)
Where B is a coefficient and G#m is the molar free energy of activation. The net flow of current depends on the difference of the actual electrode potential () and the equilibrium electrode potential , denoted by (called overpotential). (In this section, we shall only emphasize these aspects which are necessary to understand the concept of corrosion current )
G#m/ RT ] 
G#m is the molar free energy of activation. The net flow of current depends on the difference of the actual electrode potential (
) and the equilibrium electrode potential 
, denoted by 
(called overpotential). (In this section, we shall only emphasize these aspects which are necessary to understand the concept of corrosion current ) 
