Module Five of CCE 281 Corrosion: Impact, Principles, and Practical Solutions

Corrosion Kinetic Data

The use of polarization curves for the study of corrosion reactions can be traced back to the 1930's with the work of Wagner and Traud. However the representation of the mixed potential behavior is often associated with Professor Evans who has popularized this representation of corrosion polarization measurements. (reference)

These polarization diagrams can be quite useful for describing or explaining many corrosion phenomena. According to the mixed-potential theory underlying these diagrams, any electrochemical reaction can be algebraically divided into separate oxidation and reduction reactions with no net accumulation of electrical charge. Under these circumstances the net measurable current is zero and the corroding metal is charge neutral, i.e. all electrons produced by the corrosion of a metal have to be consumed by one or more cathodic processes.

In order to model a corrosion situation with mixed potential diagrams, one must first gather the information concerning the 1) activation overpotential for each process that is potentially involved and 2) any additional information for processes that could be affected by concentration overpotential. The following sections present some examples to illustrate how mixed potential models can be used to explain simple cases where corrosion processes are purely activation controlled or cases where concentration controls at least one of the corrosion processes.