Galvanic corrosion polarization resistance curve

The passage of current through an ionic electrolyte of finite resistivity results in an ohmic potential drop along the current path according to Ohm s law. There are two aspects of corrosion that are influenced by ohmic potential drops measured polarization curves and any form of corrosion in which the anodic and cathodic reactions are separated spatially, such as in galvanic corrosion. 

The main concept that most of the corrosion data interpretation is based on was first introduced by Wagner and Traud (1938), according to which galvanic corrosion is an electrochemical process with anodic and cathodic reactions taking place as statistically distributed events at the corroding surface. The corresponding partial anodic and cathodic currents are balanced so that the overall current density is zero. This concept has proven to be very useful, since it allowed all aspects of corrosion to be included into the framework of electrochemical kinetics. Directly deduced from this were the methods of corrosion rate measurement by Tafel line extrapolation, or the determination of the polarization resistance Rp from the slope of the polarization curve at the open circuit corrosion potential... 

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