Polarization Resistance Method for Determination of Instantaneous Corrosion Rates

Abstract

The polarization resistance method for the determination of instantaneous corrosion rates of metals were reviewed. The assumptions in electrode kinetics that govern the connection between the slope of steady-state applied electrochemical potential-applied current density (Eapp-iapp) measurements (i.e., the polarization resistance) and the corrosion rate were restated. Electrochemical impedance, as well as statistical and spectral electrochemical noise methods for obtaining polarization resistance, also were discussed. Traditional sources of error such as high excitation voltage amplitudes, insufficiently slow voltage ramp rates, high alternating current (AC) frequencies, inadequate polarization hold periods, high solution resistance, presence of parallel reduction-oxidation reactions, and nonuniform current and potential distributions were examined with the goal of defining some of the conditions and circumstances where these complicating factors are important. Other complicating factors such as diffusion-controlled reactions, potential-dependent film coverages, and adsorption pseudo-capacitance that affect electrochemical reaction rates were discussed. Their influence on measured interfacial resistance values and subsequent determination of corrosion rates was discussed.