The rate at which a corrosion reaction proceeds is determined by a number of factors which may act together or independently. From thermodynamic data,1,2 when available, it sometimes is feasible to calculate whether a corrosion reaction is possible, but unfortunately very little about the actual rate of reaction can be so determined. The slow steps in ion discharge, diffusion effects, and other possible polarization factors must be investigated before quantitative predictions of corrosion rates can be made.
Polarization may be defined as the production of counter potentials when the chemical energy of a cell is converted to electrical energy. The electromotive force may arise from products formed during, or by concentration changes resulting from, passage of current through the cell. The principal controlling factors in polarization include the limited solubility of a metal in a solution, the rate of proton discharge and hydrogen liberation, and diffusion of corrodant to...
