A modification of the Stern—Geary linear polarization equation

Abstract

An exact equation for the slope of the current—voltage curve at the corrosion—potential is derived. While the Stern—Geary equation is a valid approximation only if the corrosion—potential lies far from the reversible potentials of the oxidation and reduction processes which determine the corrosion process, two new formulae proposed here are valid approximations under all conditions. For given Tafel-constants these approximations introduce no error greater than 30 per cent, while the error accompanying the Stern—Geary method increases without limit as the corrosion—potential approaches either of the reversible potentials. The proposed formulae include the cases of the corroding Zn electrode in strong alkaline solution and the Fe 2+/Fe 3+-couple on stainless steel. Large discrepancies between corrosion rates determined by electrochemical and weight loss techniques reported recently are analyzed.