The Effect of Some Fundamental Aspects of the Pitting Corrosion of Stainless Steel on Electrochemical Noise Measurements

Abstract

Features of metastable pit growth on stainless steel that affect the possibilities to predict stable pit growth from electrochemical noise measurements are examined. To this end, the behavior of AISI type 304 stainless steel in chloride solutions has been studied. It is confirmed that the electrode capacitance plays a major role in fluctuations of the corrosion potential during metastable growth. This means that the size of these potential fluctuations depends primarily on the size of metastable pits and not on the peak current nor the current density during growth; this means that fluctuations in electrode potential will have little value to predict stable pitting. Electrochemical current noise from twin-electrode noise probes holds more promise. However, it is shown that the direct relationship between electrochemical current noise and pitting susceptibility breaks down when the pitting behavior is altered by a change in surface condition (heat tinting).