Further Observations on the Validity of Bare Surface Current Densities Determined by the Scratched Electrode Technique

This paper reports on a series of scratched electrode experiments carried out on a 304 stainless steel in desecrated 3.5% NaCl solution at {minus}400 mV SCE to critically address the issue of what is being measured by this technique. The results show that the current transients observed in the scratched electrode technique are primarily associated with charging of the double layer over (or interactions with) the filmed portion of the specimen surface. The procedure used by previous investigators in computing current densities yielded significant overestimates of the current densities for bare-surface reactions, and the time scale of the experiments led to overestimation of the repassivation rate. Because of the charging problem and because the repassivation reactions of interest extend well beyond the order of 10 ms, use of the scratched electrode technique is deemed to be of little value for studying the kinetics of reactions with bare steel surfaces.