Localized electrochemical impedance spectroscopy for studying pitting corrosion on stainless steels

Pitting corrosion of stainless steel has been extensively studied by electrochemical impedance spectroscopy (EIS). However, the frequency dependence of the current distribution is much different in the vicinity of a pit than on the passivated part of the surface. Therefore a localized electrochemical impedance technique has been developed and used in order to study the kinetics of pit initiation and growth on stainless steels. AC current distribution maps have been recorded during the initiation and propagation of pits. It is shown that the technique can detect localized attacks at an early stage. Traditional EIS and locally measured impedance spectra have been recorded at the same time on active and passive sites. It has been found that traditional EIS spectra contain contributions rom both the pit and the passive area. On the other hand, the locally measured impedance displays a feature which agrees with the behavior observed for the dissolution paths of iron-chromium alloys at the active current of the anodic polarization curve in chloride-containing acidic media. This approach can provide useful information on the kinetics of initiation and propagation of pitting corrosion.