Application of localised electrochemical techniques to study kinetics of initiation and propagation during pit growth

Conventional and localised electrochemical impedance spectroscopies have been used to study pitting corrosion of iron-chromium alloys, This approach has proven to be very useful since the conventional impedance spectroscopy (EIS) consists of a combination of the contribution from the passive area as well as a contribution from the active pit which are not easy to separate. Therefore localised impedance spectroscopy (LEIS) can provide valuable information on the changes of the impedance on a small area. Hence, information about the impedance behaviour; which only originates from the pit, can therefore be obtained. Different stages of pit growth have been studied, e.g. initiation and pit growth during pitting corrosion. It has been found that during pit growth the conventional EIS consists of the contribution of the pit and the surrounding passive area. The dissolution behaviour during pit growth changes with polarisation and resembles that of anodic dissolution of iron chromium alloys in acidic chloride environment near the vicinity of the anodic peak. LEIS measurements indicate that the technique is suitable to follow changes in the dissolution kinetics during pit growth. (C) 1999 Elsevier Science Ltd. All rights reserved.