Local electrochemical impedance measurement: scanning vibrating electrode technique in ac mode

The paper gives a new insight into the meaning of local impedances and the related measurement techniques. By numerical simulation it is shown that th e only fully relevant quantity is obtained through local values of both the current density and potential. A recently developed equipment based on a c ommercial SVET device modified for ac polarization is applied to corrosion situations. Under oxygen reduction control of the corrosion rate, serious a rtifacts are found on the de current density mapping and local impedance. T he drawback is explained by the contribution of a chemical term (redox pote ntial) in the probe potential. A model is elaborated accounting for the res ulting side effects in both de and ac measurements. (C) 1999 Published by E lsevier Science Ltd. All rights reserved.