Localized electrochemical impedance spectroscopy for studying the degradation of organic coatings

A localized electrochemical impedance spectroscopy technique (LEIS), which gives a measure of the local ac solution current density above the specimen surface, has been applied to study the degradation of organic coatings on metals. The technique has been used to study heterogeneities in organic coatings on steel surfaces due to underfilm-deposits and micro-blisters. The results are compared with the information obtained from traditional electrochemical impedance spectroscopy and that obtained with a scanning Kelvin probe. The results indicate that LEIS can be used to detect the onset of blistering and that it can. give a measure of the rate of water diffusion into the organic coating on a microscopic scale. LEIS also gives valuable information concerning the initiation of corrosion at a defect in an organic coating. (C) 1997 Published by Elsevier Science Ltd.