Characterization of Organic Coatings on Metal Substrates by Electrochemical Impedance Spectroscopy

Abstract

Organic coatings on phosphated and bare mild steel exposed to aqueous sodium chloride solutions were investigated by electrochemical impedance spectroscopy (EIS). The corrosion protection of coatings is well characterized by a thorough transfer function analysis of the EIS data obtained. A quasi-homogeneous and two different inhomogeneous three-dimensional surface models were used to analyze perfect and imperfect coatings, respectively. Local defects within the organic coatings and delamination effects at the substrate/coating interface were determined quantitatively even after a relatively short exposure time.