Two-electrode electrochemical impedance sensor: Part 2-impedance measurement and simulation of coatings on nonmetal substrates

Electrochemical impedance spectroscopy (EIS) has been studied extensively as a quantitative technique for evaluating protective coatings, which degrade unavoidably, regardless of their substrate type. However, most EIS studies focus on coatings on metal substrates. Consequently, on nonmetal substrates, coating evaluation is still lacking a quantitative method. Examples of the coatings on nonmetal substrates include not only those on nonconductive substrates such as plastics and composites but also the top layer of multilayer coatings on metal substrate. Here, with a two-cell EIS (TCEIS) configuration, EIS techniques are made available for evaluating coatings on nonconductive substrates, which is a progress toward future quantitative evaluation of these coatings. To test the feasibility of the TCEIS, impedance measurements were carried out on two different coatings on various nonmetal and metal (for comparison) substrates. Measurements were successful on several nonmetal substrates and all the metal substrates. A simplified two-dimensional finite element analysis (FEA) model was used to assist the interpretation of the results and study the effects on the TCEIS measurements from the relative size and position of a coating defect and the two cells of TCEIS.