Abstract: According to the experimental results and the basic concept that the capacitive contribution of the coating/metal system to EIS can reflect the change occurring at interface sensitively, the quantitative relationship between the adhesion and the analytical result of EIS is established. The approach is using the transmission line model (CR circuit) to obtain the discrete capacitance values, analyzing the physical meaning of the slope at the region in which the discrete capacitances change linearly with the discrete characteristic frequency. The data handling method is also given in detail. The relationship is validated by experiments. The results show that under certain conditions, the slopes are mainly determined by the speed of instantaneous delamination at organic coating/metal interface and are not influenced by the corrosion product built up at the artificial defect, so they have good reproducibility despite the EIS of duplicate samples showing very different configuration. The analytical results from EIS are often higher than that of mechanical measurements when adhesion is strong. Explanation of the discrepancy shows that the results from EIS are more accurate and reasonable. In regard to epoxy powder paints and A3 steel, the results also indicate that the pretreatment of substrate using silane with and without hot-dip galvanized or phosphate treatment can influence markedly the adhesion between substrate and coating.

Key words: Electrochemical impedance spectroscopy(EIS), 　Transmission line,　Interfacial adhesion, 　Organic coating, 　A3 steel