Evaluation of the Anticorrosive Behaviour of Organic Coatings by Using a Variant of Electrochemical Impedance Spectroscopy

Abstract

Electrochemical impedance spectroscopy (EIS) has been acknowledged as a modern and efficient method in the evaluation of the anticorrosive behaviour of coatings. However, difficulties in the interpretation of the complex experimental data present a significant drawback in the use of the method in field studies where quick results are required. The breakpoint frequency method is an extension of the basic EIS method, which allows rapid qualitative assessment of the condition of a coating. By the breakpoint frequency method, the behaviour of epoxy coatings containing various types of reinforcement and applied on steel specimens has been examined after long-term (up to 300 days) exposure to a corrosive environment. The parameter values obtained by the breakpoint frequency method, such as the delaminated area, have been compared with those obtained from fitting the experimental EIS data to a suitable equivalent circuit. These results have also been compared with those of the water permeability of free membranes and the diffusion coefficient determined by standard test methods (e.g. the cup test).