Protective performance of epoxy resin modified with coal tar coating studied by electrochemical impedance spectroscopy

The effect of different amounts of titanium powder, used as additive, on the protective performance in aqueous 3.5 wt.% sodium chloride solution of coal tar epoxy resin cured with polyamine has been studied by electrochemical impedance spectroscopy (EIS). In this paper, the electrochemical impedance spectra and breakpoint frequency (f_b) of the coating as a function of titanium content and immersion time, and the electrical resistance of the coating by calculating permittivity of the coating were analyzed and discussed. It is shown that EIS performance of the coating can be explained by change of the permittivity of the coating with time, and the protective performance (the protective life) is determined by the breakpoint frequency of the coating in given system.