The coating delamination mitigation of epoxy coatings by inhibiting the hydrogen evolution reaction

Abstract

The mitigation of coating delamination is one of the important challenges for epoxy coatings under the cathodic protection. Herein we report the possibility to mitigate the coating delamination of epoxy coatings by inhibiting the hydrogen evolution reaction in the presence of thioureas. The wire beam electrode method, electrochemical impedance spectroscopy and traditional delamination test were employed to evaluate the mitigation efficiency in this work. Results show that in the absence of thioureas, the delamination rate increases significantly once the cathodic protection potential is more negative than hydrogen evolution potential, suggesting that hydrogen evolution reaction plays an important role in the coating delamination. Fortunately, the coating delamination is remarkably mitigated by adding thioureas since the hydrogen evolution reaction is suppressed. WBE results show that when delamination commences, the electrodes at the defect region act as anodes, while the electrodes around the defect region act as cathodes. In the presence of thioureas the delamination area is much less than that in the absence of thioureas. Therefore, the coating delamination of epoxy coatings under the cathodic protection could be successfully suppressed through inhibiting the hydrogen evolution reaction. The finding of this work could offer a new insight to reduce the cathodic delamination rate in both theoretical research and practical application engineering applications.