EIS study of corrosion behaviour of organic coating/Dacromet composite systems

Three organic coating/Dacromet composite systems, namely two solvent-borne coatings, polyurethane, alkyd primers and a water-borne coating, styrene-acrylate emulsion, were prepared on Dacrometed carbon steel. Electrochemical impedance spectroscopy (EIS) was employed to study their corrosion behaviour in 3.5% NaCl medium. Characteristic EIS plots with two undistinguishable loops were observed for the styrene-acrylate emulsion/Dacromet system and of which the second one was greatly flatter with immersion time. The stable evolution of Rp, Cp, Cd, and a higher value of Rc illustrated an original fact that the water-borne styrene-acrylate emulsion/Dacromet system exhibited the best protective performance among the three systems. According to the investigation of thin organic film/Dacromet composite systems, a synergetic effect of multiple interface factors including the passivation, the seal and barrier function of insoluble corrosion product of Dacromet, especially the interpenetration of organic micropolymer particle with corrosion product in styrene-acrylate emulsion/Dacromet system was proposed to explain the corrosion behaviour of the composite systems.