EIS study of multilayer organic coatings on steel with different surface pretreatments
The failure process of zinc-rich epoxy/epoxy micaceous iron oxide/chlorinated rubber coatings on Q235 steels with three different surface pretreatments was investigated by electrochemical impedance spectroscopy(EIS).The Bode plots,water uptake,coating capacitance and break point frequency were determined by EIS to evaluate the protection characteristics of three coating systems.The results showed that the coatings on manually polished steel provided superior protection as compared to others due to wider saturation range,longer protection life and greater adhesion,the coatings on rusted steel ranked secondly,and the coatings on steel without pretreatment ranked thirdly.When the break point frequency increased to 1400 Hz approximately,coating resistance decreased sharply,and water uptake increased quickly,which caused serious steel corrosion.