Study on Evolution of Coating State and Role of Graphene in Graphene-Modified Low-Zinc Waterborne Epoxy Anticorrosion Coating by Electrochemical Impedance Spectroscopy

In this paper, corrosion potential and impedance response of the graphene-modified low-zinc waterborne epoxy anticorrosion coating with different compositions were measured experimentally. Microstructure impedance analysis approach was proposed, which was applied to analyze in detail the system impedance and to clarify the variation of coating state as well as the role of graphene in the coating. Results showed that the variation course of coating state was divided into four stages: activation stage; cathodic protection stage; shielding protection stage; and failure stage. Graphene formed numerous isolation layers in the coating to hinder the diffusion of aggressive particles like water and oxygen as well as corrosion products, which played a certain shielding protective role. Moreover, graphene was a good electron conductor, which enabled the outer layer zinc to continue to constitute a galvanic couple with the iron substrate after cathodic protection stage, thereby prolonging the protective effect of the coating to some extent.