Electromechanical Investigations in the Development of High Performance Coatings

By Victoria J. Gelling, Akash Saraf, Niteen Jadhav

Historically, corrosion and coatings research has been a visual, qualitative, and subjective study. ASTM B117 (Standard Test Method of Salt Spray Testing) is one of the most widely used methods in corrosion experiments, and many users visually interpret scribe creepage or blister density. Electrochemical methods offer the path-way towards quantitative corrosion measurements. Electrochemical techniques have been utilized in the past few decades as important methods in the study of corrosion and coating degradation. Electrochemical techniques allow for the determination of changes in material properties, which often occur prior to visual changes and provide information regarding corrosion mechanisms. Indeed, by using these techniques, such as electrochemical impedance spectroscopy (EIS), scanning electrochemical microscopy (SECM), and scanning vibrating electrode technique (SVET), important mechanistic information regarding protection/ failure transitions can be determined. For this study, three different powder coating systems (a one-coat DTM polyester, a two-coat system with two cure cycles, and a two-coat system with a single cure cycle) were investigated using EIS at both the intact portion (face area) of the coating and the edge of the panel. With EIS analysis, it was found that the DTM coating system exhibits signs of water ingress and the other two systems are unaffected at the face area, whereas better corrosion protection was observed for a two-coat system with two cure cycles and a two-coat system with a single cure cycle, as compared to the one-coat DTM system. Initial studies of the systems utilizing SVET exhibited a barrier type of protection for a two-coat system with two cure cycles. The most important highlight of this work was the development of an electrochemical screening method for the corrosion prediction on the panel edges.