Predicting the Anti-corrosive Performance of Zinc Rich Epoxy Primers by Electrochemical Impedance Spectroscopy

Abstract Zinc rich epoxy primers (ZREPs) protect steel substrates both by inducing a galvanic potential and acting as a physical barrier. When testing and developing ZREPs, it can be challenging to differentiate their anti-corrosion (AC) performance. Electrochemical Impedance Spectroscopy (EIS) is a well-known assessment method for evaluating the barrier properties of protective coatings. This paper aims to describe how EIS can be used to predict the AC performance of ZREPs. Potential benefits of using EIS on ZREPs are saving time during formulation development, obtaining quantitative values on their galvanic performance, and predicting lifetime. Selected ZREPs with minimum 80 weight % zinc in dry film have been evaluated. Their electrochemical properties have been assessed through EIS and compared to their performance in the accelerated corrosion tests neutral salt spray (ISO 9227) and cyclic aging (ISO 12944-9).1,2 The evaluation includes running EIS and potentiodynamic measurements on the single coat ZREPs as well as monitoring their open-circuit potential (OCP). In conclusion, the work shows that EIS is a promising assessment technique for evaluating ZREPs. Especially, the potentiodynamic EIS used to obtain an estimate on corrosion current, and the OCP measurements with time, seem to correlate well with the AC performance of the ZREPs.