Electrochemical impedance spectroscopy (EIS) as a tool for measuring corrosion of polymer-coated fasteners used in treated wood

Currently, many of the polymer-coated fasteners on the market are designed for improved corrosion performance in treated wood; yet, there is no way to evaluate their corrosion performance. In this study, a common technique for measuring the corrosion performance of polymer-coated metals, electrochemical impedance spectroscopy (EIS), was used to evaluate commercial fasteners in a water extract of treated wood. Fasteners were tested in an "out of the box" condition as well as after being driven into the wood to simulate service conditions. The EIS spectra were fit to the traditional model for polymer-coated metals where the capacitors were replaced with constant-phase elements. A low frequency corrosion-time constant was measured for all of the fasteners in the out of the box condition, which implies that the barrier properties of the coating had failed before they were used.