The importance of the time-effect in electrochemical studies of corrosion inhibitors

The corrosion protection of metallic substrates with corrosion inhibitors, either in solution or dispersed in a coating formulation, has been the focus of many research topics for many decades and has intensified in recent years even more with industry moving away from hexavalent chromium (Cr(VI))- based corrosion inhibitors. While mainly concentrating on the electrochemical behaviour and the underlying corrosion protective mechanism, the study of the time-effect, i.e. the study of how the electrochemical system behaves and the stabilization of the electrochemical system is altered over time, is often not taken into account when studying corrosion inhibitor-containing electrochemical systems. To gain a better understanding of the kinetic aspect of corrosion inhibitors changing the overall electrochemistry, this study focusses on the quantification of the time-effect of corrosion inhibitors’ electrochemical behaviour. Therefore odd random phase electrochemical impedance spectroscopy (ORP-EIS) is selected, a multisine alternative to the classical electrochemical impedance spectroscopy (EIS) technique, capable to measure and quantify the stability of electrochemical systems over time. Two different electrochemical systems are considered: lithium-based corrosion inhibitor technology on aluminium alloy AA2024-T3 and silica- and phosphate-based corrosion inhibitors for hot-dip galvanized steel. The former, already well-understood system, served as the proof of concept to design a well-defined methodology to study corrosion inhibitor-containing electrochemical systems, and gain deeper knowledge of the latter system.