Influence of anion chain length of protic ionic liquids on the corrosion resistance of API X70 steel

The objective of this paper is to evaluate the corrosion resistance of API X70 steel in three different protic ionic liquids (PILs). Protic ionic liquids cation was 2-hydroxiethylammonium, and their anion was a carboxylate where the carbon chain length was varied. The synthetised PILs were characterised by nuclear magnetic resonance. The corrosion resistance of API X70 steel was evaluated on the hand of the monitoring of the open circuit potential and electrochemical impedance spectroscopy. Results showed that PIL adsorption on the substrate surface occurs to form a film that enhances corrosion inhibition effects. However, the adsorbed film can break due to desorption that exposes the substrate surface and promotes corrosion of the substrate. In addition, it was observed that corrosion inhibition effects improve with the increase in the anion carbon chain length, since the longer is the anion the larger is the substrate coverage.