Electrochemical Corrosion Studies of Low-Alloyed Carbon Steel in Acidic Methylimidazolium Derivate Ionic Liquids with Varying Water Content

The application of ionic liquids (ILs) in a wide range of technologies requires a thorough evaluation of their corrosion behavior to typical structural steels. In this work, the corrosion effects of two acidic-type methylimidazolium derivates (potential catalyst candidates) on low-alloyed carbon steel were studied with electrochemical methods (potentiodynamic polarization and electrochemical impedance spectroscopy [EIS]). The ILs cause moderate corrosion around 0.1 mm/y at water content up to 10‰ and severe corrosion around 1 mm/y at 100‰, which underlines that before industrial applications of ILs systematic corrosion studies should be performed as part of the process design. With both ILs we found that the cathodic process exhibited apparently good linear Tafel slopes in the cathodic polarization range but in the anodic range the IL with the hydrogensulfate anion showed an active-passive transition only at the highest water concentration. In this series at lower water concentrations, under 100‰, a model assuming a potential-independent anodic current rate correctly matched with the polarization data. The EIS measurement data showed chaotic, but reproducible deviations in the low-frequency range, which were interpreted as the effect of the timely variation of distribution parameters and they apparently did not affect the charge transfer parameters essentially.