Corrosion inhibition of mild steel by coumarate‐based ionic liquids and coatings

The use of ionic liquids (ILs) as corrosion inhibitors gained attention due to their attractive properties such as high inhibition efficiency and ability to absorb onto metal surfaces. In this work, six  ILs, based on the coumarate anion combined with different nitrogen cations (triethylammonium, pyrrolidinium and imidazolium with short and long alkyl chain attached to the nitrogen atom) have been synthesized and evaluated as inhibitors for steel. The anticorrosion properties of these ILs in solution were investigated electrochemically and the metal surface was analyzed by SEM. Moreover, the IL prepared from the coumarate anion and N‐dimethyl‐N‐tetradecyl ammonium ([DTA]Cou) was incorporated into an UV‐coating formulation as an additive and by designing a similar ionic monomer which covalently links to the formulation. Impedance spectroscopy during 11 days of exposure to a solution of NaCl 0,01M, confirmed the high performance of the inhibitor in both solution and when incorporated into a coating. The synthesized ILs present efficiencies in solution exceeding 70%, in particular the ILs [DTA]Cou and tetradecyl imidazolium coumarate ([C14Im]Cou) showed efficiencies of 88% and 91% respectively. The obtained inhibitors showed interesting anticorrosion behaviors and demonstrated how different cations and an increase in the chain length affect the inhibition properties.