Corrosion properties of ammonium based ionic liquids evaluated by SEM-EDX, XPS and ICP-OES

Abstract

Two ammonium-based ionic liquids (IL) with the potential to be used as lubricants were investigated with respect to their corrosion ability. With the intention to reduce the potential negative environmental impact of lubricant ILs, (2-hydroxyethyl)-trimethyl-ammonium (choline) was chosen as the cation and compared with butyl-trimethyl-ammonium. Two commonly used metals were immersed in the selected ILs to simulate severe conditions. For each material, a corrosion inhibitor was selected and added to the respective IL to confer corrosion protection. The corrosive behavior of the ILs was determined by specially designed small-scale experiments and monitoring of the metal content in the ILs by inductively coupled plasma optical emission spectrometry (ICP-OES), showing preferable properties of the choline IL. After the corrosion experiments, the morphology and the elemental composition of the corroded metal surfaces exposed to ILs were studied by scanning electron microscopy (SEM) with energy dispersive X-ray spectrometry (EDX) and X-ray photoelectron spectroscopy (XPS). Besides ICP-OES, surface analysis to determine the chemical composition on the surface and to identify corrosion products contributed to the qualitative evaluation of the effectiveness of the corrosion inhibitors. It was also possible to show that the corrosion properties of ILs can be significantly improved by the addition of selected corrosion inhibitors.