Tribological Performance of a Lipoic Acid-Based Quaternary Phosphonium Salt as a Water-Based Lubricant Additive

Abstract To develop the lubricating performance of water-based lubricants, we synthesized a lipoic acid quaternary phosphonium salt (SP) as a water-soluble lubrication additive. This study aims to enhance the tribological performance of steel tribosystems by using an SP additive. The tribological performance of AISI 52100 steel was systematically investigated by using an SRV-IV tribotester. The tribological test conditions consisted of a 100 N load, a frequency of 25 Hz, and a sliding duration of 30 min, using a ball-on-disk configuration. The worn scar surface was examined using various analytical techniques, including 2D–3D profiles, SEM, EDS, XPS, and TOF-SIMS, to investigate the wear modes and lubrication mechanisms. Furthermore, the restricted shear simulation between the rubbing surfaces lubricated by the SP additive was studied utilizing density functional theory (DFT). The results showed that the aqueous lubricant with a 2 wt % SP additive showed a reduction in both the coefficient of friction by 76% and wear volume by 91% compared to the baseline liquid. Notably, the electrochemical results indicated that the corrosion rate was reduced by 97%, highlighting the higher corrosion resistance of the 1.0 wt % SP additive. Eventually, this study provides valuable insights into maintenance cost reductions and energy savings from reduced friction and wear in mechanical hydropower systems.