Tribological improvement using ionic liquids as additives in synthetic and bio-based lubricants for steel-steel contacts

• Main Authors: Syahir, A. Z., Mohd Zulkifli, Nurin Wahidah, Hassan, Masjuki, Abul Kalam, Mohammad, Harith, M. H., Yusoff, M. N.A.M., Zulfattah, Z. M., Jamshaid, Muhammad
• Format: Article
• Language: English; English; English
• Published: Taylor & Francis 2019
• Subjects: TJ Mechanical engineering and machinery
• Online Access: http://irep.iium.edu.my/79616/25/79616_Tribological%20Improvement%20Using%20Ionic%20Liquids_ft.pdf; http://irep.iium.edu.my/79616/19/79616_Tribological%20Improvement%20Using%20Ionic%20Liquids_scopus.pdf; http://irep.iium.edu.my/79616/3/79616_Tribological%20Improvement%20Using%20Ionic_wos.pdf; http://irep.iium.edu.my/79616/; https://www.tandfonline.com/doi/full/10.1080/10402004.2019.1679934

This study investigates the performance of three ionic liquids (ILs), trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate, trihexyl(tetradecyl)phosphonium decanoate, and 1-butyl-3-methylimidazolium tetrafluoroborate, as lubricant additives in synthetic oil polyalphaolefin (PAO8) and bio-based oil trimethylolpropane trioleate (TMPTO). The ILs were added at 0.5, 1.0, and 1.5 wt% concentrations and evaluated in terms of their miscibility with base oils as well as friction- and wear-reducing abilities. Four-ball and high-frequency reciprocating rig (HFRR) tribotesters were employed to evaluate the tribological performance under a boundary lubrication regime. Worn steel surfaces were characterized using optical microscopy, profilometry, scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) analysis. The results suggested that the addition of trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate and trihexyl(tetradecyl)phosphonium decanoate improved the tribological performance of both PAO8 and TMPTO at an optimum concentration of 1 wt%. They showed good friction reduction, lower overall surface wear, and improved surface finishing. 1-Butyl-3-methylimidazolium tetrafluoroborate managed to improve the tribological performance of both base oils only at 0.5 wt%. A further increase in 1-butyl-3-methylimidazolium tetrafluoroborate concentration caused detrimental effects on the steel surface due to the formation of halogenic compounds.