Synergistic mechanisms of wear and corrosion of bio-based phosphonium ionic liquids in sliding contacts

Abstract Bio-based phosphonium room temperature ionic liquids (PRTILs) show promise for lubrication and corrosion protection on steel, yet their combined wear-corrosion effects can accelerate surface failure. This study evaluated six PRTILs per ASTM G-119, pairing trihexyltetradecyl [P6,6,6,14] or tributyltetradecyl [P4,4,4,14] cations with saccharinate [Sacc], benzoate [Benz], or salicylate [Sali] anions, compared to SAE 10W-30 and canola oil. [Sacc]-based PRTILs achieved the lowest wear and corrosion rates. All PRTILs exhibited corrosion-accelerated wear, but [P6,6,6,14] variants—with more -CH2- groups—showed superior surface adsorption, reducing both wear and corrosion. The double-ring [Sacc] anion formed a phosphorus- and sulfur-rich tribofilm, enhancing protection. These findings clarify wear-corrosion synergism in PRTILs and support designing ionic liquids with minimized corrosion-accelerated wear for engineering use.