Oil miscible phosphonium-phosphate ionic liquid as novel antiwear and antipitting additive for low-viscosity rear axle lubricants

Abstract This study explored the feasibility of using a phosphonium phosphate ionic liquid as a candidate anti-wear and anti-pitting additive for rear axle lubrication. This particular IL was first added to a VHVI8 base oil at 2–3% concentration and demonstrated effective surface protection for wear and micro-cracking under rolling-sliding contacts. The promising results directed to a step further to produce a series of IL-containing low-viscosity (about a half of SAE 75W-90) fully formulated gear oils. Selected IL-containing experimental oils showed superior mitigation of rolling contact fatigue to a commercial SAE 75W-90 gear oil in bench-scale rolling-sliding tests. Full-scale hub dynamometer tests were conducted and demonstrated more than 3% power output and torque generation for an IL-containing low-viscosity gear oil benchmarked against commercial baselines.