Unique synergistic effects between phosphonium-alkylphosphate ionic liquids (ILs) and zinc dialkyldithiophosphate (ZDDP) are discovered when used together as lubricant additives, resulting in significant friction and wear reduction along with distinct tribofilm composition and mechanical properties. The synergism is attributed to the remarkably 30-70× higher-than-nominal concentrations of hypothetical new compounds (via anion exchange between IL and ZDDP) on the fluid surface/interface.
We have previously reported an oil-miscible phosphonium-organophosphate ionic liquid (IL) with an effective anti-wear (AW) functionality when added to a base oil by itself or combined with a conventional zinc dialkyldithiophosphate (ZDDP) for a synergistic effect. In this research, we investigated whether this synergy manifests in formulated engine oils. An experimental SAE 0W-16 engine oil was generated containing a combination of IL and ZDDP with equal phosphorus contribution. The prototype engine oil was first evaluated using tribological bench tests: AW performance in boundary lubrication (BL) and friction behavior (Stribeck curves) in elastohydrodynamic, mixed, and BL. The forthcoming standard Sequence VIE engine dynamometer test was then conducted to demonstrate improved fuel economy. Results were benchmarked against those of another experimental engine oil with almost the same formulation except using ZDDP only without the IL (similar total phosphorus content). The IL-ZDDP formulation consistently outperforms the ZDDP-only formulation in friction reduction and wear protection, and results from the bench and engine tests are well correlated.
Abstract:Effective tribofilms are desirable to protect mechanical systems. In the present research, we investigated the formation of a tribofilm through the use of α-ZrP (Zr(HPO 4 ) 2¨H2 O) as an additive. Experiments were conducted on a base oil where 0.2 wt% of the additive was used. Experimental results showed a 50% reduction in friction and a 30% reduction in wear when compared to the base oil containing 0.8 wt% ZDDP. Spectroscopic characterization indicated that the tribofilm consists of iron oxide, zirconium oxide, and zirconium phosphates. The worn surface was seen to be smooth which renders it desirable for bearing systems.
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