Surface-Functionalized Ultrafine Boehmite as Oil-Soluble Nanoadditives for Boosting the Tribological Performance of Molybdenum Dialkyldithiophosphate

The surface engineering of nanomaterials is crucial for addressing persistent issues related to their dispersion stability in base oil. In this study, the superfine boehmite (AlOOH) nanomaterials were successfully synthesized and subsequently modified by hexadecyltrimethoxysilane to achieve their dispersion stability in poly α olefin 8 (PAO8) for at least 35 days. This oil-soluble AlOOH was employed alongside molybdenum dialkyldithiophosphate (MoDTP) as additives in PAO8 to effectively reduce friction and wear. The results demonstrated that the composite additives of MoDTP and oil-soluble AlOOH exhibited remarkable friction performances in PAO8. Notably, when 1.5 wt % oil-soluble AlOOH was combined with 0.25 wt % MoDTP, the average coefficient of friction and wear rate were decreased by 80.93% and 86.34% compared to base oil, respectively. Meanwhile, the tribological properties of PAO8 containing the desired composite additive under various sliding conditions were investigated as well. Furthermore, the synergistic effect between the oil-soluble AlOOH and MoDTP facilitates the formation of a robust tribofilm composed of FePO 4 , Fe 2 (SO 4 ) 3 , MoS 2 , FeO, Al 2 O 3 , Fe 2 O 3 , MoO 3 , and Fe 3 O 4 , ultimately boosting friction-reducing and wear-resistance effects as well as load-bearing capacity.