Phosphorus-Containing Ionic Organomolybdenum Lubricant Additive for Enhancing Tribological Performance of PAO6 Base Oil

The development of environmentally friendly, sulfur-free lubricant additives has long been a critical research focus. This study reports the synthesis of a phosphorus-containing ionic organomolybdenum compound ([HBMo][DEHP]) and investigated its tribological performance in a PAO6 base oil. Moreover, molecular simulation results revealed that the additive [HBMo][DEHP] tended to adsorb onto the metal surface. The optimal concentration of [HBMo][DEHP] (0.1 wt %) was at least 10 times lower than that required for conventional additives. The tribological tests showed that the additive exhibited excellent tribological properties even under high load (490 N) and elevated temperature (175 °C) conditions. Based on molecular simulations and frictional analysis, a dual-film lubrication mechanism with an adsorption film and a tribochemical reaction film was proposed for [HBMo][DEHP].