Impact of Lubricant Additives-Soot Interactions on the Tribological Properties of Lithium Grease

Among atmospheric contaminants, soot is known to cause severe wear of mechanical components and degrade lubricating oils; however, its impact on lubricity grease remains largely unexplored. This study investigates the interactions between carbon black (as a soot surrogate) and other lubricant additives, including molybdenum disulfide (MoS 2 ) and anti-wear additive zinc dialkyldithiophosphate (ZDDP). Additionally, the effects of individual and combined additions of MoS 2 and ZDDP on the tribological properties of soot-contaminated lithium grease (LG) were compared. The lubricity of LG decreased progressively with increasing soot concentration. Conversely, incorporating MoS 2 improved the lubricity of LG, with optimal performance observed at 0.5 wt%. The individual addition of MoS 2 to LG minimally mitigated the abrasive wear caused by soot; however, the inclusion of ZDDP T202 enhances the effectiveness of MoS 2 in reducing the friction and wear. MoS 2 and ZDDP participate in tribochemical reactions to form protective films during sliding. MoS 2 contributes by reducing friction, while ZDDP reacts to form protective films that enhance wear resistance. However, the combined addition of ZDDP and MoS 2 demonstrates limited effectiveness in fully mitigating the adverse effects of soot on grease lubrication. Consequently, exploring more efficient methods to prevent lubrication failure caused by soot.