Oil-soluble sulfur-containing organic molybdenum (SOM) as lubricant additives: a review

Abstract

Abstract In situ formation of lamellar MoS2 nanomaterials between the tribocontacts during frictions through adding oil-soluble sulfur-containing organic molybdenum (SOM) additives into lubricating oils is an alternative route of dispersing pre-formed MoS2 into lubricants directly, which is difficult to disperse homogeneously in oils. In this technology, the synthesis of SOM with appropriate S and Mo contents and successful generation of enough MoS2 during friction by adjusted working conditions are two crucial factors determining the efficiency of SOM on the friction-reduction and anti-wear behaviors of the SOM-containing oils. Given the fact that SOM additives have been used intensively in both laboratory researches and engineering applications, this review discusses in detail the molecular structures, tribological behaviors, compatibility and synergistic effects with the other additives, and some application bottlenecks of the reported SOM compounds that may constrain their wide applications as lubricant additives. Moreover, some routes for overcoming these application bottlenecks are suggested. This review also concludes the basic mechanisms for the lubrication capabilities of the SOM and provides some suggestions for utilizing SOM additives in advanced lubrication systems. Finally, the future development of SOM as oil additives is proposed and summarized.