Lubrication Performance and Mechanism of Group VIA Element-Functionalized Triphenyl Phosphite as Additive

Abstract Multifunctional additives play a crucial role in enhancing the lubrication performance of lubricating oils, and chemical modification of conventional additives offers a promising solution. In this paper, two types of group VIA element (S, Se)-functionalized triphenyl phosphite (TPP)-based additives, namely, triphenyl thiophosphate (S-TPP) and triphenyl selenophosphate (Se-TPP), were successfully synthesized. Triphenyl phosphate (O-TPP) was also employed to investigate the influence of group VIA elements (O, S, and Se) on tribological and antioxidant properties. The friction experiments demonstrate that TPP-based additives can improve the antiwear and friction reduction performance of the base oil. Specifically, S-TPP further enhances antiwear performance, whereas Se-TPP exhibits superior friction reduction and antisintering properties. The antioxidant tests reveal that O-TPP and S-TPP show no antioxidant effect, whereas Se-TPP exhibits an excellent antioxidant capability. The lubrication mechanism was investigated by using SEM, 3D profiles, and XPS analyses. The results indicate the formation of an iron phosphate tribofilm on the worn surfaces. Furthermore, S-TPP and Se-TPP facilitate the formation of characteristic tribofilms containing S or Se atoms. The findings suggest that Se-TPP holds significant potential as a multifunctional additive.