Origin of the tribofilm from MoS2 nanoparticle oil additives: Dependence of oil film thickness on particle aggregation in rolling point contact

Abstract

The lubrication effectiveness of MoS2 nanoparticles as an oil additive remains unclear, restricting its application in industry to reduce friction. The goal of this work was to explore the lubrication mechanism of MoS2 nanoparticles as an oil additive. In this study, the oil film thickness behaviors of MoS2 nanoparticles in poly-alpha olefin (PAO4) base oil, PAO4 with 3 wt% dispersant (polyisobutyleneamine succinimide, PIBS), and 0W20 engine oil were investigated using an elastohydrodynamic lubrication (EHL) testing machine. Following the EHL tests, the flow patterns around the contact area and the tribofilm covering rate on contact area were studied using optical microscopy to understand the lubrication mechanism. The results indicate that both the dispersant and nanoparticle aggregation significantly affected the oil film thickness. The expected oil film thickness increase in the case of 0.1 wt% MoS2 in PAO4 base oil was obtained, with an increase from 30 to 60 nm over 15 min at a velocity of 50 mm/s. Flow pattern analysis revealed the formation of particle aggregation on the rolling path when lubricated with 0.1 wt% MoS2, which is associated with a tribofilm coverage rate of 41.5% on the contact area. However, an oil film thickness increase and particle aggregation were not observed during the tests with 0.1 wt% MoS2 blended with 3 wt% PIBS as the dispersant in PAO4 base oil, and for 0.75 wt% MoS2 in 0W20 engine oil. The results suggest that nanoparticles responsible for tribofilm formation originated from aggregates, but not the well-dispersed nanoparticles in point contact. This understanding should aid the advancement of novel lubricant additive design.

Anti-wear behaviour of silver nanoparticles on Al-Si alloy

“…Therefore, the presence of Ag element indicates the AgNPs were deposited on both worn surfaces [26]. This result confirmed formation of tribofilm on the contact area between ball and substrate materials [35,50,51]. And it might be said that tribofilm was occurred on a large surface instead of partial regions for Oil-Ag@Ctr and Oil-Ag@Pva lubricants [52].…”

An investigation on tribological properties of advanced microwave synthesized molybdenum disulfide as anti-friction additives in commercially available lubricating oils

“…Additionally, the nanoparticles contribute to the smoothening of surface roughness and asperities, facilitating improved contact between sliding surfaces and reducing friction and wear caused by plowing and cutting actions. 15,20,[33][34][35][36][37][38] By capitalizing on these mechanisms, MoS 2 nanoparticles enhance overall lubrication performance, thereby prolonging the lifespan of engine components.…”

“…Most research is currently focused on polyalphaolephin oil, which is broadly used in the engine sector. [13][14][15] In this investigation, the MoS 2 nanoparticles had synthesized using an advanced microwave platform which is an energy and time-saving method. The obtained nanoparticles are tested with four types of different lubricants such as fully synthetic, semi-synthetic, mineral, and hydraulic oil for their tribological properties using four ball tribotester.…”

Synthesis of Eco-Friendly Carbon Dots as Self-Repairing Additives of Polyalphaolefin by Means of a Green Solvation Effect

“…Luckily, the inorganic additives of nanomaterials are expected to be excellent additives for PAO because of their unique rolling, mending, and polishing effects and strong film-building ability by sintering and deposition. So far, various nanomaterials, such as metals, metal oxides, metal sulfides, metal salts, boron nitride, graphene, carbon nanotubes, carbon dots (CDs), and composites, have been used as additives of PAO with splendid performance. − Although many nanomaterials are eco-friendly according to their element compositions, there are still two issues limiting their practical application. The morphology and sizes of many nanomaterials are irregular and diverse, which is detrimental to building uniform lubricating films on rubbing surfaces .…”