Origin of the tribofilm from MoS 2 nanoparticle oil additives: Dependence of oil film thickness on particle aggregation
- PDF / 7,145,600 Bytes
- 14 Pages / 595.22 x 790.976 pts Page_size
- 89 Downloads / 139 Views
ISSN 2223-7690 CN 10-1237/TH
RESEARCH ARTICLE
Origin of the tribofilm from MoS2 nanoparticle oil additives: Dependence of oil film thickness on particle aggregation in rolling point contact Hongxing WU1, Liping WANG2, Guangneng DONG3,* 1
State Key Laboratory of Solidification Processing, Center of Advanced Lubrication and Seal Materials, Northwestern Polytechnical University, Xi’an 710072, China
2
Petro China Lanzhou Lubricating Oil R & D Institute, Lanzhou 730060, China
3
Key Laboratory of Education Ministry for Modern Design and Rotor-Bearing System, Xi'an Jiaotong University, Xi'an 710049, China
Received: 05 March 2020 / Revised: 31 May 2020 / Accepted: 03 July 2020
© The author(s) 2020. 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. Keywords: nanoparticle lubrication; oil film thickness; flow pattern; particle aggregation
1
Introduction
Low viscosity engine oil is required to reduce friction and to enhance fuel efficiency in response to global warming [1, 2]. Lubricant material design for modern engines must consider low oil viscosity, which results in low oil-film thickness and reduced
energy consumption in the hydrodynamic lubrication regime. However, this is associated with direct asperity contact in both boundary lubrication and mixed lubrication [3, 4]. Nanoparticles as an anti-friction additive have been considered as a promising candidate to reduce friction and wear in bou
Data Loading...
