Abstract
In this work, two different 2D materials, molybdenum disulfide nanoplatelets (MSNP) and graphene nanoplatelets (GNP), prepared by electrochemical exfoliation, were used as additives to prepare nanolubricants. The tribological behaviour of the nanolubricants was evaluated under two configurations (pure sliding and rolling/sliding) using two different tribometers: an Universal Macro Materials Tester (UMT-3) and a Mini Traction Machine (MTM2). Wear volume was determined, after the sliding tests, in a confocal microscope (Leica DCM 3D) and the worn surface was analyzed by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and Raman microscopy. Lubrication mechanisms of GNP and MSNP dispersed in an engine oil for improving its antifriction and antiwear capabilities are proposed. The traction coefficient determination was performed at a 50% of slide-to-roll ratio and at different temperatures. The results showed that the nanolubricants formulated with both types of additives, in their lowest concentration, improved friction and wear in sliding tests, compared to neat engine oil. In addition, only the nanolubricants with the MSNP nano additive at loadings of 0.05 and 0.2 wt% showed friction reductions compared to the commercial engine oil under the rolling/sliding tests.
Highlights
Recent studies suggested that 33% of the fuel energy in passenger cars is dissipated to overcome friction losses [1]
Lubrication are usually classified into four different regimes: boundary lubrication (BL), elastohydrodynamic lubrication (EHL), hydrodynamic lubrication (HL), and mixed lubrication (ML)
When the concentration of additives increases, the coefficient of friction (COF) worsens compared to the base oil
Summary
Recent studies suggested that 33% of the fuel energy in passenger cars is dissipated to overcome friction losses [1]. Shafi et al [14] studied the tribological behaviour of avocado oil additised with copper nanoparticles in mixed and boundary lubrication regimes They attributed the improvement in the frictional characteristics to a tribofilm formation between the sliding surfaces. Hernández Battez et al [15] evaluated the antiwear behaviour under a mixed lubrication regime of nanolubricants formed by adding metal oxide nanoparticles (CuO, ZrO2 and ZnO) to a polyalphaolefin (PAO6) The lubricant properties (traction and antiwear behaviours) of two 2D nanomaterials used as additives in a fullyformulated commercial engine oil have been evaluated Both materials, graphene and MoS2, are produced by the electrochemical exfoliation method, which allows the production of large flakes and controlled numbers of layers. This study aims to complete the tribological characterisation carried out in a previous work [27] and to check the tribological behaviour of these surfactantfree nanolubricants in mixed and elastohydrodynamic lubrication regimes
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