Abstract
To study the effect of oleic acid surface modified RGO/MoS2 composite lubricating additives on the friction and wear properties of 10# White Oil (10# WO). The influences of different concentrations of reduction graphene oxide/molybdenum disulfide (RGO–MoS2) and oleic acid surface modified reduction graphene oxide/molybdenum disulfide (OA-RGO–MoS2) on the lubricating properties in 10# WO was investigated using a four-ball long-term friction and wear tester. The microscopic morphology, lattice structure, composition and element valence of the prepared material were characterized by scanning electron microscope, Raman spectroscopy, Infrared Spectroscopy, X-ray diffractometer, X-ray photoelectron spectroscopy, element analyzer and other instruments. The diameter, structure, morphology, composition and element valence state of the wear scar were obtained by multifunctional universal tool microscope, scanning electron microscope and X-ray photoelectron spectroscopy. In the RGO–MoS2 white oil system, when 0.4 wt% RGO–MoS2 is added, the anti-friction effect is the best, and the average friction coefficient (AFC) reduced by 21.8%. When 0.2 wt% RGO–MoS2 is added, the anti-wear effect is the optimal, and the average wear scar diameter (AWSD) decreased by 12.4%. In the OA-RGO–MoS2 white oil system, when 0.2 wt% OA-RGO–MoS2 is added, the anti-friction and anti-wear effects are the best, and the AFC reduced by 33.3%, and AWSD reduced by 14.1%. Compared with RGO–MoS2, OA-RGO–MoS2 has a higher degree of graphitization, larger interlayer spacing, lower degree of layered accumulation, higher MoS2 load, and weaker thermal stability. Both lubricating additives have good anti-friction and anti-wear effects at low concentrations, and the anti-friction and anti-wear effects are more prominent after being modified by oleic acid. Analysis of friction mechanism shows that a lubricating protective film containing iron, oxygen, molybdenum, carbon, and sulfur is formed through adsorption or tribochemical reaction during the friction process, which improves the lubrication state and plays a role in reducing friction and anti-wear.
Highlights
As a typical transition metal sulfide, MoS2 is easy to slip between layers due to its unique twodimensional layered structure and weak Van der Waals force between layers, which shows an excellent anti-friction effect and has been widely used in the field of lubrication [1,2,3,4,5]
Compared with reduced graphene oxide (RGO)-MoS2, Oleic acid (OA)-RGO-MoS2 has a higher degree of graphitization, larger interlayer spacing, lower degree of layered accumulation, higher MoS2 load, and weaker thermal stability
MoS2 is highly dispersed on the lamellar RGO, mainly because MoS2 and RGO have similar two-dimensional layered structure, and RGO plays a role of nucleus and epitaxial growth substrate in the formation of molybdenum disulfide
Summary
As a typical transition metal sulfide, MoS2 is easy to slip between layers due to its unique twodimensional layered structure and weak Van der Waals force between layers, which shows an excellent anti-friction effect and has been widely used in the field of lubrication [1,2,3,4,5]. Due to its low interlaminar shear force and high elastic modulus, graphene has been widely concerned by the frictional field due to its excellent lubricity and load-bearing properties [8,9,10,11]. There are many studies on the preparation of carbon/molybdenum disulfide composites using graphite, carbon fibers, and carbon nanotubes as carrier materials as lubricating additives [12,13]. It has been reported that reduced graphene oxide/molybdenum disulfide (RGO-MoS2) materials were prepared by vapor deposition [16], hydrothermal [17], solvothermal [18], solution reduction [19], and microwave synthesis [20], with emphasis on the modulation of MoS2 nanostructures. Taking advantage of the structural similarity of these two, taking the defect site of RGO as the anchoring site and loading MoS2, it is expected to obtain the lubricant additive of RGOMoS2 with higher dispersibility
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