Tribological Behaviour of Molybdenum Disulphide Nanoparticles

Abstract

l dichalcogenides, are well known for their solid lubricating behaviour. Thin films of MoS2 exhibit extremely low coefficient of friction in dry environments, and are typically applied by mixing in oil, grease or impregnated into porous matrix of powdered materials, sputter deposition, pulsed laser ablation, evaporation or chemical vapour deposition, being essentially characteristic of either line-of-sight or high temperature processes. In this paper the authors have investigated the tribological properties of MoS2 nanoparticles with diameters of about 30 nm, under different friction conditions. The tribological properties of MoS2 nanoparticles mixed in lubricating oil were investigated using a four-ball tribometer and a block-on-ring tribometer. Obviously, the MoS2 nanoparticles can decrease the friction coefficient of lubricating oil. However the results showed that their friction reductions have do not obvious difference as compared to those obtained from the block-on-ring tribometer. The analyses of surfaces composition films, characterised by X-ray photoelectron spectroscope (XPS) and scanning electron microscopy (SEM) images, showed that deposited nanoparticles form a protective film of MoS3, allow an increase of the load capacity in friction (rubbed) pairs. XPS and SEM were used for examining morphology of the wear track after the four-ball experiment. The main advantage of the nanoparticles is ascribed to the release and furnishing of the nanoparticles from the valley onto the rubbing metal surface and their confinement at the interface. The MoS2 nanoparticles showed lower friction coefficients and higher wear resistance as compared to the common MoS2 particles (about 1.5 µm in diameter) on a four-ball machine, which were determined by the microstructure of the protective film serving as perfect intermediate lubricants between the contact surfaces.