Mechanism of Lubricating Action of Model Systems with Additives of Carbon Nanostructures under Hard Friction Conditions

Abstract

The mechanism of the lubricating effect of two model lubricants based on medical vaseline with 0.5 wt % additives of carbon nanostructures (CNSs), namely graphene oxide (GO) and shungite nanocarbon (Sh), under hard friction conditions (2070 SMT-1 friction machine, “disc–roller” friction pair made of hardened ShKh15 steel, load 2000 N) has been established. The friction surfaces were examined by confocal laser microscopy and scanning electron microscopy. The elemental composition of the friction surfaces was determined with the help of energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). The contribution of the chemical component (formation of iron oxides) to the anti-wear process was analyzed. It was found that despite the difference in the spatial structure of the used CNSs, the processes occurring in the friction zone are chemically similar. It has been demonstrated that with the use of both model lubricants, protective oxide films consisting of iron oxides (FeO, Fe₂O₃, Fe₃O₄) are formed in the contact zone. The chemical composition of the oxide film and the quantitative ratio of the formed iron oxides are not significantly affected by the type of CNS additives used. The results, together with the studies we performed earlier, demonstrate that the mechanical component, associated with the spatial organization of CNS additive, makes the decisive contribution to the anti-wear process under severe friction conditions.