A Comparative Study of the Effect of TiO2 and CuO Nanoparticles as an Additive to Mineral Oil on the Tribological Properties of Steel Friction Pairs

This study presents the effect of adding crystalline titanium dioxide (TiO2) and copper oxide (CuO) nanoparticles to SN mineral oil on the tribological properties of steel samples. X-ray diffraction confirmed the crystal structure of the nanoparticles and atomic force microscopy confirmed their nanometric size (~30 nm). Based on viscosity, surface tension, and finally micro- and macroscale ball-on-disc measurements, the optimal concentration of nanoparticles in oil samples was determined at 0.05 wt.%. The addition of TiO2 and CuO nanoparticles to SN oil reduced wear and the coefficient of friction. Moreover, macroscale tests using the XCT tribotester in a cylinder-on-ring configuration showed a higher Brugger value than in SN oil without nanoparticle additives, while a reduction in the coefficient of friction occurred. Analysis of the worn surfaces indicates that the lower coefficient of friction and wear is the result of the formation of protective anti-wear tribofilm containing nanoparticles. The conducted ball-on-disc and Brugger tests confirmed the beneficial effect of TiO2 and CuO nanoparticle addition on the tribological properties of the oil and helped explain the mechanism of lubrication of steel surfaces used in friction tests.