Experimental analysis of stable CuO nanoparticle enhanced lubricants

The tribological properties of a custom-prepared and stable nano-lubricant that consists of CuO nanoparticles (9nm average diameter) suspended in mineral base oil using sodium oleate (SOA) as a surfactant are presented. Nano-lubricants with concentrations of 0.5, 1.0 and 2.0%wt were investigated using a disk-on-disk friction and wear test. It is observed that CuO/SOA nanoparticle additives reduce the friction between the lubricated surfaces in the absence of any other conventional additives. The effect of nanoparticles is more influential at higher loads and concentrations. Also, the steady state temperature of the lubricant is lower in the presence of nanoparticles. Measurements show that the viscosity of the nano-lubricants increases as more nanoparticles are introduced in the lubricant. The Stribeck curve is utilised to generalise the friction, temperature and the viscosity results into a single plot which can help to compare the performance of different nano-lubricants. Wear analysis based on profilometry results suggests that the wear increases with the nanoparticle concentration up to a 1.0%wt and then decreases for a 2.0%wt nano-lubricant. SEM/EDS results suggest that nanoparticles bond to the surface and form protective layers. Based on the results, different possible mechanisms for nanoparticles in the boundary lubrication regime were evaluated and the reduction in the real area of contact was suggested as the possible mechanism for reducing friction.