Improving the lubricating performance of poly-alpha-olefin base oil using SnO₂ nanosized-additives

Abstract The majority of previous studies have been focused on the thermal properties of SnO 2 nanofluids. In order to understand the lubricating performance of SnO 2 nanoparticles as additives, the current study investigates the effects of the addition of SnO 2 nanoparticles on the tribological properties of poly-alpha-olefin 6 base oil. The dual-step method is utilized to disperse the SnO 2 nanoparticles in base oil with oleic acid as surfactant. The shape and size of SnO 2 nanoparticles are confirmed by transmission electron microscopy, and the dispersion stability of SnO 2 nanoparticles is examined by dynamic light scattering tests. The lubricating properties of SnO 2 nanofluids are explored on a universal mechanical tribometer with a ball-on-plate reciprocating sliding configuration. It is found that the SnO 2 nanofluids show good stability and dispersibility. The addition of SnO 2 nanoparticles decreases the friction and wear for steel-steel tribo-pairs. The positive effects on friction and wear reductions become more significant with increasing concentrations of SnO 2 nanoparticles. In this work, nanofluids containing the 5wt% SnO 2 nanoparticles and 5wt% oleic acid is considered as the optimum composition, which shows the best lubricating performance with the reductions of 13.8% in coefficient of friction and 41.4% in wear volume loss. After observing the wear tracks by scanning electron microscopy, energy dispersive spectrometer and a white-light interferometer, it is shown that the wear mechanisms are dominated by abrasive wear and adhesive wear. The enhancement in tribological properties of base oil is attributed to the formation of SnO 2 tribo-film and oleic acid tribo-layer which reduces the shearing resistance, separates the mating areas and withstands the loads. The findings obtained in this study can be used as references in the development of high-performance nanofluids.