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

The majority of previous studies have been focused on the thermal properties of SnO₂ nanofluids. In order to understand the lubricating performance of SnO₂ nanoparticles as additives, the current study investigates the effects of the addition of SnO₂ nanoparticles on the tribological properties of poly-alpha-olefin 6 base oil. The dual-step method is utilized to disperse the SnO₂ nanoparticles in base oil with oleic acid as surfactant. The shape and size of SnO₂ nanoparticles are confirmed by transmission electron microscopy, and the dispersion stability of SnO₂ nanoparticles is examined by dynamic light scattering tests. The lubricating properties of SnO₂ nanofluids are explored on a universal mechanical tribometer with a ball-on-plate reciprocating sliding configuration. It is found that the SnO₂ nanofluids show good stability and dispersibility. The addition of SnO₂ 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 SnO₂ nanoparticles. In this work, nanofluids containing the 5wt% SnO₂ 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 SnO₂ 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.