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 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.