Investigation Of Tribological Performance Of Oil-based ZnO Nanofluids

The nanometer materials are widely used due to its unique structure and properties.The concept of nanofluid arouses people’s attention. It is found that nanofluid has both unique and excellent tribological properties and good thermal conductivity. Nanoparticles added in lubricant can adsorbed easily on the surface of the friction and wear for its smaller particle size, larger surface area and low melting point, and then the lubricating film is deposited reducing the friction coefficient and wear. One of the major problems with this new classification of fluid is how to prepare stable and well-dispersed solutions.Due to their high surface activity and poor compatibility with base oils, nanoparticles in fluid tend to agglomerate into some much larger particles.In this paper, the surface of ZnO nanoparticles was modified with oleic acid as dispersant, the modification effect and modification mechanism were studied. Then different concentrations of oil-based nanofluids were prepared by mechanical stirring and ultrasonic dispersion. The dispersion, stability performance of nanofluid was investigated.The friction and wear experiment was carried out to investigate tribological performance of nanofluids. The effects of dispersant concentration, additive concentration and load on the tribological properties of the nanoparticles were systematically analyzed.Firstly, the dispersion, stability performance of nanofluids was analyzed. The surface of nanoparticles was modified with oleic acid and it was characterized by FTIR. The results show that after modification, the hydroxyl group existed on the surface of nanoparticles and the carboxyl group of oleic acid was disappeared, the new peak of the carboxylate appear in 1467 and 1567. This shows that the mechanism of the modification of nano zinc oxide particles by oleic acid is not simply physical adsorption and package,but a chemical reaction occurs between them. It shows better modification effect. The distribution of ZnO nanoparticles in the lubricant was tested by transmission electron microscopy. It can be seen that surface-capped ZnO nanoparticles exhibit no sign of obvious aggregation and maintain an average diameter. The dispersibility and stability of nanofluids were also investigated by visually examining the sedimentation process over time. The solutions can stay stably with no obvious stratification.The friction and wear properties of nanofluids were evaluated with a four-ball tester and UNMT- 1 micro/nano wear testing machine, and the morphologies of wear scars and the wear track were measured by a scanning electron microscope(SEM), VECCO wyko surface profier and a Zeiss laser confocal microscope. The results showed that fluids withZnO nanoparticles or oleic acid could reduce friction and wear under certain conditions.The nano particles as additive in lubricant exist better lubricating effect in the high load condition. And when the oleic acid adding quantity was 8wt% and ZnO nanoparticles was0.5 wt%, the nanofluids had better friction-reducing and anti-wear properties.