Tribological properties of ZnO and WS2 nanofluids using different surfactants

Previous studies have shown promising tribological performance and thermal properties of nano particles and ionic liquids when they were used separately as oil additives. However, the use of ionic liquid as a nanofluid surfactant has been rarely studied. This work investigates oil based ZnO and WS2 nanofluid tribological properties using two different surfactants: oleic acid and ionic liquid. ZnO and WS2 nanofluids were mixed and pin on disk tests were performed using 20MnCr5 carburized axle hypoid gear material. Results showed that phosphinate ionic liquid as surfactant has long term stability when mixed with ceramic nano particles. However, it was found that using phosphinate ionic liquid alone as an oil additive did not improve nanofluid tribological performance. Meanwhile, oleic acid when used as a surfactant showed lower friction and reduced wear for both ZnO nanofluids and WS2 nanofluids. SEM studies showed a film formed on the disk surface using oleic acid as surfactant which may enhance tribological performance.