Preparation and Tribological Behavior of Hydrophobic Lanthanum Borate Nanosheets in Rapeseed Oil

Oleic acid-capped lanthanum borate (abbreviated as OA/LaBO3·H2O) nanosheets were prepared by the hydrothermal method. The microstructures of as-prepared OA/LaBO3·H2O were characterized by means of SEM, TEM, EDS, FTIR and XRD, respectively. Moreover, the friction and wear properties of OA/LaBO3·H2O as a lubricant additive in rapeseed oil were evaluated on a four-ball tribotester. The tribochemical characteristics of worn surfaces were investigated by SEM and XPS. The results showed that the hydrophobic OA/LaBO3·H2O nanosheets exhibited their morphology with a diameter in the range of 100 nm to 300 nm and a thickness of about 25 nm, and displayed excellent dispersing stability in rapeseed oil. In the meantime, the rapeseed oil doped with OA/LaBO3·H2O nanosheets markedly decreased the friction and wear of steel balls, and the optimal friction-reducing and antiwear ability of rapeseed oil was obtained at an OA/LaBO3·H2O content of 1.0%. The outstanding tribological performance of OA/LaBO3·H2O in rapeseed oil was attributed to the formation of a composite boundary lubrication film mainly composed of lubricious tribochemical species of B 2O3, La2O3 and Fe2O3, and deposits of OA/LaBO3·H2O nanosheets as well as the adsorbates of rapeseed oil on rubbed surfaces.