Potential Application of Oil-Soluble LaF3 Nanoparticles as High-Performance Gear Oil Additives

This study aims to explore the potential application of LaF 3 nanoparticles as high-performance gear oil additives. Lanthanum trifluoride nanoparticles modified by di(2-ethylhexyl) phosphoric acid (D2EHPA) [denoted as LaF 3 -D2EHPA], which exhibited excellent dispersion stability, were prepared using a liquid-phase chemical method. The tribological properties of LaF 3 -D2EHPA nanoparticles in weakly polar mineral base oil (150 N), polyalphaolefin (PAO6), and strongly polar synthetic ester oil diisooctyl sebacate (DIOS) were investigated using a four-ball friction and wear tester. In combination with the adsorption experiments using a dissipative quartz crystal microbalance (QCM-D), the compatibility and action mechanisms of LaF 3 -D2EHPA nanoparticles with extreme-pressure and anti-wear additives for typical gear oils were further investigated. The results indicate that when the mass fraction of LaF 3 -D2EHPA nanoparticles is 0.2%, the tribological properties of all three base oils are improved to the greatest extent. When LaF 3 -D2EHPA nanoparticles are mixed with gear oil additives T321 (sulfurized isobutylene) and T307 (ammonium thiophosphate), they exhibit high film-forming rates and anti-wear properties, forming a boundary lubricating film on the worn surface. This film consists of a tribochemical reaction film containing sulfur and phosphorus, as well as LaF 3 -D2EHPA nanoparticles that have been deposited.