Abstract
Abstract
Lanthanum trifluoride nanoparticles surface-modified by di(2-ethylhexyl) phosphoric acid (D2EHPA) were prepared by a liquid-phase chemical route. The tribological behaviors of the as-prepared D2EHPA-LaF3 as the nano-additive in weakly polar mineral base oils 150N and poly-alpha-olefin (PAO6) as well as relatively strongly polar synthetic ester oil diisooctyl sebacate (DIOS) were evaluated with a four-ball friction and wear tester. The morphology of the worn steel surfaces as well as the composition and chemical state of typical elements thereon were analyzed by three-dimensional profilometry, scanning electron microscopy-energy dispersive spectrometry, and X-ray photoelectron spectroscopy; and the tribomechanism of the nano-additive was discussed with a view to its participation in tribochemical reactions and self-repairing effect for worn steel surfaces. The results indicate that the as-prepared D2EHPA-LaF3 nanoparticles exhibit good dispersion stability in the three kinds of tested base oils, which is due to the improvement in their compatibility with the base oils after surface-capping by the organic modifier. Besides, at a mass fraction of 0.2%, the nano-additive can improve the tribological properties of the three kinds of tested base oils to the maximum extent. This is because, on the one hand, the organic modifier D2EHPA can participate in tribochemical reactions together with the freshly exposed metal surfaces and the released LaF3 nano-core to form a tribofilm consisting of iron phosphate, iron oxides, lanthanum fluoride, and lanthanum oxide, thereby improving the anti-wear ability of the base oils. On the other hand, LaF3 nano-core can be released from D2EHPA-LaF3 nano-additive and deposited on worn steel surfaces to exert self-repairing effect, which also contributes to reducing the friction and wear of the steel-steel sliding contact.
Publisher
Research Square Platform LLC