Preparation and tribological properties of fluorosilane surface-modified lanthanum trifluoride nanoparticles as additive of fluoro silicone oil

Highlights: • Fluorosilane was selected as the modifier according to similar miscibility principle. • Fluorosilane surface-modified LaF₃ nanoparticles were successfully prepared. • Fluorosilane can enhance dispersibility of LaF₃ nanoparticles in fluorosilicone oils. • Fluorosilane can improve the stability of LaF₃ nanoparticles. • LaF₃ nanoparticles prove excellent anti-wear and friction-reducing capacities. - Abstract: LaF₃ nanoparticles surface-modified with fluorosilane were synthesized by surface modification technology. The size, morphology and phase structure of as-prepared surface-modified LaF₃ nanoparticles were analyzed by means of X-ray diffraction and transmission electron microscopy. The tribological properties of surface-modified LaF₃ nanoparticles as additive of fluoro silicone oil were evaluated with a four-ball machine, and the morphology and elemental composition of worn steel surfaces were examined with a scanning electron microscope and an X-ray photoelectron spectroscope. Results show that 3-(heptafluoroisopropoxy)propyltriethoxysilane as the modifier is able to improve the dispersibility of LaF₃ nanoparticles in fluoro silicone oil. Moreover, when the optimum concentration, 0.08 wt.% of fluorosilane surface-modified LaF₃ is added into fluoro silicone oil, as-synthesized fluorosilane surface-modified LaF₃ nanoparticles exhibit excellent anti-wear as additive in fluoro silicone oil. The wear scar diameter under the optimum concentration is always smaller than that under the lubrication of fluoro silicone oil alone. Especially, when the load is 500 N, 600 N and 700 N, the wear scar diameter is reduced by 17%, 43% and 42%, respectively. In addition, during the friction process, LaF₃ nanoparticles are deposited on the rubbed steel surface to form LaF₃ deposition layer which functions jointly with the boundary lubricating film thereby resulting in improved tribological properties