Surface Modification And Tribological Properties Of Lanthanum Trifluoride Nanoparticles

In this work, we used LaF3 nanoparticles to decorate the GO nanosheets to prepare a new water-based LaF3-GO nanohybrids lubricant additive for the poor dispersion of LaF3 nanoparticles in water. On the one hand, LaF3 nanoparticles could disperse in water due to the carbon oxygen functional groups on the surface of GO. On the other hand, the synergistic effect between LaF3 nanoparticles and GO could improve the tribological properties of nanohybrids. Moreover, because of the agglomeration and poor dispersion of LaF3 nanoparticles, we selected 3-(heptafluoroisopropoxy)propyltriethoxysilane (denoted as HFIPPTS) and tributyl phosphate (denoted as TBP) to modify LaF3 nanoparticles for different base oils and prepared HFIPPTS-LaF3 and TBP-LaF3 nanoparticles respectively. On the one hand, surface modifier could reduce the agglomeration of LaF3 nanoparticles and improve the dispersibility properties of LaF3 nanoparticles in base oil. On the other hand, the tribological synergy between modifier and LaF3 nanoparticles could improve the tribological properties of LaF3 nanoparticles in base oil. The structure and morphology of LaF3-GO, HFIPPTS-LaF3 and TBP-LaF3 were characterized by X-ray diffract, Fourier transform infrared spectrometry (FT-IR), Transmission electron microscopy (TEM) and so on. The tribological properties of three products as lubricating additive were investigated using a four-ball test machine. Moreover, the morphology of worn steel surfaces were analyzed with a scanning electron microscope (SEM) and the composition and chemical states of typical elements in the worn surfaces of the steel balls were determined with a X-ray photoelectron spectroscope (XPS), and the tribology mechanism was defined at the same time. These main research results and contents were as follows.1. Fabrication and tribological properties of LaF3-GO nanohybrids as additive in distilled waterLanthanum trifluoride (LaF3) nanoparticles decorated graphene oxide (GO) nanosheets were successfully prepared by a simple solution method. The structure and morphology characterization results of LaF3-GO nanohybrids showed that LaF3 nanoparticles are integrated with the GO nanosheets utilizing an electrostatic interaction. In addition, tribological properties of LaF3-GO nanohybrids as an additive of distilled water were evaluated with a four-ball test machine. The results showed that 1.5 wt%(quality score) is the optimum concentration of LaF3-GO nanohybrids, under this condition, both the wear scar diameter and the friction coefficient are significantly smaller than those of 1.5 wt% of GO nanosheets added into distilled water as well as distilled water alone. Moreover, the load-carrying capacity of distilled water is improved from 50 N to 400 N, and the load-carrying capacity of GO nanosheets is 200 N. The results of SEM showed that the worn steel surface is smooth and shows few furrows and grooves, showing good anti-wear properties. In addition, the results of energy dispersive spectrometer and X-ray photoelectron spectroscope revealed that during the friction process, LaF3 nanoparticles are deposited on the rubbed steel surface to form protective layer includes GO, FeF3 and LaF3, which improves the anti-friction and anti-wear properties.2. Preparation and tribological properties of HFIPPTS-LaF3 nanoparticles as additive of fluoro silicone oilLaF3 nanoparticles surface-modified with fluorosilane were synthesized by surface modification technology. The structure and morphology characterization results of HFIPPTS-LaF3 nanoparticles showed that surface modification by HFIPPTS does not change the crystal structure of LaF3 nanoparticles. Besides, HFIPPTS helps to reduce the agglomeration of LaF3 nanoparticles and changes the wettability of LaF3 nanoparticles from hydrophilicity to hydrophobic. Moreover, HFIPPTS as the modifier improves the dispersibility of LaF3 nanoparticles in fluoro silicone oil. In addition, tribological properties of HFIPPTS-LaF3 nanoparticles as an additive of fluoro silicone oil were evaluated with a four-ball test machine. The results showed that 0.08 wt%(quality score) is the optimum concentration of HFIPPTS-LaF3 nanoparticles, under this condition, the wear scar diameter is significantly 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, the results of X-ray photoelectron spectroscope revealed that during the friction process, LaF3 nanoparticles are deposited on the rubbed steel surface to form protective layer includes Fe2O3, FeF3, La2O3 and LaF3, which improves the anti-wear properties.3. Preparation of TBP-LaF3 nanoparticles and evaluation of their tribological properties as additive of liquid paraffinLaF3 nanoparticles surface-modified with TBP were synthesized by surface modification technology. The structure and morphology characterization results of TBP-LaF3 nanoparticles showed that surface modification by TBP does not change the crystal structure of LaF3 nanoparticles and TBP helps to reduce the agglomeration of LaF3 nanoparticles. Moreover, TBP as the modifier improves the dispersibility of LaF3 nanoparticles in liquid paraffin. In addition, tribological properties of TBP-LaF3 nanoparticles as an additive of liquid paraffin were evaluated with a four-ball test machine. The results showed that 0.4 wt.% (quality score) is the optimum concentration of TBP-LaF3 nanoparticles, under this condition, both the wear scar diameter and the friction coefficient are significantly smaller than that under the lubrication of liquid paraffin. In addition, the results of X-ray photoelectron spectroscope revealed that during the friction process, LaF3 nanoparticles are deposited on the rubbed steel surface to form deposited layer and active P element of TBP form a tribochemical reaction film on sliding steel surfaces, which improves the anti-friction and anti-wear properties.