How the fluorographene replaced graphene as nanoadditive for improving tribological performances of GTL-8 based lubricant oil

Abstract

Fluorographene, a new alternative to graphene, it not only inherits the 2-dimensional (2D) layered structure and outstanding mechanical properties, but also possesses controllable C–F bonds. It is meaningful to reveal the evolution processes of the tribological behaviors from graphene to fluorographene. In this work, fluorinated reduced graphene oxide nanosheets (F–rGO) with different degree of fluorination were prepared using direct gas-fluorination and they were added into gas to liquid-8 (GTL-8) base oil as lubricant additive to improve the tribological performance. According to the results, the coefficient of friction (COF) reduced by 21%, notably, the wear rate reduced by 87% with the addition of highly fluorinated reduced graphene oxide (HF–rGO) compared with rGO. It was confirmed that more covalent C–F bonds which improved the chemical stability of HF–rGO resisted the detachment of fluorine so the HF–rGO nanosheets showed less damage, as demonstrated via X-ray photoelectron spectroscopy (XPS), Raman spectra, and transmission electron microscopy (TEM). Meanwhile, the ionic liquid (IL) adsorbed on HF–rGO successfully improved the dispersibility of F–rGO in GTL-8 base oil. The investigation of tribofilm by TEM and focused ion beam (FIB) illustrated that IL displayed a synergy to participate in the tribochemical reaction and increased the thickness of tribofilm during the friction process.

Inverse Relationship between Thickness and Wear of Fluorinated Graphene: “Thinner Is Better”

“…In 2D lubricant studies, fluorinated graphene (or named fluorographene, FG) has attracted significant interest due to its superior thermal and chemical stability and large interlayer spacing. − Compared to graphene, FG shows a larger friction, which could be viewed as a disadvantage. , Nonetheless, FG offers the lower static and dynamic adhesion, lower interlayer shear strength and better corrosion resistance, which gives some edge in applications where such properties are necessary. At macroscale, FG could be used as a lubricant additive , or directly as a solid lubricant. , FG can form tribofilms at the steel–steel sliding interface via shear-induced chemical reactions. An X-ray photoelectron spectroscopy (XPS) analysis indicated the formation of metal–fluorine chemical bonds .…”

“…19,20 Nonetheless, FG offers the lower static and dynamic adhesion, 21 lower interlayer shear strength 22 and better corrosion resistance, 23 which gives some edge in applications where such properties are necessary. At macroscale, FG could be used as a lubricant additive 24,25 or directly as a solid lubricant. 26,27 FG can form tribofilms at the steel−steel sliding interface via shear-induced chemical reactions.…”

Regulating the Nb2C nanosheets with different degrees of oxidation in water lubricated sliding toward an excellent tribological performance

“…Furthermore, two-dimensional (2D) layered materials, such as graphene-based materials [8][9][10][11][12][13][14], hexagonal boron nitride, and black phosphorus, are the most common additives, and many scholars have conducted extensive studies around them. Ci et al [15] explored the tribological behaviors from graphene to fluorographene and found that fluorinated reduced graphene oxide nanosheets (F-rGO) with different degrees of fluorination display excellent tribological properties, which is due to the nanosheets with a small size easily entering the contact surface, and the large interlayer spacing makes the sample show a significant shear capability. Wang et al [16] evaluated the tribological characteristics of black phosphorus nanosheets as water-and oil-based lubricant additives and found that it exhibited an outstanding resistance to extreme pressure and bearing capacity at high loads.…”

Enhanced tribological properties of polyimide composite with carbon fiber/graphitic‐carbon nitride nanosheets

“…Furthermore, the friction coefficient and wear rate of CF/g‐C 3 N 4 /PI composite under oil lubrication are the lowest. This is because the viscosity of the oil is higher, 44 and it is easier to form an oil lubricating film, which would play excellent lubricating effect to avoid the composite occurring serious friction and wear.…”