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

Xiaojing Ci,Yangmin Wu,Zhiwen Fang,Xiulei Gao,Wenjie Zhao,Qunji Xue,Jun Luo,Tianhao Ge

doi:10.1007/s40544-019-0350-y

Xiaojing Ci, Yangmin Wu + Show 6 more

Open Access

https://doi.org/10.1007/s40544-019-0350-y

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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.

Highlights

Compared with dry friction, lubricant plays a necessary role in machinery, because it removes the friction heat and reduces unnecessary energy loss by reducing the wear and friction [1, 2]
The content of fluorine displayed a great effect on the color of fluorinated reduced graphene oxide nanosheets (F–reduced graphene oxide nanosheets (rGO)). rGO as the raw material showed a black color, while rising the content of fluorination led to a white color for highly fluorinated reduced graphene oxide (HF–rGO)
It was interesting to observe that the intensity of Tyndall effect of mixture contained HF–rGO+ionic liquid (IL) was obviously higher than HF–rGO, which illustrated that HF–rGO+IL displayed a better dispersibility in lubricant compared with HF–rGO

Summary

Introduction

Lubricant plays a necessary role in machinery, because it removes the friction heat and reduces unnecessary energy loss by reducing the wear and friction [1, 2]. Researches found that many kinds of modified graphene nanosheets displayed an excellent performance of friction reduction and anti-wear as lubricant additives, such as graphene oxide, hydrogenated grapheme, and fluorographene. Fluoro graphene (FG) as a novel graphene derived material should be emphasized that it has high fluorine density [13] It holds the properties of graphene and possesses the characteristic of fluoride such as excellent thermal and chemical stability, mechanical strength, and large interlayer distance compared with graphene [14]. Hou et al [18] prepared FG by liquid-phase exfoliating from fluorinated graphite, and the friction test results confirmed that FG could greatly enhance the anti-wear property compared with pure base oil. We utilized IL to noncovalently graft the F–G to enhance the dispersibility of F–G in lubricant and probed the role of IL during the friction tests

Materials

Synthesis of IL modified HF–rGO

Characterization techniques

Structure and morphology of F–rGO

Friction reduction and wear resistance mechanism analysis

Conclusions