Highly Exfoliated Reduced Graphite Oxide Powders as Efficient Lubricant Oil Additives

Abstract

specific surface area (SSA), good physical and chemical stability, and excellent mechanical and thermal properties. [11][12][13][14][15][16][17][18][19][20] It is expected to be an ecofriendly effective additive for antifriction and/or antiwear in lubricant systems without releasing SAPS (sulfated ash, phosphorous and sulfur; SAPS would cause air pollution such as acid rain and haze weather). [21][22][23][24][25][26][27] Actually, a variety of graphene-based lubricant oil additives have already been reported and achieved some achievements; [7,[28][29][30][31][32][33][34][35][36][37][38][39] nevertheless, most of them showed unsatisfactory performances, requiring more in-depth studies. In this paper, we report the preparation of a highly exfoliated reduced graphite oxide (heRGO) with a laminar porous microstructure and a large SSA, and its application as an additive of a poly(α-olefin) lubricant oil (type-6, PAO-6). This additive greatly decreased the coefficient of friction (COF) of PAO-6 for 44% and the wear depth by more than 90%, implying that nearly wear-free rubbing surfaces was successfully realized under boundary lubrication. Highly exfoliated reduced graphite oxide (heRGO) is prepared by thermal reduction of crude graphite oxide (GO) powders with the assistance of KOH.By using the mixtures of KOH and GO with different weight ratios (n) as the starting materials, the resulting heRGO-n powders show different microstructures and lubrication properties. The optimized heRGO-4 powders have an average particle size around 1 μm, a "loose book"-like layered microstructure, and a large specific surface area of 829.5 m 2 g −1 . The unique microstructure and tiny particle sizes have made this graphene material to be an extraordinary high-performance additive of poly(α-olefin) lubricant oil (type 6, PAO-6). By adding 0.5% (by weight, wt%) heRGO-4, the coefficient of friction of PAO-6 is decreased by 44% and the wear scar depth is reduced by more than 90%. The lubrication effect of heRGO-4 is much superior to that of thermally reduced graphite oxide. Given its facile, cheap, and scalable preparation process, heRGO-4 has a great potential for industrial applications.

The Self‐Ordered Lamellar Texture of MoS2 Transfer Film Formed in Complex Lubrication

“…When the load is up to 0.5 N, there is a steep increase of friction coefficient after a steady sliding for 1300 cycles. In this case, the rupture of boundary oil film leads to drastic increase of friction coefficient and severe wear …”

An investigation on the tribological behaviors of steel/copper and steel/steel friction pairs via lubrication with a graphene additive

“…However, the graphene in this study showed a higher degree of exfoliation because of activation by KOH at high temperature. Our previous works showed that the above graphene has good tribological properties because of its high degree of exfoliation despite some structural defects [23,25]. The highly exfoliated graphene shows much lower Van der Waals' force between layers because of larger interlayer spacing, which not only improves flexibility and self-adaptation at the friction interface but also promotes lubrication by decreasing the energy barrier of the interlayer.…”

“…The graphene (TRGO) used here was synthesized via the thermal reduction of commercially available graphene oxide (The Sixth Element Materials Technology Co., Ltd., Changzhou, China). The graphene oxide was thermally reduced at 700 °C for 4 h in Ar atmosphere via KOH, and subsequently treated with ball-milling, which was discussed in our previous work [25]. The base oil used in the experiments was hydraulic oil (Kunlun Lubricant, China) with a kinematic viscosity of 13.2 mm 2 /s at 40 °C and 4.9 mm 2 /s at 100 °C.…”

“…Graphene is a 2D laminated material that has been explored extensively as a novel lubricant additive to further improve the properties of lubrication oil [16][17][18][19][20][21][22][23][24]. It has excellent mechanical and thermal properties as well as good physical and chemical stability [25]. Although some studies on graphene lubricant additives have been conducted on steel/ copper [18,20] or steel/steel [16,17,25] friction pairs, only a few have compared the tribological behaviors of these two friction pairs as well as the differences between the lubrication mechanisms of steel/copper and steel/ steel friction pairs under graphene lubrication.…”

rGO/GO Nanosheets in Tribology: From the State of the Art to the Future Prospective

“…Patel et al, 2019, investigated the tribological effects of highly reduced graphene oxide (H-rGO) nanoplatelets as additives to mineral base oil, aiming to exploit the fewer oxygen groups present between the microlayers, allowing spacing between the surfaces to accommodate the lubricant [58]. Liñeira del Río et al, 2019, [59] studied the tribological properties of nanolubricants formed by trimethylolpropane trioleate (TMPTO) or polyalphaolefin (PAO 40) base oils with reduced graphene oxide sheets (rGO) [60][61][62][63] whose reduction was carried out in order to obtain a good stability of the nanoadditives in the fluids, observing 24% and 20% friction enhancement for the PAO 40 and the TMPTO base oils, respectively. Mungse et al, 2019, prepared alkylated graphene oxide (GO)/reduced graphene oxide (rGO) by covalent interaction with octadecyltrichlorosilane (OTCS) and octadecyltriethoxysilane (OTES), finding that the variable oxygen functionalities in the GO/rGO and hydrolysis rate of octadecylsilanes governed the grafting density of octadecyl chains on the GO and rGO.…”