MoS2–polydopamine–methoxypolyethyleneglycol amine (MoS2–PDA–MGA) was synthesized through the combination of mussel-inspired chemistry and the Michael addition reaction. The modification of MoS2 via PDA and MGA enhanced its dispersion stability in oil. The tribological properties of MoS2–PDA–MGA for use as additives in polyalkylene glycol (PAG) base oil were investigated using an oscillating reciprocating tribometer at elevated temperatures. The results indicated that the addition of 0.7 wt% MoS2–PDA–MGA in PAG resulted in excellent friction-reducing and anti-wear (AW) performances compared with PAG base oil. The tribological results of MoS2–PDA–MGA and MoS2 dispersed in PAG base oil after settling for 7 days indicate that MoS2–PDA–MGA, with its good dispersion stability, has stable friction-reducing and AW properties. XPS analysis suggested that a protective boundary film formed on the wear surfaces during the friction and wearing process, which was believed to be responsible for the excellent tribological performance of MoS2–PDA–MGA dispersed in PAG at elevated temperature.

MoS2–polydopamine–methoxypolyethyleneglycol amine (MoS2–PDA–MGA) was synthesized through the combination of mussel-inspired chemistry and the Michael addition reaction. The modification of MoS2 via PDA and MGA enhanced its dispersion stability in oil. The tribological properties of MoS2–PDA–MGA for use as additives in polyalkylene glycol (PAG) base oil were investigated using an oscillating reciprocating tribometer at elevated temperatures. The results indicated that the addition of 0.7 wt% MoS2–PDA–MGA in PAG resulted in excellent friction-reducing and anti-wear (AW) performances compared with PAG base oil. The tribological results of MoS2–PDA–MGA and MoS2 dispersed in PAG base oil after settling for 7 days indicate that MoS2–PDA–MGA, with its good dispersion stability, has stable friction-reducing and AW properties. XPS analysis suggested that a protective boundary film formed on the wear surfaces during the friction and wearing process, which was believed to be responsible for the excellent tribological performance of MoS2–PDA–MGA dispersed in PAG at elevated temperature.

The public awareness in environmental issues has been constantly growing. Lubricants are applied in many diverse areas; therefore, their environmental acceptability has become increasingly important. In this paper, a kind of eco-friendly high-temperature lubricant was prepared by mixing castor oil with lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) in molar ratios of 1:0.5, 1:1, and 1:1.5. Thermal and rheological analysis indicates that the in situ formed ILs, [Li(castor oil)]TFSI, with various molar ratios, are more resistant to high temperatures and substantially stronger than the pure castor oil. Tribological test results shown that the ILs have excellent friction reduction and antiwear properties for lubrication of steel/steel contacts at 200 °C. Moreover, the tribological performances of these lubricants were also better than those of epoxidized soybean oil fluid, which is an environment-friendly lubricant and has high oxidative stability. XPS analytical results indicated that a boundary lubrication film composed of Fe2O3, Fe3O4, FeOOH, FeSO4 or Fe2(SO4)3, FeF2, FeF3, and C–O bonding was formed on the worn steel surface, and the film is believed to be responsible for the excellent tribological properties of [Li(castor oil)]TFSI using at elevated temperature.

•A new phosphate compound was synthesized and investigated as a potential antiwear lubricant additive in aircraft engine oil.•The compound has high solubility in synthetic polyol esters.•The tribological properties of the additive are superior to the normally used tricresyl phosphate (TCP).•Tribochemical reactions were involved in the friction process and a surface protective film was generated on the lubricated metal surface.A new phosphate compound bisphenol AF bis(diphenyl phosphate) (BAFDP) has been synthesized, characterized, and its tribological behaviours as a potential additives in aircraft engine oil were investigated at elevated temperature. BAFDP has high solubility in synthetic polyol esters and it is noteworthy that BAFDP exhibited effective friction reduction and antiwear characteristics when blended with trimethylolpropyl trioleate (TMPTO) and pentaerythritol oleate (PETO). The tribological properties of BAFDP were generally superior to the traditionally used tricresyl phosphate (TCP) in TMPTO and PETO. The antiwear mechanism is tentatively proposed on the basis of the morphology features and the chemical composition of the worn surfaces by SEM and XPS.

•A novel neutral ionic liquid was synthesized and evaluated as catalyst.•The IL is fully miscible with lubricating oil after reaction, without any separation.•IL can effectively improve the tribological properties of the base oil as friction-reducing and anti-wear additives.A novel neutral ionic liquid 1-tetradecyl-3-(2-ethylhexyl)imidazolium bis(2-ethylhexyl) phosphate was synthesized and evaluated as catalyst in the esterification of trimethylolpropane (TMP) with oleic acid (OA) and anti-wear additive (AW) in trimethylolpropane oleate (TMPTO) for the first time. Results showed that the IL exhibited catalytic activity with an oleic acid conversion increased by 14% and a selectivity of 55.9% to di-ester, 44.1% to tri-ester in the esterification reaction under the optimum reaction conditions. And unlike most ILs that have little or no solubility in the synthetic ester fluids, this IL is fully miscible in TMPTO after reaction. More importantly, the IL dissolved in TMPTO significantly improved friction reducing and anti-wear properties of the base oil.

In situ formed ionic liquids (ILs) as high temperature lubricants can be obtained by mixing polyol esters (pentaerythritol oleate or trihydroxymethylpropyl trioleate) with lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) in molar ratios of 1/0.5, 1/1 and 1/1.5. Thermal and rheological analysis indicate that the in situ formed ILs, [Li(polyol ester)]TFSI, with various molar ratios are more resistant to high temperatures and substantially stronger than the polyol ester base oils. Tribological results revealed that these in situ forming ILs with molar ratios of 1/1 and 1/1.5 possessed excellent friction reduction and antiwear performance for steel/steel contact at 300 °C. Moreover, their tribological properties were significantly better than the pure polyol ester base oils and perfluoroalkyl polyether (PFPE, as a reference lubricant) under the same conditions. The results of SEM-EDS show that tribo-films formed on the worn steel discs surface lubricated by [Li(polyol ester)]TFSI. The XPS analytical results further proved the formation of a boundary lubrication films which composed of Fe2O3, Fe3O4, Fe(OH)O, FeF2, FeSO4 or Fe2(SO4)3 and C–O bonding. This surface-protective film is believed to be responsible for the excellent tribological performances of in situ forming ILs using at elevated temperature.Keywords: Biocomponent; Ionic liquids; Polyol esters; Steel/steel contacts;

By controlling the heat-treatment process, three types of lithium greases with different thickener fiber morphologies were synthesized via the saponification reaction. With increasing the cooling rate, the dimension of the thickener fiber decreased. The relationship between microstructure and tribological performance of the lubricating greases was investigated via a rheological method. The results indicated that the fiber dimension determined the level of physical entanglement and the evolution of fiber network in the friction process, further influencing the final lubricity. The grease with the large fiber dimension displayed good tribological performance under low frequency and high load conditions due to its large-scale strongly crosslinked structure. In addition, the grease with the small fiber dimension yielded a low level of fiber physical entanglements and displayed low structure strength and fast response in the rheological test. It could obviously improve the tribological performance under high frequency conditions. Through tuning the microstructure of the thickener fiber according to the lubricating conditions, the tribological performance could be obviously improved.

The alkylphenyl diphosphates pentaerythritol tetrakis(diphenyl phosphate) (PDP) and trimethylolpropane tris(diphenyl phosphate) (TDP) were evaluated as the antiwear additives in lithium complex grease and polyurea grease at 200 °C. The results indicated that both additives may effectively reduce the sliding friction and wear as compared to the base greases. The tribological performances were generally better than the normally used molybdenum disulfide (MoS2)-based additive package in lithium complex grease and also in polyurea grease. Boundary lubrication films composed of Fe(OH)O, Fe3O4, FePO4, and compounds containing the P–O bonds were formed on the worn surface, which resulted in excellent friction reduction and antiwear performance.

Naphthyl phenyl diphosphates: 1-naphthyl diphenyl phosphate (NDP) and 1,5-dihydroxynaphthalene bis(diphenyl phosphate) (DDP) were evaluated as the antiwear additives in polyalkylene glycol and polyurea grease at 200 °C. Results showed that they could effectively reduce the friction and wear of sliding pairs compared with the cases without these additives. Furthermore, the tribological properties of NDP and DDP were generally better than the normally used tricresyl phosphate (TCP) in PAG and molybdenum disulfide (MoS2) in polyurea grease. Boundary lubrication films composed of Fe(OH)O, Fe3O4, FePO4 were formed on the worn surface, which resulted in excellent friction reduction and antiwear performance.

Castor oil tris(diphenyl phosphate) (CODP) was synthesized using an environmentally friendly and renewable resource – castor oil, and its tribological properties were evaluated in lithium 12-hydroxystearate greases (LHG) and lithium complex greases (LCG) at 150 °C. The tribological behaviors of the additive for LHG and LCG application in steel/steel contacts were evaluated on an Optimol SRV-IV oscillating reciprocating friction and wear tester as well as on a MS-10J four-ball tester. The worn steel surface was analyzed by a JSM-5600LV scanning electron microscope and a PHI-5702 multifunctional X-ray photoelectron spectrometer. The results indicated that CODP as the additive could effectively reduce the friction and wear of sliding pairs in the two base greases. The tribological performances were also better than the traditional used zinc dialkyldithiophosphate (ZDDP) based additive package in LHG and also in LCG. Boundary lubrication films composed of Fe(OH)O, Fe3O4, FePO4 and compounds containing P–O bonds were formed on the worn surface, which resulted in excellent friction reduction and antiwear performance.

The tribological behaviors of hydroquinone bis(diphenyl phosphate) (HDP) and tricresyl phosphate (TCP) for polyalkylene glycol (PAG) were evaluated at 200 °C. Results showed that HDP could effectively reduce the friction coefficient and prevent wear of sliding pairs during the test. The best tribological properties of HDP achieves at the concentration of 4 wt %. At this level, the wear volume of the lower disk can be reduced by a factor of 2.4 and the load-carrying capacity can increase from 500 N to 930 N, with respect to pure PAG. Furthermore, HDP exhibited better antiwear (AW) and extreme pressure (EP) properties than TCP, despite the fact that their friction-reducing performances were similar. Boundary lubrication films composed of FeOOH, Fe2O3, FePO4, and polyether compounds were formed on the worn surface, which resulted in excellent friction reduction and AW performance.

This paper reports the tribological behavior of CaCO3 nanoparticles as a green additive in poly-alpha-olefin (PAO) base oil under variable applied load, sliding speed, sliding duration, and temperature. The tribological properties and the electrical contact resistance between the tribo-pairs lubricated with PAO alone, and PAO containing CaCO3 nanoparticles, were determined using an Optimol-SRV 4 oscillating friction and wear tester (SRV). The morphology and wear volume of the worn scar were measured simultaneously using a surface profilometer. The results showed that CaCO3 nanoparticles can dramatically improve the load-carrying capacity, as well as the anti-wear and friction-reduction properties of a PAO base oil. In addition, higher applied load, moderate frequency, longer duration time, and lower temperatures are beneficial to the deposition of CaCO3 nanoparticles accumulating on rubbing surfaces. X-ray photoelectron spectroscopy (XPS) reveals a boundary film composed of CaCO3, CaO, iron oxide, and some organic compounds on the worn surfaces.