Xinhu Wu

Tribological properties of naphthyl phenyl diphosphates as antiwear additive in polyalkylene glycol and polyurea grease for steel/steel contacts at elevated temperature

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.

Tribological properties of castor oil tris(diphenyl phosphate) as a high-performance antiwear additive in lubricating greases for steel/steel contacts at elevated temperature

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.

Investigating the tribological performance of nanosized MoS2 on graphene dispersion in perfluoropolyether under high vacuum

We report for the first time that nanosized MoS2 on graphene (MoS2/Gr) was used as an additive in perfluoropolyether (PFPE) base oil. The nanocomposite can not only form a stable dispersion in PFPE for two weeks but also dramatically improve the friction-reduction and antiwear properties of the base oil for steel/steel contact under high vacuum.

Treelike polymeric phosphate esters grafted onto graphene oxide and its tribological properties in polyalkylene glycol for steel/steel contact at elevated temperature

We report the first synthesis of a high-performance lubricant additive by grafting treelike polymeric phosphate esters (PPEs) onto graphene oxide (GO) nanosheets. Characterization of the PPEs modified GO (GO–PPEs) was performed by spectral (FT-IR, Raman, SEM, TEM, XPS), and thermogravimetric analysis (TGA). Performance evaluations of GO–PPEs as a high-temperature friction-reduction and anti-wear additive in polyalkylene glycols (PAG) were conducted by an Optimol SRV-IV oscillating reciprocating friction and wear tester. The results indicated that GO–PPEs possessed excellent tribological properties in PAG compared with pure GO and PPEs under the same conditions, which may be attributed to the good dispersion of GO–PPEs in PAG, and the excellent tribological properties of phosphate at elevated temperature. In addition, the wear mechanism was tentatively discussed according to the surface composition.

Mechanical synthesis of chemically bonded phosphorus–graphene hybrid as high-temperature lubricating oil additive

Red phosphorus (P) was covalently attached to graphene nanosheets (Gr) using high-energy ball-milling under a nitrogen atmosphere. Benefiting from the formation of phosphate and P–O–C bonds on graphene surfaces, the resulting phosphorus–graphene (P–Gr) hybrids exhibited excellent dispersion stability in polyalkylene glycol (PAG) base oil compared with graphene. Moreover, tribological measurement indicated that addition of 1.0 wt% P–Gr into PAG resulted in significant reduction in friction coefficient (up to about 12%) and wear volume (up to about 98%) for steel/steel contact at 100 °C, which was likely due to the formation of a boundary lubrication film on the sliding surfaces during the friction and wear processes. XPS analysis demonstrated that the tribofilm is composed of FeO, Fe3O4, FeOOH, FePO4, and the compounds containing C–O–C and P–O bonds.

Investigating the tribological behavior of PEGylated MoS2 nanocomposites as additives in polyalkylene glycol 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.