Imidazolium Ionic Liquids As Antiwear and Antioxidant Additive in Poly(ethylene glycol) for Steel/Steel Contacts

Abstract

Three imidazolium-based ionic liquids containing sterically hindered phenol groups were synthesized. The cation was 1-(3,5-ditert-butyl-4-hydroxybenzyl)-3-methyl-imidazolium, and the anions were tetrafluoroborates, hexafluorophosphates, and bis(trifluoromethylsulfonyl)imide. The physical properties of the synthetic products and of poly(ethylene glycol) (PEG) with the additive were evaluated. The oxidative stability of 0.5 wt % 1-(3,5-di-tert-butyl-4-hydroxybenzyl)-3-methyl-imidazolium hexafluorophosphates in PEG were assessed via rotating bomb oxidation test (RBOT), thermal analysis, and copper strip test. The tribological behaviors of the additives for PEG application in steel/steel contacts were evaluated on an Optimol SRV-IV oscillating reciprocating friction and wear tester as well as on MRS-1J four-ball testers. The worn steel surface was analyzed by a JSM-5600LV scanning electron microscope and a PHI-5702 multifunctional X-ray photoelectron spectrometer. RBOT test, thermal analysis, and copper strip test results revealed that synthesized ionic liquids possessed excellent antioxidant properties. Tribological application results revealed that these could effectively reduce friction and wear of sliding pairs compared with the PEG films used without the additives. Specifically, (BHT-1)MIMPF(6) exhibited better antiwear properties at an optimum concentration of 1 wt %. At this level, its antiwear property significantly improved by 100 times with respect to using just the PEG base oil. Boundary lubrication films composed of metal fluorides, organic fluorines, organic phosphines, and nitride compounds were formed on the worn surface, which resulted in excellent friction reduction and antiwear performance.

Oil-soluble ionic liquids as antiwear and extreme pressure additives in poly-α-olefin for steel/steel contacts

“…Furthermore, the peaks of wear scars lubricated by the three lubricants are approximately 168.8 eV, which can be ascribed to sulfate compounds [27]. The peak of P2p of ZDDP shifts from 133.5 eV to 133.3 eV after the friction test, and it is assigned to phosphate compounds and organic phosphates, respectively [10]. Moreover, the binding energies of P2p of P 888S S P and N 88816 S P vary from 132.5 eV and 133.1 eV to 132.9 eV separately, which are ascribed to organic phosphates and phosphate compounds.…”

Time-Resolved Characterization of Dynamic Tribochemical Processes for Dicationic Imidazolium Ionic Liquid

“…For ILs with fluorinated anions, Jimenez et al [26] noted that the formation of a metal fluoride-rich boundary tribolayer is necessary to achieve good tribological performance. Cai et al [8] studied the changes in the chemical composition of a steel surface subjected to rubbing under PEG lubrication with various imidazolium IL additives and provided the evidence for complicated tribochemical reactions leading to the formation of iron oxides, fluorides and sulphates. Physical adsorption of nitrogen double-bond compounds on a steel surface was also reported [45].…”

“…Room-temperature ionic liquids (ILs) are salt structures consisting of large cation and anion moieties, which are characterized by melting temperatures below 100 • C. In tribological applications, ILs have demonstrated superior performance as lubricants under both mixed and boundary conditions [1][2][3][4][5][6][7][8][9]. In severe environments, in space and at high temperatures, IL-base lubricants are especially propitious due to their exceptional thermal stability, both oxidative and nonoxidative [10][11][12][13][14].…”

“…Generally, the increase of the length of the alkyl side chains attached to a cation head group leads to the improvement of wear resistance, but this effect is not straightforward [2,22,26]. Substitution of alkyl chains by poly(ethylene glycol) (PEG) improved the tribological performance of the IL, although at the cost of decreasing its thermal stability [8,27]. Another approach relies on bridging two cationic head groups by PEG chain.…”

Physicochemistry aspects on frictional interfaces

“…| https://mc03.manuscriptcentral.com/friction these compounds were used as the anti-wear (AW) additives in polyether [79][80][81]. The molecular design is to introduce more tribochemical reactions that can inhibit oxidation and corrosion for better protection of base oils.…”