Lubrication of DLC Coatings with Two Tris(pentafluoroethyl)trifluorophosphate Anion-Based Ionic Liquids

The lubrication of a Cr-DLC coating with ethyl-dimethyl-2-methoxyethylammonium tris(pentafluoroethyl)trifluoropho-sphate [(NEMM)MOE][FAP] and 1-butyl-1-methylpyrro-lidinium tris(pentafluoroethyl)trifluorophosphate [BMP] [FAP] ionic liquids (ILs) as 1 wt% additives to a polyalphaolefin (PAO 6) was studied. Zinc dialkyldithiophosphate (ZDDP) was also used as reference in order to evaluate the effectiveness of the ILs. Reciprocating ball-on-plate tribological tests at loads of 20 and 40 N were performed. The results showed that both ILs exhibited a friction reduction, especially at the lowest load tested. Antiwear properties were also improved; the PAO 6 + 1% [BMP][FAP] mixture was slightly better, close to the values for PAO 6 + 1% ZDDP. Scanning electron microscopy (SEM) images and X-ray photoelectron spectroscopy (XPS) analysis indicated that the additive–surface interaction was responsible for the tribological improvement

Ionic liquids as tribological performance improving additive for in-service and used fully-formulated diesel engine lubricants

In recent years, several papers have been published that investigate the potential use of ionic liquids (ILs) as additives in lubricants. However, corrosive attack of ILs on lubricated metal surfaces and low miscibility of ILs in the non-polar oils are major obstacles to maintaining an optimum lubrication performance level. High miscibility and no corrosive behaviour of Trihexyltetradecyl phosphonium bis(2,4,4-tri-methylpentyl) phosphinate and Trihexyltetradecyl phosphonium bis(2-ethylhexyl) phosphate, as lubricating oil additives have recently been described in literature. This article presents work on using these phosphonium based ILs as an additive in the fully formulated diesel engine lubricants. This approach could allow the used lubricants to recover their tribological performance for further use at the end of service life. This extension of service life has the potential to generate significant economic and environmental benefits. Also it will add to the much needed knowledge about the effect of interaction between ILs and existing additives in engine-aged lubricants on the tribological performance of ring-liner tribo-system of diesel engines. Results revealed an improvement in friction and antiwear performance of used lubricant by addition of both ILs. However an increase in wear was noted for new (fresh) and in-service lubricant samples. An interesting interference between existing lubricant additives and added ILs in a boundary film formation process has been observed

FAP- Anion Ionic Liquids Used in the Lubrication of a Steel–Steel Contact

This study compares the tribological behavior of two ionic liquids ([BMP][FAP] and [(NEMM)MOE][FAP]) used as oil additive for the lubrication of a steel–steel contact. Friction and wear experiments were performed using a HFRR test machine. Friction coefficient and electrical contact resistance were measured during the tests, and the wear surface was analyzed by confocal microscopy and XPS. The tribological results showed that both ionic liquids used as additive decrease friction and wear but the [BMP][FAP] had a better performance than the [(NEMM)MOE][FAP] due to its higher reactivity with the steel

Ionic liquids as a neat lubricant applied to steel-steel contacts

This paper studies the use of 3 ionic liquids ([(NEMM)MOE][FAP], [BMP][FAP] and [BMP][NTf2]) as neat lubricant within steel-steel contact conditions. Tribological tests (at 40 and 100 C) were conducted in a HFRR tribometer and hence a complementary study was developed using a MTM tribometer. The wear surface on the discs was measured after the HFRR tests by confocal microscopy and also analyzed by SEM and XPS. The [BMP][NTf2] showed the lowest friction coefficient in the MTM and HFRR tests at 40 C but at 100 C its tribological behavior worsened due to its lowest viscosity. Similar results were found for wear behavior. Both antifriction and antiwear results were related to the tribofilms formation from the ECR and XPS measurements. © 2013 Elsevier Ltd

Ionic liquids as an additive in fully formulated wind turbine gearbox oils

This work presents the friction and wear behaviour of two fully formulated (polyalphaolefin- and mineral-based) wind turbine gearbox oils separately additivated with two ionic liquids ([Choline][NTf2] and [BMP][NTf2]) at 5wt% concentration. A tribometer using a ball-on-plate reciprocating configuration is adopted for friction and wear experiments. Friction is measured during tests and the worn surface is measured and analysed by confocal microscopy, SEM, EDS and XPS. The friction and wear results show that both ionic liquids used as an additive have a slight friction modifier character but a strong wear reducing performance, with [BMP][NTf2] performing better than [Choline][NTf2]. In addition, EDS and XPS analysis demonstrated the temperature-related chemical interactions and their influence on tribological behaviour

Phosphonium-based ionic liquids as grease additives in rolling bearing tests

Two phosphonium-derived ionic liquids: trihexyltetradecylphosphonium bis(2-ethylhexyl)phosphate (IL1) and trihexyltetradecylphosphonium tricyanomethanide (IL2) were used as additives in lithium complex- (G1) and anhydrous calcium-based (G2) greases at 5 wt%. Friction torque and wear tests were performed using a modified four-ball machine for testing rolling bearings in order to determine the friction and wear reducing properties of these grease samples in a real component. The IL2 improved the friction reduction performance of both greases, especially G1. Both ILs improved the antiwear behaviour of grease G2. Grease G2 showed higher oxidation and thermal ageing levels than G1, but the addition of the ILs, IL2 in particular, improved this issue

Isoconversional kinetic analysis applied to five phosphoniumcation-based ionic liquids

Thermal degradation of five phosphonium cation-based ionic liquids ([P66614][BEHP], [P66614][(iC8)2PO2],[P66614][NTf2], [P44414][DBS] and [P4442][DEP]) was studied using dynamic methodology (25–600◦C at 5,10 and 20◦C/min) in both inert (nitrogen) and reactive (oxygen) atmospheres. In addition, isothermalexperiments (90 min at 200, 225 and 250◦C) were carried out with [P66614][(iC8)2PO2]. Results indicatethat thermal stability is clearly dominated by the coordination ability of the anion, with [P66614][NTf2] out-performing the other ones in both pyrolytic and oxidising conditions. Although the thermal degradationmechanism is affected by atmospheric conditions, the degradation trend remains practically constant.As the dynamic methodology usually overestimates the long-term thermal stability, an isoconversionalmethodology is better for predicting the long-term thermal stability of these ionic liquids in order to beused as base oil or additive in lubricants formulation. Finally, the model-free methodology can predict atlower costs the ILs performance in isothermal conditions

Two phosphonium cation-based ionic liquids as lubricant additive to a polyalphaolefin base oil

This paper studies the tribological performance of two phosphonium cation-based ionic liquids: trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl) phosphinate ([P6,6,6,14][(iC8)2PO2]) and trihexyltetradecylphosphonium bis(2-ethylhexyl) phosphate ([P6,6,6,14][BEHP]), as lubricant additive at 1 wt% to a polyalphaolefin. A comparison of their tribological behavior was made to that of one type of zinc dialkyldithiophosphate (ZDDP). Stribeck curve tests were made in a Mini Traction Machine (MTM) tribometer at entrainment speeds ranging from 2000 to 10 mm/s, 30 N-load, slide-to-roll ratio (SRR) of 50%, and temperatures of 40, 60, 80 and 100 °C. Tribofilm formation tests were also conducted in the MTM at 100 °C, load of 50 N, entrainment speed of 150 mm/s, SRR of 50%, and duration of 60 min. Additionally, reciprocating 60-min wear tests at 60 N-load, frequency of 15 Hz, stroke length of 4 mm and at room temperature were performed with IL-containing mixtures at 0.5 and 1 wt%. Coefficient of friction was recorded during the tests, and wear on the discs surface was measured using confocal microscopy. SEM-EDS and XPS were also used for studying the lubricant-surface interactions after these tests. Lubricants including [P6,6,6,14][(iC8)2PO2] exhibited better tribological performance than [P6,6,6,14][BEHP] ones and close to the ZDDP results. SEM images of worn surfaces exhibited evidence of plastic deformation and adhesive wear and EDS analysis showed that only active elements (P, S, Zn) were detected for mixtures containing ZDDP. XPS analysis indicated a different lubrication mechanism of the blends with ionic liquids compared with the ZDDP ones

Wettability and corrosion of [NTf2] anion-based ionic liquids on steel and PVD (TiN, CrN, ZrN) coatings

Thewetting and corrosion behavior of three bis(trifluoromethylsulfonyl)imide-based ionic liquids: 1-Dodecyl-3- methylimidazolium bis(trifluoromethylsulfonyl)imide [C12MIM][NTf2], tributylmethylammonium bis(trifluoromethylsulfonyl)imide [N4441][NTf2] and methyltrioctylammonium bis(trifluoromethylsulfonyl)imide [N1888][NTf2] are tested in this research. The surface tension was measured for temperatures of 293–353 K resulting in the expected linearly decreasing behavior with temperature increase. In addition, contact angle measurements were made on AISI 52100 steel and three coatings (TiN, CrN and ZrN) obtained by PVD technique, finding the regular behavior in hydrophobic (non-polar) systems: high contact angles led to high surface tensions. Complementary parameters like spreading parameter and polarity fraction were calculated to enhance the wetting evaluation of these ionic liquids. [N1888][NTf2]/TiN resulted as the best IL-surface combination for a good wettability, due to the higher dispersion of the charge on the large size cation in this IL and the higher values of total and polar component of the surface free energy for this coating. Finally, SEM-EDS analysis determined that [N1888][NTf2]/ZrN was the best option in order to avoid corrosion problems. The evaporation of water, present as impurity in the ionic liquids, was found the main reason because of corrosion did not occur in the tests carried out at 100 °C

Antifriction and Antiwear Properties of an Ionic Liquid with Fluorine-Containing Anion Used as Lubricant Additive.

Tribological behavior of trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl) imide [P66614][NTf2] ionic liquid (IL) used as additive in a diester oil at concentrations of 0.25, 0.5 and 1 wt% was studied in this research. The IL solubility in the base oil was measured using the inductively coupled plasma mass spectrometry (ICP-MS) technique, and corrosion analysis was done at room temperature at relative humidity of 49–77%. Tribological tests were conducted for 30 min at room temperature, 15 Hz frequency, 4 mm of stroke length, a load of 80 N (corresponding to 2 GPa of maximum contact pressure) and relative humidity of 35–53%. Friction coefficient was recorded during tests, and the wear scar was measured by confocal microscopy. Worn surface was also analyzed by SEM, EDS and XPS. Results showed that a saturated solution of [P66614][NTf2] in the base oil contains about 30 wt% of IL and corrosion activity for the highest concentration of IL (1 wt%) was not found after a 20-day test. Although the base oil and the mixtures had similar friction behavior, only the 1 wt% sample exhibited slightly lower wear volume than the base oil. SEM images exhibited similar wear track width (707–796 µm) and wear mechanism (adhesive) for all samples tested. In addition, the EDS spectra only showed the elements present in the steel. Finally, the XPS measurements could not detect differences regarding iron chemical state among the samples, which is consistent with the tribological behavior obtained