Elaboration of Ionic Liquids on the Anti-Wear Performance of the Reinforced Steel-Steel Contact Surface

In this study, we used a four-ball friction and wear testing machine to test the tribological properties of [HPy]BF4 ionic liquids (ILs), low-layer graphene (G), and IL and G compounds (IL/G) as lubricant additives at variousconcentrations, loads, and speeds. The morphology of the wear scar was characterized by a white-light interferometer and a scanning electron microscope (SEM). The results showed that the optimal concentrations of IL and G were 0.10[Formula: see text]wt.% and 0.05[Formula: see text]wt.%, respectively. When the IL concentration was 0.10[Formula: see text]wt.%, the friction coefficient and the wear scar diameter (WSD) reduced by approximately 18% and 8%, respectively, compared to the base oil. When the concentration of G was 0.05[Formula: see text]wt.%, the friction coefficient and WSD reduced by approximately 23% and 12%, respectively, compared to the base oil. After adding the optimal concentration of the IL/G composite additive under the same test conditions, the average friction coefficient of the steel ball reduced by approximately 30%, and the average WSD reduced by approximately 18%. IL/G nanoadditives could be easily attached to the pit area on the friction surface of the steel ball, which made the contact surface of the friction pair smoother and the area of the oil film bearing the load larger, compared to those using the base oil. These two combined phenomena promoted synergistic antifriction and antiwear effects, which significantly improved the frictional performance of the base oil.

Synthesis of ricinoleate anion based ionic liquids and their application as green lubricating oil additives

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.

The use of imidazolium tetrafluoroborate, IMM+BF4−, and hexafluorophosphate, IMM+PF6−, ionic liquids as lubricants was investigated at 25 and 100 °C to show lower friction coefficients but higher wear rates than a reference hydrocarbon lubricant. The ionic liquids readily form tribofilms at the lower temperature but have difficulty in forming partial films at the higher temperature. Wear tracks for a Plint TE77 reciprocating ball-on-plate test using ionic liquids show smoother surfaces, with small pits developing, compared to the reference hydrocarbon lubricant test result. Similar ionic liquids not containing fluorine were found to be less effective as lubricants. Addition of ionic liquids to a base grease and a formulated high temperature grease gave surprisingly large increases in the weld load for the Four Ball extreme pressure test. Little difference between base grease and base grease+5 per cent ionic liquid was observed for the TE77 test. There was no clear indication of the effect of alkyl substituent chain length on the imidazolium cation for the Four Ball test wear scar diameter. Addition of 1 per cent tricresyl phosphate (TCP) to ionic liquids rapidly establishes a tribofilm and reduces the wear volume by 64 per cent compared to the same test for the neat ionic liquid or neat TCP. Addition of 1 per cent TCP and 1 per cent ionic liquid to a Group III base oil also establishes a substantial tribofilm and reduces wear volumes compared to the base oil with 1 per cent TCP alone or the base oil with 1 per cent ionic liquid alone. Ionic liquids show promise as neat liquid lubricants by establishing a tribolayer chemically adsorbed to the steel surfaces. They are not as effective as a reference hydrocarbon lubricant in reducing wear of those surfaces by tribocorrosion. The fluorine-free ionic liquids investigated were not as effective as those containing fluorine. The addition of ionic liquids to grease, base or fully formulated, gave a substantial improvement in performance, which indicates a synergistic interaction with the additives present in the formulated grease. There is also clear evidence of a strong synergistic effect between ionic liquids and TCP, both for the neat ionic liquids and for 1 per cent dilution of each respectively in a Group III base oil to give a thick tribofilm and substantially reduced wear in the TE77 ball-on-plate test. The nature of the synergy between ionic liquids and TCP requires further investigation.

During machining, the cutting fluids play an essential role in cooling and lubrication. In order to reduce the friction forces, the excessive amount of the cutting fluids are generally used. This, in turn, leads to wastage of the cutting fluids which results in a serious impact on the environment, health and cost of production. Therefore, the judicious use of lubricants is the foremost concern in the manufacturing industry. In order to mitigate these drawbacks, various alternatives have been developed in the last decade. In the present paper, ionic liquids have been proved as favourable sustainable alternative additives in the base oil. The effect of alkyl chain length of ionic liquids with base oil on the thermo-physical and tribological characteristics of cutting fluids including viscosity, wettability, anticorrosion behaviour, thermal stability, and coefficient of friction have been analysed. In the present study, pyrrolidinium and hexafluoro-phosphate (PF6) have been used as cation and anion, respectively, with rice bran oil as base oil. The five different ionic liquids have been dispersed in base oil by 1.0 wt%. It has been found that longer alkyl chain length showed the favourable results as compared to the shorter one. Results indicated that ionic liquid based cutting fluid attained ample enhanced thermophysical and tribological properties as compared to the neat rice bran oil. There has been 5.08% and 4.29% improvement in viscosity and thermal conductivity for IL4 + RBO in comparison to neat RBO. In addition, the wettability, coefficient of friction, and wear volume have been reduced by 20.34%, 53.79% and 57.87% correspondingly.

In the realm of lubrication, nanoparticles exert a notably positive influence on enhancing tribological performance, particularly certain oxide nanoparticles exhibit exceptional capabilities as friction and wear mitigators. However, a substantial research gap exists concerning the efficacy of oxide nanoparticles across various lubricant categories. Therefore, this study meticulously elucidates the effective integration of oxide nanoparticles in diverse lubricant categories. Using HRTEM, XRD, and FTIR, we characterize shape, size, and crystallinity. A Taguchi L18 orthogonal array is used for experimental planning, with performance characteristics of nano lubricants measured using four-ball testers. The experimental findings reveal a hierarchy of parameters governing the minimization of the coefficient of friction (COF), which are as follows: nanoparticle type, nanoparticle composition, load, speed, and lubricant, in that order. Similarly, the parameters controlling the reduction of wear scar diameter (WSD) are ranked as follows: load, nanoparticle composition, nanoparticle type, speed, and lubricant (base oil). Furthermore, an analysis of variance (ANOVA) is conducted to assess the contributions of these factors to COF and WSD. Regarding COF, 43.37% of the variance is attributed to nanoparticle type, 26.78% to nanoparticle composition, 14.49% to load, 11.8% to speed, and 2.36% to lubricant (base oil). In the case of WSD, the factor contributions are 47.67% for load, 22.4% for nanoparticle composition, 14.03% for nanoparticle type, 7.26% for lubricant (base oil), and 7.01% for speed.

The tribological properties of biobased and petroleum‐based base oils in the entire lubrication regime were investigated. High oleic sunflower oil (HOSuO) and commercially available polyalphaolefin (PAO‐6) were selected to represent biobased and petroleum‐based base oils, respectively. These two oils had similar viscosity and pressure‐viscosity coefficient at 40 °C, but differed in their chemical structures and many other properties. Tribological tests were conducted on a high frequency reciprocating rig tribometer at 40 and 75 °C, for 60 min, 1000 gf load, and variable combinations of frequency and stroke length. Lubrication regimes were quantified using the Hersey number (H) which was calculated from lubricant viscosity and test parameters (load, frequency, stroke length). The key tribological test outputs were coefficient of friction (COF); film thickness (h) expressed in % from contact resistance measurement; and ball wear scar diameter (WSD). Analysis of experimental data showed that the biobased HOSuO provided lower COF, thicker lubricant film, and lower WSD than the petroleum‐based PAO‐6, in all lubrication regimes and at both temperatures (40 and 75 °C). The difference in these properties between the two oils, [Δ(COF), Δ(WSD), Δ(h)], were the greatest in the boundary regimes (low H values) where the polar chemical structure of the biobased lubricant played a dominant role.

Ionic liquids (ILs) have been used effectively in many applications for reducing problems related to friction and wear. In this work, the potential of ILs as an anti-wear and extreme pressure lubricant additive for high load-carrying gearbox applications such as helicopter transmissions has been studied. Two halide-free ILs: {{rm{P}}_{8881}}{left({{rm{BuO}}} right)_2}{rm{PO}}_2^ - (1) and {{rm{P}}_{8881}}{left({{rm{MeO}}} right)_2}{rm{PO}}_2^ - (2), which are blended at 5 wt% each into a standard non-additivated FVA2 base oil (BO) are examined. Their solid—liquid interface, friction and load-carrying capacity, and wear (scuffing) behavior are studied on the nano-, lab-, and component-scale, respectively, at a different range of temperature and loading conditions by using the atomic force microscopy (AFM), Schwing—Reib—Verschleiß (SRV) friction tests, and Brugger tests, as well as forschungsstelle für zahnräder und getriebebau (FZG) back-to-back gear test rig. The AFM analysis shows nearly no change of adhesion over the full range of studied temperature for the IL blends compared to the BO. Similarly, IL blends demonstrate a very stable coefficient of friction (COF) of around 0.16, which even decreases with increasing test temperatures ranging from 40 to 120 °C. A clear reduction in COF up to 25% is achieved by adding only 5 wt% of the investigated ILs in the BO, and the Brugger tests also show a pronounced enhancement of load-carrying capacity. Finally, on the component-scale, a significant improvement in gear scuffing performance has been observed for both used IL blends. A detailed characterization of the wear tracks from the SRV friction tests via the transmission electron microscopy (TEM) revealed the formation of a phosphate (P—O)-based amorphous tribo-chemical layer of about 20 nm thickness. Therefore, this work may present an approach for ILs to be used as an additive in conventional lubricants due to their ability to enhance the lubrication properties, making them an alternative lubricant solution for high load-carrying gearbox applications.

Carbon quantum dots doped with silver as lubricating oil additive for enhancing tribological performance at various temperatures

The growing need for environmentally sustainable lubricants has accelerated research into vegetable oil-based alternatives to conventional mineral oils. Petroleum-derived lubricants, such as SAE 20W40, are non-biodegradable and toxic, raising ecological concerns. Vegetable oils offer advantages like renewability, biodegradability, and non-toxicity, but their limited tribological performance restricts broader application. This study systematically evaluates the tribological behavior including Coefficient of Friction (COF), Wear Scar Diameter (WSD), and Viscosity Index (VI) of ten vegetable oils: Castor, Coconut, Gingelly (Sesame), Karanja, Linseed, Mustard, Olive, Peanut (Groundnut), Rice Bran, and Sunflower. Tests were conducted using a Four Ball Tester per ASTM D4172B for COF and WSD, and a Brookfield DV2T viscometer per ASTM D2983-03 for viscosity, with VI calculated per ASTM D2270-04. A SAE 20W40 mineral oil was included as a benchmark for performance comparison. Karanja Oil showed the best performance with the lowest COF and WSD. To further enhance its properties, Copper Oxide (CuO) nanoparticles were added at concentrations ranging from 0.1% to 0.3%. Among all formulations, Karanja Oil with 0.1% CuO exhibited the lowest WSD, outperforming SAE 20W40 and base oils. The inclusion of CuO significantly improved anti-wear properties, friction reduction, and thermal stability. These findings suggest that CuO-enhanced Karanja Oil could serve as a viable, eco-friendly alternative to mineral-based lubricants in demanding industrial settings.

New metal-free nanolubricants based on carbon-dots with outstanding antiwear performance

Synergistic effects of melamine functionalized graphene oxide and imidazolium ionic liquid on the tribological performance and thermal stability of polyalphaolefin based hybrid nanolubricants

In this study, MoS2 nanosheets have been prepared and treated ultrasonically with silver ammonia solutions. The MoS2/Ag precursor was reduced using dopamine (DA) as reducing and linking agent at room temperature, and it was subjected to a hydrothermal treatment to produce MoS2/Ag nanocomposites (denoted as MoAg). The MoAg samples were functionalized with N-oleoylethanolamine to improve dispersion in the base oil component of additives. Use of the functionalized MoAg (denoted as Fc-MoAg) as a lubricant additive for steel balls resulted in effective friction reduction and anti-wear. This work avoids ion exchange during exfoliation, and the Ag+ has been reduced to nano-silver particles by dopamine to enlarge the layer spaces of MoS2. Taking the case of lubrication with base oil containing Fc-Mo0.6Ag15, the wear scar diameters and coefficients of friction of the steel balls were 0.428 and 0.098 mm, respectively, which were about three-fifths base oil. In addition, MoS2/Cu and MoS2/Ni nanocomposites were synthesized and the tribological properties associated with steel/steel balls assessed. The results demonstrate that all MoS2/metal composites exhibit enhanced tribological behavior in the steel/steel pair tests. Both nanocomposite synergy and the tribofilm containing sulfide, oxide, carbide, and other compounds play important roles in achieving reduced friction and improved anti-wear. The friction and wear properties of base oil containing Fc-MoAg and commercial additives were evaluated using a four-ball wear tester with steel/steel, steel/zirconia and zirconia/zirconia pairs. The base oil containing Fc-MoAg delivered smaller coefficients of friction (COFs) and/or scarring groove depths than those observed with the use of pure base oil and base oil containing commercial additives.

Oil-soluble ionic liquids (ILs) have been proved as effective additives in lubricant oils through tribological experiments and post-test analytical analyses. In this study, surface structures of lubricant base oil, oil-soluble ILs, and their mixtures at the air/liquid and solid/liquid interfaces have been studied using sum frequency generation (SFG) vibrational spectroscopy. At the air/base oil and air/IL interfaces, the alkyl chains of the studied compounds were shown to be conformationally disordered and their terminal methyl groups point outward at the liquid surface. The base oil dominates the air/(base oil + IL) interface due to its higher surface excess propensity and larger bulk concentration. At the solid (silica) surface, ILs adopt a structure with their charged headgroups in contact with the silica surface, while their alkyl chains are more conformationally ordered or packed compared to the air/IL interface. At the interface between silica and (base oil + IL) mixtures, ILs also preferentially adsorb to the silica surface with their layer structures somewhat different from those of ILs alone. These results showed that ILs can adsorb onto the solid surface even before tribological contacts are made. The insights obtained from this SFG study provide a better understanding of the role of ionic liquids in lubrication.

Tribologicalstudies of the 2D nanoadditives such as MoS2 and grapheneare mostly performed in base oils such as SN500, SN150,or paraffin. We have focused on their effect in lubrication propertiesof industrial oils (e.g., axle, transmission, and compressor oils)along with SN500 oil employing a four-ball tester. Two types of graphenepowders (GpowA with fewer defects than GpowC), MoS2 powder,and their physical mixtures are chosen as nanoadditives. The tribologyperformance for 0.05 wt% of additives in various industrial oils isevaluated by monitoring the coefficient of friction (COF) during rubbingand wear scar diameter (WSD) of the steel balls after rubbing. Elementalanalysis and electron microscopy have been performed on the wear surfacesfor evidence of any tribofilm formation. GpowA favors antifrictionfor axle and transmission oils with 40% reduction in axle oil, whereasit improved antiwear properties in most of the oils. GpowC shows aCOF decrement by 12% only for compressor oil, but contribute to wearreduction in all oils. The observed COF reduction is attributed tothe compatibility of nonfunctionalized GpowA with nonpolar axle oiland functionalized GpowC with polar compressor oil. MoS2 shows a decrease in the COF and WSD in most industrial oils; thebest being 60% COF and 7% WSD reduction in axle oil. For additivesin oils that favor antiwear, flakes or particles are observed on thewear surface supported by the higher elemental contribution of theconstituents from the wear region. The mixtures of GpowA or C withMoS2, however, does not seem to favor improvement in theCOF or WSD in industrial oils. With assistance from oleylamine surfactants,the lubrication properties of most additives are improved, particularlyfor the mixtures with 12–15% COF reduction and 4–7%WSD reduction in compressor oil. The study indicates that a largesheet size of high-quality graphene aids antifriction and additionof surfactant molecules facilitates a co-operative effect betweenMoS2 and graphene for improved tribology.