High-performance Lubricants Research Articles

Improving tribological efficiency of isopropyl palmitate oil with cellulose nanocrystals: a sustainable approach for high-performance lubricants

Improving tribological efficiency of isopropyl palmitate oil with cellulose nanocrystals: a sustainable approach for high-performance lubricants

Wear Characteristics Caused by Ti3AlC2 Particles under Impact-Sliding Conditions in Marine Engine

With the marine industry’s demands for carbon reduction and increased reliability, the friction and wear performance of marine engines is becoming increasingly important. MAX phase materials show great potential in marine engine tribopair materials due to their unique microstructure and performance. The typical MAX phase material Ti3AlC2 was combined with MoDTC and added to the lubricant containing ZDDP additive for the tribopair composed of chromium-based ceramic composite coated steel (CKS) piston rings and cast iron cylinder liners under impact-sliding conditions. Compared to Ti3AlC2 alone, the friction coefficient and wear depth of the designed composite additive MoDTC/Ti3AlC2 were reduced by 36.9% and 41.4%, respectively. The worn surface lubricated with the Ti3AlC2/MoDTC composite additive showed fewer scratches with significantly less plastic deformation and clearer honing grooves. The multi-component tribofilm containing FeS, MoS2, MoO3, ZnO, TiO2, Al2O3, unoxidised particles, short-chain phosphates, and some ZnS was present on the worn cylinder liner surface. The synergistic effect of Ti3AlC2, MoDTC and ZDDP additives in the lubricant can isolate the mutual contact, generate a solid tribofilm and reduce the scratching. This can provide some guidance for the development of high-performance lubricant additives under impact-sliding conditions.

Exploratory data analysis & EDS analysis on tool chip adhesion under dry and nano minimum quantity lubrication machining environment

Adhesion, abrasion, plowing and transverse displacement are the major causes of origin of friction. During dry machining of ductile materials, chips are fused with the rake face of the cutting tool and contribute to the formation of the built up edge. Built up edge protects the rake face of the tool from wear, but makes the machined surface rough. To improve the tribological properties and to decrease the tool-chip adhesion, cutting fluids are used. Cutting fluids are added to the machining zone to minimise cutting temperature and friction, but they result in environmental and health degradation. Surface texturing of tools is a potential way to modify the tribological properties of mating surfaces in order to increase the tribological qualities and decrease the tool-chip adhesion. The performance of surface textured tools depends upon orientation, dimple depth, width and pattern. Under lubrication regime, microholes in surface textured tools acts both as lubrication reservoir and traps wear debris to reduce abrasive wear. Nano Minimum Quantity Lubrication (nano-MQL) is an advanced lubrication technique used in machining processes, specifically designed to minimize the use of lubricants while maintaining effective lubrication. This method involves delivering an extremely small amount of high-performance lubricant directly to the cutting zone. The MoS2 lubricant with sunflower oil is typically in the form of nanodroplets, which are much smaller than conventional minimum quantity lubrication (MQL) droplets. The Exploratory Data Analysis (EDA) methodology enables the identification of patterns, trends, and outliers within the collected data, offering insights into the complex interplay of factors affecting the machining of Aluminium Alloy AA2024. At a spindle speed of 3500 rpm the feed force decreases by 37% under dry environment when compared with nano-MQL environment. Under dry environment average surface roughness reduces by 27% when compared with nano-MQL environment.

A green approach to synthesize polybutene lubricants from mixed C4 monomers using supported dendritic ionic liquids

Lubricants, composed of a base oil and various additives, reduce friction and abrasion between moving surfaces. High-performance lubricants, especially in the automotive and space industries, have driven advancements in synthetic oils like polyalphaolefins (PAOs), known for their high viscosity index and stability. Low molecular weight polyisobutylenes (PIBs) are used in multiple applications, including as viscosity improvers. PIBs are produced via cationic polymerization of isobutylene using Lewis acid initiators and co-initiators, often conducted at low temperatures with harmful substances like BF3. Efforts are being made to develop more eco-friendly processes, such as using AlCl3 and ionic liquids (ILs). In this research, boehmite-supported dendritic ILs (Gen1 and Gen2) were synthesized and tested as co-initiators in Raffinate-1 polymerization. The ILs improved the stability of the catalytic system, allowing for reduced AlCl3 usage, and produced PIBs with desirable molecular weight and viscosity characteristics. Density Functional Theory calculations unveiled the importance of the interaction of AlCl3 with the ionic liquids.

Tribological study of two ammonium chloride-decanoic acid deep eutectic solvents (DESs) as high-performance lubricants

Deep eutectic solvents (DESs) are acknowledged as a novel class of functional liquid. DESs share similar physical properties with ionic liquids (ILs) and have the potential to be a novel class of lubricants. In this study, two DESs, namely tetrabutylammonium chloride-decanoic acid DES (C4-DES) and methyl tricaprylmethylammonium chloride-decanoic acid DES (C8-DES), were synthesized, and their physico-chemical properties and tribological performances were evaluated. Post-analysis of the rubbing surfaces used multiple techniques to gain insights into the lubrication mechanisms. Results show that the coefficient of friction (COF) and wear were reduced by approximately 29% and 91% for the C4-DES, and 36% and 94% for the C8-DES, compared to an ester base oil. The friction reduction behavior of the DESs is attributed to the monolayer adsorption of the polar group in the decanoic acid (DEAC), whose effectiveness is affected by the component of the ammonium salts in the DESs and the operating temperatures. In addition to the adsorbed film, worn surface analysis revealed that an ultra-thin tribochemical film with a thickness of 3–7 nm was formed on the surfaces lubricated with the C8-DES. The composition of the film was studied, and the lubrication mechanisms of the two DESs were discussed.

Synthesis of complex polyolester as base stock for high-performance lubricant: Optimization, characterization, and evaluation

Synthetic esters are expected to have broad application prospects in the high-end lubrication sectors owing to their fascinating custom-tailored properties. Herein, we synthesized a novel complex polyolester (CPE) via a stepwise esterification procedure using stannous oxide as a heterogeneous catalyst. Response surface methodology coupled with the Box–Behnken design (BBD-RSM) was employed to optimize the experimental parameters and elucidate the interactions among the operating variables on the low-temperature fluidity of CPE. The optimization results indicated that the lowest pour point (−42 °C) could be obtained under the catalyst dosage of 1.2 wt%, the first step reaction temperature of 164 °C, the first step reaction time of 100 min, and the second step reaction temperature of 178 °C. Particularly, there is a significant interactive effect between the catalyst dosage and the second step reaction temperature. Followed by the molecular distillation of the crude ester prepared under the optimal conditions, the refining results revealed that the non-ideal components had been effectively removed and the total acid number of the final product was substantially reduced to below 0.1 mg KOH/g. The molecular structures of the as-synthesized esters were confirmed by FT-IR, NMR, GPC, ESI–MS, and TGA characterization and their physicochemical and tribological properties were also evaluated according to standard methods. In view of the unique molecular structural design, the developed CPE displayed plentiful prominent technological specificities, which makes it plausible to be served as a potential high-performance base stock. Therefore, the findings of this study may provide some valuable insights for expanding the application scope of synthetic esters into various special industrial scenarios.

Optimal lubricating protection and interfacial behavior for titanium alloy surface from phosphorus-based ionic liquids

The poor wear resistance of titanium alloy makes it challenging to develop high-performance lubricating materials. For the characteristic of highly designable structure, ionic liquids (ILs) are the potential lubricants with excellent physicochemical properties and lubricating performance. Herein, three protic phosphorus-based ionic liquids (PPILs) were designed and synthesized with the exploration of their interfacial lubrication behavior and interaction mechanism on the titanium substrate. The as-synthesized IL lubricants exhibit optimal tribological properties on steel-titanium friction pairs even at high load and temperature. The surface analysis showed that IL can form the lubricating protective film on the titanium-based metal surface, effectively reducing the adhesive wear. Combined with surface analysis techniques (SEM, XPS, FIB-TEM and TOF-SIMS), the lubrication mechanism was discussed systematically.

Practical Evaluation of Ionic Liquids for Application as Lubricants in Cleanrooms and under Vacuum Conditions

As part of a publicly funded cooperation project, novel high-performance lubricants (oils, greases, assembly pastes) based on ionic liquids and with the addition of specific micro- or nanoparticles are to be developed, which are adapted in their formulation for use in applications where their negligible vapor pressure plays an important role. These lubricants are urgently needed for applications in cleanrooms and high vacuum (e.g., pharmaceuticals, aerospace, chip manufacturing), especially when the frequently used perfluoropolyethers (PFPE) are no longer available due to a potential restriction of per- and polyfluoroalkyl substances (PFAS) due to European chemical legislation. Until now, there has been a lack of suitable laboratory testing technology to develop such innovative lubricants for extreme niche applications economically. There is a large gap in the tribological test chain between model testing, for example in the so-called spiral orbit tribometer (SOT) or ball-on-disk test in a high-frequency, linear-oscillation test machine (SRV-Tribometer from German “Schwing-Reib-Verschleiß-Tribometer”), and overall component testing at major space agencies (ESA—European Space Agency, NASA—National Aeronautics and Space Administration) or their service providers like the European Space Tribology Laboratory (ESTL) in Manchester. A further aim of the project was therefore to develop an application-orientated and economical testing methodology and testing technology for the scientifically precise evaluation and verifiability of the effect of ionic liquids on tribological systems in cleanrooms and under high vacuum conditions. The newly developed test rig is the focus of this publication. It forms the basis for all further investigations.

Rapid Separation and API Grades Identification of Base Oil in Low Viscosity Gasoline Engine Oil SN 0W-16.

Using low viscosity engine oil is one of the most economical and easily achievable ways to improve fuel economy. Base oil is a main component in low viscosity engine oils, and therefore, the separation and identification of its are of great significance for oil product developers to prepare high-performance lubricants. However, the extraction methods reported for base oils mainly adopt membrane dialysis, which not only fails to completely separate the base oil but also wastes a large amount of solvent. The reason for this result is that the concentration of substances inside and outside the membrane cannot always be in an imbalanced state of permeation resulting from manual operation. Additionally, most studies primarily focus on the characterization of base oil components, while there are few reports on grade identification. For the above reasons, an economically effective separation technique of base oil from low viscosity gasoline engine oil SN 0W-16 is successfully established by combining improved Soxhlet extraction and a column chromatography separation method. By applying this method, the yield of extracting base oil generally exceeds 96%, and the solvent can also save more than 3 times. Besides, an exclusion method is built through several simple characterization steps including viscosity index (VI), FT-IR, size-exclusion chromatography (SEC), and hydrocarbon composition, which can quickly identify the American Petroleum Institute (API) grade and brand of the base oils.

Ionic liquid lubricity enhancement with bio-oil derived from microwave pyrolysis of bamboo

In response to the growing demand for environmentally friendly lubrication, this study explores the potential of bio-oil-infused lubricants. The investigation focuses on the interaction between bio-oil, derived from raw bamboo (Phyllostachys edulis) through microwave pyrolysis at power levels between 500 and 800 W at 700 ∘C, and the protic ionic liquid, [Oley][Oleic]. The bio-oil, predominantly composed of diethyl phthalate (DEP) and fatty acid methyl ester (FAME), is blended with [Oley][Oleic] at concentrations of 1.0, 2.0, and 5.0 wt%. Friction measurements using a ball-on-disk setup reveal a substantial 58.9% reduction in friction and a 30.6% reduction in wear when [Oley][Oleic] is combined with bio-oil pyrolysed with a microwave power of 800 W. To maintain a low coefficient of friction (CoF) and wear for [Oley][Oleic], it is imperative to aim for an optimal DEP:FAME ratio in the bio-oil of approximately 2.0, within concentrations ranging from 0.2 to 1.0 wt%. The study highlights the complex tribological balance among viscosity, load-bearing capacity, and the chemical nature of bio-oil components, contributing to enhanced lubricity. As industries increasingly seek eco-friendly lubrication, this study offers a valuable knowledge base for developing sustainable and high-performance lubricants derived from renewable biomass sources.

Solid lubrication performance of multi-layered V2CTx coatings

MXenes induce excellent wear resistance under solid lubrication due to their distinctive surface chemistry, easy-to-shear ability, and capability to form low-friction and wear-resistant tribofilms. However, beyond the extensively studied Ti3C2Tx, other promising members of the MXene family remain largely underexplored. Therefore, we spray-coated multi-layer vanadium carbide (V2CTx) coatings (thickness ∼10.8 μm) on steel substrates and studied their tribological performance for prolonged times (10,000 cycles) using a reciprocating ball-on-disk tribometer with acting contact pressure of 445 MPa in ambient conditions. Results show that V2CTx-coated substrates demonstrate an 8-fold reduction in friction (COF of 0.11) and a 10-fold wear rate reduction (1.405 × 10−6 mm3 N−1 m−1). High-resolution materials characterization confirmed that the remarkable tribological performance of these coatings can be traced back to the formation of protective films on the substrate (tribofilm) and counterbody (transferfilm) consisting of contact pressure and frictional heat-induced degraded, deformed, exfoliated V2CTx nanosheets, nanocrystalline oxides, and amorphous carbon debris. This work fully elucidates the tribological potential of V2CTx, which is of utmost relevance for designing high-performance lubricating materials. Our work has assessed the performance of multi-layer V2CTx (M2XTx) due to its remarkable thermal stability, low molecular weight, good mechanical properties, and high interlayer spacing, thus serving as an entry point into diverse MXene compositions, including M4X3Tx (V4C3Tx).

Preparation and tribological property of MoS2@PDA@POSS core-shell-shell/Epoxy composite lubricating coating with good humidity adaptability

In this work, a humidity-adaptive additive of MoS2@PDA@POSS with core-shell-shell structure was designed and fabricated in the presence of polydopamine (PDA) interlayer. Then the composite coating of MoS2@PDA@POSS/Epoxy was prepared by introducing this additive into epoxy matrix, and its tribological properties under air and humid environments were subsequently evaluated in detail. Specially, the friction coefficient of MoS2 @PDA@POSS/Epoxy coating under high humid environment remained stable below 0.25, while its volume wear rate reduced by 91.91% compared to MoS2/Epoxy coating, and the humidity-adaptive response mechanism mainly depends on the improved mechanical properties, the alleviating effect on MoS2 oxidation, and the formation of transfer film. This work establishes a promising platform for the design and application of novel high-performance lubricating additives.

The Application of Ionic Liquids in the Lubrication Field: Their Design, Mechanisms, and Behaviors

Ionic liquids (ILs) are molten organic salts consisting of organic cations and weakly coordinating organic/inorganic anions at room temperature. ILs have excellent physical and chemical properties such as high thermal stability, high combustible temperature, high miscibility with organic compounds and so on, making them good candidates for high performance lubricants and lubricant additives. The functional designability of ILs makes them novel lubrication materials that can break through the bottleneck of the active control of friction and lubrication. This paper firstly briefly introduces how to design the physical and chemical properties of the ILs required for different friction conditions by bonding specific cations with anions. Then, the lubrication mechanisms of ILs as base lubricants and additives for oils and water are focused on. The correlation between the structure of ILs and the lubrication results are established, which can guide the structural design of ILs in different applications. The response behaviors of friction characteristics under external electric fields are analyzed, which can provide a theoretical basis for the intelligent control of friction based on ILs.

Human divergent exploration capacity for material design: A comparison with artificial intelligence

Applications of artificial intelligence (AI) to material design have attracted increasing attention in recent years. Although AI-aided material design holds great promise for some applications, whether it has surpassed human creativity remains uncertain. The aim of the current study was to compare the divergent exploration capacity of AI with that of humans on a material design task. Human participants were asked to find a high-performance lubricant molecule under searching conditions comparable to a state-of-the-art AI system. Results indicated that, on average, AI was able to find significantly better lubricant molecules. However, the best molecule found by AI fell short of the best molecule found by a human participant. Furthermore, the structural characteristics of the molecules found by AI and human participants differed significantly. These findings suggest that a state-of-the-art AI system is capable of surpassing human divergent exploration capacity in material design, as in other fields in which AI has advanced. Nevertheless, our results also demonstrate that human intelligence and AI can play complementary roles in covering a broader search space. This investigation opens up new possibilities for collaborative systems involving both AI agents and humans in material design.

Colloidally Stable Graphite Oleogels by Pyrene-Functionalized Telechelic Polymers for Friction and Wear Reduction.

Although graphite derivatives, such as graphene, graphene oxide, and reduced graphene oxide, have been widely used as lubricating oil additives to reduce friction and wear, their synthesis either proceeds with complicated procedures in low yield, suffering from high cost, or involves the utilization of highly corrosive chemicals, raising safety and environmental concerns. Therefore, the direct use of pristine graphite as a lubricating oil additive is indispensable for practical tribological applications. However, the realization of this idea has been seriously hampered by the incompatibility of graphite with lubricating base oils. In this work, we report a rational strategy to directly disperse graphite in base oils in the form of oleogels assisted by pyrene functionalized telechelic polymers under mild condition. The resulting oleogels exhibit long-time colloidal stability for more than one year, wherein the graphite has been exfoliated to in situ form graphene through π-π interactions with the pyrene-containing telechelics. Moreover, compared with the base oil, the graphite-based oleogels are found to exhibit remarkable reductions in friction and wear by up to 52% and 97%, respectively. Significantly, such tribological performances are comparable to those of exfoliated graphite derivatives. Taken collectively, directly using pristine graphite as a lubricating oil additive with superior tribological properties represents a revolutionary approach to create low-cost, green, and high-performance lubricants just based on pristine layered materials without involving any pre-exfoliations.

Interfacial adsorption and tribological response of various functional groups on titanium surface: In-depth research conducted on the lubricating mechanism of liquid lubricants

Lubricating materials for highly reactive titanium alloys are not sufficiently abundant, limiting their wide practical applications. In this work, the tribological properties for various lubricants on titanium alloy surfaces are investigated, as well as their physicochemical and adsorption properties in terms of structural composition. The results indicated that high polarity, long alkyl chain length and small spatial site resistance will be positively correlated with the tribological properties. The FIB-TEM analysis further illustrates that the film-forming mechanism of strong polar adsorption and tribo-chemical reaction is vital to high-performance lubricants on titanium alloys. This work shows great instructive significance to investigate the tribological properties and interaction mechanisms on titanium alloy surfaces from the perspective of molecular design.

Graphene Enhances the Loading Capacity and Lubrication Performance of Ionic Liquids: A Molecular Dynamics Study.

Ionic liquid (IL) combined with graphene additives have garnered extensive attention in the field of high-performance lubricating materials. However, the ambiguous mechanism of graphene influencing the load-carrying and anti-wear capacity of ILs needs further study. In this work, friction simulation shows that adding graphene causes friction coefficient to reduce by up to 88% compared with pure ILs, but lubrication performance is lost due to the destruction of graphene under high stress. Meanwhile, multilayer graphene has better friction-reducing performance and friction durability as compared to the monolayer structure, which is attributed to the easy-shear property and the reduction in the percentage of high tensile stress sites in multilayer graphene structure. In addition, it was found that excessively thick ILs film would form a three-body abrasive wear structure with graphene, which accelerated the structural destruction of graphene and caused a decline in its tribological properties. It is believed these findings can be valuable for designing of high-performance lubricating oil for practical engineering.

Influence of Base Oil Molecular Structure on the Tribological Performance of Diesel Engine Cylinder Liner and Piston Ring

Highly intensified diesel engines lead to severe lubricating condition, high performance lubricant is important to solve this problem. Base oil is the main composition of lubricant, which plays important role in lubricating performance. In this paper, three kinds of poly-α-olefin (PAO) base oil were prepared. Different olefin materials were used to produce PAO with different molecular structure. The tribological performance of diesel engine cylinder liner and piston ring lubricated with different base oil were evaluated by reciprocating test rig. Results show that PAO base oil synthesized with long carbon chain olefin has high viscosity index. The PC12 reduced the friction coefficient by 15.4%/19.6% in low speed/high speed friction compared with PC8. The wear of PC12 reduced 15.8% compared with PC8. The results were resulted from the long carbon chain of PC12, which produce high viscosity in high temperature and shear thin effect in high speed friction.

Tuning the interfacial behavior of extreme pressure lubrication by stearic acid-modified TiO2 nanoparticles

The development of high-performance lubricants under extreme pressure (EP) is of great significance for reducing energy waste and protecting ecology in heavy industries such as aerospace, large machinery, and so on. Sulfurized isobutylene (SIB) has been explored as one of the most effective EP additives for oil-based lubricants and delivered promising friction-reducing performance. However, the excessive corrosion caused by SIB on the metal surface seriously reduces the instrument’s lifetime and hinders its extensive practical application. Herein, we develop stearic acid-modified TiO2 nanoparticles (SA-TiO2) as a lubricant additive to improve the EP lubrication performance of obtained composite lubricant (CL). During EP friction, the SA-TiO2 can tune the interfacial structure of tribopair and form a high-strength nano-ceramic film to improve tribological performance. Meanwhile, the SA-TiO2 can also compensate for the high wear caused by SIB, thus significantly enhancing the antiwear, friction reduction, and EP properties by 27%, 20%, and 25%, respectively, when compared with the traditional lubricant (TL) obtained by only SIB. Benefiting from the above synergistic effects, the CL can significantly lower the SIB contents while maintaining high EP performance (4900 N weld load). These findings demonstrate a promising eco-friendly lubricant and provide new insights into the mechanism study for EP lubrication.

Synergistic lubricating behaviors of Zn-MOF/[P88814]DEHP composite used as lubricating oil additive

Use of the synergistic effect between nanomaterials and ionic liquids is of great significance for designing high-performance lubricating materials. In this work, Zn-MOF/[P88814]DEHP (zinc complexes with 2-aminoterephthalic acid nanosheets/trioctyltetradecylphosphonium bis (2-ethylhexyl) phosphate) composites were successfully synthesized by grinding the mixture of [P88814]DEHP and Zn-MOF with different mass ratios and evaluated as a new kind of the white oil additive using a four-ball testing machine. Results demonstrate that the optimal mass ratio of Zn-MOF to [P88814]DEHP was 1:1 and the Zn-MOF/[P88814]DEHP composite with 2.0 wt% addition amount into the white oil significantly reduced friction coefficient and wear. Such obvious friction-reducing and outstanding anti-wear properties of Zn-MOF/[P88814]DEHP composite could be attributed to the synergistic lubrication between Zn-MOF and [P88814]DEHP. This work investigated the synergistic lubrication between MOFs and ILs, which provided a new idea for designing and preparing new lubricating oil additives.