Four-ball Friction Tester Research Articles

Fabrication of Surface-carbonated Boron Nitride Nanosheets and Their Application as Water-based Lubrication Additives

As a typical two-dimensional layered material, hexagonal boron nitride nanosheets (BNNSs) have high mechanical strength, good conductivity, and excellent lubrication performance, which have great potential as solid nano lubricant additives in tribology. When BNNS is used as a water-based or oil-based lubricant additive, its inherent chemical inertness and poor dispersion stability make it difficult to achieve optimal anti-friction and anti-wear performance. In this paper, a simple and efficient preparation method for obtaining hexagonal boron nitride nanosheets (C-HPC-BNNSs) with surface carbonization modification and excellent dispersion stability in water-based lubricants was proposed. Using hydroxypropyl cellulose (HPC) as a modifier, a wet ball milling process combined with high-temperature carbonization treatment effectively reduced the thickness of BNNSs while uniformly modifying N-doped carbon layers on the surface of the nanosheets. Benefit from the smaller layer thickness of C-HPC-BNNSs, they exhibit excellent dispersion stability in the water-glycol solution and can maintain no significant agglomeration behavior for up to 30 days, which is the basis for the excellent lubrication performance of lubricant systems. In addition, the N-doped carbon layer modified on the surface is beneficial for enhancing the hydrophilicity of BNNSs and synergistically enhances the tribological properties of the material with BNNSs. The test results of the four-ball friction tester show that compared with the pure water-glycol solution and the water-glycol system with added C-HPC-BNNSs, the friction coefficient (COF) and wear volume of the system with added C-HPC-BNNSs could be as low as 0.095 and 1.99 × 10-4 mm3, respectively. This work has positive significance for the preparation, surface modification, and tribological application expansion of two-dimensional layered material BNNSs, which is conducive to further understanding the relationship between.

Regulatory mechanism of grafted alkyl chain length of carbon quantum dots as additives on the tribological properties of lithium greases

Carbon quantum dots (CQDs) exhibit exceptional structural properties and minimal environmental impact, garnering significant interest in the field of lubrication. In this study, four types of modified CQDs with varying alkyl chain lengths were synthesized through hydrothermal methods and subsequently mixed with lithium grease (LG) to formulate mixed greases. The influence of the alkyl chain length on the CQDs used as additives in the mixed greases was investigated with a four-ball friction and wear tester, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). Specifically, compared to pure LG, the modified CQDs with the shortest alkyl chain length reduced the coefficient of friction (COF), the diameter of abrasive spots, and the depth of abrasive scars by 33.65%, 42.11%, and 51.87%, respectively. This improvement can be attributed to the ease of these shorter-chain CQDs entering the contact area and forming a stable film containing carbon, nitrogen, and oxygen elements through friction. The tribological properties of modified CQDs can be effectively controlled by adjusting the length of the carbon chain, providing a theoretical basis for the design of environmentally friendly and sustainable grease additives in engineering applications.

Synthesis and Performance Evaluation of Metallocene Polyalphaolefins (mPAO) Base Oil with Anti-Friction and Anti-Wear Properties

Anti-wear and anti-oxidation abilities are two key properties of lubricants that play a crucial role in ensuring long-term stable equipment operation. In this study, we aimed to develop a base oil with good anti-oxidation and anti-wear properties for use under extreme pressure. The as-prepared metallocene polyalphaolefin (mPAO) was chemically modified using the trifluoromethanesulfonic acid (TfOH) catalysis through an alkylating reaction with triphenyl phosphorothioate (TPPT). During the experiments, when the reaction temperature exceeded 70 °C or the concentration of TfOH exceeded 2.67%, the β-scission reaction in the alkylation process became significantly more pronounced. The physical and chemical properties of TPPT-modified mPAO (T-mPAO) were evaluated by nuclear magnetic resonance spectroscopy, Fourier trans-form infrared spectroscopy, gel–permeation chromatography, and ASTM standards. T-mPAO showed significantly improved antioxidant capacity, with the initial oxidation temperature increasing by 32 °C compared to the base oil, and it exhibited the slowest increase in acid number in the 96-h oven oxidation test. The tribological tests showed that T-mPAO had the lowest friction coefficient, wear track, and wear rate (72.7% lower than that of mPAO) as well as the highest PB (238 kg) and PD (250 kg) among all tested samples. Compared to mPAO, the average friction coefficient of TPPT-modified mPAO in the four-ball friction test was reduced by 30.5%, and by 16.4% in the TE77 reciprocating friction test. Based on the experimental results, T-mPAO had strong anti-oxidation ability and excellent lubricating performance.The successful synthesis of multifunctional mPAO has enabled lubricant base oil additization, making it possible to use it in more demanding work scenarios, greatly broadening its application scope and making lubricant formulation blending more flexible.

Tribological and Anticorrosion Properties of N-Heterocyclic-Organophosphonic Acid Ionic Liquids as Water-Based Lubricant Additives

Four ionic liquids (ILs) were synthesized by a simple neutralization reaction using 1,8-diazabicyclo[5.4.0]undecane-7-ene as the cation and organophosphonic acids with different carbon chain lengths as the anion. The obtained ILs had an excellent water-soluble property and the tribological performance was studied by a four-ball friction tester. The results showed that the longer carbon chains, the better tribological properties of the ILs. Compared with the blank, only 0.05 wt% of ILs addition resulted in the decrease of friction coefficient and wear volume about 30% and 60%, respectively. The adsorption state of the ionic liquid on the steel surface was also investigated by molecular dynamics simulation. It is believed that the good tribological performance and corrosion inhibition was attributed to the effective physical adsorption due to the polarity of the organophosphonate, which can form an effective adsorption film and prevent the steel surface from corrosion.

Performance of Aromatic Amine-Modified Metallocene Polyalphaolefin Lubricant Base Oil

With the continuous advancement of industrial technology, higher demands have been placed on the properties of gear oils, such as oxidation stability and shear resistance. Herein, the oxidation stability of high-viscosity metallocene poly-α-olefins (mPAOs) was improved by chemical modification via aromatic amine alkylation. The modified mPAO base oils were synthesized separately with diphenylamine (mPAO-DPA) and N-phenyl-α-naphthylamine (mPAO-NPA), and their applicability in industrial gear oil formulations was evaluated. The composition and physicochemical properties of the obtained samples were assessed using 1H NMR spectroscopy, Fourier transform infrared spectroscopy, gel permeation chromatography, and the American Society for Testing and Materials standards (ASTM D445, ASTM D2270, ASTM D92, etc.) confirming the successful completion of the alkylation reaction. The oxidation stability of the samples was also evaluated using pressurized differential scanning calorimetry. The initial oxidation temperature of mPAO-NPA (230 °C) was 53 °C higher than that of mPAO, and the oxidation induction period of mPAO-DPA was nearly twice that of mPAO-NPA. Thermogravimetric analysis in air revealed the increased thermal decomposition temperature and improved thermal stability of modified mPAO. ISO VG 320 industrial gear oils were formulated using mPAO alkylated with N-phenyl-α-naphthylamine(Lub-2) and commercially purchased PAO100 (Lub-1) as base oil components. The antioxidant performance of two industrial gear oils was evaluated through oven oxidation and rotating oxygen bomb tests. The oxidation induction period of Lub-2 was 30% higher than that of Lub-1, with the latter having a lower acid number and a smaller increase in viscosity at 40 °C. Finally, the friction performance of the samples was assessed on a four-ball friction tester, revealing the synergistic effect of the mPAO-NPA base oil with the HiTEC 3339 additive, forming a more stable oil film with a smaller wear scar diameter.

Lubrication mechanism of C@Ag core–shell materials as grease additive

The preparation of a low shearing shell on the surface of carbon spheres (CS) is an attractive strategy to improve the lubrication properties of CS. In this study, core–shell structural C@Ag particles were prepared using CS as the hard core and Ag nanoparticles as the soft shell. Then, the additives were mixed with Polyalphaolefin 20 to prepare the C@Ag core–shell-enhanced lithium complex grease (C@Ag-LCG). The physicochemical properties, corrosion resistance, and tribological behaviors of LCGs were investigated. C@Ag-LCG exhibited the best high-temperature resistance and colloidal stability compared with the CS-enhanced lithium complex grease (LCG) and pure LCG. The dropping point and oil separation rate of 0.05 wt% C@Ag-LCG were 255 °C and 2.36 %, respectively. The tribological behavior of greases was tested using a four-ball friction tester, and the main damage mechanism was abrasive wear. The C@Ag additive reduced the average friction coefficient and wear spot diameter by 27.17 % and 26.12 %, respectively. The improved properties were attributed to the synergistic lubrication of hard CS core and soft Ag shell with the rolling, filling, and self-repairing effects, C@Ag deposit films and the self-lubricating oil film, as well as the thickener film and the tribochemical film at the frictional interfaces.

Synergistic Effect of Acrylate of Dialkyl Dithiophosphoric Acid Combined with Molybdenum Dialkyl Dithiocarbamate as Additives in Gear Oil

With the aim of improving the tribological properties of low-viscosity gear oil for automobiles, an acrylate of dialkyl dithiophosphoric acid (ADDP) with strong polar groups was synthesized. The tribological behavior of ADDP combined with molybdenum dialkyl dithiocarbamate (MoDTC) in gear oil was systematically studied. Tribological performances of gear oil containing different additives were assessed using a four-ball friction and wear tester. The obtained tribological characteristics reveal that ADDP and MoDTC can significantly improve the antiwear and antifriction performance of low-viscosity gear oil. Moreover, compared with using MoDTC or ADDP alone, the average friction coefficient and wear scar diameter of ADDP combined with MoDTC further decreased by 2.41–19.15% and 5.00–18.19%, respectively. Analysis of the worn surface showed that the structural characteristics and physical synergistic lubricating actions of the ADDP with MoDTC additives during the friction process can contribute to the exceptional tribological properties of the hybrid additives.

Structure–Performance Relationship of Coal-Based Lubricating Base Oils and Sensitivities to Typical Additives

The relationship between the structure characteristics and performances of coal-based hydrogenation isomeric (CTL) base oil and metallocene-catalyzed coal-based poly-alpha-olefin (mPAO) base oil is clarified in this paper. CTL and mPAO were compared with typical petroleum-based and natural gas-based commercial API III and IV base oils. Pressurized differential scanning calorimetry (PDSC), the rotary bomb oxidation test (RBOT), and a four-ball friction tester were used to evaluate the oxidation stability and lubrication performance of base oils under different working conditions. The sensitivity of different base oils to typical antioxidants and extreme-pressure antiwear agents was compared. In particular, the composition and structure of CTL base oil are clearly different from GTL and mineral base oil. The coal-based CTL and mPAO base oils exhibit commendable viscosity–temperature properties, coupled with low-temperature fluidity, fire safety, and minimal evaporation loss. The lubricating properties, oxidation stability, and sensitivity to extreme-pressure antiwear agents of CTL are close to those of similar base oils. However, the sensitivity of CTL to typical antioxidants is relatively poor. In addition, compared with commercial PAO base oil, mPAO has a lower isomerization degree and fewer isomerization types. The oxidation stability and sensitivity to typical antioxidants of mPAO base oil are comparable with those of commercial PAO base oil, while its lubrication performance and sensitivity to typical extreme-pressure antiwear agents are significantly better than those of commercial PAO base oil.

Investigation of tribological behavior of MOFs/g-C3N4 nanocomposite for insight into effect of flake-on-sheet and ball-on-sheet nanostructure

Herein, we designed two catalogs of metal organic frame materials (MOF)/carbon nitride(g-C3N4) composite nanostructures (flake-on-sheet and ball-on-sheet nanostructure appearances) to probe the effect of composite nanostructures on the cooperative friction mechanism. The tribological behaviors of MOF/g-C3N4 composite nanostructures were extensively investigated in base oil on the four-ball friction tester. The results showed that the anti-wear ability of flake-on-sheet shaped MOF/g-C3N4 in oil was superior to the ball-on-sheet shaped MOF/g-C3N4, whereas the anti-friction and load-bearing ability of latter was preferable to the former. The flake-on-sheet shaped MOF/g-C3N4 enabled the friction coefficient (COF) and wear scar diameter (WSD) of oil to reduce 31.90% and 45.46%, while the ball-on-sheet shaped MOF/g-C3N4 enabled the friction coefficient (COF) and wear scar diameter (WSD) of oil to decrease 37.07% and 42.15%, respectively. Due to the morphology difference, the anti-frition and anti-wear mechanism of the flake-on-sheet shaped MOF/g-C3N4 were reliable to the tribo-film consisting of adsorption film and tribochemical film, whereas that of ball-on-sheet shaped MOF/g-C3N4 depended on the synergistic effect of the tribo-film and the ball bearing effect of MOF nanospehere in composite structure. Moreover, the interface interaction in composite structure also had a underlying influence in the friction behavior of nanoadditive.

The Simulation of Ester Lubricants and Their Application in Weak Gel Drilling Fluids.

To enhance the performance and reduce the amount of ester-based lubricants used in weak gel drilling fluids, a shear dynamics simulation under extreme pressure conditions was employed to refine the formulation of the base oil and pressure additives. The simulation results were validated using fatty acid methyl, ethyl, and butyl esters. Fatty acid methyl ester demonstrated the lowest temperature increase and the highest load-bearing capacity post-shear. The four-ball friction test revealed that methyl oleate had a coefficient of friction of 0.0018, approximately a third of that for butyl oleate, confirming the simulation's accuracy. By using methyl oleate as the base oil and oleamide as the pressure-resistant component, the optimal shear stress was achieved with a 10% addition of oleamide. A lubricant composed of 90% methyl oleate and 10% oleamide was tested and showed a coefficient of friction of 0.03 when 0.5% was added to bentonite slurry, indicating a strong lubricating film. Adding 1% of this lubricant to a low gel drilling fluid system did not affect its rheological properties, and the gel structure remained stable after seven days of aging. Field tests at the Fu86-3 well in the Jiangsu Oilfield of Sinopec confirmed that adding 1% of the ester-based lubricant to the drilling fluid significantly improved drilling efficiency, reduced drag by an average of 33%, and increased the drilling rate to 22.12 m/h. This innovation effectively prevents drilling complications and successfully achieves the objectives of enhancing efficiency.

Effect of nano-AlN, Al2O3 on friction and wear properties of copper-steel clad plate immersed in the lubricants

PurposeThis paper aims to investigate the preparation of AlN and Al2O3, as well as the effect of nano-AlN and nano-Al2O3, on friction and wear properties of copper-steel clad plate immersed in the lubricants.Design/methodology/approachNano-AlN or nano-Al2O3 (0.1, 0.2, 0.3, 0.4 and 0.5 Wt.%) functional fluids were prepared. Their tribological properties were tested by an MRS-10A four-ball friction tester and a ball-on-plate configuration, and scanning electron microscope observed the worn surface of the plate.FindingsAn increase in nano-AlN and Al2O3 content enhances the extreme pressure and anti-wear performance of the lubricant. The best performance is achieved at 0.5 Wt.% of nano-AlN and 0.3 Wt.% of nano-Al2O3 with PB of 834 N and 883 N, a coefficient of friction (COF) of approximately 0.07 and 0.06, respectively. Furthermore, the inclusion of nano-AlN and nano-Al2O3 particles in the lubricant enhances its extreme pressure performance and reduces wear, leading to decreased wear spot depth. The lubricating effect of the nano-Al2O3 lubricant on the surface of the copper-steel composite plate is slightly superior to that of the nano-AlN lubricant, with a COF reaching 0.07. Both lubricants effectively fill and lubricate the holes on the surface of the copper-steel composite plate.Originality/valueAlN and Al2O3 as water-based lubricants have excellent lubrication performance and can reduce the COF. It can provide some reference for the practical application of nano-water-based lubricants.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2023-0255/

Adsorption Behavior and Tribological Properties of Surface-Capped Silica Nano-Additives in Rapeseed Oil

Abstract The influence of particle size and surface modifier structure on the adsorption behavior and tribological properties of surface-capped silica nano-additives in rapeseed oil was investigated. With four kinds of SiO2 nanoparticles, methyl-modified DNS-2 (particle size 14 nm) and DNS-3 (particle size 5 nm), vinyl-modified RNS-D (particle size 5 nm), and epoxy-modified RNS-E (particle size 5 nm) as the nano-additives of rapeseed oil, their adsorption behavior in rapeseed oil was studied with a quartz crystal microbalance (QCM-D), and their tribological properties were evaluated with a four-ball friction and wear tester. DNS-2 with a larger particle size can form a high-strength tribo-film on the rubbed surface through shear sintering, thereby reducing the wear scar diameter of the steel ball. DNS-3, RNS-D, and RNS-E with smaller particle sizes can form a viscoelastic adsorption layer on the rubbed steel surface, and their equilibrium adsorption mass thereon increases with the increase of the polarity of the modifiers, which corresponds to the increases in their friction-reducing and anti-wear abilities as well as extreme pressure properties therewith. Particularly, the equilibrium adsorption mass and adsorption rate of RNS-E surface-capped by an epoxy group with the largest polarity are 16 times and 34 times higher than those of DNS-3 surface-capped by methyl. This indicates that encapsulating silica nanoparticles with strongly polar organic species could help to enhance its adsorption on rubbed metal surfaces and improve its tribological properties in rapeseed oil.

Tribological Behavior and Mechanism of Surface-Modified Mullite as Polyurea Grease Additive

Abstract The excellent tribological performance of nanoparticles as additives in lubricating greases has attracted widespread attention. In this study, a silane coupling agent (KH550) was used to chemically modify nanoscale mullite (composed of Al2O3 and SiO2), and the modified nano-KH-mullite was dispersed as an additive in polyurea grease at different ratios (0.01, 0.05, 0.07, 0.1, and 0.3 wt%). The friction and wear performance of the compound polyurea greases were evaluated using a four-ball friction tester. Professional instruments will be utilized to analyze the micro-morphology, 3D profile, elemental content, and valence state of the worn surface, aiming to investigate the lubrication and antiwear mechanism of the nano-KH-mullite additive. The results indicate that nano-mullite effectively improves the antiwear and antifriction performance of the polyurea grease. When the additional content is 0.05 wt%, the friction coefficient (COF) and the wear scar diameter (WSD) are reduced by approximately 19.97% and 11.1%, respectively, and the roughness of the worn surface is also reduced. The excellent tribological performance of the composite grease is attributed not only to the good dispersibility of KH-mullite but also to its ability to promote the formation of a composite lubrication film on the friction pair surface. The component KH-Al2O3 in the KH-mullite can fill and repair scratches and grooves on the worn surface, while the other component KH-SiO2 can bear the load and convert the friction mode to rolling friction.

Onion-like carbon nanoparticles as additives in lubricant oil deform inelastically during the wear testing for improved lubrication performances

Nano-carbon has been extensively investigated as an additive to lubricant oil for improved performance. It is still far from a final verdict as to how the physicochemical features of the carbon nanomaterials affect their lubrication efficacy. Here we report the use of onion-like carbon (OLC) particles with the size of 5–10 nm as additives to lubricant oil, and their role in regulating the lubrication is elucidated through characterizing the wear-induced changes to their physiochemistry. Multiple loads are chosen for the wear testing using the four-ball friction tester. Stable dispersion of the OLC particles in lubricant oil was attained by pre-coating the particles with oleic acid molecules. Results showed that the oil with the treated OLC particles of 0.125 wt% reduced the wear scar by 30 % in diameter and the wear volume by 77 %. It was surprisingly noted that incorporation of the OLC nanoparticles particularly alleviated the heavy loading wear by remarkably reducing the friction coefficient. Raman spectroscopy characterization suggested intact chemistry of the particles after the wear testing. However, curvature changes of the particles were seen as revealed by high resolution transmission electron microscopy after the wear testing, indicating inelastic deformation of the particles triggered by the wear-squeezing.

Preparation and Tribological Behavior of Nitrogen-Doped Carbon Nanotube/Ag Nanocomposites as Lubricant Additives

In this study, nitrogen-doped carbon nanotube/Ag nanocomposites (denoted as N-C/Ag) have been synthesized in a urea solution using a hydrothermal method. The carbon nanotubes, AgNO3 solution, urea and poly-dopamine (PDA) served as carbon, silver, nitrogen and carbon sources, respectively. The results show that the diameter of the carbon tubes was about 30 nm, and the Ag nanoparticles, with a diameter of ca. 10 nm, dispersed on the carbon tube surface. The Ag particle size decreased with a lower degree of crystallinity at a high temperature in the presence of urea. The friction and wear behavior of the oil acid (OA) modified N-C/Ag (OAN-C/Ag) as an additive in liquid paraffin (LP) were studied using a four-ball friction and wear tester. The results have shown that the coefficients of friction (COFs) and wear scar diameters (WSDs) of steel balls lubricated with LP-OAN-C/Ag decreased by 27.3% and 25.3%, respectively, relative to pure LP. Tribofilms containing Ag, carbon and nitride were formed on the worn steel ball surfaces. Details, the carbon, Fe2O3, azides and nitride, Ag and alloy and other compounds on the wear scars may improve tribological properties. The synergistic effect of carbon, Ag and urea plays a critical role during sliding.

Zn2+-induced construction for highly dispersed ball-on-flake nanostructured ZIF-7/g-C3N4 nanoadditive towards improvement of tribological properties

Herein, the highly dispersed ball-on-flake nanostructured ZIF-7/g-C3N4 nanocomposites were successfully constructed by two-step approach, i.e. the electrostatic adsorption (the first step) and in-situ preparation(the second step). The composition and structure of ZIF-7/g-C3N4 nanocomposites were determined by a series of characterizations (such as XRD, FT-IR, TGA, Zeta potential, XPS, SEM, TEM, etc). The dispersibility and interface compatibility of ZIF-7/g-C3N4 nanocomposites in base oil (150SN) were intensively probed by Uv-vis spectra and optical microscope, demonstrating that the ZIF-7/g-C3N4 nanocomposites had a superior interface compatibility in oil. Furthermore, the tribological properties of ZIF-7/g-C3N4 nanocomposites as additives in base oil were detailedly evaluated on a four-ball friction tester. The experimental results showed that the ZIF-7/g-C3N4 nanocomposites at 0.05 wt% optimum adding content exerted the reduction by 46.85% of average friction coefficient and 48.74% of wear scar diameter, while exhibiting the improvement by 18.37% of bearing capacity in base oil. In terms of the characterizations of the worn surface (such as FESEM, 3D profile, elemental mapping, XPS, etc), the lubrication mechanism of ZIF-7/g-C3N4 nanocomposites were deeply discussed and proposed, are attributed to its good dispersibility in base oil, assuming the existence of synergistic lubrication.

Effectiveness of Lubricants and Fly Ash Additive on Surface Damage Resistance under ASTM Standard Operating Conditions

This study investigated the effectiveness of lubricants and additives in preventing surface damage and wear, which is critical for numerous industrial applications. The ASTM standard operation conditions were employed for a series of experiments using a four-ball friction and wear tester, testing three different oils (A, B, and C) with and without 0.5% fly ash additive. The experiments were analyzed using a microscope to evaluate the effectiveness of oils and additives in preventing surface damage. The study found that certain anti-wear additives significantly reduced the size of wear scars on the balls, indicating their effectiveness in reducing surface damage. These findings have important implications for developing new lubricant formulations and optimizing industrial processes that involve sliding and rolling contacts. The study emphasizes the importance of selecting appropriate oils and additives for specific applications to minimize surface damage and wear, which is crucial for improving the performance and lifespan of machine components.

Synthesis of Oil Soluble Boron Esters and Obtaining Lubricant Additive Packages with Anti-wear and Extreme Pressure Properties

The purpose of this work is synthesis and characterization of pryridin-yl-borate esters and investigation of tribological performance as additive. The syn-thesis of dialkyl-(2-(pyridin-2-yl) ethyl) borate esters both in the literature and the novel synthesis of dialkyl 2-(methyl (pyridin-2-yl) borate esters and dialkyl 2- (5-ethylpyridin-2-yl) ethyl borate esters were carried out. The boron esters to be obtained were characterized by using IR, 1H NMR,13C NMR spectroscopic methods as well as physical methods such as TAN and corrosion tests. The fric-tion-reducing and anti-wear properties of the synthesized lubricant additives were measured with a four-ball friction and wear tester. As a result of these stud-ies, it has been shown that the friction coefficient is reduced by about 30-40 % compared to the base oil and the wear is also reduced. In the tribological analysis performed using synthesized four molecules within the scope of the study, it was found that resistance to oxidation is increased when the synthesized molecules were added to group I base oil at 0.5 % and 1% w/w concentration. The novel synthesis of dialkyl 2-(methyl (pyridin-2-yl) borate esters and dialkyl 2- (5-ethylpyridin-2-yl) ethyl borate esters were carried out and tribological perfor-mances in base oil were analysed first time.

Effect of Cu-Doped Carbon Quantum Dot Dispersion Liquid on the Lubrication Performance of Polyethylene Glycol

Energy saving and reduced consumption of key materials such as bearings in high-end equipment can be realized by synthesizing a new lubricating functional additive, copper-doped carbon quantum dot dispersion liquid (Cu-CQDs) via hydrothermal reaction with glycerol, cupric chloride dihydrate, and choline chloride as raw materials. The influence of the dispersion liquid containing Cu-CQDs nanoparticles on the lubricating properties of polyethylene glycol (PEG200) was investigated on a four-ball friction tester. The wear scars of steel balls after friction were analyzed using a scanning electron microscope accompanied by energy dispersive spectroscopy (SEM/EDS), photoelectron microscopy, and Raman spectroscopy. The results revealed the friction and wear mechanism of Cu-CQDs. Cu-CQDs dispersion liquid can significantly enhance the lubrication performance of PEG. The average friction coefficient of PEG containing 2.0 wt% Cu-CQDs dispersion liquid was 40.99% lower than that of pure PEG. The friction and wear mechanism can be ascribed to friction, inducing Cu-CQDs to participate in the formation of boundary lubricating film, resulting in a low friction coefficient and wear scar diameter.

Preparation and Modification of Graphite-based and Coal-based Graphene and its Tribological Properties in Lubricants

Graphite-based graphene oxide (GO) and coal-based graphene oxide (GO/SiO2, which we call graphene oxide/SiO2 because the surface of the resulting coal-based GO is linked with SiO2 from the coal structure) were prepared by the conventional Hummers oxidation method and ultrasound-assisted Hummers oxidation method, respectively, using natural graphite powder and Xinjiang Wucaiwan coal as carbon sources. Furthermore, the structures of the two were studied comparatively. Afterwards, the two lamellar structure products were hydrophilically modified with octadecylamine and dicyclohexylcarbodiimide by a hydrothermal method. And then, added these products (graphite-based GO-ODA and coal-based GO/SiO2-ODA) to No.32 cycloalkyl base oils in order to comparatively investigated their tribological properties as lubricant additives. The results showed that the dispersion stability of coal-based GO/SiO2 in the lubricant was significantly better than that of graphite-based GO; meanwhile, the tribological performance of GO/SiO2-ODA in the lubricant better than that of graphite-based GO-ODA due to the surface linkage of coal-based GO/SiO2 with SiO2 particles. After 1 h - long grinding in a four-ball friction test, the lubricant friction coefficient of 0.03 wt% coal-based GO/SiO2-ODA oil reached a minimum of 0.118, which reduced 58.1% compared to pure base oil and reduced 2.8 times compared to the counterpart using graphite-based GO-ODA under the same experimental conditions.