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Purpose: This study aims to prepare thymol-based deep eutectic solvents (DESs) and use them as lubricates for friction and wear tests to simulate the wear conditions of hybrid bearings. Design/methodology/approach: Through the characterization and analysis of the morphology of wear scars and the elemental composition of friction films, the tribological behavior and wear mechanism of sample materials as lubricants were investigated and the anti-wear mechanism of thymol-based DESs was discussed. Findings: The findings demonstrate that because of the formation of a fluid lubrication film and excellent kinematic viscosity, the lubrication effect of the prepared DES is improved by about 50% compared to the base lubricating oil. The prepared [Ch]Cl-thymol DES has a better anti-friction and lubrication effect than citric-thymol, EG-thymol and urea-thymol DESs, with an average friction coefficient of about 0.04. Originality/value: In this work, the friction reduction properties of thymol-based DESs were studied as lubricants for the first time, and the lubrication mechanism of sample materials was investigated. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to prepare ZnFe2O4 nanospheres, sheet MoS2 and three ZnFe2O4@MoS2 core-shell composites with various shell thicknesses, and add them to the base oil for friction and wear tests to simulate the wear conditions of hybrid bearings. Design/methodology/approach: Through the characterization and analysis of the morphology of wear scars and the elemental composition of friction films, the tribological behavior and wear mechanism of sample materials as lubricant additives were investigated and the effects of shell thickness and sample concentration on the tribological properties of core–shell composite lubricant additives were discussed. Findings: The findings demonstrate that each of the five sample materials can, to varying degrees, enhance the lubricating qualities of the base oil and that the core–shell nanocomposite sample lubricant additive has superior lubricating properties to those of ZnFe2O4 and MoS2 alone, among them ZnFe2O4@MoS2-2 core–shell composites with moderate shell thickness performed most ideally. In addition, the optimal concentration of the ZnFe2O4@MoS2 lubricant additive was 0.5 Wt.%, and a concentration that was too high led to particle deposition and affected the friction effect. Originality/value: In this work, ZnFe2O4@MoS2 core–shell composites were synthesized for the first time using ZnFe2O4 as the carrier and the lubrication mechanism of core–shell composites and single materials were compared and studied, which illustrated the advantages of core–shell composite lubricant additives. At the same time, the influence of different shell thicknesses on the lubricant additives of core–shell composites was studied. Peer review: The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-12-2022-0367/ [ABSTRACT FROM AUTHOR]

According to the redox ability of dopamine in a weak alkaline environment, silver nanoparticles were uniformly loaded on the surface of polydopamine-modified graphene oxide (Ag/PGO). The results show that the base oil containing Ag/PGO nanoparticles exhibits a better tribological property than base oil. The maximum decrease in wear rate and friction coefficient at different temperatures amounted to 68% and 53.6%, respectively. The tribofilm containing C, O, N, and Ag exists and plays an important role in reducing friction and increasing wear resistance. Molecular dynamics simulations show that the microscopic oil film composed of Ag/PGO and n-hexadecane has low shear deformation during the shearing process, and the oil film has low interaction energy with the upper and lower shear walls. [ABSTRACT FROM AUTHOR]

Graphene has attracted attention in the field of lubrication based on its excellent properties. However, the difficulty of graphene dispersion in base oil hinders its development. In this paper, the effects of ionic liquid as additives on the dispersion and lubricating properties of graphene lubricants were investigated. Results showed that after adding ionic liquid, the graphene could be still stably dispersed in base oil even after 30 days. Molecular simulation study showed that ionic liquid tended to insert into graphene layers, and promoted the affinity of graphene and base oil. Then, the tribological friction behaviour of ionic liquid/graphene lubricants was investigated by concentration of ionic liquid, applied load and sliding velocity. Results showed that the friction and wear property was improved better after adding ionic liquid. This work provides a new method to enhance the stability of the graphene lubricating oil, and thus broaden the graphene in tribological application. [ABSTRACT FROM AUTHOR]

[Display omitted] • The CD@CuCo-MOF composites were prepared via hydrothermal and self-assembly methods, and then were dispersed in PETE oil. • The CD@CuCo-MOF additives achieved excellent lubricating performances during varying temperatures. • The tribofilm consisted of carbon dots, MOF, metal oxides, carbides and nitrides was formed to protect contact interfaces. In this study, we successfully synthesized CD@CuCo-MOF composites, which are composed of ultrathin two-dimensional (2D) nanosheets of metal-organic framework (MOF) doped with carbon dots (CDs). The synthesis process involved hydrothermal and ultrasonically assisted self-assembly with a proper solvent ratio. The composites were then dispersed into pentaerythritol ester (PETE) with the aid of ultrasonic treatment. We thoroughly evaluated the physicochemical features and tribological properties of the CD@CuCo-MOF composites using advanced testing and characterization techniques including XRD, Raman, FTIR, TG, XPS, FIB-TEM and so on. The results demonstrated that the addition of CD@CuCo-MOF resulted in a 61.1 % reduction in the coefficient of friction (COF) at a concentration of 0.1 wt% when compared to the base oil at room temperature. With the rise in temperature, CD@CuCo-MOF exhibited excellent lubricating properties due to its hybrid inorganic-organic structure and interlayer sliding effect. This led to a reduction of 59.2 % and 42.9 % in the mean COF compared to PETE oil at temperatures of 100 °C and 200 °C. This enhancement in the tribological performance of CD@CuCo-MOF could be attributed to several factors, including its superior dispersion stability, excellent lubricating properties, and involvement in the formation of a tribofilm. The tribofilm formed from a combination of CDs, CuCo-MOF, metal oxides, carbides, and nitrides promoted the rearrangement of the contact surface, thereby minimizing the friction and wear between the rubbing surfaces. These findings hold significant guiding implications for advancing the development of potential-controlled lubrication using MOFs doped with CDs across a wide temperature range. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Ag-CQDs was synthesized via a hydrothermal reaction method, and then was steady dispersed in PAO oil. • The Ag-CQDs additive exhibited excellent lubricating performance at various temperatures. • The tribofilm consisted of multiple chemical composition was formed at elevated temperatures to reduce friction. Carbon quantum dots (CQDs) doped with silver (Ag-CQDs) was prepared using a facile hydrothermal method. With the combination of ultrasound vibration and ionic liquid (IL), the dispersion stability of the Ag-CQDs additive in poly alpha olefin (PAO) was improved. The tribological performance of the CQDs and Ag-CQDs as additives over a wide temperature range were evaluated through four-ball tests and a ball-on-disk reciprocating configuration. The four-ball test results revealed that the CQDs and Ag-CQDs additives could effectively reduce the coefficient of friction (COF) of the base oil and wear scar diameter (WSD) of lower balls. When the concentration was 0.05 wt%, the Ag-CQDs additive could lead to 42.2% lower COF and 35.3% lower WSD than the base oil. Meanwhile, the tribological performance at elevated temperatures results revealed that the CQDs and Ag-CQDs additives could substantially decrease friction and wear when the ambient temperature was above 200 °C. The Ag-CQDs exhibited better lubricating performance than the CQDs. The lubricating mechanism was attributed to the formation of a tribofilm composed of Ag-CQDs, multicomponent oxides, carbonates and nitrides induced by tribochemical reactions, which provided effective protection for the rubbing pair and maintained low friction and wear. [ABSTRACT FROM AUTHOR]

Recently, the engineering structural ceramics as friction and wear components in manufacturing technology and devices have attracted much attention due to their high strength and corrosion resistance. In this study, the tribological properties of Si3N4/Si3N4 sliding pairs were investigated by adding few-layer graphene to base lubricating oil on the lubrication and cooling under different experimental conditions. Test results showed that lubrication and cooling performance was obviously improved with the addition of graphene at high rotational speeds and low loads. For oil containing 0.1 wt% graphene at a rotational speed of 3000 r·min−1 and 40 N loads, the average friction coefficient was reduced by 76.33%. The cooling effect on Si3N4/Si3N4 sliding pairs, however, was optimal at low rotational speeds and high loads. For oil containing 0.05 wt% graphene at a lower rotational speed of 500 r·min−1 and a higher load of 140 N, the temperature rise was reduced by 19.76%. In addition, the wear mark depth would decrease when adding appropriate graphene. The mechanism behind the reduction in friction and anti-wear properties was related to the formation of a lubricating protective film. [ABSTRACT FROM AUTHOR]

In this study, we use an aqueous solution synthesis method to prepare silver perrhenate powders and suspend them into a poly alpha olefin (PAO) base oil with polyoxyethylene octylphenyl ether. Four ball tests and ball-on-disk reciprocating mode are performed to determine how silver perrhenate performs tribologically as a lubricating additive over a wide range of temperatures. The physical and chemical properties, as well as the lubricating mechanisms of the silver perrhenate additive, are characterized via X-ray diffraction, scanning electron microscope, Fourier transformation infrared spectroscopy, Raman spectrum, and X-ray photoelectron spectroscopy. The four-ball test results demonstrate that the oil added with silver perrhenate additive is more effective than the base oil in reducing friction and improving wear resistance, and provides the best lubricating performance when at a concentration of 0.5 wt%. The reciprocating mode findings indicate that the hybrid lubricant exhibits distinctively better tribological properties than the base oil at high temperatures, and its low shear strength and chemical inertness allow for low friction at elevated temperatures. The resulting silver perrhenate layer that incorporates native superalloy oxides on the worn surface can provide lubrication by serving as a barrier that prevents direct contact between the rubbing surfaces at elevated temperatures. [ABSTRACT FROM AUTHOR]