Friction Reduction Research Articles

Effect of interlayer bonded bilayer graphene on friction

Abstract We study the friction properties of interlayer bonded bilayer graphene by simulating the movement of slider on the surface of bilayer graphene using molecular dynamics. The results show that the presence of the interlayer covalent bonds due to the local sp3 hybridization of carbon atoms in the bilayer graphene seriously reduced the frictional coefficient of the bilayer graphene surface to 30%, depending on the coverage of interlayer sp3 bonds and normal loads. For a certain coverage of interlayer sp3 bonds, when the normal load of the slider reaches a certain value, the surface of this interlayer bonded bilayer graphene will lose the friction reduction effect on the slider. Our findings provide guidance for the regulation and manipulation of the frictional properties of bilayer graphene surfaces through interlayer covalent bonds, which may be useful for the application of friction related graphene based nanodevices.

A biomimetic lubricating nanosystem for synergistic therapy of osteoarthritis

Failure of articular cartilage lubrication and inflammation are the main causes of osteoarthritis (OA), and integrated treatment realizing joint lubrication and anti-inflammation is becoming the most effective treat model. Inspired by low friction of human synovial fluid and adhesive chemical effect of mussels, our work reports a biomimetic lubricating system that realizes long-time lubrication, photothermal responsiveness and anti-inflammation property. To build the system, a dopamine-mediated strategy is developed to controllably graft hyaluronic acid on the surface of metal organic framework. The design constructs a biomimetic core–shell structure that has good dispersity and stability in water with a high drug loading ratio of 99%. Temperature of the solution rapidly increases to 55 °C under near-infrared light, and the hard-soft lubricating system well adheres to wear surfaces, and greatly reduces frictional coefficient by 75% for more than 7200 times without failure. Cell experiments show that the nanosystem enters cells by endocytosis, and releases medication in a sustained manner. The anti-inflammatory outcomes validate that the nanosystem prevents the progression of OA by down-regulating catabolic proteases and pain-related genes and up-regulating genes that are anabolic in cartilage. The study provides a bioinspired strategy to employ metal organic framework with controlled surface and structure for friction reduction and anti-inflammation, and develops a new concept of OA synergistic therapy model for practical applications.

Unveiling an additively manufactured open hardware pin-on-disc tribometer considering its high reproducibility

In recent years, the aspects of energy efficiency and durability have become increasingly important in the development of technical systems. From a tribological point of view, these are often linked to the reduction of wear and friction. When testing new materials, coating systems or lubricants, the underlying mechanisms and physical relationships are investigated by the deployment of simplified model tests. Advanced commercial test rigs allow high-resolution measurement of important friction and wear parameters, but also entail a considerable cost and thus a certain entry barrier to deal further with tribological aspects. In many research projects, therefore, self-developed test rigs are used, which at the same time, however, makes comparability and reproducibility with other systems considerably more difficult. For this reason, we have developed a pin-on-disc tribometer based on the open hardware approach, which can be completely additively manufactured by fused filament fabrication. In addition to presenting the customizable measurement system, we investigated the measurement capability using 50 repeated measurements on two different tribological test systems. The reproducibility of the measured values was 0.4 % and 1.1 % for friction and 0.6 % and 1.0 % for wear and was thus considerably lower than the standard deviation in the tests on a single tribometer, which was up to 7.7 % and 16.1 % for friction and wear, respectively. So, the presented tribometer can be used, for example, to perform high throughput tests and thus to detect systematic correlations, e.g., in combination with machine learning approaches. Another area of application is training and education of students and professionals.

Bio-based silsesquioxanes nano hybrids for enhancing the tribological performance of silicone oil: A DFT and experimental study

A novel, eco-friendly nanohybrid solid lubricant additive was synthesized using oleic acid, a readily available green material. By esterifying the 18-carbon chain of ethyl oleate (EO) and subjecting it to hydrosilylation with triethoxysilane (TES), the ethyl 9-(triethoxysilyl)octadecanoate (S2EO) was created. Nanosized Polymethyl silsesquioxanes (PMSQ) particles (P-NPs) were then modified with S2EO to produce the lubricant additive P-NPs-S2EO for enhancing silicone oil’s tribological performance. The synthesis processes were verified by FTIR, H-NMR, SEM, and EDS, while TGA demonstrated the nanohybrid’s superior thermal stability, showing only 1.8% weight loss at 200 °C. Tribological tests using a pin-on-disk tribometer with P-NPs and P-NPs-S2EO in silicone oil revealed a friction reduction of up to 93%, outperforming traditionally used borax and other silicone-based lubricants. The sustainable synthesis of P-NPs-S2EO, confirmed by Density Function Theory (DFT) calculations, underscores its thermal stability and efficiency as a lubricant additive.

Effect of laser shock peening on tribological properties of WC-Ni under seawater conditions: Anomalous behavior and solutions

This research investigated the effect of laser shock peening (LSP) on the tribological properties of WC-Ni under seawater lubrication. The experimental findings revealed an anomalous behavior, contrary to the existing literature, indicating that the LSP treatment actually deteriorated the tribological properties of WC-Ni. The mechanism and solutions for anomalous behavior were also examined, and the results indicated that the enhancement of material properties through LSP treatment cannot counterbalance the detrimental effects of increased surface roughness. For improved processes, the sample treated with LSP + Polish exhibits the highest residual compressive stress and the lowest surface roughness, thereby yielding the best comprehensive performance. Therefore, the experimental results demonstrate that LSP + Polish treatment can improve material performance and hydrodynamic effect, leading to reductions in friction and wear.

Utilizing photodeposition to fabricate micro-nano structured microcapsules for enhancing mechanical and high-temperature tribological performance of fabric composites

Fabric composite materials face significant challenges in maintaining excellent tribological properties at high temperatures. This study employed photodeposition to deposit gold (Au) and copper (Cu) nanoparticles on the surface of titanium dioxide-coated jojoba oil microcapsules (TiO2 @jojoba), yielding micro-nanostructured Au-TiO2 @jojoba and Cu-TiO2 @jojoba microcapsules. Subsequently, microcapsules participated in the in-situ polymerization of polyimide (PI), serving as crosslinking points in PEEK/PTFE fabric-reinforced composites. PEEK/PTFE-Au composites containing Au-TiO2 @jojoba microcapsules exhibited outstanding tribological and mechanical properties. Compared to microcapsule-free samples, PEEK/PTFE-Au composites showed a 30.26 % reduction in friction coefficient at 250 °C and a 24.28 % increase in tensile strength. In addition, mechanistic studies indicated that TiO2 underwent a friction chemical reaction converting to TiNF during friction accompanying by friction-induced phase transitions. The release of jojoba oil during friction and the occurrence of friction chemical reactions were the main friction reduction mechanisms of PEEK/PTFE-Au composites at high temperatures.

Enhancing tribological properties of lubricated contacts via synergistic interactions of green silica nanoparticles and ZDDP

Zinc dialkyldithiophosphate (ZDDP) anti-wear lubricant additive contributes to significant harmful emissions and its replacement has become a priority. In this study, green silica nanoparticles were synthesized and optimized for concentration to serve as hybrid additives alongside ZDDP in lubricants, aiming to mitigate environmental concerns. A combination of 0.5 wt% silica nanoparticles, 0.5 wt% oleic acid (OA), and 0.75 wt% ZDDP demonstrated notable improvements, reducing ZDDP usage by ∼25 % while achieving significant tribological enhancements. At room temperature, coefficient of friction (COF) was reduced by ∼60 %, and wear was reduced by ∼70 %, while at 100 °C, COF was reduced by ∼80 %, and wear was reduced by ∼96 %. Advanced characterization techniques such as FESEM with EDS mappings, EPMA, and TOF-SIMS were employed to elucidate the underlying mechanisms for observed reduction in friction and wear.

Investigation on PFAS Sources and Removal in a Municipal Wastewater Treatment Plant

PFAS (per- and poly-fluoroalkyl substances) is a complex family of manmade highly fluorinated aliphatic organic chemicals including thousands of chemical structures identified. PFASs were first synthesized in the 1940s and their physical and chemical properties such as oil and water repellency, temperature resistance, and friction reduction were then used in a wide range of products and industrial applications. Awareness about the possible health and environmental risks related to exposure to these substances has only risen in recent years and is resulting in the inclusion of such compounds in the Proposal for the recast of the Directive of the European Parliament and of the Council concerning urban wastewater treatment.A research was carried out at a municipal wastewater treatment plant (MWWTP) in Northern Italy to define the inflowing load of PFAS, the main load sources and the removal efficiency of the treatment processes.First, the contribution of the water supplied to the local population was excluded by means of specific chemical analyses. Then, the 100 industrial settlements served by the MWWTP were examined for the raw materials used, the final products and the productive cycle and 8 of them were selected as potential sources. A sampling campaign was carried out and the specific PFAS load was calculated. The total PFAS load entering the MWWTP was calculated from the analytical results and the flow. The percent contribution of each of the selected settlements to the total PFAS load was then calculated. 40% derives from a textile dyeing industry and 32% from a waste platform receiving also landfill leachates. 89% of the total PFAS load comes from the sum of such contributions and two other activities: the processing of slaughterhouse wastes and the production of chemicals for agriculture.Specific investigations lead to attribute an important role also to fire drills and fire extinguishing, using Aqueous Film Forming Foams (AFFF) containing PFAS. So, domestic contribution can be held as negligible.The removal in the WWTP was null and, in some cases, negative. As also reported in the literature some precursors can be transformed in PFAS during the biological process and some sludge accumulated compounds can be released.

Tuning Lubrication Performance of Phase‐changing Emulsion‐filled Gels by Sugar alcohols

Lubrication by hydrogels is proving to be an emerging area in colloid science. Although oil‐driven friction reduction is predominant in literature, emulsion gel‐based lubrication has attracted very little attention to date. We hypothesize that an interplay of viscolelasticity and oil volume fraction may modulate lubricity of emulsion‐filled gels. Herein, phase‐change gelatin‐based emulsion‐filled gels with different sugar alcohol and oil droplet concentrations (0‐30 wt%) were tested for their lubrication performance. The rheological and tribological tests were analysed in conjunction with spectroscopic and structural characterizations in order to reveal structure‐function relationship. Structural characterizations demonstrated that hydrogen bonding was enhanced in pure gelatin gels with the increase of sugar alcohol (glycerol)‐replacement time, which enhanced the storage modulus (G') of the gel networks. Emulsified droplets served as active fillers further strengthening the G’ and strikingly the presence of glycerol reduced the thermo‐responsiveness of the emulsion‐filled gels. Emulsion‐filled gels containing sugar alcohols, irrespective of their type, can greatly reduce the friction coefficients (μ) between hydrophobic surfaces in the boundary and mixed regimes versus the systems without sugar alcohols. In the hydrodynamic regime, the friction coefficient of the system was proportional to the second plateau shear viscosity, regulated by the oil content.This article is protected by copyright. All rights reserved.

Natural product of angelica essential oil developed as a stable Pickering emulsion for joint interface lubrication

Development of high-performance joint injection lubricants has become the focus in the field of osteoarthritis treatment. Herein, natural product of angelica essential oil combined with the graphene oxide were prepared to the stable Pickering emulsion as a biological lubricant. The tribological properties of the Pickering emulsion under different friction conditions were studied. The lubricating mechanism was revealed and the biological activities were evaluated. Results showed that the prepared Pickering emulsion displayed superior lubrication property at the Ti6Al4V biological material interface. The maximum friction reduction and anti-wear abilities of the Pickering emulsion were improved by 36% and 50% compared to water, respectively. This was primarily due to the action of the double-layer lubrication films composed of the graphene oxide and angelica essential oil molecules. It was worth noting that the friction reduction effect of the Pickering emulsion at the natural cartilage interface was higher about 19% than that of HA used in clinic for OA commonly. In addition, the Pickering emulsion also displayed antioxidant activity and cell biocompatibility, showing a good clinical application prospect in the future.

Synergistic lubrication of multilayer Ti3C2Tx@MoS2 composite coatings via hydrothermal synthesis

To reduce wear and energy loss during the movement of miniaturized devices such as wearable devices and MEMS, and to address the inherent limitations of individual categories of solid lubricating materials, a new MXene-based composite solid lubricating material was designed. In this study, Ti3C2Tx@MoS2 composites were successfully prepared via hydrothermal synthesis, with MoS2 nanosheets grown uniformly on the surface and interval of the multilayer Ti3C2Tx. The composites were deposited as a solid lubricant coating on silicon substrates using a drop coating method. Tribological behavior was evaluated by ball-on-disk reciprocating and rotating tribometer, respectively. The results revealed that the friction coefficients of the multilayer Ti3C2Tx@MoS2 composite coatings were reduced by 75%, 69%, and 58%, respectively, compared to the multilayer Ti3C2Tx, MoS2, and their mechanical mixtures. Moreover, this study proposed the excellent wear resistance of the multilayer Ti3C2Tx@MoS2 composite coatings was attributed to the synergistic lubrication of Ti3C2Tx and MoS2. MoS2 was enriched in the wear track, and the tribofilm formed during friction process played the role of friction reduction and lubrication. In comparison, the multilayer Ti3C2Tx had an excellent effect on the wear resistance and structural support.

Tribological properties of self-lubricating fabric linings prepared with GO-modified basalt fiber

The wear resistance and friction reduction of the fabric liner are important for the service life of self-lubricating spherical plain bearings. Basalt fiber was subjected to chemical modification by grafting graphene oxide onto its surface, resulting in the preparation of GO@BF. Polytetrafluoroethylene/basalt fiber and polytetrafluoroethylene/GO@BF fabric liners were prepared, and the tribological properties were investigated. The friction regions of fabric liners were characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy, and the friction and wear mechanisms were analyzed. The results show that the addition of graphene oxide can effectively improve the friction reduction and abrasion resistance of the fabric liner. During the friction process, graphene oxide and polytetrafluoroethylene transfer film form a synergistic lubrication mechanism, which effectively reduces the formation of abrasive particles on the friction surface, and improves the tribological performance of the fabric liner.

Self-dispersed molybdenum disulfide quantum dot/graphene crumpled ball as efficient high temperature lubricant additive

Inorganic nanoparticles have been proved as powerful lubricant additives at elevated temperature. However, the tribological properties are inevitably impaired due to poor dispersion and insufficient high temperature resistance of organic matter modified nanoparticles. Here, we prepare a self-dispersed molybdenum disulfide quantum dot/graphene crumpled ball (MGCB) comprising molybdenum disulfide quantum dot uniformly interspersed on the wrinkled graphene ball. The crumpled ball composite possesses excellent dispersity in polyalkylene glycol base oil without depending on surface modifiers. Compared with the conventional phosphate esters lubricant, our results indicate MGCB could vastly improve the lubrication performance of polyalkylene glycol with an extremely low concentration (0.05 wt%) at elevated temperature (150 °C), showing a friction reduction of 47% and a wear reduction of 30% compared with the conventional phosphate esters lubricant (tricresyl phosphate, TCP). This is because crumpled ball potentiates synergistic lubrication effect within the boundary lubrication. Overall, we envision our designed self-dispersed MGCB has significant potential in tribological application at elevated temperature.

Machine Learning Approach for LPRE Bearings Remaining Useful Life Estimation Based on Hidden Markov Models and Fatigue Modelling

Ball bearings are one of the most critical components of rotating machines. They ensure shaft support and friction reduction, thus their malfunctioning directly affects the machine’s performance. As a consequence, it is necessary to monitor the health conditions of such a component to avoid major degradations which could permanently damage the entire machine. In this context, HMS (Health Monitoring Systems) and PHM (Prognosis and Health Monitoring) methodologies propose a wide range of algorithms for bearing diagnosis and prognosis. The present article proposes an end-to-end PHM approach for ball bearing RUL (Remaining Useful Life) estimation. The proposed methodology is composed of three main steps: HI (Health Indicator) construction, bearing diagnosis and RUL estimation. The HI is obtained by processing non-stationary vibration data with the MODWPT (Maximum Overlap Discrete Wavelet Packet Transform). After that, a degradation profile is defined and coupled with crack initiation and crack propagation fatigue models. Lastly, a MB-HMM (Hidden Markov Model) is trained to capture the bearing degradation dynamics. This latter model is used to estimate the current degradation state as well as the RUL. The obtained results show good RUL prediction capabilities. In particular, the fatigue models allowed a reduction of the ML (Machine Learning) model size, improving the algorithms training phase.

Oxidative Hydraulic Fracturing Fluid to Enhance Production from Source Rock Reservoirs

Summary The steep production declines generally observed after hydraulic fracturing in unconventional source rock reservoirs has been attributed to several potential causes. Recently, a new additive to the stimulation fluid system was proposed to extend economical longer-term production from these formations. Oxidizer-laden fracturing fluid systems are shown to create cracks and deep channels within the organic matter present in the source rock, such as kerogen, thereby increasing the source rock permeability and enhancing the hydraulic conductivity of the exposed fracture faces. To this end, the fluid design and recommendations for its application are illustrated herein. Oxidants composed of oxychlorine (ClOn−) and oxybromine (BrOn–) (where n = 0 to 4) are effective for kerogen depolymerization or degradation at depth. This study illustrates the beneficial effects of two specific oxidizers—sodium chlorite (NaClO2) and sodium bromate (NaBrO3)—on kerogen-rich source rock subjected to in-situ reservoir conditions. Source rock samples were cut and polished to test the oxidizer’s impact on the organic and inorganic regions. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were performed on the rock surface to identify specific organic matter features. The samples were then chemically treated with varying conditions of NaClO2 or NaBrO3 (concentration range: 0.013–0.054 M; temperature: 150°C; and time: 3–24 hours). Samples were returned to the scanning electron microscope for post-treatment analysis. Furthermore, the oxidants were packaged within a slickwater hydraulic fracturing fluid system for field application, and their effects on viscosity and friction reduction were also studied. SEM images and EDS maps of kerogen-rich rock samples observed before and after treatment with oxidizing fluid showed a series of cracks formed throughout the organic matter domains, where increasing the concentration of oxidizer in the treatment fluid showed a clear increase in the prevalence of cracks throughout the surface. The effect of time was also observed, as short treatment times resulted in porosity/permeability creation in the kerogen, though longer treatment times were associated with more severe degradation. Optimal conditions for NaClO2 and NaBrO3 concentrations in the additive fluid systems were different and will be herein highlighted. Each oxidizer (10–20 pptg concentration) was added to slickwater with variable friction reducer concentration (1 gpt, 2 gpt, and 4 gpt), and shear sweeps performed at both 70°F and 180°F. A negligible difference is observed between the viscosities of the base fluid and the fluid with either oxidant at low friction reducer concentration. Meanwhile, flow loop tests demonstrated that the oxidizer did not affect the friction reducer except to slightly boost the performance due to the salt effect on the polymer. Two strong oxidants, available as commodity chemicals, are shown to be effective in cracking kerogen and any present organic matter, thus creating permeable channels and enhancing the overall permeability of the exposed source rock fracture faces. Meanwhile, the proposed fracturing fluid additives display good compatibility with other slickwater fluid components, demonstrating the potential for universal usage in unconventional stimulations. The recommendations for its application as a fluid additive in slickwater are herein illustrated.

Reduction in Powder Wall Friction by an a-C:H:Si Film

The wall friction angle is an important parameter in powder flow. In a recent study for various powders, a reduction in the wall friction angle for steel was demonstrated by the application of an a-C:H:Si film on the steel surface. This work presents the results of a study of this effect in more detail regarding the influence of the powder material, the wall normal stress and the particle size of the powder for mass median diameters from 4 µm to approximately 150 µm. The wall friction angles were measured using a Schulze ring shear tester for three different powder materials: aluminum oxide, calcium carbonate and silicon carbide. The results showed little difference with respect to powder chemistry. For the coarser powders, the reduction in the wall friction angle due to the a-C:H:Si coating was highest (10° to 12°) and rather stress-independent, while for the fine and medium-size powders the reduction was lower and stress-dependent. With increasing wall normal stress, the reduction in the wall friction angle increased. These results can be explained by the friction reduction mechanism of a-C:H:Si, which requires a certain contact pressure for superficial graphitization.

Numerical investigation of reaction driven magneto-convective flow of Sisko fluid

In many geothermal engineering applications involving exothermic chemical reactions, gravity, and buoyancy forces significantly enhance yields, especially during the thermal and catalytic cracking involving high temperature and concentration differences of some heavy hydrocarbons. This investigation deals with the numerical examination of nonlinear double convective flow, heat, and mass transfer of reactive Sisko fluid based on chemical kinetics theory for fluid flowing through a nondeformable porous medium. The governing equations are formulated and made dimensionless, and numerical results are obtained by applying the Spectral Chebyshev Collocation Method and validated with the Shooting-RK4 method. The effects of several parameters on the flow, heat, mass transfer, and thermal stability of the combustible fluid are documented in graphical and tabular forms, with detailed explanations. The computation reveals that buoyancy forces and Frank–Kamenetskii parameters encourage a velocity and temperature distribution rise. This analysis gives an insight into friction reduction in many heat and mass transfer thermophysical systems such as automobiles, power generations, and lots more.

Liquid Metal-Based Supramolecular Oleogel Lubricants Constructed by Dynamic Disulfide and Hydrogen Bonds for Antiwear and Friction Reduction

Liquid Metal-Based Supramolecular Oleogel Lubricants Constructed by Dynamic Disulfide and Hydrogen Bonds for Antiwear and Friction Reduction

Influence of Chemical Side Groups Containing Aromatic Rings: Flow-Induced Friction Enhancement or Reduction

Influence of Chemical Side Groups Containing Aromatic Rings: Flow-Induced Friction Enhancement or Reduction

Influence of Electrical Stimulation on the Friction Performance of LiPF6-Based Ionic Liquids

This work studied the influence of the voltage parameters on the friction and superlubricity performances of LiPF6-based ionic liquids (ILs). The results show that the voltage direction and magnitude greatly affected the friction performances of ILs and that macroscale superlubricity can be achieved with a stimulation of −0.1 V. The surface analysis and experiment results indicate that the voltage magnitude influences the coefficient of friction (COF) by determining the types of substances in the tribochemical film formed on the ball, while the voltage direction influences the COF by affecting the adsorption behavior of Li(PEG)+ ions on the ball. At −0.1 V, the cation group Li(PEG)+ adsorption film and FeOOH-containing tribochemical film contribute to friction reduction. The formation of FexOy within the tribochemical film results in an increase in friction at −0.8 V. The limited adsorption of Li(PEG)+ ions and the formation of FexOy contribute to the elevated COF at +0.1 V. This work proves that the friction performances of LiPF6-based ILs could be affected by voltage parameters. A lubrication model was proposed hoping to provide a basic understanding of the lubrication mechanisms of ILs in the electric environment.