Friction and wear of PPS/CNT nanocomposites with formation of electrically isolating transfer films

The effects of various fillers, i.e. short carbon fibers (SCF), graphite flakes, carbon nanotubes (CNT) and their combinations, on the tribological behavior and transfer film structures of polyphenylensulfide (PPS) were investigated. The hybrid composite filled with combined SCF, graphite and CNT shows the best tribological performance among the composites studied due to a fast formation of a groove-filling transfer film on the counterpart. Especially when measuring the electrical conductivity of the sliding contact during the friction process, a close relationship between the tribological behavior and the structure of the isolating transfer film was evident.     

Tunable friction behavior of oriented carbon nanotube films

Measured friction coefficients of carbon nanotubes vary widely from μ < 0.1–μ > 1.0 [1–6], while theoretical studies suggest intrinsically high friction coefficients, approaching unity [7]. Here we report that measured friction coefficients of MWNT films are strong functions of surface chemistry and temperature, but are not dependent on the presence of water vapor. We hypothesize that the origin of the temperature dependence arises from the interaction of the surface chemical groups on the nanotubes [8–12] and rubbing counterface. The friction coefficient of individual films can be easily tuned by changing the surface temperature and chemistry of either the countersurface or the nanotubes, we have demonstrated the ability to create and control high and low friction pairs through plasma treatments of the nanotube films with argon, hydrogen, nitrogen, and oxygen. This behavior is completely reversible, and when coupled with the superior strength, thermal, and electrical properties of nanotubes, provides a versatile tunable, multifunctional tribological system.     

Tribological behaviors of surfactant-functionalized carbon nanotubes as lubricant additive in water

The multi-walled carbon nanotubes (MWCNTs) are functionalized by self-assembled surfactant layers after sonication in anionic surfactant sodium dodecyl sulfate (SDS) aqueous solution. The tribological properties of the SDS-functionalized MWCNTs as additive in water-based lubricants were evaluated with a four-ball tester. The results show that the SDS-functionalized MWCNTs exhibit good anti-wear and friction reduction properties as well as enhanced load-carrying capacity. The maximum non-seizure load (PB value) can be raised about 3–7 times when SDS-functionalized MWCNTs were added into water. The mechanism of SDS-functionalized MWCNT additive was investigated with scanning electron microscopy (SEM), Auger electron spectroscopy (AES), and Raman spectroscopy. These preliminary results show a promise in applications of surfactant functional carbon nanotubes as an additive in water.     

聚氨酯/碳纳米管复合材料的摩擦性能

采用溶液共混法制备聚氨酯/碳纳米管复合材料,探讨碳纳米管含量和超声分散时间对聚氨酯/碳纳米管复合材料摩擦性能的影响。结果表明:随着碳纳米管含量的增加,聚氨酯/碳纳米管复合材料的摩擦因数逐渐降低,随着载荷的增大,摩擦因数有所减小;超声分散时间对聚氨酯/碳纳米管复合材料摩擦性能影响不大;碳纳米管具有较好的润滑性质,可以降低聚氨酯/碳纳米管复合材料的摩擦因数,改善聚氨酯的摩擦性能。     

Lubrication Effect of the Paraffin Oil Filled with Functionalized Multiwalled Carbon Nanotubes for Bismaleimide Resin

Multiwalled carbon nanotubes (MWCNTs) were functionalized and were used as additives in paraffin oil to improve its lubrication effect for bismaleimide resin. The tribological behavior of bismaleimide resin lubricated by the paraffin oil filled with the functionalized carbon nanotubes was investigated by friction and wear tester. The wear surface of the resin with steel ball as tribopair was analyzed by means of scanning electron microscopy (SEM). It was found that the addition of this kind of functionalized MWCNTs effectively reduced the friction coefficient. An optimal additive concentration existed in the system and was found to be 0.025 wt%. A lubrication model for the resin and steel ball system was postulated and it was the isolating effect and bearing structure of f-MWCNTs that played a key role in friction and wear reduction.     

Effect of Carbon Nanotube Addition on Tribological Behavior of UHMWPE

Carbon nanotubes (CNTs) were added to Ultra-high molecular weight polyethylene (UHMWPE) to improve the tribological properties of UHMWPE. CNTs which have a diameter of about 10–50 nm, while their length is about 3–5 nm were produced by the catalytic decomposition of acetylene gas using a tube furnace. Ball-on-disc-type wear tests were performed to evaluate the tribological performance of UHMWPE composites reinforced with CNTs. The results showed that addition of carbon nanotube up to 0.5 wt% lowered wear loss significantly and increased friction coefficient slightly. Also through the scanning electron microscope (SEM), the surfaces of UHMWPE were observed and analyzed to discuss the tribological behavior of CNT added UHMWPE.     

Influence of Surface Roughness on the Lubrication Effect of Carbon Nanoparticle-Coated Steel Surfaces

In the present study, a systematic evaluation of the influence of the surface roughness on the lubrication activity of multi-wall carbon nanotubes (MWCNT) and onion-like carbon (OLC) is performed. MWCNT and OLC are chosen as they both present an sp²-hybridization of carbon atoms, show a similar layered atomic structure, and exhibit the potential to roll on top of a surface. However, their morphology (size and aspect ratio) clearly differs, allowing for a methodical study of these differences on the lubrication effect on systematically varied surface roughness. Stainless steel platelets with different surface finishing were produced and coated by electrophoretic deposition with OLC or MWCNT. The frictional behavior is recorded using a ball-on-disk tribometer, and the resulting wear tracks are analyzed by scanning electron microscopy in order to reveal the acting tribological mechanisms. It is found that the lubrication mechanism of both types of particles is traced back to a mixture between a rolling motion on the surfaces and particle degradation, including the formation of nanocrystalline graphitic layers. This investigation further highlights that choosing the suitable surface finish for a tribological application is crucial for achieving beneficial tribological effects of carbon nanoparticle lubricated surfaces.     

Influence of the multi-walled carbon nanotube and short carbon fibre composition on tribological properties of epoxy composites

The present research work deals with the development of a novel polymer composite for brake pad applications. The composite that was used consists of epoxy resin, carbon fibre and carbon nanotubes in varying weight percentage. The tribological performance of three different samples was tested using a pin-on-disc under dry contact condition. The results indicated that the sample filled with short carbon fibres (SCF), and multi-walled carbon nanotube (MWCNT) had superior performance. Reduction in wear rate was observed due to synergism between SCF and MWCNT as compared to SCF only. Scanning electron microscopy was subsequently performed on all samples. The micrographs show changes in the structural formation after the incorporation of SCFs and MWCNT. This increased composite structural strength and explains why SCF and MWCNT’s hybrid-filled composite material has better tribological properties.     

碳纳米管直径对丁腈橡胶复合材料性能影响的分子模拟

利用分子动力学模拟研究碳纳米管(CNTs)直径改变时对丁腈橡胶(NBR)基体力学及摩擦学性能的影响。采用恒应变法考察不同复合材料模型的力学性能，结果表明复合材料力学性能随着NBR基体中CNTs直径增大呈现先增加后减小的趋势。剪切模拟结果表明，剪切后复合材料基体中分子链发生了不同程度的断裂，出现了聚合物分子链向摩擦界面聚集的现象，其中较大直径CNTs增强NBR复合材料中分子链相对完整连续，摩擦学性能改善效果更好。较大直径CNTs对NBR基体具有显著的增强效果，限制了NBR分子链的活动能力，更多的分子链聚集在CNTs周围，复合材料体系致密性及稳定性提高，从而改善了CNTs/NBR复合材料力学及摩擦学性能。其中直径(6,6)CNTs增强NBR复合材料具有更高的剪切模量，力学性能优异，表现出了更好的摩擦磨损性能。     

Various MoS2-, WS2- and C-Based Micro- and Nanoparticles in Boundary Lubrication

Various solid lubricant particles have been experimentally evaluated as possible additives to oils. However, information in terms of a direct comparison of their tribological properties is still missing. In this study, we have compared the tribological properties of seven different solid lubricant micro- and nanoparticles as additives in polyalphaolefin (PAO) oil: MoS₂ nanotubes, MoS₂ platelets (2 and 10 μm), WS₂ nanotubes, WS₂ fullerene-like nanoparticles, graphite platelets (20 μm) and multi-walled carbon nanotubes. The experiments were performed in the boundary lubrication regime under a contact pressure of 1 GPa (Hertz, max) using a ball-on-disc tribotester. In general, the particles significantly decreased the friction and wear compared to the base PAO oil. We found that it was the material of the particles that largely determined their tribological performance. The effect of the size of the particles was much less important, and the morphology (shape) of the particles had little or no influence. We have also investigated the effect of ultrasonication during suspension preparation on particle damage and found that the solid lubricant particles were not notably affected, except the MoS₂ and WS₂ nanotubes, which became somewhat shorter.     

Tribological properties of carbon-nanotube-reinforced copper composites

Tribological properties of carbon-nanotube-reinforced copper composites were investigated using a pin-on-disk test rig under dry conditions. The composites containing 4–16 vol% carbon nanotubes (CNTs) were fabricated by a powder-metallurgy technique. The tests were carried out at normal loads between 10 and 50 N, and the effect of volume fraction of CNTs on tribological behavior of the composites was examined. The composites revealed a low coefficient of friction compared with the copper matrix alloy. Due to the effects of the reinforcement and reduced friction, the wear rate of the composites decreased with increasing volume fraction of CNTs at low and intermediate loads. The composites with a high volume fraction of CNTs exhibited high porosity and their wear resistance decreased under high-load conditions.     

Effect of Humidity on the Tribological Properties of Carbide-Derived Carbon (CDC) Films on Silicon Carbide

The effect of humidity on the tribological behavior of carbide-derived carbon (CDC) films prepared by high-temperature chlorination of silicon carbide was examined. Pin-on-disk tribological tests indicate that CDC, unlike graphite or glassy carbon, performs better in dry nitrogen (less than 0.05 friction coefficient at 0% humidity) than in humid air. This versatility is explained by the onion-like structure of the nanoporous CDC coating.     

Free vibration analysis of functionally graded CNT-reinforced nanocomposite beam using Eshelby-Mori-Tanaka approach

This work deals with the effect of agglomeration and distribution of carbon nanotube on the free vibration characteristics of a functionally graded nanocomposite beams reinforced by single-walled carbon nanotubes (SWCNTs) by employing an equivalent fiber based on the Eshelby-Mori-Tanaka approach. Different SWCNTs distributions in the thickness directions are introduced to improve fundamental natural frequency of polymer composite beam. The micromechanics models used in the study include a two parameter model of agglomeration. An embedded carbon nanotube in a polymer matrix and its surrounding inter-phase is replaced with an equivalent fiber for predicting the mechanical properties of the carbon nanotube/polymer composite. The system of equations of motion is derived by using the principle of virtual work under the assumptions of the Euler-Bernoulli beam theory. The finite element method is employed to obtain a numerical approximation of the motion equation. Numerical results are presented in both tabular and graphical forms to figure out the effects of nanotube agglomeration, CNTs distribution and boundary conditions on the dynamic characteristics of the beam. The above mentioned effects play very important role on the dynamic behavior of the beam.     

Tribological Studies on Scuffing Due to the Influence of Carbon Dioxide Used as a Refrigerant in Compressors

Because hydrofluorocarbon (HFC) refrigerants in air-conditioning systems are known to have a negative effect on the environment, carbon dioxide (CO₂) is a candidate as a replacement refrigerant. Research work related to CO₂ as a refrigerant has been focused primarily on its thermodynamic performance, whereas work in the area of tribology related to carbon dioxide is absent. In this study, the effects of CO₂ used as a refrigerant on the tribological behavior of surf aces in contact in such systems were investigated. Controlled experiments were performed at constant loads in environments of CO₂ and the conventional HFC refrigerant, R134a, as well as under conditions of step-increasing loads in the presence of refrigerant (CO₂ or R134a) and polyalkylene glycol lubricant. The experiments were performed on a high-pressure tribometer that is particularly suited for tribological testing of compressor contact interfaces. The tribological behavior of contacting surfaces in a CO₂ environment was nearly identical to that in an R134a environment when tested under the same operating conditions.     

多壁碳纳米管改性UHMWPE的热膨胀和摩擦学性能研究

为了降低摩擦副用聚合物的热膨胀系数,用多壁碳纳米管(MWCNTs)改性超高分子量聚乙烯(UHM-WPE),通过热压成型法制备MWCNTs/UHMWPE复合材料.通过测量电导率计算渗流阈值来表征分散性;用热膨胀仪(DIL)测试复合材料的热膨胀率,并在干摩擦环境下,测试不同MWCNTs含量复合材料的摩擦学性能.结果表明:通...     

The surface and tribological chemistry of carbon tetrachloride on iron

The thermal decomposition of carbon tetrachloride on clean iron was studied in ultrahigh vacuum using molecular beam strategies, where it is found that carbon tetrachloride thermally decomposes on the surface to deposit iron and carbon with exactly identical kinetics as found at high pressures. No gas‐phase products are detected and the activation energy for the reaction (14.2 ± 0.5 kcal/mol) is in good agreement with the value measured at high pressures. Little carbon is detected on the surface using Auger spectroscopy following reaction and it is found that this diffuses into the surface much faster when formed from CCl₄ than from CH₂Cl₂. This effect is ascribed to the effect of co‐adsorbed chlorine on the adsorbed carbon, which is proposed to decrease the activation energy for diffusion into the bulk of the sample. This effect explains the increased tendency for carbon tetrachloride to form carbides under extreme‐pressure tribological conditions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Tribological interaction between multi-walled carbon nanotubes and silica surface using lateral force microscopy

This work presents the tribological interaction between multi-walled carbon nanotubes (MWCNTs) and silica surface using lateral manipulation in the atomic force microscope (AFM). The MWCNT is mechanically manipulated by a pyramidal silicon probe of an AFM using the same scan mechanism as in the imaging mode. With a controlled normal force of the AFM probe, it was found that lateral force applied to the MWCNT could overcome the tribological adhesion between MWCNT and silica surface, causing individual MWCNT to rotate on the silica. According to the results, the shear stresses due to tribological interacting with the MWCNTs and the silica are 59.6 MPa and 64.8 MPa for the MWCNT 1 (100 nm diameter) and the MWCNT 2 (60 nm diameter), respectively. Experimental results show that the shear stress increases with the increasing rotation angle for each manipulation, from which we determine the linear fitting function. In addition, we determine the relationship between push point and pivot point to realize the rotation behavior. The implications of tribological interaction between the MWCNTs and silica surface are discussed in detail.     

The influence of added carbon nanotubes on the properties of the carbon‐fiber‐reinforced paper‐based wet clutch friction materials

Different carbon nanotubes (CNT) content was used to investigate the influence on physical properties, microstructure, tribological behaviour and thermal endurance properties of the materials. Experimental results show that the bulk density of the specimens increase with the increase of the CNT content, and the open porosity of the samples gradually reduced, whereas the CNT content increases. When comparing the tribological properties of the specimens with different CNT content, specimens that contain 4 wt.% carbon nanotubes show the highest dynamic friction coefficient and the lowest variation coefficient of the dynamic friction coefficient. Moreover, the specimens exhibit more thermal stability and lower weight loss after adding the CNT. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of carbon nanotube addition on the tribological behavior of carbon/carbon composites

Carbon nanotube composite coatings were applied onto carbon/carbon composites to improve wear properties. Carbon nanotubes have been prepared by catalytic pyrolysis of hydrocarbons. The nanotube slurry was prepared by addition of phenolic resin and solvent to infiltrate into C/C composites. The nanotube added composites were then carbonized in a nitrogen atmosphere. Ball-on-disc type wear tests were performed to evaluate the tribological properties of the carbon nanotube added carbon composites. The result showed that addition of nanotube has the potential to increase the wear resistance of carbon composites. Changes in Raman spectra, morphology and surface damage were studied to explain observed wear behavior.     

不同维度碳纳米材料对水润滑橡胶轴承摩擦磨损性能的影响

以碳纳米管(MWNT)、多层石墨烯(MLG)和纳米石墨(NG)为填料,采用溶液共混法制备3种不同维度碳纳米材料改性的丁腈橡胶基复合材料试样。在水润滑及重载工况下对3种材料进行摩擦磨损试验,结合摩擦因数、表面形貌和磨损量等参数的测试对材料的摩擦学性能进行比较,通过SEM电镜表征,揭示不同维度碳纳米填料的作用机制。结果表明:碳纳米材料的加入能够明显降低丁腈橡胶材料低速下的摩擦因数,提高其抗磨性能,其中三维结构纳米石墨的改性效果最优。3种碳纳米填料的作用机制分别为:一维碳纳米管因长径比大,易与橡胶分子形成物理交联点,并且起到微轴承作用;二维石墨烯易于脱落转移形成良好的固体润滑膜来改善摩擦磨损性能;三维纳米石墨由于颗粒的粗糙表面与橡胶基体相互嵌入,能增加黏附力,且能减少界面脱黏现象。