Friction Properties of Fluorinated Graphitized Carbon Blacks

The tribologic properties of graphitized carbon blacks and their fluorinated derivatives are investigated as a function of the fluorination rate. Very low intrinsic friction coefficients are obtained for highly fluorinated compounds. The correlation of the tribologic results and structural investigations of the initial compounds by TEM strongly suggests that the friction mechanisms involve surface effects in the early stage of friction. Long-term tribologic experiments and Raman analyses point out an evolution of the structure and composition of the tribofilms during the friction process leading to similar friction properties of the tribofilms. Wear studies revealed that highly fluorinated derivatives appear less efficient than pristine and weakly fluorinated compounds.     

Tribological Properties of Room Temperature Fluorinated Graphite Heat-Treated Under Fluorine Atmosphere

This work is concerned with the study of the tribologic properties of room temperature fluorinated graphite heat-treated under fluorine atmosphere. The fluorinated compounds all present good intrinsic friction properties (friction coefficient in the range 0.05–0.09). The tribologic performances are optimized if the materials present remaining graphitic domains (influenced by the presence of intercalated fluorinated species) whereas the perfluorinated compounds, where the fluorocarbon layers are corrugated (armchair configuration of the saturated carbon rings) present higher friction coefficients. Raman analyses reveal that the friction process induces severe changes in the materials structure especially the partial re-building of graphitic domains in the case of perfluorinated compounds which explains the improvement of μ during the friction tests for these last materials.     

Tribological Properties of Fluorinated Carbon Nanofibres

This work is concerned with the study of the tribological properties of fluorinated carbon nanofibres with various fluorination rates. The tribological tests, carried out in the presence of pentane and in air after liquid’s evaporation demonstrate good friction properties for all the compounds (the friction coefficients ranging between 0.04 and 0.06 in the presence of pentane and between 0.07 and 0.09 in air). Raman analyses reveal that the friction process induces a partial deterioration of the carbon fibres and SEM studies show that the tribofilm is composed of individual fibres embedded in a more disordered carbonaceous matrix. The fibrous nature of the tribofilm and the experimental relationship between friction coefficient and fluorination rate strongly support that friction properties of fluorinated carbon nanofibres are governed by surface fibres interaction. The modification of the nanofibres surface tension by action of pentane or optimum fluorination rate leads to a lowering of interfibres interactions resulting in an improvement of the friction properties.     

Carbon nanotubes and other graphitic structures as contaminants on evaporated carbon films

Evaporated carbon support films for transmission electron microscopy (TEM) often contain fullerene-like structures such as nanotubes and nanoparticles. This could cause serious confusion in TEM studies of fullerene-related carbons. Other, poorly graphitized, particles are also frequently seen.     

Comparison of the efficiency of modification of SHMPE by nanofibers (C,Al<Subscript>2</Subscript>O<Subscript>3</Subscript>) and nanoparticles (Cu,SiO<Subscript>2</Subscript>) when obtaining antifriction composites

The effect of various nanofillers (nanofibers of Al₂O₃ and carbon, nanopowders of copper and SiO₂) on the physico-mechanical and tribotechnical properties of superhigh-molecular polyethylene is investigated. It is determined that the modification of superhigh-molecular polyethylene by nanofibers and nanoparticles within the limits of 0.1–05 wt % results in a substantial rise in its deformation-strength characteristics and a multifold increase in its tribotechnical characteristics. By the methods of X-ray structure analysis, infrared spectroscopy, and electron microscopy, it is shown that modification of the polymer by the mentioned nanofillers results in the formation of an ordered (lamellar) permolecular structure. It is revealed that nanofibers form a stable film of friction transfer more quickly in comparison with nanoparticles. The optimum compositions of nanofillers, which determine the high wear resistance and the low constant of friction for polymer, are determined. The mechanical activation of the binder and filler powders provides a uniform distribution of the nanopowder within the binder and additionally enhances the physico-mechanical and tribotechnical properties of the composite.     

An EELS-based study of the effects of pyrolysis on natural carbonaceous materials used for activated charcoal preparation

Electron energy‐loss spectroscopy (EELS) has been used to characterize the electronic structure of charcoal phases at the nanoscale, thus demonstrating that the technique can be applied to environmental science. Activated charcoal is extensively used to remove pollutants from liquid and gaseous sewage. It is mainly obtained by activation of coke or charcoal produced from ligneous precursors. The present study concerns the use of by‐products of local Caribbean agriculture, such as sugar cane bagasse, fruit stones and seeds, for use as activated charcoal precursors. Charcoal phases are prepared by high‐temperature pyrolysis of lignocellulosic raw materials under a nitrogen gas flow. With the aim of optimizing the pyrolysis temperature and duration and oxygen content, the concentration of carbon sp² hybridized chemical bonds and structural ordering have been followed by EELS for different treatment temperatures. To quantify the carbon sp² content, near edge structure (NES) at the carbon K edge has been measured to determine the strength of π → π* and 1s → π* transitions. Three precursors of plant origin, shells of Terminalia catappa and Acrocomia karukerana and seeds of Psidium guajava, with the pyrolysis temperatures between 600 and 900 °C, were investigated. The fraction of carbon sp² bonding is found to increase when the temperature rises from 600 °C to the range 700–750 °C and becomes stable at higher temperatures. For temperatures in excess of 700 °C, structural ordering probably occurs and well‐defined 1s → σ* NES is present, whose intensity increases with increasing preparation temperature. For the highest temperature of around 900 °C, the structure of the final product is less well organized than graphitized carbon but a few per cent of a highly ordered phase is found.     

Nonlinear viscose flow induced nonlocal vibration and instability of embedded DWCNC via DQM

Nonlinear thermo free vibration and instability of viscose fluid-conveying double-walled carbon nanocones (DWCNCs) are studied using Hamilton’s principle and differential quadrature method (DQM). The small-size effects on bulk viscosity and slip boundary conditions of nanoflow through Knudsen number (Kn) is considered. The nanocone is simulated as a clamped-clamped Euler-Bernoulli’s beam embedded in an elastic foundation of the Winkler and Pasternak type. The van der Waals (vdW) forces between the inner and outer nanocones are taken into account. The detailed parametric study is conducted, focusing on the combined effects of the nonlocal parameter, apex angles, aspect ratio, temperature change, fluid viscosity, boundary conditions and the elastic medium coefficient on the dimensionless frequency and critical fluid velocity of DWCNCs. The results show that the small-size effect on flow field is remarkable on frequency and critical fluid velocity of DWCNC. Also, the nonlinear frequency and critical flow velocity decrease with increasing the nonlocal parameter and cone semi-vertex angle. The results are in good agreement with the previous researches.     

Local lattice distortions in spherical carbon nanoparticles as studied by HRTEM image analysis

The study of lattice distortions in structures with spherical or cylindrical geometry is of growing interest in the field of carbon nanoparticles (onions, nanotubes, etc.). We report an image analysis procedure entirely performed in reciprocal space which provides a global map of the inter-shell distances in carbon nanoparticles. This procedure is applied to carbon nanoparticles with a size of 100 nm that are generated under CVD conditions and exhibit positive as well as negative curvature of the basal lattice planes. These nanoparticles are subjected to intense electron irradiation under the beam of a high-voltage electron microscope with an acceleration voltage of 1.25 MeV. We observe a compression in their centre and a dilation of the outer shells. The reciprocal-space analysis of the high-resolution electron microscopy images opens the way to investigate the stability and equilibrium structure of carbon nanoparticles and to conclude on the formation mechanism.     

类富勒烯碳薄膜的结构演变及摩擦学性能研究

通过等离子体增强化学气相沉积技术,以不同沉积时间在硅表面上制备类富勒烯碳薄膜,探究类富勒烯碳薄膜结构演变和摩擦学性能随沉积时间变化规律。利用拉曼光谱和透射电子显微镜,考察类富勒烯碳薄膜微结构和表面形貌随沉积时间的变化。结果表明:碳薄膜内类富勒烯结构含量随沉积时间先增加后保持不变;采用沉积时间为3 h的类富勒烯碳薄膜组成摩擦配伍对,当载荷从8 N增加到14 N时,摩擦因数从0.013降至0.006,即随载荷的增加实现了由低摩擦向超滑的转变。这是因为摩擦诱使类富勒烯碳薄膜发生结构转变,并形成有利于减少摩擦的类球状或外部石墨壳层闭合的纳米颗粒。     

Effects of cold working and heat treatment on microstructure and wear behaviour of Cu–Be alloy C17200

The effects of cold work process between aging and solution heat treatment on the microstructure, hardness and the tribologic behaviour of a copper–beryllium (Cu–Be) alloy C17200 were investigated. The wear behaviour of the alloys was studied using ‘pin on disc’ method under dry conditions. The results show that the formation of fine grained structure and γ phase particles enhances the mechanical properties of the alloy; nonetheless, they do not reduce the wear rate. This is attributed to the capability of the softer specimens to maintain oxygen rich compounds during the dry sliding test.     

Tribological behavior and graphitization of carbon nanotubes grown on 440C stainless steel

Vertically aligned carbon nanotube (CNT) arrays were directly grown onto 440C stainless steel substrates by plasma-enhanced chemical vapor deposition. Tribological properties of both short and long CNTs samples were studied under normal loads of 10 g, 25 g and 100 g. The CNTs had a steady-state friction coefficient of about 0.2 in humid air. In dry nitrogen, a friction of 0.2 was measured under a load of 10 g while high friction was measured at 25 g and 100 g loads. No significant variation of tribological behavior was measured between the short and long CNTs samples. SEM observations showed that rubbing caused the CNTs to align or lay down along the wear scar. They formed aggregates and were compressed by rubbing, which resulted in layer-structured graphite formations. SEM observation of the wear scars revealed loss of CNT structures accompanied by the appearance of dark areas. Micro Raman spectroscopic studies demonstrated that the dark areas were graphitized CNTs. Shear stress aligned the basal planes of the small graphene sheets in the CNT layers to the low friction orientation and eventually caused formation of more ordered graphite. The tribological formation of interfacial carbon layers increased with increasing stress from higher loads.     

Comparing electron tomography and HRTEM slicing methods as tools to measure the thickness of nanoparticles

Nanoparticles’ morphology is a key parameter in the understanding of their thermodynamical, optical, magnetic and catalytic properties. In general, nanoparticles, observed in transmission electron microscopy (TEM), are viewed in projection so that the determination of their thickness (along the projection direction) with respect to their projected lateral size is highly questionable. To date, the widely used methods to measure nanoparticles thickness in a transmission electron microscope are to use cross-section images or focal series in high-resolution transmission electron microscopy imaging (HRTEM “slicing”). In this paper, we compare the focal series method with the electron tomography method to show that both techniques yield similar particle thickness in a range of size from 1 to 5 nm, but the electron tomography method provides better statistics since more particles can be analyzed at one time. For this purpose, we have compared, on the same samples, the nanoparticles thickness measurements obtained from focal series with the ones determined from cross-section profiles of tomograms (tomogram slicing) perpendicular to the plane of the substrate supporting the nanoparticles. The methodology is finally applied to the comparison of CoPt nanoparticles annealed ex situ at two different temperatures to illustrate the accuracy of the techniques in detecting small particle thickness changes.     

类金刚石薄膜摩擦机理及其摩擦学性能影响因素的研究现状

类金刚石薄膜(DLC)具有十分优异的减摩耐磨性能,是一种极具发展潜力的固体润滑材料。但其摩擦学性能受到很多因素的影响,这些因素主要可以分为两大类:固有因素和外在因素。在不同的固有因素和外界因素影响下DLC薄膜的摩擦学性能会产生较大差异,这大大制约了人们对其摩擦学行为及摩擦机理的认识,限制了其应用范围的扩展。总结了目前有关DLC薄膜摩擦机理的三种理论,即转移膜理论、滑行界面石墨化理论和化学吸附钝化悬键理论,并在此基础上概括分析了各固有因素和外界因素对DLC薄膜摩擦学性能的影响及其机理,提出未来可以从基础理论和相关技术两方面对DLC薄膜的摩擦学性能展开深入研究。     

激光织构和碳基薄膜复合处理提高钛合金摩擦学性能研究

在重载滑动干摩擦条件下，对比不同织构密度的钛合金表面的摩擦学性能；在耐磨性最好的织构密度钛合金表面再制备碳基薄膜，并与直接在钛合金表面制备的碳基薄膜的摩擦学性能进行对比。结果表明：3种低织构密度条件下，TC4钛合金的摩擦因数减小、磨损率降低；随着织构密度的增大，钛合金材料的摩擦因数变化极小，磨损率有所增加；在织构密度5.95%的钛合金表面制备的碳基薄膜，因织构微凹处产生的小微湍流，减少了摩擦阻力，使得其摩擦因数相比直接在钛合金表面制备的碳基薄膜的摩擦因数有所减小。织构化碳基薄膜的磨损率比钛合金的磨损率降低了99.31%，比直接在钛合金表面制备碳基薄膜的磨损率也降低了约60%，这是因为高接触应力摩擦过程中触发石墨化转变，被磨损的石墨化颗粒碎片嵌入织构微凹中，抑制了摩擦接触界面的磨损行为。     

MoS2的表面修饰与摩擦学性能研究

分别用油酸（OA）、司班-60（Span-60）、十六烷基三甲基溴化铵（CTAB）-二烷基二硫代磷酸吡啶盐（Py-DDP）对MoS2纳米微粒进行表面修饰，考察了修饰后微粒的形貌、在液体石蜡中的分散稳定性和润滑性能，并采用四球摩擦磨损机测试了其摩擦学性能。结果表明，选用不同修饰剂所得到的修饰MoS2纳米微粒的稳定性和摩擦学性能均有不同程度的提高，其中以CTAB—PyDDP修饰MoS2纳米微粒的分散稳定性更佳，摩擦学性能最好。     

Mechanics of single-walled carbon nanotubes inside open single-walled carbon nanocones

This study investigates the mechanical characteristics of single-walled carbon nanotubes (CNTs) inside open single-walled carbon nanocones (CNCs). New semi-analytical expressions are presented to evaluate van der Waals (vdW) interactions between CNTs and open CNCs. Continuum approximation, along with the the Lennard-Jones (LJ) potential function, is used in this study. The effects of geometrical parameters on alterations in vdW potential energy and the interaction force are extensively examined for the concentric CNT-open CNC configuration. The CNT is assumed to enter the nanocone either through the small end or the wide end of the cone. The preferred position of the CNT with respect to the nanocone axis is fully investigated for various geometrical parameters. The optimum nanotube radius minimizing the total potential energy of the concentric configuration is determined for different radii of the small end of the cone. The examined configuration generates asymmetric oscillation; thus, the system constitutes a nano-oscillator.     

The Role of Nickel in Ni-Containing Nanotubes and Onions as Lubricant Additives

We studied tribological properties of Ni-containing single wall carbon nanotubes and carbon nano-onions. Nickel catalyst particles are often necessary to synthesize these carbon nanoparticles. Nanoparticles were used as additives dispersed in a lubricating poly-alpha-olefin base oil. We show superior tribological properties for carbon nanoparticles containing residual nickel cores. Thus, removal of nickel catalyst from carbon particles is not necessary for excellent tribological performances. Mechanisms of friction and wear reduction are discussed in the light of analytical data. Data suggest the tribo-formation of a Ni-doped carbon-like material.     

Tribological behaviour of nacre—Influence of the environment on the elementary wear processes

Nacre (so-called mother-of-pearl) is a natural organic/inorganic nanocomposite displaying exceptional high mechanical properties to weight ratio and a good biocompatibility with the human bones. Consequently, it becomes an attractive material for prosthesis design. These properties are ascribed to its highly ordered layered ‘bricks and mortar’ microstructure. This work studies the tribological behaviour of sheet nacre, rubbing on itself in dry conditions and in the presence of a liquid medium, in relation with its multiscale structure. The results show that the coefficient of friction, rather high under dry conditions (0.45), is even increasing under wet conditions (0.78). Aside a significant dissymmetry between pin and disc, the wear rates were shown to display the same trends. These changes are associated with marked differences in surface topography and in the extent of third body. The systematic study of the microstructure (by AFM, image analysis, SEM and TEM) of the worn surfaces and third bodies allows us to propose a particle detachment model where the role of the inter- and intracrystalline organic material and their interactions with the environment are emphasized.     

石油钻机盘式刹车副材料及其筛选的试验研究

开发性能优良的盘式刹车副摩擦材料是石油钻机盘式刹车技术中的一项材料分别和2种刹车块材料对偶进行摩擦学特性试验,并对各刹车副的摩擦系数及其稳定系数和波动系数以及磨损率进行了分析.试验表明,B堆焊材料的摩擦磨损性能总体优于A堆焊材料,K2刹车块材料具有较好的摩擦学特性.刹车副P20,B/K2和P35,B/K2的摩擦磨损性能明显优于其它各刹车副材料,可作为初步优选的刹车副材料.     

GaSe及相关晶体的历史、现状与未来:具有特异非线性光学特性的层状材料

概述了高度各向异性的,尤其是无掺杂和掺杂的层状半导体GaSe和相关晶体InSe,GaS和GaSe-GaS(固溶液)的结构特性、光学特性和非线性光学特性的实验研究结果,同时概述了由共焦拉曼和光致发光显微镜研究得到的结果和由声波降解法和激光消融技术得到的GaSe纳米粒的光学性质.重点讨论了E-GaSe的性质,指出其具有最大...