Improvement in hydrogen cycling properties of magnesium through added graphite

Magnesium was milled under hydrogen with three types of carbon allotropes: carbon black, graphite, and multi-walled carbon nanotubes, respectively, using a special low-energy shearing mill. Structural and phase evolution were investigated using X-ray diffractometry (XRD) and morphology was investigated by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS). Raman spectroscopy was used to investigate the changes in the nature of carbon–carbon bonding and differential scanning calorimetry (DSC) to investigate desorption characteristics. A Sieverts-type apparatus was applied to characterize the hydrogen absorption and desorption properties. It was found that graphite not only improved the hydrogen absorption, but also the desorption kinetics.     

Compressive and tensile properties of Ar filled carbon nano-peapods

In order to investigate the compressive and tensile mechanical properties of the carbon nano-peapods filled with Ar atoms outside, inside, or both outside and inside their C₆₀ fullerenes, the MD (molecular dynamics) method was used to simulate the compression and tension of the carbon peapods. According to the calculated results the effects of the filled pattern and amount of Ar atom on the mechanical properties of the carbon peapods were discussed systematically. It is shown that (1) the Ar filled nano-peapods have better compressive properties than the unfilled one, and the more Ar atoms are filled, the better the compressive properties are, (2) when the same amount of Ar atoms are filled, the carbon peapod with Ar atoms both outside and inside its C₆₀ fullerenes has the best compressive properties and the one with Ar atoms only outside has the worst compressive properties, and (3) the filled pattern and amount of Ar atom seem to have little effect on the tensile properties of the carbon peapods.     

Quantum conductance of a helically coiled carbon nanotube

Using a π-orbital tight-binding model, we investigate the transport properties of a coiled carbon nanotube (also called carbon nanotube spring), which we construct by connecting carbon nanotubes periodically in three-dimensional (3D) space. The conductance is quantized due to the translational symmetry in the coiled direction. However, the conductance behaviors differ greatly from those of pristine metallic carbon nanotubes but similar to those of carbon nanotube superlattices. We explain that conductance behaviors of the coiled carbon nanotube.     

Mechanical and tribological properties of 2-D carbon/carbon composites densified through pulse chemical vapor infiltration

This paper presents the mechanical and tribological properties of 2-D carbon/carbon composites (C/C) fabricated by the Pulse Chemical Vapor Infiltration (PCVI) process. In the PCVI process, various fabrication temperatures and different reactant pressures were adopted to investigate the influence of processing condition on physical properties, microstructure and mechanical properties. In the densification process by PCVI, holding time and pulse number are two parameters which significantly affect physical properties (such as density, porosity, and weight gain) and mechanical properties (such as interlaminar strength and wear properties). It is found that the wear properties of carbon/carbon composites can be improved obviously after the densification by 1000 pulses. Effects of initial open porosity on density of the fabricated composites are also studied. In this work, tribological performance of the specimens fabricated through the Isothermal Chemical Vapor Infiltration (ICVI) process and the PCVI process under different pulse cycles are compared. Scanning Electronic Microscopy (SEM) was used to examine the morphology of worn surface. The relationship between the tribological performance and surface morphology was studied.     

非晶金刚石薄膜的制备及其性能研究

本文利用一种新的等离子体沉积技术－真空磁过滤弧沉积制备得到一种无氢的非晶碳膜。ＥＥＬＳ分析表明，这种非晶碳膜几乎不含有ｓ０＾２和ｓｐ杂化键，呈现出高度的金刚石特征，以致可以被称为非晶金刚石膜。     

The reinforcement role of different amino-functionalized multi-walled carbon nanotubes in epoxy nanocomposites

Functionalization with different amino groups of multi-walled carbon nanotubes was achieved and nanotube-reinforced epoxy nanocomposites were prepared by mixing amino-functionalized multi-walled carbon nanotubes with epoxy resin. Differential scanning calorimetry, thermogravimetric analysis and bending tests were used to investigate the thermal and mechanical properties of the nanocomposites. The results showed that different kinds of amino-functionalized multi-walled carbon nanotubes would have different effects on the thermal and mechanical properties of the nanocomposites. The reinforcement mechanism of amino-functionalized multi-walled carbon nanotubes in epoxy resin was discussed.     

Mechanical properties improvement of carbon/carbon composites by two different matrixes

Carbon/carbon (C/C) composites with two different matrixes of pitch carbon and pyrolytic carbon were fabricated using 2-dimensional (2D) carbon felts preform. In order to study the effects of matrixes on mechanical properties, C/C composites with single matrix of pitch carbon were prepared. The mechanical properties were tested on CMT5304-30KN universal testing machine. Polarization microscope and scanning electron microscope were used to investigate the microstructures and fracture surface of C/C composites. It was resulted that the flexural strength of C/C composites with two matrixes was improved by 96% compared with that of C/C composites with single matrix. Meanwhile, better toughness was also obtained with two matrixes. For the composites, multilayer microstructures were generated after filling up of voids caused during carbonization of mesophase pitch by pyrolytic carbon. The multilayer microstructures were beneficial to the improvement of mechanical properties of C/C composites, especially the toughness. More energy could be dissipated during mechanical tests while cracks might extend along multiple paths, such as the interface between fiber and matrix or the interface between different matrixes.     

Effective mechanical properties of “fuzzy fiber” composites

In this paper we investigate the mechanical behavior of carbon fiber composites, where the carbon fibers are coated with radially aligned carbon nanotubes. For this purpose we develop a general micromechanics method for fiber composites, where fibers are coated with radially aligned microfibers (“fuzzy fiber” composites). The mechanical effective properties are computed with a special extension of the composite cylinders method. The in-plane shear modulus is determined using an extended version of the Christensen’s generalized self consistent composite cylinders method. The proposed methodology provides stress and strain concentration tensors. The results of the method are compared with numerical approaches based on the asymptotic expansion homogenization method. The combination of composite cylinders method and Mori–Tanaka method allows us to compute effective properties of composites with multiple types of “fuzzy fibers”. Numerical examples of composites made of epoxy resin, carbon fibers and carbon nanotubes are presented and the impact of the carbon nanotubes length and volume fraction in the overall composite properties is studied.     

超临界二氧化碳对芳纶纤维的表面改性

针对芳纶纤维与树脂基体界面性能差及纤维原纤化的问题,采用超临界二氧化碳分散环氧树脂对芳纶纤维进行表面改性,研究超临界二氧化碳处理对芳纶纤维结构及性能的影响。结果表明超临界二氧化碳改性处理能够提高环氧树脂对芳纶纤维的浸润效果,利用超临界二氧化碳分散环氧树脂对芳纶纤维进行处理,可以在一定程度上提高芳纶纤维的性能并改善芳纶增强树脂基复合材料的界面性能。超临界二氧化碳处理能够提高芳纶纤维表面粗糙度及比表面积,且芳纶纤维性能不受影响。     

Effects of potassium hydroxide post-treatments on the field-emission properties of thermal chemical vapor deposited carbon nanotubes

In this study, a simple potassium hydroxide treatment was applied to functionalize the surface and to modify the structure of multi-walled carbon nanotubes grown on silicon substrates by thermal chemical vapor deposition. Scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and energy dispersive spectrometry were employed to investigate the mechanism causing the modified field-emission properties of carbon nanotubes. From our experimental data, the emitted currents of carbon nanotubes after potassium hydroxide treatment are enhanced by more than one order of magnitude compared with those of untreated carbon nanotubes. The emitted current density of carbon nanotubes increases from 0.44 mA/cm2 to 7.92 mA/cm2 after 30 minutes KOH treatment. This technique provides a simple, economical, and effective way to enhance the field-emission properties of carbon nanotubes.     

Functionally graded carbon nanofiber/phenolic nanocomposites and their mechanical properties

For the first time, functionally graded carbon nanofiber/phenolic nanocomposites were designed and fabricated. The effect of compositional gradients on the flexural properties of functionally graded carbon nanofiber/phenolic composite beams was evaluated. Samples with four compositional gradients as well as a non-graded nanocomposite with the same total carbon nanofiber content and geometry were fabricated using a combination of powder stacking and compression molding techniques. Analytical and finite element models were both performed to investigate the effects of compositional gradients, boundary conditions, and external loadings on flexural properties of nanocomposite beams. Close agreement was observed between analytical solutions, finite element analyses and experiment. The morphology of the fracture surfaces was examined using a scanning electron microscope. The results showed that the flexural properties of carbon nanofiber/phenolic nanocomposites can be greatly improved by controlling the carbon nanofiber content across the thickness of the samples.     

Thickness-dependent thermoelectric power factor of polymer-functionalized semiconducting carbon nanotube thin films

The effects of polymer structures on the thermoelectric properties of polymer-wrapped semiconducting carbon nanotubes have yet to be clarified for elucidating intrinsic transport properties. We systematically investigate thickness dependence of thermoelectric transport in thin films containing networks of conjugated polymer-wrapped semiconducting carbon nanotubes. Well-controlled doping experiments suggest that the doping homogeneity and then in-plane electrical conductivity significantly depend on film thickness and polymer species. This understanding leads to achieving thermoelectric power factors as high as 412 μW m^?1 K^?2 in thin carbon nanotube films. This work presents a standard platform for investigating the thermoelectric properties of nanotubes.     

TiO_2和活性炭纤维复合物光催化降解亚甲基蓝

以粘胶基活性炭纤维(VACF)为基体,钛酸丁酯为前驱体,通过溶胶-凝胶浸渍涂覆法将二氧化钛(TiO2)负载于粘胶基活性炭纤维上,制备活性炭纤维负载的TiO2光催化复合物,通过控制活性炭纤维在溶胶中的浸泡时间,制得不同TiO2负载量的复合物。采用扫描电子显微镜(SEM)表征了制备材料的形态结构,以质量浓度为20mg/L的亚甲基蓝溶液为目标降解物,测试了材料在紫外线光照下的催化性能。结果表明:紫外光直接照射对亚甲基蓝基本无降解作用,对活性炭纤维原样有一定作用;随着TiO2负载量的增加,复合物的吸附性能得到提高,对亚甲基蓝的降解作用也得到增强。     

Electric field effects on spin transport in defective metallic carbon nanotubes

On the basis of first-principles calculations, we investigate transport properties of spin-polarized electrons in defective metallic single-wall carbon nanotubes (SWCNTs) under homogeneous transverse electric fields. Either vacancies or carbon adatoms are introduced in (10,10) SWCNT and are shown to play a role of quasi-localized magnetic impurities. The applied transverse electric fields change the relative position of the energy levels of the defects with respect to the Fermi energy so that the spin-polarized conductances are shown to be tunable. For some impurities, the orientation of the majority spin electrons in conducting channels at the Fermi energy can be switched to the opposite spin by an experimentally attainable electric field. Our results suggest that pure carbon or organic nanomagnets could be realized in SWCNTs, and their spin transport properties are controllable by transverse electric fields.     

Mechanical performance of hybrid bismaleimide composites reinforced with three-dimensional braided carbon and Kevlar fabrics

Short, unidirectional and laminated hybrid composites have been extensively investigated. However, very limited work has been conducted on three-dimensional (3-D) braided hybrid composites. In this work, 3-D braided carbon and Kevlar fibres were hybridized to reinforce a bismaleimide (BMI) resin. The purpose of this paper was to investigate the effect of carbon to Kevlar ratio on such mechanical properties as load–displacement behaviour, flexural strength and modulus, shear strength, and impact properties. The effect of surface treatment of hybrid fabrics on the flexural properties was also determined. Experimental results showed that the flexural strength and modulus of the 3-D braided carbon/Kevlar/BMI composites increased with relative carbon fibre loading up to a carbon to Kevlar ratio of 3:2 and then dropped. Positive hybrid effects were observed for both flexural strength and modulus. The results presented in this work proved that hybridization with certain amount of ductile Kevlar fibre markedly promoted the shear strength, impact energy absorption characteristics and damage tolerance of the all-carbon composite, which is of importance for the 3-D braided composites to be used in bone fixations. Fracture surfaces and microstructures of various 3-D braided hybrid composites were analyzed to interpret the experimental findings.     

TEOS/MWNT-OH杂化涂层的制备及其电化学腐蚀性能的研究

采用溶胶-凝胶(sol-gel)法制备正硅酸乙酯(TEOS)掺杂羟基化多壁碳纳米管(MWNT-OH)杂化涂层,采用电化学测试方法研究其在不同条件下的电化学腐蚀性能,通过场发射扫描电镜观察碳纳米管在涂层中的分布状况。结果表明,热处理温度、不同碳纳米管的加入方式等因素均对涂层性能产生显著的影响。用KH-550乙醇溶液对碳纳米管进行研磨处理后,碳纳米管在硅溶胶体系中呈现良好的均匀分散。涂层的热处理温度是重要因素之一,经过160℃处理后,所得涂层对铝合金基体的防护性能最佳。     

Divacancies in graphene and carbon nanotubes

Divacancies are among the most important defects that alter the charge transport properties of single-walled carbon nanotubes (SWNT), and we here study, using ab initio calculations, their properties. Two structures were investigated, one that has two pentagons side by side with an octagon (585) and another composed of three pentagons and three heptagons (555777). We investigate their stability as a function of tube diameter, and calculate their charge transport properties. The 585 defect is less stable in graphene due to two broken bonds in the pentagons. We estimate that the 555777 becomes more stable than the 585 for a diameter of about 40 A (53 A) for an armchair (zigzag) SWNTs, indicating that they will prevail in large diameter multiwalled carbon nanotubes and graphene ribbons.     

Carbon nanotube inner phase chemistry: the Cl- exchange SN2 reaction

Density functional calculations have been carried out to investigate the nature of the inner phase of a (6,6) carbon nanotube, using the Cl(-) exchange S(N)2 reaction as an indicator. Inside the carbon nanotube the classical barrier height increases by 6.6 kcal/mol due to the nanotube polarizability. This suggests that the inner phase environment can be considered a form of solid solvation, offering the possibility of obtaining altered guest properties and reactivity through dielectric stabilization.     

Field emission characteristics of chromium carbide capped carbon nanotips

In this study, field emission characteristics of two carbon based nanomaterials, carbon nanotips and chromium carbide capped carbon nanotips, were discussed. Both of these materials were synthesized by bias-assisted microwave plasma chemical vapor deposition with hydrogen and methane as reactants. Ultra-sharpness of the carbon nanotips and the composite structure of chromium carbide capped carbon nanotips have shown unique structural and electrical properties. I-V measurements were carried out to investigate the field emission characteristics. The chromium carbide capped carbon nanotips showed superior field emission stability compared to carbon nanotips under constant current emission.     

聚醚酰亚胺基炭分子筛膜的形成及其气体分离性能研究

以商用聚醚酰亚胺(PEI)作为前驱体,采用经过ZrO2-Al2O3复合溶胶修饰的陶瓷氧化铝为支撑体,浸渍涂膜制备聚合物膜,在空气中预氧化处理后,经500～800℃不同的炭化温度下制备出气体分离炭分子筛膜。为了考察炭化温度对炭膜结构和气体分离性能的影响,采用热重分析(TG)、拉曼光谱(Raman)、X射线衍射(XRD)、扫描电镜(SEM)和气体渗透等测试手段,对热解过程聚合物膜热稳定性、炭微晶结构及石墨化进程、微观形貌和气体分离性能进行了系统研究。结果表明,不同的炭化温度对所形成炭膜表现出不同物理和化学结构、炭结构和孔结构,最终影响炭分子筛膜的气体渗透性和分离选择性。