Compatibility studies between pyrolytic carbon and nickel

It is well known that carbon is graphitized by foreign substances. In previous work, graphitization of carbon fibre by nickel was found at temperatures as low as 700° C, but it was difficult to establish the graphitization rate because of the fibre's round cross-section and the variable orientation of the crystallites. In this work, pyrolytic carbon was used instead of the carbon fibre because of its flat surfaces and the preferred orientation of the carbon networks. The pyrolytic carbon which was electro-deposited with nickel, was held at high temperatures. A nickel layer was observed in the pyrolytic carbon, and the carbon area through which the nickel layer passed became graphitized. The graphitization rates were constant at each temperature. And activation energy of 39.7 kcal mol^–1 was obtained from the graphitization rates, which agrees well with the activation energy for diffusion of carbon atoms in nickel. No obvious difference of the graphitization rates was recognized between the directions parallel and normal to the carbon networks.     

Microstructure and thermal conductivity of carbon/carbon composites containing zirconium carbide

Carbon/carbon (C/C) composites containing zirconium carbide (ZrC) were prepared by a novel method. Carbon fiber felt with addition of zirconia was prepared by a microwave-hydrothermal reaction, followed by densification and graphitization. The crystalline structure of the pyrolytic carbon and morphology of the composites were investigated by X-ray diffraction, Raman spectrascope, polarized light microscope, and scanning electron microscopy. Results show that the ZrC grains with sub-micron size present a homogeneous distribution in carbon matrix. The degree of order of the pyrolytic carbon matrix is decreased due to adding ZrC into the C/C composites. Graphitization degree of the C/C composites is decreased by the addition of ZrC. ZrC grains uniformly embedded in the pyrolytic carbon matrix act as pinning particles blocking the conversion of disordered to ordered structure during graphitization. Thermal conductivity is higher in the C/C composites containing ZrC, which is attributed to the increased phonon-defect interaction produced by the thermal motion of the CO in the micropores and gaps of the composites.     

短切纤维炭/炭复合材料磁电阻特性研究

研究了经不同温度下热处理后短切纤维模压预制体炭／炭复合材料样品的磁电阻特性。研究结果表明C／C复合材料的磁电阻一位向关系曲线的形状与C／C预制体结构有关，不同预制体结构的材料，磁电阻一位向关系曲线形状不同。C／C复合材料出现磁电阻恒为0的起始温度与材料的石墨化特性有很大关系。石墨化程度越高，材料的磁电阻越大，磁电阻达到0时的测量温度越高。研究发现，磁电阻一测量温度曲线回归方程的斜率随热处理温度的增加而降低，且斜率-热处理温度的变化曲线与材料d002随热处理温度的变化曲线形状类似。     

Optimization of field emission properties of carbon nanotubes by Taguchi method

It is the purpose of this study to evaluate the field emission property of carbon nanotubes (CNTs) prepared by microwave plasma-enhanced chemical vapor deposition (MPCVD) method. Nickel layer of 5 nm in thickness on 20-nm thickness titanium nitride film was transformed into discrete islands after hydrogen plasma pretreatment. CNTs were then grown up on Ni-coated areas by MPCVD. Through the practice of Taguchi method, superior CNT films with very low emission onset electric field, about 0.7 V/μm (at J = 10 μA/cm²), are attained without post-deposition treatment. It is found that microwave power has the most important influence on the field emission characteristics of CNT films. The increase of methane flow ratio will downgrade the degree of graphitization of CNT and thus its field emission characteristics. Scanning electron microscope and transmission electron microscopy (TEM) observation and energy dispersive X-ray spectrometer analysis reveal that CNT growth by MPCVD is based on tip-growth mechanism. TEM micrographs validate the hollow, bamboo-like structure of the multi-walled CNTs.     

Template-free synthesis and supercapacitance performance of a hierachically porous oxygen-enriched carbon material

A hierarchically porous carbon material (HPCM) with plentiful pores from 0.5 to 700 nm and oxygen-enriched surfaces has been prepared starting from sodium alginate by using a sustainable and green process in which neither porous templates nor additional activation agents are utilized. While the macropores originate from the dissolution of in situ formed Na2CO3 particles during the carbonization of sodium alginate, the micropores and mesopores derive from the chemical activation process of Na ions in sodium alginate and the interspaces between the packed carbon nanoparticles, respectively. Raman spectrum and X-ray photoelectron spectroscopy reveal its nature of partial graphitization and oxygen-enriched functionalities. Electrochemical tests for electrochemical capacitors show that the present HPCM could deliver both higher energy and higher power densities than commercial activation carbon. The high energy density can be ascribed to the oxygen-enriched surfaces as well as the plentiful micropores of HPCM. While the former could provide large pseudocapacitance, the latter would strengthen the electric double layer capacitance. On the other hand, the high power density could be attributed to the excellent meso/macroporosity of HPCM.     

Fabrication and characterisation of multiwalled carbon nanotubes decorated by magnetic Ni nanoparticles

Abstract

Magnetic carbon nanotube (CNT) composites have been successfully fabricated by employing a microwave assisted method after sensitisation and activation. The phase structures and morphologies of the composites were characterised in detail by transmission electron microscope and X-ray powder diffraction. The results show that sensitisation and activation are absolutely necessary for a dense layer of magnetic nanoparticles obtained on the surface of CNTs. Magnetic measurements using a vibrating sample magnetometer demonstrate that the prepared composites are ferromagnetic.     

C/C复合材料结构显微激光喇曼光谱研究

采用显微激光喇曼光谱,以增强体为薄毡叠层、基体分别为粗糙层及光滑层结构热解炭的两种C/C复合材料为研究对象,分析、表征了两种材料炭结构的微观分布特征及其在石墨化过程中的变化状况。结果表明,不仅复合材料中不同组元,而且同一组元不同部位石墨微晶的完整度不同。在石墨化过程中,各自的石墨化进程及可石墨化能力存在差异:炭纤维体积含量较高的炭布层中的热解炭,与网胎层中的热解炭相比,石墨微晶的完整度较好,石墨化进程较快;在炭纤维体积含量较低的网胎层中,炭纤维及热解炭在其界面部位的石墨化进程较快;粗糙层结构热解炭比光滑层结构热解炭容易石墨化。借助激光喇曼光谱微区分析手段,有可能实现对复合材料中石墨化程度微观分布状态的调整和控制。     

Investigations on d.c. conductivity behaviour of milled carbon fibre reinforced epoxy graded composites

This paper reports the d.c. conductivity behaviour of milled carbon fibre reinforced polysulphide modified epoxy gradient composites. Milled carbon fibre reinforced composites having 3 vol. % of milled carbon fibre and poly sulphide modified epoxy resin have been developed. D.C. conductivity measurements are conducted on the graded composites by using an Electrometer in the temperature range from 26°C to 150°C. D.C. conductivity increases with the increase of distance in the direction of centrifugal force, which shows the formation of graded structure with the composites. D.C. conductivity increases on increase of milled carbon fibre content from 0·45 to 1·66 vol.%. At 50°C, d.c. conductivity values were 1·85 × 10⁻¹¹, 1·08 × 10⁻¹¹ and 2·16 × 10⁻¹² for samples 1, 2 and 3, respectively. The activation energy values for different composite samples 1, 2 and 3 are 0·489, 0·565 and 0·654 eV, respectively which shows decrease in activation energy with increase of fibre content.     

石墨表层对四面体非晶炭膜中受激电子的石墨建序化作用

对渗气阴极真空电弧法制备的四而体非晶炭(ta-c)膜实施氧等离子体刻蚀,消除其表面石墨层后,发现:原沉积膜中ta-C石墨表层的消除会影响其受激电子的石墨建序化.应用发射电子能耗谱,表面增强拉曼光谱和表面敏化X光吸收光谱等测量方法,测定了其表层的淌除(程度).样品的氧等离子体刻蚀阻迟了受激电子的石墨化作用,可能归因于多相成核过程中石墨晶核的缺失之故.     

碳纤维植入犬体后的结构研究

利用Ｒａｍａｎ光谱，Ｘ射线光电子能谱和Ｘ射线衍射研究了未植入和植入犬体１．５和４．５ａ后的碳纤维，结果表明随着植入时间的延长，碳纤维表面的石墨化程度逐渐下降，但碳纤维的主体结构不变，仍为良好的石墨结构。     

Development of vapor grown carbon fibers (VGCF) reinforced carbon/carbon composites

C/C composites are developed using vapor grown carbon fibers (VGCF) with two types of pitches as matrix precursor. The composites are carbonized at 1000°C by applying the isostatic pressure throughout the carbonization process and further heat treated at different temperatures up to 2500°C in the inert atmosphere. By applying iso-static pressure one can able to developed VGCF based C/C composites possessing the very high bulk density (1.80 g/cm³) and apparent density (2.01 g/cm³) only by heat treatment up to 2500°C without any densification cycle. This high value of density is due to the extremely strong fiber-matrix interactions and self sintering between the VGCF fibers during carbonization process under iso-static pressure. From the SEM study it reveals that, fiber-matrix interactions are strong and fiber boundaries merges with each other, also there is not a evidence of matrix shrinkage cracks in case 1500°C heat treated composites. On the other hand, in 2500°C heat treated composites, there is evidence of uniform fiber-matrix interfacial cracks and porosity in nanometer dimensions. This is due to the change in fiber morphology above HTT 1500°C. But the formation of nano width cracks does not affect on the mechanical properties of composites. The compressive strength increases from 95MPa of 1500°C to 105 MPa of 2500°C heat treated composites. However, hardness decreases due to the increase in the degree of graphitization of composites on 2500°C. The study reveals that by controlling processing condition and the uniform dispersion of VGCF fibers in the matrix phase, it can be possible to developed nano porosity at fiber-matrix interface.     

Graphitization of polyacrylonitrile carbon fibers and graphite irradiated by γ rays

To investigate the effect of γ-ray radiation on the microstructure of carbon fibers (CF) and graphite, the carbon fibers and graphite were irradiated by ⁶⁰Co source at room temperature. X-ray diffraction results indicate that the interlayer spacing d₀₀₂ of CF and graphite decreased after irradiation. The intensity of (002) peak in CF decreased while the peak of the (002) plane in graphite becomes sharper after irradiation. Scanning electron microscopy combined with energy dispersive X-ray spectroscopy determines that γ-ray irradiation slightly improves the carbon content of CF surface layer. Compton scattering effect and heating caused by γ-ray are proposed to be responsible for the graphitization of CF and graphite.     

石墨化处理对碳素纤维红外发射率的影响

利用自动分光辐射测量仪系统测试了两种碳素纤维在石墨化处理前后的法向光谱发射率和法向总发射率,研究了石墨化处理对碳素纤维红外发射率性能的影响.研究表明：随着石墨化过程中非碳元素的大量脱除和石墨微晶规整程度的提高,T300石墨化碳素纤维和国产石墨碳素纤维毡在2500～5000 nm和5000～6500 nm波段内的光谱发射...     

Physical properties of multiwalled carbon nanotubes

Multiwalled carbon nanotubes (MWNTs), which were prepared by hydrogen arc discharge, were purified by using an infrared radiation heating system. The morphology, structure, vibrational modes and crystalline perfection of purified MWNTs were investigated by using scanning electron microscopy, high-resolution transmission electron microscopy, an X-ray diffractometer and a Raman spectrometer. Moreover, the electrical conductivity of individual purified MWNTs was measured using a two-probe method using a micro manipulator system. It turned out that the MWNTs had a high degree of graphitization, an electrical conductivity of about 1.85×10³ S cm⁻¹ along the long axis, and an enormous current density of more than 10⁷ A cm⁻².     

炭/炭复合材料表面C/SiC/Si-Mo-Cr多层复合防氧化涂层研究(英文)

为提高炭/炭(C/C)复合材料的高温抗氧化性能,采用料浆涂刷法首先在C/C复合材料表面制备了预炭层,然后以Si粉及石墨粉(Si粉与石墨粉的质量配比为:60～80:10～25)为原材料采用包埋法经高温热处理获得C/SiC内涂层,最后在涂有C/SiC内涂层的C/C复合材料表面采用包埋法制备Si-Mo-Cr外涂层。借助扫描电镜、X射线衍射、电子能谱等分析测试手段对涂层试样的微观结构进行了分析,研究了涂层C/C复合材料在1 873 K和1 973 K下的氧化行为。结果表明:由于涂层氧化过程中表面生成了SiO2和Cr2O3复合玻璃层,其在1 873 K温度下表现出优异的防氧化性能,可以有效保护C/C复合材料达135 h。当氧化温度提高至1 973 K并氧化30 h后,该复合涂层氧化过程玻璃层完整性被破坏,涂层失效。     

Study on silicon carbide nanowires produced from carbon blacks and structure of carbon blacks

Silicon carbide nanowires were produced from carbon blacks at 1473 K and their microstructure was characterized by TEM, X-ray diffraction, FTIR and Raman spectroscopy. Nanowires of uniform diameters, the smallest averaging 10 nm, and narrow size distribution were obtained from graphitized carbon blacks, and their morphology depends on the properties of carbon black pecursors. High concentration of stacking faults and twins was detected. In addition to silicon carbide nanowires, a silicon carbide layer, about 20 nm thick, was formed on the surface of carbon black aggregates. The interior of the aggregates did not react and analysis of the data showed that it is composed of a mixture of amorphous carbon and small graphitic crystallites. The small lateral sizes of these crystallites remain unchanged during the graphitization process which is limited to the outer layer of the aggregates.     

Electroless plating and magnetic properties of Co–Zn–P coating on short carbon fibres

A layer of Co–Zn–P alloys was coated on short carbon fibre (CFs) surfaces using electroless plating method. The influence of the concentration of Co^2?+? and Zn^2?+? and reaction time on the plating rate were measured by comparing the relative mass gain rate of Co–Zn–P-coated fibres with uncoated carbon fibres prepared under different conditions. The materials characterizations were analysed by field emission scanning electron microscopy, X-ray diffraction and energy dispersive spectroscope. The magnetic properties of Co–Zn–P/CFs composites prepared in different Zn^2?+? concentration baths were measured by the vibrating sample magnetometer. The best processing parameters of electroless plating of Co–Zn–P coating on short carbon fibres were obtained.     

石墨化处理对双层热解炭基2DC/C复合材料微观结构的影响

综合采用偏光显微镜(PLM),X射线衍射仪(XRD),扫描电子显微镜(SEM),高分辨透射电子显微镜(HRTEM)等分析方法,逐层研究了2500℃高温石墨化(HTT)处理前后双层热解炭基2D C/C复合材料的不同织构以及纤维-基体界面的变化.结果表明:HTT处理后,d002值减小,石墨化度显著提高;内层低织构热解炭的断口微观形貌与晶格条纹几乎没有变化,而外层高织构热解炭晶格条纹更加平直,尤其是发现层间裂纹密度明显增大,使得处理后的高织构热解炭在受力时,裂纹易于在层间扩展和偏转,因此可有效提高材料的韧性;同时,纤维-基体界面发生弱化也是提高材料韧性的另一机制.HTT处理前后试样的三点弯曲力学性能试验结果证实了以上机制.     

Silver coating on carbon and SiC fibres

Electroless silver coating on carbon fibres using silver nitrate solutions has been studied. It was observed that the rate of silver coating depends on the degree of graphitization of carbon fibres. Fibres with a higher degree of graphitization were coated faster than those with a lower degree of graphitization. A physical model considering the number of nucleation sites on the carbon fibre surface as a function of the degree of graphitization is proposed for the silver coating process. The strength and modulus of coated and uncoated fibres have been determined using a high-sensitivity load cell with an Instron tensile testing machine. It was observed that silver coating did not alter the strength or modulus of the fibre. Aluminium matrix composites have been successfully fabricated with these fibres. The same coating technique was also used to coat silicon carbide fibres. Improvement in the infiltration during composite fabrication was observed when the fibres were silver-coated.     

C/C复合材料石墨化度P1模型的表征及测定

C/C复合材料的石墨化度反映了材料中碳结构与理想石墨晶体结构的接近程度,并且是影响其性能的一个重要结构参数,石墨化度P1是一种能够比较准确地表示碳材料石墨程度结构的参数,本文利用P1的基本原理,编制了相应的计算程序,通过X光衍射（XRD）分析,计算了不同热处理温度C／C复合材料石墨化度P1,结果表明它可以较好的表征C／C复合材料的石墨化程度,并进一步讨论了热处理温度（HTT）与石墨化度的关系。