变截面形状螺旋形炭纤维的制备和生长机理

以镍为催化剂,通过控制碳源气体乙炔的流速,在1 013 K-1 053 K温度下,制备了纤维截面形状在生长过程中由扁平形变为圆形的螺旋炭纤维,同时螺旋直径也相应的由4.2 μm变化为6.0 μm,这种变截面螺旋炭纤维的发现,为微机械系统提供了一种新型弹簧.提出了变截面螺旋炭纤维的生长机理,认为催化剂颗粒的各向异性不仅影响螺旋炭纤维螺径的大小,还影响纤维的截面形状.随着生长过程中反应条件的改变,催化剂各向异性也发生改变,长方形催化剂既可以生长扁平形也可以生长圆形截面螺旋形炭纤维,但是立方形催化剂只能生长圆形截面螺旋形炭纤维.该机制的提出不仅有助于加深对双螺旋炭纤维生长本质的认识,还对指导螺旋形炭纤维的控制生长具有重要意义.     

炭纤维表面化学的裂解气相色谱法研究

用裂解气相色谱法研究了炭纤维表面化学。与ＸＰＳ相结合,裂解色谱法可以反映炭纤维表面整个氧化层的状况。氧化后的炭纤维经５００℃裂解,色谱图中出现Ｃ３以内的气态烃及甲醛、丙酮等含氧化合物,表明炭纤维氧化后表面存在脂肪族结构。炭纤维的氧化方法或氧化时间不同,在其表面形成的化学结构也不同。     

甲烷催化裂解制备毛线状炭纤维及其微观结构

以甲烷为碳源，硫酸亚铁为催化剂前驱体，通过化学气相沉积在石墨基板上制得毛线状炭纤维。扫描电子显微镜观察得知所制炭纤维具有毛线状结构，由许多直径更小的子纤维交叉合并而成。单束毛线状炭纤维的直径为4μm-8μm。高分辨透射电子显微镜显示构成纤维的碳层排列不平直，存在偏转角，有序排列的碳层被分割成许多有序微晶区域。进一步采用X射线衍射和激光拉曼光谱等分析手段对其微观结构进行表征，表明毛线状炭纤维中碳层排列有序度较高，石墨微晶尺寸较大（La≈5nm），层间距较小（d002=0．340nm）。推测毛线状炭纤维生长机理符合“吸附-扩散-析出”过程，形成毛线状结构主要由催化剂颗粒直径决定。     

微螺旋炭纤维的制备与表征

采用溶剂热法合成出硫化镍, 并将其作为催化剂, 催化热解乙炔制备出微螺旋炭纤维. 通过SEM、FT-IR和XRD分析了催化剂和微螺旋炭纤维的形貌和微观结构. 结果表明: 硫化镍催化颗粒表面光滑、为规则的六方相结构, 直径为1~2 μm; 微螺旋炭纤维具有双螺旋结构, 截面为矩形, 具有相同的螺径. 微螺旋炭纤维分子结构中既含有不饱和的C=C双键, 又含有饱和的-CH₂-和-CH₃基团, 其微观结构整体有序度较差, 存在一定量的无定型炭和晶体缺陷, 石墨化度低.     

聚丙烯腈基炭纤维制备过程中的表面形态和结构研究

为了制备高性能的聚丙烯腈基炭纤维，用SEM和TEM等分析方法跟踪炭纤维生产全过程中纤维微观结构所发生的变化。在湿法纺丝中，控制预牵伸倍数为7倍，调整凝固浴的温度为16℃时，可纺出截面近似圆形的高质量原丝，纤维的截面和表面的微纤比较紧凑，表面缺陷和裂纹较少；原丝经过预氧化后仍保持原来的微原纤结构，纤维外部表层的石墨微晶较大，所含孔隙较少，内部的微晶较小且含有大量孔隙。用高锰酸钾改性原丝能够得到质量优异的预氧化纤维，改性预氧丝的纤维基面增加比未改性的多，基面沿纤维轴排列的程度更高。所制备的炭纤维具有由原丝演变来的微观结构，微纤沿纤维轴高度取向，微纤之间有细长的孔隙，并堆砌在一起形成枝化微纤的伸展网络，炭纤维截面形状也近似为圆形。合理调整制备工艺，得到了强度为3．6GPa-4．2GPa，断裂延伸率为1．6％-1．8％，模量为235GPa-240GPa的聚丙烯腈基炭纤维。结果表明：炭纤维的微观组织结构与原丝的微观组织结构密切相关，高强度、高取向度和结构均匀的原丝是获得高强度和高模量炭纤维的前提。     

催化裂解聚苯乙烯制备碳纳米管的研究

通过在60℃氮气气氛中催化裂解聚苯乙烯,制备了大量管径为5～40nm的高质量的碳纳米管.利用扫描电子显微镜、透射电子显微镜和拉曼光谱对所制备的碳纳米管进行了表征.研究表明,所制备的碳纳米管石墨化程度高,在碳纳米管的管壁上仅有少量的无定形碳存在.催化裂解聚苯乙烯制备碳纳米管是一种有前途、低成本的绿色化学方法.     

碳化硅纳米纤维/炭纤维共增强毡体的制备

以电镀Ni颗粒为催化剂,采用化学气相沉积(CVD)法,在炭纤维表面原位生长SiC纳米纤维(SiC-NF),制备出SiC纳米纤维/炭纤维共增强毡体.XRD和SEM分析表明生成的SiC纳米纤维物相为β-SiC,平均长度可达几十微米,直径在几十到几百个纳米之间.通过改变电镀镍的时间,研究了催化剂Ni颗粒的大小、形态及分布对SiC-NF生长情况的影响,研究结果表明,催化剂Ni颗粒分布越细小、均匀,催化活性越大,所生长的纳米SiC纤维也越细长,分布越均匀.     

短切炭纤维-炭复合材料的制备及传导性能和微观结构的研究

以中间相沥青基短切炭纤维和中间相沥青为原料,采用模压成型、炭化、致密化、高温石墨化等一系列常规工艺,制备了传导性能良好的炭/炭复合材料.主要考察了中间相沥青与中间相沥青基炭纤维质量配比对材料密度及传导性能的影响,并进一步研究了材料微晶参数的变化与材料性能的相关性.结果表明中间相沥青与纤维质量配比对材料的导热、导电性能以及微晶参数有很大影响.随着中间相沥青用量的增大,材料导热、导电性能均提高,石墨层间距d002减小,石墨微晶尺寸La、Lc增大;当中间相沥青与炭纤维质量比为 0.8时,制备出的炭/炭复合材料石墨微晶尺寸最大,常温传导性能最佳(垂直于压制方向的面向热导率为385W/(m·K),电阻率为2.85μΩ·m);进一步提高中间相沥青用量,石墨微晶尺寸La、Lc减小,材料的传导性能降低.     

气相硼催化石墨化炭纤维对其力学性能和微观结构的影响

采用间接法将硼引入炭纤维(CF)中,即先将硼引入石墨坩埚中,然后将CF放到坩埚中,升温进行石墨化处理,石墨坩埚中的硼扩散出来,进入纤维中,借助硼的催化石墨化特性,从而制备出硼掺杂石墨纤维。研究硼含量对炭纤维力学性能的影响。利用X射线光电子能谱、X射线衍射、拉曼光谱、扫描电子显微镜、高分辨透射电子显微镜对所制石墨纤维中的硼含量、结构和形貌进行表征和分析。结果表明:石墨纤维中的硼含量可控,硼的催化石墨化作用,提高了CF的石墨化度,由于硼的固溶特性引入了一些缺陷,使得CF的微结构和力学性能发生变化;通过调控CF中的硼含量(0.58%-0.68%),能够在CF强度不损失的情况下提高其模量。     

化学气相催化法生长碳纳米管及其器件的原位制备

本系统地讨论了化学气相催化法制备碳纳米管的工艺过程。讨论了化学气相催化法原位制备碳纳米管器件的技术，即先制备电极和催化剂结构，然后在电极上原位生长碳纳米管。与目前通常采用的先制备碳纳米管，然后超声分离、沉积，再光刻、蒸发制备电极的方法相比，该方法可以减少后处理工艺对碳纳米管结构带来的损伤，具有潜在的优势。     

Controllable synthesis of carbon microcoils/nanocoils by catalysts supported on ceramics using catalyzed chemical vapor deposition process

Carbon microcoils (CMCs) and carbon nanocoils (CNCs) were prepared by the catalytic pyrolysis of acetylene using Ni-based or Fe-based catalysts supported on molecular sieves by the catalyzed chemical vapor deposition (CCVD) process. The growth pattern, morphology and structure of the CMCs and CNCs (to be called by a joint name ‘carbon coils’) were examined in detail. By using a ceramic supporter, the anisotropy of the catalysts could be utilized and carbon coils could be more effectively obtained compared to non-supported alloy catalysts. Furthermore, the morphologies of the carbon coils could be controlled. The Raman spectra indicated that the structures of all these carbon coils were nanocrystalline phases in amorphous networks in spite of the different catalysts and preparation conditions.     

Enhanced field emission characteristics of nitrogen-doped carbon nanotube films grown by microwave plasma enhanced chemical vapor deposition process

Nitrogen-doped carbon nanotube (CNT) films have been synthesized by simple microwave plasma enhanced chemical vapor deposition technique. The morphology and structures were investigated by scanning electron microscopy and high resolution transmission electron microscopy. Morphology of the films was found to be greatly affected by the nature of the substrates. Vertically aligned CNTs were observed on mirror polished Si substrates. On the other hand, randomly oriented flower like morphology of CNTs was found on mechanically polished ones. All the CNTs were found to have bamboo structure with very sharp tips. These films showed very good field emission characteristics with threshold field in the range of 2.65-3.55 V/μm. CNT film with flower like morphology showed lower threshold field as compared to vertically aligned structures. Open graphite edges on the side surface of the bamboo-shaped CNT are suggested to enhance the field emission characteristics which may act as additional emission sites.     

流动催化热解法制备高质量多壁碳纳米管的研究

以甲烷为碳源,N2和H2作载气,二茂铁作催化剂前驱体,采用流动催化热解法制备出大量高质量取向性好的多壁碳纳米管(MWCNTs)。利用扫描电子显微镜(SEM),透射电子显微镜(TEM)和Raman光谱对碳纳米管的形貌和结构进行了表征。该制备过程工艺简单并且成本低廉,对实现碳纳米管的规模生产具有重要意义。     

Effect of ion irradiation on internal stress of amorphic carbon films produced by pulsed laser

Amorphic carbon films either 50 or 160 nm thick were deposited on Si(100) and glass substrates at room temperature in a high-vacuum environment using a Q-switched Nd-YAG pulse laser focused on a graphite target. These films were irradiated with Ti⁺ or C⁺ ions having kinetic energies of 35 and 75 keV, and the changes in internal stresses of the films with varying ion influence were investigated by measuring substrate bending using stylus profilometry. The ion energy and the film thickness were chosen such that the ion penetration depth, R_p, corresponded to either the film thickness or one half of the film thickness. The results indicate that there is an optimum ion fluence leading to a stress-free film for a given ion species and energy. Interpretation of the resulting stress behavior from ion irradiation was made based on the relaxation resulting from damage inside the film together with interfacial mixing. The scanning electron microscopy pictures and surface roughness measurements showed a very smooth surface for both as-deposited and ion-irradiated films. The ion-irradiated films had a Vickers hardness greater than 22 GPa, and were adherent to both Si and glass substrates. An investigation of the film characteristics using Raman scattering and electron-energy loss spectra has revealed that high-energy ion irradiation of an intermediate ion fluence can be utilized successfully to deposit an adherent and hard carbon film with controlled internal stress without changing the film structure significantly.     

Growth and microstructures of carbon nanotube films prepared by microwave plasma enhanced chemical vapor deposition process

Well-aligned carbon nanotubes (CNTs) were grown on iron coated silicon substrates by microwave plasma enhanced chemical vapor deposition. Effect of plasma composition on the growth and microstructures of CNTs were investigated by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and optical emission spectroscopy. Morphology and microstructure of nanotubes were found to be strongly dependent on the plasma composition. Aligned bamboo-shaped nanotubes consisting of regular cone shaped compartments were observed for C₂H₂/NH₃/N₂ and C₂H₂/NH₃/H₂ gas mixtures. Randomly oriented or no nanotubes growth were observed in C₂H₂/H₂ and C₂H₂/N₂ gas mixtures respectively. CNTs grown in nitrogen rich plasma had more frequent short compartments while compartment length increased with decreasing nitrogen concentration in the plasma. Raman spectroscopy of CNTs samples revealed that CNTs prepared in nitrogen rich plasma had higher degree of disorder than those in low nitrogen or nitrogen free plasma. In-situ optical emission spectroscopy investigations showed that CN and H radicals play very important role in both the growth and microstructure of CNTs. Microstructure of CNTs has been correlated as a function of CN radical concentration in the plasma. It is suggested that presence of nitrogen in the plasma enhances the bulk diffusion of carbon through the iron catalyst particles which causes compartment formation. Based on our experimental observations, growth model of nanotubes under different plasma composition has been suggested using base growth mechanism.     

Carbon dioxide as a carbon source for synthesis of carbon nanotubes by chemical vapor deposition

Carbon dioxide was successfully used as carbon source in the synthesis of carbon nanotubes (CNTs) by chemical vapor deposition (CVD) over Fe/CaO catalyst. The product was evaluated using both transmission electron microscopy (TEM) and Raman spectroscopy. Crooked and branching structures of multi-walled carbon nanotubes (MCNTs) with diameters of around 50 nm were observed on the TEM micrographs. Raman spectrum results show that the nanotubes have small defects, which is in agreement with the results of TEM. The influence of reaction variable such as furnace temperature and types of support media was also studied and the reaction mechanism was then discussed in this paper.     

Preparation of single-helix carbon microcoils by catalytic CVD process

Three-dimensional (3D) single-helix spring-like carbon microcoils (SH-CMCs) were obtained by the catalytic pyrolysis of acetylene at 800-820 °C over the Fe-Ni alloy catalysts; their growth morphologies and microstructure were examined. The diameter of carbon fiber, from which the carbon nanocoils was formed, was about 0.5 μm, the coil diameter was about 1-2 μm, and the coil pitch was about the same with the coil diameter. The SH-CMCs were generally grown by a double-directional growth mode.     

Growth of carbon nanotubes directly on a nickel surface by thermal CVD

A simple method of growing carbon nanotubes directly on nickel substrate without chemical pretreatment is reported. It is demonstrated that carbon nanotubes growth is directly affected by the roughness on the surface. Carbon nanotubes density is large in each growth zone observed on the surface; these zones being spread sparsely for coarse roughness of the surface. The density of carbon nanotubes decreases and the number of growth zones increases as the roughness on the surface is reduced. The above trend was not affected with C₂H₂ flow time changing from 10 to 2 min. A similar result was obtained using a Ni alloy as substrate, but the effect of surface roughness on the growth of CNTs was less pronounced. The CNTs grown on the Ni alloy were free of amorphous carbon and uniformly distributed.     

烧蚀过程中C/C复合材料的结构演变

利用SEM和TEM考察了3D C／C复合材料在电弧加热器上烧蚀后的材料表层显微组织结构变化。发现炭纤维和基体炭中的石墨微晶经过烧蚀后都得到了明显的发展。在距烧蚀表面几个纳米的深度范围内形成了高度取向的带状石墨织构，同时，在带状织构中间也形成了许多孔洞和缝隙。在距烧蚀表面几个微米的深度形成了卷曲柱状结构，在这些柱状结构周围有许多缺陷。在纤维和基体炭的界面区域，靠近纤维一侧形成了带状织构，且织构间的缝隙变大。     

乙炔催化裂解制备碳纳米带及其结构表征

以乙炔（C2H2）为碳源,铁为催化剂,通过化学气相沉积技术在单晶硅衬底上制备了碳纳米带.采用场发射SEM、TEM、激光Raman光谱等先进分析手段对其形态和结构进行了表征.研究发现：碳纳米带是一种准二维材料,厚度约30nm,宽度在几百纳米,长度在100μm量级.碳纳米带的碳层沿着与其生长轴方向一致的（002）晶向排列,碳层的边缘都弯曲折叠成封闭结构.碳纳米带中碳层的排列不很平直,其中存在大量的层错.由此认为碳纳米带可用于能源等领域.