改进化学气相沉积法在炭纤维表面生长碳纳米管(英文)

采用一种改进的化学气相沉积法在炭纤维表面制备碳纳米管。为了提高炭纤维表面的润湿性能,炭纤维在浸渍之前先在CVD设备中在真空下973 K的高温处理,然后在硝酸和浓硫酸体积比为3∶1的混合酸中酸处理30 min。而改进的化学气相沉积法关键在于让催化剂的还原步骤和碳纳米管的生长步骤同时进行。这样通过减小过渡金属元素与炭纤维之间的接触时间从而降低了它们之间的相互扩散,在确保了炭纤维本身的力学性能下降程度明显小于用普通化学气相法制备的情况下生长出长且茂密的碳纳米管阵列。另外,经过对工艺参数的优化发现当用乙醇作溶剂,Fe(NO3)3.9H2O溶度为100 mmol/L,氢气和碳源气体比值为4/1,而生长时间为30 min时得到最好的碳纳米管阵列。     

碳纤维表面原位生长碳纳米管的研究

采用化学气相沉积工艺在碳纤维的表面分别制备了形貌为卷曲状和直立状的原位生长碳纳米管,利用扫描电镜和透射电镜分析了碳纤维表面原位生长碳纳米管的形貌、管径和管壁状态,借助拉曼光谱分析了原位生长碳纳米管的微观结构。结果表明,卷曲状和直立状原位生长碳纳米管都完整地包裹了碳纤维的表面。卷曲状原位生长碳纳米管主要生长在碳纤维的轴向上,呈现卷曲状形貌,其长度分布在5~20μm,管径分布在10~150nm。卷曲状碳纳米管之间互相交联,形成三维网络结构。直立状碳纳米管主要生长在碳纤维的径向上,呈现放射状形貌,其长度分布在10~30μm,直径分布在10~200nm。直立状碳纳米管在纤维表面分布均匀,碳纳米管之间形成了大量的孔隙,碳纳米管在碳纤维的表面呈现出疏松的网络结构。拉曼光谱分析发现两种碳纳米管均在1350cm-1和1580cm-1附近出现了显著的碳峰位。此外,卷曲状和直立状碳纳米管的D峰和G峰的强度比例分别为0.352和0.351,两种碳纳米管均具有较高的石墨化程度。     

碳纤维布表面原位生长碳纳米管的形貌和结构

利用催化化学气相沉积的方法,在碳纤维布上原位生长了碳纳米管(CNTs);并利用扫描电子显微镜、拉曼光谱和透射电子显微镜研究了沿气流方向不同位置处生长的CNTs的形貌与结构演变。结果表明:沿气流方向不同位置处生长的CNTs呈定向排列,结构和质量相近;但不同位置处生长的CNTs的长度不同,远离进气口处生长的CNTs的长度约为进气口处CNTs长度的两倍。     

沉积条件对碳纤维表面碳纳米管生长的影响

采用化学气相沉积(CVD)法在碳纤维(CF)表面原位生长碳纳米管(CNTs)。考察了不同催化剂、沉积温度、氢气流量以及样品距进气口距离等工艺参数对CNTs-CF生长的影响。利用SEM和高分辨透射电子显微镜(HRTEM)对CNTs-CF形貌和微结构进行了表征和分析。结果表明:在CF表面原位生长的CNTs为多壁结构,其中以Ni为催化剂得到的CNTs直径小、分布均匀;在600~750℃温度范围内,随着温度的升高,CNTs直径和长度减小,产量降低;随着氢气流量的增加,CNTs直径和长度均增加;距进气口30cm,在CF表面得到的CNTs覆盖率高、直径小且分布窄,有利于制备高质量CNTs。     

单壁碳纳米管在基底表面的离散生长

通过旋涂硝酸铁异丙醇溶液于P型硅表面以获得均匀分布的催化剂颗粒,以CH4为反应气体采用CVD方法即可在P型硅表面均匀生长单壁碳纳米管,并且部分碳纳米管呈直立状.研究了催化剂浓度、生长基底、反应温度对单壁碳纳米管表面生长情况的影响.研究表明,催化剂浓度升高或采用二氧化硅替代P型硅为生长基底时,都会导致单壁碳纳米管生长的密度加大,而碳纳米管长度变短且更易贴附基底表面生长;随反应温度的提高碳纳米管的生长效率降低,并使得碳纳米管更易贴附基底表面生长.采用此方法制备的生长有直立碳纳米管的硅片作为扫描基底,在原子力显微镜敲击模式下利用拾取法成功制备了碳纳米管原子力显微镜针尖.     

Low temperature growth of SWNTs on a nickel catalyst by thermal chemical vapor deposition

Single-walled carbon nanotubes (SWNTs) have been grown on a silica-supported monometallic nickel (Ni) catalyst at temperatures ranging from as low as 450 °C to 800 °C. Different spectroscopic techniques, such as Raman, photoluminescence emission (PLE), and ultra violet-visible-near infrared (UV-vis-NIR) absorption spectroscopy were used to evaluate the diameter and quality of the SWNTs grown over the Ni catalyst at different temperatures. The analysis revealed that high quality SWNTs with a very narrow diameter distribution were obtained at a growth temperature of 500 °C. In the PLE and absorption spectra, differences were observed between the SWNTs grown on Ni and those grown on cobalt (Co). This result expands the potential of growing a specific (n, m) tube species with relatively high abundance by tuning the catalyst composition. Furthermore, the prerequisites for the low temperature growth of SWNTs over a monometallic transition metal catalyst have been elucidated.      

Multi-walled carbon nanotube growth on oxidized silicon substrates using cyclohexane precursor by chemical vapor deposition

Randomly oriented multi-walled nanotubes (MWNTs) are grown by a thermal chemical vapor deposition (CVD) process from cyclohexane precursor on a 20% copper-80% nickel (Cu-Ni) catalyst on oxidized silicon substrates. This combination of precursor and catalyst, to our knowledge, has been employed for the first time to demonstrate growth of multi-walled carbon nanotubes. The effects of annealing, gas ambient and catalyst layer thickness on the morphology of the grown carbon layers are discussed. The low resistivity values of the MWNTs grown on oxidized silicon substrates are attractive for their potential use in photonic devices and display applications.     

Multiwall and bamboo-like carbon nanotube growth by CVD using a semimetal as a catalyst

Multiwall carbon nanotubes have been synthesized on silicon substrates via atmospheric pressure chemical vapour deposition technique using bismuth as a catalyst. Field emission scanning electron microscopy analysis suggests that the samples grow through a tip growth mechanism. High-resolution transmission electron microscopy analysis shows spaghetti-like multiwall carbon nanotubes and with a bamboo-like structure obtained using the Bi catalyst. The quality, in terms of the graphitic crystallinity of the as grown carbon nanotubes, was analyzed by Raman analysis. The study shows that the catalyst, namely bismuth strongly influences the growth density and graphitic crystallinity of the grown carbon nanotubes.     

In situ growth carbon nanotube reinforced SiCf/SiC composite

Carbon nanotube (CNT) reinforced SiC_f/SiC composite was prepared by in situ chemical vapor deposition (CVD) growth of CNTs on SiC fibers then following polymer impregnation pyrolysis (PIP) process. The nature of CNTs and the microstructure of the as prepared CNT-SiC_f/SiC composite were investigated. The mechanical properties of the as prepared CNT-SiC_f/SiC composite were measured. The results reveal that the in situ CVD growth of CNTs on SiC fibers remarkably promotes the mechanical properties of SiC_f/SiC composite. The secondly pull-out of CNTs from matrix during the pull-out of the SiC fibers from matrix consumes the deformation energies, resulting in promotion of the mechanical properties for composite.     

无氢化学气相沉积法制备碳纳米管

采用无氢的化学气相沉积法（CVD）进行碳纳米管的制备技术研究,并成功地制备了由20—φ80nm左右,长度为50-100μm左右的碳纳米管。通过改变气体的流量等影响因素实现了定向碳纳米管薄膜和多层碳纳米管薄膜以及其它各种形态的碳纳米管的制备。采用微区Raman光谱、扫描电子显微镜（SEM）和透射电子显微镜（TEM）等方法对产物的形貌和结构进行了表征,结果表明采用无氢CVD法可以制备出多种形态的碳纳米管。     

化学气相沉积法快速生长定向纳米碳管

利用化学气相沉积法，采用二甲苯为碳源，二茂铁为催化剂，氮气作保护气，在石英基底上催化裂解生长定向纳米碳管，试验结果表明：在775℃，120min的条件下，可生长出长达200μm厚的定向纳米碳管薄膜；在775℃，反应时间为60min～120min时，纳米碳管的长度为100μm～200μm，而纳米碳管的直径变化不明显。而无氢气，较高的反应温度和连续的催化剂供给对快速生长定向纳米碳管有重要的影响。     

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.     

Continuous synthesis of carbon nanotubes using a metal-free catalyst by CVD

This study demonstrates the first example of the use of a metal-free catalyst for the continuous synthesis of carbon nanotubes (CNTs) by chemical vapor deposition (CVD). In this paper silica nanoparticles produced from the thermal decomposition of PSS-(2-(trans-3,4-Cyclohexanediol)ethyl)-Heptaisobutyl substituted (POSS) were used as catalyst and ethanol was served as both the solvent and the carbon source for nanotube growth. The POSS/ethanol solution was nebulized by an ultrasonic beam. The tiny mists were continuously introduced into the CVD reactor for the growth of CNTs. The morphology and structure of the CNTs have been investigated by scanning electron microscopy, high-resolution transmission electron microscopy, and Raman spectroscopy. The obtained CNTs have a multi-walled structure with diameters mainly in the size range from 13 to 16 nm. Detailed investigations on the growth conditions indicate that the growth temperature and POSS concentration are important for achieving high-quality nanotubes, and that the existing of small amount of water in ethanol is effective to remove amorphous carbon species during the formation of CNTs. The mass production of CNTs without any metal contaminant will provide a chance for investing and understanding the intrinsic properties of CNTs and applications particularly in nanoelectronics and biomedicines.     

催化剂结构与形态对碳纳米管生长的影响

采用溶胶-凝胶超临界流体干燥技术制备了含铁、钴的纳米SiO2复合气凝胶催化剂,用于碳纳米管和纳米碳包覆磁性纳米粒子的合成。利用N2物理吸附、XRD、TEM、HRTEM、EDS、SAED等手段对催化剂在不同温度下处理后晶型的转变、形态的变化进行了分析,并考察了催化剂对碳纳米管形貌、结构和碳增重率的变化。结果表明:随着处理温度从600℃升高到1000℃,催化剂比表面积从312.4m2 g降低到79.6m2 g,催化剂粒子从非晶态向晶态转变,粒径从5nm增大至60nm左右,碳的增重率从254.8%下降41.5%。采用低温处理的催化剂,碳产物中以碳纳米管为主,而采用较高温度处理后的催化剂,碳产物中则以碳包覆粒子为主,且随处理温度的升高碳包覆粒子的含量逐渐增加。     

化学气相沉积法制备碳纳米管

碳纳米管（CNTs）是一种具有独特理化性能和结构的一维纳米材料,也是当今纳米材料研究的焦点之一．在化学、生物、医药、能源、电子元件等诸多领域具有极高的应用价值．本文以有机溶剂环己烷为碳源．利用化学气相沉积法（CⅥ））在管式电阻炉内,以氩气为栽气,二茂铁为催化剂,一定温度条件下,制备了直径约为50nm,长度达几十微米以上的多壁碳纳米管（MWNTs）．采用拉曼光谱、扫描电镜、透射电镜、X-射线粉末衍射等测试手段,表征了碳纳米管的微观形貌和结构特征．通过对实验结果的分析和讨论,对CVD制备法中碳纳米管的生长机理进行了尝试性探讨。