镁钼氧化物催化剂制备多壁纳米碳管的初步研究

采用溶胶-凝胶法合成了可用来催化裂解甲烷大量制备高质量和较高纯度的多壁纳米碳管的镁钼氧化物催化剂. 实验表明该催化剂具有较高的活性和催化效率, 反应2h后, 制备的多壁纳米碳管的量接近原始催化剂量的30倍. 并用透射电镜、高分辨透射电镜、激光拉曼和热重分析对制得的粗产品进行了表征, 结果表明: 碳管的直径在10～22nm之间, 且随着反应时间的延长, 制备的纳米碳管石墨化程度增加, 反应1h后, 粗产品中碳管含量达95%, 同时, 对催化剂的特殊催化生长机理作了讨论, 生长过程中多层Mo颗粒析出在MgO载体表面是碳管成束的主要原因.     

镁-镍合金催化剂制备及纳米碳管生长模式研究

采用多元醇法制备镁-镍合金纳米粉末,并以此为催化剂制备纳米碳管,利用比表面和孔径分布测定仪、X射线衍射仪和透射电镜,研究镁-镍合金催化剂的性能和纳米碳管的生长模式。结果表明:Mg∶Ni值对镁-镍合金催化剂特性影响较大,其中Mg∶Ni为1的催化剂颗粒比表面积较大且平均粒径较小;聚乙烯吡咯烷酮(PVP)用量增大,有利于提高催化剂颗粒的比表面积、减小平均粒径,但用量过大不利于Mg2Ni合成。在以镁-镍合金为催化剂制备碳纳米管的过程中,首先在催化剂表面形成碳膜,随后形成的碳膜将前期形成的碳膜及催化剂颗粒向外推挤,催化剂颗粒移动后遗留下中空隧道,最终形成碳管,由于纳米碳管尖端的催化剂颗粒反应后失去催化活性,碳管的生长动力主要来自碳管根部。     

纳米碳管/氧化锌异质结构的合成及发光性质

以纳米碳管（CNTs）为基体、铜为催化剂,采用催化碳热还原方法直接合成出具有异质结构的纳米碳管/氧化锌（CNT/ZnO）复合材料。利用扫描电镜、透射电镜及X射线衍射等手段研究了异质结构CNT/ZnO复合材料的形态和结构。发现氧化锌纳米线在纳米碳管表面的生长过程遵循催化剂诱导的汽-液-固（VLS）机制;氧化锌纳米线与铜催化剂和纳米碳管之间分别存在明显的界面,并且氧化锌纳米线与纳米碳管均保持了规整的晶体结构。同时也发现在大直径纳米碳管上易于形成高密的氧化锌纳米线;随沉积温度的升高ZnO的形态由线到棒最后形成颗粒。异质结构CNT/ZnO复合材料的诱导发光性能不同于氧化锌纳米线和纳米碳管,在蓝光区域的发光强度远大于紫外发光强度。     

一种基于CVD法的纳米碳管微观分析及场致发射特性的研究

将化学气相沉积法（CVD）制备的纳米碳管提纯后，用透射电镜（TEM）观测了它的微观结构，通过实验对纳米碳管在不同温度下生长的结构特性进行了分析比较，得出了纳米碳管生长的最佳温度为750℃；并对纳米碳管粉体的拉曼（Raman）光谱进行了分析，得到了与透射电镜观测相一致的结论；最后测试了纳米碳管的场致发射特性．     

CVD宏观量半连续制备纳米碳管的研究

研究了以乙炔为基本原料,用Ｎ_２做载流气体;以纳米钻颗粒为催化剂在７００～８００℃常压下纳米碳管的宏观量制备．粗产品中纳米碳管的含量接近５０％,而且纳米碳管缺陷很少,直而长,石墨化好．纳米碳管的形核过程是因为碳在催化剂表面分布不均匀造成的．纳米碳管的生长极限在１５ｍｉｎ左右,然后生长变得缓慢,纳米碳管的一般长度在５～３０μｍ．     

氨气氛中镍催化剂和纳米碳管的制备

用X射线衍射仪、扫描电子显微镜和透射电子显微镜,研究了以瓷舟为载体、硝酸镍为原料、乙炔为碳源,在氨气中制备镍催化剂和纳米碳管时温度的影响,并讨论了氨气的作用.结果表明,以氨气还原硝酸镍获得镍催化剂时,最佳温度范围是700～800℃,此时催化剂的颗粒较细小且均匀,有利于纳米碳管的生长;此外,选用孔径比较细小均匀多孔的载体材料,有助于获得颗粒均匀细小的镍催化剂;在制备纳米碳管时,热分解氨得到的活性氢原子有利于维持催化剂的活性,抑制无定型碳的生成,从而促进纳米碳管生长.实验中纳米碳管的最佳制备温度为700～800℃,管径为10～25nm.     

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。     

纳米碳管储氢机理的电化学研究

对流动催化剂法制备的平均直径为6nm的多壁纲米碳管（Multi-walled carbon nanotubes,MWNTs)进行纯化处理，提纯后的多壁纳米碳管利用透射电镜（TEM）表征和电化学储氢研究。同时对该纳米碳管电极进行了自放电实验。结果表明：多壁纳米碳管具有奶高的电化学储氢容量（739mAh/g），但氢与多壁纳米碳管之间的作用力很微弱，氢很容易从多壁纳米碳管中逃逸出。另外，通过对多壁纳米碳管的气相储氢性能的测试，根据实验结果推测；纳米碳管电化学储氢和气相储氢的主要吸附机理相同，即都是物理吸附。     

气相沉积生长单壁纳米碳管束

采用流动催化热解碳氢化合物方法制备出具有一定取向的单壁纳米碳管束。研究了单壁纳米碳管束的生长过程,发现单壁纳米碳管的生长过程是在气流飘浮单个催化剂颗粒中完成。这与热解碳氢化合物制备定向的多壁纳米碳管在基体催化上生长过程有所不同。根据单壁纳米碳管生长过程,推测出单壁纳米碳管束生长速度的数量级为10^-5m/s。     

气相催化热解法制备纳米碳管的研究

以二茂铁为催化剂、苯为碳源、噻吩为生长促进剂,采用气相催化热解法制备了纳米碳管,并运用TEM、Raman、XRD等对纳米碳管的外观形貌、结构、晶化程度等进行了观察研究.结果表明:在1155℃下能制备出管径20～100nm的纳米碳管,其最大产量是催化剂用量的350%.     

Tersoff—Brenner势函数在纳米碳管研究中的应用

介绍一种以键序概念来描述原子间作用的势函数－Tersoff-Brenner势函数表达式和其碳氢系统中的参数化情况,综述了Tersoff-Brenner势函数在单壁纳米碳管的几何结构优化、力学性能、生长机理等理论研究中的应用,并且讨论了这个函数增加长程作用形式,以期能够在单壁在单壁纳米碳管储氢的理论研究中得到应用。     

MPCVD法在碳纤维上制备碳纳米管

利用微波等离子体化学气相沉积（MPCVD）法在碳纤维上制备了碳纳米管,并在此基础上系统地研究了微波功率、反应时间、催化剂前驱体的吸附时间以及吸附浓度对碳纳米管生长的影响.采用扫描电子显微镜（SEM）对样品的表面形貌进行表征.结果表明,微波功率、反应时间对碳纳米管的形貌有很大影响,此外,随着吸附时间的增加,碳纳米管的生长速度快且产量高;吸附浓度很大时,碳纤维表面上产生了大量的无定形碳和石墨,严重影响了碳纳米管的生长质量.     

真空度对碳纳米管生长过程的影响

利用等离子体增强热丝化学气相沉积系统在沉积有过渡层Ta和催化剂层NiFe的Si衬底上制备出准直碳纳米管，并用扫描电子显微镜研究了它们的生长和结构，结果表明真空度对其生长和结构有较大的影响。当真空度为4000Pa和2000Pa时，准直碳纳米管较容易生长，并且真空度为2000Pa时生长的碳纳米管平均长度大于真空度为4000Pa时碳纳米管的平均长度。但真空度为667Pa时碳纳米管生长困难。根据热力学和辉光放电理论，分析了真空度对准直碳纳米管生长和结构的影响。     

辉光放电和压强对准直碳纳米管生长的影响

利用负偏压增强热丝化学气相沉积系统在沉积有过渡层Ta和催化剂层NiFe的Si村底上制备出准直碳纳米管，并用扫描电子显微镜研完了它们的生长和结构，结果表明辉光放电和压强对其生长和结构有极大的影响。若无辉光放电产生，碳纳米管是弯曲的，有辉光放电时，碳纳米管是准直的。当压强较大时，准直碳纳米管较容易生长，并且随着压强的减小，其平均直径减小和平均长度增大。但压强为5Pa时，准直碳纳米管却不能够生长。最后，分析和讨论了辉光放电和压强对准直碳纳米管生长和结构的影响。     

Growth control of carbon nanotubes by plasma-enhanced chemical vapor deposition and reactive ion etching

A novel process for growth of carbon nanotubes using plasma processes is reported. This process consists of formation of nanotips on substrate and growth of carbon nanotubes on it. The formation of the nanotips, which were formed under an intention to control formation of catalyst nanoparticles, was carried out on substrates by reactive ion etching. After the nanotips formation, the carbon nanotubes were grown on the substrate by plasma-enhanced chemical vapor deposition. Our results showed that the introduction of the nanotips on surface gave lower density and smaller diameter growth of carbon nanotubes than those without the structure.     

The role of the gas species on the formation of carbon nanotubes during thermal chemical vapour deposition

In this paper, we investigate the several roles that hydrogen plays in the catalytic growth of carbon nanotubes from the point of view of gas species, catalyst activation and subsequent interaction with the carbon nanotubes. Carbon nanotubes and nanofibres were grown by thermal chemical vapour deposition, using methane and a mixture of hydrogen and helium, for a range of growth temperatures and pre-treatment procedures. Long, straight carbon nanotubes were obtained at 900?°C, and although the growth yield increases with the growth temperature, the growth shifts from nanotubes to nanofibres. By introducing a helium purge as part of the pre-treatment procedure, we change the gas chemistry by altering the hydrogen concentration in the initial reaction stage. This simple change in the process resulted in a clear difference in the yield and the structure of the carbon nanofibres produced. We find that the hydrogen concentration in the initial reaction stage significantly affects the morphology of carbon fibres. Although hydrogen keeps the catalyst activated and increases the yield, it prevents the formation of graphitic nanotubes.     

乙醇催化燃烧法制备竹节形碳纳米管

乙醇催化燃烧法可以方便的制备出碳纳米管和碳纳米纤维。介绍采用该方法制备出一种独特的竹节形的碳纳米管，利用乙醇作为碳源和燃料，提供材料生长所需的能量；利用Cu薄片作为基底；利用FeCl3或Fe（NO3）3作为催化剂先体。通过扫描电子显微镜（SEM），透射电子显微镜（TEM），对黑色絮状的沉积产物进行表征。实验结果表明，产物中的碳纳米管具有较好的竹节形结构。实验也表明制备的竹节形碳纳米管的形貌和微结构与其独特的制备条件有关，如：火焰的抖动，催化剂先体溶液的浓度，制备时间等。并对竹节形碳纳米管的形貌和生长机制进行了详细的讨论。     

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.     

Effects of hydrogen on the formation of aligned carbon nanotubes by chemical vapor deposition

Well-aligned carbon nanotubes with controllable properties were grown on porous silicon substrates by thermal chemical vapor deposition. The morphologies of the carbon nanotubes were varied with the introduction of H2 during the catalyst activation and/or carbon nanotube growth processes. It was found that H2 promotes the growth of carbon nanotubes while preventing the formation of spherical amorphous carbon particles. Without the introduction of H2 during the C2H2 thermal decomposition, aligned carbon nanotubes mixed with spherical carbon particles were formed on the substrate. However, with the introduction of H2, pure carbon nanotubes were synthesized. These nanotubes also had uniform diameters of 10-20 nm, which is much smaller than nanotubes synthesized without H2. The average growth rate of nanotubes was also affected by the introduction of hydrogen into the reaction chamber during nanotube growth. With the addition of hydrogen, the average growth rate changed from 78 nm/s to 145 nm/s. A possible growth mechanism, including the effect of a high ratio of H2 to C2H2, is suggested for the growth of these well-aligned carbon nanotubes with uniform diameters.     

In situ fabrication of carbon nanotube/mesocarbon microbead composites from coal tar pitch

Carbon nanotube/mesocarbon microbead composites have been synthesized from coal tar pitch with carbon nanotubes. How the carbon nanotubes affect the growth and the structure of mesocarbon microbeads are studied. The result shows that the size of beads decreases when more carbon nanotubes are added, and when the ratio of carbon nanotubes is set at 5%, we get the smallest sample with quite uniform shape. Carbon nanotubes exist both on the surface and inside of the samples and they will inhibit the growth and coalescence of these spheres. The addition of carbon nanotubes decreases the graphitization degree of the samples and makes their microtexture tend to be disordered.