纳米碳管的制备

本发明旨在提供用于制备纳米碳管和纳米碳纤维的方法以及由此制备的纳米碳管和纳米碳纤维，所述方法包括将选择性地含有表面活性剂的金属纳米粒子的胶体溶液以气相的形式与选择性的碳源一起导入热反应器。根据本发明，可容易地控制纳米碳管和纳米碳纤维的外形和结构，可大规模连续地制造纳米碳管和纳米碳纤维，简化纳米碳管和纳米碳纤维的制造设备及方法，从而可样易且成本低廉地制得具有各种外形、结构和性能的纳米碳管和纳米碳纤维。此外，本发明的方法具有高度的重现性和工业应用价值。     

一种制备碳纤维和纳米碳管的方法

本发明涉及碳纤维／纳米碳管，具体地说是一种制各碳纤维和纳米碳管的方法。它采用氢为载气、乙炔为碳源、泡沫镍为催化剂，在加碳源的同时加入含硫生长促进剂，在较低温度下反应，制备出纳米碳管、纳米碳纤维或螺旋形碳纤维。本发明工艺简单、价格低廉，产量及纯度高，本发明可应用于结构增强、微电子器件、吸波材料等，具有广阔的应用前景。     

专利文摘

一种制备碳纤维和纳米碳管的方法本发明涉及碳纤维/纳米碳管,具体地说是一种制备碳纤维和纳米碳管的方法。它采用氢为载气、乙炔为碳源、泡沫镍为催化剂,在加碳源的同时加入含硫生长促进剂,在较低温度下反应,制备出纳米碳管、纳米碳纤维或螺旋形碳纤维。本发明工艺简单、价格低     

催化化学气相沉积法合成单壁纳米碳管的研究进展

介绍了合成单壁纳米碳管的三种主要方法,总结了国内外催化化学气相沉积法合成单壁纳米碳管的研究现状,着重介绍了催化剂对合成单壁纳米碳管影响的研究情况,并分析了反应工艺条件对合成单壁纳米碳管的影响.     

化学气相沉积工艺制备绳状纳米碳管的研究

用硝酸铁作催化剂,乙炔作碳源气体,高纯氮气作稀释气体,在750℃下化学气相沉积生长了绳状纳米碳管,用高分辨扫描电镜观察了所得绳状纳米碳管的形貌.纳米碳管的直径为100～200nm,长度为10～20 μm.文中还提出了绳状纳米碳管的生长机理.     

不同金属催化炭纤维原位生长纳米炭纤维/纳米碳管的研究

为了选择合适的催化剂，来催化炭纤维生长纳米炭纤维／纳米碳管，分别以Fe、Co、Ni和Mo的金属盐为催化剂前驱体，H2为还原气体，N2为载气，采用浸渍-还原法在炭纤维表面制备纳米催化剂颗粒，再以CO为碳源，催化热解生长纳米炭纤维／纳米碳管。用扫描电镜观察了纳米催化剂颗粒的形貌和粒径及纳米炭纤维／纳米碳管的形貌，并探讨了四种金属的催化生长机制，发现四种金属的催化效果为：Ni最好，Co次之，Fe较差，Mo最差。     

火柴棒状纳米碳管的制备及其生长机理

以钨酸钠为钨源,氯化钠为诱导剂,通过水热法制备了三氧化钨(WO₃)纳米棒,再以葡萄糖为碳源,经再次水热反应对WO₃表面进行碳包覆,然后在氢气和甲烷混合气氛中反应一段时间获得了具有火柴棒状结构的纳米碳管。采用X射线衍射分析、场发射扫描电子显微镜、透射电子显微镜和X射线能量散射谱等手段对样品的晶型、形貌、微结构和表面化学元素进行了表征与分析。结果表明,样品由纳米碳管和碳化钨(WC)构成。其中,纳米碳管为火柴棒状,长度0.5～1.0 μm,直径100 nm左右;WC颗粒位于纳米碳管内部,其大小决定了火柴棒状纳米碳管的内径。这充分说明WC在碳管的生长过程中充当催化剂的作用。     

多壁纳米碳管的超声短切处理

采用超声方法对多壁纳米碳管进行短切处理，比较系统地考察了超声时间对纳米碳管的长度、孔结构和形貌的影响。结果表明，超声粉碎可以有效地短切多壁纳米碳管，随超声时间的延长，纳米碳管的长度显著减小。在超声处理120min后，纳米碳管被短切到平均长度为400nm。超声短切后的纳米碳管比表面积和孔容均显著增加。进一步延长超声时间，其比表面积和孔容反而下降。     

催化热分解法制备纳米碳管的研究

催化热分解碳氢化合物法是常见的制各纳米碳管的方法。本文以钴为催化剂、C2H2为碳源,制备出了纳米碳管。通过对该工艺较深入的研究,得到了较好的工艺过程,并对工艺参数对纳米碳等制备的影响作了探讨。     

可使纳米碳管实现工业化的新技术

使用日本国家高等工业理工研究院MorioYumura等人开发出来的热化学－蒸汽－沉积方法（简称热CVD），ShowaDenkoK．K．公司以２００g／h的速度生产了纳米碳管。这是第一次纳米碳管在这样规模下生产。ShowaDenko计划工业化该工艺。该公司在直径２００mm、连续的中试反应器中生产了纳米管。在１２００℃下将由氯化钴和复合成形剂所组成的催化剂前体连同氢气和苯，喷雾到反应器中。呈胶体状态的氯化钴还原成纳米尺寸的钴金属颗粒，在该颗粒上形成纳米碳管。合成纳米管后，再次加热该材料至１２００℃，以除去焦油，然后加热至２８００℃以…     

Carbon nanotubes and carbon nanofibers fabricated on tubular porous Al2O3 substrates

Carbon nanotubes and carbon nanofibers were grown at different temperatures on porous ceramic Al₂O₃ substrates with single channel geometry by means of a chemical vapor deposition technique using methane as carbon source and palladium as catalyst. Time-resolved in-situ Fourier transformed infrared spectroscopy was used for the investigation of methane decomposition for characterizing the catalyst’s performance. With increasing synthesis temperature, a structural transition from carbon nanofibers to carbon nanotubes was observed. At a synthesis temperature of 700 °C, solely carbon nanofibers were found, whereas at 800 °C a mixture of two types of bamboo-shaped carbon nanofibers were obtained, suggesting a structural transition. A synthesis temperature to 850 °C results in bamboo-shaped multi-walled carbon nanofibers and multi-walled carbon nanotubes. The carbon products and the observed structural transition were characterized by means of field emission scanning electron microscopy, high-resolution transmission electron microscopy, thermal gravimetric analysis, and Raman spectroscopy.     

Catalytic synthesized carbon nanostructures from methane using nanocrystalline Ni

Carbon nanostructures synthesized with nanocrystalline Ni catalyst from decomposition of methane are investigated by means of transmission electron microscopy (TEM). Two kinds of carbon nanostructures, carbon fibers and bamboo-shaped carbon nanotubes, are observed. The preferential growth direction of graphene sheets depends on the reaction conditions. The bamboo-shaped carbon nanotubes can be obtained only if the reaction temperature is higher than 1000 K, and carbon fibers can be obtained at lower temperatures. The role and state of the catalyst particles are also discussed.     

Systematic investigation of the growth mechanisms for conventional,doped and bamboo-shaped nanotubes

Fundamental physico-chemical mechanisms underlying the synthesis of nanotubes wereinvestigated, including conventional, doped, and bamboo-shaped nanotubes. The mechanisms are examined from the viewpoint of the well-known base growth (root growth) and tip growth mechanisms. The analysis of the surface characteristics of nanoparticles is key to the present approach. Surface and interface melting, surface and bulk diffusion through nanoparticle, and the formation of a hill due to over-segregation of the source species to the nanoparticle peripheral surface have also been investigated. The study may have led to an understanding of the basics and the differences between the base growth and the tip growths of nanotubes, and also of the formation of nanotube diaphragms (caps), if any. The proposed mechanisms have been used to attempt to explain various prior observations on the conventional, doped, and bamboo-shaped nanotubes. Experimental results available in the literature have been extensively employed to justify the validity of the mechanisms, and to highlight the possible appeal of these mechanisms.     

Coal as a carbon source for carbon nanotube synthesis

This article reviews the recent advances on the various processes used in the synthesis of carbon nanotubes (CNTs) from different types of coal (anthracite, bituminous, etc.) and on the role played by coal as carbon source in the production of CNTs. The molecular solid coal is inexpensive and widely available in comparison to the most widely used solid carbon precursor, graphite (a lattice solid) and high purity hydrocarbon gas sources. An account is given on the different processes involved in the synthesis of various CNTs (single and multi-walled, bamboo-shaped, branched, etc.) from different types of coal (anthracite, bituminous, etc.). Both arc-discharge and thermal plasma jet produce high quality CNTs but fundamental disadvantages limit their use as large-scale synthesis routes. Chemical vapour deposition appears to be promising but further experimental work is necessary in order to develop an understanding of the complex factors governing the formation of different carbon nanomaterials from coal. Successful utilization of CNTs in various applications is strongly dependent on the development of simple, efficient and inexpensive technology for mass production and coal as a carbon source has the potential to meet the needs.     

Fabrication of Y-junction carbon nanotubes by reduction of carbon dioxide with sodium borohydride

Y-junction carbon nanotubes with a bamboo-shaped structure have been synthesized by reduction of CO₂ with NaBH₄ at 700 °C. The X-ray power diffraction pattern indicates that the products are hexagonal graphite, and transmission electron microscope (TEM) and high-resolution transmission electron microscope (HRTEM) images reveal the morphology and structure of carbon nanotubes. The effects of reaction temperature on the growth of the Y-junction carbon nanotubes were also discussed in the paper. Reduction of supercritical CO₂ with sodium borohydride is a promising green chemical method for economically producing Y-junction carbon nanotubes.     

火焰法制备碳纳米管研究进展

火焰法是近20年来兴起的一种新颖、高能效、低成本的碳纳米管制备方法。火焰法能同时提供制备碳纳米管所需的碳源和热源,具有大规模制备碳纳米管的潜力。由于火焰中环境极其复杂,控制火焰中碳纳米管的合成仍是巨大的挑战。本工作介绍了碳纳米管的结构及其性能,综述了扩散火焰(同轴扩散火焰、反扩散火焰和对冲扩散火焰)和预混火焰(单面滞止火焰和双面滞止火焰)制备碳纳米管的研究进展,并对碳纳米管的vapor–liquid–solid、顶部和底部及空心和实心生长机理作了简要阐述,介绍了本课题组基于甲烷/空气同轴射流火焰制备碳纳米管的研究进展。分析表明,金属镍起催化作用,催化剂颗粒包覆在碳纳米管内部,火焰合成的碳纳米管基于vapor–liquid–solid生长机制,碳纳米管直径为50~90 nm,平均直径为65 nm。对火焰法制备碳纳米管的发展方向进行了展望。     

Synthesis of nanosized SiC by low-temperature magnesiothermal reduction of nanocomposites of functionalized carbon nanotubes with MCM-48

Silicon carbide synthesis by a magnesiothermal method was investigated using MCM-48 as the silica source mechanically mixed with carbon nanotubes (CNTs) as the carbon source, and nanocomposites of MCM-48/functionalized CNTs (CNTF). SiC syntheses were carried out with different molar ratios of MCM-48, carbon and magnesium at 700?°C in argon. The MCM-48 and carbon nanotube starting materials and the SiC products were characterized by BET, XRD, FESEM, EDX and TEM. The effect of the carbon content and the type of CNTs (either functionalized or unfunctionalized) on the SiC synthesis was studied. The results show that an improved yield of SiC is obtained when the carbon nanotubes are functionalized, producing a better contact with the MCM-48. This improved contact between the reactants ensures a good degree of reaction in a stoichiometric mixture of silicon and carbon, with no improvement in product formation being achieved by the use of additional carbon. These findings suggest that the degree of contact between reactants is an important factor in the magnesiothermal synthesis of SiC. The SiC products from magnesiothermal synthesis of the functionalized nanocomposite precursors were shown by TEM and FESEM to have unusual nanofiber morphologies mimicking the morphology of the CNTF nanotubes.     

Coal and carbon nanotube production

Strong expectations exist for future use of carbon nanotubes as composite materials in a large number of industries. Production cost and control of the purity and properties of such materials will influence the impacts nanotubes on the chemical, computer and construction industries. As a source material, coal is cheap and abundant, and has unique chemical structure, therefore, may be utilised in the nanotube synthesis. In the present paper, the synthesis of carbon nanotubes using coal as source material has been reviewed. Current nanotubes production largely followed the way of the production for fullerenes, most relying on plasma arcing methods. Non-arcing methods were also explored by a number of researchers. Catalytic synthesis is highlighted which has significant potential in the future nanotubes production directly from coal. Mechanism of the nanotube formation from coal is different from that using carbon graphite. Coal properties in this case are important. Weak bonds and mineral matter in the coal play an important role in the formation of the nanotubes.     

Simulation of transient processes of the catalytic synthesis of carbon nanotubes in a fluidized bed

A transient model of the catalytic synthesis of multilayer carbon nanotubes in a fluidized bed under the condition of a sharp increase in its volume during synthesis has been developed. The model is based on experimental kinetic data of the synthesis of multiwalled carbon nanotubes on metallic catalysts and takes into account the induction period of the catalyst activation, its deactivation during the synthesis, changes in the bed’s height, and the mass transfer of the gas phase components. Various modes of the periodic discharge of the product and loading of the catalyst into a reactor have been considered and, under these conditions, the dynamics of changes in the process characteristics over time have been studied. Optimal controlling parameters that allow one to achieve maximum yields from the synthesis, a high conversion level of the gaseous carbon source, and high purity of the product have been determined for cyclic operation of the reactor.     

Single-source precursor route to carbon nanotubes at mild temperature

Carbon nanotubes were synthesized via a single-source precursor route at 500 °C, using iron carbonyl both as carbon source and catalyst. The X-ray power diffraction pattern indicates that the products are hexagonal graphite. Transmission electron microscope (TEM) images of the sample reveal carbon nanotubes with an average inner (outer) diameter of 30 nm (60 nm). High-resolution TEM indicates that fabrication of the carbon nanotube walls was composed of ca. 40 graphene layers. The Raman spectrum shows two strong peaks at 1587 and 1346 cm⁻¹, corresponding to the typical Raman peaks of graphitized carbon nanotubes. This method avoids the separation of raw material from solvent and simplifies the operation process. At the same time, the research provides a new route to large-scale synthesis of carbon nanotubes.