燃料和基板对火焰法制备一维碳纳米材料的影响

以乙醇、甲醇及液化石油气为碳源，低碳钢及含Ni合金钢等为基板，采用火焰法成功地制备出了一维碳纳米材料，包括碳纳米管（CNTs）和一种新的“实心”碳纳米纤维（CNFs）。利用场发射枪高分辨扫描电镜（SEM）、透射电镜（TEM）和激光Raman光谱对碳纳米材料的结构进行了表征。发现基板材料决定燃烧生成物的性质，含Fe元素及其化合物的基板材料倾向于合成“实心”碳纳米纤维，而含Nj元素及其化合物的基板材料倾向于合成“空心”的碳纳米管，认为这是由于碳与Fe的亲和力比Ni大而造成的。不同碳源对一维碳纳米材料的形态也有影响，这与它们的含碳量和燃烧热等不同有关。     

Synthesis of carbon nanotubes on metal mesh in inverse diffusion biofuel flames

In this study, renewable biofuels (ethanol and n-butanol) were utilized to synthesize carbon nanotubes on substrate of inexpensive metal mesh (copper alloy and nickel) using inverse diffusion flame. The effects of metal mesh, synthesis time and flame temperature on growth of carbon nanotubes (CNTs) were investigated in details. The morphology and structure of CNTs were characterized by scanning electron microscopy (SEM), high resolution transmission electron microscope (HRTEM) and Raman spectroscopy. The results showed that there were no CNTs formed on nickel mesh. When the substrate was copper alloy mesh, the yield of CNTs increased from 2?min and reached maximum at about 15?min as the synthesis time increased. Under the condition of 15?min, CNTs synthesized in ethanol flame of 1023?K and in n-butanol flame of 1273?K had higher degree of graphitic structure. In addition, multi-walled carbon nanotubes (MWCNTs) with straight tube wall were synthesized in ethanol flame of 1023?K and 1273?K when the synthesis time was 15?min. For these experiments, CNTs with excellent quality could be synthesized effectively in ethanol flame with temperatures of 1023?K and 1273?K when the synthesis time was 15?min and the substrate was copper alloy mesh.     

The effect of temperature on the growth of carbon nanotubes on copper foil using a nickel thin film as catalyst

Growth of carbon nanotubes (CNTs) on bulk copper foil substrates has been achieved by sputtering a nickel thin film on Cu substrates followed by thermal chemical vapor deposition. The characteristics of the nanotubes are strongly dependent on the Ni film thickness and reaction temperature. Specifically, a correlation between the thin film nickel catalyst thickness and the CNT diameter was found. Two hydrocarbon sources investigated were methane and acetylene to determine the best conditions for growth of CNTs on copper. These results demonstrate the effectiveness of this simple method of directly integrating CNTs with highly conductive substrates for use in applications where a conductive CNT network is desirable.     

Synthesis of carbon nanotubes using SBA-15 as a template by the reaction of methane and carbon dioxide

Multiwalled carbon nanotubes (CNTs) were synthesized using Ni loaded mesoporous SBA-15 as a template by reaction of methane and carbon dioxide. The influences of nickel content on the selectivity and crystallinity of CNTs were investigated. It can be seen that the crooked CNTs with a diameter varied from 9.9, 12.5 to 36.5 nm with creasing content of Ni from 5, 15, and 30 wt%/SBA-15. A uniform diameter and good quality CNTs were obtained in our system.     

Direct synthesis of Y-junction carbon nanotubes by microwave-assisted pyrolysis of methane

Both Y-junction carbon nanotubes and individual carbon nanotubes were synthesized without any additive catalyst by microwave decomposition of methane. Detailed microstructures of as-synthesized products have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. The results show that these Y-junction CNTs possess an internal bamboo-shaped structure, and some three dimensional multi-terminal junctions are also observed on CNTs. As gas flow rate decreased to 15 sccm, only individual nanotubes could be obtained. A possible mechanism is proposed for the synthesis of the Y-junction carbon nanotubes on these observations. This technique may also have great potential in making other nano-structured carbon materials on a large scale and at low cost.     

Effects of Fuel Compositions on the Structure and Yield of Flame Synthesized Carbon Nanotubes

Flame synthesis of carbon nanostructures including nanotubes on galvanized steel was investigated utilizing laminar diffusion flames of different types of fuel. Methane (CH₄), propane (C₃H₈) and acetylene (C₂H₂) were used as fuels. Distinctive carbon nanostructures were produced depending on fuel types and fuel flow rates. The qualitative and quantitative analysis of many transmission electron microscope (TEM) and scanning electron microscope (SEM) images were performed. Methane produced thin multi wall carbon nanotubes as well as nanorods and nanofibers within the fuel flow rate range of 7.18E-07 m³/s to 9.57E-07 m³/s. Propane yielded nanotubes only at the fuel flow rate of 4.20E-07 m³/s. The nanotubes synthesized by acetylene flames were of different types that included helically coiled and twisted nanotubes.     

Synthesis of individual ultra-long carbon nanotubes and transfer to other substrates

In this article, we report the synthesis of ultra-long carbon nanotubes (CNTs) by thermal chemical vapour deposition method. Ultra-long, individual and aligned CNTs were directly grown on a flat silicon substrate. The orientation of the nanotubes was found parallel to the gas flow direction. The ultra-long CNTs were grown with different transition metallic salts, such as nickel chloride, iron (III) chloride, cobalt acetate and ruthenium acetate, as the catalysts. The influence of the growth conditions, such as growth temperature, reactive gas flow on the length and alignment of the CNTs was studied in detail. By using different catalysts, ultra-long single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs) were successfully grown. These ultra-long CNTs were transferred to other substrates by two methods. (1) The first method is to use polydimethylsiloxane as a stamp. (2) The second method is to use KOH as an etching agent. The diameter and length of the CNTs were characterised by transmission electron microscope, scanning electron microscope, atomic force microscope and Raman spectroscopy. The results indicate that the length of the CNTs can reach up to 4?mm. The diameter of the SWCNTs is in the range of 0.7–2.1?nm and the diameter of the MWCNTs is approximately 150?nm.     

Growth of carbon nanotubes via chemical vapor deposition on Co catalyst nanoparticles dispersed in CaO

Multiwalled carbon nanotubes (CNTs) have been synthesized by chemical vapor deposition (CVD) from methane and carbon monoxide. The process was catalyzed by cobalt nanoparticles produced via pyrolysis of a solid solution between cobalt and calcium tartrates. The solid solution was characterized by x-ray diffraction, thermogravimetry, and chemical analysis. As shown by transmission electron microscopy, the introduction of water vapor during synthesis increases the CNT content of the resulting material. The field emission current-voltage behavior of the CNTs is shown to depend on CVD conditions.     

堇青石载镍催化剂对燃烧合成碳纳米管的影响

借助于硝酸镍溶液, 利用浸渍法在堇青石表面均匀负载镍催化剂颗粒, 在甲烷扩散火焰中活化并催化生成碳纳米 管. 实验结果表明, 生成的多壁碳纳米管直径为30～50nm, 长度约为十几微米, 空腔比较小, 管壁石墨结晶结构良好.提高浸渍液浓度, 催化剂颗粒尺寸明显变大, 但对碳纳米管的形态影响比较小. 延长浸渍时间, 可使催化剂颗粒密度提高, 碳纳米管出现成束生长现象. 结合碳管成核生长过程和火焰燃烧的特点, 探讨了催化剂对于碳纳米管生长的影响机制.     

Bulk preparation and characterization of mesoporous carbon nanotubes by catalytic decomposition of cyclohexane on sol–gel prepared Ni–Mo–Mg oxide catalyst

Multiwalled carbon nanotubes were synthesized using Ni–Mo–Mg oxide catalyst prepared by sol–gel technique. Carbon nanotubes were formed in situ by the reduction of nickel oxide (NiO) and molybdenum oxide (MoO₃) to Ni and Mo by a gas mixture of nitrogen, hydrogen and cyclohexane at 750 °C. Scanning Electron Microscopy (SEM) was used to confirm the formation of carbon nanotubes (CNTs). The pore size distribution of carbon nanotubes (CNTs) was investigated by N₂ adsorption and desorption. It was found that the pore size fell into the mesopore range: 2 < d < 50 nm. Interpretation was also made using Raman spectroscopy, Diffuse reflectance spectroscopy, X-ray diffraction and ESR spectra. This method is found to produce a very high yield weighing over 20 times of the catalyst. Based on the experimental conditions and results obtained a possible growth mechanism of the carbon nanotubes is proposed.     

碳纳米管泛用合金晶粒细化剂的作用

综述了碳纳米管细化金属晶粒的研究现状,主要包括镁基、铝基、铅锡基、镍基、铁基等,并指出将碳纳米管加入镁、铝、铅、铁、镍基金属合金中都可以明显地细化这些合金材料的基体组织,同时阐述了目前假设的碳纳米管细化晶粒的机理:提供了较多优先形核的位置和阻碍晶粒的长大。     

Growth of carbon nanotubes on glass substrate by MPECVD

We have grown carbon nanotubes (CNTs) with a microwave plasma-enhanced chemical vapor deposition (MPECVD) method, which has been regarded as one of the most promising candidates for the synthesis of CNTs due to the vertical alignment, the low temperature and the large area growth. We had used methane (CH₄) and hydrogen (H₂) gas for the growth of CNTs. 10-nm-thick Ni catalytic layer were deposited on the Ti-coated glass substrate by RF magnetron sputtering method. In this work, we report the low-temperature growing properties of the CNTs on glass substrate with a MPECVD. We have pretreated the Ni/Ti/glass catalytic layer in different microwave power (600, 700, 800, and 900 W) and grown the CNTs in the same microwave power (800 W). SEM (Scanning electron microscopy) images of the Ni catalytic layer shows the diameter and density variation to be dependent with the pretreatment conditions. Raman spectroscopy of CNTs shows that the synthesized CNTs were multi-wall CNTs.     

The formation and characterization of palladium nanowires in growing carbon nanotubes using microwave plasma-enhanced chemical vapor deposition

Multi-wall carbon nanotubes were synthesized on electroplated palladium nanoclusters using a microwave plasma-enhanced chemical vapor deposition system in a mixture of methane and hydrogen as precursors. During the synthesis, Pd was melted to fill up the growing multi-wall carbon nanotubes. A growth mechanism was proposed to describe the Pd filling phenomenon. The multi-wall carbon nanotubes could be burned in oxygen plasma and the filled Pd nanowires could thus be collected. The surface morphology of electroplated Pd clusters and the nanostructure of multi-wall carbon nanotubes with filled Pd nanowires were examined by scanning electron microscopy and transmission electron microscopy, respectively. Raman spectra were used to study the first- and second-order signals of multi-wall carbon nanotubes. Bamboo-shaped carbon nanotubes free of filled Pd were observed under a pure methane atmosphere.     

Processing and tensile characterization of composites composed of carbon nanotube-grown carbon fibers

The growth of carbon nanotubes (CNTs) on carbon fibers was conducted via chemical vapor deposition. A solution approach has been used to distribute nickel particles on the fiber, and the carbon source was a methane gas. The resulting CNTs are about 10 μm in length and 50 nm in outer diameter. After CNT growth, a fiber bundle was impregnated with an epoxy resin to form a unidirectional composite. Tensile tests were carried out, and the induced fracture surface was examined by microscopes. Three types of CNT fracture during fiber pullout are discussed. The results show that fracture in the CNT/fiber joint is the major mode. Pullout of CNTs was also observed. While pullout of fibers leaves micro-scale holes, pullout of CNTs leaves nano-scale holes. The multi-scale fracture behavior generates new parameters for material design and processing. Some concepts regarding the microstructural design for this special composite are discussed.     

A Novel Process for High-efficient Synthesis of One-dimensional Carbon Nanoraaterials from Flames

The substrate pre-treatment plays a key role in obtaining hollow-cored carbon nanotubes (CNTs) and solidcored carbon nanofibers (CNFs) from flames. This paper introduces a simply and high-efficient process by coating a NiSO4 or FeSO4 layer on the substrate as catalyst precursors. Comparing with the regular pretreatment methods, the present experiments showed that the coating pre-treatment provided the following advantages: 1) greatly shortening the synthesis time; 2) available variant substrates and carbon sources; 3) narrowing the diameters distribution. The sulfate is considered to be a crucial factor at the growth of CNTs and CNFs, because it increases the surface energy of catalyst particles and the surface specificity of sulfurs action in metallic grains. This novel process provides a possibility for high quality and mass production of CNTs and CNFs from flames.     

A Novel Process for High-efficient Synthesis of One-dimensional Carbon Nanomaterials from Flames

The substrate pre-treatment plays a key role in obtaining hollow-cored carbon nanotubes （CNTs） and solid-cored carbon nanofibers （CNFs） from flames. This paper introduces a simply and high-efficient process by coating a NiSO4 or FeSO4 layer on the substrate as catalyst precursors. Comparing with the regular pre-treatment methods, the present experiments showed that the coating pre-treatment provided the following advantages： 1） greatly shortening the synthesis time; 2） available variant substrates and carbon sources; 3） narrowing the diameters distribution. The sulfate is considered to be a crucial factor at the growth of CNTs and CNFs, because it increases the surface energy of catalyst particles and the surface specificity of sulfurs action in metallic grains. This novel process provides a possibility for high quality and mass production of CNTs and CNFs from flames.     

Synthesis of fuel oil and carbon nanotubes in an autoclave using plastic waste as precursor

In this study, the synthesis of fuel oil and carbon nanotubes (CNTs) using waste plastic in a batch pyrolysis reactor of 750?mL capacity was carried out. Density, calorific values and FTIR spectroscopy confirmed the formation of fuel oil. The calorific value of oil was higher than the energy needed for pyrolysis process. The same reactor was used as an autoclave for the synthesis of CNTs. SEM and TEM results showed that carbon nanotubes of 40–60?nm diameters were grown on Ni/Mo/MgO catalyst. CNT yield was around 3.2?g of CNTs per 6?g of PP. The purity of CNTs was investigated by thermogravimetric analysis (TGA). The present study proposes a feasible process to convert plastic waste into furnace oil by rapid pyrolysis and synthesis of CNTs.     

Electric field induced growth of well aligned carbon nanotubes from ethanol flames

This paper introduces a process to synthesize well aligned carbon nanotubes (CNTs) from ethanol flames by using a uniform electric field generated from a DC power supply. It has been found that (1)?comparing with the other processes a small electric field is enough to align CNTs; (2)?the synthesis process becomes more controllable and repeatable; (3)?the electric field also improves the diameter uniformity and the crystallinity of graphite sheets. It is thought that the alignment mechanism is due to the electrostatic force acting upon the catalyst particles at the tips of CNTs. The present process has advantages such as convenience of applying electric field, simple experiment set-up, and large area synthesis of well aligned CNTs.     

Investigation of the effective parameters in the growth of carbon nanotubes by thermal chemical vapour deposition method

Synthesis and growth of carbon nanotubes (CNTs) from C₂H₂ by thermal chemical vapour deposition (TCVD) using a mixture of different gases were investigated. A thin film of nickel was coated as catalyst on silicon substrates by ion beam sputtering technique. Various parameters such as thickness of oxide layer and time, as well as reduction temperature were investigated in view of obtaining the best conditions for CNTs growth. C₂H₂ was very effective as carbon feedstock and NH₃ pretreatments were crucial steps towards obtaining a high density of nucleation sites for CNTs growth by inhibiting amorphous carbon generation in the initial stage of the synthesis. The substrate oxide layer was analysed by secondary ion mass spectrometry. The prepared CNTs were confirmed by Raman spectroscopy and were further characterised using scanning electron microscopy and transmission electron microscopy.     

Effects of feed gas composition and catalyst thickness on carbon nanotube and nanofiber synthesis by plasma enhanced chemical vapor deposition

Many engineering applications require carbon nanotubes with specific characteristics such as wall structure, chirality and alignment. However, precise control of nanotube properties grown to application specifications remains a significant challenge. Plasma-enhanced chemical vapor deposition (PECVD) offers a variety of advantages in the synthesis of carbon nanotubes in that several important synthesis parameters can be controlled independently. This paper reports an experimental study of the effects of reacting gas composition (percentage methane in hydrogen) and catalyst film thickness on carbon nanotube (CNT) growth and a computational study of gas-phase composition for the inlet conditions of experimentally observed carbon nanotube growth using different chemical reaction mechanisms. The simulations seek to explain the observed effects of reacting gas composition and to identify the precursors for CNT formation. The experimental results indicate that gas-phase composition significantly affects the synthesized material, which is shown to be randomly aligned nanotube and nanofiber mats for relatively methane-rich inlet gas mixtures and non-tubular carbon for methane-lean incoming mixtures. The simulation results suggest that inlet methane-hydrogen mixture coverts to an acetylene-methane-hydrogen mixture with minor amounts of ethylene, hydrogen atom, and methyl radical. Acetylene appears to be the indicator species for solid carbon formation. The simulations also show that inlet methane-hydrogen mixture does not produce enough gas-phase precursors needed to form quality CNTs below 5% CH4 concentrations in the inlet stream.