Synthesis of carbon nanocapsules and carbon nanotubes by an acetylene flame method

The fabrication of carbon nanocapsules and carbon nanotubes (CNTs) using an acetylene flame method was investigated. Carbon nanocapsules, a graphitic structure of nanoparticles with a hollow core, were synthesized using catalyst-free acetylene flames while CNTs were formed with the presence of cobalt-based catalysts in addition to acetylene flames. When the synthesis of these materials was carried out, the results showed that a massive amount of high-purity carbon nanocapsules with a particle size in the range of 15-30 nm can be produced with the acetylene flame method. The CNTs produced were multi-walled carbon nanotubes measuring a few micrometers in length and 20-30 nm in diameter. The acetylene flame method holds great potential for the cost-effective production of CNTs as well as carbon nanocapsules.     

Synthesis of single-wall carbon nanotubes and long nanotube ribbons with Ho/Ni as catalyst by arc discharge

The effect of a new bimetallic catalyst Ho/Ni for synthesis of single-walled carbon nanotubes (SWNTs) by arc discharge has been studied. Long ribbons consisting of roughly-aligned SWNT bundles were obtained by a modified arc discharge apparatus. Ribbon lengths can reach as much as 20 cm. Both elements Ho and Ni play important roles in the synthesis of SWNTs with high yield and purity. Changes in the Ho and Ni concentration in the catalyst hardly affect the diameter distribution of SWNTs, but the yield and purity of SWNTs are very sensitive to the concentration. An optimal range of Ho/Ni compositions for synthesis of SWNTs with relatively high purity and yield is given.     

Synthesis of multiwall carbon nanotubes by electric arc discharge in liquid environments

This work reports the experimental results from the production of multiwall carbon nanotubes (MWCN) synthesized by an electric arc discharge performed in liquid environments between pure graphite electrodes. Both liquid nitrogen and deionised water were suitable for a successful synthesis of this form of carbon aggregation. We report a successful synthesis of MWCN by arc discharge submerged in deionised water. Electron microscopy observations of both the reaction products and the surface of the as-synthesized raw material showed the presence of structural degradation of the MWCN, which probably operates after their growth at the cathode. The degradation is tentatively ascribed to a combination of overheating and high current density experienced by the as-synthesized MWNT, which can be caused by the loose structure of the as-deposited material. The damage appeared to be less severe in water environments, probably owing to the better cooling capacity of water relative to liquid nitrogen.     

Synthesis and characteristics of carbon-coated iron and nickel nanocapsules produced by arc discharge in ethanol vapor

Fe(C) and Ni(C) nanocapsules with low carbon content have been produced via an arc discharge process in ethanol vapor. It is clarified by X-ray diffraction that the core of the Fe(C) nanocapsules consists of γ-Fe, α-Fe and Fe₃C phase, while that of the Ni(C) nanocapsules contains only nickel. High-resolution transmission electron microscopy imaging confirms that these particles have a broad size distribution and the core/shell structure. Besides mutually independent nanocapsules with segregate graphitic shells, those with sharing shells are also observed in the Fe(C) nanocapsules. The remanence and the coercivity at room temperature of both the nanocapsules are higher than those of the corresponding microcrystallines, while the saturation magnetization is lower.     

Field emission from the film of the finely dispersed arc discharge black core material

We have studied, for the first time, the field emission from the film, prepared by a spray method, of the finely dispersed black core material, including multi-walled carbon nanotubes (MWNTs), fabricated by arc discharge. We dispersed the black core material by using an ultrasonic processor and found that the dispersed ones were much finer than those observed when treated with a ball mill and normal ultra-sonic bath. By SEM, HRTEM and Raman analyses, the MWNTs were almost not deformed and damaged during ultra-sonication. The field emission current density measured from the film of the dispersed black core material was about 15 mA/cm² at an applied field of 8 V/μm, which was about 23 times higher than that found by a ball mill. A current density of 1 mA/cm², which is required basically for flat panel display, has been obtained at 5.3 V/μm. The lifetime test of the dispersed black core material showed that the current density was almost unchanged while the field was applied. Therefore, it is concluded that a black core material fabricated by arc discharge could be used to flat panel displays as field emitters by dispersing with an ultrasonic processor, without further treatment like extraction or purification.     

Two possible emission mechanisms involved in the arc discharge method of carbon nanotube preparation

By investigating the morphologies and microstructures of the cathode deposits prepared by self-sustained arc discharge between graphite rods, we consider that there are two electron emission mechanisms occurring on the cathode: field emission and thermionic emission. The former occurs mainly on the edge of the growing surface, by which we can explain the formation of the outer hard shell of the cathode deposit; while the latter occurs mainly on the growing surface except for the edge area and it is the main cause for the growth of carbon nanotubes.     

High-efficient synthesis of double-walled carbon nanotubes by arc discharge method using chloride as a promoter

With trace halide as a promoter in an iron sulfide catalyst, relatively perfect structural integrity double-walled carbon nanotubes (DWNTs) have been synthesized in large quantity and high yield by arc discharge method. Scanning electron microscope (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and Raman spectroscopy were used for structural characterization and yield determination. The results revealed that halide was a crucial factor for selectively synthesizing high yield DWNTs. The detailed experimental parameters were systematically investigated. The possible role of halide in growth of DWNTs was discussed as well.     

Temperature and catalyst effects on the production of amorphous carbon nanotubes by a modified arc discharge

Large amounts of amorphous carbon nanotubes (ACNTs) were prepared with Co-Ni alloy powders as catalyst in hydrogen gas atmosphere by a modified arc discharging furnace which can control temperature during the electric arcing process. The experimental results indicate that the cooperative function of temperature and catalyst plays an important role in the soot production rate and the relative ACNT purity. When temperature increases from 25 °C to 700 °C, the soot production rate increases from around 1 g/h to 8 g/h, the best relative ACNT purity at 600 °C can reach up to 99% compared to the room temperature sample. Without catalyst, only plate graphite is formed at 25 °C and very few carbon nanotubes are found when temperature increases to 600 °C. TEM, SEM, HRTEM and XRD analysis showed that the as-prepared carbon nanotubes are almost amorphous. The soot production rate is 8 g/h and diameter range of amorphous carbon nanotubes is about 7-20 nm, respectively.     

Synthesis of well-aligned carbon nanotubes with open tips

Large amounts of well-aligned carbon nanotubes (CNTs) with open tips have been produced by pyrolysis of iron(II) phthalocyanine. The aligned CNTs have an average length about 10 μm and diameters ranging from 92 to 229 nm. Some of produced CNTs showed Y-junction structure due to the self-joint growth of two neighboring CNTs. The well-aligned CNTs indicated a bamboo-shaped multiwalled structure and fairly good crystallinity. The aligned CNTs follow tip growth mechanism.     

Synthesis of carbon nanotubes on pulse plated Ni nanocrystalline substrate in ethanol flames

A novel process for synthesizing carbon nanotubes (CNTs) in ethanol flames is described. The CNTs grow on a nanocrystalline Ni layer which was electro-deposited on a Ni substrate using periodic reverse (PR) pulse plating. The grain size of the plating and CNT morphology were revealed using XRD, SEM, TEM and Raman spectroscopy. It was found that the quality of the plating and the corresponding CNTs were related to two plating parameters: output pulse frequency (f) and duty cycle (r). The growth mechanism of CNTs in this process is discussed.