Effect of hydrocarbons precursors on the formation of carbon nanotubes in chemical vapor deposition
ABSTRACT High-temperature decomposition of hydrocarbons may lead to the formation of carbon deposits. However in our present studies, we found that the morphology of carbon deposits over MgO supported Fe catalyst during chemical vapor deposition (CVD) process was closely related to the thermodynamic properties and chemical structures of hydrocarbon precursors. Six kinds of hydrocarbons (methane, hexane, cyclohexane, benzene, naphthalene and anthracene) were used as carbon precursors in this study. Methane which has a pretty simple composition and is more chemically stable was favorable for the formation of high-purity single walled carbon nanotubes (SWNTs). For high-molecular weight hydrocarbons, it was found that the chemical structures rather than thermodynamic properties of carbon precursors would play an important role in nanotube formation. Specifically, the CVD processes of aromatic molecules such as benzene, naphthalene and anthracene inclined to the growth of SWNTs. While the cases of aliphatic and cyclic hydrocarbon molecules seemed a little more complicated. Based on different pyrolytic behaviors of carbon precursors and formation mechanism of SWNTs and multi-walled carbon nanotubes (MWNTs), a possible explanation of the difference in CVD products was also proposed.
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ABSTRACT: Carbon nanotube science is a new exciting subject for all the carbon community. We now have in hand 1D graphite prototypes opening a new field for basic research and increasing the technological potential of traditional carbon fibers. In addition to many open fundamental questions, one of the main difficulties resides on the technological side, since large scale synthesis, high purity samples, and manipulation at the nanoscale are not yet fully developed. In this paper, we present recent development on different nanotube aspects: prepa- ration and purification, electronic transport properties, electron spin resonance, mechanical behaviour of individual nanotubes, and field-emission.
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ABSTRACT: Rope-like bundles of single-walled carbon nanotubes (SWNTs) similar to those obtained by laser vaporization and electric-arc techniques were synthesized on a relatively large scale and at low cost by the catalytic decomposition of hydrocarbons at a temperature of about 1200 °C using an improved floating catalyst method. The SWNTs thus obtained have larger diameters and are self-organized into ropes. The addition of thiophene was found to be effective in promoting the growth of SWNTs and in increasing the yield of either SWNTs or multiwalled carbon nanotubes under different growth conditions. © 1998 American Institute of Physics.Applied Physics Letters 06/1998; 72(25):3282-3284. · 3.79 Impact Factor
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ABSTRACT: Possible pyrolysis reaction paths of cyclohexane were studied by UMP2 (FULL)/3-21G∗, UB3LYP/3-21G∗, UB3LYP/6-31G∗ and RB3LYP/6-31G∗ calculation. Pyrolysis mechanism of cyclohexane at high temperature ranges were studied by UB3LYP/6-31G∗, data ΔE0θ, ΔEθ, ΔHθ, ΔGθ and ΔE0θ≠, ΔEθ≠, ΔHθ≠, ΔGθ≠ of five reaction paths (13 reaction steps) and reaction rates at 298–1473K were obtained. The calculations show: (1) the pyrolysis temperature of cyclohexane is about 873K, and the products are 1-hexene, butadiene and butene, (2) as far as the reaction paths producing 1-hexene and producing butene are concerned, when the temperature is higher than 873K, The reaction producing butene are more feasible thermodynamically and dynamically, and the activation energy of rate-determining step is ΔE0θ≠=374.46kJ/mol. Furthermore, at 1473K, kinetic calculation suggests that the both reactions have almost equal reaction rates. (3) In the further pyrolysis reaction, reaction path D that produces butadiene from 2-butene is supported by kinetics, which means 1,3-butadiene is the main product. (4) At 298–1473K, for the reaction paths producing 1-hexene and producing butadiene, the former is supported by kinetics, and the activation energy of rate-determining step is ΔE0θ≠=374.46kJ/mol. When reaching 1473K, ΔGθ≠ of the rate-determining step of reaction path producing 1-hexene (ΔGθ≠=284.19kJ/mol) is still smaller than ΔGθ≠ of the rate-determining step of reaction path producing 1,3-butadiene (ΔGθ≠=313.10kJ/mol). The above results are basically in accord with mass spectroscopy analysis and GPC experiments.Journal of Molecular Structure-theochem - J MOL STRUC-THEOCHEM. 01/2001; 571(1):115-131.