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: The semiconductivity of carbon nanotubes has been investigated by the luminescence measurement. The nanotubes were characterized by scanning electron microscopy and X-ray diffraction. Carbon nanotubes can luminesce under laser irradiation. Using the photoluminescence measurements the emission spectrum is very wide near the infrared emission range, with a major peak at 1.3 eV. According to the temperature dependence of the photoluminescence and the thermal photoluminescence experiments, the luminescence of carbon nanotubes comes from the center of the energy trap of a defect. In view of this result, it is suggested that the technique of thermal stimulated luminescence provides a simple alternative method to obtain the energy levels in carbon nanotubes systems.Proceedings of the Institution of Mechanical Engineers Part N Journal of Nanoengineering and Nanosystems 12/2011; 225(4):145-147.
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ABSTRACT: Multi-walled carbon nanotube arrays (CNTAs) of good quality are prepared in a high yield of ∼7 wt.% by CVD at 850 °C, using rectified cyclohexane as the carbon source. All the CNTAs forming on the inner wall of a quartz tube reactor are of good quality, but those forming in the zone 40–60 cm away from the entrance of the furnace show the best degrees of graphitization and alignment. The length of these CNTAs is ∼200 µm, their average growth rate during the CVD reaction (8 min) is 25 µm min−1, and the content of MWCNTs and iron are 93.7 wt.% and 3.9 wt.%, respectively. The effect of CVD reaction temperature on the yield and quality of the CNTAs is also investigated and explained by knowledge of the chemical kinetics of reaction; four main chemical reactions are suggested for the growth of CNTAs during the process of CVD reaction, and the ratios of the active carbon species (A) to the active Fe catalyst species (C) (A:C) and the other carbon species (B) (A:B). The reasons for the high yield of CNTAs of good quality are discussed briefly.Chemical Vapor Deposition 09/2012; 18(7‐9). · 1.32 Impact Factor
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ABSTRACT: In this study, effect of ethylene and acetylene on synthesis and diameter of carbon nanotubes has been examined. The synthesis of carbon nanotubes has been carried out by chemical vapor deposition method on iron catalyst nanoparticles, at 925 °C under atmospheric pressure. Iron oxide nanoparticles have been prepared in alcohol solution containing MgO powder as a support, with a combination of 10–40 wt% by impregnation method. During synthesis of carbon nanotubes, temperature, carrier gas flow and hydrocarbon gases have been kept constant. The produced materials have been characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy.Indian Journal of Physics 09/2013; · 1.79 Impact Factor