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.
- SourceAvailable from: Binh Duong
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- "In contrast, using methane as the hydrocarbon source for CNT growth, Kong et al. showed that almost no amorphous carbon formation occurred during CNT growth . Li et al. carried out a systematic study of the effect of hydrocarbon sources (methane, hexane, cyclohexane , benzene, naphthalene and anthracene) on the formation of CNTs in the CVD process between 500 and 850 °C . They found that methane was more chemically stable than the other carbon sources and was most likely to yield high-purity SWCNTs. "
ABSTRACT: The effects of growth conditions, such as methane flow rates and type of substrate on the distribution, structure and properties of nanotubes were examined. A scanning electron microscope equipped with a Raman spectrometer enabled us to obtain critical information about the structure and electrical properties of the nanotubes simultaneously, and it was shown that these were highly dependent on the methane flow rate. At a methane flow rate of 600 cc/min, we primarily obtained double-walled carbon nanotubes having predominantly semiconducting properties. At a higher methane flow rate (700 cc/min), a mixture of single-walled and double-walled carbon nanotubes was created, most of which were semiconducting. At low methane flow rates (300 and 500 cc/min), metallic multi-walled carbon nanotubes were predominated. Carbon nanotubes grown on a quartz substrate were between 4–10 μm in length, whereas those grown on silicon were longer (∼15–20 μm). The primary growth mechanism observed was base growth, although some cap growth did occur. Based on the results of this study, it is now possible to carefully control the synthesis conditions to produce carbon nanotubes that possess specific electrical properties that suit the desired application.Carbon 09/2011; 49(11):3512-3521. DOI:10.1016/j.carbon.2011.04.050 · 6.16 Impact Factor
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- "The CNT growth in CCVD is governed by the choice of carbon source, catalyst and growth temperature although in many studies other parameters, such as growth time  , have been also proved to be crucial to the resulting carbon materials. Concerning CCVD, the catalytical decomposition of hydrocarbon gases (mainly benzene , acetylene  , ethylene,  methane  or carbon mono oxide ) is realized making use of metal particles (most commonly Fe, Ni, Mo and Co or their alloys) embedded in supports such as alumina , zeolites , CaCO 3 , mesoporous silica , silica , graphite , magnesium oxide  and clays . The use of MgO as supporting material, as extensively reported in the literature   , minimizes the formation of amorphous carbon and prevents the metal particles from aggregating. "
ABSTRACT: Fe–Co bimetallic catalysts supported on MgO were studied for the catalytic chemical vapor deposition growth of carbon nanotubes (CNTs). Different wt.% metal loadings were investigated at various deposition temperatures and times. Characterization of the products involved thermal analysis (DTA–TGA), X-ray diffraction, spectroscopy (Raman, UPS, EELS and STS) and microscopy (SEM, TEM and STM) techniques. It was found that the metal content is critical, not only to the yield and the structural quality of the synthesized carbon nanotubes, but it can be also used to tune the desired type of synthesized nanotubes. Lower (2 wt.%) loadings of Fe–Co catalysts favor the formation of single- and/or double-wall CNTs for deposition time and temperature 30 min and 800 °C, respectively. Thermal analysis and Raman measurements showed that these thin CNTs were synthesized at high amounts (CNT-per-catalyst wt.% of more than 100%), exhibiting high graphitization degree with only traces of by-products (mainly amorphous carbon) among them. Microscopy results revealed the formation of CNTs bundles, consisting of individual nanotubes with less than 2 nm outer diameter, while additional energy loss measurements pointed out that the deposited CNTs are mainly single wall. Higher (10 wt.%) Fe–Co loadings resulted to the formation of multi-wall CNTs.Carbon 10/2010; DOI:10.1016/j.carbon.2010.05.039 · 6.16 Impact Factor
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- "Li et al.  studied that SWNTs or MWNTs formation does not alone depend on the nature of hydrocarbon source. There are also other important parameters playing more crucial role in the growth of different morphology of CNT. "
ABSTRACT: One of the remarkable achievements in the field of nanotechnology is Carbon Nanotubes (CNT) synthesis. Since their discovery in 1991 by Iijima, CNTs have attracted much attention across the world. The CNTs are broadly classified into single-walled carbon nanotubes (SWNTs) and multiwalled carbon nanotubes (MWNTs). The most distinguished features of SWNTs and MWNTs are their electrical, mechanical, chemical, and electronic properties which in turn find their potential applications in almost all fields of science, engineering, and technology. Based on the previous research studies to till date, chemical vapour deposition (CVD) is considered to be the simplest method with high energy efficiency and precise control of reaction parameters compared to other different methods for synthesizing CNTs. Since production of CNTs is becoming the most important factor in the applications point of view, most industries today are opting for the CVD technique. This paper reviewed the synthesis of CNT by CVD especially focusing on methane CVD. Various parameters influencing the reaction and CNT growth were also discussed. A detailed review was made over the different types of CVD process, influence of metal, supports, metal-support interaction, effect of promoters, and reaction parameters role in CNTs growth.Journal of Nanomaterials 01/2010; DOI:10.1155/2010/395191 · 1.61 Impact Factor