Abstract
Activation of the catalyst particles during a CVD process can be anticipated from the carbon feeding rate. In this study, Fe2O3/Al2O3 catalyst was synthesized with uniformly dispersed iron over alumina support for onward production of multiwalled carbon nanotubes (MWCNTs) in a fluidized bed chemical CVD reactor. The effect of the ethylene flowrate on catalytic activity of the compound catalyst and morphology of the as-grown MWCNTs was also investigated in this study. The dispersed active phases of the catalyst and optimized gas flowrate helped in improving the tube morphology and prevented the aggregation of the as-grown MWCNTs. The flowrates, below 100 sccm, did not provide sufficient reactants to interact with the catalyst for production of defect-free CNT structures. Above 100 sccm, concentration of the carbon precursor did not show notable influence on decomposition rate of the gas molecules. The most promising results on growth and structural properties of MWCNTs were gained at ethylene flowrate of 100 sccm. At this flowrate, the ratio of G and D intensity peaks (IG/ID) was deliberated about 1.40, which indicates the growth of graphitic structures of MWCNTs.
Highlights
After their discovery by Iijima [1], carbon nanotubes (CNTs) continued to draw the tremendous attention of the research community due to their unique applications and properties
The researchers working in the field of nanotechnology have tried to synthesize CNTs through various techniques, such as arc discharge, laser excitation and ablation, chemical vapor deposition (CVD), and plasma assisted chemical vapor deposition (PECVD)
The mechanism of production of CNTs in a fluidized bed chemical vapor deposition (FBCVD) reactor is based on decomposition of the feedstock gas, dissolution of the carbon atoms in the catalyst particles, and precipitation of the carbon into nanotubes
Summary
After their discovery by Iijima [1], carbon nanotubes (CNTs) continued to draw the tremendous attention of the research community due to their unique applications and properties. CVD remains only the technique with scale-up potential for industrial scale delivery of nanotubes without compromising their selectivity, growth rate, yield, quality, and production cost [3]. The mechanism of production of CNTs in a FBCVD reactor is based on decomposition of the feedstock gas, dissolution of the carbon atoms in the catalyst particles, and precipitation of the carbon into nanotubes. The CNT production rate in a FBCVD reactor is controlled by the process temperature, variable parameters of the metal catalyst, precursor flowrate, and deliberately chosen carrier gas. The structural quality and yield of the carbon product can be improved by deliberating the process parameters, such as carbon precursor, process temperature, composition of the catalyst, catalyst preparation technique, size of the catalyst particles, and the catalyst support [4]. A detained knowledge on growth route of nanotubes and the role of the catalyst during carbon precipitation is yet to arrive at
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