“…As illustrated in Figure , the diameter of the grown CNTs increases with the partial pressure of acetylene. It is understandable that the higher coverage of carbon atoms could be responsible for the formation of large nuclei for CNTs’ growth, increasing their diameter . It should also be noted that there are some reports stating that an increase in the acetylene pressure could increase catalyst sintering, forming CNTs with larger diameters. − …”
The unpredictability of different operational parameters has rendered finding the optimum conditions for carbon nanotube (CNT) growth particularly challenging. This study attempts to explore the effect of temperature and pressure based on the growth regimes suggested by Lebedeva et al. (Carbon 2011, 49, 2508−2521. While the absorption regime resulted in premature growth, the surface-and diffusion-controlled ones showed a remarkable growth of carbon products. Along with these two regimes, the diameter, array height, and quality of CNTs generally increased with an increase in temperature, but these parameters experienced a reduction near the boundary between two regimes. Just before this reduction, the location may be considered as the optimum condition for growing tall arrays of high-quality CNTs. The quality and quantity of the grown CNTs improved as the pressure increased up to 7000 Pa.
“…As illustrated in Figure , the diameter of the grown CNTs increases with the partial pressure of acetylene. It is understandable that the higher coverage of carbon atoms could be responsible for the formation of large nuclei for CNTs’ growth, increasing their diameter . It should also be noted that there are some reports stating that an increase in the acetylene pressure could increase catalyst sintering, forming CNTs with larger diameters. − …”
The unpredictability of different operational parameters has rendered finding the optimum conditions for carbon nanotube (CNT) growth particularly challenging. This study attempts to explore the effect of temperature and pressure based on the growth regimes suggested by Lebedeva et al. (Carbon 2011, 49, 2508−2521. While the absorption regime resulted in premature growth, the surface-and diffusion-controlled ones showed a remarkable growth of carbon products. Along with these two regimes, the diameter, array height, and quality of CNTs generally increased with an increase in temperature, but these parameters experienced a reduction near the boundary between two regimes. Just before this reduction, the location may be considered as the optimum condition for growing tall arrays of high-quality CNTs. The quality and quantity of the grown CNTs improved as the pressure increased up to 7000 Pa.
“…Examples of solid nanofilaments formed from naphthalene are shown in the TEM images in Figure (d) and for phenanthrene in (e). The formation of solid carbon nanofibers has been reported in the CNTs synthesis process by many researchers. − Mori and Suzuki proposed that carbon nanofibers consist of several graphitic basal planes in carbon nanofibers synthesized by plasma-enhanced CVD. They reported that the carbon nanotubes consist of graphitic basal planes parallel to the fiber axis with a holey structure, or if the basal planes are perpendicular to the fiber axis, this leads to a platelet structure of carbon nanofibers which are not hollow.…”
The
pyrolysis–catalysis process of waste tires has been
reported to produce high value carbon nanomaterials. Tire pyrolysis
oils contain a wide range of aliphatic and aromatic compounds. To
further investigate the production of carbon nanomaterials from waste
tires, model compounds have been investigated with a 10 wt % Ni/Al2O3 catalyst to determine their influence on the
production of carbon nanomaterials. The compounds (hexadecane, decane,
styrene, naphthalene, and phenanthrene) were chosen to represent typical
aliphatic and aromatic compounds detected in tire pyrolysis oils.
It has been found that the aromatic compounds dominated solid nanocarbon
production compared with aliphatic compounds, especially for the production
of highly graphitic filamentous carbon. The filamentous carbon produced
from aliphatic compounds was in the range from 27.06 to 77.97 mg g–1 of feedstock equivalent carbon, and the filamentous
carbon produced from aromatic compounds ranged from 104.53 to 174.19
mg g–1 of feedstock equivalent carbon. The filamentous
carbon was further characterized by thermogravimetric analysis, electron
microscopy, and Raman spectroscopy, which confirmed that the filamentous
carbon was composed of both hollow carbon nanotubes and solid carbon
nanofilaments. The quality of the produced filamentous carbon was
shown by Raman spectroscopy analysis to be very similar to commercial
filamentous carbon.
“…This decrease may reduce the catalyst coverage with the carbon atoms, thereby reducing the area of the CNT growth nucleus on the catalyst surface [30]. Such a small nucleus, from which the walls of a CNT form, can reduce the diameter of the resultant CNTs [31,32]. Figure 7 (a) The average diameter of the grown CNTs as a function of total pressure.…”
While the effects of partial pressure of carbon feed on the growth of carbon nanotubes (CNTs) are well documented, the effects of total pressure in the growth chamber are not well understood. To shed some light, we investigated the growth of CNTs at different total pressures and a constant partial pressure using catalytic chemical vapour deposition method. It was observed that the growth height and diameter of CNTs decreased as the total pressure increased, probably due to the dilution of carbon feed, the increase in the boundary layer thickness and the decrease in the gas diffusion coefficient. Furthermore, the growth quality of the CNTs was found to be highest at intermediate total pressures. This can provide clues as to where the best temperature concentration is for high-quality CNTs.
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