To enhance the CNC yield further,we set the temperatures of the
three heating zones of the vertical CVD chamber to 700 C, 650 C
and 600 C, from the top to the bottom, to synthesize carbonaceous
samples. Compared with the isothermal process, this method can
facilitate the pyrolysis of ethanol and acetylene to provide more
decomposed carbon atoms in the top heating zones. Before Pd
catalysts exit the heating zone (middle and bottom stage), the
carbon atoms have more time to diffuse and precipitate to form
CNCs in the Pd catalysts. In our research, using the new heating
method achieved a CNC yield that was eightfold than that from
using the traditional heating method.
In addition, an interesting nanoscale carbon structure with a
special morphology similar an octopus tentacle was found, as
shown in Fig. 7a, b. The TEM observation shown in Fig. 7c, d reveals
that this structure contains two parts; the inner part is a hollow
structure that looks like the CNTs grown at 700 C, as shown in
Fig. 3d; the outside part looks like amorphous carbon deposit,
which surrounds the inner tube.
This structure was rarely reported in the literature. Mishra et al.
demonstrated that gas-flow fields, associated heat, and mass
transfer were not homogeneously distributed during CNF-growth
in a vertical CVD reactor [30]. They proposed a model for solving