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H. ZHANG ET AL.
carbon nanofibers grow from the catalyst particle to the
opposite directions simultaneously. While in the case of
coiled carbon nanofibers, there are several models to
explain their growth mechanism. Amelincks et al. introduced
the concept of a spatial-velocity hodograph, and proposed a
formation mechanism for a catalytically growth helix-
shaped graphite nanotubes.[5] A three-dimensional growth
model of the carbon coils based on the anisotropy for the
carbon deposition among three crystal faces was proposed
by Motojima.[12] However, other growth mechanisms of
coiled carbon nanofibers cannot be ruled out, and further
research is needed to understand the effect of catalysts.
Also, there are many uncertain factors in our experiment,
such as synthesis in air, unsteady flame, temperature
gradient, non-uniform particles size, etc., that may cause
various and abundance of morphology.
FIG. 4. EDX spectra of the catalyst particle from nickel nitrate.
CONCLUSIONS
In summary, we have synthesized straight and coiled
carbon nanofibers by ethanol catalytic combustion technique
with employing transition metal salt solution as catalyst pre-
cursors. There are two kinds of growth mechanism for growth
of both straight and coiled carbon nanofibers synthesized in
our experiment. The morphology and microstructure of the
obtained carbon nanostructures have been investigated and
their growth mechanism has been discussed. Contrasting
with the widely used CVD and other methods, the present
method has the advantage of being much simpler and more
economic.
FIG. 5. TEM images of catalyst particles on the middle part of the (a) straight
and (b) coiled carbon nanofiber.
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