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tetrahydrofuran at 500
C in the presence of Fe and Ni powders that led to carbon
nanofibers with an average diameter of 100 nm
[77]
, and the pyrolysis of tetrahydro-
furan at 600
C in the presence of Ni powders that resulted in carbon fibrils that were
formed with stacking graphite sheets of 10
40 nm in thickness
[78]
.Amorphous
CNTs with outer diameters of 50 nm and lengths up to 100
mwereprepared
through the pyrolysis of ferrocene in the presence of sulfur at 200
C. When sodium
oxalate was used instead of sulfur, the pyrolysis of ferrocene at 600
Cgenerateda
novel sandwich structure made of carbon film/Fe
3
O
4
triangular nanoplates/carbon
film.
In conjunction with solvothermal treatment, hydrothermal carbonization is yet
another way to extract carbon from carbonaceous matter, and the carbohydrates
are the best precursors to synthesize nanostructured carbon materials or carbon-
based hybrid nanomaterials via a low-temperature hydrothermal carbonization
process
[79,80]
.
Basavalingu, Gogotsi, Roy, and others have used metal carbides in the synthesis
of carbon nanoforms
[63,70
μ
-SiC powder having
specific area less than 8 m
2
/g
2
1
was used along with organic compounds. The
organic compounds used in the present investigation are of reagent grade formic
acid, oxalic acid, malonic acid, maleic acid, glycolic acid, and citric acid [58]. The
starting materials comprising of
72,81]
. The starting charge was
β
-SiC and organic compound without water were
sealed in annealed gold capsules (50
β
60 mm length and 4.5 mm i.d. having a wall
thickness of 0.1 mm), thus restricting the amount of water in the system to the
water released through the dissociation of organic compounds. We found that
the excess water in the system would decrease the yield of carbon precipitation
and the thermodynamic calculation of Jacobson et al.
[82]
indicated that the
formation of free carbon is expected in the low water to carbide ratio. Further, in
the high-pressure metal-carbon experimental system, the free excess water in the
system inhibits the formation of diamond, and the formation of graphite is more
favorable. It was found that the silicon carbide decomposes to either quartz or
cristobalite along with free carbon particles in the presence of both water and
organic compounds, but the yield of carbon particles has improved when there was
no excess water in the system. The carbon particles formed were discrete or linked
spherical shaped particles having pores, the pores were elongated irregular in shape
with pore diameter of 20
H super-
critical fluids produced through decomposition of organic compounds will have
great influence in decomposing the silicon carbide and precipitating the free ele-
mental carbon. The increased concentration of atomic hydrogen and the C
1
H
x
radi-
cals, by dissociating the organic compound in a closed system, is an ideal
environment for the stabilization of the carbon phase especially for the sp
3
-hybrid-
ized carbon under the subnatural conditions. The authors noticed not only the
improvement in the yield of carbon particles but also the change in the shape of the
carbon particles precipitated, spherical, ovoid, and scaly material having metallic
luster (
Figure 10.10
). After careful examination of these carbon particles under
high-resolution SEM, we found that some of the spherical particles are porous and
hollow, and the broken pieces of these carbon particles exhibit the growth of very
30 nm. Thus, demonstrating that the C
O
