The synthesis of carbon coils using catalyst arc discharge in an acetylene atmosphere

Article abstract of DOI:10.1016/j.ssc.2007.03.009

Novel carbon coils were synthesized by an arc discharge process on a metal plate under different gas pressures from 160 to 460?Torr. The morphology and yield of carbon coils were examined by scanning (SEM) and transmission (TEM) electron microscopy. The influence of the gas pressure and impurities such as sulfur and phosphorus on the growth of product is also discussed. It was demonstrated that the morphology and yield of the coils were greatly controlled by the gas pressure. On the other hand, a new model was proposed to describe the coil growth. Our method offers a preferable alternative for the efficient, abundant and economical growth of carbon coils.

Full text of DOI:10.1016/j.ssc.2007.03.009

Solid State Communications 142 (2007) 541–544
www.elsevier.com/locate/ssc
The synthesis of carbon coils using catalyst arc discharge in an
acetylene atmosphere
L. Zhanga, Y.B. Zhua,b,∗, C.L. Gea, C. Weia, Q.L. Wanga
a
School of Materials Science and Engineering, China University of Mining and Technology, Jiang Su 221008, PR China
b
Xuzhou Normal University, Jiang Su 221008, PR China
Received 2 September 2006; received in revised form 21 January 2007; accepted 9 March 2007 by P. Sheng
Available online 13 March 2007
Abstract
Novel carbon coils were synthesized by an arc discharge process on a metal plate under different gas pressures from 160 to 460 Torr. The
morphology and yield of carbon coils were examined by scanning (SEM) and transmission (TEM) electron microscopy. The influence of the gas
pressure and impurities such as sulfur and phosphorus on the growth of product is also discussed. It was demonstrated that the morphology and
yield of the coils were greatly controlled by the gas pressure. On the other hand, a new model was proposed to describe the coil growth. Our
method offers a preferable alternative for the efficient, abundant and economical growth of carbon coils.
c
ꢀ 2007 Elsevier Ltd. All rights reserved.
PACS: 81.05UW; 81.16-t; 60
Keywords: A. Carbon coils; A. Metal catalyst; B. Arc discharge; C. Scanning and transmission electron microscopy
1. Introduction
participation in the CVD process. In addition, it is usual to
require fine metal powders or films prepared by design as the
catalyst for the reaction [7–9].
Since coiled carbon fibers were discovered in 1953 [1],
the structure has continuously attracted much attention. These
carbon coils, as new carbon material with special DNA-like
structures and unique properties, may have many applications
such as micro sensors, hydrogen material and electromagnetic
material [2,3]. Therefore, it is valuable to explore a controlled,
reliable, efficient process to produce carbon coils on large
scales. Among various preparation processes, the chemical
vapor deposition (CVD) process has the most potential for
large scale preparation. Many researchers dedicate themselves
to synthesizing them in various CVD reaction systems, using
all kinds of catalyst, carbon sources and types of impurity as
promoter, in the presence of electromagnetic field or not [4–6].
However, the yield of carbon coils in this method is a little low
and it requires a high continual gas flow rate which results in
most of the gas being released directly into atmosphere without
In the work presented, carbon coils are produced by
decomposition of acetylene using an arc discharge process
on a metal plate at various pressures, without the complex
preparation of catalyst and introduction of impurities by design.
The aim of this paper is to investigate the synthesis and growth
model of carbon coils with arc discharge. In particular, we
attach importance to the function of the metal plate and the
morphology of products affected by reaction pressure changes.
In addition, it was found that different types of gas source
influence the forms of products.
2. Experiments
The reaction apparatus in the experiment is composed of
an electrode, reaction chamber, vacuum pump, circulatory
system, DC power supply, and so on. A spectral pure
graphite rod with size of φ 12 × 200 mm and a metal plate
(80 mm × 80 mm × 15 mm) treated by ultrasonics were
used as anode and cathode, respectively. After evacuation of
∗
Corresponding address: China University of Mining and Technology, Xu
Zhou City, Jiang Su Province, PR China. Tel.: +86 516 83892826; fax: +86 516
83995279.
E-mail address: zhuyabo@163.com (Y.B. Zhu).
c
0038-1098/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.ssc.2007.03.009

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L. Zhang et al. / Solid State Communications 142 (2007) 541–544
the system to a pressure of 0.2 Torr, the acetylene (industry-
grade acetylene) was introduced into the chamber. In succession
the arc was generated with an output current of 96 A
and voltage of 35–40 V in an acetylene atmosphere at a
pressure of 160–460 Torr. The circulatory pump operated
constantly in order to utilize the acetylene to the extreme.
Three minutes later, a large number of club-shaped products,
whose size is approximately 1 mm, developed vertically
on the surfaces of plate. They arrange with each other
with orderliness like a comb. The club-shaped samples
were characterized by X-ray diffraction (D/MAX–3B, XRD),
scanning electron microscopy (S–520, SEM), transmission
electron microscopy (JEM–100CXII, TEM), and energy
dispersive X-ray spectroscopy (JEM2010, EDS) attached to the
transmission electron microscope.
3. Results and discussion
3.1. The function of the metal plate and coil growth model
As already mentioned, the products developed vertically on
the surfaces of the plate, which serves not only as the electrode
but also as the substrate. On the other hand, experimental
findings demonstrated that the plate also provided catalyst
particles for the growth of the carbon micro coils. Fig. 1(a)
shows the representative morphology of the coils. There could
be found a dark dot locating at the node of two coiled fibers. The
result of electron diffraction confirms that the dot is Ni single
crystalline, as shown in Fig. 1(b). It is easy to deduce that the
Ni comes from the metal plate. In fact, it has been observed that
there were some small cavities in the arc area of the cathode,
indicating that the catalyst grains derive from a splash in the
arc discharge process on the metal plate.
Fig. 1. (a) TEM image of carbon coils on the metal plate, and (b) the EDS of
the dot P.
It is very interesting that two coiled fibers in Fig. 1(a) have
opposite helical state (one is left-handed, the other is right-
handed), identical cycle number, coil diameter, coil length, coil
pitch, and fiber diameter, grown from the dot. We think that the
symmetry of the crystal faces’ structure [10,11] and some other
external factors result in the enantiomorphous morphology of
the carbon coils. Moreover, the morphology of the carbon
coils shows their growing model of bottom growth. Ni comes
from the metal plate and serves as a catalyst in the growth
process. The acetylene is decomposed into carbon atoms on
the surface of the catalyst and diffuses into the Ni grains. With
the concentration of carbon in the Ni catalyst increasing, the
nucleus grows up to forms into straight fibers in the beginning,
and then the straight fibers are transformed into the filaments of
coils by outer factors.
We propose four steps to describe the formation of a carbon
coil. First (the initial stage), straight carbon fibers form from
the catalyst particles, which are attached on the plate because
of their rough surface by van der Waals forces; second, with the
van der Waals force decreasing due to temperature changing,
the stress along the fiber axis causes the distortion of fibers;
third, the elastic module of the straight fibers mainly controls
the coil diameter, coil length, coil pitch, and so on; fourth,
angular momentum conservation dictates that the two coils,
Fig. 2. (a)–(d) illustrate the growth mechanism of the carbon coils. The gray
area and dark area represent the van der Waals forces area and metal plate,
respectively.
which derive from the same catalyst grains, have opposite
helix. Fig. 2(a)–(d) illustrates the four-step model. Therefore,
in our view, carbon coil formation is influenced by not only the
anisotropy of catalyst grains but also the appropriate module
and stress of straight fibers, gas pressure, temperature field, etc.
In fact, coils with opposite handedness appear in a wide
range of biological and physical systems, such as climbing
plants [12], super-coiling of DNA structures [13,14], and morph
genesis in bacterial filaments [15,16]. The former model is in
view of these natural phenomenons [17–19].

L. Zhang et al. / Solid State Communications 142 (2007) 541–544
543
Fig. 3. SEM images of CMCs at different gas pressure: (a) 160 Torr, (b) 235 Torr, (c) 310 Torr, (d) 385 Torr and (e) 460 Torr.
3.2. The influence of gas pressure on the growth of products
Fig. 3 shows the morphology of the samples corresponding
to different acetylene gas pressure ranging from 160 to 460 Torr
in the reactor. The pressure of 160 Torr is not good for the
fabrication of carbon coils. Fig. 3(a) show that under this
pressure most of the products are other carbon forms such as
straight fibers, with just a small fraction being coils, which
have an average coil diameter and pitch of 0.5–0.8 µm and
0.8–1.2 µm, respectively. With the reaction pressure rising
to 235 Torr, some double carbon coils with the diameter of
2–4 µm and small pitch are obtained (Fig. 3(b)), but most
products are still other carbon forms such as nanofibers and
normal fibers. Fig. 3(c) and (d) show that with the pressure
of 310–385 Torr, carbon coils are in the majority, though
some straight carbon fibers or strips exist. The distribution
of the coils becomes more regular. In particular, 385 Torr is
the best pressure condition for forming the coils because the
proportion accounts for 80%–90%. It is a fact that nearly all
the products are double coils, as shown in Fig. 3(d). The coil
size become much bigger than previously, and their diameter
and length are about 6–10 µm and 50–80 µm, respectively. The
experiments also indicate that very high pressure is not helpful.
As the gas pressure becomes higher than 460 Torr, carbon coils
almost disappear from Fig. 3(e). The diameter of products is
approximately 50–100 nm; the sample turns into nanotubes,
which are testified by other TEM images (not shown here).
Fig. 4 describes concretely the influence of acetylene gas
pressure on the yield and diameter of coils. It is easy to
find that the yield and diameter of coiled fibers increase with
pressure from 160 to 375 Torr, but decrease when the value of
the pressure is beyond 375 Torr. As to the yield of the coils
decreasing, an explanation is that the density of acetylene is
so high that the catalyst is poisoned. As to the coil diameter
Fig. 4. The influence of pressure on the yield and diameter of coils. The dashed
line and the solid line show that the changes of yield and coil diameter with the
pressure increase, respectively.
changing, we think the gas pressure through controlling the
fiber module influences the coil diameter.
3.3. The influence of impurity
In experiments, we found that when pure acetylene was
substituted for industry-grade acetylene, only little amorphous
carbon was obtained, and no other products existed. Industry-
grade acetylene contains a few kinds of impurities such as
sulfur and phosphorus. The behavior of S and P may greatly
affect the formation of carbon coils. We think S and P join
together with the carbon atoms, forming an S (P)–C at the
reaction temperature. As a result, S (P)–C can be absorbed
effectively by the catalyst grains, which facilitate the formation
of the carbon coils, and in our experiments, no carbon coils
were obtained in the absence of impurities, suggesting that

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L. Zhang et al. / Solid State Communications 142 (2007) 541–544
they serve as a promoter for the preparation of carbon coils.
This finding is in agreement with the conclusion drawn by
Kawaguchi [20].
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4. Conclusions
Carbon coils were prepared by decomposition of acetylene
using an arc-discharge process with a metal catalyst. A four-
step growth model was proposed to explain the coil growing. It
is found that the diameter and the morphology of the coils are
greatly influenced by acetylene gas pressure. By comparison,
310–385 Torr is the best pressure condition for the preparation
of the carbon coils. It is also found that no coils were obtained
without S or P impurity, which should be a promoter for coil
growth.
Acknowledgements
The authors are grateful for the support of the Technological
Foundation of CUMT (ON060164), National Nature Science
Foundation of China (60376032) and Natural Science
Foundation of Jiang Su Colleges (05KJD140221).