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production of carbon nano materials
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Journal of the Korean Physical Society, Vol. 54, No. 3, March 2009, pp. 10321035
Carbon Nano Materials Produced by Using Arc Discharge in Foam
Yong-Il Kim,
Eiichi Nishikawa and Toshihide Kioka
Division of Electrical Engineering, Tokyo University of Science, Tokyo 162-8601, Japan
(Received 16 June 2008)
Nano materials are very important materials because they have a possibility of a large number
of applications not only in electric devices but also in pharmaceutical processes. If these nano
materials are to be applied to practical devices and processes, a simple synthesis method of the
nano material is of signicant importance. In this paper, we report the rst successful synthesis
of several types of nano materials the synthesis was achieved by using a simple method of an
arc discharge in foam. From the transmission electron microscopy observation, multi-walled nano
tubes, capsule materials and materials with cabbage-shaped cross sections were often found.
Furthermore, through this simple method, arc discharge in foam, several types of nano materials
could be easily collected on the surface on the foam.
PACS numbers: 52.80.Wq, 52.80.Tn
Keywords: Nano material, CNT, Capsule, Arc discharge, Foam
I. INTRODUCTION
The discovery of carbon nano materials, such as
fullerene (C
60
) [1] and carbon nanotubes (CNTs) [2],
has created new elds of materials research and devel-
opment. In recent years, the study of nano materials has
attracted considerable interest because they are needed
in microelectronic devices, metallurgy, surface modica-
tion, catalysis, biological labeling, photonics and infor-
mation storage [3,4]. If they are to be applied in practical
devices, a simple synthesis method of the nano material
is of signicant importance and several processes have
been developed to provide such nano materials. Sano
et al. have reported that nano particles with an onion-
like structure (nano-onion) of concentric atomic carbon
layers are found after dc arcing in water [5,6]. We con-
ducted a study from the unique point of view of a new
method for synthesizing nano-carbons by using an arc
discharge, with the aim of producing several types of
carbon nano materials at low cost. Here, we report the
rst successful trial of an easy to use synthesis method
for several types of carbon nano materials. The synthe-
sis method use an arc discharge in foam. The technique
used in this study facilitated the easy collection of carbon
nano materials from the foam's surface. Also, we used a
non-vacuum system, thereby eliminating almost all the
complex and expensive machinery usually required in the
arc discharge method.
E-mail: [email protected];
Tel: +81-3-3352-2307; Fax: +81-3-3352-2307
II. EXPERIMENTS
A schematic of the apparatus for the arc discharge in
foam is shown in Figure 1. The equipment is composed of
a chamber and a DC power supply. High-purity (99.9 %)
carbon rods were used as the electrodes for the arc dis-
charge. Regarding the environment of the arc discharge,
we used the foam generated by pouring \Beer" at room
temperature. We used a beer dispenser (Fukushima In-
dustries Corporation: FTN-38S1) to provide the beer
foam supply and the pressure of the carbon dioxide gas
in the dispenser was set to 2.4 kg/cm
2
. Generally, foam
can be prepared by using surfactants, which are primar-
ily proteins in the case of beer. Moreover, because the
foaming ingredients create viscous membranes, it is pos-
sible to obtain a highly dense foam phase that entraps
the carbon dioxide gas from the beer.
The arc discharge was conducted as follows: The car-
bon electrodes were placed in the middle of the chamber
after connecting them to a DC power supply and the
foam was poured into the chamber until the carbon elec-
trodes were covered. Next, an arc discharge was initiated
by applying a voltage of 20 V and a direct current of 15
A to the electrodes. The average free path of an arc dis-
charge in foam is longer than that in water; in addition,
although the surface of the foam swells due to the arc dis-
charge, its surface tension does not allow the bubbles on
the surface to break. As a result, it is possible to conne
the arc discharge within the foam, whereby we induced
a DC arc discharge that lasted for several minutes.
The products of the arc discharge attached to the foam
-1032-
Carbon Nano Materials Produced by Using Arc Discharge in Foam { Yong-Il Kim et al. -1033-
Fig. 1. Schematic of the experimental setup for the preparetion of several types of nano materials by using an DC arc
discharge method in foam.
Fig. 2. TEM images of MWNTs: (a) low-magnication view and (b) enlarged view of (a).
and as a result, there was a countless number of ne black
particles on the foam's surface. These ne particles were
typically 1000 { 5000 nm in diameter. We placed some
of the ne particles on a microscope specimen grid and
examined them by using a high-resolution transmission
electron microscopy system operating at 200 kV (HR-
TEM model H9500; Hitachi Co., Ltd.).
III. RESULTS AND DISCUSSION
From the TEM observation, three types of nano ma-
terials (multi-walled nano tubes, capsule materials and
materials with a cabbage-shaped cross section) were
observed among the ne particles of the foam's sur-
face. Figures 2(a)-(b) show typical TEM image of the
-1034- Journal of the Korean Physical Society, Vol. 54, No. 3, March 2009
Fig. 3. TEM images of capsule material: (a) low-
magnication view and (b) enlarged view of (a).
MWNTs. Figure 2(b) shows an enlarged view of (a). The
TEM images revealed that such nanotubes were MWNTs
of 10 { 20 nm in diameter and tended to be very straight
and clean.
Figures 3(a)-(b) show typical TEM images of the cap-
sule materials. Figure 3(b) shows an enlarged view of
(a). These micrographs show a well-crystallized straight
graphite layer. The capsule materials typically had a
diameter of 200 nm and consisted of 50 { 100 graphite
layers; the diameter of the inner space was approximately
150 nm. The graphite layers were of high quality, consist-
ing of long and straight parallel walls and only occasional
surface contamination.
Figures 4(a)-(b) show typical TEM images of the ma-
terial with a cabbage-shaped cross section. Figure 4(b)
shows an enlarged view of (a). We observed that the
internal structure was comprised of graphite sheets with
diameters of 20 nm folded into a multi-angle nano struc-
ture with a cabbage-shaped cross section. This material
was 20 nm in thickness and was comprised roughly of
Fig. 4. TEM images of material with a cabbage-shaped
cross section: (a) low-magnication view and (b) enlarged
view of (a).
40 layers of graphite sheets and the space between adja-
cent sheets produced the cabbage-shaped cross section.
The diameter of these cabbage-shaped materials varied
from 100 nm to above 500 nm. Since CNTs are usu-
ally observed as one-dimensional objects in the shape of
a needle and fullerenes extend radially, their structures
are dierent from that of the cabbage-shaped materi-
als. We assumed that the cabbage-shaped material was
formed when carbon vapor evaporated by the arc dis-
charge became entrapped inside ne foam bubbles and
was subsequently transformed into graphite as it shrank
and cooled down, together with the foam. Furthermore,
the cabbage-shaped materials are thought to appear in
agglomerations due to the aggregating eect of the foam.
Table 1 shows the parcents of several types of nano ma-
terials collected at the surface of the foam. We took 10
samples from the foam's surface and divided them into
three types of nano materials, MWNTs, capsule mate-
rials and materials with a cabbage-shaped cross section
Carbon Nano Materials Produced by Using Arc Discharge in Foam { Yong-Il Kim et al. -1035-
Table 1. Parcent of nano carbon materials on a foam sur-
face.
Nano carbon materials (vol%)
MWNTs 20 { 40 %
Capsule materials 10 { 30 %
Material of cabbage-shaped cross section 30 { 40 %
by using TEM observations. As seen from Table 1, we
observed 20 { 40 % MWNTs, 10 { 30 % capsule ma-
terials and 30 { 40 % material with a cabbage-shaped
cross-section. At present, the highest yield with our
method, as estimated by using TEM observations, is ap-
proximately 40 vol% for MWNTs, 30 vol% for capsules
and 30 { 40 vol% for material with a cabbage-shaped
cross section. However, at present, formation mecha-
nism was not conrmed; this will be conrmed in future
studies and further research.
IV. CONCLUSION
In summary, we reported that several types of nano
carbon materials such as MWNTs, capsule materials and
a material with a cabbage-shaped cross section, were
formed using an arc discharge method in foam. Through
this simple method, arc discharge in foam, these materi-
als could be easily collected on the foam's surface.
Since the characteristic features of the capsule mate-
rials enable the encapsulation or absorption of dierent
molecules or DNA, we expect that the capsule material
will be able to be used as a hydrogen adsorption agent or
as a drug delivery system. Also, we expect that applica-
tion of the material with a cabbage-shaped cross section,
may improve the strength of nano-sized springs. From
this study, we conclude that the proposed method may
be an ecient simple method for the fabrication of sev-
eral types of nano materials.
ACKNOWLEDGMENTS
This work was partially supported by the Center for
Drug Delivery Research (DDS), Tokyo University of Sci-
ence.
REFERENCES
[1] H. W. Kroto, J. R. Heath, S. C. O Brien, R. F. Curl and
R. E. Smalley, Nature 318, 162 (1985).
[2] S. Iijima, Nature 354, 56 (1991).
[3] I. Zalite, S. Ordanyan and G. Korb, Powder Metall. 46,
143 (2003).
[4] J. M. Capus, Powder Metall. 46, 8 (2003).
[5] N. Sano, H. Wang, M. Chhowalla, I. Alexandrou and G.
A. J. Amaratunga, Nature 414, 506 (2001).
[6] N. Sano, H. Wang, I. Alexandrou, M. Chhowalla, K. B.
K Teo and G. A. J. Amaratunga, J. Appl. Phys. 92, 2783
(2002).