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: j4306702@ed.kagu.tus.ac.jp;

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

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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.

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