S-R5-3
Production Process of Carbon Nanotube Coagulates
カーボンナノチューブ微粒子のプラズマ合成過程
Tetsu Mieno, Kazunori Koga1), Masaharu Shiratani1)
三重野 哲，古閑 一憲1)，白谷 正治1)
1)

Dept. Physics, Shizuoka University, Ooya, Suruga-ku, Shizuoka-shi 422-8529, Japan
Grad. School Info. Sci. & Electrical Eng., Kyusyu University, Motooka, Nishi-ku, Fukuoka-shi, 819-0395, Japan静岡大学理学部	 〒422-8529	  静岡市駿河区大谷	 1)
九州大学システム情報科学研究院	 〒819-0359	 福岡市西区元岡	 Control of production process of carbon nanotubes is urgent and important theme. Here, production process of carbonnanotubes by the arc-discharge method is in-situ monitored by the laser Mie-scattering method. As a result we canmeasure specio-temporal distribution of size and density of nanotube coagulates in the arc reactor. In this process thestrong heat convection modifies the flow and cooling rates of the carbon coagulates. In case of arc production ofcarbon clusters, in-situ monitoring would be important.

1. Introduction
Carbon nanotubes (CNTs) have big potential ofapplications as new functional material.
However, production of long defect-freenanotubes, control of chirality and selective
productionofmetal-nanotubes
arestillchallenging themes. In order to develop theproduction method, in-situ monitoring of theproduction processes is necessary, though thecluster size in the reaction gas phase is in therange of nm. Figure 1 shows a model figure of
the production process of single-walled carbon
nanotubes by the arc discharge method, in which
CNTs grow in the hot gas phase. [1]Not only CNTs, metallo-fullerenes, which has
potential application to contrast-media of MRI,
copper doped CNTs for the use of nano-scale
cables, [2] metal-capsulated carbons for the useof nano-sized metal powders.
Nano-sized
diamond particles have been developed by Osawagroup of Shinsyu Univ. and started to sell. [3]Watanabe and Shiratani have developed thein-situ monitoring method of silicon nanoparticles during plasma processings by silane gas,so called the Mie scattering method. [4, 5] They
successfully obtained specio-temporal distributions of silicon particles in the discharge space,and control the production and diffusion ofsilicon particles.
Here by the similar method, production processand diffusion process of nanotube coagulates in
the arc plasma reactor are investigated. [1, 6, 7]
Scattered laser light by particles at two scattering
angles are simultaneously measured andcompared with the theoretical values. [8] Then
we can confirm average size and density of thecarbon nanotubes coagulates.
2. Experimental
Schematic of the reactor is shownin Fig. 2, where a 6.5 inch diam., 270
mm high (volume of 1.8 L) metalchamber is used.
A square-type
carbon anode and a column-type
cathode are set under 0.5 atm of He gas.
A pulse-modulated green laser ( " =532 nm) is penetrated from the bottomside to the top side through the centerof the arc plasma.
Along the laser
axis (z axis), scattered! lights with
scattered angles of 15 deg. and 90 deg.
are detected using optical fibers, andaveraged by using lock’in amplifiers.

Fig. 1 A model figure of production process of CNTs by
the arc discharge method.

3. Results and discussion
Figure 3 shows vertical distribution

of estimated cluster size and density over the arc
center under the gravity-free condition.
Thecluster size d starts to grow and the cluster size
increases from z= 1 cm (above the arc plasma),where discharge current Id= 40 A and He pressure p=40 kPa.

Figure 4 shows pressure dependence of
estimated cluster size and density at z= 2 cm forthe normal-gravity condition.
By theconvection effect, the cluster size decreases byincreasing He pressure, though the cluster size iskept almost constant.
Figure 5 shows discharge current dependenceof estimated cluster size and density at z= 2 cm
for the normal-gravity condition. The cluster
size decrease by increasing the current, while thecluster density gradually increases with thecurrent.
The cluster size increases under thezero-gravity, higher-pressure, higher-discharge
current or at the large z position. Under thenormal gravity, the cluster size becomes smaller,
and the heat-convection strongly influences thecluster growth. These results are consistent
with the theoretical prediction. Development of
the laser Mie-scattering method and precise
control of the arc discharge method are underinvestigation.

Japanese).
[3] Please visit “http://nano-carbon.jp/.
[4] M. Shiratani, S. Matuo, Y. Watanabe, Jpn. J. Appl.
Phys. 30 (1991) 1887.
[5] Y. Watanabe, J. Phys. D: Appl. Phys. 39 (2006)
R329.
[6] T. Mieno & M. Takeguchi, J. Appl. Phys. 99(2006) 104301.
[7] T. Mieno, J. Jpn. Soc. Microgravity 26 (2009) 72(in Japanese).
[8] C. F. Bohren & D. R. Huffman, “Absorption andScattering of Light by Small Particle”, John WillySons, 1983.

Fig. 3 Estimated cluster diameter d & cluster density np
under gravity-free condition vs. scattering position overthe arc center.
Id= 40 A p= 40 kPa.

Fig. 4 Estimated cluster size & density vs. He pressure.
Under normal gravity condition. Id= 40 A, z= 2 cm.

Fig. 2 Schematic of the experimental setup.
Acknowledgment
This study was supported by a Grant-in-Aid
for Scientific Research from MEXT, Japan.
References[1] T. Mieno & M. Takeguchi, New Diamond &Frontier Carbon Technol. 16 (2006) 139.
[2] A. Koshio, Convertech 37, No. 4 (2009) 102 (inFig. 5 Estimated cluster size & density vs. discharge
current under normal gravity condition. p(He)= 40
kPa, z= 2 cm.