Development of Catalyst for
Synthesizing Multi-Walled Carbon Nanotubes

@@ Motoo Yumura, Ph.D., the group leader and Hiroki Ago, Ph.D., a group member of Molecular Reaction Engineering Group of Department of Chemical Systems of National Institute of Materials and Chemical Research, one of the participating research institutes of Frontier Carbon Technology Project (Main Office: Japan Fine Ceramics Center, Tokyo), have been engaged in the research and development of 'Frontier Carbon
Technology Project' for Industrial Science and Technology started under the auspice of Ministry of International Trade and Industry from the fiscal year 1998. Yumura and Ago have been developing synthetic methods of carbon nanotubes. Recently, they have succeeded in developing a catalyst for synthesizing multi-walled carbon nanotubes; the method that is expected to promote the practical use of thin wall-hanging television, and many other applications.
@@ Carbon nanotubes discovered originally by a Japanese scientist Dr. Iijima in 1991 is now drawing much attention as a high luminance, energy savings material used for the source of cold cathode electron in field emission display (FED) for wide flat panel display. The search for ample application of this material has been actively carried out.
@@ Recently, synthesizing nanotubes by chemical vapor deposition (CVD) has attracted a great interest as one of the promising synthetic methods . This technique, comparing to arc discharge or laser ablation, has the advantages of the following:
@(1) possibility of mass production
@(2) reaction occurs at relatively low temperature
@(3) possibility of orientation control
@@ When applying this technique, the key to the successful synthesis is a metal catalyst, and nanotubes are known to be produced only when ultra fine particles are used as the catalyst. To manufacture ultra fine metal particles for producing nanotubes, various methods, for example, burying in the porous materials such as zeolites or porus silicon, etching metal thin films with laser or microwave or making ultra fine particles by thermal decomposition of organometallic complex, etc., have been examined. However, in order to control the structure of nanotubes, it is favorable to utilize well-controlled ultra fine particles. Moreover, to meet the need for area enlargement of the field emission display which is in the closest to commercialization, a preparation method for easier handling ultra fine particles is highly desired.
@@ The researchers have synthesized the above mentioned ultra fine metal particles by a chemical method called "reversed micelle method" and applied them to nanotube producing catalyst.
@@ A reversed micelle method is a technique to synthesize metal nanoparticles by reducing metal ions in a water pool surrounded with surfactant. They applied this technique to cobalt which works as a nanotube catalyst, and eventually obtained the cobalt particles with an average diameters of 4nm as shown in Figure 1.
@@ The reaction of the cast film of this nanoparticles in acetylene gas at 800-900�� resulted in aligned multi-wall carbon nanotube array as shown in Figure 2�m1.2�n. As for the growth of nanobutes, it is considered that the different factors such as the condition of the cobalt or reaction temperature have the effect on the oriented films of the nanotubes; and the growth to the same direction is presumed to be the effect of the existence of adequate equilibrium relationship between the growth speed and the gas density as well as the gas supplied from one specific direction. Furthermore, depending on a reaction condition, it has been found that nanotubes grow and form a structure shown in Figure 3. The research group has already confirmed the field electron emission from oriented thin films shown in Figure 2.
@@ The catalyst solution developed here is stable in ambient atmosphere and easy to handle. Thus application of this solution combined with the screen printing method or ink jet printer facilitates the enlargement of the field area or patterning. Moreover, it is possible to apply it on curved surfaces, the property which can be profited when applying carbon nanotubes to electron sources or electrodes.