JPH0761803A - Production of fullerene and carbon nanotube - Google Patents

Abstract

PURPOSE:To synthesize fullerene and carbon nanotubes with good mass productivity. CONSTITUTION:This method for synthesizing fullerene and carbon nanotubes comprises making Ar gas flow through the interior of a reactional tube 1 made of quartz glass, making a high-frequency electric current flow through an induction coil 3 wound around the periphery thereof under >=100Torr pressure, producing a thermal plasma 4, feeding powder 6 of carbon into the thermal plasma 4, evaporating and recombining the powder. Since the thermal plasma 4 produced by the high-frequency induction has a wide plasma region at a high temperature, a large amount of the carbon powder 6 can instantaneously be evaporated to synthesize large amounts of the fullerene and carbon nanotubes in a short time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a method for synthesizing fullerene and carbon nanotubes, which are cluster molecules consisting of carbon only, with high productivity.

[0002]

2. Description of the Related Art In 1985, the existence of soccer ball-shaped cluster molecules C ₆₀ and C ₇₀ consisting only of carbon was confirmed by Kuroto. Then C _{7 6} ,
Also found similar cluster molecules such as C _{7 8,} the series of spherical shell carbon molecules became known as fullerenes. In 1990, Smolley et al. Developed a method for synthesizing fullerenes using arc discharge between carbon electrodes. In 1991, Iijima et al. Discovered a carbon skeleton (carbon nanotube) having a tubular structure. Subsequent studies have discovered that these fullerenes and carbon nanotubes have characteristics such as semiconductors and superconductors, and are expected to be applied in the future. The fullerene synthesizer, first reported by Smolli et al., Used carbon rods with a diameter of 6 mm.
It was synthesized under the arc discharge condition of helium while cooling the periphery of the carbon rod with water by passing a current of 100 to 150 A at 0 to 20V. The percentage of fullerenes present in the powder solids produced is reported to be about 10%. Carbon nanotubes can also be obtained on the negative carbon electrode of a similar synthesizer.

[0003]

It is difficult to increase the amount of carbon vaporized by the conventional method using DC arc discharge,
Further, since various clusters produced are scattered throughout the apparatus, the production amount of fullerenes and carbon nanotubes is about 0.1 g at maximum in 1 minute, and the mass production is poor and the production cost is high.

[0004]

In the synthesizing apparatus of the present invention, thermal plasma is generated using a high frequency induction coil, carbon powder is fed into it, and vaporized and recombined to synthesize fullerenes and carbon nanotubes. The thermal plasma is a plasma in which the temperatures of ions, electrons, and neutral particles are in a thermal equilibrium state, and is generated under a pressure of about 100 Torr or more, and the temperature becomes as high as 5000 to 20000K. At a pressure of about 100 Torr or less, the temperature of ions, electrons, and neutral particles becomes a non-equilibrium low-temperature plasma, and the temperature is about 100 to 1000K. Methods of generating thermal plasma include a method using DC arc discharge and a method using high frequency discharge. The thermal plasma generated by the high frequency induction coil is ICP (Inductively).
It is called a Coupled Plasma) and has a characteristic that a plasma region is wider than that of thermal plasma generated by arc discharge and that impurities are not mixed from electrodes. This ICP
With, it is possible to instantly evaporate a large amount of carbon powder. It is possible to synthesize 5 g or more of fullerene or carbon nanotube per minute, mass productivity is extremely good, and manufacturing cost is low.

[0005]

1 is a schematic view showing an example of the apparatus of the present invention. The inside of the reaction tube 1 made of a quartz glass double tube having an inner diameter of 44 mm and a length of 200 mm is evacuated to a high vacuum to completely remove oxygen and moisture, and then Ar gas is flown from the top to the bottom at a flow rate of 30 l / min. . 20kV, 10A, 4M on the induction coil 3 wound around the reaction tube with the internal pressure set to 400 Torr.
When a high frequency current of Hz is applied, ICP4 is generated at the center of the reaction tube. At this time, the temperature at the center of the ICP is about 10,000.
In order to reach K, cooling water is constantly flowed between the double tubes of the reaction tube during the experiment. Carbon powder 6 having an average particle diameter of 2 to 3 μm was fed into this ICP at a rate of 10 g per minute, and the carbon powder 9 reacted in the trap 8 was collected. When the yield of the recovered powder was measured, 80% or more of the supplied carbon powder could be recovered. When fullerenes were extracted from the recovered carbon powder with benzene, the yield of fullerenes in the powder was 5% or more.
In addition, carbon nanotubes were detected in the powder by observation with an electron microscope. The yield of fullerene and carbon nanotubes in the carbon powder after the reaction is 5 to 1 in total.
It is 0%. The pressure inside the reaction tube is 100 Torr to 76
When the experiment was performed by changing the pressure between 0 Torr, fullerenes and carbon nanotubes were formed at any pressure. FIG. 2 shows the relationship between the pressure and the combined yield of fullerene and carbon nanotubes. From this figure, it can be seen that the higher the pressure, the slightly higher the yield. Then the pressure is 76
The supply amount of carbon powder is set to 0 Torr and is 10 g / mi.
When the amount was changed from n to 100 g / min, the larger the amount supplied, the lower the yield, but the yield increased. FIG. 3 shows the relationship between the supply amount, the yield, and the yield. The yield of fullerene and carbon nanotubes is about 6 g when the supply amount of carbon powder is 100 g / min at 760 Torr.

[0006]

As described above, the present invention is different from the conventional method of using the arc discharge between the carbon electrodes, and is fed from the outside in an ICP having a wide plasma region and a high temperature of about 10000K near the center. Since a large amount of carbon powder is evaporated in a short time, it is possible to synthesize a large amount of fullerenes and carbon nanotubes at high speed.

[Brief description of drawings]

FIG. 1 is a schematic view of an apparatus showing an example of an apparatus for synthesizing fullerenes and carbon nanotubes using ICP according to the present invention.

FIG. 2 is a diagram showing the relationship between the yield of fullerene and carbon nanotubes and pressure.

FIG. 3 is a diagram showing the relationship between the supply amount of carbon powder and the yields of fullerenes and carbon nanotubes.

[Explanation of reference symbols] 1 reaction tube 2 vacuum pump 3 induction coil 4 ICP 5 feeder 6 carbon powder 7 chamber 8 trap 9 reacted carbon powder

Claims (1)

[Claims] 1. A method for synthesizing fullerenes and carbon nanotubes, which comprises synthesizing fullerenes and carbon nanotubes by feeding carbon powder into thermal plasma generated by a high frequency induction coil, vaporizing and recombining carbon powder.