JPH05238717A - Method and device for producing fullerene - Google Patents

Abstract

PURPOSE:To improve the production efficiency by supplying a graphite powder into a microwave discharge field, sublimating the powder by the discharge plasma and subjecting the sublimate to a reaction. CONSTITUTION:The microwave outputted from a microwave oscillator 5 is introduced into a cylindrical cavity resonator 1 through a waveguide 6. A graphite powder is added into a quartz discharge tube 2 for generating the electric discharge of gaseous He 4 by the electric field. The surface temp. of the graphite powder is increased by the high-temp. uniform plasma produced in the electric field formed in the resonator 1, and the graphite powder is vaporized at a temp. higher than the sublimation temp. of graphite. The vaporized graphite is subjected to a reaction in the plasma, and fullerene and soot are finally formed. The product present in a carrier gas as the fine particles is recovered by a cyclone 8 and extracted by a solvent such as toluene, and fullerene is obtained in high yield.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for producing fullerenes (spherical carbon clusters composed of C60, C70 etc.) used as catalyst carriers and electronic materials.

[0002]

2. Description of the Related Art A conventional fullerene manufacturing apparatus will be described with reference to FIG. FIG. 4 is a front view of a conventional device. In the atmosphere of the helium gas 9 of about 100 Torr in the vacuum vessel 10, the DC power supply 12 causes an arc discharge of 50 V, 100 A between the graphite electrodes 11 to evaporate the graphite. After discharging for about 1 hour at various helium pressures, the inner wall of the vacuum vessel and the water-cooled copper pipe 13
The soot containing the fullerenes attached to is collected. An example of the yield of fullerene according to the prior art is shown in FIG.

[0003]

In the prior art, fullerene generated by arc discharge scatters in the entire vacuum vessel, so the recovery rate is lowered, impurities are easily mixed, and the heating method by arc discharge causes discharge. Since the electric current is localized at a part of the graphite surface, the surface temperature of the graphite is high only in a partial area, and the sublimation amount of the graphite is not constant in a small amount, so that the reaction efficiency is lowered. Further, since the graphite rod as a raw material also serves as an electrode for arc discharge, there is a drawback that the shape of the electrode changes greatly with time due to evaporation of graphite and stable reaction conditions cannot be obtained.

In view of the above-mentioned state of the art, the present invention is to provide a method and apparatus for producing fullerenes capable of improving the reaction efficiency of fullerene production and the recovery rate of fullerenes as compared with the prior art.

[0005]

The present invention provides (1) a method for synthesizing fullerenes, characterized in that graphite powder is supplied into a microwave discharge field and the powder is sublimated and reacted by discharge plasma.

(2) Microwave oscillator, waveguide for propagating microwaves emitted by the oscillator, cavity resonator connected to the waveguide, and discharge tube inserted in the cavity resonator A fullerene synthesizing apparatus comprising: a gas supply means for introducing and flowing a discharge medium into the discharge tube; and a graphite supply means for supplying graphite powder into the discharge medium.

(3) The fullerene synthesizing apparatus as described in (2) above, wherein the discharge tube has an adiabatic expansion section near the outlet from the cavity resonator. Is.

[0008]

According to the method of the present invention, by adding graphite powder having a large specific surface area using helium gas as a carrier gas, it is possible to bring the high temperature plasma into wide contact with the high temperature plasma generated by the microwave discharge. it can. In plasma, a rapid temperature rise of the graphite powder and a uniform temperature distribution can be obtained, and the evaporation amount of graphite increases, so that the reaction efficiency of fullerene can be increased. Furthermore, since the generated fullerene can be guided to the recovery filter or the cyclone using helium gas as a carrier, the recovery rate of the fullerene can be improved.

Further, according to the device of the present invention, the microwave output from the microwave oscillator is introduced into the cavity resonator (for example, the cylindrical cavity resonator) through the waveguide, and the electric field thereof causes the helium gas to be emitted. Graphite powder is added to the inside of the discharge tube for generating a discharge, and the microwave electromagnetic field mode formed inside the cavity resonator is TM (Transvers Magneti
c) The temperature of the graphite powder surface rises due to the high temperature and spatially uniform discharge plasma generated by the electric field formed by selecting the cutoff frequency of the mode, and the graphite is evaporated at a sublimation temperature of 3500 ° C or higher. The vaporized graphite finally undergoes various reactions in plasma to form fullerenes and soot. Since the product exists as fine particles in helium as the carrier gas, the end of the discharge tube is collected as a filter structure.

In the apparatus using the microwave discharge induced by the cutoff frequency of the TM mode, the entire graphite powder diffuses into the entire discharge plasma, so that the evaporation area becomes large as compared with the case of the DC arc discharge. Moreover, the temperature distribution on the graphite surface is constant. Therefore, the molecular weights of the substances evaporated from the graphite surface are substantially equalized, and there is no variation in the products, and the reaction efficiency of fullerenes is improved. Further, the product containing the fullerene produced by the microwave discharge is recovered by a cyclone or a filter, so that the recovery rate is also improved.

Further, in the above-mentioned device, when the discharge tube has an adiabatic expansion portion near the outlet from the cavity resonator, the decomposition reaction of the generated fullerene by electrons or ions is suppressed, so that the reaction of fullerene. You can improve efficiency.

[0012]

【Example】

(Example 1) An example of fullerene production by microwave discharge according to the present invention will be described with reference to FIG. Here, a case where a cylindrical cavity resonator is used as the cavity resonator is illustrated, and FIG. 1 shows a front sectional view thereof.

The cylindrical cavity resonator 1 has an inner diameter of 86 mm and a length of 100 mm, and a graphite powder 3 is placed inside a quartz discharge tube 2 having an inner diameter of 25 mm with a pressure of 20 Torr and a flow rate of 5.
A helium gas 9 of 00 ml / min was used as a carrier and introduced from the graphite powder supply part 4 and discharged in the discharge tube 2. Microwaves were generated by the 2.45 GHz oscillator 5 and guided to the cavity resonator 1 using the waveguide 6. The deviation of the resonance frequency due to the evaporation of graphite during discharge is always obtained by the uniform discharge by the tuner 7 attached to the end plate of the cavity resonator 1. After discharging for 30 minutes, the black product in the cyclone 8 was recovered, and the fullerene was recovered by Soxhlet extraction using toluene as a solvent. The result of obtaining the yield of fullerene obtained by changing the pressure is shown in FIG.

Further, the microwave electromagnetic field mode is set to the higher order mode of TM or TE according to the shape of graphite.
The same result can be obtained by selecting the (Transvers Electric) mode and forming it inside the cavity resonator.
Further, depending on the shape of graphite, it is not necessary to form a standing wave in the cavity resonator, and graphite may be discharged in a normal traveling wave type waveguide.

(Embodiment 2) Another embodiment of the fullerene device by microwave discharge of the present invention will be described with reference to FIG. The apparatus shown in FIG. 2 is different from the apparatus shown in FIG. 1 only in that the discharge tube 2 shown in FIG. 1 uses a nozzle 4 that adiabatically expands in the vicinity of the outlet from the cavity resonator 1. Is the same.

The cylindrical cavity resonator 1 has an inner diameter of 86 mm and a length of 100 mm, and a graphite discharge tube 2 having an inner diameter of 25 mm with an adiabatic expansion nozzle 4 provided at the lower end of the cavity has a graphite powder 3 at a pressure of 20 Torr and a flow rate. 500 ml / mi
Helium gas 9 of n was introduced as a carrier from the graphite powder supply part 4 and discharged in the discharge tube 2. The microwave is generated by the 2.45 GHz oscillator 5, and the waveguide 6
Was introduced into the cavity resonator. The deviation of the resonance frequency due to the evaporation of graphite during discharge was set so that the tuner 7 attached to the end plate of the cavity resonator could always obtain a uniform discharge. The discharge plasma containing vaporized graphite generated here was ejected through a nozzle 4 into a vacuum of 10 ^-2 Torr. After discharging for 30 minutes, the black product in the cyclone 8 was recovered, and the fullerene was recovered by Soxhlet extraction using toluene as a solvent. The result of obtaining the yield of fullerene obtained by changing the pressure is shown in FIG.

Further, the microwave electromagnetic field mode is set to the higher order mode of TM or TE according to the shape of graphite.
The same result can be obtained by selecting the (Transvers Electric) mode and forming it inside the cavity resonator.
Further, depending on the shape of graphite, it is not necessary to form a standing wave in the cavity resonator, and graphite may be discharged in a normal traveling wave type waveguide.

The fullerenes produced in the present invention are K,
It is possible to obtain a superconducting material in which crystals of a large number of fullerene molecules are doped with these metals by heating together with Rb, Cs and the like in a reduced pressure sealed tube of He gas. For example, in the case of RbCs ₂ C ₆₀ , the critical temperature is 35K
Becomes

Further, fullerene, Pd, Pt (polyphenylphosphine) ₂ , in reduced toluene under Ar gas,
By stirring any of OsO ₄ (4-t-butylpyridine) ₂ , an oxidation catalyst or a reduction catalyst having fullerene crystals doped with them can be obtained. C ₆₀ Pd _n as examples thereof, C ₆₀ [Pt (poly triphenylphosphine) _2], C ₆₀ [OsO _{4 (4-t-} butylpyridine)] and the like.

Further, when La is added to the discharge plasma during the fullerene generation process, La is doped in the fullerene molecule (ie, in the spherical body) to obtain a functional material having electrical conductivity. This functional material is dimensionally controllable and highly reactive, and can be used for electrodes, wires, sensors (temperature, light,
Gas, ions, etc.), molecular devices, superconductors, etc.

[0021]

According to the present invention, in the production of fullerene, the temperature of the graphite surface can be raised uniformly by the graphite discharge in the TM mode, and the evaporation amount of graphite and the amount of graphite can be adjusted by optimizing the flow rate of helium gas. The production efficiency of fullerenes can be improved. Further, adiabatic expansion of high-temperature plasma containing vaporized graphite can cause a fullerene synthesis reaction in an appropriate plasma state. Furthermore, by appropriately selecting the cyclone shape and the mesh size of the filter, it is possible to suppress the decrease in the recovery rate of the soot containing fullerenes, which is a drawback of the prior art.

[Brief description of drawings]

FIG. 1 is an explanatory view of an embodiment of fullerene production by microwave discharge according to the present invention.

FIG. 2 is an explanatory view of another example of fullerene production by microwave discharge according to the present invention.

FIG. 3 is a graph showing the yields of fullerenes when the pressure is changed in the two examples of the present invention and the conventional method.

FIG. 4 is an explanatory view of a conventional fullerene manufacturing apparatus.

Claims (3)

[Claims] 1. A method for synthesizing fullerene, which comprises supplying a graphite powder into a microwave discharge field, and sublimating and reacting the powder by discharge plasma. 2. A microwave oscillator, a waveguide for propagating microwaves oscillated by the same, a cavity resonator connected to the waveguide, and a discharge tube inserted in the cavity resonator. A fullerene synthesizing apparatus comprising: a gas supply unit for introducing and flowing a discharge medium into the discharge tube; and a graphite supply unit for supplying graphite powder into the discharge medium. 3. The fullerene synthesizing apparatus according to claim 2, wherein the discharge tube has an adiabatic expansion portion near an outlet from the cavity resonator.