JP2004149334A - Process and apparatus for manufacturing carbon nanotube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a process for manufacturing a carbon nanotube, which process simplifies its manufacturing apparatus and increases the synthetic ratio of the produced carbon nanotube; and a manufacturing apparatus therefor. <P>SOLUTION: In the process, the carbon nanotube is synthesized by performing DC arc discharge using a cathode 1 made of a carbon material. Here, the whole of or the arc discharge part of the carbon cathode material is pre-heated before performing arc discharge between the whole or the arc discharge part of the carbon cathode material and an anode 3. The relative positions of the cathode and the anode are changed while performing DC arc discharge. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for producing carbon nanotubes for producing carbon nanotubes by an arc discharge method.
[0002]
[Prior art]
BACKGROUND ART A carbon nanotube is a graphene sheet in which carbon atoms are regularly arranged in a hexagonal shape and is rolled into a cylindrical shape, and has attracted attention as a new material because it has unique physical properties. By performing an arc discharge between two carbon materials, such carbon nanotubes may be formed in deposits that aggregate on the carbon electrode side on the cathode side and in soot that scatters around the arc. Are known. Various techniques have been proposed for improving the yield of carbon nanotubes by an arc discharge method.
[0003]
For example, arc discharge is performed in a rare gas, and when carbon is evaporated and then condensed to form a carbon nanotube, the temperature range of the reaction chamber filled with the rare gas is set to 1000 ° C. to 4000 ° C. to perform arc discharge. A device that produces carbon nanotubes having a uniform distribution of length and diameter is known (for example, see Patent Document 1).
In addition, by covering both the carbon anode and the carbon cathode with a cylindrical carbon heater and performing arc discharge so that the heat radiation temperature of the carbon heater becomes 500 ° C. to 2000 ° C., the carbon nanotube produced is In some cases, the purity and yield are increased (for example, see Patent Document 2).
Further, there is a method in which uniform carbon nanotubes can be efficiently generated by heating the tip of an anode made of a carbon electrode and then performing arc discharge (for example, see Patent Document 3).
[0004]
[Patent Document 1]
JP-A-6-157016 [Patent Document 2]
Japanese Patent Application Laid-Open No. 2000-203820 [Patent Document 3]
JP 2000-344505 A
[Problems to be solved by the invention]
When the temperature of the entire reaction chamber is increased as in Patent Document 1, there is a problem that the manufacturing apparatus becomes complicated.
In addition, when only both electrodes or the anode are heated, there is a problem that the synthesis ratio of carbon nanotubes is low in spite of the large consumption of the anode electrode.
[0006]
The present invention has been made to solve such a problem, and an object of the present invention is to simplify a manufacturing apparatus and to increase a synthesis ratio of generated carbon nanotubes.
[0007]
[Means for Solving the Problems]
The method for producing carbon nanotubes according to the present invention synthesizes carbon nanotubes by performing a DC arc discharge using a cathode made of a carbon material. After the preheating, arc discharge is performed between the anode and the anode.
[0008]
In addition, DC arc discharge is performed while moving the relative positions of the cathode and the anode.
[0009]
During the arc discharge, the whole cathode carbon material or the arc discharge portion of the cathode carbon material is heated by a heating means different from the arc discharge.
[0010]
Further, the preheating temperature is set at 500 ° C. to 2000 ° C.
[0011]
Further, the preheating method is characterized by high-frequency induction heating, arc discharge by another electrode or heating by laser irradiation, or energization heating by another power source.
[0012]
Further, the anode is cooled.
[0013]
In addition, the apparatus for producing carbon nanotubes according to the present invention includes a cathode electrode made of a carbon material, an anode electrode disposed to face the cathode electrode at a predetermined distance from the cathode electrode, and connected to the anode electrode and the cathode electrode. An arc discharge power supply for causing arc discharge between these electrodes, and a heating means for heating the entire cathode electrode or an arc discharge portion of the cathode electrode are provided.
[0014]
Further, a moving means for relatively moving the cathode electrode and the anode electrode is provided.
[0015]
Further, the heating means is a high-frequency induction heating device, an arc discharge device using another electrode, or an energization heating device using a laser or another power source.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Before describing a specific embodiment, the circumstances that led to the present invention will be described.
The general idea of carbon nanotube synthesis by arc discharge is mainly that carbon vapor and carbon ions generated from the anode carbon electrode diffuse to the cathode side and condense on the surface of the cathode electrode, which is lower in temperature than the anode. Multi-walled carbon nanotubes) are synthesized.
Therefore, it is considered that the lower the temperature of the cathode, the faster the growth rate of the carbon nanotubes, and the cathode material does not need to be a carbon material as long as it is a heat-resistant conductive material.
Based on this idea, it has been considered that increasing carbon vapor and carbon ions from the anode greatly contributes to increasing the synthesis ratio of carbon nanotubes.
For this reason, as shown in the conventional example, the entire reaction system or the anode is heated in order to increase the yield of carbon nanotubes.
[0017]
However, according to experiments performed by the inventor of the present application, even if only carbon vapor and carbon ions from the anode were increased, a large amount of graphitic carbon powder or amorphous carbon powder adhered to the cathode surface, and the synthesis ratio of carbon nanotubes was reduced. Only low ones could be generated.
Therefore, as a result of repeating various experiments, the inventor of the present application has found that the most important factor to increase the synthesis ratio of carbon nanotubes is not to increase the anode temperature, but to control the temperature of the cathode where carbon nanotubes are generated is the most important factor. Thus, it was found that maintaining the cathode temperature within an appropriate temperature range is important for producing high-purity carbon nanotubes.
[0018]
The present invention is based on such knowledge, and has been produced as a result of a change in idea from focusing on only the anode temperature in the past. Hereinafter, specific embodiments of the present invention will be described.
[0019]
Embodiment 1 FIG.
FIG. 1 is a configuration explanatory view of one embodiment of the present invention, and shows a basic configuration of a carbon nanotube manufacturing apparatus.
The apparatus for producing carbon nanotubes of the present embodiment includes a carbon cathode 1 made of a carbon material, an anode 3 made of a carbon material, a DC power supply 5 for generating arc discharge, a cathode preheating means 7, and an anode cooling means 9.
[0020]
The carbon cathode 1 and the anode 3 are arranged with an appropriate gap therebetween, and are connected to a DC power supply 5 for generating arc discharge. The carbon cathode 1 and the anode 3 may be placed in a reaction chamber, or may be in an atmosphere outside the container. The cathode heating means 7 may be any means capable of preheating or heating the discharge generating portion of the carbon cathode 1 by laser irradiation, such as a YAG laser. The anode cooling means 9 is, for example, water-cooled copper attached near the discharge generating portion of the anode 3, and cools the outer periphery of the anode near the discharge generating portion.
[0021]
Discharge gas supply means (not shown) is provided on the anode side. For example, an inert gas, preferably Ar gas, and a mixed gas containing these gases are supplied to a discharge generating space from the anode 3 to the cathode 1. In addition, it is configured such that it can be continuously supplied from the anode side to the cathode side. The term "discharge generating space" used herein refers to an arc generating space extending from the anode side to the cathode side. Thus, by continuously supplying the inert gas to the discharge generating space, the degree of ionization of the gas is increased, an arc is generated along the gas flow path, and the movement of the cathode point is suppressed. As a result, high-purity carbon nanotubes are synthesized at the fixed cathode spot.
[0022]
Next, a method of manufacturing carbon nanotubes by the carbon nanotube manufacturing apparatus configured as described above will be described.
The discharge generating part of the carbon cathode 1 is preheated by the cathode heating means 7 and the vicinity of the discharge generating part of the anode is cooled by the anode cooling means 9. In this state, an inert gas is supplied from the discharge gas supply means to the discharge generating space to perform arc discharge.
[0023]
At this time, the discharge generating portion of the carbon cathode 1 is preheated, and a region in a temperature range where carbon nanotubes are easily grown is formed on the surface of the carbon cathode. For this reason, at the same time as the start of the arc discharge, generation of carbon nanotubes is started in this region, and as a result, the amount of carbon nanotube generation increases. Here, it is considered that the reason why the amount of generated carbon nanotubes increases in the preheated region is that an arc discharge is performed in the preheated region, so that the temperature becomes such that the carbon nanotubes easily grow.
[0024]
In addition, overheating of the anode 3 can be prevented by cooling by the anode cooling means 9, and excessive evaporation of the anode 3 can be suppressed. Thus, it is possible to prevent the evaporated anode material from adhering to the surface of the generated carbon nanotube as an impurity and lowering the purity. Furthermore, the consumption of the anode 3 can be suppressed, and the life of the anode can be extended.
[0025]
(Example 1)
Hereinafter, an example of the first embodiment will be described.
The conditions of each device and the like in the present embodiment are as follows.
(1) Carbon cathode 1: plate-like carbon material (resistance value 600 μΩ · cm)
(2) Anode 3: rod-shaped carbon material (3) Discharge gas: Ar gas (supplied to anode discharge generating section)
(4) Atmospheric gas: Atmospheric atmosphere (5) Cathode heating means: YAG laser (adjusted so that the beam irradiation diameter was almost equal to the diameter of the discharge generating portion on the cathode surface)
(6) Anode cooling means: water-cooled copper
Under the above conditions, an appropriate gap was provided between the plate-like carbon material and the rod-like carbon material, current was supplied from an arc discharge power source, and arc discharge was performed for 1 second.
At this time, the laser output was changed, and the heating temperature of the plate-shaped carbon cathode and the amount of the generated carbon nanotubes were observed. As a result of the observation, it was confirmed that the amount of carbon nanotubes generated was increased by preheating the cathode surface to 500 ° C. to 2000 ° C. only by laser irradiation before starting the arc discharge.
[0027]
FIG. 2 shows the relationship between the presence or absence of heating, the heating temperature, and the state of carbon nanotube formation. FIG. 2 is an enlarged photograph of the center of the cathode point of the arc. As can be seen from FIG. 2, no carbon nanotubes were produced without preheating. It can be seen that the carbon nanotubes preheated at 500 ° C. have carbon nanotubes formed all over the surface. In addition, it can be seen that the carbon nanotubes preheated at 2000 ° C. have carbon nanotubes formed all over the surface and the tubes are growing long. Carbon nanotubes were not observed in the sample preheated at 2500 ° C. This is thought to be because if the heat generated by the arc discharge is added to the preheating at 2500 ° C., the cathode, which is the place where carbon nanotubes are generated, is overheated and the generated carbon nanotubes sublime or decompose. The amount drops significantly.
[0028]
From this example, it became clear that the amount of carbon nanotubes produced was affected by the cathode preheating temperature. It was also found that the preheating temperature of the carbon cathode was optimally set to 500 ° C to 2000 ° C.
[0029]
It should be noted that no carbon nanotubes were generated at all without preheating in this example because the arc discharge time was as short as 1 second.
Therefore, when the arc discharge is performed for a long time and the temperature of the cathode discharge section rises to reach a generation condition range similar to the case where preheating is performed, carbon nanotubes are generated.
However, whether the temperature of the cathode reaches the temperature range where carbon nanotubes are generated or not depends greatly on the size, bulk density, specific heat, thermal conductivity, discharge conditions, etc. of the cathode carbon material. It's not easy.
On the other hand, if preheating and heating are performed as in the present invention, carbon nanotubes can be produced at a high yield without being greatly affected by these fluctuation factors.
[0030]
Embodiment 2 FIG.
FIG. 3 is an explanatory view of the configuration of another embodiment of the present invention, and shows a basic configuration of a carbon nanotube manufacturing apparatus as in FIG. 3, the same components as those shown in FIG. 1 are denoted by the same reference numerals.
The carbon nanotube manufacturing apparatus of the present embodiment moves the carbon cathode 1, the anode 3, the DC power supply 5 for generating arc discharge, the cathode heating means 11, the anode cooling means 13, and the anode 3 relatively to the carbon cathode 1. The moving mechanism 15 is configured.
[0031]
The moving mechanism 15 is composed of a carriage 19 that can run on a rail 17 at a predetermined speed, and the anode 3 is attached to the carriage 19.
The cathode heating means 11 is constituted by a high-frequency induction heating device installed in front of the anode 3 in the moving direction of the carriage 19. As a method of installing the cathode heating means 11, the cathode heating means 11 may be attached to the anode cooling means 13 or may be directly attached to the carriage 19.
The anode cooling means 13 is the same as that of the first embodiment, and is made of water-cooled copper placed near the discharge generating portion of the anode 3.
[0032]
A method for manufacturing carbon nanotubes by the carbon nanotube manufacturing apparatus configured as described above will be described.
The basic operation of the apparatus is the same as that of the first embodiment. The cathode heating means 11 preheats the discharge generating part of the carbon cathode 1 and the anode cooling means 13 cools the vicinity of the discharge generating part of the anode 3. In this state, the carriage 19 is moved at a predetermined speed, for example, 10 cm / min, while performing an arc discharge by injecting an inert gas from a discharge gas supply unit (not shown) into the discharge generating space.
[0033]
According to the present embodiment, since the cathode heating means 11 is disposed in front of the anode 3, the discharge generating portion is preheated together with the movement of the carriage 19, and the effect of the first embodiment is obtained. In addition, there is an effect that carbon nanotubes can be continuously generated.
[0034]
In the above-described second embodiment, an example in which the anode 3 moves in the direction along the surface of the carbon cathode 1 has been described assuming that the carbon cathode 1 is a flat plate or a prism.
However, the present invention is not limited to this. For example, as shown in the schematic diagram of FIG. 4, a carbon cathode is used as the carbon cathode 1 and the carbon cathode 1 is rotated, and the anode 3 is connected to the axis of the cylinder. Move in the direction. At this time, both ends of the carbon cathode 1 may be connected to an AC power supply to heat the entire carbon cathode 1 by self-heating due to resistance heating. In this way, preheating and heating of the carbon cathode 1 can be realized with a simple device.
[0035]
However, when the cathode material becomes large, preheating and heating the entire cathode by resistance heating not only causes an increase in the size of the power supply, but also increases the heat loss of the cathode material due to radiation and increases the amount of electricity used. Invite.
Therefore, in such a case, as shown in FIG. 5, a laser oscillator may be installed near the anode 3 to partially heat the cathode point or the front of the cathode point of the arc discharge.
Thus, local heating is sufficient because the generation of carbon nanotubes affects only the temperature of the discharge generating portion of the cathode material. As another example of the local heating heat source, an arc discharge using an electrode different from the electrode for generating carbon nanotubes can be considered.
[0036]
(Example 2)
Hereinafter, examples of the second embodiment will be described.
The conditions of the present embodiment are as follows.
(1) Carbon cathode 1: Plate-like carbon material (2) Anode 3: Rod-like carbon material (3) Discharge gas: Ar gas (supplied to anode discharge generating section)
(4) Atmospheric gas: Atmospheric atmosphere (5) Cathode heating means: High-frequency induction heating device (interval with carbon cathode: 4 mm)
(6) Anode cooling means: water-cooled copper (7) Truck 19 Moving speed: 10 cm / min
[0037]
When heating was performed with the starting frequency of the high-frequency induction heating device being 10 kHz under the above conditions, the cathode temperature was increased to 800 ° C. only by the high-frequency induction heating.
In this state, when Ar gas is injected into the discharge space from the discharge gas supply device to generate an arc discharge between the anode and the cathode, carbon nanotubes with high density and high purity are generated.
[0038]
In this example, the discharge time in the atmosphere was set to 5 minutes. However, when the anode was not cooled, the anode was greatly consumed and continuous discharge for 2 minutes or more was impossible. On the other hand, the water-cooled anode was slightly consumed immediately after the start of the discharge, but the consumption was reduced thereafter and the discharge was possible for a long time.
[0039]
When observing the surface of the completed carbon nanotube, it was observed that the amount of adhered impurities decreased when the anode was cooled as compared with the case where the anode was not cooled. FIG. 6 is an enlarged photograph of the central portion of the arc cathode spot. From this photograph, the difference in the state of impurity deposition depending on the presence or absence of anode cooling can be clearly seen.
[0040]
From the results of this example, it was confirmed that most of the carbon impurities adhering to and depositing on the carbon nanotubes generated in the cathode discharge generating portion were flying objects from the anode. Therefore, by cooling the anode, unnecessary anode consumption can be suppressed, and not only carbon nanotubes generated on the cathode surface can be prevented from depositing scattered matter from the anode as impurities, but also the length of the anode can be reduced. It was demonstrated that the life could be extended.
[0041]
In the above embodiment, an example in which a carbon material is used as the anode has been described. However, the anode of the present invention is not limited to the carbon material, and may be a water-cooled copper electrode.
[0042]
【The invention's effect】
As described above, in the present invention, since the arc discharge is performed between the anode and the anode after preheating the entire cathode carbon material or the arc discharge part of the cathode carbon material, the yield of carbon nanotubes can be reduced with a simple device. Can be more.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a configuration according to an embodiment of the present invention.
FIG. 2 is a scanning electron microscope (SEM) photograph of a central portion of a cathode deposit obtained by the method for producing carbon nanotubes according to one embodiment of the present invention.
FIG. 3 is an explanatory diagram of a configuration of another embodiment of the present invention.
FIG. 4 is an explanatory diagram of another aspect of another embodiment of the present invention.
FIG. 5 is an explanatory diagram of another aspect of another embodiment of the present invention.
FIG. 6 is a scanning electron microscope (SEM) photograph of a central portion of a cathode deposit obtained by a method of manufacturing a carbon nanotube according to another embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Carbon cathode 3 Anode 5 Power supply for arc discharge 7, 11 Cathode heating means 9, 13 Anode cooling means 15 Moving mechanism 19 Dolly

Claims (9)

A carbon nanotube production method for synthesizing carbon nanotubes by performing a DC arc discharge using a cathode made of a carbon material,
A method for producing carbon nanotubes, wherein an arc discharge is performed between an anode and an anode after preheating the entire cathode carbon material or an arc discharge portion of the cathode carbon material. 2. The method for producing carbon nanotubes according to claim 1, wherein DC arc discharge is performed while moving the relative positions of the cathode and the anode. 3. The method for producing carbon nanotubes according to claim 1, wherein, during the arc discharge, the entire cathode carbon material or an arc discharge portion of the cathode carbon material is heated by a heating means different from the arc discharge. The method for producing carbon nanotubes according to any one of claims 1 to 3, wherein the preheating temperature is from 500C to 2000C. A method for producing carbon nanotubes, characterized in that the preheating method is high-frequency induction heating, arc discharge by another electrode or heating by laser irradiation, or energization heating by another power source. The method for producing a carbon nanotube according to any one of claims 1 to 5, wherein the anode is cooled. A cathode electrode made of a carbon material, an anode electrode opposed to the cathode electrode at a predetermined distance from the cathode electrode, and an arc electrode connected to the anode electrode and the cathode electrode to cause an arc discharge between these electrodes. An apparatus for producing carbon nanotubes, comprising: a power supply; and heating means for heating the entire cathode electrode or an arc discharge portion of the cathode electrode. The carbon nanotube manufacturing apparatus according to claim 7, further comprising a moving unit that relatively moves the cathode electrode and the anode electrode. 9. The apparatus for producing carbon nanotubes according to claim 7, wherein the heating means is a high-frequency induction heating apparatus, an arc discharge apparatus using another electrode, or an energization heating apparatus using a laser or another power supply.

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