JP2007084377A - Apparatus and method for manufacturing carbon nanotube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for manufacturing carbon nanotubes which can manufacture a large amount of carbon nanotubes by devising extension of the arc plasma region. <P>SOLUTION: The apparatus for manufacturing carbon nanotubes is provided with a hermetically closed reaction container, carbon electrodes arranged in the reaction container and perform arc discharge; and manufactures carbon nanotubes by condensing evaporated carbon after the carbon of the carbon electrodes are evaporated by using the arc discharge as a heat source; and the apparatus is further provided with a heating/warmth-keeping means which is arranged so as to surround a desired extent area spreading between electrodes and heating or warmth-keeping the desired extent area to or at a prescribed temperature to extend the arc plasma region formed between the carbon electrodes. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a carbon nanotube production apparatus and production method capable of efficiently producing a large amount of carbon nanotubes by performing arc discharge between carbon electrodes and evaporating carbon of the carbon electrode using the arc discharge as a heat source. About.

  A carbon nanotube is a substance having a shape obtained by rounding graphite with a series of carbon 6-membered rings into a cylindrical shape, and has unique physical properties. Therefore, it is expected to be applied to a wide range of technical fields in the future. It is a remarkable new material. At present, arc discharge methods, laser evaporation methods, chemical vapor deposition methods (CVD methods), etc. are used as methods for producing carbon nanotubes. Among them, production methods using arc discharge have few defects and quality. It is known that good carbon nanotubes can be obtained.

  In the production of carbon nanotubes using arc discharge, arc discharge is performed by applying electric power (arc plasma power) between carbon electrodes, and inert gas molecules such as argon and helium present in the atmosphere by the heat of the arc discharge. Is converted into plasma to form high-temperature arc plasma, and the carbon of the carbon electrode (anode) is evaporated by the thermal energy of the arc plasma. Further, after the evaporated carbon is in an atomic state in the arc plasma, it is condensed in the process of moving from the central portion of the arc plasma to the low temperature portion and being cooled, thereby generating carbon nanotubes.

  The basic reaction in the production of carbon nanotubes is the decomposition of carbon having a carbon structure (hexagonal graphite structure) evaporated from the carbon electrode by the heat of arc plasma into a plasma ion state (atomic state) in high-temperature arc plasma. Then, carbon nanotubes are generated by recombination in the crystal structure of the carbon nanotubes different from the original carbon structure in the process of cooling the carbon. Condensation means that carbon is recombined from the plasma ionized atomic state to the crystal structure of the carbon nanotube to generate carbon nanotubes. In general, in the production of carbon nanotubes by such an arc discharge method, although carbon nanotubes with good quality can be obtained as described above, the yield is very low compared to the CVD method etc. There was a problem that it was difficult to obtain efficiently.

  In the production of carbon nanotubes by the arc discharge method, for example, in Japanese Patent Application Laid-Open No. 2002-249306 (Patent Document 1), in order to improve the yield and efficiently produce carbon nanotubes, a plurality of rods are attached to a support member. An apparatus for producing carbon nanotubes has been disclosed, which is characterized in that the attached carbon nanotube collecting member is arranged around a carbon electrode and carbon nanotubes generated by arc discharge are collected by the collecting member.

  According to Patent Document 1, when carbon nanotubes are produced by the arc discharge method, the products obtained by evaporating the carbon of the electrode include impurities such as graphite, amorphous carbon, and catalytic metals in addition to the carbon nanotubes. Therefore, it takes time to remove this impurity, so that it is impossible to efficiently produce carbon nanotubes.

For this reason, by using the manufacturing apparatus described in Patent Document 1, a product containing a high content of carbon nanotubes generated by arc discharge is collected by a collecting member provided around the carbon electrode. On the other hand, graphite, amorphous carbon, catalytic metal, and the like, which are byproducts of arc discharge, pass between the carbon nanotube collecting members and adhere to the inner wall of the reaction vessel. Therefore, after the end of the arc discharge, the carbon nanotubes can be efficiently produced with high yield by collecting the product entangled with the collecting member and collected.
JP 2002-249306 A

  By the way, in the manufacturing by the conventional arc discharge method such as Patent Document 1 described above, the manufacturing apparatus itself is small-scale, and the arc plasma power applied between the carbon electrodes is as small as about 10 kW (in Patent Document 1, about 7 kW). The distance between the electrodes is set to about several millimeters.

  In order to realize mass production of carbon nanotubes by increasing the amount of carbon nanotubes produced in such an arc discharge method, the amount of carbon evaporated from the carbon electrode is increased and the evaporated carbon For this purpose, for example, the carbon evaporation from the carbon electrode can be increased, that is, the carbon evaporation region on the electrode surface can be expanded, and the plasma ionization of the evaporated carbon can be achieved. It is conceivable to expand the region, that is, the arc plasma region that promotes plasma ionization of carbon.

  However, in the arc plasma formed by the conventional arc discharge, for example, when an arc current is passed through the carbon electrode, the arc plasma diameter is narrowed down by the pinch effect due to the magnetic action, and the arc plasma region is extremely controlled. It was difficult. Therefore, simply increasing the arc plasma current flowing through the carbon electrode to increase the amount of carbon nanotubes produced cannot increase the arc plasma region, and the carbon electrode that receives thermal energy from this arc plasma region cannot be enlarged. The carbon evaporation surface could not be enlarged.

  Furthermore, when the arc plasma region is small, the plasma ionization region of carbon evaporated from the carbon electrode is also narrow, and the carbon vapor is expelled from the arc plasma region before plasma ionization and the temperature is lowered. Many things return to the carbon crystal structure. For this reason, there existed a problem that the production efficiency of a carbon nanotube was low and mass production was difficult.

  Therefore, in the production of carbon nanotubes by the arc discharge method described in Patent Document 1, a collecting member is provided around the carbon electrode as described above to improve the yield of the produced carbon nanotubes. However, since the carbon nanotube production efficiency itself is lower than that of the CVD method or the like, it is not suitable for mass production of carbon nanotubes and is limited to small-scale production.

  Furthermore, in the conventional carbon nanotube production apparatus, since the arc plasma region is small, the heat dissipation coefficient per unit energy (which can be regarded as the specific surface area of the arc plasma lump) is large, and what is the heat insulation measure for the entire apparatus. Also not given. For this reason, even if the arc plasma power is increased by increasing the size of the apparatus in order to increase the amount of carbon nanotubes generated, for example, the energy loss is very large and the power consumption efficiency is poor, resulting in a decrease in economic efficiency. Will be invited. Further, as a result, there is a problem that the heat resistance and durability of the members and materials constituting the apparatus are lowered.

  The present invention has been made in view of the above problems, and the specific object of the present invention is to expand the carbon evaporation surface of the carbon electrode, which has been difficult to achieve in the past, and the plasma ionization region of the evaporated carbon. An object of the present invention is to provide a carbon nanotube manufacturing apparatus and manufacturing method capable of efficiently mass-producing carbon nanotubes by enlarging them.

  In order to achieve the above object, a carbon nanotube production apparatus provided by the present invention includes, as a basic configuration, a sealed reaction vessel and a carbon electrode disposed in the reaction vessel and performing arc discharge. A carbon nanotube produced by evaporating carbon of the carbon electrode using the arc discharge as a heat source and then condensing the vaporized carbon, and having a desired area extending between the carbon electrodes A heating / heat-retaining means that is disposed so as to surround the region, and that heats or keeps the desired area wide at a predetermined temperature to expand an arc plasma region formed between the carbon electrodes. It is the main feature.

In the carbon nanotube production apparatus according to the present invention, it is preferable that the heating / warming means is an electric resistance heater.
Furthermore, in the manufacturing apparatus of the present invention, it is preferable that the heating / warming means heats or keeps the desired area in a temperature of 1500 ° C. or higher.

Furthermore, in the manufacturing apparatus of the present invention, the carbon electrodes can be disposed at a distance of 10 mm or more.
Moreover, in the manufacturing apparatus of this invention, it is preferable that the fireproof heat insulating material is provided in the inner surface of the said reaction container.

  Next, the carbon nanotube production method provided by the present invention has, as a basic structure, arc discharge at a carbon electrode, and after the carbon of the carbon electrode is evaporated using the arc discharge as a heat source, the carbon electrode is evaporated. A method of producing carbon nanotubes by condensing carbon, and when performing the arc discharge, using a heating and heat retaining means arranged so as to surround a desired area between the carbon electrodes, The most important feature is that the arc plasma region formed between the carbon electrodes is enlarged by heating or keeping the desired width region at a predetermined temperature.

  An apparatus for producing carbon nanotubes according to the present invention includes heating and heat retaining means arranged so as to surround a desired area extending between carbon electrodes. By using this heating and heat retaining means, a carbon nanotube is produced during arc discharge. A desired area between the electrodes is configured to be heated or kept at a predetermined temperature. In the present invention, when the arc plasma region is formed between the carbon electrodes by heating or keeping the desired area between the carbon electrodes at a predetermined temperature during arc discharge by the heating / heat holding means, The arc plasma region can be greatly enlarged as compared with the case of non-heating or non-heat-retaining.

  Here, the arc plasma control mechanism for expanding the arc plasma region by the heating and heat retaining means will be described in more detail. For example, as shown in FIG. 2 which shows an approximate relationship between the arc plasma power X and the size of the arc plasma region, the size of the arc plasma region generated between the carbon electrodes increases the arc plasma power X (kW) applied to the carbon electrodes. There is a tendency to become larger. The arc plasma power X is represented by the product of the arc plasma current Y (Amp) and the arc plasma voltage Z (Volt). When the arc plasma current Y is increased, the diameter of the arc plasma region is increased, and the arc plasma voltage Z is Increasing the length increases the length of the arc plasma region. Therefore, it is possible to expand the diameter and length of the arc plasma region by applying a larger arc plasma current to the carbon electrode and applying a higher arc plasma voltage.

  On the other hand, in the production of conventional carbon nanotubes, the arc plasma region formed between the carbon electrodes is actually narrowed by the pinch effect due to the magnetic action of the arc current as described above. Even if the plasma power was increased, the arc plasma region could not be expanded, for example, as shown in FIG.

  Therefore, in the present invention, as a countermeasure, by heating or keeping a desired area between the carbon electrodes by the heating / heat holding means, the gas molecules existing between the carbon electrodes can have other than the heat of the arc plasma itself. By applying energy by heat, that is, heat generated by the heating / heat-retaining means, the gas molecules are activated to facilitate plasma ionization. As a result, when arc discharge is performed between the carbon electrodes, an arc corresponding to the value of the arc plasma power X as shown in FIG. 2, for example, within a desired area heated or kept warm by the heating / heat keeping means. It is possible to form the arc plasma region with the dimensions (length and diameter) of the plasma or larger dimensions.

  Since the arc plasma region can be easily expanded in this way, the carbon evaporation surface on the surface of the carbon electrode can also be expanded, so that it is possible to increase the amount of evaporation of carbon that is a raw material for carbon nanotubes. Further, a large amount of carbon evaporated from the carbon electrode can be sufficiently plasma ionized in the expanded arc plasma region, and carbon nanotubes can be efficiently generated from the large amount of evaporated carbon. Therefore, according to the manufacturing apparatus of the present invention, it is possible to promote the expansion of the evaporation amount of carbon from the carbon electrode and the expansion of the plasma ionization region of the evaporated carbon, which could not be performed conventionally, and as a result, arc discharge It is possible to mass-produce carbon nanotubes by the method.

  Further, in the carbon nanotube manufacturing apparatus of the present invention, the heating and heat retaining means disposed so as to surround the arc plasma region is constituted by an electric resistance heater. Thereby, the heating or heat insulation of the space surrounded by the heating / heat insulation means can be stably performed during arc discharge. In addition, by using a carbon heating element as the electric resistance heater, the heat resistance is extremely excellent, and the effect of effectively preventing contamination of the carbon nanotubes by impurity elements can be obtained.

  Further, the heating / warming means heats or keeps a desired area surrounded by the heating / heat keeping means at a temperature of 1500 ° C. or higher, preferably 2000 ° C. or higher. In this way, by performing heating or heat insulation at a predetermined temperature of 1500 ° C. or higher by the heating and heat retaining means, the plasma ionization of carbon and gas molecules in the region is promoted during arc discharge, and the arc plasma region is stably expanded. Mass production of carbon nanotubes can be performed effectively.

  Furthermore, in the production apparatus of the present invention, the carbon electrodes can be arranged so that the distance between the carbon electrodes is 10 mm or more, preferably 100 mm or more, more preferably 200 mm or more. That is, in the past, the arc plasma diameter is reduced due to the pinch effect during arc discharge. As a result, it is difficult to increase the length of the arc plasma, and considering the power consumption efficiency, the distance between the carbon electrodes is actually In many cases, the thickness was about 2 to 3 mm.

  Also, even when trying to increase the arc plasma power by increasing the arc plasma power applied to the carbon electrode, it is necessary to apply a very large arc plasma power, for example, 100 mm or more, It was extremely difficult to form an arc plasma region between carbon electrodes separated by 200 mm or more.

  Specifically, conventionally, when an arc plasma region is formed between carbon electrodes separated by about 2 mm, an arc plasma power of about 10 kW is applied to the carbon electrodes. Based on this, for example, when an arc plasma region is formed between carbon electrodes separated by 200 mm, if the magnitude of the arc plasma power applied to the carbon electrode is simply proportionally calculated, a power of about 1000 kW is required. On the other hand, in the present invention, as will be described in detail in the following embodiment, by heating or keeping the temperature between the carbon electrodes with a heating / insulating means, the arc plasma power of about 150 kW, which is much smaller than 1000 kW, is separated by 200 mm. An arc plasma region can be formed between the carbon electrodes.

  That is, according to the present invention, a large arc plasma region having a length of 10 mm or more can be easily formed with a smaller arc plasma power than in the case of a conventional manufacturing apparatus. Thereby, the distance between carbon electrodes can be made longer than before, the arc plasma region can be expanded, and carbon nanotubes can be generated more stably.

  Moreover, in this invention, the fireproof heat insulating material is provided in the inner surface of reaction container. Thereby, the heat | fever dissipated by conducting a reaction container and dissipating outside a container can be interrupted | blocked, and the power consumption lost by heat dissipation can be suppressed. Therefore, even if a large arc plasma power is applied between the carbon electrodes to expand the arc plasma region, the heat dissipation coefficient per unit energy can be reduced and the thermal efficiency of the arc plasma can be increased. The manufacturing cost can be reduced.

  Next, the method for producing a carbon nanotube according to the present invention uses a heating / heat retaining means arranged so as to surround a desired area between the carbon electrodes when performing arc discharge. By heating or keeping the region at a predetermined temperature, the arc plasma region formed between the carbon electrodes can be expanded. As a result, the contact surface between the carbon electrode and the plasma region is increased, and the carbon evaporation surface on the surface of the carbon electrode is enlarged, so that the amount of evaporation of carbon that is a raw material for the carbon nanotube can be increased. In addition, since a large amount of carbon evaporated from the carbon electrode can be sufficiently plasma ionized in the expanded arc plasma region, carbon nanotubes can be efficiently generated from the evaporated carbon. A large amount of carbon nanotubes can be stably produced with excellent production efficiency.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings. Here, FIG. 1 is a schematic diagram schematically showing the configuration of the carbon nanotube production apparatus in the present embodiment.
As shown in FIG. 1, the carbon nanotube production apparatus 1 in the present embodiment includes a sealed reaction vessel 5, and a cathode 7 and an anode 8 made of a carbon material disposed in the reaction vessel 5 and performing arc discharge. And a heating and heat retaining means 4 arranged so as to surround a desired area (space) extending between the cathode 7 and the anode 8.

  The reaction vessel 5 is made of carbon steel or stainless steel, and this reaction vessel 5 is provided with a gas supply means (not shown) so that argon gas or helium gas can be introduced into the reaction vessel 5. The shape and dimensions of the reaction vessel 5 are not particularly limited. For example, a horizontal cylindrical reaction vessel having a predetermined diameter and length can be used. Further, a refractory heat insulating material 6 is provided on the inner surface of the reaction vessel 5 so as not to cause a gap.

  Since the refractory heat insulating material 6 provided in the reaction vessel 5 is exposed to high-temperature radiant heat or convective heat of the plasma arc or the heating / heat retaining means 4 during arc discharge, the refractory heat insulating material 6 is, for example, 1500 ° C. or more, preferably 2000 It is preferable to use a ceramic refractory heat insulating plate having a heat resistance of not lower than ° C. and a good heat insulating property, particularly an alumina bubble molded plate. By providing such a refractory heat insulating material 6, the reaction vessel 5 is conducted during arc discharge, the heat dissipated to the outside of the vessel is cut off, power consumption lost due to heat dissipation is suppressed, and at the same time the dissolution of the reaction vessel 5 is dissolved. And thermal deformation can be prevented. Furthermore, a cooling water-cooled serpentine tube may be provided on the outer surface of the reaction vessel 5 as necessary in order to further prevent thermal deformation of the reaction vessel 5.

  The shape and dimensions of the carbon cathode 7 and the carbon anode 8 are not particularly limited. For example, the carbon cathode 7 has a diameter equal to or equal to that of the carbon anode 8 so that carbon nanotubes can be stably produced. It is preferable to have a larger diameter than the carbon anode 8. The carbon anode 8 is provided with an electrode moving means (not shown) so that the carbon anode 8 can move linearly in the front-rear direction with respect to the carbon cathode 7.

  In the present embodiment, the distance between the carbon cathode 7 and the carbon anode 8 can be set to 10 mm or more, which is a longer value than before, but the distance between the carbon electrodes 7 and 8 is set to be longer, By making the arc plasma region 3 formed between the electrodes 7 and 8 longer to expand the arc plasma region 3, the production efficiency of carbon nanotubes can be further improved to meet the demand for mass production.

  As described above, the arc plasma region 3 has a larger diameter when the arc plasma current Y is increased, and a longer arc plasma region when the arc plasma voltage Z is increased. Accordingly, the interelectrode distance between the carbon cathode 7 and the carbon anode 8 should be set based on the magnitude of the arc plasma power applied to the electrodes 7 and 8 when producing the carbon nanotubes, particularly the magnitude of the arc plasma voltage. Is preferred.

  Here, FIG. 3 shows a graph showing the relationship between the arc plasma power X (kW), the arc plasma current Y (Amp), and the arc plasma voltage Z (Volt), and FIG. 4 shows the arc plasma voltage Z (Volt). ) And the interelectrode distance L (mm) between the carbon cathode 7 and the carbon anode 8 is shown.

  In the present embodiment, it is preferable that the magnitude of the arc plasma power X is 150 kW or more in order to mass-produce carbon nanotubes. Therefore, the magnitude of the arc plasma voltage Z can be set to 200 V or higher, which is higher than the carbon nanotube manufacturing conditions (operating conditions of the apparatus) that are generally performed conventionally, from the relationship shown in FIG.

  In addition, when an arc plasma voltage Z of 200 V or more is applied in this way, an arc plasma region having a length of 200 mm or more can be stably formed. Therefore, when manufacturing carbon nanotubes, considering the production efficiency, the distance L between the carbon electrodes 7 and 8 is the longest arc plasma region that can be formed by the arc plasma power applied to the carbon electrodes 7 and 8. For example, the distance L between the carbon electrodes 7 and 8 can be set to 10 mm or more, preferably 100 mm or more, and more preferably 200 mm or more as described above. In addition, the distance L between the carbon electrodes 7 and 8 can be easily changed by using, for example, the electrode moving means (not shown).

  The heating / warming means 4 is disposed so as to surround a desired area (space) extending between the carbon cathode 7 and the carbon anode 8. When the arc discharge is performed between the carbon electrodes 7 and 8, the heating / warming means 4 is activated by heating gas molecules in a region surrounded by the heating / warming means 4 and applying energy to the gas molecules by heat. By converting to plasma ionization, the arc plasma region 3 generated between the carbon electrodes 7 and 8 can be expanded.

  This heating and heat retaining means 4 is composed of an electric resistance heater, for example, a refractory metal heating element having a melting point of 3000 ° C. or higher such as tungsten, a high heat resistant carbon compound such as silicon carbide, or a carbon heating element. Among them, it is particularly preferable to use a carbon heating element in consideration of heat resistance and contamination of the product by an impurity element.

  Further, the heating / heat retaining means 4 has a cylindrical shape so as to surround a desired area extending between the carbon electrodes 7 and 8. In this heating / heat retaining means 4, the effective length of the heat generating part is preferably equal to the distance between the cathode 7 and the anode 8, and the cylindrical inner diameter is desired between the electrodes 7 and 8. It is preferable to make the diameter of the carbon electrode on the thick side, for example, 1.2 times or more the diameter of the carbon cathode 7 so as to sufficiently surround the wide area. The heating and heat retaining means 4 is provided at a predetermined position so as not to come into contact with the carbon electrodes 7 and 8 and an electrode support (not shown) that supports the carbon electrodes 7 and 8.

In the manufacturing apparatus 1 in the present embodiment, in order to manufacture a large number of carbon nanotubes, the electrode diameter D (mm) of the carbon anode 8 having a predetermined size and the arc plasma power X (kW) are selected. The electrode diameter D of the carbon anode 8 is set so that the contact surface with the arc plasma 3 (that is, the carbon evaporation surface on the surface of the carbon anode 8) is widened to increase the amount of carbon evaporation between the anode 8 and the cathode 7. It calculates | requires by following Formula (1) with respect to the arc plasma electric power X to apply.
Electrode diameter D (mm) = arc plasma power X (kW) × 0.65 (1)

  However, the arc plasma power X is preferably X ≧ 150 kW in order to stably form the arc plasma region 3 and enable mass production of carbon nanotubes. For example, the conventional carbon electrode diameter is about several millimeters and the arc plasma power applied to the carbon electrode is about 10 kW. However, the arc plasma power X is set to 150 kW or more as in this embodiment, and this arc plasma power is used. By setting the electrode diameter D of the carbon anode 8 to 97.5 mm or more according to the size of X, for example, the carbon evaporation surface of the carbon anode 8 can be expanded, and the amount of carbon evaporation from the carbon anode 8 can be increased. .

Further, the magnitude of the arc plasma power X (kW) gives sufficient energy to the carbon evaporation surface of the carbon anode 8 to increase the evaporation rate of carbon from the carbon evaporation surface. A value obtained by the following equation (2) according to S (mm ² ) or an approximate value thereof can be used.
Arc plasma power X (kW) = evaporation area S (mm ² ) × 0.076 (2)
However, the size of the evaporation area S is preferably S ≧ 2000 mm ^{2 in} order to obtain a sufficient amount of carbon evaporation.

  In the present embodiment, for example, when the electrode diameter D of the carbon anode 8 is obtained using the equation (1), a predetermined value of the arc plasma power X is selected, and separately from the equation (2) After obtaining the value of the arc plasma power X from the evaporation area S using the above, the two values are compared, and the larger value can be adopted as the value of the arc plasma power X.

In the present embodiment, by using the carbon nanotube production apparatus 1 as described above, a large number of carbon nanotubes can be produced as follows.
When carbon nanotubes are produced, first, helium gas is introduced into the reaction vessel 5 and the pressure in the reaction vessel 5 is maintained at 266 Pa (200 Torr). The space surrounded by the heating and heat retaining means 4 is heated to a temperature of 1500 ° C. or higher, preferably 2000 ° C. or higher, and the space between the carbon electrodes 7 and 8 is maintained at a predetermined temperature.

  Next, the position of the anode 8 is adjusted using an electrode moving means (not shown) such that the distance between the carbon electrodes 7 and 8 is, for example, 200 mm, and an arc plasma power of 150 kW between the carbon electrodes 7 and 8 is obtained. Arc discharge is performed by applying (arc plasma current: 750 A, arc plasma voltage: 200 V), and the arc plasma region 3 is formed between the carbon electrodes 7 and 8.

  When such arc discharge is performed, conventionally, the diameter of the arc plasma is narrowed down by the pinch effect due to the magnetic action of the arc plasma current. Therefore, for example, as shown in FIG. , 8, an arc plasma region 9 having a small diameter is formed.

  However, in this embodiment, since the space between the carbon electrodes 7 and 8 is heated by the heating and heat retaining means 4, the gas molecules existing between the carbon electrodes 7 and 8 are heated and heated by the arc plasma itself. When energy is applied by both heat from the heat retaining means 4, it is activated and plasma ionized. For this reason, it is possible to prevent the arc plasma formed between the carbon electrodes 7 and 8 from being narrowed down and to greatly expand the arc plasma region as compared with the prior art. For example, as shown in FIG. A large arc plasma region 3 can be formed between the carbon electrodes 7 and 8.

  As described above, the arc plasma region 3 formed between the carbon electrodes 7 and 8 is greatly enlarged as compared with the conventional case, so that the carbon evaporation surface in the carbon anode 8 is also enlarged, so that the amount of evaporation of carbon is increased. be able to. Further, since a large amount of carbon evaporated from the carbon electrode can be condensed after sufficiently ionized in the expanded arc plasma region 3, carbon nanotubes can be generated very efficiently from the evaporated carbon. Can do.

  That is, according to the present embodiment, by performing the arc discharge as described above for a predetermined time, the arc plasma region 3 is greatly expanded to expand the carbon evaporation region of the carbon electrode 8, and the evaporated carbon plasma. The ionization area can also be enlarged. For this reason, the production | generation of a carbon nanotube can be performed efficiently and the production amount of the carbon nanotube per unit time can be increased significantly. At the same time, by arranging the refractory heat insulating material 6 on the inner surface of the reaction vessel 5, it is possible to improve the power consumption efficiency, so that mass production of carbon nanotubes that could not be achieved in the past can be stably performed. As a result, it is possible to provide carbon nanotubes of good quality at low cost.

  Hereinafter, the present invention will be described in more detail with reference to examples. In the following examples, a case where carbon nanotubes are produced for 2 hours using the carbon nanotube production apparatus 1 shown in FIG. 1 will be described.

In this example, when manufacturing the carbon nanotubes, first, the electrode diameters of the carbon electrodes 7 and 8 were obtained based on the formula (1). In the present embodiment, the electrode diameters of the cathode 7 and the anode 8 are made equal, and the plasma arc power applied between the carbon electrodes 7 and 8 is, for example, an arc plasma region 3 formed between the carbon electrodes 7 and 8. In consideration of the size and the like, 150 kW was selected. Therefore, the electrode diameter D of the carbon electrodes 7 and 8 was calculated | required as follows according to said Formula (1).
Electrode diameter D (mm) = 150 (kW) × 0.65 = 97.5 (mm)

  In addition, since the value (97.5 mm) of the electrode diameter D obtained by the above formula (1) is a value that approximates a ready-made 4-inch diameter carbon electrode (artificial graphite electrode, diameter 102 mm), Decided to use this 4-inch diameter carbon electrode as the carbon electrodes 7,8. Further, the interelectrode distance L between the carbon electrodes 7 and 8 was set to 200 mm based on the plasma arc power value of 150 kW (that is, the arc plasma voltage was 200 V).

  Further, based on the size of the electrode diameter D of the carbon electrodes 7 and 8 obtained as described above and the distance L between the electrodes of the carbon electrodes 7 and 8, a cylindrical carbon heating element serving as the heating and heat retaining means 4 Set the dimensions. That is, the inner diameter of the cylindrical carbon heating element is set to 122.4 mm, which is 1.2 times the electrode diameter 102 mm of the carbon electrodes 7 and 8, and the effective length of the heating part of the carbon heating element is set to the carbon electrode 7, The distance between the electrodes was set to 200 mm, which is equal to the distance L between the electrodes.

Next, apart from the calculation of the electrode diameter D, a sufficient energy is given to the carbon evaporation surface of the carbon anode 8 and applied between the carbon electrodes 7 and 8 in order to increase the carbon vapor velocity from the carbon evaporation surface. The plasma arc power to be obtained was determined according to the above formula (2) based on the set size (2000 mm ² ) of the area S of the carbon evaporation surface.
Arc plasma power X (kW) = 2000 (mm ² ) × 0.076 = 152 (kW)
As a result, the magnitude 152 kW of the plasma arc power obtained based on the carbon evaporation area S is an approximate value to the magnitude 150 kW of the plasma arc power selected when the electrode diameter D is calculated. , The magnitude of the plasma arc power was set to 150 kW.

  On the other hand, as the reaction vessel 5, a horizontal cylindrical stainless steel vessel having a diameter of 1.6 m and a length of 2.2 m was used. Further, an alumina bubble molded plate having a thickness of 50 mm was pasted on the inner surface of the reaction vessel 5 including the hatch portion without any gap. Further, on the outer surface of the reaction vessel 5, in order to prevent thermal deformation of the stainless steel plate, a cooling water-cooled serpentine was disposed as a whole.

  Using the carbon nanotube production apparatus 1 having the shape and dimensions as described above, first, helium gas is introduced into the reaction vessel 5 and the pressure in the reaction vessel 5 is maintained at 266 Pa. The space surrounded by 4 was heated to 1600 ° C. with the carbon heating element 4 to maintain the temperature.

  Next, an arc discharge is performed by applying an arc plasma power of 150 kW (arc plasma current: 750 A, arc plasma voltage: 200 V) between the carbon electrodes 7 and 8, and the arc plasma region 3 between the carbon electrodes 7 and 8. The carbon nanotubes were produced by forming this and performing this arc discharge for 2 hours. In addition, in order to make it easy to grasp the manufacturing conditions of the carbon nanotubes performed this time, the manufacturing conditions are collectively described below. Note that the diameter of the arc plasma region 3 described below represents the size of the diameter at a substantially central portion of the arc plasma region 3.

(Production conditions for carbon nanotubes)
Electrode diameter D of carbon electrodes 7 and 8: 102 mm
The distance L between the carbon electrodes 7 and 8 is 200 mm.
Arc plasma power X: 150 kW
Arc plasma current: 750 Amp
Arc plasma voltage: 200 Volt
Dimensions of arc plasma region 3: Diameter 60 mm x length 200 mm
Heating and thermal insulation temperature by the carbon heating element 4: 1600 ° C
Atmospheric gas in reaction vessel 5: helium gas Atmospheric pressure in reaction vessel 5: 266 Pa

  After performing the arc discharge for 2 hours, the temperature of each part in the reaction vessel 5, particularly the temperature around the carbon electrodes 7 and 8, which is a high temperature part, fell below the ignition point temperature of the carbon powder and the carbon nanotube. After confirming the above, the reaction vessel 5 was opened to the atmospheric pressure, and the carbon nanotubes and the carbon powder generated at the periphery of the carbon electrode 7 and the carbon heating element 4 were recovered. Carbon nanotubes were selected from the collected recovered materials, and the amount of carbon nanotubes produced was measured. As a result, in this example, it was confirmed that about 60 g of carbon nanotubes could be produced in a production time of 2 hours, and it was found that the amount of carbon nanotubes produced per hour was 30 g / h. In addition, since the power consumption in the production of the carbon nanotube this time is 300 kWh, the power consumption rate was 5 kWh / g.

  The present invention can be effectively applied to the production of carbon nanotubes utilizing arc discharge.

It is a schematic diagram which represents typically the structure of the manufacturing apparatus of a carbon nanotube. It is a graph which shows the relationship between the arc plasma electric power X and the dimension of an arc plasma area | region. 5 is a graph showing the relationship between arc plasma power X, arc plasma current Y, and arc plasma voltage Z. It is a graph showing the relationship between the arc plasma voltage Z and the distance L between carbon electrodes. It is a partial schematic diagram which represents typically the shape of the arc plasma area | region formed between carbon electrodes.

Explanation of symbols

1 Carbon Nanotube Manufacturing Equipment 3 Arc Plasma Region 4 Heating / Heat Keeping Means (Carbon Heating Element)
5 Reaction vessel 6 Refractory insulation 7 Carbon electrode (cathode)
8 Carbon electrode (anode)
9 Arc plasma region

Claims (6)

A sealed reaction vessel and a carbon electrode disposed in the reaction vessel for arc discharge;
A device for producing carbon nanotubes by evaporating carbon of the carbon electrode using the arc discharge as a heat source and then condensing the evaporated carbon,
Arranged to surround a desired area extending between the carbon electrodes, and
An apparatus for producing carbon nanotubes, further comprising a heating / warming means for heating or keeping the desired area at a predetermined temperature to expand an arc plasma area formed between the carbon electrodes.   2. The carbon nanotube production apparatus according to claim 1, wherein the heating and heat retaining means is constituted by an electric resistance heater.   The carbon nanotube production apparatus according to claim 1 or 2, wherein the heating and heat retaining means heats or keeps the desired area wide at a temperature of 1500 ° C or higher.   The carbon nanotube production apparatus according to any one of claims 1 to 3, wherein the carbon electrodes are spaced apart from each other by 10 mm or more.   The apparatus for producing carbon nanotubes according to any one of claims 1 to 4, wherein a fireproof heat insulating material is provided on an inner surface of the reaction vessel. A method of producing a carbon nanotube by performing arc discharge with a carbon electrode, evaporating carbon of the carbon electrode using the arc discharge as a heat source, and then condensing the evaporated carbon,
When performing the arc discharge, using the heating and heat retaining means disposed so as to surround the desired area between the carbon electrodes, the desired area is heated or kept at a predetermined temperature, A method for producing carbon nanotubes, comprising expanding an arc plasma region formed between carbon electrodes.

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