JP4572319B2 - Carbon nanohorn manufacturing method and manufacturing apparatus - Google Patents

Description

  The present invention relates to a carbon nanoparticle production method and a production apparatus using the method, and is particularly suitable for a carbon nanohorn production method and apparatus.

  Conventional methods for producing carbon nanohorn particles include a laser ablation method, an arc discharge method between graphite electrodes in an inert gas, and an arc discharge method between graphite electrodes in liquid nitrogen. Here, it is known that carbon nanoparticles produced by the arc discharge method have few atomic arrangement defects and are suitable for field electron emission sources and fuel cell materials (Patent Document 1, Patent Document 2, and Patent Document). 3).

  In the arc discharge method between graphite electrodes in an inert gas, two graphite electrodes are placed facing each other in a container, and the container is filled with a rare gas (inert gas) such as argon or helium, between the carbon electrodes. A voltage is applied to the electrode to generate arc plasma, and carbon nanohorn particles are generated by cooling carbon vapor (soot) generated from the anode surface of the arc. The produced carbon nanohorn particles are deposited on the cathode surface or attached to the inner surface of the container, and are collected. Here, as a method of cooling the carbon vapor, a method of sucking up the carbon vapor from the container and cooling it with water, a method of cooling the arc plasma by compressing and diffusing it with an electromagnet, etc. are known (Non-Patent Document 1). Non-patent document 2).

  Also, the arc discharge method between graphite electrodes in liquid nitrogen is to apply a voltage between carbon electrodes in liquid nitrogen to generate arc plasma, and to cool the carbon vapor generated from the anode surface of the arc with liquid nitrogen Thus, carbon nanohorn particles are generated.

  In addition, a method of generating carbon nanoparticles by generating an arc discharge at a carbon electrode in water instead of in an inert gas has been developed, but what can be generated by this method is a type of carbon nano-particles. Onion (multilayer fullerene-like nanoparticles) (Non-patent Document 3). In addition, according to a recent report, it is also known that multi-walled carbon nanotubes are formed when arc discharge is generated at a carbon electrode in water (Non-patent Document 4).

JP 2002-348108 A JP 2001-064004 A JP 2003-020215 A Nikkei Sangyo Shimbun (January 24, 2003, morning edition) “Carbon nanohorn production capacity, double the joint development of an IR buoy device” Nihon Keizai Shimbun (37 pages of morning editions on February 13, 2003) “Carbon nanohorn production amount, double the conventional amount. Proceedings of the Seventh Applied Diamond Conference / Third Frontier Carbon Technology Joint Conference (ADC / FCT2003) `` Large-scale synthesis of single-walled carbon nanohorns using the arc in liquid method '' N. Sano, H. Wang, I. Alexandrou, M. Chhowalla, KBK Teo, GAJ Amaratunga, K. Iimura, `` Properties of nano carbon particles produced by an arc discharge in water '' Journal of Applied Physics, vol 92, pp. 2783-2788, year 2002.

All of the conventional methods for producing carbon nanohorns described above utilize the phenomenon that carbon nanohorns can be formed when carbon is vaporized and rapidly cooled in a relatively inert gas.
However, the laser ablation method has a problem that the cost required for the equipment increases because a CO ₂ pulse laser is used to vaporize carbon.

  In addition, the arc discharge method in liquid nitrogen is a simple method that only discharges between carbon electrodes in liquid nitrogen, and has the advantage that the cost required for equipment is low, while running because liquid nitrogen is consumed quickly. In addition to the problem of high cost, there is a problem that a replenishment liquid nitrogen tank is required for mass production of carbon nanoparticles.

  In addition, the arc discharge method in an inert gas requires a vacuum vessel, a vacuum exhaust device, etc., so that the cost required for the equipment is high, and in addition, it is necessary to repeatedly exhaust and release the atmosphere every time carbon nanoparticles are generated. In addition, there is a problem in that it is not suitable for continuous mass production because it requires a process of collecting the carbon nanoparticles deposited and deposited on the inner wall of the container and the cathode, and the manufacturing process becomes complicated. In addition, this arc discharge method has a problem that a process for producing a product, for example, carbon nanohorn, is isolated from the carbon particles, sorted and collected from the collected carbon nanoparticles.

  Furthermore, in the method for producing carbon nanoparticles by arc discharge in water, the produced carbon nanoparticles are nano-onions (multi-walled fullerene-like carbon nanoparticles) and multi-walled carbon nanotubes, and it is difficult to produce single-walled carbon nanohorns. there were.

  The carbon nanohorn manufacturing method according to the present invention solves the problem of running cost in a method of discharging between carbon electrodes in liquid nitrogen, and reduces the cost of manufacturing equipment and running cost as compared with the conventional known manufacturing method. The purpose is to greatly reduce.

  In addition, it eliminates the need for facilities such as a vacuum vessel and a vacuum evacuation device in the arc discharge method, greatly reduces the device cost, and repeats the exhaust and atmosphere release required every time the carbon nanohorn is generated, The object is to eliminate a complicated recovery step of recovering the carbon nanohorn deposited and deposited on the inner wall or the cathode.

Another object of the present invention is to easily separate and collect single-walled carbon nanohorns, multi-walled carbon nanotubes, and nanoparticles from the produced carbon nanohorns.
Furthermore, it aims at recovering single-walled carbon nanohorns at a high recovery rate, improving the production capacity of single-walled carbon nanohorns compared to conventional manufacturing methods, and ensuring production capacity capable of mass production.

  As a result of intensive research and experiments on the production method of carbon nanohorn, the present inventor sends a relatively inert gas such as nitrogen into an arc discharge field in water under the condition that water vapor does not enter the arc plasma. As a result, it was found that carbon nanohorns could be generated, and the present invention was completed. Hereinafter, means for solving the above-described problems will be described.

The first solving means includes a step of applying a voltage between the graphite cathode and the graphite anode to generate arc discharge, a step of introducing an inert gas into the arc discharge generation region, and an arc discharge generation region. A method for producing carbon nanoparticles, comprising: a step of sending carbon vapor generated by arc discharge into water together with an inert gas through a partition wall to be covered; and a step of recovering carbon nanoparticles floating or deposited in the water surface or in water It is.
The first feature here is that, in the method for producing carbon nanoparticles by arc discharge, means for introducing a gas into the arc discharge field is used. By introducing this inert gas (for example, nitrogen gas) into the arc discharge field, it is possible to create the same conditions as arc discharge in liquid nitrogen. A liquid nitrogen tank can be made unnecessary, and manufacturing equipment costs and manufacturing running costs can be significantly reduced.

  A second feature is that water vapor and air are prevented from entering the arc plasma by providing a partition wall that covers the arc discharge generation region. By blocking air and water vapor, it is possible to suppress the disappearance of the carbon nanohorn intermediate by reacting with the gas, and it is possible to generate sufficient single-layer carbon nanohorn particles that can be expanded to industrial production. It has been confirmed that single-walled carbon nanohorn particles are not generated even if an inert gas is simply blown into the arc plasma using a nozzle or the like without providing a partition wall that covers the arc discharge generation region. In addition, it has been confirmed that the generation rate of the carbon nanohorn particles varies depending on the length of the partition wall, and this point will be described in detail in Examples described later.

  Here, the manufacturing process of the single-walled carbon nanohorn particles will be described. First, carbon vapor generated by arc discharge moves and diffuses along the partition wall together with an inert gas. At this time, multi-walled carbon nanotubes and large-sized carbon particles are deposited on the partition walls. When carbon vapor is sent out into the water from the partition wall, it is cooled rapidly and single-walled carbon nanohorn particles are generated from the carbon vapor. Since single-walled carbon nanohorn particles float near the water surface, they are collected and dried. Single-walled carbon nanohorn particles can be produced by a series of these steps.

  The first solution described above is to use water and inert gas in the production of carbon nanoparticles, and greatly reduce the cost and running cost of production equipment as compared with the conventional known production methods. In addition, equipment such as a vacuum vessel and a vacuum exhaust device in the arc discharge method is not required, and the device cost can be reduced. In addition, it is possible to eliminate the process of repeating the exhaust and air release required every time the carbon nanohorn is generated and the complicated recovery process of recovering the carbon nanohorn particles deposited and deposited on the inner wall and the cathode of the container, Single-walled carbon nanohorns, multi-walled carbon nanotubes and nanoparticles can be separated and recovered from the product.

  The second solution is characterized in that the graphite cathode and the graphite anode, which are constituent elements of the first solution, are devised. Specifically, the graphite cathode 1 has a hollow portion 5 inside one end, and has a vent hole 6 penetrating to the hollow portion 5 at the other end. The inert gas is introduced into the arc discharge field through the vent hole 6, and the carbon vapor is sent into the water together with the inert gas through the hollow portion 5 as a conduit. .

  Here, by making the inside of one end of the graphite cathode 1 hollow, it is possible to easily provide a partition wall that covers an arc discharge generation region. That is, the graphite anode 2 is inserted in a non-contact manner while holding a gap for arc discharge (hereinafter referred to as “arc gap”) between the hole bottom of the hollow portion 5 and the tip of the graphite cathode 2. When an arc discharge is generated between the graphite cathode and the graphite anode, the side surface portion of the hollowed portion 5 can serve as a partition wall to cover the arc discharge generation region.

  Also, by adjusting the distance between the partition wall of the side surface portion of the hollow portion 5 of the graphite cathode 1 and the side surface portion of the graphite anode 2 so as to easily cause arc discharge, not only the tip portion of the graphite anode, Arc discharge can also be generated at the side surface portion, and there is an effect that the arc discharge generation region can be enlarged. By increasing the arc discharge region, the amount of carbon vapor generated from the graphite anode increases, and the generation rate of nanocarbon particles can be improved.

  Next, the ventilation hole 6 penetrating to the hollow portion 5 is provided in the graphite cathode 1 in order to introduce an inert gas into the arc discharge generation region. As described above, the single-walled carbon nanohorn particles are not generated even if an inert gas is simply blown into the arc plasma using a nozzle or the like without providing a partition wall that covers the arc discharge generation region. By sending an inert gas through the vent hole 6 to the hollow portion 5 of the graphite cathode 1, the inert gas can be introduced in a state where a partition wall covering the arc discharge generation region is provided.

  Further, the carbon vapor generated by the arc discharge is sent out into the water together with an inert gas using the hollow portion 5 of the graphite cathode 1 as a conduit tube. At this time, multi-walled carbon nanotubes and large-sized carbon particles are deposited and deposited on the side surfaces of the hollow portion 5 of the graphite cathode 1. As described above, the carbon vapor is rapidly cooled by being sent out into the water from the hollowed portion, and single-walled carbon nanohorn particles are generated from the carbon vapor.

  Here, in the first solution and the second solution described above, water is used as the liquid for rapidly cooling the carbon vapor, but instead, a liquid that is fluid at or below the arc discharge generation temperature. Even if is used, the same effect occurs.

  In the first and second solving means described above, the inert gas may be a gas component other than nitrogen gas, such as a rare gas such as Ar or He, or a mixed gas thereof. However, the same effect occurs. It goes without saying that even if a reactive gas is mixed in the introduced gas, there is no problem if the concentration is low and the reaction activity of the mixed gas is sufficiently low.

In the first and second solving means described above, among the generated carbon nanoparticles, it is a feature that the single-walled carbon nanohorn is floating on the water surface. The carbon particles having a large size adhere to and deposit on the side surface of the hollow portion 5 of the graphite cathode 1, and they are separated and deposited on the bottom of the water by the pressure received from the arc plasma or the flow pressure of the inert gas sent. . Unlike the case of conventional arc discharge, the characteristics of the generated carbon nanoparticles differ depending on whether they float on the water surface or deposit on the bottom of the water. In addition, since the generated carbon nanohorn particles are captured by water, unlike the case of conventional arc discharge, a complicated recovery operation such as recovery of the particles adhering to the side surface of the container is unnecessary, and the carbon nanohorn particles are completely removed with water. In other words, the carbon nanoparticle recovery rate is almost 100%, and the recovery rate is greatly improved as compared with the conventional case.
In addition, it is confirmed by microscopic observation that a very small amount of single-walled carbon nanohorns are mixed with multi-walled carbon nanotubes and large-sized carbon particles that are deposited on the bottom of the water. From the viewpoint of efficiency, it is considered more advantageous to collect the single-walled carbon nanohorn floating on the water surface.

  In the first and second solutions described above, arc discharge is generated by applying a DC voltage to the electrodes, but it goes without saying that the same effect occurs even with a DC pulse voltage. is there. In addition, when an arc discharge is generated by applying an AC voltage or an AC pulse voltage to the electrodes, the graphite cathode and the graphite anode are alternately switched, so that carbon vapor is generated from both electrodes, and both electrodes are Although it will be consumed, carbon nanoparticles are similarly generated.

Next, in the first and second solving means described above, instead of the graphite electrode (either the graphite anode or the graphite cathode or both), a graphite electrode containing or containing a metal , or In the case of using a graphite electrode in which a metal is dispersed, coated, plated or coated on a part or all of the surface, carbon nanohorn particles can be similarly produced. Also, for example, when a generation reaction is caused using a metal such as iron or nickel as an additive , carbon nanohorn particles include metal nanoparticles, that is, nano particles in which closed short single-walled carbon nanotubes are aggregated in a spherical shape. It is possible to put metal nanoparticles near the center of the carbon nanohorn particles that are particles.

  Here, the carbon electrode of the graphite cathode or the graphite anode includes a carbon electrode having a degree of graphitization or purity having conductivity to the extent that arc discharge occurs. For example, amorphous carbon or activated carbon having conductivity sufficient to cause arc discharge can be used for the electrode instead of the graphite electrode.

Next, component mechanisms necessary for a manufacturing apparatus using the carbon nanohorn manufacturing method as the first and second solving means described above are listed below.
1) A first electrode having a hollow portion 5 inside one end and a vent hole 6 penetrating to the hollow portion 5 at the other end 2) a second electrode 3) inserted loosely in the hollow portion 5 A mechanism for generating an arc discharge by applying a voltage between them 4) A mechanism for introducing an inert gas into the arc discharge field through the vent hole 5) A carbon vapor generated by the arc discharge with the cavity 5 as a conduit tube A mechanism for sending the carbon nanoparticle floating in the fluid 4 together with an inert gas. 6) A mechanism for collecting the carbon nanoparticles floating in the fluid 4. Here, the electrode diameters of the first electrode and the second electrode, the discharge current value in the arc discharge, The correlation between the flow rate of the inert gas, the depth of the hole in the hollow portion 5, the optimum value, and the like will be described in detail in the examples while showing specific examples.

Next, a description will be given of a production method that takes into account mass production to obtain uniform carbon nanoparticles continuously and stably. In the above-described method for producing carbon nanoparticles, a step of dispersing the carbon nanoparticles generated by sending carbon vapor into water by vibrating the water surface with an ultrasonic vibrator or the like, The process of stirring the water in the elutriation to prevent a rise in water temperature and the process of adjusting the water temperature to maintain the temperature of the water at a constant temperature ensure more uniform carbon nanoparticles in a continuous and stable manner. Obtainable. These steps are desirably performed constantly or periodically in the generation step.
Here, since the carbon nanohorn particles generated by the present invention float and collect on the water surface, it is difficult to prevent aggregation of the nanohorn particles during the arc discharge operation when the water stays, When moving in such a manner, there is an effect of dispersing the carbon nanoparticles by vibrating the water surface with an ultrasonic vibrator or the like.
In addition, there is an advantage that the ultrasonic vibrator can prevent the particles from being deposited on the partition walls of the hollow portion of the graphite cathode from being agglomerated. Note that pulse discharge may be used for discharge as a method for preventing the aggregation of particles deposited on the partition walls. This is because, when normal underwater arc discharge is performed, shock discharge is generated in pulse discharge as compared with continuous discharge, so that deposits on the partition walls are not formed.
As another method, since carbon nanohorn particles have a hydrophobic surface, adding a surfactant or the like to water has the advantage of preventing large aggregation on the water surface, but on the other hand, carbon nanohorn particles do not float on the water surface and do not float in water. There is a demerit that collection becomes difficult due to dispersion.

  In addition, by providing a step of stirring the water in the elutriation in order to prevent a local water temperature rise at the site where the carbon vapor is sent out, and by providing a step of adjusting the water temperature to maintain the temperature of the water at a constant temperature, More uniform carbon nanoparticles can be obtained continuously and stably. In addition, about stirring of water, it is also possible to substitute by stirring by bubbling by sending inactive gas. The change in the water temperature does not have a large effect on the carbon nanohorn particle formation reaction compared to the temperature difference between the arc temperature (about 4000 degrees) and the water temperature (0 to 100 degrees), but the mass production is sustained. If we continue, the adjustment of water temperature will be an important generation parameter.

  The method for producing a carbon nanohorn according to the present invention creates a state similar to discharging between carbon electrodes in liquid nitrogen by using the above-mentioned means, and solves the problem of running cost in the arc discharge method in liquid nitrogen. It has the effect of significantly reducing the cost and running cost of the manufacturing equipment as compared with the conventional known manufacturing method.

  Moreover, since the generated carbon particles can be recovered almost 100% with water by performing arc discharge in water, equipment such as a vacuum vessel and a vacuum exhaust device is not required, the device cost is reduced, and carbon nanohorns are generated each time. In addition to eliminating the troublesome recovery process of collecting the carbon nanohorn particles deposited and deposited on the inner wall of the container and the cathode, and the high recovery of single-walled carbon nanohorn particles. The production capacity of single-walled carbon nanohorn particles is improved as compared with the conventional production method, and the production capacity capable of mass production can be secured.

  Furthermore, since the produced single-walled carbon nanohorn particles float in water, the single-walled carbon nanohorn particles and the multi-walled carbon nanotubes and carbon particles can be easily separated and collected.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the illustrated configuration. In the conditions of a certain gas flow rate, electrode diameter, and discharge current value, there are optimum values for the dimensions shown in the figure, and various design changes can be made in the configuration of the manufacturing apparatus shown in the figure.

FIG. 1 is an apparatus for producing carbon nanohorn particles according to an embodiment of the present invention. The generation process of the carbon nanohorn in the present embodiment will be described in detail below. First, a DC power source 8 is used between the graphite cathode 1 and the graphite anode 2, and a discharge current is passed through the graphite cathode 1 and the graphite anode 2 to generate an arc discharge for a short time, for example, and is contained in the graphite anode 2. Carbon is evaporated to produce carbon vapor. At this time, a relatively inert gas 3 such as nitrogen is sent from the gas cylinder 7 to the arc discharge field 10. In the manufacturing process, the inert gas 3 is fed before the arc discharge is generated. The arc discharge field 10 is surrounded by a partition wall, and the carbon vapor generated by the arc discharge is sent to the water 4 through the partition wall together with an inert gas. After passing through the partition walls, the inert gas diffuses in the water in a bubble shape, and at the same time, the carbon vapor contained in the inert gas is quenched with water, generating carbon nanoparticles and floating near the water surface. Also, carbon vapor generated by arc discharge is cooled and deposited on the partition walls as carbon nanoparticles. Some of the deposited deposits are separated from the partition walls by the pressure received from the arc plasma or the flow pressure of the inert gas that is sent, and are deposited on the bottom of the water.
Here, the single-walled carbon nanohorn particles can be obtained by drying the suspended matter near the water surface. Moreover, when the sediment deposited on the water bottom is dried, multi-walled carbon nanotubes and carbon particles can be obtained.

FIG. 2 shows a schematic diagram of a graphite cathode. The point which devised the structure of the graphite cathode of said Example using FIG. 2 is demonstrated below. More specifically, the graphite cathode 1 has a structure having a hollow portion 5 having a hollow inside at one end and a vent hole 6 penetrating to the hollow portion 5 at the other end.
By making the inside of one end of the graphite cathode 1 hollow, it is possible to provide a partition wall covering the arc discharge generation region by the graphite cathode itself. Further, the vent hole 6 of the graphite cathode 1 is provided for introducing an inert gas into a region where arc discharge is generated. Although two holes are provided in FIG. 2, the number of the vent holes may be one or three or more.

  FIG. 3 shows a layout diagram of an arc discharge portion between the graphite cathode 1 and the graphite anode 2. The graphite anode 2 is loosely inserted into the hollow portion 5 of the graphite cathode 1, an inert gas is introduced into the arc discharge field through the vent hole 6, and the carbon vapor generated by the arc discharge uses the hollow portion 5 as a conduit tube. It has an electrode structure and arrangement that can be delivered with an inert gas. Here, the gap A for arc discharge is maintained between the hole bottom of the hollow portion 5 and the tip of the graphite cathode 2, and the graphite anode 2 is inserted without contact. When an arc discharge is generated between the graphite cathode 1 and the graphite anode 2, the side surface portion of the hollow portion 5 serves as a partition wall to cover the generation area of the arc discharge, and the arc discharge can be confined. By adjusting the distance E between the partition wall of the side surface portion of the hollow portion 5 of the graphite cathode 1 and the side surface portion of the graphite anode 2 and making it easy to cause arc discharge, not only the tip portion of the graphite anode 2, Arc discharge can also be generated at the side portion, and the area where arc discharge occurs can be enlarged.

  Here, the arc discharge gap D between the hole bottom of the graphite cathode and the tip of the graphite anode has a good distance of 1 to 2 mm, and is suitable for generation of arc discharge. Moreover, the arc discharge gap E between the side surface of the graphite cathode and the side surface of the graphite anode has a good distance of 1 to 2 mm, and is suitable for expanding the arc discharge generation region.

  Further, the optimum length F of the partition wall varies depending on the discharge current value, the electrode diameter, and the flow rate of the inert gas. For example, the graphite cathode diameter A is 3 mm, the graphite cathode diameter B is 9 mm, the partition wall thickness C is 1 mm, and the arc discharge gap D between the bottom of the graphite cathode hole and the tip of the graphite anode is 2 mm. In the case where the arc discharge gap E between the side surface of the graphite cathode and the side surface of the graphite anode is 2 mm, the results of measuring the relationship between the generation rate of carbon nanohorn, the reaction rate, the discharge current, and the length of the partition wall are described below. To do.

FIG. 6 shows the results of measuring the current dependency of the generation rate of carbon nanohorn particles by measuring the discharge time and the weight of the powder floating on the water surface containing the carbon nanohorn particles after discharge when the discharge current is changed. Show. FIG. 6 shows that the generation rate of the carbon nanohorn particles is increased by increasing the discharge current. Further, it can be seen from FIG. 6 that when the discharge current value is 65 A or more, the increase rate increases rapidly.
Here, the generation rate can be increased by increasing the discharge current. However, when the graphite anode diameter is small, if the discharge current is too large, the graphite anode is consumed too quickly and becomes unstable. It is possible to further increase the discharge current by increasing the graphite anode diameter, and by making such a design change, it is possible to increase the amount of carbon nanohorn particles produced per batch manufacturing process. .

  FIG. 7 shows the results of measuring the consumption (reduction in weight) of the graphite anode and determining the reaction rate of the carbon nanohorn particles per weight of the consumed graphite anode when the discharge current is changed in FIG. Yes. It can be seen from FIG. 7 that the reaction rate of the carbon nanohorn particles is not significantly affected by the discharge current.

  FIG. 8 shows the results of measuring the generation rate (g / h) of carbon nanohorn particles when the discharge current is fixed at 50 (A) and the length of the barrier rib (the depth of the cathode hole) is changed. ing. FIG. 8 shows that the generation rate is the fastest when the length of the partition wall due to the hollow portion of the graphite cathode is 20 mm. Although this barrier rib is considered to have an effect of widening the arc discharge field, as shown in the results of FIG. 8, even if the length of the barrier rib is increased to, for example, 30 mm, the generation rate does not increase but rather decreases. is doing. The reason for this is that if the partition wall becomes too long, the rate at which carbon vapor adheres to and accumulates on the partition wall increases, reducing the amount of carbon vapor expelled into the water together with the inert gas, and increasing the partition wall length. This is because there is a limit to the spread of the arc discharge field under the condition that the arc discharge current is constant.

  FIG. 9 shows the results of measuring the consumption of the graphite anode and determining the reaction rate of the carbon nanohorn particles per weight of the consumed graphite anode. As shown in FIG. 9, when the partition wall length is 5 mm, the reaction rate is low. When the length of the partition wall is 15 mm, the reaction rate is higher than that of 5 mm. In addition, when the length of the partition wall was changed to 15 mm, 20 mm, and 30 mm, the reaction rate did not change even when the length of the partition wall was increased, but rather the reaction rate slightly increased when the length of the partition wall was increased. Has fallen.

  FIG. 10 shows the result of obtaining the particle size distribution by dynamic light scattering when carbon nanohorn particles generated at a current of 50 A and a cathode hole depth of 15 mm are dispersed in toluene by ultrasonic waves. In the distribution of FIG. 10, there is a distribution from about 30 nm to a large diameter, and the number ratio has a peak in the vicinity of 70 nm. Also in observation with a transmission microscope, carbon nanohorn particles having a particle diameter of about 70 nm can be observed well.

Table 1 shows the results of measuring the specific surface area of the powder by nitrogen gas adsorption.
As a result, a value of about 130 m ² / g is shown, but the value of carbon nanohorn particle aggregates produced by laser evaporation is reported to be about 300 m ² / g (K. Murata et al. / Chemical Physics Letters, vol. 331, pp. 14-20 (2000)). Compared with this value, the value of the non-surface area shown in Table 1 is a low value. This assumes that the powder synthesized under the same conditions was mixed with impurities having a higher density and larger size than the carbon nanohorn particles.

  Next, the data regarding the continuous use when using the graphite cathode which has the same hollowing part, replacing | exchanging the graphite anode to wear repeatedly are shown. When a graphite anode with a diameter of 3 mm is inserted into a hollow portion of a graphite cathode having a cathode hole diameter of 7 mm and a depth of 15 mm and discharging is performed at 50 A, deposits formed on the side surfaces of the hollow portion of the cathode are peeled off for about 60 seconds. However, if the discharge is continued for a longer time, the remaining deposits are accumulated and the discharge of the hollow portion of the graphite cathode cannot be sustained. As countermeasures against this, in a long-time discharge, the gas flow rate, the length of the hollow portion of the graphite cathode, the arc with the graphite anode are controlled so as to suppress the accumulation of deposits on the side surface of the hollow portion of the graphite cathode. The arc discharge time can be extended by adjusting the gap distance or applying vibration such as ultrasonic waves to the graphite cathode.

  11 and 12 show transmission microscope images of single-walled carbon nanohorns generated using the manufacturing apparatus according to the present invention. It can be seen from the high-magnification transmission microscope image of FIG. 11 that the generated single-walled carbon nanohorn.

  FIG. 4 shows a configuration diagram of a manufacturing apparatus when arc discharge between a graphite anode and a graphite cathode is generated not on water but on the water surface. As shown in FIG. 4, even when arc discharge is performed on the water surface, the presence of the partition wall in the hollow portion of the graphite cathode and the step of introducing an inert gas into the arc discharge field cause the As in the case, air and water vapor can be blocked. For this reason, even when it is on the water surface of Example 2, it can suppress that the intermediate body of carbon nanohorn reacts with gas and lose | disappears, and can produce | generate carbon nanohorn similarly. In this case, since the carbon electrode does not enter the water, there is an effect that the process for replacing the carbon electrode in mass production is simplified.

However, in this case, since the cooling of the electrode is air cooling, the cooling efficiency is lower than that of water cooling, so that the electrode temperature is easily increased, and there is a demerit that continuous operation is difficult with a simple apparatus. That is, if the parts and gas lines that support the electrodes are not devised, they are easily damaged by heat. Further, the temperature of the partition wall itself easily becomes high, and the partition wall itself is oxidized and gasified by air, so that it is consumed for a long time.
For this reason, performing arc discharge in water as in Example 1 can efficiently cool the electrodes including the partition walls, so that an increase in the temperature of the partition walls can be suppressed and the durability can be improved.

  FIG. 5 shows another schematic view of a graphite cathode. Compared to FIG. 2, providing the air holes from the side surface has an effect that the air holes can be easily created.

Single-walled carbon nanohorns, multi-walled carbon nanotubes and the like produced by the carbon nanoparticle production method according to the present invention can be used for electron emission sources such as FED (Field Emission Display), fuel cells, hydrogen storage materials and the like.
Here, the fuel cell is suitable for use in an electrode carrying a catalyst such as platinum because the structure of the nanohorn particles has a large specific surface area and allows the catalyst fine particles to be stably attached.
As for the hydrogen storage material, in addition to the large specific surface area of the nanohorn particles, it is possible to make holes in the structure of the single-layer nanohorn by heat treatment, and as a result, a small gas such as hydrogen passes through the holes made in the nanohorn particles. It is known that molecules can be occluded inside the nanohorn, and that other fuel gases such as methane can be retained by adsorption as well as hydrogen.

Configuration of carbon nanohorn particle manufacturing equipment (1) Schematic diagram of graphite cathode (1) Arrangement of arc discharge part between graphite cathode and graphite anode Configuration diagram of carbon nanohorn particle manufacturing equipment (2) Schematic diagram of graphite cathode (2) Graph of production rate of powder containing carbon nanohorn particles Graph of reaction rate comparing the consumption weight of the graphite anode and the weight of the powder containing the generated carbon nanohorn particles Correlation graph between the generation rate of powder containing carbon nanohorn particles and the hole depth at the cavity of graphite cathode Correlation graph between the reaction rate comparing the consumption weight of the graphite anode and the weight of the powder containing the generated carbon nanohorn particles and the hole depth of the hollow portion of the graphite cathode Measurement diagram of carbon nanohorn particle size distribution by dynamic light scattering method High magnification transmission microscope image of aggregated carbon nanohorn particles Low magnification transmission microscope image of aggregated carbon nanohorn particles

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Graphite cathode 2 Graphite anode 3 Inert gas 4 Fluid 5 Cavity part 6 Vent 7 Gas cylinder 8 DC power supply 9 Valve 10 Arc discharge field 11 Floating substance containing single-walled carbon nanohorn particle 12 Multi-walled carbon nanotube and carbon particle Precipitates to be contained A Graphite anode diameter B Graphite cathode diameter C Cavity thickness of partition wall D Arc discharge gap between graphite cathode hole bottom and graphite anode tip E Side surface of graphite cathode and side surface of graphite anode Arc discharge gap between F

Claims (14)

In the method for producing carbon nanoparticles by arc discharge, a step of generating an arc discharge by applying a voltage between the graphite cathode (1) and the graphite anode (2), and an inert gas in the arc discharge generation region. A step of introducing, a step of sending the generated carbon vapor into the water together with an inert gas through the partition covering the region where the arc discharge is generated, and a step of recovering the carbon nanoparticles suspended or deposited in the water surface or in the water A method for producing carbon nanoparticles, comprising:   The graphite cathode (1) has a hollow portion (5) inside one end, and has a vent (6) penetrating to the hollow portion (5) at the other end, and the graphite anode (2) is hollow. The inert gas is introduced into the arc discharge field through the vent hole (6), and the carbon vapor is submerged with the inert gas together with the inert gas using the hollow portion (5) as a conduit. The carbon nanoparticle production method according to claim 1, wherein the carbon nanoparticle production method is performed.   The method for producing carbon nanoparticles according to claim 1 or 2, wherein a liquid that is fluid at a temperature equal to or lower than an arc discharge temperature is used instead of the water. The carbon nanoparticle according to claim 1 or 2, wherein the inert gas is a gas component having low reactivity selected from rare gases such as Ar and He and nitrogen gas, or a mixed gas thereof. Manufacturing method. The method for producing carbon nanoparticles according to claim 1, wherein the carbon nanoparticles floating on the water surface are single-walled carbon nanohorns.   The carbon nanoparticles deposited on the inner surface of the hollow portion (5) of the graphite cathode (1), separated by the pressure from the plasma and the inert gas flow pressure, and precipitated and deposited on the bottom of the water are multi-walled carbon nanotubes or The method for producing carbon nanoparticles according to claim 1 or 2, wherein the carbon nanoparticles are multi-layered carbon particles or mixed particles thereof.   The method for producing carbon nanoparticles according to claim 1 or 2, wherein the arc discharge is generated by applying a DC voltage or a DC pulse voltage to the electrode.   The method for producing carbon nanoparticles according to claim 1, wherein the arc discharge is generated by applying an AC voltage or an AC pulse voltage to the electrode. The method for producing carbon nanoparticles according to claim 1 or 2, wherein a graphite electrode containing or containing a metal instead of a graphite electrode (either the graphite anode or the graphite cathode or both), or a metal A method for producing carbon nanoparticles, characterized by using a graphite electrode that is sprayed, coated, plated or coated on a part or all of the surface.   A first electrode having a hollow portion at one end and a vent hole (6) penetrating to the hollow portion (5) at the other end, and a second electrode loosely inserted into the hollow portion (5) Electrodes, a mechanism for generating an arc discharge by applying a voltage between the electrodes, a mechanism for introducing an inert gas (3) into the arc discharge field through the vent hole (6), and a carbon vapor generated by the arc discharge And a mechanism for sending the carbon nano-particles floating or deposited in the fluid (4) to the fluid (4) and a mechanism for sending out the hollow portion (5) to the fluid (4) together with an inert gas. An apparatus for producing carbon nano-characteristics.   11. The carbon nanoparticle production apparatus according to claim 10, wherein a depth of the hollowed portion (5) is 10 to 30 mm.   The gap between the graphite cathode (1) and the graphite anode (2) loosely inserted into the hollow portion (5) (between the bottom of the hollow portion and the tip of the graphite anode and the side surface of the hollow portion and the graphite) The apparatus for producing carbon nanoparticles according to claim 10 or 11, wherein the distance between the anode and the side surface is 1 to 2 millimeters.   The method for producing carbon nanoparticles according to claim 1 or 2, further comprising a step of applying vibration such as ultrasonic waves to the graphite cathode (1). Oite the production method of carbon nano particles according to claim 1, comprising the steps of dispersing carbon nano-particles produced by vibrating the water surface by ultrasonic oscillator or the like by the carbon vapor is fed into the water, carbon vapor Sustained uniform carbon nanoparticles with a step of stirring the water in the elutriation to prevent a local rise in water temperature at the site where the water is delivered and a step of adjusting the water temperature to maintain the water temperature at a constant temperature A method for producing carbon nanoparticles, characterized by being obtained stably.