JP5328008B2 - Carbon material manufacturing method - Google Patents

Description

  The present invention relates to a carbon material obtained by thermally decomposing a hydrocarbon compound in a thermal plasma and a method for producing the same.

  Carbon materials such as carbon black and graphite use crystalline structures, physical properties such as conductivity and lubricity, etc., and by controlling the particle size and shape, conductive materials such as black pigments, rubber product reinforcements and plastics. Widely used as an adhesive filler. For example, by controlling the shape and making fine particles, paints with high light shielding properties and blackness can be obtained and used as display materials, paints using electrical conductivity, and fillers for radio wave absorbers, as well as crystallinity and electrochemical properties. It is used for battery negative materials and hydrogen storage materials that use mechanical stability, lubricants that use self-lubricating properties, and functional materials such as low-wear inks.

  Carbon materials are industrially produced by thermal decomposition of carbon-containing substances (usually mainly hydrocarbon compounds). Examples of pyrolysis of carbon-containing materials include open flame decomposition method (impingement method or channel method), closed direct flame decomposition method (furnace method), external heating surface method (continuous thermal method), plasma method, etc. Among various methods, the plasma method is particularly preferable because it has a high energy density of high-temperature plasma and a large cooling rate, and is suitable for producing fine powder.

  As a technique for producing a carbon material by this plasma method, a method of obtaining a carbon black having an amorphous internal structure by introducing a halogenated carbon compound into a zone where an inert gas is kept in an ionized state is known ( Patent Document 1).

Further, the crystallite thickness (Lc) obtained by plasma pyrolysis of a hydrocarbon compound is 100 to 160 Å, the lattice constant (a ₀ ) in the a-axis direction is 2.446 to 2.555 Å, and the lattice constant in the c-axis direction. A fine scale-like crystalline film-like carbonaceous material having a turbulent crystal structure of (c ₀ ) 6.876 to 6.885 Å has been proposed (Patent Documents 2 and 3).
Japanese Patent Publication No.43-12421 JP-A-2-307817 JP-A-5-58612

  However, the manufacturing technique of Patent Document 1 is directed to amorphous carbon black, and the obtained carbon material has a fine particle size of 36 mm, but a carbonaceous amorphous internal structure in which graphite crystallites are randomly overlapped. Presents. For this reason, although it is excellent in filling property, lubricity, etc., it is not preferable in terms of physical properties in terms of conductivity.

The carbon materials manufactured in Patent Document 2 and Patent Document 3 are macroscopically in the shape of a scale film and have a large anisotropic aspect ratio, but the crystal thickness is also 100 to 160 mm (10 to 10). 16 nm), which is relatively thick and has a turbulent crystal structure in which a ₀ is reduced by about 0.5% and c ₀ is extended by about 2.5% compared to graphite crystals. Unfortunately, it can be inferior to crystalline graphite with good electrical conductivity. For this reason, when it is used for a conductive paint using conductivity, the amount of use increases, and it becomes difficult to make a thin film or thin line. Moreover, it is conceivable that the reflectivity is lowered due to the deterioration of the electric conduction characteristics, and the light shielding property is also lowered.

  In view of the above problems, the object of the present invention is to provide a crystal thickness (Lc) that provides high conductivity, filling properties, light shielding properties, etc. when used in conductive paints, radio wave absorbers, light shielding materials, and the like. Is to provide a carbon material containing foil-like crystal pieces of 10 nm or less and a method for producing the same.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have conducted diversified studies on the mechanism by which hydrocarbons are thermally decomposed in thermal plasma and the generation conditions for conversion to carbonaceous materials. The present inventors have found that a carbon material having a desired property can be converted by varying the plasma gas temperature at the position where hydrogen compound is introduced and the ratio of the amount of introduced hydrocarbon compound to the plasma space within a certain range, thereby completing the present invention. It came to.

  (1) A crystalline carbon material obtained by plasma pyrolysis of a hydrocarbon compound, and containing a foil piece crystal piece having a crystal thickness (Lc) of 10 nm or less.

  According to the invention described in (1), the carbon material produced by thermally decomposing a hydrocarbon compound at a high plasma temperature has a crystal thickness (Lc) of 10 nm or less, and further a foil piece of 5 nm or less. Since it contains a crystal piece, it is ultrafine, flat flake, has a large aspect ratio, and has good crystallinity. For this reason, not only is it excellent in filling property and lubricity, but also it is excellent in conductivity, light shielding property, etc., and a paint having a light shielding property and high blackness is obtained. It can be widely used for fillers of electromagnetic shielding materials, lubricants utilizing self-lubricating properties, functional materials such as UV cut inks, and the like.

  (2) The carbon material according to (1), wherein the foil piece-like crystal piece has a thickness (Lc) of 5 nm or less.

  According to the invention described in (2), since the thickness of the crystal of the carbon material becomes thinner, it is finer and the aspect ratio becomes larger, so that the filling property, lubricity, conductivity, light shielding property, etc. are further improved. It will be excellent.

  (3) The carbon material according to (1) or (2), wherein the foil piece-like crystal piece contains 90% or more of the number of crystal pieces of the carbon material.

  According to the invention described in (3), since the foil piece-like crystal pieces are contained in 90% of the number of crystal pieces of the carbon material and are crystalline, they are excellent in conductivity and the like.

  (4) The carbon material according to any one of (1) to (3), wherein the hydrocarbon compound is natural gas.

  Natural gas includes methane, ethane, propane, butane and the like, and is a hydrocarbon gas mainly composed of methane, and is useful as a hydrocarbon compound raw material because of its versatility.

  (5) The carbon material according to any one of (1) to (3), wherein the hydrocarbon compound is methane and / or propane.

  Methane and propane are the main components contained in natural gas, have excellent versatility, and are advantageous in terms of cost. In addition, the hydrocarbon compound is thermally decomposed by thermal plasma to generate hydrogen together with the carbon material. However, the hydrocarbon compound has a high hydrogen content and is effective as a hydrogen source.

  (6) A method for producing a carbon material, in which a plasma is generated from an inert gas, a hydrocarbon compound is introduced into the plasma, and the hydrocarbon compound is subjected to plasma pyrolysis, the pressure in the plasma generation chamber The inert gas is supplied so that the gas flow rate in the standard state (101325 Pa at 25 ° C.) is 0.602 m / sec or more in a reduced pressure atmosphere of 6 kPa or more and 66.5 kPa or less, and the plate power is 6 kVA or more. After the application, the method for producing a carbon material according to any one of (1) to (5), wherein the hydrocarbon compound is introduced at 5 L / min or more to thermally decompose the hydrocarbon compound.

  According to the invention described in (6), using an inert gas, a hydrocarbon compound is introduced into a thermal plasma generated by inducing a high frequency at a plate power of 6 kVA or more and thermally decomposed by introducing 5 L / min or more, Since the hydrocarbon compound is thermally decomposed, the hydrocarbon compound is reformed into hydrogen and acetylene, the actual flow rate of the plasma gas is very high, and the generated hydrocarbon is quenched, so the crystal thickness ( Thus, a carbon material of a foil piece crystal piece having Lc) of 10 nm or less, and further 5 nm or less is efficiently generated.

  (7) A method for producing a carbon material, in which plasma is generated from a mixed gas of an inert gas and hydrogen, a hydrocarbon compound is introduced into the plasma, and plasma pyrolysis of the hydrocarbon compound is performed. In a reduced pressure atmosphere with a pressure in the plasma generation chamber of 6 kPa or more and 66.5 kPa or less, a mixed gas of inert gas and hydrogen is used so that the gas flow rate in the standard state (101325 Pa at 25 ° C.) is 0.602 m / sec or more. The carbon according to any one of (1) to (5), wherein after supplying and applying a high frequency of a plate power of 6 kVA or more, the hydrocarbon compound is introduced at 5 L / min or more to thermally decompose the hydrocarbon compound. Material manufacturing method.

  According to the invention described in (7), when a hydrocarbon compound is introduced to a thermal plasma generated by inducing a high frequency with a plate power of 6 kVA or more using a mixed gas of an inert gas and hydrogen, 5 L / min or more, A hydrocarbon compound is thermally decomposed by plasma to be reformed into hydrogen and acetylene, and a carbon material is generated. At this time, by mixing a diatomic molecular gas such as hydrogen with an inert gas, the pinch effect is improved, the plasma is squeezed and the temperature at the center is increased, and the actual flow velocity of the plasma gas is further increased. In addition, coupled with the fact that the generated hydrocarbon is rapidly cooled, the carbon material containing the flake-shaped crystal pieces having a crystal thickness (Lc) of 10 nm or less, and further 5 nm or less is more efficiently produced. become.

  (8) A method for producing a carbon material in which plasma is generated from a mixed gas of an inert gas and carbon dioxide, a hydrocarbon compound is introduced into the plasma, and plasma pyrolysis of the hydrocarbon compound is performed. Mixing of inert gas and carbon dioxide so that the gas flow rate is 0.602 m / sec or more in a standard condition (101325 Pa at 25 ° C.) in a reduced pressure atmosphere of 6 kPa or more and 66.5 kPa or less in the plasma generation chamber The gas according to any one of (1) to (5), wherein gas is supplied and a high frequency of 6 kVA or more of plate power is applied, and then the hydrocarbon compound is introduced at 5 L / min or more to thermally decompose the hydrocarbon compound. Carbon material manufacturing method.

  According to the invention described in (8), when a hydrocarbon compound is introduced to a thermal plasma generated by inducing a high frequency with a plate power of 6 kVA using a mixed gas of an inert gas and carbon dioxide, 5 L / min or more, The hydrocarbon compound is thermally decomposed by plasma to be reformed into hydrogen and carbon monoxide, and a carbon material is generated. When the carbon amount of the hydrocarbon compound and the carbon amount of carbon dioxide (carbon ratio of carbon of the hydrocarbon compound to carbon dioxide) exceed about 1: 1, acetylene starts to be generated and simultaneously a carbon material starts to be generated. Although the yield of the carbon material is reduced by this production method, carbon dioxide, which is a global warming gas, can be converted to carbon monoxide, which is a raw material of the mixed gas, and is similar to the invention described in (7). Thus, a carbon material containing foil-like crystal pieces having a crystal thickness (Lc) of 10 nm or less and further 5 nm or less is obtained.

  (9) The method for producing a carbon material according to any one of (6) to (8), wherein argon gas is used as the inert gas.

(10) The method for producing a carbon material according to any one of (6) to (9), wherein natural gas is used as the hydrocarbon compound.
(11) The method for producing a carbon material according to any one of (6) to (9), wherein methane and / or propane is used as the hydrocarbon compound.

  (12) The carbon material manufacturing method according to any one of (6) to (11), wherein high-frequency plasma is used as the plasma.

  When a hydrocarbon compound such as methane is mixed with an inert gas in a thermal plasma generated mainly by direct current discharge using an inert gas, when a direct current discharge is performed using a hydrocarbon compound gas such as methane, Methane and hydrocarbon compounds are decomposed to generate hydrogen, the temperature of the plasma rises due to the pinch effect, the anode copper melts, and the discharge may stop. On the other hand, when discharging is performed using a high frequency or microwave that is industrially assigned by the Radio Law, plasma can be maintained stably even in the case of such a gas. Therefore, a plasma using high frequency discharge or microwave discharge is superior to direct current discharge. Moreover, since the electrodeless discharge has no electrode, the obtained product does not contain impurities.

  (13) A radio wave absorber using the carbon material according to any one of (1) to (5).

  (14) A radio wave absorber using a carbon material obtained from the method for producing a carbon material according to any one of (6) to (12).

  According to the inventions described in (13) and (14), since the carbon material contains foil-like crystal pieces having a crystal thickness (Lc) of 10 nm or less, and further 5 nm or less, In addition, since it has a flat flake shape, a large aspect ratio, and good crystallinity, it not only has excellent filling properties and lubricity, but also has excellent conductivity and light shielding properties. For this reason, since the carbon material is uniformly dispersed and mixed in various matrix materials, it can be added without impairing the original workability and moldability of the matrix material, and it has conductivity, so that it is desired. An electromagnetic wave absorber corresponding to the frequency can be provided.

  According to the present invention, there is provided a carbon material containing a flake-like crystal piece having a crystal thickness (Lc) of 10 nm or less, further 5 nm or less, which is obtained by thermally decomposing a hydrocarbon compound with thermal plasma. Is ultrafine, is a piece of foil and has a large aspect ratio. Therefore, it is expected to be useful as a raw material for special applications such as high-value-added conductive fillers and high-performance lubricants.

  Hereinafter, embodiments of the present invention will be described in detail.

The carbon material of the present invention is obtained by plasma pyrolysis of a hydrocarbon compound, and the thickness (Lc) of the crystal is 10 nm or less, preferably 5% by mass or more of foil piece-like crystal pieces having a thickness of 90 nm or more, Preferably, it is fine crystalline containing 95% by mass or more. The crystalline carbon material is an aggregate of fine particles having a flake shape in which the lattice constant (a ₀ ) in the a-axis direction is about 0.247 nm and the lattice constant (c ₀ ) in the c-axis direction is about 0.671 nm. It is.

  The form is fine, macroscopically scaly, and has a large anisotropy and aspect ratio. For this reason, it will be excellent in filling property, lubricity, conductivity, light shielding property, etc., for example, a coating material with high light shielding property and blackness is obtained, a display material, a coating material using conductivity and an electromagnetic shielding material. It can be widely used for functional materials such as fillers, self-lubricating lubricants, UV-cutting inks, and the like.

  The carbon material of the present invention can be produced by using the following apparatus and method.

  As schematically shown in FIG. 1, the thermal plasma reactor includes a plasma torch 1 for generating plasma, a vacuum chamber 2 connected to the lower part thereof, and a high-frequency generator 3 provided at the periphery thereof. It is composed of The vacuum chamber 2 includes a vacuum pump 5 for evacuating the inside through a filter 11, and a reformed gas collection bag 4 having a filter collecting device 12 through a diaphragm vacuum pump 6. It is connected continuously. Moreover, although not shown in figure, it is cooled with the circulation type cooling water.

  Further, as shown in FIG. 2, the plasma torch 1 is a ring having a water-cooled double structure in which a quartz tube 1b is disposed outside a silicon nitride tube 1a, and is connected to a high frequency generator 3 at the outer peripheral portion thereof. The RF coil 9 is disposed in the form of a coil. Moreover, the hydrocarbon compound provided with the inert gas introduction pipe | tube 7 provided with the inert gas inlets 7a and 7b in the upper part, and the hydrocarbon compound inlet 8a for introducing the hydrocarbon compound which is source gas The introduction probe 8 is connected.

  The high-frequency generator 3 includes a high-frequency oscillator 3a and a high-frequency power source 3b. The output of the high-frequency oscillator 3a is appropriately determined depending on the type of raw material gas and the shape of the carbon material to be obtained. For example, 0.5 to 35 Kw (maximum electrode voltage (Ep) = 12 kV, maximum anode current (IP) = 5.8 A) is preferable, and the oscillation frequency is preferably 3.5 ± 0.5 Mz.

  The gas system for generating the thermal plasma should be an inert gas such as argon or helium, or a mixed gas stream obtained by adding a hydrogen gas, diatomic molecular gas such as nitrogen, or carbon dioxide gas to the inert gas. preferable.

  The hydrocarbon compound raw material for obtaining the carbon material of the present invention is not particularly limited as long as it can produce fine particles of the carbon material by a conventional method. For example, methane, ethane, propane, butane, pentane, Saturated hydrocarbons such as hexane, decane, and cyclohexane, unsaturated hydrocarbons such as ethylene, toluene, xylene, ethylbenzene, and styrene, aromatic hydrocarbons such as benzene, toluene, ethylbenzene, and styrene, polycycles such as naphthalene, anthracene, and phenanthrene An aromatic hydrocarbon etc. are mentioned. Among these, methane and propane are particularly preferable from the viewpoint of versatility and cost. Furthermore, natural gas, such as 13A used for city gas, is 88.0% methane, 4.5% ethane, 4.5% propane, and 1.7% butane. It is a hydrocarbon gas as a main component and has versatility, so it is useful as a hydrocarbon compound raw material.

  These hydrocarbon compounds or carbonaceous raw materials are preliminarily heated and vaporized and introduced into the thermal plasma stagnant region, or sprayed and introduced in the form of gas as fine droplets. In addition, the introduction of the raw material into the thermal plasma stagnation region does not necessarily require a hydrocarbon compound or a carbonaceous raw material alone, and it is mixed with a mixed gas mixed with an inert gas for generating a thermal plasma or carbon dioxide gas. It may be introduced.

  In addition, the amount of such raw material introduced depends on the output power that forms the thermal plasma stagnation zone, and the higher the frequency of the high-frequency thermal plasma, the higher the amount of raw material introduced and the higher the reforming efficiency. .

  In the manufacturing process, first, inert gas is introduced from the inert gas introduction ports 7a and 7b of the inert gas introduction pipe 7 and fed into the system, and the high frequency generator 3 supplies the RF coil 9 with a frequency of 3.5, for example. The thermal plasma 10 is generated by applying electric power at ± 0.5 Mz. Next, a hydrocarbon compound is introduced from the hydrocarbon compound introduction port 8 a and blown into the thermal plasma from the hydrocarbon compound introduction probe 8. At this stage, the hydrocarbon compound is rapidly pyrolyzed and converted into reformed gas, hydrogen, and carbon material. After the reaction is completed in the vacuum chamber 2, it is cooled by circulating cooling water, and the reformed gas and hydrogen are evacuated. It is sucked by a diaphragm vacuum pump 6 connected to the chamber 2 and collected in a reformed gas collecting bag 4. Further, after collecting the reformed gas and hydrogen gas, the carbon material is recovered from the inner wall of the vacuum chamber 2 and the filter portion of the filter collecting device 12 provided in the reformed gas collecting bag 4.

  In the above process, the raw material hydrocarbon compound is completely decomposed in the thermal plasma, and the supply amount, pressure, and output of the hydrocarbon compound are such that the recovered gas does not contain the raw material hydrocarbon compound. A foil-like crystal carbon material can be obtained. Specifically, the gas for generating the thermal plasma is supplied in such an amount that the flow rate passing through the plasma generation chamber is 0.602 m / sec or more in a standard state (101325 Pa at 25 ° C.), and carbonized in the thermal plasma. When the hydrogen compound is introduced and the pressure after the introduction is maintained at 6 kPa or more and 66.5 kPa or less, a foil piece-like crystal piece having a thickness of 10 nm or less can be stably obtained. The amount of carbon in the hydrocarbon compound to be introduced can be increased by increasing the high-frequency output. That is, the introduction amount of the hydrocarbon compound can be controlled by adjusting the output of the high frequency. The introduction amount of the hydrocarbon compound is preferably 5 L / min or more. In addition, since the amount of graphite produced increases by increasing the pressure during reforming, the production of foil piece-like crystal pieces can be controlled by controlling the pressure. The generation of thermal plasma is performed by applying a high frequency with a plate power of 6 kVA or more. In this application, it is preferable to first generate plasma at a low output, then gradually increase the output to stabilize the plasma, and then perform a reforming treatment of the hydrocarbon compound at a predetermined output.

  Since the obtained carbon material contains foil-like crystal pieces having a crystal thickness (Lc) of 10 nm or less, and further 5 nm or less, it is ultrafine, flat flaky and has a large aspect ratio, Since the crystallinity is good, not only the filling property and the lubricity are excellent, but also the conductivity and the light shielding property are excellent. Therefore, the carbon material can be homogeneously dispersed and mixed in various matrix materials, and can be added without impairing the original processability and moldability of the matrix material. Moreover, since it has electroconductivity, what was shape | molded by using as a filler in various matrix materials will be excellent in an electromagnetic wave absorption characteristic. For this reason, for example, a radio wave absorber corresponding to a desired frequency can be manufactured by using the carbon material. In particular, in a wireless LAN, when the 4.9 GHz to 5.091 GHz band, which has been prohibited from being used outdoors in the past, is released and can be used, the thickness of this frequency band is, for example, 4 to 6 mm. It is possible to provide a radio wave absorber that is thin and excellent in radio wave absorption characteristics.

  The above radio wave absorber can be manufactured by a known method by adding the carbon material of the present invention in a predetermined ratio to a matrix material. The addition ratio of the carbon material depends on the intended radio wave absorption characteristics and the matrix material to be used. For example, it is preferable to add an amount of 50 vol% or less to the matrix material.

  As a matrix material used for the above-mentioned radio wave absorber, an organic polymer having characteristics such as strength, heat resistance, and moldability according to the use is mainly used. For example, various elastomers such as chloroprene rubber, acrylonitrile-butadiene rubber, natural rubber, thermoplastic resins such as polyolefin resin, polyamide resin, PVC resin, thermosetting resins such as epoxy resin, silicone resin, urethane resin, etc. You may mix and use these as needed.

  If necessary, a solvent, a dispersant, a plasticizer, a crosslinking agent, an antiaging agent, a vulcanization accelerator, and the like may be added. Further, in addition to the organic polymer, it may be dispersed and mixed in an inorganic base material such as calcium silicate molding material, ALC or cellular concrete.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. This is merely an example, and the technical scope of the present invention is not limited to this.

<Example 1>
Using the apparatus shown in FIGS. 1 and 2, methane is used as a hydrocarbon compound, argon gas is used as an inert gas, plasma is generated with a mixed gas in which hydrogen gas is mixed, and methane is thermally decomposed by the plasma. , Produced carbon material and reformed gas (acetylene, hydrogen).

  First, after the inside of the vacuum chamber 2 is reduced to 0.13 kPa or less with the vacuum pump 5, argon gas is introduced from the inert gas introduction pipe 7 to 50 kPa, and the purge operation for reducing the pressure again is repeated three times. Argon gas was supplied into the vacuum chamber 2 from the inert gas introduction pipe 7 at 10 L / min, and the thermal plasma 10 was ignited under a pressure of about 10 kPa in the vacuum chamber 2. Next, argon gas (supply amount 60 L / min) is supplied, the pressure in the vacuum chamber is 33.2 kPa, the output of the high-frequency oscillator 3 a is increased, and then argon gas (supply) is supplied to contract the thermal plasma 10. Hydrogen gas (supply amount 10 L / min) was mixed with the amount 60 L / min), and the plate power of the high-frequency oscillator 3 a was increased to 44.0 kVA to stabilize the plasma. The flow rate at which the supplied mixed gas of argon gas and hydrogen passes through the torch in FIG. 1 is about 0.845 m / sec in the standard state (101325 Pa at 25 ° C.). As the thermal plasma reactor, a thermal plasma reactor test apparatus JEOL34KW manufactured by JEOL Ltd. was used.

  Then, after flowing argon gas as a methane carrier gas at a flow rate of 3.0 L / min to the hydrocarbon compound introduction probe 8, methane was supplied at 36.7 L / min for 2 minutes. The used hydrocarbon compound introduction probe 8 had an inner diameter of 1.76 mm. Further, the pressure in the vacuum chamber 2 was 33.2 kPa.

Acetylene gas (C ₂ H ₂ ) and hydrogen gas (H ₂ ), which are reformed gases generated by the thermal decomposition of methane, are sucked with a diaphragm vacuum pump 6 (DA-15D manufactured by ULVAC) and captured by the reformed gas. Collected in collection bag 4. After collection, the supply of methane and carrier argon gas was stopped in this order, the output of the high-frequency oscillator 3a was reduced, and the thermal plasma 10 was extinguished.

  Next, air was introduced into the vacuum chamber 2, and after the inside of the vacuum chamber 2 reached atmospheric pressure, the carbon material adhering to the inner wall of the vacuum chamber 2 and the filter portion of the filter collecting device 12 was recovered.

  About each collect | recovered carbon material, the shape of the carbon material was observed using the transmission electron microscope (TEM: EM-002B by Topcon). Observation was performed at an acceleration voltage of 200 kV. And the TEM photograph (magnification 130 thousand times) of the carbon material A collect | recovered from the filter part is shown in FIG. Moreover, the photograph of the electron beam diffraction image obtained by irradiating the particle group of the carbon material A collect | recovered from the filter part with an electron beam is shown in FIG.

  From FIG. 3, it was confirmed that all of the recovered carbon materials A are aggregates of foil piece crystal pieces each having a side length of several tens to several hundreds of nanometers and a thickness of 10 nm or less. The thickness of the crystal is obtained from the measured length and magnification by taking a cross-section of the crystal at a suitable magnification using a transmission electron microscope, printing the negative of the photograph at the same magnification, measuring the length of the target portion. It was. As a result, the thickness of almost all the particles was 5 nm or less. Further, the crystal structure was determined to be a 2H structure from an electron beam diffraction image obtained by irradiating the particle group of the carbon material A shown in FIG. 4 with an electron beam.

<Example 2>
In Example 1, except that the supply of methane was performed by mixing methane with a mixed gas of argon gas and hydrogen gas that is a plasma generating gas, methane was thermally decomposed by the same apparatus and method as in Example 1. As a result, carbon materials and reformed gas (acetylene, hydrogen) were produced.

  First, using the apparatus used in Example 1, the thermal plasma 10 was generated in the same manner as in Example 1, and then argon gas (supply amount 60 L / min) was supplied. The pressure in the vacuum chamber was 33. After setting the output of the high-frequency oscillator 3a to 2 kPa, hydrogen gas was mixed with argon gas in order to contract the plasma, and the plate power was increased to 42.1 kVA to stabilize the plasma. The flow rate at which the supplied mixed gas of argon gas and hydrogen passes through the torch in FIG. 1 is about 0.845 m / sec in the standard state (101325 Pa at 25 ° C.).

  Thereafter, 24.5 L / min of methane was mixed with a mixed gas of hydrogen gas (supply amount of 10 L / min) to argon gas (supply amount of 60 L / min), introduced from the inert gas introduction pipe 7 and supplied. The pressure in the vacuum chamber 2 was 33.2 kPa.

  Two minutes after starting the supply, reformed gas and hydrogen gas were collected in the same manner as in Example 1. After sampling, the supply of methane was stopped, the output of the high-frequency oscillator 3a was reduced, and the thermal plasma was extinguished.

  Next, in the same manner as in Example 1, after introducing the atmosphere into the vacuum chamber 2 and reaching the atmospheric pressure in the vacuum chamber 2, it adheres to the inner wall of the vacuum chamber 2 and the filter portion of the filter collector 12. The carbon material B was recovered.

  The shape of the recovered carbon material B was observed in the same manner as in Example 1. And the TEM photograph (magnification 130 thousand times) of the carbon material B is shown in FIG.

  From FIG. 5, it was confirmed that the produced carbon material B is an aggregate of foil piece-like crystal pieces having a length of one side of several tens to several hundreds of nanometers and a thickness of several nm. This foil piece crystal piece had the same shape as the carbon material obtained in Example 1. The crystal length, thickness, and crystal structure were determined in the same manner as in Example 1.

<Example 3>
In Example 1, except that a mixed gas of argon gas and carbon dioxide gas was used as a plasma generating gas, methane was thermally decomposed to generate a carbon material, a reformed gas, and the like by the same apparatus and method as in Example 1. .

  First, using the apparatus used in Example 1, thermal plasma was generated in the same manner as in Example 1, and then argon gas (supply amount 60 L / min) was supplied. The pressure in the vacuum chamber was 33. After increasing the output of the high-frequency oscillator 3a to 2 kPa, carbon dioxide gas (supply amount 51 L / min) is mixed with argon gas (supply amount 60 L / min) to contract the plasma, and the plate power is set to 41.3 kVA. To stabilize the plasma. Next, the supply amount of argon was reduced to 50 L / min. At this time, the flow rate of the supplied mixed gas of argon gas and carbon dioxide through the torch in FIG. 1 is about 1.215 m / sec in the standard state (101325 Pa at 25 ° C.).

  Then, after flowing argon gas as a methane carrier gas to the hydrocarbon compound introduction probe 8 at a flow rate of 3.0 L / min, methane was supplied at 34 L / min for 2 minutes. The pressure in the vacuum chamber 2 was 33.2 kPa.

  The reformed gas and hydrogen gas produced by the thermal decomposition of methane were collected in the same manner as in Example 1. After collection, the supply of methane and carrier argon gas was stopped in this order, the output of the high-frequency oscillator 3a was reduced, and the thermal plasma 10 was extinguished.

  Next, in the same manner as in Example 1, after introducing the atmosphere into the vacuum chamber 2 and reaching the atmospheric pressure in the vacuum chamber 2, it adheres to the inner wall of the vacuum chamber 2 and the filter portion of the filter collector 12. The carbon material C was recovered.

  The shape of the recovered carbon material C was observed in the same manner as in Example 1. And the TEM photograph (magnification 88,000 times) of the collect | recovered carbon material C is shown in FIG. Moreover, the photograph of the electron diffraction image obtained by irradiating the particle group of the carbon material C collect | recovered from the filter part with an electron beam is shown in FIG.

  From FIG. 6, it was confirmed that the generated carbon material C was an aggregate of foil piece-like crystal pieces having a side length of several tens to hundreds of tens of nm and a thickness of several nm. And this foil piece-like crystal piece was exhibiting the same shape as the carbon material obtained in Example 1, and the magnitude | size was also substantially equivalent. Further, the crystal structure was determined to be a 2H structure from an electron beam diffraction image obtained by irradiating the particle group of the carbon material C shown in FIG. 7 with an electron beam. The crystal length, thickness, and crystal structure were determined in the same manner as in Example 1.

<Example 4>
In Example 3, argon gas (supply amount 60 L / min) was supplied, the pressure in the vacuum chamber was set to 26.6 kPa, the output of the high-frequency oscillator 3 a was increased, and then argon gas ( Carbon dioxide gas was started to be mixed at a supply amount of 60 L / min), and when the plate power was 20.3 kVA, the supply amount of carbon dioxide gas was 50 L / min. Next, the pressure in the vacuum chamber was 46.5 kPa, the supply amount of argon was adjusted to 86 L / min, the amount of carbon dioxide gas was adjusted to 60 L / min, and the plate power was set to 45 kVA. The flow rate at which the mixed gas of argon gas and carbon dioxide gas passes through the torch in FIG. 1 at this time is about 1.757 m / sec in the standard state (101325 Pa at 25 ° C.).

  Then, after flowing argon gas as a methane carrier gas through the hydrocarbon compound introduction probe 8 at a flow rate of 4.0 L / min, methane was supplied at 60 L / min for 8 minutes. The pressure in the vacuum chamber 2 was 46.5 kPa.

  The reformed gas and hydrogen gas produced by the thermal decomposition of methane were collected in the same manner as in Example 1. After collection, the supply of methane and carrier argon gas was stopped in this order, the output of the high-frequency oscillator 3a was reduced, and the thermal plasma 10 was extinguished.

  Next, in the same manner as in Example 1, after introducing the atmosphere into the vacuum chamber 2 and reaching the atmospheric pressure in the vacuum chamber 2, it adheres to the inner wall of the vacuum chamber 2 and the filter portion of the filter collector 12. The carbon material D was recovered.

  About the collect | recovered carbon material D, the shape was observed using the electron microscope (JEOL Co., Ltd. product JEM-2010). Observation was performed at an acceleration voltage of 5 kV. FIG. 8 shows an SEM photograph (magnification 100000 times) of the carbon material D recovered from the filter part. For comparison, the shape of the carbon material A of Example 1 was also observed with an electron microscope. FIG. 9 shows an SEM photograph of carbon material A (magnification 100000 times, acceleration voltage at the time of observation is 15 kV). It was confirmed that the carbon material D generated from FIG. 8 is an aggregate of foil pieces of crystal pieces having a side length of several tens to several hundreds of nanometers and a thickness of several nanometers. However, compared with the carbon material A in FIG. 9, the carbon material D has a short side and a small crystal size.

<Example 5>
In Example 3, argon gas (supply amount 60 L / min) was supplied, the pressure in the vacuum chamber was set to 26.6 kPa, the output of the high-frequency oscillator 3 a was increased, and then argon gas ( When carbon dioxide gas was started to be mixed at a supply amount of 60 L / min) and the plate power was 11 kVA, the supply amount of carbon dioxide gas was 20 L / min. Next, the argon supply amount was adjusted to 86 L / min, the carbon dioxide gas amount was adjusted to 30 L / min while the pressure in the vacuum chamber was kept constant, and the plate power was set to 35.5 kVA. Next, the supply amount of argon gas was adjusted to 56 L / min. At this time, the flow rate of the mixed gas of argon and carbon dioxide is about 1.035 m / sec in the standard state (101325 Pa at 25 ° C.).

  Then, after flowing argon through the hydrocarbon compound introduction probe 8 at a flow rate of 4.0 L / min as a methane carrier gas, methane was supplied at 30 L / min for 8 minutes. The pressure in the vacuum chamber 2 was 26.5 kPa.

  The reformed gas and hydrogen gas produced by the thermal decomposition of methane were collected in the same manner as in Example 1. After collection, the supply of methane and carrier argon gas was stopped in this order, the output of the high-frequency oscillator 3a was reduced, and the thermal plasma 10 was extinguished.

  Next, in the same manner as in Example 1, after introducing the atmosphere into the vacuum chamber 2 and reaching the atmospheric pressure in the vacuum chamber 2, it adheres to the inner wall of the vacuum chamber 2 and the filter portion of the filter collector 12. The carbon material E was recovered.

  About the collect | recovered carbon material E, the shape was observed using the electron microscope. Observation was performed at an acceleration voltage of 5 kV. FIG. 10 shows an SEM photograph (magnification 100000 times) of the carbon material E recovered from the filter part. The carbon material E generated from FIG. 10 was confirmed to be an aggregate of foil-like crystal pieces having a side length of several tens to several hundreds of nanometers and a thickness of several nanometers. However, compared with the carbon material D of FIG. 8 and the carbon material A of FIG. 9, the length of one side of the carbon material E is long, and the size of the crystal is slightly large.

The nitrogen specific surface areas of the foil piece-like crystal pieces of the carbon materials A to C obtained in Examples 1 to 5 were measured, and the results are shown in Table 1. Incidentally, BET specific surface area by _{N 2} gas fast specific surface area measuring device; was measured using a (Asappu 2000 KK Shimadzu).

From the results of Table 1, it was confirmed that the specific surface area of nitrogen was 250 to 350 m ² / g, and the specific surface area was larger than that of ordinary carbon black. Accordingly, it can be said that the carbon material of the present invention is excellent in adhesion and conductivity.

The Raman spectra of the foil piece-like crystal pieces of the carbon materials A, D, and E obtained in Examples 1, 4, and 5 were measured, and the results are shown in FIG. The Raman spectrum was measured using a micro Raman (JRS-SYSTEM2000; JEOL Ltd.) and a He-Ne laser (632.8 nm) as a light source. The Raman spectrum of graphite is extremely sensitive to structural defects like no other compound, and is therefore useful as a method for evaluating carbon materials. (Source: Latest carbon material experimental technology (analysis and analysis), Chapter 11 Structural analysis by Raman spectroscopy, P91)

It is clear from the electron diffraction result of the transmission electron microscope that the carbon material A is 2H graphite. In FIG. 11, the original G band (1,580 cm ⁻¹ ) of graphite and the D band ( 1,330 cm ⁻¹ ) and D ′ band (1,620 cm ⁻¹ ) are observed. Since the carbon materials D and E show the same Raman spectrum as the carbon material A, the carbon materials D and E are also considered to be graphite. However, the carbon materials D and E are presumed to have better crystallinity than the carbon material A because the strengths of the D and D ′ bands due to the structural disorder are weaker than the carbon material A.

<Absorption characteristics of radio wave absorber>
Next, using the carbon materials A, D and E obtained in the above Examples 1, 4 and 5, the application as a radio wave absorber was verified.

First, with respect to the carbon materials A, D, and E obtained in Examples 1, 4, and 5 above, each carbon material was paraffin (melting point mp 70 to 72 at two contents of 2.5 wt% and 5.0 wt%). C., relative dielectric constant ε _r = 2.2), and molded into a hollow double cylindrical shape having an outer diameter of 7 mm, an inner diameter of 3 mm, and a thickness of about 2 mm. About this molded object, S parameter measurement by a coaxial tube method was performed using a network analyzer (Agilent Technologies 8720D) in a frequency band of 1 to 10 GHz. The intensity of the incident high frequency was 100 mW. From the obtained reflection coefficient and transmission coefficient, the complex relative dielectric constant ε _r was calculated by the Baker-Jarvis method (Document 1: Microwave Theory Tech., 38, p1096-1103 (1990)) reported in Document 1. The obtained complex relative permittivity epsilon _r of data, 8 and the relationship between the frequency and the complex relative permittivity epsilon _r at 1~10GHz frequency residence zone at 2.5 wt% and 5.0 wt% of content per It is shown in FIG. Here, FIG. 8 is a diagram showing the relationship between the frequency and the complex relative dielectric constant ε _r at a content rate of 2.5 wt% for each carbon material, and (a) is the real part of the frequency and the complex relative dielectric constant ε _r . (b) shows the relationship between the frequency and the imaginary part ε ″ of the complex relative dielectric constant ε _r . FIG. 9 shows the frequency at the content rate of 5.0 wt% and the complex relative dielectric constant ε _r. is a diagram showing for each carbon material the relationship between, (a) shows the relationship between the real part epsilon 'frequency and the complex relative permittivity ε _r, (b) is the imaginary part of the frequency and the complex relative permittivity epsilon _r epsilon "Is shown.

8 (a), 8 (b), 9 (a), and 9 (b), it was verified that the complex relative dielectric constant ε _r decreases in the order of carbon material E> carbon materials A and D.

The calculation of the reflection loss (the amount of radio wave absorption) is performed using an impedance matching type model in which a metal plate is placed behind the absorber having a thickness d. In an absorber using a filler that does not have magnetism, such as a carbon material, when radio waves are incident on the absorber vertically, the impedance Z of the sample looking into the metal plate from the absorber surface is the wavelength λ of the radio wave, the complex Using the relative dielectric constant ε _r and the characteristic impedance (impedance in free space) Z ₀ , the following expression (1) is used. In this model, the condition that absorption is maximum, that is, reflection is minimum is when the reflection coefficient S shown in the following equation (2) is minimum. Impedance Z as viewed from the incident surface this time is equal to the impedance Z ₀ of the free space. The reflection loss (S [dB]) can be written as in the following formula (3), and since S includes f (λ = c / f) and d, formulas (1) to (3) Can be used to calculate the reflection loss when the thickness d of the specimen is changed.

Therefore, from this complex relative dielectric constant ε _r , impedance Z at the surface of the absorber containing the carbon material at various sample thicknesses d is calculated from the following equation (1). The reflection loss (S [dB]) was obtained from the equation (3). Here, the reflection loss (S [dB]) is expressed in decibels (dB), and shows 90% absorption (-10% reflection) at −10 dB and 99% absorption (1% reflection) at −20 dB. A radio wave absorber can be designed and manufactured using this value as a guide.

  As an example of the absorption amount S [dB], FIG. 10 shows the absorption characteristics of an absorber sample containing 5.0 wt% of the carbon material E and having a thickness of 3.8 mm. As shown in FIG. 10, this sample has an absorption of 40 dB at a frequency of 7.7 GHz and is found to have excellent radio wave absorptivity. Thus, it was verified that if the content of the carbon material of the present invention is appropriately selected and optimized, an absorber having a large absorption amount at 1 to 10 GHz can be obtained.

<Design of electromagnetic wave absorber>
It is reported in Document 2 that the absorber can be designed by modeling and analyzing the volume fraction and frequency dependence of the dielectric constant of the carbon composite material containing the carbon material (Document 2: Transactions). of the Materials Research Society of Japan, 29 [5], p2511-2514 (2004)).

According to Document 2, the design method for the radio wave absorber is as follows. First, the complex relative permittivity ε _r for each weight fraction of the carbon material is calculated as described in the absorption characteristics of the radio wave absorber. performs fitting from the value of the ratio the real part of the dielectric constant epsilon _r epsilon 'and the imaginary part epsilon "using the following equation (4), the weight fraction and frequency of the complex relative permittivity epsilon _r using the fitting parameters determined An approximate curve based on a model formula that models the dependence and an anti-reflection curve for complete absorption using the following formula (5) are obtained, and then the non-reflection curve and the weight fraction / frequency dependence are modeled. It has been reported that the weight fraction causing the complete absorption and the absorber thickness can be calculated from the relationship with the approximated curve.

The conditional expression for complete absorption is the following expression (5). That is, in order to achieve complete absorption, the impedance Z from the surface of the radio wave absorber should be equal to the plane wave (radio wave) characteristic impedance (free space impedance) Z ₀ . it can be determined by the Z = _{Z 0.} In order to express the relationship between the frequency and the thickness, the equation (1) was modified from the wavelength λ = light speed c / frequency f.

Therefore, the inventors verified the design of the radio wave absorber using the carbon materials A, D and E obtained in Examples 1, 4 and 5. That is, as described in the absorption characteristics of the wave absorber, calculates the complex relative permittivity epsilon _r of each weight fraction of the carbon material, the real part epsilon 'and the imaginary part of the complex relative permittivity epsilon _r Fitting from ε ″ using the above equation (4), using the determined fitting parameters, an approximate curve by a model equation that models the weight fraction and frequency dependence of the complex relative permittivity ε _r , and the above From the non-reflecting curve obtained by the equation (5), a radio wave absorber that completely absorbs at a frequency of 5 GHz was designed.

By changing the frequency f and the absorber thickness d, or the wavelength λ and the absorber thickness d, the complex relative permittivity ε _r (ε _r = ε′−jε ″) The solution of the part ε ′ and the imaginary part ε ″ is obtained, the non-reflection curve plotted on the ε′−ε ″ plane is fitted with the above equation (4), and the complex relative permittivity is determined using the determined fitting parameter. A model formula that models the weight fraction / frequency dependence of ε _r , changes the weight fraction and frequency, finds solutions of the real part ε ′ and imaginary part ε ″ of the complex relative permittivity ε _r , and ε ′ The approximate curve plotted on the -ε "plane is drawn on the same ε'-ε" plane for each carbon material, and is shown in FIGS. 11, 12 and 13. And the point which these curves cross | intersect was calculated | required. This intersecting point indicates the absorber thickness and weight fraction for complete absorption.

  Here, FIG. 11 shows an anti-reflection curve when the carbon material A obtained in Example 1 is used and an approximate curve based on a model formula that models the weight fraction dependency at a frequency of 5 GHz. FIG. 12 shows an anti-reflection curve when the carbon material D obtained in Example 4 is used and an approximate curve based on a model formula modeling the weight fraction dependency at a frequency of 5 GHz. These show the approximate reflection curve by the model formula which modeled the non-reflection curve at the time of using the carbon material E obtained in Example 5, and the weight fraction dependence in frequency 5GHz.

  From these results, Table 2 shows the weight fraction and absorber thickness required for the absorber for each carbon material.

  From the above results, it has been clarified that the carbon materials A, D, and E can produce a thin absorber corresponding to a frequency of 5 GHz by appropriately selecting the weight fraction.

  In this way, the thickness of the radio wave absorber and the amount of carbon material added corresponding to the target frequency can be calculated.

It is a figure which shows typically the manufacturing apparatus of the carbon material of this invention. It is a figure which shows the cross section of the plasma torch part of the manufacturing apparatus of the carbon material of this invention. 4 is a transmission electron micrograph (130,000 times) of a carbon material recovered from the filter portion of Example 1. FIG. 2 is a photograph of an electron diffraction image obtained by irradiating a particle group of carbon material collected from the filter portion of Example 1 with an electron beam. 4 is a transmission electron micrograph (130,000 times) of a carbon material recovered from the filter portion of Example 2. FIG. 4 is a transmission electron micrograph (88,000 times) of a carbon material recovered from the filter portion of Example 3. FIG. 6 is a photograph of an electron beam diffraction image obtained by irradiating an electron beam to a particle group of a carbon material collected from a filter portion of Example 3. FIG. It is an electron micrograph (100,000 times) of the carbon material collect | recovered from the filter part of Example 4. FIG. 2 is an electron micrograph (100,000 times) of a carbon material collected from a filter portion of Example 1. FIG. It is an electron micrograph (100,000 times) of the carbon material collect | recovered from the filter part of Example 5. FIG. It is a figure of the Raman spectrum of carbon material A, D, and E collect | recovered from the filter part of Examples 1, 4, and 5. FIG. It is a figure which shows the relationship of the frequency and complex relative dielectric constant (epsilon) _{r in} content rate 2.5 wt% according to each carbon material, (a) is real part (epsilon) ', (b) is an imaginary part (epsilon)''. It is a figure which shows the relationship of the frequency in content rate 5.0 wt%, and complex dielectric constant (epsilon) _{r according} to each carbon material, (a) is real part (epsilon) ', (b) is an imaginary part (epsilon)''. It is a figure which shows the relationship between the frequency and absorption amount of an absorber with a thickness of 3.8 mm containing 5.0 wt% of carbon material E. It is a figure which shows the approximate curve by the model formula which modeled the non-reflection curve at the time of using the carbon material A obtained in Example 1, and the weight fraction dependence in the frequency of 5 GHz. It is a figure which shows the approximate curve by the model formula which modeled the non-reflection curve at the time of using the carbon material D obtained in Example 4, and the weight fraction dependence in frequency 5GHz. It is a figure which shows the approximate curve by the model formula which modeled the non-reflection curve at the time of using the carbon material E obtained in Example 5, and the weight fraction dependence in frequency 5GHz.

Explanation of symbols

1 Plasma torch (plasma generation chamber)
DESCRIPTION OF SYMBOLS 2 Vacuum chamber 3 High frequency generator 4 Reforming gas collection bag 5 Vacuum pump 6 Diaphragm vacuum pump 7 Inert gas introduction pipe 8 Hydrocarbon compound introduction probe 9 RF coil 10 Plasma 11 Filter 12 Filter collector

Claims (7)

A method for producing a crystalline carbon material in which a plasma is generated by an inert gas, a hydrocarbon compound is introduced into the plasma, and plasma thermal decomposition of the hydrocarbon compound is performed,
An inert gas is supplied so that the gas flow rate is 0.602 m / sec or more in a standard state (101325 Pa at 25 ° C.) in a reduced pressure atmosphere of 6 kPa or more and 66.5 kPa or less in the plasma generation chamber. After applying a high frequency of 6 kVA or more, the hydrocarbon compound is introduced at 5 L / min or more, and the hydrocarbon compound is thermally decomposed. A foil piece crystal piece having a crystal thickness (Lc) of 10 nm or less is obtained. The manufacturing method of the carbon material to contain . A method for producing a crystalline carbon material, in which a plasma is generated from a mixed gas of an inert gas and hydrogen, a hydrocarbon compound is introduced into the plasma, and plasma thermal decomposition of the hydrocarbon compound is performed,
In a reduced pressure atmosphere with a pressure in the plasma generation chamber of 6 kPa or more and 66.5 kPa or less, a mixed gas of inert gas and hydrogen is used so that the gas flow rate in the standard state (101325 Pa at 25 ° C.) is 0.602 m / sec or more. A foil having a crystal thickness (Lc) of 10 nm or less, which is supplied and applied with a high frequency of 6 kVA or more of plate power and then introduced with 5 L / min or more of the hydrocarbon compound to thermally decompose the hydrocarbon compound. A method for producing a carbon material containing flaky crystal pieces . A method for producing a crystalline carbon material, in which a plasma is generated from a mixed gas of an inert gas and carbon dioxide, a hydrocarbon compound is introduced into the plasma, and plasma pyrolysis of the hydrocarbon compound is performed. ,
A mixed gas of inert gas and carbon dioxide so that the gas flow rate in a standard state (101325 Pa at 25 ° C.) is 0.602 m / sec or more in a reduced pressure atmosphere of 6 kPa or more and 66.5 kPa or less in the plasma generation chamber. And a plate power of 6 kVA or more is applied, and then the hydrocarbon compound is introduced at 5 L / min or more to thermally decompose the hydrocarbon compound. The crystal thickness (Lc) is 10 nm or less. The manufacturing method of the carbon material containing foil piece-like crystal piece . The method for producing a carbon material according to claim 1, wherein argon gas is used as the inert gas. The method for producing a carbon material according to claim 1, wherein natural gas is used as the hydrocarbon compound. The method for producing a carbon material according to claim 1, wherein methane and / or propane is used as the hydrocarbon compound. The method for producing a carbon material according to claim 1, wherein high-frequency plasma is used as the plasma.