WO2011034129A1 - Process for production of carbide fine particles - Google Patents

Abstract

A process for the production of carbide fine particles, which comprises dispersing a metal oxide powder in a liquid carbonaceous substance to form a slurry, converting the slurry into liquid drops, and feeding the liquid drops into an oxygen-free thermal plasma to form carbide fine particles.

Description

Manufacturing method of carbide fine particles

The present invention relates to a method for producing nano-sized carbide fine particles, and particularly relates to a method for producing nano-sized carbide fine particles using a metal oxide as a raw material.

Currently, fine particles such as oxide fine particles, nitride fine particles, carbide fine particles are electrically insulating materials such as semiconductor substrates, printed circuit boards, various electric insulating parts, high hardness and high precision machine tool materials such as cutting tools, dies and bearings, Production of functional materials such as grain boundary capacitors and humidity sensors, production of sintered bodies such as precision sintered molding materials, production of sprayed parts such as materials that require high-temperature wear resistance such as engine valves, and fuel cell electrodes It is used in fields such as electrolyte materials and various catalysts. By using such fine particles, the bonding strength and denseness of different ceramics or different metals in the sintered body and irradiated parts are improved, and further the functionality is improved.

One method for producing such fine particles is a gas phase method. The vapor phase method includes a chemical method in which various gases are chemically reacted at a high temperature and a physical method in which particles are decomposed and evaporated by irradiation with a beam such as an electron beam or a laser to generate fine particles.

There is a thermal plasma method as one of the above gas phase methods. The thermal plasma method is a method of instantly evaporating raw materials in thermal plasma and then rapidly solidifying them to produce fine particles. Also, it is clean, highly productive, and has a high heat capacity at high temperatures. It has many advantages such as being compatible and being relatively easy to combine compared with other gas phase methods. For this reason, the thermal plasma method is actively used as a method for producing fine particles.

In the conventional method for producing fine particles using the thermal plasma method, the raw material is powdered, and the powdered raw material (powder raw material, powder) is dispersed together with a carrier gas etc. and directly charged into the thermal plasma. By doing so, fine particles are manufactured.

Patent Document 1 discloses a thermal plasma flame in which a slurry in which a fine particle manufacturing material is dispersed in a combustible material or a slurry in which the fine particle manufacturing material is dispersed in a combustible material and a combustible material is formed into droplets. A method for producing fine particles is described in which fine particles are produced by introducing into a gas phase mixture and rapidly cooling the gas phase mixture.

JP 2006-102737 A

However, Patent Document 1 does not specifically disclose a method for producing carbide fine particles. Since carbide has high hardness, it is difficult to pulverize it to produce carbide fine particles. Moreover, since many carbides have a high melting point and exceed 3000K, carbides cannot be used as raw materials when producing carbide fine particles by a vapor phase method.
In the case of producing fine particles such as carbide fine particles using a metal, if a fine metal raw material is used in order to further promote evaporation, there is a possibility of explosion depending on the substance, which is difficult to handle.
Further, studies have been made on using metal alkoxide as a solution raw material. However, since the raw material is expensive and unstable, it is difficult to handle industrially.
Furthermore, a method using a gas such as methane as a carbon source for carbonization and a method using a mixture of carbon particles in a metal as a raw material are shown. It has not been.
As described above, there is no specific manufacturing method for manufacturing carbide fine particles from oxides.

An object of the present invention is to solve the problems based on the above prior art and to provide a production method for producing nano-sized carbide fine particles using a metal oxide as a raw material.

In order to achieve the above object, the present invention provides a method for producing carbide fine particles using a metal oxide, wherein the metal oxide powder is dispersed in a liquid substance containing carbon to form a slurry. The present invention provides a method for producing carbide fine particles, characterized in that the slurry is made into droplets and supplied into a thermal plasma flame not containing oxygen.

In the present invention, examples of the metal oxide include TiO ₂ , ZrO ₂ , V ₂ O ₅ , Nb ₂ O ₅ , SiO _{2, and} WO ₃ .
In the present invention, for example, the liquid substance containing carbon includes alcohol, ketone, kerosene, octane, and gasoline.
Furthermore, in the present invention, the thermal plasma flame is preferably derived from at least one gas of hydrogen, helium and argon.

According to the present invention, nano-sized carbide fine particles can be produced with high productivity using a metal oxide as a raw material.

It is a mimetic diagram showing the whole particulates manufacture device for carrying out the manufacturing method of the carbide particulates concerning the embodiment of the present invention. It is sectional drawing which expands and shows the plasma torch vicinity in FIG. It is sectional drawing which expands and shows the top plate of the chamber in FIG. 1, and the gas injection opening vicinity provided in this top plate. It is sectional drawing which expands and shows the cyclone in FIG. It is explanatory drawing which shows the angle of the gas inject | emitted, (A) is sectional drawing of the perpendicular direction which passes along the central axis of the top plate of a chamber, (B) is the bottom view which looked at the top plate from the downward direction. (A) is a graph which shows the analysis result of the crystal structure by the X-ray diffraction method of the titanium oxide used for the manufacturing method of the carbide fine particle of the Example of this invention, (B) is obtained in the Example of this invention. It is a graph which shows the analysis result of the crystal structure by the X ray diffraction method of the obtained titanium carbide.

Below, based on the preferred embodiment shown in an accompanying drawing, the manufacturing method of the carbide particulate of the present invention is explained in detail.
FIG. 1 is a schematic diagram showing an overall configuration of a fine particle production apparatus for carrying out a method for producing carbide fine particles according to an embodiment of the present invention. FIG. 2 is a partially enlarged view of the vicinity of the plasma torch 12 shown in FIG. 3 is an enlarged cross-sectional view showing the top plate 17 of the chamber 16 shown in FIG. 1 and the vicinity of the gas injection port 28a and the gas injection port 28b provided in the top plate 17. As shown in FIG. FIG. 4 is an enlarged cross-sectional view of the cyclone 19.

A fine particle manufacturing apparatus 10 shown in FIG. 1 includes a plasma torch 12 that generates thermal plasma, a material supply device 14 that supplies a metal oxide powder in a slurry state into the plasma torch 12, as described later, and fine particles ( A chamber 16 having a function as a cooling tank for generating (primary fine particles) 15, a cyclone 19 for removing coarse particles having a particle size larger than a predetermined particle size from the generated primary fine particles 15, and a cyclone And a collection unit 20 that collects carbide fine particles (secondary fine particles) 18 having a desired particle size classified by 19.

In this embodiment, a metal oxide powder (hereinafter also referred to as a metal oxide raw material) is dispersed in a liquid substance containing carbon (hereinafter also referred to as a dispersion medium) to form a slurry, and this slurry is used. Thus, nano-sized carbide particles are manufactured by the particle manufacturing apparatus 10.

The plasma torch 12 shown in FIG. 2 includes a quartz tube 12a and a high-frequency oscillation coil 12b that surrounds the quartz tube 12a. A supply pipe 14f, which will be described later, for supplying metal oxide powder and atomizing gas into the plasma torch 12 is provided at the center of the plasma torch 12, and a plasma gas supply port 12c is provided in the periphery of the supply pipe 14f. It is formed in the part (on the same circumference).

The plasma gas is sent from the plasma gas supply source 22 to the plasma gas supply port 12c (see FIG. 2).
In the present embodiment, plasma gas does not contain oxygen in order to generate carbon by decomposing without burning a liquid substance (dispersion medium) containing carbon in a thermal plasma flame 24 to be described later. Is used. Examples of the plasma gas include hydrogen, helium, and argon. The plasma gas is not limited to a single substance, and these plasma gases may be used in combination, such as hydrogen and argon or helium and argon.

The plasma gas supply source 22 is prepared with, for example, two types of plasma gases, hydrogen and argon. The plasma gas is sent from the plasma gas supply source 22 into the plasma torch 12 as indicated by an arrow P through the ring-shaped plasma gas supply port 12c shown in FIG. Then, a high frequency voltage is applied to the high frequency oscillation coil 12b, and a thermal plasma flame 24 not containing oxygen is generated.

The outside of the quartz tube 12a is surrounded by a concentric tube (not shown), and cooling water is circulated between the tube and the quartz tube 12a to cool the quartz tube 12a. The quartz tube 12a is prevented from becoming too hot by the thermal plasma flame 24 generated in the plasma torch 12.

As shown in FIG. 1, the material supply apparatus 14 is connected to the upper part of the plasma torch 12 through a pipe 26 and a supply pipe 14f, and a slurry 14a prepared by mixing a metal oxide raw material with a dispersion medium is a material supply apparatus. 14 is uniformly supplied into the plasma torch 12.

The material supply device 14 includes a container 14b for containing the slurry 14a, a stirrer 14c for stirring the slurry 14a in the container 14b, and a pump 14d for applying high pressure to the slurry 14a via the supply pipe 14f and supplying the slurry 14a into the plasma torch 12. A spray gas supply source 14e that supplies a spray gas for spraying the slurry 14a into the plasma torch 12, and a supply pipe 14f that droplets the slurry 14a and supplies the slurry 14a into the plasma torch 12.

The spray gas subjected to the extrusion pressure is supplied from the spray gas supply source 14e together with the slurry 14a into the thermal plasma flame 24 in the plasma torch 12 through the supply pipe 14f as shown by an arrow G in FIG. The The supply pipe 14f has a two-fluid nozzle mechanism for spraying the slurry into the thermal plasma flame 24 in the plasma torch to form droplets, whereby the slurry 14a is contained in the thermal plasma flame 24 in the plasma torch 12. Spray on. That is, the slurry 14a can be formed into droplets. As the atomizing gas, for example, argon, helium, hydrogen or the like is used alone or in appropriate combination. Note that the atomizing gas is not necessarily supplied as long as the slurry 14a can be formed into droplets.

As described above, the two-fluid nozzle mechanism can apply high pressure to the slurry and spray the slurry with a spray gas which is a gas, and is used as one method for making the slurry into droplets. For example, when a nozzle having an inner diameter of 1 mm is used, if the supply pressure is 0.2 to 0.3 MPa and the slurry is flowed at 20 ml / min and the atomizing gas is sprayed at 10 to 20 liter / min, about 5 to 10 μm About a droplet is obtained.

In this embodiment, the two-fluid nozzle mechanism is used, but a one-fluid nozzle mechanism may be used. As another method, for example, a slurry is dropped on a rotating disk at a constant speed to form a droplet by centrifugal force (a droplet is formed), and a liquid is applied by applying a high voltage to the slurry surface. A method for forming droplets (generating droplets) is conceivable.

On the other hand, as shown in FIG. 1, the chamber 16 is provided adjacent to the lower side of the plasma torch 12. The dispersion medium in the slurry 14a sprayed into the thermal plasma flame 24 in the plasma torch 12 is reduced in the thermal plasma flame 24 by the carbon generated by being decomposed without burning. Further, the reduced metal material raw material reacts with carbon to become a carbide. Immediately thereafter, the carbide fine particles that have become carbide are rapidly cooled in the chamber 16 to generate primary fine particles (carbide fine particles) 15. Thus, the chamber 16 has a function as a cooling tank.

Also, here, as one of the methods for more efficiently producing carbide fine particles, a gas supply device 28 for rapidly cooling the generated carbide fine particles is provided. Hereinafter, the gas supply device 28 will be described.

The gas supply device 28 shown in FIGS. 1 and 3 has a predetermined direction toward the tail of the thermal plasma flame 24 (the end of the thermal plasma flame opposite to the plasma gas supply port 12c, that is, the end of the thermal plasma flame). A gas injection port 28a for injecting gas at an angle, a gas injection port 28b for injecting gas from the upper side to the lower side along the side wall of the chamber 16, and a compressor 28c for applying an extrusion pressure to the gas supplied into the chamber 16 The gas supply source 28d to be supplied into the chamber 16 and a pipe 28e for connecting them. The compressor 28c may be a blower.

As will be described in detail later, the gas ejected from the gas ejection port 28a has a cyclone 19 together with the gas ejected from the gas ejection port 28b, in addition to the action of rapidly cooling the primary fine particles 15 generated in the chamber 16. It has an additional action such as contributing to the classification of the primary fine particles 15.
The above-described compressor 28c and gas supply source 28d are connected to the top plate 17 of the chamber 16 through a pipe 28e.

Here, the gas injection port 28 b is a slit formed in the outer side top plate component 17 b of the gas supply device 28, and prevents the generated primary fine particles 15 from adhering to the inner wall portion of the chamber 16. It is preferable that an amount of gas can be injected so as to provide a flow rate at which the primary fine particles 15 can be classified by the downstream cyclone 19 at an arbitrary classification point. From the gas injection port 28b, gas is injected from the upper side to the lower side along the inner wall of the chamber 16.

Supplyed from the gas supply source 28d (see FIGS. 1 and 3) into the top plate 17 (specifically, the outer side top plate component 17b and the upper outer side top plate component 17c) through the pipe 28e as indicated by the arrow S. The gas thus discharged is ejected from the gas ejection port 28b (also from the gas ejection port 28a, as will be described later) through the air passage provided here.

The slurry injected into the plasma torch 12 from the material supply device 14 (droplet-formed) is reduced and carbonized in the thermal plasma flame 24 without being burned, as will be described later. It becomes carbide. The carbide is rapidly cooled in the chamber 16 by the gas injected from the gas injection port 28a (see arrow Q), and primary fine particles 15 made of carbide are generated. At this time, the primary fine particles 15 are prevented from adhering to the inner wall of the chamber 16 by the gas ejected from the gas ejection port 28 b (see arrow R).

As shown in FIG. 1, a cyclone 19 for classifying the generated primary fine particles 15 with a desired particle diameter is provided at the lower side portion of the chamber 16. As shown in FIG. 4, the cyclone 19 includes an inlet pipe 19 a that supplies the primary fine particles 15 from the chamber 16, a cylindrical outer cylinder 19 b that is connected to the inlet pipe 19 a and is positioned on the upper part of the cyclone 19, A truncated cone part 19c which is continuous from the lower part of the outer cylinder 19b to the lower side and gradually decreases in diameter, and a coarse particle which is connected to the lower side of the truncated cone part 19c and has a particle diameter equal to or larger than the desired particle diameter. The coarse particle recovery chamber 19d for recovering the gas and the inner tube 19e connected to the recovery unit 20 described in detail later and projecting from the outer cylinder 19b are provided.

From the inlet pipe 19a, an air flow containing the primary fine particles 15 generated in the chamber 16 is blown along the inner peripheral wall of the outer cylinder 19b, whereby this air flow is externally shown by an arrow T in FIG. By flowing from the inner peripheral wall of the cylinder 19b toward the truncated cone portion 19c, a swirling downward flow is formed.

Then, the above-described swirling downward flow is further accelerated by the inner peripheral wall of the truncated cone part 19c, and then reverses to become an upward flow and is discharged out of the system from the inner pipe 19e. A part of the airflow is reversed at the truncated cone part 19c before flowing into the coarse particle recovery chamber 19d, and is discharged out of the system from the inner pipe 19e. Centrifugal force is given to the particles by the swirling flow, and the coarse particles move in the wall direction due to the balance between the centrifugal force and the drag force. Further, the carbide fine particles separated from the airflow descend along the side surface of the truncated cone part 19c and are collected in the coarse particle collection chamber 19d. Here, the fine particles to which the centrifugal force is not sufficiently applied are discharged out of the system together with the reverse airflow at the inner peripheral wall of the truncated cone part 19c.

Further, a negative pressure (suction force) is generated from the collection unit 20 described in detail later through the inner tube 19e. Then, by this negative pressure (suction force), the carbide fine particles separated from the above-described swirling airflow are sucked as shown by an arrow U in FIG. 4 and sent to the recovery unit 20 through the inner tube 19e. ing.

As shown in FIG. 1, a recovery unit 20 for recovering secondary fine particles (carbide fine particles) 18 having a desired nano-sized particle diameter is provided on the extension of the inner tube 19e which is an outlet of the air flow in the cyclone 19. It has been. The recovery unit 20 includes a recovery chamber 20a, a filter 20b provided in the recovery chamber 20a, and a vacuum pump (not shown) connected via a pipe provided below the recovery chamber 20a. Yes. The fine particles sent from the cyclone 19 are drawn into the collection chamber 20a by being sucked by a vacuum pump (not shown), and are collected on the surface of the filter 20b.

Hereinafter, while describing the operation of the fine particle production apparatus 10 configured as described above, the fine particle production apparatus 10 is used to manufacture the carbide fine particles according to the embodiment of the present invention, and the carbide generated by the production method. The fine particles will be described.

Here, in this embodiment, the metal oxide raw material (metal oxide powder) is a raw material for the carbide fine particles. Examples of the metal oxide raw material (metal oxide powder) include titanium oxide (TiO ₂ ), zirconium oxide (ZrO ₂ ), vanadium oxide (V ₂ O ₅ ), niobium oxide (Nb ₂ O ₅ ), and oxidation. Examples include silicon (SiO ₂ ) and tungsten oxide (WO ₃ ).
In the present embodiment, the metal oxide is an oxide of a metal element constituting the carbide fine particles to be generated.
The metal oxide raw material has an average particle size of 50 μm or less, and preferably an average particle size of 10 μm or less so that it can be easily evaporated in a thermal plasma flame.

In the present embodiment, examples of the liquid substance (dispersion medium) containing carbon include alcohol, ketone, kerosene, octane, and gasoline.
Examples of the alcohol include ethanol, methanol, propanol, and isopropyl alcohol.
As described above, the liquid substance (dispersion medium) containing carbon acts as a carbon source for reducing the metal oxide raw material (metal oxide powder) and then supplying carbon for making a carbide. Is. For this reason, it is preferable that the liquid substance containing carbon is easily decomposed by the thermal plasma flame 24. Therefore, the liquid substance containing carbon is preferably a lower alcohol.

In the method for producing carbide fine particles of the present embodiment, first, a metal oxide raw material is dispersed in a dispersion medium to obtain a slurry. At this time, the mixing ratio of the metal oxide raw material and the dispersion medium in the slurry is, for example, 6: 4 (60%: 40%). Since the dispersion medium acts as a carbon source for reducing and carbonizing the metal oxide, the mass ratio of the metal oxide raw material and the dispersion medium is appropriately changed so that excess carbon is generated. Thus, a slurry is prepared.

Furthermore, when adjusting the slurry 14a, one or a mixture of two or more selected from the group consisting of a surfactant, a polymer, and a coupling agent may be added. As the surfactant, for example, sorbitan fatty acid ester which is a nonionic surfactant is used. For example, ammonium polyacrylate is used as the polymer. As the coupling agent, for example, a silane coupling agent or the like is used. By adding one or a mixture of two or more selected from the group consisting of a surfactant, a polymer, and a coupling agent to the slurry 14a, the metal oxide raw material is more effectively prevented from aggregating with the dispersion medium. Thus, the slurry 14a can be stabilized.

The slurry 14a prepared as described above is placed in the container 14b of the material supply apparatus 14 shown in FIG. 1 and stirred by the stirrer 14c. Thereby, it is prevented that the metal oxide raw material in a dispersion medium precipitates, and the slurry 14a in which the metal oxide raw material is dispersed in the dispersion medium is maintained. Alternatively, the slurry 14a may be continuously prepared by supplying the metal oxide raw material and the dispersion medium to the material supply device 14.

Next, the slurry 14 a is formed into droplets using the above-described two-fluid nozzle mechanism, and the slurry 14 a formed into droplets is supplied into the plasma torch 12, thereby generating heat generated in the plasma torch 12. Carbon is generated without being supplied to the plasma flame 24 and burning the dispersion medium.

The oxygen-free thermal plasma flame 24 evaporates the slurry 14a in droplets, decomposes and evaporates without burning the dispersion medium, and generates carbon. Furthermore, the thermal plasma flame 24 reduces the metal oxide raw material with the temperature and generated carbon, and then reacts with excess carbon to form a carbide. For this reason, the temperature of the thermal plasma flame 24 needs to be higher than the temperature at which the metal oxide raw material (metal oxide) contained in the slurry is reduced by carbon and carbonized.
On the other hand, the higher the temperature of the thermal plasma flame 24 is, the easier the metal oxide raw material (metal oxide) is reduced and carbonized, but the temperature is not particularly limited, and the metal oxide raw material (metal oxide) Depending on the temperature at which is reduced, it may be appropriately selected. For example, the temperature of the thermal plasma flame 24 can be set to 6000 ° C., and it is theoretically considered to reach about 10000 ° C.

Further, the pressure atmosphere in the plasma torch 12 is preferably atmospheric pressure or lower. Here, the atmosphere at atmospheric pressure or lower is not particularly limited, but may be, for example, 5 Torr to 750 Torr.

Next, the slurry 14a evaporates in the thermal plasma flame 24 not containing oxygen, and further decomposed without burning a dispersion medium such as methanol to obtain carbon. The amount of the dispersion medium in the chiller 14a is adjusted so that a larger amount of this carbon is produced than the metal oxide raw material. The generated carbon reacts with the metal oxide raw material, and the metal oxide is reduced to metal. Thereafter, excess carbon and the reduced metal react to produce carbide. The generated carbide is rapidly cooled by the gas injected in the direction indicated by the arrow Q through the gas injection port 28a and is rapidly cooled in the chamber 16, whereby the primary fine particles 15 made of carbide are obtained.

Accordingly, the amount of gas injected from the gas injection port 28a needs to be a supply amount sufficient to quench the carbide after the metal oxide is converted into carbide in the process of generating the primary fine particles 15. However, together with the amount of gas injected from the gas injection port 28b and further, the amount of gas supplied into the thermal plasma flame described later, the primary fine particles 15 are arbitrarily classified by the downstream cyclone 19. It is preferable that the flow rate is such that a flow rate that can be classified by the method is obtained and the stability of the thermal plasma flame is not disturbed.

Note that the combined amount of the gas injected from the gas injection port 28a and the amount of the gas injected from the gas injection port 28b is 200% to 5000% of the gas supplied into the thermal plasma flame. It is good to do. Here, the gas supplied into the above-described thermal plasma flame is a combination of a plasma gas that forms a thermal plasma flame, a gas that forms a plasma flow, and a spray gas.

Further, the supply method and supply position of the injected gas are not particularly limited as long as the stability of the thermal plasma flame is not hindered. In the fine particle manufacturing apparatus 10 of the present embodiment, a gas is injected by forming a circumferential slit in the top plate 17, but a method that can reliably supply gas on the path from the thermal plasma flame to the cyclone. Other methods and other positions may be used as long as they are positions.

Finally, the primary fine particles 15 made of carbides generated in the chamber 16 are blown from the inlet pipe 19a of the cyclone 19 along the inner peripheral wall of the outer cylinder 19b together with the air current. By flowing along the inner peripheral wall of the outer cylinder 19b as shown by the arrow T, the swirl flow is formed to descend. Then, this swirling flow is further accelerated at the inner peripheral wall of the truncated cone part 19c, then reverses, becomes an upward flow, and is discharged out of the system from the inner pipe 19e. A part of the airflow is reversed at the inner peripheral wall of the truncated cone part 19c before flowing into the coarse particle recovery chamber 19d, and is discharged out of the system from the inner pipe 19e.

Centrifugal force is applied to the primary fine particles 15 made of carbide by a swirling flow, and coarse particles of the primary fine particles 15 move in the wall direction due to the balance between centrifugal force and drag. In addition, among the primary fine particles 15, particles separated from the air flow descend along the side surface of the truncated cone part 19c and are collected in the coarse particle collection chamber 19d. Here, the fine particles to which the centrifugal force is not sufficiently applied are discharged out of the system as carbide fine particles (secondary fine particles) 18 from the inner tube 19e together with the reverse airflow at the inner peripheral wall of the truncated cone part 19c. The flow velocity of the airflow into the cyclone 19 at this time is preferably 10 m / sec or more.

The discharged carbide fine particles (secondary fine particles) 18 are sucked as indicated by an arrow U in FIG. 4 due to the negative pressure (suction force) from the collecting unit 20, and sent to the collecting unit 20 through the inner tube 19e. It is recovered by the filter 20b of the recovery unit 20. At this time, the internal pressure in the cyclone 19 is preferably not more than atmospheric pressure. In addition, the particle size of the carbide fine particles (secondary fine particles) 18 is defined as an arbitrary particle size at the nano-size level according to the purpose.
Thus, in this embodiment, nanosized carbide fine particles can be obtained.

In the method for producing carbide fine particles of the present invention, the number of cyclones used is not limited to one, and may be two or more.

The carbide fine particles produced by the method for producing carbide fine particles of the present embodiment have a narrow particle size distribution width, that is, a uniform particle size, and there is almost no mixing of coarse particles of 1 μm or more. Specifically, Nanosized carbide fine particles having an average particle diameter of 1 to 100 nm.
In the method for producing carbide fine particles of the present embodiment, as the carbide fine particles, for example, titanium carbide (TiC), zirconium carbide (ZrC), vanadium carbide (VC _1-x ), niobium carbide (NbC), tantalum carbide (TaC), Fine particles of silicon carbide (SiC) or tungsten carbide (WC _1-x ) can be obtained.

Carbide fine particles obtained by the method for producing carbide fine particles of the present embodiment include, for example, electrical insulation materials such as semiconductor substrates, printed boards, various electrical insulation components, cutting tools, dies, and high-hardness and high-precision machine tools. , Production of functional materials such as grain boundary capacitors and humidity sensors, production of sintered bodies such as precision sintered molding materials, production of thermal spray parts such as materials that require high-temperature wear resistance such as engine valves, and fuel cell It can be used for electrodes, electrolyte materials and various catalysts.

In this embodiment, since the particle size of the carbide fine particles can be made nano-sized, for example, when used for a sintered body, the sinterability can be improved and a high-strength sintered body can be obtained. Thus, for example, a tool with good cutting properties can be obtained. Moreover, when using for a catalyst, since a particle size can be made small, the performance of a catalyst can be improved.

Moreover, in this embodiment, since a liquid is used for the carbon source used for reduction and carbonization of the metal oxide raw material, the metal oxide raw material can be easily and uniformly supplied to the thermal plasma flame. Furthermore, since the carbon source is a liquid, it can be easily decomposed and reacted with carbon with respect to the metal oxide and the reduced metal more efficiently than a solid carbon source such as graphite. Thereby, the reaction efficiency to the carbide of a metal oxide raw material becomes high, and a carbide can be manufactured with high productivity.
In the present embodiment, the metal oxide material, for example, in the case of using TiO _2, it is possible to lower the production cost can be suppressed raw material cost.

Further, in the method for producing carbide fine particles of the present embodiment, the fine particles can be classified by a cyclone provided in the apparatus by supplying a gas and arbitrarily controlling the flow rate in the apparatus. In the method for producing carbide fine particles of the present embodiment, the coarse particles can be separated at an arbitrary classification point by changing the gas flow rate or the cyclone inner diameter without changing the reaction conditions. It becomes possible to produce high-quality fine particles with high quality and high productivity.

Furthermore, in the manufacturing method of the carbide fine particles of the present embodiment, since the swirl flow is generated in the cyclone, the residence time becomes long, and the fine particles are cooled in the cyclone. There is no need to provide it. Therefore, it is not necessary to stop the operation of the apparatus for removing the fine particles accumulated in the fins, and the operation time of the apparatus can be extended. Furthermore, the cooling effect can be further enhanced by employing a water-cooled jacket structure for the entire cyclone.

As described above, the fine particle production apparatus 10 of the present embodiment is characterized by including the gas supply device 28 whose main purpose is to rapidly cool the gas phase mixture. Hereinafter, the gas supply device 28 will be additionally described.

The gas supply device 28 shown in FIG. 1 and FIG. 3 has a gas injection port 28 a for injecting gas at a predetermined angle as described above toward the tail of the thermal plasma flame 24, and the upper side along the side wall of the chamber 16. The gas injection port 28b that injects the gas downward, the compressor 28c that applies an extrusion pressure to the gas supplied into the chamber 16, and the gas supply source 28d that is supplied into the chamber 16 are connected to each other. And a tube 28e.
The compressor 28c and the gas supply source 28d are connected to the top plate 17 of the chamber 16 through a pipe 28e. Here, the tail part of the thermal plasma flame is the end of the thermal plasma flame opposite to the plasma gas supply port 12c, that is, the terminal part of the thermal plasma flame.

As shown in FIG. 3, the gas injection port 28 a and the gas injection port 28 b are formed on the top plate 17 of the chamber 16. Here, the top plate 17 includes an inner top plate component 17a having a truncated cone shape and a part of the upper side being a cylinder, an outer top plate component 17b having a truncated cone-shaped hole, and an inner top plate component 17a. And an upper outer part top plate component 17c having a moving mechanism for moving it vertically.

Here, a screw is cut at a portion where the inner side top plate component 17a and the upper outer side top plate component 17c are in contact (in the inner side top plate component 17a, the upper cylindrical portion), and the inner top plate component 17a is By rotating, the position can be changed in the vertical direction, and the inner top plate component 17a can adjust the distance from the outer top plate component 17b. In addition, the gradient of the truncated cone part of the inner top plate part 17a and the gradient of the truncated cone part of the hole of the outer part top plate part 17b are the same, and are structured to engage with each other.

Further, the gas injection port 28a is formed in a circumferential shape that can adjust a gap formed by the inner top plate component 17a and the outer top plate component 17b, that is, a slit width, and is concentric with the top plate. Is a slit. Here, the gas injection port 28a may be any shape that can inject gas toward the tail of the thermal plasma flame 24, and is not limited to the slit shape as described above. A large number of holes may be provided.

Also, an air passage 17d through which the gas sent through the pipe 28e passes is provided inside the upper outer top plate component 17c. The gas passes through the air passage 17d and is sent to the gas injection port 28a which is a slit formed by the inner top plate component 17a and the outer top plate component 17b described above. As described above, the gas sent to the gas injection port 28a is directed in the direction indicated by the arrow Q in FIGS. 1 and 3 toward the tail portion (terminal portion) of the thermal plasma flame. It is injected at an angle of.

Here, the predetermined supply amount will be described. As described above (see paragraph 0048), the amount produced to quench the gas phase mixture is, for example, supplied into a chamber that forms a space necessary for quenching the gas phase mixture. The average flow velocity (in-chamber flow velocity) of the gas in the chamber 16 is preferably 0.001 to 60 m / sec, and more preferably 0.5 to 10 m / sec. This is a gas supply amount sufficient to rapidly cool the gas phase mixture sprayed and evaporated in the thermal plasma flame 24 to generate fine particles, and to prevent aggregation due to collision between the generated fine particles.

Note that this supply amount is sufficient to rapidly cool and solidify the gas phase mixture, and to prevent agglomeration due to collision between the microparticles immediately after solidification and formation. The amount needs to be sufficient to dilute the mixture, and the value may be appropriately determined according to the shape and size of the chamber 16.
However, this supply amount is preferably controlled so as not to hinder the stability of the thermal plasma flame.

Next, with reference to FIGS. 5A and 5B, the predetermined angle in the case where the gas injection port 28a has a slit shape will be described. FIG. 5A is a vertical sectional view passing through the central axis of the top plate 17 of the chamber 16, and FIG. 5B is a view of the top plate 17 as viewed from below. Note that FIG. 5B shows a direction perpendicular to the cross section shown in FIG. Here, a point X shown in FIGS. 5A and 5B indicates that the gas sent from the gas supply source 28d (see FIG. 1) via the air passage 17d is introduced into the chamber 16 from the gas injection port 28a. It is an injection point to be injected. Actually, since the gas injection port 28a is a circumferential slit, the gas at the time of injection forms a belt-like airflow. Therefore, the point X is a virtual emission point.

As shown in FIG. 5A, the center of the opening of the air passage 17d is the origin, the vertical upward is 0 °, the positive direction is counterclockwise on the page, and the gas injection port is in the direction indicated by the arrow Q. The angle of the gas injected from 28a is represented by angle α. This angle α is an angle with respect to the direction from the first part of the thermal plasma flame to the tail part (terminal part) described above.

Further, as shown in FIG. 5B, the thermal plasma flame with the virtual injection point X as the origin, the direction toward the center of the thermal plasma flame 24 as 0 °, and the counterclockwise direction on the paper as the positive direction. The angle of the gas ejected from the gas ejection port 28a in the direction indicated by the arrow Q in the plane direction perpendicular to the direction from the initial part 24 to the tail part (terminal part) is represented by an angle β. This angle β is an angle with respect to the central portion of the thermal plasma flame in the plane perpendicular to the direction from the initial portion to the tail portion (terminal portion) of the thermal plasma flame described above.

Using the angle α (usually the vertical angle) and the angle β (usually the horizontal angle) described above, the predetermined angle, that is, the supply direction of the gas into the chamber, , The angle α is 90 ° <α <240 ° (preferably in the range of 100 ° <α <180 °, more preferably α = 135 °) with respect to the tail (end portion) of the thermal plasma flame 24, and the angle β. Is −90 ° <β <90 ° (preferably in the range of −45 ° <β <45 °, more preferably β = 0 °).

As described above, the gas phase mixture is rapidly cooled by the gas injected toward the thermal plasma flame 24 at a predetermined supply amount and a predetermined angle, and primary particles 15 are generated. The gas injected into the chamber 16 at the predetermined angle described above does not necessarily reach the tail of the thermal plasma flame 24 at the injected angle due to the influence of turbulent flow generated inside the chamber 16. In order to effectively cool the mixture in the phase state, stabilize the thermal plasma flame 24, and operate the fine particle production apparatus 10 efficiently, it is preferable to determine the angle. The angle may be determined experimentally in consideration of conditions such as the size of the apparatus and the size of the thermal plasma flame.

When the fine particles immediately after generation collide with each other and form aggregates, non-uniform particle size causes deterioration in quality. On the other hand, in the method for producing carbide fine particles of the present invention, the fine particles are injected in the direction indicated by the arrow Q toward the tail (end portion) of the thermal plasma flame through the gas injection port 28a at a predetermined angle and supply amount. The diluted gas dilutes the primary fine particles 15 to prevent the fine particles from colliding and aggregating. That is, the gas injected from the gas injection port 28a rapidly cools the gas-phase mixture, and further prevents the generated fine particles from agglomerating, thereby reducing the particle diameter and making the particle diameter uniform. Acts on both sides.

Incidentally, the gas injected from the gas injection port 28 a has a considerable adverse effect on the stability of the thermal plasma flame 24. However, in order to continuously operate the entire apparatus, it is necessary to stabilize the thermal plasma flame. For this reason, the gas injection port 28a in the fine particle manufacturing apparatus 10 of the present embodiment is a circumferentially formed slit, and the amount of gas supply can be adjusted by adjusting the slit width. Since a uniform gas can be injected in the central direction, it can be said that it has a preferable shape for stabilizing the thermal plasma flame. This adjustment can also be performed by changing the supply amount of the injected gas.

As mentioned above, although the manufacturing method of the carbide | carbonized_material fine particle of this invention was demonstrated in detail, this invention is not limited to the said embodiment, In the range which does not deviate from the main point of this invention, it is possible to perform various improvement or a change. Of course.

Examples of the method for producing carbide fine particles of the present invention will be specifically described below.
In the present example and the comparative example, the types of plasma gas constituting the thermal plasma flame of the fine particle production apparatus 10 are shown in the columns of Examples 1 to 6 and Comparative Examples 1 to 6 shown in Table 1 below. Thus, production of titanium carbide was attempted.

In this example, a slurry having a slurry concentration of 50% by mass obtained by mixing and stirring the titanium oxide powder and methanol at a mass ratio of 1: 1 using titanium oxide powder as a raw material was used. Note that titanium oxide used as a raw material has an average particle diameter of 5 μm and a crystal structure shown in FIG.

Here, a high frequency voltage of about 4 MHz and about 80 kVA is applied to the high frequency oscillation coil 12b of the plasma torch 12, and the plasma gas shown in the following Table 1 is supplied from the plasma gas supply source 22 for each embodiment. Then, a thermal plasma flame was generated in the plasma torch 12. In addition, argon gas was supplied at 10 liters / min from the spray gas supply source 14e of the material supply apparatus 14 as the spray gas.

In this example, the titanium oxide slurry was supplied into the thermal plasma flame 24 in the plasma torch 12 together with the argon gas that is the atomizing gas.
Further, argon gas or a mixed gas of argon and helium was used as the gas supplied into the chamber 16 by the gas supply device 28. The flow rate in the chamber at this time was 5 m / sec, and the supply amount was 1 m ³ / min.
The pressure in the cyclone 19 was 50 kPa, and the supply speed of fine particles from the chamber 16 to the cyclone 19 was 10 m / sec (average value).

The ratio of hydrogen gas, helium gas, and argon gas in the plasma gas of the thermal plasma flame was such that the amount of hydrogen gas was 0 to 20 vol% with respect to the total amount of helium gas and argon gas.
In addition, when the plasma gas is two types of hydrogen gas and helium gas, the amount of hydrogen gas is 0 to 20 vol% with respect to the total amount of helium gas, and in the case of two types of hydrogen gas and argon gas, the total amount of argon gas is On the other hand, the amount of hydrogen gas was set to 0 to 20 vol%.
Note that the plasma gas supply rate was 10 to 300 liters / min for argon gas and 5 to 30 liters / min for helium gas.

Further, in the comparative example, using the same titanium oxide powder as in the example, this raw material alone or a mixture of this raw material, a reducing agent, and a graphite powder that also serves as a carbon source is used as a raw material, and the powder remains as thermal plasma. Supplied to the flame.
In the comparative example, the manufacturing conditions were the same as those in the above example except that the supply form into the thermal plasma flame 24 did not use slurry.

Next, in Examples 1 to 6 and Comparative Examples 1 to 6 shown in Table 1 below, the crystal structures of the obtained products were examined using X-ray diffraction (XRD).
In the column of carbides in Table 1 below, “○” indicates only the peak indicating the composition of titanium carbide, and peak indicating the composition of the titanium oxide derived from the raw material, although a peak indicating a part of the titanium carbide composition appears. Also, “Δ” is shown, and “x” is the one showing only the peak indicating the composition of titanium oxide.

In each of Examples 1 to 6, as shown in FIG. 6B, only titanium carbide was obtained, and the particle diameter was about 25 nm.
On the other hand, in Comparative Examples 1 to 6, compositions having compositions other than titanium carbide were also produced. Compositions other than this titanium carbide were titanium oxide that could not be carbonized and graphite derived from the raw material. Moreover, in Comparative Examples 1 to 6, the yield of titanium carbide was lower than that in Example 1.

DESCRIPTION OF SYMBOLS 10 Fine particle manufacturing apparatus 12 Plasma torch 12a Quartz tube 12b High frequency oscillation coil 12c Plasma gas supply port 14 Material supply apparatus 14a Slurry 14b Container 14c Stirrer 14d Pump 14e Spray gas supply source 14f Supply pipe 15 Primary particle 16 Chamber 17 Top plate 17a Inside Part top plate component 17b Outer part top plate part 17c Upper outer part top plate part 17d Ventilation path 18 Fine particles (secondary fine particles)
19 Cyclone 19a Inlet tube 19b Outer tube 19c Frustum 19d Coarse particle recovery chamber 19e Inner tube 20 Recovery unit 20a Recovery chamber 20b Filter 20c Tube 22 Plasma gas supply source 24 Thermal plasma flame 26 Tube 28 Gas supply device 28a Gas injection port 28b Gas injection port 28c Compressor 28d Gas supply source 28e Pipe

Claims (4)

1. A manufacturing method for manufacturing carbide fine particles using a metal oxide,
   The metal oxide powder is dispersed in a liquid substance containing carbon to form a slurry,
   A method for producing carbide fine particles, wherein the slurry is made into droplets and supplied into a thermal plasma flame not containing oxygen.
2. _{2. The} method for producing carbide fine particles according to claim 1, wherein the metal oxide is TiO ₂ , ZrO ₂ , V ₂ O ₅ , Nb ₂ O ₅ , SiO ₂ or WO ₃ .
3. 3. The method for producing carbide fine particles according to claim 1, wherein the liquid substance containing carbon is alcohol, ketone, kerosene, octane or gasoline.
4. The method for producing carbide fine particles according to any one of claims 1 to 3, wherein the thermal plasma flame is derived from at least one gas of hydrogen, helium and argon.

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