JP4963586B2 - Method for producing ultrafine particles - Google Patents

Description

  The present invention relates to a method for producing ultrafine particles coated with a thin film, and more specifically, a method for producing ultrafine particles in which a thin film comprising a carbon simple substance and / or a carbon compound is formed on the surface of ultrafine particles using a thermal plasma method. About.

  Fine particles such as oxide fine particles, nitride fine particles, and carbide fine particles are used for electrical insulation materials such as semiconductor substrates, printed circuit boards, and various electrical insulation components, high-hardness and high-precision machine tool materials such as dies and bearings, and grain boundary capacitors. , Production of sintered materials such as functional materials such as humidity sensors, precision sintered molding materials, thermal spray parts such as materials that require high-temperature wear resistance such as engine valves, and fuel cell electrodes And electrolyte materials and various catalysts. By using such fine particles, the bonding strength, denseness, or functionality of dissimilar ceramics or dissimilar metals in a sintered body or a sprayed part 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 and the like 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 or a laser to form fine particles.

  One of the gas phase methods is a thermal plasma method. 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.

  Patent Document 1 relates to a conventional technique for introducing a powdered raw material into a thermal plasma flame, compositing both powder materials of a metal fine particle and a coating layer, and making the raw material mixture a thermal plasma in an inert or reducing atmosphere. There is disclosed a method for producing oxide metal-coated fine particles by supplying into a (thermal plasma flame) to evaporate raw materials to form a gas phase mixture and then rapidly cooling the mixture.

By the way, in recent years, the various fine particles as described above are required to have a smaller size regardless of the material.
This is due to the fact that the object itself in which the fine particles are used is reduced in size, but the problem here is that the surface activity increases as the size of the fine particles decreases, and this high surface activity is Conversely, the stability of the fine particles is reduced.

  For example, when a metal such as iron or copper is atomized, if the particle size is on the order of several μm, it is well known that an oxide film is formed on the surface by gradual oxidation. On the order of tens of nanometers (hereinafter referred to as ultrafine particles to distinguish them from fine particles based on conventional sensation), oxidation is abrupt and even dangerous.

  In addition, when a low melting point metal such as gold or silver is made into fine particles, it is known that the melting point is drastically lowered when it is on the order of several nanometers. However, it becomes impossible to obtain independent ultrafine particles.

Therefore, it has become necessary to establish a method for producing such ultrafine particles stably and efficiently.
For this, for example, the technique described in Patent Document 2 is helpful.

  The technique described in Patent Document 2 is such that a uniform thickness (several atomic layer to several tens atomic layer) is formed on the surface of the ultrafine powder (which becomes a core) by vacuum deposition in the presence of a reactive gas. The ultra-thin layer) carbon atom layer is formed.

JP 2000-219901 A Japanese Patent Publication No. 5-43791

  The manufacturing method of “ultrafine powder coated with an ultra-thin carbon film” described in Patent Document 2 described above supplies a preliminarily formed ultrafine powder having a particle size of several tens of nanometers to a vapor deposition atmosphere. Atomic carbon (carbon atoms) generated by the decomposition of the reactive gas present in the atmosphere is uniformly attached to the surface of the ultrafine powder.

  As described above, the surface activity increases as the size of the microparticles decreases, and this high surface activity reduces the stability of the microparticles on the contrary, thereby forming ultrafine particles having a particle size of several nanometers, It is desired to efficiently produce various functional materials, precision sintered molding materials, etc. through an integrated manufacturing process such as coating the surface of the formed ultrafine particles with a thin film. It was not possible to produce ultrafine particles having a surface coated with a thin film by such an integrated production process.

  The present invention has been made in view of the above circumstances, and its object is to eliminate the problems based on the conventional technique, and to vapor phase the surface of ultrafine particles expected to have high surface activity and new functionality. An object of the present invention is to provide a method for producing ultrafine particles having a surface coated with a thin film by an integrated production process capable of efficiently forming a thin film and achieving high uniformity in particle size and shape.

  More specifically, an object of the present invention is to provide a method for producing ultrafine particles coated with a thin film composed of a carbon simple substance and / or a carbon compound.

  In view of the need to establish a method for stably and efficiently producing ultrafine particles that are expected to have such a high surface activity and new functionality, the present inventors have described above. As a result of intensive research to achieve the purpose, a reactive gas and a cooling gas are introduced into the end of the thermal plasma flame, which makes the ultrafine particle production material a gas-phase mixture, and is introduced to the surface. The inventors have found that it is possible to produce ultrafine particles coated with a thin film of a reactive gas component, and the present invention has been achieved.

That is, in the method for producing ultrafine particles coated with a thin film according to the present invention, a material for producing ultrafine particles is introduced and dispersed in a thermal plasma flame using an inert gas as a carrier gas under reduced pressure. The mixed gas of the hydrocarbon gas and the cooling gas excluding the hydrocarbon gas is supplied in a vertical direction parallel to the thermal plasma flame with a supply amount sufficient to rapidly cool the gaseous mixture. And an angle with respect to the center of the thermal plasma flame satisfies −90 ° and less than 90 ° in a plane perpendicular to the vertical direction of the thermal plasma flame. Thus, it introduce | transduces toward the termination | terminus part (tail part) of the said thermal plasma flame, a superfine particle is produced | generated, this produced | generated ultrafine particle and the said hydrocarbon gas are made to contact, and the thin film which consists of a hydrocarbon compound on the surface Coated with ultrafine particles And characterized in that the elephants.

  In the method for producing ultrafine particles coated with a thin film according to the present invention, the supply amount of the cooling gas sufficient to quench the gas phase mixture is as follows. That is, a space formed for quenching the gas phase mixture is called a cooling chamber (chamber), and an average flow velocity (in-chamber flow velocity) of gas introduced into the cooling chamber is set to 0.001 to 0.001. 60 m / sec is preferable, and 0.01 to 10 m / sec is more preferable.

  Further, as the direction of introducing the gas into the cooling chamber, the angle α when the vertical upper side is 0 ° with respect to the tail (end portion) of the thermal plasma flame in the cooling chamber is 90 ° <α <. In the range of 240 ° (more preferably 100 ° <α <180 °), the angle β when the direction of the thermal plasma flame viewed from the gas outlet is 0 ° is −90 ° <β <90 ° (more preferably A range of −45 ° <β <45 °) is preferable.

  According to the present invention, it is possible to efficiently form a vapor-phase thin film on the surface of ultrafine particles expected to have high surface activity and new functionality, and to achieve a thin film capable of realizing a high level of particle size and shape uniformity. The remarkable effect that the manufacturing method of the coated ultrafine particle is realizable is produced.

  More specifically, according to the present invention, under a reduced pressure, a material for producing ultrafine particles is introduced into a thermal plasma flame to form a gas phase mixture, which is sufficient to rapidly cool the gas phase mixture. The reactive gas and the cooling gas are introduced toward the tail (end part) of the thermal plasma flame with a small supply amount to generate ultrafine particles, and the generated ultrafine particles and the reactive gas are brought into contact with each other. By doing so, a step of efficiently generating ultrafine particles (core) and a carbon simple substance and / or a carbon compound generated by decomposition and reaction of reactive gas are attached to the surface of the generated ultrafine particles (core). By performing the process together, a remarkable effect is achieved that it is possible to produce ultrafine particles coated with a thin film.

  Hereinafter, the method for producing ultrafine particles according to the present invention will be described in detail based on preferred embodiments shown in the drawings.

  FIG. 1 is a schematic view showing an overall configuration of an ultrafine particle production apparatus 10 for carrying out a method for producing an ultrafine particle coated with a thin film according to an embodiment of the present invention. 2 is a partially enlarged view of the vicinity of the plasma torch 12 shown in FIG. 1, FIG. 3 is an enlarged view of the material supply device 14 shown in FIG. 1, and FIG. It is sectional drawing to which the top plate 17 of the chamber 16 shown and the gas injection port 28a with which this top plate 17 was equipped, and gas injection port 28b vicinity are expanded.

  An ultrafine particle production apparatus 10 shown in FIG. 1 generates a plasma torch 12 that generates a thermal plasma flame, a material supply apparatus 14 that supplies an ultrafine particle production material (powder material) into the plasma torch 12, and generates ultrafine particles 18. A chamber 16 having a function as a cooling chamber, a recovery unit 20 for recovering the generated ultrafine particles 18, and a gas introduction for introducing a cooling gas into the chamber 16 and ejecting it toward the thermal plasma flame 24. The apparatus 28 is comprised.

  The plasma torch 12 shown in FIG. 2 includes a quartz tube 12a and a high-frequency oscillation coil 12b surrounding the outside. In the upper part of the plasma torch 12, an introduction tube 14a, which will be described later, for introducing the ultrafine particle manufacturing material and the carrier gas into the plasma torch 12 is provided in the center thereof, and the plasma gas inlet 12c is provided in the periphery thereof. 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 inlet 12c. Examples of the plasma gas include argon, nitrogen, hydrogen, and the like. For example, two types of plasma gas are prepared in the plasma gas supply source 22. 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 inlet 12c. Then, a high frequency current is supplied to the high frequency oscillation coil 12b, and a thermal plasma flame 24 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 the enlarged view in FIG. 3, the material supply device 14 mainly includes a storage tank 142 that stores the powder material, a screw feeder 160 that quantitatively conveys the powder material, and an ultra-higher that is conveyed by the screw feeder 160. The dispersion unit 170 is configured to disperse the fine particles into primary particles before the fine particles are finally dispersed.

  Although not shown, the storage tank 142 is provided with an exhaust pipe and an air supply pipe. The storage tank 142 is a pressure vessel sealed with an oil seal or the like, and is configured so that the internal atmosphere can be controlled. In addition, an introduction port (not shown) for introducing the powder material is provided in the upper part of the storage tank 142, and the powder material 144 is introduced into the storage tank 142 from the introduction port and stored.

In the storage tank 142, a stirring shaft 146 and a stirring blade 148 connected thereto are provided in order to prevent the stored powder material 144 from agglomerating. The stirring shaft 146 is rotatably disposed in the storage tank 142 by an oil seal 150a and a bearing 152a.
Moreover, the end part of the stirring shaft 146 outside the storage tank 142 is connected to a motor 154a, and its rotation is controlled by a control device (not shown).

  A screw feeder 160 is provided in the lower part of the storage tank 142 to enable quantitative conveyance of the powder material 144. The screw feeder 160 includes a screw 162, a shaft 164 of the screw 162, a casing 166, and a motor 154 b that is a rotational power source of the screw 162. The screw 162 and the shaft 164 are provided across the lower part in the storage tank 142. The shaft 164 is rotatably disposed in the storage tank 142 by an oil seal 150b and a bearing 152b.

  Further, the end of the shaft 164 outside the storage tank 142 is connected to a motor 154b, and its rotation is controlled by a control device (not shown). Furthermore, a casing 166 that is a cylindrical passage that connects the opening of the lower portion of the storage tank 142 and a dispersion unit 170 described later and wraps the screw 162 is provided. The casing 166 extends to the middle of the dispersion unit 170 described later.

As shown in FIG. 3, the dispersion unit 170 includes an outer tube 172 that is extrapolated and fixed to a part of the casing 166, and a rotating brush 176 that is implanted at the tip of the shaft 164, and is fixed by a screw feeder 160. The conveyed powder material 144 can be primarily dispersed.
The end portion of the outer tube 172 opposite to the end portion that is fixed by extrapolation has a truncated cone shape, and also has a powder dispersion chamber 174 that is a truncated cone-shaped space. In addition, a transport pipe 182 that transports the powder material dispersed by the dispersion unit 170 is connected to the end thereof.

  The front end of the casing 166 opens, and a shaft 164 extends beyond the opening to the powder dispersion chamber 174 inside the outer tube 172, and a rotating brush 176 is provided at the front end of the shaft 164. A carrier gas supply port 178 is provided on a side surface of the outer tube 172, and a space provided by the outer wall of the casing 166 and the inner wall of the outer tube 172 serves as a carrier gas passage 180 through which the introduced carrier gas passes. It has the function of.

  The rotating brush 176 is a needle-like member made of a relatively flexible material such as nylon or a hard material such as steel wire. The rotating brush 176 extends from the vicinity of the tip of the casing 166 to the inside of the powder dispersion chamber 174. It is formed by extending radially outward and being densely planted. The length of the needle-like member at this time is such a length that the tip of the needle-like member comes into contact with the peripheral wall in the casing 166.

  In the dispersion unit 170, the gas for dispersion / conveyance is ejected from the carrier gas supply source 15 through the carrier gas supply port 178 and the carrier gas passage 180 to the rotary brush 176 from the radially outer side of the rotary brush 176, and quantitatively. The conveyed powder material 144 is dispersed into primary particles by passing between the needle-like members of the rotating brush 176.

  Here, the angle formed between the frustoconical bus of the powder dispersion chamber 174 and the shaft 164 is set to be about 30 °. In addition, it is preferable that the volume of the powder dispersion chamber 174 is small. If the volume is large, the powder material 144 dispersed by the rotating brush 176 adheres to the inner wall of the dispersion chamber before entering the transfer pipe 182 and is scattered again. There arises a problem that the concentration of the supplied dispersed powder is not constant.

  One end of the transfer tube 182 is connected to the outer tube 172, and the other end is connected to the plasma torch 12. In addition, it is preferable that the transport pipe 182 has a pipe length that is 10 times or more the pipe diameter, and at least a pipe diameter portion in which the air flow containing the dispersed powder flows at a flow velocity of 20 m / sec or more is provided. As a result, aggregation of the powder material 144 dispersed in the primary particle state by the dispersion unit 170 can be prevented, and the powder material 144 can be dispersed inside the plasma torch 12 while maintaining the above dispersion state.

  The carrier gas subjected to the extrusion pressure is supplied from the carrier gas supply source 15 together with the powder material 144 into the thermal plasma flame 24 in the plasma torch 12 through the introduction tube 14a as shown by an arrow G in FIG. Is done. The introduction tube 14 a has a nozzle mechanism for spraying the powder material into the thermal plasma flame 24 in the plasma torch, whereby the powder material 144 is sprayed into the thermal plasma flame 24 in the plasma torch 12. . As the carrier gas, argon, nitrogen, hydrogen, or the like is used alone or in appropriate combination.

  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 powder material 144 sprayed in the thermal plasma flame 24 in the plasma torch 12 evaporates into a gas phase mixture, and immediately after that, the gas phase mixture is rapidly cooled in the chamber 16 to form ultrafine particles 18. Produces. That is, the chamber 16 has a function as a cooling chamber and a function as a reaction chamber.

  By the way, the ultrafine particle production apparatus according to the present invention is characterized by including a gas introduction apparatus mainly intended to rapidly cool the gas phase mixture. Hereinafter, this gas introducing device will be described.

The gas introduction device 28 shown in FIGS. 1 and 4 includes a first gas supply source 28d, a second gas supply source 28f, and pipes 28c and 28e connecting them.
Here, argon as a cooling gas is stored in the first gas supply source 28d, and methane as a reactive gas is stored in the second gas supply source 28f.
Here, examples of the cooling gas include argon, hydrocarbon gases such as nitrogen, hydrogen, oxygen, air, carbon dioxide, water vapor, and methane, and a mixed gas thereof.

Further, the gas introduction device 28 is directed toward the tail of the thermal plasma flame 24 at a predetermined angle as described above with the gas A (here, as an example, a mixture of argon as a cooling gas and methane as a reactive gas). Gas injection port 28a for injecting gas) and the generated ultrafine particles 18 in the chamber 16 from the upper side toward the lower side along the inner wall of the chamber 16 for the purpose of preventing the inside of the chamber 16 from adhering. And a gas injection port 28b for injecting gas B (in this case, argon as an example).
Here, the tail portion of the thermal plasma flame is the end of the thermal plasma flame opposite to the plasma gas inlet 12c, that is, the end portion of the thermal plasma flame.

  In addition, as said gas A, hydrocarbon gas, such as nitrogen, hydrogen, oxygen, air, carbon dioxide, water vapor | steam, methane, etc. other than argon, and these mixed gas can be used suitably, Gas B In addition to argon, for example, hydrocarbon gas such as nitrogen, hydrogen, oxygen, air, carbon dioxide, water vapor, methane, etc., and a mixed gas thereof can be suitably used.

  In FIG. 1, 28g and 28i are pressure control valves for controlling the gas supply pressure from the first gas supply source 28d, and 28h is the gas supply pressure from the second gas supply source 28f. The pressure control valve to control is shown. The pipe 28e mixes the gas delivered from the first gas supply source 28d and the second gas supply source 28f with pressure adjustment and inserts the gas into the chamber 16. The pipe 28c The gas from the gas supply source 28d is directly inserted into the chamber 16.

  As shown in FIG. 4, the gas injection ports 28 a and 28 b are formed in the top plate 17 of the chamber 16. The top plate 17 vertically moves the inner top plate component 17a having a truncated cone shape and a part of the upper side being a cylinder, the lower top plate component 17b having a truncated cone shape hole, and the inner top plate component 17a. And an upper outer part top plate component 17c having a moving mechanism.

  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 side top plate component 17a is rotated. By doing so, the position can be changed in the vertical direction, and the distance between the inner top plate part a and the lower top plate part 17b can be adjusted. Further, the gradient of the conical portion of the inner top plate component 17a and the gradient of the conical portion of the hole of the lower top plate component 17b are the same and are structured to be combined with each other.

  The gas injection port 28a is a gap formed by the inner top plate component 17a and the lower top plate component 17b, that is, a slit, the width of which can be adjusted, and is concentric with the top plate. It is formed in a circumferential shape. Here, the gas injection port 28a may have any shape that can inject gas (here, a mixed gas of argon and methane) toward the tail of the thermal plasma flame 24, and has a slit shape as described above. It is not limited, For example, what provided many holes on the circumference may be used.

  Inside the upper outer part top plate component 17c, there are an air passage 17d through which the gas A (argon and methane) sent through the pipe 28e passes, and an air passage 17e through which the gas B (argon) passes. , Is provided. The gas A (argon and methane) sent through the pipe 28e passes through the air passage 17d and passes through the gas injection port 28a which is the slit formed by the inner top plate component 17a and the lower top plate component 17b described above. Then, it is fed into the chamber 16. The gas B (argon) sent through the pipe 28c passes through the ventilation path 17e, passes through the gas injection port 28b that is also a slit, and is sent into the chamber 16.

  The gas A (argon and methane) sent to the gas injection port 28a passes through the ventilation path 17d from the direction indicated by the arrow S in FIG. 4 and the direction indicated by the arrow Q in FIGS. That is, as described above, the thermal plasma flame is injected at a predetermined supply amount and a predetermined angle toward the tail (end portion) of the thermal plasma flame. Further, the gas B (in this case, argon) sent to the gas injection port 28b is indicated by an arrow R in FIGS. 1 and 4 from the direction indicated by the arrow T in FIG. 4 through the air passage 17e. It is ejected in the direction and supplied so as to prevent the generated ultrafine particles 18 from adhering to the inner wall surface of the chamber 16.

  Here, the predetermined supply amount of the gas A (argon and methane) will be described. As described above, as a supply amount sufficient for quenching the gas-phase mixture, for example, in the chamber 16 that forms a space necessary for quenching the gas-phase mixture, the gas introduced therein The average flow velocity in the chamber 16 (flow velocity in the chamber) is preferably supplied so as to be 0.001 to 60 m / sec, and more preferably 0.01 to 10 m / sec. In such an average flow velocity range, the powder material sprayed in the thermal plasma flame 24 evaporates, the gas phase mixture is rapidly cooled to generate ultrafine particles, and aggregation due to collision between the generated ultrafine particles is prevented. This is a sufficient gas supply amount.

The supply amount is sufficient to rapidly cool and solidify the gas phase mixture, and in order to prevent aggregation and solidification by collision of ultrafine particles immediately after production. 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.

  The supply amount of the reactive gas (here, methane) in the gas A is such that the surface of the ultrafine particles generated from a predetermined amount of the powder material (144) sprayed in the thermal plasma flame 24 is a carbon simple substance. And if it can form the thin film which consists of a carbon compound and / or, it will not be restrict | limited in particular, For example, it is preferable to contain about 0.1 to 10% with respect to the quantity of argon in the gas A.

  Next, the predetermined angle in the case where the gas injection port 28a has a slit shape will be described with reference to FIG. FIG. 5A shows a vertical sectional view passing through the central axis of the top plate 17 of the chamber 16, and FIG. 5B shows a view of the top plate 17 as viewed from below. FIG. 5B shows a direction perpendicular to the cross section shown in FIG. Here, a point X shown in FIG. 5 indicates that the mixed gas sent from the first gas supply source 28d and the second gas supply source 28f (see FIG. 1) via the air passage 17d is the gas injection port 28a. This is an injection point that is injected into the chamber 16 from the inside. 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. 5 (a), 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 formed with the direction (usually the vertical direction) from the head (starting end) to the tail (ending end) of the thermal plasma flame described above.

  Further, as shown in FIG. 5B, the thermal plasma flame with the virtual injection point X as the origin and 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 head portion (starting end portion) to the tailing portion (terminal end portion) is represented by an angle β. This angle β is an angle with respect to the center of the thermal plasma flame in the plane (usually in a horizontal plane) perpendicular to the direction from the head (starting end) to the tail (terminal) of the thermal plasma flame described above. It is.

  When the angle α (usually the angle in the vertical direction) and the angle β (usually the angle in the horizontal direction) are used, the predetermined angle, that is, the introduction direction of the gas into the chamber is set in the chamber 16. , The angle α is 90 ° <α <240 ° (more preferably in the range of 100 ° <α <180 °, most preferably α = 135 °) with respect to the tail (end portion) of the thermal plasma flame 24. β should be −90 ° <β <90 ° (more preferably in the range of −45 ° <β <45 °, most 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 the ultrafine particles 18 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 turbulence generated in the chamber 16. In order to effectively cool the mixture in the phase state and stabilize the thermal plasma flame 24 to operate the ultrafine 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.

On the other hand, the gas injection port 28b is a slit formed in the lower top plate component 17b. The gas injection port 28 b introduces the gas into the chamber 16 in order to prevent the generated ultrafine particles 18 from adhering to the inner wall of the chamber 16.
The gas injection port 28 b is a slit that is concentric with the top plate 17 and formed in a circumferential shape. However, the slit need not be a slit as long as the above-described object is sufficiently achieved.

  Here, the gas introduced into the top plate 17 (specifically, the lower top plate component 17b) from the first gas supply source 28d through the pipe 28c is supplied from the gas injection port 28b to the chamber 16 through the vent passage 17e. Injected in the direction of arrow R shown in FIG. 1 and FIG.

This action has an effect of preventing the ultrafine particles from adhering to the inner wall of the chamber 16 in the process (step) of collecting the ultrafine particles. The amount of gas injected from the gas injection port 28b may not be unnecessarily large as long as the amount is sufficient to achieve the purpose, and it is possible to prevent the ultrafine particles from adhering to the inner wall of the chamber 16. A sufficient amount is sufficient.
That is, the supply amount of the gas B may be appropriately set according to the size and state of the thermal plasma flame 24 and the size of the chamber 16 and the size and state of the inner wall surface of the chamber 16. This amount is about 5 to 5 times.

  The pressure gauge 16p provided on the side wall of the chamber 16 shown in FIG. 1 is for monitoring the pressure in the chamber 16, and mainly the amount of gas supplied into the chamber 16 as described above. It is also used to detect the fluctuation of the pressure and control the pressure in the system.

  As shown in FIG. 1, a collection unit 20 that collects the generated ultrafine particles 18 is provided on the side of the chamber 16. 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 20c provided in the upper portion of the recovery chamber 20a. The generated ultrafine particles are drawn into the collection chamber 20a by being sucked by the vacuum pump, and are collected while remaining on the surface of the filter 20b.

  Next, while describing the operation of the ultrafine particle production apparatus 10 described above, with respect to the ultrafine particle production method according to an embodiment of the present invention using the ultrafine particle production apparatus 10, and the ultrafine particles generated by this production method explain.

In the method for producing ultrafine particles according to the present embodiment, first, a powder material that is a material for producing ultrafine particles is charged into the material supply device 14.
Moreover, it is preferable here that the particle size of the powder material to be used is 10 micrometers or less, for example.

  Here, the powder material is not particularly limited as long as it can be evaporated by a thermal plasma flame, but the following materials are preferable. That is, a metal, an alloy, a single oxide, a complex oxide, a complex oxide containing at least one selected from the group consisting of elements of atomic numbers 12, 13, 26-30, 46-50, 62, 78-83, An oxide solid solution, hydroxide, carbonate compound, halide, sulfide, nitride, carbide, hydride, metal salt, or metal organic compound may be appropriately selected.

  The simple oxide means an oxide composed of one kind of element other than oxygen, the complex oxide means one composed of plural kinds of oxides, and the double oxide means two or more kinds of oxides. It is a high-order oxide made of, and is a solid in which oxides different from oxide solid solutions are uniformly dissolved. In addition, a metal means a material composed only of one or more kinds of metal elements, and an alloy means a material composed of two or more kinds of metal elements. Its structure is a solid solution, a eutectic mixture, a metal. It may form an intercalation compound or a mixture thereof.

  A hydroxide is a compound composed of a hydroxyl group and one or more metal elements, a carbonate compound is a compound composed of a carbonate group and one or more metal elements, and a halide is a halogen element. And one or more metal elements, and a sulfide means one composed of sulfur and one or more metal elements. Nitride means nitrogen and one or more metal elements, carbide means carbon and one or more metal elements, and hydride means hydrogen and one or more metal elements. It consists of metal elements. Further, a metal salt refers to an ionic compound containing at least one metal element, and a metal organic compound refers to an organic compound including a bond between at least one metal element and at least one of C, O, and N elements. And metal alkoxides and organometallic complexes.

  Next, the material for producing ultrafine particles is conveyed by gas using a carrier gas, introduced into the thermal plasma flame 24 through the introduction tube 14a for introduction into the plasma torch 12, and evaporated, and the mixture in the gas phase state To. In other words, the powder material introduced into the thermal plasma flame 24 is introduced into the thermal plasma flame 24 generated in the plasma torch 12 by being supplied into the plasma torch 12, and as a result, the gas phase is vaporized. It becomes a mixture of states.

  Since the powder material needs to be in a gas phase state in the thermal plasma flame 24, the temperature of the thermal plasma flame 24 needs to be higher than the boiling point of the powder material. On the other hand, the higher the temperature of the thermal plasma flame 24 is, the easier it is for the raw material to be in a gas phase, but the temperature is not particularly limited, and the temperature may be appropriately selected according to the raw material. 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.

  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 it may be, for example, 0.5 to 100 kPa.

  Next, the mixture in which the powder material is evaporated in the thermal plasma flame 24 to be in a gas phase is rapidly cooled in the chamber 16, thereby generating ultrafine particles 18. Specifically, the mixture in the vapor phase state in the thermal plasma 24 is rapidly cooled by the gas injected in the direction indicated by the arrow Q toward the thermal plasma flame at a predetermined angle and supply amount through the gas injection port 28a. As a result, ultrafine particles 18 are generated.

  If ultrafine particles immediately after generation collide with each other to form an aggregate, nonuniformity in particle size is a cause of quality deterioration. On the other hand, in the method for producing ultrafine particles according to the present invention, injection is performed in the direction indicated by the arrow Q toward the tail (end portion) of the thermal plasma flame at a predetermined angle and supply amount through the gas injection port 28a. The gas A to be diluted dilutes the ultrafine particles 18 to prevent the ultrafine particles from colliding with each other and aggregating.

  Further, the reactive gas contained in the gas A decomposes and reacts depending on the temperature and pressure conditions in the chamber 16 to generate or generate a carbon simple substance and / or a carbon compound on the surface of the generated ultrafine particles 18. The carbon simple substance and / or the carbon compound adsorbed on the surface of the ultrafine particles 18 prevents aggregation / fusion and oxidation of the ultrafine particles.

  That is, the gas injected from the gas injection port 28a rapidly cools the gas phase mixture, and further prevents aggregation of the generated ultrafine particles, and at the same time, carbon derived from the reactive gas contained in the injected gas. By covering the surface of ultrafine particles with a single substance and / or carbon compound, it works to make the particle size finer, make the particle size uniform, and prevent aggregation, fusion and oxidation of particles. This is a major feature of the present invention.

  By the way, 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. Therefore, the gas injection port 28a in the ultrafine particle manufacturing apparatus 10 according to the present embodiment is a slit formed in a circumferential shape, and the gas supply amount and the injection speed are 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.

  On the other hand, the second introduced gas is injected in the direction of the arrow R shown in FIGS. 1 and 4 from the upper side to the lower side along the inner wall of the chamber 16 through the gas injection port 28b. Thereby, it is possible to prevent the ultrafine particles 18 from adhering to the inner wall of the chamber 16 in the process of collecting the ultrafine particles, and to improve the yield of the generated ultrafine particles. Finally, the ultrafine particles generated in the chamber 16 are sucked by a vacuum pump (not shown) connected to the tube 20c and collected by the filter 20b of the collection unit 20.

  Here, as the carrier gas or the spray gas, generally, use of air, oxygen, nitrogen, argon, hydrogen, or the like can be considered. However, when the generated ultrafine particles are metal ultrafine particles, the carrier gas or the spray gas is used. Argon may be used.

  As the reactive gas contained in the first introduction gas, various gases can be used as long as they can be decomposed and reacted in thermal plasma to generate carbon at the atomic level. For example, in addition to the above-mentioned methane, for example, various hydrocarbon gases having 4 or less carbon atoms such as ethane, propane, butane, acetylene, ethylene, propylene, and butene can be suitably used. Further, the above-described atomic level carbon is preferably generated on the surface of the ultrafine particles generated or easily adsorbed on the surface.

  The ultrafine particles produced by the production method according to the present embodiment have a narrow particle size distribution width, that is, a uniform particle size, little contamination with coarse particles, and specifically, an average particle size of 1 ~ 100 nm. In the method for producing ultrafine particles according to the present embodiment, for example, simple inorganic substances, simple oxides, composite oxides, double oxides, oxide solid solutions, metals, alloys, hydroxides, carbonate compounds, phosphate compounds, halides, sulfides. It is possible to form a thin film on the surface of ultrafine particles such as oxides, simple nitrides, composite nitrides, simple carbides, composite carbides or hydrides.

  In the present embodiment, the reactive gas is decomposed and reacted according to the temperature and pressure conditions in the chamber 16 to generate a carbon simple substance and / or a carbon compound on the surface of the generated ultrafine particles 18, or The carbon simple substance and / or carbon compound produced is adsorbed on the surface of the ultrafine particles 18 to produce ultrafine particles having the surface coated with the carbon simple substance and / or the carbon compound.

  That is, as described above, the ultrafine particles produced by the method for producing ultrafine particles according to the present embodiment have a very large surface activity because the particle size is small as described above, and the above-described carbon simple substance and The surface coating of the ultrafine particles with the carbon compound is performed quickly in a short time.

  Note that the injected gas A can prevent the ultrafine particles generated by rapidly cooling and solidifying the gas phase mixture from colliding with each other. That is, the method for producing ultrafine particles according to the present invention comprises a process of rapidly cooling a gas phase mixture, and the surface of the produced ultrafine particles is coated with a carbon simple substance and / or a carbon compound, thereby agglomerating and fusing. In addition to preventing oxidation, it has a process to produce high-purity ultrafine particles with a fine and uniform particle size with high quality, so it reacts with the surface of the ultrafine particles generated in the above process. The carbon simple substance and / or the carbon compound derived from the decomposition / reaction of the property gas can be uniformly attached.

  Further, in the method for producing ultrafine particles according to the present embodiment, plasma gas, carrier gas, gas derived from the raw material to be supplied, and reactive gas are contained in the chamber 16 by the evacuation operation of the vacuum pump provided in the recovery unit. Not only is the cooling realized by directing the gas phase mixture from the thermal plasma flame to a location sufficiently away from the thermal plasma flame by the generated air flow, but also the gas injected toward the tail (end) of the thermal plasma flame, It also has an effect that the gas phase mixture can be rapidly cooled.

  Examples using the apparatus according to the above embodiment will be described below.

[Example 1]
First, an example in which ultrafine particles of silver are produced and aggregation / fusion of particles is prevented will be described.
As a raw material, silver powder having an average particle size of 4.5 μm was used.
Argon was used as the carrier gas.

  A high frequency voltage of about 4 MHz and about 80 kVA is applied to the high frequency oscillation coil 12 b of the plasma torch 12, and a mixed gas of argon 80 liter / min and hydrogen 5 liter / min is used as a plasma gas from the plasma gas supply source 22. And an argon / hydrogen thermal plasma flame was generated in the plasma torch 12. Here, the reaction temperature was controlled to be about 8000 ° C., and 10 liter / min of carrier gas was supplied from the carrier gas supply source 15 of the material supply device 14.

Silver powder was introduced into the thermal plasma flame 24 in the plasma torch 12 together with argon as a carrier gas.
As the gas introduced into the chamber 16 by the gas introduction device 28, the gas injected from the gas injection port 28a was mixed with argon 150 liter / min and reactive gas methane 2.5 liter / min. In addition, 50 liters / min of argon was used as the gas injected from the gas injection port 28b. At this time, the flow velocity in the chamber was 0.25 m / sec. The pressure in the chamber 16 was 50 kPa.

  The particle diameter converted from the specific surface area (surface area per gram) of the ultrafine silver particles produced under the production conditions as described above was 70 nm. 6 and 7 show electron micrographs of the particles. FIG. 6 is a photograph taken with a scanning electron microscope. When the surface of the silver ultrafine particles was observed, the fusion between the particles hardly occurred. FIG. 7 is a photograph taken with a transmission electron microscope, and a film formed on the surface of the ultrafine particles is observed. FIG. 8 shows the result of extracting the surface coating from the silver nanoparticles coated with the carbon simple substance and / or the carbon compound using chloroform, and measuring the infrared absorption spectrum thereof.

As shown in FIG. 8, the 1350～1450Cm ^-1 and 2800~3100cm ^-1, -CH ₂ - paraffin that starting with, absorption derived from the atomic olefin, 700～900Cm ^-1 and 1450 ˜1650 cm ⁻¹ , absorption derived from aromatic atomic groups including a benzene ring, and 1200 to 1300 cm ⁻¹ and 1650 to 1750 cm ⁻¹ carboxylic acid based atomic groups (—COOH). ) Appears, it can be confirmed that the surface coating film of ultrafine particles is composed of a carbon compound (hydrocarbon compound).
The yield of the ultrafine particles produced in this example was 40% because the amount of the ultrafine silver particles recovered per 100 g of the charged powder material was 40 g.

[Example 2]
Next, the Example which manufactured the ultrafine particle of silver similarly to Example 1, changed the amount of reactive gas, and controlled the particle diameter is shown.
As a raw material, silver powder having an average particle size of 4.5 μm was used.
Argon was used as the carrier gas.

  Here, the high frequency voltage applied to the plasma torch 12 and the supply amount of the plasma gas were the same as in Example 1, and an argon / hydrogen thermal plasma flame was generated in the plasma torch 12. The reaction temperature was also controlled to be about 8000 ° C., and the amount of carrier gas supplied from the carrier gas supply source 15 of the material supply device 14 was also 10 liters / min.

Silver powder was introduced into the thermal plasma flame 24 in the plasma torch 12 together with argon as a carrier gas.
As the gas introduced into the chamber 16 by the gas introduction device 28, the gas injected from the gas injection port 28a was mixed with 150 liter / min of argon and 5.0 liter / min of methane which is a reactive gas. In addition, 50 liters / min of argon was used as the gas injected from the gas injection port 28b. At this time, the flow velocity in the chamber was 0.25 m / sec. The pressure in the chamber 16 was 50 kPa.

  The particle diameter converted from the specific surface area of the ultrafine silver particles produced under the production conditions as described above was 40 nm. FIG. 9 shows a scanning electron micrograph of the particles. Further, when the surface of the silver ultrafine particles was observed with a transmission electron microscope, a layered film of a carbon simple substance and / or a carbon compound could be confirmed, and the particles were hardly fused. The yield of the ultrafine particles produced was 45% because the amount of the ultrafine silver particles collected per 100 g of the charged powder material was 45 g.

Example 3
Next, an example in which ultrafine particles of copper are produced and aggregation / fusion of particles is prevented will be described.
A copper powder having an average particle size of 5.0 μm was used as a raw material.
Argon was used as the carrier gas.

  Here, the high frequency voltage applied to the plasma torch 12, the supply amount of plasma gas, and the like were the same as those in Example 1 and Example 2, and an argon / hydrogen thermal plasma flame was generated in the plasma torch 12. The reaction temperature was also controlled to be about 8000 ° C., and the amount of carrier gas supplied from the carrier gas supply source 15 of the material supply device 14 was also 10 liters / min.

Copper powder was introduced into the thermal plasma flame 24 in the plasma torch 12 together with argon as a carrier gas.
As the gas introduced into the chamber 16 by the gas introduction device 28, the gas injected from the gas injection port 28a was mixed with 150 liter / min of argon and 5.0 liter / min of methane which is a reactive gas. In addition, 50 liters / min of argon was used as the gas injected from the gas injection port 28b. At this time, the flow velocity in the chamber was 0.25 m / sec. The pressure in the chamber 16 was 35 kPa.

The particle diameter converted from the specific surface area of the copper ultrafine particles produced under the above production conditions was 20 nm. When the surface of the copper ultrafine particles was observed with a transmission electron microscope, a layered film of a carbon simple substance and / or a carbon compound could be confirmed, and the particles were hardly fused. Further, it was confirmed that the ultrafine particles immediately after the production were copper by analysis by X-ray diffraction.
FIG. 10 shows the results of measuring the coating film on the surface of the silver nanoparticles prepared by this method by electron energy loss spectroscopy combined with a transmission electron microscope.
According to this measurement, not only the σ bond but also the π bond can be confirmed at the same time. Therefore, not only the carbon compound (see FIG. 8) confirmed by the measurement by the infrared absorption spectrum but also graphite is used for the surface coating film of the ultrafine particles. It can be confirmed that carbon simple substances such as are also included.

Further, even if the copper ultrafine particles were left in the atmosphere for 3 weeks, little oxidation occurred.
The yield of the ultrafine particles produced was 40% because the amount of the ultrafine copper particles recovered per 100 g of the charged powder material was 40 g.

In addition, from the results of Examples 1 to 3, by controlling the flow rates of the gas A and the gas B described above during the production of ultrafine particles, the size of the ultrafine particles to be generated and the coated thin film formed on the surface thereof It can be seen that the film thickness can be set to a desired value.
However, since this control condition is related to other conditions, it cannot be determined unconditionally. For now, it is necessary to determine it by trial and error.

[Comparative Example]
Next, as a comparative example, an example in which the reactive gas is mixed not with the gas injection port 28a but with the carrier gas using the apparatus according to the embodiment to produce ultrafine silver particles will be described.
As a raw material, silver powder having an average particle size of 4.5 μm was used.
As the carrier gas, a mixture of 9.0 liter / min of argon and 1.0 liter / min of methane, which is a reactive gas, was used.

  Here, the high frequency voltage applied to the plasma torch 12 and the supply amount of the plasma gas were the same as in the first to third embodiments, and an argon / hydrogen thermal plasma flame was generated in the plasma torch 12. The reaction temperature was also controlled to be about 8000 ° C., and the amount of carrier gas supplied from the carrier gas supply source 15 of the material supply device 14 was also 10 liters / min.

Silver powder was introduced into the thermal plasma flame 24 in the plasma torch 12 by a mixed gas of argon and methane as a carrier gas.
As gas introduced into the chamber 16 by the gas introduction device 28, argon of 150 liter / min is used for the gas injected from the gas injection port 28a, and argon is used for the gas injected from the gas injection port 28b. 50 liters / min was used. At this time, the flow velocity in the chamber was 0.25 m / sec. The pressure in the chamber 16 was 50 kPa.

  By observing the ultrafine silver particles generated under the above manufacturing conditions with a scanning electron microscope, not only ultrafine particles but also large particles derived from undissolved raw materials and graphite derived from methane, which is a reactive gas, are confirmed. Therefore, it was impossible to achieve uniformity in particle size and shape. FIG. 11 shows an electron micrograph of the particles.

Table 1 shows the case where the flow rate of the mixed gas (argon and methane) as the gas introduced into the chamber 16 is changed when producing the same ultrafine silver particles as shown in Examples 1 and 2. The following experimental results on the change in the particle size of the ultrafine particles were summarized. Here, the flow rate of argon is changed to 100 liter / min and 150 liter / min, and the flow rate of methane is changed to 0.5 liter / min to 5.0 liter / min.
In Table 1, BET represents the above-mentioned specific surface area, and D _BET represents the particle diameter of ultrafine particles calculated from the above.

  The above embodiments and examples are merely examples of the present invention, and the present invention is not limited thereto, and various modifications and improvements can be made without departing from the spirit of the present invention. It goes without saying that you can go.

  For example, in order to stabilize the plasma flame, it is also effective to add and mix a combustible material that is combusted by itself when the material for producing ultrafine particles is introduced into the thermal plasma flame. In this case, the mass ratio between the powder material and the combustible material may be 95: 5 as an example, but is not limited thereto.

  As for the method for supplying the cooling gas and the reactive gas into the chamber 16, the gas injection ports 28 a and 28 b in FIG. 4 are used as the cooling gas dedicated injection ports, and the reactive gas dedicated injection port is used as the injection gas, for example. Various modifications and combinations are possible, such as a method of newly providing near the outside of the outlet 28a or a method of sending reactive gas into the gas injection port 28a in the top plate 17 or the like. In this case, since each gas is guided without being mixed until it is supplied to the chamber 16, there is an advantage that a mixing operation in the middle of the piping becomes unnecessary.

  In addition, as a modification of the method for producing ultrafine particles coated with a thin film according to the present invention, a method of using a reactive gas mixed with a carrier gas as shown as a comparative example is also conceivable. Although coarse particles of the powder material may remain, it is not impossible to put to practical use if it is acceptable to add a classification operation as a post-treatment step.

It is a schematic diagram which shows the whole structure of the ultrafine particle manufacturing apparatus for enforcing the manufacturing method of the ultrafine particle which concerns on one Embodiment of this invention. It is sectional drawing of plasma torch vicinity in FIG. It is sectional drawing which shows schematic structure of a powder material supply apparatus. 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 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. It is an electron micrograph of the particle | grains concerning Example 1 (magnification 50,000 times). 2 is an electron micrograph of particles according to Example 1 (magnification 2 million times). 2 is an infrared absorption spectrum of a particle surface coating film according to Example 1. 4 is an electron micrograph of particles according to Example 2 (magnification of 50,000 times). It is a measurement result by the electron energy loss spectroscopy of the particle | grain surface coating film which concerns on Example 3. FIG. It is an electron micrograph of the particle concerning a comparative example (magnification 5000 times).

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 (Ultrafine particle) manufacturing apparatus 12 Plasma torch 12a Quartz tube 12b High frequency oscillation coil 12c Plasma gas inlet 14 Material supply apparatus 14a Introductory pipe 15 Carrier gas supply source 16 Chamber 16p Pressure gauge 17 Top plate 17a Inner part top plate component 17b Lower top plate component 17c Upper outer side top plate component 17d, 17e Ventilation path 18 Ultrafine particle 20 Collection unit 20a Collection chamber 20b Filter 20c Tube 22 Plasma gas supply source 24 Thermal plasma flame 26 Tube 28 Gas introduction device 28a, 28b Gas injection port 28c, 28e tube 28d first gas supply source 28f second gas supply source 28g, 28h, 28i pressure control valve 142 storage tank 144 powder material 146 stirring shaft 148 stirring blade 150a, 150b oil seal 152a, 152b bearing 154a, 15 4b Motor 160 Screw feeder 162 Screw 164 Shaft 166 Casing 170 Dispersion part 172 Outer tube 174 Powder dispersion chamber 176 Rotating brush 178 Carrier gas supply port 180 Carrier gas passage 182 Conveying tube

Claims (1)

Under reduced pressure, the material for producing ultrafine particles is introduced and dispersed in a thermal plasma flame using an inert gas as a carrier gas to form a gas phase mixture,
With a supply amount sufficient to quench the gas-phase mixture, a mixed gas of hydrocarbon gas and a cooling gas excluding the hydrocarbon gas is mixed at a vertical angle of 90 ° parallel to the thermal plasma flame. The thermal plasma flame is more than −90 ° and less than 90 ° in a plane perpendicular to the vertical direction of the thermal plasma flame and more than −90 ° and less than 90 ° in a plane perpendicular to the vertical direction of the thermal plasma flame. Introduced towards the end of the plasma flame (tail) to generate ultrafine particles,
A method for producing ultrafine particles, wherein the produced ultrafine particles are brought into contact with the hydrocarbon gas to produce ultrafine particles having a surface coated with a thin film made of a hydrocarbon compound .

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