Manufacturing method for fine particle and manufacturing installation for fine particle

Abstract

To provide a manufacturing method for a fine particle with controlled particle size distribution, and a manufacturing installation for a fine particle.SOLUTION: A manufacturing method for a fine particle has a droplet formation process for supplying metal oxide powder with a particle size of 500 nm or less, as measured by the BET method, and a carbon source into a space maintained at a temperature atmosphere above the reduction initiation temperature of the metal oxide powder but below its boiling point, a reduction process for reducing the metal oxide droplets generated by making the metal oxide powder into droplets by the droplet formation process using the carbon source, and a particle formation process for atomizing the reduced metal oxide droplets.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and an apparatus for producing fine particles that produce fine particles without putting raw materials into a gaseous state, and more particularly to a method and an apparatus for producing fine particles that reduce metal oxide powder after converting it into droplets. [Background technology]

[0002] Currently, fine particles such as silicon fine particles, oxide fine particles, nitride fine particles, and carbide fine particles are used in a wide variety of fields. One method for producing such fine particles is the thermal plasma method. The thermal plasma method produces fine particles by instantaneously evaporating raw materials in a thermal plasma flame and then rapidly cooling and solidifying the evaporated material. The thermal plasma method has many advantages, including being clean, highly productive, capable of handling high-melting-point materials due to its high temperature, and being relatively easy to compound compared to other gas-phase methods. For these reasons, the thermal plasma method is actively used as a method for producing fine particles.

[0003] For example, Patent Document 1 describes a method for producing non-stoichiometric titanium oxide fine particles. Patent Document 1 describes a method for producing non-stoichiometric titanium oxide microparticles using titanium oxide containing titanium dioxide, in which titanium dioxide powder is dispersed in a liquid substance containing a carbon source, water is added to form a slurry, the slurry is formed into droplets and supplied to an oxygen-free thermal plasma flame, carbon generated from the substance is reacted with the titanium dioxide in the thermal plasma flame to produce non-stoichiometric titanium oxide in a gaseous phase, and the produced non-stoichiometric titanium oxide in a gaseous phase is rapidly cooled to produce non-stoichiometric titanium oxide microparticles. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6759246 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, non-stoichiometric titanium oxide is produced in a gaseous state, and the produced non-stoichiometric titanium oxide is rapidly cooled to produce non-stoichiometric titanium oxide fine particles. When produced in a gaseous state, it is difficult to control the particle size distribution of the produced particles. In Patent Document 1, the particle size distribution of the produced particles is wide. An object of the present invention is to provide a method and an apparatus for producing fine particles with a controlled particle size distribution. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, invention [1] is a method for producing fine particles, which includes a dropletization step of supplying a metal oxide powder having a particle size of 500 nm or less as measured by the BET method and a carbon source to a space having an atmosphere at a temperature equal to or higher than the reduction initiation temperature of the metal oxide powder and lower than the boiling point of the metal oxide powder, thereby converting the metal oxide powder into droplets, a reduction step of reducing the metal oxide droplets produced by converting the metal oxide powder into droplets in the dropletization step, using a carbon source, and a particleization step of converting the reduced metal oxide droplets into particles.

[0007] Invention [2] is the method for producing fine particles according to invention [1], in which the amount of carbon source relative to the amount of metal oxide powder supplied to the temperature atmosphere space is changed in the dropletization step. Invention [3] is the method for producing microparticles according to invention [1] or [2], wherein the heat source for forming the temperature atmosphere is a thermal plasma flame or a heater. Invention [4] is the method for producing fine particles according to any one of Inventions [1] to [3], wherein the particulate forming step is a step of cooling and solidifying the metal oxide droplets to form particles. Invention [5] is the method for producing fine particles according to any one of Inventions [1] to [4], which comprises, after the particulation step, a recovery step of recovering the particles obtained in the particulation step. The invention [6] is the method for producing fine particles according to any one of the inventions [1] to [5], wherein the metal oxide powder is titanium dioxide powder. Invention [7] is a method for producing microparticles according to any one of Inventions [1] to [6], wherein the particles granulated in the granulation step after the reduction step are non-stoichiometric oxides of the metals that constitute the metal oxide powder. Invention [8] is the method for producing fine particles according to any one of Inventions [1] to [7], wherein the thermal plasma flame is a reducing atmosphere.

[0008] Invention [9] is a microparticle manufacturing apparatus that uses a metal oxide powder having a particle size of 500 nm or less as measured by the BET method and a carbon source to manufacture microparticles. The apparatus includes a chamber that forms a space with a temperature atmosphere that is equal to or higher than the reduction starting temperature of the metal oxide powder and lower than the boiling point, a material supply unit that supplies the metal oxide powder and the carbon source into the chamber that forms the space with the temperature atmosphere, and within the chamber that forms the space with the temperature atmosphere, the metal oxide powder is converted into droplets, the generated metal oxide droplets are reduced by the carbon source, and the reduced metal oxide droplets are converted into particles. Invention

[10] is the microparticle manufacturing apparatus according to invention [9], in which the material supply unit supplies metal oxide powder in a dispersed state to a space in a temperature atmosphere. Invention

[11] is the apparatus for producing fine particles according to invention [9] or

[10] , wherein the material supply unit changes the amount of the carbon source relative to the amount of metal oxide powder supplied to the temperature atmosphere space. Invention

[12] is an apparatus for producing microparticles according to any one of Inventions [9] to

[11] , which comprises a plasma torch provided above the chamber and a plasma generating unit that generates a thermal plasma flame within the plasma torch, and the thermal plasma flame forms a temperature atmosphere.

[0009] The invention

[13] is the apparatus for producing fine particles according to any one of the inventions [9] to

[12] , in which the metal oxide droplets are cooled and solidified in the chamber to form particles. The invention

[14] is the apparatus for producing fine particles according to any one of the inventions [9] to

[13] , which has a collection section connected to the chamber for collecting the granulated particles. The invention

[15] is the apparatus for producing fine particles according to any one of the inventions [9] to

[14] , wherein the metal oxide powder is titanium dioxide powder. The invention

[16] is the apparatus for producing fine particles according to any one of the inventions [9] to

[15] , wherein the granulated particles are non-stoichiometric oxides of the metals that constitute the metal oxide powder. The invention

[17] is the apparatus for producing fine particles according to any one of the inventions [9] to

[16] , wherein the thermal plasma flame is a reducing atmosphere. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a method for producing fine particles with a controlled particle size distribution, and an apparatus for producing fine particles. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram illustrating an example of a microparticle manufacturing apparatus according to an embodiment of the present invention. [Figure 2] This is an Ellingham diagram. [Figure 3] FIG. 1 is a schematic diagram showing an SEM image of titanium dioxide powder. [Figure 4] FIG. 2 is a schematic view showing an SEM image of the fine particles of Example 1. [Figure 5] FIG. 1 is a schematic view showing an SEM image of the fine particles of Example 2. [Figure 6] FIG. 10 is a schematic diagram showing an SEM image of the fine particles of Example 3. [Figure 7] 1 is a graph showing the results of analysis of the crystal structure of titanium dioxide powder and the fine particles of Examples 1 to 3 by X-ray diffraction. [Figure 8] 1 is a graph showing an enlarged view of a portion of the results of analysis of the crystal structure of titanium dioxide powder and the fine particles of Examples 1 to 3 by X-ray diffraction. [Figure 9] 1 is a graph showing the transmittance of titanium dioxide powder and the fine particles of Examples 1 to 3. DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for producing fine particles and an apparatus for producing fine particles according to the present invention will be described in detail below based on preferred embodiments shown in the accompanying drawings. It should be noted that the drawings described below are illustrative for explaining the present invention, and the present invention is not limited to the drawings shown below. In the following, the range of values ​​indicated by "~" includes the values ​​written on both sides. For example, when ε is the value ε α ~number ε β That is, the range of ε is the number ε α and the number ε β The range includes ε α ≦ε≦ε β is. Unless otherwise specified, the angles and temperatures include tolerances generally accepted in the relevant technical fields. Unless otherwise specified, the other particle sizes and flow rates also include tolerances generally accepted in the relevant technical fields. The method and apparatus for producing fine particles will be specifically described below.

[0013] [Example of microparticle manufacturing equipment] FIG. 1 is a schematic diagram showing an example of a microparticle production apparatus according to an embodiment of the present invention. The microparticle production apparatus 10 shown in FIG. 1 (hereinafter simply referred to as the production apparatus 10) is an apparatus for producing microparticles using a metal oxide powder having a particle size of 500 nm or less as measured by the BET method and a carbon source. The produced microparticles are, for example, non-stoichiometric oxides of the metals that make up the metal oxide powder. More specifically, the produced microparticles are, for example, non-stoichiometric titanium oxide microparticles.

[0014] The manufacturing apparatus 10 includes a plasma torch 12 that generates a thermal plasma flame therein, a material supply unit 14 that supplies a metal oxide powder having a particle size of 500 nm or less as measured by the BET method to the interior 16c (inside the chamber 16) of the chamber 16, the chamber 16 for generating fine particles 15, a cyclone 19 that removes coarse particles having a particle size equal to or greater than an arbitrarily specified particle size from the fine particles 15, and a recovery unit 20 that recovers fine particles 18 classified by the cyclone 19 and having a desired particle size. The fine particles 15 and the classified fine particles 18 correspond to the "fine particles" of the present invention. The classified fine particles 18 are also simply referred to as fine particles 18. For the material supply unit 14, chamber 16, cyclone 19, and recovery unit 20, various devices disclosed in Japanese Patent Application Laid-Open No. 2007-138287 can be used, for example. Furthermore, the production apparatus 10 has a carbon source supply unit 32, a plasma generation unit 33, and a raw material supply unit .

[0015] The plasma torch 12 is composed of a quartz tube 12a and a high-frequency oscillation coil 12b surrounding the quartz tube 12a. A supply pipe 14a (described later) is provided in the center of the upper part of the plasma torch 12 for supplying the raw material metal oxide powder into the plasma torch 12. A plasma gas supply port 12c is formed around the periphery (on the same circumference) of the supply pipe 14a, and the plasma gas supply port 12c is ring-shaped. A plasma generation unit 33 is electrically connected to the high-frequency oscillation coil 12b. When a high-frequency voltage is applied from the plasma generation unit 33 to the high-frequency oscillation coil 12b, a thermal plasma flame 24 is generated within the plasma torch 12.

[0016] The plasma gas supply unit 22 supplies plasma gas into the plasma torch 12. The plasma gas supply unit 22 is connected to a plasma gas supply port 12c via a pipe 22a. Although not shown, the plasma gas supply unit 22 is provided with a supply amount adjustment unit such as a valve for adjusting the supply amount. The plasma gas is supplied from the plasma gas supply unit 22 through the ring-shaped plasma gas supply port 12c into the plasma torch 12 in the directions indicated by arrows P and S.

[0017] The plasma gas used may be, for example, argon gas and hydrogen gas. In this case, argon gas and hydrogen gas are stored in plasma gas supply unit 22. Argon gas and hydrogen gas are supplied from plasma gas supply unit 22 through pipe 22a and plasma gas supply port 12c, and then into plasma torch 12 from the directions indicated by arrows P and S. The plasma gas used is not particularly limited to the above-mentioned gases, as it depends on the composition of the particles to be produced.

[0018] The plasma generating unit 33 has a high-frequency power supply (not shown), which is connected to the high-frequency oscillation coil 12b. The plasma generating unit 33 has a function of supplying a high-frequency voltage to the high-frequency oscillation coil 12b. When the high-frequency voltage is applied from the plasma generating unit 33 to the high-frequency oscillation coil 12b, a thermal plasma flame 24 is generated inside the plasma torch 12. The thermal plasma flame 24 is an induction thermal plasma flame generated by the high-frequency voltage. In the plasma generating unit 33, the high frequency voltage supplied to the high frequency oscillation coil 12b is adjusted to adjust the temperature of the thermal plasma flame 24. The plasma torch 12, which is provided above the chamber 16, generates the thermal plasma flame 24 inside by the plasma generating unit 33. The thermal plasma flame 24 is a heat source that forms a temperature atmosphere that is equal to or higher than the reduction initiation temperature and lower than the boiling point of the metal oxide powder described below. The pressure atmosphere inside the plasma torch 12 is preferably equal to or lower than atmospheric pressure. Here, the pressure of the atmosphere equal to or lower than atmospheric pressure is not particularly limited, but is, for example, 0.5 to 100 kPa. The outside of the quartz tube 12a is surrounded by a concentric tube (not shown), and cooling water is circulated between this tube and the quartz tube 12a to water-cool the quartz tube 12a and prevent the quartz tube 12a from becoming too hot due to the thermal plasma flame 24 generated inside the plasma torch 12.

[0019] The thermal plasma flame 24 in the plasma torch 12 is used as a heat source to turn the metal oxide powder into droplets, and the resulting metal oxide droplets are reduced with a carbon source such as methane gas. As described above, when a high-frequency voltage is applied from the plasma generating unit 33 to the high-frequency oscillation coil 12b, a thermal plasma flame 24 is generated within the plasma torch 12. The temperature of the thermal plasma flame 24 can be as high as 6000°C, and theoretically it is thought to reach approximately 10000°C. For this reason, when metal oxide powder is supplied into the plasma torch 12, part of the metal oxide powder evaporates, making it difficult to produce fine particles by turning the metal oxide powder into droplets within the plasma torch 12 without converting the metal oxide powder into a gaseous state.

[0020] The chamber 16 is provided adjacent to and below the plasma torch 12, and the temperature of the interior 16c of the chamber 16 is lower than that of the interior of the plasma torch 12. Therefore, the metal oxide powder can be converted into droplets in the interior 16c of the chamber 16 without being converted into a gaseous state. The interior 16c of the chamber 16 forms a space with a temperature atmosphere equal to or higher than the reduction initiation temperature of the metal oxide powder and equal to or higher than the melting point but lower than the boiling point. In the interior 16c of the chamber 16, the metal oxide powder is converted into droplets, the generated metal oxide droplets are reduced with a carbon source, and the reduced metal oxide droplets are then particleized. The chamber 16 functions as a cooling tank. During particleization, the metal oxide droplets are cooled and solidified in the interior 16c of the chamber 16, and are then particleized to generate fine particles 15. Thus, the interior 16c of the chamber 16 has a space with a temperature atmosphere that is equal to or higher than the reduction start temperature of the metal oxide powder and lower than the boiling point, and a space where the metal oxide droplets are particleized. The temperature atmosphere space and the particleization space are continuous. Furthermore, there is a temperature distribution in the interior 16c of the chamber 16, with relatively high and low temperature regions. For this reason, a region in the longitudinal direction H of the chamber 16 is identified in advance, where the metal oxide powder can be converted into droplets without being converted into a gaseous state, and where the temperature range is equal to or higher than the reduction starting temperature of the metal oxide powder and equal to or higher than the melting point and lower than the boiling point, and the metal oxide powder and the carbon source are supplied to that region.

[0021] Here, when the metal oxide powder is titanium dioxide, referring to the Ellingham diagram shown in Figure 2, straight line 40 shown in Figure 2 corresponds to the oxidation reaction of titanium. Straight line 40 indicates the reaction Ti + O2 = TiO2, and has a positive slope. The line 42 corresponds to the oxidation reaction of carbon. The line 42 shows the reaction of 2C + O2 = 2CO, and has a negative slope. 0 denotes the standard Gibbs energy of reaction. This shows that carbon can reduce titanium dioxide to elemental titanium metal at temperatures above the temperature of the intersection Pc between lines 40 and 42. Also, at temperatures above the temperature of the intersection Pc, carbon itself is oxidized to carbon monoxide (CO). The temperature of the intersection point Pc corresponds to the reduction start temperature. In the case of titanium oxide, the intersection point Pc between the lines 40 and 42 is approximately 1650°C. The melting point of titanium oxide is 1855°C, and the boiling point of titanium oxide is 2972°C. Therefore, the temperature range from the reduction start temperature of titanium oxide to below the boiling point is 1650°C to 2972°C. Considering the melting point of titanium oxide, the temperature range is above the reduction start temperature of titanium oxide and above the melting point but below the boiling point. In this case, a range of 1855°C to 2972°C is preferable. When the metal oxide powder is titanium dioxide, the temperature atmosphere above the reduction initiation temperature and below the boiling point is a temperature of 1650°C to 2972°C, preferably a temperature above the melting point, 1855°C to 2972°C. In this case, the temperature atmosphere is above the reduction initiation temperature and above the melting point but below the boiling point.

[0022] As described above, the temperature of the thermal plasma flame 24 can be set to 6000°C, so the metal oxide powder and the carbon source are supplied to a region within the above-mentioned temperature range below the longitudinal direction H of the tail 24b of the thermal plasma flame 24 in the interior 16c of the chamber 16, rather than to the center of the thermal plasma flame 24. The space having a temperature atmosphere above the reduction initiation temperature and below the boiling point of the metal oxide powder is not limited to being formed using the thermal plasma flame 24 as a heat source, and a heater or the like can be used as a heat source without using a thermal plasma flame. In this case, the temperature atmosphere is adjusted to be within the above-mentioned temperature range. The heater is not particularly limited, and an electric heater or the like can be used.

[0023] The material supply unit 14 is connected to the upper part of the plasma torch 12 via a supply pipe 14a. The material supply unit 14 supplies, for example, a metal oxide powder as a raw material to a region in the interior 16c of the chamber 16 that is in a temperature range of not less than the reduction initiation temperature of the metal oxide powder but less than the boiling point. More specifically, the material supply unit 14 supplies the metal oxide powder to a region in the interior 16c of the chamber 16 below the tail 24b of the thermal plasma flame 24 in the longitudinal direction H. As described above, for example, the one disclosed in Japanese Patent Application Laid-Open No. 2007-138287 can be used as the material supply unit 14 that supplies the metal oxide powder. In this case, the material supply unit 14 has, for example, a storage tank (not shown) that stores the metal oxide powder (raw material powder), a screw feeder (not shown) that conveys a fixed amount of the metal oxide powder (raw material powder), a dispersing unit (not shown) that disperses the metal oxide powder (raw material powder) conveyed by the screw feeder into a state of primary particles before it is finally sprayed, and a carrier gas supply source (not shown).

[0024] Metal oxide powder (raw material powder) is supplied to the interior 16c of the chamber 16 via the supply pipe 14a together with a carrier gas under extrusion pressure from a carrier gas supply source. The material supply unit 14 is not particularly limited in configuration as long as it can prevent aggregation of the metal oxide powder (raw material powder) and spray the metal oxide powder (raw material powder) into the interior 16c of the chamber 16 while maintaining the dispersed state. For example, argon gas is used as the carrier gas. The flow rate of the carrier gas can be controlled using a flow meter such as a float flow meter. The flow rate value of the carrier gas refers to the scale value of the flow meter.

[0025] The carbon source supply unit 32 has a connection pipe 32a connected to the supply pipe 14a. The carbon source supply unit 32 supplies the carbon source to a space in a temperature atmosphere, for example, the interior 16c of the chamber 16. The carbon source reduces the metal oxide powder. When a hydrocarbon gas is used as the carbon source, the thermal decomposition of the hydrocarbon is an endothermic reaction, so the carbon source also functions to cool the dropletized metal oxide powder (metal oxide droplets (not shown)). As the carbon source, various hydrocarbon gases such as methane, ethane, propane, butane, acetylene, ethylene, propylene, and butene can be used. When the carbon source is a hydrocarbon gas, the carbon source supply unit 32 is provided with a gas supply unit in which the hydrocarbon gas is stored, a regulator (pressure adjuster), an adjustment valve for controlling the amount of gas supplied, and the like, all of which are not shown.

[0026] The material supply unit 14 and the carbon source supply unit 32 supply the metal oxide powder and the carbon source to the space having a temperature atmosphere equal to or higher than the reduction initiation temperature and lower than the boiling point of the metal oxide powder. The material supply section 14 and the carbon source supply section 32 constitute a material supply unit 35 . The carbon source supply unit 32 can change the amount of carbon source relative to the amount of metal oxide powder supplied to the temperature atmosphere space, for example, the amount of methane gas supplied relative to the amount of metal oxide powder. By changing the amount of carbon source relative to the amount of metal oxide powder, for example, the amount of methane gas, the degree of reduction of the metal oxide powder can be changed, and the composition and crystallinity of the produced microparticles can be changed. Crystallinity refers to the presence or absence of a periodic arrangement of atoms and molecules that make up the fine particles, while low crystallinity refers to the loss of the periodic arrangement of atoms and molecules.

[0027] The material supply unit 35 may have a raw material supply section 34 connected to the material supply section 14 by a pipe 34a. The raw material supply unit 34 stores the metal oxide raw material that is the basis of the metal oxide powder, and supplies the metal oxide raw material to the material supply unit 14. In the configuration having the raw material supply section 34, the material supply section 14 has, for example, a jet mill (not shown) as a crusher. The jet mill crushes, pulverizes, and disperses the metal oxide raw material to obtain metal oxide powder having a particle size of 500 nm or less as measured by the BET method. The metal oxide powder is then supplied from the material supply section 14 through the supply pipe 14a into the plasma torch 12. In this case, the material supply section 14 constituting the material supply unit 35 supplies the metal oxide powder in a dispersed manner into a space in a temperature atmosphere. The jet mill may be, for example, the jet mill described in JP 2009-173979 A. However, as long as the metal oxide powder can be dispersed and supplied in a space with a certain temperature atmosphere, the jet mill is not limited to the jet mill, and a pin mill or a hammer mill may also be used. The raw material supply unit 34 is not necessarily required, and the raw material supply unit 34 does not necessarily have to be provided.

[0028] A gas supply unit 28 is connected to the chamber 16 via a pipe 28a. The gas supply unit 28 supplies a cooling gas into the chamber 16 via a pipe 28a. A thermal plasma flame 24 is used as a heat source to turn metal oxide powder (raw material powder) into droplets, and the gas supply unit 28 supplies a cooling gas (quenching gas) containing an inert gas to the droplets. The cooling gas (quenching gas) may be, for example, argon gas or hydrogen gas, similar to the plasma gas. The gas supply unit 28 has a gas supply source (not shown) in which cooling gas is stored, and a pressure applying means (not shown) that applies extrusion pressure to the cooling gas to be supplied into the chamber 16. The gas supply unit 28 is also provided with a pressure control valve (not shown) that controls the amount of gas supplied from the gas supply source. When the cooling gas is argon, for example, argon gas is stored in the gas supply source. The pressure applying means is, for example, a compressor or a blower.

[0029] The gas supply unit 28 supplies argon gas as a cooling gas toward the tail 24b of the thermal plasma flame 24, i.e., the end of the thermal plasma flame 24 opposite the plasma gas supply port 12c, i.e., the terminal end of the thermal plasma flame 24, at an angle of, for example, 45° in the direction of arrow Q, and also supplies the above-mentioned cooling gas from above to below along the inner wall 16a of the chamber 16, i.e., in the direction of arrow R shown in Figure 1.

[0030] The cooling gas supplied from the gas supply unit 28 into the chamber 16 has an additional effect of contributing to the classification of the fine particles 15 in the cyclone 19 . If the fine particle droplets collide with each other immediately after generation and form agglomerates, the particle size distribution will broaden, which will cause a decrease in quality. However, the cooling gas introduced in the direction of arrow Q toward the tail 24b (terminal end) of the thermal plasma flame 24 prevents the fine particle droplets from colliding with each other and agglomerating. Furthermore, the cooling gas in the direction of arrow R prevents adhesion of the microparticles 15 to the inner wall 16a of the chamber 16, improving the yield of the generated microparticles 15. For this reason, the cooling gas may be supplied only in the direction of arrow R without supplying the cooling gas in the direction of arrow Q.

[0031] Although argon gas was used as the cooling gas (quenching gas), the present invention is not limited to this, and any gas appropriate for the composition of the microparticles to be produced can be used. If the metal oxide droplets can be granulated, that is, if the metal oxide droplets can be cooled, solidified, and granulated in chamber 16, a cooling gas (quenching gas) may not be used. Thus, depending on the production conditions for granulating the metal oxide droplets, a cooling gas (quenching gas) may not be used. For this reason, gas supply unit 28 is not necessarily required.

[0032] 1, chamber 16 is provided with a cyclone 19 for classifying fine particles 15 into particles of a desired particle size. Cyclone 19 includes an inlet pipe 19a for supplying fine particles 15 from chamber 16, a cylindrical outer cylinder 19b connected to inlet pipe 19a and located at the top of cyclone 19, a truncated cone section 19c that extends downward from the bottom of outer cylinder 19b and has a gradually decreasing diameter, a coarse particle recovery chamber 19d connected to the bottom of truncated cone section 19c and that recovers coarse particles having a particle size equal to or larger than the desired particle size, and an inner pipe 19e connected to recovery section 20, which will be described in detail later, and protruding from outer cylinder 19b.

[0033] An airflow containing fine particles 15 is blown from the inlet pipe 19a of the cyclone 19 along the inner peripheral wall of the outer cylinder 19b, and as a result, this airflow flows from the inner peripheral wall of the outer cylinder 19b toward the truncated cone portion 19c as shown by the arrow T in Figure 1, forming a downward swirling flow. When the downward swirling flow reverses and becomes an upward flow, the balance between centrifugal force and drag prevents the coarse particles from joining the upward flow, and they descend along the side of the truncated cone portion 19c and are collected in the coarse particle collection chamber 19d. Furthermore, fine particles, which are more affected by drag than centrifugal force, are discharged from the inner pipe 19e to the outside of the cyclone 19 along with the upward flow on the inner wall of the truncated cone portion 19c.

[0034] Furthermore, a negative pressure (suction force) is generated through the inner pipe 19e from the collection unit 20, which will be described in detail later. By this negative pressure (suction force), the fine particles separated from the swirling airflow are sucked in as indicated by the symbol U and sent to the collection unit 20 through the inner pipe 19e.

[0035] A collection unit 20 for collecting fine particles 18 having a desired nanometer-order particle diameter is provided on the extension of inner pipe 19e, which is the airflow outlet within cyclone 19. Collection unit 20 includes collection chamber 20a, filter 20b provided within collection chamber 20a, and vacuum pump 30 connected via pipe 20c provided below collection chamber 20a. The fine particles sent from cyclone 19 are sucked by vacuum pump 30 and drawn into collection chamber 20a, where they remain on the surface of filter 20b and are collected. In the above-described manufacturing apparatus 10, the number of cyclones used is not limited to one, but may be two or more.

[0036] [Method of producing fine particles] Next, a description will be given of an example of a method for producing fine particles using the above-described production apparatus 10. Note that the method for producing fine particles is not particularly limited to using the above-described production apparatus 10. The raw material is a metal oxide powder having a particle size of 500 nm or less as measured by the BET method, such as titanium dioxide powder, and having a particle size of 100 nm as measured by the BET method. For example, argon gas and hydrogen gas are used as the plasma gas, and a high frequency voltage is applied from the plasma generating unit 33 to the high frequency oscillation coil 12 b to generate a thermal plasma flame 24 in the plasma torch 12 . Next, titanium dioxide powder as a raw material is gaseously transported using, for example, argon gas as a carrier gas, and is supplied via supply pipe 14a to a region in interior 16c of chamber 16 where the temperature range is equal to or higher than the reduction initiation temperature and lower than the boiling point of the metal oxide powder. Also, a metal gas as a carbon source is supplied from carbon source supply unit 32 via connecting pipe 32a and supply pipe 14a to a region in interior 16c of chamber 16 where the temperature range is equal to or higher than the reduction initiation temperature and lower than the boiling point of the metal oxide powder. As described above, the region in interior 16c of chamber 16 where the titanium dioxide powder (metal oxide powder) and methane gas (carbon source) are supplied and where the temperature range is equal to or higher than the reduction initiation temperature and lower than the boiling point of the metal oxide powder is specified in advance. In this way, the metal oxide powder and the carbon source are supplied to a region in the interior 16c of the chamber 16, which is a space in a temperature atmosphere above the reduction initiation temperature of the metal oxide powder and below its boiling point, where the temperature range is reached, to form the metal oxide powder into droplets (dropletization process). That is, the titanium dioxide powder supplied to the region in the interior 16c of the chamber 16 where the temperature range is reached is formed into droplets, generating titanium dioxide droplets. Note that, since hydrogen gas is used as the plasma gas, the thermal plasma flame 24 is a reducing atmosphere.

[0037] Next, the metal oxide droplets generated by the metal oxide powder being converted into droplets in the dropletization process are reduced with a carbon source (reduction process). In the reduction process, the titanium dioxide droplets generated by the conversion into droplets come into contact with carbon generated by the thermal decomposition of methane gas in the interior 16c of the chamber 16 and are reduced by the carbon. More specifically, the O in titanium dioxide (TiO) reacts with the C in methane gas (CH), reducing the titanium dioxide (TiO). This changes the composition of the titanium dioxide (TiO).

[0038] Next, the reduced metal oxide droplets are granulated (granulation step), thereby obtaining the above-mentioned fine particles 15. The particulate formation process is a process in which the reduced metal oxide droplets are cooled and solidified to form particles. The reduced titanium dioxide droplets are cooled and solidified to form particles. The reduced metal oxide droplets (reduced titanium dioxide droplets) are cooled and solidified to form particles in chamber 16, and the cooling in chamber 16 may be natural cooling without using a cooling gas, or forced cooling using a cooling gas.

[0039] The particles granulated in the granulation step after the reduction step, i.e., the microparticles 15, are, for example, non-stoichiometric oxides of the metals constituting the metal oxide powder. When titanium dioxide is used as the metal oxide powder, the microparticles 15 are non-stoichiometric oxides of titanium, more specifically, non-stoichiometric titanium oxide microparticles. The above-mentioned microparticles 18 are also non-stoichiometric titanium oxide microparticles like the microparticles 15.

[0040] Next, after the granulation step, the particles obtained in the granulation step are collected (collection step). In the recovery process, the fine particles 15 obtained in the interior 16c of the chamber 16 are blown together with the airflow from the inlet pipe 19a of the cyclone 19 along the inner circumferential wall of the outer cylinder 19b. As a result, this airflow flows along the inner circumferential wall of the outer cylinder 19b as indicated by arrow T in Figure 1, forming a swirling flow and descending. When the descending swirling flow reverses and becomes an ascending flow, the balance between centrifugal force and drag forces prevents coarse particles from joining the ascending flow and instead descends along the side of the truncated cone portion 19c, where they are recovered in the coarse particle recovery chamber 19d. Furthermore, fine particles that are more affected by drag than centrifugal force are expelled from the inner wall of the truncated cone portion 19c along with the ascending flow on the inner wall and out of the cyclone 19.

[0041] The discharged fine particles 18 are sucked in the direction indicated by the symbol U in Fig. 1 by the negative pressure (suction force) from the collection unit 20 by the vacuum pump 30, sent to the collection unit 20 through the inner pipe 19e, and collected by the filter 20b of the collection unit 20. In this way, the fine particles 18 are collected in the collection step. In the recovery step, the internal pressure in the cyclone 19 is preferably equal to or lower than atmospheric pressure. The particle size of the classified fine particles (fine particles) 18 is specified to any particle size on the order of nanometers depending on the purpose. In the method for producing fine particles, a cooling gas such as argon gas may be supplied from the gas supply unit 28 to the tail 24b of the thermal plasma flame 24, i.e., the end of the thermal plasma flame 24, in the direction of arrow Q, or in the direction of arrow R. Alternatively, argon gas may be supplied as a cooling gas only in the direction of arrow R.

[0042] In the above-described microparticle manufacturing apparatus and microparticle manufacturing method, the microparticles manufactured are converted into droplets during the manufacturing process but are not converted into a gaseous state. Therefore, the particle size difference between them and the raw material metal oxide powder is small, and the particle size and particle size distribution of the metal oxide powder are reflected in the particle size and particle size distribution of the manufactured microparticles. Therefore, microparticles having a particle size on the same order as the particle size of the metal oxide powder are obtained, and as a result, microparticles with a controlled particle size are obtained. Furthermore, the particle size distribution of the metal oxide powder is also reflected in the particle size distribution of the manufactured microparticles; if the particle size distribution width of the metal oxide powder is narrow, the particle size distribution width of the manufactured microparticles is also narrow.

[0043] <Metal oxide powder> Metal oxide powder is a raw material for fine particles. The metal oxide powder is a metal oxide having a particle size of 500 nm or less as measured by the BET method as described above. The particle size of the metal oxide powder as measured by the BET method is preferably 10 to 200 nm, more preferably 10 to 100 nm. The metal oxide powder is preferably spherical, but is not limited to this. For example, when the diameter of the minor axis is α and the diameter of the major axis is β, the ratio β / α of the metal oxide powder is preferably less than 3. The particle size of the metal oxide powder is the particle size measured by the BET method as described above. As described above, the metal oxide powder is, for example, titanium dioxide. In addition to titanium dioxide, examples of the metal oxide powder include boron oxide, magnesium oxide, aluminum oxide, silicon oxide, calcium oxide, vanadium oxide, chromium oxide, manganese oxide, iron oxide, cobalt oxide, nickel oxide, copper oxide, zinc oxide, gallium oxide, germanium oxide, strontium oxide, yttrium oxide, zirconium oxide, niobium oxide, molybdenum oxide, ruthenium oxide, indium oxide, tin oxide, cesium oxide, barium oxide, hafnium oxide, tantalum oxide, and tungsten oxide.

[0044] <Fine particles> The produced microparticles are particles having a particle size of 500 nm or less as measured by the BET method. The particle size as measured by the BET method is preferably 10 to 200 nm, more preferably 10 to 100 nm. The microparticles are preferably spherical, but are not limited to this. For example, when the diameter of the minor axis is α and the diameter of the major axis is β, the ratio β / α of the microparticles is preferably less than 3. The particle size of the fine particles is the particle size measured by the BET method as described above. As described above, the produced fine particles are, for example, non-stoichiometric oxides of the metals that constitute the metal oxide powder, and more specifically, non-stoichiometric titanium oxide fine particles are exemplified.

[0045] The present invention is basically configured as described above. Although the method and apparatus for producing fine particles according to the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various improvements and modifications may be made without departing from the spirit and scope of the present invention. [Example]

[0046] The features of the present invention will be explained in more detail below with reference to examples. The process contents, process procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below. In the examples, the production apparatus 10 shown in Fig. 1 was used to produce the fine particles of Examples 1 to 3. The production conditions and the like of Examples 1 to 3 will be explained below.

[0047] Example 1 In Example 1, titanium dioxide powder was used as the raw material, with a particle size of 92.8 nm measured by the BET method, as shown in the SEM image in Figure 3. The titanium dioxide powder was dispersed using a disintegrator and fed into a thermal plasma flame. A jet mill was used as the disintegrator. The disintegration conditions were a disintegration gas flow rate of 30 L / min (standard condition equivalent) and an ejector flow rate of 20 L / min (standard condition equivalent). Argon gas was used as the disintegration gas. Argon gas was used as the carrier gas to transport the titanium dioxide powder into the thermal plasma flame. The flow rate of the argon gas was 10 L / min (standard condition equivalent). The supply rate of the titanium dioxide powder was 1.0 g / min. Furthermore, the input power to the high frequency oscillation coil 12b (see FIG. 1) for generating the thermal plasma flame was kept constant at 32 kW, and the pressure inside the plasma torch was fixed at 85 kPa. Argon gas and hydrogen gas were used as plasma gases, with the flow rate of argon gas set to 240 liters / minute (standard state equivalent) and the flow rate of hydrogen gas set to 15 liters / minute (standard state equivalent). Methane gas (CH4 gas) was used as the carbon source, and the flow rate of methane gas was set to 0.5 liters / minute (standard state equivalent).

[0048] Example 2 Example 2 differs from Example 1 in that the flow rate of methane gas is 2.5 liters / minute (standard state equivalent), but other than that, Example 2 was the same as Example 1. Example 3 Example 3 differs from Example 1 in that the flow rate of methane gas is 12.5 liters / minute (standard state equivalent), but other than that, Example 3 was the same as Example 1. In Examples 1 to 3, the amount of methane gas, which is a carbon source, is changed relative to the amount of titanium dioxide powder, which is a metal oxide powder.

[0049] An SEM image of the microparticles of Example 1 is shown in Figure 4. An SEM image of the microparticles of Example 2 is shown in Figure 5. An SEM image of the microparticles of Example 3 is shown in Figure 6. The particle diameter of the microparticles of Example 1 measured by the BET method was 127 nm. The particle diameter of the microparticles of Example 2 measured by the BET method was 108 nm. The particle diameter of the microparticles of Example 3 measured by the BET method was 99.8 nm. In this way, fine particles were produced without coarsening for titanium dioxide powder (see Figure 3) with a particle size of 92.8 nm measured by the BET method. Fine particles of the same nano-order were produced from nano-order metal oxide powder. It was confirmed that the particle size distribution of the metal oxide powder was reflected in the particle size distribution of the produced fine particles. Furthermore, as shown in the SEM images of Figures 4 to 6, the fine particles of Examples 1 to 3 did not show any noticeable aggregation and were not coarsened compared to the titanium dioxide powder shown in Figure 3. The fine particles of Examples 1 to 3 tended to have smaller particle sizes when the amount of methane gas supplied was large.

[0050] Crystal structure analysis by X-ray diffraction was carried out on the titanium dioxide powder and the fine particles of Examples 1 to 3. The results are shown in Figures 7 and 8. The vertical axis in Figures 7 and 8 represents intensity, and the unit of intensity is dimensionless. In Figure 7, ▲ indicates TiO x ■ indicates the diffraction peak of TiO2 (rutile). ● indicates the diffraction peak of TiO2 (anatase). 7 shows an XRD (X-ray diffraction) spectrum 50 of titanium dioxide powder. XRD spectrum 52 shows the spectrum of the microparticles of Example 1. XRD spectrum 53 shows the spectrum of the microparticles of Example 2. XRD spectrum 54 shows the spectrum of the microparticles of Example 3. FIG. 8 shows XRD spectra 50, 52, 53, and 54 in the diffraction angle (2θ) range DL (2θ=23° to 24.5°) of FIG. In the range DL (2θ = 23° to 24.5°), TiO x The positions of the diffraction peaks are included. Figure 8 shows the diffraction peak position P1 of Ti2O3 and the 1.85 The diffraction peak position P2 of Ti2O3 is shown. The diffraction peak of Ti2O3 increases in the order of Examples 1 to 3. 1.85 The O3 diffraction peak is highest in Example 2 among Examples 1 to 3. By changing the amount of methane gas, which is the carbon source, the composition of the produced non-stoichiometric titanium oxide can be changed.

[0051] Furthermore, composition analysis was carried out using XPS (X-ray photoelectron spectroscopy) for the titanium dioxide powder and the fine particles of Examples 1 to 3. The results are shown in Table 1 below. Table 1 also shows the particle sizes measured by the BET method.

[0052] [Table 1]

[0053] As shown in Table 1, in Examples 1 to 3, the proportion of TiO2 decreased relative to the raw material titanium dioxide powder, and Ti2O3, TiO, and Ti appeared, indicating that titanium dioxide was reduced by the carbon source methane gas. The degree of reduction, from smallest to largest, is Example 3, Example 2, and Example 1. It was also shown that the composition of the produced microparticles was changed by changing the amount of methane gas, which is the carbon source, and that the crystallinity of the produced microparticles could be controlled.

[0054] The transmittance was measured for titanium dioxide powder and the fine particles of Examples 1 to 3. The results are shown in Figure 9. The horizontal axis of Figure 9 represents wavelength, and the vertical axis represents transmittance. In Figure 9, measurement line 60 represents the measurement results for the transmittance of titanium dioxide powder. Measurement line 62 represents the measurement results for the transmittance of Example 1. Measurement line 63 represents the measurement results for the transmittance of Example 2. Measurement line 64 represents the measurement results for the transmittance of Example 3. 9, in Examples 1 to 3, in the ultraviolet region with a wavelength of 400 nm or less and in the visible light region with a wavelength of more than 400 nm and around 780 nm, Examples 1 and 2 have higher transmittance than Example 3. This suggests that Example 3 has a higher TiO2 content than Examples 1 and 2. In the infrared region with wavelengths of 900 nm or more, Examples 1 and 2 have lower transmittance than Example 3. This suggests that Examples 1 and 2 contain a higher amount of TiO and Ti2O3, which are known as heat-shielding materials, than Example 3. The results of the composition analysis corresponded to the transmittance measurement results.

[0055] The method for measuring the transmittance will be described below. The transmittance was measured by first weighing 0.005 g of each of the titanium dioxide powder and the microparticles of Examples 1 to 3 to prepare a solution with ethanol added to make a total volume of 50 g. Each solution was dispersed for 5 minutes using an ultrasonic device (Tetora 150, manufactured by Nikkaki Bios Co., Ltd.). Next, 10 g of each dispersed solution was sampled, and ethanol was added to each solution to make a total volume of 50 g, followed by dispersion for 1 minute using an ultrasonic device. This resulted in measurement solutions with a mass concentration of 20 ppm for each of the titanium dioxide powder and the microparticles of Examples 1 to 3. The transmittance of each of the obtained measurement solutions at wavelengths of 200 to 1200 nm was then measured using an ultraviolet-visible-near-infrared spectrophotometer (V-770, manufactured by JASCO Corporation). [Explanation of symbols]

[0056] 10 Microparticle manufacturing equipment (manufacturing equipment) 12 Plasma Torch 12a quartz tube 12b High frequency oscillation coil 12c Plasma gas supply port 14 Material supply section 14a Supply pipe 15 Fine particles 16 Chamber 16a Inner wall 16c internal 18 Fine particles 19 Cyclone 19a Inlet pipe 19b Outer cylinder 19c Cone truncated part 19d Coarse particle collection chamber 19e inner tube 20 Collection Department 20a Recovery Room 20b filter 20c tube 22 Plasma gas supply unit 22a Piping 24 Hot Plasma Flame 24b Tail 28 Gas supply section 28a, 34a piping 30 Vacuum Pump 32 Carbon source supply unit 32a Connecting pipe 33 Plasma generating unit 34 Raw material supply department 35 Material supply unit 40, 42 straight line 50, 52, 53, 54 XRD spectra 60, 62, 63, 64 measurement lines DL range Diffraction peak positions of P1Ti2O3 P2Ti 1.85 O3 diffraction peak position Pc intersection

Claims

1. a dropletization step of supplying a metal oxide powder having a particle size of 500 nm or less as measured by a BET method and a carbon source into a space having an atmosphere at a temperature equal to or higher than the reduction initiation temperature of the metal oxide powder and lower than the boiling point of the metal oxide powder, and converting the metal oxide powder into droplets; a reduction step of reducing, with the carbon source, metal oxide droplets produced by converting the metal oxide powder into droplets in the droplet-forming step; and a particulate forming step of forming the reduced metal oxide droplets into particles.

2. The method for producing fine particles according to claim 1 , wherein the amount of the carbon source relative to the amount of the metal oxide powder supplied to the space in the temperature atmosphere is changed in the droplet-forming step.

3. 3. The method for producing fine particles according to claim 1, wherein the heat source for forming the temperature atmosphere is a thermal plasma flame or a heater.

4. The method for producing fine particles according to claim 1 or 2, wherein the particulate forming step is a step of cooling and solidifying the metal oxide droplets to form particles.

5. The method for producing fine particles according to claim 1 or 2, further comprising, after the particulation step, a recovery step of recovering the particles obtained in the particulation step.

6. 3. The method for producing fine particles according to claim 1, wherein the metal oxide powder is titanium dioxide powder.

7. The method for producing fine particles according to claim 1 or 2, wherein the particles obtained by the reduction step and the granulation step are non-stoichiometric oxides of the metals constituting the metal oxide powder.

8. The method for producing fine particles according to claim 3 , wherein the thermal plasma flame is a reducing atmosphere.

9. 1. An apparatus for producing fine particles using a metal oxide powder having a particle size of 500 nm or less as measured by a BET method and a carbon source, comprising: a chamber having an interior space with a temperature atmosphere equal to or higher than the reduction initiation temperature of the metal oxide powder but lower than the boiling point; a material supply unit that supplies the metal oxide powder and the carbon source into the chamber that constitutes the space under the temperature atmosphere; A microparticle manufacturing apparatus, in which the metal oxide powder is converted into droplets in the chamber that constitutes the space of the temperature atmosphere, the generated metal oxide droplets are reduced by the carbon source, and the reduced metal oxide droplets are converted into particles.

10. The apparatus for producing fine particles according to claim 9 , wherein the material supply unit supplies the metal oxide powder in a dispersed state to the space in the temperature atmosphere.

11. 11. The apparatus for producing fine particles according to claim 9, wherein the material supply unit changes an amount of the carbon source relative to an amount of the metal oxide powder supplied to the space in the temperature atmosphere.

12. a plasma torch provided above the chamber, and a plasma generating unit that generates a thermal plasma flame within the plasma torch; The apparatus for producing fine particles according to claim 9 or 10, wherein the thermal plasma flame forms the temperature atmosphere.

13. 11. The apparatus for producing fine particles according to claim 9, wherein the metal oxide droplets are cooled and solidified in the chamber to form particles.

14. The apparatus for producing fine particles according to claim 9 or 10, further comprising a recovery section connected to the chamber for recovering the granulated particles.

15. 11. The apparatus for producing fine particles according to claim 9, wherein the metal oxide powder is titanium dioxide powder.

16. 11. The apparatus for producing fine particles according to claim 9, wherein the granulated particles are non-stoichiometric oxides of the metals that constitute the metal oxide powder.

17. The apparatus for producing fine particles according to claim 12 , wherein the thermal plasma flame is in a reducing atmosphere.

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