JP2010131577A - Method for producing fine particles and apparatus for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing fine particles which enables highly efficient generation of fine nanoparticles having a narrow particle size distribution width, which has been hitherto difficult, and a method for producing fine particles which can be suitably used for the practise of the method. <P>SOLUTION: The method for producing fine particles includes dispersing and supplying one or more kinds of particles as a raw material for fine particle production into a thermal plasma flame, evaporating the particles for the raw material for fine particle production to prepare a mixture in a gas phase state, and cooling the mixture. A modulated induction thermal plasma device is used as the device for generating the thermal plasma flame, and amplitude modulation of coil current of the modulated induction thermal plasma device is repeated at a predetermined time interval. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a method for producing fine particles, and more specifically, a method for producing fine particles that enables complete utilization (complete evaporation) of raw materials and high-efficiency production of nanoparticles, and is preferably used for carrying out this method. The present invention relates to an apparatus for producing fine particles.

  In recent years, in conjunction with downsizing and refinement of all kinds of products including home appliances, nano-particles and complex powder designs are also used for powders used as raw materials for home appliances, cosmetics and pharmaceuticals. Is now required. There is a technique using thermal plasma as one technique for producing the nanoparticles. Thermal plasma is characterized in that the plasma as a whole has a high temperature and a large heat capacity, and can quickly heat an object to be heated.

  Above all, the greatest advantage of high-frequency induction thermal plasma is that a hot plasma space with high reactivity can be realized without an electrode, so that sputtering and melting of electrode metal is possible compared to DC plasma using arc discharge between electrodes. It is possible to form a clean, high-temperature, high-speed plasma medium that has been freed from contamination problems. This feature is very advantageous in the field of raw material production in that impurities are very little mixed and the reaction can be promoted in any medium (inert atmosphere, oxidizing atmosphere, reducing atmosphere).

In addition, the nanoparticle production also has characteristics that very excellent particles can be obtained in terms of high-purity metals, alloys, intermetallic compounds, surface clean particles and the like as compared with the production method in the liquid phase (Non-patent Document 1). reference).
Furthermore, the modulation induction thermal plasma apparatus shown in Non-Patent Document 2 can repeat the high temperature state and low temperature state of the thermal plasma on the order of microseconds to several seconds by amplitude-modulating the coil current.

Kazuo Akashi, Editor-in-Chief: Plasma Materials Science Handbook, Ohmsha (1992) Nanun et al .: 2007 Japan Electrical Engineering Association Hokuriku Branch Association Conference, A-1 (2007)

Therefore, the first object of the present invention is to use the above-described modulated induction thermal plasma, and a method for producing fine particles capable of efficiently generating fine nanoparticles having a narrow particle size distribution width, which has been difficult in the past, In addition, an object of the present invention is to provide an apparatus for producing fine particles that can be suitably used for carrying out this method.
In addition, the second object of the present invention is to reduce the material supply speed, which has been conventionally required, by reducing the amplitude modulation of the coil current of the modulated induction thermal plasma in the order of microseconds to several seconds. And a method for producing fine particles capable of efficiently producing fine nanoparticles having a narrow particle size distribution width by arbitrarily controlling the particle size of the produced nanoparticles without introducing a quenching gas. An object of the present invention is to provide an apparatus for producing fine particles that can be suitably used for carrying out the method.

  In order to achieve the above-mentioned object, the first fine particle production method according to the first aspect of the present invention is characterized in that one or more kinds of particles as a fine particle production raw material are dispersed and supplied into a thermal plasma flame. A production method of fine particles for producing fine particles by evaporating raw material particles for production into a mixture in a gas phase state, and cooling the mixture, wherein a modulation induction thermal plasma apparatus is used as the thermal plasma flame generating device. It is characterized in that the amplitude modulation of the coil current of the modulation induction thermal plasma apparatus is repeated at predetermined time intervals.

  In order to achieve the above object, the second method for producing fine particles according to the present invention comprises dissolving one or more particles as a raw material for producing fine particles in a solvent and supplying them into a thermal plasma flame. A production method of fine particles for producing fine particles by evaporating raw material particles for production into a mixture in a gas phase state, and cooling the mixture, wherein a modulation induction thermal plasma apparatus is used as the thermal plasma flame generating device. It is characterized in that the amplitude modulation of the coil current of the modulation induction thermal plasma apparatus is repeated at predetermined time intervals.

  In order to achieve the above object, the third method for producing fine particles according to the present invention includes dispersing one or more kinds of particles as a raw material for producing fine particles in a slurry and supplying the particles into a thermal plasma flame. A production method of fine particles for producing fine particles by evaporating raw material particles for production into a mixture in a gas phase state, and cooling the mixture, wherein a modulation induction thermal plasma apparatus is used as the thermal plasma flame generating device. It is characterized in that the amplitude modulation of the coil current of the modulation induction thermal plasma apparatus is repeated at predetermined time intervals.

  Here, in the method for producing fine particles according to the present invention, when the amplitude of the coil current of the modulation induction thermal plasma apparatus is amplitude-modulated, the amplitude of the coil current may be modulated by a predetermined waveform. preferable.

  Further, in the method for producing fine particles according to the present invention, a rectangular waveform, a triangular wave, a sawtooth wave, a reverse sawtooth wave, or a predetermined waveform used for amplitude modulation of the coil current of the modulation induction thermal plasma apparatus, or It is preferable to use a waveform composed of a repetitive wave including a curve including a sine wave.

  In the method for producing fine particles according to the present invention, it is preferable that the predetermined time interval for repeating the amplitude modulation of the coil current of the modulation induction thermal plasma apparatus is on the order of microseconds to several seconds.

  On the other hand, in order to achieve the above object, the fine particle production apparatus according to the second aspect of the present invention disperses one or more kinds of particles as a fine particle production raw material as they are, or dissolves them in a solvent, or A raw material supply means for producing fine particles dispersed in a slurry and fed into a thermal plasma flame, and a post-treatment for converting the raw material for producing fine particles evaporated in the thermal plasma flame into a gas phase mixture and further cooling the mixture And a fine particle collecting means for collecting fine particles generated by cooling the mixture, wherein the modulated induction thermal plasma apparatus is used as the thermal plasma flame generator, and the modulated induction thermal plasma is used. A modulation induction thermal plasma apparatus for controlling the amplitude of the coil current of the apparatus, and the control means for controlling the coil current of the modulation induction thermal plasma apparatus. Characterized in that to repeat amplitude modulation at a predetermined time interval.

  Here, in the fine particle manufacturing apparatus according to the present invention, when the amplitude of the coil current of the modulation induction thermal plasma apparatus is amplitude-modulated, the coil current may be amplitude-modulated by a predetermined waveform. preferable.

  In the fine particle manufacturing apparatus according to the present invention, a rectangular waveform, a triangular wave, a sawtooth wave, a reverse sawtooth wave, or a predetermined waveform used for amplitude modulation of the coil current of the modulation induction thermal plasma apparatus, or It is preferable to use a waveform composed of a repetitive wave including a curve including a sine wave.

  In the fine particle manufacturing apparatus according to the present invention, it is preferable that the predetermined time interval for repeating the amplitude modulation of the coil current of the modulation induction thermal plasma apparatus is on the order of microseconds to several seconds.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the microparticles | fine-particles which can produce | generate the fine particle which was difficult conventionally, and a narrow particle size distribution width | variety with high efficiency, and the microparticles manufacturing apparatus which can be used suitably for implementing this method It is an excellent effect that can be provided.
Further, according to the present invention, it is possible to provide a method for producing fine particles capable of arbitrarily controlling the particle size of the generated nanoparticles, and an apparatus for producing fine particles that can be suitably used for carrying out this method. It is effective.

The method for producing a TiO ₂ fine particles according to an embodiment of the present invention is a schematic diagram showing an overall configuration of a manufacturing apparatus for carrying out. It is sectional drawing which shows schematic structure of the raw material supply apparatus which can be used suitably when using a powder raw material as a raw material for fine particle manufacture. It is a figure which shows the example of 1 structure of the power supply of the modulation | alteration induction thermal plasma generator used for the manufacturing apparatus which concerns on embodiment. It is sectional drawing which expands and shows the plasma torch in FIG. It is explanatory drawing which shows the outline of the coil current at the time of pulse modulation. It is a figure which shows the SEM image of the particle | grains collect | recovered by the filter part as a result of the nanoparticle production | generation experiment performed using the manufacturing apparatus of FIG. It is a figure which shows the particle size frequency distribution of the particle | grains collect | recovered by the filter part as a result of the same experiment (the 1). It is a figure which shows the particle size frequency distribution of the particle | grains collect | recovered by the filter part as a result of the same experiment (the 2). It is a figure which shows the result of having calculated the raw material supply amount dependence of the average particle diameter from the SEM image of the collect | recovered particle | grains. It is a figure which shows the result of having calculated the raw material supply amount dependence of the standard deviation from the SEM image of the collect | recovered particle | grains. It is a figure which shows the current modulation factor dependence with respect to the average particle diameter of the production | generation particle | grains in each experimental condition. It is a figure which shows the duty ratio dependence with respect to the average particle diameter of a production | generation particle | grain. It is a figure which shows the calculation result of the specific surface area by BET method of the particle | grains produced | generated at each collection place. It is a figure which shows the XRD analysis result of the collect | recovered particle | grains. Is a diagram showing the raw material powder supply amount dependent weight fraction of Anatase type TiO _2. It is a schematic view showing a configuration example of a supply device of the liquid raw material used in the production apparatus for carrying out the method for producing TiO ₂ fine particles according to another embodiment.

  Hereinafter, the present invention will be described in detail based on preferred embodiments shown in the drawings.

FIG. 1 is a schematic diagram showing an overall configuration of a fine particle production apparatus (hereinafter also simply referred to as a production apparatus) 10 for carrying out a method for producing TiO ₂ fine particles according to an embodiment of the present invention.

  The manufacturing apparatus 10 shown in FIG. 1 is roughly composed of five parts. These are (1) the raw material supply unit 12, (2) the high frequency MOSFET inverter power supply 14, (3) the thermal plasma torch 16, (4) the chamber 18, and (5) the recovery unit 20.

First, the raw material supply unit 12 is connected to the upper part of the plasma torch 16 through a supply pipe, and disperses the raw material for producing fine particles into the plasma torch 16. In the manufacturing apparatus 10 according to the present embodiment, TiO ₂ fine particles are manufactured using an apparatus suitable for using a powder raw material as a raw material supply apparatus. However, here, the powder raw material needs to be dispersed when supplied into the thermal plasma flame.

  Therefore, it is preferable that the raw material supply apparatus in the present embodiment can quantitatively supply the powder raw material into the thermal plasma flame inside the plasma torch while maintaining the powder raw material in a dispersed state (so-called primary particle state). As a raw material supply apparatus having such a function, for example, an apparatus such as a powder dispersion apparatus disclosed in Japanese Patent No. 3217415 related to the applicant's application can be used.

  FIG. 2 shows a schematic configuration of a raw material supply apparatus 30 that can be suitably used when a powder raw material is used as a raw material for producing fine particles. 2 mainly includes a storage tank 32 for storing powder raw materials, a screw feeder 50 for quantitatively conveying powder raw materials, and a powder raw material conveyed by the screw feeder 50 finally. It is comprised from the dispersion | distribution part 60 which disperse | distributes this to the state of a primary particle before being spread | dispersed.

  In the storage tank 32, a stirring shaft 36 and a stirring blade 38 connected thereto are provided in order to prevent the stored powder raw material 34 from agglomerating. The stirring shaft 36 is rotatably arranged in the storage tank 32 by an oil seal 40a and a bearing 42a. Further, the end of the stirring shaft 36 outside the storage tank 32 is connected to a motor 44a, and its rotation is controlled by a control device (not shown).

  A screw feeder 50 is provided in the lower part of the storage tank 32 to enable quantitative conveyance of the powder raw material 34. The screw feeder 50 includes a screw 52, a shaft 54 of the screw 52, a casing 56, and a motor 44 b that is a rotational power source of the screw 52. The screw 52 and the shaft 54 are provided across the lower part in the storage tank 32. The shaft 54 is rotatably disposed in the storage tank 32 by an oil seal 40b and a bearing 42b.

  Further, the end of the shaft 54 outside the storage tank 32 is connected to a motor 44b, and its rotation is controlled by a control device (not shown). Further, a casing 56 that is a cylindrical passage that connects the opening of the lower portion of the storage tank 32 and a dispersion unit 60 described later and wraps the screw 52 is provided. The casing 56 is extended to the middle of the dispersion part 60 described later.

As shown in FIG. 2, the dispersing unit 60 includes an outer tube 62 that is extrapolated and fixed to a part of the casing 56, and a rotating brush 66 that is implanted at the tip of the shaft 54, and is fixed by the screw feeder 50. The conveyed powder raw material 34 can be primarily dispersed.
The end portion of the outer tube 62 opposite to the end portion that is fixed by extrapolation has a truncated cone shape, and also has a powder dispersion chamber 64 that is a truncated cone-shaped space. Further, a transport pipe 72 for transporting the powder raw material dispersed by the dispersion unit 60 is connected to the end thereof.

A gas supply port 68 is provided on the side surface of the outer tube 62, and the space provided by the outer wall of the casing 56 and the inner wall of the outer tube 62 functions as a gas passage 70 through which the supplied gas passes. Have.
The rotating brush 66 is a needle-like member made of a relatively soft material such as nylon or a hard material such as steel wire, and the shaft 54 extends from the vicinity of the tip of the casing 56 to the inside of the powder dispersion chamber 64. It is formed by extending radially outward and being densely planted.

  In the dispersion unit 60, a gas for dispersion / conveyance (carrier gas) is jetted from a pressure gas supply source (not shown) through the gas supply port 68 and the gas passage 70 to the rotary brush 66 from the outside in the radial direction of the rotary brush 66, The powder material 34 conveyed quantitatively is dispersed into primary particles by passing between the needle-like members of the rotating brush 66.

  The transfer tube 72 has one end connected to the outer tube 62 and the other end connected to the plasma torch 16. Further, it is preferable that the transport pipe 72 has a pipe length that is 10 times or more the pipe diameter, and has a pipe diameter portion at which the air flow containing the dispersed powder is at a flow velocity of 20 m / sec or more at least in the middle. As a result, the powder raw material 144 dispersed in the state of primary particles by the dispersing unit 60 can be prevented from agglomerating, and the powder raw material 34 can be dispersed inside the plasma torch 16 while maintaining the above dispersed state.

The manufacturing apparatus 10 according to this embodiment can connect the raw material supply apparatus 30 as described above to the plasma torch 16 shown in FIG. 1 and use this to implement the method for manufacturing TiO ₂ fine particles according to this embodiment. .
Here, the powder raw material used as the raw material for producing fine particles can be evaporated in a thermal plasma flame, and is preferably a powder raw material having a particle size of 100 μm or less.

Next, the high frequency MOSFET inverter power supply 14 will be described.
The high-frequency MOSFET inverter power supply 14 is a MOSFET inverter power supply having a fundamental frequency of 450 kHz, a maximum power of 50 kW, a rated voltage of 150 V, and a rated current of 460 A. Normally, the frequency used for induction thermal plasma generated using a vacuum tube power supply is several MHz, whereas in the fine particle manufacturing apparatus 10 according to the present embodiment, the one having a frequency f = 450 kHz is used.

The MOSFET inverter power supply has a power conversion efficiency of 90%, which is higher than the efficiency of the conventional vacuum tube type power supply of 30 to 60%, and overcomes the disadvantage of ICP that the energy efficiency is low. This power supply has a function of modulating the amplitude of the current.
FIG. 3 shows a configuration example for realizing the above-described function of modulating the amplitude of the power supply current.

FIG. 3 shows a configuration example used as a power source of a modulation induction thermal plasma generator, and uses a three-phase alternating current as an input power source.
In this device, after AC-DC conversion is performed by a three-phase full-wave rectifier circuit, the output voltage value is changed by a DC-DC converter using an IGBT (insulated gate bipolar transistor).

Next, DC-AC conversion is performed by the MOSFET inverter circuit. As a result, the inverter output can be AM-modulated.
A series resonance circuit composed of a capacitor and a resonance coil is connected to the output side of the inverter, and impedance matching is performed so that the resonance frequency of the load impedance including the plasma load is within the drive frequency region of the inverter power supply. .

Next, the plasma torch 16 will be described.
As shown in FIG. 4, the plasma torch 16 includes a quartz tube 16a and a high-frequency oscillation coil 16b surrounding the outside. Above the plasma torch 16, a supply pipe 16c for supplying Ti particles as a raw material for producing fine particles and a carrier gas into the plasma torch 16 is provided at the center, and a plasma gas supply port 16d is provided. It is formed in the peripheral part (on the same circumference).

  The outside of the quartz tube 16a of the plasma torch 16 is surrounded by a concentric quartz tube 16e, and cooling water 16f is circulated between the quartz tubes 16a and 16e to cool the quartz tube 16a. The quartz tube 16a is prevented from becoming too hot due to the thermal plasma flame 24 generated in the plasma torch 16.

As the plasma torch 16, a quartz tube 16a having an inner diameter of 75 mm and a length of 330 mm is used here.
In addition, the plasma generating induction coil 16b is an 8-turn one having an outer diameter of 130 mm, a coil conductor diameter of 14 mmφ, and a coil length of 155 mm.

  The coil length 155 mm is about three times longer than a general one. As described above, the advantage of increasing the coil length is that it can generate a strong electromagnetic field that is long in the axial direction, so that the plasma generated thereby becomes longer in the axial direction, and the raw material powder charged from the torch head It has advantageous characteristics for evaporation.

  A water-cooled chamber 18 is connected to the downstream portion of the plasma torch 16. As shown in FIG. 1, the chamber 18 has an upstream chamber attached in the same direction as the torch from the side closer to the plasma torch 16. In addition, a downstream chamber is provided perpendicular to the upstream chamber, and a collection unit (filter unit) 20 is provided further downstream. There are three places to collect the particles: an upstream chamber, a downstream chamber, and a filter.

Hereinafter, the manufacturing method of the TiO ₂ fine particles performed using the manufacturing apparatus 10 according to the present embodiment will be described in more detail.

  The carrier gas to which the extrusion pressure is applied is converted into plasma through a supply pipe 16c as shown in FIG. 4 together with Ti particles that are raw materials for producing fine particles from a spray gas supply source in a raw material supply device 30 (not shown). It is supplied into the thermal plasma flame 24 in the torch 16. The supply pipe 16 c has a jet nozzle mechanism for jetting the raw material for producing fine particles into the thermal plasma flame in the plasma torch 16, whereby the thermal plasma flame 24 in the plasma torch 16 is supplied with the raw material for producing fine particles. Can erupt inside. As the carrier gas, argon, nitrogen, hydrogen or the like is used alone or in appropriate combination.

As described above, the chamber 18 is provided adjacent to the lower side of the plasma torch 16, and the powder raw material sprayed into the thermal plasma flame 24 in the plasma torch 12 evaporates to form a gas phase mixture. Immediately thereafter, the mixture is quenched from the upstream chamber into the downstream chamber downstream thereof, and TiO ₂ fine particles are generated. That is, the downstream chamber downstream from the upstream chamber functions as a cooling tank.

  The fine particle production raw material injected into the plasma torch 16 from the raw material supply device 30 becomes a vapor phase mixture which is evaporated by reacting in the thermal plasma flame 24. The gas phase mixture is rapidly cooled in the downstream chamber 18 to generate fine particles. At this time, it is also desirable to prevent fine particles from adhering to the inner wall surface of the chamber 18 by injecting gas from the inner wall surface or the like of the downstream chamber 18.

  A collection unit (filter unit) 20 including a desired filter 20 a for collecting the generated fine particles is provided at a lower side portion of the chamber 18. The filter unit 20 includes a recovery chamber provided with a filter and a vacuum pump 20b connected via a pipe provided below the recovery chamber. The fine particles sent from the chamber 18 are drawn into the collection chamber by being sucked by the above-described vacuum pump 20b, and are collected while remaining on the surface of the filter.

Using the manufacturing apparatus configured as described above, an experiment of charging Ti raw material powder into thermal plasma was performed. Table 1 shows the fixed experimental conditions. The experimental conditions were such that the average input to the plasma was constant 20 kW, Ar + O ₂ was used as the sheath gas, the total flow rate was 100 L / min (converted to the standard state, the same applies hereinafter), and the flow rate composition Ar 90% + O ₂ 10%. The carrier gas was Ar, and its flow rate was 4 L / min. The pressure inside the reaction vessel was fixed at 300 torr (≈40 kPa), and the raw material Ti powder having an average diameter of 45 μm was used. The internal insertion length of the water-cooled probe into which the powder was introduced was between the fourth and fifth turns of the induction coil (insertion length: 134 mm).

Here, the definition of terms will be described based on the outline of the coil current at the time of pulse modulation using the rectangular wave shown in FIG.
First, the coil current is defined as a high value (HCL) and a low value (LCL) of the current amplitude, and in one modulation period, the time for taking the HCL is defined as the on time, and the time for taking the LCL is defined as the off time. . Furthermore, the ratio of on time in one cycle (on time / (on time + off time) × 100 (%)) is defined as a duty ratio (DF). Further, the ratio of the current amplitude of the coil (LCL / HCL × 100 (%)) is defined as a current modulation rate (SCL).

  Under the above-mentioned common fixed conditions, as shown in Table 2, a total of six experiments were conducted for the case where the coil current was not modulated and the case where the rectangular modulation with a current modulation factor (SCL) of about 70% was performed. The difference of the generated particles by the presence or absence of was investigated. For the analysis of the product, SEM (scanning electron microscope), XRD (X-ray diffraction method), and BET (Brunauer, Emmet and Teller's) method were used to examine the average particle size, crystal structure, specific surface area, etc. .

SEM observation results:
FIG. 6 shows an SEM image of particles collected by the filter unit 20 by performing a nanoparticle generation experiment under each experimental condition. The filter used was a bag filter (Microtex MT-1000) manufactured by Nippon Filter Industry. In these images, (a) and (b) correspond to no-modulation and rectangular modulation, respectively. From these images, it is understood that spherical nanoparticles with a diameter of several tens of nm are generated under any condition during rectangular modulation, but large particles with a diameter exceeding 100 nm are generated during non-modulation. From the above, it was confirmed that particles having an apparently smaller particle size were produced by applying rectangular modulation of 70% SCL.

  Note that the predetermined time interval at the time of the rectangular modulation described above, that is, the on time / off time in Table 2, can be arbitrarily determined, for example, within the range of microseconds to several seconds.

Particle size frequency distribution / average particle size:
Using the SEM image described above, 200 particles were randomly extracted and the particle size frequency distribution was examined. Specifically, two SEM images with a magnification of 100,000 in different measurements were used, and the particle diameters of a total of 200 particles were measured. 7 and 8 show the particle size frequency distribution of the recovered particles in the filter unit 20 under each experimental condition. In the figure, the average particle diameter and the standard deviation of the particle diameter are also shown.

In FIG. 7, (a), (b), and (c) correspond to each powder supply speed at the time of non-modulation, and (a), (b), and (c) in FIG. The results are shown for each powder supply rate.
From the comparison results of FIGS. 7 and 8, it is clearly recognized that the variation in particle size is smaller when the rectangular modulation is applied.

  Similarly, the average particle diameter was calculated from the SEM images of the particles generated at each collection place. FIGS. 9 and 10 show the dependency of the average particle size and standard deviation on the raw material supply amount, respectively. From both figures, when comparing the average particle size with and without rectangular modulation conditions (graph B) and without (graph A), the average particle size is clearly smaller when the rectangular modulation is applied, and the variation in particle size is also It can be confirmed that it is getting smaller.

Next, the influence of the current modulation factor (SCL) will be described with reference to FIG.
FIG. 11 is a graph showing the dependence of the current modulation rate on the average particle size of the generated particles under each experimental condition. As shown in the figure, in each of the duty ratio (DF) 90%, 80%, and 67%, the SCL value is decreased and the degree of modulation is gradually increased as compared with the case of SCL 100%. As it goes on, it can be confirmed that the average particle size tends to be smaller.

FIG. 12 is a diagram for explaining the influence of the duty ratio (DF) on various current modulation factors (SCL).
FIGS. 12A, 12B, and 12C show average particle sizes corresponding to current modulation rates of 90%, 80%, and 70%, respectively. From these figures, it can be read that there is a suitable region where the duty ratio (DF) is around 70% to 80%.

Specific surface area measurement result by BET method:
In order to cross-check such a tendency, the specific surface area of the recovered particles was determined by the BET method. The specific surface area is the total surface area with respect to all particles contained in 1 g, and the larger this value, the more particles having a smaller particle diameter.
In the BET method here, the specific surface area is calculated by adsorbing N ₂ particles. FIG. 13 shows the specific surface area measurement results by the BET method.

In FIG. 13, a graph C1 shows a case where rectangular modulation is present, and a graph C2 shows a case where rectangular modulation is not present.
From the figure, it can be seen that the specific surface area is larger when rectangular modulation is applied than when it is not modulated. This is consistent with the trend obtained from SEM images.

  Therefore, it can be said that particles with a smaller particle size can be generated under the condition of adding rectangular modulation as compared with the case of no modulation. This is considered to be because the growth of the generated particles can be suppressed and the particle size does not increase by quenching the vapor immediately after the raw material has evaporated by rapid temperature change due to plasma contraction.

XRD-generated particle surface composition:
In order to see the crystal structure and composition of the produced particles, XRD analysis was performed. FIG. 14 shows an XRD analysis result of the particles collected by the filter unit 20. From FIG. 14, under any experimental condition, the peak of Ti as a raw material was not observed, and many peaks of TiO ₂ were detected, and it was confirmed that the generated particles contained TiO ₂ .

In particular TiO ₂ peaks of Anatase-type crystal structure appear relatively large. This is considered to be due to the fact that the produced particles have a higher content of Anatase-type TiO ₂ .
Since the intensity ratio of the diffraction lines detected in the XRD analysis is related to the constituent characteristics of the substance contained in the sample, the weight fraction of the substance can be calculated using the diffraction line peak value.

In this experiment, in order to evaluate the quantitative content of Anatase-type TiO ₂ at each experimental condition / recovery place, the peak appearing at the peak 2θ = 25.280 of Anatase-type TiO _{2 and} the peak 2θ of Rutile-type TiO ₂ = Using the peak appearing at 27.445, the weight fraction of the Anatase-type TiO ₂ was calculated by the following formula.

FIG. 15 shows the dependency of the weight fraction of the Anatase type TiO _{2 on} the amount of raw material powder supplied. From the figure, it can be confirmed that the value of the weight fraction of Anatase-type TiO ₂ is about 0.85 to 0.9 under any experimental condition. From this, it is conceivable that the crystal structure and composition of the generated particles do not depend on whether there is a modulation condition (graph B) or not (graph A) or on the amount of raw material powder supplied.

The weight fraction of the Anatase type TiO2 was determined according to the following formula (1).

Here, f _A : weight fraction of Anatase type TiO ₂
I _A : Peak of Anatase type TiO 2
(2θ = 25.280, surface index: 101)
I _R : Peak of Rutile TiO ₂
(2θ = 27.445, plane index: 110)
It is.

  As described above in detail, according to the manufacturing apparatus 10 according to the present embodiment, the powder raw material is used as the raw material for fine particle manufacturing, and the above-described modulation induction thermal plasma is used. In addition, it is possible to realize a method for producing fine particles that can efficiently generate nanoparticles having a narrow particle size distribution width. In addition, it is possible to arbitrarily control the particle size of the generated nanoparticles without lowering the raw material supply rate or introducing a large amount of quenching gas, which has been necessary in the past. A method for producing fine particles capable of generating particles with high efficiency can be realized.

  In addition, this invention is not limited to the said embodiment, For example, the liquid raw material as shown in FIG. 16 which supplies in the slurry form which disperse | distributed Ti particle | grains which are fine particle manufacturing raw materials in a dispersion medium. This can also be realized by a form of supplying the plasma torch 16 using the supply device 30A. Similarly, it is also possible to supply in the form of a colloidal liquid in which Ti particles, which are raw materials for producing fine particles, are dispersed in a dispersion medium.

  Note that the liquid raw material supply device 30A shown in FIG. And a pump 30E for feeding the plasma torch 16 into the plasma torch 16.

In the above embodiment, the case of producing TiO ₂ fine particles by oxidizing Ti particles, which are raw materials for producing fine particles, has been described as an example. Needless to say, it is also possible to produce fine particles of materials, metals, nitrides, carbides and the like.

  The above embodiments and examples are only examples of the present invention, and the present invention is not limited thereto, and various modifications and changes can be made without departing from the spirit of the present invention. Needless to say, improvements may be made.

  ADVANTAGE OF THE INVENTION According to this invention, while being able to produce | generate the fine nanoparticle with a narrow particle size distribution width which was difficult conventionally, it is possible to produce | generate highly efficiently, and the particle size which makes it possible to control the particle size of the produced | generated nanoparticle arbitrarily The production method and the fine particle production apparatus that can be suitably used for carrying out this method can be provided.

The above embodiment shows an example of the present invention, and the present invention is not limited to the above embodiment, and various modifications and improvements are made without departing from the spirit of the present invention. Needless to say, it may be.
For example, the waveform of the coil current at the time of pulse modulation is not limited to the one using the rectangular wave mentioned in the embodiment, but from a repetitive wave including a curve including a triangular wave, a sawtooth wave, a reverse sawtooth wave, or a sine wave. Needless to say, the following waveform may also be used.

DESCRIPTION OF SYMBOLS 10 (Fine particle) manufacturing apparatus 12 Raw material supply part 14 High frequency MOSFET inverter power supply 16 Plasma torch 16a Quartz tube (inner tube)
16b Coil for high frequency oscillation 16c Raw material supply port 16d Plasma gas supply port 16e Quartz tube (outer tube)
16f Cooling water flow path 18 Chamber 20 Recovery part 20a Filter 20b Vacuum pump 24 Thermal plasma flame 30 Raw material supply apparatus 30A Liquid raw material supply apparatus 32 Storage tank 50 Screw feeder 60 Dispersion part

Claims (10)

Disperse one or more particles as a raw material for fine particle production and supply them into a thermal plasma flame,
A method for producing fine particles, in which the raw material particles for fine particle production are evaporated to form a gas phase mixture, and the mixture is cooled to produce fine particles,
Using a modulated induction thermal plasma device as the thermal plasma flame generator,
A method for producing fine particles, characterized in that the amplitude modulation of the coil current of this modulation induction thermal plasma apparatus is repeated at predetermined time intervals. One or more kinds of particles as a raw material for producing fine particles are dissolved in a solvent and supplied to a thermal plasma flame,
A method for producing fine particles, in which the raw material particles for fine particle production are evaporated to form a gas phase mixture, and the mixture is cooled to produce fine particles,
Using a modulated induction thermal plasma device as the thermal plasma flame generator,
A method for producing fine particles, characterized in that the amplitude modulation of the coil current of this modulation induction thermal plasma apparatus is repeated at predetermined time intervals. One or more kinds of particles as a raw material for producing fine particles are dispersed in a slurry and supplied into a thermal plasma flame,
A method for producing fine particles, in which the raw material particles for fine particle production are evaporated to form a gas phase mixture, and the mixture is cooled to produce fine particles,
Using a modulated induction thermal plasma device as the thermal plasma flame generator,
A method for producing fine particles, characterized in that the amplitude modulation of the coil current of this modulation induction thermal plasma apparatus is repeated at predetermined time intervals.   The method for producing fine particles according to any one of claims 1 to 3, wherein when the coil current of the modulation induction thermal plasma apparatus is amplitude-modulated, the coil current is amplitude-modulated by a predetermined waveform.   As a predetermined waveform used when amplitude-modulating the coil current of the modulation induction thermal plasma apparatus, a waveform comprising a repetitive wave including a curve including a rectangular wave, a triangular wave, a sawtooth wave, a reverse sawtooth wave, or a sine wave The method for producing fine particles according to claim 4, wherein   The method for producing fine particles according to any one of claims 1 to 5, wherein the predetermined time interval at which the amplitude modulation of the coil current of the modulation induction thermal plasma apparatus is repeated is in the order of microseconds to several seconds. One or more kinds of particles as a raw material for fine particle production are dispersed as they are, or dissolved in a solvent, or dispersed in a slurry and supplied into a thermal plasma flame, and a raw material production means for fine particle production,
A raw material for producing fine particles evaporated in the thermal plasma flame as a gas phase mixture, and further, a post-processing means for cooling the mixture;
A fine particle production apparatus comprising fine particle collection means for collecting fine particles generated by cooling the mixture,
Using a modulated induction thermal plasma device as the thermal plasma flame generator,
A modulation induction thermal plasma apparatus control means for modulating the amplitude of the coil current of the modulation induction thermal plasma apparatus,
The apparatus for producing fine particles, wherein the control means repeats amplitude modulation of the coil current of the modulation induction thermal plasma apparatus at predetermined time intervals.   8. The fine particle manufacturing apparatus according to claim 7, wherein when the amplitude of the coil current of the modulation induction thermal plasma apparatus is amplitude-modulated, the coil current is amplitude-modulated by a predetermined waveform.   As a predetermined waveform used when amplitude-modulating the coil current of the modulation induction thermal plasma apparatus, a waveform comprising a repetitive wave including a curve including a rectangular wave, a triangular wave, a sawtooth wave, a reverse sawtooth wave, or a sine wave The apparatus for producing fine particles according to claim 8, wherein   The apparatus for producing fine particles according to any one of claims 7 to 9, wherein a predetermined time interval at which the amplitude modulation of the coil current of the modulation induction thermal plasma apparatus is repeated is on the order of microseconds to several seconds.