JP2012055840A - Device and method for producing fine particles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production device for producing fine particles having small particle size and reduced variations in particle diameters, and to provide a method for producing fine particles.SOLUTION: The device for producing the fine particles includes: a raw material supply unit for intermittently supplying a raw material for producing the fine particles into a thermal plasma flame; a plasma torch in which the thermal plasma flame is generated, which evaporates the raw material intermittently supplied by the raw material supply unit using the thermal plasma flame to form a vapor-phase mixture; and a plasma generating unit for generating the thermal plasma flame inside the plasma torch.

Description

  The present invention relates to a nano-sized fine particle production apparatus and fine particle production method using plasma, and more particularly, to a fine particle production apparatus and a fine particle production method in which the obtained fine particles have a small particle size and small variation in particle size.

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

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

  One of the gas phase methods is a thermal plasma method. The thermal plasma method is a method of producing fine particles by instantaneously evaporating raw materials in thermal plasma and then rapidly solidifying them. In addition, the thermal plasma method is clean and highly productive, has high heat capacity at high temperatures, and therefore can be used for high melting point materials, and has many advantages such as being relatively easy to combine compared with other gas phase methods. Have For this reason, the thermal plasma method is actively used as a method for producing fine particles.

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

  Patent Document 1 discloses that a slurry in which a fine particle manufacturing material is dispersed in a combustible material, or a slurry in which the fine particle manufacturing material is used as a dispersion medium and a combustible material are continuously formed into droplets. A method for producing fine particles is described which is introduced into a thermal plasma flame to form a gas phase mixture and rapidly quenches the gas phase mixture.

JP 2006-102737 A

  In the method for producing fine particles described in Patent Document 1, although nano-sized fine particles can be produced, there is a problem that variation in the obtained fine particles cannot be controlled. In addition, there is a problem that it is difficult to produce smaller fine particles.

  An object of the present invention is to provide a production apparatus and a production method of fine particles that can solve the problems based on the above-described conventional technology and can produce fine particles having a small particle size and small variation in particle size.

  In order to achieve the above object, the present invention is an apparatus for producing fine particles, in which raw material supply means for intermittently supplying raw materials for producing fine particles into a thermal plasma flame, and the thermal plasma flame are generated inside. A plasma torch in which the raw material supplied intermittently by the raw material supply means is evaporated by the thermal plasma flame to form a gas phase mixture, and the thermal plasma flame is generated inside the plasma torch There is provided a fine particle manufacturing apparatus characterized by having plasma generating means.

  The plasma generation means includes a power supply unit that can supply an electric current for generating the thermal plasma flame to a coil provided in the plasma torch and can amplitude-modulate the electric current to the coil. The plasma generation means periodically modulates the current to the coil to change the temperature of the thermal plasma flame to a high temperature state and a low temperature state where the temperature is lower than the high temperature state. It is preferable to generate a time-modulated modulated thermal plasma flame.

  Spectral analysis means for spectrally analyzing light having a wavelength derived from the raw material with respect to the modulation induction thermal plasma flame, and based on a result of spectral analysis of light having a wavelength derived from the raw material, the raw material is supplied to the plasma generating means. It is preferable to have a control unit that relatively increases the amplitude of the current to the coil when supplied to the modulated induction thermal plasma flame, and puts the modulated induction thermal plasma flame in a high temperature state.

  Spectral analysis means for spectrally analyzing light having a wavelength derived from the raw material with respect to the modulated induction thermal plasma flame, and based on a result of spectral analysis of light having a wavelength derived from the raw material, to the raw material supply means, to the coil It is preferable to have a control unit that supplies the raw material to the modulated induction thermal plasma flame when the amplitude of the current is relatively large and the modulated induction thermal plasma flame is in a high temperature state.

Further, the raw material supply means, for example, disperses the raw material in a particle state and intermittently supplies the raw material dispersed in the particle state to the thermal plasma flame or the modulation induction thermal plasma flame. In this case, the raw material is dispersed in a particulate state by a gas.
Further, the raw material supply means, for example, is a means for dispersing the raw material in a dispersion medium to form a slurry, and forming the slurry into droplets and supplying them intermittently to the thermal plasma flame or the modulated induction thermal plasma flame. .
Furthermore, the raw material supply means, for example, disperses the raw material in a dispersion medium to form a colloidal solution, and droplets of the colloidal solution are supplied intermittently to the thermal plasma flame or the modulation induction thermal plasma flame. Is.
In addition, the raw material supply means, for example, dissolves the raw material in a solvent to form a solution, drops the dissolved solution into droplets, and intermittently supplies the solution to the thermal plasma flame or the modulation induction thermal plasma flame It is.

When the current to the coil is amplitude-modulated in the power supply unit, it is preferable that the current to the coil is amplitude-modulated with a predetermined waveform.
As a predetermined waveform used when amplitude-modulating the coil current in the power supply unit, a waveform including a repetitive wave including a curve including a rectangular wave, a triangular wave, a sawtooth wave, a reverse sawtooth wave, or a sine wave is used. Can do.
The predetermined time interval for amplitude-modulating the current to the coil is preferably in the order of microseconds to several seconds.

  The present invention also relates to a method for producing fine particles, wherein raw materials for producing fine particles are intermittently supplied into a thermal plasma flame, the raw materials are evaporated to form a gas phase mixture, and the mixture is cooled. The present invention provides a method for producing fine particles characterized by producing fine particles.

The raw material is intermittently supplied to a modulated induction thermal plasma flame in which the temperature state of the thermal plasma flame is time-modulated to periodically change to a high temperature state and a low temperature state lower than the high temperature state. preferable.
The modulated induction thermal plasma flame is spectrally analyzed for light having a wavelength derived from the raw material, and the raw material is supplied to the modulated induction thermal plasma flame based on the result of spectral analysis of the light having the wavelength derived from the raw material. Sometimes, it is preferable that the modulation induction thermal plasma flame is in a high temperature state.
Spectral analysis of light having a wavelength derived from the raw material for the modulated induction thermal plasma flame, and based on a result of spectral analysis of light having a wavelength derived from the raw material, when the modulated induction thermal plasma flame is in a high temperature state, The raw material is preferably supplied to the modulation induction thermal plasma flame.

The raw material is dispersed, for example, in a particle state and is intermittently supplied to the thermal plasma flame or the modulated induction thermal plasma flame. In this case, the raw material is dispersed in a particulate state by a gas.
Further, for example, the raw material is dispersed in a dispersion medium to form a slurry, and the slurry is made into droplets and intermittently supplied to the thermal plasma flame or the modulation induction thermal plasma flame.
Furthermore, the raw material is suspended in, for example, a dispersion medium to form a colloidal solution, and the colloidal solution is formed into droplets and intermittently supplied to the thermal plasma flame or the modulation induction thermal plasma flame.
Further, the raw material is, for example, made into a solution dissolved in a solvent, and the dissolved solution is formed into droplets and intermittently supplied to the thermal plasma flame or the modulation induction thermal plasma flame.

  According to the fine particle production apparatus and production method of the present invention, fine particles having a small particle size and a small variation in particle size can be produced.

It is a mimetic diagram showing the particulate manufacture device concerning the embodiment of the present invention. It is typical sectional drawing which shows schematic structure of the raw material supply part of the manufacturing apparatus of the microparticles | fine-particles which concerns on embodiment of this invention. It is a typical fragmentary sectional view showing the plasma torch of the particulate manufacture device concerning the embodiment of the present invention. It is a graph which shows the time change of the coil current at the time of pulse modulation. (A) is a graph which shows the pulse control signal for modulating a coil current, (b) is a graph which shows the opening and closing timing of a valve, (c) is a graph which shows supply of a raw material. It is a graph which shows an example of the result of the spectroscopic analysis of a modulation induction thermal plasma flame. (A) is a graph which shows the input waveform signal to a valve | bulb, (b) is a graph which shows an example of the time change of the radiation intensity of Ti and TiO of a modulation | alteration induction thermal plasma flame. It is a schematic diagram which shows the other example of the raw material supply part of the manufacturing apparatus of the microparticles | fine-particles which concerns on embodiment of this invention. (A)-(c) is a figure which shows the SEM image of the microparticles | fine-particles of Experimental Examples 1-3 collect | recovered with the filter (photograph substitute). (A)-(c) is a graph which shows the particle size frequency distribution of the microparticles | fine-particles of Experimental Examples 1-3 collect | recovered with the filter. It is a graph which shows the particle size of the microparticles | fine-particles of Experimental Examples 4-9.

The fine particle production apparatus and fine particle production method of the present invention will be described in detail below based on preferred embodiments shown in the accompanying drawings.
FIG. 1 is a schematic diagram showing an apparatus for producing fine particles according to an embodiment of the present invention.

A fine particle production apparatus (hereinafter simply referred to as production apparatus) 10 shown in FIG. 1 is, for example, for producing nano-sized fine particles using a powder raw material. As this powder raw material, for example, Ti powder is used.
The manufacturing apparatus 10 includes a raw material supply unit 12, a high frequency modulation induction thermal plasma generation unit (plasma generation means) 14, a plasma torch 16, a chamber 18, a recovery unit 20, an intermittent supply unit 22, and a plasma spectroscopic analysis unit. (Spectral analysis means) 28, DSP (control unit) 30, and plasma gas supply unit 32. The raw material supply unit 12 and the intermittent supply unit 22 constitute a raw material supply unit.

The raw material supply unit 12 is connected to the intermittent supply unit 22. The intermittent supply unit 22 and the plasma torch 16 are connected via a hollow water-cooled probe 24. Further, the high frequency modulation induction thermal plasma generator 14 generates a modulation induction thermal plasma flame 100 inside the plasma torch 16, and the temperature state of the thermal plasma flame is time-modulated. It becomes a high temperature state and a low temperature state.
Further, in the manufacturing apparatus 10, the modulated spectroscopic thermal plasma flame 100 is spectroscopically analyzed by the plasma spectroscopic analysis unit 28, and based on the intensity of light having a wavelength derived from the raw material out of the radiated light of the modulated induction thermal plasma flame 100 by the DSP 30. Thus, the temperature state of the modulation induction thermal plasma flame 100 is time-modulated by the high frequency modulation induction thermal plasma generator 14.

  The raw material supply unit 12, together with the intermittent supply unit 22, supplies a raw material for producing fine particles into a thermal plasma flame or a modulated induction thermal plasma flame 100 generated inside the plasma torch 16. The raw material supply unit 12 is connected to a valve 22c of the intermittent supply unit 22 provided on the upper part of the plasma torch 16 via a transfer pipe 82 (see FIG. 2).

  For example, when powder is used as a raw material for producing fine particles, the raw material needs to be dispersed when the raw material is supplied into the thermal plasma flame or the modulation induction thermal plasma flame 100 in the plasma torch 16. For this reason, the raw material is supplied dispersed in carrier gas. In this case, for example, the raw material supply unit 12 quantitatively supplies the powder raw material into the thermal plasma flame or the modulated induction thermal plasma flame 100 inside the plasma torch 16 while maintaining the powder raw material in a dispersed state. As the raw material supply unit 12 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.

  As shown in FIG. 2, the raw material supply unit 12 mainly includes a storage tank 42 for storing powder raw materials, a screw feeder 60 for quantitatively conveying powder raw materials, and a powder raw material conveyed by the screw feeder 60. It is comprised from the dispersion | distribution part 70 which disperse | distributes this to the state of a primary particle before being finally spread | dispersed.

  Inside the storage tank 42, a stirring shaft 46 and a stirring blade 48 connected thereto are provided in order to prevent the stored powder raw material 44 from agglomerating. The agitation shaft 46 is rotatably arranged in the storage tank 42 by an oil seal 50a and a bearing 52a. Moreover, the end of the stirring shaft 46 outside the storage tank 42 is connected to a motor 54a, and the rotation thereof is controlled by a control device (not shown).

  A screw feeder 60 is provided in the lower part of the storage tank 42 to enable quantitative conveyance of the powder raw material 44. The screw feeder 60 includes a screw 62, a shaft 64 of the screw 62, a casing 66, and a motor 54b that is a rotational power source of the screw 62. The screw 62 and the shaft 64 are provided across the lower part in the storage tank 42. The shaft 64 is rotatably disposed in the storage tank 42 by an oil seal 50b and a bearing 52b.

  Further, the end of the shaft 64 outside the storage tank 42 is connected to a motor 54b, and its rotation is controlled by a control device (not shown). Further, a casing 66 that is a cylindrical passage that connects the opening of the lower part of the storage tank 42 and a dispersion unit 70 described later and wraps the screw 62 is provided. The casing 66 extends to the middle of the dispersion unit 70 described later.

As shown in FIG. 2, the dispersion unit 70 includes an outer tube 72 that is extrapolated and fixed to a part of the casing 66, and a rotating brush 56 that is planted at the tip of the shaft 64, and is fixed by a screw feeder 60. The conveyed powder raw material 44 can be primarily dispersed.
The end portion of the outer tube 72 opposite to the end portion that is fixed by extrapolation has a truncated cone shape, and also has a powder dispersion chamber 74 that is a truncated cone-shaped space. Further, a transport pipe 82 for transporting the powder raw material dispersed by the dispersion unit 70 is connected to the end thereof. The transport pipe 82 is connected to the valve 22c.

A gas supply port 78 is provided on the side surface of the outer tube 72, and the space provided by the outer wall of the casing 66 and the inner wall of the outer tube 72 functions as a gas passage 80 through which the supplied gas passes. Have.
The rotating brush 56 is a needle-like member made of a relatively flexible material such as nylon or a hard material such as steel wire, and the shaft 64 extends from the vicinity of the tip of the casing 66 to the inside of the powder dispersion chamber 74. It is formed by extending radially outward and being densely planted.

  In the dispersion unit 70, a gas for dispersion / conveyance (carrier gas) is jetted from a pressure gas supply source (not shown) through the gas supply port 78 and the gas passage 80 to the rotary brush 56 from the outside in the radial direction of the rotary brush 56. The powder material 44 conveyed quantitatively is dispersed into the primary particles by passing between the needle-like members of the rotating brush 56. As the carrier gas, for example, argon (Ar) gas, nitrogen gas, hydrogen gas, or the like is used alone or in combination.

One end of the transfer tube 82 is connected to the outer tube 72, and the other end is connected to the plasma torch 16. In addition, it is preferable that the transport pipe 82 has a pipe length that is 10 times or more the pipe diameter, and at least a pipe diameter portion in which the air flow containing the dispersed powder flows at a flow velocity of 20 m / sec or more is provided. As a result, the powder raw material 44 dispersed in the primary particle state in the dispersion unit 70 is prevented from agglomerating, and the powder raw material 44 is supplied to the valve 22c while maintaining the above dispersed state, and the water-cooled probe 24 is connected to the valve 22c. Then, it is sprayed inside the plasma torch 16.
For example, the powder raw material used as the raw material for producing fine particles can be evaporated in the thermal plasma flame or the modulated induction thermal plasma flame 100, and the particle size is preferably 100 μm or less.

The plasma torch 16 has a thermal plasma flame or a modulated induction thermal plasma flame 100 generated therein, and a raw material intermittently supplied into the modulation induction thermal plasma flame 100 is a thermal plasma flame or a modulated induction thermal plasma. It is evaporated in the flame 100 to form a gas phase mixture.
The thermal plasma flame is a plasma flame whose temperature state is not time-modulated. The modulated induction thermal plasma flame is a high-temperature state in which the thermal plasma flame is periodically heated at a predetermined time interval. Also, the temperature of the thermal plasma flame is time-modulated.
As shown in FIG. 3, the plasma torch 16 includes a quartz tube 16a and a high-frequency oscillation coil 16b surrounding the outside. In the upper part of the plasma torch 16, a supply port 16c into which the water cooling probe 24 is inserted is provided at the center thereof, and a plasma gas supply port 16d is formed in the peripheral portion (on the same circumference).
For example, Ti particles as raw material powder and a carrier gas such as Ar gas are supplied into the plasma torch 16 by the water-cooled probe 24.

The plasma gas supply port 16d is connected to the plasma gas supply unit 32 by, for example, a pipe (not shown). The plasma gas supply unit 32 supplies plasma gas into the plasma torch 16 through the plasma gas supply port 16d. For example, two types of plasma gas are prepared. As the plasma gas, for example, argon gas, nitrogen gas, hydrogen gas, oxygen gas, or the like is used alone or in appropriate combination.
When a high-frequency current amplitude-modulated by the high-frequency induction thermal plasma generator 14 is applied to the high-frequency oscillation coil 16 b in a state where there is a plasma gas in the plasma torch 16, the modulated induction thermal plasma flame is placed inside the plasma torch 16. 100 is generated. When a high frequency current is simply applied to the high frequency oscillation coil 16 b by the high frequency induction thermal plasma generator 14, a thermal plasma flame is generated inside the plasma torch 16. When the plasma gas contains oxygen gas, the plasma torch 16 has an oxygen atmosphere.

  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 modulation induction thermal plasma flame 100 (thermal plasma flame) generated in the plasma torch 16.

In the plasma torch 16, for example, a quartz tube 16a having an inner diameter of 75 mm and a length of 330 mm is used.
Further, the plasma generating induction coil 16b is an 8-turn coil having an outer diameter of 130 mm, a coil conductor diameter of 14 mmφ, and a coil length of 155 mm. The tip of the water-cooled probe 24 is, for example, between the fourth and fifth turns of the plasma generating induction coil 16b.

  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. The chamber 18 rapidly cools a gas phase mixture obtained by evaporating the raw material in the thermal plasma flame or the modulated induction thermal plasma flame 100 to generate fine particles and collect the obtained fine particles.
As shown in FIG. 1, the chamber 18 has an upstream chamber 18 a attached to the plasma torch 16 in the coaxial direction from the side closer to the plasma torch 16. In addition, a downstream chamber 18b is provided perpendicular to the upstream chamber 18a, and a collection unit 20 including a desired filter 20a for collecting the generated fine particles is provided further downstream. In the manufacturing apparatus 10, the collection place of the fine particles is the filter 20a.

  The filter unit 20 includes a recovery chamber provided with a filter 20a 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 collected while remaining on the surface of the filter 20a.

  The pressure atmosphere in the plasma torch 16 is preferably not more than atmospheric pressure. Here, the atmosphere below atmospheric pressure is not particularly limited, but may be, for example, 5 Torr to 750 Torr.

The high frequency modulation induction thermal plasma generator 14 supplies a high frequency current for generating the modulation induction thermal plasma flame 100 to the high frequency oscillation coil 16b, and amplitude modulates the high frequency current to the high frequency oscillation coil 16b at predetermined time intervals. Is something that can be done. Hereinafter, the high-frequency current supplied to the high-frequency oscillation coil 16b in order to generate the modulation induction thermal plasma flame 100 is referred to as a coil current.
The high frequency modulation induction thermal plasma generator 14 includes a high frequency inverter power supply 26a, an impedance matching circuit 26b, a pulse signal generator 26c, and an FET gate signal circuit 26d.
The high frequency inverter power supply 26a 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 the high-frequency inverter power supply 26a has a frequency f = 450 kHz.

The MOSFET inverter power source constituting the high-frequency inverter power source 26a has an ICP (inductively coupled plasma) that has a power conversion efficiency of 90%, which is higher than that of a conventional vacuum tube type power source of 30 to 60%, and low in energy efficiency. It overcomes the drawbacks. The MOSFET inverter power supply has a function capable of modulating the amplitude of current. That is, the MOSFET inverter power supply can amplitude-modulate the coil current.
The high frequency inverter power supply 26a includes, for example, a rectifier circuit and a MOSFET inverter circuit. In the high-frequency inverter power supply 26a, the rectifier circuit uses, for example, a three-phase alternating current as an input power supply, and after performing AC-DC conversion by the three-phase full-wave rectifier circuit, an IGBT (insulated gate bipolar transistor) is used. The output voltage value is changed by the DC-DC converter.

The MOSFET inverter circuit is connected to a rectifier circuit and converts a direct current obtained by the rectifier circuit into an alternating current. Thereby, the inverter output, that is, the coil current is amplitude-modulated (AM-modulated).
The high frequency inverter power supply 26a has an impedance matching circuit 26b connected to the output side. The impedance matching circuit 26b is composed of a series resonance circuit including a capacitor and a resonance coil, and performs impedance matching so that the resonance frequency of the load impedance including the plasma load is within the drive frequency region of the high frequency inverter power supply 26a. Is.

The pulse signal generator 26c generates a pulse control signal for applying rectangular wave modulation to the amplitude of the coil current that maintains the high frequency modulation induction thermal plasma.
The FET gate signal circuit 26d supplies a modulation signal based on the pulse control signal generated by the pulse signal generator 26c to the MOSFET gate of the MOSFET inverter circuit of the high frequency inverter power supply 26a. Thereby, the coil current is amplitude-modulated by the pulse control signal from the pulse signal generator 26c to relatively increase or decrease the amplitude, and the coil current is reduced, for example, as in the rectangular wave 102 shown in FIG. Pulse modulation can be performed. By pulse-modulating the coil current, the modulation induction thermal plasma flame 100 can be periodically changed into a high temperature state at a predetermined time interval and a low temperature state in which the temperature is lower than the high temperature state. In the high frequency modulation induction thermal plasma generator 14, a thermal plasma flame can be generated by simply supplying a high frequency current to the high frequency oscillation coil 16b.
For example, when the raw material powder is supplied intermittently, if the raw material powder is supplied in synchronization with the high temperature state of the plasma, the raw material powder is completely evaporated at the high temperature state to be mixed in the gas phase state. The evaporated raw material powder can be rapidly cooled without supplying the raw material powder.

Note that in the rectangular wave 102 shown in FIG. 4, the current amplitude is defined as a high value (HCL) and a low value (LCL) with respect to the coil current. The time taken 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).
In the rectangular wave 102, the on time, the off time, and one cycle are all preferably on the order of microseconds to several seconds.

  Furthermore, when amplitude-modulating the coil current using the pulse control signal, it is preferable to amplitude-modulate using a predetermined waveform, for example, a rectangular wave. Needless to say, the waveform is not limited to a rectangular wave, and a waveform including a repetitive wave including a curve including a triangular wave, a sawtooth wave, a reverse sawtooth wave, or a sine wave can be used.

The intermittent supply unit 22 is for intermittently supplying the raw material into the plasma torch 16. The intermittent supply unit 22 includes a trigger circuit 22a, an electromagnetic coil 22b, and a valve 22c.
The trigger circuit 22a is connected to the pulse signal generator 26c, receives a pulse control signal from the pulse signal generator 26c, and generates a TTL level signal in synchronization with the input pulse control signal. is there.
The electromagnetic coil 22b is connected to the trigger circuit 22a, and opens and closes the valve 22c based on a TTL level signal from the trigger circuit 22a.

The valve 22c controls, for example, the entry of the raw material for producing fine particles supplied together with the carrier gas from the raw material supply unit 12 into the plasma torch 16, and the opening and closing is controlled by the electromagnetic coil 22b as described above. The Thereby, a raw material is supplied intermittently.
In the present embodiment, the pulse control signal 104 shown in FIG. 5A is output from the pulse generator 26c, and a TTL level signal synchronized with the pulse control signal 104 is generated by the trigger circuit 22a. Based on the TTL level signal, the valve 22c is opened and closed at a predetermined time interval at the timing shown in FIG. As a result, the raw material is intermittently supplied into the plasma torch 16 as shown by a waveform 108 shown in FIG.

The plasma spectroscopic analysis unit 28 performs spectroscopic analysis on the modulated induction thermal plasma flame 100 in the plasma torch 16, and measures the spectral intensity of the modulated induction thermal plasma flame 100, for example. The plasma spectroscopic analysis unit 28 includes an optical system 28a, a spectroscope 28b, and a PMT 28c. The spectroscope 28b and the PMT 28c are connected, and the PMT 28c is connected to the DSP 30.
The optical system 28a includes a lens 29a and a light guide portion 29b such as an optical fiber. The light of the plasma flame enters the light guide 29b through the lens 29a.
The spectroscope 28b is connected to the light guide unit 29b, and when the radiated light of the modulated induction thermal plasma flame 100 is inputted, the radiated light of the modulated induced thermal plasma flame 100 is dispersed at a predetermined time interval. .

The PMT 28c has a photomultiplier tube. When the spectrum of the radiated light of the modulation induction thermal plasma flame 100 is input at a predetermined time interval, it is amplified to a predetermined magnification and output to the DSP 30. It is.
In the plasma spectroscopic analysis unit 28, for example, a spectral spectrum of the modulation induction thermal plasma flame 100 shown in FIG. 6 is obtained.

The DSP 30 is for performing feedback control based on the result of the spectroscopic analysis so that the raw material supply and the plasma modulation timing coincide with each other.
The DSP 30 is input from the PMT 28c, for example, based on the spectrum of the modulation induction thermal plasma flame 100 shown in FIG. The strength of the In this case, if the raw material is Ti powder and is processed in an oxygen atmosphere, the intensity of light having a wavelength derived from Ti and TiO is required.

  The DSP 30 calculates the amount of timing deviation between the pulse control signal output from the high frequency modulation induction thermal plasma generator 14 and the emission intensity of the light having the wavelength derived from the raw material. Further, based on this timing shift amount, the phase of the pulse control signal supplied to the MOSFET gate of the MOSFET inverter circuit of the high frequency inverter power supply 26a of the high frequency induction thermal plasma generator 14, the high level time, the low level time, etc. Provide a signal that makes That is, a signal is supplied so that the length of the on time, the length of the off time, and the duty ratio in the rectangular wave 102 are appropriate. Thereby, the supply timing of a raw material can be made into the high temperature state, ie, ON time, of the modulation | alteration induction thermal plasma flame 100. FIG.

  In the present embodiment, feedback control is performed on the timing of the high temperature state and the low temperature state of the modulation induction thermal plasma flame 100. However, the present invention is not limited to this, and the opening / closing timing of the valve 22c may be controlled. Good. In this case, the DSP 30 is connected to the trigger circuit 22a. Then, the DSP 30 creates a TTL level signal created by the trigger circuit 22a based on the amount of deviation, that is, a signal that shifts the phase of the input signal to the electromagnetic coil 22b, and sends this signal to the trigger circuit 22a. Supply. Thereby, the supply timing of the raw material can be set to the high temperature state of the thermal plasma flame, that is, the on-time.

In the manufacturing apparatus 10 of the present embodiment, high frequency modulation induction thermal plasma generation is performed without operating the plasma spectroscopic analysis unit 28 and the DSP 30, that is, without performing feedback control based on the emission spectrum of the modulation induction thermal plasma flame 100. The coil current can be amplitude-modulated by the section 14, and the raw material can be intermittently supplied by the intermittent supply section 22 in synchronization with this modulation.
Further, in the manufacturing apparatus 10 of this embodiment, the high frequency modulation induction thermal plasma generation unit 14 does not amplitude-modulate the coil current, that is, the temperature of the modulation induction thermal plasma flame is kept constant, and the intermittent supply unit 22 It is also possible to intermittently supply the raw materials by operating only.

Next, the method for producing fine particles of the production apparatus 10 of the present embodiment will be described by taking as an example the production of TiO ₂ fine particles using Ti particles as a raw material.

A carrier gas, for example, Ar gas, subjected to extrusion pressure is supplied to a valve 22c from a pressure gas supply source (not shown) in the raw material supply unit 12 together with Ti particles that are raw materials for producing fine particles. At this time, the valve 22 c is kept closed, and Ti particles are not supplied into the plasma torch 16.
Next, in the high frequency modulation induction thermal plasma generation unit 14, a pulse control signal is output from the pulse signal generator 26 c to the FET gate circuit 26 d and the trigger circuit 22 a of the intermittent supply unit 22.

Next, a modulation signal based on the pulse control signal is output from the FET gate circuit 26d to the high-frequency inverter power supply 26a, and the coil current supplied to the high-frequency oscillation coil 16b is pulse-modulated as a rectangular wave 102 shown in FIG. .
At this time, as the plasma gas, for example, a mixed gas of argon gas and oxygen gas is supplied from the plasma gas supply unit 32 into the plasma torch 16. Due to the pulse-modulated coil current, the modulation induction thermal plasma flame 100 periodically becomes a high temperature state and a low temperature state at predetermined time intervals.

  The trigger circuit 22a of the intermittent supply unit 22 together with the high frequency modulation induction thermal plasma generation unit 14 creates a TTL level signal synchronized with the pulse control signal, and the valve 22c is operated by the electromagnetic coil 22b based on the TTL level signal. Opened and closed. Thereby, Ti particles and Ar gas are intermittently supplied to the modulation induction thermal plasma flame 100 in the plasma torch 16 according to the pulse control signal.

In the present embodiment, since the modulation signal of the high frequency modulation induction thermal plasma generator 14 and the opening / closing signal of the valve 22c are created using a common pulse control signal, the modulation induction thermal plasma flame 100 is in a high temperature state. In addition, a TTL level signal is generated so that Ti powder is supplied together with Ar gas and is not supplied when the modulated induction thermal plasma flame 100 is in a low temperature state. Thereby, the modulated induction thermal plasma flame 100 in a high temperature state evaporates Ti powder into a gas phase mixture, oxygen gas is contained in the plasma gas, and the evaporated Ti is rapidly cooled in a low temperature state. Formation of TiO ₂ is promoted.
Immediately thereafter, the mixture is quenched from the upstream chamber 18a into the downstream chamber 18b downstream thereof, and TiO ₂ particulates are generated. That is, the downstream chamber 18b downstream from the upstream chamber 18a functions as a cooling tank.
At this time, it is desirable to prevent the TiO ₂ 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.
Further, by being sucked by the vacuum pump 20 b, the generated TiO ₂ fine particles are recovered while remaining on the surface of the filter 20 a provided downstream of the chamber 18.

  In the present embodiment, the radiation light of the modulation induction thermal plasma flame 100 is spectrally analyzed by the plasma spectroscopic analysis unit 28. The radiated light of the modulated induction thermal plasma flame 100 is input to the spectroscope 28b by the optical system 28a, and is split at a predetermined time interval by the spectroscope 28b, and the obtained spectral spectrum is amplified by the PMT 28c to a predetermined magnification. , And output to the DSP 30.

In the DSP 30, for the light having the wavelength of the substance derived from the raw material, in this case, Ti particles are used and O ₂ gas is used for the plasma gas. Therefore, for the light having the wavelength derived from Ti and TiO, for example, FIG. As shown in (b), the time change of the Ti radiation intensity represented by the curve 110 and the time change of the TiO radiation intensity represented by the curve 112 are obtained.
When the time variation of the Ti radiation intensity (curve 110) and the time variation of the TiO radiation intensity (curve 112) shown in FIG. 7B are compared with the input waveform signal of the valve shown in FIG. The radiant intensity of Ti and the radiant intensity of TiO are higher when the valve 22c is closed than when the valve 22c is open. This indicates that Ti particles are not supplied into the plasma torch 16 when the modulated induction thermal plasma flame is in a high temperature state.

  In this case, the minimum values of Ti radiation intensity and TiO radiation intensity are about 6 ms, and the maximum values of Ti radiation intensity and TiO radiation intensity are about 13 ms. For this reason, the DSP 30 determines that the deviation of the timing at which the plasma flame reaches a high temperature is, for example, about 7 ms. This 7 ms shift time is the shift amount.

  The DSP 30 supplies a signal that shifts the phase of the pulse control signal supplied to the MOSFET gate of the MOSFET inverter circuit of the high-frequency inverter power supply 26a of the high-frequency induction thermal plasma generator 14 by, for example, 7 ms. Thus, for example, the high temperature state and the low temperature state of the modulation induction thermal plasma flame 100 so that the time variation of the Ti radiation intensity represented by the curve 110a and the time variation of the TiO radiation intensity represented by the curve 112a are obtained. The timing of the temperature state is feedback-controlled.

In this way, by performing spectroscopic analysis of the modulated induction thermal plasma flame 100 and performing feedback control, Ti powder can be supplied when the modulated induction thermal plasma flame 100 is in a high temperature state. For this reason, fine TiO ₂ fine particles having a narrow particle size distribution width can be obtained with high efficiency.

In the present embodiment, feedback control is performed on the timing of the high temperature state and the low temperature state of the modulation induction thermal plasma flame 100. However, the present invention is not limited to this, and the opening / closing timing of the valve 22c may be controlled. Good. In this case, the DSP 30 supplies a signal that shifts the phase of the TTL level signal generated by the trigger circuit 22a, that is, the phase of the input signal to the electromagnetic coil 22b, for example, 7 ms, and outputs it to the trigger circuit 22a. To do. Thereby, the supply timing of the raw material powder and the modulation timing of the plasma flame can be matched to supply the Ti powder when the thermal plasma flame is in a high temperature state. Even in this case, fine TiO ₂ fine particles having a narrow particle size distribution width can be obtained with high efficiency.

In the fine particle production method, fine particles can be produced by intermittently supplying only the raw material powder without amplitude modulation of the coil current, that is, with the temperature state of the thermal plasma flame being constant. In this case, TiO ₂ fine particles having a fine and narrow particle size distribution width can be obtained with high efficiency as compared with the conventional one in which the temperature state of the thermal plasma flame is constant and Ti powder is continuously supplied. .

Further, in the method for producing fine particles, the temperature state of the thermal plasma flame can be periodically changed between a high temperature state and a low temperature state without feedback control, and fine particles can be produced by intermittently supplying only the raw material powder. it can. In this case, TiO ₂ fine particles that are fine and have a narrow particle size distribution width can be obtained with high efficiency as compared with the case where the temperature of the thermal plasma flame is constant and Ti powder is intermittently supplied.

  In this embodiment, Ti powder is used as a raw material and dispersed with a carrier gas. However, the present invention is not limited to this, and the raw material may be a slurry or a colloidal liquid. Examples of the slurry or colloidal liquid include those in which Ti particles are dispersed or turbid in a dispersion medium. In this case, a liquid raw material supply apparatus 90 shown in FIG. This liquid raw material supply apparatus 90 is connected to the valve 22c using piping or the like.

  The liquid raw material supply device 90 is a container 94 for containing the slurry 92 (colloid liquid), an agitator 96 for stirring the slurry 92 in the container 94, and a high pressure applied to the slurry 92 (colloid liquid) to supply it to the valve 22c. It has a pump 98 and a spray gas supply source (not shown) for making the slurry 92 (colloid liquid) into droplets. Then, the slurry 92 (colloidal liquid) formed into droplets by the spray gas to which the extrusion pressure is applied is supplied into the plasma torch 16 through the valve 22c.

  In the present embodiment, the raw material may be a solution obtained by dissolving the raw material in a solvent. Also in this case, the liquid raw material supply apparatus 90 is used in the same manner as the above-described slurry or colloidal liquid. Even in this case, the solution in which the raw material is dissolved, which is formed into droplets by the spray gas to which the extrusion pressure is applied, is supplied into the plasma torch 16 through the valve 22c.

In this embodiment, Ti particles are oxidized to produce TiO ₂ fine particles as an example, but particles of other elements are used as raw materials for fine particle production, and their oxides, metals, and nitrides are used. It is also possible to produce fine particles such as products and carbides.

  For example, the raw material is not limited as long as it can be evaporated by a thermal plasma flame, but the following are preferable. That is, a simple oxide containing at least one selected from the group consisting of the elements of atomic numbers 3 to 6, 11 to 15, 19 to 34, 37 to 52, 55 to 60, 62 to 79, and 81 to 83, and a composite An oxide, a double oxide, an oxide solid solution, a metal, an alloy, a hydroxide, a carbonate compound, a halide, a sulfide, a nitride, a carbide, a hydride, a metal salt, or a metal organic compound may be appropriately selected.

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

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

For example, as a single oxide, titanium oxide (TiO ₂ ), zirconium oxide (ZrO ₂ ), calcium oxide (CaO), silicon oxide (SiO ₂ ), aluminum oxide (alumina: Al ₂ O ₃ ), silver oxide (Ag) ₂ O), iron oxide, magnesium oxide (MgO), manganese oxide (Mn ₃ O ₄ ), yttrium oxide (Y ₂ O ₃ ), cerium oxide, samarium oxide, beryllium oxide (BeO), vanadium oxide (V ₂ O ₅₎ ), Chromium oxide (Cr ₂ O ₃ ), barium oxide (BaO), and the like.

The composite oxides include lithium aluminate (LiAlO ₂ ), yttrium vanadate, calcium phosphate, calcium zirconate (CaZrO ₃ ), lead titanium zirconate, iron iron oxide (FeTiO ₃ ), and cobalt cobalt oxide (CoTiO ₃ ). As a double oxide, barium stannate (BaSnO ₃ ), (meth) barium titanate (BaTiO ₃ ), lead titanate (PbTiO ₃ ), solid solution of zirconium oxide and calcium oxide in barium titanate And so on.
Further, Zr (OH) ₄ as a hydroxide, CaCO ₃ as a carbonate compound, MgF ₂ as a halide, ZnS as a sulfide, TiN as a nitride, SiC as a carbide, TiH ₂ as a hydride. Etc.

  The present invention is basically configured as described above. The fine particle production apparatus and fine particle production method of the present invention have been described above in detail. However, the present invention is not limited to the above-described embodiment, and various improvements or modifications can be made without departing from the gist of the present invention. Of course it is also good.

Examples of the method for producing fine particles of the present invention will be specifically described below.
In this example, the production apparatus 10 shown in FIG. 1 was used for the production of fine particles.
Table 1 below shows experimental conditions common to Experimental Examples 1 to 9 shown below.

As experimental conditions, the average input to the plasma was fixed at 20 kW, Ar gas + O ₂ gas was used as the plasma gas, the total flow rate was 100 L / min (converted to the standard state, the same applies hereinafter), and the flow rate composition was Ar 90% + O ₂ 10%. It was. That is, the flow rate of argon gas was 90 L / min (standard state conversion), and O ₂ gas was 10 L / min (standard state conversion). Ar gas was used as the carrier gas, and the flow rate was 4 L / min. The internal pressure of the plasma torch 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).

In Example 1, as shown in Table 2 below, production of TiO ₂ fine particles was attempted by the production methods of Experimental Examples 1 to 3 in which the presence / absence of plasma modulation and the raw material supply method were changed.
The current modulation rate (SCL) is defined by the ratio of the coil current amplitude (LCL / HCL × 100 (%)). In Example 1, SCL = 70%.
For intermittent supply, the on time was 12 ms, the off time was 3 ms, and one cycle was 15 ms.

  Regarding the presence or absence of plasma modulation, in the manufacturing apparatus 10 shown in FIG. 1, the case where the coil current was pulse-modulated was “modulated”, and the case where the coil current was not pulse-modulated was “no modulation”. Regarding the raw material supply method, in the case of continuous supply, the electromagnetic valve was kept open, and in the case of intermittent supply, the electromagnetic valve was opened and closed under the above conditions.

  In this example, the average particle diameter and the frequency distribution of the particle diameter were examined using SEM (scanning electron microscope) for the fine particles obtained in Experimental Examples 1 to 3.

SEM observation results:
9A to 9C show SEM images of the fine particles collected by the filter 20a as a result of experiments for producing fine particles under the experimental conditions of Experimental Examples 1 to 3. FIG. 9A shows an SEM image of Experimental Example 1, FIG. 9B shows an Experimental Example 2, and FIG. 9C shows an SEM image of Experimental Example 3. As a filter 20a, a bag filter (Microtex MT-1000) manufactured by Nippon Filter Industry Co., Ltd. was used.
As shown in FIGS. 9A to 9C, spherical TiO ₂ nanoparticles having a diameter of several tens of nm could be obtained under any of the conditions of Experimental Examples 1 to 3.

Particle size frequency distribution / average particle size:
About Experimental Examples 1-3, 200 particle | grains were extracted randomly using the above-mentioned SEM image obtained, and the particle size frequency distribution was investigated. 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.
The results are shown in FIGS. 10A shows the results of Experimental Example 1, FIG. 10B shows the results of Experimental Example 2, and FIG. 10C shows the results of Experimental Example 3.
Figure 10 (a) ~ (c) is indicative of the frequency distribution and cumulative percentage of particle diameter, shows further the average particle size, also the value of the standard deviation of the d ₅₀ and particle size.

Experimental Example 1 is equivalent to the conventional example, both the average particle diameter, standard deviation of the d ₅₀ and particle size is the largest among the experimental example 1-3.
Experimental example 2 is different from experimental example 1 in that the intermittent supply is performed. Experimental Example 2 had an average particle size, both the standard deviation of the d ₅₀ and particle size smaller than Experimental Example 1. In this way, by intermittent feed, it can be reduced average particle diameter, the standard deviation of the d ₅₀ and particle size.

Experimental example 3 differs from experimental example 1 in that plasma modulation is performed. In Experimental Example 3, the average particle diameter, d _50, and standard deviation of the particle diameter are all smaller than Experimental Example 1 and smaller than Experimental Example 2.

Next, the effects of plasma modulation and raw material input were investigated. In the second embodiment, in the production of the fine particles, the signal of the DSP 30 is connected to the trigger circuit 22a in the production apparatus 10 shown in FIG. As shown in Table 3 below, the production of TiO ₂ fine particles was attempted by the production methods of Experimental Examples 4 to 9 in which the opening / closing timing of the raw material input valve was changed by the presence or absence of plasma modulation, the raw material supply method, and feedback. In Example 2, production of TiO ₂ fine particles was attempted under the same experimental conditions as Example 1 except that the SCL was 80%.

  Experiments on the production of fine particles were performed under the experimental conditions of Experimental Examples 4 to 9, and as a result, the average particle diameter of the fine particles collected by the filter 20a is shown in FIG. In Example 2, the average particle size was determined using an SEM image as in Example 1.

In the example 5 in which the coil current is pulse-modulated and with plasma modulation, and in the example 5 in which the raw material is continuously supplied and in the example 6 in which the valve opening / closing timing is not feedback-controlled in the case of intermittent charging, the average particle diameter of the manufactured fine particles Were almost equivalent.
On the other hand, in the experimental example 7 and the experimental example 8 in which feedback is performed based on the timing of the TiO radiation intensity and the valve opening / closing timing of the raw material introduction is delayed by 6 ms or 8 ms, the average particle diameter is further increased as compared with the experimental example 5. It was possible to produce fine particles with small size. In Experimental Example 9 in which the valve opening / closing timing of starting material charging was delayed by 12 ms, the average particle diameter was larger than in Experimental Examples 7 and 8. This is considered to be because, in the examples shown in FIGS. 7A and 7B, the deviation amount is about 7 ms, but the delay time is 12 ms and the valve opening / closing timing of the raw material introduction is deviated. It is done. However, the average particle size is smaller than that of Example 4 which is merely intermittently supplied.

10 Fine particle production equipment (manufacturing equipment)
DESCRIPTION OF SYMBOLS 12 Raw material supply part 14 High frequency induction thermal plasma generation part 16 Plasma torch 18 Chamber 20 Recovery part 22 Intermittent supply part 24 Water-cooled probe 28 Plasma spectroscopic analysis part 30 DSP
32 Plasma gas supply unit 100 Thermal plasma flame or modulated induction thermal plasma flame

Claims (10)

An apparatus for producing fine particles,
Raw material supply means for intermittently supplying raw materials for fine particle production into the thermal plasma flame,
A plasma torch in which the thermal plasma flame is generated, and the raw material supplied intermittently by the raw material supply means is evaporated by the thermal plasma flame to form a gas phase mixture;
An apparatus for producing fine particles, comprising: plasma generating means for generating the thermal plasma flame inside the plasma torch. The plasma generation means includes a power supply unit that can supply an electric current for generating the thermal plasma flame to a coil provided in the plasma torch and can amplitude-modulate the electric current to the coil.
The plasma generation means periodically modulates the current to the coil to change the temperature of the thermal plasma flame to a high temperature state and a low temperature state where the temperature is lower than the high temperature state. The apparatus for producing fine particles according to claim 1, which generates a time-modulated modulated induction thermal plasma flame.   Spectral analysis means for spectrally analyzing light having a wavelength derived from the raw material with respect to the modulation induction thermal plasma flame, and based on a result of spectral analysis of light having a wavelength derived from the raw material, the raw material is supplied to the plasma generating means. The fine particle according to claim 2, further comprising: a control unit that relatively increases an amplitude of a current to the coil when supplied to the modulated induction thermal plasma flame, and causes the modulated induction thermal plasma flame to be in a high temperature state. Manufacturing equipment. Spectroscopic analysis means for spectrally analyzing light having a wavelength derived from the raw material for the modulation induction thermal plasma flame;
Based on the result of spectral analysis of light having a wavelength derived from the raw material, the raw material supply means has a relatively large current amplitude to the coil, and when the modulation induction thermal plasma flame is in a high temperature state, The fine particle manufacturing apparatus according to claim 2, further comprising a control unit that supplies the raw material to the modulation induction thermal plasma flame.   The said raw material supply means disperse | distributes the said raw material to a particle state, and supplies the said raw material dispersed to the said particle state to the said thermal plasma flame or the said modulation | alteration induction thermal plasma flame intermittently. The fine particle production apparatus according to any one of the above. A method for producing fine particles,
A method for producing fine particles, characterized in that a raw material for producing fine particles is intermittently supplied into a thermal plasma flame, the raw material is evaporated to form a gas phase mixture, and the mixture is cooled to produce fine particles.   The raw material is intermittently supplied to a modulated induction thermal plasma flame in which the temperature state of the thermal plasma flame is time-modulated to periodically change to a high temperature state and a low temperature state where the temperature is lower than the high temperature state. 6. The method for producing fine particles according to 6.   The modulated induction thermal plasma flame is spectrally analyzed for light having a wavelength derived from the raw material, and the raw material is supplied to the modulated induction thermal plasma flame based on the result of spectral analysis of the light having the wavelength derived from the raw material. 8. The method for producing fine particles according to claim 7, wherein the modulation induction thermal plasma flame is at a high temperature.   Spectral analysis of light having a wavelength derived from the raw material for the modulated induction thermal plasma flame, and based on a result of spectral analysis of light having a wavelength derived from the raw material, when the modulated induction thermal plasma flame is in a high temperature state, The method for producing fine particles according to claim 7, wherein the raw material is supplied to the modulation induction thermal plasma flame.   The method for producing fine particles according to any one of claims 6 to 9, wherein the raw material is dispersed in a particle state and intermittently supplied to the thermal plasma flame or the modulation induction thermal plasma flame.