JP7570940B2 - Microparticle manufacturing apparatus, microparticle manufacturing method, and microparticle property control method - Google Patents

Description

The present invention relates to a particle manufacturing apparatus and method for manufacturing a large amount of particles at once using DC thermal plasma, and in particular to a particle manufacturing apparatus and method for manufacturing particles that maintain a stable plasma state for a long period of time and produce particles with stable quality, even when a large amount of raw material is supplied to increase production volume, and a method for controlling the physical properties of the particles.

As an example of fine particles, copper powder has traditionally been widely used as a conductive paste material. In recent years, as fine pitches have become more common in electrical circuits, there has been a demand for finer copper powder for use in conductive pastes.

The finer the copper powder is, to the submicron scale, the more severe the surface oxidation and the higher the pressed powder resistance tends to be. Therefore, when copper powder is used to form a circuit by paste printing and curing, the electrical conductivity becomes poor, and it has been an issue that it cannot be used as a circuit material for components that require reliable electrical continuity.

In order to solve these problems, as disclosed in Patent Document 1, the present inventors developed a method for producing fine particles having a large crystallite diameter, such that the ratio of the crystallite diameter to the volume cumulative particle diameter D50 (crystallite diameter/D50) is 0.15 to 0.60 (μm/μm), even though the fine copper powder has a volume cumulative particle diameter D50 of 0.20 μm to 0.70 μm as measured by a laser diffraction scattering type particle size distribution measuring device.

JP 2016-28176 A

In the method for producing microparticles as disclosed in Patent Document 1, direct current thermal plasma (hereinafter also referred to as "DC plasma") is used. Compared to methods using high frequency plasma, methods using direct current thermal plasma can reduce production costs, but it is difficult to maintain a stable plasma state over the long term, and even if there is no supply of raw material, the plasma light emission state is not necessarily constant and can become unstable. This makes it difficult to stabilize the quality of the produced microparticles, and in some cases, production has had to be stopped.

In addition, if the supply of raw material is increased to increase the production volume of microparticles, the temperature inside the chamber drops accordingly and becomes unstable. For this reason, in order to stabilize the quality of the microparticles, it is desirable to keep the temperature inside the chamber constant by increasing the plasma output, but this is difficult to achieve because there is no easy way to measure the temperature, which serves as an index for controlling the plasma output.

In view of the current situation, the present invention aims to provide a microparticle manufacturing apparatus, a microparticle manufacturing method, and a method for controlling the physical properties of microparticles that can maintain a stable plasma state for a long period of time even when a large amount of raw material is supplied, and can stabilize the quality of the microparticles manufactured, in order to increase the production volume of microparticles.

The present invention was invented to solve the problems in the prior art as described above, and includes, for example, the following aspects:

The fine particle production apparatus of the present invention is an apparatus for producing fine particles, comprising a chamber, a raw material supply device, a plasma gas supply device, a DC plasma torch, a plasma emission analysis device, and a control device,
the fine particle production apparatus is configured to produce fine particles by heating a raw material supplied from the raw material supply device using a direct current thermal plasma generated by applying a predetermined voltage by the DC plasma torch to the plasma gas supplied from the plasma gas supply device, gasifying the raw material, and cooling the raw material in the chamber;
the plasma emission analysis device analyzes the emission of the DC thermal plasma,
The control device is characterized in that it controls at least one of the supply amount of the plasma gas, the plasma output, and the supply amount of the raw material based on the output of wavelength λ resulting from the emission of light from the plasma gas or the raw material measured by the plasma emission analysis device.

In addition, the method for producing fine particles of the present invention includes the steps of: applying a predetermined voltage to a plasma gas using a DC plasma torch to generate direct current thermal plasma to heat a raw material, gasifying the raw material, and then cooling the raw material to produce fine particles;
The present invention is characterized in that at least one of the supply amount of the plasma gas, the plasma output of the DC plasma torch, and the supply amount of the raw material is controlled based on the output of the wavelength λ resulting from the emission of the plasma gas or the raw material.

In addition, the method for controlling physical properties of fine particles of the present invention includes the steps of: applying a predetermined voltage to a plasma gas using a DC plasma torch to generate direct current thermal plasma to heat a raw material, gasifying the raw material, and then cooling the raw material to produce fine particles,
The method is characterized in that at least one of the supply amount of the plasma gas, the plasma output of the DC plasma torch, and the supply amount of the raw material is adjusted based on the output of the wavelength λ resulting from the light emission of the plasma gas or the raw material, thereby controlling the physical properties of the microparticles (e.g., particle size, specific surface area, pore size, etc.) so as to obtain good results during the production of the microparticles.

According to the present invention, the plasma state can be maintained stably for a long period of time even when a large amount of raw material is supplied, so that the quality of the microparticles can be stabilized even when a large amount of raw material is supplied in order to increase the production volume of the microparticles.

FIG. 1 is a schematic diagram for explaining the configuration of a fine particle production apparatus according to the present embodiment. FIG. 2 is a graph showing an example of an emission spectrum of a plasma flame. FIG. 3 is a graph for explaining a method of control based on light emission output. FIG. 4 is a graph for explaining another control method based on light emission output. FIG. 5 is a graph showing the relationship between the specific surface area SSA and the variation σ′. FIG. 6 is a graph showing the change in the variation σ' over time in a specific example. FIG. 7 is a graph for explaining a control method based on a time average value of the output. FIG. 8 is a graph showing the change in σ'/B over time in a specific example.

Hereinafter, embodiments (examples) of the present invention will be described in more detail with reference to the drawings.
FIG. 1 is a schematic diagram for explaining a typical configuration of a fine particle production apparatus according to the present embodiment.

As shown in FIG. 1, the microparticle manufacturing apparatus 10 of this embodiment includes a chamber 12, a collection pot 14, a raw material supply device 15, a plasma gas supply device 18, a DC plasma torch 20, a plasma emission analysis device 22, and a control device 30.

In this microparticle manufacturing apparatus 10, the raw material passes from the raw material supply device 15 through the raw material supply nozzle 17 and into the DC plasma torch 20. In this embodiment, the raw material supply amount adjustment means 16 is configured to adjust the amount of raw material supplied from the raw material supply device 15 to the DC plasma torch 20.

For example, argon (Ar) gas is supplied to the DC plasma torch 20 from the plasma gas supply device 18, and a plasma flame is generated by applying a predetermined voltage to this argon gas (plasma gas) by the DC plasma torch 20. Nitrogen ( _N2 ) or the like may then be mixed in.

In addition, the raw material is gasified in the plasma flame generated by the DC plasma torch 20 and released into the chamber 12, where it is cooled and turned into fine powder, which is then stored and collected in the collection pot 14.

The inside of the chamber 12 is controlled by a pressure regulator (not shown) to maintain a negative pressure relative to the raw material supply nozzle 17, and is designed to stably generate a plasma flame. It is also possible to keep the inside of the chamber 12 at atmospheric pressure.

In the microparticle manufacturing device 10 of this embodiment, an observation window 13 is provided in the chamber 12, and the light emission from the plasma flame is observed through this observation window 13 by the plasma light emission analyzer 22.

The plasma emission analyzer 22 includes a collimator lens 23 , an optical fiber 24 , a spectroscope 25 , and a spectrum processing unit 26 .
When the light emitted from the plasma flame is input to the spectroscope 25 via the collimator lens 23 and the optical fiber 24, the spectroscope 25 measures the electromagnetic wave spectrum (emission spectrum) of this light emission. Here, the electromagnetic waves assumed are not particularly limited, but examples of the wavelength range include 200 nm to 4000 nm, and particularly 200 nm to 1700 nm. The measured emission spectrum is sent to the spectrum processing unit 26, which obtains an output at a predetermined wavelength as described below and transmits this to the control device 30.

The control device 30 is configured to control at least one of the amount of plasma gas supplied by the plasma gas supply device 18 (gas flow rate), the output of the DC plasma torch 20, and the amount of raw material supplied by the raw material supply device 15, based on the output at a specified wavelength sent from the spectral processing unit 26.

The raw materials used in such a microparticle manufacturing device 10 are appropriately selected depending on the microparticles to be manufactured, and are not particularly limited, but may contain at least one element component selected from, for example, Cu, Si, Ni, Ti, Fe, Co, Cr, Mg, Mn, Mo, W, Ta, In, Zr, Nb, B, Ge, Sn, Zn, Bi, Ag, etc.

The raw materials used in the microparticle manufacturing device 10 may be in the form of wires, powder, solution, slurry, etc. Below, we will explain the case where a powdered raw material is used as an example.

From a manufacturing standpoint, it is preferable that such raw material powder has a volume cumulative particle size D50 of 3.0 μm or more and 30 μm or less, and particularly 5.0 μm or more and 15 μm or less. The volume cumulative particle size D50 can be measured using a laser diffraction scattering type particle size distribution measuring device.

The shape of the raw material powder may be, for example, dendritic, rod-like, flake-like, cubic, or spherical or nearly spherical, but is not particularly limited. However, from the viewpoint of stabilizing the supply efficiency to the plasma torch, a spherical or nearly spherical shape is preferable.

When using the microparticle manufacturing device 10 to heat the raw material powder, it is preferable to use a mixture of argon and nitrogen gas as the plasma gas and adjust the plasma frame so that it is thick and long in a laminar flow state. By adjusting it in this way, the raw material powder that is fed is instantly gasified in the plasma flame, and sufficient energy can be supplied within the plasma flame, causing nucleation, aggregation, and condensation toward the plasma tail flame to form fine particles, especially fine particles on the submicron order.

Whether the plasma frame is in a laminar flow state can be determined by whether the aspect ratio of the frame length to the frame width (hereinafter referred to as the "frame aspect ratio") is 3 or greater when the plasma frame is observed from the side where the frame width is widest. Specifically, if the frame aspect ratio is 3 or greater, it can be determined that the plasma frame is in a laminar flow state, whereas if the frame aspect ratio is less than 3, it can be determined that the plasma frame is in a turbulent flow state.

Plasma gases used as working gases to generate thermal plasma include argon, hydrogen, nitrogen, helium, etc., and among these, it is preferable to use a mixed gas of argon and nitrogen as described above.

Here, if a mixture of argon gas and nitrogen gas is used, the nitrogen (diatomic molecule) gas can impart greater vibrational energy (thermal energy) to the raw powder particles, making the agglomeration state uniform, resulting in the production of nanoparticles with a sharper particle size distribution.

The ratio of argon to nitrogen in the plasma gas is preferably 99:1 to 10:90 in terms of flow rate, more preferably 95:5 to 60:40, and even more preferably 95:5 to 80:20. By keeping the nitrogen content in this range, it is possible to prevent the plasma flame from weakening, and it becomes easier to obtain powder with a sharp particle size distribution.

In addition, from the viewpoint of making the particle size distribution sharp, in other words, making the (D90-D10)/D50 of the produced microparticles smaller, it is preferable to adjust the ratio of argon to nitrogen in terms of flow rate ratio between 99:1 and 50:50, and especially between 95:5 and 50:50, so that the flow rate of argon is higher than that of nitrogen.

When producing oxide particles, oxygen can be added to the plasma gas. It is preferable to set the oxygen content appropriately depending on the oxide particles to be produced.

Here, D10, D50, and D90 of the fine particles are respectively D10, D50, and D90 based on the volume-based particle size distribution obtained by measuring using a laser diffraction scattering particle size distribution measurement method. In addition, (D90-D10)/D50 of the fine particles is an index showing the sharpness of the particle distribution.

In the microparticle manufacturing apparatus 10 of this embodiment configured as described above, the control device 30 controls the plasma gas supply device 18, the DC plasma torch 20, and the raw material supply device 15 as follows.

In this embodiment, the plasma gas supply device 18 has a gas flow rate adjustment means 19 for adjusting the flow rate of the plasma gas supplied to the DC plasma torch 20. The DC plasma torch 20 also has a plasma output adjustment means 21 for adjusting the plasma output. The raw material supply device 15 also has a raw material supply amount adjustment means 16 for adjusting the amount of raw material supplied. In the present invention, the "plasma output" may be the output of current, the output of voltage, or the magnitude of power, which is the product of the current and the voltage.

The raw material supply amount adjustment means 16, the gas flow rate adjustment means 19, and the plasma output adjustment means 21 are connected to a control device 30, which adjusts at least one of the flow rate of the plasma gas supplied from the plasma gas supply device 18 to the DC plasma torch 20, the plasma output of the DC plasma torch 20, and the amount of raw material supplied from the raw material supply device 15.

When producing microparticles using the microparticle production device 10, the control device 30 controls the gas flow rate adjustment means 19 and the plasma output adjustment means 21 to supply a predetermined amount of plasma gas from the plasma gas supply device 18 to the DC plasma torch 20, and the DC plasma torch 20 is set to a predetermined plasma output to generate a plasma flame.

To ensure that the plasma flame is thick and long in a laminar flow state, the plasma output is preferably 2 kW to 40 kW, and more preferably 4 kW to 15 kW. From the above viewpoint, the gas flow rate of the plasma gas is preferably 0.1 L/min to 20 L/min, and more preferably 0.5 L/min to 18 L/min.

Furthermore, in order to stably maintain the plasma flame in a laminar flow state, it is preferable to maintain the above-mentioned ranges of plasma output and gas flow rate, and to properly maintain the gas flow rate relative to the plasma output (A). For example, when a mixed gas of argon and nitrogen is used as the plasma gas, it is more preferable that the ratio of the sum of the Ar gas flow rate (B) and the _N2 gas flow rate (C), the value calculated by the formula (B+C)/A (unit: L/(min·kW)), is 0.50 to 2.00. In order to obtain the flow rate required for gasifying the raw material powder, the (B+C)/A value is preferably 0.50 or more, and in order to maintain the plasma flame in a stable laminar flow state, it is preferably 2.00 or less.
From this viewpoint, it is particularly preferable to adjust (B+C)/A to be 0.70 to 1.70, and even more preferable to adjust it to be 0.75 to 1.50.

In this state, raw material powder is supplied to the plasma flame from the raw material supply device 15 via the raw material supply nozzle 17, where it is gasified and released into the chamber 12, after which it is cooled and turned into fine particles that are stored and collected in the collection pot 14.

When producing microparticles in this manner, the state of the plasma flame is analyzed by the plasma emission analyzer 22. Then, based on the output of the wavelengths resulting from the emission of the plasma gas or raw material in the emission spectrum of the plasma flame, the control device 30 adjusts at least one of the flow rate of the plasma gas supplied from the plasma gas supply device 18 to the DC plasma torch 20, the plasma output of the DC plasma torch 20, and the supply amount of raw material supplied from the raw material supply device 15.

The wavelength λ originating from the emission of the plasma gas can be determined from the emission spectrum of the plasma flame when no raw material is being supplied. For example, when the emission spectrum is as shown in Figure 2(a), the wavelength λ originating from the emission of the plasma gas (the central wavelength of the spectrum) can be identified as wavelength _λ1 .

Moreover, the wavelength λ originating from the emission of the raw material can be determined from the emission spectrum of the plasma flame immediately after the raw material is supplied to the DC plasma torch 20. For example, when the emission spectrum appears as shown in Fig. 2(b), the wavelength λ originating from the emission of the raw material (the central wavelength of the spectrum) can be identified as wavelength _λ2 .

Based on the output of the wavelength λ resulting from the emission of the plasma gas or raw material thus identified, the flow rate of the plasma gas, the plasma output, and the supply amount of raw material can be controlled as follows. Note that the following embodiment shows an example of controlling the flow rate of the plasma gas, the plasma output, and the supply amount of raw material based on the output of the wavelength λ resulting from the emission of the plasma gas or raw material.

In addition, whether to control based on the output of the wavelength _λ1 derived from the emission of the plasma gas or based on the output of the wavelength _λ2 derived from the emission of the raw material can be appropriately selected in consideration of the correlation with the characteristics of the fine particles as described later.

As the output of the wavelength λ, the value output from the spectrometer 25 may be used as it is, but a differential value obtained by differentiating this value with respect to time, or a second-order differential value obtained by second-order differentiation with respect to time, may also be used. By using such a differential value or second-order differential value, the time change of the output of the wavelength λ becomes more noticeable. It is not limited to a first-order or second-order differential, but it is also possible to perform a higher-order differentiation (third-order, fourth-order, etc.). It is also possible to use a differential value obtained by differentiating the value output from the spectrometer 25 with respect to wavelength, or a second-order differential value obtained by second-order differentiation with respect to wavelength. It is also possible to use a value normalized by dividing the output of the wavelength λ by the output of another wavelength λ'. It is also possible to use such an output of the wavelength λ' at the same time as the time when the wavelength λ is output, or, for example, an initial output before the raw material is supplied. It is also possible to use a value obtained by moving average these values with respect to time. In this specification, such differential values and normalized values are collectively referred to as the "output of the wavelength λ".

(1) Control Based on Light Emission Output When the output of wavelength λ exceeds a preset output threshold, the control device 30 controls the light emission output to fall within the output threshold by increasing or decreasing the flow rate of plasma gas, the plasma output, and the supply amount of raw material.

Here, as the output threshold, for example, multiple outputs Y(t) at which good results are obtained are arbitrarily selected from the time change in the output of wavelength λ obtained by manufacturing microparticles multiple times (hereinafter referred to as "output Y(t)", where t represents time). Then, from N (N is a natural number of 2 or more) Yi(t) (i is a natural number from 1 to N), the average value A(t) is calculated as shown in the following formula (1).

Then, from this average value A(t), the output variation σ(t) obtained by manufacturing the microparticles multiple times is calculated as shown in the following formula (2).

Based on the variation σ(t) calculated in this way, A(t)±n×σ(t) (n is a natural number) can be set as the output threshold. Note that n is not particularly limited, but is preferably set to 3 to 6.

In addition, the "good result" when producing microparticles can be judged, for example, by the duration of production of the microparticles and the characteristics of the produced microparticles. The characteristics of the microparticles are not particularly limited, but may include, for example, image analysis particle size D _SEM , laser diffraction scattering particle size D10, D50, D90, and (D90-D10)/D50 of the microparticles calculated from these, element contents such as O ₂ and N ₂ , X-ray diffraction crystallite size, and specific surface area SSA.

The correlation between the plasma gas flow rate and the output of wavelength λ, the correlation between plasma output and the output of wavelength λ, and the correlation between the supply amount of raw material and the output of wavelength λ vary depending on the type of raw material, the type of plasma gas, the device configuration, etc. Therefore, in order to determine what control should be performed when the output of wavelength λ exceeds the output threshold, it is necessary to determine through testing what correlation the plasma gas flow rate, plasma output, and supply amount of raw material each have with the output of wavelength λ.

For example, if the output threshold is set to A(t) ±3σ(t), as shown in FIG. 3(a), when the output of wavelength λ exceeds the output threshold A(t) + 3σ(t), the control device 30 controls the plasma gas flow rate, plasma output, and raw material supply amount using the gas flow rate adjustment means 19, plasma output adjustment means 21, and raw material supply amount adjustment means 16 so that the output of wavelength λ decreases. This causes the output of wavelength λ to stay within the output threshold.

On the other hand, as shown in FIG. 3(b), when the output of wavelength λ exceeds the output threshold A(t)-3σ(t), the control device 30 controls the plasma gas flow rate, plasma output, and raw material supply rate using the gas flow rate adjustment means 19, plasma output adjustment means 21, and raw material supply rate adjustment means 16 so that the output of wavelength λ increases. This causes the output of wavelength λ to stay within the output threshold.

In this way, by controlling at least one of the plasma gas flow rate, plasma output, and raw material supply amount so that the output of wavelength λ falls within the output threshold, the plasma state can be stabilized, preventing the production of microparticles from being stopped midway and reducing productivity, and also stabilizing the quality of the microparticles produced.

In the above example, the variation is used as a function of time σ(t), but the time average of the variation σ(t) may also be used. In other words, the variation σ(t) can be averaged over time (variation σ) and set as A(t) ±m × σ (m is a natural number). Note that m is not particularly limited, but is preferably set to 3 to 6.

The output threshold can also be a constant value. The constant value can be set arbitrarily with reference to the average value A(t) and the variation σ(t) described above. For example, from the outputs Y(t) of wavelength λ obtained by manufacturing microparticles multiple times, multiple outputs Y(t) when good results are obtained can be selected, and the output threshold can be set so that these outputs Y(t) fall within them.

When the output threshold is set in this manner, for example as shown in FIG. 4(a), if the output of wavelength λ exceeds the upper output threshold, the control device 30 controls the plasma gas flow rate, plasma output, and raw material supply amount using the gas flow rate adjustment means 19, plasma output adjustment means 21, and raw material supply amount adjustment means 16 so that the output of wavelength λ decreases. This causes the output of wavelength λ to stay within the output threshold.

On the other hand, as shown in FIG. 4(b), when the output of wavelength λ exceeds the lower output threshold, the control device 30 controls the flow rate of the plasma gas, the plasma output, and the supply amount of raw material by the gas flow rate adjustment means 19, the plasma output adjustment means 21, and the raw material supply amount adjustment means 16 so that the output of wavelength λ increases. As a result, the output of wavelength λ transitions to fall within the output threshold.

When performing such control, since there is a tendency for the output of wavelength λ to vary significantly immediately after the start of microparticle production (immediately after the raw material is supplied), it is preferable to configure the control device 30 so that a predetermined judgment start time is set and the above-described control begins after this judgment start time has passed.

(2) Control based on output variation σ' The control device 30 acquires the output Y(t) of wavelength λ at regular time intervals, and when the variation σ'(t) of the time change of this output Y(t) exceeds a preset variation threshold, the flow rate of the plasma gas, the plasma output, and the supply amount of raw material are increased or decreased to control the variation σ'(t) to fall within the variation threshold.

Specifically, the variation σ'(t) is calculated by calculating the output difference ΔY(t _j ) from the output Y(t _j ) of wavelength λ at time t _j and the output Y(t _j-1 ) of wavelength λ at time t _j-1 (t _j > t _j-1 ) as shown in the following equation (3).

Such output differences ΔY(t _j ) are calculated multiple times within a predetermined time (judgment time).Then, the standard deviation is calculated from M (M is a natural number of 2 or more) ΔY(t _j ) (j is a natural number from 1 to M), and this standard deviation is set as the variation σ'(t).

By controlling the plasma gas flow rate, plasma output, and raw material supply amount so that the variation σ'(t) calculated in this manner falls within the variation threshold, the plasma state can be stabilized, and the quality of the produced microparticles can also be stabilized.

The variation threshold can be set based on the duration of microparticle production and the characteristics of the microparticles, which are correlated with the variation σ'. For example, the relationship between the variation σ' and the characteristics of the microparticles can be obtained in advance and used for the correlated characteristics of the microparticles. Such a relationship between the output variation σ' and the characteristics of the microparticles will differ depending on factors such as the type of raw material used for the microparticles.

Fig. 5 is a graph showing the relationship between the variation σ' in the output of the plasma gas at wavelength λ ₁ over the entire microparticle production time when microparticles are produced using Cu powder as a raw material, and the SSA of the produced microparticles. Here, SSA is the average value over the entire microparticle production time. As shown in Fig. 5, when Cu is used as the raw material powder, there is a correlation between the variation σ' and the SSA of the microparticles. The approximate equation of the variation σ' and the SSA of the microparticles shown in Fig. 5 is σ' = 187 x (SSA) - 437.61, and the correlation coefficient ^R2 is 0.7624.

In this embodiment, the average values of the variation σ' and SSA were calculated over the entire microparticle production time, but as long as the time ranges for both are the same, they may be calculated over a specified time range that is shorter than the entire microparticle production time.

It is known that a smaller SSA is preferable. For this reason, by arbitrarily setting the upper limit of SSA and setting the variation σ' at this point as the standard variation threshold, it becomes possible to manufacture microparticles whose SSA does not exceed the upper limit.

In this embodiment, only the upper limit of SSA is set, but the lower limit of SSA can also be set as necessary. Furthermore, such thresholds are not limited to SSA, and upper and lower limits can also be set as necessary for other particle characteristics.

(Specific example)
The output Y(t) of the wavelength λ was obtained every second, and ΔY(t _j ) was calculated. The judgment time was set to 300 seconds, and the variation σ′(t) was calculated. The judgment started after 300 seconds had elapsed.
That is, the variation σ'(600) is calculated based on the output Y(301) of the wavelength λ at 301 seconds to the output Y(600) of the wavelength λ at 600 seconds. This is calculated for each acquisition timing of the output Y(t) of the wavelength λ, thereby obtaining the variation σ'(t) from the start to the end of the production of the microparticles. This was performed seven times. The results are shown in FIG. 6.

For example, when the upper limit of the SSA of the fine particles is set to 3.2 m ² /g, the upper limit (variation threshold) of the variation σ′(t) can be set to, for example, 150 from the graph of FIG.
In this case, in Tests 5 and 6 shown in Fig. 6, the variation σ'(t) exceeds 150, and therefore fine particles with good particle size, specific surface area, pore size, etc. cannot be obtained. In the fine particle production apparatus and method of the present invention, at least one of the flow rate of the plasma gas, the plasma output, and the supply amount of the raw material is controlled so that the variation σ' does not exceed the variation threshold value, thereby stabilizing the plasma state and stabilizing the quality of the fine particles produced.

(3) Control based on time average value B of output The control device 30 acquires the output Y(t) of wavelength λ at regular time intervals and calculates the time average value B(t) of this output Y(t). If this time average value B(t) exceeds a preset average output threshold, the flow rate of the plasma gas, the plasma output, and the supply amount of raw material are increased or decreased to control the time average value B(t) to fall within the average output threshold.

Here, the average output threshold can be set based on the duration of microparticle production and the characteristics of the microparticles, which are correlated with the time average value B. For example, the relationship between the time average value B and the characteristics of the microparticles can be obtained in advance and used for the correlated characteristics of the microparticles. Such a relationship between the time average value B of the output and the characteristics of the microparticles will differ depending on factors such as the type of raw material of the microparticles.

When the average output threshold is set in this manner, for example as shown in FIG. 7(a), when the time average value B(t) of the output Y(t) exceeds the upper average output threshold, the control device 30 controls the plasma gas flow rate, plasma output, and raw material supply rate using the gas flow rate adjustment means 19, plasma output adjustment means 21, and raw material supply rate adjustment means 16 so that the output of wavelength λ decreases. As a result, the time average value B(t) of the output Y(t) changes so as to fall within the average output threshold.

On the other hand, as shown in FIG. 7(b), when the time average value B(t) of the output Y(t) exceeds the lower average output threshold, the control device 30 controls the plasma gas flow rate, plasma output, and raw material supply rate by the gas flow rate adjustment means 19, plasma output adjustment means 21, and raw material supply rate adjustment means 16 so that the output of wavelength λ increases. As a result, the time average value B(t) of the output Y(t) changes so as to fall within the average output threshold.

When performing such control, it is preferable to configure the control device 30 to set a predetermined judgment start time, as in the above-mentioned case, and to start the above-mentioned control after this judgment start time has passed.

When calculating the correlation between the time average value B and the characteristics of the microparticles, it may be calculated over the entire microparticle production time, as described above, or, if the time ranges of the two are the same, it may be calculated over a specified time range that is shorter than the entire microparticle production time.

(4) Control Based on Variation σ'/Average Value B The control device 30 acquires the output Y(t) of wavelength _λ1 at regular time intervals, and calculates a value σ'(t)/B(t) by normalizing the variation σ'(t) of the time change of this output Y(t) by the time average value B(t) of the output Y(t). If this σ'(t)/B(t) exceeds a preset σ'/B threshold, the flow rate of the plasma gas, the plasma output, and the supply amount of raw material are increased or decreased so that σ'(t)/B(t) falls within the σ'/B threshold.

Specifically, the time average value B(t) and the variance σ'(t) of the output Y(t) at the judgment time are calculated, and σ'(t)/B(t) is calculated. Note that the variance σ'(t) of the time change of the output Y(t) can be calculated in the same manner as described above.

By controlling the plasma gas flow rate, plasma output, and raw material supply rate so that the calculated σ'(t)/B(t) falls within the σ'/B threshold, the plasma state can be stabilized, and the quality of the produced microparticles can also be stabilized.

Here, the σ'/B threshold value can be set based on the characteristics of the microparticles that are correlated with σ'/B throughout the microparticle production time. The characteristics of the microparticles are not particularly limited, but can include, for example, image analysis particle size D _SEM , laser diffraction scattering particle size D10, D50, D90, and (D90-D10)/D50 of the microparticles calculated from these, element contents such as oxygen and nitrogen, X-ray diffraction crystallite size, SSA, etc., and the relationship between σ'/B and the characteristics can be obtained in advance and used for the characteristics that are correlated. The relationship between the σ'/B of such output and the characteristics of the microparticles varies depending on the type of raw material of the microparticles, etc.

When calculating the correlation between σ'/B and the characteristics of the microparticles, it may be calculated over the entire microparticle production time, as described above, or, if the time ranges for both are the same, it may be calculated over a specified time range that is shorter than the entire microparticle production time.

(Specific example)
σ'(t)/B(t) was calculated from the test data of tests 1 to 7 shown in Fig. 6. The judgment time was 300 seconds, and the judgment started after 300 seconds had elapsed. The results are shown in Fig. 8.

As shown in Figure 6, the variation σ' in tests 5 and 6 was larger than in the other tests, but as shown in Figure 8, when comparing σ'(t)/B(t), the σ'(t)/B(t) in tests 4 and 5 was larger than in the other tests.

In this way, judgment based on the variation σ' and judgment based on σ'/B will give different results. In other words, even if the characteristics of a microparticle make it impossible to judge whether it is good or bad based on the variation σ' alone, it becomes possible to judge whether it is good or bad by using σ'/B, and control can be exercised to manufacture good microparticles.

Furthermore, by combining control based on the time average value B of the output, control based on the variation σ', and control based on σ'/B, it is possible to produce microparticles while controlling multiple characteristics.

Therefore, by controlling the time average value B of the output of wavelength λ resulting from the emission of the plasma gas or raw material, and the variation in time change σ', σ'/B, using at least one of the flow rate of the plasma gas, the plasma output, and the supply amount of raw material, it is possible to produce microparticles with the desired conditions.

In the above example, the amount of plasma gas supplied, the plasma output, and the amount of raw material supplied are controlled when various thresholds are exceeded, but it is also possible to configure the amount of plasma gas supplied, the plasma output, and the amount of raw material supplied to be controlled so that the various thresholds are not exceeded.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to this, and various modifications are possible without departing from the scope of the present invention. In addition, the method of controlling the physical properties of fine particles by the above-mentioned control is also included in the embodiment of the present invention.

REFERENCE SIGNS LIST 10 Fine particle production device 12 Chamber 13 Observation window 14 Recovery pot 15 Raw material supply device 16 Raw material supply amount adjustment means 17 Raw material supply nozzle 18 Plasma gas supply device 19 Gas flow rate adjustment means 20 DC plasma torch 21 Plasma output adjustment means 22 Plasma emission analysis device 23 Collimator lens 24 Optical fiber 25 Spectroscope 26 Spectral processing unit 30 Control device

Claims (13)

A fine particle manufacturing apparatus including a chamber, a raw material supply device, a plasma gas supply device, a DC plasma torch, a plasma emission analysis device, and a control device,
a DC plasma torch is used to apply a predetermined voltage to the plasma gas supplied from the plasma gas supply device to generate DC thermal plasma, which is used to heat the raw material supplied from the raw material supply device, thereby gasifying the raw material, and then cooling the raw material in the chamber, thereby producing fine particles;
the plasma emission analysis device analyzes the emission of the DC thermal plasma,
The control device controls at least one of the supply amount of the plasma gas, the plasma output, and the supply amount of the raw material based on the output of wavelength λ derived from the light emission of the plasma gas or the raw material measured by the plasma light emission analysis device. The control device includes:
The apparatus for producing fine particles according to claim 1, characterized in that when the output of the wavelength λ exceeds a predetermined output threshold, at least one of the supply amount of the plasma gas, the plasma output, and the supply amount of the raw material is controlled. The microparticle manufacturing device according to claim 2, characterized in that the output threshold is A(t) ± n × σ(t) (n is a natural number). Here, A(t) is the average value calculated from the time change in the output of wavelength λ in multiple good results during previous microparticle manufacturing (hereinafter referred to as "output Y(t)", where t represents time), and σ(t) represents the variation calculated from the output Y(t) and the average value A(t). The microparticle manufacturing apparatus according to claim 2, characterized in that the output threshold is A(t) ± m × σ (m is a natural number). Here, A(t) is the average value calculated from the time change in the output of wavelength λ in multiple good results during previous microparticle manufacturing (hereinafter referred to as "output Y(t)", where t represents time), and σ represents the time average value of the variation σ(t) calculated from the output Y(t) and the average value A(t). The microparticle manufacturing device according to claim 2, characterized in that the output threshold is a constant value set in advance. The control device includes:
The microparticle manufacturing apparatus according to any one of claims 1 to 5, characterized in that it is configured to calculate a time average value B(t) of the output of wavelength λ at a predetermined time, and when the time average value B(t) exceeds a predetermined time average threshold, control at least one of the supply amount of the plasma gas, the plasma output, and the supply amount of the raw material. The microparticle manufacturing device according to claim 6, characterized in that the time-averaged threshold value is a value set based on good results obtained during previous microparticle manufacturing. The control device includes:
A microparticle manufacturing apparatus as described in any one of claims 1 to 7, characterized in that it is configured to calculate the variation σ'(t) of the time change in the output of wavelength λ at a predetermined time, and control at least one of the supply amount of the plasma gas, the plasma output, and the supply amount of the raw material when the variation σ'(t) exceeds a predetermined variation threshold value. The microparticle manufacturing device according to claim 8, characterized in that the variation threshold value is a value set based on good results obtained during previous microparticle manufacturing. The control device includes:
The apparatus for producing fine particles described in any one of claims 1 to 9 is configured to calculate a time average value B(t) of the output of wavelength λ at a predetermined time and a variation σ'(t) of the time change, and to calculate the variation σ'(t)/time average value B(t) (hereinafter simply referred to as "σ'(t)/B(t)"), and when σ'(t)/B(t) exceeds a predetermined σ'/B threshold value, to control at least one of the supply amount of the plasma gas, the plasma output, and the supply amount of the raw material. The microparticle manufacturing apparatus according to claim 10, characterized in that the σ'/B threshold value is a value set based on good results obtained during previous microparticle manufacturing. A method for producing fine particles by heating a raw material with a direct current thermal plasma generated by applying a predetermined voltage to a plasma gas using a DC plasma torch, gasifying the raw material, and then cooling the raw material,
A method for producing fine particles, characterized in that at least one of the supply amount of the plasma gas, the plasma output of the DC plasma torch, and the supply amount of the raw material is controlled based on the output of wavelength λ derived from the light emission of the plasma gas or the raw material. A method for producing fine particles by heating a raw material with a direct current thermal plasma generated by applying a predetermined voltage to a plasma gas using a DC plasma torch, gasifying the raw material, and then cooling the raw material,
A method for controlling the physical properties of microparticles, characterized in that at least one of the supply amount of the plasma gas, the plasma output of the DC plasma torch, and the supply amount of the raw material is adjusted based on the output of wavelength λ derived from the light emission of the plasma gas or the raw material, thereby controlling the physical properties of the microparticles to achieve good results during the production of the microparticles.

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