JP6202424B2 - Liquid plasma processing apparatus and liquid plasma processing method - Google Patents

Description

  The present invention relates to an in-liquid plasma processing apparatus and an in-liquid plasma processing method for generating a plasma in a liquid and performing a predetermined process.

Nanoparticles are fine particles having a diameter of about 1 to 100 nm. Because these nanoparticles are different from general-sized solid (bulk) materials, such as their extremely large specific surface area and their unique physical properties due to the quantum size effect, they can be used for research and application in various fields. It is being advanced.
For example, a metal nanoparticle having a small electric resistance value such as gold, silver, or copper can be formed into a paste-like ink with a dispersant or a diluent, thereby forming an electric wiring on an IC substrate or the like. In addition, gold nanoparticles have been found to exhibit catalytic activity for various reactions, and have been put into practical use, for example, as a deodorizing catalyst for toilets.

On the other hand, these gold nanoparticles are known to exhibit excellent catalytic activity when supported on base metal oxides or activated carbon.
Thus, a catalyst in which a desired metal is supported on a specific carrier is referred to as a metal-supported catalyst.
Other specific examples of the metal-supported catalyst include, for example, a platinum metal-supported catalyst using alumina nanoparticles as a support and platinum as a support target. In recent years, this metal-supported catalyst has been used in fuel cells and the like.

By the way, the applicant has applied for a patent for an apparatus for producing metal nanoparticles and a metal-supported catalyst (see, for example, Patent Document 1).
In the in-liquid plasma processing apparatus described in Patent Document 1, nanoparticles are generated based on the following principle. When the tip of an electrode formed using a metal that is a nanoparticle is immersed in a liquid contained in a container and microwaves are applied to the liquid through this electrode, the liquid is near the tip of the electrode. When heated and vaporized, bubbles are generated, and plasma is generated in the bubbles. Further, the tip portion of the electrode evaporates due to the temperature rise, and this electrode material is condensed in the bubbles or in the liquid. Thereby, nanoparticles are generated.

JP 2011-058064 A

In the in-liquid plasma processing apparatus described in Patent Document 1 described above, nanoparticles are generated through the above process.
In this process, the plasma need not be stationary because the plasma only serves as a heat source. On the other hand, the maintenance of bubbles is important and plasma is essential for this. That is, when the bubbles disappear, the tip of the electrode is exposed to the liquid, the temperature rapidly decreases, and cavitation generated at this time generates huge particles with a diameter of several μm class, which are mixed into the nanoparticles. This cavitation phenomenon is considered to be the same phenomenon as droplets in laser ablation.
Such entrainment of large particles causes the quality of the nanoparticles to deteriorate. Therefore, in order to suppress the formation of giant particles, there has been a demand for a technique that makes it possible to maintain a state where bubbles are generated near the tip of the electrode.

  The present invention has been considered in view of the above circumstances, and it is possible to maintain the bubble generation state, prevent the formation of giant particles, and prevent the deterioration of the quality of nanoparticles, and An object is to provide a plasma processing method in liquid.

To this end, liquid plasma processing apparatus of the present invention, in a liquid by generating plasma to a liquid plasma processing apparatus for generating nanoparticles, a container because videos liquid, pulsed a microwave oscillator for outputting a microwave power, Rutotomoni part is immersed in the liquid, in order to generate the plasma in a liquid, the electrode providing a pulsed microwave power output from the microwave oscillator to the liquid And an electrode formed of a material that is heated and evaporated in plasma to form nanoparticles , and the pulsed microwave power is maintained so that the liquid is vaporized and the bubbles are generated by heating. A modulation unit that periodically changes the pulse width of the pulsed microwave power by pulse width modulation so that the pulse frequency of 500 Hz or more is repeated and the bubble repeats expansion and contraction. There configured to include.

In addition, the submerged plasma treatment method of the present invention applies pulsed microwave power to a liquid via an electrode partially immersed in the liquid, generates plasma in the liquid, and heats the electrode in the plasma. In- liquid plasma processing method for generating nanoparticles by evaporation, and the pulse frequency of the pulsed microwave power is 500 Hz or more so as to maintain the state where bubbles are generated by vaporization of the liquid by heating. In other words, the pulse width of the pulsed microwave power is periodically changed by pulse width modulation so that the bubbles repeatedly expand and contract .

  According to the in-liquid plasma processing apparatus and the in-liquid plasma processing method of the present invention, since the bubble generation state is maintained, the formation of giant particles can be prevented. Thereby, since mixing of the giant particle into the nanoparticle can be prevented, deterioration of the quality of the nanoparticle can be prevented.

It is a front view which shows the structure of the in-liquid plasma processing apparatus of embodiment of this invention. It is sectional drawing which shows the structure of a coaxial waveguide exchanger and an in-liquid plasma source. It is a wave form diagram which shows the waveform of a microwave and pulse wave electric power. It is a wave form diagram which shows the waveform of the pulse wave electric power superimposed on the steady output. It is a figure which shows the control of pulse wave electric power, and the change of the magnitude | size of a bubble. It is a figure which shows the change of the pulse wave electric power and the bubble size which carried out PWM modulation. It is a wave form diagram which shows the emission spectrum of the electromagnetic waves radiated | emitted from plasma. It is a graph which shows the relationship between the duty ratio of a pulse wave, and the temperature of an electrode. It is a flowchart which shows the procedure which manufactures a metal nanoparticle with the plasma processing apparatus in a liquid in embodiment of this invention. It is a flowchart which shows the procedure which manufactures a metal carrier with the plasma processing apparatus in a liquid in embodiment of this invention. It is a scanning electron microscope (SEM) image of the platinum nanoparticle obtained by the comparative example. 2 is a scanning electron microscope (SEM) image of platinum nanoparticles obtained in Example 1. FIG. 2 is a scanning electron microscope (SEM) image of platinum nanoparticles obtained in Example 2. FIG.

  Hereinafter, preferred embodiments of an in-liquid plasma processing apparatus and an in-liquid plasma processing method according to the present invention will be described with reference to the drawings.

[In-liquid plasma processing equipment]
First, an embodiment of the in-liquid plasma processing apparatus of the present invention will be described with reference to FIG.
The figure is a front view showing the configuration of the in-liquid plasma processing apparatus of the present embodiment.
In this [in-liquid plasma processing apparatus], the schematic configuration of the in-liquid plasma processing apparatus will be described, and a detailed description of the present invention will be described in detail later in [Principle of the present invention]. .

As shown in FIG. 1, the in-liquid plasma processing apparatus 1 includes a microwave oscillator 10, a waveguide 20, a container 30, an in-liquid plasma source 40, and a temperature measuring unit 50.
Here, the microwave oscillator 10 operates as a pulse wave output unit in the present invention, and includes a magnetron box 11, a microwave power source 12, and a microwave power source controller 13.
The magnetron box 11 outputs the generated microwave as a pulse wave. The microwave generally refers to an electromagnetic wave having a wavelength of 100 μm to 1 m and a frequency of 300 MHz to 3 THz.
The microwave power source 12 supplies power for generating microwaves to the magnetron box 11.
The microwave power supply controller 13 sends a signal to the microwave power supply 12 to adjust and control the output of the microwave.

The waveguide 20 propagates the microwave output from the microwave oscillator 10 to the in-liquid plasma source 40.
A solid circuit such as an isolator 21, a power meter 22, and a tuner 23 can be attached to the waveguide 20.
The isolator 21 absorbs it with a dummy load and converts it into heat so that the microwave reflected from the load does not return to the magnetron again.
The power meter 22 measures the output and reflected microwave power.

The tuner 23 performs load impedance matching. As the tuner 23, there are a three tab tuner and an EH tuner, either of which may be used.
Further, a terminal plunger 24 or the like can be attached to the waveguide 20.
Further, a coaxial waveguide converter 25 is attached to the waveguide 20.
The structure of the coaxial waveguide converter 25 will be described in detail later in (Liquid plasma source).

The container (applicator) 30 is a container for containing a liquid.
The container 30 can be formed of, for example, a resin such as Teflon (registered trademark) or glass. Further, a stainless steel container can be provided outside the Teflon (registered trademark) container 30, or a Teflon (registered trademark) coating can be applied to the inside of the metal container.

The container 30 is charged with a solution for producing metal nanoparticles or a metal carrier.
When producing metal nanoparticles, a solvent such as water is used for the solution.
On the other hand, when producing a metal carrier, a material in which carrier particles are dispersed in the above solvent is used. The carrier includes various ceramics, glass, or carbon materials, and can be appropriately selected according to the purpose and is necessary. The concentration of the carrier can be set in the range of 10% by weight or less with respect to the solvent.
In this state, when plasma is generated in the solution, the electrode metal evaporates due to the heat of the plasma, etc., and is condensed in the bubbles or in the solution to generate metal nanoparticles, which adhere to the carrier and are supported on the metal. Is generated.

The temperature measuring means 50 includes an optical fiber 51, a spectroscope 52, and a temperature management device 53.
The optical fiber 51 is an optical transmission path that receives electromagnetic waves from plasma generated in the vicinity of the distal end portion 42-1 of the electrode 42 and sends the received electromagnetic waves to the spectroscope 52.
The spectroscope 52 obtains an emission spectrum by dispersing the electromagnetic wave.
The temperature management device 53 is an information processing device that operates under program control, and calculates the temperature of the tip portion 42-1 of the electrode 42 based on the emission spectrum obtained by the spectroscope 52. Based on the calculated temperature, the average value of the adjusted pulse wave power is determined and sent to the microwave power supply controller 13.

(Liquid plasma source)
Next, the configuration of the in-liquid plasma source 40 will be described with reference to FIG.
The in-liquid plasma source 40 is an apparatus for supplying the microwave propagating through the waveguide 20 to the liquid stored in the container 30.
As shown in FIG. 2, the submerged plasma source 40 includes a coaxial tube 41, an electrode 42, and a support 43.

The coaxial tube 41 constitutes a part of the coaxial waveguide converter 25 and receives and propagates microwaves from the waveguide 20.
Generally, in the coaxial waveguide converter 25, the waveguide 20 (tube body 25-1) and the coaxial tube 41 are connected orthogonally. For this reason, when the microwave is transmitted from the tubular body 25-1 to the coaxial tube 41, the propagation direction is changed to the orthogonal direction.

The coaxial pipe 41 is formed as a coaxial pipe structure of a coaxial pipe outer conductor 41-1 and a coaxial pipe inner conductor 41-2.
The coaxial pipe outer conductor 41-1 is a tubular member that protrudes outward from the surface of the pipe body 25-1 of the coaxial waveguide converter 25. The central axis direction of the coaxial pipe outer conductor 41-1 is perpendicular to the central axis of the tubular body 25-1 of the coaxial waveguide converter 25.
The inner diameter of the coaxial pipe outer conductor 41-1 is sized such that the characteristic impedance is 50Ω.
The characteristic impedance can be changed according to the inner / outer diameter ratio of the tube. It is also possible to adjust to match the load (plasma).

A cap-shaped support 43 is attached to the projecting direction end of the coaxial tube outer conductor 41-1 (the end of the coaxial waveguide converter 25 not connected to the tube 25-1). The opening of the projecting direction end of the coaxial pipe outer conductor 41-1 is closed.
In the support body 43, a circular hole 43-1 is formed in the center of the cap-shaped top plate portion. Moreover, the heat-resistant member 43-2 is attached to the position surrounding this hole 43-1.
The heat-resistant member 43-2 prevents the support 43 from being worn out by the plasma heat and increasing the diameter of the hole 43-1. Similar to the electrode 42, the heat-resistant member 43-2 can be formed of a metal (for example, gold or platinum) that is desired to generate nanoparticles.

An annular sealing member 44 and an annular insulating member 45 are fitted inside the cap-shaped support body 43 to prevent liquid from flowing into the coaxial tube 41 and the waveguide 20. Yes.
The insulating member 45 prevents the sealing member 44 from being directly exposed to plasma and being thermally damaged. Thereby, the lifetime of the sealing member 44 is extended, and the life of the in-liquid plasma source 40 can be extended.
As a material of the sealing member 44, for example, plastic can be used. Moreover, as a material of the insulating member 45, for example, ceramic can be used.

The coaxial pipe inner conductor 41-2 is formed in a cylindrical shape, and is disposed coaxially with the coaxial pipe outer conductor 41-1 in the hollow interior of the coaxial pipe outer conductor 41-1.
One end (container 30 side) of the coaxial pipe inner conductor 41-2 is formed in a tapered conical shape, and is in contact with the inner surface of the top plate portion of the support 43.
The other end of the coaxial tube inner conductor 41-2 is connected to the outside from a portion of the tubular body 25-1 of the coaxial waveguide converter 25 that faces the portion to which the coaxial tube outer conductor 41-1 is attached. It penetrates.

Inside the coaxial pipe inner conductor 41-2, a rod-shaped electrode 42 and a rod-shaped plunger 41-3 are also arranged in a straight line, and by screwing the plunger 41-3, the electrode 42 The distal end portion 42-1 can be extended from the hole 43-1 of the support body 43 to the outside.
Specifically, a male screw 41-4 is formed on the outer periphery of the plunger 41-3, and is formed on the inner surface of the tube protrusion 25-2 formed at a position covering the outer periphery of the plunger 41-3. Screwed into the female screw 25-3. Then, by screwing the plunger 41-3 toward the inside of the coaxial pipe inner conductor 41-2, the tip in the screwing direction of the plunger 41-3 presses the electrode 42, and the tip 42- of the electrode 42 1 is fed out through the hole 43-1 of the support 43 outward (that is, toward the liquid contained in the container 30).

By providing such a feeding mechanism of the electrode 42, even when the production amount of the metal nanoparticles is large, the tip portion 42-1 of the electrode 42 can be sequentially fed into the liquid to ensure the production amount.
The feeding mechanism of the electrode 42 is not limited to the structure shown in FIG. 2, and any conventionally known and suitable feeding structure can be used. Further, the in-liquid plasma processing apparatus 1 can be provided with a coaxial tube 41 not provided with a feeding mechanism.

The electrode 42 is formed using a metal generated as nanoparticles as a material. Further, as described above, the electrode 42 is formed in a rod shape (cylindrical shape), is coaxial with the coaxial pipe inner conductor 41-2, and is inserted into the coaxial pipe inner conductor 41-2.
A tip portion 42-1 which is a part of the electrode 42 protrudes from the hole 43-1 of the support body 43 to the outside.
And the front-end | tip part 42-1 of the electrode 42 is made into the liquid by immersing the support body 43 of the in-liquid plasma source 40 toward the inside with respect to the liquid level of the liquid stored in the container 30 from above. Immerse in. Thereby, the tip portion 42-1 of the electrode 42 is exposed in the liquid.

So far, the schematic configuration of the in-liquid plasma processing apparatus 1 of the present embodiment has been described.
In the in-liquid plasma processing apparatus 1, by supplying electric power to the liquid stored in the container 30, plasma is generated in the liquid to generate metal nanoparticles or a metal carrier.
Next, electric power supplied to the liquid will be described.

[Supply power to liquid]
The liquid is supplied with electric power for generating plasma in the liquid to generate metal nanoparticles or a metal support.
This power can be supplied by a single microwave having a frequency spectrum of 2.45 GHz, 5.8 GHz, 9.5 GHz, or the like. Thereby, high power supply efficiency becomes possible by optimizing the resonance structure and transmission line impedance.

Further, when the driving power is set to microwaves, the load on the electrode 42 can be reduced. That is, since the microwave is a single frequency, power can be supplied very efficiently.
The microwave can theoretically be made non-reflective. In this case, the power supply efficiency to the load is only the greatest loss of the oscillation efficiency of the magnetron, so the power efficiency is close to 70%. become. This number is very high compared to other methods.

  Furthermore, since microwaves absorb energy with a large relative dielectric constant (about 80) and a large dielectric loss tangent (about 10) of water to generate plasma, such a control of conductivity is unnecessary. It can be applied to many substances without the need for impurities. The fact that water is suitable as a liquid is also a feature for other systems.

As shown in FIG. 3I, the microwave is output in the form of a pulse having a plurality of cycles as one pulse. The reason why the microwave is output in a pulse form in this way is as follows.
For example, when microwave power capable of steady plasma discharge is input to the in-liquid plasma source 40, intense heat is generated by the power and the electrode 42 is destroyed. However, the electric power for generating plasma is high, and the prototype requires a peak power of 2 kW or more. In order to simultaneously realize these conflicting requirements, the power supply needs to be a microwave pulse.
On the other hand, if the pulse width of the microwave pulse is shorter than 1 μsec, the plasma becomes corona discharge, that is, non-thermal equilibrium plasma, the temperature rise is suppressed, and the wear of the electrode 42 is remarkably reduced. However, since the energy given to the liquid becomes small, there is a possibility that the reaction rate becomes slow or the metal nanoparticles and the metal support are not generated depending on the conditions.

FIG. 3 (ii) shows the waveform of the pulse wave power when the microwave is output in a pulse form. This pulse wave power is obtained by ON / OFF control of the microwave output from the microwave oscillator 10.
In addition, the peak value of the applied power is necessary for the generation of plasma, and the temperature control (described later) of the tip portion 42-1 of the electrode 42 is generally an average power. Therefore, as shown in FIG. 4, it is also possible to apply a pulsed microwave superimposed on a steady output (continuous wave CW).
In this case, as a configuration of the in-liquid plasma processing apparatus 1, an oscillator that outputs a pulsed microwave superimposed on a steady output instead of the microwave oscillator 10 is provided as the pulse wave output means of the present invention. it can.

Further, the driving power can be supplied by a direct current pulse instead of the microwave.
In this case, as a configuration of the in-liquid plasma processing apparatus 1, a DC pulse oscillator which is a pulse power source capable of outputting a DC pulse can be provided as the pulse wave output means of the present invention, instead of the microwave oscillator 10.

Thus, power is supplied to the liquid stored in the container 30 by a pulse wave such as a microwave.
The present invention makes it possible to improve the quality of the nanoparticles and increase the yield by controlling the frequency of the pulse wave, the duty ratio, and the like.
Next, the principle of the present invention having such characteristics and the details thereof will be described.

[Principle of the present invention]
The process of generating nanoparticles by plasma in liquid is as follows.
When the current flows through the electrode 42 in which the tip portion 42-1 is immersed in the liquid, the liquid is heated and vaporized, and bubbles are generated around the tip portion 42-1. Moreover, plasma is generated in the bubbles simultaneously with or immediately after the generation of the bubbles. Furthermore, the tip portion 42-1 of the electrode 42 evaporates due to the temperature rise, and the evaporated electrode material is condensed in the bubbles or in the liquid to generate nanoparticles.
The process of generating bubbles by vaporizing the liquid is that when microwaves are used for power supply, the liquids are dielectrically heated by microwaves. When DC pulses are used, Joule heating in which DC current passes through the liquids It becomes.
The generation of bubbles may be a process in which the electrode 42 itself is heated by the current flowing through the electrode 42 and the liquid in contact with the electrode 42 is vaporized.

  In this process, the plasma need not be stationary because the plasma only serves as a heat source. On the other hand, the maintenance of bubbles is important and plasma is essential for this. That is, when the bubbles disappear, the tip portion 42-1 of the electrode 42 is exposed to the liquid, the temperature rapidly decreases, and cavitation generated at this time generates huge particles with a diameter of several μm, which are nanoparticle. Mixed in. This cavitation phenomenon is considered to be the same phenomenon as droplets in laser ablation.

  In such a mechanism of nanoparticle production, the following points can be cited as important points for improving the quality of the nanoparticles and increasing the productivity.

(A) Maintaining the surface of the tip portion 42-1 of the electrode 42 at a temperature at which the vapor pressure is high and does not melt and fall off.
Since the production amount of nanoparticles is limited by the speed at which the vapor of the electrode material diffuses into the bubbles, that is, the evaporation speed, the vapor pressure needs to be increased. Generally, when the temperature is increased, the vapor pressure is increased. However, when the temperature is excessively increased, the electrode 42 is melted and falls off or deforms. It is necessary to maintain the optimum temperature during this period.

(B) Air bubbles always exist around the tip portion 42-1 of the electrode 42.
If the bubbles disappear and the tip portion 42-1 of the electrode 42 comes into contact with the liquid, it cools instantaneously. During that time, granulation stops and giant particles are generated due to cavitation or the like generated at that time. Uniformity decreases. Thereby, the quality of the produced | generated nanoparticle falls. In order to avoid such a situation, it is necessary to maintain the state where the tip portion 42-1 of the electrode 42 is not in contact with the liquid, that is, to always keep bubbles around the tip portion 42-1. is necessary.

  (C) It is considered that the evaporation rate is also accelerated by the bubble temperature and the gas vapor pressure. That is, if the bubble temperature is high and the bubbles stay, the vapor of the electrode material stays in the vicinity of the electrode 42 without condensing, and the evaporation rate decreases. Therefore, it is necessary to replace the bubbles and keep the temperature constant.

From (a), it can be seen that it is important to control the temperature of the tip part 42-1 of the electrode 42, strictly speaking, the nanoparticle material.
However, the power applied to the electrode 42 cannot be adjusted only to maintain the temperature of the electrode 42. This is because microwave power is used to maintain the temperature of the electrode 42 and is used to maintain the plasma.
If only one of them is satisfied, the granulation process may not proceed or the apparatus may be destroyed due to overheating. That is, if the electric power necessary for maintaining the discharge is continuously applied, the temperature at the tip of the in-liquid plasma source 40 may rise too much due to the amount of heat supplied and melt. For this reason, the bubble maintenance and temperature control are individually controlled by supplying power intermittently rather than applying power constantly.

Specifically, the following problems (a) to (c) are solved by realizing the following (I) to (III).
(I) The frequency of the pulse wave is set to a frequency capable of maintaining the state where bubbles are generated.
(II) Pulse width modulation (PWM) is performed on the pulse wave so that the bubble repeats expansion and contraction.
(III) The average value of the pulse wave power is controlled according to the temperature of the tip portion 42-1 of the electrode 42.
The contents of (I) to (III) will be described in order below.

[Pulse wave frequency setting]
As described in (b), it is desirable to create a state in which bubbles always exist around the tip portion 42-1 of the electrode 42 in order to prevent the generation of giant particles.
For example, when the power supply is based on the pulse wave shown in FIG. 3 (ii), the bubble expands when the pulse wave is ON, and contracts when the pulse wave is OFF.
When the OFF time is long, the bubbles disappear after contraction. As can be said from this phenomenon, if the pulse wave is turned on before the bubbles disappear, it is assumed that the bubbles turn into expansion without disappearing. In other words, the OFF time of the pulse wave is the time until the bubble disappears (to be exact, until the bubble that has been generated by the pulse wave switching from ON to OFF until the bubble disappears If the time is shorter than (the time), the bubbles will not disappear and will continue to exist around the tip portion 42-1 of the electrode 42.

Based on this inference, the inventor observed the time until the bubble that had been generated disappeared after starting to contract because the pulse wave was switched from ON to OFF. As a result, a time of 3 msec was observed.
When this observation result is taken into consideration, if the OFF time of the pulse wave is set to a time shorter than 3 msec, the bubbles will not disappear, so that the generation state can be maintained.

However, the 3 msec is the OFF time of the pulse wave and does not include the ON time of the pulse wave, that is, the pulse width.
When the frequency of the pulse wave is set, the period includes the pulse width. If the frequency is set to 333.33 Hz or more, the OFF time can be made shorter than 3 msec regardless of the pulse width.
However, when the frequency of the pulse wave is 333.33 Hz or higher and the frequency is close to 333.33 Hz, the size of the bubbles becomes very small even if they do not disappear completely. If it does so, the front-end | tip part 42-1 of the electrode 42 will contact a liquid and temperature will fall rapidly and a huge particle may arise by ablation.

Therefore, a frequency of 500 Hz or more was obtained as a frequency at which the size of the bubbles can be maintained at a certain size.
In this way, by setting the frequency of the pulse wave to 500 Hz or more, the bubbles always exist around the tip portion 42-1 of the electrode 42 in a state in which the size is maintained at a certain level or more. The situation where the tip portion 42-1 of the electrode 42 contacts the liquid and the temperature rapidly decreases is avoided, the generation of giant particles is suppressed, and the uniformity of the particle size of the generated nanoparticles is ensured. The quality of the nanoparticles is improved. In addition, as described above, while the bubbles continue to exist around the tip portion 42-1 of the electrode 42, the generation of nanoparticles is continued, so that the yield can be increased.

As described above, when the frequency of the pulse wave is set to 500 Hz or more, the size of the bubble is maintained after expanding to a certain size. And after that, the size of the bubbles hardly changes.
FIG. 5 shows a state where the size of the bubbles is maintained. The figure shows the change of the pulse wave power and the state of bubbles when the frequency of the pulse wave is 1 kHz. With reference to the figure, how the bubble size is maintained will be described according to the nanoparticle generation process.
After the plasma plasma source 40 and the tip 42-1 of the electrode 42 are immersed in the liquid, when pulse wave power is applied to the electrode 42, the liquid is heated and vaporized, and the tip 42-1 of the electrode 42 is heated. Bubbles are generated in the surroundings, and plasma is generated therein ((1) in the figure).
Bubbles containing plasma gradually increase, and the electrode metal evaporates, aggregates, and disperses within the bubbles ((2) in the figure). Then, the nanoparticles dispersed in the bubbles are dispersed in the liquid so as to be sucked into the gas-liquid interface ((3) in the figure).

Thereafter, the pulse wave power is switched from ON to OFF (or from strong to weak), but the size of the bubble is maintained with almost no apparent change. During this time, the nanoparticles dispersed in the bubbles are dispersed in the liquid.
Further, after that, when the pulse wave power is switched from OFF to ON (or from weak to strong), plasma is generated in the bubble, and the electrode metal is evaporated and aggregated by the heat, and dispersed in the bubble ((4) in the figure). )).
Thereafter, even if the control of repeatedly switching the pulse wave power between ON and OFF or switching between strong and weak is performed, the size of the bubble is apparently maintained with almost no change (see FIG. 5)).
In this way, by setting the frequency of the pulse wave to 500 Hz or more, the size of the bubbles can be maintained to some extent, so that the generation of giant particles is suppressed and the bubbles are generated. Can continue the production of nanoparticles.

Note that ON / OFF control of the pulse wave power is performed when the power is supplied by the pulse wave or DC pulse shown in FIG. 3 (ii). Further, the strength of the pulse wave power is controlled when the power is supplied by a superimposed wave of the pulse wave and the stationary power shown in FIG.
In addition, when the power supply is based on a superposed wave in which a pulse wave and a steady output are superimposed as shown in FIG. 4, the stationary power is set to a power exceeding the power at which bubbles do not disappear, thereby generating bubbles. Can be maintained.
Furthermore, when the electric power is supplied by a direct current pulse, the bubble generation state can be maintained by setting the frequency to 500 Hz or higher as in the case of the pulse wave shown in FIG. 3 (ii).

[Pulse width modulation of pulse wave]
The bubbles are cooled at the interface with the liquid and are constantly liquefied, so it is considered that the fine particles at the gas-liquid interface are always dispersed in the liquid. Here, even when the bubbles are maintained at a certain size, it is considered that the fine particles are dispersed in the liquid. From (c), it is more likely that the bubbles repeat expansion and contraction. It will promote nanoparticle diffusion into the liquid and is considered effective.
Therefore, the pulse width modulation of the pulse wave was invented as a method for promoting the expansion and contraction of the bubbles.

FIG. 6 shows the relationship between the pulse width modulated pulse wave power and the expansion and contraction of bubbles. With reference to the figure, the change of pulse-wave-modulated pulse wave power and the accompanying change of expansion and contraction of bubbles will be described.
In addition, although the figure (1) has shown the state which the bubble expanded to a certain size, the process until it reaches this state is the same as the process in FIG. 5 (1)-(3). Therefore, the description here is omitted.

After the bubble expands to a certain size ((1) in the figure), when the pulse width modulation is performed on the pulse wave so that the duty ratio gradually decreases, the bubble gradually contracts (same as in FIG. Figure (2)). At this time, the nanoparticles dispersed in the bubbles are dispersed in the liquid so as to be sucked into the gas-liquid interface.
Thereafter, when pulse width modulation is performed on the pulse wave so that the duty ratio gradually increases, the bubbles gradually expand ((3) and (4) in the figure).
Further, after that, when pulse width modulation is performed on the pulse wave so that the duty ratio is gradually reduced, the bubbles gradually contract ((5) in the figure). At this time, the nanoparticles dispersed in the bubbles are dispersed in the liquid so as to be sucked into the gas-liquid interface.

As described above, when the pulse width modulation is performed on the pulse wave, when the duty ratio of the pulse wave gradually decreases, the bubble contracts and the duty ratio of the pulse wave gradually increases. , Bubbles expand. And when a bubble shrink | contracts, the nanoparticle currently disperse | distributed in a bubble is attracted | sucked by the gas-liquid interface, and disperse | distributes to a liquid. Thereby, the diffusion of the nanoparticles from the bubbles into the liquid is promoted. Therefore, the yield of nanoparticles can be increased.
As a result of experiments conducted by the inventor, the yield of nanoparticles increased by an order of magnitude when the pulse width modulation was performed compared to the case where the pulse width modulation was not performed on the pulse wave.

Next, the configuration of the in-liquid plasma processing apparatus 1 for performing pulse width modulation on the pulse wave will be described.
The pulse width modulation is performed by the microwave power controller 13 controlling the duty ratio of the microwave pulse wave power output from the magnetron box 11.
The microwave power supply controller 13 functions as the modulation unit of the present invention, and the variable range of the duty ratio of the pulse wave power and the modulation frequency of the pulse width modulation are set, and according to the set modulation frequency, the pulse By changing the duty ratio of the wave power, the pulse width of the pulse wave is modulated.
As a specific example, for example, as shown in FIG. 6, one period of pulse width modulation (PWM) is 10 msec (modulation frequency 100 Hz), and pulse width modulation can be performed around a duty ratio of 7.7%.

Note that the pulse width modulation shown in FIG. 6 assumes that the power supply is based on the pulse wave power shown in FIG. However, the same pulse width modulation can be performed even when the power is supplied by the superimposed wave power shown in FIG. 4 or by a DC pulse.
Further, although the pulse width modulation of the pulse wave has been described here, frequency modulation can be performed instead of the pulse width modulation within a range in which heating is not excessive. However, in order to maintain the bubble generation state, the frequency of the pulse wave is preferably 500 Hz or more.

[Temperature control of electrode tip]
As described in (a) and (c), managing the temperature of the tip portion 42-1 of the electrode 42 prevents the electrode 42 from melting, falling off, and deforming, and accelerates the evaporation rate of the electrode material. Is important above.
Therefore, in order to measure the temperature of the tip portion 42-1 of the electrode 42, the in-liquid plasma processing apparatus 1 is provided with the temperature measuring means 50, and the microwave power controller 13 determines the average value of the pulse wave power based on the measurement result. By controlling this, the temperature of the electrode 42 was controlled.
This configuration will be described below.

(Temperature measuring means)
The temperature measuring means 50 is a means for measuring the temperature of the tip portion 42-1 of the electrode 42.
Here, in order to control the temperature of the electrode 42, it is necessary to strictly measure the temperature of the tip portion 42-1 of the electrode 42.
Since the microwave is applied to the tip portion 42-1 of the electrode 42 and the area is very small, a normal contact thermometer cannot be used.
As a non-contact type thermometer, there is a type that observes infrared radiation, but in the case of many solvents including water, measurement is difficult due to infrared absorption by the solvent.
In addition, calibration with emissivity is necessary for accurate measurement, and it cannot cope with changes in the situation. In general, the response of an infrared sensor is slow, which can be a problem in this application.
Therefore, the spectroscope 52 obtains a spectrum near the visible light, and calculates the temperature from the black body radiation spectrum. Since this method obtains information from a wide wavelength range, it is resistant to disturbances and can remove the absorption spectrum of the solvent and the emission spectrum from the plasma.

Specifically, as shown in FIG. 1, the end portion of the optical fiber 51 is put into the liquid, and the light receiving portion 54 that is the front end portion thereof is directly opposed to the in-liquid plasma source 40 to obtain an emission spectrum. The light receiving portion 54 is preferably covered with quartz glass or the like so as not to be damaged by plasma.
The position of the light receiving unit 54 is set at a position that does not affect the generation of plasma and is not affected by the turbidity of the solution as much as possible.
Note that a quartz glass rod can be used as a waveguide without using the optical fiber 51.

The spectroscope 52 receives the light incident on the light receiving portion 54 of the optical fiber 51 and obtains a spectrum near the visible light of this light. Then, a signal indicating the obtained spectrum is sent to the temperature management device 53.
The temperature management device 53 acquires a spectral spectrum based on the signal sent from the spectroscope 52, removes various noises, extracts only the black body radiation spectrum, and calculates it. A temperature of -1 is obtained.

In this way, a specific example of processing performed by the temperature management device 53 in order to obtain the temperature of the tip portion 42-1 of the electrode 42 will be described with reference to FIG.
This figure is a waveform diagram showing a plasma emission spectrum including blackbody radiation when the temperature of the electrode 42 is controlled by controlling the duty ratio of the pulse wave power. Specifically, the figure shows the plasma emission spectrum when the duty ratio of the pulse wave power is 15%, 12%, 10%, and 8%. The plasma emission spectrum shown in the figure is that a steady power supply is supplied to a liquid to ignite the plasma, then a pulse power supply (1 kHz, duty ratio 8 to 15%, stable discharge) is supplied, and a rotation speed is 275 rpm using a stirrer. It is the plasma emission spectrum obtained when the liquid was stirred. The distance between the tip portion 42-1 of the electrode 42 and the light receiving portion 54 of the optical fiber 51 was 22 mm.

As shown in the figure, the emission spectrum from the plasma is observed as a steep waveform at around 310 nm, 486 nm, 656 nm, and 777 nm. Moreover, in 400-600 nm, the bright line spectrum from a fluorescent lamp is observed as a steep waveform.
On the other hand, blackbody radiation has a broad spectrum in the vicinity of 500 to 900 nm, and can easily be distinguished from the above-described emission spectrum from plasma.
Therefore, the noise and the black body radiation spectrum can be separated by performing signal processing for removing the emission spectrum from the plasma and the bright line spectrum from the fluorescent lamp as noise.

The value of the black body radiation spectrum changes according to the temperature of the tip portion 42-1 of the electrode 42.
For example, when a gentle slope (slope) in the vicinity of 500 to 700 nm in the black body radiation spectrum shown in FIG. 7 is seen for each waveform, it shifts to the left and right according to the temperature of the tip portion 42-1 of the electrode 42. doing.
Specifically, when the temperature of the tip portion 42-1 of the electrode 42 is increased by increasing the duty ratio of the pulse wave power, the black body radiation spectrum shifts to the left (the photometric value at a specific wavelength, that is, Emission intensity increases). On the other hand, when the temperature of the tip portion 42-1 of the electrode 42 is decreased by reducing the duty ratio of the pulse wave power, the black body radiation spectrum shifts to the right side (the photometric value, that is, the emission intensity at a specific wavelength). Lower).
Therefore, the temperature of the tip portion 42-1 of the electrode 42 can be specified by calculating a black body radiation spectrum at a predetermined wavelength, for example, around 700 nm.
In order to perform this specification, the temperature management device 53 stores a management table in which the temperature of the tip portion 42-1 of the electrode 42 is associated with the photometric value of the black body radiation spectrum at a predetermined wavelength. When the photometric value of the black body radiation spectrum at the wavelength of is calculated, the temperature of the tip portion 42-1 of the corresponding electrode 42 can be obtained with reference to the management table.

(Control of average value of pulse wave power)
When the temperature management device 53 obtains the temperature of the tip portion 42-1 of the electrode 42, the temperature management device 53 specifies the average value of the adjusted pulse wave power.
FIG. 8 is a graph showing the relationship between the duty ratio of pulse wave power and the electrode temperature calculated from the spectrum measured by black body radiation using Planck's law. The electrode temperature shown in the figure is that liquid is supplied at a rotational speed of 275 rpm using a stirrer after supplying a pulse power supply (1 kHz, duty ratio 8 to 15%, stable discharge) after supplying a steady power supply to the liquid and igniting the plasma. Is the electrode temperature obtained when stirring.
The figure shows that changing the duty ratio of the pulse wave changes the average value of the pulse wave power and changes the temperature of the tip portion 42-1 of the electrode 42.

When specifying the average value of the adjusted pulse wave power, the temperature management device 53 is the temperature of the tip portion 42-1 of the electrode 42 calculated by Planck's law based on the emission spectrum from the spectroscope 52. When the measurement electrode temperature is lower than the target electrode temperature, which is the target temperature, the duty ratio higher than the current value is specified, and the pulse wave power when the pulse width modulation is performed according to the specified duty ratio Specify the average value of. On the other hand, when the measurement electrode temperature is higher than the target electrode temperature, the duty ratio lower than the current value is specified, and the average value of the pulse wave power when the pulse width modulation is performed according to the specified duty ratio is obtained. Identify. In the temperature management device 53, the target electrode temperature is preset and stored.
Then, the temperature management device 53 sends the specified average value of the pulse wave power to the microwave power supply controller 13.

The microwave power supply controller 13 controls the microwave power supply 12 so that the average value of the pulse wave power of the microwave output from the magnetron box 11 matches the average value of the pulse wave power received from the temperature management device 53. .
Specifically, the duty ratio of the pulse wave is controlled so that the average value of the pulse wave power shown in FIG. 3 (ii) matches the average value of the pulse wave power received from the temperature management device 53.
Thereby, the temperature of the tip portion 42-1 of the electrode 42 obtained in the temperature measuring means 50 is fed back to the microwave power source 12, the average value of the pulse wave power is controlled, and the tip portion 42-1 of the electrode 42 is controlled. The temperature becomes constant.

When the power supply is based on the pulse width modulation shown in FIG. 6, the temperature can be controlled by adjusting the average value of the duty ratio of the pulse power and controlling the average value of the pulse wave power.
On the other hand, when the power supply is based on the superimposed wave power shown in FIG. 4, the temperature can be controlled by the strength of the steady power or the duty ratio of the pulse power.
Further, although the pulse width modulation of the pulse wave has been described here, frequency modulation can be performed instead of the pulse width modulation within a range in which heating is not excessive. However, in order to maintain the bubble generation state, the frequency of the pulse wave is 500 Hz or more.

  Further, in the above description, the temperature measuring means 50 specifies the average value of the adjusted pulse wave power, and the microwave power supply controller 13 applies the pulse wave based on the specified average value of the pulse wave power. Although the pulse width modulation is performed, the present invention is not limited to this configuration. For example, the temperature measurement unit 50 specifies the duty ratio of the pulse wave for setting the average value of the pulse wave power to a predetermined average value, The microwave power supply controller 13 may be configured to control the average value of the pulse wave power by performing pulse width modulation on the pulse wave based on the specified duty ratio of the pulse wave.

[Liquid plasma treatment method]
Next, the operation (in-liquid plasma processing method) of the in-liquid plasma processing apparatus 1 of the present embodiment will be described with reference to FIGS.
FIG. 9 is a flowchart showing a procedure for generating nanoparticles using the in-liquid plasma processing apparatus 1 of the present embodiment. FIG. 10 is a flowchart showing a procedure for generating a metal carrier using the in-liquid plasma processing apparatus 1 of the present embodiment.
The metal nanoparticle manufacturing method, which is a procedure for generating nanoparticles, and the metal support manufacturing method, which is a procedure for generating a metal support, will be described in order.

(Metal nanoparticle production method)
As shown in FIG. 9, the in-liquid plasma processing apparatus 1 is attached with an electrode 42 made of a metal for which nanoparticles are to be created (step 10).
A liquid such as water is charged as a solvent into the container 30 of the in-liquid plasma processing apparatus 1 (step 11).
The in-liquid plasma source 40 is immersed in the solvent from above the liquid level.
In the microwave power supply controller 13, the frequency of the microwave pulse wave power is set to a frequency (500 Hz or more, specifically, 1 kHz) capable of maintaining the bubble generation state (step 12).
Further, the microwave power supply controller 13 sets the duty ratio of the microwave pulse wave power (or the variable range of the duty ratio) and the modulation frequency (step 13).

The microwave oscillator 10 is turned on, and a microwave is generated by the magnetron box 11. The generated microwave propagates through the waveguide 20 as a pulse wave and is supplied from the in-liquid plasma source 40 to the solvent in the container 30 (step 14).
Thereby, bubbles are generated in the vicinity of the tip portion 42-1 of the electrode 42 due to the temperature rise of the liquid. In addition, plasma is generated in the bubbles (step 15).
Furthermore, the tip portion 42-1 of the electrode 42 evaporates due to the temperature rise, and the evaporated electrode material is condensed in the bubbles or in the solvent to generate nanoparticles (step 16).

The spectroscope 52 of the temperature measuring means 50 analyzes the light received through the optical fiber 51 to obtain an emission spectrum. A signal indicating the emission spectrum is sent to the temperature management device 53.
The temperature management device 53 calculates a black body radiation spectrum based on the emission spectrum, and calculates the temperature of the tip portion 42-1 of the electrode 42 (step 17). Then, the average value of the pulse wave power to be adjusted based on the calculated temperature is specified. The specified average value of the pulse wave power is sent to the microwave power supply controller 13.
The microwave power supply controller 13 controls the microwave power supply 12 based on the specified average value of the pulse wave power, and controls the average value of the microwave pulse wave power output from the magnetron box 11 (step 18). ). Thereby, the temperature of the front-end | tip part 42-1 of the electrode 42 is controlled.

(Metal support manufacturing method)
As shown in FIG. 10, the in-liquid plasma processing apparatus 1 is provided with an electrode 42 formed of a metal for which nanoparticles are to be created (step 20).
A solvent in which carrier particles are dispersed is put into the container 30 of the in-liquid plasma processing apparatus 1 (step 21). The concentration of the carrier is set, for example, in a range of 10% by weight or less with respect to the solvent.
The in-liquid plasma source 40 is immersed in the solvent from above the liquid level.
In the microwave power supply controller 13, the frequency of the pulse wave power of the microwave is set to a frequency (500 Hz or more, specifically, 1 kHz) that can maintain the bubble generation state (step 22).
Further, the microwave power supply controller 13 sets the duty ratio of the microwave pulse wave power (or the variable range of the duty ratio) and the modulation frequency (step 23).

The microwave oscillator 10 is turned on, and a microwave is generated by the magnetron box 11. The generated microwave propagates through the waveguide 20 as a pulse wave, and is supplied from the in-liquid plasma source 40 to the solvent in the container 30 (step 24).
Thereby, bubbles are generated in the vicinity of the tip portion 42-1 of the electrode 42 due to the temperature rise of the liquid. In addition, plasma is generated in the bubbles (step 25).
Furthermore, the tip portion 42-1 of the electrode 42 evaporates due to the temperature rise, and the evaporated electrode material condenses in the bubbles or in the solvent, which adheres to and grows on the carrier dispersed in the solvent, Is generated (step 26).

The spectroscope 52 of the temperature measuring means 50 analyzes the light received through the optical fiber 51 to obtain an emission spectrum. A signal indicating the emission spectrum is sent to the temperature management device 53.
The temperature management device 53 calculates a black body radiation spectrum based on the emission spectrum, and calculates the temperature of the tip portion 42-1 of the electrode 42 (step 27). Then, the average value of the pulse wave power to be adjusted based on the calculated temperature is specified. The specified average value of the pulse wave power is sent to the microwave power supply controller 13.
The microwave power supply controller 13 controls the microwave power supply 12 based on the specified average value of the pulse wave power, and controls the average value of the pulse wave power of the microwave output from the magnetron box 11 (step 28). ). Thereby, the temperature of the front-end | tip part 42-1 of the electrode 42 is controlled.

  The inventor has proved through experiments that the present invention can be carried out and the effects described in the above embodiments can be obtained. The contents of the experiment conducted by the inventor will be specifically described below as examples and comparative examples.

<Comparative example>
An in-liquid plasma processing apparatus 1 having the configuration shown in FIG. 1 was prepared. However, the temperature measuring means 50 (the optical fiber 51, the spectroscope 52, and the temperature management device 53) are not connected.
Water was stored in the container 30 as a liquid, and the in-liquid plasma source 40 was immersed in the liquid from above the liquid level.
A peak applied power of 3500 W was applied to the electrode 42 formed using platinum (Pt) to generate plasma in the liquid, thereby generating platinum nanoparticles.
At this time, the frequency of the pulse wave was 300 Hz, and the duty ratio of the pulse wave was 20%.
In this comparative example, since the temperature measuring means 50 is not connected to the in-liquid plasma processing apparatus 1, the temperature control of the electrode 42 is not performed. Also, no pulse width modulation is performed on the pulse wave.

A scanning electron micrograph (SEM image) of platinum nanoparticles obtained by carrying out this comparative example is shown in FIG.
As shown in the figure, most of the generated particles were giant particles of several μm.
This is because the frequency of the pulse wave is 300 Hz, which is smaller than 333.33 Hz, the tip portion 42-1 of the electrode 42 comes into contact with the liquid due to the disappearance of the bubbles, and the temperature rapidly decreases. This is thought to be because particles were generated.
The particle generation rate was 1 mg / min.

<Example 1>
An in-liquid plasma processing apparatus 1 having the configuration shown in FIG. 1 was prepared. However, the temperature measuring means 50 (the optical fiber 51, the spectroscope 52, and the temperature management device 53) are not connected.
Water was stored in the container 30 as a liquid, and the in-liquid plasma source 40 was immersed in the liquid from above the liquid level.
A peak applied power of 3500 W was applied to the electrode 42 formed using platinum (Pt) to generate plasma in the liquid, thereby generating platinum nanoparticles.
At this time, the frequency of the pulse wave was 1 kHz, and the duty ratio of the pulse wave was 8%.
In the first embodiment, since the temperature measuring means 50 is not connected to the in-liquid plasma processing apparatus 1, the temperature control of the electrode 42 is not performed. Also, no pulse width modulation is performed on the pulse wave.

A scanning electron micrograph (SEM image) of the platinum nanoparticles obtained by carrying out Example 1 is shown in FIG.
As shown in the figure, the generated platinum nanoparticles had a uniform particle size, and no giant particles of several μm were observed.
This is because the frequency of the pulse wave is 1 kHz and is higher than 333.33 Hz. Therefore, since the bubbles are maintained at a certain size, the tip portion 42-1 of the electrode 42 does not come into contact with the liquid, cavitation or the like. It is thought that this is because the generation of giant particles did not occur.

However, the production rate of platinum nanoparticles was 0.07 mg / min. This value was lower than the production rate in Example 2 described below.
This is because the duty ratio of the pulse wave was kept constant at 8%, and the pulse width was not modulated, so that the bubble size did not change apparently and was maintained at a constant size. This is considered to be because the evaporation rate was lowered by maintaining the electrode in a high state and staying, and not condensing the evaporated electrode material.

<Example 2>
An in-liquid plasma processing apparatus 1 having the configuration shown in FIG. 1 was prepared. A temperature measuring means 50 (optical fiber 51, spectroscope 52, temperature management device 53) was connected to the in-liquid plasma processing apparatus 1.
Water was stored in the container 30 as a liquid, and the in-liquid plasma source 40 was immersed in the liquid from above the liquid level.
A peak applied power of 3500 W was applied to the electrode 42 formed using platinum (Pt) to generate plasma in the liquid, thereby generating platinum nanoparticles.
At this time, the frequency of the pulse wave was 1 kHz. The average duty ratio of the pulse wave was 7.7%, the duty ratio fluctuation value was 7.6%, and pulse width modulation was performed with a sawtooth wave having a modulation frequency of 100 Hz. Furthermore, the temperature of the electrode 42 was measured, and based on this temperature, the average value of the pulse wave power was controlled to control the temperature of the electrode 42.

A scanning electron micrograph (SEM image) of the platinum nanoparticles obtained by carrying out Example 2 is shown in FIG.
As shown in the figure, the generated platinum nanoparticles had a uniform particle size, and no giant particles of several μm were observed.
As in the case of Example 1, the frequency of the pulse wave is 1 kHz, which is higher than 333.33 Hz. Therefore, the bubbles are maintained at a certain size. This is considered to be because the generation of giant particles due to cavitation or the like did not occur due to the loss of contact with the liquid.

Moreover, the production rate of platinum nanoparticles was 0.37 mg / min. This value was higher than the production rate in Example 1.
This is because the bubble is repeatedly expanded and contracted by performing pulse width modulation on the pulse wave, and at the same time, the evaporation rate of the electrode material is increased by controlling the temperature of the electrode 42. This is thought to be due to this.

As described above, according to the in-liquid plasma processing apparatus and the in-liquid plasma processing method of the present embodiment, since the bubble generation state is maintained, the formation of giant particles can be prevented. Thereby, since mixing of the giant particle into the nanoparticle can be prevented, deterioration of the quality of the nanoparticle can be prevented.
Further, the yield of nanoparticles can be increased by measuring the temperature of the electrode and performing pulse width modulation of the pulse wave based on the measurement result.

The preferred embodiments of the in-liquid plasma processing apparatus and the in-liquid plasma processing method of the present invention have been described above. However, the in-liquid plasma processing apparatus and the in-liquid plasma processing method according to the present invention are limited only to the above-described embodiments. It goes without saying that various modifications can be made within the scope of the present invention.
For example, in the above-described embodiment, as shown in FIG. 1, the magnetron box, the microwave power source, and the microwave power source controller are shown in different configurations, but the present invention is not limited to the different configurations, and these are integrated. Can do.

In the above-described embodiment, the liquid plasma source is immersed in the liquid from above with respect to the liquid level of the liquid stored in the container. However, the present invention is not limited to this configuration. The tip of the plasma source in liquid can be immersed in the liquid by attaching the plasma source in liquid to the side surface of the container and introducing the liquid into the container.
Further, in the above-described embodiment, as the characteristic pulse wave control of the present invention, [frequency setting of pulse wave], [pulse width modulation of pulse wave], and [temperature control of electrode tip] are performed. Although mentioned, these can be implemented in any combination.

  The present invention can be used in an apparatus for producing metal nanoparticles or a metal support.

1 Plasma treatment equipment in liquid 10 Microwave oscillator (pulse wave output means)
13 Microwave power controller (modulator)
DESCRIPTION OF SYMBOLS 30 Container 42 Electrode 42-1 Tip part 50 Temperature measuring means 51 Optical fiber 52 Spectrometer 53 Temperature calculation apparatus

Claims (3)

An in-liquid plasma processing apparatus for generating nanoparticles by generating plasma in a liquid,
And because of the container matches the liquid,
A microwave oscillator that outputs pulsed microwave power ; and
Rutotomoni part is immersed in the liquid, in order to generate the plasma in the liquid, an electrode providing the pulsed microwave power output from the microwave oscillator to the liquid, the plasma An electrode formed of a material that is heated and evaporated to become the nanoparticles ,
The pulse frequency of the pulsed microwave power is set to 500 Hz or more so as to maintain the state in which bubbles are generated by vaporization of the liquid by heating ,
A liquid plasma processing apparatus , comprising: a modulation unit that periodically changes a pulse width of the pulsed microwave power by pulse width modulation so that the bubbles repeatedly expand and contract . A pulsed microwave power is applied to the liquid through an electrode partially immersed in the liquid to generate plasma in the liquid, and the electrode is heated and evaporated in the plasma to generate nanoparticles. A submerged plasma treatment method comprising:
The pulse frequency of the pulsed microwave power is set to 500 Hz or more so as to maintain the state in which bubbles are generated by vaporization of the liquid by heating ,
The plasma processing method in liquid , wherein the pulse width of the pulsed microwave power is periodically changed by pulse width modulation so that the bubbles repeat expansion and contraction . The electrode is formed using a metal produced as the nanoparticles as a material,
The in-liquid plasma processing method according to claim 2.