JP5472601B2 - In-liquid plasma processing apparatus, metal nanoparticle manufacturing method, and metal carrier manufacturing method - Google Patents

Description

  The present invention relates to an in-liquid plasma processing apparatus, a metal nanoparticle manufacturing method, and a metal support manufacturing method that generate metal nanoparticles or a metal support by plasma in liquid.

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, various production methods of these metal nanoparticles and metal-supported catalysts have been conventionally proposed.
For example, a solution in which a substance composed of a catalytically active component or a carrier (catalyst component) is dissolved is converted into fine droplets by ultrasonic waves, and the droplets are thermally decomposed by plasma energy. Some are precipitated and collected in an aqueous solution (see, for example, Patent Document 1).
According to this, it is possible to produce a fine particle catalyst having superior catalyst performance as compared with the conventional catalyst production methods. In addition, the particulate catalyst can be produced continuously and easily at a low cost. Furthermore, an alloy catalyst or a composite oxide catalyst having a constant composition ratio can be produced without variation between production lots.

On the other hand, many metal-supported catalyst production methods in practical use are liquid-phase chemical reduction methods. Fine particles and ultrafine particles serving as a carrier are dispersed in a metal salt solution, and metal nanoparticles are deposited on the surface of the carrier by a reduction reaction.
When obtaining metal nanoparticles, it is not necessary to use a carrier, and it is used in the production of many metal nanoparticles by using a protective agent in a colloidal form.

In addition, there is a method for purifying a metal-supported catalyst using a reduction reaction by electron beam irradiation. Specifically, a liquid containing iron oxide (Fe ₃ O ₄ ), gold oxide oxide (HAuCl ₄ ), protective polymer, reducing aid (2-propanol), and ultrapure water is placed in a glass bottle, and 4.8 MeV. A metal-supported catalyst is obtained by irradiating 6 kGy of the electron beam.

  Further, it is known that reduction occurs by gamma ray irradiation, ultrasonic vibration, or ultraviolet irradiation instead of electron beam irradiation (see, for example, Patent Documents 2 and 3). Among these, ultrasonic vibration is a simple process that can be easily mass-produced.

JP 2006-87965 A JP 2008-266214 A JP 2008-19162 A

However, the above technique has the following problems.
For example, in the technique described in Patent Document 1, the amount of catalyst generated by one treatment is very small. Specifically, for example, the catalyst activation component nickel nitrate 0.47 [g] and aluminum nitrate 1.77 [g] are dissolved in 100 [cc] water and mixed sufficiently, and then the fine particle catalyst production apparatus is used. As a result of predetermined treatment, the amount of the finished catalyst obtained was 0.5 [g / h].

  Further, the method using a reduction reaction by electron beam irradiation requires an electron beam of 4.8 MeV. The apparatus for obtaining this 4.8 MeV electron beam was large and expensive. Moreover, in many cases, the electron accelerator is about the size of a room or a building, so that it is subject to the ionizing radiation prevention regulations, and a qualified person is required for management.

Furthermore, the chemical reduction method requires a long treatment time of 20 hours.
In addition, in the chemical reduction method, the reducing agent used remains in an oxidized state, or the counter ion of the metal salt used and the ligand of the metal complex remain, and as a result, metal nanoparticles and metal support as impurities The problem of adsorbing on the surface of the material has not been solved.
Even when using an electron beam, a gamma ray, an ultrasonic wave, etc., although a reducing agent is not used, since a metal salt or a complex is used, mixing of impurities is inevitable.

  The present invention has been made to solve the above-described problems, and can reduce the cost and size of the apparatus, and can produce a high-quality metal carrier free from impurities, and An object of the present invention is to provide an in-liquid plasma processing apparatus, a metal nanoparticle manufacturing method, and a metal carrier manufacturing method that can be obtained in a sufficient amount at high speed in a short time.

  In order to achieve this object, the submerged plasma processing apparatus of the present invention is a submerged plasma processing apparatus that generates a metal nanoparticle or a metal carrier by performing a predetermined process on a solution, and a container in which the solution is stored. And a microwave oscillator for outputting microwaves, and an electrode for applying microwaves to the solution to excite plasma in the solution, and this electrode is formed of a metal that becomes nanoparticles by excitation of the plasma It is as.

  Further, the metal nanoparticle production method of the present invention is a submerged plasma treatment method for producing a nanoparticle by performing a predetermined treatment on a solution, and is disposed on a side surface of the container and a step of storing the solution in the container Supplying pulsed microwaves to the electrode whose tip protrudes into the solution, and exciting the plasma with microwaves at the tip of the electrode to crush the electrode, and the material for forming the crushed electrode as nanoparticles And a generating step.

  The method for producing a metal carrier of the present invention is a submerged plasma treatment method for producing a metal carrier by performing a predetermined treatment on a solution, the step of storing a solution in which a carrier is dispersed in a container, and a side surface of the container A step of supplying a pulsed microwave to an electrode whose tip protrudes into the solution, and plasma is excited by the microwave at the tip of the electrode to crush the electrode and form this crushed electrode And a step of supporting the material on the carrier as nanoparticles.

According to the submerged plasma processing apparatus, metal nanoparticle manufacturing method, and metal carrier manufacturing method of the present invention, a large apparatus such as an electron accelerator is not required, and therefore a small submerged plasma processing apparatus can be realized at low cost. .
In addition, since metal salts, complexes, and reducing agents are not used, impurities such as counter ions, ligands, and oxidized reducing agents derived from them are not included, and extremely high-purity metal nanoparticles and metal carriers are obtained. be able to.
Furthermore, since the plasma is generated in the solution by the in-liquid plasma source, the metal nanoparticles and the metal support can be obtained in a sufficient amount at a high speed in a short time.

It is a block diagram which shows the structure of the plasma processing apparatus in a liquid in embodiment of this invention. It is a wave form diagram which shows the waveform of a microwave electric power. It is side surface sectional drawing which shows the structure of a coaxial waveguide and a plasma source in a liquid. It is a perspective view which shows the structure of a supporting member among plasma sources in a liquid. It is side surface sectional drawing which shows the structure of an electrode vicinity among submerged plasma sources. It is side surface sectional drawing which shows the structure of the drawing | feeding-out mechanism of an electrode. It is a flowchart which shows operation | movement of the in-liquid plasma processing apparatus in embodiment of this invention. It is a flowchart which shows other operation | movement of the plasma processing apparatus in a liquid in embodiment of this invention. It is a transmission electron microscope (TEM) image of the metal nanoparticle obtained in the Example. It is a transmission electron microscope (TEM) image of the platinum metal support obtained in the Example.

  Hereinafter, preferred embodiments of an in-liquid plasma processing apparatus, a metal nanoparticle manufacturing method, and a metal carrier manufacturing 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.

As shown in the figure, the in-liquid plasma processing apparatus 1 includes a microwave oscillator 10, a waveguide 20, a container 30, and an in-liquid plasma source 40.
Here, the microwave oscillator 10 includes a magnetron box 11, a microwave power supply 12, and a microwave power supply controller 13.
The magnetron box 11 generates and outputs a microwave.
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.

In FIG. 1, the magnetron box 11, the microwave power source 12, and the microwave power source controller 13 are shown as separate configurations, but are not limited to different configurations, and can be integrated.
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 waveguide 20 propagates the microwave output from the microwave oscillator 10 to the container 30.
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.
The tuner 23 includes a three tab tuner and an EH tuner.
The three tab tuner adjusts the three stubs to maximize the power consumption of the load.
The EH tuner performs tuning by providing plungers at the E branch and the H branch of the waveguide 20 and taking them in and out.
In addition, when implementing the in-liquid plasma processing apparatus 1, you may use any of a three tab tuner and an EH tuner.

The waveguide 20 can be a corner waveguide 24, a terminal plunger 25, or the like.
Furthermore, the waveguide 20 has a coaxial waveguide converter 26.
The structure of the coaxial waveguide converter 26 will be described in detail later in (Liquid plasma source).

The container (applicator) 30 is a container for containing a liquid. Plasma is generated in the liquid stored in the container 30.
A hole 31 (see FIG. 5) for attaching a support 43 (described later) of the in-liquid plasma source 40 is formed in a part of the side surface 32 (see FIG. 5) of the container 30.
As described later, the support body 43 is formed in a cap shape, and includes a skirt portion 43-1 and a top plate portion 43-2. The hole 31 is drilled to a size that allows the top plate portion 43-2 and a part of the skirt portion 43-1 (the vicinity of the top plate portion 43-2) to be fitted.

The container 30 is preferably formed of a resin such as Teflon (registered trademark) or glass, for example. The reason for this is that if the container 30 is made of metal, the stored liquid becomes acidic water, which may cause a battery to cause electrolysis or corrosion.
A stainless steel container can be provided outside the Teflon container 30, or a Teflon coating can be applied to the inside of the metal container. Microwave leakage can be prevented by using a 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 a range of 0.1 to 10% by weight with respect to the solvent.
When plasma in the microwave liquid is generated in this state, the electrode metal is crushed by a reaction such as melting and electrolysis due to the heat and electric field of the plasma, and metal nanoparticles and a metal support are generated.

(Power supplied to liquid)
Next, the power supplied to the liquid (solution) will be described.
The liquid is supplied with electric power for generating plasma in the liquid to generate metal nanoparticles or a metal support.
This power is not a direct current pulse but a microwave having a single frequency spectrum such as 2.45 GHz, 5.8 GHz, and 9.5 GHz band. For this reason, high power supply efficiency becomes possible by optimizing the resonance structure and transmission line impedance.

In the liquid plasma, there is an example of discharge by direct current pulse as a conventional technique.
Since the DC pulse contains a fundamental frequency and an extremely wide range of frequency components that are odd multiples thereof, perfect matching with the transmission line and the load (liquid impedance) is difficult, resulting in a large reflected power and a power supply efficiency to the load. Becomes lower.
On the other hand, the load on the electrode 42 can be reduced by making the driving power microwave.
That is, since the microwave has a single frequency, it becomes possible to supply power very efficiently and to eliminate the electrode such as covering the electrode with a dielectric.
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.

Further, in the direct current pulse, it is necessary to control the conductivity of the liquid. This means that if the conductivity is low, it is necessary to mix an extra electrolyte in the liquid, or if the conductivity is already higher than necessary, plasma cannot be obtained.
On the other hand, since microwaves generate plasma by absorbing energy due to a large relative dielectric constant of water (about 80) and a large dielectric loss tangent (about 10), it is not necessary to control the conductivity. Therefore, it can be applied to many substances without introducing impurities. The fact that water is suitable as a liquid is also a feature for other systems.

As shown in FIG. 2, the microwave power is preferably in the form of a pulse having a plurality of cycles as one pulse.
When microwave power capable of steady plasma discharge is input to the plasma source, 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 required 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 support is not generated depending on the conditions.

(Liquid plasma source)
Next, the configuration of the in-liquid plasma source will be described with reference to FIGS.
FIG. 3 is a cross-sectional view showing the configuration of the in-liquid plasma source. FIG. 4 is a perspective view showing a support member constituting the in-liquid plasma source. FIG. 5 is an enlarged view of an essential part in which the electrodes constituting the plasma source in liquid and the surroundings thereof are enlarged.
In the present embodiment, it is assumed that the coaxial tube 41 of the coaxial waveguide converter 26 is included in the in-liquid plasma source 40.

The in-liquid plasma source 40 is a device for supplying the microwave that has propagated through the waveguide 20 to the liquid.
As shown in FIG. 3, the submerged plasma source 40 includes a coaxial tube 41, an electrode 42, a support 43, a sealing member 44, and an insulating member 45.
The coaxial tube 41 constitutes a part of the coaxial waveguide converter 26 and receives and propagates microwaves from the waveguide 20.
Generally, in the coaxial waveguide converter 26, the waveguide 20 (tube body 26-1) and the coaxial tube 41 are connected vertically. For this reason, when the microwave is transmitted from the tube body 26-1 to the coaxial tube 41, the propagation direction is changed to the vertical direction.

The coaxial pipe 41 is formed in a coaxial pipe structure, and includes 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 26-1 of the coaxial waveguide converter 26. The central axis direction of the coaxial pipe outer conductor 41-1 is perpendicular to the central axis of the pipe body 26-1 of the coaxial waveguide converter 26.
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).

The coaxial pipe inner conductor 41-2 is a rod-like or cylindrical member, and is disposed coaxially with the coaxial pipe outer conductor 41-1 in the hollow of the coaxial pipe outer conductor 41-1.
One end of the coaxial tube inner conductor 41-2 is on the inner surface of the tube 26-1 of the coaxial waveguide converter 26 (the surface facing the portion where the coaxial tube outer conductor 41-1 is attached). It is in contact. An electrode 42 extends from the other end.
The diameter of the coaxial pipe inner conductor 41-2 is 10 mm in the prototype, but 10 mm is not necessarily optimal, and can be changed as appropriate as described above.

A support member 50 is attached to a portion where the coaxial pipe inner conductor 41-2 is in contact with the pipe body 26-1.
As shown in FIGS. 3 and 4, the support member 50 includes a first support member 51 and a second support member 52.
The first support member 51 is formed in the shape of a truncated cone whose top is cut off, and the bottom 51-1 is fitted in the hole 26-2 of the tube 26-1. Further, a through hole 51-3 is formed in a straight line from the center of the bottom portion 51-1 toward the center of the top ridge cross section (the pier surface 51-2). One end of the coaxial waveguide inner conductor 41-2 is fitted into the through hole 51-3.

The reason why the first support member 51 is formed in the shape of a truncated cone is as follows.
The transmission fundamental mode of the rectangular waveguide is a TE mode or a TM mode. On the other hand, the transmission basic mode of the coaxial line is a TEM mode. As described above, although the transmission modes are different between the rectangular waveguide and the coaxial line, the coaxial waveguide converter 26 is able to propagate microwaves by matching them.
Although there are various matching methods, the coaxial waveguide converter 26 according to the present embodiment is matched according to the shape of the first support member 51.
There is a wine glass shape as a known shape for the first support member, but there is a drawback that the processing is difficult because the curved shape is complicated. On the other hand, the 1st support member 51 of this embodiment is a truncated cone, and a process is easy.

In addition, the wine glass type is used for a high power converter such as an average power of 1 MW or a peak power of 1 MW. However, when the high power up to that point is not handled, heat is generated even in the shape of the truncated cone. Therefore, practical matching can be achieved. This was found from the fact that the inventor conducted an electromagnetic field simulation at an average power of 500 W to 1 kW and a peak power of 5 kW, and as a result, an electromagnetic field distribution equivalent to that of a wine glass type was obtained.
Furthermore, as another advantage, since there is no edge on the surface of the first support member 51, discharge can be prevented.
In addition, by providing the three tab tuner 23, further alignment can be achieved.

The second support member 52 has a truncated cone part 52-1 and a screw part 52-2.
The truncated cone part 52-1 is formed in the shape of a truncated cone having a truncated top part, and is linearly formed from the center of the bottom part 52-3 toward the center of the top truncated section (the truncated surface). A through hole 52-4 is formed.
In addition, the truncated cone portion 52-1 is formed with a plurality of slits 52-5 along an inclination (taper), which is a kind of collet chuck. The tooth portion 52-6 between the slits supports the coaxial waveguide inner conductor 41-2 fitted in the through hole 52-4.

The screw part 52-2 is a cylindrical member extending from the bottom part 52-3 of the truncated cone part 52-1, and a male screw 52-7 is formed on the outer periphery. Moreover, the hollow 52-8 of the screw part 52-2 and the through-hole 52-4 of the truncated cone part 52-1 are connected.
On the other hand, a through hole 51-3 is formed in the center of the truncated surface 51-2 of the first support member 51, and a female screw 51-4 is formed in the through hole 51-3. Thereby, the male screw 52-7 of the second support member 52 can be screwed into the female screw 51-4 of the first support member 51, and by this screwing, the through hole 52- 4 and the hollow 52-8 communicate with the through hole 51-3 of the first support member 51.

  The diameter of the outer edge of the truncated surface 51-2 of the first support member 51 is the same as the diameter of the outer edge of the bottom 52-3 of the second support member 52. Thereby, even if the screw portion 52-2 of the second support member 52 is screwed into the female screw 51-4 of the first support member 51, an edge does not appear, so that discharge can be prevented.

As shown in FIG. 5, the electrode 42 has a barrel portion formed in a columnar shape, one end portion formed in a conical shape, and the other end portion of the other end of the coaxial tube inner conductor 41-2. The end is attached. By making one end of the electrode 42 conical, the electric field can be concentrated on the tip 46 and the electric field strength can be increased.
Then, by exposing the tip 46 of the electrode 42 in the liquid, plasma can be generated in this portion.

Since the electrode 42 is pulverized by plasma into nanoparticles, the electrode 42 is made of a metal for which a metal nanoparticle or a metal carrier is desired to produce nanoparticles.
This metal is a metal that does not react with the solvent and has a melting point that is not too high. For example, there are noble metals such as gold and platinum, which do not react with various solvents including water. When the melting point of the metal is high, the production rate of the metal nanoparticles decreases. If a solvent that reacts with these metals is used, a metal compound is formed and nanoparticles may not be produced.

The support 43 is a cap-like member attached so as to cover one end of the coaxial tube outer conductor 41-1 (the end of the coaxial waveguide converter 26 not connected to the tube 26-1). is there.
The support body 43 has a skirt portion 43-1 and a top plate portion 43-2.
The skirt part 43-3 of the skirt part 43-1 is connected to one end of the coaxial pipe outer conductor 41-1.
Of the skirt portion 43-1, the vicinity of the top plate portion 43-2 is exposed to the inside of the container 30 together with the top plate portion 43-2 when fitted into the hole 31 of the container 30. A screw groove 43-4 is formed on the outer periphery of the exposed skirt portion 43-1. The support body 43 is fixed to the side surface 32 of the container 30 by screwing the stop ring 43-5 here.
The top plate portion 43-2 and a part of the skirt portion 43-1 exposed from the hole 31 are immersed in the liquid.

Moreover, the support body 43 has the hollow part 43-6. The hollow portion 43-6 communicates with the hollow of the coaxial waveguide outer conductor 41-1.
The hollow portion 43-6 is formed in a tapered shape so that the inner diameter gradually decreases from the inner surface of the skirt portion 43-1 toward the center of the top plate portion 43-2. And the small hole 43-7 is drilled in the center of the top-plate part 43-2. Thereby, the tip 46 of the electrode 42 slightly protrudes from the hole 43-7.

Furthermore, a heat-resistant member 43-8 is attached to the surface of the top plate portion 43-2 of the support body 43.
The heat-resistant member 43-8 prevents the support 43 from being worn out by the plasma heat and increasing the diameter of the hole 43-7. Similar to the electrode 42, the heat-resistant member 43-8 can be formed of a metal (for example, gold or platinum) for which nanoparticles are desired.

The sealing member 44 is an annular member provided between the inner surface of the support 43 (the side surface of the hollow portion 43-6) and the electrode 42.
The sealing member 44 supports the electrode 42 and prevents the liquid from flowing into the coaxial tube 41.
The insulating member 45 is between the side surface of the hollow portion 43-6 of the support 43 and the electrode 42, and between the sealing member 44 and the hole 43-7 of the top plate portion 43-2 (that is, the container 30). It is an annular member provided between the sealing member 44 and the liquid when the liquid is put into the liquid.
The insulating member 45 has a function of supporting the electrode 42, a function of sealing so that liquid does not enter the coaxial tube 41 and the waveguide 20, and the sealing member 44 is directly exposed to plasma to cause thermal damage. It has a function to prevent receiving. Thereby, the lifetime of the sealing member 44 is extended, and the life of the in-liquid plasma source 40 can be extended.

Here, the sealing member 44 and the insulating member 45 will be further described.
The material of the sealing member 44 needs to be a material that is elastic enough to be deformed and in close contact with the surrounding metal and has a small dielectric loss so as not to generate heat by the microwave. In addition, it is desirable to have a certain degree of heat resistance in order to receive some heat from the plasma.
Therefore, examples of the elastic soft material include rubber, PTFE (Polytetrafluoroethylene), or a soft plastic material. However, these materials generally have a low heat resistant temperature. If these heat-resistant materials are used for this purpose, they will be destroyed in a short time due to radiant heat from plasma, creeping discharge running on the surface, high temperature of the center electrode, etc., resulting in water leakage, mixing of impurities into acidic water, etc. . On the other hand, materials having a high heat-resistant temperature are typically hard materials such as glass and ceramic, and are not suitable for sealing water by being in close contact with metal.

Further, it is conceivable to braze the insulating member 45 using ceramic or the like, but it is not suitable for this purpose.
The reason is that the center electrode 42 has a high thermal expansion due to a high temperature, and is destroyed due to strain in normal brazing. In order to absorb this shape change due to thermal expansion, a complicated structure is required. However, since the center electrode 42 becomes a consumable item, this is not suitable for this purpose.
Furthermore, if PTFE is used as the sealing member 44 and is moved backward from the plasma discharge portion toward the waveguide 20, the thermal problem can be alleviated. However, the microwave propagates through the surface of the electrode 42 due to the skin effect, and as a result also propagates to water, and therefore attenuates before propagating to the tip 46 of the electrode 42.

Therefore, the inventor has created a double structure in which plastic is used as the sealing member 44 and the liquid side is covered and protected with ceramic as the insulating member 45.
As the plastic, PTFE is used. This is because the dielectric loss in the microwave band is small, there is no excessive dielectric constant, and the heat resistance is as high as possible. However, the material is not limited to PTFE as long as it satisfies these conditions.
As the ceramic, alumina (Al ₂ 0 ₃ ) is used. This is because, like PTFE, there is little dielectric loss in the microwave band, there is no excessive dielectric constant, and there is high heat resistance and mechanical strength. With such a structure, it is possible to realize a heat-resistant structure in which only the tip 46 of the electrode 42 is exposed to the liquid and the plasma can be maintained for a long time. However, the material is not limited to alumina as long as it satisfies these conditions.

(Electrode feed mechanism)
Next, the electrode feeding mechanism will be described with reference to FIG.
This figure is a cross-sectional view showing the configuration of the feeding mechanism.
As described above, the tip of the electrode 42 is crushed by the generation of plasma. Here, when the production amount of the metal nanoparticles is small, there is no particular problem because the crushing amount of the electrode 42 is small. However, if the production amount of the metal nanoparticles is increased and plasma is generated many times, As the amount increases, the tip of the electrode 42 enters into the hole 43-7 of the support 43, and the supply of microwaves becomes insufficient, so that plasma is not generated in the solution, or the generation thereof There was a problem that it took time.
In order to solve this problem, the inventor has invented a feeding mechanism for the electrode 42.

The feeding mechanism has a structure in which the coaxial pipe inner conductor 41-2 and the electrode 42 of the in-liquid plasma source 40 are improved.
The coaxial pipe inner conductor 41-2 is formed in a cylindrical shape as shown in FIG. And the front-end | tip (container 30 side) is formed in the tapered cone shape, and the other end reaches the pipe | tube protrusion 26-3 through the through-holes 52-4 and 51-3 of the support member 50. Yes.

An electrode 42, a support member 41-3, and a plunger 41-4 are provided inside the coaxial pipe inner conductor 41-2.
The electrode 42 is formed in a cylindrical shape, and is provided coaxially with the coaxial pipe inner conductor 41-2 inside the coaxial pipe inner conductor 41-2.
One end of the electrode 42 protrudes from the hole 43-7 of the support 43 and is exposed to the solution placed in the container 30. On the other hand, the other end of the electrode 42 is terminated inside the coaxial waveguide inner conductor 41-2.
The electrode 42 is longer in the central axis direction than the electrode 42 shown in FIG. Thereby, the quantity of the metal nanoparticle which can be manufactured with one electrode 42 can be increased, and also the replacement time of the electrode 42 can be extended.

  Note that one end (solution side) of the electrode 42 is formed in a tapered conical shape in FIG. 3, but is formed in a cylindrical shape in FIG. If the taper is tapered like the electrode 42 shown in FIG. 3, the microwave can be concentrated on the tip, but if the diameter is short (thin) like the electrode 42 shown in FIG. This is because even if the taper is not tapered, the microwaves are concentrated on the tip, and the generation of plasma can be promoted sufficiently.

The support member 41-3 is formed in a cylindrical shape, and is disposed in a position surrounding the outer periphery of the electrode 42 inside the coaxial waveguide inner conductor 41-2. That is, the support member 41-3 supports the electrode 42 so that the central axis of the coaxial pipe inner conductor 41-2 and the central axis of the electrode 42 coincide.
By disposing the support member 41-3, the electrode 42 can be fed straight out in the vertical direction with respect to the hole 43-7.

The plunger 41-4 has a pusher function when the coaxial pipe inner conductor 41-2 is used as a syringe, and is coaxial with the coaxial pipe inner conductor 41-2 inside the coaxial pipe inner conductor 41-2. Is provided.
One end of the plunger 41-4 is in contact with the other end of the electrode 42, and the other end protrudes from the tubular body projection 26-3.

The tube protrusion 26-3 is a member attached so as to protrude from the tube 26 toward the outside.
The tubular protrusion 26-3 is formed in a tubular shape, and one opening is joined to the tubular body 26. And the hollow of this pipe | tube protrusion 26-3, the through-hole 51-3 of the 1st support member 51, and the through-hole 52-4 of the 2nd support member 52 are connecting.
For this reason, the other end of the coaxial pipe inner conductor 41-2 is fitted into the pipe protrusion 26-3 through the through holes 51-3 and 52-4. Moreover, the plunger 41-4 has penetrated the inside of the pipe | tube protrusion 26-3 through the through-holes 51-3 and 52-4.

Furthermore, the internal thread 26-4 is formed in the surface which contact | connects the plunger 41-4 at least among the internal side surfaces of the pipe | tube protrusion 26-3. Moreover, the external thread 41-5 is formed in a part of outer periphery of the plunger 41-4.
The plunger 41-4 is screwed into the coaxial tube inner conductor 41-2 by screwing the female screw 26-4 of the tube protrusion 26-3 and the male screw 41-5 of the plunger 41-4. Can do.

The plunger 41-4 is twisted by turning around its central axis.
When the plunger 41-4 is screwed, the electrode 42 in contact with one end of the plunger 41-4 is pushed by the plunger 41-4 and moves in the screwing direction (the central axis direction of the electrode 42). As a result, the tip of the electrode 42 protrudes from the hole 43-7 of the support member 43. In this way, the electrode 42 can be sent out in the direction of the solution.
Moreover, the length which makes the electrode 42 protrude from the hole 43-7 of the support body 43 can be finely adjusted by extending | stretching the electrode 42 by twisting.

In addition, as shown in FIG. 6, the knob part 41-6 can be provided in the other end of the plunger 41-4.
The knob portion 41-6 is a portion that is held when a person who feeds the electrode 42 turns the plunger 41-4. This knob part 41-6 can be formed in, for example, a prismatic shape, a jagged outer periphery, or a rubber can be attached. As a result, the knob portion 41-6 is easily picked up and does not slide, so that the plunger 41-4 can be easily screwed.

  In the present embodiment, the electrode feed-out structure is the structure shown in FIG. 6, but the feed-out structure is not limited to the structure shown in the figure, and various structures can be used. For example, the electrode 42 can be extended by pushing or hitting the other end of the plunger 41-4 little by little in the direction of the central axis.

[Liquid plasma treatment method]
Next, the operation (in-liquid plasma processing method) of the in-liquid plasma processing apparatus of this embodiment will be described with reference to FIGS.
FIG. 7 is a flowchart showing a procedure for generating nanoparticles using the in-liquid plasma processing apparatus of this embodiment. FIG. 8 is a flowchart showing a procedure for generating a metal carrier using the in-liquid plasma processing apparatus of this embodiment.

(Metal nanoparticle production method)
As shown in FIG. 7, the in-liquid plasma processing apparatus 1 is attached with an electrode 42 formed of a metal for which nanoparticles are to be created and a heat-resistant member 43-8 formed of a metal for which nanoparticles are to be similarly created. (Step 10).
Only the solvent is charged into the container 30 of the in-liquid plasma processing apparatus 1 (step 11).
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 and is supplied from the in-liquid plasma source 40 to the solvent in the container 30. Thereby, in the solvent, in-liquid plasma is generated in the vicinity of the tip 46 of the electrode 42 (step 12).
The metal forming the electrode 42 is crushed by a reaction such as melting or electrolysis due to the heat and electric field of the plasma in liquid, and nanoparticles are generated in the solvent (step 13).

(Manufacturing method of metal carrier formed in)
As shown in FIG. 8, in the in-liquid plasma processing apparatus 1, a metal electrode 42 for which nanoparticles are to be created and a heat-resistant member 43-8 made of a metal for which nanoparticles are to be similarly created are attached (step 20). ).
The solvent in which the carrier particles are dispersed is put into the container 30 (step 21). The concentration of the carrier is set to a range of 0.1 to 10% by weight with respect to the solvent.
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 and is supplied from the in-liquid plasma source 40 to the solvent in the container 30. Thereby, in the solvent, in-liquid plasma is generated in the vicinity of the tip 46 of the electrode 42 (step 22).
The metal forming the electrode 42 is crushed by a reaction such as melting or electrolysis due to the heat and electric field of the plasma in the liquid, and this is adhered and grows on a carrier dispersed in a solvent, thereby generating a metal support. (Step 23).

[Example]
Next, examples of the present embodiment will be described.

(Example 1: Production of metal nanoparticles)
As the apparatus, an in-liquid plasma processing apparatus 1 shown in FIG. 1 was prepared.
The in-liquid plasma processing apparatus 1 was provided with an electrode 42 made of platinum and a heat-resistant member 43-8 also made of platinum.
Further, the magnetron box 11 and the microwave power source 12 of the microwave oscillator 10 have one set configuration, and those manufactured by Micro Electronics Co., Ltd., UM-1500EC-B, production number 0101-1569 were used. As the microwave power supply controller 13, an inventor's original one was used.

500 ml of purified water was placed in the container 30 of the in-liquid plasma processing apparatus 1.
Next, the microwave oscillator 10 was turned on to generate microwaves.
The microwave propagated through the waveguide 20 and was given to purified water through the coaxial waveguide converter 26 and the in-liquid plasma source 40. Thereby, plasma was generated inside the purified water (discharge of plasma in liquid).
The microwave power at this time was 600 W, and the time was 600 seconds.
Note that when the irradiation time reached 600 seconds, the liquid temperature exceeded 80 ° C., so the microwave irradiation was terminated. This is because when the liquid temperature is 80 ° C. or higher, boiling tends to occur due to high conductivity. By the way, if the microwave irradiation is further continued, the liquid temperature exceeds 90 ° C., and the solution is completely boiled.

After the plasma ignition, the purified water began to turn black and became almost opaque at the end of the experiment.
This solution was placed in a polybin and allowed to stand for 1 day, but the solution remained uniformly black and cloudy and there was no precipitate. This means that the produced nanoparticles are tens of nanometers or less and uniform.

FIG. 9 shows an electron microscope (TEM) image of the solution in which the nanoparticles were generated.
In the figure, the solution was photographed with a transmission electron microscope (TEM) at a magnification of 300,000 times.
As shown in the figure, it was found that 2-5 nm platinum nanoparticles were generated in the solution.

(Example 2: Production of metal support)
As the apparatus, an in-liquid plasma processing apparatus 1 shown in FIG. 1 was prepared.
The in-liquid plasma processing apparatus 1 was provided with an electrode 42 made of platinum and a heat-resistant member 43-8 also made of platinum.
The magnetron box 11, the microwave power source 12, and the microwave power source controller 13 of the microwave oscillator 10 were the same as those used in Example 1.

Silica nanoparticles (average particle diameter of 50 nm) as carrier particles were mixed with 500 ml of purified water so as to be 10% by weight, and this was put in the container 30 of the in-liquid plasma processing apparatus 1.
Next, the microwave oscillator 10 was turned on and microwaves were output from the magnetron box 11. The microwave propagated through the waveguide 20 and was given to the solution via the in-liquid plasma source 40. Thereby, plasma was generated in the solution (discharge of plasma in liquid). At this time, the microwave power was 600 W and the time was 600 seconds.
Note that when the irradiation time reached 600 seconds, the liquid temperature exceeded 80 ° C., so the microwave irradiation was terminated. This is because when the liquid temperature is 80 ° C. or higher, boiling tends to occur due to high conductivity. By the way, if the microwave irradiation is further continued, the liquid temperature exceeds 90 ° C., and the solution is completely boiled.

After the plasma ignition, the solution began to become cloudy black and became almost opaque after the experiment.
This solution was placed in a polybin and left for one day, but the solution remained uniformly black and cloudy. There was no precipitate.
FIG. 10 shows an electron microscope image of the solution in which the metal support is generated. In the figure, the solution was photographed at a magnification of 150,000 times with a transmission electron microscope (TEM).
As shown in the figure, platinum was supported on the silica nanoparticles in the solution (the part indicated by the white arrow in the figure).

As described above, according to the in-liquid plasma processing apparatus, the metal nanoparticle manufacturing method and the metal carrier manufacturing method of the present embodiment, since nanoparticles can be manufactured from a metal material without passing through a metal salt from the metal, The production process can be simplified and the manufacturing time can be shortened.
In addition, since it does not contain impurities derived from metal salts, complexes, and reducing agents in the solvent, it becomes possible to produce extremely high purity metal nanoparticles and metal supports, and this is expected due to the highly active surface expected. High catalytic ability is obtained.
Furthermore, since a large device such as an electron accelerator is not required, a sufficient amount of metal nanoparticles and metal support can be manufactured with a small device at a low cost.

The preferred embodiments of the in-liquid plasma processing apparatus, the metal nanoparticle manufacturing method, and the metal carrier manufacturing method of the present invention have been described above. However, the in-liquid plasma processing apparatus, the metal nanoparticle manufacturing method, and the metal carrier according to the present invention have been described. It goes without saying that the manufacturing method is not limited to the above-described embodiment, and various modifications can be made within the scope of the present invention.
For example, in the above-described embodiment, only one container is provided. However, the number of containers is not limited to one, and two or more containers may be provided.
In the above-described embodiment, the configuration of the waveguide is the configuration shown in FIG. 1, but the configuration is not limited to this configuration, and any configuration can be used as long as microwaves can propagate to the solution. be able to.

  The present invention relates to a technology for generating metal nanoparticles or a metal support in a solution using in-liquid plasma excited by microwaves. A fuel is produced by producing a highly active catalyst using this technology. It can be used for battery price reduction and nanopaste purification.

DESCRIPTION OF SYMBOLS 1 Submerged plasma processing apparatus 10 Microwave oscillator 20 Waveguide 30 Container 31 Hole 32 Side surface 40 Submerged program source 42 Electrode 42-8 Heat-resistant member 44 Sealing member 45 Insulating member 46 Tip

Claims (7)

An in-liquid plasma processing apparatus for generating a metal nanoparticle or a metal support by applying a microwave to a solution,
A container containing the solution;
A microwave oscillator that outputs microwaves;
An electrode for applying the microwave to the solution to excite plasma in the solution;
The electrode is formed of a metal that becomes the metal nanoparticles by the excitation of the plasma. A part of the electrode is formed in a conical shape,
The in-liquid plasma processing apparatus according to claim 1, wherein the tip of the conical shape is in contact with the solution. On the side of the container, below the water surface when the solution is stored, has a hole through which the electrode passes,
A sealing member is disposed between the electrode and the hole,
The in-liquid plasma processing apparatus according to claim 1, wherein an insulating member is disposed on the solution side of the sealing member. A support for supporting the electrode and passing through the hole;
A heat-resistant member attached to a surface of the support that is in contact with the solution;
The in-liquid plasma processing apparatus according to claim 3, wherein the heat-resistant member is formed of a metal that becomes the metal nanoparticles by excitation of the plasma. The in-liquid plasma processing apparatus according to claim 1, further comprising a feeding mechanism that feeds the electrode toward the solution. A method for producing metal nanoparticles by applying a microwave to a solution to produce metal nanoparticles,
Storing the solution in a container;
Supplying a pulsed microwave to an electrode disposed on a side surface of the container and having a tip protruding into the solution;
A step of exciting the plasma by the microwave at the tip of the electrode, crushing the electrode, and generating the crushed material for forming the electrode as metal nanoparticles. Method. A metal carrier manufacturing method for producing a metal carrier by applying a microwave to a solution,
Storing the solution in which the carrier is dispersed in a container;
Supplying a pulsed microwave to an electrode disposed on a side surface of the container and having a tip protruding into the solution;
And a step of crushing the electrode by exciting the plasma with the microwave at the tip of the electrode, and supporting the crushed electrode forming material on the carrier as metal nanoparticles. A support manufacturing method.