JP2005108600A - In-liquid plasma generation device and in-liquid plasma generation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an in-liquid plasma generation device and an in-liquid plasma generation method capable of efficiently generating plasma even in a conductive liquid such as water or alcohol. <P>SOLUTION: In order to solve the problem, this in-liquid plasma generation device 1 comprises: a vessel 2 for keeping a liquid 3; an electromagnetic wave radiation means 4 for radiating electromagnetic waves into the liquid 3; an air bubble generation means for generating air bubbles 9 in the liquid; and an air bubble keeping means for keeping the air bubbles 9 in the vicinity of the electromagnetic wave radiation means 4. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a submerged plasma generator and a submerged plasma generating method for generating high-energy plasma in a conductive liquid such as water or alcohol.

Conventionally, vapor deposition technology using vapor phase plasma has been widely used as a deposition technology using plasma. For example, Patent Document 1 describes that a diamond film is formed on the surface of silicon or cubic silicon carbide by plasma CVD. Non-Patent Document 1 describes a research on generation of plasma in liquid by superposition of ultrasonic cavitation and local electromagnetic field. Furthermore, Non-Patent Document 2 describes a technique for synthesizing fullerene by inserting a graphite electrode into water and performing arc discharge.
Japanese Patent Laid-Open No. 10-81589 Nomura Shinfuku, Toyoda Hiromichi, "4th Ehime University Campus Symposium", Ehime University Campus Symposium Preparatory Committee, November 12, 2001, p. 56 N. Sano, et al, Nature 414,506 (2001)

In the plasma CVD method such as the method described in Patent Document 1, it is difficult to synthesize vapor deposition materials in large quantities. Therefore, it takes a long time to form a film having a certain thickness. In order to increase the deposition rate, supplying raw materials such as methane rapidly can be dangerous. Further, when high energy plasma is generated in the gas phase, the temperature becomes high, and it cannot be deposited on a substrate material that is vulnerable to heat. On the other hand, the generation of plasma in liquid by superimposition of ultrasonic cavitation and local electromagnetic field described in Non-Patent Document 1 is a very promising idea to generate plasma in liquid, The policy for starting the research was announced and the details were not described at all. It was completed as a concrete one in the invention according to Japanese Patent Application No. 2002-98193 made by the presenter and the present inventor. ing.

The technique of performing arc discharge in a liquid as in the example described in Non-Patent Document 2 has a problem of low energy efficiency because most of the power is consumed in the flow of electrons. In addition, when vapor deposition is performed on the substrate, there is a problem that the substrate of the target is heated by this excessive electron flow, and a substrate made of a material that is weak against heat cannot be used, and a non-conductive substrate cannot be used. The use is extremely limited.

On the other hand, the method described in Non-Patent Document 2 for generating an in-liquid plasma by irradiating an electromagnetic wave in the liquid is capable of obtaining a high synthesis rate because the liquid phase has a very high molecular density compared to the gas phase. There is expected. However, conductive liquids such as water and alcohol have the problem that eddy currents are generated in the liquid and the energy of the irradiated electromagnetic waves is consumed, and the electromagnetic waves are not absorbed because the hydroxyl groups absorb a specific frequency. There is a problem of attenuation. An object of the present invention is to provide an in-liquid plasma generating apparatus and an in-liquid plasma generating method capable of efficiently generating plasma even with a conductive liquid such as water or alcohol.

In order to solve the above problems, an in-liquid plasma generator according to the present invention generates a bubble in a liquid, a container for holding the liquid, an electromagnetic wave irradiation means for irradiating the liquid with an electromagnetic wave, and the like. A bubble generating unit for holding the bubble and a bubble holding unit for holding the bubble near the electromagnetic wave irradiation unit. As the bubble holding means, a pair of ultrasonic wave irradiation means and an ultrasonic reflector arranged above and below the bubble, a holding plate holding the bubble from above, and for electromagnetic wave irradiation arranged above and below the bubble A pair of electrodes can be used.

Furthermore, the method for generating plasma in liquid according to the present invention generates bubbles in a conductive liquid, holds the bubbles near the electromagnetic wave irradiation means, and generates plasma in the bubbles by irradiating the bubbles with electromagnetic waves. Is. Bubbles may be held by a pair of ultrasonic irradiation means and an ultrasonic reflector arranged above and below, or bubbles may be held by a pair of electrodes for electromagnetic wave irradiation arranged above and below. An aqueous solution may be used as the conductive liquid.

The submerged plasma generation apparatus and submerged plasma generation method according to the present invention of the present invention is safe and easy to handle because it is locally low in energy but macroscopically low temperature even when a conductive liquid is used. This has the effect of generating plasma in liquid.

The best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is an explanatory view showing an example of an in-liquid plasma generator according to the present invention. A liquid 3 is placed in the container 2 of the in-liquid plasma generator 1. The size of the container 2 can be appropriately selected according to the required processing capacity, and it may be a small one such as a beaker or a large processing tank for carrying out as a large plant. Here, an acrylic container is used.

The electromagnetic wave irradiation means 4 is for irradiating the liquid 3 with an electromagnetic wave. In this example, the electromagnetic wave irradiation means 4 includes an electrode pair 5a and 5b and a high frequency supply device 6 for supplying a high frequency to the electrode pair. Moreover, although the in-liquid plasma generator 1 of this invention is provided with a bubble generation means, in this example, the electrodes 5a and 5b also serve as the bubble generation means. When a high frequency is supplied to irradiate electromagnetic waves, the electrodes 5a and 5b are heated, and bubbles are generated from the liquid in contact with the electrodes 5a and 5b. As the bubble generating means, a dedicated heating means may be provided separately from the electromagnetic wave irradiation means 4. Further, as the bubble generating means, the container 2 may be covered with another container and the bubbles may be generated by reducing the pressure with a vacuum pump or the like, or a gas may be introduced from the outside, or a combination thereof. It may be.

The in-liquid plasma generator 1 of the present invention includes bubble holding means. In this example, the ultrasonic irradiation device 7 and the ultrasonic reflector 8 arranged vertically in the container 2 serve as the bubble holding means. The ultrasonic irradiation device 7 is provided below the position where the bubbles 9 are to be held, and the ultrasonic reflector 7 is provided above the position where the bubbles 9 are to be held, so that the bubbles are sandwiched from above and below. The bubble 9 receives radiation force and buoyancy due to ultrasonic irradiation from above and below, but is held at a position where they are balanced. The position where the bubbles 9 are to be held is set to be close to the electrode 5.

Next, a method for generating submerged plasma by the submerged plasma generator 1 shown in FIG. 1 will be described. Fill container 2 with liquid 3. The liquid 3 may be a non-conductive liquid such as benzene or dodecane, but in the in-liquid plasma generation method of the present invention, a conductive liquid such as water or alcohols can be used. In particular, since a large amount of water-soluble substances can be dissolved in water, an aqueous solution can be prepared according to the purpose of treatment. When a high frequency is supplied to the electrode 5 from the high frequency supply device 6, the electrode 5 is heated and bubbles are generated from the electrode 5. Furthermore, by operating the ultrasonic irradiation device 7, ultrasonic waves are irradiated from above and below between the ultrasonic irradiation device 7 and the ultrasonic reflector 8. The bubble 9 is held at a position where the radiant forces from the ultrasonic waves from above and below are balanced, and a single or several large bubbles 9 are formed and held near the electrode.

Since electromagnetic waves are irradiated between the electrodes 5a and 5b, the electromagnetic waves are also irradiated to the bubbles 9 held at the positions. Since the bubble 9 is held near the electrode 5, the electromagnetic wave reaches the bubble without being attenuated on the way and generates plasma in the bubble 9. This plasma is locally high temperature and high energy and is effective for decomposition and synthesis of substances, but on the other hand, it is macroscopically low in temperature and safe and easy to handle. .

The plasma generated in this way can be subjected to various treatments. For example, deposition can be performed on the substrate by disposing the substrate to be deposited so as to be in contact with the bubbles 9 and containing a material as a raw material for the deposited film in the liquid. Unlike conventional vapor deposition such as the CCVD method, since a liquid having a high material density is used as a raw material, the deposition rate of the deposited film is remarkably improved. It can also be used as a chemical reactor that uses carbon-containing liquids to synthesize carbon nanotubes, fullerenes, diamonds, and other substances, and to decompose harmful substances that are difficult to decompose by conventional treatment methods such as dioxin and chlorofluorocarbon. Can be used.

Next, another example of the in-liquid plasma generator will be described. FIG. 2 is an explanatory view showing another example of the in-liquid plasma generator. Description of matters common to the example shown in FIG. 1 is omitted. This example is suitable for using electromagnetic waves having a high frequency of 1 GHz to 200 GHz. A microwave concentrator 10 is used as the electromagnetic wave irradiation means 4. An electromagnetic wave is irradiated into the liquid 3 from the tip of the microwave concentration apparatus 10. As in the example of FIG. 1, the bubbles are held at a fixed position by the pair of the ultrasonic irradiation device 7 and the ultrasonic reflection plate 8, but are set to be held near the tip of the microwave concentration device 10. . Therefore, the electromagnetic waves are radiated to the bubbles 9 in a concentrated manner from the microwave concentration apparatus 10.

Furthermore, another example of the in-liquid plasma generator will be described. FIG. 3 is an explanatory view showing another example of the in-liquid plasma generator. In this example, a laser light source is used as the electromagnetic wave irradiation means 4, and laser light is irradiated to the bubbles 9 held in the liquid 3. By generating plasma using laser light, a reaction different from plasma by radio waves is realized and the scope of application of the present invention is expanded. Thus, in the present invention, the electromagnetic wave includes X-rays, infrared rays, visible light, ultraviolet rays, and the like in addition to those in the radio wave region such as short waves, medium waves, and microwaves.

A first embodiment of the in-liquid plasma generation method of the present invention will be described. FIG. 4 is an explanatory view showing an in-liquid plasma generator used in this embodiment. FIG. 5 is a circuit diagram showing a high-frequency supply device used in this embodiment. This embodiment is an example in which electromagnetic waves in the medium wave band (MF band) are used. Water is put in the acrylic container 2. The electrodes 5a and 5b are made of brass and are arranged vertically. The upper side 5a uses a columnar shape with a diameter of 40 mm, and the lower side 5b uses a nail with a diameter of 2 mm.

The resonant circuit of FIG. 5 was used. The resonance circuit unit is formed by connecting a coil (0.24Ω, 9 μH) 11, a coil 12 (1.7Ω, 57 μH) and a ceramic capacitor 13 (500 pF) in parallel, and the resonance frequency of the entire circuit is 855 kHz. The matching unit 15 is connected to the terminals A ′ and B ′, and the matching unit 15 is adjusted so that the impedance from the high frequency power source 14 side becomes 50Ω. Further, the in-liquid plasma generator 1 is connected, and the matching unit 15 is finely adjusted so that the reflected wave is minimized.

When a high frequency of 855 kHz / 200 W was supplied, a reddish purple plasma was obtained between the electrodes (distance 5 mm). Even if the power was lowered, the plasma could be stably maintained up to 100W.

A second embodiment of the in-liquid plasma generation method of the present invention will be described. FIG. 6 is a circuit diagram showing a high-frequency supply device used in this embodiment. In this embodiment, an electromagnetic wave in a short wave band (HF band) is used. The submerged plasma generator uses the one shown in FIG. The electrodes 5a and 5b are arranged vertically, and the upper 5a side is made of brass and has a columnar shape with a diameter of 40 mm, and the lower side 5b is made of aluminum with a sharply processed column having a diameter of 3 mm.

The resonant circuit of FIG. 6 was used. The capacity of the capacitor 16 is 1 nF, and the capacity of the capacitor 17 is 91 pF (11 nF in series of 11). The inductance of the coil 18 is 1.4 μH. When the submerged plasma generator 1 was connected and the resonance frequency of the entire circuit was measured, it was 12.6 MHz (the submerged plasma generator 1 has a capacity of about 30 pF, and this effect cannot be ignored). The matching unit 15 is connected to the terminals A ′ and B ′, and the matching unit 15 is adjusted so that the impedance from the high frequency power source 14 becomes 50Ω.

When a high frequency of 12.6 MHz · 200 W was supplied from the high frequency power source 14, reddish purple plasma was obtained between the electrodes 5a and 5b.

The submerged plasma generation apparatus and submerged plasma generation method of the present invention can generate high energy plasma in conductive liquids such as water and alcohols, and can be used for chemical vapor deposition, chemical reaction furnaces, or harmful. It can be applied as a material decomposition furnace.

It is explanatory drawing which shows the 1st example of a plasma generator in a liquid. It is explanatory drawing which shows the 2nd example of a plasma generator in a liquid. It is explanatory drawing which shows the 3rd example of a plasma generator in a liquid. It is explanatory drawing which shows the Example of the plasma generator in a liquid. It is a circuit diagram which shows an example of a high frequency supply apparatus. It is a circuit diagram which shows another example of a high frequency supply apparatus.

Explanation of symbols

1. Submerged plasma generator 2. Container 3. Liquid 4. Electromagnetic wave irradiation means 5a, 5b. Electrode 6. 6. High frequency supply device Ultrasonic irradiation means8. Ultrasonic reflector 9 Bubble 10. Microwave concentrator 11, 12, 18 Coil 13, 16, 17 Capacitor

Claims (8)

A container for holding a liquid, an electromagnetic wave irradiation means for irradiating an electromagnetic wave in the liquid, a bubble generation means for generating bubbles in the liquid, and a bubble for holding the bubbles near the electromagnetic wave irradiation means An in-liquid plasma generator having a holding means. The in-liquid plasma generator according to claim 1, wherein the bubble holding unit is a pair of an ultrasonic wave irradiation unit and an ultrasonic wave reflection plate arranged above and below the bubble. The in-liquid plasma generator according to claim 1, wherein the bubble holding means is a holding plate that holds bubbles from above. The in-liquid plasma generator according to claim 1, wherein the bubble holding means is an electrode for electromagnetic wave irradiation arranged above and below the bubble. A submerged plasma generation method in which bubbles are generated in a conductive liquid, the bubbles are held near an electromagnetic wave irradiation means, and the bubbles are irradiated with electromagnetic waves to generate plasma in the bubbles. The in-liquid plasma generation method according to claim 5, wherein the bubbles are held by a pair of ultrasonic irradiation means and an ultrasonic reflector arranged above and below. The method of generating plasma in liquid according to claim 5, wherein bubbles are held by a pair of electrodes for electromagnetic wave irradiation arranged above and below. 8. The in-liquid plasma generation method according to claim 5, wherein an aqueous solution is used as the conductive liquid.

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