JP2527150B2 - Microwave thermal plasma torch - Google Patents

Description

TECHNICAL FIELD The present invention relates to a microwave thermal plasma torch for synthesizing a highly efficient and highly pure substance, and particularly to a new type including ceramics and diamond. The goal is to generate materials and develop new application fields.

[Conventional technology]

While it is said that microwave plasma has higher electron density and higher reactivity than plasma generated by direct current or high frequency,
It has not been applied to thermal plasma reactions due to the very limited generation area.

There are some reports on the microwave thermal plasma generation method under atmospheric pressure. In the electrodeless method, it is common to generate a filamentary plasma with a diameter of several mm only in the reaction tube installed in the waveguide, and it was considered not suitable for processes such as film deposition. . In 1951, Cobine et al. Devised a method of generating plasma at the coaxial tip (JDCobine and DAWilber, J.Appl.Phys., 22
(1951) 835), then by Marrodineauv et al., (RM
arrodineauv and RCHughes, Spectrochim.Acta, 19 (19
63) 1309) Developed as a torch for emission spectroscopy. However, there have been few reports since then, probably because of the rise of ICP (Inductively Coupled Plasma) emission spectroscopy. The reason for this may be the stability of the plasma flame and the problem of erosion of the center conductor. None of these are suitable for high rate film deposition processes of high purity products.

[Problems to be Solved by the Invention]

It has been difficult for a device developed for conventional emission spectroscopy to stably generate a powerful plasma flame. It is an object of the present invention to provide a microwave thermal plasma torch that efficiently absorbs microwave power in a plasma flame, stabilizes it hydrodynamically, and deposits highly pure products at a high speed. .

[Means for solving the problem]

The present invention relates to a torch generator that forms a coaxial tube circuit, a means for supplying microwave power to the torch generator via an airtight dielectric window and a coaxial waveguide converter, and a circle for the torch generator. Microwave heat having means for ejecting gas in a circumferential direction and a radial direction to supply it in a spiral state, and ionizing the gas in the spiral state by the supplied microwave power to generate plasma It is a plasma torch.

According to the present invention, a coaxial waveguide converter is used to supply microwave power from a waveguide circuit to a torch generator that forms a coaxial tube circuit, and the torch generator is efficiently transmitted. Then, both the tip portion of the inner conductor and the outer conductor are narrowed down to maximize the microwave electric field at this portion.

In order to increase the stability and controllability of the plasma, the gas ejection port is provided above the torch generation section with two independent systems in the circumferential direction and the radial direction.

In the torch generating portion, gas is ionized by the microwave electric field at the tip portion of the inner conductor, that is, the electrode, and plasma is generated. The generated plasma is supplied with energy and maintained by the electric field formed around the electrodes.

[Work]

The microwave power supplied from the waveguide circuit is efficiently converted into the coaxial tube circuit of the torch generator by the coaxial waveguide converter, and the microwave electric field is maximized at the electrode portion at the tip. Gas is rotated and supplied as a vortex from two gas outlets in the circumferential direction and the radial direction, so that stable and powerful plasma is generated and blown out and maintained in the chamber.

As a result, the product has the advantage that it is less likely to contain impurities because it does not contact the electrodes.

〔Example〕

FIG. 1 shows a schematic vertical sectional view of an embodiment of the present invention. The torch generator is mainly composed of an inner conductor 1 and an outer conductor 2, and is supplied with microwave power from a waveguide circuit by an upper coaxial waveguide converter. As the coaxial waveguide converter, a ridge 5 was provided at the center of the rectangular waveguide 4 to perform impedance matching with the coaxial waveguide circuit. In the figure, 6 is an airtight dielectric window.

The inner conductor 1 is made of copper, and its tip 7 is sharpened to form an electrode. Inside the inner conductor 1, a water pipe 3 passes,
Cooling water is flowing from the cooling water inlet 17 at the upper part to the cooling water outlet 18. The outer conductor 2 is made of copper and forms a coaxial tube circuit with the inner conductor 1, and the diameter is narrowed at the torch generation portion to have the smallest diameter portion 8 to concentrate the microwave electric field and facilitate the ionization of gas. ing. Further, a cooling water reservoir 19 is provided inside this, and the cooling water is made to flow from the cooling water inlet 171 to the cooling water outlet 181.

On the other hand, in order to increase the stability and controllability of the plasma, the gas has a circumferential gas jet port 9 that produces a gas flow in the circumferential direction and a radial gas jet port 10 that produces a radial gas flow. A large number of them are provided around the wall surface of the outer conductor 2 above the torch generation portion to generate rotation and vortex in the gas. These gases are independently supplied from the gas inlets 15 and 16.

The TE01 mode microwave power applied to the rectangular waveguide 4 from the waveguide circuit is converted to the coaxial TEM mode by the ridge 5 of the coaxial waveguide converter through the airtight dielectric window 6 and the electrode The maximum voltage is reached at the portion 7, and the gas is ionized to generate plasma. Once generated plasma flame 11
Is continuously replenished with energy by the microwave electric field around the tip of the electrode and is jetted to the chamber 12.
13 is a chamber wall.

In order to charge the reactant supplied from the charging port 14 to the upper part of the torch generating part, the electrode 7 is provided with a discharging port 141 having a hole at the tip thereof. In addition, the reactant can be supplied also through the inlet 142 formed in the outer conductor 2.

In the embodiment, the inner and outer diameters of the inner conductor 1 and the outer conductor 2 forming the coaxial waveguide circuit are about 20 mm and about 57 mm, respectively, and the minimum diameter portion 8 of the torch generating portion is about 22 mm. Frequency 2.45
When a microwave power of GHz was applied and a mixed gas of hydrogen and argon was used as the plasma gas, the plasma was stably generated and maintained under atmospheric pressure.

〔The invention's effect〕

In the conventional microwave thermal plasma generator, it was only used for emission spectroscopic analysis, but was not applied to the thermal plasma reaction of substances due to the stability of the plasma flame. By using the microwave thermal plasma torch of the present invention, a powerful plasma flame can be generated and maintained,
This is possible now. The microwave thermal plasma of the present invention
The characteristics of the torch are as follows.

(1) The microwave thermal plasma torch has an advantage that impurities from the electrode are less likely to be contained in the deposit as compared with the DC arc jet.

(2) The electric power to maintain the atmospheric pressure pure hydrogen plasma is much lower than that of the DC arc jet or the high frequency plasma. That is, high-frequency plasma of 4 MHz requires 500 kw or more, while microwave requires a low power of about 1.8 kw.

(3) The microwave thermal plasma torch is suitable for substance synthesis because both the temperature gradient and the concentration gradient in plasma are considered to be quite small.

(4) Since there is almost no dissolution of the electrode, there is little problem of electrode erosion.

(5) A stable plasma flame is generated for a long time, and a highly pure reaction product is efficiently obtained.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of an embodiment of the present invention. 1 is an inner conductor, 2 is an outer conductor, 3 is a water pipe, 4 is a rectangular waveguide,
5 is a ridge, 6 is an airtight dielectric window, 7 is an electrode, 8 is a minimum diameter portion, 9 is a circumferential gas jet, 10 is a radial gas jet, 11 is a plasma flame, 12 is a chamber, 13 is 13 Chamber wall, 14/142 inlet, 141 outlet, 15/16 gas inlet, 17/171 cooling water inlet, 18/181 cooling water outlet,
19 is a cooling water reservoir

Claims (2)

(57) [Claims] 1. A torch generating portion forming a coaxial tube circuit having a minimum diameter portion by narrowing both the tip portion of the inner conductor and the outer conductor, and the outer conductor, and an airtight dielectric for the torch generating portion. A means for supplying microwave power through the body window and the coaxial waveguide converter, and means for ejecting a gas toward the torch generating portion in a circumferential direction and a radial direction to supply the gas in a spiral state, A microwave thermal plasma torch, characterized in that a gas in a spiral state is ionized by supplied microwave power to generate plasma. 2. The microwave thermal plasma torch according to claim 1, wherein two independent gas ejection ports in the circumferential direction and the radial direction are provided above the torch generating portion.