JPS63289798A - High-frequency induction plasma torch - Google Patents

Abstract

PURPOSE:To prevent the transmission of a thermal shock to a member surrounding plasma by providing a film made of the preset heat absorbing material on the plasma side of the member surrounding plasma. CONSTITUTION:A plasma cushioning tube 8 made of a heat absorbing material (e.g., Si3N4) absorbing heat by sublimation or thermal decomposition is provided inside the plasma generating unit of an outer tube 7. The interior of a torch is exhausted with an exhaust pump 14, the Ar gas is introduced through a guide section 2 to generate plasma. The Si3N4 powder is fed through a raw material lower guide section 4 and ultra-finely pulverized. Even if plasma is brought into contact with the tube 8, the heat is absorbed, and no thermal shock is applied to the outer tube 7.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a high frequency induction plasma torch, and more particularly to a plasma torch that is resistant to plasma thermal shock.

[Conventional technology]

A high-frequency induction plasma torch is an ICP (Induc) torch.
It is used for analysis (Very Coupled Plasma), for processing powder into spherical particles, for manufacturing M3 fine powder using chemical reactions, etc., and has been attracting particular attention in recent years because it can provide a heat source of 5,000°C or higher. be.

For cases such as ICP analysis, where only a small amount of raw material is needed for one analysis with an output of about 1 to 2 kW at most, a torch structure as shown in Figure 2 is sufficient to satisfy the function, and the torch is powered by the heat of the plasma. No problems such as damage occurred.

However, when used as a heat source for powder spheroidization processing or ultrafine powder production, even a laboratory-scale one has a temperature of 20 to 50K.
W class is used, and it is said that MW class is required for practical scale.

FIG. 3 shows a typical torch structure currently used for laboratory-scale ultrafine powder production equipment and powder processing. The torch has a triple structure, and a gas for plasma generation (for example, Ar) is inserted between the inner tube 5 and the middle tube 60.
This plasma gas flows through the outer tube 7.
The structure is such that cooling gas flows between the outer tube 7 and the middle tube 6 to prevent them from being damaged by contact with the outer tube 7 and the middle tube 6.

In order to have the effect of stabilizing the plasma, this cooling gas is given a swirling component and flows, and the outer tube is provided with a water cooling jacket 16 for cooling. However, in the case of a torch with such a structure, when the powder for spheroidization treatment is introduced from the plasma tail flame section through the raw material lower introduction section 4, or when the gaseous raw material is introduced from the inner tube 1, the center If the shape of the plasma is disturbed and even a small amount of plasma touches the outer tube 7, it will crack due to the thermal Wf attack and become unusable as a torch.

For this reason, efforts have been made to introduce the speed and amount of gaseous raw materials and powder, but at present no satisfactory solution has been found.

[Problem that the invention seeks to solve]

With the above-mentioned method of flowing cooling gas or devising a method of introducing gaseous raw materials or powder, if these gases and raw materials are stably supplied and no deposits are formed inside the torch, problems such as damage may occur. However, due to clogging of the powder supply system, the powder may not be introduced symmetrically to the tail flame section, or products may adhere to the gas raw material inlet (inner tube outlet), resulting in a slight If the shape of the plasma is disturbed, the plasma will come into contact with the inner wall of the outer tube, leading to damage. In addition, this way of touching causes the plasma temperature to be as high as 5,000 to 10,000 degrees Celsius, even at the moment of contact.
The problem is that cracks occur.

In the present invention, such slight disturbance of plasma is an unavoidable phenomenon when operating for a long time, and it is better to have a structure that will not be damaged even if a small amount of solder comes into contact with the plasma. It is unique in that it was thought to be a good idea and its structure and materials were devised.

[Means for solving problems]

The above-mentioned problem is solved by a high-frequency induction plasma torch in which a film made of a heat absorbing material is provided on the plasma side of a member surrounding the plasma.

[Effect]

By providing a film made of a heat absorbing material on the plasma side of the member surrounding the plasma, even if the plasma touches the film, the heat of the plasma is absorbed by the film and no thermal shock is transmitted to the member surrounding the plasma.

〔Example〕

Hereinafter, the present invention will be explained based on examples.

The apparatus shown in FIG. 1 is a reaction apparatus using a plasma torch. The device configuration is roughly divided into a plasma torch section, a reaction vessel 11, a product recovery section 12, and an exhaust gas recovery pump 14.
Consists of.

The plasma torch section includes an inner tube 5 having an introduction part 16 for introducing the gaseous raw material 1 into the upper part, a middle tube 6 that wraps around the inner tube 5 and has an introduction part 17 for introducing the plasma gas 2 into the upper part, and a middle tube 6 having an introduction part 17 for introducing the plasma gas 2 into the upper part. tube 6
The basic structure is an outer tube 7 which encloses the outer tube 7 and has a space below which the plasma 10 is generated. An introduction part 18 for introducing cooling gas 3 for cooling the inner surface of the outer tube is provided at the upper part of the outer tube 7, and a plasma buffer tube 8 according to the present invention is provided in the plasma 10 generation range of the outer tube 7. . Further, on the outer periphery of the outer tube 7, a high frequency coil 9 for generating plasma 10 is provided in the plasma generation part, a lower raw material introduction part 19 is provided for introducing the raw material 4 into the plasma tail flame part, and the temperature rising part is cooled by cooling water 15. A water cooling jacket 16 is provided.

[Example 1] Plasma is generated by flowing Ar gas for plasma generation from the introduction part 2 and increasing the output of the high-frequency induction coil while reducing the pressure inside the torch using the exhaust pump 14. . When the high-frequency output reached approximately 5KW, cooling Ar gas was gradually started to flow, the exhaust pump was stopped, and the high-frequency output was gradually increased.Atmospheric pressure thermal plasma was generated at the device's maximum output of 30KW. occurs. In addition, the cold ready-to-use gas is constructed to flow in a tangential direction so as to have a swirling component in order to increase its effect. In this state, SL 3 N having a particle size of approximately 1 to 5 μm is introduced from the raw material lower introduction part 4.
4' Start feeding powder.

Then, when the plasma started supplying raw materials, the tail flame part into which the powder entered was disturbed, causing distortion in the radial direction and slightly touching the plasma buffer tube 8 of 5i3NJJ, but the plasma disturbance disappeared after that. This made it possible to stably maintain the powder's spherical shape and refinement experiments without damaging the torch section.

Comparative experiments were conducted twice using a torch without a built-in plasma buffer tube 8. The first time was immediately after introducing the powder raw material, and the second time was about 2 hours after entering steady operation, when the powder supply system was blocked. This caused a slight disturbance in the plasma, causing microcracks to occur in the outer tube, which subsequently progressed and made the experiment impossible.

[Example 2] After generating plasma in the same manner as in Example 1, 5iCu and Ar gas were introduced from the gaseous raw material introduction part 1 as a carrier gas, and NHi gas was introduced from the lower raw material introduction part. After pouring it in, we conducted a Si3N synthesis experiment, and the experiment continued for a total of about 50 hours without damaging the torch.

If you use a plasma buffer tube, it will be stable for a long time.
The reason why plasma can continue to be generated is that even if the plasma hits the wall, the heat is used to sublimate (or decompose) the buffer tube, and no thermal shock phenomenon occurs in the outer tube. It is from.

In order for heat absorption by sublimation to be carried out efficiently and for the heat of the plasma to not be transferred to the outer tube, the material must have a large latent heat of sublimation, a material with a sublimation temperature that can sublimate at the plasma temperature, and a material with a high heat resistance. A material with low conductivity is suitable.

Ceramics such as BN, AQN, Si, N, and SiC are heat resistant and have a sublimation (decomposition) temperature of 1.900~.
At 3,000°C, both are temperatures at which sublimation can be expected when plasma contact occurs, but Si3N4 has the lowest thermal conductivity and is the most suitable tube material for plasma buffering. From the point of view of not reducing the purity of the product, it is best to choose a plasma buffer tube made of the same material as the product, and the material is selected based on the balance between the probability of damage due to the thermal characteristics mentioned above and the purity of the product. Should.

In addition, in the conventional method, in order to prevent damage to the outer tube due to plasma, it was necessary to flow cooling gas approximately 5 to 10 times the amount of plasma gas, but with the present invention, this amount of plasma gas can be saved. be able to.

In other embodiments of the present invention, instead of fitting the cylindrical plasma buffer material, there is a method of attaching it as a film, and a method of applying a powder.

Suitable materials include substances that sublime at 2,000 to 3,000°C, such as BN, AQN, and 5i3N41SiC. In this case, the construction is easy, and even if the buffer material is damaged by the heat of the plasma, it is easy to repair.

Furthermore, although the structure shown in FIG. 1 is such that the outer tube is cooled with cooling water, a system that does not use cooling water is also possible by applying a buffer material over the entire length of the plasma. .

According to the above embodiment, the problem of breakage, which was the biggest drawback of the thermal plasma torch, can be solved, and at the same time, the problem of contamination of products by cooling water flowing in when the torch breaks can be solved.

Furthermore, since the amount of cooling water for the outer tube can be reduced or eliminated, it is also excellent in terms of thermal efficiency, which is a very big advantage when considering upsizing and industrialization.

〔Effect of the invention〕

According to the present invention, by providing a film made of a heat absorbing material on the plasma side of the member surrounding the plasma, even if the plasma touches the pancreas, the heat of the plasma is absorbed by the film, causing a thermal shock to the member surrounding the plasma. is not transmitted, so there is an excellent effect that members surrounding the plasma are not damaged by the thermal shock of the plasma.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 is a sectional view of a conventional torch, and FIG. 3 is a sectional view showing an application example of the conventional torch. 7... Outer tube, 8... Plasma buffer tube, 9... Induction coil, 10... Plasma.

Claims (3)

[Claims] (1) A high-frequency induction plasma torch characterized in that a film made of a heat absorbing material is provided on the plasma side of a member surrounding the plasma. (2) The high frequency induction plasma torch according to claim 1, wherein the heat absorbing material absorbs heat by sublimation or thermal decomposition. (3) In a high-frequency induction plasma torch in which the member surrounding the plasma constitutes an outermost cylinder and a high-frequency induction coil is provided outside the outermost cylinder, the length of the membrane in the axial direction of the outermost cylinder is the outermost cylinder. The high frequency induction plasma torch according to claim 1 or 2, characterized in that the diameter is 1 to 3 times the inner diameter of the cylinder, and the mounting range of the high frequency induction coil is included within the mounting range of the membrane. .