JPH03291367A - Operating method for high-frequency plasma reaction device - Google Patents

Abstract

PURPOSE:To stabilize the supply of raw material powder by introducing gaseous hydrogen together with the raw material into a plasma flame at the time of introducing the raw material powder into high-frequency plasma to melt the powder. CONSTITUTION:The gaseous hydrogen is introduced together with the raw material powder (for example, Si-Al alloy powder) into the plasma flame at the time of melting or evaporating the raw material powder by introducing the raw material powder into the high-frequency plasma or the hybrid plasma formed by bonding plural DC plasmas and the high-frequency plasma. The amt. of the gaseous hydrogen to be introduced is set at about 2 to 5l/min when the plate power of the high-frequency plasma is about 100Kw. The gaseous hydrogen and the raw material powder are directly charged into the plasma flame by using copper pipes of water cooled double structures. The stable supply of the raw material powder is possible in this way and the long-term use of the quartz pipes to be used without breaking is possible as well.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention utilizes the high temperature of high-frequency plasma or a hybrid plasma that combines multiple direct current plasmas and high-frequency plasmas to evaporate or melt powder to reduce particle size and size. It relates to processes such as obtaining different powders, thermal spraying, surface treatment/modification of powders, or reacting powders with second substances having different components. In particular, it relates to a method of introducing powder into a plasma flame.

Conventional technology High-frequency plasma, or hybrid plasma that combines multiple DC plasmas and high-frequency plasma, has been used in many high-temperature processes recently because it is relatively easy to obtain high-temperature ranges of several thousand degrees or more. It is not easy to efficiently introduce raw material powder into these plasma flames. Plasma flames are a stream of ultra-high temperature gas, and the high temperature gas has a high viscosity, which inhibits the introduction of powder. be.

The flame of high-frequency plasma and hybrid plasma is generated inside a water-cooled quartz tube by electromagnetic induction from an external work coil, but if the powder cannot be efficiently introduced into the flame, the powder will adhere to the quartz tube wall and cause damage to the quartz tube. An induced current is generated, the temperature rises, and the quartz tube wall is damaged.

In addition, if the deposits on the quartz tube wall are fused,
After the plasma is extinguished, stress is generated due to the difference in thermal expansion coefficient between the deposits and the quartz tube, and the quartz tube wall may be damaged. As a method to prevent these problems, the inventors have already proposed in Japanese Patent Application No. 82-53985 a hybrid plasma in which multiple DC plasma flows are merged on the central axis of a high-frequency plasma work coil to transfer powder into a plasma flame. Discloses how to efficiently introduce the system.

This method uses a combined flame of DC plasma ejected toward the center of a high-frequency plasma flame to introduce powder. Although this method is significantly improved compared to the case of high-frequency plasma alone, it It is not possible to completely capture the powder in the frame, and some of the powder is thrown out of the frame, which has the disadvantage that if a large amount of powder is introduced for a long time, the powder will gradually adhere to the quartz walls.

Problems to be Solved by the Invention The present invention provides high-frequency plasma or hybrid plasma that combines multiple DC plasmas and high-frequency plasmas.
The purpose is to introduce powder stably over a long period of time.

Means for Solving the Problems The present invention provides a high-frequency plasma characterized in that raw material powder is introduced together with hydrogen gas when powder is introduced into a high-frequency plasma or a hybrid plasma that combines a plurality of DC plasmas and high-frequency plasmas. This is a method of introducing powder into the

Plasma flames are ultra-high temperature gas flows, but high-temperature gases have high viscosity, so when raw powder is introduced from outside the plasma flame, some of the powder is repelled by the plasma flame surface.To prevent this phenomenon, requires direct introduction of the raw material powder into the plasma flame.

For this purpose, it is necessary to insert the raw material introduction nozzle into the plasma flame, but this can be solved by using a copper pipe with a water-cooled double structure. The material is not particularly limited to copper, but in order to enhance the water cooling effect, copper is preferable because of its good thermal conductivity.

Even if the raw material powder is introduced into the plasma flame in this manner, there will naturally be some powder that has low viscosity and will fly out of the plasma flame. In order to prevent this, it is preferable to introduce hydrogen gas together with the powder from the raw material introduction nozzle into the plasma center.

Hydrogen gas is preferably introduced through the same nozzle as the raw material powder, but may be introduced using a double pipe system or directly near the raw material powder nozzle.

Argon is usually used as the working plasma gas, but when hydrogen gas is introduced into the argon plasma flame, the plasma density in that area becomes low. This is thought to be because hydrogen is a diatomic molecule, but the hydrogen gas introduced together with the raw material generates a region with low plasma density on the central axis of the plasma flame. In other words, the plasma density increases in an annular shape around the central axis.

High plasma density naturally means high temperature, and as mentioned above, the higher the temperature of the gas flow, the higher the viscosity, so a plasma flame is formed where the viscosity is low on the central axis and the annular part around it is highly viscous. The present invention creates such a low viscosity area on the central axis of the plasma flame by introducing hydrogen, and by introducing the raw material powder into this area, it is possible to prevent the raw material powder from flying out of the plasma flame. This is to prevent

The present invention introduces hydrogen gas from a raw material introduction nozzle to form a plasma flame having a cylindrical low viscosity portion formed at the central axis of the plasma flame to prevent raw material powder from scattering from the flame, and This was completed by discovering that a raw material introduction nozzle was inserted into the plasma flame to directly introduce the powder into the flame. Furthermore, when the plate power of the high-frequency plasma is about 1100K, the introduction speed of hydrogen gas is approximately 2 to 5 M.
/sin is appropriate. If the amount of hydrogen gas introduced is smaller than this, the effect of making the plasma flame into an annular shape will be small, and if it is too large, the hydrogen gas will spread throughout the plasma flame, reducing the effect.

The amount of hydrogen gas introduced is changed as appropriate depending on the plasma output. Furthermore, in addition to hydrogen gas, inert gas such as Ar, He
Introducing such gas has no effect on the plasma flame and can be used as a carrier gas for raw material powder. Furthermore, in the present invention, since the powder raw material can be stably introduced into the plasma, it has become possible to process a significantly larger amount of raw material powder than in the case where hydrogen is not introduced.

Example A hybrid plasma device in which three direct current plasmas (9 km) were arranged on the circumference and a high frequency plasma (100 kl) was placed below them was heated through a water-cooled copper raw material introduction nozzle inserted into the upper part of the plasma flame. -M alloy powder (
(average particle size: 10 gm) was introduced, and its state was observed.

At was introduced as a plasma working gas at a rate of about 1501/min. The results are shown in Table 1.
When hydrogen is introduced in addition to Ar gas, the amount of powder adhering to the quartz tube wall is smaller than when hydrogen is not introduced, and the effect is especially remarkable when the hydrogen amount is 2.5 and 5 cm/min. .

In addition, the raw material introduction nozzle is not inserted into the plasma flame,
When placed outside the plasma flame, the amount of powder adhering to the quartz tube wall increases by several grams under all conditions, and No.
Under the same conditions as above, after the plasma was extinguished, cracks appeared in the quartz tube from the part where the powder was attached.

As a result of electron microscopic observation, the produced powder was found to have a spherical shape of 0.1 to 0.
．． It was 54m of 5i-A1 alloy powder. Since the raw material powder has a particle size of 10 ILm, it is considered that the powder was evaporated in plasma and then cooled and precipitated.

In addition, the particle size distribution of the produced powder is better when hydrogen is introduced.
It was small.

(Hereinafter in the margin) Effects of the Invention The present invention has made it possible to stably supply raw material powder into a high-frequency plasma flame, and to enable long-term operation without damage to the quartz tube wall. Furthermore, it has become possible to introduce a larger amount of raw material powder than in the past.

Claims (2)

[Claims] (1) In the operation process in which raw material powder is introduced into high-frequency plasma or a hybrid plasma that combines multiple DC plasmas and high-frequency plasma, and the powder is melted or evaporated, hydrogen gas is added to the plasma flame along with the raw material powder. A method of operating a high-frequency plasma reactor, characterized by introducing the high-frequency plasma reactor into a plasma reactor. (2) A method for operating a high-frequency plasma reactor according to claim (1), characterized in that hydrogen gas and raw material powder are introduced into a plasma flame through a nozzle charged therein.