JPS5825045B2 - Method for producing SiC ultrafine particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing ultrafine SiC particles, and more specifically, to a method for producing ultrafine SiC particles with high purity by reacting raw material gas with plasma in the gas phase. It is.

Conventionally, methods for producing such SiC fine particles include (a) pulverization of 8 i C coarse particles, (b) solid phase reaction of silicon powder and carbon powder, and (c) solid phase reaction of silicon oxide powder and carbon powder. (d) Various gas phase reactions are known.

However, in the method (a) of pulverizing SiC coarse particles, it is extremely difficult to produce ultrafine particles, and it is almost impossible to produce ultrafine particles with an IPm or less.

Also, (b) solid phase reaction between silicon powder and carbon powder, (c)
In the case of a solid phase reaction such as a solid phase reaction between silicon oxide powder and carbon powder, finer particles can be obtained than the method of pulverizing SiC coarse particles, and it is also possible to produce Zabumicron particles, but it is still sufficient. The particle size cannot be said to be small, and in addition,
Because it must be manufactured at high temperatures, it has the disadvantage of being more likely to be contaminated with impurities than the surrounding environment.

Compared to the above-mentioned methods, (d) a method using a gas phase reaction has the following advantages: ultrafine SiC particles can be obtained, the atmosphere can be easily controlled, high purity products can be easily obtained, and dispersibility has improved. There are advantages such as being good.

However, in the method using this gas phase reaction,
Generally, the feed gas must be heated to a high temperature.

For example, one of the gas phase methods is to sublimate SiC to obtain ultrafine particles, but in this case, if heating is not performed, S
iC ultrafine particles can only be obtained in extremely small quantities.

Conventionally, an arc or a plasma jet has been used as a heating means.

However, these methods require high power, a large amount of plasma gas, and large equipment, and have the disadvantage that they cannot prevent contamination of impurities from carbon, metal, etc. used in the electrodes.

The present invention aims to eliminate these drawbacks.

Specifically, the purpose of the present invention is to provide a method for producing medium-sized, high-purity SiC ultrafine particles in the amount of several tens of grams per day using a small device, small amount of gas, and low power using a plasma gas phase reaction. .

Therefore, the method for producing ultrafine SiC particles according to the present invention is characterized in that after plasma is generated in the reaction system, a raw material gas is introduced into the reaction system.

According to the method for producing SiC ultrafine particles according to the present invention, a stable plasma is generated in the reaction system in advance (that is, unlike a method using an arc or the like, electric discharge is not repeated during the reaction, After the plasma is generated, the electrode is removed from the reaction system, eliminating the possibility of contamination with impurities such as the electrode.

Moreover, it has the advantage of requiring less gas and electricity.
In addition, it has the advantage that the device can be made smaller.

To explain the present invention in more detail, SiC in the present invention
The method for producing ultrafine particles first involves generating plasma in a reaction system.

Although the method of plasma generation and stabilization is not limited in the present invention, it can be carried out using, for example, a reaction torch whose cross-sectional view is shown in FIG.

FIG. 1 is a cross-sectional view of an example of a reaction torch for carrying out the method for producing SiC ultrafine particles in the present invention, and in the figure,
1 is a reaction torch, 2 is an external quartz glass tube, 3 is an intermediate quartz glass tube, 4 is an internal quartz glass tube, 5 is a reaction chamber, 6 is a water-cooled mold, 7 is a plasma gas inlet, 8 is a source gas introduction 9 is a graphite rod, 10 is a work coil, and 11 is a powder deposition chamber.

As is clear from FIG. 1, this reaction torch 1 includes an intermediate quartz glass tube 3 and an internal quartz glass tube 4 inserted concentrically and spaced apart from an external quartz glass tube 2. A reaction chamber 5 is provided below the lower ends of the tube 3 and the inner quartz glass tube 4, and the upper ends of the outer quartz glass tube 2, the intermediate quartz glass tube 3, and the inner quartz glass tube 4 are covered with a water-cooled mold 6 in a stepped manner. It is integrated with quartz glass.

Further, this water-cooled mold 6 is provided with a plasma gas introduction lower for introducing plasma gas into a gas passage formed by the inner wall of the intermediate quartz glass tube 3 and the outer wall of the inner quartz glass tube 4. A raw material gas inlet 8 for introducing raw material gas into a gas path constituted by the inner wall of the external quartz glass tube 2 and the outer wall of the intermediate quartz glass tube 3 is bored.

A graphite rod 9, which is an electric electrode, is inserted into the internal glass tube 4 from the top of the water-cooled mold 6 so as to be able to move up and down, and the work coil 10, which is the other electrode, is inserted into the external quartz glass tube corresponding to the reaction chamber 5. It is wrapped in two parts.

Below the reaction chamber 5 is a powder deposition chamber 11 for depositing the produced SiC ultrafine particles.

To use this reaction torch 1, first, a plasma gas (for example, argon, etc.) is introduced from the plasma gas introduction lower.
is introduced into the reaction chamber 5, the graphite rod 9 is made to protrude into the reaction chamber 5 from inside the internal quartz glass 4, and plasma is generated by the action with the work coil 10.

Thereafter, the graphite rod 9 is pulled up and removed from the reaction chamber 5, and the raw material gas is introduced from the raw material gas inlet 8.

By introducing the raw material gas, a reaction occurs in the reaction chamber 5, and the generated SiC ultrafine particles are deposited in the powder deposition chamber 11.

In this way, plasma is generated and stabilized, but the stability of the plasma depends on the shape of the reaction torch 1, the shape of the work coil 10, power frequency, output, output impedance, type of plasma gas, and flow rate. Among these, the shape of the reaction torch 1 is the most important.

To give an example of specific conditions for plasma stability when using the reaction torch 1 described above, when argon is used as the plasma gas, the internal quartz glass tube 4 has a diameter of 235 mm, the intermediate quartz glass tube 3 has a diameter of 35 mm, When the external quartz glass tube 2 has a diameter of 45mm, the frequency of the power supply is 4MHz, and the number of turns of the work coil 10 is 4, if argon gas is flowed over 13#/m to the plasma gas introduction lower, the output will be over IKW. A stable plasma can be obtained.

A part of this argon gas (plasma gas) is used to heat the insulation between the plasma and the external quartz glass tube 2.
plays the role of cooling.

Therefore, it is possible to minimize deterioration of the external quartz glass tube 2 and to generate plasma over a long period of time.

When this reaction torch 1 is used, the concentration or flow rate of the raw material gas can be changed appropriately.

However, if the concentration is too high, there is a risk that the plasma will disappear, but this will vary depending on the flow rate of the plasma gas, the amount of applied power, etc.

Further, in this reaction torch 1, it is also possible to introduce the raw material gas from inside the internal glass tube 4 through which the graphite rod 9 is inserted.

In this case, the stability of the plasma is the same as when the source gas is introduced from the source gas inlet 8, but the stability decreases when the flow rate becomes too high.

In this way, plasma stability can be obtained under various conditions in addition to the above-mentioned specific conditions.

Furthermore, even if the reaction torch 1 is shaped without the intermediate quartz glass tube 3, stable plasma can be obtained.

By making the reaction torch 1 have a double structure and reducing the diameter of the quartz glass tube, the flow rate of the plasma gas can be reduced.

For example, the internal quartz glass tube 4 in Fig. 1 has a diameter of 22rtynφ.
, assuming that the external quartz glass tube 2 is 35++ mφ, when using argon gas, the flow rate is 213/1 or more, 1.4 K
Plasma becomes stable with a power of W or more.

However, if the diameter of the external quartz glass tube 2 is too small, the heat of the plasma will affect the external quartz glass tube 2, leading to devitrification or melting under unfavorable conditions.

When using this double-structured plasma torch, plasma is generated, and the raw material gas is mixed with the plasma gas before the reaction torch 1 and introduced into the reaction torch 1 to perform a plasma gas phase reaction.

In this case as well, the flow rate or concentration of the raw material gas can be changed as appropriate in the same manner as in the triple structure reaction torch (FIG. 1), and the diameter of the obtained particles is also the same value.

In the present invention, the raw material gas is introduced into the plasma in this way, and this raw material gas is thermodynamically
Anything that generates this can be used.

For example, it is possible to use one or more of methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, etc., or a combination of one or more of silane, silicon tetrachloride, and one or more of methane, ethane, etc. Many compounds and combinations of compounds containing and carbon can be used.

Next, a schematic illustration of the implementation of the method of the invention will be explained based on the drawings.

FIG. 2A is a schematic diagram of an apparatus for carrying out the method for producing SiC ultrafine particles according to the present invention, in which 12 is a high frequency power source;
3 is an exhaust pipe, 14 is a plasma gas introduction pipe, 15 is a flow meter, 16 is a raw material gas introduction pipe, 17 is a thermostatic chamber, 18 is a liquid raw material tank, and the other parts are the same as those shown in FIG.

The reaction torch 1 is a triple-structured or double-structured reaction torch shown in FIG.
Connected to 2.

In addition, an exhaust pipe 1 is provided at the bottom of the powder deposition chamber 11 of the reaction torch 1.
There are 3.

Further, the plasma gas introduction pipe 14 is connected to the reaction torch 1 via a flow meter 15.

The raw material gas introduction pipe 16 passes through a liquid raw material tank 18 whose temperature is adjusted in a constant temperature bath 17 via a flow meter 15 and is connected to the reaction torch 1 .

First, the flow rate is measured from the plasma gas introduction pipe 14 to the flow meter 1.
The plasma gas adjusted in step 5 is introduced into the reaction torch 1, and plasma is generated in the reaction torch 1 using the graphite rod 9, work coil 10, and high frequency power source 12.

Next, the graphite rod 9 is pulled up, and from the raw material gas introduction pipe 16,
A carrier gas whose flow rate is adjusted by a flow meter 15 is caused to flow, and the liquid raw material in the liquid raw material tank 18 is vaporized and introduced into the reaction torch 1.

The SiC ultrafine particles generated within the reaction torch 1 are deposited in the powder deposition chamber 11, while the gas is exhausted from the exhaust pipe 13.

FIG. 2B is a schematic diagram of a manufacturing apparatus in which the raw material is gas from the beginning, and the raw material gas introduction pipe 16 is directly connected to the reaction torch 1 via a flow meter 15.

In this case, since the raw material is a gas from the beginning,
and the liquid raw material tank 18 are no longer necessary.

The device is otherwise similar to the device of FIG. 2A and operates similarly.

Next, an example will be explained.

Example 1 Liquid methyltrichlorosilane containing silicon and carbon in a 1:1 ratio was used as a raw material, and argon gas was used as a carrier.1. I x 10" mol/mvt and 151/71 u!t of argon gas as the plasma gas were introduced into the triple structure reaction torch shown in FIG.
Using a high-frequency power source and a work coil with a diameter of 507 nm and 4 turns, a plasma gas phase reaction was carried out at an output of 3.5 KW, and a solid product was deposited below the torch.

This was heat-treated at about 1200° C. in an argon gas atmosphere and then at about 650° C. in air to obtain a light gray powder.

According to a transmission electron microscope observation of this powder, the particle size of the powder was 100 to 1000 particles, and no increase in particle size was observed due to heat treatment.

According to powder X-ray diffraction, this powder mainly contained β-3iC.

Similar results were obtained using silane and methane as gaseous feedstocks.

Example 2 Methyltrichlorosilane using argon gas as a carrier 1. Argon gas I
This was mixed into the QA/mvt and introduced into the double structure reaction torch, and the
．． Plasma gas phase reaction was carried out using a 5-turn work coil at a power of 2.9 KW for 1 hour to deposit a solid product below the torch.

After the same heat treatment as in Example 1, the powder is light gray in color and the particle size is between 150 and 750 particles,
It was mainly β-3iC.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an example of a reaction torch for carrying out the method for producing ultrafine SiC particles according to the present invention, and FIGS. 2A and 2B are cross-sectional views for carrying out the method for producing ultrafine SiC particles according to the present invention. FIG. 2 is a schematic diagram of the device. 1... Reaction torch, 2... External quartz glass tube, 3... Intermediate quartz glass tube, 4...
...Internal quartz glass tube, 5...Reaction chamber, 6...
...Water-cooled mold, 7...Plasma gas inlet, 8...Raw material gas inlet, 9...Graphite rod, 10... Work coil, 11...
・Powder deposition chamber, 12...High frequency power supply, 13...
... Exhaust pipe, 14 ... Plasma gas introduction pipe, 15 ... Flowmeter, 16 ... Raw material gas introduction pipe, 17 ... Constant temperature Tank, 18...
Liquid raw material tank.

Claims (1)

[Claims] 1. A work coil and an electrode are used in the reaction system to stably generate plasma by a lucky discharge, and after the electrode is extracted from the reaction system, a raw material gas containing silicon and carbon is introduced into the reaction system. A method for producing SiC ultrafine particles.