JPH0124727B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing ultrafine SiC powder suitable as a high-temperature structural material.

SiC is chemically stable at room and high temperatures and has excellent mechanical strength, so it can be used in ceramic engines,
It is expected to be used as another high-temperature structural material.

Since SiC is inherently difficult to sinter, it is sintered by adding sintering aids such as boron or alumina, or by applying high pressure by hot pressing, HIP, etc. However, the strength of products sintered with the addition of sintering aids decreases at high temperatures, and hot pressing and HIP sintering methods have the problem of making it difficult to sinter large, complex-shaped products. Therefore, in the production of SiC sintered bodies with high density, uniform phase, and fine particle size, the raw material SiC powder is required to be of high purity, submicron or smaller particles, narrow particle size distribution, and little agglomeration. It became like that.

Conventional technology The conventional manufacturing method of SiC fine powder is as follows: (1) SiC reduction reaction method (2) Grinding method of SiC coarse particles (3) Solid phase reaction method of Si and C (4) Various gas phase reaction methods etc. are known.

However, methods (1) to (3) above include a pulverization step in the manufacturing process, making it difficult to manufacture ultrafine powder of submicron size or less, and also having the disadvantage that impurities are likely to be mixed in.

On the other hand, method (4) has the advantage that it is easy to obtain fine particles because it is precipitated from the gas phase, and that it is easy to obtain high-purity powder because it is easy to purify at the raw material stage. In the gas phase reaction method, a gas is introduced into a reaction chamber as a raw material and reacted under temperature and pressure conditions such that the substance to be synthesized (e.g. silicon carbide) is stable in the solid phase and other chemical species are stable in the gas phase. It's a method. The gas phase reaction method is suitable for synthesizing thin films and powders.

In normal gas phase reaction methods, the reaction proceeds by heating, but in some cases light, laser, electron beam, plasma, etc. can be used in addition to temperature to excite the reaction. In particular, when using plasma, the gas itself is in an ultra-high temperature state, which provides various advantages. However, since the use of plasma is the latest technology, it often involves technical difficulties in its handling and stability. In particular, the conventional plasma method requires a large amount of gas and uses electrodes, which have the disadvantage of introducing impurities.

OBJECT OF THE INVENTION The present invention seeks to overcome the drawbacks of the conventional methods, and its purpose is to provide a simple and small-scale device,
The object of the present invention is to provide a method for producing high-purity SiC ultrafine powder whose particle size, composition, and crystal phase are controlled.

Structure of the Invention As a result of intensive research to achieve the above object, the present inventors found that in addition to high frequency power acting on plasma,
It has been found that by controlling the pressure of the reaction system, the amount of gas consumed can be reduced, and the particle size, composition, and crystal phase of the produced powder can be controlled. The present invention was completed based on this knowledge.

The gist of the present invention is to introduce raw material gases of hydrogen silicide or silicon halide and hydrocarbon into plasma in a non-oxidizing atmosphere created using non-polar discharge of high frequency induction method, and to reduce the pressure of the reaction system to 1. below atmospheric pressure
The present invention provides a method for producing ultrafine SiC powder, which is characterized by carrying out a gas phase reaction while controlling the pressure within a range of 0.1 torr or more.

In order to produce fine particles, it is desirable to control the reaction rate, nucleation rate, and particle growth rate, so a plasma generation method that allows atmosphere control, temperature control, and generation enthalpy control is desirable.
Plasma generation methods include high frequency induction method (400kHz to 3GHz), high frequency induction method, DC arc method,
There are alternating current arc methods, laser methods, etc., but among these methods, argon plasma, which is created using non-polar discharge using a high frequency induction method, is used because it is easy to control enthalpy by controlling the cleanliness of the atmosphere, electric power, gas pressure, etc. Further, hydrogen plasma, hydrocarbon plasma, or a mixed plasma of these may be used, but the atmosphere must be non-oxidizing and only need to be neutral or reducing.

Hydrogen silicide or silicon halide used as raw materials include SiCl ₄ , Si ₂ H ₆ , SiH ₃ Cl, SiCl ₂ H ₂ , SiCl ₃ H,
Examples of hydrocarbons include SiCl ₄ , etc.
Examples include CH ₄ , C ₂ H ₄ , C ₃ H ₆ and C ₃ H ₈ . However, it is not limited to these compounds.

When the high frequency power source is 4MHz and 15kW, the mixing ratio of the raw material gas mixed into the plasma gas is as follows:
A ratio of 0.001 to 1 vol. is desirable. When the degree of contamination is greater than 1, the plasma becomes unstable, and when it is less than 0.001, the reaction rate becomes poor.

The method of generating plasma is to reduce the pressure inside the furnace to 0.1 torr or less, generate a glow discharge by applying a voltage of 4 kV to the anode electrode, then introduce plasma gas and pressurize the inside of the furnace to 1.5 torr. You will get a frame.

A source gas is introduced into the obtained non-oxidizing plasma gas.

The pressure of the atmosphere is controlled to a pressure in the range of less than 1 atm and more than 0.1 torr, which allows gas convection to be controlled, so that the plasma is stable and almost no source gas introduced into the plasma comes out of the plasma. When this pressure exceeds 1 atm, it becomes difficult to control the gas convection described above, and a large amount of SiC adheres to the furnace walls, such as the quartz tube walls, which prevents plasma radiation and lowers the temperature of the quartz tube. Raising the temperature will shorten the life of the quartz tube, and if the temperature exceeds, for example, 2 atmospheres, the plasma temperature will rise, but the plasma will become unstable and the resulting SiC powder will often have a particle radius of 1000 Å or more. Moreover, if this pressure is lower than 0.1 torr, the yield of the obtained powder will be low.

When the atomic molar ratio of hydrogen silicide in the raw material gas and C to Si in the hydrocarbon ranges from 1 to 5, the SiC generation region tends to expand as the pressure in the furnace increases, but as the pressure approaches 1 atm, the plasma temperature decreases. As the temperature rises, decomposition of SiC begins to occur, and the area where SiC is produced becomes narrower. A similar trend can also be seen in the effect of the power supplied by the high-frequency power supply on the SiC generation region.

When the in-furnace gas pressure and supply power are constant, Si generation is recognized when the atomic molar ratio of C and Si in the raw material gas is less than 1, and in the molar ratio range of 1 to 3, only SiC is generated, and 5. If the atomic molar ratio of C and Si is 1 to 1, the atomic molar ratio of C and Si tends to expand.
5, preferably 1 to 3 molar ratio.

On the other hand, the crystalline phase of the produced SiC powder is a homogeneous beta phase when the furnace pressure is low, but when the pressure is close to 1 atmosphere, there is a tendency for a slight alpha phase to coexist.

In addition, the particle size of the generated SiC powder is determined by the furnace gas pressure,
As the supplied power increases, crystal growth is promoted due to the rise in plasma temperature, so it tends to become larger.

Example 1 After evacuating the furnace to 0.1 torr, the anode voltage was
A high frequency wave of 4kV, anode current of 1.5A, grid current of 30mA, and frequency of 3.6MHz was applied to the work coil to create a glow using non-polar discharge.

Next, flow argon gas at a flow rate of 58.4ml/min.
Anode voltage 6kV, anode current 1.5A, grit current 40
Argon gas plasma was created by passing a high frequency wave of mA and frequency of 3.6 MHz through the work coil. A mixture of 1.22 ml/min of SiH ₄ gas and _1.79 ml/min (C/Si = 2.9) of SiH ₄ gas and 1.79 ml/min (C/Si = 2.9) of argon gas (concentration 4.9%) was introduced into the argon gas, and a plasma gas phase reaction was carried out at a gas pressure of 5 torr. SiC fine powder was synthesized.

According to powder X-ray diffraction, this powder has mostly β
-It was SiC. In addition, the particle size of this powder was 150 Å to 250 Å according to transmission electron mirror observation, and the average particle size calculated from the peak half width by powder X-ray diffraction was 70 Å.

Example 2 In Example 1, argon gas 177.1ml/
min, silane gas 2.07ml/min, ethylene gas
SiC fine powder was synthesized by setting the gas pressure to 10 torr at a flow rate of 2.42 ml/min (C/Si = 2.34, concentration 2.5%).

The obtained powder was mostly β-SiC and had a particle diameter of 200 Å to 250 Å as determined by transmission electron microscopy, and an average particle diameter of 100 Å calculated from the peak half width by powder X-ray diffraction.

Example 3 The power supply conditions were set to anode voltage 6.5kV, anode current 1.6A, grit current 55mA, and frequency 3.6MHz.
Argon gas 236.4ml/min, silane gas 2.04ml/min
min, ethylene gas 2.07ml/min (C/Si=2.03,
SiC fine powder was synthesized at a flow rate of 1.7%) and a gas pressure of 50 torr.

The obtained powder was mostly β-SiC and had a particle diameter of 250 Å to 350 Å as determined by transmission electron microscopy, and an average particle diameter of 160 Å calculated from the peak half-width by powder X-ray diffraction.

Example 4 Argon gas 1087.6ml/min in Example 3
Silane gas 1.83ml/min, ethylene gas 2.76ml/min
SiC fine powder was synthesized by setting the gas pressure to 360 torr at a flow rate of min (C/Si = 3.02, concentration 0.4%).

β-SiC accounts for 86% of the obtained powder, and the remaining 14
% was Si. The average particle size of β-SiC is powder
Calculated from the peak half width by line diffraction: 200 Å
It was hot.

Comparative example Power supply conditions are set to anode voltage 7kV, anode current 1.7A, grit current 55mA, frequency 3.6MHz, argon gas 1091.9ml/min, silane gas 4.09ml/min.
min, ethylene gas flow rate of 4.8 ml/min (C/Si = 2.35, concentration 0.8%) and gas pressure set to 1 atm.
A fine powder was synthesized.

The obtained powder is 75% β-SiC, 18% Si, and about 7% graphite, with a small amount of 15R-SiC.
The formation of was also observed.

The average particle diameter of β-SiC was 512 Å when calculated from the peak half-width by powder X-ray diffraction.

Effects of the Invention According to the method of the present invention, (1) Since the plasma temperature and the amount of enthalpy generated are controlled not only by the supplied power but also by the gas pressure, the control range is expanded and the mean free path of the active gas species can also be controlled. Therefore, it is easy to control the particle size, composition, and crystallinity of the produced powder.

(2) By controlling the pressure of the reaction system, a gentle plasma flame can be generated, so the amount of sheath gas used can be reduced.
That is, the conventional method required a large amount of sheath gas due to the intense jet-like plasma flame, but this drawback can be eliminated.

(3) By introducing the raw material gas into the center of the plasma, which has a temperature of 10,000 to 20,000 K, molecules and atoms are decomposed into ions, which can be rapidly cooled, making it possible to obtain particles as small as 100 Å in diameter.

For example, in the conventional method, the raw material gas was introduced into the vicinity of the plasma at a temperature of 2000 to 3000 K, which did not fully utilize the extremely high temperature and high enthalpy of the plasma, which was inefficient. Obtained.

(4) Since plasma generators such as arc electrodes are not used, high-purity SiC ultrafine powder can be produced without contamination with impurities, and the equipment is simple and small-scale, with improved operability. Longer lifespan.

It is possible to achieve excellent effects that cannot be obtained with conventional methods such as the following.

Claims (1)

[Claims] 1. Introducing raw material gases of hydrogen silicide or silicon halide and hydrocarbon into plasma in a non-oxidizing atmosphere created by non-polar discharge using high-frequency induction method, and reducing the pressure of the reaction system to less than 1 atmosphere. SiC is characterized by a gas phase reaction that is controlled within a range of 0.1 torr or more.
Method for producing ultrafine powder. 2. The method for producing ultrafine SiC powder according to claim 1, wherein hydrogen silicide and hydrocarbon are introduced into the plasma at an atomic molar ratio of C to Si of 1 to 5.