JPS60246212A - Ultrafine particles of amorphous silicon nitride and its production - Google Patents

Abstract

PURPOSE:A silicon halide is blown into a plasma stream of a nitrogen-hydrogen mixed gas to cause the reactions with nitrogen and hydrogen whereby uniform silicon nitride excellent in heat resistance and corrosion resistance is obtained. CONSTITUTION:A silicon halide is blown into a plasma stream of a nitrogen- hydrogen mixed gas to effect the reaction with activated nitrogen and hydrogen. The plasma gas stream is formed by high-frequency induction heating. The through-put of the gas for plasma naturally depends upon the capacity of the plasma torch employed, however, the feed of the silicon halide is kept in a range from 0.05-0.2 at a gas volume ratio of the halide to the plasma calculated under normal conditions. The amount of the hydrogen in the plasma gas preferably ranges from 0.3 to 1.0 time the mole of the halogen atom.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to amorphous ultrafine particle silicon nitride and a method for producing the same. More specifically, the present invention relates to amorphous ultrafine particulate silicon nitride produced by injecting a halogenated silicon compound into a mixed plasma gas flow of nitrogen and hydrogen and reacting these three raw materials, and a method for producing the same.

Silicon nitride is known to be a material that is excellent in heat resistance and corrosion resistance, and particularly in thermal shock resistance. Therefore, it is expected to be used as a heat-resistant high-temperature structural material for automobile or industrial gas turbine or reciprocating engine parts, as well as for industrial high-temperature heat exchanger parts.

The following methods are known as conventional methods for producing silicon nitride powder. That is, a method in which metallic silicon is directly nitrided with nitrogen gas, a method in which a mixture of silica powder and carbon powder is nitrided with nitrogen gas11, or a method in which silicon imide is formed from silicon tetrachloride and ammonia and this is thermally decomposed. etc. However, these methods have the problem that super W1 particles suitable for sintering cannot be obtained.

Another method is (1) a method in which silicon halide or silicon hydride (silane) and ammonia gas are subjected to a gas phase reaction in a gas phase reaction tube heated to a high temperature (Japanese Patent Application Laid-Open No. 54-13
4.089, 57-82, 108), or (method of reacting the same raw materials by contacting them with ultra-high temperature plasma (JP-A-1983-16.604, JP-A No. 57-209,
810) has been proposed. According to these methods, it is expected that silicon nitride in the form of ultrafine powder can be obtained. However, since all of the II compounds are produced through an imide production reaction, the resulting amorphous powder material contains many NH groups. Therefore, the visible powder material is unstable, prone to hydrolysis due to moisture absorption or reaction with oxygen in the air, and cannot be used for sintering until it is produced. need to be done.

In addition, in these plasma utilization methods, the velocity of the plasma flow passing through the plasma torch (see the explanation in the drawings below) is always fast, such as 10 to 20 m/sec.

Therefore, when introducing the reactant source 4 into the plasma flow,
If the force n is blown from the periphery of the torch supernatant as described in the above-mentioned prior art, the reaction material gas will be swept away by the plasma flow and will only flow to the wall of the reactor, causing the temperature to drop. is further cooled from the wall by 1:IL per minute.

Therefore, the reaction raw material gas cannot react in minutes.

The inventors of the present invention have investigated the following problems, and as a result of intensive research to obtain 1-quality ultrafine particulate silicon nitride that is chemically stable and can be used for immediate sintering, All of the problems of the prior art described above have been solved by injecting a silicon halogenide compound into a mixed plasma gas flow of nitrogen and hydrogen to cause these rare substances to react. The present invention was completed knowing that silicon nitride could be obtained.

As is clear from the description below, an object of the present invention is to provide homogeneous amorphous ultrafine particle silicon nitride that can be produced under stable operating conditions and a method for producing the same. teeth,
This will become clear from the description below.

The present invention (-invention) has the following main configurations (1) and (5) and the embodiment configurations (2) to (4).

(1) An amorphous superstructure characterized by injecting a silicon halide compound into a mixed plasma gas stream of nitrogen and hydrogen, and causing the silicon halide to react with activated nitrogen and hydrogen in the plasma gas stream. A method for producing particulate silicon nitride.

(2) The manufacturing method according to item 1 above, wherein the plasma gas flow is formed by high-frequency induction heating.

(3) The method according to item 1, wherein the ratio of the silicon halide compound to the plasma gas is 0.05 to 0.2 in terms of gas volume ratio converted to a standard state.

(4) Number of moles of hydrogen gas and halogenated silicon compound molecules
The manufacturing method according to the above item 1, wherein the ratio of the number of halogen atoms therein is 0.3 to 1.0.

(5) Amorphous ultrafine particulate nitridation obtained by blowing a silicon halide compound into a mixed plasma gas flow of nitrogen and hydrogen, and reacting the silicon halide with activated nitrogen and hydrogen in the plasma gas flow. silicon.

In the method of the present invention, a gas mixture of nitrogen and hydrogen is used to first form a plasma gas stream. Therefore, a plasma forming device is used. Although the apparatus is not limited, one example of the apparatus used in the method of the present invention will be explained with reference to the drawings.

In the figure, reference numeral 1 designates a high-frequency induction plasma torch, which is partially equipped with a nozzle head 2 having plasma-operated gas nozzles 2a, 2b, and 2C. The head 2 further includes a raw material gas supply pipe 3 having a double pipe structure with a partition wall.
is inserted through the center of the head 2 in the 1-down direction. The outer pipe of the supply pipe 3 is a cooling pipe, and the cooling water supplied from the cooling water port 3a reaches the tip of the chain pipe through the partition wall, and then returns to the upper end through the opposite side of the partition wall, and the cooling water is returned to the upper end. It is discharged from output r+3.

Subsequently, 4 is the innermost cylinder made of quartz installed in the plasma torch 1, and has a water cooling jacket 7 on the outside thereof. The jacket has a cooling water inlet lower d and a cooling water outlet [17b] bored in the torch I, and the cooling water is passed therethrough during operation of the torch.

Further, a high-frequency induction coil 5 is provided outside the innermost cylinder 4 within the water-cooling jacket 7, and the coil is connected to a high-frequency transmitter (not shown) provided outside the device using conductive wires 6a and 6b. The frequency of the high frequency to be oscillated when carrying out the present invention varies depending on the size of the device, but is in the range of several hundred KHz to 5 MHz.

The plasma formation method is such that plasma operating gas (note: nitrogen and hydrogen) supplied from nozzles 2a, 2b, and 2C attached to the head 2 is placed in a corresponding position in the coil 5 in the innermost cylinder 4. When passing through, the plasma flame 14 having an annular or doughnut-shaped ultra-high temperature part 15 is formed by receiving energy based on the high-frequency current applied to the coil. Preliminary feed nozzles 8a and 8b are provided at the lower part of the plasma torch l, and these nozzles are used for supplying waste for quenching or as a third feed nozzle.
Used for adding ingredients. The lower end of the plasma torch 1 is removably connected to a reaction cooling device 10. Its innermost cylinder 11 is made of quartz like the aforementioned innermost cylinder 4, and its outer side (engineering cooling device lO (inside the main body) is a water-cooled jacket i.12.The jacket has cooling water containers 1:112a and +112a drilled in the cooling device 10.
2b, and the cooling water is passed therethrough while the torch 1 is in operation.

The lower part of the plasma flame 14 mentioned above is a torch L and a cooling bag M1.
It penetrates through the joint part 0 and reaches the 12 part of the innermost cylinder 11. It is then cooled in III and returns from the plasma flame to a normal mixed gas flow. cooling'! The F part of the A position 10 is a lower flange 13, and is connected to a powder collecting device (not shown). As the powder collecting device #A, for example, but not limited to, a cyclone, a bag filter, a static electricity collecting device, or a combination thereof can be used.

In carrying out the method of the invention, for example, using the apparatus described above, hydrogen gas '4! Supply raw gas or hydrogen-nitrogen mixed gas. The amount of plasma forming gas that can be supplied is
Although it is automatically determined by the quality of the equipment (plasma torch) used, the supply acid of the silicon halide compound is 0 in terms of the gas volume ratio converted to the standard state with respect to the plasma gas amount.
．． Keep it within the range of 0.05 to 0.2. Further, in order to improve the mixing of the silicon halide compound and the plasma forming gas, a carrier gas such as nitrogen or hydrogen may be introduced together. The ratio of hydrogen used in the plasma forming gas is 0.3 to 1.0 to 1.0 to 1.0 per the number of halogen atoms contained in the silicon halide supplied as a raw material.
A range of 0 times the mole is preferred.

The mixed gas supplied as explained in the above figure absorbs the high frequency energy loaded on the high frequency induction coil 5 (hereinafter referred to as RF coil), and the component gases are dissociated and ionized into their original states, and 1 It becomes a high-temperature plasma flow exceeding 10,000 degrees Celsius. This state is explained by Plasma Chemist
ry and Plasma ProcessingV
ol l, No, l, 1981 T, Yoshid
As shown in the research report of a, a donut-shaped highest temperature distribution portion 15 is generated in the innermost cylinder 4 corresponding to the height of the RF coil 5, and the temperature distribution as the plasma flame 14 is located downstream of the plasma flow. The average value is 4,000 to 50,000 near the exit of the plasma torch.

When looking at a detailed cross-section of the plasma flame at this exit portion, the temperature is high at the concentric central portion, and the temperature is suddenly low at the portion close to the inner wall surface of the innermost cylinder 4.

On the other hand, the velocity of the plasma flow passing through the torch is 10-2
Since the speed is about 0 m/sec, the reaction master 4 cannot be sufficiently heated by the method of introducing the reaction raw material into the plasma flow from the periphery of the torched flow as described above. it is obvious.

The woody feature of the method of the present invention is that the silicon halide raw material is introduced into the straight portion 16 of the donut-shaped high temperature portion 15 in the plasma flame within the torch. By supplying the raw material to the portion, the high-temperature energy of the plasma can be utilized to the maximum extent, and the reaction between the silicon halide compound and nitrogen and hydrogen, which are already in an active state at the time of the introduction, is promoted.

The silicon halide used in the present invention is not limited to, but may be 5iX4 (where x is CI, Br or
), 5iHXi, or S i H2Xa. Among them, 5iCl+ is preferable, and the method of supplying the silicon halide to the reaction device, that is, the plasma torch, is to spray a liquid and blow it in, or to use a gas as it is, or by using nitrogen, hydrogen, etc. It can be supplied diluted with a carrier gas.

The reaction equations related to the above-mentioned raw materials according to the method of the present invention are shown by the following equations. (When using Tagushi 5iCI+).

3SiCI+ +4(N)+12(H)→S h N4
+12MCl...(1)SiCl+" 4(H)
→Si(g)+4HCI...(2)SiCI+
→Si(g)+4((:I)...(2).

4(CI) + 4(H) → 4HC1...(2)
3Si(g) ” 4(N)” −” 5h14 −(
3) In other words, most of the nitrogen-hydrogen mixture gas supplied into the plasma torch is dissociated in the formed high-temperature plasma flame and becomes atomic or ionic, with some NH or NH2 ions being no longer present. 1 has been completed. The generation of silicon nitride is expressed by equation (1) and equation (2) or (2) °
The gaseous silicon produced by the formula reacts with the raw r-form nitrogen (3)
It consists of a ceremony.

The silicon nitride thus obtained has the following characteristics in terms of X-rays.

Amorphous and particle size 0. O1~0.02 it l! It is an ultrafine powder of -F, and is suitable for producing a high-strength structural material 1 by sintering. In addition, nitrided 11 obtained by the reaction of the present invention
Because there are very few N)I groups as impurities in the element,
Although the silicon nitride is amorphous ultrafine particles, it maintains sufficient stability to be handled in air. Tarishi,
Depending on the reaction conditions, minute amounts of NH groups may be mixed into the fine powder, but the reason for this is that N)
This is because ions or NH2 ions are generated.

This amorphous ultrafine powder silicon nitride can of course be used for sintering as described above, but it can also be heat-treated (note, see examples below) if necessary. A silicon nitride fine powder with a high α-crystal content can be easily obtained.

The present invention will be explained below using Examples.

Example frequency 4MHz, output? Manufacturing equipment was used, which was equipped with an OK-high frequency oscillator, a 56-type plasma torch manufactured by TAFA Co., USA, and a separately manufactured reaction cooling device and powder collection device as shown in the figure. First, the pressure inside the system is reduced, and then the atmosphere is replaced with argon gas.

Next, flow 201/■1n of argon gas through nozzle 2a (spouts vertically) and 25cm/■11 of argon gas through nozzle 2c (spouts in a swirling flow), raise the power of the high-frequency induction coil, and then Ignite the plasma using the method. To maintain the stability of the plasma flame, gradually increasing the power, add 25 cycles/1n of nitrogen to nozzle 2C, and then add 35 cycles/1n of nitrogen to nozzle 2b (radially ejecting).
After that, the argon gas flowing through the nozzles 2a and 2C was gradually lowered, and finally a nitrogen-only plasma flow was obtained. Next, 15Jlj/wi of hydrogen is added to the nozzle 2a.
A nitrogen-hydrogen mixed gas plasma flow was obtained. The electric power applied to the high-frequency induction coil was adjusted to about 87 KW, and the plasma flame was adjusted to have a cylindrical shape so that the lower end of the flame would not spread. After the plasma flame stabilizes, silicon tetrachloride gas 8 is supplied from the raw material supply pipe 3.
9/in and nitrogen 3.1/so as carrier gas
A mixed gas of n was introduced and reacted. The tip of the supply pipe was located 51 points below the lower end of the RF coil. As a result, the fine powder collected by the powder collector had a particle diameter of 0.01 to 0.02 P as measured by electron micrograph, and was found to be amorphous by X-ray diffraction. Also, as a result of elemental analysis, silicon is 59.2%
.

The nitrogen was confirmed to be 37.6% silicon nitride.

A part of this powder was heated at 1550°C in a nitrogen stream in an electric furnace.
X-ray diffraction analysis of the powder heat-treated for 2 hours revealed that the α-crystal content was approximately 85%, with the remainder being β-crystalline silicon nitride.

[Brief explanation of drawings]

The figure is an explanatory diagram of a plasma torch used to implement the method of the present invention. In the figure, ■... High frequency induction plasma torch 2... Nozzle hends 2a, 2b and 2C... Plasma operation gas nozzle 3
... raw material z1 gas supply pipe 4 ... quartz innermost cylinder 5.
・High frequency induction coils 6a and 6b ・Conductor 7 ・Water cooling jacket IO ・Reaction cooling device 11 ・
...Innermost cylinder 12...Water cooling jacket 14...Plasma flame 15...Doughnut-shaped high temperature part or above Patent applicant Chisso Corporation representative Patent attorney Yatabe Sasai 1- Katsuhiko Nonaka 5

Claims (5)

[Claims] (1) An amorphous superstructure characterized by injecting a silicon halide compound into a mixed plasma gas stream of nitrogen and hydrogen, and causing the silicon halide to react with activated nitrogen and hydrogen in the plasma gas stream. A method for producing particulate silicon nitride. (2) The manufacturing method according to claim 1, wherein the plasma gas flow is formed by high-frequency induction heating. (3) The method according to claim 1, wherein the ratio of the silicon halide compound to the plasma gas is 0.05 to 0.2 in terms of gas volume ratio converted to a standard state. (4) The manufacturing method according to claim 1, wherein the ratio of the number of moles of hydrogen gas to the number of halogen atoms in the halogenated silicon compound molecule is 0.3 to 1.0. (5) Amorphous ultrafine particulate nitridation obtained by blowing a silicon halide compound into a mixed plasma gas flow of nitrogen and hydrogen, and reacting the silicon halide with activated nitrogen and hydrogen in the plasma gas flow. f1 element.