JPH0536363B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing finely powdered silicon nitride.

[Prior Art] Silicon nitride is used in various fields due to its low coefficient of thermal expansion, high temperature strength, etc. Also,
When using it, the particle size of the raw material particles must be adjusted in order to facilitate sintering at low temperatures and increase catalytic activity.
It is desirable that the particle size be 1000 Å or less, and a silicon nitride powder having such a small particle size has been desired.

Conventionally, when producing silicon nitride powder, there is a method as shown in equation (1), in which silicon metal is directly reacted with nitrogen to produce silicon nitride.

3Si+2N ₂ →Si ₃ N ₄ ...(1) There is also a method of producing silicon nitride by reacting silicon tetrachloride with ammonia, as shown in equation (2).

3SiCl ₄ +4NH ₃ → Si ₃ N ₄ +12HCl...(2) [Problems to be solved by the invention] The above method had the following problems.

In the method of formula (1), it was necessary to use highly pure and fine metallic silicon powder. The particle size distribution of the obtained powdered silicon nitride is often not wide, and it is quite difficult to obtain fine particles of 1000 Å or less. Furthermore, it is difficult to obtain fine metallic silicon of high purity, and the problem of contamination with impurities cannot be avoided.

Furthermore, in the manufacturing method of formula (2), silicon tetrachloride, which is a raw material, is expensive, and thus the silicon nitride obtained is also expensive. Another problem was that harmful hydrogen chloride gas was generated, and its treatment required many man-hours.

The present invention has been made in view of the above-mentioned problems, and provides a manufacturing method for easily obtaining fine particulate silicon nitride powder.

[Means for Solving the Problems] The method for producing silicon nitride powder of the present invention involves mixing metal silicon powder and oxidizing gas and igniting the mixture to form a reaction flame and producing ultrafine particles or gaseous particles. The method is characterized in that an oxidation step for forming silicon oxide and a nitridation step for nitriding silicon monoxide by supplying a reaction flame into a reducing gas atmosphere containing a nitrogen element are performed in sequence.

The oxidation step referred to in the present invention is one of the features of the present invention, and is a step in which metallic silicon powder is oxidized in an oxidizing gas atmosphere to form silicon monoxide. The finer the particles of this metal silicon powder, the more preferable it is, and the one with a particle size of 200 mesh or less is particularly desirable.
If you use metallic silicon powder with such particles,
The particle size of the obtained silicon nitride powder is also 100 Å to 1000 Å.
This is a preferable range. Note that it is not necessary to use particularly high purity metal silicon powder.

Typical oxidizing gases include oxidizing gas and ozone gas, and those that oxidize metal silicon powder to form silicon monoxide can be used. Various methods can be considered to cause the metal silicon powder and the oxidizing gas to react, but it is possible to form a dust cloud with the metal silicon powder and the oxidizing gas, and ignite this dust cloud. It is preferable to oxidize by exploding or burning. According to this method, the heat generated during the oxidation reaction promotes the oxidation of other metal silicon powders, and the resulting high temperature produces ultrafine particle or gaseous silicon monoxide. Then, it becomes possible to carry out the nitriding process described later using the thermal energy of the reaction flame during oxidation. As this ignition means, a burner, plasma jet, arc discharge, laser light, etc. can be used. Further, it is desirable to determine the optimum concentration of the dust cloud depending on the particle size of the metal silicon powder used, the ignition means, etc. Note that the metal silicon powder may be supplied intermittently over very short periods of time, or may be supplied continuously. However, from the standpoint of thermal efficiency, it is desirable to form the reaction flame continuously.

The nitriding step is a step in which the silicon monoxide obtained in the oxidation step is reduced and nitrided to form silicon nitride. The nitrogen-containing reducing gas used in this nitriding step is a gas that has both reducing and nitriding functions, and various combinations of one or more types of substances can be selected. For example, carbon monoxide gas, hydrogen gas, hydrocarbon gas, etc. can be used as the reducing gas. Further, as the nitriding gas, ammonia gas, amine gas, etc. can be used. It is also possible to use a compound having a nitrogen element in the molecule of a hydrocarbon compound. In this case, with one type of gas, a reduction reaction occurs with the carbon element and the hydrogen element, and a nitriding reaction occurs with the nitrogen element. In addition, in these cases, by using the carbon element in excess of the reduction reaction equivalent, it is also possible to generate silicon carbide and produce a mixture of silicon nitride and silicon carbide. Further, the composition ratio of this mixture can be freely adjusted by adjusting the equivalent ratio of nitrogen element and carbon element. Note that in order to prevent the reaction system from being cooled by the reducing gas containing nitrogen, it is desirable to heat the gas in advance.

When silicon monoxide comes into contact with the nitrogen-containing reducing gas at high temperature, it is reduced and nitrided to become silicon nitride. In this case, it is desirable to carry out the oxidation step and the nitridation step successively in order to utilize the heat of the oxidation step. When a dust cloud is formed by metal silicon powder and oxidizing gas in the oxidation process,
A continuous reaction flame containing a large amount of silicon monoxide is formed. Therefore, by generating this continuous reaction flame in the above-mentioned reducing atmosphere, reduction and nitriding reactions proceed continuously due to the thermal energy of this continuous reaction flame, and ultrafine particle or gaseous silicon monoxide is It can be silicon nitride in the form of a fine powder.

The obtained silicon nitride can be collected by a well-known collection device such as a bag filter. Note that since the gas that has passed through the collection device usually contains unreacted oxidizing gas and reducing gas containing nitrogen, it is desirable to discharge it after processing such as combustion.

[Operations and Effects of the Invention] According to the manufacturing method of the present invention, by simply using an ignition means such as a burner or a plasma jet, the heat generated during the reaction between the metal silicon powder and the oxidizing gas causes the metal silicon powder to ignite other metal silicon powder. reaction is promoted. Therefore, thermal efficiency is extremely high and costs can be reduced.
Then, a reaction flame containing ultrafine particulate or gaseous silicon monoxide is continuously formed, and by contacting this reaction flame with a reducing gas containing nitrogen, a large amount of fine particulate silicon nitride powder is continuously formed. is manufactured. Therefore, the effects of the present invention are significant, such as the ability to obtain homogeneous silicon nitride powder extremely efficiently and with good mass production.

[Example] FIG. 1 shows a manufacturing apparatus related to the manufacturing method of the present invention. This manufacturing device includes a reactor 10 whose inner wall is surrounded by heat-resistant bricks 15 and a discharge passage 30 on one side wall, and a reactor 10 provided on the other side wall of the reactor 10.
It mainly consists of a burner 20 that sends flame to the reactor 10. The burner 20 is provided with a powder supply device 21 for supplying metal silicon powder, an oxygen supply pipe 22 for supplying oxygen, and an LPG supply pipe 23 for supplying LPG for pilot fire. A reducing/nitriding gas supply pipe 12 for supplying a mixed gas of methane gas and ammonia gas via a preheating furnace 11 is provided on the upper wall of the reactor 10 so as to open into the reactor 10 .

Further, a powder collecting device 31 is provided in the discharge passage 30, and a bag filter 32 is provided behind the powder collecting device 31 to collect uncollected silicon nitride powder. The exhaust gas that has passed through the bag filter 32 is configured to be discharged outdoors after passing through a combustion processing section 34 by a blower 33.

Using the reaction apparatus configured as described above, a reaction was carried out in the following manner to produce silicon nitride powder.

First, the valves 24 and 25 of the oxygen supply pipe 22 and the LPG supply pipe 23 were opened, and the burner 20 was ignited to sufficiently dry the inside of the reactor 10 to remove oxygen. Thereafter, the powder supply device 21 continuously supplies the metal silicon powder at a supply rate of 10 to 30 kg/hour, and at the same time, the oxygen supply pipe 22 supplies oxygen in an amount equal to the reaction equivalent of the metal silicon powder (4 to 12 Nm ³ /hour). ) supplied. And valve 1 of reducing/nitriding gas supply pipe 12
3 was opened, and a mixed gas of methane gas and ammonia gas heated to about 1000° C. by the preheating furnace 11 was supplied at a flow rate of 8 to 24 Nm ³ /hour for methane gas and 11 to 32 Nm ³ /hour for ammonia gas.

At this time, a reaction flame 26 is continuously formed in front of the burner 20 due to the oxidation reaction of the metal silicon powder.
The silicon nitride powder obtained by obtaining the thermal energy is reduced by the carbon element and hydrogen element of the methane gas and the hydrogen element of the ammonia gas, and is nitrided by the nitrogen element of the ammonia gas. and 16 to 40 in bug filter 32
A yield of Kg/hour was collected.

In addition, the exhaust gas that has passed through the bag filter 32 is
After being sent to the combustion processing section 34 by the blower 33 and subjected to combustion processing, it was discharged outdoors.

When the obtained powder was analyzed by electron microscopy and X-ray diffraction, it was found to be a silicon nitride powder with a particle size distribution of 100 Å to 1000 Å and an amorphous structure.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a manufacturing apparatus according to an embodiment of the present invention. 10...Reaction furnace, 12...Reducing/nitriding gas supply pipe, 20...Burner, 21...Powder supply device,
22...Oxygen supply pipe, 23...LPG supply pipe, 3
0...Discharge passage, 31...Powder collection device.

Claims (1)

[Claims] 1. An oxidation step in which a metal silicon powder and an oxidizing gas are mixed and ignited to form a reaction flame to form ultrafine particle or gaseous silicon monoxide; A method for producing silicon nitride powder, comprising sequentially performing a nitriding step of nitriding the silicon monoxide by supplying the silicon monoxide into a reducing gas atmosphere containing elements. 2. The method for producing silicon nitride powder according to claim 1, wherein the reducing gas containing nitrogen element is a mixed gas of a hydrocarbon gas and ammonia. 3. The method for producing silicon nitride powder according to claim 1, wherein the reaction flame is formed by igniting, exploding and burning a dust cloud formed of metal silicon powder and oxidizing gas. 4. The method for producing silicon nitride powder according to claim 3, wherein ignition is performed using a burner or a plasma jet. 5. The method for producing silicon nitride powder according to claim 1, wherein the metal silicon powder has a particle size of 200 mesh or less. 6. The method for producing silicon nitride powder according to claim 1, wherein the reducing gas containing nitrogen element is supplied after being heated in advance.