JPS61178408A - Production of silicon nitride powder - Google Patents

Abstract

PURPOSE:To produce finely divided uniform powder of silicon nitride efficiently and easily, by oxidizing metallic silicon powder to give finely divided particles of silicon monoxide, reducing and nitrogenizing it. CONSTITUTION:Oxygen and LPG are fed from the feed pipes 22 and 23, respectively, to the burner 20, which is ignited, so the reaction furnace 10 is dried and deoxidized. Then, metallic silicon powder (<=200 meshes) is continuously fed from the feeder 21 to the furnace, and simultaneously oxygen is fed from the feed pipe 22 to form dust cloud. The dust cloud is ignited, exploded, burned, and oxidized to give ultrafine or gaseous silicon monoxide. A mixed gas of a hydrocarbon gas and an ammonia gas heated by the preheating furnace 11 is fed to a position just before the burner 20 by the feed pipe 12. Consequently, silicon monoxide is reduced and nitrogenized, to synthesize silicon nitride powder, which is collected by the collector 31 and the bag filter 32.

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. In addition, when using it, it is desirable that the particle size of the raw material particles be 1000 Å or less in terms of ease of sinterability at low temperatures and increase in catalytic activity. Silicon nitride powder was desired.

Conventionally, in manufacturing silicon nitride powder, (1)
There is a method of producing silicon nitride by directly reacting nitrogen with metal silicon, as shown in the formula below.

3Si +2Nt →3i 3N4 ... (1
) There is also a method of producing silicon nitride by reacting silicon tetrachloride with ammonia, as shown in formula (2).

38! C14+4NH3→Si 3N4+12HC1 (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 purified and fine metal silicon powder. The particle size distribution of the obtained powdered silicon nitride is often 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 as a raw material is expensive, and thus the silicon nitride obtained is also expensive. Another problem is that harmful hydrogen chloride gas is generated, and its treatment requires a lot of 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 production method of the present invention includes an oxidation step of oxidizing metal silicon powder in an oxidizing gas atmosphere to form ultrafine particulate or gaseous silicon monoxide, and the silicon monoxide. and a nitriding step of nitriding in a reducing gas atmosphere containing nitrogen.

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.

It is preferable that this metal silicon powder has fine particles, and 2
00 mesh or less is particularly desirable.

If metal silicon powder with such particles is used, the particle size of the obtained silicon nitride powder will also be in a preferable range of 100 to 1000 particles. Note that it is not necessary to use gold coin silicon powder with particularly high purity.

Typical oxidizing gases include oxygen gas, ozone gas, etc., 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 the metal silicon powder and the oxidizing gas form a dust cloud, and this dust cloud is ignited to cause an explosion. , it is desirable to oxidize it by burning it. 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 preferable 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 that the reaction flame be formed 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 the dominant class or a plurality 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 the metal silicon powder and the oxidizing gas in the oxidation step, a continuous reaction flame is formed by the metal silicon powder and the oxidizing gas, which contains a large amount of -1ift silicon. Therefore, by generating this continuous reaction flame in the above-mentioned reducing atmosphere, the reduction and nitriding reactions proceed continuously due to the thermal energy of this continuous reaction flame, and the additional particulate or gaseous silicon monoxide is It can be made into powdered silicon nitride.

1q of 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 by the reaction between the metal silicon powder and the oxidizing gas can be used to ignite other metal silicon powder. Powder reaction is accelerated. 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 productivity.

[Example] FIG. 1 shows a manufacturing apparatus related to the manufacturing method of the present invention. This manufacturing apparatus includes a reactor 10 whose inner wall is surrounded by heat-resistant bricks 15 and which has a discharge passage 30 on one side wall;
The burner 20 is provided on the other side wall of the reactor 10 and sends flame to the reactor 10. burner 20
A powder supply device 21 for supplying metal silicon powder, an oxygen supply pipe 22 for supplying oxygen, and an LPd supply pipe 23 for supplying LPG for a pilot flame are disposed in the fuel cell. A reducing/nitriding gas supply pipe 12 for supplying a mixed gas of methane gas and ammonia gas through the total heat 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 for collecting uncollected silicon nitride powder is provided behind the powder collecting device [31]. 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 of the oxygen supply pipe 22 and the LPG supply pipe 23.
25 was opened and the burner 20 was ignited to sufficiently dry the inside of the reactor 10 and deoxidize it.

After that, the powder supply device 21 supplies 1 portion of metal silicon powder.
It was continuously supplied at a supply rate of 0 to 30 kQ/hour, and at the same time, oxygen was supplied from the oxygen supply pipe 22 in an amount corresponding to the reaction equivalent of the metal silicon powder (4 to 12 Nm<3>/hour). Then, the valve 13 of the reducing/nitriding gas supply pipe 12 is opened, and a mixed gas of methane gas and ammonia gas heated to about 1000°C by the preheating furnace 11 is supplied at a rate of 8 to 24 Ns3/hour of methane gas and a rate of 11 to 32Ns3/hour of ammonia gas. It was supplied at a flow rate of

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, and the thermal energy is obtained and reduced by the carbon element and hydrogen element of methane gas and the hydrogen element of ammonia gas, and the ammonia gas Silicon nitride powder synthesized by nitriding with nitrogen element was collected in a powder collector 31 and a bag filter 32 at a collection rate of 16 to 40 km hours.

Furthermore, the exhaust gas that has passed through the bag filter 32 is transferred to the blower 3
After being sent to the combustion processing section 34 by 3 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 between 100 and 1000 particles 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.

Claims (6)

[Claims] (1) An oxidation process in which metallic silicon powder is oxidized in an oxidizing gas atmosphere to form ultrafine particle or gaseous silicon monoxide, and a nitriding process in which the silicon monoxide is nitrided in a reducing gas atmosphere containing nitrogen. A method for producing silicon nitride powder, comprising: (2) The method for producing silicon nitride powder according to claim 1, wherein the reducing gas containing nitrogen is a mixed gas of a hydrocarbon gas and an ammonia gas. (3) Production of silicon nitride powder according to claim 1, wherein the oxidation step is performed by forming a dust cloud with metal silicon powder and an oxidizing gas, and igniting the dust cloud to cause it to explode and burn. Method. (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 is heated in advance and then supplied.