JPH04240106A - Production of silicon nitride powder - Google Patents

Abstract

PURPOSE:To provide the production of silicon nitride powder with a high nitriding ratio attained. CONSTITUTION:A silicon nitride reactor 1 is packed with seed silicon nitride powder of 50 to 1000mum average particle diameter and non-oxidizing gas is supplied from a reaction gas inlet 4 to the reactor 1 to form a fluidized bed 6. After the formation of the fluidized bed 6, metal silicon of <=150mum average particle diameter entrained and dispersed by non-oxidizing gas is continuously fed to the fluidized bed 6 through a raw material inlet pipe 10 and silicon nitride obtained from the fluidized bed 6 is entrained by waste gas to take it out through a silicon nitride powder outlet pipe 11. Silicon nitride powder with uniform quality can be produced on an industrial scale by using metal silicon powder of <=150mum average particle diameter industrially obtained as it is.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing silicon nitride powder that can nitride fine metal silicon powder at a high nitriding rate.

0002

2. Description of the Related Art Hitherto, a method using a fluidized bed has been known as one of the methods for industrially producing silicon nitride powder by directly nitriding metallic silicon. In this method, a fluidized bed is formed between metallic silicon powder and a reaction gas, and then heated. However, in this fluidized bed reaction type silicon nitride powder manufacturing method, the metallic silicon powder as a raw material is directly exposed to a high temperature atmosphere. As a result, the metal silicon powder introduced into the fluidized bed melts immediately, and particles fuse and aggregate, resulting in a decrease in specific surface area and a significant drop in reaction rate, forming a fluidized bed. The problem is that it is difficult to In this case, lowering the temperature of the fluidized bed significantly reduces the nitriding reaction rate.

[0003] Conventionally, in order to solve this problem, a fluidized bed was formed with metal silicon powder and a reactive gas, and when this was heated, the temperature increase rate was set at 30 to 150°C/
A method for obtaining silicon nitride powder of stable quality by controlling the Hr to prevent melting and agglomeration of metal silicon powder
No. 97110) has been proposed, but this method requires a long time to heat up and cool down the furnace, resulting in poor productivity.

0004

[Problems to be Solved by the Invention] As a method for solving the above-mentioned problems of the conventional manufacturing method, an improved method for manufacturing silicon nitride powder using a fluidized bed method previously proposed by the present applicant (Japanese Patent Application Laid-Open No. 1-195954) No.). This manufacturing method preferably uses metal silicon powder with a particle size of 149 μm to 4 m.
granulated to about m, and formed from silicon nitride powder and a non-oxidizing reaction gas containing nitrogen gas or ammonia gas,
The nitrided product is continuously supplied into a first fluidized bed whose temperature is maintained at 1000 to 1400°C, and after the first nitriding reaction is performed in the first fluidized bed, the nitrided product is continuously supplied from this first fluidized bed. At the same time, this is further supplied to a second fluidized bed formed from silicon nitride powder and a non-oxidizing reaction gas containing nitrogen gas or ammonia gas, and the unreacted nitriding raw material is nitrided in the second fluidized bed. A secondary nitriding reaction is performed, and according to this method, silicon nitride powder with less variation in quality such as α phase ratio can be stably and efficiently produced.

However, the above-mentioned method of the prior application recommends granulating the metallic silicon powder, and the reasons for granulating the metallic silicon in advance are as follows: (1) good fluidization state in the fluidized bed; (2)
) Preventing the surface area from decreasing due to melting of metal silicon and preventing clogging in the fluidized bed. However, the general form of the reaction performed using a fluidized bed is to use nitrogen gas or nitrogen gas as a fluidizing gas. Air between ammonia gas and metal silicon
Considering that the reaction is a solid-state reaction, it is preferable to reduce the particle size of the metal silicon powder as a raw material and increase the specific surface area in order to improve the reaction rate. Furthermore, since silicon nitride obtained by a gas-solid reaction must ultimately be pulverized to a particle size having an appropriate distribution on the submicron order, it is desirable that the metal silicon particles be fine. Metallic silicon, which is a raw material, is pulverized as finely as possible using industrially available pulverization equipment, but usually the economically obtainable fine particles have a BET specific surface area of 4 m2/g and an average particle size. It is about 1 to 44 μm.

[0006] Therefore, it is desired to efficiently produce silicon nitride powder using such fine metal silicon powder as it is.

[0007] The present invention was made in response to the above-mentioned needs, and it is possible to efficiently directly nitride fine metallic silicon with an average particle size of 150 μm or less, particularly 50 μm or less, and achieve a high nitridation rate of metallic silicon. It is an object of the present invention to provide a method for producing silicon nitride powder that is both possible and economically advantageous.

[0008]

[Means and effects for solving the problem] The present inventors have
As a result of intensive studies to achieve the above objective, we found that a fluidized bed was formed in advance from seed silicon nitride powder with an average particle size of 50 to 1000 μm and a non-oxidizing gas containing nitrogen or ammonia, and the raw material was added to the fluidized bed. The average particle size of
Metallic silicon powder of 50 μm or less, particularly 50 μm or less, is entrained and dispersed in a non-oxidizing gas containing nitrogen or ammonia and continuously introduced into the fluidized bed to produce silicon nitride, and at the same time, the silicon nitride is converted into exhaust gas. It has been found that by entraining and continuously discharging the fine metal silicon powder, silicon nitride powder can be produced at low cost with a high nitriding rate using the fine metal silicon powder as it is.

That is, in the production method of silicon nitride powder using a fluidized bed reaction type, fine powder of metallic silicon having a particle size that can be obtained industrially has a strong interparticle force, so if it is left as it is, it will cause channeling, etc. It is difficult to maintain a good fluidized bed. Generally, the fluidized bed has a different fluid state depending on the density, particle size, and particle size distribution of the fluidized particles. For example, Geldart's classification “Pow
der Technology, 7, 285 (197
3); 19, 133 (1978)”, “A
” particles are suitable for forming a good fluidized bed,
Furthermore, "A'" particles containing an appropriate amount of particles with a particle size of 44 μm or less, which is called a "good fraction," are said to be particles particularly suitable for forming a good fluidized bed. According to this classification, the above-mentioned industrially obtained pulverized metallic silicon particles having an average particle diameter of 1 to 44 μm belong to “C” particles. "C" particles are said to have strong interparticle forces that cause channeling in the fluidized bed, making it extremely difficult to form a good fluid state.

On the other hand, the starting temperature of the nitriding reaction of metallic silicon at approximately normal pressure is around 1200°C, and the melting temperature of metallic silicon is thought to be 1300 to 1400°C. In a gas-solid reaction in which metallic silicon is nitrided with nitrogen or ammonia gas, nitriding starts from the surface and progresses as nitrogen diffuses into the interior. This reaction is 140-18
This is an exothermic reaction that generates a large amount of heat, 0 kcal/mol, and it is very important that the heat is removed smoothly. This is because if metal silicon reaches the melting temperature before the nitriding reaction progresses uniformly and a silicon nitride film is formed on the surface of metal silicon, melting and coalescence between metal silicon particles will occur, and the specific surface area will drastically decrease. At the same time, the fluidized bed becomes blocked, and the nitriding reaction can no longer be continued.

[0011] In the present invention, the average particle diameter is set in advance from 50 to 1000.
A fluidized bed is formed with seed silicon nitride powder of 150 μm or less, and fine metal silicon powder with an average particle size of 150 μm or less is entrained and dispersed in a non-oxidizing gas containing nitrogen or ammonia to continuously form a fluidized bed. By introducing metal silicon into a liquid, it is possible to form a good fluidized bed of metal silicon using the particle size that makes it difficult to form a uniform fluidized bed, and it is possible to form a good fluidized bed of metal silicon, which prevents agglomeration and coarsening of fine metal silicon powder. In addition, the metal silicon fine powder is allowed to adhere to and grow on the seed silicon nitride powder to cause nitridation, and the silicon nitride obtained by nitriding is accompanied by the exhaust gas and continuously discharged. As a result, there is no need to perform a pretreatment step of granulating, drying, and calcining the metal silicon powder, and the above-mentioned "C" having an average particle size of 50 μm or less is eliminated.
Even when using metal silicon powder, which is classified as particles, it is possible to maintain a good fluidized state in the fluidized bed, increasing the cost advantage of using a fluidized bed reaction, and having a large specific surface area and a small average particle size. The inventors have discovered that silicon nitride powder can be efficiently obtained at a high reaction rate by using small metallic silicon powder as it is, and have accomplished the present invention.

Therefore, in the present invention, a fluidized bed is formed in advance from seed silicon nitride powder having an average particle size of 50 to 1000 μm and a non-oxidizing gas containing nitrogen or ammonia at the start of the reaction, and the average particle size is Nitriding characterized by continuously supplying fine metal silicon powder of 150 μm or less, nitriding the fine metal silicon powder to obtain silicon nitride, and continuously discharging the silicon nitride to obtain silicon nitride powder. A method for producing silicon powder is provided.

[0013] The present invention will be explained in more detail below. The seed silicon nitride powder used in the present invention has an average particle diameter of 50
~1000 μm, particularly preferably 200 to 500 μm. When the average particle size is less than 50 μm, it is difficult for the fluidized bed to maintain a good fluid state due to channeling, etc. On the other hand, when the average particle size exceeds 1000 μm, the fluidization start speed increases and the gas flow rate becomes difficult to maintain. As the bubble size increases, slugging occurs, and 50
As in the case of less than μm, it becomes difficult to maintain a good fluid state. Note that by repeating growth and destruction, the seed silicon nitride powder can always exist in the fluidized bed with an average particle diameter of 50 to 1000 μm.

In the present invention, the seed silicon nitride powder is used to form a fluidized bed in advance using a non-oxidizing gas before starting the reaction. In this case, the fluidized bed can be formed by a conventional method, and it is preferable to raise the temperature while fluidizing the seed silicon nitride powder.

The non-oxidizing gas contains nitriding or ammonia, but if necessary, an inert gas such as Ar or He, or a non-oxidizing gas such as H2 may be mixed. In this case, the concentration of nitrogen or ammonia in the non-oxidizing gas is preferably 20 to 100% by volume, particularly 50 to 100% by volume.

Next, in the present invention, metal silicon powder is continuously fed into the fluidized bed, and a nitriding reaction is carried out in the fluidized bed to convert the metal silicon powder into silicon nitride powder. Here, the average particle size of the metallic silicon fine powder is 150 μm or less, and preferably 1 to 44 μm. If the average particle diameter exceeds 150 μm, the progress of the nitriding reaction may be hindered. In addition, it is desirable that the specific surface area of metal silicon be large, but since pulverization costs too much,
It is preferably 15 m2/g, particularly 1 to 4 m2/g. By using fine particles of silicon metal obtained using a normal pulverizer instead of granulated particles, the specific surface area of silicon metal can be significantly increased, which can substantially improve the reaction rate. . The supply amount of the above metal silicon fine powder is 1 to 100 g of seed silicon nitride powder.
It is preferable to set it as 100g/Hr, especially 10-50g/Hr.

The metal silicon powder is preferably continuously supplied to the fluidized bed while being accompanied by a non-oxidizing gas containing nitrogen or ammonia. This non-oxidizing gas can be configured in the same manner as the non-oxidizing gas constituting the fluidized bed. Although the linear velocity of the non-oxidizing gas is not limited, it is preferably 0.5 to 10 m/s, particularly 2 to 5 m/s, and the linear velocity of the non-oxidizing gas is preferably 0.5 to 5 g/liter, In particular, it is preferable to supply it at a rate of 1 to 3 g/liter.

In the nitriding reaction of the metal silicon powder,
The reaction temperature is 1000-1500°C, especially 1200-13
The temperature is preferably 50°C.

The silicon nitride obtained in this nitriding reaction is continuously discharged and recovered together with the exhaust gas, but the silicon nitride obtained is subjected to the above operation twice or multiple times as necessary to carry out the nitriding reaction. be able to.

[0020]

[Examples] The present invention will be specifically explained below with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[Examples 1 to 3, Comparative Examples 1 to 3] Silicon nitride powder was produced using the continuous silicon nitride production machine shown in FIG. First, the inner diameter is 80 mm, and the length of the soaking part is 500 m.
Reactor 1 having a reaction chamber 2 made of mullite tubes of m
Inside, seed silicon nitride or metal silicon powder 5 for comparison.
00g was loaded. The reaction chamber 2 was heated to the temperature shown in Table 1 by a heater 3 installed around it. Next, a mixed gas of nitrogen and hydrogen was supplied as a reaction gas and a fluidizing gas to the reactor 1 from the reaction gas supply port 4 at the flow rates shown in Table 1. The supplied mixed gas flowed above the reactor 1 and formed a fluidized bed 6 above the gas distribution plate 5 provided in the gas reaction chamber 2. At the same time as the fluidized bed 6 is formed, the disperser 7 is operated (8 in the figure is a mixing mechanism equipped with a hopper 9), and the raw metal silicon having the size shown in Table 1 is entrained and dispersed in nitrogen gas. The raw material is continuously supplied to the fluidized bed 6 through the raw material supply pipe 10 at a rate of 200 g/Hr, and while the height of the fluidized bed 6 is maintained at 300 mm, silicon nitride is entrained in the exhaust gas from the fluidized bed 6, and the silicon nitride powder is discharged. It was taken out through tube 11. The extracted silicon nitride is transferred to a separator 12
It was separated into silicon nitride powder and gas. The silicon nitride powder was recovered by a recovery device 13, and the gas was sent to a gas purification device 14. In addition, for Example 2, the above operation was repeated to perform two-stage nitriding.

Table 2 shows the physical properties and fluidity of the above silicon nitride.
It was shown to. As seen from Table 2, a good fluidized bed 6
In order to form The nitriding rate improves. For example, when the average particle diameter is 37 μm, the nitriding rate is 95% (Example 1)
When the average particle diameter was 2.7 μm, the nitridation rate was 98% (Example 3). In addition, by installing another reaction chamber in the above-mentioned apparatus and performing two-stage nitriding on the nitrided product discharged from the silicon nitride powder discharge pipe 11, the nitriding rate can be maintained at 100 even if the average particles of metallic silicon are somewhat large. %, and a high α phase ratio silicon nitride powder with an α phase ratio of 92% (Example 2) could be stably obtained.

However, when metallic silicon was used as fluidized particles at the start of the reaction (Comparative Examples 1 and 2), silicon nitride was not discharged because the inside of the fluidized bed was agglomerated and clogged. Similarly, even when silicon nitride is used as fluidized particles at the start of the reaction, the average particle diameter is less than 50 μm (Comparative Example 3
), the silicon nitride discharge pipe 10 was blocked due to the generation of fine powder, and silicon nitride was not discharged.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

[Effects of the Invention] As explained above, the method for producing silicon nitride powder of the present invention has a uniform quality represented by the α phase ratio even when using industrially obtained fine metal silicon powder as a raw material. This makes it possible to produce silicon nitride powder on an industrial scale at low cost.

[Brief explanation of the drawing]

FIG. 1 shows a continuous silicon nitride production machine used in the practice of the present invention.

[Explanation of symbols]

1 Reactor 2 Reaction chamber 3 Heater 4 Reaction gas supply port 5 Gas distribution plate 6 Fluidized bed 7 Dispersion machine 8 Mixing mechanism 9 Hopper 10 Raw material supply pipe 11 Silicon nitride powder discharge pipe 12 Separator 13 Recovery device 14 Gas purification equipment

Claims (1)

[Claims] Claim 1: At the start of the reaction, the average particle diameter is 50~
A fluidized bed is formed from a seed silicon nitride powder of 1000 μm and a non-oxidizing gas containing nitrogen or ammonia, and fine metallic silicon powder having an average particle size of 150 μm or less is continuously supplied into the fluidized bed. A method for producing silicon nitride powder, which comprises nitriding fine powder to obtain silicon nitride, and continuously discharging the silicon nitride to obtain silicon nitride powder.