JPH0360410A - Method for manufacturing silicon nitride powder - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for stably and efficiently producing silicon nitride powder with little variation in quality by a direct nitriding method using a fluidized bed.

Conventionally, as a method for industrially producing silicon nitride powder by directly nitriding metal silicon powder, a fixed bed batch method has mainly been adopted. However, silicon nitride powder obtained by a fixed bed batch method has a problem in terms of quality variations. That is, the α phase ratio differs between batches, and even within the same batch there are variations in the temperature distribution in the furnace and the degree of progress of the nitriding reaction, which often causes variations in the quality of the silicon nitride powder. Such variations in the quality of silicon nitride powder tend to increase as the batch size increases. Furthermore, in the fixed bed batch system, it is difficult to automate operations such as inputting raw materials and taking out products, and therefore there is a risk that impurities may be mixed in during these operations.

Therefore, when adopting a fixed bed batch system, in order to increase the scale and expand the production scale, the quality variation of the silicon nitride powder obtained increases as the size increases, and the work is also extensive. This requires a lot of effort, long heating and cooling periods, etc.
There are many problems.

Various manufacturing methods have been proposed to solve these problems. For example, a method using a vertical furnace (Japanese Unexamined Patent Publication No. 5
8-151311).

Method using a pusher type tunnel furnace (JP-A-60-1
86406) Method using a two-rotation kiln (Japanese Unexamined Patent Publication No. 1983
-266305), a method using a fluidized bed (Japanese Unexamined Patent Publication No. 61-97110), etc.

However, even with these methods, there are almost no methods that can simultaneously solve the problems of the quality of the obtained silicon nitride powder and the problems of its productivity. For example, in a method using a vertical furnace, the temperature distribution and the degree of progress of the nitriding reaction vary widely, resulting in large variations in the α phase ratio of the silicon nitride powder. Although the method using a pusher type tunnel furnace can obtain silicon nitride powder with a relatively stable α phase ratio, its productivity is not industrially sufficient. In the method using a rotary kiln, it is difficult to control the residence time, and therefore quality such as α phase ratio tends to vary widely, and stable operation is difficult. The method using a fluidized bed can obtain silicon nitride powder with a stable alpha phase ratio, but it requires a long time to heat up and cool down the furnace, and the nitriding reaction rate is slow, so its productivity is not suitable for industrial use. It's not enough.

In other words, in the conventional method described above, if the variation in quality such as α phase ratio is stabilized to a satisfactory level, productivity will decrease, whereas if productivity is improved to an industrially satisfactory level, the quality will decrease. Control becomes difficult and variations in quality become large.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing silicon nitride powder that can produce silicon nitride powder with high productivity with less variation in quality such as alpha phase ratio.

In order to achieve the above object, the present invention is made by forming a nitriding raw material containing metal silicon powder from silicon nitride powder and a non-oxidizing reaction gas containing nitrogen gas or ammonia gas, and heating the nitriding raw material at a temperature of 1000 to 1000. After being continuously supplied to a first fluidized bed maintained at 1400°C and carrying out a first nitriding reaction in the first fluidized bed,
The nitrided product is continuously taken out from this first fluidized bed, and 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. A method for producing silicon nitride powder is provided, which is characterized by carrying out a secondary nitriding reaction in which unreacted nitriding raw materials are nitrided in two fluidized beds.

In other words, in the fluidized bed reaction method for manufacturing silicon nitride powder, the raw material silicon powder is directly exposed to a high temperature atmosphere, so the surface of the metal silicon powder introduced into the fluidized bed immediately melts, resulting in a decrease in specific surface area. There are problems in that the reaction rate decreases significantly, and it becomes difficult to form a fluidized bed due to fusion and agglomeration between particles.

In this case, lowering the temperature of the fluidized bed significantly reduces the nitriding reaction rate. 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 50°C.
/Hr to prevent melting and agglomeration of metal silicon powder,
Method for obtaining silicon nitride powder with stable quality (Japanese Patent Application Laid-Open No. 61
97110) has been proposed, but as mentioned above, this method requires a long time for heating and cooling, and the nitriding reaction rate is slow, resulting in poor productivity. On the other hand,
According to the production method of the present invention, the temperature is as high as possible below the melting point of metallic silicon and at which the specific surface area of metallic silicon powder does not decrease significantly, that is, at a temperature of 1000 to 1400°C, preferably 1200 to 1350°C. A first nitriding reaction is carried out in the fluidized bed of By performing several-order nitriding reactions to improve the nitriding rate, it is possible to obtain silicon nitride powder with a high nitriding rate and stable quality without causing melting or agglomeration of particles.
Continuously supplying metal silicon powder to a first fluidized bed in a heated state, continuously taking out nitrided silicon nitride powder from the first fluidized bed, and continuously supplying it to a second fluidized bed. As a result, a cooling step is not necessary, and silicon nitride powder can be obtained with high productivity. In this case, in the fluidized bed reaction type, the particles in the bed are vigorously stirred and mixed, resulting in almost complete mixing in the bed.
Although it is difficult to achieve a high nitriding rate in the first fluidized bed, the nitriding rate of the final product can be increased by performing the nitriding reaction in two or multiple stages.

Therefore, according to the production method of the present invention, silicon nitride powder with a high nitriding rate and with little variation in quality can be produced with excellent productivity sufficient for industrial use.

The present invention will be explained in more detail below.

As described above, the method for producing silicon nitride powder of the present invention involves supplying a nitriding raw material containing metallic silicon powder to a plurality of heated fluidized beds formed from silicon nitride powder and a reaction gas containing nitrogen gas or ammonia gas. By sequentially and continuously supplying and discharging, the nitriding reaction is carried out in stages over multiple stages.

The metal silicon powder used as the nitriding raw material is not particularly limited, but those having an average particle size of 1494 to 4 mm are preferably used. In this case, a binder such as polyvinyl alcohol is added to finely powdered metal silicon powder of 444 mm or less to granulate it to an average particle size of 149 to 4 nn, and this granulated product is
It is possible to use a material that has been sintered at 1300° C. for a short time so that the silicon powders stick together but do not melt. In addition, for this nitriding raw material, 5-5% of silicon nitride powder with an average particle size of about 149μ to 4m is added to the metal silicon powder.
A mixed powder containing 0% by weight, preferably 10 to 30% by weight can be used. By adding such silicon nitride powder, even if the supply rate of the nitriding raw material is increased and the residence time in the fluidized bed is shortened, the average nitriding rate in the first nitriding reaction in the first fluidized bed can be improved. is possible,
Furthermore, fusion and aggregation of metal silicon powder can be more effectively prevented. Note that if the addition rate of silicon nitride powder exceeds 50% by weight, the production rate may be reduced, while if it is less than 5% by weight, it is difficult to obtain a substantial effect by adding silicon nitride powder.

In the method of the present invention, the nitriding raw material is subjected to a nitriding reaction in a plurality of fluidized beds in multiple steps. In this case, each fluidized bed is formed from silicon nitride powder and a non-oxidizing reaction gas containing nitrogen gas or ammonia gas, and is heated and maintained to a nitriding reaction temperature. Here, the temperature of the first fluidized bed into which the nitriding raw material is first introduced is 1000
~■400℃, preferably 1200-1350℃,
Nitride is formed on the surface of the metal silicon powder particles by the first nitriding reaction in the first fluidized bed. Note that if the temperature of the fluidized bed is less than 1000°C, nitrides cannot be formed on the surface of the metal silicon powder particles, while if it exceeds 1400°C, the particles will melt.

Agglomeration will occur. Further, the temperature of the second fluidized bed and subsequent fluidized beds formed as necessary is not particularly limited, but is 1200 to 1700°C, particularly 1350 to 1300°C.
It is preferable to set the temperature to 500°C, and it is preferable to set the temperature so that the temperature increases sequentially. In addition, the number of fluidized beds,
That is, from the viewpoint of productivity, it is preferable that the nitriding reaction order is second or third order. Furthermore, the non-oxidizing reaction gas that forms this fluidized bed contains nitrogen gas or ammonia gas, but hydrogen gas can be mixed with this reaction gas, and in this case, the content of nitrogen gas or ammonia gas can be 10 to 100% by volume, especially 60 to 90% by volume.

In the method for producing silicon nitride powder of the present invention, the nitriding raw material is sequentially and continuously supplied to the fluidized bed and then continuously discharged to nitride the metal silicon powder in stages, but the nitriding conditions other than the above are normal conditions. It can be done.

As explained above, according to the production method of the present invention, it is possible to stably and efficiently produce silicon nitride powder with less variation in quality such as α phase ratio. .

EXAMPLES Hereinafter, the present invention will be specifically explained by showing examples and comparative examples, but the present invention is not limited to the following examples.

[Example 1] Polyvinyl alcohol was added in an amount of 1% by weight in terms of solid content to metal silicon powder having a particle size of 44- or less, and then kneaded, and then granulated to an average particle size of 0.5 m+ using an extrusion granulator. This is 150
After drying at °C to remove moisture, it was placed in a sintering furnace and sintered at 1300 °C for 1 hour under argon gas flow, and this was used as a nitriding raw material.

On the other hand, 500 g of silicon nitride powder was charged into a first reactor and a second reactor each having an inner diameter of 8' Otm and a scorching part length of 500 m.
A mixture of NQ/min is supplied as a reaction gas,
A fluidized bed (bed height 300 mm) was formed in each case, and one reactor was heated to create a fluidized bed at 1250°C and 1
It was maintained at 400°C. The above nitriding raw material is continuously supplied to the fluidized bed in this first reactor at a rate of 200 g/hr, and the bed height is 300 g/hr from the fluidized bed in this first reactor.
The nitrided product is continuously taken out so that the nitrided product is maintained at a temperature of 300,111 mm.
The product was removed continuously so that it was maintained at n.

The above final product was a silicon nitride powder with constant quality of nitridation rate of 95% and alpha phase rate of 80%. Note that the nitridation rate of the nitrided product taken out from the first reactor was 50%.

[Example 2] Silicon nitride powder was prepared in the same manner as in Example 1, except that the fluidized bed temperature in the first reactor and the fluidized bed temperature in the second reactor were set to 1300°C and 1,450°C, respectively. Manufactured.

The obtained silicon nitride powder has a nitridation rate of 98% and an α phase rate of 75%.
It was of a certain quality. Note that the nitridation rate of the nitrided product taken out from the first reactor was 65%.

[Comparative example]

The same operation as in Example 1 was performed except that the fluidized bed temperature in the first reactor and the fluidized bed temperature in the second reactor were set to 1420°C and 1450°C, respectively. After a certain period of time, it became impossible to maintain the fluidized bed in the first reactor. After the operation was stopped, the inside of the first reactor was examined and a lump of metallic silicon was found at the bottom of the cylinder.

[Example 3] As a nitriding raw material, a mixed powder obtained by mixing 30% by weight of silicon nitride powder (average particle size 0.5 m) with that used in Example 1 was used, and 400 g of this was placed in a fluidized bed in the first reactor. Silicon nitride powder was produced in the same manner as in Example 2 except that the powder was supplied at a rate of /hr.

The obtained silicon nitride powder had a nitriding rate of 98% and was of constant quality.

[Example 4] A third reactor with an inner diameter of 80 ng++ and a scorching part length of 500 mm was prepared, and a third fluidized bed consisting of 500 g of silicon nitride powder and a reaction gas was formed therein. The temperature was ↓450'C, and the flow fVJ temperature in the first and second reactors was 1300°C, respectively.

1350°C, and the nitride produced in the second reactor is continuously fed as it is into the fluidized bed in the third reactor, and the nitrided product is continuously fed from the fluidized bed in the third reactor. In addition, silicon nitride powder (average particle size 0.5n) was used as the nitriding raw material in Example 1.
Silicon nitride powder was produced under the same conditions as in Example Y except that a mixed powder containing 30% by weight of m) was used.

The obtained silicon nitride powder had a constant quality with a nitridation rate of 99%.

Claims (1)

[Claims] 1. A nitriding raw material containing metal silicon powder is continuously supplied to a first fluidized bed formed from silicon nitride powder and a non-oxidizing reaction gas containing nitrogen gas or ammonia gas and maintained at a temperature of 1000 to 1400°C. After performing the first nitriding reaction in the first fluidized bed, the nitrided product is continuously taken out from the first fluidized bed, and is further treated with a non-oxidizing product containing silicon nitride powder and nitrogen gas or ammonia gas. A method for producing silicon nitride powder, which comprises supplying silicon nitride powder to a second fluidized bed formed from a reaction gas, and performing a second nitriding reaction in which unreacted nitriding raw material is nitrided in the second fluidized bed.