JPS5915114B2 - Method for manufacturing silicon nitride sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a silicon nitride sintered body containing β'-sialon and/or silicon nitride.

Conventionally, this type of silicon nitride sintered body has been produced by firing a silicon nitride sintered body in a normal pressure nitrogen atmosphere or a non-oxidizing gas atmosphere, or by sintering the sintered body in a vacuum, a nitrogen atmosphere, or a non-oxidizing gas atmosphere. It is manufactured either by hot pressing in a non-oxidizing gas atmosphere or by hot pressing in a non-oxidizing gas atmosphere.

In this case, the body to be sintered is left bare in the above-mentioned atmosphere, or is made of boron nitride (BN), aluminum nitride (AlN),
It is embedded in a stuffing powder made of one or more of silicon carbide (SiC) and carbon, then fired and hot pressed.

In particular, when producing a sintered body mainly composed of β'-sialon as a silicon nitride-based sintered body, a mixed powder of silicon nitride and aluminum nitride and one or both of alumina and silica is used as the raw material. After molding this into a predetermined shape using various methods, drying, and removing the binder, the molded body was buried in a graphite container filled with boron nitride powder, and the graphite container was placed in a nitrogen atmosphere. So 160
Calcinate at a temperature of 0 to 1800°C.

However, the above-mentioned method has the disadvantage that a porous white portion is formed on the surface layer of the sintered body during firing.

When such white areas occur, not only do firing cracks occur around the white areas, but they also cause deterioration of various physical properties such as oxidation resistance, alkali corrosion resistance, strength, and hardness of the obtained sintered body. .

For this reason, the present inventor has conducted various studies on the formation of white parts on the sintered body during firing, and has found that the white parts are caused by silicon nitride, silica, or both components from the surface of the sintered body. The inventors have investigated that this is caused by the volatilization and dissipation of these components, and have discovered that the volatilization and dissipation of these components cannot be suppressed by the above-mentioned filling powder such as boron nitride.

Based on the above investigation results, the present inventor conducted further research and tried using silicon nitride, silica, or a powder consisting of silicon nitride and silica as a packing powder, and found that the No white portion was formed on the surface layer of the sintered body, and a dense sintered body without firing cracks was obtained.

However, it has been found that such a filling powder made of silicon nitride and/or silica sinteres itself during the firing of the sintered body, making it impossible to take out the silicon nitride sintered body after firing.

Therefore, as a result of further intensive research, the present inventors found a mixed powder containing one or more of boron nitride powder, aluminum nitride powder, silicon carbide powder bed, and carbon powder together with silicon nitride powder and/or silica powder. By using the silicon nitride powder as a filling powder, white parts are not formed on the surface layer of the silicon nitride sintered object during firing, thereby preventing firing cracks and suppressing sintering of the packing powder itself. It has been found that a dense silicon nitride sintered body to which no powder adheres can be obtained by doing so.

This effect of preventing the formation of white parts on the surface layer of the sintered object is due to the fact that the silicon nitride and/or silica powder mixed in the powder is decomposed and diffused during the firing of the sintered object. This is thought to be because the concentration of gas phase components in the atmosphere around the body is sufficiently increased, thereby suppressing volatilization of silicon nitride components and/or silica components from the surface of the silicon nitride-based sintered body.

In addition, the sintering prevention effect of the packing powder itself is due to the fact that during the firing of the object to be sintered, boron nitride powder, etc., which is difficult to sinter and mixed with silicon nitride powder and/or silica powder, intervenes in the silica powder, etc., which is easy to sinter. It is thought that this is to prevent silica powder and the like from directly contacting each other and sintering.

Hereinafter, the non-invention will be explained in detail.

First, a mixed powder obtained by mixing one or both of silicon nitride powder and silica powder with one or more selected from the group of boron nitride powder, aluminum nitride powder, silicon carbide powder, and carbon powder is used as a powder. Pre-formed β iron component, silicon nitride component or β
After a silicon nitride sintered body consisting of a sialon component, a silicon nitride component, etc. is buried, it is fired by an atmospheric pressure sintering method or a hollow press method to produce a silicon nitride sintered body.

When using the normal pressure firing method, a graphite container is filled with the above-mentioned packing powder, a silicon nitride-based sintered body is buried in this packing powder, and then the graphite container is almost tightly sealed. The product is heated and fired in a nitrogen atmosphere or a non-oxidizing gas atmosphere such as an inert gas.

On the other hand, when a hot press method is adopted, a hot press mold is filled with the powder, a silicon nitride sintered body is buried in the powder, and the inside of the mold is evacuated, for example.

After evacuating the outer periphery of the mold as necessary, the mold is heated and fired from the outer periphery while being pressurized with a graphite push rod or the like.

The particle size of the silicon nitride powder and/or silica powder in the packed powder used in the present invention is such that it can be easily decomposed and diffused efficiently during firing, and even if it is too small, from the viewpoint of suppressing its own sinterability. Too coarse is not good, usually 50-500
It is desirable to set it to around μ.

The particle size of one or more powders selected from the group of boron nitride powder, aluminum nitride powder, silicon carbide powder, and carbon powder in the packed powder used in the invention may also be about the same.

In the present invention, the blending ratio of silicon nitride powder, etc. and boron nitride powder, etc. in the packed powder is preferably such that the silicon nitride powder, etc. has a weight ratio of 3 to 60%, and the weighted boron powder, etc., has a weight ratio of 97 to 40%. .

In other words, if the number of layers of silicon nitride powder, etc. in the packed powder is less than three times the maximum, the concentration of gaseous silicon in the atmosphere around the sintered object will not be sufficient during firing of the sintered object, and the silicon nitride powder etc. will not be absorbed from the surface of the sintered object. It can sufficiently suppress the volatilization of the silicon nitride component and/or silica component, but if the amount exceeds 60% by weight at most, not only will the powder itself be easily sintered, but the amount of volatile components in the powder will increase too much. This is because the actual volume of the stuffed powder decreases greatly during baking, and the volume of cavities in the stuffed powder increases.

The firing humidity in the present invention may be appropriately selected depending on the components in the object to be sintered.

For example, when the object to be sintered consists of a silicon nitride component, the firing humidity is set to 1500°C or higher, and when the object to be sintered consists of a β'-SiAlON component, the firing humidity is set to 1600 to 180°C.
The temperature may be about 0°C.

Next, the present invention will be explained in detail.

Example 1 First, fine powders of silicon nitride, aluminum nitride, and alumina were prepared as raw materials, and 20 mol% of each of these was prepared.
(Si3N, ), 40 mol% (AlN), 40 mol% (
A1203), wet-pulverized in an alumina pot for 96 hours, dried and crushed until the average particle size is 0.
．． A mixed fine powder raw material of 5 μm was prepared.

Next, 20 parts by weight of vinyl acetate was added to this raw material and kneaded, and the mixture was granulated using a 36-mesh nylon sieve.
This granulated raw material is pressed into a mold press (pressure 500Kp/cr/l).
The molded body was molded into a plate shape with dimensions of 40 W x 70 L x 10 TT nm under the conditions of A sintered body was made.

Next, a graphite container filled with a packing powder (Example 1) consisting of silicon nitride powder (15 weight maximum) and boron nitride powder (85 weight maximum), and a graphite container filled with a packing powder (comparative example) consisting only of boron nitride powder. After burying and sealing the silicon nitride sintered bodies, the containers were heated in a nitrogen atmosphere for 10 minutes.
Two types of iron components were heated to 1750°C at a temperature increase rate of 0°C/Hr, heated at that temperature for 4 hours, and then heated and slowly cooled at a falling rate of 200°C/Hr to release β. A silicon nitride sintered body was obtained.

The obtained silicon nitride sintered body of the present invention (Example 1) had no white parts on the surface, was grayish-black in color as a whole, and was homogeneous and dense with a porosity of 0.4.

Furthermore, there were no firing cracks in the sintered body.

On the other hand, in the conventional silicon nitride sintered body (comparative example) obtained using only boron nitride powder as a packing powder, a white part with a thickness of about 1 to 2 mm is formed on the surface, and the inside is gray. It was a dense black part, and the porosity of the white part was 20 to 30%, and the porosity of only the gray black part was 0.3%.

Additionally, several firing cracks were present over a wide area on the surface of this sintered body.

In addition, as a result of identifying the above white part and gray black part with X-ray, the white part is 15R-AIN polytype-Sialon and α
-Alumina, while the gray black part was mainly composed of β'-sialon and also contained a small amount of α-alumina.

Example 2 Nitriding consisting of β iron component was carried out in the same manner as in Example 1 above, except that a mixed powder consisting of silicon nitride powder 15 weight maximum silica powder 5 hereditary and boron nitride powder 80 weight candy was used as the packing powder. A silicon sintered body was obtained.

The obtained silicon nitride sintered body, like that of Example 1, had no white parts on the surface, no firing cracks, and was extremely dense with a porosity of 0.4.

As detailed above, according to the present invention, during firing, the silicon nitride component and/or the silica component are prevented from volatilizing from the surface of the silicon nitride-based sintered body, and the surface layer of the sintered body is It can prevent the formation of white parts, prevent the occurrence of firing cracks, and prevent the filling powder itself from forming into sintered lumps, and has remarkable physical properties such as oxidation resistance, alkali corrosion resistance, strength, and hardness. It has remarkable effects such as being able to obtain an excellent homogeneous and dense silicon nitride sintered body.

Claims (1)

[Claims] 1 A mixed powder obtained by mixing one or both of silicon nitride powder and silica powder with one or more selected from the group of boron nitride powder, aluminum nitride powder, silicon carbide powder, and carbon powder is used as a packing powder, and the packing is 1. A method for producing a silicon nitride sintered body, which comprises embedding a silicon nitride sintered body in powder and then heating and firing it.