JPS5838387B2 - Method for producing a sintered body of silicon nitride or silicon carbide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for producing a sintered body of silicon nitride or silicon carbide;
Furthermore, the present invention relates to a method for producing a sintered body of silicon nitride or silicon carbide, which is characterized in that the process of burning a silicon nitride or silicon carbide rod is carried out in a specific casing material.

In recent years, sintered bodies of silicon nitride or silicon carbide have been developed for various uses as engineering ceramics, and various methods of manufacturing them have been proposed accordingly.

Specifically, various improvement methods have been proposed for the normal sintering method, reaction sintering method, hot press method, etc. Among these, the present invention proposes an improved method for the normal sintering method. It is.

For example, the normal sintering method for silicon nitride involves adding a number of sintering aids such as magnesia, alumina, and yttria to silicon nitride powder, and applying various molding methods such as press molding, casting molding, and injection molding. The material is shaped by a method and then fired at a temperature of 1,600 to 1,900° C. in a non-oxidizing atmosphere such as nitrogen.

Various proposals have been made regarding this stage of burning the precepts.

As is well known, silicon nitride does not have sufficient oxidation resistance at high temperatures, and also has the property of decomposing and producing silicon and nitrogen at high temperatures.

This silicon becomes silicon monoxide (Sin) if oxygen is present.
It becomes steam.

Regarding the former problem of oxidation resistance, it is sufficient that oxygen does not exist in the firing atmosphere, so firing may be performed in a nitrogen atmosphere or a non-oxidizing atmosphere such as argon, and in some cases, firing may be performed in a vacuum. It is also possible to do so.

However, regarding the latter problem of decomposition of silicon nitride, a fully satisfactory method has not yet been proposed.

One possible solution to this problem is to replace the air inside the box with a non-oxidizing gas and make the box completely airtight, but this method is difficult and non-oxidizing. Be realistic.

Further, in obtaining a sintered body of silicon carbide, the problem is almost the same in that silicon carbide decomposes into silicon and carbon at high temperatures.

The present invention solves various problems associated with the decomposition of silicon nitride or silicon carbide, and includes storing a round body whose main part is silicon nitride or silicon carbide in a silicon nitride casing material, and The material is further stored in a carbonaceous box material having an opening,
In addition, the diameter of the opening is 2 mm or less, or the opening is filled with a carbonaceous porous material such as carbon fiber or carbon particles, and the hollow shaped body is burned in a non-oxidizing atmosphere. The gist of the present invention is a method for producing a characteristic sintered body of silicon nitride or silicon carbide.

High-temperature decomposition of silicon nitride is influenced by the partial pressure of silicon vapor and nitrogen gas around silicon nitride. Naturally, if the partial pressure of silicon vapor and nitrogen gas is high, the decomposition of silicon nitride is suppressed and the decomposition of silicon carbide is suppressed. High-temperature decomposition of silicon is also suppressed in substantially the same way if the partial pressure of silicon vapor is high.

The present invention is characterized by using a special double-structured case material, in which the inner case material is made of silicon nitride material, the outer case material is made of carbonaceous material, and the outer case material and the inner case material are made of silicon nitride material. Although they may be in close contact with each other, it is better to separate them a little so that a space exists between the outer casing material and the inner casing material.

Then, an opening is provided in the carbonaceous material that is the outer casing material, and the diameter of the opening is 2 mm or less, or the opening is made of carbonaceous porous material such as carbon fiber or carbon particles. It is characterized by being filled with

Alternatively, the opening may be directly connected to the outside of the furnace using a carbonaceous tube or the like.

The present invention is characterized by the use of the box material having the structure described above, and by adopting such a structure, the following advantages can be obtained and the above-mentioned problems can be solved. be.

That is, the internal space formed by the inner casing material is filled with silicon vapor that is evaporated and decomposed from the casing material and the object to be burned at high temperatures, and the partial pressure of the silicon vapor is maintained at a high state, so that the Decomposition of silicon nitride or silicon carbide from substances will be suppressed.

However, silicon vapor is generated from the outer surface of the casing material (inner casing) due to the decomposition of silicon nitride, and silicon vapor also comes out from the inside.If the outer carbonaceous casing material is not used, this silicon vapor will Steam adheres to the furnace wall or, in the case of an electric furnace, to the heating element, shortening the furnace life.

It also affects temperature measurement, and when using an optical pyrometer, it can clog the temperature hole, fog up the side heat hole window glass, and distort the measured temperature if gas is present in the field of view. be.

When using a thermocouple, it is also undesirable to deteriorate the thermocouple, so it is necessary to prevent silicon vapor from floating in the furnace.

For this purpose, the present invention uses a carbonaceous material as the outer case.

As is known, carbon easily reacts with silicon or silicon monoxide at high temperatures, and is harmful to silicon carbide.

The present invention takes advantage of this reaction and uses a carbonaceous outer casing to trap silicon vapor, but in order to better trap silicon vapor in the outer casing, an opening is provided in the outer casing. It is necessary to provide

In other words, if the outer casing does not have an opening, for example, when a large number of silicon nitride hollow bodies are burned, the decomposition of the hollow bodies and the inner casing will generate a considerable amount of silicon vapor and nitrogen gas. The inside of the box becomes pressurized, and in search of an outlet, silicon carbide deposits are formed in the pores of the outer case, which are not necessarily airtight, to block these pores, and then, in search of an outlet, the top lid of the outer case is closed. As a result, silicon vapor fills and floats in a wide area in the furnace, causing the above-mentioned disadvantages as shown in Comparative Example 2.

However, by providing an opening in the outer casing, silicon vapor and nitrogen gas are guided to this opening, and the silicon vapor can be mainly collected in this opening, thereby avoiding the above-mentioned disadvantages.

It is preferable that the openings have as many small diameters as possible and are evenly distributed.

Further, depending on the case, an opening with a large diameter may be used, but in this case, it is necessary to fill the opening with a carbonaceous porous material such as carbon fiber or carbon particles.

This is because silicon vapor escapes to the outside of the outer casing without coming into contact with carbon through the large-diameter opening and contaminates the inside of the furnace.

,Of course. It is also effective to fill a small-diameter opening with a carbonaceous porous material such as the one described above.

Particularly when the object to be burned is large or in large quantity, filling with carbon fibers, carbon particles, etc. is easy and highly effective.

As a result of repeated experiments by the present inventors, we found that the opening diameter is preferably 2u or less when a carbonaceous porous material is not used, and that when a carbonaceous porous material is used, the opening diameter It was found that no particular restrictions were necessary.

The reason for limiting the value to the above numerical range is that in the opening having a diameter larger than the second diameter, there is silicon vapor that escapes from the outer casing to the outside without coming into contact with carbon.

Silicon nitride or silicon carbide molded bodies contain organic binders such as CMC (carboxymethyl cellulose) as bonding agents, so these binders decompose at high temperatures and produce hydrocarbons and other forms. Since it is desirable that oxygen gas inside the body be removed from the space formed by the inner box, the incinerator atmosphere is kept in a vacuum until about 1000°C.
These carbonaceous arsenic fractions are sucked out of the casing material.

It is important to provide an opening to facilitate operations for adjusting the atmosphere.

The use of the special double box material of the present invention ensures sufficient air permeability for the above purpose.

The present invention is applicable not only to the firing of silicon nitride or silicon carbide shaped bodies, but also to other silicon-containing materials.

In addition, if the silicon nitride or silicon carbide body contains easily decomposed substances other than silicon, the substance that reacts with the substance may be present in the opening of the carbonaceous outer casing and collected. .

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Silicon nitride powder (average particle size 2 μ, purity 98 weight φ) 100
To parts by weight, 5 parts by weight of ¥203 powder (average particle size 2μ), A
After adding 5 parts by weight of l203 powder (average particle size 0.5μ) and mixing well, 8 parts by weight of CMC2φ aqueous solution was added as a binder, and the kneaded clay was mixed at a pressure of 200 kg/1 for 10 minutes.
It was shaped into a flat plate of 0x50x15 mm using a mechanical press.

Ten of these hollow bodies were housed in a silicon nitride box material with an internal volume of 150x150x200.

Next, this silicon nitride inner casing was cut into 6 small holes with a diameter of 17nrlL.
It was housed in a graphite outer box with a top cover made of a graphite plate with a thickness of 30 mrIL distributed uniformly over the area of the barrel of 30 m in the center at a density of 30 m/d.

The inner volume of this outer box was 200x200x250.

Next, this graphite outer box was placed in an electric furnace and heated to 1000°C in a vacuum, then filled with nitrogen gas to atmospheric pressure, heated to 1750°C, and held at this temperature for 1 hour. did.

Comparative Example 1 Completely the same as Example 1 except that the diameter of the small holes provided in the graphite plate of the outer box was 8 mm, and the density of the small holes was 1 hole/d and uniformly distributed over an area of 30 mm. A silicon nitride sintered body was obtained by the process.

Comparative Example 2 A silicon nitride sintered body was obtained by the same process as in Example 1, except that instead of using the graphite outer case in Example 1, an ordinary graphite outer case without any special design was used for the top cover.

Further, the number of samples was set to 40 so that the silicon nitride inner box was filled.

Example 2 A silicon nitride sintered body was obtained by the same process as in Example 1 except that the graphite outer case in Example 1 was replaced with the outer case shown below.

The number of samples was 40.

The outer box used in this example is as follows.

The material is graphite and the surface has no holes except for the top lid.The top surface has a hole with a diameter of 301 nm in the center, and the inner diameter is 50 mm and the height is 80 mm. A L11L graphite cylinder (thickness: 10 mπ) was placed on the lid with its center aligned with the hole in the lid, and the inside of the inner cylinder was densely filled with carbon fibers (average diameter: 10 μm).

Example 3 Everything was the same as in Example 1 except for the number of upper lid samples of the graphite outer box.

There are 6 small holes with a diameter of 2 in the center of the top cover of the graphite outer box.
A cylinder made of graphite, which is the same as that in Example 2, is placed on the upper lid with its center aligned with the center of the small hole.

Furthermore, graphite particles with an average particle diameter of 3 are filled into this cylinder.

The number of samples is 40 as in Example 2.

Table 1 shows the firing results obtained in the above Examples and Comparative Examples.

Claims (1)

[Scope of Claims] 1. A guard-shaped body mainly made of silicon nitride or silicon carbide is housed in a silicon nitride casing material, and the silicon nitride casing material is further housed in a carbonaceous casing material having an opening. A method for producing a sintered body of silicon nitride or silicon carbide, characterized in that the diameter of the opening is 2 mm or less, and the shaped body is burned in a non-oxidizing atmosphere. 2. A hollow body mainly made of silicon nitride or silicon carbide is housed in a silicon nitride casing material, and the silicon nitride casing material is further housed in a carbonaceous casing material having an opening; 1. A method for producing a sintered body of silicon nitride or silicon carbide, which comprises filling a carbonaceous porous material such as carbon fiber or carbon particles, and sintering the shaped body in a non-oxidizing atmosphere.