JPS6036377A - Manufacture of high density silicon carbide sintered body - 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 producing a high-density silicon carbide sintered body.

Silicon carbide has higher hardness than conventional silicon carbide, excellent wear resistance, low coefficient of thermal expansion, high decomposition temperature, high 11W oxidation property, chemical stability, and generally high electrical conductivity. It is known as a useful ceramic material with properties.

In addition to the above-mentioned properties, this high-density sintered body made of silicon carbide has high strength up to high temperatures and excellent thermal shock resistance, making it a promising high-temperature structural material, and attempts are being made to apply it to various uses including gas turbines. It is being

The silicon carbide sintered body is produced by methods such as hot press sintering, pressureless sintering, reaction sintering, recrystallization, and chemical vapor deposition. Among these methods, the most industrially advantageous method is considered to be the pressureless sintering method. The pressureless sintering method can be molded using methods commonly used for molding ceramic materials, such as pressing, slurry casting, extrusion molding, and injection molding. Thick-walled products can be manufactured most easily and with high productivity. Furthermore, products produced by this method can be expected to have higher performance than products produced by reaction sintering and recrystallization methods.

One day! However, since silicon carbide is a compound with strong covalent bonding, it is difficult to sinter it alone in the case of normal pressure sintering method and hot press sintering method, and it is difficult to sinter it by itself. In order to obtain a sintered body, it is necessary to add some kind of sintering aid. Boron or boron compounds are known as sintering aids. Furthermore, carbon may be added to these.

However, in the case of pressureless sintering, even if such a sintering aid is added, it is difficult to obtain a good high-performance, high-density sintered body using normal methods. Particularly during sintering, a silicon carbide molded body containing a sintering aid is easily decomposed, which causes a problem in that the molded body is not sufficiently densified.

This problem is true when making small sample molded bodies, but it becomes a particularly big problem when trying to manufacture products with complex shapes, large quantities, or thick walls as homogeneous, high-density quantities with good productivity. Become.

The present invention relates to a silicon carbide molded body (however, aluminum and/or
(excluding those containing an aluminum compound as a sintering aid) to prevent the molded body from decomposing and suppressing densification when sintering at normal pressure, and to obtain a high-density sintered body. This method provides a method for

Silicon carbide begins to decompose at the sintering temperature of the silicon carbide compact. In other words, silicon carbide does not melt under atmospheric pressure and has a temperature of 20
At temperatures above 00°C, it begins to sublimate, and at even higher temperatures it decomposes into carbon and silicon-rich vapor. The sintering temperature of the molded body required to obtain a high-density sintered body of silicon carbide is generally 1
The temperature is 800 to 2300°C, and in this high temperature range, silicon carbide sublimes, decomposes, and generates gases such as silicon and Si2C. Therefore, the silicon carbide molded body is made of silicon, Si2
By firing in an atmosphere containing a gas such as C, sublimation and decomposition of silicon carbide in the molded body can be suppressed. However, in reality, decomposition of silicon carbide is not simple. That is, an interaction occurs with the sintering aid contained in the molded body, the silica layer on the surface of the silicon carbide particles, other impurities, or the weak butyric acid contained in the atmosphere.

Therefore, in order to prevent the decomposition of the molded body during firing and to create a sintered body with higher density, it is necessary to place the gas generated by the decomposition of the molded body in an equilibrium vapor position. Preferably, the partial pressure of those gases in the atmosphere is maintained.

For the reasons described in 1-, oxygen is often involved in the decomposition of silicon carbide, and when oxygen is present, gases such as -silicon oxide (Sin) and -carbon oxide (CO) are thought to be generated. Therefore, it is necessary to increase the partial pressure of these gases in the firing atmosphere in order to suppress the decomposition of the compact.

As a result of various studies on preventing the decomposition of silicon carbide molded bodies from the following points of view, the present invention was developed. The gist of this article is a method for producing a high-density carbonized sintered body, in which the material (excluding those containing it as an agent) is fired in an atmosphere containing silicon and/or carbon as a component. be.

Next, the implementation method will be explained.

An atmosphere containing silicon and/or carbon as a component can be created by various methods, but one method is to introduce or enclose these gases into a firing furnace. The gas containing silicon is Si, 5iC14.

5il14. In addition to SiO, carbon-containing residues can be introduced as hydrocarbons, CO, and the like. Usually, the atmosphere is an inert gas such as nitrogen, argon, helium, etc. mixed with these gases. Another effective method is to arrange a powder, compact, or sintered compact around the silicon carbide compact that generates these gases at the sintering temperature. Such a powder, molded body, or sintered body preferably consists of one or more of silicon and a silicon compound, and/or one or more of carbon and a carbon compound.

Methods for placing these powders around a silicon carbide molded body include embedding the molded body in the powder, and placing the molded body in a carbon or silicon carbide pod coated with the powder on its inner surface. There are ways to do this. The method of embedding in the powder is preferred because it effectively suppresses decomposition of the molded body. However, it is unsuitable for molded products of large dimensions and complex shapes. On the other hand, the method in which the powder is applied to the sheath material is suitable for manufacturing various shapes, and it is possible to obtain a high-density sintered body equivalent to that obtained by embedding the powder in the powder. In the powder coating method, the powder may be mixed with an organic solvent such as alcohol, acetone, or water to form a slurry and then applied to the pod material.

At this time, a binder such as polyvinyl alcohol can also be combined with 4fQ in the slurry.

In the above powder embedding method, silicon carbide is used as powder,
Although various materials such as silica, -resistant silicon, and carbon can be used, powders made of silicon carbide powder and/or carbon powder are preferred.

In the case of powder coating, in addition to silicon carbide powder and carbon powder, it is also possible to use a polymeric aromatic compound with a large amount of residual iRM, such as phenol resin and polymethylphenylene. Also,
Instead of using powder or unsintered compacts, it is also possible to use sintered compacts.

1j Feminized silicon powder is commercially available with a purity of 98% and an average particle size of 1
A material of micron or smaller was used. This silicon carbide powder was mixed with a sintering aid in the proportions shown in Table 1, placed in a plastic pot, and thoroughly mixed with a plastic ball in the presence of acetone. Next, this was dried and molded using a mechanical press at 200Kg/cv+t to form a 20X
1) A molded object of 20 x 40 mm. (However, no
6 is rubber press molded at a pressure of 2000Kg/cffl to have an outer diameter of 50mm, an inner diameter of 40), and a length of 150m.
A pipe-shaped molded body of m was obtained. ) Next, this was heated in a resistance heating furnace for 2,000 degrees under various atmospheric conditions shown in Table 1.
It was baked at 'C for 1 hour.

As a result of the following 1-, it can be seen that a silicon carbide sintered body having a higher density can be obtained by the method of the present invention than by the conventional method shown in the comparative example.

Table 1 Llt No.1. is Comparative Example F2. Side weight ratio of SiC, C, etc. to the weight of powder 3
The density of the sintered compact is relative to the theoretical density in Table 1. No atmospheric conditions: The compact is placed in the furnace without a container and buried: The compact is placed in the powder according to the type and amount in the right column of the method. Buried coating '1Ij = Apply a slurry made by adding ethyl alcohol to the powder according to the type and compounding amount in the right column of the method on the inner surface of the carbon container, and after drying, apply this slurry.

Claims (5)

[Claims] (1) A silicon carbide molded body (excluding those containing aluminum and/or an aluminum compound as a sintering aid) is fired in an atmosphere containing silicon and/or carbon as a component. A method for producing a high-density silicon carbide sintered body. (2) an atmosphere containing one or more of silicon and silicon compounds arranged around the silicon carbide molded body] and/or
The manufacturing method according to claim (1), wherein the material is formed from one or more of carbon and carbon compounds. (3) Claim No. 1 in which the atmosphere contains an inert gas
) or the manufacturing method in paragraph (2). (4) The manufacturing method according to claim (2), wherein the silicon compound is silicon carbide, silica, or silicon oxide. (5) The manufacturing method according to claim (2), wherein the carbon compound is a polymeric androaromatic compound such as a phenol resin or polymethylphenylene.