JPH0582346B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a silicon carbide refractory material.

Silicon carbide has been conventionally used as a refractory material with excellent heat resistance and thermal shock resistance. The manufacturing method is pressure sintering or pressureless sintering, but while pressure sintering can produce dense and high-strength products, it can only produce products with simple shapes and requires complicated equipment. It's expensive.

Pressureless sintering has also been carried out, but since it involves the addition of boron and carbon and is a solid phase reaction, the properties are affected by the dispersion state of the additives, and its reliability is not always satisfactory. Ta.

This invention is a method of manufacturing a highly reliable, high-density, high-strength sintered body by sintering at normal pressure by taking advantage of the inherent heat resistance and thermal shock resistance of silicon carbide. .

In the conventional pressureless sintering method, ultrafine powder is used,
Because it is sintered using a solid phase reaction, the volume shrinks by approximately 20%. For this reason, strain tends to remain in the sintered body.

The inventors investigated the cause of this strain and found that it is greatly affected by the surface oxidation state of SiC, the main raw material.

The surface of silicon carbide particles is oxidized by air even at room temperature, and this is more noticeable in the case of ultrafine particles of 1 μm or less. That is, it is clear that the amount of oxidation is proportional to surface area as well as time and temperature.

This oxygen on the surface of silicon carbide affects the reaction with boric acid and other sintering aids, and is particularly noticeable when AlN is used. AlN is SiC−AlN
In the -C system, the reaction proceeds in the liquid phase at 2000 to 2200°C, so it is clearly a more preferable sintering aid than boric acid in terms of homogeneity, but as mentioned above, it is susceptible to interference by oxygen on the SiC surface. .

This interference can be suppressed by incorporating C into the reaction system, but this alone is not sufficient.

It is known that AlN is used as a sintering aid in the conventional pressureless sintering method, but in this case
It is used together with other sintering aids such as WC, BC, B, Al ₂ O ₃ , etc., and it is not possible to obtain a sufficiently dense product (more than 90% of the theoretical density) with AlN-C alone as in the present invention. Ta. This is because no consideration was given to the influence of moisture in the molded article.

Therefore, in the present invention, a dried blended powder is used, and the moisture content in the binder is suppressed to 1% or less. This is because the amount of oxidation on the SiC surface tends to increase when moisture is present, and this is to reduce the interference caused by oxygen.AlN, in particular, easily reacts with moisture and decomposes in mixtures even at room temperature. This is because it has become clear that the AlN blended with water changes in quality due to moisture and becomes ineffective as a sintering aid. Therefore, in order to prevent moisture from entering the molded article, consideration must be given to moisture not only in the raw material powder but also in the binder used.

When SiC, AlN, and powder are added, they are C granules, so it is relatively easy to dry them. Such drying can be carried out by a known method, such as by holding the particles at 150° C. for about 10 hours in a constant temperature bath, to volatilize water from the surface of the particles. Dry raw material powder has a moisture content of 0.1%
degree or less.

However, even though ordinary binders are hydrophobic, they often contain water, and even during firing, they do not volatilize as easily as the water attached to the particle surface. Even if silicon powder with low surface oxidation is used, it will be easily oxidized by the moisture in the binder, which will have an adverse effect on the SiC-AlN-C reaction system.

The binder can be used as it is or diluted with a solvent, etc., but the water content that does not affect the above reaction or can be ignored is 1% or less, preferably substantially no water content. shall not be included. Such a binder can be obtained by dehydrating a generally commercially available binder. This dehydration treatment may be carried out by a known method, such as adding a desiccant such as silica gel to the binder, or adding concentrated sulfuric acid if no reaction occurs.

The C added in the present invention may be in powder form, or may be C included in the binder and mixed as residual carbon during firing, or both may be used. In any case, the total amount of C added is 1 to 10
% by weight.

This invention will be explained below with reference to Examples.

Example: 90 parts of SiC powder with an average particle size of 0.5μ 5 parts of AlN powder with an average particle size of 4.0μ Dehydrated mixed powder (moisture content 0.1%) with a carbonization rate of 50%, phenol resin ( 10 parts of acetone (water content: 0.3%) and 100 parts of acetone (water content: 0.2%) were added and granulated.

This compact was pressureless sintered at 2100°C in an Ar atmosphere. The density of this material was 3.15 (corresponding to 98% of the theoretical density), the bending strength at room temperature was 550 MPa, and the bending strength at 1200°C was 650 MPa.

As a comparative example, commonly used phenol resin (water content 1.1%) and acetone (water content 1.3%) were used.
%), and a sintered body was obtained in the same manner as in the example.

This material had a density of 2.75 and a room temperature strength of 250 MPa. The addition ratio of AlN and C is preferably within the range of 1 to 10% by weight relative to SiC, and if it deviates from this range, high density and high strength cannot be obtained. Firing temperature is also 2000-2200℃
If the range is exceeded, the same desirable density and strength cannot be obtained.

Claims (1)

[Claims] 1 80 to 98% by weight of SiC powder in dry state
And 1-10% by weight of AlN powder, a total of 1-10% by weight of dry C powder and/or C raw material which is mixed as residual carbon during firing with low moisture content is added and mixed, and the moisture content is 1% or less. 1. A method for producing a silicon carbide refractory material, which comprises mixing and molding a viscous binder, followed by firing at 2000 to 2200°C in a non-oxidizing atmosphere. 2. The method for producing a silicon carbide refractory material according to claim 1, wherein the binder contains substantially no water.