JPS5891060A - Manufacture of 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-strength silicon carbide sintered body.

Silicon carbide is harder, more cylindrical, has better wear resistance, has a lower coefficient of thermal expansion, has a higher decomposition temperature, has greater oxidation resistance, is chemically stable, and generally has considerable electrical conductivity. It is known as a ceramic H material for oak. In addition to the above-mentioned properties, this highly marketable sintered body of carbonized + A: cable has high strength up to high temperatures, has a thermal shock resistance of 1,000 yen, and is considered promising as a high-temperature structural material, including for gas turbines. Various applications have been attempted as a result.

Carbonized t)/element I Akita compact is hot press sintered, pressureless sintered,
Fabricated by methods such as reactive sintering, recrystallization, and chemical vapor deposition. Among these methods, the pressureless sintering method is considered to be the industrially most advantageous method. The pressureless sintering method is generally used to mold ceramic materials, such as the press method, slurry casting method, extrusion molding method, and injection molding method. Large-sized products and thick-walled products can be manufactured easily and with high productivity. Furthermore, products produced by this method are expected to have higher performance than products produced by reaction sintering and recrystallization methods.

However, since silicon carbide is a compound with strong covalent bonding properties, it is difficult to sinter the same amount in both the pressureless sintering method and the hot press sintering method, or it is difficult to sinter it alone. In order to obtain this, it is necessary to add a sintering aid. Known examples of the sintering aid 1 include boron, diboron compounds, aluminum, and aluminum compounds. Furthermore, carbon may be added to these.

However, in the case of the pressureless sintering method, even if such a sintering aid is added, it is difficult to obtain a good high-performance, high-density sintered body using the normal method. Particularly during sintering, the silicon carbide molded body containing the 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 dimensions, or thick walls as homogeneous, high-density products with good productivity. .

The present inventors have previously succeeded in obtaining a high-strength carbide t1-prime compact containing aluminum and/or an aluminum compound by pressureless sintering, or have developed a method to make this possible. As a preferable method, we have also found an effective method for preventing the molded body from decomposing and suppressing densification during pressureless sintering.

The present invention was discovered as a result of various studies aimed at further improving these methods, and is by no means the most effective of these improvements. In the present invention, sintering may be carried out at normal pressure or by hot press, and it is also effective to carry out sintering in various non-oxidizing atmospheres.

The present invention will be mainly described below as the most effective sintering method, which is carried out under normal pressure in an atmosphere containing aluminum as a component.

The gist of the present invention is to always use two types of silicon carbide raw materials, alpha and beta crystals, and to use aluminum and/or a compound containing aluminum as a sintering aid for these raw materials. Because it is
These will be explained below.

First of all, silicon carbide (SiO) raw material has a purity of 98% or more, preferably 90-98%.
You can also use the one with a % degree.

Regarding particle size, in the case of super eI powder, it is appropriate to express the average particle diameter in terms of surface area, and the bending strength at room temperature and 1400°C, which is the object of the present invention, is at least 25/'2 or more. Preferably, in order to obtain a sintered body with a specific surface area of 5.27'fF or more, preferably i, J: 10 rn2/
′? The above is good.

The purpose of the present invention is to use α-crystal (type) and β-crystal as this silicon carbide raw material.
Two types of crystals are mixed and used in a predetermined mixing ratio, and the ratio is based on weight (the same applies hereinafter), and α is 65 to 95.
%, β should be 35 to 5, especially ri: α70
-85% and β30-15%.

This is because if these mixing ratios are exceeded, it is difficult to produce an effective effect compared to using α alone or β alone. In relation to this, is there a sintered body that has higher strength even when pressure-free sintered than when using either crystal alone? I found out that I was q.

In particular, it is relatively easy to improve Hatatetsu IM: by 50% or more than that which can be obtained by using it alone, and depending on the conditions, it is possible to achieve a strength that is more than twice as high. Furthermore, it has been confirmed that an improvement in room temperature strength of about 10 to 20% can be easily achieved, although the improvement in high temperature strength is not particularly significant.

Next, the sintering aid) used in the present invention is aluminum or a compound containing aluminum, and examples of this compound include alumina, aluminum silicate, aluminum carbide, aluminum silicon carbide, aluminum boride, Aluminum phosphide etc. can be used. These - free oxygen-free aluminum, aluminum nitride, aluminum carbide, aluminum silicon carbide,
Aluminum chloride, aluminum phosphide, and oxygen-containing alumina are classified into two types, but the most convenient to use is (
-J, alumina (Al1xO3), hereafter Ajl!
This will be explained as 203.

Aluminum oxide (A40a) B corantum (α
-All-203) can be conveniently used, but other crystal forms such as the gamma form may also be used. In addition, an alumina source such as aluminum hydroxide, which easily turns into aluminum oxide even when heated in a non-acidic atmosphere, can also be used.
It also includes compounds that readily yield aluminum oxide of % or more. The aluminum oxide is preferably one with a purity of IW of 98% or more and a low particle size, with an average particle size of 1p.
l]] The following are highly preferable: 11J [1,2,
um or less.

In the present invention, carbonization of aluminum oxide (combined with keishin)
The blending ratio in ゛ is A/! It is 05 to 35% by weight as 203. If this l-J:n is less than 5%, densification will not proceed sufficiently during sintering, and a high-density sintered body that provides high strength will not be produced.
When the temperature is higher than 1900°C, the power and strength of densification is low even when sintered.

If 35% or more of AA20aM is mixed and sintered at 1900 to 2300℃, the decomposer will increase, become porous, and a large amount of unnecessary AA20aM will remain in the sintered body. be.

Similarly, the generally desirable range for the amount of A^03 source is A
It is 2 to 2 Owt in terms of 1,03.

In the present invention, it is desirable to prepare a mixture of raw material 1, in which the remainder, except for aluminum oxide, consists essentially of silicon carbide;
Of course, it may also contain other ingredients that are inevitably included as impurities in the silicon carbide raw material or mixed in during the grinding process, and some ingredients such as silicon oxide. In one aspect, it is an advantage that there is no problem even if it is contained in a relatively large amount.

As the molding method, all LA ceramics molding and rolling methods can be used. That is, press molding, slurry casting, injection molding, extrusion molding, etc. are commercially available. Firing can be carried out at 1900 to 2300° C. in a non-oxidizing atmosphere without pressure. Nitrogen, argon, helium, carbon oxide, hydrogen, and the like can be used as the non-oxidizing surrounding atmosphere, but an atmosphere using an inert gas such as argon or helium is convenient and preferred.

In addition, as described later, 5iO7i including rkoA7,403
It has been found that it is preferable to treat the shape in an atmosphere containing AA components, and it is even more preferable to use an atmosphere that contains carbon and silicon in addition to the atmosphere containing AA.
4 was given.

Sintering temperature i-J: more preferably 1 (19s 0-210
It is 0°C. If the degree of deviation is lower than 1900°C, densification will not proceed sufficiently and a high-density IW sintered body cannot be obtained, whereas if it is higher than 2300°C, the molded body will decompose too much and become porous, which is not preferable.

The travel time required is 1 to 48 hours, more preferably 2 to 48 hours.
It is 24 hours.

This is because if the length is too short, it will not be densified, and even if it is densified, it will not produce sufficient optical intensity, and if it is too long, it will decompose too much and become porous, which is often undesirable.

Is this the most promising way to develop the present invention? y=rExplanation J-ru. That is, since the A/L203 source such as AA203 is added as a sintering aid, in the normal method, this A7!203JiX rapidly decomposes or evaporates during the sintering process, and is removed from the molded body. It may be removed before contributing to the densification of the molded body.

It has been found that, for this reason, it may not be possible to obtain the desired high-density sintered body in which the sintered body is sufficiently densified.

After making various attempts to solve this problem, we found that it is effective to sinter a silicon carbide molded body containing a compound containing an alumina source in an atmosphere containing aluminum as a component. By firing in an atmosphere containing one or more of aluminum and compounds containing aluminum, it was possible to easily produce a sintered body with higher density. This method reduces the amount of alumina that is removed from the compact before densification, making it possible to develop a high-density sintered compact with a stable structure.

On the other hand, silicon carbide itself also begins to decompose at the sintering temperature of the silicon carbide molded body. In other words, silicon carbide does not melt in a bath under atmospheric pressure, but begins to sublimate at temperatures above 2000°C, and
c At high temperatures, it decomposes into carbon- and silicon-rich vapor. The sintering temperature of the compact required to obtain the silicon carbide high-density sintered body targeted in the present invention is 1900 to 2300°C, and in this high temperature range, silicon carbide undergoes sublimation, decomposition, etc. , S
1 + 8120, etc., and the silicon carbide molded body is fired in an atmosphere containing gases such as Si, Si20, etc., thereby suppressing sublimation and decomposition of silicon carbide in the molded body. However, in reality, the decomposition of silicon carbide is simple; that is, the sintering aid contained in the molded body, the alumina in 1-, the silica layer on the surface of the silicon carbide grains, or 1, other impurities or the atmosphere. An interaction occurs with trace amounts of acid contained therein.

Therefore, in order to prevent the decomposition of the compact during firing and to produce a sintered compact with a higher density, V'c is set so that the amount of gas in the atmosphere exceeds the equilibrium vapor pressure of the gas generated by the decomposition of the compact. It has been found that it is preferable to maintain the partial pressure of the gas.

When silicon carbide containing alumina etc. is sintered, it is difficult to investigate what kind of reaction actually occurs and what kind of gas is generated, but various tests have shown that silicon carbide containing alumina etc. It has also been found that it is very preferable to sinter a quality compact in an atmosphere containing aluminum, silicon, and/or carbon to produce a sintered body having a high density and uniform composition, composition, and strength. Ta.

Here, a specific method for creating an atmosphere containing AA as a component will be explained.

In general, it is sufficient to introduce or enclose a gas containing the 1-aluminum component into the firing furnace, and the gas containing aluminum can be introduced as A4, Ago@, A420゜AbO, etc., resulting in a normal inert gas atmosphere. These gases can be used in combination with an inert gas such as nitrogen, argon, or helium.

Alternatively, these gases can be fused into powder, compacted or sintered bodies which are generated at the sintering temperature.
It can also be done automatically by distributing it around the H-1 material molded body, or by coating it with a layer that brings in straw gas.

The structure of the sintered body of the present invention thus obtained is mainly composed of fine equiaxed αSiO crystals, with some columnar or plate-like βEIiO crystals remaining. The glass phase (mainly ATO3) that should remain as the second phase is present at the grain boundaries consisting of the first phase, SiO.
It was observed that the amount of carbon (n) produced from the silicon carbide raw material was very small.

It was found that β was more pronounced than when either one was used alone. Although it is not certain whether the effects of the present invention are brought about by accident, it is possible that the difference between the two sides has an effect.

The present invention thus provides a method which makes it possible to obtain higher strengths in the case of sintering silicon carbide using aluminum and/or aluminum-containing compounds as sintering aids. , the industrial value is enormous.

Next, Example (C) will be further explained.

Actual Cases 1 to 4, Comparative Examples 5 to 6 The Examples and Comparative Examples shown in Table 1 were made using α and β crystalline silicon carbide powder (purity of 98% or more, specific surface area of 10 2/2 or more).
) with the specified angle of I'11 degrees of 95% or more and the average particle size of 1. Aluminum oxide powder (corundum) of um or less was thoroughly mixed in the presence of ethyl alcohol, and this was mixed at 2000 kg/1.
Hydraulic molding was performed using yn2 to form a 20 x 40 x 15 m compact, which was then placed in a carbon container with a lid that had a slightly larger volume than the compact, placed in an argon gas atmosphere, and fired as shown in Table 1. It was obtained by υ sintering according to the conditions. Table 1 shows the density and bending strength of each sintered body.

1.1 Table Examples 7 to 10, Comparative Examples 11 to 12 The same conditions as Examples 1 to 4 and Comparative Examples 5 to 6, except for the firing atmosphere in Table 1, and the conditions shown in Table 2. Table 2 shows the bending strength of the sintered body obtained as an addition.

Table 2 (Note 1) In Tables 1 and 2, sample height 1 → 7.2 →
8゜、、、、 6C Town, 12 (corresponds to Chino (Note 2)
In Table 2, the embedding and coating methods are as follows.

Embed two molded bodies in a mixed powder according to the type and amount shown in the right column of the method. Apply a slurry made by adding ethyl alcohol to the above mixed powder on the inner surface of the carbon container, and after drying, mold it into a powder mixture. Place the body, coating thickness is approximately 051+III+

Claims (1)

[Claims] 1. By weight, 65 to 95% α crystals and 35 to 5% β crystals.
Aluminum and/or
Alternatively, a method for producing a high-strength silicon carbide sintered body, characterized in that the shape is fired in a non-oxidizing atmosphere. 2. The manufacturing method according to claim 1, wherein the mixing ratio is 70 to 85% of α crystal and 60 to 15% of β crystal. 6. The manufacturing method according to claim 1 or 2, wherein the atmosphere is an atmosphere containing an inert gas. 4. The manufacturing method according to any one of claims 1 to 3, wherein the firing temperature is 1900 to 2500°C. 5. The manufacturing method according to any one of claims 1 to 4, in which the body is pressure-coated and baked. 6 The aluminum-containing compound contained in the silicon carbide molded body is alumina, aluminum nitride, aluminum carbide, aluminum silicon carbide (A 114 S 1-04
), aluminum chloride, aluminum phosphide, and one or more selected from aluminum phosphide. 1) The manufacturing method according to any one of claims 1 to 426, wherein the sintered body is fired in an atmosphere containing aluminum as a component.