JPS61106459A - 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] [Industrial application field] The present invention relates to a high-density silicon carbide sintered body.

[Prior art] Silicon carbide has higher hardness than before, has excellent wear resistance, has a small coefficient of thermal expansion, has a high decomposition temperature, has high oxidation resistance, is chemically stable, and generally has considerable electrical conductivity. It is known as a useful ceramic material with In addition to the above-mentioned properties, this high-density sintered body of silicon carbide has high strength up to high temperatures and excellent thermal shock resistance, making it promising as a high-temperature structural material, and attempts have been 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 industrially most advantageous method is considered to be the pressureless sintering method. According to the pressureless sintering method, certain temporary materials of ceramic materials can be formed by commonly used methods such as press method, slurry casting method, extrusion molding method, injection molding method, etc., and it is possible to mold products with complex shapes and large dimensions. Thick-walled products can be manufactured 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.

However, silicon carbide is a compound with strong covalent bonding properties, so it is difficult to sinter it alone, and it is difficult to sinter it by itself, even in the case of normal pressure sintering method and hot press sintering method. The addition of some sintering aid is necessary to obtain the desired shape.

As the sintering aid, boron or a boron compound, aluminum or an aluminum compound, etc. are known. In the case of pressureless sintering, carbon is further added to these.

[Problems to be Solved by the Invention] 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 by a normal method. - Particularly during sintering, the silicon carbide molded body containing the sintering aid 4 is easily decomposed, which causes the problem that the molded body is not sufficiently densified. This problem is true when making small sample moldings, 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 invention provides a high-density sintered body that prevents decomposition of a silicon carbide molded body containing aluminum and/or an aluminum compound from being suppressed from being densified when the molded body is sintered under normal pressure. It is something to do.

The present invention relates to the use of aluminum or aluminum compounds as sintering aids. As the aluminum compound, alumina, aluminum nitride, aluminum carbide, aluminum silicon carbide, aluminum boride, aluminum phosphide, etc. can be used. These are classified into two categories: oxygen-free aluminum, aluminum nitride, aluminum carbide, aluminum silicon carbide, aluminum boride, thaliminium phosphide and oxygen-free alumina. In either case, 0.5 to 5 weights of carbon is usually added, and in the case of the former system, which does not contain oxygen, carbon may be added.

In addition, regarding the latter case where alumina is used,
Although a method for obtaining a high-density sintered body by pressureless sintering has not been established at all, the present invention provides a high-density sintered body in this case as well.

Aluminum or an aluminum compound is added to silicon carbide as a sintering aid, but in a normal method, this aluminum or aluminum compound is evaporated,
It is easily decomposed and removed from the molded body, and therefore densification does not proceed sufficiently, making it difficult to obtain a high-density sintered body.

[Means for solving the problem] Various attempts were made to solve this problem, and it was found that a silicon carbide molded body containing aluminum or an aluminum compound was placed in an atmosphere containing aluminum as a component,
That is, it has been found that a higher density sintered body can be produced by firing four times in an atmosphere containing one or more of aluminum and aluminum compounds.

According to this method, aluminum is removed from the compact,
Alternatively, the amount of aluminum compound can be reduced, and a high-density sintered body with a stable composition and structure can be obtained.

On the other hand, silicon carbide itself also begins to decompose at the sintering temperature of the silicon carbide compact. That is, silicon carbide does not melt under atmospheric pressure, begins to sublimate at temperatures above 2000° C., and decomposes into carbon and silicon-rich vapor at even higher temperatures. The sintering temperature of the molded body required to obtain a high-density sintered body of silicon carbide is generally 1800 to 2300°C, and in this high temperature range silicon carbide undergoes sublimation, decomposition, and gases such as Si and Si20. Occur. Therefore, the silicon carbide molded body is made of Si.

By firing in an atmosphere containing gas such as 5i2C, sublimation and decomposition of silicon carbide in the molded body can be suppressed. However, in reality, the decomposition of silicon carbide is not simple; that is, aluminum or aluminum compounds are used as sintering aids in the compact, or silica on the surface of silicon carbide particles is used.
Alternatively, mutual reactions occur with other impurities or trace amounts of oxygen contained in the atmosphere.

Therefore, in order to prevent the decomposition of the compact during firing and to produce a sintered compact with higher density, it is necessary to maintain the partial pressure of the gases in the atmosphere above the equilibrium vapor pressure of the gases generated by the decomposition of the compact. It is preferable.

When sintering a silicon carbide molded body containing aluminum or an aluminum compound, it is difficult to investigate what kind of reactions actually occur and what kind of gases are generated, but various tests have shown that aluminum and/or It is more preferable to sinter a silicon carbide molded body containing an aluminum compound in an atmosphere containing aluminum, silicon and/or carbon in order to produce a sintered body having a high density and a uniform composition and structure. Understood. A case where alumina is used as an aluminum compound will be explained. The decomposition of the compact during sintering is thought to occur mainly through the following reaction: SiG + Al2 (h → Al2O + SiO◆CO) In this case, Al2O in the atmosphere during sintering.

If the partial pressure of the Sin and GO gases is made equal to or higher than the equilibrium vapor pressure of these gases generated by decomposition of the molded body, decomposition of the molded body is suppressed and a higher density sintered body is produced.

Next, the implementation method will be explained.

An atmosphere containing aluminum as a component or an atmosphere containing aluminum and silicon and/or carbon as components can be achieved by introducing or enclosing these gases into the firing furnace. Gases containing aluminum are AI, AICh, ^1
20. As AIO etc., silicon-containing gas is Si, 5i
Carbon-containing gases can be introduced as hydrocarbons, GO, etc. as CIa, EiHs, SiO, etc. The atmosphere is usually a mixture of these gases with an inert gas such as nitrogen, argon, helium, etc. Another effective method is to arrange a silicon carbide material such as powder, molded body, or sintered body around one side of the main mold which generates these gases at the sintering temperature.

That is, (1) the atmosphere is formed from one or more of aluminum powder or aluminum compound powder arranged around a silicon carbide molded body, or a molded body made of these powders; (2) the atmosphere is formed from a silicon carbide molded body; One or more of aluminum powder, aluminum compound powder and one or more of silicon powder, silicon compound powder, carbon powder, carbon compound powder disposed around the body.

Or one formed from an unfired compact made of these powders (3) An atmosphere obtained by sintering a silicon carbide compact containing aluminum and/or an aluminum compound arranged around the silicon carbide compact. It is also good to be formed from a sintered body.

Methods for placing these powders around a silicon carbide molded body include embedding the molded body in the powder, and molding the powder into a 1k-6 sided carbon or silicon carbide sheath material. There are ways to place the body. The method of embedding in the powder is preferable because it effectively suppresses the decomposition of the molded body, but it is not suitable for molded bodies of large size and complex shapes. On the other hand, the method of applying the powder to the pod material is suitable for manufacturing various shapes,
Moreover, the surface condition of the sintered body becomes good, and a high-density sintered body equivalent to that obtained when the sintered body is embedded in the powder can be obtained. 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.

A binder such as polyvinyl alcohol can also be mixed into the slurry at this time.

In the powder embedding and coating methods, various powders such as those mentioned above can be used, but preferred is a powder obtained by mixing aluminum or aluminum compound powder with silicon carbide powder and/or carbon powder. In this case, it is preferable to use the same aluminum or aluminum compound powder as that used as the sintering aid, but it is not necessarily limited to the same powder. For example, if alumina is used as the sintering aid, In addition to alumina, aluminum hydroxide, aluminum nitride,
Aluminum carbide or the like may be used, and in the case of powder coating, it is also convenient to use a polymeric aromatic compound with a large amount of residual carbon, such as phenol resin or polymethylphenylene, instead of carbon powder.

When blending silicon carbide powder and/or carbon powder with aluminum or aluminum compound powder, the preferred blending amount of aluminum or aluminum compound is 2 to 40% by weight in terms of aluminum. If it is less than 2%, the effect of suppressing the decomposition of the molded body is small, and a sufficiently high-density sintered body cannot be obtained, and if it is more than 40%, the decomposition rate of the blended powder increases, resulting in a large weight loss even when the density is high. Moreover, if aluminum, alumina, etc. are used and buried, impregnation of these into the molded body as a liquid phase occurs, which is undesirable.

It is also preferable to use a sintered body instead of a powder or an unfired compact.

As the sintered body, it is convenient to use a silicon carbide sintered body containing aluminum or an aluminum compound. In this case, it is preferable to surround the molded body with a sintered body of the same quality as the molded body to be fired, but it may be of a different type.When using a sintered body, powder or unfired molded Compared to when using a molded body, the surface area relative to the weight is smaller, so the decomposition rate is lower and the atmosphere around the molded body can be effectively maintained in a good condition for a long time. Suitable.

Although the case using the normal pressure firing method has been described above, the present invention can of course also be applied to the case of the hot press method.

[Example] Commercially available silicon carbide powder with a purity of 88% and a particle size of 1 micron or less was used. This silicon carbide powder (brittle jig additive was mixed in the proportions shown in Table 1), placed in a plastic pot, thoroughly mixed with a plastic pole in the presence of acetone, and then dried and machined. Molded by press at 300Kg/cm2 20X 20X
The 4 mm compact was then fired in a resistance heating furnace at 2000° C. for 1 hour under various atmospheric conditions shown in Table 1.

The above results show that a silicon carbide sintered body with a higher density can be obtained by the method of the present invention than by the conventional method shown in the comparative example.

Book 1 Comparative example Book 2 The sintering temperature is the relative density to the theoretical density of the obtained sintered body Wood 3 Al2O3 is impregnated into the molded body and it is defective Book 4 No atmospheric conditions in Table 1 of the carbon equivalent amount: No container for the molded body Place in a furnace and bury: Embed the molded body in a mixed (or single) powder according to the type and amount in the right column of the method. Add ethyl alcohol to the above mixed (or single) powder on the inner surface of a two-carbon container. After drying, place the molded body in the slurry (approximately 0.5 ms + molded body 2).

Claims (1)

[Claims] 1. A high-density silicon carbide sintered body, which is obtained by firing a silicon carbide molded body containing aluminum and/or an aluminum compound in an atmosphere containing aluminum as a component. 2. The sintered body according to claim 1, wherein the atmosphere contains an inert gas. 3. Powder containing one or more of aluminum powder and aluminum compound powder arranged in an atmosphere around a silicon carbide compact, or a compact containing these powders, or obtained by sintering the compact. A sintered body according to claim 1 or 2, which is formed from a sintered body. 4. Aluminum compound powder is alumina, aluminum nitride, aluminum carbide, aluminum silicon carbide (Al
The sintered body according to claim 3, which is one or more selected from _4SiC_4), aluminum boride, and aluminum phosphide. 5. A powder containing one or more of aluminum powder and aluminum compound powder, a molded body containing these powders, or a sintered body obtained by sintering the molded body has a powder content of 2 to 40% in terms of aluminum. Claim 3 containing % by weight of aluminum and/or aluminum compounds
Term sintered body. 6. Claims in which the aluminum compound contained in the silicon carbide molded body is one or more selected from alumina, aluminum nitride, aluminum carbide, aluminum silicon carbide (A1_4SiC_4), aluminum boride, and aluminum phosphide. A sintered body according to any one of Items 1 to 5. 7. The sintered body according to claim 1, wherein the atmosphere is an atmosphere containing aluminum, silicon and/or carbon as components. 8. The sintered body according to claim 7, wherein the atmosphere contains an inert gas. 9. Powder containing one or more of aluminum powder, aluminum compound powder, silicon powder, silicon compound powder, carbon powder, in which the atmosphere is arranged around the silicon carbide compact;
Claim 7, which is formed from one or more powders selected from carbon compound powders, a molded body containing these powders, or a sintered body obtained by sintering the molded body. or the sintered body of item 8. 10. Aluminum compound powder is alumina, aluminum nitride, aluminum carbide, aluminum silicon carbide (A
The sintered body according to claim 9, which is one or more selected from l_4SiC_4), aluminum boride, and aluminum phosphide. 11. The sintered body according to claim 9, wherein the silicon compound powder is one or more selected from silicon carbide, silica, and silicon monoxide. 12. The carbon compound is one or two selected from polymeric aromatic compounds such as phenol resin and polymethylphenylene.
The sintered body according to claim 9, which is more than one. 13. Aluminum powder, aluminum compound powder 1
A powder containing one or more of these powders, a molded body containing these powders, or a sintered body obtained by sintering the molded body,
The sintered body according to claim 9, which contains 2 to 40% by weight of aluminum and/or an aluminum compound in terms of aluminum. 14. Claims in which the aluminum compound contained in the silicon carbide molded body is one or more selected from alumina, aluminum nitride, aluminum carbide, aluminum silicon carbide (Al_4SiC_4), aluminum boride, and aluminum phosphide. The sintered body according to any one of items 7 to 13.