JPH0329743B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing 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, and has a high decomposition temperature.
It is known as a useful ceramic material that has high oxidation resistance, is chemically stable, and generally has considerable electrical conductivity. 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. The pressureless sintering method can be molded using methods commonly used to mold ceramic materials, such as the press method, slurry casting method, extrusion molding method, and injection molding method. Thick 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, since silicon carbide is a compound with strong covalent bonding properties, it is difficult to sinter it alone, even in the case of pressureless sintering method and hot press sintering method, and it is difficult to sinter it alone. In order to obtain this, it is necessary to add some sintering aid. 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 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 by a normal method. 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 sintering small compacts, but it becomes a particularly big problem when trying to manufacture complex-shaped products, large-sized products, and thick-walled products as homogeneous, high-density products with good productivity. Become. In the present invention, when a silicon carbide molded body containing one or more selected from aluminum aluminum nitride, aluminum carbide, aluminum silicon carbide (Al ₄ SiC ₄ ), and aluminum boride is sintered under pressure, the molded body is The present invention provides a method for producing a high-density sintered body that prevents decomposition and densification. Aluminum, aluminum nitride, aluminum carbide, aluminum silicon carbide, aluminum boride used as sintering aids usually 0.5 to 5% by weight
and carbon may be added if it does not contain carbon. These aluminum or aluminum compounds are added to silicon carbide as a sintering aid, but in the normal method, this aluminum or aluminum compound easily evaporates and decomposes during sintering and is easily removed from the compact. development has not progressed sufficiently,
It is 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 the silicon carbide formed body containing aluminum or an aluminum compound was placed in an atmosphere containing aluminum as a component, that is, aluminum,
It has been found that a higher density sintered body can be obtained by firing in an atmosphere containing one or more selected from Al ₂ O and AlO. According to this method, the amount of aluminum or aluminum compound removed from the compact is reduced, and a high-density sintered compact 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. In other words, silicon carbide does not melt under atmospheric pressure, begins to sublimate at temperatures above 2000°C, and decomposes into carbon and silicon 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 1900 to 2300℃, and in this high temperature range silicon carbide sublimates, decomposes, and forms other substances such as Si and Si ₂ C. Generates gas. Therefore, by firing the silicon carbide molded body in an atmosphere containing a gas such as Si or Si ₂ 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 between silicon carbide and aluminum or an aluminum compound as a sintering aid contained in the compact, a silica layer or other impurities on the surface of silicon carbide particles, or a trace amount of oxygen contained in the atmosphere. Therefore, the decomposition of the molded body during firing is prevented,
In order to produce a sintered body with higher density, it is preferable to maintain the partial pressure of the gases in the atmosphere above the equilibrium vapor pressure of the gases generated by decomposition of the compact. 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 A silicon carbide molded body containing an aluminum compound is mixed with Al, Al ₂ O, AlO and silicon and/or
Alternatively, it has been found that firing in an atmosphere containing carbon is more preferable in producing a sintered body having a high density and a uniform composition and structure. When alumina is present as an aluminum compound, it is thought that the following reaction mainly occurs during decomposition of the compact during sintering. SiC + Al ₂ O ₃ → Al ₂ O + SiO + CO Therefore, in this case, Al ₂ O in the atmosphere during sintering,
If the partial pressure of SiO and CO gases is made equal to or higher than the equilibrium vapor pressure of these gases generated by decomposition of the compact, decomposition of the compact will be suppressed and a sintered compact with higher density will be obtained. It is thought that a similar phenomenon occurs when an aluminum compound other than alumina or aluminum is used. Next, the implementation method will be explained. An atmosphere containing Al, Al ₂ O, and AlO as components, or an atmosphere containing Al, Al ₂ O, AlO, and silicon and/or carbon as components can be achieved by introducing or sealing these gases into the firing furnace. Gases containing aluminum can be introduced as Al, AlCl ₃ , Al ₂ O, AlO, etc., gases containing silicon can be introduced as Si, SiCl ₄ , SiH ₄ , SiO, etc., and gases containing carbon can be introduced as hydrocarbons, CO, etc. can. The atmosphere is usually a mixture of an inert gas such as nitrogen, argon, or helium. Another effective method is to arrange powder, compacts, or sintered compacts that generate these gases at the sintering temperature around the silicon carbide compact. That is, (1) the atmosphere is formed from one or more of aluminum powder and aluminum compound powder arranged around a silicon carbide compact, or a compact made of these powders; (2) the atmosphere is a silicon carbide compact; Formed from one or more of aluminum powder, aluminum compound powder and one or more of silicon powder, silicon compound powder, carbon powder, carbon compound powder arranged around the compact, or an unfired compact consisting of these powders. (3) A sintered body obtained by sintering a silicon carbide molded body containing aluminum and/or an aluminum compound in an atmosphere arranged around the silicon carbide molded body is preferable. There are two methods for placing these powders around a silicon carbide compact: burying the compact in the powder, and placing the compact in a carbon or silicon carbide pod whose inner surface is coated with the powder. One possible method is to place the The method of embedding in the powder is preferable because it effectively suppresses decomposition of the compact. However, it is unsuitable for molded objects of large dimensions and complex shapes. On the other hand, the method of applying the powder to the pod material is suitable for manufacturing sintered bodies of various shapes, and also provides a good surface condition of the sintered body, resulting in high-density sintering equivalent to the case of embedding the powder in the powder. You can get a body. As a method of applying the powder, the powder may be mixed with an organic solvent such as alcohol or acetone, or water to form a slurry, which may be 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, when alumina is used as a sintering aid, in addition to alumina, aluminum hydroxide, aluminum nitride, aluminum carbide, etc. may also be used. Furthermore, in the case of powder coating, it is convenient to use a high-molecular aromatic compound with a large amount of residual carbon, such as phenolic 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 decomposition of the molded body is small, and a sintered body with a sufficiently high density cannot be obtained. 40% again
The above is undesirable because the decomposition rate of the blended powder increases, and even if the powder has a high density, the weight of the powder decreases greatly and the inside of the furnace gets dirty. Furthermore, if aluminum, alumina, or the like is used for embedding, a phenomenon such as impregnation of these materials 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 disposed around it, 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 a different type of sintered body may be used. When using a sintered body, the surface area relative to the weight is smaller than when using powder or unfired compacts, so the rate of decomposition is lower and it is effective in keeping the atmosphere around the compact for a long time in a good condition. Suitable when long-term firing is required. 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 99% and a particle size of 1
A material of micron or smaller was used. A sintering aid is blended into this silicon carbide powder in the proportions shown in Table 1,
The mixture was placed in a plastic pot and thoroughly mixed using a plastic bowl in the presence of acetone. This is then dried and mechanically pressed to 300
Kg/cm ² to obtain a 20×20×4 mm compact. Next, this was 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 in Table 1. Note that in Table 1, Nos. 12 to 20 are reference examples. As can be seen from this reference example, the manufacturing method of the present invention is also effective for manufacturing a sintered body by firing a silicon carbide molded body containing alumina as a sintering aid. A sintered body obtained by firing a silicon carbide molded body containing alumina as a sintering aid can be easily made into a high-density and high-strength sintered body by the manufacturing method of the present invention, but it is generally heated at 1400°C. At higher temperatures, the strength tends to decrease as the temperature rises. On the other hand, sintered silicon carbide compacts that do not contain alumina or contain aluminum compounds other than alumina have a characteristic that there is little tendency for strength to decrease at temperatures above 1400°C.

【table】

【table】

[Table] No atmospheric conditions in Table 1: The molded body is placed in a furnace without a container Burial: The molded body is buried in a mixed (or single) powder of the type and amount in the right column of the method Coating: Carbon Mix the above (or use it alone) on the inside of the container
Apply a slurry made by adding ethyl alcohol to the powder, and after drying, place the molded body in this, coating thickness is approximately 0.5 mm. Molded body: Unfired molded body made of the above mixed powder. Place the molded body in a container. Sintered body: A molded body is placed in a sintered body container made of the above mixed powder.

Claims (1)

[Claims] 1 Aluminum, aluminum nitride, aluminum carbide, aluminum silicon carbide (Al ₄ SiC ₄ ),
A silicon carbide molded body containing one or more selected from aluminum boride is fired in an atmosphere containing one or more selected from Al, Al ₂ O, and AlO. A method for producing a high-density silicon carbide sintered body. 2. The manufacturing method according to claim 1, wherein the atmosphere contains an inert gas. 3. The atmosphere is one of aluminum powder and aluminum compound powder arranged around the silicon carbide molded body.
The manufacturing method according to claim 1 or 2, which is formed from 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. Method. 4. The production according to claim 3, wherein the aluminum compound powder is one or more selected from alumina, aluminum nitride, aluminum carbide, aluminum silicon carbide (A1 ₄ SiC ₄ ), aluminum boride, and aluminum phosphide. Method. 5 Powder containing one or more of aluminum powder and aluminum compound powder, or a molded body containing these powders, or a sintered body obtained by sintering the molded body, has a particle size of 2 to 40% in terms of aluminum.
3. The method according to claim 3, comprising % by weight of aluminum and/or aluminum compounds. 6. Claim 1, wherein the atmosphere contains one or more selected from Al, Al ₂ O, and AlO, and contains silicon and/or carbon as a component.
Manufacturing method of section. 7 The atmosphere is one of aluminum powder and aluminum compound powder arranged around the silicon carbide molded body.
one or more powders selected from silicon powder, silicon compound powder, carbon powder, carbon compound powder, a molded body containing these powders, or a molded body obtained by sintering the molded body. The manufacturing method according to claim 6, which is formed from the obtained sintered body. 8. The production according to claim 7, wherein the aluminum compound powder is one or more selected from alumina, aluminum nitride, aluminum carbide, aluminum silicon carbide (A1 ₄ SiC ₄ ), aluminum boride, and aluminum phosphide. Method. 9. The manufacturing method according to claim 7, wherein the silicon compound powder is one or more selected from silicon carbide, silica, and silicon monoxide. 10. The manufacturing method according to claim 7, wherein the carbon compound is one or more selected from polymeric aromatic compounds such as phenol resin and polymethylphenylene. 11 Powder containing one or more of aluminum powder and aluminum compound powder, or a molded body containing these powders, or a sintered body obtained by sintering the molded body, has an aluminum content of 2 to
The manufacturing method according to claim 7, comprising 40% by weight of aluminum and/or an aluminum compound.