JPS6034515B2 - Manufacturing method of silicon carbide ceramic sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a silicon carbide sintered body, particularly a dense and high-strength silicon carbide bran body obtained by so-called normal firing in which the compact is bonded without pressure after molding. .

Silicon carbide is useful because it has higher hardness than before, has excellent wear resistance, has a coefficient of thermal expansion of 4.0, has a high decomposition temperature, has high oxidation resistance, is chemically stable, and generally has considerable electrical conductivity. It is known as a ceramic material.

In addition to the above-mentioned properties, this high-density composite 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 have been made to apply it to a variety of applications including gas turbines. It is being Silicon carbide is a compound with strong covalent bonds, so it is difficult to sinter it alone, and it is difficult to sinter it to a high density.In order to obtain a high density brick, it is necessary to add some kind of sintering aid. is necessary. In the case of the hot press method, boron, B4C, aluminum, AIN, etc. are known as competitive additives. Furthermore, in the case of pressureless sintering, it is known that carbon is further added to these materials. However, the conventional brazed products are not sufficient in terms of performance or manufacturing method, as will be described later. Therefore, the present inventor conducted repeated experiments with the aim of finding silicon carbide ant aggregates with superior properties than conventional ones even when using a normal firing method instead of the hot press method, and as a result, the present invention was achieved. In the present invention, aluminum oxide is contained in an amount of 0.5 to 35% by weight, and the balance has a specific surface area of 5〆/g.
The gist of the present invention is to provide a method for producing a silicon carbide-based ceramic briquette having a specific strength by forming the above-mentioned mixture substantially consisting of silicon carbide and then sintering it without applying pressure.

Incidentally, although it has been known in the past to use aluminum oxide as an auxiliary agent for silicon carbide, the present invention is only completely different in performance and method as described below.

That is, one of the subordinate products belongs to the so-called refractory brick category shown in JP-A-47-442Y and JP-A-49-129703, and is composed of coarse aggregate of silicon carbide. Mix and mold aluminum oxide to 1200~150
It is obtained by firing at a temperature of about 1,000 ℃, and has low strength because a large amount of aluminum oxide or silicon oxide layer exists around silicon carbide particles.

On the other hand, an example of using aluminum oxide as a solidifying agent for hot pressing in high-density silicon carbide ceramics was previously studied by AIlie et al. Am. CeramCoc, 39(11)386~
389, 1956.

Regarding this truth, at the beginning of the development, the present inventor thought that the effect of aluminum oxide on silicon carbide is the same in the case of hot pressing and the case of normal sintering without using pressure. In general, when a mixture and a molded body having the same composition are hot-pressed and normally sintered at the same temperature, the resultant body produced by hot-pressing is more fibrous than the sintered body produced by normal sintering due to the effect of pressure application. It was thought that the density would increase and the strength would also increase. However, as a result of various studies carried out by the present inventors, it has been found that a sintered body having higher strength can be obtained by the normal sintering method than by the hot pressing method. As will be described later in the Examples, the difference in high temperature strength was particularly large. It is thought that the sintering mechanism is different between the ordinary brazing method and the hot pressing method of the present invention, and the microstructure of the obtained sintered body is also different. In the case of the hot press method, pressure is applied in the presence of a liquid phase mainly composed of aluminum oxide, and the sintered body is easily sufficiently densified. It has a microstructure consisting of equiaxed grains. Therefore, at high temperatures, the aluminum oxide at the silicon carbide grain boundaries softens, resulting in a significant decrease in strength. On the other hand, in the case of the conventional sintered silk method of the present invention, the sintering mechanism has not yet been fully elucidated;
During crystallization, favorable grain growth of silicon carbide particles occurs in the presence of a sufficient amount of liquid phase mainly composed of aluminum oxide, and at the same time, components mainly composed of aluminum oxide decompose and evaporate, resulting in oxidation that contributed to densification. It is thought that a strong microstructure in which columnar or plate-like particles are entangled is formed as aluminum desorbs from the compact. Further, according to electron microscopic observation, although aluminum oxide grains were sometimes observed between silicon carbide grains in this sintered body, no second phase such as aluminum oxide was found at the silicon carbide grain boundaries.

From the above, it was found that the silicon carbide ceramic obtained by the present invention is a material with characteristics different from conventional silicon carbide aluminum monoxide refractories and aluminum oxide-added hot-pressed silicon carbide ceramics.

The present invention will be specifically explained below.

First, as a silicon carbide (SIC) raw material, either type Q or type B crystal type can be used, but type 6 is preferable.

A purity of 98% or more is preferred, but purity of 90 to 98% can also be used effectively. In the case of extremely fine particles, it is more appropriate to express the particle size in terms of specific surface area than average particle diameter, and the bending strength at room temperature and 1400°C, which is the object of the present invention, is at least 25 k9/m or more, preferably 30 k9/m or more. In order to obtain an interlocking body with a density of 90% or more, it is necessary to have a specific surface area of 5〆/ta or more, and preferably, to obtain a bending strength of 35k9/m or more at room temperature and 1400℃, oxidation is necessary. If aluminum is 6 to 35%, it is 10〆/ta or more,
40 when aluminum oxide is about 0.5 to 5% by weight
In order to obtain a strength of at least 15 kg/h, it is desirable that the specific surface area is 15/t or more. Next, aluminum oxide (mountain 2)
Corundum is conveniently used for 03), but other crystal forms such as gamma form may also be used.

Aluminum hydroxide, aluminum sulfate, etc., which become aluminum oxide when heated, can also be used, and in the present invention, aluminum oxide includes compounds that produce these aluminum oxides. The purity is preferably 98% or more and low soda content, and the particle size is preferably 1 mm or less, preferably 0.2 mm or less. In the present invention, the ratio of aluminum oxide to silicon carbide is A
It is 0.5 to 35% by weight as I203. If this is less than 0.5%, densification will not progress sufficiently during sintering, and 90%
This is because it is not possible to obtain a high density sintered body with a density higher than %.
On the other hand, if it exceeds 35%, it will become dense even if sintered at a low temperature of 190,000 or less, but the strength will be low;
This is because the amount of decomposition increases when the material is brazed with 0.00%, resulting in porosity. Furthermore, in these ranges, especially when aluminum oxide is 6 to 35%, in combination with silicon carbide with a specific surface area of 10〆/ta or more and a purity of 98% or more, the density is 90% or more; at room temperature and 140,000 ml. The bending strength of
It becomes possible to easily obtain more than 5k9/masu,
When aluminum oxide is 0.5 to 5%, the specific surface area is 1
5〆/ta or more: In combination with silicon carbide with a purity of 98% or more, it became possible to easily obtain a product with a density of 90% or more and a bending strength of 40 kg/ta or more at room temperature and 1400 qo.

In the present invention, it is desirable to prepare a mixture consisting essentially of silicon carbide other than aluminum oxide in terms of raw materials, and one feature is that it is sufficient to obtain the desired object.Of course, for example, There is no problem even if small amounts of other components that are unavoidably included as impurities in the silicon carbide raw material or mixed in during the pulverization process are included, and as will be described later, some components such as silicon oxide may contain relatively large amounts. One advantage is that there is no problem with this.

As the molding method, all methods commonly used for molding ceramics can be used. That is, press molding, molding, injection molding, extrusion molding, etc. are suitable. The firing is
It is necessary to carry out the process at 1900 to 230000 in a non-oxidizing atmosphere without pressure. Nitrogen as a non-oxidizing atmosphere,
Argon, helium, carbon monoxide, hydrogen, etc. can be used, but among them, argon and helium are convenient and preferred. The temperature is more preferably 1950 to 2100 oo. This is because if the temperature is lower than 190,000, densification will not proceed sufficiently and a high-density sintered body cannot be obtained, and if the temperature is higher than 230,000, the molded body will decompose too much and become porous, which is not preferable. Incidentally, the time required is usually 1 to 24 hours, and more preferably 2 to 1 hour. This is because if the time is too short, the material will not be densified, and even if it is densified, sufficient strength will not be produced, and if the time is too long, it will decompose too much and become porous, which is often undesirable. Here, the features and advantages of the present invention will be further explained as follows. 1 Easily achieves high density through normal firing without applying pressure.
Silicon carbide ceramics having high strength can be obtained.

For example, additives such as Yama, NN, B, and B4C require hot pressing, making it impossible to produce products with complex shapes or large dimensions.Also, AI easily oxidizes and is difficult to use, and reacts and foams when it comes in contact with water. , Fine powder is dangerous to handle, etc.B.
B4C, Yama-N, etc. each have their own problems, such as being expensive, difficult to obtain fine particles, and difficult to crush.

2. Products with higher strength than conventional sintered products can be easily obtained.

For example, additives such as B+C, B4C1C, AI1C, and AIN1C can usually be sintered, but C usually uses high-molecular aromatic compounds such as polymethylphenylene and phenolic resin, so it must be handled carefully. Mixing with B-C requires sufficient time, and the strength is particularly low in the B-C additive system, at around 40-50k9/masu at room temperature, and when these additives are used, The raw material SIC powder has a specific surface area of 15〆/ta or more, which is very fine, and Sio2
There are also problems such as the need to use extremely small amounts of ingredients that are acceptable in the present invention.

3 Aluminum oxide is a very stable material, and it does not react with water, so it can be freely used in manufacturing processes that involve contact with water, and it can be used in wet mixing, pulverization, and mud-mixing using water as a medium, and the atmosphere in which it is handled can be controlled. You also need to be careful.

4 Even if the purity of the raw material silicon carbide powder is somewhat low (higher is better, even 98% or less) or particle size is somewhat coarse (higher is better, even if the specific surface area is 15% or less), the oxidation property and performance will be improved. It is not necessary to remove the silicon oxide film on the surface of the silicon carbide powder particles, and there is no problem even if silicon oxide is added.

As described above, the present invention is industrially extremely advantageous, and this will be further understood from the Examples shown below.

(Example) Examples 1 to 6 shown in Table 1 are silicon carbide powder and purity 95.
Aluminum oxide powder (corundum) having an average particle diameter of 1 mound or less by weight% or more was mixed and this was twill pressed at 2000k9/uniform to form a 20 x 40 x 15 skin molded body, and this molded body was passed through argon gas, It was obtained by agglomerating under the firing conditions shown in Table 1.

Moreover, in Comparative Examples 7 and 8, 2.
It was obtained by hot pressing at a pressure of 00k9/ground. Table 1 shows the density and bending strength of each Akatsuki compact. Table 1 *7 and 8 are comparative examples

Claims (1)

[Scope of Claims] 1 A mixture of 0.5 to 35% by weight of aluminum oxide and the remainder consisting essentially of silicon carbide with a specific surface area of 5 m^2/g or more is molded and then sintered without applying pressure at room temperature or 1400
A method for producing a high-density and high-strength silicon carbide ceramic sintered body having a bending strength of 25 kg/mm^2 or more at °C. 2. The mixture consists of 6 to 35% by weight of aluminum oxide and the balance is silicon carbide with a specific surface area of 10 m^2/g or more and a purity of 98% or more, and the sintered body has a density of 90% or more and can be bent at room temperature and 1400 ° C. A method for producing a silicon carbide ceramic sintered body according to claim 1, which has a strength of 35 kg/mm^2 or more. 3. The mixture consists of 0.5 to 5% by weight of aluminum oxide and the balance is silicon carbide with a specific surface area of 15 m^2/g or more and a purity of 98% or more, and the sintered body has a density of 90% or more and is sintered at room temperature and 1400°C. The method for producing a sintered silicon carbide ceramic body according to claim 1, which has a bending strength of 40 kg/mm^2 or more.