JPS63392B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a sintered body of silicon carbide, particularly a sintered body of ultrafine polycrystalline particles of silicon carbide produced by a gas phase thermal decomposition reaction of a methylhydrogensilane compound. Silicon carbide has extremely stable properties both chemically and physically, and has excellent oxidation resistance, corrosion resistance, thermal conductivity, and strength, especially at high temperatures, and has a low coefficient of thermal expansion, making it suitable for use in gas turbine blades, It is said to be useful as automobile parts, components for corrosive liquids (gases), fireproof materials, components for high-temperature reactions, and various electronic components. However, this silicon carbide has been put to practical use as a sintered body, and this sintered body is produced using a reaction sintering method in which molten silicon reacts with a molded mixture of silicon carbide and carbon, and a silicon compound is heated at high temperature. Vapor deposition method that thermally decomposes
Furthermore, it is manufactured by adding metals such as aluminum and their oxides, or sintering aids such as carbon and boron to fine silicon carbide powder, and sintering the mixture under normal pressure or pressure. In the case of this reaction sintering method, various shapes can be obtained because the calcined body is molded before reacting with silicon, but since the molded body contains free silicon, high-temperature strength and durability cannot be obtained. The disadvantage is that the alkalinity is poor, and the vapor deposition method has the disadvantage that the strength is inferior because the vapor does not reach the inside of the compact, and the sintered compact obtained by the method using a sintering aid has the disadvantage that If the strength exceeds the melting point of the metal or metal oxide used in the material, the strength will decrease, and if boron and carbon are added, a high-density sintered body can be obtained, but this boron reduces it by 0.15% by weight. % or more, boron is present at the grain boundaries, which has the disadvantage that it cannot be used for semiconductor-related applications that require high purity. The present invention relates to a silicon carbide sintered body that solves these disadvantages, and it has crystallites of 50 Å.
It is an aggregate consisting of the following, which is made by sintering ultrafine polycrystalline silicon carbide particles with a uniform spherical shape with an average particle size of 0.1 to 1μ at 1750 to 2500℃ in an inert atmosphere. This is a characteristic feature. To explain this, the present inventors have conducted various studies on the manufacturing method of silicon carbide sintered bodies, and have found that the main raw material, ultrafine powdered silicon carbide, has a crystallite size of 50 Å.
The present invention was completed by confirming that an ultrafine polycrystallite having an average particle size of 0.1 to 1 μm is sufficient as an aggregate consisting of the following. The ultrafine silicon carbide particles used to obtain _the sintered body of the present invention are said to have the above _- mentioned _{physical properties} .
=1~3, 2b+1≧a, a≧b, 2b+1≧c≧
1. Methylhydrodiene silanes represented by a+c=2b+2) were heated to 750 to 1600 in a reducing atmosphere.
It can be obtained by gas-phase pyrolysis at ℃, and since the raw silane contains silicon-hydrogen bonds but no silicon-chlorine bonds, it is rapidly decomposed at relatively low temperatures. However, hydrogen chloride is not generated during this thermal decomposition,
Therefore, since the silicon carbide powder, which is a thermal decomposition product, does not come into contact with these active gases, ultrafine particles having a substantially spherical and uniform particle size with high surface activity can be obtained. The silicon carbide particles obtained by this method are polycrystalline bodies with crystallites of 50 Å or less, and the average particle size is 0.1 to 1 μm, and since they are ultrafine particles, they can be refined. It has the advantage of not requiring a pulverization process to process the product, and therefore can be obtained as a highly pure product.
The sintered body of the present invention is obtained by molding this ultrafine silicon carbide powder and sintering it under normal pressure or pressure, so it is useful as a member that requires high purity. Ru. This molding may be performed by a method known in the ceramic industry, such as a die press method. This molding can be carried out without using any additives, but if necessary, stearate alone or a lubricant prepared by dissolving stearate in a solvent such as benzene may be used. In addition, in order to make complex molded products such as tubes and crucibles, it is possible to mold them using a rubber press, but in order to obtain more precise molded products, it is necessary to It is preferable to perform mechanical processing such as grinding or slicing. Note that this molding may be performed by a slip cast method, but in this case, a plasticizer such as polyethylene glycol, a low molecular weight cellulose derivative, or paraffin, and a binder such as polyvinyl butyral are added to the silicon carbide powder.
The paste may be dispersed in water and poured into calcined plaster molds, and the moldable paste may be extruded, injection molded or roll formed. Furthermore, the compact obtained in this way is then sintered to form a sintered body, but this sintering can be performed under normal pressure, gas pressure, press pressure, or other pressure. It's okay to get old. However, if the heating temperature is lower than 1750°C, sintering will be insufficient.For the purpose of obtaining high-density products, it is better to set the heating temperature as high as possible;
If the temperature is 2300°C or higher, the strength may decrease due to particle growth, and it is also economically disadvantageous, so it is preferable to set the temperature to 1750 to 2300°C. Furthermore, sintering requires these to be under an inert atmosphere, but this may be done in the presence of argon, nitrogen, or helium gas. In addition, when cutting the molded product described above prior to this sintering step, it may be calcined if necessary, but this temperature is preferably 1500°C or higher; The temperature may be determined depending on the strength required for the machining. On the other hand, the sintered body of the present invention would be expensive if manufactured only from the above-mentioned ultrafine silicon carbide particles, so even if commercially available silicon carbide particles with an average particle size of 5 μm or less were added. This often provides industrial advantages in terms of price. but,
When sintering this type of commercially available silicon carbide, it is necessary to add a sintering aid as described above, for example, 0.15 to 5% by weight of boron and the amount of boron contained in this raw material powder. to remove free oxygen
It is necessary to add 0.1 to 5% by weight of carbon, but in the case of the present invention, the amount of commercially available silicon carbide added to 100 to 50 parts by weight of the above-mentioned ultrafine silicon carbide particles is 50 parts by weight. Even in this case, the amount of boron and carbon that should be added is 0.15% by weight each.
Below, the amount can be set to 0.1% by weight or less, which is advantageous in that the amount added can be reduced along with the amount of commercially available silicon carbide, and the disadvantages caused by the coexistence of boron and carbon can be minimized. is also given. Note that the boron added in this case may be either metallic boron or a boron compound, and the carbon may be either carbon powder or an organic polymer compound that provides carbon through thermal decomposition. The latter is often used for effective dispersion.Also, when metals or metal oxides are used as auxiliaries, a sintered body can be obtained by adding a smaller amount than normally used, so these should be used. The above-mentioned disadvantages due to the use of auxiliary agents are improved. Molding when using this commercially available silicon carbide together,
Sintering may be carried out in the same manner as described above, but the sintering temperature is preferably 1800 to 2500, since the sintering start temperature becomes higher due to differences in surface activity. In summary, the present invention uses silicon carbide in particular in aggregates whose crystallites are 50 Å or less and whose particle size is 0.1 to 0.1.
It is made by using 1μ ultrafine polycrystalline particles and sintering them, but according to this, the density is
Since 2.4 g/cc (75% of theoretical density) or more can be easily obtained, it can be used as gas turbine blades and automobile parts that require strength, but also does not require particular strength. For heat radiation
It can be used for IC substrates, various reaction tubes, etc. Next, examples of the present invention will be given. Examples 1 to 9 A vertical tubular electric furnace equipped with an alumina core tube with an inner diameter of 52 mm and a length of 1000 mm was heated to 1350°C, and 2 volumes of tetramethyldisilane [(CH ₃ ) ₄ Si ₂ H ₂ ] was added thereto. When gas phase pyrolysis was carried out by introducing 300 c.c./min of hydrogen containing 100 c.c./min. The ultrafine particles of silicon carbide shown in the electron microscopy dark field image by β-SiC (111) diffraction corresponding to the bright field image were obtained.
An electron micrograph shows that the crystallite size of this particle is 40 Å.
It is an aggregate with a particle size of 0.1 to 0.3μ,
It had a specific surface area of 37.3 m ² /g. Next, 15 g of the ultrafine silicon carbide particles were placed in a carbon mold for hot press with a diameter of 40 mm without adding any sintering aid, and degassed under reduced pressure.
Next, this system was placed under an argon gas atmosphere, and then heated at 2300°C for 30 minutes under a pressure of 100 kg/cm ² to sinter it, and after cooling, it was taken out and the density of the obtained sintered body was measured. This is 3.00g/cc (93% of theoretical density) and the specific resistance of this is 10 ³ Ωcm
It was hot. Further, an electron micrograph of this sintered body is shown in FIG. 3, and it can be seen that there was no grain growth and the sintered body was cleanly sintered. When the above ultrafine silicon carbide powder (u-SiC) was used and sintered under the conditions shown in Table 1, the results shown in Table 1 were obtained, and these results were was also sintered to a high density. In addition, for comparison, commercially available β-type silicon carbide [manufactured by Ibiden Co., Ltd., specific surface area 16 m ² /g] and α-type silicon carbide [manufactured by Showa Denko KK, specific surface area 11 m ² /g] were compared with the above. Although sintering was carried out under the conditions shown in Table 1, a high-density sintered body could not be obtained in this case. (Note) In Table 1 below, BN...manufactured by Showa Denko Co., Ltd., boron nitride B ₄ C...manufactured by Rare Metallic Co., Ltd., boron carbide B...manufactured by Rare Metallic Co., Ltd., boron C...manufactured by Gunei Kagaku Co., Ltd., phenol resin ( Carbonization yield 55
%) respectively.

[Table] Example 10 The same vertical electric furnace as in Example 1 was heated to 1050℃,
When hydrogen gas containing 10% by volume of tetramethyldisilane was introduced at a rate of 400c.c./min to cause gas phase thermal decomposition, the crystallite size was less than 20Å and the particle size was 0.5~0.
Ultrafine silicon carbide powder with a spherical shape of 0.6μ was obtained.
This had a specific surface area of 14.2 m ² /g. Next, this was heated and sintered at 1900°C for 30 minutes under a pressure of 100 kg/cm ² as in Example 1, and a sintered body with a density of 2.96 (92% of theoretical density) was obtained. Ta. Examples 11 to 15 To 5 g of ultrafine silicon carbide particles obtained in Example 1,
Commercially available β-type silicon carbide [manufactured by IBIDEN Co., Ltd., specific surface area
16m ² /g] 5g, metallic boron [Rare Metallic Co., Ltd.
[manufactured by Gunei Chemical Co., Ltd.] 0.015g, phenolic resin [manufactured by Gunei Chemical Co., Ltd.]
Carbonization yield: 55%] 0.019g and 70g of hexane were added, and these were heated in a polyethylene ball mill for 24 hours.
After mixing for a period of time, the solvent was evaporated off and the mixture was crushed. Next, put this into a mold and make it 40 x 50 x 450 mm.
After being molded into a rod-shaped body and pressurized at 1.5Kg/ ^cm2 using a rubber press, it was heated at 800℃ in a nitrogen gas atmosphere.
When the phenolic resin was carbonized by heating for 1 hour, it had a density of 1.57 g/cc. Next, put this sample into a carbon die,
When heated and sintered at 2000℃ for 1 hour in an argon gas atmosphere, the density was 2.63g/cc (relative to theoretical density 82
%), which has a specific resistance of 10 ⁶ Ωcm
It was hot. In addition, in the above, silicon carbide ultrafine particles (A) and β
When the blending ratio of type silicon carbide (B) is changed, this β type silicon carbide can be changed to α type silicon carbide (C) [Showa Denko K.K.
When ^a sintered body was produced in the same manner as described above, the results shown in Table 2 below were obtained.

[Table] For comparison, in Example 10 above, silicon carbide ultrafine particles were not used, only commercially available β-type silicon carbide was used as silicon carbide, and the results were molded and processed under the same conditions. When heated under pressure, the density of the product obtained in this case was 1.80 g/cc, and it did not become a sintered body. Example 16 A similar treatment was performed except that tetramethyldisilane in Example 1 was replaced with dimethylsilane [(CH ₃ ) ₂ SiH ₂ ], resulting in an aggregate of crystallites of 40 Å or less and a particle size of 0.2
30g of silicon carbide ultrafine particles with a particle size of ~0.8μ and a specific surface area of 43.9m ² /g were added to methylcellulose MC-400.
[Manufactured by our company, trade name] 1 g and 1 g of glycerin were dispersed in a solution of 6 g of water, mixed with three rolls, and taken out as a sheet. Next, this sheet was cut into a shape of 50 x 2 x 50 mm, calcined in nitrogen gas at 1200°C for 1 hour, and then pressureless sintered at 2300°C for 1 hour in this nitrogen gas atmosphere. A sheet with a density of 2.65 g/cc (83% of theoretical density) was obtained.

[Brief explanation of the drawing]

Figures 1 and 2 show electron micrographs of ultrafine silicon carbide particles, which are the raw material for the sintered body of the present invention, with Figure 1 being a bright field image and Figure 2 being a β
- This is a dark field image obtained by SiC (111) diffraction, and FIG. 3 shows an electron micrograph image of the sintered body of the present invention.

Claims (1)

[Scope of Claims] 1. Ultrafine polycrystalline particles of silicon carbide having a spherical shape with an aggregate of crystallites of 50 Å or less and an average particle size of 0.1 to 1 μ are grown in an inert atmosphere at a temperature of 1750 Å or less.
A silicon carbide sintered body characterized by being fired at a temperature of 2500℃. 2 Silicon carbide ultrafine polycrystalline particles have the general formula (CH ₃ ) _a Si _b H _c (where b=1 to 3, 2b+1≧a,
a≧b, 2b+1≧c≧1, a+c=2b+2) from 750 to
The silicon carbide sintered body according to claim 1, which is obtained by vapor phase pyrolysis at a temperature of 1600°C. 3 To 100 to 50 parts by weight of ultrafine polycrystalline particles of silicon carbide, which are aggregates consisting of crystallites of 50 Å or less and have a spherical shape with an average particle size of 0.1 to 1 μ, add (a) an average particle size of 5 μ or less; 0.5 to 50 parts by weight of silicon carbide fine powder,
(b) less than 0.15 parts by weight of boron or 0.15 as the amount of boron
A boron compound in an amount equivalent to 0.1 part by weight or less, (c) 0.1 part by weight or less of carbon, or a carbon compound in an amount equivalent to 0.1 part by weight or less as carbon content is added in an inert atmosphere at 1750 to 2500°C. A silicon carbide sintered body characterized by being formed by firing at a high temperature.