JPH0534307B2 - - Google Patents

Description

[Detailed description of the invention]

(Technical Field) The present invention relates to a novel method for producing a silicon carbide sintered body having an excellent microstructure. (Background Art) Ceramic sintered bodies obtained by sintering fine powder of silicon carbide are expected to have expanded applications as high-temperature structural materials. Notable advantages of silicon carbide sintered bodies include high strength at high temperatures, excellent corrosion resistance, high thermal conductivity, and low coefficient of thermal expansion. Therefore, silicon carbide sintered bodies having these advantages can be used as gas turbine parts and engine parts for automobiles.
Research and development is actively underway for applications such as high-temperature heat exchangers, bearings, and burners for combustion furnaces. A pressureless sintering method is suitable for industrially producing ceramic sintered bodies with complex shapes. However, since silicon carbide powder is a typical material that is difficult to sinter, special measures are required to enable pressureless sintering. Conventionally, several methods including patents have been proposed for sintering silicon carbide, and representative methods include the following two U.S. patents that use boron and carbon as sintering aids; There is a Japanese patent for this. Namely: (1) U.S. Patent No. 4004934, (Japanese Patent Publication No. 57-32035) (2) U.S. Pat. , 0.3~
After adding and mixing a boron compound in an amount equivalent to 3.0% by weight of elemental boron and a carbon source in an amount equivalent to 0.1 to 1.0% by weight of elemental carbon, this mixture is shaped and heated under an inert atmosphere without any additives. 1900～ at pressure
This method involves heating to a high temperature of 2100°C to obtain a silicon carbide sintered body. Method (2) uses a boron compound in an amount equivalent to 0.15 to 3.0 weight % of elemental boron and an amount equivalent to 0.5 to 5.0 weight % of elemental carbon to silicon carbide powder containing 5 weight % or more of α crystals. A carbon compound is added and heated to a high temperature to form a silicon carbide powder and a sintered body without substantially changing the crystal form, that is,
This is a method for obtaining a silicon carbide sintered body by making the crystalline form of silicon carbide in silicon carbide powder, which is a starting material, have essentially the same proportion as the crystalline form in the final sintered body. The silicon carbide sintered body obtained by these methods is
It is a dense sintered body with more than 95% of the theoretical density of silicon carbide. However, the silicon carbide sintered bodies obtained by these methods have problems of low mechanical strength and too large variations in strength for applications that require heavy mechanical loads such as gas turbines for automobiles, and are not suitable for industrial use. This has become an obstacle to practical application. It is generally known that there is a strong relationship between the mechanical properties of ceramic sintered bodies and the microstructure of sintered bodies.
In order to obtain a sintered body with high strength, it is said that it is preferable that its microstructure satisfies the following three conditions (a) to (c). Here, the microstructure of a sintered body refers to a three-dimensional structure of particles and defects (voids) that constitute the sintered body. (a) The defects contained in the sintered body are few and small. (b) The particle size of the single particles constituting the sintered body is small. (c) There are no specifically grown coarse particles exceeding 50μ in the sintered body. Furthermore, the following condition (d), which has recently become established theory, must be satisfied. (d) There is anisotropy in the shape of the particles that make up the sintered body. Here, the generation of coarse particles in (c) above has conventionally been considered to be caused by phase transition during sintering, and efforts have been made to understand sintering conditions that do not cause phase transition. For example, in the above-mentioned Japanese Patent Publication No. 57-32035, it states that the phase transition from β crystal to α crystal causes grains to grow coarsely.
A method of preventing this using a nitrogen atmosphere is proposed on the right side of the page. Furthermore, on the left side of page 3 of Japanese Patent Publication No. 59-34147, it is stated that ``The crystalline form of silicon carbide in the starting material has essentially the same proportion as the crystalline form of the final non-pressure sintered body.'' clearly stated. Furthermore, the condition (d), that the particle shape is anisotropic, means that the fracture surface that occurs when the sintered body breaks increases; It is presumed that this is to increase the energy required for destruction. In other words, the sintered body is difficult to break. Here, the anisotropy of particle shape refers to the presence of three-dimensional anisotropy in the shape of particles, such as plate-like or rod-like shape. Needless to say, the sintered body as a whole must have no grain orientation in a specific direction. Conventional techniques have not produced a silicon carbide sintered body that satisfies all of the above conditions (a) to (d). For example, according to experiments conducted by the present inventors, method (1) described above (method disclosed in Japanese Patent Publication No. 57-32035) cannot overcome the drawback that coarse particles are likely to be generated; The method 2) (the method disclosed in Japanese Patent Publication No. 59-34147) has the problem that a single particle of the sintered body has no anisotropy, and a sintered body with high strength cannot be obtained. (Basic idea) The present inventors aimed to obtain a silicon carbide sintered body with high mechanical strength and small variations in mechanical strength, and the microstructure of the particles constituting the sintered body has been used as a guideline for this purpose. As a result of intensive studies with the goal of obtaining a sintered body that satisfies all of the proposed conditions (a) to (d) above, we determined that the following raw material powders were used and the sintering conditions were specified. By doing this, we found that a microstructure that satisfies the conditions (a) to (d) above can be obtained with good reproducibility, and furthermore, it is true that a sintered body with a microstructure that satisfies the conditions (a) to (d) above is It was confirmed that the mechanical strength was high and the variation was small, and the present invention was completed. (Detailed Disclosure of the Invention) That is, according to the present invention, (1) 0.05 to 0.3 parts by weight of boron and 0.5 to 3.0 parts by weight of carbon are added and mixed to 100 parts by weight of silicon carbide powder, and then the mixture is molded. In the method of obtaining a silicon carbide sintered body by heating and sintering at 1900 to 2050°C, the physical properties of the silicon carbide powder are as shown below (a):
It satisfies the conditions (b) and (c): (a) The average particle diameter ρ is 0.1 to 0.2μ. (b) The standard deviation of particle diameter is 0.8×ρ or less. (c) The crystal form must contain 97 to 80% by weight of β crystals and 3 to 20% by weight of low-temperature α crystals. When heating and raising the temperature of the mixture molded body, 1750
In the temperature range of ~1900℃, after maintaining the heating rate of 1~10℃/min, it is heated and sintered at 1900~2050℃: Characterized by the following characteristics (d), (e), and (f). A novel method for producing a silicon carbide sintered body, which comprises obtaining a sintered body that can be removed. (d) The density of the sintered body must be 3.10g/cc or more. (e) The average grain size of the microstructure is 3 to 15μ and the aspect ratio is 5 to 20. (f) The crystal form must contain 80% by weight or more of β crystals and 20% by weight or less of high-temperature α crystals. is provided. The present invention will be explained in detail below. First, the raw material silicon carbide powder used in the present invention is required to satisfy the following three requirements. The first requirement is that the average particle diameter ρ of the powder is 0.1 to 0.2μ.
It is to be. The reason is that when ρ exceeds 0.2μ, the density of the silicon carbide sintered body obtained is 3.10g/
This is because it is difficult to exceed cc, and if ρ is less than 0.1 μ, the driving force for sintering is too large, or coarse particles are likely to be generated in the sintered body. It cannot be achieved. The second requirement is that the standard deviation of the powder particle size is 0.8×
The particle size distribution must be narrow below ρ.
This is based on the experimental findings of the present inventors that in order to prevent the generation of coarse particles, the particle size distribution of the fine structure of the sintered body is narrow, and that it is essential that the particle size distribution of the raw material powder is narrow. be. As a method for measuring the particle size, it is preferable to employ a method of determining the particle size from an electron microscope image, as detailed in the section [Particle Size Measurement Method] below. The third requirement is that the crystal form of silicon carbide powder is 97
It contains ~80% by weight or more of β crystals and 3 to 20% by weight of low-temperature α crystals (2H). 3 to 20% by weight of low-temperature α-crystals (2H) means that, apart from the final crystal form during sintering, it contains 3 to 20% by weight of crystal forms that can undergo a phase transition to β-crystals. means. This is based on the experimental findings of the present inventors that anisotropy (indicated by aspect ratio) occurs in the particles of the sintered body only when this third requirement is satisfied. Furthermore, the content of high-temperature α crystals (4H, 6H, 15R) contained in silicon carbide powder is
Preferably, the amount is at a trace level of 1% or less. Silicon carbide powder that satisfies the above three requirements is
Basically, the method proposed by the present inventors in Japanese Patent Application Laid-Open No. 59-83922 is used, that is, once a decomposable silicon compound and a decomposable carbon compound are combined into a silicon oxide and an elemental carbon through a chemical reaction. It can be easily obtained by producing an extremely finely mixed powder, compressing this powder to a bulk density of 0.15 g/cc or more, and then heating it to about 1600 to 1900°C. Note that, as other methods for producing fine silicon carbide powder containing β crystals as a main component, the following two methods are conventionally known as typical methods. That is, (a) After mechanically mixing silicon oxide and carbon or silicon and carbon, heating to 2000°C or less,
A method of finely pulverizing the silicon carbide produced. (b) Silicon compounds such as SiH ₄ and Si(CH ₃ ) ₄ and CH ₄ ,
A method in which silicon carbide is produced by introducing a carbon compound such as C ₂ H ₆ into a plasma atmosphere heated to over 1200°C and causing a gas phase reaction in the presence of hydrogen. However, according to the results of follow-up experiments conducted by the present inventors on the two methods (a) and (b) above, the powder obtained by method (a) has two types: particles pulverized to 0.1 μm or less and particles of several μm. It is a powder with a wide particle size distribution in which
Although the size is small, the particles are strongly aggregated, and the apparent particle size is large and the powder has a wide particle size distribution. Therefore, neither of the silicon carbide powders obtained by the above methods (a) and (b) is suitable as a raw material for the present invention. Now, a silicon carbide sintered body is obtained by forming silicon carbide powder into a desired shape and then sintering it, but in the present invention, elemental boron or a boron compound and elemental carbon are added to silicon carbide powder prior to shaping. A small amount is added and mixed as a sintering aid to accelerate sintering to form a mixture. The amount added is 0.05 to 0.3 parts by weight of the former and 0.5 to 3.0 parts by weight of the latter in terms of elemental boron, per 100 parts of silicon carbide powder. Naturally, the purpose of the sintering aid is to
It is desirable to mix it with silicon carbide powder as uniformly as possible, and for this purpose, when expressed in terms of specific surface area, elemental boron or boron compounds must have a specific surface area of 3 m ² /g or more, and elemental carbon must have a specific surface area of 30 m 2 /g. ² /g or more in fine powder form is preferred. The silicon carbide powder and the above-mentioned sintering aid are mixed using a ball mill, vibration mill, etc., but in order to obtain a more homogeneous mixture, water or an organic solvent such as methanol or ethanol is added and a wet ball mill is used. , a method of mixing using a vibrating mill or the like is preferred. That is, it is a method in which water or an organic solvent such as methanol is added to and mixed with elemental boron fine powder, boron compound fine powder, elemental carbon fine powder, and silicon carbide fine powder, and then the water or the organic solvent is evaporated. Preferable examples of the boron compound that can be used in the present invention include finely powdered B ₄ C, BN, BP, AlB ₂ and the like. Preferable examples of fine powdered elemental carbon include carbon black and acetylene black. The thus obtained mixture of silicon carbide powder containing a small amount of sintering aid is then molded into a desired shape, and then molded in vacuum or in an inert gas atmosphere such as argon or helium without pressure. That is, a silicon carbide sintered body is obtained by heating and sintering at 1900 to 2050°C without applying mechanical pressure to the surface of the molded body. In the present invention, in this case, the 1900 to 2050°C
The heating rate in the heating process up to the heating temperature of 1750
In the temperature range of ~1900°C, it is required to maintain the temperature within a specific range of 1~10°C/min. However, if the heating rate is too high and exceeds 10°C/min, the phase transition from low-temperature α-crystals to high-temperature α-crystals will occur more easily than the phase transition from low-temperature α-crystals to β-crystals, and the sintering This is because there is a problem in that the anisotropy of the particles of the solid body is insufficiently ensured. On the other hand, according to the experimental findings of the present inventors, if the heating rate is too low and it is less than 1°C/min, the particles of the sintered body tend to become coarse and the object of the present invention cannot be achieved. It is. According to the method of the present invention as described in detail above,
A silicon carbide sintered body having the following three properties can be obtained. Namely: First, the density of the sintered body is 3.10 g/cc or more, and second, the average particle size of the microstructure is 3 to 15 μm.
It is large and has an aspect ratio of 5 to 20. As mentioned above, the microstructure refers to the three-dimensional structure of the particles and defects that make up the sintered body, but the measurement of the average particle diameter and aspect ratio is carried out by smoothing the surface of the sintered body and The particle size is determined from an image magnified (usually 100 to 1000 times) with a microscope, and the particle size is the average value of the maximum length L and minimum length D of each particle in this image. The arithmetic mean value of the diameter, and the aspect ratio is L/
This is the arithmetic mean value of D. These are usually
It is sufficient to calculate for 300 or more particles. Furthermore, thirdly, the crystal form of the sintered body of the present invention is 80
It is a sintered body containing at least 20% by weight of β crystals and 20% or less of high-temperature α crystals, and more preferably a sintered body containing 5% or less of high-temperature α crystals by weight. According to the experimental findings of the present inventors, the low-temperature α
If silicon carbide powder containing 3 to 20% by weight or less of crystals (the rest is β crystals), more preferably 5 to 20% by weight or less, is used as a raw material and sintered under the conditions described above, high-temperature α crystals will be 20% by weight. % (the remainder being β crystals), more preferably 5% by weight or less, can be obtained with extremely good reproducibility. It goes without saying that this sintered body has the excellent microstructure that is the object of the present invention. (Operations and Effects of the Invention) The present invention is directed to the production of a silicon carbide sintered body having an excellent microstructure, which has been strongly desired as a technical concept, but for which no production method has been established in reality. The method was established by specifying the physical properties of the raw material silicon carbide powder and the sintering conditions. The results of measuring the mechanical strength of the sintered body obtained by the method of the present invention show that the strength is clearly higher than that of the conventional sintered body and the variation is small, as shown in the examples below. It was confirmed that the toughness value (K _IC ) was also high. The silicon carbide sintered body obtained by the method of the present invention has an excellent microstructure as described above, and the reason for this is presumed to be as follows. (b) Since the raw material powder is easily sinterable, sintering can be performed with the added amount of boron, which is a sintering aid, of 0.05 to 0.3 parts by weight, which is smaller than that in conventional technology, and therefore the sintered body can be easily sintered. The generation of coarse particles inside is suppressed. (b) Since raw material powder that is easily sinterable is used, the sintering temperature can be lowered to 1,900 to 2,050°C, which is lower than before, and therefore, coarsening of the sintered body particles can be suppressed. (c) During the sintering process, the low-temperature α-crystal undergoes a phase transition to a β-crystal, and as a result, anisotropy occurs in the sintered particles. (Examples and Comparative Examples) Hereinafter, more specific embodiments of the present invention will be described with reference to Examples. Silicon Carbide Powder Silicon carbide powder having the quality shown in Table 1 was used in the Examples and Comparative Examples. Powders 1 to 3 in Table 1 are prepared using the method previously proposed by the present inventors in JP-A-59-83922.
That is, 33.6% SiO ₂ was obtained by simultaneously injecting SiCl ₄ as a silicon compound and C ₉ fraction as a carbon compound into a fire obtained by burning hydrogen with air.
Once a soot-like extremely fine mixture containing 66.3% elemental carbon was compressed to a bulk density of 0.5 g/cc,
Heated to 1700℃, 1800℃, and 1900℃, respectively, and the following
It is obtained by burning off excess carbon after producing silicon carbide according to the reaction formula shown in equation (1). SiO ₂ +3C→SiC+2CO...(1) Powder 4 is obtained by directly reacting SiH ₄ , CH ₄ and H ₂ in the gas phase using a conventionally known method [for example, Journal of the Chemical Society of Japan, 2, 188- 193 (1980)] at a reaction temperature of 1400°C. Powders 5 and 6 are commercially available products, and their microscopic images indicate that they are made by mixing silicon dioxide or silicon with elemental carbon, heating the resulting coarse particles of silicon carbide, and grinding them for a long time using a vibrating mill or the like. It is assumed that the

[Table] As shown by the values in Table 1, Powders 1 to 3 satisfy all physical property conditions (a), (b), and (c) as raw materials of the present invention. In comparison, powders 4 to 6 have an average particle size ρ
and its standard deviation are both larger than the specified values of the present invention. Powder 6 does not contain any β-crystals and is only high-temperature α-crystals. Like this powder 4-6
does not satisfy any of the physical property conditions as a raw material specified in the present invention. The method for measuring the average particle diameter ρ and the standard deviation of particle diameter shown in Table 1 is described in the [Particle diameter measurement method] described in the summary of analysis methods below. I turned and asked. Transmission electron microscope images of powders 1, 4, and 5 are shown in Figures 1, 2, and 3, respectively, and a powder X-ray diffraction image of powder 1 is shown in Figure 4. Examples 1 to 3 To 100 g of each of powders 1 to 3 shown in Table 1,
B ₄ C powder with a specific surface area of 10.4 m ² /g as a boron source
0.25g and a specific surface area of 120.5m ² /
2g of carbon black and more ethanol
50 c.c. were added and mixed in a resin ball mill for 20 hours. 50 g of the powder obtained by heating the resulting mixture to remove ethanol by evaporation was placed in a cylindrical container and uniaxially compressed under a load of 0.5 T/cm ^{2 .}
Rubber pressed and molded using hydrostatic pressure. Table 2 shows the density of each powder compact obtained. Next, these powder compacts are heated using a high-frequency heating furnace.
A silicon carbide sintered body was obtained by heating at a temperature of 1950° C. for 30 minutes in a nitrogen atmosphere under a vacuum of 10 ⁻¹ to 1 Torr.
The heating rate is 50℃/min from room temperature to 1750℃,
The rate was 5°C/min from 1750°C to 1900°C. Thereafter, the temperature was further increased to 1950°C and sintered for 30 minutes. Table 2 shows the density, average grain size aspect ratio of the microstructure, and crystal shape of the obtained sintered body. In addition, a powder compact identical to each of the above powder compacts was heated at the same temperature increase rate as above, and when the temperature reached 1900°C, the heating was stopped and allowed to cool to form a silicon carbide sintered intermediate. I got it. The crystal form of the obtained sintered intermediate is shown in Table 2. It was presumed that the crystal form of this sintered intermediate represented one intermediate state of the silicon carbide sintered body obtained by heating at 1950° C. for 30 minutes. 20 pieces each from each silicon carbide sintered body obtained.
A test piece was cut out and its bending strength was measured according to the method of JIS R-1601. Similarly, fracture toughness values were determined using the Bitkers indentation method from each of the 20 test pieces.
K _IC was measured. These measured values are shown in Table-2. As shown by the values in Table 2, any silicon carbide sintered body produced by using raw material powder with physical properties that meet the conditions of the present invention and sintered under the conditions specified by the present invention satisfies the purpose of the present invention. It was something that had the characteristics of

[Table] Comparative Examples 1 to 2 When heating the same powder compact as used in Example 3 in a high-frequency heating furnace, the heating temperature was higher than 1750°C.
A silicon carbide sintered body was obtained in exactly the same manner as in Example 3, except that the temperature increase rate up to 1900°C was set to the value shown in Table 2. The density of the obtained sintered body, the average particle diameter of the microstructure, etc. are shown in Table 2. In addition, in the same manner as in Example 3, the crystal form of the sintered intermediate was estimated at the stage when the temperature reached 1900° C., and the bending strength and K _IC of the sintered body were also measured. These measured values are shown in Table-2. As shown by the values in Table 2, Comparative Example 1 has a faster temperature increase rate from 1750℃ to 1900℃ than specified by the present invention.
In the case of , the content of α crystals in the sintered intermediate was high. Furthermore, the aspect ratio of the particles constituting the sintered body was low, and perhaps because of this, the obtained silicon carbide sintered body had low bending strength and a large standard deviation. On the other hand, in the case of Comparative Example 2, where the temperature increase rate is slower than specified in the present invention, the average particle diameter of the particles constituting the sintered body is large, and the resulting silicon carbide sintered body is The bending strength was even lower than that of No. 1, and its standard deviation was also large. Comparative Examples 3 to 5 Using powders 4, 5, and 6 shown in Table 1 that do not meet the conditions specified in the present invention, the same method as in the example,
A silicon carbide sintered body was obtained under the same conditions. The results of measuring the density of the obtained sintered body are shown in Table-
As shown in Figure 3, all of them are significantly below the target value of 3.10 g/cc or more of the present invention.

[Table] Comparative Examples 6 to 10 Using powders 4, 5, and 6 shown in Table 1, which do not meet the conditions specified in the present invention, sintering conditions etc. were searched to increase the density of the sintered body, and the results were obtained in Table 4. A silicon carbide sintered body was obtained by changing the conditions to those shown in (same conditions as in the example except for the conditions listed in Table 3). As shown in Table 3, the density of the obtained sintered body can be increased by increasing the amount of B ₄ C added for powder 4 (comparative example 6), and for powders 5 and 6 ( Comparative Examples 7 to 10), it was recognized that the heating temperature could be increased by increasing the heating temperature.

[Table] Therefore, for the sintered bodies obtained in Comparative Examples 6, 8, and 10, in which the sintered body density reached 3.10 g/cc or more, the average particle size of the microstructure, , bending strength, etc. were measured and shown in Table 5. As a result, the density of the sintered body increased and it was possible to satisfy the requirement (d), but Comparative Examples 6 and 8
In the comparative example, the average particle diameter is higher than the specified value.
10, the aspect ratio is lower than the specified value, and in both cases,
It has been found that a sintered body that achieves the objectives of the invention cannot be obtained. Furthermore, in comparison with Examples 1 to 3,
The average bending strength is low, the standard deviation is large, and the K _IC is also low.

【table】

[Particle size measurement]

In the present invention, the particle diameter is measured using a microscope image, which is the only method for directly observing particles, and a transmission electron microscope is used as the microscope. As is well known, when powder particles are supported on a sample support of an electron microscope, agglomeration and segregation of particles tend to occur, making it quite difficult to prepare a sample that represents the entire powder. In order to prevent this problem, studies have been carried out in the past (for example, "Powder Particle Size Measurement Method" edited by the Powder Engineering Research Group (published by Yokendo, 1962))
Various methods are described in Chapter 4). As a result of intensive study of these various methods, the present inventors sprayed a slurry in which powder particles were dispersed onto a sheet mesh using collodion as a support film using a nebulizer, and the powder particles were supported on the collodion film. It was confirmed that the sample gave the best results. In the present invention, the particle size of the powder is determined from an electron microscope image of a sample obtained by this spraying method. The slurry preferably uses isobutanol as a dispersion medium, and the powder slurry concentration is preferably in the range of 0.3 to 0.7%. When dispersing the powder, it is preferable to use a powerful ultrasonic dispersion device such as an ultrasonic cell disrupter and allow it to act for several minutes. The particle size of the powder is determined from the microscopic image of the sample obtained in this way, and here the particle size is defined as the equivalent circle diameter. The equivalent circle diameter is a value expressed by measuring the area of a particle image, assuming a circle with the same area as the image, and expressing the diameter of the circle. Here, in the present invention, in order to eliminate the possibility of arbitrariness as to whether a certain image is regarded as a single particle or a plurality of particles, for example, when an image is partially connected, such as a gourd-shaped image, All shall be considered as a single particle. Note that as the amount of powder supported on the support film increases, the probability that multiple particles will apparently connect and appear as a single particle increases, so the particle diameter in the present invention is defined as the area of the particle image in the entire image. It shall be determined from a sample prepared such that it is in the range of 5 to 15%. Note that the average particle diameter is the arithmetic mean value of equivalent circle diameters. [Crystal form determination method] Low-temperature α contained in silicon carbide powder and sintered body
crystal (2H), β crystal (3C), high temperature α crystal (4H, 6H,
15R) is determined from the pattern obtained by powder X-ray diffraction using CuKα radiation as the light source and a monochromator on the receiving side. The method of calculating each component from the height of each peak of the figure is described in Nitrogen Industry Association Journal, 87, 576-582.
(1979) shall be followed. In addition,
When measuring a sintered body using powder X-ray diffraction, the sintered body is ground into 100 meshes or less.

[Brief explanation of the drawing]

FIGS. 1 to 3 are enlarged photographs showing the state of particles of powders 1, 4, and 5 used in Examples and Comparative Examples of the present invention, respectively, taken with a transmission electron microscope. The magnification is 8000x in both cases. FIG. 4 shows the powder X-ray diffraction pattern of Powder 1. 5 to 7 are enlarged photographs showing the surface structures of the surfaces of the sintered bodies obtained in Example 1 and Comparative Examples 6 and 10, respectively, taken with an optical microscope. The magnification is 500x in both cases. FIG. 8 shows a powder X-ray diffraction diagram of the sintered body obtained in Example 1. FIG. 9 is a graph showing the relationship between (standard deviation of particle diameter/ρ) and the average particle diameter of the microstructure.
FIG. 10 is a diagram showing the relationship between the α crystal content and the aspect ratio of the microstructure of the sintered intermediate.

Claims (1)

[Claims] 1. After carbonizing and mixing 100 parts by weight of silicon carbide powder with 0.05 to 0.3 parts by weight of boron and 0.5 to 3.0 parts by weight, the mixture is molded and heated and sintered at 1900 to 2050°C. In the method for obtaining a silicon carbide sintered body, the physical properties of the silicon carbide powder are as shown below (a):
It satisfies the conditions (b) and (c): (a) The average particle diameter ρ is 0.1 to 0.2μ. (b) The standard deviation of particle diameter is 0.8×ρ or less. (c) The crystal form must contain 97 to 80% by weight of β crystals and 3 to 20% by weight of low-pitched α crystals. When heating and raising the temperature of the mixture molded body, 1750
In the temperature range of ~1900℃, after maintaining the heating rate of 1~10℃/min, it is heated and sintered at 1900~2050℃: Characterized by the following characteristics (d), (e), and (f). A novel method for producing a silicon carbide sintered body, which comprises obtaining a sintered body that can be removed. (d) The density of the sintered body must be 3.10g/cc or more. (e) The average grain size of the microstructure is 3 to 15μ and the aspect ratio is 5 to 20. (f) The crystal form must contain 80% by weight or more of β crystals and 20% by weight or less of high-temperature α crystals. 2 There are 5 to 5 low-temperature α crystals in the raw material silicon carbide powder.
20% by weight, and the resulting silicon carbide sintered body contains 5% by weight or less of high-temperature α crystals.