JPS63182257A - Novel manufacture of 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 (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 find expanded use 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 with these advantages are being actively researched and developed for use in automobile gas turbine parts and engine parts, high-temperature heat exchangers, bearings, burners for combustion furnaces, etc. There is.

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. 4,004,934,
(2) U.S. Patent No. 4,321,954, (Japanese Patent Publication No. 7-32035)
9-34147) Method (1) uses 0.3 to 3
．． After adding and mixing a boron compound in an amount equivalent to 0 weight percent elemental boron and a carbon source in an amount equivalent to 0.1 to 1.0 weight percent elemental carbon, this mixture is molded and This is a method of obtaining a silicon carbide sintered body by heating to a high temperature of 1900 to 2100° C. in an atmosphere without pressure.

Method (2) is based on silicon carbide powder containing 5% by weight or more of α crystals, and a boron compound in an amount equivalent to 0.15% to 3.0% by weight of elemental boron and 0.5% to 5.0% by weight. of carbon compound in an amount equivalent to the elemental carbon and heated to high temperature,
The silicon carbide powder and the sintered body do not substantially change in crystal form, that is, the crystal form of silicon carbide in the starting material silicon carbide powder changes to the crystal form in the final sintered body. This is a method of obtaining a silicon carbide sintered body by making the shape jump essentially the same ratio.

The silicon carbide sintered body obtained by these methods is a dense sintered body that reaches 95% or more of the theoretical density of silicon carbide. However, the silicon carbide sintered bodies obtained by these methods have low mechanical strength and too large variations in strength for applications that require large mechanical loads such as gas turbines for automobiles, so they are not suitable for industrial use. This is an obstacle to practical application.

It is generally known that there is a strong relationship between the mechanical properties of a ceramic sintered body and the microstructure of the sintered body, and for a sintered body to have high strength, its microstructure must meet the following conditions (a). ~(
It is said that it is preferable to satisfy the three conditions 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 an established theory, must be satisfied.

(d) The shape of the particles constituting the sintered body has anisotropy.

Here, the generation of coarse particles in (c) above has traditionally been thought to be caused by phase transition during sintering, and efforts have been made to understand sintering conditions that do not cause phase transition. 0
For example, in the above-mentioned Japanese Patent Publication No. 57-32035, it states that the phase transition from β-crystal to 7-crystalline crystals causes the grains to grow coarsely, and on the right side of page 5, the publication states that this problem can be prevented by using a nitrogen atmosphere. proposing a law. Also, special public service 59-341
On the left side of page 3 of Publication No. 47, it is clearly 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." There is.

Furthermore, the condition (d) that the particle shape is anisotropic means that the fracture surface that occurs when the sintered body breaks increases, and therefore, this increase in the fracture surface increases the 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 the experiments conducted by the present inventors, the method (1) described above (the method disclosed in Japanese Patent Publication No. 57-32035) cannot overcome the drawback that coarse particles are likely to be generated;
The method 2) (method disclosed in Japanese Patent Publication No. 59-34147) has a problem in 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 study with the goal of obtaining a sintered body that satisfies all of the proposed conditions (a) to (d) above, we used the raw material powder described below and specified the sintering conditions. It has been found that a microstructure satisfying the conditions (a) to (d) above can be obtained with good reproducibility by
The present invention has been completed based on the fact that a sintered body having a microstructure under the conditions of ) to (d) has high mechanical strength and small variations in mechanical strength.

(Detailed disclosure of the invention) That is, according to the present invention, after adding and mixing 0.05 to 0.3 parts by weight of boron and 0.5 to 3.0 parts by weight to 100 parts by weight of silicon carbide powder. In the method of obtaining a silicon carbide sintered body by molding the mixture and heating and sintering it at 1900 to 2050°C, the physical properties of the cored silicon powder are shown below (a) and (b).
, and (c), and (i) the average particle diameter ρ is 0.1 to 0.2 μ.

(b) The standard deviation of particle diameter is 0.8×ρ or less.

(c) The crystal form must contain 80% by weight or more of β crystals and 20% by weight or less of low-temperature α crystals.

■When heating the core compound molded product, r 1750
In the temperature range of ~1900°C, a heating rate of 1 to 10'C/min is maintained, and in this heating process, the content of α crystals is passed through an intermediate state of 5% by weight or less. , 190
Heat sintering at 0 to 2050"C: ■ A novel method of silicon carbide sintered bodies, which consists of obtaining a sintered body characterized by the following properties (2), (e), and (f). Production method.

(d) The density of the sintered body is 3.10 g/cc or more.

(e) The average particle diameter of the microstructure is 3 to 15 μm and the aspect ratio is 5 to 20.

(f) The crystal form must contain 1% or more of 8I 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 powder has an average particle diameter ρ of 0.1 to 0.2 μ. The reason is that when ρ exceeds 0.2μ, the density of the silicon carbide sintered body obtained is 3, LOg/cc.
If ρ is less than 0.1 μ, this is because the driving force for sintering is too large or coarse particles are likely to be generated in the sintered body. cannot achieve its purpose.

The second requirement is that the powder has a narrow particle size distribution with a standard deviation of particle size of 0.8×ρ or less.

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 fibers of the sintered body is narrow and that it is essential that the particle size distribution of the raw material powder is narrow. It is. 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 the silicon carbide powder contains 80% or more of β crystals and 7 low-temperature types (2H). 20% or less of low-temperature α-crystals (2H) means that 20% or less of crystal forms, most of which undergo a phase transition into three products during sintering, are included. The reason for this is based on the experimental findings of the present inventors that anisotropy (represented by aspect ratio) occurs in the particles of the sintered body only when this third requirement is satisfied. It is. 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 produced by the method previously proposed by the present inventors in JP-A No. 59-83922, that is, by chemically processing a decomposable silicon compound and a decomposable carbon compound. After producing a powder containing an extremely fine mixture of silicon oxide and elemental carbon by reaction, and then compressing this powder to a bulk density of 0.15 g/cc or more, 16
It can be easily obtained by heating to about 00 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 representative methods. That is, (a) after mechanically mixing silicon oxide and carbon or silicon and carbon, 200
A method of heating to below 0°C and pulverizing the generated silicon carbide.

(b) A silicon compound such as 5iHa, 5i(CHi)4 and a carbon compound such as CH4°C2116 are combined at 120
A method of introducing silicon carbide into a plasma atmosphere heated to 0'C or higher and causing a gas phase reaction in the presence of hydrogen to produce silicon carbide.

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 that coexists with particles, and (b)
The powder obtained by this method has a single particle size of about 0.1 μ, but the particles are tightly aggregated, giving the appearance of a powder with a large upper particle size and a wide particle size distribution. It is. 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 molding silicon carbide powder into a desired shape and then sintering it, but in the present invention,
Prior to molding, a small amount of elemental boron or a boron compound and elemental carbon are added and mixed as sintering aids to promote sintering to silicon carbide powder to form a mixture. The amount of the former is 0.05 to 0.3 parts in terms of elemental boron, and the latter is 0.5 to 3.0 parts per 100 parts of silicon carbide powder.
Department.

Naturally, for its purpose, it is desirable to mix the sintering aid with the silicon carbide powder as uniformly as possible.
For this purpose, when expressing this in terms of specific surface area, elemental boron or boron compounds must have a specific surface area of 3n (/g or more),
Further, the elemental carbon is preferably in the form of a fine powder with a specific surface area of 3 On (/g or more).

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 preferable, that is, after adding and mixing water or an organic solvent such as methanol to fine elemental boron powder, fine boron compound powder, fine elemental carbon powder, and fine silicon carbide powder. This is a method of removing water or organic solvent by evaporation.

The boron compounds that can be used in the present invention include:
Preferable examples include fine powder B4C, BN, BP 1AIB2, and the like. In addition, fine powdered elemental carbon includes carbon wine rank, acetylene rank,
etc. are listed as preferred.

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, 1900 to 2050 without applying mechanical pressure to the surface of the molded product.
A silicon carbide sintered body is obtained by heating to ℃.

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 to 10'C/min. However, if the heating rate is too high and exceeds 10'C/min, the phase transition from low temperature α crystal to high temperature α crystal will occur more easily than the phase transition from low temperature α crystal to β crystal. For this reason, it becomes difficult to pass through an intermediate state in which the α crystal content is 5% or less as specified in the present invention, and there is a disadvantage that the anisotropy of the particles of the sintered body is insufficiently ensured. It is. On the other hand, according to the experimental findings of the present inventors, if the heating rate is too low and less than 1° C./min, the particles of the sintered body tend to enlarge and the object of the present invention cannot be achieved. It is. Note that the α crystal in this intermediate state means the sum of both the low-temperature type and the high-temperature type.

As described in detail above, by following the method of the present invention, it is possible to obtain a silicon carbide sintered body having the following three characteristics. That is; firstly, the density of the sintered body is 3.10 g / cc or more, and secondly, the average particle size of the fine fibers is 3 to 15μ and the aspect ratio is 5 to 20. It is.

In addition, it is minute! As mentioned above, JI weave refers to the three-dimensional structure of particles and defects that make up a sintered body, but the average particle diameter and aspect ratio are measured by smoothing the surface of the sintered body and using a microscope. (usually 100-1000)
The particle size is determined from the image seen (times), and the particle diameter is the maximum length (L) and minimum length (D) of each particle in this image.
The average particle diameter is the arithmetic mean value of particle diameters, and the aspect ratio is the arithmetic mean value of L/Ill. It is usually sufficient to determine these for 300 or more particles.

Furthermore, thirdly, the crystal form of the sintered body of the present invention is a sintered body containing 80% or more of three types and 20% or less of high-temperature α crystals,
More preferably, the sintered body contains 5% or less of high-temperature α crystals.

According to the experimental findings of the present inventors, the low-temperature α crystal is 20
% (the remainder is β crystals), more preferably 5 to 20%. If silicon carbide powder is used as a raw material and sintered under the conditions described above, high-temperature α crystals will be 20% or less (the remainder is β crystals), More preferably, a silicon carbide sintered body having a composition of 5% or less can be obtained with extremely high reproducibility. It goes without saying that this sintered body has the excellent microstructure that is the object of the present invention.

(Actions and Effects of the Invention) Although the present invention has been strongly desired as a technical idea, in reality, a manufacturing method thereof has not been established.
A method for manufacturing silicon carbide sintered bodies with excellent microstructure,
This was established by specifying the physical properties and sintering conditions of the raw material silicon carbide powder.

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, and the fracture toughness value is It was confirmed that (K+c) 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.

(a) Since the raw material powder is easily sinterable, sintering can be carried out with the addition of boron, which is a sintering aid, in an amount of 0.05 to 0.3 parts by weight, which is smaller than in the conventional technology. Therefore, generation of coarse particles in the sintered body is suppressed.

(b) Since an easily sinterable raw material powder is used, the sintering temperature is 1
It is possible to lower the temperature to 900 to 2050'C, which is lower than the conventional temperature, and therefore the enlargement of the sintered particles can be suppressed.

(c) During the sintering process, the sintered particles undergo an intermediate state in which the α crystal content is 5% or less, so 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.

Disaster ± Missing Earth Work■ Silicon carbide powder of the quality shown in Table 1 was used for unexamined 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, in which 5iCI4 is added as a silicon compound into a flame obtained by burning hydrogen with air. , 33.6% SiO□ and 66.3% obtained by simultaneously injecting C9 fraction as carbon compounds.
A very fine soot-like mixture containing elemental carbon is once heated to zero.
．． 170 respectively after tightening to a bulk density of 5 g/cc.
Heat to 0'C21800℃11900℃ and perform the following (1)
It is obtained by burning off excess carbon after producing silicon carbide according to the reaction formula shown in the formula.

5iOz÷3C-+SiC+2CO・・・・・・・・・
-(1) Powder 4 is obtained by directly reacting 5iHa, CHa, and H2 in the gas phase, using a conventionally known method [e.g., Journal of the Chemical Society of Japan,'' 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

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 diameter ρ and a standard deviation thereof each larger than the specified values of the present invention. Powder 6 does not contain any β-crystals and is only high-temperature α-crystals. As described above, powders 4 to 6 do not satisfy any of the physical property conditions as raw materials 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 will be described in the summary of analysis methods below [Particle diameter measurement method]
Similarly, the percentage of crystal form was determined by [crystal form determination method].

Transmission electron microscope images of powders 1, 4, and 5 are shown in Figure 1.
, 2, 3, and the powder X-ray diffraction image of Powder 1 is shown in Figure 4.

84G powder with a specific surface area of 10.4 m''/g as a boron source was added to 100 g of each of powders 1 to 3 shown in Table 1.
．． 25g and a specific surface area of 120.5m as a single carbon source.
”/g carbon blank and 5 ethanol.
0 cc was added and mixed in a resin ball mill for 20 hours. The obtained mixture was heated to remove ethanol by evaporation, and 50 g of the powder was placed in a cylindrical container and the amount of 0.57
After being uniaxially compressed under a load of /cffl, it was rubber pressed and molded under a hydrostatic pressure of 2T/CIII. Table 2 shows the density of each powder compact obtained.

Next, these powder compacts were heated in a high-frequency heating furnace for 10-
'~ITorr under vacuum in a nitrogen atmosphere at a temperature of 1950° C. for 30 minutes to obtain a silicon carbide sintered body.

The heating rate was 50'C/min from room temperature to 1750'C, and 5°C/min from 1750'C to 1900'C.

After that, the temperature was further raised to 1950°C and sintered for 30 minutes. The density of the obtained sintered body, the average particle diameter aspect ratio of the fine fibers, and the crystal form are shown in Table 2.

The same powder compact as 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. The crystal form of this sintered intermediate was changed to 3 at 1950'C.
Carbonization Table 2 obtained by heating for 0 minutes It was assumed that this shows one intermediate state of the silicon sintered body.

Twenty test pieces were cut out from each of the obtained silicon carbide sintered bodies, and the bending strength was measured according to the method of JIS R-1601. Similarly, the fracture toughness value (K+c) was measured using the Binkers indentation method for each of the 20 test pieces. 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 had the characteristics of

In heating the same powder compact as used in Example 3 above, using a high-frequency heating furnace, the temperature was lowered from 1750'C to 1900'C.
Except that the heating rate up to 'C is the value shown in Table 2,
A silicon carbide sintered body was obtained in exactly the same manner as in Example 3. Table 2 shows the density of the obtained sintered body, the average particle size of the microstructure, etc.
It was shown to.

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 KIC of the sintered body were also measured. These measured values are shown in Table-2.

As shown in Table 2, 1750'C to 1900'C
In the case of Comparative Example 1, in which the rate of temperature increase to The resulting 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.

Comparison Charcoal Main 21 A silicon carbide sintered body was obtained using the powders 4 and 5.6 shown in Table 1, which do not meet the conditions specified in the present invention, in the same manner and under the same conditions as in the examples. The density of the obtained sintered bodies was measured, and as shown in Table 3, all of the densities were significantly below the target value of 3.10 g/cc or more of the present invention.

Table-3 Using powders 4 and 5.6 shown in Table-1 that do not meet the conditions stipulated by the present invention, sintering conditions etc. were searched to increase the density of the sintered compact, and the conditions were changed to the conditions shown in Table-4. A silicon carbide sintered body was obtained (under the 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 and C added for powder 4 (comparative example 6), and for powder 5.6. (
Comparative Examples 7 to 10), it was recognized that the heating temperature could be increased by increasing the heating temperature.

Table 4 Therefore, for the sintered bodies obtained in Comparative Examples 6 and 8.10 in which the sintered body density reached 3.10 g/cc or more, the average particle diameter of the fine m-weave was determined in exactly the same manner as in the example. The crystal shape, bending strength, etc. were measured and are shown in Table 5.

As a result, the sintered body density increased and the requirement (d) was satisfied, but in Comparative Example 6.8, the average particle diameter was higher than the specified value, and in Comparative Example 10, the aspect ratio was It was found that the ratio was lower than the specified value, and a sintered body that achieved the object of the present invention could not be obtained in either case. Furthermore, compared to Examples 1 to 3, the average bending strength is low, the standard deviation is large, and Kle is also roughly low.

Table-5 Powder 2 and Powder 5 with the same average particle diameter ρ and α crystal content
were mixed in various ratios to prepare powders with different particle size distributions. B, C and carbon black were added to these powders in exactly the same manner as in the examples, and then molded, and then heated and sintered using a high frequency heating furnace in the same manner as in the examples. The relationship between (standard deviation of particle diameter)/ρ and the average particle diameter of the microstructure of the obtained silicon carbide sintered body is shown in FIG. From Figure 9, it can be seen that there is a positive correlation between the two.

α3A U Powder 1 and Powder 6 were mixed at various ratios to prepare powders with different crystal forms. 84C and carbon black were added to these powders and molded in exactly the same manner as in the examples, and then sintered using a high frequency heating furnace in the same manner as in the examples.

Further, in exactly the same manner as in Examples, heating was stopped when each powder compact reached 1900° C., and the crystal form of the obtained sintered intermediate was measured.

The relationship between the α-crystal content of the sintered intermediate obtained from these mixed powders and the aspect ratio of the sintered body microstructure is shown in Figure 10. From Figure 10, it can be seen that when the α-crystal content of the sintered intermediate exceeds 5%, the aspect ratio of the sintered body microstructure is difficult to become 5 or more.

(Summary of analytical methods) The analysis methods used in the present invention are summarized below.

(Particle Size Measurement) In the present invention, the particle size 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, many studies have been carried out in the past (
For example, various methods are described in Chapter 4 of ``Powder Particle Size Measurement Methods'' (published by Yokendo, 1962), edited by the Powder Technology Study Group).

As a result of intensive studies on 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 in a positive direction and appear as a single particle increases. It shall be determined from a sample prepared such that the area 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 crystal (2H) contained in silicon carbide powder and sintered body
), 3 products (3C), high temperature α crystal (4H, 6B, x
sR) is determined by Cuf! The method of calculating each component from the peak height of the 0 figure obtained from the figure obtained by powder X-ray diffraction using α-rays as a light source and a monochromator on the receiving side is described in Ceramics Association Journal, Gong, 576-582 ( 1979
)) shall be followed. In addition, when measuring a sintered compact by powder X-ray diffraction method, the sintered compact is crushed into 100 meshes or less.

[Brief explanation of the drawing]

Figures 1 to 3 are enlarged photographs of powders 1 and 4.5 used in the Examples and Comparative Examples of the present invention, respectively, showing the state of the particles in the highest shadow under a transmission electron microscope.
It is 0 times. 421 shows the powder X-ray diffraction pattern of Powder 1, and FIGS. 5 to 7121 show the powder X-ray diffraction pattern of Example 1. Comparative example 6
．． This is an enlarged photograph showing the surface structure of the surface of the sintered body obtained in step 10, taken with an optical microscope, and the magnification is 500 times. FIG. 8 shows a powder X-ray diffraction pattern of the sintered body obtained in Example 1. FIG. 9 is a graph showing the relationship between (standard deviation of particle size/ρ) and the average particle size of the microstructure. It is. The 10th is
FIG. 3 is a diagram showing the relationship between the α-convex gold fi of the sintered intermediate and the aspect ratio of the microstructure. Patent applicant Mitsui Toatsu Chemical Co., Ltd. Figure 1 Figure 2 Figure 31! ] Figure 5 Figure 6 Figure 7i: So 1 Figures 4 to 8■ Zel ("ノ

Claims (2)

[Claims] (1) 0.05 to 0.3 per 100 parts by weight of silicon carbide powder
After adding and mixing parts by weight of boron and 0.5 to 3.0 parts by weight of carbon, the mixture is molded and heated at 1900 to 2050°C.
[1] 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 0.2 μ; (b) The standard deviation of particle diameter is 0.8×ρ or less. (c) The crystal form must contain 80% by weight or more of β crystals and 20% by weight or less of low-temperature α crystals. [2] When heating the mixture molded product, i175
In the temperature range of 0 to 1900 °C, a heating rate of 1 to 10 °C/min is maintained, ii. and after passing through an intermediate state in which the content of α crystals is 5% by weight or less in this temperature raising process. , 190
Heat sintering at 0 to 2050°C: [3] Following (
A novel method for producing a silicon carbide sintered body, which comprises obtaining a sintered body characterized by the properties of (d), (e), and (f). (d) The density of the sintered body is 3.10 g/cc or more. (e) The average particle diameter of the microstructure is 3 to 15 μm 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 20 low-temperature α crystals in the raw material silicon carbide powder.
2. The method according to claim 1, wherein the resulting silicon carbide sintered body contains 5% by weight or less of high-temperature α crystals.