JPS63206353A - Novel manufacture of silcion 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 have expanded uses 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, there have been several patents proposed regarding sintering methods for silicon carbide, including the following two U.S. patents and U.S. patents that use boron and carbon as sintering aids. Japanese patent applications corresponding to this can be cited, namely: (1) U.S. Patent No. 4,004,934,
7-32035) (2) U.S. Patent No. 4,321.954, (Equity [5
9-34147) Method (1) uses 0.3 to 3
．． After adding and mixing a boron compound in an amount equivalent to 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 molded and placed in an inert atmosphere. In this method, a silicon carbide sintered body is obtained by heating to a high temperature of 1900 to 2100° C. without applying 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 crystalline form, that is, the crystalline form of silicon carbide in the starting material silicon carbide powder is the same as the crystalline form in the final sintered body. This is a method of obtaining a silicon carbide sintered body by keeping the ratio essentially the same.

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 the problem of low mechanical strength and too large variations in strength for applications that require large mechanical loads such as gas turbines for automobiles. This is an obstacle to industrial 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 (a) to (
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) Fewer and smaller defects are included in the sintered body (b)
) The particle size of the single particles constituting the sintered body is small.

(c) There are no specifically grown coarse particles with a diameter exceeding 0μ 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 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. 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 the particle shape refers to the fact that the particle shape has three-dimensional anisotropy, such as plate-like or rod-like shape.It goes without saying that the sintered body as a whole can be It is necessary that the particles have no orientation.

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 of the present inventors, the method (1) described above The method (method disclosed in Japanese Patent Publication No. 57-32035) cannot overcome the drawback that coarse particles are likely to be generated, and the method (2) (method disclosed in Japanese Patent Publication No. 59-34147) cannot overcome the drawback that coarse particles are likely to be generated.
However, there is a problem that a single particle of the sintered body has no anisotropy (and a sintered body with high strength cannot be obtained).

Furthermore, recently, the sintered bodies obtained by the non-pressure methods of (1) and (2) have been subjected to HIP (Hot l5ostatic) process.
We have also developed a method of heating the sintered body to around 2000°C in an inert gas atmosphere of several thousand atmospheres to reduce the internal defects contained in the sintered body and make it denser (for example, the 3rd press). This method is effective in reducing internal defects in a sintered body by heating the surface of the sintered body while pressurizing it with high-pressure gas. This is a great method. However, in the case of a sintered body with many defects, the high pressure gas permeates into the inside of the sintered body and the densification effect is difficult to appear.According to the experiments conducted by the present inventors, It has been found that a density of 3.05 g/cc or more is desirable.

The method (1) above has the disadvantage that coarse particles are generated before the sintered body density reaches 3.05 g/cc,
In method (2), anisotropy does not occur in the particle shape even if the old P treatment is performed.

(Basic idea) The present inventors aimed to obtain a silicon carbide sintered body with high mechanical strength (and small variation in mechanical strength), and the microstructure of the particles constituting the sintered body was used as a guideline for achieving this goal. As a result of intensive studies with the goal of obtaining a sintered body that satisfies all of the conditions (a) to (d) that have been proposed by It has been found that by specifying the above, a microstructure satisfying the conditions (a) to (d) above can be obtained with good reproducibility, and furthermore, (a)
It was confirmed that the sintered bodies having the microstructures under the conditions of ) to (d) actually have high mechanical strength and small variations in mechanical strength, and the present invention was completed.

(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 of carbon 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 silicon carbide powder are as shown below (a) and (b).
, (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) and once heated in an inert gas atmosphere to a temperature range such that the α crystal content in the silicon carbide powder does not exceed 5% by weight, and the following conditions (d) and (e) are satisfied. Obtain a sintered intermediate that: (d) has a density of 3.05 g/cc or more.

(e) The crystal form must contain 95% by weight or more of β crystals and 5% by weight or less of α crystals.

(3) After that, it is heated to 1800-2000°C in an inert gas atmosphere of 100 atmospheres or more, and the next step (
A novel method for producing a silicon carbide sintered body, which comprises obtaining a sintered body characterized by the properties of (g) and (h).

(f) The density of the sintered body is 3. Must be more than Log/cc.

(g) The average grain size of the microstructure is 3 to 15 μm and the asvect ratio is 5 to 20.

(h) The crystal form must contain 50% by weight or more of β crystals and less than 50% by weight 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 0.2 μ, the density of the silicon carbide sintered body obtained is 3.10 g/cc.
If ρ is less than 0.1H, this is because the driving force for sintering is too large or coarse particles are likely to be generated in the sintered body. It is not possible to achieve the goal.

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 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 the silicon carbide powder contains 80% or more of β crystals and low temperature α crystals (2H). 20% or less of low-temperature α-crystals (20% by weight) means that 20% or less of crystal forms, most of which undergo a phase transition to β-crystals during sintering, are included. The reason is that the particles of the sintered body have anisotropy (
This is based on the experimental findings of the present inventors that the aspect ratio (expressed in terms of aspect ratio) occurs. Further, the content of high-temperature type α crystals (48, 68, 15R) contained in the silicon carbide powder is preferably about a trace 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 finely pulverizing the silicon carbide produced.

(b) A silicon compound such as SiH4, St (CHa) a and a carbon compound such as CH4°CJi are combined at 120%
A method of producing silicon carbide by introducing it into a plasma atmosphere heated to 0°C or higher 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 that coexists with particles, and (b)
The powder obtained by this method has a single particle size of about 0.1H, but the particles are tightly agglomerated, and it appears to be a powder with a large upper particle size and a wide particle size distribution. be. 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.

The silicon carbide powder and the sintering aid can be mixed using a ball mill or the like, but for that purpose it is desirable to mix the sintering aid with the silicon carbide powder as uniformly as possible. has a specific surface area of 3
A fine powder of nf/g or more is preferable. As boron compounds, BaC, BN, BP, AIB
Examples include z.

In addition, as a method for adding elemental carbon, hydrocarbons with relatively high carbon content, such as phenol-formaldehyde condensates, resorcinol-formaldehyde condensates, glycerin, tar pitch, furan resins, etc., can be added to water or toluene, acetone, ethanol, etc. Dissolve in the solvent of
This is added to the silicon carbide powder mixed with a small amount of elemental boron or boron compound powder, mixed in a wet state using a ball mill, etc., then the water or solvent is removed by drying, and then the inert gas at 500 to 600°C is added. This can be carried out by heating in an atmosphere to carbonize the hydrocarbon.

As another method of adding elemental carbon, it is also possible to use finely powdered elemental carbon itself. In this case, carbon black, acetylene black, etc. with a specific surface area of 30rd/g or more is used as the elemental carbon to achieve a more uniform mixture. In order to get
It is preferable to add water or an organic solvent such as methanol or ethanol and mix the mixture wet using a ball mill, vibration mill, etc. This is a method in which water or an organic solvent is added and mixed, and then the water or organic solvent is removed by evaporation.

The thus obtained silicon carbide powder containing a small amount of sintering aid is then molded into a desired shape and then heated with an inert gas such as argon, helium, nitrogen, etc. at about atmospheric pressure or below atmospheric pressure or under vacuum. By heating in a gas atmosphere, a sintered intermediate having a density of 3.05 g/cc or more and containing 95% by weight or more of β crystals and 5% by weight or less of α crystals can be obtained.

Here, the heating temperature is basically α in the silicon carbide fine powder.
It is required to maintain the temperature within a range such that the crystal content does not exceed 5%, but usually this heating temperature is 185%.
A temperature in the range of 0 to 2,000"C is generally good. However, it is more preferable to select the appropriate temperature depending on the physical properties of the silicon carbide powder. According to the experimental findings of the present inventors, the heating temperature should be set at a density of 3. In order to prevent the generation of coarse particles in the sintered intermediate, it is preferable to set the temperature between the minimum temperature required to reach .05 g/cc (hereinafter referred to as Ts) to Ts + 50°C. Experiments conducted by the present inventors According to our findings, there is a positive correlation between (standard deviation of particle size) /ρ and Ts of silicon carbide powder, as shown in Figure 12 of the attached drawings, and powders with narrow particle size distribution have lower There is a tendency for the density to reach 3.05 g/cc at a certain temperature.The α crystal in this sintered intermediate means the sum of both the low-temperature type and the high-temperature type.

Next, in the present invention, the sintered intermediate having the predetermined characteristic values obtained as described above is heated in a sufficiently high pressure inert gas atmosphere such as argon, helium, nitrogen, etc.
The desired sintered body can be obtained.

Here, the pressure of the inert gas is at least 100 atmospheres or more,
More preferably, the pressure is 500 atmospheres or more.

Although it is not necessary to particularly set an upper limit of the pressure, setting it to 10,000 atmospheres or more is less effective considering the increase in equipment costs.

As mentioned above, the heating temperature is 1800-2000°
A range of C is generally good, but in consideration of the above Ts, it is more preferable to set it in a range of Ts-50 to Ts+50°C.

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. Namely: First of all, the density of the sintered body is 3. Log/cc or more, and secondly, the average grain size of the microstructure is 3 to 15 μ and the aspect ratio is 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 performed by smoothing the surface of the sintered body and The particle diameter is determined from an image magnified (usually 100 to 1000 times) with a microscope, and the particle diameter is the average value of the maximum length (L) and minimum length (D) of each particle in this image. The diameter is the arithmetic mean value of particle diameters, and the aspect ratio is the arithmetic mean value of L/D. 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 β crystals and 20% or less 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 the silicon carbide powder is sintered under the conditions described above, the high-temperature α crystals are 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 it is clearly higher in strength than the conventional sintered body (and its variation is small, and the fracture toughness is It was confirmed that the value (Lc) 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.

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

(b) Since an easily sinterable raw material powder is used, the sintering temperature is 1
It is possible to reduce the temperature to 900 to 2050°C, which is lower than the conventional temperature, thereby suppressing enlargement of the sintered particles.

(c) In the sintering process, the sintered particles pass through a sintered intermediate containing 5% or less of α crystals, so that 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 of the quality shown in Table 1 was used in the non-experimental examples and comparative examples.

Powders 1 to 3 in Table 1 were prepared using the method previously proposed by the present inventors in JP-A-59-83922, in which 5iC1n was added as a silicon compound in a flame obtained by burning hydrogen with air. , 33.6% stag and 66.3% obtained by simultaneous injection of C9 fraction as carbon compound.
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.
Heating to 0℃, 1800℃, 1900℃, following (1)
It is obtained by burning off excess carbon after producing silicon carbide according to the reaction formula shown in the formula.

SiO□+3C-+SiC+2GO・-・-・・・・・-
-----・(1) Powder 4 is SiH4, C)+4 and h
It is obtained by direct reaction of
0)) 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 1 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 proportion of crystal forms was determined by [crystal form determination method].

Transmission electron microscope images of Powders 1 and 4.5 are shown in FIGS. 1, 2, and 3, respectively, and FIG. 4 shows a powder X-ray diffraction image of Powder 1.

84C 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 120.5+ as a single carbon source
*"/g of carbon black and 50 cc of ethanol were added and mixed in a resin ball mill for 20 hours. The resulting mixture was heated to remove ethanol by evaporation, and 50 g of the powder was obtained. 0.5 in a cylindrical container
After being uniaxially compressed with a load of 7/c+1, it was rubber pressed and molded with a hydrostatic pressure of 2 T/cd. Table 2 shows the density of each powder compact obtained.

Next, these powder compacts were heated for 30 minutes at a temperature of 1900° C. in a nitrogen atmosphere under a vacuum of 10 −1 to I Torr to obtain a silicon carbide sintered intermediate. Table 2 shows the density and crystal form of the obtained sintered intermediate. The Ts (minimum temperature necessary for the density to reach 3.051/cc) of each powder compact was the value shown in Table 2.
Ts was determined by the method described in the section below.

Next, each of the sintered intermediates was heated at 1,880° C. for 30 minutes in a nitrogen atmosphere of 1,500 atmospheres to obtain a silicon carbide sintered body.

Table 2 shows the density, average grain size aspect ratio of the microstructure, and crystal shape of the obtained 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, KIC was measured using the Vickers indentation method using 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

The powder X-ray diffraction images of the sintered intermediate and sintered body obtained in Example 1 are shown in FIG. 5 and FIG. 6, respectively.

Table 2 This m21 A silicon carbide sintered intermediate was obtained using the powder 4.5.6 shown in Table 1, which does not meet the conditions specified in the present invention, by the same method and under the same conditions as in the example. . The density of the obtained sintered intermediates was measured, and as shown in Table 3, it was found that all the densities were significantly below the target value of 3.05 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 specified in the present invention, sintering conditions etc. were searched to increase the density of the sintered compact, and the results are shown in Table 4. A silicon carbide sintered body was obtained by changing the conditions to those shown (same conditions as in Examples except for the conditions listed in Table 4). As shown in Table 4, the density of the obtained sintered body can be increased by increasing the amount of B and C added for powder 4 (comparative example 4), and for powders 5 and 6 (comparative example 4). Example 5.6) It was found that the heating temperature could be increased by increasing the heating temperature. In addition, in the powder compact of Comparative Example 1 using Powder 4, in which the amount of 84G added was 0.25 parts, the density did not reach 3.051/cc even if the heating temperature was increased.

The sintered intermediates with a density of 3.05 g/cc or more obtained in Comparative Examples 4 to 6 were heated to the heating temperature shown in Table 5 in a nitrogen atmosphere of 1500 atm in the same manner as in the examples. hold for 30 minutes,
Next, the mechanical properties of these sintered bodies were measured in the same manner as in the examples, and the results in Table 5 were obtained. As shown by the numerical values in Table 5, It can be seen that the fine structure of any of the sintered bodies does not exhibit the physical property values targeted by the present invention, and the mechanical properties are also poor.

As a result, the sintered body density increased and the requirement (d) was satisfied, but in Comparative Examples 7 and 8, the average particle diameter was higher than the specified value, and in Comparative Example 9, 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, Example 1
-3, the average bending strength is low (and the standard deviation is large, and Kle is also low.

Table 5 Powder 2 and Powder 5, which have the same α-crystal content, were mixed at various ratios to prepare powders with different particle size distributions.

BaC and carbon black were added to these powders in exactly the same manner as in the examples, and then molded, and the Ts of each powder compact was measured as follows. A powder compact obtained from the same batch of mixed powder is heated in a vacuum of 10-1 Torr in a nitrogen atmosphere for 30 minutes, and after cooling, the density is measured. The heating temperature is increased from 1800°C in 10"C increments. The heating temperature at which the density reaches 3.05 g/cc is Ts. Thus obtained, Ts and (standard deviation of particle size)/ρ The relationship between the two is shown in Fig. 12. It can be seen from the figure that there is a positive correlation between the two.

Powder 2 and Powder 6 were mixed at various ratios to prepare powders with different crystal forms. B, C and carbon black were added to these powders in exactly the same manner as in the examples, and then molded, and heated under vacuum in the same manner as in the examples to obtain sintered intermediates. Next, these sintered intermediates were heated to 150 mm in the same manner as in the example.
A sintered body was obtained by heating under a pressure of 0 atm.

FIG. 13 shows the relationship between the α crystal content of the sintered intermediate obtained from these mixed powders and the aspect ratio of the fine structure of the sintered body. From the figure, 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.

After adding B, C and carbon black to Powder 1 and molding it in exactly the same manner as in Example, it was heated to 1800 to 1900 m
These sintered intermediates were heated at various temperatures of °C to obtain sintered intermediates with different densities.Next, these sintered intermediates were heated under a pressure of 1500 atm in exactly the same manner as in the example to obtain sintered bodies. . The relationship between the density of these sintered intermediates and the density of the sintered body is shown in FIG. From the figure, it can be seen that unless the density of the sintered intermediate is 3.05 g/cc or more, the density of the sintered body is difficult to reach 3.10 g/cc or more.

From the electron microscope images of silicon carbide powder shown in Figures 1 to 3, powder 1 (Figure 1) has a narrow particle size distribution with no secondary agglomeration, and powder 4 (Figure 2) has a narrow particle size distribution with no secondary agglomeration. It can be seen that powder 6 (Figure 3) has a relatively uniform single particle size but developed secondary agglomeration, and powder 6 (Figure 3) has no secondary agglomeration but has a wide particle size distribution. The following can be seen from the optical microscope images of the fine structure of the sintered body shown in FIGS. 7 to 9. In the sintered body of Example 1 (Figure 7), the particles are fine and anisotropic, whereas in Comparative Example 8 (Figure 8), the particles are anisotropic but coarse; 9
(Figure 9) shows that although the particles are fine, there is no anisotropy. Further, from the optical microscope images of the fine structure of the sintered intermediate shown in FIGS. 10 and 11, it is clear that the particles in Example 1 (FIG. 10) are fine and uniform, whereas the particles in Comparative Example 2 (FIG. 11) are fine and uniform.
Figure) shows that coarse particles with anisotropy are generated.

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

[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, many studies have been carried out in the past (
For example, various methods are described in Chapter 4 of "Powder Particle Size Measurement Method" published by the Powder Technology Research Association (published by Yokendo, 1962).

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%. A method using an ultrasonic disperser for several minutes is preferred.

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 upwards 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 the five diameters of the circular phase.

[Crystal form determination method]

Low-temperature α crystal (2H) contained in silicon carbide powder and sintered body
), β crystal (3C), high temperature α crystal (4H, 6H, 15
Quantification of R) is carried out using a monochromator using CuKα radiation as a light source.
The method of calculating each component from the height of each peak of the 0 figure obtained from the figure obtained by powder X-ray diffraction method using a powder on the receiving side is described in Ceramics Association Journal, Gong, 576-582 (1979))
The method described in shall be followed. In addition, the sintered body is powder
When measuring by the linear diffraction method, the sintered body is pulverized into 100 meshes or less.

[Brief explanation of the drawing]

FIGS. 1 to 3 are photographs showing the state of particles of powders 1, 4, and 6 used in Examples and Comparative Examples of the present invention, respectively, taken with a transmission electron microscope. Both magnifications are 8000
It's double. FIG. 4 shows the powder X-ray diffraction pattern of Powder 1. FIGS. The diffraction pattern is shown. FIGS. 7 to 9 show Example 1, respectively. Comparative example 8. The 0 magnification of the photos taken with an optical microscope showing the fine structure of the surface structure of the cross section of the sintered body obtained in Comparative Example 9 is 500 times. FIGS. 10 to 11 show Example 1, respectively. The 0 magnification of the photos taken by an optical microscope showing the fine structure of the surface structure of the cross section of the sintered intermediate obtained in Comparative Example 1 is 150 times. FIG. 12 is a graph showing the relationship between Ts and (standard deviation of particle diameter/ρ). FIG. 13 is a graph showing the relationship between the high α content of the sintered intermediate and the aspect ratio of the microstructure of the crystal. FIG. 14 is a graph showing the relationship between the density of the sintered intermediate and the density of the sintered body. Patent applicant: Mitsui Toatsu Chemical Co., Ltd. Figure 1: Engraving of the drawings in Figure 2 - Engraving of the drawings in Figure 7 Figure 8: 1412I Procedural amendment (method) May 19, 1985 Commissioner of the Japan Patent Office Black 1) Akira Mr. Yu 1, Indication of the case Patent Application No. 39131 filed in 1988 2, Title of the invention: New manufacturing method for silicon carbide sintered body 3, Relationship with the case by the person making the amendment Patent address: Kasumigaseki, Chiyoda-ku, Tokyo 3-chome 2-5 name (31
2) Mitsui Toatsu Chemical Co., Ltd. 4. Number of inventions increased by amendment 0 7. Contents of amendment [Attachment] 4. Brief explanation of drawings Figures 1 to 3 show examples and comparative examples of the present invention. These are photographs taken with a transmission electron microscope showing the particle state of powders 1 and 4.6 used in
It is 0 times. FIG. 4 shows the powder X-ray diffraction pattern of Powder 1. FIGS. The diffraction pattern is shown. FIGS. 7 to 9 show Example 1, respectively. Comparative example 8. The zero magnification of the photos taken with an optical microscope showing the grain structure of the cross section of the sintered body obtained in Comparative Example 9 is 500 times. FIGS. 10 to 11 show Example 1, respectively. The 0 magnification of the photos taken with an optical microscope showing the grain structure of the cross section of the sintered intermediate obtained in Comparative Example 1 is 150 times. FIG. 12 is a graph showing the relationship between Ts and (standard deviation lρ of particle diameter). FIG. 13 is a graph showing the relationship between the α-crystal content of the sintered intermediate and the aspect ratio of the microstructure of the crystal. FIG. 14 is a graph showing the relationship between the density of the sintered intermediate and the density of the sintered body. (2) Figures 7 to 11 of the drawings are replaced with drawings without tally marks as shown in the attached sheet. that's all

Claims (4)

[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) and once heated in an inert gas atmosphere to a temperature range such that the α crystal content in the silicon carbide powder does not exceed 5% by weight, and the following conditions (d) and (e) are satisfied. Obtain a sintered intermediate that: (d) has a density of 3.05 g/cc or more. (e) The crystal form must contain 95% by weight or more of β crystals and 5% by weight or less of α crystals. (3) After that, it is heated to 1800 to 2000°C in an inert gas atmosphere of 100 atmospheres or more to obtain a sintered body characterized by the following properties (f), (g), and (h). A novel manufacturing method for silicon carbide sintered bodies, which comprises: (f) The density of the sintered body is 3.10 g/cc or more. (g) The average particle diameter of the microstructure is 3 to 15 μm and the aspect ratio is 5 to 20. (h) The crystal form must contain 50% by weight or more of β crystals and less than 50% by weight of high-temperature α crystals. (4) 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.