JP2812546B2 - Ceramics molded body and method of manufacturing ceramics molded body - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a ceramic molded body and a method for producing a ceramic molded body, and more particularly, to a main raw material such as silicon nitride or silicon carbide and a sintering aid. By baking and heat-treating the raw material powder comprising the additives of the above, a strong whisker single crystal having a shape such as a hexagonal columnar crystal having a different size is grown in the ceramic molded body, thereby increasing strength and toughness. The present invention relates to a ceramic molded body capable of obtaining an excellent ceramic molded body and a method for producing the same.

[Prior art] Conventionally, excellent corrosion resistance and heat resistance of ceramic molded bodies containing covalent bonding compounds silicon carbide and silicon nitride have been noticed, and in particular, use under severe conditions in high-temperature gas is inevitable. There is an increasing interest in the use of internal combustion engines for structural materials and component materials.

Therefore, it has been desired for a long time to provide the ceramic molded body with high strength and high toughness so that the ceramic molded body can be used as a structural material and a component material of an internal combustion engine.

For example, Japanese Patent Application Laid-Open No. 59-54675 discloses a "method for producing a fiber-reinforced silicon carbide sintered body". That is, according to this technical idea, a whisker generator that becomes whiskers by heat treatment in granular form is used as the raw material powder and sintering aid without mixing the granular raw material powder and the sintering aid with the fibrous whiskers. After mixing and forming into a predetermined shape, the formed body is heat-treated at a temperature of 1300 ° C. or more, preferably 1500 ° C. to 1750 ° C., in a non-oxidizing atmosphere having a partial pressure of nitrogen gas. As a result, fibrous whiskers are formed in the molded body from the mixed granular whisker forming agent, and thereafter, the temperature is further increased, and densification and sintering are performed in a non-oxidizing atmosphere, whereby the fiber-reinforced silicon carbide firing is performed. It is to get the union.

[Problems to be Solved by the Invention] However, in the method for producing a fiber-reinforced silicon carbide sintered body according to the conventional technique, since fibrous whiskers are generated in the ceramic molded body, the orientation in the same direction is reduced. Even when the whiskers have entanglement and twisting of the whiskers, mutual physicochemical interference occurs, and as a result,
It turned out that it was difficult to see a dense and defect-free ceramic molded body with good reproducibility. That is, according to this conventional technique, the ceramic molded body defines a defect having a void of several μm to several tens μm, and sometimes several hundred μm.

By the way, since ceramics are brittle, they have high notch sensitivity, and when actually using ceramic molded bodies, defects are limited to at most 30 μm, preferably
It is required that the thickness be 10 μm or less. Further, a technical idea of confirming the presence or absence of the defect without destroying the ceramic molded body and excluding the defect from the ceramic molded body has not been disclosed yet.

Therefore, in actual use of the ceramic molded article by the manufacturing method according to the technical idea disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 59-54675, the safety factor is largely estimated and limited to only a portion having a very small working stress. Can only be used. That is, it is hard to say that the purpose of imparting high toughness and high strength to the ceramic molded body has been completely achieved.

In addition, as a general means for improving the strength, a method of suppressing grain growth using a raw material powder which is extremely finely adjusted to generate fine crystals in a ceramic molded body, for example, a so-called nanocomposite is adopted. Have been. According to the above-described method, it is possible to improve the strength by substantially reducing the defect size and the number of defects.

However, in the above method, in order to obtain a finely adjusted raw material powder such as a nanocomposite, for example, a Si-CN composite powder, after adding ammonia to hexamethyldisilazane, a gas phase reaction is performed at 1000 ° C. Further, as is clear from the fact that the heat treatment must be performed at 1350 ° C. for 4 hours in nitrogen gas, there is a problem that the production cost rises because a complicated reaction step is required. Further, in order to mold ceramics by the above method, the method is limited to a molding method using hot pressing or a capsule method HIP, so that the shape of the obtained ceramic molded body is limited. Furthermore, the fracture toughness value that serves as a guide for toughness is K
_IC = 6 to 7.8 MPam _1/2 only, and it is hard to say that sufficient toughness was obtained.

In addition, as a general means to improve toughness,
The method of sintering and mixing whiskers in the raw material by adding 20 to 40% by weight is used, but the production cost rises,
For inconveniences such as limitation of the shape that can be formed and deterioration of the working environment due to whisker scattering into the atmosphere, the fracture toughness value is
K _IC = about 7 to 8 MPma _1/2 and its effect is not considered significant.

Therefore, an object of the present invention is to suppress the solid solution of impurities in a single crystal as much as possible in a ceramic molded body, high purity and a whisker-like shape having a shape of a plurality of hexagonal columnar crystals of different sizes. A ceramic compact having both high toughness and high strength by generating single crystal grains, forming a skeleton with large crystal grains among the crystal grains, and forming a filling structure that fills the gaps with small crystal grains. And a method for producing a ceramic molded body.

[Means for Solving the Problems] In order to solve the above problems, the present invention relates to a method for producing a sintered body containing at least one selected from the group consisting of silicon nitride (Si ₃ N ₄ ) and silicon carbide (SiC). And the minor axis length obtained by heat treatment is 0.1 μm or more and 0.6 μm or less, and the major axis length is 0.5 μm
a first crystal grain having a shape of not less than m and not more than 3 μm and an aspect ratio of not less than 5 and not more than 10, and at least one selected from the group consisting of silicon nitride (Si ₃ N ₄ ) and silicon carbide (SiC); The length of the minor axis obtained by sintering and heat treatment is 0.3 μm to 0.8 μm, the major axis is 4.0 μm to 7.0 μm, and the aspect ratio is 5 to 20.
A second crystal grain having the following shape, and containing one or more selected from the group consisting of silicon nitride (Si ₃ N ₄ ) and silicon carbide (SiC), and having a short diameter obtained by sintering and heat treatment. And a third crystal grain having a shape with a length of 0.8 μm or more and 4 μm or less, a major axis length of 8 μm or more and 20 μm or less, and an aspect ratio of 5 or more and 20 or less.

Further, the present invention relates to silicon nitride (Si ₃ N ₄ ) and silicon carbide (SiC).
Containing at least one selected from the group consisting of a plurality of crystal grains having different shapes obtained by sintering and heat treatment, and Al ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ , CeO ₂ , Si
_{O 2, Cr 2 O 3,} Dy 2 O 3, Sm 2 O 3, Nd 2 O 3, TiO 2, MgO, ZrO 2, H
at least one composition selected from the group consisting of fO ₂ and Ti, T
a, a method of producing a ceramic molded body containing at least one composition selected from the group consisting of carbides, nitrides, and carbonitrides of Cr and Zr, wherein the firing and heat treatment steps are performed at 1400 ° C. to 1550 ° C. A first step in which the temperature is maintained for 0.5 hours or more in the following temperature range, and a second step in which the temperature is increased and then maintained for 1 hour or more in a temperature range of 1600 ° C. or more and 1780 ° C. or less, and then the temperature is further increased A third step of maintaining the temperature in a temperature range of 1800 ° C. or higher and 1950 ° C. or lower for 0.5 hour or more, and a fourth step of lowering the temperature and maintaining the temperature in a temperature range of 1000 ° C. or higher and 1500 ° C. or lower for 0.5 hour or longer; It is characterized by consisting of.

[Specific Description of Configuration] The strength of the ceramic molded body depends on the bonding strength of crystal grains, and is determined by the defect size and defect distribution. For example, in the fracture strength σ _{f which} is a guide of the strength, Y: Coefficient depending on defect shape C: Defect size K _IC : Fracture toughness value, and the relationship is shown. The fracture toughness value K _IC described in the above formula is a guideline indicating toughness, and is defined as follows.

r: surface energy of fracture E: Young's modulus of the material Note that r described in the above equation is defined as follows.

r = Sr ₁ + r ₂ + r ₃ + r ₄ r ₁ : fracture energy when completely cracked flat S: shape factor r ₂ : plastic deformation energy at crack tip r ₃ : energy such as sound light consumed at fracture r ₄ : Energy consumed by intentionally introduced.From the factors shown in the definition of the fracture strength and fracture toughness and the relationship between the above two formulas, to improve the strength and toughness It is desirable that the crystal grains themselves be formed firmly and that the crystal grains be firmly bonded to each other so as to reduce the defect size, thereby increasing the surface energy of destruction.

That is, actually, by growing crystal grains into a whisker-like shape, which is a single crystal, an increase in apparent fracture energy due to a whisker pulling effect or a crack branching effect leads to an increase in strength and toughness. I can do it.

By the way, the whisker grows substantially as a single crystal, and its strength reaches 350 kgf / mm ^2. Therefore, it can be determined that the whisker is a strongly formed crystal grain.

Therefore, in the examples according to the present invention, basically, three types of whisker-like single crystals having different sizes are grown by firing to form crystal grains having a shape, and are used as main constituent particles of the ceramic molded body.

In addition, not adding the whisker-shaped crystal grains at the raw material stage, such as entanglement of whiskers and anisotropy due to orientation, mutual physicochemical interference, it is not possible to obtain a dense molded body or defects occur This is for avoiding the problem and facilitating the removal of the binder and the decomposition and removal of impurities. As a result, it becomes possible to grow main constituent particles composed of whisker-like crystal grains of a desired shape and size in the ceramic molded body.

In the examples according to the present invention, the main constituent particles composed of the whisker-like crystal grains were grown in three different sizes. As a result, the third crystal grains composed of the large-diameter whiskers form a basic skeleton, and the second crystal grains composed of the medium-diameter whiskers form a secondary skeleton between the basic skeletons. Since the first crystal grains composed of the small-diameter whiskers fill the space between the whiskers and the medium-diameter whiskers, the filling property, that is, the density per fixed volume is significantly increased, and at the same time, the gap is significantly reduced.

Further, due to the improvement of the filling property, the defect size is reduced from 1/20 to 1/100 as compared with the conventional example using whiskers having the same diameter as main constituent particles.

Furthermore, due to the improvement of the filling property, the bonding force between the whiskers increases, and more than doubles as compared with the conventional example.

In the toughness, the third whiskers made of large diameter whiskers were used.
Due to an increase in apparent fracture energy of crystal grains, a whisker pull-out effect, a crack branching effect, and the like, toughness twice or three times that of the conventional example can be achieved.

Next, the shapes of the first to third crystal grains and their mutual relationship will be described.

The first crystal grains composed of small-diameter whiskers grown by sintering in a ceramic compact have a minor axis of 0.1 μm or more.
0.6 μm or less, the major axis is 0.5 μm or more and 3 μm or less, it is possible to be composed of a whisker-like single crystal in the range where the aspect ratio is 5 or more and 10 or less, more preferably the minor axis is 0.2 μm or more 0.4 μm or less, major axis 1 μm or more and 2 μm
Hereinafter, it is composed of a whisker-like single crystal having an aspect ratio of 5 or more and 10 or less.

The second crystal grains composed of medium diameter whiskers have a minor axis of 0.3μ.
m or more and 0.8 or less, a major axis of 4 μm or more and 7 μm or less, and a whisker-like single crystal having an aspect ratio of 5 or more and 20 or less, and more preferably a minor axis of 0.5 μm or more and 0.8 μm or less. μm or less, major axis 4μm or more and 6μ
m and a whisker-like single crystal having an aspect ratio of 5 or more and 20 or less.

The third crystal grains composed of large diameter whiskers have a minor axis of 0.8.
μm or more and 4 or less, a major axis of 8 μm or more and 20 μm or less, and a whisker-like single crystal having an aspect ratio of 5 or more and 20 or less, and more preferably a minor diameter of 1.4 μm or more and 3.7 μm or less. μm or less, major axis 7μm or more and 8μ
m and a whisker-like single crystal having an aspect ratio of 5 or more and 20 or less.

The second crystal grains have grown by a factor of 2 to 6 times the volume of the first crystal grains, and the third crystal grains have grown by a factor of 3 to 20 times the first crystal grains. .

If the first to third crystal grains deviate from the above range, voids are generated, resulting in a decrease in strength and toughness, and inconveniences such as a decrease in mixing ability and scattering due to deterioration of fluidity, and This leads to difficulties in the handling of raw materials, and causes a rise in raw material prices. Therefore, the shape of the size of the first to third crystal grains is limited to the above range.

Further, in the first to third crystal grains, the composition ratio between each crystal grain in the minor axis direction and the major axis direction from the filling state is as follows, where the minor axis of the first crystal grain is 1 in the minor axis. The first crystal grain: the second crystal grain = 1: 1.5-3 The ratio of the first crystal grain: the third crystal grain = 1: 4-7 is obtained. One crystal grain: second crystal grain = 1: 4 to 6 First crystal grain: third crystal grain = 1: 7 to 10

If the composition ratio of the first to third crystal grains deviates from the range of the composition ratio, voids are generated as the crystal grains grow, so that strength and toughness are reduced. Therefore, the range of the composition ratio of each of the first to third crystal grains is limited to the above range.

Further, in the first to third crystal grains, the volume ratio of each crystal grain from the filling structure and the filling curve is as follows: the first crystal grain is 20 v / v% or more and 75 v / v% or less, the second crystal grain is 20 v / v%. Not less than 40 v / v% Third crystal grain is in the range of not less than 5 v / v% and not more than 40 v / v%.

If the first to third crystal grains deviate from the above range, it becomes practically impossible to include desired crystal grains in the ceramic molded body unless whiskers are added at the raw material stage. Therefore, the volume ratio of the first to third crystal grains is limited to the above range.

In addition, the first ceramic body after firing
From 30% by weight to 98% by weight of the total of the third to third crystal grains
The remainder in the range of not more than% by weight is occupied by a complexing agent comprising a sintering aid and an additive for suppressing crystal growth. In the above range, when the weight ratio is 30% by weight or less, a large improvement in physical properties cannot be expected, and when the weight ratio is 98% by weight or more,
Since it is not fired sufficiently densely, it contains voids and defects. Therefore, the weight ratio occupied by the total of the first to third crystal grains in the fired ceramic molded body is limited to the above range.

By the way, silicon nitride (Si
₃ N ₄ ) and silicon carbide (SiC) are covalent substances having a very strong covalent bond between atoms, so they are difficult to fire, and in order to obtain a dense sintered body, Use is essential. In addition, since the sintering of the nitride is performed at a high temperature through the interface by forming a liquid phase and a glass phase at the interface of the nitride particles, the additive is used to form the liquid phase or the glass phase. It is composed of a sintering aid for promoting sintering and a crystallization inhibitor for suppressing crystallization of the liquid phase and the glass phase. Therefore, in the ceramic molded body, Al ₂ O ₃ , Y ₂ O ₃ , La _{2
O 3, CeO 2, SiO 2} , Cr 2 O 3, Dy 2 O 3, Sm 2 O 3, Nd 2 O 3, TiO 2,
It contains oxides such as MgO, ZrO ₂ and HfO ₂ singly or in combination, and further contains oxides such as Ti, Ta, Cr and Zr, nitrides, carbonitrides and the like.

The first to third crystal grains are made of silicon nitride or silicon carbide, but it is also possible to form a solid solution of some oxides.

The ceramic molded body needs to be extremely densely fired in order to eliminate voids and defects. Therefore, the first to third crystal grains need to be grown into a shape composed of hexagonal columnar whiskers. . This is because, as shown in FIG. 1a, the hexagonal columnar whiskers are composed of flat surfaces, so that gaps between the crystal grains are less likely to be generated as compared with the circular or other crystal grains shown in FIG. 1b. This can be easily understood.

Therefore, in order to surely obtain hexagonal columnar crystal whiskers, it is necessary to suppress solid solution and to strictly control the heating pattern and the blending of additives.

When sialon or Ce ₅ Si ₃ O ₁₂ N is used as a raw material, it is difficult to grow crystal grains into hexagonal columnar whiskers. The use of sialon and Ce ₅ Si ₃ O ₁₂ N must be avoided because the shape becomes close to that of, and anxiety of including defects and extremely reducing the strength becomes apparent.

Examples Next, preferred examples of the ceramic molded body according to the present invention and the method for manufacturing the ceramic molded body will be described.
This will be described in detail below with reference to the accompanying drawings.

First, a ceramic molded body serving as a test specimen to be subjected to various tests in this example was produced by the method for producing a ceramic molded body according to the present invention.

As a raw material, silicon nitride (Si ₃ N ₄ ) 89 with an average particle size of 0.8 μm
Aluminum oxide (Al ₂ O ₃ ) with weight%, average particle size 0.4 μm
Yttrium oxide (Y
₂ O ₃ ) 4% by weight, dysprosium oxide (Dy ₂ O ₃ ) having an average particle size of 1.0 μm 2% by weight, cesium oxide (CeO ₂ ) having an average particle size of 1.2 μm 1% by weight, lanthanum oxide having an average particle size of 1.5 μm (L
a ₂ O ₃ ) Each was weighed so as to be 1% by weight, water was added, and the mixture was mixed using a ball mill to make a raw material slurry.

Next, the slurry-like raw material was processed by slip casting to obtain a plate-like molded body having a shape of 40 × 20 × 100 mm.

After drying and degreasing the plate-like molded body, the molded body was sintered according to the firing pattern shown by the solid line 10 in FIG. 2 to obtain a ceramic molded body.

In addition, a ceramic molded body as a specimen used as a comparative example in various tests in this example was produced according to a conventional method of the related art. As a raw material of a test sample as a comparative example, the same material as the test sample was used, and its plasticity was 89% by weight of silicon nitride (Si ₃ N ₄ ) and aluminum oxide (Al ₂ O ₃ ).
Each was weighed so as to be 5% by weight and 6% by weight of yttrium oxide (Y ₂ O ₃ ), and a molded body was obtained using the same molding method as the test specimen, dried, and degreased. Firing was performed in the firing pattern shown by the dashed line 12 in FIG. 2 to obtain a ceramic molded body.

Experimental Example 1 A strength test was performed using the test specimen and the comparative specimen. The number of tests for each was 30 cases, and processing such as surface roughness and chamfering for each test specimen and comparative example specimen was JISR1601
According to. The density was measured by Archimedes' method and the bending strength was measured as span 30 mm.

The test results are shown in FIG. As can be easily understood from the test results, the strength, toughness, bending strength,
In any of the physical property values, the test specimen, that is, the ceramic molded article according to the present invention has a property value superior to that of the comparative specimen, that is, the ceramic molded article manufactured according to a conventional method of the related art. I was able to judge.

Experimental Example 2 The surfaces of the test specimen and the comparative specimen were mirror-finished, and defects in the surface and cross-sectional directions were observed using an optical microscope and an electron microscope (SEM).

The results are shown in FIGS. 4a and 4b. FIG. 4a
Is an observation result using an optical microscope in the range of the investigation area of 40 × 100 mm ^{2 in the} surface direction and 40 × 20 mm ^{2 in} the cross section direction.
FIG. 4b shows the peripheral part where the maximum defect was observed by observation with an optical microscope, using a SEM, and a visual field area of 20 mm diameter (10 ² π mm ² ).
This is the result of observation.

Test specimens for observation using any microscope,
That is, it was easily understood that the shape of the defect was smaller in the ceramic molded body according to the present example than in the comparative sample, that is, the ceramic molded body according to the conventional method. From this, it was determined that the ceramic molded body according to the present example was less likely to form a defect and was fired densely.

Experimental Example 3 The test specimen and the comparative specimen were 25% HNO ₃ and HF 10
% Of the mixed solution for 4 hours, and the particle size distribution was observed by SEM.

FIG. 5A is a graph showing the observation results of the test specimen, and FIG. 5B is a graph showing the observation results of the comparative specimen as the frequency of the particle size distribution.

According to the observation using the SEM, the constituent grains of the test specimen were observed as single crystals composed of hexagonal columnar whiskers having three different sizes as shown in the graph of FIG.
The surface was also visible.

And among the three types of hexagonal columnar whiskers,
The third crystal grains composed of the large diameter whiskers form a basic skeleton, the second crystal grains composed of the medium diameter whiskers form a secondary skeleton between the basic skeletons, and the large diameter whiskers and the medium diameter whiskers are further formed. The first crystal grains made of small-diameter whiskers are filled in between.

On the other hand, the constituent particles of the comparative sample were needle-like or rod-like, and the surface could not be visually recognized. From this, it is determined that the additive of the grain boundary layer forming material has a large solid solution in the growing particles and a large intragranular fracture in the comparative sample.

The following items were determined from Experimental Examples 1 to 5.

That is, by growing the main constituent particles consisting of single crystal grains of hexagonal columnar whiskers into three different sizes, the third crystal grains consisting of large diameter whiskers form the basic skeleton, and the basic skeleton The second crystal grains composed of medium-diameter whiskers form a secondary skeleton in between, and the first crystal grains composed of small-diameter whiskers are further filled between the large-diameter whiskers and the medium-diameter whiskers. That is,
The density per volume was significantly increased, while the gaps could be significantly reduced. Further, due to the improvement in the filling property, the defect size is 1 / compared to the comparative example according to the related art.
It was reduced from 20 to 1/100.

Furthermore, in the toughness, the toughness is twice to three times as large as that of the comparative example due to the reduction of the apparent fracture energy of the third crystal grains composed of the large diameter whiskers, the effect of pulling out the whiskers, the effect of crack branching, and the like. Was done.

Experimental Example 4 The compositions of silicon nitride (Si ₃ N ₄ ), silicon carbide (SiC), and the remaining additives, which are the main components of the crystal grains, were adjusted as shown in the table of FIG. Was fired according to the sintering temperature pattern to obtain a ceramic molded body. In addition, the manufacturing method of the plate-shaped molded body, the method of drying and the degreasing treatment were the same as those in Experimental Example 1, and the firing was performed in a nitrogen atmosphere.

After firing, the composition ratios of the first to third crystal grains grown in the ceramic molded body were as shown in the table of FIG.

Regarding various physical property values of the fired ceramic molded body, the results shown in the table of FIG. 8 were obtained.

If the composition of silicon nitride (Si ₃ N ₄ ) and silicon carbide (SiC), which are the main constituents, is 98% by weight or more based on the composition ratio and physical properties of the first to third crystal grains, the ceramic molded body will have a sufficient content. Densification is not achieved, and the intended growth of crystal grains cannot be achieved. Therefore, since many voids and defects are included, the strength is weak and the toughness is so small that the measurement of the fracture toughness value is difficult. When the composition is 30% by weight or less, the crystal grains tend to grow into spheres, which makes it difficult to grow hexagonal columnar whiskers. Therefore, the shape of the crystal grains promotes the formation of voids and defects, resulting in a decrease in strength and toughness. That is, when forming the composite material by increasing the additive, it can be understood that the additive is dissolved in the crystal grains.

[Effects of the Invention] As described above, according to the ceramic molded body and the method of manufacturing the ceramic molded body according to the present invention, crystals are firmly formed during the firing process without adding whisker-shaped crystal grains at the raw material stage. The main constituent particles composed of whisker-like single crystal grains of hexagonal columnar crystals to be formed are grown to three different sizes, and a basic skeleton is formed in the crystal grains composed of large diameter whiskers, and a medium diameter is formed between the basic skeletons. A skeleton is formed secondarily on the crystal grains made of whiskers, and the space between the large diameter whiskers and the medium diameter whiskers is filled with crystal grains made of small diameter whiskers. As a result, the strength and toughness can be remarkably improved, and the number of defects and the size of the defects can be reduced, so that stress concentration can be reduced,
Further, it has an effect of slowing down the notch sensitivity.

In addition, this has the effect of improving the safety factor and the durability.

[Brief description of the drawings]

FIG. 1a is a schematic diagram showing a sintered state of a ceramic molded body according to the present invention, FIG. 1b is a schematic diagram showing a sintered state of a ceramic molded body according to the prior art, and FIG. FIG. 3 is a graph showing firing patterns of a preferred embodiment and a comparative example according to the ceramic molded body and the method of manufacturing the ceramic molded body. FIG. 3 is a table showing test results of Experimental Example 1 among the preferred embodiments according to the present invention. 4a and 4b are tables showing test results of Experimental Example 2 among preferred embodiments according to the present invention, and FIGS. 5a and b are Experimental Tables 3 among preferred embodiments according to the present invention. FIG. 6 is a table showing the composition of the ceramic molded body of Experimental Example 4 among preferred examples according to the present invention, and FIGS. 7 and 8 are graphs showing the present invention. In a table showing test results of Experimental Example 4 among preferred examples according to is there. 10: firing pattern of the embodiment 12: firing pattern of the prior art

Claims (5)

(57) [Claims] 1. A material containing at least one member selected from the group consisting of silicon nitride (Si ₃ N ₄ ) and silicon carbide (SiC), wherein the length of the minor axis obtained by sintering and heat treatment is 0.1 μm to 0.6 μm. Hereinafter, selected from the group consisting of a first crystal grain having a shape with a major axis having a length of 0.5 μm or more and 3 μm or less and an aspect ratio of 5 or more and 10 or less, and silicon nitride (Si ₃ N ₄ ) and silicon carbide (SiC). The major axis length obtained by sintering and heat treatment is 0.3 μm or more and 0.8 μm or less, the major axis length is 4.0 μm or more and 7.0 μm or less, and the aspect ratio is 5 or more and 20 or less. Containing at least one selected from the group consisting of silicon nitride (Si ₃ N ₄ ) and silicon carbide (SiC), and having a minor axis length of 0.8 obtained by sintering and heat treatment. μm or more and 4 μm or less, length of major axis is 8 μm or more and 20 μm or less, and aspect ratio is 5 or more and 20 or less. A ceramic molded article comprising: a third crystal grain; 2. The ceramic compact according to claim 1, wherein said crystal grains have a composition range of 30% by weight or more and 98% by weight or less, and Al ₂ O ₃ , Y ₂ O ₃ , La
₂ O ₃ , CeO ₂ , SiO ₂ , Cr ₂ O ₃ , Dy ₂ O ₃ , Sm ₂ O ₃ , Nd ₂ O ₃ , Ti
O ₂ , MgO, ZrO ₂ , one or more compositions selected from the group consisting of HfO ₂ and Ti, Ta, Cr, one or more compositions selected from the group consisting of carbides, nitrides and carbonitrides of Zr A ceramic molded article characterized by containing a composition. 3. The ceramic molded body according to claim 1, wherein the crystal grains are whisker-like single crystals having a shape such as a hexagonal columnar crystal. 4. The ceramic compact according to claim 1, wherein the volume ratio of the first crystal grains, the volume ratio of the second crystal grains, and the volume ratio of the third crystal grains is 100 v / v.
%, The first crystal grains occupy a volume ratio of 20 v / v% to 75 v / v%, the second crystal grains occupy a volume ratio of 20 v / v% to 40 v / v%, and the third crystal grains A ceramic molded body characterized in that grains occupy a volume ratio of 5 v / v% or more and 40 v / v% or less. 5. A plurality of crystal grains having at least one selected from the group consisting of silicon nitride (Si ₃ N ₄ ) and silicon carbide (SiC) and having different shapes obtained by sintering and heat treatment; Al ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ , CeO ₂ , SiO ₂ ,
Cr ₂ O ₃ , Dy ₂ O ₃ , Sm ₂ O ₃ , Nd ₂ O ₃ , TiO ₂ , MgO, ZrO ₂ , HfO ₂
One or more compositions selected from the group consisting of: Ti, Ta,
In a method for producing a ceramic molded body containing at least one composition selected from the group consisting of Cr, Zr carbide, nitride and carbonitride, the steps of firing and heat treatment are performed at a temperature of 1400 ° C to 1550 ° C. A first step of maintaining the temperature in the temperature range for 0.5 hour or more; and a second step of maintaining the temperature in a temperature range of 1600 ° C. or more and 1780 ° C. or less for 1 hour or more. A third step of maintaining the temperature in a temperature range of 1800 ° C or more and 1950 ° C or less for 0.5 hours or more;
A fourth step of holding for 0.5 hours or more;