JP3005650B2 - Chemically modified silicon carbide ceramic powder and method for producing silicon carbide ceramic - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chemically modified silicon carbide ceramic powder for producing silicon carbide ceramics having excellent heat resistance and oxidation resistance, which is used in gas turbines for power generation and the like. And a method for producing a silicon carbide ceramic using the same, which can obtain a sintered body relatively easily and has no limitation on the shape, and relates to a method for adding an auxiliary agent in liquid phase sintering without pressure application It is.

[0002]

2. Description of the Related Art Silicon carbide ceramics are structural materials that are excellent in chemical stability, wear resistance and high-temperature strength.
It is used for materials such as gas turbines for power generation. Since silicon carbide ceramics have a strong covalent bond, a small diffusion coefficient, and are difficult to sinter, they hardly sinter even when a compact of pure silicon carbide powder is heated. Therefore, a sintering aid is generally added during sintering. By adding the sintering aid, the sintered body is densified and the strength can be improved. Usually, sintering is performed by hot pressing, but sintering without pressure has also been studied. Examples of pressureless sintering include solid phase sintering in which boron and carbon are added as assistants, and liquid phase sintering in which alumina and rare earth oxides are added as assistants.

There have been many attempts to introduce a metal or metal oxide into the skeleton or side chain of an organosilicon compound and then produce ceramics such as silicon carbide and silicon nitride. For example, Japanese Patent Publication No. 56-13645 proposes a method for producing a silicon carbide sintered body from an organosilicon polymer containing Si, B and O as main skeleton components and having a group containing C in a side chain. I have. Also, JP-B-57-38549
Then, there is a method of producing a silicon carbide ceramic from a material in which at least one element selected from B, Al, Fe, or Ti or a compound containing the same is chemically bonded to polycarbosilane, which is a kind of an organosilicon compound. Proposed. JP-A-57-22169 proposes a method for producing a heat-resistant ceramic sintered body by mixing a polycarbosilane partially containing a vanadio-siloxane bond (VO-Si) with a non-oxide ceramic powder. ing. In Japanese Patent Publication No. 59-10945, Si, B and O
There has been proposed a method for obtaining a heat-resistant ceramic sintered compact by mixing a semi-inorganic polymer containing, with a ceramic powder such as an oxide, carbide, nitride, boride, or silicide. Furthermore, Japanese Patent Application Laid-Open No. 60-151276 proposes a method of obtaining a silicon carbide sintered body from a homogeneously dispersed mixture of silicon carbide powder and an organometallic polymer containing silicon, carbon, boron and nitrogen as main components.

[0004]

In the prior art described above, sintering by hot pressing effectively applies pressure together with heat, so that sintering occurs effectively, but there is a problem that the shape of ceramics is limited. In this regard, pressureless solid-phase sintering does not have a problem of shape limitation and can be said to be a versatile technique. However, among pressureless sintering, boron,
Solid phase sintering by adding carbon as an auxiliary agent has a problem in that the temperature range for obtaining a dense sintered body is extremely narrow, and the conditions must be strictly controlled. On the other hand, in non-pressurized liquid phase sintering by addition of a composite oxide such as alumina, rare earth oxide, YAG (Y ₃ Al ₅ O ₁₂ ), or two or more oxides, non-pressurized solid phase The sintering conditions are relatively wide compared to sintering. However, in order to obtain a dense sintered body, it is necessary to add a certain amount or more of an auxiliary agent. At this time, there is a problem that the auxiliary component forms a second phase at the grain boundary, and this grain boundary phase causes grain boundary slip due to viscous flow at a high temperature. Grain boundary slip is a kind of plastic deformation, but it is a non-uniform deformation, so it causes stress concentration and causes a decrease in strength. Auxiliary components segregated at the grain boundary triple point pose a serious problem from the viewpoint of oxidation resistance.

In Japanese Patent Publication Nos. 56-13645 and 57-38549, since methods for producing silicon carbide ceramics only from an organic silicon compound, there are many portions that are removed during the formation of ceramics, and the yield is high. There is a problem in the point. JP-A-57-22169 discloses a VO-Si
Is a method of producing a heat-resistant ceramic sintered body by mixing a polycarbosilane partially containing non-oxide ceramic powder with a non-oxide ceramic powder. Difficult to get body. Also, even with the method of Japanese Patent Publication No. 59-10945, it is difficult to obtain a dense sintered body by pressureless sintering. Further, JP-A-60-151
In 276, a dense sintered body can be obtained even by pressureless sintering, but there is a problem that the sintering temperature requires a high temperature of 2100 ° C. or higher.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned prior art, and is capable of relatively easily obtaining a silicon carbide ceramic sintered body, and having no limitation on the shape. The present invention relates to a method of adding an auxiliary agent in liquid phase sintering by pressure. That is, the present invention provides a chemically modified polycarbosilane having a structure in which silicon is contained as a main component in a main chain of a basic skeleton, a hydrocarbon group is included in a side chain, and the basic skeleton has a structure crosslinked with a group containing a metal. Coating at least one selected from polysilazane or polysilane-based organosilicon compound on the surface of silicon carbide ceramic particles, followed by heat treatment to bond the organosilicon compound to the silicon carbide ceramic particles. And a chemically modified silicon carbide ceramic powder. Further, the present invention provides the above chemically modified silicon carbide ceramic powder, wherein the metal contains at least one of Al and rare earth elements. Chemically modified silicon carbide ceramic powder, characterized in that the amount of metal in the coating layer with respect to silicon is in the range of 3% to 10% in elemental ratio, and particles in which the crystal system of the silicon carbide ceramic particles is mainly composed of β-type silicon carbide. Each of the chemically modified silicon carbide ceramic powders is a preferred embodiment. Further, the present invention provides a chemically modified polycarbosilane having a structure in which silicon is contained as a main component in a main chain of a basic skeleton, a hydrocarbon group is contained in a side chain, and the basic skeleton has a structure crosslinked with a group containing a metal. After coating at least one selected from polysilazane or a polysilane-based organosilicon compound on the surface of the silicon carbide ceramic particles, the organic silicon compound is bonded to the silicon carbide ceramic particles by heat treatment in an inert gas. And a method of producing a chemically modified silicon carbide ceramic powder. Further, in the present invention, in the above method, the heat treatment may be performed at 800 ° C. to 1500 ° C.
A method for producing a chemically modified silicon carbide ceramic powder, which is carried out at a temperature of ° C., is a preferred embodiment.
Furthermore, the present invention provides a method for producing silicon carbide ceramics, which comprises using the above chemically modified silicon carbide ceramic powder, molding and heating the powder. Further, the present invention is characterized in that, in the above method, a method for producing silicon carbide ceramics, wherein the heating is performed in an inert gas, wherein the heating step includes a step of maintaining the temperature at one or more stages for a certain period of time. A method for producing silicon carbide ceramics, in which at least a step before heating and holding in the final stage, and a phase transition of silicon carbide ceramics during a subsequent heating step or a silicon carbide α phase serving as a nucleus for grain growth are generated. A method for producing silicon carbide ceramics,
A method for producing silicon carbide ceramics, wherein at least one heating is performed at a temperature of 1500 to 1800 ° C., wherein at least one heating at a temperature of 1500 to 1800 ° C. is performed for 5 minutes or more. The preferred embodiments of the present invention are methods for producing silicon carbide ceramics.

Examples of the organosilicon compound used in the present invention include the following formulas (1), (2) and (3)

[0008]

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[0009]

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[0010]

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(In the formulas (1) to (3), R ₁ is a metal or a group composed of a metal and oxygen, R ₂ , R ₃ and R ₄ are hydrocarbon groups, p is an integer of 1 or more, and the formula (1) In (2), m and n are each zero or more and represent m + n = 1), and the basic skeleton is represented by a metal or a group containing a metal such as a group containing metal and oxygen as main components. Has a crosslinked structure, and in formulas (1) and (2), metal and silicon have an element ratio of m:
Chemically modified polycarbosilane, polysilazane, or polysilane-based organosilicon compounds having a ratio of (m + n) can be used. Here, as a material having a structure in which the basic skeleton is cross-linked by a group containing a metal, for example, a chemically modified polycarbosilane (PCOAl), a chemically modified polysilazane (PSNOA)
l), chemically modified polysilane (PSOAl) and the like are exemplified as suitable ones. Also, for example, chemically modified polycarbosilane (PCOAl)
C) is dissolved in carbon tetrachloride (CCl ₄ ), and chlorinated polycarbosilane (PCCl) is prepared by reacting with benzoyl peroxide (BPO), and then hydrolyzed polycarbosilane is obtained. (PCO
By reacting H) with a metal alkoxide such as Al (OC ₃ H ₇ ) ₃ , a structure having a metal oxide in the side chain can be obtained. Chemically modified polysilazane (PSNOAl) is composed of polysilazane (PSN) and AlN.
By reacting a metal alkoxide such as (OC ₃ H ₇ ), a structure having a metal oxide in a side chain can be obtained. Also, chemically modified polysilane (PSOAl)
Is a polysilane having a hydroxyl group in the side chain and Al (OC
By reacting a metal alkoxide such as ₃ H ₇ ), a structure having a metal oxide in a side chain can be obtained. In the present invention, at least one selected from the above-mentioned organosilicon compounds is used.
Species are used by appropriately combining them, that is, a chemically modified polycarbosilane and polysilazane, or a chemically modified polycarbosilane and polysilane, or a combination of two each of chemically modified polysilazane and polysilane,
Alternatively, it means that a combination of three kinds of chemically modified polycarbosilane, polysilazane, and polysilane can be used.

Preferred examples of the metal include Al and Ti, and examples of the rare earth element include Y and Yb. Here, that the metal contains at least one or more of Al and rare earth elements means that they are used in an appropriate combination. For example, Y _3, which is a kind of a complex oxide of Al and Y, is used. Al ₅ O ₁₂ (YAG) is particularly effective. Further, as an example of the silicon carbide ceramic particles, for example, particles made of β-silicon carbide having a crystal system of 3C are desirable. The coating treatment is performed by dissolving an organosilicon compound in an organic solvent, immersing silicon carbide ceramic particles therein, and stirring. In this case, it is desirable that the amount of metal in the coating layer with respect to silicon in the entire chemically modified silicon carbide ceramic powder is in the range of 3% to 10% in elemental ratio. The heat treatment is preferably performed by raising the temperature to 800 ° C. to 1500 ° C. in an inert gas such as argon or helium.

Next, a silicon carbide ceramic is produced by molding and heating the chemically modified silicon carbide ceramic powder. In this case, as the molding, a method of performing CIP molding after uniaxial molding is exemplified. As the heating, a method in which heating is preferably performed at least once at a temperature of 1500 ° C. to 1800 ° C. for 5 minutes or more in an inert gas such as argon or helium is exemplified. In the present invention, the term “the heating step includes a step of maintaining the temperature at one or more stages for a certain period of time” is specifically from 1500 ° C. to 1800 ° C.
After holding at an arbitrary temperature of ° C. for a certain period of time, the process of holding at a higher temperature for a certain period of time is included at least once or more. In addition, at least in the process before heating and holding in the final stage, the phase transition of silicon carbide ceramics in the subsequent heating process, or to generate a silicon carbide α phase that is a nucleus for grain growth, specifically, , Chemically modified polycarbosilane, polysilazane, polysilane
Although SiC microcrystals can be generated, the presence of a metal such as Al at the atomic level in the vicinity of the generated β-SiC microcrystals makes it possible for Al to easily form a solid solution in SiC. Is transferred to α-SiC. The α-SiC generated here becomes a base point of phase transition with other β-SiC or grain growth of SiC particles at the time of processing at a higher temperature.

[0014]

Next, the operation of the present invention will be described. A structure in which silicon is contained as a main component in a main chain of a basic skeleton, a hydrocarbon group is contained in a side chain, and the basic skeleton is cross-linked with a group containing a metal, for example, a group mainly containing a metal and oxygen. At least one selected from the group consisting of chemically modified polycarbosilane, polysilazane, or polysilane-based organosilicon compound,
After coating the surface of the silicon carbide ceramic particles, heat treatment is performed to use the chemically modified silicon carbide ceramic powder characterized in that the organic silicon compound is bonded to the silicon carbide ceramic particles. Can be One is that by using an organic silicon compound which itself turns into a ceramic, a new ceramic component is generated between the ceramic particles during sintering, and the reliability of sintering is improved. By introducing a metal or a metal oxidizing component into the organic silicon compound, a cross-linking point can be formed between the main chains of the organic silicon compound, and the yield of the chemically modified organic silicon compound is improved. By coating the surface of the silicon carbide ceramic particles with the chemically modified organic silicon compound as a precursor and performing a heat treatment, a bond is formed between the ceramic particles and the organic silicon compound, and furthermore, desorption due to thermal decomposition is suppressed, and The yield of the silicon compound is improved, and ceramicification is effectively caused. At this time, when the heat treatment is performed in an inert gas such as argon or helium at a temperature of 800 ° C. to 1500 ° C., excess organic components of the organic silicon compound can be removed without mixing of unnecessary oxygen components. . Further, in the course of this heat treatment, a strong chemical bond is generated between the organic silicon compound and the silicon carbide ceramic particles, and a chemically modified silicon carbide ceramic powder can be obtained relatively easily.

By the presence of the sintering aid component in the organosilicon compound, uniform addition of the sintering aid component can be realized,
Since sintering can be performed by adding a necessary minimum amount of an auxiliary agent, problems such as deterioration in high-temperature characteristics and oxidation resistance due to segregation of auxiliary agent components, which are problems in the powder mixing method, are solved. In addition, a chemically modified organosilicon compound which itself turns into ceramics to produce silicon carbide ceramics is converted to silicon carbide ceramics at 1000 ° C to 1200 ° C.
In the vicinity, it precipitates as very fine β-SiC crystals. Since this β-SiC microcrystal is very active, improvement in sinterability can be expected first. Next, the very active β-SiC
Since the auxiliary component is present in the vicinity of the microcrystal at the atomic level, it can be expected that the β → α phase change of the silicon carbide ceramic is more effectively caused than in the case of the powder mixing method.
In the chemically modified organosilicon compound coated on the surface of the silicon carbide ceramic particles, if the metal is characterized by containing at least one or more of rare earth elements such as Al or Y, Al or Y or the like Rare earth elements,
Since these oxides or composite oxides are effective as an aid for silicon carbide and silicon nitride ceramics, they can be used for producing those ceramics. When the ratio of silicon to metal in the entire chemically modified silicon carbide ceramic powder is 3% to 10% in elemental ratio, it works sufficiently effectively. If the amount is larger than this, the ratio of the organosilicon compound contained in the ceramic molded body is too large, and the amount of the organosilicon compound is too large relative to the silicon carbide powder in terms of yield, and the powder is not effectively coated. There is a problem that an organic silicon compound component is excessively present. If it is 3% or less, the amount of the organosilicon compound is too small, and the amount of the α component generated during the first-stage heat treatment becomes relatively small, so that the effect as a grain growth nucleus cannot be effectively exhibited.

If the crystal system of the silicon carbide ceramic particles coated with the organic silicon compound is β-type (3C system),
The phase transition of the ceramic particles can be controlled by utilizing the β → α phase transition of the organosilicon compound. by this,
A silicon carbide ceramic having a controlled phase transition can be obtained. When the phase transition can be controlled, the grain growth of the silicon carbide ceramic accompanying the phase transition can be controlled, and therefore, the microstructure of the obtained ceramic can also be controlled. At this time, an arbitrary amount of the α component serving as a nucleus of the phase transition can be produced by using an arbitrary amount of the organosilicon compound in the molded body. In the subsequent heating stage, phase transition and grain growth can be performed using the α component created first as nuclei, so if the amount and size of nuclei can be controlled by controlling the nucleation process of any first stage A silicon carbide ceramic having a microstructure based thereon can be obtained.
Here, heating which is a process of generating the α component is performed at 1500 ° C. to 1 ° C.
By performing at a temperature of 800 ° C. for 5 minutes to 10 hours, any phase transition state can be created. By performing the heating in an inert gas, the ceramics to be manufactured can be heat-treated without being oxidized. Since the heating step includes a step of maintaining the temperature at one or more stages for a certain period of time, the α phase generated before the final heating stage can be used as a nucleus to grow grains in the subsequent heating stages.
When the heating is performed at 1500 ° C. or higher, α components are generated. At a temperature higher than 1800 ° C., α phases of various polytypes such as 4H and 6H are generated. This makes it difficult to control grain growth. The α component does not appear unless the heating is performed for a longer time as the temperature is lower. However, when the temperature is higher, the α component effectively appears by heating for a shorter time. The amount of the α component can be controlled by the amount of the organosilicon compound and the amount, temperature and time of the metal contained therein.

[0017]

Next, the present invention will be specifically described based on examples, but the present invention is not limited to the examples. Example 1 (Preparation of chemically modified silicon carbide ceramic powder) 10 g of polycarbosilane (PC) and 50 g of carbon tetrachloride (CCl ₄ )
In benzoyl peroxide (BPO).
By reacting 1 g, the Si—H bond is changed to Si—
Chlorinated polycarbosilane (PC
Cl) was prepared. By hydrolyzing PCCl, hydroxylated polycarbosilane (PCOH) in which Si-Cl bonds were replaced with Si-OH bonds was produced. This PC
8 g of OH and 20 g of Al (OC ₃ H ₇ ) ₃ are reacted to form polycarbosilane (PCOA) having a metal oxide in a side chain.
1) was synthesized. A β-SiC powder (3C type) having a particle diameter of 500 nm was added to the toluene solution of PCOAl thus obtained. Although the synthesized PCOAl had a ratio of Al to Si of 2%, the weight loss when the heating temperature was changed was examined. At a heating temperature of 800 ° C., the weight reduction was almost completed. The yield at 1000 ° C. was about 80%. Compared with the polycarbosilane used as a raw material having a yield of only 19% at 1000 ° C., the yield was greatly improved through a chemical reaction. Further, since the yield of PCOAl before coating on the silicon carbide ceramic particles was 70%, the yield was further improved by coating. This is because PCOAl was bonded to the silicon carbide ceramic particles and the interaction worked.

Examples 2 to 5 and Comparative Examples 7 to 10 (Production of silicon carbide ceramics) PCOAl produced by the method of Example 1 was prepared by reducing the proportion of Al to Si from 0 to 15%.
Coated on silicon carbide particles so that
The chemically modified silicon carbide ceramic powder treated for 3 hours was granulated and uniaxially molded, then subjected to CIP molding and then heat treated at 1800 ° C. for 30 minutes to examine the change in crystal structure. These samples were further heated to 1900 ° C. and examined for density when held for 30 minutes. Table 1 shows the results. 1 when the amount of Al in the chemically modified silicon carbide ceramic powder is 3% or more
By treating at 800 ° C. for 30 minutes, 4H became the main phase. On the other hand, the density improved up to an Al content of 10%, but decreased slightly above that. FIG. 1 shows changes in the ratio of the crystal phase to the Al amount and the relative density.

[0019]

[Table 1]

Examples 11 to 12 and Comparative Examples 13 to 17 (Preparation of Silicon Carbide Ceramics) PCOAl prepared by the method of Example 1 was coated on silicon carbide particles so that the ratio of Al to Si was 5%. The chemically modified silicon carbide ceramic powder treated at 800 ° C. for 3 hours was granulated, uniaxially formed, then CIP-molded, and then subjected to a heat treatment at a predetermined temperature for an arbitrary period to examine the crystal structure change. The densities of these samples after further treatment at 1900 ° C. for 30 minutes were examined. Table 2 shows the results. A high-density ceramic can be obtained with a processing time of 5 minutes or more, and 1500 ° C.
To 1800 ° C. was desirable for densification.
FIG. 2 shows changes in the ratio of the crystal phase and the relative density with respect to the processing temperature.

[0021]

[Table 2]

Example 18 (Production of Chemically Modified Silicon Carbide Ceramic Powder) PC 10 g
Was dissolved in 50 g of CCl ₄ , and 0.1 g of BPO was reacted to prepare PCCl in which Si—H bonds were replaced by Si—Cl bonds. By hydrolyzing PCCl, PCOH was produced in which Si-Cl bonds were replaced with Si-OH bonds. A toluene solution was prepared from Al (OC ₃ H ₇ ) ₃ and Y (OC ₃ H ₇ ) ₃ in an Al: Y elemental ratio of 5: _3.
The same amount of water as H ₇ ) ₃ and a catalytic amount of hydrochloric acid were added thereto, and the mixture was refluxed to prepare a YAG precursor. This YAG precursor and P
PCYAG with metal oxide in side chain by reacting COH
Was synthesized. SiC powder having a particle diameter of 500 nm was added to the toluene solution of PCYAG thus obtained, and the mixture was stirred and mixed to prepare a chemically modified ceramic powder coated on the powder surface. Although the synthesized PCYAG had a ratio of Al to Si of 2%, the weight loss when the heating temperature was changed was examined. PCYAG has a heating temperature of 8 like PCOAl.
The weight loss was almost completed at 00 ° C, and the yield at 1000 ° C was about 80%. Compared with the polycarbosilane used as a raw material having a yield of only 19% at 1000 ° C., the yield was greatly improved through a chemical reaction. Also,
PC before coating on silicon carbide ceramic particles
The yield was further improved by coating since the yield of YAG was 70%.

Example 19 (Production of Silicon Carbide Ceramics) PCYAG produced by the method of Example 18 was produced by adding 5% of YAG to SiC.
The chemically modified silicon carbide ceramic particles coated on the silicon carbide ceramic particles so as to correspond to t% and treated at 800 ° C. for 3 hours are heated at 1700 ° C. for 30 minutes,
Then, it heated at 1900 degreeC for 30 minutes. As in the case of using Al alone, the 4H phase was generated by the first stage heat treatment, and 1900
By the treatment at ℃, a dense sintered body was obtained.

[0024]

As described above in detail, according to the present invention, by using a chemically modified silicon carbide ceramic powder obtained by coating the surface of silicon carbide ceramic particles with a metal oxide-containing organosilicon compound as a precursor. It is also excellent in sinterability, and a silicon carbide ceramic sintered body in which the microstructure, particle size and grain shape of silicon carbide ceramic are arbitrarily controlled can be obtained relatively easily by pressureless sintering.

[Brief description of the drawings]

FIG. 1 shows the results obtained in Examples 2 to 5 and Comparative Examples 7 to 10.
The ratio of the crystal phase to the amount and the change in the relative density are shown.

FIG. 2 shows changes in the ratio of the crystal phase and the relative density with respect to the processing temperature in Examples 11 to 12 and Comparative Examples 13 to 17.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinichi Hirano Nagoya University, Nagoya-shi, Aichi Pref. Reference JP-A-63-201056 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C04B 35/626-35/636 C04B 35/565-35/577

Claims (12)

(57) [Claims] 1. A chemically modified polycarbosilane containing silicon as a main component in a main chain of a basic skeleton, having a hydrocarbon group in a side chain, and having a structure in which the basic skeleton is crosslinked with a group containing a metal. After coating at least one selected from polysilazane or a polysilane-based organosilicon compound on the surface of the silicon carbide ceramic particles, heat treatment is performed on the surface to bond the organosilicon compound to the silicon carbide ceramic particles. Chemically modified silicon carbide ceramic powder. 2. The chemically modified silicon carbide ceramic powder according to claim 1, wherein the metal contains at least one of Al and rare earth elements. 3. The amount of metal in the coating layer with respect to silicon in the entire chemically modified silicon carbide ceramic powder is 3 in elemental ratio.
The chemically modified silicon carbide ceramic powder according to claim 1, wherein the content is in the range of 10% to 10%. 4. The chemically modified silicon carbide ceramic powder according to claim 1, wherein the crystal system of the silicon carbide ceramic particles is particles mainly composed of β-type silicon carbide. 5. A chemically modified polycarbosilane containing silicon as a main component in a main chain of a basic skeleton, having a hydrocarbon group in a side chain, and having a structure in which the basic skeleton is crosslinked by a group containing a metal. After coating the surface of silicon carbide ceramic particles with at least one selected from polysilazane or polysilane-based organic silicon compound, the organic silicon compound is bonded to the silicon carbide ceramic particles by heat treatment in an inert gas. A method for producing a chemically modified silicon carbide ceramic powder, characterized in that: 6. The method for producing a chemically modified silicon carbide ceramic powder according to claim 5, wherein the heat treatment is performed at a temperature of 800 ° C. to 1500 ° C. 7. A method for producing silicon carbide ceramics, comprising using the chemically modified silicon carbide ceramic powder according to claim 1 and molding and heating it. 8. The method for producing a silicon carbide ceramic according to claim 7, wherein the heating is performed in an inert gas. 9. The method for producing a silicon carbide ceramic according to claim 7, wherein the heating step includes a step of maintaining the temperature at one or more stages for a predetermined time. 10. A silicon carbide α-phase which forms a phase transition of silicon carbide ceramics or a nucleus for grain growth at least in a process before heating and holding in a final stage, and in a subsequent heating process. The method for producing a silicon carbide ceramic according to claim 9. 11. Heating at least once at 1500 ° C.
The method for producing silicon carbide ceramics according to claim 9, wherein the method is performed at a temperature of 1800 ° C. 12. The method for producing a silicon carbide ceramic according to claim 11, wherein at least one heating at a temperature of 1500 ° C. to 1800 ° C. is performed for 5 minutes or more.