JPS6138143B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a high-density silicon carbide sintered body. Silicon carbide sintered bodies have extremely excellent chemical and physical properties such as thermal conductivity, coefficient of thermal expansion, hot strength, oxidation resistance, and corrosion resistance, and are used, for example, in gas turbine parts and high-temperature heat exchangers. This material is suitable for use in high-temperature structures such as vessels. Since silicon carbide is a material that is difficult to sinter, a pressure sintering method has conventionally been mainly employed. This method not only makes it difficult to produce a sintered body with a complicated shape, but also has the disadvantage of poor productivity. For this purpose, a pressureless sintering method was proposed, and
- No. 78609 "Production method of high-density silicon carbide ceramics" and then JP-A No. 52-6716 "Silicon carbide sintered bodies", submicron ( A method is disclosed in which a mixed powder having a particle size of 1 micron or less is compacted and pressure-free sintered at about 1950 to 2300° C. in an inert atmosphere. By the way, according to the pressureless sintering method, a carbonaceous additive is added to improve the sinterability between silicon carbide particles by reducing and removing the silica film coated on silicon carbide particles with carbon even at room temperature. However, the amount of carbon added is extremely small at 0.1 to 1.0% by weight based on the weight of silicon carbide powder, and the particle size is submicron and has a huge surface area. Generally speaking, the method of uniformly dispersing the silicon carbide particles by dispersing them with an organic compound solution is followed by heating and decomposing the organic substances in the solution to precipitate carbon. It does not cover the surface. As a result, the reduction and removal of the silica film becomes localized, and during the sintering stage, the residual silica film impedes grain growth and reduces sinterability, and also forms an intervening phase within the sintered body, which improves the physical properties of the sintered body, such as strength. etc. have a harmful effect. Therefore, as mentioned above, the pressureless sintering method has the drawback that the intervening phase consisting of the residual silica film is unevenly distributed at the grain boundaries and tends to impair the physical properties of the sintered body. The present inventors have previously applied for patents for ``Method for manufacturing sintered silicon carbide'' (Japanese Patent Application No. 15883-1983) and ``Method for manufacturing high-density sintered silicon carbide'' (Patent Application No. 15883-1983).
No. 41330), we proposed a new pressureless sintering method that eliminates and improves the above-mentioned drawbacks of the previously known pressureless sintering methods. The purpose of the present invention is to provide a new pressureless sintering method that is a further improvement over the conventional pressureless sintering method proposed by the present inventors. A first step of preparing a mixed powder containing 1.0 to 15.0 parts by weight of a temporary binder in terms of solid content, a second step of molding the mixed powder into a green body, and a second step of molding the green body into a 1750 to 2100 a third step of sintering within the temperature range of The present invention relates to a method for producing a sintered silicon carbide body, which is dried by contacting the silicon carbide body, and in which the atmosphere from at least the drying of the hydrofluoric acid to the completion of sintering is non-oxidizing. Next, the present invention will be explained in detail. According to the present invention, it is preferable that the silicon carbide powder, which is the starting material, has an average particle size of 3 microns or less; if the particle size is larger than that, it is difficult to obtain a sintered body having a dense and uniform crystal structure. In particular, to obtain a sintered body with high density and high strength, the average grain size is 1.0.
It is more preferable to use powder of micron size or less. Silicon carbide has an α type, which belongs to a hexagonal system, and a β type, which belongs to a cubic system, depending on its crystal structure, and according to the present invention, either one of them or a mixture thereof can be used as the starting material. The silicon carbide can be produced by, for example, a method in which a mixture of metal silicon powder and fine carbon powder or silica powder and fine carbon powder is subjected to a heat reaction, a method in which a mixed gas such as a silicon halide and a hydrocarbon is subjected to a gas phase reaction, or the Acheson method. It is possible to use a method of finely pulverizing and classifying α-type silicon carbide particles obtained in can. It is preferable that free carbon, free silica, or free silicon contained in the silicon carbide powder thus obtained be removed and purified as much as possible by a conventional method. According to the present invention, silicon carbide powder is brought into contact with hydrofluoric acid by kneading with hydrofluoric acid or immersed in hydrofluoric acid before being formed into a green body, and then dried. It is necessary to let it happen. The reason why silicon carbide powder is brought into contact with hydrofluoric acid is that the surface of silicon carbide particles is generally covered with a silica film even at room temperature, so this silica film is removed to expose the silicon carbide particles themselves, and then the silicon carbide particles are baked. The goal is to increase cohesion. The mechanism by which the silica film is removed by hydrofluoric acid is as shown in the following reaction formula (1) or (2). SiO ₂ +4HF→SiF ₄ +2H ₂ O ...(1) SiO ₂ +6HF→H ₂ SiF ₆ +2H ₂ O ...(2) The silicon carbide particles from which the silica film has been removed are very easily oxidized, and at room temperature It is also easily oxidized by oxygen in the atmosphere according to the reaction formula below and is covered again with a silica film. 2SiC + 3O ₂ → 2SiO ₂ + 2CO ... (3) However, according to the present invention, by contacting with hydrofluoric acid and drying, the silicon carbide particles from which the silica film has been removed remain non-sintered until the end of sintering. Since the process is carried out in an oxidizing atmosphere, the surface of the silicon carbide particles is not coated with a silica film again, and as a result, a high-density sintered body in which the silicon carbide particles are strongly self-sintered can be obtained. . The purpose of removing the silica film using hydrofluoric acid of the present invention is completely different from the method of removing and purifying granular free silica contained in silicon carbide powder using hydrofluoric acid. It is something to do. The silica particles are generally removed by immersion in hydrofluoric acid or a mixed acid of hydrofluoric acid and nitric acid, followed by washing with water and drying. Even if such a method is used, the silica film covering the silicon carbide surface is temporarily removed according to reaction formula (1) or (2), but after that it is exposed to the atmosphere or washed with water. This is because it reacts with oxygen dissolved in the water and is coated with the silica film again. According to experiments conducted by the present inventors, the formed body made of silicon carbide powder from which silica grains were removed using hydrofluoric acid using the conventional method did not exhibit significant grain growth even when fired at a high temperature of 2100°C. Approximately 1.9
Only a sintered body with a low density of g/cc could be obtained. According to the conventional pressureless sintering method, a higher temperature of approximately 100 to 150° C. is required to reach approximately the same density as the sintered body of the present invention. As described above, the necessity of increasing the sintering temperature in the conventional method compared to the method of the present invention impedes self-sintering between silicon carbide particles and impairs the mechanical properties of the sintered body, such as This is because the silica film, which reduces strength, is removed only locally. In the present invention, it is preferable to contact 100 parts by weight of silicon carbide powder with hydrofluoric acid in an amount equivalent to 0.2 parts by weight or more of hydrogen fluoride.
This is because if the amount is less than 0.2 parts by weight, the silica film on the surface of the silicon carbide particles cannot be sufficiently removed, resulting in poor sintering properties and making it difficult to obtain a sintered body with high density and a uniform crystalline state. Note that a non-oxidizing mineral acid can be used in combination with the hydrofluoric acid for the purpose of removing impurities other than silica in the silicon carbide powder. According to the invention, it is necessary to add a temporary binder to the silicon carbide powder in order to obtain a sintered body with high density and high strength. The temporary binder used in the present invention is, for example, a novolak type phenolic resin, and this temporary binder has the function of temporarily exerting an adhesive effect between silicon carbide particles at the initial stage of sintering. The finally obtained sintered body is strongly sintered by self-sintering. In the sintered body in which no temporary binder was added to the silicon carbide powder, remarkable grain growth was observed as shown in the scanning electron micrograph shown in Fig. 1, but almost no firing shrinkage occurred. It becomes a porous body, making it difficult to obtain a high-density sintered body. On the other hand, under the same conditions, a sintered body to which a temporary binder was added undergoes overall firing shrinkage due to grain growth, resulting in a high-density sintered body, as shown in Figure 2. . Conventional pressureless sintering methods generally do not require the use of a temporary binder and produce a dense sintered body with overall firing shrinkage even without the inclusion of a temporary binder. is obtained. The reason for this is that at the initial stage of sintering, when a network is formed between silicon carbide particles,
This is thought to be due to the remaining silica film acting as a viscous binder on the surface of the silicon carbide particles. As mentioned above, the temporary binder acts so that a neck is formed at each contact point between silicon carbide particles instead of a silica film, and without the temporary binder, there are places where no neck is formed at the contact point. It is thought that grain growth occurs locally and that overall firing shrinkage does not occur. In addition, the temporary binder has the function of increasing the strength of the resulting form and making it easier to handle. Therefore, the mixed powder prepared in the first step of the present invention must contain 0.5 to 15.0 parts by weight of temporary binder in terms of solid content. The reason for keeping the temporary binder within the above range is that if it is less than 0.5 parts by weight, the action as the binder will not be sufficiently exerted and it will be difficult to obtain a high-density sintered body, whereas if it is more than 15.0 parts by weight. This is because it inhibits the sintering action and forms an intervening phase within the sintered body, reducing the physical properties of the sintered body.
A range of 1.0 to 7.0 parts by weight is more preferred. When using an inorganic temporary binder such as sodium silicate, colloidal silica, alumina sol and aluminum phosphate as the temporary binder, it is advantageous to add it after treatment with hydrofluoric acid. be. Organic temporary binders can be advantageously used because they are not easily attacked by hydrofluoric acid, such as polyvinyl alcohol, cornstarch, molasses,
Various organic temporary binders can be used, such as coal tar pitch, phenolic resins, lignosulfonates, stearates, or alginates. The method of adding the temporary binder is to dissolve it in an aqueous solution, a mixed solution with hydrofluoric acid, or an organic solvent and mix it with the silicon carbide powder in the form of a solution, or to carbonize the temporary binder in the form of a powder. After mixing with silicon powder, water, hydrofluoric acid or an organic solvent can be added and kneaded. The temporary binder may be added to the silicon carbide powder at any time before contacting with hydrofluoric acid, before drying the hydrofluoric acid, or after contacting with hydrofluoric acid and drying. I can do it. The temporary binder in solution form added in this manner is dried to form a solid temporary binder before or after shaping into the product. In the method of the invention, the silicon carbide powder that has been contacted with hydrofluoric acid needs to be dried in a non-oxidizing atmosphere to evaporate the hydrofluoric acid before being shaped into a green body. The reason why the drying is performed in a non-oxidizing atmosphere is that when hydrofluoric acid is dried and evaporated in the air, the surfaces of the silicon carbide particles are reoxidized. As a method for drying the silicon carbide powder that has been brought into contact with the hydrofluoric acid, heating it in a non-oxidizing atmosphere or a non-oxidizing air stream to a temperature of about 110°C or higher, which is the boiling point of hydrofluoric acid, or Either heating under reduced pressure may be employed. The mixed powder prepared in the first step of the present invention needs to contain at least silicon carbide powder and a temporary binder, but in addition to this, a sintering aid such as boron carbide may be added. You can also do it.
The function of the sintering aid is to diffuse into silicon carbide particles to increase the number of pores during sintering at high temperatures, thereby facilitating sintering. As the sintering aid other than boron carbide, for example, boron, aluminum, or aluminum carbide can be used, but the sintering aid that is chemically unstable to hydrofluoric acid is hydrofluoric acid. It is preferable to add the boron-containing material after drying, and it is preferable to use a boron-containing material as a sintering aid because it does not significantly reduce the oxidation resistance of the sintered body. When adding a boron-containing material, if the boron-containing material is added in an amount equivalent to more than 3.0 parts by weight, the oxidation resistance of the sintered body will deteriorate, so it is preferable to add 3.0 parts by weight or less, and the average particle size Optimally, the material is selected from boron, boron carbide, or a mixture thereof, with a diameter of 1 micron or less. In many cases, silicon carbide particles contain a small amount of aluminum compounds and other unavoidable impurities, or intentional impurities such as aluminum and boron to improve sinterability.
These impurities act as sintering agents,
The present invention does not preclude the presence of such a sintering aid. As a method for molding the mixed powder prepared in the first step of the present invention into a green body, various conventionally known molding methods can be applied, such as stamp molding, extrusion molding, casting molding, and injection molding. It can be formed into any shape by a method such as molding or isostatic pressing. When using the embossing molding method, a pressure of about 250 to 2000 kg/cm ² can usually be used, and the density of the molded product in that case will be about 1.6 to 1.9 g/cc. Increasing the density of the compact as much as possible is very advantageous in obtaining a high-density sintered compact, and therefore it is recommended to add a small amount of lubricant such as stearate to the mixed powder before compaction. can. In the isostatic pressing method, the mixed powder is charged into a container made of, for example, a rubber bag, the pressure inside the container is reduced, and then molding is performed, which is advantageous in obtaining a uniform and high-density product. In the present invention, in order to prevent re-oxidation of the silicon carbide powder from which the silica film has been removed using hydrofluoric acid, the atmosphere from at least the drying of the hydrofluoric acid to the completion of sintering is made non-oxidizing. It is necessary to do so. As the non-oxidizing atmosphere, a gas atmosphere consisting of at least one selected from argon, helium, neon, nitrogen, hydrogen, carbon monoxide, and hydrogen fluoride, or a vacuum can be used. It is necessary to prevent the mixed powder dried in the non-oxidizing atmosphere from being exposed to the atmosphere when forming it into a green body or charging it into a firing furnace. This method can be carried out by placing the mixed powder and the resulting form in a container and sealing it. As containers it is possible to use, for example, rubber bags, plastic bags, plastic containers, ceramic containers or metal containers. In addition, as the container used when charging the material into the firing furnace, a container or bag that can be fired can be selected, or a container made of ceramic, such as graphite, that can withstand temperatures of about 2000 degrees Celsius can be used. According to the present invention, in order to obtain a high-density and high-strength silicon carbide sintered body, it is necessary to sinter the formed body in a non-oxidizing atmosphere within a temperature range of 1750 to 2100°C. The reason why the firing temperature is limited to the above temperature range is that if it is lower than 1750°C, sufficient grain growth will not occur, making it impossible to obtain a high-density sintered body.
This is because if the temperature is higher than 2100°C, the coarsening phenomenon of crystal grains becomes significant, resulting in a high density but a decrease in mechanical strength. In particular, in order to obtain a sintered body having a density higher than 2.5 g/cc and a uniform and fine crystal structure, a temperature range of 1800 to 2000°C is more suitable. According to experiments conducted by the present inventors, it has been found that the formed body of the present invention reaches almost the same density at a firing temperature approximately 100 to 150°C lower than that of the conventional formed body using carbon as a solid reducing agent. Ta. However, according to the conventional method, when β-type silicon carbide powder is used as a starting material, the transition from β-type to α-type progresses during sintering, resulting in a coarse and elongated plate shape that is extremely undesirable in terms of mechanical properties. It tends to become a coarse crystal weave containing crystals. According to the present invention, there is an advantage that even if β-type silicon carbide powder is used, a sintered body consisting of uniform fine crystals can be obtained with almost no transformation to α-type. The firing time within the temperature range of 1,750 to 2,100°C is determined mainly by the desired crystal structure and density; generally, firing at a lower temperature for a longer time will result in a more uniform and finer crystal structure. Since it is easy to obtain a high-density sintered body, it is optimal to perform the firing within the temperature range of 1800 to 2000°C for at least 10 minutes. Furthermore, increasing the temperature in a temperature range of 1500° C. or higher over time is advantageous in obtaining a high-density sintered body. As the firing furnace for firing the formed body, various conventionally known high-temperature firing furnaces capable of controlling the firing temperature and atmosphere are used, such as a firing furnace such as a Tammann furnace equipped with a graphite core tube and a heating element. can be used. Next, the present invention will be explained by comparing examples with comparative examples. Example 1 As a starting material, β-type silicon carbide was produced by the continuous production method described in JP-A No. 52-142697, and was further purified and classified in terms of particle size. β-type silicon carbide powder having the crystal structure shown in FIG. 5 was used.

【table】

[Table] 30.00 g of the β-type silicon carbide powder and 0.90 g of novolak type phenol resin were mixed in advance with about 20 g of acetone.
The entire solution in ml was mixed in an agate mortar to allow the acetone to evaporate and then mixed for an additional 30 minutes. The mixed powder was transferred to a glove box in an argon gas atmosphere, placed in an open container made of fluororesin, and 7.5 g of hydrofluoric acid (hydrogen fluoride content: 10% by weight) was added and mixed uniformly for 30 minutes. It was left for another 1 hour. The wet mixture was then heated to a final temperature of 150° C. over 2 hours in a stream of argon gas to evaporate the hydrofluoric acid to dryness, cooled and mixed again in an agate mortar for 30 minutes. An appropriate amount of this dried mixed powder was taken, and then a disk-shaped compact with a diameter of 20.3 mm was produced using a press machine in a glove box at a pressure of 1500 kg/cm ² . The density of the molded body was found to be 1.73 g/cc (relative theoretical density ratio of about 54%). The molded body was sealed in a graphite airtight container in a glove box, and then charged into a Tammann-type firing furnace, and fired after creating an argon gas atmosphere in the furnace. The temperature raising process during firing was from room temperature to 600°C for 60 minutes, from 600 to 1500°C for 22 minutes, and then from 1500 to 1900°C over 80 minutes, held at the maximum temperature of 1900°C for 60 minutes, and then cooled. The obtained sintered body had a firing shrinkage rate of 13.3%,
It was confirmed that it had a density of 2.68 g/cc (relative theoretical density ratio of about 84%). The flow sheet of this embodiment is shown in FIG. 8. Example 2 29.73 g of β-type silicon carbide powder described in Example 1
0.27 g of boron carbide prepared by crushing commercially available 200-mesh boron carbide grains (manufactured by Denki Kagaku Kogyo Co., Ltd.) to an average particle size of 0.62 microns was placed in an agate mortar for 30 minutes.
Mixed for a minute. The mixed powder was transferred to a glove box under an argon gas atmosphere, placed in an open container made of fluororesin, and 7.5 g of hydrofluoric acid described in Example 1 was added thereto and mixed uniformly for 30 minutes. The wet mixture was then heated to a final temperature of 150° C. for 2 hours in a stream of argon gas to dry it. A total solution of 0.90 g of novolak type phenolic resin dissolved in about 20 ml of acetone was added to the thus obtained dry powder and mixed, and after the acetone was evaporated, the mixture was further mixed for 30 minutes. Using this mixed powder, a molded body was created in the same manner as in Example 1, and the molded body was charged into a Tammann-type firing furnace in an argon gas atmosphere. Next, the temperature was raised in the same temperature raising process as in Example 1, and the maximum temperature was reached.
The temperature was increased to 1920°C and baked for 60 minutes. The density of this sintered body was 3.04 g/cc (relative theoretical density ratio of about 95%), and the firing shrinkage rate was 17.1%. Further, it was confirmed that the crystal structure of the sintered body had a fine structure consisting of crystals of about 3 to 5 microns, as shown in the scanning electron micrograph of FIG. 2 (5,000 times magnification). Further, from the powder X-ray diffraction diagram of this sintered body shown in FIG. 6, it was found that almost no β-type silicon carbide was transferred to α-type silicon carbide during the firing process. Example 3 The formulation was similar to that described in Example 2, but the amount of novolac type phenolic resin added was changed to 1.80.
Two types of mixed powders were prepared in the same manner as in Example 2, with the amounts changed to 0.45 g and 0.45 g. Using this mixed powder, a molded body was created in the same manner as in Example 1, and the molded body was charged into a Tammann-type firing furnace in an argon gas atmosphere. Next, the temperature was raised in the same temperature raising process as in Example 1, and the product was fired for 60 minutes at a maximum temperature of 1920°C. Among the obtained sintered bodies, the density of the former sintered body with increased novolak type phenolic resin was 2.99 g/cc.
(relative theoretical density rate approximately 93%), shrinkage rate is 16.7%, and the density of the latter sintered body with reduced novolak type phenolic resin is 2.86 g/cc (relative theoretical density rate approximately 89%), shrinkage after firing. The rate was 15.3%. Comparative Example 1 A mixed powder was prepared using the same mixture as described in Example 2 but without novolac type phenolic resin as a temporary binder, and hydrofluoric acid was added in the same manner as in Example 1. After mixing and drying, a molded body was created. Next, the product was placed in a Tammann-type firing furnace, the inside of the furnace was made into an argon gas atmosphere, the temperature was raised in the same temperature raising process as in Example 1, and the product was fired at a maximum temperature of 1920°C for 60 minutes. This sintered body has a firing shrinkage rate of 7.7% and 2.18g/cc.
(relative theoretical density ratio of about 68%), and as shown in the scanning electron micrograph in Figure 1 (5000x magnification), remarkable grain growth can be seen, but it is porous with gaps between grains. A fine structure was recognized. Comparative Example 2 A mixed powder having the same formulation as described in Example 2 but omitting the treatment with hydrofluoric acid was molded and fired in the same manner as in Example 1. The maximum temperature was 1920°C and baking was performed for 60 minutes. This sintered body had a firing shrinkage rate of 10.9% and a low density of 2.47 g/cc (relative theoretical density rate of about 77%). Comparative Example 3 A mixed powder having the same formulation as described in Example 2 but omitting the treatment with hydrofluoric acid was heated to 800°C in a nitrogen gas atmosphere to thermally decompose the phenolic resin, and then cooled. Afterwards, the mixture was mixed again in an agate mortar for 15 minutes. This mixed powder was molded into a disk shape with a diameter of 20.3 mm using a graphite mold at a pressure of 700 kg/cm ² . The density of this molded body is 1.70g/cc
(relative theoretical density ratio of approximately 53%). The molded body was placed in a graphite crucible, placed in a Tammann-type firing furnace to create an argon gas atmosphere, heated at a rate of 40°C per minute, and fired at a maximum temperature of 1920°C for 60 minutes. This sintered body has a firing shrinkage rate of 10.9% and a density of 2.41 g/cc (relative theoretical density rate approximately 75%), and the shape of its crystals is shown in the scanning electron micrograph shown in Figure 3. As can be seen from 5000x magnification), the particles were irregular and the particle size was non-uniform. Furthermore, the sintered body fired at the maximum temperature of 2050℃ for 45 minutes has a firing shrinkage rate of 17.4% and a density of 3.05g/cc.
(relative theoretical density rate of approximately 95%), and has a microstructure consisting of irregularly shaped crystals without clear bonding surfaces, as shown in the scanning electron micrograph (5000x) in Figure 4. Ta. Furthermore, from the powder X-ray diffraction diagram of this sintered body shown in Figure 7, β
It was confirmed that most of the type silicon carbide was transformed into α-type silicon carbide. Example 4 29.27 g of β-type silicon carbide powder described in Example 1
and 0.73 g of boron carbide described in Example 2 were mixed in an agate mortar for 30 minutes. Transfer the mixed powder into a glove box with an argon gas atmosphere,
Place lignin sulfonate (manufactured by Sanyo Kokusaku Pulp Company, Sun Extract) in an open container made of fluororesin.
P201), 1.7 g of hydrofluoric acid described in Example 1, and 5.8 g of distilled water were added and mixed for 30 minutes. The wet mixture was then heated to a final temperature of 150° C. for 2 hours in a stream of argon gas to dry it. This mixed powder was further mixed in an agate mortar for 30 minutes, and then a molded body was prepared in the same manner as in Example 1 but at a pressure of 700 Kg/cm ² and placed in a Tammann furnace in an argon gas atmosphere. Next, firing was performed under the same firing conditions as in Example 2. The firing shrinkage rate of the obtained sintered body was 16.3%, and the density was 2.94.
g/cc (relative theoretical density rate approximately 92%). Example 5 The β-type silicon carbide described in Example 1 as a starting material was further classified with water to give an average particle size of 0.25 microns.
β-type silicon carbide powder prepared to have a maximum particle size of 0.68 microns was used. 0.3 g of aluminum stearate and 0.27 g of boron carbide described in Example 2 were mixed with 29.73 g of this β-type silicon carbide powder in an agate mortar for 30 minutes. The mixed powder was mixed and dried with 0.90 g of novolac type phenolic resin in the same manner as in Example 1, and then the hydrofluoric acid described in Example 1 was added.
A molded article was prepared by adding and mixing 7.5 g. The density of this molded body is 1.80 g/cc (relative theoretical density rate approximately 56
%). This compact was placed in a Tammann-type firing furnace in an argon gas atmosphere, heated in the same temperature-raising process as in Example 1, and fired at a maximum temperature of 1900°C for 60 minutes. The firing shrinkage rate of the obtained sintered body was 16.4%, and the density was 3.08 g/cc (relative theoretical density rate approximately 96%).
It was hot. Example 6 As a starting material, a commercially available α-type silicon carbide powder (manufactured by Waha Abrasives Industry Co., Ltd., particle size: No. 3000) was further ground and classified, and the purified product was used. This α
The purity of type silicon carbide powder is 98.5%, the average particle size is 0.59
It was micron. A molded body was produced using this silicon carbide powder in the same manner as described in Example 2. Next, this molded body was placed in a Tammann-type firing furnace in an argon atmosphere, and the temperature was raised in the same temperature raising process as in Example 1, and fired at a maximum temperature of 1940°C for 60 minutes. The density of the obtained sintered body was 2.96 g/cc (relative theoretical density ratio of about 92%), and the firing shrinkage rate was 16.4%. As mentioned above, in order to sinter silicon carbide powder without pressure, high temperature firing at around 2050°C,
Whereas submicron silicon carbide ultrafine powder of about 0.5 microns or less, which is expensive and difficult to obtain, was required, the present invention can achieve micron-level carbonization in a relatively low temperature range of about 1850 to 1900°C. Even if silicon powder is used, pressureless sintering produces silicon carbide with high density and extremely few intervening phases consisting of silica films that degrade the physical properties of the sintered body, and whose crystals are strongly bonded to each other. A sintered body can be stably produced, and the present invention is extremely useful industrially.

[Brief explanation of the drawing]

Figure 1 is a scanning electron micrograph (5000x) of the sintered body described in Comparative Example 1, and Figure 2 is a scanning electron micrograph (5000x) of the sintered body described in Example 2.
3 is a scanning electron micrograph (5000x magnification) of the sintered body described in Comparative Example 3, and FIG. 4 is a scanning electron micrograph of another sintered body described in Comparative Example 3. (5000 times), FIG. 5 is an X-ray diffraction diagram of the β-type silicon carbide powder used in Example 1, and FIG. 6 is a powder X-ray diffraction diagram of the sintered body described in Example 2. and FIG. 7 shows the powder X of the sintered body described in Comparative Example 3.
It is a line diffraction diagram, and FIG. 8 is a flow sheet diagram showing an example of the method of the present invention.

Claims (1)

[Claims] 1. Silicon carbide powder 100 with an average particle size of 3 microns or less
a first step of preparing a mixed powder containing 0.5 to 15.0 parts by weight of a temporary binder in solids;
a second step of molding the mixed powder into a green body;
a third step of sintering the green body at a temperature range of 1,750 to 2,100°C, and at least silicon carbide among the silicon carbide and temporary binder is sintered with hydrogen fluoride before being molded into the green body in the second step. A method for producing a silicon carbide sintered body, which is dried by contacting with an acid, and the atmosphere from at least the drying of the hydrofluoric acid to the completion of sintering is non-oxidizing. 2. The manufacturing method according to claim 1, wherein in the first step, 100 parts by weight of silicon carbide powder is brought into contact with 0.2 parts by weight or more of hydrofluoric acid corresponding to hydrogen fluoride. 3. The manufacturing method according to claim 1 or 2, wherein in the first step, the silicon carbide powder and the temporary binder are uniformly mixed and then brought into contact with hydrogen fluoride and dried. 4. The manufacturing method according to claim 1 or 2, wherein in the first step, silicon carbide powder, temporary binder and hydrofluoric acid are uniformly mixed and then dried. 5. The manufacturing method according to claim 1 or 2, wherein in the first step, silicon carbide powder and hydrogen fluoride are uniformly mixed and dried, and then a temporary binder is mixed therein. 6 In the first step, the mixed powder has a solid content of 1.0~
6. A method according to any one of claims 1 to 5, containing 7.0 parts by weight of temporary binder. 7 The temporary binder used in the first step is:
The manufacturing method according to any one of claims 1 to 6, which is made of an organic material. 8. The manufacturing method according to any one of claims 1 to 7, wherein the silicon carbide powder used in the first step has an average particle size of 1.0 microns or less. 9. The manufacturing method according to any one of claims 1 to 8, wherein in the first step, the mixed powder contains a boron-containing material corresponding to 3.0 parts by weight or less of boron. 10. The manufacturing method according to any one of claims 1 to 9, wherein the boron-containing material is selected from boron, boron carbide, or a mixture thereof having an average particle size of 1 micron or less. 11 In the third step, the formed body is heated to 1800-2000℃
11. The manufacturing method according to any one of claims 1 to 10, wherein the manufacturing method is sintered for at least 15 minutes within a temperature range of . 12 The non-oxidizing atmosphere is a gas atmosphere consisting of at least one selected from argon, helium, neon, nitrogen, hydrogen, carbon monoxide, and hydrogen fluoride, or vacuum.
The manufacturing method according to any one of Item 11.