JPH0158155B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a silicon carbide sintered body,
In particular, the present invention relates to a method for producing a high-strength and homogeneous silicon carbide sintered body. Silicon carbide has extremely good chemical and physical properties, making it particularly suitable for applications as high-temperature structural materials used under harsh conditions, such as in gas turbine components and high-temperature heat exchangers. It is the material. Conventionally, the pressure sintering method and the reaction sintering method are widely known as methods for manufacturing silicon carbide sintered bodies. However, the former pressure sintering method makes it difficult to produce sintered bodies with complex shapes and has low productivity, while the latter reaction sintering method produces high-strength sintered bodies. Since it is difficult to obtain and contains a large amount of free silicon, it has the disadvantage that its strength deteriorates in a high temperature range. By the way, silicon carbide is a material that is difficult to sinter.
Until now, it has been difficult to use the no-pressure sintering method, which is commonly used to manufacture oxide ceramics, in which a formed body is molded at room temperature and sintered under no pressure, for sintering silicon carbide. However, recently a pressureless sintering method has been reported in which a mixed powder consisting of silicon carbide, a boron-containing additive, and a carbonaceous additive is compacted and sintered in an inert atmosphere. There is. For example, according to the invention described in Japanese Patent Application Laid-Open No. 78609/1983, which claimed priority based on Patent Application No. 409073 filed in the United States on October 24, 1973, silicon carbide was added to a boron-containing additive ( 0.3-3.0 wt% B) and a carbon-containing additive (0.1-1.0 wt% C), and then the molded body was heated at 1900 °C in an inert atmosphere.
A method for obtaining a silicon carbide sintered body having at least 85% of the theoretical density by pressureless sintering at a temperature of ~2100°C is disclosed. As mentioned above, in the pressureless sintering method of silicon carbide, boron-containing additives and carbonaceous additives are added to the raw materials as the main sintering aids, and in addition, beryllium, aluminum, etc. There are also examples where additives containing it have been used. The reason why the boron-containing additive is added to the starting materials as an additive is that by allowing boron to coexist at each contact point of the silicon carbide particles during sintering, an adhesive layer is formed on the surface of the silicon carbide particles, and the network This is because it has the effect of adhering each particle during formation and promoting uniform shrinkage.On the other hand, the reason why carbonaceous additives are added is that silicon carbide particles are always covered with a silica film at room temperature, and this silica Since self-sintering of silicon carbide is inhibited by the film, the silica film is reduced and removed to improve sinterability between silicon carbide particles and to suppress coarsening of crystal grains during sintering. It is from. Therefore, it is effective that the densification aid and the carbonaceous additive are uniformly dispersed in the silicon carbide fine powder. The carbonaceous organic compound is widely used because it has the advantage that the surface of silicon carbide particles can be uniformly coated with carbon by adding the carbonaceous organic compound in the form of a solution. However, when carbonaceous organic compounds such as those mentioned above are used as carbonaceous additives, they tend to segregate as the solvent moves during drying, and they are thermally decomposed in advance to remove free carbon before molding the resulting product. When molding a formed body without generating or thermally decomposing it, there is a drawback that the temperature increase rate and the atmosphere in the furnace must be strictly controlled during the thermal decomposition stage during firing. On the other hand, among the conventionally known methods for producing pressureless sintered bodies of silicon carbide, in particular, there is no method for producing high-strength sintered bodies using inorganic carbonaceous additives as carbonaceous additives. , for example, JP-A-54-67598
The methods described in Japanese Patent Application Laid-open No. 54-67599 are known, but these methods all start with β-type silicon carbide obtained by thermally decomposing an extremely expensive organosilicon polymer compound. This method uses silicon carbide as a raw material, which is synthesized by a normal method using silica and carbon, an inorganic carbonaceous additive, and a densification aid added as necessary to produce high-strength silicon carbide. There was no known method for producing a pressureless sintered body. The present inventor has proposed a non-pressure sintered body of silicon carbide produced by using silicon carbide fine powder synthesized by a normal method using silica and carbon as a starting material and using inorganic carbonaceous fine powder as carbonaceous fine powder. As a result of various studies, it has been found that there are variations in density or crystal grain size due to non-uniform microscopic dispersion of carbonaceous fine powder, as described below, which causes a significant decrease in the physical properties of the sintered body, especially the bending strength. We newly discovered that this is the case. That is, as described above, the sintering raw materials used in producing the pressureless silicon carbide sintered body are as follows:
It is important that the silicon carbide fine powder and the carbonaceous fine powder are uniformly dispersed in the mixture, but since the silicon carbide fine powder and the inorganic carbonaceous fine powder have extremely strong cohesive properties, it is necessary to sufficiently loosen the agglomeration and disperse them uniformly. It is difficult to obtain a mixture of silicon carbide particles, and the raw materials for sintering silicon carbide that have been used in the past partially contain agglomerated silicon carbide powder and inorganic carbonaceous powder. If a pressureless silicon carbide sintered body is manufactured using such a raw material for sintering, the effect of the carbonaceous fine powder during sintering will be uneven, resulting in variations in density, crystal grain size, etc. The inorganic carbonaceous fine powder that causes microscopic variations in physical properties and forms the agglomerated particles remains in the sintered body, resulting in defects in the sintered body. Therefore, in order to obtain a particularly high-strength silicon carbide pressureless sintered body using inorganic carbonaceous fine powder as carbonaceous fine powder, dispersion of silicon carbide fine powder and inorganic carbonaceous fine powder in the raw material for sintering is necessary. It is extremely important that the conditions be uniform. Incidentally, a method for producing a pressureless sintered body of silicon carbide using inorganic carbonaceous fine powder as the carbonaceous fine powder has been reported in the past. For example, according to Japanese Patent Application Laid-open No. 52-6716, which claimed priority based on patent application No. 591840 filed in the United States on June 30, 1975, in a solution of polyethylene glycol added to benzene, A method is described in which a mixed powder of β-type silicon carbide, acetylene black, and amorphous boron is ground in a ball mill, and then a slurry containing the mixed powder is spray-dried, shaped, and then sintered. However, this method does not take into account any means of loosening the agglomeration of acetylene black, making it difficult to loosen it sufficiently, and furthermore, no means of stabilizing the dispersion state and preventing aggregation in the subsequent steps are considered. However, it has been difficult to form a mixed powder in which silicon carbide fine powder and carbonaceous additive are sufficiently uniformly dispersed. As mentioned above, in a method for producing a raw material for silicon carbide sintering that uses inorganic carbonaceous fine powder as carbonaceous fine powder, there is no known method for loosening the agglomeration of silicon carbide fine powder and inorganic carbonaceous fine powder and dispersing them sufficiently uniformly. Ta. The present invention provides a dispersion having a surprising effect of loosening agglomeration of the silicon carbide fine powder and inorganic carbonaceous additive and maintaining a uniform dispersion state when inorganic carbonaceous fine powder is used as the carbonaceous fine powder. A raw material for silicon carbide sintering in which fine silicon carbide powder and fine carbonaceous powder are dispersed in an extremely uniform state is produced by using a chemical agent, and then this raw material for silicon carbide sintering is sintered without pressure. The object of the present invention is to provide a method for producing a homogeneous and high-strength silicon carbide sintered body. According to the first aspect of the present invention, a mixture of silicon carbide fine powder and a carbonaceous additive is molded into a green body, and the green body is sintered without pressure to produce a silicon carbide sintered body. In the method, silicon carbide fine powder and inorganic carbonaceous fine powder are added to a dispersion medium containing a dispersant and uniformly dispersed to create a suspension, and then this suspension is dried to form the dispersion medium. Mainly removes only the medium inside,
Silicon carbide sintering is characterized in that a part of the dispersant remains, thereby creating a dry mixture in a uniformly mixed state while maintaining a uniformly mixed state, followed by molding and pressureless sintering. The above object can be achieved by the method of manufacturing the body. Furthermore, according to the second aspect of the present invention, a mixture consisting of fine silicon carbide powder and a carbonaceous additive is molded into a green body, and this green body is sintered without pressure to produce a silicon carbide sintered body. In the manufacturing method, when the silicon carbide fine powder and the inorganic carbonaceous fine powder are suspended and mixed in a dispersion medium containing a dispersant, at least one selected from cyclohexane and benzene or water is used as a medium. A suspension is created by uniformly dispersing the mixture in a dispersion medium prepared by adding and mixing a dispersant, and then this suspension is freeze-dried in an atmosphere maintained at a temperature lower than the melting point of the dispersion medium. Then, by sublimating and drying only the dispersion medium from the freeze-dried mixture under reduced pressure, a dry mixture is created in which a uniformly dispersed state is maintained with the dispersant remaining, and this is molded into any shape. The above object can be achieved by a method for producing a silicon carbide sintered body, which is characterized in that a molded body having the shape of is formed and the molded body is sintered under no pressure. Next, the present invention will be explained in detail. As mentioned above, it is important that the raw material for silicon carbide sintering is a mixture in which silicon carbide fine powder, inorganic carbonaceous fine powder, and a densification aid added as necessary are uniformly dispersed. However, the silicon carbide fine powder and the inorganic carbonaceous fine powder are highly cohesive powders, and even when suspended in a dispersion medium, conventional dispersion methods cannot efficiently disperse them uniformly, and No suitable method for maintaining uniform dispersion was known. The present inventor has conducted various studies to obtain a mixture in which silicon carbide fine powder, inorganic carbonaceous fine powder, and a densification aid added as necessary are uniformly dispersed.
It has an extremely good affinity with the silicon carbide fine powder or inorganic carbonaceous fine powder, and even with a relatively small amount added, it can produce a suspension in an extremely uniform and long-term stable dispersion state that was previously unimaginable. We have newly discovered a dispersant that is easily obtainable and exhibits surprising effects, and we have also discovered that by using the dispersant, we can obtain extremely high-strength sintered bodies that have been difficult to obtain in the past. They found out that it is possible and completed the present invention. According to the present invention, when a dispersion medium made of an organic substance is used as a dispersion medium, an organic substance having at least one of an amino group, a sulfonic acid group, a carboxylic acid group, and an ester group is used as a dispersant. Among the dispersants, those having the effect of loosening the agglomeration of silicon carbide fine powder and dispersing it uniformly include, for example, polyoxyethylene fatty acid amine, sorbitan fatty acid ester, dialkyl sulfosuccinate salt, fatty acid, and alkyl amine. salt or benzenesulfonic acid,
Examples of substances that have the effect of loosening agglomeration and uniformly dispersing inorganic carbonaceous fine powder include polyoxysorbitan fatty acid ester, polyoxyethylene glycerin fatty acid ester, polyethylene glycol fatty acid ester, polyoxyethylene fatty acid amine, sorbitan fatty acid ester, and pentaerythritol. There are fatty acid esters, propylene glycol fatty acid esters, sucrose fatty acid esters, polyglycerin fatty acid esters, fatty acid alkanolamides, and amine oxides, and these can be used alone or in combination. According to the present invention, the organic dispersion medium includes acetone, ethanol, methanol, butanol, hexane, heptane, nonane, toluene, xylene, ethyl methyl ketone, ethyl benzene,
Preferably, at least one selected from trichloroethylene, cyclohexane, benzene, and carbon tetrachloride is used. On the other hand, when using water as the dispersion medium,
As a dispersant, organic substances with amino groups, organic substances with sulfonic acid groups, organic substances with carboxylic acid groups, organic substances with ether groups, organic substances with ammonium groups, aluminates, phosphates, phosphoric acid It is preferable to use one or more selected from complex salts, sulfonates, and silicates, and examples of the dispersants having the effect of loosening agglomeration and uniformly dispersing silicon carbide fine powder include: Tetramethylammonium hydroxide, monoethanolamine, monoethylamine, diethylamine, triethylamine, propylamine, isobutylamine, monobutylamine, di-n-propylamine, tannic acid, sodium alginate, ammonium alginate, polyacrylic acid, polyacrylic acid amine , polyacrylic ester, ammonium polyacrylate,
Examples include sodium ligninsulfonate, ammonium ligninsulfonate, sodium aluminate, carboxymethyl cellulose, and water glass. Examples of substances that have the effect of loosening agglomeration and uniformly dispersing inorganic carbonaceous fine powder include fatty acid salts, alkylbenzene sulfonates, There are linear alkylbenzene sulfonates, α-olefin sulfonates, naphthalene-formalin condensate sulfonates, polyoxyethylene alkyl ethers, and polyoxyethylene alkyl phenyl ethers, and these can be used alone or in combination. Can be done. Note that the dispersion state can also be improved by adjusting the pH value of the dispersion medium using aqueous ammonia or the like. According to the present invention, the amount of the dispersant added is preferably within the range of 0.05 to 4 parts by weight based on 100 parts by weight of the total weight of the silicon carbide fine powder and the inorganic carbonaceous fine powder. The reason for this is that if the amount of the dispersant added is less than the above range, it will not be possible to sufficiently loosen the agglomeration of the silicon carbide fine powder and inorganic carbonaceous fine powder in the dispersion medium and maintain a uniform dispersion state. It is difficult to produce raw materials for silicon carbide sintering in a well-mixed state, and if the amount exceeds the above range, it is not only uneconomical to add more dispersant than necessary, but also the dispersant may remain in the formed body. This is because it has an adverse effect on sintering. Among the dispersants, the amount of the dispersant intended to loosen the agglomeration of the silicon carbide fine powder and disperse it uniformly is advantageously within the range of 0.02 to 3 parts by weight per 100 parts by weight of the silicon carbide fine powder. Further, it is advantageous that the amount of a substance added for the purpose of loosening agglomeration and uniformly dispersing the inorganic carbonaceous fine powder is within the range of 0.03 to 300 parts by weight per 100 parts by weight of the inorganic carbonaceous fine powder. It is advantageous to use a dispersant whose purpose is to loosen the agglomeration of the inorganic carbonaceous fine powder and disperse it uniformly, by mixing it with the inorganic carbonaceous fine powder in advance.
The reason for this is that by mixing the dispersant with the inorganic carbonaceous fine powder in advance, the surface of the inorganic carbonaceous fine powder can be efficiently coated, and the amount of the dispersant adhering to the surface of the silicon carbide fine powder and other additives can be reduced. This is because even with a relatively small amount of dispersant, it is possible to efficiently deagglomerate and uniformly disperse the inorganic carbonaceous fine powder. According to the present invention, it is advantageous that the content of silicon carbide fine powder and inorganic carbonaceous fine powder in the suspension is in the range of 3 to 50% by volume. The reason why it is advantageous for the content to be within the range of 3 to 50% by volume is that the silicon carbide fine powder and the inorganic carbonaceous fine powder in the suspension have extremely strong cohesiveness. If it is higher, the amount of silicon carbide particles present per unit volume increases, so the silicon carbide fine powder and the inorganic carbonaceous fine powder are extremely likely to aggregate, making it difficult to obtain the uniform dispersion state that is the objective of the present invention. On the other hand, considering the purpose of the present invention to form a suspension in a uniformly dispersed state, it is advantageous to keep the content as low as possible; however, if it is lower than 3% by volume, there will be substantial carbonization per unit equipment. This is because the manufacturing capacity of raw materials for silicon sintering is extremely low and uneconomical, and more suitable results can be obtained in the range of 5 to 45% by volume. As a dispersion means for obtaining a suspension in a uniformly dispersed state, which is the object of the present application, it is possible to use a device having a strong shearing force capable of loosening the agglomeration of the silicon carbide fine powder and the inorganic carbonaceous fine powder. It is advantageous to use at least one of a vibrating mill, an attritor, a ball mill, a colloid mill, or a high-speed mixer, for example, to mix silicon carbide fine powder, inorganic carbonaceous fine powder, and a densification aid added as necessary with a dispersion medium. By charging it into a liquid and mixing it in the presence of a dispersant, it is possible to easily obtain the uniform dispersion state that is the object of the present invention in a short time. According to the present invention, it is preferable to use at least one selected from gas black, oil furnace black, naphthalene black, anthracene black, and acetylene black as the inorganic carbonaceous fine powder, and the amount added is equal to or less than silicon carbide. It is advantageous that the amount is 0.3 to 4.0 parts by weight based on 100 parts by weight of the fine powder, and more suitable results are obtained within the range of 1.0 to 3.0 parts by weight. According to the present invention, as the silicon carbide fine powder, silicon carbide consisting of one or more types selected from α-type crystals, β-type crystals, and amorphous crystals can be used. In particular, in order to produce a high-strength silicon carbide sintered body, it is advantageous to use silicon carbide fine powder mainly composed of β-type crystals as a starting material. The densification aid added as necessary is mainly a boron-containing additive, and other conventionally known additives containing beryllium, aluminum, etc. can also be used as the densification aid.
As the boron-containing additive, it is advantageous to add, for example, at least one selected from boron and boron carbide in an amount of 0.1 to 3.0 parts by weight based on 100 parts by weight of silicon carbide fine powder in terms of boron content. According to the invention, shaping aids can be added to the suspension. The molding aid is used as a lubricant or a binder during molding by being blended into the powder, and exhibits the effect of reducing molding defects that occur in the formed body. Among the above-mentioned molding aids, for example, those having a lubricating effect include carbo wax, magnesium stearate, barium stearate, aluminum stearate, zinc stearate, stearic acid, cellulose acetate, glycerin, polyethylene glycol, etc., and have a binding effect. Examples include starch, dextrin, gum arabic, casein, molasses, Na-carboxymethyl cellulose,
Methyl cellulose, cellulose acetate, glycerin, polyvinyl alcohol, polyvinyl methyl ether, polyacrylic acid amide, polyethylene glycol, tannic acid, liquid paraffin, wax emulsion, ethyl cellulose, polyvinyl acetate, phenol resin, etc. are used alone or in combination. can be used. According to the present invention, it is advantageous for the dispersant or molding aid to contain as little metal elements as possible. The reason for this is that the metal elements remain in the sintered body and deteriorate the physical properties of the sintered body, particularly properties such as strength and oxidation resistance in a high temperature range. According to the present invention, it is necessary to remove the dispersion medium while maintaining a uniform mixing state from the suspension that has been uniformly dispersed and mixed. Methods for removing the dispersion medium while maintaining a more uniform mixing state than the suspension include (1) a spray drying method that evaporates and removes the dispersion medium within an extremely short period of time; This can be advantageously carried out by a freeze-drying method in which the dispersion medium is frozen in an atmosphere maintained at a temperature lower than the melting point of the dispersion medium, and then the dispersion medium is sublimated and removed from the frozen product. According to the spray drying method (1), in order to prevent carbonaceous fine powder, densification aid, etc. from segregating due to the movement of the dispersion medium due to evaporation, it is necessary to disperse the carbonaceous fine powder, densification aid, etc. while maintaining a uniform mixing state. It is advantageous to concentrate the suspension by removing part of the medium and then spray drying said concentrated suspension, further reducing the drying time by reducing the particle size of the sprayed droplets. It is advantageous to make it as small as possible. Note that this drying method has the advantage that it is possible to obtain a granular silicon carbide sintering raw material with extremely good fluidity. In this case, the content of solids in the concentrated suspension is preferably in the range of 10 to 50% by volume. The freeze-drying method (2) can be advantageously applied when at least one selected from cyclohexane and benzene or water is used as the dispersion medium. According to this method, the suspension is sprayed into an atmosphere maintained at a temperature lower than the melting point of the dispersion medium and then frozen, and then the dispersion medium in the frozen material is sublimated under reduced pressure. Drying is advantageous. The reason for spraying the suspension is that by spraying the suspension into fine droplets, heat exchange can be performed quickly;
As a result, it is possible to easily prevent the drawbacks of agglomeration and segregation of silicon carbide fine powder, carbonaceous fine powder, and the densification aid added as necessary when freezing. Furthermore, the reason why the dispersion medium is sublimated and dried under reduced pressure from the frozen material is that by freeze-drying, the silicon carbide fine powder, the carbonaceous fine powder, and the densification aid added if necessary are not segregated, and the dispersion medium is uniformly dried. This is because the dispersion medium can be removed while maintaining a good mixed state. Another advantage of spraying the suspension in this drying method is that by spraying the suspension with a solid content in the range of 15 to 50% by volume, it improves fluidity and moldability. It is possible to obtain a granular raw material for silicon carbide sintering which has extremely excellent properties. Advantageously, the temperature in the atmosphere in which the suspension is frozen is maintained at least 5° C. below the melting point of the dispersion medium. By maintaining the temperature at least 5°C lower than the melting point of the dispersion medium, the time required for the suspension to freeze can be relatively shortened. This is because the disadvantages of aggregation and segregation of each agent can be easily prevented. In addition, the lower the temperature in the atmosphere, the faster the suspension can be frozen, but cooling the atmosphere requires a large amount of cost and is uneconomical. Particularly suitable results can be obtained within a range of 10 to 100°C lower than the melting point of the dispersion medium. According to the present invention, the powder mixture produced as described above is granulated as necessary to form a formed product of any shape, and then charged into a sintering furnace and heated for 1900 minutes in an inert gas stream. By sintering within the temperature range of ~2300°C, a high-strength and homogeneous silicon carbide sintered body can be easily produced. There are various molding methods that can be used for forming the formed body depending on the shape of the desired pressureless sintered body, but according to the present invention, tape casting, extrusion, vibration molding, and injection molding can be used. Means such as molding, dust press molding or dry press molding can be applied, among which it is advantageous to apply injection molding or dry press molding. Next, the present invention will be specifically explained using Examples and Comparative Examples. Example 1 Silicon carbide was produced by the method for producing silicon carbide mainly composed of β-type crystals described in Japanese Patent Publication No. 55-40527, and a silicon carbide fine powder that was further purified and classified in particle size was used. The silicon carbide fine powder consists of 96.2% by weight of β-type crystals, 0.38% by weight of free carbon, and 0.18% by weight of free carbon.
It contained % oxygen by weight and had a specific surface area of 14.2 m ² /g. Inorganic carbonaceous fine powder has an average particle size of 210A and a specific surface area of 125.
m ² /g oil furnace black was used. 1 g of polyoxyethylene dodecylamine and benzene for 10 g of the above oil furnace black.
100 ml was added and mixed for 3 hours using a ball mill. Next, the silicon carbide fine powder is added to the mixture.
500 g of commercially available 200-mesh boron carbide grains were crushed and classified to have a specific surface area of 21.4 m ² /g, and 6.5 g of boron carbide powder was added with 470 ml of benzene and 5.0 g of polyethylene glycol using a vibration mill. Dispersion treatment was carried out for 4 hours. Discharging the suspension from the vibration mill while operating the vibration mill,
Frozen granules were obtained by spraying into a container maintained at -50°C. The obtained frozen granules had an average particle size of 0.11 mm. Then, the frozen granules are
Freeze-drying was carried out by placing the sample in a container maintained at 0.11-20 mmHg and 0-5°C. The resulting dry mixture has a powder bulk density of 0.53 g/cm ³
It was a hot granule. An appropriate amount was taken from this dry mixture and pre-molded using a metal mold at a pressure of 0.15 t/cm ² , and then molded using an isostatic press at a pressure of 2.0 t/cm ² . The formed body was placed in a Tammann type sintering furnace and sintered in an argon gas stream. Sintering was maintained at a maximum temperature of 2100°C for 30 minutes. The obtained sintered body had a density of 3.14 g/cm ³ . Process this sintered body into a rod shape of 3 x 3 x 30 mm,
Finally polished with 1μm diamond abrasive grain, span 20mm, crosshead speed 0.5mm/
When the three-point bending strength was measured under the conditions of min., it had an average strength of 68.3 Kg/mm ² at room temperature. Example 2, Comparative Example 1 A suspension was prepared using the same formulation as Example 1, but with different amounts of dispersant as shown in Table 1.
A dry mixture was obtained in the same manner as in Example 1. An appropriate amount was taken from this dry mixture, and a sintered body was obtained in the same manner as in Example 1. The physical properties of the obtained sintered body were measured in the same manner as shown in Example 1, and are shown in Table 1.

[Table] Example 3 Propylene glycol fatty acid ester for 8 g of oil furnace black used in Example 1
0.5 g and 100 ml of acetone were added and mixed for 1 hour using a vibrating mill. Next, 500 g of the silicon carbide fine powder used in Example 1, 6.5 g of the boron carbide powder used in Example 1, 470 ml of acetone, 5.0 g of polyethylene glycol, and 1 g of sodium dioctyl sulfosuccinate were added to the mixture, and the mixture was mixed using an attritor. Dispersion treatment was performed for 4 hours to obtain a suspension. The suspension was sprayed into a container maintained at 80°C to obtain a granular dry mixture. An appropriate amount was taken from this dry mixture and a sintered body was obtained in the same manner as in Example 1. The obtained sintered body had a density of 3.10 g/cm ³ . Further, the three-point bending strength measured in the same manner as in Example 1 had an average strength of 63.2 Kg/mm ² at room temperature. Example 4 The formulation was the same as in Example 3, but polyoxysorbitan fatty acid ester, polyoxyethylene glycerin fatty acid ester, polyethylene glycol fatty acid ester, sorbitan fatty acid ester, pentaerythritol fatty acid ester, and salt were used instead of propylene glycol fatty acid ester. A suspension was prepared by adding a sugar fatty acid ester, a polyglycerin fatty acid ester, a fatty acid alkanolamide, and an amine oxide, respectively, and a dry mixture was obtained in the same manner as in Example 3. An appropriate amount was taken from these dry mixtures and a sintered body was obtained in the same manner as in Example 1. The physical properties of the sintered bodies thus obtained were measured in the same manner as shown in Example 1, and it was found that both sintered bodies were manufactured using the dry mixture obtained without adding the above-mentioned dispersant as a starting material. It was observed that the average strength was significantly improved compared to the body. Example 5 Silicon carbide was commercially available α-type silicon carbide powder (GC
#6000) was further pulverized, purified, and classified for particle size, and a fine silicon carbide powder was used. The silicon carbide fine powder is 0.42
Contains wt% free carbon, 0.14wt% oxygen,
It had a specific surface area of 15.4 m ² /g. The inorganic carbonaceous fine powder used was obtained by crushing acetylene black to have a specific surface area of 90 m ² /g. 1.6 g of polyoxyethylene nonylphenol ether and 100 ml of distilled water were added to 8 g of the acetylene black and mixed for 24 hours using a ball mill. Next, the silicon carbide fine powder is added to the mixture.
500g and 6.5g of boron carbide powder used in Example 1
Then, 190 ml of distilled water, 5.0 g of cellulose acetate, and 1 g of tetramethylammonium hydroxide were added, and a dispersion treatment was performed for 4 hours using an attritor. The suspension was sprayed into a container maintained at -60°C to obtain frozen granules with an average particle size of 0.12 mm. The frozen granules were then placed in a container maintained at 0.01 to 20 mmHg and -5 to -10°C, and freeze-dried. The resulting dry mixture has a powder bulk density of 0.70 g/cm ³
The granules were hot. An appropriate amount was taken from this dry mixture and a sintered body was obtained in the same manner as in Example 1, except that the maximum temperature during sintering was changed to 2150°C. The obtained sintered body had a density of 3.16 g/cm ³ . Further, the three-point bending strength measured in the same manner as in Example 1 had an average strength of 57.7 Kg/mm ² at room temperature. Example 6 Same formulation as Example 5, but fatty acid salt, alkylbenzene sulfonate, linear alkylbenzene sulfonate, α-olefin sulfonate, and naphthalene-formalin condensate were used instead of polyoxyethylene nonylphenol ether. A suspension was prepared by adding the sulfonate and polyoxyethylene alkyl ether, respectively, and a dry mixture was obtained in the same manner as in Example 5. An appropriate amount was taken from these dry mixtures and a sintered body was obtained in the same manner as in Example 1. The physical properties of the sintered bodies thus obtained were measured in the same manner as shown in Example 1, and it was found that both sintered bodies were manufactured using the dry mixture obtained without adding the above-mentioned dispersant as a starting material. It was observed that the average strength was significantly improved compared to the body. Example 7 Same formulation as Example 5, but monoethanolamine, monoethylamine, diethylamine, triethylamine, propylamine, isobutylamine, monobutylamine, di-n-propylamine, tannin instead of tetramethylammonium hydroxide. Acid, sodium alginate, ammonium alginate, polyacrylic acid, amine polyacrylate, polyacrylic ester, ammonium polyacrylate, sodium ligninsulfonate, ammonium ligninsulfonate, carboxymethyl cellulose, sodium aluminate,
A suspension was prepared by adding water glass, and a dry mixture was obtained in the same manner as in Example 5. An appropriate amount was taken from these dry mixtures and a sintered body was obtained in the same manner as in Example 1. The physical properties of the sintered bodies thus obtained were measured in the same manner as shown in Example 1, and it was found that both sintered bodies were manufactured using the dry mixture obtained without adding the above-mentioned dispersant as a starting material. It was observed that the average strength was significantly improved compared to the body. As described above, according to the method of the present invention, it is possible to produce a homogeneous mixture in which silicon carbide fine powder and inorganic carbonaceous fine powder are deagglomerated and sufficiently uniformly dispersed. It is possible to obtain a high-strength and homogeneous pressureless sintered body of silicon carbide with extremely little microscopic variation in crystal grain size, etc., and is extremely useful industrially.

Claims (1)

[Claims] 1. A method for producing a silicon carbide sintered body by molding a mixture of fine silicon carbide powder and a carbonaceous additive into a green body, and sintering the green body without pressure, A suspension is created by adding silicon carbide fine powder and inorganic carbonaceous fine powder to a dispersion medium containing a dispersant and uniformly dispersing the same, and then drying this suspension to remove the medium in the dispersion medium. Mainly removes only the liquid,
A method for producing a silicon carbide sintered body, characterized in that a part of the dispersant remains, thereby creating a dry mixture that maintains a uniform mixed state, and then molding and sintering without pressure. . 2. The dispersion medium contains at least one of an amino group, a sulfonic acid group, a carboxylic acid group, and an ester group as a dispersant for the organic medium.
The method for producing a sintered silicon carbide body according to claim 1, characterized in that a seed organic substance is used. 3 The dispersion medium is water, and the dispersant is an organic substance having an amino group, an organic substance having a sulfonic acid group, an organic substance having a carboxylic acid group, an organic substance having an ether group, or an ammonium group. Claim 1, characterized in that one or more selected from organic substances, aluminates, phosphates, phosphate complexes, sulfonates, and silicates are used. The method for producing the described silicon carbide sintered body. 4 The amount of the dispersant added is 0.05 to 100 parts by weight of the total weight of silicon carbide fine powder and inorganic carbonaceous fine powder.
Claims 1 to 3 within the range of 4 parts by weight
A method for producing a silicon carbide sintered body according to any one of the items. 5. The dispersion medium liquid made of an organic substance includes acetone,
Claim 2 is at least one selected from ethanol, methanol, butanol, hexane, heptane, nonane, toluene, xylene, ethyl methyl ketone, ethylbenzene, trichloroethylene, cyclohexane, benzene, and carbon tetrachloride. The method for producing the described silicon carbide sintered body. 6. The silicon carbide according to claim 1 or 4, wherein the inorganic carbonaceous fine powder is at least one selected from gas black, oil furnace black, naphthalene black, anthracene black, and acetylene black. A method for producing a sintered body. 7. A method of manufacturing a silicon carbide sintered body by molding a mixture consisting of fine silicon carbide powder and a carbonaceous additive to form a green body, and sintering the green body without pressure, comprising: fine silicon carbide powder and inorganic carbon; When suspending and mixing the fine powder in a dispersion medium containing a dispersant, a dispersion medium prepared by adding and mixing a dispersant to at least one selected from cyclohexane and benzene or water as a medium. A suspension is prepared by uniformly dispersing the suspension in a liquid, and then this suspension is freeze-dried in an atmosphere maintained at a temperature lower than the melting point of the dispersion medium, and then the freeze-dried mixture is then freeze-dried. By sublimating only the dispersion medium under reduced pressure, a dry mixture is created in which a uniformly dispersed state is maintained with the dispersant remaining, and this is molded into a molded object of any shape. A method for producing a silicon carbide sintered body, characterized by pressureless sintering. 8. Silicon carbide sintering according to claim 7, characterized in that the uniformly dispersed suspension is sprayed into an atmosphere maintained at a temperature lower than the melting point of the dispersion medium and frozen. How the body is manufactured.