JPH0224781B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing easily sinterable silicon carbide fine powder, and in particular, the present invention involves heating a raw material in which an aluminum source is uniformly dispersed in a raw material in a vertical furnace to continuously form mainly β-type crystals. The present invention also relates to a method for producing easily sinterable silicon carbide fine powder containing aluminum as a solid solution. Conventionally, as a method for manufacturing easily sinterable silicon carbide powder for silicon carbide sintered bodies, for example, (a) JP-A-55-
136174 and (b) JP-A-55-20268 are disclosed. According to JP-A No. 55-136174 in (a) above,
``Silicon carbide containing 0.2 to 0.6% aluminum as a solid solution is made into a fine powder of 3 microns or less, and this is used as a sintering raw material, and sintering is performed without adding a sintering accelerator during sintering. A method for producing a characterized silicon carbide sintered body.'' is disclosed. However, the manufacturing method described in the publication in (a) above,
If the carbon or silica used as the raw material contains a large amount of nitrogen dissolved in solid solution, the aluminum and nitrogen may react to form AlN, resulting in insufficient aluminum as a sintering agent, resulting in carbonization. It cannot be said to be optimal as a raw material for manufacturing silicon sintered bodies. On the other hand, according to Japanese Patent Application Laid-Open No. 55-20268, "Boron-based and aluminum-based sintering accelerators are added to silicon raw materials and carbon raw materials, and boron is added to the produced silicon carbide."
Adding 0.05 to 0.25% by weight and aluminum in an amount of 0.05 to 0.40% by weight, under a non-oxidizing atmosphere,
A method for producing easily sinterable silicon carbide powder, which comprises heating to ~2600°C and pulverizing. ' has been disclosed. However, the manufacturing method described in the above publication (b) does not take into account the amount of solid solution nitrogen contained in the carbon and silica raw materials, and the nitrogen that acts as a sintering aid, such as boron and aluminum, is dissolved in solid solution. They are not paying attention to the fact that they are consumed in response to this. On the other hand, many methods for continuously producing silicon carbide have been proposed, such as West German Patent No.
No. 1186447 for the purpose of obtaining α-type silicon carbide,
A method for continuously producing β-type silicon carbide using a vertical furnace in an intermediate process is disclosed, but this method is characterized by raw material processing in which silica sand is coated with carbon material for continuous production, which will be described in detail later. However, since the behavior of SiO gas is not taken into consideration, the raw material yield and thermal efficiency are low, and the exhaust gas passage is blocked due to the precipitation reaction of SiO gas, making it unsuitable for stable continuous operation. On the other hand, a method using silicon carbide containing 10% or more of 2H-type crystals as a starting material is also known, but as mentioned above, the silicon carbide used in this method is essentially a chemical vapor phase reaction deposition method or carbon It is produced by the reaction of black and colloidal silica, and is considered to be very expensive industrially. In the present invention, it is preferable to use silicon carbide mainly composed of β-type crystals. Conventionally, β-type silicon carbide has mainly been used academically as a sample produced by a chemical vapor phase reaction deposition method, but industrially it has never been put to practical use because it is very expensive.
However, an economical and industrial-scale method for continuously producing silicon carbide consisting of β-type crystals is not yet known. From this point of view, the present inventors have previously published a method for continuous production of β-type silicon carbide in Japanese Patent Application No. 49-126425, and
No. 54-60501 proposes an invention relating to a continuous production method of silicon carbide mainly consisting of β-type crystals. The present invention relates to an improvement of the method previously invented and patented by the present inventors, and the present invention improves the thermal efficiency in the preheating zone and the dead weight drop of the charged raw materials, and maintains stable furnace conditions. Moreover, the purpose is to provide a method for continuously producing silicon carbide mainly consisting of β-type crystals in which a certain amount of aluminum is dissolved in solid solution using a low power source unit, and also to provide a method for continuously producing silicon carbide mainly composed of β-type crystals in which a certain amount of aluminum is dissolved. The object is to eliminate and improve the drawbacks of the manufacturing method, and by providing the manufacturing method described in the claims above, the above object can be achieved. The manufacturing method of the present invention will be explained in detail below. According to the present invention, the above-mentioned conventional silicon carbide is produced in which aluminum is contained as a solid solution in silicon carbide obtained by heating a raw material containing carbon and silica in a predetermined molar ratio in a non-oxidizing atmosphere. In the method,
It is necessary to keep the aluminum partial pressure or aluminum oxide partial pressure constant by continuously or intermittently charging a raw material with an aluminum source uniformly dispersed into the raw material from the upper part of the vertical furnace. The reason is that in order for aluminum to be dissolved in some form in the obtained silicon carbide fine powder, Al
This is because it is considered that maintaining the partial pressure of aluminum or the partial pressure of aluminum oxide within the region of the phase diagram of the -O-C system is an important condition. That is, the forms in which aluminum is dissolved in silicon carbide fine powder include Al ₄ C ₃ , Al-O-Si compounds, and Al-
It is thought that it is either Si, but the following factors are considered to be the factors contributing to their solid solution. (b) The reaction temperature is approximately 2000°C to 2700°C (b) The PAl ₂ O and/or Psio partial pressure is constant (c) PAl ₂ O/Pco is in the range of 0.03 to 1.0 ( d) The atmosphere of the reactor must be relatively airtight. (e) The generation of Al ₂ O gas is caused by
Or it needs to be a mixture of silica and other raw materials. Therefore, when producing silicon carbide fine powder industrially, it contains a certain amount of unavoidable impurities derived from various raw materials, such as silica stone and coke as a carbon material. It is an unavoidable problem that trace amounts of oxygen existing as a SiO ₂ film and nitrogen dissolved in solid solution are contained on the surface of the substrate. On the other hand, it is also possible to adjust the aluminum content by appropriately selecting the type of silica stone and coke as the carbon material. Therefore, in conventional methods of manufacturing silicon carbide fine powder and sintered bodies using the same, impurities such as oxygen and nitrogen present on the surface of silicon carbide fine powder have an adverse effect on sintering, for example. Focusing on the drawback that boron added as an auxiliary agent reacts with nitrogen solidly dissolved on the surface of silicon carbide fine powder to form BN bonds and lose the effect of acting as a densification auxiliary agent, the conventional The present inventors confirmed through various experiments that the relatively large amount of boron used in this method can eliminate and improve the causes of deterioration of the oxidation resistance and electrical properties of sintered bodies. The present invention was completed based on the novel findings shown below. That is, the present inventors selectively form AlN by adding or replenishing aluminum to the raw material composition in an amount slightly in excess of that required by the nitrogen content. Either use a silicon carbide powder with a specific content, or contain a certain amount of aluminum in the formed body for sintering. By using silicon carbide fine powder as a starting material, it is possible to uniformly generate sintering initiation bonding points, that is, nets, which occur at the mutual contact areas of silicon carbide fine powder particles when sintering is started, and to prevent sintering. To promote the solid-state diffusion of SiC during solidification, to achieve high density at a relatively low temperature, and to generate plate-shaped crystal grains along with the solid-state diffusion, resulting in a structure in which the plate-shaped crystal grains intersect with each other. Can be done. Furthermore, if carbon is added in excess of the amount required by the oxygen content of conventional silicon carbide fine powder, carbon may remain in the silicon carbide sintered body in the form of free carbon, degrading the physical properties, especially the strength, of the sintered body. The previously thought carbonaceous additive was added in excess of the amount required by the oxygen content of the silicon carbide fine powder, and was actively incorporated in the form of free carbon into the silicon carbide sintered body. As a result, the phase transformation of β-type crystals to α-type crystals is optimized, and the coarsening of plate-shaped crystals caused by conversion of β-type crystals to α-type is prevented, and plate-shaped crystals with relatively uniform grain size are mutually bonded. By intersecting each other and filling the gaps with crystal grains having a finer grain size, we have discovered that it is possible to provide a raw material that has a homogeneous structure and a fine structure, making it possible to obtain a high-density, high-quality sintered body. This is what I found out. That is, according to the present invention, the blended raw material is blended with carbon and silica in a molar ratio of C/SiO ₂ in the range of 3.0 to 4.5, and the aluminum source is preliminarily added to the carbon or silica raw material in the blended raw material. The aluminum source must be either aluminum or an aluminum compound or a mixture of these. Therefore, it is necessary that the blended raw materials contain 0.3 to 3.5% by weight in terms of aluminum. Next, the present invention will be explained in detail. Many crystal types of silicon carbide are known.
Conventionally, it has been roughly divided into two types: the hexagonal α type and the cubic β type. For the former α type, high temperatures such as 2000
High-temperature stable silicon carbide such as 4H and 6H types, which are stable even above 1500°C, and 2H type silicon carbide, which is stable at 1500°C or below, are known. On the other hand, the latter β type is known to be the 3C type, which is stable up to approximately 2000°C. Conventionally, in the pressureless sintering method of silicon carbide, it has been reported that it is easy to stably obtain a relatively high-density sintered body by using high-temperature stable type α-type silicon carbide as the starting material. Type α silicon carbide does not undergo a crystal transformation transition during sintering, and the sintering speed is slow. Therefore, in order to obtain a high-density sintered body, it is necessary to sinter at a high sintering temperature. The sintered body obtained using high-temperature stable type α-type silicon carbide as a starting material has a structure consisting of pseudospherical relatively coarse crystal grains without anisotropy, so it is difficult to obtain a high-strength sintered body. Ta. In addition, when silicon carbide containing mainly β-type crystals is used as a starting material, the β-type crystals tend to change to α-type during sintering, making it difficult to achieve high density. Although it is said that it is necessary to maintain the atmosphere in a nitrogen gas atmosphere or to add 0.05 to 5% by weight of α-type silicon carbide fine powder to the starting material, β-type silicon carbide is used as the starting material, and β-type silicon carbide is used as the starting material. Conventionally, there is no known method for converting most of type silicon carbide into α-type and obtaining a high-density sintered body. That is, according to the present invention, it is necessary that the aluminum source is blended into the carbon or silica raw material, or supplementary added to the raw material, and contained in an amount of 0.3 to 3.5% by weight in terms of aluminum. If the aluminum content is less than 0.3% by weight, all of the solid solution nitrogen contained in the silicon carbide fine powder cannot be fixed as AlN, so when producing a sintered body using this silicon carbide fine powder as raw material, B and N are The effect of B will be lost due to the reaction, while aluminum
If the amount is more than 3.5% by weight, unreacted aluminum will reduce the high-temperature strength of the silicon carbide sintered body. Note that the nitrogen contained in the silicon carbide fine powder is
The amount is preferably about 0.02 to 0.3% by weight.
Although it is possible to reduce the nitrogen content to 0.02% by weight or less, it requires the use of extremely expensive industrial raw materials, and the control of the manufacturing conditions for silicon carbide fine powder is extremely severe, making it impractical.
On the other hand, if nitrogen is contained in an amount of 0.3% by weight or more, an excessive amount of aluminum is required, which adversely affects the properties of the silicon carbide sintered body as described above, which is not preferable. In addition, if the aluminum content is more than 0.7% by weight, the solid-state diffusion of SiC during sintering will be significantly promoted, and plate crystals will grow abnormally rapidly, making it difficult to obtain a high-density sintered body. This is because not only is it difficult, but also the high temperature properties of the sintered body are deteriorated. Therefore, more suitable results are obtained with the amount of aluminum within the above range. The aluminum-containing additive may be any additive that releases aluminum during sintering, and may be a compound of aluminum and boron. In addition, in the present invention, silicon carbide fine powder manufactured by adding an aluminum-containing enrichment agent to the raw material for manufacturing silicon carbide or using a raw material containing a certain amount of aluminum in advance may be used. is advantageous. Although various aluminum-containing salts and metal aluminum can be used as the aluminum-containing enrichment agent, it is economically advantageous to use alumina (aluminum oxide), mullite, and the like. As described above, according to the present invention, by containing or adding a certain amount of aluminum to the raw material composition, AlN can be formed by reacting with solid solution nitrogen present in silicon carbide fine powder. is important. As a result, there is an advantage that boron as a sintering aid can be prevented from reacting with solid solution nitrogen to form BN. This is because Al has a stronger bond with N than B, so by reacting with N, Al can be prevented from reacting with B during the sintering reaction and becoming BN, which means that the amount of B added can be reduced. This is because it can be considered a thing. In addition, it is more preferable that the aluminum source is contained in the carbon or silica source material or other additives in a total amount of 0.3 to 3.5% by weight in terms of aluminum. If it is less than 0.005% by weight, all of the solid solution nitrogen cannot be converted to AlN,
This is because if the amount is more than 0.5% by weight, unreacted Al will remain and deteriorate the properties of the sintered body. Then, 0.015% of the silicon carbide fine powder is added to the nitrogen.
It is more preferable that the content is 0.25% by weight. Due to its synergistic effect with boron, it acts as a densification aid, and also has various effects such as forming grain boundary phases in the early stages of sintering, preventing coarsening of crystals, and removing SiO ₂ films. To do this,
This is because it has been confirmed that the addition and use of the above-mentioned carbon fine powder is effective. According to the present invention, it is necessary to use a manufacturing apparatus characterized by a vertical furnace as shown in FIG. Here, one example of a manufacturing apparatus that can be used to carry out the present invention will be described with reference to the drawings. As shown in FIG. 1, the apparatus used in the method of the present invention has a raw material charging port 1, a pre-heating zone 2, a heating zone 3, a cooling zone 4, and a sealable product discharge port 5, which are arranged vertically. The tubes 8 forming the heating zone are made of graphite, and the means 1 for indirectly electrically heating the charge in the heating zone are provided.
0, 11, and 12, and has a heat insulating layer 9 made of carbon or graphite fine powder on at least the outside of the heating zone 3. The reaction vessel 6 is installed in the center of the apparatus, and the indirect heating means 10, 11, 12 include a graphite heating element 10 vertically disposed outside a tube 8 forming a heating zone, and a heating section of the heating zone 10. Graphite reflective tube 1 provided close to the outside of 11 and inside the heat insulating layer.
Consists of 2. The graphite heating element 10 has a U-shape,
Close to the outside of the cylinder forming the heating zone, the heat generating part 11 of the heating element is provided so as to face the heating zone in the vertical direction and to heat the charge in the heating zone as uniformly as possible. There is. The graphite heating element 10 is located in a space surrounded by a cylinder 8 forming a heating zone and a graphite reflection cylinder 12, and a non-oxidizing gas filling port 1 is provided in the space.
3, a non-oxidizing gas such as argon, helium, nitrogen, carbon monoxide, hydrogen, or the like is sealed, thereby preventing the graphite heating element from being oxidized and consumed due to the intrusion of air. In other words, the vertical furnace is a vertical reaction vessel that has at least a raw material input port in the upper part, a pre-heating zone, a heating zone, and a cooling zone in the downward direction, and a sealed port in the lower part for taking out the product. characterized by something. The reason for this is that in the present invention, the height of the raw material-filled layer in the pre-preparation zone is maintained within the range of 0.2 to 0.9 m, and the amount of CO gas and SiO gas passing through the raw material-filled layer in the pre-preparation zone is increased. death,
This is because precipitates from SiO gas condense in the raw material layer at a high concentration, making it difficult to maintain the smooth fall of the raw material over a long period of time. In other words, it is not preferable in the present invention to increase the production amount by using a reaction vessel that is long in the vertical direction, as this will result in poor weight-lowering properties of the raw materials. In the present invention, the height of the raw material filling layer in the preheating zone is determined from the means for indirectly electrically heating the charge in the heating zone, that is, from the heating part of the heating element or the upper end of the induction coil to the surface of the raw material filling layer. It is the vertical length of In the present invention, the surface of the raw material-filled layer may be held at a constant position for a long time within the height range of the raw material-filled layer, or the position of the raw material-filled layer surface may be pulsated intermittently. According to the present invention, the raw materials blended as described above are continuously or intermittently charged into the preheating zone from the upper part of the reaction vessel, which has a preheating zone, a heating zone, and a cooling zone, and the charged raw materials are The preheating zone of the reaction vessel is continuously or intermittently lowered by its own weight until it reaches the heating zone, and the SiC formation reaction is carried out within the temperature range of 1650 to 2100℃ by indirect electrical heating in the horizontal direction within the heating zone. The most important thing in this invention is to set the height of the raw material filling layer in the preheating zone to 0.2~
It is necessary to maintain the distance within 0.9m. If the height of the raw material packed layer is lower than 0.2 m, high-temperature CO gas will not be sufficiently exchanged with the raw material and will be released outside the system, and the amount of heat transmitted through the reaction vessel and dissipated in the preheating zone will also be reduced. This increases the thermal efficiency, and at the same time increases the amount of SiO gas released outside the system together with the CO gas, increasing heat loss and raw material loss, making it difficult to economically produce β-type silicon carbide. The height of the raw material filling layer
When operating at a height higher than 0.9 m, most of the SiO gas rising from the heating zone becomes the precipitate and is not released outside the system, so the partial pressure of SiO gas inside the reaction vessel gradually increases, and the amount of precipitation in the pre-heating zone increases. As a result, the smooth fall of the raw material under its own weight is significantly inhibited, making long-term stable continuous operation difficult. Therefore, the height of the raw material filling layer in the preheating zone must be maintained within the range of 0.2 to 0.9 m. Best results are obtained within a range of ~0.7m. In addition, the reaction formula of silicon carbide produced from silica and carbon in the production method of the present invention is generally as shown below (1).
It is shown by Eq. SiO ₂ +3C→SiC+2CO...(1) However, the actual main generation mechanism is that SiO gas is generated according to equation (2) below, and the SiO gas and carbon react according to equation (3). It is known that silicon carbide is produced. SiO ₂ +C→SiO+CO...(2) SiO+2C→SiC+CO...(3) In the present invention, high-purity silica selected from silica stone, silica sand, or powder thereof, and various granular or powdered silica are used as starting materials. Carbon selected from carbonaceous materials is used. When blending this raw material, it is not preferable to use a blended raw material in which the blending ratio of carbon to silica is close to or low in chemical equivalent, as in the conventional method using an Acheson furnace. This is because, in the present invention, if a blended raw material similar to the conventional method is used, more of the SiO gas generated according to the above equation (2) will not be converted to SiC, and the amount of SiO gas in the reaction vessel will increase. . Said
SiO gas causes the reactions shown in the following equations (4), (5), and (6) in the preheating zone. 2SiO→SiO ₂ +Si...(4) SiO+CO→SiO ₂ +C...(5) 3SiO+CO→2SiO ₂ +SiC...(6) As a result, the amount of precipitated semi-molten mixed SiO ₂ , Si, SiC, C, etc. increase. Because the precipitates are sticky, the raw materials coagulate with each other, significantly impeding the smooth movement and descent of the most important raw materials for the continuous production of silicon carbide, making long-term stable continuous operation difficult. Become. Therefore, according to the present invention, the blended raw material consisting of silica and carbon is a mixture of silica particles and carbon particles,
Use a product made by mixing silica powder and carbon powder and forming it into aggregates, or add one or more of the following, such as wood chips, rice husks, coconut shells, charcoal particles, coke particles, and lime particles to the aggregates. However, it is necessary that the blended raw materials are blended with an excess of carbon, and the blended molar ratio C/SiO ₂ is within the range of 3.2 to 5.0.
The reason for this is that if the blending ratio is smaller than 3.2, it will be difficult to react the silica sufficiently and maintain the smooth fall of the raw material over a long period of time as described above, while if it is larger than 5.0, carbon will not contribute to the reaction. This is not preferable for economical production of β-type silicon carbide because the thermal efficiency is lowered due to heating to a high temperature and the cost required for the carbon raw material increases. As described above, according to the present invention, raw materials containing silica and carbon in a C/SiO ₂ molar ratio within the range of 3.0 to 4.5 are continuously or intermittently fed into a reaction vessel having a preheating zone, a heating zone, and a cooling zone. 1650 while lowering its own weight to
In a method for producing silicon carbide mainly composed of β-type crystals in which SiC formation reaction is performed by indirect electrical heating to a temperature of ~2100°C, the bulk specific gravity of the blended raw materials is 0.45 ~
The object of the present invention can be achieved by operating while maintaining the height of the material-filled layer in the preheating zone within the range of 0.2 to 0.9 m. Further, according to the present invention, the silicon carbide fine powder needs to contain 90% or more of β-type crystal silicon carbide. The silicon carbide fine powder contains 90% β-type crystal silicon carbide.
The reason why it is necessary to contain the above will be explained. Usually, the crystals mixed in silicon carbide, which mainly consists of β-type crystals, are 2H-type crystals, which are more stable at lower temperatures than β-type crystals, or α-type crystals, such as 4H and 6H types, which are more stable at higher temperatures than β-type crystals. The above-mentioned 2H type silicon carbide is extremely unstable in the temperature range where normal sintering reactions occur, and tends to cause abnormal grain growth during sintering. For example, the optimal range of 2000 is extremely narrow.
On the other hand, if high temperature stable type α-type silicon carbide such as 4H or 6H type is contained, the phase transformation from β-type crystal to α-type crystal will be promoted during sintering. It is difficult to obtain a sintered body having a microstructure in which plate-shaped crystals having relatively uniform grain sizes intersect with each other and the gaps between them are filled with crystal grains having finer grain sizes. Therefore, in order to obtain a sintered body having the above-mentioned microstructure and high strength, which is the object of the present invention, a silicon carbide fine powder containing 90% or more of β-type crystal silicon carbide should be used as a starting material. Among these, silicon carbide fine powder containing 95% or more of β-type crystal silicon carbide is more suitable. Next, examples of the present invention will be described. Example 1 Silica powder (SiO ₂ = 99.7%, 80 mesh or less)
100 parts by weight, petroleum coke powder, (C = 98.7%, aluminum (ash) = 0.5%, 325 mesh or less) 76
and 7 parts by weight of high pitch flour (C = 50.4%, 200 mesh or less) were mixed in a vertical screw mixer for 10 minutes. While spraying a 0.5% aqueous solution of carbomethylcellulose on the above-mentioned blended raw materials, the mixture is molded using a dish-type granulator, sized using a sieve and a burr grizzly, and then placed in a band-type ventilation dryer and dried with hot air at 150°C for 90 minutes. with an average particle size of 10.5mm,
A molding raw material having a bulk specific gravity of 0.60 and a C/SiO ₂ molar ratio of 4.0 was obtained. The molding raw material was charged from the top of the manufacturing equipment with the specifications shown in Table 1, the height of the packed layer in the preheating zone of the raw material layer was 0.5 m, and the mass velocity of CO gas was
While maintaining the temperature within the range of 250 to 260 Kg/m ² hr, and lowering the outer wall temperature of the graphite cylinder in a heating zone controlled to 2150°C, indirect electrical heating is performed to perform the SiC formation reaction at approximately 1850°C. After cooling to 450°C in the generated CO gas, the reaction product was continuously discharged from the outlet. The composition ratio of the obtained product excluding impurities is
SiC is 71.6%, SiO ₂ is 2.3%, free carbon (FC) is 26.1%, and of the SiC, β-type crystal is 96.5%.
%, and the average particle size was 10.3μ.

【table】

[Table] Example 2 and Comparative Example 1 The same operations as in Example 1 were carried out using the same raw materials as in Example 1 and changing the bulk specific gravity by changing the particle size distribution. The results are shown in Table 2.

[Table] Example 3 and Comparative Example 2 Using the same manufacturing equipment as used in Example 1, the same operations as in Example 1 were performed by changing the height of the packed layer in the pre-heating zone of the raw material layer. The results are shown in Table 3.

[Table] These are the values.
2 The power unit shown in Table 3 above is 85%Si
This shows the value converted to C.
In Examples 1 and 2 using the method of the present invention, extremely smooth continuous operation was possible for a long period of time. In the case of Comparative Example 1 using raw materials with large bulk specific gravity,
Even if only a small amount of precipitates are deposited between the SiO gas and raw material particles, cross-linking will occur between the raw material particles due to the agglomerates, which will significantly worsen the drop in the weight of the raw material and cause the blow-up phenomenon of gas and raw materials to occur frequently, resulting in continuous operation. It was difficult to do so, and there were also safety issues in terms of work. According to the method of the present invention as in Examples 1, 3-1, and 3-2, continuous operation could be carried out very smoothly over a long period of time. When operating with the raw material layer kept low as in Comparative Example 2-1, high-temperature CO gas is discharged, and at the same time, SiO gas discharged outside the system is observed, resulting in poor power consumption and economical problems. It wasn't the point. In addition, when the raw material layer is high as in Comparative Example 2-2, it is expected that the heat exchange efficiency between the reaction product gas and the raw material will improve, but in reality, more SiO gas in the reaction product gas is precipitated in the preheating zone than necessary. As a result, the amount of precipitates increased, and troubles due to adhesion and adhesion between raw material particles frequently occurred, resulting in a stagnation in the weight loss of the raw material, making continuous operation difficult. As explained above, according to the method of the present invention,
It has the effect of continuously producing silicon carbide consisting of α-type silicon carbide and fine β-type crystals with a uniform particle size and a low content of impurities in a stable furnace condition for a long period of time and at a high yield, and is suitable for industrial use. Above all, it is extremely useful.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of a vertical continuous manufacturing apparatus used in Examples and Comparative Examples of the present invention. 1... Raw material charging port, 2... Pre-preparation zone, 3... Heating zone, 4
...Cooling zone, 5...Product outlet, 6...Reaction vessel, 8
...Cylinder forming a heating zone, 9...Insulating layer, 10...Graphite heating element, 11...Heating part of graphite heating element, 12...
Graphite reflector tube, 13...Non-oxidizing gas filling port, 14
... Guide electrode, 15 ... Bus bar, 16 ... Temperature measurement hole, 1
8...Produced gas outlet.

Claims (1)

[Claims] 1. Silicon carbide containing aluminum as a solid solution in silicon carbide obtained by heating a raw material containing carbon and silica in a predetermined molar ratio in a non-oxidizing atmosphere. In the manufacturing method, a raw material with an aluminum source uniformly dispersed in the raw material is continuously or intermittently introduced from the top of a vertical furnace,
A method for producing easily sinterable silicon carbide fine powder, which is characterized by producing silicon carbide fine powder mainly composed of β-type crystals and containing aluminum as a solid solution, by keeping aluminum partial pressure or aluminum oxide partial pressure constant. . 2. The aluminum source is either aluminum or an aluminum compound, or a mixture thereof, and the amount of aluminum contained in the raw materials in terms of aluminum is
The manufacturing method according to claim 1, characterized in that the content is 0.3 to 3.5% by weight. 3 The blended raw materials are carbon and silica combined with C/SiO ₂
The aluminum source is blended in a molar ratio of 3.0 to 4.5, and the aluminum source is pre-contained in the blended carbon or silica raw material, or the aluminum source is 0.3 in terms of aluminum as aluminum or an aluminum compound in the raw material. The manufacturing method according to claim 1, wherein 3.5% by weight is added and mixed. 4. The vertical furnace is a vertical reaction vessel having a raw material input port at least in the upper part, a pre-heating zone and a heating zone sequentially downward, and a sealed port for taking out the product in the lower part. A manufacturing method according to claim 1. 5. The aluminum partial pressure is maintained constant through operation while maintaining the height of the raw material packed bed in the preheating zone within a range of 0.2 to 0.9 m. manufacturing method. 6 The solid solution of aluminum is 0.1 to 0.1 of silicon carbide.
The manufacturing method according to claim 1, characterized in that the amount is equivalent to 0.7% by weight. 7 The silicon carbide fine powder mainly composed of β-type crystals is
The manufacturing method according to claim 1, characterized in that the method contains at least 90% of β-type crystals and has an average particle size of submicron size.