JPH0118005B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention mainly relates to a method for producing ultrafine silicon carbide powder that is excellent as a raw material for silicon carbide sintered bodies.
In particular, the present invention relates to a method for producing ultrafine silicon carbide powder having an average particle size of significantly less than 1 μm. The present inventors previously proposed an invention relating to a method for producing silicon carbide mainly composed of β-type crystals in Japanese Patent Application Laid-Open No. 54-33899 and Japanese Patent Publication No. 55-40527,
For the first time in the world, we established an industrial continuous manufacturing method for silicon carbide made of β-type crystals. By the way, silicon carbide consisting of β-type crystals has recently been recognized to have extremely excellent properties when used as a raw material for producing pressureless sintered bodies, and according to such uses, the finer the silicon carbide, the easier it is to sinter. Or, because of its excellent uniform shrinkability, particularly fine particles are required. For example, according to Japanese Patent Application Laid-Open No. 160200/1987, β-type particles with submicron particle size are produced by plasma jet reaction from silicon halides and hydrocarbons. Silicon carbide powder and its manufacturing method were also published in Japanese Unexamined Patent Publication No. 1983
Publication No. 67599 discloses a method for producing high purity β-type silicon carbide powder of 1 μm or less obtained by thermally decomposing an organosilicon polymer compound. However, the starting materials used in the methods described in the above-mentioned publications are all extremely expensive, and there is no industrial method that can supply ultrafine silicon carbide powder consisting of β-type crystals that satisfies such requirements at low cost. The manufacturing method is still unknown. Based on this viewpoint, one of the present inventors previously proposed an invention relating to ``a method for producing ultrafine silicon carbide powder consisting mainly of β-type crystals'' in Japanese Patent Application No. 113615/1982. According to the method of the invention, silica and carbon are
Raw materials with a _SiO2 molar ratio in the range of 3.2 to 5.0 are charged into a reaction vessel having a pre-heating zone, a heating zone, and a cooling zone, and the reaction temperature is controlled within the range of 1650 to 2100℃ to produce SiC. In the method for producing silicon carbide mainly composed of β-type crystals, which undergoes a chemical reaction, the raw materials are granulated, and the porosity of the granules is 40 to 55%, and the bulk density of the granules is in the range of 0.40 to 0.90 g/cm ³ Then, the granular raw material is charged from the top of the reaction vessel until the filling width of the charge in the heating zone is 0.10~
Within the range of 0.35 m, the charging width (Wm) is the descending speed (Um/hr) of the charge in the heating zone.
and heating zone height (Hm) within the range shown by the following relational expression. 17.9 (W-0.31) ² +0.23≦U≦53.1H (W-0.31
) ² +1.24 By the way, as a method for producing fine silicon carbide powder, for example, Japanese Patent Publication No. 45-10413 discloses an invention related to a "method for producing pigment silicon carbide," and according to the invention, It is stated that in order to produce fine silicon carbide powder, it is important to use carbon powder as fine as possible. Therefore, the present inventors attempted to apply extremely fine carbon powder for the purpose of further improving the method proposed by one of the present inventors. However, in the method proposed by one of the present inventors, especially when extremely fine carbon powder with a specific surface area of 1 m ² /g or more is used, the crushing strength of the granular raw material in the reaction zone is significantly deteriorated and it collapses. It was discovered that stable continuous operation could not be carried out due to deterioration of outgassing in the reaction zone. That is, in the above method, granular raw materials made of silica and carbon are charged from the top of a vertical reaction vessel and continuously heated.
This is a method of carrying out a SiC conversion reaction, in which the granular raw material does not disintegrate during handling and reaction,
It needs to have enough strength to maintain its original shape. In addition, in order to produce fine silicon carbide powder, it is preferable to carry out the reaction at as low a reaction temperature as possible, but the method of carrying out the continuous SiC formation reaction as proposed by one of the inventors mentioned above is For the reasons mentioned above, it was not possible to use fine carbon powder, and we had to use carbon powder with a relatively coarse particle size and poor reactivity. This method had the disadvantage that it had to be operated at a relatively high reaction temperature. The present inventors have conducted various studies to improve the crushing strength in the reaction zone of granular raw materials using extremely fine carbon powder, with the aim of further improving the method previously proposed by one of the present inventors. As a result, when granulating raw materials using extremely fine carbon powder as a starting material, a carbon-based binder containing an organic solvent-soluble component is used as a binder for the granular raw material, and when the starting materials are mixed, Alternatively, we have discovered that by using an organic solvent during granulation, it is possible to create a granular raw material that has strong crushing strength even in the reaction zone and can maintain its original shape. As a result, we have completed the present invention, which enables the continuous production of silicon carbide powder consisting of extremely fine β-type crystals at low cost and easily. That is, according to the present invention, a raw material prepared by blending silica, carbon, and a carbon-based binder and molded into granules is charged from above a reaction vessel having a preheating zone, a heating zone, and a cooling zone, and The charged raw materials are allowed to fall continuously or intermittently under their own weight in the pre-heating zone of the reaction vessel until they reach the heating zone, where they are indirectly electrically heated horizontally in the heating zone, and the charged raw materials and the raw materials in the reaction zone are The power load and the rate of descent of the charging materials and reaction products are controlled so that the horizontal temperature distribution of the reaction products is almost uniform.
Production of silicon carbide by carrying out a SiC conversion reaction, then dropping the reaction product into a cooling zone, cooling it in a non-oxidizing atmosphere, and then discharging the reaction product continuously or intermittently from the lower part of the cooling zone of the reaction vessel. In the method, the carbon contained in the raw material formed into granules is a carbon powder with a specific surface area in the range of 1 to 1000 m ² /g, and at the latest when granulated, the carbon-based binder and organic It is mixed using a solvent,
The above object can be achieved by a method for producing ultrafine silicon carbide powder, which is characterized in that the reaction temperature in the heating zone is controlled within the range of 1500 to 2000°C. Next, the present invention will be explained in detail. A reaction for producing silicon carbide using silica and carbon as starting materials is generally represented by the following formula (1). SiO ₂ +3C→SiC+2CO... (1) However, the actual main generation mechanism is that SiO gas is generated according to the following formula (2), and the SiO gas and carbon react according to the following formula (3). It is known that silicon carbide is produced by SiO ₂ +C→SiO+CO ...(2) SiO+2C→SiC+CO ...(3) By the way, according to the present invention, the SiO gas generated according to the above formula (2) is quickly converted according to the above formula (3). It is desirable that the SiO gas partial pressure in the reaction vessel not be increased so much during the SiC conversion reaction. This is because, in the present invention, when the SiO gas partial pressure in the reaction vessel increases, the equation (3)
However, in this case, the reaction according to equation (3) above is mainly a reaction in which SiC crystals grow and become coarse, so under conditions of high SiO gas partial pressure, fine It becomes difficult to obtain SiC particles, and in even more serious cases, a part of the SiO gas rises to the pre-preparation zone and causes reactions as shown in equations (4), (5), and (6) below, causing pre-preparation. In the tropics, SiO ₂ , Si,
SiC, C, etc. are precipitated in a mixed state. Since the precipitate is sticky, the raw materials coagulate together,
The smooth movement and descent of the most important raw material in the continuous production of silicon carbide is significantly hindered, making stable continuous operation over a long period of time difficult. 2SiO→SiO ₂ +Si ……(4) SiO+CO→SiO ₂ +C ……(5) 3SiO+CO→2SiO ₂ +SiC ……(6) According to the present invention, the rise in the SiO gas partial pressure is suppressed, and extremely fine To obtain silicon carbide powder,
It is necessary to use carbon powder with a specific surface area within the range of 1 to 1000 m ² /g. The reason for this is that when the specific surface area is smaller than 1 m ² /g, there are few places where the reaction according to the above formula (3) occurs, and the SiC production reaction due to crystal growth becomes the main reaction, which is the object of the present invention. It is difficult to produce fine silicon carbide powder, and on the other hand, carbon powder with a specific surface area larger than 1000 m ² /g is considered to be extremely suitable from the viewpoint of reactivity. This is because it is not only difficult to obtain, but also has an extremely low bulk specific gravity, which has the disadvantage of increasing the porosity of the granules and significantly lowering the crushing strength.
Among them, carbon powder in the range of 10 to 500 m ² /g is relatively easy to obtain, and suitable results can be obtained. The carbon powder is mainly used as contact black,
It is preferable to use at least one type of carbon black selected from furnace black, thermal black, and lamp black. Among them, thermal black has a chain structure or chain structure of carbon black particles, that is, a low structure and high crushing strength. This is the most suitable method because it allows easy production of granular raw materials. According to the present invention, a raw material obtained by blending silica and carbon and granulating the mixture is used. If silica and carbon are used as powder without granulation, they will be generated during the reaction.
This is because it has the disadvantage that the outgassing of CO gas deteriorates, making it difficult for the reaction to proceed. Therefore, it is advantageous for the average particle diameter of the granules to be within the range of 3 to 18 mm. The reason for this is that if the average particle diameter of the granules is smaller than 3 mm, there is almost no effect as a granule, while if it is larger than 18 mm, the reaction rate within the granules slows down.
This is because it is not economical. According to the present invention, it is important that the granules maintain their original shape even when exposed to high temperatures in the reaction zone, and the carbon powder is mixed with a carbon-based binder and an organic It is necessary to mix using a solvent. The reason for this is that the carbon powder used in the present invention, which has an extremely large specific surface area, has extremely strong agglomeration properties and usually exists in the form of secondary particles, which are agglomerated large numbers of fine particles, and cannot be mixed with silica. When granulating, it is difficult to loosen the agglomeration of the carbon powder and disperse the binder uniformly by simply blending and mixing a fine powder binder, but as mentioned above, using an organic solvent This is thought to be due to the fact that by mixing, the organic solvent-soluble components of the carbon-based binder can be eluted and mixed, so that they can be uniformly dispersed even inside the secondary particles of the carbon powder. According to the present invention, the carbon-based binder preferably contains at least 30% by weight of organic solvent-soluble components and 20 to 80% by weight of fixed carbon. The reason why the organic solvent soluble component is preferably at least 30% by weight is that if the organic solvent soluble component is less than 30% by weight, it is difficult to uniformly disperse the binder even inside the secondary particles of carbon powder. This is because a large amount of carbon-based binder is required to obtain the desired crushing strength. On the other hand, the reason why it is preferable to use fixed carbon in an amount of 20 to 80% by weight is that if the fixed carbon is less than 20% by weight, a large amount must be added in order to obtain the desired crushing strength, resulting in poor workability. Not only is the binder occupying a large volume in the granular raw material, it is difficult to maintain crushing strength in a high temperature range. This is because it is extremely low and difficult to apply efficiently. According to the present invention, the carbon-based binder is preferably at least one selected from petroleum pitch, coal tar pitch, wood tar pitch, asphalt, phenolic resin, petroleum tar, coal tar, and wood tar. . According to the present invention, the granular raw material is prepared by blending silica, carbon powder, a carbon-based binder, and an organic solvent, and then forming the mixture into granules, or by mixing the carbon-based binder and an organic solvent. It can be suitably produced by any method in which a liquid mixture in which organic solvent-soluble components of a carbon-based binder are eluted is added to a mixture of silica and carbon powder, mixed, and then formed into granules. Further, according to the present invention, the organic solvent may be removed from the mixture by drying, then crushed and re-pulverized, and a water-soluble binder may be added to the resulting mixture for granulation. According to the present invention, the amount of fixed carbon in the carbon-based binder eluted into the organic solvent during the mixing is 1.5 with respect to 100 parts by weight of the silica and carbon powder in total.
It is preferable to set it as 30 parts by weight. The reason is,
If the amount of fixed carbon is less than 1.5 parts by weight, the crushing strength of the granular raw material in the reaction zone will be insufficient, while if it is more than 30 parts by weight, the carbon generated from the binder will envelop the carbon powder, resulting in This is because the specific surface area of the carbon powder decreases, and coarse silicon carbide particles are likely to be produced. According to the present invention, it is preferable to mix 5 to 50 parts by weight of the carbon-based binder with respect to a total of 100 parts by weight of silica and carbon powder. The reason for this is that if the amount is less than 5 parts by weight, the crushing strength of the granular raw material in the reaction zone will be low and the product will easily collapse in the reaction vessel, while if it is more than 50 parts by weight, the cost of the binder will be high. This is because the amount of carbon generated by thermal decomposition of the binder increases, making it easier to generate coarse silicon carbide particles, and the best results are obtained within the range of 10 to 40 parts by weight. It will be done. According to the present invention, the organic solvent is
It is preferable to add at least 10 parts by weight. The reason for this is that if the amount of the organic solvent blended is less than 10 parts by weight, it is difficult to uniformly disperse the binder. Note that the amount of the organic solvent to be blended is preferably as large as possible in consideration of the uniform dispersibility of the binder; however, if it is too large, it is uneconomical, so it is advantageous that the amount to be blended is 100 parts by weight or less. According to the present invention, the organic solvent is advantageously one that can elute as much of the organic solvent-soluble components of the carbon-based binder as possible, such as benzene, acetone, toluene, hexane, isohexane, heptane, isoheptane, isooctane, cyclohexane, etc. , ethylbenzene, chloroform, carbon tetrachloride, dichloroethane, dichloroethylene, trichloroethylene, nonane, xylene, methyl alcohol, ethyl alcohol, butyl alcohol, isobutyl alcohol, propyl alcohol, isopropyl alcohol, ethyl ether, isopropyl ether, ethyl formate, methyl acetate, acetic acid ethyl, isopropyl acetate, ethyl propionate,
Amyl propionate, butyl butyrate, diethyl carbonate, fluorinated acetic acid, diethylene dimethyl ether,
Ethyl methyl ketone, quinoline and those having equivalent functions can be used. In addition, if we consider coal tar as the binder and use benzene as the organic solvent,
The insoluble content in benzene is about 7.2%, and when quinoline is used as the organic solvent, the insoluble content is about 3.5%. Therefore, most of the coal tar is composed of organic solvent-soluble components such as benzene, ethylbenzene, toluene, m/p-xylene, o-xylene, styrene, methylcyclohexane, n-heptane, cyclohexane, and ethylcyclohexane. Therefore, it is suitable for eluting the organic solvent-soluble component and mixing it with silica and carbon powder, which is an embodiment of the present invention. According to the present invention, in order to suppress the increase in the SiO gas partial pressure, it is effective to increase the amount of carbon in the raw material to increase the number of places where the formula (3) occurs, and It is advantageous for the C/SiO ₂ molar ratio to be in the range from 3.2 to 5.0. Said C/SiO ₂
The reason why it is advantageous to set the molar ratio within the range of 3.2 to 5.0 is that when the C/SiO ₂ molar ratio is smaller than 3.2, the reaction according to the formula (3) can be sufficiently carried out, and SiO
It is difficult to maintain the gas partial pressure low, while
This is because if it is larger than 5.0, excess carbon that does not contribute to the reaction will be heated to a high temperature, resulting in lower thermal efficiency and increased costs for carbon raw materials, which is uneconomical. The present inventors conducted various studies on the silica and carbon used as starting materials in the present invention and the reaction conditions, and found that the specific surface area of the carbon powder was 1 to 1000 m ² /
When operating within the range ^of C/SiO ₂ of silica and carbon
It has been found that extremely good results can be obtained when the molar ratio (R) satisfies the following relational expression (7). S ^-1 ≦3.1×10 ^-2 R・X+1.1×10 ⁴ T ^-1 ...(7) Furthermore, according to the present invention, the SiO gas partial pressure in the reaction vessel can be reduced by improving the permeability in the raw materials. In order to make the porosity of the granules uniform, the raw materials are granulated, and the porosity of the granules is
It is preferable that the granular raw material has a bulk density of 0.40 to 1.13 g/cm ³ and a bulk density of 10 to 60%. The above blended raw materials are granulated, and the porosity of the granules is reduced to 10~10.
The reason why it is preferable to set it within the range of 60% is that if the porosity is lower than 10%, the permeability in the granules will be poor, making it difficult for the reaction product gas to be released, and the SiO gas partial pressure will locally decrease within the granules. This is because the porosity becomes high, which tends to cause coarsening of the crystal grains as described above. On the other hand, it is preferable that the porosity is as high as possible in consideration of the release of reaction product gas, but if it is higher than 60%, the grains become coarser. This is because the strength of the material is extremely low, and it will collapse in the reaction vessel and the breathability will deteriorate significantly.
Best results are obtained within a range of 55%. The granular bulk density of the granular raw material is 0.40 to 1.13 g/
The reason why it is preferable to set it within the range of cm ³ is that the lower the bulk density is, the more preferable it is in terms of air permeability and other aspects.
In order to obtain a granular raw material with a lower value than 0.40 g/cm ³ , it is necessary to significantly increase the porosity of the granules or make the particle size of the granules extremely uniform.
This is because if the porosity is too high, the strength of the granules will drop significantly as described above, and making the particle size uniform will lead to ^a significant increase in raw material cost. If the temperature is high, the permeability of the reaction product gas will be poor, and the flow of the high-temperature gas in the preheating zone will become uneven, resulting in insufficient heat exchange between the raw material and the high-temperature gas.
This is because it becomes susceptible to the effects of precipitates from SiO gas, which inhibits the smooth fall of the raw material under its own weight, making it difficult to maintain stable operation over a long period of time. The best results can be obtained when the bulk density of the granules is within the range of 0.50 to 0.90 g/cm ³ . According to the present invention, the bulk density of the granules (D
g/cm ³ ) is the charging width (W
More suitable results can be obtained when the following relational expression (8) expressed by m) and the porosity (A%) of the granular material is satisfied. 0.0146A (W-0.82) ³ +0.3≦D≦-2.52A (W-
0.22) ³ +1.0...(8) The porosity of the granular material is the volume ratio occupied by pores per unit bulk volume, and the bulk volume includes the solids and internal voids in the granular material. It is volume. The bulk density of the granules is the weight of a given volume of the granules, ie the weight per unit volume including solids, internal voids and external voids. The filling width of the charge is twice the distance from the side wall of the reaction vessel to the farthest horizontal charge. According to the present invention, the granular raw material is charged from above a reaction vessel having a preheating zone, a heating zone, and a cooling zone,
The charged raw materials are allowed to fall continuously or intermittently under their own weight in the pre-heating zone of the reaction vessel until they reach the heating zone, and are indirectly electrically heated horizontally within the heating zone to cool the charged raw materials in the reaction zone. In addition, the SiC conversion reaction is carried out by controlling the power load and the rate of descent of the charged raw materials and reaction products that descend through the reaction zone so that the horizontal temperature distribution of the reaction products is almost uniform. After being lowered into a cooling zone and cooled in a non-oxidizing atmosphere, the reaction product is continuously or intermittently discharged from the lower part of the cooling zone of the reaction vessel. According to the present invention, in producing extremely fine silicon carbide powder, the reaction temperature in the heating zone is set at 1500-
It is necessary to control the temperature within the range of 2000℃. The reason for this is that when the reaction temperature is lower than 1500°C, the reaction rate of the reaction represented by formula (2) is extremely slow and it is difficult to efficiently produce silicon carbide powder; This is because if the temperature is too high, silicon carbide once produced undergoes crystal growth and changes to α-type silicon carbide, making it difficult to produce extremely fine β-type silicon carbide powder, which is the object of the present invention. Note that the reaction temperature is lower than that required in the conventional continuous operation method for silicon carbide invented and proposed by the present inventors, and the amount of energy required for operation is small, and the production equipment is It also has advantages such as significantly improved durability. In addition, the rate of descent of the charge in the heating zone (Um/hr) can be calculated using the following relational expression (9) between the filling width of the charge in the heating zone (Wm) and the height of the heating zone (Hm).
It is advantageous to keep the value within the range shown in . H(8.3W ² −5.8W+1.16)≦U≦H(50W ² −36.7W
+7.3)...(9) The height of the heating zone is the length in the height direction of the means for heating the charge, that is, the heating part of the heating element. Next, an example of a manufacturing apparatus directly used for carrying out the method of the present invention will be described with reference to the drawings. The apparatus directly used for carrying out the method of the present invention has a raw material charging port 1, a preheating zone 2, a heating zone 3, a cooling zone 4, and a sealable product outlet 5, as shown in FIG. The tube 7 forming the heating zone is made of graphite and is equipped with means 8, 9 for indirectly electrically heating the charge in the heating zone, and is provided with means 8, 9 for indirectly electrically heating the charge in the heating zone, and at least A heat insulating layer 1 made of carbon or graphite fine powder is provided on the outside of the heating zone.
0. The reaction vessel 6 is installed in the center of the apparatus, and the indirect heating means 8 and 9 are composed of a graphite heating element 8 and a graphite reflection tube 9 provided close to the outside of the heating element. In the space surrounded by the cylinder forming the heating zone and the graphite reflector cylinder, for example, argon, helium, nitrogen, carbon monoxide,
Hydrogen and other non-oxidizing gases are sealed to prevent the graphite heating element from being consumed by oxidation due to air intrusion. Hereinafter, the present invention will be described with reference to examples. Example 1 100 parts by weight of silica powder (SiO ₂ =99.7% by weight) with an average particle size of 153 μm, 63 parts by weight of thermal black powder (FC = 98.5% by weight) with a specific surface area of 25 m ² /g, and an average particle size of 40 μm 35 parts by weight of high pitch powder (benzene soluble component = 65.7% by weight, FC = 50.4% by weight) and 140 parts by weight of benzene were mixed for a period of time using a fret mill and then dried to obtain a solid mixture. . Next, the crushed product obtained by crushing the solid mixture was put into a pan-type granulator and granulated while spraying a 0.5% CMC aqueous solution, and after being sized with a sieve and Burr Grizzly, it was passed through a band-type aerated dryer. put it in
It was dried with hot air at 150°C for 90 minutes. The obtained granular raw material had an average particle size of 10.3 mm, a porosity of 51%,
The bulk density of the granules is 0.64 g/cm ³ and the C/SiO ₂ molar ratio is
It was 4.0. This granular raw material is charged from the top of a vertical indirect heating furnace as shown in Fig. 1, and is continuously lowered by its own weight inside the heating furnace until it reaches a heating zone where the reaction temperature is controlled at 1650°C. The charge in the heating zone is 0.60
After the SiC formation reaction was carried out by indirect heating in the horizontal direction while descending under its own weight at a rate of descent of m/hr, it was allowed to descend under its own weight into a cooling zone, and the reaction product was continuously discharged from the discharge port. The specifications of the indirect heating furnace used are as shown in Table 1, and the filling width of the charge in the heating zone is 0.24.
It is m.

[Table] After removing free carbon from the obtained reaction product, the rotation speed was measured using a ball mill with an inner diameter of 250 mmφ.
Wet crushing at 48 rpm for 5 hours, and further into 10% HF aqueous solution.
Free silica was removed and purified by immersion for 3 hours. The content of silicon carbide consisting of β-type crystals in the purified silicon carbide was measured by X-ray diffraction and was 96.6%, and the particle shape was determined using a scanning electron microscope as shown in Figure 2. As shown in the photograph (2700x), it was a fine powder with an extremely round shape and relatively uniform particle size, and its specific surface area was 36.2 m ² /g. Comparative Example 1 100 parts by weight of silica powder (SiO ₂ = 99.7% by weight) with an average particle size of 153 μm, 76 parts by weight of petroleum coke powder (FC = 98.7% by weight) with an average particle size of 29 μm, and 76 parts by weight of silica powder (FC = 98.7% by weight) with an average particle size of 43 μm Pituchi powder (FC=50.4% by weight)
Mix 7 parts by weight and mix 10 parts by weight in a vertical screw mixer.
Mixed for a minute. While spraying a 0.5% CMC aqueous solution onto the above-mentioned blended raw materials, the mixture is molded using a pan-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. The average particle diameter is 10.5 mm, the porosity of the granules is 47%, the bulk density of the granules is 0.62 g/cm ³ , and the C/SiO ₂ molar ratio is 4.0.
A granular raw material was obtained. The process was almost the same as in Example 1 using the granular raw material, but the reaction temperature was controlled at 1900°C, and the SiC formation reaction was carried out by lowering the charge in the heating zone by its own weight at a rate of descent of 0.60 m/hr. I set it. The physical properties of the obtained reaction product were measured in the same manner as in Example 1. The results are shown in Table 2. The particle shape is shown in the scanning electron micrograph (2700
times). Comparative Example 2 A reaction product was obtained in the same manner as in Comparative Example 1, but the reaction temperature was controlled lower than in Comparative Example 1 to 1650° C., and the rate of descent of the charge was slowed to 0.40 m/hr. The physical properties of the obtained reaction product were measured in the same manner as in Example 1. As shown in Table 2, we were able to obtain relatively fine silicon carbide powder with a specific surface area of 22.7 m ² /g, but the free silica content in the product was 21.7% by weight, which contained a large amount of unreacted silica. In addition, a large amount of precipitates from SiO gas were formed in the preheating zone, making it difficult to lower the charge smoothly under its own weight. Example 2, Comparative Example 3 A reaction product was obtained using the same method as in Example 1, but using granular raw materials prepared with different amounts of high pitch powder and benzene as shown in Table 2. The physical properties of the obtained reaction product were measured in the same manner as in Example 1, and the results are shown in Table 2. Example 2 was able to operate stably and continuously for a long period of time. On the other hand, in Comparative Example 3, the charge collapsed within the reaction vessel, making continuous operation difficult. Example 3 A granular raw material similar to Example 1 but having physical properties as shown in Table 2 was obtained. The granular raw material was charged into the indirect heating furnace used in Example 1 and operated under the conditions shown in Table 2 to obtain a reaction product. The physical properties of the obtained reaction product were measured in the same manner as in Example 1, and the results are shown in Table 2. Example 4 The same procedure as in Example 1 was carried out, except that the granular raw material was prepared using silica (SiO ₂ =99.6% by weight) with an average particle size of 2 μm as shown in Table 2, and the same procedure as in Example 1 was carried out. A reaction product was obtained under these conditions. The physical properties of the obtained reaction product were measured in the same manner as in Example 1, and the results are shown in Table 2. Example 5 A reaction product was obtained in the same manner as in Example 1, except that the reaction temperature was controlled higher than in Example 1, and the rate of descent of the charge was increased. The physical properties of the obtained reaction product were measured in the same manner as in Example 1. The results are shown in Table 2, although the specific surface area of the silicon carbide powder was slightly smaller at 29.8 m ² /g, the dead weight of the charge fell smoothly and stable continuous operation was possible for a long period of time. We were able to improve the production capacity per unit of equipment. Example 6 A granular raw material was prepared as in Example 1, but using coal tar pitch, wood tar pitch, asphalt, phenolic resin, petroleum tar, coal tar, and wood tar instead of high pitch flour as the binder. A reaction product was obtained in the same manner as in Example 1. All of the silicon carbide powders obtained by purifying the reaction products were extremely fine and fully satisfied the purpose of the present invention. In addition, stable operation was possible for a long period of time. The C/SiO ₂ molar ratio in each of the granular raw materials was adjusted to 4.0. As described above, according to the present invention, it is possible to produce ultrafine silicon carbide powder with an extremely large specific surface area and an average particle diameter of much less than 1 μm at a high yield, and by using this powder, it is possible to produce ultrafine silicon carbide powder with an extremely large specific surface area, which has an average particle diameter of much less than 1 μm. It is possible to produce silicon carbide sintered bodies that have extremely high strength and excellent thermal shock resistance compared to pressureless silicon carbide sintered bodies made using The effect that contributes to the above is extremely large.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of the vertical continuous manufacturing apparatus used in the examples and comparative examples of the present invention, and FIG. 2 is a scanning electron micrograph (2700x) of the silicon carbide powder described in Example 1. Figure 3 is a scanning electron micrograph (2700x magnification) of the silicon carbide powder described in Comparative Example 1. 1... Raw material charging port, 2... Pre-preparation zone, 3... Heating zone, 4... Cooling zone, 5... Product discharge port, 6...
Reaction vessel, 7...Cylinder forming a heating zone, 8...Heating element made of graphite, 9...Reflector tube made of graphite, 10...Insulating layer, 11...Non-oxidizing gas charging port, 12...Guiding electrode , 13... Flexible conductor, 14... Bus bar,
15... Temperature measuring pipe, 16... Outer shell, 17... Refractory brick, 18... Exhaust duct, 19... Raw material hopper.

Claims (1)

[Claims] 1. Blending silica, carbon, and a carbon-based binder,
The raw material formed into granules is charged from above into a reaction vessel having a preheating zone, a heating zone, and a cooling zone, and the charged raw material is lowered by its own weight continuously or intermittently within the preheating zone of the reaction vessel. while reaching a heating zone, and indirectly electrically heating in the horizontal direction within the heating zone,
The SiC formation reaction is carried out by controlling the power load and the rate of descent of the charged raw materials and reaction products in the reaction zone so that the horizontal temperature distribution of the charged raw materials and reaction products in the reaction zone is almost uniform. Then, the reaction product is lowered into a cooling zone, and after cooling in a non-oxidizing atmosphere, the ultrafine reaction product of much less than 1 μm is continuously or intermittently discharged from the lower part of the cooling zone of the reaction vessel. In the manufacturing method, the carbon contained in the raw material formed into granules is carbon powder with a specific surface area in the range of 1 to 1000 m ² /g, and contains an organic solvent soluble component at the latest when granulated. It is mixed using the carbon-based binder and organic solvent, and the reaction temperature in the heating zone is controlled.
A method for producing ultrafine silicon carbide powder, characterized by controlling the temperature within a range of 1500 to 2000°C. 2. The carbon powder is mainly at least one selected from contact black, furnace black, thermal black, and lamp black.
The manufacturing method according to claim 1, which is a seed. 3. The carbon-based binder contains at least 30% by weight of organic solvent-soluble components and 20 to 20% of fixed carbon.
The manufacturing method according to claim 1 or 2, containing 80% by weight. 4 The carbon-based binder includes petroleum pitch, coal tar pitch, wood tar pitch, asphalt,
The manufacturing method according to any one of claims 1 to 3, wherein at least one selected from phenolic resin, petroleum tar, coal tar, and wood tar is used. 5. The manufacturing method according to any one of claims 1 to 4, characterized in that silica, carbon powder, a carbon-based binder, and an organic solvent are blended, mixed, and then formed into granules. 6. A mixture of a carbon-based binder and an organic solvent is added to the mixture of silica and carbon powder, and the mixed liquid obtained by eluting the organic solvent-soluble components of the carbon-based binder is formed into granules. A manufacturing method according to any one of claims 1 to 4, characterized in that: 7. The amount of fixed carbon in the carbon-based binder eluted into the organic solvent during the mixing is within the range of 1.5 to 30 parts by weight based on the total of 100 parts by weight of the silica and carbon powder. The manufacturing method according to any one of items 1 to 6. 8. The manufacturing method according to any one of claims 1 to 7, wherein 5 to 50 parts by weight of the carbon-based binder is added to a total of 100 parts by weight of silica and carbon powder. 9. Claim 1, wherein the organic solvent is blended in an amount of at least 10 parts by weight based on 100 parts by weight of carbon powder.
The manufacturing method according to any one of items 1 to 8. 10 The porosity of the raw material formed into granules is 10
9. The manufacturing method according to any one of claims 1 to 9, wherein the bulk density of the granules is within the range of 0.40 to 1.13 g/cm ³ .