JPH022802B2 - - 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 producing sintered silicon carbide, and 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. It is. 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. Silicon carbide consisting of the 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 better the sinterability or In order to have excellent uniform shrinkability, a particularly fine material is required. For example, according to Japanese Patent Application Laid-open No. 160200/1987, β-type silicon carbide with a submicron particle size produced by a plasma jet reaction than silicon halides and hydrocarbons is required. Powder and its manufacturing method are also disclosed in Japanese Patent Application Laid-Open No. 1986-67599.
According to the publication, a method for producing high purity β-type silicon carbide powder of 1 μm or less obtained by thermally decomposing an organosilicon polymer compound is disclosed. However, the starting materials used in the method described in the above-mentioned publication are all extremely expensive, and an industrial manufacturing method that can inexpensively supply ultrafine silicon carbide powder consisting of β-type crystals that satisfies such requirements is required. The method is still unknown. By the way, as a method for producing fine silicon carbide powder using silica and carbon as starting materials, for example, Japanese Patent Publication No. 10413/1977 discloses an invention related to a "method for producing pigment silicon carbide"; According to the publication, it is described that it is important to use carbon powder as fine as possible in order to produce fine silicon carbide powder. The present inventors previously attempted to use extremely fine carbon powder in the method proposed by the present inventors. However, in the method previously proposed by the present inventors, 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 deteriorates significantly and collapses. It was discovered that stable continuous operation could not be performed due to deterioration of gas leakage.
In other words, in the method described above, granular raw materials made of silica and carbon are charged from the top of a vertical reaction vessel and continuously processed.
This is a method of carrying out a SiC conversion reaction, and the granular raw material needs to have a strength that allows it to maintain its original shape without collapsing during handling and reaction. 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 SiC conversion reaction continuously as proposed by the present inventors is not suitable for the reasons mentioned above. Because it is not possible to use fine carbon powder, and it is necessary to use carbon powder with a relatively coarse particle size and poor reactivity, the reaction temperature is relatively high considering production efficiency and workability during operation. The disadvantage was that the operation had to be carried out at Based on this viewpoint, the present inventors conducted various studies to improve the crushing strength in the reaction zone of granular raw materials using fine carbon powder, and first published a patent application.
No. 57-75324, when granulating a raw material 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 the starting material is By using an organic solvent during mixing or 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. According to the invention and Japanese Patent Application No. 147701/1989, which enables continuous production at low cost and easily, when granulating raw materials using extremely fine carbon powder as a starting material, the carbon powder and a carbon-based binder are combined. By using a surfactant that can significantly improve wettability with the dissolved dispersion medium, it is easy to produce a granular raw material that has strong crushing strength even in the reaction zone and can maintain its original shape. The present invention proposes an invention that enables continuous production of silicon carbide powder consisting of extremely fine β-type crystals at low cost and easily. By the way, according to the method previously proposed by the present inventors, it is necessary to mix a relatively large amount of carbon-based binder in order to produce a granular raw material that has sufficient crushing strength even in the reaction zone. . However, if too much of the carbon-based binder is blended, fine carbon powders will be bound to each other by the carbon produced when the binder carbonizes, forming integrated coarse particles. It has the disadvantage that it tends to contain relatively coarse silicon carbide particles caused by the coarse particles. The present invention further improves the method previously proposed by the inventors, further reduces the amount of carbon-based binder used when producing granular raw materials, and enables stable production of fine silicon carbide powder. The purpose is to provide a method. A raw material made by blending silica, carbon, and a carbon-based binder and forming it into granules is charged from above the reaction vessel, which has a pre-heating zone, a heating zone, and a cooling zone. While lowering its own weight, it reaches the heating zone, and is indirectly electrically heated horizontally within the heating zone, and at the same time, electric power is applied so that the horizontal temperature distribution of the charged raw materials and reaction products in the reaction zone is almost uniform. The SiC formation reaction is carried out by controlling the rate of descent of the charged raw materials and reaction products, and then the reaction products are lowered into a cooling zone under a non-oxidizing atmosphere to be cooled, and then the reaction products are transferred to the lower part of the cooling zone. In a method for producing silicon carbide in which silicon carbide is discharged more continuously or intermittently, the raw materials to be formed into granules include (a) carbon powder having a specific surface area within the range of 1 to 1000 m ² /g and a carbon-based binder; or (b) mixing a carbon powder having a specific surface area within the range of 1 to 1000 m ² /g and a carbon-based binder using water or an organic A process of mixing using a dispersion medium containing a solvent as a main component and a surfactant; After passing through either of the above steps (a) and (b), the resulting mixture is bonded with silica and carbon. The reaction temperature in the heating zone is set to 1500 to 2000.
The above object can be achieved by controlling the temperature within the range of .degree. 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 suitable SiC particles, and in even more extreme 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. precipitate 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 in 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 preferred 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 raw material formed into granules maintains its original shape even when exposed to the high temperature of the reaction zone, and the raw material formed into granules has a size of (a) 1 to 1000 m ^{2 .} a step of mixing carbon powder having a specific surface area within the range of /g and a carbon-based binder using a dispersion medium mainly composed of water; or
(b) A step of mixing carbon powder having a specific surface area within the range of 1 to 1000 m ² /g and a carbon-based binder using a dispersion medium mainly composed of water or an organic solvent and a surfactant. ; It is necessary that the mixture obtained after passing through either of the above steps (a) and (b) is mixed with silica and a carbon-based binder and then granulated. The reason why a carbon-based binder is added in the step (a) or (b) and the granulation step when forming the raw materials into granules is that in the step (a) or (b), the carbon powder is not mutually mixed. This is the process of mixing a carbon-based binder for bonding, and the granulation process is the same as described above.
This is a process of mixing a carbon-based binder to bond silica with the mixture obtained after passing through either process (a) or (b), and the process of (a) or (b) and granulation. This is because by blending a carbon-based binder in each step, it is possible to efficiently blend the carbon-based binder in an optimum amount according to each purpose. Note that the carbon powder and the carbon-based binder are used in the above (a).
Either the step of mixing using a dispersion medium mainly composed of water or the step of mixing using a dispersion medium mainly composed of water or an organic solvent and a surfactant as described in (b) above. The reason for mixing is
The carbon powder used in the present invention, which has an extremely large specific surface area, has a strong cohesive property and usually exists in the form of a particle group in which many fine particles are aggregated, that is, in the form of secondary particles. Therefore, a fine powder binder is simply added. It is difficult to loosen the agglomeration of the carbon powder and disperse the binder uniformly by simply mixing the carbon powder, and since the bonds between the carbon powders are extremely weak, it is difficult to maintain the crushing strength of the granular raw material in the reaction zone. Although it is difficult, it is possible to use the above (a) mixing process using a dispersion medium mainly composed of water or (b) using a dispersion medium mainly composed of water or an organic solvent and a surfactant. By mixing the carbon powder and the carbon-based binder in any of the mixing steps, the carbon-based binder can be uniformly dispersed even inside the secondary particles of the carbon powder. be. According to the present invention, the carbon-based binder in step (a) or (b) contains at least 30% by weight of dispersion medium soluble components and 5 to 80% by weight of fixed carbon. It is preferable. The reason why it is preferable to contain the dispersion medium soluble component at least 30% by weight is that if the dispersion medium soluble component is less than 30% by weight, the binder can be uniformly dispersed even inside the secondary particles of the carbon powder. This is because it is difficult and requires a large amount of carbon-based binder to obtain the desired crushing strength.On the other hand, the reason why it is preferable to use a binder containing 5 to 80% by weight of fixed carbon is as follows. If the fixed carbon content is less than 5% by weight, a large amount of binder must be added to obtain the desired crushing strength, which not only deteriorates workability but also increases the volume of binder in the granular raw material. Therefore, it is difficult to maintain crushing strength in a high temperature range, and if the amount exceeds 80% by weight, the practical effect as a binder is low and it is difficult to apply it efficiently. According to the present invention, the blending amount of the carbon-based binder in the step (a) or (b) is within the range of 0.1 to 10 parts by weight based on 100 parts by weight of carbon powder in terms of fixed carbon amount. It is preferable to do so. The reason for this is that if the blended amount converted to the amount of fixed carbon is less than 0.1 part by weight, the crushing strength of the granular raw material in the reaction zone will be low.
The product tends to disintegrate in the reaction vessel, and on the other hand, if the amount exceeds 10 parts by weight, the carbon produced when the binder carbonizes tends to bond fine carbon powder to each other and form integrated coarse particles. This is because it becomes easier to contain relatively coarse silicon carbide particles caused by the coarse particles in the product, and the best results can be obtained within the range of 0.5 to 8 parts by weight. According to the present invention, when mixing carbon powder and a carbon-based binder, it is important to uniformly disperse and mix the carbon-based binder even inside the secondary particles of the carbon powder. According to step a), it is preferable to use a water-soluble carbon-based binder with surfactant-like properties, and according to step (b), either an organic solvent or water is used. It is preferable to use a dispersion medium as a main component and a surfactant for improving the wettability of the dispersion medium to the carbon powder. According to step (a) of the present invention, the carbon powder and the carbon-based binder are mixed using a dispersion medium containing water as a main component. According to the present invention, in which a dispersion medium mainly composed of water is used in the step (a), lignin sulfonate, saccharide, alginate is used as a water-soluble carbon-based binder having surfactant-like properties. etc. can be used. According to step (b) of the present invention, carbon powder and a carbon-based binder are mixed using a dispersion medium containing either an organic solvent or water as a main component and a surfactant. When using a dispersion medium containing an organic solvent as a main component in step (b) above, the carbon-based binder may be petroleum pitch, coal tar pitch, wood tar pitch, asphalt, phenolic resin, petroleum tar, or coal tar. It is preferable to use at least one selected from , wood tar, and at least one selected from amines, organic compounds having a carboxyl group, organic compounds having a sulfo group, and esters as a surfactant. . The surfactants include, for example, polyoxy fatty acid amines, sorbitan fatty acid esters, dialkyl sulfosuccinic acid ester salts, fatty acids, alkyl amine salts, benzene sulfonic acid, polyoxysorbitan fatty acid esters, polyoxyethylene glycerin fatty acid esters, polyethylene glycol fatty acid esters, penta Erythritol fatty acid ester, propylene glycolic acid ester, sucrose fatty acid ester, polyglycerin fatty acid ester,
There are fatty acid alkanolamides and amine oxides, and these can be used alone or in combination. 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, 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, formic acid ester, acetic acid Methyl, ethyl acetate, isopropyl acetate, ethyl propionate, amyl propionate, butyl butyrate, diethyl carbonate, acetic acid fluoride,
Diethylene dimethyl ether, ethyl methyl ketone, quinoline and those having equivalent functions can be used. When using a dispersion medium mainly composed of water in step (b) above, the carbon-based binder contains at least one selected from phenolic resin, lignin sulfonate, sugar, and alginate. It is preferable to use at least one selected from amines, organic compounds having a carboxyl group, organic compounds having a sulfo group, esters, ammonium compounds, and organic compounds having an ether bond as a surfactant. Examples of the surfactants include fatty acid salts, alkylbenzene sulfonates, linear alkylbenzene sulfonates, α-olefin sulfonates, naphthalene-formalin condensate sulfonates, and polyoxyethylene alkyl phenyl ethers. They can be used alone or in combination. According to the present invention, the amount of surfactant blended in the step (b) is 0.05 parts by weight per 100 parts by weight of carbon powder.
It is preferably within the range of 5 parts by weight. If the amount of the surfactant added is less than the above range, the effect of improving the wettability between the carbon powder and the dispersion medium is insufficient, while if it is more than the above range, the surfactant may be added more than necessary. It is uneconomical. According to the present invention, the blending amount of the dispersion medium in the step (a) or (b) is 100% by weight of the carbon powder, considering the effect of uniformly dispersing the carbon-based binder and the carbon powder and economical efficiency. 10 to 700 parts by weight. According to the present invention, the mixture obtained after passing through the step (a) or (b) is mixed with silica and a carbon-based binder in the granulation step, and granulated. According to the present invention, the binder used in the granulation step needs to be a carbon-based binder. The reason for this is that the carbon-based binder can maintain strong bonding strength even in high-temperature ranges, and when this granulation raw material undergoes a reaction to form SiC and becomes a reaction product, the carbon in the binder becomes SiO2. This is because it reacts with gas to form SiC and maintains its shape, so it can maintain a constant shape even in the reaction zone without collapsing and re-powdering. The fixed carbon content of the carbon-based binder used in the granulation step is preferably in the range of 5 to 80% by weight. The reason for this is that if the fixed carbon content is less than the above range, a large amount must be blended in order to obtain the desired crushing strength, whereas if it is greater than the above range, the actual action as a binder will be reduced. This is because it is difficult to apply efficiently. According to the present invention, the blending amount of the carbon-based binder in the granulation step is within the range of 1 to 20 parts by weight based on the total of 100 parts by weight of silica and carbon powder in terms of fixed carbon amount. is preferred. The reason for this is that if the blended amount converted to the amount of fixed carbon is less than 1 part 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.
This is because if the amount is more than 20 parts by weight, the cost required for the binder increases and coarse silicon carbide particles due to carbon generated when the binder is carbonized are likely to be generated. The best results are obtained within this range. According to the present invention, the carbon-based binder used in the granulation step can be mixed in either solution or fine powder form. Furthermore, a sticky solution such as CMC can also be used during granulation in the granulation step. The above-mentioned sticky solution has the effect of increasing the crushing strength of the granulated raw material at room temperature and prevents the granulated raw material from collapsing during handling until it is charged into a reaction vessel. As the above-mentioned adhesive solution, in addition to the CMC solution, for example, starch, PVA, vinyl acetate, and other solutions can be used. According to the present invention, in producing fine silicon carbide powder, the amount of carbon in the raw material is increased to increase the number of locations where the reaction of formula (3) occurs, thereby suppressing the increase in the SiO gas partial pressure. It is effective to change the C/SiO ₂ molar ratio of silica and carbon in the blended raw materials.
Advantageously, it is in the range 3.2 to 5.0. The reason why it is advantageous to set the C/SiO ₂ 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; It is difficult to maintain the SiO gas partial pressure low, and on the other hand, if it is greater than 5.0, excess carbon that does not contribute to the reaction is heated to a high temperature, resulting in low thermal efficiency and an increase in the cost of carbon raw materials, which is uneconomical. This is because. 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 permeability in the raw materials is improved to reduce the SiO gas partial pressure in the reaction vessel. In order to make the mixture uniform, the raw materials are granulated to reduce the porosity of the granules.
It is advantageous to use a granular raw material with a bulk density of 0.40 to 1.13 g/cm ³ . The above blended raw materials are granulated, and the porosity of the granules is reduced to 10~10.
The reason why it is advantageous to keep the porosity 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 SiO gas will be generated locally within the granules. This is because the partial pressure becomes high, which tends to cause coarsening of crystal grains as described above.On the other hand, the porosity is preferably as high as possible considering the release of reaction product gas, but it is higher than 60%. This is because the strength of the granules is extremely low, and they will collapse in the reaction vessel, resulting in a marked deterioration of air permeability.
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 advantageous to keep the bulk density within the range ^{of 0.40 g/cm 3 is} that the lower the bulk density is, the more advantageous it is in terms of air permeability and other aspects. Significantly increase the porosity of the material, or
Alternatively, the particle size of the granules must be made extremely uniform, and if the porosity is too high, the strength of the granules will decrease significantly as described above, and making the granules uniform in size also costs raw materials. On the other hand, if it is higher than 1.13 g/ ^cm3 , the permeability of the reaction product gas will be poor and the flow of 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 influence of precipitates from the 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 ) satisfies the following relational expression (8), which is expressed by the charging width (Wm) of the charging material in the heating zone and the porosity (A%) of the granular material, to obtain more favorable results. can. 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. The bulk volume is the volume including the solids occupied in the granules and the internal voids. 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 into a reaction vessel having a preheating zone, a heating zone, and a cooling zone,
The charged raw material is allowed to fall continuously or intermittently under its own weight in the pre-heating zone of the reaction vessel until it reaches the heating zone, and is indirectly electrically heated horizontally within the heating zone to cool the charged raw material 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 descending through the reaction zone so that the horizontal temperature distribution of the reaction products is almost uniform. After being lowered into the 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, the produced silicon carbide will undergo crystal growth and change into 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 durability of the production equipment is improved. It also has advantages such as significantly improved performance. 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 it 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 heat generating 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 explained 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 and 9 for indirectly electrically heating the charge in the heating zone, and includes at least A heat insulating layer 10 made of carbon or graphite is provided outside the heating zone. 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 thermal black powder with a specific surface area of 25 m ² /g (FC = 98.5% by weight), 10 parts by weight of novolak type phenolic resin (FC = 51.6% by weight) and 1 part by weight of polyoxyethylene alkyl phenyl ether and 400 parts by weight of isopropyl alcohol, and after thorough mixing using a high-speed mixer,
Spray drying gave a granular mixture with an average particle size of about 0.3 mm. Next, 110 parts by weight of the granular mixture, 140 parts by weight of silica powder (SiO ₂ =99.7% by weight) with an average particle size of 153 μm, and 40 parts by weight of high pitch powder were blended,
Pour into a pan-type granulator and granulate while spraying a 0.5% CMC aqueous solution. After granulating with a sieve and burr grizzly, put into a band-type aerated dryer and dry at 150°C.
Dry with hot air for 90 minutes. The obtained granular raw material had an average particle diameter of 11 mm, a porosity of the granules of 50%, a bulk density of the granules of 0.61 g/cm ³ , and a C/SiO ₂ molar ratio of 4.4. This granular raw material is charged from the top of a vertical indirect heating furnace as shown in Figure 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. and the charge in the heating zone.
After the SiC formation reaction was performed by indirect heating in the horizontal direction while lowering the reactor by its own weight at a descending speed of 0.60 m/hr, the reactor was lowered by its own weight into a cooling zone, and the reaction product was continuously discharged from the outlet. 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. After removing free carbon from the obtained reaction product, the rotation speed was reduced using a ball mill with an inner diameter of 250 mmφ.
Wet crushing at 48 rpm for 5 hours, and then into a 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 to be 97.2%, and the specific surface area was 35.3 m ² /g. Furthermore, when the particle count was observed using a scanning electron microscope, it was found that it was a fine powder with an extremely round shape. 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】

[Table] Example 2, Comparative Example 1 Granules were prepared in the same manner as in Example 1, but by changing the blending amounts of the surfactant and dispersion medium when producing the granule mixture as shown in Table 2. The mixture was used to obtain the 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. All of the above-mentioned Example 2 were able to operate stably and continuously for a long period of time. On the other hand, in Comparative Example 1, the charge collapsed in the reaction vessel, making continuous operation difficult.

[Table] Example 3 Same as Example 1, but fatty acid salt, alkylbenzene sulfonate, linear alkylbenzene sulfonate, α-olefin sulfonate, naphthalene-formalin were used instead of polyoxyethylene alkyl phenyl ether. Granular raw materials were prepared using the sulfonic acid salt of the condensate and polyoxyethylene nonylphenol ether, respectively, to obtain a reaction product. 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. Example 4 A granular raw material was prepared in the same manner as in Example 1, except that lignin sulfonate, liquid sugar, and alginic acid were used as the binder instead of the phenolic resin, and water was used as the dispersion medium. A reaction product was obtained in the same manner as in 1. Although the crushing strength of the reaction products was slightly lower than that of the reaction product obtained in Example 1, the silicon carbide powders obtained by purification were all extremely fine and could not meet the purpose of the present invention. This was fully satisfactory, and the operation could be carried out stably for a long period of time. The C/SiO ₂ molar ratio in each of the granular raw materials was adjusted to 4.0. Example 5 Thermal black powder 100 used in Example 1
A granular mixture was obtained in the same manner as in Example 1 using 15 parts by weight of petroleum tar (FC=19.6% by weight), 0.5 parts by weight of polyoxyethylene dodecylamine, and 300 parts by weight of toluene. Next, 115 parts by weight of the granular mixture and the same novolac type phenolic resin used in Example 1 (average particle size = approx.
A granular raw material was prepared in the same manner as in Example 1, and a reaction product was obtained in the same manner as in Example 1. The physical properties of the obtained reaction product were measured in the same manner as in Example 1, and the content of silicon carbide consisting of β-type crystals was 98.3%, and its specific surface area was 34.1%.
m ² /g. Example 6 Same as Example 5, but propylene glycol fatty acid ester, polyoxysorbitan fatty acid ester, polyoxyethylene glycerin fatty acid ester, polyethylene glycol fatty acid ester, pentaerythritol fatty acid ester, sucrose instead of polyoxydodecylamine. A granular raw material was prepared using a fatty acid ester, a polyglycerin fatty acid ester, a fatty acid alkanolamide, and an amine oxide, and a reaction product was obtained in the same manner as in Example 1. All of the reaction products had a crushing strength suitable for continuous operation, and it was possible to carry out stable continuous operation for a long period of time. Note that the silicon carbide obtained by purifying the reaction product was extremely fine. As described above, according to the present invention, ultrafine silicon carbide powder with an extremely large specific surface area and an average particle diameter well below 1 μm, which is suitable for producing a pressureless sintered silicon carbide body, can be easily produced in high yield. Therefore, the effect of contributing to industry is extremely large.

[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, 7
...Cylinder forming a heating zone, 8...Graphite heating element, 9...
Graphite reflector, 10... Heat insulating layer, 11... Non-oxidizing gas charging port, 12... Guide electrode, 13... Flexible conductor,
14...Bus bar, 15...Temperature measuring pipe, 16...Outer shell, 17...Firebrick, 18...Exhaust duct, 19...
Raw material hopper.

Claims (1)

[Claims] 1. A raw material prepared by blending silica, carbon, and a carbon-based binder and molding it into granules is charged from above a reaction vessel having a preheating zone, a heating zone, and a cooling zone. is brought to the heating zone while continuously or intermittently lowering its own weight, and is indirectly electrically heated horizontally within the heating zone, so that the horizontal temperature distribution of the charged raw materials and reaction products in the reaction zone is almost uniform. At the same time, the SiC formation reaction is carried out by applying electric power so as to control the rate of descent of the charged raw materials and reaction products, and then cooling the reaction products by lowering them into a cooling zone under a non-oxidizing atmosphere. In a method for producing silicon carbide in which a reaction product is discharged continuously or intermittently from the lower part of a cooling zone, the raw material to be formed into granules is (a) carbon powder having a specific surface area within the range of 1 to 1000 m ² /g. and ^a carbon-based binder using a dispersion medium containing water as a main component; A step of mixing a binder with a dispersion medium mainly composed of water or an organic solvent and a surfactant; the mixture obtained after passing through either of the steps (a) and (b) above. A granulated mixture of silica and a carbon-based binder is used, and the reaction temperature in the heating zone is set to 1500 to 2000.
1. A method for producing ultrafine silicon carbide powder, characterized in that the SiC formation reaction is controlled within a temperature range of °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 in step (a) or (b) contains at least 30% by weight of dispersion medium soluble components and 5 to 80% by weight of fixed carbon. The manufacturing method according to item 1 or 2. 4 The blending amount of the carbon-based binder in the step (a) or (b) above is calculated by converting the amount of fixed carbon into carbon powder.
The manufacturing method according to any one of claims 1 to 3, characterized in that the amount is in the range of 0.1 to 10 parts by weight per 100 parts by weight. 5 In the step (b) above, a dispersion medium containing water as a main component is used, and at least one selected from phenol resin, lignin sulfonate, saccharide, and alginate is used as a carbon-based binder. A manufacturing method according to any one of claims 1 to 4. 6 In the step (b) above, a dispersion medium containing an organic solvent as a main component is used, and as a carbon-based binder, petroleum pitch, coal tar pitch, wood tar pitch,
At least one selected from asphalt, phenolic resin, petroleum tar, coal tar, and wood tar is used, and as a surfactant, amine,
Claim 1 in which at least one selected from an organic compound having a carboxyl group, an organic compound having a sulfo group, and an ester is used.
~The manufacturing method according to any one of Items 4 to 4. 7 In the step (b) above, a dispersion medium containing water as a main component is used, and at least one selected from phenolic resin, lignin sulfonate, saccharide, and alginate is used as a carbon-based binder. , Claims 1 to 3 use as a surfactant at least one selected from amines, organic compounds having a carboxyl group, organic compounds having a sulfo group, esters, ammonium compounds, and organic compounds having an ether bond. Fourth
The manufacturing method according to any one of paragraphs. 8. Any one of claims 1 to 4, 6, or 7, wherein the amount of the surfactant is within the range of 0.05 to 5 parts by weight per 100 parts by weight of carbon powder. The manufacturing method described in. 9. The manufacturing method according to any one of claims 1 to 8, wherein the fixed carbon content of the carbon-based binder used in the granulation step is within the range of 5 to 80% by weight. . 10 The blending amount of the carbon-based binder in the granulation step is within the range of 1 to 20 parts by weight based on a total of 100 parts by weight of silica and carbon powder in terms of fixed carbon amount. -The manufacturing method according to any one of Items 9 to 9.