JPH0135773B2 - - 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. 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. 160200/1983, 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. 1983-67599.
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 organic silicon polymer compound is disclosed. however,
The starting materials used in the methods described in the above-mentioned publications are all extremely expensive, and an industrial production method that can inexpensively supply ultrafine silicon carbide powder consisting of β-type crystals that satisfies such requirements is needed. is still unknown. By the way, as a method for producing fine silicon carbide powder using silica, carbon, and starting materials, for example, an invention related to a "manufacturing method of pigmented silicon carbide" is disclosed in Japanese Patent Publication No. 10413/1983, For example, it is stated that it is important to use carbon powder as fine as possible in order to produce fine silicon carbide powder. Therefore, the present inventors attempted to use extremely fine carbon powder in the method previously proposed by the present inventors. However, in the method previously proposed by the present inventors, especially when the specific surface area is 1
If extremely fine carbon powder of m ² /g or more is used, the crushing strength of the granular raw material in the reaction zone will significantly deteriorate and collapse, and gas release in the reaction zone will worsen, making stable continuous operation impossible. I found out that. That is, in the above method, a granular raw material made of silica and carbon is charged from the upper part of a vertical reaction vessel and a SiC conversion reaction is continuously performed. It needs to have enough strength to maintain its original shape without collapsing. Furthermore, in order to produce fine silicon carbide powder, it is preferable to carry out the reaction at as low a reaction temperature as possible;
The method of carrying out the SiC conversion reaction cannot use fine carbon powder for the reasons mentioned above, and has had to use carbon powder with a relatively coarse particle size and poor reactivity. In consideration of production efficiency and workability, this method had the disadvantage that it had to be operated at a relatively high reaction temperature. Based on this viewpoint, the present inventors conducted various studies to improve the crushing strength in the reaction zone of granular raw materials using extremely fine carbon powder. When granulating the granular raw materials, a carbon-based binder containing an organic solvent-soluble component is used as a binder for the granular raw materials, and an organic solvent is used during mixing or granulating the starting materials to form a reaction zone. We have newly discovered that it is possible to make a granular raw material that has high crushing strength and can maintain its original shape even in the case of granular raw materials. Having completed an invention that can be manufactured easily and continuously, the inventors proposed an invention relating to a ``method for manufacturing ultrafine silicon carbide powder'' in Japanese Patent Application No. 75324/1983. However, according to the method previously proposed by the present inventors, a carbon-based binder containing an organic solvent-soluble component is used as the binder for the granular raw materials, and the organic It was necessary to use a solvent. By the way, as a result of various research aimed at further improving the method proposed by the present inventors,
When granulating raw materials using extremely fine carbon powder as a starting material, a surfactant that can significantly improve the wettability between the carbon powder and a dispersion medium in which a carbon-based binder is dissolved is used. By newly discovering and using the above-mentioned surfactant, it is possible to use a dispersion medium other than an organic solvent as a dispersion medium, and the crushing strength is strong even in the reaction zone, and the original shape is maintained. By being able to easily produce the obtained granular raw material, the present invention has been completed, which allows silicon carbide powder consisting of extremely fine β-type crystals to be continuously produced 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 SiC conversion reaction is carried out by controlling the power load and the rate of descent of the charged raw materials and reaction products falling through the reaction zone so that the horizontal temperature distribution of the reaction products is almost uniform. In a method for producing silicon carbide, the reaction product is discharged continuously or intermittently from the lower part of the cooling zone of the reaction vessel after being lowered into a cooling zone and cooled in a non-oxidizing atmosphere. The specific surface area of carbon is in the range of 1 to 1000 m ² /g, and this raw material is mixed with at least 10 parts by weight of dispersion medium per 100 parts by weight of carbon powder at the latest when it is granulated. liquid, and a surfactant that is at least one selected from amines, organic compounds having carboxyl groups, organic compounds having sulfo groups, and esters in an amount corresponding to 0.05 to 5 parts by weight per 100 parts by weight of carbon powder. As a medium, a carbon-based binder containing an organic solvent-soluble component in an amount of 10 to 40 parts by weight is mixed with a total of 100 parts by weight of silica and carbon powder,
Then, the reaction temperature in the heating zone was set to 1500 to 2000℃.
Ultrafine silicon carbide powder can be produced by controlling the SiC formation reaction within the range of . 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) According to the present invention, the SiO gas generated according to the above formula (2) is converted according to the above formula (3). It is desirable to carry out the SiC formation reaction quickly and not to increase the SiO gas partial pressure in the reaction vessel to a large extent. 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, suppressing the increase in the SiO gas partial pressure, In order to obtain extremely fine 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 the high temperature of the reaction zone, and the carbon powder is mixed with a dispersion medium and a surfactant at the latest when granulated. It is necessary to mix it with a carbon-based binder as a medium. 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. By mixing the agent as a medium, the wettability between the carbon powder and the dispersion medium can be improved, and the dispersion medium soluble components of the carbon-based binder can be uniformly distributed inside the secondary particles of the carbon powder. This is thought to be due to the fact that it can be dispersed into According to the present invention, the carbon-based binder preferably contains at least 30% by weight of dispersion medium soluble components and 5 to 80% by weight of fixed carbon. The reason why it is preferable to contain at least 30% by weight of the dispersion medium soluble component is that if the dispersion medium soluble component is less than 30% by weight, it is difficult to disperse the binder into the secondary particles of carbon powder. Therefore, 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 5 to 80% by weight is that if the fixed carbon content is less than 5% by weight, a large amount must be added to obtain the desired crushing strength. Not only is the binder's properties inferior, but also the volume of the binder in the granular raw material increases, making it difficult to maintain crushing strength in high temperature ranges, and if it exceeds 80% by weight, it does not effectively act as a binder. This is because the effectiveness is extremely low and it is difficult to apply efficiently. According to the present invention, when using a dispersion medium containing an organic liquid as a main component, petroleum pitch, coal tar pitch, wood tar pitch, asphalt, phenolic resin, petroleum tar, coal tar, It is preferable to use at least one kind selected from wood tar, and to use at least one kind selected from amines, organic compounds having a carboxyl group, organic compounds having a sulfo group, and esters as a surfactant. According to the present invention, the surfactant may include, for example, polyoxy fatty acid amine, sorbitan fatty acid ester, dialkyl sulfone succinate salt,
Fatty acid, alkylamine salt, benzene sulfonic acid, polyoxysorbitan fatty acid ester, polyoxyethylene glycerin fatty acid ester, polyethylene glycol fatty acid ester, pentaerythritol fatty acid ester, propylene glycol acid ester, sucrose fatty acid ester, polyglycerin fatty acid ester, fatty acid There are alkanolamides and amine oxides, and these can be used alone or in combination. It is effective for the organic liquid to be one that can elute as much of the 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. According to the present invention, when using a dispersion medium mainly composed of water, at least one selected from phenolic resin, lignin sulfonate, molasses, and alginate is used as a carbon-based binder. However, 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 the surfactant. According to the present invention, the surfactant may be, for example, a fatty acid salt, an alkylbenzene sulfonate, a linear alkylbenzene sulfonate, an α-olefin sulfonate, a sulfonate of a naphthalene-formalin condensate, a polyoxyethylene alkyl phenyl There are ethers, and these can be used alone or in combination. According to the present invention, the amount of the surfactant added is preferably within the range of 0.05 to 5 parts by weight per 100 parts by weight of carbon powder. 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 will be extremely small, and the carbon-based binder will not be uniformly dispersed even inside the secondary particles of the carbon powder. If the amount exceeds the above range, more surfactant will be added than necessary, which is uneconomical. According to the present invention, the granular raw material is produced by adding a dispersion medium and a surfactant to a mixture of silica, carbon powder, and a carbon-based binder, mixing the mixture, and then forming the mixture into granules. A method of mixing a binder, a dispersion medium, and a surfactant, and adding the mixed solution in which the soluble components of the carbon-based binder have been eluted to a mixture of silica and carbon powder, mixing, and then forming the mixture into granules. It can be suitably manufactured by either method. Further, according to the present invention, the dispersion medium can be dried and removed from the mixture, then crushed and re-pulverized, and a binder can be added to the resulting mixture for granulation. Note that the surfactant can also be used by being mixed with carbon powder in advance. According to the present invention, the amount of fixed carbon in the carbon-based binder eluted into the dispersion medium 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 10 to 40 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 10 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 40 parts by weight, the cost of the binder will be high. This is because the amount of carbon produced by thermal decomposition of the binder increases, making it easier to produce coarse silicon carbide particles. According to the present invention, the dispersion medium liquid is mixed with carbon powder 100
It is preferable to add at least 10 parts by weight. The reason for this is that if the blending amount of the dispersion medium is less than 10 parts by weight, it is difficult to uniformly disperse the binder. In addition, it is preferable that the blending amount of the dispersion medium liquid be as large as possible considering the uniform dispersibility of the binder, but since it is uneconomical if it is too large, it is advantageous that the blending amount is 500 parts by weight or less. . In addition, the above-mentioned amounts of the "dispersion medium" and "surfactant" are sufficient if the relationship with the carbon powder is taken into consideration.
The amount is based on 100 parts by weight of carbon powder,
On the other hand, with regard to the binder for bonding silica and carbon powder, it was decided to show the amount to be blended based on 100 parts by weight (silica + carbon powder) because it was necessary to clarify the relationship between the blending amounts of both. 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 content in the reaction vessel. In order to make the pressure uniform, the above-mentioned blended raw materials are granulated, and the porosity of the granules is
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. Either the porosity of the granules must be significantly increased or the particle size of the granules must be made extremely uniform; if the porosity is too high, the strength of the granules will decrease significantly as described above, and the porosity of the granules must be made extremely uniform. This is because making the particle size uniform leads to a significant increase in raw material cost ^;
If the temperature is higher, the permeability of the reaction product gas will be poor, the flow of the high temperature gas in the pre-heating zone will be uniform, and the heat exchange between the raw material and the high temperature gas will be insufficient.Furthermore, the precipitates from the SiO gas will be This is because the raw material becomes susceptible to the influence and the smooth fall of its own weight is inhibited, making it difficult to maintain stable operation for 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 occupied by pores per unit bulk volume. The bulk volume is the volume that includes solids and internal voids in the granules. 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 material is automatically lowered continuously or intermittently through 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, 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 silicon carbide method invented and proposed by the present inventors, requires less energy for operation, and reduces the durability of production equipment. It also has advantages such as significantly improved properties. 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 means for heating the charge, that is, the heat generation of the heating element. This is the length in the height direction at the part. 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 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 explained 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 novolac type phenolic resin ( FC=51.6% by weight) 34 parts by weight, 1 part by weight of polyoxyethylene alkyl phenyl ether, and isopropyl alcohol
140 parts by weight were blended, thoroughly mixed using a fret mill, and then dried to obtain a solid mixture. Next, the crushed product obtained by crushing the solid mixture was placed in a pan-type granulator and granulated while spraying a 0.5% CMC aqueous solution, and then placed in a band-type ventilation dryer and dried with hot air for 90 minutes. The obtained granular raw material had an average particle diameter of 10.5 mm, a porosity of the granules of 52%, a granular bulk density of 0.62 g/cm ³ , and a C/SiO ₂ molar ratio of 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 conversion reaction was carried out by indirect heating in the horizontal direction while lowering the reactor by its own weight at a descending rate of 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 charging width in the heating zone is 0.24.
It is m.

【table】

[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 determined by X-ray diffraction to be 96.1%, and the specific surface area was 35.6 m ² /g. Furthermore, when the particle shape was observed using a scanning electron microscope, it was found to be a fine powder with an extremely round shape and relatively uniform particle size. Example 2, Comparative Example 1 Same as Example 1, but as shown in Table 2, reaction production was performed using granular raw materials prepared by changing the blending amounts of surfactant, binder, or dispersion medium. I got something. In other words, in Table 2, Example 2-1 is an example in which the blending amount of the surfactant was lowered to the lower limit of the present invention, and although the reaction efficiency of SiC is improved, the specific surface area becomes small, and this blending amount was found to be the limit. Furthermore, in Comparative Example 1-1, the amount of the surfactant blended was significantly reduced (0.02 parts by weight), but the effect of the addition of the binder was not exhibited and the raw material collapsed in the heating furnace. Therefore, it was found that the amount of this surfactant to be blended is required to be 0.05 parts by weight or more per 100 parts by weight of carbon powder. Next, Example 2-2 is an example in which the blending amount of the surfactant is close to the upper limit of the present invention, and Example 2-3 is an example in which the blending amount of the dispersion medium is reduced. In both cases, although the reaction efficiency of SiC has improved slightly, the specific surface area has become smaller. Next, Example 2-4 is an example in which the blending amount of the dispersion medium was increased to 200 parts by weight per 100 parts by weight of carbon powder. Although both the SiC reaction efficiency and specific surface area were improved, the amount used was It is economically disadvantageous because there are many Comparative Example 1-2 is an example in which only 7 parts by weight of the binder is added to the total of 100 parts by weight of silica and carbon, and the effect of adding the binder is not apparent and the raw material disintegrates in the heating furnace. However, it turned out to be undesirable.

【table】

[Table] 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 heating furnace, making continuous operation difficult. Example 3 Same as Example 1, but fatty acid salt, alkylbenzene sulfonate, linear alkylbenzene sulfonate, α-olefin sulfonate, naphthalene-formalin condensate was used instead of polyoxyethylene alkyl phenyl ether. Granular raw materials were prepared using sulfonic acid salts and polyoxyethylene nonylphenol ether, respectively, and reaction products were obtained. 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 material was prepared as in Example 1, but using lignin sulfonate, molasses and alginic acid instead of phenolic resin as the binder and water as the dispersion medium. A reaction product was obtained in the same manner as above. 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 Same as Example 1, but channel black powder (specific surface area = 128 m ² /g, FC =
The reaction product was obtained using a granular raw material prepared using 98.1% by weight). The properties of the reaction product obtained are shown in Table 2.
Additionally, operations remained stable for an extremely long period of time. Example 6 A reaction product was obtained in the same manner as in Example 1, except that the reaction temperature was controlled at 1900°C, which was higher than in Example 1, and the rate of descent of the charge was increased to 0.80 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, the specific surface area of the silicon carbide powder was slightly smaller at 28.6 m ² /g, but the dead weight of the charge fell smoothly and stable continuous operation was possible for a long period of time. The production capacity per unit of equipment was high. Example 7 100 parts by weight of silica powder similar to that used in Example 1, 67 parts by weight of thermal black powder similar to that used in Example 1, and high pitch powder (benzene soluble component = 65.7% by weight, FC = 50.4% by weight) %), 0.5 parts by weight of polyoxyethylene dodecylamine, and 150 parts by weight of benzene were mixed thoroughly using a fret mill, and then dried to obtain a solid mixture. Then Example 1 was prepared from the solid mixture.
A granular raw material was obtained in the same manner as above. The obtained granular raw material had an average particle diameter of 11.7 mm, a porosity of the granules of 49%, a bulk density of the granules of 0.60 g/cm ³ , and a C/SiO ₂ molar ratio of 3.8.
It was hot. A reaction product was obtained in the same manner as in Example 1 using the granular raw material. 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. Example 8 A granular raw material was prepared in the same manner as in Example 7, but using 50 parts by weight of petroleum tar (FC = 19.6% by weight) as a binder and 180 parts by weight of toluene as a dispersion medium. A reaction product was obtained in the same manner. 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. Both Example 7 and Example 8 were able to operate stably and continuously for a long period of time. Example 9 Same as Example 7, 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 body of silicon carbide, can be easily produced in high yield. The effect of contributing to industry is extremely large.

[Brief explanation of drawings]

The figure 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 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)

[Scope of Claims] 1. A raw material made of mainly silica and carbon formed into granules is charged into a reaction vessel and allowed to fall under its own weight continuously or intermittently in a preheating zone until it reaches a heating zone. In the reaction zone of the heating zone, indirect electrical heating is applied while controlling the rate of descent while applying a power load so that the horizontal temperature distribution of the charged raw materials and 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 specific surface area of carbon in the raw material formed into granules is in the range of 1 to 1000 m ² /g, and this raw material, when granulated at the latest, contains 100 parts by weight of carbon powder. a dispersion medium in an amount corresponding to at least 10 parts by weight based on the carbon powder, and an amine in an amount corresponding to at least 0.05 to 5 parts by weight based on 100 parts by weight of the carbon powder,
Using a surfactant selected from at least one of an organic compound having a carboxyl group, an organic compound having a sulfo group, and an ester as a medium, 10
A carbon-based binder containing an organic solvent-soluble component in an amount of ~40 parts by weight was mixed, and the reaction temperature in the heating zone was 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 contains at least 30% by weight of dispersion medium soluble components and 5% by weight of fixed carbon.
The manufacturing method according to claim 1 or 2, wherein the content is 80% by weight. 4 Using a dispersion medium mainly composed of organic liquid, and using carbon-based binders such as petroleum pitch, coal tar pitch, wood tar pitch, asphalt,
At least one selected from phenolic resin, petroleum tar, coal tar, and wood tar is used, and as a surfactant, one selected from amines, organic compounds having a carboxyl group, organic compounds having a sulfo group, and esters. The manufacturing method according to any one of claims 1 to 3, wherein at least one type is used. 5 A dispersion medium containing water as a main component is used, at least one selected from phenolic resin, lignin sulfonate, molasses, and alginate is used as a carbon-based binder, and amine, Claims 1 to 3 in which at least one selected from an organic compound having a carboxyl group, an organic compound having a sulfo group, an ester, an ammonium compound, and an organic compound having an ether bond are used. manufacturing method. 6 The organic liquid is 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, formate, methyl acetate, ethyl acetate,
The manufacturing method according to claim 4, which is at least one selected from isopropyl acetate, ethyl propionate, amyl propionate, butyl butyrate, diethyl carbonate, fluorinated acetic acid, diethylene dimethyl ether, ethyl methyl ketone, and quinoline. .