JP4683195B2 - Method for producing silicon carbide powder - Google Patents

Description

  The present invention provides an improved method for producing silicon carbide powder which can obtain a silicon carbide powder having a low particle size and a sharp particle size distribution and having excellent moldability at low cost.

  Silicon carbide ceramics have excellent corrosion resistance and oxidation resistance, and particularly excellent strength properties at high temperatures. Therefore, wear resistant parts such as mechanical seals and valves, corrosion resistant parts, gas turbine engines, etc. It is attracting attention as a high-temperature structural material. High-purity treated silicon carbide is also used for semiconductor manufacturing parts and vacuum device parts.

  It is known that silicon carbide ceramics are difficult-to-sinter substances, and powder properties such as purity, particle size and particle size distribution of silicon carbide powder as a raw material affect the sinterability. In particular, silicon carbide for semiconductors is required to be highly purified.

  Production methods of silicon carbide powder include 1) a gas phase reaction method in which a silicon halide compound and a hydrocarbon are reacted by heating, 2) a gas phase thermal decomposition method in which an organosilicon compound is subjected to a thermal decomposition reaction, and 3) a silica and carbon. A silica reduction method by reaction is known. Among these production methods, the gas phase reaction method 1) and the gas phase pyrolysis method 2) can obtain fine silicon carbide powder having a fine particle, but a silicon halide compound used as a starting material. And organosilicon compounds are industrially disadvantageous because they are expensive and difficult to handle. The silica reduction method of 3) has long been known as the Acheson method. However, since it requires a pulverization process, it has the disadvantages that it is difficult to make fine particles and that impurities cannot be avoided.

  In recent years, a production method for obtaining silicon carbide having fine particles and high purity by a silica reduction method has been proposed, a method using a mixture of silica and carbon powder as a starting material (Patent Documents 1 to 4), and a silicon source. A method using a liquid silicon compound such as ethyl silicate and a precursor obtained using a novolac type phenol resin as a carbon source (Patent Documents 5 and 6) is disclosed.

JP-A-62-221213 JP 63-170207 A JP-A-2-267109 Japanese Patent Laid-Open No. 5-132307 JP 60-226406 A JP-A-9-48605

  A manufacturing method capable of obtaining a silicon carbide powder having a sharp particle size distribution with few impurities and an excellent moldability while being a relatively inexpensive manufacturing method is currently the most demanded, but is still in demand. Not obtained.

  That is, in Patent Documents 1 to 4, a mixture of silica and carbon powder is used as a starting material for a method for producing silicon carbide powder by a silica reduction method. In any method, silica particles and carbon black are used. Since the carbon component is simply mixed and the carbon component is not uniformly present on the surface of the silica particle, the deoxygenation reaction due to carbon from the silica particle shown in the following reaction formula 1 becomes uneven and insufficient. It is difficult to obtain high purity silicon carbide powder.

<Reaction Formula 1>
SiO ₂ + 3C → SiC + 2CO

  In Patent Documents 5 and 6, a liquid silicon compound such as ethyl silicate is used as a silicon source as a starting material for a method for producing silicon carbide powder by a silica reduction method, and a borak type phenol resin is used as a carbon source. However, the organosilicon compound used as a starting material is expensive and is industrially disadvantageous because the reaction is not uniform and multi-stage heat treatment is required.

  Therefore, the present invention is technically intended to provide a production method capable of obtaining a silicon carbide powder having a sharp particle size distribution with few impurities and excellent moldability while being a relatively inexpensive production method. Let it be an issue.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the surface of the silica particle powder is coated with a surface modifier in the method for producing silicon carbide powder in the silica reduction method, and the surface. By using composite particle powder with carbon powder adhering to the surface of modifier-coated silica particles as a starting material, silicon carbide powder with low impurities and sharp particle size distribution and excellent moldability can be obtained at low cost. The present inventors have found that it is possible to achieve the present invention.

  That is, the present invention provides a method for producing silicon carbide powder in a silica reduction method, wherein the particle surface of silica particle powder is coated with a surface modifier as a starting material, and the surface modifier-coated silica particle surface is coated with carbon powder. This is a method for producing a silicon carbide powder characterized by using a composite particle powder to which is adhered (Invention 1).

  The present invention also provides the method for producing a silicon carbide powder according to the present invention 1, wherein the weight ratio of silica and carbon powder in the composite particle powder is 1.0: 0.6 to 1.0: 1.0. (Invention 2).

  The method for producing silicon carbide powder according to the present invention has a sharp particle size distribution with few impurities, and can obtain silicon carbide powder having excellent moldability at low cost, so wear-resistant parts such as mechanical seals and valves It is suitable as a method for producing silicon carbide powder for silicon carbide ceramics used for high temperature structural materials such as corrosion resistant parts, gas turbine engines, semiconductor manufacturing parts, vacuum device parts and the like.

  The configuration of the present invention will be described in more detail as follows.

  First, a method for producing silicon carbide powder according to the present invention will be described.

  The silicon carbide powder having a sharp particle size distribution with few impurities in the present invention and having excellent moldability is obtained by coating the surface of the silica particle powder with a surface modifier in the method for producing silicon carbide powder in the silica reduction method. And a composite particle powder in which carbon powder is adhered to the surface modifier-coated silica particle surface as a starting material.

  As the silica particle powder in the present invention, any white carbon such as silicic anhydride, hydrous silicic acid, anhydrous silicate and hydrous silicate, or a substance mainly composed of silica, such as silica gel, can be used. Can also be used. Considering the purity of the obtained silicon carbide, anhydrous silicic acid and hydrous silicic acid containing no salt are preferred.

  The particle shape of the silica particle powder may be any shape such as a spherical shape, a granular shape, an indefinite shape, a needle shape, and a plate shape. Considering the uniform treatment of the carbon powder on the surface of the silica particles, the particle shape is preferably spherical or granular.

  The average particle size of the silica particle powder is 0.001 to 1.0 μm, preferably 0.002 to 0.5 μm, and more preferably 0.003 to 0.2 μm.

When the average particle diameter exceeds 1.0 μm, the proportion of SiO _{2 in} the particles not in contact with the carbon powder increases, so the carbonization rate of the resulting silicon carbide powder decreases. When the average particle size is less than 0.001 μm, aggregation is likely to occur due to an increase in intermolecular force due to particle miniaturization. Therefore, uniform carbon powder adhesion treatment to the silica particle surface via the surface modifier is performed. It becomes difficult.

The BET specific surface area value of the silica particle powder is preferably 3 m ² / g or more, more preferably 6 m ² / g or more, and still more preferably 15 m ² / g or more. When the BET specific surface area is less than 3 m ² / g, the silica particles are coarse and the proportion of SiO ₂ inside the particles not in contact with the carbon powder increases, so the carbonization rate of the resulting silicon carbide powder decreases. To do. In consideration of the uniform carbon powder adhesion treatment to the silica particle surface via the surface modifier, the upper limit is preferably 800 m ² / g, more preferably 600 m ² / g, and even more preferably 400 m ² / g. is there.

  As a silica particle powder, it is preferable that the moisture content in particle powder is 10% or less, More preferably, it is 7% or less, More preferably, it is 5% or less. When the water content in the silica particle powder exceeds 10%, unreacted silica tends to remain, which is not preferable because the purity is lowered.

  Any surface modifier may be used as the surface modifier in the present invention as long as the carbon powder can be attached to the surface of the silica particles. Preferably, organosilicon such as alkoxysilane, silane coupling agent and organopolysiloxane is used. Compounds, polymer compounds and the like are preferably used.

  Examples of organosilicon compounds include methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, ethyltriethoxysilane, propyl Alkoxysilanes such as triethoxysilane, butyltriethoxysilane, isobutyltrimethoxysilane, hexyltriethoxysilane, octyltriethoxysilane and decyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, γ-aminopropyltriethoxysilane , Γ-glycidoxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-methacryloyloxypropyltrime Silane coupling agents such as xylsilane, N- (β-aminoethyl) -γ-aminopropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, polysiloxane, methylhydrogenpolysiloxane, modified polysiloxane, etc. And organopolysiloxane.

  Examples of the polymer compound include polyvinyl alcohol, polyacrylic acid, carboxymethyl cellulose, acrylic acid-maleic acid copolymer, and olefin-maleic acid copolymer.

  The coating amount of the surface modifier is preferably 0.01 to 15.0% by weight in terms of C with respect to the silica particle powder. In the case of less than 0.01% by weight, it is difficult to attach 60 parts by weight or more of carbon powder to 100 parts by weight of silica particle powder. Since 0.01 to 15.0% by weight of the coating allows 60 to 100 parts by weight of the carbon powder to adhere to 100 parts by weight of the silica particle powder, there is no meaning to cover more than necessary. More preferably, it is 0.02-12.5 weight%, More preferably, it is 0.03% -10.0 weight%.

  As the carbon powder in the present invention, carbon black particle powder such as furnace black, channel black and acetylene black, and graphite powder can be used.

The adhesion amount of the carbon powder in the present invention is 60 to 100 parts by weight with respect to 100 parts by weight of the silica particle powder. When the amount is less than 60 parts by weight, the amount of carbon components relative to the silica particles is too small, so that the deoxygenation reaction from SiO ₂ by carbon becomes insufficient, and the unreacted SiO ₂ remains, resulting in a decrease in purity. On the other hand, when the amount exceeds 100 parts by weight, the amount of carbon components remaining as impurities without contributing to the reaction increases, which is disadvantageous for high purity, which is not preferable. Considering high purification of the resulting silicon carbide powder, the amount of carbon powder attached to 100 parts by weight of the silica particle powder is preferably 62 to 90 parts by weight, more preferably 64 to 80 parts by weight.

  The composite particle powder in the present invention is a mixture of silica particle powder and a surface modifier, the particle surface of the silica particle powder is coated with the surface modifier, and then the silica particle powder coated with the surface modifier and It can be obtained by mixing with carbon powder.

  The surface of the silica particle powder with the surface modifier is coated by mechanically mixing and stirring the silica particle powder and the surface modifier or a solution of the surface modifier. What is necessary is just to mix and stir mechanically, spraying a solution or a surface modifier.

  As equipment for mixing and stirring the silica particle powder and the surface modifier, and mixing and stirring the carbon powder and the silica particle powder whose surface is coated with the surface modifier, shear force is applied to the powder layer. A device that can be added is preferable, and in particular, a device capable of simultaneously performing shearing, spatula and compression, for example, a wheel-type kneader, a ball-type kneader, a blade-type kneader, and a roll-type kneader can be used. A wheel-type kneader can be used more effectively.

  Examples of the wheel-type kneader include an edge runner (synonymous with “mix muller”, “simpson mill”, “sand mill”), multi-mal, stotz mill, wet pan mill, conner mill, ring muller, etc., preferably edge Runners, multi-mals, stocks mills, wet pan mills and ring mullers, more preferably edge runners. Examples of the ball kneader include a vibration mill. Examples of the blade-type kneader include a Henschel mixer, a planetary mixer, and a nauter mixer. Examples of the roll-type kneader include an extruder.

  The condition at the time of mixing and stirring the silica particle powder and the surface modifier is such that the line load is 19.6 to 1960 N / cm, preferably so that the surface modifier is coated as uniformly as possible on the particle surface of the silica particle powder. May be adjusted appropriately in the range of 98 to 1470 N / cm, more preferably 147 to 980 N / cm, and the treatment time is 5 minutes to 24 hours, preferably 10 minutes to 20 hours. In addition, what is necessary is just to adjust process conditions suitably in the range of stirring speed 2-2000rpm, Preferably 5-1000rpm, More preferably, it is 10-800rpm.

  After the surface modifier is coated on the surface of the silica particle powder, the carbon powder is added, mixed and stirred to adhere the carbon powder to the surface modifier-coated silica particle surface. If necessary, drying or heat treatment may be further performed.

  The carbon powder is added little by little over a period of 5 minutes to 24 hours, preferably 5 minutes to 20 hours, or 5 to 25% by weight with respect to 100 parts by weight of the silica particle powder. Part of the carbon powder is preferably added in portions until the desired addition amount is reached.

  The conditions at the time of mixing and stirring are such that the linear load is 19.6 to 1960 N / cm, preferably 98 to 1470 N / cm, more preferably 147 to 980 N / cm, and the treatment time is 5 minutes so that the carbon powder adheres uniformly. The treatment conditions may be appropriately adjusted in a range of ˜24 hours, preferably 10 minutes to 20 hours. In addition, what is necessary is just to adjust process conditions suitably in the range of stirring speed 2-2000rpm, Preferably 5-1000rpm, More preferably, it is 10-800rpm.

  In the case of performing drying or heat treatment, the heating temperature is usually preferably 40 to 80 ° C, more preferably 50 to 70 ° C, and the heating time is preferably 10 minutes to 6 hours, more preferably 30 minutes to 3 hours. .

  If an alkoxysilane or silane coupling agent is used as the surface modifier, the coating process finally becomes an organosilane compound produced from the alkoxysilane or silane coupling agent through these steps. Has been.

  The particle shape and particle size of the composite particles in the present invention greatly depend on the particle shape and particle size of the silica particles, and have a particle form similar to the silica particles.

  The particle shape of the composite particle powder in the present invention may be any shape such as a spherical shape, a granular shape, an indefinite shape, a needle shape, and a plate shape.

The average particle size of the composite particle powder in the present invention is 0.001 to 1.0 μm, preferably 0.002 to 0.5 μm, more preferably 0.003 to 0.2 μm. When the average particle diameter exceeds 1.0 μm, the proportion of SiO ₂ inside the particles not in contact with the carbon powder increases, so that the purity of the obtained silicon carbide powder decreases.

The BET specific surface area value of the composite particle powder in the present invention is preferably 3 to 800 m ² / g, more preferably 6 to 600 m ² / g, and still more preferably 15 to 400 m ² / g. When the BET specific surface area value is less than 3 m ² / g, the silica particles are coarse and the proportion of SiO _{2 in} the particles not in contact with the carbon powder increases, so the purity of the resulting silicon carbide powder decreases. .

  The water content with respect to the silica particles in the composite particle powder in the present invention is preferably 10% or less, more preferably 7% or less, and even more preferably 5% or less. When the water content in the composite particle powder exceeds 10%, unreacted silica tends to remain, which is not preferable because purity decreases.

  The desorption rate of the carbon powder of the composite particle powder in the present invention is preferably 20% or less, more preferably 15% or less, and still more preferably 10% or less. When the desorption rate of the carbon powder exceeds 20%, the carbon powder that exists non-uniformly without contacting with silica increases, and the purity of the resulting silicon carbide powder decreases.

  The silicon carbide powder according to the present invention is a composite particle powder in which the particle surface of the silica particle powder is coated with a surface modifier and carbon powder is adhered to the surface modifier-coated silica particle surface. It is reduced and carbonized by heating and firing at a predetermined temperature in a non-oxidizing atmosphere. If necessary, the decarbonization treatment and / or the residual silica dissolution / removal treatment with hydrofluoric acid or the like may be performed by heating at 600 to 800 ° C. in an oxidizing atmosphere.

  The composite particle powder as the starting material may have a granulated body formed in advance if necessary. By forming a granulated body, the handleability of the obtained silicon carbide can be improved. Examples of the granulation method include compression granulation, extrusion granulation, rolling granulation, spray granulation and the like.

  As a binder used when forming a granulated body, a binder that does not remain as an impurity in the obtained silicon carbide is preferable. Specifically, starch, polyvinyl alcohol, phenol resin, or the like can be used.

  As the gas for forming the nitrogen atmosphere, an inert gas such as He gas or Ar gas can be used.

  The heating and firing temperature in a non-oxidizing atmosphere is preferably in the range of 1500 to 2000 ° C, more preferably 1550 to 1950 ° C, and even more preferably 1600 to 1900 ° C. When the heating and baking temperature is 1500 ° C. or lower, the formation reaction of the silicon carbide powder hardly occurs, and unreacted silica and carbon tend to remain, which is not preferable. When the temperature is 2000 ° C. or higher, particle growth progresses and pulverization becomes difficult, and α-type silicon carbide is generated and mixed with β-type silicon carbide.

  End point determination of the reductive nitriding reaction by heating and baking in a non-oxidizing atmosphere is performed by monitoring the amount of CO generated in the reaction furnace, and the amount of CO generated is preferably 50 ppm or less, more preferably 30 ppm or less, and even more preferably The end point was the time when it became 10 ppm or less.

  The silicon carbide powder in the present invention, if necessary, is cooled after the above-mentioned reduction carbonization treatment for further decarbonization treatment in an oxidizing atmosphere at a temperature range of 600 to 800 ° C. for 1 hour or more, preferably 3 Heat treatment for more than an hour.

  The crystal form of silicon carbide obtained by the production method of the present invention is β-type, and the particle shape can be obtained in various particle shapes such as granular, indeterminate and needle-like depending on the production conditions.

  The particle size of the silicon carbide powder obtained by the production method of the present invention is 0.001 to 10 μm, preferably 0.005 to 8 μm, more preferably 0.01 to 5 μm.

The BET specific surface area value of the silicon carbide powder obtained by the production method of the present invention is preferably 0.1 to ²⁰⁰ m ² / g, more preferably 0.5 to 150 m ² / g.

  The particle size distribution of the silicon carbide powder obtained by the production method of the present invention has a geometric standard deviation value of the particle diameter of 2.5 or less, preferably 2.3 or less, more preferably 2.0 or less. When the geometric standard deviation value of the particle diameter exceeds 2.5, it is not preferable because the sintering characteristics at the time of sintering of the compact are deteriorated by the existing coarse particles.

  The residual silica of the silicon carbide powder obtained by the production method of the present invention is 1% or less, preferably 0.8% or less, more preferably 0.6% or less.

  The residual carbon of the silicon carbide powder obtained by the production method of the present invention is 1.5% or less, preferably 1.3% or less, more preferably 1.1% or less.

<Action>
The most important point in the present invention is that in the method for producing silicon carbide powder in the silica reduction method, the particle surface of the silica particle powder is coated with a surface modifier and the surface modifier-coated silica particle surface is coated with carbon powder. This is the fact that by using the composite particle powder with the adhering as a starting material, a silicon carbide powder having a sharp particle size distribution with few impurities and excellent moldability can be obtained at low cost.

The present inventor considers the following as the reason why the silicon carbide powder impurities obtained by the production method according to the present invention are small. Production of silicon carbide powder by the silica reduction method is a reaction represented by the following formula 2, and it is known that SiO ₂ is first reduced by carbon and then a nitriding reaction occurs. According to the production method of the present invention, a composite particle powder in which a carbon powder serving as a carbon supply source is uniformly attached to a particle surface of a silica particle powder via a surface modifier is used as a starting material. Compared to a simple mixture of silica particle powder and carbon components such as carbon black, the reduction reaction by carbon from the silica particles occurs uniformly, so that silicon carbide with little residual silica and residual carbon could be obtained. Estimated. The reaction rate can also be improved by selecting a silica particle having a low water content in the composite particle powder.

<Formula 2>
SiO ₂ + C → SiO + CO (1)
SiO + 2C → SiC + CO (2)

  Hereinafter, the present invention will be described in detail with reference to examples.

  The average particle diameters of the silica particle powder, carbon powder, composite particle powder, and silicon carbide powder were all measured by measuring the particle diameters of 350 particles shown in the electron micrograph, and the average value thereof was indicated.

  The particle size distribution of the particle size of the silicon carbide powder was indicated by a geometric standard deviation value obtained by the following method.

  That is, the value measured for the particle size of the particle shown in the above enlarged photograph is calculated from the measured value and the particle size is plotted on the horizontal axis on the lognormal probability paper according to the statistical method from the actual particle size and number of particles obtained. The diameter is plotted on the vertical axis, and the cumulative number of particles belonging to each of the predetermined particle diameter sections (under the integrated sieve) is plotted as a percentage. Then, from this graph, the particle diameter values corresponding to the number of particles of 50% and 84.13% are read, and the geometric standard deviation value = particle diameter under integrated fluid 84.13% / under integrated fluid 50%. The value was calculated according to the particle diameter (geometric mean diameter). The closer the geometric standard deviation value is to 1, the better the particle size distribution of the particles.

  The specific surface area value was indicated by a value measured by the BET method.

  The water content of the silica particle powder in the silica particle powder and the composite particle powder was represented by the value obtained by measuring the weight of the silica particle powder before and after heating for 2 hours at 1000 ° C. In the case of composite particle powder, the weight of the silica particles in the composite particle powder is determined by measuring the amount of carbon powder and surface modifier adhering in advance by the method described later and subtracting from the weight of the composite particle powder. It is obtained by calculating.

<Equation 1>
Water content of silica powder (%) = {(Wa-We) / Wa} × 100
Wa: Weight of silica particle powder We: Weight of silica particle powder after heating at 1000 ° C. for 2 hours

  The coating amount of the surface modifier coated on the particle surface of the silica particle powder and the adhesion amount of the carbon powder adhered to the silica particle powder are “Horiba Metal Carbon / Sulfur Analyzer EMIA-2200 Model” (Inc. It was obtained by measuring the carbon content using HORIBA, Ltd.

  The desorption rate (%) of the carbon powder adhering to the composite particle powder was indicated by the value obtained by the following method. The closer the desorption rate of the carbon powder is to 0%, the smaller the desorption amount of the carbon powder from the particle surface.

  3 g of the composite particle powder and 40 ml of ethanol were placed in a 50 ml settling tube, subjected to ultrasonic dispersion for 20 minutes, and then allowed to stand for 120 minutes, whereby the composite particle powder and detached carbon powder were separated due to the difference in specific gravity. Next, 40 ml of ethanol was again added to the composite particle powder, and after ultrasonic dispersion for 20 minutes, the composite particle powder was allowed to stand for 120 minutes to separate the composite particle powder from the detached carbon powder. This composite particle powder was dried at 100 ° C. for 1 hour, and the carbon amount was measured using the above-mentioned “Horiba Metal Carbon / Sulfur Analyzer EMIA-2200 type” (manufactured by Horiba, Ltd.). The value was defined as the carbon powder desorption rate (%).

<Equation 2>
Desorption rate of carbon powder (%) = {(Wa-We) / Wa} × 100
Wa: Carbon powder adhesion amount of composite particle powder We: Carbon powder adhesion amount of composite particle powder after desorption test

  The crystal phase of the silicon carbide powder was confirmed by powder X-ray diffraction using an “X-ray diffractometer RINT 2500” (Rigaku Corporation).

  The residual silica (% by weight) of the silicon carbide powder was determined by measuring the oxygen content using “O / N analyzer TC-436” (manufactured by LECO Corporation).

  Residual carbon (% by weight) of the silicon carbide powder is determined by measuring the total carbon amount using “Horiba Metal Carbon / Sulfur Analyzer EMIA-2200” (manufactured by Horiba, Ltd.) and obtaining the amount of residual carbon The amount of carbon required for the reaction was calculated from the amount of silica (calculated from the amount of silica obtained by removing unreacted residual silica from the total amount of silica), and the value obtained by subtracting the amount of carbon used in the reaction from the total amount of carbon was shown. .

<Composite Particle 1: Production of Composite Particle Powder>
To 10 kg of silica particle powder (silica particle 1) (particle shape: spherical, average particle size: 0.012 μm, BET specific surface area value: 209.5 m ² / g, water content 0.4%), methyl hydrogen polysiloxane ( 400 g (trade name: TSF484: manufactured by GE Toshiba Silicone Co., Ltd.) was added to the silica particle powder while operating the edge runner, and mixed and stirred at a linear load of 588 N / cm for 40 minutes. The stirring speed at this time was 22 rpm.

Next, 6.4 kg of carbon powder (type: carbon black, particle shape: granular, particle diameter 0.022 μm, BET specific surface area value 133.5 m ^{2 /} g) is added over 10 minutes while the edge runner is running. Further, after mixing and stirring for 90 minutes at a linear load of 588 N / cm, carbon black was adhered to the methylhydrogenpolysiloxane coating, and then dried at 105 ° C. for 60 minutes using a dryer to obtain composite particle powder. It was. The stirring speed at this time was 22 rpm.

The obtained composite particle powder was a granular particle having an average particle diameter of 0.016 μm. The BET specific surface area value is 132.6 m ² / g, the moisture content of the silica particles in the composite particle powder is 0.21% by weight, the desorption rate of the carbon powder is 5.6%, and SiO ₂ and C are mixed by weight. The ratio was 1.0: 0.638. From the observation result of the electron micrograph, since almost no carbon black was observed, it was confirmed that almost the entire amount of carbon black was adhered to the particle surface of the silica particle powder through the methyl hydrogen polysiloxane coating.

<Example 1: Production of silicon carbide powder>
The composite particle powder was put into a graphite container as a starting material, and calcination was carried out at 1650 ° C. for 5 hours while flowing Ar gas to perform reduction nitriding treatment. The CO concentration at the end of the reaction was 9 ppm. The obtained powder was heat-treated in air at 700 ° C. for 3 hours to burn off unreacted carbon to obtain silicon carbide powder.

The obtained silicon carbide powder was granular particles having an average particle size of 0.72 μm. The geometric standard deviation value was 1.96, the BET specific surface area value was 14.6 m ² / g, the crystal form was β-form, the residual silica was 0.4% by weight, and the residual carbon was 0.81% by weight.

  In accordance with the composite particles 1 to Example 1, composite particle powder and silicon carbide powder as starting materials were prepared. Various production conditions and various characteristics of the obtained composite particle powder and silicon carbide powder are shown.

Silica particles 1-3:
A silica particle powder having the characteristics shown in Table 1 was prepared as a silica particle powder.

Carbon powders A to C:
A carbon powder having the characteristics shown in Table 2 was prepared as the carbon powder.

<Composite particle>
Composite particles 2-3, comparative composite particles 1:
Type of silica particle powder, type of additive in coating process with surface modifier, amount added, line load and time of edge runner treatment, type of carbon powder in carbon powder adhesion process, amount added, edge runner treatment line A composite particle powder was obtained in the same manner as the composite particle 1 except that the load and time were variously changed.

  The production conditions at this time are shown in Table 3, and various characteristics of the obtained composite particle powder are shown in Table 4.

<Method for producing silicon carbide>
Examples 2-3 and Comparative Example 1:
The same procedure as in the manufacture of silicon carbide of Example 1 except that the type of starting material, the mixing ratio of seed crystals, the reaction temperature and reaction time in the reduction nitriding treatment, and the heating temperature and heating time in the decarbonization treatment were variously changed. Thus, silicon carbide powder was obtained.

  The production conditions at this time are shown in Table 5, and the various characteristics of the obtained silicon carbide powder are shown in Table 6.

Claims (2)

In the method for producing silicon carbide powder in the silica reduction method, a composite in which the particle surface of silica particle powder is coated with a surface modifier as a starting material and carbon powder is adhered to the surface modifier-coated silica particle surface A method for producing silicon carbide powder, characterized by using a particle powder. 2. The method for producing silicon carbide powder according to claim 1, wherein the weight ratio of silica to carbon powder in the composite particle powder is 1.0: 0.6 to 1.0: 1.0.