JP2021147283A - Composite particle and manufacturing method thereof - Google Patents

Abstract

To provide a composite particle that has a small content of impurities, is excellent in reactivity between silica and carbon during sintering, and has large specific gravity and its manufacturing method.SOLUTION: A composite particle includes silicate particles 11, and a mixture 12 that covers the silicate particles 11 and is formed of amorphous silica and carbon, in which a true density of silicate particles is 2.2 g/cm3 or larger and smaller than 2.7 g/cm3, the true density of the mixture is 1.6 g/cm3 or larger and smaller than 2.3 g/cm3, and the impurity content is smaller than 200 ppm or smaller. As is described above, the composite particle 10 has a small content of impurities and is excellent in reactivity between silica and carbon during firing, and has a greater specific gravity. Therefore, it is suitable as a production material for silicon carbide or silicon.SELECTED DRAWING: Figure 1

Description

The present invention relates to silicon carbide or composite particles used in the production of silicon and a method for producing the same.

In recent years, awareness of energy saving and power saving has increased, and the demand for power semiconductors using silicon, silicon carbide, etc. has increased. Silicon carbide and silicon can be produced by firing a mixture of _{silica (SiO 2) and carbon (C).} Of the various known silica manufacturing methods, the method of manufacturing from alkali silicate is preferable in order to prepare a large amount of inexpensive and high-quality silica in response to the widespread use and application fields of power semiconductors. ..

Methods for producing silicon carbide or silicon include the following. For example, there is known a method of producing silicon carbide by heating inexpensive silica and carbon such as coke to 1500 to 1900 ° C. and causing a reduction reaction between carbon and silica (Patent Document 3). Further, silica obtained by purifying sodium silicate with a chelate or the like and carbon obtained from a flammable gas or a carbonaceous substance are heated to a temperature exceeding 1700 ° C. in a submerged arc furnace to cause a reduction reaction between carbon and silica. A method for producing silicon is known (Patent Document 4).

Further, a method for obtaining pure silicon monoxide that can be used as a raw material for silicon is known (Patent Document 5). When silicon is produced from silicon monoxide (SiO), the purity of silicon usually depends on the purity of the raw material silicon monoxide.

According to Patent Document 5, a method of recovering silicon monoxide by firing a mixture of a material containing carbon and silicon dioxide as a main component under a pressure of 5000 Pa or less in a temperature range of 1300 ° C. or higher and 1800 ° C. or lower. Proposed. In this method, silicon monoxide gas and carbon monoxide gas are generated by the reaction at the contact surface between the two substances of the mixture. Then, this gas is cooled to solidify a part of silicon monoxide into a bulk and recover it, and other silicon monoxide is exhausted.

As described above, there are various methods for reaching the material of the power semiconductor, but especially when silica is mixed with carbon in the production of silicon carbide, the raw materials are not separated due to the influence of the difference in the specific gravity of the raw materials and the particle size. It is preferable to treat it as such. Therefore, a method of producing a powder in which silica and carbon are composited in advance is known (Patent Document 1 and Patent Document 2).

International Publication No. 2013/005741 Japanese Unexamined Patent Publication No. 2013-567792 Japanese Unexamined Patent Publication No. 2000-0442223 JP-A-2009-530218 Japanese Unexamined Patent Publication No. 2005-206441

However, the powder obtained by combining silica and carbon described in Patent Documents 1 and 2 is light and bulky, and the material is easily separated by crushing or crushing. In addition, the compounding does not reduce the content of impurities.

High purity is required for silicon carbide and silicon used in semiconductors and the like. If the amount of impurities contained in the raw material can be reduced at the same time (in the same process), the manufacturing process can be simplified.

Usually, in the mixed raw material obtained by dry-mixing silica particles and carbon particles, particles having different specific densities are present independently of each other, so that material separation is likely to occur particularly when the diameters of these particles are large. Even in the composite powder described in Patent Documents 1 and 2 described above, when the stirring is strengthened in order to increase the cleaning efficiency when removing impurities by cleaning with an acid, the composite powder is crushed and crushed. Silica and carbon separate. When silica and carbon are separated in this way, the reactivity at the time of firing is lowered.

Furthermore, when the silica particles and carbon particles in the mixing raw material are refined for the purpose of enhancing the reactivity at the time of firing, the metal components constituting the crusher and the impurities remaining in the crusher are mixed during the work. May be mixed with raw materials.

Further, when the particles are made finer, the bulk density becomes smaller and the amount of raw material charged into the manufacturing apparatus becomes smaller. For example, the amount that can be washed at one time is small, or the amount that can be put into the firing furnace is small, and the production amount per process is limited.

The present invention has been made in view of such circumstances, and provides composite particles having a small impurity content, excellent reactivity between silica and carbon at the time of firing, and a large specific density, and a method for producing the same. The purpose is.

(1) In order to achieve the above object, the composite particles of the present invention include silicate particles and a mixture obtained by coating the silicate particles and formed of amorphous silica and carbon. , The true density of the silicate particles is 2.2 g / cm ³ or more and less than 2.7 g / cm ³ , and the true density of the mixture is 1.6 g / cm ³ or more and less than 2.3 g / cm ^3. It is characterized in that the content of impurities is 200 ppm or less. As described above, the composite particles have a small content of impurities, excellent reactivity between silica and carbon at the time of firing, and a large specific gravity. Therefore, it is suitable as a raw material for producing silicon carbide or silicon.

(2) Further, the composite particles of the present invention are characterized in that the apparent density is 1.1 g / cm ³ or more and 2.1 g / cm ³ or less. As a result, the composite particles can be put into the crucible at high density, and SiC can be efficiently produced.

(3) Further, in the method for producing composite particles of the present invention, carbon and silicate particles are mixed with an alkaline silicate aqueous solution having a Si concentration of 10% by mass or more in the liquid content, and the carbon-containing alkaline silicate aqueous solution is used. The first step of obtaining the particles, the second step of mixing the carbon-containing alkaline silicate aqueous solution and the mineral acid, and precipitating C and Si as particles composed of silica and carbon to obtain a particle-containing liquid substance, and the particle-containing It is characterized by including a third step of solid-liquid separation of liquid matter. As a result, it is possible to obtain composite particles having a small impurity content, excellent reactivity between silica and carbon during firing, and a large specific density.

(4) Further, the method for producing composite particles of the present invention is characterized in that the carbon-containing alkaline silicate aqueous solution is added to the mineral acid in the second step. By adding an alkaline aqueous solution to the strong acid in this way, the precipitated mixture can be made uniform and impurities can be dissolved in the acid. This makes it possible to dissolve impurities.

(5) Further, the method for producing composite particles of the present invention is characterized in that, in the second step, the carbon-containing alkaline silicate aqueous solution and the mineral acid are mixed while keeping the pH at 1.0 or less.

(6) Further, the method for producing composite particles of the present invention is characterized by further including a fourth step of dissolving solid impurities by the solid-liquid separation using an acid aqueous solution having a pH of less than 3.0. .. As a result, impurities can be further dissolved.

(7) Further, the method for producing composite particles of the present invention is characterized in that hydrogen peroxide is added to the acid aqueous solution in the second step and the fourth step. As a result, impurities can be further dissolved.

According to the present invention, it is possible to realize composite particles having a small impurity content, excellent reactivity between silica and carbon during firing, and a large specific gravity. As a result, high-purity silicon carbide and silicon can be obtained in large quantities by a simple method.

It is a schematic diagram which shows an example of the cross section (core) of the composite particle of this invention. It is a schematic diagram which shows an example of the cross section (dispersion) of the composite particle of this invention. It is a flowchart which shows the manufacturing method of the composite particle of this invention.

As a result of diligent research, the present inventors have made particles composed of silica, carbon and silicate particles, which have a low impurity content, excellent reactivity at the time of firing, and a high true density (bulk density). Invented. Since the particles of the present invention are completely settled in mineral acid, particles having a low impurity content and excellent reactivity between silica and carbon during firing can be produced easily and at low cost.

Further, the present inventors mix a specific alkaline silicate aqueous solution, silicate particles and carbon, and then mix the obtained mixture and mineral acid to form particles composed of silica, silicate particles and carbon. Was then precipitated, and then solid-liquid separation was performed on the liquid material containing the composite particles to obtain a solid content containing an aggregate of the composite particles. Hereinafter, embodiments of the present invention will be described in detail.

[Composition of composite particles]
1 and 2 are schematic views showing an example of a cross section of the composite particle 10, respectively. The composite particle 10 includes a silicate particle 11 and a mixture 12. The apparent density of the composite particles 10 ^{is preferably 1.1 g / cm 3} or more and 2.1 g / cm ³ or less. The bulk density of the aggregate of the composite particles 10 ^{is preferably 0.8 g / cm 3} or more and 1.8 g / cm ³ or less. As for each density, the apparent density is the gas substitution method of JIS R 1620 "Particle density measurement method of fine ceramic powder", the true density is the pycnometer method of the same JIS, and the bulk density is JIS R 1628 "bulk density of fine ceramic powder". Measure based on the tap bulk density measurement method in "Measurement method" (the same applies hereinafter).

As described above, since the specific gravity is large, the cleaning efficiency can be increased, and the composite particles 10 can be put into the crucible at a high density, so that silicon carbide and silicon can be efficiently produced. The content of impurities in the composite particles 10 is 200 ppm or less. As described above, the composite particle 10 is suitable as a raw material for manufacturing a semiconductor because the content of impurities is small.

The silicate particles 11 are included in the composite particles 10 and constitute core particles in the example shown in FIG. Further, in the example shown in FIG. 2, the silicate particles 11 are dispersed inside the composite particles 10. The true density of the silicate particles 11 is 2.2 g / cm ³ or more. By including the silicate particles 11, the composite particles 10 have an apparent density of 1.1 g / cm ³ or more.

The silicate particles 11 are, for example, silica stone and silica sand. The silicate particles 11 may contain impurities. The silicate particles 11 do not necessarily have to be crystalline particles, and may be silicate glass or a molten silicic acid product.

The mixture 12 coats the silicate particles 11 and is made of amorphous silica and carbon. In the example shown in FIG. 1, the mixture 12 forms a layer around the core particles. Further, in the example shown in FIG. 2, the mixture 12 forms a base material that fills the space between the dispersed particles.

Since the mixture 12 adheres to the silicate particles 11 without being separated into each material as described above, the reactivity between silica and carbon at the time of firing is improved. The true density of the mixture 12 is less than ^{2.3 g / cm 3.} Further, with such a configuration, the specific gravity of the aggregate of the composite particles 10 becomes high, and the container such as a crucible can be filled with a high density.

[Manufacturing method of composite particles]
A method for producing the composite particles 10 configured as described above will be described. FIG. 3 is a flowchart showing a method for producing the composite particles 10. As shown in FIG. 3, carbon and silicate particles are mixed with an alkaline silicate aqueous solution (water glass) having a Si concentration of 10% by mass or more in the liquid to obtain a slurry-like carbon-containing alkaline silicate aqueous solution. Obtain (first step). In this step, it is preferable to mix the three materials at once.

Next, a carbon-containing alkaline silicate aqueous solution and a mineral acid are mixed, and C and Si are precipitated as particles composed of silica and carbon to obtain a particle-containing liquid substance (second step). By this step, three solids are compounded. As the mineral acid, for example, sulfuric acid is preferably used.

In the second step, it is preferable to add a carbon-containing alkaline silicate aqueous solution to the mineral acid. By adding an alkaline aqueous solution to the strong acid in this way, the precipitated mixture can be made uniform and impurities can be dissolved in the acid. Further, in the second step, it is preferable to mix the carbon-containing alkaline silicate aqueous solution and the mineral acid while keeping the pH at 1.0 or less. Further, it is preferable to add hydrogen peroxide. As a result, impurities can be dissolved.

Then, the particle-containing liquid material is solid-liquid separated (third step). By solid-liquid separation, a solid content containing a mixture of silica and carbon and a liquid content containing impurities can be obtained. As a result, it is possible to obtain composite particles having a small impurity content, excellent reactivity between silica and carbon during firing, and a large specific density.

The solid impurities thus obtained are dissolved using an acid aqueous solution having a pH of less than 3.0 (fourth step). As a result, impurities can be further dissolved. In the fourth step, hydrogen peroxide may be added to the acid aqueous solution. As a result, impurities can be further dissolved. As a result, high-purity silicon carbide and silicon can be obtained in large quantities by a simple method.

Since this manufacturing method is simple in operation and has high processing efficiency, the composite particles 10 can be obtained at a low manufacturing cost. Further, the composite particles 10 obtained by this production method have impurities such as aluminum (Al), iron (Fe), magnesium (Mg), calcium (Ca), titanium (Ti), boron (B) and phosphorus (P). It has the feature that the content of calcium is small.

[Examples, comparative examples]
Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples.

[Example 1] Add 25 g of water to 100 g of a water glass solution containing 30% natural silica stone (manufactured by Fuji Chemical Co., Ltd .: SiO ₂ / Na ₂ O (molar ratio) = 3.20), and mix them to obtain a Si concentration. A 10 mass% water glass solution was obtained. In the obtained water glass solution, 12.2 g of silicic acid (Mitsubishi Shoji Building Materials, Fratary Sand, average particle size 180 μm, true density 2.6 g / cm ³ ) and carbon (manufactured by Tokai Carbon Co., Ltd., average particle size: 1 mm, 2 mm) 27.0 g of particles having the following particle size (ratio of particles of 90% by mass or more) was added and mixed to obtain a carbon-containing alkaline silicate aqueous solution.

66.2 g of the obtained carbon-containing alkaline silicate aqueous solution was added dropwise to 200 g of sulfuric acid having a sulfuric acid concentration of 10.7% by volume (a mixture of 165.6 ml of water and 20 ml of concentrated sulfuric acid), and silica was added at room temperature (25 ° C.). After precipitating particles composed of silica and carbon (carbon-containing precipitated silica), solid-liquid separation is performed using a Buchner funnel under reduced pressure, and a solid containing a mixture of silica and carbon, which is an aggregate of particles composed of silica and carbon. A minute of 35.7 g and a liquid content of 233.3 g containing impurities were obtained. The pH was maintained at 1.0 or less until the end of the dropping.

To the obtained solid content containing a mixture of silica and carbon, 200 g of sulfuric acid having a sulfuric acid concentration of 10.7% by volume was added at room temperature (25 ° C.) to prepare a slurry having a pH of less than 3.0 (because it precipitated). No stirring). After solid-liquid separation of this slurry, the obtained solid content was washed with distilled water. Then, the solid content washed with water was dried at 105 ° C. for 1 day to obtain 27.5 g of a mixture of silica and carbon ^{having a true density of 1.9 g / cm 3.}

The concentrations of aluminum (Al), iron (Fe), titanium (Ti), boron (B), and phosphorus (P) in the obtained mixture of silica and carbon were measured. The results are shown in Table 1. Further, the obtained mixture of silica and carbon ( _{molar ratio of C / SiO 2} : 3.5) was placed in a carbon crucible having a volume of 50 cm ³ and calcined in a tubular furnace at 1650 ° C. for 5 hours in an argon atmosphere. Table 2 shows the quantity before and after firing.

[Example 2] To 126 g of a water glass solution containing 10% silica stone (manufactured by Fuji Chemical Co., Ltd .: SiO ₂ / Na ₂ O (molar ratio) = 3.20), 32 g of water is added and mixed, and the Si concentration is 10 mass. % Water glass solution was obtained. In the obtained water glass solution, 4.1 g of silicic acid (Mitsubishi Shoji Building Materials, Fratary Sand, average particle size 2 mm, true density 2.6 g / cm ³ ) and carbon (manufactured by Tokai Carbon Co., Ltd., average particle size: 1 mm, 2 mm) 27.0 g of particles having the following particle size (ratio of particles of 90% by mass or more) was added and mixed to obtain a carbon-containing alkaline silicate aqueous solution.

66.2 g of the obtained carbon-containing alkaline silicate aqueous solution was added dropwise to 200 g of sulfuric acid having a sulfuric acid concentration of 10.7% by volume (a mixture of 165.6 ml of water and 20 ml of concentrated sulfuric acid), and silica was added at room temperature (25 ° C.). After precipitating particles composed of silica and carbon (carbon-containing precipitated silica), solid-liquid separation is performed using a Buchner funnel under reduced pressure, and a solid containing a mixture of silica and carbon, which is an aggregate of particles composed of silica and carbon. A minute of 35.0 g and a liquid content of 233.3 g containing impurities were obtained. The pH was maintained at 1.0 or less until the end of the dropping.

To the obtained solid content containing a mixture of silica and carbon, 200 g of sulfuric acid having a sulfuric acid concentration of 10.7% by volume was added at room temperature (25 ° C.) to prepare a slurry having a pH of less than 3.0 (because it precipitated). No stirring). After solid-liquid separation of this slurry, the obtained solid content was washed with distilled water. Then, the solid content washed with water was dried at 105 ° C. for 1 day to obtain 23.7 g of a mixture of silica and carbon ^{having a true density of 1.6 g / cm 3.}

The concentrations of aluminum (Al), iron (Fe), titanium (Ti), boron (B), and phosphorus (P) in the obtained mixture of silica and carbon were measured. The results are shown in Table 1. Further, the obtained mixture of silica and carbon ( _{molar ratio of C / SiO 2} : 3.5) was placed in a carbon crucible having a volume of 50 cm ³ and fired in a tubular furnace at 1650 ° C. for 5 hours in an argon atmosphere. Table 2 shows the quantity before and after firing.

[Example 3] To 42 g of a water glass solution containing 70% silica stone (manufactured by Fuji Chemical Co., Ltd .: SiO ₂ / Na ₂ O (molar ratio) = 3.20), 11 g of water was added and mixed, and the Si concentration was 10 mass. % Water glass solution was obtained. In the obtained water glass solution, 28.4 g of silicic acid (Mitsubishi Shoji Building Materials, Fratary Sand, average particle size 500 μm, true density 2.6 g / cm ³ ) and carbon (manufactured by Tokai Carbon Co., Ltd., average particle size: 1 mm, 2 mm) 27.0 g of particles having the following particle size (ratio of particles of 90% by mass or more) was added and mixed to obtain a carbon-containing alkaline silicate aqueous solution.

66.2 g of the obtained carbon-containing alkaline silicate aqueous solution was added dropwise to 200 g of sulfuric acid having a sulfuric acid concentration of 10.7% by volume (a mixture of 165.6 ml of water and 20 ml of concentrated sulfuric acid), and silica was added at room temperature (25 ° C.). After precipitating particles composed of silica and carbon (carbon-containing precipitated silica), solid-liquid separation is performed using a Buchner funnel under reduced pressure, and a solid containing a mixture of silica and carbon, which is an aggregate of particles composed of silica and carbon. 45.0 g of a fraction and 233.3 g of a liquid containing impurities were obtained. The pH was maintained at 1.0 or less until the end of the dropping.

To the obtained solid content containing a mixture of silica and carbon, 200 g of sulfuric acid having a sulfuric acid concentration of 10.7% by volume was added at room temperature (25 ° C.) to prepare a slurry having a pH of less than 3.0 (because it precipitated). No stirring). After solid-liquid separation of this slurry, the obtained solid content was washed with distilled water. Then, the solid content washed with water was dried at 105 ° C. for 1 day to obtain 41.2 g of a mixture of silica and carbon ^{having a true density of 2.2 g / cm 3.}

The concentrations of aluminum (Al), iron (Fe), titanium (Ti), boron (B), and phosphorus (P) in the obtained mixture of silica and carbon were measured. The results are shown in Table 1. Further, the obtained mixture of silica and carbon ( _{molar ratio of C / SiO 2} : 3.5) was placed in a carbon crucible having a volume of 50 cm ³ and fired in a tubular furnace at 1650 ° C. for 5 hours in an argon atmosphere. Table 2 shows the quantity before and after firing.

[Comparative Example 1] 35 g of water is added to 140 g of a silica stone-free water glass solution (manufactured by Fuji Chemical Co., Ltd .: SiO ₂ / Na ₂ O (molar ratio) = 3.20) and mixed to obtain a Si concentration of 10% by mass. A water glass solution was obtained. 27.0 g of carbon (manufactured by Tokai Carbon Co., Ltd., average particle size: 1 mm, ratio of particles having a particle size of 2 mm or less: 90% by mass or more) was added to the obtained water glass solution and mixed to obtain a carbon-containing water glass solution. rice field.

66.2 g of the obtained carbon-containing water glass solution was added dropwise to 200 g of sulfuric acid having a sulfuric acid concentration of 10.7% by volume (a mixture of 165.6 ml of water and 20 ml of concentrated sulfuric acid), and silica was added at room temperature (25 ° C.). After precipitating particles made of carbon (carbon-containing precipitated silica), solid-liquid separation is performed using a Buchner funnel under reduced pressure, and the solid content containing a mixture of silica and carbon, which is an aggregate of particles made of silica and carbon. 35.8 g and 232.3 g of a liquid containing impurities were obtained. The pH was maintained at 1.0 or less until the end of the dropping.

To the obtained solid content containing a mixture of silica and carbon, 200 g of sulfuric acid having a sulfuric acid concentration of 10.7% by volume was added at room temperature (25 ° C.) to obtain a slurry having a pH of less than 3.0. Most of the carbon mixture surfaced on the liquid surface. After solid-liquid separation of this slurry, the obtained solid content was washed with distilled water. Then, the solid content washed with water was dried at 105 ° C. for 1 day to obtain 22.6 g of a mixture of silica and carbon ^{having a true density of 1.5 g / cm 3.}

The concentrations of aluminum (Al), iron (Fe), titanium (Ti), boron (B), and phosphorus (P) in the obtained mixture of silica and carbon were measured. The results are shown in Table 1. Further, the obtained mixture of silica and carbon ( _{molar ratio of C / SiO 2} : 3.5) was placed in a carbon crucible having a volume of 50 cm ³ and fired in a tubular furnace at 1650 ° C. for 5 hours in an argon atmosphere. Table 2 shows the quantity before and after firing.

[Comparative Example 2] 30% added after silica stone
To 140 g of a water glass solution (manufactured by Fuji Chemical Co., Ltd .: SiO ₂ / Na ₂ O (molar ratio) = 3.20), 35 g of water was added and mixed to obtain a water glass solution having a Si concentration of 10% by mass. 66.2 g of the obtained water glass aqueous solution was added dropwise to 200 g of sulfuric acid (a mixture of 165.6 ml of water and 20 ml of concentrated sulfuric acid) having a sulfuric acid concentration of 10.7% by volume, and precipitated silica was added at room temperature (25 ° C.). After precipitation, solid-liquid separation was performed using a Buchner funnel under reduced pressure to obtain 28.9 g of solid content (precipitated silica) containing _{SiO 2 and 237.3 g of liquid content containing impurities.} The pH was maintained at 1.0 or less until the end of the dropping.

To the obtained _{solid content containing SiO 2} , 200 g of sulfuric acid having a sulfuric acid concentration of 10.7% by volume was added at room temperature (25 ° C.) to prepare a slurry having a pH of less than 3.0. After solid-liquid separation of this slurry, the obtained solid content was washed with distilled water. Then, the solid content washed with water was dried at 105 ° C. for 1 day to obtain 18.5 g of high-purity silica.

In addition to 11.7 g of the obtained high-purity silica, 4.9 g of silica stone (Mitsubishi Corporation building materials, flattery sand, average particle size 180 μm, true density 2.6 g / cm ³ ) and carbon (manufactured by Tokai Carbon Co., Ltd., average particle size: 1 mm) 10.9 g of particles having a particle size of 2 mm or less: 90% by mass or more) was added and mixed to obtain a mixture of high-purity silica, silica stone and carbon.

The high-purity silica, silica stone and carbon mixture obtained by mixing the high-purity silica, silica stone and carbon powders separated each powder during the measurement of apparent density, true density and bulk density. Therefore, it was not possible to measure the apparent density, true density and bulk density as a mixture of high-purity silica, silica stone and carbon.

The concentrations of aluminum (Al), iron (Fe), titanium (Ti), boron (B), and phosphorus (P) in the obtained mixture of high-purity silica and carbon were measured. The results are shown in Table 1. Further, the obtained mixture of high-purity silica and carbon ( _{molar ratio of C / SiO 2} : 3.5) was placed in a carbon crucible having a volume of 50 cm ³ and fired in a tubular furnace at 1650 ° C. for 5 hours in an argon atmosphere. .. Table 2 shows the quantity before and after firing.

Table 1 shows the amount of impurities in each composite particle. As shown in Table 1, the amount of impurities in Example 1 in which the composite particles in which silica stone was contained in the mixture was formed was smaller than that in Comparative Example 2 in which silica stone was added separately from the mixture.

Table 2 shows the weight of the raw material (aggregate of composite particles or mixture of silica and carbon) before firing in a density crucible. Table 2 shows the weight of the product (SiC) after firing. The weight before firing represents the weight of the raw material when the crucible is filled as much as possible.

In Example 1 in which silica stone was included in the mixture, the amount of SiC produced after firing was increased as compared with Comparative Example 1 without silica stone. Further, comparing Examples 1, 2 and 3 with Comparative Example 1, it can be seen that by incorporating silica stone in the mixture, the bulk density is increased and the yield of SiC is increased.

Table 3 shows the results of measuring the impurity content of silica stone. Since the composite particles have undergone the cleaning step, the amount of impurities in the composite particles is less than this amount of impurities. Further, the amount of impurities in the composite particles is larger than the amount of impurities in Comparative Example 1. As described above, by carrying out the production method of the present invention, the purity of the composite particles can be increased and the yield of SiC can be increased.

10 Composite particles 11 Silicate particles 12 Mixture

Claims (7)

With silicate particles,
A mixture coated with the silicate particles and formed of amorphous silica and carbon.
The true density of the silicate particles is 2.2 g / cm ³ or more and less than 2.7 g / cm ^3.
The true density of the mixture is 1.6 g / cm ³ or more and less than 2.3 g / cm ^3.
A composite particle characterized by having an impurity content of 200 ppm or less. The composite particle according to claim 1, wherein the apparent density is 1.1 g / cm ³ or more and 2.1 g / cm ^{3 or less.} The first step of mixing carbon and silicate particles with an alkaline silicate aqueous solution having a Si concentration of 10% by mass or more in the liquid to obtain a carbon-containing alkaline silicate aqueous solution.
The second step of mixing the carbon-containing alkaline silicate aqueous solution and the mineral acid and precipitating C and Si as particles composed of silica and carbon to obtain a particle-containing liquid substance.
A method for producing composite particles, which comprises a third step of solid-liquid separation of the particle-containing liquid material. The method for producing composite particles according to claim 3, wherein in the second step, the carbon-containing alkaline silicate aqueous solution is added to the mineral acid. The method for producing a composite particle according to claim 3 or 4, wherein in the second step, the carbon-containing alkaline silicate aqueous solution and the mineral acid are mixed while maintaining the pH at 1.0 or less. The composite particle according to any one of claims 3 to 5, further comprising a fourth step of dissolving solid impurities by solid-liquid separation using an acid aqueous solution having a pH of less than 3.0. Manufacturing method. The method for producing composite particles according to claim 6, wherein hydrogen peroxide is added to the acid aqueous solution in the second step and the fourth step.

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