KR101627371B1 - Preparing method of size-controlled silicon carbide powder - Google Patents

Abstract

The present invention relates to a method of producing a silicon carbide powder with size-adjustable particles, and more particularly, to a method of producing a silicon carbide powder including the following steps: i) preparing a liquid silicon source and a solid carbon source as raw materials; ii) gelling a liquid silicon source in a dispersion solution of the raw material to prepare a gel in which a solid carbon is evenly distributed; iii) heat treating the gel to prepare SiO2-C composite powder; and iv) performing carbothermal reduction on the SiO2-C composite powder to prepare a silicon carbide powder, wherein a SiO2-C composite powder is adjustable to a desired particle size by classifying particles by size and/or adjusting temperature and time of thermal carbon reduction reaction.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method of preparing a silicon carbide powder,

The present invention relates to a method for producing silicon carbide powder capable of controlling particle size.

Silicon carbide (SiC) has been used for materials such as high temperature materials, abrasion resistant materials, automotive parts, corrosion resistance of chemical plants and chemical resistant parts because of its excellent thermal mechanical properties and chemical resistance. In recent years, due to the characteristics of the semiconductor process, precise control of high-temperature processes is required, and thus silicon carbide is attracting attention as a material replacing conventional quartz and alumina materials.

Representative methods for producing silicon carbide powder include Acheson method, solid-liquid reaction method, gas phase reaction method, liquid phase reaction method and the like.

As a first method, the Acheson method is a kind of solid phase reaction method. Is a method of preparing a silicon carbide powder by mixing a solid silicon source (mainly silica (SiO ₂ )) with a solid carbon source (mainly carbon black, graphite, etc.) and performing a carbothermal reduction reaction. The silicon carbide powder produced by the Acheson method has a large average particle diameter of 1 to 100 mm. Therefore, there is a disadvantage that it is difficult to further produce a silicon carbide nano powder having an average particle diameter of 1 mu m or less even when pulverized.

A solid-liquid reaction method as a second method is disclosed in U.S. Patent No. 6,730,283. According to U.S. Patent No. 6,730,283, solid phase expanded graphite is impregnated with a liquid organosilicon compound and then calcined at a temperature of 1300 ° C or higher to prepare a silicon carbide powder. The average particle size of the silicon carbide powder produced by the above method is 100 to 1000 nm.

As a third method, a meteorological reaction method is disclosed in Japanese Patent Application Laid-open No. 61-127616 and Korean Patent No. 0318350. The gas phase reaction requires an additional apparatus for heating and vaporizing the silicon source, which is expensive, and there is a risk that the reaction temperature is maintained at a high temperature of 1600 DEG C or higher.

As a fourth method, a liquid phase reaction method is disclosed in U.S. Patent No. 6,627,169 and U.S. Patent No. 7,029,643. In U.S. Patent No. 6,627,169, a silicon carbide powder is produced by reacting ethyl silicate as a liquid silicon and a phenol resin as a liquid carbon source, which is a resole type. In addition, U.S. Patent No. 7,029,643 discloses a silicon carbide powder produced by reacting alkoxysilane, which is liquid silicon, with a resole type xylene resin, which is a liquid carbon source.

According to the conventional manufacturing method as described above, there is a high possibility that impurities are introduced in the mixing process of the solid raw material, and the synthesis yield is low because the silicon source used as the raw material and the carbon source are not uniformly mixed. And it is difficult to control the particle size of the silicon carbide to be produced.

U.S. Patent No. 6,730,283 entitled " Process for producing β-silicon carbide fine powder " Japanese Patent Application Laid-Open No. 61-127616 "Process for producing silicon carbide fine powder" Korean Patent No. 0318350 "A method for producing a silicon carbide powder from a vaporized polysiloxane U.S. Patent No. 6,627,169 entitled " Silicon Carbide Powder and Its Manufacturing Method " U.S. Patent No. 7,029,643 entitled " Silicon Carbide Powder and Its Manufacturing Method "

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing silicon carbide powders capable of controlling various purity and particle size with high economic efficiency.

In order to solve the above problems,

I) preparing a liquid silicon source and a solid carbon source so that the C / Si molar ratio ranges from 2.3 to 4.0 as the raw material;

Ii) preparing a gel in which a solid carbon source is uniformly dispersed in a gelled liquid silicon source;

Ⅲ) by heating the gel to a temperature of 300~1000 ℃ to prepare a SiO ₂ -C composite powder; And

Iv) subjecting the SiO ₂ -C composite powder to a thermal carbon reduction reaction at 1300-2200 ° C to produce a silicon carbide powder; The method comprising the steps of: preparing a silicon carbide powder;

In the production method of the present invention, since a liquid silicon source and a solid carbon source are used as a reaction raw material, homogeneous mixing of raw materials is easy, and there is an economical advantage that an expensive mixer is not used.

In the production method of the present invention, the liquid silicon source is gelated in a solution in which the liquid silicon source and the solid-phase carbon source are uniformly dispersed, There is an effect of uniformly dispersing the solid carbon source in the gel phase. In addition, SiO ₂ -C composites prepared by drying and heat treatment of the gel have an effect of increasing the efficiency of the thermal carbon reduction reaction due to the proximity of the silicon source to the carbon source.

The production method of the present invention has an effect of controlling the particle size of the silicon carbide powder through classification of the particle size of the SiO ₂ -C composite powder. In addition, the particle size of the silicon carbide powder can be controlled by controlling the reaction temperature and time in the thermal carbon reduction reaction of the SiO ₂ -C composite.

Therefore, the present invention is superior in that high purity silicon carbide powder can be produced at a high yield, and it is easy to control the particle size of the silicon carbide powder within a size range of several tens nm to several tens of 탆.

1 is for the manufacturing method of the silicon carbide powder of the present invention, (a) a mixing step of the liquid silicon source and a solid carbon source, (b) gelation step of the liquid silicon source, and (c) SiO ₂ -C complexing step FIG.

The present invention relates to a process for producing a silicon carbide powder using a liquid silicon source and a solid carbon source as raw materials. Specifically, in the process according to the invention to prepare a liquid silicon source and a solid phase SiO ₂ -C composite powder of the carbon source is homogeneously subjected to the gelation of the silicon source in a mixed state to the solid state carbon is dispersed homogeneously, and the SiO ₂ - C composite according to the particle size or the thermal carbon reduction reaction conditions to control the particle size of the silicon carbide powder to a desired size.

The method for producing a silicon carbide powder according to the present invention comprises:

I) preparing a liquid silicon source and a solid carbon source so that the C / Si molar ratio ranges from 2.3 to 4.0 as the raw material;

Ii) preparing a gel in which a solid carbon source is uniformly dispersed in a gelled liquid silicon source;

Ⅲ) by heating the gel to a temperature of 300~1000 ℃ to prepare a SiO ₂ -C composite powder; And

Iv) subjecting the SiO ₂ -C composite powder to a thermal carbon reduction reaction at 1300-2200 ° C to produce a silicon carbide powder; .

The method for producing the silicon carbide powder according to the present invention will be described in more detail as follows.

In step i), the raw material is prepared.

In the present invention, a liquid silicon source and a solid carbon source are used as raw materials.

The liquid silicon source is a silane compound containing a hydrolyzable functional group. Specifically, the liquid silicon source is selected from the group consisting of monoalkoxysilane, dialkoxysilane, trialkoxysilane and tetraalkoxysilane, One or more silane compounds may be used. Specifically, at least one selected from methoxysilane, ethoxysilane, propoxysilane, dimethyldimethoxysilane, dichlorodiethoxysilane, chlorotrimethoxysilane, tetraethylorthosilicate and the like can be used.

[Chemical Formula 1]

(In Formula 1, R _1, R _2, R ₃ and R ₄ is selected from hydrogen atom, halogen atom, C ₁ ~C ₆ alkyl group and a C ₁ ~C ₆ alkoxy group, but R _1, R _2, R at least one of the ₃ and R ₄ is a C ₁ ~C ₆ alkoxy group)

The solid carbon source may be a nano-sized powdery carbon compound. Specifically, at least one selected from the group consisting of carbon black powder, carbon nanotube (CNT) and graphite powder may be used.

It is preferable that the solid carbon source is dispersed in a solvent selected from water, a C _{1 to} C ₆ alcohol and an aqueous C _{1 to} C ₆ alcohol solution, so that it is easier to homogeneously mix the liquid silicon source and the solid carbon source, This is because the surface area of the carbon source is increased and the reaction activity can be further increased in the silicon carbide synthesis reaction. At this time, the amount of the solvent for dispersing the solid carbon source is preferably less than 20 mole ratio, preferably 4 to 20 mole ratio based on 1 mole of the liquid silicon source. If the amount of the solvent is less than 4 mol, uniform dispersion and surface area equivalent effects of the solid carbon source can not be obtained. If the solvent is used in excess of 20 molar ratio, the liquid silicon compound increases the gelation time in the gelation step .

The liquid silicon source and the solid carbon source used as raw materials in the present invention can be variously used from a low purity material to a high purity material. In the production method of the present invention, the silicon carbide synthesized through controlling the purity of the solid carbon source used as a raw material The purity of the powder can be controlled. The liquid silicon source used as the raw material and the solid carbon source may be mixed so that the molar ratio of C / Si ranges from 2.3 to 4.0. As the molar ratio of C / Si increases, the synthesis yield of silicon carbide increases. The particle size tends to decrease. If the molar ratio of C / Si is less than 2.3, the synthesis yield of silicon carbide powder may be lowered. If the molar ratio of C / Si is less than 2.3, Molar ratio exceeds 4.0, unreacted carbon may remain after the synthesis of the silicon carbide powder, thereby lowering the purity of the product.

In the step ii), a gel having uniform solid carbon sources is prepared.

The gel prepared in the present invention is uniformly dispersed in a solid carbon source on a SiO ₂ gel having a network structure formed by hydrolyzing a liquid silicon source with an aqueous acid solution or an aqueous base. In addition, the solid carbon source is trapped in a SiO ₂ gel having a network structure, and the movement is inhibited.

The method for producing a gel according to the present invention will be described in detail. The liquid silicon source can be gelated by adding an aqueous acid solution or an aqueous base solution to a solution in which a liquid silicon source and a solid carbon source are uniformly dispersed while stirring. Or a liquid silicon source is firstly hydrolyzed by adding an aqueous acid solution or an aqueous base solution to the liquid silicon source, and then the solid carbon source is added and stirred to disperse the solid carbon source in the gel structure.

The acid aqueous solution used for gelation of the liquid silicon source is an aqueous solution in which at least one acid selected from common organic acids or inorganic acids is dissolved in a molar ratio of 0.001 to 0.14 mol based on 1 mol of water. The acid may be at least one selected from the group consisting of inorganic acids including nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid and the like and organic acids including oxalic acid, acetic acid, and toluenesulfonic acid. Use an aqueous acid / silicon mixture molar ratio for gelation ranging from 1 to 10 so that the silicon source is sufficiently gelled.

The base aqueous solution used for gelation of the liquid silicon source may be prepared by dissolving at least one base selected from conventional organic bases or inorganic bases in an aqueous solution at a molar concentration of 0.001 to 0.14 mol based on 1 mol of water to be. The base may be specifically at least one selected from the group consisting of alkali metal salts such as sodium hydroxide, ammonia, and amines such as hexamethylenetetramine (HMTA). The aqueous base solution / silicon source molar ratio for gelation ranges from 1 to 16, so that the silicon source is sufficiently gelated.

In the present invention, the gelation temperature is preferably maintained in the range of 20 to 50 ° C in the range of 300 to 600 rpm to sufficiently disperse the liquid silicon source and the solid carbon source in the gelation process.

As described above, in the present invention, the raw material can be easily mixed with the conventional solid-phase reaction method by selectively using a liquid silicon source and a solid carbon source. Therefore, in the gelation process of the present invention, instead of using an expensive mixer, mixing can be performed homogeneously even using a general mixing method in which the rotational force and rotation speed of the mixer are relatively low. For example, it is possible to use conventional mixing means including magnetic stirring with Teflon coating, impeller stirring with Teflon coating, ultrasonic mixing and the like. Particularly, when impeller coated with Teflon is used and stirred at a speed of 300-600 rpm by a general stirring method, impurities introduced during mixing of raw materials can be controlled. Also, mixing and dispersing the mixture by repeating the impeller stirring method and the ultrasonic mixing method coated with Teflon at about 3 times at room temperature may be more advantageous for producing high purity silicon carbide powder.

When the above-mentioned liquid silicon source starts to gel, stirring is stopped. When the gelation is completed, the gel is dried at a temperature of 25 to 100 DEG C and atmospheric pressure or a vacuum atmosphere for 24 to 72 hours to obtain a gel.

In step iii), the gel is heat-treated to prepare a SiO ₂ -C composite powder.

In the present invention, a solvent (for example, water, alcohol or the like) remaining in the gel is evaporated by heat treatment to shrink the volume of the gel to produce a SiO ₂ -C composite powder having a close distance between the silicon source and the carbon source.

The SiO ₂ -C composite powder produced by the above-mentioned heat treatment is composed of amorphous SiO ₂ having a very large contact area between the silicon raw material and the carbon raw material particles and a nano-sized carbon powder of a solid phase. Therefore, the SiO _{2 -} C composite can maximize the contact between SiO ₂ and the carbon powder, thereby improving the reaction efficiency in the thermal carbon reduction reaction for synthesizing the silicon carbide powder.

The heat treatment for the preparation of the SiO ₂ -C composite powder is conducted in an inert atmosphere or a vacuum atmosphere at 300 to 1000 ° C for 1 to 6 hours. Specifically, a gel in which a carbon source is uniformly dispersed is placed in a graphite crucible, charged into a quartz reaction furnace, heated in an inert atmosphere or a vacuum atmosphere at a rate of 8 to 12 캜 / min to 300 to 1000 캜, To prepare a SiO ₂ -C composite powder.

In addition, when the SiO ₂ -C composite powder is applied to the thermal carbon reduction reaction, it may be easier to control the particle size of the synthesized silicon carbide by classifying it according to the particle size. The SiO ₂ -C composites can be sieved to a predetermined size using a ball mill, an impact mill, a planetary mill or the like, and sieved to classify the particles by particle size. Specifically, the SiO ₂ -C composite powder can be classified by size in a size of 5 mm or more, a particle size of 0.5 to 5 mm, a particle size of 200 to 500 μm, and a particle size of less than 200 μm.

Depending on the particle size of the SiO ₂ -C composite powder, the synthesis temperature and the synthesis time of the silicon carbide powder in the thermal carbon reduction reaction may be affected. If a SiO ₂ -C composite powder is applied to a thermal carbon reduction reaction without a classification process, a high temperature or a long reaction time is required for the thermal carbon reduction reaction of a SiO ₂ -C composite having a large particle size. However, when the classified SiO ₂ -C complex is used, the temperature of the thermal carbon reduction reaction and the reaction time are controlled by the particle size, so that it is possible to produce the silicon carbide powder economically. According to the present invention, the smaller the particle size of the SiO ₂ -C composite is, the lower the synthesis temperature and time of the silicon carbide powder by the thermal carbon reduction reaction, and the silicon carbide powder having a small particle size is synthesized.

Therefore, the present invention is advantageous in that the particle size of the silicon carbide powder can be more easily controlled by classifying SiO ₂ -C composite powder.

FIG. 1 is a conceptual diagram of a step of mixing a liquid silicon source with a solid carbon source, a step of gelling a liquid silicon source, and a step of forming a SiO ₂ -C complex in the method of producing the silicon carbide powder of the present invention.

1 (a), the solid carbon source is uniformly dispersed in the liquid silicon source and the liquid phase / the solid phase coexist.

1 (b), the liquid silicon source is converted into a gel phase which is hydrolyzed by an aqueous acid solution or an aqueous base solution to form a network structure with Si-O-H bonds between the uniformly dispersed solid carbon source particles. As shown in the figure, the solid carbon source is trapped in the gel phase of the mesh structure and is inhibited from moving, so that a gel in which the solid carbon source is uniformly dispersed can be produced.

In (c) SiO ₂ -C complex formation step of FIG. 1, the solvent remaining in the gel is evaporated by high-temperature heat treatment, and SiO ₂ is shrunk to form SiO ₂ -C composites. The composite prepared through this heat treatment maximizes the contact area between SiO ₂ and the carbon source, so that the reaction efficiency in the subsequent thermal carbon reduction reaction can be further improved.

Step iv) is a thermal carbon reduction reaction of the SiO ₂ -C composite to produce silicon carbide powder.

The thermal carbon reduction reaction is conducted in an inert atmosphere or a vacuum atmosphere at a temperature of 1400 to 2200 ° C for 1 to 6 hours. Specifically, the SiO ₂ -C composites are placed in a graphite crucible and charged in a high-temperature vacuum (for example, graphite vacuum furnace) to raise the temperature to 1400 to 2200 ° C at a rate of 8 to 12 ° C / min in an inert or vacuum atmosphere And maintained for 1 to 6 hours, followed by cooling to prepare silicon carbide powder.

According to the production method of the present invention, the particle size of the silicon carbide powder to be produced can be sufficiently controlled. Specifically, by controlling the temperature and time of the thermal carbon reduction reaction, the particle size of the silicon carbide powder is controlled within an average particle size range of 50 nm to 400 μm by using SiO ₂ -C composites classified by particle size of 100 μm to 10 mm do. For example, as the temperature is increased up to the synthesis temperature of 2000 ° C., the size of the synthesized silicon carbide powder gradually increases from 50 nm to 20 μm, and at 2200 ° C., the particle size of the silicon carbide powder rapidly increases to a maximum of 200 μm.

As described above, according to the method for producing silicon carbide powder according to the present invention, the synthesis yield of silicon carbide relative to the silicon atoms of the silicon source is high and the particle size of silicon carbide can be controlled.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

[Example]

Examples 1-5. Synthesis of silicon carbide powder

Tetraethyl orthosilicate (TEOS) was used as a liquid silicon source, and carbon black powder (purity 99.992%) was used as a solid carbon source. As shown in Table 1 below, TEOS and carbon black were each measured to have a C / Si molar ratio of 2.3 to 3.3, thereby preparing five raw materials.

division Composition of raw material Acidic aqueous solution TEOS
(mol) Carbon black
(mol) C / Si
(Molar ratio) Nitric acid (mol) Water (mol) Example 1 One 2.3 2.3 0.007 2 Example 2 One 2.5 2.5 0.007 2 Example 3 One 2.8 2.8 0.007 2 Example 4 One 3.0 3.0 0.007 2 Example 5 One 3.3 3.3 0.007 2

1 mol of TEOS was added to carbon black, and the mixture was stirred in a magnetic stirrer at a speed of 400 rpm for 10 minutes at room temperature, followed by mixing for 10 minutes in an ultrasonic mixer. To the fully mixed raw material, an aqueous acid solution prepared by mixing 0.007 mol of the measured nitric acid and 2 mol of water was added and stirred at room temperature until the gel was obtained. The gel was dried at about 100 < 0 > C for about 24 hours to prepare a gel.

The prepared gel was charged in a graphite crucible and charged into a quartz reaction furnace. The temperature was raised at a rate of 10 ° C / min under a nitrogen gas atmosphere and heat treatment was conducted at 900 ° C for 1 hour to prepare a SiO ₂ -C complex. A SiO ₂ -C composite powder with a size of 5 mm or more was selected and used for the thermal carbon reduction reaction.

SiO ₂ -C composite powder was placed in a graphite furnace and charged into a graphite furnace. The temperature was raised to a silicon carbide synthesis temperature at a rate of 10 ° C / min in a vacuum atmosphere (10 ^-2 torr) After maintaining the carbon reduction reaction conditions, the silicon carbide powder was prepared by low-temperature cooling.

Thermal carbon reduction reaction conditions division Heating rate
(° C / min) Reaction temperature
(° C) atmosphere Reaction time (h) Synthetic condition 1 10 1600 vacuum 3 Synthetic condition 2 10 1800 vacuum 3 Synthetic condition 3 10 2000 vacuum One Synthetic condition 4 10 2200 vacuum One

The results of Examples 1 to 5 are as follows.

As the C / Si molar ratio increased, the yield of SiC synthesis ranged from about 67% to 95% based on silicon source. In the case of raw materials having a C / Si molar ratio of 2.3 to 3.0, residual carbons in the synthesized silicon carbide powder were not observed, but in the case of raw materials having a C / Si molar ratio of 3.3, residual carbons in the silicon carbide powder synthesized due to excessive use of carbon sources About 5% were present. The crystal phase analysis of the silicon carbide powder synthesized by using a raw material having a C / Si molar ratio of 2.5 and a C / Si molar ratio of 3.0 was carried out using a diffraction pattern of XRD. As a result, all of β-phase silicon carbide was synthesized, No image was observed. The silicon carbide powder observed by SEM was spherical and the particle size was observed to have a size of about 200 to 500 nm. The silicon carbide powder synthesized by using a raw material having a C / Si molar ratio of 3.0 was selected and measured to have a purity of about 99.997 in the purity analysis using the GDMS analysis method.

As the C / Si molar ratio increased, the yield of SiC synthesis was in the range of about 58% to 93% based on silicon source. In the case of raw materials having a C / Si molar ratio of 2.3 to 3.0, residual carbons in the synthesized silicon carbide powder were not observed, but in the case of raw materials having a C / Si molar ratio of 3.3, residual carbons in the silicon carbide powder synthesized due to excessive use of carbon sources About 3% were present. The crystal phase analysis of the silicon carbide powder synthesized by using a raw material having a C / Si molar ratio of 2.5 and a C / Si molar ratio of 3.0 was carried out using a diffraction pattern of XRD. As a result, all of β-phase silicon carbide was synthesized, No image was observed. The silicon carbide powder observed by SEM was spherical, and the particle size was observed to have a size of about 1 탆 to 5 탆.

As the C / Si molar ratio increased, the yield of SiC synthesis was in the range of about 53% to 84% based on silicon source. In the case of raw materials having a C / Si molar ratio of 2.3 to 3.0, residual carbons in the synthesized silicon carbide powder were not observed, but in the case of raw materials having a C / Si molar ratio of 3.3, residual carbons in the silicon carbide powder synthesized due to excessive use of carbon sources About 1.5% were present. The crystal phase analysis of the silicon carbide powder synthesized by using a raw material having a C / Si molar ratio of 2.5 and a C / Si molar ratio of 3.0 was carried out using a diffraction pattern of XRD. As a result, all of β-phase silicon carbide was synthesized, No image was observed. The silicon carbide powder observed by SEM was spherical, and the particle size was observed to have a size of about 10 탆 to 20 탆.

As the C / Si mole ratio increased, the yield of SiC synthesis was in the range of about 49% to 79% based on the silicon source. In the case of raw materials having a C / Si molar ratio of 2.3 to 3.0, residual carbons in the synthesized silicon carbide powder were not observed, but in the case of raw materials having a C / Si molar ratio of 3.3, residual carbons in the silicon carbide powder synthesized due to excessive use of carbon sources About 1% were present. The crystal phase analysis of the silicon carbide powder synthesized by using a raw material having a C / Si molar ratio of 2.5 and a C / Si molar ratio of 3.0 was carried out using a diffraction pattern of XRD. As a result, it was observed that silicon carbide of? Phase was synthesized. The silicon carbide powder observed by SEM was mixed with a typical α-SiC phase shape and a spherical shape on a hexagonal plate, and the powder particle size was observed to have a size of about 100 μm to 200 μm.

Example 6 Synthesis of Silicon Carbide Powder

High purity carbon black powder (purity: 99.99923%) was used as a solid phase carbon source and tetraethyl orthosilicate (TEOS) was used as a liquid silicon source.

1 mol of TEOS and 3 mol of carbon black were weighed and mixed in a Teflon beaker. The mixture was stirred at room temperature for about 1 hour at a rate of 400 rpm using a magnetic stirrer in an environment of a small amount of impurities. For the preparation of aqueous acid solution to be used for the hydrolysis of TEOS, 0.007 mol of high purity nitric acid and 2 mol of distilled water were weighed and mixed in a Teflon beaker to minimize the influx of impurities. To the mixed solution of TEOS and carbon black, an aqueous acid solution was added and stirred at room temperature until the gel became a gel. The gel was completely dried at a temperature of about 100 ° C in an environment of low inflow of impurities to prepare a gel.

The prepared gel was charged in a graphite crucible and charged into a quartz reaction furnace. The temperature was raised at a rate of 10 ° C / min under a high purity nitrogen gas atmosphere and heat treatment was conducted at 900 ° C for 1 hour to prepare a SiO ₂ -C complex. A SiO ₂ -C composite powder with a size of 5 mm or more was selected and used for the thermal carbon reduction reaction.

The SiO ₂ -C composite powder was placed in a high purity graphite furnace in a high purity graphite crucible, and the temperature was raised to 1800 ° C at a rate of 10 ° C / min in a vacuum atmosphere (10 ^-2 torr) and maintained for 3 hours Followed by low-temperature cooling to prepare a high purity silicon carbide powder.

The results of Example 6 are as follows. The synthesis yield of the silicon carbide powders produced was in the range of about 93% based on silicon source, and unreacted carbon was not observed. As a result of crystal phase analysis using XRD diffraction pattern, β-phase silicon carbide having excellent crystallinity was observed to be synthesized, and unreacted carbon and unreacted SiO ₂ were not observed. The silicon carbide powder observed by SEM was spherical and the particle size was observed to be 200 nm in size. The purity of the finally synthesized silicon carbide powder was analyzed using the GDMS method and measured to have a purity of about 99.99994.

Examples 7-11. Synthesis of silicon carbide powder

Tetraethyl orthosilicate (TEOS) was used as a liquid silicon source, and carbon black powder (purity 99.992%) was used as a solid carbon source. As shown in Table 3 below, TEOS and carbon black were each measured to have a C / Si molar ratio of 2.3 to 3.3, thereby preparing five raw materials.

division Composition of raw material Aqueous base solution TEOS
(mol) Carbon black
(mol) C / Si
(Molar ratio) ammonia
(mol) Water (mol) Example 7 One 2.3 2.3 0.07 4 Example 8 One 2.5 2.5 0.07 4 Example 9 One 2.8 2.8 0.07 4 Example 10 One 3.0 3.0 0.07 4 Example 11 One 3.3 3.3 0.07 4

1 mol of TEOS, 4 mol of ethanol and 16 mol of distilled water were added to carbon black, and the mixture was stirred in a magnetic stirrer at a speed of 400 rpm for 10 minutes at room temperature, followed by mixing in an ultrasonic mixer for 10 minutes. Respectively. To the fully mixed raw material, an aqueous base solution prepared by mixing 0.07 mol of the measured ammonia water and 4 mol of water was added, and the mixture was stirred at room temperature until it became a gel. The gel was dried at about 100 < 0 > C for about 24 hours to prepare a gel.

The prepared gel was charged into a graphite crucible and charged into a quartz reaction furnace. The furnace was heated at a rate of 10 ° C / min under a nitrogen gas atmosphere and heat-treated at 900 ° C for 0.5 hour to prepare a SiO ₂ -C composite. The SiO ₂ -C composites were selected for powders> 5 mm and used for the thermal carbon reduction reaction.

SiO ₂ -C composite powder was placed in a graphite furnace and heated in a vacuum atmosphere (10 ^-2 torr) at a rate of 10 ° C / min to a silicon carbide synthesis temperature, After maintaining the carbon reduction reaction conditions, the silicon carbide powder was prepared by low-temperature cooling.

Thermal carbon reduction reaction conditions division Heating rate
(° C / min) Reaction temperature
(° C) atmosphere Reaction time (h) Synthetic condition 1 10 1600 vacuum 3 Synthetic condition 2 10 1800 vacuum 3 Synthetic condition 3 10 2000 vacuum One Synthetic condition 4 10 2200 vacuum One

The results of Examples 7 to 11 are as follows.

As the C / Si molar ratio increased, the yield of SiC synthesis ranged from about 70% to 93% based on silicon source. In the case of raw materials having a C / Si molar ratio of 2.3 to 3.0, residual carbons in the synthesized silicon carbide powder were not observed, but in the case of raw materials having a C / Si molar ratio of 3.3, residual carbons in the silicon carbide powder synthesized due to excessive use of carbon sources About 3% were present. The crystal phase analysis of the silicon carbide powder synthesized by using a raw material having a C / Si molar ratio of 2.5 and a C / Si molar ratio of 3.0 was carried out using a diffraction pattern of XRD. As a result, all of β-phase silicon carbide was synthesized, No image was observed. The silicon carbide powder observed by SEM was spherical and the particle size was observed to be about 50 to 150 nm in size. The silicon carbide powder synthesized by using a raw material having a C / Si molar ratio of 3.0 was selected and found to have a purity of about 99.995 in the purity analysis using the GDMS analysis method.

As the C / Si molar ratio increased, the yield of SiC synthesis ranged from about 62% to 91% based on the silicon source. In the case of raw materials having a C / Si molar ratio of 2.3 to 3.0, residual carbons in the synthesized silicon carbide powder were not observed, but in the case of raw materials having a C / Si molar ratio of 3.3, residual carbons in the silicon carbide powder synthesized due to excessive use of carbon sources About 5% were present. The crystal phase analysis of the silicon carbide powder synthesized by using a raw material having a C / Si molar ratio of 2.5 and a C / Si molar ratio of 3.0 was carried out using a diffraction pattern of XRD. As a result, all of β-phase silicon carbide was synthesized, No image was observed. The silicon carbide powder observed by SEM was spherical and the particle size was observed to be about 200 nm to 800 nm in size.

As the C / Si molar ratio increased, the yield of SiC synthesis ranged from 59% to 89% based on the silicon source. In the case of raw materials having a C / Si molar ratio of 2.3 to 3.0, residual carbons in the synthesized silicon carbide powder were not observed, but in the case of raw materials having a C / Si molar ratio of 3.3, residual carbons in the silicon carbide powder synthesized due to excessive use of carbon sources About 3% were present. The crystal phase analysis of the silicon carbide powder synthesized by using a raw material having a C / Si molar ratio of 2.5 and a C / Si molar ratio of 3.0 was carried out using a diffraction pattern of XRD. As a result, all of β-phase silicon carbide was synthesized, No image was observed. The silicon carbide powder observed by SEM was spherical and the particle size was observed to have a size of about 1.2 탆 to 4 탆.

As the C / Si mole ratio increased, the yield of SiC synthesis was in the range of about 54% to 83% based on silicon source. In the case of raw materials having a C / Si molar ratio of 2.3 to 3.0, residual carbons in the synthesized silicon carbide powder were not observed, but in the case of raw materials having a C / Si molar ratio of 3.3, residual carbons in the silicon carbide powder synthesized due to excessive use of carbon sources About 2.5% were present. The crystal phase analysis of the silicon carbide powder synthesized by using a raw material having a C / Si molar ratio of 2.5 and a C / Si molar ratio of 3.0 was carried out using a diffraction pattern of XRD. As a result, it was observed that silicon carbide of? Phase was synthesized. The silicon carbide powder observed by SEM was mixed with a typical α-SiC phase and spherical shape on the hexagonal plate, and the powder particle size was observed to have a size of about 3 ㎛ to 6 ㎛.

Claims (14)

(I) at least one liquid silicon source selected from the group consisting of a silane compound represented by the following formula (1) and a carbon black powder, a carbon nanotube (CNT) and a graphite powder Preparing at least one solid carbon source selected from the group consisting of:
Ii) reacting the prepared raw material with an aqueous solution of an acid or base to prepare a gel in which a solid carbon source is uniformly dispersed in a SiO ₂ gel having a network structure formed by hydrolysis of a liquid silicon source;
Ⅲ) by heating the gel to a temperature of 300~1000 ℃ to prepare a SiO ₂ -C composite powder; And
Iv) subjecting the SiO ₂ -C composite powder to a thermal carbon reduction reaction at 1300-2200 ° C to produce a silicon carbide powder;
≪ / RTI >
[Chemical Formula 1]

(In Formula 1, R _1, R _2, R ₃ and R ₄ is selected from hydrogen atom, halogen atom, C ₁ ~C ₆ alkyl group and a C ₁ ~C ₆ alkoxy group, but R _1, R _2, R at least one of the ₃ and R ₄ is a C ₁ ~C ₆ alkoxy group)
delete delete The method according to claim 1,
The solid carbon source is water, C ₁ ~C ₆ alcohol or C ₁ ~C ₆ The method for producing the silicon carbide powder is characterized by using a dispersed aqueous alcohol solution.
delete The method according to claim 1,
Wherein the acid aqueous solution is an aqueous solution in which at least one acid selected from the group consisting of nitric acid, hydrochloric acid, oxalic acid, acetic acid, and toluenesulfonic acid is dissolved.
The method according to claim 1,
Wherein the acid aqueous solution is dissolved in a molar ratio of 0.001 to 0.14 mol based on 1 mol of water and the acid aqueous solution is used so that an aqueous solution of an acid / silicon is in a molar ratio of 1 to 10. [ .
The method according to claim 1,
Wherein the base aqueous solution is an aqueous solution in which at least one base selected from the group consisting of sodium hydroxide, ammonia, and hexamethylenetetramine (HMTA) is dissolved.
The method according to claim 1,
Wherein the base aqueous solution is dissolved in a molar ratio of 0.001 to 0.14 mol based on 1 mol of water and the base aqueous solution is used so that the base aqueous solution / silicon single molar ratio is in the range of 1 to 16. Way.
The method according to claim 1,
Wherein the mixing means selected from the group consisting of Teflon coated magnetic stirring, Teflon coated impeller stirring, and ultrasonic mixing is used in the step ii).
The method according to claim 1,
Wherein the heat treatment in the steps iii) and iv) is performed in an inert atmosphere or a vacuum atmosphere.
The method according to claim 1,
Wherein the particle size of the silicon carbide powder is controlled by controlling the temperature and time of the thermal carbon reduction reaction in the step iv).
The method according to claim 1,
Wherein the SiO ₂ -C complex is classified according to the particle size in the step iv).
14. The method of claim 13,
In the step iv), the SiO ₂ -C composites are classified by particle size in the range of 100 μm to 10 mm and used in the thermal carbon reduction reaction to adjust the particle size of the silicon carbide powder within the range of the average particle size of 50 nm to 400 μm Wherein the silicon carbide powder is a silicon carbide powder.

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