METHOD FOR PRODUCING LARGE GRANULAR ALPHA-PHASE SILICON CARBIDE POWDERS WITH A HIGH-PURITY

Abstract

The present disclosure provide a method for producing large granular high-purity α-phase silicon carbide powders using a silicon dioxide/carbon composite, the method including: producing a gel in which the carbonaceous compound is dispersed in a silicon dioxide network structure through a sol-gel process using starting materials including liquid phase silicon containing compounds and liquid phase carbonaceous compounds; subjecting the gel to first heat treatment to thermally decompose the carbon carbonaceous compound, thereby producing a silicon dioxide/carbon composite including nano-sized carbon particles; and subjecting the silicon dioxide/carbon composite to second heat treatment at a higher temperature than that of the first heat treatment to obtain large granular high-purity α-phase silicon carbide powders.

Claims

1. A method for producing large granular high-purity α-phase silicon carbide powders, the method comprising steps of: (i) producing a gel in which the carbonaceous compound is dispersed in a silicon dioxide network structure through a sol-gel process using starting materials including liquid phase silicon containing compounds and liquid phase carbonaceous compounds; (ii) subjecting the gel to first heat treatment to thermally decompose the carbonaceous compound, thereby producing a silicon dioxide/carbon composite including nano-sized carbon particles; and; (iii) subjecting the silicon dioxide/carbon composite to second heat treatment at a higher temperature than that of the first heat treatment to obtain large granular high-purity α-phase silicon carbide powders.

2. The method of claim 1, wherein the silicon containing compound comprises one selected from the group consisting of tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS), and combinations thereof.

3. The method of claim 1, wherein the carbonaceous compound comprises one selected from the group consisting of phenolic resin, sucrose, maltose, fructose, lactose, polyimide, xylene, and combinations thereof.

4. The method of claim 1, wherein a molar ratio of carbon atom to Si atom (C/Si) in the starting materials is 1:1.6 to 3.0.

5. The method of claim 1, wherein the sol-gel process is performed by introducing the starting materials into a solvent and adding a catalyst thereto, followed by stirring.

6. The method of claim 5, wherein the catalyst comprises: an acid selected from the group consisting of oxalic acid, maleic acid, nitric acid, hydrochloric acid, acrylic acid, toluenesulfonic acid, and combinations thereof; or a base selected from the group consisting of an alkali metal hydroxide, ammonia water, hexamethylenetetramine, and combinations thereof.

7. The method of claim 5, wherein the stirring is performed at a speed of 400 to 2,000 RPM and a temperature of 25 to 60° C.

8. The method of claim 1, further comprising a step of drying the gel, before subjecting the gel to the first heat treatment.

9. The method of claim 1, wherein the first heat treatment is performed by heating the gel to the temperature of 1,100 to 1,250° C. at a heating rate of 2 to 5° C./min to produce the silicon dioxide/carbon composite.

10. The method of claim 1, wherein the carbon particles included in the silicon dioxide/carbon composite have an average particle size of 5 nm or less.

11. The method of claim 1, further comprising a step of classifying the silicon dioxide/carbon composite to a size of 300 μm or less, before subjecting the silicon dioxide/carbon composite to the second heat treatment.

12. The method of claim 1, wherein the second heat treatment is performed by heating the silicon dioxide/carbon composite to the temperature of 2,000 to 2,100° C. at a heating rate of 5 to 15° C./min to obtain large granular high-purity α-phase silicon carbide powders.

13. The method of claim 1, which is free of introduction of an additional raw material.

14. The method of claim 1, wherein the large granular α-phase silicon carbide powder has an average particle size of 70 to 500 μm, a particle size distribution (d.sub.90/d.sub.10) of 5 or less, and a purity of 99.9995 wt % or more.

Description

EXAMPLES 1 to 3

[0059] To produce large granular high-purity α-phase silicon carbide powder, tetraethyl orthosilicate (TEOS) having metallic impurity content of 20 ppm or less was used as a liquid phase silicon containing compound, and a solid state phenol resin (novolac type) having a metallic impurity content of about 100 ppm was used as a carbonaceous compound. The TEOS and the phenol resin were prepared in consideration of the amount of carbon remaining after heat treatment such that the molar ratio of carbon atom to Si atom (C/Si) in starting materials was 1:1.6 to 3.0.

[0060] Specifically, according to the content ratio shown in Table 1 below, the carbonaceous compound and the silicon containing compound were mixed together and stirred. That is, phenol resin was dissolved in 4 moles of ethanol relative to 1 mole of Si atom in the silicon containing compound, and then TEOS was added to the solution, which was then sufficiently mixed and stirred at a stirring speed of 2000 rpm at room temperature.

[0061] To the sufficiently mixed starting material solution, an aqueous nitric acid solution obtained by mixing 0.07 mol of nitric acid and 2 mol of water relative to 1 mol of Si atom in the silicon containing compound was added, and the mixture was stirred at room temperature until a gel was formed.

[0062] The gel in which the phenol resin was uniformly dispersed was placed in high-purity distilled water to lower the alcohol content, and the gel was dried at about 80° C. for about 24 hours. The dried gel was placed in a high-purity graphite crucible which was then placed in a quartz reactor. Then, the dried gel was subjected to a first heat treatment in which the gel was heated to 1,200° C. at a rate of 5° C./min under a nitrogen gas atmosphere and maintained at that temperature for 0.5 hours, thereby producing a silicon dioxide/carbon (SiO.sub.2—C) composite. The size of the thermally decomposed carbon in the above-produced silicon dioxide/carbon composite was 2 nm or less, and the silicon dioxide/carbon composite was classified to have a size of 300 μm or less and used in a heat-treatment process for producing large granular α-phase silicon carbide powder.

[0063] The above classified silicon dioxide/carbon composite was placed in a high-purity graphite crucible at a filling rate of 60% and charged into a high-purity graphite furnace. Then, the classified silicon dioxide/carbon composite was subjected to a second heat treatment in which the composite was heated to the temperature of 2,000° C. at a rate of 10° C./min under a vacuum atmosphere (10.sup.−2 Torr) and maintained at that temperature for 3 hours, thereby producing large granular α-phase silicon carbide powder.

[0064] The properties of the large granular α-phase silicon carbide powders produced using the silicon dioxide/carbon composites in Examples 1 to 3 are summarized in Table 1 below.

TABLE-US-00001 TABLE 1 Example 1 2 3 Starting C atom in carbon source (mol) 1.6 2.3 3.0 materials Si atom in silicon source (mol) 1 1 1 C/Si (molar ratio) 1.6 2.3 3.0 Nitric acid Nitric acid (mol) 0.07 0.07 0.07 aqueous Water (mol) 2 2 2 solution α-Silicon Average particle size (μm) 90 100 150 carbide Particle size distribution (d.sub.90/d.sub.10) 4.1 4.3 4.5 powder Purity (GDMS, wt %) 99.9995 to 99.9998

EXAMPLES 4 and 5

[0065] A silicon dioxide/carbon composite was produced in the same manner as in Example 1, except that the molar ratio of carbon atom to Si atom (C/Si) in the starting materials was fixed to 2.3.

[0066] The silicon dioxide/carbon composite was placed in a high-purity graphite crucible at a filling rate of 60% and charged into a high-purity graphite furnace. Then, the silicon dioxide/carbon composite was subjected to a second heat treatment in which the composite was heated to 2,100° C. at a heating rate of 10° C./min under a vacuum atmosphere (10.sup.−2 Torr) and maintained at that temperature for each of 1 hour and 3 hours, thereby producing large granular high-purity α-phase silicon carbide powder.

[0067] The properties of the large granular α-phase silicon carbide powders produced using the silicon dioxide/carbon composites in Examples 4 and 5 are summarized in Table 2 below.

TABLE-US-00002 TABLE 2 Example 4 5 Heat treatment Atmosphere Vacuum Vacuum Heating rate (° C./min) 10 10 Peak temperature (° C.) 2100 2100 Heating time (h) 1 3 α-Silicon Average particle size (μm) 250 450 carbide powder Particle size distribution 2.5 3 (d.sub.90/d.sub.10) Purity (GDMS, wt %) 99.99995 99.99994

[0068] As described above, the large granular α-phase silicon carbide powder according to the present disclosure may be applied as a raw material for the fabrication process of a silicon carbide single crystal by the PVT method.

[0069] According to the production method of the present disclosure, large granular high-purity α-phase silicon carbide powder having an average particle size of 70 to 500 μm, a uniform particle size distribution of (d.sub.90/d.sub.10) of 5 or less, and an impurity content of 10 ppm or less may be produced through a simplified process without a complicated heat-treatment process or a process of introducing additional raw materials, making it possible to improve economic efficiency and yield.

[0070] In addition, according to the production method of the present disclosure, it is possible to effectively control the size, particle size distribution, and purity of silicon carbide powder by changing the composition of the silicon source and the carbon source that are used for the production of the silicon dioxide/carbon composite and controlling the heat-treatment temperature and the heating time.