Method for manufacturing SiC powders with high purity
Disclosed herein is a method for manufacturing SiC powders with a high purity, and more particularly, a method for manufacturing SiC powders with a high purity by reating a solid phase carbon source as raw materials with gas phase silicon sources generated from a starting material composed of metallic silicon and silicon dioxide powders and, in which it is easy to control the size and crystalline phase of the SiC powders by changing the compositions of the gas phase silicon source to the solid phase carbon source mole ratio, and the temperature and time for the heat treatment.
1. A method for synthesizing SiC powders, comprising:
i) mixing and drying metallic silicon, silicon dioxide (SiO 2 ) powders and a thermoplastic resin to prepare a starting material for generating gas phase silicon sources, wherein a ratio of the metallic silicon to silicon dioxide (SiO 2 ) powders is in a range from 1:0.8 to 2.0 by a molar ratio;
ii) placing the starting material for generating gas phase silicon sources at a lower part of a graphite crucible, placing a graphite separator on the starting material for generating gas phase silicon sources, placing a solid phase carbon source at an upper part of the graphite separator, and then closing a cover of the graphite crucible to constitute a reaction system for manufacturing SiC powders; and
iii) subjecting the reaction system under vacuum atmosphere or argon atmosphere to perform heat treatment to synthesize the SiC powders.
2. The method of claim 1 , wherein in step ii), the graphite separator has a thickness from 0.5 mm to 5 mm and holes having a diameter from 1 mm to 4 mm are present at 4 ea/cm 2 to 30 ea/cm 2 on a surface thereof.
3. The method of claim 1 , wherein the metallic silicon and silicon dioxide powder used in step i) produce silicon gas and silicon monoxide gas by the heat treatment in step iii), and the produced silicon gas and silicon monoxide gas pass through the holes of the graphite separator and are reacted with the carbon source placed at the upper part thereof to prepare the SiC powders.
4. The method of claim 1 , wherein in step i), the thermoplastic resin is used in a range from 0.2% by weight to 2% by weight based on the starting material for generating gas phase silicon sources.
5. The method of claim 1 , wherein in step i), the thermoplastic resin is one selected from phenol resins, phenol resins, polyethylene resins, and acrylic resins.
6. The method of claim 1 , wherein in step i), the mixing is performed as a process of adding water or ethanol in an amount from 20% by weight to 40% by weight and then stirring the mixture at a speed from 100 rpm to 400 rpm and the drying is performed at a temperature from 60° C. to 90° C.
7. The method of claim 1 , wherein in step ii), a C/Si element molar ratio of the silicon source and the carbon source to be charged in the crucible is in the range from 0.7 to 2.0/1.
8. The method of claim 1 , wherein in step iii), the heat treatment is performed under vacuum atmosphere at a temperature from 1,200° C. to 1,400° C. for 1 hour to 5 hours, and then under vacuum or argon atmosphere at a temperature from 1,700° C. to 2,100° C. for 1 hour to 5 hours.
9. The method of claim 1 , wherein the SiC powders are prepared in the form of beta phase SiC powders having an average diameter from 1 μm to 20 μm or a mixture of beta and alpha phase SiC powders having an average diameter from 30 μm to 50 μm.