A preparation process of high-purity silicon carbide powder

Abstract

The invention discloses a preparation process of high-purity silicon carbide powder, comprising the following steps: (1) wet-mixing high-purity carbon powder and high-purity silicon powder, drying and pressing to form a green body; (2) placing two green bodies in a graphite crucible of an electromagnetic induction furnace, heating to 1450°C and keeping the temperature for 2 hours under vacuum, then heating to 1600°C and keeping the temperature for 2 hours, then heating to 2050-2250°C and keeping the temperature for 2 hours; cooling to room temperature. In the preparation process of the invention, two green bodies are stacked up and down, and the temperature gradient distribution inside the crucible is utilized during re-sintering, and the silicon carbide at the bottom is decomposed to produce a large amount of Si that passes through the upper stacked sample, thereby reducing the residual carbon content of the upper sample and increasing the SiC generation of the upper sample. The high-purity silicon carbide powder prepared by the process of the invention has a purity higher than 99.999%, which fully meets the requirements for the growth of silicon carbide single crystals and the requirements for the use level of electronic ceramic raw materials.

Description

Technical Field

[0001] The invention relates to a preparation process of high-purity silicon carbide powder, belonging to the field of high-tech ceramics. Background Art

[0002] High-purity silicon carbide powder is the main raw material for preparing silicon carbide single crystals and SiC electronic ceramics. The preparation methods of high-purity SiC powder include Acheson method, self-propagating high-temperature synthesis method, chemical vapor deposition method, plasma method, sol-gel method and polymer thermal decomposition method. The most widely used is the solid-phase Acheson method, but this type of method introduces more impurities during the preparation process and the carbon residue is also high, resulting in low product purity and failure to meet the use requirements. In the prior art, Liu Guangliang and others loosely piled the silicon carbide raw materials into a crucible, and used the material transfer characteristics along the axial direction caused by the axial temperature difference inside the crucible to prepare pure silicon carbide ceramics by re-sintering. Dai Peiyun and others used the high temperature at the bottom of the crucible to cause the silicon carbide at the bottom to decompose and produce a large amount of volatile gases, which were deposited on the crucible cover to obtain dense pure silicon carbide ceramics. Liu Guangliang, Liu Bobo and others used silicon nitride as a pore-forming agent to prepare pure directional porous SiC ceramics. Silicon nitride as a pore-forming agent provides a large amount of silicon source, which effectively supplements the excessively high residual carbon content caused by the decomposition of SiC in porous ceramics. However, the purity of silicon carbide powder obtained by these methods is still not ideal. Summary of the invention

[0003] In view of the above prior art, the present invention provides a process for preparing high-purity silicon carbide powder

[0004] The present invention is achieved through the following technical solutions:

[0005] A process for preparing high-purity silicon carbide powder comprises the following steps:

[0006] (1) Preparation of green body: high purity carbon powder and high purity silicon powder are wet mixed in a molar ratio of 1:1.0 to 1.2, and then pressed after drying to form a green body;

[0007] (2) placing two blanks stacked up and down in a graphite crucible of an electromagnetic induction furnace, heating them to 1450°C under vacuum and keeping them warm for 2 hours, then heating them to 1600°C and keeping them warm for 2 hours (to promote liquid-solid reaction), then heating them to 2050-2250°C and keeping them warm for 2 hours (to promote the volatile gas generated by the blank in the bottom high temperature zone to be transmitted axially); cooling them to room temperature to obtain high-purity silicon carbide powder.

[0008] Furthermore, in the step (1), the specific operation of the wet mixing is: placing high-purity carbon powder and high-purity silicon powder in a ball mill made of phenolic resin, using deionized water as the grinding medium, and using grinding balls made of phenolic resin for grinding.

[0009] Furthermore, during the grinding, the water-to-material ratio is 0.8:1, mass ratio; and the grinding time is 2 hours.

[0010] Furthermore, in the step (1), a mold made of phenolic resin is used for pressing.

[0011] Furthermore, during the pressing, the molding pressure is 5t, and the mixed material green body is formed after holding the pressure for 1 minute.

[0012] Furthermore, in the step (1), the size of the blank is φ30 mm×16~80 mm.

[0013] Furthermore, in step (2), the heating rate is 25°C / min.

[0014] The preparation process of high-purity silicon carbide powder of the present invention adopts phenolic resin ball mill, grinding ball and dry pressing mold for wet mixing and dry pressing molding process. Compared with dry mixing or simple rough mixing, wet mixing can effectively promote material dispersion, more easily achieve dispersion and mixing of particles with smaller particle size, effectively increase the contact area of ​​heterogeneous particles, reduce the reaction distance between particles, and be more conducive to high-temperature reaction. The impurities introduced in the ball milling mixing and dry pressing molding process are phenolic resin, and the porous carbon formed by the high-temperature insulation cracking of phenolic resin is conducive to the formation of high-purity silicon carbide. Two blanks are stacked up and down (if there is only one blank, a large amount of graphite exists at the bottom after high-temperature sintering, which is difficult to separate from the upper sample), and the temperature gradient distribution inside the crucible during re-sintering is utilized (the temperature field inside the crucible of the electromagnetic induction furnace is distributed along the axial gradient reduction), and the bottom silicon carbide decomposes to produce a large amount of Si passing through the upper superimposed sample, reducing the residual carbon content of the upper sample; at the same time, the bottom silicon carbide decomposes to produce a large amount of Si2C and SiC2 gas, which also passes through the upper sample and is deposited to generate SiC, increasing the SiC generation amount of the upper sample. The high-purity silicon carbide powder prepared by the process of the present invention has a purity higher than 99.999%, which fully meets the requirements for silicon carbide single crystal growth and the use level requirements for electronic ceramic raw materials.

[0015] Various terms and phrases used herein have the general meanings that are well known to those skilled in the art. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 : Microscopic morphology of high-purity silicon carbide powder of Example 1. DETAILED DESCRIPTION

[0017] The present invention will be further described below in conjunction with the embodiments. However, the scope of the present invention is not limited to the following embodiments. It will be appreciated by those skilled in the art that various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention.

[0018] The instruments, reagents, and materials involved in the following examples, unless otherwise specified, are all conventional instruments, reagents, and materials available in the prior art and can be obtained through regular commercial channels. The experimental methods, detection methods, etc. involved in the following examples, unless otherwise specified, are all conventional experimental methods and detection methods available in the prior art.

[0019] The high-purity carbon powder and high-purity silicon powder used in the present invention are both purchased from the conventional market. The high-purity carbon powder is purchased from Graphite with a purity of 99.9999%; the high-purity silicon powder is purchased from Zhejiang Yamei Nano Technology Co., Ltd. with a purity of 99.9999%.

[0020] Example 1 Preparation process of high-purity silicon carbide powder

[0021] Here are the steps:

[0022] (1) Preparation of green body: High-purity carbon powder and high-purity silicon powder were wet mixed in a molar ratio of 1:1.0, dried at 120°C for 2 h, and then pressed (using a mold made of phenolic resin and a molding pressure of 5 t). After holding the pressure for 1 min, a cylindrical green body was formed. In this embodiment, two types of cylindrical green bodies were prepared, with dimensions of φ30 mm×80 mm and φ30 mm×16 mm, respectively.

[0023] The specific operation of the wet mixing is: placing high-purity carbon powder and high-purity silicon powder in a ball mill made of phenolic resin, using first-class deionized water as the grinding medium (water-to-material ratio is 0.8:1, mass ratio), with a purity greater than 99.9%, using phenolic resin grinding balls for grinding, and the grinding time is 2 hours.

[0024] (2) Two blanks are stacked up and down (the size of the upper blank is φ30mm×80mm, and the size of the lower blank is φ30mm×16mm) and placed in a graphite crucible (φ40mm×100mm) of an electromagnetic induction furnace. The temperature is raised to 1450°C under vacuum and kept at this temperature for 2 hours, then raised to 1600°C and kept at this temperature for 2 hours, and then raised to 2150°C and kept at this temperature for 2 hours, with a heating rate of 25°C / min. The temperature is cooled to room temperature, and the sintered product of the upper blank is taken and crushed to obtain high-purity silicon carbide powder. The specific microscopic morphology is as follows: Figure 1 shown.

[0025] Conventional sintered blanks are placed in a sagger or crucible for direct sintering. The present invention stacks the blanks, with the upper blank being the target product and the lower blank being the sacrificial product. This placement is closely related to the unique temperature field distribution inside the crucible of the electromagnetic induction furnace. According to research, the temperature inside the crucible is distributed in a descending gradient along the axial direction, which causes the temperature inside the sample to be distributed along the axial gradient. After stacking, the bottom sacrificial blank is in the high temperature zone, while the upper blank is at a normal sintering temperature. The bottom sacrificial blank produces a large amount of silicon vapor, SiC2 and Si2C gas that evaporate along the axial direction and inevitably pass through the upper sample. During the crossing process, the silicon vapor will inevitably react with the residual carbon in the upper sample to reduce the amount of residual carbon and further improve the purity; and part of Si2C and SiC2 can also be deposited inside the upper sample to increase the yield of silicon carbide.

[0026] Embodiments 2 to 5

[0027] Compared with Example 1, the sintering temperature is changed, as shown in Table 1. Others are the same as Example 1. The bulk porosity, volume density, ignition loss rate and SiC purity of the high-purity silicon carbide powder prepared in each example are shown in Table 1.

[0028] Generally speaking, the higher the re-sintering temperature, the higher the burn-out rate, resulting in an increase in porosity and a decrease in bulk density. However, the decrease in bulk density during re-sintering in the present invention means that a large amount of volatile gas in the sacrificial body reacts with the sample to produce new SiC grains, resulting in an increase in bulk density and a decrease in burn-out rate.

[0029] Table 1

[0030]

[0031] The above examples are provided to those skilled in the art to fully disclose and describe how to make and use the claimed embodiments, and are not intended to limit the scope of the disclosure herein. Modifications that are obvious to those skilled in the art will fall within the scope of the appended claims.

Claims

1. A process for preparing high-purity silicon carbide powder, characterized in that: The following steps are involved: (1) Preparation of green body: high purity carbon powder and high purity silicon powder are wet mixed in a molar ratio of 1:1.0 to 1.2, and then pressed after drying to form a green body; (2) Place two blanks stacked up and down in a graphite crucible of an electromagnetic induction furnace, heat them up to 1450°C under vacuum and keep them warm for 2 hours, then heat them up to 1600°C and keep them warm for 2 hours, then heat them up to 2050-2250°C and keep them warm for 2 hours; cool them down to room temperature, take out the sintered blank on the top, and crush it to obtain high-purity silicon carbide powder.

2. The process for preparing high-purity silicon carbide powder according to claim 1, characterized in that: In the step (1), the specific operation of the wet mixing is: placing high-purity carbon powder and high-purity silicon powder in a ball mill made of phenolic resin, using deionized water as the grinding medium, and using grinding balls made of phenolic resin for grinding.

3. The process for preparing high-purity silicon carbide powder according to claim 2, characterized in that: During the grinding, the water-to-material ratio is 0.8:1, mass ratio; and the grinding time is 2 hours.

4. The process for preparing high-purity silicon carbide powder according to claim 1, characterized in that: In the step (1), a mold made of phenolic resin is used for pressing.

5. The process for preparing high-purity silicon carbide powder according to claim 4, characterized in that: During the pressing, the molding pressure is 5t, and the mixed material green body is formed after holding the pressure for 1 min.

6. The process for preparing high-purity silicon carbide powder according to claim 1, characterized in that: In the step (1), the blank is a cylindrical blank, and the size of the blank is φ30 mm×16-80 mm.

7. The process for preparing high-purity silicon carbide powder according to claim 6, characterized in that: Of the two blanks in step (2), the size of the upper blank is φ30 mm×80 mm, and the size of the lower blank is φ30 mm×16 mm.

8. The process for preparing high-purity silicon carbide powder according to claim 1, characterized in that: In the step (2), the heating rate is 25°C / min.

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