A silicon carbide powder synthesis crucible and a silicon carbide powder synthesis method

Abstract

The application discloses a synthesis crucible for silicon carbide powder and a synthesis method of silicon carbide powder. High-purity graphite powder and high-purity silicon powder are mixed uniformly according to a proportion, and then are laid on the bottom of the crucible. The high-purity graphite powder is laid in a containing cavity surrounded by a supporting cylinder, a ventilation cylinder and an annular support, and an upper cover of the crucible is covered. The crucible is placed in a furnace body, vacuumized, heated, and repeatedly pumped and filled with a protective gas for cleaning. Then, the temperature is raised, and the temperature is kept for 30-50 hours. During the period, the protective gas is introduced, the temperature in the furnace is kept at 2000-2600 DEG C, and the pressure is kept at 50-800 mbar. The silicon carbide powder is synthesized. By placing extra graphite powder on the upper part of the crucible, the Si atmosphere escaped from the powder during the synthesis process preferentially reacts with the graphite powder placed outside the ventilation cylinder to generate extra silicon carbide powder, so that the utilization efficiency of the raw material is improved, and the cost of the raw material is reduced. In addition, since the Si atmosphere escaped preferentially reacts with the graphite powder placed outside the ventilation cylinder, the possibility of corrosion of the crucible and the heat insulation felt is reduced, and the service life of the crucible and the heat insulation felt can be significantly improved.

Description

Technical Field

[0001] This invention relates to the synthesis of silicon carbide powder, specifically a silicon carbide powder synthesis crucible and a method for synthesizing silicon carbide powder. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Silicon carbide (SiC), as a typical representative of third-generation wide-bandgap semiconductor materials, possesses excellent properties such as wide bandgap, high electron saturation drift velocity, high critical breakdown voltage, high thermal conductivity, and high temperature resistance. Based on these characteristics, silicon carbide has irreplaceable advantages in electronic applications such as high temperature, high pressure, high frequency, high power, optoelectronics, radiation resistance, and microwave, as well as in extreme environments such as aerospace, military, and nuclear energy.

[0004] Currently, the high-temperature self-propagating method is the mainstream method for synthesizing silicon carbide powder. The specific process is as follows: High-purity graphite powder and high-purity silicon powder are mixed evenly and placed in a crucible, then heated under an inert gas atmosphere. When the temperature rises to the melting point of Si, C begins to dissolve in the Si liquid, increasing the ignition contact area and thus increasing the diffusion rate. When the temperature reaches the ignition temperature, Si and C undergo an exothermic reaction instantaneously, igniting the surrounding reactants layer by layer, causing more Si to melt, C to continue dissolving, and the reaction to continue, thereby synthesizing silicon carbide powder.

[0005] During the synthesis of silicon carbide powder, as the temperature rises, Si in the mixed powder begins to escape in gaseous form, which will cause the following effects: (1) Crucible corrosion and crystallization: The escaping Si atmosphere will severely corrode the crucible cover and the crucible body. At high temperatures, the Si atmosphere reacts with the crucible material to form atmospheric crystals. These crystals not only adhere to the inner wall of the upper part of the crucible and the cover, but also cause the crucible cover and the crucible body to stick together, making it impossible to open normally. Long-term corrosion and crystallization will cause cracks in the upper part of the crucible cover and the crucible body, which will seriously affect the sealing performance and mechanical strength of the crucible, and ultimately significantly reduce the service life of the crucible. (2) Corrosion and damage of insulation felt: The Si atmosphere escaping from the outside of the crucible will also corrode the insulation felt. This corrosion will cause structural damage to the insulation felt, thereby reducing its insulation performance and service life. Damage to the insulation felt will increase energy loss, reduce process efficiency, and increase the cost of equipment maintenance and replacement. (3) Imbalance in silicon-carbon ratio leads to a decrease in the purity of silicon carbide powder: The escape of Si atmosphere will disrupt the balance of silicon-carbon ratio in the reaction system, reduce the amount of Si in the actual reaction, and leave residual carbon in the prepared silicon carbide product, which will reduce the purity of the final silicon carbide powder and make it difficult to meet the requirements.

[0006] Chinese patent CN109336114B discloses a method for improving the synthesis efficiency of high-purity silicon carbide powder. The specific steps include pretreatment, introducing a mixed gas for a high-temperature self-propagating reaction, and cooling to room temperature under mixed gas protection. The method is characterized by the effective suppression of powder carbonization caused by carbon-silicon ratio imbalance during synthesis through the introduction of high-purity silane, thereby improving the quality and synthesis efficiency of the silicon carbide powder. However, the introduction of high-purity silane results in excessive Si atmosphere inside the crucible, exacerbating corrosion of the crucible's inner wall and significantly reducing its service life.

[0007] Chinese patent CN115520871A discloses a method for synthesizing high-purity silicon carbide powder, the main steps of which are: (1) Batching: High-purity silicon powder and graphite powder are mixed in a specific molar ratio. (2) Mixing: Mixing is carried out using a three-dimensional motion mixer for 1-24 hours. (3) Crucible pretreatment: The graphite crucible is heated to 1873-2400℃ and argon gas is introduced. (4) Synthesis: The process is carried out in four stages, including vacuuming, heating, heat preservation and cooling. (5) Post-treatment: Ball milling, cleaning and sieving. However, the embedded connection between the crucible lid and the crucible body may not be completely sealed. Under high temperature conditions, the Si atmosphere escaping from the powder will crystallize with the crucible lid and the crucible body, and the Si atmosphere escaping from the outside of the crucible will corrode the insulation felt, affecting the life of the crucible and the insulation felt.

[0008] The patents disclosed above all use the high-temperature self-propagating method to synthesize silicon carbide powder. During the high-temperature synthesis process, Si atmosphere will escape, which will cause severe corrosion of the crucible and insulation felt, affecting the service life and sealing performance of the overall structure, increasing the cost of maintenance and replacement, and also disrupting the silicon-carbon ratio balance in the reaction system, resulting in a decrease in the purity of the synthesized silicon carbide. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide a silicon carbide powder synthesis crucible and a method for synthesizing silicon carbide powder. By using this crucible and synthesis method, high-purity silicon carbide powder can be obtained, and the problem of crucible corrosion by Si atmosphere in existing technologies is effectively solved, greatly improving the service life of the crucible and insulation.

[0010] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0011] In a first aspect, the present invention provides a silicon carbide powder synthesis crucible, comprising a crucible body, a crucible top cover, a venting cylinder, a supporting cylinder, and a graphite sheet, wherein...

[0012] The crucible lid is used to cover the crucible body;

[0013] The upper part of the inner wall of the crucible body is provided with a stepped structure;

[0014] The ventilation cylinder is mounted on the stepped structure via an annular support, and the diameter of the ventilation cylinder is smaller than the diameter of the crucible body.

[0015] The outer diameter of the supporting cylinder is smaller than the inner diameter of the crucible body. The supporting cylinder is installed on the annular support of the venting cylinder, and the height of the supporting cylinder is higher than the height of the venting cylinder. The supporting cylinder, the venting cylinder, and the annular support together form a chamber for holding graphite powder.

[0016] The graphite sheet is placed on top of the support cylinder, between the support cylinder and the crucible lid.

[0017] Because graphite powder has a large specific surface area, carbon atoms can come into more full contact with silicon atoms. Placing graphite powder between the ventilation cylinder and the support cylinder allows the Si atmosphere escaping from the mixed powder to react preferentially with the graphite powder, thus slowing down the corrosion of the graphite sheet or crucible cover by the Si component.

[0018] In some embodiments, the crucible cover and the crucible body are made of isostatic graphite and are connected by threads or screws.

[0019] In some embodiments, the graphite sheet is made of isostatically pressed graphite. The presence of the graphite sheet not only further blocks the Si atmosphere that has not reacted with the graphite powder, but also effectively prevents the Si atmosphere from reacting with the connection between the crucible cover and the crucible body, thereby reducing corrosion of the crucible and extending its lifespan.

[0020] In some embodiments, the supporting cylinder, the venting cylinder, and the annular support are made of tantalum carbide or have tantalum-plated surfaces. This can significantly reduce the reaction between the support cylinder and the Si atmosphere, extending the lifespan of the components.

[0021] In some embodiments, the height of the supporting cylinder is 40-60mm and the thickness is 10-15mm.

[0022] Preferably, the supporting cylinder is 5-15 mm higher than the venting cylinder. This allows the graphite powder to react with the escaping Si atmosphere.

[0023] In some embodiments, the diameter of the crucible body is 350-400 mm and the wall thickness is 15-30 mm.

[0024] Secondly, the present invention provides a method for synthesizing silicon carbide powder, comprising the following steps:

[0025] The synthesis was carried out using the aforementioned silicon carbide powder synthesis crucible;

[0026] High-purity graphite powder and high-purity silicon powder are mixed in a certain proportion and then spread at the bottom of the crucible.

[0027] High-purity graphite powder is laid in the container chamber formed between the supporting cylinder, the venting cylinder and the annular support, and the crucible lid is then closed.

[0028] Place the crucible into the furnace body, evacuate it, heat it to 800-1000℃, introduce protective gas, and then repeatedly evacuate and purge it.

[0029] Continue heating to 2000-2600℃ and holding for 30-50 hours, during which protective gas is introduced to maintain the furnace pressure at 50-800 mbar, thus synthesizing silicon carbide powder.

[0030] The purpose of repeated filling and cleaning is to thoroughly remove nitrogen from the inside of the crucible.

[0031] In some embodiments, the atomic molar ratio of high-purity graphite powder to high-purity silicon powder is 1:1.05-1.30. Since Si in the mixed powder begins to escape in gaseous form as the temperature increases, the molar ratio of Si to C in the gaseous component inside the crucible is greater than 1 to ensure sufficient Si to react with C at high temperatures. Furthermore, the graphite powder and silicon powder are of high purity (5N, ≥99.999%), which improves the purity of the synthesized silicon carbide powder.

[0032] In some embodiments, after synthesis, the temperature is lowered to room temperature, a protective gas is introduced, and the pressure inside the furnace is increased to 800-1000 mbar.

[0033] In some embodiments, the crucible is placed in the furnace body, and the vacuuming time is 8-10 hours, with a vacuum value of 5×10⁻⁶. -5 ~10 -6 mbar.

[0034] In some embodiments, the method of repeated purging and cleaning is as follows: a protective gas is introduced to bring the furnace pressure to 200-500 mbar and maintain it for 0.5-1 hour, followed by evacuation to a vacuum level below 5 × 10⁻⁶ mbar. -5 mbar, maintain for 1-2 hours, repeat this process 3-5 times.

[0035] In some embodiments, high-purity graphite powder is laid in the holding chamber formed between the supporting cylinder, the venting cylinder, and the annular support. The mass of the laid high-purity graphite powder is 5%-30% of the high-purity graphite powder in the bottom carbon-silicon mixed powder. This ensures that the graphite powder here reacts fully with the Si atmosphere escaping from the bottom of the crucible, improving the utilization rate of raw materials.

[0036] Preferably, high-purity graphite powder is laid in the holding chamber formed between the supporting cylinder, the venting cylinder and the annular support, and the molar ratio of the laid high-purity graphite powder to the excess high-purity silicon powder in the bottom carbon-silicon mixed powder (high-purity silicon powder with a silicon-carbon ratio greater than 1 in the mixed powder) is 0.8-1:1.

[0037] In some embodiments, the protective gas is Ar, H2, He, or a mixture of Ar / H2 and He / H2; when a mixture is used, the volume percentage of H2 is less than 20%.

[0038] In some embodiments, the crucible, insulation felt, etc., are pretreated before first use. The pretreatment temperature is 2200-2600℃, the pretreatment chamber pressure is 1-30 mbar, and the pretreatment time is 20-40 h. This removes adsorbed nitrogen and impurity elements from the surface, thereby improving the purity of the silicon carbide powder.

[0039] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows:

[0040] 1. The assembly structure of the venting cylinder, supporting cylinder, and graphite sheet of the present invention reduces the corrosion of the crucible's inner wall by the Si atmosphere, significantly extending the crucible's service life. Furthermore, this structure reduces the escape of Si atmosphere into the insulation felt, thereby reducing corrosion of the insulation felt and increasing its service life. The extended lifespan of the crucible and insulation felt directly reduces production costs.

[0041] 2. In the process of silicon carbide synthesis, this invention adds a slightly excessive amount of silicon to enrich the raw materials with silicon. The crucible of this invention effectively reduces the escape of Si atmosphere, maintains the balance of silicon and carbon ratio in the raw materials, which is conducive to obtaining silicon carbide powder with higher purity and is more suitable for growing high-quality SiC single crystals. The silicon remaining at the end of the reaction can be sublimated from the silicon carbide to the top of the crucible by heating, and reacts with the graphite powder above it to ensure that the synthesized SiC powder does not contain silicon, carbon and other phases, effectively improving the quality and product consistency of silicon carbide.

[0042] 3. In this invention, by placing additional graphite powder on the upper part of the crucible, the large specific surface area and high activity of graphite powder are fully utilized. During the synthesis process, the Si atmosphere escaping from the powder reacts preferentially with the graphite powder placed on the outside of the ventilation cylinder to generate additional silicon carbide powder, which can produce 5% to 30% more SiC powder, improving the utilization efficiency of raw materials and reducing raw material costs. The reaction between the graphite powder and the excess Si atmosphere in the crucible reduces the amount of Si component leaking into the insulation layer through the crucible, reducing the corrosion of the crucible and its insulation layer by the Si component and extending the life of the crucible. Since the insulation performance is not affected, energy consumption is also saved to a certain extent.

[0043] 4. The crucible of the present invention has a simple structure, is convenient for material handling, and is easy to operate and maintain, making it suitable for mass production of silicon carbide powder. Attached Figure Description

[0044] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0045] Figure 1 This is a schematic diagram of the crucible structure in an embodiment of the present invention;

[0046] Figure 2 This is a cross-sectional view of the assembly of the supporting cylinder, the venting cylinder, and the graphite sheet in an embodiment of the present invention;

[0047] Figure 3 This is a cross-sectional view of the crucible body in an embodiment of the present invention;

[0048] Figure 4 The Raman spectrum of the silicon carbide powder synthesized in the embodiments of the present invention is shown below.

[0049] In the diagram, 1-graphite powder; 2-crucible lid; 3-graphite sheet; 4-support cylinder; 5-ventilation cylinder; 6-crucible body; 7-mixed powder. Detailed Implementation

[0050] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0051] The present invention will be further described below with reference to the embodiments.

[0052] Example 1

[0053] like Figure 1 As shown, the crucible consists of a crucible cover 2, a graphite sheet 3, a supporting cylinder 4, a venting cylinder 5, and a crucible body 6. The crucible cover is used to cover the crucible body.

[0054] The upper part of the inner wall of the crucible body 6 is provided with a stepped structure;

[0055] The ventilation cylinder 5 is mounted on the stepped structure by an annular support, and the outer diameter of the ventilation cylinder 5 is smaller than the inner diameter of the crucible body 6.

[0056] The outer diameter of the supporting cylinder 4 is smaller than the inner diameter of the crucible body 6. The supporting cylinder 4 is installed on the annular support of the venting cylinder 5. The height of the supporting cylinder 4 is higher than the height of the venting cylinder 5. The supporting cylinder 4 and the venting cylinder 5 form a chamber for holding graphite powder.

[0057] The graphite sheet 3 is placed on top of the support cylinder 4, between the support cylinder 4 and the crucible cover 2.

[0058] Mixed powder 7 is placed at the bottom of the crucible body 6, while graphite powder 1 is placed on the outside of the venting cylinder. In addition, the crucible cover 2 is connected to the crucible body 6 by threads, screws, etc., and the venting cylinder is directly snapped onto the stepped structure of the crucible body by an annular support.

[0059] like Figure 2 As shown, graphite sheet 3, support cylinder 4 and ventilation cylinder 5 are assembled. The inner diameter of ventilation cylinder 5 is 60-80mm and the height is 30-50mm, while the height of support cylinder 4 is 40-60mm and the thickness is 10-15mm. Graphite powder 1 is placed in the space between ventilation cylinder 5 and support cylinder 4, which can react with Si atmosphere.

[0060] like Figure 3 As shown, the diameter of the crucible body 6 is 350-400mm, the wall thickness is 15-30mm, and there is a stepped structure on the upper part with a step width of 10-15mm, which facilitates the placement of the ventilation cylinder 5, and the height of the stepped structure is no more than 1 / 4 of the total height of the crucible.

[0061] When using it for the first time, the crucible and the insulation felt structure are placed in the synthesis furnace for high-temperature pretreatment. The heating temperature is 2200-2600℃, the pressure in the pretreatment chamber is 1-30mbar, and the holding time is 20-40h.

[0062] The crucible cover 2 and the crucible body 6 are made of isostatic graphite, and the two are connected by threads or screws.

[0063] The supporting cylinder 4, the ventilation cylinder 5, and the annular support are made of tantalum carbide or have tantalum plating on their surface.

[0064] Example 2

[0065] The method for synthesizing silicon carbide powder includes the following steps:

[0066] (1) Mix high-purity graphite powder and high-purity silicon powder evenly in a molar ratio of 1:1.05 and place them at the bottom of the graphite crucible. Then, spread high-purity graphite powder on the outside of the ventilation cylinder, with a mass of 5% of the high-purity graphite powder in the bottom mixed powder.

[0067] (2) Place the assembled graphite crucible into the synthesis furnace and perform vacuum treatment for 8 hours to reduce the vacuum value inside the furnace to below 5 × 10⁻⁶. -5 mbar.

[0068] (3) Heat the inside of the crucible to 800℃, maintain the pressure inside the furnace at 200mbar for 0.5h, and then evacuate to a vacuum below 5×10⁻⁶ mbar. -5 mbar, maintain for 1 hour, repeat this process 3 times to remove nitrogen from inside the crucible.

[0069] (4) After the pumping and cleaning process is completed, the temperature is raised to 2200℃ and kept for 50 hours. Protective gas is introduced to maintain the pressure inside the furnace at 50mbar.

[0070] (5) After the synthesis is completed, the temperature is slowly lowered to room temperature, and protective gas is continuously introduced to raise the pressure inside the furnace to 1000 mbar, so as to obtain the required high-purity silicon carbide powder.

[0071] Tests were conducted using powder X-ray diffraction and Raman spectroscopy, such as... Figure 4 As shown, the powder contains only SiC and no impurities such as Si or C. Since no corrosion was observed in the crucible and insulation felt, their estimated service life is twice that of ordinary crucibles.

[0072] Example 3

[0073] The method for synthesizing silicon carbide powder includes the following steps:

[0074] (1) Mix high-purity graphite powder and high-purity silicon powder evenly in a molar ratio of 1:1.15 and place them at the bottom of the crucible. The mass of high-purity graphite powder spread on the outside of the ventilation cylinder is 15% of the high-purity graphite powder in the bottom mixed powder.

[0075] (2) Place the assembled graphite crucible into the synthesis furnace and evacuate it for 8 hours to ensure that the vacuum value inside the furnace is below 5 × 10⁻⁶. -5 mbar.

[0076] (3) Heat the inside of the crucible to 900℃, maintain the pressure inside the furnace at 300mbar for 0.5h, and then evacuate to a vacuum below 5×10⁻⁶ mbar. -5 mbar, maintain for 1.5h, repeat this process 4 times to remove nitrogen from inside the crucible.

[0077] (4) After the pumping and cleaning process is completed, the temperature is raised to 2400℃ and kept for 40 hours. Protective gas is introduced to maintain the pressure inside the furnace at 300mbar.

[0078] (5) After the synthesis is completed, the temperature is slowly lowered to room temperature, and protective gas is continuously introduced to raise the pressure inside the furnace to 1000 mbar, so as to obtain the required high-purity silicon carbide powder.

[0079] Testing using powder X-ray diffraction and Raman spectroscopy revealed that the powder contained only SiC and no impurities such as Si or C. The estimated service life of the crucible and insulation felt can reach 2.5 times that of ordinary crucibles.

[0080] Example 4

[0081] The method for synthesizing silicon carbide powder includes the following steps:

[0082] (1) Mix high-purity graphite powder and high-purity silicon powder evenly in a molar ratio of 1:1.3 and place them at the bottom of the crucible. The mass of high-purity graphite powder spread on the outside of the ventilation cylinder is 30% of the high-purity graphite powder in the bottom mixed powder.

[0083] (2) Place the assembled graphite crucible into the synthesis furnace and perform vacuum treatment for 9 hours to ensure that the vacuum value inside the furnace is below 5 × 10⁻⁶. -6 mbar.

[0084] (3) Heat the inside of the crucible to 1000℃, maintain the pressure inside the furnace at 500mbar for 0.5h, and then evacuate to a vacuum below 5×10⁻⁶ mbar. -5 mbar, maintain for 1.5h, repeat this process 5 times to remove nitrogen from inside the crucible.

[0085] (4) After the pumping and cleaning process is completed, the temperature is raised to 2600℃ and kept for 30 hours. Protective gas is introduced to maintain the pressure inside the furnace at 800mbar.

[0086] (5) After the synthesis is completed, the temperature is slowly reduced to room temperature, and protective gas is continuously introduced to raise the pressure in the furnace to 900 mbar, so as to obtain high-purity silicon carbide powder.

[0087] Testing using powder X-ray diffraction and Raman spectroscopy revealed that the powder contained only SiC and no impurities such as Si or C. The estimated service life of the crucible and insulation felt can reach 2.5 times that of ordinary crucibles.

[0088] Comparative Example 1

[0089] Compared with Example 2, the crucible structure of Comparative Example 1 is different. In Comparative Example 1, there is no venting cylinder and no additional high-purity graphite powder is placed on the top of the crucible.

[0090] The synthesized SiC powder was tested and characterized. The results of powder X-ray diffraction and Raman spectroscopy both revealed characteristic peaks of carbon, indicating that there are still C impurities in the powder and the powder purity is low.

[0091] Meanwhile, severe corrosion was found on the upper part of the crucible, with obvious corrosion pits of Si component visible on the crucible wall, and SiC powder residue was also found in the insulation felt. This indicates that during the powder synthesis process of Comparative Example 1, excess Si component corroded the crucible and leaked into the insulation, leading to a certain degree of carbonization of the powder and reducing the amount of usable powder; the lifespan of the crucible and insulation was also affected.

[0092] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A silicon carbide powder synthesis crucible, characterized in that: It includes the crucible body, crucible lid, venting cylinder, support cylinder, and graphite sheet, among which, The crucible lid is used to cover the crucible body; The upper part of the inner wall of the crucible body is provided with a stepped structure; The ventilation cylinder is mounted on the stepped structure via an annular support, and the diameter of the ventilation cylinder is smaller than the diameter of the crucible body. The outer diameter of the supporting cylinder is smaller than the inner diameter of the crucible body. The supporting cylinder is installed on the annular support of the venting cylinder, and the height of the supporting cylinder is higher than the height of the venting cylinder. The supporting cylinder, the venting cylinder, and the annular support together form a chamber for holding graphite powder. The graphite sheet is placed on top of the support cylinder, between the support cylinder and the crucible lid.

2. The silicon carbide powder synthesis crucible according to claim 1, characterized in that: The crucible lid and the crucible body are made of isostatic graphite, and the two are connected by threads or screws.

3. The silicon carbide powder synthesis crucible according to claim 1, characterized in that: The graphite sheet is made of isostatically pressed graphite.

4. The silicon carbide powder synthesis crucible according to claim 1, characterized in that: The supporting cylinder, ventilation cylinder, and annular support are made of tantalum carbide or have tantalum plating on their surface.

5. The silicon carbide powder synthesis crucible according to claim 1, characterized in that: The height of the supporting cylinder is 40-60mm and the thickness is 10-15mm.

6. The silicon carbide powder synthesis crucible according to claim 1, characterized in that: The supporting cylinder is 5-15mm higher than the venting cylinder.

7. The silicon carbide powder synthesis crucible according to claim 1, characterized in that: The diameter of the crucible body is 350-400mm, and the wall thickness is 15-30mm.

8. A method for synthesizing silicon carbide powder, characterized in that: Includes the following steps: The synthesis was carried out using the silicon carbide powder synthesis crucible described in any one of claims 1-7; High-purity graphite powder and high-purity silicon powder are mixed in a certain proportion and then spread at the bottom of the crucible. High-purity graphite powder is laid in the container chamber formed between the supporting cylinder, the venting cylinder and the annular support, and the crucible lid is then closed. Place the crucible into the furnace body, evacuate it, heat it to 800-1000℃, introduce protective gas, and then repeatedly evacuate and purge it. Then, the temperature is raised to 2000-2600℃ and held for 30-50 hours. During this period, a protective gas is introduced to maintain the pressure inside the furnace at 50-800 mbar, thereby synthesizing silicon carbide powder.

9. The method for synthesizing silicon carbide powder according to claim 8, characterized in that: The atomic molar ratio of high-purity graphite powder to high-purity silicon powder is 1:1.05-1.

3.

10. The method for synthesizing silicon carbide powder according to claim 8, characterized in that: After synthesis, cool to room temperature, introduce protective gas, and increase the furnace pressure to 800-1000 mbar.

11. The method for synthesizing silicon carbide powder according to claim 8, characterized in that: The method of repeated purging and cleaning is as follows: A protective gas is introduced to bring the furnace pressure to 200-500 mbar, and this pressure is maintained for 0.5-1 hour. Then, a vacuum is drawn down to below 5 × 10⁻⁶ mbar. - 5 mbar, maintain for 1-2 hours, repeat this process 3-5 times.

12. The method for synthesizing silicon carbide powder according to claim 8, characterized in that: The mass of high-purity graphite powder laid in the holding chamber formed between the supporting cylinder, the venting cylinder and the annular support is 5%-30% of the high-purity graphite powder in the bottom carbon-silicon mixed powder.

13. The method for synthesizing silicon carbide powder according to claim 8, characterized in that: High-purity graphite powder is laid in the holding chamber formed between the supporting cylinder, the venting cylinder and the annular support. The molar ratio of the laid high-purity graphite powder to the excess high-purity silicon powder in the bottom carbon-silicon mixed powder is 0.8-1:

1.

14. The method for synthesizing silicon carbide powder according to claim 8, characterized in that: The protective gas is Ar, H2, He, or a mixture of Ar / H2 and He / H2; when a mixture is used, the volume percentage of H2 is less than 20%.

15. The method for synthesizing silicon carbide powder according to claim 8, characterized in that: When the crucible and insulation felt structure are used for the first time, they are pretreated at a temperature of 2200-2600℃, a pressure of 1-30 mbar in the pretreatment chamber, and a time of 20-40 h.

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