A method for synthesizing high-purity silicon carbide powder

Abstract

The present invention relates to the technical field of silicon carbide powder manufacturing, and particularly relates to a method for synthesizing high-purity silicon carbide powder, which includes: S1. Paste graphite paper or carbon fiber cloth on the resistance heating material and / or the inner wall of the deposition chamber, and connect the resistance heating material to the electrode; S2. Adjust the pressure in the deposition chamber to a vacuum state or replace it with an argon atmosphere, and heat the temperature to 900 - 1300 °C; S3. Transport methyltrichlorosilane, silicon chloride, hydrogen, argon, and hydrocarbon gas into the deposition chamber in proportion for deposition for 10 - 150 h to obtain a silicon carbide block; S4. Perform crushing treatment and cleaning treatment on the obtained silicon carbide block in sequence to obtain silicon carbide powder; S5. Perform high-temperature treatment on the silicon carbide powder to obtain the silicon carbide powder used for silicon carbide single crystal growth. This method can improve the production efficiency of silicon carbide powder and reduce the production cost; the synthesized silicon carbide powder has a controllable particle size and a high purity.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon carbide powder manufacturing, and particularly to a method for synthesizing high-purity silicon carbide powder materials. Background Art

[0002] Currently, physical vapor transport (PVT) method is usually used to prepare silicon carbide substrates; and the growth source of silicon carbide single crystals is usually silicon carbide powder materials. Therefore, the purity, particle size, etc. of silicon carbide powder materials play a crucial role in the growth of silicon carbide single crystals, and will directly affect the crystal quality of the grown silicon carbide single crystals. At present, the existing silicon carbide powder materials are generally synthesized by self-propagating high-temperature synthesis (SHS) method. The self-propagating high-temperature synthesis method is also called combustion synthesis technology, which is a technology for synthesizing materials by using the self-heating and self-conduction effects of high chemical reaction heat between reactants. Once the reactants are ignited, they will automatically spread to the unreacted area until the reaction is complete; that is, silicon carbide is obtained by uniformly mixing high-purity silicon powder and carbon powder and then heating at high temperature. However, due to the high preparation costs of high-purity graphite powder and silicon powder, the synthesis cost of silicon carbide powder materials remains high; in addition, due to the process limitations of self-propagating high-temperature synthesis, the purity of silicon carbide powder materials may be affected by activators, and it is difficult to synthesize large-particle-size and high-purity silicon carbide powder materials; for example, the patent publication number DE112012002094B4 discloses a method for synthesizing high-purity silicon carbide powder materials by high-temperature synthesis using high-purity carbon powder and silicon powder. The obtained silicon carbide powder materials have a particle size in the range of 0.01 - 2 mm. To prepare high-purity silicon carbide powder materials, the gas-phase reaction method has been further explored, such as using chemical vapor deposition (CVD) method to produce high-quality silicon carbide fine powder, etc., and the components of the obtained silicon carbide fine powder are easy to control; however, when using the chemical vapor deposition method to prepare silicon carbide powder materials, it requires high temperature and complex equipment, with high production costs and low yields, and it is not easy to mass-produce industrially. For example, the patent publication number CN116815318A discloses a technology for preparing silicon carbide powder materials by chemical vapor deposition method. By adjusting or changing the chemical vapor deposition process, the synthesis yield can be improved, but this adjustment or change will reduce the purity of the synthesized silicon carbide powder materials; in addition, since the synthesized silicon carbide block is deposited on graphite, an additional new graphite removal process is required subsequently, increasing the process difficulty. Therefore, there is an urgent need to provide a method for synthesizing silicon carbide powder materials for batch synthesizing large-particle-size and high-purity silicon carbide powder materials.

[0003] The present invention provides a method for synthesizing high-purity silicon carbide powder materials to solve the problem in the prior art that the existing synthesis methods cannot synthesize large-particle-size and high-purity silicon carbide powder materials. Summary of the Invention

[0004] The object of the present invention is to provide a method for synthesizing high-purity silicon carbide powder, so as to solve the problem in the prior art that the existing synthesis methods cannot synthesize large-sized and high-purity silicon carbide powder.

[0005] The technical solution of the present invention is: a method for synthesizing high-purity silicon carbide powder, comprising the following steps:

[0006] S1. Paste graphite paper or carbon fiber cloth on the resistance heating material and / or the inner wall of the deposition chamber. Then, place the resistance heating material in the deposition chamber and connect the resistance heating material to the electrode through a mechanical structure;

[0007] S2. Adjust the pressure in the deposition chamber to a vacuum state or replace the atmosphere in the deposition chamber with an argon atmosphere. Then, heat the temperature in the deposition chamber to 900 - 1300 °C;

[0008] S3. Transport methyltrichlorosilane, silicon tetrachloride, hydrogen, argon, and hydrocarbon gas into the deposition chamber in proportion for deposition, and control the temperature and pressure in the deposition chamber. After depositing for 10 - 150 h, obtain a silicon carbide block; wherein, the transport flow ratio of the methyltrichlorosilane, the silicon tetrachloride, the hydrogen, the argon, and the hydrocarbon gas is 1:(0 - 0.1):(1 - 15):(0 - 1):(0 - 0.1); the feeding rate of the methyltrichlorosilane is 10 - 5000 g / min;

[0009] S4. Perform crushing treatment and cleaning treatment on the obtained silicon carbide block in sequence. After the cleaning is completed, obtain silicon carbide powder;

[0010] S5. Put the obtained silicon carbide powder into the reaction chamber for high-temperature treatment, and regulate the crystal form and carbon-silicon ratio of the silicon carbide powder to obtain the silicon carbide powder used for growing silicon carbide single crystals.

[0011] Preferably, in S3, the hydrocarbon gas is any one or a combination of propylene, ethylene, and butadiene.

[0012] Preferably, in S3, during the deposition process, the pressure in the deposition chamber is 0.9 - 10 atm; the temperature in the deposition chamber is 1000 - 1300 °C.

[0013] Preferably, the purity of the methyltrichlorosilane is greater than 99.99%, and the metal impurity content in the methyltrichlorosilane is less than 1 ppm.

[0014] Preferably, in step S5, for the high-temperature treatment process, the treatment temperature is 1500 - 2300 °C, the treatment duration is 5 - 50 h, and the pressure in the reaction chamber during the treatment process is 0.01 - 1 atm.

[0015] Preferably, the resistive heating material is a single element or compound containing any one of C, W, Mo, and Ta elements; the diameter of the resistive heating material is 0.1-10 mm.

[0016] Preferably, in the step S1, the operation process of pasting the graphite paper or the carbon fiber cloth on the resistive heating material includes the following steps:

[0017] a. Polish the surface of the resistive heating material to make the surface finish of the resistive heating material ≥ 8 levels;

[0018] b. Coat the resistive heating material with an adhesive or a mixture of an adhesive and an organic solvent. Then, cut the graphite paper or the carbon fiber cloth into a suitable size and adhere it to the resistive heating material;

[0019] c. Dry the resistive heating material adhered with the graphite paper or the carbon fiber cloth.

[0020] Preferably, the adhesive is any one or a combination of thermosetting phenolic resin, epoxy resin, polyurethane, polyester resin, acrylic resin, and polyvinyl butyral; the metal impurity content in the adhesive is less than 1 ppm;

[0021] The coating method of coating the resistive heating material with the adhesive or the mixture of the adhesive and the organic solvent is any one of brush coating, electrostatic spraying, ultrasonic spraying, and air spraying.

[0022] Preferably, the drying treatment includes a low-temperature drying stage and a high-temperature drying stage; the drying temperature in the low-temperature drying stage is 30-250 °C, and the drying time is 1-24 h; the drying temperature in the high-temperature drying stage is 200-900 °C, and the drying time is 0.5-5 h, and the high-temperature drying stage is carried out in an inert atmosphere or a vacuum environment.

[0023] Preferably, the thickness of the graphite paper is 0.1-5 mm.

[0024] Compared with the prior art, the advantages of the present invention are:

[0025] (1) A method for synthesizing high-purity silicon carbide powder provided by the present invention uses methyltrichlorosilane as the main raw material for depositing silicon carbide powder, and is deposited under conditions of a relatively large feeding rate and a relatively large pressure. This can not only improve the conversion rate of the methyltrichlorosilane atmosphere and the production efficiency of silicon carbide powder, but also effectively separate the silicon carbide block from the heating element, enabling the heating element to be recycled and reused, thereby effectively reducing production costs. At the same time, the synthesized silicon carbide powder not only has a relatively large particle size, but also the particle size of the silicon carbide powder is adjustable, and it also has a very high purity, solving the problem in the prior art that existing synthesis methods cannot synthesize silicon carbide powder with a large particle size and high purity.

[0026] (2) A method for synthesizing high-purity silicon carbide powder provided by the present invention is deposited based on conditions of a relatively large feeding rate and a relatively large pressure. Compared with traditional synthesis methods based on relatively low air pressure and low feeding flow rate conditions, the relatively large feeding rate and relatively large air pressure can not only fully mix the methyltrichlorosilane atmosphere with hydrogen, improving the conversion rate of the methyltrichlorosilane atmosphere, but also weaken the influence of homogeneous thermal decomposition of the atmosphere in the deposition chamber on the yield of synthesized silicon carbide powder caused by excessive heating sources and slow atmosphere circulation rate, and at the same time weaken the problem of blockage of the gas transmission holes by fine powders formed by homogeneous thermal decomposition of the atmosphere in the deposition chamber.

[0027] (3) A method for synthesizing high-purity silicon carbide powder provided by the present invention adds gases such as chlorosilane and hydrocarbon gases to the atmosphere introduced into the deposition chamber during the deposition process. This can not only regulate the carbon-silicon ratio in the silicon carbide block during the deposition process, but also significantly improve the deposition rate of the silicon carbide powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be further described below in conjunction with the drawings and embodiments:

[0029] Figure 1 is a flow chart of a method for synthesizing high-purity silicon carbide powder according to the present invention;

[0030] Figure 2 is a picture of the silicon carbide powder prepared in Example 3 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The content of the present invention will be further described in detail below in conjunction with specific embodiments:

[0032] In the description of the present invention, it should be noted that methyltrichlorosilane, silicon chloride, hydrogen, argon, hydrocarbon gas, etc. transported into the deposition chamber are all in gaseous state; "4N", "6N", etc. used to represent the purity of atmospheres such as methyltrichlorosilane, silicon chloride, hydrogen, etc., where "N" is "Nine". For example, "4N" is 99.99%, "6N" is 99.9999%, and so on.

[0033] A method for synthesizing high-purity silicon carbide powder, the synthesis method includes multiple synthesis steps as shown in Figure 1 the following. Example 1

[0034] S1. Select a resistance heating rod with a diameter of 8 mm and made of graphite material as the heating element, polish the surface of the resistance heating rod to make the surface finish of the resistance heating rod reach level 8; immediately, brush epoxy resin on the resistance heating rod and the inner wall of the chamber, and cut the graphite paper with a thickness of 1 mm into appropriate sizes and adhere it to the resistance heating rod and the inner wall of the chamber; then, put the resistance heating rod with the adhered graphite paper and the chamber into an oven for drying treatment, and first bake at 200 °C for 30 min, then bake at a high temperature of 900 °C in a vacuum environment for 30 min; finally, set the deposition chamber in the deposition device, set the resistance heating rod with the adhered graphite paper in the deposition chamber, and connect the resistance heating rod to the electrode through a mechanical structure.

[0035] S2. Replace the atmosphere in the deposition chamber with an argon atmosphere, and then heat the temperature in the deposition chamber to 1100 °C.

[0036] S3. Transport methyltrichlorosilane (MTS) and hydrogen into the deposition chamber in proportion for deposition. During the deposition process, control the temperature and pressure in the deposition chamber. After 20 h of deposition, obtain a silicon carbide block; among them, the feeding rate of methyltrichlorosilane is 20 g / min; the transport flow ratio of methyltrichlorosilane to hydrogen is 1:10; the purity of the used methyltrichlorosilane is 4N, and the purity of the used hydrogen is 6N; and during the deposition process, in order to ensure that methyltrichlorosilane can be fully and quickly converted into silicon carbide and deposited on the heating element, the temperature and pressure in the deposition chamber should not have too large fluctuations, and the temperature in the deposition chamber needs to be controlled within the range of 1050 - 1150 °C, and the pressure is controlled at 0.9 - 1 atm.

[0037] S4. Perform crushing treatment and cleaning treatment on the obtained silicon carbide block in sequence. After the cleaning is completed, obtain silicon carbide powder.

[0038] S5. Put the obtained silicon carbide powder into the reaction chamber, adjust the pressure in the reaction chamber to 500 Pa, and at the same time heat the temperature in the reaction chamber to 2200 °C to perform high-temperature treatment on the silicon carbide powder. After 10 hours of treatment, 6 Kg of silicon carbide powder suitable for the growth of silicon carbide single crystals is obtained, and the purity of the silicon carbide powder is 6N, and the particle size is about 5 mm.

[0039] In this embodiment, the thickness of the graphite paper is 1 mm. In other embodiments, the thickness of the graphite paper can be 0.1 - 10 mm.

[0040] In this embodiment, adhering the graphite paper to the resistance heating rod not only helps to effectively peel off the silicon carbide block deposited on the resistance heating rod from the resistance heating rod subsequently, but also facilitates the recycling and reuse of the resistance heating rod. At the same time, since the temperature in the deposition chamber needs to be controlled within the range of 1050 - 1150 °C during the deposition process, it can be inferred that the temperature on the periphery of the heating element in the deposition chamber must be within the range of 1050 - 1150 °C, and the temperature of the inner wall of the deposition chamber may also reach above 900 °C. At this time, on the one hand, the formed silicon carbide will be deposited on the inner wall of the deposition chamber, and on the other hand, the silicon powder, silicon carbide powder, and carbon powder formed in the inner cavity of the chamber will also adhere to the inner wall of the chamber under the action of heat convection; to effectively peel off the silicon carbide block and dust deposited on the inner wall of the deposition chamber subsequently, avoid damage to the inner wall of the deposition chamber and extend the service life of the material of the inner wall of the deposition chamber, graphite paper also needs to be pasted on the inner wall of the deposition chamber. In other embodiments, if the temperature on the inner wall of the deposition chamber is relatively low and no silicon carbide will be deposited, there is no need to paste graphite paper; or, if the heating element is the inner wall of the deposition chamber, only graphite paper needs to be pasted on the inner wall of the chamber.

[0041] In addition, since the graphite paper itself is a flexible porous material, it helps to relieve the thermal stress caused by the difference in the coefficient of thermal expansion between the silicon carbide deposition block and the heating element. If the thermal stress is too large, it will cause the heating element to break during and after the deposition process. If the heating element breaks during the deposition process, the current circuit will disappear, the heating element will not be able to continue heating, and then the deposition process will end prematurely, ultimately affecting the output of silicon carbide powder. At the same time, if the thermal stress is too large, it may also cause the deposition block on the heating element to fall off, damaging the deposition chamber and posing a safety hazard. Therefore, pasting a layer of graphite paper on the heating element also helps to reduce the probability of phenomena such as the breakage of the heating element or the falling off of the deposition block on the heating element during the deposition process, improving the production efficiency of silicon carbide powder to a certain extent and extending the service life of the inner wall material of the deposition chamber. At the same time, through a large number of experimental verifications, it is known that to avoid the graphite paper being too thin and easily torn, unable to fully relieve the thermal stress, or the graphite paper being too thick and affecting the heat transfer effect of the heating element, the thickness of the graphite paper is preferably 0.1 - 5 mm. And using carbon fiber cloth instead of graphite paper can achieve the same effect. The thickness of the carbon fiber cloth is 0.1 - 5 mm. Therefore, carbon fiber cloth can be selected for use in other embodiments.

[0042] In this embodiment, epoxy resin is used to adhere the graphite paper to the inner walls of the resistance heating rod and the deposition chamber. In other embodiments, any one or more of other adhesives such as thermosetting phenolic resin, polyurethane, polyester resin, acrylic resin, polyvinyl butyral, etc. can be selected; a mixture of an adhesive and an organic solvent can also be selected, etc. And in this embodiment, the adhesive is brush-coated on the resistance heating material, while in other embodiments, the coating method of applying the adhesive or the mixture of the adhesive and the organic solvent on the resistance heating material is one of brush coating, electrostatic spraying, ultrasonic spraying, air spraying, etc.

[0043] In this embodiment, in step S2, the atmosphere in the deposition chamber is replaced with an argon atmosphere, and then subsequent processes such as heating and deposition are carried out. The main role of the argon atmosphere during the deposition process is to promote the flow of the atmosphere in the deposition chamber, fully convert methyltrichlorosilane into silicon carbide, and thus increase the deposition rate of silicon carbide. In other embodiments, since the feeding rate of methyltrichlorosilane is relatively large and the flow rate of methyltrichlorosilane is relatively high, after methyltrichlorosilane is transported into the deposition chamber, methyltrichlorosilane can flow in the deposition chamber and come into full contact with hydrogen. Therefore, in step S2, the pressure in the deposition chamber can also be directly adjusted to a vacuum state, or an argon atmosphere can be transported into the deposition chamber while transporting atmospheres such as methyltrichlorosilane and hydrogen into the deposition chamber.

[0044] In this embodiment, since the deposited silicon carbide bulk is a polycrystalline structure and is β-silicon carbide; while the silicon carbide powder used for crystal growth is usually α-silicon carbide; therefore, in order to promote the transformation of the deposited silicon carbide bulk from β-silicon carbide to α-silicon carbide, the deposited silicon carbide bulk needs to be crushed, cleaned and then placed in a reaction chamber for high-temperature treatment process; at the same time, due to the different saturated vapor pressures of carbon, silicon, silicon carbide, etc., during the high-temperature treatment process, the excess silicon element in the silicon carbide powder will sublime and flow out. Therefore, the high-temperature treatment can also adjust the carbon-silicon ratio in the silicon carbide powder, so as to obtain a raw material more suitable for the growth of silicon carbide single crystals. In other embodiments, it is also necessary to perform crushing, cleaning treatment and high-temperature treatment process on the deposited silicon carbide bulk; and during the high-temperature treatment process, the treatment temperature needs to be in the range of 1500-2300 °C, and the treatment duration is controlled within the range of 5-50 h; at the same time, during the high-temperature treatment process, the pressure in the reaction chamber needs to be controlled within the range of 0.01-1 atm. Example 2

[0045] S1. Select a resistance heating wire with a diameter of 1 mm and made of tungsten metal material as the heating element, polish the surface of the resistance heating wire so that the surface finish of the resistance heating wire reaches grade 8; then, brush phenolic resin on the resistance heating wire, cut the graphite paper with a thickness of 2 mm into appropriate sizes and adhere it to the resistance heating wire; then, place the resistance heating wire with the graphite paper adhered on it in an oven for drying treatment, and first bake it at 200 °C for 30 min, and then bake it at a high temperature of 700 °C in a vacuum environment for 30 min; finally, set the resistance heating wire with the graphite paper adhered on it in the deposition chamber, and connect the resistance heating wire to the electrode through a mechanical structure;

[0046] S2. Adjust the pressure in the deposition chamber to a vacuum state, and then heat the temperature in the deposition chamber to 1150 °C;

[0047] S3. Transport methyltrichlorosilane and hydrogen into the deposition chamber in proportion for deposition. After depositing for 100 h, a silicon carbide bulk is obtained; among them, during the deposition process, the feeding rate of methyltrichlorosilane is 200 g / min; the transport flow ratio of methyltrichlorosilane to hydrogen is 1:10; the purity of the used methyltrichlorosilane is 4N, and the purity of the used hydrogen is 6N; and during the deposition process, the temperature and pressure in the deposition chamber should not fluctuate too much, the temperature needs to be controlled within the range of 1100-1200 °C, and the pressure is controlled at 4.5-5 atm.

[0048] S4. Perform crushing treatment and cleaning treatment on the obtained silicon carbide bulk in sequence. After the cleaning is completed, silicon carbide powder is obtained;

[0049] S5. Place the obtained silicon carbide powder into the reaction chamber, adjust the pressure in the reaction chamber to 500 Pa, and at the same time heat the temperature in the reaction chamber to 2200 °C to perform high-temperature treatment on the silicon carbide powder. After 10 h of treatment, 100 Kg of silicon carbide powder suitable for the growth of silicon carbide single crystals is obtained, and the purity of the silicon carbide powder is 6N, and the particle size is about 8 mm.

[0050] In the present invention, the particle size of the synthesized silicon carbide powder is adjustable and is controlled by a crusher during the crushing treatment of the silicon carbide block in step S4; the particle size of the synthesized silicon carbide powder can be adjusted according to actual usage requirements. In the present invention, the particle size of the silicon carbide powder is preferably controlled within the range of 1-20 mm. Example 3

[0051] S1. Select a resistance heating wire with a diameter of 0.5 mm and made of tantalum metal material as the heating element, and polish the surface of the resistance heating wire to make the surface finish of the resistance heating wire reach grade 8; immediately afterwards, brush phenolic resin on the resistance heating wire, and cut a graphite paper with a thickness of 2 mm into a suitable size and adhere it to the resistance heating wire; then, place the resistance heating rod adhered with graphite paper into an oven for drying treatment, and first bake it at 200 °C for 30 min, and then bake it at a high temperature of 800 °C in a vacuum environment for 30 min; finally, set the resistance heating wire adhered with graphite paper in the deposition chamber, and connect the resistance heating wire to the electrode through a mechanical structure;

[0052] S2. Adjust the pressure in the deposition chamber to a vacuum state, and then heat the temperature in the deposition chamber to 1200 °C;

[0053] S3. Feed methyltrichlorosilane and hydrogen into the deposition chamber in proportion for deposition, control the temperature and pressure in the deposition chamber, and after 100 h of deposition, obtain a silicon carbide block; wherein, during the deposition process, the feeding rate of methyltrichlorosilane is 200 g / min; the feeding flow ratio of methyltrichlorosilane to hydrogen is 1:10; the purity of the used methyltrichlorosilane is 4N, and the purity of the used hydrogen is 6N; and during the deposition process, the temperature and pressure in the deposition chamber should not fluctuate too much, and the temperature needs to be controlled within the range of 1100-1200 °C, and the pressure is controlled at 4.5-5 atm.

[0054] S4. Perform crushing treatment and cleaning treatment on the obtained silicon carbide block in sequence. After the cleaning is completed, obtain silicon carbide powder; and, as Figure 2 shown, the prepared silicon carbide powder has a relatively large particle size.

[0055] S5. Put the obtained silicon carbide powder into the reaction chamber, adjust the pressure in the reaction chamber to 200 Pa, and at the same time heat the temperature in the reaction chamber to 2200 °C. Conduct high-temperature treatment on the silicon carbide powder. After 10 hours of treatment, 120 Kg of silicon carbide powder suitable for the growth of silicon carbide single crystals is obtained, and the purity of the silicon carbide powder is 6N. Example 4

[0056] S1. Select a resistance heating wire with a diameter of 0.2 mm and made of molybdenum alloy material as the heating element, and polish the surface of the resistance heating wire to make the surface finish of the resistance heating wire reach grade 8; immediately afterwards, spray phenolic resin on the resistance heating wire by electrostatic spraying method, and cut the graphite paper with a thickness of 2 mm into appropriate sizes and then adhere it to the resistance heating wire; then, put the resistance heating rod adhered with graphite paper into the oven for drying treatment, and first bake it at 200 °C for 30 min, and then bake it at 900 °C under vacuum environment for 30 min; finally, set the resistance heating wire pasted with graphite paper in the deposition chamber, and connect the resistance heating wire to the electrode through a mechanical structure;

[0057] S2. Adjust the pressure in the deposition chamber to a vacuum state, and then heat the temperature in the deposition chamber to 1050 °C;

[0058] S3. Transport methyltrichlorosilane and hydrogen into the deposition chamber in proportion for deposition, control the temperature and pressure in the deposition chamber. After 100 hours of deposition, a silicon carbide block is obtained; among them, during the deposition process, the feeding rate of methyltrichlorosilane is 200 g / min; the transport flow ratio of methyltrichlorosilane to hydrogen is 1:10; the purity of the methyltrichlorosilane used is 4N, and the purity of the hydrogen used is 6N; and during the deposition process, the temperature in the deposition chamber needs to be controlled within the range of 1000 - 1100 °C, and the pressure is controlled at 8 - 8.5 atm.

[0059] S4. Conduct crushing treatment and cleaning treatment on the obtained silicon carbide block in sequence. After the cleaning is completed, silicon carbide powder is obtained;

[0060] S5. Put the obtained silicon carbide powder into the reaction chamber, adjust the pressure in the reaction chamber to 200 Pa, and at the same time heat the temperature in the reaction chamber to 2200 °C. Conduct high-temperature treatment on the silicon carbide powder. After 10 hours of treatment, 120 Kg of silicon carbide powder suitable for the growth of silicon carbide single crystals is obtained, and the purity of the silicon carbide powder is 6N. Example 5

[0061] S1. Select a resistance heating wire with a diameter of 0.2 mm and made of molybdenum alloy material as the heating element, and polish the surface of the resistance heating wire to make the surface finish of the resistance heating wire reach grade 8. Immediately afterwards, spray phenolic resin on the resistance heating wire by electrostatic spraying method, and cut a graphite paper with a thickness of 2 mm into appropriate size and then adhere it to the resistance heating wire. Then, place the resistance heating rod with the adhered graphite paper into an oven for drying treatment, and first bake it at 200 °C for 30 min, and then bake it at a high temperature of 900 °C in a vacuum environment for 30 min. Finally, set the resistance heating wire with the adhered graphite paper in the deposition chamber, and connect the resistance heating wire to the electrode through a mechanical structure.

[0062] S2. Adjust the pressure in the deposition chamber to a vacuum state, and then heat the temperature in the deposition chamber to 1050 °C.

[0063] S3. Feed methyltrichlorosilane, hydrogen and silicon chloride (SiCl 4 ) into the deposition chamber in proportion for deposition. Control the temperature and pressure in the deposition chamber. After depositing for 100 h, a silicon carbide block is obtained. Among them, during the deposition process, the feeding rate of methyltrichlorosilane is 200 g / min; the feeding flow ratio of methyltrichlorosilane, hydrogen and silicon chloride is 1:10:0.1; the purity of the used methyltrichlorosilane is 4N, the purity of the used silicon chloride is 4N, and the purity of the used hydrogen is 6N; and during the deposition process, the temperature in the deposition chamber needs to be controlled within the range of 1000 - 1100 °C, and the pressure is controlled at 8 - 8.5 atm.

[0064] S4. Perform crushing treatment and cleaning treatment on the obtained silicon carbide block in sequence. After the cleaning is completed, silicon carbide powder is obtained.

[0065] S5. Put the obtained silicon carbide powder into the reaction chamber, adjust the pressure in the reaction chamber to 200 Pa, and at the same time heat the temperature in the reaction chamber to 2200 °C to perform high-temperature treatment on the silicon carbide powder. After treating for 10 h, 150 Kg of silicon carbide powder suitable for growing silicon carbide single crystals is obtained, and the purity of the silicon carbide powder is 6N.

[0066] In this embodiment, a silicon chloride atmosphere is added to the atmosphere introduced into the deposition chamber to adjust the carbon-silicon ratio in the silicon carbide block. In other embodiments, the carbon-silicon ratio in the silicon carbide block can also be adjusted by adding hydrocarbon gases or adding hydrocarbon gases and silicon chloride atmosphere simultaneously. Among them, the hydrocarbon gases can be olefin gases, such as one or more of propylene, ethylene, butadiene, etc.; or saturated hydrocarbon gases, such as one or more of methane, ethane, etc. Example 6

[0067] S1. Select a resistance heating wire with a diameter of 0.2 mm and made of molybdenum alloy material as the heating element. Polish the surface of the resistance heating wire to make the surface finish reach grade 8. Immediately afterwards, spray phenolic resin on the resistance heating wire by electrostatic spraying, and cut a graphite paper with a thickness of 2 mm into a suitable size and then adhere it to the resistance heating wire. Then, place the resistance heating rod with the adhered graphite paper in an oven for drying treatment, and first bake it at 200 °C for 30 min, and then bake it at a high temperature of 900 °C in a vacuum environment for 30 min. Finally, set the resistance heating wire with the adhered graphite paper in the deposition chamber, and connect the resistance heating wire to the electrode through a mechanical structure;

[0068] S2. Adjust the pressure in the deposition chamber to a vacuum state, and then heat the temperature in the deposition chamber to 1050 °C;

[0069] S3. Transport methyltrichlorosilane, hydrogen, silicon chloride and ethylene to the deposition chamber in proportion for deposition. Control the temperature and pressure in the deposition chamber. After depositing for 100 h, a silicon carbide block is obtained. Among them, during the deposition process, the feeding rate of methyltrichlorosilane is 1000 g / min; the transport flow ratio of methyltrichlorosilane, hydrogen, silicon chloride and ethylene is 1:6:0.1:0.1; the purity of the used methyltrichlorosilane is 4N, the purity of the used silicon chloride is 4N, the purity of the used hydrogen is 6N; the purity of the used ethylene is 4N; and during the deposition process, the temperature in the deposition chamber needs to be controlled within the range of 1000 - 1100 °C, and the pressure is controlled at 4.5 - 5 atm.

[0070] S4. Perform crushing treatment and cleaning treatment on the obtained silicon carbide block in sequence. After the cleaning is completed, silicon carbide powder is obtained;

[0071] S5. Put the obtained silicon carbide powder into the reaction chamber, adjust the pressure in the reaction chamber to 200 Pa, and at the same time heat the temperature in the reaction chamber to 2200 °C to perform high-temperature treatment on the silicon carbide powder. After treating for 10 h, 700 Kg of silicon carbide powder suitable for growing silicon carbide single crystals is obtained, and the purity of the silicon carbide powder is 6N.

[0072] Comparative Example 1

[0073] S1. Select a resistance heating rod with a diameter of 8 mm and made of graphite material as the heating element. Set the resistance heating rod in the deposition furnace, and connect the resistance heating rod to the electrode through a mechanical structure.

[0074] S2. Replace the atmosphere in the deposition furnace with an argon atmosphere, and then heat the temperature in the deposition furnace to 1200 °C;

[0075] S3. Transport methyltrichlorosilane and hydrogen into the deposition furnace in proportion for deposition. Control the temperature and pressure in the deposition chamber. After 24 hours of deposition, a silicon carbide block is obtained. Among them, during the deposition process, the feeding rate of methyltrichlorosilane is 500 g / h; the transport flow ratio of methyltrichlorosilane to hydrogen is 1:10; the purity of the used methyltrichlorosilane is 98%, and the purity of the used hydrogen is 3N; and during the deposition process, the temperature in the deposition furnace needs to be controlled within the range of 1150 - 1250 °C, and the pressure is controlled at 0.7 - 1 atm.

[0076] S4. Successively perform crushing treatment and cleaning treatment on the obtained silicon carbide block. After the cleaning is completed, 2.4 kg of silicon carbide powder is obtained, and the purity of the silicon carbide powder is 99%.

[0077] Comparing Example 1 with Comparative Example 1 shows that during the deposition process, increasing the feeding rate of methyltrichlorosilane can significantly improve the conversion efficiency of methyltrichlorosilane, that is, increase the deposition rate of silicon carbide powder, and thus increase the yield of silicon carbide powder. And compared with Comparative Example 1, the silicon carbide powder prepared in Example 1 has a higher purity. Comparing Example 1 with Examples 2 - 4 shows that during the deposition process, increasing the pressure in the deposition chamber and simultaneously increasing the feeding rate of methyltrichlorosilane can significantly increase the deposition rate of silicon carbide powder; at the same time, comparing Examples 2, 3 with Example 4 shows that when the feeding rate of methyltrichlorosilane is the same and the deposition time is the same, increasing the temperature in the deposition chamber or increasing the pressure in the deposition chamber both contribute to increasing the deposition rate of silicon carbide powder. Comparing Examples 5, 6 with Example 4 shows that adding a silicon chloride atmosphere and / or an olefin atmosphere to the atmosphere input into the deposition chamber can not only regulate the carbon-silicon ratio in the silicon carbide block during the deposition process, but also significantly increase the deposition rate of silicon carbide powder. In addition, compared with Comparative Example 1, in Examples 1 - 6, the feeding rates of atmospheres such as methyltrichlorosilane are relatively high; a larger feeding rate helps to alleviate the problem that the homogeneous pyrolysis of the atmosphere in the deposition chamber due to too many heating sources and slow atmosphere flow rate affects the yield of silicon carbide powder.

[0078] The above embodiments are only used to illustrate the technical concept and features of the present invention. The purpose is to enable those who are familiar with this technology to understand the content of the present invention and implement it accordingly, and it cannot be used to limit the protection scope of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic features of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to embrace all changes that fall within the meaning and scope of the equivalent elements of the claims in the present invention.

Claims

1. A method for synthesizing high-purity silicon carbide powder, characterized in that: The steps include: S1, pasting graphite paper or carbon fiber cloth on the resistance heating material and / or the inner wall of the deposition chamber, then placing the resistance heating material in the deposition chamber, and connecting the resistance heating material to the electrode through a mechanical structure; the operation process of pasting the graphite paper or the carbon fiber cloth on the resistance heating material includes the following steps: a. polishing the surface of the resistance heating material so that the surface finish of the resistance heating material is ≥ level 8; b. applying an adhesive or a mixture of an adhesive and an organic solvent on the resistance heating material, and then cutting the graphite paper or the carbon fiber cloth into a suitable size and adhering it to the resistance heating material; c. drying the resistance heating material to which the graphite paper or the carbon fiber cloth is adhered; S2, adjusting the pressure in the deposition chamber to a vacuum state or replacing the atmosphere in the deposition chamber with an argon atmosphere, and then heating the temperature in the deposition chamber to 900-1300° C.; S3, delivering methyltrichlorosilane, silicon chloride, hydrogen, argon, and hydrocarbon gas into a deposition chamber for deposition at a delivery flow ratio of 1:(0-0.1):(1-15):(0-1):(0-0.1), and controlling the temperature and pressure in the deposition chamber; After 10-150 hours of deposition, a silicon carbide block is obtained; the feed rate of methyltrichlorosilane is 10-5000 g / min; the pressure in the deposition chamber is 0.9-10 atm; the hydrocarbon gas is any one or more of propylene, ethylene, and butadiene; the temperature in the deposition chamber is 1000-1300° C.; S4, crushing and cleaning the obtained silicon carbide block in sequence, and obtaining silicon carbide powder after cleaning; S5. Put the obtained silicon carbide powder into a reaction chamber for high temperature treatment, adjust the crystal form and carbon-silicon ratio of the silicon carbide powder, and obtain silicon carbide powder used for growing silicon carbide single crystals.

2. The method for synthesizing high-purity silicon carbide powder according to claim 1, characterized in that: The purity of the methyltrichlorosilane is greater than 99.99%, and the content of metal impurities in the methyltrichlorosilane is less than 1 ppm.

3. The method for synthesizing high-purity silicon carbide powder according to claim 1, characterized in that: In step S5, the high temperature treatment process has a treatment temperature of 1500-2300° C., a treatment time of 5-50 hours, and a pressure in the reaction chamber of 0.01-1 atm during the treatment.

4. The method for synthesizing high-purity silicon carbide powder according to claim 1, characterized in that: The resistance heating material is a single substance or a compound containing any one of C, W, Mo, and Ta elements; and the diameter of the resistance heating material is 0.1-10 mm.

5. The method for synthesizing high-purity silicon carbide powder according to claim 1, characterized in that: The adhesive is any one or more combinations of thermosetting phenolic resin, epoxy resin, polyurethane, polyester resin, acrylic resin, and polyvinyl butyral; the content of metal impurities in the adhesive is less than 1ppm; The adhesive or the mixed solution of the adhesive and the organic solvent is coated on the resistance heating material by any one of brushing, electrostatic spraying, ultrasonic spraying and air spraying.

6. The method for synthesizing high-purity silicon carbide powder according to claim 1, characterized in that: The drying process includes a low-temperature drying stage and a high-temperature drying stage; the drying temperature of the low-temperature drying stage is 30-250°C, and the drying time is 1-24h; the drying temperature of the high-temperature drying stage is 200-900°C, and the drying time is 0.5-5h, and the high-temperature drying stage is carried out in an inert atmosphere or a vacuum environment.

7. The method for synthesizing high-purity silicon carbide powder according to claim 1, characterized in that: The graphite paper has a thickness of 0.1-5 mm.

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