Synthesis method of high-purity silicon carbide powder

Abstract

The invention relates to the technical field of silicon carbide powder manufacturing, in particular to a high-purity silicon carbide powder synthesis method which comprises the steps that S1, graphite paper or carbon fiber cloth is pasted to a resistance heating material and / or the inner wall of a deposition chamber, and the resistance heating material is connected to an electrode; s2, the pressure in the deposition chamber is adjusted to a vacuum state or replaced with an argon atmosphere, and the temperature is increased to 900-1300 DEG C; s3, methyl trichlorosilane, silicon chloride, hydrogen, argon and hydrocarbon gas are conveyed into the deposition chamber in proportion for deposition for 10-150 h, and a silicon carbide block is obtained; s4, the obtained silicon carbide blocks are sequentially subjected to crushing treatment and cleaning treatment, and silicon carbide powder is obtained; and S5, carrying out high-temperature treatment on the silicon carbide powder to obtain the silicon carbide powder for silicon carbide single crystal growth. The method can improve the production efficiency of the silicon carbide powder and reduce the production cost; the synthesized silicon carbide powder has controllable particle size and high purity.

Description

Technical Field

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

[0002] At present, the physical vapor transport method (PVT) is usually used to prepare silicon carbide substrates; and the growth source of silicon carbide single crystals is usually silicon carbide powder. Therefore, the purity and particle size of silicon carbide powder play a vital 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 is generally synthesized by self-propagating high-temperature synthesis (SHS). Self-propagating high-temperature synthesis is also called combustion synthesis technology. It is a technology that uses the self-heating and self-conduction effect of high chemical reaction heat between reactants to synthesize materials. 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 heating them at high temperature. However, due to the high preparation cost of high-purity graphite powder and silicon powder, the synthesis cost of silicon carbide powder is also high. In addition, due to the process limitations of self-propagating high-temperature synthesis, the purity of silicon carbide powder may be affected by the activator, making it difficult to synthesize large-particle, high-purity silicon carbide powder. For example, patent publication number DE112012002094B4 discloses a method for high-temperature synthesis of high-purity silicon carbide powder using high-purity carbon powder and silicon powder, and the prepared silicon carbide powder has a particle size in the range of 0.01-2mm. In order to prepare high-purity silicon carbide powder, the gas phase reaction method was further explored, such as the use of chemical vapor deposition (CVD) to produce high-quality silicon carbide micropowder, and the components of the prepared silicon carbide micropowder are easy to control. However, when using chemical vapor deposition to prepare silicon carbide powder, high temperature and complex equipment are required, the production cost is high, and the output is low, which is not easy to mass produce in industry. For example, the patent publication number is CN116815318A, which discloses a technology for preparing silicon carbide powder using chemical vapor deposition. By adjusting or changing the chemical vapor deposition process, the yield of the synthesis can be increased. However, this adjustment or change will reduce the purity of the synthesized silicon carbide powder. In addition, since the synthesized silicon carbide block is deposited on graphite, a new graphite removal process needs to be added later, which increases the difficulty of the process. Therefore, it is urgent to provide a method for synthesizing silicon carbide powder for batch synthesis of large-particle-size, high-purity silicon carbide powder.

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

[0004] The purpose of the present invention is to provide a method for synthesizing high-purity silicon carbide powder to solve the problem that the existing synthesis method in the prior art cannot synthesize large-particle-size, 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: 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; 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, conveying methyltrichlorosilane, silicon chloride, hydrogen, argon, and hydrocarbon gas into a deposition chamber in proportion for deposition, and controlling the temperature and pressure in the deposition chamber; after deposition for 10-150 hours, a silicon carbide block is obtained; wherein the conveying flow ratio of the methyltrichlorosilane, the silicon chloride, the hydrogen, the argon, and the hydrocarbon gas is 1:(0-0.1):(1-15):(0-1):(0-0.1); the feed rate of the methyltrichlorosilane is 10-5000 g / min; 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.

[0006] Preferably, in S3, the hydrocarbon gas is any one or more combinations of propylene, ethylene and butadiene.

[0007] 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.

[0008] Preferably, the purity of the methyltrichlorosilane is greater than 99.99%, and the content of metal impurities in the methyltrichlorosilane is less than 1 ppm.

[0009] Preferably, 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.

[0010] Preferably, the resistance heating material is a single substance or a compound containing any one of the elements C, W, Mo, and Ta; and the diameter of the resistance heating material is 0.1-10 mm.

[0011] Preferably, in S1, the operation process of pasting the graphite paper or the carbon fiber cloth onto the resistance heating material comprises 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.

[0012] Preferably, the adhesive is any one or more combinations of thermosetting phenolic resin, epoxy resin, polyurethane, polyester resin, acrylic resin, 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.

[0013] Preferably, 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.

[0014] Preferably, the graphite paper has a thickness of 0.1-5 mm.

[0015] Compared with the prior art, the advantages of the present invention are: (1) The present invention provides a method for synthesizing high-purity silicon carbide powder. The method uses methyltrichlorosilane as the main raw material for depositing silicon carbide powder, and the deposition is carried out under conditions of a relatively high feed rate and a relatively high pressure. This method can not only increase the conversion rate of methyltrichlorosilane atmosphere and improve the production efficiency of silicon carbide powder, but also achieve effective separation of silicon carbide blocks and heating elements, so that the heating elements can 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 has an adjustable particle size and is also of very high purity. This method solves the problem in the prior art that the existing synthesis method cannot synthesize large-particle-size, high-purity silicon carbide powder.

[0016] (2) The present invention provides a method for synthesizing high-purity silicon carbide powder. The method is based on deposition under conditions of a relatively large feed rate and a relatively large pressure. Compared with the conventional synthesis method based on conditions of a relatively small gas pressure and a low feed flow rate, the relatively large feed rate and the relatively large gas pressure can not only fully mix the methyltrichlorosilane atmosphere with the hydrogen gas, thereby increasing the conversion rate of the methyltrichlorosilane atmosphere, but also can reduce the influence of the homogeneous pyrolysis of the atmosphere in the deposition chamber caused by excessive heating sources and slow atmosphere circulation rate on the yield of the synthesized silicon carbide powder, and at the same time reduce the problem of fine powder formed by the homogeneous pyrolysis of the atmosphere in the deposition chamber blocking the gas transmission holes.

[0017] (3) The present invention provides a method for synthesizing high-purity silicon carbide powder. During the deposition process, chlorosilane and hydrocarbon gases are added to the atmosphere introduced into the deposition chamber. This can not only control the carbon-silicon ratio in the silicon carbide block during the deposition process, but also significantly increase the deposition rate of the silicon carbide powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will be further described below in conjunction with the accompanying drawings and embodiments: Figure 1 This is a flow chart of a method for synthesizing high-purity silicon carbide powder according to the present invention; Figure 2 This is a picture of the silicon carbide powder prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0019] The present invention is further described in detail below in conjunction with specific embodiments: In the description of the present invention, it should be noted that the methyltrichlorosilane, silicon chloride, hydrogen, argon and hydrocarbon gases transported into the deposition chamber are all in gaseous state; "4N", "6N" and the like are used to indicate the purity of the atmospheres such as methyltrichlorosilane, silicon chloride, hydrogen, etc., where "N" stands for "Nine", for example, "4N" is 99.99%, "6N" is 99.9999%, and so on.

[0020] A method for synthesizing high-purity silicon carbide powder, the method comprising: Figure 1 Multiple synthetic steps are shown. Example 1

[0021] S1. Select a resistance heating rod with a diameter of 8 mm and made of graphite material as the heating element, and polish the surface of the resistance heating rod to make the surface smoothness of the resistance heating rod reach level 8; then, 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 to a suitable size and adhere it to the resistance heating rod and the inner wall of the chamber; then, put the resistance heating rod and the chamber adhered with graphite paper into an oven for drying, and first bake it at 200°C for 30 minutes, and then bake it in a vacuum environment and at a high temperature of 900°C for 30 minutes; finally, set the deposition chamber in the deposition device, set the resistance heating rod adhered with graphite paper in the deposition chamber, and connect the resistance heating rod to the electrode through a mechanical structure.

[0022] S2. Replace the atmosphere in the deposition chamber with an argon atmosphere, and then heat the temperature in the deposition chamber to 1100°C.

[0023] S3. Methyltrichlorosilane (MTS) and hydrogen are transported into a deposition chamber in proportion for deposition. During the deposition process, the temperature and pressure in the deposition chamber are controlled. After 20 hours of deposition, a silicon carbide block is obtained. The feed rate of methyltrichlorosilane is 20 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. 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 cannot fluctuate too much. The temperature in the deposition chamber needs to be controlled within the range of 1050-1150°C, and the pressure is controlled within the range of 0.9-1atm.

[0024] S4, crushing and cleaning the obtained silicon carbide block in sequence, and obtaining silicon carbide powder after cleaning.

[0025] S5. Put the obtained silicon carbide powder into a reaction chamber, adjust the pressure in the reaction chamber to 500Pa, and 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 growing silicon carbide single crystals is obtained, and the purity of the silicon carbide powder is 6N and the particle size is about 5 mm.

[0026] In this embodiment, the thickness of the graphite paper is 1 mm. In other embodiments, the thickness of the graphite paper may be 0.1-10 mm.

[0027] In this embodiment, the graphite paper is adhered to the resistance heating rod, which not only helps to realize the effective stripping of the silicon carbide block deposited on the resistance heating rod from the resistance heating rod, 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 in the deposition chamber, the temperature around the heating element 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 cavity inside the chamber will also adhere to the inner wall of the chamber under the action of thermal convection; in order to realize the effective stripping of the silicon carbide block and dust deposited on the inner wall of the deposition chamber from the inner wall of the deposition chamber, avoid the damage of the inner wall of the deposition chamber, and extend the service life of the inner wall material of the deposition chamber, the inner wall of the deposition chamber also needs to be pasted with graphite paper. In other embodiments, if the temperature on the inner wall of the deposition chamber is low and silicon carbide will not be deposited, there is no need to paste graphite paper; or, if the heating element is the inner wall of the deposition chamber, it is only necessary to paste graphite paper on the inner wall of the chamber.

[0028] In addition, since graphite paper itself is a flexible porous material, it helps to alleviate the thermal stress caused by the difference in thermal expansion coefficients between the silicon carbide deposition block and the heating element; if the thermal stress is too large, the heating element will break during the deposition process and after the deposition is completed; if the heating element breaks during the deposition process, the current circuit will disappear, and the heating element will not be able to continue to generate heat, which will cause the deposition process to end prematurely, and ultimately affect the production of silicon carbide powder; at the same time, excessive thermal stress may also cause the deposition block deposited on the heating element to fall off, causing damage to the deposition chamber and posing a safety hazard; therefore, sticking a layer of graphite paper on the heating element can also help reduce the probability of the heating element breaking or the deposition block on the heating element falling off during the deposition process, thereby 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, a large number of experiments have shown that in order to avoid the graphite paper being too thin and easy to tear, 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 0.1-5mm; and the use of carbon fiber cloth instead of graphite paper can achieve the same effect; the thickness of the carbon fiber cloth is 0.1-5mm; therefore, carbon fiber cloth can be selected for use in other embodiments.

[0029] In this embodiment, epoxy resin is used to adhere graphite paper to the resistance heating rod and the inner wall of 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 adhesive and organic solvent can also be selected. In addition, in this embodiment, the adhesive is brushed on the resistance heating material, while in other embodiments, the adhesive or the mixture of adhesive and organic solvent is applied to the resistance heating material by brushing, electrostatic spraying, ultrasonic spraying, air spraying, etc.

[0030] 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 performed; the role of the argon atmosphere in the deposition process is mainly to promote the flow of the atmosphere in the deposition chamber, so that methyltrichlorosilane is fully converted into silicon carbide, thereby increasing the deposition rate of silicon carbide. In other embodiments, since the feed rate of methyltrichlorosilane is relatively large, the flow rate of methyltrichlorosilane is relatively high. After methyltrichlorosilane is transported into the deposition chamber, methyltrichlorosilane can flow in the deposition chamber and fully contact with hydrogen; therefore, in step S2, the pressure in the deposition chamber can also be directly adjusted to a vacuum state, or, while transporting methyltrichlorosilane, hydrogen and other atmospheres into the deposition chamber, an argon atmosphere can be transported into the deposition chamber.

[0031] In this embodiment, since the silicon carbide block obtained by deposition is a polycrystalline structure and is β-silicon carbide; and the silicon carbide powder used for crystal growth is usually α-silicon carbide; therefore, in order to promote the conversion of the deposited silicon carbide block from β-silicon carbide to α-silicon carbide, the deposited silicon carbide block needs to be crushed, cleaned and placed in the 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 sublimate and flow out, so the high-temperature treatment can also adjust the carbon-silicon ratio in the silicon carbide powder, thereby obtaining a raw material more suitable for the growth of silicon carbide single crystals. In other embodiments, the deposited silicon carbide block also needs to be crushed, cleaned and high-temperature treated; and during the high-temperature treatment process, the treatment temperature needs to be in the range of 1500-2300℃, and the treatment time is controlled in the range of 5-50h; at the same time, during the high-temperature treatment process, the pressure in the reaction chamber needs to be controlled in the range of 0.01-1atm. Example 2

[0032] S1. Select a resistance heating wire with a diameter of 1 mm and made of tungsten 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 level 8; then, 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, put the resistance heating wire with the graphite paper in an oven for drying, and first bake it at 200°C for 30 minutes, and then bake it in a vacuum environment and at a high temperature of 700°C for 30 minutes; finally, set the resistance heating wire with the graphite paper in a deposition chamber, and connect the resistance heating wire to the electrode through a mechanical structure; S2, adjusting the pressure in the deposition chamber to a vacuum state, and then heating the temperature in the deposition chamber to 1150° C.; S3. Methyltrichlorosilane and hydrogen are transported into a deposition chamber in proportion for deposition, and the temperature and pressure in the deposition chamber are controlled. After 100 hours of deposition, a silicon carbide block is obtained; wherein, during the deposition process, the feed 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 and pressure in the deposition chamber cannot fluctuate too much, the temperature needs to be controlled within the range of 1100-1200°C, and the pressure is controlled within 4.5-5atm.

[0033] 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, adjust the pressure in the reaction chamber to 500Pa, and 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, 100 kg of silicon carbide powder suitable for growing silicon carbide single crystals is obtained, and the purity of the silicon carbide powder is 6N and the particle size is about 8 mm.

[0034] In the present invention, the particle size of the synthesized silicon carbide powder is adjustable and is controlled by a crusher when the silicon carbide block is crushed 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 to 20 mm. Example 3

[0035] S1. A resistance heating wire with a diameter of 0.5 mm and made of tantalum metal material is selected as the heating element, and the surface of the resistance heating wire is polished to make the surface finish of the resistance heating wire reach level 8; then, phenolic resin is brushed on the resistance heating wire, and graphite paper with a thickness of 2 mm is cut into a suitable size and adhered to the resistance heating wire; then, the resistance heating rod adhered with graphite paper is placed in an oven for drying, and first baked at 200°C for 30 minutes, and then baked in a vacuum environment and a high temperature of 800°C for 30 minutes; finally, the resistance heating wire with graphite paper is set in a deposition chamber, and the resistance heating wire is connected to the electrode through a mechanical structure; S2, adjusting the pressure in the deposition chamber to a vacuum state, and then heating the temperature in the deposition chamber to 1200° C.; S3. Methyltrichlorosilane and hydrogen are transported into a deposition chamber in proportion for deposition, and the temperature and pressure in the deposition chamber are controlled. After 100 hours of deposition, a silicon carbide block is obtained; wherein, during the deposition process, the feed 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 and pressure in the deposition chamber cannot fluctuate too much, the temperature needs to be controlled within the range of 1100-1200°C, and the pressure is controlled within 4.5-5atm.

[0036] S4, crushing and cleaning the obtained silicon carbide block in sequence, and obtaining silicon carbide powder after cleaning; and Figure 2 As shown, the prepared silicon carbide powder has a larger particle size.

[0037] S5. Put the obtained silicon carbide powder into a reaction chamber, adjust the pressure in the reaction chamber to 200Pa, and heat the temperature in the reaction chamber to 2200°C. Perform high-temperature treatment on the silicon carbide powder. After 10 hours of treatment, 120 kg of silicon carbide powder suitable for growing silicon carbide single crystals is obtained, and the purity of the silicon carbide powder is 6N. Example 4

[0038] S1. A resistance heating wire with a diameter of 0.2 mm and made of molybdenum alloy material is selected as the heating element, and the surface of the resistance heating wire is polished to make the surface finish of the resistance heating wire reach level 8; then, phenolic resin is sprayed on the resistance heating wire by electrostatic spraying, and graphite paper with a thickness of 2 mm is cut into a suitable size and adhered to the resistance heating wire; then, the resistance heating rod adhered with graphite paper is placed in an oven for drying, and first baked at 200°C for 30 minutes, and then baked in a vacuum environment and a high temperature of 900°C for 30 minutes; finally, the resistance heating wire with graphite paper is set in a deposition chamber, and the resistance heating wire is connected to the electrode through a mechanical structure; S2, adjusting the pressure in the deposition chamber to a vacuum state, and then heating the temperature in the deposition chamber to 1050° C.; S3. Methyltrichlorosilane and hydrogen are transported into a deposition chamber in proportion for deposition, and the temperature and pressure in the deposition chamber are controlled. After 100 hours of deposition, a silicon carbide block is obtained; wherein, during the deposition process, the feed 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 within the range of 8-8.5 atm.

[0039] 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, adjust the pressure in the reaction chamber to 200Pa, and heat the temperature in the reaction chamber to 2200°C. Perform high-temperature treatment on the silicon carbide powder. After 10 hours of treatment, 120 kg of silicon carbide powder suitable for growing silicon carbide single crystals is obtained, and the purity of the silicon carbide powder is 6N. Example 5

[0040] S1. A resistance heating wire with a diameter of 0.2 mm and made of molybdenum alloy material is selected as the heating element, and the surface of the resistance heating wire is polished to make the surface finish of the resistance heating wire reach level 8; then, phenolic resin is sprayed on the resistance heating wire by electrostatic spraying, and graphite paper with a thickness of 2 mm is cut into a suitable size and adhered to the resistance heating wire; then, the resistance heating rod adhered with graphite paper is placed in an oven for drying, and first baked at 200°C for 30 minutes, and then baked in a vacuum environment and a high temperature of 900°C for 30 minutes; finally, the resistance heating wire with graphite paper is set in a deposition chamber, and the resistance heating wire is connected to the electrode through a mechanical structure; S2, adjusting the pressure in the deposition chamber to a vacuum state, and then heating the temperature in the deposition chamber to 1050° C.; S3. Methyltrichlorosilane, hydrogen and silicon chloride (SiCl4) are transported into a deposition chamber in proportion for deposition, and the temperature and pressure in the deposition chamber are controlled. After 100 hours of deposition, a silicon carbide block is obtained; wherein, during the deposition process, the feed rate of methyltrichlorosilane is 200 g / min; the transport flow ratio of methyltrichlorosilane, hydrogen and silicon chloride is 1:10:0.1; the purity of the methyltrichlorosilane used is 4N, the purity of the silicon chloride 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 within the range of 8-8.5 atm.

[0041] 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, adjust the pressure in the reaction chamber to 200Pa, and heat the temperature in the reaction chamber to 2200°C. Perform high-temperature treatment on the silicon carbide powder. After 10 hours of treatment, 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.

[0042] 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 gas or adding hydrocarbon gas and silicon chloride atmosphere at the same time; wherein the hydrocarbon gas can be an olefin gas, such as one or more of propylene, ethylene, butadiene, etc.; or it can be a saturated hydrocarbon gas, such as one or more of methane, ethane, etc. Example 6

[0043] S1. A resistance heating wire with a diameter of 0.2 mm and made of molybdenum alloy material is selected as the heating element, and the surface of the resistance heating wire is polished to make the surface finish of the resistance heating wire reach level 8; then, phenolic resin is sprayed on the resistance heating wire by electrostatic spraying, and graphite paper with a thickness of 2 mm is cut into a suitable size and adhered to the resistance heating wire; then, the resistance heating rod adhered with graphite paper is placed in an oven for drying, and first baked at 200°C for 30 minutes, and then baked in a vacuum environment and a high temperature of 900°C for 30 minutes; finally, the resistance heating wire with graphite paper is set in a deposition chamber, and the resistance heating wire is connected to the electrode through a mechanical structure; S2, adjusting the pressure in the deposition chamber to a vacuum state, and then heating the temperature in the deposition chamber to 1050° C.; S3. Methyltrichlorosilane, hydrogen, silicon chloride and ethylene are transported into a deposition chamber in proportion for deposition, and the temperature and pressure in the deposition chamber are controlled. After 100 hours of deposition, a silicon carbide block is obtained; wherein, during the deposition process, the feed 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 methyltrichlorosilane used is 4N, the purity of the silicon chloride used is 4N, the purity of the hydrogen used is 6N; the purity of the ethylene used 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 within 4.5-5atm.

[0044] 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, adjust the pressure in the reaction chamber to 200Pa, and heat the temperature in the reaction chamber to 2200°C. Perform high-temperature treatment on the silicon carbide powder. After 10 hours of treatment, 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.

[0045] Comparative Example 1 S1. A resistance heating rod with a diameter of 8 mm and made of graphite material is selected as a heating element, the resistance heating rod is arranged in a deposition furnace, and the resistance heating rod is connected to an electrode through a mechanical structure.

[0046] S2, replacing the atmosphere in the deposition furnace with an argon atmosphere, and then heating the temperature in the deposition furnace to 1200° C.; S3. Methyltrichlorosilane and hydrogen are transported to a deposition furnace in proportion for deposition, and the temperature and pressure in the deposition chamber are controlled. After 24 hours of deposition, a silicon carbide block is obtained; wherein, during the deposition process, the feed rate of methyltrichlorosilane is 500 g / h; the transport flow ratio of methyltrichlorosilane to hydrogen is 1:10; the purity of the methyltrichlorosilane used is 98%, and the purity of the hydrogen used 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 within the range of 0.7-1atm.

[0047] S4. The obtained silicon carbide block is crushed and cleaned in sequence. After cleaning, 2.4 kg of silicon carbide powder is obtained, and the purity of the silicon carbide powder is 99%.

[0048] Comparing Example 1 with Comparative Example 1, it can be seen that during the deposition process, increasing the feed rate of methyltrichlorosilane can significantly improve the conversion efficiency of methyltrichlorosilane, that is, increase the deposition rate of silicon carbide powder, and then increase the output 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, it can be seen that during the deposition process, increasing the pressure in the deposition chamber and increasing the feed rate of methyltrichlorosilane can significantly increase the deposition rate of silicon carbide powder; at the same time, comparing Example 2, Example 3 with Example 4, it can be seen that when the feed 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 can help to increase the deposition rate of silicon carbide powder. Comparing Example 5 and Example 6 with Example 4, it can be seen that adding silicon chloride atmosphere and / or 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 improve the deposition rate of silicon carbide powder. In addition, compared with Comparative Example 1, in Examples 1-6, the feed rates of atmospheres such as methyltrichlorosilane are all higher; a larger feed rate helps to alleviate the problem of homogeneous pyrolysis of the atmosphere in the deposition chamber affecting the yield of silicon carbide powder due to excessive heating sources and slow atmosphere circulation rate.

[0049] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the scope of protection 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 the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is limited by the attached claims rather than the above description, and it is intended to include all changes 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, It is 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; 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, conveying methyltrichlorosilane, silicon chloride, hydrogen, argon, and hydrocarbon gas into a deposition chamber in proportion for deposition, and controlling the temperature and pressure in the deposition chamber; after deposition for 10-150 hours, a silicon carbide block is obtained; wherein the conveying flow ratio of the methyltrichlorosilane, the silicon chloride, the hydrogen, the argon, and the hydrocarbon gas is 1:(0-0.1):(1-15):(0-1):(0-0.1); the feed rate of the methyltrichlorosilane is 10-5000 g / min; 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. A method for synthesizing high-purity silicon carbide powder according to claim 1, Features: In S3, the hydrocarbon gas is any one or more combinations of propylene, ethylene, and butadiene.

3. A method for synthesizing high-purity silicon carbide powder according to claim 1, Features: 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.

4. A method for synthesizing high-purity silicon carbide powder according to claim 3, Features: The purity of the methyltrichlorosilane is greater than 99.99%, and the content of metal impurities in the methyltrichlorosilane is less than 1 ppm.

5. A method for synthesizing high-purity silicon carbide powder according to claim 3, Features: 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.

6. A method for synthesizing high-purity silicon carbide powder according to claim 3, Features: 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.

7. A method for synthesizing high-purity silicon carbide powder according to claim 3, Features: In S1, 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.

8. A method for synthesizing high-purity silicon carbide powder according to claim 7, Features: 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.

9. A method for synthesizing high-purity silicon carbide powder according to claim 7, Features: 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.

10. A method for synthesizing high-purity silicon carbide powder according to claim 7, Features: The graphite paper has a thickness of 0.1-5 mm.

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