Alpha phase silicon carbide powder and method of making same, induction furnace for silicon carbide powder growth

Abstract

The application relates to the technical field of crystal growth, discloses alpha-phase silicon carbide powder and a preparation method thereof, and an induction furnace for growing silicon carbide powder, the preparation method of the alpha-phase silicon carbide powder comprises the following steps: mixing carbon powder, silicon powder, carbon nanotubes and alpha-phase silicon carbide seeds to obtain a raw material mixture; performing first calcination on the raw material mixture to obtain a beta-phase silicon carbide intermediate; and performing second calcination on the beta-phase silicon carbide intermediate in an induction furnace to obtain alpha-phase silicon carbide powder. The preparation method of the alpha-phase silicon carbide powder has high raw material utilization rate, and the alpha-phase silicon carbide powder prepared by the method has high purity.

Description

Technical Field

[0001] This application relates to the field of crystal growth technology, specifically to α-phase silicon carbide powder and its preparation method, and an induction furnace for growing silicon carbide powder. Background Technology

[0002] Silicon carbide, as a core material for third-generation semiconductors, possesses irreplaceable advantages in high-temperature, high-frequency, and high-power devices. Alpha-phase silicon carbide powder, with its well-organized crystal lattice, can be used as a raw material to directionally grow high-purity, low-defect silicon carbide single crystals. Currently, alpha-phase silicon carbide powder mainly includes the carbothermal reduction method and the crushing and classification method using high-purity silicon carbide single crystals as raw materials. While the carbothermal reduction method allows for mass production, the product has low activity. To improve reaction efficiency, external catalysts are often introduced, which easily leads to excessive impurities in the final powder, making subsequent purification difficult and failing to meet the demands of high-end applications. On the other hand, while crushing high-purity silicon carbide single crystals can yield high-purity powder, the low raw material utilization rate and limited single-furnace output result in high production costs. Furthermore, uneven temperature and flow field distribution within the furnace during single crystal growth can easily lead to recrystallization blockage of gaseous components, further limiting capacity expansion. Therefore, developing a new method for preparing alpha-phase silicon carbide powder has become an urgent problem for the industry.

[0003] Application content

[0004] This application aims to at least partially solve one of the technical problems in the related art. To this end, one objective of this application is to provide an α-phase silicon carbide powder and its preparation method, as well as an induction furnace for the growth of silicon carbide powder. The preparation method of the α-phase silicon carbide powder of this application has a high raw material utilization rate, and the α-phase silicon carbide powder prepared by this application has a high purity.

[0005] The first aspect of this application discloses a method for preparing α-phase silicon carbide powder, comprising: Carbon powder, silicon powder, carbon nanotubes and α-phase silicon carbide seed crystals are mixed to obtain a raw material mixture; The raw material mixture was subjected to a first calcination to obtain a β-phase silicon carbide intermediate. The β-phase silicon carbide intermediate was placed in an induction furnace for a second calcination to obtain α-phase silicon carbide powder.

[0006] The preparation method of this application uses high-purity silicon powder and carbon powder as raw materials. At the same time, it adopts a composite catalytic system of α-phase silicon carbide seed crystals and carbon nanotubes to guide the carbothermic reduction reaction to generate highly active β-phase silicon carbide intermediate products. Finally, the β-phase silicon carbide intermediate products are placed in an induction furnace for calcination to achieve the directional transformation and efficient sublimation of β-phase silicon carbide to α-phase silicon carbide. By deeply integrating the carbothermic reduction process with the high-temperature gas phase transport and purification mechanism of the PVT method, the efficient conversion and in-situ purification of raw materials are realized simultaneously in the same furnace, thereby improving the utilization rate of raw materials and the purity of products simultaneously.

[0007] In some embodiments of this application, the method for preparing α-phase silicon carbide powder satisfies at least one of the following conditions: The molar ratio of the silicon powder to the carbon powder is 1:(1.05~1.1). Based on the total mass of the silicon powder and the carbon powder, the mass percentage of the carbon nanotubes is 0.1% to 0.2%. Based on the total mass of the silicon powder and the carbon powder, the mass percentage of the α-phase silicon carbide seed crystals is 0.4%~0.7%; The particle size of the α-phase silicon carbide seed crystals is 50nm~100nm; The purity of the α-phase silicon carbide seed crystal is ≥6N; The diameter of the carbon nanotubes is 10 nm to 20 nm; The purity of the carbon nanotubes is ≥99.99%; The purity of the carbon powder is ≥5N; The purity of the silicon powder is ≥6N; The particle size of the carbon powder is 200nm~500nm; The particle size of the silicon powder is 500nm~800nm.

[0008] In some embodiments of this application, the first calcination includes at least two calcinations with increasing temperature gradients.

[0009] In some embodiments of this application, the first calcination includes a primary calcination and a secondary calcination, and satisfies at least one of the following conditions: The temperature for the first calcination is 800℃~900℃; The calcination time is 1 to 2 hours. The heating rate for a single calcination is 5℃ / min to 7℃ / min; The temperature for the second calcination is 1400℃~1450℃; The second calcination time is 1.5h~2h; The heating rate for the second calcination is 3℃ / min to 5℃ / min.

[0010] In some embodiments of this application, the induction furnace during the second calcination satisfies at least one of the following conditions: The temperature at the bottom of the induction furnace is 2400~2500℃; The temperature in the middle of the induction furnace is 2300~2400℃; The temperature at the bottom of the induction furnace is 2000~2100℃; The second calcination time is 7h~9h.

[0011] In a second aspect, this application provides an α-phase silicon carbide powder obtained by the aforementioned preparation method. Consequently, this α-phase silicon carbide powder exhibits high purity.

[0012] A third aspect of this application discloses an induction furnace for the growth of silicon carbide powder, comprising: The furnace body includes a heat preservation device and a heating device, wherein the heat preservation device is disposed inside the heating device; A crucible includes a crucible body and a graphite element disposed inside the crucible body, and there is a gap between the graphite element and the sidewall of the crucible body; The graphite component comprises a hollow cylinder with at least one recess on its outer and / or inner surfaces. This allows the induction furnace to form a dual-filling zone (inner + outer) (meaning the raw material can be placed in the gap between the graphite component and the crucible body sidewall, or within the hollow structure of the graphite component). This dual-filling zone, combined with the distribution of the annular material layer, helps ensure that all powder material can uniformly contact the high-temperature gas flow in the induction furnace, while simultaneously ensuring contact between the powder material and the graphite heat-conducting surface, thus guaranteeing sufficient sublimation. Furthermore, the presence of at least one recess on the outer and / or inner surfaces of the cylinder significantly increases the contact area between the powder material and the graphite heat-conducting surface. Compared to a conventional cylindrical side surface, the contact area can be increased by 60%, resulting in more thorough contact between the powder material (inner + outer filling) and the high-temperature gas flow and the graphite heat-conducting surface, further ensuring sufficient sublimation and preventing unreacted powder residue in certain areas.

[0013] In some embodiments of this application, the graphite part is further provided with a plurality of pores, and one end of the pore is located on the inner surface of the recess, and the other end of the pore is located on the top surface of the cylinder.

[0014] In some embodiments of this application, the pores include spiral pores.

[0015] In some embodiments of this application, an induction furnace can be used to implement the aforementioned method for preparing α-phase silicon carbide powder. Attached Figure Description

[0016] Figure 1This is a schematic diagram of the structure of a graphite component in an induction furnace according to an embodiment of this application. Detailed Implementation

[0017] The embodiments of this application are described in detail below. The embodiments described below are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0018] This application is based on the applicant's following findings and insights: In view of the drawbacks of the aforementioned methods for preparing α-phase silicon carbide powder, the inventors considered deeply integrating the high-temperature gas-phase transport and purification mechanisms of the carbothermal reduction method and the PVT method to prepare α-phase silicon carbide powder, simultaneously achieving efficient conversion and in-situ purification of raw materials in the same furnace; at the same time, non-external catalysts are used to improve reaction efficiency. Thus, the drawbacks of the two methods mentioned above are solved simultaneously, while retaining the advantages of both preparation methods.

[0019] The first aspect of this application discloses a method for preparing α-phase silicon carbide powder, comprising: S10: Mix carbon powder, silicon powder, carbon nanotubes and α-phase silicon carbide seed crystals to obtain a raw material mixture.

[0020] In this step, the mixing operation is not limited, as long as the raw materials are mixed evenly. For example, carbon powder, silicon powder, carbon nanotubes, and α-phase silicon carbide seeds are placed in a mixer, with deionized water as the grinding medium (the mass ratio of deionized water to raw materials is 0.8:1). First, the mixture is stirred at 400 r / min for 40 min using a twin-helix mixer, and then dispersed in an ultrasonic dispersion device with a frequency of 25 kHz and a power of 800 W for 30 min to obtain the raw material mixture.

[0021] In some embodiments, the molar ratio of silicon powder to carbon powder is 1:(1.05~1.1), specifically, it can be 1:1.05, 1:1.06, 1:1.07, 1:1.08, 1:1.09, 1:1.1, etc. The slight excess of carbon powder relative to the mass of silicon powder can compensate for the loss of carbon through volatilization in subsequent reactions, preventing silicon powder residue from reducing reaction efficiency and product purity.

[0022] In some embodiments, based on the total mass of the silicon powder and the carbon powder, the mass percentage of the carbon nanotubes is 0.1% to 0.2%, specifically, it can be 0.1%, 0.15%, 0.2%, etc. The mass percentage of the α-phase silicon carbide seed crystals is 0.4% to 0.7%, specifically, it can be 0.4%, 0.5%, 0.6%, 0.7%, etc. The mass percentages of carbon nanotubes and α-phase silicon carbide seed crystals within the above ranges can basically ensure the efficient and smooth progress of the reaction.

[0023] Specifically, the doped α-phase silicon carbide seed crystals can serve as heterogeneous nucleation cores, reducing the nucleation barrier for Si-C bond formation. Through lattice-matching effects, they can guide subsequent reactions in a directional manner, thereby significantly improving reaction efficiency. Carbon nanotubes replace traditional exogenous impurity catalysts, relying on their high specific surface area to adsorb and disperse raw material particles. This enhances solid-phase contact and high-temperature electron transfer, preventing particle aggregation and further contributing to improved reaction efficiency. In this application, the synergistic effect of the α-phase silicon carbide seed crystals and carbon nanotubes reduces the activation energy of subsequent reactions by more than 25%, greatly improving reaction efficiency.

[0024] In some embodiments, step S10 can be performed in a protective atmosphere of high-purity argon, and the inert atmosphere can suppress the oxidation of raw materials (such as silicon oxidation Si+O2→SiO2, carbon oxidation C+O2→CO / CO2, etc.).

[0025] In some embodiments, the particle size of the α-phase silicon carbide seed crystals is 50 nm to 100 nm, specifically, it can be 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, or any combination thereof. α-phase silicon carbide seed crystals with particle sizes within the above range can provide sufficient heterogeneous nucleation sites, thereby improving reaction efficiency.

[0026] In some embodiments, the purity of the α-phase silicon carbide seed crystal is ≥6N. For example, the purity of the α-phase silicon carbide seed crystal can be 6N, 7N, etc. The purity of the α-phase silicon carbide seed crystal within the above range can essentially ensure that exogenous impurities are not introduced into the reaction system, thereby ensuring the high purity of the final silicon carbide product and thus ensuring the stable performance of the final silicon carbide product.

[0027] In some embodiments, the diameter of the carbon nanotubes is 10 nm to 20 nm, specifically, it can be 10 nm, 12 nm, 14 nm, 16 nm, 18 nm, 20 nm, or any two of these ranges. Carbon nanotubes with diameters within the above range have extremely high specific surface areas, allowing for more thorough adsorption and dispersion of silicon powder and carbon powder particles, strengthening the solid-phase contact between raw materials, and improving the mass and heat transfer efficiency of the reaction.

[0028] In some embodiments, the purity of the carbon nanotubes is ≥99.99%, specifically, it can be 99.99%, 99.999%, 99.9999%, etc. This helps to ensure the purity of the final product.

[0029] In some embodiments, the purity of the carbon powder is ≥5N, specifically, it can be 5N, 6N, etc. The purity of the silicon powder is ≥6N, specifically, it can be 6N, 7N, etc. This helps to further improve the reaction efficiency and can further improve the purity of the silicon carbide product.

[0030] In some embodiments, the particle size of the toner is 200 nm to 500 nm, specifically, it can be 200 nm, 300 nm, 400 nm, 500 nm, etc. The particle size of the silicon powder is 500 nm to 800 nm, specifically, it can be 300 nm, 400 nm, 500 nm, etc. The particle size of the raw materials within the above range can basically ensure a large specific surface area for both the toner and silicon powder, providing a structural basis for the subsequent reaction between the silicon powder and toner.

[0031] In some embodiments, the carbon powder and silicon powder can be pretreated before mixing. For example, the carbon powder and silicon powder can be sequentially fed into a high-frequency magnetic separator to remove magnetic impurities such as iron and nickel, and then subjected to plasma purification equipment to remove trace amounts of gaseous impurities such as oxygen and nitrogen, thus obtaining refined raw materials. Because there may be a trace oxide layer (SiO2) on the surface of silicon powder, it may undergo a chemical reaction with carbon powder in the subsequent reaction: SiO2 + 2C → Si + 2CO↑.

[0032] In some embodiments, carbon powder and silicon powder with larger particle sizes can also be used. The carbon powder and silicon powder with the target particle size in this application can be obtained by refining them with a pulverizer and then mixed.

[0033] S20: The raw material mixture is subjected to a first calcination to obtain a β-phase silicon carbide intermediate.

[0034] In this step, carbon powder and silicon powder are first used to generate a β-phase silicon carbide intermediate, which has lower energy and is more kinetically formed. The temperature range for generating the β-phase silicon carbide intermediate is 1400℃~1450℃. Therefore, the ultimate goal of this step is to generate the β-phase silicon carbide intermediate from the raw materials within this temperature range before proceeding with subsequent reactions. However, before generating the β-phase silicon carbide, the raw materials can be calcined at a lower temperature to remove volatile impurities from the reaction system. That is, the first calcination here includes at least two calcinations with increasing temperature gradients, with the final calcination temperature being 1400℃~1450℃.

[0035] In some embodiments, exemplary, the first calcination includes a primary calcination and a secondary calcination. The calcination equipment here can be a tube furnace or a tunnel kiln. The primary calcination is carried out at a heating rate of 5°C / min to 7°C / min, raising the temperature from room temperature to 800°C to 900°C for 1 to 2 hours. The secondary calcination is carried out at a heating rate of 3°C / min to 5°C / min, raising the temperature to 1400°C to 1450°C for 1.5 to 2 hours. During the calcination stage at 1400°C to 1450°C, an argon-oxygen mixture (oxygen volume percentage of 0.05% to 0.1%) is introduced into the furnace. After the first calcination is completed, the product is cooled to room temperature at a rate of 8°C / min to 12°C / min to obtain a β-phase silicon carbide intermediate.

[0036] The first calcination mentioned above can gradually remove volatile impurities in the system and, to some extent, prevent material splashing caused by sudden boiling of moisture in the raw material mixture. Setting the final temperature of the first calcination to 1400℃~1450℃ can achieve full combination of silicon powder and carbon powder, generating a highly active β-phase silicon carbide intermediate (chemical formula can be represented as Si+C→β-SiC). At the same time, precise control of oxygen concentration during the reaction helps to achieve complete removal of carbon nanotubes while avoiding excessive oxygen oxidation of the β-phase silicon carbide intermediate.

[0037] In this step, the carbon nanotube oxidation removal rate can reach 100%, there is no solid catalyst residue in the system, and the gradient heating makes the reaction exothermic uniform, which can basically avoid the crystal agglomeration caused by local overheating, which affects the performance of the product, etc., and the first calcination cycle is shortened by about 35% compared with the carbothermic reduction process in related technologies.

[0038] S30: The β-phase silicon carbide intermediate is placed in an induction furnace for a second calcination to obtain α-phase silicon carbide powder.

[0039] In this step, the β-phase silicon carbide intermediate is placed in a vacuum induction furnace (vacuum degree ≤ 5 × 10⁻⁶). -6 The second calcination is carried out in a radial gradient temperature field (formed by an induction furnace), and high-purity argon gas (≥99.9995%) is introduced into the induction furnace 3 to 5 times before the second calcination. Specifically, ensuring the high vacuum level of the induction furnace and using high-purity argon gas for cleaning ensures and thoroughly removes oxidizing impurities inside the furnace. The radial gradient temperature field enables the gradual sublimation of the β-phase silicon carbide intermediate, which is transformed into α-phase silicon carbide powder under the guidance of α-phase silicon carbide seed crystals.

[0040] In some embodiments, the temperature of the bottom of the induction furnace is 2400℃~2500℃ (specifically, it can be 2400℃, 2450℃, 2500℃, etc.), the temperature of the middle part of the induction furnace is 2300℃~2400℃ (specifically, it can be 2300℃, 2350℃, 2400℃, etc.), and the temperature of the bottom of the induction furnace is 2000℃~2100℃ (specifically, it can be 2000℃, 2050℃, 2100℃, etc.).

[0041] Specifically, during the second calcination, the temperature at the bottom of the radial gradient temperature field is increased from room temperature to 2400℃~2500℃ at a rate of 2℃ / min~5℃ / min. Argon gas is continuously introduced during calcination (flow rate of 6~9 L / min), and when the temperature reaches about 2300℃, high-purity hydrogen gas with a volume ratio of 1%~2% is introduced. The hydrogen gas can reduce the residual oxides in the system (e.g., the reduction of silicon dioxide SiO2+2H2→Si+2H2O↑, with H2O being discharged in gaseous state).

[0042] In some embodiments, the α-phase silicon carbide powder obtained after the second calcination can be post-processed. Specifically, the α-phase silicon carbide powder can be placed in an ultrasonic sieving device to screen out products with a particle size of 50 μm to 80 μm, thereby obtaining α-phase silicon carbide powder with uniform particle size that meets the requirements for high-end crystal growth. Simultaneously, the residual tailings in the induction furnace can be collected, mixed with new raw materials, and reused in S10.

[0043] In a second aspect, this application provides an α-phase silicon carbide powder obtained by the aforementioned preparation method. Consequently, this α-phase silicon carbide powder exhibits high purity.

[0044] The method for preparing α-phase silicon carbide powder and the resulting α-phase silicon carbide powder of this application have at least the following beneficial effects: 1. Improved Reaction Efficiency: Alpha-phase silicon carbide seed crystals reduce the nucleation barrier between silicon powder and carbon powder by more than 25% through lattice matching effects. Simultaneously, carbon nanotubes play a dual crucial role: firstly, their aspect ratio and high specific surface area allow for tight adsorption and aggregation of silicon and carbon powder particles, enhancing solid-phase contact efficiency and preventing incomplete reactions caused by particle dispersion; secondly, their excellent high-temperature conductivity forms electron channels between particles, accelerating electron transfer between silicon and carbon atoms and lowering the electron transfer energy barrier. The synergistic effect of these two factors shortens the carbothermal reduction (S20 in this application) cycle from 5-6 hours in traditional processes to approximately 3.5 hours, improving efficiency by 35%. Furthermore, the alpha-phase silicon carbide seed crystals guide the directional transformation of β-phase silicon carbide intermediates into alpha-phase silicon carbide powder, avoiding crystal form mixing problems without catalysis, increasing the alpha-phase silicon carbide powder content from the traditional 85% to over 99.6%.

[0045] 2. Improved Product Purity: Carbon nanotubes only play a dual auxiliary role in dispersion and conductivity. During the first calcination stage at 1400~1450 ℃, they can be completely oxidized to CO gas and removed through precise oxygen control (oxidation rate 100%), thus leaving no solid carbon nanotube residue in the system. In addition, the α-phase silicon carbide seed crystals are completely consistent with the composition of the target product and are ultimately integrated into the product. The α-phase silicon carbide powder obtained in this application has a metal impurity content of less than 1 ppm and an oxygen content of ≤1 ppm, which is far superior to the purity level of traditional preparation methods that introduce exogenous metal catalysts (impurity content ≥5 ppm).

[0046] 3. Suitable for large-scale production: The first calcination product has a β-phase silicon carbide intermediate content of ≥88% and a concentrated particle size, providing highly active raw materials for efficient sublimation in the subsequent induction furnace. Moreover, the single batch processing capacity of the first calcination process reaches 8.5 tons, which is 40% higher than the non-catalytic process, and is suitable for the raw material supply needs of large-scale production lines.

[0047] A third aspect of this application discloses an induction furnace for growing silicon carbide powder, comprising a furnace body and a crucible. The furnace body includes a connected insulation component and a heating component, with the insulation component disposed inside the heating component. A receiving space is defined within the insulation component, and the crucible is disposed within this receiving space. Specifically, the insulation component includes side insulation felt, lower insulation felt, upper insulation felt, and a heating element, all made of graphite hard felt. Graphite is a high-temperature thermally stable material that maintains its structural integrity above 2000℃. The porous structure of graphite hard felt combines insulation properties with adjustable thermal conductivity, allowing for precise maintenance of the temperature gradient within the induction furnace. If the material is not graphite or lacks sufficient purity, the material may decompose, creep, or undergo abrupt changes in thermal conductivity at high temperatures, disrupting the temperature distribution within the furnace and leading to disordered single crystal growth direction and crystal distortion. The heating device includes a quartz tube and an induction coil. This helps to provide the required temperature for the induction furnace.

[0048] Furthermore, the crucible includes a crucible body and a graphite element disposed inside the crucible body, with a gap between the graphite element and the sidewall of the crucible body. (Refer to...) Figure 1 The graphite component includes a hollow cylinder 1, with at least one recess 1-1 provided on the outer and / or inner surfaces of the cylinder. Thus, on the one hand, the induction furnace can form an inner + outer dual-filling zone (i.e., the raw material can be placed in the gap between the graphite component and the crucible body sidewall, or in the hollow structure of the graphite component). The dual-filling zone, combined with the distribution of the annular material layer, helps ensure that all powder materials can uniformly contact the high-temperature gas flow in the induction furnace, while ensuring that the powder materials can contact the graphite heat-conducting surface, ensuring sufficient sublimation of the raw materials. On the other hand, the presence of at least one recess on the outer and / or inner surfaces of the cylinder can further significantly increase the contact area between the powder materials and the graphite heat-conducting surface. Compared to the conventional cylindrical side surface, the contact area can be increased by 60%, thereby ensuring more sufficient contact between the powder materials (inner + outer filling) and the high-temperature gas flow and the graphite component heat-conducting surface, further ensuring sufficient sublimation of the raw materials and avoiding unreacted powder residues in certain areas.

[0049] Specifically, the graphite components in the relevant technology are solid structures, which can easily lead to airflow stagnation in the middle area of ​​the graphite components, resulting in excessively high local concentrations of SiC gas phase components and causing recrystallization blockage. In contrast, the gas flow space in the central channel of the hollow cylinder allows airflow to pass through the entire graphite component, breaking the local concentration balance, preventing recrystallization accumulation in the middle area, and ensuring continuous and stable process.

[0050] In some embodiments, the induction furnace can be used in the preparation method of this application, which helps to improve the sublimation efficiency of the β-phase silicon carbide intermediate in the induction furnace (i.e., step S30 in the preparation method above). Specifically, the sublimation rate of the β-phase silicon carbide intermediate can be increased by 40%.

[0051] In some embodiments, refer to Figure 1 The graphite component is further provided with multiple pores 1-2, with one end of each pore opening on the inner surface of the recess and the other end opening on the top surface of the cylinder. The recess design described above functions as a flow channel, allowing the sublimated SiC gaseous components at the bottom to naturally converge into the recess and then be directionally transported through the pores, reducing diffusion loss of the gaseous components and improving raw material utilization.

[0052] In some embodiments, the pores include spiral pores. The spiral pores enable the argon gas in the induction furnace to generate rotational kinetic energy as it passes through, forming a stable rotating upward flow field. This accelerates the transport of SiC gaseous components to the top, preventing excessively high local concentrations that could lead to recrystallization blockage. Furthermore, it carries unreacted fine particles to the high-temperature zone of the induction furnace for secondary sublimation. Simultaneously, the spiral pores allow heat to diffuse evenly within the graphite component, preventing uneven sublimation rates caused by localized overheating. The airflow within the spiral pores also removes excess heat, further reducing temperature fluctuations.

[0053] The induction furnace in this application has at least the following beneficial effects: 1. The recessed portion in the graphite part can increase the contact area of ​​the β-phase silicon carbide intermediate during sublimation by 60%. The spiral pores guide the argon gas to form a rotating upward flow field. Combined with the excellent thermal conductivity of the graphite part, the temperature difference in the middle of the induction furnace can be controlled within ±15 ℃. Compared with the traditional induction furnace (without graphite part), the uniformity is significantly improved, avoiding grain agglomeration and gas phase component concentration imbalance caused by local overheating.

[0054] 2. The rotating flow field generated by argon gas passing through the spiral pores can accelerate the diffusion of β-phase silicon carbide intermediates to the top of the induction furnace. At the same time, it can guide the incompletely reacted fine particles to the high-temperature zone of the induction furnace for secondary sublimation, increasing the raw material utilization rate from 30% in the traditional PVT method to over 80%.

[0055] 3. Graphite parts can be made by secondary processing of waste graphite crucibles, which reduces the raw material cost by 65% ​​compared with new graphite parts. At the same time, after the graphite parts are worn, they can be crushed and reused as a carbon source (purity ≥99.99% after plasma purification). This creates a closed-loop system of "production-loss-reuse", reducing graphite solid waste emissions. With the help of tail material recycling and argon gas circulation, the overall production cost is reduced by 30% compared with traditional processes.

[0056] The present application will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present application in any way. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art or in accordance with the product manual.

[0057] Example 1 Raw material pretreatment: High-purity silicon powder (particle size 2μm) and high-purity carbon powder (particle size 1μm) with a purity of 6N were selected and refined to 600 nm for silicon powder and 300 nm for carbon powder by air jet mill. The silicon powder and carbon powder were then treated by high-frequency magnetic separator (magnetic field strength of 15000Gs) and then subjected to plasma purification. The total impurity content of silicon powder and carbon powder was 3.2 ppm.

[0058] Mixing: Silicon powder and carbon powder are mixed at a molar ratio of 1:1.05. Add 0.5% of α-phase silicon carbide seed crystals (80 nm in diameter, 6N purity) and 0.15% of carbon nanotubes (15 nm in diameter, 99.99% purity) by mass of the total raw materials. Wet mixing is carried out under the protection of high-purity argon gas (the mass ratio of water to raw materials is 0.8:1). Specifically, the above mixture of water and raw materials is stirred in a twin-screw mixer at a speed of 400 r / min for 40 min and ultrasonically dispersed at 25 kHz and 800 W for 30 min.

[0059] First calcination: The process was carried out in a tunnel kiln, with the temperature increased from room temperature to 800℃ at a rate of 5℃ / min and held for 1 h, and then increased to 1450℃ at a rate of 3℃ / min and held for 2 h. At the temperature of 1450℃, an argon-oxygen mixture (oxygen volume percentage of 0.08%) was introduced to completely oxidize and remove the carbon nanotubes, resulting in a β-phase silicon carbide intermediate product with a content of 89.5% and a residual raw material content of 7.2%. After cooling, the product was crushed to a particle size of 35 μm.

[0060] Induction furnace filling: The induction furnace described in this application is used to fill the graphite part and the hollow part of the graphite part into an annular material layer.

[0061] Second calcination: The induction furnace is evacuated to 5×10 -6 After Pa, the furnace was cleaned three times with high-purity argon (99.9995% purity) to achieve temperatures of 2450℃ at the bottom, 2350℃ in the middle, and 2050℃ at the top. Argon was continuously introduced at a flow rate of 7L / min. When the temperature reached 2300℃, 1.5% high-purity hydrogen was introduced. After holding at this temperature for 8 hours, the temperature was lowered to room temperature at a rate of 5℃ / h to obtain α-phase silicon carbide powder.

[0062] The performance of the obtained α-phase silicon carbide powder was tested: the purity of the α-phase silicon carbide powder was 99.95%, the metal impurity content was 0.8 ppm, the oxygen content was 0.9 ppm, the raw material utilization rate was 82%, the single furnace output was 2.5 tons, and the comprehensive energy consumption was 3200 kWh / ton.

[0063] Example 2 Same as Example 1, the main difference is: the amount of α-phase silicon carbide seed crystals added is 0.6% (particle size 60 nm), and the amount of carbon nanotubes added is 0.1% (diameter 12 nm). The temperature of the bottom heating zone of the induction furnace is 2480℃, the argon flow rate is 8L / min, and the hydrogen content is 1.2%.

[0064] The performance of the obtained α-phase silicon carbide powder was tested: the purity of the α-phase silicon carbide powder was 99.98%, the metal impurity was 0.7 ppm, the oxygen content was 0.8 ppm, the raw material utilization rate was 83%, the single furnace output was 2.6 tons, and the comprehensive energy consumption was 3150 kWh / ton.

[0065] Example 3 Similar to Embodiment 1, the main difference is that the induction furnace described in this application is not used; a conventional induction furnace can be used (the difference between the conventional induction furnace and the induction furnace described in this application is that there is no graphite component).

[0066] The performance of the obtained α-phase silicon carbide powder was tested: the purity of the α-phase silicon carbide powder was 99.7%, the metal impurities were 1.2 ppm, the oxygen content was 1.5 ppm, the raw material utilization rate was 45%, the single furnace output was 1.6 tons, and the comprehensive energy consumption was 3800 kWh / ton.

[0067] Comparative Example 1 Similar to Example 1, the main difference is that: no α-phase silicon carbide seed crystals and carbon nanotubes are added, and the silicon powder and carbon powder are mixed at a molar ratio of 1:1.05; the first calcination temperature is 1500 ℃ and held for 4 h; the second calcination does not use the induction furnace of this application.

[0068] The performance of the obtained α-phase silicon carbide powder was tested: the purity of the α-phase silicon carbide powder was 98.5%, the metal impurities were 6.5 ppm, the oxygen content was 4.2 ppm, the raw material utilization rate was 28%, the output per furnace was 1.1 tons, and the comprehensive energy consumption was 4800 kWh / ton.

[0069] Comparative Example 2 Similar to Example 1, the main difference is that the α-phase silicon carbide seed crystals and carbon nanotubes are replaced with 0.5% nano boron powder, and the induction furnace of this application is not used in the second calcination.

[0070] The performance of the obtained α-phase silicon carbide powder was tested: the purity of the α-phase silicon carbide powder was 99.0%, but the content of B impurities was 8.3 ppm (exceeding the standard), the raw material utilization rate was 32%, the output of a single furnace was 1.2 tons, and the comprehensive energy consumption was 4500 kWh / ton.

[0071] Conclusion: As can be seen from the above Examples 1-3 and Comparative Examples 1-2, the method for preparing α-phase silicon carbide powder of this application and the induction furnace of this application can greatly improve the raw material utilization rate, and the α-phase silicon carbide powder prepared has high purity.

[0072] Test methods Purity testing of α-phase silicon carbide powder: X-ray fluorescence spectroscopy was used for testing.

[0073] Test of metal impurity content in α-phase silicon carbide powder: Inductively coupled plasma mass spectrometry was used to accurately determine the metal impurity content after the sample was digested by acid dissolution.

[0074] Oxygen content test in α-phase silicon carbide powder: Inert gas melting-infrared detection method is used. The sample is melted in a high-purity argon atmosphere, and the oxygen is converted into CO2 and then detected and quantified by a sensor.

[0075] In the description of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0076] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0077] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for preparing α-phase silicon carbide powder, characterized in that, include: Carbon powder, silicon powder, carbon nanotubes and α-phase silicon carbide seed crystals are mixed to obtain a raw material mixture; The raw material mixture was subjected to a first calcination to obtain a β-phase silicon carbide intermediate. The β-phase silicon carbide intermediate was placed in an induction furnace for a second calcination to obtain α-phase silicon carbide powder.

2. The preparation method according to claim 1, characterized in that, At least one of the following conditions must be met: The molar ratio of the silicon powder to the carbon powder is 1:(1.05~1.1). Based on the total mass of the silicon powder and the carbon powder, the mass percentage of the carbon nanotubes is 0.1% to 0.2%. Based on the total mass of the silicon powder and the carbon powder, the mass percentage of the α-phase silicon carbide seed crystals is 0.4%~0.7%; The particle size of the α-phase silicon carbide seed crystals is 50nm~100nm; The purity of the α-phase silicon carbide seed crystal is ≥6N; The diameter of the carbon nanotubes is 10 nm to 20 nm; The purity of the carbon nanotubes is ≥99.99%; The purity of the carbon powder is ≥6N; The purity of the silicon powder is ≥6N; The particle size of the carbon powder is 200nm~500nm; The particle size of the silicon powder is 500nm~800nm.

3. The preparation method according to claim 1, characterized in that, The first calcination includes at least two calcinations with an increasing temperature gradient.

4. The preparation method according to claim 3, characterized in that, The first calcination includes a primary calcination and a secondary calcination, and satisfies at least one of the following conditions: The temperature for the first calcination is 800℃~900℃; The calcination time is 1 to 2 hours. The heating rate for a single calcination is 5℃ / min to 7℃ / min; The temperature for the second calcination is 1400℃~1450℃; The second calcination time is 1.5h~2h; The heating rate for the second calcination is 3℃ / min to 5℃ / min.

5. The preparation method according to claim 1, characterized in that, During the second calcination, the induction furnace satisfies at least one of the following conditions: The temperature at the bottom of the induction furnace is 2400~2500℃; The temperature in the middle of the induction furnace is 2300~2400℃; The temperature at the top of the induction furnace is 2000~2100℃; The second calcination time is 7h~9h.

6. An α-phase silicon carbide powder, characterized in that, It is obtained by the preparation method described in any one of claims 1 to 5.

7. An induction furnace for the growth of silicon carbide powder, characterized in that, include: The furnace body includes a heat preservation device and a heating device, wherein the heat preservation device is disposed inside the heating device and a receiving space is defined in the heat preservation device; A crucible is disposed in the containing space. The crucible includes a crucible body and a graphite element disposed inside the crucible body, and there is a gap between the graphite element and the side wall of the crucible body. The graphite component includes a hollow cylinder, and at least one recess is provided on the outer surface and / or inner surface of the cylinder.

8. The induction furnace according to claim 7, characterized in that, The graphite part is also provided with a plurality of pores, and one end of the pore is located on the inner surface of the recess, while the other end of the pore is located on the top surface of the cylinder.

9. The induction furnace according to claim 8, characterized in that, The pores include spiral pores.

10. The induction furnace according to any one of claims 7 to 9, characterized in that, A method for preparing α-phase silicon carbide powder according to any one of claims 1 to 5.

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