Silicon carbide powder, silicon carbide powder synthesis system and synthesis method

Abstract

This invention discloses silicon carbide powder, a silicon carbide powder synthesis system, and a synthesis method, relating to the field of semiconductor technology. The silicon carbide powder synthesis method provided by this invention employs an integrated condensation and recovery chamber design within the synthesis system, and implements precise temperature gradient control. By separating the hot gas flow rising zone from the condensation reflux zone, it effectively improves silicon condensation efficiency while preventing condensate from clogging the gas rising channel, thus achieving in-situ recycling of silicon resources. This fundamentally solves the industry problems of silicon resource waste and purity degradation in silicon carbide synthesis, achieving breakthroughs in raw material utilization, product quality, overall energy consumption, and environmental protection, demonstrating significant economic benefits and industrialization prospects.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and more specifically, to silicon carbide powder, a silicon carbide powder synthesis system, and a synthesis method. Background Technology

[0002] Silicon carbide (SiC) is widely used in abrasives, refractory materials, high-temperature structural ceramics, power semiconductor devices, and third-generation semiconductor substrates due to its excellent thermal stability, chemical inertness, high hardness, and wide bandgap semiconductor properties. With the surge in demand for high-performance SiC devices from new energy vehicles, 5G communications, and photovoltaic inverters, the market demand for high-purity (≥99.9%) SiC powder with controllable particle size is becoming increasingly urgent.

[0003] Currently, the mainstream methods for synthesizing SiC powder in industry include: the Acheson method (electric resistance furnace method), the self-propagating high-temperature synthesis method (SHS), chemical vapor deposition (CVD), and the liquid phase / sol-gel method. Among these, the Acheson method and the self-propagating high-temperature synthesis method generally share a common technical challenge: silicon vapor phase escape loss. Because the SiC synthesis temperature is usually higher than the boiling point of silicon (approximately 2355℃) or significantly increases the vapor pressure of silicon, some silicon escapes from the reaction zone in gaseous form (such as Si, SiO, Si2C, etc.), and is either emitted with the exhaust gas or deposited in the low-temperature region of the furnace. This phenomenon leads to the following problems: (1) Silicon loss usually accounts for 5%-15% of the total silicon content of raw materials, and can even reach 20% in the Acheson process, which significantly increases production costs and results in low raw material utilization. (2) The escaped silicon vapor condenses in the inner wall of the furnace or in the exhaust pipe to form a silicon deposit layer, which may peel off and mix into the product in subsequent operations, causing impurity pollution and reducing product purity. (3) Silicon deposits adhere to the furnace wall, pipes and valves, requiring regular shutdown for cleaning, which reduces equipment utilization and production efficiency. (4) Direct emission of silicon-containing tail gas not only wastes resources but may also form silicon dust pollution, increase tail gas treatment costs, and increase environmental pressure.

[0004] Existing technologies attempt to control the problem caused by the volatilization of gaseous silicon through various methods. For example, the tail gas condensation and recovery method involves installing a condensation device at the end of the exhaust pipe to collect the escaped silicon vapor as solid silicon. However, this approach is an "end-of-pipe treatment," requiring the recovered silicon to be added back as raw material, increasing the process and energy consumption. Furthermore, the condensation location is far from the reaction zone, making in-situ recycling impossible. The inert gas purging method uses inert gases such as argon to carry silicon vapor away from the high-temperature reaction zone, reducing its deposition in the reactor. However, this method only changes the migration path of the silicon vapor and does not achieve recovery, instead increasing gas consumption and subsequent processing burden. Additionally, the sealed reactor design uses a fully enclosed reaction vessel to suppress silicon vapor escape, but sealing is difficult under high temperature and pressure conditions, and the silicon vapor condensing on the inner wall of the reactor is difficult to automatically return, still requiring manual cleaning. While these methods alleviate the silicon volatilization problem to some extent, they all have significant limitations.

[0005] Therefore, in the process of silicon carbide powder synthesis, how to achieve in-situ, continuous, and efficient recovery of fumed silicon and return it directly to the reaction zone has become a key technical challenge to improve raw material utilization, enhance product purity, reduce energy consumption, and reduce environmental pollution.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide silicon carbide powder, a silicon carbide powder synthesis system, and a synthesis method to solve or improve the above-mentioned technical problems.

[0008] This invention is implemented as follows: In a first aspect, the present invention provides a silicon carbide powder synthesis system, the synthesis system including a crucible, a heating system and a cooling system, the crucible including a flow guide and a flow guide shroud; wherein, the flow guide shroud is installed on the top inner side of the crucible lid; The flow guide is detachably installed on the side of the crucible near the bottom of the crucible at the center; the area between the side wall of the flow guide and the center of the flow guide is the reaction zone, and the area between the side wall of the flow guide and the side wall of the crucible is the flow guiding zone; on the outside of the crucible, a heating system is provided on the side near the flow guide and connected to the crucible, and a cooling system is provided on the side near the crucible lid and connected to the crucible.

[0009] In an optional embodiment, a plurality of graphite slots are fixedly provided on the inner side of the bottom of the crucible for fixing the flow guide; along the axial direction, the sidewall of the flow guide extends outward toward the bottom of the flow guide, and the extended portion matches the graphite slots.

[0010] In an optional embodiment, the top of the flow guide is in communication with the interior of the crucible; the flow guide includes a constant diameter sidewall near the bottom of the flow guide and a variable diameter sidewall near the crucible lid; wherein, the diameter of the constant diameter sidewall is smaller than the inner diameter of the crucible; the variable diameter sidewall extends from the constant diameter sidewall toward the crucible lid, and the diameter on the side near the crucible lid is smaller than the diameter on the side away from the crucible lid. And / or, the flow guide extends from the inside of the top of the crucible lid toward the bottom of the crucible and comes closer together to form an inverted triangular structure; the vertical height of the inverted triangular structure is higher than the vertical height of the small-diameter side of the flow guide.

[0011] In an optional embodiment, the refrigeration system includes a multi-ring pipe arranged in a ring for filling with a refrigeration medium; wherein the refrigeration medium is selected from either water or an inert gas; the inlet of the refrigeration medium is on the side near the crucible lid, and the outlet is on the side away from the crucible lid. And / or, the heating method of the heating system is selected from induction heating or resistance heating.

[0012] In an optional embodiment, the synthesis system has a vent for supplying a protective gas to the interior of the synthesis system; the protective gas is selected from at least one of nitrogen, helium, and argon.

[0013] In an optional embodiment, temperature sensors are independently provided on the top of the flow guide and the through area inside the crucible, as well as on the heating system and the cooling system. And / or, the synthesis system also includes a monitoring system, which includes a pressure monitor, a gas flow monitor, and a gas purity monitor.

[0014] Secondly, the present invention provides a method for synthesizing silicon carbide powder using a silicon carbide powder synthesis system as described in any of the foregoing embodiments, comprising the following steps: Assemble the crucible and the flow guide, and the flow guide cover and the crucible cover separately; A crucible lid with a flow guide shroud is assembled in a reaction zone by filling it with a silicon source and a carbon source mixed in proportion. Start the heating system, cooling system and monitoring system. The heating system raises the temperature of the reaction zone to 1800℃-2000℃ at a rate of 5℃ / min-20℃ / min. At the same time, control the cooling system so that the temperature on the side near the cooling system is 200℃-500℃ lower than the temperature of the top of the guide and the through area inside the crucible. The reaction is carried out for 10-14 hours to obtain silicon carbide powder.

[0015] In an optional implementation, the ratio of silicon source to carbon source is (1-1.05):1; The silicon source is selected from high-purity silicon powder or silicon blocks, with a purity of ≥99.99%; the carbon source is selected from graphite or carbon black. And / or, the materials of the shroud, the flow guide, and the crucible are selected from graphite or boron nitride.

[0016] In an optional embodiment, during the reaction, the gas pressure of the synthesis system is 0.1 atm-0.5 atm, the oxygen content is ≤10 ppm, and the flow rate of the protective gas is 0.1 L / min-5.0 L / min. And / or, the temperature of the top of the flow guide and the through area inside the crucible is 1800℃-2000℃, and the temperature on the side near the refrigeration system is 1300℃-1500℃.

[0017] Thirdly, the present invention provides a silicon carbide powder, which is prepared by the silicon carbide powder synthesis method as described in any of the foregoing embodiments; The purity of silicon carbide powder is ≥99.5%.

[0018] The present invention has the following beneficial effects: The silicon carbide powder synthesis method provided by this invention adopts an integrated condensation and recovery chamber design in the synthesis system and performs precise temperature gradient control. By separating the hot gas rising zone from the condensation reflux zone, the silicon condensation efficiency is effectively improved, while preventing condensate from blocking the gas rising channel, thus realizing the in-situ recycling of silicon resources. It fundamentally solves the industry problems of silicon resource waste and purity reduction in silicon carbide synthesis, and achieves breakthroughs in raw material utilization, product quality, comprehensive energy consumption and environmental protection, with significant economic benefits and industrialization prospects. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the crucible structure in a silicon carbide powder synthesis system. Figure 2 The XRD test results are for the silicon carbide powder prepared in Example 1.

[0021] Icons: 1-Crucible; 101-Crucible lid; 3-Flow guide; 5-Refrigeration system; 501-Inlet; 502-Outlet; 7-Flow guide; 701-Variable diameter sidewall; 702-Equal diameter sidewall; 9-Heating system; 11-Graphite slot. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0023] In a first aspect, the present invention provides a silicon carbide powder synthesis system, the synthesis system including a crucible 1, a heating system 9 and a cooling system 5, the crucible 1 including a flow guide 7 and a flow guide shroud 3; wherein, the flow guide shroud 3 is installed on the inner side of the top of the crucible cover 101; The flow guide 7 is detachably installed on the side of the center of the crucible 1 near the bottom of the crucible 1; the area between the side wall of the flow guide 7 and the center of the flow guide 7 is the reaction zone, and the area between the side wall of the flow guide 7 and the side wall of the crucible 1 is the flow guiding zone; on the outside of the crucible 1, a heating system 9 is provided on the side near the flow guide 7 and connected to the crucible 1, and a cooling system 5 is provided on the side near the crucible cover 101 and connected to the crucible 1.

[0024] It should be noted that when the temperature reaches the reaction temperature, the silicon source and the carbon source undergo a solid-phase or gas-solid-phase reaction to generate SiC. At the same time, some silicon escapes due to the increase in vapor pressure at high temperature, forming silicon vapor (the main components of which are gaseous species such as Si and Si2C).

[0025] The silicon carbide powder synthesis system provided by this invention adopts an integrated condensation and recovery chamber design. By separating the hot gas rising zone from the condensation reflux zone, it effectively improves the silicon condensation efficiency while preventing condensate from clogging the gas rising channel, thus enabling the recycling of silicon resources. A detailed analysis follows: The guide zone inside crucible 1 serves as a recovery zone for condensed products, directly integrating an adjustable temperature condensation chamber without the need for an external condenser, resulting in a compact structure. The condensed silicon material flows back naturally by gravity, avoiding pollution and energy consumption associated with mechanical transport. All condensed silicon material is recovered and directly returned to the reaction zone, constructing a closed-loop recycling system for silicon, converting the condensed silicon material back into raw materials, thus achieving efficient utilization of silicon throughout the entire process while reducing the introduction of impurities. Through zoned cooling and real-time temperature control, a continuous gradient from high to low temperature is formed between the top of the guide component 7 and the through-flow area inside crucible 1, allowing for selective condensation of gaseous silicon in specific areas and improving condensation efficiency (theoretical recovery rate >95%).

[0026] In an optional embodiment, a plurality of graphite slots 11 are fixedly provided on the inner side of the bottom of the crucible 1 for fixing the flow guide 7; along the axial direction, the side wall of the flow guide 7 extends outward toward the bottom of the flow guide 7, and the extended portion matches the graphite slots 11.

[0027] Furthermore, the number of graphite slots 11 is at least 3, which are evenly and equally spaced at the bottom of the crucible 1 to ensure the stability of the guide 7.

[0028] The height of the sidewall extension of the flow guide 7 corresponds to the depth of the graphite slot 11, the length of the sidewall extension of the flow guide 7 corresponds to the length of the graphite slot 11, and the thickness of the sidewall of the flow guide 7 corresponds to the width of the graphite slot 11.

[0029] In other embodiments of the present invention, it is also permissible if the length of the graphite slot 11 is greater than or less than the length of the sidewall extension of the guide member 7.

[0030] It should be noted that in areas where the graphite slots 11 are not provided, the bottom of the guide member 7 is suspended. This area facilitates the return of condensed silicon material to the reaction zone, enabling reuse. In other embodiments of the present invention, the number of graphite slots 11 is reasonably set according to actual needs.

[0031] In an optional embodiment, the top of the flow guide 7 is in communication with the interior of the crucible 1; the flow guide 7 includes a constant diameter sidewall 702 near the bottom of the flow guide 7 and a variable diameter sidewall 701 near the crucible cover 101; wherein, the diameter of the constant diameter sidewall 702 is smaller than the inner diameter of the crucible 1; the variable diameter sidewall 701 extends from the constant diameter sidewall 702 toward the crucible cover 101, and the diameter on the side near the crucible cover 101 is smaller than the diameter on the side away from the crucible cover 101. The variable diameter sidewall 701 of the flow guide 7 helps to reduce the impact of the silicon material falling after condensation on the flow guide 7; the condensed silicon material is affected by gravity and falls to the variable diameter sidewall 701 of the flow guide 7, and then falls further along the flow guide area to the bottom of the crucible 1, and is further fed back to the reaction zone to participate in the reaction.

[0032] It should be noted that the bottom of the guide member 7 near the equal diameter sidewall 702 is provided with a through hole that passes through the guide member 7 and the crucible 1. The number and diameter of the through holes are reasonably set according to the actual particle size of the material.

[0033] And / or, the flow guide 3 extends from the inner side of the top of the crucible cover 101 toward the bottom of the crucible 1 and comes closer together to form an inverted triangular structure; the vertical height of the inverted triangular structure is higher than the vertical height of the small diameter side of the flow guide 7.

[0034] The design of the flow guide shroud 3, which is lower in the middle and higher on both sides, helps to change the direction of silicon gas flow back, allowing silicon vapor to enter the low-temperature zone for condensation. The condensed silicon material flows back to the bottom of the crucible 1 along the lower flow guide 7 to replenish the silicon raw material.

[0035] In optional embodiments, the present invention does not particularly limit the installation form of the flow guide shroud 3 and the crucible cover 101. It can be selected to be integrally molded or detachably assembled according to actual needs. If it is a detachable assembly form, it can be selected as needed, such as snap-fit ​​connection, threaded connection or interference fit connection.

[0036] In an optional embodiment, the refrigeration system 5 includes a multi-ring pipe arranged in a ring for filling with a refrigeration medium; wherein the refrigeration medium is selected from either water or an inert gas; the inlet 501 of the refrigeration medium is on the side close to the crucible cover 101, and the outlet 502 is on the side away from the crucible cover 101.

[0037] And / or, the heating method of the heating system 9 is selected from induction heating or resistance heating.

[0038] The multi-loop pipe arrangement expands the coverage area of ​​the condensation zone in the axial direction of crucible 1. The pipes are interconnected and snake-shaped, encircling the outer perimeter of crucible 1 near the end of crucible cover 101. The refrigeration medium flows from top to bottom along the axial direction of crucible 1, which is opposite to the upward flow of the escaping silicon vapor, thus facilitating the full condensation of gaseous silicon.

[0039] In an optional embodiment, the synthesis system has a vent for supplying a protective gas to the interior of the synthesis system; the protective gas is selected from at least one of nitrogen, helium, and argon.

[0040] In an optional embodiment, temperature sensors are independently provided on the top of the flow guide 7, the through area inside the crucible 1, the heating system 9, and the cooling system 5. And / or, the synthesis system also includes a monitoring system, which includes a pressure monitor, a gas flow monitor, and a gas purity monitor.

[0041] Secondly, the present invention provides a method for synthesizing silicon carbide powder using a silicon carbide powder synthesis system as described in any of the foregoing embodiments, comprising the following steps: Assemble crucible 1 with flow guide 7 and flow guide shroud 3 with crucible cover 101 respectively; A crucible lid 101 with a flow guide shroud 3 is assembled in a reaction zone by filling it with a silicon source and a carbon source mixed in proportion. Start the heating system 9, the cooling system 5 and the monitoring system. The heating system 9 raises the temperature of the reaction zone to 1800℃-2000℃ at a rate of 5℃ / min-20℃ / min. At the same time, control the cooling system 5 so that the temperature on the side near the cooling system 5 is 200℃-500℃ lower than the temperature of the top of the guide 7 and the through area inside the crucible 1. The reaction is carried out for 10-14 hours to obtain silicon carbide powder.

[0042] It should be noted that after the high-purity silicon source and carbon source are mixed evenly according to the stoichiometric ratio, they are placed into crucible 1. High-purity protective gas is then introduced into the synthesis system as a carrier gas and protective atmosphere. A cooling system 5 is installed on the side of crucible 1 near the crucible cover 101. This cooling system 5 is made of high-temperature resistant material and includes multiple coils of pipes. It can transport a cooling medium internally and is equipped with a temperature sensor to monitor the temperature of the side of crucible 1 near the cooling system 5 in real time, ensuring that the temperature of the top of the guide 7 and the through area inside the crucible 1 is 200℃-500℃ higher than the temperature of the corresponding area of ​​the cooling system 5.

[0043] The temperature sensor monitors the temperature in real time, which not only prevents the overall temperature from being too high, thus avoiding incomplete condensation of silicon vapor and the large amount of silicon vapor escaping outside the crucible with the carrier gas, reducing the recovery rate, but also prevents the temperature in the low-temperature zone from being too low, causing the silicon vapor to condense into solid powder instantly, adhering to the cavity wall and guide groove, which can easily block the return channel and require frequent shutdowns for cleaning. Reasonable temperature difference control ensures that the silicon vapor is completely condensed in the low-temperature zone, and that the liquid silicon has good fluidity and smooth return flow.

[0044] The area near the cooling system 5 is designated as the low-temperature zone, while the area connecting the top of the guide vane 7 to the interior of the crucible 1 is designated as the high-temperature zone. This temperature gradient helps prevent excessively small temperature differences, which could lead to insufficient condensation driving force and cause some silicon vapor to be discharged with the carrier gas before reaching the low-temperature zone, resulting in a recovery rate at an intermediate level. Furthermore, it helps prevent excessively low temperatures in the low-temperature zone, which could cause silicon vapor to condense instantly into solid powder, adhering to the cavity wall and the sidewall of the guide vane 7, easily clogging the bottom of the guide vane 7 and requiring frequent shutdowns for cleaning.

[0045] The heating rate of heating system 9 is too slow, resulting in uniform grain growth but a long production cycle and high energy consumption; the heating rate of heating system 9 is too fast, which will cause local overheating, and a large amount of silicon vapor will escape instantly, exceeding the processing limit of the condensation chamber and reducing the recovery rate.

[0046] Furthermore, the heating rate of the heating system 9 is 8℃ / min-15℃ / min, and can be selected from any one of 8℃ / min, 10℃ / min, 12℃ / min and 15℃ / min, or other values ​​within the range of 8℃ / min-15℃ / min, as needed.

[0047] By setting the appropriate heating rate and synthesis temperature in the reaction zone, the silicon carbide powder produced has fine and uniform grains, minimal silicon loss, and optimal overall performance. If the temperature in the reaction zone is too low, the reaction will be incomplete, resulting in more residual free silicon and free carbon, and a decrease in purity. If the temperature in the reaction zone is too high, the silicon vapor pressure will increase sharply, exceeding the operating limit of the condensation system, and the high temperature will also intensify the reaction between silicon and the material in crucible 1, causing grain coarsening.

[0048] Furthermore, the temperature of the reaction zone is 1800℃-2000℃, which can be selected from any one of 1850℃, 1900℃, 1950℃ and 2000℃, or other values ​​within the range of 1800℃-2000℃, as needed.

[0049] Setting a reasonable reaction time can ensure high purity of the silicon carbide powder, making it easy to use directly as a high-purity powder. If the reaction time is insufficient, the reaction will be incomplete, resulting in more residual free silicon and free carbon, requiring subsequent acid washing and purification, which increases input costs. If the reaction time is too long, although the reaction will be complete, the grains will become coarser, significantly increasing energy consumption and reducing economic efficiency.

[0050] For example, the reaction time is 10h-14h, and can be selected from any one of 10h, 11h, 12h, 13h and 14h, or other values ​​within the range of 10h-14h, as needed.

[0051] It should be noted that after the set reaction time is completed, heating is stopped, and the synthesis system is allowed to cool naturally to room temperature with the furnace. Turn off the cooling system 5, open the synthesis system, and remove the silicon carbide powder from crucible 1.

[0052] In an optional implementation, the ratio of silicon source to carbon source is (1-1.05):1; The silicon source is selected from high-purity silicon powder or silicon blocks, with a purity of ≥99.99%; the carbon source is selected from graphite or carbon black. And / or, the materials of the flow guide 3, the flow guide 7, and the crucible 1 are selected from graphite or boron nitride.

[0053] In an optional embodiment, during the reaction, the gas pressure of the synthesis system is 0.1 atm-0.5 atm, the oxygen content is ≤10 ppm, and the flow rate of the protective gas is 0.1 L / min-5.0 L / min.

[0054] It should be noted that the gas pressure inside the synthesis system is slightly positive. This setting ensures that the gas flow rises from the bottom of the crucible 1 through the reaction zone, and then is transported from the top of the guide 7 (which belongs to the high-temperature zone) in the upper part of the reaction zone to the guide zone (which belongs to the low-temperature zone) through the internal area of ​​the crucible 1.

[0055] Setting the appropriate gas pressure can effectively suppress the free diffusion of silicon vapor, allowing it to flow directionally into the flow zone without hindering reaction kinetics. If the pressure is too low, silicon vapor is prone to leaking from equipment gaps, and the airflow's ability to "carry" silicon vapor is weak, with some silicon vapor remaining in the reaction zone and being consumed by secondary reactions. If the pressure is too high, although silicon loss is less, it suppresses gas-phase mass transfer, leading to a decrease in the reaction rate, and imposes stringent requirements on equipment sealing.

[0056] Furthermore, the gas pressure of the synthesis system is 0.2atm-0.4atm, which can be selected from any one of 0.2atm, 0.3atm and 0.4atm, or other values ​​within the range of 0.2atm-0.4atm, as needed.

[0057] During the synthesis of silicon carbide powder, the synthesis system is periodically replenished with a small amount of fresh protective gas to compensate for system leaks, and the oxygen purity in the synthesis system is monitored by a gas purity monitor to ensure that the oxygen content is below 10 ppm.

[0058] The gas purity monitor used in this embodiment of the invention is an online dew point meter. In other embodiments of the invention, the appropriate device can be selected as needed.

[0059] If the protective gas flow rate is too low, the carrier gas cannot carry the silicon vapor into the condensation zone in time, causing the silicon vapor to stay in the high-temperature zone for too long, resulting in homogeneous nucleation and the formation of nano-silicon powder mixed into the product. If the protective gas flow rate is too high, the airflow will violently scour the material surface, easily entraining fine SiC powder particles into the condensation chamber, and increasing the load on the cooling system and energy consumption.

[0060] Furthermore, the flow rate of the protective gas is 1.0 L / min to 3.0 L / min, and can be selected from any one of 1.0 L / min, 1.5 L / min, 2.0 L / min and 3.0 L / min, or other values ​​within the range of 1.0 L / min to 3.0 L / min, as needed.

[0061] And / or, the temperature of the area where the top of the flow guide 7 penetrates the interior of the crucible 1 is 1800℃-2000℃, and the temperature on the side near the refrigeration system 5 is 1300℃-1500℃.

[0062] It should be noted that the temperature of the area connecting the top of the flow guide 7 with the interior of the crucible 1 is a high-temperature zone, which is higher than the dew point of silicon, preventing premature condensation of silicon vapor and blockage of the airflow channel. The temperature near the cooling system 5 is a low-temperature zone, lower than the condensation temperature of silicon, which is conducive to the full condensation of silicon vapor. Silicon vapor escaping from the reaction zone enters the flow guide zone, and under the action of the temperature gradient, the silicon vapor re-condenses into liquid silicon or solid silicon droplets in a specific low-temperature zone. The condensed silicon material flows back to the reaction zone under the action of gravity along the inclined reaction zone cavity wall (i.e., the variable diameter part of the reaction zone) and the flow guide zone, realizing the in-situ recovery of silicon.

[0063] In an optional embodiment, the materials of the flow guiding region, the flow guiding element 7, and the crucible 1 are selected from graphite or boron nitride.

[0064] In optional embodiments, the raw material utilization rate of the silicon carbide powder synthesis method provided by the present invention is ≥98%, the purity of the obtained product is ≥99.5%, and the overall energy consumption is reduced by 15%-25% compared with the traditional silicon carbide powder synthesis method.

[0065] Thirdly, the present invention provides a silicon carbide powder, which is prepared by the silicon carbide powder synthesis method as described in any of the foregoing embodiments; The purity of silicon carbide powder is ≥99.5%.

[0066] Furthermore, the purity of the silicon carbide powder is ≥99.9%.

[0067] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0068] Example 1 This embodiment provides a silicon carbide powder, the synthesis method of which includes the following steps: In the reaction zone of crucible 1, a silicon source (high-purity silicon powder, 99.99%) and a carbon source (graphite) mixed in a ratio of 1.05:1 are loaded, and crucible lid 101 is installed. The heating system 9, the cooling system 5, and the monitoring system are started. The heating system 9 heats the temperature of the reaction zone to 1900℃ at a rate of 10℃ / min. At the same time, the cooling system 5 is controlled so that the temperature on the side near the cooling system 5 is 400℃ lower than the temperature of the through area. The temperature of the through area is 1900℃, and the temperature on the side near the cooling system 5 is 1500℃. The gas pressure of the synthesis system is 0.3 atm, and the oxygen content is ≤10ppm. The flow rate of the protective gas is 2.0L / min.

[0069] After reacting for 12 hours, heating was stopped, and the synthesis system was allowed to cool naturally to room temperature with the furnace. The refrigeration system was then turned off. The synthesis system was then opened, and the silicon carbide powder in crucible 1 was removed to obtain silicon carbide powder.

[0070] Comparative Example 1 This comparative example provides a silicon carbide powder, the synthesis method of which includes the following steps: (1) Raw material preparation and pretreatment Natural quartz sand (SiO2≥99.2%) is coarsely crushed to a particle size <5mm by a crusher; petroleum coke (fixed carbon≥95%) is crushed to <3mm by a hammer crusher; after weighing according to SiO2:C=1:1.5 (mass ratio), it is put into a twin-screw mixer, 3wt% wood chips are added as a pore-forming agent, and dry-mixed for 2 hours until uniform.

[0071] (2) Charging of the resistance furnace A 20cm thick coke layer is laid at the bottom of the rectangular graphite furnace body as a conductive bed; a 30cm diameter graphite electrode is vertically inserted; the mixture is filled in layers, and compacted every 30cm thickness, with a 50cm diameter cavity reserved in the center as the reaction core area; the top layer is covered with 20cm coke as a heat insulation layer, and the sides of the furnace body are sealed with refractory clay.

[0072] (3) High-temperature synthesis reaction A 10kV / 50kA AC current was applied to the electrode, and the temperature was increased to 1400℃ at a rate of 50℃ / h (taking 28 hours); the temperature was kept constant at 1900±100℃ for 12 hours, and the reaction occurred: SiO2+3C→SiC+2CO↑; the temperature was further increased to 2500℃ at a rate of 30℃ / h and maintained for 48 hours to ensure the reaction was complete; the total power consumption was approximately 6500kWh / ton of product.

[0073] (4) Cooling and furnace opening After power failure, allow the material to cool naturally for 72 hours to below 80°C; remove the side fire-resistant walls and use an excavator to remove the outer layer of unreacted material (approximately 40% of the total); manually chisel out the silicon carbide crystal blocks (in a radial columnar crystal structure) from the central reaction zone.

[0074] (5) Crushing and grading The crystalline blocks are coarsely crushed to <2cm particles by a crusher; then they are medium crushed to <5mm by a double roll crusher; wet-milled in a ball mill (water-to-material ratio 2:1) for 24 hours to D50≈5μm; and classified by a hydrocyclone to remove coarse particles >10μm.

[0075] (6) Chemical purification The treated powder was transferred to an acid-resistant reactor, and a mixture of 20wt% hydrofluoric acid (HF) and 15wt% nitric acid (HNO3) was added. The mixture was stirred and acid-washed at 80°C for 6 hours to dissolve the metal oxides and free silicon: SiO2 + 6HF → H2SiF6 + 2H2O. After dehydration in a filter press, the powder was washed with deionized water until the conductivity of the filtrate was <50μS / cm.

[0076] (7) Drying and sieving The filter cake enters the spray drying tower (inlet air temperature is 250℃) to produce powder with a moisture content of <0.5%; hard agglomerates are removed by an ultrasonic vibrating screen (400 mesh screen); iron impurities are removed by a magnetic separator (magnetic field strength is 1.2T).

[0077] The following comparative analysis was conducted on Example 1 and Comparative Example 1, and the results are summarized in Table 1. The comparative dimensions include raw material utilization rate, product purity, comprehensive energy consumption, environmental protection and safety, equipment life and maintenance, and process controllability.

[0078] Table 1 Analysis Results

[0079] Experimental Example 1 This experiment was conducted to investigate the effects of heating rate and synthesis temperature on the synthesis of silicon carbide powder. The test items included silicon recovery rate, product purity, average particle size and energy consumption. The conclusions and impact analysis were also conducted, and the relevant results are summarized in Table 2.

[0080] The silicon recovery rate is calculated using the mass conservation method: Silicon recovery rate (%) = (m Si,回流 + m Si,产物 ) / m Si,投入 ×100%); Product purity, i.e., the purity of silicon carbide powder, is measured by GDMS; Average particle size is measured by laser diffraction; Comprehensive energy consumption is measured by direct metering: a three-phase energy meter is installed at the main power supply of the equipment, and the total power consumption (kWh) of the entire synthesis cycle (heating + heat preservation + cooling) is recorded and divided by the mass (kg) of silicon carbide powder produced.

[0081] Table 2 Results of the study on the relationship between heating rate and synthesis temperature

[0082] As shown in Table 2, the optimal process conditions are a heating rate of 10°C / min and a synthesis temperature of 1900°C. At this temperature, the silicon recovery rate is 98.2%, the purity of the silicon carbide powder is 99.9%, the average particle size is 1.8 μm, and the crystal structure is pure. If the heating rate is too rapid (20°C / min), silicon vapor escapes instantaneously, reducing the recovery rate to 95.0%. If the synthesis temperature is too high (2000°C), side reactions are exacerbated, and the grain size coarsens to 5.0 μm.

[0083] Experimental Example 2 This experiment was conducted to investigate the effects of system pressure and gas flow rate on the synthesis of silicon carbide powder. The test items included silicon recovery rate, product purity, and particle size distribution. The conclusions and impact analysis were presented, and the relevant results are summarized in Table 3.

[0084] The testing methods for silicon recovery rate and product purity are the same as those in Experiment 1; the testing method for particle size distribution is laser diffraction: the cumulative distribution curve is measured, and D50 (median diameter) and D90 (particle size corresponding to 90% cumulative diameter) are read, and the D50 / D90 data are summarized.

[0085] Table 3. Results of the study on pressure and gas flow rate in the synthesis system.

[0086] As shown in Table 3, the optimal conditions for the synthesis system are a slightly positive pressure of 0.3 atm and a gas flow rate of 2.0 L / min. Under these conditions, the silicon recovery rate is 98.2%, and the purity is 99.9%. Too low a pressure (0.1 atm) leads to silicon vapor leakage, resulting in a recovery rate of only 96.0%; too low a flow rate (0.5 L / min) causes silicon vapor to remain in the reaction zone, resulting in the formation of nano-silicon powder which mixes into the product, reducing the product purity to 99.5%.

[0087] Experimental Example 3 This experiment was conducted to investigate the effect of temperature gradients in the high-temperature and low-temperature zones on recovery efficiency. The test items included silicon recovery rate and reflux silicon purity. The results of the experiment, including the summarization of the blockage frequency in the flow channel and the analysis of the conclusions and impacts, are summarized in Table 4.

[0088] The silicon recovery rate was tested using the same method as in Example 1; the purity of the refluxed silicon was tested and analyzed using inductively coupled plasma optical emission spectrometry (ICP-OES).

[0089] Table 4. Results of the effect of temperature gradient on recovery efficiency

[0090] As shown in Table 4, the optimal conditions are 1900°C in the high-temperature zone and 1500°C in the low-temperature zone (a temperature difference of 400°C). At this temperature, the silicon recovery rate is 98.2%, the purity of the refluxed silicon is 99.9%, and there is no blockage. If the temperature difference is too small (200°C), the condensation driving force is insufficient, and the recovery rate is only 95.0%; if the temperature difference is too large (600°C), the silicon vapor instantly condenses into solid powder, blocking the reflux channel.

[0091] Test Example 4 This experiment was conducted to investigate the effects of reaction time on product conversion rate and energy consumption. The test items included silicon recovery rate, product purity, free carbon content, free silicon content, and overall energy consumption. The conclusions and impact analysis were then presented, and the relevant results are summarized in Table 5.

[0092] The testing methods for silicon recovery rate, product purity, and overall energy consumption are the same as those in Experiment 1; free carbon content and free silicon content are measured using GDMS.

[0093] Table 5. Results of the effect of reaction time on product conversion rate and energy consumption

[0094] As shown in Table 5, a reaction time of 12 hours is optimal. At this time, the product purity is 99.9%, and the contents of free carbon and free silicon both decrease to 0.1%, indicating that the raw material reaction is complete. If the time is insufficient (10 hours), more impurities remain, and the purity is only 97.5%. If the reaction time exceeds 12 hours, the purity no longer improves, but energy consumption increases from 11.0 kWh / kg to 13.5 kWh / kg, grain coarsening occurs, and economic efficiency decreases.

[0095] Test Example 1 This test example uses XRD analysis to analyze the silicon carbide powder prepared in Example 1. The test results are shown in [Figure 1]. Figure 2 .

[0096] After cleaning and drying, the powder was found to be β-SiC crystalline powder by XRD analysis.

[0097] Test Example 2 This test example analyzes the purity of the silicon carbide powder prepared in Example 1 using GDMS. Specific purity data are shown in Table 6.

[0098] Table 6. Purity data of silicon carbide powder

[0099] In summary, this invention, through the synergistic design of "condensation recovery + gas circulation," fundamentally solves the industry problems of silicon resource waste and purity decline in silicon carbide synthesis. It achieves breakthroughs in raw material utilization, product quality, energy consumption, and environmental protection, and has significant economic benefits and industrialization prospects.

[0100] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A silicon carbide powder synthesis system, characterized in that, The synthesis system includes a crucible, a heating system, and a cooling system. The crucible includes a flow guide and a flow guide shroud; wherein the flow guide shroud is installed on the top inner side of the crucible lid. The flow guide is detachably installed on the side of the crucible center near the bottom of the crucible; the area between the side wall of the flow guide and the center of the flow guide is the reaction zone, and the area between the side wall of the flow guide and the side wall of the crucible is the flow guiding zone; on the outside of the crucible, a heating system is provided on the side near the flow guide and connected to the crucible, and a cooling system is provided on the side near the crucible lid and connected to the crucible.

2. The silicon carbide powder synthesis system according to claim 1, characterized in that, Multiple graphite slots are fixedly provided on the inner bottom side of the crucible for fixing the flow guide; along the axial direction, the side wall of the flow guide extends outward towards the bottom of the flow guide, and the extended part matches the graphite slots.

3. The silicon carbide powder synthesis system according to claim 1, characterized in that, The top of the flow guide is connected to the interior of the crucible; the flow guide includes a constant diameter sidewall near the bottom of the flow guide and a variable diameter sidewall near the crucible lid; wherein, the diameter of the constant diameter sidewall is smaller than the inner diameter of the crucible; the variable diameter sidewall extends from the constant diameter sidewall toward the crucible lid, and the diameter on the side closer to the crucible lid is smaller than the diameter on the side farther from the crucible lid. And / or, the flow guide extends from the inner side of the top of the crucible lid toward the bottom of the crucible and comes closer together to form an inverted triangular structure; the vertical height of the inverted triangular structure is higher than the vertical height of the small-diameter side of the flow guide.

4. The silicon carbide powder synthesis system according to claim 1, characterized in that, The refrigeration system includes multiple rings of pipe arranged in a ring, which are used to fill the refrigeration medium; wherein the refrigeration medium is selected from either water or an inert gas; the inlet of the refrigeration medium is on the side closer to the crucible lid, and the outlet is on the side farther from the crucible lid; And / or, the heating method of the heating system is selected from induction heating or resistance heating.

5. The silicon carbide powder synthesis system according to claim 1, characterized in that, The synthesis system is provided with a vent for supplying a protective gas to the interior of the synthesis system; the protective gas is selected from at least one of nitrogen, helium and argon.

6. The silicon carbide powder synthesis system according to claim 1, characterized in that, Temperature sensors are independently installed at the top of the flow guide and in the through area inside the crucible, as well as in the heating and cooling systems. And / or, the synthesis system further includes a monitoring system, which includes a pressure monitor, a gas flow monitor, and a gas purity monitor.

7. A method for synthesizing silicon carbide powder using the silicon carbide powder synthesis system as described in any one of claims 1-6, characterized in that, Includes the following steps: Assemble the crucible and the flow guide, and the flow guide cover and the crucible cover separately; A crucible lid with a flow guide shroud is assembled in a reaction zone by filling it with a silicon source and a carbon source mixed in proportion. Start the heating system, cooling system and monitoring system. The heating system raises the temperature of the reaction zone to 1800℃-2000℃ at a rate of 5℃ / min-20℃ / min. At the same time, control the cooling system so that the temperature on the side near the cooling system is 200℃-500℃ lower than the temperature of the top of the guide and the through area inside the crucible. The reaction is carried out for 10-14 hours to obtain silicon carbide powder.

8. The method for synthesizing silicon carbide powder according to claim 7, characterized in that, The ratio of the silicon source to the carbon source is (1-1.05):1; The silicon source is selected from high-purity silicon powder or silicon ingots, and the purity of the silicon source is ≥99.99%; the carbon source is selected from graphite or carbon black. And / or, the materials of the shroud, the flow guide, and the crucible are selected from graphite or boron nitride.

9. The method for synthesizing silicon carbide powder according to claim 7, characterized in that, During the reaction, the gas pressure of the synthesis system is 0.1 atm-0.5 atm, and the oxygen content is ≤10 ppm; the flow rate of the protective gas is 0.1 L / min-5.0 L / min. And / or, the temperature of the top of the flow guide and the through area inside the crucible is 1800℃-2000℃, and the temperature on the side near the refrigeration system is 1300℃-1500℃.

10. A silicon carbide powder, characterized in that, It is prepared by the silicon carbide powder synthesis method according to any one of claims 7-9; The purity of silicon carbide powder is ≥99.5%.

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