Recovery method for residual waste after silicon carbide crystal growth

Abstract

The invention relates to the technical field of silicon carbide crystal growth, in particular to a method for recovering residual waste after silicon carbide crystal growth, which comprises the following steps: step 1, free carbon oxidation: carrying out oxidation treatment on free carbon in an oxidizing atmosphere to generate gaseous carbon dioxide; 2, directional oxidation of the blocks: oxidizing the silicon carbide blocks into silicon oxide powder through combination of directional oxygen introduction and physical oscillation; 3, regenerating the heat-insulating layer, oxidizing silicon carbide in micropores of the heat-insulating layer by external directional oxygen introduction, and generating silicon oxide; step 4, separating and purifying waste materials, carrying out size grading on recycled powder, and carrying out electric separation and acid pickling to obtain high-purity silicon carbide powder and silicon oxide powder; and step 5, raw material re-synthesis: doping the recycled silicon carbide powder in different proportions, doping the silicon carbide powder into unmixed silicon powder and carbon powder according to a process proportion, mixing, and carrying out secondary synthesis in a silicon carbide raw material synthesis path. The technical problems that the interior of the growth furnace is difficult to clean and the waste recovery rate is low are solved.

Description

Technical Field

[0001] The invention relates to the technical field of silicon carbide crystal growth, and in particular to a method for recovering residual waste after silicon carbide crystal growth. Background Art

[0002] As a new semiconductor material, SiC has excellent application prospects in the electrical field due to its advantages such as large bandgap, high breakdown voltage, high thermal conductivity, high electron saturation drift rate, and low dielectric constant. Currently, the main method for preparing SiC crystals in China is the physical vapor transport method (PVT method). The principle is to volatilize SiC powder into gaseous components by heating the high-temperature zone and adjusting the temperature. Then, a temperature gradient is established in the crucible, and silicon carbide single crystals are crystallized in the seed crystal area, ultimately producing large-scale silicon carbide single crystals.

[0003] However, in actual use, after silicon carbide crystal growth, lumps that are difficult to clean will form on the side walls of the growth furnace, and silicon carbide crystals will also penetrate into its insulation layer, which cannot be recovered and is not conducive to multiple crystal growth. Summary of the Invention

[0004] The purpose of the present invention is to address the shortcomings of the existing technology. By introducing oxygen, the silicon carbide that is difficult to clean remaining in the growth furnace is oxidized at high temperature into silicon oxide that is easy to clean, and the silicon carbide is removed and recovered, thereby solving the technical problems of the difficulty in cleaning the interior of the growth furnace and the low waste recovery rate.

[0005] In response to the above technical problems, the technical solutions adopted are as follows: A method for recovering waste remaining after silicon carbide crystal growth comprises the following steps: Step 1: Free carbon oxidation, wherein the free carbon is oxidized in an oxidizing atmosphere to generate gaseous carbon dioxide; Step 2: Directional oxidation of agglomerates, which involves oxidizing the silicon carbide agglomerates into silicon oxide powder through directed oxygen flow combined with physical vibration; Step 3: Regeneration of the insulation layer, external oxygen directional oxidation of the micropores of the insulation layer to participate in silicon carbide and generate silicon oxide; Step 4: separation and purification of waste materials, particle size classification of the recovered powder, and electrostatic separation and weak acid washing to obtain high-purity silicon carbide powder and silicon oxide powder; Step 5: Resynthesize the raw materials. The recovered silicon carbide powder is mixed with different proportions, mixed with unmixed silicon powder and carbon powder according to the process proportion, and then a secondary synthesis is carried out in the silicon carbide raw material synthesis path.

[0006] Preferably, in the free carbon oxidation step, excess oxygen is introduced into the crucible, the temperature is raised to 600-800° C. at a rate of 5° C. / min and kept at that temperature for 2 hours, and the oxygen concentration is greater than 10%.

[0007] Preferably, the agglomeration directional oxidation step comprises the following steps: A. Heat the crucible to 1100-1200℃ and keep it warm for 15 minutes; B. Move the oxygen injection port close to the side wall of the agglomerate and continue to spray oxygen at multiple points; C. Roll the surface silicon oxide to promote the shedding of silicon oxide and oxidation of deep silicon carbide.

[0008] Preferably, the insulation layer regeneration step comprises the following steps: a. While step A is being performed, the reflective layer of the inner layer of the insulation layer is opened to heat the insulation layer; b. The opening rate of the insulation layer is adjusted to the maximum, and oxygen is introduced from the outer layer of the insulation layer; c. The silicon carbide in the gaps of the insulation layer is oxidized into silicon oxide and collected; Preferably, the waste separation and purification step comprises the following steps: ①. After step 1, the remaining silicon carbide at the bottom of the crucible is recovered and crushed and sieved again.

[0009] ②. The mixed powder of silicon oxide and silicon carbide formed in step 2 and step 3 is crushed and ground to D 50 ≤10μm, then the powder is classified by air flow according to density, and then silicon carbide and silicon oxide are further separated by high-voltage electric separation, and the silicon oxide is output; ③ A carbonic acid solution is used to pickle silicon carbide to remove metal impurities therein. The carbonic acid solution is obtained by passing the carbon dioxide generated in steps 1, 2 and 3 into an aqueous solution containing carbonic anhydrase.

[0010] Preferably, the raw material resynthesis step comprises the following steps: (1) The used silicon carbide raw materials were crushed and screened, and silicon carbide powder with a particle size of less than 0.18 mm was screened out using an 80-mesh nylon screen and collected.

[0011] (2) The silicon carbide powder synthesized by the high-temperature self-propagating method was crushed and sieved, and the silicon carbide powder with a particle size of less than 0.18 mm was screened out using an 80-mesh nylon screen and collected.

[0012] (3) High-purity carbon powder and high-purity silicon powder are mixed with silicon carbide powder in an atomic molar ratio of 1:1, and mixed for 8 hours using a mixer at a speed of 30 revolutions per minute.

[0013] (4) The collected silicon carbide fine powder and the mixed silicon carbide powder are mixed in a mass ratio of 1:9, and the mixing is carried out for 4 hours using a mixer at a speed of 30 revolutions per minute.

[0014] (5) Charging the furnace: Place the mixed raw materials into the crucible and load the furnace.

[0015] (6) Raw material synthesis.

[0016] Preferably, the (6) raw material synthesis comprises the following steps: Ⅰ. Gas washing: Use a vacuum pump to evacuate the furnace chamber to a pressure of <1×10-4Pa, maintain this pressure for 4 hours, introduce Ar, and increase the furnace chamber pressure to 60kPa~80kPa, maintaining the pressure for 1h~3h minutes; Ⅱ. Second gas purge: Use a vacuum pump to evacuate the furnace chamber to a pressure of <1×10-4Pa, maintain this pressure for 4 hours, introduce Ar, and increase the furnace chamber pressure to 60kPa~80kPa, maintaining the pressure for 2h~5h minutes; III. Heating: Under a pressure of 50kPa~800kPa, raise the temperature to 600℃~800℃ at a heating rate of 1℃ / min~10℃ / min and maintain for 1h~2h; continue heating, control the temperature at 1300℃~1400℃, and evacuate with a mechanical pump, maintaining for 5~7h. Under this condition, the silicon carbide powder is removed to the maximum extent possible; within 2h~3h, raise the temperature to 2200℃ and maintain for 15h~25h. Synthesize the silicon carbide powder using the high-temperature self-propagating method; Ⅳ. Cooling, maintaining the furnace chamber pressure at 2kPa~20kPa, adjusting the gas flow rate introduced through the graphite pipe, maintaining the argon flow rate at 200sccm~800sccm and cooling; when the temperature drops to room temperature, then directly introduce argon into the furnace chamber to atmospheric pressure, open the furnace door and remove the raw materials; V. Post-processing of raw materials: crushing, screening, cleaning, drying and packaging the taken out silicon carbide.

[0017] Preferably, the oxidation mechanism involved in step 2 is arranged inside the growth furnace and is used for directionally controlling oxygen output; The oxidation mechanism includes two sets of sealing covers horizontally slidably connected to both sides of the crucible, a cover plate vertically slidably connected to the top of the crucible, an air outlet arranged on the edge of the cover plate, a control frame vertically slidably connected to the cover plate, an air jet ring rotatably connected to the control frame, multiple sets of rolling wheels evenly arranged around the control frame, and multiple sets of balls evenly arranged around the paint spraying ring; The heat preservation mechanism involved in step 3 is arranged outside the crucible and is used to dynamically control the collection and dissipation of thermal radiation; The separation mechanism involved in step 4 is arranged at the bottom of the growth furnace and is used to separate and purify the waste.

[0018] Preferably, the heat preservation mechanism includes a reflective assembly arranged outside the crucible and a heat-insulating assembly arranged outside the reflective assembly, the reflective assembly including a plurality of groups of reflective sheets rotatably connected to the periphery of the crucible, a reel arranged at the bottom of each group of reflective sheets, a reflective film wound on the reel, and a control rod rotatably connected to the top of the reflective sheet and fixedly connected to one end of the reflective film on the control rod; The thermal insulation assembly includes a fixed layer, a plurality of adjustment layers rotatably connected to the outside of the fixed layer and arranged from top to bottom, a lifting ring vertically slidably connected to the outside of the adjustment ring, and an air jet arranged on the inside of the lifting ring.

[0019] As another preferred embodiment, the separation mechanism includes a discharge table vertically slidably connected to the bottom of the crucible, multiple groups of ball mills arranged around the discharge table, an air flow separator arranged inside the ball mill, an electrostatic separator arranged above the air flow separator, and a pickling chamber arranged inside the air flow separator.

[0020] Beneficial effects of the present invention: (1) The present invention provides a free carbon oxidation step, introduces oxygen into the growth furnace, and maintains a high temperature to completely oxidize the excess carbon particles generated after the growth of the silicon carbide waste. Within the temperature gradient within which the free carbon can be oxidized, silicon carbide is not easily oxidized, ensuring that the carbon particles are completely oxidized and removed into carbon dioxide while ensuring that no new impurities are mixed into the residual silicon carbide. (2) The present invention provides a step of directional oxidation of agglomerates, wherein the hard silicon carbide agglomerates formed on the inner sidewall of the growth furnace are first subjected to overall high-temperature oxidation, and then the local agglomerates are struck by physical knocking. This, on the one hand, promotes the rapid shedding of surface agglomerates, and on the other hand, promotes deep silicon carbide agglomerates to contact oxygen and undergo oxidation, thereby ensuring the cleaning efficiency of the sidewall agglomerates. (3) In the present invention, a reflective layer capable of dynamically adjusting the reflection angle and an insulating layer capable of dynamically adjusting the opening ratio are provided through the step of regenerating the insulating layer. The establishment of an axial temperature gradient in the crucible is facilitated by the provision of the reflective layer and the insulating layer. By controlling the temperature dissipation and combining with the input of oxygen from the outside, the silicon carbide crystals in the micropores of the insulating layer are oxidized and removed, thereby achieving the regeneration of the insulating layer and improving the service life of the insulating layer. (4) In the present invention, by setting up a waste separation and purification step, the carbon dioxide generated in the previous oxidation process is recycled and utilized, the carbon dioxide is made into carbonic acid, and the recovered silicon carbide is pickled with carbonic acid, thereby removing metal impurities in the silicon carbide, recycling it, and reducing costs.

[0021] In summary, the equipment has the advantages of being green and environmentally friendly, and is particularly suitable for the field of silicon carbide crystal growth. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 The present invention is a schematic structural diagram of a growth furnace used in a method for recycling residual waste after silicon carbide crystal growth.

[0024] Figure 2 Schematic diagram of the internal structure of the growth furnace.

[0025] Figure 3 Schematic diagram of the oxidation mechanism.

[0026] Figure 4 Schematic cross-section of the oxidation mechanism.

[0027] Figure 5 Schematic diagram of the working status of the control frame.

[0028] Figure 6 Schematic diagram of the position of the reflective layer.

[0029] Figure 7 Schematic diagram of the structure of the reflective layer.

[0030] Figure 8 Schematic diagram of the working state of the reflective layer.

[0031] Figure 9 Schematic diagram of the structure of the insulation layer.

[0032] Figure 10 Schematic diagram of the separation mechanism.

[0033] Figure 11 The present invention is a flow chart of a method for recycling waste materials remaining after silicon carbide crystal growth. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present invention are clearly and completely described below with reference to the accompanying drawings.

[0035] Example 1 like Figure 11 As shown, a method for recovering waste remaining after silicon carbide crystal growth comprises the following steps: Step 1: Free carbon oxidation, wherein the free carbon is oxidized in an oxidizing atmosphere to generate gaseous carbon dioxide; Step 2: Directional oxidation of agglomerates, which involves oxidizing the silicon carbide agglomerates into silicon oxide powder through directed oxygen flow combined with physical vibration; Step 3: Regeneration of the insulation layer, external oxygen directional oxidation of the micropores of the insulation layer to participate in silicon carbide and generate silicon oxide; Step 4: separation and purification of waste materials, particle size classification of the recovered powder, and electrostatic separation and weak acid washing to obtain high-purity silicon carbide powder and silicon oxide powder; Step 5: Resynthesize the raw materials. The recovered silicon carbide powder is mixed with different proportions, mixed with unmixed silicon powder and carbon powder according to the process proportion, and then a secondary synthesis is carried out in the silicon carbide raw material synthesis path.

[0036] In the free carbon oxidation step, excess oxygen is introduced into the crucible, the temperature is raised to 600-800° C. at a rate of 5° C. / min and kept at that temperature for 2 hours, and the oxygen concentration is greater than 10%.

[0037] In this embodiment, the free carbon in the waste is removed by high-temperature oxidation. By controlling the temperature and oxygen concentration, the free carbon therein is encouraged to fully react while avoiding oxidation of the residual silicon carbide, and carbon dioxide rather than carbon monoxide is produced.

[0038] The agglomeration directional oxidation step comprises the following steps: A. Heat the crucible to 1100-1200℃ and keep it warm for 15 minutes; B. Move the oxygen injection port close to the side wall of the agglomerate and continue to spray oxygen at multiple points; C. The grinding wheel 16 moves along the side wall to grind the surface silicon oxide, promoting the shedding of silicon oxide and the oxidation of deep silicon carbide.

[0039] In this embodiment, the crucible is further heated to reach the temperature range for silicon carbide oxidation to achieve oxidation of silicon carbide. The physical crushing of the grinding wheel 16 and the impact of the airflow generated by the oxygen injection port are used to promote the rapid shedding of silicon oxide and accelerate the oxidation of deep silicon carbide.

[0040] The thermal insulation layer regeneration step comprises the following steps: a. While step A is being performed, the reflective layer of the inner layer of the insulation layer is opened to heat the insulation layer; b. The opening rate of the insulation layer is adjusted to the maximum, and oxygen is introduced from the outer layer of the insulation layer; c. The silicon carbide in the gaps of the insulation layer is oxidized into silicon oxide and collected; In this embodiment, by adjusting the porosity of the insulation layer and the reflection angle of the reflection layer, the inside of the insulation layer can also be rapidly heated. At the same time, oxygen is passed from the outside. The oxygen passes through the micropores of the insulation layer, oxidizes the silicon carbide and takes it out of the micropores, thereby achieving the cleaning and regeneration of the insulation layer.

[0041] The waste separation and purification step comprises the following steps: ①. After step 1, the remaining silicon carbide at the bottom of the crucible is recovered and crushed and sieved again.

[0042] ②. The mixed powder of silicon oxide and silicon carbide formed in step 2 and step 3 is crushed and ground to D 50 ≤10μm, then the powder is classified by air flow according to density, and then silicon carbide and silicon oxide are further separated by high-voltage electric separation, and the silicon oxide is output; ③ A carbonic acid solution is used to pickle silicon carbide to remove metal impurities therein. The carbonic acid solution is obtained by passing the carbon dioxide generated in steps 1, 2 and 3 into an aqueous solution containing carbonic anhydrase.

[0043] Due to the large difference in density and hardness between silicon carbide and silicon oxide, after grinding, silicon carbide can be enriched into coarse powder and silicon oxide can be enriched into fine powder. The coarse powder and fine powder are then preliminarily separated by airflow, and then further separated by high-voltage electric separation. Finally, the carbon dioxide generated in the previous step is converted into carbonic acid, which is used to pickle the silicon carbide to remove metal impurities and complete the recovery of silicon carbide.

[0044] The raw material resynthesis step comprises the following steps: (1) The used silicon carbide raw materials were crushed and screened, and silicon carbide powder with a particle size of less than 0.18 mm was screened out using an 80-mesh nylon screen and collected.

[0045] (2) The silicon carbide powder synthesized by the high-temperature self-propagating method was crushed and sieved, and the silicon carbide powder with a particle size of less than 0.18 mm was screened out using an 80-mesh nylon screen and collected.

[0046] (3) High-purity carbon powder and high-purity silicon powder are mixed with silicon carbide powder in an atomic molar ratio of 1:1, and mixed for 8 hours using a mixer at a speed of 30 revolutions per minute.

[0047] (4) The collected silicon carbide fine powder and the mixed silicon carbide powder were mixed in a mass ratio of 1:9, and mixed at a speed of 30 revolutions per minute using a mixer for 4 hours.

[0048] (5) Charging the furnace: Place the mixed raw materials into the crucible and load the furnace.

[0049] (6) Raw material synthesis.

[0050] The (6) raw material synthesis comprises the following steps: Ⅰ. Gas washing: Use a vacuum pump to evacuate the furnace chamber to a pressure of <1×10-4Pa, maintain this pressure for 4 hours, introduce Ar, and increase the furnace chamber pressure to 60kPa~80kPa, maintaining the pressure for 1h~3h minutes; Ⅱ. Second gas purge: Use a vacuum pump to evacuate the furnace chamber to a pressure of <1×10-4Pa, maintain this pressure for 4 hours, introduce Ar, and increase the furnace chamber pressure to 60kPa~80kPa, maintaining the pressure for 2h~5h minutes; III. Heating: Under a pressure of 50kPa~800kPa, raise the temperature to 600℃~800℃ at a heating rate of 1℃ / min~10℃ / min and maintain for 1h~2h; continue heating, control the temperature at 1300℃~1400℃, and evacuate with a mechanical pump, maintaining for 5~7h. Under this condition, the silicon carbide powder is removed to the maximum extent possible; within 2h~3h, raise the temperature to 2200℃ and maintain for 15h~25h. Synthesize the silicon carbide powder using the high-temperature self-propagating method; Ⅳ. Cooling, maintaining the furnace chamber pressure at 2kPa~20kPa, adjusting the gas flow rate introduced through the graphite pipe, maintaining the argon flow rate at 200sccm~800sccm and cooling; when the temperature drops to room temperature, then directly introduce argon into the furnace chamber to atmospheric pressure, open the furnace door and remove the raw materials; V. Post-processing of raw materials: crushing, screening, cleaning, drying and packaging the taken out silicon carbide.

[0051] In this embodiment, by setting up three steps of free carbon oxidation, agglomeration directional oxidation, and insulation layer regeneration, the waste recovery of the inner wall of the growth furnace and the insulation layer is achieved, while improving the waste recovery rate and ensuring the cleanliness of the growth furnace.

[0052] Specifically, when the gas phase reaches the relatively cool furnace sidewalls or crucible walls, its temperature drops dramatically. At the cold wall, the supersaturation of the gas phase increases significantly, disrupting the chemical reaction equilibrium. These gas molecules lose their stability and undergo deposition reactions or condensation directly onto the cooler wall material, forming solid Si-C compounds. Liquid silicon, with a relatively high silicon content, comes into contact and reacts with the solid carbon, ultimately forming a new SiC layer that clings to the existing sidewalls, forming a hard crust.

[0053] At the same time, in addition to flowing toward the sidewalls, some of the gaseous matter also accompanies the airflow into (or reaches through diffusion) the edge areas of the insulation material. The insulation material has a porous structure, allowing these gas molecules to penetrate into the pore network of the insulation material. When they penetrate deep into the insulation material, the ambient temperature is significantly lower than the temperature required to maintain the gaseous state. In the relatively low temperature and confined pore space, these gaseous substances directly undergo a gas-solid phase transition, transforming into tiny solid crystals. Because these depositions occur deep within the pores or even in dead spaces, the newly formed SiC nanocrystals firmly adhere to the fibers / pore walls of the insulation material, forming residues that are difficult to remove using conventional physical methods.

[0054] This application introduces oxygen into the growth furnace and uses high-temperature oxidation to oxidize the residual silicon carbide into silicon oxide. The oxidation process causes volume expansion and generates carbon dioxide. The escaping carbon dioxide forms a porous structure within the silicon oxide. Compared to silicon carbide, the carbon dioxide is harder and chemically inert, making it easier to clean. This promotes the shedding of silicon carbide agglomerates on the sidewalls and the discharge of silicon carbide within the insulation layer.

[0055] At the same time, in the silicon carbide PVT method for crystal growth, due to the high temperature in the later stage of crystal growth and the different evaporation temperatures of the silicon and carbon components of the silicon carbide powder, excess carbon particles remain in the later stage of crystal growth. These carbon particles are removed by producing carbon dioxide through high-temperature oxidation.

[0056] Example 2 like Figures 1-10 As shown, the components identical or corresponding to those in the first embodiment are designated by the corresponding reference numerals in the first embodiment. For simplicity, only the differences from the first embodiment are described below. The second embodiment differs from the first embodiment in that: Further, if Figure 1 、 Figure 2 、 Figure 3 、 Figure 4 、 Figure 5 As shown, the oxidation mechanism 1 involved in the step 2 is arranged inside the growth furnace and is used to directionally control the output of oxygen; The oxidation mechanism 1 includes two sets of sealing covers 11 horizontally slidably connected to both sides of the upper part of the crucible, a cover plate 12 vertically slidably connected to the top of the crucible, an air outlet 13 arranged at the edge of the cover plate 12, a control frame 14 vertically slidably connected to the cover plate 12, an air injection ring 15 rotatably connected to the control frame 14, multiple sets of rollers 16 evenly arranged around the control frame 14, and multiple sets of balls 17 evenly arranged around the paint spraying ring; The heat preservation mechanism 2 involved in step 3 is arranged outside the crucible and is used to dynamically control the collection and dissipation of thermal radiation; The separation mechanism 3 involved in step 4 is arranged at the bottom of the growth furnace and is used to separate and purify the waste.

[0057] In this embodiment, the interior of the growth furnace includes a crucible and an insulation layer, wherein silicon carbide is adhered to the side wall of the crucible, an openable furnace cover is provided on the growth furnace, a vertically movable support plate for crystal growth is provided on the furnace cover, a closing cover is fixed on the support plate, a cover plate 12 is vertically slidably connected to the furnace cover, and a sealing cover 11 slides horizontally on both sides of the top of the crucible.

[0058] In detail, when the crystal grows, the support plate moves down, and the sealing covers 11 on both sides slide closed to form a seal together with the closing cover. After the crystal growth is completed and the crystal is taken out, the furnace cover is closed, the control frame 14 enters the crucible, the cover plate 12 moves down and forms a seal with the closing cover again. After oxidation is completed, the control frame 14 continues to move down, and the air injection ring 15 on it rotates at the same time. The control frame 14 moves down, and the control frame 14 moves down. The grinding wheel 16 on it rolls over the agglomerates on the side wall surface, causing the agglomerates to crack. At the same time, a plurality of balls 17 are provided on the air injection ring 15. The balls 17 are arranged on the outside of the air injection ring 15 through a telescopic rod and a spring. When the air injection ring 15 rotates, the balls 17 squeeze and crush the agglomerates on the side wall surface, thereby causing the agglomerates on the surface to fall off quickly, improving the cleanliness of the side wall and avoiding a large amount of residue. The air injection ring 15 sprays oxygen. On the one hand, the oxygen is directly sprayed on the surface of the agglomerate, thereby promoting the contact between the inside of the agglomerate and the oxygen, thereby quickly oxidizing. On the other hand, the impact force of the air flow is used to accelerate the falling off of the agglomerate.

[0059] It should be noted that an air outlet 13 is provided at the edge of the lower bottom surface of the cover plate 12 to output oxygen downward. Oxygen is released downward through the air outlet 13, thereby enabling oxygen to quickly contact the agglomerates on the side wall surface, and at the same time blow the dust generated by the falling of the agglomerates downward to reduce the upward movement.

[0060] It is worth mentioning that an exhaust port is provided in the middle of the cover plate 12 to control the gas concentration in the crucible, thereby removing the carbon dioxide produced by the oxidation reaction from the tube and utilizing it.

[0061] like Figure 6 、 Figure 7 、 Figure 8 、 Figure 9 As shown, the heat preservation mechanism 2 includes a reflective assembly 21 arranged outside the crucible and a heat insulation assembly 22 arranged outside the reflective assembly 21. The reflective assembly 21 includes multiple groups of reflective sheets 211 rotatably connected to the four sides of the crucible, a reel 212 arranged at the bottom of each group of reflective sheets 211, a reflective film 213 wound on the reel 212, and a control rod 214 rotatably connected to the top of the reflective sheet 211, with one end of the reflective film 213 fixedly connected to the control rod 214. The thermal insulation assembly 22 includes a fixed layer 221, a plurality of adjustment layers 222 rotatably connected to the outside of the fixed layer 221 and arranged from top to bottom, a lifting ring 223 vertically slidably connected to the outside of the adjustment ring, and an air jet 224 arranged on the inside of the lifting ring.

[0062] In this embodiment, by providing a dynamically adjustable reflective layer and an insulating layer, protection against thermal radiation and adjustment of the opening rate are achieved, so that the thermal insulation layer can be more adapted to the heat distribution requirements during crystal growth and waste recycling.

[0063] In detail, during the crystal growth process, the heat in the furnace presents a vertical temperature gradient. The heat source is located at the bottom of the furnace body and is provided with energy by an induction coil or a resistance heater to form a high-temperature core area. The heat energy is transferred to the interior of the furnace cavity by thermal radiation and gas convection.

[0064] The insulation layer arranged on the outside of the crucible can be divided into three layers: the innermost layer is the reflective layer, the middle layer is high-density carbon felt, and the outer layer is soft graphite felt. The inner reflective layer is usually made of tantalum foil to reflect infrared radiation to the crucible.

[0065] The core purpose of the opening design of the insulation layer is to establish an axial temperature gradient: the openings form local heat dissipation channels, forcing heat to escape vertically. This creates a decreasing temperature difference within the furnace from the high-temperature raw material zone at the bottom to the low-temperature seed crystal zone at the top, driving the directional diffusion and deposition growth of SiC vapor toward the seed crystal. The porosity of the insulation layer is the percentage of the opening area to the total surface area of ​​the insulation layer. A low porosity results in insufficient heat dissipation, a weak axial temperature gradient, slowed gas phase transport, and reduced crystal growth. A high porosity results in rapid heat dissipation, resulting in overcooling at the top, premature gas phase deposition, and the formation of polycrystalline or inclusions. Therefore, it is necessary to set an ideal porosity.

[0066] Based on this, multiple groups of reflective components 21 are set on the outside of the crucible, and each group of reflective components 21 is provided with multiple groups of reflective sheets 211. The angles of each reflective sheet 211 are controlled by a motor or other device, so that the heat radiation is concentrated to the bottom of the crucible, thereby assisting in the formation of a temperature gradient. At the same time, since the angles between the reflective sheets 211 are different, a reel 212 is set on the reflective sheet 211, and a reflective film 213 is rolled up on the reel 212. The outer end of the reflective film 213 is fixed on the control rod 214, and the control rod 214 rotates the reel 212 set at the bottom. On the reflective sheet 211, when crystals are growing, the reflective sheet 211 is rotated to a preset angle. At this time, the control rod 214 is tightly attached to the reflective sheet 211 below, pulling open the reflective film 213, and using the reflective film 213 to seal the pores in the middle of each group of reflective sheets 211. When the crystal growth is completed and the insulation layer is regenerated, the reflective sheet 211 is opened, and the control rod 214 is rotated at the same time to fully open the pores in the middle of the reflective sheet 211, so that heat radiation is dissipated, heating the insulation layer in the middle, and thus oxidizing the silicon carbide in the pores of the insulation layer.

[0067] Meanwhile, the insulation layer outside the reflective layer has openings inside. By configuring the insulation layer as a double layer, with the outer layer arranged in multiple groups from top to bottom and rotatable along the center, the openings in the inner and outer layers align, connecting the openings and increasing the porosity. Misalignment reduces the porosity. By configuring multiple groups, different porosity ratios can be achieved, thereby achieving an axial temperature gradient.

[0068] A lifting ring 223 is provided outside the insulation layer. An air outlet 13 is provided inside the lifting ring 223. The air outlet 13 outputs oxygen. The oxygen passes through the openings to oxidize the silicon carbide in the openings and is taken out by airflow.

[0069] like Figure 10 As shown, the separation mechanism 3 includes a discharge table 31 vertically slidably connected to the bottom of the crucible, a plurality of ball mills 32 arranged around the discharge table 31, an air flow separator 33 arranged inside the ball mill 32, an electrostatic separator 34 arranged above the air flow separator 33, and a pickling chamber 35 arranged inside the air flow separator 33.

[0070] In this embodiment, an electrostatic separator 34 and a pickling chamber 35 are provided to separate silicon oxide and silicon carbide, and then impurities are removed from the silicon carbide.

[0071] In detail, the discharge table 31 is set at the bottom of the crucible and can move up and down. After the free carbon oxidation step, the discharge table 31 moves down, and the silicon carbide waste therein is input into the ductile iron mill for crushing, and then collected. After the agglomeration, directional peroxidation and insulation layer regeneration, the discharge table 31 moves down again, so that the upper silicon oxide and silicon carbide fall into the ball mill 32 below for crushing. Due to the difference in hardness between silicon oxide and silicon carbide, silicon oxide is enriched in fine powder and silicon carbide is enriched in coarse powder. It is output from the ball mill 32 to the air flow separator 33. After passing through the air flow separator 33, it is finely divided and output to the electrostatic separator 34 for further precise separation. The obtained silicon carbide powder enters the pickling chamber 35, is pickled with carbonic acid, and is output together with silicon oxide after removing metal impurities. Silicon carbide is synthesized as raw material.

[0072] It should be noted that the carbonic acid used for pickling is prepared from the carbon dioxide generated by oxidation in steps one, two and three. By passing the carbon dioxide into an aqueous solution containing carbonic anhydrase, efficient preparation of carbonic acid can be achieved, and then the carbonic acid is introduced into the pickling chamber 35 to pickle the silicon carbide.

[0073] It should be noted that since the oxidation mechanism 1, the heat preservation mechanism 2 and the separation mechanism 3 are all arranged inside the electromagnetic coil, the mechanical components in the device need to be isolated and shielded to prevent damage caused by coil heating.

[0074] In the description of the present invention, it should be understood that the terms "front and back", "left and right", etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the equipment or components referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they cannot be understood as limitations on the invention.

[0075] Of course, in this technical solution, those skilled in the art should understand that the term "one" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element may be one, while in another embodiment, the number of the element may be multiple, and the term "one" should not be understood as a limitation on the quantity.

[0076] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art based on the technical guidance of the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for recovering waste remaining after silicon carbide crystal growth, characterized in that: The following steps are involved: Step 1: Free carbon oxidation, wherein the free carbon is oxidized in an oxidizing atmosphere to generate gaseous carbon dioxide; Step 2: Directional oxidation of agglomerates, which involves oxidizing the silicon carbide agglomerates into silicon oxide powder through directed oxygen flow combined with physical vibration; Step 3: Regeneration of the insulation layer, directing oxygen flow from the outside to oxidize the silicon carbide in the micropores of the insulation layer and generate silicon oxide; Step 4: separation and purification of waste materials, particle size classification of the recovered powder, and electrostatic separation and weak acid washing to obtain high-purity silicon carbide powder and silicon oxide powder; Step 5: Resynthesize the raw materials. The recovered silicon carbide powder is mixed with different proportions, mixed with unmixed silicon powder and carbon powder according to the process proportion, and then a secondary synthesis is carried out in the silicon carbide raw material synthesis path.

2. The method for recycling residual waste after silicon carbide crystal growth according to claim 1, characterized in that: In the free carbon oxidation step, excess oxygen is introduced into the crucible, the temperature is raised to 600-800° C. at a rate of 5° C. / min and kept at that temperature for 2 hours, and the oxygen concentration is greater than 10%.

3. The method for recycling residual waste after silicon carbide crystal growth according to claim 2, characterized in that: The agglomeration directional oxidation step comprises the following steps: A. Heat the crucible to 1100-1200℃ and keep it warm for 15 minutes; B. Move the oxygen injection port close to the side wall of the agglomerate and continue to spray oxygen at multiple points; C. Roll the surface silicon oxide to promote the shedding of silicon oxide and oxidation of deep silicon carbide.

4. The method for recycling residual waste after silicon carbide crystal growth according to claim 1, characterized in that: The thermal insulation layer regeneration step comprises the following steps: a. While step A is being performed, the reflective layer of the inner layer of the insulation layer is opened to heat the insulation layer; b. The opening rate of the insulation layer is adjusted to the maximum, and oxygen is introduced from the outer layer of the insulation layer; c. Silicon carbide in the gaps of the insulation layer is oxidized into silicon oxide and collected.

5. The method for recycling waste remaining after silicon carbide crystal growth according to claim 1, characterized in that: The waste separation and purification step comprises the following steps: ① After step one, the remaining silicon carbide at the bottom of the crucible is recovered and crushed and sieved again; ②. The mixed powder of silicon oxide and silicon carbide formed in step 2 and step 3 is crushed and ground to D 50 ≤10μm, then the powder is classified by air flow according to density, and then silicon carbide and silicon oxide are further separated by high-voltage electric separation, and the silicon oxide is output; ③ A carbonic acid solution is used to pickle silicon carbide to remove metal impurities therein. The carbonic acid solution is obtained by passing the carbon dioxide generated in steps 1, 2 and 3 into an aqueous solution containing carbonic anhydrase.

6. The method for recycling residual waste after silicon carbide crystal growth according to claim 1, characterized in that: The raw material resynthesis step comprises the following steps: (1) Crushing and screening the used silicon carbide raw materials, using an 80-mesh nylon screen to screen out silicon carbide powder with a particle size of less than 0.18 mm and collect it; (2) The silicon carbide powder synthesized by the high-temperature self-propagating method was crushed and sieved, and the silicon carbide powder with a particle size of less than 0.18 mm was screened out using an 80-mesh nylon screen and collected; (3) High-purity carbon powder and high-purity silicon powder are mixed with silicon carbide powder in an atomic molar ratio of 1:1, and mixed in a mixer at a speed of 30 revolutions per minute for 8 hours; (4) The collected silicon carbide fine powder and the mixed silicon carbide powder were mixed in a mass ratio of 1:9, and mixed at a speed of 30 revolutions per minute using a mixer for 4 hours; (5) Charging the furnace: Put the mixed raw materials into the crucible and load the furnace; (6) Raw material synthesis.

7. The method for recycling residual waste after silicon carbide crystal growth according to claim 6, characterized in that: The (6) raw material synthesis comprises the following steps: Ⅰ. Gas washing: Use a vacuum pump to evacuate the furnace chamber to a pressure of <1×10-4Pa, maintain this pressure for 4 hours, introduce Ar, and increase the furnace chamber pressure to 60kPa~80kPa, maintaining the pressure for 1h~3h minutes; Ⅱ. Second gas purge: Use a vacuum pump to evacuate the furnace chamber to a pressure of <1×10-4Pa, maintain this pressure for 4 hours, introduce Ar, and increase the furnace chamber pressure to 60kPa~80kPa, maintaining the pressure for 2h~5h minutes; III. Heating: Under a pressure of 50 kPa to 800 kPa, raise the temperature to 600°C to 800°C at a heating rate of 1°C / min to 10°C / min and maintain for 1 to 2 hours; continue heating, control the temperature at 1300°C to 1400°C, and evacuate with a mechanical pump for 5 to 7 hours, in which state the silicon carbide powder is removed to the maximum extent possible; raise the temperature to 2200°C within 2 to 3 hours and maintain for 15 to 25 hours; and synthesize the silicon carbide powder by a high-temperature self-propagating method; Ⅳ. Cooling, maintaining the furnace chamber pressure at 2kPa~20kPa, adjusting the gas flow rate introduced through the graphite pipe, maintaining the argon flow rate at 200sccm~800sccm and cooling; when the temperature drops to room temperature, then directly introduce argon into the furnace chamber to atmospheric pressure, open the furnace door and remove the raw materials; V. Post-processing of raw materials: crushing, screening, cleaning, drying and packaging the taken out silicon carbide.

8. The method for recycling residual waste after silicon carbide crystal growth according to claim 1, characterized in that: The oxidation mechanism (1) involved in step 2 is arranged inside the growth furnace and is used to directionally control the output of oxygen; The oxidation mechanism (1) comprises two sets of sealing covers (11) horizontally slidably connected to both sides of the crucible, a cover plate (12) vertically slidably connected to the top of the crucible, an air outlet (13) arranged at the edge of the cover plate (12), a control frame (14) vertically slidably connected to the cover plate (12), an air jet ring (15) rotatably connected to the control frame (14), a plurality of rollers (16) evenly arranged around the control frame (14), and a plurality of balls (17) evenly arranged around the spray ring. The heat preservation mechanism (2) involved in step 3 is arranged outside the crucible and is used to dynamically control the collection and dissipation of thermal radiation; The separation mechanism (3) involved in step 4 is arranged at the bottom of the growth furnace and is used to separate and purify the waste.

9. The method for recycling waste remaining after silicon carbide crystal growth according to claim 8, characterized in that: The heat preservation mechanism (2) comprises a reflective assembly (21) arranged outside the crucible and a heat insulation assembly (22) arranged outside the reflective assembly (21), wherein the reflective assembly (21) comprises a plurality of groups of reflective sheets (211) rotatably connected to the periphery of the crucible, a reel (212) arranged at the bottom of each group of reflective sheets (211), a reflective film (213) wound on the reel (212), and a control rod (214) rotatably connected to the top of the reflective sheet (211), with one end of the reflective film (213) fixedly connected to the control rod (214); The thermal insulation assembly (22) comprises a fixed layer (221), a plurality of adjustment layers (222) rotatably connected to the outside of the fixed layer (221) and arranged from top to bottom, a lifting ring (223) vertically slidably connected to the outside of the adjustment ring, and an air jet (224) arranged on the inside of the lifting ring.

10. The method for recycling waste remaining after silicon carbide crystal growth according to claim 8, characterized in that: The separation mechanism (3) includes a discharge table (31) vertically slidably connected to the bottom of the crucible, a plurality of ball mills (32) arranged around the discharge table (31), an air flow separator (33) arranged inside the ball mill (32), an electrostatic separator (34) arranged above the air flow separator (33), and a pickling chamber (35) arranged inside the air flow separator (33).

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