Silicon carbide powder and preparation method thereof

Abstract

The invention belongs to the field of silicon carbide crystal growth, and particularly relates to silicon carbide powder and a preparation method thereof. The method comprises the steps that reaction raw materials are added into a crucible, the reaction raw materials comprise a plurality of composite material layers arranged in a stacked mode, and each composite material layer comprises a silicon powder layer, a carbon powder layer and a silicon carbide seed crystal layer which are sequentially arranged in a stacked mode; and heating and synthesizing the crucible containing the composite material layer to obtain the silicon carbide powder. The method is simple to operate, and the prepared silicon carbide powder has both large size and high purity.

Description

Technical Field

[0001] The present invention relates to the field of silicon carbide crystal growth, and specifically to a silicon carbide powder and a preparation method thereof. Background Art

[0002] In the field of silicon carbide crystal growth, silicon carbide powder is the core raw material that determines crystal quality. Large-particle silicon carbide powder, particularly due to its superior sublimation uniformity during the crystal growth process, is a key prerequisite for improving silicon carbide crystal quality. However, current conventional silicon carbide powder synthesis processes have significant limitations. To increase the particle size of the synthesized powder to meet the large particle size requirement, the reaction temperature must be increased and the synthesis time must be prolonged. However, this approach results in significant silicon loss, significantly reducing the yield of silicon carbide powder and making it difficult to strike a balance between particle size and yield. Furthermore, the preparation of high-purity silicon carbide powder requires hydrogen to participate in the reaction. In existing processes, hydrogen gradually permeates through the outer insulation layer and the crucible into the reaction zone, resulting in extremely low permeation efficiency. Most of the hydrogen is discharged from the system with the purge gas before entering the crucible to participate in the reaction. This not only results in waste of hydrogen raw material, but also, due to insufficient hydrogen supply in the reaction zone, it can easily lead to failure in the synthesis of high-purity powder, further hindering the stable production of high-purity, large-sized silicon carbide powder. Therefore, the preparation method of silicon carbide powder needs further improvement. Summary of the Invention

[0003] The present application aims to solve at least one of the technical problems in the related art to a certain extent. To this end, the present application proposes a large-sized, high-purity silicon carbide powder and a preparation method thereof.

[0004] In a first aspect of the present application, a method for preparing silicon carbide powder is proposed, which comprises: adding reaction raw materials into a crucible, wherein the reaction raw materials include a plurality of stacked composite material layers, each of the composite material layers includes a silicon powder layer, a carbon powder layer and a silicon carbide seed layer stacked in sequence; heating and synthesizing the crucible containing the composite material layers to obtain silicon carbide powder.

[0005] The present application achieves efficient and uniform synthesis of large-sized silicon carbide powder by setting up a composite material layer with a stacked structure. On the one hand, since the vaporization temperature of silicon powder is relatively low, during the reaction process, the silicon powder in the bottom layer first vaporizes at high temperature to form gaseous silicon. The gaseous silicon rises and reacts chemically with the carbon powder to generate gaseous silicon carbide. Subsequently, the gaseous silicon carbide sublimates to the silicon carbide seed crystal area and begins to crystallize and grow. As the reaction proceeds, the growing silicon carbide vaporizes again and continues to move upward driven by the axial temperature gradient, and recrystallizes in a higher temperature area. Through repeated recrystallization processes, the particle size of the silicon carbide powder will continue to increase, and eventually an ideal large-sized silicon carbide powder is obtained. On the other hand, the stacked composite material layers can not only ensure that the reaction raw materials are fully contacted and reacted during the heating process, but also can effectively control the order and rate of the reaction, thereby making the reaction more uniform and further improving the purity and performance consistency of the silicon carbide powder.

[0006] According to an embodiment of the present application, the molar ratio of the silicon powder in the silicon powder layer to the carbon powder in the carbon powder layer is 1:1-1.2:1. Therefore, within the above molar ratio range, the silicon powder and carbon powder are facilitated to fully react, thereby improving the utilization rate of the raw materials.

[0007] According to an embodiment of the present application, the mass ratio of the silicon carbide seeds in the silicon carbide seed layer to the reaction raw materials is 1%-10%, specifically 3%-7%. Therefore, within the above mass ratio range, it helps to promote the crystal growth of silicon carbide powder and improve the purity and performance consistency of the product.

[0008] According to an embodiment of the present application, the particle size of the silicon powder in the silicon powder layer is 0.5 mm to 5 mm, and more specifically, the particle size of the silicon powder is 1 mm to 3 mm. Therefore, a suitable silicon powder particle size helps slow down the gasification rate of silicon during the reaction, thereby reducing silicon loss and improving raw material utilization.

[0009] According to an embodiment of the present application, the purity of the silicon powder is ≥99.99999999%, thereby facilitating the production of silicon carbide powder with higher purity.

[0010] According to an embodiment of the present application, the carbon powder in the carbon powder layer has a particle size of 10 μm to 100 μm, and more specifically, a particle size of 20 μm to 60 μm. Therefore, a suitable carbon powder particle size helps ensure that the carbon powder and silicon powder can fully contact and react during the reaction process, thereby improving reaction efficiency and the purity of the silicon carbide powder.

[0011] According to an embodiment of the present application, the purity of the carbon powder is ≥99.9999%, thereby facilitating the production of silicon carbide powder with higher purity.

[0012] According to embodiments of the present application, the particle size of the silicon carbide seeds in the silicon carbide seed layer is 0.2mm-1mm, and specifically, the particle size of the silicon carbide seeds is 0.3mm-0.6mm. In this way, the appropriate particle size of the silicon carbide seeds helps to provide sufficient surface area to promote uniform crystallization and growth of the silicon carbide powder, thereby improving the purity and performance consistency of the silicon carbide powder.

[0013] According to embodiments of the present application, the purity of the silicon carbide seeds is ≥99.9999%. In this way, it is helpful to generate silicon carbide powder with high purity.

[0014] According to embodiments of the present application, the number of the composite material layers is 3-7, and specifically, the number of the composite material layers is 3-5. In this way, the process flow can be simplified while ensuring the synthesis effect, so as to improve the production efficiency and reduce the operation complexity.

[0015] According to embodiments of the present application, the heating synthesis includes purging, one-stage synthesis and two-stage synthesis performed in sequence. In this way, in the purging stage, a large amount of mixed gas is used to purge the furnace cavity and the hot field of the silicon carbide growth device to remove air and impurities therein, so as to ensure the purity of the reaction environment. Subsequently, in the one-stage synthesis stage, the silicon carbide powder is preliminarily synthesized by reacting under high pressure conditions. Finally, in the two-stage synthesis stage, the small particles of the silicon carbide powder are continuously vaporized and recrystallized, and through this process, the large-size silicon carbide powder is finally obtained.

[0016] According to embodiments of the present application, the total amount of the purging mixed gas introduced in the purging stage is less than the total amount of the first mixed gas introduced in the one-stage synthesis stage. In this way, the total amount of the gas in the purging stage is sufficient to remove impurities in the furnace cavity and the hot field, and more mixed gas is introduced in the one-stage synthesis stage, which is conducive to sufficient hydrogen participating in the reaction to promote the vaporization and reaction of the silicon powder and the carbon powder to generate silicon carbide.

[0017] According to embodiments of the present application, the proportion of hydrogen in the purging mixed gas is greater than the proportion of hydrogen in the first mixed gas. In this way, the higher proportion of hydrogen in the purging stage helps to more efficiently remove impurities in the hot field. The lower proportion of hydrogen in the first mixed gas is because the reaction of hydrogen with the hot field material (such as graphite) will cause the loss and structural damage of the hot field material, affecting the stability and service life of the hot field. By reducing the proportion of hydrogen in the first mixed gas, the erosion can be reduced, while still ensuring sufficient hydrogen to participate in the reaction.

[0018] According to embodiments of the present application, the proportion of hydrogen in the second mixed gas introduced in the two-stage synthesis stage is lower than the proportion of hydrogen in the first mixed gas. In this way, it is helpful to reduce the erosion of the hot field structure by hydrogen, thereby maintaining the stability of the reaction temperature.

[0019] According to an embodiment of the present application, the pressure of the second-stage synthesis is lower than that of the first-stage synthesis. This increases the axial temperature gradient, prompting small-particle silicon carbide powder and some incompletely reacted silicon powder and carbon powder to sublime upward, allowing them to continue to react or recrystallize, thereby obtaining large-particle silicon carbide powder.

[0020] According to an embodiment of the present application, the purging comprises: introducing a purging gas mixture containing hydrogen and argon at a temperature below 1200°C, and maintaining the pressure at 500mbar, 100mbar, and 10mbar for 30-60 minutes respectively. The pressure is then backfilled to 100mbar and 500mbar and maintained for 30-60 minutes respectively, and then vacuumed to 10 -6 mbar.

[0021] This helps hydrogen fully react with impurities such as oxygen and nitrogen within the aforementioned timeframe. Argon also dilutes the hydrogen, reducing its concentration and the rate at which it reacts with the thermal field materials, thereby minimizing thermal field losses and providing a pure environment for subsequent processes. Furthermore, gradually reducing the pressure prevents damage to the thermal field caused by drastic pressure changes. Gradually backfilling the pressure and maintaining it for a certain period of time can reduce thermal stress in the thermal field and equipment caused by drastic pressure changes, while ensuring a stable reaction environment and reducing fluctuations in the reaction environment caused by pressure and temperature changes. This helps improve reaction stability and repeatability.

[0022] According to an embodiment of the present application, the flow ratio of hydrogen to argon in the mixed gas is 15:85-30:70, specifically 20:80-30:70, thereby ensuring that impurities are completely removed while also helping to reduce hydrogen erosion of the thermal field structure.

[0023] According to an embodiment of the present application, the one-stage synthesis includes: raising the temperature to 1800°C-2000°C within 2h-4h (specifically, within 2h-3h), maintaining the pressure at 200mbar-500mbar (specifically, the pressure is 200mbar-300mbar), introducing a first mixed gas containing hydrogen and argon, and heating the synthesis time for 10h-20h.

[0024] Therefore, reaching the desired synthesis temperature within the aforementioned heating time allows for the timely locking of silicon gas, allowing it to fully react with carbon and prevent its loss. Within this temperature range, silicon powder and carbon powder achieve high vaporization and reaction rates, allowing for full reaction to produce high-purity β-silicon carbide. Higher pressures, on the other hand, reduce the vaporization and loss of silicon atoms, ensuring more silicon atoms participate in the reaction and improving raw material utilization.

[0025] According to the embodiments of the present application, the flow ratio of hydrogen and argon in the first mixed gas is 30:170-40:160. Thus, within the above range, hydrogen is fully involved in the growth reaction of silicon carbide, while the excessive hydrogen is quickly removed, avoiding excessive erosion of the hot field. If the proportion of hydrogen is too high, the structure of the hot field may be damaged, thereby reducing the service life of the equipment; if the proportion of argon is too large, the concentration of hydrogen will be reduced, and the reaction rate of silicon carbide growth may be slowed down, resulting in a prolonged reaction time.

[0026] According to the embodiments of the present application, the second synthesis includes: heating to 2000-2200℃ within 0.5-1h (specifically, within 2-3h), maintaining the pressure at 50-100mbar (specifically, the pressure is 60-80mbar), and flowing in the second mixed gas containing hydrogen and argon, and the heating synthesis time is 15-40h (specifically, the synthesis time is 20-25h).

[0027] Thus, within the above temperature range and pressure range, it is easier for small particles of silicon carbide powder to be gasified and recrystallized. And sufficient synthesis time also helps to generate large-size silicon carbide powder.

[0028] According to the embodiments of the present application, the flow ratio of hydrogen and argon in the second mixed gas is 10:190-20:180, and specifically, the flow ratio is 10:190-15:185. Thus, within the above range, hydrogen is fully involved in the growth reaction of silicon carbide, while avoiding excessive erosion of hydrogen to the hot field.

[0029] According to the embodiments of the present application, at least one of the following conditions is met: the purity of the hydrogen is ≥99.9999999%; the purity of the argon is ≥99.9999999%. Thus, the above purity can reduce the mixing of impurities, improve the selectivity and efficiency of the reaction, and thereby improve the purity of the silicon carbide powder.

[0030] In the second aspect of the present application, a silicon carbide powder is provided, which is prepared by the method described above. All the features and advantages of the silicon carbide powder are consistent with the method described above, and will not be repeated here.

[0031] According to the embodiments of the present application, the particle size of the silicon carbide powder is 10-30mm. Thus, the large-size silicon carbide powder particles have higher mechanical strength and thermal conductivity, making them have wide application prospects in the fields of optical devices, electronic devices, high-temperature-resistant materials, etc.

[0032] According to the embodiments of the present application, the purity of the silicon carbide powder is not less than 99.9999%.

[0033] According to the embodiment of the present application, the N concentration of the silicon carbide powder is ≤5×10 -15 atoms / cm 3 . BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic diagram of the synthesis principle of silicon carbide powder of this application.

[0035] Figure 2 These are photos of the silicon carbide powder of Example 1 and Comparative Example 1 of the present application.

[0036] Reference numerals: 10: silicon powder layer; 20: carbon powder layer; 30: silicon carbide seed layer; 40: silicon carbide powder. DETAILED DESCRIPTION

[0037] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0038] In the first aspect of the present application, a method for preparing silicon carbide powder is proposed. The schematic diagram of the synthesis principle of the method is shown in FIG. Figure 1 The method comprises: adding reaction raw materials into a crucible, wherein the reaction raw materials include a plurality of stacked composite material layers, each of the composite material layers including a silicon powder layer 10, a carbon powder layer 20, and a silicon carbide seed layer 30 stacked in sequence; and heating the crucible containing the composite material layers to synthesize and obtain silicon carbide powder 40.

[0039] The present application achieves efficient and uniform synthesis of large-sized silicon carbide powder by setting up a composite material layer with a stacked structure. On the one hand, since the vaporization temperature of silicon powder is relatively low, during the reaction process, the silicon powder in the bottom layer first vaporizes at high temperature to form gaseous silicon. The gaseous silicon rises and reacts chemically with the carbon powder to generate gaseous silicon carbide. Subsequently, the gaseous silicon carbide sublimates to the silicon carbide seed crystal area and begins to crystallize and grow. As the reaction proceeds, the growing silicon carbide vaporizes again and continues to move upward driven by the axial temperature gradient, and recrystallizes in a higher temperature area. Through repeated recrystallization processes, the particle size of the silicon carbide powder will continue to increase, and eventually an ideal large-sized silicon carbide powder is obtained. On the other hand, the stacked composite material layers can not only ensure that the reaction raw materials are fully contacted and reacted during the heating process, but also can effectively control the order and rate of the reaction, thereby making the reaction more uniform and further improving the purity and performance consistency of the silicon carbide powder.

[0040] According to an embodiment of the present application, in the reaction raw materials, the molar ratio of the silicon powder in the silicon powder layer to the carbon powder in the carbon powder layer is 1:1-1.2:1, specifically 1:1, 1.1:1, 1.2:1 or any range between them. Therefore, within the above molar ratio range, it is helpful for the silicon powder and carbon powder to fully react and improve the utilization rate of the raw materials. If the molar ratio is too high, that is, the silicon powder is excessive, the by-product Si2C may be produced during the reaction, and the presence of the by-product will reduce the purity of the silicon carbide powder; if the molar ratio is too low, that is, the carbon powder is excessive, the by-product SiC2 may be produced during the reaction, and the presence of this by-product will also reduce the purity of the silicon carbide powder.

[0041] According to an embodiment of the present application, the mass ratio of the silicon carbide seeds in the silicon carbide seed layer in the reaction raw materials is 1%-10%, specifically, 3%-7%. Specifically, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any range between them. Therefore, within the above-mentioned mass ratio range, it helps to promote the crystallization growth of silicon carbide powder and improve the purity and performance consistency of the product. If the mass ratio is too high, it may cause the concentration of silicon carbide seeds in the reaction system to be too high, thereby causing mutual interference between the seeds, affecting the uniformity of the crystallization process, and thus reducing the quality of silicon carbide powder; if the mass ratio is too low, the number of silicon carbide seeds is insufficient, and it may not be able to effectively induce crystal growth, resulting in an insufficient crystallization process.

[0042] According to an embodiment of the present application, the particle size of the silicon powder in the silicon powder layer is 0.5 mm to 5 mm, specifically, the particle size of the silicon powder is 1 mm to 3 mm, specifically 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, or any range therebetween. Thus, a suitable silicon powder particle size helps to slow down the gasification rate of the silicon powder during the reaction, thereby reducing silicon loss and improving the utilization rate of the raw materials. If the particle size of the silicon powder is too large, it may cause incomplete gasification of the silicon powder during the reaction, affecting the efficiency of silicon carbide powder generation; if the particle size of the silicon powder is too small, it may accelerate the gasification rate of the silicon powder, resulting in excessive loss of silicon powder, thereby reducing the utilization rate of the raw materials.

[0043] According to an embodiment of the present application, the purity of the silicon powder is ≥99.99999999%, thereby facilitating the production of silicon carbide powder with higher purity.

[0044] According to an embodiment of the present application, the particle size of the carbon powder in the carbon powder layer is 10μm-100μm, specifically, the particle size of the carbon powder is 20μm-60μm, specifically 10μm, 20μm, 40μm, 60μm, 80μm, 100μm or any range between two thereof. Therefore, a suitable particle size of the carbon powder helps to ensure that the carbon powder and the silicon powder can fully contact and react during the reaction process, thereby improving the reaction efficiency and the purity of the silicon carbide powder. If the particle size of the carbon powder is too large, it may cause uneven reaction and affect the crystallization quality of the silicon carbide powder; if the particle size of the carbon powder is too small, it may increase the specific surface area of ​​the carbon powder, resulting in excessive consumption of carbon powder during the reaction, thereby reducing the utilization rate of the raw materials.

[0045] According to an embodiment of the present application, the purity of the carbon powder is ≥99.9999%, thereby facilitating the production of silicon carbide powder with higher purity.

[0046] According to an embodiment of the present application, the particle size of the silicon carbide seeds in the silicon carbide seed layer is 0.2mm-1mm, and the specific particle size of the silicon carbide seeds is 0.3mm-0.6mm, such as 0.2mm, 0.4mm, 0.6mm, 0.8mm, 1mm or any range between them. Thus, a suitable particle size of the silicon carbide seeds helps to provide sufficient surface area to promote uniform crystallization and growth of silicon carbide powder, thereby improving the purity and performance consistency of the silicon carbide powder. If the particle size of the silicon carbide seeds is too large, it may cause uneven crystallization growth, affecting the particle size distribution and performance of the final silicon carbide powder; if the particle size of the silicon carbide seeds is too small, it may not be able to effectively induce crystallization growth, resulting in an insufficient crystallization process, which will also affect the purity and performance of the silicon carbide powder.

[0047] According to an embodiment of the present application, the purity of the silicon carbide seed crystal is ≥99.9999%, thereby facilitating the production of silicon carbide powder with higher purity.

[0048] According to an embodiment of the present application, the number of the composite material layers is 3-7, specifically, the number of the composite material layers is 3-5, specifically 3, 4, 5, 6, and 7. In this way, while ensuring the synthesis effect, the process flow can be simplified to improve production efficiency and reduce operational complexity.

[0049] According to an embodiment of the present application, a method for obtaining a composite material layer includes first laying a layer of silicon powder on the bottom of a crucible, then flattening it so that the height difference between its four corners is no more than 2 mm, and then sequentially laying carbon powder and silicon carbide seed layers, similarly ensuring that the height difference between the four corners of the carbon powder layer and the silicon carbide seed layer is no more than 2 mm. This optimizes the spatial uniformity of the raw materials, thereby providing stable conditions for the subsequent synthesis reaction and crystal growth of the silicon carbide powder.

[0050] It is understood that there is no specific limitation on the flattening method, as long as each layer has a certain flatness and the height difference of the four corners of each layer is no more than 2 mm. In some embodiments, a pressing tray can be used for flattening.

[0051] According to an embodiment of the present application, the heating synthesis includes a purge, a first-stage synthesis, and a second-stage synthesis performed sequentially. Thus, in the purge stage, a large amount of mixed gas is used to purge the furnace chamber and the thermal field of the silicon carbide growth device to remove air and impurities therein, thereby ensuring the purity of the reaction environment. Subsequently, in the first-stage synthesis stage, silicon carbide powder is initially synthesized by reacting under high pressure conditions. Finally, in the second-stage synthesis stage, small particles of silicon carbide powder are continuously vaporized and recrystallized. After this process, large-sized silicon carbide powder is finally obtained.

[0052] According to an embodiment of the present application, the total amount of the purge mixed gas introduced during the purge phase is less than the total amount of the first mixed gas introduced during the first synthesis phase. Thus, the total amount of gas introduced during the purge phase is sufficient to remove impurities from the furnace chamber and the heat field, while the introduction of more mixed gas during the first synthesis phase facilitates sufficient gas participation in the reaction, thereby promoting the gasification and reaction of silicon powder and carbon powder to form silicon carbide.

[0053] According to an embodiment of the present application, the proportion of hydrogen in the purge mixed gas is greater than the proportion of hydrogen in the first mixed gas. Thus, the higher proportion of hydrogen in the purge stage helps to more efficiently remove impurities in the thermal field. The reason why the proportion of hydrogen in the first mixed gas is low is that the reaction of hydrogen with thermal field materials (such as graphite) will cause loss and structural damage of thermal field materials, affecting the stability and service life of the thermal field. By reducing the proportion of hydrogen in the first mixed gas, this erosion can be reduced while still ensuring that sufficient hydrogen participates in the reaction.

[0054] According to an embodiment of the present application, the proportion of hydrogen in the second mixed gas introduced in the second-stage synthesis is lower than the proportion of hydrogen in the first mixed gas. This helps reduce the corrosion of hydrogen on the thermal field structure, thereby maintaining a stable reaction temperature.

[0055] According to an embodiment of the present application, the pressure of the second-stage synthesis is lower than that of the first-stage synthesis. This increases the axial temperature gradient, prompting small-particle silicon carbide powder and some incompletely reacted silicon powder and carbon powder to sublime upward, allowing them to continue to react or recrystallize, thereby obtaining large-particle silicon carbide powder.

[0056] According to an embodiment of the present application, the purging comprises: introducing a purging gas mixture containing hydrogen and argon at a temperature below 1200°C, and maintaining the pressure at 500mbar, 100mbar, and 10mbar for 30-60 minutes respectively. The pressure is then backfilled to 100mbar and 500mbar and maintained for 30-60 minutes respectively, and then vacuumed to 10 -6 mbar.

[0057] This helps hydrogen fully react with impurities such as oxygen and nitrogen within the aforementioned timeframe. Argon also dilutes the hydrogen, reducing its concentration and the rate at which it reacts with the thermal field materials, thereby minimizing thermal field losses and providing a pure environment for subsequent processes. Furthermore, gradually reducing pressure can prevent damage to the thermal field caused by drastic pressure changes. Gradually backfilling the pressure and maintaining it for a certain period of time can reduce thermal stress in the thermal field and equipment caused by drastic pressure changes, while ensuring a stable reaction environment and minimizing fluctuations in the reaction environment caused by pressure and temperature changes, helping to improve reaction stability and repeatability.

[0058] According to an embodiment of the present application, the flow ratio of hydrogen and argon in the mixed gas is 15:85-30:70, specifically, the flow ratio is 20:80-30:70, specifically 15:85, 20:80, 25:75, 30:70 or any range between them. In this way, it can not only ensure that impurities are completely removed, but also help reduce the erosion of hydrogen on the thermal field structure. If the proportion of hydrogen is too large, the thermal field structure may be destroyed, thereby reducing the service life of the equipment; if the proportion of argon is too large, the impurities in the thermal field may not be completely removed, affecting the crystal growth of silicon carbide powder.

[0059] According to an embodiment of the present application, the one-stage synthesis includes: raising the temperature to 1800°C-2000°C within 2h-4h (specifically, within 2h-3h), maintaining the pressure at 200mbar-500mbar (specifically, the pressure is 200mbar-300mbar), introducing a first mixed gas containing hydrogen and argon, and heating the synthesis time for 10h-20h.

[0060] Therefore, reaching the desired synthesis temperature within the aforementioned heating time allows for the timely locking of silicon gas, allowing it to fully react with carbon and prevent its loss. Within this temperature range, silicon powder and carbon powder achieve high vaporization and reaction rates, allowing for full reaction to produce high-purity β-silicon carbide. Higher pressures, on the other hand, reduce the vaporization and loss of silicon atoms, ensuring more silicon atoms participate in the reaction and improving raw material utilization.

[0061] According to an embodiment of the present application, the flow ratio of hydrogen and argon in the first mixed gas is 30:170-40:160, specifically 30:170, 35:165, 40:160 or any range between two of them. Thus, within the above range, it helps hydrogen to fully participate in the growth reaction of silicon carbide, and at the same time helps to quickly remove excess hydrogen and avoid excessive erosion of the thermal field. If the proportion of hydrogen is too high, it may cause the thermal field structure to be destroyed, thereby reducing the service life of the equipment; if the proportion of argon is too large, the concentration of hydrogen will decrease, and the reaction rate of silicon carbide growth may slow down, resulting in a longer reaction time.

[0062] According to an embodiment of the present application, the two-stage synthesis includes: heating to 2000°C-2200°C within 0.5h-1h (specifically, within 2h-3h), maintaining the pressure at 50mbar-100mbar (specifically, the pressure is 60mbar-80mbar), introducing a second mixed gas containing hydrogen and argon, and heating the synthesis time for 15h-40h (specifically, the synthesis time is 20h-25h).

[0063] Therefore, within the above temperature and pressure ranges, small-particle silicon carbide powder is more easily vaporized and recrystallized, and sufficient synthesis time is also conducive to the production of large-sized silicon carbide powder.

[0064] According to an embodiment of the present application, the flow ratio of hydrogen and argon in the second mixed gas is 10:190-20:180, specifically, the flow ratio is 10:190-15:185. Specifically, such as 10:190, 15:185, 20:180 or the range between any two of them. Thus, within the above range, it helps hydrogen to fully participate in the growth reaction of silicon carbide while avoiding excessive erosion of the thermal field by hydrogen. If the proportion of hydrogen is too high, the thermal field structure may be destroyed, thereby reducing the service life of the equipment; if the proportion of argon is too large, the concentration of hydrogen will decrease, and the reaction rate of silicon carbide growth may slow down, resulting in a prolonged reaction time.

[0065] According to an embodiment of the present application, the purity of the hydrogen is ≥99.9999999%. Thus, the above purity can reduce the mixing of impurities, improve the selectivity and efficiency of the reaction, and thus improve the purity of the silicon carbide powder.

[0066] According to an embodiment of the present application, the purity of the argon gas is ≥99.9999999%. This purity can reduce the mixing of impurities, improve the selectivity and efficiency of the reaction, and thus improve the purity of the silicon carbide powder.

[0067] In a second aspect of the present application, a silicon carbide powder is provided, wherein the silicon carbide powder is prepared by the method described above. All the features and advantages of the silicon carbide powder are consistent with those of the method described above and are not described in detail here.

[0068] According to an embodiment of the present application, the silicon carbide powder has a particle size of 10 mm to 30 mm, specifically 10 mm, 20 mm, 30 mm, or any range therebetween. As a result, these large silicon carbide powder particles have higher mechanical strength and thermal conductivity, making them promising for broad application in optical devices, electronic devices, high-temperature resistant materials, and other fields.

[0069] According to an embodiment of the present application, the purity of the silicon carbide powder is not less than 99.9999%, which can be obtained by glow discharge mass spectrometry (GDMS) testing.

[0070] According to the embodiment of the present application, the N concentration of the silicon carbide powder is ≤5×10 -15 atoms / cm 3 The specific results can be obtained through secondary ion mass spectrometry (SIMS) testing.

[0071] The embodiments of the present application are described in detail below.

[0072] Example 1:

[0073] Silicon powder (purity > 99.9999999%), carbon powder (purity > 99.9999%) and silicon carbide seeds (purity ≥ 99.9999%) are used as reaction raw materials, and the total weight of the reaction raw materials is 10kg. Among them, the molar ratio of silicon powder to carbon powder is 1.1:1, and the mass proportion of silicon carbide seeds in the reaction raw materials is 5%. After calculation, the weights of silicon powder, carbon powder and silicon carbide seeds are 6.84kg, 2.66kg and 0.5kg respectively. The above silicon powder, carbon powder and silicon carbide seeds are equally divided into 5 parts, and the weights of silicon powder, carbon powder and seeds in each part are 1.368kg, 0.532kg and 0.1kg respectively. The charging process is as follows: first take a portion of silicon powder (1.368kg) and spread it flat on the bottom of the crucible. Use a 0.7kg pressure tray to press it gently. Use the weight of the pressure tray to flatten the silicon powder. Measure the height of the four points of the flattened silicon powder to make the height difference less than 2mm. After the silicon powder is filled, fill a layer of 0.532kg of carbon powder on the surface of the silicon powder. The carbon powder is flattened in the same way as the silicon powder to ensure that the height difference of the four points of the flattened carbon powder is less than 2mm. After the carbon powder is filled, fill a layer of 0.1kg of silicon carbide seeds on top of the carbon powder. The flattening requirements are the same as above to obtain a composite material layer. Repeat this method to form a total of 5 composite material layers. Finally, the materials in the crucible are silicon powder to silicon carbide seeds from bottom to top, and the top layer is silicon carbide seeds. After the loading is completed, the crucible is transferred to the synthesis furnace for synthesis.

[0074] Before the start of the synthesis, the tightness of the furnace is tested to ensure that there is no leakage during the synthesis process. The temperature is raised to 1200℃ in 8 hours. During the heating process, a mixture of hydrogen and argon with a flow rate ratio of 20:80 is introduced; at the same time, the furnace chamber is purged and the pressure is reduced to 500mbar, 100mbar, and 10mbar in turn. Each pressure stage is maintained for 60 minutes; then the pressure is backfilled to 100mbar and 500mbar in turn. Each pressure stage is also maintained for 60 minutes. Finally, the furnace chamber is evacuated until the pressure is less than 10 -6 mbar. The power was then increased, and the temperature was raised to 2000°C over 2 hours. A single-stage synthesis was conducted at 2000°C, with a pressure of 300 mbar, a hydrogen to argon flow ratio of 35:165, and a duration of 15 hours. Following the completion of the first-stage synthesis, the temperature was raised to 2200°C over 1 hour, and a second-stage synthesis was conducted at this temperature. The synthesis pressure was set to 70 mbar, the hydrogen to argon flow ratio was 10:190, and the duration was 30 hours.

[0075] Comparative Example 1

[0076] The same as Example 1, except that 6.84 kg of silicon powder, 2.66 kg of carbon powder, and 0.5 kg of silicon carbide seed crystals were mixed and stirred in a stirring device for 3 hours to uniformly mix to obtain a raw material mixture. The raw material mixture was transferred to a crucible and loaded into a synthesis furnace for synthesis.

[0077] After loading the furnace, the airtightness of the furnace was tested. After the test, the temperature was raised to 2200°C for 10 hours and synthesis began. The synthesis pressure was 100 mbar, the ratio of hydrogen to argon was 10:90, and the synthesis time was 30 hours.

[0078] The silicon carbide powders prepared in Example 1 and the comparative example were crushed, sieved, washed and dried. Figure 2 It can be seen that the morphology of the silicon carbide powder of Example 1 is white and columnar; while the morphology of the silicon carbide powder of Comparative Example 1 is light green and needle-shaped.

[0079] Two samples of silicon carbide powder prepared in Example 1 and Comparative Example 1 were randomly taken to test their nitrogen concentrations. As shown in Table 1, the nitrogen concentrations of Example 1 were less than 5×10 -15 atoms / cm 3 , while the N element concentration in Comparative Example 1 was 7.60×10 16 atoms / cm 3 This shows that the silicon carbide powder prepared by the method of the present application can effectively reduce the nitrogen concentration.

[0080] The purity of the silicon carbide powder prepared in Example 1 and Comparative Example 1 was tested, yielding the data in Tables 2 and 3, respectively. Comparison shows that the purity of the silicon carbide powder in Example 1 was 99.99995%, while the purity of the silicon carbide powder in Comparative Example 1 was 99.9998%. This demonstrates that the silicon carbide powder prepared by the method of the present application has a relatively high purity.

[0081] Performance testing:

[0082] Nitrogen concentration: obtained by secondary ion mass spectrometry (SIMS).

[0083] Purity of silicon carbide powder: obtained by glow discharge mass spectrometry (GDMS) testing.

[0084] Table 1

[0085]

[0086] Table 2

[0087]

[0088]

[0089] Table 3

[0090]

[0091]

[0092] Note: In Tables 1 and 2, Matrix refers to the main components of silicon carbide, namely C and Si; Binder (In) refers to the substrate material used in glow discharge mass spectrometry testing.

[0093] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0094] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A method for preparing silicon carbide powder, characterized in that: include: Adding reaction raw materials into the crucible, wherein the reaction raw materials include a plurality of stacked composite material layers, each of the composite material layers includes a silicon powder layer, a carbon powder layer, and a silicon carbide seed layer stacked in sequence; The crucible containing the composite material layer is heated and synthesized to obtain silicon carbide powder.

2. The method according to claim 1, characterized in that In the reaction raw materials, the molar ratio of silicon powder in the silicon powder layer to carbon powder in the carbon powder layer is 1:1-1.2:

1.

3. The method according to claim 1, characterized in that The silicon carbide seeds in the silicon carbide seed layer account for 1% to 10% by mass of the reaction raw materials, preferably 3% to 7% by mass.

4. The method according to claim 1, characterized in that Meet at least one of the following conditions: The particle size of the silicon powder in the silicon powder layer is 0.5 mm to 5 mm, preferably 1 mm to 3 mm; The purity of the silicon powder is ≥99.9999999%; The particle size of the carbon powder in the carbon powder layer is 10 μm-100 μm, preferably 20-60 μm; The purity of the carbon powder is ≥99.9999%; The particle size of the silicon carbide seeds in the silicon carbide seed layer is 0.2 mm to 1 mm, preferably 0.3 mm to 0.6 mm; The purity of the silicon carbide seed crystal is ≥99.9999%.

5. The method according to claim 1, characterized in that: The number of the composite material layers is 3-7, preferably 3-5.

6. The method according to claim 1, characterized in that The heating synthesis includes purging, one-stage synthesis and two-stage synthesis which are performed in sequence.

7. The method according to claim 6, characterized in that Meet at least one of the following conditions: The total amount of the purge mixed gas introduced in the purge is less than the total amount of the first mixed gas introduced in the first stage synthesis; The proportion of hydrogen in the purge mixed gas is greater than the proportion of hydrogen in the first mixed gas; The proportion of hydrogen in the second mixed gas introduced in the second-stage synthesis is lower than the proportion of hydrogen in the first mixed gas; The pressure of the second-stage synthesis is lower than the pressure of the first-stage synthesis.

8. The method according to claim 6, characterized in that Meet at least one of the following conditions: The purging comprises: when the temperature is lower than 1200°C, introducing a purging mixed gas at a flow ratio of hydrogen to argon of 15:85-30:70, preferably 20:80-30:70, and keeping the pressure at 500mbar, 100mbar, and 10mbar for 30min-60min respectively; then backfilling the pressure to 100mbar and 500mbar and keeping them for 30min-60min respectively, and then evacuating to 10 -6 mbar; The one-stage synthesis comprises: heating to 1800° C.-2000° C. within 2 h-4 h, preferably 2 h-3 h, maintaining the pressure at 200 mbar-500 mbar, preferably 200 mbar-300 mbar, introducing the first mixed gas at a flow ratio of hydrogen to argon of 30:170-40:160, and heating the synthesis time for 10 h-20 h; The two-stage synthesis comprises: heating to 2000° C.-2200° C. within 0.5 h-1 h, preferably 2 h-3 h, maintaining the pressure at 50 mbar-100 mbar, preferably 60 mbar-80 mbar, introducing the second mixed gas at a flow ratio of hydrogen to argon of 10:190-20:180, preferably 10:190-15:185, and heating the synthesis time for 15 h-40 h, preferably 20 h-25 h; Wherein, the purity of the hydrogen is ≥99.9999999%; The purity of the argon gas is ≥99.99999999%.

9. A silicon carbide powder, characterized in that: It is prepared by the method according to any one of claims 1 to 8.

10. The silicon carbide powder according to claim 9, characterized in that Meet at least one of the following conditions: The particle size of the silicon carbide powder is 10mm-30mm; The purity of the silicon carbide powder is not less than 99.9999%; The N concentration in the silicon carbide powder is ≤5×10 -15 atoms / cm 3 .

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