Crucible synthesized by silicon carbide powder and using method thereof

Abstract

The invention belongs to the field of silicon carbide powder synthesis, and particularly relates to a silicon carbide powder synthesis crucible and a use method. The silicon carbide powder synthetic crucible is formed by vertically stacking single-layer crucibles with the same structure along the central axis of a graphite crucible; the single-layer crucible comprises a crucible upper cover, a graphite sheet and a crucible main body; the crucible upper cover and the crucible main body are nested; the bottom of the inner cavity of the crucible main body is used for placing silicon powder and graphite powder; and the graphite flake is clamped between the crucible upper cover and the crucible main body. By designing the height of the single-layer crucible and the structure of the multi-layer crucible, a proper temperature gradient is favorably constructed, and by controlling parameters such as heat preservation time and pressure, batch production of large-particle-size and high-uniformity silicon carbide powder is realized, and an ideal raw material is provided for growth of high-quality silicon carbide crystals.

Description

Technical Field

[0001] The invention belongs to the field of silicon carbide powder synthesis, and in particular relates to a silicon carbide powder synthesis crucible and a use method thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] As a typical wide bandgap semiconductor, silicon carbide has been widely used in many fields such as renewable energy generation, high-voltage inverters, communications and radar systems, aerospace, etc., due to its wide bandgap, high critical breakdown voltage, high thermal conductivity, high saturated electron mobility and excellent chemical stability. It plays a key role in these fields and promotes technological progress and application development.

[0004] At present, the mainstream method for growing silicon carbide crystals is physical vapor transport (PVT). In the PVT method, the particle size and uniformity of silicon carbide powder are key factors. Silicon carbide powder with large and uniform particle size plays an important role in improving the quality and physical properties of silicon carbide crystals. Silicon carbide powder with large particle size helps to reduce the decomposition rate of the powder and reduce the carbonization rate of the powder. Silicon carbide powder with uniform particle size helps to control the growth rate of the crystal, reduce the introduction of lattice defects, and improve the quality of the crystal.

[0005] In the synthesis process of silicon carbide powder, obtaining large particles with uniform particle size faces many challenges. Traditional synthesis methods usually cannot achieve large particle size and uniform particle size at the same time. Due to the different temperature fields inside the crucible, the temperature at different positions of the crucible is different. Generally, only large particles appear on the surface of the powder, while the particles inside the powder are smaller. This unevenness not only affects the quality of the overall powder, but may also lead to instability in the subsequent crystal growth process.

[0006] Patent CN107640773B discloses a method for directly synthesizing large-particle silicon carbide powder, which uses the principle of sublimation to recrystallize silicon carbide powder in the holes of graphite crystal plates. However, this method is limited by the temperature field distribution, and only the powder particle size at the graphite crystal plate is larger, while the powder particle size inside the crucible is still smaller. This results in uneven distribution of the particle size of the overall powder, which cannot meet the demand for uniform powder for high-quality silicon carbide crystal growth.

[0007] Patent CN117342561A discloses a method for preparing high-purity silicon carbide powder, in which perforated graphite cylinders and carbon-silicon mixed raw materials are placed alternately along the diameter direction of the crucible. Although this method improves the temperature field by perforating the graphite cylinder, it also brings new problems. Due to the discontinuous distribution of the powder (separated by the graphite cylinder), the powder particle size in different areas will be quite different. This discontinuity is not conducive to improving the uniformity of the overall powder particle size.

[0008] Patent CN117695973A discloses a silicon carbide powder synthesis device, which uses an inclined splitter plate structure to divide the reaction zone into an upper reaction zone and a lower recovery zone, and uses the splitter plate to grade and screen the silicon carbide powder generated by the reaction to collect silicon carbide powder with uniform particle size. However, the screening of silicon carbide powder by the splitter plate may cause small-sized silicon carbide powder to enter the collection bin, thereby failing to ensure the uniformity of the particle size of the overall silicon carbide powder.

[0009] The current mainstream silicon carbide powder synthesis method can only obtain large-size silicon carbide powder locally, and the uniformity of the powder particle size cannot be guaranteed. Due to the poor consistency of the powder, the stability of the quality of the grown single crystal cannot be guaranteed. Summary of the invention

[0010] In order to solve the above technical problems, the purpose of the present invention is to provide a silicon carbide powder synthesis crucible and a method of use. The silicon carbide powder prepared by this crucible and method has the characteristics of large particle size and high particle size uniformity, and can meet the growth requirements of high-quality silicon carbide crystals.

[0011] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0012] According to a first aspect of the present invention, a synthetic crucible for silicon carbide powder is provided, wherein the synthetic crucible for silicon carbide powder is formed by stacking single-layer crucibles of the same structure up and down along the central axis of a graphite crucible; the single-layer crucible comprises a crucible cover, a graphite sheet and a crucible body; the crucible cover and the crucible body are nested; the bottom of the inner cavity of the crucible body is used to place silicon powder and graphite powder; the graphite sheet is clamped between the crucible cover and the crucible body.

[0013] Preferably, the crucible upper cover of the single-layer crucible is composed of a graphite gas distributor and a graphite disc, which are connected by threads and have a vent hole in the center.

[0014] Preferably, the single-layer crucible with the same structure is composed of 3 to 5 single-layer crucible structures assembled along the central axis of the graphite crucible.

[0015] Preferably, the crucible cover and the crucible body of the single-layer crucible are both made of isostatic graphite.

[0016] Preferably, the graphite sheet is made of porous graphite or medium-coarse graphite, and has a thickness of 3 to 10 mm.

[0017] Preferably, the single-layer crucible body has a height of 100-120 mm, an inner diameter of 280-350 mm, and a wall thickness of 15-30 mm.

[0018] Preferably, the diameter of the vent hole in the center of the crucible upper cover of the single-layer crucible is 100-140 mm.

[0019] Preferably, the filling amount of the mixed powder formed by the silicon powder and the graphite powder is 1 / 3-2 / 3 of the height of the single-layer crucible.

[0020] In a second aspect of the present invention, a method for using a silicon carbide powder synthesis crucible is provided, comprising the following steps:

[0021] S1. Mix high-purity silicon powder and high-purity graphite powder evenly and place them in each single-layer crucible;

[0022] S2, assembling the single-layer crucible and placing it in a synthesis furnace, introducing a protective gas into the synthesis furnace, performing a first heating treatment and a second heating treatment, and performing a heat preservation treatment after reaching a first pressure value to obtain β-SiC;

[0023] S3, introducing protective gas into the synthesis furnace, performing a third heating treatment, and performing a heat preservation treatment after reaching the second pressure value; after the heat preservation is completed, the pressure is raised to a third pressure value, and then the temperature is lowered to room temperature to obtain α-SiC powder.

[0024] Preferably, in step S1, the purity of the high-purity graphite powder and the high-purity silicon powder are both 6N level, wherein the particle size of the graphite powder is 5-200 μm, and the particle size of the silicon powder is 20-500 μm; the molar ratio of the high-purity silicon powder to the high-purity graphite powder is 1:1.

[0025] Preferably, in step S2, the protective gas is selected from one of argon (Ar), hydrogen (H2), and a mixed gas of hydrogen and argon, and the flow ratio of hydrogen in the mixed gas is 0 to 20%.

[0026] Preferably, in step S2, the temperature of the first heat treatment is 800-1000°C; the temperature of the second heat treatment is 1400-1800°C; the first pressure value is 0-10 mbar; and the insulation time is 6-10 h.

[0027] Preferably, in step S3, the temperature of the third heat treatment is 2000-2500° C.; the second pressure value is 50-800 mbar; the insulation time is 20-60 h; and the third pressure value is 800-1000 mbar.

[0028] The beneficial effects achieved by one or more technical solutions of the present invention are as follows:

[0029] (1) The present invention adopts a multi-layer crucible structure formed by stacking multiple single-layer crucibles. Each single-layer crucible effectively weakens the influence of heat convection, reduces local temperature fluctuations, and maintains a stable temperature distribution. This design creates a uniform temperature field inside each single-layer crucible, provides consistent crystallization conditions for the entire reaction space, and effectively promotes the uniformity of the particle size of silicon carbide powder.

[0030] (2) The height of the single-layer crucible is designed in the present invention to facilitate the construction of a suitable temperature gradient, which not only ensures a sufficient temperature difference to drive the transformation of small particles into large particles, but also avoids the uneven growth that may be caused by excessive temperature gradients. In addition, the single-layer crucible promotes the effective diffusion and uniform distribution of the gas phase, so that the small particles in the entire reaction space can fully participate in the growth process and achieve uniform transformation into large particles. In the multi-layer crucible structure, the internal temperature gradient of each independent single-layer crucible is appropriate, ensuring that large and uniform silicon carbide powder can be synthesized in each single-layer crucible.

[0031] (3) The single-layer crucible in the present invention has a relatively low height, which effectively shortens the diffusion path of impurity elements, and the vent hole design of the crucible cover provides a direct channel for impurity discharge, thereby greatly improving the purity of silicon carbide powder.

[0032] (4) In the present invention, each single-layer crucible is an independent unit and can be disassembled and replaced individually. If a single-layer crucible is damaged during use, it can be replaced individually. This design reduces the cost of use and extends the service life of the multi-crucible structure.

[0033] (5) In the two-step synthesis of silicon carbide powder, proper heat preservation during the β-SiC synthesis stage promotes uniform nucleus formation and initial growth, which lays the foundation for the subsequent α-SiC transformation and is conducive to the formation of large particles. The full formation of β-SiC reduces unreacted raw materials and improves the purity of subsequent α-SiC. By controlling parameters such as heat preservation time and pressure, high-quality, large-particle α-SiC powder can be obtained.

[0034] (6) The multi-layer crucible of the present invention has a simple and efficient structure, which enables the mass production of large-particle-size, high-uniformity silicon carbide powder, and provides an ideal raw material for the growth of high-quality silicon carbide crystals. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0036] Figure 1This is a schematic diagram of the structure of a multi-layer crucible for synthesizing high-purity silicon carbide powder with large particle size and high particle size uniformity provided in Example 1 of the present invention;

[0037] Figure 2 It is an assembly diagram of the crucible upper cover of the single-layer crucible structure in Example 1 of the present invention and a cross-sectional diagram of each component;

[0038] Figure 3 It is a cross-sectional view of a graphite sheet in a single-layer crucible structure in Example 1 of the present invention;

[0039] Figure 4 It is a cross-sectional view of the crucible body in the single-layer crucible structure in Example 1 of the present invention;

[0040] Figure 5 This is a temperature field diagram of a crucible for synthesizing silicon carbide powder obtained by numerical simulation in Example 1 of the present invention;

[0041] In the figure, 100: single crucible structure; 110: crucible cover; 111: graphite gas distribution plate, 112: graphite ring; 120: graphite sheet (crystallization plate); 130: crucible body; 200: multi-crucible structure; 310: carbon-silicon mixed powder. DETAILED DESCRIPTION

[0042] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0043] As mentioned above, the current mainstream method for synthesizing silicon carbide powder can only obtain large-particle silicon carbide powder locally, and the uniformity of the particle size of the powder cannot be guaranteed. Due to the poor consistency of the powder, the stability of the quality of the grown single crystal cannot be guaranteed. Therefore, those skilled in the art are in urgent need of preparing a crucible for synthesizing silicon carbide powder that can achieve both uniformity of the powder and large particle size.

[0044] A first typical embodiment of the present invention provides a synthetic crucible for silicon carbide powder, wherein the synthetic crucible for silicon carbide powder is formed by stacking single-layer crucibles of the same structure up and down along the central axis of a graphite crucible; the single-layer crucible comprises a crucible cover, a graphite sheet and a crucible body; the crucible cover and the crucible body are nested; the bottom of the inner cavity of the crucible body is used to place silicon powder and graphite powder; the graphite sheet is clamped between the crucible cover and the crucible body.

[0045] In one or more embodiments of this implementation mode, the crucible cover of the single-layer crucible is composed of a graphite gas distributor and a graphite disc, which are connected by threads and have an air vent in the center to facilitate the removal of impurity elements inside the crucible and balance the internal pressure.

[0046] In one or more embodiments of this implementation mode, the single-layer crucible with the same structure is assembled along the central axis of the graphite crucible by 3 to 5 single-layer crucible structures. After the single-layer crucibles are stacked to form a multi-layer crucible, since each single-layer crucible has a low height, the temperature field inside each single-layer crucible is uniform, which is conducive to the synthesis of silicon carbide powder with large and uniform particle size. When the number of stacked single-layer crucibles exceeds 5, the overall height of the stacked crucibles is too large, which increases the temperature field difference between different single-layer crucibles, resulting in poor furnace uniformity of the synthesized material; when the number of stacked single-layer crucibles is less than 3, the height of the single-layer crucible is prioritized, and the output of synthesized silicon carbide powder is low.

[0047] In one or more examples of this implementation manner, the crucible upper cover and the crucible body of the single-layer crucible are both made of isostatic graphite.

[0048] In one or more embodiments of this embodiment, the graphite sheet is made of porous graphite or medium-coarse graphite with a thickness of 3 to 10 mm. During the synthesis process, the nitrogen element and impurity elements inside the mixed powder can escape from the crucible better. In addition, during the synthesis process, crystallization is prone to occur at the upper cover of the crucible. The presence of the graphite sheet can effectively reduce the occurrence of crystallization at the connection between the upper cover of the crucible and the crucible body, thereby increasing the service life of the crucible.

[0049] In one or more embodiments of this implementation, the height of the single-layer crucible body is 100-120 mm, the inner diameter is 280-350 mm, and the wall thickness is 15-30 mm. Since the height of the single-layer crucible is relatively low, not only can the heat conduction path be shortened, so that the heat can be distributed more evenly, but also the longitudinal temperature gradient can be significantly reduced, so that the temperature field inside the single-layer crucible is more uniform. In addition, the low crucible height can effectively shorten the diffusion path of impurity elements and improve the purity of silicon carbide powder.

[0050] In one or more embodiments of this implementation, the diameter of the vent hole in the center of the crucible cover of the single-layer crucible is 100-140 mm, and the vent hole provides a direct channel to allow more nitrogen and other impurity elements to escape from the crucible. In addition, the vent hole also helps to balance the pressure inside and outside the crucible.

[0051] In one or more embodiments of this implementation mode, the filling amount of the mixed powder formed by the silicon powder and the graphite powder is 1 / 3-2 / 3 of the height of the single-layer crucible. During the pumping process, since the powder accumulation thickness is small, the gas can be more easily penetrated and exchanged, thereby improving the discharge of nitrogen and impurity elements.

[0052] A second typical embodiment of the present invention provides a method for using a silicon carbide powder synthesis crucible, comprising the following steps:

[0053] S1. Mix high-purity silicon powder and high-purity graphite powder evenly and place them in each single-layer crucible;

[0054] S2, assembling the single-layer crucible and placing it in a synthesis furnace, introducing a protective gas into the synthesis furnace, performing a first heating treatment and a second heating treatment, and performing a heat preservation treatment after reaching a first pressure value to obtain β-SiC;

[0055] S3, introducing protective gas into the synthesis furnace, performing a third heating treatment, and performing a heat preservation treatment after reaching the second pressure value; after the heat preservation is completed, the pressure is raised to a third pressure value, and then the temperature is lowered to room temperature to obtain α-SiC powder.

[0056] In one or more embodiments of this implementation mode, in step S1, the purity of the high-purity graphite powder and the high-purity silicon powder are both at 6N level, wherein the particle size of the graphite powder is 5-200 μm, and the particle size of the silicon powder is 20-500 μm; the molar ratio of the high-purity silicon powder to the high-purity graphite powder is 1:1.

[0057] In one or more examples of this implementation mode, in step S2, the protective gas is selected from one of argon (Ar), hydrogen (H2), and a mixed gas of hydrogen and argon, and the flow ratio of hydrogen in the mixed gas is 0-20%.

[0058] In one or more examples of this embodiment, in step S2, the temperature of the first heat treatment is 800-1000°C; the temperature of the second heat treatment is 1400-1800°C; the first pressure value is 0-10 mbar; and the insulation time is 6-10 hours.

[0059] In one or more examples of this implementation mode, in step S3, the temperature of the third heat treatment is 2000-2500°C; the second pressure value is 50-800 mbar; the insulation time is 20-60 hours; and the third pressure value is 800-1000 mbar.

[0060] In one or more embodiments of this embodiment, the method of use is specifically divided into two steps to synthesize silicon carbide powder. First, β-SiC is synthesized at a synthesis temperature of 1400 to 1800°C, a synthesis pressure of 0 to 10 mbar, and a reaction time of 6 to 10 hours. This stage is conducive to the uniform nucleus formation and initial growth of β-SiC. In addition, the full formation of β-SiC reduces unreacted raw materials and improves the purity of subsequent α-SiC. Subsequently, α-SiC is synthesized at a synthesis temperature of 2000 to 2500°C, a synthesis pressure of 50 to 800 mbar, and a synthesis time of 20 to 60 hours. The early synthesis of β-SiC is conducive to the formation of large and uniform particles of α-SiC, which fully improves the quality of α-SiC.

[0061] The present invention will be further described in detail below in conjunction with specific embodiments. It should be noted that the specific embodiments are intended to explain the present invention rather than to limit it.

[0062] Example 1

[0063] like Figure 1 As shown, the multi-layer crucible structure 200 is composed of three single-layer crucibles 100 with the same internal structure stacked and assembled along the central axis, and the mixed powder is placed at the bottom of each single-layer crucible. In addition, the temperature field inside the crucible changes little, which is conducive to improving the particle size uniformity of the silicon carbide powder. In addition, since the stacking thickness of the mixed powder inside each single-layer crucible is small, each single-layer crucible has the same crucible cover (graphite gas distribution plate and graphite ring structure), which can allow more impurity elements to escape from the crucible, which is helpful to obtain higher purity silicon carbide powder.

[0064] like Figure 2 As shown, the single-layer crucible upper cover 110 is composed of a graphite gas distribution plate 111 and a graphite ring 112, which are connected by internal threads. The diameter of the vent hole is 100-140 mm, and the design of the vent hole provides a direct channel for impurities to be discharged.

[0065] like Figure 3 As shown, the graphite sheet 120 has a thickness of 3 to 10 mm and is made of porous graphite or medium-coarse graphite, which can allow impurities inside the crucible to escape from the powder, thereby improving the purity of the silicon carbide powder. In addition, during the synthesis process, crystallization is prone to occur at the crucible cover. The presence of the graphite sheet can effectively reduce the occurrence of crystallization at the connection between the crucible cover and the crucible body, thereby increasing the service life of the crucible.

[0066] like Figure 4 As shown, the height of the single-layer crucible body 130 is 100-120 mm, and the connection with the crucible cover 110 is a snap-fit ​​structure. There is a gap at the connection between the crucible cover 110 and the crucible body 130, which is where the graphite sheet 120 is placed. This can prevent crystallization between the crucible cover and the crucible body, causing the crucible cover to be unable to be opened.

[0067] like Figure 5 As shown in the figure, this is the temperature field diagram of the synthetic silicon carbide powder crucible obtained by numerical simulation. It can be clearly seen from the figure that in the multi-layer crucible structure, the temperature distribution inside each single-layer crucible is very uniform, and the temperature difference between the layers of crucibles is very small, which ensures that the reaction conditions in the entire multi-layer crucible structure are basically consistent, which is conducive to obtaining silicon carbide powder with large and uniform particle size.

[0068] In addition, when the synthetic crucible and the heat preservation structure are used for the first time, they are subjected to high-temperature pretreatment, the treatment temperature is 2400-2600° C., and the treatment time is 30-60 hours.

[0069] By combining a multi-layer crucible structure and a two-step synthesis method, the preparation of large-particle-size uniform silicon carbide powder was successfully achieved. The multi-layer crucible structure is composed of multiple single-layer crucibles stacked together, and each single-layer crucible has a low height, which ensures the uniformity of the internal temperature field and creates ideal conditions for the uniform growth of silicon carbide powder. At the same time, the two-step synthesis method first synthesizes β-SiC at a lower temperature, laying a good foundation for the subsequent formation of α-SiC. In the second step of high-temperature synthesis, β-SiC is transformed into α-SiC, and large-particle growth is achieved under optimized temperature and pressure conditions. This method not only promotes the formation of large particles, but also ensures the uniformity of the overall particle size distribution.

[0070] The specific method for using the above-mentioned silicon carbide powder synthetic crucible includes the following steps:

[0071] (1) The height of the single-layer crucible used is 100 mm, the inner diameter of the crucible is 280 mm, and the wall thickness of the crucible is 15 mm. The material of the graphite sheet (crystallization plate) is porous graphite, and the diameter of the vent hole on the crucible cover is 140 mm. Three single-layer crucibles with the same internal structure are stacked vertically along the central axis to form a multi-crucible structure.

[0072] (2) High-purity graphite powder and high-purity silicon powder were weighed in a molar ratio of 1:1, placed in a three-dimensional mixer and mixed for 8 hours, and then transferred into a graphite crucible after being mixed evenly.

[0073] (3) The carbon-silicon mixed powder is filled with 2 / 3 of the height of the single-layer crucible. The assembled multi-layer crucible is placed in the synthesis furnace and vacuumed for 6 hours to make the vacuum value less than 5×10 -5 mbar.

[0074] (4) Raise the temperature to 800°C, introduce protective gas, make the pressure in the furnace 300 mbar, maintain it for 1 hour, and then evacuate it to less than 5×10 -5 mbar, maintain for 2 h, and repeat this process 3 times.

[0075] (5) The temperature is continued to rise to 1500°C. During the heating process, protective gas is continuously introduced to maintain the pressure in the furnace at 0.5 mbar. The holding time is 10 h. In this step, β-SiC is synthesized.

[0076] (6) The temperature is further raised to 2300°C, while the protective gas is introduced and the pressure in the furnace is maintained at 50 mbar for 60 hours. In this step, α-SiC is synthesized.

[0077] (7) After the synthesis is completed, the temperature is slowly lowered to room temperature. During this stage, protective gas is introduced to increase the pressure in the furnace to 800 mbar.

[0078] (8) The synthesized silicon carbide powder is taken out. The powder has high overall purity, large and uniform crystal grain size, and can be used to grow silicon carbide single crystals.

[0079] The silicon carbide powder prepared by this method has a particle size between 5 and 10 mm, accounting for 76%, and the silicon carbide powder with a particle size ≤ 1 mm accounts for only 2%.

[0080] Example 2

[0081] The difference from Example 1 is that the crucible structure prepared in this example increases the number of stacking layers on the basis of maintaining the size of the single-layer crucible unchanged, so as to improve the yield.

[0082] Specifically, the height of the single-layer crucible is maintained at 100 mm, the inner diameter of the crucible is 280 mm, and the wall thickness of the crucible is 15 mm. The material of the graphite sheet (crystallization plate) is changed to medium-coarse graphite, and the diameter of the vent hole on the crucible cover is 140 mm. Four single-layer crucibles with the same internal structure are stacked vertically along the central axis to form a multi-crucible structure. The remaining steps and conditions are the same as those in Example 1.

[0083] The prepared silicon carbide powder has a particle size between 5 and 10 mm, accounting for 72%, and the silicon carbide powder with a particle size ≤ 1 mm accounts for only 3%.

[0084] Example 3

[0085] The difference from Example 1 is that the size of each single-layer crucible in the crucible structure is changed in this example.

[0086] Specifically, the height of a single-layer crucible is 120 mm, the inner diameter of the crucible is 300 mm, the wall thickness of the crucible is 15 mm, the graphite sheet (crystallization plate) remains unchanged, and the diameter of the vent hole on the crucible cover is reduced to 100 mm. Three single-layer crucibles with the same internal structure are stacked vertically along the central axis to form a multi-crucible structure.

[0087] The remaining steps and conditions are the same as those in Example 1. The proportion of the prepared silicon carbide powder with a particle size between 5 and 10 mm is 72%, and the proportion of the silicon carbide powder with a particle size of ≤1 mm is only 5%.

[0088] Example 4

[0089] The difference from Example 1 is that this example changes the α-SiC synthesis time and pressure in the synthesis method.

[0090] Specifically: in step (6), the synthesis temperature of α-SiC is changed to 2400° C., and the synthesis pressure is changed to 200 mbar.

[0091] The remaining steps and conditions are the same as those in Example 1. The proportion of the prepared silicon carbide powder with a particle size between 5 and 10 mm is 75%, and the proportion of the silicon carbide powder with a particle size of ≤1 mm is only 5%.

[0092] Comparative Example 1

[0093] The difference from Example 1 is that the crucible structure height in Comparative Example 1 is 350 mm, the inner diameter is 320 mm, the crucible wall thickness is 15 mm, the material of the graphite sheet (crystallization plate) remains unchanged, which is a porous graphite material, and the crucible cover is provided with a 140 mm vent. The synthesis method still adopts a two-step synthesis, first synthesizing β-SiC and then converting it into α-SiC.

[0094] After the synthesis, the obtained silicon carbide powder is not uniform, with large particles in the upper part of the crucible, while the grains in the middle and bottom are too small. This single-layer crucible structure makes it difficult to achieve uniform temperature field and uniform particle size. The particle size of silicon carbide powder between 5 and 10 mm accounts for 30%, the particle size between 1 and 5 mm accounts for 50%, and the particle size of silicon carbide powder ≤ 1 mm accounts for 20%.

[0095] Comparative Example 2

[0096] Compared with Example 1, the crucible structure of Comparative Example 2 is the same, and a multi-layer crucible is formed by stacking multiple single-layer crucibles of the same structure. In the synthesis method, the synthesis step of β-SiC is not performed, and the temperature is directly raised to 2000-2400° C. while maintaining the pressure at 50 mbar to perform the transformation of α-SiC.

[0097] After the synthesis is completed, only large-particle powder exists on the outer side of the upper part of the crucible, and the inner part of the powder is large-particle, but not uniform. The multi-layer crucible structure provides a uniform temperature field, but lacks the formation and initial growth of β-SiC nuclei, resulting in unsatisfactory α-SiC transformation and large-particle growth, and thus cannot achieve uniform large-particle silicon carbide powder. The particle size of silicon carbide powder between 5 and 10 mm accounts for 60%, the particle size between 1 and 5 mm accounts for 25%, and the particle size of silicon carbide powder ≤ 1 mm accounts for 15%.

[0098] Comparative Example 3

[0099] Compared with Example 1, the crucible structure of Comparative Example 3 increases the number of stacking layers while keeping the size of the single-layer crucible unchanged to verify the synthesis effect. The height of the single-layer crucible is maintained at 100 mm, the inner diameter of the crucible is 280 mm, and the wall thickness of the crucible is 15 mm. In addition, the material of the graphite sheet (crystallization plate) is changed to medium-coarse graphite, and the diameter of the vent hole on the crucible cover is 140 mm. Six single-layer crucibles with the same internal structure are stacked vertically along the central axis to form a multi-crucible structure.

[0100] In the synthesized powder, due to the large overall height of the crucible, the temperature field difference between the single-layer crucibles at different positions is large, resulting in the upper crucible temperature being lower than the bottom crucible temperature. The powder particles in the top crucible are small, with a small proportion of large particles, while the powder particles in the bottom crucible are large, resulting in an overall uneven phenomenon. The particle size of silicon carbide powder between 5 and 10 mm accounts for 55%, the particle size between 1 and 5 mm accounts for 30%, and the particle size of silicon carbide powder ≤ 1 mm accounts for 15%.

[0101] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A silicon carbide powder synthesis crucible, characterized in that: The silicon carbide powder synthesis crucible is formed by stacking single-layer crucibles of the same structure up and down along the central axis of a graphite crucible; the single-layer crucible comprises a crucible cover, a graphite sheet and a crucible body; the crucible cover and the crucible body are nested; the bottom of the inner cavity of the crucible body is used to place silicon powder and graphite powder; the graphite sheet is clamped between the crucible cover and the crucible body.

2. The silicon carbide powder synthesis crucible according to claim 1, characterized in that: The crucible upper cover of the single-layer crucible is composed of a graphite gas distribution plate and a graphite disc, which are connected by threads and have a vent hole in the center.

3. The silicon carbide powder synthesis crucible according to claim 1, characterized in that: The single-layer crucible with the same structure is composed of 3 to 5 single-layer crucible structures assembled along the central axis of the graphite crucible.

4. The silicon carbide powder synthesis crucible according to claim 1, characterized in that: The crucible cover and the crucible body of the single-layer crucible are both made of isostatic graphite; Preferably, the graphite sheet is made of porous graphite or medium-coarse graphite, with a thickness of 3 to 10 mm; Preferably, the height of the single-layer crucible body is 100-120 mm, the inner diameter is 280-350 mm, and the wall thickness is 15-30 mm; Preferably, the diameter of the vent hole in the center of the crucible upper cover of the single-layer crucible is 100-140 mm.

5. The silicon carbide powder synthesis crucible according to claim 1, characterized in that: The filling amount of the mixed powder formed by the silicon powder and the graphite powder is 1 / 3-2 / 3 of the height of the single-layer crucible.

6. A method for using a silicon carbide powder synthesis crucible, characterized in that: The following steps are involved: S1. Mix high-purity silicon powder and high-purity graphite powder evenly and place them in each single-layer crucible; S2, assembling the single-layer crucible and placing it in a synthesis furnace, introducing a protective gas into the synthesis furnace, performing a first heating treatment and a second heating treatment, and performing a heat preservation treatment after reaching a first pressure value to obtain β-SiC; S3, introducing protective gas into the synthesis furnace, performing a third heating treatment, and performing a heat preservation treatment after reaching a second pressure value; After the heat preservation is completed, the pressure is raised to a third pressure value, and then the temperature is lowered to room temperature to obtain α-SiC powder.

7. The method of use according to claim 6, characterized in that: In step S1, the purity of the high-purity graphite powder and the high-purity silicon powder are both 6N level, wherein the particle size of the graphite powder is 5-200 μm, and the particle size of the silicon powder is 20-500 μm; the molar ratio of the high-purity silicon powder to the high-purity graphite powder is 1:

1.

8. The method of use according to claim 6, characterized in that: In step S2, the protective gas is selected from one of argon (Ar), hydrogen (H2), and a mixed gas of hydrogen and argon, and the flow rate ratio of hydrogen in the mixed gas is 0-20%.

9. The method of use according to claim 6, characterized in that: In step S2, the temperature of the first heat treatment is 800-1000°C; the temperature of the second heat treatment is 1400-1800°C; the first pressure value is 0-10 mbar; and the insulation time is 6-10 hours.

10. The method of use according to claim 6, characterized in that: In step S3, the temperature of the third heat treatment is 2000-2500°C; the second pressure value is 50-800 mbar; the insulation time is 20-60 hours; and the third pressure value is 800-1000 mbar.

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