Method for synthesizing flaky monocrystal silicon carbide powder

Abstract

The invention provides a synthetic method of flaky monocrystal silicon carbide powder. The synthesis method sequentially comprises the steps of pretreatment of reaction materials, filling of the reaction materials, heating synthesis of powder and the like. The pre-treatment of the reaction materials comprises the following steps: preparing graphite powder and silicon blocks with different particle sizes, soaking by utilizing a silane coupling agent ethanol solution, drying, ball-milling and mixing the dried graphite powder, a solid-phase substance, a dispersing agent and the ethanol solution, and drying and screening to obtain a solid-phase mixture; the reaction material filling comprises the following steps: sequentially placing silicon blocks with particle sizes from large to small in layers along the direction from the bottom to the top of the crucible, and filling a solid phase mixture with the same layer height into gaps of the silicon blocks when each layer of silicon blocks is placed; the powder heating synthesis comprises the following steps: putting a crucible into a silicon carbide powder synthesis furnace, and heating and synthesizing to obtain a reaction mixture. According to the synthesis method provided by the invention, the crystal quality and particle size uniformity of the silicon carbide powder are obviously improved, and the stacking density is effectively kept stable.

Description

Technical Field

[0001] This invention relates to the field of semiconductor materials technology, specifically to the field of silicon carbide synthesis technology, and more particularly to a method for synthesizing sheet-like single-crystal silicon carbide powder. Background Technology

[0002] Silicon carbide single crystals, as an important functional material, have broad application prospects in wide-bandgap semiconductor devices, high-temperature, high-frequency, high-power electronic devices, light-emitting devices, and lasers. Physical vapor deposition (PVT), a method for preparing silicon carbide, has attracted widespread attention due to its advantages of high efficiency, low cost, and high crystal quality. This method involves heating high-purity silicon carbide powder to a high temperature, causing it to volatilize into gaseous components such as gaseous Si, gaseous Si₂C, and gaseous SiC₂. These gaseous components are then transported to a low-temperature cooling zone, where they are deposited onto a seed crystal, ultimately forming a silicon carbide single crystal of a certain thickness.

[0003] Currently, the industrial preparation of silicon carbide powder mainly relies on self-propagating high-temperature synthesis or carbothermal reduction. Although these methods have cost advantages, they have significant limitations in terms of powder quality. The silicon carbide powder used in the silicon carbide single crystal growth process is mostly needle-shaped or porous spherical, with a crystal structure that is mainly polycrystalline or amorphous and has many grain boundaries. This type of silicon carbide usually needs to be processed by crushing and screening to obtain silicon carbide powder that can be used for crystal growth. However, the subsequent crushing and screening process may introduce other impurities, increase the metal content, and increase the processing time and cost.

[0004] Meanwhile, silicon carbide powder synthesized by conventional methods has unstable packing density and generally poor particle size uniformity, making it difficult to pack tightly in the growth crucible and forming a large number of pores. This leads to uneven heat conduction and ineffective sublimation of the powder in the porous areas. In particular, the internal pores of needle-shaped silicon carbide particles may collapse or close at high temperatures, causing fluctuations in crystal growth rate. Moreover, their high specific surface area due to their porous structure makes them more prone to adsorbing metallic impurities and volatile organic compounds.

[0005] Therefore, there is a need to develop a method for synthesizing sheet-like single-crystal silicon carbide powder that can significantly improve the crystal quality and particle size uniformity of silicon carbide powder, maintain stable packing density, and improve the quality of silicon carbide crystal growth. Summary of the Invention

[0006] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a method for synthesizing sheet-like single-crystal silicon carbide powder. This powder synthesis method introduces solid phase materials, which allow silicon carbide grains to preferentially nucleate on the surfaces of these materials during the synthesis process. This heterogeneous nucleation method can promote uniform nucleation of grains and help form silicon carbide powder with more uniform particle size. Furthermore, silicon blocks of different particle sizes are placed in the growth crucible from bottom to top in multiple levels. By gradually reducing the size of the silicon blocks, a balanced release of silicon vapor is achieved. At the same time, the bottom and top of the crucible are filled with a mixture of solid solvent and graphite powder with different concentration ratios. The high concentration at the bottom enhances heterogeneous nucleation and inhibits the growth of large grains, while the low concentration at the top allows for moderate grain merging, balancing the reaction rate. By matching the silicon vapor diffusion rate through the concentration gradient, a uniform transition of grain size from bottom to top is achieved.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] A method for synthesizing sheet-like single-crystal silicon carbide powder includes the following steps:

[0009] Step 1, Pre-treatment of reaction materials: Prepare graphite powder and silicon blocks of different particle sizes. Soak the graphite powder in ethanol solution of silane coupling agent and dry it. Ball mill and mix the dried graphite powder with solid phase material, dispersant and ethanol solution. After drying and sieving, a solid phase mixture is obtained. The solid phase material includes at least one of hexagonal boron nitride, silicon nitride, boron carbide, polycarbosilane or carbon nanotubes.

[0010] In step 1, the amount of silane coupling agent is 1-5% of the mass of graphite powder; the silane coupling agent ethanol solution is used to enhance the surface activity of graphite powder; the mass ratio of solid phase material to graphite powder is between 1:100 and 1:1000; the solid phase material is used to preferentially nucleate on the surface of the former during the synthesis of silicon carbide powder, promoting the uniform nucleation of silicon carbide grains.

[0011] This invention introduces a solid phase material with a similar lattice structure to silicon carbide crystals, which significantly reduces the nucleation interface energy, allowing silicon carbide grains to preferentially undergo heterogeneous nucleation on their surfaces. Furthermore, ball milling highly disperses the solid phase material within the graphite powder, creating uniformly distributed nucleation sites in the reaction system. This ensures that crystal nuclei form spatially uniformly, avoiding size differentiation caused by localized explosive nucleation. The increased density of heterogeneous nucleation sites shortens the diffusion paths of carbon and silicon atoms, suppressing overgrowth of individual grains, thereby significantly improving the monodispersity and grain size uniformity of the silicon carbide powder.

[0012] Step 2, Filling the reactants: Place silicon blocks of decreasing size in layers from bottom to top of the crucible. After each layer of silicon blocks is placed, fill the gaps between the silicon blocks with a solid phase mixture of the same height. The concentration of solid phase substances in the solid phase mixture gradually decreases from bottom to top of the crucible. After all the filling is completed, seal the crucible.

[0013] In step 2, the silicon block particle size ranges from 1 to 3 cm, the difference in silicon block particle size between the same layer does not exceed 0.5 cm, and the difference in silicon block particle size between adjacent layers does not exceed 1 cm.

[0014] In step 2, the mass ratio of solid phase material to graphite powder in the solid phase mixture filled at the bottom of the crucible is between 1:100 and 1:500, and the mass ratio of solid phase material to graphite powder in the solid phase mixture filled at the top of the crucible along the direction from the bottom to the top is between 1:500 and 1:1000.

[0015] This invention achieves gradient control of silicon vapor release by filling a crucible with silicon blocks of different sizes. Larger silicon blocks at the bottom of the crucible have a smaller specific surface area and a slower vaporization rate, providing a continuous and stable supply of silicon vapor. Smaller silicon blocks at the top of the crucible have a larger specific surface area and a faster vaporization rate, compensating for the concentration decay as vapor diffuses to the top. Correspondingly, this invention controls the gradient distribution of solid phase material concentration. The high-concentration solid phase material at the bottom of the crucible enhances heterogeneous nucleation density, rapidly consuming silicon vapor in the high-temperature region and suppressing large grain formation. The low-concentration solid phase material at the top of the crucible reduces the density of nucleation sites, allowing for moderate grain merging and avoiding low density caused by excessively fine grain size. The solid phase material concentration gradient is negatively correlated with the silicon vapor diffusion rate, ensuring a consistent nucleation growth rate per unit volume along the silicon vapor diffusion path and achieving a continuous and uniform transition in grain size from the bottom to the top of the crucible.

[0016] Step 3: Heating and synthesizing silicon carbide powder: After placing the crucible into the silicon carbide powder synthesis furnace, heating and synthesizing to obtain the reaction mixture.

[0017] In step 3, before placing the crucible into the silicon carbide powder synthesis furnace, the position of the heating coil is first adjusted to ensure that the temperature gradient during the heating synthesis process is [value missing]. After placing the crucible into the silicon carbide powder synthesis furnace, the furnace cavity was sealed and a vacuum was drawn. The furnace was gradually heated to T1, and then argon gas was introduced until the pressure inside the furnace cavity reached P1. Argon gas was then continuously introduced at a flow rate of Q, and the temperature was further increased to T2 while the pressure was increased to P2. After holding at this temperature for a time t, the mixture was cooled to T3 to obtain the reaction mixture.

[0018] In step 3, the temperature gradient The temperature range is 3-5℃ / cm; the temperature range of T1 is 900~1500℃; the temperature range of T2 is 2100~2400℃; the temperature range of T3 is 20~40℃; the holding time of t is 10~30h.

[0019] In step 3, the pressure range of P1 is 800-950 mbar; the pressure range of P2 is 300-600 mbar; and the flow rate range of Q is 10-1000 sccm.

[0020] Step 4, Post-treatment of silicon carbide powder: The reaction mixture is acid-washed with a mixture of hydrofluoric acid and hydrochloric acid to obtain silicon carbide powder.

[0021] The silicon carbide powder obtained in step 4 is a plate-like polygonal single crystal with a bulk density of 1.45-1.95 g / cm³. 3 The single crystal ratio is 90-99%, the thickness is 10-100um, and the side length is 100-500um.

[0022] In step 4, the mass ratio of hydrofluoric acid to hydrochloric acid is 1:1-1:4, the concentration of hydrofluoric acid is 5-10wt%, the concentration of hydrochloric acid is 15-20wt%, and the cleaning time is 2-4h.

[0023] Compared with existing technical solutions, the present invention has at least the following beneficial effects:

[0024] 1. This invention introduces solid phase materials, which enable silicon carbide grains to preferentially nucleate on the surfaces of these materials during the synthesis process. This heterogeneous nucleation can promote uniform nucleation of grains, thereby helping to form silicon carbide powder with more uniform particle size.

[0025] 2. This invention places silicon blocks of different particle sizes in multiple levels from the bottom to the top of the growth crucible. By gradually reducing the size of the silicon blocks, a balanced release of silicon vapor is achieved. The top and bottom are filled with a mixture of solid solvent and graphite powder at different concentration ratios. The high concentration at the bottom enhances heterogeneous nucleation and inhibits the growth of large grains, while the low concentration at the top allows for moderate grain merging, balancing the reaction rate. By matching the concentration gradient with the silicon vapor diffusion rate, a uniform transition of grain size from bottom to top is achieved, which significantly improves the crystal quality and particle size uniformity of silicon carbide powder and maintains stable packing density.

[0026] 3. This invention uses a silane coupling agent to pretreat graphite powder, enhancing the interfacial bonding with the solid phase and increasing the reaction contact area. Simultaneously, a dispersant is introduced to improve the mixing uniformity of the solid phase and graphite powder, ensuring that the solid phase particles uniformly coat the graphite surface, increasing the density of effective nucleation sites, and thus optimizing the efficiency and product quality of the silicon carbide synthesis reaction. Attached Figure Description

[0027] Figure 1This invention relates to the method of filling the crucible with reactants in a method for synthesizing sheet-like single-crystal silicon carbide powder.

[0028] Among them: 1. solid phase mixture; 2. silicon block; 3. crucible. Detailed Implementation

[0029] The present invention will now be described in further detail with reference to the accompanying drawings and specific preferred embodiments.

[0030] In the description of this invention, it should be understood that the terms "left side," "right side," "upper part," "lower part," "top," and "bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Terms such as "first" and "second" do not indicate the importance of components and therefore should not be construed as limitations on the invention. The specific dimensions used in this embodiment are only for illustrating the technical solution and do not limit the scope of protection of this invention. Those skilled in the art should understand that the embodiments described are merely to help understand the invention and should not be considered as specific limitations on the invention.

[0031] Example 1

[0032] This embodiment provides a method for synthesizing sheet-like single-crystal silicon carbide powder, and the synthesis method includes:

[0033] Step 1: Prepare graphite powder and silicon blocks of different particle sizes 2. Soak the graphite powder in an ethanol solution containing a silane coupling agent, controlling the amount of silane coupling agent to be 5% of the graphite powder mass. After soaking, dry the graphite powder. Divide the dried graphite powder into equal groups, and ball-mill each group with a solid phase material, dispersant, and ethanol solution. After drying and sieving, obtain a solid phase mixture 1. Adjust the mass ratio of the solid phase material to graphite powder in each group, resulting in 6 groups with the following mass ratios: 1:100, 1:280, 1:460, 1:640, 1:820, and 1:1000. The solid phase material selected is hexagonal boron nitride.

[0034] Step 2: Place silicon blocks 2 in layers from bottom to top of crucible 3, with particle sizes decreasing sequentially. Use four sets of silicon blocks 2 of different sizes. The particle sizes of each layer of silicon blocks 2 from bottom to top of crucible 3 are 2.5cm-3cm, 2cm-2.5cm, 1.5cm-2cm, and 1cm-1.5cm, respectively. The particle size difference of silicon blocks 2 in the same layer should not exceed 0.5cm. After each layer of silicon blocks 2 is placed, fill the gaps between the silicon blocks 2 with a solid phase mixture 1 of the same height. The concentration of solid phase material in the solid phase mixture 1 gradually decreases from bottom to top of crucible 3. After all filling is completed, seal crucible 3.

[0035] Step 3: First, adjust the position of the heating coil to achieve a temperature gradient of 5℃ / cm during the heating and synthesis process. Place crucible 3 into the silicon carbide powder synthesis furnace, seal the furnace cavity, and evacuate. Gradually raise the temperature inside the furnace to 1200℃, then introduce argon gas until the pressure inside the furnace cavity reaches 800mbar. Continue to introduce argon gas at a flow rate of 50-200 sccm, and continue to raise the temperature to 2300℃ while reducing the pressure to 300mbar. After holding at this temperature for 15 hours, cool to 40℃ to obtain the reaction mixture.

[0036] Step 4: The reaction mixture is acid-washed at 80°C and 0.2 MPa for 2 hours using a mixture of hydrofluoric acid (5 wt%) and hydrochloric acid (15 wt%) (mass ratio 1:1) to obtain silicon carbide powder.

[0037] Example 2

[0038] Step 1: Prepare graphite powder and silicon blocks of different particle sizes 2. Soak the graphite powder in an ethanol solution containing a silane coupling agent, controlling the amount of silane coupling agent to be 5% of the graphite powder mass. After soaking, dry the graphite powder. Divide the dried graphite powder into equal groups, and ball-mill each group with a solid phase material, dispersant, and ethanol solution. After drying and sieving, obtain a solid phase mixture 1. Adjust the mass ratio of the solid phase material to graphite powder in each group, resulting in 6 groups with the following mass ratios: 1:100, 1:240, 1:380, 1:520, 1:660, and 1:800. The solid phase material selected is hexagonal boron nitride.

[0039] Step 2: Place silicon blocks 2 in layers from bottom to top of crucible 3, with particle sizes decreasing sequentially. Use four sets of silicon blocks 2 of different sizes. The particle sizes of each layer of silicon blocks 2 from bottom to top of crucible 3 are 2.5cm-3cm, 2cm-2.5cm, 1.5cm-2cm, and 1cm-1.5cm, respectively. The particle size difference of silicon blocks 2 in the same layer should not exceed 0.5cm. After each layer of silicon blocks 2 is placed, fill the gaps between the silicon blocks 2 with a solid phase mixture 1 of the same height. The concentration of solid phase material in the solid phase mixture 1 gradually decreases from bottom to top of crucible 3. After all filling is completed, seal crucible 3.

[0040] Step 3: First, adjust the position of the heating coil to achieve a temperature gradient of 5℃ / cm during the heating and synthesis process. Place crucible 3 into the silicon carbide powder synthesis furnace, seal the furnace cavity, and evacuate. Gradually raise the temperature inside the furnace to 1200℃, then introduce argon gas until the pressure inside the furnace cavity reaches 800mbar. Continue to introduce argon gas at a flow rate of 50-200 sccm, and continue to raise the temperature to 2300℃ while reducing the pressure to 300mbar. After holding at this temperature for 15 hours, cool to 40℃ to obtain the reaction mixture.

[0041] Step 4: The reaction mixture is acid-washed with a mixture of hydrofluoric acid (8 wt%) and hydrochloric acid (16 wt%) (mass ratio 1:2) to obtain silicon carbide powder.

[0042] Example 3

[0043] This embodiment provides a method for synthesizing sheet-like single-crystal silicon carbide powder, and the synthesis method includes:

[0044] Step 1: Prepare graphite powder and silicon blocks of different particle sizes 2. Soak the graphite powder in an ethanol solution containing a silane coupling agent, controlling the amount of silane coupling agent to be 5% of the graphite powder mass. After soaking, dry the graphite powder. Divide the dried graphite powder into equal groups, and ball-mill each group with a solid phase material, dispersant, and ethanol solution. After drying and sieving, obtain a solid phase mixture 1. Adjust the mass ratio of the solid phase material to graphite powder in each group, resulting in 6 groups with the following mass ratios: 1:100, 1:280, 1:460, 1:640, 1:820, and 1:1000. The solid phase material selected is hexagonal boron nitride.

[0045] Step 2: Place silicon blocks 2 in layers from bottom to top of crucible 3, with particle sizes decreasing sequentially. Use four sets of silicon blocks 2 of different sizes. The particle sizes of each layer of silicon blocks 2 from bottom to top of crucible 3 are 2.7cm-3cm, 2.4cm-2.7cm, 2.1cm-2.4cm, and 1.8cm-2.1cm, respectively. The particle size difference of silicon blocks 2 in the same layer should not exceed 0.3cm. After each layer of silicon blocks 2 is placed, fill the gaps between the silicon blocks 2 with a solid phase mixture 1 of the same height. The concentration of solid phase material in the solid phase mixture 1 gradually decreases from bottom to top of crucible 3. After all filling is completed, seal crucible 3.

[0046] Step 3: First, adjust the position of the heating coil to achieve a temperature gradient of 5℃ / cm during the heating and synthesis process. Place crucible 3 into the silicon carbide powder synthesis furnace, seal the furnace cavity, and evacuate. Gradually raise the temperature inside the furnace to 1200℃, then introduce argon gas until the pressure inside the furnace cavity reaches 800mbar. Continue to introduce argon gas at a flow rate of 50-200 sccm, and continue to raise the temperature to 2300℃ while reducing the pressure to 300mbar. After holding at this temperature for 15 hours, cool to 40℃ to obtain the reaction mixture.

[0047] Step 4: The reaction mixture is acid-washed for 2 hours using a mixture of hydrofluoric acid (10wt%) and hydrochloric acid (20wt%) (mass ratio 1:4) to obtain silicon carbide powder.

[0048] Example 4

[0049] This embodiment provides a method for synthesizing sheet-like single-crystal silicon carbide powder, and the synthesis method includes:

[0050] Step 1: Prepare graphite powder and silicon blocks 2 of different particle sizes. Soak the graphite powder in an ethanol solution containing a silane coupling agent, controlling the amount of silane coupling agent to be 5% of the graphite powder mass. After soaking, dry the graphite powder. Divide the dried graphite powder into equal groups, and ball-mill each group with a solid phase material, dispersant, and ethanol solution. After drying and sieving, obtain a solid phase mixture 1. Adjust the mass ratio of the solid phase material to graphite powder in each group, dividing it into 10 groups. The mass ratios of the solid phase material to graphite powder in each group are: 1:100, 1:200, 1:300, 1:400, 1:500, 1:600, 1:700, 1:800, 1:900, and 1:1000. The solid phase material is hexagonal boron nitride.

[0051] Step 2: Place silicon blocks 2 in layers from bottom to top of crucible 3, with particle sizes decreasing sequentially. Use 6 sets of silicon blocks 2 with different particle sizes. The particle sizes of each layer of silicon blocks 2 from bottom to top of crucible 3 are: 2.5cm-3cm, 2.2cm-2.7cm, 1.9cm-2.4cm, 1.6cm-2.1cm, 1.3cm-1.8cm, and 1cm-1.5cm, respectively. The particle size difference of silicon blocks 2 in the same layer should not exceed 0.5cm. After each layer of silicon blocks 2 is placed, fill the gaps in the silicon blocks 2 with a solid phase mixture 1 of the same height. The concentration of solid phase material in the solid phase mixture 1 gradually decreases from bottom to top of crucible 3. After all filling is completed, seal crucible 3.

[0052] Step 3: First, adjust the position of the heating coil to achieve a temperature gradient of 5℃ / cm during the heating and synthesis process. Place crucible 3 into the silicon carbide powder synthesis furnace, seal the furnace cavity, and evacuate. Gradually raise the temperature inside the furnace to 1200℃, then introduce argon gas until the pressure inside the furnace cavity reaches 800mbar. Continue to introduce argon gas at a flow rate of 50-200 sccm, and continue to raise the temperature to 2300℃ while reducing the pressure to 300mbar. After holding at this temperature for 15 hours, cool to 40℃ to obtain the reaction mixture.

[0053] Step 4: The reaction mixture is acid-washed with a mixture of hydrofluoric acid (6wt%) and hydrochloric acid (16wt%) (mass ratio 1:3) to obtain silicon carbide powder.

[0054] Example 5

[0055] This embodiment provides a method for synthesizing sheet-like single-crystal silicon carbide powder. In step 1 of the synthesis method, the solid phase material is selected as carbon nanotubes. Except for the above, the other conditions are exactly the same as in Example 1.

[0056] Comparative Example 1

[0057] This embodiment provides a method for synthesizing sheet-like single-crystal silicon carbide powder. In step 1 of the synthesis method, no solid phase material is used. Only graphite powder, dispersant and ethanol solution are ball-milled and mixed. Except for the above, the other conditions are exactly the same as in Example 1.

[0058] Comparative Example 2

[0059] This embodiment provides a method for synthesizing sheet-like single-crystal silicon carbide powder. In step 1 of the synthesis method, the mass ratio of solid phase material to graphite powder is kept constant at 1:500. In step 2, a single-concentration solid phase mixture 1 is filled into a crucible 3 with no concentration change. Except for the above, the other conditions are exactly the same as in Example 1.

[0060] Comparative Example 3

[0061] This embodiment provides a method for synthesizing sheet-like single-crystal silicon carbide powder. In step 2 of the synthesis method, silicon blocks 2 with the same particle size are placed along the direction from the bottom to the top of the crucible 3. Except for the above, the other conditions are exactly the same as those in Embodiment 1.

[0062] Comparative Example 4

[0063] This embodiment provides a method for synthesizing sheet-like single-crystal silicon carbide powder. In step 2 of the synthesis method, the concentration of solid phase material in the solid phase mixture 1 gradually increases from the bottom to the top of the crucible 3. Except for the above, the other conditions are exactly the same as in Example 1.

[0064] Comparative Example 5

[0065] This embodiment provides a method for synthesizing sheet-like single-crystal silicon carbide powder. In step 3 of the synthesis method, the temperature of T2 is adjusted from 2200℃ to 2000℃. Apart from the above, the other conditions are exactly the same as in embodiment 1.

[0066] Comparative Example 6

[0067] This embodiment provides a method for synthesizing sheet-like single-crystal silicon carbide powder. In step 1 of the synthesis method, the amount of silane coupling agent is controlled to be 0.1% of the mass of graphite powder. Except for the above, the other conditions are exactly the same as those in Example 1.

[0068] Comparative Example 7

[0069] This embodiment provides a method for synthesizing sheet-like single-crystal silicon carbide powder. In step 1 of the synthesis method, the amount of silane coupling agent is controlled to be 10% of the mass of graphite powder. Apart from the above, the other conditions are exactly the same as those in Example 1.

[0070] Comparative Example 8

[0071] This embodiment provides a method for synthesizing sheet-like single-crystal silicon carbide powder. In step 3 of the synthesis method, the position of the heating coil is adjusted to create a temperature gradient during the heating synthesis process. The temperature was 1℃ / cm, and all other conditions were exactly the same as in Example 1.

[0072] Comparative Example 9

[0073] This embodiment provides a method for synthesizing sheet-like single-crystal silicon carbide powder. In step 3 of the synthesis method, the position of the heating coil is adjusted to create a temperature gradient during the heating synthesis process. The temperature was 10℃ / cm, and all other conditions were exactly the same as in Example 1.

[0074] Comparative Example 10

[0075] This embodiment provides a method for synthesizing sheet-like single-crystal silicon carbide powder. In step 3 of the synthesis method, after heating to T2, the pressure is simultaneously increased to P2, where the pressure is set to 1200 mbar. Apart from the above, the other conditions are exactly the same as in Embodiment 1.

[0076] The test results obtained by performing grain size detection, Span value calculation, single crystal ratio detection, and packing density detection on the silicon carbide powders obtained in Examples 1-5 and Comparative Examples 1-5 are shown in Table 1.

[0077] Table 1

[0078]

[0079]

[0080] The comparison of the test results shows that:

[0081] Example 2, based on Example 1, reduced the concentration range of the solid phase mixture 1 within crucible 3, thus decreasing the concentration gradient and consequently reducing particle size uniformity and packing density. Example 3 further reduced the particle size difference among silicon blocks 2 in the same layer, effectively eliminating vapor pressure fluctuations and improving the quality of the synthesized silicon carbide powder. Example 4 used more grouped solid phase mixture 1 and silicon blocks 2, further reducing vapor pressure fluctuations and concentration deviations, effectively eliminating grain size defects. Example 5 replaced the solid phase material with hexagonal boron nitride. Due to the higher surface energy of carbon nanotubes, the heterogeneous nucleation efficiency decreased, resulting in a decline in the quality of the synthesized silicon carbide powder.

[0082] In Comparative Example 1, due to the lack of solid phase material, there are no heterogeneous nucleation sites during the powder synthesis process, which leads to a decrease in the contact efficiency between graphite powder and silicon block 2, a significant increase in the mass fraction of free carbon, and a significant decrease in the quality of silicon carbide powder.

[0083] In Comparative Example 2, the concentration of the solid phase mixture 1 remains constant, which cannot effectively match the distribution of silicon blocks 2 with different particle sizes. This results in coarse crystals at the top and fine powder at the bottom, with a large span in the grain size distribution, which cannot effectively guarantee the uniformity of the silicon carbide powder particle size.

[0084] In Comparative Example 3, the silicon block 2 with a single particle size cannot balance the release of silicon vapor, resulting in a pulsed change in the silicon evaporation rate. This leads to intermittent nucleation and growth, and the grains are prone to fracture structures, with a significant reduction in particle size uniformity.

[0085] In Comparative Example 4, selecting a reverse concentration gradient for powder growth will further lead to a difference in particle size between the top and bottom of the crucible 3. The bottom solid phase mixture 1 has a lower concentration, and the silicon block 2 has a larger particle size, making the coarsening phenomenon at the bottom more obvious. The high-concentration solid phase mixture 1 at the top and the small-particle silicon block 2 will synthesize ultrafine powder with a particle size of less than 1 μm, which cannot be mixed.

[0086] In Comparative Example 5, the reaction temperature was reduced to 2000℃, which could not make the phase transformation complete. The proportion of β-SiC phase exceeded 30%, polycrystalline agglomeration was severe, the single crystal rate was significantly reduced, and the polycrystalline interface would further hinder the densification of silicon carbide powder.

[0087] In Comparative Examples 6 and 7, the amount of silane coupling agent was controlled to be 0.1% and 10% of the graphite powder mass, respectively. Too low an amount of silane coupling agent would result in insufficient coverage of the graphite powder surface, failing to effectively anchor the solid phase particles, leading to uneven dispersion of the solid phase material, failure of nucleation sites, and thus low Span value and packing density. On the other hand, too high an amount of silane coupling agent would lead to the formation of a large number of clusters, adsorbing a large amount of solid phase material. These clusters would not only nucleate densely on their surface, but also coat the SiC particles with residue after powder synthesis. In terms of Span value, due to the uneven distribution of the solid phase material, the synthesized silicon carbide powder would have various morphologies, resulting in a multi-peak distribution of its Span value. Similarly, the corresponding packing density would also decrease significantly.

[0088] In Comparative Examples 8 and 9, the temperature gradient during the synthesis of silicon carbide powder was controlled at 1℃ / cm and 10℃ / cm, respectively. When the temperature gradient was set too high, the temperature difference between the high-temperature and low-temperature zones in crucible 3 increased, the area of ​​intense reaction became highly concentrated, and the nucleation rate in the high-temperature zone was much higher than the growth rate, which led to an excessive number of fine particles, irregular particle shapes, a significant increase in the Span value, and a significant decrease in its packing density. When the temperature gradient was set lower, the temperature distribution in crucible 3 was more uniform, the reaction rate difference was small, and the nucleation and growth rates were close to equilibrium, which could ensure improved particle size uniformity. However, the lower temperature gradient resulted in more unreacted impurities remaining, leading to a decrease in the purity of silicon carbide powder crystals and a decrease in the single crystal rate.

[0089] In Comparative Example 10, the pressure was increased to above standard atmospheric pressure during the heating process of silicon carbide powder synthesis. The high pressure setting increased the partial pressure of the gas phase and the supersaturation, which made the nucleation rate much higher than the growth rate. This resulted in a sharp increase in the proportion of finer particles. Furthermore, the gas diffusion resistance increased accordingly under high pressure, which confined the reaction to the high-temperature region. This led to a large difference in particle size between the high-temperature core region and the edge, resulting in a significant deterioration in the Span value and packing density.

[0090] As can be seen from the above, this invention not only introduces solid phase material, enabling silicon carbide grains to preferentially nucleate on the surface of the solid phase material during the synthesis process, thus promoting uniform grain nucleation and helping to form silicon carbide powder with more uniform particle size, but also places silicon blocks 2 of different particle sizes in multiple levels from the bottom to the top of the crucible 3. By gradually reducing the size of the silicon blocks 2, a balanced release of silicon vapor is achieved. The top and bottom are filled with a mixture of solid solvent and graphite powder with different concentration ratios. The high concentration at the bottom enhances heterogeneous nucleation and inhibits the growth of large grains, while the low concentration at the top allows for moderate grain merging, balancing the reaction rate. By matching the concentration gradient with the silicon vapor diffusion rate, a uniform transition of grain size from bottom to top is achieved, which significantly improves the crystal quality and particle size uniformity of silicon carbide powder and maintains stable packing density.

[0091] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0092] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0093] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for synthesizing sheet-like single-crystal silicon carbide powder, characterized in that: Includes the following steps: Step 1, Pre-treatment of reactants: Prepare graphite powder and silicon blocks of different particle sizes. Soak the graphite powder in an ethanol solution of silane coupling agent and dry it. Ball mill and mix the dried graphite powder with solid phase material, dispersant and ethanol solution. After drying and sieving, a solid phase mixture is obtained. The solid phase material includes at least one of hexagonal boron nitride, silicon nitride, boron carbide, polycarbosilane or carbon nanotubes. Step 2, Filling the reactants: Place silicon blocks of decreasing size in layers from bottom to top of the crucible. After each layer of silicon blocks is placed, fill the gaps between the silicon blocks with a solid phase mixture of the same height. The concentration of solid phase substances in the solid phase mixture gradually decreases from bottom to top of the crucible. After all the filling is completed, seal the crucible. Step 3: Heating synthesis of silicon carbide powder: After placing the crucible into the silicon carbide powder synthesis furnace, heating and synthesizing to obtain the reaction mixture; Step 4, Post-treatment of silicon carbide powder: The reaction mixture is acid-washed under heated and pressurized conditions using a mixture of hydrofluoric acid and hydrochloric acid to obtain silicon carbide powder.

2. The method for synthesizing sheet-like single-crystal silicon carbide powder according to claim 1, characterized in that: In step 1, the amount of silane coupling agent is 1-5% of the mass of graphite powder; the silane coupling agent ethanol solution is used to enhance the surface activity of graphite powder; the mass ratio of solid phase material to graphite powder is between 1:100 and 1:1000; the solid phase material is used to preferentially nucleate on the surface of the former during the synthesis of silicon carbide powder, promoting the uniform nucleation of silicon carbide grains.

3. The method for synthesizing sheet-like single-crystal silicon carbide powder according to claim 2, characterized in that: In step 2, the silicon block particle size ranges from 1 to 3 cm, the difference in silicon block particle size between the same layer does not exceed 0.5 cm, and the difference in silicon block particle size between adjacent layers does not exceed 1 cm.

4. The method for synthesizing sheet-like single-crystal silicon carbide powder according to claim 2, characterized in that: In step 2, the mass ratio of solid phase material to graphite powder in the solid phase mixture filled at the bottom of the crucible is between 1:100 and 1:500, and the mass ratio of solid phase material to graphite powder in the solid phase mixture filled at the top of the crucible along the direction from the bottom to the top is between 1:500 and 1:1000.

5. The method for synthesizing sheet-like single-crystal silicon carbide powder according to any one of claims 1 to 4, characterized in that: In step 3, before placing the crucible into the silicon carbide powder synthesis furnace, the position of the heating coil is first adjusted to ensure that the temperature gradient during the heating synthesis process is [value missing]. ∇T After placing the crucible into the silicon carbide powder synthesis furnace, the furnace cavity is sealed and a vacuum is drawn. The temperature inside the furnace is then gradually increased to [temperature missing]. T 1 Argon gas was then introduced until the pressure inside the furnace reached the required level. P 1 After that, the continuous inflow was Q Argon gas was added, and the temperature was further increased to... T 2 At the same time, reduce the pressure P 2 Insulation time t Then, cool to T 3 The reaction mixture was obtained.

6. The method for synthesizing sheet-like single-crystal silicon carbide powder according to claim 5, characterized in that: In step 3, the temperature gradient ∇T 3-5℃; T 1 The temperature range is 900~1500℃; T 2 The temperature range is 2100~2400℃; T 3 The temperature range is 20~40℃; t The heat preservation time is 10~30 hours.

7. The method for synthesizing sheet-like single-crystal silicon carbide powder according to claim 6, characterized in that: In step 3, P 1 The pressure range is 800-950 mbar; P 2 The pressure range is 300-600 mbar; Q The flow rate range is 10~1000 sccm.

8. The method for synthesizing sheet-like single-crystal silicon carbide powder according to claim 7, characterized in that: The silicon carbide powder obtained in step 4 is a plate-like polygonal single crystal with a bulk density of 1.45-1.95 g / cm³. 3 The single crystal ratio is 90-99%, the thickness is 10-100um, and the side length is 100-500um.

9. The method for synthesizing sheet-like single-crystal silicon carbide powder according to claim 7, characterized in that: In step 4, the mass ratio of hydrofluoric acid to hydrochloric acid is 1:1-1:4, the concentration of hydrofluoric acid is 5-10wt%, the concentration of hydrochloric acid is 15-20wt%, and the cleaning time is 2-4h.

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