A controllable synthesis method of high-purity polyhedral SiC powder particles

Abstract

The application discloses a controllable synthesis method of high-purity polyhedral SiC powder particles, and particularly relates to the technical field of silicon carbide powder preparation. The method comprises the following steps: mixing high-purity silicon powder and a carbon source according to a specific molar ratio, adding a dispersing agent and performing dry ball milling to obtain a mixed powder; performing high-temperature synthesis reaction on the mixed powder by heating to 1800 DEG C to 2400 DEG C in a vacuum and inert protective gas atmosphere through a staged temperature program; and after the reaction, performing gradient cooling, multi-stage acid washing, water washing, drying and airflow grading treatment to obtain a final product. The method can prepare silicon carbide powder with a purity of not less than 99.99%, regular polyhedral morphology and concentrated particle size distribution by systemically controlling the purity of raw materials, reaction atmosphere, temperature program and post-treatment process, and the process flow is simple and controllable.

Description

Technical Field

[0001] This invention belongs to the field of silicon carbide powder preparation technology, specifically relating to a controllable synthesis method for high-purity polyhedral SiC powder particles. Background Technology

[0002] Silicon carbide powder is a key raw material for the fabrication of high-performance semiconductor devices, precision ceramics, and high-end abrasives. Among them, polyhedral SiC particles with complete crystal structure and regular morphology have attracted much attention due to their unique advantages in subsequent applications.

[0003] Currently, the widely used high-temperature synthesis method in industry typically involves directly heating a mixture of silicon and carbon sources. This method generally operates at reaction temperatures of 1900-2200℃ and is often protected by an inert gas atmosphere or atmospheric pressure. However, this method often faces several problems in its implementation. First, the temperature distribution within conventional reactors is not uniform enough, easily leading to variations in local reaction progress. The resulting powder morphology is often irregular, mostly broken lumps or flakes, with a very low proportion of regular polyhedral crystals. Second, the reaction process is often carried out under atmospheric or simple protective atmospheres, making raw materials and products susceptible to oxidation contamination. Furthermore, trace impurities in the raw materials are difficult to remove effectively, resulting in limited purity of the final powder, typically failing to consistently reach above 99.5%, thus restricting its application in high-end fields such as semiconductors. Third, existing processes handle the post-reaction products relatively simply, insufficiently removing residual unreacted substances, metallic impurities, and oxides, and lacking effective classification methods, resulting in a wide particle size distribution and requiring improvement in batch consistency.

[0004] While vapor deposition can prepare high-purity SiC, it suffers from problems such as complex equipment, high cost, low production capacity, and difficulty in controlling particle morphology, making it unsuitable for large-scale production. Wet chemical methods, such as the sol-gel method, have issues including lengthy process flows, easy introduction of impurities, and particle agglomeration during high-temperature sintering, making it difficult to obtain well-dispersed, independent polyhedral particles.

[0005] Therefore, how to achieve synergistic control of SiC powder purity, morphology and particle size through process optimization while ensuring production efficiency and controllable costs has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a controllable synthesis method for high-purity polyhedral SiC powder particles.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A controllable synthesis method for high-purity polyhedral SiC powder particles includes the following steps: (1) Raw material pretreatment and mixing: Select silicon powder with a purity of not less than 99.99% and carbon source with a purity of not less than 99.9%, mix the silicon powder and the carbon source at a Si to C molar ratio of 1:1 to 1:1.5, add a dispersant, and then perform dry ball milling to obtain mixed powder; (2) High-temperature synthesis reaction: The mixed powder is placed in the reaction chamber, and the reaction chamber is evacuated to a pressure not exceeding 10 Pa. Then, an inert protective gas is introduced into the reaction chamber and its internal pressure is maintained at 0.1-0.15 MPa. Then, the mixed powder is heated to 1800-2400℃ and kept at this temperature for 3-6 hours. (3) Post-processing and classification: The mixed powder after the reaction in step (2) is cooled to room temperature, and then acid washing, water washing and drying are performed in sequence. Finally, air classification is performed to obtain the high-purity polyhedral SiC powder particles.

[0008] Furthermore, in step (1), the particle size of the silicon powder is 5-20 μm; the carbon source is flake graphite or activated carbon with a particle size of 1-10 μm.

[0009] Furthermore, in step (1), the dispersant is zinc stearate or talc, and its addition amount is 0.3-1.5% of the total mass of the silicon powder and carbon source.

[0010] Furthermore, in step (1), the parameters of the dry ball mill are: rotation speed 400-600 r / min, time 6-12 hours, and ball-to-material ratio 15:1-25:1.

[0011] Furthermore, the grinding media used in the dry ball mill is polyurethane balls.

[0012] Furthermore, in step (1), before mixing, the silicon powder and the carbon source are respectively subjected to acid washing, water washing and vacuum drying.

[0013] Furthermore, in step (2), the heating process includes: First stage: Increase the temperature from room temperature to 1000℃ at a rate of 5-8℃ / min; The second stage involves heating from 1000℃ to 1800-2400℃ at a rate of 2-7℃ / min.

[0014] Furthermore, in step (2), the inert protective gas is argon or nitrogen, and the flow rate is 0.5-5 L / min.

[0015] Furthermore, in step (3), the cooling process includes: First stage: Cool down from the reaction temperature to 1000℃ at a rate of 3-5℃ / min; Second stage: Cool down from 1000℃ to room temperature at a rate of 5-10℃ / min.

[0016] Further, in step (3), the pickling includes: first soaking in a hydrochloric acid solution with a mass concentration of 5-10% for 2-4 hours, and then soaking in a hydrofluoric acid solution with a mass concentration of 5-8% for 1-2 hours; the water washing is washing with deionized water until the washing solution is neutral.

[0017] Beneficial effects of this invention: 1. Simplified process flow and improved process controllability: This method adopts a dry powder mixing and direct high-temperature reaction path, avoiding the complex steps of slurry preparation and spray granulation in traditional wet processes, thus shortening the production cycle. By systematically combining and parameterizing raw material pretreatment, vacuum and atmosphere control, segmented temperature management, and multi-step post-treatment, key aspects of the entire synthesis process can be effectively monitored and adjusted, enhancing the stability and repeatability of the process.

[0018] 2. Facilitates the formation of regular polyhedral crystal forms: The segmented heating procedure employed in the method first eliminates volatile components at a relatively gentle heating rate, and then raises the temperature to the reaction high temperature at an even slower rate. This helps to homogenize the internal thermal field of the reaction system and reduce crystal defects caused by thermal stress. Conducting the synthesis reaction within the set high-temperature range and with sufficient holding time provides conditions for the full growth of SiC grains and the balanced development of each crystal face, thereby promoting the formation of regular polyhedral morphologies.

[0019] 3. Ensures high purity of the final product: The method selects high-purity silicon powder and carbon source from the source and optionally performs pre-cleaning, reducing the initial impurity content. High vacuum degassing and continuous inert gas protection before the reaction effectively isolate oxygen and moisture, preventing oxidation of the materials at high temperatures. A specific acid washing process is then employed, using different acids to sequentially remove metallic and silicon oxide impurities, thereby systematically increasing the product purity to over 99.99%, far exceeding the 99.5% of existing technologies.

[0020] 4. Achieved a concentrated distribution of product particle size: By limiting the initial particle size of the raw materials and combining it with dry ball milling assisted by a dispersant, a uniformly mixed powder precursor was obtained, laying the foundation for the reaction to generate a product with uniform particle size. Introducing an air classification step after synthesis allows the particle size distribution of the final powder to be controlled within a narrow range as needed, improving product consistency. Attached Figure Description

[0021] Figure 1 The image shows the morphology of the polyhedral SiC powder particles prepared in Example 1 using a scanning electron microscope (SEM).

[0022] Figure 2The image shows the morphology of the polyhedral SiC powder particles prepared in Example 2 using a scanning electron microscope (SEM).

[0023] Figure 3 The image shows the morphology of the polyhedral SiC powder particles prepared in Example 3 using a scanning electron microscope (SEM). Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0025] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, all materials and reagents used are commercially available.

[0026] Example 1 This embodiment provides a controllable synthesis method for high-purity polyhedral SiC powder particles, the specific steps of which are as follows: (1) Raw material pretreatment and mixing: Electronic-grade silicon powder with a purity of 99.995% and a particle size D50 of approximately 10 μm, and flake graphite with a purity of 99.95% and a particle size D50 of approximately 5 μm were selected as carbon sources. First, the silicon powder and graphite were stirred and washed with 5% dilute hydrochloric acid and deionized water, respectively, and then dried in a vacuum drying oven at 80℃ and a vacuum degree of 10-100 Pa for 12 hours to remove impurities adsorbed on the surface. Subsequently, according to the stoichiometric ratio of Si to C of 1:1.2, 100 g of the treated silicon powder and approximately 51.31 g of graphite were weighed (calculated according to the Si:C molar ratio of 1:1.2). Zinc stearate (approximately 1.51 g) was added to the mixture as a dispersant, accounting for 1.0% of the total mass (sum of silicon powder and graphite). The mixture was placed in a dry ball mill and milled for 10 hours at a speed of 500 r / min using polyurethane grinding balls (ball-to-material mass ratio of 20:1) to obtain a uniformly mixed gray-black powder.

[0027] (2) High-temperature synthesis reaction: The mixed powder obtained in step (1) is evenly spread in a graphite powder support frame with a thickness of about 10 mm. The powder support frame is pushed into the constant temperature zone of the tubular atmosphere furnace (reaction chamber) and the furnace tube is sealed. First, the vacuum system is started to pump the pressure in the furnace tube to 5 Pa and maintain it for 30 minutes. Then, the vacuum valve is closed and high-purity argon gas (purity ≥99.999%) is introduced into the furnace tube. The gas flow rate is controlled at 2.0 L / min by the mass flow meter, and the back pressure valve is adjusted to stabilize the pressure in the furnace at 0.13 MPa. After purging for 30 minutes, the temperature program is started: in the first stage, the temperature is increased from room temperature to 1000℃ at a rate of 7℃ / min; in the second stage, the temperature is increased from 1000℃ to the target temperature of 1950℃ at a rate of 3℃ / min, and the temperature is kept constant at 1950℃ for 4 hours to carry out the synthesis reaction.

[0028] (3) Post-treatment and classification: After the reaction is completed, the temperature program is started: in the first stage, the temperature is reduced from 1950℃ to 1000℃ at a rate of 4℃ / min; in the second stage, the temperature is reduced from 1000℃ to room temperature (approximately 25℃) at a rate of 8℃ / min. After the furnace temperature drops to room temperature, the protective gas is turned off and the reaction product is removed. The product powder is first soaked in 8% hydrochloric acid solution for 3 hours, filtered and rinsed with deionized water until the filtrate is neutral (pH≈7), and then soaked in 6% hydrofluoric acid solution for 1.5 hours to remove possible free silicon and oxides. After filtration again, it is repeatedly washed with deionized water until the washing solution is neutral (pH≈7) when tested with pH paper. The washed wet powder is dried in a vacuum drying oven at 100℃ and a vacuum degree of 10-100Pa for 10 hours. Finally, the dried SiC powder is fed into an air classifier, the classifier speed is set, and powder with a target particle size range of 5-12μm is collected to obtain the final high-purity polyhedral SiC powder particles.

[0029] Example 2 (1) Raw material pretreatment and mixing: The silicon powder has a purity of 99.99% and a particle size D50 of approximately 15 μm; the carbon source is activated carbon with a purity of 99.9% and a particle size D50 of approximately 3 μm. The molar ratio of Si to C is 1:1. Talc is used as the dispersant, and the amount added is 0.5% of the total mass. The dry ball milling parameters are: rotation speed 550 r / min, time 8 hours, and ball-to-material ratio 18:1. During the raw material pretreatment, the raw materials are dried in a vacuum drying oven at 80℃ and a vacuum degree of 10-100 Pa for 12 hours.

[0030] (2) High-temperature synthesis reaction: The mixed powder is laid to a thickness of about 8 mm. The protective gas is high-purity nitrogen with a flow rate of 1.5 L / min, and the pressure inside the furnace is maintained at 0.15 MPa. The heating program is as follows: heat up to 1000 °C at 5 °C / min, then heat up to 1850 °C at 4 °C / min, and hold at 1850 °C for 5 hours.

[0031] (3) Post-treatment and classification: The cooling program was as follows: from 1850℃ to 1000℃ at a rate of 3℃ / min, and then to room temperature at a rate of 6℃ / min. The pickling step was as follows: soaking in 10% hydrochloric acid for 2.5 hours, and then soaking in 5% hydrofluoric acid for 2 hours. The target particle size range for airflow classification was set to 1-10 μm. The drying step was carried out in a vacuum drying oven at 100℃ and a vacuum degree of 10-100 Pa. The remaining steps were the same as in Example 1.

[0032] Example 3 (1) Raw material pretreatment and mixing: The silicon powder has a purity of 99.99% and a particle size D50 of approximately 8 μm; the carbon source is flake graphite with a purity of 99.96% and a particle size D50 of approximately 8 μm. The molar ratio of Si to C is 1:1.4. The dispersant is zinc stearate, with an addition amount of 1.2% of the total mass. The dry ball milling parameters are: rotation speed 450 r / min, time 12 hours, and ball-to-material ratio 22:1. During raw material pretreatment, the raw materials are dried in a vacuum drying oven at 80℃ and a vacuum degree of 10-100 Pa for 12 hours.

[0033] (2) High-temperature synthesis reaction: The mixed powder is laid to a thickness of about 15 mm. The protective gas is argon with a flow rate of 3.0 L / min, and the pressure inside the furnace is maintained at 0.14 MPa. The heating program is as follows: heat up to 1000 °C at 6 °C / min, then heat up to 2250 °C at 2 °C / min, and hold at 2250 °C for 3.5 hours.

[0034] (3) Post-treatment and classification: The cooling procedure was as follows: from 2250℃ to 1000℃ at a rate of 5℃ / min, and then to room temperature at a rate of 10℃ / min. The pickling step was as follows: soaking in 5% hydrochloric acid for 4 hours, and then soaking in 8% hydrofluoric acid for 1 hour. The target particle size range for airflow classification was set to 120-200μm. The drying step was carried out in a vacuum drying oven at 100℃ and a vacuum degree of 10-100Pa. The remaining steps were the same as in Example 1.

[0035] Comparative Example 1 Step (1): Industrial silicon powder with a purity of 99.9% (particle size of about 50 μm) and metallurgical coke (particle size of about 100 μm) were simply mechanically mixed for 30 minutes at a Si:C molar ratio of 1:1.05. No dispersant was added and no fine ball milling was performed.

[0036] Step (2): Place the mixture into a common graphite crucible and then into a box-type resistance furnace. After closing the furnace door, directly introduce atmospheric pressure nitrogen (99.9% purity) for protection, without high vacuum pretreatment. Heat directly to 2000℃ at a single heating rate of 10℃ / min and hold for 4 hours.

[0037] Step (3): After the reaction is complete, the furnace is allowed to cool naturally. The product is simply soaked once in dilute hydrochloric acid, washed with water and dried. No hydrofluoric acid washing or gas flow classification is performed.

[0038] Comparative Example 2 Step (1) is the same as in Example 1.

[0039] Step (2): Place the mixed powder in a tube furnace and evacuate it (to 5 Pa). Then, without filling it with any protective gas, heat it to 1950°C and hold it for 4 hours under dynamic high vacuum (keeping the mechanical pump running) using the same procedure as in Example 1.

[0040] Step (3) is the same as in Example 1.

[0041] Comparative Example 3 Step (1) is the same as in Example 1.

[0042] Step (2): Atmosphere control is the same as in Example 1. However, the heating program is changed to directly raise the temperature from room temperature to 1950°C at a constant rate of 5°C / min and hold for 4 hours. The two-stage heating is eliminated.

[0043] Step (3) is the same as in Example 1.

[0044] The performance of the final powders obtained in Examples 1-3 and Comparative Examples 1-3 was tested, and the results are recorded in Table 1 below.

[0045] Table 1: Performance Test and Characterization Results of Examples and Comparative Examples Note: The particle size distribution span is characterized by (D90-D10) / D50. The smaller the value, the more concentrated the particle size distribution.

[0046] In summary, the method of this invention effectively solves the problems of low purity, irregular morphology, and wide particle size distribution existing in the prior art through the synergistic effect of multiple technical features, including high-purity and homogenization pretreatment of raw materials, a synthesis atmosphere protected by high vacuum and inert gas, a segmented heating and cooling program, and a system post-treatment including multi-stage acid washing and airflow classification. This achieves the controllable preparation of high-purity polyhedral SiC powder particles. The results of each embodiment and comparative example fully verify the effectiveness and necessity of the technical solution of this invention.

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A controllable synthesis method for high-purity polyhedral SiC powder particles, characterized in that, Includes the following steps: (1) Raw material pretreatment and mixing: Select silicon powder with a purity of not less than 99.99% and carbon source with a purity of not less than 99.9%, mix the silicon powder and the carbon source at a Si to C molar ratio of 1:1 to 1:1.5, add a dispersant, and then perform dry ball milling to obtain mixed powder; (2) High-temperature synthesis reaction: The mixed powder is placed in the reaction chamber, and the reaction chamber is evacuated to a pressure not exceeding 10 Pa. Then, an inert protective gas is introduced into the reaction chamber and its internal pressure is maintained at 0.1-0.15 MPa. Then, the mixed powder is heated to 1800-2400℃ and kept at this temperature for 3-6 hours. (3) Post-processing and classification: The mixed powder after the reaction in step (2) is cooled to room temperature, and then acid washing, water washing and drying are performed in sequence. Finally, air classification is performed to obtain the high-purity polyhedral SiC powder particles.

2. The controllable synthesis method of high-purity polyhedral SiC powder particles according to claim 1, characterized in that, In step (1), the particle size of the silicon powder is 5-20 μm; the carbon source is flake graphite or activated carbon with a particle size of 1-10 μm.

3. The controllable synthesis method of high-purity polyhedral SiC powder particles according to claim 1, characterized in that, In step (1), the dispersant is zinc stearate or talc, and its addition amount is 0.3-1.5% of the total mass of the silicon powder and carbon source.

4. The controllable synthesis method of high-purity polyhedral SiC powder particles according to claim 1, characterized in that, In step (1), the parameters of the dry ball mill are: rotation speed 400-600 r / min, time 6-12 hours, and ball-to-material ratio 15:1-25:

1.

5. The controllable synthesis method of high-purity polyhedral SiC powder particles according to claim 4, characterized in that, The grinding media used in the dry ball mill are polyurethane balls.

6. The controllable synthesis method of high-purity polyhedral SiC powder particles according to claim 1, characterized in that, In step (1), before mixing, the silicon powder and the carbon source are respectively subjected to acid washing, water washing and vacuum drying.

7. The controllable synthesis method of high-purity polyhedral SiC powder particles according to claim 1, characterized in that, In step (2), the heating process includes: First stage: Increase the temperature from room temperature to 1000℃ at a rate of 5-8℃ / min; The second stage involves heating from 1000℃ to 1800-2400℃ at a rate of 2-7℃ / min.

8. The controllable synthesis method of high-purity polyhedral SiC powder particles according to claim 1, characterized in that, In step (2), the inert protective gas is argon or nitrogen, and the flow rate is 0.5-5 L / min.

9. The controllable synthesis method of high-purity polyhedral SiC powder particles according to claim 1, characterized in that, In step (3), the cooling process includes: First stage: Cool down from the reaction temperature to 1000℃ at a rate of 3-5℃ / min; Second stage: Cool down from 1000℃ to room temperature at a rate of 5-10℃ / min.

10. The controllable synthesis method of high-purity polyhedral SiC powder particles according to claim 1, characterized in that, In step (3), the pickling includes: first soaking in a hydrochloric acid solution with a mass concentration of 5-10% for 2-4 hours, and then soaking in a hydrofluoric acid solution with a mass concentration of 5-8% for 1-2 hours; the water washing is washing with deionized water until the washing solution is neutral.

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