A method for preparing high-efficiency silicon nitride powder

Abstract

This invention relates to the field of silicon nitride powder production technology. The invention discloses a highly efficient method for preparing silicon nitride powder, comprising the following steps: Step 1: Crystalline silicon is loaded into a ball mill, milling media are added, and the mixture is ball-milled to form silicon powder with a particle size of less than 30 micrometers; Step 2: Nitrogen gas is introduced into a high-temperature container to remove air from the container, and then the container is heated to 300-500°C and held for 5-10 minutes; Step 3: The crushed silicon powder is removed and dried to obtain dry silicon powder. This invention grinds high-purity crystalline silicon into ultrafine silicon powder, and sprays the dried silicon powder into a high-temperature container containing nitrogen gas through spray granulation. This suspends the silicon powder in nitrogen gas for nitriding, increasing the contact area and improving the nitriding rate of the silicon powder. Furthermore, the nitriding process facilitates heat release. The nitrided silicon powder is then subjected to secondary pulverization using an airflow mill, resulting in a smaller average particle size and achieving rapid and efficient preparation of silicon nitride powder.

Description

Technical Field

[0001] This invention relates to the field of silicon nitride powder production technology, and in particular to a method for preparing high-efficiency silicon nitride powder. Background Technology

[0002] Silicon nitride possesses advantages such as high mechanical strength, good thermal stability, and good chemical stability, making it particularly suitable for high-temperature, high-speed, highly corrosive, and highly abrasive working environments frequently encountered in modern technology. Silicon nitride has a wide range of industrial applications, including metallurgy, machinery, chemical engineering, semiconductors, aerospace, and automotive industries, serving as turbine blades, high-temperature bearings, high-speed cutting tools, heat-resistant components, and wear- and corrosion-resistant parts. With the continuous expansion of silicon nitride applications and the increasing demands for its quality, the preparation of silicon nitride powder is receiving increasing attention.

[0003] Among existing methods for producing silicon nitride powder, direct nitriding is the most commonly used. In this method, silicon powder reacts directly with nitrogen in a high-temperature nitrogen atmosphere to produce silicon nitride powder. In the initial stage of the reaction, the silicon nitride powder layer formed on the surface of the silicon powder hinders the diffusion of nitrogen to the center of the particles, resulting in a low yield of silicon nitride powder. In addition, the reaction between silicon and nitrogen is a strongly exothermic reaction, and the released heat can cause the powder to self-sinter and form agglomerates, thereby coarsening the powder particles and affecting the performance of silicon nitride powder. Summary of the Invention

[0004] To overcome the technical defects of the existing technology, the present invention provides a high-efficiency silicon nitride powder preparation method to solve the problem mentioned in the background art that the direct nitriding method is commonly used in the existing silicon nitride powder production. The direct nitriding method involves silicon powder reacting directly with nitrogen in a high-temperature nitrogen atmosphere to generate silicon nitride powder. In the initial stage of the reaction, the silicon nitride powder layer formed on the surface of the silicon powder hinders the diffusion of nitrogen to the center of the particles, resulting in a low yield of silicon nitride powder.

[0005] The technical solution adopted in this invention is as follows: This invention provides a method for preparing high-efficiency silicon nitride powder, comprising the following steps:

[0006] Step 1: Load crystalline silicon into a ball mill, add grinding media, and use the ball mill to grind and crush it into silicon powder smaller than 30 micrometers.

[0007] Step 2: Introduce nitrogen into the high-temperature container to purge the air inside, then turn on the power to raise the temperature of the high-temperature container to 300-500℃ and keep it at that temperature for 5-10 minutes.

[0008] Step 3: Take out the crushed silicon powder and dry it to obtain silicon dry powder. At the same time, heat the high-temperature container to 1500-1600℃. Then, under the protection gas, spray the silicon dry powder into the high-temperature container and continue to introduce nitrogen into the high-temperature container. Under the condition of stable nitrogen flow rate in the furnace, the silicon dry powder and nitrogen react fully.

[0009] Step 4: After the reaction, the silicon powder is cooled to room temperature in the furnace, then the nitrogen gas is stopped, the silicon nitride product is collected, crushed and sieved to obtain high-purity silicon nitride powder.

[0010] Preferably, the surface of the crystalline silicon is inspected before it is crushed. Crystalline silicon without any adhering substances is sent to an ultrasonic cleaner for cleaning, while crystalline silicon with impurities is placed in an acid bath for 1-3 hours. After ultrasonic cleaning and acid bath, the crystalline silicon is rinsed clean in a water bath.

[0011] Preferably, the ball mill rotates at 100-120 revolutions per minute, and the milling time is 5-8 hours. Water equal to 50% of the weight of the crystalline silicon is added during the ball milling process, and the temperature is controlled below 50°C during the ball milling process.

[0012] Preferably, the ball mill is a planetary ball mill or a rolling ball mill, using agate balls or silicon nitride balls as the grinding media.

[0013] Preferably, the crystalline silicon has a silicon content of ≥99.6%, the nitrogen gas introduced has a purity of ≥99.9%, and the nitriding reaction time is 2-3 hours.

[0014] Preferably, the silicon powder is dried in an oven at 50-70°C for 10-12 hours, with a moisture content of less than 10%, and the silicon powder is preheated to 200-300°C before spraying.

[0015] Preferably, the feed rate of the silicon dry powder when it is blown into the high-temperature container is 10-12 kg / h, and the protective gas is argon with a flow rate of 40-60 liters / minute.

[0016] Preferably, the pressure inside the high-temperature container is maintained at 3-6 MPa, and the nitrogen concentration inside the high-temperature container is greater than 80%.

[0017] Preferably, during the pulverization process, the silicon nitride product is fed into an air jet mill at a feed rate of 20-30 kg / h and a feed pressure of 0.8-1.2 MPa. The silicon nitride product is then discharged after being impact-pulverized with high-pressure gas in the air jet mill.

[0018] Preferably, the obtained silicon nitride product is high-purity silicon nitride with an average particle size of 5-20 micrometers and an impurity content of less than 2%.

[0019] The high-efficiency silicon nitride powder preparation method of the present invention adopts different cleaning methods according to the surface condition of crystalline silicon to ensure the cleaning quality of crystalline silicon, without the introduction of other impurities, reduce the loss of crystalline silicon, save costs, make its impurity content low, and the whole process is stable and suitable for industrial production.

[0020] The beneficial effects of this invention are:

[0021] This invention grinds high-purity crystalline silicon into ultrafine silicon powder, and then sprays the dried silicon powder into a high-temperature container containing nitrogen gas through spray granulation. This allows the silicon powder to be suspended in nitrogen gas for nitriding, which not only increases the contact area and improves the nitriding rate of the silicon powder, but also facilitates the release of heat during nitriding. The nitrided silicon powder is then pulverized twice using an airflow mill, resulting in a smaller average particle size, thus achieving rapid and efficient preparation of silicon nitride powder. Detailed Implementation

[0022] The present invention will be further described below with reference to embodiments:

[0023] Example 1.

[0024] This embodiment of the invention provides a method for preparing high-efficiency silicon nitride powder, comprising the following steps:

[0025] Step 1: Load crystalline silicon into a ball mill, add ball milling media, and use the ball mill to grind and crush it to form 25-micron silicon powder.

[0026] Step 2: Introduce nitrogen into the high-temperature container to purge the air inside, then turn on the power to raise the temperature of the high-temperature container to 300°C and hold it at that temperature for 5 minutes.

[0027] Step 3: Take out the crushed silicon powder and dry it to obtain silicon dry powder. At the same time, heat the high-temperature container to 1500°C. Then, under the protection gas, spray the silicon dry powder into the high-temperature container and continue to introduce nitrogen into the high-temperature container. Under the condition that the nitrogen flow rate in the furnace is stable, the silicon dry powder reacts fully with the nitrogen.

[0028] Step 4: After the reaction, the silicon powder is cooled to room temperature in the furnace, then the nitrogen gas is stopped, the silicon nitride product is collected, crushed and sieved to obtain high-purity silicon nitride powder.

[0029] In this embodiment, the surface of the crystalline silicon is inspected before crushing. Crystalline silicon without surface deposits is sent to an ultrasonic cleaner for cleaning, while crystalline silicon with surface impurities is immersed in an acid bath for 1 hour. After ultrasonic cleaning and acid immersion, the crystalline silicon is rinsed clean in a water bath.

[0030] In this embodiment, the ball mill rotates at 100 revolutions per minute and the milling time is 5 hours. Water equal to 50% of the weight of the crystalline silicon is added during the ball milling process, and the temperature is controlled below 50°C.

[0031] In this embodiment, a planetary ball mill or a rolling ball mill is selected, and agate balls or silicon nitride balls are used as the grinding media.

[0032] In this embodiment, the silicon content of the crystalline silicon is ≥99.6%, the purity of the nitrogen gas introduced is ≥99.9%, and the nitriding reaction time is 2 hours.

[0033] In this embodiment, the silicon powder is dried in an oven at 50°C for 10 hours until the moisture content is less than 10%. Before spraying, the silicon powder is preheated to 200°C.

[0034] In this embodiment, the feed rate of the silicon dry powder when it is blown into the high-temperature container is 10 kg / h, the protective gas is argon, and the argon flow rate is 40 liters / minute.

[0035] In this embodiment, the pressure inside the high-temperature container is maintained at 3 MPa, and the nitrogen concentration inside the high-temperature container is greater than 80%.

[0036] In this embodiment, the silicon nitride product is fed into an air jet mill at a feed rate of 20 kg / h and a feed pressure of 0.8 MPa. The silicon nitride product is then discharged after being impact-crushed with high-pressure gas in the air jet mill.

[0037] The silicon nitride product obtained in this embodiment is high-purity silicon nitride with an average particle size of 20 micrometers and an impurity content of less than 2%.

[0038] Example 2.

[0039] This embodiment of the invention provides a method for preparing high-efficiency silicon nitride powder, comprising the following steps:

[0040] Step 1: Load crystalline silicon into a ball mill, add grinding media, and use the ball mill to grind and crush it into silicon powder smaller than 20 micrometers.

[0041] Step 2: Introduce nitrogen into the high-temperature container to purge the air inside, then turn on the power to raise the temperature of the high-temperature container to 350°C and hold it at that temperature for 8 minutes.

[0042] Step 3: Take out the crushed silicon powder and dry it to obtain silicon dry powder. At the same time, heat the high-temperature container to 1550°C. Then, under the protection gas, spray the silicon dry powder into the high-temperature container and continue to introduce nitrogen into the high-temperature container. Under the condition that the nitrogen flow rate in the furnace is stable, the silicon dry powder reacts fully with the nitrogen.

[0043] Step 4: After the reaction, the silicon powder is cooled to room temperature in the furnace, then the nitrogen gas is stopped, the silicon nitride product is collected, crushed and sieved to obtain high-purity silicon nitride powder.

[0044] In this embodiment, the surface of the crystalline silicon is inspected before crushing. Crystalline silicon without surface deposits is sent to an ultrasonic cleaner for cleaning, while crystalline silicon with surface impurities is immersed in an acid bath for 2 hours. After ultrasonic cleaning and acid immersion, the crystalline silicon is rinsed clean in a water bath.

[0045] In this embodiment, the ball mill rotates at 110 revolutions per minute and the milling time is 7 hours. Water equal to 50% of the weight of the crystalline silicon is added during the ball milling process, and the temperature is controlled below 50°C.

[0046] In this embodiment, a planetary ball mill or a rolling ball mill is selected, and agate balls or silicon nitride balls are used as the grinding media.

[0047] In this embodiment, the silicon content of the crystalline silicon is ≥99.6%, the purity of the nitrogen gas introduced is ≥99.9%, and the nitriding reaction time is 2.5 hours.

[0048] In this embodiment, the silicon powder is dried in an oven at 60°C for 11 hours, with a moisture content of less than 10%. Before spraying, the silicon powder is preheated to 250°C.

[0049] In this embodiment, the feed rate of the silicon dry powder when it is blown into the high-temperature container is 11 kg / h, the protective gas is argon, and the argon flow rate is 50 liters / minute.

[0050] In this embodiment, the pressure inside the high-temperature container is maintained at 5 MPa, and the nitrogen concentration inside the high-temperature container is greater than 80%.

[0051] In this embodiment, the silicon nitride product is fed into an air jet mill at a feed rate of 25 kg / h and a feed pressure of 1 MPa. The silicon nitride product is then discharged after being impact-crushed with high-pressure gas in the air jet mill.

[0052] The silicon nitride product obtained in this embodiment is high-purity silicon nitride with an average particle size of 12 micrometers and an impurity content of less than 2%.

[0053] Example 3.

[0054] This embodiment of the invention provides a method for preparing high-efficiency silicon nitride powder, comprising the following steps:

[0055] Step 1: Load crystalline silicon into a ball mill, add grinding media, and use the ball mill to grind and crush it into silicon powder smaller than 15 micrometers.

[0056] Step 2: Introduce nitrogen into the high-temperature container to purge the air inside, then turn on the power to raise the temperature of the high-temperature container to 500°C and keep it at that temperature for 10 minutes.

[0057] Step 3: Take out the crushed silicon powder and dry it to obtain silicon dry powder. At the same time, heat the high-temperature container to 1600°C. Then, under the protection gas, spray the silicon dry powder into the high-temperature container and continue to introduce nitrogen into the high-temperature container. Under the condition that the nitrogen flow rate in the furnace is stable, the silicon dry powder reacts fully with the nitrogen.

[0058] Step 4: After the reaction, the silicon powder is cooled to room temperature in the furnace, then the nitrogen gas is stopped, the silicon nitride product is collected, crushed and sieved to obtain high-purity silicon nitride powder.

[0059] In this embodiment, the surface of the crystalline silicon is inspected before crushing. Crystalline silicon without surface deposits is sent to an ultrasonic cleaner for cleaning, while crystalline silicon with surface impurities is immersed in an acid bath for 3 hours. After ultrasonic cleaning and acid immersion, the crystalline silicon is rinsed clean in a water bath.

[0060] In this embodiment, the ball mill rotates at 120 revolutions per minute and the milling time is 8 hours. Water equal to 50% of the weight of the crystalline silicon is added during the ball milling process, and the temperature is controlled below 50°C.

[0061] In this embodiment, a planetary ball mill or a rolling ball mill is selected, and agate balls or silicon nitride balls are used as the grinding media.

[0062] In this embodiment, the silicon content of the crystalline silicon is ≥99.6%, the purity of the nitrogen gas introduced is ≥99.9%, and the nitriding reaction time is 3 hours.

[0063] In this embodiment, the silicon powder is dried in an oven at 70°C for 12 hours, with a moisture content of less than 10%. Before spraying, the silicon powder is preheated to 300°C.

[0064] In this embodiment, the feed rate of the silicon dry powder when it is blown into the high-temperature container is 12 kg / h, the protective gas is argon, and the argon flow rate is 60 liters / minute.

[0065] In this embodiment, the pressure inside the high-temperature container is maintained at 6 MPa, and the nitrogen concentration inside the high-temperature container is greater than 80%.

[0066] In this embodiment, the silicon nitride product is fed into an air jet mill at a feed rate of 30 kg / h and a feed pressure of 1.2 MPa. The silicon nitride product is then discharged after being impact-crushed with high-pressure gas in the air jet mill.

[0067] The silicon nitride product obtained in this embodiment is high-purity silicon nitride with an average particle size of 8 micrometers and an impurity content of less than 2%.

[0068] Comparative Example 1.

[0069] Unlike Example 3, the surface of the crystalline silicon is not inspected or cleaned before it is crushed.

[0070] Comparative Example 2.

[0071] Unlike Example 3, the silicon dry powder is not preheated before spraying.

[0072] Comparative Example 3.

[0073] Unlike Example 3, the silicon nitride product was pulverized using a conventional pulverizer.

[0074] The products of Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests;

[0075] Silicon nitride powder samples were prepared for Examples 1-3 and Comparative Examples 1-3 and numbered A / B / C / D / E / F. The silicon nitride powder samples in groups A / B / C / D / E / F were then tested, and the test results are shown in the table below.

[0076] Average particle size Nitrogenation rate impurity content A 18 98.1％ 0.8％ B 15 98.3％ 0.6％ C 12 98.7％ 0.5％ D 14 98.6％ 1.2％ E 13 96.8％ 0.6％ F 22 98.5％ 0.5％

[0077] As can be seen from Examples 1-3, the silicon powder prepared by the high-efficiency silicon nitride powder preparation method of the present invention has a high nitride rate, a small average particle size, and a low impurity content, and can achieve rapid and efficient preparation of silicon nitride powder.

[0078] As can be seen from Comparative Example 1 and Example 3, different cleaning methods are used according to the surface condition of the crystalline silicon to ensure the cleaning quality of the crystalline silicon, prevent the introduction of other impurities, reduce the loss of crystalline silicon, and save costs.

[0079] Furthermore, Comparative Examples 2-3 show that the processing method is also particularly important in the preparation of high-efficiency silicon nitride powder. By preheating the silicon dry powder in advance, it can quickly reach the ideal nitriding temperature. After nitriding, it is pulverized a second time using an air jet mill, resulting in a smaller average particle size and improved silicon nitride powder performance.

[0080] The innovation of this invention lies in:

[0081] This invention employs different cleaning methods based on the surface condition of crystalline silicon to ensure the cleaning quality of the crystalline silicon, prevent the introduction of other impurities, reduce the loss of crystalline silicon, save costs, and reduce its impurity content. High-purity crystalline silicon is ground into ultrafine silicon powder, which is then sprayed into a high-temperature container containing nitrogen gas through spray granulation. This allows the silicon powder to be suspended in nitrogen gas for nitriding, which not only increases the contact area and improves the nitriding rate of the silicon powder, but also facilitates the release of heat during nitriding. The nitrided silicon powder is then pulverized twice using an air jet mill, resulting in a small average particle size. The entire process is stable and suitable for industrial production, achieving rapid and efficient preparation of silicon nitride powder.

[0082] The foregoing has shown and described the basic principles and main features of the present invention, as well as its advantages. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope. All such changes and modifications fall within the scope of the present invention as claimed, which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing high-efficiency silicon nitride powder, characterized in that, Includes the following steps: Step 1: Load crystalline silicon into a ball mill, add grinding media, and use the ball mill to grind and crush it into silicon powder smaller than 30 micrometers. Step 2: Introduce nitrogen into the high-temperature container to purge the air inside, then turn on the power to raise the temperature of the high-temperature container to 300-500℃ and keep it at that temperature for 5-10 minutes. Step 3: Take out the crushed silicon powder and dry it to obtain silicon dry powder. At the same time, heat the high-temperature container to 1500-1600℃. Then, under the protection gas, spray the silicon dry powder into the high-temperature container and continue to introduce nitrogen into the high-temperature container. Under the condition of stable nitrogen flow rate in the furnace, the silicon dry powder and nitrogen react fully. Step 4: After the reaction, the silicon powder is cooled to room temperature in the furnace, then the nitrogen gas is stopped, the silicon nitride product is collected, crushed and sieved to obtain high-purity silicon nitride powder; in: The silicon powder is dried in an oven at 50-70℃ for 10-12 hours, with a moisture content of less than 10%. Before spraying, the silicon powder is preheated to 200-300℃. The feed rate of the silicon dry powder when it is blown into the high-temperature container is 10-12 kg / h, and the protective gas is argon with a flow rate of 40-60 L / min. The pressure inside the high-temperature container is maintained at 3-6 MPa, and the nitrogen concentration inside the high-temperature container is greater than 80%. During the pulverization process, the silicon nitride product is fed into an air jet mill at a feed rate of 20-30 kg / h and a feed pressure of 0.8-1.2 MPa. The silicon nitride product is then discharged after being impact-pulverized with high-pressure gas in the air jet mill.

2. The method for preparing high-efficiency silicon nitride powder according to claim 1, characterized in that, Before crushing, the surface of the crystalline silicon is inspected. Crystalline silicon without any adhering substances is sent to an ultrasonic cleaner for cleaning. Crystalline silicon with impurities is placed in an acid bath for 1-3 hours. After ultrasonic cleaning and acid soaking, the crystalline silicon is rinsed clean in a water bath.

3. The method for preparing high-efficiency silicon nitride powder according to claim 1, characterized in that, The ball mill rotates at 100-120 revolutions per minute for 5-8 hours. Water equal to 50% of the weight of the crystalline silicon is added during the ball milling process, and the temperature is controlled below 50°C.

4. The method for preparing high-efficiency silicon nitride powder according to claim 1, characterized in that, The ball mill is either a planetary ball mill or a rolling ball mill, using agate balls or silicon nitride balls as the grinding media.

5. The method for preparing high-efficiency silicon nitride powder according to claim 1, characterized in that, The crystalline silicon has a silicon content of ≥99.6%, the nitrogen gas introduced has a purity of ≥99.9%, and the nitriding reaction time is 2-3 hours.

6. The method for preparing high-efficiency silicon nitride powder according to claim 1, characterized in that, The obtained silicon nitride product is high-purity silicon nitride with an average particle size of 5-20 micrometers and an impurity content of less than 2%.