A method for preparing high-performance silicon nitride powder

Abstract

This invention relates to the field of silicon nitride powder preparation technology, and provides a method for preparing high-performance silicon nitride powder, solving the problem that it is difficult to synthesize silicon nitride powder with high α phase content and no free Si in the prior art; the preparation process includes: 1) selection of raw materials; 2) addition of diluent; 3) first nitriding reaction; 4) second nitriding reaction; 5) acid washing and purification.

Description

Technical Field

[0001] This invention relates to the field of silicon nitride powder preparation technology, and more particularly to a method for preparing high-performance silicon nitride powder. Background Technology

[0002] Silicon nitride (Si3N4) is a typical strongly covalent compound, possessing not only high melting point, high hardness, and wear resistance, but also high flexural strength and good thermal conductivity, making it irreplaceable in key fields such as national defense, military industry, and electronic information. High-quality powder is the primary prerequisite for preparing high-performance Si3N4 ceramics. High-quality Si3N4 powder typically needs to meet the following criteria: high purity, low oxygen content, ultrafine particle size, narrow distribution, high α-phase content, and low impurity content. The quality of the powder is closely related to the preparation process and conditions. Currently, there are four different preparation methods: SiO2 carbothermal nitriding, direct nitriding of Si powder, chemical vapor phase synthesis, and high-temperature decomposition of silane precursors. Among these, the direct nitriding method, where Si powder reacts with N2 to produce Si3N4 powder, has gained widespread recognition and adoption in the scientific and industrial communities due to its simple and easy-to-implement production process, easy-to-operate equipment, low production cost, and high powder synthesis efficiency. The direct nitriding method can be divided into three steps: the first step is to nitrid silicon powder in nitrogen to produce silicon nitride; the second step is to crush and grind the silicon nitride block produced by the reaction; and the third step is to acid wash and purify the crushed and ground silicon nitride powder. These three steps correspond to the performance requirements of higher α content, finer particle size, narrower particle size distribution, and higher purity of silicon nitride powder.

[0003] Application number 201110296695.9, publication number CN102503434B, discloses a method for synthesizing silicon nitride powder by nitriding silicon powder under medium-temperature, slightly positive pressure conditions. The method uses silicon powder and nitrogen-containing compounds as raw materials, formulated into reaction mixtures according to different component ratios. After short-term grinding and mixing, the mixture is placed in a boat and then placed in a sealed, heatable, and pressure-resistant reaction furnace. After vacuuming, a nitrogen-containing non-oxidizing gas at a certain pressure is introduced. The mixture is preheated by electricity, raising the temperature to 500–900°C. A combustion synthesis reaction is initiated through local heating or by pre-embedded ignition blocks. The synthesized silicon nitride product is cooled with the furnace and, after initial crushing, yields the silicon nitride powder. This invention combines the advantages of high-temperature silicon powder nitriding and silicon powder combustion synthesis of silicon nitride, reducing the nitriding reaction temperature and the required synthesis pressure, shortening the production cycle, and significantly reducing the production cost of silicon nitride powder. However, it is difficult to synthesize silicon nitride powder with high α phase content and no free Si.

[0004] Application number 202010282836.0, publication number CN113493191B, this Chinese invention discloses a method for preparing high-purity α-silicon nitride powder and the high-purity α-silicon nitride powder itself. A catalyst is added to fine silicon powder with a particle size of less than 100 micrometers. The catalyst can reversibly react to generate metal compounds under the reaction conditions for preparing silicon nitride powder, resulting in the presence of metal halides. The fine silicon powder with the added catalyst is placed in a nitriding furnace and held at a temperature of 1050–1400℃ for 50–180 hours under a mixed atmosphere of nitrogen and argon to undergo a nitriding reaction and obtain silicon nitride powder. The method utilizes the unique effect of fully catalyzing the surface reaction with fewer metal impurities to ensure the purity of the product. The reduced metal impurities make the α→β crystal transformation less likely to occur, increasing the α-phase content of the product and meeting the requirements for high-purity silicon nitride powder. However, the silicon nitride powder still contains free Si. Summary of the Invention

[0005] Therefore, in view of the above problems, the present invention provides a method for preparing high-performance silicon nitride powder, which solves the problem that it is difficult to synthesize silicon nitride powder with high α phase content and no free Si in the prior art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing high-performance silicon nitride powder includes the following steps:

[0008] S1. Porous silicon powder is used as the raw material for the nitriding reaction. The porous silicon powder is ball-milled, separated, and dried.

[0009] S2. Add diluent to the dried porous silica powder, mix well, and then separate and dry.

[0010] S3. Weigh the mixture obtained in step S2 and carry out the first nitriding reaction in a tube furnace. After the reaction is completed, cool it.

[0011] S4. Take out the cooled product, crush it in a mortar, grind it evenly, carry out a second nitriding reaction in a tube furnace, and obtain crude silicon nitride powder after cooling.

[0012] S5. Weigh the crude silicon nitride powder, ball mill it, and then separate and dry it.

[0013] S6. The mixture of ammonia, HF and HNO3, and HCl solution was used for acid washing in sequence, while sonicating. After centrifugation, the mixture was washed with deionized water until neutral and dried to obtain high-performance silicon nitride powder.

[0014] Furthermore, the preparation process of porous silica powder is as follows:

[0015] a. Preparation of Mg2Si: Silicon powder and magnesium powder, both with a purity of 99%, are added to a ball mill at a molar ratio of 1:2 to 3 and mixed evenly. The ball-to-material ratio is 6 to 8:1, the rotation speed is 500 to 600 r / min, and the mixture is ball-milled for 6 to 8 hours. The mixture is then placed in a heat treatment furnace for vacuum heat treatment. Ar protective gas is introduced, and the gas is repeatedly evacuated three times. The temperature is raised to 500 to 600℃, the reaction time is 2 to 3 hours, and the mixture is cooled to room temperature to obtain Mg2Si.

[0016] b. Preparation of porous silica powder: Weigh 0.5-1.0g of Mg2Si obtained in step a and place it in a ceramic boat. Put the boat into a heat treatment furnace and introduce nitrogen and oxygen in a gas volume ratio of 20-25:1. Exhaust the gas for 30-60 minutes, raise the temperature to 600-700℃, set the temperature program to 5℃ / min, and the reaction time to 10-12 hours. After the reaction is completed, cool to room temperature.

[0017] c. Take out the product after the reaction and add it to a mixture of 0.2-0.5 mol / L HCl solution and 2-5 wt% HF solution. Treat with acid for 2-3 hours, then wash with deionized water and ethanol 2-3 times, and then separate and dry.

[0018] Further, in step S2, the diluent is: nano-silicon with a particle size of 30-50 nm, and the mass ratio of nano-silicon to porous silicon powder is 1:4-5; the mixing is: mixing in a ball mill for 30-60 min, adding 200-300 g of grinding balls with a diameter of 5-6 mm and 100-200 ml of anhydrous ethanol, and rotating at a speed of 100-120 r / min.

[0019] Furthermore, the specific process of the first nitriding reaction is as follows: In a high-temperature tube furnace, 40-50g of the mixture obtained in step S2 is weighed and added to an Al2O3 corundum ceramic boat. The furnace tube is pushed in, and after the furnace tube is closed, a vacuum is drawn 2-3 times. High-purity Ar is introduced into the furnace, and when the temperature is raised to 1200-1300℃, the furnace tube is rotated at a speed of 5-10 r / min. Ar is then removed, and high-purity N2 is introduced at a flow rate of 0.2 L / min. Nitriding is carried out for 10-15 hours.

[0020] Furthermore, the specific process of the second nitriding reaction is as follows: it is carried out in a high-temperature tube furnace. The powder obtained in step S3 is added to an Al2O3 corundum ceramic boat, pushed into the furnace tube, and after the furnace tube is closed, a vacuum is drawn 2 to 3 times. High-purity Ar is introduced into the furnace, and when the temperature is raised to 1300 to 1400°C, the furnace tube is rotated at a speed of 5 to 10 r / min. Ar is then removed, and high-purity N2 is introduced at a flow rate of 0.2 L / min. Nitriding is carried out for 15 to 20 hours.

[0021] Further, the pickling process is as follows: 1-5 wt% ammonia solution is added to the pickling tank, and the prepared crude silicon nitride powder is added for a first round of water washing for 5-6 hours, with simultaneous ultrasonic treatment, and centrifugation to remove the supernatant; then, a mixed solution of HF and HNO3 with a volume ratio of 1:5-6 is added to the pickling tank, and the silicon nitride powder is subjected to a second round of water washing for 5-6 hours, with simultaneous ultrasonic treatment, and centrifugation to remove the supernatant; finally, 1-5 wt% HCl solution is added, and the silicon nitride powder is subjected to a third round of water washing for 5-6 hours, with simultaneous ultrasonic treatment, and centrifugation to remove the supernatant.

[0022] Further, the ball milling process is as follows: weigh 80-120g of powder, add 400-500g of silicon nitride ceramic grinding balls with a diameter of 1-2mm, add 100-200ml of anhydrous ethanol, rotate at 200-300r / min, and mill for 10-20h.

[0023] Separation is achieved by using a screen to separate the grinding balls from the material;

[0024] Drying is carried out in a vacuum drying oven at a temperature of 80–100℃ for 8–12 hours.

[0025] Cooling is achieved by shutting down the heating system under N2 protection, allowing the tubular furnace to cool completely and naturally.

[0026] Grinding: Use an agate mortar and pestle to grind for 20-30 minutes.

[0027] By adopting the aforementioned technical solution, the beneficial effects of the present invention are as follows:

[0028] 1. The silicon nitride powder obtained by the preparation method of this invention has a high α-phase content. The principle is as follows: the silicon powder nitriding reaction is not only very slow, but also a strongly exothermic reaction. The temperature at which the nitriding reaction occurs (1300℃~1400℃) is very close to the melting point of silicon powder (1415±2℃). Once the nitriding reaction occurs, the large amount of heat released by the reaction will drive the internal temperature of the silicon powder to rise in a short time. The increase in temperature promotes the occurrence of the nitriding reaction, thus exothermically driving the temperature to rise further. This is the principle of self-propagating silicon powder nitriding. The overheating inside the reaction system makes it easier for the structurally stable β-phase to appear in the product, thus reducing the α-phase content. Sometimes, the internal overheating even causes the temperature to exceed the melting point of silicon. At this time, the fine silicon powder will melt and agglomerate, further hindering the occurrence of the nitriding reaction. If a liquid phase appears in the reaction system, the nitriding product often contains large, unnitrided silicon particles. To prevent overheating within the reaction system, this invention employs a scheme involving the addition of a silicon nitride diluent to the silicon powder, the use of a rotary furnace, and a two-step nitriding process. This aims to maximize the heat dissipation capacity of the system and promote an increase in the α-phase content of the nitriding product. Furthermore, nano-silicon is added as a raw material for the nitriding reaction. In this case, the nano-sized silicon powder reacts first to produce silicon nitride and disperses around the micron-sized silicon powder. This also acts as a silicon nitride diluent, simultaneously promoting an increase in the α-phase content of the nitriding product.

[0029] 2. The silicon nitride powder obtained by the preparation method of this invention does not contain free Si. The principle is as follows: using porous silicon as the raw material for the nitriding reaction can achieve complete nitriding, thus eliminating the presence of free Si. However, due to the oxidation products generated during the nitriding reaction and other impurities such as metals introduced during the silicon nitride crushing and grinding process, including free silicon, SiO2, and metal elements represented by Fe and Al, remain on the surface of silicon nitride or in the pores of the surface, which can be removed by acid washing. Therefore, this invention employs a three-round acid washing method, using strong oxidizing nitric acid to oxidize the inert metal elements on the particle surface into metal ions, and hydrochloric acid can successfully extract the metal elements; nitric acid and hydrofluoric acid can partially dissolve the surface of silicon nitride, dissolving impurities remaining below the surface or in the surface pores, and hydrofluoric acid can effectively dissolve free Si and SiO2. Furthermore, ultrasonic treatment was carried out simultaneously during the pickling process. Ultrasonic cavitation bubbles preferentially nucleate at the grain boundary slits and defects. When the cavitation bubbles collapse, they generate high temperature, high pressure, strong impact, and micro-jets, which can effectively destroy the surface tension, passivation film, and wettability at these locations, thereby improving the pickling effect. Detailed Implementation

[0030] Example 1

[0031] A method for preparing high-performance silicon nitride powder, characterized by comprising the following steps:

[0032] (1) Selection of raw materials: Porous silicon powder is used as the raw material for the nitriding reaction. The porous silicon powder is ball-milled, separated and dried.

[0033] (1-1) Preparation of Mg2Si: Silicon powder and magnesium powder with a purity of 99% were added to a ball mill at a molar ratio of 1:2 and mixed evenly. The ball-to-material ratio was 6:1 and the rotation speed was 500 r / min. After ball milling for 6 hours, the mixture was placed in a heat treatment furnace for vacuum heat treatment. Ar protective gas was introduced and the gas was repeatedly evacuated three times. The temperature was raised to 500℃ and the reaction time was 2 hours. After cooling to room temperature, Mg2Si was obtained.

[0034] (1-2) Preparation of porous silicon powder: Weigh 0.5g of Mg2Si and place it in a ceramic boat. Put it into a heat treatment furnace and introduce nitrogen and oxygen in a gas volume ratio of 20:1. Exhaust the gas for 30min and raise the temperature to 600℃. Set the heating program to 5℃ / min and the reaction time to 10h. After the reaction is completed, cool to room temperature.

[0035] (1-3) Take out the product after the reaction, add it to a mixture of 0.2 mol / L HCl solution and 2 wt% HF solution, treat with acid for 2 h, then wash with deionized water and ethanol 3 times, separate and dry.

[0036] (2) Add diluent: Add nano-silicon with a particle size of 30nm to the dried porous silica powder. The mass ratio of nano-silicon to porous silica powder is 1:4. Add 200g of grinding balls with a diameter of 5mm and 100ml of anhydrous ethanol. Mix in a ball mill for 30min at a speed of 100r / min. Then, use a mesh screen to separate the grinding balls from the material. Dry in a vacuum drying oven at a temperature of 80℃ for 8h.

[0037] (3) First nitriding reaction: carried out in a high-temperature tube furnace. Weigh 50g of the mixture obtained in step S2, add it to an Al2O3 corundum ceramic boat, push in the furnace tube, close the furnace tube, evacuate 3 times, fill the furnace with high-purity Ar, raise the temperature to 1200℃, rotate the furnace tube at a speed of 5r / min, remove the Ar, fill with high-purity N2 at a flow rate of 0.2L / min, nitrid for 10h, after the reaction is completed, under N2 protection, turn off the heating system and allow the tube furnace to cool completely naturally.

[0038] (4) Second nitriding reaction: Take out the cooled product, grind it for 30 min using an agate mortar, and then carry out the second nitriding reaction in a high-temperature tube furnace. Add the ground powder to an Al2O3 corundum ceramic boat, push it into the furnace tube, close the furnace tube, evacuate 3 times, fill the furnace with high-purity Ar, raise the temperature to 1300℃, rotate the furnace tube at a speed of 5 r / min, remove the Ar, fill with high-purity N2 at a flow rate of 0.2 L / min, nitrid for 15 h, and after the reaction is completed, turn off the heating system under N2 protection and let the tube furnace cool completely naturally to obtain crude silicon nitride powder;

[0039] (5) Acid washing and purification: Weigh the crude silicon nitride powder, ball mill it, separate and dry it, and then acid wash it in sequence with ammonia water, a mixed solution of HF and HNO3, and HCl solution, while sonicating it. After centrifugation, wash it with deionized water until neutral, and dry it to obtain high-performance silicon nitride powder.

[0040] (5-1) Weigh 100g of crude silicon nitride powder, add 500g of silicon nitride ceramic grinding balls with a diameter of 2mm, add 100ml of anhydrous ethanol, rotate at 200r / min for 15h, use a mesh screen to separate the grinding balls from the material, and then dry them in a vacuum drying oven at 80℃ for 8h.

[0041] (5-2) Add 1 wt% ammonia water to the pickling tank, put in the prepared crude silicon nitride powder, and perform a first round of water washing for 5 hours, while simultaneously performing ultrasonic treatment. Remove the supernatant by centrifugation. Then add a mixed solution of HF and HNO3 with a volume ratio of 1:5 to the pickling tank, and perform a second round of water washing for 5 hours, while simultaneously performing ultrasonic treatment. Remove the supernatant by centrifugation. Finally, add 1 wt% HCl solution, and perform a third round of water washing for 5 hours, while simultaneously performing ultrasonic treatment. Remove the supernatant by centrifugation.

[0042] (5-3) Wash with deionized water until neutral, and dry in a vacuum drying oven at 80°C for 8 hours to obtain high-performance silicon nitride powder.

[0043] Example 2

[0044] (1) Selection of raw materials: Porous silicon powder is used as the raw material for the nitriding reaction. The porous silicon powder is ball-milled, separated and dried.

[0045] (1-1) Preparation of Mg2Si: Silicon powder and magnesium powder with a purity of 99% were added to a ball mill at a molar ratio of 1:2 and mixed evenly. The ball-to-material ratio was 6:1 and the rotation speed was 500 r / min. After ball milling for 7 h, the mixture was placed in a heat treatment furnace for vacuum heat treatment. Ar protective gas was introduced and the gas was repeatedly evacuated three times. The temperature was raised to 550℃ and the reaction time was 2 h. After cooling to room temperature, Mg2Si was obtained.

[0046] (1-2) Preparation of porous silicon powder: Weigh 0.5g of Mg2Si and place it in a ceramic boat. Put it into a heat treatment furnace and introduce nitrogen and oxygen in a gas volume ratio of 20:1. Exhaust the gas for 30min and raise the temperature to 650℃. Set the heating program to 5℃ / min and the reaction time to 10h. After the reaction is completed, cool to room temperature.

[0047] (1-3) Take out the product after the reaction, add it to a mixture of 0.2 mol / L HCl solution and 2 wt% HF solution, treat with acid for 2 h, then wash with deionized water and ethanol 3 times, separate and dry.

[0048] (2) Add diluent: Add nano-silicon with a particle size of 30nm to the dried porous silica powder. The mass ratio of nano-silicon to porous silica powder is 1:4.5. Add 200g of grinding balls with a diameter of 5mm and 100ml of anhydrous ethanol. Mix in a ball mill at a speed of 100r / min for 30min. Then, use a mesh screen to separate the grinding balls from the material. Dry in a vacuum drying oven at a temperature of 80℃ for 8h.

[0049] (3) First nitriding reaction: carried out in a high-temperature tube furnace. Weigh 50g of the mixture obtained in step S2, add it to an Al2O3 corundum ceramic boat, push in the furnace tube, close the furnace tube, evacuate 3 times, fill the furnace with high-purity Ar, raise the temperature to 1250℃, rotate the furnace tube at a speed of 5r / min, remove the Ar, fill with high-purity N2 at a flow rate of 0.2L / min, nitrid for 10h, and after the reaction is completed, turn off the heating system under N2 protection to allow the tube furnace to cool completely naturally.

[0050] (4) Second nitriding reaction: Take out the cooled product, grind it for 30 min using an agate mortar, and then carry out the second nitriding reaction in a high-temperature tube furnace. Add the ground powder to an Al2O3 corundum ceramic boat, push it into the furnace tube, close the furnace tube, evacuate 3 times, fill the furnace with high-purity Ar, raise the temperature to 1350℃, rotate the furnace tube at a speed of 5 r / min, remove the Ar, fill with high-purity N2 at a flow rate of 0.2 L / min, nitrid for 15 h, and after the reaction is completed, turn off the heating system under N2 protection and let the tube furnace cool completely naturally to obtain crude silicon nitride powder;

[0051] (5) Acid washing and purification: Weigh the crude silicon nitride powder, ball mill it, separate and dry it, and then acid wash it in sequence with ammonia water, a mixed solution of HF and HNO3, and HCl solution, while sonicating. After centrifugation, wash it with deionized water until neutral, and dry it to obtain high-performance silicon nitride powder.

[0052] (5-1) Weigh 100g of crude silicon nitride powder, add 500g of silicon nitride ceramic grinding balls with a diameter of 2mm, add 100ml of anhydrous ethanol, rotate at 200r / min for 15h, use a mesh screen to separate the grinding balls from the material, and then dry them in a vacuum drying oven at 80℃ for 8h.

[0053] (5-2) Add 2wt% ammonia water to the pickling tank, put in the prepared crude silicon nitride powder, and perform a first round of water washing for 5 hours, while simultaneously performing ultrasonic treatment. Remove the supernatant by centrifugation. Then add a mixed solution of HF and HNO3 with a volume ratio of 1:5.5 to the pickling tank, and perform a second round of water washing for 5 hours, while simultaneously performing ultrasonic treatment. Remove the supernatant by centrifugation. Finally, add 2wt% HCl solution, and perform a third round of water washing for 5 hours, while simultaneously performing ultrasonic treatment. Remove the supernatant by centrifugation.

[0054] (5-3) Wash with deionized water until neutral, and dry in a vacuum drying oven at 80°C for 8 hours to obtain high-performance silicon nitride powder.

[0055] Example 3

[0056] (1) Selection of raw materials: Porous silicon powder is used as the raw material for the nitriding reaction. The porous silicon powder is ball-milled, separated and dried.

[0057] (1-1) Preparation of Mg2Si: Silicon powder and magnesium powder with a purity of 99% were added to a ball mill at a molar ratio of 1:2 and mixed evenly. The ball-to-material ratio was 6:1 and the rotation speed was 500 r / min. After ball milling for 8 hours, the mixture was placed in a heat treatment furnace for vacuum heat treatment. Ar protective gas was introduced and the gas was repeatedly evacuated three times. The temperature was raised to 600℃ and the reaction time was 2 hours. After cooling to room temperature, Mg2Si was obtained.

[0058] (1-2) Preparation of porous silicon powder: Weigh 0.5g of Mg2Si and place it in a ceramic boat. Put it into a heat treatment furnace and introduce nitrogen and oxygen in a gas volume ratio of 20:1. Exhaust the gas for 30min and raise the temperature to 700℃. Set the heating program to 5℃ / min and the reaction time to 10h. After the reaction is completed, cool to room temperature.

[0059] (1-3) Take out the product after the reaction, add it to a mixture of 0.2 mol / L HCl solution and 2 wt% HF solution, treat with acid for 2 h, then wash with deionized water and ethanol 3 times, separate and dry.

[0060] (2) Add diluent: Add nano-silicon with a particle size of 30nm to the dried porous silica powder. The mass ratio of nano-silicon to porous silica powder is 1:4. Add 200g of grinding balls with a diameter of 5mm and 100ml of anhydrous ethanol. Mix in a ball mill for 30min at a speed of 100r / min. Then, use a mesh screen to separate the grinding balls from the material. Dry in a vacuum drying oven at a temperature of 80℃ for 8h.

[0061] (3) First nitriding reaction: carried out in a high-temperature tube furnace. Weigh 50g of the mixture obtained in step S2, add it to an Al2O3 corundum ceramic boat, push in the furnace tube, close the furnace tube, evacuate 3 times, fill the furnace with high-purity Ar, raise the temperature to 1300℃, rotate the furnace tube at a speed of 5r / min, remove the Ar, fill with high-purity N2 at a flow rate of 0.2L / min, nitrid for 10h, and after the reaction is completed, turn off the heating system under N2 protection to allow the tube furnace to cool completely naturally.

[0062] (4) Second nitriding reaction: Take out the cooled product, grind it for 30 min using an agate mortar, and then carry out the second nitriding reaction in a high-temperature tube furnace. Add the ground powder to an Al2O3 corundum ceramic boat, push it into the furnace tube, close the furnace tube, evacuate 3 times, fill the furnace with high-purity Ar, raise the temperature to 1400℃, rotate the furnace tube at a speed of 5 r / min, remove the Ar, fill with high-purity N2 at a flow rate of 0.2 L / min, nitrid for 15 h, and after the reaction is completed, turn off the heating system under N2 protection and let the tube furnace cool completely naturally to obtain crude silicon nitride powder;

[0063] (5) Acid washing and purification: Weigh the crude silicon nitride powder, ball mill it, separate and dry it, and then acid wash it in sequence with ammonia water, a mixed solution of HF and HNO3, and HCl solution, while sonicating. After centrifugation, wash it with deionized water until neutral, and dry it to obtain high-performance silicon nitride powder.

[0064] (5-1) Weigh 100g of crude silicon nitride powder, add 500g of silicon nitride ceramic grinding balls with a diameter of 2mm, add 100ml of anhydrous ethanol, rotate at 200r / min for 15h, use a mesh screen to separate the grinding balls from the material, and then dry them in a vacuum drying oven at 80℃ for 8h.

[0065] (5-2) Add 3wt% ammonia water to the pickling tank, put in the prepared crude silicon nitride powder, and perform a first round of water washing for 5 hours, while simultaneously performing ultrasonic treatment. Remove the supernatant by centrifugation. Then add a mixed solution of HF and HNO3 in a volume ratio of 1:6 to the pickling tank, and perform a second round of water washing for 5 hours, while simultaneously performing ultrasonic treatment. Remove the supernatant by centrifugation. Finally, add 3wt% HCl solution, and perform a third round of water washing for 5 hours, while simultaneously performing ultrasonic treatment. Remove the supernatant by centrifugation.

[0066] (5-3) Wash with deionized water until neutral, and dry in a vacuum drying oven at 80°C for 8 hours to obtain high-performance silicon nitride powder.

[0067] Comparative Example 1

[0068] The differences from Example 1 are as follows: Porous silicon powder is not used as the raw material for the nitriding reaction; commercially available silicon powder is used instead; nano-silicon is not added as a diluent; the nitriding reaction does not use a two-stage reaction method, but a traditional one-stage reaction method, and the furnace tube remains stationary during the reaction; the acid washing and purification process does not use a three-stage water washing method, but a traditional one-stage water washing method. Other technical solutions are the same as in Example 1.

[0069] The performance test results of the products of Example 1, Example 2, Example 3 and Comparative Example 1 are shown in the table below.

[0070] Table 1

[0071]

[0072] As can be seen from the test data in Table 1:

[0073] The α-phase content of the products in Examples 1, 2, and 3 is all greater than 92%, which is much higher than that in Comparative Example 1. The nitriding rate is as high as 100%, which can achieve complete nitriding. There are no free Si diffraction peaks. The purity of silicon nitride powder is as high as 99%, and the total metal impurity content is much lower than that in the comparative example, indicating that the silicon nitride powder prepared by the present invention is of good quality.

[0074] Although the invention has been specifically shown and described in conjunction with preferred embodiments, those skilled in the art should understand that various changes in form and detail may be made to the invention without departing from the spirit and scope of the invention as defined in the appended claims, all of which shall be within the scope of protection of the invention.

Claims

1. A method for preparing high-performance silicon nitride powder, characterized in that, Includes the following steps: S1. Porous silicon powder is used as the raw material for the nitriding reaction. The porous silicon powder is ball-milled, separated, and dried. S2. Add diluent to the dried porous silica powder, mix well, and then separate and dry. S3. Weigh the mixture obtained in step S2 and carry out the first nitriding reaction in a tube furnace. After the reaction is completed, cool it. S4. Take out the cooled product, crush it in a mortar, grind it evenly, carry out a second nitriding reaction in a tube furnace, and obtain crude silicon nitride powder after cooling. S5. Weigh the crude silicon nitride powder, ball mill it, and then separate and dry it. S6. The mixture of ammonia, HF and HNO3, and HCl solution was used sequentially for washing. The mixture was sonicated while washing with water. After centrifugation, it was washed with deionized water until neutral and dried to obtain high-performance silicon nitride powder. The preparation process of the porous silicon powder is as follows: a. Preparation of Mg2Si: Silicon powder and magnesium powder, both with a purity of 99%, are added to a ball mill at a molar ratio of 1:2~3 and mixed evenly. The ball-to-material ratio is 6~8:1, the rotation speed is 500~600 r / min, and the mixture is ball-milled for 6~8 h. The mixture is then placed in a heat treatment furnace for vacuum heat treatment. Ar protective gas is introduced, and the gas is repeatedly evacuated three times. The temperature is raised to 500~600℃, the reaction time is 2~3 h, and the mixture is cooled to room temperature to obtain Mg2Si. b. Preparation of porous silica powder: Weigh 0.5~1.0g of Mg2Si obtained in step a and place it in a ceramic boat. Put the boat into a heat treatment furnace and introduce nitrogen and oxygen in a gas volume ratio of 20~25:

1. Exhaust the gas for 30~60min, raise the temperature to 600~700℃, set the temperature rise program to 5℃ / min, and the reaction time is 10~12h. After the reaction is completed, cool to room temperature. c. Take out the product after the reaction, add it to a mixture of 0.2~0.5mol / L HCl solution and 2~5wt% HF solution, treat with acid for 2~3h, then wash with deionized water and ethanol 2~3 times, separate and dry. The washing process is as follows: 1-5 wt% ammonia solution is added to the pickling tank, followed by the prepared crude silicon nitride powder. A first wash is performed for 5-6 hours, with simultaneous ultrasonic treatment. The supernatant is then removed by centrifugation. Next, a mixed solution of HF and HNO3 in a volume ratio of 1:5-6 is added to the pickling tank, and the silicon nitride powder is washed a second time for 5-6 hours, with simultaneous ultrasonic treatment. The supernatant is then removed by centrifugation. Finally, a 1-5 wt% HCl solution is added, and the silicon nitride powder is washed a third time for 5-6 hours, with simultaneous ultrasonic treatment. The supernatant is then removed by centrifugation. In step S2, the diluent is nano-silicon with a particle size of 30-50 nm, and the mass ratio of nano-silicon to porous silicon powder is 1:4-5; the mixing is carried out by mixing in a ball mill for 30-60 min, adding 200-300 g of grinding balls with a diameter of 5-6 mm and 100-200 ml of anhydrous ethanol, and rotating at a speed of 100-120 r / min.

2. The method for preparing high-performance silicon nitride powder according to claim 1, characterized in that, The specific process of the first nitriding reaction is as follows: In a high-temperature tube furnace, 40-50g of the mixture obtained in step S2 is weighed and added to an Al2O3 corundum ceramic boat. The furnace tube is pushed in, and after the furnace tube is closed, a vacuum is drawn 2-3 times. High-purity Ar is introduced into the furnace, and when the temperature is raised to 1200-1300℃, the furnace tube is rotated at a speed of 5-10 r / min. Ar is then removed, and high-purity N2 is introduced at a flow rate of 0.2 L / min. Nitriding is carried out for 10-15 hours.

3. The method for preparing high-performance silicon nitride powder according to claim 1, characterized in that, The specific process of the second nitriding reaction is as follows: it is carried out in a high-temperature tube furnace. The powder that has been ground evenly in step S4 is added to an Al2O3 corundum ceramic boat, pushed into the furnace tube, and after the furnace tube is closed, a vacuum is drawn 2 to 3 times. High-purity Ar is introduced into the furnace and the temperature is raised to 1300 to 1400°C. The furnace tube is rotated at a speed of 5 to 10 r / min. Ar is removed and high-purity N2 is introduced at a flow rate of 0.2 L / min. Nitriding is carried out for 15 to 20 hours.

4. The method for preparing high-performance silicon nitride powder according to claim 1, characterized in that, In step S1, the ball milling is performed as follows: weigh 80-120g of porous silica powder, add 400-500g of silicon nitride ceramic grinding balls with a diameter of 1-2mm, add 100-200ml of anhydrous ethanol, rotate at 200-300r / min, and mill for 10-20h.

5. The method for preparing high-performance silicon nitride powder according to claim 1, characterized in that: In steps S1 and S5, the separation is achieved by using a mesh screen to separate the grinding balls from the material.

6. The method for preparing high-performance silicon nitride powder according to claim 1, characterized in that, In steps S1, S2, S5 and S6, the drying is carried out in a vacuum drying oven at a temperature of 80~100℃ for 8~12 hours.

7. The method for preparing high-performance silicon nitride powder according to claim 1, characterized in that: In steps S3 and S4, cooling is achieved by shutting down the heating system under N2 protection, allowing the tubular furnace to cool completely and naturally. The grinding process involves using an agate mortar and pestle to grind for 20-30 minutes.

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