A method for preparing high-purity silicon nitride powder assisted by ultrasonic pickling

Abstract

The present invention discloses a method for preparing high-purity silicon nitride powder with the aid of ultrasonic pickling, comprising the following steps: S1: preparing raw materials for preparation; S2: preparing equipment for preparation; S3: pretreatment of raw materials; S4: pickling treatment; S5: preparation of blank; S6: drying; S7: sintering synthesis. The method for preparing high-purity silicon nitride powder with the aid of ultrasonic pickling of the present invention has high requirements on the purity of nitrogen during the preparation process, and no oxides are generated during the preparation, so the quality of the finished product can be guaranteed, and the blank molding pressure has a significant effect on the nitridation rate of silicon powder. As the density of the blank increases, the nitridation rate of metal silicon powder gradually decreases. As the initial particle size of silicon powder decreases, the dependence of the nitridation rate of metal silicon powder on pressure is significantly reduced. The method is more advantageous for preparing blanks under a pressure of 40Mpa, and the prepared silicon nitride powder is conducive to improving the nitridation rate of silicon powder.

Description

Technical Field

[0001] The invention relates to the field of preparation of high-purity silicon nitride powder, and in particular to a method for preparing high-purity silicon nitride powder with the assistance of ultrasonic pickling. Background Art

[0002] Silicon nitride has excellent oxidation resistance, good thermal and chemical stability, high strength and hardness, and self-lubricating properties. It is widely used as high-temperature resistant, corrosion-resistant and wear-resistant parts, high-speed cutting tools, radar antenna covers, etc. Its application fields involve machinery, chemical, electronics, military and other industries. As a refractory material, silicon nitride combined with silicon carbide began to be used in the tuyere of blast furnaces. Due to its excellent performance, large and medium-sized blast furnaces around the world still use this refractory material. In addition, it is also used as a horizontal continuous casting separation ring. However, compared with other refractory materials, its usage and scope are relatively small. The important factor restricting the large-scale promotion and application of silicon nitride materials in the above-mentioned fields is its high production cost, including the cost of raw materials and preparation and processing. Therefore, it is very necessary to find a suitable technology for mass production of silicon nitride powder.

[0003] There are many methods for preparing silicon nitride powder. The most common ones are direct nitridation of silicon powder, carbon thermal reduction, gas phase method and self-propagating method. In addition, there are thermal decomposition method, solvent thermal synthesis method, direct nitridation of silicon powder based on fluidization technology, etc. To select a suitable method from these synthesis routes to organize batch production of Si3N4 powder, several basic principles such as high product quality, low cost and large production scale should be considered comprehensively. From the current research and application situation, the gas-solid phase reaction of direct nitridation of silicon powder is a relatively mature process, but its product quality is subject to certain limitations. Summary of the invention

[0004] The main purpose of the present invention is to provide a method for preparing high-purity silicon nitride powder assisted by ultrasonic pickling, which can effectively solve the problems in the background technology.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for preparing high-purity silicon nitride powder by ultrasonic pickling, comprising the following steps:

[0007] S1: Prepare the raw materials for preparation: including silicon oxide, silicon powder, high-purity nitrogen, ammonium chloride, ferric chloride, distilled water, polyvinyl alcohol solution, anhydrous ethanol, and dilute hydrochloric acid;

[0008] S2: Prepare the equipment for preparation: constant temperature magnetic stirrer, electronic balance, planetary four-head fast ball mill, drying oven, vacuum hot pressing sintering furnace, stainless steel grinding tank, oven;

[0009] S3: Pretreatment of raw materials: weigh a certain amount of silicon powder in a stainless steel grinding jar so that the ball-to-material mass ratio is 10:1, use anhydrous ethanol as the medium, just enough to submerge the balls and silicon powder, perform wet grinding or dry grinding after passing Ar gas, take out the material after stopping, rinse and filter repeatedly with 0.1 mol / L dilute hydrochloric acid, and then place it in an oven to dry at 60°C;

[0010] Weigh a certain amount of silicon oxide in a stainless steel grinding jar so that the ball-to-material mass ratio is 5:1. Use anhydrous ethanol as the medium, just enough to submerge the balls and silicon powder. Wet grind or dry grind after passing Ar gas. Take out the material after stopping, rinse and filter repeatedly with 0.5 mol / L dilute hydrochloric acid, and then dry it in an oven at 60°C.

[0011] S4: Pickling treatment: The dried silicon oxide and silicon powder are placed in a sealed constant temperature condition and subjected to high temperature ultrasonic pickling. The ultrasonic time lasts for 3-10 hours and the temperature is 120°C.

[0012] S5: Preparation of green body: adding 5% polyvinyl alcohol solution to the mixed powder at a ratio of 4%, stirring and rolling to make the mixture uniform, and preparing the green body by machine pressing, using a stainless steel mold with an inner diameter of 30 mm and a pressure of 40 MPa to press it into a round cake shape;

[0013] S6: Drying: Place the formed round cake-shaped body into an oven and keep it at 100°C for 2 hours until the body is completely dry;

[0014] S7: Sintering synthesis: Use a vacuum hot pressing sintering furnace for nitriding synthesis, introduce high-purity nitrogen with a purity of 99.9%, and perform nitriding treatment on it. The nitriding temperature is 1350℃, the nitriding time is 90min, and a catalyst is added to prepare a green body under a pressure of 40Mpa. Put the green body into a vacuum hot pressing sintering furnace, first evacuate and then fill with nitrogen, and then heat and keep in stages, and nitridate at 1420℃ for 2h in a slow heating system. At this time, the pressure in the furnace increases at the initial stage of heating due to gas expansion and decomposition of NH4CL and FeCl3. No exhaust treatment is performed, and the temperature is continued to rise until the nitriding reaction begins. As the reaction proceeds, nitrogen is consumed and the pressure begins to drop. Nitrogen is continuously filled to maintain the pressure at 0.05Mpa until the nitriding reaction is completed, thereby completing the sintering work.

[0015] Preferably, in step S1, the purity of silicon oxide is 99%, the purity of silicon powder is 99%, the purity of high-purity nitrogen is 99.99%, the ammonium chloride is analytically pure, the ferric chloride is analytically pure, the purity of distilled water is 99%, and the purity of polyvinyl alcohol solution is 99%.

[0016] Preferably, in step S3, the silicon powder needs to be ground for 3 hours, and a diluent is added to perform pressure molding on the silicon powder. The added ratio of the diluent is 30%, and the diluent is α-Si3N4.

[0017] Preferably, the material used for pickling in step S4 is a mixture of HF, hydrochloric acid and HNO3, and the ratio of HF: hydrochloric acid: HNO3 is 1:9:0.3.

[0018] Preferably, the catalyst in step S7 is a mixture of NH4CL and FeCl3, and the ratio of NH4CL:FeCl3 is 2:3.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] This method has high requirements on the purity of nitrogen during the preparation process, so that no oxides are produced during the preparation, thereby ensuring the quality and accuracy of the finished product. At the same time, the blank molding pressure has a significant effect on the nitriding rate of silicon powder. As the density of the blank increases, the nitriding rate of metal silicon powder gradually decreases. As the initial particle size of silicon powder decreases, the dependence of the nitriding rate of metal silicon powder on pressure is significantly reduced. This method is more advantageous for preparing blanks under a pressure of 40Mpa. The slow heating ammoniation system through staged heating and heat preservation is beneficial to the improvement of the nitriding rate of silicon powder. The silicon nitride powder prepared by using ball-milled silicon powder and adding a quantitative diluent in a certain proportion is beneficial to the improvement of the nitriding rate of silicon powder, thereby preventing the nitriding rate of silicon powder from being increased due to excessive temperature. , silicon powder shows self-sintering phenomenon, and the added diluent can effectively avoid the self-sintering and silicon flow phenomenon of silicon powder, and with the extension of nitriding time, it is beneficial to increase the content of β-Si3N4 in the powder. At this temperature, the content of β-Si3N4 in the powder prepared by nitriding for 2h is 70.3%. The addition of diluent can significantly increase the nitriding rate of silicon powder, and will not cause the content of β-Si3N4 to decrease rapidly. The added catalyst is beneficial to reduce the temperature of nitriding reaction, and its effect is more obvious when the relative addition ratio of FeCl3 is less than 4%, and then it tends to be slow. Gas is generated by the catalyst during the nitriding process, resulting in a porous structure of the green body, which is beneficial to the improvement of nitriding rate. DETAILED DESCRIPTION

[0021] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Specific embodiment one:

[0023] A method for preparing high-purity silicon nitride powder by ultrasonic pickling, comprising the following steps:

[0024] S1: Prepare the raw materials for preparation: including silicon oxide, silicon powder, high-purity nitrogen, ammonium chloride, ferric chloride, distilled water, polyvinyl alcohol solution, anhydrous ethanol, and dilute hydrochloric acid. The purity of silicon oxide is 99%, the purity of silicon powder is 99%, the purity of high-purity nitrogen is 99.99%, the ammonium chloride is analytical grade, the ferric chloride is analytical grade, the purity of distilled water is 99%, the purity of polyvinyl alcohol solution is 99%, and the ratio of silicon oxide to silicon powder is 2:1.

[0025] S2: Prepare the equipment for preparation: constant temperature magnetic stirrer, electronic balance, planetary four-head fast ball mill, drying oven, vacuum hot pressing sintering furnace, stainless steel grinding tank, oven.

[0026] S3: Pretreatment of raw materials: weigh 100g of silicon powder in a stainless steel grinding jar, grind the silicon powder for 3h, and add 10 parts of diluent to perform pressure molding treatment. The diluent addition ratio is 30%, and the diluent is α-Si3N4, so that the ball-to-material mass ratio is 10:1. Use 80ml of anhydrous ethanol as the medium, just enough to submerge the balls and silicon powder. Wet grind it or dry grind it after passing Ar gas. Take out the material after stopping, rinse and filter it repeatedly with 0.1mol / L dilute hydrochloric acid, and then dry it in an oven at 60℃.

[0027] Weigh 200g of silicon oxide into a stainless steel grinding jar so that the mass ratio of balls to materials is 5:1. Use 80ml of anhydrous ethanol as the medium, just enough to submerge the balls and silicon powder. Perform wet grinding or dry grinding after passing Ar gas. After stopping, take out the material, rinse and filter it repeatedly with 0.5mol / L dilute hydrochloric acid, and then dry it in an oven at 60℃.

[0028] S4: Pickling treatment: The dried silicon oxide and silicon powder are placed in a closed constant temperature condition for high temperature ultrasonic pickling. The ultrasonic time lasts for 3-10 hours at a temperature of 120°C. The pickling material is a mixture of HF, hydrochloric acid and HNO3. The ratio of HF: hydrochloric acid: HNO3 is 1:9:0.3.

[0029] S5: Preparation of the green body: Add 50 ml of 5% polyvinyl alcohol solution at a 4% addition ratio to the mixed powder, stir and roll to mix evenly, and prepare the green body by machine pressing, using a stainless steel mold with an inner diameter of 30 mm and a pressure of 40 MPa to press it into a round cake shape.

[0030] S6: Drying: Place the formed round cake-shaped body into an oven and keep it at 100°C for 2 hours until the body is completely dry.

[0031] S7: Sintering synthesis: Nitriding synthesis is carried out in a vacuum hot pressing sintering furnace, and high-purity nitrogen with a purity of 99.9% is introduced to perform nitriding treatment on the product. The nitriding temperature is 1350°C and the nitriding time is 90min. 12 parts of catalyst are added to prepare a green body under a pressure of 40Mpa. The green body is placed in a vacuum hot pressing sintering furnace, first evacuated and then filled with nitrogen, and then heated and maintained in stages, and nitrided at 1420°C for 2h in a slow heating system. At this time, the pressure in the furnace increases at the initial stage of heating due to gas expansion and decomposition of NH4CL and FeCl3. No exhaust treatment is performed, and the temperature is continued to rise until the nitriding reaction begins. As the reaction proceeds, nitrogen is consumed and the pressure begins to drop. Nitrogen is continuously filled to maintain the pressure at 0.05Mpa until the nitriding reaction is completed, thereby completing the sintering work. The catalyst is a mixture of NH4CL and FeCl3, and the ratio of NH4CL:FeCl3 is 2:3. Specific embodiment 2:

[0033] A method for preparing high-purity silicon nitride powder by ultrasonic pickling, comprising the following steps:

[0034] S1: Prepare the raw materials for preparation: including silicon oxide, silicon powder, high-purity nitrogen, ammonium chloride, ferric chloride, distilled water, polyvinyl alcohol solution, anhydrous ethanol, and dilute hydrochloric acid. The purity of silicon oxide is 99%, the purity of silicon powder is 99%, the purity of high-purity nitrogen is 99.99%, the ammonium chloride is analytical grade, the ferric chloride is analytical grade, the purity of distilled water is 99%, the purity of polyvinyl alcohol solution is 99%, and the ratio of silicon oxide to silicon powder is 2:1.

[0035] S2: Prepare the equipment for preparation: constant temperature magnetic stirrer, electronic balance, planetary four-head fast ball mill, drying oven, vacuum hot pressing sintering furnace, stainless steel grinding tank, oven.

[0036] S3: Pretreatment of raw materials: weigh 200g of silicon powder in a stainless steel grinding jar, grind the silicon powder for 3h, and add 20 parts of diluent to perform pressure molding treatment. The diluent addition ratio is 30%, and the diluent is α-Si3N4, so that the ball-to-material mass ratio is 10:1. Use 160ml of anhydrous ethanol as the medium, just enough to submerge the balls and silicon powder. Wet grind it or dry grind it after passing Ar gas. Take out the material after stopping, rinse and filter it repeatedly with 0.1mol / L dilute hydrochloric acid, and then dry it in an oven at 60℃.

[0037] Weigh 400g of silicon oxide into a stainless steel grinding jar so that the mass ratio of balls to materials is 5:1. Use 160ml of anhydrous ethanol as the medium, just enough to submerge the balls and silicon powder. Perform wet grinding or dry grinding after passing Ar gas. After stopping, take out the material, rinse and filter it repeatedly with 0.5mol / L dilute hydrochloric acid, and then dry it in an oven at 60℃.

[0038] S4: Pickling treatment: The dried silicon oxide and silicon powder are placed in a closed constant temperature condition for high temperature ultrasonic pickling. The ultrasonic time lasts for 3-10 hours at a temperature of 120°C. The pickling material is a mixture of HF, hydrochloric acid and HNO3. The ratio of HF: hydrochloric acid: HNO3 is 1:9:0.3.

[0039] S5: Preparation of the green body: Add 50 ml of 5% polyvinyl alcohol solution at a 4% addition ratio to the mixed powder, stir and roll to mix evenly, and prepare the green body by machine pressing, using a stainless steel mold with an inner diameter of 30 mm and a pressure of 40 MPa to press it into a round cake shape.

[0040] S6: Drying: Place the formed round cake-shaped body into an oven and keep it at 100°C for 2 hours until the body is completely dry.

[0041] S7: Sintering synthesis: Nitriding synthesis is carried out in a vacuum hot pressing sintering furnace, and high-purity nitrogen with a purity of 99.9% is introduced to perform nitriding treatment on the product. The nitriding temperature is 1350°C and the nitriding time is 90 minutes. 25 parts of catalyst are added to prepare a green body under a pressure of 40Mpa. The green body is placed in a vacuum hot pressing sintering furnace, first evacuated and then filled with nitrogen, and then heated and maintained in stages, and nitrided at 1420°C for 2 hours in a slow heating system. At this time, the pressure in the furnace increases at the initial stage of heating due to gas expansion and decomposition of NH4CL and FeCl3. No exhaust treatment is performed, and the temperature is continued to rise until the nitriding reaction begins. As the reaction proceeds, nitrogen is consumed and the pressure begins to drop. Nitrogen is continuously filled to maintain the pressure at 0.05Mpa until the nitriding reaction is completed, thereby completing the sintering work. The catalyst is a mixture of NH4CL and FeCl3, and the ratio of NH4CL:FeCl3 is 2:3.

[0042] The performance of the silicon nitride powder prepared by the method is compared with the common silicon nitride powder on the market, wherein the silicon nitride powder prepared by the method is an example, and the common silicon nitride powder on the market is a comparative example. The following is a comparison table:

[0043] Composite thermal conductivity Average particle size Sphericity Embodiment 1 3.2 6.0 0.88 Embodiment 2 2.8 5.6 0.9 Comparative Example 0.6 3.2 0.79 .

[0044] This method has high requirements on the purity of nitrogen during the preparation process, so that no oxides are produced during the preparation, thereby ensuring the quality and accuracy of the finished product. At the same time, the blank molding pressure has a significant effect on the nitriding rate of silicon powder. As the density of the blank increases, the nitriding rate of metal silicon powder gradually decreases. As the initial particle size of silicon powder decreases, the dependence of the nitriding rate of metal silicon powder on pressure is significantly reduced. This method is more advantageous for preparing blanks under a pressure of 40Mpa. The slow heating ammoniation system through staged heating and heat preservation is beneficial to the improvement of the nitriding rate of silicon powder. The silicon nitride powder prepared by using ball-milled silicon powder and adding a quantitative diluent in a certain proportion is beneficial to the improvement of the nitriding rate of silicon powder, thereby preventing the nitriding rate of silicon powder from being increased due to excessive temperature. , silicon powder shows self-sintering phenomenon, and the added diluent can effectively avoid the self-sintering and silicon flow phenomenon of silicon powder, and with the extension of nitriding time, it is beneficial to increase the content of β-Si3N4 in the powder. At this temperature, the content of β-Si3N4 in the powder prepared by nitriding for 2h is 70.3%. The addition of diluent can significantly increase the nitriding rate of silicon powder, and will not cause the content of β-Si3N4 to decrease rapidly. The added catalyst is beneficial to reduce the temperature of nitriding reaction, and its effect is more obvious when the relative addition ratio of FeCl3 is less than 4%, and then it tends to be slow. Gas is generated by the catalyst during the nitriding process, resulting in a porous structure of the green body, which is beneficial to the improvement of nitriding rate.

[0045] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing high-purity silicon nitride powder by ultrasonic pickling, characterized in that: The steps include: S1: Prepare the raw materials for preparation: including silicon oxide, silicon powder, high-purity nitrogen, ammonium chloride, ferric chloride, distilled water, polyvinyl alcohol solution, anhydrous ethanol, and dilute hydrochloric acid; The purity of silicon oxide is 99%, the purity of silicon powder is 99%, the purity of high-purity nitrogen is 99.99%, ammonium chloride is analytically pure, ferric chloride is analytically pure, the purity of distilled water is 99%, and the purity of polyvinyl alcohol solution is 99%; S2: Prepare the equipment for preparation: constant temperature magnetic stirrer, electronic balance, planetary four-head fast ball mill, drying oven, vacuum hot pressing sintering furnace, stainless steel grinding tank, oven; S3: Pretreatment of raw materials: weigh a certain amount of silicon powder in a stainless steel grinding jar so that the ball-to-material mass ratio is 10:1, use anhydrous ethanol as the medium, just enough to submerge the balls and silicon powder, perform wet grinding or dry grinding after passing Ar gas, take out the material after stopping, rinse and filter repeatedly with 0.1 mol / L dilute hydrochloric acid, and then place it in an oven to dry at 60°C; Weigh a certain amount of silicon oxide in a stainless steel grinding jar so that the ball-to-material mass ratio is 5:

1. Use anhydrous ethanol as the medium, just enough to submerge the balls and silicon powder. Wet grind or dry grind after passing Ar gas. Take out the material after stopping, rinse and filter repeatedly with 0.5 mol / L dilute hydrochloric acid, and then dry it in an oven at 60°C. The silicon powder needs to be ground for 3 hours and then pressure-formed by adding a diluent. The diluent addition ratio is 30%, and the diluent is α-Si3N4. S4: Pickling treatment: The dried silicon oxide and silicon powder are placed in a sealed constant temperature condition and subjected to high temperature ultrasonic pickling. The ultrasonic time lasts for 3-10 hours and the temperature is 120°C. The pickling material is a mixture of HF, HCl and HNO3, wherein the ratio of HF:HCl:HNO3 is 1:9:0.3; S5: Preparation of green body: adding 5% polyvinyl alcohol solution to the mixed powder at a ratio of 4%, stirring and rolling to make the mixture uniform, and preparing the green body by machine pressing, using a stainless steel mold with an inner diameter of 30 mm and a pressure of 40 MPa to press it into a round cake shape; S6: Drying: Place the formed round cake-shaped body into an oven and keep it at 100°C for 2 hours until the body is completely dry; S7: Sintering synthesis: Use a vacuum hot pressing sintering furnace for nitriding synthesis, introduce high-purity nitrogen with a purity of 99.9%, perform nitriding treatment on it, the nitriding temperature is 1350℃, the nitriding time is 90min, add a catalyst, prepare a green body under a pressure of 40MPa, put the green body into a vacuum hot pressing sintering furnace, first evacuate and then fill with nitrogen, then heat and keep in stages, and nitridate at 1420℃ for 2h in a slow heating system. At this time, the pressure in the furnace increases at the initial stage of heating due to gas expansion and decomposition of NH4Cl and FeCl3. No exhaust treatment is performed, and the temperature is continued to rise until the nitriding reaction begins. As the reaction proceeds, nitrogen is consumed and the pressure begins to drop. Nitrogen is continuously filled to maintain the pressure at 0.05Mpa until the nitriding reaction is completed, thereby completing the sintering work; The catalyst is a mixture of NH4Cl and FeCl3, wherein the ratio of NH4Cl to FeCl3 is 2:3.