A method for processing a reaction sintered silicon nitride wafer

Abstract

The application relates to the technical field of silicon nitride ceramic sheets, in particular to a reaction sintering silicon nitride ceramic sheet processing method which comprises the following steps: S1, spherical boron nitride powder and a dispersing agent are added into a solvent to be mixed to obtain a spherical boron nitride solution; S2, the spherical boron nitride solution and a yttrium solution are mixed to obtain a mixed solution; S3, a sintering aid, silicon powder and the mixed solution are put into a ball mill to be slurried to obtain slurry; S4, the slurry is flow-casted by a flow-casting machine to be formed into a flow-cast green body; S5, the flow-cast green body is put on a powder coating machine to be coated with powder to obtain a flow-cast green body after powder coating; S6, the flow-cast green body after powder coating is stacked and then put into a hot air glue removal furnace to be subjected to glue removal treatment to obtain a stacked green body; and S7, the stacked green body is subjected to sintering treatment to obtain a silicon nitride ceramic sheet. The spherical boron nitride powder is used to locally coat a yttrium-containing substance, a reaction sintering silicon nitride ceramic sheet processing method is provided, and the prepared silicon nitride ceramic sheet has a compact structure and excellent bending strength performance.

Description

Technical Field

[0001] This invention relates to the field of silicon nitride ceramic sheet technology, specifically to a method for processing reaction-sintered silicon nitride ceramic sheets. Background Technology

[0002] The fabrication processes of silicon nitride ceramic sheets are mainly divided into three categories: gas pressure sintering, hot pressing sintering, and reaction sintering. Among them, reaction sintering uses silicon powder as the main raw material. After being cast and debinded, it is placed in a sintering furnace, where it first reacts with nitrogen at 1200℃~1400℃, and then sintered at a high temperature of 1700℃~1900℃. This is currently the most advanced fabrication technology in this field. However, this method still has significant problems in the nitriding stage: excessively high temperatures can cause the silicon powder to exotherm violently and melt; while insufficient temperatures or time can lead to incomplete nitriding, thus affecting the final sintering effect. In addition, an excessively long nitriding cycle can significantly increase production costs.

[0003] To control the nitriding process of silicon powder in reaction sintering, catalytic nitriding technology is commonly used. Commonly used catalysts include silicon nitride powder, iron powder, zirconium oxide powder, nickel powder, and yttrium oxide. However, these catalysts often come with a series of negative effects, such as difficulty in ceramic densification, reduced electrical properties, and a significant decrease in thermal conductivity.

[0004] Therefore, finding a suitable catalyst for silicon powder nitriding sintering has become a critical issue that the industry urgently needs to address. Boron nitride powder, containing nitrogen, theoretically possesses catalytic potential and can effectively suppress the melting phenomenon of silicon powder during nitriding. However, conventional boron nitride powder has low activity, may have compatibility issues with the silicon nitride ceramic interface, and is not conducive to material densification. Literature research indicates that using spherical powder particles in the early stages of silicon nitride sintering can significantly improve the densification of the green body by promoting particle rearrangement.

[0005] To address the aforementioned technical challenges, this invention provides a method for processing reaction-sintered silicon nitride ceramic sheets. This method utilizes spherical boron nitride powder as a catalyst, effectively promoting the densification process. Simultaneously, by locally coating the surface of the boron nitride particles with yttrium-containing substances, interfacial compatibility during high-temperature sintering is improved. This method not only significantly enhances nitriding efficiency but also successfully eliminates the adverse effects of boron nitride on densification and interfacial bonding. Under high-temperature conditions, the yttrium-containing substances can generate yttrium oxide in situ, which has low volatility and is less likely to form pores in specific areas, thereby further ensuring the uniformity and density of the ceramic structure. Summary of the Invention

[0006] The purpose of this invention is to provide a method for processing reaction-sintered silicon nitride ceramic sheets to solve the problems raised in the prior art.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] Step S1: Mix spherical boron nitride powder, dispersant and solvent, and place in a high-speed mixer to obtain spherical boron nitride solution;

[0009] Step S2: Mix the spherical boron nitride solution and yttrium solution, and place them in a high-speed mixer to obtain a mixture;

[0010] Step S3: Add sintering aid, silicon powder and mixture to ball mill and ball mill to obtain a well stirred slurry. Degas the well stirred slurry under vacuum to obtain a degassed slurry.

[0011] Step S4: The degassed slurry is coated onto the film belt by a casting machine, dried in the drying section to form a casting green body, and then cut into shape to obtain the cut casting green body;

[0012] Step S5: Place the cut cast green body on a powder coating machine and apply spherical boron nitride powder onto the green body by spraying powder to obtain the powder-coated green body;

[0013] Step S6: Stack the powdered green bodies in layers of 10-25 pieces each, frame them, and place them in a hot air de-glue oven for de-glue removal to obtain stacked green bodies;

[0014] Step S7: Nitriding and sintering the laminated green body to obtain reaction-sintered silicon nitride ceramic sheets.

[0015] Furthermore, the spherical boron nitride particles have a diameter of 5~21μm, the dispersant is sodium polyacrylate, the solvent is one or more of ethanol, isopropanol, and ethyl acetate, and the sintering aid is yttrium oxide.

[0016] Furthermore, the yttrium solution contains 0.005% to 0.01% polyvinyl butyral powder, which is the same mass as the solvent in step S1. The yttrium solution is one or more of yttrium nitrate solution, yttrium oxalate solution, and yttrium acetate solution, and the mass of the yttrium solution is 10% to 20% of the solvent in step S1.

[0017] Furthermore, in step S1, the mass of the spherical boron nitride is 5% to 10% of the solvent mass, and the mass of the dispersant is 0.1% to 0.5% of the spherical boron nitride mass.

[0018] Furthermore, in step S3, the sintering aid is 2%~5% by mass percentage, the silicon powder is 87%~93%, and the mixture is 5%~8%.

[0019] Furthermore, in step S1, the stirring conditions for placing the material in the high-speed mixer are: speed 200~5000 rpm, time 2~6 h; in step S2, the stirring conditions for the high-speed mixer are: speed 50~100 rpm, time 4~12 h; in step S3, the ball milling conditions are: time 6~12 h, speed 50~220 r / min; in step S4, the green body thickness is 0.20~0.50 mm; in step S5, the powder coating amount is 0.05~0.3 g / piece; in step S6, the debinding process parameters are: temperature 500~600℃, time 48~72 h; in step S7, the nitriding treatment is performed with nitrogen gas introduced at a nitriding temperature of 1250~1300℃ for 6~12 h, followed by raising the temperature to 1350~1400℃ for 3~9 h; and the sintering treatment temperature is 1800~1900℃ for 2~7 h.

[0020] In the above technical solution, the stirring speed and time in step S1 have a crucial impact on the coating effect: too slow a speed is not conducive to particle dispersion, while too fast a speed can easily lead to the breakage of spherical particles; too long a time will result in an excessively thick coating layer, while too short a time will result in insufficient coating amount. This involves the site-selective adsorption mechanism of the dispersant—the dispersant molecules first interact with specific groups on the surface of boron nitride, preferentially adsorbing at certain sites. Subsequently, in the yttrium-containing solution, the sites where the dispersant has been adsorbed shield the yttrium molecules from coating, allowing yttrium to selectively deposit in the blank areas. Through this two-step coating method, precise local coating of yttrium is achieved. In the subsequent debinding and sintering processes, the dispersant volatilizes and escapes, exposing its original occupied sites, which directly interact with the silicon powder, promoting nitriding and providing insulation; while the yttrium-coated area generates yttrium oxide in situ at high temperature, effectively improving the compatibility between boron nitride and silicon nitride grains, inhibiting porosity formation, and thus significantly improving the densification level of the ceramic.

[0021] Furthermore, the spherical boron nitride undergoes a modification treatment, the specific modification steps of which are as follows:

[0022] 1): Dissolve sodium hydroxide in water and sonicate it to obtain a 5 mol / L sodium hydroxide solution; mix the sodium hydroxide solution with spherical boron nitride in a beaker and stir, then transfer it to a hydrothermal reactor and react at 120~125℃ for 48~50 h. After the reaction is completed, vacuum filter the solution and wash it with water until the pH of the filtrate is 6.9~7.1. Dry the filtrate at 70~80℃ for 12~14 h to obtain hydroxylated spherical boron nitride.

[0023] 2): Disperse polyvinylpyrrolidone in water, add hydroxylated spherical boron nitride, stir and mix, then add carboxymethyl cellulose, stir at 60~65℃ for 1~2h to dissolve it, and obtain a mixture; treat the mixture with ultrasound, then transfer it to a ball mill jar containing zirconia balls, and ball mill on a planetary ball mill for 18~20h to obtain a suspension; wash the suspension with water by centrifugation and repeat centrifugation 3~5 times, and dry at 80~85℃ for 24~26h to obtain modified spherical boron nitride.

[0024] Furthermore, the sodium hydroxide solution is mixed with spherical boron nitride at a mass ratio of 50:3, and polyvinylpyrrolidone, water, hydroxylated spherical boron nitride and carboxymethyl cellulose are mixed at a mass ratio of 1:50:1:0.25.

[0025] Furthermore, the silicon powder undergoes modification treatment, and the specific modification steps are as follows:

[0026] Weigh silicon powder, add anhydrous ethanol, and disperse by ultrasonication to obtain a dispersion. Add the dispersion dropwise to a 0.25 mol / L ferrous ammonium sulfate solution and stir continuously for 4-6 hours to allow the reaction to mix and obtain a mixture. After the reaction is complete, wash the mixture 4-6 times with anhydrous ethanol, dry it in a drying oven, and then pulverize it to obtain modified silicon powder.

[0027] Furthermore, the solid-liquid ratio of the silicon powder to anhydrous ethanol is 0.04~0.06 g / mL, and the dispersion is mixed with ferrous ammonium sulfate solution at a mass ratio of 1:0.2.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] 1. This invention describes a method for processing reaction-bonded silicon nitride ceramic sheets. This method utilizes spherical boron nitride powder to locally coat yttrium-containing materials, providing a method for processing reaction-bonded silicon nitride ceramic sheets. This method fully leverages the positive role of boron nitride powder in promoting the nitriding process while effectively avoiding its adverse effects on material densification. Furthermore, this processing technology can significantly reduce production costs, especially by increasing the stack size to 25 sheets / stack, further enhancing the feasibility of industrial applications.

[0030] 2. This invention describes a reaction-sintered silicon nitride ceramic wafer processing method. During the sintering process, modified silicon powder first promotes matrix formation through catalytic nitriding and liquid-phase sintering effects. Simultaneously, spherical boron nitride is hydroxylated, transforming it from highly hydrophobic to hydrophilic, fundamentally solving its dispersion problem in aqueous slurries and effectively suppressing agglomeration. The modified spherical boron nitride, through surface polymer coating, not only achieves uniform dispersion but also acts as an inert filler embedded in the forming matrix. Furthermore, the entire chemical modification process is mild and controllable, avoiding damage to the spherical structure of boron nitride and fully preserving its excellent thermal conductivity. The two complement each other in terms of dispersibility, structural construction, and functional performance, ultimately giving the material comprehensive properties of "high thermal conductivity, high strength, and easy processing," making it suitable for high-performance electronic device heat dissipation substrates, high-temperature structural ceramics, and other high-end fields.

[0031] 3. This invention describes a method for processing reaction-sintered silicon nitride ceramic wafers, which involves chemically depositing a nanoscale iron oxide film onto the surface of silicon powder using ferrous ammonium sulfate. This Fe-based compound film acts as a highly efficient catalyst for the nitriding reaction, significantly reducing the nitriding activation energy and increasing the nitriding rate. This allows the silicon powder to be more completely converted to silicon nitride at a lower temperature and in a shorter time during subsequent sintering. Simultaneously, the Fe-Si-ON liquid phase formed by the catalyst at high temperature promotes grain rearrangement and mass migration through a liquid-phase sintering mechanism, significantly improving the density of the ceramic body, reducing porosity, and thus enhancing the material's mechanical strength and thermal conductivity. Furthermore, the surface coating may alter the surface electrical properties of the silicon powder, helping to improve its dispersion stability in aqueous slurries. Attached Figure Description

[0032] Figure 1 This is a process flow diagram of a reaction sintering silicon nitride ceramic sheet processing method according to the present invention;

[0033] Figure 2 This is a scanning electron microscope image of the spherical boron nitride powder described in Example 1 of the reaction sintering silicon nitride ceramic sheet processing method of the present invention;

[0034] Figure 3 This is a schematic diagram of the two-step local coating mechanism of a reaction sintering silicon nitride ceramic sheet processing method of the present invention. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] The sources of raw materials in the following examples and comparative examples:

[0037] Spherical boron nitride powder: sourced from Shanghai Jiadeer Chemical Technology Co., Ltd.;

[0038] Sodium polyacrylate: Product number S30249, sourced from Shanghai Yuanye Biotechnology Co., Ltd.;

[0039] Isopropanol, sodium hydroxide, and anhydrous ethanol were all of analytical grade.

[0040] Yttrium nitrate: analytical grade, catalog number BX2854, sourced from Shanghai Baoyang Baoxin Biotechnology Co., Ltd.

[0041] Yttrium oxide: Item number ds20230222, sourced from Shandong Desheng New Materials Co., Ltd.

[0042] Silicon powder: Product number PA07355, sourced from Guangdong Wengjiang Chemical Reagent Co., Ltd.;

[0043] Polyvinylpyrrolidone: Product No. S30268, sourced from Shanghai Yuanye Biotechnology Co., Ltd.;

[0044] Carboxymethyl cellulose: Product number RM-C011800, sourced from Shenzhen Zhenqiang Biotechnology Co., Ltd.;

[0045] Zirconia balls: sourced from Zibo Xinrunqing Chemical Co., Ltd.

[0046] Ferrous ammonium sulfate: sourced from Hubei Xinhongli Chemical Co., Ltd.

[0047] Example 1: This invention provides a technical solution for processing reaction-sintered silicon nitride ceramic sheets, comprising the following steps:

[0048] Step S1: Mix 20g of spherical boron nitride powder, 0.02g of sodium polyacrylate and 400mL of isopropanol, place them in a high-speed mixer, stir at 200rpm for 2h to obtain a spherical boron nitride solution.

[0049] Step S2: Mix the spherical boron nitride solution and 40 mL of yttrium nitrate solution, place them in a high-speed mixer, stir at 50 rpm for 4 hours to obtain a mixture;

[0050] Step S3: Add 2% yttrium oxide, 93% silicon powder and 5% mixed liquid to the ball mill by mass percentage, ball mill for 6 hours, ball mill speed is 50 r / min, ball mill volume is 2L, and degas the stirred slurry under a specific vacuum environment to obtain the degassed slurry;

[0051] Step S4: The degassed slurry is coated onto the film belt by a casting machine, dried in the drying section to form a casting green body with a thickness of 0.20 mm, and then cut into shape to obtain the cut casting green body;

[0052] Step S5: Place the cut cast green blank on a powder coating machine and apply spherical boron nitride powder to the green blank by spraying powder. The amount of powder applied is 0.05g / piece, and the powdered green blank is obtained.

[0053] Step S6: Stack the powdered green bodies in layers of 10 pieces each, frame them, and place them in a hot air de-glue furnace for de-glue removal. The de-glue removal process parameters are set as follows: temperature 500℃, time 48h, to obtain the stacked green bodies.

[0054] Step S7: Nitriding the laminated green body at 1250℃ for 6 hours while maintaining nitrogen gas flow. Then, the temperature is raised to 1350℃ for 3 hours, followed by sintering at 1800℃ for 2 hours to obtain reaction-sintered silicon nitride ceramic sheets.

[0055] Example 2: This invention provides a technical solution for processing reaction-sintered silicon nitride ceramic sheets, comprising the following steps:

[0056] Step S1: Mix 20g of spherical boron nitride powder, 0.02g of sodium polyacrylate and 400mL of isopropanol, place them in a high-speed mixer, stir at 200rpm for 2h to obtain a spherical boron nitride solution.

[0057] Step S2: Mix the spherical boron nitride solution and 40 mL of yttrium nitrate solution, place them in a high-speed mixer, stir at 50 rpm for 4 hours to obtain a mixture;

[0058] Step S3: Add 2% yttrium oxide, 93% silicon powder and 5% mixed liquid to the ball mill by mass percentage, ball mill for 6 hours, ball mill speed is 50 r / min, ball mill volume is 2L, and degas the stirred slurry under a specific vacuum environment to obtain the degassed slurry;

[0059] Step S4: The degassed slurry is coated onto the film belt by a casting machine, dried in the drying section to form a casting green body with a thickness of 0.20 mm, and then cut into shape to obtain the cut casting green body;

[0060] Step S5: Place the cut cast green blank on a powder coating machine and apply spherical boron nitride powder to the green blank by spraying powder. The amount of powder applied is 0.05g / piece, and the powdered green blank is obtained.

[0061] Step S6: Stack the powdered green bodies in layers of 15 pieces each, frame them, and place them in a hot air de-glue oven for de-glue removal. The de-glue removal process parameters are set as follows: temperature 500℃, time 48h, to obtain the stacked green bodies.

[0062] Step S7: Nitriding the laminated green body at 1250℃ for 6 hours while maintaining nitrogen gas flow. Then, the temperature is raised to 1350℃ for 3 hours, followed by sintering at 1800℃ for 2 hours to obtain reaction-sintered silicon nitride ceramic sheets.

[0063] Example 3: This invention provides a technical solution for processing reaction-sintered silicon nitride ceramic sheets, comprising the following steps:

[0064] Step S1: Mix 20g of spherical boron nitride powder, 0.02g of sodium polyacrylate and 400mL of isopropanol, place them in a high-speed mixer, stir at 200rpm for 2h to obtain a spherical boron nitride solution.

[0065] Step S2: Mix the spherical boron nitride solution and 40 mL of yttrium nitrate solution, place them in a high-speed mixer, stir at 50 rpm for 4 hours to obtain a mixture;

[0066] Step S3: Add 2% yttrium oxide, 93% silicon powder and 5% mixed liquid to the ball mill by mass percentage, ball mill for 6 hours, ball mill speed is 50 r / min, ball mill volume is 2L, and degas the stirred slurry under a specific vacuum environment to obtain the degassed slurry;

[0067] Step S4: The degassed slurry is coated onto the film belt by a casting machine, dried in the drying section to form a casting green body with a thickness of 0.20 mm, and then cut into shape to obtain the cut casting green body;

[0068] Step S5: Place the cut cast green blank on a powder coating machine and apply spherical boron nitride powder to the green blank by spraying powder. The amount of powder applied is 0.05g / piece, and the powdered green blank is obtained.

[0069] Step S6: Stack the powdered green bodies in layers of 25 pieces each, frame them, and place them in a hot air de-glue oven for de-glue removal. The de-glue removal process parameters are set as follows: temperature 500℃, time 48h, to obtain the stacked green bodies.

[0070] Step S7: Nitriding the laminated green body at 1250℃ for 6 hours while maintaining nitrogen gas flow. Then, the temperature is raised to 1350℃ for 3 hours, followed by sintering at 1800℃ for 2 hours to obtain reaction-sintered silicon nitride ceramic sheets.

[0071] Example 4: This invention provides a technical solution for processing reaction-sintered silicon nitride ceramic sheets, comprising the following steps:

[0072] Step S1: Mix 20g of spherical boron nitride powder, 0.02g of sodium polyacrylate and 400mL of isopropanol, place them in a high-speed mixer, stir at 1500rpm for 4h to obtain a spherical boron nitride solution.

[0073] Step S2: Mix the spherical boron nitride solution and 40 mL of yttrium nitrate solution, place them in a high-speed mixer, stir at 60 rpm for 6 hours to obtain a mixture;

[0074] Step S3: Add 3% yttrium oxide, 91% silicon powder and 6% mixed liquid to a ball mill by mass percentage, ball mill for 8 hours, ball mill speed is 100 r / min, ball mill volume is 2L, and degas the stirred slurry under a specific vacuum environment to obtain the degassed slurry;

[0075] Step S4: The degassed slurry is coated onto the film belt by a casting machine, dried in the drying section to form a casting green body with a thickness of 0.30 mm, and then cut into shape to obtain the cut casting green body;

[0076] Step S5: Place the cut cast green blank on a powder coating machine and apply spherical boron nitride powder to the green blank by spraying powder. The amount of powder applied is 0.1g / piece, and the powdered green blank is obtained.

[0077] Step S6: Stack the powdered green bodies in layers of 15 pieces each, frame them, and place them in a hot air de-glue oven for de-glue removal. The de-glue removal process parameters are set as follows: temperature 520℃, time 55h, to obtain the stacked green bodies.

[0078] Step S7: Nitriding the laminated green body at 1260°C for 8 hours while maintaining nitrogen gas flow, then raising the temperature to 1370°C for 5 hours, followed by sintering at 1830°C for 4 hours to obtain reaction-sintered silicon nitride ceramic sheets.

[0079] The spherical boron nitride is modified, and the specific modification steps are as follows:

[0080] 1): Dissolve 10g of sodium hydroxide in 50mL of water and sonicate for 10min to ensure complete dissolution, obtaining a 5mol / L sodium hydroxide solution; take 50mL of this sodium hydroxide solution and mix it with 3g of spherical boron nitride in a beaker and stir, then transfer the mixture to a hydrothermal reactor and react at 120℃ for 48h. After the reaction is completed, vacuum filter the mixture and wash it with water until the pH of the filtrate is 6.9. Dry the filtrate at 70℃ for 12h to obtain hydroxylated spherical boron nitride.

[0081] 2): Disperse 1g of polyvinylpyrrolidone in 50mL of water, add 1g of hydroxylated spherical boron nitride, stir thoroughly, then add 0.25g of carboxymethyl cellulose, stir at 60℃ for 1h to completely dissolve, and obtain a mixture; sonicate the mixture for 20min, then transfer it to a 250mL ball mill jar containing 100g of zirconia balls, and ball mill at 400rpm for 18h on a planetary ball mill to obtain a suspension; centrifuge the suspension at 5000rpm for 10min, wash with water and repeat centrifugation 3 times to remove residual modifier, and dry at 80℃ for 24h to obtain modified spherical boron nitride;

[0082] The silicon powder undergoes modification treatment, and the specific modification steps are as follows:

[0083] Weigh silicon powder and add anhydrous ethanol at a solid-liquid ratio of 0.04 g / mL. Disperse the powder by ultrasonication for 60 min to obtain a dispersion. Add the dispersion dropwise to a 0.25 mol / L ferrous ammonium sulfate solution at a mass ratio of 1:0.2 and stir continuously at 540 r / min for 4 h to allow it to react and mix thoroughly to obtain a mixture. After the reaction is complete, wash the mixture four times with anhydrous ethanol, dry it in a drying oven, and then pulverize it to obtain modified silicon powder.

[0084] Example 5: This invention provides a technical solution for processing reaction-sintered silicon nitride ceramic sheets, comprising the following steps:

[0085] Step S1: Mix 20g of spherical boron nitride powder, 0.02g of sodium polyacrylate and 400mL of isopropanol, place them in a high-speed mixer, stir at 3000rpm for 5h to obtain a spherical boron nitride solution.

[0086] Step S2: Mix the spherical boron nitride solution and 40 mL of yttrium nitrate solution, place them in a high-speed mixer, stir at 70 rpm for 8 hours to obtain a mixture;

[0087] Step S3: Add 4% yttrium oxide, 89% silicon powder and 7% mixed liquid to a ball mill by mass percentage, ball mill for 10 hours, ball mill speed is 150 r / min, ball mill volume is 2L, and degas the stirred slurry under a specific vacuum environment to obtain the degassed slurry;

[0088] Step S4: The degassed slurry is coated onto the film belt by a casting machine, dried in the drying section to form a casting green body with a thickness of 0.40 mm, and then cut into shape to obtain the cut casting green body;

[0089] Step S5: Place the cut cast green blank on a powder coating machine and apply spherical boron nitride powder to the green blank by spraying powder. The amount of powder applied is 0.2g / piece, and the powder-coated green blank is obtained.

[0090] Step S6: Stack the powdered green bodies in layers of 20 pieces each, frame them, and place them in a hot air de-glue oven for de-glue removal. The de-glue removal process parameters are set as follows: temperature 550℃, time 60h, to obtain the stacked green bodies.

[0091] Step S7: Nitriding the laminated green body is carried out at a temperature of 1270°C for 10 hours while nitrogen is being introduced. Then the temperature is raised to 1380°C for 7 hours and then sintered at a temperature of 1850°C for 5 hours to obtain reaction-sintered silicon nitride ceramic sheets.

[0092] The spherical boron nitride is modified, and the specific modification steps are as follows:

[0093] 1): Dissolve 10g of sodium hydroxide in 50mL of water and sonicate for 11min to ensure complete dissolution, obtaining a 5mol / L sodium hydroxide solution; take 50mL of this sodium hydroxide solution and mix it with 3g of spherical boron nitride in a beaker and stir, then transfer the mixture to a hydrothermal reactor and react at 123℃ for 49h. After the reaction is completed, vacuum filter the mixture and wash it with water until the pH of the filtrate is 7.0. Dry the filtrate at 75℃ for 13h to obtain hydroxylated spherical boron nitride.

[0094] 2): Disperse 1g of polyvinylpyrrolidone in 50mL of water, add 1g of hydroxylated spherical boron nitride, stir thoroughly, then add 0.25g of carboxymethyl cellulose, stir at 63℃ for 1.5h to completely dissolve, and obtain a mixture; sonicate the mixture for 23min, then transfer it to a 250mL ball mill jar containing 100g of zirconia balls, and ball mill at 430rpm for 19h on a planetary ball mill to obtain a suspension; centrifuge the suspension at 5300rpm for 11min, wash with water and repeat centrifugation 4 times to remove residual modifier, and dry at 83℃ for 25h to obtain modified spherical boron nitride;

[0095] The silicon powder undergoes modification treatment, and the specific modification steps are as follows:

[0096] Weigh silicon powder and add anhydrous ethanol at a solid-liquid ratio of 0.05 g / mL. Disperse the powder by ultrasonication for 75 min to obtain a dispersion. Add the dispersion dropwise to a 0.25 mol / L ferrous ammonium sulfate solution at a mass ratio of 1:0.2 and stir continuously at 545 r / min for 5 h to allow it to react and mix thoroughly to obtain a mixture. After the reaction is complete, wash the mixture five times with anhydrous ethanol, dry it in a drying oven, and then pulverize it to obtain modified silicon powder.

[0097] Example 6: This invention provides a technical solution for processing reaction-sintered silicon nitride ceramic sheets, comprising the following steps:

[0098] Step S1: Mix 20g of spherical boron nitride powder, 0.02g of sodium polyacrylate and 400mL of isopropanol, place them in a high-speed mixer, stir at 5000rpm for 6h to obtain a spherical boron nitride solution.

[0099] Step S2: Mix the spherical boron nitride solution and 40 mL of yttrium nitrate solution, place them in a high-speed mixer, stir at 100 rpm for 12 hours to obtain a mixture;

[0100] Step S3: Add 5% yttrium oxide, 87% silicon powder and 8% mixed liquid to a ball mill by mass percentage, ball mill for 12 hours, ball mill speed is 220 r / min, ball mill volume is 2L, and degas the stirred slurry under a specific vacuum environment to obtain the degassed slurry;

[0101] Step S4: The degassed slurry is coated onto the film belt by a casting machine, dried in the drying section to form a casting green body with a thickness of 0.50 mm, and then cut into shape to obtain the cut casting green body.

[0102] Step S5: Place the cut cast green blank on a powder coating machine, and apply spherical boron nitride powder to the green blank by spraying powder. The amount of powder applied is 0.3g / piece, and the powdered green blank is obtained.

[0103] Step S6: Stack the powdered green bodies in layers of 25 pieces each, frame them, and place them in a hot air de-glue oven for de-glue removal. The de-glue removal process parameters are set as follows: temperature 600℃, time 72h, to obtain the stacked green bodies.

[0104] Step S7: Nitriding the laminated green body at 1300℃ for 12 hours while maintaining nitrogen gas flow. Then, the temperature is raised to 1400℃ for 9 hours and sintering is performed at 1900℃ for 7 hours to obtain reaction-sintered silicon nitride ceramic sheets.

[0105] The spherical boron nitride is modified, and the specific modification steps are as follows:

[0106] 1): Dissolve 10g of sodium hydroxide in 50mL of water and sonicate for 12min to ensure complete dissolution, obtaining a 5mol / L sodium hydroxide solution; take 50mL of this sodium hydroxide solution and mix it with 3g of spherical boron nitride in a beaker and stir, then transfer the mixture to a hydrothermal reactor and react at 125℃ for 50h. After the reaction is completed, perform vacuum filtration and wash with water until the pH of the filtrate is 7.1. Dry at 80℃ for 14h to obtain hydroxylated spherical boron nitride.

[0107] 2): Disperse 1g of polyvinylpyrrolidone in 50mL of water, add 1g of hydroxylated spherical boron nitride, stir thoroughly, then add 0.25g of carboxymethyl cellulose, stir at 65℃ for 2h to completely dissolve, and obtain a mixture; sonicate the mixture for 25min, then transfer it to a 250mL ball mill jar containing 100g of zirconia balls, and ball mill at 450rpm for 20h on a planetary ball mill to obtain a suspension; centrifuge the suspension at 5500rpm for 12min, wash with water and repeat centrifugation 5 times to remove residual modifier, and dry at 85℃ for 26h to obtain modified spherical boron nitride;

[0108] The silicon powder undergoes modification treatment, and the specific modification steps are as follows:

[0109] Weigh silicon powder and add anhydrous ethanol at a solid-liquid ratio of 0.06 g / mL. Disperse the powder by ultrasonication for 90 min to obtain a dispersion. Add the dispersion dropwise to a 0.25 mol / L ferrous ammonium sulfate solution at a mass ratio of 1:0.2 and stir continuously at 550 r / min for 6 h to allow it to react and mix thoroughly to obtain a mixture. After the reaction is complete, wash the mixture 6 times with anhydrous ethanol, dry it in a drying oven, and then pulverize it to obtain modified silicon powder.

[0110] Comparative Example 1: Step S2 is removed, and the other steps are the same as in Example 1.

[0111] Comparative Example 2: Steps S1 and S2 are removed. In step S3, the sintering aid is 5% by mass percentage and the silicon powder is 95%. The other steps are the same as in Example 1.

[0112] Comparative Example 3: The green blanks after powdering in step S6 are stacked, with 30 pieces per layer, and the remaining steps are the same as in Example 1.

[0113] Experiment: Reaction-sintered silicon nitride ceramic sheets obtained in Examples 1-6 and Comparative Examples 1-3 were used to prepare samples. Their properties were tested, and the results were recorded.

[0114] Ceramic tiles for the presence of dissolved silica (visual inspection): Visually inspect for black spherical silica particles;

[0115] Ceramic tile density test: The density was tested using the water displacement method, with GB / T 25995-2010 as the reference standard.

[0116] Ceramic tile flexural strength test: Based on GB / T 6569-2006 as the reference standard, the three-point flexural method was used for testing. The sample length was 35 mm, the width was 4 mm, the thickness was 0.32 mm, and the loading rate of the sample testing machine was 0.5 mm / min.

[0117] Ceramic sheet thermal conductivity test: GB / T 22588-2008 was used as the reference standard, and the laser flash method was adopted for testing. The sample was square, with a length and width of 9.8 mm and a thickness of 0.32 mm.

[0118] All experimental results are shown in Table 1.

[0119] Table 1

[0120]

[0121] As shown in Table 1, compared with Example 1, Comparative Example 1 did not use yttrium solution to locally coat the spherical boron nitride powder, resulting in a decrease in the density and flexural strength of the ceramic sheet. This indicates that the local coating of yttrium molecules used in this invention can improve the interfacial compatibility of the green body during high-temperature sintering and eliminate the adverse effects of spherical boron nitride powder on sintering densification and interfacial compatibility. Comparative Example 2 did not use spherical boron nitride powder, and the resulting ceramic sheet exhibited silica dissolution. This indicates that the spherical boron nitride powder added in this invention can prevent silica dissolution caused by the reaction between silicon powder and nitrogen, thereby improving the density of the ceramic sheet.

[0122] Compared to Example 1, Examples 4-6 show excellent results, achieving 25° azid sintering. The resulting ceramic tiles have higher density, better compactness, superior flexural strength, and thermal conductivity that meets the usage standards (>80W / (m×K)). This indicates that modifying spherical boron nitride and silicon powder can improve their dispersibility, enhance the compactness of the ceramic tiles, and strengthen their mechanical properties.

[0123] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for processing reaction-sintered silicon nitride ceramic sheets, characterized in that: Includes the following steps: Step S1: Mix spherical boron nitride powder, dispersant and solvent, and place in a high-speed mixer to obtain spherical boron nitride solution; Step S2: Mix the spherical boron nitride solution and yttrium solution, and place them in a high-speed mixer to obtain a mixture; Step S3: Add sintering aid, silicon powder and mixture to ball mill and ball mill to obtain a well stirred slurry. Degas the well stirred slurry under vacuum to obtain a degassed slurry. Step S4: The degassed slurry is coated onto the film belt by a casting machine, dried in the drying section to form a casting green body, and then cut into shape to obtain the cut casting green body; Step S5: Place the cut cast green body on a powder coating machine and apply spherical boron nitride powder onto the green body by spraying powder to obtain the powder-coated green body; Step S6: Stack the powdered green bodies in layers of 10-25 pieces each, frame them, and place them in a hot air de-glue oven for de-glue removal to obtain stacked green bodies; Step S7: The laminated green body is subjected to nitriding and sintering treatment to obtain reaction-sintered silicon nitride ceramic sheet; In step S3, the sintering aid is 2%~5% by mass percentage, the silicon powder is 87%~93%, and the mixture is 5%~8%.

2. The method for processing reaction-sintered silicon nitride ceramic sheets according to claim 1, characterized in that: The spherical boron nitride particles have a diameter of 5~21μm, the dispersant is sodium polyacrylate, the solvent is one or more of ethanol, isopropanol, and ethyl acetate, and the sintering aid is yttrium oxide.

3. The method for processing reaction-sintered silicon nitride ceramic sheets according to claim 1, characterized in that: The yttrium solution contains 0.005% to 0.01% polyvinyl butyral powder, which is the same mass as the solvent in step S1. The yttrium solution is one or more of yttrium nitrate solution, yttrium oxalate solution, and yttrium acetate solution, and the mass of the yttrium solution is 10% to 20% of the solvent in step S1.

4. The method for processing reaction-sintered silicon nitride ceramic sheets according to claim 1, characterized in that: In step S1, the mass of the spherical boron nitride is 5% to 10% of the solvent mass, and the mass of the dispersant is 0.1% to 0.5% of the spherical boron nitride mass.

5. The method for processing reaction-sintered silicon nitride ceramic sheets according to claim 1, characterized in that: The mixing conditions in step S1 for placing the material in the high-speed mixer are: speed 200-5000 rpm, time 2-6 h; the mixing conditions in step S2 for the high-speed mixer are: speed 50-100 rpm, time 4-12 h; the ball milling conditions in step S3 are: time 6-12 h, speed 50-220 r / min; the green body thickness in step S4 is 0.20-0.50 mm; the powder coating amount in step S5 is 0.05-0.3 g / piece; the debinding process parameters in step S6 are: temperature 500-600℃, time 48-72 h; the nitriding treatment in step S7 is: nitriding temperature 1250-1300℃, time 6-12 h, under nitrogen gas purging, followed by heating to... The temperature is 1350~1400℃ for 3~9 hours; the sintering temperature is 1800~1900℃ for 2~7 hours.

6. The method for processing reaction-sintered silicon nitride ceramic sheets according to claim 1, characterized in that: The spherical boron nitride is modified, and the specific modification steps are as follows: 1): Dissolve sodium hydroxide in water and sonicate it to obtain a 5 mol / L sodium hydroxide solution; mix the sodium hydroxide solution with spherical boron nitride in a beaker and stir, then transfer it to a hydrothermal reactor and react at 120~125℃ for 48~50 h. After the reaction is completed, vacuum filter the solution and wash it with water until the pH of the filtrate is 6.9~7.

1. Dry the filtrate at 70~80℃ for 12~14 h to obtain hydroxylated spherical boron nitride. 2): Disperse polyvinylpyrrolidone in water, add hydroxylated spherical boron nitride, stir and mix, then add carboxymethyl cellulose, stir at 60~65℃ for 1~2h to dissolve it, and obtain a mixture; treat the mixture with ultrasound, then transfer it to a ball mill jar containing zirconia balls, and ball mill on a planetary ball mill for 18~20h to obtain a suspension; wash the suspension with water by centrifugation and repeat centrifugation 3~5 times, and dry at 80~85℃ for 24~26h to obtain modified spherical boron nitride.

7. The method for processing reaction-sintered silicon nitride ceramic sheets according to claim 6, characterized in that: The sodium hydroxide solution is mixed with spherical boron nitride at a mass ratio of 50:3, and polyvinylpyrrolidone, water, hydroxylated spherical boron nitride and carboxymethyl cellulose are mixed at a mass ratio of 1:50:1:0.

25.

8. The method for processing reaction-sintered silicon nitride ceramic sheets according to claim 1, characterized in that: The silicon powder undergoes modification treatment, and the specific modification steps are as follows: Weigh silicon powder, add anhydrous ethanol, and disperse by ultrasonication to obtain a dispersion. Add the dispersion dropwise to a 0.25 mol / L ferrous ammonium sulfate solution and stir continuously for 4-6 hours to allow the reaction to mix and obtain a mixture. After the reaction is complete, wash the mixture 4-6 times with anhydrous ethanol, dry it in a drying oven, and then pulverize it to obtain modified silicon powder.

9. A method for processing reaction-sintered silicon nitride ceramic sheets according to claim 8, characterized in that: The solid-liquid ratio of the silicon powder to anhydrous ethanol is 0.04~0.06 g / mL, and the dispersion is mixed with ferrous ammonium sulfate solution at a mass ratio of 1:0.2.

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