A method for preparing a reaction-sintered silicon nitride wafer

Abstract

This invention relates to the field of silicon nitride ceramic sheet technology, specifically a method for preparing reaction-sintered silicon nitride ceramic sheets, comprising the following steps: S1 preparing a nano-dispersion; S2 adding hexagonal porous boron nitride to the nano-dispersion for mixing; S3 placing the sintering aid, silicon powder, and hexagonal porous boron nitride nano-mixture into a ball mill for slurry preparation; S4 casting the slurry into a cast green body using a casting machine; S5 coating the cast green body with powder using a powder coating machine to obtain a powder-coated green body; S6 stacking the powder-coated green bodies in a hot air debinding furnace for debinding treatment to obtain a stacked green body; S7 sintering the stacked green bodies to obtain a reaction-sintered silicon nitride ceramic sheet. This invention uses hexagonal porous boron nitride as a catalyst aid for silicon powder nitridation, providing a new method for preparing reaction-sintered silicon nitride ceramic sheets, resulting in silicon nitride ceramic sheets with high thermal conductivity and flexural strength.

Description

Technical Field

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

[0002] Insulated Gate Bipolar Transistor (IGBT), as the core device of modern energy conversion systems, is known as the "central processing unit" of the power electronics field. It is a key product of my country's emerging industries and plays an irreplaceable role in high-end fields such as new energy electric vehicles, ultra-high voltage power transmission, smart grids and rail transit.

[0003] In the field of IGBT supporting materials, silicon nitride ceramic substrates have become a key basic material for the third-generation semiconductor industry due to their excellent comprehensive performance. Currently, product quality on the market varies greatly, and further improvements are needed in terms of consistency and reliability.

[0004] Silicon nitride ceramics are mainly prepared using three process routes: gas pressure sintering, hot pressing sintering, and reaction sintering. Among them, the reaction sintering process uses silicon powder as raw material. After being formed by tape casting, it first undergoes a nitriding reaction in a nitrogen atmosphere at 1200–1400℃, and then sintersects at a high temperature of 1700–1900℃. This represents the most advanced technology in the industry at present. However, this process has significant technical challenges: too high a temperature will cause silicon to melt, while too low a temperature will result in incomplete nitriding, and extending the nitriding time will significantly increase production costs.

[0005] To optimize the nitriding process, catalytic nitriding technology is widely used in the industry. Commonly used catalysts include silicon nitride powder, iron powder, zirconium oxide powder, nickel powder, and yttrium oxide, but these additives often lead to negative effects such as decreased ceramic density, deterioration of electrical properties, and reduction in thermal conductivity. Against this backdrop, developing novel and highly efficient catalysts has become a key issue for industrial development. Boron nitride, due to its nitrogen-containing properties, theoretically possesses catalytic potential. Coupled with its excellent high-temperature thermal conductivity and thermal stability, it can effectively suppress silicon melting. However, its insufficient surface activity may affect the densification process of the final product, and this technical challenge remains to be solved.

[0006] To address the aforementioned technical challenges, this invention proposes a method for preparing reaction-sintered silicon nitride ceramic sheets: Hexagonal porous boron nitride prepared by a template method is used as a catalyst for silicon powder nitridation. The hexagonal porous boron nitride is then activated, and through pre-dispersion and adsorption, nano-sized silicon nitride powder is embedded within the hexagonal porous boron nitride to form a composite structure. A small amount of highly active nano-silicon nitride effectively enhances the compatibility between the hexagonal porous boron nitride and the matrix, ensuring that the hexagonal porous boron nitride does not interfere with the normal densification process of the ceramic sheet. Simultaneously, since only a very small amount of nano-silicon nitride is added, it neither affects the thermal conductivity of the ceramic sheet nor hinders the densification effect. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing reaction-sintered silicon nitride ceramic sheets to solve the problems raised in the prior art.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] Step S1: Add nano-silicon nitride powder and dispersant to ethanol, sonicate at 100-200W for 30-120 minutes to obtain nano-dispersion;

[0010] Step S2: After mixing the nano-dispersion with hexagonal porous boron nitride, the mixture is subjected to ultrasonic treatment to obtain an ultrasonicated mixture; the ultrasonicated mixture is then transferred to a planetary ball mill for mechanical grinding to obtain a hexagonal porous boron nitride nano-mixture.

[0011] Step S3: Add the sintering aid, silicon powder and hexagonal porous boron nitride nano mixture into a ball mill and ball mill at a speed of 50-220 r / min for 6-12 h to obtain a uniformly mixed slurry; place the uniformly mixed slurry in a vacuum environment for degassing treatment to obtain a degassed slurry;

[0012] Step S4: The degassed slurry is evenly coated onto the film belt through a casting machine and then sent to the drying section for drying to obtain a casting green body with a thickness of 0.20-0.50 mm, which is then cut into shape.

[0013] Step S5: Using a powder spraying process, hexagonal porous boron nitride powder is evenly sprayed onto the surface of the cut cast green body on a powder coating machine to obtain the powder-coated green body.

[0014] Step S6: Stack the powdered green bodies into layers of 10-30 pieces each. After fixing them in a frame, place them in a hot air de-glue oven for de-glue removal to obtain stacked green bodies.

[0015] Step S7: Sinter the stacked green blanks to obtain reaction-sintered silicon nitride ceramic sheets.

[0016] Furthermore, the dispersant is ammonium polyacrylate, and the sintering aid is lutetium oxide.

[0017] Furthermore, the hexagonal porous boron nitride has a particle size of 5 μm to 10 μm, a porosity of 10% to 30%, and a pore size of 100 nm to 1 μm.

[0018] Further, in step S1, the amount of dispersant is 10% to 20% of the mass of the nano-silicon nitride powder, preferably 5% to 10% of the mass of the nano-silicon nitride powder, and the mass of ethanol is 1000 to 5000 times the mass of the nano-silicon nitride powder; in step S2, the mass of the hexagonal porous boron nitride is 20 to 50 times the mass of the nano-silicon nitride powder in step S1; in step S3, the mass of the sintering aid is 2% to 4% of the mass of the silicon powder, and the silicon powder and hexagonal porous boron nitride are mixed at a mass ratio of 20 to 50:1.

[0019] Furthermore, the process parameters for ultrasonic treatment in step S2 are: ultrasonic power 150-400W, treatment time 30-200min; the process parameters for planetary ball mill mechanical grinding are: ball mill jar capacity 2-50L, rotation speed 50-220r / min, grinding time 2-6h; the powder application amount in step S5 is 0.05-0.3g / piece; and the process parameters for glue removal treatment in step S6 are: temperature 500-600℃, pressure -10-10Pa, treatment time 48-72h.

[0020] Furthermore, the sintering treatment in step S7 is divided into nitriding and sintering. The first stage of nitriding is controlled at a temperature of 1250-1300℃, a pressure of 0.1-0.9MPa, and a time of 6-12h. The second stage of nitriding is controlled at a temperature of 1350-1400℃, a pressure of 0.5-2MPa, and a time of 3-9h. The final sintering temperature is controlled at 1800-1900℃, a pressure of 0.9-2MPa, and a time of 2-8h.

[0021] Furthermore, the nano-silicon nitride undergoes a modification treatment, the specific modification steps of which are as follows:

[0022] γ-glycidoxypropyltrimethoxysilane was dissolved in a 90% acetone aqueous solution, and nano-silicon nitride powder was added. The mixture was dispersed at a high speed of 2000 r / min for 2-3 min to form a suspension. The suspension was continuously shaken at 30-35℃ for 5-6 h, filtered, and dried to obtain modified nano-silicon nitride.

[0023] Furthermore, the mass of the γ-glycidyl etheroxypropyltrimethoxysilane is 1% of the mass of the nano-silicon nitride powder.

[0024] Furthermore, the hexagonal porous boron nitride undergoes a modification treatment, the specific modification steps of which are as follows:

[0025] 1) Add hexagonal porous boron nitride to a 5 mol / L sodium hydroxide aqueous solution, stir magnetically at 80-85℃ for 48-50 h, filter after the reaction is complete, wash with deionized water until the pH of the filtrate is 6.9-7.1, dry at 120-125℃ for 24-26 h to obtain hydroxylated hexagonal porous boron nitride, grind for later use.

[0026] 2) Take a 95% ethanol solution, add γ-aminopropyltriethoxysilane, stir in a water bath at 60-65℃ for 3-4 hours, then add hydroxylated hexagonal porous boron nitride, continue stirring at 60-65℃ for 3-4 hours, filter and wash after the reaction is complete, and dry at 90-100℃ for 12-14 hours to obtain silane coupling agent modified hexagonal porous boron nitride.

[0027] 3) Disperse the silane coupling agent-modified hexagonal porous boron nitride in deionized water, add anhydrous ethanol, and sonicate for 1-2 hours. Add dopamine hydrochloride and tris(hydroxymethyl)aminomethane hydrochloride, adjust the pH to 8-8.5, stir at 80-85℃ for 6-7 hours, filter and wash until the filtrate is colorless and the pH is 6.9-7.1, dry at 60-65℃ for 24-26 hours, and grind to obtain the modified hexagonal porous boron nitride.

[0028] Furthermore, the hexagonal porous boron nitride and sodium hydroxide aqueous solution are mixed at a mass ratio of 1:10; γ-aminopropyltriethoxysilane, hydroxylated hexagonal porous boron nitride and 95% ethanol solution are mixed at a mass ratio of 0.1:2:10; silane coupling agent modified hexagonal porous boron nitride, deionized water, anhydrous ethanol, dopamine hydrochloride and tris(hydroxymethyl)aminomethane hydrochloride are mixed at a mass ratio of 1:100:100:0.2:0.3.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] 1. This invention describes a method for preparing reaction-sintered silicon nitride ceramic sheets, using hexagonal porous boron nitride with specific structural parameters as a catalyst for silicon powder nitridation. The hexagonal porous boron nitride has a particle size of 5–10 μm, a porosity controlled within the range of 10%–30%, and a pore size of 100 nm–1 μm. Excessive porosity will affect its thermal insulation performance, while insufficient porosity will reduce the loading capacity of the activating material. Optimized pore size selection is beneficial for the effective loading of nanoparticles. The mass ratio of silicon powder to boron nitride is optimized to 20:1 to 50:1. This ratio range effectively suppresses silicon dissolution without affecting the final densification of the ceramic sheet. This method combines the material advantages of nano-silicon nitride and porous boron nitride: on the one hand, it utilizes the excellent thermal insulation performance of boron nitride to control the reaction temperature; on the other hand, it significantly improves the nitridation reaction efficiency through nano-silicon nitride. In particular, by optimizing the material ratio and process parameters, this invention successfully increased the number of green blanks stacked to 25 pieces / layer, which significantly reduced production costs while ensuring product quality. It effectively solved the technical problem that increasing the number of stacks in traditional processes easily leads to silicon dissolution. This technological breakthrough provides a new solution for the large-scale production of high-performance silicon nitride ceramics.

[0031] 2. The present invention describes a method for preparing reaction-sintered silicon nitride ceramic sheets, which uses γ-glycidyl etheroxypropyltrimethoxysilane to modify nano-silicon nitride, preventing the agglomeration of nano-silicon nitride, reducing the use of dispersants, and improving the sintering density of the ceramic sheets; silanol (-Si(OH)3) condenses with the SiO2 layer on the surface of nano-silicon nitride to form Si-O-Si covalent bonds, and the retained epoxy groups open and react with hexagonal porous boron nitride modified by γ-aminopropyltriethoxysilane to improve the interfacial bonding strength between nano-silicon nitride and hexagonal porous silicon nitride.

[0032] 3. This invention describes a method for preparing reaction-sintered silicon nitride ceramic sheets. The hexagonal porous boron nitride used undergoes a three-step modification process: sodium hydroxide hydroxylation generates B-OH / NH active sites, enhancing the adsorption of subsequent modifiers; γ-aminopropyltriethoxysilane introduces amino groups, providing anchoring sites for dopamine polymerization; and then dopamine self-polymerization forms a dopamine coating layer, improving the adhesion of polydopamine and enhancing the bonding force between the hexagonal porous boron nitride and nano-silicon nitride. Before sintering, the amino group of γ-aminopropyltriethoxysilane undergoes a ring-opening reaction with the epoxy group of γ-glycidoxypropyltrimethoxysilane. Simultaneously, the catechol / amino groups of polydopamine interact with the modified hexagonal porous boron nitride and nano-silicon nitride through hydrogen bonds and coordination bonds, enhancing the mechanical properties of the silicon nitride ceramic sheet. Attached Figure Description

[0033] Figure 1 This is a process flow diagram of a reaction-sintered silicon nitride ceramic sheet preparation method according to the present invention;

[0034] Figure 2 This is a schematic diagram of the hexagonal porous boron nitride and nano-silicon nitride embedded in Example 1 of the method for preparing reaction-sintered silicon nitride ceramic sheets according to the present invention;

[0035] Figure 3 This is a scanning electron microscope image of nano-silicon nitride powder in Example 1 of the method for preparing reaction-sintered silicon nitride ceramic sheets according to the present invention;

[0036] Figure 4 This is a microscope image of the green blank prepared in Example 1 of the reaction sintering silicon nitride ceramic sheet preparation method of the present invention;

[0037] Figure 5 These are electron microscope (EM) images of Example 1 and Comparative Example 1 in the method for preparing reaction-sintered silicon nitride ceramic sheets according to the present invention. Detailed Implementation

[0038] 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.

[0039] Raw material sources for examples and comparative examples:

[0040] Nano silicon nitride powder: particle size 20nm, product number: XH-Si3N4-20, sourced from Shanghai Xiaohuang Nanotechnology Co., Ltd.

[0041] Silicon powder: Product number PA07355, sourced from Guangdong Wengjiang Chemical Reagent Co., Ltd.;

[0042] Ammonium polyacrylate: Product number S68736, sourced from Shanghai Yuanye Biotechnology Co., Ltd.;

[0043] Hexagonal porous boron nitride: sourced from Xi'an Qiyue Biotechnology Co., Ltd.;

[0044] Lutene oxide: Product number S41402, sourced from Shanghai Yuanye Biotechnology Co., Ltd.;

[0045] γ-glycidyl etheroxypropyltrimethoxysilane: Product No. C034963, sourced from Shanghai Kedi Chemical Technology Co., Ltd.;

[0046] Acetone: Product No. 10000418, sourced from Sinopharm Chemical Reagent Co., Ltd.;

[0047] Sodium hydroxide: Product number 10019718, sourced from Sinopharm Chemical Reagent Co., Ltd.;

[0048] γ-aminopropyltriethoxysilane: Product No. 21321, sourced from Hubei Wande Chemical Co., Ltd.;

[0049] Dopamine hydrochloride: Product number D103111, sourced from Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0050] Anhydrous ethanol: Product number 10009218, sourced from Sinopharm Chemical Reagent Co., Ltd.;

[0051] Tris(hydroxymethyl)aminomethane hydrochloride: Product No. S16004, sourced from Shanghai Yuanye Biotechnology Co., Ltd.

[0052] Example 1: As Figures 1-5 As shown, the present invention provides a method for preparing reaction-sintered silicon nitride ceramic sheets, comprising the following steps:

[0053] Step S1: Add 1g of nano-silicon nitride powder and 0.1g of ammonium polyacrylate to 1L of ethanol, and sonicate for 30min on an ultrasonic homogenizer with an ultrasonic power of 100W to obtain a nano-dispersion.

[0054] Step S2: Mix the nano-dispersion with 20g of hexagonal porous boron nitride, and then place it in an ultrasonic homogenizer for ultrasonic treatment. The parameters are set as follows: ultrasonic power 150W, treatment time 30min, to obtain the ultrasonicated mixture. Transfer the ultrasonicated mixture to a planetary ball mill for mechanical grinding. Select a ball mill jar capacity of 2L, control the rotation speed at 50r / min, and grind for 2h to obtain a hexagonal porous boron nitride nano-mixture.

[0055] Step S3: Add 8g of lutetium oxide, 400g of silicon powder and hexagonal porous boron nitride nano-mixture to a ball mill and ball mill at 50r / min for 6h. The volume of the ball mill jar is 2L to obtain a uniformly mixed slurry. Place the uniformly mixed slurry in a specific vacuum environment for degassing treatment to obtain a degassed slurry.

[0056] Step S4: The degassed slurry is evenly coated onto the film belt through the casting machine and then sent to the drying section to dry, so as to obtain a casting green body with a thickness of 0.20mm, which is then cut into shape.

[0057] Step S5: Using a powder spraying process, hexagonal porous boron nitride powder is evenly sprayed onto the surface of the cut cast green body on a powder coating machine. The powder coating amount is 0.05g / piece, and the powder-coated green body is obtained.

[0058] Step S6: Stack the powdered green bodies into layers of 10 pieces each. After fixing them in a frame, 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℃, pressure -10Pa, and processing time 48h to obtain the stacked green bodies.

[0059] Step S7: The laminated green body is sintered. Sintering is divided into nitriding and sintering. The first stage of nitriding is controlled at 1250℃, pressure of 0.1MPa and time of 6h. The second stage of nitriding is controlled at 1350℃, pressure of 0.5MPa and time of 3h. The final sintering temperature is 1800℃, pressure of 0.9MPa and time of 2h. After sintering is completed, reaction sintered silicon nitride ceramic sheet is obtained.

[0060] Example 2: Figures 1-5 As shown, the present invention provides a method for preparing reaction-sintered silicon nitride ceramic sheets, comprising the following steps:

[0061] Step S1: Add 1g of nano-silicon nitride powder and 0.05g of ammonium polyacrylate to 1L of ethanol, and sonicate for 60min on an ultrasonic homogenizer with an ultrasonic power of 150W to obtain a nano-dispersion.

[0062] Step S2: Mix the nano-dispersion with 20g of hexagonal porous boron nitride, and then place it in an ultrasonic homogenizer for ultrasonic treatment. The parameters are set as follows: ultrasonic power 300W, treatment time 90min, to obtain the ultrasonicated mixture. Transfer the ultrasonicated mixture to a planetary ball mill for mechanical grinding. Select a ball mill jar capacity of 2L, control the rotation speed at 100r / min, and grind for 4h to obtain a hexagonal porous boron nitride nano-mixture.

[0063] Step S3: Add 8g of lutetium oxide, 400g of silicon powder and hexagonal porous boron nitride nano-mixture into a ball mill and ball mill at 100r / min for 8h. The volume of the ball mill jar is 2L to obtain a uniformly mixed slurry. Place the uniformly mixed slurry in a specific vacuum environment for degassing treatment to obtain a degassed slurry.

[0064] Step S4: The degassed slurry is evenly coated onto the film belt through the casting machine and then sent to the drying section to dry, so as to obtain a casting green body with a thickness of 0.30mm, which is then cut into shape.

[0065] Step S5: Using a powder spraying process, hexagonal porous boron nitride powder is evenly sprayed onto the surface of the cut cast green blank on a powder coating machine. The powder coating amount is 0.15g / piece, and the powder-coated green blank is obtained.

[0066] Step S6: Stack the powdered green bodies into layers of 15 pieces each. After being framed and fixed, 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℃, pressure -5Pa, and processing time 55h to obtain the stacked green bodies.

[0067] Step S7: The laminated green body is sintered. Sintering is divided into nitriding and sintering. The first stage of nitriding is controlled at 1260℃, pressure of 0.5MPa, and time of 8h. The second stage of nitriding is controlled at 1360℃, pressure of 1MPa, and time of 5h. The final sintering temperature is 1850℃, pressure of 1.5MPa, and time of 4h. After sintering, reaction-sintered silicon nitride ceramic sheet is obtained.

[0068] The nano-silicon nitride undergoes modification treatment, and the specific modification steps are as follows:

[0069] 0.1 g of γ-glycidoxypropyltrimethoxysilane was dissolved in a 90% acetone aqueous solution, and 10 g of nano-silicon nitride powder was added. The mixture was dispersed at a high speed of 2000 r / min for 2 min using a high-shear mixer to form a suspension. The suspension was transferred to a constant temperature shaking oven and shaken continuously at 30℃ for 5 h. After filtration and drying, modified nano-silicon nitride was obtained.

[0070] The hexagonal porous boron nitride underwent modification treatment, and the specific modification steps are as follows:

[0071] 1) Take 25g of hexagonal porous boron nitride and add it to 250mL of 5mol / L sodium hydroxide aqueous solution. Stir magnetically at 80℃ for 48h. After the reaction is completed, filter and wash with deionized water until the pH of the filtrate is 6.9. Dry at 120℃ for 24h to obtain hydroxylated hexagonal porous boron nitride. Grind it for later use.

[0072] 2) Take 50 mL of 95% ethanol solution, add 0.5 g of γ-aminopropyltriethoxysilane, stir in a water bath at 60 °C for 3 h to allow it to fully hydrolyze, then add 10 g of hydroxylated hexagonal porous boron nitride, continue stirring at 60 °C for 3 h, filter and wash after the reaction is complete, and dry at 90 °C for 12 h to obtain silane coupling agent modified hexagonal porous boron nitride.

[0073] 3) Disperse 4g of silane coupling agent modified hexagonal porous boron nitride in 400mL of deionized water, add 400mL of anhydrous ethanol, sonicate for 1h, add 0.8g of dopamine hydrochloride and 1.2g of tris(hydroxymethyl)aminomethane hydrochloride, adjust the pH to 8, stir at 80℃ for 6h, filter and wash until the filtrate is colorless and the pH is 6.9, dry at 60℃ for 24h, and grind to obtain modified hexagonal porous boron nitride.

[0074] Example 3: As Figures 1-5 As shown, the present invention provides a method for preparing reaction-sintered silicon nitride ceramic sheets, comprising the following steps:

[0075] Step S1: Add 1g of nano-silicon nitride powder and 0.05g of ammonium polyacrylate to 1L of ethanol, and sonicate for 90min on an ultrasonic homogenizer with an ultrasonic power of 170W to obtain a nano-dispersion.

[0076] Step S2: Mix the nano-dispersion with 20g of hexagonal porous boron nitride, and then place it in an ultrasonic homogenizer for ultrasonic treatment. The parameters are set as follows: ultrasonic power 350W, treatment time 150min, to obtain the ultrasonicated mixture. Transfer the ultrasonicated mixture to a planetary ball mill for mechanical grinding. Select a ball mill jar capacity of 2L, control the rotation speed at 190r / min, and grind for 5h to obtain a hexagonal porous boron nitride nano-mixture.

[0077] Step S3: Add 8g of lutetium oxide, 400g of silicon powder and hexagonal porous boron nitride nano-mixture to a ball mill and ball mill at 190r / min for 10h. The volume of the ball mill jar is 2L to obtain a uniformly mixed slurry. Place the uniformly mixed slurry in a specific vacuum environment for degassing treatment to obtain a degassed slurry.

[0078] Step S4: The degassed slurry is evenly coated onto the film belt through the casting machine and then sent to the drying section to dry, so as to obtain a casting green body with a thickness of 0.40mm, which is then cut into shape.

[0079] Step S5: Using a powder spraying process, hexagonal porous boron nitride powder is evenly sprayed onto the surface of the cut cast green body on a powder coating machine. The powder coating amount is 0.20g / piece, and the powder-coated green body is obtained.

[0080] Step S6: Stack the powdered green bodies into layers of 25 pieces each. After being framed and fixed, place them in a hot air de-glue oven for de-glue removal. The de-glue removal process parameters are set as follows: temperature 570℃, pressure 5Pa, and processing time 65h to obtain the stacked green bodies.

[0081] Step S7: The laminated green body is sintered. Sintering is divided into nitriding and sintering. The first stage of nitriding is controlled at 1280℃, pressure of 0.7MPa, and time of 10h. The second stage of nitriding is controlled at 1380℃, pressure of 1.5MPa, and time of 7h. The final sintering temperature is 1870℃, pressure of 1.7MPa, and time of 6h. After sintering, reaction-sintered silicon nitride ceramic sheet is obtained.

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

[0083] 0.15 g of γ-glycidoxypropyltrimethoxysilane was dissolved in a 90% acetone aqueous solution, and 15 g of nano-silicon nitride powder was added. The mixture was dispersed at a high speed of 2000 r / min for 2.5 min using a high-shear mixer to form a suspension. The suspension was transferred to a constant temperature shaking oven and shaken continuously at 33℃ for 5.6 h. After filtration and drying, modified nano-silicon nitride was obtained.

[0084] The hexagonal porous boron nitride underwent modification treatment, and the specific modification steps are as follows:

[0085] 1) Take 30g of hexagonal porous boron nitride and add it to 300mL of 5mol / L sodium hydroxide aqueous solution. Stir magnetically at 83℃ for 49h. After the reaction is complete, filter and wash with deionized water until the pH of the filtrate is 7.0. Dry at 123℃ for 25h to obtain hydroxylated hexagonal porous boron nitride, grind and set aside.

[0086] 2) Take 100 mL of 95% ethanol solution, add 1 g of γ-aminopropyltriethoxysilane, stir in a water bath at 63°C for 3.5 h to allow it to fully hydrolyze, then add 20 g of hydroxylated hexagonal porous boron nitride, continue stirring at 63°C for 3.5 h, filter and wash after the reaction is complete, and dry at 95°C for 13 h to obtain silane coupling agent modified hexagonal porous boron nitride;

[0087] 3) Disperse 5g of silane coupling agent modified hexagonal porous boron nitride in 500mL of deionized water, add 500mL of anhydrous ethanol, sonicate for 1.5h, add 1g of dopamine hydrochloride and 1.5g of tris(hydroxymethyl)aminomethane hydrochloride, adjust the pH to 8.3, stir at 83℃ for 6.5h, filter and wash until the filtrate is colorless and the pH is 7.0, dry at 63℃ for 25h, and grind to obtain modified hexagonal porous boron nitride.

[0088] Example 4: Figures 1-5 As shown, the present invention provides a method for preparing reaction-sintered silicon nitride ceramic sheets, comprising the following steps:

[0089] Step S1: Add 1g of nano-silicon nitride powder and 0.05g of ammonium polyacrylate to 1L of ethanol, and sonicate for 120min on an ultrasonic homogenizer with an ultrasonic power of 200W to obtain a nano-dispersion.

[0090] Step S2: Mix the nano-dispersion with 20g of hexagonal porous boron nitride, and then place it in an ultrasonic homogenizer for ultrasonic treatment. The parameters are set as follows: ultrasonic power 400W, treatment time 200min, to obtain the ultrasonicated mixture. Transfer the ultrasonicated mixture to a planetary ball mill for mechanical grinding. Select a ball mill jar capacity of 2L, control the rotation speed at 220r / min, and grind for 6h to obtain a hexagonal porous boron nitride nano-mixture.

[0091] Step S3: Add 8g of lutetium oxide, 400g of silicon powder and hexagonal porous boron nitride nano-mixture to a ball mill and ball mill at 220r / min for 12h. The volume of the ball mill jar is 50L to obtain a uniformly mixed slurry. Place the uniformly mixed slurry in a specific vacuum environment for degassing treatment to obtain a degassed slurry.

[0092] Step S4: The degassed slurry is evenly coated onto the film belt through the casting machine and then sent to the drying section to dry, so as to obtain a casting green body with a thickness of 0.50mm, which is then cut into shape.

[0093] Step S5: Using a powder spraying process, hexagonal porous boron nitride powder is evenly sprayed onto the surface of the cut cast green body on a powder coating machine. The powder coating amount is 0.3g / piece, and the powder-coated green body is obtained.

[0094] Step S6: Stack the powdered green bodies into layers of 25 pieces each. After being framed and fixed, 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℃, pressure 10Pa, and processing time 72h to obtain the stacked green bodies.

[0095] Step S7: The laminated green body is sintered. Sintering is divided into nitriding and sintering. The first stage of nitriding is controlled at 1300℃, pressure of 0.9MPa, and time of 12h. The second stage of nitriding is controlled at 1400℃, pressure of 2MPa, and time of 9h. The final sintering temperature is 1900℃, pressure of 2MPa, and time of 8h. After sintering is completed, reaction-sintered silicon nitride ceramic sheet is obtained.

[0096] The nano-silicon nitride undergoes modification treatment, and the specific modification steps are as follows:

[0097] 0.2 g of γ-glycidoxypropyltrimethoxysilane was dissolved in a 90% acetone aqueous solution, and 20 g of nano-silicon nitride powder was added. The mixture was dispersed at a high speed of 2000 r / min for 3 min using a high-shear mixer to form a suspension. The suspension was transferred to a constant temperature shaking oven and shaken continuously at 35℃ for 6 h. After filtration and drying, modified nano-silicon nitride was obtained.

[0098] The hexagonal porous boron nitride underwent modification treatment, and the specific modification steps are as follows:

[0099] 1) Take 30g of hexagonal porous boron nitride and add it to 300mL of 5mol / L sodium hydroxide aqueous solution. Stir magnetically at 85℃ for 50h. After the reaction is completed, filter and wash with deionized water until the pH of the filtrate is 7.1. Dry at 125℃ for 26h to obtain hydroxylated hexagonal porous boron nitride, grind and set aside.

[0100] 2) Take 150 mL of 95% ethanol solution, add 1.5 g of γ-aminopropyltriethoxysilane, stir in a water bath at 65 °C for 4 h to allow it to fully hydrolyze, then add 30 g of hydroxylated hexagonal porous boron nitride, continue stirring at 65 °C for 4 h, filter and wash after the reaction is complete, and dry at 100 °C for 14 h to obtain silane coupling agent modified hexagonal porous boron nitride.

[0101] 3) Disperse 6g of silane coupling agent modified hexagonal porous boron nitride in 600mL of deionized water, add 600mL of anhydrous ethanol, sonicate for 2h, add 1.2g of dopamine hydrochloride and 1.8g of tris(hydroxymethyl)aminomethane hydrochloride, adjust the pH to 8.5, stir at 85℃ for 7h, filter and wash until the filtrate is colorless and the pH is 7.1, dry at 65℃ for 26h, and grind to obtain modified hexagonal porous boron nitride.

[0102] Comparative Example 1: Steps S1 and S2 were not used, i.e., hexagonal porous boron nitride and nano silicon nitride powder were not added. The remaining steps were the same as in Example 1.

[0103] Comparative Example 2: In step S3, the hexagonal porous boron nitride nano-mixture was replaced with hexagonal porous boron nitride, and the remaining steps were the same as in Example 1.

[0104] Comparative Example 3: In step S3, the hexagonal porous boron nitride nano-mixture was replaced with a nano-dispersion, and the remaining steps were the same as in Example 1.

[0105] Experiment: Reaction-sintered silicon nitride ceramic sheets obtained in Examples 1-4 and Comparative Examples 1-3 were used to prepare samples. Their properties were tested, and the results were recorded.

[0106] Green compact density test: The density was tested using the water displacement method, with a sample volume of 0.4 cm³, in accordance with GB / T 25995-2010 as the reference standard. 3 ;

[0107] Ceramic tiles for the presence of dissolved silica (visual inspection): Visually inspect for black spherical silica particles;

[0108] Ceramic tile density test: The density was tested using the water displacement method, with a sample volume of 0.4 cm³, in accordance with GB / T 25995-2010 as the reference standard. 3 ;

[0109] Ceramic tile flexural strength test: Based on GB / T 6569-2006 as the reference standard, the three-point flexural strength test was adopted. The sample length was 35mm, the width was 4mm, the thickness was 2mm, and the loading rate of the sample testing machine was 0.5mm / min.

[0110] Ceramic sheet thermal conductivity test: GB / T 22588-2008 was used as the reference standard, and the laser flash method was used for testing. The sample was a circular disc with a diameter of 6 mm and a thickness of 2 mm.

[0111] All experimental results are shown in Table 1.

[0112] Table 1

[0113]

[0114] According to the data in Table 1, the silicon nitride ceramic sheets prepared in Examples 1 to 3 have good performance and can achieve 25 layers of nitride sintering. Compared with Example 1, the density, flexural strength and thermal conductivity of the silicon nitride ceramic sheets prepared in Examples 2 to 4 are higher than those in Example 1. This indicates that the modified hexagonal porous boron nitride and nano silicon nitride can effectively improve the compactness, interfacial strength and thermal conductivity of the ceramic sheets.

[0115] 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 preparing reaction-sintered silicon nitride ceramic sheets, characterized in that: Includes the following steps: Step S1: Add nano-silicon nitride powder and dispersant to ethanol, sonicate at 100~200W for 30~120min to obtain nano-dispersion; Step S2: After mixing the nano-dispersion with hexagonal porous boron nitride, the mixture is subjected to ultrasonic treatment to obtain an ultrasonicated mixture; the ultrasonicated mixture is then transferred to a planetary ball mill for mechanical grinding to obtain a hexagonal porous boron nitride nano-mixture. Step S3: Add the sintering aid, silicon powder and hexagonal porous boron nitride nano mixture into a ball mill and ball mill at a speed of 50~220 r / min for 6~12 h to obtain a uniformly mixed slurry; place the uniformly mixed slurry in a vacuum environment for degassing treatment to obtain a degassed slurry; Step S4: The degassed slurry is evenly coated onto the film belt through the casting machine and then sent to the drying section to dry, so as to obtain a casting green body with a thickness of 0.20~0.50mm, which is then cut into shape; Step S5: Using a powder spraying process, hexagonal porous boron nitride powder is evenly sprayed onto the surface of the cut cast green body on a powder coating machine to obtain the powder-coated green body. Step S6: Stack and assemble the powdered green bodies, with 10 to 30 pieces per layer. After fixing them in a frame, place them in a hot air de-glue oven for de-glue removal to obtain stacked green bodies. Step S7: Sinter the laminated green body to obtain reaction-sintered silicon nitride ceramic sheet; The nano-silicon nitride undergoes modification treatment, and the specific modification steps are as follows: γ-glycidoxypropyltrimethoxysilane was dissolved in a 90% acetone aqueous solution, and nano-silicon nitride powder was added. The mixture was dispersed at a high speed of 2000 r / min for 2-3 min to form a suspension. The suspension was continuously shaken at 30-35℃ for 5-6 h, filtered, and dried to obtain modified nano-silicon nitride. The hexagonal porous boron nitride underwent modification treatment, and the specific modification steps are as follows: 1) Add hexagonal porous boron nitride to a 5 mol / L sodium hydroxide aqueous solution, stir magnetically at 80~85℃ for 48~50h, filter after the reaction is complete, wash with deionized water until the pH of the filtrate is 6.9~7.1, dry at 120~125℃ for 24~26h to obtain hydroxylated hexagonal porous boron nitride, grind for later use. 2) Take a 95% ethanol solution, add γ-aminopropyltriethoxysilane, stir in a water bath at 60-65℃ for 3-4 hours, then add hydroxylated hexagonal porous boron nitride, continue stirring at 60-65℃ for 3-4 hours, filter and wash after the reaction is complete, and dry at 90-100℃ for 12-14 hours to obtain silane coupling agent modified hexagonal porous boron nitride. 3) Disperse the silane coupling agent-modified hexagonal porous boron nitride in deionized water, add anhydrous ethanol, and sonicate for 1-2 hours. Add dopamine hydrochloride and tris(hydroxymethyl)aminomethane hydrochloride, adjust the pH to 8-8.5, stir at 80-85℃ for 6-7 hours, filter and wash until the filtrate is colorless and the pH is 6.9-7.1, dry at 60-65℃ for 24-26 hours, and grind to obtain the modified hexagonal porous boron nitride.

2. The method for preparing reaction-sintered silicon nitride ceramic sheets according to claim 1, characterized in that: The dispersant is ammonium polyacrylate, and the sintering aid is lutetium oxide.

3. The method for preparing reaction-sintered silicon nitride ceramic sheets according to claim 1, characterized in that: The hexagonal porous boron nitride has a particle size of 5μm~10μm, a porosity of 10%~30%, and a pore size of 100nm~1μm.

4. The method for preparing reaction-sintered silicon nitride ceramic sheets according to claim 1, characterized in that: In step S1, the amount of dispersant is 10% to 20% of the mass of the nano-silicon nitride powder, and the mass of ethanol is 1000 to 5000 times the mass of the nano-silicon nitride powder; in step S2, the mass of the hexagonal porous boron nitride is 20 to 50 times the mass of the nano-silicon nitride powder in step S1; in step S3, the mass of the sintering aid is 2% to 4% of the mass of the silicon powder, and the silicon powder and hexagonal porous boron nitride are mixed at a mass ratio of 20 to 50:

1.

5. The method for preparing reaction-sintered silicon nitride ceramic sheets according to claim 1, characterized in that: The ultrasonic treatment process parameters in step S2 are: ultrasonic power 150~400W, treatment time 30~200min; the planetary ball mill mechanical grinding process parameters are: ball mill jar capacity 2~50L, rotation speed 50~220r / min, grinding time 2~6h; the powder application amount in step S5 is 0.05~0.3g / piece; the glue removal process parameters in step S6 are: temperature 500~600℃, pressure -10~10Pa, treatment time 48~72h.

6. The method for preparing reaction-sintered silicon nitride ceramic sheets according to claim 1, characterized in that: The sintering process described in step S7 is divided into nitriding and sintering. The first stage of nitriding is controlled at a temperature of 1250~1300℃, a pressure of 0.1~0.9MPa, and a time of 6~12h. The second stage of nitriding is controlled at a temperature of 1350~1400℃, a pressure of 0.5~2MPa, and a time of 3~9h. The final sintering temperature is controlled at 1800~1900℃, a pressure of 0.9~2MPa, and a time of 2~8h.

7. The method for preparing reaction-sintered silicon nitride ceramic sheets according to claim 1, characterized in that: The mass of the γ-glycidyl etheroxypropyltrimethoxysilane is 1% of the mass of the nano-silicon nitride powder.

8. The method for preparing reaction-sintered silicon nitride ceramic sheets according to claim 1, characterized in that: The hexagonal porous boron nitride and sodium hydroxide aqueous solution are mixed at a mass ratio of 1:10; γ-aminopropyltriethoxysilane, hydroxylated hexagonal porous boron nitride and 95% ethanol solution are mixed at a mass ratio of 0.1:2:10; silane coupling agent modified hexagonal porous boron nitride, deionized water, anhydrous ethanol, dopamine hydrochloride and tris(hydroxymethyl)aminomethane hydrochloride are mixed at a mass ratio of 1:100:100:0.2:0.3.

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