A method for producing a silicon nitride ceramic

Abstract

The application discloses a preparation method of silicon nitride ceramic. The silicon nitride ceramic is prepared through the steps of configuring an organic glue, recycling slurry treatment, recycling material treatment, ball milling mixing, defoaming aging, flow casting, punching and coating isolation powder, air degumming, pressure sintering and sand blasting treatment. The silicon nitride substrate prepared by the method has good flatness, low roughness and high mechanical properties. The use of acrylonitrile-butadiene-styrene copolymer and polyaspartic acid ester composite adhesive improves the fracture toughness of the material; the use of ytterbium fluoride and strontium hexaboride composite sintering aids reduces the roughness of the material; the use of organic silicon fluoride and BYK-3902P composite leveling agent reduces the warpage of the material and improves the flatness of the material.

Description

Technical Field

[0001] This invention belongs to the field of silicon nitride ceramic preparation technology, and specifically relates to a method for preparing silicon nitride ceramics. Background Technology

[0002] Silicon nitride ceramics possess numerous advantages, including high strength, high hardness, high thermal conductivity, low coefficient of thermal expansion, low high-temperature creep, good oxidation resistance, good hot corrosion resistance, and low coefficient of friction. They hold an irreplaceable position in key fields such as national defense, military industry, and electronic information. However, the large investment required for equipment and the relatively high manufacturing cost of silicon nitride ceramics currently limit their large-scale application, confining them primarily to the high-end application of IGBTs in automotive manufacturing.

[0003] To further expand the applications of silicon nitride ceramics, the key lies in using highly efficient, large-scale production equipment and significantly reducing manufacturing costs through various methods. Therefore, researching a low-cost, scalable silicon nitride ceramic manufacturing technology is particularly important.

[0004] The cost of silicon nitride ceramics mainly lies in the raw and auxiliary materials, including silicon nitride powder, and the production efficiency and yield rate of the molding and sintering processes, which require significant equipment investment. Firstly, due to equipment and process limitations, aluminum nitride ceramics manufacturing inevitably generates many semi-finished products at various stages. These semi-finished products, after proper processing, can be reused essentially as new powder without affecting the performance of the final product. This semi-finished product processing significantly reduces the input of new powder, thereby lowering manufacturing costs. Secondly, the use of highly efficient tape casting technology ensures continuous large-scale production while maintaining high efficiency. Finally, the use of multi-layered, alternating lamination and a single-sintering process maximizes the utilization of the kiln's effective sintering volume and reduces pre-sintering processes, significantly reducing manufacturing costs. However, reusing new powder can also lead to a decline in the performance of the final material, necessitating optimization of raw material formulations or processes.

[0005] Patent 201310241572.4 discloses a low-cost method for producing silicon nitride ceramics. This patent merely mentions replacing cerium oxide and lanthanum oxide with inexpensive monazite, and the flux addition ratio is only 6-9 wt%, resulting in a very limited cost reduction. Patent 201910323311.4 discloses a low-cost method for preparing silicon nitride ceramics, using analytical grade anhydrous ethanol as the solvent, requiring spray drying granulation, employing isostatic pressing (which is not a continuous production method and has low efficiency), and requiring pre-sintering at 800-1400 degrees Celsius. The cost advantage is not significant. Patent 202080011345.0 discloses a method for manufacturing single green sheets, a method for manufacturing silicon nitride sintered bodies, and single green sheets and silicon nitride sintered bodies. It uses laser cutting to process the green blanks, which is not only inefficient but also requires large equipment investment, making it unsuitable for mass production. Patent 201910223395.4 discloses a method for producing high-strength, high-thermal-conductivity silicon nitride substrates. After sintering, additional machining and surface polishing are used to process the substrate surface, adding a step and increasing costs. Patent 202011118907.X discloses a high-thermal-conductivity silicon nitride ceramic substrate and its preparation method. This method requires preheating at a high temperature of 1200-1500℃ followed by high-temperature sintering at 1750-1950℃, reducing the efficiency of the expensive furnace and adding a heating step, thus increasing costs. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing silicon nitride ceramics.

[0007] A method for preparing silicon nitride ceramics, comprising the following steps:

[0008] (1) Preparation of organic adhesive: Add adhesive, plasticizer and organic solvent into a container and stir evenly; the mass ratio of the adhesive, plasticizer and organic solvent is (15-25):(10-20):(80-120);

[0009] (2) Recycled slurry treatment: Add organic solvent to the slurry remaining in each process before casting, add it to a container and stir evenly. The mass ratio of the recycled slurry to the organic solvent is (30-50): (10-20).

[0010] (3) Recycled material treatment: Add the scraps from casting and pressure sintering, green waste and organic solvents to the ball mill in a mass ratio of (10-20): (10-20): (30-50). Ball mill for 24-48 hours, and use a device with a multi-stage filter to discharge the material from the ball mill into a clean bucket.

[0011] (4) Ball milling and mixing: Organic solvent, silicon nitride powder, recycled slurry, recycled material, sintering aid, dispersant and leveling agent are added to a ball mill in sequence and ball milled for 12-24 hours to obtain a mixed slurry; the organic adhesive prepared in step (1) is added and ball milled for another 24-36 hours to obtain a cast slurry; the mass ratio of the organic solvent, silicon nitride powder, recycled slurry, recycled material, sintering aid, dispersant and leveling agent is (90-130):(60-120):(20-30):(20-30):(5-15):(5-10):(5-15); the mass ratio of the mixed slurry to the organic adhesive is (1-5):1;

[0012] (5) Degassing and aging: Degas the casting slurry prepared in step (4) for 10-30 min under vacuum, and stir and age it for 10-15 h at a speed of 5-10 rpm, controlling the viscosity at 6000-20000 cps, the solid content at 55-75%, and the temperature at 10-25℃.

[0013] (6) Casting: The slurry prepared in step (5) is cast using a casting machine, and the green body is wrapped with a paper tube; the process parameters for this step are: casting speed 0.1-0.2 m / min, temperature of zone 1 of casting drying chamber 15-35℃, temperature of zone 2 of casting drying chamber 55-85℃, and temperature of zone 3 of casting drying chamber 70-110℃;

[0014] (7) Punching and applying isolation powder: Select a punching die according to the drawing requirements, cut the green blank prepared in step (6), and transport it to the powder application line by conveyor belt for powder application. The powder application pressure is 0.05-0.1Mpa and the powder application temperature is 55-85℃.

[0015] (8) Air debinding: Place the leveled green body into an intermittent furnace for debinding; the process parameters for this step are: debinding temperature 450-650℃, total time: 15-25h, and heating rate <5℃ / min between 220-350℃.

[0016] (9) Pressure sintering: The debinding product is placed into a sintering furnace for sintering; the process parameters for this step are: sintering temperature 1650-1850℃, sintering time: 15-25h, pressure: 0.5-1.0Mpa;

[0017] (10) Sandblasting: Use sandblasting equipment to remove the isolation powder on the surface of the sintered silicon nitride ceramic.

[0018] The adhesive is a mixture of acrylonitrile-butadiene-styrene copolymer and polyaspartic acid ester in a mass ratio of (1-5):1.

[0019] The plasticizer is one or more of methyl phthalate, di(2-ethylhexyl) terephthalate, dibutyl sebacate, and di(2-ethylhexyl) cyclohexane-1,4-dicarboxylic acid.

[0020] The organic solvent is one or more of toluene, xylene, isopropanol, ethanol, and ethyl acetate.

[0021] The sintering aid is a mixture of ytterbium fluoride and strontium hexaboride in a mass ratio of (1-3):1.

[0022] The dispersant is one or more of polyethyleneimine, ammonium citrate, ammonium persulfate, sodium tripolyphosphate, tetraethyl ethylenediamine, ammonium acrylate, trioleic acid glyceride, and phosphate esters.

[0023] The leveling agent is a mixture of silicone fluorine leveling agent and BYK-3902P leveling agent at a mass ratio of 1:(1-3); the molecular structural formula of the silicone fluorine leveling agent is as follows:

[0024]

[0025] The raw material composition and ratio of the isolation powder in step (7) are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1: (0.015-0.025): (3-5).

[0026] The sandblasting process in step (10) is as follows: sand type: alumina, zirconium oxide, silicon dioxide, mass ratio 1:1:1; sand mesh: 100-3000 mesh; pressure = 0.01-0.5Mpa.

[0027] The beneficial effects of this invention are: the silicon nitride substrate prepared by this invention has good flatness, low roughness, and high mechanical properties. The use of an acrylonitrile-butadiene-styrene copolymer and a polyaspartic acid ester composite adhesive improves the fracture toughness of the material; the use of a ytterbium fluoride and strontium hexaboride composite sintering aid reduces the roughness of the material; and the use of organosilicon fluorine and BYK-3902P composite leveling agent reduces the warpage of the material and improves its flatness. Detailed Implementation

[0028] To facilitate understanding of the present invention, a more comprehensive description will be given below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0029] Example 1

[0030] A method for preparing silicon nitride ceramics, comprising the following steps:

[0031] (1) Preparation of organic adhesive: Add adhesive, methyl phthalate and ethanol into a container and stir evenly; the mass ratio of the adhesive, methyl phthalate and ethanol is 20:15:100; the adhesive is a mixture of acrylonitrile-butadiene-styrene copolymer and polyaspartic acid ester in a mass ratio of 3:1.

[0032] (2) Recycled slurry treatment: Add ethanol to the slurry remaining from each process before casting, add it to a container and stir evenly. The mass ratio of the recycled slurry to ethanol is 40:15.

[0033] (3) Recycled material treatment: Add the scraps from casting and pressure sintering, green waste and ethanol to the ball mill at a mass ratio of 15:15:40, ball mill for 36 hours, and use a device with a multi-stage filter to discharge the material from the ball mill into a clean bucket;

[0034] (4) Ball milling and mixing: Ethanol, silicon nitride powder, recycled slurry, recycled material, sintering aid, polyethyleneimine, and leveling agent are added to a ball mill in sequence and milled for 18 hours to obtain a mixed slurry; the organic adhesive prepared in step (1) is added, and the mixture is milled for another 28 hours to obtain a casting slurry; the mass ratio of ethanol, silicon nitride powder, recycled slurry, recycled material, sintering aid, polyethyleneimine, and leveling agent is 110:80:25:25:10:8:10; the mass ratio of the mixed slurry to the organic adhesive is 3:1; the sintering aid is a mixture of ytterbium fluoride and strontium hexaboride in a mass ratio of 2:1; the leveling agent is a mixture of organosilicon fluorine leveling agent and BYK-3902P leveling agent in a mass ratio of 1:2; the molecular structure of the organosilicon fluorine leveling agent is as follows:

[0035]

[0036] (5) Degassing and aging: The casting slurry prepared in step (4) is vacuum degassed for 20 min and aged for 12 h by stirring at 8 rpm, with the viscosity controlled at 10000 cps, the solid content at 65%, and the temperature at 18℃.

[0037] (6) Casting: The slurry prepared in step (5) is cast using a casting machine, and the green body is wrapped with a paper tube. The process parameters for this step are: casting speed 0.15m / min, temperature of zone 1 of casting drying chamber 25℃, temperature of zone 2 of casting drying chamber 65℃, and temperature of zone 3 of casting drying chamber 90℃.

[0038] (7) Punching and applying isolation powder: Select a punching die according to the drawing requirements, cut the green blank prepared in step (6), and transport it to the powder application line by conveyor belt for powder application. The powder application pressure is 0.08 MPa and the powder application temperature is 65℃. The raw material composition and ratio of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1:0.02:4.

[0039] (8) Air debinding: The leveled green body is placed into an intermittent furnace for debinding; the process parameters for this step are: debinding temperature 500℃, total time: 20h, heating rate <5℃ / min between 280℃.

[0040] (9) Pressure sintering: The debinding product is placed into a sintering furnace for sintering; the process parameters for this step are: sintering temperature 1750℃, sintering time: 20h, pressure: 0.8Mpa;

[0041] (10) Sandblasting: Remove the isolation powder from the surface of the sintered silicon nitride ceramic using sandblasting equipment. The sandblasting process is as follows: sand type: alumina, zirconium oxide, silicon dioxide, mass ratio 1:1:1; sand mesh: 800 mesh; pressure = 0.03 MPa.

[0042] Example 2

[0043] A method for preparing silicon nitride ceramics, comprising the following steps:

[0044] (1) Preparation of organic adhesive: Add the adhesive, di(2-ethylhexyl) terephthalate, and xylene into a container and stir evenly; the mass ratio of the adhesive, di(2-ethylhexyl) terephthalate, and xylene is 15:11:85; the adhesive is a mixture of acrylonitrile-butadiene-styrene copolymer and polyaspartic acid ester mixed in a mass ratio of 1:1;

[0045] (2) Recycled slurry treatment: Add xylene to the slurry remaining from each process before casting, add it to a container and stir evenly. The mass ratio of the recycled slurry to xylene is 30:11.

[0046] (3) Recycled material treatment: Add the scraps from casting and pressure sintering, green waste and xylene to the ball mill at a mass ratio of 10:10:32, ball mill for 24 hours, and use a device with a multi-stage filter to discharge the material from the ball mill into a clean bucket;

[0047] (4) Ball milling and mixing: Xylene, silicon nitride powder, recycled slurry, recycled material, sintering aid, tetraethyl ethylenediamine, and leveling agent are added sequentially to a ball mill and ball milled for 12 hours to obtain a mixed slurry; the organic adhesive prepared in step (1) is added, and the mixture is ball milled for another 24 hours to obtain a casting slurry; the mass ratio of xylene, silicon nitride powder, recycled slurry, recycled material, sintering aid, tetraethyl ethylenediamine, and leveling agent is 90:60:20:20:5:5:5; the mass ratio of the mixed slurry to the organic adhesive is 1:1; the sintering aid is a mixture of ytterbium fluoride and strontium hexaboride mixed in a mass ratio of 1:1; the leveling agent is a mixture of organosilicon fluorine leveling agent and BYK-3902P leveling agent mixed in a mass ratio of 1:1; the molecular structure of the organosilicon fluorine leveling agent is as follows:

[0048]

[0049] (5) Degassing and aging: The casting slurry prepared in step (4) is vacuum degassed for 10 min and aged for 10 h by stirring at 5 rpm, with the viscosity controlled at 8000 cps, the solid content at 55%, and the temperature at 10℃.

[0050] (6) Casting: The slurry prepared in step (5) is cast using a casting machine, and the green body is wrapped with a paper tube. The process parameters for this step are: casting speed 0.1 m / min, temperature of zone 1 of the casting drying chamber 15℃, temperature of zone 2 of the casting drying chamber 55℃, and temperature of zone 3 of the casting drying chamber 70℃.

[0051] (7) Punching and applying isolation powder: Select a punching die according to the drawing requirements, cut the green blank prepared in step (6), and transport it to the powder application line by conveyor belt for powder application. The powder application pressure is 0.05 MPa and the powder application temperature is 55℃. The raw material composition and ratio of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1:0.015:3.

[0052] (8) Air debinding: The leveled green body is placed into an intermittent furnace for debinding; the process parameters for this step are: debinding temperature 450℃, total time: 15h, and heating rate <5℃ / min between 220℃.

[0053] (9) Pressure sintering: The debinding product is placed into a sintering furnace for sintering; the process parameters for this step are: sintering temperature 1650℃, sintering time: 15h, pressure: 0.5Mpa.

[0054] (10) Sandblasting: Remove the isolation powder from the surface of the sintered silicon nitride ceramic using sandblasting equipment. The sandblasting process is as follows: sand type: alumina, zirconium oxide, silicon dioxide, mass ratio 1:1:1; sand mesh: 500 mesh; pressure = 0.03 MPa.

[0055] Example 3

[0056] A method for preparing silicon nitride ceramics, comprising the following steps:

[0057] (1) Preparation of organic adhesive: Add the adhesive, cyclohexane-1,4-dicarboxylic acid di(2-ethylhexyl) ester, and ethyl acetate into a container and stir evenly; the mass ratio of the adhesive, cyclohexane-1,4-dicarboxylic acid di(2-ethylhexyl) ester, and ethyl acetate is 25:20:120; the adhesive is a mixture of acrylonitrile-butadiene-styrene copolymer and polyaspartic acid ester mixed in a mass ratio of 4:1;

[0058] (2) Recycled slurry treatment: Add ethyl acetate to the slurry remaining from each process before casting, add it to a container and stir evenly. The mass ratio of the recycled slurry to ethyl acetate is 50:20.

[0059] (3) Recycled material treatment: Add the scraps from casting and pressure sintering, green waste and ethyl acetate to the ball mill at a mass ratio of 20:20:50. Ball mill for 48 hours, and use a device with a multi-stage filter to discharge the material from the ball mill into a clean bucket;

[0060] (4) Ball milling and mixing: Ethyl acetate, silicon nitride powder, recycled slurry, recycled material, sintering aid, sodium tripolyphosphate, and leveling agent are added to a ball mill in sequence and milled for 24 hours to obtain a mixed slurry; the organic adhesive prepared in step (1) is added, and the mixture is milled for another 36 hours to obtain a casting slurry; the mass ratio of ethyl acetate, silicon nitride powder, recycled slurry, recycled material, sintering aid, sodium tripolyphosphate, and leveling agent is 130:120:30:30:15:10:15; the mass ratio of the mixed slurry to the organic adhesive is 4:1; the sintering aid is a mixture of ytterbium fluoride and strontium hexaboride in a mass ratio of 3:1; the leveling agent is a mixture of organosilicon fluorine leveling agent and BYK-3902P leveling agent in a mass ratio of 1:3; the molecular structure of the organosilicon fluorine leveling agent is as follows:

[0061]

[0062] (5) Degassing and aging: The casting slurry prepared in step (4) is vacuum degassed for 30 min and aged for 15 h by stirring at 10 rpm, with the viscosity controlled at 20000 cps, the solid content at 75%, and the temperature at 25℃.

[0063] (6) Casting: The slurry prepared in step (5) is cast using a casting machine, and the green body is wrapped with a paper tube. The process parameters for this step are: casting speed 0.2 m / min, temperature of zone 1 of the casting drying chamber 35℃, temperature of zone 2 of the casting drying chamber 85℃, and temperature of zone 3 of the casting drying chamber 110℃.

[0064] (7) Punching and applying isolation powder: Select a punching die according to the drawing requirements, cut the green blank prepared in step (6), and transport it to the powder application line by conveyor belt for powder application. The powder application pressure is 0.1 MPa and the powder application temperature is 85℃. The raw material composition and ratio of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1:0.025:5.

[0065] (8) Air debinding: The leveled green body is placed into an intermittent furnace for debinding; the process parameters for this step are: debinding temperature 650℃, total time: 25h, and heating rate <5℃ / min between 300℃.

[0066] (9) Pressure sintering: The debinding product is placed into a sintering furnace for sintering; the process parameters for this step are: sintering temperature 1850℃, sintering time: 25h, pressure: 1.0Mpa;

[0067] (10) Sandblasting: Use sandblasting equipment to remove the isolation powder on the surface of the sintered silicon nitride ceramic. At the same time, the sandblasting equipment performs sandblasting on the product surface according to customer requirements. The roughness Ra = 1.2um; The sand type: alumina, zirconium oxide, silicon dioxide, mass ratio 1:1:1; sand mesh: 2500 mesh; pressure = 0.45Mpa.

[0068] Comparative Example 1

[0069] A method for preparing silicon nitride ceramics, comprising the following steps:

[0070] (1) Preparation of organic adhesive: Add acrylonitrile-butadiene-styrene copolymer, methyl phthalate and ethanol into a container and stir evenly; the mass ratio of acrylonitrile-butadiene-styrene copolymer, methyl phthalate and ethanol is 20:15:100;

[0071] (2) Recycled slurry treatment: Add ethanol to the slurry remaining from each process before casting, add it to a container and stir evenly. The mass ratio of the recycled slurry to ethanol is 40:15.

[0072] (3) Recycled material treatment: Add the scraps from casting and pressure sintering, green waste and ethanol to the ball mill at a mass ratio of 15:15:40, ball mill for 36 hours, and use a device with a multi-stage filter to discharge the material from the ball mill into a clean bucket;

[0073] (4) Ball milling and mixing: Ethanol, silicon nitride powder, recycled slurry, recycled material, sintering aid, polyethyleneimine, and leveling agent are added to a ball mill in sequence and milled for 18 hours to obtain a mixed slurry; the organic adhesive prepared in step (1) is added, and the mixture is milled for another 28 hours to obtain a casting slurry; the mass ratio of ethanol, silicon nitride powder, recycled slurry, recycled material, sintering aid, polyethyleneimine, and leveling agent is 110:80:25:25:10:8:10; the mass ratio of the mixed slurry to the organic adhesive is 3:1; the sintering aid is a mixture of ytterbium fluoride and strontium hexaboride in a mass ratio of 2:1; the leveling agent is a mixture of organosilicon fluorine leveling agent and BYK-3902P leveling agent in a mass ratio of 1:2; the molecular structure of the organosilicon fluorine leveling agent is as follows:

[0074]

[0075] (5) Degassing and aging: The casting slurry prepared in step (4) is vacuum degassed for 20 min and aged for 12 h by stirring at 8 rpm, with the viscosity controlled at 10000 cps, the solid content at 65%, and the temperature at 18℃.

[0076] (6) Casting: The slurry prepared in step (5) is cast using a casting machine, and the green body is wrapped with a paper tube. The process parameters for this step are: casting speed 0.15m / min, temperature of zone 1 of casting drying chamber 25℃, temperature of zone 2 of casting drying chamber 65℃, and temperature of zone 3 of casting drying chamber 90℃.

[0077] (7) Punching and applying isolation powder: Select a punching die according to the drawing requirements, cut the green blank prepared in step (6), and transport it to the powder application line by conveyor belt for powder application. The powder application pressure is 0.08 MPa and the powder application temperature is 65℃. The raw material composition and ratio of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1:0.02:4.

[0078] (8) Air debinding: The leveled green body is placed into an intermittent furnace for debinding; the process parameters for this step are: debinding temperature 500℃, total time: 20h, heating rate <5℃ / min between 280℃.

[0079] (9) Pressure sintering: The debinding product is placed into a sintering furnace for sintering; the process parameters for this step are: sintering temperature 1750℃, sintering time: 20h, pressure: 0.8Mpa;

[0080] (10) Sandblasting: Use sandblasting equipment to remove the isolation powder on the surface of the sintered silicon nitride ceramic. At the same time, the sandblasting equipment performs sandblasting on the product surface according to customer requirements. The roughness Ra = 0.6um; The sandblasting: sand type: alumina, zirconium oxide, silicon dioxide, mass ratio 1:1:1; sand mesh: 800 mesh; pressure = 0.03Mpa.

[0081] Comparative Example 2

[0082] A method for preparing silicon nitride ceramics, comprising the following steps:

[0083] (1) Preparation of organic adhesive: Add polyaspartic acid ester, methyl phthalate and ethanol into a container and stir evenly; the mass ratio of polyaspartic acid ester, methyl phthalate and ethanol is 20:15:100.

[0084] (2) Recycled slurry treatment: Add ethanol to the slurry remaining from each process before casting, add it to a container and stir evenly. The mass ratio of the recycled slurry to ethanol is 40:15.

[0085] (3) Recycled material treatment: Add the scraps from casting and pressure sintering, green waste and ethanol to the ball mill at a mass ratio of 15:15:40, ball mill for 36 hours, and use a device with a multi-stage filter to discharge the material from the ball mill into a clean bucket;

[0086] (4) Ball milling and mixing: Ethanol, silicon nitride powder, recycled slurry, recycled material, sintering aid, polyethyleneimine, and leveling agent are added to a ball mill in sequence and milled for 18 hours to obtain a mixed slurry; the organic adhesive prepared in step (1) is added, and the mixture is milled for another 28 hours to obtain a casting slurry; the mass ratio of ethanol, silicon nitride powder, recycled slurry, recycled material, sintering aid, polyethyleneimine, and leveling agent is 110:80:25:25:10:8:10; the mass ratio of the mixed slurry to the organic adhesive is 3:1; the sintering aid is a mixture of ytterbium fluoride and strontium hexaboride in a mass ratio of 2:1; the leveling agent is a mixture of organosilicon fluorine leveling agent and BYK-3902P leveling agent in a mass ratio of 1:2; the molecular structure of the organosilicon fluorine leveling agent is as follows:

[0087]

[0088] (5) Degassing and aging: The casting slurry prepared in step (4) is vacuum degassed for 20 min and aged for 12 h by stirring at 8 rpm, with the viscosity controlled at 10000 cps, the solid content at 65%, and the temperature at 18℃.

[0089] (6) Casting: The slurry prepared in step (5) is cast using a casting machine, and the green body is wrapped with a paper tube. The process parameters for this step are: casting speed 0.15m / min, temperature of zone 1 of casting drying chamber 25℃, temperature of zone 2 of casting drying chamber 65℃, and temperature of zone 3 of casting drying chamber 90℃.

[0090] (7) Punching and applying isolation powder: Select a punching die according to the drawing requirements, cut the green blank prepared in step (6), and transport it to the powder application line by conveyor belt for powder application. The powder application pressure is 0.08 MPa and the powder application temperature is 65℃. The raw material composition and ratio of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1:0.02:4.

[0091] (8) Air debinding: The leveled green body is placed into an intermittent furnace for debinding; the process parameters for this step are: debinding temperature 500℃, total time: 20h, heating rate <5℃ / min between 280℃.

[0092] (9) Pressure sintering: The debinding product is placed into a sintering furnace for sintering; the process parameters for this step are: sintering temperature 1750℃, sintering time: 20h, pressure: 0.8Mpa;

[0093] (10) Sandblasting: Use sandblasting equipment to remove the isolation powder on the surface of the sintered silicon nitride ceramic. At the same time, the sandblasting equipment performs sandblasting on the product surface according to customer requirements. The roughness Ra = 0.6um; The sandblasting: sand type: alumina, zirconium oxide, silicon dioxide, mass ratio 1:1:1; sand mesh: 800 mesh; pressure = 0.03Mpa.

[0094] Comparative Example 3

[0095] A method for preparing silicon nitride ceramics, comprising the following steps:

[0096] (1) Preparation of organic adhesive: Add adhesive, methyl phthalate and ethanol into a container and stir evenly; the mass ratio of the adhesive, methyl phthalate and ethanol is 20:15:100; the adhesive is a mixture of acrylonitrile-butadiene-styrene copolymer and polyaspartic acid ester in a mass ratio of 3:1.

[0097] (2) Recycled slurry treatment: Add ethanol to the slurry remaining from each process before casting, add it to a container and stir evenly. The mass ratio of the recycled slurry to ethanol is 40:15.

[0098] (3) Recycled material treatment: Add the scraps from casting and pressure sintering, green waste and ethanol to the ball mill at a mass ratio of 15:15:40, ball mill for 36 hours, and use a device with a multi-stage filter to discharge the material from the ball mill into a clean bucket;

[0099] (4) Ball milling and mixing: Ethanol, silicon nitride powder, recycled slurry, recycled material, ytterbium fluoride, polyethyleneimine, and leveling agent are added to a ball mill in sequence and milled for 18 hours to obtain a mixed slurry; the organic adhesive prepared in step (1) is added, and the mixture is milled for another 28 hours to obtain a casting slurry; the mass ratio of ethanol, silicon nitride powder, recycled slurry, recycled material, ytterbium fluoride, polyethyleneimine, and leveling agent is 110:80:25:25:10:8:10; the mass ratio of the mixed slurry to the organic adhesive is 3:1; the leveling agent is a mixture of organosilicon fluorine leveling agent and BYK-3902P leveling agent mixed in a mass ratio of 1:2; the molecular structure of the organosilicon fluorine leveling agent is as follows:

[0100]

[0101] (5) Degassing and aging: The casting slurry prepared in step (4) is vacuum degassed for 20 min and aged for 12 h by stirring at 8 rpm, with the viscosity controlled at 10000 cps, the solid content at 65%, and the temperature at 18℃.

[0102] (6) Casting: The slurry prepared in step (5) is cast using a casting machine, and the green body is wrapped with a paper tube. The process parameters for this step are: casting speed 0.15m / min, temperature of zone 1 of casting drying chamber 25℃, temperature of zone 2 of casting drying chamber 65℃, and temperature of zone 3 of casting drying chamber 90℃.

[0103] (7) Punching and applying isolation powder: Select a punching die according to the drawing requirements, cut the green blank prepared in step (6), and transport it to the powder application line by conveyor belt for powder application. The powder application pressure is 0.08 MPa and the powder application temperature is 65℃. The raw material composition and ratio of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1:0.02:4.

[0104] (8) Air debinding: The leveled green body is placed into an intermittent furnace for debinding; the process parameters for this step are: debinding temperature 500℃, total time: 20h, heating rate <5℃ / min between 280℃.

[0105] (9) Pressure sintering: The debinding product is placed into a sintering furnace for sintering; the process parameters for this step are: sintering temperature 1750℃, sintering time: 20h, pressure: 0.8Mpa;

[0106] (10) Sandblasting: Use sandblasting equipment to remove the isolation powder on the surface of the sintered silicon nitride ceramic. At the same time, the sandblasting equipment performs sandblasting on the product surface according to customer requirements. The roughness Ra = 0.6um; The sandblasting: sand type: alumina, zirconium oxide, silicon dioxide, mass ratio 1:1:1; sand mesh: 800 mesh; pressure = 0.03Mpa.

[0107] Comparative Example 4

[0108] A method for preparing silicon nitride ceramics, comprising the following steps:

[0109] (1) Preparation of organic adhesive: Add adhesive, methyl phthalate and ethanol into a container and stir evenly; the mass ratio of the adhesive, methyl phthalate and ethanol is 20:15:100; the adhesive is a mixture of acrylonitrile-butadiene-styrene copolymer and polyaspartic acid ester in a mass ratio of 3:1.

[0110] (2) Recycled slurry treatment: Add ethanol to the slurry remaining from each process before casting, add it to a container and stir evenly. The mass ratio of the recycled slurry to ethanol is 40:15.

[0111] (3) Recycled material treatment: Add the scraps from casting and pressure sintering, green waste and ethanol to the ball mill at a mass ratio of 15:15:40, ball mill for 36 hours, and use a device with a multi-stage filter to discharge the material from the ball mill into a clean bucket;

[0112] (4) Ball milling and mixing: Ethanol, silicon nitride powder, recycled slurry, recycled material, strontium hexaboride, polyethyleneimine, and leveling agent are added to a ball mill in sequence and milled for 18 hours to obtain a mixed slurry; the organic adhesive prepared in step (1) is added, and the mixture is milled for another 28 hours to obtain a casting slurry; the mass ratio of ethanol, silicon nitride powder, recycled slurry, recycled material, strontium hexaboride, polyethyleneimine, and leveling agent is 110:80:25:25:10:8:10; the mass ratio of the mixed slurry to the organic adhesive is 3:1; the leveling agent is a mixture of organosilicon fluorine leveling agent and BYK-3902P leveling agent mixed in a mass ratio of 1:2; the molecular structure of the organosilicon fluorine leveling agent is as follows:

[0113]

[0114] (5) Degassing and aging: The casting slurry prepared in step (4) is vacuum degassed for 20 min and aged for 12 h by stirring at 8 rpm, with the viscosity controlled at 10000 cps, the solid content at 65%, and the temperature at 18℃.

[0115] (6) Casting: The slurry prepared in step (5) is cast using a casting machine, and the green body is wrapped with a paper tube. The process parameters for this step are: casting speed 0.15m / min, temperature of zone 1 of casting drying chamber 25℃, temperature of zone 2 of casting drying chamber 65℃, and temperature of zone 3 of casting drying chamber 90℃.

[0116] (7) Punching and applying isolation powder: Select a punching die according to the drawing requirements, cut the green blank prepared in step (6), and transport it to the powder application line by conveyor belt for powder application. The powder application pressure is 0.08 MPa and the powder application temperature is 65℃. The raw material composition and ratio of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1:0.02:4.

[0117] (8) Air debinding: The leveled green body is placed into an intermittent furnace for debinding; the process parameters for this step are: debinding temperature 500℃, total time: 20h, heating rate <5℃ / min between 280℃.

[0118] (9) Pressure sintering: The debinding product is placed into a sintering furnace for sintering; the process parameters for this step are: sintering temperature 1750℃, sintering time: 20h, pressure: 0.8Mpa;

[0119] (10) Sandblasting: Use sandblasting equipment to remove the isolation powder on the surface of the sintered silicon nitride ceramic. At the same time, the sandblasting equipment performs sandblasting on the product surface according to customer requirements. The roughness Ra = 0.6um; The sandblasting: sand type: alumina, zirconium oxide, silicon dioxide, mass ratio 1:1:1; sand mesh: 800 mesh; pressure = 0.03Mpa.

[0120] Comparative Example 5

[0121] A method for preparing silicon nitride ceramics, comprising the following steps:

[0122] (1) Preparation of organic adhesive: Add adhesive, methyl phthalate and ethanol into a container and stir evenly; the mass ratio of the adhesive, methyl phthalate and ethanol is 20:15:100; the adhesive is a mixture of acrylonitrile-butadiene-styrene copolymer and polyaspartic acid ester in a mass ratio of 3:1.

[0123] (2) Recycled slurry treatment: Add ethanol to the slurry remaining from each process before casting, add it to a container and stir evenly. The mass ratio of the recycled slurry to ethanol is 40:15.

[0124] (3) Recycled material treatment: Add the scraps from casting and pressure sintering, green waste and ethanol to the ball mill at a mass ratio of 15:15:40, ball mill for 36 hours, and use a device with a multi-stage filter to discharge the material from the ball mill into a clean bucket;

[0125] (4) Ball milling and mixing: Ethanol, silicon nitride powder, recycled slurry, recycled material, sintering aid, polyethyleneimine, and leveling agent are added to a ball mill in sequence and milled for 18 hours to obtain a mixed slurry; the organic adhesive prepared in step (1) is added, and the mixture is milled for another 28 hours to obtain a casting slurry; the mass ratio of ethanol, silicon nitride powder, recycled slurry, recycled material, sintering aid, polyethyleneimine, and leveling agent is 110:80:25:25:10:8:10; the mass ratio of the mixed slurry to the organic adhesive is 3:1; the sintering aid is a mixture of ytterbium fluoride and strontium hexaboride in a mass ratio of 2:1; the leveling agent is an organosilicon fluorinated leveling agent with the following molecular structure:

[0126]

[0127] (5) Degassing and aging: The casting slurry prepared in step (4) is vacuum degassed for 20 min and aged for 12 h by stirring at 8 rpm, with the viscosity controlled at 10000 cps, the solid content at 65%, and the temperature at 18℃.

[0128] (6) Casting: The slurry prepared in step (5) is cast using a casting machine, and the green body is wrapped with a paper tube. The process parameters for this step are: casting speed 0.15m / min, temperature of zone 1 of casting drying chamber 25℃, temperature of zone 2 of casting drying chamber 65℃, and temperature of zone 3 of casting drying chamber 90℃.

[0129] (7) Punching and applying isolation powder: Select a punching die according to the drawing requirements, cut the green blank prepared in step (6), and transport it to the powder application line by conveyor belt for powder application. The powder application pressure is 0.08 MPa and the powder application temperature is 65℃. The raw material composition and ratio of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1:0.02:4.

[0130] (8) Air debinding: The leveled green body is placed into an intermittent furnace for debinding; the process parameters for this step are: debinding temperature 500℃, total time: 20h, and heating rate <5℃ / min between 280℃.

[0131] (9) Pressure sintering: The debinding product is placed into a sintering furnace for sintering; the process parameters for this step are: sintering temperature 1750℃, sintering time: 20h, pressure: 0.8Mpa;

[0132] (10) Sandblasting: Use sandblasting equipment to remove the isolation powder on the surface of the sintered silicon nitride ceramic. At the same time, the sandblasting equipment performs sandblasting on the product surface according to customer requirements. The roughness Ra = 0.6um; The sandblasting: sand type: alumina, zirconium oxide, silicon dioxide, mass ratio 1:1:1; sand mesh: 800 mesh; pressure = 0.03Mpa.

[0133] Comparative Example 6

[0134] A method for preparing silicon nitride ceramics, comprising the following steps:

[0135] (1) Preparation of organic adhesive: Add adhesive, methyl phthalate and ethanol into a container and stir evenly; the mass ratio of the adhesive, methyl phthalate and ethanol is 20:15:100; the adhesive is a mixture of acrylonitrile-butadiene-styrene copolymer and polyaspartic acid ester in a mass ratio of 3:1.

[0136] (2) Recycled slurry treatment: Add ethanol to the slurry remaining from each process before casting, add it to a container and stir evenly. The mass ratio of the recycled slurry to ethanol is 40:15.

[0137] (3) Recycled material treatment: Add the scraps from casting and pressure sintering, green waste and ethanol to the ball mill at a mass ratio of 15:15:40, ball mill for 36 hours, and use a device with a multi-stage filter to discharge the material from the ball mill into a clean bucket;

[0138] (4) Ball milling and mixing: Ethanol, silicon nitride powder, recycled slurry, recycled material, sintering aid, polyethyleneimine, and BYK-3902P leveling agent are added to a ball mill in sequence and ball milled for 18 hours to obtain a mixed slurry; the organic adhesive prepared in step (1) is added and ball milled for another 28 hours to obtain a casting slurry; the mass ratio of ethanol, silicon nitride powder, recycled slurry, recycled material, sintering aid, polyethyleneimine, and BYK-3902P leveling agent is 110:80:25:25:10:8:10; the mass ratio of the mixed slurry to the organic adhesive is 3:1; the sintering aid is a mixture of ytterbium fluoride and strontium hexaboride mixed in a mass ratio of 2:1;

[0139] (5) Degassing and aging: The casting slurry prepared in step (4) is vacuum degassed for 20 min and aged for 12 h by stirring at 8 rpm, with the viscosity controlled at 10000 cps, the solid content at 65%, and the temperature at 18℃.

[0140] (6) Casting: The slurry prepared in step (5) is cast using a casting machine, and the green body is wrapped with a paper tube. The process parameters for this step are: casting speed 0.15m / min, temperature of zone 1 of casting drying chamber 25℃, temperature of zone 2 of casting drying chamber 65℃, and temperature of zone 3 of casting drying chamber 90℃.

[0141] (7) Punching and applying isolation powder: Select a punching die according to the drawing requirements, cut the green blank prepared in step (6), and transport it to the powder application line by conveyor belt for powder application. The powder application pressure is 0.08 MPa and the powder application temperature is 65℃. The raw material composition and ratio of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1:0.02:4.

[0142] (8) Air debinding: The leveled green body is placed into an intermittent furnace for debinding; the process parameters for this step are: debinding temperature 500℃, total time: 20h, and heating rate <5℃ / min between 280℃.

[0143] (9) Pressure sintering: The debinding product is placed into a sintering furnace for sintering; the process parameters for this step are: sintering temperature 1750℃, sintering time: 20h, pressure: 0.8Mpa;

[0144] (10) Sandblasting: Use sandblasting equipment to remove the isolation powder on the surface of the sintered silicon nitride ceramic. At the same time, the sandblasting equipment performs sandblasting processing on the product surface according to customer requirements. The sandblasting process is as follows: sand type: alumina, zirconium oxide, silicon dioxide, mass ratio 1:1:1; sand mesh: 800 mesh; pressure = 0.03Mpa.

[0145] Experimental Example 1:

[0146] The fracture toughness of the silicon nitride substrates prepared in Examples 1-3 and Comparative Examples 1-2 was tested using the indentation method. A load of 196 N was applied, and each experiment was performed in triplicate. Statistical analysis was conducted using SPSS 24.0 software. The quantitative data were analyzed using... (mean ± standard deviation) represents the mean. The Kolmogorov-Smirnov test was used to test the normality of the data. For normally distributed data, the t-test was used to compare the differences in means between the two groups. P < 0.05 was considered statistically significant.

[0147] The test results are shown in Table 1:

[0148] Table 1

[0149]

[0150]

[0151] Note: * indicates P<0.05 compared to Example 1 group.

[0152] Experimental Example 2:

[0153] The surface roughness of the silicon nitride substrates prepared in Examples 1-3 and Comparative Examples 3-4 was tested. The surface roughness was measured by selecting at least five test points on both sides of the silicon nitride substrate, and the average roughness of all test points was taken as the test result. All test points included a central point located in the center, with the remaining test points located around the central point and close to the edges of the silicon nitride substrate. The test results are shown in Table 2.

[0154] Table 2

[0155]

[0156] Note: * indicates P<0.05 compared to Example 1 group.

[0157] Experimental Example 3:

[0158] The warpage (mm / 25.4mm) of the silicon nitride substrates prepared in Examples 1-3 and Comparative Examples 5-6 was tested. The test results are shown in Table 3.

[0159] Table 3

[0160]

[0161]

[0162] Note: * indicates P<0.05 compared to Example 1 group.

[0163] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing silicon nitride ceramics, characterized in that, Follow these steps: (1) Preparation of organic adhesive: Add adhesive, plasticizer and organic solvent into a container and stir evenly; the mass ratio of the adhesive, plasticizer and organic solvent is (15-25):(10-20):(80-120); (2) Recycled slurry treatment: Add organic solvent to the slurry remaining from each process before casting, add it to a container and stir evenly. The mass ratio of the recycled slurry to the organic solvent is (30-50):(10-20). (3) Recycled material treatment: Add the scraps from casting and pressure sintering, green waste and organic solvents to the ball mill in a mass ratio of (10-20): (10-20): (30-50), and ball mill for 24-48 hours. Use a device with a multi-stage filter to discharge the material from the ball mill into a clean bucket. (4) Ball milling and mixing: Organic solvent, silicon nitride powder, recycled slurry, recycled material, sintering aid, dispersant and leveling agent are added to the ball mill in sequence and ball milled for 12-24 hours to obtain a mixed slurry; the organic adhesive prepared in step (1) is added and ball milled for another 24-36 hours to obtain a casting slurry; the mass ratio of the organic solvent, silicon nitride powder, recycled slurry, recycled material, sintering aid, dispersant and leveling agent is (90-130):(60-120):(20-30):(20-30):(5-15):(5-10):(5-15); the mass ratio of the mixed slurry to the organic adhesive is (1-5):1; (5) Degassing and aging: The casting slurry prepared in step (4) is degassed under vacuum for 10-30 min and aged for 10-15 h by stirring at 5-10 rpm, with the viscosity controlled at 6000-20000 cps, the solid content at 55-75%, and the temperature at 10-25℃. (6) Casting: The slurry prepared in step (5) is cast using a casting machine, and the green body is wrapped with a paper tube; the process parameters for this step are: casting speed 0.1-0.2 m / min, temperature of zone 1 of casting drying chamber 15-35℃, temperature of zone 2 of casting drying chamber 55-85℃, and temperature of zone 3 of casting drying chamber 70-110℃; (7) Punching and applying isolation powder: Select the punching die according to the drawing requirements, cut the green blank prepared in step (6), and transport it to the powder application line by conveyor belt for powder application. The powder application pressure is 0.05-0.1MPa and the powder application temperature is 55-85℃. (8) Air debinding: Place the leveled green body into an intermittent furnace for debinding; the process parameters for this step are: debinding temperature 450-650℃, total time: 15-25h, and heating rate <5℃ / min between 220-350℃. (9) Pressure sintering: The debinding product is placed into a sintering furnace for sintering; the process parameters for this step are: sintering temperature 1650-1850℃, sintering time: 15-25h, pressure: 0.5-1.0MPa; (10) Sandblasting: Remove the insulating powder from the surface of the sintered silicon nitride ceramic using sandblasting equipment; The adhesive is a mixture of acrylonitrile-butadiene-styrene copolymer and polyaspartic acid ester in a mass ratio of (1-5):1; The sintering aid is a mixture of ytterbium fluoride and strontium hexaboride in a mass ratio of (1-3):1; The leveling agent is a mixture of silicone fluorine leveling agent and BYK-3902P leveling agent at a mass ratio of 1:(1-3); the molecular structural formula of the silicone fluorine leveling agent is as follows: 。 2. The method for preparing silicon nitride ceramic according to claim 1, characterized in that, The plasticizer is one or more of methyl phthalate, di(2-ethylhexyl) terephthalate, dibutyl sebacate, and di(2-ethylhexyl) cyclohexane-1,4-dicarboxylic acid.

3. The method for preparing silicon nitride ceramic according to claim 1, characterized in that, The organic solvent is one or more of toluene, xylene, isopropanol, ethanol, and ethyl acetate.

4. The method for preparing silicon nitride ceramic according to claim 1, characterized in that, The dispersant is one or more of polyethyleneimine, ammonium citrate, ammonium persulfate, sodium tripolyphosphate, tetraethyl ethylenediamine, ammonium acrylate, trioleic acid glyceride, and phosphate esters.

5. The method for preparing silicon nitride ceramic according to claim 1, characterized in that, The raw material composition and ratio of the isolation powder in step (7) are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1: (0.015-0.025): (3-5).

6. The method for preparing silicon nitride ceramic according to claim 1, characterized in that, The sandblasting in step (10) is as follows: sand type: alumina, zirconium oxide, silicon dioxide, mass ratio 1:1:1; sand mesh: 100-3000 mesh; pressure = 0.01-0.5MPa.

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