Anti-cracking silicon nitride ceramic glue discharging process

Abstract

The invention discloses an anti-cracking silicon nitride ceramic degumming process, and belongs to the technical field of ceramic materials, by adding a self-synthesized modified binder and a modified sintering aid in the process of preparing a silicon nitride ceramic green body, the residual carbon amount can be reduced, and the influence on the purity of the silicon nitride ceramic caused by the generation of an impurity phase due to the existence of carbon is avoided; the prepared silicon nitride ceramic substrate has good mechanical strength and thermal conductivity, and is good in density and not easy to crack; the modified binder disclosed by the invention can be gradually decomposed to form uniform pores, so that the residual carbon amount is reduced; the modified sintering agent is provided with an inert shell, the situation that traditional fluoride easily reacts with water molecules to generate HF gas in the rubber discharging stage can be avoided, silicon dioxide can generate silicon nitride with nitrogen in the rubber discharging process, loss of silicon atoms in powder caused by the silicon flowing phenomenon is avoided, the content of silicon nitride in the powder is further reduced, and the service life of the powder is prolonged. And the purity of the silicon nitride is ensured.

Description

Technical Field

[0001] This invention belongs to the field of ceramic materials technology, specifically a process for removing adhesive from silicon nitride ceramics to prevent cracking. Background Technology

[0002] Silicon nitride is an inorganic compound with high thermal and chemical stability. It is a ceramic material composed of silicon and nitrogen, and its unique crystal structure endows it with excellent physical and chemical properties. Silicon nitride has a very high melting point and hardness, allowing it to maintain stability even under extreme temperatures and harsh environments. In the ceramics industry, silicon nitride is widely used in various fields, including electronics, optics, aerospace, and chemical engineering. Its excellent mechanical properties and chemical stability make it an ideal choice for manufacturing advanced electronic devices, high-temperature resistant materials, and corrosion-resistant components. Of particular note is the increasingly sophisticated production process of silicon nitride ceramics, including advancements in silicon nitride powder synthesis and ceramic forming technologies, which further improves its production efficiency and performance, making silicon nitride ceramics promising for both scientific research and industrial applications.

[0003] During the sintering process of silicon nitride, the green preform needs to be placed in a debinding furnace to remove organic additives. These additives undergo chemical reactions such as cracking, carbonization, and oxidation within the furnace, producing gases such as carbon dioxide. Of particular note is that in existing technology, the furnace temperature gradually decreases from 600°C to 150°C during the debinding process. This means that during the cooling period, the debinding furnace needs to draw in at least 3 parts of air from the outside, confirming that the debinding furnace is not sealed in actual production; it exchanges air with the outside. During this time, the gases inside the furnace cannot escape, while cold outside air and its carried water vapor continuously enter the furnace. This water vapor reacts with the organic matter inside the furnace in an oxidation reaction, producing gaseous water, which circulates within the furnace.

[0004] Chinese Patent No. CN118084507B discloses a process for removing binder from silicon nitride ceramic green bodies. This solution optimizes the binder removal process to overcome the shortcomings of existing processes, reduces the formation of silica during the binder removal process, and results in high yield, low cracking rate, low residual carbon content, and less warping and deformation of the green bodies obtained after binder removal. However, the binder used in this solution is polyvinyl butyral, which has a high residual carbon content. The presence of carbon can easily generate impurity phases and reduce density. Summary of the Invention

[0005] The purpose of this invention is to provide a debinding process for silicon nitride ceramics to prevent cracking. By adding a self-synthesized modified binder and a modified sintering aid during the preparation of the silicon nitride ceramic green body, the residual carbon content can be reduced, avoiding the formation of impurity phases by the presence of carbon, which would affect the purity of the silicon nitride ceramic. This results in a silicon nitride ceramic substrate with good mechanical strength and thermal conductivity, as well as good density and resistance to cracking.

[0006] The objective of this invention can be achieved through the following technical solutions: A process for removing binder from silicon nitride ceramics to prevent cracking includes the following steps: Step 1: The isocyanate groups at both ends of isophorone diisocyanate react with the hydroxyl groups of p-hydroxybenzaldehyde and the amino groups of 3-dimethylaminopropenal, respectively, to obtain a modified intermediate containing double bonds.

[0007] Step 2: Modified polyacrylic acid is obtained by copolymerizing the double bonds on the modified intermediate with an acrylic acid solution under an initiator; the modified binder is obtained by directly reacting polyvinyl butyral and modified polyacrylic acid through an aldol condensation reaction.

[0008] Step 3: Using the sol-gel method, fluorides are coated with silica to obtain modified sintering aids.

[0009] Step 4: After mixing and ball milling the modified sintering aid, silicon nitride with a particle size of 0.4-0.7μm, modified binder, dispersant polyvinylpyrrolidone, plasticizer polyethylene glycol and ethanol, a silicon nitride ceramic preform is prepared.

[0010] Step 5: Place the silicon nitride ceramic blank in a muffle furnace and remove the binder in sections to obtain a silicon nitride ceramic substrate, thus completing a silicon nitride ceramic binder removal process that prevents cracking.

[0011] Furthermore, the ratio of modified sintering aid, silicon nitride, modified binder, polyvinylpyrrolidone, polyethylene glycol and ethanol is 3-5g: 55-65g: 18-20g: 4-6g: 6-8g: 20-25g.

[0012] Furthermore, the specific preparation steps of the modified intermediate are as follows: Isophorone diisocyanate, p-hydroxybenzaldehyde, and ethyl acetate were added to a reaction vessel and stirred for 1-2 hours at 60-70℃ and 500-600 r / min. Then, 3-dimethylaminopropenal was added, and the reaction was continued for 3-4 hours. The mixture was then naturally cooled to room temperature and frozen in a -20℃ freezer for 8-9 hours. After crystals appeared in the solution, the mixture was filtered, and the filter cake was dried at 70-80℃ for 1-2 hours to obtain the modified intermediate.

[0013] Furthermore, the ratio of isophorone diisocyanate, p-hydroxybenzaldehyde, ethyl acetate and 3-dimethylaminopropenal is 22.4-22.6g: 12.2-12.8g: 100-110mL: 21.7-22.8g.

[0014] Furthermore, the specific preparation steps for modified polyacrylic acid are as follows: The modified intermediate, acrylic acid solution, and deionized water were added to a reaction vessel, and nitrogen gas was introduced for protection. The reaction was stirred at 95-100℃ and 500-600 r / min for 1-2 h. After cooling to 55-65℃, ammonium persulfate and N,N-methylenebisacrylamide were added, and the mixture was heated to 70-80℃ and stirred for another 3-4 h. The mixture was then filtered, and the filter cake was washed 2-3 times with deionized water and anhydrous ethanol, respectively. The mixture was then vacuum dried at 60-80℃ for 1-2 h to obtain modified polyacrylic acid.

[0015] Furthermore, the ratio of the modified intermediate, acrylic acid solution, deionized water, ammonium persulfate and N,N-methylenebisacrylamide is 15-20g: 70-80mL: 500-600mL: 1-2g: 1-2g.

[0016] Furthermore, the specific preparation steps of the modified binder are as follows: Polyvinyl butyral and deionized water were added to a reaction vessel and stirred at 60-70℃ and 500-600 r / min for 1-2 h. Then, a 1 mol / L hydrochloric acid solution was added and stirring was continued for 30-40 min. Modified polyacrylic acid was then added and stirring was continued for 2-3 h. After the reaction was complete, sodium hydroxide solution was added to adjust the pH to 4-5 to quench the reaction. The mixture was then kept at the same temperature for another 2-3 h. The mixture was filtered, and the filter cake was washed 2-3 times with deionized water and anhydrous ethanol, respectively. The cake was then vacuum dried at 60-80℃ for 1-2 h to obtain the modified binder.

[0017] Furthermore, the ratio of polyvinyl butyral, hydrochloric acid solution and modified polyacrylic acid is 100-120g: 900-950mL: 8-10mL: 50-60g.

[0018] Furthermore, the specific preparation steps of the modified sintering aid are as follows: Fluoride with a particle size of 3-5 μm and hexadecyltrimethylammonium bromide are added to a reaction vessel and stirred at 60-70℃ and 500-600 r / min for 1-2 h. Then deionized water and anhydrous ethanol are added and stirring is continued for 1-2 h. Then ammonia and tetraethyl orthosilicate are added and stirring is continued for 24-26 h. After filtration, the filter cake is washed 2-3 times with deionized water and anhydrous ethanol, respectively, and then vacuum dried at 60-80℃ for 1-2 h to obtain the modified sintering aid.

[0019] Furthermore, the ratio of fluoride, hexadecyltrimethylammonium bromide, deionized water, anhydrous ethanol, ammonia, and tetraethyl orthosilicate is 10-20g: 5-7g: 300-400mL: 2-3L: 50-60mL: 80-90g.

[0020] Furthermore, the fluoride is any one or more of magnesium fluoride, ytterbium fluoride, yttrium fluoride, lanthanum fluoride, and cerium fluoride in any ratio.

[0021] Furthermore, the specific preparation steps for segmented glue removal are as follows: The silicon nitride ceramic preform is placed in a muffle furnace and heated to 200-220°C at a rate of 0.4-0.6°C / min under an atmosphere of 1-3 Pa and a nitrogen flow rate of 400-500 L / min. The temperature is held for 2-3 hours, then further heated to 500-550°C and held for 2-3 hours. Then, air is introduced at a flow rate of 300-400 L / min, and the temperature is increased to 550-600°C and held for 4-6 hours. Finally, the temperature is lowered to 150-170°C under an atmosphere of 4-6 Pa and an air flow rate of 220-250 L / min for 20-24 hours. The furnace door is then opened to obtain the silicon nitride ceramic substrate, thus completing a process for removing adhesive from silicon nitride ceramics to prevent cracking.

[0022] The beneficial effects of this invention are: 1. The anti-cracking silicon nitride ceramic debinding process provided by the present invention reduces the residual carbon content by adding a self-synthesized modified binder and modified sintering aid during the preparation of silicon nitride ceramic green body, thereby avoiding the generation of impurity phases by carbon and affecting the purity of silicon nitride ceramic. This results in silicon nitride ceramic substrates with good mechanical strength and thermal conductivity, as well as good density and resistance to cracking.

[0023] 2. The modified sintering agent of the present invention modifies fluorides by coating them with inert silica to form an inert shell. This avoids the common occurrence of fluorides reacting with water molecules to generate HF gas during the debinding stage. HF has strong reducing properties and will corrode the Si-N bonds on the surface of the silicon nitride blank, resulting in a porous surface. Furthermore, silica can react with nitrogen gas to generate silicon nitride during the debinding process, avoiding the loss of silicon atoms in the powder due to silicon flow, thereby reducing the silicon nitride content in the powder and ensuring the purity of silicon nitride.

[0024] 3. The modified binder of the present invention is obtained by grafting polyacrylic acid and polyvinyl butyral through an aldol condensation reaction. The polyacrylic acid segments have low heat resistance and preferentially decompose into volatile substances. These molecules are small in size and highly volatile, and can quickly escape from the gaps between the green body particles. During the escape process, a large number of interconnected micron-sized pores are left inside the green body, providing a direct path for the discharge of subsequent polyvinyl butyral decomposition products and reducing the residual carbon content. Furthermore, the polyvinyl butyral grafted with polyacrylic acid has higher bonding strength and can promote the direct and uniform bonding of various additives. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1: A process for removing binder from silicon nitride ceramics to prevent cracking, comprising the following steps: S1: 22.4 g of isophorone diisocyanate, 12.2 g of p-hydroxybenzaldehyde and 100 mL of ethyl acetate were added to a reaction vessel and stirred at 60 °C and 500 r / min for 1 h. Then 21.7 g of 2-methylpropenal was added and the reaction was continued for 3 h. The mixture was naturally cooled to room temperature and then frozen at -20 °C for 8 h. After crystals appeared in the solution, the mixture was filtered and the filter cake was dried at 70 °C for 1 h to obtain the modified intermediate.

[0027] S2: Add 15g of modified intermediate, 70mL of acrylic acid solution and 500mL of deionized water to a reaction vessel, purge with nitrogen for protection, and stir at 95℃ and 500r / min for 1h. Cool to 55℃, add 1g of ammonium persulfate and 1g of N,N-methylenebisacrylamide, heat to 70℃, continue stirring for 3h, filter, wash the filter cake twice with deionized water and anhydrous ethanol respectively, and vacuum dry at 60℃ for 1h to obtain modified polyacrylic acid.

[0028] S3: Add 100g of polyvinyl butyral and 900mL of deionized water to a reaction vessel and stir for 1h at 60℃ and 500r / min. Then add 8mL of 1mol / L hydrochloric acid solution and continue stirring for 30min. Then add 50g of modified polyacrylic acid and continue stirring for 2h. After the reaction is complete, add sodium hydroxide solution to adjust the pH to 4 to quench the reaction. Continue to keep warm for 2h, filter, wash the filter cake twice with deionized water and anhydrous ethanol, and vacuum dry at 60℃ for 1h to obtain the modified binder.

[0029] S4: Add 10g of ytterbium fluoride with a particle size of 3μm and 5g of hexadecyltrimethylammonium bromide to a reaction vessel, stir and react for 1h at 60℃ and 500r / min, then add 300mL of deionized water and 2L of anhydrous ethanol, continue stirring for 1h, then add 50mL of ammonia water and 80g of tetraethyl orthosilicate, continue stirring for 24h, filter, wash the filter cake twice with deionized water and anhydrous ethanol respectively, and dry it under vacuum at 60℃ for 1h to obtain the modified sintering aid.

[0030] S5: 3g of modified sintering aid, 55g of silicon nitride with a particle size of 0.4μm, 18g of modified binder, 4g of dispersant polyvinylpyrrolidone, 6g of plasticizer polyethylene glycol and 20g of ethanol are stirred and mixed. After ball milling in a nitrogen protective atmosphere, the mixture is placed in a degassing tank to remove bubbles and obtain a mixed slurry. The mixed slurry is formed by a scraper in a casting machine, dried, wound up, vacuum sealed and statically pressed to obtain a silicon nitride ceramic preform.

[0031] S6: Place the silicon nitride ceramic blank in a muffle furnace. Under an atmosphere of 1 Pa pressure and 400 L / min nitrogen flow rate, heat the blank to 200 °C at a heating rate of 0.4 °C / min and hold for 2 hours. Then continue heating to 500 °C and hold for 2 hours. Next, introduce air at a flow rate of 300 L / min and heat the blank to 550 °C and hold for 4 hours. Then, under an atmosphere of 4 Pa ​​pressure and 220 L / min air flow rate, cool the blank to 150 °C for 20 hours. Open the furnace door to obtain the silicon nitride ceramic substrate, thus completing a silicon nitride ceramic adhesive removal process to prevent cracking.

[0032] Example 2: A process for removing binder from silicon nitride ceramics to prevent cracking, comprising the following steps: S1: 22.5g isophorone diisocyanate, 12.5g p-hydroxybenzaldehyde and 105mL ethyl acetate were added to a reaction vessel and stirred at 65℃ and 550r / min for 1.5h. Then 22.25g 2-methylpropenal was added and the reaction was continued for 3.5h. The mixture was naturally cooled to room temperature and then frozen at -20℃ for 8.5h. After crystals appeared in the solution, the mixture was filtered and the filter cake was dried at 75℃ for 1.5h to obtain the modified intermediate.

[0033] S2: 17.5g of modified intermediate, 75mL of acrylic acid solution and 550mL of deionized water were added to a reaction vessel, and nitrogen gas was introduced for protection. The mixture was stirred at 97.5℃ and 550r / min for 1.5h. After cooling to 60℃, 1.5g of ammonium persulfate and 1.5g of N,N-methylenebisacrylamide were added. The mixture was heated to 75℃ and stirred for another 3.5h. After filtration, the filter cake was washed 2.5 times with deionized water and anhydrous ethanol, respectively, and dried under vacuum at 70℃ for 1.5h to obtain modified polyacrylic acid.

[0034] S3: Add 110g of polyvinyl butyral and 925mL of deionized water to a reaction vessel and stir for 1.5h at 65℃ and 550r / min. Then add 9mL of 1mol / L hydrochloric acid solution and continue stirring for 35min. Then add 55g of modified polyacrylic acid and continue stirring for 2.5h. After the reaction is complete, add sodium hydroxide solution to adjust the pH to 4.5 to quench the reaction. Continue to keep warm for another 2.5h, filter, and wash the filter cake 2.5 times with deionized water and anhydrous ethanol respectively. Dry under vacuum at 70℃ for 1.5h to obtain the modified binder.

[0035] S4: Add 15g of ytterbium fluoride with a particle size of 4μm and 6g of hexadecyltrimethylammonium bromide to a reaction vessel and stir for 1.5h at 65℃ and 550r / min. Then add 350mL of deionized water and 2.5L of anhydrous ethanol and continue stirring for 1.5h. Then add 55mL of ammonia water and 85g of tetraethyl orthosilicate and continue stirring for 25h. Filter and wash the filter cake 2.5 times with deionized water and anhydrous ethanol, respectively. Dry under vacuum at 70℃ for 1.5h to obtain the modified sintering aid.

[0036] S5: 4g of modified sintering aid, 60g of silicon nitride with a particle size of 0.55μm, 19g of modified binder, 5g of dispersant polyvinylpyrrolidone, 7g of plasticizer polyethylene glycol and 22.5g of ethanol are stirred and mixed. After ball milling in a nitrogen protective atmosphere, the mixture is placed in a degassing tank to remove bubbles and obtain a mixed slurry. The mixed slurry is formed by a scraper in a casting machine, dried and wound, vacuum sealed and statically pressed to obtain a silicon nitride ceramic preform.

[0037] S6: Place the silicon nitride ceramic blank in a muffle furnace and heat it to 210°C at a rate of 0.5°C / min under an atmosphere of 2 Pa and 450 L / min nitrogen. Hold the temperature for 2.5 h, then continue heating to 525°C and hold for 2.5 h. Then, introduce air at a flow rate of 350 L / min and heat to 575°C, hold for 5 h. Finally, cool the temperature to 160°C under an atmosphere of 5 Pa and 235 L / min air for 22 h. Open the furnace door to obtain the silicon nitride ceramic substrate, thus completing a process for removing adhesive from silicon nitride ceramics to prevent cracking.

[0038] Example 3: A process for removing adhesive from silicon nitride ceramics to prevent cracking, comprising the following steps: S1: 22.6 g of isophorone diisocyanate, 12.8 g of p-hydroxybenzaldehyde and 110 mL of ethyl acetate were added to a reaction vessel and stirred at 70 °C and 600 r / min for 2 h. Then 22.8 g of 2-methylpropenal was added and the reaction was continued for 4 h. The mixture was naturally cooled to room temperature and then frozen at -20 °C for 9 h. After crystals appeared in the solution, the mixture was filtered and the filter cake was dried at 80 °C for 2 h to obtain the modified intermediate.

[0039] S2: Add 20g of modified intermediate, 80mL of acrylic acid solution and 600mL of deionized water to a reaction vessel, purge with nitrogen for protection, and stir at 100℃ and 600r / min for 2h. Cool to 65℃, add 2g of ammonium persulfate and 2g of N,N-methylenebisacrylamide, heat to 80℃, continue stirring for 4h, filter, wash the filter cake three times with deionized water and anhydrous ethanol respectively, and vacuum dry at 80℃ for 2h to obtain modified polyacrylic acid.

[0040] S3: Add 120g of polyvinyl butyral and 950mL of deionized water to a reaction vessel and stir for 2h at 70℃ and 600r / min. Then add 10mL of 1mol / L hydrochloric acid solution and continue stirring for 40min. Then add 60g of modified polyacrylic acid and continue stirring for 3h. After the reaction is complete, add sodium hydroxide solution to adjust the pH to 5 to quench the reaction. Continue to keep warm for 3h, filter, wash the filter cake three times with deionized water and anhydrous ethanol respectively, and vacuum dry at 80℃ for 2h to obtain the modified binder.

[0041] S4: Add 20g of ytterbium fluoride with a particle size of 5μm and 7g of hexadecyltrimethylammonium bromide to a reaction vessel and stir for 2h at 70℃ and 600r / min. Then add 400mL of deionized water and 3L of anhydrous ethanol and continue stirring for 2h. Then add 60mL of ammonia water and 90g of tetraethyl orthosilicate and continue stirring for 26h. Filter and wash the filter cake three times with deionized water and anhydrous ethanol respectively. Dry under vacuum at 80℃ for 2h to obtain the modified sintering aid.

[0042] S5: Mix 5g of modified sintering aid, 65g of silicon nitride with a particle size of 0.7μm, 20g of modified binder, 6g of dispersant polyvinylpyrrolidone, 8g of plasticizer polyethylene glycol and 25g of ethanol. After ball milling in a nitrogen protective atmosphere, place the mixture in a degassing tank to remove bubbles and obtain a mixed slurry. The mixed slurry is then formed by a scraper in a casting machine, dried, wound up, vacuum sealed and statically pressed to obtain a silicon nitride ceramic preform.

[0043] S6: Place the silicon nitride ceramic blank in a muffle furnace and heat it to 220°C at a rate of 0.6°C / min under an atmosphere of 3 Pa and 500 L / min nitrogen. Hold the temperature for 3 hours, then continue heating to 550°C and hold for 3 hours. Then, introduce air at a rate of 400 L / min and heat to 600°C, hold for 6 hours. Finally, cool the temperature to 170°C under an atmosphere of 6 Pa and 250 L / min air for 24 hours. Open the furnace door to obtain the silicon nitride ceramic substrate, thus completing a process for removing adhesive from silicon nitride ceramics to prevent cracking.

[0044] Comparative Example 1: Based on Example 3, the modified binder in step S5 was replaced with polyvinyl butyral, while the other steps remained unchanged, resulting in a silicon nitride ceramic substrate, thus completing a silicon nitride ceramic adhesive removal process to prevent cracking.

[0045] Comparative Example 2: Based on Example 3, the modified sintering aid in step S5 was replaced with magnesium fluoride, while the other steps remained unchanged, resulting in a silicon nitride ceramic substrate, thus completing a silicon nitride ceramic adhesive removal process to prevent cracking.

[0046] The silicon nitride ceramic substrates prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to performance tests. Thermal conductivity was tested according to GB / T 22588-2008; three-point bending strength was tested according to GB / T6569-2006; residual carbon content was tested according to GB / T 14849.10-2016 "Industrial Silicon Chemical Analysis Methods Part 10: Determination of Carbon Content by Infrared Absorption Method"; density was tested according to GB / T 25995-2010 "Test Methods for Density and Apparent Porosity of Fine Ceramics"; and body cracking rate was tested according to GB / T 3810.15-2016 "Test Methods for Ceramic Tiles Part 15: Determination of Crack Resistance of Glazed Tiles".

[0047] The results are shown in Table 1: Table 1 project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Thermal conductivity (W / m·K) 86.98 87.32 88.12 77.56 80.23 Three-point bending strength (MPa) 728 738 743 662 695 Residual carbon content (wt%) 0.07 0.06 0.05 0.28 0.09 Density (%) 93.2 93.8 94.5 87.6 89.3 Crack rate of billet (%) 1.2 0.9 0.7 8.5 5.3 As can be seen from Table 1, the thermal conductivity, three-point bending strength, and density of the silicon nitride ceramic substrates prepared in Examples 1-3 are significantly better than those in the comparative example, while the residual carbon content and green body cracking rate are significantly lower than those in the comparative example. This indicates that the silicon nitride ceramic substrates prepared by the anti-cracking silicon nitride ceramic debinding process provided by the present invention have good mechanical strength and thermal conductivity, and good density and are not prone to cracking.

[0048] In Comparative Example 1, the modified binder in step S5 was replaced with polyvinyl butyral. Pure polyvinyl butyral does not contain polyacrylic acid segments, so it cannot achieve early decomposition and pore formation. The decomposition temperature of polyvinyl butyral is concentrated, and the decomposition products contain viscous intermediates that are difficult to escape quickly, resulting in an increase in residual carbon. Residual carbon is prone to generating impurity phases, which destroys the continuous structure of ceramics and leads to a decrease in the density of silicon nitride ceramics. Polyvinyl butyral has low bonding strength and cannot promote the uniform dispersion of various additives. There are defects such as particle agglomeration and uneven pores inside the green body, which are prone to cracking under external force or thermal stress. At the same time, uneven pores lead to obstruction of heat conduction paths.

[0049] In Comparative Example 2, the modified sintering aid in step S5 was replaced with magnesium fluoride. Ordinary magnesium fluoride does not have a silicon dioxide shell for protection. During the debinding stage, under air conditions, magnesium fluoride reacts with trace amounts of moisture in the blank to generate HF gas. HF is highly corrosive and will break the Si-N bonds on the surface of the silicon nitride blank, resulting in a loose surface and microcracks inside the blank. Silicon flow is likely to occur during high-temperature debinding.

[0050] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A silicon nitride ceramic de-binding process to prevent cracking, characterized by, It comprises the following steps: Step one: through the isophorone diisocyanate two end isocyanate groups respectively with the hydroxyl group of p-hydroxy benzaldehyde and the amino group of 3-dimethylamino acrolein, a modified intermediate containing double bond is obtained; Step two: through the double bond on the modified intermediate and acrylic acid solution copolymerization under initiator, a modified polyacrylic acid is obtained; through the aldehyde condensation reaction between polyvinyl butyral and the modified polyacrylic acid, a modified adhesive is obtained; Step three: through sol-gel method, using silica to coat fluoride, a modified sintering aid is obtained; Step four: after stirring and mixing ball milling of the modified sintering aid, silicon nitride with particle size of 0.4-0.7 microns, modified adhesive, dispersant polyvinylpyrrolidone, plasticizer polyethylene glycol and ethanol, a silicon nitride ceramic body is prepared; Step five: the silicon nitride ceramic body is placed in a muffle furnace, through the segmented degassing process, a silicon nitride ceramic substrate is prepared, and a silicon nitride ceramic degassing process preventing cracking is completed.

2. The process for preventing cracking of silicon nitride ceramic de-binding according to claim 1, wherein The amount ratio of the modified sintering aid, silicon nitride, modified adhesive, polyvinylpyrrolidone, polyethylene glycol and ethanol is 3-5g:55-65g:18-20g:4-6g:6-8g:20-25g.

3. The process for preventing cracking of silicon nitride ceramic de-binding according to claim 1, wherein The specific preparation steps of the modified intermediate are as follows: Isophorone diisocyanate, p-hydroxy benzaldehyde and ethyl acetate are added into a reaction kettle, stirred at 60-70℃ and 500-600r / min for 1-2h, then 3-dimethylamino acrolein is added, and the reaction is continued for 3-4h, and then the solution is naturally cooled to room temperature and placed in a-20℃ freezer for 8-9h, after the crystallization appears in the solution, the filter cake is placed in a 70-80℃ drying oven for 1-2h to obtain the modified intermediate.

4. The process for preventing cracking of silicon nitride ceramic according to claim 3, wherein The amount ratio of the isophorone diisocyanate, p-hydroxy benzaldehyde, ethyl acetate and 3-dimethylamino acrolein is 22.4-22.6g:12.2-12.8g:100-110mL:21.7-22.8g.

5. The process for preventing cracking of silicon nitride ceramic as claimed in claim 1, wherein, The specific preparation steps of the modified polyacrylic acid are as follows: The modified intermediate, acrylic acid solution and deionized water are added into a reaction kettle, and nitrogen is introduced for protection, and then the reaction is stirred at 95-100℃ and 500-600r / min for 1-2h, and then the temperature is cooled to 55-65℃, and then ammonium persulfate and N,N-methylene bisacrylamide are added, and then the temperature is heated to 70-80℃, and then the stirring is continued for 3-4h, and then the filter cake is washed with ionized water and anhydrous ethanol for 2-3 times respectively, and then the filter cake is vacuum dried at 60-80℃ for 1-2h to obtain the modified polyacrylic acid.

6. The process for preventing cracking of silicon nitride ceramic as claimed in claim 5, wherein The amount ratio of the modified intermediate, acrylic acid solution, deionized water, ammonium persulfate and N,N-methylene bisacrylamide is 15-20g:70-80mL:500-600mL:1-2g:1-2g.

7. The process for preventing cracking of silicon nitride ceramic by using a photoresist according to claim 1, wherein The specific preparation steps of the modified adhesive are as follows: Polyvinyl butyral and deionized water are added to the reaction kettle, stirred at 60-70℃ and 500-600r / min for 1-2h, then 1mol / L hydrochloric acid solution is added, continue to stir for 30-40min, then add modified polyacrylic acid, continue to stir for 2-3h, after the reaction is completed, add sodium hydroxide solution to adjust the pH value to 4-5, quench the reaction, continue to keep warm for 2-3h, filter, wash the filter cake with ion water and anhydrous ethanol for 2-3 times, vacuum drying at 60-80℃ for 1-2h, to obtain the modified adhesive; The amount ratio of polyvinyl butyral, hydrochloric acid solution and modified polyacrylic acid is 100-120g:900-950mL:8-10mL:50-60g.

8. The process for preventing cracking of silicon nitride ceramic de-binding according to claim 1, wherein The specific preparation steps of the modified sintering aid are as follows: Fluoride and cetyltrimethylammonium bromide with a particle size of 3-5μm are added to the reaction kettle, stirred at 60-70℃ and 500-600r / min for 1-2h, then deionized water and anhydrous ethanol are added, continue to stir for 1-2h, then add ammonia and tetraethyl orthosilicate, continue to stir for 24-26h, filter, wash the filter cake with ion water and anhydrous ethanol for 2-3 times, vacuum drying at 60-80℃ for 1-2h, to obtain the modified sintering aid.

9. The process for preventing cracking of silicon nitride ceramic de-greasing according to claim 8, wherein The amount ratio of fluoride, cetyltrimethylammonium bromide, deionized water, anhydrous ethanol, ammonia and tetraethyl orthosilicate is 10-20g:5-7g:300-400mL:2-3L:50-60mL:80-90g; the fluoride is any one or more of magnesium fluoride, ytterbium fluoride, yttrium fluoride, lanthanum fluoride and cerium fluoride in any ratio.

10. The process for preventing cracking of silicon nitride ceramic by using a photoresist according to claim 1, wherein The specific process of the segmented degassing process is as follows: The silicon nitride ceramic body is placed in a muffle furnace, heated to 200-220℃ at a heating rate of 0.4-0.6℃ / min under an atmosphere of 1-3Pa pressure and 400-500L / min nitrogen flow, then heated to 500-550℃, and kept for 2-3h, then air is introduced at a flow rate of 300-400L / min, and the temperature is raised to 550-600℃, and kept for 4-6h, then the temperature is lowered to 150-170℃ under an atmosphere of 4-6Pa pressure and 220-250L / min air flow, and the cooling time is 20-24h, to complete the segmented degassing process.