A debinding process for silicon nitride ceramic green bodies

Abstract

The present invention discloses a debinding process for silicon nitride ceramic green bodies, which includes: (1) After the silicon nitride raw powder is formed by tape casting, a silicon nitride ceramic green body is made. The silicon nitride ceramic green body is placed in a crucible, and a layer of boron nitride powder is applied on the surface of the green body; (2) Debinding is carried out in stages in a muffle furnace; The debinding of the silicon nitride ceramic green body is realized, the generation of silicon dioxide in the debinding process is reduced, and the quality of batch production of silicon nitride ceramic substrates is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic materials, and particularly to a debinding process for silicon nitride ceramic green bodies. Background Art

[0002] Silicon nitride (Si3N4) is an inorganic compound with high thermal stability and chemical stability. It is a ceramic material composed of silicon and nitrogen elements, and its special crystal structure endows it with excellent physical and chemical properties. Silicon nitride has a very high melting point and hardness, enabling it to maintain stability under extremely high temperatures and harsh environments. In the ceramic industry, silicon nitride is widely used in various fields, including electronics, optics, aerospace, and chemical engineering, etc. Its excellent mechanical properties and chemical stability make it an ideal choice for preparing advanced electronic devices, high-temperature resistant materials, and corrosion-resistant components. Notably, the production process of silicon nitride ceramics is becoming increasingly perfect, including the synthesis of silicon nitride powder and the development of ceramic forming technology, which further improves the efficiency and performance of its preparation, making silicon nitride ceramics have broad prospects in scientific research and industrial applications.

[0003] During the sintering process of silicon nitride, the green body needs to be first placed in a debinding furnace to remove the organic additives therein. These additives will undergo chemical reactions such as cracking, carbonization, and oxidation in the furnace, and at the same time, gases such as carbon dioxide will be generated. It is particularly noteworthy that in the prior art, during the debinding process, the temperature in the furnace gradually drops from 600 °C to 150 °C. According to the ideal gas state equation PV = nRT, when the temperature drops to 150 °C, the amount of gas in the furnace is 4 times that at 600 °C. This means that during the cooling period, the debinding furnace needs to inhale at least 3 parts of air from the outside, which can prove that the debinding furnace is not airtight during actual production and there is an exchange with the outside air (because in the prior art, the normal debinding furnace pressure is controlled within -20 to 10 Pa relative to the atmospheric pressure. If it is an airtight debinding furnace, according to PV = nRT, it can be calculated that the pressure will reach -75750 Pa during the cooling section. Obviously, it is impossible to use such a debinding furnace in the industrial process because the equipment cost will be hundreds of thousands more). After on-site inspection and verification, it is found that cold air does indeed enter through the debinding valve of the debinding furnace to make up for the gradually consumed oxygen in the furnace. In the prior art, during the heat preservation and slow burning stage at 600 °C and the subsequent cooling stage, the debinding furnace takes 30 hours; during this period, the gas in the furnace cannot be discharged, and cold air from the outside and the water vapor it carries will continuously enter the furnace. These water vapors react with the organic substances in the furnace to produce gaseous water, and these gaseous waters will circulate in the furnace (Reaction Formulas 1, 2). Due to the gases and moisture generated by the reaction, the surface of the silicon nitride covered by silica will become loose, which not only reduces the thermal conductivity of the product but also increases the glass phase and changes the composition between the crystal phases, thus seriously affecting the appearance quality of the sintered body. Therefore, optimizing the debinding process to make up for the deficiencies in the existing debinding process and ensuring the controllability of the debinding process is of great significance for improving the quality of batch production of silicon nitride ceramic substrates.

[0004] C X H Y O Z (s)+O2(g)→CO2+H2O(g) (1)

[0005] Si3N4(s)+6H2O(g)→3SiO2(s)+4NH3(g) (2) Summary of the Invention

[0006] In view of the apparent defects of silicon nitride ceramics, the present invention provides a debinding process for silicon nitride ceramic green bodies, which makes up for the deficiencies of the prior art by optimizing the debinding process, reduces the generation of silica during the debinding process, and improves the quality of batch production of silicon nitride ceramic substrates.

[0007] A debinding process for silicon nitride ceramic green bodies, comprising:

[0008] (1) The silicon nitride green powder is formed into a silicon nitride ceramic green body by tape casting. The silicon nitride ceramic green body is placed in a crucible, and a layer of boron nitride powder is applied on the surface of the green body.

[0009] (2) The crucible containing the silicon nitride ceramic green body in step (1) is placed in a muffle furnace for staged debinding. The specific steps are as follows:

[0010] (a) First, under an atmosphere with a muffle furnace pressure of 1 - 3 Pa and a nitrogen flow rate of 200 - 500 L / min, the temperature is raised from room temperature to 200 °C at a heating rate of 0.4 - 0.6 °C / min and held for 2 - 3 hours.

[0011] (b) Under an atmosphere with a muffle furnace pressure of 1 - 3 Pa and a nitrogen flow rate of 200 - 500 L / min, the temperature is raised from 200 °C to 500 °C at a heating rate of 0.1 - 0.4 °C / min and held for 2 - 3 hours.

[0012] (c) Subsequently, under an atmosphere with a muffle furnace pressure of 1 - 3 Pa and a compressed air flow rate of 100 - 400 L / min, the temperature is raised from 500 °C to 550 - 600 °C at a heating rate of 0.4 - 0.6 °C / min and held for 2 - 6 hours.

[0013] (d) Under an atmosphere with a muffle furnace pressure of 3 - 6 Pa and a compressed air flow rate of 100 - 250 L / min, the temperature is lowered to 120 - 170 °C, and the cooling time is 16 - 24 hours.

[0014] (e) After the cooling is completed, the furnace door is opened.

[0015] The tape casting of the silicon nitride ceramic green body includes the following steps: Based on the total mass percentage of the slurry, prepare raw materials of 3 - 5 wt% sintering aid, 37 - 65 wt% silicon nitride, 8 - 20 wt% binder, 1 - 6 wt% dispersant, 2 - 8 wt% plasticizer, and 10 - 25 wt% ethanol solvent. After ball milling and mixing in a nitrogen - protected atmosphere and then defoaming in a defoaming tank to obtain a mixed slurry, the mixed slurry is formed by a doctor blade in a tape casting machine, dried, wound, then vacuum - sealed and cold isostatically pressed to obtain the silicon nitride ceramic green body.

[0016] The sintering aid is at least one of oxides or fluorides. The oxides are at least one of ZrO2, MgO, Yb2O3, Y2O3, Gd2O3, and the fluorides are at least one of MgF2, YbF3, YF3. The binder is polyvinyl butyral, the dispersant is polyvinylpyrrolidone, the plasticizer is polyethylene glycol. The particle size of the sintering aid is 1 - 5 μm, and the particle size of the silicon nitride is 0.4 - 0.7 μm.

[0017] By optimizing the debinding process, the present invention makes up for the deficiencies in the existing debinding process, reduces the generation of silicon dioxide during debinding, and enables the obtained green body after debinding to have a high yield, a low cracking rate, a small amount of residual carbon, and is not easily warped and deformed. The production method of the present invention is simple, easy to realize industrial production, and reduces the production cost. Detailed Embodiments

[0018] In the present invention, the deficiencies in the existing debinding technology due to the defects of debinding equipment are made up by optimizing the debinding process, and the generation of silicon dioxide impurities is reduced. The present invention will be further described below in conjunction with specific embodiments:

[0019] A debinding process for a silicon nitride ceramic green body includes:

[0020] (1) After the silicon nitride raw powder is formed by tape casting, a silicon nitride ceramic green body is made. The silicon nitride ceramic green body is placed in a crucible, and a layer of boron nitride powder is applied on the surface of the green body.

[0021] (2) The crucible containing the silicon nitride ceramic green body in step (1) is placed in a muffle furnace for staged debinding. The specific steps are as follows:

[0022] (a) First, under the atmosphere with a muffle furnace pressure of 1 - 3 Pa and a nitrogen flow rate of 200 - 500 L / min, the temperature is raised from room temperature to 200 °C at a heating rate of 0.4 - 0.6 °C / min, and held for 2 - 3 hours.

[0023] (b) Under the atmosphere with a muffle furnace pressure of 1 - 3 Pa and a nitrogen flow rate of 200 - 500 L / min, the temperature is raised from 200 °C to 500 °C at a heating rate of 0.1 - 0.4 °C / min, and held for 2 - 3 hours.

[0024] (c) Subsequently, under the atmosphere with a muffle furnace pressure of 1 - 3 Pa and a compressed air flow rate of 100 - 400 L / min, the temperature is raised from 500 °C to 550 - 600 °C at a heating rate of 0.4 - 0.6 °C / min, and held for 2 - 6 hours.

[0025] (d) Under the atmosphere with a muffle furnace pressure of 3 - 6 Pa and a compressed air flow rate of 100 - 250 L / min, the temperature is lowered to 120 - 170 °C, and the cooling time is 16 - 24 hours.

[0026] (e) After the cooling is completed, the furnace door is opened.

[0027] The tape casting of the silicon nitride ceramic green body comprises the following steps: Based on the total mass percentage of the slurry, 3-5 wt% of sintering aids, 37-65 wt% of silicon nitride, 8-20 wt% of binder, 1-6 wt% of dispersant, 2-8 wt% of plasticizer, and 10-25 wt% of ethanol solvent are ball-milled and mixed in a nitrogen protection atmosphere and then placed in a degassing tank for degassing to obtain a mixed slurry. The mixed slurry is formed by a doctor blade in a tape casting machine, dried, and wound up, and then vacuum-sealed and cold isostatically pressed to obtain a silicon nitride ceramic green body.

[0028] The sintering aids are at least one of oxides or fluorides. The oxides are ZrO2, MgO, Yb2O3, Y2O3, Gd2O3, and the fluorides are MgF2, YbF3, YF3. The binder is polyvinyl butyral, the dispersant is polyvinyl pyrrolidone, the plasticizer is polyethylene glycol. The particle size of the sintering aids is 1-5 μm, and the particle size of the silicon nitride is 0.4-0.7 μm.

[0029] Example 1

[0030] First, according to the material ratio shown in Table 1, it is ball-milled and mixed in a nitrogen protection atmosphere and then placed in a degassing tank for degassing to obtain a mixed slurry. The mixed slurry is formed by a doctor blade in a tape casting machine, dried, and wound up, and then vacuum-sealed and cold isostatically pressed to obtain a silicon nitride ceramic green body. The silicon nitride ceramic green body is placed in a crucible, and a layer of boron nitride powder is coated on the surface of the green body.

[0031] Secondly, the crucible containing the silicon nitride ceramic green body is placed in a muffle furnace. The muffle furnace is an atmospheric non-closed furnace type, including a degassing valve and a pressure relief valve. The crucible of the silicon nitride ceramic green body is degassed in stages in the muffle furnace. The specific steps are as follows:

[0032] (a) First, in an atmosphere with a muffle furnace pressure of 1 Pa and a nitrogen flow rate of 200 L / min, it is heated from room temperature to 200 °C at a heating rate of 0.4 °C / min and held for 2 hours;

[0033] (b) In an atmosphere with a muffle furnace pressure of 1 Pa and a nitrogen flow rate of 200 L / min, it is heated from 200 °C to 500 °C at a heating rate of 0.1 °C / min and held for 2 hours;

[0034] (c) Subsequently, in an atmosphere with a muffle furnace pressure of 1 Pa and a compressed air flow rate of 100 L / min, it is heated from 500 °C to 550 °C at a heating rate of 0.4 °C / min and held for 2 hours;

[0035] (d) In an atmosphere with a muffle furnace pressure of 3 Pa and a compressed air flow rate of 250 L / min, it is cooled to 120 °C, and the cooling time is 24 hours;

[0036] (e) After the temperature reduction is completed, open the furnace door.

[0037] Example 2

[0038] First, mix by ball milling in a nitrogen protection atmosphere according to the material ratio shown in Table 1, and then place it in a degassing tank to remove bubbles to obtain a mixed slurry. The mixed slurry is formed by a doctor blade in a casting machine, dried, wound up, and then vacuum-sealed and cold isostatically pressed to obtain a silicon nitride ceramic blank. Place the silicon nitride ceramic blank in a crucible and apply a layer of boron nitride powder on the surface of the blank.

[0039] Secondly, place the crucible containing the silicon nitride ceramic blank in a muffle furnace. The muffle furnace is of an atmospheric pressure non-closed furnace type and includes a degassing valve and a pressure relief valve. The crucible of the silicon nitride ceramic blank is degassed in sections in the muffle furnace. The specific steps are as follows:

[0040] (a) First, in an atmosphere with a muffle furnace pressure of 3 Pa and a nitrogen flow rate of 500 L / min, heat from room temperature to 200 °C at a heating rate of 0.6 °C / min and hold for 3 hours;

[0041] (b) In an atmosphere with a muffle furnace pressure of 3 Pa and a nitrogen flow rate of 500 L / min, heat from 200 °C to 500 °C at a heating rate of 0.4 °C / min and hold for 3 hours;

[0042] (c) Subsequently, in an atmosphere with a muffle furnace pressure of 3 Pa and a compressed air flow rate of 400 L / min, heat from 500 °C to 550 °C at a heating rate of 0.6 °C / min and hold for 6 hours;

[0043] (d) In an atmosphere with a muffle furnace pressure of 6 Pa and a compressed air flow rate of 100 L / min, cool down to 170 °C, and the cooling time is 16 hours;

[0044] (e) After the temperature reduction is completed, open the furnace door.

[0045] Example 3

[0046] First, mix by ball milling in a nitrogen protection atmosphere according to the material ratio shown in Table 1, and then place it in a degassing tank to remove bubbles to obtain a mixed slurry. The mixed slurry is formed by a doctor blade in a casting machine, dried, wound up, and then vacuum-sealed and cold isostatically pressed to obtain a silicon nitride ceramic blank. Place the silicon nitride ceramic blank in a crucible and apply a layer of boron nitride powder on the surface of the blank.

[0047] Secondly, place the crucible containing the silicon nitride ceramic blank in a muffle furnace. The muffle furnace is of an atmospheric pressure non-closed furnace type and includes a degassing valve and a pressure relief valve. The crucible of the silicon nitride ceramic blank is degassed in sections in the muffle furnace. The specific steps are as follows:

[0048] (a) First, under the atmosphere of a muffle furnace pressure of 3 Pa and a nitrogen flow rate of 400 L / min, heat from room temperature to 200 °C at a heating rate of 0.4 °C / min and hold for 3 hours;

[0049] (b) Under the atmosphere of a muffle furnace pressure of 3 Pa and a nitrogen flow rate of 400 L / min, heat from 200 °C to 500 °C at a heating rate of 0.4 °C / min and hold for 3 hours;

[0050] (c) Subsequently, under the atmosphere of a muffle furnace pressure of 3 Pa and a compressed air flow rate of 400 L / min, heat from 500 °C to 600 °C at a heating rate of 0.4 °C / min and hold for 6 hours;

[0051] (d) Under the atmosphere of a muffle furnace pressure of 3 Pa and a compressed air flow rate of 250 L / min, cool down to 170 °C, and the cooling time is 16 hours;

[0052] (e) After the cooling is completed, open the furnace door.

[0053] Example 4

[0054] First, mix the materials according to the material ratio shown in Table 1 in a nitrogen protection atmosphere by ball milling, and then place them in a degassing tank for degassing to obtain a mixed slurry. The mixed slurry is formed by a doctor blade in a casting machine, dried, wound up, then vacuum sealed and cold isostatically pressed to obtain a silicon nitride ceramic blank. Place the silicon nitride ceramic blank in a crucible and apply a layer of boron nitride powder on the surface of the blank.

[0055] Secondly, place the crucible containing the silicon nitride ceramic blank into a muffle furnace. The muffle furnace is an atmospheric non-closed furnace type, including a degumming valve and a pressure relief valve. The crucible of the silicon nitride ceramic blank is degummed in sections in the muffle furnace. The specific steps are as follows:

[0056] (a) First, under the atmosphere of a muffle furnace pressure of 1 Pa and a nitrogen flow rate of 400 L / min, heat from room temperature to 200 °C at a heating rate of 0.4 °C / min and hold for 3 hours;

[0057] (b) Under the atmosphere of a muffle furnace pressure of 1 Pa and a nitrogen flow rate of 400 L / min, heat from 200 °C to 500 °C at a heating rate of 0.4 °C / min and hold for 3 hours;

[0058] (c) Subsequently, under the atmosphere of a muffle furnace pressure of 1 Pa and a compressed air flow rate of 400 L / min, heat from 500 °C to 600 °C at a heating rate of 0.4 °C / min and hold for 6 hours;

[0059] (d) Under the atmosphere of a muffle furnace pressure of 3 Pa and a compressed air flow rate of 250 L / min, cool down to 170 °C, and the cooling time is 16 hours;

[0060] (e) After the temperature reduction is completed, open the furnace door.

[0061] Example 5

[0062] First, mix the materials according to the material ratio shown in Table 1 in a nitrogen protection atmosphere by ball milling, and then place them in a degassing tank for degassing to obtain a mixed slurry. The mixed slurry is formed by a doctor blade in a casting machine, dried, wound, and then vacuum-sealed and cold isostatically pressed to obtain a silicon nitride ceramic blank. Place the silicon nitride ceramic blank in a crucible and apply a layer of boron nitride powder on the surface of the blank.

[0063] Secondly, place the crucible containing the silicon nitride ceramic blank into a muffle furnace. The muffle furnace is of an atmospheric pressure non-closed furnace type and includes a degassing valve and a pressure relief valve. The crucible of the silicon nitride ceramic blank is degassed in segments in the muffle furnace. The specific steps are as follows:

[0064] (a) First, under the atmosphere of a muffle furnace pressure of 3 Pa and a nitrogen flow rate of 400 L / min, heat from room temperature to 200 °C at a heating rate of 0.4 °C / min and hold for 3 hours;

[0065] (b) Under the atmosphere of a muffle furnace pressure of 3 Pa and a nitrogen flow rate of 400 L / min, heat from 200 °C to 500 °C at a heating rate of 0.4 °C / min and hold for 3 hours;

[0066] (c) Subsequently, under the atmosphere of a muffle furnace pressure of 3 Pa and a compressed air flow rate of 400 L / min, heat from 500 °C to 600 °C at a heating rate of 0.4 °C / min and hold for 6 hours;

[0067] (d) Under the atmosphere of a muffle furnace pressure of 6 Pa and a compressed air flow rate of 250 L / min, cool down to 170 °C, and the cooling time is 16 hours;

[0068] (e) After the temperature reduction is completed, open the furnace door.

[0069] Example 6

[0070] First, mix the materials according to the material ratio shown in Example 3 of Table 1 in a nitrogen protection atmosphere by ball milling, and then place them in a degassing tank for degassing to obtain a mixed slurry. The mixed slurry is formed by a doctor blade in a casting machine, dried, wound, and then vacuum-sealed and cold isostatically pressed to obtain a silicon nitride ceramic blank. Place the silicon nitride ceramic blank in a crucible and apply a layer of boron nitride powder on the surface of the blank.

[0071] Secondly, place the crucible containing the silicon nitride ceramic blank into a muffle furnace. The muffle furnace is of an atmospheric pressure non-closed furnace type and includes a degassing valve and a pressure relief valve. The crucible of the silicon nitride ceramic blank is degassed in segments in the muffle furnace. The specific steps are as follows:

[0072] (a) First, under the atmosphere with a muffle furnace pressure of 3 Pa and a nitrogen flow rate of 400 L / min, heat from room temperature to 200 °C at a heating rate of 0.4 °C / min and hold for 3 hours;

[0073] (b) Under the atmosphere with a muffle furnace pressure of 3 Pa and a nitrogen flow rate of 400 L / min, heat from 200 °C to 500 °C at a heating rate of 0.4 °C / min and hold for 3 hours;

[0074] (c) Subsequently, under the atmosphere with a muffle furnace pressure of 3 Pa and a compressed air flow rate of 400 L / min, heat from 500 °C to 550 °C at a heating rate of 0.4 °C / min and hold for 6 hours;

[0075] (d) Under the atmosphere with a muffle furnace pressure of 3 Pa and a compressed air flow rate of 250 L / min, cool down to 170 °C and the cooling time is 16 hours;

[0076] (e) After the cooling is completed, open the furnace door.

[0077] Table 1

[0078]

[0079] Comparative Example 1

[0080] First, after mixing according to the material ratio of Example 3, a silicon nitride ceramic green body is obtained by tape casting. Place the silicon nitride ceramic green body in a crucible and apply a layer of boron nitride powder on the surface of the green body.

[0081] Secondly, place the crucible with the silicon nitride ceramic green body in a muffle furnace. The muffle furnace is of normal pressure non-closed furnace type, including a degreasing valve and a pressure relief valve, and degrease in stages. The specific steps are as follows:

[0082] (a) First, under the atmosphere with a muffle furnace pressure of -1 Pa and a nitrogen flow rate of 200 L / min, heat from room temperature to 650 °C at a heating rate of 0.6 °C / min and hold for 12 hours;

[0083] (b) Open the furnace door and cool down naturally.

[0084] Comparative Example 2

[0085] First, after mixing according to the material ratio of Example 3, a silicon nitride ceramic green body is obtained by tape casting. Place the silicon nitride ceramic green body in a crucible and apply a layer of boron nitride powder on the surface of the green body.

[0086] Secondly, place the crucible with the silicon nitride ceramic green body in a muffle furnace. The muffle furnace is of normal pressure non-closed furnace type, including a degreasing valve and a pressure relief valve, and degrease in stages. The specific steps are as follows:

[0087] (a) First, under the atmosphere with a muffle furnace pressure of 5 Pa and a nitrogen flow rate of 200 L / min, heat from room temperature to 650 °C at a heating rate of 0.6 °C / min and hold for 12 hours;

[0088] (b) Open the furnace door and let it cool naturally.

[0089] Comparative Example 3

[0090] The raw material ratio, mixing conditions and preparation process are the same as those in Example 3, except that: in steps (a), (b), and (c), the pressure of the muffle furnace is 0 Pa.

[0091] Comparative Example 4

[0092] The raw material ratio, mixing conditions and preparation process are the same as those in Example 3, except that: in steps (a), (b), and (c), the pressure of the muffle furnace is 4 Pa.

[0093] Comparative Example 5

[0094] The raw material ratio, mixing conditions and preparation process are the same as those in Example 3, except that: in step (d), the pressure of the muffle furnace is 2 Pa.

[0095] Comparative Example 6

[0096] The raw material ratio, mixing conditions and preparation process are the same as those in Example 3, except that: in step (d), the pressure of the muffle furnace is 7 Pa.

[0097] Comparative Example 7

[0098] The raw material ratio, mixing conditions and preparation process are the same as those in Example 3, except that: step (d) is to open the furnace door and let it cool naturally.

[0099] Comparative Example 8

[0100] The raw material ratio, mixing conditions and preparation process are the same as those in Example 3, except that: the steps in step (c) are: under the atmosphere with a muffle furnace pressure of 3 Pa and a compressed air flow rate of 400 L / min, heat from 500 °C to 540 °C at a heating rate of 0.4 °C / min and hold for 6 hours.

[0101] Comparative Example 9

[0102] The raw material ratio, mixing conditions and preparation process are the same as those in Example 3, except that: the steps in step (c) are: under the atmosphere with a muffle furnace pressure of 3 Pa and a compressed air flow rate of 400 L / min, heat from 500 °C to 610 °C at a heating rate of 0.4 °C / min and hold for 6 hours.

[0103] Comparative Example 10

[0104] The raw material ratio, mixing conditions and preparation process are the same as those in Example 3, except that: the steps in step (d) are: cooling to 180°C under the atmosphere with a muffle furnace pressure of 3 Pa and a compressed air flow rate of 250 L / min, and the cooling time is 16 hours.

[0105] The silicon nitride ceramic green bodies were mass-produced according to the methods of Examples 1-6 and Comparative Examples 1-10. After debinding, the silicon nitride ceramic green bodies were sintered to obtain silicon nitride ceramic substrates. The thermal conductivity and three-point bending strength of the ceramic substrates prepared in Examples 1-6 were also tested.

[0106] Table 2 Apparent performance parameters of the silicon nitride ceramic substrates prepared by the present invention:

[0107]

[0108]

[0109] Table 3 Performance parameters of the silicon nitride ceramic substrates prepared in Examples 1-6:

[0110] Thermal conductivity (W / m*K) Three-point bending strength (MPa) Example 1 83.52 736 Example 2 85.79 725 Example 3 84.38 718 Example 4 85.69 711 Example 5 86.15 724 Example 6 85.11 721

[0111] As can be seen from Table 2 and Table 3, the ceramic substrates prepared in Examples 1-6 have excellent apparent performance, thermal conductivity and bending strength, the cracking rate is 1.7-2.9%, there is no warping deformation on the surface of the substrate, and the number of white spots on the surface of a single ceramic substrate is 0-6.

[0112] For Comparative Examples 1 - 2 and Example 3, the raw material ratios and preparation processes of the ceramic green bodies used for debinding are the same, but the process parameters during the debinding process are different. During the debinding process in Comparative Examples 1 and 2, under an atmosphere where the muffle furnace pressure is -1 to 5 Pa and the nitrogen flow rate is 200 L / min, the temperature is raised from room temperature to 650°C at a heating rate of 0.6°C / min, held for 12 hours, and then the furnace door is opened and the temperature is allowed to drop naturally. The thermal conductivity and three-point bending strength of the ceramic substrates obtained by debinding in Comparative Examples 1 and 2 meet the existing standard requirements. Comparative Examples 1 and 2 are actually existing traditional debinding methods, and after verification, Comparative Example 1 is the optimal debinding process. Comparing the ceramic substrates obtained in Comparative Examples 1 and 2 and Example 3, the thermal conductivities of the substrates obtained by the three methods are 74.23, 70.54, and 84.38 W / m*K respectively, and the three-point bending strengths are 682, 673, and 718 Mpa respectively. The thermal conductivity and three-point bending strength properties of the ceramic substrates obtained in Comparative Examples 1 and 2 are lower than those of the ceramic substrate obtained in Example 3. The crack rate of the ceramic substrate obtained in Example 3 is 1.7%, the probability of white spots appearing on the ceramic substrate during mass production is 3%, the number of white spots on the surface of the ceramic substrate with white spots is 1 - 3 per piece, and there is no warping deformation; however, the ceramic substrates obtained in Comparative Examples 1 and 2 have apparent defects. The crack rate of Comparative Example 1 is 5.4%, the warping degree is 0.8%, there are white spots on the surface of each ceramic substrate after batch sintering, and the number of white spots on the surface of the ceramic substrate is 9 - 12 per piece. The crack rate of Comparative Example 2 is 8.6%, the warping degree is 1.1%, there are white spots on the surface of each ceramic substrate after sintering, and the number of white spots on the surface of the ceramic substrate is 10 - 12 per piece. Additionally, through experimental verification, when the heating temperature in step (a) of Comparative Example 1 is changed from 650°C to 580°C, the crack rate of the obtained ceramic substrate is 12%, the warping degree is 3.8%, there are white spots on the surface of each ceramic substrate after sintering, and the number of white spots on the surface of the ceramic substrate is 18 - 20 per piece. The thermal conductivity and three-point bending strength of the ceramic substrate do not meet the standard requirements, indicating that: when debinding according to the existing method, if the debinding temperature is lower than 600°C, the appearance, thermal conductivity, and strength of the obtained ceramic substrate do not meet the standard requirements, while the debinding temperature of the present invention is lower than 600°C, being 550 - 600°C, and the appearance, thermal conductivity, and strength of the obtained ceramic substrate meet the standard requirements.

[0113] The material compositions and ratios of the silicon nitride ceramic green bodies used in Example 3 and Example 4 are the same, and there are only differences in the muffle furnace pressure during the heating process (steps a, b, c). The muffle furnace pressure in Example 3 is 3 Pa, and the muffle furnace pressure in Example 4 is 1 Pa. The apparent properties of the ceramic substrates prepared in Example 3 and Example 4 are good, and the cracking rates are 1.7% and 2.1% respectively. The probability of white spots appearing on the ceramic substrate after batch sintering according to the method of Example 3 is 3%, and the number of white spots on the surface of the ceramic substrate with white spots is 1 - 3 per piece. The probability of white spots appearing on the ceramic substrate after batch sintering according to the method of Example 4 is 5%, and the number of white spots on the surface of the ceramic substrate with white spots is 1 - 5 per piece. There is no warping deformation, indicating that the ceramic substrate prepared when the muffle furnace pressure is 1 - 3 Pa in the heating stage of the debinding process has good apparent properties. The material compositions and ratios of the silicon nitride ceramic green bodies used in Comparative Example 3 and Comparative Example 4 are the same as those in Example 3, but the muffle furnace pressures are 0 Pa and 4 Pa respectively, which are not within the preferable range of 1 - 3 Pa. The apparent properties of the prepared ceramic substrates are defective, and the cracking rate, warping rate, number of white spots, thermal conductivity, and three-point bending strength do not meet the requirements of the existing technical standards. Therefore, in the heating stage of debinding, a muffle furnace pressure of 1 - 3 Pa is preferable.

[0114] The material compositions and ratios of the silicon nitride ceramic green bodies used in Example 3 and Example 5 are the same, and only the pressure in the muffle furnace during the cooling process (step d) is different. The pressure in the muffle furnace of Example 3 is 3 Pa, and the pressure in the muffle furnace of Example 5 is 6 Pa. The apparent properties of the ceramic substrates prepared in Example 3 and Example 5 are good, and the fracture rates are 1.7% and 2.4% respectively. The probability of white spots appearing on the ceramic substrates after batch sintering according to the method of Example 3 is 3%, and the number of white spots on the surface of the ceramic substrates with white spots is 1 - 3 per piece. The probability of white spots appearing on the ceramic substrates after batch sintering according to the method of Example 5 is 6%, and the number of white spots on the surface of the ceramic substrates with white spots is 1 - 4 per piece, and there is no warping deformation, indicating that the apparent properties of the ceramic substrates prepared when the pressure in the muffle furnace is 3 - 6 Pa in the cooling stage of the debinding process are good. The material compositions and ratios of the silicon nitride ceramic green bodies used in Comparative Example 5 and Comparative Example 6 are the same as those in Example 3, but the pressures in the muffle furnace in the cooling stage of the debinding process are 2 Pa and 7 Pa respectively, which are not within the preferred range of 3 - 6 Pa. The thermal conductivities and three-point bending strengths of the ceramic substrates prepared in Comparative Example 5 and Comparative Example 6 do not meet the standard requirements, and there are also defects in appearance. Among them, the fracture rate of Comparative Example 5 is 8.4%, the warpage rate is 1.4%, and there are white spots on the surface of each ceramic substrate after sintering, and the number of white spots on the surface of the ceramic substrate is 11 - 14 per piece; the fracture rate of Comparative Example 6 is 10.2%, the warpage rate is 1.2%, and there are white spots on the surface of the sintered ceramic substrates, and the number of white spots on the surface of the ceramic substrate is 12 - 15 per piece. The fracture rates, warpage rates and the number of white spots of Comparative Example 5 and Comparative Example 6 are higher than those of Example 3. Therefore, in the cooling stage of debinding, a muffle furnace pressure of 3 - 6 Pa is preferred.

[0115] In Example 3 and Comparative Example 7, the material components and ratios of the silicon nitride ceramic green bodies used are the same, and the only difference lies in the cooling method during the cooling process (Step d). In Example 3, the method of "cooling to 170°C in an atmosphere with a muffle furnace pressure of 3 Pa and a compressed air flow rate of 250 L / min for 16 hours" is adopted, while in Comparative Example 7, "the furnace door is opened and natural cooling is carried out". The ceramic substrate prepared in Example 3 has good apparent properties, with a fracture rate of 1.7%, a probability of 3% of white spots appearing on the ceramic substrate after batch sintering, 1 - 3 white spots per piece on the surface of the ceramic substrate with white spots, and no warping deformation; the ceramic substrate prepared in Comparative Example 7 has defective apparent properties, with a fracture rate of 12%, a warping degree of 1.5%, white spots on the surface of each ceramic substrate after sintering, 15 - 19 white spots per piece on the surface of the ceramic substrate, and the apparent properties of the obtained ceramic substrate are poorer compared with Example 3. This is because, starting from 600°C when the furnace door is opened in Comparative Example 7, water vapor in the air will react with silicon nitride under the condition of a temperature above 200°C, generating a large amount of silicon dioxide, resulting in relatively large defects in the apparent properties of the prepared Comparative Example 7, and the thermal conductivity and three-point bending strength of the prepared ceramic substrate do not meet the standard requirements. Therefore, in the cooling stage of debinding, it is preferred to "cool to 170°C in an atmosphere with a muffle furnace pressure of 3 Pa and a compressed air flow rate of 250 L / min for 16 hours".

[0116] In Example 3 and Example 6, the material components and ratios of the silicon nitride ceramic green bodies used are the same, and the only difference lies in the maximum temperature during heating (Step c). In Example 3, the temperature is raised to 600°C, and in Example 6, the temperature is raised to 550°C. The thermal conductivity and three-point bending strength of the ceramic substrates prepared in Example 3 and Example 6 meet the standard requirements, and there are no defects in appearance, indicating that the heating process in Step (c) can be heated from 500°C to 550 - 600°C. Comparing the debinding processes of Example 3 and Example 6 with Comparative Example 8 and Comparative Example 9, the difference is that the maximum temperatures in the heating stage of debinding in Comparative Example 8 and Comparative Example 9 are not within the range of 550 - 600°C. The temperature in Comparative Example 8 is lower than 550°C, and the temperature in Comparative Example 9 is higher than 600°C. The ceramic substrates prepared in Comparative Example 8 and Comparative Example 9 have certain defects in appearance, and their thermal conductivity and three-point bending strength also do not meet the standard requirements. The fracture rate of Comparative Example 8 is 6.6%, the warping degree is 2.1% (not available), and there are white spots on the surface of each ceramic substrate after sintering, with 13 - 16 white spots per piece on the surface of the ceramic substrate; the fracture rate of Comparative Example 9 is 8.6%, the warping degree is 1.6%, and there are white spots on the surface of the ceramic substrate after sintering, with 12 - 14 white spots per piece on the surface of the ceramic substrate, and the apparent properties are poorer compared with Example 3 and Example 6. Therefore, the maximum temperature during the heating process of debinding is preferably 550 - 600°C.

[0117] The material composition, ratio, and debinding process of the silicon nitride ceramic green bodies used in Example 3 and Comparative Example 10 are the same. There is only a difference in the temperature before opening the furnace door during the cooling stage of step (d) in the debinding process. In Example 3, the furnace door is opened after cooling to 170 °C, while in Comparative Example 10, the furnace door is opened after cooling to 180 °C. There are certain defects in the appearance of the ceramic substrate prepared by the method of Comparative Example 10, and its thermal conductivity and three-point bending strength also do not meet the standard requirements. The cracking rate of the ceramic substrate prepared in Comparative Example 10 is 9.8%, and the warpage is 1.9%. After batch sintering, there are white dots on the surface of the ceramic substrate, and the number of white dots on the surface of the ceramic substrate is 11 - 14 per piece. Since a large amount of air carrying water vapor enters the muffle furnace after the furnace door is opened, when the temperature is above 170 °C, silicon nitride reacts with water to form silicon dioxide, resulting in defects in the appearance of the ceramic substrate; while when the temperature of opening the furnace door is lower than 170 °C, less silicon dioxide is formed on the surface of silicon nitride, so it has better apparent properties. Therefore, the temperature of opening the furnace door is preferably below 170 °C.

[0118] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A debinding process for silicon nitride ceramic green bodies, characterized in that, Including: (1) The silicon nitride green body is made by tape casting the silicon nitride raw powder. The silicon nitride green body is placed in a crucible, and a layer of boron nitride powder is coated on the surface of the green body. (2) The crucible containing the silicon nitride green body in step (1) is placed in a muffle furnace for staged debinding. The specific steps are as follows: (a) First, under the atmosphere with a muffle furnace pressure of 1 - 3 Pa and a nitrogen flow rate of 200 - 500 L / min, the temperature is raised from room temperature to 200 °C at a heating rate of 0.4 - 0.6 °C / min and held for 2 - 3 hours. (b) Under the atmosphere with a muffle furnace pressure of 1 - 3 Pa and a nitrogen flow rate of 200 - 500 L / min, the temperature is raised from 200 °C to 500 °C at a heating rate of 0.1 - 0.4 °C / min and held for 2 - 3 hours. (c) Subsequently, under the atmosphere with a muffle furnace pressure of 1 - 3 Pa and a compressed air flow rate of 100 - 400 L / min, the temperature is raised from 500 °C to 550 - 600 °C at a heating rate of 0.4 - 0.6 °C / min and held for 2 - 6 hours. (d) Under the atmosphere with a muffle furnace pressure of 3 - 6 Pa and a compressed air flow rate of 100 - 250 L / min, the temperature is lowered to 120 - 170 °C, and the cooling time is 16 - 24 hours. (e) After the cooling is completed, the furnace door is opened.

2. The debinding process of the silicon nitride ceramic green body according to claim 1, characterized in that, The tape casting of the silicon nitride green body includes the following steps: Based on the total mass percentage of the slurry, prepare raw materials of 3 - 5 wt% sintering aid, 37 - 65 wt% silicon nitride, 8 - 20 wt% binder, 1 - 6 wt% dispersant, 2 - 8 wt% plasticizer, and 10 - 25 wt% ethanol solvent. After ball milling and mixing in a nitrogen protection atmosphere, it is placed in a degassing tank for degassing to obtain a mixed slurry. The mixed slurry is formed by a doctor blade in a tape casting machine, dried, wound up, then vacuum sealed and cold isostatically pressed to obtain the silicon nitride green body.

3. The debinding process of the silicon nitride ceramic green body according to claim 2, characterized in that, The sintering aid is at least one of oxides or fluorides. The oxides are at least one of ZrO2, MgO, Yb2O3, Y2O3, Gd2O3, and the fluorides are at least one of MgF2, YbF3, YF3.

4. The debinding process of the silicon nitride ceramic green body according to claim 2, characterized in that, The binder is polyvinyl butyral.

5. The debinding process of a silicon nitride ceramic green body according to claim 2, characterized in that, The dispersant is polyvinylpyrrolidone.

6. The debinding process of the silicon nitride ceramic green body according to claim 2, wherein, The plasticizer is polyethylene glycol.

7. The debinding process of the silicon nitride ceramic green body according to claim 2, characterized in that, The particle size of the sintering aid is 1 - 5 μm, and the particle size of the silicon nitride is 0.4 - 0.7 μm.

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