Method for preparing aluminum oxide ceramic substrate through gel casting by using three-stage drying method

Abstract

The invention relates to a method for preparing an aluminum oxide ceramic substrate through gel casting by using a three-stage drying method, which effectively reduces capillary force in a water evaporation process through replacement drying of polyethylene glycol, relieves the problem of rapid shrinkage of the surface of a green body, and avoids the phenomenon of internal high stress concentration through uniform diffusion of a replacement solution; in the microwave drying stage, synchronous migration of moisture inside and outside the green body is achieved through temperature control adjustment, the dry shell effect is avoided, finally hot air drying is carried out, and the compactness and dimensional precision of the finally sintered ceramic substrate are further improved. And the replacement drying and the microwave drying are combined, so that the moisture removal rate is obviously increased. Compared with a traditional natural drying mode or a single hot air drying mode, the whole drying time of the process is shortened by 30% or above. Through a scientifically designed three-stage drying process, the problems of cracks, deformation, low drying efficiency and the like in the preparation of the gel-casting aluminum oxide ceramic substrate are comprehensively solved, and the yield and the performance of the substrate are remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of preparation technology, in particular to a method for preparing an alumina ceramic substrate by gel injection molding using a three-stage drying method. Background Art

[0002] As an advanced ceramic molding process, gel casting has been widely used in the preparation of ceramic substrates, complex structural parts and porous materials in recent years. It solidifies ceramic particles through the polymerization reaction of monomer solution, overcomes the limitations of traditional molding processes (such as pressing and extrusion molding) in complex shape parts, and can be applied to complex geometric shapes and thin-walled ceramic products. Due to the uniformity of the gel network, the particles inside the green body are evenly distributed, which helps to form a dense structure during the sintering process. It is suitable for advanced ceramics including alumina, zirconia, silicon nitride, etc. Drying is an important and complex issue because the ceramic green body shrinks, involving mass-heat coupling transfer and the green body has dimensional changes and induced stress. It has been studied for a long time. Although gel casting has excellent molding ability, during the green body drying stage, since the green body contains a lot of water, the water removal process easily induces internal stress, resulting in cracks or deformation of the green body. This problem is one of the important technical bottlenecks in the development of gel casting technology.

[0003] At present, the drying technology closely related to the preparation of alumina ceramic substrates has been studied and improved, especially for the characteristics of gel casting molded green bodies, but the cracking and deformation problems during the drying process have not been completely solved. The drying of small-particle ceramic powder green bodies has a high pressure gradient in the internal liquid due to the small pore size and low permeability, which produces high capillary stress and may cause defects such as cracks.

[0004] Currently, the most mainstream traditional drying methods include natural drying, hot air drying, microwave drying and displacement drying.

[0005] 1. Natural drying: The water removal rate is slow, and stress is easily accumulated inside the blank due to capillary force, causing cracks.

[0006] 2. Hot air drying: It can accelerate the evaporation of water, but the drying rate of the surface and the interior does not match, which often leads to surface hardening or even cracking.

[0007] 3. Microwave drying: The heating is uniform, but the power is difficult to control accurately. Under high power conditions, thermal gradients can easily induce structural stress inside and outside the green body.

[0008] 4. Replacement drying: chemical solutions (such as polyethylene glycol) are used to replace the water in the green body to reduce the damage to the green body structure caused by capillary force. However, during the replacement process, it is inevitable that the chemical solution will enter the green body, thereby introducing new impurities.

[0009] Insufficient stress relief during the drying process: When the green body is drying, water migrates to the surface through the pores and evaporates. The liquid-water interface in the pores forms a capillary force. The faster the water evaporates, the greater the capillary force, which causes strong tensile stress in the green body structure. Especially under rapid drying conditions, the capillary force is too large to be released, which is the main reason for the formation of cracks.

[0010] Poor drying uniformity: The surface moisture evaporates too quickly, and the internal moisture migrates outward slowly, resulting in surface shrinkage and hardening (dry shell effect), closure of water outlet pores, and inability to discharge internal moisture in time, forming internal and external stress differences, further aggravating crack formation and green body damage.

[0011] Limitations of microwave drying technology: Microwave drying uses the interaction between electromagnetic waves and polar molecules in the material (vibration of water molecules) to generate heat to vaporize water. Due to the uneven distribution of microwave energy in microwave equipment, the moisture content inside the green body is also uneven, and the area with high moisture content inside the green body is prone to local overheating.

[0012] Chemical replacement drying is easy to introduce impurities and has low drying efficiency: Chemical replacement drying may introduce new impurities, affecting the sintering performance of ceramics, and the replacement efficiency is low. For large-sized green bodies, the solvent replacement effect is not ideal. After the organic solvent replaces the water, its volatilization rate is closely related to the properties of the solvent. If the volatilization is too fast, it will still cause surface hardening problems, and if the volatilization is too slow, the process time will be extended.

[0013] The problems with the existing technology are mainly due to the following core reasons:

[0014] (1) Insufficient control of capillary force and drying rate: Lack of effective control of capillary force during the drying process leads to cracks and stress concentration problems.

[0015] (2) Lack of refined management of drying conditions: The uneven distribution of temperature, humidity and airflow makes it impossible to achieve overall uniformity in the drying of the green body.

[0016] (3) Single technical route: Existing technologies fail to effectively integrate the advantages of chemical replacement, hot air drying, microwave drying and other methods.

[0017] (4) Insufficient adaptability of equipment and processes: Lack of customized solutions for complex billet shapes and specific process requirements. Summary of the invention

[0018] In view of the above problems, a three-stage drying method for preparing alumina ceramic substrates by gel casting was proposed. The multi-stage drying process can take into account both efficiency and quality to achieve more uniform and efficient green body drying and avoid cracking and deformation problems.

[0019] The technical solution of the present invention is: a method for preparing an alumina ceramic substrate by gel casting using a three-stage drying method.

[0020] The following steps are involved:

[0021] Step 1: Weigh 1μm Al2O3 powder with a purity of >99.99% and small-size zirconium beads of 0.2-1mm with a mass that is 50% of the mass of the Al2O3 powder;

[0022] Step 2: preparing a premixed solution by mixing an organic monomer acrylamide, a crosslinking agent N,N'-methylenebisacrylamide, a dispersant, deionized water, and a lubricant glycerol in a ratio of 2wt%, 0.2wt%, 1wt%, 20wt%, and 2wt% to the powder;

[0023] Step 3: Add the premix prepared in step 2 and the zirconium beads weighed in step 1 to the ball mill, turn on the circulating cooling water of the ball mill to control the temperature of the ball mill to prevent the friction during ball milling from generating heat and polymerizing the monomers, add 1 / 3 of the Al2O3 powder weighed in step 1 in batches for every half an hour of stirring to mix the powders evenly to prevent the powders from agglomerating and condensing after a large amount of powder is added at one time, and ball mill at a speed of 160r / min for 16h;

[0024] Step 4: 2 hours after the ball milling in step 3, add acetylene glycol defoamer, the mass of which is 0.2% of the mass of Al2O3 powder; and assemble the injection mold at this time;

[0025] Step 5: The ball-milled slurry, whose solid content is 53 vol%, is extracted with a vacuum filter, and then added into a vacuum mixer and stirred for 30 minutes for degassing to eliminate micron-sized bubbles in the slurry;

[0026] Step 6: Add 10% initiator APS with a mass of 0.15% of the mass of Al2O3 powder and half the mass of catalyst tetramethylethylenediamine to the slurry after degassing in step 5, stir for 3 minutes at room temperature of 25°C and then inject into the mold;

[0027] Step 7: Place the mold after injection molding in step 6 into a 50°C constant temperature water bath for 15-30 minutes, and demould the green body after the monomer polymerization is completed;

[0028] Step 8: Place the substrate after demoulding in step 7 into a polyethylene glycol solution with a molecular weight of 400 and a mass fraction of 25wt% to 55wt% for displacement drying for 2 hours to relieve the internal capillary force and further harden the surface of the blank;

[0029] Step 9: Place the green body after replacement drying in step 8 into a microwave device for temperature-controlled microwave drying to further dry the moisture inside the green body. The microwave power is 119-442W. The green body surface is detected in real time. The surface temperature of the green body is controlled to be 60°C by switching the microwave device on and off. After the green body weight does not change, the green body is placed in an oven and dried with hot air at the same temperature of 60°C as microwave drying for 4 hours to ensure that the inside and outside of the green body are evenly dried.

[0030] Step 10: Debinding and sintering the ceramic body after hot air drying in step 9 to finally obtain a uniform Al2O3 ceramic substrate blank.

[0031] Furthermore, the injection molding mold in the step three includes a mold main body shell with an opening on one side and several layered steel bars inserted on both sides of the main body shell, the mold main body shell and the steel bars are both 304 stainless steel, a glass plate for layered partitions is inserted in the middle of the layered steel bars, the two glass plates and the steel bars on both sides constitute an injection molding cavity, and the thickness of each injection molding cavity is controlled with a 25% margin based on the required thickness of the substrate production.

[0032] Furthermore, the amount of initiator and catalyst added in step six needs to be adjusted according to the preparation environment temperature. When the indoor temperature is too high, a smaller amount of initiator and catalyst can be added. When the indoor temperature is low, a larger amount of initiator and catalyst can be added to overcome the effect of temperature on the monomer polymerization reaction.

[0033] Furthermore, during the displacement drying in step eight, the polyethylene glycol solution can be circulated by slightly stirring the polyethylene glycol to improve the displacement uniformity.

[0034] Furthermore, the replacement drying time is increased or decreased according to the length of the water migration distance.

[0035] A three-stage drying method for preparing an alumina ceramic substrate based on a gel casting process, wherein the alumina blank is first subjected to chemical displacement drying for a period of time, and after the chemical displacement drying relieves the internal capillary force and further hardens the surface of the blank, temperature-controlled microwave drying is performed to further dry the moisture inside the blank. After microwave drying until the weight of the blank remains substantially unchanged, hot air drying is performed to ensure that the inside and the surface of the blank are evenly dried.

[0036] Furthermore, the chemical displacement drying is carried out by placing the product in a polyethylene glycol solution with a molecular weight of 400 and a mass fraction of 25 wt% to 55 wt%.

[0037] Furthermore, the temperature-controlled microwave drying is to place the blank after displacement drying into a microwave device for temperature-controlled microwave drying, the microwave power is 119-442W, the surface of the blank is detected in real time, the surface temperature of the blank is controlled to 60°C by switching the microwave device, and the microwave is used until the weight of the blank does not change.

[0038] Furthermore, the hot air drying is performed in an oven at the same temperature as the temperature-controlled microwave drying.

[0039] The beneficial effects of the present invention are as follows: the three-stage drying method of the present invention is used for the method of preparing alumina ceramic substrates by gel injection molding. Through a scientifically designed three-stage drying process, the problems of cracks, deformation and low drying efficiency in the preparation of alumina ceramic substrates by gel injection molding are comprehensively solved, and the yield and performance of the substrates are significantly improved, providing a reliable technical guarantee for the large-scale industrial production of high-quality ceramic substrates. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a process diagram of the three-stage drying method of the present invention for preparing an alumina ceramic substrate by gel casting;

[0041] Figure 2 This is a diagram of the gel injection mold used in the method of the present invention. DETAILED DESCRIPTION

[0042] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0043] The gel casting process is a ceramic molding method based on chemical gelation reaction, which has significantly high fluidity and good particle dispersion. The core principle is to introduce chemical gelling agents (such as acrylamide and its copolymers) to induce a rapid gelation reaction in the ceramic slurry, forming a high-viscosity three-dimensional network structure in situ, so that the ceramic particles are stably and evenly dispersed in the colloid. The formed green body is uniform, and the ceramic substrate has a simple shape and suitable size, which can perfectly combine the three drying methods to achieve the unity of production quality and efficiency.

[0044] The present invention proposes a three-stage drying process for preparing alumina ceramic substrates based on gel injection molding process, wherein the alumina blank is first subjected to chemical replacement drying for a period of time, and after the chemical replacement drying is performed to relieve the capillary force of the internal part and further harden the surface of the blank, temperature-controlled microwave drying is performed to further dry the moisture inside the blank, and microwave drying is performed until the weight of the blank remains substantially unchanged, and then hot air drying is performed, and finally debinding sintering is performed. The three-stage drying method is used for the process of preparing alumina ceramic substrates by gel injection molding. Figure 1 shown.

[0045] Embodiment 1, a method for preparing an alumina substrate by gel casting process using alumina powder as raw material, comprising the following steps:

[0046] Step 1: Weigh high-purity 1μm Al2O3 powder (purity>99.99%) and small-size zirconium beads (0.2mm) with a mass of 50% of the mass of the Al2O3 powder.

[0047] Step 2: Prepare a premixed solution by mixing organic monomer acrylamide, crosslinking agent N,N'-methylenebisacrylamide, dispersant, deionized water and lubricant glycerol in the following proportions: 2wt%, 0.2wt%, 1wt%, 20wt% and 2wt% of the powder mass.

[0048] Step 3: Add the premix prepared in step 2 and the zirconium beads weighed in step 1 to the ball mill, turn on the circulating cooling water of the ball mill to control the temperature of the ball mill to prevent the friction during ball milling from generating heat and causing polymerization of the monomers. Add 1 / 3 of the Al2O3 powder weighed in step 1 in batches for ball milling every half an hour to mix the powders evenly and prevent the powders from agglomerating and condensing after a large amount of powder is added at one time. Ball mill for 16 hours at a speed of 160r / min.

[0049] Step 4: 2 hours after the ball milling in step 3, add defoamer (acetylene glycol) with a mass of 0.2% of the powder mass. At this time, assemble the injection mold. The injection mold is as follows: Figure 2 As shown, the mold main body shell with an opening on one side and several layered steel bars inserted on both sides of the main body shell are made of 304 stainless steel, and a glass plate used for layered partitions is inserted in the middle of the layered steel bars. The two glass plates and the steel bars on both sides constitute an injection mold cavity. The thickness of each injection mold cavity is controlled with a 25% margin based on the required thickness of the substrate production, because the wet blank shrinks by about 22% to the final product.

[0050] Step 5: After ball milling, the slurry with a solid content of 53 vol% is extracted with a vacuum filter, and then added to a vacuum mixer and vacuum-stirred for 30 minutes for degassing treatment to eliminate micron-sized bubbles in the slurry.

[0051] Step 6: Add initiator APS (concentration 10%) with a mass of 0.15% of the mass of Al2O3 powder and catalyst tetramethylethylenediamine with a mass of half the mass of the initiator to the slurry after degassing in step 5, and inject the mold after stirring for 3 minutes at room temperature of 25°C. Note that when the room temperature is too high, you can add less initiator and catalyst, and when the room temperature is low, you can add more initiator and catalyst. Temperature has a greater impact on the polymerization reaction of monomers.

[0052] Step 7: Place the mold after injection molding in step 6 into a 50℃ constant temperature water bath for about 15-30 minutes, and demould after the monomer polymerization is completed and the green body has a certain strength. Note that the time of monomer polymerization is significantly related to the temperature. You can touch the surface of the green body and demould it when the surface is smooth, solidified, and has a certain elasticity but is not liquid.

[0053] Step 8: Place the substrate after demoulding in step 7 into a polyethylene glycol solution with a molecular weight of 400 and a mass fraction of 25wt% for displacement drying for 2 hours to relieve the capillary force of the internal part and further harden the surface of the body. The size of the ceramic substrate blank produced in this embodiment is 50*50*0.5 (length*width*thickness). The displacement drying time can be reduced for blanks smaller than this size because the water migration path is short. The polyethylene glycol concentration and displacement time can be appropriately increased for blanks larger than this size or high-density blanks that have undergone a certain drying process. The polyethylene glycol solution can be circulated by gently stirring the polyethylene glycol to improve the uniformity of the displacement.

[0054] Step nine: Place the green body obtained after replacement drying in step eight into a microwave device for temperature-controlled microwave drying to further dry the moisture inside the green body. The microwave power is 119 W. The green body surface is monitored in real time. The surface temperature of the green body is controlled to be 60°C by switching the microwave device on and off. Microwave until the weight of the green body does not change. Then, place the green body in an oven and dry it with hot air at the same temperature of 60°C as microwave drying for 4 hours to ensure that the inside and outside of the green body are evenly dried.

[0055] Step 10: Debinding and sintering the ceramic body after hot air drying in step 9 to finally obtain a uniform Al2O3 ceramic substrate blank.

[0056] Embodiment 2, a method for preparing an alumina substrate by gel casting process using alumina powder as raw material, comprising the following steps:

[0057] Step 1: Weigh high-purity 1μm Al2O3 powder (purity>99.99%) and small-size zirconium beads (0.2mm) with a mass of 50% of the mass of the Al2O3 powder.

[0058] Step 2: Prepare a premixed solution by mixing organic monomer acrylamide, crosslinking agent N,N'-methylenebisacrylamide, dispersant, deionized water and lubricant glycerol in the following proportions: 2wt%, 0.2wt%, 1wt%, 20wt% and 2wt% of the powder mass.

[0059] Step 3: Add the premix prepared in step 2 and the zirconium beads weighed in step 1 to the ball mill, turn on the circulating cooling water of the ball mill to control the temperature of the ball mill to prevent the friction during ball milling from generating heat and causing polymerization of the monomers. Add 1 / 3 of the Al2O3 powder weighed in step 1 in batches for ball milling every half an hour to mix the powders evenly and prevent the powders from agglomerating and condensing after a large amount of powder is added at one time. Ball mill for 16 hours at a speed of 160r / min.

[0060] Step 4: After the ball milling in step 3, add defoamer (acetylene glycol) at a mass of 0.2% of the powder mass. At this time, assemble the injection mold. The injection mold is as follows: Figure 2 shown.

[0061] Step 5: After ball milling, the slurry with a solid content of 53 vol% is extracted with a vacuum filter, and then added to a vacuum mixer and vacuum-stirred for 30 minutes for degassing treatment to eliminate micron-sized bubbles in the slurry.

[0062] Step 6: Add initiator APS (concentration 10%) with a mass of 0.15% of the mass of Al2O3 powder and catalyst tetramethylethylenediamine with a mass of half the mass of the initiator to the slurry after degassing in step 5, and inject the mold after stirring for 3 minutes at room temperature of 25°C. Note that when the room temperature is too high, you can add less initiator and catalyst, and when the room temperature is low, you can add more initiator and catalyst. Temperature has a greater impact on the polymerization reaction of monomers.

[0063] Step 7: Place the mold after injection molding in step 6 into a 50℃ constant temperature water bath for about 15-30 minutes, and demould after the monomer polymerization is completed and the green body has a certain strength. Note that the time of monomer polymerization is significantly related to the temperature. You can touch the surface of the green body and demould it when the surface is smooth, solidified, and has a certain elasticity but is not liquid.

[0064] Step 8: Place the substrate demolded in step 7 into a polyethylene glycol solution with a molecular weight of 400 and a mass fraction of 40wt% for displacement drying for 2 hours to relieve the internal capillary force and further harden the surface of the blank. Small-sized blanks can reduce the displacement drying time because of the short water migration path. Large-sized blanks or high-density blanks that have undergone a certain drying process can appropriately increase the polyethylene glycol concentration and displacement time. The polyethylene glycol solution can be circulated by gently stirring the polyethylene glycol to improve the uniformity of the displacement.

[0065] Step nine: Place the green body obtained after replacement drying in step eight into a microwave device for temperature-controlled microwave drying to further dry the moisture inside the green body. The microwave power is 259W. The green body surface is monitored in real time. The surface temperature of the green body is controlled to be 60°C by switching the microwave device on and off. Microwave until the weight of the green body does not change. Place the green body in an oven and dry it with hot air at the same temperature of 60°C as microwave drying for 4 hours to ensure that the inside and outside of the green body are evenly dried.

[0066] Step 10: After debinding and sintering the ceramic body after hot air drying in step 9, a uniform Al2O3 ceramic substrate blank is finally obtained.

[0067] Embodiment 3, a method for preparing an alumina substrate by gel casting process using alumina powder as raw material, comprising the following steps:

[0068] Step 1: Weigh high-purity 1μm Al2O3 powder (purity>99.99%) and small-size zirconium beads (0.2mm) with a mass of 50% of the mass of the Al2O3 powder.

[0069] Step 2: Prepare a premixed solution by mixing organic monomer acrylamide, crosslinking agent N,N'-methylenebisacrylamide, dispersant, deionized water and lubricant glycerol in the following proportions: 2wt%, 0.2wt%, 1wt%, 20wt% and 2wt% of the powder mass.

[0070] Step 3: Add the premix prepared in step 2 and the zirconium beads weighed in step 1 to the ball mill, turn on the circulating cooling water of the ball mill to control the temperature of the ball mill to prevent the friction during ball milling from generating heat and causing polymerization of the monomers. Add 1 / 3 of the Al2O3 powder weighed in step 1 in batches for ball milling every half an hour to mix the powders evenly and prevent the powders from agglomerating and condensing after a large amount of powder is added at one time. Ball mill for 16 hours at a speed of 160r / min.

[0071] Step 4: After the ball milling in step 3, add defoamer (acetylene glycol) at a mass of 0.2% of the powder mass. At this time, assemble the injection mold. The injection mold is as follows: Figure 2 shown.

[0072] Step 5: After ball milling, the slurry with a solid content of 53 vol% is extracted with a vacuum filter, and then added to a vacuum mixer and vacuum-stirred for 30 minutes for degassing treatment to eliminate micron-sized bubbles in the slurry.

[0073] Step 6: Add initiator APS (concentration 10%) with a mass of 0.15% of the mass of Al2O3 powder and catalyst tetramethylethylenediamine with a mass of half the mass of the initiator to the slurry after degassing in step 5, and inject the mold after stirring for 3 minutes at room temperature of 25°C. Note that when the room temperature is too high, you can add less initiator and catalyst, and when the room temperature is low, you can add more initiator and catalyst. Temperature has a greater impact on the polymerization reaction of monomers.

[0074] Step 7: Place the mold after injection molding in step 6 into a 50℃ constant temperature water bath for about 15-30 minutes, and demould after the monomer polymerization is completed and the green body has a certain strength. Note that the time of monomer polymerization is significantly related to the temperature. You can touch the surface of the green body and demould it when the surface is smooth, solidified, and has a certain elasticity but is not liquid.

[0075] Step 8: Place the substrate demolded in step 7 into a polyethylene glycol solution with a molecular weight of 400 and a mass fraction of 55wt% for displacement drying for 2 hours to relieve the internal capillary force and further harden the surface of the blank. Small-sized blanks can reduce the displacement drying time because of the short water migration distance. Large-sized blanks or high-density blanks that have undergone a certain drying process can appropriately increase the polyethylene glycol concentration and displacement time. The polyethylene glycol solution can be circulated by gently stirring the polyethylene glycol to improve the uniformity of the displacement.

[0076] Step nine: Place the green body obtained after replacement drying in step eight into a microwave device for temperature-controlled microwave drying to further dry the moisture inside the green body. The microwave power is 462W. The green body surface is monitored in real time. The surface temperature of the green body is controlled to be 60°C by switching the microwave device on and off. Microwave until the weight of the green body does not change. Then, place the green body in an oven and dry it with hot air at the same temperature of 60°C as microwave drying for 4 hours to ensure that the inside and outside of the green body are evenly dried.

[0077] Step 10: After debinding and sintering the ceramic body after hot air drying in step 9, a uniform Al2O3 ceramic substrate blank is finally obtained.

[0078] Step 6: The viscosity of the slurry after adding the initiator and the catalyst and stirring was measured by a rotary digital viscometer before injection molding. The density of the final Al2O3 ceramic blank sample was measured by the Archimedes drainage method for 10 samples and the average value was taken. The three-point bending strength was measured for 10 samples and the average value was taken. The following table shows the test data of the three embodiments:

[0079] <![CDATA[Slurry viscosity (mpa·s -1 )]]> <![CDATA[Density of the sintered sample (g / cm 3 )]]> Three-point bending strength (Mpa) Example 1 141.6 3.957 323.30 Example 2 141.4 3.960 341.70 Example 3 148.9 3.955 338.80

[0080] The three-stage drying process proposed in the present invention is used for preparing alumina ceramic substrates by gel casting. By organically combining polyethylene glycol (PEG) displacement drying, temperature-controlled microwave drying and hot air drying, the efficiency of the drying process and the quality of the green body are significantly improved, and the technical bottlenecks such as drying cracks, warping and lack of uniformity in the traditional process are solved, achieving the following technical effects:

[0081] 1. Significantly reduce drying cracks and deformation rate

[0082] The first stage of polyethylene glycol displacement drying effectively reduces the capillary force during the evaporation of water. Displacement drying alleviates the rapid shrinkage problem of the green body surface and avoids the internal high stress concentration phenomenon through the uniform diffusion of the displacement solution.

[0083] 2. Improve drying uniformity

[0084] In the microwave drying stage, the temperature is controlled (microwave power 119-442W, surface temperature is controlled at 60℃) to achieve the synchronous migration of moisture inside and outside the green body, avoiding the occurrence of dry shell effect, and finally perform hot air drying. The density and dimensional accuracy of the ceramic substrate after the final sintering are further improved.

[0085] 3. Shorten drying time and improve production efficiency

[0086] The combination of displacement drying and microwave drying in the process of the present invention significantly accelerates the rate of water removal. Compared with traditional natural drying or single hot air drying, the overall drying time of this process is shortened by more than 30%. Taking a 0.5mm thick alumina substrate as an example, the total drying time is reduced from 24 hours in the traditional method to less than 16 hours, meeting the needs of industrial production.

[0087] The above-mentioned embodiments only express the specific implementation of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A method for preparing an alumina ceramic substrate by gel casting using a three-stage drying method, characterized in that: The following steps are involved: Step 1: Weigh 1μm Al2O3 powder with a purity of >99.99% and small-size zirconium beads of 0.2-1mm with a mass that is 50% of the mass of the Al2O3 powder; Step 2: preparing a premixed solution by mixing an organic monomer acrylamide, a crosslinking agent N,N'-methylenebisacrylamide, a dispersant, deionized water, and a lubricant glycerol in a ratio of 2wt%, 0.2wt%, 1wt%, 20wt%, and 2wt% to the powder; Step 3: Add the premix prepared in step 2 and the zirconium beads weighed in step 1 to the ball mill, turn on the circulating cooling water of the ball mill to control the temperature of the ball mill to prevent the friction during ball milling from generating heat and polymerizing the monomers, add 1 / 3 of the Al2O3 powder weighed in step 1 in batches for every half an hour of stirring to mix the powders evenly to prevent the powders from agglomerating and condensing after a large amount of powder is added at one time, and ball mill at a speed of 160r / min for 16h; Step 4: 2 hours after the ball milling in step 3, add acetylene glycol defoamer, the mass of which is 0.2% of the mass of Al2O3 powder; and assemble the injection mold at this time; Step 5: The ball-milled slurry, whose solid content is 53 vol%, is extracted with a vacuum filter, and then added into a vacuum mixer and stirred for 30 minutes for degassing to eliminate micron-sized bubbles in the slurry; Step 6: Add 10% initiator APS with a mass of 0.15% of the mass of Al2O3 powder and half the mass of catalyst tetramethylethylenediamine to the slurry after degassing in step 5, stir for 3 minutes at room temperature of 25°C and then inject into the mold; Step 7: Place the mold after injection molding in step 6 into a 50°C constant temperature water bath for 15-30 minutes, and demould the green body after the monomer polymerization is completed; Step 8: Place the substrate after demoulding in step 7 into a polyethylene glycol solution with a molecular weight of 400 and a mass fraction of 25wt% to 55wt% for displacement drying for 2 hours to relieve the internal capillary force and further harden the surface of the blank; Step 9: Place the green body after replacement drying in step 8 into a microwave device for temperature-controlled microwave drying to further dry the moisture inside the green body. The microwave power is 119-442W. The green body surface is detected in real time. The surface temperature of the green body is controlled to be 60°C by switching the microwave device on and off. After the green body weight does not change, the green body is placed in an oven and dried with hot air at the same temperature of 60°C as microwave drying for 4 hours to ensure that the inside and outside of the green body are evenly dried. Step 10: Debinding and sintering the ceramic body after hot air drying in step 9 to finally obtain a uniform Al2O3 ceramic substrate blank.

2. The method for preparing an alumina ceramic substrate by gel casting using the three-stage drying method according to claim 1, characterized in that: The injection molding mold in the step three includes a mold main body shell with an opening on one side and several layered steel bars inserted on both sides of the main body shell. The mold main body shell and the steel bars are both made of 304 stainless steel. A glass plate for layered partitions is inserted in the middle of the layered steel bars. The two glass plates and the steel bars on both sides constitute an injection molding cavity. The thickness of each injection molding cavity is controlled with a 25% margin based on the required thickness of the substrate production.

3. The method for preparing an alumina ceramic substrate by gel casting using the three-stage drying method according to claim 1, characterized in that: The amount of initiator and catalyst added in step six needs to be adjusted according to the preparation environment temperature. When the indoor temperature is too high, a smaller amount of initiator and catalyst can be added. When the indoor temperature is low, an appropriate amount of initiator and catalyst can be added to overcome the effect of temperature on the monomer polymerization reaction.

4. The method for preparing an alumina ceramic substrate by gel casting using the three-stage drying method according to claim 1, characterized in that: When the displacement drying in step eight is performed, the polyethylene glycol solution can be circulated by slightly stirring the polyethylene glycol to improve the uniformity of the displacement.

5. The method for preparing an alumina ceramic substrate by gel casting using the three-stage drying method according to claim 4, characterized in that: The replacement drying time is increased or decreased according to the length of the water migration distance.

6. A three-stage drying method for preparing an alumina ceramic substrate based on a gel casting process, characterized in that: The alumina blank is first subjected to chemical replacement drying for a period of time. After the internal capillary force is relieved and the surface of the blank is further hardened, temperature-controlled microwave drying is performed to further dry the moisture inside the blank. After microwave drying until the weight of the blank remains basically unchanged, hot air drying is performed to ensure that the inside and outside of the blank are evenly dried.

7. The three-stage drying method for preparing an alumina ceramic substrate based on a gel casting process according to claim 6, characterized in that: The chemical displacement drying is carried out by placing the mixture in a polyethylene glycol solution with a molecular weight of 400 and a mass fraction of 25wt% to 55wt%.

8. The three-stage drying method for preparing an alumina ceramic substrate based on a gel casting process according to claim 6 or 7, characterized in that: The temperature-controlled microwave drying is to place the green body after displacement drying into a microwave device for temperature-controlled microwave drying, the microwave power is 119-442W, the green body surface is detected in real time, the green body surface temperature is controlled to be 60°C by switching the microwave device, and the microwave is used until the green body weight does not change.

9. The three-stage drying method for preparing an alumina ceramic substrate based on a gel casting process according to claim 8, characterized in that: The hot air drying is performed by placing the product in an oven and performing hot air drying at the same temperature as the temperature-controlled microwave drying.

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