A gel-bonding method for pressureless sintering of silicon carbide

Abstract

The present application belongs to the technical field of processing silicon carbide ceramic material, and particularly relates to a gel connection method for pressureless sintering silicon carbide. The gel connection method for pressureless sintering silicon carbide uses a first mold and a second mold to prepare a silicon carbide product through pouring connection and pressureless sintering. According to the slurry solidification shrinkage-time curve, the method of the present application more scientifically and reasonably performs gel connection, uses gel injection molding to complete connection and re-induction during the reaction period, and eliminates the oxygen block polymerization layer. Meanwhile, the drying and pressureless sintering process of two-zone temperature control is adopted, according to the characteristics that the heat flow is always upward, a certain hysteresis is set for the upper zone temperature control than the lower zone, temperature uniformity is realized, stress is released, the shrinkage of each zone is consistent, the connection layer is uniform, the finished product is defect-free, and the method has the characteristics of easy operation and simple process. The method of the present application has high efficiency and simple operation, and has great application prospect in the connection of large-size silicon carbide ceramic parts.

Description

Technical Field

[0001] This invention belongs to the field of silicon carbide ceramic material processing technology, specifically the field of gel casting processing technology, and particularly relates to a gel bonding method for pressureless sintering of silicon carbide. Background Technology

[0002] Compared to reaction-bonded silicon carbide (RBSiC), pressureless sintered silicon carbide (SSiC) has higher operating temperature, stronger resistance to acid and alkali corrosion, high resistivity and antistatic properties, and higher purity without free Si. It is more suitable for processing steps such as photolithography, etching, deposition, diffusion and polishing in integrated circuit semiconductor equipment, and is the most promising sintering method in SiC ceramic preparation.

[0003] Gel casting is a near-net-shape forming technology that is becoming increasingly sophisticated. For precision ceramic components, many complex internal or hollow structures cannot be machined. Using gel bonding to connect and combine various SiC structures during the material forming stage is an effective method. However, gel-formed SiC preforms shrink during drying and approximately 0.5% during slurry curing. When preparing complex-shaped, high-precision ceramic structural parts through pressureless sintering, the uniformity of shrinkage in the bonding layer and the consistency of deformation in the base material are particularly important. In processes involving temperature changes, such as drying, debinding, and sintering, improper process control can easily lead to defects such as cracking and porosity in the bonding area.

[0004] Chinese patent CN104924412A provides a method for bonding by re-gelling the green blank after moisturizing. This moisturizing method addresses the shrinkage of the silicon carbide green blank during drying, but does not consider the deformation during the slurry curing stage. More importantly, it is only applicable to reaction sintering, a sintering method with low net dimensions and internal stress. Silicon carbide green blanks experience a relatively large shrinkage of 15% to 20% during pressureless sintering, which significantly affects the precision of ceramic structural parts. At the same time, the effect of small internal stresses is very obvious on a macroscopic scale, and it is impossible to effectively judge whether the internal stress has been truly eliminated. Therefore, this method is not very applicable.

[0005] Based on this, this application explores a more scientific and refined gel bonding method and pressureless sintering process to ensure that the bonding layer of the sintered green body is free of defects and stress, thereby solving the technical problems existing in the prior art. Summary of the Invention

[0006] The purpose of this invention is to address the technical problems existing in the gel casting green body connection method and pressureless sintering method in the prior art, and to provide a gel bonding method for pressureless sintering silicon carbide. Based on the slurry curing shrinkage-time curve, gel bonding is carried out more scientifically and rationally. The gel casting completes the bonding during the reaction period and induces it again, eliminating the oxygen inhibition layer. At the same time, a two-zone temperature-controlled drying and pressureless sintering process is adopted. Based on the characteristic that the heat flow is always upward, the temperature control of the upper zone is set to have a certain lag compared with the lower zone, so as to achieve temperature uniformity and release stress, so that the shrinkage of each zone is consistent and the bonding layer is uniform, resulting in a defect-free finished product. It is easy to operate and the process is simple.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A gel bonding method for pressureless sintered silicon carbide involves preparing silicon carbide products by casting and pressureless sintering using a first mold and a second mold. In use, a first ceramic blank is first prepared in the first mold, demolded, and then the second mold is fixed to one end of the first ceramic blank. A second ceramic blank is then prepared in the second mold, followed by gel bonding through drying, degumming, and pressureless sintering processes.

[0009] The method includes the following steps:

[0010] S1: Set up the first mold, apply the initiator solution, use the first mold to solidify the slurry using the gel casting method to prepare the first ceramic green body, demold, and perform surface treatment;

[0011] S2: Set up a second mold, use the second mold to prepare a second ceramic blank at one end of the first ceramic blank by using a gel casting method and solidification, demold to obtain a ceramic connected blank;

[0012] S3: The ceramic connected green body obtained in step S2 is dried, degummed, and sintered without pressure to obtain the sintered finished product.

[0013] Specifically, the ceramic refers to SiC.

[0014] Specifically, in step S1, the matrix raw material and the gel system raw material are mixed to prepare a slurry, which is then injected into the first mold to prepare the first ceramic blank using the gel casting method.

[0015] Specifically, the matrix material is surface-modified silicon carbide micro powder with a particle size of submicron; the gel system used is a water-based gel system, which includes crosslinking system components, polymerization inhibitors, additives, dispersants and other reagents.

[0016] Furthermore, in the crosslinking system components, the monomer is acrylamide, the crosslinking agent is methylene bisacrylamide; the polymerization inhibitor is one or both of catechol and phenothiazine; the additive is at least one of carbon black, boron nitride, boron carbide, alumina, yttrium oxide, and titanium dioxide; the dispersant is at least two of polyethylene glycol, n-butanol, and tetramethylammonium hydroxide; and the other reagents are at least three of urea, melamine, dimethylformamide, glycerol, and isopropanol.

[0017] Preferably, the slurry comprises the following raw materials in the following percentages by mass: 8-10% pure water, 5-7% crosslinking system, 0.18-0.36% polymerization inhibitor, 0.1-0.3% urea, 0.5-1% boron carbide, 0.05-0.1% melamine, 0.4-0.6% n-butanol, 0.8-1% glycerol, 1.2-1.4% tetramethylammonium hydroxide, with the balance being surface-modified silicon carbide micro powder.

[0018] Preferably, the volume solids content of the slurry is 45-50%.

[0019] Preferably, in the crosslinking system, the mass ratio of acrylamide to methylene bisacrylamide is (8~10):1.

[0020] Preferably, the mass ratio of catechol to phenothiazine in the polymerization inhibitor is (4~5):1.

[0021] Specifically, in step S1, before injecting the slurry into the first mold, the initiator solution coated on the inner surface of the first mold is at least one of hydrogen peroxide solution, ammonium persulfate solution, and benzoyl peroxide solution; the initiator solution includes raw materials in the following mass percentages: 10-20% initiator, 10-20% tetramethylammonium hydroxide, and 70-78% ice water, the role of which is to neutralize the exothermic reaction of the initiator during dissolution.

[0022] Specifically, during demolding in step S1, the slurry shrinkage-curing-time curve is measured, and demolding is performed at the moment corresponding to the inflection point of the shrinkage rate in the slurry shrinkage-curing-time curve, at which point the slurry is cured.

[0023] Preferably, in step S1, the inflection point time is obtained from the slurry shrinkage-curing-time curve based on the pre-determined slurry curing time; the curing temperature is 16~30℃, the inflection point time is 17~45min, and the inflection point time is the time when the slurry surface has a certain strength but the core has not yet shrunk significantly; that is, the curing time in step S1 is 17~45min.

[0024] Preferably, in step S1, the release agent used during demolding is syrup.

[0025] Specifically, in step S1, the surface treatment is rinsing, which is used to clean the oxygen inhibition layer. In step S1, 1~2mm of the oxygen inhibition layer is rinsed away.

[0026] Specifically, in step S2, before casting, an initiator solution is applied to the inner surface of the second mold; the initiator solution is at least one of hydrogen peroxide solution, ammonium persulfate solution, and benzoyl peroxide solution; the initiator solution includes raw materials in the following mass percentages: 10-20% initiator, 10-20% tetramethylammonium hydroxide, and 70-78% ice water, the role of which is to neutralize the heat released during the dissolution of the initiator.

[0027] Specifically, the curing time in step S2 is 35~90 min, and the curing temperature is 16~30℃.

[0028] Specifically, the total amount of initiator solution used in steps S1 and S2 is 0.5% to 1% of the total mass of the slurry.

[0029] Specifically, the drying and pressureless sintering in step S3 both require a two-zone temperature control method, i.e., the temperature of the upper zone corresponds to the temperature of the first ceramic blank, and the temperature of the lower zone corresponds to the temperature of the second ceramic blank. It is preset that the cooling stage of the upper zone is controlled with a certain lag compared to the lower zone to ensure the uniformity of the bonding layer and low internal stress. The first ceramic blank and the second ceramic blank do not deform and interfere with each other, so that the resulting ceramic bonding blank shrinks evenly.

[0030] Specifically, the drying process in step S3 is as follows: the upper and lower zones are simultaneously heated to a first preset temperature of 100~120℃ and held for 0.5~3h; then the lower zone begins to cool at a fixed cooling rate of 5~20℃ / h until room temperature, while the upper zone continues to be held for 0.1~0.5h, and then the upper zone begins to cool at the same cooling rate of 5~20℃ / h until room temperature.

[0031] Specifically, the degumming process in step S3 is as follows: first, the temperature is raised to 320-350℃ at a rate of 5-20℃ / h and held for 1-2 hours, then the temperature is controlled in the above drying process, and finally the temperature is reduced to room temperature (in addition, in actual production, the temperature can be raised to 320-350℃ and held for 1-2 hours, and then directly cooled to room temperature with the furnace).

[0032] Specifically, the pressureless sintering process in step S3 is as follows: The upper and lower zones are simultaneously heated to a first preset temperature of 1950~2200℃ and held for 0.5~2 hours; then the lower zone begins to cool at a fixed cooling rate of 20~200℃ / h to a second preset temperature of 1600~1900℃, while the upper zone is held for 0.1~1 hours; then the upper zone begins to cool at the same cooling rate of 20~200℃ / h to the second preset temperature of 1600~1900℃, while both zones are held for 0.5~2 hours simultaneously; then… The lower zone begins to cool at a fixed cooling rate of 20~200℃ / h to the third preset temperature of 1100~1300℃, while the upper zone is held at that temperature for 0.1~1h. Then the upper zone begins to cool at the same cooling rate of 10~20℃ / h to the third preset temperature of 1100~1300℃, and both the upper and lower zones are held at that temperature for 0.1~0.5h. Then the lower zone begins to cool at a fixed cooling rate until room temperature, while the upper zone is held at that temperature for 0.1~1h. Then the upper zone begins to cool at the same cooling rate until room temperature.

[0033] Alternatively, the present invention also employs an integrated degumming and pressureless sintering method for sintering, specifically as follows: After drying in step S3, both upper and lower zones are simultaneously heated to a first preset temperature of 600~700℃ and held for 0.5~2h; then, both upper and lower zones are simultaneously heated to a second preset temperature of 1950~2200℃ and held for 0.5~2h; then, the lower zone begins to cool at a fixed cooling rate of 20~200℃ / h to a third preset temperature of 1600~1900℃, while the upper zone is held for 0.1~1h; then, the upper zone begins to cool at the same cooling rate of 20~200℃ / h to the third preset temperature. The temperature is set at 1600~1900℃, and both the upper and lower zones are held at the same temperature for 0.5~2h. Then, the lower zone is cooled at a fixed cooling rate of 20~200℃ / h to the fourth preset temperature of 1100~1300℃, while the upper zone is held at the same temperature for 0.1~1h. Then, the upper zone is cooled at the same cooling rate of 20~200℃ / h to the fourth preset temperature of 1100~1300℃, and both the upper and lower zones are held at the same temperature for 0.1~0.5h. Then, the lower zone is cooled at a fixed cooling rate until room temperature, while the upper zone is held at the same temperature for 0.1~1h. Then, the upper zone is cooled at the same cooling rate until room temperature.

[0034] Furthermore, based on a general inventive concept, the present invention also provides a silicon carbide product prepared by the above method.

[0035] Specifically, the silicon carbide product is a layered ceramic structure or a precision component containing a complex hollow structure, such as an anti-static vacuum chuck for semiconductor testing equipment or a high-purity SiC ceramic precision component, used to adsorb, transfer, and fix Si wafers.

[0036] Compared with the prior art, the beneficial effects of the present invention are:

[0037] 1. The gel bonding method for pressureless sintered silicon carbide of the present invention, based on the curing shrinkage-time curve of the slurry, performs gel bonding in a more scientific and reasonable manner. It utilizes gel casting to complete the bonding during the reaction period and induces it again, eliminating the oxygen-inhibiting layer. At the same time, it adopts a two-zone temperature-controlled drying and pressureless sintering process. Based on the characteristic that the heat flow is always upward, the upper zone temperature control is set to produce a certain lag compared with the lower zone, so as to achieve temperature uniformity and release stress, making the shrinkage of each zone consistent and the bonding layer uniform, resulting in a defect-free finished product. It is also easy to operate and has a simple process.

[0038] 2. The silicon carbide product prepared by this invention has high bonding strength; the method of this invention is highly efficient and simple to operate, and has great application prospects in the connection of large-size silicon carbide ceramic parts.

[0039] 3. The process method of the present invention is environmentally friendly and easy to promote and apply in the field of silicon carbide ceramic material processing. Attached Figure Description

[0040] Figure 1 SEM images of the attachment area of ​​a silicon carbide preform bonded by a gel method in the prior art;

[0041] Figure 2 This is a SEM image of the connection area after pressureless sintering of the connector according to the method of Example 1;

[0042] Figure 3 This is a schematic diagram of the drying process and pressureless sintering process curves in Example 1;

[0043] Figure 4 This is a schematic diagram of the S-type curing shrinkage rate (temperature)-time curve in steps S1 and S2 of Example 1. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention.

[0045] To make the description of this disclosure more detailed and complete, illustrative descriptions of embodiments and specific examples of the present invention are provided below; however, these are not the only forms of implementing or utilizing the specific examples of the present invention. The embodiments cover features of multiple specific examples and methods and steps for constructing and operating these specific examples, and their order. However, other specific examples may also be used to achieve the same or equivalent functions and order of steps.

[0046] Unless otherwise specified, all instruments and equipment used in the following examples are commercially available conventional instruments and equipment; all other reagents and materials used are commercially available conventional reagents and materials.

[0047] Example 1

[0048] Example 1 provides a gel bonding method for pressureless sintering of silicon carbide. The product is prepared using a first mold and a second mold through casting bonding and pressureless sintering. The first mold is the lower mold with an upward opening, and the second mold is the upper mold with a downward opening. In use, a first ceramic blank is first prepared in the first mold, demolded, and then the second mold is fixed to the top of the first ceramic blank. A second ceramic blank is then prepared in the second mold, followed by drying, debonding, and pressureless sintering for gel bonding. In this example, the ceramic refers to SiC. The method in this example also prepares an anti-static vacuum chuck for a semiconductor testing device. The vacuum chuck is made of silicon carbide and contains a complex hollow structure.

[0049] The specific steps of the method are as follows:

[0050] S1: Set up the first mold, apply the initiator solution, use the first mold to prepare the first ceramic blank by gel casting method, and measure the slurry shrinkage-curing-time curve. Demold at the moment corresponding to the inflection point of the shrinkage rate in the slurry shrinkage-curing-time curve. At this time, the slurry is cured to obtain the first ceramic blank, and then perform surface treatment.

[0051] In step S1, the matrix raw material and the gel system raw material are mixed to prepare a slurry, which is then injected into the first mold to prepare the first ceramic blank using the gel casting method.

[0052] The matrix raw material is surface-modified XF series silicon carbide micro powder from Shandong Xinfang Group Co., Ltd., with a particle size of submicron. The gel system used is a water-based gel system, which includes crosslinking system components, crosslinking agent, polymerization inhibitor, additives, dispersant and other reagents. The monomer in the crosslinking system components is acrylamide, and the crosslinking agent is methylene bisacrylamide.

[0053] Specifically, the slurry comprises 9.5% pure water, 6% acrylamide, 0.6% methylenebisacrylamide, 0.3% catechol, 0.06% phenothiazine, 0.3% urea, 1% boron carbide, 0.05% melamine, 0.6% n-butanol, 0.8% glycerol, and 1.4% tetramethylammonium hydroxide, with the balance being surface-modified silicon carbide micropowder; the volume solids content of the slurry is 50%.

[0054] In step S1, before the slurry is injected into the first mold, the initiator solution coated on the inner surface of the first mold is an ammonium persulfate solution, and its formula is (mass ratio) 5% ammonium persulfate, 15% tetramethylammonium hydroxide, and 80% ice water;

[0055] In step S1, based on the actual pre-tested slurry shrinkage-curing-time curve, the curing-time curve is an S-shaped curing curve, and the curing temperature measured under this formula is 24℃, and the time corresponding to the inflection point is 38min, that is, the curing time in step S1 is 38min.

[0056] In step S1, the release agent used during demolding is syrup;

[0057] In step S1, the surface treatment is rinsing, which is used to clean the oxygen inhibition layer. In step S1, about 2 mm of the oxygen inhibition layer is rinsed away.

[0058] S2: Set up a second mold, use the second mold to prepare a second ceramic blank on the top of the first ceramic blank using the gel casting method and solidification, demold to obtain a ceramic connected blank;

[0059] In step S2, before casting, an ammonium persulfate solution is coated on the inner surface of the second mold as an initiator. The formula is (by mass ratio) 5% ammonium persulfate, 15% tetramethylammonium hydroxide, and 80% ice water.

[0060] The preparation start time in step S2 is 38 minutes (i.e., the time when the slurry solidifies in step S1); the solidification time in step S2 is 80 minutes, and the solidification temperature is 25°C; wherein, the total amount of initiator solution used in steps S1 and S2 is 0.5% of the total mass of the slurry;

[0061] S3: The ceramic connecting green body obtained in step S2 is dried, degummed, sintered without pressure, cooled and then precision milled to obtain the final product (i.e., vacuum chuck product).

[0062] In step S3, both drying and pressureless sintering require a two-zone temperature control method, where the upper zone temperature corresponds to the temperature of the first ceramic blank and the lower zone temperature corresponds to the temperature of the second ceramic blank. The upper zone cooling stage is pre-set to have a certain lag compared to the lower zone to ensure the uniformity of the bonding layer and low internal stress. The first and second ceramic blanks do not deform or interfere with each other, resulting in uniform shrinkage of the obtained ceramic bonding blank.

[0063] The drying process in step S3 is as follows: the upper and lower zones are simultaneously heated to the first preset temperature of 105℃ and kept at that temperature for 2 hours; then the lower zone begins to cool at a fixed cooling rate of 20℃ / h until it reaches room temperature, while the upper zone continues to be kept at that temperature for 0.3 hours, and then the upper zone begins to cool at the same cooling rate of 20℃ / h until it reaches room temperature.

[0064] In this embodiment, the degumming process in step S3 is as follows: first, the temperature is raised to 350°C at a rate of 20°C / h and held for 2 hours, then the temperature control method in the above-mentioned drying process is used, and finally the temperature is reduced to room temperature (in addition, in actual production, the method of directly cooling to room temperature with the furnace after raising the temperature to 350°C and holding for 2 hours can also be used).

[0065] The pressureless sintering process in step S3 is as follows: the upper and lower zones are simultaneously heated to the first preset temperature of 2100℃ and held for 2 hours; then the lower zone begins to cool at a fixed cooling rate of 20℃ / h to the second preset temperature of 1800℃, while the upper zone is held for 0.5 hours; then the upper zone begins to cool at the same cooling rate of 20℃ / h to the second preset temperature of 1800℃, while the upper and lower zones are held for 0.5 hours; then the lower zone begins to cool at a fixed cooling rate of 20℃ / h to the third preset temperature of 1200℃, while the upper zone is held for 0.5 hours; then the upper zone begins to cool at the same cooling rate of 20℃ / h to the third preset temperature of 1200℃, while the upper and lower zones are held for 0.5 hours; then the lower zone begins to cool at a fixed cooling rate until room temperature, while the upper zone is held for 0.5 hours; then the upper zone begins to cool at the same cooling rate until room temperature.

[0066] Performance testing

[0067] 1. The vacuum chuck product prepared in Example 1 has a size of Ф330mm. The total warpage of the product after sintering was less than 0.1mm, as measured by feeler gauge. This indicates that the upper and lower two-zone temperature control method has a significant effect and helps to improve the product structure.

[0068] 2. Performance tests were conducted on multiple samples prepared according to the method in Example 1, based on GB / T 25995 "Test Method for Density and Apparent Porosity of Fine Ceramics" and GB / T 6569 "Test Method for Flexural Strength of Fine Ceramics". The performance of the samples prepared in the furnace was tested by cutting them. The connecting layer was located in different positions in the multiple samples, and the fracture was always in the middle of the sample. During the test, the average flexural strength of the 12 30mm*40mm*70mm samples was found to be 442MPa, and the average density was 3.16g / cm³. 3 This meets the product usage requirements.

[0069] 3. By using air adsorption, the wafer is adsorbed onto the vacuum chuck, which effectively suppresses vibration and prevents deformation caused by clamping.

[0070] Figure 1 The image shows a SEM image of the fracture surface near the bonding area of ​​a silicon carbide preform sample bonded by a gel method in the prior art. It can be seen that the bonding layer is not obvious, there is almost no oxygen inhibition, and it exhibits the same intergranular cleavage fracture mechanism as the parent material.

[0071] Figure 2 The image shows an SEM image of a product sample after pressureless sintering using the method described in Example 1. It can be seen that the location of the connection area cannot be distinguished at the microscopic level after sintering, indicating that the connection effect is good and the material structure is uniform.

[0072] Figure 3 This is a schematic diagram of the temperature curves for the drying and pressureless sintering processes in Example 1.

[0073] Figure 4 This is a schematic diagram of the S-type curing shrinkage rate (temperature)-time curve in steps S1 and S2, used to determine the inflection point and the time to complete curing.

[0074] This invention demonstrates that the method of the present invention can achieve the technical effect of consistent shrinkage in each area during connection, uniform connection layer, and defect-free finished product.

[0075] Example 2

[0076] Example 2 provides a gel bonding method for pressureless sintering of silicon carbide. The difference between the process method of Example 2 and Example 1 is that the method in Example 2 is used to prepare high-purity SiC ceramics.

[0077] Specifically, the slurry in step S1 comprises (by mass fraction) 9% pure water, 6% acrylamide, 0.6% methylene bisacrylamide, 0.15% catechol, 0.03% phenothiazine, 0.6% n-butanol, 1.4% tetramethylammonium hydroxide, and the balance being surface-modified silicon carbide micro powder; no impurities other than Si and C are introduced, and the volume solids content of the slurry is 52%.

[0078] In step S1, the curing time is determined based on the actual pre-tested slurry shrinkage S-shaped curing-time curve, and the curing temperature of the slurry is 24℃, the inflection point corresponds to the time of 17min, that is, the curing time in step S1 is 17min.

[0079] In step S2, before casting, an ammonium persulfate solution is coated on the inner surface of the second mold as an initiator. The formula is (by mass ratio) 10% ammonium persulfate, 15% tetramethylammonium hydroxide, and 75% ice water.

[0080] The preparation start time in step S2 is 17 min (i.e., the time when the slurry solidifies in step S1); the curing time in step S2 is 35 min, and the curing temperature is 24℃.

[0081] In Example 2, sintering was performed using an integrated degumming and pressureless sintering method. Specifically, after drying in step S3, both the upper and lower zones were simultaneously heated to a first preset temperature of 620°C and held for 2 hours; then, both zones were simultaneously heated to a second preset temperature of 2200°C and held for 2 hours; then, the lower zone began to cool at a fixed cooling rate of 20°C / h to a third preset temperature of 1850°C, while the upper zone was held for 0.5 hours; then, the upper zone began to cool at the same cooling rate of 20°C / h to the third preset temperature of 1850°C. The temperature is set at 850℃, and both the upper and lower zones are held at this temperature for 0.5 hours. Then, the lower zone is cooled at a fixed rate of 20℃ / h to the fourth preset temperature of 1300℃, while the upper zone is held at this temperature for 0.5 hours. The upper zone is then cooled at the same rate of 20℃ / h to the fourth preset temperature of 1300℃, and both the upper and lower zones are held at this temperature for 0.5 hours. The lower zone is then cooled at a fixed rate until it reaches room temperature, while the upper zone is held at this temperature for 0.5 hours. The upper zone is then cooled at the same rate until it reaches room temperature.

[0082] Performance testing

[0083] According to GB / T 25995 "Test Method for Density and Apparent Porosity of Fine Ceramics" and GB / T 6569 "Test Method for Bending Strength of Fine Ceramics", the performance of multiple samples prepared by the method in Example 2 was tested. The results showed that the measured ceramic density, strength, etc. were comparable to those in Example 1.

[0084] According to GB / T 3045 "Chemical Analysis Methods for Silicon Carbide in Ordinary Abrasives", the SiC content of the products prepared in Examples 1 and 2 can reach 99.7%, which is slightly higher than the market average. This indicates that the method of the present invention achieves the purpose of uniform and defect-free bonding layer and improved purity.

[0085] The above embodiments are illustrative examples of the implementation of the present invention. The implementation of the present invention is not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and are included within the protection scope of the present invention.

Claims

1. A gel bonding method for pressureless sintering of silicon carbide, characterized in that, Includes the following steps: S1: Set up the first mold, apply the initiator solution, use the first mold to solidify the slurry using the gel casting method to prepare the first ceramic green body, demold, and perform surface treatment; S2: Set up a second mold, use the second mold to prepare a second ceramic blank at one end of the first ceramic blank by using a gel casting method and solidification, demold to obtain a ceramic connected blank; S3: The ceramic connected green body obtained in step S2 is dried, degummed, and sintered without pressure to obtain the sintered finished product. The ceramic refers to SiC; In step S1, the matrix raw material and the gel system raw material are mixed to prepare a slurry, which is then injected into the first mold to prepare the first ceramic blank using the gel casting method. The matrix material is surface-modified silicon carbide micro powder with a particle size in the submicron range; the gel system used is a water-based gel system. The slurry comprises the following raw materials in the following percentages by mass: 8-10% pure water, 5-7% crosslinking system, 0.18-0.36% polymerization inhibitor, 0.1-0.3% urea, 0.5-1% boron carbide, 0.05-0.1% melamine, 0.4-0.6% n-butanol, 0.8-1% glycerol, 1.2-1.4% tetramethylammonium hydroxide, with the balance being surface-modified silicon carbide micro powder; The crosslinking system includes the monomer acrylamide and the crosslinking agent methylenebisacrylamide; In the crosslinking system, the mass ratio of acrylamide to methylene bisacrylamide is (8~10):1; in the polymerization inhibitor, the mass ratio of catechol to phenothiazine is (4~5):

1. The volumetric solids content of the slurry is 45-50%; In step S3, both drying and pressureless sintering require a two-zone temperature control method, i.e., the temperature of the upper zone corresponds to the temperature of the first ceramic blank, and the temperature of the lower zone corresponds to the temperature of the second ceramic blank. The drying process in step S3 is as follows: the upper and lower zones are simultaneously heated to the first preset temperature of 100~120℃ and kept at that temperature for 0.5~3h; then the lower zone begins to cool at a fixed cooling rate of 5~20℃ / h until room temperature, while the upper zone continues to be kept at that temperature for 0.1~0.5h, and then the upper zone begins to cool at the same cooling rate of 5~20℃ / h until room temperature. The degumming process in step S3 is as follows: first, the temperature is raised to 320-350℃ at a rate of 5-20℃ / h and kept at that temperature for 1-2 hours; then, the temperature is controlled in the drying process; and finally, the temperature is lowered to room temperature. The pressureless sintering process in step S3 is as follows: The upper and lower zones are simultaneously heated to a first preset temperature of 1950~2200℃ and held for 0.5~2 hours; then the lower zone begins to cool at a fixed rate of 20~200℃ / h to a second preset temperature of 1600~1900℃, while the upper zone is held for 0.1~1 hours; then the upper zone begins to cool at the same rate of 20~200℃ / h to a second preset temperature of 1600~1900℃, while both zones are held for 0.5~2 hours; then the lower zone... The first zone begins to cool at a fixed cooling rate of 20~200℃ / h to the third preset temperature of 1100~1300℃, while the second zone is held at that temperature for 0.1~1h. Then the second zone begins to cool at the same cooling rate of 10~20℃ / h to the third preset temperature of 1100~1300℃, while both zones are held at that temperature for 0.1~0.5h. Then the third zone begins to cool at a fixed cooling rate until room temperature, while the second zone is held at that temperature for 0.1~1h. Finally, the third zone begins to cool at the same cooling rate until room temperature.

2. The gel bonding method for pressureless sintered silicon carbide as described in claim 1, characterized in that, In step S1, before the slurry is injected into the first mold, the initiator solution coated on the inner surface of the first mold is an ammonium persulfate solution; the initiator solution is prepared from the following raw materials by mass percentage: 5% ammonium persulfate, 15% tetramethylammonium hydroxide, and 80% ice water.

3. The gel bonding method for pressureless sintered silicon carbide as described in claim 1, characterized in that, In step S1, during demolding, the slurry shrinkage-curing-time curve is measured. Demolding is performed at the moment corresponding to the inflection point of the shrinkage rate in the slurry shrinkage-curing-time curve, at which point the slurry is cured.

4. The gel bonding method for pressureless sintered silicon carbide as described in claim 1, characterized in that, In step S1, the curing temperature is 16~30℃; the curing time in step S1 is 17~45min.

5. The gel bonding method for pressureless sintered silicon carbide as described in claim 1, characterized in that, In step S1, the release agent used during demolding is syrup.

6. The gel bonding method for pressureless sintered silicon carbide as described in claim 1, characterized in that, In step S2, before casting, an initiator solution is applied to the inner surface of the second mold; the initiator solution is an ammonium persulfate solution; the initiator solution is prepared from the following raw materials by mass percentage: 5% ammonium persulfate, 15% tetramethylammonium hydroxide, and 80% ice water.

7. The gel bonding method for pressureless sintered silicon carbide as described in claim 1, characterized in that, In step S2, the curing temperature is 16~30℃; the curing time in step S2 is 35~90min.

8. A silicon carbide product prepared by any one of claims 1-7, characterized in that, The silicon carbide product is an anti-static vacuum chuck for semiconductor testing equipment.

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