Silicon carbide ceramic green body and process for producing the same

Abstract

The application relates to the field of silicon carbide ceramic preparation, and provides a preparation process of a silicon carbide ceramic blank and the silicon carbide ceramic blank prepared through the preparation process; the preparation process comprises the following steps: S1: configuring a premixed solution; S2: adding silicon carbide powder, uniformly mixing, and obtaining a slurry; S3: performing vacuum extraction treatment on the slurry; S4: adding a catalyst and an initiator into the slurry after the vacuum extraction treatment, uniformly mixing, pouring into a mold for solidification, simultaneously performing ultrasonic treatment during the solidification, and obtaining a formed blank; and S5: after the formed blank is dried, performing high-temperature sintering and degreasing, and obtaining the silicon carbide ceramic blank; the application introduces ultrasonic waves into gel injection molding silicon carbide ceramics; the ultrasonic operation is simple, new impurities cannot be introduced; the operation process is economical and environment-friendly, and environmental pollution cannot be caused; the solidification speed is improved, the preparation efficiency of the blank is improved, and the defects of the ceramic material are effectively reduced.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide ceramic preparation, and provides a process for preparing silicon carbide ceramic blanks and the silicon carbide ceramic blanks obtained by the process. Background Technology

[0002] Silicon carbide (SiC) materials possess advantages such as high elastic modulus, moderate density, low coefficient of thermal expansion, high thermal conductivity, and thermal shock resistance. They also exhibit high specific stiffness and excellent dimensional stability, making them an ideal material for space optical remote sensor mirrors. In recent years, they have been widely used in the fabrication of space mirror blanks. There are many methods for preparing SiC materials, among which reaction-bonded SiC is the earliest structural ceramic to achieve large-scale industrial application due to its simple process, short sintering time, low sintering temperature and cost, net-size sintering, and ease of fabricating large and complex shapes. It has broad application prospects. However, defects are unavoidable in actual processing and production. Ceramic materials are far more sensitive to defects than metals; even minute defects can easily cause stress concentration at the defect location, leading to rapid damage, especially in optical materials where quality requirements are even more stringent. Therefore, controlling product quality is particularly important.

[0003] In recent years, many research institutions and companies have introduced ultrasound into injection molding processes, enabling significant improvements in the quality of micro-injection molded parts while maintaining consistent process parameters. The EU's ULTRA-MELT institute was the first to discover that ultrasound can improve the flowability of melts in molds. Subsequently, with continued research by international and domestic researchers, it was found that the introduction of ultrasound can reduce material viscosity, improve flowability, promote sample crystallization, and enhance weld line strength. However, current research mainly focuses on the molding processes of organic materials and has not yet applied it to ceramic materials. Summary of the Invention

[0004] This invention addresses the technical problems existing in existing preparation methods by providing a preparation process that can effectively reduce defects in ceramic materials. It mainly involves introducing ultrasonic action during the gel casting combined with reactive sintering process to prepare silicon carbide. Ultrasonic action is applied during the slurry curing stage, allowing the slurry to expel internally trapped air bubbles through cavitation. This mechanical action homogenizes the material, while the ultrasonic thermal effect increases the slurry temperature, reducing the slurry's contact time with air, accelerating curing, reducing oxygen resistance, and thus reducing defects.

[0005] This invention provides a process for preparing silicon carbide ceramic green bodies, the process comprising the following steps:

[0006] S1: Prepare the premixed solution;

[0007] S2: Add silicon carbide powder to the premixed liquid and mix evenly to obtain a slurry; the solid content of the slurry is above 60%;

[0008] S3: Vacuum treatment is performed on the slurry;

[0009] S4: Add catalyst and initiator to the slurry after vacuum treatment, mix evenly, pour into a mold for curing, and perform ultrasonic treatment during the curing process to obtain a shaped blank;

[0010] S5: After drying the formed blank, it is subjected to high-temperature sintering and degreasing to obtain the silicon carbide ceramic blank.

[0011] Preferably, the solvent of the premixed liquid is water, and the solute of the premixed liquid includes acrylamide, methylenebisacrylamide, and tetramethylammonium hydroxide.

[0012] Preferably, the pH value of the slurry is at the high point of the absolute value of the Zeta potential of SiC, and preferably, the purity of the silicon carbide powder is greater than 99%.

[0013] Preferably, the vacuum pressure of the vacuuming process is between -0.08 MPa and -0.06 MPa.

[0014] Preferably, the vacuuming time is 15 to 20 minutes.

[0015] Preferably, the ultrasonic treatment time is 10 to 15 minutes; the ultrasonic treatment frequency is 10 kHz to 15 kHz.

[0016] Preferably, the ultrasonic treatment is water bath ultrasonic treatment or direct ultrasonic treatment.

[0017] Preferably, the drying time of the formed blank is controlled to be more than one month.

[0018] Preferably, the high-temperature sintering degreasing process includes: heating to 200°C at a rate of 25°C / h, then heating to 600°C at a rate of 10°C / h, then heating to 1800°C at a rate of 25°C / h and holding at that temperature for 2 hours; and then cooling to room temperature at a rate of 25°C / h.

[0019] The present invention also provides a silicon carbide ceramic preform, which is prepared by the silicon carbide ceramic preform preparation process of the present invention.

[0020] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0021] This invention provides a novel process for preparing silicon carbide ceramic green bodies. By introducing ultrasound into gel-molded silicon carbide ceramics, the ultrasound operation is simple and does not introduce new impurities. The process is economical and environmentally friendly, without causing environmental pollution. By introducing ultrasound treatment during the curing process, finer air bubbles can be removed, while the silicon carbide ceramic green body is more uniformly dispersed, and the curing speed is increased, thereby improving the green body preparation efficiency. The curing speed can be increased by an average of about 35.7%. At the same time, it can effectively reduce defects in ceramic materials. Attached Figure Description

[0022] Figure 1 This is a picture of a silicon carbide ceramic green body prepared according to a specific embodiment of the present invention;

[0023] Figure 2 These are flaw detection images of silicon carbide ceramic green bodies prepared according to specific embodiments of the present invention. Detailed Implementation

[0024] In the following description, embodiments of the invention will be described with reference to the accompanying drawings. In the description below, the same modules are denoted by the same reference numerals. Where the same reference numerals are used, their names and functions are also the same. Therefore, their detailed description will not be repeated.

[0025] 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 constitute a limitation thereof.

[0026] In a specific embodiment of the present invention, a process for preparing a silicon carbide ceramic green body is provided, the process comprising the following steps:

[0027] S1: Prepare a premixed solution; the solvent of the premixed solution is water, and the solute of the premixed solution includes acrylamide, methylenebisacrylamide, and tetramethylammonium hydroxide; wherein, tetramethylammonium hydroxide is added in appropriate excess, for example, by increasing the solvent volume by 1% to 3% while ensuring the pH of the slurry; this ensures that the silicon carbide powder can be uniformly dispersed in the premixed solution after being added, and at the same time ensures that the solid content of the final slurry can reach more than 60%; in the premixed solution prepared in this invention, by appropriately adding some small molecule organic matter, it is better ensured that the long-chain organic matter will not break due to the action of ultrasound during the curing process of acrylamide, thus preventing the formation of a network structure.

[0028] S2: Add silicon carbide powder to the premixed liquid and mix evenly to obtain a slurry; the solid content of the slurry is above 60%; the purity of the silicon carbide powder is greater than 99%, the particles are uniform, and the solution after adding water is neutral or weakly alkaline; specifically, the mixture is stirred evenly, and the slurry after stirring should not have obvious sedimentation, and the powder in each part of the slurry should be evenly dispersed, without clumping or large particle agglomeration; the pH value of the slurry is the highest absolute value of the Zeta potential of SiC.

[0029] S3: Vacuum treatment is performed on the slurry; the vacuum pressure of the vacuum treatment is between -0.08MPa and -0.06MPa; the vacuum treatment time is between 15 minutes and 20 minutes to ensure that large air bubbles in the slurry can be expelled.

[0030] S4: Add catalyst and initiator to the vacuum-treated slurry, mix evenly, pour into a mold for curing, and simultaneously perform ultrasonic treatment to obtain a shaped green body; specifically, the initiator can be ammonium persulfate, and the catalyst can be N,N,N′,N′-tetramethylethylenediamine; the ultrasonic treatment time is 10 to 15 minutes; the ultrasonic treatment frequency is 10 kHz to 15 kHz; using this ultrasonic frequency not only achieves better ultrasonic effect, but also avoids excessive ultrasonic heat effect, allowing for better control of the sample curing speed, thereby controlling the stress, and preventing defects such as cracking in the green body during subsequent processes; specifically, ultrasonic treatment can be applied by direct contact or using a room temperature water bath. When applying directly, the application location should be kept away from the molding requirements as much as possible. If using a water bath, the slurry mold must be waterproof and not obstruct the conduction of ultrasound, and contact between the slurry and the water bath must be avoided.

[0031] Normally, there are certain limitations on the vacuum level during vacuuming processes, and excessively high vacuum levels are not used, otherwise some organic matter will volatilize and affect the dispersion of silicon carbide. Ultrasonic treatment does not have this problem. The silicon carbide ceramic green body preparation process provided by this invention uses ultrasonic treatment during the curing process. During the curing process, some of the slurry has already become solid, and ultrasonic treatment will not cause changes to the dispersion of the slurry. Therefore, it will not have a significant impact on the dispersion.

[0032] S5: After drying the formed green body, high-temperature sintering and degreasing are performed to obtain the silicon carbide ceramic green body. In a preferred embodiment, the drying speed should be as slow as possible, and the drying time of the formed green body should be controlled to more than one month to avoid new defects caused by excessively fast drying. The temperature range of high-temperature sintering and degreasing is 1600℃~2000℃. Specifically, the high-temperature sintering and degreasing process includes: heating to 200℃ at a rate of 25℃ / h, then heating to 600℃ at a rate of 10℃ / h, then heating to 1800℃ at a rate of 25℃ / h and holding for 2h; then cooling to room temperature at a rate of 25℃ / h. By reducing the heating rate during the organic matter decomposition stage, new cracks are avoided.

[0033] The present invention also provides a silicon carbide ceramic preform, which is prepared by the silicon carbide ceramic preform preparation process of the present invention.

[0034] This invention provides a novel process for preparing silicon carbide ceramic green bodies. By introducing ultrasound into gel-molded silicon carbide ceramics, the ultrasound operation is simple and does not introduce new impurities. The operation process is economical and environmentally friendly, and does not generate environmental pollution. The curing speed is increased, which improves the efficiency of green body preparation and effectively reduces defects in ceramic materials.

[0035] The following detailed description, in conjunction with specific embodiments, provides further details.

[0036] Example 1

[0037] S1: Prepare a premixed solution using water, acrylamide, methylenebisacrylamide, and an appropriate excess of TMAH; the ratio of acrylamide to methylenebisacrylamide is 1:15, use 1000ml of water, and add 5ml of TMAH.

[0038] S2: Add 99% pure silicon carbide powder to the prepared premixed liquid. The ratio of powder with D50 of 40 microns and 3 microns is 3:1, with a total powder weight of 5000g. Stir continuously until it is uniformly mixed; the solid content of the slurry is 60%.

[0039] S3: Pour the well-mixed slurry into a vacuum filtration flask and vacuum for 20 minutes;

[0040] S4: Add a catalyst and an initiator to the slurry after vacuuming. The initiator is ammonium persulfate and the catalyst is tetramethylethylenediamine. After stirring for a period of time, pour the mixture into a mold and place the mold in a water bath for ultrasonic treatment for 20 minutes. Select a region in the middle of the slurry for ultrasonic treatment for 5 minutes to distinguish between internal ultrasonic treatment and water bath ultrasonic treatment.

[0041] S5: After curing, place it in a constant temperature and humidity chamber for slow drying, continuously adjusting the chamber parameters to control the dehydration rate. Once the green body is completely dry, place it in a vacuum sintering furnace for degreasing, heating it to 200℃ at a rate of 25℃ / h, then to 600℃ at a rate of 10℃ / h, and finally to 1800℃ at a rate of 25℃ / h, holding for 2 hours. Cool it to room temperature at a rate of 25℃ / h to obtain the silicon carbide ceramic green body.

[0042] The silicon carbide ceramic green body prepared in this embodiment is shown in the image below. Figure 1 As shown, the flaw detection images are as follows: Figure 2 As shown in the figure, at the location where ultrasound is applied, the formed blank in contact with the ultrasound becomes significantly thicker and without defects.

[0043] This invention provides a novel process for preparing silicon carbide ceramic green bodies. By introducing ultrasound into gel-molded silicon carbide ceramics, the ultrasound operation is simple and does not introduce new impurities. The process is economical and environmentally friendly, without causing environmental pollution. By introducing ultrasound treatment during the curing process, finer air bubbles can be removed, while the silicon carbide ceramic green body is more uniformly dispersed, and the curing speed is increased, thereby improving the green body preparation efficiency. The curing speed can be increased by an average of about 35.7%. At the same time, it can effectively reduce defects in ceramic materials.

[0044] Although embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

[0045] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A process for preparing silicon carbide ceramic green bodies, characterized in that, The silicon carbide ceramic green body preparation process includes the following steps: S1: Prepare a premixed solution; the solvent of the premixed solution is water, and the solute of the premixed solution includes acrylamide, methylenebisacrylamide, and tetramethylammonium hydroxide; S2: Add silicon carbide powder with a purity greater than 99% to the premixed liquid, mix evenly to obtain a slurry; the solid content of the slurry is above 60%, and the pH value is the highest absolute value of the Zeta potential of SiC. S3: Vacuum treatment is performed on the slurry; S4: Add catalyst and initiator to the vacuum-treated slurry, mix evenly, pour into a mold for curing, and simultaneously perform ultrasonic treatment to obtain a shaped green body; the ultrasonic treatment time is 10 minutes to 15 minutes; the ultrasonic treatment frequency is 10KHz to 15KHz; S5: After drying the formed green body, high-temperature sintering and degreasing are performed to obtain the silicon carbide ceramic green body; the high-temperature sintering and degreasing process includes: heating to 200°C at a rate of 25°C / h, then heating to 600°C at a rate of 10°C / h, then heating to 1800°C at a rate of 25°C / h, holding at that temperature for 2h; and then cooling to room temperature at a rate of 25°C / h.

2. The silicon carbide ceramic green body preparation process according to claim 1, characterized in that, The vacuum pressure of the vacuuming process is between -0.08MPa and -0.06MPa; the vacuuming time is between 15 minutes and 20 minutes.

3. The silicon carbide ceramic green body preparation process according to claim 1, characterized in that, The ultrasonic treatment is either water bath ultrasonic treatment or direct ultrasonic treatment.

4. The silicon carbide ceramic green body preparation process according to claim 1, characterized in that, The drying time of the formed blank is controlled to be more than one month.

5. A silicon carbide ceramic green body, characterized in that, The silicon carbide ceramic preform is prepared by the silicon carbide ceramic preform preparation process according to any one of claims 1 to 4.

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