A method for repairing microcracks in silicon carbide porous ceramics isopressed
By using a repair solution of silicon carbide aggregate, inorganic columnar fibers, and metal oxide nanoparticles, capillary infiltration, and high-temperature sintering methods to repair microcracks in silicon carbide porous ceramics prepared by isostatic pressing, the problems of low yield and insufficient mechanical strength were solved, enabling the industrial application of high-strength silicon carbide porous ceramics.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NANJING TECH UNIV
- Filing Date
- 2024-06-17
- Publication Date
- 2026-07-21
AI Technical Summary
When preparing porous silicon carbide ceramics using the existing isostatic pressing method, microcracks are difficult to repair, resulting in low yield and insufficient mechanical strength, which affects the product's service life.
The repair solution, which contains silicon carbide aggregate, inorganic columnar fibers, metal oxide nanoparticles and an aqueous solution of organic binder, is used to heal microcracks through capillary penetration and high-temperature sintering.
It improves the flexural strength of porous silicon carbide ceramics, enhances the mechanical properties of the product, increases the yield, and reduces production losses, making it suitable for large-scale industrial production.
Smart Images
Figure CN118580100B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for repairing microcracks in isostatic pressing of silicon carbide porous ceramics, belonging to the field of porous ceramic preparation. Background Technology
[0002] Silicon carbide porous ceramic materials possess advantages such as high temperature resistance, thermal shock resistance, corrosion resistance, high mechanical strength, wear resistance, and high filtration accuracy, making them one of the most widely used liquid-solid and gas-solid separation filtration materials in process industries. The forming methods for silicon carbide porous ceramics are mainly divided into three types: isostatic pressing, gel casting, and extrusion molding. Isostatic pressing and extrusion molding are suitable for large-scale industrial production. Based on the characteristics of the two forming methods and the different requirements for the moisture content and plasticity of the pre-pressed powder, isostatic pressing is more suitable for preparing single-channel tubular filter elements, while extrusion molding is suitable for preparing multi-channel tubular or honeycomb filter elements. In extrusion molding, a plasticized clay material, after mixing and refining, is placed into an extruder. The clay material is extruded through the extruder to obtain a ceramic green body. After thorough drying, it is sintered at high temperature to obtain silicon carbide porous ceramics. This method is similar to the forming and preparation method of alumina porous ceramics, with a relatively mature process and a high yield. Isostatic pressing involves adding mixed, granulated, and sieved silicon carbide granules into an elastic mold with a central metal mandrel. After sealing, the mold is placed in an isostatic pressing cylinder and pressed to obtain a ceramic green body of the desired shape. The green body is then demolded twice, once through the mold and once through the mandrel, to obtain a ceramic green body. After drying, it undergoes high-temperature sintering to obtain porous silicon carbide ceramic products. Silicon carbide porous ceramics prepared by this method have high mechanical strength and can achieve near-net-shape molding of complex structures in a single step. However, it requires extremely high control over processes such as filling, pressing, and demolding. Factors such as powder viscosity, filler density, pressure application and depressurization rates, and demolding methods inevitably cause microcracks in the green body. These microcracks cannot be eliminated after high-temperature sintering, resulting in a low product yield. Therefore, how to repair and heal microcracks in silicon carbide porous ceramics during isostatic pressing, improve product yield and mechanical strength, reduce the risk of breakage during application, and significantly increase the service life of silicon carbide porous ceramics is crucial. Summary of the Invention
[0003] The technical problem this invention aims to solve is to address the shortcomings of existing preparation techniques by providing a method for repairing microcracks in the isostatic pressing of silicon carbide porous ceramics. This method introduces inorganic columnar fibers and repairs microcracks on the surface of porous ceramics through sol-gel impregnation, improving the yield rate in the isostatic pressing process, solving the problem of low strength due to stress concentration caused by the presence of microcracks during molding, and extending the service life of silicon carbide porous ceramics under complex working conditions.
[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for repairing microcracks in isostatic pressing of silicon carbide porous ceramics. The method involves capillary penetration of a repair solution into the microcracks. After the microcracks are filled with the repair solution, they are dried, and finally sintered in a high-temperature furnace to obtain a fully healed silicon carbide porous ceramic. The repair solution comprises silicon carbide aggregate, inorganic columnar fibers, metal oxide nanoparticles, and an aqueous solution of an organic binder.
[0005] The preparation method of this repair solution includes the following steps: (1) First, prepare an aqueous solution of organic binder of a certain concentration, then disperse silicon carbide aggregate into an appropriate amount of organic binder solution, and stir thoroughly at room temperature for 6-12 hours to obtain dispersion A; (2) Then weigh an appropriate amount of inorganic columnar fiber and add it to dispersion A. Stir thoroughly at 40-60℃ for 2-3 hours to obtain dispersion B. (3) Finally, weigh an appropriate amount of metal oxide nanoparticles and add them to dispersion B. Stir thoroughly at 60-80℃ for 4-6 hours and finally cool to obtain the repair solution.
[0006] The main components of the repair solution are in the following mass ratio: 10-20 parts silicon carbide aggregate, 1-5 parts inorganic columnar fibers, 5-10 parts metal oxide nanoparticles, and 70-80 parts organic binder aqueous solution.
[0007] The organic binder is polyvinyl alcohol, methylcellulose or carboxymethylcellulose, and the aqueous solution of the organic binder has a mass concentration of 0.5%-5%.
[0008] The silicon carbide aggregate has a particle size of 1-20 μm.
[0009] The inorganic columnar fibers are silicon carbide fibers, silicon carbide whiskers or mullite fibers, with a fiber length of 3-5 μm and a diameter of 200-500 nm.
[0010] The metal oxide nanoparticles are zirconium oxide, magnesium oxide, aluminum oxide or yttrium oxide, with a particle size of 100-500 nm.
[0011] The repair drying temperature is 60-80 ºC, and the drying time is 12-24 hours.
[0012] The repair sintering temperature is 1300-1500 ºC, the heating rate is 1-3ºC / min, and the holding time is 2-6h.
[0013] In this invention, the flexural strength of silicon carbide porous ceramics is determined using the following method: The flexural strength test method involves measuring the average flexural strength at three points using a flexural strength tester, with a span of 40 mm and a loading speed of 0.5 mm / min. Specific test procedures are in accordance with the national standard GB / T1965-1996 (National Standard of the People's Republic of China, Test Method for Flexural Strength of Porous Ceramics). Beneficial effects
[0014] 1. The repair method of the present invention has a simple preparation process, a short process flow, and low requirements for production equipment, making it suitable for large-scale industrial production.
[0015] 2. The silicon carbide porous ceramic prepared by this invention has a flexural strength of over 20 MPa, making it suitable for gas purification applications under high-temperature and complex working conditions in process industries.
[0016] 3. The repair method of this invention overcomes the problem of microcracks in silicon carbide porous ceramics prepared by the mesostatic pressing method in the prior art. By reinforcing and repairing the microcracks, high-temperature self-healing is achieved, which increases the bending strength of silicon carbide porous ceramics, improves the yield of the whole cycle from product molding and sintering to the coating stage by 100%, reduces production losses and improves production efficiency. Attached Figure Description
[0017] Appendix Figure 1 This is a schematic diagram of the repair and high-temperature sintering healing of microcracks in silicon carbide porous ceramics.
[0018] Appendix Figure 2 These are before-and-after photos of a silicon carbide porous ceramic tube before and after microcrack repair.
[0019] Explanation of reference numerals in the attached figures: 1—Microcracks; 2—Repair solution; 2-1—Aqueous binder solution; 2-2—Silicon carbide aggregate; 2-3—Inorganic columnar fibers; 2-4—Metal oxide nanoparticles. Detailed Implementation
[0020] The present invention will be further explained below with reference to the embodiments. The following embodiments are only used to illustrate the present invention, but are not intended to limit the scope of the present invention. Example 1
[0021] like Figure 1 As shown, this embodiment uses a repair solution to capillary-penetrate the microcracks in silicon carbide porous ceramic. After the microcracks are filled with the repair solution, they are dried, and finally sintered in a high-temperature furnace to obtain a fully healed silicon carbide porous ceramic. The specific microcrack repair process includes the following steps: Step 1: First, measure 600ml of deionized water into a beaker with a magnetic stirrer and heat it to 80ºC. Then, weigh 30g of polyvinyl alcohol granules and slowly add them to the beaker in batches while heating and stirring. After the polyvinyl alcohol granules melt, allow it to cool naturally to obtain a 5wt% polyvinyl alcohol aqueous solution for later use.
[0022] Step 2: First, weigh 70 parts of 5 wt% polyvinyl alcohol and put them into a beaker with magnetic stirring. Then, weigh 20 parts of silicon carbide aggregate with a particle size of 1 μm and put them into the beaker. Stir thoroughly at room temperature for 12 hours. Next, weigh 5 parts of silicon carbide fiber with a fiber length of 3 μm and a diameter of 200 nm and put them into the beaker. The above proportions are in the mass ratio. Heat to 40 ºC and stir thoroughly for 2 hours. Finally, weigh 5 parts of 100 nm zirconium oxide nanoparticles and put them into the beaker. Heat to 60 ºC and stir thoroughly for 4 hours to obtain the repair solution.
[0023] Step 3: Use a pipette to draw up the repair solution and penetrate it into the porous silicon carbide ceramic sample with microcracks until the microcracks are filled and no longer absorbed. Finally, place the sample in a 60 ºC oven to dry for 12 hours. Then, place the sample in a high-temperature furnace and heat it to 1500ºC at a rate of 1 ºC / min and hold it at that temperature for 6 hours. After natural cooling, obtain the sample and then polish the surface to obtain the final product.
[0024] Tests showed that the silicon carbide porous ceramic prepared in this embodiment had no obvious microcracks, and the bending strength of the material increased from 12.8 MPa before repair to 24.5 MPa, which meets the standards for industrial application. Example 2
[0025] This embodiment primarily employs a repair solution to capillary-permeate the microcracks in silicon carbide porous ceramics. After the microcracks are filled with the repair solution, they are dried, and finally sintered in a high-temperature furnace to obtain a fully healed silicon carbide porous ceramic. The specific microcrack repair process includes the following steps: Step 1: First, measure 74 parts of 5wt% polyvinyl alcohol prepared in Example 1 and put them into a beaker with magnetic stirring. Then, weigh 15 parts of silicon carbide aggregate with a particle size of 1 μm and put them into the beaker. Stir thoroughly at room temperature for 12 hours. Next, weigh 1 part of silicon carbide fiber with a fiber length of 3 μm and a diameter of 200 nm and put it into the beaker. Heat to 40 ºC and stir thoroughly for 2 hours. Finally, weigh 10 parts of magnesium oxide nanoparticles with a particle size of 100 nm and put them into the beaker. The above proportions are in the mass ratio. Heat to 60 ºC and stir thoroughly for 4 hours to obtain the repair solution.
[0026] Step 2: Use a pipette to draw up the repair solution and penetrate it into the porous silicon carbide ceramic sample with microcracks until the microcracks are filled and no longer absorbed. Finally, place the sample in a 60 ºC oven to dry for 12 hours. Then, place the sample in a high-temperature furnace and heat it to 1500ºC at a rate of 1 ºC / min and hold it at that temperature for 6 hours. After natural cooling, obtain the sample and then polish the surface to obtain the final product.
[0027] Tests showed that the silicon carbide porous ceramic prepared in this embodiment had no obvious microcracks, and the bending strength of the material was increased to 18.6 MPa, indicating that the inorganic columnar fiber component reduced the bending strength of the silicon carbide porous ceramic. Example 3
[0028] This embodiment primarily employs a repair solution to capillary-permeate the microcracks in silicon carbide porous ceramics. After the microcracks are filled with the repair solution, they are dried, and finally sintered in a high-temperature furnace to obtain a fully healed silicon carbide porous ceramic. The specific microcrack repair process includes the following steps: Step 1: First, measure 80 parts of 5wt% polyvinyl alcohol prepared in Example 1 and put them into a beaker with magnetic stirring. Then, weigh 10 parts of silicon carbide aggregate with a particle size of 1 μm and put them into the beaker. Stir thoroughly at room temperature for 12 hours. Next, weigh 5 parts of mullite fiber with a fiber length of 3 μm and a diameter of 200 nm and put them into the beaker. Heat to 40 ºC and stir thoroughly for 2 hours. Finally, weigh 5 parts of alumina nanoparticles with a particle size of 100 nm and put them into the beaker. The above proportions are in the mass ratio. Heat to 60 ºC and stir thoroughly for 4 hours to obtain the repair solution.
[0029] Step 2: Use a pipette to draw up the repair solution and penetrate it into the porous silicon carbide ceramic sample with microcracks until the microcracks are filled and no longer absorbed. Finally, place the sample in a 60 ºC oven to dry for 12 hours. Then, place the sample in a high-temperature furnace and heat it to 1500ºC at a rate of 1 ºC / min and hold it at that temperature for 6 hours. After natural cooling, obtain the sample and then polish the surface to obtain the final product.
[0030] Tests showed that the silicon carbide porous ceramic prepared in this embodiment had no obvious microcracks, and the bending strength of the material was increased to 22.3 MPa. Compared with Example 1, this indicates that the reduction in the liquid-solid content of the repair solution has a certain impact on the bending strength. Example 4
[0031] This embodiment primarily employs a repair solution to capillary-permeate the microcracks in silicon carbide porous ceramics. After the microcracks are filled with the repair solution, they are dried, and finally sintered in a high-temperature furnace to obtain a fully healed silicon carbide porous ceramic. The specific microcrack repair process includes the following steps: Step 1: First, measure 70 parts of 5wt% polyvinyl alcohol prepared in Example 1 and put them into a beaker with magnetic stirring. Then, weigh 20 parts of silicon carbide aggregate with a particle size of 20 μm and put them into the beaker. Stir thoroughly at room temperature for 6 hours. Next, weigh 5 parts of silicon carbide whiskers with a fiber length of 5 μm and a diameter of 500 nm and put them into the beaker. Heat to 60 ºC and stir thoroughly for 3 hours. Finally, weigh 5 parts of zirconia nanoparticles with a particle size of 500 nm and put them into the beaker. The above proportions are in the mass ratio. Heat to 80 ºC and stir thoroughly for 6 hours to obtain the repair solution.
[0032] Step 2: Use a pipette to draw up the repair solution and penetrate it into the porous silicon carbide ceramic sample with microcracks until the microcracks are filled and no longer absorbed. Finally, place the sample in a 60 ºC oven to dry for 12 hours. Then, place the sample in a high-temperature furnace and heat it to 1500ºC at a rate of 1 ºC / min and hold it at that temperature for 6 hours. After natural cooling, obtain the sample and then polish the surface to obtain the final product.
[0033] Tests showed that the silicon carbide porous ceramic prepared in this embodiment had no obvious microcracks and the bending strength of the material reached 21.9 MPa. Compared with Example 1, this indicates that the increased particle size of the main components of the repair solution reduced the bending strength of the material. Example 5
[0034] This embodiment primarily employs a repair solution to capillary-permeate the microcracks in silicon carbide porous ceramics. After the microcracks are filled with the repair solution, they are dried, and finally sintered in a high-temperature furnace to obtain a fully healed silicon carbide porous ceramic. The specific microcrack repair process includes the following steps: Step 1: First, measure 70 parts of 5wt% polyvinyl alcohol prepared in Example 1 and put them into a beaker with magnetic stirring. Then, weigh 20 parts of silicon carbide aggregate with a particle size of 10 μm and put them into the beaker. Stir thoroughly at room temperature for 6 hours. Next, weigh 5 parts of silicon carbide fiber with a fiber length of 3 μm and a diameter of 200 nm and put them into the beaker. Heat to 60 ºC and stir thoroughly for 3 hours. Finally, weigh 5 parts of zirconia nanoparticles with a particle size of 100 nm and put them into the beaker. The above proportions are in the mass ratio. Heat to 80 ºC and stir thoroughly for 6 hours to obtain the repair solution.
[0035] Step 2: Use a pipette to draw up the repair solution and penetrate it into the porous silicon carbide ceramic sample with microcracks until the microcracks are filled and no longer absorbed. Finally, place the sample in a 60 ºC oven to dry for 12 hours. Then, place the sample in a high-temperature furnace and heat it to 1300ºC at a rate of 3ºC / min and hold it at that temperature for 2 hours. After natural cooling, obtain the sample and then polish the surface to obtain the final product.
[0036] Tests showed that the silicon carbide porous ceramic prepared in this embodiment had no obvious microcracks and the bending strength of the material reached 19.4 MPa. Compared with Example 1, this indicates that lower sintering temperature, faster sintering rate and shorter holding time are not conducive to improving the bending strength of the material. Example 6
[0037] This embodiment primarily employs a low-concentration repair solution to capillary-permeate the microcracks in silicon carbide porous ceramics. After the microcracks are filled with the repair solution, they are dried, and finally sintered in a high-temperature furnace to obtain fully healed silicon carbide porous ceramics. The specific microcrack repair process includes the following steps: Step 1: First, measure 600ml of deionized water into a beaker with a magnetic stirrer and heat it to 80ºC. Then, weigh 3g of polyvinyl alcohol granules and slowly add them to the beaker in batches while heating and stirring. After the polyvinyl alcohol granules melt, allow it to cool naturally to obtain a 0.5wt% polyvinyl alcohol aqueous solution for later use.
[0038] Step 2: First, weigh 70 parts of 0.5 wt% polyvinyl alcohol and put them into a beaker with magnetic stirring. Then, weigh 20 parts of silicon carbide aggregate with a particle size of 1 μm and put them into the beaker. Stir thoroughly at room temperature for 12 hours. Next, weigh 5 parts of silicon carbide fiber with a fiber length of 3 μm and a diameter of 200 nm and put them into the beaker. Heat to 40 ºC and stir thoroughly for 2 hours. Finally, weigh 5 parts of 100 nm zirconium oxide nanoparticles and put them into the beaker. The above proportions are in the mass ratio. Heat to 60 ºC and stir thoroughly for 4 hours to obtain the repair solution.
[0039] Step 3: Use a pipette to draw up the repair solution and penetrate it into the porous silicon carbide ceramic sample with microcracks until the microcracks are filled and no longer absorbed. Finally, place the sample in a 60 ºC oven to dry for 12 hours. Then, place the sample in a high-temperature furnace and heat it to 1500ºC at a rate of 1 ºC / min and hold it at that temperature for 6 hours. After natural cooling, obtain the sample and then polish the surface to obtain the final product.
[0040] Testing revealed the presence of microcracks in the silicon carbide porous ceramic prepared in this embodiment, with a flexural strength of only 16.3 MPa. This indicates a decrease in binder concentration, significant particle sedimentation, and uneven dispersion, which is detrimental to improving the flexural strength of the repaired material.
Claims
1. A method for repairing microcracks in isostatic pressing of silicon carbide porous ceramics, characterized in that, This method involves capillary penetration of a repair solution into microcracks. After the microcracks are filled with the repair solution, they are dried and finally sintered in a high-temperature furnace to obtain a fully healed porous silicon carbide ceramic. The repair solution comprises silicon carbide aggregate, inorganic columnar fibers, metal oxide nanoparticles, and an aqueous solution of an organic binder. The mass ratio of the repair solution components is 10-20 parts silicon carbide aggregate, 1-5 parts inorganic columnar fibers, 5-10 parts metal oxide nanoparticles, and 70-80 parts aqueous solution of organic binder. The inorganic columnar fibers are silicon carbide fibers, silicon carbide whiskers, or mullite fibers, with a fiber length of 3-5 μm and a diameter of 200-500 nm. The metal oxide nanoparticles are zirconium oxide, magnesium oxide, aluminum oxide, or yttrium oxide, with a particle size of 100-500 nm. The organic binder is polyvinyl alcohol, methylcellulose, or carboxymethyl cellulose, and the aqueous solution of the organic binder has a mass concentration of 5 wt%.
2. The method for repairing microcracks in isostatic pressing of silicon carbide porous ceramics according to claim 1, characterized in that, The preparation method of the repair solution includes the following steps: (1) First, prepare an aqueous solution of organic binder, then disperse silicon carbide aggregate into the organic binder solution, and stir thoroughly at room temperature for 6-12 hours to obtain dispersion A; (2) Then weigh the inorganic columnar fibers and add them to dispersion A. Stir at 40-60℃ for 2-3 hours to obtain dispersion B. (3) Finally, weigh the metal oxide nanoparticles and add them to the dispersion B. Stir at 60-80℃ for 4-6 hours and finally cool to obtain the repair solution.
3. The method for repairing microcracks in isostatic pressing of silicon carbide porous ceramics according to claim 1, characterized in that, The silicon carbide aggregate has a particle size of 1-20 μm.
4. The method for repairing microcracks in isostatic pressing of silicon carbide porous ceramics according to claim 1, characterized in that, The drying temperature is 60-80℃, the drying time is 12-24h, the sintering temperature is 1300-1500℃, the heating rate is 1-3℃ / min, and the holding time is 2-6h.