Directional hole silicon carbide filter element and preparation method thereof

Abstract

The invention provides a directional hole silicon carbide filter element and a preparation method thereof, and belongs to the technical field of silicon carbide filter elements. The preparation method comprises the steps of preparing the supporting body and preparing the composite membrane layer. The step of preparing the support body comprises the steps of preparing a mixture and needling; the preparation of the mixture comprises the following steps: mixing siloxane-treated silicon carbide, organic-treated silicon nitride, polyacrylamide, carbon nanotubes and microcrystalline wax, adding modified organic silicon resin, and uniformly mixing to obtain the mixture; the preparation method of the organically treated silicon nitride comprises the following steps: adding silicon nitride into absolute ethyl alcohol, uniformly stirring, adding hydroxyethyl acrylate and ammonium persulfate, heating to 78-82 DEG C, carrying out reflux condensation reaction for 2.8-3.4 hours, cooling to 50-54 DEG C, adding trimethylolpropane triacrylate, and carrying out irradiation treatment under ultraviolet light to obtain the organically treated silicon nitride. The directional-hole silicon carbide filter element prepared by the invention is uniform in porosity and aperture, high in strength and excellent in high temperature resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of silicon carbide filter elements, and in particular relates to a silicon carbide filter element with directional holes and a preparation method thereof. Background Art

[0002] Silicon carbide (SiC) porous ceramic is a high-performance ceramic material with a special microporous structure. It not only inherits the excellent properties of silicon carbide such as high hardness, high strength, small thermal expansion coefficient, high thermal conductivity, and good chemical stability, but also has high specific surface area, good permeability and filtration efficiency due to its porous structure. These characteristics give it broad application prospects in metallurgy, chemical industry, environmental protection, energy and other fields.

[0003] The preparation methods of silicon carbide porous ceramics mainly include particle stacking method, freeze drying method, 3D printing method, and organic foam impregnation method; The particle stacking method uses the sintering properties of the ceramic particles themselves to form sintering necks between the particles, thereby forming a porous structure. This method has a simple process, but the porosity is low, and the pore structure is greatly affected by the shape and particle size distribution of the raw material particles; the freeze-drying method is to freeze the ceramic slurry and then dry it under reduced pressure or vacuum to sublime the ice crystals to form a directionally arranged pore structure. This method can control the pore structure, but has high requirements on the solid phase content and cooling rate of the slurry; the 3D printing method uses computer-aided design to spray a binder through a print head to stack the raw material powder layer by layer. This method can achieve the preparation of complex shapes and uniform pore structures, but the current process parameters still need to be optimized and the cost is relatively high; the organic foam impregnation method uses organic foam as a template, coats or impregnates the ceramic slurry on the template, and removes the template after sintering to form a porous structure. This method cannot prepare small-pore closed-pore products, and the performance of the preform is greatly affected by the raw materials.

[0004] Directional pore ceramics exhibit high filtration efficiency because their pores are arranged in a certain direction. They are particularly suitable for scenarios with high requirements for fluid directionality. However, their manufacturing is complex and costly, and they may not be effective when processing multi-directional fluids. Therefore, providing a directional pore silicon carbide ceramic to reduce costs, simplify processes, and improve multi-directional fluid effects is a research topic for technicians.

[0005] At present, the preparation methods of silicon carbide porous ceramics with directional pores are mainly freeze-drying and 3D printing; Although the freezing method has unique advantages in preparing anisotropic porous structures, the solid content of the slurry in the freezing method needs to be strictly controlled. If the solid content is too high, the slurry viscosity will be too high, making it easy for particles to be swallowed during ice crystal growth, and thus it is impossible to obtain an ideal porous structure. If the solid content is too low, the strength of the porous green body after sublimation will be too low, and it will easily collapse and fail to maintain the desired shape. Secondly, during the freezing process, the growth rate and direction of ice crystals are affected by many factors, such as temperature gradient and cooling rate. Uneven cooling rate can lead to uneven pore structure, affecting the performance of the material. During the preparation process, the thermal resistance of the solidified layer in the single-sided cooling method can easily cause the pore structure spacing to gradually increase, resulting in uneven product structure and limiting its application range. Furthermore, the porous ceramic green body obtained by the freezing method requires precise control of the sintering temperature during the sintering process. If the sintering temperature is too high, the green body will shrink too much, reducing the porosity and increasing energy consumption. If the sintering temperature is too low, the green body cannot be densified, affecting the mechanical properties of the material. It can be seen that the preparation of directional porous ceramics by freezing method requires precise control of parameters such as temperature and cooling rate during the freezing process and pressure during the sublimation process. The process is complex and has high requirements on equipment. Since freeze-drying equipment and precise temperature control system are required, the preparation cost is relatively high.

[0006] The 3D printing method for preparing directional porous ceramics has significant advantages and certain limitations; 3D printing technology can achieve high-precision manufacturing of complex structures, has extremely high design flexibility, and can customize porosity, pore size and distribution according to needs. Its integrated molding feature reduces the assembly steps in traditional processes and improves production efficiency. At the same time, it has high material utilization and is suitable for small-batch customized production. In addition, when preparing porous ceramics, 3D printing technology can achieve structures with complex shapes, high porosity and good pore connectivity, especially in aerospace, biomedicine and other fields, showing broad application prospects.

[0007] However, 3D printing of porous ceramics has technical disadvantages. Its printing accuracy is limited, especially when preparing submicron or nanometer pores. The post-processing process is complex and requires steps such as high-temperature sintering, which can cause deformation of the pore structure and reduced strength. In addition, 3D printing equipment is expensive, has relatively low production efficiency, and has high requirements for the particle size and fluidity of ceramic materials. These factors have limited its large-scale industrial application to a certain extent.

[0008] It can be seen that the existing technology for preparing directional pore silicon carbide ceramics has problems such as uneven pore size and porosity, unstable pore structure, poor mechanical properties, and high cost. Summary of the Invention

[0009] In order to solve the above technical problems, the present invention provides a directional pore silicon carbide filter element and a preparation method thereof, which ensure uniform pore size and porosity, high mechanical properties, and excellent high temperature resistance.

[0010] In order to solve the above technical problems, the present invention adopts the following technical solutions: A method for preparing a directional pore silicon carbide filter element includes preparing a support body and preparing a composite membrane layer. The specific operations are as follows: 1. Prepare the support (1) Preparation of mixture The siloxane-treated silicon carbide, organic-treated silicon nitride, polyacrylamide, carbon nanotubes, and microcrystalline wax are mixed evenly, and then the modified silicone resin is added. After mixing evenly, the mixture is processed by a kneader for 3-5 times, each time for 25-35 minutes, to obtain a mixture; The mass ratio of the siloxane-treated silicon carbide, organic-treated silicon nitride, modified silicone resin, polyacrylamide, carbon nanotubes, and microcrystalline wax is 86-93:4-6:2-4:0.4-0.6:0.4-0.7:0.3-0.6; The preparation method of the siloxane-treated silicon carbide comprises placing 2.3-2.7 g of silicon carbide in a plasma device, introducing argon gas, controlling the argon flow rate to 40-45 sccm, the treatment power to 86-92 W, and the treatment time to 4.5-5.5 minutes. After the treatment is completed, the argon gas is turned off, and octamethylcyclotetrasiloxane gas is introduced, controlling the gas flow rate to 25-30 sccm, the treatment power to 72-77 W, the treatment pressure to 10-14 Pa, and the treatment time to 16-20 minutes. After the treatment is completed, the siloxane-treated silicon carbide is obtained. The preparation method of the organically treated silicon nitride comprises the following steps: introducing anhydrous ethanol into a reaction container, then adding silicon nitride and stirring evenly, adding hydroxyethyl acrylate and stirring evenly, adding ammonium persulfate, raising the temperature to 78-82° C., and conducting a condensation reflux reaction for 2.8-3.4 hours. After the stirring reaction is completed, lowering the temperature to 50-54° C., adding trimethylolpropane triacrylate, stirring evenly, and placing the reaction container under ultraviolet light for irradiation treatment, wherein the irradiation time is 6-10 minutes, the ultraviolet wavelength is 340-360 nm, and the irradiation power is 13-18 mW / cm 2 , filtered, washed and dried to obtain organic-treated silicon nitride; The mass ratio of anhydrous ethanol, silicon nitride, hydroxyethyl acrylate, ammonium persulfate, and trimethylolpropane triacrylate is 200:8-12:3.4-3.6:0.2-0.5:1.5-1.8; The modified silicone resin is prepared by adding phenyltrimethoxysilane and trifluoropropyltrimethoxysilane to anhydrous ethanol and mixing them evenly; then adding γ-glycidyl ether propyltrimethoxysilane, bis(dioctyloxypyrophosphate)ethylene titanate and tetramethylguanidine; raising the temperature to 32-37° C., stirring at 510-540 rpm for 37-42 minutes; then adding nano-titanium dioxide and performing ultrasonic dispersion; the ultrasonic time is 35-45 minutes, the ultrasonic frequency is 30-38 kHz, and the ultrasonic power is 210-225 W; after the ultrasonication is completed, performing reduced pressure distillation at 48-52° C. for 1.4-1.6 hours, and the pressure of the reduced pressure distillation is -0.06 to -0.09 MPa, to obtain the modified silicone resin; The particle size of the nano titanium dioxide is 20-50 nm; The mass ratio of the anhydrous ethanol, phenyltrimethoxysilane, trifluoropropyltrimethoxysilane, γ-glycidyl ether propyltrimethoxysilane, bis(dioctyloxypyrophosphate)ethylene titanate, tetramethylguanidine, and nano-titanium dioxide is 15-20:40-50:40-50:5-10:0.5-1:0.5-1:5-11; (2) Acupuncture The mixed material is placed in an extruder for extrusion molding, the extrusion speed is controlled to be 0.5-2.0 m / min, the extrusion pressure is 10-30 MPa, and a cylinder with a wall thickness of 10-20 mm is extruded. A directional hole is punctured on the cylinder with a special-shaped needle to obtain a green body. The diameter and spacing of the hole are adjusted by the structure of the needle. The diameter of the straight end hole is 1-2 mm, the diameter of the hexagonal circumscribed circle is 3-4 mm, the hole spacing is 1-2 mm, and the hexagonal depth is 1 mm. The green body is sintered at 1300-1450°C for 4.8-5.3 hours to obtain a support body.

[0011] 2. Preparation of composite film layer The silicon carbide fiber is placed in deionized water to prepare a silicon carbide fiber slurry, and the support body is placed in the silicon carbide fiber slurry for suction. The silicon carbide fiber slurry completely immerses the support body, one end of the support body is completely sealed, and the other end is connected to a suction pump. The suction pump is started, and the suction negative pressure is controlled to be -0.08 to -0.09 MPa. The thickness of the silicon carbide fiber layer is controlled to be 1.5-2.0 mm. The support body is removed, excess slurry is drained, and dried at 78-82° C. for 10-14 hours to obtain a silicon carbide fiber composite support body; The silicon carbide fiber has a length of 1-2 mm and a diameter of 10-14 μm; The mass ratio of the silicon carbide fiber to deionized water is 0.1-0.5:100; Silicon carbide particles and polyacrylamide are added to the acidic silica sol and the acidic aluminum sol, and the mixture is stirred to obtain a mixed slurry; a silicon carbide fiber composite support is placed in the mixed slurry for suction, and the mixed slurry is completely immersed in the silicon carbide fiber composite support. The suction negative pressure is controlled to be -0.08 to -0.09 MPa, and the suction time is 1 to 2 minutes. After the suction is completed, the silicon carbide fiber composite support is removed, the excess slurry is drained, and the mixture is dried at 78 to 82° C. for 10 to 14 hours, and then sintered at 1200 to 1400° C. for 4.8 to 5.2 hours to obtain a directional pore silicon carbide filter element; The particle size of the silicon carbide particles is 20-80 μm; The acidic silica sol has a pH value of 2-3 and a solid content of 28-32%; The acidic aluminum sol has a pH value of 3-4 and a solid content of 23-28%; The mass ratio of the acidic silica sol, the acidic aluminum sol, the silicon carbide particles and the polyacrylamide is 48-52:48-53:4-8:1-2.

[0012] A directional pore silicon carbide filter element is manufactured using the above-mentioned preparation method.

[0013] Compared with the prior art, the present invention has achieved the following beneficial effects: 1. The present invention performs siloxane treatment on silicon carbide, where octamethylcyclotetrasiloxane is cracked under the action of plasma and combines with hydroxyl groups on the surface of silicon carbide, thereby achieving siloxane modification of silicon carbide, improving the surface activity of silicon carbide, and enhancing compatibility with silicone resin. Silicon nitride is then subjected to organic treatment, specifically, ammonium persulfate is used to initiate polymerization of hydroxyethyl acrylate, trimethylolpropane triacrylate generates active free radicals under ultraviolet light, and cross-links with polyhydroxyethyl acrylate to obtain a polymer network-coated silicon nitride, thereby improving the dispersibility and interfacial bonding strength of silicon nitride. In the step of modifying the silicone resin, silane is used as a modification matrix, wherein phenylsilane provides a skeleton and hydrophobic properties, enhancing thermal stability, and fluorosilane introduces the low surface energy characteristics of fluorine element, enhancing compatibility with other components. During the mixing process, the two are combined through hydrogen bonds to form a physical pre-polymer network, providing a basis for subsequent cross-linking; γ- Glycidyl ether propyl trimethoxysilane is used as a bridging agent. Its epoxy group can react with the hydroxyl groups on the surface of silicon carbide and silicon nitride to enhance the interfacial bonding between the inorganic component and the organic resin. The epoxy group can also form a polyether cross-linked network through ring-opening polymerization under the action of tetramethylguanidine, thereby enhancing the toughness of the support. The titanate coupling agent can improve the dispersion performance of titanium dioxide in the organic phase, thereby obtaining a modified silicone resin with both the flexibility of the organic phase and the high strength of the inorganic phase. Combined with components such as carbon nanotubes, the toughness of the support is enhanced, and the mechanical properties, high temperature resistance and resistance to heating and water cooling of the support are improved. Then, a needle-punching process is used to prepare directional pore porous ceramics to obtain a green body with uniform pores. A suction process is used to prevent excess particles from clogging the pores, and a composite layer of fibers and aggregates can be formed, with an aggregate accumulation layer formed on the outermost layer. Due to the gradient pore structure design, the air permeability resistance is reduced and the filtration effect is improved. 2. The directional pore silicon carbide filter element prepared by the present invention has a porosity of 38-45%, a membrane pore size of 20-30 μm, and an air permeability resistance of 150-370 Pa; 3. The directional pore silicon carbide filter element prepared by the present invention has a flexural strength of 18.5-23.6 MPa and a fracture toughness of 2.45-2.67 MPa·m at 26°C. 1 / 2 The flexural strength was measured at 17.6-22.7 MPa and the fracture toughness was 2.34-2.58 MPa·m after being kept at 1100℃ for 120 hours. 1 / 2 After 20 heating-water cooling treatments, the flexural strength was 17.2-22.3 MPa and the fracture toughness was 2.28-2.52 MPa·m 1 / 2 . BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is the outer surface structure of the supporting body tube; Figure 2 It is the cross-sectional structure of the supporting body; Figure 3 The needle structure includes a cylindrical part and a hexagonal prism part. DETAILED DESCRIPTION

[0015] In order to more clearly understand the technical features, purposes and effects of the present invention, the specific implementation methods of the present invention are first described.

[0016] Example 1 1. Prepare the support (1) Preparation of mixture 90 g of siloxane-treated silicon carbide, 5 g of organic-treated silicon nitride, 0.5 g of polyacrylamide, 0.5 g of carbon nanotubes, and 0.5 g of microcrystalline wax were mixed uniformly, and then 3 g of modified silicone resin was added. After mixing uniformly, the mixture was processed by a kneader four times, each time for 30 minutes, to obtain a mixture; The preparation method of the siloxane-treated silicon carbide comprises placing 2.5 g of silicon carbide in a plasma device, introducing argon gas, controlling the argon gas flow rate to 42 sccm, the processing power to 90 W, and the processing time to 5.0 min. After the treatment is completed, the argon gas is turned off, and octamethylcyclotetrasiloxane gas is introduced, controlling the gas flow rate to 28 sccm, the processing power to 75 W, the processing pressure to 12 Pa, and the processing time to 18 min. After the treatment is completed, the siloxane-treated silicon carbide is obtained; The preparation method of the organically treated silicon nitride comprises the following steps: introducing 200 g of anhydrous ethanol into a reaction container, then adding 10 g of silicon nitride and stirring evenly, adding 3.5 g of hydroxyethyl acrylate and stirring evenly, adding 0.3 g of ammonium persulfate, raising the temperature to 80° C., and reacting under condensation reflux for 3.0 hours. After the stirring reaction is completed, lowering the temperature to 52° C., adding 1.7 g of trimethylolpropane triacrylate, stirring evenly, and placing the reaction container under ultraviolet light for irradiation treatment, wherein the irradiation time is 8 minutes, the ultraviolet wavelength is 350 nm, and the irradiation power is 15 mW / cm 2 , filtered, washed and dried to obtain organic-treated silicon nitride; The modified silicone resin is prepared by adding 45 g of phenyltrimethoxysilane and 46 g of trifluoropropyltrimethoxysilane to 18 g of anhydrous ethanol and mixing evenly, then adding 8 g of γ-glycidyl ether propyltrimethoxysilane, 0.7 g of bis(dioctyloxypyrophosphate)ethylene titanate and 0.8 g of tetramethylguanidine, raising the temperature to 34° C., stirring at 520 rpm for 40 minutes, then adding 7 g of nano-titanium dioxide and performing ultrasonic dispersion, wherein the ultrasonic time is 40 minutes, the ultrasonic frequency is 35 kHz, and the ultrasonic power is 220 W. After the ultrasonication is completed, the mixture is subjected to reduced pressure distillation at 50° C. for 1.5 hours, and the pressure of the reduced pressure distillation is -0.07 MPa, to obtain the modified silicone resin. The particle size of the nano titanium dioxide is 30 nm; (2) Acupuncture The mixture was placed in an extruder for extrusion molding, the extrusion speed was controlled to be 1.0 m / min, the extrusion pressure was 20 MPa, a cylinder with a wall thickness of 10 mm was extruded, and a directional hole was punctured on the cylinder with a special-shaped needle to obtain a green body. The diameter and spacing of the hole were adjusted by the structure of the needle. The diameter of the straight end hole was 1 mm, the diameter of the hexagonal circumscribed circle was 3 mm, the hole spacing was 1 mm, and the hexagonal depth was 1 mm. The green body was sintered at 1380°C for 5 h to obtain a support body.

[0017] 2. Preparation of composite film layer 0.3 g of silicon carbide fiber was placed in 100 g of deionized water to prepare a silicon carbide fiber slurry. The support was placed in the silicon carbide fiber slurry and suction was performed. The silicon carbide fiber slurry completely submerged the support. One end of the support was completely sealed, and the other end was connected to a suction pump. The suction pump was started, and the suction negative pressure was controlled to -0.08 MPa. The thickness of the silicon carbide fiber layer was controlled to 1.8 mm. The support was removed, the excess slurry was drained, and the support was dried at 80° C. for 12 h to obtain a silicon carbide fiber composite support. The silicon carbide fiber has a length of 1.5 mm and a diameter of 12 μm; 6 g of silicon carbide particles and 1.5 g of polyacrylamide were added to 50 g of acidic silica sol and 50 g of acidic aluminum sol, and the mixture was stirred to obtain a mixed slurry. A silicon carbide fiber composite support was placed in the mixed slurry for suction, and the mixed slurry was completely immersed in the silicon carbide fiber composite support. The suction negative pressure was controlled to -0.08 MPa, and the suction time was 1.5 min. After the suction was completed, the silicon carbide fiber composite support was removed, the excess slurry was drained, and the mixture was dried at 80°C for 12 h, and then sintered at 1300°C for 5.0 h to obtain a directional pore silicon carbide filter element. The particle size of the silicon carbide particles is 30 μm; The acidic silica sol has a pH value of 2.5 and a solid content of 30%; The acidic aluminum sol has a pH value of 3.5 and a solid content of 25%.

[0018] Example 2 1. Prepare the support (1) Preparation of mixture 86 g of siloxane-treated silicon carbide, 4 g of organic-treated silicon nitride, 0.4 g of polyacrylamide, 0.4 g of carbon nanotubes, and 0.3 g of microcrystalline wax were mixed uniformly, and then 2 g of modified silicone resin was added. After mixing uniformly, the mixture was processed by a kneader three times, each time for 35 minutes, to obtain a mixture; The preparation method of the siloxane-treated silicon carbide comprises placing 2.3 g of silicon carbide in a plasma device, introducing argon gas, controlling the argon gas flow rate to 40 sccm, the processing power to 86 W, and the processing time to 4.5 minutes. After the treatment is completed, the argon gas is turned off, and octamethylcyclotetrasiloxane gas is introduced, controlling the gas flow rate to 25 sccm, the processing power to 72 W, the processing pressure to 10 Pa, and the processing time to 16 minutes. After the treatment is completed, the siloxane-treated silicon carbide is obtained. The preparation method of the organically treated silicon nitride comprises the following steps: introducing 200 g of anhydrous ethanol into a reaction container, then adding 8 g of silicon nitride and stirring evenly, adding 3.4 g of hydroxyethyl acrylate and stirring evenly, adding 0.2 g of ammonium persulfate, raising the temperature to 78° C., and reacting under condensation and reflux for 3.4 hours. After the stirring reaction is completed, lowering the temperature to 50° C., adding 1.5 g of trimethylolpropane triacrylate, stirring evenly, and then irradiating the reaction under ultraviolet light for 6 minutes, with an ultraviolet wavelength of 340 nm and an irradiation power of 13 mW / cm 2 , filtered, washed and dried to obtain organic-treated silicon nitride; The modified organic silicone resin is prepared by adding 40 g of phenyltrimethoxysilane and 40 g of trifluoropropyltrimethoxysilane to 15 g of anhydrous ethanol and mixing evenly, then adding 5 g of γ-glycidyl ether propyltrimethoxysilane, 0.5 g of bis(dioctyloxypyrophosphate)ethylene titanate and 0.5 g of tetramethylguanidine, raising the temperature to 32° C., stirring at 510 rpm for 37 minutes, then adding 5 g of nano-titanium dioxide and performing ultrasonic dispersion, wherein the ultrasonic time is 35 minutes, the ultrasonic frequency is 30 kHz, and the ultrasonic power is 210 W. After the ultrasonication is completed, the mixture is subjected to reduced pressure distillation at 48° C. for 1.4 hours, and the pressure of the reduced pressure distillation is -0.09 MPa, to obtain the modified organic silicone resin. The particle size of the nano titanium dioxide is 20 nm; (2) Acupuncture The mixture was placed in an extruder for extrusion molding, the extrusion speed was controlled to be 0.5 m / min, the extrusion pressure was 10 MPa, a cylinder with a wall thickness of 10 mm was extruded, and a directional hole was punctured on the cylinder with a special-shaped needle to obtain a green body. The diameter and spacing of the hole were adjusted by the structure of the needle. The diameter of the straight end hole was 1.5 mm, the diameter of the hexagonal circumscribed circle was 3.5 mm, the hole spacing was 1.5 mm, and the hexagonal depth was 1 mm. The green body was sintered at 1300°C for 5.3 h to obtain a support body.

[0019] 2. Preparation of composite film layer 0.1 g of silicon carbide fiber was placed in 100 g of deionized water to prepare a silicon carbide fiber slurry. The support was placed in the silicon carbide fiber slurry and suction was performed. The silicon carbide fiber slurry completely submerged the support. One end of the support was completely sealed, and the other end was connected to a suction pump. The suction pump was started and the suction negative pressure was controlled to -0.09 MPa. The thickness of the silicon carbide fiber layer was controlled to 1.5 mm. The support was removed, the excess slurry was drained, and the support was dried at 78° C. for 14 h to obtain a silicon carbide fiber composite support. The silicon carbide fiber has a length of 1 mm and a diameter of 10 μm; 4 g of silicon carbide particles and 1 g of polyacrylamide were added to 50 g of acidic silica sol and 53 g of acidic aluminum sol, and the mixture was stirred to obtain a mixed slurry. A silicon carbide fiber composite support was placed in the mixed slurry for suction, and the mixed slurry was completely immersed in the silicon carbide fiber composite support. The suction negative pressure was controlled to -0.08 MPa, and the suction time was 1 min. After the suction was completed, the silicon carbide fiber composite support was removed, the excess slurry was drained, and the oriented pore silicon carbide filter element was dried at 78°C for 14 h, and then sintered at 1200°C for 4.8 h. The particle size of the silicon carbide particles is 20 μm; The acidic silica sol has a pH value of 2 and a solid content of 28%; The acidic aluminum sol has a pH value of 3 and a solid content of 23%.

[0020] Example 3 1. Prepare the support (1) Preparation of mixture 93 g of siloxane-treated silicon carbide, 6 g of organic-treated silicon nitride, 0.6 g of polyacrylamide, 0.7 g of carbon nanotubes, and 0.6 g of microcrystalline wax were mixed uniformly, and then 4 g of modified silicone resin was added. After mixing uniformly, the mixture was processed by a kneader 5 times, each time for 25 minutes, to obtain a mixture; The preparation method of the siloxane-treated silicon carbide comprises placing 2.7 g of silicon carbide in a plasma device, introducing argon gas, controlling the argon gas flow rate to 45 sccm, the processing power to 92 W, and the processing time to 5.5 minutes. After the treatment is completed, the argon gas is turned off, and octamethylcyclotetrasiloxane gas is introduced, controlling the gas flow rate to 30 sccm, the processing power to 77 W, the processing pressure to 14 Pa, and the processing time to 20 minutes. After the treatment is completed, the siloxane-treated silicon carbide is obtained. The preparation method of the organically treated silicon nitride comprises the following steps: introducing 200 g of anhydrous ethanol into a reaction container, then adding 12 g of silicon nitride and stirring evenly, adding 3.6 g of hydroxyethyl acrylate and stirring evenly, adding 0.5 g of ammonium persulfate, raising the temperature to 82° C., and reacting under condensation and reflux for 2.8 hours. After the stirring reaction is completed, lowering the temperature to 54° C., adding 1.8 g of trimethylolpropane triacrylate, stirring evenly, and then irradiating the reaction under ultraviolet light for 10 minutes, with an ultraviolet wavelength of 360 nm and an irradiation power of 18 mW / cm 2 , filtered, washed and dried to obtain organic-treated silicon nitride; The modified silicone resin is prepared by adding 50 g of phenyltrimethoxysilane and 50 g of trifluoropropyltrimethoxysilane to 20 g of anhydrous ethanol and mixing evenly, then adding 10 g of γ-glycidyl ether propyltrimethoxysilane, 1 g of bis(dioctyloxypyrophosphate)ethylene titanate, and 1 g of tetramethylguanidine, raising the temperature to 37° C., stirring at 540 rpm for 42 minutes, then adding 11 g of nano-titanium dioxide and performing ultrasonic dispersion, wherein the ultrasonic time is 45 minutes, the ultrasonic frequency is 38 kHz, and the ultrasonic power is 225 W. After the ultrasonication is completed, the mixture is subjected to reduced pressure distillation at 52° C. for 1.6 hours, and the pressure of the reduced pressure distillation is -0.06 MPa, to obtain the modified silicone resin. The particle size of the nano titanium dioxide is 50 nm; (2) Acupuncture The mixture was placed in an extruder for extrusion molding, the extrusion speed was controlled to 2.0 m / min, the extrusion pressure was 30 MPa, a cylinder with a wall thickness of 15 mm was extruded, and a directional hole was punctured on the cylinder with a special-shaped needle to obtain a green body. The diameter and spacing of the hole were adjusted by the structure of the needle. The diameter of the straight end hole was 2 mm, the diameter of the hexagonal circumscribed circle was 4 mm, the hole spacing was 2 mm, and the hexagonal depth was 1 mm. The green body was sintered at 1450°C for 4.8 hours to obtain a support body.

[0021] 2. Preparation of composite film layer 0.5 g of silicon carbide fiber was placed in 100 g of deionized water to prepare a silicon carbide fiber slurry. The support was placed in the silicon carbide fiber slurry and suction was performed. The silicon carbide fiber slurry completely submerged the support. One end of the support was completely sealed, and the other end was connected to a suction pump. The suction pump was started, and the suction negative pressure was controlled to -0.08 MPa. The thickness of the silicon carbide fiber layer was controlled to 2.0 mm. The support was removed, the excess slurry was drained, and the support was dried at 82° C. for 10 h to obtain a silicon carbide fiber composite support. The silicon carbide fiber has a length of 2 mm and a diameter of 14 μm; 8 g of silicon carbide particles and 2 g of polyacrylamide were added to 52 g of acidic silica sol and 48 g of acidic aluminum sol, and the mixture was stirred to obtain a mixed slurry. A silicon carbide fiber composite support was placed in the mixed slurry for suction, and the mixed slurry was completely immersed in the silicon carbide fiber composite support. The suction negative pressure was controlled to -0.098 MPa, and the suction time was 2 minutes. After the suction was completed, the silicon carbide fiber composite support was removed, the excess slurry was drained, and the directional pore silicon carbide filter element was dried at 82°C for 10 hours, and then sintered at 1400°C for 5.2 hours to obtain a directional pore silicon carbide filter element. The particle size of the silicon carbide particles is 80 μm; The acidic silica sol has a pH value of 3 and a solid content of 32%; The acidic aluminum sol has a pH value of 4 and a solid content of 28%.

[0022] Comparative Example 1-1 On the basis of Example 1, the changes are as follows: 1. Preparation of Support (1) Preparation of mixture 90 g of silicon carbide, 5 g of organically treated silicon nitride, 0.5 g of polyacrylamide, 0.5 g of carbon nanotubes, and 0.5 g of microcrystalline wax were mixed uniformly, and then 3 g of the silane mixture was added. After mixing uniformly, the mixture was processed by a kneader 4 times, each time for 30 minutes, to obtain a mixture; The preparation method of organically treated silicon nitride is exactly the same as that in Example 1; The silane mixture is prepared by uniformly stirring phenyltrimethoxysilane and trifluoropropyltrimethoxysilane, wherein the mass ratio of phenyltrimethoxysilane to trifluoropropyltrimethoxysilane is 45:46; (2) Acupuncture Exactly the same as Example 1.

[0023] The steps for preparing the composite film layer are exactly the same as those in Example 1.

[0024] Comparative Example 1-2 1. Preparation of Support (1) Preparation of mixture 90 g of siloxane-treated silicon carbide, 5 g of silicon nitride, 0.5 g of polyacrylamide, 0.5 g of carbon nanotubes, and 0.5 g of microcrystalline wax were mixed uniformly, and then 3 g of modified silicone resin was added. After mixing uniformly, the mixture was processed by a kneader four times, each time for 30 minutes, to obtain a mixture; The preparation method of the siloxane-treated silicon carbide and the preparation method of the modified silicone resin are exactly the same as those in Example 1; (2) Acupuncture Exactly the same as Example 1; 2. Preparation of composite film layer The preparation steps of the silicon carbide fiber composite support are exactly the same as those in Example 1; 6 g of silicon carbide particles and 1.5 g of polyacrylamide were added to 100 g of acidic silica sol and stirred to obtain a mixed slurry. The silicon carbide fiber composite support was placed in the mixed slurry for suction, and the mixed slurry was completely immersed in the silicon carbide fiber composite support. The suction negative pressure was controlled to -0.08 MPa, and the suction time was 1.5 min. After the suction was completed, the silicon carbide fiber composite support was removed, the excess slurry was drained, and the oriented pore silicon carbide filter element was dried at 80°C for 12 h, and then sintered at 1300°C for 5.0 h to obtain a silicon carbide filter element. The particle size of the silicon carbide particles is 30 μm; The acidic silica sol has a pH value of 2.5 and a solid content of 30%; The acidic aluminum sol has a pH value of 3.5 and a solid content of 25%.

[0025] Performance Testing (1) The porosity, membrane pore size, and air permeability resistance of the products prepared in Examples 1-3 were tested. The test results are as follows:

[0026] (2) The flexural strength and fracture toughness of the products obtained in Example 1-3, Comparative Example 1-1, and Comparative Example 1-2 were tested, and the high temperature resistance and high and low temperature cycle resistance of the products were tested. The test results are as follows:

[0027] Among them, the resistance to heating and cooling water is to raise the temperature of the products prepared in Examples 1-3, Comparative Example 1-1, and Comparative Example 1-2 to 1000°C at a rate of 30°C / min, keep warm for 30 minutes, and then immediately place them in 20°C deionized water for 10 minutes, with the deionized water completely immersing the products; the above operation is a heating-cooling cycle, and the heating-cooling cycle is repeated 20 times, and the flexural strength and fracture toughness are measured again; The present invention performs siloxane treatment on silicon carbide, octamethylcyclotetrasiloxane is cracked under the action of plasma, and combines with hydroxyl groups on the surface of silicon carbide, thereby realizing siloxane modification of silicon carbide, improving the surface activity of silicon carbide, and enhancing compatibility with organic silicone resin; then, silicon nitride is subjected to organic treatment, specifically, hydroxyethyl acrylate is polymerized by initiating polymerization of hydroxyethyl acrylate through ammonium persulfate, trimethylolpropane triacrylate generates active free radicals under ultraviolet light, and cross-links with polyhydroxyethyl acrylate to obtain polymer network-coated silicon nitride, thereby improving the dispersibility and interfacial bonding strength of silicon nitride; in the step of modifying the organic silicone resin, silane is used as a modification matrix, wherein phenylsilane can provide a skeleton and hydrophobic properties, thereby enhancing thermal stability, and fluorosilane introduces the low surface energy characteristics of fluorine element, thereby enhancing compatibility with other components, and the two are combined through hydrogen bonds during mixing to form a physical prepolymer network, thereby providing a basis for subsequent cross-linking; γ-condensation Hydroglycerol ether propyl trimethoxysilane is used as a bridging agent. Its epoxy group can react with the hydroxyl groups on the surface of silicon carbide and silicon nitride to enhance the interfacial bonding between the inorganic component and the organic resin. The epoxy group can also form a polyether cross-linked network through ring-opening polymerization under the action of tetramethylguanidine, thereby enhancing the toughness of the support. The titanate coupling agent can improve the dispersion performance of titanium dioxide in the organic phase, thereby obtaining a modified silicone resin with both the flexibility of the organic phase and the high strength of the inorganic phase. Combined with components such as carbon nanotubes, the toughness of the support is enhanced, and the mechanical properties, high temperature resistance and resistance to heating and water cooling of the support are improved. Then, a needle-punching process is used to prepare directional pore porous ceramics to obtain a green body with uniform pores. A suction process is used to prevent excess particles from clogging the pores, and a composite layer of fibers and aggregates can be formed, with an aggregate accumulation layer formed in the outermost layer. Due to the gradient pore structure design, the air permeability resistance is reduced and the filtration effect is improved.

[0028] Compared with Example 1, Comparative Example 1-1 omitted the siloxane modification of silicon carbide and the modification of the silicone resin. The interfacial bonding ability between the silicon carbide particles and the silicone resin was weak, and there was a lack of an effective toughening mechanism, thereby reducing the toughness and strength of the product, and also reducing the stability of the product. Its high and low temperature cycling performance was poor; Compared with Example 1, Comparative Example 1-2 omits the organic modification step of silicon nitride, which results in poor interface bonding of silicon nitride and increased crack incidence. In addition, the aluminum sol component is omitted in the film layer, which weakens the overall strength and toughness. The reduction rate of its strength and fracture toughness is less than that of Comparative Example 1-1.

[0029] Unless otherwise specified, all ratios and percentages described in the present invention are by mass.

[0030] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a directional pore silicon carbide filter element, characterized in that: The method comprises the steps of preparing a support body and preparing a composite film layer; The preparation of the support body includes the steps of preparing a mixture and needling; The step of preparing the mixture comprises mixing siloxane-treated silicon carbide, organic-treated silicon nitride, polyacrylamide, carbon nanotubes, and microcrystalline wax, adding modified organic silicone resin, and mixing uniformly to obtain a mixture; The modified silicone resin is prepared by adding phenyltrimethoxysilane and trifluoropropyltrimethoxysilane to anhydrous ethanol and mixing them evenly, then adding γ-glycidyl ether propyltrimethoxysilane, bis(dioctyloxypyrophosphate)ethylene titanate and tetramethylguanidine, stirring at 32-37° C. for 37-42 minutes, then adding nano-titanium dioxide for ultrasonic dispersion, and performing reduced pressure distillation to obtain the modified silicone resin; The preparation method of the organically treated silicon nitride comprises adding silicon nitride to anhydrous ethanol, stirring uniformly, adding hydroxyethyl acrylate and ammonium persulfate, heating to 78-82° C., condensing and refluxing for 2.8-3.4 hours, cooling to 50-54° C., adding trimethylolpropane triacrylate, and irradiating under ultraviolet light to obtain the organically treated silicon nitride; The steps of preparing the composite membrane layer are as follows: firstly placing the support body in the silicon carbide fiber slurry for suction, then placing the support body in the mixed slurry for suction, and sintering to obtain the directional pore silicon carbide filter element; The mixed slurry is prepared by stirring acidic silica sol, acidic aluminum sol, silicon carbide particles and polyacrylamide.

2. The method for preparing a directional pore silicon carbide filter element according to claim 1, characterized in that: In the step of preparing the mixture, the mass ratio of the siloxane-treated silicon carbide, organic-treated silicon nitride, modified silicone resin, polyacrylamide, carbon nanotubes, and microcrystalline wax is 86-93:4-6:2-4:0.4-0.6:0.4-0.7:0.3-0.

6.

3. The method for preparing a directional pore silicon carbide filter element according to claim 1, characterized in that: In the preparation method of organically treated silicon nitride, the irradiation treatment has an irradiation time of 6-10 minutes, an ultraviolet wavelength of 340-360 nm, and an irradiation power of 13-18 mW / cm 2 ; The mass ratio of the anhydrous ethanol, silicon nitride, hydroxyethyl acrylate, ammonium persulfate and trimethylolpropane triacrylate is 200:8-12:3.4-3.6:0.2-0.5:1.5-1.

8.

4. The method for preparing a directional pore silicon carbide filter element according to claim 1, characterized in that: In the preparation method of the modified silicone resin, the ultrasonic dispersion has an ultrasonic time of 35-45 min, an ultrasonic frequency of 30-38 kHz, and an ultrasonic power of 210-225 W; The particle size of the nano titanium dioxide is 20-50 nm; The mass ratio of the anhydrous ethanol, phenyltrimethoxysilane, trifluoropropyltrimethoxysilane, gamma-glycidyl ether propyltrimethoxysilane, bis(dioctyloxypyrophosphate)ethylene titanate, tetramethylguanidine and nano titanium dioxide is 15-20:40-50:40-50:5-10:0.5-1:0.5-1:5-11.

5. The method for preparing a directional pore silicon carbide filter element according to claim 1, characterized in that: The preparation method of the siloxane-treated silicon carbide comprises placing 2.3-2.7 g of silicon carbide in a plasma device, introducing argon gas, controlling the argon gas flow rate to 40-45 sccm, the treatment power to 86-92 W, and the treatment time to 4.5-5.5 minutes. After the treatment, the argon gas is turned off, and octamethylcyclotetrasiloxane gas is introduced, controlling the gas flow rate to 25-30 sccm, the treatment power to 72-77 W, the treatment pressure to 10-14 Pa, and the treatment time to 16-20 minutes. After the treatment, the siloxane-treated silicon carbide is obtained.

6. The method for preparing a directional pore silicon carbide filter element according to claim 1, characterized in that: The needling step comprises placing the mixed material into an extruder for extrusion molding, controlling the extrusion speed to be 0.5-2.0 m / min, the extrusion pressure to be 10-30 MPa, extruding a cylinder with a wall thickness of 10-20 mm, and using a special-shaped needle to needle-puncture directional holes in the cylinder to obtain a green body. The diameter and spacing of the holes are adjusted by the structure of the needle. The diameter of the straight end hole is 1-2 mm, the diameter of the hexagonal circumscribed circle is 3-4 mm, the hole spacing is 1-2 mm, and the hexagonal depth is 1 mm. The green body is sintered at 1300-1450° C. for 4.8-5.3 hours to obtain a support body.

7. The method for preparing a directional pore silicon carbide filter element according to claim 1, characterized in that: The steps of preparing the composite membrane layer include placing silicon carbide fibers in deionized water to prepare a silicon carbide fiber slurry, placing a support body in the silicon carbide fiber slurry for suction, completely immersing the support body in the silicon carbide fiber slurry, completely sealing one end of the support body, connecting the other end to a suction pump, starting the suction pump, controlling the suction negative pressure to -0.08 to -0.09 MPa, controlling the thickness of the silicon carbide fiber layer to 1.5 to 2.0 mm, removing the support body, draining excess slurry, and drying at 78 to 82° C. for 10 to 14 hours to obtain a silicon carbide fiber composite support body; The silicon carbide fiber has a length of 1-2 mm and a diameter of 10-14 μm; The mass ratio of the silicon carbide fiber to deionized water is 0.1-0.5:

100.

8. The method for preparing a directional pore silicon carbide filter element according to claim 1, characterized in that: The step of preparing the composite membrane layer further includes adding silicon carbide particles and polyacrylamide to the acidic silica sol and the acidic aluminum sol, stirring uniformly to obtain a mixed slurry; placing a silicon carbide fiber composite support body in the mixed slurry for suction, wherein the mixed slurry completely immerses the silicon carbide fiber composite support body, controlling the suction negative pressure to be -0.08 to -0.09 MPa, and the suction time to be 1 to 2 minutes. After the suction is completed, removing the silicon carbide fiber composite support body, draining excess slurry, drying at 78-82° C. for 10-14 hours, and then sintering at 1200-1400° C. for 4.8-5.2 hours to obtain a directional pore silicon carbide filter element; The particle size of the silicon carbide particles is 20-80 μm; The acidic silica sol has a pH value of 2-3 and a solid content of 28-32%; The acidic aluminum sol has a pH value of 3-4 and a solid content of 23-28%; The mass ratio of the acidic silica sol, the acidic aluminum sol, the silicon carbide particles and the polyacrylamide is 48-52:48-53:4-8:1-2.

9. A directional pore silicon carbide filter element, prepared by the preparation method according to any one of claims 1 to 8.

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