An oriented hole silicon carbide filter element and a method of making the same

Abstract

The application 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 a support body and preparing a composite film layer; the step of preparing the support body comprises the steps of preparing a mixture and needle punching; in the step of preparing the mixture, siloxane treated silicon carbide, organic treated silicon nitride, polyacrylamide, carbon nanotubes and microcrystalline wax are mixed, modified silicone resin is added, and the mixture is uniformly mixed to obtain the mixture; the preparation method of the organic treated silicon nitride comprises the following steps: adding silicon nitride into anhydrous ethanol, uniformly stirring, adding hydroxyethyl acrylate and ammonium persulfate, heating to 78-82 DEG C, condensing and refluxing for 2.8-3.4 h, cooling to 50-54 DEG C, adding trimethylolpropane triacrylate, and performing irradiation treatment under ultraviolet light to obtain the organic treated silicon nitride; the directional hole silicon carbide filter element prepared by the application has uniform porosity and pore size, high strength and excellent high-temperature resistance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of silicon carbide filter elements, and particularly relates to a directional hole silicon carbide filter element and a preparation method thereof. BACKGROUND

[0002] Silicon carbide (SiC) porous ceramics is a high-performance ceramic material with a special micro-porous 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 make it have broad application prospects in the fields of metallurgy, chemical industry, environmental protection, energy and the like.

[0003] The preparation methods of silicon carbide porous ceramics mainly include a particle accumulation method, a freeze-drying method, a 3D printing method and an organic foam impregnation method.

[0004] The particle accumulation method is to form sintering necks between ceramic particles to form a porous structure through the sintering performance of the ceramic particles. This method is simple in process, but has low porosity, and the pore structure is greatly affected by the particle shape and particle size distribution of raw materials. The freeze-drying method is to freeze ceramic slurry and then perform pressure reduction or vacuum drying treatment to make ice crystals sublimate and form a directional arrangement of pore structures. This method can control the pore structure, but has high requirements for the solid content of the slurry and the cooling rate. The 3D printing method is to use computer-aided design to spray binder on the raw material powder layer by layer through a printing head to form a product. This method can realize the preparation of complex shapes and uniform pore structures, but the process parameters still need to be optimized, and the cost is high. The organic foam impregnation method is to use an organic foam as a template, coat or impregnate ceramic slurry on the template, and then remove the template after sintering to form a porous structure. This method cannot prepare small-pore-diameter closed-pore products, and the performance of the preform is greatly affected by the raw materials.

[0005] Directional hole ceramics have high filtration efficiency due to the arrangement of pores in a certain direction, and are particularly suitable for scenes with high fluid directionality requirements. However, the manufacturing process is complex, the cost is high, and the effect may not be good when dealing with multi-directional fluid. Therefore, it is a research subject for technical personnel to provide a directional hole silicon carbide ceramic, reduce the cost, simplify the process, and improve the multi-directional fluid effect.

[0006] At present, the preparation methods of directional hole silicon carbide porous ceramics mainly include the freeze-drying method and the 3D printing method.

[0007] Although the freezing method has unique advantages in preparing anisotropic pore structures, the solid content of the slurry needs to be strictly controlled in the freezing method. If the solid content is too high, the viscosity of the slurry will be too large, and the particle phagocytosis phenomenon will easily occur during the growth of ice crystals, so that the ideal porous structure cannot be obtained. If the solid content is too low, the strength of the porous body after sublimation will be too low, and the desired shape cannot be maintained.

[0008] Secondly, during the freezing process, the growth rate and direction of ice crystals are affected by various factors such as temperature gradient and cooling rate. Uneven cooling rate will lead to unevenness of the pore structure, affecting the performance of the material. The single-sided cooling method is prone to cause the pore structure distance to gradually increase due to the thermal resistance of the solidified layer during the preparation process, resulting in uneven product structure and limiting its application range.

[0009] Furthermore, the sintering temperature of the porous ceramic body obtained by the freezing method needs to be precisely controlled during the sintering process. If the sintering temperature is too high, the body will shrink too much, reducing the porosity and increasing energy consumption. If the sintering temperature is too low, the body cannot be densified, affecting the mechanical properties of the material.

[0010] It can be seen that the preparation of directional porous ceramics by the freezing method requires precise control of parameters such as temperature, cooling rate and pressure during the freezing process, and the process is complex and requires high equipment. Due to the use of freeze-drying equipment and precise temperature control system, the preparation cost is relatively high.

[0011] 3D printing method for preparing directional pore porous ceramics has significant advantages and certain limitations.

[0012] 3D printing technology can realize high-precision manufacturing of complex structures, has high design flexibility, and can customize porosity, pore size and distribution according to demand. The characteristics of integrated forming reduce the assembly steps in traditional process, improve production efficiency, and have high material utilization, which is suitable for small-batch customized production. In addition, 3D printing technology can realize complex shape, high porosity and good pore connectivity when preparing porous ceramics, which has broad application prospects in aerospace, biomedicine and other fields.

[0013] However, 3D printing of porous ceramics has technical shortcomings, such as limited printing accuracy, especially in preparing submicron or nanoscale pore size, complex post-processing process, and the need for high-temperature sintering, which will cause deformation of the pore structure and reduce the strength. In addition, the cost of 3D printing equipment is high, the production efficiency is relatively low, and the particle size and fluidity of ceramic materials are required to be high. These factors to some extent limit its large-scale industrial application.

[0014] It can be seen that the prior art has problems of uneven pore size and porosity, unstable pore structure, poor mechanical properties and high cost. SUMMARY

[0015] To solve the above technical problems, the present application provides a directional pore silicon carbide filter element and a preparation method thereof, which ensures uniform pore size and porosity, high mechanical properties and excellent high temperature resistance.

[0016] To solve the above technical problems, the present application adopts the following technical solutions:

[0017] A preparation method of a directional pore silicon carbide filter element, comprising preparing a support body and a composite film layer, and the specific operation is as follows:

[0018] 1. Preparing a support body

[0019] (1) Preparing a mixture

[0020] The siloxane treated silicon carbide, organically treated silicon nitride, modified silicone resin, polyacrylamide, carbon nanotubes and microcrystalline wax are uniformly mixed, then the modified silicone resin is added, and after uniform mixing, the mixture is processed by a kneader for 3-5 times, each time for 25-35 min, to obtain the mixture;

[0021] The mass ratio of the siloxane treated silicon carbide, organically 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;

[0022] The preparation method of the siloxane treated silicon carbide is as follows: 2.3-2.7 g of silicon carbide is placed in a plasma device, argon gas is introduced, the argon gas flow is controlled at 40-45 sccm, the treatment power is 86-92 W, and the treatment time is 4.5-5.5 min; after the treatment is completed, the argon gas is turned off, octamethylcyclotetrasiloxane gas is introduced, the gas flow is controlled at 25-30 sccm, the treatment power is 72-77 W, the treatment pressure is 10-14 Pa, and the treatment time is 16-20 min; after the treatment is completed, the siloxane treated silicon carbide is obtained;

[0023] The preparation method of the organically treated silicon nitride is as follows: anhydrous ethanol is introduced into a reaction container, then silicon nitride is added and stirred uniformly, hydroxyethyl acrylate is added, after stirring uniformly, ammonium persulfate is added, the temperature is raised to 78-82℃, and the condensation reflux reaction is carried out for 2.8-3.4 h; after the stirring reaction is completed, the temperature is lowered to 50-54℃, trimethylolpropane triacrylate is added, and after stirring uniformly, it is placed under ultraviolet light for irradiation treatment; the irradiation time is 6-10 min, the ultraviolet wavelength is 340-360 nm, and the irradiation power is 13-18 mW / cm 2, filtration, washing, drying to obtain the organic treated silicon nitride;

[0024] The mass ratio of the anhydrous ethanol, silicon nitride, hydroxyethyl acrylate, ammonium persulfate, trimethylolpropane triacrylate is 200:8-12:3.4-3.6:0.2-0.5:1.5-1.8;

[0025] The preparation method of the modified silicone resin is that phenyltrimethoxysilane and trifluoropropyltrimethoxysilane are uniformly mixed in anhydrous ethanol, then γ-glycidoxypropyltrimethoxysilane, bis(dioctyloxyphosphato)ethyl titanate and tetramethylguanidine are added, the temperature is raised to 32-37℃, stirring is carried out at 510-540 rpm for 37-42 min, nano titanium dioxide is added for ultrasonic dispersion, the ultrasonic time is 35-45 min, the ultrasonic frequency is 30-38 kHz, the ultrasonic power is 210-225 W, after ultrasonic, distillation is carried out at 48-52℃ under reduced pressure for 1.4-1.6 h, the pressure of the reduced pressure distillation is-0.06~-0.09 MPa, to obtain the modified silicone resin;

[0026] The particle size of the nano titanium dioxide is 20-50 nm;

[0027] The mass ratio of the anhydrous ethanol, phenyltrimethoxysilane, trifluoropropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, bis(dioctyloxyphosphato)ethyl titanate, tetramethylguanidine, nano titanium dioxide is 15-20:40-50:40-50:5-10:0.5-1:0.5-1:5-11;

[0028] (2) needle punching

[0029] The mixture is put into an extruder for extrusion molding, the extrusion speed is controlled to be 0.5-2.0 m / min, the extrusion pressure is controlled to be 10-30 MPa, and the extrusion wall thickness is controlled to be 10-20 mm of a cylinder, a directional hole is punched on the cylinder by a special-shaped needle to obtain a green body, the diameter and the 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 circumscribed circle of the hexagon is 3-4 mm, the hole spacing is 1-2 mm, and the hexagon depth is 1 mm, the green body is sintered at 1300-1450℃ for 4.8-5.3 h to obtain the support body.

[0030] 2. Preparation of the composite membrane layer

[0031] The silicon carbide fibers are placed in deionized water to prepare a silicon carbide fiber slurry, the support is placed in the silicon carbide fiber slurry to perform suction, the silicon carbide fiber slurry completely immerses the support, one end of the support is completely sealed, the other end is connected to a suction pump, the suction pump is started, 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 to 2.0 mm, the support is taken out, the excess slurry is drained, and the support is dried at 78 to 82 ℃ for 10 to 14 h to obtain a silicon carbide fiber composite support;

[0032] The length of the silicon carbide fibers is 1 to 2 mm, and the diameter is 10 to 14 μm;

[0033] The mass ratio of the silicon carbide fibers to the deionized water is 0.1 to 0.5:100;

[0034] The acid silicon sol and the acid aluminum sol are added with silicon carbide particles and polyacrylamide, and after uniform stirring, a mixed slurry is obtained; the silicon carbide fiber composite support is placed in the mixed slurry to perform suction, the mixed slurry completely immerses the silicon carbide fiber composite support, the suction negative pressure is controlled to be -0.08 to -0.09 MPa, the suction time is 1 to 2 min, after the suction is completed, the silicon carbide fiber composite support is taken out, the excess slurry is drained, and the silicon carbide fiber composite support is dried at 78 to 82 ℃ for 10 to 14 h, and then sintered at 1200 to 1400 ℃ for 4.8 to 5.2 h to obtain a directional pore silicon carbide filter element;

[0035] The particle size of the silicon carbide particles is 20 to 80 μm;

[0036] The acid silicon sol has a pH value of 2 to 3 and a solid content of 28 to 32%;

[0037] The acid aluminum sol has a pH value of 3 to 4 and a solid content of 23 to 28%;

[0038] The mass ratio of the acid silicon sol, the acid aluminum sol, the silicon carbide particles and the polyacrylamide is 48 to 52:48 to 53:4 to 8:1 to 2.

[0039] A directional pore silicon carbide filter element is prepared by the preparation method.

[0040] Compared with the prior art, the present application has the following beneficial effects:

[0041] 1.The silicon carbide is subjected to siloxane treatment, octamethylcyclotetrasiloxane is cracked under the action of plasma and combined with the hydroxyl group on the surface of silicon carbide, thereby realizing the siloxane modification of the silicon carbide, improving the surface activity of the silicon carbide and enhancing the compatibility with the organic silicon resin; then the silicon nitride is subjected to organic treatment, specifically, ammonium persulfate is used to initiate the polymerization of hydroxyethyl acrylate, trimethylolpropane triacrylate generates active free radicals under ultraviolet light, and is crosslinked with polyhydroxyethyl acrylate, thereby obtaining a polymer network coated silicon nitride, and improving the dispersibility and interfacial bonding force of the silicon nitride; in the step of modifying the organic silicon resin, silane is used as a modified matrix, the phenyl silane in the silane can provide a skeleton and hydrophobic properties, enhance the thermal stability, the fluorosilane introduces the low surface energy characteristics of fluorine elements, enhances the compatibility with other components, and the two are combined to form a physical prepolymer network through hydrogen bonding during the mixing process, thereby providing a basis for subsequent crosslinking; the epoxy group of gamma-glycidoxypropyltrimethoxysilane as a bridging agent can react with the hydroxyl group on the surface of the silicon carbide and the silicon nitride, thereby enhancing the interfacial bonding between the inorganic components and the organic resin, the epoxy group can also undergo ring-opening polymerization under the action of tetramethyl guanidine to form a polyether crosslinking network, thereby enhancing the toughness of the support body, and the titanate coupling agent can improve the dispersibility of titanium dioxide in the organic phase, thereby obtaining a modified organic silicon resin with the flexibility of the organic phase and the high strength of the inorganic phase, and combining with components such as carbon nanotubes, thereby enhancing the toughness of the support body and improving the mechanical properties, high temperature resistance and temperature rise-water cooling resistance of the support body; then a needle punching process is used to prepare a directional hole porous ceramic, thereby obtaining a green body with uniform pores, and using a suction process, the excess particles will not block the pore channels, and a composite layer of fibers and aggregates can be formed, and an aggregate accumulation layer can be formed on the outermost layer, due to the gradient pore structure design, the air permeation resistance is reduced, and the filtration effect is improved;

[0042] 2.The directional hole silicon carbide filter element prepared by the method has a porosity of 38-45%, a membrane layer pore size of 20-30μm, and an air permeation resistance of 150-370Pa.

[0043] 3.The directional hole silicon carbide filter element prepared by the method has a bending strength of 18.5-23.6MPa and a fracture toughness of 2.45-2.67MPa·m 1 / 2 at 26℃, a bending strength of 17.6-22.7MPa and a fracture toughness of 2.34-2.58MPa·m 1 / 2 after 20 times of temperature rise-water cooling treatment, and a bending strength of 17.2-22.3MPa and a fracture toughness of 2.28-2.52MPa·m 1 / 2 . BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 It is the structure of the outer surface of the support body pipe;

[0045] Figure 2 to support the cross-sectional structure of the body;

[0046] Figure 3 to support the cross-sectional structure of the body; DETAILED DESCRIPTION

[0047] In order to more clearly understand the technical features, objectives and effects of the present application, a specific embodiment of the present application will be described first.

[0048] Example 1

[0049] 1. Preparation of the support

[0050] (1) Preparation of the mixture

[0051] 90 g of siloxane-treated 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 modified silicone resin was added. After mixing uniformly, the mixture was processed by a kneader for 4 times, 30 min each time, to obtain the mixture;

[0052] The preparation method of the siloxane-treated silicon carbide is as follows: 2.5 g of silicon carbide was placed in a plasma device, argon gas was introduced, the argon gas flow was controlled at 42 sccm, the processing power was 90 W, and the processing time was 5.0 min. After the processing was completed, the argon gas was turned off, octamethylcyclotetrasiloxane gas was introduced, the gas flow was controlled at 28 sccm, the processing power was 75 W, the processing pressure was 12 Pa, and the processing time was 18 min. After the processing was completed, the siloxane-treated silicon carbide was obtained;

[0053] The preparation method of the organically treated silicon nitride is as follows: 200 g of anhydrous ethanol was introduced into a reaction container, and then 10 g of silicon nitride was added and stirred uniformly. Then 3.5 g of hydroxyethyl acrylate was added, and after stirring uniformly, 0.3 g of ammonium persulfate was added. The temperature was raised to 80℃, and the condensation reflux reaction was carried out for 3.0 h. After the stirring reaction was completed, the temperature was lowered to 52℃, 1.7 g of trimethylolpropane triacrylate was added, and after stirring uniformly, it was placed under ultraviolet light for irradiation treatment. The irradiation time was 8 min, the ultraviolet wavelength was 350 nm, and the irradiation power was 15 mW / cm 2 After filtration, washing and drying, the organically treated silicon nitride was obtained;

[0054] The preparation method of the modified silicone resin is as follows: 45 g of phenyltrimethoxysilane, 46 g of trifluoropropyltrimethoxysilane are uniformly mixed in 18 g of anhydrous ethanol, then 8 g of γ-glycidyl ether propyltrimethoxysilane, 0.7 g of bis(dioctyloxy diphosphate) ethylene titanate, and 0.8 g of tetramethyl guanidine are added, the temperature is raised to 34℃, and stirring is performed at 520 rpm for 40 min, then 7 g of nano titanium dioxide is added for ultrasonic dispersion, the ultrasonic time is 40 min, the ultrasonic frequency is 35 kHz, the ultrasonic power is 220 W, after ultrasonic treatment, distillation is performed at 50℃ under reduced pressure for 1.5 h, the pressure of the reduced pressure distillation is -0.07 MPa, and the modified silicone resin is obtained;

[0055] The particle size of the nano titanium dioxide is 30 nm;

[0056] (2) needle punching

[0057] The mixture is placed into an extruder for extrusion molding, the extrusion speed is controlled to be 1.0 m / min, the extrusion pressure is 20 MPa, and a cylindrical body with a wall thickness of 10 mm is obtained, a special-shaped needle is used to needle punch directional holes on the cylindrical body 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 mm, the diameter of the circumscribed circle of the hexagon is 3 mm, the hole spacing is 1 mm, and the depth of the hexagon is 1 mm, and the green body is sintered at 1380℃ for 5 h to obtain the support body.

[0058] 2. Preparation of a composite membrane layer

[0059] 0.3 g of silicon carbide fibers are placed in 100 g of deionized water to prepare a silicon carbide fiber slurry, 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, the other end is connected to a suction pump, the suction pump is started, the suction negative pressure is controlled to be -0.08 MPa, and the thickness of the silicon carbide fiber layer is controlled to be 1.8 mm, the support body is taken out, the excess slurry is drained, and drying is performed at 80℃ for 12 h to obtain a silicon carbide fiber composite support body.

[0060] The length of the silicon carbide fiber is 1.5 mm, and the diameter is 12 μm.

[0061] 6 g of silicon carbide particles and 1.5 g of polyacrylamide are added to 50 g of an acidic silicon sol and 50 g of an acidic aluminum sol, the mixture is uniformly stirred, and a mixed slurry is obtained; the silicon carbide fiber composite support body is placed in the mixed slurry for suction, the mixed slurry completely immerses the silicon carbide fiber composite support body, the suction negative pressure is controlled to be -0.08 MPa, the suction time is 1.5 min, after the suction is completed, the silicon carbide fiber composite support body is taken out, the excess slurry is drained, drying is performed at 80℃ for 12 h, and then sintering is performed at 1300℃ for 5.0 h to obtain a directional hole silicon carbide filter element.

[0062] The particle size of the silicon carbide particles is 30 μm;

[0063] The acidic silicon sol has a pH value of 2.5 and a solid content of 30%;

[0064] The acidic aluminum sol has a pH value of 3.5 and a solid content of 25%.

[0065] Example 2

[0066] 1. Preparation of the support body

[0067] (1) Preparation of the mixture

[0068] 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 uniform mixing, the mixture was processed by a kneader for 3 times, each for 35 min, to obtain the mixture;

[0069] The preparation method of the siloxane-treated silicon carbide is as follows: 2.3 g of silicon carbide was placed in a plasma device, argon gas was introduced, the argon gas flow was controlled at 40 sccm, the processing power was 86 W, and the processing time was 4.5 min. After the processing was completed, the argon gas was turned off, octamethylcyclotetrasiloxane gas was introduced, the gas flow was controlled at 25 sccm, the processing power was 72 W, the processing pressure was 10 Pa, and the processing time was 16 min. After the processing was completed, the siloxane-treated silicon carbide was obtained;

[0070] The preparation method of the organic-treated silicon nitride is as follows: 200 g of anhydrous ethanol was introduced into a reaction container, and then 8 g of silicon nitride was added and stirred uniformly. Then, 3.4 g of hydroxyethyl acrylate was added, and after uniform stirring, 0.2 g of ammonium persulfate was added. The temperature was raised to 78°C, and the reaction was carried out under reflux condensation for 3.4 h. After the stirring reaction was completed, the temperature was lowered to 50°C, 1.5 g of trimethylolpropane triacrylate was added, and after uniform stirring, it was placed under ultraviolet light for irradiation treatment. The irradiation time was 6 min, the ultraviolet wavelength was 340 nm, and the irradiation power was 13 mW / cm 2 After filtration, washing, and drying, the organic-treated silicon nitride was obtained;

[0071] The preparation method of the modified silicone resin is as follows: 40 g of phenyltrimethoxysilane and 40 g of trifluoropropyltrimethoxysilane are uniformly mixed in 15 g of anhydrous ethanol, and then 5 g of γ-glycidyl ether propyltrimethoxysilane, 0.5 g of bis(dioctyloxy diphosphate) ethylene titanate, and 0.5 g of tetramethyl guanidine are added. The temperature is raised to 32°C, and stirring is performed at 510 rpm for 37 min. Then, 5 g of nano titanium dioxide is added for ultrasonic dispersion, with an ultrasonic time of 35 min, an ultrasonic frequency of 30 kHz, and an ultrasonic power of 210 W. After ultrasonic treatment, the mixture is distilled at 48°C under reduced pressure for 1.4 h, with a reduced pressure of -0.09 MPa, to obtain the modified silicone resin.

[0072] The particle size of the nano titanium dioxide is 20 nm.

[0073] (2) Needle punching

[0074] The mixture is placed into an extruder for extrusion molding, with an extrusion speed of 0.5 m / min, an extrusion pressure of 10 MPa, and an extrusion wall thickness of 10 mm to form a cylindrical body. A special-shaped needle is used to punch directional holes on the cylindrical body 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 holes is 1.5 mm, the diameter of the circumscribed circle of the hexagonal holes is 3.5 mm, the hole spacing is 1.5 mm, and the depth of the hexagonal holes is 1 mm. The green body is sintered at 1300°C for 5.3 h to obtain the support body.

[0075] 2. Preparation of the composite membrane layer

[0076] 0.1 g of silicon carbide fibers is placed in 100 g of deionized water to prepare a silicon carbide fiber slurry. 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, the suction negative pressure is controlled to be -0.09 MPa, and the thickness of the silicon carbide fiber layer is controlled to be 1.5 mm. The support body is taken out, the excess slurry is drained, and dried at 78°C for 14 h to obtain a silicon carbide fiber composite support body.

[0077] The length of the silicon carbide fibers is 1 mm, and the diameter is 10 μm.

[0078] 4 g of silicon carbide particles and 1 g of polyacrylamide are added to 50 g of acidic silicon sol and 53 g of acidic aluminum sol. After uniform stirring, a mixed slurry is obtained. The silicon carbide fiber composite support body is placed in the mixed slurry for suction. The mixed slurry completely immerses the silicon carbide fiber composite support body, the suction negative pressure is controlled to be -0.08 MPa, and the suction time is 1 min. After suction, the silicon carbide fiber composite support body is taken out, the excess slurry is drained, and dried at 78°C for 14 h. Then, the silicon carbide fiber composite support body is sintered at 1200°C for 4.8 h to obtain a directional hole silicon carbide filter element.

[0079] The particle size of the silicon carbide particles is 20 μm;

[0080] The acidic silicon sol has a pH value of 2 and a solid content of 28%;

[0081] The acidic aluminum sol has a pH value of 3 and a solid content of 23%.

[0082] Example 3

[0083] 1. Preparation of the support

[0084] (1) Preparation of the mixture

[0085] 93 g of siloxane-treated silicon carbide, 6 g of organically 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 uniform mixing, the mixture was processed by a kneader for 5 times, each time for 25 min, to obtain the mixture;

[0086] The preparation method of the siloxane-treated silicon carbide is as follows: 2.7 g of silicon carbide was placed in a plasma device, argon gas was introduced, the argon gas flow was controlled at 45 sccm, the processing power was 92 W, and the processing time was 5.5 min. After the processing was completed, the argon gas was turned off, octamethylcyclotetrasiloxane gas was introduced, the gas flow was controlled at 30 sccm, the processing power was 77 W, the processing pressure was 14 Pa, and the processing time was 20 min. After the processing was completed, the siloxane-treated silicon carbide was obtained;

[0087] The preparation method of the organically treated silicon nitride is as follows: 200 g of anhydrous ethanol was introduced into a reaction container, and then 12 g of silicon nitride was added and stirred uniformly. Then, 3.6 g of hydroxyethyl acrylate was added, and after uniform stirring, 0.5 g of ammonium persulfate was added. The temperature was raised to 82°C, and the condensation reflux reaction was carried out for 2.8 h. After the stirring reaction was completed, the temperature was lowered to 54°C, 1.8 g of trimethylolpropane triacrylate was added, and after uniform stirring, it was placed under ultraviolet light for irradiation treatment. The irradiation time was 10 min, the ultraviolet wavelength was 360 nm, and the irradiation power was 18 mW / cm 2 After filtration, washing, and drying, the organically treated silicon nitride was obtained;

[0088] The preparation method of the modified silicone resin is as follows: 50 g of phenyltrimethoxysilane and 50 g of trifluoropropyltrimethoxysilane are uniformly mixed in 20 g of anhydrous ethanol, and then 10 g of γ-glycidyl ether propyltrimethoxysilane, 1 g of bis(dioctyloxy diphosphate) ethylene titanate, and 1 g of tetramethyl guanidine are added. The temperature is raised to 37℃, and stirring is performed at 540 rpm for 42 min. Then, 11 g of nano-titanium dioxide is added for ultrasonic dispersion, with an ultrasonic time of 45 min, an ultrasonic frequency of 38 kHz, and an ultrasonic power of 225 W. After ultrasonic treatment, the mixture is distilled at 52℃ under reduced pressure for 1.6 h, with a reduced pressure of -0.06 MPa, to obtain the modified silicone resin.

[0089] The particle size of the nano-titanium dioxide is 50 nm.

[0090] (2) Needle punching

[0091] The mixture is placed into an extruder for extrusion molding, with an extrusion speed of 2.0 m / min, an extrusion pressure of 30 MPa, and an extrusion wall thickness of 15 mm to form a cylindrical body. A special-shaped needle is used to punch directional holes on the cylindrical body 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 holes is 2 mm, the diameter of the circumscribed circle of the hexagonal holes is 4 mm, the spacing between the holes is 2 mm, and the depth of the hexagonal holes is 1 mm. The green body is sintered at 1450℃ for 4.8 h to obtain the support body.

[0092] 2. Preparation of the composite membrane layer

[0093] 0.5 g of silicon carbide fibers are placed in 100 g of deionized water to prepare a silicon carbide fiber slurry. 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, the suction negative pressure is controlled to be -0.08 MPa, and the thickness of the silicon carbide fiber layer is controlled to be 2.0 mm. The support body is taken out, the excess slurry is drained, and dried at 82℃ for 10 h to obtain a silicon carbide fiber composite support body.

[0094] The length of the silicon carbide fibers is 2 mm, and the diameter is 14 μm.

[0095] 8 g of silicon carbide particles and 2 g of polyacrylamide are added to 52 g of acidic silicon sol and 48 g of acidic aluminum sol. After uniform stirring, a mixed slurry is obtained. The silicon carbide fiber composite support body is placed in the mixed slurry for suction. The mixed slurry completely immerses the silicon carbide fiber composite support body, the suction negative pressure is controlled to be -0.098 MPa, and the suction time is 2 min. After suction, the silicon carbide fiber composite support body is taken out, the excess slurry is drained, and dried at 82℃ for 10 h. Then, the silicon carbide fiber composite support body is sintered at 1400℃ for 5.2 h to obtain a directional hole silicon carbide filter element.

[0096] The particle size of the silicon carbide particles is 80 μm;

[0097] The acidic silicon sol has a pH value of 3 and a solid content of 32%;

[0098] The acidic aluminum sol has a pH value of 4 and a solid content of 28%.

[0099] Comparative Example 1-1

[0100] On the basis of Example 1, the changes are that,

[0101] 1. Preparation of the support

[0102] (1) Preparation of the mixture

[0103] 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 a silane mixture was added. After mixing uniformly, the mixture was processed by a kneader for 4 times, 30 min each time, to obtain a mixture;

[0104] The organically treated silicon nitride was prepared by the same method as in Example 1.

[0105] The silane mixture was prepared by stirring uniformly phenyltrimethoxysilane and trifluoropropyltrimethoxysilane, and the mass ratio of the phenyltrimethoxysilane to the trifluoropropyltrimethoxysilane was 45:46.

[0106] (2) Needle punching

[0107] The same as in Example 1.

[0108] The steps of preparing the composite film layer were the same as in Example 1.

[0109] Comparative Example 1-2

[0110] 1. Preparation of the support

[0111] (1) Preparation of the mixture

[0112] 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 a modified silicone resin was added. After mixing uniformly, the mixture was processed by a kneader for 4 times, 30 min each time, to obtain a mixture;

[0113] The preparation method of the siloxane-treated silicon carbide and the preparation method of the modified silicone resin were the same as in Example 1.

[0114] (2) Needle punching

[0115] The same as in Example 1.

[0116] 2. Preparation of composite membrane layer

[0117] The preparation steps of the silicon carbide fiber composite support are completely same as those in Example 1;

[0118] 6 g of silicon carbide particles and 1.5 g of polyacrylamide were added into 100 g of acidic silica sol, and after stirring uniformly, a mixed slurry was obtained; the silicon carbide fiber composite support was placed in the mixed slurry for suction, the mixed slurry completely immersed the silicon carbide fiber composite support, the suction negative pressure was controlled to be -0.08 MPa, the suction time was 1.5 min, after the suction was completed, the silicon carbide fiber composite support was taken out, the excess slurry was drained, and then dried at 80℃ for 12 h, and then sintered at 1300℃ for 5.0 h, to obtain a directional pore silicon carbide filter element;

[0119] The particle size of the silicon carbide particles is 30 μm;

[0120] The acidic silica sol has a pH value of 2.5 and a solid content of 30%;

[0121] The acidic aluminum sol has a pH value of 3.5 and a solid content of 25%.

[0122] Performance test

[0123] (1) The products prepared in Examples 1-3 were tested for porosity, membrane layer pore size and air permeation resistance, and the test results are as follows:

[0124]

[0125] (2) The products prepared in Examples 1-3, Comparative Examples 1-1 and 1-2 were tested for flexural strength and fracture toughness, and the high temperature resistance and high-low temperature cycle resistance of the products were tested, and the test results are as follows:

[0126]

[0127] Among them, the temperature resistance-water cooling resistance is that the products prepared in Examples 1-3, Comparative Examples 1-1 and 1-2 are raised to 1000℃ at a rate of 30℃ / min, and then immediately placed in 20℃ deionized water for 10 min, and the deionized water completely immersed the products; the above operation is one temperature-water cooling cycle, and the temperature-water cooling cycle is repeated for 20 times, and then the flexural strength and fracture toughness are tested again;

[0128] The silicon carbide is subjected to siloxane treatment, octamethylcyclotetrasiloxane is cleaved under the action of plasma and combined with the hydroxyl group on the surface of the silicon carbide, thus realizing the siloxane modification of the silicon carbide, improving the surface activity of the silicon carbide and enhancing the compatibility with the organic silicon resin; then the silicon nitride is subjected to organic treatment, specifically, ammonium persulfate is used to initiate the polymerization of hydroxyethyl acrylate, trimethylolpropane triacrylate generates active free radicals under ultraviolet light, and is crosslinked with the polyhydroxyethyl acrylate, thus obtaining a polymer network coated silicon nitride, improving the dispersibility and interface bonding force of the silicon nitride; in the modification step of the organic silicon resin, silane is used as a modified matrix, the phenyl silane in the silane can provide a skeleton and hydrophobic property, enhance the thermal stability, the fluorosilane introduces the low surface energy property of fluorine element, enhances the compatibility with other components, and the two are combined through hydrogen bonds to form a physical prepolymer network during the mixing process, thus providing a basis for subsequent crosslinking; the epoxy group of gamma-glycidoxypropyltrimethoxysilane as a bridging agent can react with the hydroxyl group on the surface of the silicon carbide and the silicon nitride, thus enhancing the interface bonding between the inorganic components and the organic resin, the epoxy group can also undergo ring-opening polymerization under the action of tetramethyl guanidine to form a polyether crosslinking network, thus enhancing the toughness of the support body, and the titanate coupling agent can improve the dispersibility of titanium dioxide in the organic phase, thus obtaining a modified organic silicon resin with the flexibility of the organic phase and the high strength of the inorganic phase, and combining with components such as carbon nanotubes, thus enhancing the toughness of the support body and improving the mechanical properties, high-temperature resistance and temperature-rise-water-cooling resistance of the support body; then a needle punching process is used to prepare a porous ceramic with directional holes, thus obtaining a green body with uniform pores, and an aspiration process is used, so that the excess particles will not block the pores and can form a composite layer of fibers and aggregates, and an aggregate accumulation layer is formed on the outermost layer, due to the gradient pore structure design, the air permeation resistance is reduced and the filtration effect is improved.

[0129] Comparative Example 1-1 is compared with Example 1, the siloxane modification of the silicon carbide and the modification step of the organic silicon resin are omitted, the interface bonding capacity between the silicon carbide particles and the organic silicon resin is weak, and there is a lack of effective toughening mechanism, thus reducing the toughness and strength of the product and also reducing the stability of the product, and the low-temperature resistance and high-temperature resistance cycle performance is poor;

[0130] Comparative Example 1-2 is compared with Example 1, the organic modification step of the silicon nitride is omitted, which leads to poor interface bonding of the silicon nitride, an increased crack occurrence rate, and the omission of the aluminum sol component in the film layer, which weakens the overall strength and toughness, and the strength and fracture toughness reduction rate is less than that of Comparative Example 1-1.

[0131] Unless otherwise specified, the proportions described in the present application are mass proportions, and the percentages described are mass percentages.

[0132] Finally, it should be noted that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art will appreciate that modifications can be made to the technical solutions described in the foregoing embodiments, or some of the technical features thereof can be replaced equivalently, without departing from the spirit and principle of the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a directional porous silicon carbide filter element, characterized in that, This includes the steps of preparing the support and preparing the composite film. The preparation of the support includes the preparation of a mixture and a needle punching step; The preparation of the mixture involves mixing siloxane-treated silicon carbide, organic-treated silicon nitride, polyacrylamide, carbon nanotubes, and microcrystalline wax, adding modified organosilicon resin, and mixing evenly to obtain the mixture. The mass ratio of the siloxane-treated silicon carbide, the organic-treated silicon nitride, the modified organosilicon resin, the polyacrylamide, the carbon nanotubes, and the microcrystalline wax is 86-93:4-6:2-4:0.4-0.6:0.4-0.7:0.3-0.

6. The method for preparing siloxane-treated silicon carbide is as follows: 2.3-2.7g of silicon carbide is placed in a plasma device, argon gas is introduced, the argon gas flow rate is controlled at 40-45 sccm, the treatment power is 86-92W, the treatment time is 4.5-5.5min, after the treatment is completed, the argon gas is turned off, octamethylcyclotetrasiloxane gas is introduced, the gas flow rate is controlled at 25-30 sccm, the treatment power is 72-77W, the treatment pressure is 10-14Pa, the treatment time is 16-20min, after the treatment is completed, siloxane-treated silicon carbide is obtained; The modified organosilicon resin is prepared by adding phenyltrimethoxysilane and trifluoropropyltrimethoxysilane to anhydrous ethanol and mixing them evenly. Then, γ-glycidyl ether propyltrimethoxysilane, bis(dioctyloxypyrophosphate) ethylene titanate and tetramethylguanidine are added and stirred at 32-37°C for 37-42 min. Then, nano-titanium dioxide is added and ultrasonically dispersed for 35-45 min, ultrasonic frequency of 30-38 kHz, and ultrasonic power of 210-225 W. The modified organosilicon resin is obtained by vacuum distillation. The particle size of the nano-titanium dioxide is 20-50 nm; The mass ratio of anhydrous ethanol, phenyltrimethoxysilane, trifluoropropyltrimethoxysilane, γ-glycidyl etherpropyltrimethoxysilane, 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. The method for preparing the organically treated silicon nitride is as follows: silicon nitride is added to anhydrous ethanol and stirred until homogeneous. Hydroxyethyl acrylate and ammonium persulfate are then added. The mixture is heated to 78-82°C and refluxed for 2.8-3.4 hours. The mixture is then cooled to 50-54°C, and trimethylolpropane triacrylate is added. The mixture is then irradiated under ultraviolet light for 6-10 minutes at a wavelength of 340-360 nm and a power of 13-18 mW / cm². 2 Organically treated silicon nitride is obtained; 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 steps for preparing the composite membrane include: preparing a silicon carbide fiber slurry by placing silicon carbide fibers in deionized water; placing a support in the silicon carbide fiber slurry and performing suction, ensuring the silicon carbide fiber slurry completely submerges the support; sealing one end of the support completely and connecting the other end to a suction pump; starting the suction pump and controlling the suction negative pressure to -0.08 to -0.09 MPa; controlling the thickness of the silicon carbide fiber layer to 1.5-2.0 mm; removing the support, draining excess slurry, and drying at 78-82℃ for 10-14 hours to obtain a silicon carbide fiber composite support. The silicon carbide fiber has a length of 1-2 mm and a diameter of 10-14 μm; The mass ratio of silicon carbide fiber to deionized water is 0.1-0.5:100; Silicon carbide particles and polyacrylamide are added to acidic silica sol and acidic aluminum sol, and stirred evenly to obtain a mixed slurry. The silicon carbide fiber composite support is placed in the mixed slurry for suction, and the mixed slurry completely submerges the silicon carbide fiber composite support. The suction negative pressure is controlled at -0.08 to -0.09 MPa, and the suction time is 1-2 minutes. After the suction is completed, the silicon carbide fiber composite support is removed, excess slurry is drained, and it is dried at 78-82℃ for 10-14 hours. Then it is sintered at 1200-1400℃ for 4.8-5.2 hours to obtain a directional pore silicon carbide filter element. The silicon carbide particles have a particle size of 20-80 μm; The acidic silica sol has a pH of 2-3 and a solid content of 28-32%. The acidic aluminum sol has a pH of 3-4 and a solid content of 23-28%. The mass ratio of the acidic silica sol, acidic aluminum sol, silicon carbide particles, and polyacrylamide is 48-52:48-53:4-8:1-2.

2. The method for preparing a directional porous silicon carbide filter element according to claim 1, characterized in that, The needle punching step involves placing the mixture into an extruder for extrusion molding, controlling the extrusion speed at 0.5-2.0 m / min and the extrusion pressure at 10-30 MPa, extruding a cylinder with a wall thickness of 10-20 mm, and using a shaped needle to punch directional holes in the cylinder to obtain a blank. 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 circumscribed circle of the hexagon is 3-4 mm, the hole spacing is 1-2 mm, and the hexagonal depth is 1 mm. The blank is sintered at 1300-1450℃ for 4.8-5.3 h to obtain a support.

3. A directional porous silicon carbide filter element, prepared by the method of any one of claims 1-2.

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