Cordierite ceramic with gradient pore structure and method of making same

Abstract

This invention provides a cordierite ceramic with a gradient pore structure and its preparation method, relating to the field of porous cordierite ceramics. The preparation method of the cordierite ceramic with a gradient pore structure includes the following steps: adding alumina, magnesium oxide, and silica to a polymer dispersion containing polyvinyl alcohol microspheres, ball milling until uniform, then adding functional additives and ball milling until uniform to obtain a phase inversion slurry; the polymer dispersion containing polyvinyl alcohol microspheres is prepared by uniformly dispersing polyvinyl alcohol in a mixture of polyphenylene ether sulfone, N-methylpyrrolidone, and polyvinylpyrrolidone. This invention effectively avoids uneven pores or closed pores during sintering, achieving a uniform and controllable pore size distribution, low closed-pore rate, and enabling gradient changes in porosity, simultaneously improving porosity and flexural strength. It also avoids cracking or deformation of the green body after phase inversion, improving process stability.

Description

Technical Field

[0001] This invention relates to the field of porous cordierite ceramics, and in particular to a cordierite ceramic with a gradient pore structure and its preparation method. Background Technology

[0002] Cordierite is a magnesium aluminum silicate mineral composed of silicon dioxide (SiO2), aluminum oxide (Al2O3), and magnesium oxide (MgO). Its silicon dioxide (SiO2) content is approximately 51 wt%, aluminum oxide (Al2O3) content is approximately 35%, and magnesium oxide (MgO) content is approximately 14%. Cordierite possesses a unique cyclic silicate structure, with its framework consisting of six-membered rings formed by Si(Al)O4 tetrahedra stacked in parallel, creating one-dimensional channels along the c-axis of the crystal. Furthermore, cordierite exhibits excellent adsorption and filtration properties, and demonstrates good resistance to acids, alkalis, and corrosion. It can operate stably for extended periods in most wastewater environments without causing secondary pollution due to ion dissolution. It performs exceptionally well in treating organic dye wastewater and other industrial wastewater, and is widely used in the water treatment field.

[0003] Cordierite, as a ceramic material for water treatment, requires high porosity and high water flux. Therefore, a pore-forming agent must be used in its preparation process. Through experimental research, the inventors discovered that existing preparation processes for cordierite ceramic materials generally use starch, graphite, or other components as pore-forming agents, mixing the pore-forming agent with cordierite raw material powder using dry or wet mixing methods. However, during the mixing process, due to the significant difference in density and specific gravity between the cordierite raw material powder and the aforementioned pore-forming agent, it is difficult to achieve uniformity and stability during mixing, easily leading to agglomeration or stratification. In the subsequent sintering process, this results in the formation of uneven pores with a wide pore size distribution and a large number of non-connected pores, resulting in a high closed-pore rate. This not only limits water flux but also severely affects the mechanical properties of cordierite ceramics. Furthermore, since the mechanical strength of cordierite ceramics is strongly negatively correlated with porosity, it is difficult to simultaneously optimize to obtain high porosity and high flexural strength.

[0004] Furthermore, in the wet mixing process of pore-forming agent and cordierite raw material powder, not only are the aforementioned technical defects present, but there are also problems such as the green body being prone to swelling, cracking or deformation after phase transformation of the mixed slurry, low mechanical strength of the green body, low yield of molded products, poor stability of the preparation process, and unfavorable conditions for large-scale industrial production.

[0005] Based on this, a method for preparing cordierite ceramics with a gradient pore structure is provided. This method can overcome the agglomeration or stratification that easily occurs when mixing pore-forming components with cordierite raw material powder in existing methods. It effectively avoids uneven pores or closed pores during sintering, resulting in a uniform and controllable pore size distribution, low closed pore rate, and the ability to achieve a gradient change in porosity. This simultaneously improves porosity and flexural strength, which is beneficial for water treatment filtration. Furthermore, it can avoid the swelling, cracking, or deformation of the green body after phase transformation of the mixed slurry during the preparation process, thus improving process stability and facilitating large-scale production. This method has significant technical significance and research value. Summary of the Invention

[0006] To address the technical problems existing in the prior art, this invention provides a method for preparing cordierite ceramics with a gradient pore structure. This method overcomes the agglomeration or stratification that easily occurs when mixing pore-forming components with cordierite raw material powder. It effectively avoids uneven pores or closed pores during sintering, resulting in a uniform and controllable pore size distribution, low closed pore rate, and the ability to achieve a gradient change in porosity. This simultaneously improves porosity and flexural strength, which is beneficial for water treatment filtration. Furthermore, it avoids the swelling, cracking, or deformation of the green body after phase transformation of the mixed slurry during the preparation process, improving process stability and facilitating large-scale production.

[0007] The present invention also provides cordierite ceramics with a gradient pore structure prepared by the aforementioned preparation method.

[0008] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A method for preparing cordierite ceramics with a gradient pore structure includes the following steps: preparing a phase transformation slurry, performing a phase transformation treatment, and drying and sintering. The method for preparing the phase inversion slurry is as follows: alumina, magnesium oxide, and silica are added to a polymer dispersion containing polyvinyl alcohol microspheres, ball-milled until uniform, and then functional additives are added and ball-milled until uniform to obtain the phase inversion slurry. The polymer dispersion containing polyvinyl alcohol microspheres is prepared by uniformly dispersing polyvinyl alcohol in a mixture of polyphenylene ether sulfone, N-methylpyrrolidone and polyvinylpyrrolidone. The functional additive is a mixture of terpineol, glycerin, and oleic acid; The phase transformation treatment method is as follows: the phase transformation slurry is introduced into the molding mold, the mold containing the phase transformation slurry is placed in deionized water for phase transformation treatment, and the mold is demolded to obtain the green body; The green body is dried and sintered to obtain cordierite ceramic with a gradient pore structure.

[0009] Preferably, in the polymer dispersion containing polyvinyl alcohol microspheres, the weight ratio of polyphenylene ether sulfone, N-methylpyrrolidone, polyvinylpyrrolidone, and polyvinyl alcohol is 5-8:1-2:85-90:3-5. The degree of polymerization of the polyvinyl alcohol is 1700-2400, and the degree of alcoholysis is 88-99% (molar percentage).

[0010] Preferably, in the functional additives, the weight ratio of terpineol, glycerin, and oleic acid is 4-5:2-3:1-2.

[0011] Preferably, in the preparation of the phase inversion slurry, the weight ratio of alumina, magnesium oxide, and silicon dioxide is 30-32:10-12:56-58.

[0012] Preferably, in the preparation of the phase inversion slurry, the weight ratio of the polymer dispersion containing polyvinyl alcohol microspheres to the total weight of alumina, magnesium oxide and silica is 2-2.5:1. The weight ratio of the functional additives used to the total weight of aluminum oxide, magnesium oxide and silicon dioxide is 8-10:100.

[0013] Preferably, in the phase inversion treatment, the volume ratio of the mold containing the phase inversion slurry to deionized water is 1:10-15; The phase transformation temperature is 25-35℃, and the holding time for phase transformation treatment is 12-24h.

[0014] Furthermore, in the drying and sintering process, the green body is first pre-dried and then dried with hot air to obtain a dry green body with a moisture content of ≤1wt%. The pre-drying temperature is 40-50℃, and the pre-drying time is 6-8 hours; The hot air drying temperature is 60-70℃, the hot air drying speed is 0.5-1m / s, and the hot air drying time is 12-16h.

[0015] Furthermore, in the drying and sintering process, after the green body is dried to obtain a dry green body, it is placed in an air atmosphere environment, heated from room temperature to 500-550℃, and sintered at that temperature; then the temperature is further increased to 1000-1050℃, and sintered at that temperature; then the temperature is further increased to 1250-1300℃, and sintered at that temperature, and then cooled to obtain cordierite ceramic with a gradient pore structure.

[0016] Preferably, the rate of heating from room temperature to 500-550℃ is 1-2℃ / min, and the holding and sintering time is 2-3h; The heating rate continues to rise to 1000-1050℃ at a rate of 2-3℃ / min, and the holding sintering time is 1-1.5h; The temperature is increased to 1250-1300℃ at a rate of 1-2℃ / min, and the holding time for sintering is 4-6h. The cooling rate is 2-3℃ / min.

[0017] A cordierite ceramic with a gradient pore structure prepared by the aforementioned method.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The method for preparing cordierite ceramics with gradient pore structure of the present invention involves combining polyvinyl alcohol (PVA) with polyphenylene ether sulfone (PPS), N-methylpyrrolidone (N-methylpyrrolidone), and PPS. Utilizing the insolubility of PVA in PPS, a polymer dispersion containing PVA solid microspheres is prepared and then mixed with cordierite ceramic powder raw materials to improve the uniformity of the pore-forming agent distribution in the ceramic slurry. Simultaneously, functional additives containing terpineol, glycerol, and oleic acid are added to prevent ceramic powder agglomeration, reduce slurry viscosity, improve slurry leveling, regulate the replacement rate of organic solvent and water, and reduce green defects. Furthermore, during the phase transformation process, PVA is used as the core pore-forming component, combined with a terpineol-glycerol-oleic acid auxiliary pore-forming system, supplemented by N-methylpyrrolidone during the phase transformation process. The pores formed by the displacement of methylpyrrolidone with water form the basic pore structure, and the polyvinyl alcohol forms secondary micropores after sintering and burning, effectively improving the uniformity of micropore size. This creates a composite gradient pore structure of "basic pores + secondary micropores" inside the cordierite ceramic. The aforementioned technologies work together synergistically to overcome the agglomeration or stratification that easily occurs when mixing existing pore-forming components with cordierite raw material powder. This effectively avoids uneven pores or closed pores during sintering, resulting in a uniform and controllable pore size distribution, low closed pore rate, and the ability to achieve a gradient change in porosity. This simultaneously improves porosity and flexural strength, which is beneficial for water treatment filtration. Furthermore, it avoids the swelling, cracking, or deformation of the green body after phase transformation of the mixed slurry during the preparation process, improving process stability and facilitating large-scale production.

[0019] (2) The cordierite ceramic with gradient pore structure of the present invention has a permeation pore diameter of 50-80 μm and a dense pore diameter of 5-10 μm; a porosity of 70-85%, an open pore rate of ≥90%, and a closed pore rate of <5%; a porosity gradient change rate of 8-10% / cm; and a water flux (25℃) from the permeation surface to the dense surface of ≥800 L / (m²). 2 • h·MPa); removal rate of particles with a diameter ≥5μm ≥99%; flexural strength (three-point bending method) ≥15MPa, compressive strength ≥30MPa; weight loss rate after soaking in boiling water for 24h <1%; cordierite crystal phase purity ≥95%; weight loss rate after soaking in 5wt% HCl solution / 5wt% NaOH solution for 24h is not higher than 2%. Attached Figure Description

[0020] Figure 1 The image shows an electron microscope image of the cordierite ceramic with a gradient pore structure prepared in Example 1. Detailed Implementation

[0021] To provide a clearer understanding of the technical features, objectives, and effects of this invention, specific embodiments are now described. It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0022] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, "first," "second," etc., are used to distinguish similar objects and are not used to describe a particular order or sequence. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0023] This invention provides a method for preparing cordierite ceramics with a gradient pore structure, comprising the following steps: preparing a polymer dispersion, preparing a functional additive, preparing a phase inversion slurry, performing a phase inversion treatment, and drying and sintering.

[0024] The method for preparing the polymer dispersion is as follows: polyphenylene ether sulfone, N-methylpyrrolidone, polyvinylpyrrolidone, and polyvinyl alcohol are mixed and stirred at 50-100℃ for 2-6 hours until the dispersion is uniform, thereby obtaining a polymer dispersion containing polyvinyl alcohol microspheres.

[0025] In the preparation of the polymer dispersion, the weight ratio of polyphenylene ether sulfone, N-methylpyrrolidone, polyvinylpyrrolidone, and polyvinyl alcohol is 5-8:1-2:85-90:3-5.

[0026] In the prepared polymer dispersion, the degree of polymerization of polyvinyl alcohol is 1700-2400, and the degree of alcoholysis is 88-99% (molar percentage).

[0027] The method for preparing the functional additive is as follows: terpineol, glycerin, and oleic acid are stirred and mixed evenly at room temperature in a weight ratio of 4-5:2-3:1-2 to obtain the functional additive.

[0028] The method for preparing the phase inversion slurry is as follows: weigh each ceramic powder according to the weight ratio of alumina, magnesium oxide, and silicon dioxide of 30-32:10-12:56-58; add alumina, magnesium oxide, and silicon dioxide to a polymer dispersion containing polyvinyl alcohol microspheres; use a planetary ball mill to ball mill for 6-10 hours; then add functional additives and ball mill for 1-2 hours to obtain the phase inversion slurry.

[0029] In the preparation of the phase inversion slurry, the total weight ratio of ceramic powder (alumina, magnesium oxide, and silicon dioxide) to the weight ratio of the polymer dispersion containing polyvinyl alcohol microspheres is 1:2-2.5. The total weight ratio of ceramic powder (alumina, magnesium oxide, silicon dioxide) to functional additives is 100:8-10.

[0030] The phase inversion treatment method involves introducing a phase inversion slurry into a molding mold, then placing the mold containing the phase inversion slurry in 10-15 times its volume of deionized water, and maintaining the temperature at 25-35℃ for 12-24 hours for phase inversion treatment. After demolding, a green body is obtained. During this process, N-methylpyrrolidone in the phase inversion slurry dissolves into the deionized water through capillary action, forming a green body with gradient channels.

[0031] The drying and sintering method is as follows: the green body is first pre-dried at a temperature of 40-50℃ for 6-8 hours; then it is dried by hot air circulation at a temperature of 60-70℃ for 12-16 hours to remove the bound water inside the green body and obtain a dry green body with a moisture content ≤1wt%; then the dried green body is placed in a sintering furnace and heated from room temperature to 500-550℃ at a heating rate of 1-2℃ / min in an air atmosphere, and held for 2-3 hours; then the temperature is further increased to 1000-1050℃ at a heating rate of 2-3℃ / min and held for 1-1.5 hours; then the temperature is further increased to 1250-1300℃ at a heating rate of 1-2℃ / min and held for 4-6 hours, and then cooled to room temperature at a cooling rate of 2-3℃ / min to obtain cordierite ceramic with a gradient pore structure.

[0032] The method for preparing cordierite ceramics with a gradient pore structure according to embodiments of the present invention firstly involves using polyphenylene ether sulfone, N-methylpyrrolidone, polyvinylpyrrolidone, and polyvinyl alcohol in combination. Taking advantage of the insolubility of polyvinyl alcohol in polyvinylpyrrolidone, a polymer dispersion containing polyvinyl alcohol solid microspheres is prepared. Then, terpineol, glycerol, and oleic acid are used to prepare functional additives. These functional additives are then ball-milled and mixed with the polymer dispersion containing polyvinyl alcohol solid microspheres to prepare a phase inversion slurry. Terpineol is a nonionic dispersant; its long carbon chains can be adsorbed onto the surface of ceramic powder, inhibiting agglomeration between ceramic particles caused by van der Waals forces through steric hindrance, thereby reducing slurry viscosity and improving dispersion stability. Glycerol is a polar co-dispersant that can form a hydrogen bond network with N-methylpyrrolidone, regulating the replacement rate of N-methylpyrrolidone and increasing the concentration of N-methylpyrrolidone solid microspheres in the polymer dispersion. Polyvinyl alcohol (PVA) improves stability and enhances the mechanical strength of green bodies. The carboxyl groups of oleic acid can coordinate with the hydroxyl groups on the surface of ceramic powders (alumina / magnesia / silica), achieving directional coating of the ceramic powders, improving their wettability and dispersibility, and regulating the rate of water penetration into the green body, thus preventing cracking and deformation caused by excessively rapid replacement. Through the synergistic effect of these three factors, ceramic powder agglomeration is prevented, the uniformity of ceramic powder mixing in polymer dispersions containing PVA microspheres is improved, slurry viscosity is reduced, slurry leveling is improved, replacement rate is regulated, and green body defects are reduced. Then, during the phase transformation process, polyvinyl alcohol (PVA) is used as the core pore-forming component, combined with a terpineol-glycerol-oleic acid auxiliary pore-forming system. The pores formed by the replacement of N-methylpyrrolidone with water during the phase transformation are used as the basic pore structure. After sintering and burning off, PVA forms secondary micropores, which effectively improves the uniformity of micropore size and realizes the composite pore-forming of "basic pores + secondary micropores". Specifically, as a water-soluble polymer, PVA can partially swell with water during the phase transformation process. Its swelling property can regulate the replacement rate of N-methylpyrrolidone with water: water first penetrates into the PVA microspheres on the surface of the slurry, causing the PVA microspheres to swell and rupture to form micropores, while promoting the replacement of N-methylpyrrolidone. The swelling rate of PVA microspheres inside the slurry is slow, and the replacement rate of N-methylpyrrolidone is also slow. This achieves a continuous gradient decrease in the replacement rate from the surface to the interior of the slurry, thereby effectively controlling the formation rate and size of the pores and ultimately forming a continuous gradient change in pore size.

[0033] This invention also provides cordierite ceramics with a gradient pore structure prepared by the aforementioned method. Specific properties of the cordierite ceramics are shown in the table below:

[0034] The present invention will be further described below with reference to some specific embodiments.

[0035] Example 1 This embodiment provides a method for preparing cordierite ceramics with a gradient pore structure, specifically as follows: 1. Preparation of polymer dispersion First, polyphenylene ether sulfone, N-methylpyrrolidone, and polyvinylpyrrolidone are mixed, heated to 60°C, and stirred for 2 hours. Then, polyvinyl alcohol PVA-1799 is added, and the mixture is stirred for another 2 hours to obtain a polymer dispersion containing polyvinyl alcohol microspheres.

[0036] The weight ratio of polyphenylene ether sulfone, N-methylpyrrolidone, polyvinylpyrrolidone, and polyvinyl alcohol PVA-1799 is 5:1:90:4.

[0037] 2. Preparation of functional additives Terpineol, glycerin, and oleic acid were mixed at room temperature for 30 minutes in a weight ratio of 4:2:1 to obtain the functional additive.

[0038] 3. Preparation of phase inversion slurry Weigh out each ceramic powder according to the weight ratio of alumina, magnesium oxide, and silicon dioxide of 31:11:58; add alumina, magnesium oxide, and silicon dioxide to a polymer dispersion containing polyvinyl alcohol microspheres, control the ball-to-particle ratio at 4:1, and ball mill at 300 rpm. After ball milling for 8 hours using a planetary ball mill, add functional additives and ball mill for another 2 hours to obtain a phase inversion slurry.

[0039] The total weight ratio of ceramic powder (alumina, magnesium oxide, and silicon dioxide) to the weight ratio of polymer dispersion containing polyvinyl alcohol microspheres is 1:2.

[0040] The total weight ratio of ceramic powder (alumina, magnesium oxide, silicon dioxide) to functional additives is 100:8.

[0041] 4. Phase transformation treatment The phase inversion slurry is introduced into the molding mold, and then the mold containing the phase inversion slurry is placed in 10 times its volume of deionized water. The phase inversion is carried out at 25°C and 50 rpm with low stirring. After soaking for 18 hours, the phase inversion is determined to be complete after the conductivity has remained unchanged for 2 hours by monitoring the conductivity. A green body with gradient channels is obtained.

[0042] 5. Drying and sintering After pre-drying the green body at 40℃ for 6 hours, the green body is dried by hot air circulation, with the hot air temperature controlled at 60℃, the hot air velocity at 0.5m / s, and the drying time at 12 hours to remove the bound water inside the green body, obtaining a dry green body with a moisture content ≤1wt%. Then, the dried green body is placed in a sintering furnace and heated from room temperature to 500℃ in an air atmosphere at a heating rate of 1℃ / min, and held for 2 hours. Then, the temperature is further increased to 1000℃ at a heating rate of 2℃ / min, and held for 1 hour. Then, the temperature is further increased to 1250℃ at a heating rate of 1℃ / min, and held for 4 hours. Finally, the temperature is cooled to room temperature at a cooling rate of 2℃ / min to obtain cordierite ceramic with a gradient pore structure.

[0043] This embodiment also provides cordierite ceramics with a gradient pore structure prepared by the aforementioned method, as shown in the electron microscope image below. Figure 1 As shown; the obtained cordierite ceramics had a permeation pore size of 65 μm and a dense pore size of 8 μm; a porosity of 78%, an open pore rate of 92%, and a closed pore rate of 3%; a porosity gradient change rate of 9% / cm; and a water flux (25℃) from the permeation surface to the dense surface of 850 L / (m²). 2 The removal rate of particles with a diameter ≥5μm was 99.2%; the bending strength (three-point bending method) was 16MPa, and the compressive strength was 32MPa; the weight loss rate after soaking in boiling water for 24h was 0.8%; the purity of cordierite crystal phase was 96%; the weight loss rate after soaking in 5wt% HCl solution / 5wt% NaOH solution for 24h was not higher than 1.5%.

[0044] Example 2 This embodiment provides a method for preparing cordierite ceramics with a gradient pore structure, specifically as follows: 1. Preparation of polymer dispersion First, polyphenylene ether sulfone, N-methylpyrrolidone, and polyvinylpyrrolidone are mixed, heated to 80°C, and stirred for 3 hours. Then, polyvinyl alcohol PVA-1799 is added, and the mixture is stirred for another 3 hours to obtain a polymer dispersion containing polyvinyl alcohol microspheres.

[0045] The weight ratio of polyphenylene ether sulfone, N-methylpyrrolidone, polyvinylpyrrolidone, and polyvinyl alcohol PVA-1799 is 6:2:88:4.

[0046] 2. Preparation of functional additives Terpineol, glycerin, and oleic acid were mixed at room temperature for 30 minutes in a weight ratio of 5:3:2 to obtain the functional additive.

[0047] 3. Preparation of phase inversion slurry Weigh out each ceramic powder according to the weight ratio of alumina, magnesium oxide, and silicon dioxide of 32:12:56; add alumina, magnesium oxide, and silicon dioxide to a polymer dispersion containing polyvinyl alcohol microspheres, control the ball-to-particle ratio at 5:1, and ball mill at 350 rpm. After ball milling for 6 hours using a planetary ball mill, add functional additives and ball mill for another 2 hours to obtain a phase inversion slurry.

[0048] The total weight ratio of ceramic powder (alumina, magnesium oxide, and silicon dioxide) to the weight ratio of polymer dispersion containing polyvinyl alcohol microspheres is 1:2.2.

[0049] The total weight ratio of ceramic powder (alumina, magnesium oxide, silicon dioxide) to functional additives is 100:9.

[0050] 4. Phase transformation treatment The phase inversion slurry is introduced into the molding mold, and then the mold containing the phase inversion slurry is placed in 12 times the volume of deionized water. The phase inversion is carried out at 30°C and 80 rpm with low stirring. After soaking for 20 hours, the phase inversion is determined to be complete after the conductivity has remained unchanged for 2 hours by monitoring the conductivity. A green body with gradient channels is obtained.

[0051] 5. Drying and sintering After pre-drying the green body at 45℃ for 7 hours, the green body is dried by hot air circulation, with the hot air temperature controlled at 65℃, the hot air velocity at 0.8 m / s, and the drying time at 14 hours to remove the bound water inside the green body, obtaining a dry green body with a moisture content ≤1wt%. Then, the dried green body is placed in a sintering furnace and heated from room temperature to 500℃ in an air atmosphere at a heating rate of 1.5℃ / min, and held for 2 hours. Then, the temperature is further increased to 1000℃ at a heating rate of 2.5℃ / min, and held for 1 hour. Then, the temperature is further increased to 1280℃ at a heating rate of 1.5℃ / min, and held for 5 hours. Finally, the temperature is cooled to room temperature at a cooling rate of 2.5℃ / min to obtain cordierite ceramic with a gradient pore structure.

[0052] This embodiment also provides cordierite ceramics with a gradient pore structure prepared by the aforementioned method; the obtained cordierite ceramics have a permeation pore diameter of 75 μm and a dense pore diameter of 9 μm; a porosity of 82%, an open pore rate of 93%, and a closed pore rate of 2%; a porosity gradient change rate of 9.5% / cm; and a water flux (25℃) from the permeation surface to the dense surface of 900 L / (m²). 2The removal rate of particles with a diameter ≥5μm was 99.3%; the bending strength (three-point bending method) was 17MPa, and the compressive strength was 34MPa; the weight loss rate after soaking in boiling water for 24h was 0.7%; the purity of cordierite crystal phase was 97%; the weight loss rate after soaking in 5wt% HCl solution / 5wt% NaOH solution for 24h was not higher than 1.3%.

[0053] Example 3 This embodiment provides a method for preparing cordierite ceramics with a gradient pore structure, specifically as follows: 1. Preparation of polymer dispersion First, polyphenylene ether sulfone, N-methylpyrrolidone, and polyvinylpyrrolidone are mixed, heated to 100°C, and stirred for 2 hours. Then, polyvinyl alcohol PVA-1799 is added, and the mixture is stirred for another 2 hours to obtain a polymer dispersion containing polyvinyl alcohol microspheres.

[0054] The weight ratio of polyphenylene ether sulfone, N-methylpyrrolidone, polyvinylpyrrolidone, and polyvinyl alcohol PVA-1799 is 8:1.5:85.5:5.

[0055] 2. Preparation of functional additives Terpineol, glycerin, and oleic acid were mixed at room temperature for 30 minutes in a weight ratio of 4.5:2.5:1.5 to obtain the functional additive.

[0056] 3. Preparation of phase inversion slurry Weigh out each ceramic powder according to the weight ratio of alumina, magnesium oxide, and silicon dioxide of 30:10:58; add alumina, magnesium oxide, and silicon dioxide to a polymer dispersion containing polyvinyl alcohol microspheres, control the ball-to-particle ratio at 4.5:1, and ball mill at 400 rpm. After ball milling for 10 hours using a planetary ball mill, add functional additives and ball mill for another 2 hours to obtain a phase inversion slurry.

[0057] The total weight ratio of ceramic powder (alumina, magnesium oxide, and silicon dioxide) to the weight ratio of the polymer dispersion containing polyvinyl alcohol microspheres is 1:2.5.

[0058] The total weight ratio of ceramic powder (alumina, magnesium oxide, silicon dioxide) to functional additives is 100:10.

[0059] 4. Phase transformation treatment The phase inversion slurry is introduced into the molding mold, and then the mold containing the phase inversion slurry is placed in 15 times its volume of deionized water. The phase inversion is carried out at 35°C and 100 rpm with low stirring. After soaking for 24 hours, the phase inversion is determined to be complete after the conductivity has remained unchanged for 2 hours by monitoring the conductivity. A green body with gradient channels is obtained.

[0060] 5. Drying and sintering After pre-drying the green body at 50℃ for 8 hours, the green body is dried by hot air circulation, with the hot air temperature controlled at 70℃, the hot air velocity at 1m / s, and the drying time at 16 hours to remove the bound water inside the green body, obtaining a dry green body with a moisture content ≤1wt%. Then, the dried green body is placed in a sintering furnace and heated from room temperature to 550℃ in an air atmosphere at a heating rate of 2℃ / min, and held for 2 hours. Then, the temperature is further increased to 1050℃ at a heating rate of 3℃ / min, and held for 1 hour. Then, the temperature is further increased to 1300℃ at a heating rate of 2℃ / min, and held for 6 hours. Finally, the temperature is cooled to room temperature at a cooling rate of 3℃ / min to obtain cordierite ceramic with a gradient pore structure.

[0061] This embodiment also provides cordierite ceramics with a gradient pore structure prepared by the aforementioned method; the obtained cordierite ceramics have a permeation pore diameter of 80 μm and a dense pore diameter of 10 μm; a porosity of 85%, an open pore rate of 91%, and a closed pore rate of 4%; a porosity gradient change rate of 10% / cm; and a water flux (25℃) from the permeation surface to the dense surface of 920 L / (m²). 2 The particle size distribution (·h·MPa) was 99.1% for particles with a diameter ≥5μm; the bending strength (three-point bending method) was 15MPa, and the compressive strength was 31MPa; the weight loss rate after soaking in boiling water for 24h was 0.9%; the purity of the cordierite crystal phase was 95%; and the weight loss rate after soaking in 5wt% HCl solution / 5wt% NaOH solution for 24h was no higher than 1.8%.

[0062] Comparative Example 1 Comparative Example 1 uses the cordierite ceramic preparation scheme of Example 1, with the following differences: 1) Polyvinyl alcohol PVA-1799 is not used. Polyphenylene ether sulfone, N-methylpyrrolidone and polyvinylpyrrolidone are mixed evenly at a weight ratio of 5:1:94. Then, 4% of the total weight of the ceramic powder is added as a pore-forming agent starch. After mixing evenly, the mixture is ball-milled with the ceramic powder to prepare a phase inversion slurry; 2) The preparation and addition of functional additives are omitted.

[0063] Testing revealed that the cordierite ceramics prepared in Comparative Example 1 exhibited uneven pore size distribution, with permeation pores ranging from 40-90 μm and dense pores from 10-25 μm, showing no continuous gradient change. The porosity was 55%, with an open-pore ratio of 75% and a closed-pore ratio of 18%. No clear porosity gradient was observed. The water flux (25℃) from the permeation surface to the dense surface was 350 L / (m²·h·MPa). The removal rate for particles ≥5 μm was 90.5%. The flexural strength (three-point bending method) was 9 MPa, and the compressive strength was 18 MPa. The weight loss rate after immersion in boiling water for 24 hours was 1.5%. The cordierite crystal phase purity was 88% (starch ignition residue carbon affected crystal phase development). The weight loss rates after immersion in 5wt% HCl solution / 5wt% NaOH solution for 24 hours were both higher than 3.2%.

[0064] Unless otherwise stated, all percentages used in this invention are mass percentages.

[0065] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing cordierite ceramics with a gradient pore structure, characterized in that, The process includes the following steps: preparation of phase inversion slurry, phase inversion treatment, drying and sintering; The method for preparing the phase inversion slurry is as follows: alumina, magnesium oxide, and silica are added to a polymer dispersion containing polyvinyl alcohol microspheres, ball-milled until uniform, and then functional additives are added and ball-milled until uniform to obtain the phase inversion slurry. The polymer dispersion containing polyvinyl alcohol microspheres is prepared by uniformly dispersing polyvinyl alcohol in a mixture of polyphenylene ether sulfone, N-methylpyrrolidone and polyvinylpyrrolidone. The functional additive is a mixture of terpineol, glycerin, and oleic acid; The phase transformation treatment method is as follows: the phase transformation slurry is introduced into the molding mold, the mold containing the phase transformation slurry is placed in deionized water for phase transformation treatment, and the mold is demolded to obtain the green body; The green body is dried and sintered to obtain cordierite ceramic with a gradient pore structure.

2. The method for preparing cordierite ceramics with a gradient pore structure according to claim 1, characterized in that, In the polymer dispersion containing polyvinyl alcohol microspheres, the weight ratio of polyphenylene ether sulfone, N-methylpyrrolidone, polyvinylpyrrolidone, and polyvinyl alcohol is 5-8:1-2:85-90:3-5. The degree of polymerization of the polyvinyl alcohol is 1700-2400, and the degree of alcoholysis is 88-99%.

3. The method for preparing cordierite ceramics with a gradient pore structure according to claim 1, characterized in that, In the functional additives, the weight ratio of terpineol, glycerin, and oleic acid is 4-5:2-3:1-2.

4. The method for preparing cordierite ceramics with a gradient pore structure according to claim 1, characterized in that, In the preparation of the phase inversion slurry, the weight ratio of alumina, magnesium oxide, and silicon dioxide is 30-32:10-12:56-58.

5. The method for preparing cordierite ceramics with a gradient pore structure according to claim 1, characterized in that, In the preparation of the phase inversion slurry, the weight ratio of the polymer dispersion containing polyvinyl alcohol microspheres to the total weight of alumina, magnesium oxide and silica is 2-2.5:

1. The weight ratio of the functional additives used to the total weight of aluminum oxide, magnesium oxide and silicon dioxide is 8-10:

100.

6. The method for preparing cordierite ceramics with a gradient pore structure according to claim 1, characterized in that, In the phase inversion treatment, the volume ratio of the mold containing the phase inversion slurry to deionized water is 1:10-15. The phase transformation temperature is 25-35℃, and the holding time for phase transformation treatment is 12-24h.

7. The method for preparing cordierite ceramics with a gradient pore structure according to claim 1, characterized in that, In the drying and sintering process, the green body is first pre-dried and then dried with hot air to obtain a dry green body with a moisture content of ≤1wt%. The pre-drying temperature is 40-50℃, and the pre-drying time is 6-8 hours; The hot air drying temperature is 60-70℃, the hot air drying speed is 0.5-1m / s, and the hot air drying time is 12-16h.

8. The method for preparing cordierite ceramics with a gradient pore structure according to claim 1, characterized in that, In the drying and sintering process, after the green body is dried, it is placed in an air atmosphere environment and heated from room temperature to 500-550℃ and held for sintering; then the temperature is further increased to 1000-1050℃ and held for sintering; then the temperature is further increased to 1250-1300℃ and held for sintering, and then cooled to obtain cordierite ceramic with a gradient pore structure.

9. The method for preparing cordierite ceramics with a gradient pore structure according to claim 8, characterized in that, The rate of heating from room temperature to 500-550℃ is 1-2℃ / min, and the holding time for sintering is 2-3h; The heating rate continues to rise to 1000-1050℃ at a rate of 2-3℃ / min, and the holding sintering time is 1-1.5h; The temperature is increased to 1250-1300℃ at a rate of 1-2℃ / min, and the holding time for sintering is 4-6h. The cooling rate is 2-3℃ / min.

10. A cordierite ceramic with a gradient pore structure, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.

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