A multi-level porous alumina foam ceramic and a preparation method and application thereof

Abstract

The application provides a multi-level pore alumina foam ceramic and a preparation method and application thereof, and the preparation method comprises the following steps: S1, mixing boehmite nanoparticles with a solvent, and obtaining a boehmite nanoparticle sol after dispersion treatment; S2, adding a surfactant and a pH regulator to the boehmite nanoparticle sol, and obtaining a foam sol ceramic slurry after foaming treatment; S3, adding an oil phase to the foam sol ceramic slurry, and obtaining a foam emulsion ceramic slurry after emulsification treatment; S4, injecting the foam emulsion ceramic slurry into a mold, and performing drying treatment on a green body after demolding, so as to obtain a foam ceramic green body; and S5, performing sintering on the foam ceramic green body, so as to obtain a multi-level pore alumina foam ceramic. The method provided by the application is simple and green, the obtained product has high porosity and high connected open porosity, and can be applied to the fields of fluid heat preservation, medium dispersion, fine filtration, adsorption, catalysis and the like.

Description

Technical Field

[0001] This invention belongs to the field of porous ceramic preparation technology, and relates to a multi-level porous alumina foam ceramic, its preparation method and application. Background Technology

[0002] Foam ceramics combine the advantages of both foam materials and structural ceramics, possessing characteristics such as low density, high specific surface area, high specific strength, high temperature resistance, and corrosion resistance. They are widely used in industries such as filtration, adsorption, catalysis, and thermal insulation.

[0003] Currently, the mainstream preparation processes for open-cell foam ceramics in the industry mainly include three types: the pore-forming agent addition method, the organic foam impregnation method, and the direct foaming method. However, each of these methods has obvious shortcomings: the pore-forming agent addition method can flexibly control the pore size and morphology, but the overall porosity of the finished product is usually less than 50%, and it is only suitable for conventional filters; the organic foam impregnation method can prepare open-cell foam ceramics with high porosity, but the decomposition of organic matter during the preparation process can easily cause environmental pollution, and the pore size of the product is relatively large, resulting in poor filtration effect for fine particles; the direct foaming method is simple and environmentally friendly, and can prepare open-cell foam ceramics with high porosity and high strength, but it is still difficult to achieve the integrated preparation of multi-level gradient pore structures.

[0004] Therefore, the industry urgently needs to develop a process for preparing open-cell foam ceramics that can simultaneously improve the strength of the green body, the strength of the sintered finished product, and the overall porosity, so as to meet the demand for high-porosity, high-strength porous ceramic materials in fields such as building insulation, industrial filtration, and catalyst carriers. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a multi-level porous alumina foam ceramic, its preparation method, and its applications. The method provided by this invention is simple, environmentally friendly, and yields a product with both high porosity and high interconnectivity, applicable to fluid insulation, media dispersion, fine filtration, adsorption, and catalysis.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing multi-level porous alumina foam ceramic, the method comprising the following steps:

[0008] S1. Boehmite nanoparticles are mixed with solvent and dispersed to obtain boehmite nanoparticle sol.

[0009] S2. Add surfactant and pH adjuster to the boehmite nanoparticle sol, and obtain foam sol ceramic slurry after foaming treatment;

[0010] S3. Add an oil phase to the foam sol ceramic slurry, and obtain a foam emulsion ceramic slurry after emulsification treatment;

[0011] S4. The foam emulsion ceramic slurry is injected into the mold, and after demolding, the green body is dried to obtain a foam ceramic green body.

[0012] S5. The foam ceramic blank is sintered to obtain multi-level porous alumina foam ceramic.

[0013] This invention uses boehmite (γ-AlO(OH)) nanoparticle sol as a foam stabilizer. After foaming treatment, an oil phase is added to the foam sol ceramic slurry and emulsified to obtain a particle-stabilized foam emulsion with an oil-in-water structure. This increases the multi-level ratio of the pore structure of the multi-level porous alumina foam ceramic. After drying and sintering, open-cell alumina foam ceramic with high porosity and excellent mechanical properties can be obtained.

[0014] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0015] Preferably, the average particle size of the boehmite nanoparticles in step S1 is 2nm to 8nm, such as 2nm, 3nm, 4nm, 5nm, 6nm, 7nm or 8nm.

[0016] Preferably, the solvent in step S1 includes deionized water.

[0017] Preferably, the dispersion process in step S1 includes ultrasonic dispersion.

[0018] Preferably, the dispersion processing time in step S1 is 10 min to 60 min, for example, 10 min, 20 min, 30 min, 40 min, 50 min or 60 min.

[0019] Preferably, the solid content of the boehmite nanoparticle sol in step S1 is 3wt% to 30wt%, such as 3wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, or 30wt%.

[0020] Preferably, the surfactant in step S2 includes sodium α-olefin sulfonate.

[0021] Preferably, the amount of surfactant added in step S2 is 0.02wt% to 0.85wt% of the mass of the boehmite nanoparticles, for example, 0.02wt%, 0.1wt%, 0.2wt%, 0.3wt%, 0.5wt%, 0.6wt%, 0.8wt%, or 0.85wt%.

[0022] Preferably, the pH adjuster in step S2 includes any one or a combination of at least two of ammonia, ammonium carbonate, ammonium bicarbonate, or tetramethylammonium hydroxide.

[0023] Preferably, the pH value of the foam sol ceramic slurry is 7-9.

[0024] Preferably, the rotation speed of the first mechanical stirring is 800 r / min to 1200 r / min, such as 800 r / min, 900 r / min, 1000 r / min, 1100 r / min or 1200 r / min, and the time is 5 min to 20 min, such as 5 min, 8 min, 10 min, 12 min, 15 min, 18 min or 20 min.

[0025] Preferably, the oil phase in step S3 includes any one or a combination of at least two of the following: n-octane, n-decane, n-dodecane, olive oil, triglycerides, oleic acid, or palm oil.

[0026] Preferably, the amount of oil phase added in step S3 is 0.1 to 2 times the volume of the foam sol ceramic slurry, for example, 0.1 times, 0.3 times, 0.5 times, 0.8 times, 1 time, 1.3 times, 1.5 times or 2 times.

[0027] Preferably, the emulsification process in step S3 includes a second mechanical stirring.

[0028] Preferably, the rotation speed of the second mechanical stirring is 1500 r / min to 2200 r / min, such as 1500 r / min, 1600 r / min, 1700 r / min, 1800 r / min, 1900 r / min, 2000 r / min, 2100 r / min or 2200 r / min, and the time is 15 min to 40 min, such as 15 min, 20 min, 25 min, 30 min, 35 min or 40 min.

[0029] In this invention, by controlling the rotation speed and time within the above-mentioned preferred range, it is more beneficial to obtain a uniform and stable foam emulsion ceramic slurry.

[0030] Preferably, the mold in step S4 is made of either a metal or an organic material. The metal material includes any one of aluminum alloy, stainless steel, or high carbon steel, and the organic material includes any one of polytetrafluoroethylene, polypropylene, or polycarbonate.

[0031] Preferably, the drying process is carried out at a temperature of 20°C to 40°C for 72 hours to 240 hours. For example, the temperature can be 20°C, 25°C, 30°C, 35°C, or 40°C, and the time can be 72 hours, 100 hours, 120 hours, 150 hours, 180 hours, 200 hours, or 240 hours.

[0032] Preferably, the sintering temperature in step S5 is 1200℃~1550℃, the heating rate is 0.5℃ / min~10℃ / min, and the holding time is 0.5h~2h. For example, the temperature is 1200℃, 1250℃, 1300℃, 1350℃, 1400℃, 1450℃, 1500℃ or 1550℃, the heating rate is 0.5℃ / min, 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min, and the holding time is 0.5h, 1h, 1.5h or 2h.

[0033] In a second aspect, the present invention provides a multi-level porous alumina foam ceramic prepared by the preparation method described in the first aspect.

[0034] Preferably, the multi-level porous alumina foam ceramic includes primary macropores formed by support pillars, secondary spherical pores located on the support pillars and pore walls, windows located on the pore walls for connecting adjacent primary macropores, and tertiary pores located between the grains of the pore walls.

[0035] Preferably, the diameter of the primary macropore is 20μm to 250μm, such as 20μm, 30μm, 50μm, 80μm, 100μm, 150μm, 200μm, or 250μm, and the diameter of the secondary spherical pore is 2μm to 20μm, such as 2μm, 5μm, 8μm, 10μm, 12μm, 15μm, 17μm, or 20μm, etc. The aperture of the window is 1μm to 10μm, for example, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm, etc., and the aperture of the tertiary pores is 0.01μm to 1μm, for example, 0.01μm, 0.1μm, 0.2μm, 0.3μm, 0.5μm, 0.6μm, 0.8μm or 1μm, etc.

[0036] Preferably, the multi-level porous alumina foam ceramic includes open-cell and closed-cell structures, with a total porosity of 80% to 95%, and the proportion of open-cell structures to total pores is greater than 90%, for example, a total porosity of 80%, 83%, 85%, 90%, 93%, or 95%.

[0037] Preferably, the hierarchical porous alumina foam ceramic includes hierarchical porous α-Al2O3 foam ceramic.

[0038] Preferably, the compressive strength of the multi-level porous alumina foam ceramic is 2MPa to 50MPa, such as 2MPa, 10MPa, 20MPa, 30MPa, 40MPa or 50MPa.

[0039] Preferably, the thermal conductivity of the hierarchical porous alumina foam ceramic is 0.3 W·m. -1 ·K -1 ~1.5W·m -1 ·K -1 For example, 0.3 W·m -1 ·K -1 0.5W·m -1 ·K -1 0.8 W·m -1 ·K -1 1W·m -1 ·K -1 1.2 W·m -1 ·K -1 Or 1.5 W·m -1 ·K -1 wait.

[0040] Thirdly, the present invention provides an application of multi-level porous alumina foam ceramic as described in the second aspect in building insulation, industrial filtration or catalyst carrier.

[0041] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] This invention uses γ-AlO(OH) nanoparticle sol as raw material to prepare foam preforms. The resulting foam preforms have high strength, facilitating subsequent machining, transportation, and on-site application. The finished product has a three-level interconnected open-cell structure with a reasonable pore size gradient distribution, exhibiting excellent filtration capabilities for fine particles in both gas and liquid phases. It is also suitable for functional scenarios such as adsorption and catalysis. The entire process is environmentally friendly, with no high-temperature sol removal step and no pollutant emissions, making it green and low-carbon. By controlling the sol solid content, porosity, pore structure, and mechanical strength can be flexibly adjusted to obtain a series of products with different parameters, adapting to the needs of multiple fields. The pore wall crystals are generated by the in-situ reaction of colloidal particles, and the particle bonding strength is significantly better than that of traditional powder sintering processes. Under the same porosity conditions, the overall strength of the finished product is higher. Attached Figure Description

[0044] Figure 1 This is a large-scale SEM image of the alumina foam ceramic prepared in Example 1.

[0045] Figure 2 This is a small-scale SEM image of the alumina foam ceramic prepared in Example 1.

[0046] Figure 3 This is a SEM image of the pore structure of the alumina foam ceramic prepared in Example 1.

[0047] Figure 4 These are SEM images of the pore walls of the alumina foam ceramic prepared in Example 1.

[0048] Figure 5 These are SEM images of the grains on the pore walls and the pores between the grains in the alumina foam ceramic prepared in Example 1. Detailed Implementation

[0049] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0050] "The scope of this invention can be defined by a lower limit and an upper limit. The selected lower limit and upper limit define the boundary of a specific range. The range defined in this way can be defined by the inclusion or exclusion of endpoints. Any endpoint can be independently selected for inclusion or exclusion, and all lower limit and upper limit values ​​can be arbitrarily combined to form a new range. That is, any lower limit value can be combined with any upper limit value to form an effective range. For example, if the ranges of 60~120 and 80~110 are listed for specific parameters, it should be understood that the ranges of 60~110 and 80~120 also fall within the scope of this invention. In addition, if the minimum range values ​​1 and 2 are listed, and the maximum range values ​​3, 4 and 5 are also listed, then 1~3, 1~4, and 2~3, 1~4, 2~5 ... All ranges from 1 to 5, 2 to 3, 2 to 4, and 2 to 5 fall within the scope of this invention. In this invention, the numerical range "a to b" represents a shortened representation of any combination of real numbers between a and b, where both a and b are real numbers. For example, the numerical range "0 to 5" indicates that all real numbers between 0 and 5 have been fully listed in this document; "0 to 5" is merely a shortened representation of this numerical combination. When a parameter is expressed as an integer ≥ 2, it is equivalent to listing positive integers that meet the requirements, such as 2, 3, 4, 5, 6, 7, 8, 9, and 10. When a parameter is expressed as an integer selected from "2 to 10", it is equivalent to listing any integer among 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0051] In this invention, "a combination of at least two" refers to a quantity greater than or equal to 2 unless otherwise specified. For example, "any one or a combination of at least two" means that any one of the listed items can be selected, or a combination of at least two of the listed items formed in a manner that does not conflict and enables the implementation of this invention. In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" cover any one of two or more related listed items, as well as any and all combinations of the related listed items. The arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" means a set consisting of A, B, and combinations of A and B, where "containing A and / or B" can be understood, depending on the context of the statement, as containing A, containing B, or simultaneously containing both A and B. In this invention, "optional" means that the corresponding feature, component, step or solution is not necessary, that is, it is selected from either "with" or "without". If there are multiple "optional" limitations in a technical solution, unless otherwise specified and there is no technical conflict or mutual constraint, each "optional" limitation is independent and does not affect the others.

[0052] In this invention, technical features or solutions described using open-ended terms such as "comprising" or "including" do not exclude additional non-conflicting elements beyond the listed elements unless otherwise specified. They are considered to disclose both closed-ended features or solutions consisting solely of the listed elements and open-ended features or solutions that may include additional non-conflicting elements beyond the listed elements. For example, if A includes a1, a2, and a3, unless otherwise specified, this means that A can consist only of a1, a2, and a3, or it can include other non-conflicting elements based on a1, a2, and a3. This corresponds to the disclosure of technical solutions such as "A consists of a1, a2, and a3," "A is selected from a1, a2, and a3," and "A not only includes a1, a2, and a3, but may also include other non-conflicting elements." All embodiments and optional embodiments of this invention, unless otherwise specified and without technical conflict, can be combined to form new technical solutions, and such combinations fall within the scope of this invention. The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various locations throughout the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this invention can be combined with other embodiments that do not conflict with the technology. The ordinal numbers "first," "second," "third," and "fourth," etc., used in the expressions "first aspect," "second aspect," "third aspect," and "fourth aspect" in this invention are for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly specifying the importance or quantity of the indicated technical features. They serve only as a non-exhaustive enumeration and do not constitute a closed limitation on quantity.

[0053] In this invention, the order in which the steps are written in the methods described in each embodiment does not imply a strict execution order. The actual execution order of each step should be determined based on its function and possible internal logic. Unless otherwise specified, all steps of this invention can be executed in the order they are written, or in any order without technical conflict. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) executed sequentially, or it may include steps (b) and (a) executed sequentially. If the method also includes step (c), then step (c) can be added to the method in any order without conflict, including but not limited to the execution order of steps (a), (b), and (c), steps (a), (c), and (b), steps (c), (a), and (b), etc.

[0054] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0055] In this invention, "room temperature" generally refers to 4℃~35℃, and can refer to 20℃±5℃. In some embodiments of this invention, room temperature refers to 20℃~30℃.

[0056] Example 1

[0057] This embodiment provides a method for preparing multi-level porous alumina foam ceramic, including the following steps:

[0058] S1. Mix 5g of boehmite nanoparticle powder (particle size 5nm) with 95g of deionized water, and disperse by ultrasonication at 300W for 40min to obtain a stable γ-AlO(OH) nanoparticle sol with a solid mass fraction of 5wt%.

[0059] S2. Add 0.01g of sodium α-alkenylsulfonate to the γ-AlO(OH) nanoparticle sol, add a few drops of 2mol / L ammonium bicarbonate to adjust the pH of the system to 8, and mechanically stir at 800r / min for 5min.

[0060] S3. Add 20 mL of n-octane (accounting for 21% of the volume of the foam sol ceramic slurry) to the sol, and mechanically stir at 1800 r / min for 10 min to obtain a foam emulsion ceramic slurry with uniform and stable foam.

[0061] S4. Inject the slurry into the aluminum alloy mold, let it stand for 24 hours under normal temperature and pressure (25℃, 101.3kPa) to complete the demolding, and then dry it under constant temperature and humidity (25℃, 45%RH) and normal pressure for 192 hours to obtain the foam ceramic green body.

[0062] S5. The foam ceramic blank is sintered at 1300℃ in an air atmosphere at a heating rate of 2℃ / min and held at that temperature for 1.5h to complete the crystallization and obtain a multi-level porous alumina foam ceramic product.

[0063] Example 2

[0064] This embodiment provides a method for preparing multi-level porous alumina foam ceramic, including the following steps:

[0065] S1. Mix 15g of boehmite nanoparticle powder (particle size 5nm) with 85g of deionized water, and disperse by ultrasonication at 300W for 30min to obtain a stable γ-AlO(OH) nanoparticle sol with a solid mass fraction of 15wt%.

[0066] S2. Add 0.045g of sodium α-olefin sulfonate to the γ-AlO(OH) nanoparticle sol, add a few drops of 1mol / L ammonium carbonate to adjust the pH to 8.5, stir at 1000r / min for 10min to obtain foam sol ceramic slurry;

[0067] S3. Add 35 mL of n-dodecane (accounting for 41% of the volume of the foam sol ceramic slurry) to the sol, and stir at 1900 r / min for 15 min to obtain a foam emulsion ceramic slurry with uniform and stable foam.

[0068] S4. Inject the slurry into the polypropylene mold, let it stand for 24 hours at room temperature and pressure to complete the demolding, and then dry it at constant temperature and humidity (25℃, 45%RH) and normal pressure for 120 hours to obtain the foamed ceramic green body.

[0069] S5. Sintering is carried out at 1500℃ in an air atmosphere with a heating rate of 2℃ / min and a holding time of 2h to complete crystallization and obtain a multi-level porous alumina foam ceramic product.

[0070] Example 3

[0071] This embodiment provides a method for preparing multi-level porous alumina foam ceramic, including the following steps:

[0072] S1. Mix 30g of boehmite nanoparticle powder (particle size 5nm) with 70g of deionized water, and disperse by ultrasonication at 300W for 30min to obtain a stable γ-AlO(OH) nanoparticle sol with a solid mass fraction of 30wt%.

[0073] S2. Add 0.15g of sodium α-olefin sulfonate to the γ-AlO(OH) nanoparticle sol, add a few drops of 0.5mol / L ammonia to adjust the pH to 9, stir at 1100r / min for 8min to obtain foam sol ceramic slurry;

[0074] S3. Add 50 mL of triglyceride (accounting for 71% of the volume of the foam sol ceramic slurry) to the sol, and stir at 2200 r / min for 20 min to obtain a foam emulsion ceramic slurry with uniform and stable foam.

[0075] S4. Inject the slurry into a stainless steel mold, let it stand for 24 hours at room temperature and pressure to complete demolding, and then dry it at constant temperature and humidity (25℃, 45%RH) and normal pressure for 72 hours to obtain the foamed ceramic green body.

[0076] S5. Sintering is carried out at 1450℃ in air atmosphere with a heating rate of 2℃ / min and holding for 2 hours to complete crystallization and obtain multi-level porous alumina foam ceramic product.

[0077] Example 4

[0078] This embodiment provides a method for preparing multi-level porous alumina foam ceramic, including the following steps:

[0079] S1. Mix 15g of boehmite nanoparticle powder (particle size 2nm) with 85g of deionized water, and disperse by ultrasonication at 300W for 60min to obtain a stable γ-AlO(OH) nanoparticle sol with a solid mass fraction of 15wt%.

[0080] S2. Add 0.003g of sodium α-alkenylsulfonate to the γ-AlO(OH) nanoparticle sol, add a few drops of 2mol / L ammonium bicarbonate to adjust the pH of the system to 8, and mechanically stir at 800r / min for 20min.

[0081] S3. Add 8.5 mL of n-octane (accounting for 10% of the volume of the foam sol ceramic slurry) to the sol, and mechanically stir at 1500 r / min for 40 min to obtain a foam emulsion ceramic slurry with uniform and stable foam.

[0082] S4. Inject the slurry into the aluminum alloy mold, let it stand for 24 hours under normal temperature and pressure to complete the demolding, and then dry it under constant temperature and humidity (25℃, 45%RH) and normal pressure for 192 hours to obtain the foam ceramic green body.

[0083] S5. The foam ceramic blank is sintered at 1200℃ in an air atmosphere at a heating rate of 0.5℃ / min and held at that temperature for 1.5h to complete the crystallization and forming, thereby obtaining a multi-level porous alumina foam ceramic product.

[0084] Example 5

[0085] This embodiment provides a method for preparing multi-level porous alumina foam ceramic, including the following steps:

[0086] S1. Mix 3g of boehmite nanoparticle powder (particle size 8nm) with 97g of deionized water, and disperse by ultrasonication at 300W for 10min to obtain a stable γ-AlO(OH) nanoparticle sol with a solid mass fraction of 3wt%.

[0087] S2. Add 0.0255g of sodium α-alkenylsulfonate to the γ-AlO(OH) nanoparticle sol, add a few drops of 2mol / L ammonium bicarbonate to adjust the pH of the system to 8, and mechanically stir at 1100r / min for 8min.

[0088] S3. Add 194 mL of n-octane to the sol (twice the volume of the foam sol ceramic slurry), and mechanically stir at 1800 r / min for 10 min to obtain a foam emulsion ceramic slurry with uniform and stable foam.

[0089] S4. Inject the slurry into the aluminum alloy mold, let it stand for 24 hours under normal temperature and pressure to complete the demolding, and then dry it under constant temperature and humidity (25℃, 45%RH) and normal pressure for 192 hours to obtain the foam ceramic green body.

[0090] S5. The foam ceramic blank is sintered at 1300℃ in air atmosphere, with a heating rate of 10℃ / min and a holding time of 0.5h to complete crystallization and obtain a multi-level porous alumina foam ceramic product.

[0091] Example 6

[0092] The difference between this embodiment and Embodiment 1 is that 0.075g of sodium α-olefin sulfonate is added in step S2;

[0093] The remaining preparation methods and parameters are consistent with those in Example 1.

[0094] Example 7

[0095] The difference between this embodiment and Embodiment 1 is that 20 mL of toluene is added in step S3;

[0096] The remaining preparation methods and parameters are consistent with those in Example 1.

[0097] Example 8

[0098] The difference between this embodiment and Embodiment 1 is that in step S3, 285 mL of n-octane is added, making it occupy 3 times the volume of the foam sol ceramic slurry;

[0099] The remaining preparation methods and parameters are consistent with those in Example 1.

[0100] Comparative Example 1

[0101] The difference between this comparative example and Example 1 is that step S3 is omitted;

[0102] The remaining preparation methods and parameters are consistent with those in Example 1.

[0103] Comparative Example 2

[0104] The difference between this comparative example and Example 1 is that in step S1, 5g of boehmite nanoparticles were replaced with 4.8g of α-Al2O3 and 0.2g of boehmite nanoparticles.

[0105] The remaining preparation methods and parameters are consistent with those in Example 1.

[0106] Structural characterization

[0107] The multi-level porous alumina foam ceramic prepared in Example 1 was subjected to SEM testing, and the test results are as follows: Figures 1-5 As shown.

[0108] The total porosity and open-cell ratio (the proportion of open cells to total pores) of the multi-level porous alumina foam ceramics prepared in Examples 1-8 and Comparative Examples 1-2 were tested using the Archimedes method (impregnation method); the compressive strength was tested using a universal testing machine, and the results are shown in Table 1.

[0109] Table 1

[0110]

[0111]

[0112] Depend on Figure 1 and Figure 2 It can be seen that the hierarchical porous alumina foam ceramic prepared in Example 1 has a three-dimensional interconnected open-pore structure, with uniformly distributed primary macropores and an average macropore diameter of approximately 35 μm; Figure 3 and Figure 4 It can be seen that the support column and the hole walls have a large number of spherical holes and windows. The average diameter of the spherical holes is about 4 μm, and the average diameter of the windows is about 2.5 μm. The windows are clear and complete, and adjacent large holes are interconnected through the windows. Figure 5 It can be seen that the grains constituting the pore walls are of uniform size, and a large number of uniform tertiary pores are distributed between the grains, with an average porosity of approximately 50 nm. In summary... Figures 1-5 It can be seen that the hierarchical porous alumina foam ceramic prepared in Example 1 has orderly and uniformly distributed pores at each level, forming a complete hierarchical porous structure. In addition, SEM tests were also performed on the hierarchical porous alumina foam ceramics prepared in Examples 2 and 3, and the results showed that they also have a complete hierarchical porous structure, with average pore diameters of 65 μm and 50 μm for the first-level macropores, respectively.

[0113] As can be seen from the comparison of the data of Example 1 and Comparative Examples 1-2 in Table 1, the addition of the oil phase is a key step in forming secondary spherical pores and achieving a complete hierarchical pore structure in this invention. Comparative Example 1 did not add an oil phase, and the resulting product only had primary macropores and windows, without secondary spherical pores. The proportion of open pores to total pores and the compressive strength were significantly lower than those of Example 1. Meanwhile, Comparative Example 2, with α-Al₂O₃ as the main component and boehmite as only a small amount of additive, also showed significantly lower open pore ratios and compressive strength compared to Example 1 due to insufficient phase transformation during sintering. This indicates that boehmite, as the sole ceramic powder raw material, has significant advantages over the traditional α-Al₂O₃-based raw material system, enabling the acquisition of a more uniform and stable hierarchical pore structure and superior mechanical properties.

[0114] Furthermore, a comparison of the data from Examples 1 and 6-8 in Table 1 shows that in this invention, the amount of surfactant added, the type of oil phase, and the amount of oil phase added also affect the formation of the hierarchical porous structure and the overall performance of the product. Although a hierarchical porous structure can still be formed even when deviating from the preferred range of this invention, its total porosity and / or open pore ratio are lower than those in Example 1, indicating that the process parameters within the preferred range can achieve synergistic optimization of each level of pores, thereby obtaining better overall performance.

[0115] In summary, by designing parameters such as the foaming process, type and content of the second phase, the present invention produces porous alumina foam ceramics with a significant hierarchical pore structure, as well as high porosity, an open pore ratio of more than 90%, and high compressive strength.

[0116] In summary, this invention has produced alumina foam ceramics with a multi-level pore structure by synergistically controlling parameters such as foaming process and oil phase type and dosage. This material has excellent comprehensive properties, including high porosity, high open cell ratio (>90%), and high compressive strength.

[0117] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing hierarchical porous alumina foam ceramic, characterized in that, The preparation method includes the following steps: S1. Boehmite nanoparticles are mixed with solvent and dispersed to obtain boehmite nanoparticle sol. S2. Add surfactant and pH adjuster to the boehmite nanoparticle sol, and obtain foam sol ceramic slurry after foaming treatment; S3. Add an oil phase to the foam sol ceramic slurry, and obtain a foam emulsion ceramic slurry after emulsification treatment; S4. The foam emulsion ceramic slurry is injected into the mold, and after demolding, the green body is dried to obtain a foam ceramic green body. S5. The foam ceramic blank is sintered to obtain multi-level porous alumina foam ceramic.

2. The preparation method according to claim 1, characterized in that, The average particle size of the boehmite nanoparticles described in step S1 is 2 nm to 8 nm. Preferably, the solvent in step S1 includes deionized water; Preferably, the dispersion treatment in step S1 includes ultrasonic dispersion treatment; Preferably, the dispersion treatment time in step S1 is 10 min to 60 min; Preferably, the solid content of the boehmite nanoparticle sol in step S1 is 3wt%~30wt%.

3. The preparation method according to claim 1 or 2, characterized in that, The surfactant mentioned in step S2 includes sodium α-olefin sulfonate; Preferably, the amount of surfactant added in step S2 is 0.02wt%~0.85wt% of the mass of the boehmite nanoparticles; Preferably, the pH adjuster in step S2 includes any one or a combination of at least two of ammonia, ammonium carbonate, ammonium bicarbonate, or tetramethylammonium hydroxide; Preferably, the pH value of the foam sol ceramic slurry is 7-9.

4. The preparation method according to any one of claims 1-3, characterized in that, The foaming process described in step S2 includes a first mechanical stirring; Preferably, the first mechanical stirring speed is 800 r / min to 1200 r / min, and the time is 5 min to 20 min.

5. The preparation method according to any one of claims 1-4, characterized in that, The oil phase in step S3 includes any one or a combination of at least two of the following: n-octane, n-decane, n-dodecane, olive oil, triglycerides, oleic acid, or palm oil; Preferably, the amount of oil phase added in step S3 is 0.1 to 2 times the volume of the foam sol ceramic slurry; Preferably, the emulsification process in step S3 includes a second mechanical stirring; Preferably, the second mechanical stirring speed is 1500 r / min to 2200 r / min, and the time is 10 min to 40 min.

6. The preparation method according to any one of claims 1-5, characterized in that, The mold material in step S4 includes metal or organic materials. The metal material includes any one of aluminum alloy, stainless steel or high carbon steel, and the organic material includes any one of polytetrafluoroethylene, polypropylene or polycarbonate. Preferably, the drying process is carried out at a temperature of 20°C to 40°C for a duration of 72 hours to 240 hours.

7. The preparation method according to any one of claims 1-6, characterized in that, The sintering temperature in step S5 is 1200℃~1550℃, the heating rate is 0.5℃ / min~10℃ / min, and the holding time is 0.5h~2h.

8. A multi-level porous alumina foam ceramic prepared by the preparation method according to any one of claims 1-7.

9. The multi-level porous alumina foam ceramic according to claim 8, characterized in that, The multi-level porous alumina foam ceramic includes a primary macropore formed by a support column, a secondary spherical pore located on the support column and the pore wall, a window located on the pore wall for connecting adjacent primary macropores, and a tertiary pore located between the grains of the pore wall. Preferably, the diameter of the primary macropore is 20μm~250μm, the diameter of the secondary spherical pore is 2μm~20μm, the diameter of the window is 1μm~10μm, and the diameter of the tertiary pore is 0.01μm~1μm; Preferably, the multi-level porous alumina foam ceramic includes open-cell and closed-cell structures, with a total porosity of 80%~95%, and open-cell structures accounting for >90% of the total porosity. Preferably, the hierarchical porous alumina foam ceramic comprises hierarchical porous α-Al2O3 foam ceramic; Preferably, the compressive strength of the multi-level porous alumina foam ceramic is 2 MPa to 50 MPa; Preferably, the thermal conductivity of the hierarchical porous alumina foam ceramic is 0.3 W·m. -1 ·K -1 ~1.5W·m -1 ·K -1 .

10. The application of a multi-level porous alumina foam ceramic as described in claim 8 or 9 in building insulation, industrial filtration, or catalyst carrier.

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