A method for preparing open-cell gamma-alumina foam ceramics based on microwave heating technology

Abstract

The application relates to the technical field of porous ceramics, in particular to a method for preparing open-pore gamma-alumina foam ceramics based on microwave heating technology. (1) An aluminum sol is prepared; (2) a surfactant is added into the aluminum sol; (3) a pH regulator is added under mechanical stirring to adjust the pH value of the obtained slurry, and then the stirring is continued to obtain stable foam slurry; (4) the obtained foam slurry is injected into a mold, and after solidification, demolding and drying, a foam ceramic body is obtained; (5) the body is subjected to microwave sintering, and finally open-pore gamma-alumina foam ceramics are obtained. The gamma-Al2O3 foam ceramics prepared by the method have a pore structure mainly composed of macropores with a size of dozens of microns; the size of the 'window' type open pores on the pore wall is several microns to dozens of microns; and the foam ceramics with the structure can be applied to the fields of adsorption filtration, sound absorption and noise reduction, catalysts and catalyst carriers and the like.

Description

Technical Field

[0001] This invention relates to the field of porous ceramics technology, specifically a method for preparing open-cell gamma-alumina foam ceramics based on microwave heating technology. Background Technology

[0002] Foam ceramics combine the characteristics of both foam and ceramic materials, possessing advantages such as low density, high specific surface area, high specific strength, high temperature resistance, corrosion resistance, and wear resistance. They can be widely used in filtration, adsorption, catalysis, and thermal insulation. Traditional sintering processes for foam ceramics often suffer from temperature gradients between the inside and outside of the product, leading to problems such as cracking and uneven internal and external structures, resulting in unstable performance. Microwave heating technology, with its overall heating characteristic, eliminates temperature differences, achieves uniform sintering, and improves product performance. It also significantly shortens the holding time, thereby reducing energy consumption and saving costs. This has positive implications for the large-scale production of foam ceramics. Summary of the Invention

[0003] To address the aforementioned problems, the present invention aims to provide a method for preparing open-cell gamma-alumina foam ceramics based on microwave heating technology. This foam ceramic exhibits high porosity and high open-cell porosity while maintaining a high specific surface area, making it suitable for applications such as fluid insulation, dispersion, filtration, adsorption, and catalysis. This method is simple, convenient, low-cost, and environmentally friendly.

[0004] A method for preparing open-cell gamma-alumina foam ceramics based on microwave heating technology specifically includes the following steps: (1) Preparation of aluminum sol; (2) Add a surfactant to the aluminum sol obtained in step (1); (3) Add pH adjuster under mechanical stirring and adjust the pH value of the resulting slurry, then continue stirring to obtain a stable foam slurry; (4) Inject the foam slurry obtained in step (3) into the mold, and after solidification, demold and dry to obtain a foam ceramic blank; (5) The blank obtained in step (4) is microwave sintered to finally obtain open-pore gamma alumina foam ceramic, denoted as γ-Al2O3 foam ceramic.

[0005] Furthermore, in step (1), the aluminum sol is prepared by dissolving boehmite powder in deionized water to obtain aluminum sol. The colloidal particles in the aluminum sol are γ-AlO(OH), and the particle size is 4-10 nm. The solid content of the aluminum sol is 3-30 wt%.

[0006] Furthermore, in step (2), the surfactant is sodium α-olefin sulfonate, and its addition amount is 0.02-0.85 wt% of the aluminum sol mass; Further, in step (3), the pH value of the obtained slurry is adjusted to 4-9. The pH adjuster includes one or more of inorganic acids, inorganic bases and inorganic salts. The inorganic acids include one or more of hydrochloric acid, nitric acid and sulfuric acid. The inorganic bases include one or more of ammonia, sodium hydroxide and potassium hydroxide. The inorganic salts include one or more of ammonium chloride and potassium chloride.

[0007] Furthermore, in step (3), the stirring rate of the mechanical stirring is 1500-2000 r / min, and the stirring continues for 5-20 min after adjusting the pH value.

[0008] Furthermore, the drying process described in step (4) involves drying at room temperature for more than 48 hours.

[0009] Furthermore, the microwave sintering conditions described in step (5) are a power of 0.5-30KW, a frequency of 915MHz, and a holding time of 1-30min.

[0010] The prepared γ-Al2O3 foam ceramics have a porosity of 81.0-93.6%, with an open-cell porosity of over 90%, and a compressive strength of 0.5-4.8 MPa.

[0011] The γ-Al2O3 foam ceramic has a connected open-pore structure with a macropore diameter of 30-120 μm, a window-type open pore diameter of 1-60 μm on the pore wall, a grain size of nanoscale that makes up the pore wall, and obvious micro-wrinkle structure on the pore wall.

[0012] The γ-Al2O3 foam ceramic prepared by this invention can be used in the fields of adsorption filtration, sound absorption and noise reduction, or as a catalyst or catalyst support.

[0013] Compared with the prior art, the present invention has the following beneficial effects: (1) The foam blank obtained by mechanical stirring and foaming with boehmite sol as raw material has high strength and high porosity, and can be used for machining, transportation and application.

[0014] (2) γ-Al2O3 foam ceramics have a typical window-type open-cell structure and can be widely used in fluid dispersion and filtration. Because of its suitable pore size and open-cell size, it is suitable for filtering microparticles in air and water, as well as in adsorption, catalysis and other fields.

[0015] (3) The added surfactant is an environmentally friendly sodium α-alkenyl sulfonate. The added pH adjusters include inorganic acids such as hydrochloric acid, nitric acid, and sulfuric acid, inorganic bases such as ammonia, sodium hydroxide, and potassium hydroxide, and inorganic salts such as ammonium chloride and potassium chloride. Moreover, no debinding process is required, so it will not cause pollution to the environment.

[0016] (4) By controlling the solid content of the sol, foam ceramics with different porosities and pore structures can be prepared, which have different strengths and open-cell porosities and can be applied to a wider range of fields.

[0017] (5) The crystals that make up the pore walls of the foam ceramic prepared in this invention are obtained by in-situ reaction of colloidal particles. The bonding strength between the particles is much greater than that obtained by sintering alone, thus obtaining foam ceramics with a strength much greater than that prepared by other methods at the same porosity.

[0018] (6) In this invention, the blank is solidified by the gel of the sol during molding, which can prepare samples of different shapes and the internal structure of the samples is more uniform, and can be applied to a wider range of fields.

[0019] (7) The sintering conditions of foam ceramics based on microwave heating technology in this invention are significantly better than those of traditional sintering methods, which reduces energy consumption, saves energy, and does not emit harmful gases during sintering, thus causing no pollution to the environment. Attached Figure Description

[0020] Figure 1 This is a photograph of the open-cell gamma-alumina foam ceramic prepared in Example 1 of this invention; Figure 2 This is a SEM image of the open-cell gamma-alumina foam ceramic prepared in Example 1 of this invention; Figure 3 This is a SEM image of the pore structure of the open-cell gamma-alumina foam ceramic prepared in Example 1 of this invention; Figure 4 This is a SEM image of the pore walls of the open-cell gamma-alumina foam ceramic prepared in Example 1 of the present invention. Detailed Implementation

[0021] To better understand the content of this invention, the invention will be further described below with reference to specific embodiments and accompanying drawings. The following embodiments are based on the technology of this invention and provide detailed implementation methods and operating steps, but the scope of protection of this invention is not limited to the following embodiments.

[0022] Example 1: (1) Boehmite powder was dissolved in deionized water to obtain aluminum sol with a solid content of 5wt%. The aluminum sol colloidal particles were γ-AlO(OH) and the average particle size of the colloidal particles was 4.7nm. (2) Add 0.2 wt% sodium α-alkenylsulfonate to the sol, that is, sodium α-alkenylsulfonate accounts for 0.2 wt% of the mass of the above aluminum sol; (3) Add 2 mol / L dilute ammonia water under mechanical stirring at 2000 r / min and adjust the pH of the resulting slurry to 8. Then continue stirring for 5 min to obtain a stable foam slurry. (4) The obtained slurry is injected into the mold, and after the slurry solidifies, it is demolded and dried at room temperature for more than 48 hours to obtain a foam ceramic blank; (5) The obtained foam ceramic blank was microwave sintered at a power of 0.5KW, a frequency of 915MHz and a holding time of 20min to finally obtain open-pore gamma alumina foam ceramic, denoted as γ-Al2O3 foam ceramic.

[0023] The obtained γ-Al2O3 foam ceramics were tested and found to have a porosity of 93.6%, an open-cell porosity of 98%, a pore size of 106 μm, a window-type open-cell pore size of approximately 52 μm, a uniform and stable pore structure, and the foam ceramics were intact without cracks. The compressive strength was 0.5 MPa.

[0024] Example 2: (1) Boehmite powder was dissolved in deionized water to obtain aluminum sol with a solid content of 15wt%. The aluminum sol colloidal particles were γ-AlO(OH) and the average particle size of the colloidal particles was 5.5nm. (2) Add 0.3 wt% sodium α-alkenyl sulfonate to the sol, that is, sodium α-alkenyl sulfonate accounts for 0.3 wt% of the above aluminum sol by mass; (3) Add 2 mol / L dilute ammonia water under mechanical stirring at 2000 r / min and adjust the pH of the resulting slurry to 8. Then continue stirring for 5 min to obtain a stable foam slurry. (4) The obtained slurry is injected into the mold, and after the slurry solidifies, it is demolded and dried at room temperature for more than 48 hours to obtain a foam ceramic blank; (5) The obtained foam ceramic blank was microwave sintered at a power of 3KW, a frequency of 915MHz and a holding time of 5min to finally obtain γ-Al2O3 foam ceramic.

[0025] The obtained γ-Al2O3 foam ceramics were tested and found to have a porosity of 88.4%, an open-cell porosity of 96%, a pore size of 73 μm, a window-type open-cell size of approximately 35 μm, a uniform and stable pore structure, and the foam ceramics were intact without cracks. The compressive strength was 2.3 MPa.

[0026] Example 3: (1) Boehmite powder was dissolved in deionized water to obtain aluminum sol with a solid content of 30 wt%. The aluminum sol colloidal particles were γ-AlO(OH) and the average particle size of the colloidal particles was 6.2 nm. (2) Add 0.5 wt% sodium α-alkenylsulfonate to the sol, that is, sodium α-alkenylsulfonate accounts for 0.5 wt% of the above aluminum sol by mass; (3) Add 2 mol / L dilute ammonia water under mechanical stirring at 2000 r / min and adjust the pH of the resulting slurry to 8. Then continue stirring for 5 min to obtain a stable foam slurry. (4) The obtained slurry is injected into the mold, and after the slurry solidifies, it is demolded and dried at room temperature for more than 72 hours to obtain a foam ceramic blank; (5) The obtained foam ceramic blank was microwave sintered at a power of 30KW, a frequency of 915MHz and a holding time of 3min to finally obtain γ-Al2O3 foam ceramic.

[0027] The obtained γ-Al2O3 foam ceramics were tested and found to have a porosity of 81.0%, an open-cell porosity of over 95%, a macropore size of 52 μm, a window-type open-cell diameter of approximately 16 μm, a uniform and stable pore structure, and the foam ceramics were intact without cracks. The compressive strength was 4.8 MPa.

[0028] Figure 1 This is a photograph of the open-cell gamma-alumina foam ceramic prepared in Example 1 of this invention. It can be seen that the sintered foam ceramic has a complete overall structure without obvious defects, and can be prepared into different shapes.

[0029] Figure 2 This is a SEM image of the open-cell gamma-alumina foam ceramic prepared in Example 1 of this invention. As can be seen, the foam ceramic has a very uniform pore structure and a high open-cell porosity, exceeding 98%.

[0030] Figure 3 This is a SEM image of the open-cell gamma-alumina foam ceramic prepared in Example 1 of this invention. It can be seen that the pore structure of the foam ceramic is very uniform, and the pore size on the pore walls is approximately 50 μm.

[0031] Figure 4 This is a SEM image of the pore walls of the alumina foam ceramic prepared in Example 1 of this invention. It can be seen that the grain size constituting the pore walls is at the nanometer scale, and there are obvious microscopic wrinkles on the pore walls.

[0032] Comprehensive Appendix Figures 1-4 As can be seen, the alumina foam ceramic prepared by the method of the present invention has an open-pore structure with high porosity, and has wide applications in the fields of pollutant adsorption and filtration, high-temperature flue gas filtration, automobile exhaust treatment, catalyst carrier, and molten metal filtration.

[0033] The above description is merely an embodiment of the present invention and is not intended to limit the present invention in any way. The present invention can also have other embodiments based on the above structure and function, which will not be listed hereafter. Therefore, any simple modifications, equivalent changes, and alterations made by those skilled in the art to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing open-cell gamma-alumina foam ceramics based on microwave heating technology, characterized in that, Specifically, the following steps are included: (1) Preparation of aluminum sol; (2) Add a surfactant to the obtained aluminum sol; (3) Add pH adjuster under mechanical stirring and adjust the pH value of the resulting slurry, then continue stirring to obtain a stable foam slurry; (4) The obtained foam slurry is injected into the mold, cured, demolded and dried to obtain a foam ceramic blank; (5) The obtained blank is microwave sintered to finally obtain open-pore gamma alumina foam ceramic.

2. The method for preparing open-cell gamma-alumina foam ceramics based on microwave heating technology as described in claim 1, characterized in that, In step (1), the aluminum sol is prepared by dissolving boehmite powder in deionized water to obtain aluminum sol. The colloidal particles in the aluminum sol are γ-AlO(OH), and the particle size is 4-10 nm. The solid content of the aluminum sol is 3-30 wt%.

3. The method for preparing open-cell gamma-alumina foam ceramics based on microwave heating technology as described in claim 1, characterized in that, In step (2), the surfactant is sodium α-olefin sulfonate, and its addition amount is 0.02-0.85 wt% of the aluminum sol mass.

4. The method for preparing open-cell gamma-alumina foam ceramics based on microwave heating technology as described in claim 1, characterized in that, Step (3) Adjust the pH value of the obtained slurry to 4-9. The pH adjuster includes one or more of inorganic acids, inorganic bases and inorganic salts.

5. The method for preparing open-cell gamma-alumina foam ceramic based on microwave heating technology as described in claim 4, characterized in that, The inorganic acid includes one or more of hydrochloric acid, nitric acid, and sulfuric acid; the inorganic base includes one or more of ammonia, sodium hydroxide, and potassium hydroxide; and the inorganic salt includes one or more of ammonium chloride and potassium chloride.

6. The method for preparing open-cell gamma-alumina foam ceramics based on microwave heating technology as described in claim 1, characterized in that, In step (3), the stirring rate of mechanical stirring is 1500-2000 r / min, and stirring is continued for 5-20 min after adjusting the pH value; the drying in step (4) is drying at room temperature for more than 48 hours.

7. The method for preparing open-cell gamma-alumina foam ceramics based on microwave heating technology as described in claim 1, characterized in that, The microwave sintering conditions described in step (5) are: power 0.5-30KW, frequency 915MHz, and holding time 1-30min.

8. The method for preparing open-cell gamma-alumina foam ceramics based on microwave heating technology as described in claim 1, characterized in that, The prepared open-cell gamma alumina foam ceramics have a porosity of 81.0-93.6%, with an open-cell porosity of over 90%, and a compressive strength of 0.5-4.8 MPa.

9. The method for preparing open-cell gamma-alumina foam ceramics based on microwave heating technology as described in claim 1, characterized in that, The prepared open-cell gamma alumina foam ceramic has a connected open-cell structure with a macropore diameter of 30-120 μm, a window-type open-cell diameter of 1-60 μm on the pore wall, a grain size of nanoscale that makes up the pore wall, and obvious micro-wrinkle structure on the pore wall.

10. The method for preparing open-cell gamma-alumina foam ceramic based on microwave heating technology as described in claim 1, characterized in that, The prepared open-cell gamma alumina foam ceramics are used in adsorption filtration, sound absorption and noise reduction, or as catalysts and catalyst supports.

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