A method for preparing porous ceramics by a stirring-foaming method

Abstract

This invention relates to a method for preparing porous ceramics by stirring and foaming, belonging to the field of porous ceramic preparation technology. The method for preparing porous ceramics by stirring and foaming of this invention includes the following steps: (1) mixing ceramic powder, deionized water, dispersant, regulator, organic monomer, crosslinking agent, and water-based polymer material to form a ceramic slurry; (2) placing the ceramic slurry into a ball mill jar for ball milling, discharging the slurry after completion, adding a surfactant to the ceramic slurry, mixing it evenly, placing it into a foaming device, adding a mixture of ammonium persulfate and tetramethylammonium hydroxide powder, mixing it evenly, adding tetramethylethylenediamine dropwise, stirring evenly, and then pouring it into a mold made of non-permeable and non-inhibiting material for curing. After curing, demolding is performed to obtain a ceramic green body; (3) drying and sintering the ceramic green body to obtain porous ceramics. The curing process of the porous ceramic green body of this invention can be achieved at room temperature, with low equipment requirements and convenient operation.

Description

Technical Field

[0001] This invention relates to a method for preparing porous ceramics by stirring and foaming, belonging to the field of porous ceramics preparation technology. Background Technology

[0002] In the early 1990s, Oak Ridge National Laboratory in the United States invented gel casting technology for ceramic green bodies. This technology combines traditional organic green body slip casting technology with polymer chemistry theory. Organic monomers and cross-linking agents capable of forming gels are mixed with organic solvents or water to form a premix, which is then mixed with ceramic powder to prepare a ceramic slurry. This slurry is poured into a non-permeable mold and polymerized in situ under certain conditions to form a cross-bonded gel, thus shaping the ceramic green body. This technology is suitable for the precision molding of ceramic green bodies of various complex shapes. However, as a free radical polymerization reaction, the monomers come into contact with air during polymerization, and the oxygen in the air hinders the polymerization reaction, making it difficult for the ceramic slurry to polymerize within air bubbles.

[0003] To overcome the problem of surface oxygen hindering polymerization, Chinese invention patent 200810016714.6 discloses a method for preparing alumina foam ceramics, specifically a method for preparing porous ceramics using nitrogen-protected free radical polymerization foaming. This method requires heating and curing during the gelation process (curing temperature 60-150℃), resulting in a long gelation time, long production and experimental cycles, and high equipment requirements. Chinese invention patent 201410602514.4 discloses a method and apparatus for preparing porous ceramics using heavy gas-protected direct foaming, specifically a heavy gas-protected stirring foaming method. It uses a heavy gas upward air displacement method to remove air from the slurry environment and cleverly utilizes the gap between the rotating rod of the mixer and the top cover as an air outlet, simplifying the process operation.

[0004] A novel method for preparing porous ceramic preforms by foaming and gelling ceramic slurry in an argon or carbon dioxide gas environment is proposed, providing a new approach for the research and application of porous ceramic materials. This method utilizes heavy gases (with molecular weights greater than the average molecular weight of air), such as argon or carbon dioxide, to remove air from the slurry environment during preparation. The gelation process requires an ambient temperature below 40℃, unlike previous nitrogen-protected methods (requiring temperatures of 60-150℃). During the solidification process of the foamed ceramic slurry, the density of the heavy gas is greater than that of air, making it less likely to overflow from the surface of the foamed slurry, resulting in a more stable slurry. Furthermore, no external protective gas is required during the mold gelation process. However, this direct heavy gas foaming method for preparing porous ceramics requires specific equipment and gas pipeline connections, making the operation relatively complex. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing porous ceramics by stirring and foaming to solve the above-mentioned technical problems.

[0006] The technical solution provided by this invention is as follows: A method for preparing porous ceramics by stirring and foaming, comprising the following steps:

[0007] (1) Ceramic slurry is formed by mixing ceramic powder, deionized water, dispersant, regulator, organic monomer, crosslinking agent and water-based polymer material;

[0008] (2) The ceramic slurry is put into a ball mill jar for ball milling. After the slurry is finished, the material is discharged. A surfactant is added to the ceramic slurry, and after mixing, it is put into a foaming device. A mixture of ammonium persulfate and tetramethylammonium hydroxide powder is added and mixed. Then, tetramethylethylenediamine is added dropwise, stirred evenly, and poured into a mold for curing. After curing, the mold is removed to obtain a ceramic green body.

[0009] (3) The ceramic blank is dried and sintered to obtain porous ceramic.

[0010] The effect of the above technical solution is that adding water-soluble polymer materials to ceramic powder can improve the viscosity and stability of ceramic slurry and form a covering layer that reduces oxygen dissolution and diffusion, enabling the ceramic slurry to gel and solidify under the coexistence of gas (air), liquid, and solid phases, thereby producing ceramic green bodies. While introducing excess ammonium persulfate eliminates the inhibitory effect of oxygen in the air on the gelation process of the ceramic slurry, ammonium persulfate is an acidic reagent, and excessive addition can easily cause local flocculation of the slurry, resulting in uneven pore size distribution in the prepared porous ceramics. By introducing the alkaline reagent tetramethylammonium hydroxide into the ammonium persulfate powder and adjusting the mixed powder of ammonium persulfate and tetramethylammonium hydroxide to alkalinity, the problem of slurry flocculation is overcome.

[0011] Based on the above technical solution, the present invention can be further improved as follows:

[0012] Further, in step (1), the weight of the deionized water is 15-70% of the weight of the ceramic powder, the weight of the dispersant is 0.1-5% of the weight of the ceramic powder, the weight of the regulator is 0.1-5% of the weight of the ceramic powder, the weight of the organic monomer is 0.1-8% of the weight of the ceramic powder, the ratio of the organic monomer to the crosslinking agent is 10:1-30:1, and the weight of the water-based polymer material is 1-5% of the weight of the ceramic powder.

[0013] Furthermore, in step (2), the ball milling time is 10-24 hours, the ball-to-material ratio is 1:1-5:1, and the weight of the surfactant is 0.1-5% of the weight of the ceramic slurry.

[0014] Further, in step (2), the weight ratio of ammonium persulfate and tetramethylammonium hydroxide is 10:0.5-2, and the weight of the mixed powder of ammonium persulfate and tetramethylammonium hydroxide is 0.5-5% of the weight of the ceramic slurry.

[0015] Furthermore, in step (2), the weight of the tetramethylethylenediamine is 0.05-0.5% of the weight of the ceramic slurry.

[0016] Furthermore, in step (2), the mold is made of a non-permeable and non-resistant material, which is metal, glass or dense plastic; the curing temperature is 25-30℃ and the curing time is 30-60min.

[0017] The advantage of adopting the above-mentioned further solution is that the ceramic body does not need to be heated during curing; it can be carried out at room temperature of 25-30℃.

[0018] Further, in step (3), the drying time is 5-10 days; the sintering temperature is 1200-2200℃, and the time is 2-4 hours. Specifically, the drying involves placing the foamed ceramic blank on a screen with open top and bottom for drying; oxide ceramics are sintered in an air furnace at a temperature of 1200-1800℃; silicon nitride ceramics are sintered under nitrogen protection at a temperature of 1600-1800℃; and silicon carbide ceramics are sintered under argon protection at a temperature of 1500-2200℃.

[0019] Furthermore, the ceramic powder is one or more of alumina, yttrium oxide, zirconium oxide, silicon nitride, silicon carbide, and mullite; the average particle size of the ceramic powder is 0.1-10 μm.

[0020] Furthermore, the dispersant is polyacrylate or polymethacrylate; the regulator is ammonia or tetramethylammonium hydroxide; the organic monomer is acrylamide or methacrylamide; the crosslinking agent is N,N-methylenebisacrylamide or ethylene glycol dimethacrylate; and the waterborne polymer material is polyvinylpyrrolidone, polyvinyl alcohol, or polyacrylamide.

[0021] Furthermore, the surfactant is an alkylbenzene sulfonate anionic surfactant, a protein surfactant, or a combination of an alkylbenzene sulfonate anionic surfactant and a protein surfactant.

[0022] The technical solution provided by this invention has the following advantages compared with the prior art:

[0023] The method for preparing porous ceramics using the stirring foaming method of the present invention is a consumable method. It involves introducing excess ammonium persulfate and tetramethylammonium hydroxide mixed powder to consume oxygen in the foam slurry and introducing water-soluble polymer materials to form a covering layer that reduces oxygen dissolution and diffusion. This allows the foam ceramic slurry to gel and solidify under a three-phase coexistence condition of gas (air), liquid, and solid phases, thereby preparing the ceramic green body. Specifically, ammonium persulfate reacts with oxygen to chemically isolate the slurry from oxygen in the air. By adding excess ammonium persulfate initiator and tetramethylammonium hydroxide composite powder, a portion of the ammonium persulfate is used to consume oxygen in the bubbles, overcoming the oxygen inhibition effect of oxygen on free radical polymerization, while another portion is used to initiate the free radical polymerization reaction. Tetramethylammonium hydroxide is used to adjust the local acidity and alkalinity of the slurry, achieving the gelation and solidification reaction of the foam slurry. Furthermore, the introduction of water-soluble polymer materials increases the viscosity and stability of the foam slurry, while effectively reducing the dissolution and diffusion rate of oxygen within the foam, thus forming a porous foam ceramic green body.

[0024] Free radical polymerization initiators are typically compounds that exhibit appropriate thermal decomposition rates at polymerization temperatures, generating free radicals and initiating monomer polymerization. Ammonium persulfate, as a free radical polymerization initiator, contains weak bonds and readily decomposes to generate free radicals. In the preparation of porous ceramics using the stirred foaming method, air gradually disperses into the ceramic slurry during stirring, forming a solid-liquid-gas three-phase coexisting suspension system. Oxygen in the gas phase reacts with dissolved polymer chain free radicals in the liquid phase to generate non-free radicals, thus completely stopping the free radical polymerization reaction. To overcome the inhibitory effect of oxygen and ensure the smooth progress of the free radical polymerization reaction within the water-based porous ceramic slurry, this invention adds excess ammonium persulfate initiator to consume oxygen in the gas phase, reducing the oxygen concentration. Simultaneously, water-soluble polymer materials are added to reduce oxygen dissolution and diffusion. Furthermore, no inert gas protection is required. The water-based foam ceramic slurry undergoes a free radical polymerization reaction and gels solidifies within a short time at room temperature, thus achieving the preparation of porous ceramic green bodies.

[0025] The method for preparing porous ceramics of the present invention can achieve the solidification process of the porous ceramic green body at room temperature, with low equipment requirements and convenient operation. Attached Figure Description

[0026] Figure 1 Here is a scanning electron microscope image of the porous ceramic obtained in Example 1 of this invention;

[0027] Figure 2 Here is a scanning electron microscope image of the porous ceramic obtained in Example 2 of this invention;

[0028] Figure 3 This is a scanning electron microscope image of the porous ceramic obtained in Comparative Example 1 of the present invention;

[0029] Figure 4 This is a scanning electron microscope image of the porous ceramic obtained in Comparative Example 2 of the present invention. Detailed Implementation

[0030] The principles and features of the present invention are described below with reference to examples. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0031] Example 1

[0032] A method for preparing porous ceramics by stirring and foaming includes the following steps:

[0033] (1) 2000g of alumina powder (average particle size of 0.5μm), 1g of yttrium oxide powder (average particle size of 1.1μm), 550g of deionized water, 40g of ammonium acrylate dispersant, 40g of tetramethylammonium hydroxide regulator, 100g of acrylamide organic monomer, 5g of N,N-methylenebisacrylamide crosslinking agent, and 20g of polyvinylpyrrolidone waterborne polymer material are mixed to form a ceramic slurry;

[0034] (2) Place the ceramic slurry into a ball mill jar and ball mill for 24 hours (ball-to-material ratio of 2:1). After completion, discharge the material, weigh 1250g of ceramic slurry, add 3g of surfactant alkylbenzene sulfonate, mix well and place it in a foaming device. Add 15g of ammonium persulfate and 2g of tetramethylammonium hydroxide and mix well. Then place it in a mixer with a speed of 100r / min and stir for 20min. Adjust the speed of the mixer to 1500r / min. When the slurry foams to 2500ml, add 2g of tetramethylethylenediamine, stir evenly and pour it into a glass mold for curing for 1 hour (curing temperature of 25℃). After curing, demold to obtain the ceramic green body.

[0035] (3) The ceramic green body was placed on a screen with open top and bottom and allowed to dry freely for 10 days; the completely dried green body was then sintered in an air furnace at 1500℃ for 3 hours to obtain porous ceramics. Scanning electron microscope images of the obtained porous ceramics are shown below. Figure 1 As shown.

[0036] Example 2

[0037] A method for preparing porous ceramics by stirring and foaming includes the following steps:

[0038] (1) Mix 2000g of silicon nitride powder (average particle size 0.5μm), 20g of alumina powder (average particle size 0.5μm), 36g of yttrium oxide powder (average particle size 1.1μm), 900ml of deionized water, 60g of ammonium acrylate dispersant, 60g of ammonia water conditioner, 120g of acrylamide organic monomer, 10g of N,N-methylenebisacrylamide crosslinking agent, and 20g of polyvinylpyrrolidone waterborne polymer material to form a ceramic slurry;

[0039] (2) Place the ceramic slurry into a ball mill jar and ball mill for 15 hours (ball-to-material ratio of 2:1). After completion, discharge the material, weigh 379g of ceramic slurry, add 1.5g of surfactant alkylbenzene sulfonate, mix well, and place it in a foaming device. Add 5g of ammonium persulfate and 0.5g of tetramethylammonium hydroxide, mix well, and place it in a mixer with a speed of 100r / min and stir for 20 minutes. Then, adjust the speed of the mixer to 1500r / min. When the slurry foams to 1000ml, add 1.5g of tetramethylethylenediamine, stir evenly, and pour it into a glass mold for curing for 1 hour (curing temperature of 30℃). After curing, demold to obtain the ceramic green body.

[0040] (3) The ceramic green body was placed on a permeable sieve and allowed to dry freely for 8 days; the completely dried green body was then sintered in a nitrogen furnace at 1750℃ for 2 hours to obtain porous ceramics. Scanning electron microscope images of the obtained porous ceramics are shown below. Figure 2 As shown.

[0041] Comparative Example 1

[0042] (1) 2000g of alumina powder (average particle size of 0.5μm), 1g of yttrium oxide powder (average particle size of 1.1μm), 550g of deionized water, 40g of ammonium acrylate dispersant, 40g of tetramethylammonium hydroxide regulator, 100g of acrylamide organic monomer, 5g of N,N-methylenebisacrylamide crosslinking agent, and 25g of polyvinylpyrrolidone waterborne polymer material are mixed to form a ceramic slurry;

[0043] (2) Place the ceramic slurry in a ball mill jar and ball mill for 24 hours (ball-to-material ratio of 2:1). After completion, discharge the slurry, weigh 1250g of ceramic slurry, add 3g of surfactant alkylbenzene sulfonate, mix well, and place it in a foaming device. Add 15g of ammonium persulfate, and place it in a mixer with a speed of 100r / min. Stir for 20 minutes, then adjust the speed of the mixer to 1500r / min. When the slurry foams to 2500ml, add 2g of tetramethylethylenediamine, stir evenly, and pour into a glass mold for curing for 1 hour (curing temperature is 25°C). ℃ After curing, the ceramic blank is demolded to obtain the ceramic body.

[0044] (3) The ceramic green body was placed on a screen with open top and bottom and allowed to dry freely for 10 days; the completely dried green body was then sintered in an air furnace at 1500℃ for 3 hours to obtain porous ceramics. Scanning electron microscope images of the obtained porous ceramics are shown below. Figure 1 As shown. The scanning electron microscope (SEM) image of the obtained porous ceramic is as follows. Figure 3 As shown.

[0045] Comparative Example 2

[0046] (1) 2000g of alumina powder (average particle size of 0.5μm), 1g of yttrium oxide powder (average particle size of 1.1μm), 550g of deionized water, 40g of ammonium acrylate dispersant, 40g of tetramethylammonium hydroxide regulator, 100g of acrylamide organic monomer, and 5g of N,N-methylenebisacrylamide crosslinking agent;

[0047] (2) Place the ceramic slurry into a ball mill jar and ball mill for 24 hours (ball-to-material ratio of 2:1). After completion, discharge the material, weigh 1250g of ceramic slurry, add 3g of surfactant alkylbenzene sulfonate, mix well and place it in a foaming device. Add 15g of ammonium persulfate and 2g of tetramethylammonium hydroxide and mix well. Then place it in a mixer with a speed of 100r / min and stir for 20min. Adjust the speed of the mixer to 1500r / min. When the slurry foams to 2500ml, add 2g of tetramethylethylenediamine, stir evenly and pour it into a glass mold for curing for 1 hour (curing temperature of 30℃). After curing, demold to obtain the ceramic green body.

[0048] (3) The ceramic green body was placed on a screen with open top and bottom and allowed to dry freely for 10 days; the completely dried green body was then sintered in an air furnace at 1500℃ for 3 hours to obtain porous ceramics. Scanning electron microscope images of the obtained porous ceramics are shown below. Figure 4 As shown.

[0049] The porosity and pore size of the porous ceramics prepared in Examples 1-2 and Comparative Examples 1-2 are shown in Table 1:

[0050] Table 1. Porosity and pore size of the porous ceramics prepared in Examples 1-2 and Comparative Examples 1-2.

[0051] Porosity 85％ 88％ 80％ 78％ Hole condition Uniform pore size distribution Uniform pore size distribution The pore structure was destroyed Poor uniformity of pore structure

[0052] As can be seen from Table 1, the porous ceramics prepared in Examples 1 and 2 have uniform pore distribution and porosity >85%. In Comparative Example 1, because only ammonium persulfate was added and tetramethylammonium hydroxide was not added, flocculation occurred in the microstructure, and the pore structure was destroyed. In Comparative Example 2, because no water-based polymer material was added, the stability of the ceramic slurry was poor, resulting in phenomena such as foam coalescence, rupture, and pore wall coalescence, and the uniformity of the pore structure deteriorated.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. 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 porous ceramics by stirring and foaming, characterized in that, Includes the following steps: (1) A ceramic slurry is formed by mixing ceramic powder, deionized water, dispersant, regulator, organic monomer, crosslinking agent and water-based polymer material; the weight of the water-based polymer material is 1-5% of the weight of the ceramic powder; the regulator is ammonia or tetramethylammonium hydroxide; the water-based polymer material is polyvinylpyrrolidone, polyvinyl alcohol or polyacrylamide; (2) The ceramic slurry is placed in a ball mill jar for ball milling. After the slurry is finished, the slurry is discharged. A surfactant is added to the ceramic slurry and mixed. The mixture is then placed in a foaming device and mixed with a powder of ammonium persulfate and tetramethylammonium hydroxide. The mixture is then placed in a mixer with a speed of 100 r / min and stirred for 20 min. The speed of the mixer is then adjusted to 1500 r / min. When the slurry foams to 2500 ml or 1000 ml, tetramethylethylenediamine is added dropwise. After stirring evenly, the mixture is poured into a mold and cured at a temperature of 25-30℃ for 30-60 min. After curing, the slurry is demolded to obtain a ceramic green body. The weight ratio of ammonium persulfate to tetramethylammonium hydroxide is 10:0.5-2, and the weight of the powder of ammonium persulfate and tetramethylammonium hydroxide is 0.5-5% of the weight of the ceramic slurry. (3) The ceramic blank is dried and sintered to obtain porous ceramic.

2. The method for preparing porous ceramics by stirring and foaming according to claim 1, characterized in that, In step (1), the weight of the deionized water is 15-70% of the weight of the ceramic powder, the weight of the dispersant is 0.1-5% of the weight of the ceramic powder, the weight of the regulator is 0.1-5% of the weight of the ceramic powder, the weight of the organic monomer is 0.1-8% of the weight of the ceramic powder, and the ratio of the organic monomer to the crosslinking agent is 10:1-30:

1.

3. The method for preparing porous ceramics by stirring and foaming according to claim 1, characterized in that, In step (2), the ball milling time is 10-24 hours, the ball-to-material ratio is 1:1-5:1, and the weight of the surfactant is 0.1-5% of the weight of the ceramic slurry.

4. The method for preparing porous ceramics by stirring and foaming according to claim 1, characterized in that, In step (2), the weight of the tetramethylethylenediamine is 0.05-0.5% of the weight of the ceramic slurry.

5. The method for preparing porous ceramics by stirring and foaming according to claim 1, characterized in that, In step (2), the mold is made of a non-permeable and non-resistant material, which is metal, glass or dense plastic.

6. The method for preparing porous ceramics by stirring and foaming according to claim 1, characterized in that, In step (3), the drying time is 5-10 days; the sintering temperature is 1200-2200℃ and the time is 2-4 hours.

7. The method for preparing porous ceramics by stirring and foaming according to claim 1, characterized in that, The ceramic powder is one or more of alumina, yttrium oxide, zirconium oxide, silicon nitride, silicon carbide, and mullite; the average particle size of the ceramic powder is 0.1-10 μm.

8. The method for preparing porous ceramics by stirring and foaming according to claim 1, characterized in that, The dispersant is polyacrylate or polymethacrylate; the organic monomer is acrylamide or methacrylamide; and the crosslinking agent is N,N-methylenebisacrylamide.

9. The method for preparing porous ceramics by stirring and foaming according to claim 1, characterized in that, The surfactant is an alkylbenzene sulfonate anionic surfactant, a protein surfactant, or a combination of an alkylbenzene sulfonate anionic surfactant and a protein surfactant.

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