Method for preparing porous ceramic through gel casting of emulsion

Abstract

The invention provides a method for preparing porous ceramic through gel casting of emulsion, and belongs to the technical field of porous ceramic materials, and the method comprises the following steps: adding a catalyst and an initiator into the emulsion, carrying out mechanical stirring and injection molding, and then putting the emulsion into a drying oven for heating and curing to obtain a porous ceramic biscuit; degreasing and sintering the obtained biscuit to obtain porous ceramic; the emulsion comprises ceramic powder and / or sol nanoparticles, an organic monomer, a cross-linking agent, a binder, a defoaming agent, deionized water, an oil phase and a surfactant. According to the invention, rapid curing molding of the emulsion is realized through a cross-linking polymerization reaction of the organic monomer and the cross-linking agent, the advantages of simple and convenient operation and adjustable pore structure of an emulsion template method are retained, and a novel efficient technical route is provided for rapid and controllable preparation of porous ceramics with a complex structure and high porosity.

Description

Technical Field

[0001] This invention relates to a method for preparing porous ceramics by gel casting of emulsions, belonging to the technical field of porous ceramic materials. Background Technology

[0002] Porous ceramics, with their high specific surface area, low density, high temperature resistance, corrosion resistance and excellent chemical stability, combined with the advantages of low thermal conductivity, low dielectric constant and high specific strength imparted by the porous structure, are widely used in gas / liquid filtration, catalyst carriers, biological scaffolds and heat exchangers. However, their application is still limited by insufficient control over the pore structure.

[0003] Traditional methods for preparing porous ceramics, including organic foam impregnation, freeze-drying, adding pore-forming agents, and direct foaming, have limitations in terms of pore structure uniformity, pore size control, and process complexity, making it difficult to meet the demands for high-performance ceramics integrating structure and function. Emulsions, as a soft template system, possess excellent stability due to the ultra-high desorption energy of some hydrophobic particles at the water-oil interface, effectively enabling pore structure control. Furthermore, the micro- and nano-scale pore structures derived from emulsion droplet templates provide an efficient and controllable pathway for optimizing the structure and performance of porous ceramics. However, they suffer from long production cycles and difficulties in molding complex structures; therefore, the curing and molding of emulsions is crucial.

[0004] The curing process of an emulsion must meet a series of key requirements to ensure the formation and stability of the final porous structure. First, the curing process should exhibit good structural retention, effectively fixing the morphology and distribution of emulsion droplets and preventing droplet aggregation or phase separation, thereby ensuring the integrity and controllability of the pore structure. Second, the curing conditions must be compatible with the ceramic powder and various additives used to avoid adverse phenomena such as particle sedimentation, agglomeration, or emulsion demulsification. Simultaneously, the curing process should be carried out under mild operating conditions, such as suitable temperature, pH, or light intensity, to avoid compromising emulsion stability. Finally, the cured emulsion should possess sufficient mechanical strength to facilitate subsequent demolding, drying, and sintering, effectively reducing the risk of structural deformation and cracking.

[0005] Current emulsion curing technologies mainly include solvent evaporation curing, freeze curing (freeze-drying), UV curing, and thermosetting. Solvent evaporation curing is the most traditional emulsion curing method. Under controlled conditions, the continuous and dispersed phases (usually water or organic solvents) are gradually evaporated, promoting the bonding and formation of droplets. This method requires high emulsion stability and is prone to structural collapse. Freeze curing rapidly freezes the emulsion, freezing the water / oil phase, and then sublimates it under vacuum, retaining the template structure. It has good structure retention and is suitable for microporous / macroporous structure shaping, but the cycle is relatively long. Chinese invention patent CN111559918B combines microemulsion with freeze-drying to prepare porous ceramic green bodies. UV curing uses a photoinitiator to polymerize monomers under UV irradiation, achieving structural fixation. The reaction is rapid, but the penetration depth is limited, making it suitable for thin-layer structures. Thermosetting uses thermosensitive monomers or initiators to complete polymerization and crosslinking under heating conditions. It has high molding efficiency, but requires high temperature control and high emulsion thermal stability. Chinese invention patent CN119118684A uses a thermosensitive emulsion combined with direct-write printing to prepare multi-level porous ceramics, utilizing the thermosetting properties of epoxy resin to cure the emulsion into shape.

[0006] Gel casting is an advanced molding technology that introduces polymerizable monomers into a ceramic suspension, which are then chemically cross-linked and cured in situ within a mold to form a three-dimensional network structure, thus achieving the shaping of the green body. This process is simple and highly adaptable. It offers significant advantages such as high molding precision and applicability to complex structures. The gel system exhibits uniform internal cross-linking, resulting in high strength of the cured green body, which is beneficial for structural retention during demolding and drying.

[0007] This invention proposes a method for preparing porous ceramics by combining emulsion and gel casting, integrating the advantages of emulsion molding (simplicity and controllable structure) with the high precision, rapid, and uniform molding characteristics of gel casting. This technology enables efficient in-situ solidification of emulsions, providing a feasible new approach for rapidly constructing porous ceramics with uniform structure, controllable pore structure, and high porosity. Summary of the Invention

[0008] This invention addresses the challenge of preparing porous ceramics with complex shapes by proposing a method for preparing porous ceramics using emulsion gel casting. This invention introduces organic monomers and crosslinking agents into the emulsion, followed by in-situ crosslinking with a catalyst and initiator to form a three-dimensional gel network, achieving rapid emulsion curing while preserving the pore structure formed by the emulsion droplet template. The pore structure derived from the emulsion droplet template is controlled by adjusting parameters such as solid phase content, oil phase type and content, and the curing process is effectively controlled by adjusting parameters such as organic monomers, crosslinking agents, catalysts, initiators, and curing temperature, enabling rapid curing and molding of porous ceramics with complex shapes.

[0009] To achieve the above objectives, the specific technical solution is as follows:

[0010] This invention provides a method for preparing porous ceramics by gel casting of an emulsion, comprising the following steps:

[0011] Step 1: Add catalyst and initiator to emulsion, mechanically stir and pour into mold, then place in oven for heating and curing to obtain porous ceramic green body;

[0012] Step 2: The green body obtained in Step 1 is degreased and sintered to obtain porous ceramics;

[0013] The emulsion comprises ceramic powder and / or sol nanoparticles, organic monomers, crosslinking agents, binders, defoamers, deionized water, an oil phase, and surfactants, and is formed by mechanical stirring and emulsification.

[0014] Optionally, the ceramic powder and / or sol-gel nanoparticles account for 5 to 85 wt.% of the sum of the mass of deionized water and the ceramic powder and / or sol-gel nanoparticles.

[0015] Optionally, the surfactant accounts for 0.01 to 10.0 wt.% of the mass of the ceramic powder and / or sol-gel nanoparticles.

[0016] Optionally, the volume ratio of the oil phase to deionized water is 1:19 to 99:1;

[0017] Optionally, the binder accounts for 0.01 to 10 wt.% of the mass of deionized water.

[0018] Optionally, the defoamer accounts for 0.01 to 10 wt.% of the mass of deionized water.

[0019] Optionally, the mass ratio of crosslinking agent to organic monomer is 1:5 to 1:90. The amount of catalyst added is 0.1 to 1 mL relative to 1 g of organic monomer, and the amount of initiator added is 0.1 to 1 mL. The organic monomer and initiator are added in the form of aqueous solutions of the corresponding substances, with the organic monomer solution having a mass fraction of 0.05 to 30 wt.% and the initiator solution having a concentration of 3 wt.%.

[0020] Optionally, the ceramic powder is an oxide ceramic powder, a non-oxide ceramic powder, or a composite ceramic powder, selected from one or more of the following: alumina, silicon oxide, zirconium oxide, cerium oxide, magnesium oxide, yttrium oxide, titanium dioxide, silicon nitride, boron nitride, silicon carbide, boron carbide, aluminum titanate, hydroxyapatite, tricalcium β-phosphate, fly ash, coal gangue, secondary alumina ash, kaolin, tailings, and metallurgical slag.

[0021] Optionally, the sol nanoparticles are one or a mixture of two or more of aluminum sol, silica sol, zirconium sol, titanium sol, and cerium sol.

[0022] Optionally, the oil phase is one or a mixture of two or more of the following: n-hexane, n-heptane, n-octane, n-decane, cyclohexane, polydimethylsiloxane, glyceryl caprylate, liquid paraffin, silicone oil, soybean oil, rapeseed oil, olive oil, corn oil, sunflower oil, toluene, and styrene.

[0023] Optionally, the surfactant is one or a mixture of two or more of the following: valeric acid, hexylamine, octadecanoic acid, trimethylchlorosilane, sodium dodecyl sulfate, sodium dodecyl (benzene) sulfonate, sodium fatty alcohol polyoxyethylene ether sulfate, sodium α-alkenyl sulfonate, triethanolamine dodecyl sulfate, hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, superdispersant 41000, cocamidopropyl betaine, Tween series such as Tween 20 / 40 / 60 / 80, Span series such as Span 20 / 40 / 60 / 80.

[0024] Optionally, the organic monomer is one of acrylamide, methacrylamide, dimethacrylamide, hydroxyethyl 2-methacrylate, N-hydroxymethylacrylamide, N-isopropylacrylamide, hydroxyethyl methacrylate, methacrylic acid, acrylic acid, dimethylaminoisobutylene ester, and hydroxyethyl acrylate; the crosslinking agent is one of N,N'-methylenebisacrylamide, ethylene glycol dimethacrylate, and diethylenetriaminevalerate; the catalyst is N,N,N',N'-tetramethylethylenediamine; and the initiator is ammonium persulfate or potassium persulfate.

[0025] Optionally, the adhesive is one or a mixture of two or more of the following: polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone, sodium pyrophosphate, sodium carboxymethyl / ethyl cellulose, ethylene glycol, and glycerol.

[0026] Optionally, the defoamer is one or a mixture of two or more of tert-butanol, polydimethylsiloxane, polyoxypropylene glycerol ether, and polyoxypropylene ethylene oxide glycerol ether.

[0027] If the ceramic powder, sol nanoparticles, surfactants, binders, and defoamers mentioned above are mixtures of two or more of the specific substances listed above, the proportions of the mixtures can be arbitrary.

[0028] Optionally, the emulsion is prepared by mixing ceramic powder and / or sol nanoparticles, organic monomers, crosslinking agents, binders, defoamers, deionized water, surfactants, and oil phases, and then mechanically stirring to obtain a uniform and stable emulsion.

[0029] Optionally, the mechanical stirring emulsification process of the emulsion in step 1 is carried out at a speed of 300~3000 rpm for 5 min~12 h; after adding the catalyst and initiator, the mechanical stirring speed is 100~2000 rpm for 10 s~10 min; and the heating curing temperature is 30℃~99℃ for 1 min~6 h.

[0030] Optionally, in step 2, the organic monomers and crosslinking agents react under the action of a catalyst and an initiator to generate an organic polymer, which requires degreasing to remove organic matter. During the degreasing process, the heating rate is 0.01 ~ 10 ℃ / min, the degreasing temperature is 300 ~ 900℃, and the holding time is 10 min ~ 12 h; during the sintering process, the heating rate is 0.1 ~ 20 ℃ / min, the sintering temperature is 800 ~ 2000℃, the sintering atmosphere is air, nitrogen, or argon, and the holding time is 10 min ~ 8 h.

[0031] The present invention also provides porous ceramics prepared by the method, with a porosity of 10% to 99.9%.

[0032] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0033] This invention provides a method for preparing porous ceramics by gel casting of emulsions, which combines the advantages of both emulsion templates and gel casting.

[0034] First, it enables precise control of pore structure. The emulsion utilizes droplet templates formed by the stable distribution of surface-modified hydrophobic particles at the water / oil interface. By adjusting parameters such as oil phase content, particle hydrophobicity and concentration, and emulsification process conditions, the distribution of particles at the phase interface can be controlled at multiple scales, achieving control over pore size distribution, pore morphology, and porosity, thus constructing a uniformly distributed pore structure. Second, it simplifies the molding process and adapts to complex shapes. Gel casting can achieve rapid curing of emulsions and obtain products with complex structures under low energy consumption and mild conditions, overcoming the limitations of traditional template methods in terms of molding freedom and pore structure stability, providing a research foundation for constructing structure-function integrated ceramic components. Attached Figure Description

[0035] To more clearly illustrate the technical solutions of the experimental examples of the present invention, the accompanying drawings in the description of the embodiments are now briefly explained.

[0036] Figure 1 This is a SEM image of the silicon nitride porous ceramic preform prepared in Example 1.

[0037] Figure 2 SEM image of the silicon nitride ceramic green body prepared in Comparative Example 1. Detailed Implementation

[0038] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be described in detail below with reference to specific embodiments. It should be understood that the selection of embodiments is merely an example of the feasibility of the technical solution and does not constitute any limitation on the invention.

[0039] Example 1

[0040] (1) A stable emulsion is prepared by mixing ceramic powder, organic monomer, crosslinking agent, binder, defoamer, deionized water, surfactant and oil phase and mechanically stirring at 3000 rpm for 1 h.

[0041] The ceramic powder is silicon nitride, the organic monomer is acrylamide, the crosslinking agent is N,N'-methylenebisacrylamide, the catalyst is N,N,N',N'-tetramethylethylenediamine, the initiator is ammonium persulfate, the binder is polyvinyl alcohol, the defoamer is tert-butanol, the surfactant is hexadecyltrimethylammonium bromide, and the oil phase is n-hexane.

[0042] The composition of the catalyst is as follows: silicon nitride powder accounts for 22 wt.% of the total mass of deionized water and silicon nitride powder; hexadecyltrimethylammonium bromide accounts for 0.2 wt.% of silicon nitride powder; the volume ratio of n-hexane to deionized water is 1:5; polyvinyl alcohol accounts for 7 wt.% of the mass of deionized water; tert-butanol accounts for 5 wt.% of the mass of deionized water; acrylamide has a mass fraction of 20 wt.%; the mass ratio of crosslinking agent to organic monomer is 1:15; and the catalyst and initiator are added at a rate of 0.6 mL per 1 g of organic monomer.

[0043] (2) After the emulsion preparation is complete, reduce the stirring speed to 2000 rpm, add N,N,N',N'-tetramethylethylenediamine and ammonium persulfate sequentially, and stir for 5 min. Pour the emulsion into a mold and heat to 45℃ for 1 h to cure, obtaining a silicon nitride ceramic preform. Its cross-sectional SEM image is shown below. Figure 1 It can be seen that the interior has a regular and uniform pore structure before sintering. The green body was heated to 600℃ at a heating rate of 0.2 ℃ / min and held for 4 h to remove the binder. Then, it was sintered in a nitrogen atmosphere at a heating rate of 5 ℃ / min to 1900℃ and held for 1 h to obtain silicon nitride porous ceramic with a porosity of 45.47%.

[0044] Example 2

[0045] (1) A stable emulsion is prepared by mixing ceramic powder, organic monomer, crosslinking agent, binder, defoamer, deionized water, surfactant and oil phase and mechanically stirring at 1500 rpm for 2 h.

[0046] The ceramic powder is alumina, the organic monomer is methacrylamide, the crosslinking agent is ethylene glycol dimethacrylate, the catalyst is N,N,N',N'-tetramethylethylenediamine, the initiator is potassium persulfate, the binder is polyethylene glycol, the defoamer is polydimethylsiloxane, the surfactant is sodium dodecyl sulfate, and the oil phase is n-heptane.

[0047] The composition of the alumina powder is 15 wt.% of the total mass of deionized water and alumina powder, sodium dodecyl sulfate is 3.5 wt.% of the powder, n-heptane is 10:1 of the volume of deionized water, polyethylene glycol is 10 wt.% of the mass of deionized water, polydimethylsiloxane is 10 wt.% of the mass of deionized water, methacrylamide is 10 wt.% of the mass, the crosslinking agent to organic monomer mass ratio is 1:48, the catalyst addition is 0.5 mL relative to 1 g of organic monomer, and the initiator addition is 0.5 mL.

[0048] (2) After the emulsion preparation is completed, the stirring speed is reduced to 300 rpm, and N,N,N',N'-tetramethylethylenediamine and potassium persulfate are added sequentially and stirred for 10 min. The above emulsion is injected into a mold and heated to 80℃ for 30 min to obtain a ceramic green body. The green body is heated to 900℃ at a heating rate of 0.5℃ / min and held for 2 h to remove the binder. Then, it is sintered in air at a heating rate of 0.1℃ / min to 1650℃ and held for 10 min to obtain alumina porous ceramic with a porosity of 87.64%.

[0049] Example 3

[0050] (1) Mix ceramic powder, organic monomer, crosslinking agent, binder, defoamer, deionized water, surfactant and oil phase, and mechanically stir at 2000 rpm for 5 min to obtain a stable emulsion;

[0051] The ceramic powder is silicon dioxide, the organic monomer is dimethylacrylamide, the crosslinking agent is diethylenetriaminevalerate, the catalyst is N,N,N',N'-tetramethylethylenediamine, the initiator is ammonium persulfate, the binder is polyvinylpyrrolidone, the defoamer is polyoxypropylene ethylene glycerol ether, the surfactant is trimethylchlorosilane, and the oil phase is n-octane.

[0052] The composition of the catalyst is as follows: silica powder accounts for 5 wt.% of the total mass of deionized water and silica powder; trimethylchlorosilane accounts for 10 wt.% of the ceramic powder; the volume ratio of n-octane to deionized water is 99:1; polyvinylpyrrolidone accounts for 1 wt.% of the deionized water; polyoxypropylene ethylene glycerol ether accounts for 3 wt.% of the deionized water; dimethacrylamide has a mass fraction of 30 wt.%; the mass ratio of crosslinking agent to organic monomer is 1:5; and the catalyst and initiator are added in amounts of 1 mL per 1 g of organic monomer.

[0053] (2) After the emulsion preparation is completed, the stirring speed is reduced to 500 rpm, and N,N,N',N'-tetramethylethylenediamine and ammonium persulfate are added sequentially and stirred for 10 s. The above emulsion is injected into a mold and heated to 30℃ for 1 min to obtain a ceramic green body. The green body is heated to 700℃ at a heating rate of 0.01℃ / min and held for 5 h to remove the binder. Then, it is sintered in an argon atmosphere at a heating rate of 10℃ / min to 800℃ and held for 4 h to obtain a silica porous ceramic with a porosity of 99.32%.

[0054] Example 4

[0055] (1) A stable emulsion is prepared by mixing ceramic powder, organic monomer, crosslinking agent, binder, defoamer, deionized water, surfactant and oil phase and mechanically stirring at 800 rpm for 2 h.

[0056] The ceramic powder consists of hydroxyapatite and tricalcium phosphate, the organic monomer is dimethylaminoisobutylene ester, the crosslinking agent is ethylene glycol dimethacrylate, the catalyst is N,N,N',N'-tetramethylethylenediamine, the initiator is potassium persulfate, the binder is sodium carboxymethyl cellulose, the defoamer is polyoxypropylene glycerol ether, the surfactant is superdispersant 41000, and the oil phase is n-decane.

[0057] The composition of the catalyst is as follows: hydroxyapatite and tricalcium phosphate powder account for 45 wt.% of the total mass of deionized water and ceramic powder; superdispersant 41000 accounts for 2 wt.% of the powder; the volume ratio of n-decane to deionized water is 1:3; sodium carboxymethyl cellulose accounts for 3 wt.% of the deionized water; polyoxypropylene glycerol ether accounts for 7 wt.% of the deionized water; dimethylaminoisobutylene ester has a mass fraction of 25 wt.%; the mass ratio of crosslinking agent to organic monomer is 1:68; and the catalyst and initiator are added at a rate of 0.8 mL per 1 g of organic monomer.

[0058] (2) After the emulsion preparation is completed, the stirring speed is reduced to 100 rpm, and N,N,N',N'-tetramethylethylenediamine and potassium persulfate are added sequentially and stirred for 8 min. The above emulsion is injected into a mold and cured at 60℃ for 4.5 h to obtain a ceramic green body. The green body is heated to 800℃ at a heating rate of 1℃ / min and held for 6 h to remove the binder. Then, it is sintered in air at a heating rate of 15℃ / min to 1400℃ and held for 3 h to obtain a porous ceramic with a porosity of 62.26%.

[0059] Example 5

[0060] (1) A stable emulsion is prepared by mixing ceramic powder, organic monomer, crosslinking agent, binder, defoamer, deionized water, surfactant and oil phase and mechanically stirring at 2500 rpm for 3 h.

[0061] The ceramic powder is kaolin, the organic monomer is hydroxyethyl acrylate, the crosslinking agent is N,N'-methylenebisacrylamide, the catalyst is N,N,N',N'-tetramethylethylenediamine, the initiator is ammonium persulfate, the binder is sodium pyrophosphate, the defoamer is polydimethylsiloxane, the surfactant is cocamidopropyl betaine, and the oil phase is silicone oil.

[0062] The composition of the catalyst is as follows: 75 wt.% of the total mass of deionized water and kaolin powder; 6.3 wt.% of the powder is cocamidopropyl betaine; the volume ratio of silicone oil to deionized water is 1:14; 5 wt.% of the deionized water is sodium pyrophosphate; 1 wt.% of the deionized water is polydimethylsiloxane; 2 wt.% of hydroxyethyl acrylate is hydroxyethyl acrylate; the mass ratio of crosslinking agent to organic monomer is 1:82; and the catalyst and initiator are added at a ratio of 0.35 mL to 1 g of organic monomer.

[0063] (2) After the emulsion preparation is completed, the stirring speed is reduced to 1500 rpm, and N,N,N',N'-tetramethylethylenediamine and ammonium persulfate are added sequentially and stirred for 4 min. The above emulsion is injected into a mold and cured at 70℃ for 6 h to obtain a ceramic green body. The green body is heated to 400℃ at a heating rate of 8 ℃ / min and held for 12 h to remove the binder. Then, it is sintered in air at a heating rate of 1 ℃ / min to 1500℃ and held for 2 h to obtain a porous ceramic with a porosity of 31.66%.

[0064] Example 6

[0065] (1) A stable emulsion was prepared by mixing sol nanoparticles, organic monomers, crosslinking agents, binders, defoamers, deionized water, surfactants and oil phases and mechanically stirring at 300 rpm for 12 h.

[0066] The sol nanoparticles are zirconium sol, the organic monomer is acrylamide, the crosslinking agent is diethylenetriaminevalerate, the catalyst is N,N,N',N'-tetramethylethylenediamine, the initiator is potassium persulfate, the binder is ethylene glycol, the defoamer is tert-butanol, the surfactant is valerate, and the oil phase is liquid paraffin.

[0067] The zirconium sol nanoparticles account for 85 wt.% of the total mass of deionized water and zirconium sol nanoparticles, valeric acid accounts for 8 wt.% of the zirconium sol nanoparticles, the volume ratio of liquid paraffin to deionized water is 1:9, ethylene glycol accounts for 0.01 wt.% of the mass of deionized water, tert-butanol accounts for 0.01 wt.% of the mass of deionized water, acrylamide has a mass fraction of 0.05 wt.%, the mass ratio of crosslinking agent to organic monomer is 1:90, the catalyst addition amount is 0.1 mL relative to 1 g of organic monomer, and the initiator addition amount is 0.1 mL.

[0068] (2) After the emulsion preparation is completed, the stirring speed is increased to 1000 rpm, and N,N,N',N'-tetramethylethylenediamine and potassium persulfate are added sequentially and stirred for 6 min. The above emulsion is injected into a mold and cured at 99℃ for 3 h to obtain a ceramic green body. The green body is heated to 300℃ at a heating rate of 10 ℃ / min and held for 10 min to remove the binder. Then, it is sintered in air at a heating rate of 10 ℃ / min to 1600℃ and held for 6 h to obtain a zirconia porous ceramic with a porosity of 50.78%.

[0069] Example 7

[0070] (1) A stable emulsion is prepared by mixing ceramic powder, sol nanoparticles, organic monomers, crosslinking agents, binders, defoamers, deionized water, surfactants and oil phases and mechanically stirring at 1000 rpm for 4 h.

[0071] The ceramic powder is alumina, the sol nanoparticles are silica sol, the organic monomer is N-isopropylacrylamide, the crosslinking agent is ethylene glycol dimethacrylate, the catalyst is N,N,N',N'-tetramethylethylenediamine, the initiator is ammonium persulfate, the binder is glycerol, the defoamer is polyoxypropylene glycerol ether, the surfactant is sodium α-olefin sulfonate, and the oil phase is sunflower seed oil.

[0072] The alumina powder and silica sol accounted for 55 wt.% of the total mass of deionized water and all powders, sodium α-olefin sulfonate accounted for 5 wt.% of the powders and nanoparticles, the volume ratio of sunflower seed oil to deionized water was 1:19, glycerol accounted for 8 wt.% of the mass of deionized water, polyoxypropylene glycerol ether accounted for 2 wt.% of the mass of deionized water, N-isopropylacrylamide accounted for 5 wt.%, the mass ratio of crosslinking agent to organic monomer was 1:35, and the amount of catalyst added was 0.2 mL and the amount of initiator added was 0.2 mL relative to 1 g of organic monomer.

[0073] (2) After the emulsion preparation is completed, the stirring speed is reduced to 800 rpm, and N,N,N',N'-tetramethylethylenediamine and ammonium persulfate are added sequentially and stirred for 9 min. The above emulsion is injected into a mold and cured at 50℃ for 1.5 h to obtain a ceramic green body. The green body is heated to 600℃ at a heating rate of 5℃ / min and held for 9 h to remove the binder. Then, it is sintered in air at a heating rate of 20℃ / min to 1300℃ and held for 8 h to obtain a porous ceramic with a porosity of 20.31%.

[0074] Example 8

[0075] (1) A stable emulsion is prepared by mixing ceramic powder, organic monomer, crosslinking agent, binder, defoamer, deionized water, surfactant and oil phase and mechanically stirring at 1200 rpm for 8 hours.

[0076] The ceramic powder is titanium dioxide, the organic monomer is dimethylacrylamide, the crosslinking agent is N,N'-methylenebisacrylamide, the catalyst is N,N,N',N'-tetramethylethylenediamine, the initiator is ammonium persulfate, the binder is sodium carboxyethyl cellulose, the defoamer is tert-butanol, the surfactant is hexylamine, and the oil phase is cyclohexane.

[0077] The composition of the catalyst is as follows: titanium dioxide powder accounts for 65 wt.% of the total mass of deionized water and titanium dioxide; hexylamine accounts for 0.01 wt.% of the powder; the volume ratio of cyclohexane to deionized water is 40:1; sodium carboxyethyl cellulose accounts for 0.6 wt.% of the deionized water; tert-butanol accounts for 8.5 wt.% of the deionized water; dimethylacrylamide accounts for 15 wt.% of the mass; the mass ratio of crosslinking agent to organic monomer is 1:25; and the catalyst and initiator are added at a ratio of 0.27 mL per 1 g of organic monomer.

[0078] (2) After the emulsion preparation is completed, N,N,N',N'-tetramethylethylenediamine and ammonium persulfate are added sequentially while maintaining a stirring speed of 1200 rpm and stirred for 2 min. The above emulsion is injected into a mold and heated to 85℃ for 15 min to obtain a ceramic green body. The green body is heated to 550℃ at a heating rate of 3℃ / min and held for 1 h to remove the binder. Then, it is sintered in an argon atmosphere at a heating rate of 7℃ / min to 1250℃ and held for 5 h to obtain a porous ceramic with a porosity of 93.23%.

[0079] Comparative Example 1

[0080] (1) A stable emulsion is prepared by mixing ceramic powder, organic monomer, crosslinking agent, binder, defoamer, deionized water, surfactant and oil phase and mechanically stirring at 1500 rpm for 2 h.

[0081] The ceramic powder is silicon nitride, the organic monomer is acrylamide, the crosslinking agent is ethylene glycol dimethacrylate, the catalyst is N,N,N',N'-tetramethylethylenediamine, the initiator is ammonium persulfate, the binder is polyethylene glycol, the defoamer is polydimethylsiloxane, the surfactant is hexadecyltrimethylammonium chloride, and the oil phase is liquid paraffin.

[0082] The composition of the mixture is as follows: silicon nitride powder accounts for 90 wt.% of the total mass of deionized water and silicon nitride powder; hexadecyltrimethylammonium chloride accounts for 1 wt.% of the silicon nitride powder; the volume ratio of liquid paraffin to deionized water is 1:9; polyethylene glycol accounts for 6 wt.% of the mass of deionized water; polydimethylsiloxane accounts for 5 wt.% of the mass of deionized water; acrylamide has a mass fraction of 15 wt.%; the mass ratio of crosslinking agent to organic monomer is 1:25; and the amount of catalyst and initiator added is 0.5 mL relative to 1 g of organic monomer.

[0083] (2) After the emulsion preparation is completed, the stirring speed is reduced to 1000 rpm, and N,N,N',N'-tetramethylethylenediamine and ammonium persulfate are added sequentially and stirred for 1 min. The above emulsion is injected into a mold and cured in an oven at 70℃ for 3 h to obtain a ceramic green body. The porosity of the obtained sample is 2.35%. This indicates that when the solid content exceeds the parameter range of 5 ~ 85 wt.% specified in this invention, the preparation of porous ceramic materials with the technical effect described in this invention cannot be achieved. The SEM image of its green body cross section is shown below. Figure 2 As shown, a non-porous structure can be observed.

[0084] Comparative Example 2

[0085] (1) Mix ceramic powder, organic monomer, crosslinking agent, binder, defoamer, deionized water, surfactant and oil phase, and mechanically stir at 2000 rpm for 30 min to obtain a stable emulsion;

[0086] The ceramic powder is cerium oxide, the organic monomer is methacrylamide, the crosslinking agent is N,N'-methylenebisacrylamide, the catalyst is N,N,N',N'-tetramethylethylenediamine, the initiator is potassium persulfate, the binder is polyvinyl alcohol, the defoamer is tert-butanol, the surfactant is sodium dodecyl sulfate, and the oil phase is n-octane.

[0087] The composition of the catalyst is as follows: cerium oxide powder accounts for 50 wt.% of the total mass of deionized water and cerium oxide powder; sodium dodecyl sulfate accounts for 3 wt.% of the powder; the volume ratio of n-octane to deionized water is 1:25; polyvinyl alcohol accounts for 4 wt.% of the mass of deionized water; tert-butanol accounts for 3 wt.% of the mass of deionized water; methacrylamide accounts for 20 wt.% of the mass; the mass ratio of crosslinking agent to organic monomer is 1:15; and the catalyst and initiator are added at a rate of 0.3 mL per 1 g of organic monomer.

[0088] (2) After the emulsion preparation is completed, the stirring speed is reduced to 500 rpm, and N,N,N',N'-tetramethylethylenediamine and potassium persulfate are added sequentially, and stirred for 1 min. The above emulsion is injected into a mold and heated and cured in an oven at 60℃ for 2 h to obtain a ceramic green body. The porosity of the obtained sample is 2.12%. This indicates that when the volume ratio of oil phase to deionized water is not within the parameter range of 1:19 to 99:1, the cross-section of the green body has no porous structure, and the porous ceramic material with the technical effect described in this invention cannot be prepared.

[0089] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing porous ceramics by gel casting of an emulsion, characterized in that, Includes the following steps: Step 1: Add catalyst and initiator to emulsion, mechanically stir and pour into mold, then place in oven for heating and curing to obtain porous ceramic green body; Step 2: The green body obtained in Step 1 is degreased and sintered to obtain porous ceramics; The emulsion comprises ceramic powder and / or sol nanoparticles, organic monomers, crosslinking agents, binders, defoamers, deionized water, an oil phase, and surfactants, and is formed by mechanical stirring and emulsification.

2. The method for preparing porous ceramics by gel casting of an emulsion according to claim 1, characterized in that, The ceramic powder and / or sol nanoparticles comprise 5 to 85 wt.% of the sum of the mass of deionized water and the ceramic powder and / or sol nanoparticles. Optionally, the surfactant accounts for 0.01 to 10.0 wt.% of the mass of the ceramic powder and / or sol-gel nanoparticles. Optionally, the volume ratio of the oil phase to deionized water is 1:19 to 99:1; Optionally, the binder accounts for 0.01 to 10 wt.% of the mass of deionized water. Optionally, the defoamer accounts for 0.01 to 10 wt.% of the mass of deionized water. Optionally, the mass ratio of the crosslinking agent to the organic monomer is 1:5 to 1:90; Optionally, the amount of catalyst added is 0.1 to 1 mL relative to 1 g of organic monomer, and the amount of initiator added is 0.1 to 1 mL.

3. The method for preparing porous ceramics by gel casting of an emulsion according to claim 2, characterized in that, The organic monomer and the initiator were added in the form of aqueous solutions of the corresponding substances, with the organic monomer solution having a mass fraction of 0.05~30 wt.% and the initiator solution having a concentration of 3 wt.%.

4. The method for preparing porous ceramics by gel casting of an emulsion according to claim 1, characterized in that, The ceramic powder is an oxide ceramic powder, a non-oxide ceramic powder, or a composite ceramic powder, selected from one or more of the following: alumina, silicon oxide, zirconium oxide, cerium oxide, magnesium oxide, yttrium oxide, titanium dioxide, silicon nitride, boron nitride, silicon carbide, boron carbide, aluminum titanate, hydroxyapatite, tricalcium β-phosphate, fly ash, coal gangue, secondary alumina ash, kaolin, tailings, and metallurgical slag. Optionally, the sol nanoparticles are one or a mixture of two or more of aluminum sol, silica sol, zirconium sol, titanium sol, and cerium sol. Optionally, the oil phase is one or a mixture of two or more of the following: n-hexane, n-heptane, n-octane, n-decane, cyclohexane, polydimethylsiloxane, glyceryl caprylate, liquid paraffin, silicone oil, soybean oil, rapeseed oil, olive oil, corn oil, sunflower oil, toluene, and styrene. Optionally, the surfactant is one or a mixture of two or more of the following: valeric acid, hexylamine, octadecanoic acid, trimethylchlorosilane, sodium dodecyl sulfate, sodium dodecyl (benzene) sulfonate, sodium fatty alcohol polyoxyethylene ether sulfate, sodium α-alkenyl sulfonate, triethanolamine dodecyl sulfate, hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, superdispersant 41000, cocamidopropyl betaine, Tween series such as Tween 20 / 40 / 60 / 80, Span series such as Span 20 / 40 / 60 / 80; Optionally, the organic monomer is one of acrylamide, methacrylamide, dimethacrylamide, hydroxyethyl methacrylate, N-hydroxymethylacrylamide, N-isopropylacrylamide, hydroxyethyl methacrylate, methacrylic acid, acrylic acid, dimethylaminoisobutylene acrylate, and hydroxyethyl acrylate; the crosslinking agent is one of N,N'-methylenebisacrylamide, ethylene glycol dimethacrylate, and diethylenetriaminevalerate; the catalyst is N,N,N',N'-tetramethylethylenediamine; and the initiator is ammonium persulfate or potassium persulfate. Optionally, the adhesive is one or a mixture of two or more of the following: polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone, sodium pyrophosphate, sodium carboxymethyl / ethyl cellulose, ethylene glycol, and glycerol. Optionally, the defoamer is one or a mixture of two or more of tert-butanol, polydimethylsiloxane, polyoxypropylene glycerol ether, and polyoxypropylene ethylene oxide glycerol ether.

5. The method for preparing porous ceramics by gel casting of an emulsion according to claim 1, characterized in that, The mechanical stirring emulsification process of the emulsion in step 1 is carried out at a speed of 300~3000 rpm for 5 min~12 h; after adding the catalyst and initiator, the mechanical stirring speed is 100~2000 rpm for 10 s~10 min; the heating curing temperature is 30℃~99℃ for 1 min~6 h.

6. The method for preparing porous ceramics by gel casting of an emulsion according to claim 1, characterized in that, In the degreasing process described in step 2, the heating rate is 0.01 ~ 10 ℃ / min, the degreasing temperature is 300 ~ 900℃, and the holding time is 10 min ~ 12 h.

7. The method for preparing porous ceramics by gel casting of an emulsion according to claim 6, characterized in that, In the sintering process described in step 2, the heating rate is 0.1 ~ 20 ℃ / min, the sintering temperature is 800 ~ 2000℃, the sintering atmosphere is air, nitrogen or argon, and the holding time is 10 min ~ 8 h.

8. Porous ceramics prepared by the method according to any one of claims 1 to 7.

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