Preparation method of gradient porous composite ceramic thermal insulation material

Abstract

The present application relates to the technical field of composite thermal insulation material preparation, and particularly relates to a preparation method of gradient-pore composite ceramic thermal insulation material, which is prepared from 68-76 parts of ceramic matrix raw material, 8-12 parts of polycrystalline mullite fiber reinforcement, 14-18 parts of composite pore-forming agent, 1.5-2.5 parts of silica sol binder and 0.3-0.5 parts of dispersant by mass fraction; the ceramic matrix raw material comprises alumina, zirconia and mullite, the composite pore-forming agent is a combination of two or more selected from polystyrene microspheres, stearic acid, sodium chloride and graphite powder, and the dispersant is one or a combination of two selected from sodium polycarboxylate and sodium dodecylbenzenesulfonate; the material forms a gradient-pore structure along the thickness direction. The present application adopts a composite pore-forming system combined with a gradient forming process to accurately construct a pore structure gradually changing along the thickness direction, so that the internal pore distribution of the material is uniform and regular, and the structural strength and use adaptability of the material are balanced from the structural level.

Description

Technical Field

[0001] This invention relates to the field of composite thermal insulation material preparation technology, specifically to a method for preparing a gradient porosity composite ceramic thermal insulation material. Background Technology

[0002] High-temperature insulation materials are key basic materials in the fields of aluminum alloy heat treatment and high-end industrial thermal protection. Ceramic-based insulation materials, with their excellent high-temperature resistance, chemical stability, and structural durability, have become the core application materials in this field. However, ceramic insulation materials currently used in industrial settings generally suffer from a single pore structure design, often employing a uniform pore structure. This makes it difficult to achieve an effective balance between insulation capacity and mechanical load-bearing performance, leading to insufficient insulation or structural damage in practical applications.

[0003] Existing manufacturing processes mostly employ a single uniform pore system, which makes it difficult to precisely control the distribution and gradient changes of pores. This results in poor uniformity of pores within the material, weak interlayer bonding, and a tendency for delamination and cracking to occur after long-term use. Traditional molding processes rely on constant pressure or grouting methods, which have insufficient control over the molding precision of gradient structures and cannot meet the customized thermal insulation requirements under complex working conditions.

[0004] Meanwhile, existing technologies mostly use high-purity mineral raw materials, resulting in high raw material costs and failing to achieve resource utilization of industrial solid waste, which contradicts the trend of green and low-carbon industrial development. Furthermore, conventional drying and sintering processes lack gradient control, making the green body prone to deformation and cracking during processing. The material's thermal stability and operating temperature are insufficient to meet the requirements of harsh high-temperature environments. Given the shortcomings in the overall performance of existing ceramic insulation materials, the industry urgently needs a new ceramic insulation material preparation technology that can balance insulation structure, mechanical properties, preparation cost, and process stability. Summary of the Invention

[0005] The primary objective of this invention is to provide a method for preparing gradient porosity composite ceramic thermal insulation materials.

[0006] A further objective of this invention is to provide a gradient-pore composite ceramic thermal insulation material, comprising, by weight, 68-76 parts of ceramic matrix raw material, 8-12 parts of polycrystalline mullite fiber reinforcement, 14-18 parts of composite pore-forming agent, 1.5-2.5 parts of silica sol binder, and 0.3-0.5 parts of dispersant; wherein the ceramic matrix raw material comprises alumina, zirconium oxide, and mullite, the composite pore-forming agent is a combination of two or more selected from polystyrene microspheres, stearic acid, sodium chloride, and graphite powder, and the dispersant is one or a combination of two selected from sodium polycarboxylate and sodium dodecylbenzenesulfonate; the material forms a gradient-pore structure along its thickness direction.

[0007] Preferably, the ceramic matrix raw material also includes harmlessly treated waste incinerator bottom ash, pulverized waste glass, and yttrium oxide; the particle size of the waste incinerator bottom ash is ≤90μm, the particle size of the waste glass is ≤100μm, and the particle size of the yttrium oxide is ≤50μm.

[0008] Preferably, the polycrystalline mullite fiber reinforcement has a diameter of 3μm-6μm and a length of 5mm-12mm.

[0009] Preferably, the gradient pore structure is a three-layer structure, with a surface porosity of 30%-45%, a middle layer porosity of 45%-60%, and an inner layer porosity of 60%-75%.

[0010] Preferably, the gradient pore structure is a six-layer structure, with the porosities of each layer being approximately 32%, approximately 40%, approximately 48%, approximately 56%, approximately 64%, and approximately 70%, respectively.

[0011] A method for preparing a gradient porosity composite ceramic thermal insulation material includes the following steps: (1) Raw material preparation: ceramic matrix raw materials, polycrystalline mullite fiber reinforcement, composite pore-forming agent, silica sol binder, dispersant and deionized water are mixed to prepare slurry; (2) Gradient molding: Layered slurry vacuum filtration molding is adopted, or photopolymerization 3D printing with vacuum filtration combined with 405nm ultraviolet laser, layer thickness 25μm, exposure power 250mW, scanning speed 5000mm / s, external wall scanning speed 2000mm / s, and filling scanning speed 5000mm / s is adopted to prepare gradient green bodies, and silica sol is used to bond the layers of the green bodies. (3) Gradient drying: Gradient temperature drying is performed on the gradient green body; (4) bisque firing: The dried green body is placed in an air atmosphere and fired bisquely; (5) High-temperature sintering: The bisquered blank is heated and sintered under a protective atmosphere, and the target material is obtained after cooling.

[0012] Preferably, in step (1), the raw material mixing is carried out at 25℃±2℃. First, the ceramic matrix raw material and polycrystalline mullite fiber are mixed at a speed of 3000r / min for 15min. Then, the composite pore-forming agent, silica sol binder and dispersant are added and mixed for 20min. Finally, deionized water is added to adjust the viscosity of the slurry.

[0013] Preferably, in step (2), the vacuum filtration pressure is 0.06MPa-0.08MPa, the filtration time is 12min-18min, and the thickness of the interlayer silica sol coating is 0.05mm-0.1mm.

[0014] Preferably, in step (3), the gradient drying is carried out at a heating rate of 5℃ / h, first drying at 60℃ for 6h-10h, and then heating to 100℃-130℃ for 2h-6h. After drying, the moisture content of the green body is ≤0.5%.

[0015] Preferably, in step (4), the sintering process is carried out at a heating rate of 4℃ / min-6℃ / min, and after heating to 680℃-780℃, it is held for 1.0h-1.3h; in step (5), the high-temperature sintering is carried out in a nitrogen or argon atmosphere with a purity of ≥99.99%, the gas flow rate is 5L / min, the high-temperature sintering heating rate is 2℃ / min-5℃ / min, the sintering temperature is 1550℃-1620℃, the holding time is 2.5h-4.0h, and the cooling rate is 2℃ / min-2.5℃ / min.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention uses a composite pore-forming system combined with a gradient forming process to accurately construct a pore structure that gradually changes along the thickness direction, so that the pores inside the material are evenly and regularly distributed, thus balancing the structural strength and usability of the material from a structural level.

[0017] 2. This invention adopts a molding method that combines layered slurry vacuum filtration or photopolymerization 3D printing with vacuum filtration, which greatly improves the molding accuracy of gradient preforms. Combined with interlayer bonding treatment, it effectively enhances the interlayer bonding force and avoids delamination and cracking during material use.

[0018] 3. This invention introduces industrial solid waste as a matrix component into the raw materials, realizing the resource utilization of waste, reducing the raw material preparation cost, and at the same time not affecting the structural stability of the material, which is in line with the green and environmentally friendly production concept.

[0019] 4. The synergistic process of gradient drying, segmented sintering and gradient high-temperature sintering of the present invention can effectively eliminate stress in the billet, avoid cracks and deformation in the billet during the processing, and ensure the dimensional accuracy and structural integrity of the material.

[0020] 5. The preparation process of this invention has strong stability and a wide range of adjustable parameters. The pore gradient and structural parameters can be adjusted according to different application scenarios to adapt to various high-temperature thermal protection conditions. This invention achieves synergistic optimization of structural design, raw material formulation and preparation process. The prepared material has both good structural stability and process adaptability, which can meet the needs of high-end industrial fields such as aluminum alloy heat treatment and has good prospects for industrial application. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1: Raw material preparation: By weight, 70 parts of ceramic matrix raw material are taken, including 40 parts of alumina, 15 parts of zirconium oxide, and 15 parts of mullite. The alumina purity is ≥98% and the particle size is 10-20μm. The zirconium oxide purity is ≥97% and the particle size is 15-25μm. The mullite purity is ≥96% and the particle size is 20-30μm. 10 parts of reinforcement raw material are industrial-grade polycrystalline mullite fibers with a purity of ≥95%, a fiber diameter of 3μm, and a length of 5mm. 18 parts of composite pore-forming agent are taken, including 8 parts of polystyrene microspheres and 6 parts of stearic acid. 4 parts sodium chloride, polystyrene microspheres with a particle size of 50-80 μm, stearic acid purity ≥99%, sodium chloride purity ≥99.5%, particle size 30-50 μm; 2 parts binder, industrial grade silica sol, silica mass concentration 25%, viscosity 100-200 mPa·s; 0.3 parts dispersant, industrial grade sodium polycarboxylate, molecular weight 2000-3000; appropriate amount of deionized water, adjust the slurry viscosity to 7000 mPa·s, and test using a rotational viscometer under constant temperature conditions of 25℃.

[0023] Using a high-speed mixer, the ceramic matrix and reinforcing raw materials are first mixed at 3000 r / min for 15 min at 25±2℃. Then, the composite pore-forming agent, binder, and dispersant are added and the mixture is continued for 20 min. Finally, deionized water is gradually added and stirred at 2000 r / min until the preset viscosity is reached, ensuring uniform mixing without lumps.

[0024] Gradient molding: A three-layer gradient preform with a total thickness of 15mm was prepared using a layered slurry-vacuum filtration molding process and a 100mm×100mm×15mm polished stainless steel mold. The first layer, the surface layer, consisted of 12 parts of pore-forming agent, including 3 parts of polystyrene microspheres, 6 parts of stearic acid, and 3 parts of sodium chloride, with a porosity of 35%. The second layer, the middle layer, consisted of 18 parts of pore-forming agent, including 6 parts of polystyrene microspheres, 4 parts of stearic acid, and 8 parts of sodium chloride, with a porosity of 50%. The third layer, the inner layer, consisted of 24 parts of pore-forming agent, including 15 parts of polystyrene microspheres, 8 parts of stearic acid, and 1 part of sodium chloride, with a porosity of 65%. Each layer was 5mm thick, with a slurry-laying speed of approximately 5mm / min. After slurry-laying, the preform was filtered for 15 minutes under a vacuum filtration machine at a pressure of 0.06MPa. A 0.1mm thick silica sol was then applied between the layers for bonding at a speed of 2mm / s. After standing for 5 minutes, the next layer was laid.

[0025] Drying treatment: The green body and mold are placed in a constant temperature forced air drying oven and a gradient drying method is adopted. First, it is dried at 60℃ and forced air rate of 2m / s for 8 hours, and then the temperature is raised to 110℃ for 4 hours. The heating rate is 5℃ / h. After drying, the moisture content of the green body is 0.4%, which is tested with a moisture meter. A plastic scraper is used to assist in demolding.

[0026] Bisque firing: Place the dried green body into a high-temperature furnace and heat it to 700°C at a heating rate of 5°C / min in an air atmosphere. Hold it at this temperature for 1 hour and then let it cool naturally to below 200°C before removing it. Ensure that the green body is free of cracks and deformation.

[0027] High-temperature sintering: The bisquered green body is placed in the high-temperature furnace and sintered in a nitrogen atmosphere with a nitrogen purity ≥99.99% and a flow rate of 5L / min. The temperature is increased to 1580℃ at a heating rate of 3℃ / min, held for 3h, and then cooled to room temperature at a cooling rate of 2℃ / min to obtain a gradient pore composite ceramic thermal insulation material.

[0028] Example 2: Raw material preparation: By weight, the ceramic matrix raw material consisted of 72 parts, including 42 parts alumina, 14 parts zirconium oxide, and 16 parts mullite, with specifications consistent with Example 1; the reinforcing material consisted of 10 parts industrial-grade polycrystalline mullite fiber with a purity ≥95%, a fiber diameter of 4 μm, and a length of 7 mm; the composite pore-forming agent consisted of 16 parts polystyrene microspheres, 3 parts graphite powder, 5 parts stearic acid, and 3 parts sodium chloride, with the graphite powder having a purity ≥98% and a particle size of 10-20 μm, and the specifications of the remaining raw materials consistent with Example 1; the binder and dispersant specifications were consistent with Example 1. The slurry viscosity was adjusted to 6500 mPa·s with deionized water and tested under constant temperature conditions of 25℃. The graphite powder was first dried at 105℃ and a blower speed of 2 m / s for 2 h, and then the raw materials were mixed according to the mixing parameters of Example 1.

[0029] Gradient molding: A three-layer gradient preform with a total thickness of 15 mm was prepared using a layered slurry-vacuum filtration molding process with mold specifications consistent with Example 1. The first layer consisted of 11 parts of pore-forming agent, including 2 parts of polystyrene microspheres, 1 part of graphite powder, 5 parts of stearic acid, and 3 parts of sodium chloride, with a porosity of 38%. The second layer consisted of 16 parts of pore-forming agent, including 4 parts of polystyrene microspheres, 2 parts of graphite powder, 4 parts of stearic acid, and 6 parts of sodium chloride, with a porosity of 52%. The third layer consisted of 21 parts of pore-forming agent, including 10 parts of polystyrene microspheres, 4 parts of graphite powder, 5 parts of stearic acid, and 2 parts of sodium chloride, with a porosity of 68%. The interlayer treatment and filtration parameters were consistent with Example 1, with a slurry flow rate of approximately 4 mm / min. After slurry spreading, the surface was smoothed with a scraper.

[0030] Drying treatment: The drying parameters were the same as in Example 1. After drying, the moisture content of the green body was 0.4%, and it was demolded without damage.

[0031] Bisque firing: The bisque firing parameters are the same as in Example 1. After bisque firing, the green body is free from deformation and cracking.

[0032] High-temperature sintering: Sintering is carried out under a nitrogen atmosphere with a nitrogen purity ≥99.99% and a flow rate of 5L / min. The temperature is increased to 1580℃ at a heating rate of 3℃ / min, held for 3.5h, and then cooled to room temperature at a cooling rate of 2℃ / min to obtain the target material.

[0033] Example 3: Raw material preparation: By weight, the ceramic matrix raw material consisted of 72 parts, including 38 parts alumina, 12 parts zirconium oxide, 12 parts mullite, 8 parts waste incinerator bottom ash, and 2 parts waste glass. The waste incinerator bottom ash was treated to be harmless and had a particle size ≤90μm. The waste glass was crushed and had a particle size ≤100μm. The specifications of the remaining matrix raw materials were the same as in Example 1. The reinforcing material consisted of 10 parts industrial-grade polycrystalline mullite fiber with a purity ≥95%, a fiber diameter of 5μm, and a length of 10mm. The composite pore-forming agent consisted of 16 parts, with specifications the same as in Example 2. The binder specifications were the same as in Example 1. The dispersant consisted of 0.4 parts sodium polycarboxylate and sodium dodecylbenzenesulfonate in a 1:1 ratio, both of which were industrial-grade. The slurry viscosity was adjusted to 7000mPa·s with deionized water and tested under constant temperature conditions of 25℃.

[0034] The bottom ash of the waste incinerator is first dried at 110°C and a blower speed of 2m / s for 4 hours, then ground and passed through a 90-mesh sieve; waste glass is crushed and ground to a particle size of ≤100 mesh, and after pretreatment, it is mixed with other raw materials according to the mixing parameters of Example 1.

[0035] Gradient molding: Layered slurry spreading-vacuum filtration molding was adopted. The mold specifications were the same as in Example 1, and the proportion of pore-forming agent and porosity of each layer were the same as in Example 2. The interlayer treatment and filtration parameters were the same as in Example 2. Before spreading the slurry, a 0.05mm thin layer of silica sol was applied to the inner wall of the mold, and the surface was smoothed after spreading the slurry.

[0036] Drying process: Gradient drying method is adopted. First, dry at 60℃ and blower speed of 2m / s for 8 hours, then raise the temperature to 110℃ and dry for 5 hours. The heating rate is 5℃ / h. After drying, the moisture content of the green body is 0.35%, and there is no damage when demolding.

[0037] Bisque firing: In an air atmosphere, heat to 750℃ at a heating rate of 5℃ / min, hold for 1.2h, and then let cool naturally to below 200℃ before removing the blank. The blank should be free of cracks and deformation.

[0038] High-temperature sintering: Sintering is carried out under a nitrogen atmosphere with a nitrogen purity ≥99.99% and a flow rate of 5L / min. The temperature is increased to 1580℃ at a heating rate of 3℃ / min, held for 3.5h, and then cooled to room temperature at a cooling rate of 2℃ / min to obtain the target material.

[0039] Example 4: Raw material preparation: By weight, the ceramic matrix raw material consisted of 72.5 parts, including 38 parts alumina, 12 parts zirconium oxide, 12 parts mullite, 8 parts waste incinerator bottom ash, 2 parts waste glass, and 0.5 parts yttrium oxide. The yttrium oxide had a purity of ≥99% and a particle size of ≤50μm. The specifications of the remaining raw materials were the same as in Example 3. The reinforcing material consisted of 10 parts industrial-grade polycrystalline mullite fiber with a purity of ≥95%, a fiber diameter of 4μm, and a length of 8mm. The specifications of the composite pore-forming agent, binder, and dispersant were the same as in Example 3. The slurry viscosity was adjusted to 6800 mPa·s with deionized water and tested under constant temperature conditions of 25℃.

[0040] Yttrium oxide was ground to a particle size ≤50 mesh, dried at 110°C for 2 hours, and then mixed with other pretreated raw materials according to the mixing parameters of Example 1.

[0041] Gradient molding: A molding method combining photopolymer 3D printing and vacuum filtration was adopted. A photopolymer 3D printer was selected, using a 405nm ultraviolet laser, a layer thickness of 25μm, an exposure power of 250mW, a scanning speed of 5000mm / s (2000mm / s for the outer wall and 5000mm / s for the infill), to prepare a three-layer gradient preform with a total thickness of 15mm. The proportion of pore-forming agent and the porosity of each layer were consistent with those in Example 3. After printing, a vacuum filter was used to filter the preform at a pressure of 0.07MPa for 12 minutes, and a 0.05mm thin layer of silica sol was applied between the layers.

[0042] Drying treatment: Gradient drying method is adopted. First, dry at 60℃ and blower speed of 2m / s for 6h, then dry at 100℃ for 3h, and finally dry at 120℃ for 2h. The heating rate is 5℃ / h. After drying, the moisture content of the green body is ≤0.3% and the dimensions are stable.

[0043] Firing treatment: In an air atmosphere, heat to 750°C at a heating rate of 5°C / min and hold for 1.2 hours to ensure that pore-forming agents and impurities are fully removed.

[0044] High-temperature sintering: Sintering is carried out in a nitrogen atmosphere using a gradient heating method. The nitrogen purity is ≥99.99% and the flow rate is 5L / min. The heating rate is 5℃ / min from room temperature to 500℃, 3℃ / min from 500℃ to 1200℃, and 2℃ / min from 1200℃ to 1600℃. After holding at this temperature for 4 hours, the temperature is lowered to room temperature at a rate of 2℃ / min.

[0045] Example 5: Raw material preparation: By weight, the ceramic matrix raw material consists of 68 parts, including 35 parts alumina, 10 parts zirconium oxide, 15 parts mullite, 5 parts waste incinerator bottom ash, 2 parts waste glass, and 0.5 parts yttrium oxide. The raw material specifications are consistent with those in Example 4. The reinforcing material consists of 8 parts industrial-grade polycrystalline mullite fiber with a purity ≥95%, a fiber diameter of 3 μm, and a length of 6 mm. The composite pore-forming agent consists of 14 parts polystyrene microspheres, 2 parts graphite powder, 5 parts stearic acid, and 3 parts sodium chloride. The binder consists of 1.5 parts industrial-grade silica sol with a silica mass concentration of 25%. The dispersant consists of 0.3 parts sodium polycarboxylate and sodium dodecylbenzenesulfonate in a 1:1 ratio. Deionized water is used to adjust the slurry viscosity to 6000 mPa·s.

[0046] The raw material mixing and pretreatment methods are the same as those in Examples 3 and 4.

[0047] Gradient molding: A molding method combining photopolymerization 3D printing and vacuum filtration was adopted. The printer parameters were the same as in Example 4. A three-layer gradient preform with a total thickness of 10 mm was prepared, with a surface porosity of 30%, a middle layer of 45%, and an inner layer of 60%. The filtration parameters were 0.07 MPa and 12 min. Silica sol was applied between the layers.

[0048] Drying treatment: Gradient drying method is adopted, first drying at 50℃ for 10h, then drying at 100℃ for 4h, with a heating rate of 5℃ / h, and the moisture content is controlled at 0.5%, and the green body is free from cracks.

[0049] Firing process: In an air atmosphere, heat to 680°C at a heating rate of 4°C / min, hold for 1.0h, and then remove after natural cooling to below 200°C.

[0050] High-temperature sintering: Sintering is carried out in an argon atmosphere using a gradient heating method. The argon purity is ≥99.99% and the flow rate is 5L / min. The heating rate is 5℃ / min from room temperature to 500℃, 3℃ / min from 500℃ to 1200℃, and 2℃ / min from 1200℃ to 1550℃. After holding at 1550℃ for 2.5h, the temperature is lowered to room temperature at a rate of 2℃ / min.

[0051] Example 6: Raw material preparation: By weight, the ceramic matrix raw material consists of 76 parts, including 42 parts alumina, 16 parts zirconium oxide, 15 parts mullite, 5 parts waste incinerator bottom ash, 2 parts waste glass, and 0.5 parts yttrium oxide. The raw material specifications are consistent with those in Example 4. The reinforcing material consists of 12 parts industrial-grade polycrystalline mullite fiber with a purity ≥95%, a fiber diameter of 6 μm, and a length of 12 mm. The composite pore-forming agent consists of 18 parts polystyrene microspheres, 4 parts graphite powder, 3 parts stearic acid, and 3 parts sodium chloride. The binder consists of 2.5 parts industrial-grade silica sol with a silica mass concentration of 25%. The dispersant consists of 0.5 parts sodium polycarboxylate and sodium dodecylbenzenesulfonate in a 1:1 ratio. Deionized water is used to adjust the slurry viscosity to 9000 mPa·s.

[0052] The raw material mixing and pretreatment methods are the same as in Example 4.

[0053] Gradient molding: A molding method combining photopolymerization 3D printing and vacuum filtration was adopted. The printer parameters were the same as in Example 4. A three-layer gradient preform with a total thickness of 20 mm was prepared, with a surface porosity of 45%, a middle layer of 60%, and an inner layer of 75%. The filtration parameters were 0.08 MPa and 18 min. Silica sol was applied between the layers.

[0054] Drying treatment: Gradient drying method is adopted, first drying at 60℃ for 8 hours, then drying at 130℃ for 6 hours, with a heating rate of 5℃ / h, and the moisture content is controlled at 0.4%, and the green body size is stable.

[0055] Firing process: In an air atmosphere, heat to 780°C at a heating rate of 6°C / min, hold for 1.3 hours, and then allow to cool naturally to below 200°C before removing.

[0056] High-temperature sintering: Sintering is carried out in a nitrogen atmosphere using a gradient heating method. The nitrogen purity is ≥99.99% and the flow rate is 5L / min. The heating rate is 5℃ / min from room temperature to 500℃, 3℃ / min from 500℃ to 1200℃, and 2℃ / min from 1200℃ to 1620℃. After holding at 1620℃ for 4.0h, the temperature is lowered to room temperature at a rate of 2.5℃ / min.

[0057] Example 7: Raw material preparation: By weight, the ceramic matrix raw material is 72.5 parts, including 38 parts alumina, 12 parts zirconium oxide, 12 parts mullite, 5 parts waste incinerator bottom ash, 2 parts waste glass, and 0.5 parts yttrium oxide. The raw material specifications are the same as in Example 4. The specifications of the reinforcing agent, composite pore-forming agent, binder, and dispersant are the same as in Example 4. Deionized water is used to adjust the slurry viscosity to 7500 mPa·s.

[0058] The raw material mixing and pretreatment methods are the same as in Example 4.

[0059] Gradient molding: A molding method combining photopolymerization 3D printing and vacuum filtration was adopted. The printer parameters were the same as in Example 4. A six-layer gradient preform with a total thickness of 18 mm was prepared with porosities of 32%, 40%, 48%, 56%, 64%, and 70% respectively. The proportion of pore-forming agent was adjusted as the porosity increased. The filtration parameters were 0.07 MPa and 15 min. Silica sol was applied between the layers.

[0060] Drying treatment: Gradient drying method is adopted, first drying at 60℃ for 6 hours, then drying at 100℃ for 3 hours, and finally drying at 120℃ for 2 hours. The heating rate is 5℃ / h. After drying, the moisture content of the green body is ≤0.3% and the dimensions are stable.

[0061] Firing treatment: In an air atmosphere, the temperature is raised to 750℃ at a heating rate of 5℃ / min and held for 1.2h. The green body is free from deformation and cracks.

[0062] High-temperature sintering: Sintering is carried out in a nitrogen atmosphere using a gradient heating method. The nitrogen purity is ≥99.99% and the flow rate is 5L / min. The heating rate is 5℃ / min from room temperature to 500℃, 3℃ / min from 500℃ to 1200℃, and 2℃ / min from 1200℃ to 1600℃. After holding at this temperature for 4 hours, the temperature is lowered to room temperature at a rate of 2℃ / min.

[0063] The composite pore-forming agent of this invention is selected from two or more combinations of polystyrene microspheres, stearic acid, sodium chloride, and graphite powder; the dispersant is selected from one or two of sodium polycarboxylate and sodium dodecylbenzenesulfonate; the photopolymerization 3D printing process parameters are: 405nm ultraviolet laser, layer thickness 25μm, exposure power 250mW, scanning speed 5000mm / s, external wall scanning speed 2000mm / s, and filling scanning speed 5000mm / s.

[0064] The pretreatment method for bottom ash from waste incinerators is as follows: dry at 110℃ and a blowing speed of 2m / s for 4 hours, then grind and pass through a 90-mesh sieve; the pretreatment method for waste glass is as follows: crush and grind to a particle size ≤100 mesh; the pretreatment method for yttrium oxide is as follows: grind to a particle size ≤50 mesh, and dry at 110℃ for 2 hours.

[0065] After the silica sol between the gradient green body layers is bonded, it is left to stand for 5 minutes before the next layer of slurry is applied. Before applying the slurry, a 0.05mm thick layer of silica sol can be applied to the inner wall of the mold. After applying the slurry, the surface of the green body is smoothed with a scraper.

[0066] The high-temperature sintering adopts a gradient heating method: the heating rate from room temperature to 500℃ is 5℃ / min, the heating rate from 500℃ to 1200℃ is 3℃ / min, and the heating rate from 1200℃ to the sintering endpoint temperature is 2℃ / min.

[0067] The composite pore-forming agent of this invention is a combination of two or more selected from polystyrene microspheres, stearic acid, sodium chloride, and graphite powder; the dispersant is one or a mixture of two selected from sodium polycarboxylate and sodium dodecylbenzenesulfonate. The photopolymerization 3D printing of this invention uses a 405nm ultraviolet laser, with a layer thickness of 25μm, an exposure power of 250mW, a scanning speed of 5000mm / s, an external wall scanning speed of 2000mm / s, and a filling scanning speed of 5000mm / s. The pretreatment of the bottom ash from the waste incinerator is as follows: drying at 110℃ and a blower speed of 2m / s for 4 hours, followed by grinding and sieving through a 90-mesh sieve; the pretreatment of waste glass is as follows: crushing and grinding to a particle size ≤100 mesh; the pretreatment of yttrium oxide is as follows: grinding to a particle size ≤50 mesh and drying at 110℃ for 2 hours.

[0068] After bonding the gradient green body layers with silica sol, let it stand for 5 minutes before laying the next layer of slurry. Before laying the slurry, apply a 0.05mm thick layer of silica sol to the inner wall of the mold. After laying the slurry, use a scraper to smooth the surface of the green body.

[0069] The high-temperature sintering adopts a gradient heating method, with a heating rate of 5℃ / min from room temperature to 500℃, a heating rate of 3℃ / min from 500℃ to 1200℃, and a heating rate of 2℃ / min from 1200℃ to the sintering endpoint temperature.

[0070] Performance testing and results analysis: Test sample: The test samples were gradient pore composite ceramic thermal insulation materials prepared in Examples 1 to 7. Three parallel samples were prepared for each sample, with the same size as the mold in the corresponding example. Before testing, the surface was polished and impurities were removed. The test results were taken as the average value, and the deviation of the parallel samples was ≤5%.

[0071] Test standards and methods: All tests were conducted at 25±2℃ and 50±5% relative humidity. The testing equipment was calibrated and qualified. The specific methods are as follows: (1) Bulk density: According to GB / T5480-2017, the volumetric mass method was adopted. The sample size was 30mm×30mm×corresponding blank thickness. The mass was tested by an electronic balance with an accuracy of 0.001g. The size was tested and the volume was calculated by a vernier caliper with an accuracy of 0.02mm. Each sample was tested 3 times and the average value was taken.

[0072] (2) Porosity: According to GB / T16400-2020, the immersion method combined with the bulk density calculation was used to test the average porosity of each gradient layer and the whole. Each sample was tested 3 times and the average value was taken. The calculation deviation was ≤1%.

[0073] (3) Thermal conductivity: According to ASTM C518, a heat flow meter was used for testing. The test temperature was 25℃ (room temperature) and 1000℃ (high temperature). The sample size was 300mm×300mm×corresponding blank thickness. The hot plate was set to test temperature and the cold plate to 50℃. After holding for 30 minutes, the data was recorded. Each sample was tested 3 times and the average value was taken.

[0074] (4) Compressive strength: According to GB / T3003-2022, the universal testing machine was used for testing. The loading rate was 10 mm / min. The sample size was 50 mm × 50 mm × corresponding blank thickness. The maximum fracture load was recorded and the strength was calculated. Each sample was tested 3 times and the average value was taken.

[0075] (5) Thermal stability: According to GB / T3003-2022, the high temperature furnace aging method was used for testing. The sample was kept at 1200℃ for 24 hours in a high temperature furnace. After cooling, the dimensional changes were tested and the linear shrinkage rate was calculated. Each sample was tested 3 times and the average value was taken.

[0076] (6) Maximum operating temperature: The maximum operating temperature is determined by thermogravimetric analysis combined with differential scanning calorimetry. The test conditions are 25-1600℃, heating rate 10℃ / min, nitrogen atmosphere. The temperature at which the sample mass loss rate is ≥5% and a clear thermal decomposition peak appears is the maximum operating temperature. Each sample is tested 3 times and the average value is taken.

[0077] (7) Interlayer bonding strength: Refer to GB / T3003-2022 and optimize the test method. Use a universal testing machine for testing. The loading rate is 5 mm / min. The sample size is 100 mm × 50 mm × corresponding blank thickness. Test the interlayer peel strength. Each sample is tested 3 times and the average value is taken.

[0078] The test results are shown in Table 1 below: Table 1: Results analysis: Based on the above test results, the gradient porosity composite ceramic thermal insulation materials prepared in each embodiment of the present invention exhibit excellent comprehensive performance. The preparation process demonstrates good stability and repeatability, fully proving the feasibility and practicality of the preparation method provided by the present invention, and meeting the requirements for the practicality of inventions under patent law. The test data of each embodiment show good matching with the corresponding preparation process parameters, following the basic laws of industrial production, and can be directly applied to industrial production. Furthermore, by comparing the performance of each embodiment with that of corresponding comparative embodiments, the technical advantages of the preparation method of the present invention are further highlighted. None of the comparative embodiments adopted the optimized process or raw material system of the present invention, resulting in their comprehensive performance being inferior to that of the corresponding embodiments.

[0079] Example 1, as the basic embodiment of the present invention, employs a combination of layered slurry spreading-vacuum filtration molding process and a composite porogen system. The prepared material has a reasonable bulk density and uniform pore distribution, effectively balancing thermal insulation performance and mechanical strength, providing a reliable foundation for optimization in subsequent embodiments. Comparative Example 1, without using a composite porogen, only uses a single sodium chloride porogen, resulting in decreased material porosity, increased bulk density, significantly increased thermal conductivity at both room and high temperatures, and decreased interlayer bonding strength and maximum service temperature. This demonstrates the crucial optimizing role of the composite porogen system in material performance.

[0080] Example 2, by adding graphite powder and extending the high-temperature sintering holding time, further optimized the internal structure of the material, resulting in a simultaneous improvement in compressive strength and thermal insulation, as well as an increase in the maximum service temperature. Comparative Example 2, without adding graphite powder and shortening the sintering holding time, exhibited a less dense internal structure, decreased compressive strength, increased thermal conductivity, and poorer thermal stability, highlighting the beneficial effects of adding graphite powder and maintaining a suitable sintering time on material performance.

[0081] Example 3 introduces two solid wastes, waste incinerator bottom ash and waste glass, as components of the ceramic matrix raw materials, achieving waste recycling and reuse, reducing material preparation costs, and without negatively impacting the material's core thermal insulation, mechanical, and thermal stability properties, aligning with the trend of green and environmentally friendly industrial development. Comparative Example 3, without adding solid waste and using only pure alumina, zirconium oxide, and mullite as matrix raw materials, not only increased preparation costs but also reduced porosity and increased thermal conductivity, demonstrating that the appropriate introduction of solid waste can reduce costs while ensuring material performance.

[0082] Example 4 incorporates yttrium oxide as a sintering aid into the raw material system. A combined photopolymerization 3D printing and vacuum filtration molding method effectively improves the molding accuracy of the preform and the thermal stability of the material, significantly enhancing interlayer bonding strength and further optimizing the overall performance of the material. Comparative Example 4, without the addition of yttrium oxide and using only single vacuum filtration molding, suffers from insufficient molding accuracy, decreased material thermal stability and interlayer bonding strength, and a lower maximum operating temperature, demonstrating the technological value of yttrium oxide and the composite molding method.

[0083] Examples 5 to 7, by reasonably adjusting the raw material ratio, total body thickness, porosity gradient distribution, and process parameters at each stage, were adapted to the thermal insulation and protection requirements under different high-temperature environments. The prepared materials all maintained stable performance, demonstrating that the preparation method of the present invention possesses good flexibility and adaptability, and can be specifically adjusted according to the needs of actual application scenarios, thus expanding the application range of the materials. In contrast, Examples 5 to 7 did not adjust the raw material ratio or process parameters according to the parameter range of the present invention; either the raw material ratio was unbalanced, or the porosity gradient was unreasonable, resulting in the overall performance of the materials being lower than that of the corresponding examples. This further verifies the rationality and optimization effect of the process parameters of the present invention.

[0084] In summary, by optimizing the raw material system, molding process and sintering parameters, this invention successfully solves the technical problems of the prior art, which make it difficult to balance the thermal insulation performance and mechanical strength of ceramic thermal insulation materials and the high preparation cost. Each embodiment shows better thermal insulation performance, mechanical properties and thermal stability compared with the corresponding embodiment.

[0085] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention.

Claims

1. A gradient porosity composite ceramic thermal insulation material, characterized in that, The material is composed of 68-76 parts by weight of ceramic matrix raw material, 8-12 parts of polycrystalline mullite fiber reinforcement, 14-18 parts of composite pore-forming agent, 1.5-2.5 parts of silica sol binder, and 0.3-0.5 parts of dispersant. The ceramic matrix raw material includes alumina, zirconium oxide, and mullite. The composite pore-forming agent is a combination of two or more selected from polystyrene microspheres, stearic acid, sodium chloride, and graphite powder. The dispersant is one or a combination of two selected from sodium polycarboxylate and sodium dodecylbenzene sulfonate. The material forms a gradient pore structure along the thickness direction.

2. The gradient porosity composite ceramic thermal insulation material according to claim 1, characterized in that, The ceramic matrix raw materials also include harmlessly treated waste incinerator bottom ash, crushed waste glass and yttrium oxide; the particle size of waste incinerator bottom ash is ≤90μm, the particle size of waste glass is ≤100μm, and the particle size of yttrium oxide is ≤50μm.

3. The gradient porosity composite ceramic thermal insulation material according to claim 1, characterized in that, The diameter of the polycrystalline mullite fiber reinforcement is 3μm-6μm and the length is 5mm-12mm.

4. The gradient porosity composite ceramic thermal insulation material according to claim 1, characterized in that, The gradient porosity structure is a three-layer structure, with a surface porosity of 30%-45%, a middle layer porosity of 45%-60%, and an inner layer porosity of 60%-75%.

5. The gradient porosity composite ceramic thermal insulation material according to claim 1, characterized in that, The gradient pore structure is a six-layer structure, with porosities of approximately 32%, 40%, 48%, 56%, 64%, and 70% for each layer, respectively.

6. A method for preparing a gradient-pore composite ceramic thermal insulation material, used to prepare the material according to any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Raw material preparation: ceramic matrix raw materials, polycrystalline mullite fiber reinforcement, composite pore-forming agent, silica sol binder, dispersant and deionized water are mixed to prepare slurry; (2) Gradient molding: Layered slurry vacuum filtration molding is adopted, or photopolymerization 3D printing with vacuum filtration combined with 405nm ultraviolet laser, layer thickness 25μm, exposure power 250mW, scanning speed 5000mm / s, external wall scanning speed 2000mm / s, and filling scanning speed 5000mm / s is adopted to prepare gradient green bodies, and silica sol is used to bond the layers of the green bodies. (3) Gradient drying: Gradient temperature drying is performed on the gradient green body; (4) bisque firing: The dried green body is placed in an air atmosphere and fired bisquely; (5) High-temperature sintering: The bisquered blank is heated and sintered under a protective atmosphere, and the target material is obtained after cooling.

7. The preparation method according to claim 6, characterized in that, Step (1) The raw material mixing is carried out at 25℃±2℃. First, the ceramic matrix raw material and polycrystalline mullite fiber are mixed at a speed of 3000r / min for 15min. Then, the composite pore-forming agent, silica sol binder and dispersant are added and mixed for 20min. Finally, deionized water is added to adjust the viscosity of the slurry.

8. The preparation method according to claim 6, characterized in that, Step (2) The vacuum filtration pressure is 0.06MPa-0.08MPa, the filtration time is 12min-18min, and the thickness of the interlayer silica sol coating is 0.05mm-0.1mm.

9. The preparation method according to claim 6, characterized in that, Step (3) Gradient drying: First, dry at 60℃ for 6h-10h at a heating rate of 5℃ / h, then heat to 100℃-130℃ for 2h-6h. After drying, the moisture content of the green body is ≤0.5%.

10. The preparation method according to claim 6, characterized in that, Step (4) The sintering process is carried out at a heating rate of 4℃ / min-6℃ / min, and after heating to 680℃-780℃, it is held for 1.0h-1.3h; Step (5) The high-temperature sintering is carried out in a nitrogen or argon atmosphere with a purity of ≥99.99%, the gas flow rate is 5L / min, the high-temperature sintering heating rate is 2℃ / min-5℃ / min, the sintering temperature is 1550℃-1620℃, the holding time is 2.5h-4.0h, and the cooling rate is 2℃ / min-2.5℃ / min.

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