High-temperature-resistant low-thermal-conductivity low-dielectric alumina aerogel thermal insulation composite material and preparation method thereof

Abstract

The application discloses a kind of high-temperature-resistant low-thermal-conductivity low-dielectric alumina aerogel heat-insulating composite material and preparation method thereof, belong to aerogel material technical field.The application uses aluminum-silicon-zirconium ternary aqueous sol as matrix precursor, introduces boron source to construct boron-silicon and boron-zirconium cooperative lattice stable system, inhibits material crystallization sintering under 1000 DEG C high temperature;Low-dielectric core-shell structure infrared sunscreen is prepared by hydrolysis deposition method, and the characteristics of infrared shielding and low dielectric, low loss are considered;Collaborate reinforced fiber and whisker multistage interpenetrating reinforced skeleton or reinforced fiber preform skeleton to improve mechanical properties, compatible with a variety of drying processes, and the target composite material is obtained by subsection gradient heating treatment.The application has strong process adaptability, controllable cost, and is suitable for aerospace wave-transparent heat protection, high-end electronic packaging, new energy equipment and industrial high-temperature insulation fields.

Description

Technical Field

[0001] This invention belongs to the field of aerogel material technology, specifically relating to a high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material and its preparation method. Background Technology

[0002] New high-speed aircraft, high-end radar radomes, new energy equipment, and industrial high-temperature equipment maintain surface temperatures of around 1000℃ during operation, requiring matching thermal insulation materials to possess comprehensive properties such as high temperature resistance, low thermal conductivity, low dielectric constant, lightweight, and good mechanical properties. Alumina aerogel, with its high porosity, low density, low thermal conductivity, and high temperature resistance, is considered one of the most promising materials for medium- and high-temperature thermal insulation.

[0003] Currently, several key technical issues still exist in the practical application of alumina aerogel: 1. Alumina aerogel is prone to crystal phase transformation, particle sintering and pore collapse at high temperatures of 1000℃, which leads to a sharp increase in thermal conductivity and makes it impossible to use stably for a long time. 2. To reduce the thermal conductivity at high temperatures, light-blocking agents need to be added. Ordinary single-powder light-blocking agents will significantly increase the dielectric constant and dielectric loss tanδ, which cannot meet the requirements of wave-transparent and low-dielectric packaging. 3. Pure alumina aerogel is brittle and has low mechanical strength, making it prone to cracking and breakage under assembly, vibration, and thermal shock conditions; 4. Existing preparation methods mostly rely on supercritical drying alone, which results in high equipment costs, limited processes, and incompatibility with more low-cost drying methods; 5. The process is complex, the precursor cost is high, and the batch stability is poor, making it difficult to achieve large-scale production.

[0004] The above problems prevent existing alumina aerogel materials from simultaneously achieving high temperature resistance, low thermal conductivity, low dielectric constant, high strength, and process versatility within the 1000℃ temperature range, severely limiting their application in aerospace, electronics, new energy, and industrial high-temperature insulation fields.

[0005] Existing technologies cannot overcome all the aforementioned technical pain points simultaneously, and this invention proposes improvements to address these multiple deficiencies. Therefore, developing an alumina aerogel composite material with a temperature resistance of 1000℃, low thermal conductivity, low dielectric constant, high strength, and compatibility with various drying processes has become an urgent technical problem to be solved in this field. Summary of the Invention

[0006] To address the problems of existing alumina aerogels, such as easy sintering and collapse at 1000℃, high high-temperature thermal conductivity, increased dielectric strength due to opacifiers, poor mechanical properties, limited drying processes, and high preparation costs, this invention provides a high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material and its preparation method. This invention mainly includes three core improvements: constructing a borosilicate-boron-zirconium dual-lattice synergistic stabilizing system to suppress high-temperature sintering; employing a low-dielectric core-shell infrared opacifier to balance thermal insulation and low dielectric properties; and using a multi-level interpenetrating skeleton of reinforcing fibers and whiskers or a reinforcing fiber preform skeleton to improve mechanical properties. The resulting material can be used stably for a long time at 1000℃, exhibits wide-temperature-range low thermal conductivity, low dielectric strength and low loss, and excellent mechanical properties. It is also compatible with various drying processes, has controllable costs, and can be used in aerospace thermal protection, radar transparent structures, high-end electronic packaging, new energy equipment, and industrial high-temperature pipeline insulation.

[0007] The technical solution of the present invention is as follows: A high-temperature resistant, low-thermal-conductivity, and low-dielectric alumina aerogel thermal insulation composite material is prepared using an in-situ composite sol of aqueous alumina sol, aqueous silica sol, and aqueous zirconium sol as a precursor. A borosilicate and boron-zirconium dual-lattice synergistic stabilization system is employed to suppress high-temperature crystallization and sintering. A low-dielectric core-shell structure infrared shielding agent is introduced, balancing infrared shielding with low dielectric and low-loss characteristics. The composite material is further enhanced by a multi-level interpenetrating reinforcing skeleton of reinforcing fibers and whiskers or a reinforcing fiber preform skeleton to improve mechanical properties and structural stability. Through precise sol control, dual-path skeleton molding, gradient impregnation with gel, multiple types of mild drying, and segmented heat treatment, a high-temperature stable, low-dielectric, low-thermal-conductivity, and high-strength vibration-resistant alumina aerogel composite material is obtained. At the microscopic level, the alumina matrix of the composite material is an amorphous-partially crystalline composite phase; the core-shell opacifier is uniformly dispersed inside the matrix without obvious agglomeration; and the reinforcing fibers and whiskers intertwine to form a continuous interpenetrating skeleton.

[0008] The present invention discloses a method for preparing a high-temperature resistant, low-thermal-conductivity, low-dielectric alumina aerogel thermal insulation composite material, comprising five steps: composite sol preparation, fiber-reinforced porous skeleton molding, composite sol impregnation and gel aging, multi-mode drying, and segmented high-temperature heat treatment.

[0009] The objective of this invention is achieved through the following technical solution: A method for preparing a high-temperature resistant, low-thermal-conductivity, low-dielectric-resistance alumina aerogel thermal insulation composite material includes the following steps: S1. Preparation of composite sol: S1-1. Slowly add the measured alcohol to the aqueous aluminum sol, stir evenly, then add the aqueous silica sol and aqueous zirconium sol, and continue stirring to form an aluminum-silicon-zirconium ternary in-situ composite sol. S1-2. Add a measured amount of boron source to the composite sol and stir until the boron source is completely dissolved. S1-3. Add acid or base catalyst to adjust the pH value. The pH of the acidic system is controlled at 4.0-6.5, and the pH of the alkaline system is controlled at 9.0-11.0. Continue stirring to obtain a uniform and stable ternary composite alumina sol. S2, Fiber-reinforced porous skeleton molding: S2-1. Add the organic and inorganic adhesives to deionized water in proportion and stir under water bath conditions to form a uniform, stable dispersion with the designed viscosity. S2-2. Add the reinforcing fibers and whiskers slowly in batches to the above dispersion. Stir after each batch is added, and continue stirring until the dispersion is uniform after the addition is complete, so as to obtain a stable slurry without clumping or sedimentation. S2-3. Inject the slurry into the mold, shape it, and dry it to obtain a fiber preform; preheat the fiber preform at 700-900℃, and after cooling, obtain a fiber-reinforced porous skeleton with interconnected pores. Alternatively, reinforced fiber preforms can be used directly as the skeleton, and then used after degumming pretreatment at 550℃~650℃. S3, Composite Sol Impregnation and Gel Aging: First, a low-dielectric core-shell structure infrared shading agent with controllable core-shell thickness is prepared; then, the low-dielectric core-shell structure infrared shading agent is uniformly dispersed in the composite sol prepared in S1, and the fiber-reinforced porous skeleton obtained in S2 is impregnated using a multi-mode impregnation process, and gelation and isothermal aging are completed in sequence to obtain a wet gel composite with uniform structure and no obvious agglomeration. S4. Multi-mode drying: The wet gel composite is placed in a drying device for drying to remove the liquid phase inside the pores of the wet gel composite, so as to obtain an aerogel preform that does not crack and does not collapse. S5. Segmented high-temperature heat treatment: The aerogel preform is placed in a high-temperature furnace and subjected to a three-stage heat treatment with gradient heating in air or an inert atmosphere; the solvent organic matter is removed in sequence, the gel network is stabilized, and the crystal phase is regulated. After cooling, a high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material is obtained.

[0010] Further: S1 involves diluting alcohols in an aqueous alumina sol, then adding aqueous silica sol, aqueous zirconium sol, and a boron source to form a stable borosilicate and boron-zirconium bilattice system. This system can create a barrier structure on the surface of alumina particles, inhibiting crystallization and sintering at 1000℃. The pH is then adjusted to obtain a composite sol, in which: In S1-1, the stirring is carried out at a speed of 200 r / min to 800 r / min for 10 min to 30 min; the continued stirring is carried out at a speed of 200 r / min to 800 r / min for 15 min to 40 min. S1-2 involves constructing a borosilicate and boron-zirconium synergistic lattice stabilization system; the introduction of a boron source forms a borosilicate and boron-zirconium synergistic stabilization system, creating a barrier structure on the surface of alumina particles to suppress crystallization and sintering at 1000℃; the stirring speed is 200r / min~800r / min, and the time is 20min~50min. In S1-3, the stirring speed is 200 r / min to 800 r / min, and the time is 30 min to 60 min; The alcohol, aqueous aluminum sol, aqueous silica sol, aqueous zirconium sol, and catalyst are disposed in a mass ratio of (2-3):(4-5):(4-5):(1-2):(0.5-1). The boron source is selected from at least one of boric acid, metaboric acid, boron oxide, borates, and borate esters; The alcohols mentioned are one or more of ethanol, methanol, isopropanol, n-propanol, n-butanol, isobutanol, sec-butanol, tert-butanol, ethylene glycol, propylene glycol, and glycerol, and can be mixed in any proportion. The aqueous aluminum sol has a solid content of 30%–50%, the aqueous silica sol has a solid content of 15%–40%, and the aqueous zirconium sol has a solid content of 25%–35%. The average particle size of the aqueous aluminum sol particles is 35nm to 150nm, the average particle size of the aqueous silica sol particles is 25nm to 100nm, and the average particle size of the aqueous zirconium sol particles is 30nm to 120nm. The aqueous aluminum sol, aqueous silica sol, and aqueous zirconium sol maintain the same acidity or alkalinity to prevent premature gelation of the sol system; an alkaline catalyst is added to the acidic system, and an acid catalyst is added to the alkaline system. The acid catalyst is one of hydrochloric acid, nitric acid, acetic acid, citric acid, oxalic acid, and phosphoric acid. The alkaline catalyst is one of ammonia, urea, organic amine, or alkali metal hydroxide.

[0011] S2 is achieved by preheating after slurry molding, or by using a reinforced fiber preform as a skeleton, wherein: In S2-1, the stirring is carried out under water bath conditions, with the water bath temperature being 50℃~90℃ and the stirring time being 30min~60min; In S2-2, stir for 10 to 20 minutes after each batch is added, and continue stirring for 40 to 90 minutes until the mixture is evenly dispersed. In S2-3, the molding process is selected from vacuum filtration, molding, injection, extrusion or spraying. The drying process involves drying in an oven at 80℃ to 120℃ for 2 to 8 hours; the preheating process takes 1 to 3 hours. The reinforcing fiber preform described in S2 is selected from at least one of alumina fiber preform, silica fiber preform, zirconia fiber preform, and mullite fiber preform. The organic adhesive, inorganic adhesive, and deionized water are mixed in a mass ratio of (2-3):(4-5):(4-5); The organic adhesive is selected from at least one of gelatin, starch, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl alcohol, polyethylene glycol, acrylic resin, phenolic resin, and aqueous emulsion. The inorganic binder is selected from at least one of alumina sol, zirconium oxide sol, silica sol, aluminum dihydrogen phosphate, sodium silicate, boric acid, borate, and low melting point glass powder. The reinforcing fiber is selected from at least one of chopped alumina fiber, silicon oxide fiber, zirconium oxide fiber, mullite fiber, quartz fiber, silicon-aluminum composite fiber, and aluminum-zirconium doped fiber; The whiskers are selected from at least one of alumina whiskers, zirconia whiskers, and silicon carbide whiskers.

[0012] The low-dielectric core-shell infrared shading agent described in S3 is selected from at least one of TiO2@SiO2, ZrO2@SiO2, BN@SiO2, Al2O3@SiO2, TiO2@BN, and ZrO2@BN; The core of the low-dielectric core-shell infrared shading agent performs the infrared shading function, and the outer shell is made of low-dielectric material to avoid the degradation of the overall dielectric performance caused by directly using high-dielectric powder; the shell thickness of the low-dielectric core-shell infrared shading agent is 10nm to 50nm, preferably 20nm to 40nm; the addition amount of the low-dielectric core-shell infrared shading agent is 1wt% to 3wt%, preferably 1.5wt% to 2.5wt%.

[0013] The steps for preparing the low-dielectric core-shell infrared shading agent in S3 are as follows: The core phase powder is added to an ethanol-water mixed solvent (ethanol to water volume ratio of 1:2 to 2:1) and dispersed evenly. The pH is adjusted to 8.5 to 11.0, and a silicate ester or boron source precursor is slowly added dropwise. The mixture is refluxed at 40℃ to 80℃ for 2 to 6 hours. The product is centrifuged, washed, dried at 80℃ to 120℃, and heat-treated at 400℃ to 600℃ for 2 to 4 hours to obtain a low-dielectric core-shell infrared shading agent with a shell thickness of 10 nm to 50 nm. The above-mentioned low-dielectric core-shell structure infrared shading agent was added to the composite sol prepared in S1, and the shading agent was uniformly dispersed by ultrasonic dispersion for 10 min to 30 min and mechanical stirring for 30 min to 60 min. The fiber-reinforced porous skeleton obtained from S2 is placed in an impregnation device and fully impregnated using any one of the following methods: atmospheric pressure impregnation, vacuum impregnation, pressure impregnation, vacuum-pressure composite impregnation, spraying, or curtain coating. The vacuum degree of vacuum impregnation is -0.05MPa to -0.1MPa, the pressure of pressure impregnation is 0.1MPa to 0.5MPa, and the pressure holding impregnation is 30min to 120min. After impregnation, the composite is placed at 60℃~80℃ for gelation and aging for 30min~24h to obtain a wet gel composite with uniform structure. The drying process described in S4 is selected from at least one of the following: supercritical ethanol drying, supercritical CO2 drying, freeze drying, microwave drying, vacuum drying, atmospheric pressure drying, and infrared drying. S4. Multi-method drying: The wet gel is placed in a drying device and at least one combination of supercritical, freezing, vacuum, microwave, and atmospheric pressure drying is selected to remove the liquid phase inside the pores and obtain an aerogel preform that does not crack or collapse.

[0014] The gradient heating three-stage heat treatment described in S5 has the following specific process: First stage: Heat to 500℃ at a rate of 1℃ / min to 5℃ / min, hold for 1 hour, and remove solvent and organic components; Second stage: Heat up to 800℃ at 2℃ / min~8℃ / min, hold for 1h, and stabilize the amorphous network structure; The third stage involves heating at 3℃ / min to 10℃ / min to 1000℃ and holding for 1h to 2h to regulate the crystal phase structure and enhance the lattice stabilization effect; after holding, the furnace is cooled to room temperature.

[0015] This invention also relates to a high-temperature resistant, low-thermal-conductivity, low-dielectric alumina aerogel thermal insulation composite material, obtained by the above-mentioned preparation method of the high-temperature resistant, low-thermal-conductivity, low-dielectric alumina aerogel thermal insulation composite material, and has the following properties: ① The long-term operating temperature is 1000℃, and the linear shrinkage rate after heat treatment at 1000℃ for 2 hours is ≤1.8%; ② Thermal conductivity at room temperature ≤ 0.028 W / (m K), thermal conductivity at 1000℃ ≤ 0.060 W / (m K); ③ Dielectric constant ε≤1.67 (10GHz), dielectric loss tanδ≤0.009 (10GHz); ④ Density 0.30 g / cm³ 3 ~0.35g / cm 3 10% deformation compressive strength ≥0.6MPa.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. The high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material of the present invention: Good high-temperature stability: The borosilicate and boron-zirconium dual-lattice stabilization system can make the material structurally stable, with low shrinkage and no collapse at 1000℃; Balancing low thermal conductivity and low dielectric properties: The core-shell structure infrared shielding agent is used, with the core achieving infrared radiation shielding and the low dielectric shell isolating the high dielectric core, overcoming the technical contradiction of the deterioration of dielectric constant and dielectric loss tanδ caused by traditional shielding agents. Mechanical property improvement: Multi-level interpenetrating reinforcement of reinforcing fibers and whiskers or pre-reinforcing fiber skeleton improves strength and vibration and thermal shock resistance; High process adaptability: It is compatible with multiple drying paths such as supercritical, freezing, vacuum, microwave, and atmospheric pressure, and does not have to rely entirely on expensive supercritical equipment, thus reducing production costs and adapting to the large-scale preparation of large-size components.

[0017] 2. The advantages of the preparation method of the high temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material described in this invention are: the entire preparation process is controllable, it can be adapted to a variety of industrial equipment, and it is conducive to engineering scale-up preparation. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0019] Figure 1 This is a schematic diagram of the microstructure of a high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material according to the present invention (including reinforcing fibers, whiskers, aerogel matrix, and low dielectric core-shell infrared shading agent). Figure 2 This is a schematic diagram of the preparation process of a high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material according to the present invention. Detailed Implementation

[0020] The present invention will be further illustrated by the following examples. These examples are intended to illustrate the present invention and not to limit it.

[0021] Test environment description: The test samples for each embodiment and comparative example were taken from the same batch of finished products; the high-temperature heat treatment and linear shrinkage test atmosphere were both air atmosphere; the dielectric property test condition was 10GHz; the compressive strength test was conducted under room temperature conditions; the thermal conductivity test was conducted under room temperature conditions.

[0022] Example 1: A method for preparing a high-temperature resistant, low-thermal-conductivity, low-dielectric-resistance alumina aerogel thermal insulation composite material, such as... Figure 2 As shown, it includes the following steps: S1. Preparation of composite sol: The solution was prepared by mixing ethanol, aqueous aluminum sol, aqueous silica sol, aqueous zirconium sol, and ammonia in a mass ratio of 2:5:4:1:0.5. Ethanol was added to the aluminum sol for dilution, and silica sol and zirconium sol were added in sequence and stirred evenly to form an aluminum-silicon-zirconium ternary in-situ composite sol. Boric acid was added as a boron source, and ammonia was added dropwise to adjust the pH to obtain the composite sol. S2. Fiber-reinforced porous skeleton molding: Gelatin and alumina sol are used as the bonding system to prepare a slurry by blending short alumina fibers and alumina whiskers; the mass ratio of short alumina fibers to alumina whiskers is 4:1; the slurry is injected into a mold, vacuum filtered and molded, dried and preheated at 800℃, and cooled to obtain a fiber-reinforced porous skeleton with a multi-level interpenetrating structure composed of short reinforcing fibers and whiskers; S3. Composite sol impregnation and gel aging: TiO2@SiO2 core-shell structure low dielectric infrared opacifier was prepared by hydrolysis deposition method, with an addition amount of 2wt%; the opacifier was dispersed in composite sol, and the framework was vacuum impregnated at a vacuum degree of -0.08MPa for 60min; gel aging was carried out at 80℃ to obtain a wet gel composite. S4. Drying: Supercritical CO2 drying is used; S5. Segmented high-temperature heat treatment: Heating and heat preservation in three stages: 500℃, 800℃, and 1000℃. First stage: Increase the temperature to 500℃ at a rate of 1℃ / min, and hold for 1 hour; Second stage: Increase the temperature to 800℃ at a rate of 8℃ / min and hold for 1 hour; The third step involves heating the material at 3℃ / min to 1000℃, holding it at that temperature for 2 hours, and then cooling it to room temperature with the furnace after the holding period to obtain a high-temperature resistant, low-thermal-conductivity, low-dielectric alumina aerogel thermal insulation composite material.

[0023] The properties of the prepared high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material are as follows: Density 0.31 g / cm³ 3 Thermal conductivity at room temperature: 0.026 W / (m K), thermal conductivity at 1000℃ is 0.057 W / (m). K), dielectric constant 1.58 (10GHz), dielectric loss tanδ=0.006 (10GHz), compressive strength at 10% deformation 0.9MPa, linear shrinkage rate at 1000℃ for 2h after heat treatment 1.3%.

[0024] Figure 1This is a schematic diagram of the microstructure of a high-temperature resistant, low-thermal-conductivity, and low-dielectric alumina aerogel thermal insulation composite material prepared in Example 1. It can be seen that the material has a continuous porous network inside, with alumina aerogel uniformly coating short-cut alumina fibers and alumina whiskers, and the pores are interconnected. The low-dielectric core-shell structure infrared shading agent is uniformly dispersed. The multi-level interpenetrating skeleton constructed by short-cut alumina fibers and alumina whiskers is tightly bonded to the aerogel interface, effectively suppressing high-temperature structural collapse and reducing thermal conductivity and dielectric loss tanδ.

[0025] Example 2: A method for preparing a high-temperature resistant, low-thermal-conductivity, low-dielectric-resistance alumina aerogel thermal insulation composite material includes the following steps: S1. Preparation of composite sol: The composite sol was prepared by mixing isopropanol, aqueous aluminum sol, aqueous silica sol, aqueous zirconium sol, and nitric acid in a mass ratio of 3:4:4:1.5:1; boron oxide was added as a boron source, and the pH was adjusted to obtain the composite sol. S2. Fiber-reinforced porous skeleton molding: Continuous alumina fiber felt is used as a porous skeleton after being pretreated by degumming at 600℃. S3. Composite sol impregnation and gel aging: ZrO2@SiO2 core-shell structure low dielectric infrared opacifier was prepared by hydrolysis deposition method, with an addition amount of 2wt%; the opacifier was dispersed in the sol, impregnated under normal pressure, and gel aged at 80℃. S4. Drying: Supercritical ethanol drying is used; S5. Segmented high-temperature heat treatment: The temperature is raised and held in three stages at 500℃, 800℃ and 1000℃, and then cooled in the furnace to obtain a high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material.

[0026] The properties of the prepared high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material are as follows: Density 0.32 g / cm³ 3 Thermal conductivity at room temperature: 0.027 W / (m K), thermal conductivity at 1000℃ is 0.058 W / (m²). K), dielectric constant 1.62 (10GHz), dielectric loss tanδ=0.007 (10GHz), compressive strength at 10% deformation 0.8MPa, linear shrinkage rate at 1000℃ for 2h heat treatment 1.5%.

[0027] Example 3: A method for preparing a high-temperature resistant, low-thermal-conductivity, low-dielectric-resistance alumina aerogel thermal insulation composite material includes the following steps: S1. Preparation of composite sol: The sol was prepared by mass ratio of tert-butanol:aqueous aluminum sol:aqueous silica sol:aqueous zirconium sol:acetic acid = 3:5:4:1:1; tert-butanol was added to the aluminum sol to dilute it and form an aluminum-based composite sol; borax was added as a boron source and acetic acid was added dropwise to adjust the pH to obtain the composite sol. S2. Fiber-reinforced porous skeleton molding: Mullite fiber pulping and molding is used, and a porous skeleton is obtained after preheating at 800℃. S3. Composite sol impregnation and gel aging: Al2O3@SiO2 core-shell structure low dielectric infrared opacifier was prepared by hydrolysis deposition method, with an addition amount of 2wt%; the opacifier was dispersed in sol, impregnated under pressure, and gel aged at 80℃. S4. Drying: Drying is carried out under normal pressure; S5. Segmented high-temperature heat treatment: The temperature is raised and held in three stages at 500℃, 800℃ and 1000℃, and then cooled in the furnace to obtain a high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material.

[0028] The properties of the prepared high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material are as follows: Density 0.30 g / cm³ 3 Thermal conductivity at room temperature: 0.028 W / (m²) K), thermal conductivity at 1000℃ is 0.059 W / (m). K), dielectric constant 1.67 (10GHz), dielectric loss tanδ=0.008 (10GHz), compressive strength at 10% deformation 0.7MPa, linear shrinkage rate at 1000℃ for 2h after heat treatment 1.8%.

[0029] Example 4: A method for preparing a high-temperature resistant, low-thermal-conductivity, low-dielectric-resistance alumina aerogel thermal insulation composite material includes the following steps: S1. Preparation of composite sol: Prepare the sol by mass ratio of ethanol: ethylene glycol: aqueous aluminum sol: aqueous silica sol: aqueous zirconium sol: nitric acid = 1:1:4:4:1.8:1; dilute the aluminum sol with ethanol and ethylene glycol, then add silica sol and zirconium sol in sequence and stir evenly to form a ternary in-situ composite sol of aluminum sol-silica sol-zirconium sol. Add borate ester as boron source, and adjust the pH by adding nitric acid dropwise to obtain the composite sol. S2. Fiber-reinforced porous skeleton molding: 3D quartz fiber preforms are used after degumming pretreatment at 600℃. S3. Composite sol impregnation and gel aging: TiO2@BN core-shell structured low dielectric infrared opacifier was prepared by hydrolysis deposition method, with an addition amount of 2wt%; the opacifier was dispersed in the sol, impregnated under vacuum pressure, and gel aged at 80℃. S4. Drying: Freeze-drying is employed; S5. Segmented high-temperature heat treatment: Heating and holding in three stages at 500℃, 800℃, and 1000℃, followed by furnace cooling, yields a high-temperature resistant, low-thermal-conductivity, low-dielectric-content alumina aerogel thermal insulation composite material.

[0030] The properties of the prepared high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material are as follows: Density 0.33 g / cm³ 3 Thermal conductivity at room temperature: 0.026 W / (m K), thermal conductivity at 1000℃ is 0.056 W / (m). K), dielectric constant 1.50 (10GHz), dielectric loss tanδ=0.005 (10GHz), compressive strength at 10% deformation 1.0MPa, linear shrinkage at 1000℃ for 2h after heat treatment 1.2%.

[0031] Example 5: A method for preparing a high-temperature resistant, low-thermal-conductivity, low-dielectric-resistance alumina aerogel thermal insulation composite material includes the following steps: (1) The preparation of the composite sol, the skeleton forming, and the impregnation process are the same as in Example 1; (2) The type and amount of infrared shielding agent for the core-shell structure are the same as in Example 1; (3) Drying: Vacuum drying is used; (4) The segmented high-temperature heat treatment is the same as in Example 1.

[0032] The properties of the prepared high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material are as follows: Density 0.33 g / cm³ 3 Thermal conductivity at room temperature: 0.027 W / (m K), thermal conductivity at 1000℃ is 0.059 W / (m). K), dielectric constant 1.60 (10GHz), dielectric loss tanδ=0.007 (10GHz), compressive strength at 10% deformation 0.7MPa, linear shrinkage rate at 1000℃ for 2h after heat treatment 1.8%.

[0033] Example 6: A method for preparing a high-temperature resistant, low-thermal-conductivity, low-dielectric-resistance alumina aerogel thermal insulation composite material includes the following steps: (1) The preparation of the composite sol, the skeleton forming, and the impregnation process are the same as in Example 1; (2) The type and amount of infrared shielding agent for the core-shell structure are the same as in Example 1; (3) Drying: Microwave drying is used; (4) The segmented high-temperature heat treatment is the same as in Example 1.

[0034] The properties of the prepared high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material are as follows: Density 0.32 g / cm³ 3 Thermal conductivity at room temperature: 0.027 W / (m K), thermal conductivity at 1000℃ is 0.058 W / (m²). K), dielectric constant 1.59 (10GHz), dielectric loss tanδ=0.006 (10GHz), compressive strength at 10% deformation 0.8MPa, linear shrinkage at 1000℃ for 2h after heat treatment 1.6%.

[0035] Example 7: A method for preparing a high-temperature resistant, low-thermal-conductivity, low-dielectric-resistance alumina aerogel thermal insulation composite material includes the following steps: (1) The preparation of the composite sol, the skeleton forming, and the impregnation process are the same as in Example 1; (2) The type and amount of infrared shielding agent for the core-shell structure are the same as in Example 1; (3) Drying: Infrared drying is used; (4) The segmented high-temperature heat treatment is the same as in Example 1.

[0036] The properties of the prepared high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material are as follows: Density 0.34 g / cm³ 3 Thermal conductivity at room temperature: 0.028 W / (m²) K), thermal conductivity at 1000℃ is 0.060 W / (m). K), dielectric constant 1.65 (10GHz), dielectric loss tanδ=0.009 (10GHz), compressive strength at 10% deformation 0.6MPa, linear shrinkage rate at 1000℃ for 2h heat treatment 2.0%.

[0037] Example 8: A method for preparing a high-temperature resistant, low-thermal-conductivity, low-dielectric-resistance alumina aerogel thermal insulation composite material includes the following steps: (1) The preparation of the composite sol is the same as in Example 1; (2) The fiber-reinforced porous skeleton is formed in the same way as in Example 1; (3) Composite sol impregnation and gel aging: The process parameters of the core-shell opaque agent hydrolysis deposition were adjusted to prepare a TiO2@SiO2 low dielectric core-shell infrared opaque agent with a shell thickness of 10 nm and an opaque agent addition amount of 1 wt%; the opaque agent was dispersed in the composite sol; the subsequent vacuum impregnation and gel aging conditions were consistent with those in Example 1; (4) Drying is the same as in Example 1, using supercritical CO2 drying; (5) The segmented high-temperature heat treatment process is the same as in Example 1.

[0038] The properties of the prepared high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material are as follows: Density 0.30 g / cm³ 3 Thermal conductivity at room temperature: 0.027 W / (m K), thermal conductivity at 1000℃ is 0.059 W / (m). K), dielectric constant 1.54 (10GHz), dielectric loss tanδ=0.005 (10GHz), compressive strength at 10% deformation 0.85MPa, linear shrinkage rate at 1000℃ for 2h after heat treatment 1.4%.

[0039] Example 9: A method for preparing a high-temperature resistant, low-thermal-conductivity, low-dielectric-resistance alumina aerogel thermal insulation composite material includes the following steps: (1) The preparation of the composite sol is the same as in Example 1; (2) The fiber-reinforced porous skeleton is formed in the same way as in Example 1; (3) Composite sol impregnation and gel aging: The process parameters of the core-shell opaque agent hydrolysis deposition were adjusted to prepare a TiO2@SiO2 low dielectric core-shell infrared opaque agent with a shell thickness of 50nm and an opaque agent addition amount of 3wt%; the opaque agent was dispersed in the composite sol; the subsequent vacuum impregnation and gel aging conditions were consistent with those in Example 1; (4) Drying is the same as in Example 1, using supercritical CO2 drying; (5) The segmented high-temperature heat treatment process is the same as in Example 1.

[0040] The properties of the prepared high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material are as follows: Density 0.34 g / cm³ 3 Thermal conductivity at room temperature: 0.028 W / (m²) K), thermal conductivity at 1000℃ is 0.060 W / (m). K), dielectric constant 1.66 (10GHz), dielectric loss tanδ=0.009 (10GHz), compressive strength at 10% deformation 0.75MPa, linear shrinkage rate at 1000℃ for 2h after heat treatment 1.7%.

[0041] Comparative Example 1: Compared with Example 1, the difference is that no boron source and borosilicate and boron zirconium synergistic lattice stabilizing system were added, while the rest of the preparation process is the same as in Example 1.

[0042] Properties of the prepared composite material: The linear shrinkage rate after heat treatment at 1000℃ for 2 hours is 5.2%, and the thermal conductivity at 1000℃ is 0.086 W / (m). At high temperatures, the structure exhibits significant sintering and pore collapse, with a dielectric constant of 1.82 (10 GHz) and a dielectric loss of tanδ=0.011 (10 GHz).

[0043] Comparative Example 2: Compared with Example 1, the difference is that ordinary TiO2 powder is used and a low dielectric core-shell structure opaque agent is not used, while the rest of the preparation process is the same as in Example 1.

[0044] Properties of the prepared composite material: With a dielectric constant of 1.95 (10GHz) and a dielectric loss of tanδ=0.014 (10GHz), it cannot meet the requirements for low dielectric wave transmission.

[0045] Comparative Example 3: Compared with Example 1, the difference is that no reinforcing fibers and whisker reinforcing phases were added, while the rest of the preparation process is the same as that of Example 1.

[0046] Properties of the prepared composite material: With 10% deformation, the compressive strength is only 0.25 MPa. The material is brittle and prone to cracking and breakage. The dielectric constant is 1.78 (10 GHz) and the dielectric loss is tanδ=0.010 (10 GHz).

[0047] Results and Discussion: Table 1: Properties of the composite materials prepared in the examples and comparative examples

[0048] The results show that: 1. As can be seen from the examples, the high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material of the present invention can be used stably at 1000℃, taking into account low thermal conductivity, low dielectric, low loss and high strength, good adaptability to drying process, and good application prospects.

[0049] 2. By comparing Example 1 and Comparative Example 1, it can be seen that: without the boron source, there is no boron-silicon-boron-zirconium synergistic lattice stabilization system. The material undergoes significant sintering collapse at high temperature, and the thermal conductivity and shrinkage rate deteriorate significantly. This confirms that the boron-silicon-boron-zirconium synergistic lattice stabilization system is a key technical feature for inhibiting the crystallization sintering of alumina aerogel at 1000℃ and controlling high-temperature shrinkage.

[0050] 3. By comparing Example 1 and Comparative Example 2, it can be seen that: directly using ordinary TiO2 powder to replace the low dielectric core-shell structure infrared shading agent significantly increases the dielectric constant and dielectric loss tanδ, confirming that the core-shell structure shading agent, by relying on the low dielectric shell to isolate the high dielectric core, can take into account both infrared shading and heat insulation and low dielectric wave transmission performance.

[0051] 4. By comparing Example 1 and Comparative Example 3, it can be seen that without the introduction of a multi-level interpenetrating reinforcing skeleton of reinforcing fibers and whiskers, the compressive strength of the material decreases significantly, and it becomes brittle and prone to cracking. This confirms that a multi-level interpenetrating reinforcing skeleton of reinforcing fibers and whiskers is a necessary condition to ensure the mechanical and thermal shock resistance properties of the material.

[0052] The comparative examples of this invention are used to verify the impact of the key technical features within this application on performance; the comprehensive performance combination of low shrinkage, low thermal conductivity and low dielectric constant achieved by this invention at 1000℃ is difficult to achieve simultaneously in existing alumina aerogel materials.

[0053] This invention uses an aluminum-silicon-zirconium ternary in-situ composite sol as a precursor, employs a borosilicate and boron-zirconium dual-lattice stabilization system to suppress high-temperature sintering, and prepares a low-dielectric core-shell structure infrared shading agent via hydrolysis deposition, maintaining low dielectric and low-loss characteristics while ensuring thermal insulation performance. It is combined with a fiber / whisker multi-level interpenetrating reinforcement framework and is compatible with various drying methods. A three-stage heat treatment process yields an aerogel material that can be stably used at 1000℃. The resulting composite material possesses low thermal conductivity, low dielectric, low loss, and high strength, exhibits strong process adaptability, and is cost-controllable, making it suitable for aerospace, high-end electronics, new energy, and industrial high-temperature insulation applications.

[0054] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. Various process solutions that are not substantially different from the concept of the present invention are all within the scope of protection of the present invention.

Claims

1. A method for preparing a high-temperature resistant, low-thermal-conductivity, low-dielectric-resistance alumina aerogel thermal insulation composite material, characterized in that: Includes the following steps: S1. Preparation of composite sol: S1-1. Slowly add the measured alcohol to the aqueous aluminum sol, stir evenly, then add the aqueous silica sol and aqueous zirconium sol, and continue stirring to form an aluminum-silicon-zirconium ternary in-situ composite sol. S1-2. Add a measured amount of boron source to the composite sol and stir until the boron source is completely dissolved. S1-3. Add acid or base catalyst to adjust the pH value. The pH of the acidic system is controlled at 4.0-6.5, and the pH of the alkaline system is controlled at 9.0-11.

0. Continue stirring to obtain a uniform and stable ternary composite alumina sol. S2, Fiber-reinforced porous skeleton molding: S2-1. Add the organic and inorganic adhesives to deionized water in a certain proportion and stir under water bath conditions to form a uniform, stable dispersion with the designed viscosity. S2-2. Add the reinforcing fibers and whiskers slowly in batches to the above dispersion. Stir after each batch is added, and continue stirring until the dispersion is uniform after the addition is complete, so as to obtain a stable slurry without clumping or sedimentation. S2-3. Inject the slurry into the mold, shape it, and dry it to obtain a fiber preform; preheat the fiber preform at 700-900℃, and after cooling, obtain a fiber-reinforced porous skeleton with interconnected pores. Alternatively, reinforced fiber preforms can be used directly as the skeleton, and then used after degumming pretreatment at 550℃~650℃. S3, Composite Sol Impregnation and Gel Aging: First, a low-dielectric core-shell structure infrared shading agent with controllable core-shell thickness is prepared; then, the low-dielectric core-shell structure infrared shading agent is uniformly dispersed in the composite sol prepared in S1, and the fiber-reinforced porous skeleton obtained in S2 is impregnated using a multi-mode impregnation process, and gelation and isothermal aging are completed in sequence to obtain a wet gel composite with uniform structure and no obvious agglomeration. S4. Multi-mode drying: The wet gel composite is placed in a drying device for drying to remove the liquid phase inside the pores of the wet gel composite, so as to obtain an aerogel preform that does not crack and does not collapse. S5. Segmented high-temperature heat treatment: The aerogel preform is placed in a high-temperature furnace and subjected to a three-stage heat treatment with gradient heating in air or an inert atmosphere; the solvent organic matter is removed in sequence, the gel network is stabilized, and the crystal phase is regulated. After cooling, a high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material is obtained.

2. The preparation method of the high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material according to claim 1, characterized in that: The alcohols, aqueous aluminum sol, aqueous silica sol, aqueous zirconium sol, and catalyst mentioned in S1 are disposed in a mass ratio of (2-3):(4-5):(4-5):(1-2):(0.5-1). The boron source is selected from at least one of boric acid, metaboric acid, boron oxide, borates, and borate esters; The alcohols mentioned are one or more of ethanol, methanol, isopropanol, n-propanol, n-butanol, isobutanol, sec-butanol, tert-butanol, ethylene glycol, propylene glycol, and glycerol, and can be mixed in any proportion. The aqueous aluminum sol has a solid content of 30%–50%, the aqueous silica sol has a solid content of 15%–40%, and the aqueous zirconium sol has a solid content of 25%–35%. The average particle size of the aqueous aluminum sol particles is 35nm to 150nm, the average particle size of the aqueous silica sol particles is 25nm to 100nm, and the average particle size of the aqueous zirconium sol particles is 30nm to 120nm. The aqueous aluminum sol, aqueous silica sol, and aqueous zirconium sol maintain the same acidity and alkalinity; an alkaline catalyst is added to the acidic system, and an acid catalyst is added to the alkaline system. The acid catalyst is one of hydrochloric acid, nitric acid, acetic acid, citric acid, oxalic acid, and phosphoric acid. The alkaline catalyst is one of ammonia, urea, organic amine, or alkali metal hydroxide.

3. The preparation method of the high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material according to claim 1, characterized in that: In S1-1, the stirring is carried out at a speed of 200 r / min to 800 r / min for 10 min to 30 min; the continued stirring is carried out at a speed of 200 r / min to 800 r / min for 15 min to 40 min. In S1-2, the stirring speed is 200 r / min to 800 r / min, and the time is 20 min to 50 min; In S1-3, the stirring speed is 200 r / min to 800 r / min, and the time is 30 min to 60 min.

4. The preparation method of a high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material according to claim 1, characterized in that: S2 is achieved by preheating after slurry molding, or by using a reinforced fiber preform as a skeleton, wherein: In S2-1, the stirring is carried out under water bath conditions, with the water bath temperature being 50℃~90℃ and the stirring time being 30min~60min; In S2-2, stir for 10 to 20 minutes after each batch is added, and continue stirring for 40 to 90 minutes until the mixture is evenly dispersed. In S2-3, the molding process is selected from vacuum filtration, molding, injection, extrusion or spraying. The drying process involves drying in an oven at 80℃ to 120℃ for 2 to 8 hours; the preheating process takes 1 to 3 hours.

5. The preparation method of a high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material according to claim 1, characterized in that: The reinforcing fiber preform described in S2 is selected from at least one of alumina fiber preform, silica fiber preform, zirconia fiber preform, and mullite fiber preform. The organic adhesive, inorganic adhesive, and deionized water are mixed in a mass ratio of (2-3):(4-5):(4-5); The organic adhesive is selected from at least one of gelatin, starch, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl alcohol, polyethylene glycol, acrylic resin, phenolic resin, and aqueous emulsion. The inorganic binder is selected from at least one of alumina sol, zirconium oxide sol, silica sol, aluminum dihydrogen phosphate, sodium silicate, boric acid, borate, and low melting point glass powder. The reinforcing fiber is selected from at least one of chopped alumina fiber, silica fiber, zirconium oxide fiber, mullite fiber, quartz fiber, silica-alumina composite fiber, and alumina-zirconium doped fiber; The whiskers are selected from at least one of alumina whiskers, zirconia whiskers, and silicon carbide whiskers.

6. The preparation method of a high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material according to claim 1, characterized in that: The low-dielectric core-shell infrared shading agent described in S3 is selected from at least one of TiO2@SiO2, ZrO2@SiO2, BN@SiO2, Al2O3@SiO2, TiO2@BN, and ZrO2@BN; The shell thickness of the low-dielectric core-shell infrared shading agent is 10nm to 50nm; the addition amount of the low-dielectric core-shell infrared shading agent is 1wt% to 3wt%.

7. The preparation method of a high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material according to claim 1, characterized in that: In S3, the steps for preparing a low-dielectric core-shell infrared shading agent are as follows: the core phase powder is added to an ethanol-water mixed solvent and dispersed evenly, with an ethanol to water volume ratio of 1:2 to 2:

1. The pH is adjusted to 8.5 to 11.0, and a silicate ester or boron source precursor is slowly added dropwise. The mixture is refluxed at 40℃ to 80℃ for 2 to 6 hours. The product is centrifuged, washed, dried at 80℃ to 120℃, and heat-treated at 400℃ to 600℃ for 2 to 4 hours to obtain a low-dielectric core-shell infrared shading agent with a shell thickness of 10 nm to 50 nm. The above-mentioned low-dielectric core-shell structure infrared shading agent was added to the composite sol prepared in S1, and the shading agent was uniformly dispersed by ultrasonic dispersion for 10 min to 30 min and mechanical stirring for 30 min to 60 min. The fiber-reinforced porous skeleton obtained from S2 is placed in an impregnation device and fully impregnated using any one of the following methods: atmospheric pressure impregnation, vacuum impregnation, pressure impregnation, vacuum-pressure composite impregnation, spraying, or curtain coating. The vacuum degree of vacuum impregnation is -0.05MPa to -0.1MPa, the pressure of pressure impregnation is 0.1MPa to 0.5MPa, and the pressure holding impregnation is 30min to 120min. After impregnation, the composite is placed at 60℃~80℃ for gelation and aging for 30min~24h to obtain a uniformly structured wet gel composite.

8. The preparation method of a high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material according to claim 1, characterized in that: The drying process described in S4 is selected from at least one of the following: supercritical drying of ethanol, supercritical drying of CO2, freeze drying, microwave drying, vacuum drying, atmospheric pressure drying, and infrared drying.

9. The preparation method of a high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material according to claim 1, characterized in that: The gradient heating three-stage heat treatment described in S5 has the following specific process: First stage: Heat to 500℃ at a rate of 1℃ / min to 5℃ / min, hold for 1 hour, and remove solvent and organic components; Second stage: Heat up to 800℃ at 2℃ / min~8℃ / min, hold for 1h, and stabilize the amorphous network structure; The third stage involves heating at 3℃ / min to 10℃ / min to 1000℃ and holding for 1h to 2h to regulate the crystal phase structure and enhance the lattice stabilization effect; after holding, the furnace is cooled to room temperature.

10. A high-temperature resistant, low-thermal-conductivity, low-dielectric-conductivity alumina aerogel thermal insulation composite material, characterized in that: The high-temperature resistant, low thermal conductivity, and low dielectric alumina aerogel thermal insulation composite material obtained according to any one of claims 1-9 has the following properties: ① The long-term operating temperature is 1000℃, and the linear shrinkage rate after heat treatment at 1000℃ for 2 hours is ≤1.8%; ② Thermal conductivity at room temperature ≤ 0.028 W / (m K), thermal conductivity at 1000℃ ≤ 0.060 W / (m K); ③ Dielectric constant ε≤1.67, 10GHz; Dielectric loss tanδ≤0.009, 10GHz; ④ Density 0.30 g / cm³ 3 ~0.35g / cm 3 10% deformation compressive strength ≥0.6MPa.

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