Multiphase gradient coating reinforced aerogel composite material and preparation method thereof
Through sandwich gradient coating design and multiphase coating reinforcement method, the problem of performance conflict of aerogel materials in single coating modification was solved, and aerogel composite materials with high strength, low thermal conductivity and high electrical conductivity were achieved, expanding its application range.
Patent Information
- Application Number
- CN202510898571.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-01
- Publication Date
- 2025-09-19
AI Technical Summary
Existing aerogel materials are difficult to simultaneously meet the requirements of high strength and low thermal conductivity after single coating modification, and the traditional multi-coating method leads to a serious decrease in porosity, limiting the expansion of its application areas.
A sandwich gradient coating design is adopted to modify the aerogel substrate layer by layer to form a chemical bonding layer, a functional transition layer and a protective layer. TiO2, carbon precursor and polymer solution are used for multiphase coating reinforcement. Combined with hydrothermal treatment and heat treatment technology, it ensures that each coating is evenly distributed in the aerogel pores.
The synergistic improvement of the high mechanical properties, low thermal conductivity and high electrical conductivity of aerogel materials has been achieved, making it suitable for fields such as spacecraft thermal protection and flexible electronic devices, and enhancing the strength and performance adaptability of composite materials.
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Figure CN120664901A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of silica aerogel preparation, and relates to a multiphase gradient coating reinforced aerogel composite material and a preparation method thereof. Background Art
[0002] Aerogels are materials with excellent properties, including high porosity, low density, low thermal conductivity, good adsorption properties, and high-temperature stability. They are widely used in a variety of high-end applications, including ultralight insulation, electromagnetic shielding, and aerospace, and hold broad application prospects. To meet the demands of diverse applications, aerogel substrates are typically treated with various surface treatments to achieve varying properties, including high-temperature resistance, corrosion resistance, low-temperature resistance, and high strength. However, limited materials and processes typically limit the application of a single coating on an aerogel substrate. The limitations of a single coating and performance conflicts restrict the application of aerogel composites. For example, conventional SiO2 or Al2O3 aerogels modified with a single hydrophobic coating cannot simultaneously meet the requirements for high strength (>2 MPa) and low thermal conductivity (<0.025 W / m·k). Patent application CN110950377A utilizes a multi-coating process using CVD-deposited carbon layers. However, this method results in a porosity reduction of >30%, significantly impacting the thermal conductivity of the aerogel. Therefore, it is necessary to study a processing method that can achieve aerogel multi-coating. Summary of the Invention
[0003] To solve the above problems, the present invention provides a multiphase gradient coating reinforced aerogel composite material and a preparation method thereof. Through the "sandwich gradient coating" design method, the aerogel skeleton is modified layer by layer to achieve a synergistic improvement in mechanical, thermal and electrical properties.
[0004] A multiphase gradient coating reinforced aerogel composite material comprises an aerogel substrate, a chemical bonding layer, a functional transition layer, and a protective layer. The chemical bonding layer, the functional transition layer, and the protective layer form a sandwich gradient coating, which improves the mechanical, thermal, and electrical properties of the aerogel material. The chemical bonding layer is formed by immersing the aerogel substrate in a metal oxide solution and then treating it; the functional transition layer is formed by immersing the aerogel substrate with the chemical bonding layer in a carbon precursor solution and then treating it; and the protective layer is formed by immersing the aerogel substrate with the functional transition layer in a polymer solution and then treating it. The chemical bonding layer, the functional transition layer, and the protective layer are sequentially coated on the aerogel substrate from the inside out.
[0005] To achieve optimal performance improvement, the metal oxide in the metal oxide solution is TiO2. The carbon precursor solution is a glucose aqueous solution containing boric acid or CTAB. The polymer solution is a functionalized DMF solution or DMAC solution.
[0006] The preparation method of the multiphase gradient coating reinforced aerogel composite material specifically comprises the following steps: S1. Prepare the aerogel substrate by uniformly mixing ethyl orthosilicate with water and methanol in a certain proportion. Add hydrochloric acid to adjust the pH value of the solution to 2-4. Wait for it to be fully hydrolyzed to obtain a SiO2 aerogel precursor solution. Then, place the precursor solution at 50-60°C, add ammonia solution to adjust the pH value to 8-10, and use ultrasonic treatment to gel the precursor solution to obtain the aerogel substrate.
[0007] In this step, after adding an ammonia solution to adjust the pH value, the precursor solution is first poured on the quartz fiber felt for infiltration, and then ultrasonically treated to obtain an aerogel substrate. By adding quartz fiber felt inside the aerogel substrate, the strength of the aerogel material is further increased.
[0008] S2. Prepare a metal oxide solution for impregnating the aerogel substrate. Mix anhydrous ethanol and deionized water in a volume ratio of 4:1. Ultrasonic degassing is performed to remove dissolved oxygen to obtain an ethanol-water mixed solvent. Under nitrogen protection, TBT (tetrabutyl titanate) is slowly added to the mixed solvent. Stir at a temperature of ≤25°C and 300-500 rpm. During stirring, dilute nitric acid is added dropwise to adjust the pH of the solvent to 3.5-4.0. Continuous stirring is performed to obtain a clear solution containing TiO2. The clear solution is then stirred continuously. APTES (3-aminopropyl) triethoxysilane) and KH-550 (silane coupling agent) are then added sequentially while stirring. The molar ratio of TBT, APTES, and KH-550 is controlled to be 3:1:0.5. The temperature is continuously increased during stirring until the viscosity of the clear solution increases significantly. The solution is then allowed to stand at room temperature for 12 hours and filtered to obtain a metal oxide solution.
[0009] After the metal oxide solution is prepared, the aerogel substrate is completely immersed in the metal oxide solution under the conditions of 0.1 MPa and 60° C. for 2 to 4 hours, and a chemical bonding layer is coated on the aerogel substrate.
[0010] S3. First, prepare a carbon precursor solution for impregnating the aerogel substrate. Dissolve glucose in deionized water at 60°C and stir until completely transparent to obtain a 1 mol / L glucose aqueous solution. Add boric acid or CTAB (hexadecyltrimethylammonium bromide) to the glucose aqueous solution and completely disperse it under ultrasound. Then, add dilute sulfuric acid to adjust the pH value to 2.5-4.0 to obtain a carbon precursor solution.
[0011] After the carbon precursor solution is prepared, the aerogel substrate treated in step S2 is immersed in the carbon precursor solution, and the hydrothermal reaction is maintained at 180-200° C. for 10-12 hours, and a functional transition layer is coated on the aerogel substrate.
[0012] S4. First, prepare a polymer solution. Two different polymer solutions can be used during the preparation.
[0013] One is a functionalized DMF (N,N-dimethylformamide) solution. First, 15 wt% of PI (polyimide) precursor is added to 80 wt% of DMF, and then 5 wt% of carbon nanotubes pretreated with KH-550 are added. The mixture is magnetically stirred at a speed of 500 rpm for 2 hours, and then ultrasonically dispersed for 30 minutes. The functionalized DMF solution is obtained after filtration through a filter membrane.
[0014] The other method involves a DMAC (N,N-dimethylacetamide) solution. DMAC is soaked through 4Å molecular sieves for 24 hours to obtain a solvent, which is then used for monomer dissolution and polymerization. Under nitrogen, the diamine monomer is slowly added to the solvent. Stirring is carried out at 200 rpm and 50°C for 1–2 hours to accelerate dissolution, until the solvent becomes transparent. The dianhydride monomer is then ground to a particle size of less than 200 mesh. The dianhydride monomer powder is then added to the solvent in 3–5 batches, separated by 15 minutes, at ≤30°C. The solvent is stirred continuously at room temperature for 12–24 hours to maintain a solution viscosity of 4000–8000 cP. The treated solvent is then degassed under low vacuum at -0.1 MPa for 40 minutes. The solvent is then filtered through 10μm, 5μm, and 1μm polytetrafluoroethylene filters, yielding a defoamed DMAC solution.
[0015] The prepared polymer solution is selected, the aerogel substrate treated in step S3 is placed in the polymer solution for complete immersion, and a protective layer is covered on the aerogel substrate.
[0016] In step S4, vacuum treatment can be performed when the aerogel substrate is impregnated, and the penetration of the coating into the pores of the aerogel substrate is increased by vacuum assistance. Specifically, after the aerogel substrate is placed in the polymer solution, it is first slowly vacuumed to reduce the air pressure to -0.08MPa and maintain it for 10 minutes, and then gradually reduced to -0.1MPa for 40 minutes, and then the "vacuum-release" process is repeated 3 times to ensure that the polymer solution fully fills the pores of the aerogel substrate. After the impregnation is completed, the aerogel substrate is taken out, the residual polymer solution on the surface is removed, and it is placed at room temperature for ventilation and drying to remove free DMF, and then vacuum treated for 10 hours at -0.1MPa and 50°C. After treatment, it is stepped to 150°C at a heating rate of 2°C / min and cured for 2 hours to complete the protective layer coating of the aerogel substrate.
[0017] S5. Heat-treating the aerogel substrate treated in step S4 to achieve layer-by-layer functionalization by performing staged heat treatment to obtain a multiphase gradient coating reinforced aerogel. The specific steps are: first, the aerogel substrate is heated at a rate of 3°C / min in air or a mixed atmosphere of 5% O2 and N2, and the temperature is raised to 400°C and kept warm for 2 hours; then, at a rate of 5°C / min, in Ar or N2 gas with an oxygen content of less than 10 ppm, the flow rate is maintained at 60 mL / min, and the temperature is raised to 800°C and kept warm for 2 hours; finally, at a rate of 2°C / min, the temperature is raised to 350°C under the protection of N2 and kept warm for 4 hours.
[0018] The multiphase gradient coating reinforced aerogel composite material provided by the present invention has high mechanical properties, low thermal conductivity and high electrical conductivity, and can be applied to the fields of spacecraft thermal protection, flexible electronic devices, etc. The preparation method provided by the present invention solves the multi-scale synergy problem of aerogel material coating, can be adapted to fiber-reinforced substrates to improve the strength of composite materials, and can achieve precise control of carbon resistance layer ratio through hydrothermal temperature, and ensure uniform distribution of each coating within the pores of the aerogel through gradient impregnation technology. The addition of boric acid during the hydrothermal carbonization process realizes in-situ carbonization control and promotes the orderly growth of sp2 carbon. The chemical coupling of -NH2 and carbon layer is achieved by adding APTES to the inner layer TiO2 sol. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The present invention will be further described in detail below with reference to the accompanying drawings.
[0020] Figure 1 This is a process step diagram of Example 1; Figure 2 This is a process step diagram of Example 2. DETAILED DESCRIPTION
[0021] To further illustrate the concept of the present invention, the present invention will be further described in detail below through specific examples. The following examples are merely exemplary illustrations and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the contents of the present invention are included in the scope of protection intended by the present invention. Example 1
[0022] S1: Preparation of aerogel substrate: Tetraethyl orthosilicate, water, and methanol were mixed in a molar ratio of 1:4:6, the pH value was adjusted to 2 with 0.01M hydrochloric acid, and the mixture was kept at 50°C for 4 hours for full hydrolysis to obtain a SiO2 aerogel precursor solution. The SiO2 aerogel precursor solution was then placed at 60°C, the pH value was adjusted to 10 by adding 0.5M ammonia solution, and gelation was performed by ultrasonic treatment to obtain a SiO2 aerogel substrate.
[0023] S2: Prepare a metal oxide sol for impregnating the SiO2 aerogel substrate to form an inner chemical bonding layer. The first step in preparing the metal oxide solution is to mix anhydrous ethanol and deionized water in a volume ratio of 4:1, and use ultrasonic degassing for 10 minutes to remove dissolved oxygen. The second step is to slowly add TBT to the ethanol-water mixed solvent under nitrogen protection, and stir at a temperature of ≤25°C and 300rpm. During the stirring process, 0.1M dilute nitric acid is added dropwise, and the pH value is adjusted to 3.5-4.0. Stirring is continued for 1 hour until the solution is clear to form a TiO2 sol precursor. The third step is to add APTES and KH-550 dropwise to the TiO2 sol precursor in a stirring state. The molar ratio of TBT, APTES and KH-550 is controlled to be 3:1:0.5. In the fourth step, the TiO2 sol precursor was heated to 50°C and stirred continuously for 4 hours until the viscosity increased significantly. In the fifth step, the TiO2 sol precursor was aged at room temperature for 12 hours and filtered through a 0.22μm polytetrafluoroethylene filter to obtain a uniform and transparent metal oxide sol. After the metal oxide sol was prepared, the SiO2 aerogel substrate was immersed in the mixed solution under vacuum conditions of 0.1MPa and 60°C for 2 hours to form a chemical bonding layer on the surface of the SiO2 aerogel substrate.
[0024] S3: Prepare a carbon precursor solution for the SiO2 impregnation aerogel substrate to form a functional transition layer in the middle layer. The first step in preparing the carbon precursor solution is to dissolve 20wt% glucose in 60wt% deionized water at 60°C, and stir it magnetically until it is completely transparent to obtain a 1mol / L glucose aqueous solution. The second step is to add 2wt% boric acid to the glucose aqueous solution, perform ultrasonic dispersion at 40KHz for 30 minutes, and add dilute sulfuric acid to adjust the pH to 2.5 to obtain a glucose aqueous solution containing boric acid as a carbon precursor solution.
[0025] The glucose aqueous solution containing boric acid was then transferred into a high-pressure reactor, and the SiO2 aerogel substrate impregnated with the metal oxide sol was immersed therein. The hydrothermal reaction was carried out at 180°C for 12 hours to form a functional transition layer on the surface of the SiO2 aerogel substrate.
[0026] S4: Prepare a polymer solution for impregnating the SiO2 aerogel substrate to form an outer protective layer. The polymer solution is prepared by adding 15 wt% of PI precursor to 80 wt% of DMF, followed by 5 wt% of carbon nanotubes pretreated with KH-550. The mixture is magnetically stirred at 500 rpm for 2 hours, then ultrasonically dispersed for 30 minutes, and filtered through a 0.45 μm filter membrane to obtain a functionalized DMF solution as the polymer solution.
[0027] After the polymer solution is prepared, the SiO2 aerogel substrate, which has been impregnated with the carbon precursor solution, is placed in a DMF-resistant mesh container. DMF solution is added to the container until the SiO2 aerogel substrate is completely immersed in the DMF solution. Vacuuming is then performed, initially slowly pumping the pressure down to -0.08 MPa for 10 minutes to expel the gas from the macropores of the SiO2 aerogel substrate. Deep penetration is then performed, gradually decreasing the pressure to -0.1 MPa and maintaining it for 40 minutes. The "vacuum-release" process is repeated three times to ensure that the solution fully fills the pores of the SiO2 aerogel substrate. The impregnated SiO2 aerogel substrate was then placed at an angle for 30 minutes to allow the residual solution on the surface to drip clean. The SiO2 aerogel substrate was then placed in a fume hood at 25°C for 2 hours to remove free DMF. It was then vacuum treated at -0.1MPa and 50°C for 10 hours, and then the temperature was increased stepwise to 150°C at a heating rate of 2°C / min for curing for 2 hours to obtain a layer-by-layer modified aerogel material, completing the coating of the chemical bonding layer, functional transition layer and protective layer.
[0028] S5: The coating is enhanced by heat treatment. The first step is to crystallize the metal oxide layer by heating it to 400°C in air at a heating rate of 3°C / min and keeping it warm for 2 hours. The second step is to carbonize the carbon precursor by heating it to 800°C at a heating rate of 5°C / min in high-purity Ar with an oxygen content of less than 10ppm and a flow rate of 60mL / min and keeping it warm for 2 hours. The third step is to cure the polymer layer by heating it to 350°C at a heating rate of 2°C / min in N2 atmosphere and keeping it warm for 4 hours. Through multiple heat treatment steps, an aerogel material reinforced with a multiphase gradient coating is obtained. Example 2
[0029] S1: Preparation of aerogel substrate: The first step is to mix ethyl orthosilicate, water and methanol in a molar ratio of 1:4:6, adjust the pH to 4 with 0.01M hydrochloric acid, and then keep it at 55°C for 4 hours to fully hydrolyze to obtain a SiO2 aerogel precursor solution. The SiO2 aerogel precursor solution is then placed at 55°C and a 0.5M ammonia solution is added to adjust the pH to 10. A piece of quartz fiber felt with a specification of 300*300*10mm is then placed in the mold, and the treated SiO2 aerogel precursor solution is quickly poured on the quartz fiber felt to ensure that the quartz fiber felt is completely soaked in the aerogel precursor solution, and then subjected to ultrasonic treatment at 55-60°C to gel, thereby obtaining a quartz fiber aerogel substrate.
[0030] S2: Prepare a metal oxide solution. The first step is to mix anhydrous ethanol and deionized water in a volume ratio of 4:1, and ultrasonically degas for 10 minutes to remove dissolved oxygen to obtain an ethanol-water mixed solvent. The second step is to slowly add TBT to the ethanol-water mixed solvent under nitrogen protection, and stir at a temperature of ≤25°C and 500rpm. While stirring, add 0.1M dilute nitric acid dropwise, adjust the pH to 3.5, and continue stirring for 1 hour until the solution becomes clear to obtain a TiO2 sol precursor solution. The third step is to continue to add APTES and KH-550 dropwise to the TiO2 sol precursor solution under stirring, wherein the molar ratio of TBT, APTES and KH-550 is 3:1:0.5. The fourth step is to heat the TiO2 sol precursor solution to 50°C and continue stirring for 4 hours until the viscosity of the solution increases significantly. In the fifth step, the TiO2 sol precursor solution was aged at room temperature for 12 hours and filtered using a 0.22 μm polytetrafluoroethylene filter membrane to obtain a uniform and transparent metal oxide solution.
[0031] The quartz fiber aerogel substrate was vacuum immersed in the metal oxide solution at 0.1 MPa and 60°C for 4 h.
[0032] S3: Prepare a carbon precursor solution by first dissolving 40 wt% glucose in 80 wt% deionized water at 60°C and magnetically stirring until the solution is completely transparent to obtain a glucose aqueous solution. Then, add 0.3 wt% CTAB to the glucose aqueous solution and ultrasonically disperse it at 40 kHz for 30 minutes. Finally, add dilute sulfuric acid to adjust the pH to 4.0 to obtain a glucose aqueous solution containing CTAB.
[0033] The glucose aqueous solution containing CTAB was then transferred into a high-pressure reactor, and the quartz fiber aerogel substrate impregnated with the metal oxide sol was placed in it and immersed in the glucose aqueous solution containing CTAB, and hydrothermally reacted at 200°C for 10 hours.
[0034] S4: Prepare the polymer solution. First, soak DMAC through 4Å molecular sieves for 24 hours to obtain a solvent. Under nitrogen protection, slowly add 4,4'-ODA to the solvent and stir at 200 rpm and 50°C for 2 hours to accelerate dissolution until the solution is transparent. Grind PMDA to a size of less than 200 mesh and add it to the solution in five batches, each with a 15-minute interval, at ≤30°C. Stir continuously at room temperature for 24 hours to control the solution viscosity to 4000-8000 cP to obtain a polymer solution. Degas the polymer solution at -0.1 MPa for 40 minutes and then filter it multiple times through 10μm, 5μm, and 1μm polytetrafluoroethylene filters to remove unreacted monomers or gel particles, obtaining a defoamed polymer solution.
[0035] Then, the quartz fiber aerogel substrate was immersed in the polymer solution at 50 °C for 12 h.
[0036] S5: Heat treatment: The first step is to heat the temperature to 500°C at a rate of 3°C / min in a mixed atmosphere of 5% O2 and N2 and keep it warm for 3 hours. The second step is to heat the temperature to 1000°C at a rate of 5°C / min in a high-purity N2 with an oxygen content of less than 10ppm and a flow rate of 70mL / min and keep it warm for 2 hours. The third step is to heat the temperature stepwise at a rate of 2°C / min in a N2 protective atmosphere, raising the temperature to 150°C and holding it for 1 hour, to 250°C and holding it for 1 hour, and to 350°C and holding it for 2 hours to obtain a multiphase gradient coating reinforced quartz fiber aerogel material.
[0037] Comparative Example 1: TEOS, water, and methanol were mixed in a molar ratio of 1:4:6, the pH adjusted to 4 with 0.01M hydrochloric acid, and then fully hydrolyzed at 50-60°C for 2 hours to produce a SiO2 aerogel precursor solution. The SiO2 aerogel precursor solution was placed at 60°C, the pH adjusted to 10 with 0.5M ammonia solution, and then gelled through ultrasonic treatment to produce a SiO2 aerogel wet gel material. The obtained SiO2 aerogel wet gel material was supercritically dried at 55°C and 14MPa for 6 hours to obtain a SiO2 aerogel material.
[0038] Comparative Example 2: S1: Mix ethyl orthosilicate, water, and methanol in a molar ratio of 1:4:6, adjust the pH to 2 with 0.01M hydrochloric acid, and then maintain at 60°C for 4 hours to allow for complete hydrolysis to produce a SiO2 aerogel precursor solution. The SiO2 aerogel precursor solution is placed at 50°C, and 0.5M ammonia solution is added to adjust the pH to 8. The solution is then ultrasonically treated to gel, yielding a SiO2 aerogel substrate.
[0039] S2: Glucose was dissolved in deionized water at 60°C and magnetically stirred until completely transparent to prepare a 1 mol / L glucose aqueous solution. 0.4 wt% CTAB was added to the glucose aqueous solution and ultrasonically dispersed at 40 kHz for 30 minutes. The pH was adjusted to 2.5 with dilute sulfuric acid to prepare a glucose aqueous solution containing CTAB. The glucose aqueous solution containing CTAB was transferred to an autoclave and the aerogel substrate was immersed in the glucose aqueous solution containing CTAB. The aerogel substrate was hydrothermally reacted at 200°C for 10 hours to obtain a single-layer carbonized aerogel precursor.
[0040] S3: Heat treatment: Place the aerogel material precursor that has undergone single-layer carbonization treatment in a heat treatment furnace, and heat it to 800°C at a heating rate of 5°C / min in high-purity Ar with an oxygen content of less than 10 ppm and a flow rate of 60 mL / min, and keep it warm for 2 hours to obtain an aerogel material that has undergone single-layer carbonization treatment.
[0041] The prepared aerogel material was subjected to experimental tests, and properties such as compressive strength, thermal conductivity, surface resistance and porosity were compared. The results are shown in the following table:
[0042] It can be seen from the test results that the aerogel material prepared by the method provided by the present invention has a greatly improved compressive strength, and has little effect on thermal conductivity while maintaining a high porosity. In particular, Example 2 also has a high surface resistance. Although Comparative Example 1 has high porosity, high surface resistance, and low thermal conductivity, its compressive strength is weak and is not suitable for scenarios with high structural strength requirements. The comprehensive performance of the aerogel material provided by the present invention can meet the requirements of most usage scenarios.
[0043] There are many methods and approaches to implement the technical solutions of the present invention, and the above are only preferred embodiments provided by way of example. Those skilled in the art may conceive of many changes, modifications and substitutions without departing from the present invention. It should be understood that various alternatives to the embodiments of the present invention described herein may be adopted in the practice of the present invention. The attached claims are intended to limit the scope of the present invention and therefore cover methods within the scope of these claims and their equivalents. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.
Claims
1. A multiphase gradient coating reinforced aerogel composite material, comprising an aerogel substrate, a chemical bonding layer, a functional transition layer and a protective layer, characterized in that: The chemical bonding layer is formed by immersing the aerogel substrate in a metal oxide solution; The functional transition layer is formed by immersing the aerogel substrate having the chemical bonding layer in a carbon precursor solution; The protective layer is formed by immersing the aerogel substrate with the functional transition layer in a polymer solution.
2. The multiphase gradient coating reinforced aerogel composite material according to claim 1, characterized in that: The metal oxide in the metal oxide solution is TiO2.
3. The multiphase gradient coating reinforced aerogel composite material according to claim 1, characterized in that: The carbon precursor solution is a glucose aqueous solution containing boric acid or CTAB.
4. The multiphase gradient coating reinforced aerogel composite material according to claim 1, characterized in that: The polymer solution is a functionalized DMF solution or a DMAC solution.
5. A method for preparing a multiphase gradient coating reinforced aerogel composite material, characterized in that: The following steps are involved: S1. Preparing an aerogel substrate: After mixing ethyl orthosilicate with water and methanol in proportion, adding hydrochloric acid to adjust the pH value of the solution to 2-4, hydrolyzing to obtain a precursor solution, adding an ammonia solution at 50-60° C. to adjust the pH value of the precursor solution to 8-10, and then ultrasonically treating to obtain an aerogel substrate; S2. Anhydrous ethanol and deionized water are mixed in a volume ratio of 4:1, and the dissolved oxygen is removed by ultrasound to obtain a mixed solvent. TBT is added to the mixed solvent under nitrogen protection and stirred at a temperature of ≤25°C and 300-500 rpm. During the stirring process, dilute nitric acid is added to adjust the pH value to 3.5-4.0 to obtain a clear solution containing TiO2. APTES and KH-550 are added in sequence while stirring the clear solution. The temperature is continuously raised and stirred until the viscosity of the clear solution increases. The molar ratio of TBT, APTES and KH-550 is 3:1:0.
5. The mixture is then allowed to stand and age at room temperature for 12 hours. After filtration, a metal oxide solution is obtained. The aerogel substrate is immersed in the metal oxide solution at 0.1 MPa and 60°C for 2-4 hours. S3, dissolving glucose in 60°C deionized water and stirring until transparent to obtain a 1 mol / L glucose aqueous solution, then adding boric acid or CTAB to disperse under ultrasound, adjusting the pH value to 2.5-4.0 with dilute sulfuric acid to obtain a carbon precursor solution, and immersing the aerogel substrate treated in step S2 in the carbon precursor solution for hydrothermal reaction at 180-200°C for 10-12 hours; S4, preparing a polymer solution, and immersing the aerogel substrate treated in step S3 into the polymer solution; S5. Heat-treating the aerogel substrate treated in step S4 to obtain a multiphase gradient coating reinforced aerogel.
6. The method for preparing a multiphase gradient coating reinforced aerogel composite material according to claim 5, characterized in that: In the step S1, after the pH value of the precursor solution is adjusted by adding ammonia water, the precursor solution is poured on the quartz fiber felt to soak it, and then ultrasonically treated to obtain the aerogel substrate.
7. The method for preparing a multiphase gradient coating reinforced aerogel composite material according to claim 5, characterized in that: The polymer solution used in step S4 is a functionalized DMF solution. 15 wt% of PI precursor is added to 80 wt% of DMF, and then 5 wt% of carbon nanotubes pretreated with KH-550 are added. The mixture is stirred at 500 rpm for 2 h, then ultrasonically dispersed for 30 min, and filtered to obtain a functionalized DMF solution.
8. The method for preparing a multiphase gradient coating reinforced aerogel composite material according to claim 5, characterized in that: The polymer solution used in step S4 is a DMAC solution. DMAC is soaked in a 4Å molecular sieve for 24 hours to obtain a solvent. The diamine monomer is slowly added to the solvent under nitrogen protection and stirred at 200 rpm and 50°C for 1-2 hours until the solvent is transparent. The dianhydride monomer is ground to less than 200 mesh and the solvent is added in 3-5 batches at intervals of 15 minutes at ≤30°C. The solvent is continuously stirred at room temperature for 12-24 hours to adjust the solution viscosity to 4000-8000 cP. The solvent is then degassed at -0.1 MPa for 40 minutes and then filtered using 10 μm, 5 μm, and 1 μm polytetrafluoroethylene filter membranes in sequence to obtain a defoamed DMAC solution.
9. The method for preparing a multiphase gradient coating reinforced aerogel composite material according to claim 5, characterized in that: In step S4, the aerogel substrate is immersed in the polymer solution and subjected to vacuum treatment, first slowly pumping to -0.08 MPa, maintaining for 10 minutes, gradually reducing to -0.1 MPa, maintaining for 40 minutes, and repeating the "vacuum-release" cycle three times; the immersed aerogel substrate is removed to remove the surface solution, and the substrate is dried under ventilation at room temperature to remove free DMF, and then vacuum treated at -0.1 MPa and 50°C for 10 hours, and then heated to 150°C at a heating rate of 2°C / min for curing for 2 hours.
10. The method for preparing a multiphase gradient coating reinforced aerogel composite material according to claim 5, characterized in that: The heat treatment in step S5 is to heat the aerogel substrate to 400°C at a heating rate of 3°C / min under the control of air or a mixed atmosphere of 5% O2 and N2 and keep it warm for 2 hours; then heat it to 800°C at a heating rate of 5°C / min at a flow rate of 60 mL / min in Ar or N2 with an oxygen content of less than 10 ppm and keep it warm for 2 hours; then heat it to 350°C at a heating rate of 2°C / min under the protection of N2 and keep it warm for 4 hours.