Preparation method of silicon-boron composite aerogel with network structure regulated and controlled by carbosilane

Abstract

The invention discloses a preparation method of silicon-boron composite aerogel with a carbosilane-containing regulation network structure, and belongs to the field of high-temperature-resistant thermal protection materials. According to the method, on the basis of a sol-gel process, carbosilane and triethanolamine borate are introduced for modification regulation, and the silicon-boron composite aerogel is prepared through specific aging and drying processes. Through deep crosslinking of a polyfunctional group silane blending system and a boron-nitrogen molecular source, the ultrahigh heat resistance (1100 DEG C +) of the aerogel is ensured, the two core pain points of high brittleness and complex hydrophobic modification process of the traditional aerogel are solved, and a three-dimensional network structure with toughness, in-situ hydrophobicity and thermal stability is constructed. In addition, a macroscopic reinforced framework is constructed by introducing the fiber felt, so that the mechanical toughness and the thermal stability of the material are remarkably improved, and long-acting heat insulation application in an extremely high-temperature environment is realized.

Description

Technical Field

[0001] This invention relates to the field of high-temperature resistant thermal insulation materials, and in particular to a method for preparing a silicon-boron composite aerogel with a network structure regulated by carbon silane. Background Technology

[0002] Aerogel is a three-dimensional nanonetwork structure material formed by the aggregation of nanoscale primary particles. It possesses high porosity, high specific surface area, and extremely low density, earning it the reputation of a "miracle material that changes the world." Due to its unique porous structure, aerogel exhibits excellent thermal insulation properties at room temperature, with a thermal conductivity far lower than that of static air. In aerospace, petrochemical, and building energy conservation fields, aerogel is considered one of the most promising high-efficiency thermal insulation materials. Especially in the fire protection of critical infrastructure such as bridge cables, lightweight and efficient aerogel materials can significantly reduce structural temperature rise, buying valuable time for emergency response.

[0003] Although conventional oxide aerogels (SiO2) possess excellent primary thermal insulation properties, their thermal stability is poor. In extreme fire environments (such as tanker explosions), the highest fire temperature can reach over 1100℃. Under sustained exposure to such high temperatures, the siloxane bonds (Si-O-Si) within conventional aerogels undergo violent condensation, leading to the collapse of the nano-network framework, severe sintering, and volume shrinkage, ultimately resulting in the loss of their thermal insulation function. Another major drawback of conventional aerogels is their low mechanical strength, high brittleness, lack of toughness, and extreme hygroscopicity. After moisture absorption, their pore structure undergoes irreversible collapse due to capillary forces generated by water molecules. Traditional improvement methods typically require secondary hydrophobic modification after drying, which not only significantly extends the production cycle but also makes it difficult for modifiers to penetrate deep into the aerogel.

[0004] Based on the aforementioned problems, there is an urgent need to propose a new method for preparing aerogel materials that can simultaneously achieve high-temperature thermal stability, excellent mechanical properties, and in-situ hydrophobic characteristics. This would provide a new generation of protection for bridge cables that is "high-temperature resistant, high-strength, tough, and corrosion-resistant," and would have significant practical implications for improving the structural thermal protection safety of bridge cables and other structures in extreme environments. Summary of the Invention

[0005] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, this invention proposes a method for preparing silicon-boron composite aerogels and their fiber-reinforced composite materials, which can solve the problems of skeleton collapse, significant bulk mechanical brittleness, and excessively long hydrophobic modification cycle of traditional oxide aerogels at high temperatures. It can meet the application requirements of aerogels and composite materials to achieve long-term and reliable thermal protection in harsh environments with extreme high temperatures and complex conditions.

[0006] The objective of this invention is achieved through the following technical solution: a method for preparing a silicon-boron composite aerogel with a network structure regulated by carbon-containing silanes, comprising the following steps: (a) A mixture of carbon-containing silane, ethanol and deionized water was prepared, and an acidic catalyst was added to adjust the mixture to a weakly acidic state. The mixture was then subjected to hydrolysis under water bath heating and stirring conditions. Subsequently, an organosilicon source was added to continue the hydrolysis reaction to obtain a silicon-carbon sol. (b) Triethanolamine borate, ethanol and deionized water were mixed and hydrolyzed under water bath heating conditions to obtain boron nitrogen sol; (c) The silicon carbide sol obtained in step (a) is mixed with the boron nitrogen sol obtained in step (b). The weak alkalinity of the boron nitrogen sol is used to promote cross-linking to obtain a uniform silicon boron composite sol. Then, it is allowed to stand to gel and obtain a silicon boron composite wet gel. (d) Immerse the silicon-boron composite wet gel in an aging solution for aging treatment; after aging, immerse the silicon-boron composite wet gel in a modification solution for modification treatment. (e) The silicon-boron composite wet gel treated in step (d) is subjected to supercritical drying or vacuum freeze-drying to obtain silicon-boron composite aerogel; The density of the silicon-boron composite aerogel is 0.08~0.49 g / cm³, and the specific surface area is 200~800 m² / g; the volume shrinkage rate of the silicon-boron composite aerogel is less than 3% after being heated at 1300℃ for 30 min.

[0007] Preferably, in step (a), the carbon-containing silane is selected from one or more of methyltrimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, and ethoxytrimethylsilane; and the organosilicon source is selected from one or more of tetraethyl orthosilicate, methyl orthosilicate, and 3-aminopropyltriethoxysilane.

[0008] Preferably, in step (a), the molar ratio of the carbon-containing silane, ethanol, and deionized water is 1~2:5~12:2~11, and the molar ratio of the carbon-containing silane to the organosilicon source is 1~2:1; in step (b), the molar ratio of the triethanolamine borate, ethanol, and deionized water is 1~5:10~30:10~30.

[0009] Preferably, in step (a), the hydrolysis temperature of the silicon carbide sol is 10~50℃ and the total hydrolysis time is 3~6 hours; in step (b), the hydrolysis temperature of the boron nitrogen sol is 40~75℃ and the hydrolysis time is 3~6 hours.

[0010] This invention also provides a method for preparing a silicon-boron composite aerogel fiber reinforced composite material, comprising the following steps: S1. Provide cleaned fiber felt; S2. Immerse the fiber felt in the silicon-boron composite sol prepared by the above method, and after vacuum treatment, let it stand at room temperature to gel, and obtain silicon-boron composite gel fiber felt. S3. The silicon-boron composite gel fiber felt obtained in step S2 is immersed in aging solution and modification solution in sequence to carry out aging treatment and hydrophobic modification treatment respectively. S4. The material treated in step S3, namely the silicon-boron composite aerogel fiber felt, is subjected to supercritical drying or vacuum freeze-drying to obtain the silicon-boron composite aerogel fiber reinforced composite material.

[0011] Preferably, the aging solution is prepared by mixing organosilane and anhydrous ethanol in a volume ratio of 0.5~1.5:6~10; the modification solution contains polymethylsilane and anhydrous ethanol, wherein the volume ratio of polymethylsilane to anhydrous ethanol is 0.5~2:8~12, and wherein the polymethylsilane is selected from one or more of hexamethyldisilazane, hexamethyldisiloxane and trimethylchlorosilane.

[0012] Preferably, the aging conditions are: aging in an aging solution at 50~75℃ for 24~48 hours; the hydrophobic modification conditions are: modification in a modification solution at 50~75℃ for 24~48 hours; the liquid is replaced every 8~12 hours during the aging and modification process; the volumes of the aging solution and the modification solution are 1~5 times the volume of the silicon boron composite wet gel or the silicon boron composite gel fiber felt, respectively.

[0013] Preferably, the supercritical drying uses carbon dioxide as the drying medium and ethanol as the intermediate solvent, with a drying temperature of 40~60℃, a drying pressure of 10~20MPa, and a drying time of 3~12 hours; the vacuum freeze-drying has a pre-cooling temperature of -85~-50℃, a freezing time of 12~24 hours, a vacuum degree of 10~20Pa during the drying stage, and a drying time of 24~48 hours.

[0014] Preferably, in step S1, the method for cleaning the fiber felt is as follows: after soaking in deionized water, ethanol and sodium hydroxide for 5 to 10 hours, the fiber felt is rinsed with deionized water until neutral, and then dried; wherein the fiber felt is selected from mullite fiber felt, high silica fiber felt or aluminum silicate fiber felt.

[0015] Preferably, the silicon-boron composite aerogel fiber reinforced composite material has a thermal conductivity of 0.0264~0.0312 W / (m·K) at room temperature; a compressive strength (50% compression deformation) of 0.5~1.6 MPa; and a volume shrinkage rate of less than 3% after being heated at 1300℃ for 30 minutes.

[0016] Beneficial effects: (1) The silicon-boron composite aerogel material prepared by this method achieves molecular-level doping by introducing triethanolamine borate. The introduction of boron can form high-bond-energy chemical bonds (such as Si-OB, Si-N, etc.) with silicon, oxygen, and nitrogen atoms. These structures with higher thermal stability can play an in-situ reinforcing role, significantly suppressing structural shrinkage and collapse under high temperature, so that the aerogel can still maintain structural integrity at extreme temperatures above 1100℃. The high carbon content can participate in the formation of Si-CO / Si-BCN amorphous system during high-temperature pyrolysis, further synergistically enhancing the overall heat resistance and oxidation resistance of the material with boron.

[0017] (2) The silicon-boron composite aerogel prepared by this method can be microscopically controlled at the molecular scale by adjusting the proportion of organic functional groups (such as methyl groups) in the backbone. Since methyl groups do not participate in the reaction, they will reduce the crosslinking density of the network and increase the compliance of the backbone during the polycondensation process, which can effectively alleviate the capillary forces during the drying process.

[0018] (3) The silicon-boron composite aerogel prepared by this method utilizes the hydrophobic groups naturally present in the carbon source to achieve "in-situ hydrophobicity" directly during the gelation process, eliminating the tedious secondary modification steps and greatly improving production efficiency. Attached Figure Description

[0019] Figure 1 A scanning electron microscope image of the silicon-boron composite aerogel with a network structure regulated by methyltrimethoxysilane provided in Example 1; Figure 2 Scanning electron microscope image of the silicon-boron composite aerogel felt with a network structure regulated by methyltrimethoxysilane provided in Example 2; Figure 3 Scanning electron microscope image of the silicon-boron composite aerogel felt with a network structure regulated by dimethyldimethoxysilane provided in Example 3; Figure 4 Transmission electron microscope image of silicon boron composite aerogel felt with uncontrolled network structure provided for Comparative Example 3; Figure 5 A flowchart illustrating the preparation method of a silicon-boron composite aerogel and its fiber-reinforced composite material provided by the present invention. Detailed Implementation

[0020] The embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments of the present invention not only demonstrate specific technical solutions but also aim to present the creation of a high-end new material for protection against extreme thermal environments such as bridge tanker fires. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0021] Example 1, see Figure 5 A method for preparing a silicon-boron composite aerogel with a network structure regulated by carbon silane includes the following steps: S1: Mix methyltrimethoxysilane, ethanol, and deionized water in a molar ratio of 0.3:7:3, add hydrochloric acid solution to adjust the pH to 2.5, and hydrolyze in a 55°C water bath for 4 hours. Then add tetraethyl orthosilicate in a molar ratio of methyltrimethoxysilane to tetraethyl orthosilicate of 3:7, and hydrolyze in a 55°C water bath for 2 hours with a stirring rate of 300 r / min. Mix triethanolamine borate, ethanol, and deionized water in a molar ratio of 1:3.3:3.3, and hydrolyze in a 55°C water bath for 5 hours with a stirring rate of 300 r / min.

[0022] S2: Mix and stir the two hydrolyzed solutions to obtain a homogeneous silicon-boron composite sol. Allow the sol to stand at a constant temperature of 65℃ to obtain a silicon-boron composite wet gel. Place the silicon-boron composite wet gel in a constant temperature oven at 70℃ for 48 hours. The aging solution is a mixture of tetraethyl orthosilicate and anhydrous ethanol in a volume ratio of 1:4.

[0023] S3: The aged silicon-boron composite wet gel was dried using supercritical CO2 at a temperature of 45℃, a supercritical pressure of 15MPa, and a drying time of 4 hours. A silicon-boron composite aerogel with a methyltrimethoxysilane-regulated network structure was obtained. Its microstructure under a scanning electron microscope is shown in [Figure number missing]. Figure 1 .

[0024] In this embodiment, the density of the methyltrimethoxysilane-regulated network structure of the silicon-boron composite aerogel is 0.0806 g / cm³. 3 Its specific surface area is 538.134 m². 2 / g.

[0025] Example 2: A method for preparing a silicon-boron composite aerogel fiber reinforced composite material includes the following steps: S1: Mix methyltrimethoxysilane, ethanol, and deionized water in a molar ratio of 0.6:7:5, add hydrochloric acid solution to adjust the pH to 2.5, and hydrolyze in a 60°C water bath for 4 hours. Then add tetraethyl orthosilicate in a molar ratio of methyltrimethoxysilane to tetraethyl orthosilicate of 3:5, and hydrolyze in a 55°C water bath for 2 hours with a stirring rate of 350 r / min. Mix triethanolamine borate, ethanol, and deionized water in a molar ratio of 1:10:10, and hydrolyze in a 60°C water bath for 5 hours with a stirring rate of 350 r / min.

[0026] S2: Mix the two hydrolyzed solutions to obtain a boron-silicon composite sol. Immerse the cleaned fiber felt in the boron-silicon composite sol and allow it to stand to gel, thus obtaining a boron-silicon composite gel fiber felt. Place the boron-silicon composite gel fiber felt in a 65°C constant temperature oven for 48 hours. The aging solution is a mixture of tetraethyl orthosilicate and anhydrous ethanol in a volume ratio of 1:5.

[0027] S3: The aged silicon-boron composite aerogel fiber felt was dried using supercritical CO2 at a temperature of 50°C and a supercritical pressure of 10 MPa for 5 hours to obtain a silicon-boron composite aerogel fiber reinforced composite material, namely a silicon-boron composite aerogel felt with a methyltrimethoxysilane-regulated network structure. Its microstructure under a scanning electron microscope is shown in [Figure number missing]. Figure 2 .

[0028] In this embodiment, the density of the methyltrimethoxysilane-regulated network structure of the silicon-boron composite aerogel felt is 0.209 g / cm3, the specific surface area is 422 m2 / g, the thermal conductivity is 0.02984 W / m·K, the compressive strength (50% compression deformation) is 1.610 MPa, and its volume shrinkage rate is approximately 2.85% after being exposed to a flame gun at 1300℃ for 30 minutes.

[0029] Example 3: A method for preparing a silicon-boron composite aerogel fiber reinforced composite material, which differs from Example 2, comprises the following steps: S1: Mix dimethyldimethoxysilane, ethanol, and deionized water in a molar ratio of 0.3:7:7, add hydrochloric acid solution to adjust the pH to 3, and hydrolyze in a 55°C water bath for 5 hours. Then add methyltrimethoxysilane and tetraethyl orthosilicate in a molar ratio of 3:7, and hydrolyze in a 55°C water bath for 2 hours with a stirring rate of 300 r / min. Mix triethanolamine borate, ethanol, and deionized water in a molar ratio of 3:10:10, and hydrolyze in a 55°C water bath for 5 hours with a stirring rate of 300 r / min.

[0030] S2: Mix the two hydrolyzed solutions to obtain a boron-silicon composite sol. Immerse the cleaned fiber felt in the boron-silicon composite sol and allow it to stand to gel, thus obtaining a boron-silicon composite gel fiber felt. Place the boron-silicon composite gel fiber felt in a 70°C constant temperature oven for 48 hours. The aging solution is a mixture of tetraethyl orthosilicate and anhydrous ethanol in a volume ratio of 1:5.

[0031] S3: The aged silicon-boron composite wet aerogel fiber felt was dried using supercritical CO2 fluid at a temperature of 45℃, a supercritical pressure of 15MPa, and a drying time of 8 hours to obtain a silicon-boron composite aerogel fiber reinforced composite material, namely a silicon-boron composite aerogel felt with a dimethyldimethoxysilane-regulated network structure. Its microstructure under a scanning electron microscope is shown in [Figure number missing]. Figure 3 .

[0032] In this embodiment, the density of the silicon-boron composite aerogel felt with a dimethyldimethoxysilane-regulated network structure is 0.226 g / cm³. 3 Specific surface area is 264 m² 2 It has a thermal conductivity of 0.0307 W / m·K and a compressive strength (50% compression deformation) of 0.956 MPa. When exposed to a flame gun at 1300℃ for 30 minutes, its volume shrinkage rate is approximately 2.97%.

[0033] Comparative Example 1: Same as Example 1, except that in step S1, methyltrimethoxysilane, ethanol, and deionized water are mixed in a molar ratio of 0.8:7:3, hydrochloric acid solution is added to make the pH value 2.5, and hydrolysis is carried out in a 55°C water bath for 5 hours. Then, tetraethyl orthosilicate with a molar ratio of methyltrimethoxysilane to tetraethyl orthosilicate of 4:5 is added, and hydrolysis is carried out in a 55°C water bath for 2 hours with a water bath stirring rate of 300 r / min. Triethanolamine borate, ethanol, and deionized water are mixed in a molar ratio of 1:3.3:3.3, and hydrolyzed in a 55°C water bath for 5 hours with a water bath stirring rate of 300 r / min.

[0034] In this comparative example, the molar ratio of carbon-containing silanes was increased. In this embodiment, the density of the silicon-boron composite aerogel with a methyltrimethoxysilane-regulated network structure is 0.127 g / cm³. 3 The specific surface area is 491.235 m². 2 / g.

[0035] Comparative Example 2: Unlike Example 2, Comparative Example 2 is a pure mullite fiber felt that is not combined with aerogel. After being cleaned with a mixture of sodium hydroxide solution, anhydrous ethanol and deionized water, its thermal conductivity is 0.0352 W / m·K and its compressive strength (50% compression deformation) is 0.010 MPa.

[0036] Comparative Example 3: Unlike Example 2, Comparative Example 3 did not add carbon-containing silanes to regulate the network structure. The main implementation steps are as follows: S1: Mix tetraethyl orthosilicate, ethanol, and deionized water in a molar ratio of 1:7:5, add hydrochloric acid solution to adjust the pH to 2.5, and hydrolyze in a 60°C water bath for 4 hours with a stirring rate of 350 r / min; mix triethanolamine borate, ethanol, and deionized water in a molar ratio of 1:10:10, and hydrolyze in a 60°C water bath for 5 hours with a stirring rate of 350 r / min.

[0037] S2: Mix the two hydrolyzed solutions to obtain a silicon-boron composite sol. Immerse the cleaned fiber felt in the silicon-boron composite sol and allow it to stand to gel. Place the gelled silicon-boron composite gel fiber felt in a 65°C constant temperature oven for 48 hours. The aging solution is a mixture of tetraethyl orthosilicate and anhydrous ethanol in a volume ratio of 1:5.

[0038] S3: The aged silicon-boron composite aerogel fiber felt was dried using supercritical CO2 at a temperature of 50℃ and a supercritical pressure of 10MPa for 5 hours. This yielded a silicon-boron composite aerogel felt without a carbosilane-regulated network structure. Its microstructure under a scanning electron microscope is shown in [Figure number missing]. Figure 4 .

[0039] The difference between Comparative Example 3 and Example 2 is that, in the preparation process of Comparative Example 3, the specific surface area of ​​the uncontrolled network structure silicon-boron composite aerogel felt was 803 m². 2 / g, with a thermal conductivity of 0.0306 W / m·K at room temperature, and a compressive strength (50% compression deformation) of 0.406 MPa, which is 74.8% lower than the compressive strength of the aerogel felt with a network structure controlled by carbon silane used in Example 2.

[0040] Furthermore, the material of this invention, in conjunction with the real-time mixed vehicle-fire-wind test platform and implementation method for long-span bridge substructures disclosed in Chinese Invention Patent Application No. 2025111956407, was used to conduct wind-fire-force synergistic fire resistance tests simulating actual bridge conditions. During the experiments, the thermal barrier integrity and ablation resistance evolution behavior of the material of this invention under continuous thermal shock were observed. It was found that the material of this invention possesses excellent thermal insulation and flame-retardant performance under complex multi-physics field coupling, which can meet the protection requirements of key bridge components under extreme fire conditions, and demonstrates high fire resistance applicability in long-span bridge engineering.

[0041] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0042] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0043] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a silicon-boron composite aerogel with a network structure regulated by carbon-silane, characterized in that, Includes the following steps: (a) A mixture of carbon-containing silane, ethanol and deionized water was prepared, and an acidic catalyst was added to adjust the mixture to a weakly acidic state. The mixture was then subjected to hydrolysis under water bath heating and stirring conditions. Subsequently, an organosilicon source was added to continue the hydrolysis reaction to obtain a silicon-carbon sol. (b) Triethanolamine borate, ethanol and deionized water were mixed and hydrolyzed under water bath heating conditions to obtain boron nitrogen sol; (c) The silicon carbide sol obtained in step (a) is mixed with the boron nitrogen sol obtained in step (b). The weak alkalinity of the boron nitrogen sol is used to promote cross-linking to obtain a uniform silicon boron composite sol. Then, it is allowed to stand to gel and obtain a silicon boron composite wet gel. (d) Immerse the silicon-boron composite wet gel in an aging solution for aging treatment; After aging, the silicon-boron composite wet gel is then immersed in a modifying solution for modification treatment. (e) The silicon-boron composite wet gel treated in step (d) is subjected to supercritical drying or vacuum freeze-drying to obtain silicon-boron composite aerogel.

2. The method for preparing silicon-boron composite aerogel with a network structure regulated by carbon-silane according to claim 1, characterized in that, In step (a), the carbon-containing silane is selected from one or more of methyltrimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, and ethoxytrimethylsilane; the organosilicon source is selected from one or more of tetraethyl orthosilicate, methyl orthosilicate, and 3-aminopropyltriethoxysilane. In step (a), the molar ratio of the carbon-containing silane, ethanol and deionized water is 1~2:5~12:2~11, and the molar ratio of the carbon-containing silane to the organosilicon source is 1~2:1; in step (b), the molar ratio of the triethanolamine borate, ethanol and deionized water is 1~5:10~30:10~30.

3. The method for preparing silicon-boron composite aerogel with a network structure regulated by carbon-silane according to claim 1, characterized in that, In step (a), the hydrolysis temperature of the silicon carbide sol is 10~50℃ and the total hydrolysis time is 3~6 hours; in step (b), the hydrolysis temperature of the boron nitrogen sol is 40~75℃ and the hydrolysis time is 3~6 hours.

4. A method for preparing a silicon-boron composite aerogel fiber reinforced composite material, characterized in that, Includes the following steps: S1. Provide cleaned fiber felt; S2. Immerse the fiber felt in the silicon-boron composite sol prepared according to any one of the methods in claims 1-3, and after vacuum treatment, allow it to stand at room temperature to gel, thereby obtaining silicon-boron composite gel fiber felt. S3. The silicon-boron composite gel fiber felt obtained in step S2 is immersed in aging solution and modification solution in sequence for aging treatment and hydrophobic modification treatment, respectively. S4. The silicon-boron composite aerogel fiber felt treated in step S3 is subjected to supercritical drying or vacuum freeze-drying to obtain silicon-boron composite aerogel fiber reinforced composite material.

5. The method for preparing the silicon-boron composite aerogel with a network structure regulated by carbon silane according to claim 1, or the method for preparing the silicon-boron composite aerogel fiber-reinforced composite material according to claim 4, characterized in that, The aging solution is prepared by mixing organosilane and anhydrous ethanol in a volume ratio of 0.5~1.5:6~10; the modification solution contains polymethylsilane and anhydrous ethanol, wherein the volume ratio of polymethylsilane to anhydrous ethanol is 0.5~2:8~12, and wherein the polymethylsilane is selected from one or more of hexamethyldisilazane, hexamethyldisiloxane and trimethylchlorosilane; The aging conditions are: aging in an aging solution at 50~75℃ for 24~48 hours; the hydrophobic modification conditions are: modification in a modification solution at 50~75℃ for 24~48 hours; the liquid is replaced every 8~12 hours during the aging and modification process; the volumes of the aging solution and the modification solution are 1~5 times the volume of the silicon boron composite wet gel or silicon boron composite gel fiber felt, respectively.

6. The method for preparing the silicon-boron composite aerogel with a network structure regulated by carbon silane according to claim 1, or the method for preparing the silicon-boron composite aerogel fiber-reinforced composite material according to claim 4, characterized in that, The supercritical drying uses carbon dioxide as the drying medium and ethanol as the intermediate solvent, with a drying temperature of 40~60℃, a drying pressure of 10~20MPa, and a drying time of 3~12 hours; the vacuum freeze-drying uses a pre-cooling temperature of -85~-50℃, a freezing time of 12~24 hours, a vacuum degree of 10~20Pa during the drying stage, and a drying time of 24~48 hours.

7. The method for preparing the silicon-boron composite aerogel fiber reinforced composite material according to claim 4, characterized in that, In step S1, the fiber felt is cleaned by soaking it in deionized water, ethanol and sodium hydroxide for 5 to 10 hours, rinsing it with deionized water until it is neutral, and then drying it; wherein the fiber felt is selected from mullite fiber felt, high silica fiber felt or aluminum silicate fiber felt.

8. A silicon-boron composite aerogel fiber reinforced composite material prepared by the method for preparing the silicon-boron composite aerogel fiber reinforced composite material according to any one of claims 4-7, characterized in that, The silicon-boron composite aerogel fiber reinforced composite material has a thermal conductivity of 0.0264~0.0312 W / (m·K) at room temperature; a compressive strength of 0.5~1.6 MPa; a specific surface area of ​​200~800 m² / g; and a volume shrinkage rate of less than 3% when subjected to a 1300℃ flame for 30 minutes.

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