Carbon fiber reinforced silica aerogel composite material and preparation method thereof

Abstract

This invention belongs to the field of thermal insulation composite materials technology, and discloses a carbon fiber reinforced silica aerogel composite material and its preparation method. The preparation method combines carbon fiber as a reinforcement with silica aerogel. Carbon fiber is a high-light-shielding material that can effectively reduce heat radiation, while silica aerogel is currently the most widely studied type of aerogel, exhibiting low solid-phase and gas-phase thermal conductivity. Combining the thermal insulation advantages of fibers and aerogels results in a composite material with even lower thermal conductivity. The obtained carbon fiber reinforced silica aerogel composite material has a lower density compared to ceramic matrix fibers; the density of the carbon fiber reinforced silica aerogel composite material can be controlled at 0.11 g / cm³. 3 ~0.22g / cm 3 It has a low thermal conductivity at high temperatures, with a thermal conductivity of 0.025 W / (m·K) to 0.035 W / (m·K) at 600℃.

Description

Technical Field

[0001] This invention belongs to the field of thermal insulation composite materials technology, specifically relating to a carbon fiber reinforced silica aerogel composite material and its preparation method. Background Technology

[0002] Aircraft typically face environmental challenges such as high temperatures and vibrations during operation. Aerogel composite materials, with their three-dimensional network skeleton and nanoscale porous structure, are widely used in the thermal insulation layers of aircraft.

[0003] Silica aerogel is currently the most widely used type of aerogel. However, due to its relatively high brittleness, the skeleton of silica aerogel is prone to fracture under external forces. The most common method is to composite silica aerogel with fibers. Fiber-reinforced silica aerogel composites typically use ceramic fibers with a coefficient of thermal expansion close to that of silica aerogel, such as quartz fibers and alumina fibers.

[0004] Carbon fiber materials possess advantages such as lightweight, high strength, high modulus, low density, and high temperature resistance. In the field of thermal insulation, carbon materials are inherently highly light-shielding. However, due to the significant difference in thermal expansion coefficients between carbon fiber and ceramic-based aerogel substrates such as silica and alumina, composite materials prepared by combining ceramic-based aerogels (e.g., silica and alumina aerogels) with carbon fiber exhibit shrinkage / expansion mismatch under high-temperature conditions, leading to problems such as material cracking. Therefore, in practical applications, carbon fiber composites are rarely combined with ceramic-based aerogels. Summary of the Invention

[0005] To address the issues of mismatched expansion coefficients between silica aerogel and carbon fiber in existing technologies, and the high radiative thermal conductivity of ceramic fiber-reinforced silica aerogel composites under high-temperature conditions, this invention provides a carbon fiber reinforced silica aerogel composite material and its preparation method. The carbon fiber reinforced silica aerogel composite material prepared by this method does not crack with temperature changes. At the same time, the material exhibits low thermal conductivity and low density under high-temperature conditions.

[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0007] A method for preparing a carbon fiber reinforced silica aerogel composite material includes the following steps:

[0008] (1) Polymethylsilane is impregnated into polyacrylonitrile-based pre-oxidized fiber preforms by vacuum impregnation to obtain fiber preforms impregnated with polymethylsilane;

[0009] (2) The fiber preform impregnated with polymethylsilane is cured and then pyrolyzed under vacuum to obtain a SiC-carbon fiber preform with a SiC film on its surface.

[0010] (3) Mix tetraethyl orthosilicate, anhydrous ethanol and water to obtain a silicon-based solution, add an inorganic acid catalyst solution to adjust the pH to acidic, and then let it stand to obtain a silica sol;

[0011] (4) Add an alkaline catalyst solution to the silica sol to perform gel condensation, stir evenly, and obtain silica sol;

[0012] (5) The SiC-carbon fiber preform is laid in the mold, and the silica sol is impregnated and filled into the SiC-carbon fiber preform in the mold under negative pressure to obtain silica sol-carbon fiber wet gel composite material.

[0013] (6) The silica sol-carbon fiber wet gel composite material is subjected to gelation, aging, and supercritical drying to obtain the carbon fiber reinforced silica aerogel composite material.

[0014] This invention involves impregnating polymethylsilane onto polyacrylonitrile-based pre-oxidized fibers, followed by high-temperature curing and pyrolysis to form a SiC film on the surface of the polyacrylonitrile fibers. Furthermore, the polyacrylonitrile fibers carbonize after pyrolysis, and the preform shrinks after carbonization, with a shrinkage rate of approximately 10%. The carbonized fiber preform maintains good structural stability under high-temperature conditions, and the coefficient of thermal expansion of the SiC layer formed on the surface is 4–4.7 × 10⁻⁶ from room temperature to 1000℃. -6 / K) and the coefficient of thermal expansion of silica aerogel (0.5~5×10) -6 The coefficient of thermal expansion (C / K) is close to that of silica aerogel and carbon fiber, which solves the problem of mismatch in the coefficient of thermal expansion between the two materials in the prior art.

[0015] Further, in step (1), the polyacrylonitrile-based pre-oxidized fiber preform is prepared by the following method: polyacrylonitrile-based pre-oxidized fiber is needle-punched, and the needle-punching density is controlled at 200 needles / cm. 2 ~400 thorns / cm 2 The density of the polyacrylonitrile-based pre-oxidized fiber preform is controlled to be 0.06 g / cm³. 3 ~0.08g / cm 3 The vacuum degree of the vacuum impregnation is -0.09MPa to -0.1MPa, and the pressure is maintained for more than 2 hours.

[0016] Furthermore, in step (2), the curing temperature is 200℃~300℃ and the curing time is 1h~2h.

[0017] Furthermore, in step (2), the pyrolysis procedure is as follows: first, the temperature is raised from room temperature to 350°C for 60 min; then, the temperature is raised from 350°C to 1000°C for 650 min; finally, the temperature is maintained at 1000°C for 2 h.

[0018] Furthermore, in step (3), the molar ratio of tetraethyl orthosilicate, anhydrous ethanol and water is 1:(10-50):(1-3), and the mixing is carried out by stirring at room temperature for 10-30 minutes; the inorganic acid catalyst solution is a nitric acid solution with a concentration of 0.1 mol / L to 2 mol / L; the pH of the silicon-based solution is adjusted to 1-3; and the standing time is 0.5-8 hours.

[0019] Step (3) The solid content in silica aerogel is controlled by adjusting the ratio of tetraethyl orthosilicate, anhydrous ethanol and water to prepare silica aerogel substrate with low solid content and low density. Increasing the proportion of anhydrous ethanol reduces the density of the aerogel, while too high a proportion of anhydrous ethanol results in poor structural stability of the gel.

[0020] Furthermore, in step (4), the alkaline catalyst solution is ammonia or sodium hydroxide solution with a concentration of 0.1 mol / L to 2 mol / L.

[0021] Furthermore, in step (5), the density of the SiC-carbon fiber preform is controlled at 0.08 g / cm³ using a molding die. 3 ~0.16g / cm 3 .

[0022] Furthermore, in step (5), the negative pressure condition is -0.08MPa to -0.1MPa, and the negative pressure condition is maintained for ≥0.5h.

[0023] Furthermore, in step (6), the gel aging temperature is 5℃~40℃ and the time is 48h~96h; the supercritical drying temperature is 260℃~320℃, the drying pressure is 8 MPa~12MPa, and the time is 4h~12h.

[0024] Based on a general inventive concept, the present invention also provides a carbon fiber reinforced silica aerogel composite material obtained by the aforementioned preparation method, having a density of 0.11 g / cm³. 3 ~0.22g / cm 3 The thermal conductivity at 600℃ is 0.025W / (m·K)~0.035W / (m·K).

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. The preparation method of the present invention uses carbon fiber as a reinforcement and combines it with silica aerogel. Carbon fiber is a high light-shielding material that can effectively reduce heat radiation, while silica aerogel is the most widely studied type of aerogel. Silica aerogel has low solid-phase thermal conductivity and low gas-phase thermal conductivity. By combining the thermal insulation advantages of fiber and aerogel, the prepared aerogel composite material has even lower thermal conductivity.

[0027] 2. The preparation method of the present invention involves pyrolyzing polyacrylonitrile-based pre-oxidized fiber and polymethylsilane to form a SiC layer on the surface of the fiber preform. On the one hand, pyrolyzing the pre-oxidized fiber can ensure that the fiber preform does not shrink significantly under high temperature conditions. On the other hand, after the materials are combined, the SiC layer on the carbon fiber surface is in contact with the silica aerogel. The difference in their coefficients of thermal expansion is small, and the shrinkage and expansion matching during the alternating hot and cold process is good, so that cracks will not be generated inside the aerogel composite material during use.

[0028] 3. The density of the ceramic used in this invention is usually more than one times that of the polyacrylonitrile polymer. The weight loss rate of the polyacrylonitrile pre-oxidized fiber after pyrolysis is about 50%, and the volume retention rate is about 70%. The fiber after pyrolysis has a lower density than the ceramic fiber. On the other hand, the silica aerogel with a low density is prepared by the ratio of tetraethyl orthosilicate, anhydrous ethanol and deionized water, and the carbon fiber reinforced silica aerogel composite material has a low density.

[0029] 4. The carbon fiber reinforced silica aerogel composite material prepared by this invention has a lower density than that of ceramic matrix fibers. The density of the carbon fiber reinforced silica aerogel composite material can be controlled at 0.11 g / cm³. 3 ~0.22g / cm 3 It has a low thermal conductivity at high temperatures, with a thermal conductivity of 0.025 W / (m·K) to 0.035 W / (m·K) at 600℃. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a process flow diagram of Embodiment 1 of the present invention;

[0032] Figure 2 This is a scanning electron microscope image of the polyacrylonitrile pre-oxidized fiber (before pyrolysis) used in this invention;

[0033] Figure 3These are scanning electron microscope images of the polyacrylonitrile pre-oxidized fiber (after pyrolysis) used in this invention;

[0034] Figure 4 This is a scanning electron microscope image of SiC-carbon fiber (after pyrolysis) used in this invention. Detailed Implementation

[0035] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0036] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0037] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0038] Example 1:

[0039] A carbon fiber reinforced silica aerogel composite material and its preparation method, such as Figure 1 As shown, it includes the following steps:

[0040] (1) The density is 0.08 g / cm³ 3 The needle-punched polyacrylonitrile-based pre-oxidized fiber preforms were placed in a vacuum impregnation chamber, and polymethylsilane was impregnated into the fiber preforms under vacuum conditions of -0.09MPa to -0.1MPa for more than 2 hours.

[0041] (2) Take out the fiber preform impregnated with polymethylsilane and place it in an oven at 200℃~300℃ for 1h~2h for curing. After curing, place the cured fiber preform in a high-temperature pyrolysis furnace and pyrolyze it under vacuum. The pyrolysis procedure is as follows: 1) Increase the temperature from room temperature to 350℃ in 60min; 2) Increase the temperature from 350℃ to 1000℃ in 2650min; 3) Hold at 1000℃ for 2h. The resulting pyrolyzed fiber preform is the SiC-carbon fiber preform with a SiC film on its surface.

[0042] (3) Mix tetraethyl orthosilicate, anhydrous ethanol and deionized water in a molar ratio of 1:30:2, stir at room temperature for 30 min to obtain a silicon-based solution, slowly add an inorganic acid catalyst, adjust the pH of the solution to 1-3, and let stand for 2 h.

[0043] The inorganic acid catalyst is nitric acid, and the concentration of the inorganic acid catalyst solution is 1 mol / L;

[0044] (4) Add an alkaline catalyst to the silica sol obtained in the previous step to promote gel condensation and stir evenly to obtain silica sol;

[0045] The alkaline catalyst is ammonia (sodium hydroxide can also be used), and the concentration of the alkaline catalyst solution is 1 mol / L;

[0046] (5) The silica sol obtained in step (4) is impregnated and filled into the SiC-carbon fiber preform obtained in step (2) under a negative pressure of -0.08MPa to -0.1MPa. The density of the preform is 0.12g / cm³. 3 The pressure conditions were maintained for 2 hours to obtain a silica sol-carbon fiber wet gel composite material.

[0047] (6) The silica sol-carbon fiber wet gel composite material obtained in the above steps is subjected to gel aging and supercritical drying under high temperature conditions. The gel aging temperature is 30°C and the time is 72h; the supercritical drying temperature is 280°C, the drying pressure is 10MPa and the time is 8h to obtain carbon fiber reinforced silica aerogel composite material.

[0048] Example 2:

[0049] A carbon fiber reinforced silica aerogel composite material and its preparation method, comprising the following steps:

[0050] (1) The density is 0.06 g / cm³ 3 The needle-punched polyacrylonitrile-based pre-oxidized fiber preforms were placed in a vacuum impregnation chamber, and polymethylsilane was impregnated into the fiber preforms under vacuum conditions of -0.09MPa to -0.1MPa for more than 2 hours.

[0051] (2) Take out the fiber preform impregnated with polymethylsilane and place it in an oven at 200℃~300℃ for 1h~2h for curing. After curing, place the cured fiber preform in a high-temperature pyrolysis furnace and pyrolyze it under vacuum. The pyrolysis procedure is as follows: 1) Increase the temperature from room temperature to 350℃ in 60min; 2) Increase the temperature from 350℃ to 1000℃ in 650min; 3) Hold at 1000℃ for 2h. The resulting pyrolyzed fiber preform is the SiC-carbon fiber preform with a SiC film on its surface.

[0052] (3) Mix tetraethyl orthosilicate, anhydrous ethanol and deionized water in a molar ratio of 1:50:3, stir at room temperature for 30 min to obtain a silicon-based solution, slowly add an inorganic acid catalyst, adjust the pH of the solution to 1-3, and let stand for 2 h.

[0053] The inorganic acid catalyst is nitric acid, and the concentration of the inorganic acid catalyst solution is 1 mol / L;

[0054] (4) Add an alkaline catalyst to the silica sol obtained in the previous step to promote gel condensation and stir evenly to obtain silica sol;

[0055] The alkaline catalyst is ammonia (sodium hydroxide can also be used), and the concentration of the alkaline catalyst solution is 1 mol / L;

[0056] (5) The silica sol obtained in step (4) is impregnated and filled into the SiC-carbon fiber preform obtained in step (2) under a negative pressure of -0.08MPa to -0.1MPa. The density of the preform is 0.08g / cm³. 3 The pressure conditions were maintained for 2 hours to obtain a silica sol-carbon fiber wet gel composite material.

[0057] (6) The silica sol-carbon fiber wet gel composite material obtained in the above steps is subjected to gel aging and supercritical drying under high temperature conditions. The gel aging temperature is 30°C and the time is 72 h. The supercritical drying temperature is 280°C, the drying pressure is 10 MPa and the time is 8 h to obtain carbon fiber reinforced silica aerogel composite material.

[0058] Example 3:

[0059] A carbon fiber reinforced silica aerogel composite material and its preparation method, comprising the following steps:

[0060] (1) The density is 0.08 g / cm³ 3 The needle-punched polyacrylonitrile-based pre-oxidized fiber preforms were placed in a vacuum impregnation chamber, and polymethylsilane was impregnated into the fiber preforms under vacuum conditions of -0.09MPa to -0.1MPa for more than 2 hours.

[0061] (2) Take out the fiber preform impregnated with polymethylsilane and place it in an oven at 200℃~300℃ for 1h~2h for curing. After curing, place the cured fiber preform in a high-temperature pyrolysis furnace and pyrolyze it under vacuum. The pyrolysis procedure is as follows: 1) Increase the temperature from room temperature to 350℃ in 60min; 2) Increase the temperature from 350℃ to 1000℃ in 650min; 3) Hold at 1000℃ for 2h. The resulting pyrolyzed fiber preform is the SiC-carbon fiber preform with a SiC film on its surface.

[0062] (3) Mix tetraethyl orthosilicate, anhydrous ethanol and deionized water in a molar ratio of 1:10:1, stir at room temperature for 30 min to obtain a silicon-based solution, slowly add an inorganic acid catalyst, adjust the pH of the solution to 1-3, and let stand for 2 h.

[0063] The inorganic acid catalyst is nitric acid, and the concentration of the inorganic acid catalyst solution is 1 mol / L;

[0064] (4) Add an alkaline catalyst to the silica sol obtained in the previous step to promote gel condensation and stir evenly to obtain silica sol;

[0065] The alkaline catalyst is ammonia (sodium hydroxide can also be used), and the concentration of the alkaline catalyst solution is 1 mol / L;

[0066] (5) The silica sol obtained in step (4) is impregnated and filled into the SiC-carbon fiber preform obtained in step (2) under a negative pressure of -0.08MPa to -0.1MPa. The density of the preform is 0.16g / cm³. 3 The pressure conditions were maintained for 2 hours to obtain a silica sol-carbon fiber wet gel composite material.

[0067] (6) The silica sol-carbon fiber wet gel composite material obtained in the above steps is placed under high temperature conditions for gelation, aging, and supercritical drying. The gel aging temperature is 30℃ and the time is 72h; the supercritical drying temperature is 280℃, the drying pressure is 10MPa, and the time is 8h to obtain carbon fiber reinforced silica aerogel composite material.

[0068] Comparative Example 1:

[0069] The difference between this comparative example and Example 1 is that the fiber preform is different, and the fiber used is quartz fiber; otherwise, it is the same as Example 1.

[0070] Comparative Example 2:

[0071] The difference between this comparative example and Example 2 is that the fiber preform is different, and the fiber used is mullite fiber; otherwise, it is the same as Example 2.

[0072] Comparative Example 3:

[0073] The difference between this comparative example and Example 1 is that the fiber preform is different; it uses directly pyrolyzed polyacrylonitrile pre-oxidized fiber that has not been impregnated with polycarbosilane. Otherwise, it is the same as Example 1.

[0074] Comparative Example 4:

[0075] The difference between this comparative example and Example 1 is that the fiber preform is different. The polyacrylonitrile-based pre-oxidized fiber preform is not impregnated with polymethylsilane and does not crack. Otherwise, it is the same as Example 1.

[0076] Results and Discussion:

[0077] The aerogel composite materials prepared in Examples 1, 2, 3, 1 (Comparative Example), 2 (Comparative Example), 3 (Comparative Example), and 4 have the following properties, as shown in Table 1:

[0078] Table 1: Comparison of the performance of aerogel composite materials in the examples and comparative examples

[0079]

[0080] Depend on Figure 2 It can be seen that the diameter of the pre-oxidized polyacrylonitrile fiber before pyrolysis is between 11 μm and 13 μm. Figure 3 It is known that the diameter of the pre-oxidized polyacrylonitrile fiber after pyrolysis is between 7 μm and 9 μm, and the fiber pyrolysis shrinkage rate is approximately 30%. Figure 4 It is known that the diameter of SiC-carbon fiber is about 12μm, and a SiC layer is coated on the surface of polyacrylonitrile pre-oxidized fiber.

[0081] The results show that the carbon fiber reinforced silica aerogel composite material of the present invention exhibits good performance at low densities (0.11 g / cm³). 3 ~0.21g / cm 3 The aerogel composites prepared using ceramic fibers (such as quartz and mullite) as reinforcement exhibit low high-temperature thermal conductivity. Due to the high density of the fibers, it is difficult to control the fiber density during molding, resulting in delamination of the composites. Furthermore, the high radiative thermal conductivity at high temperatures leads to high overall thermal conductivity, and the low fiber density results in significant thickness shrinkage after high-temperature testing, leading to structural instability. Additionally, the low density of mullite fibers makes them difficult to mold, causing delamination and cracking of the resulting aerogel composites. Comparative Example 4 directly uses unimpregnated polyacrylonitrile pre-oxidized fibers combined with silica aerogel. The large shrinkage of the pre-oxidized fibers at high temperatures prevents proper bonding between the aerogel and fibers, causing delamination and cracking. Comparative Example 3 first undergoes high-temperature pyrolysis of unimpregnated pre-oxidized fibers before combining them with silica aerogel. During high-temperature thermal conductivity testing, the mismatch in thermal expansion coefficients between the carbon fibers and silica aerogel at high temperatures leads to numerous cracks, resulting in a significant increase in the composite's thermal conductivity.

[0082] In summary, the preparation method of the carbon fiber reinforced silica aerogel composite material of the present invention produces a carbon fiber reinforced SiO2 aerogel composite material with low density and low thermal conductivity at high temperatures. The present invention prepares the carbon fiber reinforced silica aerogel composite material by pretreating carbon fiber felt and then compounding it with silica sol, followed by processes such as sol-gel and supercritical drying. This solves the problem of mismatched thermal expansion coefficients between carbon fiber and silica aerogel, which easily leads to interfacial debonding under high and low temperature cycling.

Claims

1. A method for preparing a carbon fiber reinforced silica aerogel composite material, characterized in that, Includes the following steps: (1) Polymethylsilane is impregnated into polyacrylonitrile-based pre-oxidized fiber preforms by vacuum impregnation to obtain fiber preforms impregnated with polymethylsilane; The polyacrylonitrile-based pre-oxidized fiber preforms were prepared by the following method: polyacrylonitrile-based pre-oxidized fibers were needle-punched, with the needle-punching density controlled at 200 needles / cm². 2 ~400 thorns / cm 2 The density of the polyacrylonitrile-based pre-oxidized fiber preform is controlled to be 0.06 g / cm³. 3 ~0.08 g / cm 3 The vacuum degree of the vacuum impregnation is -0.09 MPa to -0.1 MPa, and the pressure is maintained for more than 2 hours. (2) The fiber preform impregnated with polymethylsilane is cured and then pyrolyzed under vacuum to obtain a SiC-carbon fiber preform with a SiC film on its surface. The pyrolysis procedure is as follows: First, the temperature is raised from room temperature to 350 °C over a period of 60 min; then, the temperature is raised from 350 °C to 1000 °C over a period of 650 min; finally, the temperature is held at 1000 °C for 2 h. (3) Mix tetraethyl orthosilicate, anhydrous ethanol and water to obtain a silicon-based solution, add an inorganic acid catalyst solution to adjust the pH to acidic, and then let it stand to obtain a silica sol; The molar ratio of tetraethyl orthosilicate, anhydrous ethanol, and water is 1:(10-50):(1-3), and the mixing is carried out by stirring at room temperature for 10-30 minutes; the inorganic acid catalyst solution is a nitric acid solution with a concentration of 0.1 mol / L to 2 mol / L; the pH of the silicon-based solution is adjusted to 1-3; and the standing time is 0.5-8 hours. (4) Add an alkaline catalyst solution to the silica sol to perform gel condensation, stir evenly, and obtain silica sol; (5) The SiC-carbon fiber preform is laid in the mold, and the silica sol is impregnated and filled into the SiC-carbon fiber preform in the mold under negative pressure to obtain silica sol-carbon fiber wet gel composite material. (6) The silica sol-carbon fiber wet gel composite material is subjected to gel aging and supercritical drying to obtain the carbon fiber reinforced silica aerogel composite material. The gel aging temperature is 5 ℃~40 ℃, and the time is 48 h~96 h; the supercritical drying temperature is 260 ℃~320 ℃, the drying pressure is 8 MPa~12 MPa, and the time is 4 h~12 h.

2. The method of claim 1, wherein the carbon fiber-reinforced silica aerogel composite is prepared by the steps of: In step (2), the curing temperature is 200 ℃~300 ℃ and the curing time is 1 h~2 h.

3. The method for preparing the carbon fiber reinforced silica aerogel composite material according to claim 1, characterized in that, In step (4), the alkaline catalyst solution is ammonia or sodium hydroxide solution with a concentration of 0.1 mol / L to 2 mol / L.

4. The method for preparing the carbon fiber reinforced silica aerogel composite material according to claim 1, characterized in that, In step (5), the density of the SiC-carbon fiber preform is controlled to be 0.08 g / cm 3 ~ 0.16 g / cm 3 by a molding die.

5. The method for preparing the carbon fiber reinforced silica aerogel composite material according to claim 1, characterized in that, In step (5), the negative pressure condition is -0.08 MPa to -0.1 MPa, and the negative pressure condition is maintained for ≥0.5 h.

6. The carbon fiber-reinforced silica aerogel composite material produced by the production method according to any one of claims 1 to 5, characterized by, Its density is 0.11 g / cm³. 3 ~0.22 g / cm 3 The thermal conductivity at 600 ℃ is 0.025 W / (m·K)~0.035 W / (m·K).

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