High-temperature-resistant super-elastic silicon carbide composite aerogel and preparation method thereof

Abstract

The application discloses a high-temperature-resistant super-elastic silicon carbide composite aerogel, which comprises a synergistically reinforced cell-like wall structure formed by micro-nano hybrid fibers, wherein the micro-nano hybrid fibers are composed of micron fibers and nanofibers, and a modified sol is used for high-temperature bonding to form a three-dimensional multi-level micro-nano fiber network structure.The high-temperature-resistant super-elastic silicon carbide composite aerogel is formed by a directional freezing casting technology to form a micro-nano fiber synergistically reinforced cell-like wall structure.When subjected to a compression stress, the micron fibers serve as a framework to bear the main stress load, thereby reducing stress concentration in the matrix, and local stress can be transmitted to the silicon carbide nanofiber network through cross-linking nodes, so that the overall mechanical strength is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ceramic aerogels, and particularly relates to a high-temperature-resistant super-elastic silicon carbide composite aerogel and a preparation method thereof. BACKGROUND

[0002] Ceramic aerogels can be used as an efficient thermal insulation material due to their high porosity, large specific surface area, low density, low thermal conductivity and oxidation resistance, and have attracted extensive attention in many fields such as aerospace, industrial pipelines and civil buildings. However, the three-dimensional network skeleton structure of traditional ceramic aerogels is composed of pearl necklace-like structures formed by the aggregation of nanoparticles. The low continuity of the skeleton structure leads to high brittleness, and the aerogel is prone to sintering and structure collapse in extreme environments, thereby affecting its thermal insulation performance. Generally, the addition of fiber reinforcement in ceramic aerogels can effectively enhance the mechanical properties of the aerogels, but will correspondingly increase the density of the aerogels, thereby reducing the thermal insulation performance. In addition, the weak interfacial interaction between the fibers and the matrix leads to easy peeling of the aerogel particles, which seriously limits the practical application of the aerogels.

[0003] In recent years, in order to solve the above problems, relevant technical personnel in the field have made some research. A new type of ceramic fiber aerogel with one-dimensional nanofiber as the building unit has attracted extensive attention, which combines the advantages of ceramic materials and high continuity of nanofibers and successfully overcomes the brittleness and force-heat mutual exclusion problems that are difficult to avoid in the forming and processing of traditional aerogels. Generally, silicon carbide materials have excellent properties such as chemical corrosion resistance, high specific strength and high specific modulus, and have high application value in the fields of aerospace, national defense and military industry. In addition, compared with oxide ceramic materials, silicon carbide materials have higher thermal stability and thermal shock resistance. At the same time, silicon carbide materials exhibit high extinction coefficient for infrared radiation with a wavelength of less than 7.5 um, which can effectively improve the problem of high infrared radiation thermal conductivity of aerogels in high temperature environment. These comprehensive properties make silicon carbide fiber aerogels one of the most excellent thermal insulation materials in harsh applications such as building insulation and aerospace thermal protection, and are ideal candidates for building multifunctional ceramic aerogels.

[0004] Currently, silicon carbide fiber aerogels are mainly prepared by chemical vapor deposition technology. For example, patent CN202011612437.2 discloses a method of using fluffy carbon fiber felt as a growth template for silicon carbide nanofibers. By combining chemical vapor deposition, a silicon carbide fiber aerogel is prepared, which is constructed by randomly interweaving nanofiber three-dimensional space. The pore structure of the silicon carbide fiber aerogel prepared by this method is controllable and easy to realize large-scale industrial production. Patent CN202111342210.5 discloses a method of growing silicon carbide nanofibers in situ on the surface of a graphite crucible cover using chemical vapor deposition. The fibers self-assemble to form a three-dimensional silicon carbide fiber aerogel with high porosity and high thermal stability. This method does not require the use of carbon fibers as a growth template, thereby reducing production costs. Su et al. used chemical vapor deposition to form a layer of silicon carbide ceramic nanowire film on the surface of a graphite crucible cover, and used the film to stack layer by layer to form a super-light, high-temperature-resistant elastic silicon carbide fiber aerogel (ACS Nano 2018, 12, 3103-3111). However, the preparation process of chemical vapor deposition usually requires harsh experimental conditions, which is not conducive to industrial production, and the lack of effective bonding points between fibers leads to poor high-temperature structural stability, and large plastic deformation and strength reduction during stress. In addition, the silicon carbide fiber aerogel prepared by this method is only a simple stacking of two-dimensional structures, and the weak interlayer interaction leads to easy delamination between layers, making it difficult to meet the processing requirements of complex shapes in actual applications. This method cannot build an ordered arrangement of organizational structure, and the internal microstructure is randomly assembled by fibers, which cannot accurately control its density and pore structure, resulting in a large energy dissipation during compression. Su et al. further improved the preparation process by combining chemical vapor deposition and directional freeze casting technology in 2020, successfully constructing a super-light, elastic and low-thermal-conductivity silicon carbide fiber aerogel with a honeycomb-like pore structure, achieving a recoverable elastic strain of 80% and a high-temperature resistance of 1200℃. However, the poor connection between fibers leads to poor mechanical properties, with a maximum compression strength of only 8.5kPa, making it difficult to resist thermal shock and large mechanical stress under extreme conditions (Su et al., Sci. Adv. 2020; 6: eaay6689). Guo et al. combined a 3D printing process with a chemical vapor deposition-like process in 2022 to manufacture an elastic silicon carbide nanowire aerogel with a three-dimensional multi-level complex structure. This method allows the silicon carbide fiber aerogel to have programmable geometry and adjustable force / thermal performance, making it suitable for specific application scenarios. However, due to the simple random winding and lapping of fibers to form a three-dimensional network structure, there is still a lack of effective interface bonding points between fibers, resulting in a maximum recoverable elastic strain of only 20% (ACS Nano 2022, 16, 6625-6633).Therefore, although the above aerogel makes outstanding contributions to the enhancement of network structure and thermal insulation performance through microstructure design, its elastic mechanical properties and use durability need to be further improved. SUMMARY

[0005] The present application aims to solve the above problems, and provide a kind of operation process simple, low to equipment requirement, the aerogel material prepared not only has the characteristics such as high porosity, low density and extremely low thermal conductivity of traditional ceramic aerogel, simultaneously, through microstructure construction, form micro-nano fiber synergistically enhanced cell wall structure, greatly enhance the mechanical properties of elastic ceramic aerogel, effectively improve the overall high temperature structural stability of ceramic aerogel, high temperature super-elastic silicon carbide composite aerogel and its preparation method.

[0006] To solve the above technical problems, the technical scheme of the present application is: a kind of high temperature super-elastic silicon carbide composite aerogel, including synergistically enhanced cell wall structure of micro-nano hybrid fiber composite, and micro-nano hybrid fiber is composed of micron fiber and nanofiber, and is formed three-dimensional multistage micro-nano fiber network structure by high temperature bonding of a modified sol.

[0007] Preferably, the micron fiber in the micro-nano hybrid fiber is composed of one or more of Si3N4 fiber, ZrO2 fiber, silicate fiber, TiO2 fiber and Al2O3 fiber;The nanofiber is silicon carbide fiber.

[0008] Preferably, the modified sol is a composite of silica sol and fluxing agent, and the fluxing agent is composed of one or more of boric acid, sodium oxide and potassium oxide.

[0009] Preferably, the preparation method of the high temperature super-elastic silicon carbide composite aerogel comprises the following steps:

[0010] S1, a thickening agent is added to an aqueous solution and stirred uniformly, then micro-nano fiber is added for ultrasonic dispersion, to obtain a fiber suspension;

[0011] S2, tetraethyl orthosilicate, water, anhydrous ethanol, oxalic acid and fluxing agent are mixed to carry out hydrolysis reaction, to obtain a modified sol;The modified sol is added dropwise to the fiber suspension, and then directional freezing casting and high temperature calcination are carried out, the calcination temperature is 700-1100 DEG C, to obtain high temperature super-elastic silicon carbide composite aerogel.

[0012] Preferably, the thickening agent in S1 is one of polyethylene oxide, polyvinyl alcohol, polyacrylamide and sodium polyacrylate;The content of thickening agent is 0.2-0.7wt%.

[0013] Preferably, the aspect ratio of the microfibers in S1 is 20-250; the diameter of the silicon carbide nanofibers is 200-600 nm, and the total mass fraction of the micro / nanofibers is 1%, wherein the mass ratio of the micro / nanofibers is 2:1, 1:1 and 1:2, respectively.

[0014] Preferably, the mass ratio of tetraethyl orthosilicate, water, anhydrous ethanol, oxalic acid and fluxing agent in S2 is 1:(2-5):(2-5):(0.03-0.09):(0.02-0.05), and the stirring time and temperature are 1-2 h and 25-50℃, respectively; the content of the modified sol is 0.1-0.3 wt%, and the stirring time is 5-10 min.

[0015] Preferably, the strength and density of the silicon carbide fiber-based composite aerogel in S2 can be adjusted, which is embodied in: by changing the content of the modified sol or the crosslinking degree, the strength and density of the silicon carbide fiber-based composite aerogel are adjusted; or, by changing the aspect ratio of the microfibers, the strength and density of the silicon carbide fiber-based composite aerogel are adjusted; or, by changing the mass ratio of the microfibers to the nanofibers, the strength and density of the silicon carbide fiber-based composite aerogel are adjusted.

[0016] The beneficial effects of the present application are:

[0017] 1. The high-temperature-resistant super-elastic silicon carbide composite aerogel provided by the present application forms a micro / nano fiber synergistically reinforced cell-like wall structure through directional freeze casting technology. When subjected to compressive stress, the microfibers act as a skeleton to bear the main stress load, thereby reducing stress concentration in the matrix, and local stress can be transmitted to the silicon carbide nanofiber network through the crosslinking nodes, thereby improving the overall mechanical strength; the directional pore structure formed by the directional freeze casting technology realizes the extremely low thermal conductivity of the aerogel in the radial direction.

[0018] 2. The present application uses modified sol as a high-temperature binder to build stable bonding points between fibers. Compared with conventional silica sol binders, the fluxing agent can reduce the melting temperature and improve the fluidity of the melt during the heat treatment process, thereby reducing the preparation time and economic cost.

[0019] 3. The preparation method of the high-temperature-resistant super-elastic silicon carbide composite aerogel described in the present application has a simple operation process and low equipment requirements, and can be applied to large-scale industrial production.

[0020] 4. The present application uses micro / nano hybrid fibers to interweave and form a synergistically reinforced cell-like wall structure, uses a modified high-temperature binder to reinforce the fiber network interweaving points, and constructs a three-dimensional multi-level micro / nano fiber network to prepare a silicon carbide fiber-based composite aerogel.

[0021] 5、The composite aerogel has excellent mechanical resilience, low thermal conductivity and high temperature structural stability. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a flow chart of the high-temperature-resistant super-elastic silicon carbide composite aerogel and a preparation method thereof. DETAILED DESCRIPTION

[0023] The application will be further described below in combination with the drawings and specific examples:

[0024] Example 1

[0025] The application provides a high-temperature-resistant super-elastic silicon carbide composite aerogel, which comprises a synergistically reinforced cell wall structure formed by micro-nano hybrid fibers, the micro-nano hybrid fibers are composed of micron fibers and nano fibers, and a modified sol is used for high-temperature bonding to form a three-dimensional multi-level micro-nano fiber network structure. In this embodiment, the three-dimensional multi-level micro-nano fiber network structure is composed of the synergistically reinforced cell wall structure and a directional pore structure. The directional pore structure in the application is formed by the directional pore structure formed in the directional freeze casting process.

[0026] The micron fibers in the micro-nano hybrid fibers are composed of one or more of Si3N4 fibers, ZrO2 fibers, silicate fibers, TiO2 fibers and Al2O3 fibers; and the nano fibers are silicon carbide fibers.

[0027] The modified sol is a composite of silica sol and a fluxing agent, and the fluxing agent is composed of one or more of boric acid, sodium oxide and potassium oxide.

[0028] The application further discloses a preparation method of the high-temperature-resistant super-elastic silicon carbide composite aerogel, which comprises the following steps:

[0029] S1, a thickening agent is added into an aqueous solution and stirred uniformly, then micro-nano fibers are added for ultrasonic dispersion to prepare a fiber suspension.

[0030] In S1, the thickening agent is one of polyethylene oxide, polyvinyl alcohol, polyacrylamide and sodium polyacrylate; the content of the thickening agent is 0.2-0.7 wt%; the length-diameter ratio of the micron fibers is 20-250; the diameter of the silicon carbide nano fibers is 200-600 nm; the total mass fraction of the micro-nano fibers is 1%, and the mass ratio of the micro / nano fibers is 2:1, 1:1 and 1:2 respectively.

[0031] S2, tetraethyl orthosilicate, water, anhydrous ethanol, oxalic acid and a fluxing agent are mixed to perform a hydrolysis reaction to prepare a modified sol; the modified sol is added dropwise into the fiber suspension, then directional freeze casting and high-temperature calcination are performed, the calcination temperature is 700-1100 DEG C, and a high-temperature-resistant super-elastic silicon carbide composite aerogel is obtained.

[0032] The mass ratio of tetraethyl orthosilicate, water, anhydrous ethanol, oxalic acid and fluxing agent in S2 is 1:(2-5):(2-5):(0.03-0.09):(0.02-0.05), and the stirring time and temperature are 1-2h and 25-50℃, respectively; the content of the modified sol is 0.1-0.3wt%, and the stirring time is 5-10min. The strength and density of the silicon carbide fiber-based composite aerogel can be adjusted, which is embodied in: by changing the content or cross-linking degree of the modified sol, the strength and density of the silicon carbide fiber-based composite aerogel are adjusted; or, by changing the aspect ratio of the micron fibers, the strength and density of the silicon carbide fiber-based composite aerogel are adjusted; or, by changing the mass ratio of micron fibers to nanofibers, the strength and density of the silicon carbide fiber-based composite aerogel are adjusted.

[0033] In the embodiment, the micro-nanofiber synergistically reinforced cell-like wall structure is obtained by directional freeze casting technology. The cell wall structure is composed of micron fibers and silicon carbide nanofibers as a supporting skeleton. The synergistic effect of micro-nanofibers is beneficial to improve the ability of the fiber cell wall to resist buckling deformation, thereby improving the mechanical strength of the ceramic fiber aerogel. At the same time, the silicon carbide fiber network reinforces the micron fiber network, thereby improving the mechanical stability of the cell wall connection. By controlling the temperature gradient to realize directional growth of the ice template, the directional pore structure is formed after drying, which is beneficial to reduce the thermal conductivity of the aerogel in the radial direction. After high-temperature calcination, the high-temperature molten SiO2 after low-temperature solidification forms stable bonding points between the fibers, preventing the sliding action between the fibers during stress, thereby improving the high-temperature structural stability of the overall structure.

[0034] Taking the preparation of Si3N4 micron fibers and Si / B modified sol as an example, the preparation method of the application is as follows:

[0035] In the first step, a certain amount of thickening agent is added to 30mL of aqueous solution and stirred at 65℃ on a heating stirring table for 1-2h to form a 0.2wt%-0.7wt% thickening agent solution, then Si3N4 micron fibers and silicon carbide nanofibers are added for ultrasonic dispersion, and after stirring uniformly, a fiber suspension is obtained, wherein the total content of micro-nanofibers is 1%.

[0036] The second step is to mix tetraethyl orthosilicate, water, anhydrous ethanol, oxalic acid and boric acid according to the mass ratio of 1:(2-5):(2-5):(0.03-0.09):(0.02-0.05) and fully stir for 1-2 hours to prepare Si / B modified sol; a certain amount of modified sol is added dropwise into the fiber suspension, then the sol / fiber suspension is poured into a polytetrafluoroethylene mold with the bottom brass half immersed in liquid nitrogen for directional freezing, the freezing time is 3-5 minutes, then the frozen sample is vacuum dried for at least 3 days; finally, it is put into a muffle furnace for high-temperature calcination, the calcination temperature is 700-1100 DEG C and the heating rate is 2-5 DEG C / min, to obtain the high-temperature-resistant super-elastic silicon carbide composite aerogel.

[0037] The present application prepares a high-temperature-resistant super-elastic silicon carbide composite aerogel with a density of 0.162 g / cm 3 , and the size and density can be adjusted, the aspect ratio of Si3N4 microfibers is about 200, the diameter of silicon carbide nanofibers is about 300 nm, the mass ratio of micro-nano fibers is 1:1, and the content of Si / B modified sol is 0.26 wt%.

[0038] S1, 0.075 g of polyethylene oxide is added to 30 mL of aqueous solution and stirred at 65 DEG C on a heating stirring table for 2 hours, then 0.15 g of Si3N4 microfiber with an aspect ratio of about 200 and 0.15 g of silicon carbide nanofiber are added respectively for ultrasonic dispersion, and the stirring is uniform to obtain a fiber suspension, wherein the total content of micro-nano fibers is 1%.

[0039] S2, tetraethyl orthosilicate, water, anhydrous ethanol, oxalic acid and boric acid are mixed according to the mass ratio of 1:5:5:0.07:0.02 and fully stirred for 2 hours to prepare Si / B modified sol; a certain amount of modified sol is added dropwise into the fiber suspension (the content of Si / B sol is 0.26 wt%), then the sol / fiber suspension is poured into a polytetrafluoroethylene mold with the bottom brass half immersed in liquid nitrogen for directional freezing, the freezing time is 3-5 minutes, then the frozen sample is vacuum dried for 3 days; finally, it is put into a muffle furnace for high-temperature calcination, the calcination temperature is 800 DEG C and the heating rate is 2 DEG C / min.

[0040] Example two

[0041] This example prepares a high-temperature-resistant super-elastic silicon carbide composite aerogel with a density of 0.296 g / cm 3 , and the size and density can be adjusted, the aspect ratio of Si3N4 microfibers is about 20, the diameter of silicon carbide nanofibers is about 300 nm, the mass ratio of micro-nano fibers is 1:1, and the content of Si / B modified sol is 0.26 wt%.

[0042] S1, 0.075 g of polyethylene oxide was added to 30 mL of aqueous solution, stirred at 65℃ for 2h on a heating stirrer, then 0.15 g of Si3N4 microfiber with an aspect ratio of about 20 and 0.15 g of silicon carbide nanofiber were added respectively for ultrasonic dispersion, and the fiber suspension was obtained by stirring uniformly, wherein the total content of micro-nanofiber was 1%.

[0043] S2, tetraethyl orthosilicate, water, anhydrous ethanol, oxalic acid and boric acid were mixed according to the mass ratio of 1:5:5:0.07:0.02 and stirred thoroughly for 2h to prepare Si / B modified sol; a certain amount of modified sol was added dropwise into the fiber suspension (Si / B sol content 0.26wt%), then the sol / fiber suspension was poured into a polytetrafluoroethylene mold with the bottom brass half immersed in liquid nitrogen for directional freezing, the freezing time was 3-5min, then the frozen sample was vacuum dried for 3 days; finally, it was put into a muffle furnace for high temperature calcination, the calcination temperature was 800℃ and the heating rate was 2℃ / min.

[0044] Example Three

[0045] In this example, a high-temperature-resistant super-elastic silicon carbide composite aerogel with a density of 0.195 g / cm 3 , and size and density adjustable, was prepared, which was the same as example one except that the aspect ratio of the Si3N4 microfiber was about 150.

[0046] The preparation method of the high-temperature-resistant super-elastic silicon carbide composite aerogel was changed accordingly, which was the same as example one except that the aspect ratio of the Si3N4 microfiber was about 150.

[0047] Example Four

[0048] In this example, a high-temperature-resistant super-elastic silicon carbide composite aerogel with a density of 0.147 g / cm 3 , and size and density adjustable, was prepared, which was the same as example one except that the mass ratio of micro-nanofiber was 1:2.

[0049] The preparation method of the high-temperature-resistant super-elastic silicon carbide composite aerogel was changed accordingly, which was the same as example one except that the mass ratio of micro-nanofiber was 1:2.

[0050] Example Five

[0051] In this example, a high-temperature-resistant super-elastic silicon carbide composite aerogel with a density of 0.243 g / cm 3 , and size and density adjustable, was prepared, which was the same as example 1 except that the mass ratio of micro-nanofiber was 2:1.

[0052] The preparation method of the high-temperature-resistant super-elastic silicon carbide composite aerogel is changed accordingly, so that the mass ratio of the micro-nano fiber is 2:1, and the rest is the same as in Example 1.

[0053] Example Six

[0054] In this example, a high-temperature-resistant super-elastic silicon carbide composite aerogel with a density of 0.239 g / cm 3 The high-temperature-resistant super-elastic silicon carbide composite aerogel with adjustable size and density is prepared, and except that the content of the Si / B modified sol is 0.14wt%, the rest is the same as in Example 1.

[0055] The preparation method of the high-temperature-resistant super-elastic silicon carbide composite aerogel is changed accordingly, so that the content of the Si / B modified sol is 0.14wt%, and the rest is the same as in Example 1.

[0056] Example Seven

[0057] This example is a comparative example, which relates to a preparation method of a silicon carbide fiber aerogel. The diameter and proportion of the silicon carbide fiber are the same as in Example 1, and the preparation method is the same as in Example 1, except that the micro-nano hybrid fiber matrix is replaced by only silicon carbide nanofiber.

[0058] The sample density, room temperature thermal conductivity and maximum compressive strength under 60% compressive strain of the high-temperature-resistant super-elastic silicon carbide composite aerogel material and the comparative example silicon carbide fiber aerogel material are tested respectively.

[0059] The test results of the present application are shown in Table 1:

[0060] Table 1

[0061]

[0062]

[0063] As can be seen from Table 1:

[0064] (1) As can be seen from the comparison between Example 1 and Comparative Example 7, by compounding rigid microfibers and flexible nanofibers, the microfibers play a supporting role, reducing the local stress load in the matrix, thereby further improving the mechanical strength of the aerogel.

[0065] (2) From Example 1 to Example 3, it can be known that the aspect ratio of the microfiber is controlled, so that the mechanical strength of the high-temperature-resistant super-elastic silicon carbide composite aerogel can be accurately regulated. From Example 1, Example 4 and Example 5, it can be known that the mass ratio of the micro-nano fiber is controlled, so that the mechanical strength of the high-temperature-resistant super-elastic silicon carbide composite aerogel can be accurately regulated. From Example 1 and Example 6, it can be known that the addition amount of the high-temperature binder is controlled, so that the mechanical strength of the high-temperature-resistant super-elastic silicon carbide composite aerogel can be accurately regulated.

[0066] In summary, through Example 1 to Example 5, it can be found that the high-temperature-resistant super-elastic silicon carbide composite aerogel prepared by the preparation method of the present application has the advantages of low density, excellent mechanical properties and low thermal conductivity. The present application forms a micro-nano fiber synergistically enhanced cell wall structure by compounding micro-nano fibers, combining directional freeze casting technology and a modified high-temperature binder, which can effectively enhance the mechanical resilience of the prepared composite aerogel through the synergistic effect of micro-nano fibers during the stress process. The directional pore structure formed by the directional freeze casting technology can effectively reduce the thermal conductivity of the aerogel in the radial direction. The modified sol constructs stable crosslinking points between the fibers, so that it has excellent high-temperature structural stability. At the same time, by changing the fiber aspect ratio, the micro-nano fiber mass ratio and the sol content, the strength and density of the aerogel can be adjusted.

[0067] Those skilled in the art will appreciate that the examples described herein are presented to aid the reader in understanding the principles of the present application and should be understood as not limiting the scope of the present application to such specifically recited examples and embodiments. Those skilled in the art can make various other specific modifications and combinations according to the technical inspiration disclosed in the present application without departing from the spirit of the present application, and these modifications and combinations are still within the scope of protection of the present application.

Claims

1. A high-temperature resistant, superelastic silicon carbide composite aerogel, characterized in that: This includes a synergistically enhanced cavity wall-like structure formed by micro- and nano-hybrid fibers. The micro- and nano-hybrid fibers are composed of micron-fibers and nanofibers, and are bonded together at high temperature using a modified sol to form a three-dimensional multi-level micro- and nano-fiber network structure. The micro-nano hybrid fibers are composed of one or more of Si3N4 fibers, ZrO2 fibers, silicate fibers, TiO2 fibers, and Al2O3 fibers; the nanofibers are silicon carbide fibers. The preparation method of the high-temperature resistant superelastic silicon carbide composite aerogel includes the following steps: S1. Add the thickener to the aqueous solution and stir until uniform. Then add the micro-nano hybrid fibers and disperse them by ultrasonication to obtain a fiber suspension. S2. Tetraethyl orthosilicate, water, anhydrous ethanol, oxalic acid and flux are mixed and hydrolyzed to obtain a modified sol. The modified sol is added dropwise to the fiber suspension, and then subjected to directional cryogenic casting and high-temperature calcination at a temperature of 700-1100℃ to obtain a high-temperature resistant superelastic silicon carbide composite aerogel.

2. The high-temperature resistant, superelastic silicon carbide composite aerogel according to claim 1, characterized in that: The modified sol is a composite of silica sol and flux, wherein the flux is composed of one or more of boric acid, sodium oxide and potassium oxide.

3. The high-temperature resistant, superelastic silicon carbide composite aerogel according to claim 1, characterized in that: The thickener in S1 is one of polyethylene oxide, polyvinyl alcohol, polyacrylamide, and sodium polyacrylate; the thickener content is 0.2-0.7 wt%.

4. The high-temperature resistant, superelastic silicon carbide composite aerogel according to claim 1, characterized in that: The aspect ratio of the microfibers in S1 is 20 to 250; the diameter of the silicon carbide nanofibers is 200 to 600 nm; the total mass fraction of the micro / nano hybrid fibers is 1%; and the mass ratio of micro / nano fibers is 2:1, 1:1, or 1:

2.

5. The high-temperature resistant, superelastic silicon carbide composite aerogel according to claim 4, characterized in that: The mass ratio of tetraethyl orthosilicate, water, anhydrous ethanol, oxalic acid, and flux in S2 is 1:(2-5):(2-5):(0.03-0.09):(0.02-0.05), and the stirring time and temperature are 1-2 h and 25-50 °C, respectively; the content of the modified sol is 0.1-0.3 wt%, and the stirring time is 5-10 min.

6. The high-temperature resistant, superelastic silicon carbide composite aerogel according to claim 1, characterized in that: The strength and density of the high-temperature resistant superelastic silicon carbide composite aerogel in S2 are adjustable, which is reflected in: controlling the strength and density of the high-temperature resistant superelastic silicon carbide composite aerogel by changing the content or degree of cross-linking of the modified sol; or, controlling the strength and density of the high-temperature resistant superelastic silicon carbide composite aerogel by changing the aspect ratio of the microfibers; or, controlling the strength and density of the high-temperature resistant superelastic silicon carbide composite aerogel by changing the mass ratio of microfibers to nanofibers.

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