Triaxially spun superelastic high-temperature resistant composite carbon nanofiber aerogel and preparation method thereof

Abstract

The present invention discloses a triaxially spun superelastic and high-temperature resistant composite carbon nanofiber aerogel and a preparation method thereof. The aerogel is formed by interweaving curly fibers with a core layer of carbon and a shell layer of oxide ceramic. The present invention utilizes electrostatic spinning technology to prepare composite carbon nanofiber aerogels. First, an inner layer polyacrylonitrile solution is prepared, and the water / alcohol ratio is adjusted to prepare a middle layer ceramic sol with controllable water content, thereby obtaining a spinning solution with compatibility in the initial spinning stage. The temperature and humidity of the airflow of the outer nozzle are then regulated, and the water content of the ceramic sol is further adjusted during the spinning process, so that the spinning solution becomes incompatible. The spinning solution jet is fast and solidified in advance, thereby obtaining a curly interwoven structure nanofiber aerogel precursor. Finally, the final product is obtained by changing the atmosphere and performing rapid and continuous heat treatment. The present invention solves the problems of insufficient mechanical properties and easy oxidation of carbon nanofiber aerogels. The preparation method is simple and easy to implement, and the process is continuous, and can be carried out on existing electrostatic spinning production equipment.

Description

Technical Field

[0001] The invention relates to a triaxially spun superelastic high-temperature resistant composite carbon nanofiber aerogel and a preparation method thereof, belonging to the technical field of nanomaterials. Background Art

[0002] Carbon aerogel, a porous material with a three-dimensional network structure, has become an ideal material for high-temperature thermal protection due to its excellent thermal stability and thermal insulation properties. However, existing carbon aerogels still suffer from poor three-dimensional network stability and easy oxidation, which seriously affects their mechanical and thermal insulation properties.

[0003] Regarding the construction of three-dimensional carbon aerogel networks, weak-necked aerogels constructed from traditional nanoparticles are brittle and cannot be used alone. Aerogel powders that incorporate reinforcing / toughening components such as whiskers and fibers are prone to shedding and have poor deformation capabilities. Self-supporting aerogels, such as carbon nanotubes and graphene nanosheets, offer some improvements in mechanical properties, but these structures induce continuous heat conduction after compaction, which can lead to a decrease in the material's thermal insulation performance and limit their practical application. Using flexible nanofibers with high aspect ratios and good continuity as building blocks, a stable, self-supporting elastic structure with interwoven and relatively slippable connections can be formed within the aerogel, potentially addressing the issue of carbon aerogel's poor mechanical properties. Chinese invention patent application CN202211050959.7 discloses a carbon nanofiber aerogel and its application in fireproof and thermal insulation materials. The carbon nanofiber aerogel is prepared through a series of processes, including electrospinning, carbonization, homogenization, and freeze-drying, which improves the material's mechanical properties. However, this preparation method is cumbersome and the process is discontinuous. The Chinese invention patent application with publication number CN202011386739.2 applies for a method for rapidly preparing graphene fiber aerogel. The air flow jet spinning method is used to form a self-supporting carbon nanofiber aerogel precursor in one step, and then the final product is obtained by high-temperature calcination. However, this method has insufficient drawing force, and the obtained fiber aerogel has a loose and irregular structure. The connection structure between fibers is unstable and easy to slip, and the overall uniformity of the material is poor. When facing mechanical shock or heat flow shock, the structure is extremely easy to collapse, which will cause a decrease in mechanical properties.

[0004] In terms of improving the oxidation resistance of nanofiber aerogels, since ceramic materials have excellent oxidation resistance, post-processing methods such as chemical vapor deposition, atomic layer deposition, and impregnation are often used to achieve a ceramic antioxidant layer coating on the surface of the nanofiber. The Chinese invention patent application with publication number CN202210954448.1 applies for a high-temperature resistant and highly elastic silicon carbide @ oxide ceramic core-shell nanofiber aerogel material and its preparation method. Silicon carbide nanofiber aerogel covered with an oxide ceramic shell is prepared through chemical vapor deposition, oxidation, atomic layer deposition, fiber homogeneous dispersion, and freeze drying. However, this method is complex and slow, and it is difficult to deposit antioxidant materials in fiber aerogels with a larger thickness. The Chinese invention patent application with publication number CN202410246752.X applies for a carbon @ silicon carbide nanofiber aerogel and its preparation method and application. Carbon nanofiber aerogel covered with a silicon carbide shell is prepared through impregnation, drying, and high-temperature calcination, but this method is prone to the problem of uneven fiber impregnation.

[0005] Therefore, it is necessary to develop a simple, easy and continuous process method to prepare high-temperature resistant elastic carbon nanofiber aerogel with an antioxidant protective layer to meet the application requirements of high-temperature thermal protection fields such as aerospace. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a triaxially spun super-elastic and high-temperature resistant composite carbon nanofiber aerogel and a preparation method thereof, which solves the problems of insufficient mechanical properties of traditional carbon nanofiber aerogel materials, inability to cope with extreme temperature aerodynamic thermal shock, and easy oxidation in an aerobic environment and low temperature resistance limit. The method is highly universal, simple and easy to implement, and has a continuous process, and can be carried out on existing electrospinning production equipment.

[0007] In order to solve the above problems, the present invention is implemented by the following technical solutions:

[0008] The present invention provides a triaxially spun superelastic and high-temperature resistant composite carbon nanofiber aerogel. The composite carbon nanofiber aerogel uses curled fibers with a carbon core layer and an oxide ceramic shell layer as building blocks, and the curled fibers are interwoven to form an elastic network connection structure.

[0009] Preferably, the triaxially spun superelastic and high-temperature resistant composite carbon nanofiber aerogel consists of a carbon core layer, a surface continuously and evenly covered with an oxide ceramic protective shell layer with a thickness of 10 to 200 nm, an aspect ratio ≥ 1000, and curled fibers with a diameter of 50 to 2000 nm, and a curling rate of 10 to 40%.

[0010] Preferably, the curled interwoven structure density of the triaxially spun superelastic high temperature resistant composite carbon nanofiber aerogel is 100 to 1000 per cm 3, pore size is 1-5 μm, volume density is 5-200 mg / cm 3 , thickness is 2~50mm.

[0011] Preferably, the triaxially spun superelastic and high-temperature resistant composite carbon nanofiber aerogel has a temperature resistance limit of 1200-1350°C in an aerobic environment, and a thermal conductivity of 0.031-0.080W / (m·K) in an atmospheric environment at 300°C; the compressive strength of the composite carbon nanofiber aerogel is 170-1100kPa, the compression rebound rate is 98-100%, and the plastic deformation is ≤10% after 1000 loading-unloading compression cycles under 60% strain; the tensile breaking strength of the composite carbon nanofiber aerogel is 10-50kPa, and it can be fully recovered when the tensile strain is ≤150%, and the plastic deformation is ≤10% after 1000 loading-unloading stretching cycles under 50% strain.

[0012] The present invention also provides a method for preparing the above-mentioned triaxially spun superelastic and high-temperature resistant composite carbon nanofiber aerogel, comprising the following steps:

[0013] Step 1): dissolving polyacrylonitrile in a solvent and stirring thoroughly to prepare a polyacrylonitrile solution;

[0014] Step 2): fully stirring the inorganic source, solvent, spinning aid, and pH regulator to prepare a low water / alcohol ratio ceramic sol with rapid gelation reaction characteristics in the jet whipping drawing stage;

[0015] Step 3): Using a three-axis spinning needle, the polyacrylonitrile solution obtained in step 1) is used as the inner pipe spinning solution, which is ejected from the inner hole of the three-axis nozzle, and the ceramic sol obtained in step 2) is used as the middle pipe spinning solution, which is ejected through the middle hole. The inner layer polyacrylonitrile solution and the middle layer ceramic sol are merged at the nozzle of the three-axis spinning needle to obtain a spinning solution with compatibility in the initial spinning stage. At this time, the inner layer polyacrylonitrile solution will not undergo phase separation and solidification;

[0016] Step 4): The spinning solution obtained in step 3) is subjected to electrospinning. While the hydroxyl groups in the inorganic source of the middle ceramic sol are rapidly condensed, a temperature and humidity-controlled airflow is ejected through the outer hole of the triaxial structure spinning needle, so that the water content in the middle ceramic sol jet is at the level of phase separation of the inner polyacrylonitrile solution, thereby inducing the spinning solution to become incompatible. The inner polyacrylonitrile solution jet and the middle ceramic sol jet are rapidly and prematurely solidified to form core-shell structured curly fibers that are interwoven into a composite carbon nanofiber aerogel precursor.

[0017] Step 5): The composite carbon nanofiber aerogel precursor obtained in step 4) is placed in a continuous calcination furnace for atmosphere-changing, microwave-assisted rapid thermal treatment. After an oxygen atmosphere pre-oxidation stage and an oxygen-deficient atmosphere microwave-assisted rapid ceramicization and carbonization stage, a densified oxide ceramic shell layer is obtained while preventing oxygen molecules from penetrating into the core layer carbon fibers, thereby preparing a super-elastic and high-temperature resistant composite carbon nanofiber aerogel.

[0018] Preferably, in step 1), the concentration of polyacrylonitrile in the polyacrylonitrile solution is 5 to 20 wt%; the solvent is N,N-dimethylformamide; the stirring rate is 120 to 1000 rpm, and the stirring time is 2 to 10 h.

[0019] Preferably, in step 2), the inorganic source includes tetraethyl orthosilicate, vinyltriethoxysilane, titanium tetrachloride, tetrabutyl titanate, isopropyl titanate, tetraethyl titanate, titanyl sulfate, zirconium n-propoxide, zirconium n-butoxide, zirconyl nitrate, zirconium oxychloride octahydrate, zirconium acetylacetonate, zirconium chloride, zirconium acetate, aluminum powder, aluminum isopropoxide, aluminum nitrate nonahydrate, aluminum chloride hexahydrate, aluminum acetylacetonate, stannous chloride dihydrate, tin tetrachloride, tributyltin chloride, stannous sulfate, antimony pentachloride, antimony trichloride, antimony acetate, lanthanum acetylacetonate, lanthanum oxide. , lanthanum chloride, lanthanum nitrate, lanthanum acetate, neodymium nitrate hexahydrate, neodymium chloride, neodymium acetate, neodymium sulfate octahydrate, manganese acetylacetonate, manganese chloride, manganese acetate, manganese carbonate, manganese sulfate monohydrate, manganese chloride tetrahydrate, iron powder, ferric acetylacetonate, ferrocene, ferric chloride, ferric nitrate nonahydrate, cerium ammonium nitrate, cerium chloride heptahydrate, cerium chloride, cerium carbonate, cerium acetate, cerium oxalate, praseodymium nitrate, praseodymium chloride, cobalt acetate, cobalt sulfate heptahydrate, cobalt oxalate, cobalt acetylacetonate, cobalt nitrate hexahydrate, cobalt chloride hexahydrate, copper powder, copper citrate, acetic acid monohydrate Any one or more of copper, copper tartrate, copper nitrate trihydrate, copper sulfate pentahydrate, chromium acetate, chromium sulfate, chromium nitrate nonahydrate, chromium trichloride hexahydrate, zinc chloride, zinc nitrate hexahydrate, zinc phosphate hexahydrate, zinc acetylacetonate, zinc sulfate monohydrate, zinc acetate dihydrate or zinc sulfate heptahydrate; the solvent includes any one or more of deionized water, methanol, ethanol, propanol, N,N-dimethylformamide, N,N-dimethylacetamide, acetone or acetylacetone; the spinning aid includes polyvinyl pyrrolidone, polyvinyl alcohol , polyethylene oxide, polyvinyl acetate or polyurethane; the pH regulator includes any one or more of formic acid, acetic acid, hydrochloric acid, sulfuric acid, nitric acid, sodium hydroxide, potassium hydroxide or ammonia water; the concentration of the inorganic source is 5 to 70wt%; the water / alcohol ratio is 1:10 to 1:3; the concentration of the spinning aid is 0.1 to 5wt%; the concentration of the pH regulator is 1 to 10wt%; the stirring rate is 120 to 1000rpm, and the stirring time is 2 to 10h.

[0020] Preferably, in step 3), the pore size of the inner layer pipe of the triaxial structure spinning needle is 0.1-1 mm, and the pore size of the middle layer pipe is 0.5-1.5 mm; the inner layer polyacrylonitrile solution and the middle layer ceramic sol are quantitatively introduced through two pumps respectively, with a flow rate of 1-100 ml / h and a flow ratio of 1:10-1:1.

[0021] Preferably, in step 4), the aperture of the outer layer pipe of the triaxial structure spinning needle is 1 to 2.5 mm, the temperature of the outer hole jet air flow is 20 to 35°C, and the air flow humidity is 30 to 60%; the electrospinning environment temperature is 20 to 35°C, and the ambient humidity is 30 to 60%; the electrospinning process parameters are: voltage is 5 to 100 kV, and the receiving distance is 5 to 50 cm.

[0022] Preferably, in step 5), the temperature of the oxygen atmosphere pre-oxidation stage is 180-300°C, and the holding time is 60-120 min; the inert atmosphere in the oxygen-deficient atmosphere microwave-assisted rapid ceramicization and carbonization stage is nitrogen or argon, and the volume concentration of oxygen is 0.5-5%; the microwave-assisted rapid thermal treatment is microwave heating treatment or microwave plasma thermal treatment, and the temperature is raised to a high temperature of 400-1350°C at a heating rate of 1-10°C / min, and the holding time at high temperature is 60-120 min.

[0023] The principles of the present invention are as follows:

[0024] The present invention adopts triaxial spinning technology to prepare super-elastic and high-temperature resistant composite carbon nanofiber aerogel, wherein the inner layer of the three-layer coaxial spinning nozzle is a polyacrylonitrile solution, the middle layer is a ceramic sol, and the outer layer is a temperature and humidity controllable airflow jet layer. Since the water content in the hydrolysis-condensation reaction of the middle-layer ceramic sol will affect the compatibility of the inner-layer polyacrylonitrile solution, and then determine the phase separation solidification rate and solidification site of the inner-layer polyacrylonitrile solution, it has an important influence on the smooth progress of spinning and the structure of the obtained fiber material. Therefore, the present invention adopts a two-step water content control method to adjust the water content of the middle-layer ceramic sol in stages to control the phase separation solidification rate and site of the inner-layer polyacrylonitrile solution at different stages of triaxial spinning, thereby ensuring the integrity of the fiber core-shell structure and the formation of the highly curled interwoven structure of the fiber material. The first step involves controlling the water content of the ceramic sol. During the initial spinning phase, the water content of the middle ceramic sol is reduced to a low threshold, below the level required for complete hydrolysis of the alkoxide. Simultaneously, the proportion of alcohol solution in the middle ceramic sol is increased, increasing the hydroxyl storage capacity within the sol. This results in a ceramic sol that is compatible with the inner polyacrylonitrile solution and rapidly solidifies during the whipping and stretching phase. The second step involves controlling the water content of the ceramic sol jet. By injecting a temperature- and humidity-controlled airflow close to the surface of the ceramic sol, the water content of the jet, generated by the condensation of the different ceramic sols in the middle layer, is further adjusted to a level that allows for rapid phase separation and solidification of the inner polyacrylonitrile solution. This results in poor compatibility with the inner polyacrylonitrile solution, and both the inner and middle jets of the spinning solution rapidly and prematurely solidify, resulting in a composite carbon nanofiber aerogel precursor. This composite carbon nanofiber aerogel precursor undergoes a variable-atmosphere, rapid, and continuous heat treatment to produce the final product.

[0025] The complete core-shell structure of the curled single fibers and the highly interwoven three-dimensional network between them achieved in this invention are key to the superelasticity and high-temperature resistance of the composite carbon nanofiber aerogel. First, in the first step, when controlling the water content of the middle ceramic sol, the water / alcohol ratio influences the compatibility of the inner polyacrylonitrile solution when the spinning solutions merge, determining whether the initial spinning process can proceed smoothly. When the water / alcohol ratio in the ceramic sol is high, a large amount of water in the sol quickly diffuses into the inner polyacrylonitrile solution, causing the compatibility of the polyacrylonitrile solution to decrease rapidly, triggering the phase separation of the inner solution at the nozzle, causing the needle to be blocked, and affecting the spinning efficiency; when the water / alcohol ratio of the middle ceramic sol is at a low threshold, its internal water content is moderate, and the water molecules can participate in the full hydrolysis-condensation of the ceramic sol while not triggering the phase separation of the inner polyacrylonitrile solution, ensuring that the compatibility of the polyacrylonitrile solution is improved when the spinning solution converges at the nozzle, and the initial spinning can proceed smoothly; when the water / alcohol ratio of the middle ceramic sol further decreases, the water content inside the sol is insufficient, and after the middle ceramic sol and the inner polyacrylonitrile solution converge at the nozzle, they are easily directly transformed into a mixed spinning solution, and the obtained fiber does not have a core-shell structure.

[0026] In the second step of regulating the water content of the ceramic sol jet, based on the differences in water production in the condensation reactions of different ceramic sol systems, a temperature and humidity-controlled airflow is further sprayed through the outermost nozzle to finely regulate the water content in the middle-layer ceramic sol jet, thereby affecting the compatibility of the inner-layer polyacrylonitrile solution and controlling the phase separation and solidification rate and location of the inner-layer polyacrylonitrile solution during the jet whipping and stretching process to ensure the formation of curled fibers and their interwoven structures. When the middle layer ceramic sol system condenses and produces too much water, although the compatibility of the inner layer polyacrylonitrile solution decreases and the solidification rate of the inner layer polyacrylonitrile solution accelerates, due to the excessive amount of water, the solvent evaporation rate of the entire jet is slow, and the jet is continuously subjected to the electric field force in the axial direction, resulting in the curling structure being slowly stretched, the degree of fiber curling is reduced, and a highly interwoven elastic network connection structure cannot be formed between the fibers. At this time, the high-temperature airflow sprayed through the outermost nozzle will cause the excessive water produced by condensation to evaporate quickly, ensuring that the fiber curling shape is maintained; when the middle layer ceramic sol system condenses and produces moderate water, the inner and middle layer jets of the spinning solution are quickly and prematurely solidified, The jet can undergo sufficient whipping and stretching while flying in the spinning area, while retaining its curled shape during the violent whipping process, thereby obtaining a nanofiber aerogel precursor composed of highly interwoven curled fibers; when the middle layer ceramic sol system condenses and produces too little water, the inner layer polyacrylonitrile solution has a certain compatibility, and the inner layer polyacrylonitrile spinning liquid jet solidification rate is slow, then the overall spinning liquid jet solidification site is delayed, and due to insufficient jet whipping and stretching, straight fibers are obtained, and an elastic network connection structure of interwoven curled fibers cannot be formed. At this time, low-temperature moisture can be sprayed through the outermost nozzle to make up for the insufficient water production of the middle layer ceramic sol condensation, thereby ensuring the curling and forming of the fibers.

[0027] The high-temperature heat treatment stage in the present invention needs to carry out microwave-assisted rapid ceramicization and carbonization under an oxygen-poor atmosphere, which is the key to ensuring that the fiber shell oxide ceramics are dense and defect-free and the core carbon is not easily oxidized. When the oxygen concentration is too high, although the oxygen atmosphere releases heat after combustion, which is conducive to breaking through the energy barrier and promoting grain growth, the oxygen negative ion concentration at the grain boundary increases continuously during the heat treatment, which can cause the grain boundary movement speed to accelerate. Therefore, an inert atmosphere such as nitrogen and argon is introduced to form an oxygen-poor atmosphere with a low oxygen concentration, which avoids the increase of excessive growth of grain size and fiber pore defects, thereby covering the fiber surface with a dense oxide ceramic protective shell. In addition, when the heat treatment speed is too slow, oxygen molecules easily penetrate into the core carbon fiber, causing oxidation of carbon fiber and reducing the temperature resistance of fiber. By microwave-assisted heat treatment technology, the volume diffusion mode of grains is converted to grain boundary diffusion. Since the grain boundary diffusion activation energy is lower, the densification heat treatment speed is improved, and the core carbon fiber oxidation caused by long-term heat treatment is avoided.

[0028] The composite carbon nanofiber aerogel obtained by the present invention has a highly elastic curled morphology, and when subjected to tensile and compressive stress, it can dissipate external stress through the elongation and torsional deformation of the curled fiber structure, and return to its original shape after the stress is removed. The rich interwoven structure between the curled fibers allows the fibers to slip, but limits the fiber slippage. At the same volume density, the material has better compression and tensile mechanical properties, avoiding thermal protection failure caused by structural collapse after stress. At the same time, the composite carbon nanofiber aerogel has excellent oxidation resistance and temperature resistance, which improves the practical applicability of carbon nanofiber aerogel in high-temperature thermal protection fields such as aircraft.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) The triaxially spun superelastic high-temperature resistant composite carbon nanofiber aerogel and its preparation method of the present invention are universal, simple and easy to operate, and have a continuous process. They can be obtained by using the corresponding spinning solution on existing electrospinning production equipment and regulating the spinning process.

[0031] (2) The triaxially spun superelastic high-temperature resistant composite carbon nanofiber aerogel prepared by the present invention has excellent elasticity and oxidation resistance. It has stronger resistance to aerodynamic thermal shock in extreme temperature environments and higher temperature resistance limit in aerobic environments, which can meet the application requirements of carbon nanofiber aerogel in the field of high-temperature thermal protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A flow chart of the preparation method of the triaxially spun superelastic and high-temperature resistant composite carbon nanofiber aerogel provided by the present invention;

[0033] Figure 2 This is an electron microscope image of a coiled fiber with a carbon core and an oxide ceramic shell prepared in Example 1;

[0034] Figure 3 This is a physical photo of the triaxially spun superelastic and high-temperature resistant composite carbon nanofiber aerogel prepared in Example 1. DETAILED DESCRIPTION

[0035] To make the present invention more clearly understood, preferred embodiments are described in detail below with reference to the accompanying drawings.

[0036] Example 1

[0037] A method for preparing triaxially spun superelastic and high-temperature resistant composite carbon nanofiber aerogel comprises the following steps:

[0038] Step 1): dissolving polyacrylonitrile in N,N-dimethylformamide and stirring thoroughly (stirring rate 120 rpm, stirring time 2 h) to prepare a polyacrylonitrile solution, wherein the concentration of the polyacrylonitrile is 5 wt%;

[0039] Step 2): tetraethyl orthosilicate (an inorganic source), deionized water and methanol (a solvent), polyvinyl pyrrolidone (a spinning aid), and formic acid (a pH regulator) were mixed and stirred thoroughly (stirring speed: 120 rpm, stirring time: 2 h) to prepare a ceramic sol, wherein the inorganic source concentration was 5 wt%, the water / alcohol ratio was 1:10, the spinning aid concentration was 0.1 wt%, and the pH regulator concentration was 1 wt%;

[0040] Step 3): The polyacrylonitrile solution obtained in step 1) and the ceramic sol obtained in step 2) are respectively introduced into the inner layer pipe and the middle layer pipe of the triaxial structure spinning needle (the inner layer pipe pore diameter is 0.1 mm, the inner layer pipe flow rate is 1 ml / h, the middle layer pipe pore diameter is 0.5 mm, the middle layer pipe flow rate is 10 ml / h, and the flow ratio is 1:10). The inner layer polyacrylonitrile solution and the middle layer ceramic sol are merged at the nozzle of the triaxial spinning needle to form a spinning solution with compatibility in the initial spinning stage;

[0041] Step 4): The spinning solution obtained in step 3) is subjected to electrospinning, and the outer pipe of the triaxial structure spinning needle sprays an airflow with controllable temperature and humidity (the outer pipe aperture is 1 mm, the airflow temperature is 20°C, and the airflow humidity is 30%). The water content in the middle layer ceramic sol jet is at the phase separation level of the inner layer polyacrylonitrile solution, and the spinning solution is rapidly transformed into an incompatible state. The inner layer polyacrylonitrile solution jet and the middle layer ceramic sol jet are quickly and prematurely solidified to form core-shell structured curly fibers that are interwoven into a composite carbon nanofiber aerogel precursor. The electrospinning environment temperature is 20°C and the ambient humidity is 30%. The electrospinning process parameters are: voltage 5kV, receiving distance 5cm;

[0042] Step 5): The composite carbon nanofiber aerogel precursor obtained in step 4) is placed in a continuous calcination furnace for atmosphere change and microwave-assisted rapid thermal treatment, and undergoes an oxygen atmosphere pre-oxidation stage (temperature 180°C, holding time 60 minutes), and an oxygen-deficient atmosphere microwave-assisted rapid ceramicization and carbonization stage (the inert atmosphere is nitrogen, the volume concentration of oxygen is 0.5%, and the microwave-assisted rapid thermal treatment is microwave heating treatment, heating to a high temperature of 400°C at a heating rate of 1°C / min, and maintaining the high temperature for 60 minutes) to prepare a super-elastic and high-temperature resistant composite carbon nanofiber aerogel.

[0043] The composite carbon nanofiber aerogel uses curled fibers with a core layer of carbon and a shell layer of oxide ceramic as building blocks, and the curled fibers are interwoven to form an elastic network connection structure.

[0044] The composite carbon nanofiber aerogel consists of a carbon core layer, a continuous and uniform surface covered with a 30nm thick oxide ceramic protective shell layer, an aspect ratio of ≥1000, and a 120nm diameter curly fiber with a curvature of 10%. The curly interwoven structure density of the composite carbon nanofiber aerogel is 100 per cm 3 , pore size 5μm, volume density 16mg / cm 3 , thickness 20mm.

[0045] The composite carbon nanofiber aerogel has a temperature resistance limit of 1200°C in an aerobic environment, and a thermal conductivity of 0.050W / (m·K) in an atmospheric environment at 300°C; the composite carbon nanofiber aerogel has a compressive strength of 270kPa, a compression rebound rate of 98%, and a plastic deformation of ≤10% after 1000 loading-unloading compression cycles at 60% strain; the composite carbon nanofiber aerogel has a tensile fracture strength of 15kPa, can fully recover when the tensile strain is 50%, and a plastic deformation of ≤10% after 1000 loading-unloading stretching cycles at 50% strain.

[0046] Example 2

[0047] A method for preparing triaxially spun superelastic and high-temperature resistant composite carbon nanofiber aerogel comprises the following steps:

[0048] Step 1): dissolving polyacrylonitrile in N,N-dimethylformamide and stirring thoroughly (stirring rate 1000 rpm, stirring time 10 h) to prepare a polyacrylonitrile solution, wherein the concentration of the polyacrylonitrile is 20 wt%;

[0049] Step 2): Mixing an inorganic source of titanium tetrachloride, solvents of deionized water and ethanol, a spinning aid of polyvinyl alcohol, and a pH regulator of hydrochloric acid, and stirring thoroughly (stirring speed 1000 rpm, stirring time 10 hours) to prepare a ceramic sol, wherein the inorganic source concentration is 70 wt%, the water / alcohol ratio is 1:3, the spinning aid concentration is 5 wt%, and the pH regulator concentration is 10 wt%;

[0050] Step 3): The polyacrylonitrile solution obtained in step 1) and the ceramic sol obtained in step 2) are respectively introduced into the inner layer pipe and the middle layer pipe of the triaxial structure spinning needle (the inner layer pipe pore diameter is 1 mm, the inner layer pipe flow rate is 100 ml / h, the middle layer pipe pore diameter is 1.5 mm, the middle layer pipe flow rate is 100 ml / h, and the flow ratio is 1:1). The inner layer polyacrylonitrile solution and the middle layer ceramic sol are merged at the nozzle of the triaxial spinning needle to form a compatible spinning solution for the initial spinning stage;

[0051] Step 4): The spinning solution obtained in step 3) is subjected to electrospinning, and the outer layer pipe of the triaxial structure spinning needle sprays an airflow with controllable temperature and humidity (the outer layer pipe aperture is 2.5 mm, the airflow temperature is 35°C, and the airflow humidity is 60%). The water content in the middle layer ceramic sol jet is at the phase separation level of the inner layer polyacrylonitrile solution, and the spinning solution is rapidly transformed into an incompatible state. The inner layer polyacrylonitrile solution jet and the middle layer ceramic sol jet are quickly and prematurely solidified to form core-shell structured curly fibers that are interwoven into a composite carbon nanofiber aerogel precursor; the electrospinning environment temperature is 35°C and the ambient humidity is 60%; the electrospinning process parameters are: voltage 100 kV, receiving distance 50 cm;

[0052] Step 5): The composite carbon nanofiber aerogel precursor obtained in step 4) is placed in a continuous calcination furnace for atmosphere change and microwave-assisted rapid thermal treatment. After an oxygen atmosphere pre-oxidation stage (temperature 300°C, holding time 120 min), and an oxygen-deficient atmosphere microwave-assisted rapid ceramicization and carbonization stage (the inert atmosphere is nitrogen, the volume concentration of oxygen is 5%, and the microwave-assisted rapid thermal treatment is microwave plasma heat treatment, heating to a high temperature of 1350°C at a heating rate of 10°C / min, and maintaining time at high temperature for 120 min), a super-elastic and high-temperature resistant composite carbon nanofiber aerogel is prepared.

[0053] The composite carbon nanofiber aerogel uses curled fibers with a core layer of carbon and a shell layer of oxide ceramic as building blocks, and the curled fibers are interwoven to form an elastic network connection structure.

[0054] The composite carbon nanofiber aerogel consists of a carbon core layer, a 200nm-thick oxide ceramic protective shell layer continuously and evenly covered on the surface, and is composed of curly fibers with an aspect ratio of ≥1500 and a diameter of 2000nm. The curly fiber curvature is 40%. The curly interwoven structure density of the composite carbon nanofiber aerogel is 1000 / cm 3 , pore size 1 μm, volume density 200 mg / cm 3 , thickness 50mm.

[0055] The composite carbon nanofiber aerogel has a temperature resistance limit of 1350°C in an aerobic environment and a thermal conductivity of 0.031W / (m·K) in an atmospheric environment at 300°C. The composite carbon nanofiber aerogel has a compressive strength of 1100kPa, a compression rebound rate of 100%, and a plastic deformation of ≤5% after 1000 loading-unloading compression cycles at 60% strain. The composite carbon nanofiber aerogel has a tensile fracture strength of 50kPa, can fully recover at a tensile strain of 150%, and a plastic deformation of ≤5% after 1000 loading-unloading stretching cycles at 50% strain.

[0056] Example 3

[0057] A method for preparing triaxially spun superelastic and high-temperature resistant composite carbon nanofiber aerogel comprises the following steps:

[0058] Step 1): dissolving polyacrylonitrile in N,N-dimethylformamide and stirring thoroughly (stirring rate 600 rpm, stirring time 6 h) to prepare a polyacrylonitrile solution, wherein the concentration of the polyacrylonitrile is 16 wt %;

[0059] Step 2): an inorganic source zirconium n-propoxide, solvents of deionized water, ethanol, N,N-dimethylformamide, a spinning aid polyethylene oxide, and a pH regulator sodium hydroxide were mixed and stirred thoroughly (stirring speed 600 rpm, stirring time 6 hours) to prepare a ceramic sol, wherein the inorganic source concentration was 40 wt%, the water / alcohol ratio was 1:5, the spinning aid concentration was 2.5 wt%, and the pH regulator concentration was 4 wt%;

[0060] Step 3): The polyacrylonitrile solution obtained in step 1) and the ceramic sol obtained in step 2) are respectively introduced into the inner layer pipe and the middle layer pipe of the triaxial structure spinning needle (the inner layer pipe pore diameter is 0.4 mm, the inner layer pipe flow rate is 1 ml / h, the middle layer pipe pore diameter is 1 mm, the middle layer pipe flow rate is 1 ml / h, and the flow ratio is 1:1). The inner layer polyacrylonitrile solution and the middle layer ceramic sol are merged at the nozzle of the triaxial spinning needle to form a compatible spinning solution in the initial spinning stage;

[0061] Step 4): The spinning solution obtained in step 3) is subjected to electrospinning, and the outer layer pipe of the triaxial structure spinning needle sprays an airflow with controllable temperature and humidity (the outer layer pipe aperture is 2mm, the airflow temperature is 25°C, and the airflow humidity is 45%). The water content in the middle layer ceramic sol jet is at the phase separation level of the inner layer polyacrylonitrile solution, and the spinning solution is rapidly transformed into an incompatible state. The inner layer polyacrylonitrile solution jet and the middle layer ceramic sol jet are quickly and prematurely solidified to form core-shell structured curly fibers that are interwoven into a composite carbon nanofiber aerogel precursor; the electrospinning environment temperature is 25°C and the ambient humidity is 50%; the electrospinning process parameters are: voltage 20kV, receiving distance 40cm;

[0062] Step 5): The composite carbon nanofiber aerogel precursor obtained in step 4) is placed in a continuous calcination furnace for atmosphere change and microwave-assisted rapid thermal treatment, and undergoes an oxygen atmosphere pre-oxidation stage (temperature 230°C, holding time 65 minutes), and an oxygen-deficient atmosphere microwave-assisted rapid ceramicization and carbonization stage (the inert atmosphere is nitrogen, the volume concentration of oxygen is 4%, and the microwave-assisted rapid thermal treatment is microwave heating treatment, heating to a high temperature of 900°C at a heating rate of 7°C / min, and maintaining time at high temperature for 65 minutes) to prepare a super-elastic and high-temperature resistant composite carbon nanofiber aerogel.

[0063] The composite carbon nanofiber aerogel uses curled fibers with a core layer of carbon and a shell layer of oxide ceramic as building blocks, and the curled fibers are interwoven to form an elastic network connection structure.

[0064] The composite carbon nanofiber aerogel consists of a carbon core layer, a 50nm-thick oxide ceramic protective shell layer continuously and evenly covered on the surface, and is composed of curly fibers with an aspect ratio of ≥2500 and a diameter of 1000nm. The curly fiber curvature is 27%. The curly interwoven structure density of the composite carbon nanofiber aerogel is 450 per cm 3 , pore size 3.6μm, volume density 141mg / cm 3 , thickness 28mm.

[0065] The composite carbon nanofiber aerogel has a temperature resistance limit of 1250°C in an aerobic environment and a thermal conductivity of 0.049W / (m·K) in an atmospheric environment at 300°C. The composite carbon nanofiber aerogel has a compressive strength of 300kPa, a compression rebound rate of 99%, and a plastic deformation of ≤7% after 1000 loading-unloading compression cycles at 60% strain. The composite carbon nanofiber aerogel has a tensile fracture strength of 46kPa, can fully recover at a tensile strain of 129%, and a plastic deformation of ≤8% after 1000 loading-unloading stretching cycles at 50% strain.

[0066] Example 4

[0067] A method for preparing triaxially spun superelastic and high-temperature resistant composite carbon nanofiber aerogel comprises the following steps:

[0068] Step 1): dissolving polyacrylonitrile in N,N-dimethylformamide and stirring thoroughly (stirring rate 400 rpm, stirring time 8 h) to prepare a polyacrylonitrile solution, wherein the concentration of the polyacrylonitrile is 10 wt%;

[0069] Step 2): The inorganic source aluminum isopropoxide, the solvents deionized water, methanol, acetone, the spinning aid polyvinyl acetate, and the pH regulator potassium hydroxide were mixed and stirred thoroughly (stirring speed 400 rpm, stirring time 8 hours) to prepare a ceramic sol, wherein the inorganic source concentration was 60 wt%, the water / alcohol ratio was 1:8, the spinning aid concentration was 3 wt%, and the pH regulator concentration was 6 wt%;

[0070] Step 3): The polyacrylonitrile solution obtained in step 1) and the ceramic sol obtained in step 2) are respectively introduced into the inner layer pipe and the middle layer pipe of the triaxial structure spinning needle (the inner layer pipe pore diameter is 0.7 mm, the inner layer pipe flow rate is 20 ml / h, the middle layer pipe pore diameter is 1.3 mm, the middle layer pipe flow rate is 60 ml / h, and the flow ratio is 1:3). The inner layer polyacrylonitrile solution and the middle layer ceramic sol are merged at the nozzle of the triaxial spinning needle to form a spinning solution with compatibility in the initial spinning stage;

[0071] Step 4): The spinning solution obtained in step 3) is subjected to electrospinning, and the outer pipe of the triaxial structure spinning needle sprays an airflow with controllable temperature and humidity (the outer pipe aperture is 2.2 mm, the airflow temperature is 30°C, and the airflow humidity is 55%). The water content in the middle ceramic sol jet is at the phase separation level of the inner polyacrylonitrile solution, and the spinning solution is rapidly transformed into an incompatible state. The inner polyacrylonitrile solution jet and the middle ceramic sol jet are rapidly and prematurely solidified to form core-shell structured curly fibers that are interwoven into a composite carbon nanofiber aerogel precursor. The electrospinning environment temperature is 30°C and the ambient humidity is 30%. The electrospinning process parameters are: voltage 90 kV, receiving distance 15 cm;

[0072] Step 5): The composite carbon nanofiber aerogel precursor obtained in step 4) is placed in a continuous calcination furnace for atmosphere change and microwave-assisted rapid thermal treatment, and undergoes an oxygen atmosphere pre-oxidation stage (temperature 280°C, holding time 100 min), and an oxygen-deficient atmosphere microwave-assisted rapid ceramicization and carbonization stage (the inert atmosphere is argon, the volume concentration of oxygen is 1%, and the microwave-assisted rapid thermal treatment is microwave heating treatment, heating to a high temperature of 960°C at a heating rate of 5°C / min, and maintaining the high temperature for 100 min) to prepare a super-elastic and high-temperature resistant composite carbon nanofiber aerogel.

[0073] The composite carbon nanofiber aerogel uses curled fibers with a core layer of carbon and a shell layer of oxide ceramic as building blocks, and the curled fibers are interwoven to form an elastic network connection structure.

[0074] The composite carbon nanofiber aerogel consists of a carbon core layer, a continuous and uniform surface covered with a 110nm thick oxide ceramic protective shell layer, and a length-to-diameter ratio of ≥3500. The fibers are 1800nm ​​in diameter and have a curling rate of 38%. The density of the curled interwoven structure of the composite carbon nanofiber aerogel is 700 per cm 3 , pore size 2.8μm, volume density 159mg / cm 3 , thickness 40mm.

[0075] The composite carbon nanofiber aerogel has a temperature resistance limit of 1300°C in an aerobic environment, and a thermal conductivity of 0.049W / (m·K) in an atmospheric environment at 300°C; the composite carbon nanofiber aerogel has a compressive strength of 720kPa, a compression rebound rate of 99%, and a plastic deformation of ≤6% after 1000 loading-unloading compression cycles at 60% strain; the composite carbon nanofiber aerogel has a tensile fracture strength of 47kPa, can fully recover at a tensile strain of 145%, and a plastic deformation of ≤7% after 1000 loading-unloading stretching cycles at 50% strain.

[0076] Comparative Example 1

[0077] Carbon nanofiber aerogel was prepared according to the method of Example 1, except that the water / alcohol ratio of the middle ceramic sol was 1:2. After the spinning process began, the needle became clogged, resulting in inability to continuously produce fibers. A small amount of the resulting carbon nanofiber material was collected and subjected to a rapid, continuous heat treatment with a variable atmosphere.

[0078] The carbon nanofibers obtained in this example have an aspect ratio of 1000, a diameter of 2300 nm, an oxide ceramic protective shell thickness of 250 nm, a curling rate of 4%, and a curling interwoven structure density of 15 / cm 3 The obtained carbon nanofiber material has a pore size of 6 μm and a volume density of 205 mg / cm 3 , material thickness of 0.5mm, temperature resistance limit in an aerobic environment of 300°C, thermal conductivity in an atmospheric environment at 300°C of 0.085W / (m·K), compressive strength of 50kPa, compression rebound rate of 45%, plastic deformation ≤22% after 1000 load-unload compression cycles at 60% strain, tensile fracture strength of 1kPa, complete recovery at a tensile strain of 10%, and plastic deformation ≤25% after 1000 load-unload stretching cycles at 50% strain. This comparative example shows that under the condition of a ceramic sol water / alcohol ratio of 1:2, the compatibility of the inner polyacrylonitrile solution decreases rapidly due to the excessive water content within the sol. The inner solution undergoes phase separation at the nozzle, polymer enrichment and precipitation, resulting in clogging of the spinning needle, affecting spinning continuity and production efficiency.

[0079] Comparative Example 2

[0080] A carbon nanofiber aerogel was prepared according to the method of Example 1, except that the water / alcohol ratio of the middle ceramic sol was 1:11, resulting in a carbon nanofiber aerogel precursor without a core-shell structure. The collected carbon nanofiber aerogel precursor without a core-shell structure was subjected to a variable atmosphere, rapid, continuous heat treatment.

[0081] The carbon nanofibers obtained in this example have an aspect ratio of 1000, a diameter of 2200 nm, an oxide ceramic protective shell thickness of 300 nm, a curling rate of 1%, and a curling interwoven structure density of 10 / cm 3 The obtained carbon nanofiber material has a pore size of 6 μm and a volume density of 205 mg / cm 3The material thickness is 1mm, the temperature resistance limit in an aerobic environment is 300°C, the thermal conductivity in an atmospheric environment at 300°C is 0.089W / (m·K), the compressive strength is 65kPa, the compression rebound rate is 55%, the plastic deformation after 1000 load-unload compression cycles at 60% strain is ≤20%, the tensile fracture strength is 3kPa, the tensile strain can be completely recovered at 15%, and the plastic deformation after 1000 load-unload stretching cycles at 50% strain is ≤23%. This comparative example shows that when the water / alcohol ratio of the ceramic sol is 1:11, the water content in the sol is insufficient. After the middle ceramic sol and the inner polyacrylonitrile solution merge at the needle nozzle, they directly become a mixed spinning solution, and the resulting fiber does not have a core-shell structure. Therefore, when the water / alcohol ratio of the middle ceramic sol is too low, the composite carbon nanofiber aerogel with the desired properties of the present invention cannot be obtained.

[0082] Comparative Example 3

[0083] A carbon nanofiber aerogel was prepared according to the method of Example 1, except that the temperature of the airflow ejected from the outer orifice of the triaxial spinning needle was 15°C and the humidity was 65%. A composite carbon nanofiber aerogel precursor composed of low-crimp fibers was obtained. The collected composite carbon nanofiber aerogel precursor composed of low-crimp fibers was subjected to a variable atmosphere, rapid, continuous heat treatment.

[0084] The carbon nanofibers obtained in this example have an aspect ratio of 1100, a diameter of 2100 nm, an oxide ceramic protective shell thickness of 350 nm, a curling rate of 5%, and a curling interwoven structure density of 40 per cm. 3 The obtained carbon nanofiber material has a pore size of 5.5 μm and a volume density of 210 mg / cm 3 , the material thickness is 1.5mm, the temperature resistance limit in an aerobic environment is 300℃, the thermal conductivity in an atmospheric environment at 300℃ is 0.081W / (m·K), the compressive strength is 80kPa, the compression rebound rate is 90%, the plastic deformation after 1000 loading-unloading compression cycles at 60% strain is ≤13%, the tensile fracture strength is 7kPa, it can be fully recovered at a tensile strain of 40%, and the plastic deformation after 1000 loading-unloading stretching cycles at 50% strain is ≤17%. It can be seen from this comparative example that under the conditions that the temperature of the air flow jetted from the outer hole of the triaxial structure spinning needle is 15°C and the air flow humidity is 65%, due to the excessive water content of the outer air flow, the compatibility of the inner polyacrylonitrile solution decreases. Although the solidification rate of the inner solution jet is accelerated, the overall spinning liquid jet has a high water content and the solvent evaporation rate is slow. Therefore, the jet solidification site is delayed, the fiber curvature is reduced, and a highly curled and interwoven elastic network connection structure cannot be formed between the fibers. The obtained material has poor elasticity compared to Example 1 and does not meet the requirements for the material developed in the present invention.

[0085] Comparative Example 4

[0086] A carbon nanofiber aerogel was prepared according to the method of Example 1, except that the temperature of the airflow ejected from the outer orifice of the triaxial spinning needle was 40°C and the humidity was 25%. A composite carbon nanofiber aerogel precursor composed of straight fibers was obtained. The collected composite carbon nanofiber aerogel precursor composed of straight fibers was subjected to a variable atmosphere, rapid, continuous heat treatment.

[0087] The carbon nanofibers obtained in this embodiment have an aspect ratio of 1100, a diameter of 2200 nm, an oxide ceramic protective shell thickness of 300 nm, a curling rate of 4%, and a curling interwoven structure density of 10 / cm 3 The obtained carbon nanofiber material has a pore size of 5.5 μm and a volume density of 205 mg / cm 3 , the material thickness is 1mm, the temperature resistance limit in an aerobic environment is 300℃, the thermal conductivity in the atmospheric environment at 300℃ is 0.082W / (m·K), the compressive strength is 70kPa, the compression rebound rate is 80%, the plastic deformation after 1000 loading-unloading compression cycles at 60% strain is ≤17%, the tensile fracture strength is 5kPa, it can be fully recovered at a tensile strain of 29%, and the plastic deformation after 1000 loading-unloading stretching cycles at 50% strain is ≤20%. From this comparative example, it can be seen that under the conditions that the temperature of the jet air flow from the outer hole of the triaxial structure spinning needle is 40°C and the humidity of the air flow is 25%, due to the small amount of water in the outer air flow, the inner polyacrylonitrile solution has a certain compatibility, and the jet solidification rate of the inner polyacrylonitrile solution is slow, then the overall spinning liquid jet solidification site is delayed, and due to insufficient jet whipping and stretching, straight fibers are obtained. The carbon nanofiber aerogel precursor constructed by the straight fibers has an interlaced stacking structure, resulting in poor uniformity of the material, easy stratification and other problems. The obtained material has poor elasticity compared to Example 1, and does not meet the requirements for the preparation of the material of the present invention.

Claims

1. A triaxially spun superelastic high temperature resistant composite carbon nanofiber aerogel, characterized in that: The composite carbon nanofiber aerogel is constructed with curled fibers with a carbon core layer and an oxide ceramic shell layer as the building blocks. The curled fibers are interwoven to form an elastic network connection structure, and the curling rate of the curled fibers is 10-40%. The temperature resistance limit of the composite carbon nanofiber aerogel in an aerobic environment is 1200-1350°C, and the thermal conductivity in an atmospheric environment at 300°C is 0.031-0.080W / (m·K). The composite carbon nanofiber aerogel has a compressive strength of 170-1100kPa, a compression rebound rate of 98-100%, and a plastic deformation of ≤10% after 1000 loading-unloading compression cycles at 60% strain. The composite carbon nanofiber aerogel has a tensile fracture strength of 10-50kPa, can fully recover when the tensile strain is ≤150%, and a plastic deformation of ≤10% after 1000 loading-unloading stretching cycles at 50% strain.

2. The triaxially spun superelastic and high temperature resistant composite carbon nanofiber aerogel according to claim 1, characterized in that: The composite carbon nanofiber aerogel is composed of a carbon core layer, a surface continuously and evenly covered with an oxide ceramic protective shell layer with a thickness of 10-200 nm, and curled fibers with an aspect ratio of ≥1000 and a diameter of 50-2000 nm.

3. The triaxially spun superelastic and high temperature resistant composite carbon nanofiber aerogel according to claim 1, characterized in that: The density of the curled interwoven structure of the composite carbon nanofiber aerogel is 100 to 1000 per cm 3 , pore size is 1~5μm, volume density is 5~200mg / cm 3 , thickness is 2~50mm.

4. The method for preparing the triaxially spun superelastic and high temperature resistant composite carbon nanofiber aerogel according to any one of claims 1 to 3, characterized in that: The following steps are involved: Step 1): Dissolve polyacrylonitrile in a solvent and stir thoroughly to prepare a polyacrylonitrile solution; Step 2): The inorganic source, solvent, spinning aid, and pH regulator are fully stirred to prepare a ceramic sol having a rapid gelation reaction characteristic in the jet whipping drawing stage; Step 3): Using a three-axis spinning needle, the polyacrylonitrile solution obtained in step 1) is used as the inner pipe spinning solution and is ejected from the inner hole of the three-axis nozzle. The ceramic sol obtained in step 2) is used as the middle pipe spinning solution and is ejected through the middle hole. The inner layer polyacrylonitrile solution and the middle layer ceramic sol are merged at the nozzle of the three-axis spinning needle to obtain a spinning solution with compatibility in the initial spinning stage. At this time, the inner layer polyacrylonitrile solution will not undergo phase separation and solidification; Step 4): The spinning solution obtained in step 3) is subjected to electrospinning. While the hydroxyl groups in the inorganic source of the middle-layer ceramic sol are rapidly condensed, a temperature and humidity-controlled airflow is ejected through the outer hole of the triaxial structure spinning needle, so that the water content in the middle-layer ceramic sol jet is at the phase separation level of the inner-layer polyacrylonitrile solution, inducing the spinning solution to become an incompatible state. The inner-layer polyacrylonitrile solution jet and the middle-layer ceramic sol jet are quickly and prematurely solidified to form core-shell structured curly fibers that are interwoven into a composite carbon nanofiber aerogel precursor; Step 5): The composite carbon nanofiber aerogel precursor obtained in step 4) is placed in a continuous calcination furnace for atmosphere-changing, microwave-assisted rapid thermal treatment. After an oxygen atmosphere pre-oxidation stage and an oxygen-deficient atmosphere microwave-assisted rapid ceramicization and carbonization stage, a densified oxide ceramic shell layer is obtained while preventing oxygen molecules from penetrating into the core layer carbon fibers to prepare an ultra-elastic and high-temperature resistant composite carbon nanofiber aerogel.

5. The preparation method according to claim 4, characterized in that In step 1), the concentration of polyacrylonitrile in the polyacrylonitrile solution is 5-20 wt %; the solvent is N,N-dimethylformamide; the stirring rate is 120-1000 rpm, and the stirring time is 2-10 h.

6. The preparation method according to claim 4, characterized in that In step 2), the inorganic source includes tetraethyl orthosilicate, vinyltriethoxysilane, titanium tetrachloride, tetrabutyl titanate, isopropyl titanate, tetraethyl titanate, titanyl sulfate, zirconium n-propoxide, zirconium n-butoxide, zirconyl nitrate, zirconium oxychloride octahydrate, zirconium acetylacetonate, zirconium chloride, zirconium acetate, aluminum powder, aluminum isopropoxide, aluminum nitrate nonahydrate, aluminum chloride hexahydrate, aluminum acetylacetonate, stannous chloride dihydrate, tin tetrachloride, tributyltin chloride, stannous sulfate, antimony pentachloride, antimony trichloride, antimony acetate, lanthanum acetylacetonate, lanthanum oxide, chloride Lanthanum, lanthanum nitrate, lanthanum acetate, neodymium nitrate hexahydrate, neodymium chloride, neodymium acetate, neodymium sulfate octahydrate, manganese acetylacetonate, manganese chloride, manganese acetate, manganese carbonate, manganese sulfate monohydrate, manganese chloride tetrahydrate, iron powder, ferric acetylacetonate, ferrocene, ferric chloride, ferric nitrate nonahydrate, cerium ammonium nitrate, cerium chloride heptahydrate, cerium chloride, cerium carbonate, cerium acetate, cerium oxalate, praseodymium nitrate, praseodymium chloride, cobalt acetate, cobalt sulfate heptahydrate, cobalt oxalate, cobalt acetylacetonate, cobalt nitrate hexahydrate, cobalt chloride hexahydrate, copper powder, copper citrate, copper acetate monohydrate, Any one or more of copper tartrate, copper nitrate trihydrate, copper sulfate pentahydrate, chromium acetate, chromium sulfate, chromium nitrate nonahydrate, chromium trichloride hexahydrate, zinc chloride, zinc nitrate hexahydrate, zinc phosphate hexahydrate, zinc acetylacetonate, zinc sulfate monohydrate, zinc acetate dihydrate or zinc sulfate heptahydrate; the solvent includes any one or more of deionized water, methanol, ethanol, propanol, N,N-dimethylformamide, N,N-dimethylacetamide, acetone or acetylacetone; the spinning aid includes polyvinyl pyrrolidone, polyvinyl alcohol, Any one or more of polyethylene oxide, polyvinyl acetate or polyurethane; the pH regulator includes any one or more of formic acid, acetic acid, hydrochloric acid, sulfuric acid, nitric acid, sodium hydroxide, potassium hydroxide or ammonia water; the concentration of the inorganic source is 5-70wt%; the water / alcohol ratio is 1:10-1:3; the concentration of the spinning aid is 0.1-5wt%; the concentration of the pH regulator is 1-10wt%; the stirring rate is 120-1000rpm, and the stirring time is 2-10h.

7. The preparation method according to claim 4, characterized in that In step 3), the inner layer pipe pore diameter of the triaxial structure spinning needle is 0.1-1 mm, and the middle layer pipe pore diameter is 0.5-1.5 mm; the inner layer polyacrylonitrile solution and the middle layer ceramic sol are quantitatively introduced through two pumps respectively, with a flow rate of 1-100 ml / h and a flow ratio of 1:10-1:

1.

8. The preparation method according to claim 4, characterized in that In step 4), the outer tube aperture of the triaxial structure spinning needle is 1-2.5 mm, the temperature of the outer hole jet air flow is 20-35°C, and the air flow humidity is 30-60%; the electrospinning environment temperature is 20-35°C, and the ambient humidity is 30-60%; the electrospinning process parameters are: voltage is 5-100 kV, and the receiving distance is 5-50 cm.

9. The preparation method according to claim 4, characterized in that In step 5), the temperature of the oxygen atmosphere pre-oxidation stage is 180-300°C, and the holding time is 60-120 minutes; the inert atmosphere in the oxygen-deficient microwave-assisted rapid ceramicization and carbonization stage is nitrogen or argon, and the volume concentration of oxygen is 0.5-5%; the microwave-assisted rapid thermal treatment is microwave heating treatment or microwave plasma thermal treatment, and the temperature is increased to a high temperature of 400-1350°C at a heating rate of 1-10°C / min, and the high temperature is maintained for 60-120 minutes.

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