Broadband wave-absorbing and heat-insulating type Si-C-N-based nanofiber membrane intercalation foamed ceramic as well as preparation method and application thereof

Abstract

The invention discloses broadband wave-absorbing and heat-insulating Si-C-N-based nanofiber membrane intercalated foamed ceramic as well as a preparation method and application thereof, and particularly relates to the field of foamed ceramic. Dipping organic foam in the ceramic slurry to obtain a dry foam blank, and cracking the dry foam blank to obtain Si-C-N-based foamed ceramic with a hollow skeleton structure; mixing the SiC phase precursor, polyimide and a spinning auxiliary agent in a solvent to obtain a spinning solution; performing spinning on the spinning solution to obtain a precursor nanofiber membrane, and performing ceramic treatment on the precursor nanofiber membrane to obtain a Si-C-N-based nanofiber membrane; a plurality of Si-C-N-based nanofiber membranes are sequentially arranged on the surface of Si-C-N-based foamed ceramic, and a layer of Si-C-N-based foamed ceramic is placed on the nanofiber membranes to form the nanofiber membrane intercalation foamed ceramic.

Description

Technical Field

[0001] The present application relates to the field of wave-absorbing and heat-insulating materials, and in particular to a broadband wave-absorbing and heat-insulating Si-CN based nanofiber membrane intercalated foam ceramic, and a preparation method and application thereof. Background Art

[0002] The rapid development of aerospace technology has created an urgent need for integrated high-temperature absorbing and thermal insulation materials. Porous structures, due to their excellent electromagnetic impedance matching characteristics and low solid-phase and convective heat transfer, are currently considered the most advantageous structures for achieving synergistic thermal insulation and absorption. Porous materials primarily include porous ceramics, aerogels, and nanofiber membranes. Porous ceramics, among others, possess rigidity and are resistant to strong stress impacts, holding great potential for application in aerospace. Foam ceramics, a type of porous ceramic with a high porosity (greater than 70%), offer excellent lightweight properties and good load-bearing capacity. Foam ceramics are typically produced using either a foaming or template method. The template method involves impregnating a porous template with a slurry, subjecting it to high-temperature treatment, and then removing the template. This creates a hollow structure similar to polar bear hair, offering advantages in thermal insulation. However, the large pores of commonly used organic foam templates enhance internal gas-phase heat conduction and convection, hindering thermal insulation. Furthermore, homogeneous ceramic foams are limited by their dispersion properties, making broadband absorption difficult, especially across low frequencies (typically 4 to 18 GHz). Consequently, existing ceramic foams cannot achieve both high-efficiency thermal insulation and broadband absorption while maintaining basic mechanical properties. Summary of the Invention

[0003] The main purpose of this application is to provide a broadband wave-absorbing and heat-insulating Si-CN based nanofiber membrane intercalated foam ceramic and its preparation method and application, aiming to solve the problem in the prior art that it is impossible to take into account both the requirements of high-efficiency heat insulation and broadband wave-absorbing performance while ensuring basic mechanical properties.

[0004] To achieve the above objectives, the present application provides a broadband wave-absorbing and heat-insulating Si-CN-based nanofiber membrane intercalated foam ceramic, comprising at least two foam ceramic layers, with a nanofiber membrane layer disposed between the two adjacent foam ceramic layers; wherein the foam ceramic layer is a Si-CN-based foam ceramic having a hollow skeleton structure; the nanofiber membrane layer comprises a plurality of periodically arranged nanofiber membranes, wherein the plurality of nanofiber membranes form a pattern; The preparation method of Si-CN based foam ceramics is as follows: immersing organic foam in ceramic slurry to obtain a foam dry blank, and cracking the foam dry blank to obtain Si-CN based foam ceramics; the preparation method of Si-CN based nanofiber membrane is as follows: mixing SiC phase precursor, polyimide and spinning aid in a solvent to obtain a spinning solution; spinning the spinning solution to obtain a precursor nanofiber membrane, and ceramicizing the precursor nanofiber membrane to obtain a Si-CN based nanofiber membrane.

[0005] Optionally, the spacing between each Si-CN based nanofiber membrane is 0-10 mm; the density of the Si-CN based nanofiber membrane intercalated foam ceramic is 0.3-0.5 g / cm 3 , compressive strength is 5-12 MPa, thermal insulation temperature is greater than or equal to 700℃, effective absorption frequency band is 4-18 GHz; the thickness of the foam ceramic layer is 3-10mm, and the thickness of the nanofiber membrane is 0.05-0.2mm.

[0006] To achieve the above-mentioned objectives, the present application also provides a method for preparing broadband wave-absorbing and heat-insulating Si-CN-based nanofiber membrane intercalated foam ceramics, comprising: preparing Si-CN-based foam ceramics and Si-CN-based nanofiber membranes; arranging multiple Si-CN-based nanofiber membranes in sequence on the surface of the Si-CN-based foam ceramics, and placing a layer of Si-CN-based foam ceramics on the nanofiber membranes to form an initial nanofiber membrane intercalated foam ceramics; keeping the initial nanofiber membrane intercalated foam ceramics at 800-1200°C for 100-300 h to obtain the nanofiber membrane intercalated foam ceramics.

[0007] Optionally, the preparation method of Si-CN based foam ceramics is: placing the foam dry blank in a silicon-based ceramic deposition furnace, heating the silicon-based ceramic deposition furnace to 800-1200°C, introducing gas, and keeping the temperature for 100-300 hours to obtain Si-CN based foam ceramics.

[0008] Optionally, the organic foam has a residual carbon rate of less than 5%, and its material is polyurethane, polyethylene or polypropylene.

[0009] Optionally, the ceramic slurry includes a ceramic component and graphene-modified carbon nanotubes, and the mass fraction of the graphene-modified carbon nanotubes in the ceramic component is 0~5%; the ceramic component includes the following components in terms of mass fraction: the mass fractions of ceramic powder, solvent, binder, dispersant, thickener, and defoaming agent are 30~40%, 40~60%, 1~5%, 0.1~2%, 0.5~3%, and 0.05~0.5%, respectively, and the sum of the mass fractions of the above components is 100%.

[0010] Optionally, the preparation method of graphene-modified carbon nanotubes includes: placing carbon nanotubes in a deposition furnace, heating the deposition furnace to 1040-1100° C., introducing a carbon source, and maintaining the temperature for 3-10 hours to obtain graphene-modified carbon nanotubes.

[0011] Optionally, in the spinning solution, the SiC phase precursor accounts for 7-12w% of the solvent; the spinning aid accounts for 3-5w% of the solvent; the polyimide accounts for 1-5w% of the solvent; the SiC phase precursor includes polycarbosilane or polyborocarbosilane; during the spinning process, the inner diameter of the spinning needle is 0.3-0.5 mm; the liquid output rate is 30-60 µL / min; the collection distance between the needle and the receiver is 16~20 cm; the DC positive voltage is 18~22 kV, and the negative voltage is -2~-4 kV.

[0012] Optionally, the ceramic treatment process is as follows: drying the precursor nanofiber membrane and curing it at 190-230 ° C for 1-2 h; placing the cured precursor nanofiber membrane in a tubular furnace, introducing a nitrogen atmosphere, and keeping it at 1300-1600 ° C for 1-5 h to obtain a Si-CN based nanofiber membrane.

[0013] To achieve the above objectives, the present application also provides an application of broadband wave-absorbing and heat-insulating Si-CN based nanofiber membrane intercalated foam ceramics in heat-insulating and wave-absorbing materials.

[0014] Compared with the prior art, the present invention has the following advantages: The broadband wave-absorbing and heat-insulating Si-CN based nanofiber membrane intercalated foam ceramic of the present invention uses a foam ceramic layer with a hollow skeleton structure as a dielectric layer, and intercalates the nanofiber membrane into the foam ceramic, which increases the number of reflections of electromagnetic waves, effectively enhances the resonance of electromagnetic waves, and broadens the effective absorption band of electromagnetic waves; the interlayer interface between the foam ceramic and the nanofiber membrane provides interface thermal resistance, increases heat scattering, and improves thermal insulation performance; the foam ceramic and the nanofiber membrane are both made of the Si-CN system, which has excellent temperature resistance, can be used for a long time at 1400°C and maintain stable structural functionality, thereby ensuring basic mechanical properties.

[0015] The method for preparing broadband wave-absorbing and heat-insulating Si-CN-based nanofiber membrane intercalated foam ceramics of the present invention adopts a CVD process to prepare a ceramic matrix with very good continuity and uniformity, and can connect dispersed ceramic particles to form a ceramic skeleton with strong bearing capacity; an organic foam with a low residual carbon rate is used as a template, and the template decomposes during the CVD process to form a hollow skeleton structure, which is conducive to multiple scattering of electromagnetic waves and phonons, and is very beneficial to wave absorption and heat insulation; the foam ceramics are prepared by slurry impregnation and CVD method, which has the advantages of large size and large-scale manufacturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a structural diagram of a broadband microwave-absorbing and heat-insulating Si-CN based nanofiber membrane intercalated foam ceramic in this application; Figure 2 This is a schematic flow chart of a method for preparing a broadband wave-absorbing and heat-insulating Si-CN based nanofiber membrane intercalated foam ceramic according to the present application; Figure 3 This is a distribution diagram of a broadband microwave-absorbing and heat-insulating Si-CN-based nanofiber membrane intercalated with foam ceramics in this application; Figure 4 The shape of the nanofiber membrane in the nanofiber membrane-intercalated foam ceramic obtained in Example 1 of the present application; Figure 5 These are macroscopic and microscopic photos of the foam ceramic obtained in Example 1 of the present application; Figure 6 These are macroscopic and microscopic photos of the nanofiber membrane obtained in Example 1 of the present application; Figure 7 These are macroscopic and microscopic photos of the nanofiber membrane intercalated ceramic foam obtained in Example 1 of the present application; Figure 8 This is an infrared photograph of the nanofiber membrane intercalation foam obtained in Example 1 of the present application under a ceramic butane spray gun; Figure 9 is the reflection loss curve of Example 5 of the present application; Figure 10 This is the reflection loss curve of the comparative example of this application.

[0017] The realization of the objectives, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0018] To make the objectives, technical solutions, and advantages of this application more clear, the technical solutions of this application will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

[0019] The first embodiment of the present invention provides a broadband wave absorbing and heat insulating Si-CN based nanofiber membrane intercalated foam ceramic, such as Figure 1As shown, it includes at least two foam ceramic layers, with a nanofiber membrane layer disposed between the two adjacent foam ceramic layers; wherein the foam ceramic layer is a Si-CN-based foam ceramic with a hollow skeleton structure; the nanofiber membrane layer includes multiple nanofiber membranes arranged in a periodic pattern. The spacing between each Si-CN-based nanofiber membrane is 0-10mm; the density of the Si-CN-based nanofiber membrane intercalated foam ceramic is 0.3-0.5 g / cm 3 , a compressive strength of 5-12 MPa, a thermal insulation temperature greater than or equal to 700°C, and an effective absorption frequency band of 4-18 GHz; the thickness of the ceramic foam layer is 3-10 mm, and the thickness of the nanofiber membrane is 0.05-0.2 mm. Furthermore, the number of ceramic foam layers is 2-10. Preferably, the spacing between the Si-CN-based nanofiber membranes is 9 mm, the thickness of the ceramic foam layer is 3.2 mm, and the thickness of the nanofiber membrane is 0.1 mm.

[0020] The second embodiment of the present invention provides a method for preparing a broadband wave absorbing and heat insulating Si-CN based nanofiber membrane intercalated foam ceramic, such as Figure 2 As shown, the specific steps include: Step S1, impregnating the organic foam in ceramic slurry to obtain a foam dry blank, and cracking the foam dry blank to obtain a Si-CN based foam ceramic; the specific process is as follows.

[0021] Step S11: placing carbon nanotubes into a deposition furnace, heating the deposition furnace to 1040-1100° C., introducing a carbon source, and maintaining the temperature for 3-10 hours to obtain graphene-modified carbon nanotubes; wherein the carbon source is methane, ethylene, or propylene.

[0022] Step S12: mixing ceramic powder, a binder, a dispersant, a thickener, and a defoaming agent in a solvent to obtain a mixture; adding graphene-modified carbon nanotubes to the mixture, and ball milling for 10 to 20 hours to obtain a ceramic slurry; wherein the mass fractions of the ceramic powder, solvent, binder, dispersant, thickener, and defoaming agent are 30 to 40%, 40 to 60%, 1 to 5%, 0.1 to 2%, 0.5 to 3%, and 0.05 to 0.5%, respectively, and the sum of the mass fractions of the above components is 100%; the mass fraction of the graphene-modified carbon nanotubes in the mixture is 0.2 to 5%.

[0023] Exemplarily, the ceramic powder includes SiC whiskers, SiC particles or Si particles, the length of the SiC whiskers is 5-10 μm, and the size of the SiC particles and Si particles is 1-3 μm; the solvent is water or dibutyl ketone; the binder is polyvinyl alcohol (PVA), polyacrylate (PAA) or carboxymethyl cellulose (CMC); the dispersant is polyammonium acrylate (NH4PAA) or tetramethylammonium hydroxide (TMAH); the thickener is polyacrylamide (PAM) or silica sol; and the defoaming agent is ethanol or isopropyl alcohol.

[0024] Step S13, impregnating the organic foam in a ceramic slurry to obtain a foam dry blank, and cracking the foam dry blank to obtain a Si-CN based foam ceramic; Specifically, in step S131, the organic foam is washed with deionized water and then dried, and placed in the ceramic slurry obtained in step S12. After repeated extrusion and dipping, excess slurry is squeezed out with a roller machine, and the foam is naturally dried in a dry environment at 30-40°C for 12 hours to obtain a foam dry blank; wherein the residual carbon rate of the organic foam is less than 5%, and the material thereof is polyurethane, polyethylene or polypropylene.

[0025] In step S132, the foam dry blank is placed in a silicon-based ceramic deposition furnace, the temperature of the silicon-based ceramic deposition furnace is raised to 800-1200°C, and gas is introduced, and the temperature is kept for 100-300 hours. The gas source is turned off, and the Si-CN-based foam ceramic is obtained after the temperature of the deposition furnace drops to room temperature.

[0026] Silicon-based ceramic deposition furnaces include Si3N4, SiC, SiCN, or SiBCN deposition furnaces. When the substrate of a silicon-based ceramic deposition furnace is Si3N4, the deposition process parameters are limited to: a deposition temperature of 900-1200°C, a deposition time of 120-200 hours, and the inlet gases are NH3, Ar, carrier gas H2, and reaction gas H2, with a controlled flow ratio of 7:10:8:4. The carrier gas H2 carries SiCl4.

[0027] When the substrate of the silicon-based ceramic deposition furnace is low-loss SiC, the deposition process parameters are limited to: deposition temperature of 900~1200 ℃, deposition time of 100~180 h, the inlet gas is Ar, carrier gas H2 and reaction gas H2, and the flow ratio is controlled at 2:1:6, in which the carrier gas H2 brings in CH3SiCl3 (MTS).

[0028] When the substrate of the silicon-based ceramic deposition furnace is SiCN, the deposition process parameters are limited to: deposition temperature of 800~1200℃, deposition time of 180~300 h, the gases introduced are C3H6, NH3, Ar, carrier gas H2 and reaction gas H2, and their flow ratio is controlled to be 4:6:12:150:20, among which carrier gas H2 brings in SiCl4.

[0029] When the substrate of the silicon-based ceramic deposition furnace is low-loss SiBCN, the deposition process parameters are limited to: deposition temperature of 900-1200 °C, deposition time of 180-300 h, the gases introduced are BCl3, NH3, Ar, carrier gas H2 and reaction gas H2, and their flow ratio is controlled to be 1:3:23:15:80, among which carrier gas H2 is brought into MTS.

[0030] In this embodiment, an organic foam with a low residual carbon rate is used as a template. During the CVD process, the template decomposes to form a hollow skeleton structure, which is conducive to the multiple scattering of electromagnetic waves and phonons, and is very beneficial for wave absorption and heat insulation. The ceramic matrix prepared by the CVD process has very good continuity and uniformity, and can connect the dispersed ceramic particles to form a ceramic skeleton with a strong load-bearing capacity. The organic foam manufacturing process is highly mature, making it low-cost, accessible, and highly reliable. The combination of slurry impregnation and CVD method to prepare foam ceramics has the advantages of large size and large-scale manufacturing. The G-CNTs in the ceramic slurry have stronger electrical conductivity than CNTs, which can greatly improve the electrical conductivity, thereby reducing their content in the slurry, improving the fluidity of the slurry, and ensuring the uniformity of impregnation. Step S2: Mixing a SiC precursor, a polyimide, and a spinning aid in a solvent to obtain a spinning solution (precursor solution); wherein the SiC precursor comprises polycarbosilane or polyboronocarbosilane, the SiC precursor accounts for 7-12% by weight of the solvent; the spinning aid accounts for 3-5% by weight of the solvent; and the polyimide accounts for 1-5% by weight of the solvent; the spinning aid is polyvinyl pyrrolidone, and the solvent is a mixture of chloroform and N,N-dimethylformamide; Specifically, chloroform and N,N-dimethylformamide are mixed in a mass ratio of 3-9:1 to obtain a solvent, a spinning aid, polycarbosilane and polyimide are added to the solvent in sequence and magnetic stirring is performed for 30-45 hours to obtain a spinning solution.

[0031] Step S3, electrospinning the spinning solution to obtain a precursor nanofiber membrane, and ceramicizing the precursor nanofiber membrane to obtain a Si-CN based nanofiber membrane; Specifically, in step S31, the spinning solution is poured into the needle tube, and a spinning needle with an inner diameter of 0.3-0.5 mm is equipped, and the needle is placed on a propeller with a liquid discharge rate of 30-60 μL / min; a certain DC voltage is applied to the needle and the flat receiver respectively, wherein the DC positive voltage is 18-22 kV and the negative voltage is -2~-4 kV. After the spinning solution is pushed out, it will be split and stretched into filaments under the action of the high voltage electric field and move to the flat receiver, wherein the collection distance between the needle and the receiver is 16-20 cm, and the precursor nanofiber membrane is collected.

[0032] In step S31, the precursor nanofiber membrane is dried at 80°C for 2 hours to ensure that the solvent is fully evaporated; then the temperature is increased to 190-230°C at a heating rate of 3-5°C / min and kept warm for 1-2 hours to complete the curing; thereafter, the cured precursor nanofiber membrane is placed in a tubular furnace, and a nitrogen atmosphere is introduced, and the temperature is increased to 1300-1600°C at a heating rate of 1-3°C / min and kept warm for 1-5 hours to complete the ceramic transformation to obtain a Si-CN based nanofiber membrane.

[0033] According to the above method, n layers of Si-CN based nanofiber membrane layers and n+1 layers of Si-CN based foam ceramics are prepared and assembled according to the method of step S4, as follows.

[0034] Step S4, as Figure 3 As shown in FIG, multiple Si-CN based nanofiber membranes are sequentially arranged on the surface of Si-CN based foam ceramics, and a layer of Si-CN based foam ceramics is placed on the nanofiber membranes to form nanofiber membrane intercalated foam ceramics. The Si-CN based nanofiber membranes are attached to the surface of Si-CN based foam ceramics by electrostatic adsorption; Figure 4 As shown, the Si-CN-based nanofiber membranes are shaped like centrosymmetric circles, squares, crosses, or square rings; multiple Si-CN-based nanofiber membranes are arranged in a periodic pattern on the surface of the Si-CN-based foam ceramic. When n is greater than 1, the Si-CN-based nanofiber membrane layers and Si-CN-based foam ceramic are stacked in the above manner to form a multilayer nanofiber membrane-intercalated foam ceramic.

[0035] In this embodiment, a low-loss, absorbing Si-CN-based ceramic foam serves as the dielectric layer. A low-resistance Si-CN-based nanofiber membrane, identical in composition to the Si-CN-based ceramic foam, serves as the resistive layer, creating a uniform three-dimensional conductive structure within the nanofiber membrane. Both the ceramic foam and the nanofiber membrane utilize the Si-CN system, which exhibits excellent temperature resistance and can withstand extended use at temperatures up to 1400°C while maintaining stable structural functionality. The nanofiber membrane is intercalated within the ceramic foam, increasing the number of electromagnetic wave reflections, effectively enhancing electromagnetic wave resonance and broadening the effective absorption band. The interface between the ceramic foam and the nanofiber membrane provides interfacial thermal resistance, increasing heat dissipation and improving thermal insulation performance.

[0036] Step S5: placing the nanofiber membrane intercalated foam ceramic in a mold, placing it in a deposition furnace, introducing gas, and keeping the temperature at 800-1200° C. for 100-300 h to obtain the final nanofiber membrane intercalated foam ceramic.

[0037] Example 1 Step S10, placing carbon nanotubes in a graphite crucible and placing it in a graphene deposition furnace, heating the deposition furnace to 1060° C., introducing methane, and keeping the temperature for 5 hours before turning off the gas. After the deposition furnace cools to room temperature, graphene-modified carbon nanotubes are obtained; Step S20, mixing SiC whiskers, deionized water, polyvinyl alcohol, tetramethylammonium hydroxide, and polyethylene glycol in mass fractions of 40%, 55%, 2%, 2%, and 1% in sequence to obtain a mixture; adding 2% by mass of graphene-modified carbon nanotubes to the mixture, and ball milling for 10 hours to obtain a ceramic slurry; Step S30: wash the polyurethane foam with a thickness of 5 mm with deionized water and then dry it, place it in the ceramic slurry, repeatedly squeeze and immerse it, squeeze out the excess slurry with a roller, and naturally dry it in a dry environment at 35°C for 12 hours to obtain a foam dry blank; place the foam dry blank in a CVD Si3N4 ceramic deposition furnace, heat the silicon-based ceramic deposition furnace to 1000°C, and simultaneously introduce NH3, Ar, carrier gas H2 and reaction gas H2, and control their flow ratio to be 7:10:8:4, wherein the carrier gas H2 carries SiCl4. After keeping the temperature for 150 hours, turn off the gas source, and wait until the deposition furnace temperature drops to room temperature to obtain a Si-CN-based foam ceramic with a thickness of 5 mm. Figure 5 , Figure 5 a is a macroscopic photograph of large-scale foam ceramics, demonstrating its ability to be manufactured on a large scale. Figure 5 b is a microscopic photograph of foam ceramics, from which we can see that its skeleton structure is continuous and has high load-bearing potential.

[0038] Step S40, mixing chloroform and N,N-dimethylformamide in a mass ratio of 5:1 to obtain a solvent, sequentially adding 10% by mass of polyvinyl pyrrolidone, 3% by mass of polycarbosilane as a SiC ceramic precursor, and 2% by mass of polyimide to the solvent, and performing magnetic stirring for 30 hours to obtain a spinning solution; Step S50: Pour the spinning solution into a needle tube, equip it with a spinning needle with an inner diameter of 0.3 mm, and place it on a propeller with a liquid discharge rate of 40 μL / min; apply a positive high voltage of 20 kV to the needle tube and a negative high voltage of -2 kV to the flat plate receiver. Under the action of the high voltage electric field, the spinning solution is split and stretched into filaments, which are then moved to the flat plate receiver; In step S60, the precursor nanofiber membrane is dried at 80 °C for 2 h; then the temperature is raised to 200 °C at a heating rate of 5 °C / min and kept at this temperature for 2 h to complete the curing; then the cured precursor nanofiber membrane is placed in a tubular furnace, and a nitrogen atmosphere is introduced, and the temperature is raised to 1300 °C at a heating rate of 3 °C / min and kept at this temperature for 2 h to complete the ceramic transformation, thereby obtaining a Si-CN based nanofiber membrane with a thickness of 0.1 mm. Figure 6 , Figure 6 a is a macroscopic photo of the nanofiber membrane. Figure 6 b is a microscopic photograph of the nanofiber membrane. It can be seen from the figure that the nanofibers are randomly distributed and overlap with each other to form a three-dimensional network.

[0039] In step S70, the nanofiber membrane is processed into a 21 mm × 21 mm square piece, and multiple square pieces are bonded to the surface of the foam ceramic with an interval of 9 mm by electrostatic adsorption force. Another layer of foam ceramic is placed on the nanofiber membrane to form a nanofiber membrane intercalated foam ceramic. Then, the nanofiber membrane intercalated foam ceramic is placed in a lightweight graphite tooling mold for shaping, and then placed again in a CVD Si3N4 ceramic deposition furnace. After the deposition furnace temperature is raised to 1000 ° C, NH3, Ar, carrier gas H2 and reaction gas H2 are introduced, and the flow ratio is controlled to be 7:10:8:4, wherein the carrier gas H2 carries SiCl4. After keeping the temperature for 40 hours, the gas source is turned off. After the deposition furnace cools to room temperature, the sample is taken out to obtain the nanofiber membrane intercalated foam ceramic. Figure 7 , Figure 7 a is a macroscopic photo of nanofiber membrane intercalated foam ceramics. Figure 7 b is a microscopic photograph of the nanofiber membrane intercalated foam ceramic. It can be seen from the figure that the CVDSi3N4 foam ceramic and the nanofiber membrane are successfully bonded.

[0040] like Figure 8 As shown, a butane spray gun was used to test the thermal insulation performance of nanofiber membrane intercalated foam ceramics. Figure 8 a. Thermal insulation performance test results are as follows Figure 8 As shown in Figures 8b and 8c, the surface temperature of the ceramic foam intercalated with the nanofiber membrane reached over 1000°C. After 5 minutes, the backside temperature of the ceramic foam stabilized at approximately 400°C, a temperature drop of more than 600°C compared to the surface temperature. The microwave absorption performance was tested using the bow-shaped frame method, and the test results showed that the effective absorption frequency band covered 6.2 to 18 GHz. The compressive strength of the ceramic foam intercalated with the nanofiber membrane was tested using a universal testing machine, and the compressive strength was 7.35 MPa.

[0041] Example 2 Step S10, placing carbon nanotubes in a graphite crucible and placing it in a graphene deposition furnace, heating the deposition furnace to 1060° C., introducing methane, and keeping the temperature for 5 hours before turning off the gas. After the deposition furnace cools to room temperature, graphene-modified carbon nanotubes are obtained; Step S20, mixing SiC whiskers, SiC particles, deionized water, polyvinyl alcohol, tetramethylammonium hydroxide, and polyethylene glycol in mass fractions of 25%, 15%, 55%, 2%, 2%, and 1% in sequence to obtain a mixture; adding 2% by mass of graphene-modified carbon nanotubes to the mixture, and ball milling for 15 hours to obtain a ceramic slurry; Step S30: wash the polyurethane foam with a thickness of 5 mm with deionized water and then dry it, place it in the ceramic slurry, repeatedly squeeze and immerse it, squeeze out the excess slurry with a roller, and naturally dry it in a dry environment at 35°C for 12 hours to obtain a foam dry blank; place the foam dry blank in a CVD SiBCN ceramic deposition furnace, heat the silicon-based ceramic deposition furnace to 1000°C, and simultaneously introduce BCl3, NH3, Ar, carrier gas H2 and reaction gas H2, and control their flow ratio to be 1:3:23:15:80, wherein the carrier gas H2 is brought into the MTS, and after keeping the temperature for 200 hours, the gas source is turned off, and after the temperature of the deposition furnace drops to room temperature, a Si-CN-based foam ceramic with a thickness of 5 mm is obtained; Step S40, mixing chloroform and N,N-dimethylformamide in a mass ratio of 5:1 to obtain a solvent, sequentially adding 10% by mass of polyvinyl pyrrolidone, 3% by mass of polycarbosilane as a SiC ceramic precursor, and 2% by mass of polyimide to the solvent, and performing magnetic stirring for 30 hours to obtain a spinning solution; Step S50: Pour the spinning solution into a needle tube, equip it with a spinning needle with an inner diameter of 0.3 mm, and place it on a propeller with a liquid discharge rate of 40 μL / min; apply a positive high voltage of 20 kV to the needle tube and a negative high voltage of -2 kV to the flat plate receiver. Under the action of the high voltage electric field, the spinning solution is split and stretched into filaments, which are then moved to the flat plate receiver; Step S60: Dry the precursor nanofiber membrane at 80°C for 2 hours; then heat it to 200°C at a heating rate of 5°C / min and keep it at that temperature for 2 hours to complete the curing; then place the cured precursor nanofiber membrane in a tubular furnace, introduce nitrogen atmosphere, heat it to 1300°C at a heating rate of 3°C / min, and keep it at that temperature for 2 hours to complete the ceramic transformation, thereby obtaining a Si-CN based nanofiber membrane with a thickness of 0.1 mm; In step S70, the nanofiber membrane is processed into 21 mm × 21 mm square pieces. Multiple square pieces are bonded to the surface of the ceramic foam using electrostatic adsorption at intervals of 9 mm. A layer of ceramic foam is then placed on the nanofiber membrane to form a nanofiber membrane-intercalated ceramic foam. The nanofiber membrane-intercalated ceramic foam is then placed in a lightweight graphite tooling mold for shaping. The nanofiber membrane-intercalated ceramic foam is then placed in a CVD SiBCN-based ceramic deposition furnace. The furnace temperature is raised to 1000°C, and BCl₃, NH₃, Ar, carrier gas H₂, and reactant gas H₂ are introduced at a controlled flow ratio of 1:3:23:15:80. The carrier gas H₂ is introduced into the MTS. After holding the temperature for 60 hours, the gas source is turned off. Once the deposition furnace cools to room temperature, the sample is removed to obtain the nanofiber membrane-intercalated ceramic foam.

[0042] Compared to Example 1, this example modified the ceramic slurry composition and CVD ceramic substrate. The former enhanced the slurry's fluidity and increased the amount of slurry attached to the organic foam; the latter improved the ceramic substrate's stability and facilitated long-term use in an aerobic environment. After oxidation at 1000°C for 10 hours, its absorption performance showed no significant degradation, and the effective absorption frequency band still covered 6.8 to 18 GHz, demonstrating that this material can be used for extended periods in high-temperature environments.

[0043] Example 3 Step S10, placing carbon nanotubes in a graphite crucible and placing it in a graphene deposition furnace, heating the deposition furnace to 1060° C., introducing methane, and keeping the temperature for 5 hours before turning off the gas. After the deposition furnace cools to room temperature, graphene-modified carbon nanotubes are obtained; Step S20, mixing SiC whiskers, deionized water, polyvinyl alcohol, tetramethylammonium hydroxide, and polyethylene glycol in mass fractions of 40%, 55%, 2%, 2%, and 1% in sequence to obtain a mixture; adding 1% by mass of graphene-modified carbon nanotubes to the mixture, and ball milling for 10 hours to obtain a ceramic slurry; Step S30: A 5 mm thick polyurethane foam is washed with deionized water and then dried. The foam is placed in a ceramic slurry, repeatedly squeezed and impregnated, and then excess slurry is squeezed out with a roller. The foam is then naturally dried in a dry environment at 35°C for 12 hours to obtain a foam dry blank. The foam dry blank is placed in a CVD SiC ceramic deposition furnace, the silicon-based ceramic deposition furnace is heated to 1050°C, and Ar, carrier gas H2, and reaction gas H2 are introduced simultaneously, and their flow ratio is controlled to be 2:1:6, wherein the carrier gas H2 is introduced into the MTS. After the temperature is maintained for 120 hours, the gas source is turned off, and after the deposition furnace temperature drops to room temperature, a Si-CN-based foam ceramic with a thickness of 5 mm is obtained. Step S40, mixing chloroform and N,N-dimethylformamide in a mass ratio of 5:1 to obtain a solvent, sequentially adding 10% by mass of polyvinyl pyrrolidone, 3% by mass of polycarbosilane as a SiC ceramic precursor, and 2% by mass of polyimide to the solvent, and performing magnetic stirring for 30 hours to obtain a spinning solution; Step S50: Pour the spinning solution into a needle tube, equip it with a spinning needle with an inner diameter of 0.3 mm, and place it on a propeller with a liquid discharge rate of 40 μL / min; apply a positive high voltage of 20 kV to the needle tube and a negative high voltage of -2 kV to the flat plate receiver. Under the action of the high voltage electric field, the spinning solution is split and stretched into filaments, which are then moved to the flat plate receiver; Step S60: Dry the precursor nanofiber membrane at 80°C for 2 hours; then heat it to 200°C at a heating rate of 5°C / min and keep it at that temperature for 2 hours to complete the curing; then place the cured precursor nanofiber membrane in a tubular furnace, introduce nitrogen atmosphere, heat it to 1300°C at a heating rate of 3°C / min, and keep it at that temperature for 2 hours to complete the ceramic transformation, thereby obtaining a Si-CN based nanofiber membrane with a thickness of 0.1 mm; In step S70, the nanofiber membrane is processed into 21 mm × 21 mm square pieces. Multiple square pieces are bonded to the surface of the foam ceramic at intervals of 9 mm using electrostatic adsorption. A further layer of foam ceramic is placed on the nanofiber membrane to form a nanofiber membrane-intercalated foam ceramic. The nanofiber membrane-intercalated foam ceramic is then placed in a lightweight graphite tooling mold for shaping and then placed again in a CVD SiC ceramic deposition furnace. The silicon-based ceramic deposition furnace is heated to 1050°C and simultaneously introduced with Ar, carrier gas H2, and reactive gas H2 at a controlled flow ratio of 2:1:6. The carrier gas H2 is introduced into the MTS. After holding the temperature for 40 hours, the gas source is turned off. After the deposition furnace cools to room temperature, the sample is removed to obtain the nanofiber membrane-intercalated foam ceramic.

[0044] Compared to Example 1, this example modified the CVD ceramic substrate. Because the CVD SiC substrate exhibits strong electromagnetic wave loss, the G-CNT content was reduced compared to Example 1 for impedance matching. The absorption performance was tested using the bow-shaped frame method, and the results showed an effective absorption frequency band covering 5.4–14.8 GHz. Due to the rapid deposition rate and high substrate strength of CVD SiC, a high-strength, microwave-absorbing and thermally insulating nanofiber membrane-intercalated foam ceramic was obtained in a short preparation cycle, achieving a compressive strength of 11.37 MPa.

[0045] Example 4 Step S10, placing carbon nanotubes in a graphite crucible and placing it in a graphene deposition furnace, heating the deposition furnace to 1060° C., introducing methane, and keeping the temperature for 5 hours before turning off the gas. After the deposition furnace cools to room temperature, graphene-modified carbon nanotubes are obtained; Step S20, mixing SiC whiskers, deionized water, polyvinyl alcohol, tetramethylammonium hydroxide, and polyethylene glycol in mass fractions of 40%, 55%, 2%, 2%, and 1% in sequence to obtain a mixture; adding 2% by mass of graphene-modified carbon nanotubes to the mixture, and ball milling for 10 hours to obtain a ceramic slurry; Step S30: A 3.2 mm thick polyurethane foam is washed with deionized water and then dried, and placed in a ceramic slurry. After repeated extrusion and dipping, excess slurry is squeezed out with a roller, and the foam is naturally dried for 12 hours in a dry environment at 35°C to obtain a foam dry blank. The foam dry blank is placed in a CVD Si3N4 ceramic deposition furnace, the silicon-based ceramic deposition furnace is heated to 1000°C, and NH3, Ar, carrier gas H2 and reaction gas H2 are introduced simultaneously, and the flow ratio is controlled to be 7:10:8:4, wherein the carrier gas H2 carries SiCl4. After keeping the temperature for 150 hours, the gas source is turned off, and after the deposition furnace temperature drops to room temperature, a Si-CN-based foam ceramic with a thickness of 3.2 mm is obtained. Step S40, mixing chloroform and N,N-dimethylformamide in a mass ratio of 5:1 to obtain a solvent, sequentially adding 10% by mass of polyvinyl pyrrolidone, 3% by mass of polycarbosilane as a SiC ceramic precursor, and 2% by mass of polyimide to the solvent, and performing magnetic stirring for 30 hours to obtain a spinning solution; Step S50: Pour the spinning solution into a needle tube, equip it with a spinning needle with an inner diameter of 0.3 mm, and place it on a propeller with a liquid discharge rate of 40 μL / min; apply a positive high voltage of 20 kV to the needle tube and a negative high voltage of -2 kV to the flat plate receiver. Under the action of the high voltage electric field, the spinning solution is split and stretched into filaments, which are then moved to the flat plate receiver; Step S60: Dry the precursor nanofiber membrane at 80°C for 2 hours; then heat it to 200°C at a heating rate of 5°C / min and keep it at that temperature for 2 hours to complete the curing; then place the cured precursor nanofiber membrane in a tubular furnace, introduce nitrogen atmosphere, heat it to 1300°C at a heating rate of 3°C / min, and keep it at that temperature for 2 hours to complete the ceramic transformation, thereby obtaining a Si-CN based nanofiber membrane with a thickness of 0.1 mm; In step S70, the nanofiber membrane is processed into 21 mm × 21 mm square pieces. Multiple square pieces are bonded to the surface of the foam ceramic using electrostatic adsorption at intervals of 9 mm. A layer of foam ceramic is then placed on the nanofiber membrane. A further layer of periodically dispersed nanofiber membrane and foam ceramic is then bonded on top of the foam ceramic to form a nanofiber membrane-intercalated foam ceramic. The nanofiber membrane-intercalated foam ceramic is then placed into a lightweight graphite tooling mold for shaping and then placed again in a CVD Si3N4 ceramic deposition furnace. After the furnace temperature is raised to 1000°C, NH3, Ar, carrier gas H2, and reactive gas H2 are introduced at a controlled flow ratio of 7:10:8:4. The carrier gas H2 carries SiCl4. After maintaining the temperature for 40 hours, the gas source is turned off. After the deposition furnace cools to room temperature, the sample is removed to obtain the nanofiber membrane-intercalated foam ceramic.

[0046] Compared to Example 1, this embodiment increases the number of nanofiber membrane and foam ceramic layers and reduces the thickness of each foam ceramic layer, ensuring that the total thickness remains essentially unchanged. Thermal insulation performance test results show that the surface temperature of the nanofiber membrane intercalated foam ceramic reaches over 1000°C, and the back surface temperature of the foam ceramic stabilizes at approximately 300°C after 5 minutes, a decrease of more than 700°C compared to the surface. Wave absorption performance test results show that the effective absorption frequency band covers 5.4 to 18 GHz. This shows that changing the number of layers does not affect the overall thermal insulation and wave absorption performance of the nanofiber membrane intercalated foam ceramic.

[0047] Example 5 Step S10, placing carbon nanotubes in a graphite crucible and placing it in a graphene deposition furnace, heating the deposition furnace to 1060° C., introducing methane, and keeping the temperature for 5 hours before turning off the gas. After the deposition furnace cools to room temperature, graphene-modified carbon nanotubes are obtained; Step S20, mixing SiC whiskers, deionized water, polyvinyl alcohol, tetramethylammonium hydroxide, and polyethylene glycol in mass fractions of 40%, 55%, 2%, 2%, and 1% in sequence to obtain a mixture; adding 2% by mass of graphene-modified carbon nanotubes to the mixture, and ball milling for 10 hours to obtain a ceramic slurry; Step S30: Wash a 3.2 mm thick polyurethane foam with deionized water and then dry it. The foam is placed in a ceramic slurry, repeatedly squeezed and impregnated, and then excess slurry is squeezed out with a roller. The foam is then naturally dried in a dry environment at 35°C for 12 hours to obtain a foam dry blank. The foam dry blank is placed in a CVD Si3N4 ceramic deposition furnace, the silicon-based ceramic deposition furnace is heated to 1000°C, and NH3, Ar, carrier gas H2, and reaction gas H2 are introduced simultaneously, and their flow ratio is controlled to be 7:10:8:4, wherein the carrier gas H2 carries SiCl4. After the temperature is maintained for 150 hours, the gas source is turned off, and after the deposition furnace temperature drops to room temperature, a Si-CN-based foam ceramic with a thickness of 3.2 mm is obtained. Step S40, mixing chloroform and N,N-dimethylformamide in a mass ratio of 5:1 to obtain a solvent, sequentially adding 10% by mass of polyvinyl pyrrolidone, 3% by mass of polycarbosilane as a SiC ceramic precursor, and 2% by mass of polyimide to the solvent, and performing magnetic stirring for 30 hours to obtain a spinning solution; Step S50: Pour the spinning solution into a needle tube, equip it with a spinning needle with an inner diameter of 0.3 mm, and place it on a propeller with a liquid discharge rate of 40 μL / min; apply a positive high voltage of 20 kV to the needle tube and a negative high voltage of -2 kV to the flat plate receiver. Under the action of the high voltage electric field, the spinning solution is split and stretched into filaments, which are then moved to the flat plate receiver; Step S60, drying the precursor nanofiber membrane at 80°C for 2 hours; then heating it to 200°C at a heating rate of 5°C / min and holding it for 2 hours to complete the curing; then placing the cured precursor nanofiber membrane in a tubular furnace, introducing a nitrogen atmosphere, heating it to 1300°C at a heating rate of 3°C / min, and holding it for 2 hours to complete the ceramic transformation, thereby obtaining a Si-CN based nanofiber membrane, which is denoted as C1; in order to prepare a multi-layer nanofiber membrane intercalated foam ceramic with a gradient change, another batch of precursor nanofiber membranes is placed in a high-temperature tubular furnace, introduced a nitrogen atmosphere, and heated to 1500°C at a rate of 3°C / min and held for 2 hours to obtain a Si-CN based nanofiber membrane with a thickness of 0.1 mm (denoted as C2); In step S70, the C1 nanofiber membrane is processed into 21 mm × 21 mm square pieces. Multiple square pieces are bonded to the surface of the ceramic foam using electrostatic adsorption at intervals of 9 mm. A layer of ceramic foam is then placed on the nanofiber membrane. A periodically dispersed layer of C2 nanofiber membrane and ceramic foam is bonded on top of the ceramic foam to form a multi-layer gradient nanofiber membrane-intercalated ceramic foam. The nanofiber membrane-intercalated ceramic foam is then placed into a lightweight graphite tooling mold for shaping and then placed back into a CVD Si3N4 ceramic deposition furnace. After the furnace temperature is raised to 1000°C, NH3, Ar, carrier gas H2, and reactive gas H2 are introduced at a controlled flow ratio of 7:10:8:4. The carrier gas H2 carries SiCl4. After holding the temperature for 40 hours, the gas source is turned off. After the deposition furnace cools to room temperature, the sample is removed to obtain the nanofiber membrane-intercalated ceramic foam.

[0048] Compared with Example 4, this embodiment inserts two different layers of nanofiber membranes. By changing the ceramicization temperature of the nanofibers, different electrical properties are obtained, thereby achieving different absorption response characteristics for electromagnetic waves. Wave absorption performance test results Figure 9 As shown in the figure, the effective absorption frequency band covers 4 to 18 GHz, which is significantly wider than that of Example 4. Thermal insulation performance test results show that the surface temperature of the nanofiber membrane-intercalated foam ceramic reaches over 1000°C, and the back surface temperature of the foam ceramic stabilizes at approximately 300°C after 5 minutes, a decrease of more than 700°C compared to the surface.

[0049] Comparative Example Step S10, placing carbon nanotubes in a graphite crucible and placing it in a graphene deposition furnace, heating the deposition furnace to 1060° C., introducing methane, and keeping the temperature for 5 hours before turning off the gas. After the deposition furnace cools to room temperature, graphene-modified carbon nanotubes are obtained; Step S20, mixing SiC whiskers, deionized water, polyvinyl alcohol, tetramethylammonium hydroxide, and polyethylene glycol in mass fractions of 40%, 55%, 2%, 2%, and 1% in sequence to obtain a mixture; adding 2% by mass of graphene-modified carbon nanotubes to the mixture, and ball milling for 10 hours to obtain a ceramic slurry; Step S30: wash a 10 mm thick polyurethane foam with deionized water and then dry it, place it in a ceramic slurry, repeatedly squeeze and immerse it, squeeze out excess slurry with a roller, and naturally dry it in a dry environment at 35°C for 12 hours to obtain a foam dry blank; place the foam dry blank in a CVD Si3N4 ceramic deposition furnace, heat the silicon-based ceramic deposition furnace to 1000°C, and simultaneously introduce NH3, Ar, carrier gas H2 and reaction gas H2, and control their flow ratio to be 7:10:8:4, wherein the carrier gas H2 carries SiCl4. After keeping the temperature for 150 hours, turn off the gas source, and wait until the temperature of the deposition furnace drops to room temperature to obtain the foam ceramic.

[0050] The thermal insulation and microwave absorption properties of the foam ceramic were tested using a butane spray gun and a bow-shaped frame method. The thermal insulation test results showed that the back surface temperature of the foam ceramic reached a stable level of approximately 500°C after 5 minutes, which was more than 500°C lower than that of the surface. The microwave absorption test results are shown in Figure 2. Figure 10 As shown in FIG, the effective absorption frequency band covers 4.4-8.8 GHz. The heat insulation and wave absorption performance are significantly reduced compared with Example 1.

[0051] The third embodiment of the present invention provides an application of the broadband wave-absorbing and heat-insulating Si-CN based nanofiber membrane intercalated foam ceramic in a heat-insulating and wave-absorbing material.

[0052] The above are only preferred embodiments of the present application and do not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A broadband wave-absorbing and heat-insulating Si-CN based nanofiber membrane intercalated foam ceramic, characterized in that: It comprises at least two foam ceramic layers, with a nanofiber membrane layer disposed between two adjacent foam ceramic layers; Wherein, the foam ceramic layer is a Si-CN based foam ceramic with a hollow skeleton structure; The preparation method of the Si-CN based foam ceramic comprises the following steps: impregnating an organic foam in a ceramic slurry to obtain a foam dry blank; and cracking the foam dry blank to obtain the Si-CN based foam ceramic; The nanofiber membrane layer includes a plurality of periodically arranged Si-CN based nanofiber membranes; The preparation method of the Si-CN based nanofiber membrane is as follows: A SiC phase precursor, polyimide and a spinning aid are mixed in a solvent to obtain a spinning solution; the spinning solution is spun to obtain a precursor nanofiber membrane; and the precursor nanofiber membrane is ceramicized to obtain a Si-CN based nanofiber membrane.

2. The broadband wave-absorbing and heat-insulating Si-CN based nanofiber membrane intercalated foam ceramic according to claim 1, characterized in that: The spacing between each of the Si-CN based nanofiber membranes is 0-10 mm; The density of the Si-CN based nanofiber membrane intercalated foam ceramic is 0.3-0.5 g / cm 3 , compressive strength is 5-12MPa, thermal insulation temperature is greater than or equal to 700℃, effective absorption frequency band is 4-18 GHz; the thickness of the foam ceramic layer is 3-10mm, and the thickness of the nanofiber membrane is 0.05-0.2mm.

3. A method for preparing the broadband wave-absorbing and heat-insulating Si-CN based nanofiber membrane intercalated foam ceramic according to claim 1, characterized in that: include: Preparation of Si-CN based foam ceramics and Si-CN based nanofiber membranes; Arranging a plurality of the Si-CN based nanofiber membranes in sequence on the surface of the Si-CN based foam ceramic to form a nanofiber membrane layer, and placing a layer of the Si-CN based foam ceramic on the nanofiber membrane layer to form an initial nanofiber membrane intercalated foam ceramic; The initial nanofiber membrane intercalated foam ceramic is kept at 800-1200° C. for 100-300 h to obtain the nanofiber membrane intercalated foam ceramic.

4. The method for preparing the broadband wave-absorbing and heat-insulating Si-CN based nanofiber membrane intercalated foam ceramic according to claim 3, characterized in that: The preparation method of the Si-CN based foam ceramic is as follows: The foam dry blank is placed in a silicon-based ceramic deposition furnace, the silicon-based ceramic deposition furnace is heated to 800-1200° C., gas is introduced, and the temperature is maintained for 100-300 hours to obtain a Si-CN based foam ceramic.

5. The method for preparing the broadband wave-absorbing and heat-insulating Si-CN based nanofiber membrane intercalated foam ceramic according to claim 3, characterized in that: The residual carbon rate of the organic foam is less than 5%, and the material thereof is polyurethane, polyethylene or polypropylene.

6. The method for preparing the broadband wave-absorbing and heat-insulating Si-CN based nanofiber membrane intercalated foam ceramic according to claim 3, characterized in that: The ceramic slurry includes a ceramic component and graphene-modified carbon nanotubes, wherein the mass fraction of the graphene-modified carbon nanotubes in the ceramic component is 0.2-5%. The ceramic component includes the following components in terms of mass fraction: The mass fractions of the ceramic powder, solvent, binder, dispersant, thickener and defoamer are 30-40%, 40-60%, 1-5%, 0.1-2%, 0.5-3% and 0.05-0.5%, respectively, and the sum of the mass fractions of the above components is 100%.

7. The method for preparing the broadband wave-absorbing and heat-insulating Si-CN based nanofiber membrane intercalated foam ceramic according to claim 6, characterized in that: The preparation method of the graphene-modified carbon nanotubes comprises: The carbon nanotubes are placed in a deposition furnace, the temperature of the deposition furnace is raised to 1040-1100° C., a carbon source is introduced, and the temperature is maintained for 3-10 hours to obtain graphene-modified carbon nanotubes.

8. The method for preparing the broadband wave-absorbing and heat-insulating Si-CN based nanofiber membrane intercalated foam ceramic according to claim 3, characterized in that: In the spinning solution, the SiC phase precursor accounts for 7-12w% of the solvent; the spinning aid accounts for 3-5w% of the solvent; the polyimide accounts for 1-5w% of the solvent; the SiC phase precursor includes polycarbosilane or polyborocarbosilane; During the spinning process, the inner diameter of the spinning needle is 0.3-0.5 mm; the liquid discharge rate is 30-60 μL / min; the collection distance between the needle and the receiver is 16-20 cm; the DC positive voltage is 18-22 kV, and the negative voltage is -2-4 kV.

9. The method for preparing the broadband wave-absorbing and heat-insulating Si-CN based nanofiber membrane intercalated foam ceramic according to claim 3, characterized in that: The process of the ceramic treatment is as follows: The precursor nanofiber membrane is dried and cured at 190-230° C. for 1-2 h; The solidified precursor nanofiber membrane is placed in a tubular furnace, introduced into a nitrogen atmosphere, and kept at 1300-1600° C. for 1-5 h to obtain a Si-CN based nanofiber membrane.

10. Use of the broadband wave-absorbing and heat-insulating Si-CN based nanofiber membrane intercalated foam ceramic according to claim 1 in heat-insulating and wave-absorbing materials.

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