Ceramic aerogel with multi-scale heterostructure and preparation method thereof

Abstract

The invention relates to a ceramic aerogel with a multi-scale heterostructure and a preparation method thereof, and the preparation method comprises the following steps: dipping carbon fibers in a reduced graphene oxide aqueous solution, and drying to obtain a Cf / RGO composite material; the preparation method comprises the following steps: by taking methyltriethoxysilane and dimethyldimethoxysilane as silicon sources, deionized water as a hydrolytic agent and tetramethylammonium hydroxide as a catalyst, mixing to obtain siloxane gel, and drying to obtain siloxane dry aerogel; and placing the Cf / RGO stacked layer by layer on the siloxane dry aerogel, carrying out high-temperature gas phase siliconizing to obtain a SiC / C composite fiber material, and carrying out air atmosphere heat treatment to obtain the layered hollow fiber skeleton based SiC-coated SiO2 nanowire aerogel. The aerogel disclosed by the invention has the characteristics of light weight, high temperature resistance, strong mechanical property and the like, collaborative optimization of mechanical-thermal-electromagnetic properties is realized, and a new thought is provided for cross-scale design of stealth materials under a high-temperature multi-physical field coupling condition.

Description

Technical Field

[0001] The present invention relates to the technical field of new materials, and in particular to a ceramic aerogel with a multi-scale heterogeneous structure and a preparation method thereof. Background Art

[0002] Modern technological advances have increased the probability of detection and destruction of military facilities and weapons, with infrared and radar being the primary detection methods. This has made infrared / radar-compatible stealth material technology crucial for enhancing battlefield survivability. Simultaneously, demand for materials adaptable to extreme environments is increasing for applications such as spacecraft thermal protection, civil aviation electromagnetic compatibility optimization, and disaster relief equipment. This is driving stealth material technologies (such as thermal radiation regulation and electromagnetic wave absorption) towards collaborative innovation between the military and civilian sectors. Against this backdrop, the rapid development of dual-use military and civilian equipment, such as hypersonic vehicles and reusable spacecraft, has created an increasingly urgent need for materials that combine mechanical resistance and infrared / radar compatibility with stealth in high-temperature environments. Traditional stealth materials (such as stealth coatings and organic materials) often suffer from oxidation failure, a sharp drop in mechanical properties, and reduced stealth performance at high temperatures, making them unable to meet the stringent requirements of extreme thermal, mechanical, and electromagnetic multi-field coupling conditions. Therefore, the development of new high-temperature structural stealth materials urgently requires overcoming the technical bottleneck of collaboratively optimizing mechanical, thermal, and electromagnetic properties, aiming to create a multifunctional, integrated system that combines lightweighting, high-temperature resistance, and infrared / radar compatibility with stealth.

[0003] Ceramic-based materials are a typical high-temperature stealth material. Traditional ceramic-based high-temperature stealth materials often face bottlenecks such as high density, high brittleness, high thermal conductivity, and a limited stealth frequency band, making them difficult to meet the requirements of lightweight, broadband compatibility, and multifunctional integration. In recent years, ceramic aerogels have shown promising application prospects in high-temperature stealth due to their ultra-low density, high porosity, and excellent heat resistance. However, single-component and single-structure aerogels suffer from insufficient mechanical strength at high temperatures, limited ability to regulate infrared thermal radiation, and a lack of multi-scale attenuation mechanisms for electromagnetic waves, severely restricting their application in stealth scenarios. To overcome these limitations, multi-level structural designs have been widely investigated. For example, the introduction of nanowire networks can enhance the mechanical toughness of ceramic aerogels; layered interfaces can extend the scattering path of electromagnetic waves; and hollow fibers can not only effectively enhance electromagnetic wave dissipation but also hinder heat transfer, thereby suppressing thermal radiation. However, achieving the precise integration of these multi-scale structures through controlled synthesis techniques remains a challenge.

[0004] Furthermore, combining rational component design with structural regulation is a more effective technical approach for constructing multifunctional systems that combine lightweight, high-temperature resistance, load-bearing properties, broadband electromagnetic loss, and infrared suppression. For example, ceramic aerogels can be layered together to achieve high-temperature infrared suppression and optimized impedance matching. Furthermore, surface oxidation of ceramic aerogels forms an interface layer, which optimizes thermal-electromagnetic synergistic stealth performance through multiple reflection / absorption mechanisms between different materials. The core challenge of current research lies in how to collaboratively address the technical challenges of lightweighting, mechanical load-bearing properties, high-temperature stability, and broadband stealth through multi-scale structural design and component optimization, while also achieving dynamic compatibility and long-term maintenance of cross-band stealth capabilities. New high-temperature structural stealth materials are a key area of ​​current stealth materials, but their development is hampered by key issues such as structural failure, mechanical property degradation, and multi-band stealth performance mismatch caused by thermal-mechanical coupling in traditional materials.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of the present invention is to provide a ceramic aerogel with a multi-scale heterogeneous structure and a preparation method thereof, which can prepare a layered hollow fiber skeleton-based SiC@SiO2 nanowire aerogel, realizing the coordinated optimization of "mechanical-thermal-electromagnetic properties".

[0007] A first aspect of the present invention provides a method for preparing a ceramic aerogel having a multi-scale heterogeneous structure, comprising the following steps: S1. Adding ascorbic acid to a graphene oxide aqueous solution to obtain a reduced graphene oxide aqueous solution, immersing carbon fiber in the reduced graphene oxide aqueous solution, and drying to obtain a Cf / RGO composite material; S2, using methyltriethoxysilane and dimethyldimethoxysilane as silicon sources, deionized water as a hydrolyzing agent, and tetramethylammonium hydroxide as a catalyst, mixing them and stirring them uniformly to obtain a siloxane gel, and drying the siloxane gel to obtain a siloxane dry aerogel; S3. The stacked Cf / RGO composite material is placed on the siloxane dry aerogel for high-temperature vapor phase siliconization to obtain a SiC / C composite fiber material. The SiC / C composite fiber material is heat-treated in an air atmosphere to obtain a layered hollow fiber skeleton-based SiC@SiO2 nanowire aerogel.

[0008] Preferably, step S1 includes: S11, dissolving graphene oxide in deionized water to obtain a graphene oxide aqueous solution; S12, adding ascorbic acid to the graphene oxide aqueous solution and stirring thoroughly to obtain a reduced graphene oxide aqueous solution; S13. Immersing the carbon fiber in an aqueous solution of reduced graphene oxide, and drying the carbon fiber in an oven at 50-70° C. (preferably 60° C.) to obtain a Cf / RGO composite material.

[0009] Preferably, the concentration of the graphene oxide aqueous solution is 10-20 mg / ml, more preferably 15 mg / ml.

[0010] Preferably, the mass ratio of ascorbic acid to graphene oxide aqueous solution is (1.5-2.5):1, more preferably 2:1.

[0011] Preferably, step S2 includes: S21, mixing methyltriethoxysilane, dimethyldimethoxysilane, deionized water, and tetramethylammonium hydroxide and stirring uniformly to obtain a siloxane gel; S22. Place the silicone gel in an oven at 50-70°C (preferably 60°C) and dry it to obtain a silicone dry aerogel.

[0012] Preferably, the mass ratio of methyltriethoxysilane, dimethyldimethoxysilane, deionized water and tetramethylammonium hydroxide is (1-3): (0.5-1.5): (1.5-4.5): (0-0.05), more preferably 2:1:3:0.02.

[0013] Preferably, step S3 includes: S31, placing the stacked Cf / RGO composite material on the siloxane dry aerogel and placing the composite material in a crucible, placing the crucible in a high-temperature atmosphere furnace, and performing high-temperature vapor-phase siliconization to obtain a SiC / C composite fiber material; S32. Place the SiC / C composite fiber material in a muffle furnace for air atmosphere heat treatment to obtain a layered hollow fiber skeleton-based SiC@SiO2 nanowire aerogel.

[0014] Preferably, the high-temperature vapor phase siliconizing is carried out in an inert gas atmosphere at a temperature of 1500-1600° C. for a holding time of 2-3 hours; more preferably, the temperature is 1550° C. for a holding time of 2.5 hours.

[0015] Preferably, the inert gas is argon.

[0016] Preferably, the air atmosphere heat treatment is performed by heating the temperature to 800-1000°C at a rate of 1-3°C / min and keeping the temperature for 2-4 hours; more preferably, the temperature is increased to 950°C at a rate of 2°C / min and keeping the temperature for 3 hours.

[0017] The second aspect of the present invention provides a ceramic aerogel with a multi-scale heterogeneous structure, which is prepared by the above-mentioned preparation method. The ceramic aerogel is a layered hollow fiber skeleton-based SiC@SiO2 nanowire aerogel, the average spacing between each layer is 350~450μm, the average diameter of the nanowire is 200~250 nm, the nanowire exhibits a core-shell structure, an amorphous SiO2 layer is generated on the SiC surface, and the thickness of the SiO2 layer is distributed between 5~10 nm.

[0018] The third aspect of the present invention provides an application of the ceramic aerogel having a multi-scale heterogeneous structure.

[0019] Specifically, the applications include but are not limited to: A. Used as a thermal protection material for aerospace structures. During space exploration, the surface of spacecraft may be exposed to high temperatures and mechanical shocks. This material is lightweight, highly elastic, and resistant to high temperatures, making it promising for use in aerospace structural thermal protection materials. B. Used as thermal insulation / stealth material in the engine area of ​​ships / aircraft and other equipment. This area requires materials with good high temperature resistance, fire resistance and load-bearing properties, and this material has these properties. In addition, military ships and military aircraft also have certain requirements for their high-temperature stealth performance. This material also has good infrared stealth performance at high temperatures; C. Used as refractory material for steam turbine furnace. Generally, the furnace wall temperature of steam turbine is 1100~1200℃. At the same time, it has a certain load-bearing capacity. This material has good fireproof and heat-insulating properties and a certain load-bearing capacity, and is expected to be used as refractory material for furnace.

[0020] The present invention has at least the following beneficial effects: (1) This invention uses carbon fiber and siloxane dry gel as raw materials, and combines the in-situ conversion and attachment growth mechanisms in SiC fiber synthesis to successfully prepare a multi-scale heterogeneous structure material - layered hollow fiber skeleton-based SiC@SiO2 nanowire aerogel (LHSNA). The aerogel structure uses hollow SiC fiber as a layered skeleton, and a large number of SiC nanowires are assisted to grow on its surface. The dual construction of hollow structure and heterogeneous interface is achieved by heat treatment. This cross-scale (nanowire-hollow micron fiber-millimeter-scale layered) microstructure and dual-composition (SiC, SiO2) collaborative design realizes the functional integration of electromagnetic loss, infrared stealth and mechanical load-bearing, that is, the coordinated optimization of "mechanical-thermal-electromagnetic properties" is achieved.

[0021] (2) The aerogel prepared by the present invention has light weight (17.92 mg / cm 3), high temperature resistance (1200°C), and strong mechanical properties. At room temperature, the material has the advantages of low matching thickness (1.8 mm), wide absorption bandwidth (5.46 GHz), and strong reflection loss (-67.62 dB). At 800°C, it still has the characteristics of low matching thickness (2.5 mm) and high absorption efficiency (3.2 GHz) in the X-band (8-12 GHz).

[0022] (3) The aerogel prepared by the present invention is designed through dual optimization of structure and components, which effectively reduces the amount of infrared radiation at 1100°C and can achieve a thermal gradient exceeding 1000°C.

[0023] (4) The preparation process of the present invention is simple and has low energy consumption, which enables the simplified preparation of SiC-based fiber aerogels with complex structures and two components, and provides a new idea for the cross-scale design of stealth materials under high-temperature multi-physical field coupling conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 This is an optical photograph of the layer-by-layer stacked Cf / RGO provided by the present invention.

[0026] Figure 2 These are photos of Cf provided by the present invention before and after being impregnated with RGO aqueous solution.

[0027] Figure 3 This is an SEM image of Comparative Example 2 of the present invention after Cf vapor-phase siliconization without impregnation of RGO.

[0028] Figure 4 The results of the vapor phase siliconization of the siloxane xerogel provided by the present invention are shown; wherein, (a) is an optical image of the siloxane xerogel before and after the vapor phase siliconization reaction, and (b) is the XRD spectrum of the product after the reaction.

[0029] Figure 5 Photos of LHSNAs of different shapes and sizes provided by the present invention.

[0030] Figure 6 This is a load-bearing demonstration photo of the LHSNA provided by the present invention.

[0031] Figure 7 These are SEM images of the hollow skeleton provided by the present invention at different stages of preparation.

[0032] Figure 8 This is the EDS element distribution diagram of the SiC@SiO2 nanowires provided by the present invention.

[0033] Figure 9 σ-ε curves (at 800°C) of the LHSNA provided by the present invention at 40% deformation and 50 compressions perpendicular to the lamellar plane.

[0034] Figure 10 The preparation of the sample provided by the present invention and the characterization diagram of its material composition; wherein, (a) is a schematic diagram of the preparation of the sample; (b) is a demonstration of the lightweighting of the sample; (c) is the XRD spectrum of the product at different stages; (d) is the FT-IR spectrum of the product at different stages; (e) is the Raman spectrum of the product at different stages; (f)-(i) are the XPS spectra of the sample; and (j) is the pore distribution diagram of the sample.

[0035] Figure 11 SEM and TEM images of the samples provided by the present invention; wherein, (a) is the SEM image of the sample; (b)-(c) are SEM images of hollow fibers; (d)-(e) are SEM images of nanowires; (f) is the diameter distribution of nanowires; (g1)-(g2) are TEM images of SiC@SiO2 nanowires; (h1)-(h2) are TEM images of hollow SiC@SiO2 fibers; (i1)-(i2) are TEM images of lamellar SiC@SiO2.

[0036] Figure 12 Graphs showing the mechanical properties of the LHSNA provided by the present invention; wherein, (a) is a σ-ε curve of the LHSNA under different compression deformations perpendicular to the layered surface; (b) is a comparison of the compression modulus of the LHSNA with that of other elastic ceramic aerogels; (c) is a σ-ε curve of the LHSNA under 100 compressions with a 40% deformation perpendicular to the layered surface; (d) is a curve showing the change in stress and modulus of the LHSNA under 100 compressions with a 40% deformation perpendicular to the layered surface; (e) is a curve showing the change in stress of the LHSNA under 50 compressions with a 40% deformation perpendicular to the layered surface (at 800°C); (f) is a σ-ε curve of the LHSNA compressed parallel to the layered surface; (g) is an optical photograph of the compression rebound of the LHSNA on a butane torch flame surface (1000°C); and (h) is an optical photograph of the compression rebound of the LHSNA on a liquid nitrogen surface (-196°C).

[0037] Figure 13Figures 1 and 2 show the radar stealth performance of the LHSNA provided by the present invention; (a)-(c) are the microwave reflection loss curves of the LHSNA; (d) is a comparison of the microwave absorption performance of the LHSNA and SiC-based materials with different structures; (e) is a 3D radar wave scattering model of the LHSNA; (f) is the RCS curve of the LHSNA at -90°~90°; (g)-(h) are the microwave reflection loss curves of the LHSNA at 800°C and 8-12 GHz; (i) is the effective absorption bandwidth of the LHSNA at 800°C, 400°C, 600°C, and 800°C, from 8 to 12 GHz.

[0038] Figure 14 Figure 1 shows the infrared stealth performance of the LHSNA provided by the present invention; (a) shows the infrared emissivity of the LHSNA at different temperatures; (b) shows the thermal conductivity of the LHSNA at different temperatures; (c) shows the temperature curve of the LHSNA at approximately 1100°C; (d) shows the thermal imaging of the LHSNA at 100°C to 300°C; (e) shows the thermal imaging of the LHSNA at different times at 1100°C; and (f) shows the thermogravimetric curve of the LHSNA.

[0039] Figure 15 This is a microstructure diagram of the aerogel obtained in Comparative Example 1 of the present invention.

[0040] Figure 16 This is a microstructure diagram of the aerogel obtained in Comparative Example 4 of the present invention.

[0041] Figure 17 This is the overall appearance of the aerogel obtained in Comparative Example 4 of the present invention. DETAILED DESCRIPTION

[0042] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0043] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form also includes the plural form. In addition, it should be understood that when the terms "comprise", "include", "have", "contain" are used in this specification, it is indicated that there are features, steps, operations, devices, components and / or combinations thereof, which are open terms, that is, they mean including but not limited to. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the range are also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0044] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention. Example

[0045] This embodiment provides a method for preparing a ceramic aerogel having a multi-scale heterogeneous structure, comprising the following steps: S1. Preparation of the carbon source: Commercial carbon fiber (Cf), industrial-grade graphene oxide (GO), L-ascorbic acid, and deionized water were used as raw materials. A 15 mg / ml GO aqueous solution was prepared. A certain amount of ascorbic acid (mLAA:mGO = 2:1) was added to the GO aqueous solution and stirred thoroughly for 6 hours to obtain a reduced graphene oxide (RGO) aqueous solution. The commercial carbon fiber was then immersed in the RGO aqueous solution and then dried in an oven at 60°C for 48 hours to obtain a Cf / RGO composite.

[0046] S2. Preparation of silicon source (siloxane xerogel): Methyltriethoxysilane (MTES) and dimethyldimethoxysilane (DMES) were used as silicon sources, deionized water was used as a hydrolyzing agent, and tetramethylammonium hydroxide (TMAOH) was used as a catalyst. They were mixed in a mass ratio of 2:1:3:0.02 and stirred to obtain siloxane gel. The gel was dried in an oven at 60 °C for 48 hours to obtain siloxane dry aerogel.

[0047] S3, stacking the layers of Cf / RGO (such as Figure 1The siloxane aerogel (shown in Figure 1) was placed on top of the dry siloxane aerogel and placed in a crucible. The crucible was then placed in a high-temperature atmosphere furnace for high-temperature vapor-phase siliconization at 1550°C for 2.5 hours in an Ar atmosphere, resulting in a SiC / C composite fiber material. The composite fiber material obtained in the previous step was placed in a muffle furnace and heated to 900°C at a rate of 2°C / min. The temperature was then held for 3 hours, ultimately yielding a layered hollow fiber skeleton-based SiC@SiO2 (ceramic) nanowire aerogel.

[0048] The layered hollow fiber skeleton-based SiC@SiO2 nanowire aerogel (LHSNA) prepared in this example is formed by in-situ conversion of stacked carbon fibers (Cf) impregnated with reduced graphene oxide (RGO). The preparation diagram is shown in FIG. Figure 10 As shown in (a) in the figure. The preparation process mainly includes the following three stages: impregnation of RGO, vapor phase siliconization, and air atmosphere heat treatment. Impregnation of RGO on the surface of Cf is a clever step of the present invention (Cf before and after impregnation of RGO is as shown in Figure 2 As shown in the figure), the RGO on the Cf surface first reacts with SiO and CO2, which plays an important role in maintaining the hollow fiber-based skeleton in the later stage. In the high-temperature gas-phase siliconization, the silicone aerogel pyrolyzes and releases SiO, CO2 and CO gas. RGO and Cf react with SiO as carbon sources to generate SiC, and the reaction formula is shown in formula (1). The silicone aerogel acts as both a carbon source and a silicon source. The SiO and CO gas produced by the decomposition of the silicone aerogel react continuously to grow into ultra-long SiC nanowires, and the reaction formula is shown in formula (2). In addition, the CO2 gas produced by the pyrolysis of the silicone aerogel can also react with Cf and RGO, and the reaction formula is shown in formula (3). On the one hand, it provides a large amount of CO for reaction formula (2), and on the other hand, the reaction leads to the consumption of carbon reaction sites in Cf and RGO. The present invention also found that powdered silica xerogel can not only be used as a silicon source, but also form bulk SiOC ceramics after vapor phase siliconization (optical images of siloxane xerogel before and after vapor phase siliconization reaction are shown in Figure 2). Figure 4 As shown in (a), the XRD pattern of the product after the reaction is as follows Figure 4 (b) in Figure 1). The transformation of powdered siloxane xerogel into bulk SiOC ceramics is a synergistic effect of pyrolysis chemical reactions and thermal stress-induced physical densification. This allows the preparation of multiple different products from a single reaction, significantly improving resource utilization. The heat treatment not only removes unreacted carbon from the carbon fibers, creating a hollow structure, but also forms a SiO2 layer on the SiC surface, creating a core-shell structure. This achieves multiple goals at once.

[0049] SiO (g) + 2C (s) → SiC (s) + CO (g) Formula (1); SiO (g) + 3CO (g) → SiC (s) + 2CO2 (g) Formula (2); C (s) + CO2 (g) → 2CO (g) Formula (3); like Figure 10 As shown in (b), the density of LHSNA is 17.92 mg / cm 3 , can be placed on peach blossoms. LHSNA can achieve larger size preparation and has the characteristics of easy processing (such as Figure 5 At the same time, LHSNA can withstand a weight 1500 times greater than its own without deformation; this shows that it has the characteristics of light weight and high strength (such as Figure 6 The preparation process mainly includes the following three stages: impregnation of RGO, vapor siliconization, and heat treatment. The material composition of different stages is analyzed below. Figure 10 (c) in the figure is the XRD spectrum of different stages. It can be seen from the figure that after Cf is impregnated with RGO, the intensity of the amorphous peak of C near 26.5° increases significantly. After CVI, the product shows strong and sharp diffraction peaks at 35.8°, 41.6°, 60.2°, 71.9°, and 75.6°, which correspond to the (111), (200), (220), (311), and (222) crystal planes of β-SiC, respectively. The intensity of the main diffraction peaks is (111), (220), (311), (200), and (222) from strong to weak, which is consistent with JCPDS 29-1129. At the same time, a diffraction peak is observed at 33.8°, which can be attributed to the stacking fault of SiC on the (111) crystal plane. No diffraction peak of C is observed. After heat treatment in air atmosphere, the product showed a broad peak at 22°, indicating the formation of amorphous silicon dioxide oxide.

[0050] Microstructural analysis of samples: The microscopic morphology of the sample is Figure 11 As shown in (a)-(e) in the figure, the overall morphology of the sample shows a nanowire-filled layered structure, with an average spacing of about 400 μm (0.4 mm) between the layers. First, the layered structure is analyzed, and its microscopic morphology is shown in Figure 11 As shown in (b) and (c), the layered structure is composed of a hollow fiber skeleton. The hollow fiber is transformed from C fiber, with a diameter of about 7.3 μm and a wall thickness of about 1.2 μm. The hollow fiber is composed of a large number of slender fibers. There are also a large number of pore structures between the slender fibers, which may be due to the growth of SiC on the surface of the C fiber. There is a small amount of lamellar network structure around the hollow fiber, which is transformed from RGO. The SEM images of the hollow skeleton at different stages of preparation are shown in Figure 2. Figure 7As shown in Figure 2, combined with the material composition analysis above, the morphology transformation path can be obtained as “solid C fiber-RGO coated C fiber-C@SiC core-shell fiber-hollow SiC@SiO2 fiber”. Figure 11 As shown in (d) and (e) in the figure, it can be seen that the nanowires present a long-range and continuous structure. In addition, these nanowires also show good flexibility and present a curved shape. This is caused by the bending of ultra-long single-crystal silicon carbide fibers under the action of gravity and external forces. In addition, due to the heat treatment in an air atmosphere, the SiO2 layer formed by oxidation on the surface of the SiC nanowires causes a large number of nanowires to form connection points, that is, the transition from virtual overlap to real connection. These structures all contribute to the improvement of its electromagnetic, thermal and mechanical properties. The diameter distribution of the nanowires is shown in Figure 11 As shown in (f) in the figure, the diameter of most nanowires is distributed between 200 and 250 nm, with an average diameter of 226.53 nm. To further clarify the composition of the sample, TEM analysis was performed. In the final product, SiC@SiO2 exists in three forms. The first is the SiC@SiO2 nanowires generated by gas phase reaction. Its TEM and HRTEM are as follows: Figure 11 As shown in (g1) and (g2), the EDS element distribution is as follows Figure 8 As shown in the figure, the nanowires show a significant core-shell structure, with an amorphous SiO2 layer formed on the SiC surface, and the thickness of the SiO2 layer is distributed between 5 and 10 nm. The second is the hollow SiC@SiO2 fiber formed by the transformation of C fibers. Its TEM and HRTEM are as follows Figure 11 As shown in (h1) and (h2) in the figure, the hollow fiber is composed of a large number of slender fibers with pores between the fibers. The fibers are also composed of SiC and SiO2 formed by surface oxidation. The thickness of the SiO2 layer is distributed between 4 and 10 nm. Finally, a lamellar network structure is formed by the transformation of RGO. Its TEM and HRTEM are as follows Figure 11 As shown in (i1) and (i2) in . The distribution and thickness of the SiO2 layer are consistent with the previous two forms of existence. The reason for the formation of such a structure is mainly due to the gas-solid growth mechanism and adhesion growth mechanism of SiC. It is worth noting that black shadow areas of varying degrees and quantities appeared in the TEM of the RGO-derived SiC@SiO2 lamellar structure and the SiC@SiO2 nanowires synthesized by gas-phase reaction. This may be due to the high-density state of SiC grain growth during the gas-phase siliconization process. In summary, the final sample is a SiC@SiO2 nanowire aerogel (LHSNA) with a layered hollow fiber skeleton. In summary, the use of a clever carbon fiber template conversion method can achieve efficient structural control of SiC fiber-based aerogels. Its preparation process is simple and has low energy consumption, which realizes the simplified preparation of SiC-based fiber aerogels with complex structures and two components.

[0051] Mechanical properties analysis of LHSNA: Thanks to its microstructure, LHSNA exhibits good mechanical properties. Figure 12 As shown in (a), LHSNA exhibits good resilience perpendicular to the layered surface and can achieve 100% rebound under a compressive strain of 60%. Figure 12 (a) in the figure is the compressive stress-strain (σ-ε) curve of LHSNA, which is a closed-loop curve and can be divided into three stages. The first stage is the initial linear stage, that is, under a compressive strain of less than 40%; the second stage is the transition region, with gradually increasing compressive stress and stress growth rate between 40% and 60% strain. In this stage, the nanowires in the lamellar gaps are squeezed and in close contact, resulting in an increase in the stress growth rate. The third stage is the densification stage (ε>60%), and the σ value shows a sharp increase trend. This is because the lamellar gaps are compressed and gradually reduced by external forces, resulting in the densification of the pore structure. At the same time, it was observed that when the compressive strain was 80%, the σ-ε curve fluctuated, which may be due to the rupture of the hollow fiber skeleton under high compression. The compression modulus of LHSNA along the lamellar direction calculated by the linear elastic system is 49.2±3.1 Kpa, which is higher than the compression modulus of elastic ceramic aerogels, such as Figure 12 As shown in (b) in . Figure 12 As shown in (c) and (d) in the figure, NLSA also exhibits good fatigue resistance in LHSNA perpendicular to the layered surface. Under the condition of 100 times of 40% compression deformation, its stress and modulus can be restored to 83% of the initial value. The structural design of the nanowire-filled layered hollow fiber skeleton enables the aerogel to undergo flexibly deformed nanowires in the layered gaps when subjected to external forces, thereby effectively dispersing and absorbing external energy. At the same time, the gaps in the layered structure provide sufficient space for the nanowires, enabling them to maintain structural stability during deformation, further improving the energy dissipation efficiency of the material. Therefore, this unique structural design not only gives the aerogel good elasticity, enabling it to maintain stable performance after multiple cycles of loading, but also significantly improves its fatigue resistance, enabling it to maintain excellent mechanical properties under extreme conditions. LHSNA also has good compression performance under high temperature conditions. Its stress value can be restored to 85% of the initial value under 50 compressions with 40% deformation at 800°C. Its σ-ε curve and stress change curve are shown as follows. Figure 9 and Figure 12 The anisotropic structure makes LHSNA have excellent mechanical properties along the layered surface, and its σ-ε curve is shown in Figure 12As shown in (f) in the figure. As can be seen from the figure, when ε is 1.7%, its stress is as high as 119.1 kPa and its modulus is as high as 7005.9 kPa. This is because the nanowires and the hollow fiber layer form a continuous reinforcement network, and its high intrinsic modulus directly improves the in-plane bearing capacity; secondly, the layered confinement of the hollow fiber skeleton effectively constrains the spatial freedom of the nanowires, suppresses in-plane buckling instability, and realizes efficient stress transfer through the cross-linking of the hollow fibers and nanowires. This makes LHSNA have ultra-high stiffness along the layered surface ( 32 ). When ε is 1.7%, the outer edge of LHSNA begins to bend and the stress growth rate decreases. When ε is 7.8%, LHSNA fails by fracture. In order to further investigate the mechanical properties of LHSNA under harsh conditions, compression tests were carried out on the NLSA under 50% deformation on the surface of a butane torch flame (1000°C) and a liquid nitrogen surface (-196°C). The experimental results show that after removing the external stress, LHSNA can recover to its original geometric shape, as shown in Figure 2. Figure 12 In summary, LHSNA exhibits good mechanical properties in different dimensions and under different environments.

[0052] Electromagnetic wave absorption performance of LHSNA: The electromagnetic wave absorption performance of LHSNA in the direction perpendicular to the layered direction, such as Figure 13 As shown in (a)-(c) in the figure. As can be seen from the figure, when the matching thickness is 1.55 mm, the LHSNA achieves a minimum reflection loss (RLmin) of -67.62 dB at 16.12 GHz. When the matching thickness is 1.8 mm, its maximum effective absorption bandwidth (EABmax) is 5.46 GHz. The LHSNA prepared by the present invention is compared with other SiC-based materials with different structures in terms of matching thickness, effective absorption bandwidth, and minimum reflection loss. Figure 13 As shown in (d) in the figure. As can be seen from the figure, the present invention has significant comprehensive advantages, which shows that LHSNA has the characteristics of strong absorption loss (-67.62 dB) and broadband absorption (5.46 GHz) at low filling ratio (5%) and low matching thickness (1.8 mm). In order to further demonstrate the practical application value of the LHSNA prepared in this study, the Radar Cross Section (RCS) simulation of the samples at 16.12 GHz was performed using CST Studio Suite 2023 software to obtain its true electromagnetic wave absorption performance (the thickness of the added sample was 1.55 mm). The results are shown in Figure 2. Figure 13As shown in (e)-(f) in the figure. It can be seen from the figure that the addition of LHSNA with a thickness of only 1.55 mm can significantly attenuate the RCS signal. Compared with the RCS value of the pure PEC conductive layer, the RCS value can be reduced by 20 dB·m² after adding LHSNA. It is worth noting that the average RCS value after adding LHSNA can be completely reduced to below -10 dB m² in the range of θ from -60° to 60°, which shows that LHSNA has excellent radar wave stealth capability. Microwave absorption performance at high temperature has always been a key and difficult issue in current research. The microwave absorption performance of LHSNA at 800 ℃ is shown in Figure 13 As shown in (g)-(h) in Figure 3, when the matching thickness is 2.5 mm, the EABmax of HFSNA can reach 3.2 GHz in the range of 8-12 GHz at 800 ℃. Figure 13 As shown in (i) of Figure 1, the LHSNA achieves an effective absorption bandwidth of at least 3 GHz in the 8-12 GHz range at temperatures of 200°C, 400°C, 600°C, and 800°C, and the effective absorption bandwidth shifts toward lower frequencies as temperature increases. These results demonstrate that the LHSNA is temperature-insensitive and exhibits excellent microwave absorption performance over a wide temperature range.

[0053] LHSNA's infrared stealth performance: The cross-scale multi-structure and dual-component (SiC, SiO2) collaborative design not only helps the material exhibit good mechanical properties and microwave absorption properties, but also helps it exhibit excellent infrared stealth performance. The infrared stealth performance of the material is related to the temperature and infrared emissivity of the material, which requires reducing the infrared emissivity of the material and improving the thermal insulation performance of the material. First, the infrared emissivity at different temperatures was examined, such as Figure 14 As shown in (a) of Figure 1, the infrared emissivity of the LHSNA increases with increasing temperature. This is likely due to the intensified thermal motion of free electrons in the material as temperature rises, which may increase the interaction between electrons and electromagnetic waves, thereby enhancing the absorption and emission of infrared light. Thermal conductivity is an important indicator of a material's thermal insulation performance. Figure 14 Panel (b) shows the thermal conductivity of the LHSNA at different temperatures perpendicular to the layer (room temperature in air, high temperature in argon). The figure shows that the solid-state thermal conductivity of the LHSNA perpendicular to the layer is 20 mW·m-1·k-1, lower than the thermal conductivity of air (26 mW·m-1·k-1). Its thermal conductivity at 1200°C is only 101 mW·m-1·k-1. To further examine its thermal protection performance under extreme conditions, its ultra-high-temperature infrared stealth performance was simultaneously investigated using high-temperature thermocouples and an infrared thermal imager. Figure 14Figure (c) shows the temperature distribution curve on both sides of the sample. As can be seen from the figure, when a high temperature of about 1100 °C is applied to one side perpendicular to the layered structure, the temperature of the LHSNA on the other side is only about 75 °C for 10 minutes and the sample thickness is 2.5 cm. The temperature gradient is greater than 1000 °C. The infrared thermal imaging of LHSNA at 100~300 °C perpendicular to the layered direction is shown in Figure 2. Figure 14 As shown in (d) (sample thickness is 1 cm), it exhibits excellent infrared stealth performance at 100~300℃. At 300℃, the surface radiation temperature is only 106℃, and the radiation is reduced to 1 / 3 of the ambient temperature. LHSNA applies infrared thermal imaging at about 1100℃ perpendicular to the layer direction for different times. Figure 14 As shown in (e) in the figure, when the time is 10 minutes, the infrared radiation temperature of the heated surface is about 1120 ℃, and the temperature of the back is about 55 ℃. This has a certain error with the results of the thermocouple test in the previous article. This is because the thermocouple test is the surface temperature of the material. The infrared radiation temperature of the material is also related to the emissivity, and its emissivity also helps to reduce the infrared radiation temperature. Excellent thermal stability is also a necessary condition for the application of materials in high temperature environments. Figure 14 (f) is the thermogravimetric curve of LHSNA in air atmosphere. It can be seen from the figure that its weight increases by only 3% at 1200 ℃. In order to further investigate the high temperature resistance of LHSNA, an ultra-high temperature thermal ablation experiment was carried out on it. Figure 14 As shown in (f) in the figure, under the conditions of approximately 1200°C and single-sided ablation for 60 min, no significant changes were found in its appearance and size, and the sample weight gain and linear shrinkage were both less than 0.5%.

[0054] In summary, this invention successfully developed a layered hollow fiber skeleton-based SiC@SiO2 nanowire aerogel (LHSNA) through a multiscale heterostructure design strategy, combining high-temperature resistance, mechanical strength, and infrared-radar-compatible stealth performance. By combining a simple high-temperature vapor-phase siliconization technique with a heat treatment process, a multi-component structure (layered + hollow fiber + nanowire + core-shell structure) and a dual-component structure (SiC + SiO2) were easily and efficiently prepared. This resulted in a lightweight material system (density 17.92 mg / cm³), excellent mechanical properties (excellent compression resilience and fatigue resistance), and a high operating temperature (1200°C). By leveraging polarization losses at the core-shell heterojunction interface and loss enhancement of the multi-component structure, the LHSNA achieves an effective absorption bandwidth of 5.46 GHz at room temperature with a thickness of 1.8 mm. Even at high temperatures (800°C), it maintains an effective absorption bandwidth of 3.2 GHz in the X-band (with a thickness of 2.5 mm). Through heat loss from the multi-layered structure and phonon scattering effects at heterogeneous interfaces, LHSNA exhibits excellent infrared stealth performance at high temperatures, achieving a thermal gradient exceeding 1000°C at 1100°C (with a thickness of 2.5 cm). The "mechanical-thermal-electromagnetic" collaborative optimization strategy proposed in this work is of great significance for the development of stealth protective materials for aerospace hot-end components, and will contribute to the development of new lightweight, high-performance, structurally compatible stealth materials.

[0055] Comparative Example 1: S1. Preparation of a carbon source: Commercial carbon fiber (Cf), industrial-grade graphene oxide (GO), L-ascorbic acid, and deionized water were used as raw materials. A 15 mg / ml GO aqueous solution was prepared. A certain amount of ascorbic acid (mLAA:mGO = 2:1) was added to the GO aqueous solution and stirred thoroughly for 6 hours to obtain a reduced graphene oxide (RGO) aqueous solution. The commercial carbon fiber was then immersed in the RGO aqueous solution and dried in an oven at 60°C for 48 hours to obtain a Cf / RGO composite.

[0056] S2. Preparation of silicon source (siloxane xerogel): Methyltriethoxysilane (MTES) and dimethyldimethoxysilane (DMES) were used as silicon sources, deionized water was used as a hydrolyzing agent, and tetramethylammonium hydroxide (TMAOH) was used as a catalyst. They were mixed in a mass ratio of 2:1:3:0.02 and stirred to obtain siloxane gel. The gel was dried in an oven at 60 °C for 48 hours to obtain siloxane dry aerogel.

[0057] S3. Place the stacked Cf / RGO layers on top of the dry siloxane aerogel and place them in a crucible. Place the crucible in a high-temperature atmosphere furnace for high-temperature vapor-phase siliconization at 1550°C for 2.5 hours in an Ar atmosphere to obtain a SiC / C composite fiber material. Place the composite fiber material obtained in the previous step in a muffle furnace and heat it to 600°C at a rate of 2°C / min for 3 hours.

[0058] In this comparative example, the air atmosphere heat treatment temperature was changed to 600 ° C, and the layered hollow fiber skeleton-based SiC nanowire aerogel was obtained. The microstructure is as follows Figure 15 shown.

[0059] Comparative Example 2: S1. Preparation of carbon source: Commercial carbon fiber (Cf) was used as the carbon source.

[0060] S2. Preparation of silicon source (siloxane xerogel): Methyltriethoxysilane (MTES) and dimethyldimethoxysilane (DMES) were used as silicon sources, deionized water was used as a hydrolyzing agent, and tetramethylammonium hydroxide (TMAOH) was used as a catalyst. They were mixed in a mass ratio of 2:1:3:0.02 and stirred to obtain siloxane gel. The gel was dried in an oven at 60 °C for 48 hours to obtain siloxane dry aerogel.

[0061] S3. Place the stacked Cf / RGO layers on top of the dry siloxane aerogel and place them in a crucible. Place the crucible in a high-temperature atmosphere furnace for high-temperature vapor-phase siliconization at 1550°C for 2.5 hours in an Ar atmosphere to obtain a SiC / C composite fiber material. Place the composite fiber material obtained in the previous step in a muffle furnace and heat it to 900°C at a rate of 2°C / min for 3 hours.

[0062] The results of this comparative example are as follows Figure 3 As shown in the figure, it can be seen that when commercial carbon fiber (Cf) is directly used as the carbon source without impregnation with RGO, although a nanowire structure can be formed, the fiber structure is fragile, and it is difficult for the product to maintain its continuous and complete fiber structure after vapor phase siliconization.

[0063] Comparative Example 3: S1. Preparation of a carbon source: Commercial carbon fiber (Cf), industrial-grade graphene oxide (GO), L-ascorbic acid, and deionized water were used as raw materials. A 15 mg / ml GO aqueous solution was prepared. A certain amount of ascorbic acid (mLAA:mGO = 2:1) was added to the GO aqueous solution and stirred thoroughly for 6 hours to obtain a reduced graphene oxide (RGO) aqueous solution. The commercial carbon fiber was then immersed in the RGO aqueous solution and then dried in an oven at 60°C for 48 hours to obtain a Cf / RGO composite.

[0064] S2. Preparation of silicon source: Use silicon powder as the silicon source.

[0065] S3. Place the stacked Cf / RGO layers on top of the dry siloxane aerogel and place them in a crucible. Place the crucible in a high-temperature atmosphere furnace for high-temperature vapor-phase siliconization at 1550°C for 2.5 hours in an Ar atmosphere to obtain a SiC / C composite fiber material. Place the composite fiber material obtained in the previous step in a muffle furnace and heat it to 900°C at a rate of 2°C / min for 3 hours.

[0066] In this comparative example, silicon powder was directly used as the silicon source, and the results showed that only a small amount of nanowires were formed.

[0067] Comparative Example 4: S1. Preparation of carbon source: Commercial carbon fiber (Cf) was used as the carbon source.

[0068] S2. Preparation of silicon source: Use silicon powder as the silicon source.

[0069] S3. Place the stacked Cf / RGO layers on top of the dry siloxane aerogel and place them in a crucible. Place the crucible in a high-temperature atmosphere furnace for high-temperature vapor-phase siliconization at 1550°C for 2.5 hours in an Ar atmosphere to obtain a SiC / C composite fiber material. Place the composite fiber material obtained in the previous step in a muffle furnace and heat it to 900°C at a rate of 2°C / min for 3 hours.

[0070] In this comparative example, commercial carbon fiber (Cf) was used as the carbon source, and silicon powder was used as the silicon source. The results showed that only a very small amount of agglomerated nanowires were formed, and their microstructure was as follows: Figure 16 As shown, the overall appearance of the sample is as Figure 17 shown.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a ceramic aerogel having a multi-scale heterogeneous structure, characterized in that: The steps include: S1. Adding ascorbic acid to a graphene oxide aqueous solution to obtain a reduced graphene oxide aqueous solution, immersing carbon fiber in the reduced graphene oxide aqueous solution, and drying to obtain a Cf / RGO composite material; S2, using methyltriethoxysilane and dimethyldimethoxysilane as silicon sources, deionized water as a hydrolyzing agent, and tetramethylammonium hydroxide as a catalyst, mixing them and stirring them uniformly to obtain a siloxane gel, and drying the siloxane gel to obtain a siloxane dry aerogel; S3. The stacked Cf / RGO composite material is placed on the siloxane dry aerogel for high-temperature vapor phase siliconization to obtain a SiC / C composite fiber material. The SiC / C composite fiber material is heat-treated in an air atmosphere to obtain a layered hollow fiber skeleton-based SiC@SiO2 nanowire aerogel.

2. The preparation method according to claim 1, characterized in that Step S1 includes: S11, dissolving graphene oxide in deionized water to obtain a graphene oxide aqueous solution; S12, adding ascorbic acid to the graphene oxide aqueous solution and stirring thoroughly to obtain a reduced graphene oxide aqueous solution; S13. Immersing the carbon fiber in a reduced graphene oxide aqueous solution, and drying the carbon fiber in an oven at 50-70° C. to obtain a Cf / RGO composite material.

3. The preparation method according to claim 1, characterized in that The concentration of the graphene oxide aqueous solution is 10-20 mg / ml; the mass ratio of ascorbic acid to the graphene oxide aqueous solution is (1.5-2.5):

1.

4. The preparation method according to claim 1, characterized in that Step S2 includes: S21, mixing methyltriethoxysilane, dimethyldimethoxysilane, deionized water, and tetramethylammonium hydroxide and stirring uniformly to obtain a siloxane gel; S22. Place the silicone gel in an oven at 50-70° C. and dry it to obtain a silicone dry aerogel.

5. The preparation method according to claim 1, characterized in that The mass ratio of the methyltriethoxysilane, dimethyldimethoxysilane, deionized water and tetramethylammonium hydroxide is (1-3): (0.5-1.5): (1.5-4.5): (0-0.05).

6. The preparation method according to claim 1, characterized in that Step S3 includes: S31, placing the stacked Cf / RGO composite material on the siloxane dry aerogel and placing the composite material in a crucible, placing the crucible in a high-temperature atmosphere furnace, and performing high-temperature vapor-phase siliconization to obtain a SiC / C composite fiber material; S32. Place the SiC / C composite fiber material in a muffle furnace for air atmosphere heat treatment to obtain a layered hollow fiber skeleton-based SiC@SiO2 nanowire aerogel.

7. The preparation method according to claim 1, characterized in that The high-temperature vapor phase siliconizing is carried out in an inert gas atmosphere at a temperature of 1500-1600° C. and a holding time of 2-3 hours.

8. The preparation method according to claim 1, characterized in that The air atmosphere heat treatment is carried out by heating the material to 800-1000° C. at a rate of 1-3° C. / min and keeping the temperature for 2-4 hours.

9. A ceramic aerogel with a multi-scale heterogeneous structure, characterized in that: The ceramic aerogel is prepared by the preparation method according to any one of claims 1 to 8, wherein the ceramic aerogel is a layered hollow fiber skeleton-based SiC@SiO2 nanowire aerogel, the average spacing between each layer is 350~450μm, the average diameter of the nanowire is 200~250 nm, the nanowire exhibits a core-shell structure, an amorphous SiO2 layer is generated on the SiC surface, and the thickness of the SiO2 layer is distributed between 5~10 nm.

10. Use of the ceramic aerogel with multi-scale heterogeneous structure according to claim 9 in the manufacture of spacecraft, ships, and steam turbines.

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