A core-shell structure ceramic aerogel and a preparation method thereof

Abstract

This invention belongs to the technical field of composite ceramic aerogel materials, and discloses a core-shell structured ceramic aerogel and its preparation method. The method involves freeze-drying a precursor solution containing nitrogen and boron sources to obtain a precursor aerogel; subjecting the precursor aerogel to high-temperature heat treatment to obtain a boron nitride aerogel serving as the core framework; depositing a pyrolytic carbon layer on the surface of the boron nitride aerogel using chemical vapor deposition to form a pyrolytic carbon shell layer covering the surface of the boron nitride aerogel, thus obtaining a core-shell structured aerogel; immersing the core-shell structured aerogel in a precursor solution containing silicon and aluminum sources, performing vacuum impregnation and freeze-drying, followed by high-temperature heat treatment to form an aluminum-silicon-oxygen ceramic shell layer on the surface of the pyrolytic carbon shell layer, thus obtaining the core-shell structured ceramic aerogel. The core-shell structured ceramic aerogel of this invention exhibits low density, low strain, superelasticity, low thermal conductivity, and excellent high-temperature insulation properties.

Description

Technical Field

[0001] This invention belongs to the technical field of composite ceramic aerogel materials, specifically relating to a core-shell structured ceramic aerogel and its preparation method. Background Technology

[0002] From thermal protection for deep space probes to thermal management in extreme environments, the demand for advanced thermal insulation materials has gradually shifted from simply pursuing lightweight and high-temperature resistance to comprehensive optimization that balances mechanical properties and multifunctionality. Ceramic aerogels, due to their high porosity, low density, and excellent thermal stability, are considered highly promising candidate materials for extreme environment applications. However, traditional ceramic aerogels still have significant limitations in practical applications: on the one hand, the pure ceramic framework is prone to brittle fracture under external forces, resulting in insufficient material mechanical reliability and limited service life; on the other hand, the thermal insulation performance and structural stability of single-component aerogels in complex thermal environments still need further improvement. Therefore, how to synergistically improve their mechanical stability and high-temperature insulation capabilities has become a key issue that urgently needs to be addressed in this field.

[0003] Introducing a second phase to enhance network support or regulate the microstructure of constituent units can effectively improve the overall performance of ceramic aerogels. Patent CN202210087367.6 discloses a superelastic aerogel and its preparation method, which uses chemical vapor deposition to deposit a pyrolytic carbon layer on the surface of SiC nanowires or Si3N4 nanoribbons, achieving a "welding" connection between nanowires or nanoribbons to construct a three-dimensional network structure. The resulting aerogel can achieve complete recovery under compressive strain up to 80% and exhibits excellent fatigue resistance. However, a single pyrolytic carbon coating layer is prone to oxidation failure in high-temperature aerobic environments and has limited ability to regulate heat conduction paths, making it difficult to meet the thermal insulation requirements under high-temperature service conditions. Patent CN202511527884.0 discloses an antioxidant composite ceramic aerogel and its preparation method, which involves impregnating boron nitride nanoribbon aerogel in a xylene solution of tetraethyl orthosilicate and silicon tetrachloride, followed by hydrolysis and inert atmosphere pyrolysis to form a silica layer on its surface, thereby obtaining a silica@boron nitride nanoribbon aerogel. This method improves the oxidation resistance of materials to some extent, but the synergistic effect of the single-shell design on thermal insulation performance, structural stability and multifunctional integration capability is still insufficient.

[0004] Therefore, there is an urgent need to develop a simple, efficient and scalable control strategy to achieve a synergistic improvement in the mechanical properties and thermal stability of ceramic aerogels, and to endow them with excellent thermal insulation performance and multifunctional integration capabilities in extreme environments, so as to meet the application needs of aerospace, energy storage and high temperature protection and other fields. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a core-shell structured ceramic aerogel and its preparation method. By constructing a multi-layered composite structure, namely a ceramic aerogel with a core-shell three-layer composite structure, the material properties are synergistically improved.

[0006] To achieve the above objectives, the present invention specifically adopts the following technical solution: A method for preparing a core-shell structured ceramic aerogel includes the following steps: Precursor solutions containing nitrogen and boron sources were freeze-dried to obtain precursor aerogels. The precursor aerogel was heat-treated at 1100–1400°C for 2–6 hours in a protective atmosphere to obtain boron nitride aerogel as the core framework. A pyrolytic carbon layer was deposited on the surface of the boron nitride aerogel using chemical vapor deposition to form a pyrolytic carbon M layer covering the surface of the boron nitride aerogel, thus obtaining a core-M structure aerogel. The core-shell structured aerogel is impregnated in a precursor solution containing silicon and aluminum sources, vacuum impregnated, freeze-dried, and then heat-treated at 800–950°C for 30–90 min to form an aluminum-silicon-oxygen ceramic shell on the surface of the pyrolytic carbon-shell layer, thus obtaining the core-shell structured ceramic aerogel.

[0007] Preferably, in a precursor solution containing both a nitrogen source and a boron source: The nitrogen source is melamine or urea, and the boron source is boric acid; the molar ratio of the nitrogen source to the boron source is 1:6 to 2:1. The solvent is a mixture of water and a polar solvent, wherein the polar solvent is methanol, ethanol, ethylene glycol, n-propanol, isopropanol, isobutanol, sec-butanol, tert-butanol, or dimethyl sulfoxide, and the volume ratio of water to polar solvent is 1:2 to 2:1.

[0008] Preferably, when the precursor aerogel is subjected to high-temperature heat treatment, the protective atmosphere is a mixed atmosphere composed of one or more of nitrogen, ammonia and argon in any proportion.

[0009] Preferably, when using chemical vapor deposition to deposit a pyrolytic carbon layer on the surface of the boron nitride aerogel, the specific process includes: heating to 900–1200°C at a heating rate of 2–10°C / min in a flowing protective atmosphere, and depositing for 0.1–5 h; wherein the carbon source precursor is methane or propylene, and the carbon source precursor gas flow rate is 50–200 mL / min.

[0010] Preferably, in the precursor solution containing silicon and aluminum sources: The silicon source is tetraethyl orthosilicate, the aluminum source is aluminum chloride hexahydrate, aluminum sulfate or aluminum nitrate, and the solvent is deionized water. The mass ratio of the silicon source, aluminum source and deionized water is 1:(5-10):(30-80).

[0011] Preferably, when the core-shell aerogel is impregnated in a precursor solution containing silicon and aluminum sources, the vacuum impregnation time is 6 to 12 hours.

[0012] Preferably, the freeze-drying is carried out under vacuum, and the freeze-drying temperature is -196~-20℃; When freeze-drying the precursor solution containing nitrogen and boron sources, the freeze-drying time is 12–48 h. After impregnation of the nuclear-shell aerogel, the freeze-drying time is 24–72 hours.

[0013] The present invention also provides a core-shell structured ceramic aerogel, which is prepared by the preparation method described above.

[0014] Preferably, the thickness of the pyrolytic carbon layer is 30–120 nm.

[0015] Preferably, the bulk density of the core-shell structured ceramic aerogel is 20–35 mg / cm³. 3 The room temperature thermal conductivity is 30–35 mW / (m·K).

[0016] The present invention has the following technical effects: This invention presents a method for preparing core-shell structured ceramic aerogels. By constructing a three-layer composite structure (core-shell) stepwise and precisely controlling the process parameters at each step, it effectively solves the technical problems of insufficient mechanical reliability, poor high-temperature insulation and structural stability of traditional ceramic aerogels, and the difficulty of achieving synergistic performance improvement in existing composite modification schemes. Its innovation lies in the synergistic adaptation of each structure and process. The specific principle is as follows: First, a precursor solution containing nitrogen and boron sources is freeze-dried and heat-treated at 1100–1400℃ for 2–6 hours to prepare a boron nitride aerogel with both lightweight and heat-resistant properties, which serves as the core framework and provides stable three-dimensional support for the material. Then, a pyrolytic carbon shell layer with excellent toughness is deposited on its surface by chemical vapor deposition to improve the brittleness of the boron nitride core layer and achieve flexible connection between nanounits. Finally, the core-shell structured aerogel is vacuum impregnated. After freeze-drying, the precursor solution containing silicon and aluminum sources is subjected to high-temperature heat treatment at 800–950°C for 30–90 minutes to form an aluminum-silicon-oxygen ceramic shell layer that combines rigidity and structural stability. This further fixes the interlayer connections and increases the effective contact area for bearing stress. The synergistic effect of this three-layer structure enables the aerogel to maintain its ultra-lightweight properties while possessing excellent superelasticity and fatigue resistance, effectively solving the problem of brittle fracture in pure ceramic aerogels. In the core-shell structure ceramic aerogel of this invention, the boron nitride core layer provides basic heat-resistant support, the pyrolytic carbon shell layer assists in regulating the heat conduction path, and the aluminum-silicon-oxygen shell layer effectively blocks heat radiation and heat conduction and provides antioxidant protection for the inner layer. With precise control of the heat treatment parameters of the core and shell layers, the aerogel has excellent high-temperature thermal insulation performance, effectively solving the defect that existing single-coating aerogels cannot simultaneously achieve thermal insulation and antioxidant properties. In this invention, the pyrolytic carbon shell layer acts as a transition layer, connecting the boron nitride aerogel core layer and the aluminum silicon oxide ceramic shell layer, enabling the three layers to work synergistically. Specifically, the pyrolytic carbon shell layer serves as an intermediate functional layer for toughening, transition, and synergistic protection: First, the pyrolytic carbon shell layer is formed on the surface of the boron nitride aerogel through chemical vapor deposition, forming stable C–B and C–N covalent bonds with the boron and nitrogen atoms on the boron nitride surface, rather than being a physical attachment. At the same time, a flexible welding structure is formed at the cross contact sites of the boron nitride nanoribbons. The pyrolytic carbon itself possesses the interfacial slip and plastic deformation capabilities of a disordered carbon structure, which can dissipate stress and avoid stress under external forces. First, the pyrolytic carbon-based shell improves the inherent brittleness of the boron nitride core layer from a mechanistic perspective, achieving flexible connections between nanounits and enhancing the material's elasticity and mechanical stability. Second, the pyrolytic carbon-based shell has moderate surface energy and good wettability with silicon and aluminum source precursors, enabling the precursor liquid to spread and coat the framework surface evenly. Simultaneously, the thermal expansion coefficient of pyrolytic carbon is between that of boron nitride and aluminum-silicon-oxygen ceramics, buffering interfacial thermal stress during shell heat treatment at 800–950℃. Combined with its surface nanoscale roughness, it provides physical anchoring sites, effectively preventing cracking, warping, or detachment of the aluminum-silicon-oxygen shell, providing a stable transition substrate for shell formation. Finally, the pyrolytic carbon-based shell can introduce solid... The solid-interface thermal resistance enhances phonon scattering to reduce solid-phase thermal conductivity, while simultaneously acting as an intermediate barrier for oxygen diffusion. Together with the outer aluminum-silicon-oxygen ceramic shell, it extends the oxygen transport path, initially protecting the inner boron nitride structure and maintaining skeletal porosity stability at high temperatures. Combined with the thermal radiation barrier and anti-oxidation effects of the aluminum-silicon-oxygen shell, it achieves a synergistic improvement in mechanical properties, high-temperature thermal insulation performance, and structural stability. This invention overcomes the shortcomings of traditional ceramic aerogels, such as brittleness and easy fracture, easy oxidation of a single pyrolytic carbon coating at high temperatures, and limited thermal insulation performance, through the aforementioned step-by-step preparation process and the synergistic mechanism of the three-layer structure. The resulting material possesses ultralight weight, high elasticity, low thermal conductivity, and high-temperature thermal protection capabilities. The preparation process parameters are well-defined, highly controllable, and easy to scale up for production, demonstrating significant technical advantages and application value. Attached Figure Description

[0017] Figure 1 An optical photograph of the core-shell structured ceramic aerogel obtained in Example 1 of this invention; Figure 2 The image shows the SEM and energy dispersive spectroscopy (EDS) of the core-shell ceramic aerogel prepared in Example 1 of this invention. Figure 3 The compressive stress-strain curve of the core-shell structured ceramic aerogel according to an embodiment of the present invention; Figure 4 The back-temperature curve of the thermal insulation performance of the core-shell structured ceramic aerogel prepared in Example 1 of the present invention under a butane torch flame at 1300℃ is shown. Detailed Implementation

[0018] The following examples will provide a more detailed explanation of the specific content of the present invention. It should be noted that: unless otherwise specified, the conditions in the following examples are performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following examples are all from commercially available sources.

[0019] The method for preparing core-shell structured ceramic aerogels provided by this invention includes the following steps: Step 1: Melamine or urea is used as the nitrogen source, and boric acid is used as the boron source. The nitrogen source and boron source are dissolved in a mixed solvent of water and a polar solvent at a molar ratio of 1:6 to 2:1 to obtain a precursor solution. The polar solvent is selected from methanol, ethanol, ethylene glycol, n-propanol, isopropanol, isobutanol, sec-butanol, tert-butanol, and dimethyl sulfoxide. The volume ratio of water to polar solvent is 1:2 to 2:1.

[0020] Step 2: The precursor solution obtained in Step 1 is freeze-dried under vacuum at -196 to -20°C for 12 to 48 hours to obtain precursor aerogel; then the precursor aerogel is placed in one or any two mixed atmospheres of nitrogen, ammonia, and argon and heat-treated at 1100 to 1400°C for 2 to 6 hours to obtain boron nitride aerogel as the core framework.

[0021] Step 3: Place the boron nitride aerogel obtained in Step 2 into a chemical vapor deposition apparatus. Under a flowing argon atmosphere, heat the aerogel to 900–1200°C at a rate of 2–10°C / min. Introduce methane or propylene as a carbon source precursor and control the gas flow rate to 50–200 mL / min. Deposit for 0.1–5 h to form a pyrolytic carbon layer with a thickness of 30–120 nm on the surface of the boron nitride aerogel, thus obtaining a core-shell structured aerogel coated with a pyrolytic carbon shell.

[0022] Step 4: Tetraethyl orthosilicate is used as the silicon source, and aluminum chloride hexahydrate, aluminum sulfate, or aluminum nitrate is used as the aluminum source. It is mixed with deionized water at a mass ratio of 1:(5-10):(30-80) and stirred for 3-6 hours to obtain a precursor solution containing silicon and aluminum sources. The core-shell structured aerogel obtained in Step 3 is immersed in the precursor solution and vacuum impregnated for 6-12 hours. After being removed, it is frozen until completely solidified and then freeze-dried for 24-72 hours. Finally, the dried sample is placed in a muffle furnace and heat-treated at 800-950℃ for 30-90 minutes to form an aluminum-silicon-oxygen ceramic shell on the surface of the pyrolytic carbon layer, thus obtaining a core-shell structured ceramic aerogel.

[0023] Example 1 The preparation method of core-shell structured ceramic aerogel in this embodiment includes the following steps: Step 1: Melamine and boric acid were dissolved in a mixed solvent of water and tert-butanol in a molar ratio of 1:1, with the volume ratio of water to tert-butanol being 1:1. The mixture was stirred to form a transparent precursor solution. The resulting precursor solution was frozen at -60°C and then freeze-dried in a freeze dryer for 48 hours to obtain a precursor aerogel. Subsequently, the precursor aerogel was placed under a nitrogen atmosphere and heated to 1300°C at a rate of 5°C / min, and held at this temperature for 2 hours to obtain boron nitride nanoribbon aerogel, which served as the core framework.

[0024] Step 2: Place the boron nitride aerogel obtained in Step 1 in the heating zone of a chemical vapor deposition apparatus. Under the protection of flowing argon, heat it to 1000℃ at a heating rate of 10℃ / min. Then, introduce methane as a carbon source precursor at a flow rate of 60mL / min and deposit for 2 hours to form a pyrolytic carbon layer on the surface of the boron nitride framework, thus obtaining a core-methane structure aerogel.

[0025] Step 3: Tetraethyl orthosilicate, aluminum nitrate, and deionized water were mixed at a mass ratio of 1:5:60 and stirred at room temperature for 4 hours to obtain a homogeneous aluminum-silicon-oxygen precursor solution. The core-shell structured aerogel obtained in Step 2 was immersed in the precursor solution. After the core-shell structured aerogel reached adsorption saturation, it was impregnated under vacuum for 12 hours. Then, the sample was placed in a freeze dryer to freeze until solidified, and then vacuum dried for 48 hours to remove moisture. Finally, the freeze-dried sample was placed in a muffle furnace and calcined at 900°C at a rate of 10°C / min in air for 60 minutes to form an aluminum-silicon-oxygen ceramic shell on the surface of the pyrolytic carbon layer, thus obtaining the core-shell structured ceramic aerogel of this embodiment.

[0026] Experimental testing showed that the bulk density of the core-shell structured ceramic aerogel prepared in this embodiment was 30 mg / cm³. 3 ,like Figure 1 As shown, the aerogel can be stably placed on fine plant fibers, fully demonstrating its ultra-lightweight properties. Figure 2 The microstructure and elemental distribution of the single hybrid nanoribbon are shown. It can be seen that the BN surface is uniformly covered by a continuous and dense coating layer, which exhibits a distinct bilayer structure: an inner layer of pyrolytic carbon and an outer layer of aluminosilicate ceramic. The interface between the two layers is clear, and no obvious cracks or peeling were observed, indicating good bonding between the layers. Furthermore, the coating layer is uniformly distributed along the axial direction and has a consistent thickness, confirming the successful construction of a "core-shell" structure. Thanks to the dual coating of the pyrolytic carbon shell and the aluminosilicate ceramic shell, the aerogel exhibits excellent mechanical stability: after 100 cycles of 10% strain compression, no permanent deformation occurred. Figure 3 The compression resilience of the aerogel under low strain was demonstrated; it completely recovered to its original state after compression without significant deformation loss. The significant improvement in its mechanical properties and excellent fatigue resistance are mainly attributed to the structural evolution of the stress-bearing unit. The mechanical response behavior of the original boron nitride nanoribbons was effectively improved after sequentially coating the surface with a tough pyrolytic carbon shell and an aluminosilicate ceramic shell; simultaneously, the effective contact area for stress bearing increased, enabling the aerogel to withstand higher stress loads. In addition to enhanced mechanical properties, this double-shell structure also endows the aerogel with excellent high-temperature thermal insulation capabilities. The room temperature thermal conductivity of the aerogel in this embodiment is 30 mW / (m·K), exhibiting good thermal insulation performance; Figure 4 As shown, in this embodiment, the temperature of the aerogel's unexposed surface remained stable at 250°C under continuous erosion by a butane torch flame at 1300°C, demonstrating excellent high-temperature thermal protection performance.

[0027] Example 2 The preparation method of core-shell structured ceramic aerogel in this embodiment includes the following steps: Step 1: Urea and boric acid were dissolved in a mixed solvent of water and tert-butanol at a molar ratio of 2:1, with the volume ratio of water to tert-butanol being 1:2. The mixture was stirred to form a transparent precursor solution. The resulting precursor solution was frozen at -20°C and then freeze-dried in a freeze dryer for 48 hours to obtain a precursor aerogel. Subsequently, the precursor aerogel was placed under a nitrogen atmosphere and heated to 1400°C at a rate of 5°C / min, and held at this temperature for 2 hours to obtain boron nitride nanoribbon aerogel, which served as the core framework.

[0028] Step 2: Place the boron nitride aerogel obtained in Step 1 in the heating zone of a chemical vapor deposition apparatus. Under the protection of flowing argon, heat it to 1100℃ at a heating rate of 10℃ / min. Then, introduce methane as a carbon source precursor at a flow rate of 30mL / min and deposit for 3h to form a pyrolytic carbon layer on the surface of the boron nitride framework, thus obtaining a core-methane structure aerogel.

[0029] Step 3: Tetraethyl orthosilicate, aluminum nitrate, and deionized water were mixed at a mass ratio of 1:8:70 and stirred at room temperature for 6 hours to obtain a homogeneous aluminum-silicon-oxygen precursor solution. The core-shell structured aerogel obtained in Step 2 was immersed in the precursor solution. After the core-shell structured aerogel reached adsorption saturation, it was impregnated under vacuum for 6 hours. Then, the sample was placed in a freeze dryer to freeze until solidified, and then vacuum dried for 48 hours to remove moisture. Finally, the freeze-dried sample was placed in a muffle furnace and calcined at 800°C at a rate of 10°C / min in air for 90 minutes to form an aluminum-silicon-oxygen ceramic shell on the surface of the pyrolytic carbon layer, thus obtaining a core-shell structured ceramic aerogel.

[0030] Experimental results showed that the bulk density of the core-shell structured ceramic aerogel prepared in this embodiment was 32 mg / cm³. 3 It can fully recover after 100 cycles of 10% compressive strain, exhibiting excellent superelasticity. In addition, the aerogel has a room temperature thermal conductivity of 32 mW / (m·K), and under the erosion of a butane torch flame at 1300℃, the temperature of the aerogel's unexposed surface remains stable at 260℃, demonstrating excellent high-temperature thermal insulation performance.

[0031] Example 3 The preparation method of core-shell structured ceramic aerogel in this embodiment includes the following steps: Step 1: Melamine and boric acid were dissolved in a mixed solvent of water and tert-butanol at a molar ratio of 1:1, with a water to tert-butanol volume ratio of 2:3. The mixture was stirred to form a transparent precursor solution. The resulting precursor solution was frozen at -60°C and freeze-dried in a freeze dryer for 48 hours to obtain a precursor aerogel. Subsequently, the precursor aerogel was placed under a nitrogen atmosphere and heated to 1400°C at a rate of 5°C / min, and held at this temperature for 3 hours to obtain boron nitride nanoribbon aerogel, which served as the core framework.

[0032] Step 2: Place the boron nitride aerogel obtained in Step 1 in the heating zone of a chemical vapor deposition apparatus. Under the protection of flowing argon, heat it to 1200°C at a heating rate of 10°C / min. Then, introduce methane as a carbon source precursor at a flow rate of 60 mL / min and deposit for 1 h to form a pyrolytic carbon layer on the surface of the boron nitride framework, thus obtaining a core-methane structure aerogel.

[0033] Step 3: Tetraethyl orthosilicate, aluminum chloride hexahydrate, and deionized water were mixed at a mass ratio of 1:10:80 and stirred at room temperature for 4 hours to obtain a homogeneous aluminum-silicon-oxygen precursor solution. The core-shell structured aerogel obtained in Step 2 was immersed in the precursor solution. After the core-shell structured aerogel reached adsorption saturation, it was impregnated under vacuum for 12 hours. Then, the sample was placed in a freeze dryer and frozen until solidified, followed by vacuum drying for 48 hours to remove moisture. Finally, the freeze-dried sample was placed in a muffle furnace and calcined at 950°C at a rate of 10°C / min in air for 30 minutes to form an aluminum-silicon-oxygen ceramic shell on the surface of the pyrolytic carbon layer, thus obtaining a core-shell structured ceramic aerogel.

[0034] Experimental testing showed that the bulk density of the core-shell structured ceramic aerogel prepared in this embodiment was 35 mg / cm³. 3 It can fully recover after 100 cycles of 10% compressive strain, exhibiting excellent superelasticity. In addition, the aerogel has a room temperature thermal conductivity of 35 mW / (m·K), and under the erosion of a butane torch flame at 1300℃, the temperature of the aerogel's unexposed surface remains stable at 270℃, demonstrating excellent high-temperature thermal insulation performance.

[0035] In summary, this invention successfully constructed a core by sequentially building a pyrolytic carbon-methyl layer and an aluminum-silicon-oxygen ceramic shell on the surface of a boron nitride aerogel core layer. First A novel ceramic aerogel with a three-layer composite shell structure achieves integrated properties of lightweight, superelasticity, low thermal conductivity, and high-temperature insulation. The core structure proposed in this invention... First The three-layered shell structure has a clear division of labor and synergistic effect. The boron nitride core layer provides a lightweight and heat-resistant three-dimensional framework for the material, the pyrolytic carbon shell layer endows the material with excellent toughness and elastic response, and the aluminum-silicon-oxygen ceramic shell layer undertakes the functions of efficient thermal protection and thermal insulation enhancement. From the structural level, the overall performance of the material is comprehensively improved. The prepared aerogel has a bulk density of 30-35 mg / cm³. While maintaining its ultra-lightweight properties, it also has superelasticity that fully recovers after 100 cycles of 10% compressive strain. The improvement in its mechanical properties comes from the formation of C-B and C-N covalent bonds between the pyrolytic carbon shell layer and the boron nitride surface, and the formation of flexible cross-sections at the boron nitride nanoribbons. The welded structure effectively dissipates stress through interfacial slip and plastic deformation. Simultaneously, the double-layer inorganic coating toughens brittle ceramic nanounits, increases the stress-bearing area, and significantly improves the material's elasticity and mechanical stability. The pyrolytic carbon oxide layer also plays a crucial transitional role; its moderate surface energy, good wettability with the silicon-aluminum precursor, and thermal expansion coefficient between boron nitride and aluminum-silicon-oxygen ceramics allow it to buffer interfacial thermal stress during shell heat treatment. Combined with surface nano-roughness, it forms a physical anchor, preventing cracking, warping, or detachment of the aluminum-silicon-oxygen shell, providing a stable and reliable substrate for shell formation. Furthermore, the aerogel has a low room temperature thermal conductivity of 30–35 mW / (m²). K), under the action of a high-temperature heat source of 1300℃, the temperature of the unexposed surface can be controlled below 280℃, thanks to the ability of the pyrolytic carbon shell to introduce solids. The solid-state interface provides thermal resistance and enhances phonon scattering to reduce solid-phase thermal conduction. Simultaneously, it synergistically constructs an oxygen diffusion barrier and extends the oxygen transport path in conjunction with the aluminum-silicon-oxygen ceramic shell. Combined with the effective blocking of thermal radiation and conduction by the aluminum-silicon-oxygen shell, it provides ample anti-oxidation protection for the inner structure, maintaining pore structure stability even at high temperatures. Ultimately, this achieves a synergistic improvement in mechanical properties, high-temperature insulation performance, and structural stability, fundamentally overcoming the shortcomings of traditional ceramic aerogels, such as brittleness and easy fracture, easy oxidation of a single pyrolytic carbon coating at high temperatures, and limited insulation performance. The preparation method provided by this invention is simple, with well-defined parameters, strong controllability, and easy to scale up production. The resulting core... First Shell-structured ceramic aerogels possess multiple advantages, including lightweight, high elasticity, low thermal conductivity, and high-temperature thermal protection. They have significant technical advantages and broad application prospects in fields such as thermal protection for aerospace vehicles, thermal insulation for high-temperature industrial kilns, flexible thermal management devices, and special thermal protection equipment.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions 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 core-shell structured ceramic aerogel, characterized in that, The process includes the following: Precursor solutions containing nitrogen and boron sources were freeze-dried to obtain precursor aerogels. The precursor aerogel was heat-treated at 1100–1400°C for 2–6 hours in a protective atmosphere to obtain boron nitride aerogel as the core framework. A pyrolytic carbon layer was deposited on the surface of the boron nitride aerogel using chemical vapor deposition to form a pyrolytic carbon M layer covering the surface of the boron nitride aerogel, thus obtaining a core-M structure aerogel. The core-shell structured aerogel is impregnated in a precursor solution containing silicon and aluminum sources, vacuum impregnated, freeze-dried, and then heat-treated at 800–950°C for 30–90 min to form an aluminum-silicon-oxygen ceramic shell on the surface of the pyrolytic carbon-shell layer, thus obtaining the core-shell structured ceramic aerogel.

2. The method for preparing a core-shell structured ceramic aerogel according to claim 1, characterized in that, In precursor solutions containing nitrogen and boron sources: The nitrogen source is melamine or urea, and the boron source is boric acid; the molar ratio of the nitrogen source to the boron source is 1:6 to 2:

1. The solvent is a mixture of water and a polar solvent, wherein the polar solvent is methanol, ethanol, ethylene glycol, n-propanol, isopropanol, isobutanol, sec-butanol, tert-butanol, or dimethyl sulfoxide, and the volume ratio of water to polar solvent is 1:2 to 2:

1.

3. The method for preparing a core-shell structured ceramic aerogel according to claim 1, characterized in that, When the precursor aerogel is subjected to high-temperature heat treatment, the protective atmosphere is a mixture of one or more of nitrogen, ammonia and argon in any proportion.

4. The method for preparing a core-shell structured ceramic aerogel according to claim 1, characterized in that, When depositing a pyrolytic carbon layer on the surface of the boron nitride aerogel using chemical vapor deposition, the specific process includes: heating to 900–1200°C at a heating rate of 2–10°C / min in a flowing protective atmosphere, and depositing for 0.1–5 h; wherein the carbon source precursor is methane or propylene, and the carbon source precursor gas flow rate is 50–200 mL / min.

5. The method for preparing a core-shell structured ceramic aerogel according to claim 1, characterized in that, In the precursor solution containing silicon and aluminum sources: The silicon source is tetraethyl orthosilicate, the aluminum source is aluminum chloride hexahydrate, aluminum sulfate or aluminum nitrate, and the solvent is deionized water. The mass ratio of the silicon source, aluminum source and deionized water is 1:(5-10):(30-80).

6. The method for preparing a core-shell structured ceramic aerogel according to claim 1, characterized in that, The core-shell aerogel was impregnated in a precursor solution containing silicon and aluminum sources, and the vacuum impregnation time was 6 to 12 hours.

7. The method for preparing a core-shell structured ceramic aerogel according to claim 1, characterized in that, Freeze-drying is carried out under vacuum, and the freeze-drying temperature is -196~-20℃. When freeze-drying the precursor solution containing nitrogen and boron sources, the freeze-drying time is 12–48 h. After impregnation of the nuclear-shell aerogel, the freeze-drying time is 24–72 hours.

8. A core-shell structured ceramic aerogel, characterized in that, The core-shell structured ceramic aerogel is prepared by any one of the preparation methods of claims 1-7.

9. A core-shell structured ceramic aerogel according to claim 8, characterized in that, The thickness of the pyrolytic carbon layer is 30–120 nm.

10. A core-shell structured ceramic aerogel according to claim 8 or 9, characterized in that, The bulk density of the core-shell structured ceramic aerogel is 20–35 mg / cm³. 3 The room temperature thermal conductivity is 30–35 mW / (m·K).

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