A large-aspect-ratio shell-core structure in-situ embedded porous silicon carbide foam bi-continuous network composite aerogel and a preparation method thereof

Abstract

This invention provides a dual-continuous network composite aerogel with a high aspect ratio core-shell structure in situ embedded in porous silicon carbide foam, belonging to the field of high-temperature resistant composite aerogel technology. It includes a core-shell structure and a framework. The core-shell structure comprises a core and a shell layer. The shell layer is a ceramizable silicone rubber layer, and the core is a continuous network of SiC nanowires. The framework is a continuous network of porous silicon carbide foam. The core-shell structure is in situ embedded within the framework structure, forming an interpenetrating dual-continuous network composite structure. The invention also provides a preparation method that precisely designs the mechanical distribution and coupling characteristics of the nanowires, ceramic framework, and porous structure, synergistically optimizing the multifunctionality, energy absorption, and high-temperature resistance of the composite aerogel. This method offers significant advantages in the control of sound waves, electromagnetic waves, and light waves, as well as high-temperature oxidation resistance and vibration resistance, making it widely applicable in aerospace, military protection, electronic equipment, and building vibration isolation.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature resistant composite aerogel technology, and particularly relates to a dual continuous network composite aerogel with a large aspect ratio shell-core structure and in-situ embedded porous silicon carbide foam and its preparation method. Background Technology

[0002] With the increasing demand for high-performance fireproof and thermal insulation materials in modern industry, existing inorganic composite aerogel materials are widely used due to their excellent high-temperature resistance and thermal insulation properties. However, traditional inorganic composite aerogel preparation methods often employ simple blending modes of zero-dimensional to one-dimensional, one-dimensional to one-dimensional, and two-dimensional to one-dimensional nanostructures. While achieving high performance and multifunctionality, this inevitably leads to the formation of numerous weakly bonded structures within the material, resulting in accelerated performance degradation and a short service life under long-term vibration conditions. Furthermore, with increasing energy demands, integrating high performance, multifunctionality, high strength, and high toughness into a single structure has become a crucial requirement in the field of lightweight composite structures. Therefore, the development of lightweight composite aerogels for high-temperature thermal insulation is of great significance. Currently, in the design of high-strength, high-flexibility, and multifunctional structures for high-temperature resistance, the composite of ceramizable silicone rubber with inorganic templates is an important technical solution. However, existing ceramizable silicone rubber composites still face problems such as thermal expansion mismatch, weak interfacial bonding, and easy oxidation. Therefore, reinforcing phases such as carbon foam and SiC nanowires are introduced into the design of ceramicizable silicone rubber composites to improve their overall performance.

[0003] Chinese Patent Application No. CN202411019183.1 discloses a ceramicized silicone rubber composite tape. This invention develops a ceramicized silicone rubber composite tape and further synthesizes a novel organic-inorganic hybrid flame retardant. This allows the product to maintain excellent mechanical properties while further improving flame retardant and ceramic-forming properties. The resulting product is used to wrap and encapsulate the copper busbars of high-voltage connectors in new energy vehicle battery packs, providing fireproofing and insulation. Chinese Patent Application No. CN202311535978.3 discloses a high-efficiency fire-resistant silicone rubber composite sleeve and its preparation method. This solves the problems of existing silicone rubber sleeves being unable to withstand prolonged high-temperature impacts above 1600℃, significant reduction in the bonding strength between silicone rubber and high-temperature resistant fiber tubes before and after high-temperature flame attack, severe damage to the sleeve structure, and environmental pollution caused by solvent dilution in the preparation process using dip-coating. This invention, by combining ceramicizable silicone rubber with high-silica fiber tubes, imparts higher fire resistance to the material while also possessing good mechanical properties, water resistance, aging resistance, and low-temperature resistance. Chinese Patent Application No. CN202111180454.8 discloses a method for preparing a ceramizable silicone rubber composite material. The ceramizable silicone rubber composite material of this invention exhibits good dimensional stability and mechanical properties under high-temperature conditions; the ablation products can support a load twice their own weight at 500–1000℃, and it has excellent residual strength at room temperature, with a flexural strength ≥2.69 MPa; it also exhibits excellent electrical insulation properties at all temperatures, with a volume resistivity ≥8.7 × 10¹¹ Ω·cm after ablation at 500–1000℃. Chinese Patent Application No. CN109734478A discloses a silicon carbide-coated carbon foam resin-based composite material substrate and its preparation method. This invention uses silicon carbide-coated carbon foam as a reinforcing phase to improve the high-temperature resistance and compressive strength of the composite material substrate, and improves the overall dielectric properties of the composite material substrate by filling with resin.

[0004] In basic research, Chen Zhaofeng, Zhang Junxiong, Li Binbin, and others have conducted extensive research on SiC nanowire / lightweight foamed carbon composite materials (SnwLCF) based on chemical vapor infiltration technology, depositing SiC nanowires onto the three-dimensional framework of lightweight foamed carbon composite materials. The results show that silicon carbide nanowires divide the macropores of LCF and form many smaller pores inside it. The division of pores is the key to improving the thermal insulation performance of LCF. In addition, the content of SiC nanowires also has an important influence on the compressive and thermal properties of SnwLCF (Journal of Alloys and Compounds, 2020, 829: 154609; Journal of Materials Science, 2020, 55: 4170-4178; Rare Metals, 2023, 42(10): 3354-3363). Wang Yang et al. successfully synthesized ultralight and high-strength SiCnw@SiC foam materials with efficient microwave absorption and thermal insulation properties using template sacrificial method and chemical vapor deposition method. Its microstructure is a novel double-network structure formed by the coupling of morphology-controllable SiCnw and SiC framework. The introduction of SiCnw can not only provide more interfacial polarization and dielectric loss for SiC foam, greatly enhancing the microwave absorption capability of composite foam, but also make it an excellent radiation absorber, which can effectively reduce the thermal conductivity of foam (ACS Applied Materials & Interfaces, 2021, 13(18): 22017-22030).

[0005] However, existing nanowire-embedded carbon foam materials still suffer from problems such as insufficient high-temperature water and oxygen resistance, poor seismic performance, inability to balance rigidity and toughness, and the need to improve thermal insulation and multifunctionality. These issues limit their application in high-temperature and harsh environments, and there is an urgent need to further optimize the structure and performance of the materials to improve their comprehensive functions and reliability. Summary of the Invention

[0006] Technical solution: In order to solve the above-mentioned technical problems, the present invention provides a dual continuous network composite aerogel with a large aspect ratio shell-core structure in situ embedded porous silicon carbide foam, specifically comprising a shell-core structure and a framework;

[0007] The shell-core structure includes a core and a shell, with the shell wrapping around the core. The shell is a ceramicizable silicone rubber layer structure, and the core is a continuous network structure of SiC nanowires.

[0008] The skeleton is a porous silicon carbide foam with a continuous network structure.

[0009] The shell-core structure is embedded in situ on the skeleton structure, forming an interpenetrating double continuous network composite structure.

[0010] As an improvement, a silicon carbide coating is also included, which is attached to the skeleton surface by a chemical vapor deposition method.

[0011] As an improvement, the composite aerogel has an open porosity greater than 95% and a density of 10 kg / m³. 3 ~30kg / m 3 Compressive strength: 0.03MPa~0.5MPa.

[0012] As an improvement, the shell has a thickness of 10-20 nm, the core has an amorphous structure with a diameter of 30-70 nm, and the aspect ratio of the core is 2000-4000.

[0013] As an improvement, the shell layer includes at least one of organosilicon rubber, siloxane-containing silicone rubber, fluorinated modified silicone rubber, and metal oxide modified silicone rubber.

[0014] As an improvement, the skeleton is a quasi-topological structure formed by three-dimensional repeating of hollow multi-rings, and the thickness of the silicon carbide coating is no more than 15 nm.

[0015] As an improvement, the hollow multi-element ring is at least one of a regular pentagon or a regular hexagon with a side length of 10μm to 30μm and a side diameter of 600nm to 1200nm.

[0016] As a specific embodiment of the present invention, a method for preparing a dual-continuous network composite aerogel with a high aspect ratio shell-core structure in situ embedded porous silicon carbide foam is also provided. The preparation method produces the above-mentioned composite aerogel, and the specific steps of the method include:

[0017] (1) Preparation of carbon foam matrix

[0018] Melamine foam is placed in a high-temperature furnace, evacuated and protected with inert gas. Protective gas is introduced at a flow rate of 20 sccm to 80 sccm, and the temperature is slowly raised to 800℃ to 1100℃. After holding at this temperature for 0.5h to 2h, the furnace is cooled to obtain a carbon foam skeleton matrix.

[0019] (2) Preparation of silicon carbide coating

[0020] The matrix obtained in (1) is placed in a chemical vapor deposition apparatus. An inert gas is introduced into a methyltrichlorosilane (MTS) solution and then into the deposition apparatus. The gas is continued until the valves on both sides of the deposition apparatus are closed. The temperature is slowly increased. After deposition for a period of time, the temperature is slowly cooled to room temperature to obtain a porous carbon foam skeleton structure coated with a silicon carbide coating.

[0021] (3) Pyrolysis treatment

[0022] The porous carbon foam skeleton structure coated with silicon carbide obtained in (2) was placed in a high-temperature furnace and heated to 500℃~800℃ in an air atmosphere for 2h~4h to obtain a porous silicon carbide foam skeleton.

[0023] (4) Nickel salt immersion treatment

[0024] The porous silicon carbide foam skeleton obtained in (3) was immersed in nickel salt solution for 5 min to 120 min, and then dried in an environment of 40℃ to 100℃ until the ethanol solvent was completely evaporated.

[0025] (5) Preparation of silicon carbide nanowires

[0026] The material obtained in (4) was placed in a vacuum furnace and heated slowly to 900℃ to 1200℃ with an inert gas flow rate of 30 sccm to 70 sccm. After evacuation, H2 and MTS were introduced at the same time. The material was kept at the temperature for 1 h to 3 h and then cooled to room temperature to obtain a high aspect ratio SiC nanowire embedded porous silicon carbide foam double continuous network composite aerogel.

[0027] (6) Silicone rubber filling and degassing

[0028] The high aspect ratio SiC nanowire embedded porous silicon carbide foam dual continuous network composite aerogel obtained in (5) was placed in a vacuum device, and a mixture of ceramicizable silicone rubber and solvent was drawn in. The aerogel was degassed at a certain temperature and a certain vacuum to obtain a high aspect ratio shell-core structure SiC@CSR nanowire embedded porous silicon carbide foam dual continuous network composite aerogel.

[0029] (7) Curing and molding

[0030] The composite aerogel obtained in (6) is cured at 80℃~200℃ for 6h~10h to form the final composite aerogel.

[0031] As an improvement, in step (4), the nickel salt solution is one or a mixture of nickel nitrate, nickel chloride, nickel acetate or nickel sulfate, and the solvent is ethanol.

[0032] As an improvement, in step (6), the degassing temperature is 40℃~80℃ and the vacuum degree is 0.01MPa~0.08MPa.

[0033] Beneficial effects: By precisely designing the mechanical distribution and coupling characteristics of nanowires, ceramic skeletons and porous structures, this invention synergistically optimizes the multifunctionality, energy absorption and high temperature resistance of composite aerogels. It has significant advantages in the control of sound waves, electromagnetic waves and light waves, as well as high temperature oxidation resistance and vibration resistance, which makes it have broad application potential in aerospace, military protection, electronic equipment, building vibration isolation and other fields.

[0034] Meanwhile, the composite aerogel and its preparation method proposed in this invention have the following advantages compared with conventional methods:

[0035] (1) The present invention is lightweight and multifunctional, specifically: it adopts a design scheme of multi-dielectric material combined with multi-level pore structure. Based on the characteristics of high wave transmittance silicone rubber, semiconductor silicon carbide nanowires electronic transport and Young's modulus, it can form a coordinated response to mechanical waves, light waves and radar waves at a low frequency (≤200Hz), as well as rapid thermal energy conversion and dissipation of various wavebands, realizing the logical design of multifunctional characteristics.

[0036] Furthermore, based on the hollow template and the large aspect ratio nanowires for homogenization and effective multi-level segmentation of the composite aerogel, high thermal insulation performance can be achieved under relatively lightweight conditions by effectively limiting gas heat conduction.

[0037] (2) The excellent energy absorption and vibration resistance characteristics of this invention are specifically reflected in the design of a multi-level pore size and mechanical wave coupling unit with large aspect ratio nanowires embedded in the homogeneous micron-pores of the porous silicon carbide template, which can achieve mechanical wave response over a wide frequency range (as shown in the appendix to the specification). Figure 6 (As shown).

[0038] Furthermore, the outer silicone rubber coating not only enhances vibration resistance but also provides multi-level energy buffering under external forces, enabling the material to dissipate energy step by step under impacts and vibrations of varying intensities, thereby reducing damage to the structure. It is particularly suitable for applications such as vibration damping, impact resistance, and vibration resistance.

[0039] (3) The present invention has mild antioxidant capacity, specifically: it adopts an all-ceramic structure, has excellent high temperature resistance, and can work stably for a long time in high temperature environment.

[0040] Furthermore, the silicone rubber layer can transform into a ceramic phase at high temperatures, further enhancing the material's high-temperature resistance and oxidation resistance. This solves the temperature resistance problem of traditional carbon-based materials in high-temperature oxidizing environments, allowing for a longer service life in applications under high-temperature and corrosive conditions. Attached Figure Description

[0041] Figure 1 This is a flowchart illustrating the preparation process of the SiC@CSR nanowire-embedded porous silicon carbide foam composite aerogel of the present invention.

[0042] Figure 2 This is a schematic diagram of the SiC@CSR nanowire embedded porous silicon carbide foam composite aerogel structure of the present invention.

[0043] Figure 3 This is a schematic diagram of a single SiC nanowire coated with a ceramicizable silicone rubber coating.

[0044] Figure 4 This describes the microstructure of the SiC embedded porous carbon foam material prepared in Example 2 of this invention.

[0045] Figure 5 These are the statistical results of the SiC nanowires prepared in Example 2 of this invention.

[0046] Figure 6 This refers to the compressive strength of the composite aerogel prepared in Example 2 of this invention.

[0047] Figure 7 This refers to the reflection loss of the composite aerogel prepared in Example 3 of this invention.

[0048] In the figure: 21, core-shell structured SiC@CSR nanowires; 22, porous silicon carbide foam skeleton; 31, SiC nanowires; 32, ceramicized silicon rubber coating. Detailed Implementation

[0049] The technical solutions in the embodiments of the present invention will be clearly and completely described below, so that those skilled in the art can better understand the advantages and features of the present invention, thereby making a clearer definition of the scope of protection of the present invention. The embodiments described in this invention are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0050] This invention provides a dual continuous network composite aerogel with a high aspect ratio shell-core structure in situ embedded porous silicon carbide foam, comprising a shell-core structure and a framework; the shell-core structure comprises a core and a shell layer, wherein the shell layer wraps around the core, the shell layer is a ceramicizable silicone rubber layer structure, and the core is a continuous network structure of SiC nanowires.

[0051] The skeleton is a porous silicon carbide foam with a continuous network structure.

[0052] The shell-core structure is embedded in situ within the skeleton structure, forming a composite structure of interwoven double continuous networks.

[0053] In this invention, on the one hand, a composite structure of a continuous network of silicon carbide nanowires in the core-shell structure and a porous silicon carbide foam structure with a continuous network framework is designed; on the other hand, by embedding the core-shell structure in situ into the framework, a chemical bond with strong bonding effect is formed, which is not easy to fall off, thus realizing the shock resistance and good energy absorption effect of the entire structure.

[0054] Meanwhile, the core-shell structure in this invention uses a criticizable silicone rubber (CSR) layer as the shell and silicon carbide nanowires as the core, namely the SiC@CSR nanowire structure in this invention. The CSR nanowires are designed with a large aspect ratio, ranging from 2000 to 4000. The large aspect ratio has the following two main effects: 1. Under the condition of the same fiber diameter, a large aspect ratio can maximize the path of freedom of the nanowires under mechanical deformation, thereby increasing the energy absorption value of the aerogel; in addition, the interpenetrating fiber network with a large aspect ratio will allow the fibers to curl and entangle over a large range, forming more prestress points, changing the fiber's response frequency to sound waves, and enabling the material to form effective acoustic modulation characteristics over a wide frequency range; 2. The fiber structure with a large aspect ratio is conducive to more uniformly dividing the micron-sized pores inside the SiC template, thereby improving the reflection behavior of different signals (electromagnetic waves, sound waves, and mechanical waves) after entering the material, which is conducive to the synergistic optimization of different signals.

[0055] In a specific embodiment of the present invention, the framework is a structure formed by attaching a silicon carbide coating onto a carbon foam substrate via chemical vapor deposition, followed by foaming. Preferably, the framework is a quasi-topological structure formed by three-dimensional repeating stacks of hollow multi-rings, wherein the multi-rings are one of regular pentagons or regular hexagons with a side length of 10μm to 30μm and a side diameter of 600nm to 1200nm; the shell layer of the hollow multi-rings, i.e., the silicon carbide coating, is an amorphous SiC layer with a thickness not exceeding 15nm.

[0056] As a specific embodiment of the present invention, the shell-core structure has a shell layer of ceramizable silicone rubber CSR with a thickness of 10nm to 20nm and a core of SiC nanowires with a diameter of 30nm to 70nm.

[0057] Preferably, the ceramizable silicone rubber is one or a mixture of organosilicon silicone rubber, siloxane silicone rubber, fluorinated modified silicone rubber, and metal oxide modified silicone rubber.

[0058] The following specific embodiments illustrate the preparation method of the dual continuous network composite aerogel with a large aspect ratio shell-core structure and in-situ embedded porous silicon carbide foam in this invention.

[0059] I. Preparation method (process as follows) Figure 1 (As shown)

[0060] Example 1

[0061] (1) Place melamine foam in a high-temperature furnace, evacuate and protect with inert gas, introduce protective gas at a flow rate of 20 sccm, slowly heat to 800℃, keep warm for 0.5h and then cool to obtain carbon foam skeleton structure.

[0062] (2) A porous silicon carbide coating was prepared by chemical vapor deposition. The carbon foam skeleton structure prepared in step (1) was placed in the deposition apparatus, and an inert gas was introduced into the methyltrichlorosilane (MTS) solution at a flow rate of 20 sccm, thereby introducing it into the deposition apparatus. The gas was continued for 5 min. Then the valves on both sides of the deposition apparatus were closed, the temperature was slowly raised to 1000℃, deposition was carried out for 5 min, and the temperature was slowly cooled to room temperature to obtain a silicon carbide coating covering the porous carbon foam skeleton structure.

[0063] (3) The porous carbon foam skeleton structure coated with silicon carbide obtained in step (2) is placed in a high-temperature furnace and heated to 500°C for 2 hours in an air atmosphere to obtain a porous silicon carbide foam skeleton.

[0064] (4) Immerse the porous silicon carbide foam skeleton in nickel salt solution for 5 minutes, and then dry it in an environment of 40°C until the solvent is completely evaporated.

[0065] (5) Preparation of SiC nanowire filling phase. The material obtained in step (4) was placed in a vacuum furnace and heated slowly to 900°C with an inert gas flow rate of 30 sccm. After evacuation, H2 and MTS were introduced simultaneously. After holding at the temperature for 1 h, the temperature was cooled to room temperature to obtain a high aspect ratio SiC nanowire embedded porous silicon carbide foam bicontinuous network composite aerogel.

[0066] (6) The ceramicizable silicone rubber is mixed with a solvent to ensure that the viscosity of the mixture is less than 4000 mPa·s and has high fluidity. Then, the high aspect ratio SiC nanowire embedded porous silicon carbide foam dual continuous network composite aerogel obtained in step (5) is placed in a vacuum device, and the mixed ceramicizable silicone rubber mixture is drawn in. The mixture is degassed at 40°C and 0.01 MPa to obtain the high aspect ratio shell and core structure SiC@CSR nanowire embedded porous silicon carbide foam dual continuous network composite aerogel.

[0067] (7) The composite aerogel obtained in step (6) was cured at 80°C for 6 hours to form the final composite aerogel. The porosity of the composite aerogel was measured to be 96.7%, and the density was 12 kg / m³. 3 Reflection loss -60dB.

[0068] Example 2

[0069] (1) Place melamine foam in a high-temperature furnace, evacuate and protect with inert gas, introduce protective gas at a flow rate of 50 sccm, slowly heat to 1000℃, keep warm for 1 hour and then cool to obtain carbon foam skeleton structure.

[0070] (2) A porous silicon carbide coating was prepared by chemical vapor deposition. The carbon foam skeleton structure prepared in step (1) was placed in the deposition apparatus, and an inert gas was introduced into the methyltrichlorosilane (MTS) solution at a flow rate of 30 sccm, thereby introducing it into the deposition apparatus. The gas was continued for 10 min. Then the valves on both sides of the deposition apparatus were closed, the temperature was slowly raised to 1100℃, deposition was carried out for 8 min, and the temperature was slowly cooled to room temperature to obtain a silicon carbide coating covering the porous carbon foam skeleton structure.

[0071] (3) The porous carbon foam skeleton structure coated with silicon carbide obtained in step (2) is placed in a high-temperature furnace and heated to 700°C for 3 hours in an air atmosphere to obtain a porous silicon carbide foam skeleton.

[0072] (4) Immerse the porous silicon carbide foam skeleton in nickel salt solution for 60 min, and then dry it in an environment of 80°C until the solvent is completely evaporated.

[0073] (5) Preparation of SiC nanowire filling phase. The material obtained in step (4) was placed in a vacuum furnace and heated slowly to 1050℃ with an inert gas flow rate of 350 sccm. After evacuation, H2 and MTS were introduced at the same time. After holding at the temperature for 2 hours, it was cooled to room temperature to obtain a high aspect ratio SiC nanowire embedded porous silicon carbide foam bicontinuous network composite aerogel.

[0074] (6) The ceramicizable silicone rubber is mixed with a solvent to ensure that the viscosity of the mixture is less than 4000 mPa·s and has high fluidity. Then, the high aspect ratio SiC nanowire embedded porous silicon carbide foam dual continuous network composite aerogel obtained in step (5) is placed in a vacuum device, and the mixed ceramicizable silicone rubber mixture is drawn in. The aerogel is degassed at 60°C and 0.05 MPa to obtain the high aspect ratio shell and core structure SiC@CSR nanowire embedded porous silicon carbide foam dual continuous network composite aerogel.

[0075] (7) The composite aerogel obtained in step (6) was cured at 140℃ for 8 hours to form the final composite aerogel. The porosity of the composite aerogel was measured to be 97.4%, and the density was 23 kg / m³. 3 Reflection loss -20dB.

[0076] Example 3

[0077] (1) Place melamine foam in a high-temperature furnace, evacuate and protect with inert gas, introduce protective gas at a flow rate of 80 sccm, slowly heat to 1100℃, keep warm for 2 hours and then cool to obtain carbon foam skeleton structure.

[0078] (2) A porous silicon carbide coating was prepared by chemical vapor deposition. The carbon foam skeleton structure prepared in step (1) was placed in the deposition apparatus, and an inert gas was introduced into the methyltrichlorosilane (MTS) solution at a flow rate of 50 sccm, thereby carrying it into the deposition apparatus. The gas was continued for min. Then the valves on both sides of the deposition apparatus were closed, the temperature was slowly raised to 1300℃, deposition was carried out for 10 min, and the temperature was slowly cooled to room temperature to obtain a silicon carbide coating covering the porous carbon foam skeleton structure.

[0079] (3) The porous carbon foam skeleton structure coated with silicon carbide obtained in step (2) is placed in a high-temperature furnace and heated to 800°C in an air atmosphere for 4 hours to obtain a porous silicon carbide foam skeleton.

[0080] (4) Immerse the porous silicon carbide foam skeleton in nickel salt solution for 120 min, and then dry it in an environment of 100°C until the solvent is completely evaporated.

[0081] (5) Preparation of SiC nanowire filling phase. The material obtained in step (4) was placed in a vacuum furnace and heated slowly to 1200℃ with an inert gas flow rate of 70 sccm. After evacuation, H2 and MTS were introduced at the same time. After holding at the temperature for 3 hours, it was cooled to room temperature to obtain a high aspect ratio SiC nanowire embedded porous silicon carbide foam dual continuous network composite aerogel.

[0082] (6) The ceramizable silicone rubber is mixed with a solvent to ensure that the viscosity of the mixture is less than 4000 mPa·s and has high fluidity. Then, the high aspect ratio SiC nanowire embedded porous silicon carbide foam dual continuous network composite aerogel obtained in step (5) is placed in a vacuum device, and the well-mixed ceramizable silicone rubber mixture is drawn in. The mixture is degassed at 80°C and a vacuum of 0.08 MPa to obtain the high aspect ratio shell-core structure SiC@CSR nanowire embedded porous silicon carbide foam dual continuous network composite aerogel.

[0083] (7) The composite aerogel obtained in step (6) was cured at 200℃ for 10 hours to form the final composite aerogel. The porosity of the composite aerogel was measured to be 98.8%, and the density was 30 kg / m³. 3 Reflection loss -70dB.

[0084] II. Experimental Testing

[0085] Multiple composite aerogels prepared in Examples 1 to 3 were used for performance testing experiments.

[0086] 2.1 Microscopic morphology

[0087] See Figures 2-3It can be clearly seen that the composite aerogel structure includes a porous silicon carbide foam framework 22 with in-situ grown core-shell structure SiC@CSR nanowires 21 embedded within it. After SEM analysis of the composite aerogels prepared in this invention, such as the group of products in Example 2, the following can be observed... Figure 4 As shown, it is possible to obtain: SiC nanowires with a large aspect ratio are embedded in situ within a porous silicon carbide foam framework.

[0088] 2.2 Compressive strength test

[0089] Figures 5-6 , Figure 5 The statistics on the diameter of the SiC nanowires in Example 2 show that the average diameter of the nanowires is 64 nm. Figure 6 Compression tests were conducted on the product from Example 1. The compression performance was tested using a computer-controlled universal testing machine (E43.104, MTS, China). The sample size was 10mm x 10mm, and the compressive strain was 75%. The compressive stress was obtained by dividing the pressure from the sensor by the sample area. The stress-strain curves show that the compressive strength reaches 50 kPa when the deformation is 50%, and increases with increasing deformation. No destructive fractures occurred during compression, reflecting the structural stability of the composite aerogel.

[0090] 2.3 Absorption Performance Test

[0091] Figure 7 The reflection loss of the composite aerogel prepared in Example 3 was measured using a vector network analyzer (Ceyear 3672B, CETC Science Instrument), following standard GB / T 35679-2017. The sample was prepared by mixing fibers and paraffin wax in a 4:6 ratio to form concentric rings with an outer diameter of 7 mm and an inner diameter of 3.04 mm. The electromagnetic parameters were plotted using Origin. It can be seen that it possesses excellent electromagnetic wave absorption performance.

[0092] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A dual-continuous network composite aerogel with a high aspect ratio shell-core structure and in-situ embedded porous silicon carbide foam, characterized in that: Including shell and core structure, and framework; The core-shell structure includes a core and a shell, with the shell wrapping around the core. The shell is a ceramicizable silicone rubber layer structure, and the core is a continuous network structure of SiC nanowires. The framework is a continuous network structure of porous silicon carbide foam. The core-shell structure is embedded in situ on the framework structure, forming an interpenetrating double continuous network composite structure. The skeleton is a structure formed by attaching a silicon carbide coating onto a carbon foam matrix using a chemical vapor deposition method, followed by a foaming process. The composite aerogel has an open porosity greater than 95% and a density of 10~30 kg / m³. 3 Compressive strength 0.03~0.5 MPa; The shell has a thickness of 10~20 nm, the core has an amorphous structure with a diameter of 30~70 nm, and the aspect ratio of the core is 2000~4000; The shell layer includes at least one of organosilicon rubber, siloxane-containing silicone rubber, fluorinated modified silicone rubber, and metal oxide modified silicone rubber. The framework is a topological structure formed by three-dimensional repeating stacks of hollow multi-rings, and the thickness of the silicon carbide coating does not exceed 15 nm. The hollow multi-element ring is at least one of a regular pentagon or a regular hexagon with a side length of 10-30 μm and a side diameter of 600-1200 nm.

2. The method for preparing a dual-continuous network composite aerogel with a high aspect ratio shell-core structure and in-situ embedded porous silicon carbide foam according to claim 1, characterized in that: Includes the following steps: (1) Preparation of carbon foam matrix: Melamine foam is placed in a high-temperature furnace, vacuumed and protected with inert gas, and protective gas is introduced at a flow rate of 20~80 sccm. The temperature is slowly raised to 800~1100 ℃, and the temperature is maintained for 0.5~2 h before cooling to obtain carbon foam skeleton matrix; (2) Preparation of silicon carbide coating: The substrate obtained in (1) is placed in a chemical vapor deposition device, and an inert gas is introduced into a methyltrichlorosilane (MTS) solution and then introduced into the deposition device. The gas is continued until the valves on both sides of the deposition device are closed. The temperature is slowly increased, and after deposition for a period of time, the temperature is slowly cooled to room temperature to obtain a silicon carbide coating covering a porous carbon foam skeleton structure. (3) Pyrolysis treatment: The porous carbon foam skeleton structure coated with silicon carbide obtained in (2) is placed in a high-temperature furnace and heated to 500~800 ℃ in an air atmosphere for 2~4 h to obtain a porous silicon carbide foam skeleton. (4) Nickel salt impregnation treatment: The porous silicon carbide foam skeleton obtained in (3) is impregnated in nickel salt solution for 5~120 min, and then dried in an environment of 40~100 ℃ until the solvent ethanol is completely evaporated; (5) Preparation of silicon carbide nanowires: The material obtained in (4) is placed in a vacuum furnace and an inert gas is introduced at a flow rate of 30~70 sccm. The temperature is slowly raised to 900~1200 ℃. Then, after evacuation, H2 and MTS are introduced at the same time. After keeping the temperature for 1~3 h, it is cooled to room temperature to obtain a composite aerogel with a large aspect ratio SiC nanowire embedded porous silicon carbide foam double continuous network. (6) Silicone rubber filling and degassing: The high aspect ratio SiC nanowire embedded porous silicon carbide foam double continuous network composite aerogel obtained in (5) is placed in a vacuum device, and a mixture of ceramicizable silicone rubber and ethanol is drawn in. Degassing is performed at a certain temperature and a certain vacuum to obtain a high aspect ratio shell and core structure SiC@CSR nanowire embedded porous silicon carbide foam double continuous network composite aerogel. (7) Curing and molding: The composite aerogel obtained in (6) is cured at 80~200 ℃ for 6~10 h to form the final composite aerogel.

3. The method for preparing the dual continuous network composite aerogel with a large aspect ratio shell-core structure and in-situ embedded porous silicon carbide foam according to claim 2, characterized in that: In step (4), the nickel salt solution is one or a mixture of nickel nitrate, nickel chloride, nickel acetate or nickel sulfate, and the solvent is ethanol.

4. The method for preparing the dual continuous network composite aerogel with a large aspect ratio shell-core structure and in-situ embedded porous silicon carbide foam according to claim 2, characterized in that: In step (6), the degassing temperature is 40~80 ℃ and the vacuum degree is 0.01~0.08MPa.

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