SiC composite aerogel-based electromagnetic wave absorbing material and preparation method thereof

Abstract

The application relates to a SiC composite aerogel-based electromagnetic wave absorbing material and a preparation method thereof, and comprises the following steps: uniformly stirring amine-based bridged siloxane, organosilane and an organic solvent, adding water and continuously stirring until uniformity to obtain a sol, and obtaining a gel after standing; placing the obtained gel in an oven for aging, cleaning with an organic solvent to remove residual impurities, and performing drying treatment to obtain silicon-carbon in-situ hybrid aerogel; performing high-temperature carbonization and pyrolysis on the obtained silicon-carbon in-situ hybrid aerogel under a protective atmosphere; and performing high-temperature carbon thermal reduction on the obtained product under a protective atmosphere to obtain the SiC composite aerogel-based electromagnetic wave absorbing material. The SiC composite aerogel-based electromagnetic wave absorbing material prepared by the application exhibits excellent wave absorbing performance, and has the advantages of wide raw material sources, low cost, simple synthesis process, mild preparation conditions and the like, and provides a new scheme for the preparation of SiC aerogel.

Description

Technical Field

[0001] This invention relates to the field of new materials technology, and in particular to a SiC composite aerogel-based electromagnetic absorbing material and its preparation method. Background Technology

[0002] Silicon carbide (SiC) is an important third-generation wide-bandgap semiconductor material with a series of advantages, including low density, high temperature resistance, oxidation resistance, high strength, corrosion resistance, low coefficient of thermal expansion, and designable dielectric properties, making it highly promising for applications in the field of high-temperature broadband microwave absorbing materials. Current research on SiC absorbing materials includes morphologies such as particles, fibers, whiskers, nanowires, foams, core-shell composites, and aerogels. Among these, aerogels possess a three-dimensional nano-hierarchical porous network structure. This unique structure provides ample porous space for reflecting and scattering electromagnetic waves and helps improve impedance matching. Furthermore, it exhibits excellent properties such as low density and low thermal conductivity, making SiC aerogel a highly promising high-temperature electromagnetic wave absorbing material. However, research on SiC aerogel materials in the field of microwave absorption is still in its early stages, and its research and industrialization face multiple challenges and limitations, mainly reflected in complex preparation processes, high costs, poor high-temperature resistance, and fragile mechanical properties.

[0003] In existing technologies, patent documents (publication number CN119118696A and CN102351506A) use silicon and carbon precursors as raw materials. First, a composite aerogel is obtained through a one-pot sol-gel process, aging, and drying. Then, SiC aerogel material is obtained through a carbothermic reduction reaction under argon protection. This method suffers from problems such as a large variety of raw materials, uneven mixing of silicon and carbon precursors at the nanoscale, mismatched shrinkage of the two precursors, and unadjustable dielectric properties of SiC. Patent document (publication number CN114230379A) ​​uses polycarbosilane as the silicon source and vinyl compounds as the carbon source. The silicon and carbon source precursors are first prepared into a solution, and then a hydrosilylation reaction is carried out under anaerobic conditions at 90-150 °C with a Pt catalyst to form a precursor gel. After drying and high-temperature calcination at 1000-1600 °C under anaerobic conditions, SiC aerogel is obtained. This method also suffers from the problems of requiring a wide variety of raw materials and stringent precursor gelation conditions, and the high cost of precursors hinders large-scale industrial applications. Patent literature (publication number CN118846976A) describes the preparation of SiC / Fe-3Si composite aerogel absorbing materials by doping with Fe-3Si. While the addition of magnetic components improves the material's absorption performance, it is highly susceptible to oxidation and failure at high temperatures, significantly reducing the material's operating temperature. Therefore, the preparation process of SiC aerogels is relatively complex. Developing a simple and low-cost preparation technique is of great significance for the research and application of SiC aerogels in microwave absorption.

[0004] The information disclosed in this background section is intended only to enhance the understanding of the general background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide a SiC composite aerogel-based electromagnetic absorbing material and its preparation method, so as to solve the problems of complex process, low yield and high cost in the existing SiC aerogel preparation technology.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a SiC composite aerogel-based electromagnetic absorbing material, comprising the following steps: S1. Thoroughly mix the amino-bridged siloxane, organosilane and organic solvent, add water and continue stirring until uniform to obtain a sol, and then let it stand to obtain a gel. S2. The gel obtained in step S1 is placed in an oven for aging, cleaned with an organic solvent to remove residual impurities, and then dried to obtain silicon-carbon in-situ hybrid aerogel thermal insulation material. S3. The silicon-carbon in-situ hybrid aerogel obtained in step S2 is subjected to high-temperature carbonization and pyrolysis under a protective atmosphere. S4. The product obtained in step S3 is subjected to high-temperature carbothermal reduction under a protective atmosphere to obtain SiC composite aerogel-based electromagnetic absorbing material.

[0007] The present invention provides a method for preparing SiC composite aerogel-based electromagnetic absorbing materials. Using amino-bridged siloxanes and organosilanes as silicon sources, a silicon-carbon in-situ hybrid aerogel containing both Si and C elements in its molecular structure is prepared through autocatalytic gelation and drying processes. The SiC composite aerogel-based electromagnetic absorbing material is then obtained through high-temperature carbonization pyrolysis and high-temperature carbothermal reduction reactions. This method has significant advantages such as wide availability of raw materials, low cost, simple synthesis process, and mild precursor gel preparation conditions, and has potential application prospects in the field of SiC aerogel preparation.

[0008] Preferably, in step S1, the amino-bridged siloxane includes one or more of the following: bis[3-(trimethoxysilyl)propyl]amine, bis(3-triethoxysilylpropyl)amine, 3-aminopropyltrimethoxysilane, and 3-aminopropyltriethoxysilane.

[0009] Preferably, in step S1, the organosilane includes one or more of tetramethoxysilane, tetraethoxysilane, methyltriethoxysilane, and methyltrimethoxysilane.

[0010] Preferably, in steps S1 and S2, the organic solvent includes one or more of ethanol, methanol, acetone, n-heptane, and n-hexane.

[0011] Preferably, in step S1, the molar ratio of the organosilane, organic solvent, water and amino-bridged siloxane is (0~5):(6~80):(6~15):1.

[0012] Preferably, in step S1, the temperature during the settling period is 30~60 ℃ and the time is 0.1~24h.

[0013] In step S1 of this invention, the amino groups in the amino-bridged siloxane molecule bind hydrogen ions (H+) from water molecules, releasing hydroxide ions (OH-). These OH- ions, in turn, promote the de-alcoholization and hydrolysis of the two silicon sources, converting alkoxy groups into highly reactive silanol groups. The silanol groups then undergo dehydration condensation and cross-linking reactions, transforming the solution into a sol. As the hydrolysis and condensation reactions continue, the silicon source molecules cross-link to form a silicon-carbon in-situ hybrid aerogel containing Si and C elements. Furthermore, by adjusting the ratio of organosilanes and amino-bridged siloxanes, the relative contents of Si, C, N, and O elements in the precursor can be directly changed, thereby achieving precise control of the microwave absorption properties of the SiC composite aerogel through N doping regulation.

[0014] Preferably, in step S2, the aging temperature is 30~60℃ and the time is 24~48h.

[0015] Preferably, in step S2, the drying process includes one or more of the following: supercritical carbon dioxide drying, supercritical ethanol drying, or vacuum freeze drying.

[0016] Preferably, in step S3, the protective atmosphere is argon or nitrogen, and the gas flow rate is 5~20 mL / min.

[0017] Preferably, in step S3, the high-temperature carbonization pyrolysis specifically involves heating to 800-1000 °C at a rate of 1-10 °C / min.

[0018] In step S3 of this invention, the silicon-carbon in-situ hybrid aerogel undergoes a high-temperature carbonization and pyrolysis reaction, producing a large amount of amorphous free carbon and SiO2. During this process, the breaking of carbon-carbon bonds and carbon-hydrogen bonds also generates some small molecule gases (CO, H2, etc.). The argon atmosphere can be used as a protective gas and at the same time promotes the discharge of pyrolysis gases.

[0019] Preferably, in step S4, the protective atmosphere is argon, and the gas flow rate is 5~20 mL / min.

[0020] Preferably, in step S4, the high-temperature carbothermic reduction specifically involves: continuing to heat to 1200-1600 °C at a rate of 5-10 °C / min, holding at this temperature for 2-4 hours, and then naturally cooling to room temperature.

[0021] In step S4 of this invention, the silicon-carbon in-situ hybrid aerogel continues to undergo a carbothermic reduction reaction at a temperature higher than 1200 °C. The free carbon in step S3 diffuses to the SiO2 interface, realizing the gradual reduction and carbonization of silicon atoms, and finally forming a SiC composite aerogel-based electromagnetic absorbing material with in-situ N doping.

[0022] Secondly, the present invention provides a SiC composite aerogel-based electromagnetic absorbing material obtained by the preparation method of the SiC composite aerogel described above.

[0023] By adopting the above technical solution, the present invention has at least the following beneficial effects: 1. The method for preparing SiC composite aerogel-based electromagnetic absorbing materials provided by this invention uses amino-bridged siloxanes as silicon sources to obtain in-situ silicon-carbon hybrid aerogels containing both Si and C in their molecular structure through autocatalytic gelation. Then, SiC composite aerogels are obtained through high-temperature carbonization pyrolysis and high-temperature carbothermal reduction reactions. Compared with common SiC aerogel preparation methods such as template methods, organic / SiO2 composite aerogel carbothermal reduction methods, and polymer precursor pyrolysis methods, this method has significant advantages such as wide availability of raw materials, low cost, simple synthesis process, and mild precursor gelation conditions, providing a new approach for the preparation of SiC aerogels.

[0024] 2. The preparation method of SiC composite aerogel-based electromagnetic absorbing material provided by the present invention can directly change the relative content of Si, C, N and O elements in the precursor by introducing organosilicon into amino-bridged siloxane, thereby conveniently realizing the precise control of N doping in SiC composite aerogel, and thus adjusting its absorption performance, so that the absorption frequency band can be suitable for different application scenarios.

[0025] 3. Compared with other forms of SiC absorbing materials, the SiC composite aerogel prepared by this invention has the characteristics of being lightweight, and the three-dimensional nanostructure enhances the reflection loss of the multi-level pores, which helps to enhance the electromagnetic absorption performance.

[0026] 4. The SiC composite aerogel-based electromagnetic absorbing material provided by this invention exhibits excellent wave absorption performance. Attached Figure Description

[0027] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0028] Figure 1 These are microscopic morphology images of the SiC composite aerogel-based electromagnetic absorbing material at different stages during the preparation process in Example 1 of this invention. Figure 2 XPS spectra and elemental contents at different stages during the preparation of the SiC composite aerogel-based electromagnetic absorbing material in Example 1 of this invention; Figure 3 The diagram shows the microwave absorption performance of the SiC composite aerogel-based electromagnetic absorbing material in Example 1 of this invention. Figure 4 The nitrogen adsorption-desorption isotherm and pore size distribution curves of the SiC composite aerogel-based electromagnetic absorbing materials in Examples 1-3 of this invention are shown. Detailed Implementation

[0029] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and implementations of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of the present invention.

[0030] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0031] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0032] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0033] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to. Example 1

[0034] This embodiment provides a method for preparing a SiC composite aerogel-based electromagnetic absorbing material, including the following steps: S1. Mix bis[3-(trimethoxysilyl)propyl]amine and ethanol thoroughly, then add water and continue stirring until homogeneous to obtain a sol. Let it stand at 30°C for 5 hours to obtain a gel. The molar ratio of the raw materials is as follows: ethanol:water:bis[3-(trimethoxysilyl)propyl]amine = 15:8:1.

[0035] S2. The gel obtained in step S1 is aged in a 40°C oven for 48 hours, washed with ethanol to remove residual impurities, and then dried with supercritical carbon dioxide to obtain silicon-carbon in-situ hybrid aerogel thermal insulation material.

[0036] S3. Place the silicon-carbon in-situ hybrid aerogel obtained in step S2 into a tube furnace, and heat it to 1000 °C at a rate of 5 °C / min in an argon atmosphere with a gas flow rate of 10 mL / min for high-temperature carbonization and pyrolysis.

[0037] S4. The product obtained in step S3 is subjected to high-temperature carbothermal reduction in an argon atmosphere with a gas flow rate of 10 mL / min and a rate of 5 °C / min, and then naturally cooled to room temperature after holding at this temperature for 3 h to obtain the SiC composite aerogel-based electromagnetic absorbing material.

[0038] The results show that the SiC composite aerogel-based electromagnetic absorbing material prepared in this embodiment has a porosity of 87.5% and a specific surface area of ​​191.24 m². 2 The Si, O, N and C elements are 38.03%, 14.97%, 4.26% and 42.74% respectively. With a thickness of 1.8 mm, the minimum reflection loss is -49.2 dB at 14.0 GHz and the effective absorption bandwidth is 5.2 GHz (12.8 GHz~18 GHz).

[0039] Figure 1The figures show the microstructure of the SiC composite aerogel-based electromagnetic absorbing material at different stages during its preparation in this embodiment. (ab) represents the silicon-carbon in-situ hybrid aerogel prepared in step S2, (cd) represents the high-temperature carbonization and pyrolysis stage in step S3, and (eh) represents the high-temperature carbothermal reduction stage in step S4. As can be seen from the figures, the precursor hybrid aerogel possesses a typical pearl-chain network framework structure and a three-dimensional nanoporous network structure, with uniform and evenly distributed framework and pore sizes. For the sample at 1000 °C, its structure is still mainly composed of nanoparticles, but the pore size is very small. This is because the sample underwent carbonization and pyrolysis at high temperatures, causing a dramatic shrinkage of the microstructure and the original nanoporous structure of the aerogel. For the sample at 1400 °C, its microstructure re-exhibits a typical aerogel morphology. The framework structure is assembled from uniformly cross-linked nanoparticles, and a rich and well-developed nanoporous structure is formed between the framework structures. This is because the sample, after dramatic shrinkage, continued to undergo pyrolysis and carbothermal reduction reactions, removing a large number of unstable structures and thus forming a rich pore structure. The sample at 1500 °C retains the microstructure of the sample pyrolyzed at 1400 °C, maintaining a three-dimensional porous network structure. However, the framework structure is primarily composed of irregular rod-shaped whiskers and nanoparticles. This is because the continuous carbothermal reduction reaction causes the nucleated SiC to grow along its dominant direction. Since the raw materials required for its growth originate from amorphous carbon and SiO2 on a randomly cross-linked, curved framework structure, rod-shaped whiskers are formed that grow irregularly along a certain direction. The sample at 1500 °C exhibits a typical aerogel porous network structure and can therefore be termed a SiC composite aerogel.

[0040] Figure 2The figures show XPS spectra and elemental contents at different stages during the preparation of the SiC composite aerogel-based electromagnetic absorbing material in this embodiment. As can be seen from the figures, the atomic ratio of Si, O, N, and C in the hybrid aerogel precursor is approximately 2:3:1:6. At 1000 °C, the C and N contents in the sample significantly decreased, while the Si and O contents increased, indicating that C and N elements were largely decomposed and removed during the carbonization and pyrolysis process, while Si and O remained relatively stable under the high-temperature argon inert atmosphere, hence their relatively higher contents. At 1400 °C, the O content in the pyrolysis sample significantly decreased because a carbothermic reduction reaction occurred at this temperature, generating SiC and removing O, thus increasing the Si and C contents relatively. Furthermore, the N content further decreased due to high-temperature pyrolysis or the carbothermic reduction reaction. As the carbothermic reduction reaction continued, the O content in the 1500 °C pyrolysis sample continued to decrease, while the Si and C contents continued to increase, and the N content remained essentially unchanged. The atomic contents of Si, O, N and C elements in the SiC composite aerogel prepared at 1500 °C are 38.03%, 14.97%, 4.26% and 42.74%, respectively.

[0041] Figure 3 The graph shows the reflection loss curve and absorption performance of the SiC composite aerogel-based electromagnetic absorbing material in this embodiment. As can be seen from the graph, at a thickness of 1.8 mm, the minimum reflection loss of the sample is -49.2 dB at 14.0 GHz, and the effective absorption bandwidth is as high as 5.2 GHz (12.8 GHz ~ 18 GHz) at a thickness of 1.7 mm, indicating that the SiC composite aerogel has excellent electromagnetic wave absorption performance. Example 2

[0042] This embodiment provides a method for preparing a SiC composite aerogel-based electromagnetic absorbing material, including the following steps: S1. Mix bis[3-(trimethoxysilyl)propyl]amine, methyltrimethoxysilane and ethanol thoroughly, then add water and continue stirring until homogeneous to obtain a sol. Let it stand at 30°C for 5 hours to obtain a gel. The molar ratio of the raw materials is as follows: methyltrimethoxysilane: ethanol: water: bis[3-(trimethoxysilyl)propyl]amine = 0.5: 15: 8: 1.

[0043] S2. The gel obtained in step S1 is aged in a 40°C oven for 48 hours, washed with ethanol to remove residual impurities, and then dried with supercritical carbon dioxide to obtain silicon-carbon in-situ hybrid aerogel thermal insulation material.

[0044] S3. Place the silicon-carbon in-situ hybrid aerogel obtained in step S2 into a tube furnace, and heat it to 1000 °C at a rate of 5 °C / min in an argon atmosphere with a gas flow rate of 10 mL / min for high-temperature carbonization and pyrolysis.

[0045] S4. The product obtained in step S3 is subjected to high-temperature carbothermal reduction in an argon atmosphere with a gas flow rate of 10 mL / min and a rate of 5 °C / min, and then naturally cooled to room temperature after holding at this temperature for 3 h to obtain the SiC composite aerogel-based electromagnetic absorbing material.

[0046] The results show that the SiC composite aerogel-based electromagnetic absorbing material prepared in this embodiment has a porosity of 87.1% and a specific surface area of ​​188.96 m². 2 The Si, O, N and C elements are 40.21%, 20.86%, 2.19% and 36.74% respectively. With a thickness of 5.4 mm, the minimum reflection loss is -35.4 dB at 14.5 GHz and the effective absorption bandwidth is 5.1 GHz (12.1 GHz ~ 17.2 GHz). Example 3

[0047] This embodiment provides a method for preparing a SiC composite aerogel-based electromagnetic absorbing material, including the following steps: S1. Mix bis[3-(trimethoxysilyl)propyl]amine, methyltrimethoxysilane and ethanol thoroughly, then add water and continue stirring until homogeneous to obtain a sol. Let it stand at 30°C for 5 hours to obtain a gel. The molar ratio of the raw materials is as follows: methyltrimethoxysilane: ethanol: water: bis[3-(trimethoxysilyl)propyl]amine = 1:15:8:1.

[0048] S2. The gel obtained in step S1 is aged in a 40°C oven for 48 hours, washed with ethanol to remove residual impurities, and then dried with supercritical carbon dioxide to obtain silicon-carbon in-situ hybrid aerogel thermal insulation material.

[0049] S3. Place the silicon-carbon in-situ hybrid aerogel obtained in step S2 into a tube furnace, and heat it to 1000 °C at a rate of 5 °C / min in an argon atmosphere with a gas flow rate of 10 mL / min for high-temperature carbonization and pyrolysis.

[0050] S4. The product obtained in step S3 is subjected to high-temperature carbothermal reduction in an argon atmosphere with a gas flow rate of 10 mL / min and a rate of 5 °C / min, and then naturally cooled to room temperature after holding at this temperature for 3 h to obtain the SiC composite aerogel-based electromagnetic absorbing material.

[0051] The results show that the SiC composite aerogel-based electromagnetic absorbing material prepared in this embodiment has a porosity of 86.7% and a specific surface area of ​​181.24 m². 2The Si, O, N and C elements are 42.08%, 24.13%, 0.85% and 32.94% respectively. With a thickness of 5.0 mm, the minimum reflection loss is -32.5 dB at 14.6 GHz and the effective absorption bandwidth is 3.2 GHz (11.5 GHz~14.7 GHz).

[0052] Figure 4 The figures show the nitrogen adsorption-desorption isotherms and pore size distribution curves of the SiC composite aerogel-based electromagnetic absorbing materials in Examples 1-3. As can be seen from the figures, the nitrogen adsorption curves of the SiC composite aerogels prepared with different raw material ratios in Examples 1-3 exhibit typical mesoporous adsorption-desorption characteristics, i.e., a significant hysteresis loop forms in the adsorption-desorption curves within the relative pressure range of 0.4-0.9. Furthermore, the nitrogen adsorption amounts in the three examples are similar, and the nitrogen adsorption-desorption curves are similar. The pore size distribution curves further indicate that the pore size distribution curves of the three examples are similar, the pore size distribution is relatively uniform, and the nanopore size is concentrated around 9.3 nm. Comparative Example 1

[0053] This comparative example is basically the same as Example 1, except that only steps S1 and S2 were performed, while steps S3 and S4 were not performed. Specifically, bis[3-(trimethoxysilyl)propyl]amine and ethanol were thoroughly stirred until homogeneous, then water was added, and stirring continued until homogeneous to obtain a sol. This sol was then allowed to stand at 30°C for 5 hours to obtain a gel. The molar ratio of the raw materials was as follows: ethanol:water:bis[3-(trimethoxysilyl)propyl]amine = 15:8:1. The gel was aged in a 40°C oven for 48 hours, washed with ethanol to remove residual impurities, and then dried using supercritical carbon dioxide to obtain a silicon-carbon in-situ hybrid aerogel insulation material.

[0054] The results show that, since it has not undergone high-temperature carbonization and pyrolysis reactions and high-temperature carbothermal reduction reactions, the silicon-carbon in-situ hybrid aerogel is mainly composed of a continuous silicon oxide phase and has no magnetic phase. This results in a lack of effective electrical conduction loss, dielectric loss and magnetic loss mechanisms, and it has no electromagnetic wave absorption properties, thus belonging to the category of wave-transparent materials. Comparative Example 2

[0055] This comparative example is basically the same as Example 2, except that in step S1, the molar ratio of methyltrimethoxysilane to bis[3-(trimethoxysilyl)propyl]amine is 6:1. The specific process is as follows: bis[3-(trimethoxysilyl)propyl]amine, methyltrimethoxysilane and ethanol are thoroughly stirred evenly, then water is added and stirring is continued until uniform to obtain a sol. The sol is then placed at 30°C and allowed to stand for 5 hours to obtain a gel. The molar ratio of the raw materials is as follows: methyltrimethoxysilane: ethanol: water: bis[3-(trimethoxysilyl)propyl]amine = 6:15:8:1.

[0056] The results show that the low nitrogen doping content in the SiC composite aerogel leads to a low dielectric constant and weak dielectric loss, resulting in poor electromagnetic wave absorption performance as it cannot effectively attenuate incident electromagnetic waves. At a thickness of 5.0 mm, the minimum reflection loss is -3.7 dB at 6.5 GHz. Comparative Example 3

[0057] This comparative example is basically the same as Example 1, except that in step S1, the molar ratio of water to bis[3-(trimethoxysilyl)propyl]amine is 1:1. The specific process is as follows: bis[3-(trimethoxysilyl)propyl]amine and ethanol are thoroughly stirred until homogeneous, then water is added, and stirring is continued until homogeneous to obtain a sol. The sol is then placed at 30°C and allowed to stand for 5 hours to obtain a gel. The molar ratio of the raw materials is as follows: ethanol:water:bis[3-(trimethoxysilyl)propyl]amine = 15:1:1.

[0058] The results show that due to the low proportion of water, the silicon source cannot be fully hydrolyzed, resulting in incomplete gelation and the inability to form a silicon-carbon in-situ hybrid aerogel with a certain strength. Comparative Example 4

[0059] This comparative example is basically the same as Example 1, except that in step S2, the aerogel is dried at normal pressure. The specific process is as follows: the gel after displacement in step S3 is placed in an oven and the temperature is increased in a gradient order of 30℃-40℃-50℃-60℃-70℃-80℃, and each temperature is maintained for 3 hours, finally obtaining silicon-carbon in-situ hybrid aerogel.

[0060] The results showed that due to the rapid evaporation rate of ethanol under normal pressure drying, the capillary force within the gel increased sharply, leading to pore collapse and a large shrinkage rate. The resulting silicon-carbon in-situ hybrid aerogel had a porosity of 67.1% and a specific surface area of ​​94.35 m². 2 / g, and the surface has obvious cracks. Comparative Example 5

[0061] This comparative example is basically the same as Example 1, except that a carbon dioxide atmosphere is used in steps S3 and S4. Specifically, the silicon-carbon in-situ hybrid aerogel described in step S2 is placed in a tube furnace and heated to 1300 °C at a rate of 5 °C / min in a carbon dioxide atmosphere with a gas flow rate of 10 mL / min for high-temperature carbonization and pyrolysis. The temperature is then further increased to 1600 °C for high-temperature carbothermal reduction. After holding at this temperature for 3 hours, the material is naturally cooled to room temperature to obtain the SiC composite aerogel-based electromagnetic absorbing material.

[0062] The results show that the oxidizing properties and high-temperature reactivity of carbon dioxide lead to the oxidation and loss of the carbon skeleton, the failure of SiC formation, the complete failure of the electromagnetic wave absorption function, and also cause the aerogel structure to collapse and lose its mechanical properties. Comparative Example 6

[0063] This comparative example is basically the same as Example 1, except that: in step S4, the temperature is raised to 1100°C for high-temperature carbothermal reduction. The specific process is as follows: the product described in step S3 is heated to 1100°C in an argon atmosphere with a gas flow rate of 10 mL / min and then heated at a rate of 5 °C / min for high-temperature carbothermal reduction. After holding at this temperature for 3 h, it is naturally cooled to room temperature to obtain the SiC composite aerogel-based electromagnetic absorbing material.

[0064] The results show that the carbothermic reduction reaction has an extremely low reaction rate at 1100°C, which leads to a significant decrease in SiC yield. The product contains a large amount of unreacted SiO2 and free carbon, causing the material to lose its electromagnetic wave absorption function. Comparative Example 7

[0065] This comparative example is basically the same as Example 1, except that in steps S3 and S4, the temperature is increased at a rate of 20 °C / min. Specifically, the silicon-carbon in-situ hybrid aerogel described in step S2 is placed in a tube furnace and heated to 1000 °C at a rate of 20 °C / min in an argon atmosphere with a gas flow rate of 10 mL / min for high-temperature carbonization and pyrolysis. The temperature is then further increased to 1500 °C for high-temperature carbothermal reduction. After holding at this temperature for 3 hours, the material is naturally cooled to room temperature to obtain the SiC composite aerogel-based electromagnetic absorbing material.

[0066] The results show that rapid heating can cause the temperature difference between the inner and outer layers of the aerogel to exceed 200°C, generating huge thermal stress, which in turn leads to structural collapse. In addition, it can also lead to insufficient carbothermic reduction reaction, a significant decrease in SiC yield, and a decrease in the microwave absorption performance of the aerogel.

[0067] In summary, the method for preparing SiC composite aerogel-based electromagnetic absorbing materials provided by this invention utilizes amino-bridged siloxanes as the silicon source to obtain an in-situ silicon-carbon hybrid aerogel containing both Si and C in its molecular structure through autocatalytic gelation. The SiC composite aerogel is then obtained through high-temperature carbonization pyrolysis and high-temperature carbothermal reduction reactions. Compared with common SiC aerogel preparation methods such as template methods, organic / SiO2 composite aerogel carbothermal reduction methods, and polymer precursor pyrolysis methods, this method offers significant advantages, including a wide range of raw material sources, low cost, simple synthesis process, and mild precursor gelation conditions. It provides a novel approach for SiC aerogel preparation. Furthermore, the method for preparing SiC composite aerogel-based electromagnetic absorbing materials provided by this invention allows for the direct alteration of the relative contents of Si, C, N, and O elements in the precursor by introducing organosilanes into the amino-bridged siloxanes. This facilitates precise control of N doping in the SiC composite aerogel, thereby adjusting its absorption performance and enabling the absorption frequency band to be suitable for different application scenarios. The SiC composite aerogel prepared in this invention is lightweight compared to other forms of SiC absorbing materials. Its three-dimensional nanostructure enhances the reflection loss of the hierarchical pores, thus contributing to improved electromagnetic absorption performance. The SiC composite aerogel-based electromagnetic absorbing material provided by this invention exhibits excellent absorption performance.

[0068] 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; 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 SiC composite aerogel-based electromagnetic absorbing material, characterized in that, Includes the following steps: S1. Thoroughly mix the amino-bridged siloxane, organosilane and organic solvent, add water and continue stirring until uniform to obtain a sol, and then let it stand to obtain a gel. S2. The gel obtained in step S1 is aged in an oven, cleaned with an organic solvent to remove residual impurities, and then dried to obtain silicon-carbon in-situ hybrid aerogel. S3. The silicon-carbon in-situ hybrid aerogel obtained in step S2 is subjected to high-temperature carbonization and pyrolysis under a protective atmosphere. S4. The product obtained in step S3 is subjected to high-temperature carbothermal reduction under a protective atmosphere to obtain SiC composite aerogel-based electromagnetic absorbing material.

2. The preparation method of the SiC composite aerogel-based electromagnetic absorbing material according to claim 1, characterized in that, In step S1, the amino-bridged siloxane includes one or more of bis[3-(trimethoxysilyl)propyl]amine, bis(3-triethoxysilylpropyl)amine, 3-aminopropyltrimethoxysilane, and 3-aminopropyltriethoxysilane; the organosilane includes one or more of tetramethoxysilane, tetraethoxysilane, methyltriethoxysilane, and methyltrimethoxysilane; in steps S1 and S2, the organic solvent includes one or more of ethanol, methanol, acetone, n-heptane, and n-hexane.

3. The preparation method of the SiC composite aerogel-based electromagnetic absorbing material according to claim 1, characterized in that, In step S1, the molar ratio of the organosilane, organic solvent, water and amino-bridged siloxane is (0~5):(6~80):(6~15):

1.

4. The preparation method of the SiC composite aerogel-based electromagnetic absorbing material according to claim 1, characterized in that, In step S1, the temperature during the settling period is 30~60 ℃ and the time is 0.1~24 h.

5. The preparation method of the SiC composite aerogel-based electromagnetic absorbing material according to claim 1, characterized in that, In step S2, the aging temperature is 30~60℃ and the time is 24~48h.

6. The preparation method of the SiC composite aerogel-based electromagnetic absorbing material according to claim 1, characterized in that, In step S2, the drying process includes one or more of the following: supercritical carbon dioxide drying, supercritical ethanol drying, or vacuum freeze drying.

7. The preparation method of the SiC composite aerogel-based electromagnetic absorbing material according to claim 1, characterized in that, In step S3, the protective atmosphere is argon or nitrogen, and the gas flow rate is 5~20 mL / min; in step S4, the protective atmosphere is argon, and the gas flow rate is 5~20 mL / min.

8. The preparation method of the SiC composite aerogel-based electromagnetic absorbing material according to claim 1, characterized in that, In step S3, the high-temperature carbonization pyrolysis specifically involves heating to 800-1000 °C at a rate of 1-10 °C / min.

9. The preparation method of the SiC composite aerogel-based electromagnetic absorbing material according to claim 1, characterized in that, In step S4, the high-temperature carbothermic reduction specifically involves: continuing to raise the temperature to 1200-1600 °C at a rate of 5-10 °C / min, holding at this temperature for 2-4 hours, and then naturally cooling to room temperature.

10. A SiC composite aerogel-based electromagnetic absorbing material prepared by the preparation method of the SiC composite aerogel-based electromagnetic absorbing material according to any one of claims 1 to 9.

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