Composite wave-absorbing and heat-insulating material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of preparation of electromagnetic wave-absorbing and heat-insulating materials, and discloses a composite wave-absorbing and heat-insulating material and a preparation method and application thereof.The preparation method comprises the steps that coconut fiber carbon aerogel is prepared, then C / SiC nanowire composite aerogel is prepared from the coconut fiber carbon aerogel and silicon dioxide dry gel powder, the pretreated C / SiC nanowire composite aerogel is soaked in a ZIF-8 precursor solution, and the ZIF-8 precursor solution is dried to obtain the composite wave-absorbing and heat-insulating material. The composite wave-absorbing and heat-insulating material with specific orientation arrangement is obtained. The prepared composite material has a three-dimensional connected network structure arranged in a specific orientation mode, is high in wave absorbing performance, wide in absorption frequency band, good in heat insulation performance and low in density, can effectively absorb electromagnetic waves of different wave bands by adjusting the ZIF-8 loading capacity, and has important application value in the fields of electromagnetic wave absorbing, high-temperature heat insulation and the like.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic wave absorbing heat insulation material preparation technology, and relates to a composite wave absorbing heat insulation material, its preparation method and application. Background Technology

[0002] Silicon carbide (SiC) nanomaterials, due to their low density, high thermal conductivity, excellent mechanical properties, and chemical stability, have significant application value in fields such as stealth fighters, 5G communications, and high-power electronic devices. However, traditional bulk SiC materials are difficult to meet the requirements of lightweight and broadband electromagnetic wave absorption due to their high density and brittleness. While SiC nanowires can optimize absorption performance through high specific surface area and quantum confinement effects, their controllable synthesis and macroscopic assembly still face challenges such as difficulty in morphology control and poor structural stability. Three-dimensional porous aerogels offer a new approach to solving these problems; their high porosity, low density, and interconnected channels can enhance electromagnetic wave loss.

[0003] Researchers have attempted to use biomass materials with porous structures as templates to prepare SiC-based microwave absorbing materials. For example, Chinese patent CN116396079A discloses a method for preparing SiC nanowire aerogels using biomass (eggplant, winter melon, loofah, grapefruit peel, sugarcane, and wood) carbon aerogels as templates via carbothermal reduction, followed by chemical vapor deposition to modify the surface with carbon nanotube-coated magnetic nanoparticles to introduce a magnetic loss mechanism. While this method improves microwave absorption performance, the magnetic particles used are mainly physically bonded to the SiC nanowires, resulting in weak interfacial bonding. This makes them prone to detachment or performance degradation at high temperatures or during long-term use, affecting the material's stability and durability. Although this method improves the material's microwave absorption performance to some extent, its strongest reflection loss is only -47.75 dB, and its maximum effective absorption bandwidth is 8.96 GHz. There is still room for optimization in terms of broadband and strong absorption, and the thermal insulation performance needs improvement.

[0004] In addition, although existing biomass templates (such as loofah sponge, eggplant, etc.) have a certain porous structure, their pore distribution is uneven and their structure is simple. After carbonization, their specific surface area is limited, making it difficult to achieve uniform and oriented growth of SiC nanowires, and also not conducive to the loading and interface control of subsequent functional components.

[0005] Therefore, developing a microwave absorbing and heat-insulating material that combines strong absorption, wide bandwidth, excellent heat insulation, controllable structure, simple process, and low cost remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides a composite microwave absorbing and heat-insulating material, its preparation method, and its applications. The prepared composite microwave absorbing and heat-insulating material exhibits strong microwave absorption performance, wide absorption bandwidth, good heat insulation performance, and low density. Furthermore, by adjusting the ZIF-8 loading, it can effectively absorb electromagnetic waves of different wavebands, making it valuable for applications in electromagnetic wave absorption and high-temperature heat insulation. The preparation method is green, efficient, and scalable.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for preparing a composite microwave absorbing and heat-insulating material, wherein ZIF-8 is grafted onto the surface of a C / SiC nanowire composite aerogel pretreated with 3-aminopropyltriethoxysilane, and ZIF-8 particles are firmly grown on the surface of the C / SiC nanowire composite aerogel through an impregnation and aging process, thereby obtaining a composite microwave absorbing and heat-insulating material. The preparation method includes the following steps: (1) The cleaned and dried coconut fiber mat is placed in a high-temperature tube furnace for carbonization treatment to obtain coconut fiber carbon aerogel; the coconut fiber carbon aerogel material is graphitized coconut fiber carbon aerogel, and the carbon aerogel material has a natural three-dimensional hierarchical porous structure.

[0008] (2) Tetraethoxysilane (TEOS), distilled water and anhydrous ethanol were mixed, and expandable graphite and silicon powder were added. After stirring, the mixture was dried and ground to prepare silica (SiO2) dry gel powder. Coconut fiber carbon aerogel with a mass ratio of 1:4-6 was mixed with silica dry gel powder and placed in a graphite crucible. After calcination in a high-temperature tube furnace, C / SiC nanowire composite aerogel was obtained. (3) The C / SiC nanowire composite aerogel from step (2) is immersed in an ethanol solution of 3-aminopropyltriethoxysilane (APTES), aged at room temperature for 1-3 h, and dried for 10-14 h to obtain C / SiC-NH2 material.

[0009] (4) The C / SiC-NH2 material in step (3) is immersed in ZIF-8 precursor solution and stirred for 1-3 h. After stirring, it is aged at room temperature for 24 h. After aging, the product is cleaned and dried to obtain composite microwave absorbing and heat insulation material.

[0010] Preferably, in step (1), the carbonization temperature is 600-800℃, more preferably 700℃, and the carbonization time is 1-3h, more preferably 2h.

[0011] Preferably, in step (2), the ratio of tetraethoxysilane, distilled water, anhydrous ethanol, expandable graphite, and silicon powder is 90-110 mL:25-35 mL:15-25 mL:5 g:6 g, and more preferably 100 mL:30 mL:20 mL:5 g:6 g.

[0012] Preferably, in step (2), the calcination temperature is 1400-1600 ℃, more preferably 1500 ℃, and the calcination time is 5-8h, more preferably 6h.

[0013] Preferably, in step (2), the mass ratio of coconut fiber carbon aerogel to silica dry gel powder is 1:5.

[0014] Preferably, in step (3), the volume ratio of ethanol to 3-aminopropyltriethoxysilane in the ethanol solution of 3-aminopropyltriethoxysilane is 95:5.

[0015] Preferably, zinc nitrate hexahydrate and 2-methylimidazole (2-MIM) in a molar ratio of 1:8 are dissolved in methanol solution and then mixed to obtain ZIF-8 precursor solution.

[0016] Secondly, the present invention provides a composite microwave absorbing and heat insulation material prepared by the above preparation method, which has a three-dimensional interconnected network structure with a specific orientation arrangement, using natural coconut fiber carbon aerogel as the skeleton, SiC nanowires as the three-dimensional network reinforcement, and ZIF-8 particles grafted on the surface as the functional modification layer.

[0017] Thirdly, the present invention provides an application of the composite microwave absorbing and heat-insulating material in the preparation of an integrated device that combines electromagnetic wave absorption and heat insulation functions.

[0018] This invention utilizes porous coconut fiber as a template to construct a three-dimensional interconnected network structure with a specific orientation, consisting of natural coconut fiber carbon aerogel as the skeleton, SiC nanowires as the three-dimensional network reinforcement, and ZIF-8 particles grafted onto the surface as a functional modification layer. This results in a composite microwave absorbing and heat-insulating material that combines broadband strong absorption and thermal insulation. The coconut fiber, with its natural three-dimensional hierarchical porous structure (hollow microtubes, surface micropores, and nanoscale gaps), directly forms a three-dimensional porous carbon skeleton with high specific surface area and interconnected pores after carbonization. This hierarchical porous structure guides nucleation, surface functional groups adsorb silicon sources, and local gas release regulates the microenvironment, synergistically promoting the uniform orientation growth of SiC nanowires. The interconnected structure of SiC nanowires provides an effective transmission path for electrons, and the natural three-dimensional hierarchical porous structure enables the composite material to be lightweight and heat-resistant. The combination of ZIF-8 and SiC nanowires synergistically regulates the electromagnetic parameters of SiC nanowire aerogel materials, improves the impedance matching degree of SiC nanowire aerogel materials, and solves the problem that the dielectric constant of single SiC nanowire aerogel materials is large, which is not conducive to impedance matching and thus results in poor wave absorption performance.

[0019] The advantages and beneficial effects of this invention are: (1) The composite microwave absorbing and heat-insulating material prepared by this invention has excellent broadband electromagnetic wave absorption capability (effective absorption bandwidth up to 13.52 GHz, reflection loss as low as -65.77 dB) and good high-temperature heat insulation performance (the average back surface temperature can be maintained at 125-130 ℃ under butane flame heating at 1300 ℃), solving the technical problem of traditional materials having single function and difficulty in achieving multiple functions. Moreover, by simply adjusting the concentration of ZIF-8 precursor liquid, the loading morphology and content of ZIF-8 on the surface of SiC nanowires can be precisely controlled, thereby achieving directional optimization of the material's microwave absorption characteristics and heat insulation performance, meeting the differentiated needs of different application scenarios.

[0020] (2) The preparation method of the present invention breaks through the limitations of traditional templates in terms of porosity, mechanical properties and process complexity. Moreover, the process is simple and low-cost, does not require complex synthesis equipment, and is more green, efficient and can be mass-produced. Attached Figure Description

[0021] Figure 1 The X-ray diffraction patterns of the products obtained in Comparative Examples 1-3 and Example 4 of this invention are shown. Figure 2 This is a SEM image of the coconut fiber carbon aerogel prepared according to the present invention. Figure 3 These are SEM images of the products obtained in Comparative Examples 1-2 and Examples 1-4 of this invention; Figure 4Infrared power variation curves of the products obtained in Comparative Examples 1, 3, and Examples 1-4 of this invention; Figure 5 Infrared thermal images of the products obtained in Comparative Examples 1, 3, and Examples 1-4 of this invention. Figure 6 These are reflection loss images of the products obtained in Comparative Examples 1, 3, and Examples 1-4 of this invention. Detailed Implementation

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the embodiments described below are only some embodiments of the present invention and are not limiting, and cannot be used to limit the protection scope of the present invention.

[0023] Comparative Example 1 A method for preparing C / SiC nanowire composite aerogel, comprising the following steps: Step 1: Place the cleaned and dried coconut fiber mat into a high-temperature tube furnace at 700℃ for 2 hours to carbonize it, thereby obtaining coconut fiber carbon aerogel.

[0024] Step 2: Mix 100 mL of tetraethoxysilane (TEOS), 30 mL of distilled water, and 20 mL of anhydrous ethanol. Add 5 g of expandable graphite and 6 g of silicon powder, stir at room temperature for 24 h, and dry at 90 °C for 12 h to obtain SiO2 dry gel; Step 3: The coconut fiber carbon aerogel from Step 1 and the SiO2 dry gel from Step 2, with a mass ratio of 1:5, are placed together in a graphite crucible and calcined at 1500℃ for 6 h in a high-temperature tube furnace to prepare C / SiC nanowire composite aerogel, denoted as S-0.

[0025] like Figure 1 As shown, the C / SiC nanowire composite aerogel S-0 prepared in Comparative Example 1 includes characteristic diffraction peaks of 3C-SiC (β-SiC), proving that the obtained material is a SiC nanowire aerogel material.

[0026] like Figure 2 As shown, the coconut fiber carbon aerogel prepared in Comparative Example 1 has a natural three-dimensional hierarchical porous structure (hollow microtubes, surface micropores and nanoscale gaps) in a single coconut fiber carbon.

[0027] like Figure 3 As shown in Figure (a), the product S-0 obtained in Comparative Example 1 is composed of SiC nanowires with high aspect ratio (diameter generally exceeding 100 nm) and relatively smooth surface, which form a more complex three-dimensional network through interlacing.

[0028] like Figure 4 As shown, the product S-0 obtained in Comparative Example 1 was continuously heated for 240 s under a butane spray gun at 1300 ℃. At a distance of 3 cm from the back of the sample, the laser power value corresponding to the thermal radiation of the material was recorded using a laser power meter. The average laser power value was 1.476 mW.

[0029] like Figure 5 As shown in Figure (a), the product S-0 obtained in Comparative Example 1 was continuously heated at 1300 °C under a butane spray gun for 240 s, and an infrared thermal image of the back side of the material was taken using an infrared thermal imager. After heating for about 80 s, the rate of temperature rise on the back side slowed down significantly and gradually entered a relatively stable dynamic equilibrium stage, with the lowest average temperature on the back side of the material being 125.5 °C.

[0030] like Figure 6 As shown, the product S-0 obtained in Comparative Example 1 exhibits excellent microwave absorption at a thickness of 3 mm and a frequency of 9.92 GHz. min It has a sensitivity as low as -15.77 dB and an effective bandwidth (RL < -10 dB) of 8.96 GHz.

[0031] Comparative Example 2 The preparation methods of ZIF-8 material include: Step 1, Zn 2+ / 2-MIM was prepared by dissolving 1.19 g of zinc nitrate hexahydrate and 2.626 g of 2-methylimidazole in 50 mL of methanol at a fixed molar ratio of 1:8 to obtain zinc nitrate hexahydrate solution and 2-methylimidazole solution.

[0032] Step 2: Mix zinc nitrate hexahydrate solution and 2-methylimidazole solution to obtain ZIF-8 precursor solution. After stirring for 2 h, age at room temperature for 24 h. Centrifuge the aged ZIF-8 precursor solution again using a high-speed centrifuge. Wash the precipitate twice with methanol and dry it in a vacuum drying oven at 80℃ for 6 h to obtain dry ZIF-8 material, denoted as S.

[0033] like Figure 1 As shown, the product S obtained in Comparative Example 2 has characteristic diffraction peaks of ZIF-8, proving that a pure ZIF-8 sample with good crystallinity and no impurity phases was successfully synthesized.

[0034] like Figure 3 As shown in (b), the product S obtained in Comparative Example 2 is composed of ZIF-8 particles in the form of regular dodecahedrons.

[0035] Comparative Example 3 A method for preparing a ZIF-8 / SiC nanowire aerogel composite material, comprising: Step 1, Zn2+ With a fixed molar ratio of 1:8, 1.19 g of zinc nitrate hexahydrate and 2.626 g of 2-methylimidazole were dissolved in 50 mL of methanol, respectively, and mixed to obtain a 50 mM ZIF-8 precursor solution.

[0036] Step 2: The product S-0 obtained in Comparative Example 1 was immersed in ZIF-8 precursor solution and stirred for 2 h. After stirring, it was aged at room temperature for 24 h. After aging, the product was washed and dried to obtain a ZIF-8 / SiC nanowire aerogel composite material with a specific orientation, denoted as S-00.

[0037] like Figure 4 As shown, the product S-00 obtained in Comparative Example 3 was continuously heated for 240 s under a butane spray gun at 1300 ℃. At a distance of 3 cm from the back of the sample, the laser power value corresponding to the thermal radiation of the material was recorded using a laser power meter. The average laser power value was 3.361 mW.

[0038] like Figure 5 As shown in Figure (f), the product S-00 obtained in Comparative Example 3 was continuously heated at 1300 °C under a butane spray gun for 240 s, and an infrared thermal image of the back side of the material was taken using an infrared thermal imager. After heating for about 80 s, the rate of temperature rise on the back side slowed down significantly and gradually entered a relatively stable dynamic equilibrium stage, with the lowest average temperature on the back side of the material being 190.2 °C.

[0039] like Figure 6 As shown, the product S-00 prepared in Comparative Example 3 exhibits excellent microwave absorption at a thickness of 3 mm and a frequency of 6.48 GHz. min It has a sensitivity as low as -23.08 dB and an effective bandwidth (RL < -10 dB) of 13.28 GHz.

[0040] Example 1 A method for preparing a composite microwave absorbing and heat-insulating material includes: Step 1: The product S-0 obtained in Comparative Example 1 was immersed in an ethanol solution of 3-aminopropyltriethoxysilane (APTES) with a concentration of 5 vol% for 2 h at room temperature and then dried for 12 h to obtain C / SiC-NH2 material.

[0041] Step 2, Zn 2+ With a fixed molar ratio of 1:8, 0.238 g of zinc nitrate hexahydrate and 0.525 g of 2-methylimidazole were dissolved in 50 mL of methanol and mixed to obtain a 10 mM ZIF-8 precursor solution.

[0042] Step 3: The C / SiC-NH2 material obtained in Step 1 is immersed in ZIF-8 precursor solution and stirred for 2 h. After stirring, it is aged at room temperature for 24 h. After aging, the product is washed and dried to obtain a composite microwave absorbing and heat insulation material, namely a ZIF-8 / SiC nanowire aerogel composite material with a specific orientation, denoted as S-1.

[0043] like Figure 3 As shown in Figure (c), the product S-1 obtained in Example 1 shows that although ZIF-8 crystals successfully nucleated and grew on the surface of SiC nanowire aerogel, a continuous and dense coating layer was not formed. At the same time, the original surface of the SiC nanowires and the numerous void structures in the three-dimensional network of the aerogel are still clearly visible.

[0044] like Figure 4 As shown, the product S-1 obtained in Example 1 was continuously heated for 240 s under a butane spray gun at 1300 ℃. At a distance of 3 cm from the back of the sample, the laser power value corresponding to the thermal radiation of the material was recorded using a laser power meter. The average laser power value was 2.035 mW.

[0045] like Figure 5 As shown in Figure (b), the product S-1 obtained in Example 1 was continuously heated at 1300 °C under a butane spray gun for 240 s, and an infrared thermal image of the back side of the material was taken using an infrared thermal imager. After heating for about 80 s, the rate of temperature rise on the back side slowed down significantly and gradually entered a relatively stable dynamic equilibrium stage, with the lowest average temperature on the back side of the material being 160.4 °C.

[0046] like Figure 6 As shown, product S-1 obtained in Example 1 exhibits excellent microwave absorption at a thickness of 3 mm and a frequency of 9.36 GHz. min It has a low sensitivity of -29.86 dB and an effective bandwidth (RL < -10 dB) of 12.44 GHz.

[0047] Example 2 describes a method for preparing a composite microwave absorbing and heat-insulating material. The only difference from Example 1 is the ZIF-8 precursor solution. 0.595 g of zinc nitrate hexahydrate and 1.313 g of 2-methylimidazole were dissolved in 50 mL of methanol, respectively, and mixed to obtain a 25 mM ZIF-8 precursor solution. The resulting composite microwave absorbing and heat-insulating material is designated S-2.

[0048] like Figure 3As shown in Figure (d), the product S-2 obtained in Example 2 demonstrates that ZIF-8 successfully achieved a basically continuous and complete coating on the surface of the SiC nanowire aerogel framework. This coating effectively covers most of the SiC nanowire surface, essentially filling the original voids, although some tiny pits exist in certain areas of the coating. Overall, the linear texture of the coated SiC nanowires is still clearly discernible.

[0049] like Figure 4 As shown, the product S-2 obtained in Example 2 was continuously heated for 240 s under a butane spray gun at 1300 ℃. At a distance of 3 cm from the back of the sample, the laser power value corresponding to the thermal radiation of the material was recorded using a laser power meter. The average laser power value was 2.408 mW.

[0050] like Figure 5 As shown in (c), the product S-2 obtained in Example 2 was continuously heated at 1300 °C under a butane spray gun for 240 s, and an infrared thermal image of the back side of the material was taken using an infrared thermal imager. After heating for about 80 s, the rate of temperature rise on the back side slowed down significantly and gradually entered a relatively stable dynamic equilibrium stage, with the lowest average temperature on the back side of the material being 180.3 °C.

[0051] like Figure 6 As shown, product S-2 obtained in Example 2 exhibits excellent microwave absorption at a thickness of 3 mm and a frequency of 7.68 GHz. min It has a low sensitivity of -29.27 dB and an effective bandwidth (RL < -10 dB) of 12.72 GHz.

[0052] Example 3 A method for preparing a composite microwave absorbing and heat-insulating material differs from Example 1 only in the ZIF-8 precursor solution. 1.19 g of zinc nitrate hexahydrate and 2.626 g of 2-methylimidazole are dissolved in 50 mL of methanol, respectively, and mixed to obtain a 50 mM ZIF-8 precursor solution. The resulting composite microwave absorbing and heat-insulating material is designated S-3.

[0053] like Figure 3 As shown in Figure (e), the product S-3 obtained in Example 3 shows that ZIF-8 achieves a more thorough coating of SiC nanowires. The original gaps are completely filled, forming a continuous and dense composite structure. However, a small number of tiny pits can still be observed on the surface of the coating layer, but this does not affect the overall integrity. Moreover, the initial texture of the coated SiC nanowires is no longer discernible, indicating that the ZIF-8 layer has reached a certain thickness and completely encapsulates the underlying structure.

[0054] like Figure 4As shown, the product S-3 obtained in Example 3 was continuously heated for 240 s under a butane spray gun at 1300 ℃. At a distance of 3 cm from the back of the sample, the laser power value corresponding to the thermal radiation of the material was recorded using a laser power meter. The average laser power value was 1.534 mW.

[0055] like Figure 5 As shown in Figure (d), the product S-3 obtained in Example 3 was continuously heated at 1300 °C under a butane spray gun for 240 s, and an infrared thermal image of the back side of the material was taken using an infrared thermal imager. After heating for about 80 s, the rate of temperature rise on the back side slowed down significantly and gradually entered a relatively stable dynamic equilibrium stage, with the lowest average temperature on the back side of the material being 128.3 °C.

[0056] like Figure 6 As shown, the product S-3 obtained in Example 3 exhibits excellent absorption when the thickness is 3 mm and the frequency is 9.28 GHz, with an RLmin as low as -65.77 dB and an effective bandwidth (RL<-10 dB) of 7.98 GHz.

[0057] Example 4 A method for preparing a composite microwave absorbing and heat-insulating material differs from Example 1 only in the ZIF-8 precursor solution. 2.38 g of zinc nitrate hexahydrate and 5.252 g of 2-methylimidazole are dissolved in 50 mL of methanol, respectively, and mixed to obtain a 100 mM ZIF-8 precursor solution. The resulting composite microwave absorbing and heat-insulating material is designated S-4.

[0058] like Figure 1 As shown, in the product S-4 obtained in Example 4, it can be found that the ZIF-8 crystals have undergone preferential orientation growth, so that the specific crystal planes of ZIF-8 preferentially match and attach with the surface lattice of SiC nanowires to reduce the total energy of the system. This causes the ZIF-8 crystals to no longer be randomly distributed, but uniformly arranged with their (222), (114), and (134) crystal planes parallel to the substrate surface, resulting in a ZIF-8 / SiC nanowire aerogel composite material with a specific orientation arrangement.

[0059] like Figure 3 As shown in Figure (f), the product S-4 obtained in Example 4 shows that when the concentration of ZIF-8 precursor is further increased to 100 mM, its growth behavior changes significantly. The ZIF-8 crystal undergoes preferred orientation, forming a unidirectional overgrowth structure. This uneven growth mode consumes a large amount of precursor, which in turn causes some SiC nanowires to fail to be effectively coated, and their surfaces remain exposed.

[0060] like Figure 4As shown, the product S-4 obtained in Example 4 was continuously heated for 240 s under a butane spray gun at 1300 ℃. At a distance of 3 cm from the back of the sample, the laser power value corresponding to the thermal radiation of the material was recorded using a laser power meter. The average laser power value was 1.386 mW.

[0061] like Figure 5 As shown in (e), the product S-4 obtained in Example 4 was continuously heated at 1300 °C under a butane spray gun for 240 s, and an infrared thermal image of the back side of the material was taken using an infrared thermal imager. After heating for about 80 s, the rate of temperature rise on the back side slowed down significantly and gradually entered a relatively stable dynamic equilibrium stage, with the lowest average temperature on the back side of the material being 125.6 °C.

[0062] like Figure 6 As shown, the product S-4 obtained in Example 4 exhibits excellent absorption when the thickness is 3 mm and the frequency is 7.12 GHz, with an RLmin as low as -37.67 dB and an effective bandwidth (RL<-10 dB) of 13.52 GHz.

[0063] Examples 1-4 show that composite microwave absorbing and heat-insulating materials were prepared by setting four gradient concentrations of ZIF-8 precursor solution: 10 mM, 25 mM, 50 mM, and 100 mM. The results show that the ZIF-8 loading can effectively control its coating morphology on the SiC nanowire surface, thereby achieving directional optimization of the material's microwave absorbing and heat-insulating properties. In Example 1, at a low concentration of 10 mM, the material achieved an effective absorption bandwidth of up to 12.44 GHz. In Example 3, at a concentration of 50 mM, ZIF-8 formed a dense coating layer, significantly enhancing the interfacial polarization effect, with a peak reflection loss of -65.77 dB, exhibiting optimal strong absorption capacity and good thermal insulation (average back surface temperature 128.3℃). In Example 4, at a high concentration of 100 mM, ZIF-8 underwent preferred orientation growth, and while maintaining excellent thermal insulation, the effective absorption bandwidth was further broadened to 13.52 GHz. This demonstrates that the system of this invention can achieve controllable design and fabrication of composite materials with different performance focuses, such as broadband strong absorption, ultra-wideband, or high-efficiency thermal insulation, by simply adjusting the concentration of the precursor liquid according to the requirements of thermal insulation and wave absorption performance.

[0064] In summary, the composite microwave absorbing and heat-insulating material prepared by this invention possesses a three-dimensional interconnected network structure. This interconnected structure provides an effective transmission path for electrons, and the natural three-dimensional hierarchical porous structure achieves the lightweight and heat-resistant properties of the composite material. Simultaneously, the magnetic zinc-based material in ZIF-8 also imparts certain magnetic loss characteristics to the material. The synergistic effect of these two factors significantly influences the electromagnetic wave absorption capability.

[0065] The embodiments of the present invention have been shown and described above. Those skilled in the art can make improvements or modifications based on the above description. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a composite microwave absorbing and heat-insulating material, characterized in that, ZIF-8 was grafted onto the surface of C / SiC nanowire composite aerogel pretreated with 3-aminopropyltriethoxysilane. An impregnation and aging process was then used to ensure the ZIF-8 particles firmly grew on the SiC nanowire aerogel surface, thus obtaining a composite microwave absorbing and heat-insulating material. The specific steps included are as follows: (1) The cleaned and dried coconut fiber mat is placed in a high-temperature tube furnace for carbonization treatment to obtain coconut fiber carbon aerogel. (2) Tetraethoxysilane, distilled water and anhydrous ethanol were mixed, and expandable graphite and silicon powder were added. After stirring, the mixture was dried and ground to prepare silica dry gel powder. Coconut fiber carbon aerogel with a mass ratio of 1:4-6 was mixed with silica dry gel powder and placed in a graphite crucible. After high-temperature calcination, C / SiC nanowire composite aerogel was prepared. (3) The C / SiC nanowire composite aerogel from step (2) is immersed in an ethanol solution of 3-aminopropyltriethoxysilane, aged at room temperature, and dried to obtain C / SiC-NH2 material; (4) The C / SiC-NH2 material in step (3) is immersed in ZIF-8 precursor liquid and stirred, aged at room temperature, and the resulting product is cleaned and dried to obtain composite microwave absorbing and heat insulation material.

2. The method for preparing the composite microwave absorbing and heat-insulating material according to claim 1, characterized in that, In step (1), the carbonization temperature is 600-800℃ and the carbonization time is 1-3 h.

3. The method for preparing the composite microwave absorbing and heat-insulating material according to claim 1, characterized in that, In step (2), the ratio of tetraethoxysilane, distilled water, anhydrous ethanol, expandable graphite, and silicon powder is 90-110 mL: 25-35 mL: 15-25 mL: 5 g: 6 g.

4. The method for preparing the composite microwave absorbing and heat-insulating material according to claim 1, characterized in that, In step (2), the calcination temperature is 1400-1600 ℃ and the calcination time is 5-8h.

5. The method for preparing the composite microwave absorbing and heat-insulating material according to claim 1, characterized in that, In step (3), the volume ratio of ethanol to 3-aminopropyltriethoxysilane in the ethanol solution of 3-aminopropyltriethoxysilane is 95:

5.

6. The method for preparing the composite microwave absorbing and heat-insulating material according to claim 1, characterized in that, In step (3), the soaking and aging process is carried out for 1-3 hours, and the drying process is carried out for 10-14 hours.

7. The method for preparing the composite microwave absorbing and heat-insulating material according to claim 1, characterized in that, In step (4), the ZIF-8 precursor solution is prepared by adding zinc nitrate hexahydrate and 2-methylimidazole in a molar ratio of 1:8 to a methanol solution for dissolution, and then mixing them to obtain a 10-100mM ZIF-8 precursor solution.

8. A composite microwave absorbing and heat-insulating material, characterized in that, A three-dimensional interconnected network structure with a specific orientation arrangement was prepared by the preparation method described in any one of claims 1-7, using natural coconut fiber carbon aerogel as the skeleton, SiC nanowires as the three-dimensional network reinforcement, and ZIF-8 particles grafted on the surface as the functional modification layer.

9. The application of the composite microwave absorbing and heat-insulating material as described in claim 8 in the preparation of an integrated device that combines electromagnetic wave absorption and heat insulation functions.

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