Dielectric adjustable graphene / ceramic composite aerogel and preparation method thereof

Abstract

The invention discloses dielectric adjustable graphene / ceramic composite aerogel and a preparation method thereof, and belongs to the technical field of functional composite materials. The preparation method comprises the following steps: S1, mixing a reduced graphene oxide dispersion liquid with a silicon carbide whisker dispersion liquid, and carrying out ultrasonic treatment and centrifugation to obtain a composite precipitate; s2, performing directional freezing treatment on the composite precipitate, inducing to form a three-dimensional communicated porous structure, and then performing freeze drying to prepare a graphene / ceramic composite aerogel precursor; and S3, performing chemical vapor infiltration on the graphene / ceramic composite aerogel precursor to prepare the silicon carbide protective layer. The preparation method is simple, and the prepared material has excellent performances such as light weight, high strength, dielectric adjustability and high-temperature oxidation resistance, has application prospects in the fields of aerospace thermal protection and the like, and solves the problems that in the prior art, SiC whiskers are damaged in the preparation process, and the service life of the SiC whiskers is prolonged. The mechanical property, the dielectric property and the high-temperature oxidation resistance of the composite aerogel are insufficient, and the like.

Description

Technical Field

[0001] This invention relates to the field of functional composite materials technology, specifically to a dielectrically tunable graphene / ceramic composite aerogel and its preparation method. Background Technology

[0002] Graphene aerogels, with their high porosity (typically >90%) and the intrinsic electrical conductivity of graphene (500-800 S / m), have become a research focus for lightweight, multifunctional materials. Their three-dimensional porous structure can block heat conduction paths, providing a foundation for thermal insulation; their conductive network creates conditions for electromagnetic function modulation, making them valuable for applications in aerospace, electronic equipment, and other fields.

[0003] However, pure graphene aerogels have three major drawbacks that restrict their practical applications: First, they are mechanically fragile. Their three-dimensional network relies solely on the van der Waals forces between graphene sheets, lacking an effective stress transfer path, resulting in low compressive strength and a tendency to collapse and crack during assembly, transportation, and service. Second, they have limited dielectric properties. The dielectric constant of a single graphene is high and difficult to control, failing to meet the diverse dielectric parameter requirements of different scenarios. Third, they lack high-temperature oxidation resistance. Graphene is easily oxidized and degraded in oxygen-rich environments above 500°C, limiting its application in high-temperature scenarios.

[0004] To address the shortcomings of pure graphene aerogels, a "reinforcement-graphene composite" approach is commonly employed. Existing reinforcements are mainly categorized into metals, traditional ceramics, and carbon materials. While metal reinforcements (such as Fe3O4 and Ni nanoparticles) can improve microwave absorption performance through magnetic loss, their high density (e.g., Fe3O4 reaches 5.18 g / cm³) makes the resulting composite material's density insufficient for lightweighting, and metal particles are prone to oxidation, exhibiting poor stability under humid and hot conditions. Traditional ceramic reinforcements (such as Al2O3 and ZrO2) have lower densities but extremely weak dielectric loss capabilities, failing to achieve dielectric synergy with graphene. Carbon material reinforcements (such as carbon fibers and carbon nanotubes) have dimensions that do not match the graphene sheets, easily disrupting the porous structure of the aerogel. SiC materials form a dielectric gradient transition with graphene, reducing electromagnetic wave reflectivity, with a theoretical density of 3.21 g / cm³. 3 Similar to graphene, it ensures lightweight design and excellent environmental stability, making it an enhancer that meets the triple requirements of "dielectric synergy - lightweight design - stability".

[0005] Zero-dimensional SiC powder typically has a particle size of 1-5 μm, no aspect ratio, and cannot form a continuous stress transfer path. It can only improve the compressive strength to ≤0.3 MPa and is prone to agglomeration, which destroys the structural uniformity. Low aspect ratio SiC chopped fibers have a diameter >1 μm and a length >20 μm, which is mismatched with the size of graphene sheets (1-5 μm in diameter). If they are too long, they will easily penetrate the porous structure, leading to a decrease in porosity and an increase in density. If they are too coarse, they cannot be embedded in the interlayer gaps, resulting in weak interfacial bonding and easy peeling under external force. High aspect ratio SiC whiskers are compatible with the size of graphene sheets. They can be embedded in the interlayer gaps to form a "microscopic steel reinforcement" support network, improving mechanical properties, and can also be uniformly dispersed to reduce agglomeration. They can also be hydroxylated to form hydrogen bonds with graphene, enhancing interfacial bonding.

[0006] However, existing technologies still have shortcomings: First, the traditional "ball milling-high-temperature sintering" process easily leads to graphene sheet damage and SiC whisker oxidation; second, in the chemical vapor infiltration (CVI) step, temperatures above 1000℃ easily cause SiC whiskers to melt, and the relationship between the protective layer thickness and the protective effect is not clearly defined; third, dielectric modulation is only attributed to the ratio of the reinforcing body, ignoring the effect of the porous structure. Therefore, developing a composite aerogel preparation technology that synergistically solves mechanical reinforcement, dielectric modulation, and high-temperature oxidation resistance, with controllable process parameters, has become crucial for promoting the engineering applications of this type of material. Summary of the Invention

[0007] To address the aforementioned technical problems, the present invention aims to provide a dielectrically tunable graphene / ceramic composite aerogel and its preparation method, thereby solving the problems that existing technologies cause damage to SiC whiskers during the preparation process, resulting in insufficient mechanical properties, dielectric properties, and high-temperature oxidation resistance of the composite aerogel.

[0008] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: In a first aspect, the present invention provides a method for preparing dielectrically tunable graphene / ceramic composite aerogel, comprising the following steps: S1. Mix the reduced graphene oxide dispersion with the silicon carbide whisker dispersion, sonicate, and centrifuge to obtain a composite precipitate. S2. The composite precipitate obtained in S1 is subjected to directional freezing treatment to induce the formation of a three-dimensional interconnected porous structure, and then freeze-dried to obtain a graphene / ceramic composite aerogel precursor. S3. The graphene / ceramic composite aerogel precursor obtained in S2 is subjected to chemical vapor infiltration to prepare a silicon carbide protective layer, thereby obtaining the graphene / ceramic composite aerogel.

[0009] The beneficial effects of this invention are as follows: The preparation method of this invention is simple. It is composed of reduced graphene oxide nanosheets and silicon carbide whiskers. The whiskers form a three-dimensional skeleton structure between the two-dimensional graphene sheets, which improves the mechanical properties of the material. At the same time, through dielectric synergy with reduced graphene oxide, the composite material has tunable dielectric properties. The resulting material has superior properties such as lightweight and high strength, tunable dielectric, and resistance to high temperature oxidation, and has application prospects in aerospace thermal protection and other fields.

[0010] Furthermore, the reduced graphene oxide nanosheets in S1 have 1-5 layers, a sheet diameter of 1-5 μm, and an electrical conductivity of 500-800 S / m.

[0011] Furthermore, the reduced graphene oxide in S1 is prepared through the following steps: A monolayer graphene oxide dispersion was prepared using the modified Hummers method, and then reduced graphene oxide was obtained by sequentially subjecting it to hydrothermal reduction and freeze-drying.

[0012] Furthermore, improving the Hummers method includes the following steps: (1) First, mix and stir concentrated hydrochloric acid and graphite powder under ice-water bath conditions, then add potassium permanganate in batches, continue stirring, and finally react in a constant temperature water bath. (2) After the reaction in step (1) is completed, deionized water is added dropwise to the reaction system, then the system is stirred and hydrogen peroxide solution is added and stirred continuously. Finally, the system is centrifuged and washed to obtain a single-layer graphene oxide dispersion.

[0013] The beneficial effects of adopting the above-mentioned further technical solutions are as follows: By improving the Hummers method to control the addition of oxidant and the reaction temperature, the present invention can effectively reduce the defects of graphene oxide sheets, while ensuring that the monolayer rate of graphene oxide is ≥90%, laying the foundation for the subsequent reduction preparation of reduced graphene oxide.

[0014] Furthermore, in step (1), the temperature of the ice-water bath is 0-5℃, the temperature of the constant temperature water bath is 30-50℃, the mixing and stirring time is 20-40 min, the stirring time is 30-90 min, and the reaction time in the constant temperature water bath is 3-5 h.

[0015] Furthermore, in step (1), the mass-to-volume ratio of concentrated hydrochloric acid, graphite powder, and potassium permanganate is 40-60 mL: 1-3 g: 5-15 g.

[0016] Furthermore, in step (1), each batch is added at intervals of 10-15 minutes.

[0017] The beneficial effects of adopting the above-mentioned further technical solution are as follows: the present invention avoids the decomposition of oxidant due to excessively high local temperature by adding the oxidant in batches.

[0018] Furthermore, in step (2), the dropping rate of deionized water is 1-2 mL / min, while the temperature of the reaction system is controlled to not exceed 80℃.

[0019] The beneficial effects of adopting the above-mentioned further technical solutions are as follows: This application prevents the solution from boiling violently due to a sudden increase in the temperature of the reaction system by limiting the acceleration of the deionized water droplets and the temperature of the reaction system.

[0020] Furthermore, in step (2), the stirring time is 20-40 min, and the stirring time continues for 30-90 min.

[0021] Furthermore, in step (2), the centrifugal washing speed is 6000-10000 rpm and the time is 15-20 min.

[0022] Furthermore, the method for preparing reduced graphene oxide by hydrothermal reduction and freeze-drying specifically includes the following steps: (a) Add ammonia to the graphene oxide dispersion to adjust the pH and obtain an alkaline graphene oxide dispersion. (b) Add hydrazine hydrate to the alkaline graphene oxide dispersion and mix well to obtain a mixed suspension; (c) The suspension was kept at 150-250℃ for 10-15 h, then centrifuged, washed, and freeze-dried to obtain reduced graphene oxide.

[0023] The beneficial effects of adopting the above-mentioned further technical solution are as follows: The reduced graphene oxide nanosheets obtained in this application have 1-5 layers and a sheet diameter of 1-5 μm. Some oxygen-containing functional groups are retained on the surface, which not only ensures that the material has good electrical conductivity, with an electrical conductivity of 500-800 S / m, but also promotes the synergistic composite of the two by forming a strong bonding interface with the hydroxyl groups on the surface of SiC whiskers through the functional groups.

[0024] Furthermore, both steps (a) and (b) are performed with ultrasound assistance, and the ultrasound power is 300-350 W.

[0025] Further, in step (a), the concentration of the graphene oxide dispersion is 1-3 mg / mL, the mass concentration of ammonia is 25%-28%, and the pH is adjusted to 9-10.

[0026] Furthermore, the freeze-drying conditions in step (c) are: -50~-40℃, vacuum degree ≤10 Pa, 20-30 h.

[0027] Furthermore, the silicon carbide whiskers in S1 have a crystal form of β-SiC and undergo surface hydroxylation treatment, with a hydroxyl content of 0.5-1.0 mmol / g.

[0028] Furthermore, the hydroxylation treatment includes the following steps: First, SiC whiskers are stirred and refluxed in a 10%-15% hydrochloric acid solution at 80-90℃ for 4-6 h; then washed with deionized water until neutral, and dried at 60-70℃ for 8-10 h to obtain hydroxylated SiC whiskers.

[0029] The beneficial effects of adopting the above-mentioned further technical solution are as follows: The present invention removes impurities and oxide layers on the surface of SiC whiskers by hydrochloric acid reflux treatment, while introducing a large number of hydroxyl groups on the surface of the whiskers, providing binding sites for subsequent composite with reduced graphene oxide, and effectively improving the composite uniformity.

[0030] Furthermore, the mass ratio of reduced graphene oxide to silicon carbide whiskers in S1 is (2-4):1; the concentration of the reduced graphene oxide dispersion is 0.5-2 mg / mL, and the concentration of silicon carbide whiskers is 0.5-2 mg / mL.

[0031] The beneficial effects of adopting the above-mentioned further technical solutions are as follows: This application optimizes and verifies the mass ratio of reduced graphene oxide and silicon carbide whiskers. When the ratio is less than 1:4, the mechanical property enhancement effect is insufficient. When the ratio is greater than 1:2, the material density increases significantly, which is not conducive to the demand for lightweighting.

[0032] Furthermore, the cooling rate of the directional freezing treatment in S2 is 5-10℃ / min.

[0033] Furthermore, the reaction conditions for chemical vapor infiltration in S3 are as follows: using trichloromethylsilane as a precursor, hydrogen as a carrier gas, and argon as a dilution and protective gas, the reaction is carried out at 900-1100℃ and 0.1-1kPa for 1-3 hours.

[0034] Furthermore, the heating rate of chemical vapor infiltration is 10-20 °C / min.

[0035] Furthermore, the molar ratio of hydrogen to trichloromethylsilane is (5-10):1.

[0036] Furthermore, the flow rate ratio of hydrogen to argon is 1:(1-3).

[0037] Furthermore, the thickness of the silicon carbide protective layer in S3 is 50-500 nm.

[0038] In a second aspect, the present invention provides a dielectrically tunable graphene / ceramic composite aerogel, which is prepared by the method described above.

[0039] The present invention has the following beneficial effects: 1. This invention provides a structurally complete graphene unit: a reduced graphene oxide nanosheet with a small number of layers and uniform sheet size was independently prepared. The reduced graphene oxide not only has good conductivity, but the functional groups retained on its surface also provide abundant active sites for subsequent composites.

[0040] 2. This invention constructs an integrated thermal insulation and load-bearing structure: by combining silicon carbide whiskers and reduced graphene oxide under mild conditions to construct a composite aerogel with a high porosity three-dimensional network structure, the whiskers form effective support between graphene sheets in this structure, enhancing the mechanical strength of the material and enabling it to bear loads; at the same time, the pore structure inside the material also realizes the integration of thermal insulation and load-bearing functions.

[0041] 3. This invention achieves lightweight and adjustable performance: by changing the proportion of silicon carbide whiskers, various dielectric combinations can be formed with reduced graphene oxide, so that while maintaining thermal insulation and mechanical properties, it can adapt to different electromagnetic environments, and its comprehensive performance is superior to traditional single-function materials. Attached Figure Description

[0042] Figure 1 This is a flowchart illustrating the preparation process of dielectrically tunable graphene / ceramic composite aerogels. Figure 2 SEM image of silicon carbide whiskers; Figure 3 SEM image of reduced graphene oxide; Figure 4 SEM image of the dielectrically tunable graphene / ceramic composite aerogel prepared in Example 1; Figure 5 The real part dielectric constant of the dielectrically tunable graphene / ceramic composite aerogels prepared in Examples 1-3 is characterized. Figure 6 The imaginary part dielectric constant of the dielectrically tunable graphene / ceramic composite aerogels prepared in Examples 1-3 is characterized. Figure 7 The dielectric loss tangent characterization results are for the dielectrically tunable graphene / ceramic composite aerogels prepared in Examples 1-3. Detailed Implementation

[0043] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0044] Example 1: A method for preparing dielectrically tunable graphene / ceramic composite aerogel (preparation flow chart as shown) Figure 1(As shown), including the following steps: Preparation of S1, hydroxylated SiC whiskers SiC whiskers were weighed and placed in a beaker, and a 12% (w / w) hydrochloric acid solution was added. The mixture was stirred and refluxed at 85°C for 5 hours to remove impurities and oxide layers from the surface of the SiC whiskers. The pretreated SiC whiskers were then washed with deionized water until neutral and placed in a vacuum drying oven at 65°C for 9 hours to obtain hydroxylated SiC whiskers. SEM images are shown below. Figure 2 As shown.

[0045] S2. Preparation of monolayer graphene oxide The preparation of monolayer graphene oxide using the modified Hummers method specifically includes the following steps: S201. Add 50 mL of concentrated sulfuric acid to a three-necked flask, place the three-necked flask in water, control the temperature at about 2℃, slowly add 2 g of graphite powder, and stir for 30 min until the graphite powder is completely dispersed. S202. Keep the water bath in place and add 10 g of potassium permanganate in batches, with an interval of 12 min between each batch to avoid local overheating that could cause the oxidant to decompose. After the addition is complete, continue stirring for 1 h. S203. Remove the ice-water bath and transfer the three-necked flask to a constant temperature water bath. Control the temperature at 40°C and keep the reaction at this temperature for 4 hours. Stir once every 30 minutes during the reaction to ensure uniform reaction. S204. After the reaction is complete, slowly add 100 mL of deionized water to the three-necked flask at a rate of 1.5 mL / min. At the same time, use a constant temperature water bath to control the system temperature to not exceed 80°C to prevent the solution from boiling violently due to a sudden temperature rise. S205. After the deionized water has been added, continue stirring for 30 min. Then add 30 mL of 30% hydrogen peroxide solution. At this time, the solution color changes from brown to bright yellow. Continue stirring for 1 h to completely reduce the unreacted potassium permanganate. S206. Dilute the reacted solution to 5000 mL with deionized water, then centrifuge at 8000 rpm for 18 min, discard the supernatant, and repeat the centrifugation and washing until the solution pH is neutral to obtain a monolayer graphene oxide dispersion.

[0046] S3, Preparation of Reduced Graphene Oxide Nanosheets S301. Dilute the monolayer graphene oxide dispersion obtained in S206 with deionized water to a concentration of 2 mg / mL, and then place it in an ultrasonic cleaner and sonicate at 320 W for 10 min to obtain the graphene oxide dispersion. S302. Add 10 mL of 27% ammonia water to the graphene oxide dispersion obtained in S301, adjust the pH to 9.5, and then continue to sonicate for 20 min under the same ultrasonic power to allow the ammonia water to fully react with the graphene oxide to obtain an alkaline graphene oxide dispersion. S303. While maintaining the ultrasonic state, slowly add 1 ml of hydrazine hydrate dropwise to the alkaline graphene oxide dispersion obtained in S302. After the addition is complete, continue ultrasonic treatment for 10 min to obtain a mixed suspension. S304. The mixed suspension obtained in S303 is transferred to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene, sealed, and placed in a forced-air drying oven. The reaction is carried out at 200℃ for 12 h to complete the reduction of graphene oxide. S305. After the reaction is complete, allow the autoclave to cool naturally to room temperature. Remove the reaction solution and wash it with deionized water by centrifugation until neutral. Then, place the precipitate in a freeze dryer and freeze-dry it for 24 hours at -50℃ and a vacuum degree ≤10 Pa to obtain reduced graphene oxide nanosheets with an electrical conductivity of approximately 700 S / m. SEM images are shown below. Figure 3 As shown.

[0047] Preparation of S4, silicon carbide whiskers and reduced graphene oxide dispersion The hydroxylated silicon carbide whiskers obtained in S1 and the reduced graphene oxide obtained in S3 were weighed at a mass ratio of 1:2, and dispersed in an alcohol solution with a water content of ≤0.05%. The solutions were ultrasonically treated at 60 W for 10 min to prepare silicon carbide whisker dispersions and reduced graphene oxide dispersions with a concentration of 1 mg / mL.

[0048] S5. Preparation of composite precipitates The reduced graphene oxide dispersion obtained from S4 was slowly added to the silicon carbide whisker dispersion at a rate of 1 drop / s. After mixing, the mixture was further ultrasonically combined at 60 W for 12 h and centrifuged at 6000 rpm for 30 min to obtain the composite precipitate.

[0049] S6, directional freezing treatment The composite precipitate obtained from S5 was transferred to a custom-designed directional freezing mold and placed in a liquid nitrogen environment. It was then directionally frozen at a cooling rate of 8 °C / min for 90 min to form a porous structure arranged along the freezing direction. Finally, it was freeze-dried at -50 °C for 48 h to obtain a graphene / ceramic composite aerogel precursor.

[0050] S7, Chemical Vapor Permeation First, the graphene / ceramic composite aerogel precursor obtained from S6 was placed in a chemical vapor deposition furnace. The reaction chamber was evacuated to 0.08 kPa, and the temperature was increased to 1000℃ at a heating rate of 15℃ / min. Then, a gas was introduced into the reaction chamber, in which trichloromethylsilane was used as the precursor and carried by hydrogen as the carrier gas, with a hydrogen to trichloromethylsilane molar ratio of 8:1. Argon was introduced simultaneously as a dilution gas, with an argon to hydrogen flow rate ratio of 1:2. Deposition was carried out for 2 h. Finally, after deposition, the furnace was cooled to room temperature to obtain a dielectrically tunable graphene / ceramic composite aerogel. SEM images are shown below. Figure 4 As shown.

[0051] Example 2: A method for preparing dielectrically tunable graphene / ceramic composite aerogel includes the following steps: The basic preparation method is the same as in Example 1, except that the mass ratio of silicon carbide whiskers to reduced graphene oxide in S4 of this example is changed to 1:3, while the other steps remain unchanged.

[0052] Example 3: A method for preparing dielectrically tunable graphene / ceramic composite aerogel includes the following steps: The basic preparation method is the same as in Example 1, except that the mass ratio of silicon carbide whiskers to reduced graphene oxide in S4 of this example is changed to 1:4, while the other steps remain unchanged.

[0053] Comparative Example 1: A method for preparing reduced graphene oxide aerogel includes the following steps: S1. The preparation method of reduced graphene oxide nanosheets is the same as in Example 1.

[0054] S2. Reduced graphene oxide nanosheets were dispersed in alcohol at a concentration of 1 mg / mL, sonicated at 60 W for 10 min, centrifuged, and then frozen in liquid nitrogen at a cooling rate of 8 °C / min for 1.5 h. Subsequently, the nanosheets were freeze-dried at -50 °C for 48 h to obtain the reduced graphene oxide aerogel precursor.

[0055] S3, Chemical Vapor Permeation The reduced graphene oxide aerogel precursor obtained in S2 was placed in a chemical vapor deposition furnace. The reaction chamber was evacuated to 0.08 kPa and heated to 1000℃ at a heating rate of 15℃ / min. Then, a gas was introduced into the reaction chamber, in which trichloromethylsilane was used as the precursor and carried by hydrogen as the carrier gas, with a molar ratio of hydrogen to trichloromethylsilane of 8:1. At the same time, argon was introduced as a dilution gas, with a flow rate ratio of argon to hydrogen of 1:2. Deposition was carried out for 2 h. After the deposition was completed, the furnace was cooled to room temperature to obtain the reduced graphene oxide aerogel.

[0056] Comparative Example 2: A method for preparing silicon carbide whisker aerogel includes the following steps: S1, the preparation method of hydroxylated SiC whiskers is the same as in Example 1.

[0057] Preparation of S2 and SiC whisker aerogel precursors Hydroxylated SiC whiskers were dispersed in alcohol (concentration 1 mg / mL), sonicated at 60 W for 10 min, centrifuged, and then frozen in liquid nitrogen at a cooling rate of 8 °C / min for 1.5 h. Subsequently, they were freeze-dried at -50 °C for 48 h to obtain pure SiC whisker aerogel precursor.

[0058] S3, Chemical Vapor Deposition The silicon carbide whisker aerogel precursor obtained in S2 was placed in a chemical vapor deposition furnace. The reaction chamber was evacuated to 0.08 kPa and heated to 1000℃ at a heating rate of 15℃ / min. Then, a gas was introduced into the reaction chamber, in which trichloromethylsilane was used as the precursor and carried by hydrogen as the carrier gas, with a molar ratio of hydrogen to trichloromethylsilane of 8:1. At the same time, argon was introduced as a dilution gas, with a flow rate ratio of argon to hydrogen of 1:2. Deposition was carried out for 2 h. After the deposition was completed, the furnace was cooled to room temperature to obtain silicon carbide whisker aerogel.

[0059] Experimental example: The aerogels prepared in Examples 1-3 and Comparative Examples 1-2 were characterized for density, porosity, compressive strength, dielectric properties, and high-temperature oxidation resistance. The experimental results are as follows: Figures 4-7 As shown.

[0060] The aerogel prepared in Comparative Example 1 has a density of approximately 0.11 g / cm³. 3 It has a porosity of about 94%, but a compressive strength of only 0.7-0.9 MPa, a mass retention rate of less than 65% in an oxygen-rich environment at 800℃, and a real part of dielectric constant as high as 28-32, which cannot meet the requirements of mechanical strength and oxidation resistance in complex scenarios. The aerogel prepared in Comparative Example 2 had a mass retention rate of ≥95% after oxidation at 800℃, a compressive strength of only 0.4-0.6 MPa, a real part of dielectric constant as low as 3-5 and an imaginary part <0.5, and a weak dielectric loss capability, making it difficult to meet the requirements of electromagnetic functions. The aerogels prepared in Examples 1-3 of this application have a density ≤0.15 g / cm³. 3Porosity ≥88%, meeting lightweight requirements; compressive strength ≥2.0 MPa, mechanical properties improved by 2-5 times compared to pure system; X-band dielectric constant real part adjustable within the range of 8-22 and imaginary part adjustable within the range of 3-8, adaptable to different electromagnetic scenarios; 800℃ oxidation mass retention rate ≥87%, high temperature stability superior to pure reduced graphene oxide system, meeting the integrated performance requirements of "lightweight and high strength - adjustable dielectric - high temperature oxidation resistance" in aerospace thermal protection and electronic packaging fields.

[0061] according to Figure 4 As can be seen from the SEM images, the aerogel prepared in Example 1 of this application has a high-porosity three-dimensional network structure composed of silicon carbide whiskers and reduced graphene oxide. In this structure, the graphene sheets form an effective support, enhancing the mechanical properties of the material. The porous structure achieves integrated thermal insulation and load-bearing functions. According to Figures 5-7 The dielectric performance characterization results show that this application can form various dielectric combinations with reduced graphene oxide by changing the proportion of silicon carbide whiskers, so that while maintaining thermal insulation and mechanical properties, it can adapt to different electromagnetic environments and its comprehensive performance is significantly better than that of single-function materials.

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing dielectrically tunable graphene / ceramic composite aerogels, characterized in that, The method comprises the following steps: S1, mixing a reduced graphene oxide dispersion liquid and a silicon carbide whisker dispersion liquid, ultrasonic treatment, centrifugation, and obtaining a composite precipitate; S2, directional freezing treatment is performed on the composite precipitate obtained in S1 to induce formation of a three-dimensional interconnected porous structure, and then freeze-drying is performed to obtain a graphene / ceramic composite aerogel precursor; S3, a silicon carbide protective layer is prepared by chemical vapor infiltration on the graphene / ceramic composite aerogel precursor obtained in S2 to obtain a graphene / ceramic composite aerogel.

2. The method of claim 1, wherein the dielectrically tunable graphene / ceramic composite aerogel is prepared by the steps of: The reduced graphene oxide in S1 is prepared by the following steps: A single-layer graphene oxide dispersion liquid is prepared by using an improved Hummers method, and then hydrothermal reduction and freeze-drying are sequentially performed to obtain the reduced graphene oxide.

3. The method of claim 2, wherein the dielectrically tunable graphene / ceramic composite aerogel is prepared by the steps of: The improved Hummers method comprises the following steps: (1) first, mix concentrated hydrochloric acid and graphite powder under the condition of an ice water bath, then add potassium permanganate in batches, continue to stir, and finally constant temperature water bath reaction; (2) first, add deionized water to the reaction system after the reaction in step (1) is completed, then stir and add hydrogen peroxide solution to continue stirring, and finally centrifugal washing to obtain a single-layer graphene oxide dispersion liquid.

4. The method of claim 1, wherein the dielectrically tunable graphene / ceramic composite aerogel is prepared by the steps of: The crystal form of the silicon carbide whisker in S1 is β-SiC, and the surface is hydroxylated, and the hydroxyl content is 0.5-1.0 mmol / g.

5. The method of claim 1, wherein the dielectrically tunable graphene / ceramic composite aerogel is prepared by the steps of: The mass ratio of the reduced graphene oxide and the silicon carbide whisker in S1 is (2-4):1; the concentration of the reduced graphene oxide dispersion liquid is 0.5-2 mg / mL, and the concentration of the silicon carbide whisker is 0.5-2 mg / mL.

6. The method of claim 1, wherein the dielectrically tunable graphene / ceramic composite aerogel is prepared by the steps of: The cooling rate of the directional freezing treatment in S2 is 5-10℃ / min.

7. The method of claim 1, wherein the dielectrically tunable graphene / ceramic composite aerogel is prepared by the steps of: The reaction conditions of the chemical vapor infiltration in S3 are as follows: trichloromethylsilane is used as a precursor, hydrogen is used as a carrier gas, argon is used as a dilution gas and a protective gas, the reaction is carried out at 900-1100℃ and a pressure of 0.1-1kPa for 1-3 hours.

8. The method of claim 1, wherein the dielectrically tunable graphene / ceramic composite aerogel is prepared by the steps of: The thickness of the silicon carbide protective layer in S3 is 50-500 nm.

9. A dielectrically tunable graphene / ceramic composite aerogel, characterized in that, The graphene / ceramic composite aerogel is prepared by using the preparation method in any one of claims 1-8.

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