A wave-absorbing composite material with a multi-level pore structure and a preparation method thereof
By constructing a multi-level porous absorbing composite material, combined with a three-dimensional graphene network and silicon carbide nanowires, the impedance matching and loss insufficiency problems of single silicon carbide nanowires were solved, and the combination of multiple scattering and loss mechanisms was realized, thereby improving the absorption performance of electromagnetic waves.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANGHAI INST OF CERAMIC CHEM & TECH CHINESE ACAD OF SCI
- Filing Date
- 2023-01-06
- Publication Date
- 2026-05-12
Smart Images
Figure CN118306981B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of microwave absorbing composite materials, specifically relating to a microwave absorbing composite material with a multi-level porous structure and its preparation method. Background Technology
[0002] The rapid development of electronic technology has brought about problems such as electromagnetic pollution and electromagnetic information leakage, leading to widespread attention on high-performance microwave absorbing composite materials. Silicon carbide, as a wide-bandgap semiconductor material, possesses characteristics such as low density, high strength, corrosion resistance, and oxidation resistance, while also exhibiting suitable electrical conductivity and excellent dielectric properties. Based on these properties, silicon carbide nanowires, due to their large specific surface area, high surface atomic ratio, and numerous surface dangling bonds, can construct interconnected conductive network structures, making them considered an ideal high-temperature microwave absorbing material. However, the electromagnetic parameters of single silicon carbide nanowires are insufficient to achieve impedance matching characteristics, and their electromagnetic wave loss mechanism is singular with insufficient dielectric loss strength, resulting in strong reflection and weak absorption, which fails to meet the practical application requirements of microwave absorbing materials. Therefore, introducing multiple absorption mechanisms and constructing composite materials with multi-dimensional structures and multi-phase compositions are considered effective ways to optimize microwave absorption performance.
[0003] Graphene's unique electronic structure and tunable dielectric properties endow it with excellent electromagnetic wave absorption characteristics, thus making it an ideal structural unit for microwave absorbing composite materials. Graphene's large specific surface area effectively extends the propagation path of electromagnetic waves, and its three-dimensional network structure enhances multiple scattering of electromagnetic waves, improving conductivity loss. The combination of three-dimensional graphene and silicon carbide nanowires constructs a hierarchical porous structure, effectively increasing electromagnetic wave scattering. The destructive interference caused by scattering significantly increases the loss of electromagnetic waves during propagation. Simultaneously, it improves the impedance matching of the composite material, and the introduced interfacial polarization and dipole polarization contribute to dielectric loss reduction. However, the construction of the three-dimensional graphene structure and its distribution within the silicon carbide nanowires are difficult to precisely control, and the matching of the intrinsic dielectric properties of graphene and silicon carbide materials still requires further optimization. Summary of the Invention
[0004] To address the above problems, this invention provides a microwave absorbing composite material with a multi-level porous structure and its preparation method.
[0005] In a first aspect, the present invention provides a method for preparing a microwave absorbing composite material with a hierarchical porous structure, comprising: mixing graphene oxide, iron oxide, and nickel nitrate in a solvent to obtain a composite printing slurry; then obtaining a composite hydrogel structure by 3D printing the composite printing slurry; obtaining a composite aerogel by freeze-drying and vacuum drying; and then introducing boron nitride interface and silicon carbide nanowires in situ in the composite aerogel by chemical vapor deposition to obtain the microwave absorbing composite material with a hierarchical porous structure.
[0006] Preferably, the mass ratio of iron(III) oxide to graphene oxide is 3:1 to 1:3, more preferably 1:1; the mass ratio of nickel nitrate to graphene oxide is 1:10 to 60, more preferably 1:50.
[0007] Preferably, the nozzle air pressure of the 3D printing is 0.1-0.4 MPa, the nozzle diameter is 0.3-0.6 mm, the nozzle moving speed is 10-30 mm / s, the intralayer monofilament spacing is 0.3-0.6 mm, and the interlayer spacing is 0.3-0.6 mm.
[0008] Preferably, the composite hydrogel is freeze-dried at a temperature of -80℃ to -30℃ for 24 to 72 hours; and vacuum-dried for 24 to 48 hours.
[0009] Preferably, the temperature of the boron nitride interface in the chemical vapor deposition is 800–900°C, the reaction pressure is 1–2 kPa, and the reaction time is 0.5–2 hours; the flow rate of the ammonia gas is 40–80 mL / min, and the flow rate of the boron chloride gas is 10–20 mL / min.
[0010] Preferably, the temperature for chemical vapor deposition of silicon carbide nanowires is 1000–1100 °C, the reaction pressure is 3–6 kPa, and the reaction time is 1–8 hours; the flow rate of the reaction gas methyltrichlorosilane is 220–360 mL / min.
[0011] Secondly, the present invention provides a microwave absorbing composite material with a multi-level porous structure obtained by the above preparation method. The microwave absorbing composite material with a multi-level porous structure has a porosity of 20% to 50%, a minimum reflection loss of -17.7 to -33.6 dB, and a maximum effective absorption bandwidth of 2.0 to 6.2 GHz.
[0012] Beneficial effects
[0013] This invention introduces iron(II,III) oxide (Fe3O4) to provide a magnetic loss mechanism. 3D printing and cryogenic self-assembly techniques are used to construct a macroscopically ordered, microscopically porous network structure of three-dimensional graphene. This microscopic network enables electromagnetic wave conductivity loss. In chemical vapor deposition, boron nitride interfaces and silicon carbide nanowires are introduced in situ into the three-dimensional graphene structure. The complementary dielectric constants optimize the impedance matching of the composite material, ensuring that electromagnetic waves can penetrate more deeply into the material and undergo loss. Simultaneously, the formed interfaces exhibit interfacial polarization and dipole polarization, resulting in dielectric loss. The nanowire framework structure, combining magnetic, dielectric, and conductivity loss mechanisms, enables multiple scattering of electromagnetic waves, effectively enhancing the composite material's electromagnetic wave loss intensity. Attached Figure Description
[0014] Figure 1 Optical images of the three-dimensional graphene and the three-dimensional graphene / boron nitride / silicon carbide nanowire absorbing composite material in Example 1;
[0015] Figure 2 This is a cross-sectional SEM image of the three-dimensional graphene in Example 1;
[0016] Figure 3 This is a cross-sectional SEM image of the three-dimensional graphene / boron nitride / silicon carbide nanowire microwave absorbing composite material in Example 1;
[0017] Figure 4 The values represent the reflection loss of the three-dimensional graphene / boron nitride / silicon carbide nanowire composite material in Example 1 at different simulated thicknesses.
[0018] Figure 5 The graph shows the trend of the maximum effective absorption bandwidth of the composite materials prepared in Examples 1-7 and Comparative Examples 1-6. Detailed Implementation
[0019] The present invention will be further described below with reference to the accompanying drawings and the following embodiments. It should be understood that the accompanying drawings and the following embodiments are for illustrative purposes only and are not intended to limit the present invention.
[0020] This invention provides a method for preparing a microwave absorbing composite material with a hierarchical porous structure. The method uses graphene oxide, iron oxide, and nickel nitrate as raw materials and deionized water as a solvent to prepare a uniformly dispersed composite slurry by ultrasonication. Then, a composite aerogel structure is constructed using 3D printing and cryogenic self-assembly technology. By controlling the macroscopic structural parameters of the printing process and the temperature parameters of the cryogenic self-assembly process, macroscopic / microscopic control of the graphene oxide sheets is achieved to construct a graphene aerogel with a through-network structure. Finally, high-purity boron nitride interfaces and silicon carbide nanowires are grown in situ sequentially using chemical vapor deposition to obtain a three-dimensional graphene / boron nitride / silicon carbide nanowire microwave absorbing composite material with a hierarchical porous structure.
[0021] The following exemplarily illustrates a method for preparing a microwave absorbing composite material with a multi-level porous structure provided by the present invention, which may include the following steps.
[0022] (1) Preparation of composite printing paste. Graphene oxide, iron oxide and nickel nitrate were added to deionized water and mixed uniformly by ultrasonication to prepare a composite printing paste with uniformly dispersed components.
[0023] In an optional embodiment, the mass ratio of graphene oxide to deionized water solvent can be 1:30 to 80. An appropriate amount of solvent can yield a composite slurry with uniformly dispersed components and self-supporting properties.
[0024] The mass ratio of iron(III) oxide to graphene oxide can be 3:1 to 1:3, preferably 1:1; the mass ratio of nickel nitrate to graphene oxide can be 1:10 to 60, preferably 1:50. An appropriate amount of nickel nitrate loading allows the subsequently grown silicon carbide nanowires to uniformly fill the pores of the three-dimensional graphene network, forming a hierarchical porous structure. Excessive nickel nitrate loading leads to overly dense growth of the silicon carbide nanowires, making it difficult for the composite material to form a porous structure; insufficient nickel nitrate loading results in discontinuous growth of the silicon carbide nanowires, making it difficult to form a continuous scattering network.
[0025] In some embodiments, the ultrasonic power can be 200–600 W, and the ultrasonic time can be 0.5–2 hours. Since graphene oxide forms a gel structure in water, resulting in a high viscosity of the composite slurry, appropriately increasing the ultrasonic power and extending the ultrasonic time helps to achieve more uniform dispersion of the components.
[0026] (2) Preparation of composite hydrogel. The composite printing slurry prepared in step (1) is stacked as needed by 3D printing to prepare a macroscopically densely packed composite hydrogel. During the 3D printing process, a pre-edited three-dimensional model can be imported into the software, and by setting parameters such as printing air pressure and moving speed, the slurry is stacked according to the path set by the program to obtain a dense structure.
[0027] In an optional embodiment, the 3D printing process parameters can be: nozzle air pressure of 0.1–0.4 MPa, nozzle diameter of 0.3–0.6 mm, nozzle movement speed of 10–30 mm / s, intralayer monofilament spacing of 0.3–0.6 mm, and interlayer spacing of 0.3–0.6 mm. Preferably, to prevent leakage in the macrostructure, the nozzle diameter, intralayer monofilament spacing, and interlayer spacing can be kept consistent to construct a macroscopically dense composite hydrogel structure.
[0028] In some embodiments, the length and width of the 3D-printed hydrogel material can be 12–18 mm, preferably 14 mm; the height can be 1.8–2.5 mm, preferably 2.0 mm. Suitable three-dimensional dimensions are beneficial for subsequent electromagnetic wave absorption performance testing of the material.
[0029] (3) Preparation of composite aerogel. The composite hydrogel obtained in step (2) was placed in a freeze dryer, and the microscopic control of the graphene oxide sheets was achieved through the freeze self-assembly process to construct a three-dimensional network structure with interconnected sheets; then, the solvent in the composite hydrogel structure was removed by vacuum drying to prepare a composite aerogel with a lightweight structure.
[0030] In optional embodiments, the freeze-drying temperature of the composite hydrogel can be -80℃ to -30℃, and the time can be 24 to 72 hours; the vacuum drying time can be 24 to 48 hours. Freeze-drying can regulate the self-assembly process of graphene oxide sheets, significantly affecting the pore size of the network structure in the aerogel.
[0031] (4) Preparation of microwave absorbing composite material with hierarchical porous structure. Boron nitride interface and silicon carbide nanowires were introduced in situ into the composite aerogel prepared in step (3) by chemical vapor deposition to prepare a three-dimensional graphene / boron nitride / silicon carbide nanowire microwave absorbing composite material with hierarchical porous structure.
[0032] The high temperatures during chemical vapor deposition (CVD) reduce graphene oxide to graphene, further constructing a continuous porous network structure. Complementary dielectric constants optimize the impedance matching of the composite material. Simultaneously, the interface between boron nitride and graphene sheets introduces dielectric loss mechanisms such as interfacial polarization and dipole polarization. The constructed silicon carbide nanowire framework and the three-dimensional graphene network form a hierarchical porous structure, enabling multiple scattering of electromagnetic waves and effectively improving the microwave absorption performance of the composite material.
[0033] In an optional embodiment, the temperature of the boron nitride interface in the chemical vapor deposition can be 800-900°C, the reaction pressure can be 1-2 kPa, and the reaction time can be 0.5-2 hours; the flow rate of the ammonia gas can be 40-80 mL / min, and the flow rate of the boron chloride gas can be 10-20 mL / min.
[0034] In an optional embodiment, the temperature for chemical vapor deposition of silicon carbide nanowires can be 1000–1100°C, the reaction pressure can be 3–6 kPa, and the reaction time can be 1–8 hours; the flow rate of the reaction gas methyltrichlorosilane can be 220–360 mL / min. The length of the silicon carbide nanowire framework constructed in the three-dimensional graphene network structure can be controlled to be above 11.6 μm, preferably 12–20 μm; the diameter can be controlled to be 560–640 nm, preferably 590 nm.
[0035] This invention uses graphene oxide as raw material and combines 3D printing technology with cryogenic self-assembly technology to achieve synergistic control of the macroscopic and microscopic structures of the material, forming porous three-dimensional graphene with controllable macroscopic structure and interconnected microscopic structures. Simultaneously, the in-situ growth of boron nitride on the surface of the graphene sheets effectively modulates the dielectric constant of graphene and introduces an interfacial polarization electromagnetic wave loss mechanism. Furthermore, in-situ deposition of silicon carbide nanowires constructs a porous nanonetwork structure, forming a hierarchical porous structure with the three-dimensional graphene, achieving multiple scattering of incident electromagnetic waves and increasing electromagnetic wave loss during transmission.
[0036] The microwave absorbing composite material with a multi-level porous structure obtained by the preparation method provided by the present invention has a porosity of 20% to 50%, a minimum reflection loss of -17.7 to -33.6 dB, and a maximum effective absorption bandwidth of 2.0 to 6.2 GHz.
[0037] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values in the examples below.
[0038] Example 1
[0039] (1) Preparation of composite printing paste. 0.6g graphene oxide, 0.6g iron oxide and 0.02g nickel nitrate were added to 20ml deionized water and ultrasonically dispersed at 500W for 1 hour to prepare a composite printing paste with uniformly dispersed components.
[0040] (2) Preparation of composite hydrogel. Import the pre-edited three-dimensional model into the 3D printing software. The size is designed to be 14mm×14mm×2mm. The composite printing paste prepared in step (1) is stacked as needed to prepare a macroscopically densely stacked composite hydrogel. The printing nozzle pressure of the 3D printing is 0.2MPa, the printing nozzle diameter is 0.5mm, the printing nozzle moving speed is 20mm / s, the intralayer monofilament spacing is 0.5mm, and the upper and lower layer spacing is 0.5mm.
[0041] (3) Preparation of composite aerogel. The composite hydrogel obtained in step (2) was placed in a freeze dryer, where the freezing temperature was -60℃ and the freezing time was 36 hours; then, it was vacuum dried for 24 hours to obtain a composite aerogel with an ultralight structure.
[0042] (4) Preparation of microwave absorbing composite material with hierarchical porous structure. The composite aerogel prepared in step (3) was placed in a chemical vapor deposition reactor, and boron nitride was grown in situ at 800℃, with a reaction pressure of 1 kPa and a reaction time of 1 hour. The flow rate of the reaction gas ammonia was 50 mL / min, and the flow rate of the reaction gas boron chloride was 15 mL / min. Then, the temperature was raised to 1100℃ and silicon carbide nanowires were grown in situ at a reaction pressure of 3 kPa and a reaction time of 2 hours. The flow rate of the reaction gas methyltrichlorosilane was 320 mL / min. A three-dimensional graphene / boron nitride / silicon carbide nanowire microwave absorbing composite material with hierarchical porous structure was prepared.
[0043] A circular structure with an inner diameter of 3 mm and an outer diameter of 7 mm was cut from a cubic composite material structure using a laser cutting machine.
[0044] Example 2
[0045] Referring to Example 1, the main difference is that 1.8g of iron(III) oxide is added in step (1).
[0046] Example 3
[0047] Referring to Example 1, the main difference is that 1.8g of graphene oxide is added in step (1).
[0048] Example 4
[0049] Referring to Example 1, the main difference is that 0.06g of nickel nitrate is added in step (1).
[0050] Example 5
[0051] Referring to Example 1, the main difference is that 0.01g of nickel nitrate is added in step (1).
[0052] Example 6
[0053] Referring to Example 1, the main difference is that the deposition time of silicon carbide nanowires in step (4) is 6 hours.
[0054] Example 7
[0055] Referring to Example 1, the main difference is that the deposition time of boron nitride in step (4) is 2 hours.
[0056] Comparative Example 1
[0057] Referring to Example 1, the main difference is that the freeze-drying temperature in step (3) is -20°C.
[0058] Comparative Example 2
[0059] Referring to Example 1, the main difference is that the freezing time in step (3) is 12 hours and the vacuum drying time is 12 hours.
[0060] Comparative Example 3
[0061] Referring to Example 1, the main difference is that boron nitride was not deposited in step (4).
[0062] Comparative Example 4
[0063] Referring to Example 1, the main difference is that the deposition time of boron nitride in step (4) is 4 hours.
[0064] Comparative Example 5
[0065] Referring to Example 1, the main difference is that silicon carbide nanowires were not deposited in step (4).
[0066] Comparative Example 6
[0067] Referring to Example 1, the main difference is that: in step (1), nickel nitrate catalyst was not added, and in step (4), silicon carbide interface was deposited instead of silicon carbide nanowires.
[0068] Figure 1 Optical images of the three-dimensional graphene and the three-dimensional graphene / boron nitride / silicon carbide nanowire absorbing composite material in Example 1 are shown. As can be seen from the images, the three-dimensional graphene has a periodic cubic structure, with adjacent filaments within each layer maintaining close contact with adjacent layers above and below, without any visible gaps, ensuring that incident electromagnetic waves cannot directly pass through the material. The prepared three-dimensional graphene / boron nitride / silicon carbide nanowire composite material maintains a similar structure to the three-dimensional graphene and did not experience structural collapse during high-temperature deposition, indicating that the graphene sheets formed a mutually supporting interconnected network structure.
[0069] Figure 2 This is a cross-sectional SEM image of the three-dimensional graphene in Example 1. As can be seen from the image, the cryogenic self-assembly process of the composite hydrogel achieves microscopic control of the graphene oxide sheets, constructs a porous network structure that is interconnected throughout, provides a huge specific surface area, and can effectively achieve multiple scattering of incident electromagnetic waves.
[0070] Figure 3 This is a cross-sectional SEM image of the three-dimensional graphene / boron nitride / silicon carbide nanowire absorbing composite material in Example 1. As can be seen from the image, silicon carbide nanowires are grown in situ inside the composite material. These nanowires are over 11.6 μm in length and approximately 590 nm in diameter. The silicon carbide nanowires form an intersecting framework structure with micron-level pores. Together with the three-dimensional graphene, they form a hierarchical porous structure, which is beneficial for enhancing the multiple scattering intensity of incident electromagnetic waves.
[0071] Figure 4The figures show the reflection loss values of the three-dimensional graphene / boron nitride / silicon carbide nanowire composite material in Example 1 at different simulated thicknesses. As can be seen from the figures, the composite material exhibits the lowest reflection loss value of -47.2 dB at 12.1 GHz when the simulated thickness is 3 mm, demonstrating excellent electromagnetic wave loss intensity. When the simulated thickness is 2.6 mm, it exhibits the lowest reflection loss value of -31.9 dB at 15.3 GHz. Its effective absorption bandwidth (reflection loss value less than -10 dB) is 11.8 GHz to 18.0 GHz, with a bandwidth reaching 6.2 GHz, demonstrating excellent broadband (high-frequency) absorption performance. The excellent electromagnetic wave absorption performance of the three-dimensional graphene / boron nitride / silicon carbide nanowire composite material can be attributed to multiple loss mechanisms, including electrical conductance loss, magnetic loss, and dielectric loss.
[0072] Figure 5 The graph shows the trend of the maximum effective absorption bandwidth of the composite materials prepared in Examples 1-7 and Comparative Examples 1-6. As can be seen from the graph, Examples 2-5, by changing the amount of iron oxide and silicon carbide nanowires introduced into the composite material, can affect the magnetic loss strength and dielectric loss strength of the composite material. Compared to Example 1, the reduction in effective absorption bandwidth in Examples 2-5 is attributed to the decrease in impedance matching of the composite material and the reduction in magnetic loss phase. Examples 6 and 7 extended the deposition time of silicon carbide nanowires and boron nitride within the protection range, resulting in the introduction of relatively excessive silicon carbide nanowires and boron nitride, and a slight impedance mismatch in the composite material. In Comparative Examples 1 and 2, the self-assembly process of the graphene oxide sheets was insufficient, and a stable interconnected porous scattering network was not formed, resulting in a weakening of the multiple scattering intensity of the incident electromagnetic waves. In Comparative Example 3, the boron nitride interface was not introduced in situ, resulting in a weakening of the dielectric loss effect of the composite material. In Comparative Example 4, excessive boron nitride was introduced, resulting in impedance mismatch in the composite material. In Comparative Example 5, the silicon carbide nanowires were not introduced in situ, which not only significantly weakened the impedance matching of the composite material, but also weakened the multiple scattering intensity of the electromagnetic waves. Compared to Example 1, Comparative Example 6 introduced a silicon carbide interface instead of silicon carbide nanowires, and its reduction in effective absorption bandwidth is attributed to the effect of conductivity loss and the weakening of the multiple scattering intensity of the electromagnetic waves.
[0073] The table below shows the effective absorption band and minimum reflection loss of the composite materials prepared in Examples 1-7 and Comparative Examples 1-6:
[0074]
[0075]
Claims
1. A method for preparing a microwave absorbing composite material with a hierarchical porous structure, characterized in that, include: Graphene oxide, iron oxide, and nickel nitrate are mixed in a solvent to obtain a composite printing paste. The composite printing paste is then 3D printed to obtain a composite hydrogel structure. After freeze-drying and vacuum drying, a composite aerogel is obtained. Then, boron nitride interface and silicon carbide nanowires are introduced in situ into the composite aerogel by chemical vapor deposition to obtain the microwave absorbing composite material with a multi-level porous structure. The mass ratio of iron(II,III) oxide to graphene oxide is 3:1 to 1:3, and the mass ratio of nickel nitrate to graphene oxide is 1:10 to 60. The nozzle air pressure of the 3D printer is 0.1-0.4 MPa, the nozzle diameter is 0.3-0.6 mm, the nozzle moving speed is 10-30 mm / s, the intralayer monofilament spacing is 0.3-0.6 mm, and the interlayer spacing is 0.3-0.6 mm. The temperature of the boron nitride interface in the chemical vapor deposition is 800–900℃, the reaction pressure is 1–2 kPa, and the reaction time is 0.5–2 hours; the flow rate of the ammonia gas is 40–80 mL / min, and the flow rate of the boron chloride gas is 10–20 mL / min.
2. The preparation method according to claim 1, characterized in that, The mass ratio of iron(III) oxide to graphene oxide is 1:1; the mass ratio of nickel nitrate to graphene oxide is 1:
50.
3. The preparation method according to claim 1, characterized in that, The composite hydrogel is freeze-dried at a temperature of -80℃ to -30℃ for 24 to 72 hours; vacuum drying takes 24 to 48 hours.
4. The preparation method according to claim 1, characterized in that, The temperature for chemical vapor deposition of silicon carbide nanowires is 1000–1100℃, the reaction pressure is 3–6 kPa, and the reaction time is 1–8 hours; the flow rate of the reaction gas methyltrichlorosilane is 220–360 mL / min.
5. A microwave absorbing composite material with a hierarchical porous structure obtained by the preparation method of claim 1, characterized in that, The microwave absorbing composite material with a multi-level porous structure has a porosity of 20% to 50%, a minimum reflection loss of -17.7 to -33.6 dB, and a maximum effective absorption bandwidth of 2.0 to 6.2 GHz.