Lightweight broadband electromagnetic absorption composite material and preparation method thereof

Abstract

The invention discloses a lightweight broadband electromagnetic absorption composite material and a preparation method thereof. The lightweight broadband electromagnetic absorption composite material is a graded magnetoelectric network formed by a three-dimensional porous carbon skeleton with a hierarchical pore structure and iron-nickel alloy nanoparticles; the three-dimensional porous carbon skeleton is a three-dimensional porous carbon skeleton with a hierarchical pore structure, which is formed after delignification treatment by taking natural balsa wood as a biological template, and retains a directional conduit structure of the natural balsa wood; iron-nickel alloy nanoparticles are loaded in channels and on the surfaces of hole walls of the three-dimensional porous carbon skeleton in situ. The method is particularly suitable for radar wave-absorbing interlayers, electromagnetic compatibility panels and aerospace stealth structures.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic functional materials technology, specifically to a lightweight broadband electromagnetic absorption composite material and its preparation method. Background Technology

[0002] With the rapid development of electronic devices and wireless communication technologies, electromagnetic radiation and interference problems are becoming increasingly prominent. Developing high-performance electromagnetic absorbing materials is of great significance for fields such as radar stealth, aerospace, and electromagnetic compatibility. Traditional absorbing materials typically rely on high-density metals or magnetic fillers (such as iron-based alloys, ceramics, and carbon composites) to enhance electromagnetic loss capability. However, while this method can improve attenuation performance, it often leads to increased material density and deteriorated impedance matching, resulting in narrow absorption bandwidth and difficulty in integration with lightweight composite structures, thus limiting its application in advanced equipment.

[0003] To balance lightweight properties with broad-band absorption characteristics, porous and mesoporous materials have attracted widespread attention due to their unique structural advantages. For example, porous carbon and biochar, through their hierarchical pore structures, can promote multiple scattering and interfacial polarization of electromagnetic waves, thereby improving absorption performance. However, these materials often rely on complex template methods for preparation, which suffer from cumbersome processes, insufficient structural stability, and difficulty in large-scale production.

[0004] In recent years, inspired by natural biological structures, hierarchical porous absorber materials prepared using wood, lotus root, and other materials as templates have shown great potential. Wood itself possesses oriented xylem channels and multi-scale pore wall structures, which can extend the propagation path of electromagnetic waves, achieve multiple reflections, and rely on its natural pore-solid gradient structure to achieve smooth impedance matching. Building upon this, introducing magnetic components (such as Fe and Ni) can construct a magnetoelectric synergistic loss mechanism, further enhancing absorption efficiency. Nevertheless, how to uniformly embed magnetic nanoparticles into the wood mesoporous framework through controllable and stable processes, and achieve synergistic optimization of structure, impedance, and loss, remains a crucial technical challenge to be solved in this field. Summary of the Invention

[0005] 1. The technical problem to be solved:

[0006] To address the aforementioned technical problems, this invention provides a lightweight broadband electromagnetic absorbing composite material based on the graded structure design of natural wood and its preparation method, which is particularly suitable for radar absorbing sandwich layers, electromagnetic compatibility panels, and aerospace stealth structures.

[0007] 2. Technical Solution:

[0008] A lightweight broadband electromagnetic absorption composite material is characterized by: a hierarchical magnetoelectric network formed by a three-dimensional porous carbon skeleton with a multi-level porous structure and iron-nickel alloy nanoparticles; the three-dimensional porous carbon skeleton is formed by using natural balsa wood as a biological template and undergoing lignin removal treatment to form a three-dimensional porous carbon skeleton with a multi-level porous structure, which retains the directional vascular structure of natural balsa wood; and iron-nickel alloy nanoparticles are loaded in situ in the channels and on the surface of the pore walls of the three-dimensional porous carbon skeleton.

[0009] Furthermore, the iron-nickel alloy nanoparticles are prepared by an impregnation-sintering process; the mass ratio of Fe to Ni in the iron-nickel alloy nanoparticles is (4-9):1.

[0010] Furthermore, the three-dimensional porous carbon skeleton has a vessel diameter of 5-8 μm and a cell wall thickness of 2-3 μm.

[0011] Furthermore, the electromagnetic absorption composite material has a minimum reflection loss of ≤-42dB in the frequency range of 2-18GHz and an effective absorption bandwidth of ≥6.4GHz.

[0012] A method for preparing a lightweight broadband electromagnetic absorption composite material includes the following steps:

[0013] Step 1: Template preparation: Natural balsa wood blocks are treated with delignification and then dried to obtain a balsa wood skeleton with an open mesoporous structure;

[0014] Step 2: Preparation of precursor solution: Dissolve iron salt and nickel salt in solvent according to the target mass ratio of Fe to Ni to form a homogeneous precursor solution;

[0015] Step 3: Impregnation and Loading: Immerse the balsa wood skeleton obtained in Step 1 into the precursor solution prepared in Step 2, allowing the solution to fully penetrate into the interior of the skeleton;

[0016] Step 4: Post-treatment and carbonization: The impregnated balsa wood skeleton is removed and cleaned, and then sintered in an inert atmosphere to obtain a lightweight broadband electromagnetic absorption composite material.

[0017] Further, in step one, the delignification treatment involves placing the natural balsa wood blocks in an alkaline sodium sulfite solution and treating them under heating conditions for 6-12 hours; the concentration of sodium hydroxide in the alkaline sodium sulfite solution is 2.0-3.0 mol / L, and the concentration of sodium sulfite is 0.3-0.5 mol / L; the heating temperature is 130-150℃.

[0018] Furthermore, in step three, ultrasonic-assisted treatment is applied during the impregnation process.

[0019] Furthermore, in step four, the sintering temperature is 700-900℃, and the holding time is 1-3 hours.

[0020] 3. Beneficial effects:

[0021] (1) The present invention provides a lightweight broadband electromagnetic absorption composite material, which is a biomimetic composite material based on the graded structure of natural wood. It consists of a balsa wood skeleton treated with lignin removal and Fe / Ni alloy nanoparticles uniformly loaded thereon, wherein the mass ratio of Fe to Ni is (4-9):1.

[0022] (2) The lightweight broadband electromagnetic absorption composite material prepared by the present invention constructs a multi-level porous structure with 5-8 μm mesopores and directional channels by removing lignin from balsa wood. This structure can significantly extend the electromagnetic wave propagation path, induce multiple reflections, and achieve smooth impedance matching through the natural pore-solid gradient. Fe / Ni nanoparticles are generated and fixed in situ on the channel and pore wall surface of the skeleton through impregnation and sintering processes, forming a stable hierarchical magnetoelectric network. The Fe / Ni nanoparticles provide magnetic loss through magnetic domain resonance and eddy current effect, which works synergistically with the dielectric loss of the carbonized wood skeleton to dissipate electromagnetic energy. Through the synergistic design of structure, composition and process, the intrinsic coupling of anisotropic waveguide, gradient impedance and magnetoelectric synergistic effect is realized.

[0023] (3) The lightweight broadband electromagnetic absorption composite material prepared by the present invention exhibits excellent electromagnetic wave absorption performance in the 2-18GHz frequency band. Under a specific matching thickness, its minimum reflection loss can reach -42.58dB and its maximum effective absorption bandwidth reaches 6.42GHz. It also has the characteristics of being lightweight, high-strength, and structurally stable. It is particularly suitable for radar absorbing sandwich, aerospace stealth structure and electromagnetic compatibility (EMC) panel where there are strict requirements for weight and broadband performance. Attached Figure Description

[0024] Figure 1 SEM images of the lightweight broadband electromagnetic absorption composite material of the embodiment; where (a) shows the longitudinal pores, (b) shows the surface of the transverse pores, and (c) shows the adhesion of iron-nickel alloy nanoparticles;

[0025] Figure 2 The X-ray diffraction pattern is shown in the example. Detailed Implementation

[0026] The present invention will now be described in detail with reference to the embodiments.

[0027] A lightweight broadband electromagnetic absorption composite material is characterized by: a hierarchical magnetoelectric network formed by a three-dimensional porous carbon skeleton with a multi-level porous structure and iron-nickel alloy nanoparticles; the three-dimensional porous carbon skeleton is formed by using natural balsa wood as a biological template and undergoing lignin removal treatment to form a three-dimensional porous carbon skeleton with a multi-level porous structure, which retains the directional vascular structure of natural balsa wood; and iron-nickel alloy nanoparticles are loaded in situ in the channels and on the surface of the pore walls of the three-dimensional porous carbon skeleton.

[0028] Furthermore, the iron-nickel alloy nanoparticles are prepared by an impregnation-sintering process; the mass ratio of Fe to Ni in the iron-nickel alloy nanoparticles is (4-9):1.

[0029] Furthermore, the three-dimensional porous carbon skeleton has a vessel diameter of 5-8 μm and a cell wall thickness of 2-3 μm.

[0030] Furthermore, the electromagnetic absorption composite material has a minimum reflection loss of ≤-42dB in the frequency range of 2-18GHz and an effective absorption bandwidth of ≥6.4GHz.

[0031] A method for preparing a lightweight broadband electromagnetic absorption composite material includes the following steps:

[0032] Step 1: Template preparation: Natural balsa wood blocks are treated with delignification and then dried to obtain a balsa wood skeleton with an open mesoporous structure;

[0033] Step 2: Preparation of precursor solution: Dissolve iron salt and nickel salt in solvent according to the target mass ratio of Fe to Ni to form a homogeneous precursor solution;

[0034] Step 3: Impregnation and Loading: Immerse the balsa wood skeleton obtained in Step 1 into the precursor solution prepared in Step 2, allowing the solution to fully penetrate into the interior of the skeleton;

[0035] Step 4: Post-treatment and carbonization: The impregnated balsa wood skeleton is removed and cleaned, and then sintered in an inert atmosphere to obtain a lightweight broadband electromagnetic absorption composite material.

[0036] Further, in step one, the delignification treatment involves placing the natural balsa wood blocks in an alkaline sodium sulfite solution and treating them under heating conditions for 6-12 hours; the concentration of sodium hydroxide in the alkaline sodium sulfite solution is 2.0-3.0 mol / L, and the concentration of sodium sulfite is 0.3-0.5 mol / L; the heating temperature is 130-150℃.

[0037] Furthermore, in step three, ultrasonic-assisted treatment is applied during the impregnation process.

[0038] Furthermore, in step four, the sintering temperature is 700-900℃, and the holding time is 1-3 hours.

[0039] Example 1:

[0040] The preparation of mesoporous wood-based composite material (FNWMs-1) with a Fe / Ni mass ratio of 5:1 includes the following steps:

[0041] (1) The balsa wood blocks were cut into small pieces of 20mm×20mm×10mm and placed in a prepared alkaline sodium sulfite solution (NaOH 2.5mol / L, Na2SO3 0.4mol / L). The solution was heated and stirred at 140℃ for 9 hours. After treatment, the balsa wood was removed, washed with deionized water, and freeze-dried to obtain a lignin-free mesoporous balsa wood skeleton.

[0042] (2) Weigh out ferric chloride and nickel chloride hexahydrate according to the molar ratio of Fe:Ni=5:1, dissolve them in deionized water, prepare a precursor solution with a total metal ion concentration of 0.5mol / L, and ultrasonically disperse for 30 minutes.

[0043] (3) Immerse the mesoporous balsa wood skeleton obtained in step (1) into the above precursor solution, place it in an ultrasonic cleaner for ultrasonic treatment for 1 hour, and then let it stand and soak for 24 hours.

[0044] (4) Take out the soaked wood block, rinse the surface lightly with deionized water, then soak it in dilute NaOH solution (0.1mol / L) for 1 hour to neutralize any residual acid, and finally wash it with deionized water.

[0045] (5) The treated sample was placed in a tube furnace and heated to 800°C at a rate of 5°C / min under argon protection. The temperature was maintained for 2 hours for carbonization and alloying. Then it was naturally cooled to room temperature to obtain the target composite material FNWMs-1.

[0046] Example 2:

[0047] A lightweight broadband electromagnetic absorption composite material, unlike Example 1, has a Fe:Ni molar ratio controlled at 4:1 when preparing the precursor solution in step (2). The remaining steps are the same as in Example 1, resulting in the composite material FNWMs-2.

[0048] Example 3:

[0049] A lightweight broadband electromagnetic absorption composite material, unlike Example 1, has a Fe:Ni molar ratio controlled at 9:1 when preparing the precursor solution in step (2). The remaining steps are the same as in Example 1, resulting in the composite material FNWMs-3.

[0050] Comparative Example 1 (pure carbonized wood, non-magnetic load):

[0051] A comparative material, unlike Example 1, does not undergo the impregnation processes in steps (2) and (3). The mesoporous balsa wood skeleton obtained in step (1) of Example 1 is directly subjected to the carbonization treatment in step (5) to obtain a purely carbonized porous wood material.

[0052] Comparative Example 2 (prepared by physical mixing method):

[0053] A comparative material was prepared by crushing the mesoporous balsa wood skeleton obtained in step (1) of Example 1 into powder. Commercial Fe / Ni alloy micropowder was then physically and mechanically mixed with the wood powder according to the metal ratio of Example 1, and subsequently mixed with paraffin wax and pressed into test rings. This method does not involve an in-situ impregnation loading process.

[0054] Result detection

[0055] The structural characterization and electromagnetic property tests of the samples prepared in the examples and comparative examples were performed, and the main results are as follows:

[0056] 1. Microstructure analysis:

[0057] As attached Figure 1 The images shown are SEM images of the lightweight broadband electromagnetic absorption composite material obtained in Example 1; (a) is a SEM image of its longitudinal pores; (b) is a SEM image of the transverse pore surface; and (c) is a SEM image of the iron-nickel alloy nanoparticles. The images show that it possesses a wood-like anisotropic porous structure, forming a hierarchical magnetoelectric network with the distributed iron-nickel alloy nanoparticles.

[0058] SEM observations showed that the lightweight broadband electromagnetic absorbing composite materials (FNWMs) obtained in Examples 1-3 successfully retained the inherent anisotropic porous structure of balsa wood. The cross-section revealed neatly arranged elliptical vessels (5-8 μm in diameter), while the longitudinal section showed continuous through-channels. Fe / Ni nanoparticles were uniformly distributed on the vessel cavities and mesopore walls, without significant agglomeration, forming a stable hierarchical magnetoelectric network. The sample in Comparative Example 1 only exhibited a porous structure with a carbon skeleton and no magnetic particles. In the sample in Comparative Example 2, the commercial Fe / Ni micropowder was unevenly mixed with the wood charcoal powder, resulting in loose interfacial bonding.

[0059] 2. Phase and composition analysis:

[0060] As attached Figure 2 The figure shows X-ray diffraction patterns of iron-nickel alloy nanoparticles attached to the crystalline phases of lightweight broadband electromagnetic absorbing composites prepared with different Fe:Ni ratios. Numbers 1, 2, and 3 in the figure correspond to Fe:Ni ratios of 5:1, 4:1, and 9:1, respectively.

[0061] XRD analysis showed that the example samples exhibited broad peaks of amorphous carbon at 20°-30°, and distinct characteristic diffraction peaks of NiFe2O4 and γ-Fe2O3 at 30.3°, 35.7°, and 43.5°, confirming the successful formation of the Fe / Ni ferrite phase. Among them, the ferrite diffraction peaks of Example 1 (Fe / Ni=5:1) were the strongest and sharpest, indicating the highest crystallinity.

[0062] 3. Electromagnetic wave absorption performance test:

[0063] Vector network analyzers were used to test in the 2-18 GHz frequency band. Composite material powder and paraffin were mixed at a mass ratio of 3.6:7.4 and pressed into a coaxial ring. The reflection loss (RL) was calculated. The results are compared in the table below:

[0064] Sample number Fe / Ni mass ratio Minimum reflection loss (RLmin) / dB Maximum effective absorption bandwidth (EABmax) / GHz Achieving the matching thickness / mm of RLmin Example 1 5:1 -42.58 6.42 2.5 Example 2 4:1 -25.39 3.95 3.0 Example 3 9:1 -31.31 6.63 2.0 Comparative Example 1 none >-10 none none Comparative Example 2 5:1 -18.50 2.10 4.5

[0065] Performance Analysis:

[0066] Examples 1-3 were obtained according to the specific implementation method of the present invention. The Fe / Ni ratio was adjusted within the range specified in the present invention to produce significant differences in the electromagnetic parameters and absorption performance of the composite material. Example 1 (Fe / Ni=5:1) exhibited an optimal balance between absorption intensity (RLmin=-42.58dB) and good bandwidth (EABmax=6.42GHz), attributed to its optimized magnetoelectric synergy and optimal impedance matching.

[0067] Comparative Examples 1 and 2 were not operated entirely according to the technical solution of this invention. Comparative Example 1 (pure carbonized wood) lacked magnetic loss centers and relied solely on dielectric loss, failing to achieve effective absorption. Comparative Example 2 (physical mixing) suffered from poor interfacial bonding due to the magnetic particles only having physical contact with the carbon skeleton, failing to form an effective hierarchical network and abundant heterogeneous interfaces, resulting in deteriorated impedance matching and absorption performance far lower than Example 1, which used in-situ loading. This strongly demonstrates the synergistic advantages and necessity of the technical solution combining the "biological template method for preparing hierarchical porous skeletons" and the "in-situ impregnation-sintering structure for building a magnetoelectric network" used in this invention.

[0068] Based on the above test results, it can be seen that the lightweight broadband electromagnetic absorbing composite material proposed in this invention has successfully achieved comprehensive performance of lightweight, strong absorption, and wide bandwidth through biomimetic structural design and multi-scale component control. It effectively solves the problems of traditional absorbing materials being heavy, having narrow bandwidth, and being difficult to integrate with lightweight structures, and has broad application prospects in the fields of radar stealth, aerospace, and electromagnetic compatibility protection.

[0069] Although the present invention has been disclosed above with reference to preferred embodiments, these are not intended to limit the invention. Any person skilled in the art can make various changes or modifications without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention should be defined by the scope of the claims of this application.

Claims

1. A lightweight broadband electromagnetic absorption composite material, characterized in that: A hierarchical magnetoelectric network is formed by a three-dimensional porous carbon skeleton with a multi-level porous structure and iron-nickel alloy nanoparticles; the three-dimensional porous carbon skeleton is formed by using natural balsa wood as a biological template and undergoing lignin removal treatment to form a three-dimensional porous carbon skeleton with a multi-level porous structure, which retains the directional vascular structure of natural balsa wood; iron-nickel alloy nanoparticles are loaded in situ in the channels and on the surface of the pore walls of the three-dimensional porous carbon skeleton.

2. The lightweight broadband electromagnetic absorption composite material according to claim 1, characterized in that: The iron-nickel alloy nanoparticles are prepared by an impregnation-sintering process; the mass ratio of Fe to Ni in the iron-nickel alloy nanoparticles is (4-9):

1.

3. The lightweight broadband electromagnetic absorption composite material according to claim 1, characterized in that: The three-dimensional porous carbon skeleton has a vessel diameter of 5-8 μm and a cell wall thickness of 2-3 μm.

4. The lightweight broadband electromagnetic absorption composite material according to claim 1, characterized in that: The electromagnetic absorption composite material has a minimum reflection loss of ≤-42dB in the frequency range of 2-18GHz and an effective absorption bandwidth of ≥6.4GHz.

5. A method for preparing a lightweight broadband electromagnetic absorption composite material as described in any one of claims 1-4, characterized in that: Includes the following steps: Step 1: Template preparation: Natural balsa wood blocks are treated with delignification and then dried to obtain a balsa wood skeleton with an open mesoporous structure; Step 2: Preparation of precursor solution: Dissolve iron salt and nickel salt in solvent according to the target mass ratio of Fe to Ni to form a homogeneous precursor solution; Step 3: Impregnation and Loading: Immerse the balsa wood skeleton obtained in Step 1 into the precursor solution prepared in Step 2, allowing the solution to fully penetrate into the interior of the skeleton; Step 4: Post-treatment and carbonization: The impregnated balsa wood skeleton is removed and cleaned, and then sintered in an inert atmosphere to obtain a lightweight broadband electromagnetic absorption composite material.

6. The method for preparing a lightweight broadband electromagnetic absorption composite material according to claim 5, characterized in that: In step one, the delignification treatment involves placing natural balsa wood blocks in an alkaline sodium sulfite solution and treating them under heating conditions for 6-12 hours; the concentration of sodium hydroxide in the alkaline sodium sulfite solution is 2.0-3.0 mol / L, and the concentration of sodium sulfite is 0.3-0.5 mol / L; the heating temperature is 130-150℃.

7. The method for preparing a lightweight broadband electromagnetic absorption composite material according to claim 5, characterized in that: In step three, ultrasonic-assisted treatment is applied during the impregnation process.

8. The method for preparing a lightweight broadband electromagnetic absorption composite material according to claim 5, characterized in that: In step four, the sintering temperature is 700-900℃, and the holding time is 1-3 hours.

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