Ni3Al-PPy composite wave-absorbing material as well as preparation method and application thereof

Abstract

The invention discloses a Ni3Al-PPy composite wave-absorbing material as well as a preparation method and application thereof, and belongs to the technical field of electromagnetic wave-absorbing materials. The Ni3Al-PPy composite wave-absorbing material with a core-shell structure is successfully synthesized by combining a thermit reaction with a chemical oxidation polymerization method and hydrochloric acid modification. By regulating and controlling the addition amount of the pyrrole monomer in the range of 0.25-0.75 mL, the continuous regulation and control of the thickness of the PPy shell layer from 0.22 [mu] m to 0.31 [mu] m is realized. When the thickness of a PPy shell layer is 0.27 mu m and the matching thickness of the composite wave-absorbing material is 3.0 mm, the minimum reflection loss and absorptivity gt of-40.0 dB are obtained at 9.27 GHz; and when the matching thickness is 2.0 mm, the effective absorption bandwidth reaches 3.02 GHz. According to the invention, the effect of the shell layer thickness in regulating and controlling the performance of the wave-absorbing material with the core-shell structure is illustrated, and a feasible strategy is provided for designing a high-performance light-weight wave-absorbing material with adjustable electromagnetic parameters and enhanced durability.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic absorbing materials technology, specifically relating to a Ni3Al@PPy composite absorbing material, its preparation method, and its application. Background Technology

[0002] With the rapid development of modern electronic devices and communication technologies, more and more information is transmitted in the form of electromagnetic waves. The microwave pollution and information leakage caused by excessive electromagnetic radiation are attracting more and more attention, and the demand for electromagnetic wave absorbing materials (wave-absorbing materials) is growing day by day.

[0003] Traditional microwave absorbing materials include metal-based materials, carbon-based materials, and polymer composites. However, single materials often struggle to balance impedance matching and loss mechanisms, resulting in strong electromagnetic wave reflection and weak absorption. Therefore, combining magnetic and dielectric materials to construct binary or ternary materials with significant synergistic effects has become a current research hotspot. Furthermore, heterostructures, particularly core-shell structures, which have found wide applications in catalysis, energy storage, and biosensing, have also been found to effectively convert electromagnetic energy into heat energy in microwave absorption, providing a feasible solution for mitigating microwave pollution and signal interference.

[0004] Currently, among the conductive polymers used for modification, polypyrrole (PPy) stands out for its excellent mechanical properties, making the construction of high-performance microwave absorbers based on magnetic materials / PPy composites a research hotspot. For example, invention patent CN114314679A discloses a polypyrrole-coated iron(III) oxide nanoflower absorbing material, its preparation method, and its application. This polypyrrole-coated iron(III) oxide nanoflower absorbing material, with a thickness of 2.077 mm, exhibits a reflectivity RL ≤ -10 dB in the frequency range of 12-18 GHz, achieving broadband absorption at a relatively thin thickness, but its absorption is not strong enough. Another example is invention patent CN115867010A, which discloses a core-shell structured dendritic Fe2O3@PPy absorbing composite material and its preparation method. This dendritic Fe2O3@PPy absorbing composite material, with a reflectivity RL ≤ -10 dB in the frequency range of approximately 5.7-8 GHz at a thickness of 4.0 mm, has an RLmin of -46.53 dB. While it achieves strong absorption at a relatively thin thickness, its absorption frequency is not wide. An ideal absorbing material should simultaneously possess strong absorption, broadband, and lightweight characteristics, but existing material systems still have significant shortcomings. While polypyrrole (PPy) is widely used in combination with ferromagnetic materials to obtain microwave absorbers, the resulting absorbing materials still cannot simultaneously possess ideal characteristics of strong absorption, wide bandwidth, and lightweight. Furthermore, the intrinsic conductivity of PPy is insufficient to meet the requirements for direct applications.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a Ni3Al@PPy composite microwave absorbing material, its preparation method, and its applications. The Ni3Al@PPy composite microwave absorbing material is successfully synthesized via an aluminothermic reaction combined with chemical oxidative polymerization and hydrochloric acid modification, exhibiting a core-shell structure. By controlling the amount of pyrrole monomer added within the range of 0.25-0.75 mL, the PPy shell thickness was continuously adjustable from 0.22 μm to 0.31 μm. When the PPy shell thickness is 0.27 μm, the composite microwave absorbing material with a matching thickness of 3.0 mm achieves a minimum reflection loss of -40.0 dB at 9.27 GHz, with an absorption rate >99.99%. At a matching thickness of 2.0 mm, the effective absorption bandwidth reaches 3.02 GHz, simultaneously possessing strong absorption, wide bandwidth, and lightweight characteristics.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, a Ni3Al@PPy composite microwave absorbing material includes a micron-sized Ni3Al core and a modified PPy shell coating the surface of the Ni3Al core. The modified PPy shell is a hydrochloric acid-modified PPy shell, and the thickness of the modified PPy shell is 0.22~0.31μm.

[0008] Furthermore, the thickness of the modified PPy shell is 0.27 μm.

[0009] Furthermore, the Ni3Al@PPy composite microwave absorbing material is obtained through aluminothermic reaction, oxidative polymerization reaction, and hydrochloric acid doping modification.

[0010] Furthermore, the concentration of hydrochloric acid used in the hydrochloric acid doping modification is 0.04~0.06 mol / L.

[0011] Furthermore, the preparation of the Ni3Al core includes: mixing aluminum powder and nickel powder, pressing them into a blank, and then carrying out an aluminothermic reaction in a protective atmosphere. The resulting reaction product is then ground, washed, and dried to obtain the Ni3Al core.

[0012] Furthermore, the mixing involves three-dimensionally mixing nickel powder and aluminum powder with a molar ratio of 3 to 3.2:1 using Al2O3 as the grinding ball and at a rotation speed of 140 to 160 r / min. And / or, the pressing pressure is 30~40MPa; And / or, the protective atmosphere is argon; And / or, the temperature of the aluminothermic reaction is 250~270℃; And / or, the mass ratio of the igniter of the aluminothermic reaction to the total mass of the aluminum powder and nickel powder is 1:15~17.

[0013] Furthermore, when the thickness of the modified PPy shell is 0.27 μm, the Ni3Al@PPy composite absorbing material with a matching thickness of 3.0 mm achieves a minimum reflection loss of -40.0 dB at 9.27 GHz and an absorption rate of >99.99%, while the effective absorption bandwidth reaches 3.02 GHz when the matching thickness is 2.0 mm.

[0014] Secondly, a method for preparing the Ni3Al@PPy composite microwave absorbing material as described in the first aspect includes the following steps: S1. Mix Ni3Al core and pyrrole monomer in deionized water, then add FeCl3·6H2O solution to carry out oxidative polymerization reaction to obtain composite material I; S2. After washing the composite material I obtained in S1, hydrochloric acid doping modification was carried out to obtain Ni3Al@PPy composite microwave absorbing material.

[0015] Further, in step S1, the reaction ratio of the Ni3Al core, pyrrole monomer and FeCl3·6H2O solution is 2g:0.25~0.75ml:30ml; And / or, in step S1, the mass percentage of FeCl3·6H2O in the FeCl3·6H2O solution is 6%~17%; And / or, in step S2, the concentration of hydrochloric acid used in the hydrochloric acid doping modification is 0.04~0.06 mol / L.

[0016] Thirdly, the application of the Ni3Al@PPy composite absorbing material described in the first aspect, or the Ni3Al@PPy composite absorbing material prepared by the preparation method described in the second aspect, in electromagnetic absorbing materials or electromagnetic absorbing devices.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: 1. This invention relates to a Ni3Al@PPy composite microwave absorbing material with a core-shell structure. Using micron-sized Ni3Al as the core material, it significantly enhances the magnetic loss capability while also improving the oxidation resistance of the magnetic components, demonstrating significant industrial application value. Using hydrochloric acid-doped modified PPy as the shell layer significantly improves its conductivity: the resistivity of the Ni3Al@PPy composite material is consistently lower than that of pure Ni3Al (4.915 Ω·cm), and gradually decreases with increasing shell thickness. When the shell thickness gradually increases within the range of 0.22~0.31 μm, the resistivity of the composite material decreases from 4.622 Ω·cm to 4.101 Ω·cm. This invention effectively optimizes impedance matching by systematically controlling the PPy shell thickness, thereby significantly improving the electromagnetic wave attenuation performance of the Ni3Al@PPy composite material. When the PPy shell thickness is 0.27 μm, the composite material with a matching thickness of 3.0 mm achieves a minimum reflection loss of -40.0 dB at 9.27 GHz (absorption rate >99.99%), while the effective absorption bandwidth reaches 3.02 GHz with a matching thickness of 2.0 mm. It also exhibits strong absorption, wide bandwidth, and lightweight characteristics. This lays a theoretical foundation for the development of core-shell structure absorbers with electromagnetic synergistic effects and demonstrates broad application prospects.

[0018] 2. The preparation method of this invention successfully synthesizes Ni3Al@PPy composite microwave absorbing material with a core-shell structure through aluminothermic reaction combined with chemical oxidative polymerization and hydrochloric acid modification. By controlling the amount of pyrrole monomer added within the range of 0.25-0.75 mL, the thickness of the PPy shell layer can be continuously controlled from 0.22 μm to 0.31 μm. Systematically modulating the thickness of the polypyridine shell effectively optimizes the impedance matching of the Ni3Al@PPy composite material and improves its electromagnetic wave attenuation performance. This preparation method has lower energy consumption in the aluminothermic reaction and does not require a continuous high-temperature heat source. The phase formation rate is fast, the purity is high, and there are few impurities. The rapid heating and cooling characteristics of the aluminothermic reaction prevent the generated Ni3Al grains from growing, ultimately obtaining a fine-grained or even nanocrystalline structure. Furthermore, the surface of this structure is rough and highly active, which can form mechanical interlocking and chemical bonding with the subsequently coated PPy shell layer, improving the bonding strength of the core-shell interface. In addition, the method of this invention directly initiates the polymerization of pyrrole monomer on the surface of Ni3Al particles. This process eliminates the need for additional surfactants or complex organic modifiers to stabilize particle dispersion, avoiding the drawbacks of additives (such as surfactants and stabilizers) requiring subsequent removal through complex processes. This novel and simplified preparation method has significant practical implications. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] In the following figures, S0 refers to the Ni3Al microwave absorbing material prepared in Comparative Example 1, and S1, S2 and S3 refer to the Ni3Al@PPy composite microwave absorbing materials prepared in Examples 1-3, respectively.

[0021] Figure 1 The images are SEM and TEM images, where a and e, b and f, c and g, d and h are scanning electron microscope (SEM) images (low-magnification SEM and high-magnification SEM) of S0, S1, S2 and S3, respectively; il are transmission electron microscope (TEM) images of S0, S1, S2 and S3, respectively.

[0022] Figure 2 The figures are XRD and FT-IR spectra, where a is the XRD spectrum of S0, S1, S2 and S3; and b is the FT-IR spectrum of S0 and S2.

[0023] Figure 3 The hysteresis loops of S0, S1, S2 and S3 at 25°C are given.

[0024] Figure 4 S0, S1, S2, and S3 at different frequencies ε′ , ε ″、tan δ ε , μ ′、 μ "and tan δ μ Curve, where a is ε′ Curve graph, b is ε "Curve graph, c is tan " δ ε Curve graph, d is μ 'Curve graph, e is μ "Curve graph, f is tan " δ μ Line graph.

[0025] Figure 5 Let a be the Cole-Cole curve and C0 curve for S0, S1, S2 and S3, where a is the Cole-Cole curve and b is the C0 curve.

[0026] Figure 6The diagrams show the three-dimensional / two-dimensional reflection loss curves and impedance matching plots. A1-A4 represent the three-dimensional reflection loss curves for S0, S1, S2, and S3, respectively; B1-B4 represent the two-dimensional reflection loss curves for S0, S1, S2, and S3, respectively; and C1-C4 represent the impedance matching plots for S0, S1, S2, and S3, respectively.

[0027] Figure 7 The XRD patterns of the Ni3Al@PPy composite microwave absorbing materials prepared in Example 2 and Comparative Example 2 are shown, where HCl represents the XRD pattern of Example 2 and TsOH represents the XRD pattern of Comparative Example 2.

[0028] Figure 8 Ni3Al@PPy composite microwave absorbing materials prepared for Example 2 (HCl) and Comparative Example 2 (TsOH) at different frequencies ε′ , ε ″、tan δ ε , μ ′、 μ "and tan δ μ Curve, where a is ε′ Curve graph, b is ε "Curve graph, c is tan " δ ε Curve graph, d is μ 'Curve graph, e is μ "Curve graph, f is tan " δ μ Line graph.

[0029] Figure 9 The figures show the three-dimensional reflection loss curves (RL) of the Ni3Al@PPy composite microwave absorbing materials prepared in Example 2 and Comparative Example 2. In Example 2, a is the three-dimensional reflection loss curve of Ni3Al@PPy prepared by hydrochloric acid immersion modification, and b is the three-dimensional reflection loss curve of Ni3Al@PPy prepared by p-toluenesulfonic acid immersion modification in Comparative Example 2.

[0030] Figure 10 The figures show the interference destructive curves of the Ni3Al@PPy composite absorbing materials prepared in Example 2 and Comparative Example 2, where a and c are the reflection loss-frequency curves and matching thickness-frequency curves of Ni3Al@PPy prepared by hydrochloric acid immersion modification in Example 2 at different thicknesses, respectively; b and d are the reflection loss-frequency curves and matching thickness-frequency curves of Ni3Al@PPy prepared by p-toluenesulfonic acid immersion modification in Comparative Example 2 at different thicknesses, respectively. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments of this invention are implemented based on the technical solutions of this invention, and detailed implementation methods and processes are given. The described embodiments are only a part of the embodiments of this invention, not all of them. Those skilled in the art should understand that the embodiments are merely helpful in understanding this invention and should not be considered as specific limitations on this invention. Furthermore, the scope of protection of this invention is not limited to the following embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0032] In the embodiments of this invention, process parameters not specifically specified are generally performed under conventional conditions. Unless otherwise specified and / or stated, all numerical values ​​relating to component amounts are "values ​​or ratios by weight or mass" throughout. Unless otherwise stated, all raw materials used in this invention are available from commercially available products.

[0033] In this invention, the endpoints and any values ​​of the disclosed ranges are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0034] According to a first aspect of the present invention, the present invention first provides a Ni3Al@PPy composite microwave absorbing material, the Ni3Al@PPy composite microwave absorbing material comprising a micron-sized Ni3Al core and a modified PPy shell coating the surface of the Ni3Al core, the modified PPy shell being a hydrochloric acid modified PPy shell, the thickness of the modified PPy shell being 0.22~0.31μm.

[0035] Ni3Al, as a nickel-aluminum intermetallic compound, differs significantly from traditional aluminides due to its unique combination of high-temperature stability, excellent corrosion resistance, and superior oxidation resistance. These superior properties have led to its widespread application in various industrial fields. Its excellent performance stems from the strong aluminum-nickel bond, which remains stable even at high temperatures, giving Ni3Al characteristics similar to both high-temperature alloys and ceramics: including high melting point, low density, high strength, and excellent corrosion and oxidation resistance. However, Ni3Al also has limitations such as inherently weak magnetism and poor impedance matching, restricting its practical application in electromagnetic wave absorption. The Ni3Al@PPy composite absorbing material provided by this invention has a core-shell structure, using micron-sized Ni3Al as the core material. This significantly improves the oxidation resistance of the magnetic components while enhancing magnetic loss capability, demonstrating significant industrial application value. Simultaneously, by modifying PPy as the shell layer of the Ni3Al core with hydrochloric acid doping, the saturation magnetization (Ms) and coercivity decrease. This weakening of magnetic properties is related to the introduction of a non-magnetic polymer layer. This moderate adjustment of the magnetic response promotes a more favorable balance between the dielectric loss of the PPy shell and the magnetic loss of the Ni3Al core, which is crucial for optimizing impedance matching and improving overall electromagnetic wave absorption performance.

[0036] Secondly, it exhibits good electromagnetic wave energy storage and dissipation capabilities. This performance improvement is attributed to the enhanced conductivity brought about by the PPy shell. Furthermore, hydrochloric acid doping of PPy can further significantly improve its conductivity; the resistivity of the Ni3Al@PPy composite material is consistently lower than that of pure Ni3Al (4.915 Ω·cm). This enhanced conductivity is beneficial for the generation of electromagnetic waves and induces eddy currents under alternating electromagnetic fields. Acid doping can effectively regulate the charge distribution of PPy, increase the carrier concentration, and thus enhance its conductivity. The protons introduced during the doping process can increase the charge carrier density of the polymer backbone and promote the structural ordering of the molecular chain, thereby improving carrier transport performance by enhancing the charge delocalization effect.

[0037] Third, it exhibits superior dielectric loss performance compared to magnetic loss, which is the dominant attenuation mechanism in Ni3Al@PPy composites. The introduction and controllable growth of the PPy shell successfully introduces an additional relaxation mechanism, thereby significantly enhancing dielectric loss. Furthermore, this Ni3Al@PPy composite microwave absorbing material possesses a heterogeneous core-shell structure: interfacial polarization at the Ni3Al-PPy interface, dipole polarization within the PPy phase, and conductivity loss jointly regulate the dielectric response. The core-shell structure exhibits multiple advantages, including interfacial polarization effects, confinement effects, complementary performance behavior, and core corrosion protection. Particularly noteworthy is its ability to integrate multiple loss mechanisms, forming a high-performance composite material with outstanding microwave absorption performance. The core-shell structure of the Ni3Al@PPy composite material creates abundant heterogeneous interfaces and structural defects between the conductive PPy shell and the magnetic Ni3Al core, providing favorable conditions for interfacial polarization under alternating electromagnetic fields. When the material is exposed to electromagnetic radiation, charge carriers accumulate at the interface, forming a significant electric dipole moment, altering the charge density distribution and thus enhancing the interfacial relaxation process. Furthermore, the polar nature of PPy molecules results in a large number of intrinsic electric dipoles, which can generate significant dipole polarization when oriented under an applied electromagnetic field. The disordered arrangement of covalent bonds in the amorphous region and the presence of polar functional groups may induce additional dipole moments, further enhancing the overall dipole polarization effect.

[0038] Fourth, impedance matching was optimized, improving absorption performance. When the thickness of the modified PPy shell was controlled to be 0.22~0.31 μm (e.g., 0.23 μm, 0.24 μm, 0.25 μm, 0.26 μm, 0.27 μm, 0.28 μm, 0.29 μm, 0.30 μm, etc.), the resistivity of the Ni3Al@PPy composite absorbing material gradually decreased with increasing shell thickness. When the shell thickness increased from 0.22 μm to 0.31 μm, the resistivity of the composite material decreased from 4.622 Ω·cm to 4.101 Ω·cm. When the PPy shell thickness was 0.27 μm, the composite material with a matching thickness of 3.0 mm achieved a minimum reflection loss of -40.0 dB at 9.27 GHz (absorption rate >99.99%), while the effective absorption bandwidth reached 3.02 GHz when the matching thickness was 2.0 mm. This invention effectively optimizes impedance matching by systematically controlling the thickness of the PPy shell, thereby significantly improving the electromagnetic wave attenuation performance of the Ni3Al@PPy composite absorbing material. This lays a theoretical foundation for the development of core-shell structure absorbers with electromagnetic synergistic effects and shows broad application prospects.

[0039] As an optional embodiment of the Ni3Al@PPy composite microwave absorbing material of the present invention, the Ni3Al@PPy composite microwave absorbing material is obtained through aluminothermic reaction, oxidative polymerization reaction, and hydrochloric acid doping modification. Further, the concentration of hydrochloric acid used in the hydrochloric acid doping modification is 0.04~0.06 mol / L (e.g., 0.041 mol / L, 0.043 mol / L, 0.045 mol / L, 0.047 mol / L, 0.049 mol / L, 0.051 mol / L, 0.053 mol / L, 0.055 mol / L, 0.057 mol / L, 0.059 mol / L, etc.).

[0040] This invention successfully synthesizes a core-shell structured Ni3Al@PPy composite microwave absorbing material via an aluminothermic reaction combined with chemical oxidative polymerization (e.g., using ferric chloride hexahydrate as the oxidant and hydrochloric acid as the dopant). The use of a micron-sized Ni3Al magnetic core enhances magnetic loss capability and improves the oxidation resistance of the magnetic components, demonstrating significant industrial applicability. Simultaneously, hydrochloric acid doping and modification of polypyrrole improves its conductivity. The material exhibits good interfacial polarization and stability. Systematic modulation of the polypyridine shell thickness effectively optimizes the impedance matching of the Ni3Al@PPy composite material, enhancing its electromagnetic wave attenuation performance. This preparation method consumes less energy in the aluminothermic reaction and does not require a continuous high-temperature heat source. It achieves rapid phase formation, high purity, and few impurities. The rapid heating and cooling characteristics of the aluminothermic reaction prevent the generated Ni3Al grains from growing too large, ultimately resulting in a fine-grained or even nanocrystalline structure. Furthermore, the surface of these particles is rough and highly active, enabling them to form mechanical and chemical bonds with the subsequently coated PPy shell, enhancing the bonding strength at the core-shell interface. Furthermore, the method of this invention directly initiates the polymerization of pyrrole monomers on the surface of Ni3Al particles. This process eliminates the need for additional surfactants or complex organic modifiers to stabilize particle dispersion, avoiding the drawbacks of additives (such as surfactants and stabilizers) requiring subsequent removal through complex processes. This novel and simplified preparation method has significant practical implications.

[0041] As an optional embodiment of the Ni3Al@PPy composite microwave absorbing material of the present invention, the preparation of the Ni3Al core includes: mixing aluminum powder and nickel powder, pressing them into a blank, and then carrying out an aluminothermic reaction in a protective atmosphere. The resulting reaction product is then ground, washed, and dried to obtain the Ni3Al core.

[0042] Further optionally, the mixing involves using Al2O3 as the grinding ball and mixing nickel powder and aluminum powder in a three-dimensional ratio of 3 to 3.2:1 (e.g., 3.05:1, 3.1:1, 3.15:1, 3.2:1, etc.) at a rotation speed of 140 to 160 r / min (e.g., 141 r / min, 143 r / min, 145 r / min, 147 r / min, 149 r / min, 151 r / min, 153 r / min, 155 r / min, 157 r / min, 159 r / min, etc.) at a rotation speed of 140 to 160 r / min. And / or, the pressing pressure is 30~40MPa (e.g., 31MPa, 33MPa, 35MPa, 37MPa, 39MPa, etc.). And / or, the protective atmosphere is argon; And / or, the temperature of the aluminothermic reaction is 250~270℃ (e.g., 251℃, 253℃, 255℃, 257℃, 260℃, 262℃, 265℃, 267℃, 269℃, etc.); And / or, the ratio of the total mass of the aluminum powder and nickel powder to the mass of the igniter for the aluminothermic reaction is 15~17:1 (e.g., 15.1:1, 15.3:1, 15.7:1, 15.9:1, 16.1:1, 16.3:1, 16.5:1, 16.7:1, 16.9:1, etc.).

[0043] According to a second aspect of the present invention, the present invention further provides a method for preparing the Ni3Al@PPy composite microwave absorbing material, comprising the following steps: S1. Mix Ni3Al core and pyrrole monomer in deionized water, then add FeCl3·6H2O solution to carry out oxidative polymerization reaction to obtain composite material I; S2. After washing the composite material I obtained in S1, hydrochloric acid doping modification was carried out to obtain Ni3Al@PPy composite microwave absorbing material.

[0044] In the above preparation method, as an optional implementation, in step S1, the reaction ratio of the Ni3Al core, pyrrole monomer, and FeCl3·6H2O solution is 2g:0.25~0.75ml:30ml (e.g., 2g:0.25ml:30ml, 2g:0.3ml:30ml, 2g:0.35ml:30ml, 2g:0.4ml:30ml, 2g:0.45ml:30ml, 2g:0.5ml:30ml, 2g:0.55ml:30ml, 2g:0.6ml:30ml, 2g:0.65ml:30ml, 2g:0.7ml:30ml, 2g:0.75ml:30ml, etc.). And / or, in step S1, the mass percentage of FeCl3·6H2O in the FeCl3·6H2O solution is 6%~17% (e.g., 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, etc.). And / or, in step S2, the concentration of hydrochloric acid used in the hydrochloric acid doping modification is 0.04~0.06 mol / L (such as 0.041 mol / L, 0.043 mol / L, 0.045 mol / L, 0.047 mol / L, 0.049 mol / L, 0.051 mol / L, 0.053 mol / L, 0.055 mol / L, 0.057 mol / L, 0.059 mol / L, etc.).

[0045] In the above technical solution, by adjusting the amount of pyrrole monomer added within the range of 0.25-0.75 mL, the thickness of the PPy shell can be continuously adjusted from 0.22 μm to 0.31 μm.

[0046] According to a third aspect of the present invention, the present invention also includes the application of the above-mentioned Ni3Al@PPy composite absorbing material in electromagnetic absorbing materials or electromagnetic absorbing devices.

[0047] The present invention will now be described in further detail with reference to specific embodiments.

[0048] Example 1 A Ni3Al@PPy composite microwave absorbing material is prepared by the following steps: Preparation of Ni3Al micron-sized particles (1) Using Al2O3 as the grinding ball, nickel powder and aluminum powder with a molar ratio of 3:1 were mixed in a three-dimensional vortex mixer for 8 h at a rotation speed of 150 r / min. Then, 80 g of the nickel powder and aluminum powder mixture was pressed into a compact on a copper substrate under a pressure of 30 MPa. The compact was placed in a combustion synthesis reactor. Simultaneously, a mixture of 5 g of aluminum powder, sulfur powder and MnO2 was pressed into small balls as an igniter (the mass ratio of MnO2:aluminum powder:sulfur powder was 1:2:1.5; the igniter used in the following examples and comparative examples was the same as that in Example 1), and placed in the combustion synthesis reactor. The reactor was heated to 260°C under an argon atmosphere to initiate the igniter reaction, which in turn triggered the aluminothermic reaction. After the reaction was completed, the product was naturally cooled in the reactor to obtain a mixed block product. The block was crushed and ground, and then repeatedly washed with hydrochloric acid and sodium hydroxide solution and dried to obtain Ni3Al micron particles.

[0049] Preparation of Ni3Al@PPy composite microwave absorbing material (2) Disperse a mixture of 2 g Ni3Al micron particles and 0.25 mL pyrrole monomer in 170 mL deionized water and stir continuously for 30 min. Then slowly add 30 mL of FeCl3·6H2O solution with a mass concentration of 6%~7% to initiate the oxidative polymerization reaction and continue stirring at room temperature for 12 h. (3) After stirring, composite material I was collected by magnetic separation. After washing with deionized water and anhydrous ethanol alternately, the obtained product was placed in 50 mL of 0.05 mol / L hydrochloric acid solution for 24 h for acid doping modification. (4) After the acid doping modification is completed, magnetic separation is performed again to obtain composite material II, which is thoroughly rinsed with deionized water and anhydrous ethanol, and finally dried overnight in a vacuum oven at 60°C to obtain Ni3Al@PPy composite microwave absorbing material, numbered S1.

[0050] Example 2 A Ni3Al@PPy composite microwave absorbing material is prepared by the following steps: Preparation of Ni3Al micron-sized particles (1) Using Al2O3 as the grinding ball, nickel powder and aluminum powder with a molar ratio of 3:1 were mixed in a three-dimensional vortex mixer for 8 h at a rotation speed of 150 r / min. Then, 80 g of the nickel powder and aluminum powder mixture was pressed into a compact on a copper substrate under a pressure of 30 MPa. The compact was placed in a combustion synthesis reactor. Simultaneously, a mixture of 5 g of aluminum powder, sulfur powder and MnO2 was pressed into small balls as an igniter and placed in the combustion synthesis reactor. The reactor was heated to 260 °C under an argon atmosphere to initiate the igniter reaction, which in turn triggered the aluminothermic reaction. After the reaction was completed, the product was naturally cooled in the reactor to obtain a mixed block product. The block was crushed and ground, and then repeatedly washed with hydrochloric acid and sodium hydroxide solution and dried to obtain Ni3Al micron particles.

[0051] Preparation of Ni3Al@PPy composite microwave absorbing material (2) Disperse a mixture of 2 g Ni3Al micron particles and 0.5 mL pyrrole monomer in 170 mL deionized water and stir continuously for 30 min. Then slowly add 30 mL of FeCl3·6H2O solution with a mass concentration of 11%~12% to initiate the oxidative polymerization reaction and continue stirring at room temperature for 12 h. (3) After stirring, composite material I was collected by magnetic separation. After washing with deionized water and anhydrous ethanol alternately, the obtained product was placed in 50 mL of 0.05 mol / L hydrochloric acid solution for 24 h for acid doping modification. (4) After the acid doping modification is completed, magnetic separation is performed again to obtain composite material II, which is thoroughly rinsed with deionized water and anhydrous ethanol, and finally dried overnight in a vacuum oven at 60°C to obtain Ni3Al@PPy composite microwave absorbing material, numbered S2.

[0052] Example 3 A Ni3Al@PPy composite microwave absorbing material is prepared by the following steps: Preparation of Ni3Al micron-sized particles (1) Using Al2O3 as the grinding ball, nickel powder and aluminum powder with a molar ratio of 3:1 were mixed in a three-dimensional vortex mixer for 8 h at a rotation speed of 150 r / min. Then, 80 g of the nickel powder and aluminum powder mixture was pressed into a compact on a copper substrate under a pressure of 30 MPa. The compact was placed in a combustion synthesis reactor. Simultaneously, a mixture of 5 g of aluminum powder, sulfur powder and MnO2 was pressed into small balls as an igniter and placed in the combustion synthesis reactor. The reactor was heated to 260 °C under an argon atmosphere to initiate the igniter reaction, which in turn triggered the aluminothermic reaction. After the reaction was completed, the product was naturally cooled in the reactor to obtain a mixed block product. The block was crushed and ground, and then repeatedly washed with hydrochloric acid and sodium hydroxide solution and dried to obtain Ni3Al micron particles.

[0053] Preparation of Ni3Al@PPy composite microwave absorbing material (2) Disperse a mixture of 2 g Ni3Al micron particles and 0.75 mL pyrrole monomer in 170 mL deionized water and stir continuously for 30 min. Then slowly add 30 mL FeCl3·6H2O solution with a mass concentration of 16~17% to initiate the oxidative polymerization reaction and continue stirring at room temperature for 12 h. (3) After stirring, composite material I was collected by magnetic separation. After washing with deionized water and anhydrous ethanol alternately, the obtained product was placed in 50 mL of 0.05 mol / L hydrochloric acid solution for 24 h for acid doping modification. (4) After the acid doping modification is completed, magnetic separation is performed again to obtain composite material II, which is thoroughly rinsed with deionized water and anhydrous ethanol, and finally dried overnight in a vacuum oven at 60°C to obtain Ni3Al@PPy composite microwave absorbing material, numbered S3.

[0054] Comparative Example 1 A method for preparing Ni3Al micron-sized particles includes the following steps: Using Al2O3 as the grinding ball, nickel powder and aluminum powder with a molar ratio of 3:1 were mixed in a three-dimensional vortex mixer for 8 h at a speed of 150 r / min. Then, 80 g of the nickel and aluminum powder mixture was pressed into a compact on a copper substrate under a pressure of 30 MPa. The compact was placed in a combustion synthesis reactor. Simultaneously, a mixture of 5 g of aluminum powder, sulfur powder, and MnO2 was pressed into small balls as an igniter and placed in the combustion synthesis reactor. The reactor was heated to 260℃ under an argon atmosphere to initiate the igniter reaction, which in turn triggered the aluminothermic reaction. After the reaction, the product was allowed to cool naturally in the reactor, yielding a mixed bulk product. The bulk was crushed, ground, repeatedly washed with hydrochloric acid and sodium hydroxide solution, and dried to obtain Ni3Al micron-sized particles, designated S0.

[0055] Comparative Example 2 The method for preparing Ni3Al@PPy composite microwave absorbing materials using p-toluenesulfonic acid doping modification includes the following steps: Preparation of Ni3Al micron-sized particles (1) Using Al2O3 as the grinding ball, nickel powder and aluminum powder with a molar ratio of 3:1 were mixed in a three-dimensional vortex mixer for 8 h at a rotation speed of 150 r / min. Then, 80 g of the nickel powder and aluminum powder mixture was pressed into a compact on a copper substrate under a pressure of 30 MPa. The compact was placed in a combustion synthesis reactor. Simultaneously, a mixture of 5 g of aluminum powder, sulfur powder and MnO2 was pressed into small balls as an igniter and placed in the combustion synthesis reactor. The reactor was heated to 260 °C under an argon atmosphere to initiate the igniter reaction, which in turn triggered the aluminothermic reaction. After the reaction was completed, the product was naturally cooled in the reactor to obtain a mixed block product. The block was crushed and ground, and then repeatedly washed with hydrochloric acid and sodium hydroxide solution and dried to obtain Ni3Al micron particles.

[0056] Preparation of Ni3Al@PPy composite microwave absorbing material (2) Disperse 2 g of Ni3Al micron particles and 0.5 mL of pyrrole monomer in 170 mL of deionized water and stir continuously for 30 min. Then transfer the mixed solution to a three-necked flask and slowly add 30 mL of FeCl3·6H2O solution with a mass concentration of 11%~12% to initiate the oxidative polymerization reaction. Continue stirring at room temperature for 12 h. (3) After stirring, composite material I was collected by magnetic separation. After washing with deionized water and anhydrous ethanol alternately, the obtained product was placed in 50 mL of 0.05 mol / L p-toluenesulfonic acid solution for 24 h for acid doping modification. (4) After the acid doping modification is completed, magnetic separation is performed again to obtain composite material II, which is thoroughly rinsed with deionized water and anhydrous ethanol, and finally dried overnight in a vacuum oven at 60°C to obtain Ni3Al@PPy composite microwave absorbing material.

[0057] Tests and Results 1. SEM and TEM The Ni3Al@PPy composite microwave absorbing materials (S1, S2, and S3) prepared in Examples 1-3 and the Ni3Al microwave absorbing material (S0) prepared in Comparative Example 1 were characterized by SEM, and the results are as follows: Figure 1 As shown in ah, where a and e, b and f, c and g, d and h are scanning electron microscope (low-magnification SEM and high-magnification SEM) images of S0, S1, S2 and S3, respectively; il are transmission electron microscope (TEM) images of S0, S1, S2 and S3, respectively. Figure 1 The image shows that the particle size distribution of Ni3Al particles (S0) ranges from hundreds to tens of micrometers, which is significantly different from that of nanomaterials. (High-magnification SEM image) Figure 1 Ball milling sintering traces can be identified in e). Figure 1 bd and Figure 1 fh indicates that after acid-modified PPy coating, as the polypyrrole content increases, the particle size of Ni3Al@PPy composite microwave absorbing materials (S1, S2 and S3), especially S2 and S3, increases significantly, the sintering morphology of the original Ni3Al surface disappears, and a large number of wrinkles gradually appear on the surface.

[0058] TEM micrographs vividly illustrate the microstructure of pure Ni3Al(S0) and Ni3Al@PPy composite microwave absorbing materials (S1, S2, and S3), such as... Figure 1 As shown in il. The Ni3Al surface is smooth and has no coating layer ( Figure 1 i), while the introduction of acid-modified PPy forms an irregular shell on the Ni3Al surface. When the amount of pyrrole added increases from 0.25 mL to 0.75 mL, the average shell thickness is 0.22 μm, 0.27 μm and 0.31 μm respectively. Figure 1 The results show that a core-shell structure can be successfully constructed by chemical oxidation, and the shell thickness can be precisely controlled by adjusting the amount of pyrrole added, thereby adjusting the electromagnetic parameters and impedance matching, and ultimately achieving effective control of microwave absorption performance.

[0059] 2. XRD and FT-IR XRD and FT-IR tests were performed on the microwave absorbing materials (S0, S1, S2, and S3) prepared in Examples 1-3 and Comparative Example 1. The results are as follows: Figure 2 As shown. Figure 2XRD patterns of samples S0, S1, S2, and S3 are shown. All samples exhibit significant diffraction peaks at 2θ = 24.9°, 35.6°, 44.0°, 51.2°, 57.9°, and 64.0°, corresponding to the (100), (110), (111), (200), (210), and (211) crystal planes of Ni3Al (PDF#97-015-1385), respectively. The diffraction patterns of S1-S3 are essentially consistent with those of S0, with identical peak positions, indicating that the Ni3Al crystal structure remained stable during preparation without phase transition or introduction of impurities. Furthermore, no obvious PPy characteristic diffraction peaks were observed in the S1-S3 patterns, attributed to the amorphous PPy shell formed through chemical oxidative polymerization and hydrochloric acid doping modification. However, slight variations in the intensity of Ni3Al diffraction peaks were observed in the XRD patterns, which may be influenced by the thickness of the PPy shell coating.

[0060] Figure 2 b shows the FT-IR spectra of S0 and S2. Since pure Ni3Al does not contain PPy, the S0 curve does not show characteristic peaks for organic matter; however, after PPy coating (shell thickness 0.27 μm), the S2 spectrum exhibits a clear characteristic PPy absorption band: 613 cm⁻¹. -1 The absorption peak at 1124 cm⁻¹ is attributed to out-of-plane bending vibrations of the C-plane. -1 1400 cm -1 and 1617 cm -1 The absorption peaks at 3230 cm⁻¹ correspond to the in-plane deformation vibration of CH, the in-ring deformation vibration of CN, and the stretching vibration of the pyrrole ring skeleton, respectively. -1 With 3469cm -1 The absorption band at this location originates from the stretching vibrations of the NH bonds in PPy. These results collectively demonstrate the successful preparation of the Ni3Al@PPy composite microwave absorbing material.

[0061] 3. Study on the microwave absorption performance of the microwave absorbing materials (S0, S1, S2 and S3) prepared in Examples 1-3 and Comparative Example 1 Figure 3 The hysteresis loops of S0, S1, S2, and S3 at 25 °C are shown. Under an applied magnetic field of 15000 Oe, the saturation magnetization (Ms) of S0, S1, S2, and S3 are 2.95 emu / g, 2.76 emu / g, 2.54 emu / g, and 2.34 emu / g, respectively. Furthermore, the coercivity (H) of all samples is... CWith a coercivity less than 95 Oe, the Ni3Al@PPy composite microwave absorbing materials (S1, S2, and S3) exhibit lower coercivity than pure Ni3Al (S0). A decrease in saturation magnetization and coercivity was observed after coating the Ni3Al particles with a PPy shell. This weakening of magnetic properties is related to the introduction of the non-magnetic polymer layer. This moderate modulation of the magnetic response promotes a more favorable balance between the dielectric loss of the PPy shell and the magnetic loss of the Ni3Al core, which is crucial for optimizing impedance matching and improving overall electromagnetic wave absorption performance.

[0062] The absorption characteristics of electromagnetic waves (EMWs) are controlled by the electromagnetic parameters of materials, which are determined by the principles of energy conversion. These parameters are the complex permittivity ε. r (ε) r = ε′ - jε″, where ε′ represents the real part of the complex permittivity, ε″ represents the imaginary part of the complex permittivity, and j represents the imaginary unit) and the complex permeability μ r (μ) r = μ′ - jμ″, where μ′ represents the real part of the complex permeability, μ″ represents the imaginary part of the complex permeability, and j represents the imaginary unit. These components are crucial in determining the interaction between a material and electromagnetic waves. The real parts (ε′ and μ′) represent the ability to store electromagnetic energy, while the imaginary parts (ε″ and μ″) quantify the dissipation or loss of energy. Therefore, the overall absorption performance is a function of the combined effect of these energy storage and dissipation capabilities. Figure 4 The curves showing how electromagnetic parameters change with frequency are displayed. For example... Figure 4 As shown in Figure a, the ε′ values ​​of samples S0-S3 fluctuate within the ranges of 21.5-9.1, 12.5-6.1, 12.3-8.4, and 16-7.8, respectively, exhibiting significant frequency dispersion characteristics. This phenomenon is generally attributed to the hysteresis of dipole orientation polarization relative to the periodic changes in the electric field, and the relaxation peaks observed in these curves may be related to various polarization relaxation mechanisms. Figure 4 b shows that the ε″ values ​​of samples S0-S3 vary within the ranges of 13.2-2.5, 7.1-0.1, 10.2-1.8, and 10.3-3.1, respectively. Among the three Ni3Al@PPy composite microwave absorbing materials, S3 exhibits the highest ε′ and ε″ values ​​in most frequency bands, indicating its better electromagnetic wave energy storage and dissipation capabilities. This is attributed to the thicker conductive PPy shell providing more charge carriers and polarization sites, and the fluctuation of the complex permittivity increases with the increase of the PPy shell thickness, highlighting the influence of the PPy shell thickness on the dielectric properties of the Ni3Al@PPy composite microwave absorbing material.

[0063] Figure 4As shown in d and 4e, the μ′ and μ″ of samples S0-S3 exhibit significant oscillations in the frequency range of 2.0-18.0 GHz. All samples have μ′ values ​​close to 1, indicating limited magnetic energy storage capacity determined by the weakly magnetic Ni3Al core. Sample S2 shows the most significant μ′ value among all samples, indicating its superior ability to store magnetic energy from incident electromagnetic radiation relative to other samples. Furthermore, at specific frequencies, samples S0, S1, and S3 exhibit negative μ″ values ​​(reaching as low as -0.4), a negative magnetic loss typically characteristic of diamagnetic systems. Measurements using the Vibrating Sample Magnetometer (VSM) of this invention confirm that both pure Ni3Al (S0) and Ni3Al@PPy composite microwave absorbing materials (S1, S2, S3) exhibit weak ferromagnetism. This apparent contradiction suggests that the observed negative μ″ values ​​may originate from the Fabry-Perot resonance effect, which is frequently observed in high dielectric constant composite materials.

[0064] In addition, the dielectric loss tangent tan δ ε (tan) δ ε = ε″ / ε′, where ε′ represents the real part of the complex permittivity and ε″ represents the imaginary part of the complex permittivity) and the magnetic loss tangent tan δ μ (tan) δ μ = μ″ / μ′, where μ′ represents the real part of the complex permeability and μ″ represents the imaginary part of the complex permeability, is an important indicator for evaluating the contribution of dielectric loss and magnetic loss to electromagnetic wave absorption. For example... Figure 4 As shown in c and 4f, the tan δ of S1 and S3 ε The value increases with increasing frequency, while its tan δ μ The value shows the opposite decreasing trend. This weakening of magnetic loss capability can be attributed to the coating effect of the nonmagnetic PPy shell on the ferromagnetic Ni3Al particles. Although S2 deviates from this general trend, by comparing tan δ ε With tan δ μ As can be seen from the curves, all samples exhibit dielectric loss performance superior to magnetic loss in the 2.0–18.0 GHz range, tan δ ε >> tan δμ confirms that dielectric loss is the dominant attenuation mechanism for all materials.

[0065] The frequency-dependent dielectric response can be quantitatively described using Debye relaxation theory, and its expression is: (1) (2) (3) Where ε ∞ ε s τ and τ represent the high-frequency limiting capacitance, static capacitance, and polarization relaxation time, respectively, and ƒ represents the frequency of the alternating magnetic field.

[0066] like Figure 5 As shown in Figure a, the Cole-Cole curves of all composite samples exhibit distorted arcs that significantly deviate from the ideal Debye behavior, indicating the existence of multiple polarization relaxation processes and non-Debye characteristics. This phenomenon originates from the heterogeneous core-shell structure of the composite material: interfacial polarization at the Ni3Al-PPy interface, dipole polarization within the PPy phase, and conductivity loss jointly regulate the dielectric response. Sample S3 exhibits the widest arc range along the ε′ axis, suggesting superior polarization capability compared to other samples. The gradual change in curve morphology from S0 to S3 reflects the successful introduction and controllable growth of the PPy shell, resulting in the successful introduction of an additional relaxation mechanism and significantly enhanced dielectric loss. In the low-frequency region (high ε′ value), polarization is mainly dominated by interfacial effects, while in the high-frequency region (low ε′ value), it is influenced by a rapid polarization mechanism. These results confirm that the dielectric properties and relaxation dynamics of Ni3Al@PPy composites can be precisely tuned by controlling the PPy shell. The core-shell structure of the Ni3Al@PPy composite material creates abundant heterogeneous interfaces and structural defects between the conductive PPy shell and the magnetic Ni3Al core. These features provide favorable conditions for interfacial polarization under alternating electromagnetic fields. When the material is exposed to electromagnetic radiation, charge carriers accumulate at the interface, forming a significant electric dipole moment, which alters the charge density distribution and enhances the interfacial relaxation process. Furthermore, the polar nature of the PPy molecules results in a large number of intrinsic electric dipoles, which can generate significant dipole polarization when oriented under an applied electromagnetic field. The disordered arrangement of covalent bonds in the amorphous region and the presence of polar functional groups may induce additional dipole moments, further strengthening the overall dipole polarization effect.

[0067] Regarding the magnetic loss mechanism—another key contributor to electromagnetic wave absorption—five main phenomena need to be considered: domain wall resonance, hysteresis loss, exchange resonance, eddy current effect, and natural resonance. To quantitatively distinguish these mechanisms, equation (4) is typically used for analysis: (4) Where C0 is the ratio of the square of the imaginary part to the square of the real part of the complex permeability and the frequency, its variation with frequency is used to determine the loss type of the material, μ0 represents the absolute permeability of space, σ represents the conductivity, d represents the thickness of the material, and ƒ represents the frequency of the alternating magnetic field. Figure 5As shown in b, the C0 curves of the four samples show a decreasing trend with increasing frequency, accompanied by several obvious fluctuation peaks, indicating that eddy current loss is not the main mechanism of magnetic loss. Specifically, the resonance peaks observed in the 4.5-9.0 GHz frequency range can be attributed to natural resonance, while the resonance peaks appearing at 12.8 and 16.2 GHz may be caused by exchange resonance.

[0068] Based on transmission line theory, the RL (reflection loss) values ​​of the Ni3Al@PPy samples are determined using the following formula, and their microwave absorption characteristics are evaluated: (5) (6) (7) (8) In this theoretical model, ε r μ represents the complex permittivity. r Z represents the complex permeability. in Z0 represents the input impedance of the absorbing material, Z0 is the characteristic impedance in free space, c, d and ƒ represent the speed of light in vacuum, the sample thickness and the incident microwave frequency, respectively, j represents the imaginary unit; RL represents the reflection loss, and the unit is dB.

[0069] Figure 6 The diagram shows the electromagnetic wave absorption performance of S0, S1, S2, and S3 at different frequencies and matching thicknesses, presented in 3D / 2D reflection loss curves and impedance matching plots. Matching thickness refers to the physical thickness of the electromagnetic wave absorbing material that enables optimal matching between the input impedance and free-space impedance at a specific frequency, thereby minimizing reflection loss (or meeting specific absorption requirements). It represents the thickness corresponding to the "valley" on the RL curve and constitutes the thickness dimension of the RL "valley" in the 3D diagram. Generally, a material is considered to have excellent absorption capability when it can absorb more than 90% of the incident wave (i.e., RL ≤ -10 dB). Figure 6 The 3D and 2D RL plots (a1-b4) show that S0, S1, and S3 have lower RL values ​​and narrower effective absorption bandwidths (EAB), while S2 exhibits the best absorption characteristics. Figure 6The Ni3Al@PPy composite absorbing material (S2) prepared in Example 2 shown in a3 and 6b3 achieved a minimum reflection loss of -40.0 dB at a matching thickness of 3.0 mm and a frequency of 9.27 GHz. The EAB reached 3.02 GHz (11.73-14.75 GHz) when the matching thickness was 2 mm. This result shows that the core-shell structure significantly improves the absorption performance of Ni3Al micron particles. Furthermore, by comparing the data of S2 with those of S1 and S3, it was found that when the thickness of the modified PPy shell is 0.22~0.31 μm, shells that are too thin or too thick may have a negative impact on the absorption performance: (1) a shell that is too thin leads to discontinuity of the conductive network, insufficient dielectric loss capacity, low density of interface polarization sites and weak dipole polarization; (2) a shell that is too thick may achieve strong local absorption, but it will cause high conductivity, severe skin effect and material-air interface impedance mismatch, resulting in strong surface reflection, reduced magnetic loss contribution, limited bandwidth and increased optimal thickness. In this case, electromagnetic waves only penetrate the surface layer, the proportion of magnetic components decreases, the contribution of magnetic loss weakens, and the severe impedance mismatch between the material surface and free space triggers strong electromagnetic wave reflection.

[0070] Typically, excellent impedance matching is a prerequisite for high-performance microwave absorbing materials. Impedance matching ratio Z = |Z in / Z0| can be calculated according to formula (7) and is used for impedance matching assessment. When Z=1 (Z in When ≈Z0), it means that the incident electromagnetic wave can penetrate into the material to the maximum extent, thus minimizing surface reflection. Figure 6 c1-c4 are impedance matching diagrams for S0, S1, S2 and S3, respectively. The red area represents the region where the Z value is close to 1 (0.8-1.2). It can be clearly observed that the Z values ​​of S1, S2 and S3 are better than those of S0. This indicates that the core-shell structure effectively optimizes the impedance matching of the Ni3Al@PPy composite material and plays a key role in enhancing its electromagnetic wave absorption performance.

[0071] 4. Comparison and performance analysis of acid-doped modification (1) XRD XRD tests were performed on the Ni3Al@PPy composite material prepared in Comparative Example 2 and the Ni3Al@PPy composite material prepared in Example 2. The results are as follows: Figure 7 As shown. Figure 7 In the study, both samples showed significant diffraction peaks at 2θ = 24.9°, 35.6°, 44.0°, 51.2°, 57.9°, and 64.0°, which correspond to the (100), (110), (111), (200), (210), and (211) crystal planes of Ni3Al (PDF#97-015-1385), respectively.

[0072] (2) Study on absorption performance Figure 8 The electromagnetic parameters of the Ni3Al@PPy composite microwave absorbing material prepared by doping PPy with hydrochloric acid and p-toluenesulfonic acid (TsOH) are shown. Regarding dielectric properties, the real part of the complex dielectric constant of the HCl-doped system is also shown. ε′ virtual part ε′′ and dielectric loss tangent tan δ ε Both were significantly higher than the TsOH doped system. This is because small molecule HCl can more easily enter the PPy chain structure, effectively increasing the carrier concentration and introducing more polarization centers, thereby enhancing dielectric storage and loss capabilities. Even though the amount of TsOH in Comparative Example 2 was greater than the amount of HCl in Example 2, its effect was not as good as that of Example 2. In terms of magnetic properties, the real part of the complex permeability of the two doped systems was significantly higher. μ′ virtual part μ′′ and magnetic loss tangent tan δ μ The values ​​are all at a low level, indicating that the absorption mechanism of this composite system is mainly based on dielectric loss, with limited contribution from magnetic loss. In terms of absorption performance, the HCl-doped system achieves lower reflection loss (with a minimum RL value of -40 dB) and a wider effective absorption bandwidth due to its superior dielectric loss characteristics, and can satisfy the interference destructive condition at a thinner thickness. In contrast, the macromolecular TsOH has a weaker dielectric loss due to its low doping efficiency and insufficient carrier concentration, and its absorption performance can only reach a moderate level of RL equal to -15.2 dB. Its effective bandwidth and lightweight potential are inferior to those of the HCl-doped system.

[0073] Figure 9 Figures a and 9b show the three-dimensional reflection loss (RL) curves of Ni3Al@PPy composite absorbing materials prepared by hydrochloric acid and p-toluenesulfonic acid doping, respectively. The composite material prepared by p-toluenesulfonic acid doping achieved a minimum reflection loss of -15.2 dB at 14.7 GHz and a matching thickness of 5.5 mm, with an EAB of 1.41 GHz (14.05-15.46 GHz). The hydrochloric acid doped system exhibits significantly better absorption intensity and effective bandwidth.

[0074] Figure 10 a and 10c Figure 10 b and 10d are the interference destructive phase diagrams of Ni3Al@PPy composite microwave absorbing materials prepared by hydrochloric acid and p-toluenesulfonic acid doping and modification of PPy, respectively. These diagrams show the relationship between material thickness and electromagnetic wave recombination. When the / 4 model curves are consistent, the incident electromagnetic wave and the reflected electromagnetic wave will exhibit destructive interference. Both systems exhibit thickness-frequency dependent destructive interference: as the thickness increases, the RL valley shifts to lower frequencies; as the frequency increases, the matching thickness decreases, which conforms to the physical law that t≈λ / 4 (where t represents the matching thickness and λ represents the incident wavelength).

[0075] 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 Ni3Al@PPy composite microwave absorbing material, characterized in that, It includes a micron-sized Ni3Al core and a modified PPy shell coating the surface of the Ni3Al core. The modified PPy shell is a hydrochloric acid-modified PPy shell with a thickness of 0.22~0.31μm.

2. The Ni3Al@PPy composite microwave absorbing material as described in claim 1, characterized in that, The thickness of the modified PPy shell is 0.27 μm.

3. The Ni3Al@PPy composite microwave absorbing material as described in claim 1, characterized in that, The Ni3Al@PPy composite microwave absorbing material was obtained through aluminothermic reaction, oxidative polymerization reaction, and hydrochloric acid doping modification.

4. The Ni3Al@PPy composite microwave absorbing material as described in claim 3, characterized in that, The concentration of hydrochloric acid used in the hydrochloric acid doping modification is 0.04~0.06 mol / L.

5. The Ni3Al@PPy composite microwave absorbing material as described in claim 1, characterized in that, The preparation of the Ni3Al core includes: mixing aluminum powder and nickel powder, pressing them into a blank, and then carrying out an aluminothermic reaction in a protective atmosphere. The resulting reaction product is then ground, washed, and dried to obtain the Ni3Al core.

6. The Ni3Al@PPy composite microwave absorbing material as described in claim 5, characterized in that, The mixing process involves three-dimensionally mixing nickel powder and aluminum powder with a molar ratio of 3 to 3.2:1 using Al2O3 as grinding balls at a rotation speed of 140 to 160 r / min. And / or, the pressing pressure is 30~40MPa; And / or, the protective atmosphere is argon; And / or, the temperature of the aluminothermic reaction is 250~270℃; And / or, the mass ratio of the igniter of the aluminothermic reaction to the total mass of the aluminum powder and nickel powder is 1:15~17.

7. The Ni3Al@PPy composite microwave absorbing material as described in claim 1, characterized in that, When the thickness of the modified PPy shell is 0.27 μm, the Ni3Al@PPy composite absorbing material achieves a minimum reflection loss of -40.0 dB at 9.27 GHz and an absorption rate of >99.99% when the matching thickness is 3.0 mm, while the effective absorption bandwidth reaches 3.02 GHz when the matching thickness is 2.0 mm.

8. A method for preparing the Ni3Al@PPy composite microwave absorbing material as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Mix Ni3Al core and pyrrole monomer in deionized water, then add FeCl3·6H2O solution to carry out oxidative polymerization reaction to obtain composite material I; S2. After washing the composite material I obtained in S1, hydrochloric acid doping modification was carried out to obtain Ni3Al@PPy composite microwave absorbing material.

9. The preparation method according to claim 8, characterized in that, In step S1, the reaction ratio of the Ni3Al core, pyrrole monomer, and FeCl3·6H2O solution is 2g:0.25~0.75ml:30ml; And / or, in step S1, the mass percentage of FeCl3·6H2O in the FeCl3·6H2O solution is 6%~17%; And / or, in step S2, the concentration of hydrochloric acid used in the hydrochloric acid doping modification is 0.04~0.06 mol / L.

10. The Ni3Al@PPy composite absorbing material according to any one of claims 1 to 7, or the Ni3Al@PPy composite absorbing material prepared by the preparation method according to any one of claims 8 to 9, is used in electromagnetic absorbing materials or electromagnetic absorbing devices.

Images