Preparation method of wave-absorbing composite material and wave-absorbing composite material

Abstract

The application provides a wave-absorbing composite material preparation method and a wave-absorbing composite material, and the method comprises the following steps: placing foamed nickel in a hydrochloric acid solution for ultrasonic treatment; sequentially performing ultrasonic cleaning treatment on the foamed nickel by using deionized water and anhydrous ethanol, and drying the foamed nickel to obtain pretreated foamed nickel; dissolving iron nitrate nonahydrate, nickel nitrate hexahydrate, polyvinylpyrrolidone and urea in deionized water to obtain a uniform mixed solution; performing hydrothermal reaction on the uniform mixed solution and the pretreated foamed nickel to obtain an intermediate product; performing ultrasonic cleaning and drying treatment on the intermediate product to obtain FeNi layered double metal hydroxide / foamed nickel, and placing the FeNi layered double metal hydroxide / foamed nickel in an inert atmosphere tube furnace for high-temperature calcination treatment, naturally cooling to room temperature for second heat preservation treatment, and obtaining a FeNi-based composite metal oxide / foamed nickel composite material, so as to solve the problem that current wave-absorbing materials are difficult to simultaneously consider excellent impedance matching and strong electromagnetic wave attenuation capability, and the wave-absorbing effect is not ideal.

Description

Technical Field

[0001] This application relates to the field of microwave absorbing materials technology, and in particular to a method for preparing a microwave absorbing composite material and the microwave absorbing composite material. Background Technology

[0002] With the widespread application and rapid development of 5G communication and electronic equipment in military, communications, aerospace and other fields, electromagnetic radiation and electromagnetic pollution problems are becoming increasingly serious. Electromagnetic radiation not only interferes with the normal operation of precision electronic equipment, leading to performance degradation or even malfunction, but also poses potential harm to human health, such as affecting the nervous and cardiovascular systems. Against this backdrop, developing high-performance absorbing materials that are "thin, lightweight, wide-bandwidth, and have strong absorption" to effectively absorb and attenuate electromagnetic waves and reduce the hazards of electromagnetic radiation has become a key issue to be solved in the field of electromagnetic functional materials.

[0003] Nickel foam (NF), a typical three-dimensional interconnected porous metallic material, has attracted attention due to its large specific surface area, good mechanical stability, low density, and excellent conductivity. Its three-dimensional conductive network provides multiple reflection and scattering paths for incident electromagnetic waves, and achieves electromagnetic wave energy attenuation through conductive losses. Meanwhile, layered bimetallic hydroxides (LDHs), as inorganic functional materials with typical layered structures, have advantages such as strong compositional tunability and good ion exchange capacity. High-temperature calcination can yield composite metal oxides, forming a high specific surface area porous structure. Abundant heterointerfaces and lattice defects can enhance interfacial polarization and dipole polarization losses, while magnetic metal oxides can also provide effective magnetic losses, making them highly promising electromagnetic wave loss media. There are already reports on the preparation of microwave absorbing materials by combining LDH-derived metal oxides with nickel foam.

[0004] However, when combining LDH-derived metal oxides with nickel foam to prepare microwave absorbing materials, it is impossible to achieve optimal matching of the electromagnetic parameters of the composite material by precisely controlling the proportion of metal components. This makes it difficult to simultaneously achieve excellent impedance matching and strong electromagnetic wave attenuation capabilities, resulting in unsatisfactory absorption effects. Moreover, the absorption performance of the obtained material needs improvement; it is impossible to achieve both strong absorption and broadband absorption at ultra-thin thicknesses, making it difficult to meet the stringent requirements of high-performance and practical microwave absorbing materials for real-world engineering applications. Summary of the Invention

[0005] This application provides a method for preparing a microwave absorbing composite material and the microwave absorbing composite material, in order to solve the technical problem that existing microwave absorbing materials cannot simultaneously achieve excellent impedance matching and strong electromagnetic wave attenuation capabilities, resulting in unsatisfactory microwave absorption effects.

[0006] The first aspect of this application provides a method for preparing a microwave absorbing composite material, comprising: The nickel foam was subjected to ultrasonic treatment in a hydrochloric acid solution. The ultrasonically treated nickel foam was sequentially ultrasonically cleaned with deionized water and anhydrous ethanol and then dried to obtain pretreated nickel foam. Ferric nitrate nonahydrate, nickel nitrate hexahydrate, polyvinylpyrrolidone and urea were dissolved in deionized water to obtain a homogeneous mixed solution. The homogeneous mixed solution and the pretreated nickel foam were placed in a hydrothermal reactor for hydrothermal reaction. After the reaction was completed, the mixture was naturally cooled to room temperature for a first heat preservation treatment to obtain an intermediate product. The intermediate product was subjected to ultrasonic cleaning and drying to obtain FeNi layered bimetallic hydroxide / nickel foam. The FeNi layered bimetallic hydroxide / nickel foam was placed in an inert atmosphere tube furnace for high-temperature calcination. After calcination, the FeNi layered bimetallic hydroxide / nickel foam was naturally cooled to room temperature for a second heat preservation treatment to obtain the FeNi-based composite metal oxide / nickel foam composite material.

[0007] In some embodiments, the concentration of the hydrochloric acid solution is in the range of 1 mol / L to 5 mol / L, and the ultrasonic treatment time of the nickel foam in the hydrochloric acid solution is in the range of 3 min to 7 min.

[0008] In some embodiments, the ultrasonically treated nickel foam is sequentially ultrasonically cleaned with deionized water and anhydrous ethanol for 20 minutes each.

[0009] In some embodiments, Fe in the homogeneous mixed solution 3+ with Ni 2+ The total molar amount is in the range of 1 mmol to 3 mmol, Fe 3+ with Ni 2+ The molar ratio is in the range of 1:3 to 3:1.

[0010] In some embodiments, the amount of urea added to the homogeneous mixed solution is 10 mmol, the amount of polyvinylpyrrolidone added is 0.1 g, and the volume of deionized water is 70 mL.

[0011] In some embodiments, the temperature of the hydrothermal reaction is in the range of 100°C to 140°C, and the duration of the first heat preservation treatment is 12 hours.

[0012] In some embodiments, the steps of ultrasonically cleaning and drying the intermediate product include: The intermediate product was ultrasonically cleaned twice with deionized water and anhydrous ethanol and then dried. The drying temperature was 60°C and the drying time was between 10 and 14 hours.

[0013] In some embodiments, the inert atmosphere is an argon atmosphere, the temperature of the high-temperature calcination treatment is in the range of 400°C to 600°C, the heating rate is 5°C / min, and the time of the second heat preservation treatment is in the range of 1h to 3h.

[0014] A second aspect of this application provides a microwave absorbing composite material, comprising: Using three-dimensional porous nickel foam as a substrate, FeNi-based composite metal oxide nanoflower structures assembled from two-dimensional nanosheets are grown in situ on the substrate surface; the phase composition of the microwave absorbing composite material varies with the molar ratio of Fe and Ni in the raw materials. The microwave absorbing composite material is prepared by a microwave absorbing composite material preparation method according to any one of the first aspects above.

[0015] In some embodiments, the microwave absorbing composite material is a composite of NiO and NiFe2O4 or a composite of Fe3O4 and NiO.

[0016] This application provides a method for preparing a microwave absorbing composite material and the microwave absorbing composite material. The method includes: ultrasonically treating nickel foam in a hydrochloric acid solution; ultrasonically cleaning the ultrasonically treated nickel foam sequentially with deionized water and anhydrous ethanol and drying it to obtain pretreated nickel foam; dissolving ferric nitrate nonahydrate, nickel nitrate hexahydrate, polyvinylpyrrolidone, and urea in deionized water to obtain a homogeneous mixed solution; placing the homogeneous mixed solution and the pretreated nickel foam in a hydrothermal reactor for hydrothermal reaction, and after the reaction, naturally cooling to room temperature for a first heat preservation treatment to obtain an intermediate product; ultrasonically cleaning and drying the intermediate product to obtain FeNi layered bimetallic hydroxide / nickel foam; placing the FeNi layered bimetallic hydroxide / nickel foam in an inert atmosphere tube furnace for high-temperature calcination, and after the FeNi layered bimetallic hydroxide / nickel foam is calcined, naturally cooling to room temperature for a second heat preservation treatment to obtain a FeNi-based composite metal oxide / nickel foam composite material, so that the microwave absorbing material simultaneously possesses excellent impedance matching and strong electromagnetic wave attenuation capability, thereby improving the microwave absorption effect. Attached Figure Description

[0017] To more clearly illustrate the technical solution of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart of the method for preparing the microwave absorbing composite material in this application; Figure 2(a) and Figure 2(b) are XRD characterization diagrams of the FeNi-MMO / NF microwave absorbing composite materials obtained in Examples 1-3 of this application; Figure 3 These are SEM images of the FeNi-MMO / NF microwave absorbing composite materials obtained in Examples 1-3 of this application; Figure 4 This is an EDS elemental mapping diagram of the Fe1Ni1-MMO / NF microwave absorbing composite material obtained in Example 2 of this application; Figures 5(a) to 5(f) are 3D and 2D reflection loss diagrams of the FeNi-MMO / NF microwave absorbing composite materials obtained in Examples 1 to 3 of this application; Figures 6(a) and 6(b) are absorption bandwidth diagrams of the FeNi-MMO / NF microwave absorbing composite materials obtained in Examples 1-3 of this application; Figures 7(a) to 7(c) are impedance matching diagrams of the FeNi-MMO / NF microwave absorbing composite materials obtained in Examples 1 to 3 of this application; Figures 8(a) to 8(c) are radar scattering cross-section attenuation diagrams of the FeNi-MMO / NF absorbing composite materials obtained in Examples 1 to 3 of this application. Detailed Implementation

[0019] To enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this application.

[0020] In some technologies, it is difficult for absorbing materials to simultaneously achieve excellent impedance matching and strong electromagnetic wave attenuation capabilities, resulting in unsatisfactory absorption effects. To address this technical problem, this application provides a method for preparing a microwave absorbing composite material and the microwave absorbing composite material itself. The preparation method and the microwave absorbing composite material are described below: like Figure 1 The diagram shown is a flowchart of the method for preparing microwave absorbing composite materials in this application.

[0021] The first aspect of this application provides a method for preparing a microwave absorbing composite material, comprising: S100: The nickel foam is placed in a hydrochloric acid solution for ultrasonic treatment; the concentration of the hydrochloric acid solution is in the range of 1 mol / L to 5 mol / L, more preferably 2 to 4 mol / L, and more preferably 3 mol / L; the ultrasonic treatment time of the nickel foam in the hydrochloric acid solution is in the range of 3 min to 7 min, more preferably 4 to 6 min, and more preferably 5 min.

[0022] S200: The ultrasonically treated nickel foam is sequentially ultrasonically cleaned with deionized water and anhydrous ethanol and then dried to obtain pretreated nickel foam; the ultrasonic cleaning time for the ultrasonically treated nickel foam is 20 min for each step.

[0023] S300: Ferric nitrate nonahydrate, nickel nitrate hexahydrate, polyvinylpyrrolidone, and urea are dissolved in deionized water to obtain a homogeneous mixed solution; the homogeneous mixed solution contains Fe... 3+ with Ni 2+ The total molar amount is in the range of 1 mmol to 3 mmol, more preferably 1.5 to 2.5 mmol, and more preferably 2 mmol; Fe 3+ with Ni 2+ The molar ratio is in the range of 1:3 to 3:1. The amount of urea added to the homogeneous mixed solution is 10 mmol, the amount of polyvinylpyrrolidone added is 0.1 g, and the volume of deionized water is 70 mL.

[0024] S400: The homogeneous mixed solution and the pretreated nickel foam are placed in a hydrothermal reactor for hydrothermal reaction. After the reaction is completed, the mixture is naturally cooled to room temperature for a first heat preservation treatment to obtain an intermediate product. The temperature of the hydrothermal reaction is in the range of 100°C to 140°C, more preferably 110 to 130°C, and more preferably 120°C. The time of the first heat preservation treatment is 12 hours.

[0025] S500: The intermediate product is subjected to ultrasonic cleaning and drying to obtain FeNi layered bimetallic hydroxide / nickel foam.

[0026] The step of ultrasonically cleaning and drying the intermediate product includes the following steps: S510: The intermediate product is ultrasonically cleaned twice with deionized water and anhydrous ethanol and then dried; the drying temperature is 60°C and the drying time is in the range of 10h to 14h, more preferably 11h to 13h, and more preferably 12h.

[0027] S600: The FeNi layered bimetallic hydroxide / nickel foam is placed in an inert atmosphere tube furnace for high-temperature calcination. After calcination, the FeNi layered bimetallic hydroxide / nickel foam is naturally cooled to room temperature for a second heat preservation treatment to obtain a FeNi-based composite metal oxide / nickel foam composite material. The inert atmosphere is argon atmosphere, the temperature of the high-temperature calcination treatment is in the range of 400°C to 600°C, more preferably 450 to 550°C, and more preferably 500°C; the heating rate is 5°C / min, and the time of the second heat preservation treatment is in the range of 1h to 3h, more preferably 1.5 to 2.5h, and more preferably 2h.

[0028] This application provides a method for preparing microwave absorbing composite materials, the specific process of which is as follows: First, pretreatment of nickel foam is carried out: the nickel foam is placed in a 1-5 mol / L hydrochloric acid solution and ultrasonically treated for 3-7 minutes to remove the surface oxide layer. Then, it is ultrasonically cleaned with deionized water and anhydrous ethanol for 20 minutes in sequence. After drying, the pretreated nickel foam is obtained.

[0029] Secondly, a hydrothermal reaction was carried out to prepare the precursor: ferric nitrate nonahydrate, nickel nitrate hexahydrate, 0.1 g polyvinylpyrrolidone (PVP-K30), and 10 mmol urea were dissolved in 70 ml of deionized water to obtain a homogeneous mixed solution. Among them, Fe... 3+ with Ni 2+ The molar ratio was (1:3) to (3:1), and the total molar amount was 1 to 3 mmol. The mixed solution and the pretreated nickel foam were placed together in a hydrothermal reactor and hydrothermally reacted at 100 to 140°C for 12 h. After the reaction was completed, the mixture was naturally cooled to room temperature. The product was ultrasonically cleaned twice with deionized water and anhydrous ethanol, and dried at 60°C for 10 to 14 h to obtain (FeNi-LDH / NF).

[0030] Finally, the target product was prepared by high-temperature calcination: the FeNi-LDH / NF precursor was placed in an argon atmosphere tube furnace and heated to 400~600°C at a heating rate of 5°C / min for 1~3 hours. After natural cooling, the FeNi-based composite metal oxide / nickel foam (FeNi-MMO / NF) composite material was obtained.

[0031] This application provides a method for preparing a microwave absorbing composite material. The composite material uses three-dimensional porous nickel foam (NF) as a substrate, with FeNi-based composite metal oxide (MMO) nanoflower structures assembled from two-dimensional nanosheets grown in situ on the surface. First, a FeNi layered double hydroxide (LDH) precursor is grown in situ on the surface of the nickel foam using a hydrothermal method, followed by high-temperature calcination in an inert atmosphere to obtain the FeNi-MMO / NF composite material. By adjusting the Fe / Ni molar ratio, the electromagnetic parameters of the composite material are optimized, thereby improving its electromagnetic wave attenuation capability. The resulting Fe1Ni1-MMO / NF composite material achieves a minimum reflection loss (RL) of -68.18 dB at a matching thickness of 2.4 mm and an effective absorption bandwidth (EAB) of 4.16 GHz at a thickness of 1.5 mm, while simultaneously reducing the radar cross section (RCS) of the metal plate by 30.47 dB m². The microwave absorbing composite material provided in this application has a simple preparation process and good structural stability, showing broad application prospects in the fields of electromagnetic protection and radar stealth.

[0032] This application provides a method for preparing microwave absorbing composite materials, which has the following beneficial effects: 1. This application flexibly controls the phase composition and electromagnetic parameters of the composite material by adjusting the Fe / Ni molar ratio, introducing a low-conductivity magnetic composite metal oxide onto the surface of nickel foam. This optimizes the impedance matching characteristics of the material, allowing more electromagnetic waves to penetrate the material and achieve effective attenuation. Simultaneously, the porous nanoflower structure formed by the vertically oriented growth of two-dimensional nanosheets, together with the three-dimensional porous network of nickel foam, forms a hierarchical porous structure, providing abundant multiple reflection and scattering paths for incident electromagnetic waves, thus extending the propagation path of electromagnetic waves within the material.

[0033] 2. The Fe1Ni1-MMO / NF composite material with the best performance obtained in this application has the lowest reflection loss (RL) at a matching thickness of 2.4 mm. min The effective absorption bandwidth (EAB, RL≤-10dB) can reach -68.18 dB; with an ultra-thin thickness of 1.5 mm, the effective absorption bandwidth (EAB, RL≤-10dB) is as wide as 4.16 GHz, covering the main frequency bands of the X-band and Ku-band; at the same time, the radar cross section (RCS) simulation results show that the material can reduce the RCS value of the metal plate by 30.47 dB m², and has excellent radar stealth performance.

[0034] 3. The method for preparing microwave absorbing composite materials provided in this application has a simple process operation, uses commercially available conventional chemicals as raw materials, which are easy to obtain and have low cost, and the hydrothermal and calcination process conditions are mild, requiring no complex equipment, and has strong repeatability, making it suitable for large-scale industrial production.

[0035] This application provides a method for preparing microwave absorbing composite materials, the specific implementation of which is as follows: Example 1

[0036] (1) Place 2cm×3cm×2mm nickel foam in a 3mol / L hydrochloric acid solution and sonicate for 5 minutes to remove the surface oxide layer. Then sonicate in deionized water and anhydrous ethanol for 20 minutes each to remove surface impurities. After drying, pretreated nickel foam is obtained.

[0037] (2) 0.5 mmol ferric nitrate nonahydrate, 1.5 mmol nickel nitrate hexahydrate, 0.1 g polyvinylpyrrolidone (PVP-K30) and 10 mmol urea were added to 70 mL of deionized water and stirred at room temperature until completely dissolved to obtain a homogeneous mixed solution. The mixed solution and pretreated nickel foam were placed together in a 100 mL stainless steel hydrothermal reactor lined with polytetrafluoroethylene, sealed and placed in a forced-air drying oven, and kept at 120°C for 12 h for hydrothermal reaction. After the reaction was completed, the mixture was naturally cooled to room temperature, the product was taken out, and ultrasonically cleaned twice each with deionized water and anhydrous ethanol. It was then dried in a forced-air drying oven at 60°C for 12 h to obtain the Fe1Ni3-LDH / NF precursor.

[0038] (3) The Fe1Ni3-LDH / NF precursor was placed in a corundum crucible and placed in an argon atmosphere tube furnace. The temperature was raised to 500°C at a rate of 5°C / min and kept at that temperature for 2 hours. After the calcination was completed, it was naturally cooled to room temperature to obtain the Fe1Ni3-MMO / NF composite material.

[0039] Example 2

[0040] In this embodiment, the FeNi-based composite metal oxide microwave absorbing material (denoted as Fe1Ni1-MMO / NF) loaded on the nickel foam surface was prepared using the same method as in Example 1. The only difference was that the amount of ferric nitrate nonahydrate and nickel nitrate hexahydrate added in step (2) was 1 mmol.

[0041] Example 3

[0042] In this embodiment, the FeNi-based composite metal oxide microwave absorbing material (denoted as Fe3Ni1-MMO / NF) loaded on the nickel foam surface was prepared using the same method as in Example 1. The only difference was that the amount of ferric nitrate nonahydrate and nickel nitrate hexahydrate added in step (2) was 1.5 mmol and 0.5 mmol, respectively.

[0043] The samples obtained in Examples 1-3 were characterized by XRD crystal structure to analyze the phase composition of the microwave absorbing composite material. Figure 2(a) shows the XRD patterns of Example 1 (Fe1Ni3-MMO / NF) and Example 2 (Fe1Ni1-MMO / NF). As can be seen from the figure, since the material substrate is nickel foam, the characteristic peaks of nickel in the XRD pattern are relatively strong, corresponding to the (111), (200), and (220) crystal planes of Ni at 44.5°, 51.8°, and 76.4°. When the Fe / Ni ratio is 1:3 and 1:1, the metal oxides formed are NiO and NiFe2O4. The characteristic peaks at 37.3°, 43.3°, and 62.9° correspond to the (111), (200), and (220) crystal planes of NiO. The characteristic peaks at 30.3°, 35.7°, 43.4°, 57.4°, and 63.0° correspond to the (220), (311), (400), (511), and (440) crystal planes of NiFe2O4. It can be observed that the characteristic peak intensity of NiFe2O4 in the XRD pattern of Fe1Ni1-MMO / NF is significantly higher than that in Fe1Ni3-MMO / NF. This is because the molar ratio of Fe in the Fe1Ni1-MMO / NF composite material is larger, resulting in more NiFe2O4 in the product. As the molar ratio of Fe continues to increase, the XRD pattern of Example 3 (Fe3Ni1-MMO / NF), as shown in Figure 2(b), also shows obvious characteristic peaks of nickel foam. The metal oxides formed after calcination are Fe3O4 and NiFe2O4. The characteristic peaks at 30.2°, 35.6°, 37.2°, 43.2°, 53.2°, and 62.6° correspond to the (114), (016), (024), (220), (232), and (228) crystal planes of Fe3O4. The characteristic peaks at 37.2°, 43.2°, and 62.8° correspond to the (111), (200), and (220) crystal planes of NiO.

[0044] To further investigate the morphology and structure of the composite material, SEM characterization was performed on the material. Figure 3 Middle (a) to Figure 3 Figure (l) presents SEM images of FeNi-MMO / NF composites with different Fe and Ni metal ion ratios. It can be seen that the three-dimensional network framework structure of NF is well preserved. Despite hydrothermal reaction and high-temperature calcination at 500°C, the NF framework did not collapse or break, indicating its good mechanical stability. Figure 3 Middle (a) to Figure 3As shown in (d), when the Fe / Ni ion ratio is 1:3, the surface of the nickel foam mesh is covered with very dense, fine lamellar nanoflowers. These nanoflowers are tightly packed together, leaving almost no large gaps. Figure 3 Middle (e) to Figure 3 In (h), it can be found that when Fe 3+ With further increases in Fe / Ni ion content, when the Fe / Ni ion ratio is 1:1, more Fe... 3+ Within the layers of metal oxide plates, the nanoflowers become larger and their surface loading increases. These structures are not simply stacked but exhibit a tendency to grow outwards perpendicular to the substrate. This indicates that Fe... 3+ The increase of Fe can improve the directional growth ability of nanosheets and reduce their self-aggregation. This is mainly because Fe... 3＋ Replaced Ni on the plate 2+ This process imparts a positive charge to the LDH sheets, suppressing their self-aggregation under electrostatic forces, thus increasing the dispersibility of the nanosheets. Figure 3 middle (i) to Figure 3 As can be seen in (l), with Fe 3+ As the ratio of Fe to Ni continued to increase, when the ratio was 3:1, more agglomeration of nanoflowers appeared on the nickel foam mesh, while the non-agglomerated areas were thinner nanosheets, and the size of the nanoflowers was also larger than that of the nanoflowers when the ratio of Fe to Ni was 1:1.

[0045] To investigate the elemental distribution of the composite material, the material was characterized by EDS. Figure 4 The EDS elemental mapping of Fe1Ni1-MMO / NF is presented. It can be seen that the sample is composed of six elements: Fe, Ni, C, N and O, and they are uniformly distributed. This is consistent with the results of XRD spectrum and SEM image.

[0046] To evaluate the microwave absorption performance of the composite materials, the electromagnetic absorption characteristics of three samples were investigated. Figures 5(a), 5(c), and 5(e) show the three-dimensional minimum reflection loss (RL) plots of Fe1Ni3-MMO / NF, Fe1Ni1-MMO / NF, and Fe3Ni1-MMO / NF in the 2-18 GHz range for thicknesses of 0-5 mm. Figures 5(b), 5(d), and 5(e) show the two-dimensional RL plots of the three samples for thicknesses of 2-3 mm. As shown in Figures 5(a) and 5(b), the RL of Fe1Ni3-MMO / NF at a matching thickness of 2.2 mm... minThe RLmin is -30.36 dB, and the EAB is only 2.68 GHz. As shown in Figures 5(e) and 5(f), the RLmin of Fe3Ni1-MMO / NF with a matching thickness of 2.5 mm is -45.5 dB, and the EAB is only 2.48 GHz. As shown in Figures 5(c) and 5(d), the RLmin of Fe1Ni1-MMO / NF with a matching thickness of 2.4 mm is -30.36 dB, and the EAB is only 2.68 GHz. min The electromagnetic interference (EMI) was -68.18 dB, and the energy level (EAB) was 3.08 GHz, significantly better than the other two composite materials. This indicates that the appropriate amounts of NiO and NiFe2O4 in the Fe1Ni1-MMO / NF composite material balanced the overall electromagnetic parameters of the material. Furthermore, the tight and uniform bonding of the three-dimensional nickel foam network of metal oxides constructs a multiphase heterogeneous interface. After entering the porous nickel foam framework, electromagnetic waves undergo multiple reflections and scattering between the MMO nanosheet layers and on the surface of the NF framework.

[0047] As shown in Figures 6(a) and 6(b), the effective absorption bandwidth (EAB) of the three FeNi-MMO / NF composites in thicknesses of 1.4–2.6 mm was calculated. Figure 6(a) shows that the EAB value of Fe1Ni1-MMO / NF in the 1.4–2.6 mm thickness range is greater than that of the other two samples, indicating that it can absorb more electromagnetic waves over a wider frequency range. Notably, Fe1Ni3-MMO / NF and Fe3Ni1-MMO / NF also exhibit good RL values ​​at the same thickness. This result demonstrates the effective synergistic effect between the three-dimensional nickel foam network and the multi-component metal oxide, resulting in excellent EMA performance. Figure 6(b) shows the material thicknesses corresponding to the maximum EAB for the three samples. It can be seen that all three samples exhibit excellent effective absorption bandwidth at relatively thin thicknesses. The EAB for Fe1Ni3-MMO / NF at a thickness of 1.4 mm is 3.6 GHz, and the EAB for Fe3Ni1-MMO / NF at a thickness of 1.3 mm is 3.28 GHz. Among them, Fe1Ni1-MMO / NF achieved an EAB of 4.16 GHz at a material thickness of only 1.5 mm. Combined with the previous test analysis of its RL, it can be intuitively seen that Fe1Ni1-MMO / NF has a higher RL in a thinner matching thickness range. min and EAB max It can simultaneously meet the above requirements for evaluating the properties of microwave absorbing materials, which also proves that this material can be considered an excellent functional EMW microwave absorbing material.

[0048] Figures 7(a) to 7(c) show the curves of normalized impedance modulus versus frequency for the three samples. As can be seen from the figures, the Z-value of Fe1Ni1-MMO / NF is closest to 1 across the entire frequency range, indicating that the composite material exhibits excellent impedance matching characteristics. This means that the higher the impedance matching degree between the material surface and the air, the more electromagnetic waves can penetrate the material surface into its interior. The results show that the presence of porous nickel foam can effectively balance the impedance between the material and free space, allowing more electromagnetic waves to enter the foam interior. A reasonable balance of the impedance matching coefficient can improve the electromagnetic response capability of the material.

[0049] Figures 8(a) to 8(c) show the simulated RCS (Radar Target Cross Section) curves of metal PEC plates coated with Fe1Ni3-MMO / NF, Fe1Ni1-MMO / NF, and Fe3Ni1-MMO / NF absorbing coatings. The Fe1Ni3-MMO / NF coating thickness is 2.2 mm, with a simulation frequency of 9.68 GHz; the Fe1Ni1-MMO / NF coating thickness is 2.4 mm, with a simulation frequency of 9.16 GHz; and the Fe3Ni1-MMO / NF coating thickness is 2.5 mm, with a simulation frequency of 7.92 GHz. The planar scattering signals of the three coated models are relatively weak, indicating that the three samples have a certain absorption capability for radar signals at specific frequency bands and thicknesses. The RCS simulation curves in Figures 8(a) to 8(c) more intuitively show that, compared with the pure PEC board, the RCS value of the PEC board coated with the Fe1Ni3-MMO / NF absorbing layer decreased by 25.59 dBm. 2 The maximum RCS value in the range of -90° to 90° is -11.9 dBm. 2 The RCS value of the PEC plate coated with the Fe3Ni1-MMO / NF absorbing layer decreased by 28.07 dBm. 2 The maximum RCS value in the range of -90° to 90° is -15.7 dBm. 2 It is worth noting that the RCS value of the PEC plate coated with the Fe1Ni1-MMO / NF absorbing layer decreased by 30.47 dBm. 2 The maximum RCS value in the range of -90° to 90° is -16.5 dBm. 2 This indicates that it has extremely high absorption and attenuation capabilities for incident radar waves.

[0050] As demonstrated by the above embodiments, the preparation process of this application is simple and cost-controllable. The FeNi-based composite metal oxide microwave absorbing material with a foamed nickel surface loaded with FeNi has a reflection loss of -68.18 dB at a thickness of 2.4 mm. This material can reduce the RCS value by 30.47 dB m², exhibiting excellent radar wave stealth potential. The FeNi-based composite metal oxide microwave absorbing material with a foamed nickel surface loaded with FeNi has broad application prospects as a novel absorber.

[0051] A second aspect of this application provides a microwave absorbing composite material, comprising: Using three-dimensional porous nickel foam as a substrate, FeNi-based composite metal oxide nanoflower structures assembled from two-dimensional nanosheets are grown in situ on the substrate surface; the phase composition of the microwave absorbing composite material varies with the molar ratio of Fe and Ni in the raw materials. The microwave absorbing composite material is prepared by a method for preparing microwave absorbing composite materials as described in any of the above embodiments. The microwave absorbing composite material is a composite of NiO and NiFe2O4 or a composite of Fe3O4 and NiO.

[0052] It is worth noting that the effects of the above-mentioned microwave absorbing composite material embodiments can be found in the effects of the above-mentioned microwave absorbing composite material preparation method embodiments, and will not be repeated here.

[0053] The above detailed embodiments further illustrate the purpose, technical solution, and beneficial effects of the embodiments of this application. It should be understood that the above are merely specific embodiments of the embodiments of this application and are not intended to limit the protection scope of the embodiments of this application. Any modifications, equivalent substitutions, improvements, etc., made on the basis of the technical solutions of the embodiments of this application should be included within the protection scope of the embodiments of this application.

Claims

1. A method for preparing a microwave absorbing composite material, characterized in that, include: The nickel foam was subjected to ultrasonic treatment in a hydrochloric acid solution. The ultrasonically treated nickel foam was sequentially ultrasonically cleaned with deionized water and anhydrous ethanol and then dried to obtain pretreated nickel foam. Ferric nitrate nonahydrate, nickel nitrate hexahydrate, polyvinylpyrrolidone and urea were dissolved in deionized water to obtain a homogeneous mixed solution. The homogeneous mixed solution and the pretreated nickel foam were placed in a hydrothermal reactor for hydrothermal reaction. After the reaction was completed, the mixture was naturally cooled to room temperature for a first heat preservation treatment to obtain an intermediate product. The intermediate product was subjected to ultrasonic cleaning and drying to obtain FeNi layered bimetallic hydroxide / nickel foam. The FeNi layered bimetallic hydroxide / nickel foam was placed in an inert atmosphere tube furnace for high-temperature calcination. After calcination, the FeNi layered bimetallic hydroxide / nickel foam was naturally cooled to room temperature for a second heat preservation treatment to obtain the FeNi-based composite metal oxide / nickel foam composite material.

2. The method for preparing a microwave absorbing composite material according to claim 1, characterized in that, The concentration of the hydrochloric acid solution is in the range of 1 mol / L to 5 mol / L, and the ultrasonic treatment time of the nickel foam in the hydrochloric acid solution is in the range of 3 min to 7 min.

3. The method for preparing a microwave absorbing composite material according to claim 1, characterized in that, The ultrasonically treated nickel foam is then ultrasonically cleaned sequentially with deionized water and anhydrous ethanol for 20 minutes each.

4. The method for preparing a microwave absorbing composite material according to claim 1, characterized in that, Fe in the homogeneous mixed solution 3+ with Ni 2+ The total molar amount is in the range of 1 mmol to 3 mmol, Fe 3+ with Ni 2+ The molar ratio is in the range of 1:3 to 3:

1.

5. The method for preparing a microwave absorbing composite material according to claim 1, characterized in that, The homogeneous mixed solution contains 10 mmol of urea, 0.1 g of polyvinylpyrrolidone, and 70 mL of deionized water.

6. The method for preparing a microwave absorbing composite material according to claim 1, characterized in that, The temperature of the hydrothermal reaction is in the range of 100°C to 140°C, and the first heat preservation treatment lasts for 12 hours.

7. The method for preparing a microwave absorbing composite material according to claim 1, characterized in that, The steps of ultrasonic cleaning and drying the intermediate product include: The intermediate product was ultrasonically cleaned twice with deionized water and anhydrous ethanol and then dried. The drying temperature was 60°C and the drying time was between 10 and 14 hours.

8. The method for preparing a microwave absorbing composite material according to claim 1, characterized in that, The inert atmosphere is argon, the temperature of the high-temperature calcination treatment is in the range of 400°C to 600°C, the heating rate is 5°C / min, and the time of the second heat preservation treatment is in the range of 1h to 3h.

9. A microwave absorbing composite material, characterized in that, include: Using three-dimensional porous nickel foam as a substrate, FeNi-based composite metal oxide nanoflower structures assembled from two-dimensional nanosheets are grown in situ on the substrate surface; the phase composition of the microwave absorbing composite material varies with the molar ratio of Fe and Ni in the raw materials. The microwave absorbing composite material is prepared by a method for preparing a microwave absorbing composite material according to any one of claims 1 to 8.

10. The microwave absorbing composite material according to claim 1, characterized in that, The microwave absorbing composite material is a composite of NiO and NiFe2O4 or a composite of Fe3O4 and NiO.

Images