A magnetic medium synergistic FeOx@SiO2@NC microsphere electromagnetic wave absorbing material, a preparation method and application thereof

Abstract

This invention relates to a magnetically synergistic FeOx@SiO2@NC microsphere electromagnetic wave absorbing material, its preparation method, and its applications, relating to the field of electromagnetic wave absorbing composite materials. The magnetically synergistic FeOx@SiO2@NC microsphere electromagnetic wave absorbing material... x The SiO2@NC microsphere electromagnetic wave absorbing material is a microsphere structure consisting of a core layer, a middle layer, and a shell layer, with heterogeneous interfaces formed at the interfaces between adjacent layers. The core layer is a microsphere core layer composed of a mixture of FeO and Fe3O4 phases; the middle layer is a SiO2 layer; and the shell layer is a nitrogen-doped carbon layer, denoted as the NC layer. This magnetically-coordinated FeO... x @SiO2@NC microsphere electromagnetic wave absorbing materials comprehensively improve the overall absorption performance and environmental adaptability of absorbing materials by combining the advantages of interface polarization loss, magnetic-dielectric synergistic loss and corrosion resistance. For example, with a matching thickness of 2.0 mm, the effective absorption bandwidth can reach 5.91 GHz, the frequency range is 12.09-18.00 GHz, and the minimum reflection loss is as low as -43.02 dB.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic wave absorbing composite materials, and in particular to a magnetically synergistic FeOx@SiO2@NC microsphere electromagnetic wave absorbing material, its preparation method, and its application. Background Technology

[0002] As high-end equipment in aerospace, electronics, and power industries upgrade towards high speed, high temperature, and lightweight, the demand for electromagnetic protection under complex operating conditions is becoming increasingly urgent. Traditional metal-based absorbing materials have excellent magnetic loss, but they are dense, have poor oxidation resistance, and are prone to the skin effect; single iron oxide magnetic materials have insufficient dielectric properties, impedance mismatch, and weak corrosion resistance; pure carbon-based materials, although low in density, have a narrow absorption bandwidth due to the lack of a magnetic loss mechanism, all of which are insufficient to meet the requirements of complex operating conditions. Therefore, the development of composite materials that combine magnetic-dielectric synergistic loss, broadband absorption, corrosion resistance, and structural stability has become a core research direction in the field of electromagnetic wave absorption.

[0003] Currently, the design of core-shell structures in composite materials can utilize precise magnetic phase composites to create heterogeneous interfaces that enhance polarization loss and regulate the balance of magnetic parameters. However, existing core-shell materials still suffer from problems such as loose interfacial bonding, insufficient heterogeneous interfaces, lack of functional buffer layers, poor corrosion resistance, and inadequate synergistic regulation of magnetic phases. These issues make it difficult to achieve broadband strong absorption at thin thicknesses, necessitating improvements. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a magnetically synergistic FeOx@SiO2@NC microsphere electromagnetic wave absorbing material, its preparation method, and its application. By combining the multiple advantages of interface polarization loss, magnetically synergistic loss, and corrosion resistance, the overall absorption performance and environmental adaptability of the absorbing material are comprehensively improved.

[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: A magnetically synergistic FeO x The @SiO2@NC microsphere electromagnetic wave absorbing material is a microsphere structure consisting of a core layer, a middle layer, and a shell layer, with a heterojunction interface formed at the interface between adjacent layers. The core layer is a microsphere core layer composed of a mixture of FeO and Fe3O4 phases, the middle layer is a SiO2 layer, and the shell layer is a nitrogen-doped carbon layer, denoted as the NC layer.

[0006] Furthermore, the diameter of the microsphere structure is 300-500 nm.

[0007] This application also provides magnetically synergistic FeO. x The preparation method of @SiO2@NC microsphere electromagnetic wave absorbing material includes the following steps: (1) Fe3O4 nanospheres were prepared by hydrothermal method and denoted as product A; (2) Add product A to a mixed solution of ethanol and deionized water, sonicate until uniformly dispersed, then add ammonia and tetraethyl silicate, stir thoroughly at room temperature, centrifuge and filter to obtain product B with SiO2 coated on the surface of Fe3O4 nanospheres. (3) Product B and dopamine hydrochloride were uniformly dispersed in Tris buffer solution, stirred thoroughly at room temperature and filtered under reduced pressure to obtain product C, which was coated with SiO2 layer and PDA layer in sequence on the outside of Fe3O4 nanospheres, wherein the PDA layer was a dopamine layer. (4) Place product C in a tube furnace filled with argon gas for high-temperature calcination. Calcination conditions: heat to 600-800 ℃ at a heating rate of 5 ℃ / min, and hold for 0.5-1.5h to obtain the product.

[0008] Further, step (1) specifically involves: using anhydrous ferric chloride as the iron source, sodium acetate and polyvinylpyrrolidone as solutes, and ethylene glycol as the solvent, mixing thoroughly in proportion, then transferring to a high-pressure reactor for reaction, followed by centrifugation, filtration, and washing with ethanol multiple times to obtain product A.

[0009] Furthermore, in step (1), the mass ratio of anhydrous ferric chloride, polyvinylpyrrolidone, and sodium acetate is 2:1:1, and the volume of ethylene glycol is 55-65 ml based on 4 g of anhydrous ferric chloride; the reaction conditions in the high-pressure reactor are: reaction at 180-200℃ for 8-10 h.

[0010] Furthermore, in step (2), the volume ratio of ammonia, tetraethyl silicate, ethanol and deionized water is 1:(0.04-0.15):40:10; based on 0.5g of product A, the total volume of ammonia, tetraethyl silicate, ethanol and deionized water used is 408.3-409.2ml.

[0011] Furthermore, the molar concentration of the Tris buffer solution is 0.1 mol / L. The specific preparation method is as follows: first, add a certain amount of tris(hydroxymethyl)aminomethane to deionized water to dissolve it, and then adjust the pH of the solution to 8.5 with 1 mol / L dilute hydrochloric acid.

[0012] Further, in step (3), 0.4-0.6 g of product B and 0.4-0.8 g of dopamine hydrochloride are uniformly dispersed in 250 ml of Tris buffer.

[0013] Furthermore, in step (2), the ultrasonic time is 1-2 hours and the stirring time is 3-5 hours; in step (3), the mechanical stirring is performed at room temperature for 10-14 hours.

[0014] This application is a magnetically coupled FeO xApplication of SiO2@NC microsphere electromagnetic wave absorbing materials in electromagnetic wave absorption.

[0015] The present invention employs the above-described structure and has the following advantages: 1. The electromagnetic wave absorbing material of the present invention, consisting of a magnetically synergistic three-layer core-shell microsphere, FeO x The multi-level, layered core-shell structure formed by the core, SiO2 intermediate layer, and NC outer layer enables FeO to... x The outer FeO core forms rich and tightly bonded heterojunctions with SiO2 and NC. These heterojunctions can effectively induce strong interfacial polarization under the action of an electromagnetic field. The polarization relaxation process can efficiently dissipate electromagnetic wave energy, thereby significantly improving electromagnetic wave absorption performance. The outer NC, as an excellent dielectric material, has high dielectric loss characteristics, which can further dissipate electromagnetic energy through conductivity loss and defect-induced polarization. x As a magnetic component, it induces magnetic moment reversal and resonance in alternating electromagnetic fields, generating a significant magnetic loss effect. Through the synergistic effect of dielectric loss and magnetic loss, a multi-faceted synergistic energy dissipation mechanism is constructed, greatly enhancing the material's ability to attenuate electromagnetic waves. The intermediate SiO2 buffer layer not only optimizes the impedance matching characteristics of the material and reduces the reflection of electromagnetic waves on the material surface, but also forms a dense protective barrier, significantly improving the material's corrosion resistance and preventing the core absorbing component from degrading due to environmental erosion. At the same time, the multi-level core-shell structure gives the material a reasonable microstructure and size distribution, further optimizing the electromagnetic parameter matching. Through the superposition of multiple advantages of interface polarization loss, magnetic-dielectric synergistic loss, and corrosion protection, the overall absorbing performance and environmental adaptability of the absorbing material are comprehensively improved.

[0016] 2. With a matching thickness of 2.0 mm, the microsphere electromagnetic wave absorbing material has an effective absorption bandwidth of up to 5.91 GHz, a frequency range of 12.09-18.00 GHz (wide frequency range with wide applicability and high application value), and a minimum reflection loss as low as -43.02 dB. Attached Figure Description

[0017] Figure 1 Optical image of FeOx@SiO2@NC microspheres from Example 1; Figure 2 FeO from Example 1 x Scanning electron microscope image of @SiO2@NC microspheres; Figure 3 FeO from Example 1 x X-ray diffraction pattern of @SiO2@NC microspheres; Figure 4 FeO from Example 1 x Transmission electron microscopy morphology and elemental distribution of @SiO2@NC microspheres; Figure 5 FeO from Example 1 x Transmission electron microscopy morphology and lattice fringes of @SiO2@NC microspheres; Figure 6 FeO from Example 1 x @SiO2@NC and FeO x Curves showing the dielectric constant and dielectric tangent loss angle variation of SiO2; Figure 7 FeO from Example 1 x @SiO2@NC and FeO x Curves showing the variation of magnetic permeability and magnetic permeability tangent loss angle of SiO2; Figure 8 FeO from Example 1 x @SiO2@NC and FeO x Minimum reflection loss diagram of @SiO2; Figure 9 FeO from Example 1 x @SiO2@NC and FeO x @SiO2 effective absorption bandwidth diagram; Figure 10 FeO (as in Example 4) x Scanning electron microscope image of @SiO2@NC microspheres; Figure 11 FeO (as in Example 4) x Transmission electron microscopy morphology and elemental distribution of @SiO2@NC microspheres; Figure 12 FeO (as in Example 4) x Curves showing the dielectric constant, dielectric tangent loss, permeability, and permeability tangent loss angle of @SiO2@NC microspheres; Figure 13 FeO (as in Example 4) x Minimum reflection loss diagram and effective absorption bandwidth diagram of @SiO2@NC microspheres. Detailed Implementation

[0018] To clearly illustrate the technical features of this solution, the invention will be described in detail below through specific implementation methods and in conjunction with the accompanying drawings.

[0019] 1. Preparation of the electromagnetic wave absorbing material of the magnetic-dielectric synergistic three-layer core-shell microspheres of this application.

[0020] 1.1 Preparation of Samples in Example 1

[0021] (1) Dissolve 4.0 g of anhydrous ferric chloride, 4.0 g of polyvinylpyrrolidone and 2.0 g of sodium acetate in 60 ml of ethylene glycol. After stirring for 1 h to form a homogeneous solution, transfer it to a high-pressure reactor lined with polytetrafluoroethylene and react at 200 °C for 8 h. Collect Fe3O4 nanoparticles by centrifugation and wash them with ethanol multiple times to obtain product A. (2) 0.5 g of product A was dispersed in a mixed solution consisting of 320.0 ml ethanol and 80.0 ml deionized water and ultrasonically treated for 1 h to achieve uniform dispersion of nanoparticles; then 8.0 ml ammonia and 1.2 ml tetraethyl silicate were added to the mixed solution and mechanically stirred at room temperature for 4 h. The black precipitate Fe3O4@SiO2 was collected by centrifugation to obtain product B.

[0022] (3) First, 0.605 g of tris(hydroxymethyl)aminomethane was added to 50 ml of deionized water to dissolve it. Then, the pH was adjusted to 8.5 with 1 mol / L dilute hydrochloric acid to prepare a 0.1 mol / L Tris buffer solution. Subsequently, 0.5 g of product B and 0.4 g of dopamine hydrochloride were added to the solution and stirred for 12 h. Finally, under reduced pressure, the Fe3O4@SiO2@PDA composite material was collected by filtration to obtain product C, in which the PDA was the dopamine layer. (4) Place product C in a tube furnace filled with argon gas, raise the temperature to 600-800℃ at a rate of 5℃ / min, and hold for 1.0 h to obtain the electromagnetic wave absorbing material FeO with magnetic-medium synergistic three-layer core-shell microspheres. x @SiO2@NC.

[0023] 1.2 Sample Preparation in Example 2

[0024] (1) Dissolve 4.0 g of anhydrous ferric chloride, 4.0 g of polyvinylpyrrolidone and 2.0 g of sodium acetate in 60 ml of ethylene glycol. After stirring for 1 h to form a homogeneous solution, transfer it to a high-pressure reactor lined with polytetrafluoroethylene and react at 200 °C for 8 h. Collect Fe3O4 nanoparticles by centrifugation and wash them with ethanol multiple times to obtain product A. (2) 0.5 g of product A was dispersed in a mixed solution consisting of 320.0 ml of ethanol and 80.0 ml of deionized water and sonicated for 1 h to achieve uniform dispersion of nanoparticles; then 8.0 ml of ammonia and 0.3 ml of tetraethyl silicate were added to the mixed solution and mechanically stirred at room temperature for 4 h. The black precipitate Fe3O4@SiO2 was collected by centrifugation to obtain product B. (3) First, 0.605 g of tris(hydroxymethyl)aminomethane was added to 50 ml of deionized water to dissolve it. Then, the pH was adjusted to 8.5 with 1 mol / L dilute hydrochloric acid to prepare a 0.1 mol / L Tris buffer solution. Subsequently, 0.5 g of product B and 0.8 g of dopamine hydrochloride were added to the solution and stirred for 12 h. Finally, under reduced pressure, the Fe3O4@SiO2@PDA composite material was collected by filtration to obtain product C. (4) Place product C in a tube furnace filled with argon gas, raise the temperature to 600-800 ℃ at a rate of 5 ℃ / min, and hold for 1.0 h to obtain the electromagnetic wave absorbing material FeO with magnetic-medium synergistic three-layer core-shell microspheres. x @SiO2@NC.

[0025] 1.3 Preparation of Samples in Example 3

[0026] (1) Dissolve 4.0 g of anhydrous ferric chloride, 4.0 g of polyvinylpyrrolidone and 2.0 g of sodium acetate in 60 ml of ethylene glycol. After stirring for 1 h to form a homogeneous solution, transfer it to a high-pressure reactor lined with polytetrafluoroethylene and react at 200 °C for 8 h. Collect Fe3O4 nanoparticles by centrifugation and wash them with ethanol multiple times to obtain product A. (2) 0.5 g of product A was dispersed in a mixed solution consisting of 320.0 ml of ethanol and 80.0 ml of deionized water and sonicated for 1 h to achieve uniform dispersion of nanoparticles; then 8.0 ml of ammonia and 0.5 ml of tetraethyl silicate were added to the mixed solution and mechanically stirred at room temperature for 4 h. The black precipitate Fe3O4@SiO2 was collected by centrifugation to obtain product B. (3) First, 0.605 g of tris(hydroxymethyl)aminomethane was added to 50 ml of deionized water to dissolve it. Then, the pH was adjusted to 8.5 with 1 mol / L dilute hydrochloric acid to prepare a 0.1 mol / L Tris buffer solution. Subsequently, 0.5 g of product B and 0.6 g of dopamine hydrochloride were added to the solution and stirred for 12 h. Finally, under reduced pressure, the Fe3O4@SiO2@PDA composite material was collected by filtration to obtain product C. (4) Place product C in a tube furnace filled with argon gas, raise the temperature to 600-800 ℃ at a rate of 5 ℃ / min, and hold for 1.0 h to obtain the electromagnetic wave absorbing material FeO with magnetic-medium synergistic three-layer core-shell microspheres. x @SiO2@NC.

[0027] 1.4 Preparation of Samples in Example 4

[0028] (1) Dissolve 4.0 g of anhydrous ferric chloride, 4.0 g of polyvinylpyrrolidone and 2.0 g of sodium acetate in 60 ml of ethylene glycol. After stirring for 1 h to form a homogeneous solution, transfer it to a high-pressure reactor lined with polytetrafluoroethylene and react at 200 °C for 8 h. Collect Fe3O4 nanoparticles by centrifugation and wash them with ethanol multiple times to obtain product A. (2) 0.5 g of product A was dispersed in a mixed solution consisting of 320.0 ml of ethanol and 80.0 ml of deionized water, and sonicated for 1 h to achieve uniform dispersion of nanoparticles; then 8.0 ml of ammonia and 0.7 ml of tetraethyl silicate were added to the mixed solution, and the mixture was mechanically stirred at room temperature for 4 h. The black precipitate Fe3O4@SiO2 was collected by centrifugation to obtain product B. (3) First, 0.605 g of tris(hydroxymethyl)aminomethane was added to 50 ml of deionized water to dissolve it. Then, the pH was adjusted to 8.5 with 1 mol / L dilute hydrochloric acid to prepare a 0.1 mol / L Tris buffer solution. Subsequently, 0.5 g of product B and 0.6 g of dopamine hydrochloride were added to the solution and stirred for 12 h. Finally, under reduced pressure, the Fe3O4@SiO2@PDA composite material was collected by filtration to obtain product C. (4) Place product C in a tube furnace filled with argon gas, raise the temperature to 600-800 ℃ at a rate of 5 ℃ / min, and hold for 1.0 h to obtain the electromagnetic wave absorbing material FeO with magnetic-medium synergistic three-layer core-shell microspheres. x @SiO2@NC.

[0029] 1.5 Preparation of Samples in Example 5

[0030] (1) Dissolve 4.0 g of anhydrous ferric chloride, 4.0 g of polyvinylpyrrolidone and 2.0 g of sodium acetate in 60 ml of ethylene glycol. After stirring for 1 h to form a homogeneous solution, transfer it to a high-pressure reactor lined with polytetrafluoroethylene and react at 200 °C for 8 h. Collect Fe3O4 nanoparticles by centrifugation and wash them with ethanol multiple times to obtain product A. (2) 0.5 g of product A was dispersed in a mixed solution consisting of 320.0 ml of ethanol and 80.0 ml of deionized water and sonicated for 1 h to achieve uniform dispersion of nanoparticles; then 8.0 ml of ammonia and 0.9 ml of tetraethyl silicate were added to the mixed solution and mechanically stirred at room temperature for 4 h. The black precipitate Fe3O4@SiO2 was collected by centrifugation to obtain product B. (3) First, 0.605 g of tris(hydroxymethyl)aminomethane was added to 50 ml of deionized water to dissolve it. Then, the pH was adjusted to 8.5 with 1 mol / L dilute hydrochloric acid to prepare a 0.1 mol / L Tris buffer solution. Subsequently, 0.5 g of product B and 0.5 g of dopamine hydrochloride were added to the solution and stirred for 12 h. Finally, under reduced pressure, the Fe3O4@SiO2@PDA composite material was collected by filtration to obtain product C. (4) Place product C in a tube furnace filled with argon gas, raise the temperature to 600-800 ℃ at a rate of 5 ℃ / min, and hold for 1.0 h to obtain the electromagnetic wave absorbing material FeO with magnetic-medium synergistic three-layer core-shell microspheres. x @SiO2@NC.

[0031] 2. Preparation of comparative samples

[0032] Preparation method: First, product B was obtained through steps (1) and (2) of Example 1. Then, it was heated to 600-800 ℃ at a heating rate of 5 ℃ / min and held at that temperature for 1.0 h to obtain the control sample FeO. x @SiO2 composite material.

[0033] 3. Characterization and Results Analysis

[0034] The FeOx@SiO2@NC composite material prepared in Example 1 and the FeO prepared in Example 2 were compared. x The microstructure and properties of the @SiO2 comparative composite material were characterized.

[0035] Figure 1 Optical images of the FeOx@SiO2@NC microspheres in Example 1. (From...) Figure 1 It can be observed that the magnetically-mediated three-layered core-shell microspheres are black in appearance.

[0036] Figure 2 FeO in Example 1 x Scanning electron microscope image of SiO2@NC microspheres. (Source: [Insert image here]) Figure 2 As can be seen in (a)-(c), all prepared samples exhibit a regular spherical morphology. Among them, Figure 2 (b) Some microspheres showed shell damage, and a distinct layered structure was clearly observed in the damaged areas, with each layer tightly bonded together, confirming the successful construction of the layered structure. In addition, the surface of the microspheres exhibited certain roughness, which is attributed to the process of carbonization of dopamine hydrochloride to form nitrogen-doped carbon.

[0037] Figure 3 FeO in Example 1 x X-ray diffraction pattern of @SiO2@NC microspheres. Figure 3Characteristic diffraction peaks of FeO (PDF#06-0615), Fe3O4 (PDF#99-0073), and Fe2SiO4 (PDF#99-0049) were clearly observed in the sample. The reason for this is that during the heat treatment process, some Fe3O4 cores can undergo interfacial reactions with the SiO2 interlayer to generate Fe2SiO4 and FeO phases, which also indirectly proves that FeO... X There is a strong interfacial bonding between the SiO2 layer and the graphene. The broadened diffuse diffraction bulge at 21.2° is attributed to the characteristic peak of graphitized carbon, indicating that the outermost dopamine hydrochloride layer has been fully carbonized. In addition, no characteristic diffraction peaks of amorphous SiO2 were observed in the spectrum, which is attributed to the amorphous structure of SiO2.

[0038] Figure 4 FeO in Example 1 x Transmission electron microscopy (TEM) images and elemental distribution maps of @SiO2@NC microspheres (to more intuitively determine the structure and composition of the sample). The elemental distribution map is generated by controlling the electron beam to scan point-by-point in a selected area using a TEM, with EDS acquiring the characteristic signals at each point in real time. The software then converts the signal intensity into a color image to display the distribution of elements in the sample. Figure 4 The transmission electron microscopy (TEM) image in (a) clearly shows a three-layered core-shell structure. Figure 4 The EDS elemental distributions in (b)-(f) reveal that the interior is composed of irregular Fe3O4 and FeO nanoparticles, while the middle and outermost layers are composed of SiO2 and NC, respectively, with both shell layers having a thickness of approximately 30 nm. These results demonstrate a high degree of agreement between the elemental distribution of the microspheres and the core-shell structure distribution in the transmission morphology images.

[0039] Figure 5 FeO in Example 1 x Transmission electron microscopy (TEM) images and lattice fringes of @SiO2@NC microspheres. Figure 5 (a) clearly shows a three-layered core-shell structure. Figure 5 A distinct lattice is clearly visible in (bd), with interplanar spacings of 0.296 nm and 0.264 nm corresponding to the (220) plane of Fe3O4 (see [reference]). Figure 5 b) and the (111) crystal plane of FeO (see Figure 5 c), the crystal plane with an interplanar spacing of 0.237 nm belongs to the (222) crystal plane of Fe2SiO4 (see Figure 5 d), combined Figure 3 The X-ray diffraction pattern can prove that the composite material FeO x Successful synthesis of @SiO2@NC.

[0040] Figure 6FeO in Example 1 x @SiO2@NC and FeO x The dielectric constant and dielectric tangent loss angle of SiO2 are shown in Figure 6(a). Figure 6(a) shows the real part curves of the dielectric constants of the two materials. Figure 6 (b) shows the imaginary part curves of the dielectric constants of the two materials, and Figure 6(c) shows the corresponding dielectric loss tangent curves. FeO x The real and imaginary parts of the dielectric constant of @SiO2@NC are in the ranges of 8.0-16.0 and 3.0-9.0, respectively, and the decay rate with increasing frequency is gradual, indicating that this material has excellent dispersion characteristics, which is beneficial for optimizing impedance matching characteristics. Its dielectric loss tangent is greater than 0.3, indicating strong dielectric loss capability, mainly attributed to multiple interface polarization and the conductivity loss introduced by the carbon shell. FeO x The real and imaginary parts of the dielectric constant of SiO2 are only 5.0-10.5 and 1.2-3.8, respectively, compared to FeO. x Both SiO2 and NC showed significant decreases. The reason for this is that the lack of carbon layers weakens the material's conductivity and polarization loss capabilities; at the same time, its dielectric loss tangent in the high-frequency range is less than 0.3, further confirming that its electromagnetic wave loss performance has declined.

[0041] Figure 7 FeO in Example 1 x @SiO2@NC and FeO x The permeability and permeability tangent loss angle of SiO2. Figure 7 (a) is the curve showing the real part of the permeability. Figure 7 (b) is the imaginary part curve of the permeability. Figure 7 (c) shows the variation curve of the permeability tangent loss angle. As the test frequency increases, both the real and imaginary parts of the permeability of the two materials exhibit significant fluctuations, and the permeability tangent loss angle also fluctuates greatly. This indicates that the material possesses excellent electromagnetic wave magnetic loss performance, and its magnetic loss mechanism mainly originates from the resonance loss and eddy current loss generated by the core Fe3O4 and FeO.

[0042] Figure 8 In the diagram, (a) and (b) are FeO, respectively. x @SiO2@NC and FeO x Minimum reflection loss diagram for @SiO2. Figure 9 In the diagram, (a) and (b) are FeO, respectively. x @SiO2@NC and FeO x The effective absorption bandwidth diagram of @SiO2. The results show that FeO xThe minimum reflection loss of @SiO2@NC is as low as -43.02 dB; with a matching thickness of 2.0 mm, the effective electromagnetic wave absorption bandwidth reaches 5.91 GHz, corresponding to a frequency range of 12.09-18.00 GHz. In comparison, FeO... x The SiO2 material exhibits a minimum reflection loss of only -38.70 dB and an effective absorption bandwidth of 4.63 GHz with a matching thickness of 2.2 mm, ranging from 12.87 to 17.50 GHz. These results clearly demonstrate that carbon layer coating modification can significantly impart and enhance the electromagnetic wave absorption performance of the material, which is of great value for broadening the practical application scenarios and promoting the engineering application of this type of absorbing material.

[0043] Figure 10 FeO in Example 4 x Scanning electron microscope image of SiO2@NC microspheres. (Source: [Insert image here]) Figure 10 As shown in (a) and (b), all prepared samples exhibit a regular spherical morphology. Some microspheres showed adhesion, which is due to the increased amount of tetraethyl orthosilicate, which led to a thicker SiO2 layer and thus an increased probability of adhesion between the microspheres.

[0044] Figure 11 FeO in Example 4 x Transmission electron microscopy (TEM) images and elemental distribution maps of @SiO2@NC microspheres. Figure 11 The transmission electron microscopy (TEM) image in (a) clearly shows a three-layered core-shell structure. Figure 11 The EDS elemental distributions in (b) to (f) show that the interior is composed of irregular Fe3O4 and FeO nanoparticles, while the middle and outermost layers are composed of SiO2 and NC, respectively. The thickness of the SiO2 layer reaches 50 nm, which is significantly increased compared to Example 1. This indicates that adjusting the amount of Si source can effectively adjust the thickness of the shell, and the method has good universality.

[0045] Figure 12 FeO in Example 4 x The dielectric constant, dielectric loss tangent, permeability, and permeability loss tangent of @SiO2@NC are shown in Figure 12(a). Figure 12(b) shows the real and imaginary parts of the dielectric constant, and Figure 12(a) shows the corresponding dielectric loss tangent curve. FeO xThe real and imaginary parts of the dielectric constant of @SiO2@NC are in the ranges of 5.5-13.8 and 2.1-8.0, respectively, and the decay rate with increasing frequency is gradual, indicating that the material has excellent dispersion characteristics, which is beneficial for optimizing impedance matching characteristics. Its dielectric loss tangent is greater than 0.3, indicating strong dielectric loss capability, mainly attributed to multiple interface polarization effects and the conductivity loss introduced by the carbon shell. However, its values ​​are significantly lower than those in Example 1. The reason for this is that the increase in the SiO2 layer and the decrease in the carbon layer will reduce the dielectric loss performance of the material to a certain extent. Figure 12 (c) shows the spectrum curves of the real and imaginary parts of the permeability. Figure 12 (d) shows the variation curve of the permeability tangent loss angle. As the test frequency increases, both the real and imaginary parts of the permeability of the two materials exhibit significant fluctuations, and the permeability tangent loss angle also fluctuates greatly. This indicates that the material possesses excellent electromagnetic wave magnetic loss performance, and its magnetic loss mechanism mainly originates from the resonance loss and eddy current loss generated by the core Fe3O4 and FeO.

[0046] Figure 13 In the figures, (a) and (b) are FeO samples from Example 4. x Minimum reflection loss and effective absorption bandwidth plot of @SiO2@NC. The results show that FeO x The minimum reflection loss of @SiO2@NC is as low as -45.32 dB; with a matching thickness of 2.2 mm, the effective electromagnetic wave absorption bandwidth is as high as 5.53 GHz, corresponding to a frequency range of 12.47-18.00 GHz. Comparative Example 1 and FeO x The performance of SiO2 demonstrates that changes in SiO2 and the carbon layer can adjust the electromagnetic wave absorption performance of the material in real time, enabling it to meet different usage environments. This is of great value for broadening the practical application scenarios of this type of microwave absorbing material and promoting its engineering applications.

[0047] The specific embodiments described above should not be construed as limiting the scope of protection of this invention. Any alternative modifications or variations made to the embodiments of this invention by those skilled in the art will fall within the scope of protection of this invention. All aspects not detailed in this invention are well-known to those skilled in the art.

Claims

1. A magnetically synergistic FeO x @SiO2@NC microsphere electromagnetic wave absorbing material, characterized in that... It is a microsphere structure consisting of a core layer, a middle layer and a shell layer, with a heterogeneous interface formed at the interface between adjacent layers; The core layer is a microsphere core layer composed of a mixture of FeO and Fe3O4 phases, the middle layer is a SiO2 layer, and the shell layer is a nitrogen-doped carbon layer, denoted as the NC layer.

2. The magnetically-coordinated FeO according to claim 1 x @SiO2@NC microsphere electromagnetic wave absorbing material, characterized in that... The diameter of the microsphere structure is 300-500 nm.

3. A magnetically cooperating FeO as described in claim 1 or 2 x The method for preparing SiO2@NC microsphere electromagnetic wave absorbing materials is characterized by... Includes the following steps: (1) Fe3O4 nanospheres were prepared by hydrothermal method and denoted as product A; (2) Add product A to a mixed solution of ethanol and deionized water, sonicate until uniformly dispersed, then add ammonia and tetraethyl silicate, stir thoroughly at room temperature, centrifuge and filter to obtain product B with SiO2 coated on the surface of Fe3O4 nanospheres. (3) Product B and dopamine hydrochloride were uniformly dispersed in Tris buffer solution, stirred thoroughly at room temperature and filtered under reduced pressure to obtain product C, which was coated with SiO2 layer and PDA layer in sequence on the outside of Fe3O4 nanospheres, wherein the PDA layer was a dopamine layer. (4) Place product C in a sintering device with argon gas for high-temperature calcination. Calcination conditions: heat up to 600-800 ℃ at a heating rate of 5 ℃ / min, and hold for 0.5-1.5h to obtain the product.

4. The magnetically synergistic FeO as described in claim 3 x The method for preparing SiO2@NC microsphere electromagnetic wave absorbing materials is characterized by... Step (1) is as follows: anhydrous ferric chloride is used as the iron source, sodium acetate and polyvinylpyrrolidone are used as solutes, and ethylene glycol is used as the solvent. The mixture is stirred and mixed thoroughly in proportion, then transferred to a high-pressure reactor for reaction. After centrifugation and filtration, the product A is obtained by washing with ethanol multiple times.

5. The magnetically-mediated FeO according to claim 4 x The method for preparing SiO2@NC microsphere electromagnetic wave absorbing materials is characterized by... In step (1), the mass ratio of anhydrous ferric chloride, polyvinylpyrrolidone, and sodium acetate is 2:1:

1. Based on 4g of anhydrous ferric chloride, the volume of ethylene glycol is 55-65ml. The reaction conditions in the high-pressure reactor are: reaction at 180-200℃ for 8-10h.

6. The magnetically-mediated FeO according to claim 3 x The method for preparing SiO2@NC microsphere electromagnetic wave absorbing materials is characterized by... In step (2), the volume ratio of ammonia, tetraethyl silicate, ethanol and deionized water is 1:(0.04-0.15):40:10; Based on 0.5g of product A, the total volume of ammonia, tetraethyl silicate, ethanol and deionized water used is 408.3-409.2ml.

7. The magnetically-mediated FeO according to claim 3 x The method for preparing SiO2@NC microsphere electromagnetic wave absorbing materials is characterized by... The molar concentration of Tris buffer is 0.1 mol / L. The specific preparation method is as follows: first, add a certain amount of tris(hydroxymethyl)aminomethane to deionized water to dissolve it, and then adjust the pH of the solution to 8.5 with 1 mol / L dilute hydrochloric acid.

8. The magnetically-mediated FeO according to claim 3 x The method for preparing SiO2@NC microsphere electromagnetic wave absorbing materials is characterized by... In step (3), 0.4-0.6 g of product B and 0.4-0.8 g of dopamine hydrochloride are uniformly dispersed in 250 ml of Tris buffer.

9. The magnetically co-located FeO as described in claim 3 x The method for preparing SiO2@NC microsphere electromagnetic wave absorbing materials is characterized by... In step (2), the ultrasonic time is 1-2 hours and the stirring time is 3-5 hours; in step (3), the mechanical stirring is carried out at room temperature for 10-14 hours.

10. A magnetically cooperating FeO as described in claim 1 or 2 x Application of SiO2@NC microsphere electromagnetic wave absorbing materials in electromagnetic wave absorption.

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