Composite wave-absorbing material and preparation method thereof

Abstract

The invention provides a composite wave-absorbing material and a preparation method thereof, and belongs to the technical field of wave-absorbing materials. The preparation method comprises the following steps: mixing a ferric salt solution and an ethylenediamine tetraacetic acid solution to obtain a mixed solution 1; mixing the ferrous salt solution and the ethylenediamine tetraacetic acid solution to obtain a mixed solution 2; and finally, mixing the mixed solution 1 and the mixed solution 2, drying and sintering to obtain the composite wave-absorbing material. Fe < 3 + > / Fe < 2 + > nanoparticles are fixed on EDTA (Ethylene Diamine Tetraacetic Acid) through a simple and convenient chemical one-step method (COSM) to construct a multiphase heterojunction structure, so that the synergistic enhancement of an interface polarization effect is realized, and electromagnetic energy is promoted to be converted into heat energy. The composite wave-absorbing material can realize high reflection loss (-45 dB to-50 dB) and wide effective absorption bandwidth (3.0-3.5 GHz) under the condition of a thin layer (1.6-2.8 mm).

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wave-absorbing materials, and particularly relates to a composite wave-absorbing material and a preparation method thereof. BACKGROUND

[0002] With the popularization of 5G / 6G communication, Internet of Things, high-power radar and other technologies, the utilization rate of electromagnetic wave spectrum resources has been significantly improved (0.1-100 GHz coverage rate is over 90%), leading to the intensification of electromagnetic interference (EMI) and electromagnetic pollution problems. The intensity of electromagnetic radiation has increased by 3 orders of magnitude compared with 20 years ago, and traditional reflective shielding materials are easy to cause secondary pollution. Wave-absorbing materials are a class of materials that can attenuate electromagnetic radiation, and their core function is to reduce the reflection and scattering effects of electromagnetic waves on the target interface. Such substances have important application value in the fields of electromagnetic compatibility and stealth technology due to their unique energy conversion characteristics. The demand for stealth technology in modern warfare has driven the development of wave-absorbing materials, such as the need to reduce the radar cross section (RCS) of stealth warplanes by 10-100 times, which traditional ferrite materials cannot meet.

[0003] In summary, the research and development of electromagnetic wave absorbing materials is a strategic requirement to address electromagnetic pollution and military challenges, and is also a core driving force to promote innovation in the fields of communication, medical treatment, new energy and others. Its development needs to aim at "thin, light, wide and strong", and optimize the dielectric / magnetic loss synergy mechanism, machine learning driven design through innovative paths such as biomass derivatives to build an efficient electromagnetic protection system. However, due to the limited impedance matching performance of single-loss mechanism wave-absorbing materials, it is difficult to achieve ideal wave-absorbing effect. Therefore, researchers have developed multifunctional composite wave-absorbing materials by compounding two or more wave-absorbing materials with different loss mechanisms. Such composite materials not only retain the advantages of each component, but also optimize the impedance matching through synergistic effect, prompting more incident electromagnetic waves to enter the material interior and be effectively dissipated. This design strategy enables the composite wave-absorbing material to have comprehensive performance of "thin, light, wide and strong", meeting the development needs of modern wave-absorbing materials.

[0004] Iron-based heteroatom-doped carbon composites have become a research focus due to their unique electromagnetic wave absorption characteristics. Through the synergistic effect of iron elements and nitrogen, carbon and other heteroatoms, the wave absorption performance of the material is significantly improved. The Fe-N-C single-atom material with a reflection loss of-60 dB has been successfully developed by the Chinese Academy of Sciences. The Fe / Fe3C@N-C core-shell material with a wide frequency absorption characteristic of 5.2 GHz has been developed by Harbin Institute of Technology using MOFs derivation technology. The Fe-N / S-C composite material with light weight (density less than 0.8 g / cm³) and high absorption performance has been prepared by Northwest Industrial University using biomass raw materials. These achievements effectively improve the dielectric-magnetic synergistic loss performance of the material by precisely regulating the combination mode of iron element form (single atom or nanoparticle) and carbon matrix. In addition, the polarization loss principle of Fe-N4 active center has been clarified by in-situ XAS technology used by the American Argonne National Laboratory. The Fe@Al2O3 / C core-shell material with oxidation resistance has been successfully prepared by the Korean Sungkyunkwan University using atomic layer deposition process. The Fe-N-P-C composite material that can realize full-band absorption in the Ku band at a thickness of 1.5 mm has been developed by the German Max Planck Institute. At present, there are still three technical problems in this field: iron element is easy to oxidize, low frequency band absorption effect is poor, and preparation cost is high. Therefore, it is of great significance to research a composite wave-absorbing material and a preparation method thereof. SUMMARY

[0005] The purpose of the present application is to provide a composite wave-absorbing material and a preparation method thereof, so as to solve the problems of iron element easy to oxidize and poor absorption effect in the prior art of iron-based heteroatom-doped carbon composite wave-absorbing material.

[0006] In order to achieve the above-mentioned purpose of the application, the present application provides the following technical solutions: The present application provides a preparation method of a composite wave-absorbing material, comprising the following steps: S1: mixing a ferric salt solution and an ethylenediaminetetraacetic acid solution to obtain a mixed solution 1; S2: mixing a ferrous salt solution and an ethylenediaminetetraacetic acid solution to obtain a mixed solution 2; S3: drying and sintering the mixed solution 1 and the mixed solution 2 to obtain a composite wave-absorbing material.

[0007] Preferably, in the mixed solution 1, the molar ratio of ethylenediaminetetraacetic acid and Fe 3+ is 1-2:1-2.

[0008] Preferably, in the mixed solution 2, the molar ratio of ethylenediaminetetraacetic acid and Fe 2+ is 1-2:1-2.

[0009] Preferably, an antioxidant vitamin C is added to the ferrous salt solution.

[0010] Preferably, the ferric salt in the ferric salt solution is ferric chloride; and the ferrous salt in the ferrous salt solution is ferrous sulfate.

[0011] Preferably, the drying step comprises standing the mixed solution at room temperature until the water evaporates.

[0012] Preferably, the drying step further comprises a grinding step.

[0013] Preferably, the sintering comprises a first sintering and a second sintering.

[0014] Preferably, the first sintering is performed at a temperature of 300-700℃ for 1-3 hours; and the second sintering is performed at a temperature of 500-900℃ for 1-3 hours.

[0015] The application also provides a composite wave-absorbing material prepared by the method.

[0016] The application has the following advantages: (1) Fe 3+ / Fe 2+ nanoparticles are fixed on EDTA by a simple one-step chemical method (COSM), a multi-phase heterojunction structure is constructed, the interface polarization effect is synergistically enhanced, and electromagnetic energy is converted into heat.

[0017] (2) The controllable pyrolysis and doping regulation of the chelate precursor successfully prepare a composite material in which magnetic particles are uniformly dispersed in an N, O-doped carbon matrix. The molecular confinement effect of the chelate effectively inhibits the agglomeration of the magnetic particles, allowing them to be uniformly embedded in the carbon matrix at the nanoscale. N, O co-doping not only regulates the electronic structure of the carbon matrix, but also enhances the interface polarization effect by introducing defects and polar functional groups, thereby improving the dielectric loss ability. The excellent wave-absorbing performance of the composite wave-absorbing material is due to the magnetic-dielectric synergistic loss mechanism: the embedded magnetic particles contribute to high-frequency magnetic loss through natural resonance and eddy current loss, and the optimized particle size and distribution significantly improve the imaginary part of magnetic permeability (μ '' ). The N, O-doped carbon matrix realizes wide-band dielectric response through conductive loss, dipole polarization, and interface polarization (such as the carbon / magnetic particle interface). By adjusting the ratio of magnetic particles to the carbon matrix, the application realizes the matching of the intrinsic impedance of the composite wave-absorbing material to the free space, and the composite wave-absorbing material can achieve high reflection loss (-45 dB to -50 dB) and wide effective absorption bandwidth (3.0-3.5 GHz) under thin layer (1.6-2.8 mm) conditions. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1SEM and TEM images of the composite wave-absorbing material prepared in Examples 1~3, wherein a is the SEM image of the composite wave-absorbing material of Example 1, b is the SEM image of the composite wave-absorbing material of Example 2, c is the SEM image of the composite wave-absorbing material of Example 3, e is the TEM image of the composite wave-absorbing material of Example 1, f is the TEM image of the composite wave-absorbing material of Example 2, and g is the TEM image of the composite wave-absorbing material of Example 3; Figure 2 2D reflection loss (RL) curve graph of the composite wave-absorbing material of Example 1 having a thickness of 1.0~5.5 mm in a frequency range of 2.0~18.0 GHz; Figure 3 3D reflection loss (RL) curve graph of the composite wave-absorbing material of Example 1 having a thickness of 1.0~5.5 mm in a frequency range of 2.0~18.0 GHz; Figure 4 2D reflection loss (RL) curve graph of the composite wave-absorbing material of Example 2 having a thickness of 1.0~5.5 mm in a frequency range of 2.0~18.0 GHz; Figure 5 3D reflection loss (RL) curve graph of the composite wave-absorbing material of Example 2 having a thickness of 1.0~5.5 mm in a frequency range of 2.0~18.0 GHz; Figure 6 2D reflection loss (RL) curve graph of the composite wave-absorbing material of Example 3 having a thickness of 1.0~5.5 mm in a frequency range of 2.0~18.0 GHz; Figure 7 3D reflection loss (RL) curve graph of the composite wave-absorbing material of Example 3 having a thickness of 1.0~5.5 mm in a frequency range of 2.0~18.0 GHz; Figure 8 Graphs of the real part ε ' and the imaginary part ε '' of the complex permittivity, the real part μ ' and the imaginary part μ '' of the complex permeability, the frequency-dielectric loss tangent tanε, and the frequency-magnetic loss tangent tanμ of the composite wave-absorbing materials of Examples 1~3, wherein a is the graph of the real part ε ' , b is the graph of the imaginary part ε '' , c is the graph of the frequency-dielectric loss tangent tanε, d is the graph of the real part μ ' of the complex permeability, e is the graph of the imaginary part μ '' , and f is the graph of the frequency-magnetic loss tangent tanμ. DETAILED DESCRIPTION

[0019] The present invention provides a method for preparing a composite wave-absorbing material, comprising the following steps: S1: mixing the iron salt solution and the ethylenediaminetetraacetic acid solution to obtain a mixed solution 1; S2: mixing the ferrous salt solution and the ethylenediaminetetraacetic acid solution to obtain a mixed solution 2; S3: Mixing the mixed solution 1 and the mixed solution 2, drying and sintering the mixture to obtain a composite absorbing material.

[0020] In the present invention, in the mixed solution 1, ethylenediaminetetraacetic acid and Fe 3+ The molar ratio is 1~2:1~2, preferably 1:1, 1:2, 2:1.

[0021] In the present invention, in the mixed solution 2, ethylenediaminetetraacetic acid and Fe 2+ The molar ratio is 1~2:1~2, preferably 1:1, 1:2, 2:1.

[0022] In the present invention, the antioxidant vitamin C is added to the ferrous salt solution; the amount of the antioxidant vitamin C added is preferably 0.5g. The role of vitamin C is to avoid Fe 2+ Oxidized in solution.

[0023] In the present invention, the ferric salt in the ferric salt solution is ferric chloride; and the ferrous salt in the ferrous salt solution is ferrous sulfate.

[0024] In the present invention, the specific step of drying is: leaving the mixed solution to stand at room temperature until the water evaporates.

[0025] In the present invention, the step of grinding is further included after the drying.

[0026] In the present invention, the sintering includes a first sintering and a second sintering.

[0027] In the present invention, the temperature of the first sintering is 300-700° C., and the time is 1-3 hours; the temperature of the second sintering is 500-900° C., and the time is 1-3 hours.

[0028] The present invention uses a simple chemical one-step method (COSM) to convert Fe 3+ / Fe 2+ Nanoparticles are fixed on EDTA to construct multiple heterojunction structures, achieving synergistic enhancement of the interface polarization effect and promoting the conversion of electromagnetic energy into thermal energy. Prepare two EDTA solutions, then mix the iron salt solution and the ferrous salt solution with the EDTA solution respectively, and finally mix the two mixed solutions. 3+ and Fe 2+The four oxygen atoms and two ethylenediamine groups of EDTA can form coordination bonds with iron ions to form [Fe (EDTA) complexes.

[0029] The application further provides a composite wave-absorbing material prepared by the preparation method of the composite wave-absorbing material.

[0030] The technical solutions provided by the application are described in detail below in combination with examples, but they should not be understood as limitations to the protection scope of the application.

[0031] Example 1

[0032] Two portions of 2.9224 g (0.01 mol) of ethylenediaminetetraacetic acid (EDTA) were weighed into 50 mL of distilled water respectively until completely dissolved, to obtain two portions of ethylenediaminetetraacetic acid solution; 2.702 g (0.01 mol) of iron trichloride hexahydrate was weighed into 5 mL of distilled water until completely dissolved, to obtain an iron chloride solution; 1.52 g (0.01 mol) of ferrous sulfate was weighed into 5 mL of distilled water until completely dissolved, and 0.5 g of an antioxidant (VC) was added, to obtain a ferrous sulfate solution.

[0033] The iron trichloride solution was poured into one portion of the EDTA solution and stirred thoroughly, to obtain a mixed solution 1; the ferrous sulfate solution was poured into the other portion of the EDTA solution and stirred thoroughly, to obtain a mixed solution 2. The mixed solution 1 and the mixed solution 2 were mixed uniformly, and electromagnetic stirring was performed at room temperature for 24 h until the water evaporated; if the final sample was moist, it could be placed in an oven at 35 ℃ to continue evaporating, and after complete evaporation, it was ground into a powder, placed in a tube furnace, sintered at a temperature of 300 ℃ for 2 h, and then sintered at a temperature of 500 ℃ for 2 h to obtain a composite wave-absorbing material, which is denoted as EDTA / Fe 2+ / Fe 3+ 1:1:1300℃-500℃.

[0034] Example 2

[0035] The difference from Example 1 is that the sintering temperature is different: sintering at 500 ℃ for 2 h, and then sintering at a temperature of 700 ℃ for 2 h, and the other conditions are the same, and the prepared composite wave-absorbing material is denoted as EDTA / Fe 2+ / Fe 3+ 1:1:1500℃-700℃.

[0036] Example 3

[0037] The difference from Example 1 is that the sintering temperature is different: sintering at 700℃ for 2h, and then sintering at 900℃ for 2h, and the other conditions are the same, and the prepared composite wave-absorbing material is denoted as EDTA / Fe 2+ / Fe 3+ 1:1:1700℃-900℃.

[0038] Field emission scanning electron microscopy (FESEM, ZEISS Gemini SEM500) and transmission electron microscopy (TEM JEOL) were used to characterize the surface morphology and elemental composition. X-ray powder diffraction (XRD, LabXRD-6100, CuKa, scanning rate: 5°·min -1 ) and Raman spectroscopy (Renishaw, InVia) were used to analyze the crystal structure and chemical composition of the samples. X-ray photoelectron spectroscopy (XPS, Escalab250 Xi, ThermmoFisher Scientifc) was used to determine the valence states of C, N, and Fe. Vibrating sample magnetometry (VSM, Lakeshore 7404) was used to measure the magnetic properties of the composite materials. Coaxial method was used to collect electromagnetic parameters in the frequency range of 2-18GHz (N5224A, Agilent, USA), and based on these parameters, the reflection loss (RL) values were calculated using transmission line theory.

[0039] From Figure 1 It can be seen that from Figure 1 a and 1e, when the sintering temperature is 300℃-500℃, the composite wave-absorbing material presents a circular shape, and the agglomeration phenomenon is reduced. At the same time, the particle size shows a decreasing trend. Continue to increase the sintering temperature (500℃-700℃) (b and 1f), the morphology of the composite wave-absorbing material changes from circular to cylindrical, and some particles present cylindrical shape, most of them are still compact circular. When the temperature reaches 700℃-900℃ (c and 1g), the morphology of the composite wave-absorbing material has changed greatly, the overall shape becomes cylindrical, and there is a relatively large distance, which proves that the sintering temperature has a great relationship with the morphology of the composite wave-absorbing material. Figure 1 Figure 1

[0040] Reflection loss (RL) is a key parameter for evaluating the electromagnetic wave absorption (EMWA) ability of the absorber. RL is calculated using transmission line model (TLM), and the specific formula is as follows (Eg.1-Eg.2):

[0041] Where Z0 represents the impedance in vacuum, Z in represents the input impedance, μ r represents the complex relative permeability, and ε r ​​represents the complex relative permittivity. The variables f, d, and c represent the frequency of the electromagnetic wave, the thickness of the material, and the speed of the electromagnetic wave in a vacuum, respectively. in It is an absorber, and Z0 is the impedance match to free space. Generally, an RL value below -10dB means that 90% of the incident electromagnetic wave energy is absorbed. The effective absorption bandwidth (EAB) is defined as the frequency range over which attenuation occurs.

[0042] Figure 2 and Figure 3 The 2D and 3D reflection back (RL) curves of the composite absorbing material of Example 1 in the frequency range of 2.0 to 18.0 GHz are shown when the thickness is 1.0 to 5.5 mm. Figure 4 and Figure 5 The 2D and 3D reflection back (RL) curves of the composite absorbing material of Example 2 in the frequency range of 2.0 to 18.0 GHz are shown when the thickness is 1.0 to 5.5 mm. Figure 6 and Figure 7 The 2D and 3D reflection (RL) curves for the composite absorber of Example 3, with a thickness of 1.0 to 5.5 mm, are shown over the frequency range of 2.0 to 18.0 GHz. It can be seen that for the composite absorber of Example 2, with a thickness of 2.1 mm, the RL is -46.86 dB at 11.84 GHz.

[0043] Usually, the complex dielectric constant is expressed as ε r = ε '- jε '', the complex magnetic permeability is expressed as μ r = μ '- jμ '' is the preferred parameter for characterizing electromagnetic behavior and elucidating the underlying mechanism of EMW attenuation within materials. ε ' 'and μ ' is a measure of electromagnetic stored energy, ε ''and μ '' indicates the tendency to dissipate electromagnetic energy. Figure 8 It can be seen that the dielectric constant of the composite absorbing material prepared at different sintering temperatures at frequencies of 2.0~18.0GHZ is ε 'and ε ''The change of the amount. Obviously, EDTA / Fe 2+ / Fe 3+ 1:1:1500℃-700℃ composite materials ε 'and ε '' is superior to other ratios in performance at the next level temperature, EDTA / Fe 2+ / Fe 3+1:1:1500℃-700℃ composite material has a significant contribution to the dielectric properties. The ratio of energy loss to storage is called the dielectric loss tangent (tan δ ε ), as shown in equation Eg.3.

[0044]

[0045] From Figure 8 a and Figure 8 b, it can be seen that the tan δ ε of Example 2 and Example 3 is higher than Example 1, indicating that the higher the sintering temperature, the better the dielectric loss performance of the composite material. ε ', ε '' and tan δ ε The curves show multiple polarization relaxation peaks, indicating that the dielectric behavior is complex. The oxygen-rich functional groups act as polarization and scattering centers, enhancing the dipole polarization. The combined effect of dipole and interfacial polarization enhances the dielectric loss, thereby improving the absorption capacity.

[0046] Figure 8 c and Figure 8 d are the analysis of magnetic properties, including μ' and μ" and tan μ r . The composite wave-absorbing material of Example 2 exhibits higher μ' and μ" and tan μ r values in the low frequency range compared to the composite wave-absorbing material of Example 3. With the increase of frequency, there is a significant drop, followed by fluctuations within a defined bandwidth.

[0047] In the composite material, the main source of electromagnetic energy loss is dielectric loss and magnetic loss, as shown by the corresponding loss tangent. In addition, the attenuation constant (a) factor can further illustrate the ability of attenuation loss, as shown in equation Eg.4:

[0048] To obtain a higher attenuation constant, equation Eg.4 shows that it can be achieved by increasing εThe values of ε" and μ" are required to achieve. Effective impedance matching, higher attenuation coefficient and dielectric loss and magnetic loss are essential for achieving the best electromagnetic wave absorption performance. The absorption performance of the material to electromagnetic waves depends on the synergy of its dielectric loss factor ε" and magnetic loss factor μ", which represent the dissipation ability of electromagnetic energy in the medium. Increasing the values of ε" and μ" can enhance the electromagnetic attenuation performance inside the material, but the interface impedance matching characteristics need to be optimized to achieve the maximum transmission of the incident wave. When there is a significant wave impedance mismatch on the surface of the material, the incident electromagnetic wave cannot enter the medium layer due to the reflection effect, at this time, simply improving the loss parameter cannot improve the wave absorption performance. Therefore, the design of high-performance wave absorber needs to build a dynamic balance of attenuation characteristics and impedance adaptation, and realize the dual optimization of electromagnetic wave energy transmission at the interface and internal dissipation through composite parameter regulation. Impedance matching determines the degree of electromagnetic wave penetration into the material: poor impedance matching will cause serious reflection of electromagnetic waves on the surface of the material, thereby reducing the electromagnetic wave absorption performance. Impedance matching is usually evaluated using the ratio Z in / Z 0| | The ratio compares the input impedance to the impedance of free space. The closer the ratio is to 1, the better the impedance matching, and the easier it is for electromagnetic waves to penetrate the material. Z in / Z 0| | Z in / Z 0|The ratio of the four samples, the thickness range is 1.0~5.5mm. The yellow area represents the best impedance matching area. Obviously, EDTA / Fe 2+ / Fe 3+ 1:1:1500℃-700℃ composite material shows more excellent impedance matching.

[0049] The composite wave absorbing material of Example 2 exhibits excellent dielectric loss characteristics, which is mainly because a large number of interfaces are formed inside the material, which effectively promote the interface polarization effect. The synergistic effect of material dipole polarization and interface polarization improves the interface loss performance, so that the material has stronger electromagnetic wave absorption capacity.

[0050] The above only describes the preferred embodiments of the present application, and it should be pointed out that for ordinary skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, which should be considered as the protection scope of the present application.

Claims

1. A method for preparing a composite absorbing material, characterized in that: The steps include: S1: mixing the iron salt solution and the ethylenediaminetetraacetic acid solution to obtain a mixed solution 1; S2: mixing the ferrous salt solution and the ethylenediaminetetraacetic acid solution to obtain a mixed solution 2; S3: Mixing the mixed solution 1 and the mixed solution 2, drying and sintering the mixture to obtain a composite absorbing material.

2. The method for preparing a composite absorbing material according to claim 1, wherein: In the mixed solution 1, ethylenediaminetetraacetic acid and Fe 3+ The molar ratio is 1~2:1~2.

3. The method for preparing a composite absorbing material according to claim 1 or 2, characterized in that: In the mixed solution 2, ethylenediaminetetraacetic acid and Fe 2+ The molar ratio is 1~2:1~2.

4. The method for preparing a composite absorbing material according to claim 3, wherein: Antioxidant vitamin C is added to the ferrous salt solution.

5. The method for preparing a composite absorbing material according to claim 1, 2 or 4, wherein: The ferric salt in the ferric salt solution is ferric chloride; the ferrous salt in the ferrous salt solution is ferrous sulfate.

6. The method for preparing a composite absorbing material according to claim 5, characterized in that: The specific step of drying is: leaving the mixed solution to stand at room temperature until the water evaporates.

7. The method for preparing a composite absorbing material according to claim 4 or 6, characterized in that: The method further comprises a grinding step after the drying.

8. The method for preparing a composite absorbing material according to claim 7, wherein: The sintering includes a first sintering and a second sintering.

9. The method for preparing a composite absorbing material according to claim 8, wherein: The temperature of the first sintering is 300-700° C., and the time is 1-3 hours; the temperature of the second sintering is 500-900° C., and the time is 1-3 hours.

10. A composite absorbing material obtained by the method for preparing a composite absorbing material according to any one of claims 1 to 9.

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