A metal organic framework (MOFs) derived carbon coated FeSi-based composite magnetic wave-absorbing material and a preparation method thereof

Abstract

The application relates to a metal organic framework (MOFs) derived carbon coated FeSi-based composite magnetic wave-absorbing material and a preparation method thereof. The surface oxidized flaky FeSi-based magnetic wave-absorbing powder is combined with MOFs derived carbon as a core to improve interface polarization, dipole polarization, increase complex permittivity, strengthen multi-level structure interface scattering, and optimize impedance matching of the composite material. When the content of the prepared material is 10% and the coating thickness is 1.5 mm, the reflectivity is optimized from -2 dB to -36.5 dB. The material prepared by the application can realize effective absorption of electromagnetic waves at low thickness, has good chemical stability, and has a simple preparation method. After the surface of the flaky FeSi-based magnetic wave-absorbing powder is oxidized, the FeSi-based core can be prevented from being eroded in the MOFs combination process, and the existence of the oxidation layer improves the stability and corrosion resistance of the material.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of magnetic wave-absorbing materials, in particular to a metal-organic framework (MOFs) derived carbon-coated FeSi-based composite magnetic wave-absorbing material and a preparation method thereof. BACKGROUND

[0002] With the advent of the 5G era, electronic products have been more widely applied in the fields of national defense, medical treatment, military affairs, civil use and the like. Meanwhile, serious electromagnetic wave interference and radiation pollution and the like problems are also brought. According to reports, long-term staying in an electromagnetic wave environment will cause calcium loss of a human being, and further cause visual impairment, leukemia and the like diseases. In the military aspect, electromagnetic wave interference brings adverse effects on the reliability of a weapon system. For example, intelligence is inaccurate, an enemy target cannot be detected, an airplane flight is out of control and the like. Therefore, how to prevent electromagnetic wave interference and solve the problems of radiation pollution and the like is concerned, and electromagnetic wave-absorbing materials have become a hot spot of current research and development.

[0003] Ferrite has the advantages of good thermal stability, high magnetic permeability, large resistivity, simple preparation process and the like, and is an excellent electromagnetic wave-absorbing material, and therefore has important applications in many fields such as pigments, photocatalysts and electromagnetic wave absorption. Although great achievements have been made in the research and application of ferrite materials in the past few decades and some have been successfully applied to weapon equipment, ferrite materials also have defects such as poor temperature stability and large density, and need to be further developed to meet the requirements of the current complex and changeable war state, military technology progress and arms race. Researchers improve the deficiencies of ferrite wave-absorbing materials through doping modification of ferrite itself, and compounding with a second phase material, such as loading ferrite on carbon nanotubes, mechanically grinding mixing of alloy and ferrite, and preparing core-shell structure ferrite materials. Among them, the core-shell structure nano ferrite wave-absorbing material is one of the current research hotspots.

[0004] Metal-organic framework (MOFs) derived material is a new type of wave-absorbing material, has the advantages of simple synthesis process, low production cost, good thermal stability, large specific surface area, high porosity and the like, and the derived porous carbon / magnetic metal particle composite material overcomes the characteristics of uneven dispersion of magnetic particles, and through high-temperature calcination, a light porous carbon material with special microstructure can be prepared, and therefore the material is widely concerned in the wave-absorbing field. Combining MOFs with single metals such as iron and cobalt is beneficial to the synthesis of porous composite materials, and the porous composite material has well-dispersed nanoparticles and an ordered structure, and exhibits good electromagnetic wave absorption performance. However, in the chemical reaction process of compounding MOFs with soft magnetic alloy matrix, the soft magnetic alloy matrix is eroded. SUMMARY

[0005] The purpose of this invention is to provide a FeSi-based magnetic absorbing material coated with metal-organic frameworks (MOFs)-derived carbon and its preparation method. A core-shell structured sheet-like FeSi-based composite MOF magnetic powder is prepared by compositing FeSi-based magnetic powder and MOFs using a hydrothermal method. This sheet-like FeSi-based composite MOF magnetic powder is then annealed to obtain a FeSi-based composite magnetic absorbing material coated with metal-organic frameworks (MOFs)-derived carbon. This structure improves the dielectric loss of the material and optimizes its impedance matching, resulting in a significant improvement in the material's microwave absorption performance.

[0006] The embodiments of the present invention are implemented as follows:

[0007] A FeSi-based composite magnetic absorbing material coated with metal-organic framework (MOF)-derived carbon is disclosed. The FeSi-based composite magnetic absorbing material uses surface-oxidized sheet-like FeSi-based magnetic absorbing powder as its core and high-dielectric-constant MOF-derived carbon as its coating layer. The MOF-derived carbon has the unit molecular formula C2. 24 H 12 ClFe3O 13 The iron-based frame material is MIL-101 (Fe).

[0008] Furthermore, in the above technical solution, the mass ratio of the core to the coating layer is (7-27):3.

[0009] Furthermore, in the above technical solution, the FeSi-based magnetic powder is a high-permeability sheet-like FeSiAl, FeSiCr, or FeSi.

[0010] Furthermore, in the above technical solution, when the core is FeSiAl, the mass percentages of Fe, Si, and Al are 85.8 wt.%, 10.1 wt.%, and 4.1 wt.%, respectively.

[0011] A method for preparing a metal-organic framework (MOF)-derived carbon-coated FeSi-based composite magnetic microwave absorbing material includes the following steps:

[0012] Step S1: Ball mill the micron-sized water-atomized FeSi-based magnetic powder for 12-36 hours to obtain flake-shaped FeSi-based magnetic powder;

[0013] Step S2: The sheet-like FeSi-based magnetic powder prepared in step S1 is heated from room temperature to 300℃-600℃ at a heating rate of 2-5℃ / min under an oxygen atmosphere and calcined for 2h-4h, and then cooled to room temperature to obtain the core, which is a sheet-like FeSi-based magnetic microwave absorbing powder with surface oxidation.

[0014] Step S3: The sheet-like FeSi-based magnetic absorbing powder obtained in step S2, ferric nitrate nonahydrate (Fe(NO3)3·9H2O), and terephthalic acid (PTA) are sequentially dissolved in N,N-dimethylformamide (DMF). After mechanical stirring until dissolved, a hydrothermal reaction is carried out. After the hydrothermal reaction is completed, the powder is cooled, filtered, washed, dried, and ground to obtain sheet-like FeSi-based composite MOFs magnetic powder.

[0015] Step S4: The sheet-like FeSi-based composite MOF magnetic powder obtained in step S3 is annealed by heating from room temperature to 500℃-700℃ at a heating rate of 2-5℃ / min under argon atmosphere protection and calcining for 1-3h. After annealing, it is cooled to room temperature to obtain the preparation method of FeSi-based composite magnetic microwave absorbing material with metal-organic framework (MOF) derived carbon coating.

[0016] Furthermore, in the above technical solution, in step S3, the hydrothermal reaction is carried out under the condition of heating at 110-160℃ for 12-24 hours.

[0017] Furthermore, in the above technical solution, the ball milling time in step S1 is 24 hours.

[0018] Furthermore, in the above technical solution, in step S2, the heating rate during oxidation annealing is 5℃ / minute, the oxidation annealing temperature is 600℃, and the holding time is 3 hours.

[0019] Furthermore, in the above technical solution, in step S2, the oxygen introduced during the oxidation annealing treatment is always in a flowing state.

[0020] Furthermore, in the above technical solution, in step S4, the heating rate during annealing is 5℃ / minute, the annealing temperature is 500℃, and the holding time is 2 hours.

[0021] The beneficial effects of this invention are as follows: The metal-organic framework (MOFs)-derived carbon-coated FeSi-based composite magnetic absorbing material of this invention possesses the advantages of high magnetic permeability of ferrite alloys, the size effect of nanomaterials, and the characteristics of a core-shell structure, comprehensively considering multiple factors to improve the absorption performance of the material. Furthermore, because the metal powder is pre-coated with an oxide layer after oxidation heat treatment to form a sheet-like FeSi-based magnetic absorbing powder with an oxidized surface, the soft magnetic alloy matrix will not be eroded during the subsequent MOFs composite process, thus achieving the goal of compositing the soft magnetic alloy powder with the MOFs-derived carbon material. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is the X-ray diffraction pattern of the carbon-coated FeSiAl composite MOFs composite magnetic microwave absorbing material in this invention;

[0024] Figure 2 This is a comparison diagram of the absorption performance of the FeSiAl magnetic nano-absorbing material in this invention before and after carbon coating. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings to facilitate a further understanding of the present invention. Unless otherwise specified, all experimental methods used in the following embodiments are conventional methods. Unless otherwise specified, all materials and reagents used in the following embodiments are commercially available.

[0026] Example 1

[0027] In this embodiment, the MOFs are MIL-101(Fe) (the unit molecular formula of MIL-101(Fe) is C). 24 H 12 ClFe3O 13 ).

[0028] This embodiment includes a metal-organic framework (MOF)-derived carbon-coated FeSiAl composite magnetic absorbing material. The core of the material is 90 wt.% FeSiAl, and the coating layer is 10 wt.% MOFs (wt.% is mass percentage). The mass percentages of Fe, Si, and Al are 85.8 wt.%, 10.1 wt.%, and 4.1 wt.%, respectively.

[0029] This embodiment also includes a method for preparing a metal-organic framework (MOF)-derived carbon-coated FeSiAl composite magnetic microwave absorbing material, comprising the following steps:

[0030] Step 1: The readily available micron-sized water-atomized FeSiAl soft magnetic alloy powder is ball-milled for 24 hours to obtain sheet-like FeSi-based soft magnetic alloy powder.

[0031] Step S2: Place the flake-shaped FeSiAl magnetic powder obtained in step S1 into a quartz tube and evacuate it in a tube furnace. Then fill it with oxygen until the gas pressure inside the quartz tube reaches atmospheric pressure. Then, keep the oxygen flowing into the quartz tube at a flow rate of 0.1 L / min. Then, raise the temperature from room temperature to 500℃ at a heating rate of 5℃ / min and calcine for 3 hours. Then, let it cool naturally to room temperature to obtain the core. The core is a flake-shaped FeSiAl magnetic microwave absorbing powder with surface oxidation.

[0032] Step S3: Hydrothermal Coating: Take 0.9g of FeSiAl magnetic powder absorbing material obtained in Step S2, 0.17g of ferric nitrate nonahydrate (Fe(NO3)3·9H2O) and 0.07g of terephthalic acid (PTA) and dissolve them in 40ml of N,N-dimethylformamide (DMF). After stirring mechanically at 320r / min for 30 minutes, transfer the mixture to a stainless steel reactor lined with polytetrafluoroethylene. Then place it in a constant temperature drying oven and heat at 110℃ for 24 hours. After the reactor cools to room temperature, the product is centrifuged and washed three times with DMF and anhydrous ethanol, respectively. It is then dried in a vacuum drying oven at 60℃ for 12 hours and ground to obtain flake-shaped FeSiAl composite MOFs magnetic powder.

[0033] Step S4: The sheet-like FeSiAl composite MOFs magnetic powder obtained in step S3 is evacuated in a tube furnace and then filled with argon gas until the gas pressure inside the quartz tube reaches atmospheric pressure. Under the protection of argon atmosphere, the temperature is raised from room temperature to 500℃ at a heating rate of 5℃ / min and calcined for 2 hours for annealing. After annealing, it is naturally cooled to room temperature to obtain FeSiAl composite magnetic microwave absorbing material with metal-organic framework (MOFs) derived carbon coating.

[0034] Example 2

[0035] In this embodiment, the MOFs are MIL-101(Fe) (the unit molecular formula of MIL-101(Fe) is C). 24 H 12 ClFe3O 13 ).

[0036] This embodiment includes a metal-organic framework (MOF)-derived carbon-coated FeSiAl composite magnetic absorbing material. The core of the material is 80 wt.% FeSiAl, and the coating layer is 20 wt.% MOFs (wt.% is mass percentage).

[0037] This embodiment also includes a method for preparing a metal-organic framework (MOF)-derived carbon-coated FeSiAl composite magnetic microwave absorbing material, comprising the following steps:

[0038] Step 1: The readily available micron-sized water-atomized FeSiAl soft magnetic alloy powder is ball-milled for 12 hours to obtain sheet-like FeSi-based soft magnetic alloy powder.

[0039] Step S2: The sheet-like FeSiAl soft magnetic alloy powder obtained in step S1 is placed in a quartz tube and a vacuum is drawn in a tube furnace. Oxygen is then introduced until the gas pressure inside the quartz tube reaches atmospheric pressure. Oxygen is then introduced into the quartz tube at a flow rate of 0.1 liters / minute. The temperature is then increased from room temperature to 300°C at a heating rate of 2°C / minute and calcined for 4 hours. After that, it is naturally cooled to room temperature to obtain the core. The core is a sheet-like FeSiAl magnetic absorbing powder with an oxidized surface.

[0040] Step S3: Hydrothermal Coating: Take 1.0g of FeSiAl magnetic powder absorbing material obtained in Step S2, 0.426g of ferric nitrate nonahydrate (Fe(NO3)3·9H2O) and 0.175g of terephthalic acid (PTA) and dissolve them in 50ml of N,N-dimethylformamide (DMF). After stirring mechanically at 300r / min for 40 minutes, transfer the mixture to a stainless steel reactor lined with polytetrafluoroethylene. Then place it in a constant temperature drying oven and heat it at 160℃ for 12 hours. After the reactor cools to room temperature, the product is centrifuged and washed three times with DMF and anhydrous ethanol, respectively. It is then dried in a vacuum drying oven at 60℃ for 14 hours and ground to obtain sheet-like FeSiAl composite MOFs magnetic powder.

[0041] Step S4: The sheet-like FeSiAl composite MOFs magnetic powder obtained in step S3 is evacuated in a tube furnace and then filled with argon gas until the gas pressure inside the quartz tube reaches atmospheric pressure. Under the protection of argon atmosphere, the temperature is raised from room temperature to 700℃ at a heating rate of 2℃ / min and calcined for 1 hour for annealing. After annealing, it is naturally cooled to room temperature to obtain FeSiAl composite magnetic microwave absorbing material with metal-organic framework (MOFs) derived carbon coating.

[0042] Example 3

[0043] In this embodiment, the MOFs are MIL-101(Fe) (the unit molecular formula of MIL-101(Fe) is C). 24 H 12 ClFe3O 13 ).

[0044] This embodiment includes a FeSiAl composite magnetic microwave absorbing material with carbon coating derived from metal-organic frameworks (MOFs). The core of the material is 70 wt.% FeSiAl, and the coating layer is 30 wt.% MOFs (wt.% is mass percentage).

[0045] This embodiment also includes a method for preparing a metal-organic framework (MOF)-derived carbon-coated FeSiAl composite magnetic microwave absorbing material, comprising the following steps:

[0046] Step 1: The readily available micron-sized water-atomized FeSiAl soft magnetic alloy powder is ball-milled for 36 hours to obtain sheet-like FeSi-based soft magnetic alloy powder.

[0047] Step S2: The sheet-like FeSiAl soft magnetic alloy powder obtained in step S1 is placed in a quartz tube and a vacuum is drawn in a tube furnace. Oxygen is then introduced until the gas pressure inside the quartz tube reaches atmospheric pressure. Oxygen is then introduced into the quartz tube at a flow rate of 0.1 liters / minute. The temperature is then increased from room temperature to 600°C at a heating rate of 3°C / minute and calcined for 2 hours. After that, it is naturally cooled to room temperature to obtain the core. The core is a sheet-like FeSiAl magnetic absorbing powder with an oxidized surface.

[0048] Step S3: Hydrothermal Coating: Take 0.7g of FeSiAl magnetic powder absorbing material obtained in Step S2, 0.5112g of ferric nitrate nonahydrate (Fe(NO3)3·9H2O) and 0.21g of terephthalic acid (PTA) and dissolve them in 45ml of N,N-dimethylformamide (DMF). After stirring mechanically at 300r / min for 40 minutes, transfer the mixture to a stainless steel reactor lined with polytetrafluoroethylene. Then place it in a constant temperature drying oven and heat it at 130℃ for 18 hours. After the reactor cools to room temperature, the product is separated by centrifugation and washed three times with DMF and anhydrous ethanol, respectively. It is then dried in a vacuum drying oven at 60℃ for 10 hours and ground to obtain sheet-like FeSiAl composite MOFs magnetic powder.

[0049] Step S4: The sheet-like FeSiAl composite MOFs magnetic powder obtained in step S3 is evacuated in a tube furnace and then filled with argon until the gas pressure inside the quartz tube reaches atmospheric pressure. Under the protection of argon atmosphere, the temperature is raised from room temperature to 600℃ at a heating rate of 3℃ / min and calcined for 3 hours for annealing. After annealing, it is naturally cooled to room temperature to obtain FeSiAl composite magnetic microwave absorbing material with metal-organic framework (MOFs) derived carbon coating.

[0050] Example 4

[0051] In this embodiment, the MOFs are MIL-101(Fe) (the unit molecular formula of MIL-101(Fe) is C). 24 H 12 ClFe3O 13 ).

[0052] This embodiment includes a metal-organic framework (MOF)-derived carbon-coated FeSiCr composite magnetic absorbing material. The core of the material is 90 wt.% FeSiCr, and the coating layer is 10 wt.% MOFs (wt.% is mass percentage). The mass percentage of the FeSiCr soft magnetic core is 87.2 wt.% Fe, 9.5 wt.% Si, and 3.3 wt.% Cr.

[0053] This embodiment also includes a method for preparing a metal-organic framework (MOF)-derived carbon-coated FeSiCr composite magnetic microwave absorbing material, comprising the following steps:

[0054] The difference between Example 4 and Example 1 is that FeSiAl in steps S1, S2 and S3 is replaced with FeSiCr, and the stoichiometry of the FeSiCr soft magnetic core is by mass percentage, with Fe being 87.2 wt.%, Si being 9.5 wt.% and Cr being 3.3 wt.%. All other steps are the same as in Example 1.

[0055] Example 5

[0056] In this embodiment, the MOFs are MIL-101(Fe) (the unit molecular formula of MIL-101(Fe) is C). 24 H 12 ClFe3O 13 ).

[0057] This embodiment includes a metal-organic framework (MOF)-derived carbon-coated FeSiCr composite magnetic absorbing material. The core of the material is 80 wt.% FeSiCr, and the coating layer is 20 wt.% MOFs (wt.% is mass percentage). The mass percentage of the FeSiCr soft magnetic core is 87.2 wt.% Fe, 9.5 wt.% Si, and 3.3 wt.% Cr.

[0058] This embodiment also includes a method for preparing a metal-organic framework (MOF)-derived carbon-coated FeSiCr composite magnetic microwave absorbing material, comprising the following steps:

[0059] The difference between Example 5 and Example 2 is that FeSiAl in steps S1, S2 and S3 is replaced with FeSiCr, the mass percentage of the FeSiCr soft magnetic core is 87.2 wt.%, Si is 9.5 wt.% and Cr is 3.3 wt.%, and the FeSiCr magnetic powder is adjusted to 1 g. All other steps are the same as in Example 2.

[0060] Example 6

[0061] In this embodiment, the MOFs are MIL-101(Fe) (the unit molecular formula of MIL-101(Fe) is C). 24 H 12 ClFe3O 13 ).

[0062] This embodiment includes a metal-organic framework (MOF)-derived carbon-coated FeSiCr composite magnetic absorbing material. The core of the material is 70 wt.% FeSiCr, and the coating layer is 30 wt.% MOFs (wt.% is mass percentage). The mass percentage of the FeSiCr soft magnetic core is 87.2 wt.% Fe, 9.5 wt.% Si, and 3.3 wt.% Cr.

[0063] This embodiment also includes a method for preparing a metal-organic framework (MOF)-derived carbon-coated FeSiCr composite magnetic microwave absorbing material, comprising the following steps:

[0064] The difference between Example 6 and Example 3 is that FeSiAl in steps S1, S2 and S3 is replaced with FeSiCr, the mass percentage of the FeSiCr soft magnetic core is 87.2 wt.%, Si is 9.5 wt.% and Cr is 3.3 wt.%, and the FeSiCr magnetic powder is adjusted to 0.7 g. All other steps are the same as in Example 3.

[0065] Example 7

[0066] In this embodiment, the MOFs are MIL-101(Fe) (the unit molecular formula of MIL-101(Fe) is C). 24 H 12 ClFe3O 13 ).

[0067] This embodiment includes a metal-organic framework (MOF)-derived carbon-coated FeSi composite magnetic absorbing material. The core of the material is 90 wt.% FeSi, and the coating layer is 10 wt.% MOFs (wt.% is mass percentage). The mass percentage of the FeSi soft magnetic core is 86.7 wt.% Fe and 13.3 wt.% Si.

[0068] This embodiment also includes a method for preparing a metal-organic framework (MOF)-derived carbon-coated FeSi composite magnetic microwave absorbing material, comprising the following steps:

[0069] The difference between Example 7 and Example 1 is that the FeSiAl composite magnetic absorbing material in steps S1, S2 and S3 is replaced with FeSi composite magnetic absorbing material, and the mass percentage of the FeSi soft magnetic core is 86.7 wt.% for Fe and 13.3 wt.% for Si. All other steps are the same as in Example 1.

[0070] Example 8

[0071] In this embodiment, the MOFs are MIL-101(Fe) (the unit molecular formula of MIL-101(Fe) is C). 24 H 12 ClFe3O 13 ).

[0072] This embodiment includes a metal-organic framework (MOF)-derived carbon-coated FeSi composite magnetic absorbing material. The core of the material is 80 wt.% FeSi, and the coating layer is 20 wt.% MOFs (wt.% is mass percentage). The mass percentage of the FeSi soft magnetic core is 86.7 wt.% Fe and 13.3 wt.% Si.

[0073] This embodiment also includes a method for preparing a metal-organic framework (MOF)-derived carbon-coated FeSi composite magnetic microwave absorbing material, comprising the following steps:

[0074] The difference between Example 8 and Example 2 is that the FeSiAl composite magnetic absorbing material in steps S1, S2, and S3 is replaced with FeSi composite magnetic absorbing material. The mass percentage of the FeSi soft magnetic core is 86.7% Fe and 13.3% Si, with the sum of the percentages of the two components being 100%. All other steps are the same as in Example 2. The amount of FeSi composite magnetic absorbing material is adjusted to 1g, and all other steps are the same as in Example 1.

[0075] Example 9

[0076] In this embodiment, the MOFs are MIL-101(Fe) (the unit molecular formula of MIL-101(Fe) is C 24 H 12 ClFe3O 13 ).

[0077] This embodiment includes a metal-organic framework (MOF)-derived carbon-coated FeSi composite magnetic absorbing material. The core of the material is 70 wt.% FeSi, and the coating layer is 30 wt.% MOFs (wt.% is mass percentage). The mass percentage of the FeSi soft magnetic core is 86.7 wt.% Fe and 13.3 wt.% Si.

[0078] This embodiment also includes a method for preparing a metal-organic framework (MOF)-derived carbon-coated FeSi composite magnetic microwave absorbing material, comprising the following steps:

[0079] The difference between Example 9 and Example 1 is that the FeSiAl composite magnetic absorbing material in steps S1, S2, and S3 is replaced with FeSi composite magnetic absorbing material. The mass percentage of the FeSi soft magnetic core is 86.7% Fe and 13.3% Si, with the sum of the percentages of the two components being 100%. All other steps are the same as in Example 3. The amount of FeSi composite magnetic absorbing material is adjusted to 0.7g, and all other steps are the same as in Example 3.

[0080] Experimental Example 1

[0081] All of these experimental examples are for characterizing the materials used in each step of Example 1.

[0082] The phase composition of the metal-organic framework (MOF)-derived carbon-coated FeSiAl composite magnetic microwave absorbing material obtained in step 4 of Example 1 was characterized using a PANalytical-Empyrean X-ray diffractometer. The results are as follows: Figure 1 As shown.

[0083] The electromagnetic parameters of the materials were tested and the reflectivity was calculated using an Agilent PNA-L5230C vector network analyzer. The sheet-like FeSiAl magnetic absorbing powder prepared in step 2 of Example 1, and the metal-organic framework (MOFs)-derived carbon-coated FeSiAl composite magnetic absorbing material prepared in step 4 of Example 1, were mixed with paraffin wax at a mass ratio of 1:1 to prepare coaxial samples with outer and inner diameters of 7 mm and 3 mm respectively, and a thickness of approximately 2.5 mm. The complex permeability and complex permittivity of the samples were measured in the 1-18 GHz frequency band. The reflectivity R of the monolayer absorbing material was calculated and simulated using the following formula. The results are as follows: Figure 2 As shown.

[0084] (1)

[0085] In equation (1), εr, μr and d are the complex permittivity, complex permeability and thickness of the absorbing material, respectively, f is the frequency of the electromagnetic wave, c is the propagation speed of the electromagnetic wave in vacuum and j is the imaginary unit.

[0086] from Figure 1 It can be seen that the main phase composition of the metal-organic framework (MOFs)-derived carbon-coated FeSi composite magnetic microwave absorbing material synthesized in Example 1 is FeSiAl, carbon, and Fe3O4. From... Figure 2As can be seen, after MOF-derived carbon coating, the reflectivity of the MOF-derived carbon-coated FeSi-based magnetic absorbing material with a MIL-101 content of 10% and a coating thickness of 1.5 mm was optimized from -2 dB to -36.5 dB. This demonstrates that the complex permittivity of the MOF-derived carbon-coated FeSi composite magnetic absorbing material was significantly improved. This indicates that the MOF-derived carbon-coated FeSi-based composite magnetic absorbing material prepared in this invention can achieve effective absorption of electromagnetic waves at low thickness.

[0087] In summary, using MOFs as a carbon source, a FeSi-based composite magnetic absorbing material with MOF-derived carbon coating is obtained through high-temperature carbonization. This material possesses the advantages of high magnetic permeability of ferrite alloys, the size effect of nanomaterials, and the characteristics of MOF composite materials, comprehensively considering multiple factors to improve the material's microwave absorption performance. Furthermore, because the metal powder is pre-coated with an oxide layer after oxidation heat treatment to form a sheet-like FeSi-based magnetic absorbing powder with an oxidized surface, the soft magnetic alloy matrix is ​​not corroded during the subsequent MOF composite process, thus achieving the goal of combining magnetic absorbing powder and MOF-derived carbon materials. Moreover, the material's stability and corrosion resistance are improved, making it more suitable for practical applications and industrial production requirements, thus demonstrating good development prospects and application value. The MOF-derived carbon-coated FeSi-based magnetic absorbing material prepared by this invention exhibits good chemical stability and has a simple preparation method, making it a preferred choice as a microwave absorbing material.

Claims

1. A FeSi-based composite magnetic microwave absorbing material with carbon coating derived from metal-organic frameworks (MOFs), characterized in that: The FeSi-based composite magnetic absorbing material uses surface-oxidized, sheet-like FeSi-based magnetic absorbing powder as its core and high-dielectric-constant MOF-derived carbon as its coating layer. The MOF-derived carbon has a unit molecular formula of C2. 24 H 12 ClFe3O 13 The iron-based frame material is MIL-101(Fe).

2. The FeSi-based composite magnetic microwave absorbing material with carbon coating derived from metal-organic frameworks (MOFs) as described in claim 1, characterized in that: The mass ratio of the core to the coating layer is (7-27):

3.

3. The FeSi-based composite magnetic microwave absorbing material with carbon coating derived from metal-organic frameworks (MOFs) as described in claim 2, characterized in that: The FeSi-based magnetic powder is a high-permeability sheet-like FeSiAl, FeSiCr, or FeSi.

4. The FeSi-based composite magnetic microwave absorbing material with carbon coating derived from metal-organic frameworks (MOFs) as described in claim 3, characterized in that: When the core is FeSiAl, the mass percentages of Fe, Si, and Al are 85.8 wt.%, 10.1 wt.%, and 4.1 wt.%, respectively.

5. A method for preparing FeSi-based composite magnetic microwave absorbing materials with carbon coating derived from metal-organic frameworks (MOFs) as described in claims 2-4, characterized in that: Includes the following steps: Step S1: Ball mill the micron-sized water-atomized FeSi-based magnetic powder for 12-36 hours to obtain flake-shaped FeSi-based magnetic powder; Step S2: The sheet-like FeSi-based magnetic powder prepared in step S1 is heated from room temperature to 300℃-600℃ in an oxygen atmosphere at a heating rate of 2-5℃ / min and calcined for 2h-4h, and then cooled to room temperature to obtain a core, wherein the core is a sheet-like FeSi-based magnetic microwave absorbing powder with surface oxidation. Step S3: The sheet-like FeSi-based magnetic absorbing powder obtained in step S2, ferric nitrate nonahydrate (Fe(NO3)3·9H2O), and terephthalic acid (PTA) are sequentially dissolved in N,N-dimethylformamide (DMF). After mechanical stirring until dissolved, a hydrothermal reaction is carried out. After the hydrothermal reaction is completed, the powder is cooled, filtered, washed, dried, and ground to obtain sheet-like FeSi-based composite MOFs magnetic powder. Step S4: The sheet-like FeSi-based composite MOF magnetic powder obtained in step S3 is heated from room temperature to 500℃-700℃ at a heating rate of 2-5℃ / min under argon atmosphere protection and calcined for 1-3h for annealing. After annealing, it is cooled to room temperature to obtain FeSi-based composite magnetic absorbing material with metal-organic framework (MOF) derived carbon coating.

6. The method for preparing the FeSi-based composite magnetic microwave absorbing material with carbon coating derived from metal-organic frameworks (MOFs) as described in claim 5, characterized in that: In step S3, the hydrothermal reaction is carried out under the condition of heating at 110-160℃ for 12-24 hours.

7. The method for preparing the FeSi-based composite magnetic microwave absorbing material with carbon coating derived from metal-organic frameworks (MOFs) as described in claim 5, characterized in that: In step S1, the ball milling time is 24 hours.

8. The method for preparing the FeSi-based composite magnetic microwave absorbing material with carbon coating derived from metal-organic frameworks (MOFs) as described in claim 5, characterized in that: In step S2, the heating rate during oxidation annealing is 5℃ / min, the oxidation annealing temperature is 600℃, and the holding time is 3 hours.

9. The method for preparing the FeSi-based composite magnetic microwave absorbing material with carbon coating derived from metal-organic frameworks (MOFs) as described in claim 5, characterized in that: In step S2, the oxygen introduced during the oxidation annealing process is always in a continuous flow state.

10. The method for preparing the FeSi-based composite magnetic microwave absorbing material with carbon coating derived from metal-organic frameworks (MOFs) as described in claim 5, characterized in that: In step S4, the heating rate during annealing is 5℃ / minute, the annealing temperature is 500℃, and the holding time is 2 hours.

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