A Fe3O4 chain-like microwave absorbing material with ultra-high aspect ratio and its preparation method

Abstract

This invention discloses a Fe3O4 chain-like microwave absorbing material with an ultra-high aspect ratio and its preparation method. The preparation method includes the following steps: mixing iron pentacarbonyl solution and ethanol evenly, then placing the mixture in a hydrothermal reaction apparatus and reacting it under the presence of a magnetic field; after the reaction, cooling, washing, and drying are performed to obtain the Fe3O4 chain-like microwave absorbing material with an ultra-high aspect ratio. In the method of this invention, a magnetic field is applied during the hydrothermal process. Under the induction of the external magnetic field, magnetic Fe3O4 nanoparticles assemble and arrange themselves, transforming from disordered polycrystalline particles into chain-like crystals oriented along the direction of the magnetic field. Due to its unique chain-like structure, a conductive network can be formed, thereby greatly enhancing the conductivity of the material and facilitating multiple scattering and absorption of electromagnetic waves, thus improving the material's ability to absorb electromagnetic waves.

Description

Technical Field

[0001] This invention relates to the field of microwave absorbing materials technology, specifically to a Fe3O4 chain-like microwave absorbing material with an ultra-high aspect ratio and its preparation method. Background Technology

[0002] With the increasing prevalence of electronic devices and the growing prominence of electromagnetic radiation issues, the development of highly efficient microwave absorbing materials has become an urgent priority. Excellent microwave absorbing materials can effectively absorb and convert electromagnetic wave energy, providing shielding and protection, and can also be applied in fields such as stealth technology and electromagnetic compatibility. Traditional microwave absorbing materials suffer from narrow absorption frequency bands and performance limitations due to angle variations. Therefore, developing new microwave absorbing materials is of great significance, and is expected to improve the safety and efficiency of electromagnetic wave applications, promoting technological innovation and development in related fields.

[0003] Nanomaterials have attracted widespread interest in the field of electromagnetic wave absorption over the past few years. Due to their unique structure and size effects, nanomaterials are considered a potential option for improving wave absorption performance. In this context, Fe3O4, with its low cost and excellent dual electromagnetic properties (dielectric constant and magnetic permeability), which contribute to the rapid attenuation and dissipation of electromagnetic waves, possesses great potential as a highly efficient electromagnetic wave absorber.

[0004] Chinese patent application CN107638851A discloses a bell-shaped Fe3O4@void@SiO2 nanochain and its preparation method. Under the induction of an external magnetic field, magnetic Fe3O4 nanoparticles are assembled and arranged. Simultaneously, core-shell Fe3O4@P(DVB-MAA) nanochains are formed through distillation precipitation polymerization. Subsequently, a sol-gel method is used to coat the SiO2 shell, achieving the preparation of a double-shell Fe3O4@P(DVB-MAA)@SiO2 nanochain. Finally, the nanochain structure is protected by salt recrystallization, and pyrolysis is performed in an argon atmosphere. The final product is the bell-shaped Fe3O4@void@SiO2 nanochain, with a minimum reflection loss of -45.03 dB (13.57 GHz) and an effective absorption bandwidth of up to 5.5 GHz. However, existing technologies involve multiple composite materials, making preparation more complex, and there is room for improvement in both absorption intensity and bandwidth.

[0005] Chinese patent application CN113511689A discloses a magnetite nanoribbon microwave absorber and its preparation method. This absorber is a continuous ribbon structure composed of tightly packed magnetite nanocrystals. Microscopically, the magnetite nanoribbon absorber has a thickness of 10–40 nm and a lateral dimension between 0.2–2 μm. The preparation method involves preparing a precursor solution using polyvinylpyrrolidone, ferric nitrate nonahydrate, and N,N-dimethylformamide as raw materials, followed by electrospinning to obtain composite nanoribbons. These nanoribbons are then heated in a high-temperature furnace, annealed to obtain ferric oxide nanoribbons, and thermally reduced to magnetite nanoribbons in an Ar / H2 atmosphere. By controlling the proportion of the precursor solution, nanoribbons with different lateral dimensions can be prepared controllably. This absorber achieves a reflection attenuation below -50 dB and an effective bandwidth of 4.93 GHz when the mass filling amount in the absorbing material is as low as 20%, but there is room for improvement in both absorption intensity and bandwidth. Summary of the Invention

[0006] The technical problem to be solved by this invention is how to prepare a Fe3O4 microwave absorbing material with a single composition and excellent absorption intensity and bandwidth.

[0007] The present invention solves the above-mentioned technical problems through the following technical means:

[0008] A method for preparing a Fe3O4 chain-like microwave absorbing material with an ultra-high aspect ratio includes the following steps: mixing a pentacarbonyl iron solution and ethanol evenly, then placing them in a hydrothermal reaction apparatus and reacting them under the presence of a magnetic field; wherein the strength of the magnetic field is 0.05-6T; after the reaction is completed, cooling, washing, and drying are performed to obtain the Fe3O4 chain-like microwave absorbing material with an ultra-high aspect ratio.

[0009] Preferably, the volume ratio of the iron pentacarbonyl solution to ethanol is 20-30:1.

[0010] Preferably, the pentacarbonyl iron solution and ethanol are mixed evenly by ultrasound or stirring.

[0011] Preferably, the ultrasound duration is ≥0.5h; the stirring temperature is 15-30℃, and the stirring time is ≥0.5h.

[0012] Preferably, the reaction temperature is 160-200℃ and the time is 2-8h.

[0013] Preferably, the reaction is cooled in air after completion.

[0014] Preferably, water and ethanol are used sequentially for centrifugal washing; the centrifugation speed is 4000-6000 revolutions per minute, and the centrifugation washing is performed 4-8 times, each time for 3-5 minutes.

[0015] Preferably, the drying temperature is 50-80℃ and the time is 10-20 hours.

[0016] The present invention also proposes an ultra-high aspect ratio Fe3O4 chain-like microwave absorbing material, which is prepared by the preparation method of the ultra-high aspect ratio Fe3O4 chain-like microwave absorbing material.

[0017] Preferably, the aspect ratio of the Fe3O4 chain-like microwave absorbing material with an ultra-large aspect ratio is 200-500.

[0018] In the method of this invention, a magnetic field is applied during the hydrothermal process. Under the induction of the external magnetic field, magnetic Fe3O4 nanoparticles assemble and arrange themselves, transforming from disordered polycrystalline particles into chain-like crystals oriented along the direction of the magnetic field. Due to its unique chain-like structure, a conductive network can be formed, thereby greatly enhancing the conductivity of the material and facilitating multiple scattering and absorption of electromagnetic waves, thus improving the material's ability to absorb electromagnetic waves.

[0019] This invention provides a novel, high-efficiency, wide-frequency-domain nano-absorbing material with a single composition, simple preparation process, low cost, and easy industrial production and application.

[0020] Compared with existing microwave absorbing materials, the advantages of this invention are:

[0021] 1) The one-dimensional orientation and high aspect ratio of Fe3O4 chain crystals are like countless microwave antennas, providing a directional channel for the transmission of electromagnetic waves and extending the transmission time, which is beneficial to the dissipation of electromagnetic energy.

[0022] 2) Nanochains self-assemble easily to form a three-dimensional network structure, causing electromagnetic waves to be scattered and absorbed multiple times inside the material, increasing the loss of electromagnetic waves.

[0023] 3) The special micro-nano structure endows the material with excellent microwave absorption performance. When the coating thickness is 3.66 mm, the strongest reflection loss value of -60.84 dB (8.45 GHz) is obtained, and the absorption bandwidth (RL < -5 dB) is 7.43 GHz. When the coating thickness is between 5.12 and 5.71 mm, the effective absorption bandwidth (RL < -10 dB) is greater than 5.5 GHz, which effectively solves the problems of low absorption intensity and narrow bandwidth of existing magnetic microwave absorbing materials. Attached Figure Description

[0024] Figure 1 This is a SEM image of the Fe3O4 chain-like microwave absorbing material prepared in Example 1 of this invention;

[0025] Figure 2 The minimum reflection loss and maximum absorption bandwidth of the Fe3O4 chain-like microwave absorbing material prepared in Example 1 of this invention are shown in the diagram.

[0026] Figure 3 The minimum reflection loss and maximum absorption bandwidth of the Fe3O4 chain-like microwave absorbing material prepared in Example 3 of this invention are shown in the diagram.

[0027] Figure 4 The minimum reflection loss and maximum absorption bandwidth of the Fe3O4 chain-like microwave absorbing material prepared in Example 4 of this invention are shown in the diagram.

[0028] Figure 5 This is a SEM image of the Fe3O4 chain-like microwave absorbing material prepared in Example 5 of the present invention;

[0029] Figure 6 The minimum reflection loss and maximum absorption bandwidth of the Fe3O4 chain-like microwave absorbing material prepared in Example 5 of this invention are shown in the diagram.

[0030] Figure 7 This is a SEM image of the Fe3O4 chain-like microwave absorbing material prepared in Example 6 of the present invention;

[0031] Figure 8 The minimum reflection loss and maximum absorption bandwidth of the Fe3O4 chain-like microwave absorbing material prepared in Example 6 of this invention are shown in the diagram.

[0032] Figure 9 This is a SEM image of the Fe3O4 microwave absorbing material prepared in Comparative Example 1 of this invention;

[0033] Figure 10 The diagram shows the minimum reflection loss and maximum absorption bandwidth of the Fe3O4 microwave absorbing material prepared in Comparative Example 1 of this invention.

[0034] Figure 11 This is a SEM image of the Fe3O4 microwave absorbing material prepared in Comparative Example 2 of this invention;

[0035] Figure 12 The minimum reflection loss and maximum absorption bandwidth of the Fe3O4 microwave absorbing material prepared in Comparative Example 2 of this invention are shown in the diagram.

[0036] Figure 13 The diagram shows the minimum reflection loss and maximum absorption bandwidth of the Fe3O4 absorbing material prepared in Comparative Example 3 of this invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0039] Unless otherwise specified in the embodiments, the techniques or conditions described in the literature in this field or in accordance with the product manual may be followed.

[0040] Example 1

[0041] A method for preparing a Fe3O4 chain-like microwave absorbing material with an ultra-high aspect ratio includes the following steps:

[0042] (1) Take 25 mL of iron pentacarbonyl solution and 1 mL of ethanol, and sonicate for 0.5 h to obtain a well mixed solution;

[0043] (2) Place the well-mixed solution in a polytetrafluoroethylene-lined stainless steel sealed reactor and place it in a 1T magnet. Perform a solvothermal reaction at 180℃ for 6 hours;

[0044] (3) After the reaction was completed, the reactor was cooled in air. It was then centrifuged twice each with distilled water and ethanol at 6000 rpm for 5 minutes each time. The resulting black precipitate was dried in an oven at 50°C for 20 hours to obtain the Fe3O4 chain-like microwave absorbing material with an ultra-high aspect ratio. Its SEM image is shown below. Figure 1 As shown, by Figure 1 It can be seen that Fe3O4 particles form Fe3O4 chain-like microwave absorbing materials with ultra-large aspect ratios under magnetic fields, with aspect ratios of 200-500.

[0045] Example 2

[0046] A method for preparing a Fe3O4 chain-like microwave absorbing material with an ultra-high aspect ratio includes the following steps:

[0047] (1) Take 25 mL of iron pentacarbonyl solution and 1 mL of ethanol, stir in a water bath at 30°C for 0.5 h at a stirring speed of 300 r / min to obtain a uniformly mixed solution;

[0048] (2) Place the well-mixed solution in a polytetrafluoroethylene-lined stainless steel sealed reactor and place it in a 1T magnet. Perform a solvothermal reaction at 180℃ for 6 hours;

[0049] (3) After the reaction was completed, the reactor was cooled in the air. It was centrifuged twice with distilled water and twice with ethanol at 6000 rpm for 5 min each time. The black precipitate obtained was dried in an oven at 50°C for 20 hours to obtain the Fe3O4 chain microwave absorbing material with ultra-high aspect ratio.

[0050] Example 3

[0051] A method for preparing a Fe3O4 chain-like microwave absorbing material with an ultra-high aspect ratio includes the following steps:

[0052] (1) Take 30 mL of iron pentacarbonyl solution and 1 mL of ethanol, and sonicate for 0.6 h to obtain a well mixed solution;

[0053] (2) Place the well-mixed solution in a polytetrafluoroethylene-lined stainless steel sealed reactor and place it in a 1.5T magnet. Perform a solvothermal reaction at 160℃ for 2 hours.

[0054] (3) After the reaction was completed, the reactor was cooled in the air. The reactor was centrifuged four times each with distilled water and ethanol at 5000 rpm for 3 minutes each time. The black precipitate obtained was dried in an oven at 80°C for 10 hours to obtain the Fe3O4 chain-like microwave absorbing material with a large aspect ratio.

[0055] Example 4

[0056] A method for preparing a Fe3O4 chain-like microwave absorbing material with an ultra-high aspect ratio includes the following steps:

[0057] (1) Take 20 mL of ferric pentacarbonyl solution and 1 mL of ethanol, and sonicate for 0.5 h to obtain a homogeneous solution;

[0058] (2) Place the well-mixed solution in a polytetrafluoroethylene-lined stainless steel sealed reactor and place it in a 0.8T magnet. Perform a solvothermal reaction at 200℃ for 8 hours.

[0059] (3) After the reaction was completed, the reactor was cooled in the air. It was centrifuged twice with distilled water and twice with ethanol at 6000 rpm, each time for 5 min. The black precipitate obtained was dried in an oven at 60℃ for 18 hours to obtain the Fe3O4 chain microwave absorbing material with ultra-high aspect ratio.

[0060] Example 5

[0061] The only difference from Example 1 is that in (2), it is placed in a magnet of 0.05T.

[0062] Example 6

[0063] The only difference from Example 1 is that in (2), it is placed in a 6T magnet.

[0064] Comparative Example 1

[0065] A method for preparing Fe3O4 microwave absorbing material includes the following steps:

[0066] (1) Take 25 mL of iron pentacarbonyl solution and 1 mL of ethanol, stir in a water bath at 15 °C for 0.5 h at a stirring speed of 300 r / min to obtain a uniformly mixed solution.

[0067] (2) Place the well-mixed solution in a sealed stainless steel reactor lined with polytetrafluoroethylene, without applying a magnetic field. Perform a solvothermal reaction at 180°C for 6 hours.

[0068] (3) After the reaction was completed, the reactor was cooled in the air. It was centrifuged twice with distilled water and twice with ethanol at 4000 rpm, each time for 4 min. The resulting black precipitate was dried in an oven at 50°C for 20 hours.

[0069] Comparative Example 2

[0070] The only difference from Example 1 is that in (2), it is placed in a 7T magnet.

[0071] Comparative Example 3

[0072] The only difference from Example 1 is that in (1), water is used instead of ethanol; the product is a non-chain structure.

[0073] The performance of the absorbing materials in the examples and comparative examples was tested. The specific test method is as follows: The specific absorbing test method is the coaxial cable method based on transmission line theory. The test sample is mixed with paraffin and pressed into a ring-shaped columnar sample with an inner diameter of 3.04 mm, an outer diameter of 7 mm, and a thickness of 2 mm.

[0074] Figure 2 This is a diagram showing the minimum reflection loss and maximum absorption bandwidth of the Fe3O4 chain-like absorbing material in Example 1 of this invention; (The diagram is from...) Figure 2 It can be seen that the special micro-nano structure endows the material with excellent microwave absorption performance. When the coating thickness is 3.66 mm, the strongest reflection loss value is obtained -60.84 dB (8.45 GHz) and the absorption bandwidth (RL < -5 dB) is 7.43 GHz. When the coating thickness is 5.25 mm, the effective absorption bandwidth (RL < -10 dB) is 5.53 GHz.

[0075] Figure 3 This is a diagram showing the minimum reflection loss and maximum absorption bandwidth of the Fe3O4 chain-like absorbing material in Example 3 of the present invention; (The diagram is from...) Figure 3 It can be seen that the prepared sample has good electromagnetic wave absorption capability, with a minimum reflection loss RL = -52.84dB (8.65GHz) and an effective absorption bandwidth EAB = 4.79GHz.

[0076] Figure 4 This is a diagram showing the minimum reflection loss and maximum absorption bandwidth of the Fe3O4 chain-like absorbing material in Example 4 of the present invention; (The diagram is from...) Figure 4It can be seen that the prepared sample has good electromagnetic wave absorption ability, RL = -53.25 dB (12.05 GHz), and EAB = 5.13 GHz.

[0077] Figure 5 This is the SEM image of the Fe3O4 chain-like wave-absorbing material prepared in Example 5 of the present invention. Figure 5 It can be seen that the prepared sample of Fe3O4 nanoparticles shows a chain-like arrangement under a 0.5 T magnetic field, and the aspect ratio is within the range of 200 - 500. Figure 6 This is the minimum reflection loss and maximum absorption bandwidth diagram of the Fe3O4 chain-like wave-absorbing material prepared in Example 5 of the present invention. Figure 6 It can be seen that the prepared sample has good electromagnetic wave absorption ability, RL = -52.75 dB (6.15 GHz), and EAB = 4.79 GHz.

[0078] Figure 7 This is the SEM image of the Fe3O4 chain-like wave-absorbing material prepared in Example 6 of the present invention. Figure 7 It can be seen that the prepared sample of Fe3O4 nanoparticles shows a chain-like arrangement under a 6 T magnetic field, and the aspect ratio is within the range of 200 - 500. Figure 8 This is the minimum reflection loss and maximum absorption bandwidth diagram of the Fe3O4 chain-like wave-absorbing material prepared in Example 6 of the present invention. Figure 8 It can be seen that the prepared sample has good electromagnetic wave absorption ability, RL = -45.29 dB (9.15 GHz), and EAB = 4.44 GHz.

[0079] Figure 9 This is the SEM image of the Fe3O4 wave-absorbing material prepared in Comparative Example 1. Figure 9 It can be seen that the prepared sample is relatively dispersed and not in a chain-like shape.

[0080] Figure 10 This is the minimum reflection loss and maximum absorption bandwidth diagram of the wave-absorbing material prepared in Comparative Example 1. Figure 10 It can be seen that the wave absorption performance and effective absorption bandwidth of the prepared sample are both decreased compared with Example 1, RL = -12.52 dB (6.7 GHz), and EAB = 2.14 GHz.

[0081] Figure 11 This is the SEM image of the Fe3O4 wave-absorbing material prepared in Comparative Example 2. Figure 11 It can be seen that the prepared sample of Fe3O4 nanoparticles has aggregation and stacking. Figure 12 This is the minimum reflection loss and maximum absorption bandwidth diagram of the Fe3O4 wave-absorbing material in Comparative Example 2 of the present invention. Figure 12It can be seen that the absorption performance and bandwidth of the prepared sample are lower than those of Example 1, with RL = -41.65dB (8.75GHz) and EAB = 2.89GHz.

[0082] Figure 13 This diagram shows the minimum reflection loss and maximum absorption bandwidth of the Fe3O4 non-chain absorbing material prepared in Comparative Example 3 of this invention; (The diagram is from...) Figure 13 It can be seen that the absorption performance and bandwidth of the prepared sample are lower than those of Example 1, with RL = -13.22dB (1.0GHz) and EAB = 0.62GHz.

[0083] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a Fe3O4 chain-like microwave absorbing material with an ultra-high aspect ratio, characterized in that: The process includes the following steps: mixing a ferric pentacarbonyl solution and ethanol evenly, then placing the mixture in a hydrothermal reaction apparatus and reacting it under the presence of a magnetic field; wherein the strength of the magnetic field is 0.8-6T; after the reaction is completed, cooling, washing, and drying are performed to obtain the Fe3O4 chain-like microwave absorbing material with an ultra-high aspect ratio; the aspect ratio of the Fe3O4 chain-like microwave absorbing material with an ultra-high aspect ratio is 200-500; the volume ratio of the ferric pentacarbonyl solution to ethanol is 20-30:

1.

2. The method for preparing the Fe3O4 chain-like microwave absorbing material with an ultra-high aspect ratio according to claim 1, characterized in that: The pentacarbonyl iron solution and ethanol are mixed evenly by ultrasound or stirring.

3. The method for preparing the Fe3O4 chain-like microwave absorbing material with an ultra-high aspect ratio according to claim 2, characterized in that: The ultrasound duration is ≥0.5h; the stirring temperature is 15-30℃, and the stirring time is ≥0.5h.

4. The method for preparing the Fe3O4 chain-like microwave absorbing material with an ultra-high aspect ratio according to claim 1, characterized in that: The reaction is carried out at a temperature of 160-200℃ for 2-8 hours.

5. The method for preparing the Fe3O4 chain-like microwave absorbing material with an ultra-large aspect ratio according to claim 1, characterized in that: After the reaction is complete, cool in air.

6. The method for preparing the Fe3O4 chain-like microwave absorbing material with an ultra-high aspect ratio according to claim 1, characterized in that: The mixture is washed by centrifugation with water and ethanol in sequence; the centrifugation speed is 4000-6000 revolutions per minute, and the washing is performed 4-8 times, each time for 3-5 minutes.

7. The method for preparing the Fe3O4 chain-like microwave absorbing material with an ultra-large aspect ratio according to any one of claims 1-6, characterized in that: The drying temperature is 50-80℃, and the time is 10-20 hours.

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