A method for broadening the effective bandwidth of a wave-absorbing material

Abstract

The application provides a method for widening the effective bandwidth of a wave-absorbing material, and comprises a preparation method of a composite material: mixing magnetic metal hydrotalcite and expanded graphite into a multiphase fluid, then introducing the multiphase fluid into a high-speed shearing microcavity in a circulation mode, using the high-speed fluid boundary layer shearing force to realize the interlayer peeling of the magnetic metal hydrotalcite and the expanded graphite, and self-assembling into a two-dimensional / two-dimensional stacked sheet-shaped magnetic particle / few-layer graphite electromagnetic wave absorbing powder. The application proposes a two-dimensional / two-dimensional structure formed by sheet-shaped magnetic nanoparticles and few-layer graphite for a carbon-based magnetic particle composite material. The two-dimensional electron gas is easy to form at the interface, and the resonance loss different from the interface relaxation can be realized by the resonance of the plasmon and the incident microwave. On the other hand, the magnetic performance of the sheet-shaped magnetic nanoparticles can be secondarily regulated, the mode of Aharoni exchange resonance is changed, the dielectric loss and the magnetic loss are improved in an integrated manner, and the effective bandwidth of the material for absorbing electromagnetic waves is widened.

Description

Technical Field

[0001] This invention relates to the field of carbon-based magnetic particle composite material preparation technology, and in particular to a method for broadening the effective bandwidth of microwave absorbing materials. Background Technology

[0002] Absorbing electromagnetic waves using absorbing materials is an effective method for solving electromagnetic pollution. Focusing on the requirements of being "thin, wide, light, and strong," carbon-based electromagnetic wave absorbing materials possess advantages such as light weight, tunable frequency range, and good compatibility with the organic / inorganic interface of the matrix, making them a promising new type of absorbing material to replace traditional ferrite, carbonyl iron, and other absorbing materials. However, carbon-based materials generally have high dielectric constants and poor impedance matching, which limits their practical application. Therefore, combining them with magnetic nanoparticles to form composite materials, accommodating both dielectric and magnetic losses, and improving impedance matching to enhance the material's absorption performance, is currently the main design approach for carbon-based absorbing materials. Co-precipitation, in-situ growth, and self-assembly methods have all achieved the composite of carbon-based materials and magnetic nanoparticles, improving absorption performance. However, these composite materials are mostly multiphase materials of spherical magnetic particles and various carbon-based materials; dielectric loss mainly comes from interfacial relaxation, and magnetic loss is mainly due to natural resonance. Limited by the Snoek limit of spherical particles, the effective absorption frequency band is concentrated in the X-band and part of the Kμ-band. It is of great significance to further extend the absorption frequency band to the S, C and Kμ high-frequency bands. Summary of the Invention

[0003] The purpose of this invention is to solve the technical problem that in the prior art, composite materials are mostly multiphase materials of spherical magnetic particles and various carbon-based materials, the dielectric loss mainly comes from interface relaxation, the magnetic loss is mainly due to natural resonance, and the effective absorption frequency band is concentrated in the X-band and part of the Kμ-band due to the limitation of the Snoek limit of spherical particles.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method for preparing a composite material, characterized by comprising the following steps:

[0006] Magnetic metal hydrotalcite and expanded graphite are blended into a multiphase fluid, which is then circulated into a high-speed shearing microcavity. The boundary layer shearing force of the high-speed fluid is used to achieve interlayer delamination of magnetic metal hydrotalcite and expanded graphite, which then self-assemble into two-dimensional / two-dimensional stacked sheet-like magnetic particles / few-layer graphite electromagnetic wave absorbing powder.

[0007] Preferably, the specific steps are as follows:

[0008] S1: Magnetic metal hydrotalcite is ultrasonically dispersed in ultrapure water to obtain suspension L1, which is then ultrasonically treated.

[0009] S2: Treat expanded graphite in hydrogen peroxide for 1 hour to obtain suspension L2;

[0010] S3: Ultrasonic mixing of L1 and L2 forms a multiphase mixed liquid L3;

[0011] S4: L3 is cyclically added to the high-speed shearing microcavity for high-speed shearing to obtain the sheared suspension L4;

[0012] S5: L4 was repeatedly washed with ultrapure water until the center was reached, then centrifuged and vacuum dried to obtain sheet-like magnetic particles / few-layer graphite electromagnetic wave absorbing powder.

[0013] Preferably, the magnetic metal hydrotalcite in S1 is one of NiFe hydrotalcite, NiCo hydrotalcite, FeCo hydrotalcite, or a doped form thereof, and the ultrasonic treatment time is 2 hours.

[0014] Preferably, the expanded graphite is 80-200 mesh, and the hydrogen peroxide concentration is 15%.

[0015] Preferably, the mass density of both L1 and L2 is 0.15 g / ml.

[0016] Preferably, the ratio of L1 to L2 in S3 is 1:1 to 2.

[0017] This application also provides a composite material prepared using the composite material preparation method described above.

[0018] This application also provides an application of a composite material, which is the composite material described above, for absorbing electromagnetic waves to solve electromagnetic pollution.

[0019] This application proposes a two-dimensional / two-dimensional structure formed by sheet-like magnetic nanoparticles and few-layer graphite in carbon-based magnetic particle composites. This structure readily forms a two-dimensional electron gas at the interface, enabling the resonance formation of plasmons and incident microwaves with resonance losses different from interface relaxation. Furthermore, the magnetic properties of the sheet-like magnetic nanoparticles can be further modulated, altering the Aharoni exchange resonance mode and comprehensively improving both dielectric and magnetic losses, thus broadening the effective bandwidth for electromagnetic wave absorption. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the synthesis path of a method for preparing a composite material according to one embodiment of the present invention;

[0021] Figure 2 This is a schematic diagram of a shearing device according to one embodiment of the present invention;

[0022] Figure 3The images shown are scanning electron microscope images, imaginary part of dielectric constant, imaginary part of magnetic permeability, and curves showing the variation of reflection loss with frequency for the sheet-like magnetic particles / few-layer graphite electromagnetic wave absorbing powder in Embodiment 1 of the present invention.

[0023] Figure 4 The images shown are scanning electron microscope images, imaginary part of dielectric constant, imaginary part of magnetic permeability, and reflection loss versus frequency curves of the sheet-like magnetic particles / few-layer graphite electromagnetic wave absorbing powder in Embodiment 2 of the present invention.

[0024] In the diagram, 1 is the stationary disk; 2 is the shearing microcavity; 3 is the moving disk; 4 is the cavity; 5 is the suspension; and 6 is the cooling circulation system. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments.

[0026] Numerous specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways than those described herein, and therefore the invention is not limited to the specific embodiments disclosed in the following specification.

[0027] For a method of preparing a composite material, please refer to [link / reference]. Figure 1 It includes the following steps:

[0028] S1: A layered magnetic metal hydrotalcite was ultrasonically dispersed in ultrapure water to obtain a suspension L1 with a mass density of 0.15 g / ml. The ultrasonic time was 2 hours to ensure the uniformity of the suspension as much as possible.

[0029] In one embodiment, the layered magnetic metal hydrotalcite is NiFe hydrotalcite, and the NiFe ratio in the NiFe hydrotalcite is 3:1; in other embodiments, the layered magnetic metal hydrotalcite can also be NiCo, FeCo, or doped based on them, such as Co-doped NiFe hydrotalcite, etc.

[0030] The magnetic metal hydrotalcite described above can be prepared using a hydrothermal method or directly customized during hydrotalcite production. Since the preparation of hydrotalcite has been well studied, this invention does not involve the research of hydrotalcite.

[0031] S2: 80-200 mesh expanded graphite is treated in 15% hydrogen peroxide for 1 hour, while maintaining the temperature at 50-100℃, with a mass density of 0.05 g / ml, to obtain a suspension L2;

[0032] S3: Ultrasonic mixing of L1 and L2 forms a multiphase mixed liquid L3;

[0033] In one embodiment, the ratio of L1 to L2 is 1:1 to 2.

[0034] S4: The mixed liquid L3 is circulated and dripped into the high-speed shearing microcavity for high-speed shearing. The spacing between the shearing disks is 50-100 μm, and the shearing speed is 8000-10000 rpm. The shearing cycle is 10-20 times to obtain the sheared suspension L4.

[0035] In one embodiment, a high-speed liquid phase shearing device is used to shear the L3. (See [link to relevant documentation]). Figure 2 The high-speed liquid phase shearing device includes a cavity 4 and a cooling circulation system 6. The cooling circulation system 6 is connected to the top and bottom of the cavity 4 at both ends for cooling the cavity 4. A moving disk 3 and a stationary disk 1 are arranged inside the cavity 4. The projections of the moving disk 3 and the stationary disk 1 on the vertical plane overlap each other. The distance between the moving disk 3 and the stationary disk 1 is adjustable, ranging from tens of micrometers to hundreds of micrometers. A shearing microcavity 2 is arranged between the moving disk 3 and the stationary disk 1. During use, the suspension 5 enters the high-speed shearing microcavity 2 through the cooling circulation system 6. The high-speed rotating moving disk 3 drags in the microcavity to form a Couette swirling flow field, generating a boundary layer near the surfaces of the moving disk 3 and the stationary disk 1. The micrometer-level spacing provides a large velocity gradient. The suspended particles in the boundary layer are peeled off by the liquid phase shearing force. The surface of the NiFe LDH layer is positively charged, while the surface of the peeled graphite sheet is negatively charged, thereby achieving electrostatic assembly between the two to obtain the NiFeLDH / LLG composite material.

[0036] S5: L4 is repeatedly washed with ultrapure water until neutral, centrifuged and vacuum dried at a temperature of 60-100℃ to obtain flake magnetic particles / few-layer graphite electromagnetic wave absorbing powder, which is the composite material.

[0037] This application also provides a composite material prepared using the above-described preparation method. The composite material is a sheet-like magnetic particle / few-layer graphite electromagnetic wave absorbing powder. The scanning electron microscope image and the curves showing the changes in the imaginary part of the dielectric constant, the imaginary part of the permeability, and the reflection loss as a function of frequency are shown below. Figure 3 and Figure 4 As shown, both the dielectric constant and permeability exhibit frequency domain oscillations, indicating that this material possesses both plasmon resonance and Aharoni exchange resonance, with the effective bandwidth effectively extended in the C and Kμ bands.

[0038] This application also provides an application of a composite material, wherein the composite material is the above-mentioned sheet-like magnetic particles / few-layer graphite electromagnetic wave absorber, and the composite material is used to absorb electromagnetic waves to solve electromagnetic pollution.

[0039] The present application will be described in detail below with reference to specific embodiments:

[0040] Example 1:

[0041] 1. NiFe hydrotalcite with a NiFe ratio of 3:1 was ultrasonically dispersed in ultrapure water until the suspension L1 had a mass density of 0.15 g / ml. The ultrasonic time was 2 hours to ensure the uniformity of the suspension as much as possible.

[0042] 2. 80-mesh expanded graphite was treated in 15% hydrogen peroxide for 1 hour while maintaining the temperature at 50-100℃, resulting in a mass density of 0.05 g / ml, to obtain a suspension L2.

[0043] 3. 100ml L1 and 100ml L2 are ultrasonically mixed to form a multiphase mixed liquid L3;

[0044] 4. The mixed liquid L3 was circulated and dripped into the high-speed shearing microcavity for high-speed shearing. The spacing between the shearing disks was 80 μm, and the shearing speed was 90,000 rpm. The shearing cycle was repeated 15 times to obtain the sheared suspension L4.

[0045] 5. L4 was repeatedly washed with ultrapure water until neutral, centrifuged, and vacuum dried at 70℃ to obtain m. NiFe-LDH ∶m llg = 3:1 flake magnetic particles / few-layer graphite electromagnetic wave absorbing powder, where m NiFe-LDH The mass of NiFe hydrotalcite, m llg Refers to the quality of few-layer graphite.

[0046] The scanning electron microscope image of the material and the graphs showing the imaginary part of the dielectric constant, the imaginary part of the permeability, and the reflection loss as a function of frequency are shown below. Figure 3 As shown.

[0047] Example 2:

[0048] 1. NiFe hydrotalcite with a NiFe ratio of 3:1 was ultrasonically dispersed in ultrapure water until the suspension L1 had a mass density of 0.15 g / ml. The ultrasonic time was 2 hours to ensure the uniformity of the suspension as much as possible.

[0049] 2. 200-mesh expanded graphite was treated in 15% hydrogen peroxide for 1 hour while maintaining the temperature at 50-100℃, resulting in a mass density of 0.05 g / ml, to obtain a suspension L2.

[0050] 3. 50 ml L1 and 100 ml L2 are ultrasonically mixed to form a multiphase mixed liquid L3;

[0051] 4. The mixed liquid L3 was circulated and dripped into the high-speed shearing microcavity for high-speed shearing. The spacing between the shearing disks was 80 μm, and the shearing speed was 90,000 rpm. The shearing cycle was repeated 15 times to obtain the sheared suspension L4.

[0052] 5. L4 was repeatedly washed with ultrapure water until neutral, centrifuged and vacuum dried at 70℃ to obtain mass ratio m. NiFe-LDH ∶m llg =3:2 flake magnetic particles / few-layer graphite electromagnetic wave absorbing powder.

[0053] The scanning electron microscope image of the material and the graphs showing the imaginary part of the dielectric constant, the imaginary part of the permeability, and the reflection loss as a function of frequency are shown below. Figure 4 As shown.

[0054] According to solid-state theory, the plasmon dispersion relation of a two-dimensional electron gas is expressed as: In the formula, Let ω be the angular frequency of the collective electron oscillation, m* be the effective mass, ε be the dielectric constant, n be the electron density, and q be the wavenumber. The bandgap-free dispersion relation determines its ease of excitation, a characteristic widely confirmed in semiconductor MOS inversion layers. From the dispersion relation perspective, adjusting the electron density and effective mass can yield a considerably wide frequency range. When the incident electromagnetic wave and plasmon frequency match, resonant absorption occurs. Extending this resonant absorption mechanism to absorbing materials is beneficial for broadening the effective bandwidth. On the other hand, the upper limit of the absorption frequency for magnetic loss in materials follows the Snoek limit. Anisotropic, sheet-like magnetic particles are beneficial for increasing magnetic saturation, thereby enhancing the material's magnetic response performance at high frequencies and strengthening the high-frequency loss of the absorbing material in the Kμ band through Aharoni exchange resonance.

[0055] Based on the mechanism of plasmon resonance absorption, this application proposes a design strategy that combines sheet-like magnetic particles with few-layer graphite, taking into account both magnetic loss and impedance matching. A two-dimensional / two-dimensional structure is formed between the sheet-like magnetic particles and the few-layer graphite. The significant difference in their macroscopic electromagnetic parameters facilitates the formation of a two-dimensional electron gas at the interface. Furthermore, the sheet-like magnetic particles overcome the Snoek limit of spherical particles, thereby broadening the effective bandwidth for electromagnetic wave absorption.

[0056] While mechanical ball milling of Fe, Co, and Ni magnetic metal powders in different proportions can yield flake-like magnetic particles, successful preparation requires over 100 hours of grinding time, resulting in excessive energy consumption and low efficiency. Layered magnetic metal hydrotalcites, such as NiFe hydrotalcite (not limited to NiFe hydrotalcite, but can also be NiCo, FeCo, or doped forms like Co-doped NiFe hydrotalcite), have weak interlayer bonding. Ultrasonic or high-speed liquid-phase shearing can achieve interlayer exfoliation, resulting in two-dimensional positively charged plates with micro-nano thicknesses. Expanded graphite, being flake graphite with increased interlayer spacing, exhibits weakened interlayer forces, also allowing for interlayer exfoliation via ultrasonic or high-speed liquid-phase shearing. This invention recommends using a high-speed liquid-phase shearing method to blend magnetic metal hydrotalcite and expanded graphite into a multiphase fluid. This multiphase fluid is circulated into a high-speed shearing microcavity, utilizing the boundary layer shearing force of the high-speed fluid to achieve interlayer exfoliation of the hydrotalcite and expanded graphite, which then self-assembles into two-dimensional / two-dimensional stacked flake-like magnetic particles / few-layer graphite electromagnetic wave absorbing powders.

[0057] The composite material in this application is a carbon-based magnetic particle composite material. It proposes a two-dimensional / two-dimensional structure formed by sheet-like magnetic nanoparticles and few-layer graphite. This structure readily forms a two-dimensional electron gas at the interface, enabling the resonance formation of plasmons and incident microwaves with resonance losses different from interface relaxation. Furthermore, the magnetic properties of the sheet-like magnetic nanoparticles can be further modulated, altering the Aharoni exchange resonance mode and comprehensively improving both dielectric and magnetic losses, thus broadening the effective bandwidth for electromagnetic wave absorption.

[0058] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A method for preparing a composite material, characterized in that: Includes the following steps: Magnetic metal hydrotalcite and expanded graphite are blended into a multiphase fluid, and then the multiphase fluid is circulated into a high-speed shearing microcavity. The boundary layer shearing force of the high-speed fluid is used to achieve interlayer delamination of magnetic metal hydrotalcite and expanded graphite, and they self-assemble into sheet-like magnetic particles / few-layer graphite electromagnetic wave absorbing powder. The specific steps are as follows: S1: Magnetic metal hydrotalcite is ultrasonically dispersed in ultrapure water to obtain suspension L1, which is then ultrasonically treated; the magnetic metal hydrotalcite is NiFe hydrotalcite, NiCo hydrotalcite, FeCo hydrotalcite, or a dopant of one of the above three types, and the ultrasonic treatment time is 2 hours. S2: Treat expanded graphite in hydrogen peroxide for 1 hour to obtain suspension L2; S3: Ultrasonic mixing of L1 and L2 forms a multiphase mixed liquid L3; S4: L3 is cyclically added to the high-speed shearing microcavity for high-speed shearing to obtain the sheared suspension L4; S5: L4 was repeatedly washed with ultrapure water until neutral, centrifuged and vacuum dried to obtain sheet-like magnetic particles / few-layer graphite electromagnetic wave absorbing powder.

2. The method for preparing the composite material according to claim 1, characterized in that: The expanded graphite is 80-200 mesh, and the hydrogen peroxide concentration is 15%.

3. The method for preparing the composite material according to claim 1, characterized in that: The mass density of both L1 and L2 is 0.15 g / ml.

4. The method for preparing the composite material according to claim 1, characterized in that: The ratio of L1 to L2 in S3 is 1:1~2.

5. A composite material, characterized in that: It is prepared using the method for preparing the composite material according to any one of claims 1-4.

6. An application of a composite material, characterized in that: The composite material is the composite material described in claim 5, and the composite material is used to absorb electromagnetic waves to solve the problem of electromagnetic pollution.

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