Spherical complex structure wave-absorbing agent and preparation method thereof

Abstract

The invention discloses a preparation method of a spherical wave-absorbing agent with a complex structure. The preparation method comprises the following steps: preparing MAX phase powder into a spherical template through a spray granulation process; taking the spherical template as an inner core, and performing in-situ growth of a ferrite shell layer on the surface of the spherical template by a hydrothermal method to obtain the spherical composite structure composite wave-absorbing agent, wherein the particle size of the inner core is 8-12 microns, and the thickness of the shell layer is 400-600 nanometers. Through unique material system design and microstructure regulation and control, a core-shell composite structure with dielectric MAX-phase spherical particles as a matrix and a magnetic Fe3O4 nano layer as a coating shell layer is constructed. According to the bi-component heterostructure design, gradient matching of electromagnetic parameters of the material is achieved, and multiple electromagnetic wave dissipation mechanisms are innovatively constructed through geometric configuration.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic wave absorbing materials, specifically a spherical complex structure wave absorbing agent and its preparation method. Background Technology

[0002] With the rapid development of modern electronic information technology and military stealth technology, the demand for electromagnetic wave absorbing materials in electromagnetic shielding, anti-interference, and stealth coatings is becoming increasingly urgent. Traditional absorbing materials (such as ferrites, carbon-based materials, and conductive polymers) often suffer from problems such as narrow absorption bandwidth, high density, and poor environmental stability, making it difficult to meet the high-performance absorption requirements of wide bandwidth, lightweight design, and complex service environments.

[0003] In recent years, researchers have attempted to improve microwave absorption performance by constructing synergistic loss mechanisms in magnetic-dielectric composite systems. For example, ferrites are combined with dielectric materials such as carbon nanotubes and graphene, or magnetic layers are coated onto the surface of ceramic particles using chemical deposition. However, these composite materials often employ simple physical mixing or disordered coating structures, making it difficult to achieve uniform dispersion of magnetic-dielectric components and maximize interfacial coupling effects. Furthermore, asymmetric morphologies (such as sheet-like or rod-like) of microwave absorbers are prone to anisotropy, leading to uneven electromagnetic field distribution and reduced effective absorption bandwidth.

[0004] The geometry of the absorbing agent directly affects the electromagnetic wave propagation path and interfacial polarization effect. In existing technologies, spherical structures are considered advantageous for forming a uniform electromagnetic field distribution and multiple scattering due to their isotropic characteristics; however, their fabrication is mostly limited to single-component (e.g., hollow Fe3O4 microspheres) or simple combinations of core-shell structures (e.g., SiO2@Fe3O4). For composite systems of MAX phase and ferrite, how to achieve synergistic enhancement of magnetic loss, dielectric loss, and interfacial polarization while controlling impedance matching through precise spherical coating structure design remains a pressing technical challenge. Summary of the Invention

[0005] In view of this, the present invention provides a spherical complex structure microwave absorber and its preparation method to solve the problems mentioned in the background art. To achieve the above objectives, the present invention provides the following technical solution: This invention discloses a method for preparing a spherical complex structure microwave absorber, comprising the following steps: (1) The MAX phase powder was prepared into a spherical template by spray granulation process; (2) Using a spherical template as the core, a ferrite shell is grown in situ on its surface by hydrothermal method to obtain a spherical composite microwave absorber with a complex structure; wherein the core particle size is 8-12 micrometers and the shell thickness is 400-600 nanometers.

[0006] As a further aspect of the present invention: the MAX phase powder is at least one of Ti3SiC2, Ti2AlC or Ti2SnC.

[0007] As a further aspect of the present invention: in step (1), the spray granulation process includes: mixing MAX phase powder with pure water to form a slurry, spraying the slurry into granules in a spray granulation tower to obtain spherical droplets, and sintering the spherical droplets to form a spherical template.

[0008] As a further aspect of the present invention: the slurry has a solid content of 50-70%, the atomizing disc rotates at a speed of 40-50 Hz, the inlet temperature is 200-250°C, and the exhaust temperature is 100-120°C.

[0009] As a further aspect of the present invention: in step (1), the sintering temperature is 1100-1300℃ and the sintering time is 3-5h.

[0010] As a further aspect of the present invention: in step (1), the MAX phase powder is pre-processed by ball milling.

[0011] As a further aspect of the present invention: in step (2), the hydrothermal method specifically includes the following steps: A spherical template was dispersed in a mixed iron source solution containing Fe³⁺ and Fe²⁺ to obtain a suspension; Add alkali to the suspension to adjust its pH to 8.5-10.5, and react at 80-100℃ for 0.5-1 hour; After the reaction is complete, the products are magnetically separated, washed and dried to obtain a core-shell structured composite microwave absorber.

[0012] As a further aspect of the present invention: the molar ratio of Fe³⁺ to Fe²⁺ in the spherical template and the mixed iron source solution is (0.03-0.04):(2.5-3.5):1.

[0013] On the other hand, the present invention discloses a spherical complex structure microwave absorber, which is prepared by the above-described preparation method.

[0014] Compared with the prior art, the beneficial effects of the present invention are: Compared to existing technologies that commonly use magnetic materials to simply coat dielectric materials or create single spherical structures, this invention constructs a core-shell composite structure with dielectric MAX phase spherical particles as the matrix and magnetic Fe3O4 nanolayers as the coating shell through unique material system design and microstructure control. This two-component heterogeneous structure design achieves gradient matching of material electromagnetic parameters and innovatively constructs multiple electromagnetic wave dissipation mechanisms through geometric configuration.

[0015] Electromagnetic wave absorption mechanism: The outer Fe3O4 magnetic shell effectively reduces the reflection loss of electromagnetic waves on the material surface by adjusting the surface impedance characteristics, and significantly improves the capture efficiency of incident electromagnetic waves; the electromagnetic waves entering the material are initially attenuated by the hysteresis loss of the Fe3O4 layer, and then multiple dielectric loss mechanisms such as interface polarization and dipole polarization are excited in the MAX phase dielectric matrix; the specially designed hollow spherical structure greatly extends the propagation path of electromagnetic waves by constructing multiple internal reflection interfaces, so that electromagnetic energy is gradually dissipated in the process of repeated reflection.

[0016] This composite structure design enables the material to exhibit excellent electromagnetic wave absorption characteristics, with a significantly improved reflection loss value compared to traditional absorbers. In particular, by controlling the ratio between the MAX phase matrix particle size and the Fe3O4 coating layer thickness, the electromagnetic parameters of the material can be controlled and adjusted to meet the absorption requirements of different frequency bands.

[0017] The technological breakthrough of this invention is not only reflected in the significant improvement of microwave absorption performance, but also in the good scalability of the spray granulation combined with the in-situ surface growth process, which provides an innovative idea for the development of new composite microwave absorbing materials. It is particularly suitable for high-performance electromagnetic protection needs in aerospace, electronic communications and other fields. Attached Figure Description

[0018] Figure 1 The reflection loss variation of the absorbing agent with different coating thicknesses in Example 1 in the frequency range of 2-18 GHz is shown, with the lowest reflectivity reaching -57.2 dB at 16.6 GHz. Figure 2 The variation of reflection loss of the absorbing agent with different coating thicknesses in the frequency range of 2-18 GHz is shown in Comparative Example 1. Figure 3 To compare the reflection loss variation of absorbing agents with different coating thicknesses in Example 2 within the frequency range of 2.5-17.5 GHz; the dielectric loss of the material is more significant in the high-frequency region (≥10Hz). Detailed Implementation

[0019] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0021] Example 1 1. Ball milling: Put Ti2AlC powder (particle size 1 micrometer) into a ball mill with a material-to-ball ratio of 5:1; add grinding balls with a diameter of 3 mm and ball mill for 3 hours.

[0022] 2. Atomization granulation: The ball-milled powder is mixed with pure water to form a slurry, which is then sprayed in a spray granulation tower to obtain spherical droplets. The process parameters for spray granulation are: atomizing disc speed 45HZ, inlet air temperature 230℃, exhaust air temperature 110℃, pure water is used to prepare the slurry, and the solid content of the slurry is controlled to be 60%.

[0023] 3. Sintering: Sinter the spherical droplets to form Ti2AlC spheres with a particle size of 8 micrometers; the sintering temperature is 1200℃ and the sintering time is 4h.

[0024] 4. 0.018 mol anhydrous ferric chloride and 0.006 mol ferrous chloride tetrahydrate were added as iron sources to 150 ml of distilled water. Under stirring, 5 g (approximately 0.037 mol) of sintered Ti2AlC spheres were added. The temperature was raised to 90 °C, and 9 ml of 1 M ammonia water was added to adjust the reaction system to an alkaline environment. The reaction was continued for 30 minutes, cooled to room temperature, and magnetically collected. The collected powder was washed three times with pure water and dried to obtain the product, namely the spherical complex structure microwave absorber. The shell thickness of this spherical complex structure microwave absorber was measured to be 500 nm.

[0025] The obtained spherical complex structure absorbing agent was coated onto an aluminum substrate using a coaxial method, with coating thicknesses ranging from 0.9 to 1.9 mm. The reflection loss of the spherical complex structure absorbing agent with different coating thicknesses at different frequencies was detected using a vector network analyzer. The results are shown in [Figure number missing]. Figure 1 .from Figure 1 As can be seen, reflection loss typically decreases with increasing frequency, implying that the material may exhibit better absorption performance at higher frequencies. Furthermore, materials of different thicknesses exhibit varying reflection losses at different frequencies, indicating that material thickness significantly impacts its absorption performance. The point marked in the figure (16.6 GHz, -57.2 dB) shows the reflection loss of the material at that frequency with a specific thickness; this is a very low reflection loss value, indicating excellent absorption performance at that frequency.

[0026] Example 2 1. Ball milling: Put Ti2AlC powder (particle size 1 micrometer) into a ball mill with a material-to-ball ratio of 5:1; add grinding balls with a diameter of 3 mm and ball mill for 3 hours.

[0027] 2. Atomization granulation: The ball-milled powder is mixed with pure water to form a slurry, which is then sprayed in a spray granulation tower to obtain spherical droplets. The process parameters for spray granulation are: atomizing disc speed 40HZ, inlet air temperature 210℃, exhaust air temperature 100℃, pure water is used to prepare the slurry, and the solid content of the slurry is controlled to be 70%.

[0028] 3. Sintering: Sinter the spherical droplets to form Ti2AlC spheres with a particle size of 10 micrometers; the sintering temperature is 1100℃ and the sintering time is 4h.

[0029] 4. 0.015 mol anhydrous ferric chloride and 0.006 mol ferrous chloride tetrahydrate were added as iron sources to 150 ml of distilled water. Under stirring, 5 g (approximately 0.037 mol) of sintered Ti₂AlC spheres were added. The temperature was raised to 90 °C, and 9 ml of 1 M ammonia water was added to adjust the reaction system to an alkaline environment. The reaction was continued for 30 minutes, cooled to room temperature, and magnetically collected. The collected powder was washed three times with pure water and dried to obtain the product, namely the spherical complex structure microwave absorber. The shell thickness of this spherical complex structure microwave absorber was measured to be 400 nm.

[0030] Example 3 3. Ball milling: Put Ti2AlC powder (particle size 1 micrometer) into a ball mill with a material-to-ball ratio of 5:1; add grinding balls with a diameter of 3 mm and ball mill for 3 hours.

[0031] 4. Atomization granulation: The ball-milled powder is mixed with pure water to form a slurry, which is then sprayed in a spray granulation tower to obtain spherical droplets. The process parameters for spray granulation are: atomizing disc speed 50HZ, inlet air temperature 250℃, exhaust air temperature 100℃, pure water is used to prepare the slurry, and the solid content of the slurry is controlled to be 70%.

[0032] 3. Sintering: Sinter the spherical droplets to form Ti2AlC spheres with a particle size of 12 micrometers; the sintering temperature is 1300℃ and the sintering time is 4h.

[0033] 4. 0.021 mol anhydrous ferric chloride and 0.006 mol ferrous chloride tetrahydrate were added as iron sources to 150 ml of distilled water. Under stirring, 5 g (approximately 0.037 mol) of sintered Ti2AlC spheres were added. The temperature was raised to 90 °C, and 9 ml of 1 M ammonia water was added to adjust the reaction system to an alkaline environment. The reaction was continued for 30 minutes, cooled to room temperature, and magnetically collected. The collected powder was washed three times with pure water and dried to obtain the product, namely the spherical complex structure microwave absorber. The shell thickness of this spherical complex structure microwave absorber was measured to be 600 nm.

[0034] Comparative Example 1 1. Ball milling: Put Ti2AlC powder (particle size 1 micrometer) into a ball mill with a material-to-ball ratio of 5:1; add grinding balls with a diameter of 3 mm and ball mill for 3 hours.

[0035] 2. Atomization granulation: The ball-milled powder is mixed with pure water to form a slurry, which is then sprayed in a spray granulation tower to obtain spherical droplets. The process parameters for spray granulation are: atomizing disc speed 45HZ, inlet air temperature 230℃, exhaust air temperature 110℃, pure water is used to prepare the slurry, and the solid content of the slurry is controlled to be 60%.

[0036] 3. Sintering: Sinter the spherical droplets to form Ti2AlC spheres with a particle size of 8 micrometers; the sintering temperature is 1200℃ and the sintering time is 4h.

[0037] 4. 0.018 mol anhydrous ferric chloride and 0.006 mol ferrous chloride tetrahydrate were added as iron sources to 150 ml of distilled water. Under stirring, 3.5 g (approximately 0.026 mol) of sintered Ti2AlC spheres were added. The temperature was raised to 90 °C, and 9 ml of 1 M ammonia water was added to adjust the reaction system to an alkaline environment. The reaction was continued for 30 minutes, cooled to room temperature, and magnetically collected. The collected powder was washed three times with pure water and dried to obtain the product, namely the spherical complex structure microwave absorber. The shell thickness of this spherical complex structure microwave absorber was measured to be 1 micrometer.

[0038] The obtained spherical complex structure absorbing agent was coated onto an aluminum substrate using a coaxial method, with coating thicknesses ranging from 0.9 to 1.9 mm. The reflection loss of the spherical complex structure absorbing agent with different coating thicknesses at different frequencies was detected using a vector network analyzer. The results are shown in [Figure number missing]. Figure 2 .from Figure 2 It can be seen that the overall reflection loss is relatively high.

[0039] Comparative Example 2 3. Ball milling: Put Ti2AlC powder (particle size 1 micrometer) into a ball mill with a material-to-ball ratio of 5:1; add grinding balls with a diameter of 3 mm and ball mill for 3 hours.

[0040] 4. Atomization granulation: The ball-milled powder is mixed with pure water to form a slurry, which is then sprayed in a spray granulation tower to obtain spherical droplets. The process parameters for spray granulation are: atomizing disc speed 45HZ, inlet air temperature 230℃, exhaust air temperature 110℃, pure water is used to prepare the slurry, and the solid content of the slurry is controlled to be 60%.

[0041] 3. Sintering: Sinter the spherical droplets to form Ti2AlC spheres with a particle size of 8 micrometers; the sintering temperature is 1200℃ and the sintering time is 4h.

[0042] 4. 0.018 mol anhydrous ferric chloride and 0.006 mol ferrous chloride tetrahydrate were added as iron sources to 150 ml of distilled water. Under stirring, 6 g (approximately 0.045 mol) of sintered Ti2AlC spheres were added. The temperature was raised to 90 °C, and 9 ml of 1 M ammonia water was added to adjust the reaction system to an alkaline environment. The reaction was continued for 30 minutes, cooled to room temperature, and magnetically collected. The collected powder was washed three times with pure water and dried to obtain the product, namely the spherical complex structure microwave absorber. The shell thickness of this spherical complex structure microwave absorber was measured to be 200 nm.

[0043] The obtained spherical complex structure absorbing agent was coated onto an aluminum substrate using a coaxial method, with coating thicknesses ranging from 1.3 mm to 2 mm. The reflection loss of the spherical complex structure absorbing agent with different coating thicknesses at different frequencies was detected using a vector network analyzer. The results are shown in [Figure number missing]. Figure 3 .from Figure 3 It can be seen that the reflection loss values ​​of some curves increase significantly after the frequency exceeds 10 GHz.

[0044] Although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0045] Therefore, the above description is only a preferred embodiment of this application and is not intended to limit the scope of this application; that is, all equivalent modifications made in accordance with the scope of the claims of this application shall be within the protection scope of the claims of this application.

Claims

1. A method for preparing a spherical complex structure microwave absorbing agent, characterized in that, Includes the following steps: (1) The MAX phase powder was prepared into a spherical template by spray granulation process; (2) Using a spherical template as the core, a ferrite shell is grown in situ on its surface by hydrothermal method to obtain a spherical composite microwave absorber with a complex structure; wherein the core particle size is 8-12 micrometers and the shell thickness is 400-600 nanometers.

2. The preparation method according to claim 1, characterized in that, The MAX phase powder is at least one of Ti3SiC2, Ti2AlC or Ti2SnC.

3. The preparation method according to claim 1, characterized in that, In step (1), the spray granulation process includes: mixing MAX phase powder with pure water to form a slurry, spraying the slurry into granules in a spray granulation tower to obtain spherical droplets, and sintering the spherical droplets to form a spherical template.

4. The preparation method according to claim 3, characterized in that, The slurry has a solid content of 50-70%, the atomizing disc rotates at 40-50 Hz, the inlet temperature is 200-250℃, and the exhaust temperature is 100-120℃.

5. The preparation method according to claim 3, characterized in that, In step (1), the sintering temperature is 1100-1300℃ and the sintering time is 3-5h.

6. The preparation method according to claim 1, characterized in that, In step (1), the MAX phase powder is pre-processed by ball milling.

7. The preparation method according to claim 1, characterized in that, In step (2), the hydrothermal method specifically includes the following steps: A spherical template was dispersed in a mixed iron source solution containing Fe³⁺ and Fe²⁺ to obtain a suspension; Add alkali to the suspension to adjust its pH to 8.5-10.5, and react at 80-100℃ for 0.5-1 hour; After the reaction is complete, the products are magnetically separated, washed and dried to obtain a core-shell structured composite microwave absorber.

8. The preparation method according to claim 1, characterized in that, The molar ratio of Fe³⁺ to Fe²⁺ in the spherical template and the mixed iron source solution is (0.03-0.04):(2.5-3.5):

1.

9. A spherical complex structure microwave absorber, which is prepared by the preparation method according to any one of claims 1-8.

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