A layered high-absorption electromagnetic shielding composite material and its preparation method

Abstract

A layered, highly absorptive electromagnetic shielding composite material and its preparation method involve selectively etching the Al layer of Ti3AlC2 to obtain an MX solution. Fe3O4 and MX are then assembled into a composite material, FM. Melamine foam is then carbonized to obtain a carbonized foam, CF. FM is then assembled onto a CF skeleton via an impregnation method to form a composite foam, FM@CF. Finally, MX is deposited on the bottom of FM@CF via vacuum filtration to form the layered, highly absorptive electromagnetic shielding composite material, FM@CF / MX. The preparation process is simple and easy to operate. The layered structure achieves a "low reflection-high absorption-high reflection-reabsorption" strategy for electromagnetic waves, successfully achieving a combination of high electromagnetic absorption and high electromagnetic shielding efficiency, significantly reducing secondary electromagnetic contamination and helping to address the hazards of electromagnetic radiation. This material is widely used in aerospace, military equipment, microelectronic devices, consumer electronics, and other fields.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic shielding composite materials, and in particular to a high-absorption electromagnetic shielding composite material with a layered structure and a preparation method thereof. Background Art

[0002] With the rapid development of communications technology and wearable electronic devices, highly integrated electronic systems generate electromagnetic waves of varying frequencies, resulting in significant electromagnetic radiation. This radiation can severely impact the normal operation of adjacent devices. Furthermore, long-term exposure to electromagnetic radiation can cause serious harm to the human body, including nausea, headaches, eye diseases, and cancer. Electromagnetic radiation, also known as "electromagnetic pollution," has become the fourth largest public hazard after air pollution, water pollution, and noise pollution. Therefore, the development of high-performance materials that shield electromagnetic waves and reduce electromagnetic radiation is crucial.

[0003] Reflection and absorption are the primary methods for shielding electromagnetic waves. Current electromagnetic shielding materials primarily include metals, carbon materials, and conductive polymer composites. However, these materials primarily shield electromagnetic waves through reflection, with reflectivity typically exceeding 90% and absorption rates below 10%. Such high reflectivity can cause severe secondary electromagnetic pollution and complicate the electromagnetic environment, making it difficult to fundamentally eliminate the hazards of electromagnetic radiation. Therefore, the development of electromagnetic shielding materials that primarily rely on absorption is urgent.

[0004] Chinese patent CN116041780A discloses a "method for preparing a multi-layered, porous, electromagnetic shielding composite foam material with adjustable heterogeneous structure": polydopamine is modified on the surface of a melamine foam skeleton, melted paraffin is impregnated into the polydopamine-modified melamine foam, and the paraffin is partially coated on the foam skeleton. This foam is then subjected to chemical silver plating, resulting in in-situ deposition of silver nanoparticles on the surface of the foam skeleton not coated with the paraffin. The paraffin is removed, and the foam is encapsulated with an aqueous polyurethane suspension of carbon nanofiller and freeze-dried to obtain the multi-layered, porous electromagnetic shielding composite foam material with adjustable heterogeneous structure. However, this material exhibits good electromagnetic wave absorption performance only at low electromagnetic shielding performance levels, and exhibits very low electromagnetic wave absorption at high electromagnetic shielding performance levels. For example, a material with an electromagnetic shielding performance of 47 dB in the X-band has an electromagnetic wave absorption rate of only 7%. Furthermore, the preparation process for this material is complex and time-consuming, making it difficult to achieve large-scale production. Summary of the Invention

[0005] The present invention aims to address the problem of severe secondary electromagnetic wave pollution caused by the high reflectivity of existing electromagnetic shielding materials. The present invention provides a layered, highly absorptive electromagnetic shielding composite material and its preparation method. The MX solution is obtained by selectively etching the Al layer of Ti3AlC2, and Fe3O4 and MX are assembled into a composite material (FM). Melamine foam is carbonized to obtain a carbonized foam (CF). FM is then assembled onto a CF skeleton by an impregnation method to obtain a composite foam material (FM@CF). Finally, MX is deposited on the bottom of the FM@CF by vacuum filtration to obtain a layered, highly absorptive electromagnetic shielding composite material (FM@CF / MX). This electromagnetic shielding composite material has a simple preparation process and is easy to operate. Its layered structure achieves a "low reflection-high absorption-high reflection-reabsorption" strategy for electromagnetic waves, successfully achieving a combination of high electromagnetic absorption and high electromagnetic shielding efficiency, significantly reducing secondary electromagnetic wave pollution and helping to address the hazards of electromagnetic radiation. The material can be widely used in aerospace, military equipment, microelectronic equipment, consumer electronics, and other fields.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing a layered high-absorption electromagnetic shielding composite material comprises the following steps:

[0008] 1) Add LiF and Ti3AlC2 to HCl solution, stir, centrifuge, wash, disperse the resulting precipitate in water, and collect the supernatant by centrifugation. The resulting supernatant is the MX dispersion;

[0009] 2) modifying Fe3O4 particles in an aqueous solution of a cationic modifier, washing them by centrifugation to obtain positively charged Fe3O4 particles, mixing the positively charged Fe3O4 particles with an MX dispersion, and vibrating them thoroughly to ensure complete electrostatic self-assembly to obtain an FM dispersion;

[0010] 3) Carbonizing the melamine foam under nitrogen to obtain CF, immersing the CF in a FM dispersion, and vacuum drying the CF to obtain a FM-loaded composite foam material FM@CF;

[0011] 4) MX was deposited on the bottom of FM@CF and vacuum dried to obtain FM@CF / MX.

[0012] In step 2), the cationic modifier is one or both of hexadecyltrimethylammonium bromide and octadecyltrimethylammonium chloride.

[0013] In step 2), the concentration of the aqueous solution of the cationic modifier is 1 to 10 mg / mL.

[0014] In step 2), the mass ratio of Fe3O4 to MX is 0.25 to 2:1.

[0015] In step 2), the concentration of the FM dispersion is 1-10 mg / mL.

[0016] In step 3), the CF is immersed in the FM dispersion at least once.

[0017] In step 4), MX is deposited by vacuum filtration to deposit the MX dispersion on the bottom of FM@CF.

[0018] In step 4), the thickness of MX deposition is controlled by the mass of MX.

[0019] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0020] The present invention effectively loads the FM composite onto CF through an impregnation method, and then deposits MX at the bottom of the FM@CF through vacuum filtration to achieve a layered structure. Compared to conductive layers prepared by methods such as dip coating and electroless plating, the MX deposited layer prepared by vacuum filtration is denser, thinner, and more conductive, resulting in superior electromagnetic shielding performance.

[0021] The present invention constructs a layered structure of "low reflection-high absorption-high reflection-reabsorption". The FM@CF layer has suitable conductivity and good magnetic properties. Its high-porosity foam structure can significantly extend the transmission path of electromagnetic waves, causing them to reflect multiple times inside the material, converting electromagnetic waves into heat through dielectric loss and magnetic loss. The electromagnetic waves passing through the FM@CF layer will be reflected back to the FM@CF layer by the highly conductive MX deposited layer to form secondary reflected electromagnetic waves, and will be absorbed by the FM@CF layer again, thereby achieving high absorption of electromagnetic waves. This significantly reduces secondary electromagnetic pollution and helps to solve the hazards caused by electromagnetic radiation. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is one of the scanning electron microscope images of the layered high-absorption electromagnetic shielding composite material prepared in Example 2.

[0023] Figure 2 This is the second scanning electron microscope image of the layered high-absorption electromagnetic shielding composite material prepared in Example 2.

[0024] Figure 3 This is a diagram of the electromagnetic shielding effectiveness of the layered high-absorption electromagnetic shielding composite material prepared in Example 2 in the X-band.

[0025] Figure 4 This is a diagram of the power coefficient of the layered high-absorption electromagnetic shielding composite material prepared in Example 2 in the X-band. DETAILED DESCRIPTION

[0026] In order to make the technical solution of the present invention more clear, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0027] The CF used in the following examples was melamine foam carbonized at 500°C for 2 hours under nitrogen atmosphere, with a size of 30 × 20 × 5 mm. Fe₃O₄ particles were purchased from MCC New Materials Co., Ltd., with a size of 20 nm. Ti₃AlC₂ was purchased from Foshan Xinxi Technology Co., Ltd., with a size of 400 mesh. MX was prepared by the following method: 2 g of LiF and 2 g of Ti₃AlC₂ were added sequentially to 40 mL of 9 mol / L HCl solution. The mixture was stirred at 35°C for 48 hours. The resulting reaction solution was centrifuged and washed with water until the supernatant had a pH ≥ 6. The resulting precipitate was dispersed in deionized water, sonicated for 1 hour, and centrifuged at 3500 rpm for 1 hour. The supernatant was collected to obtain the MX dispersion. A certain volume of the MX dispersion was measured and filtered to form an MX membrane. The mass of the MX membrane was used to calculate the concentration of the MX dispersion and the total mass of MX in the MX dispersion.

[0028] Example 1

[0029] (1) 40 mg of Fe3O4 particles were added to 10 mL of 2 mg / mL hexadecyltrimethylammonium bromide aqueous solution and ultrasonicated for 2 h to allow adsorption onto the Fe3O4 particles. The particles were then centrifuged and washed to obtain positively charged Fe3O4 particles. The positively charged Fe3O4 particles were then mixed with MX dispersion at a Fe3O4 to MX mass ratio of 1:2 and fully shaken to ensure complete electrostatic self-assembly to obtain FM dispersion.

[0030] (2) CF was immersed in 30 mL of 5 mg / mL FM dispersion for 1 h and then taken out and vacuum dried to obtain FM1@CF.

[0031] (3) The MX dispersion containing 75 mg of MX was deposited on the bottom of FM1@CF by vacuum filtration and vacuum dried to obtain FM1@CF / MX, where the thickness of the MX deposition layer was about 30 μm.

[0032] Example 2

[0033] (1) 40 mg of Fe3O4 particles were added to 10 mL of 2 mg / mL hexadecyltrimethylammonium bromide aqueous solution and ultrasonicated for 2 h to allow adsorption onto the Fe3O4 particles. The particles were then centrifuged and washed to obtain positively charged Fe3O4 particles. The positively charged Fe3O4 particles were then mixed with MX dispersion at a Fe3O4 to MX mass ratio of 1:2 and fully shaken to ensure complete electrostatic self-assembly to obtain FM dispersion.

[0034] (2) CF was immersed in 30 mL of 5 mg / mL FM dispersion for 1 h and then vacuum dried to obtain FM1@CF. FM1@CF was immersed in 30 mL of 5 mg / mL FM dispersion for 1 h and then vacuum dried to obtain FM2@CF.

[0035] (3) The MX dispersion containing 75 mg of MX was deposited on the bottom of FM2@CF by vacuum filtration and vacuum dried to obtain FM2@CF / MX, where the thickness of the MX deposition layer was about 30 μm.

[0036] Example 3

[0037] (1) 40 mg of Fe3O4 particles were added to 10 mL of 5 mg / mL hexadecyltrimethylammonium bromide aqueous solution and ultrasonicated for 2 h to allow adsorption of Fe3O4 particles on the Fe3O4 particles. The particles were then centrifuged and washed to obtain positively charged Fe3O4 particles. The positively charged Fe3O4 particles were mixed with MX dispersion at a Fe3O4 to MX mass ratio of 1:2 and then fully shaken to ensure complete electrostatic self-assembly to obtain FM dispersion.

[0038] (2) CF was immersed in 30 mL of 5 mg / mL FM dispersion for 1 h and then taken out and vacuum dried to obtain FM1@CF.

[0039] (3) The MX dispersion containing 75 mg of MX was deposited on the bottom of FM1@CF by vacuum filtration and vacuum dried to obtain FM1@CF / MX, where the thickness of the MX deposition layer was about 30 μm.

[0040] Example 4

[0041] (1) 40 mg of Fe3O4 particles were added to 10 mL of 5 mg / mL hexadecyltrimethylammonium bromide aqueous solution and ultrasonicated for 2 h to allow adsorption of Fe3O4 particles on the Fe3O4 particles. The particles were then centrifuged and washed to obtain positively charged Fe3O4 particles. The positively charged Fe3O4 particles were mixed with MX dispersion at a Fe3O4 to MX mass ratio of 1:2 and then fully shaken to ensure complete electrostatic self-assembly to obtain FM dispersion.

[0042] (2) CF was immersed in 30 mL of 5 mg / mL FM dispersion for 1 h and then vacuum dried to obtain FM1@CF. FM1@CF was immersed in 30 mL of 5 mg / mL FM dispersion for 1 h and then vacuum dried to obtain FM2@CF.

[0043] (3) The MX dispersion containing 75 mg of MX was deposited on the bottom of FM1@CF by vacuum filtration and vacuum dried to obtain FM1@CF / MX, where the thickness of the MX deposition layer was about 30 μm.

[0044] Example 5

[0045] (1) 40 mg of Fe3O4 particles were added to 10 mL of 5 mg / mL hexadecyltrimethylammonium bromide aqueous solution and ultrasonicated for 2 h to allow adsorption of Fe3O4 particles on the Fe3O4 particles. The particles were then centrifuged and washed to obtain positively charged Fe3O4 particles. The positively charged Fe3O4 particles were mixed with MX dispersion at a Fe3O4 to MX mass ratio of 1:2 and then fully shaken to ensure complete electrostatic self-assembly to obtain FM dispersion.

[0046] (2) CF was immersed in 30 mL of 10 mg / mL FM dispersion for 1 h and then vacuum dried to obtain FM1@CF. FM1@CF was immersed in 30 mL of 10 mg / mL FM dispersion for 1 h and then vacuum dried to obtain FM2@CF.

[0047] (3) The MX dispersion containing 75 mg of MX was deposited on the bottom of FM1@CF by vacuum filtration and vacuum dried to obtain FM1@CF / MX, where the thickness of the MX deposition layer was about 30 μm.

[0048] Example 6

[0049] (1) 40 mg of Fe3O4 particles were added to 10 mL of 2 mg / mL hexadecyltrimethylammonium bromide aqueous solution and ultrasonicated for 2 h to allow adsorption onto the Fe3O4 particles. The particles were then centrifuged and washed to obtain positively charged Fe3O4 particles. The positively charged Fe3O4 particles were then mixed with MX dispersion at a Fe3O4 to MX mass ratio of 1:2 and fully shaken to ensure complete electrostatic self-assembly to obtain FM dispersion.

[0050] (2) CF was immersed in 30 mL of 5 mg / mL FM dispersion for 1 h and then vacuum dried to obtain FM1@CF. FM1@CF was immersed in 30 mL of 5 mg / mL FM dispersion for 1 h and then vacuum dried to obtain FM2@CF.

[0051] (3) The MX dispersion containing 25 mg of MX was deposited on the bottom of FM2@CF by vacuum filtration and vacuum dried to obtain FM2@CF / MX, where the thickness of the MX deposition layer was about 10 μm.

[0052] Example 7

[0053] (1) 40 mg of Fe3O4 particles were added to 10 mL of 2 mg / mL hexadecyltrimethylammonium bromide aqueous solution and ultrasonicated for 2 h to allow adsorption onto the Fe3O4 particles. The particles were then centrifuged and washed to obtain positively charged Fe3O4 particles. The positively charged Fe3O4 particles were then mixed with MX dispersion at a Fe3O4 to MX mass ratio of 1:2 and fully shaken to ensure complete electrostatic self-assembly to obtain FM dispersion.

[0054] (2) CF was immersed in 30 mL of 5 mg / mL FM dispersion for 1 h and then vacuum dried to obtain FM1@CF. FM1@CF was immersed in 30 mL of 5 mg / mL FM dispersion for 1 h and then vacuum dried to obtain FM2@CF.

[0055] (3) The MX dispersion containing 50 mg of MX was deposited on the bottom of FM2@CF by vacuum filtration and vacuum dried to obtain FM2@CF / MX, where the thickness of the MX deposition layer was about 20 μm.

[0056] Example 8

[0057] (1) 40 mg of Fe3O4 particles were added to 10 mL of 2 mg / mL hexadecyltrimethylammonium bromide aqueous solution and ultrasonicated for 2 h to allow adsorption onto the Fe3O4 particles. The particles were then centrifuged and washed to obtain positively charged Fe3O4 particles. The positively charged Fe3O4 particles were then mixed with MX dispersion at a Fe3O4 to MX mass ratio of 1:2 and fully shaken to ensure complete electrostatic self-assembly to obtain FM dispersion.

[0058] (2) CF was immersed in 30 mL of 5 mg / mL FM dispersion for 1 h and then vacuum dried to obtain FM1@CF. FM1@CF was immersed in 30 mL of 5 mg / mL FM dispersion for 1 h and then vacuum dried to obtain FM2@CF.

[0059] (3) The MX dispersion containing 100 mg of MX was deposited on the bottom of FM2@CF by vacuum filtration and vacuum dried to obtain FM2@CF / MX, where the thickness of the MX deposition layer was approximately 40 μm.

[0060] The present invention discloses a layered high-absorption electromagnetic shielding composite material and a preparation method thereof. The preparation method is simple and easy to operate. The layered high-absorption electromagnetic shielding composite material is assembled from FM@CF composite foam and MX deposited layers. Fe3O4 particles are modified with a cationic surface modifier, and the positively charged Fe3O4 particles are mixed with an MX dispersion to form an FM composite by electrostatic self-assembly. The FM composite is then impregnated on a carbonized melamine foam (CF) skeleton to obtain a composite foam material FM@CF. Finally, MX is deposited on the bottom of the FM@CF composite foam by vacuum filtration to obtain a layered composite material FM@CF / MX with both high absorption and high electromagnetic shielding properties.

[0061] Figures 1-2 This is a scanning electron microscope image of the layered high-absorption electromagnetic shielding composite material prepared in Example 2. Figure 3This is a diagram of the electromagnetic shielding effectiveness of the layered high-absorption electromagnetic shielding composite material prepared in Example 2 in the X-band. Figure 4 This is a diagram of the power coefficient of the layered high-absorption electromagnetic shielding composite material prepared in Example 2 in the X-band.

[0062] The FM@CF layer's suitable conductivity and highly open-pore structure provide excellent impedance matching with air, resulting in low primary reflectivity of electromagnetic waves. Furthermore, the FM@CF's three-dimensional, porous mesh structure allows for multiple reflections of electromagnetic waves within the foam, significantly increasing the propagation path within the foam. This allows the FM@CF to absorb a significant amount of electromagnetic waves through both magnetic and electrical losses. Electromagnetic waves that pass through the FM@CF layer are reflected back by the highly conductive MX deposited layer, forming secondary reflected electromagnetic waves, which are then absorbed again by the FM@CF layer. This achieves a "low reflection-high absorption-high reflection-reabsorption" strategy for electromagnetic waves. The layered structure of the FM@CF / MX electromagnetic shielding composite material successfully combines high electromagnetic absorption with high electromagnetic shielding performance. Its absorption rate reaches 81% with an X-band electromagnetic shielding performance of 71dB, significantly reducing secondary electromagnetic contamination and thus significantly minimizing the harm caused by electromagnetic radiation.

Claims

1. A method for preparing a layered high-absorption electromagnetic shielding composite material, characterized in that The following steps are involved: 1) Add LiF and Ti3AlC2 to HCl solution, stir, centrifuge, wash, disperse the resulting precipitate in water, and collect the supernatant by centrifugation. The resulting supernatant is the MX dispersion; 2) Fe3O4 particles are modified in an aqueous solution of a cationic modifier, centrifuged and washed to obtain positively charged Fe3O4 particles, and the positively charged Fe3O4 particles are oscillated with an MX dispersion to obtain an FM dispersion; 3) Carbonizing melamine foam under nitrogen to obtain CF, impregnating the CF in FM dispersion, and vacuum drying to obtain FM-loaded composite foam material FM@CF; 4) Depositing MX on the bottom of FM@CF and vacuum drying it to obtain FM@CF / MX; In step 2), the cationic modifier is one or both of hexadecyltrimethylammonium bromide and octadecyltrimethylammonium chloride.

2. The method for preparing a layered high-absorption electromagnetic shielding composite material according to claim 1, wherein: In step 2), the concentration of the aqueous solution of the cationic modifier is 1-10 mg / mL.

3. The method for preparing a layered high-absorption electromagnetic shielding composite material according to claim 1, wherein: In step 2), the mass ratio of Fe3O4 to MX is 0.25~2:

1.

4. The method for preparing a layered high-absorption electromagnetic shielding composite material according to claim 1, wherein: In step 2), the concentration of the FM dispersion is 1-10 mg / mL.

5. The method for preparing a layered high-absorption electromagnetic shielding composite material according to claim 1, wherein: In step 3), the CF is immersed in the FM dispersion at least once.

6. The method for preparing a layered high-absorption electromagnetic shielding composite material according to claim 1, wherein: In step 4), MX is deposited on the bottom of FM@CF by vacuum filtration.

7. The method for preparing a layered high-absorption electromagnetic shielding composite material according to claim 1, wherein: In step 4), the thickness of MX deposition is controlled by the mass of MX.

8. A layered high-absorption electromagnetic shielding composite material, characterized by: Prepared by the preparation method according to any one of claims 1 to 7.

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