Electromagnetic double-gradient composite material containing Ni and CFC as well as preparation method and application of electromagnetic double-gradient composite material

Abstract

The invention discloses an electromagnetic double-gradient composite material containing Ni and CFC and a preparation method and application thereof, and relates to the technical field of electromagnetic shielding materials. The preparation method comprises the following steps: (1) cutting carbon fiber cloth into small blocks, polishing carbon fibers through abrasive paper, immersing a sample into a sensitizing solution at room temperature for 15 minutes, and soaking the sample into an activating solution for 90 seconds; a sensitizer used in the chemical nickel plating process comprises nickel sulfate hexahydrate and diluted hydrochloric acid; and (2) ammonia water is added to adjust the pH of the chemical nickel plating solution, chemical nickel plating treatment is carried out at the temperature of 60 DEG C, nickel deposition is carried out for 1-4 times and 20 min each time, after the reaction is completed, deionized water is used for washing for 2 min, then pressing is carried out for 48 h, and finally drying is carried out in a drying oven, so that the electromagnetic double-gradient composite material is obtained. By depositing Ni on the CFC substrate, the dielectric loss, magnetic loss and heterogeneous interface loss performances are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic shielding materials technology, and more specifically to an electromagnetic dual-gradient composite material containing Ni and CFC, its preparation method, and its application. Background Technology

[0002] The rapid development of 5G / 6G communication technologies, coupled with the widespread adoption of miniature mobile electronic devices, has led to considerable challenges related to electromagnetic shielding. To mitigate the destructive effects of electromagnetic radiation on highly sensitive and precision equipment and its potential harm to human health, advancing the development of efficient electromagnetic shielding (EMI) materials is crucial. The development of advanced and highly integrated fifth-generation (5G) wireless systems in recent decades has created opportunities for lightweight, thin, easily handled, and efficient EMI shielding solutions.

[0003] Traditional electromagnetic shielding materials are usually made of metallic elements such as copper, iron, cobalt, nickel and silver, which have limited ability to absorb electromagnetic waves, resulting in primary reflection and subsequent secondary electromagnetic pollution.

[0004] Furthermore, the dwindling reserves of these metals, coupled with their inherent limitations, including high density, limited flexibility, and insufficient corrosion resistance, severely hinder their practical applications. While carbon nanotubes, graphene, and MXene exhibit high electrical conductivity, this property can cause significant impedance mismatch at the air-material interface.

[0005] Therefore, most incident electromagnetic waves are reflected at the surface, generating considerable secondary pollution. Conductive polymer composites (CPCs) require nanoscale components dispersed in a flexible polymer matrix, such as polydimethylsiloxane (PDMS), waterborne polyurethane (WPU), aramid fibers (AF), and polyimide (PI). These typically involve complex processing, increased costs, and reliance on unsustainable base materials, severely limiting their industrial applications. Therefore, there is an urgent need to design high-performance electromagnetic shielding materials with comprehensive multifunctionality. For example, materials combining electromagnetic interference shielding with Joule heating and infrared camouflage capabilities are crucial for military applications, especially in demanding outdoor combat environments.

[0006] Applications of nanomaterials in the development of multifunctional electronic textiles. These conductive nanomaterials include silver nanowires, MXenes, ferrite compounds, graphene, and carbon nanotubes. While AgNWs and MXenes exhibit excellent conductivity, their high cost and complex synthesis present obstacles. Graphene and carbon nanotubes exhibit weak interfacial interactions with the substrate due to insufficient surface functional groups. Ferrites and carbonyl iron particles have been identified as key electromagnetic wave absorbers, but their individual application cannot provide the required strong broadband absorption performance, thus significantly limiting practical applications.

[0007] Conductive polymers, such as polyaniline (PANI), polypyrrole (PPy), and polyacetylene, are frequently used as flexible conductive materials due to their inherent flexibility and foldability; however, they often require the addition of additional conductive substances to improve their electrical properties. Given the deployment of EMI materials in complex environments, developing auxiliary functions such as hydrophobicity, mechanical strength, and antimicrobial properties is crucial for ensuring environmental stability. Summary of the Invention

[0008] In view of this, the present invention provides a Ni- and CFC-containing electromagnetic dual-gradient composite material with high-performance electromagnetic shielding and infrared camouflage effects, its preparation method and application.

[0009] A flexible electroless nickel-plated CFC structure was fabricated by electroless nickel plating on carbon fiber fabric (CFC). Ni deposition on the CFC substrate significantly improved dielectric loss, magnetic loss, and heterojunction loss performance. This comprehensive strategy successfully integrated dielectric loss, magnetic loss, and internal multiple reflection mechanisms into the material, thereby enhancing its electromagnetic interference shielding effectiveness (EMI SE). Consequently, this composite material achieved a peak EMI SE of 64.3 dB at a thickness of 0.49 mm in the X-band frequency range.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing an electromagnetic dual-gradient composite material containing Ni and CFC includes the following steps: (1) Pretreatment: The carbon fiber cloth was cut into small pieces, and then the carbon fiber was polished with sandpaper. Next, the sample was immersed in the sensitizing solution for 15 minutes at room temperature, and then the sample was immersed in the activation solution for 90 seconds. The sensitizers used in the electroless nickel plating process include nickel sulfate hexahydrate and dilute hydrochloric acid. (2) Electroless nickel plating: Ammonia was added to adjust the pH of the electroless nickel plating solution. Electroless nickel plating was performed at 60°C, with nickel deposition repeated 1-4 times for 20 minutes each time. The carbon fiber cloth was turned over every 3 minutes. After the reaction was completed, the solution was washed with deionized water for 2 minutes, then pressed for 48 hours, and finally dried in an oven to obtain the electromagnetic dual gradient composite material.

[0011] Preferably, the sensitizing solution is a mixture of nickel sulfate hexahydrate and hydrochloric acid, with a concentration of 0.7-0.9 mL / g.

[0012] Preferably, the activating solution is a mixture of sodium hydroxide and sodium borohydride, with a mass ratio of sodium hydroxide to sodium borohydride of (0.7-0.9):(0.9-1.1).

[0013] Preferably, the electroless nickel plating solution is prepared by adding 9.9 g of nickel sulfate, 9.0 g of sodium citrate, 8.4 g of sodium hypophosphite, and 9.0 mg of thiourea to 300 mL of distilled water, and finally adding ammonia water to adjust the pH of the plating solution to 9.0.

[0014] Preferably, the pressing is performed using a 2-3 kg weight; the drying temperature is 70-90℃.

[0015] Another object of the present invention is to provide the application of the electromagnetic dual gradient composite material prepared by the above-mentioned method of preparing Ni- and CFC-containing electromagnetic dual gradient composite material in construction, flexible wearable devices, precision electronic instruments, aerospace technology and military instruments.

[0016] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects: (1) The maximum electrical conductivity and tensile strength of the flexible electromagnetic dual gradient composite material are 589.91 S / cm and 11.7 MPa, respectively.

[0017] (2) In the X-band, the average electromagnetic shielding effectiveness (SE) of the electromagnetic double-gradient composite material with a thickness of 0.49 mm. T The dielectric strength reached 64.3 dB, while the electroless nickel plating time was only 20 min. This was mainly due to the large dielectric loss, magnetic loss and heterojunction loss.

[0018] (3) The electromagnetic dual gradient composite material has excellent Joule heating capability (220°C at 2.0 V) and still maintains good magnetic properties after being subjected to high temperature treatment at 1000°C for 90 s.

[0019] (4) The construction gradient of the electromagnetic duality alleviates the impedance mismatch at the air-film interface, resulting in a decrease in the reflectivity of electromagnetic waves (EMWs), while the unique network structure promotes the “absorption-reflection-reabsorption” process of electromagnetic waves. In addition, it also exhibits excellent mechanical properties, effective thermal management, Joule heating capability, and significant passive and active infrared camouflage performance. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0021] Figure 1(a) is a schematic diagram of the preparation process of electromagnetic dual-gradient composite material, (b) is magnetic detection, (c) is high temperature resistance detection, (d) is hydrophobic detection, (e) is electrical conductivity detection, and (f) is infrared stealth detection.

[0022] Figure 2 (a) is a SEM image of carbon fiber cloth with Ni deposited once, (b) is a SEM image of carbon fiber cloth with Ni deposited twice, (c) is a SEM image of carbon fiber cloth with Ni deposited three times, (d) is a SEM image of carbon fiber cloth with Ni deposited four times, and (e) is a surface scan image of carbon fiber cloth with Ni deposited twice.

[0023] Figure 3 (a) is a low-magnification SEM image of electroless nickel-plated carbon fiber, (b) is a high-magnification SEM image of electroless nickel-plated carbon fiber, (c) is a low-magnification SEM image of a single electroless nickel-plated carbon fiber, (d) is a high-magnification SEM image of a single electroless nickel-plated carbon fiber, and (e) is a cross-sectional morphology and cross-sectional scan of a carbon fiber electroless nickel-plated composite material with a core-shell structure layer.

[0024] Figure 4 (a) is the XRD pattern of the electromagnetic dual-gradient composite material, (b) is the full XPS spectrum of the electromagnetic dual-gradient composite material, (c) is the Ni 2p XPS spectrum, (d) is the FT-IR spectrum of the electromagnetic dual-gradient composite material with different Ni deposition times, (e) is the O 1s XPS spectrum, (f) is the C 1s XPS spectrum, (g) is the conductivity at different electroless nickel plating times, (h) is the conductivity at different deposition times, and (i) is the hysteresis loop of the electromagnetic dual-gradient composite material in the region from -20,000 to 20,000 Oe.

[0025] Figure 5 (a) Comparison curves of total electromagnetic shielding effectiveness (SET) for different Ni deposition times; (b) Comparison curves of electromagnetic absorption loss (SEA) for different Ni deposition times; (c) Reflection coefficient (R), absorption coefficient (A), and transmission coefficient (T) of composite materials for different Ni deposition times; (d) Comparison curves of electromagnetic reflection loss (SER) for different Ni deposition times; (e) Comparison of average values ​​of SET, SEA, and SER in the X-band; (f) Evaluation of SET, SER, SEA, material thickness, and absorption value A; (g) SET of composite materials prepared with different Ni deposition times in the X-band; (h) SEA for different Ni deposition times; (i) R, A, and T of composite materials prepared with different Ni deposition times; (j) SER for different Ni deposition times; (k) Average values ​​of SET, SEA, and SER; (l) Comparative evaluation of SET, SER, SEA, thickness, and absorption value A; (m) Schematic diagram of electromagnetic shielding mechanism.

[0026] Figure 6 (a) Surface roughness of carbon fiber cloth, (b) Surface roughness of electromagnetic dual-gradient composite material with single-layer Ni deposition, (c) Surface roughness of electromagnetic dual-gradient composite material with double-layer Ni deposition, (d) Surface roughness of electromagnetic dual-gradient composite material with triple-layer Ni deposition, (e) Surface roughness of electromagnetic dual-gradient composite material with quadruple-layer Ni deposition, (f) Average surface roughness, (g) Contact angle of carbon fiber cloth, (h) Contact angle of electromagnetic dual-gradient composite material with single-layer Ni deposition, (i) Contact angle of electromagnetic dual-gradient composite material with double-layer Ni deposition, (j) Contact angle of electromagnetic dual-gradient composite material with triple-layer Ni deposition, (k) Contact angle of electromagnetic dual-gradient composite material with quadruple-layer Ni deposition, and (l) Average contact angle.

[0027] Figure 7 (a) shows the stress-strain diagram of electromagnetic dual-gradient composite materials with different Ni deposition times, (b) shows the tensile strength diagram of electromagnetic dual-gradient composite materials with different Ni deposition times, (c) shows the torsional test photograph, (d) shows the elasticity test photograph, (e) shows the tensile test photograph, and (f) shows the optical and infrared camera photographs taken at different temperatures, a schematic diagram of passive infrared thermal camouflage, and the infrared camouflage performance of the target under simulated room temperature background.

[0028] Figure 8 (a) Photograph of carbon fiber cloth, (b) Schematic diagram of Tesla coil, (c) Appearance change of a small light bulb exposed to Tesla coil when the switch is on, (d) Appearance change of a small light bulb exposed to Tesla coil when the switch is off, (e) Electric and magnetic fields of a chassis containing electromagnetic dual-gradient composite material tested by an electromagnetic radiation tester, (f) Electric and magnetic fields of a chassis without electromagnetic dual-gradient composite material tested by an electromagnetic radiation tester, (g) Comparison of electromagnetic shielding effectiveness and high temperature resistance performance, (h) Comparison of magnetic performance of electromagnetic dual-gradient composite material under high temperature treatment, (i) Schematic diagram of self-cleaning mechanism of hydrophobic surface of electromagnetic dual-gradient composite material, self-cleaning performance tested by adding methylene blue solution to the surface.

[0029] Figure 9 (a) shows the relationship between time and temperature for the electromagnetic dual-gradient composite material at 0.5-2V; (b) shows the experimental data and linear fitting of TSS for U2; (c) shows the time-temperature curves at different voltages; (d) shows the stability spectrum of the electromagnetic dual-gradient composite material under heating and cooling cycles at 1.25V; (e) shows the temperature curve after heating at 1.25V for 3600 s; and (f) shows the infrared temperature photograph of the electromagnetic dual-gradient composite material at 0.5-2V.

[0030] Figure 10 This is a schematic diagram of the synergistic effect of electromagnetic shielding in electromagnetic dual-gradient composite materials. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and 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.

[0032] Example 1 Preparation of electromagnetic dual-gradient composite materials containing Ni and CFC: (1) Pretreatment: Carbon fiber cloth (CFC) measuring 10cm x 15cm was cut into small pieces, each measuring 5cm x 5cm, and then polished with 600-grit sandpaper. Next, the samples were immersed in a sensitization solution at room temperature for 15 minutes. Afterward, the samples were immersed in an activation solution for 90 seconds. The sensitizers used in the electroless nickel plating process included nickel sulfate hexahydrate and dilute hydrochloric acid.

[0033] (2) Electroless nickel plating: In the electroless nickel plating process, ammonia was added to adjust the pH of the electroless nickel plating solution (pH=9). Nickel deposition times at 60℃ were 5 min, 10 min, 15 min, 20 min, and 25 min. Ni was deposited in single, double, triple, and quadruple cycles, each lasting 20 min. After the reaction was complete, the inorganic nickel CFC-based composite material was washed with deionized water for 2 min, then pressed with a heavy object for 48 h, and finally dried in an oven.

[0034] Experimental Analysis: exist Figure 1 (a) illustrates the process of synthesizing electromagnetic dual-gradient composite materials via electroless nickel plating. First, CFCs were cut into 5cm × 5cm pieces. Then, the CFCs were activated in a prepared activation solution, and a nickel layer was formed through one to four electroless nickel plating depositions. The deposition times during the electroless nickel plating process were 5 min, 10 min, 15 min, 20 min, and 25 min, and the electroless nickel plating time was used as a variable for testing. The composites were named CFCCs-5, CFCCs-10, CFCCs-15, CFCCs-20, and CFCCs-25 according to the time required for each electroless nickel plating step.

[0035] Furthermore, electroless nickel plating was performed 1 to 4 times, each lasting 20 minutes, and the number of electroless nickel plating operations was used as a variable in the test. To characterize the samples, CFCs were deposited twice. Additionally, examples of CFCCs with two depositions are provided to illustrate the characteristics of the samples. Figure 1 In (b), CFCCs are attracted by a magnet, indicating the presence of a magnetic component. Figure 1 In (c), the CFCCs sample with two depositions exhibits high-temperature usability. Figure 1 In (d), the water droplets can stably adhere to the sample surface, indicating that the sample is hydrophobic. For example... Figure 1 As shown in (e), the sample exhibits excellent conductivity, such as Figure 1 As shown in (f), the sample has effective infrared camouflage capabilities.

[0036] The microstructure of CFCs with different Ni depositions was characterized by scanning electron microscopy.

[0037] After one deposition cycle lasting 20 minutes, a small amount of nickel particles were clearly deposited on the CFC surface. With increasing deposition cycles, the carbon fiber surface after two deposition cycles was completely covered by nickel particles. After the carbon fiber surface was covered, the nickel particles gradually filled the gaps between the carbon fibers. After four deposition cycles, the gaps between the carbon fibers were completely filled, as shown in the image. Figure 2 (a) Figure 2 (b) Figure 2 (c) and Figure 2 As shown in (d). According to Figure 2 The surface scan shown in (e) shows an elemental composition of approximately 5.84% carbon, 1.71% oxygen, 2.98% phosphorus, and 89.47% nickel. During electroless nickel plating, the active reaction sites form a nickel-phosphorus composition with autocatalytic properties, and the redox reaction continues until the entire active surface is covered, promoting the formation of a nickel layer. The deposited nickel nanoparticles are spherical, and the shape of the nanoparticles is attributed to the appearance of tiny protrusions at the nanoscale during nickel deposition. With increasing deposition, the CFC surface is covered with metallic Ni, and it is evident that the gaps between the fibers are covered by metallic Ni. Furthermore, after the second nickel plating, the amount of metallic Ni deposited on the CFC surface further increases.

[0038] The electroless Ni electromagnetic dual-gradient composite material was characterized using scanning electron microscopy (SEM). Low- and high-magnification SEM images of the electromagnetic dual-gradient composite material clearly show the compactness of the composite surface. Figure 3 (a) and 3(b)). Cross-sectional SEM images of the electromagnetic dual-gradient composite material show that the carbon fiber core is covered by a tough shell with a thickness of approximately 0.1 μm. Figure 3 (c) and 3 (d)).

[0039] The core layer is composed of carbon fibers with a good orientation along the confined space constructed by the Ni shell. In general, the mixture of carbon fibers and nickel provides heterogeneous lamellar connections and improves layer alignment through synergistic interfacial interactions of nickel-oxygen-carbon covalent bonds and π-π bridges, contributing to the excellent compactness of the nickel core layer. High-magnification SEM images of the carbon fiber shell reveal a high degree of order. Low-magnification and high-magnification SEM images of the carbon fibers further confirm their core-shell structure, where the core and shell layers are tightly connected, forming a coaxial cylindrical shape. Figure 3 (e)). The tightly connected nickel core layer and highly ordered carbon fiber shell endow the carbon fiber fabric with uniform, large-area, and orderly interconnected conductive channels.

[0040] Figure 4 (a) shows the XRD pattern of the electromagnetic dual-gradient composite material. During the 25-minute electroless nickel plating process, three new diffraction peaks appeared at 44.5°, 51.8°, and 76.3°, corresponding to the (111), (200), and (220) crystal planes of the face-centered cubic nickel lattice. A two-stage deposition method was used for testing, and X-ray photoelectron spectroscopy (XPS) analysis was performed to determine the chemical composition and oxidation state of the electromagnetic dual-gradient composite material. The two-stage deposited electromagnetic dual-gradient composite material is mainly composed of nickel, oxygen, and carbon. Figure 4 (b) In the nickel (Ni) 2p spectrum of the electromagnetically double-gradient composite material with two depositions, two significant peaks appear at 855.64 eV and 873.14 eV, indicating the binding energy associated with nickel. The accompanying peaks observed at 878.75 eV and 861.11 eV in the nickel (Ni) 2p spectrum indicate the presence of a high-spin divalent nickel state. Figure 4 (c)

[0041] Figure 4 (d) shows the FT-IR spectra of electromagnetic dual-gradient composite materials with different Ni deposition times after electroless nickel plating, at 2363 cm⁻¹. - 1 and 2330 cm - 1 The resonant frequency of nickel was observed at 663 cm⁻¹, while the nickel-oxygen lattice vibration appeared at 663 cm⁻¹. - 1 This indicates that the carbon fiber cloth has been fully coated after the electroless nickel plating process.

[0042] O 1sXPS Atlas ( Figure 4 (e) indicates that no significant material accumulation occurred on the CFC surface after activation. High-resolution C1s spectroscopy ( Figure 4Characteristic peaks at 284.79 eV and 288.21 eV are observed in (f), corresponding to C=C and C=O bonds in the bilayer electromagnetic gradient composite material. XRD and XPS results confirm that nickel nanoparticles have been effectively anchored on the CFC surface.

[0043] The conductivity of the electromagnetic dual-gradient composite material demonstrates its dissipation capability; the higher the electromagnetic wave energy, the stronger the conductivity, and the more likely it is to cause higher levels of electromagnetic interference. The conductivity was 71.43 S / cm, 139.24 S / cm, 187.32 S / cm, 212.22 S / cm, and 301.8 S / cm during Ni deposition times ranging from 5 min to 25 min. This indicates that the functional conductive network has been effectively conducted (…). Figure 4 (g)). For example Figure 4 As shown in (h), the conductivity of the sample without electroless nickel plating was 32.59 S / cm. After one, two, three, and four electroless nickel plating processes, the conductivity increased to 184.88 S / cm, 212.22 S / cm, 311.78 S / cm, and 589.91 S / cm, respectively. By extending the plating duration and increasing the number of depositions, conductivity can be improved, thereby increasing electromagnetic shielding efficiency. Magnetism plays a crucial role in reducing electromagnetic interference, such as... Figure 4 As shown in (i), after electroless nickel plating, all tested electromagnetic dual-gradient composite material samples exhibited typical soft magnetic properties. The saturation magnetization of the nanocomposite materials after one, two, three, and four depositions were 5.25 emu / g, 7.86 emu / g, 9.40 emu / g, and 10.34 emu / g, respectively. The sample after the four deposition process showed the maximum saturation magnetization, which was mainly due to the presence of nickel metal particles added by the electroless nickel plating deposition method.

[0044] To analyze the electromagnetic shielding mechanism, the SE in the X-band frequency range was calculated. T SE A and SE R .like Figure 5 As shown in (a), 5(b), and 5(d), the overall shielding effectiveness continues to increase with the extension of electroless nickel plating time and the increase of repeated deposition times. The effectiveness of absorption and shielding indicates that the incident wave still exists even after bouncing off the main surface and then propagates to the internal loss region of the shield. Absorption loss is caused by the absorption of electromagnetic waves at the material's internal interface or by reflection within the material. It is generally understood that surface plasmon resonance (SPR) is generated by the direct coupling between electromagnetic waves and charge carriers, and more conductive materials tend to exhibit more effective reflection shielding. Figure 5The data in (c) and 5(d) suggest that the increase in reflective shielding effectiveness may be due to enhanced reflection caused by increased conductivity, while the increase in absorbent shielding effectiveness may be related to stronger dielectric polarization and magnetic loss. Figure 5 As shown in (e), the average total shielding effectiveness values ​​of the original sample, and the samples deposited with nickel one, two, three, and four times sequentially were 44.2 dB, 49.3 dB, 64.3 dB, 53.6 dB, and 51.5 dB, respectively. The electromagnetic shielding effectiveness of the composite materials CFCCs-5, CFCCs-10, CFCCs-15, CFCCs-20, and CFCCs-25 after one nickel deposition followed by sequential deposition for 5 min, 10 min, 15 min, 20 min, and 25 min were 44.2 dB, 47 dB, 51.8 dB, 53.6 dB, 49.3 dB, and 54.3 dB, respectively. Figure 5 As shown in (k).

[0045] The electromagnetic dual-gradient composite material provided by this invention comprises a composite film with a thickness of 0.49 mm, consisting of two deposited electromagnetic layers. It exhibits a reflection loss (SET) of 64.29 dB and an absorption loss (SE) as low as 15.61 dB. R The shielding follows a path of absorption, reflection, and reabsorption. Increased reflection directs more energy outward, reducing overall shielding effectiveness. Figure 5 The results shown in (i) confirm these observations, and the correlation curves are as follows: Figure 5 As shown in (g), 5(h), and 5(j), the shielding effectiveness (SE) of commercially available shielding materials is typically... T The absorbance exceeds 20 dB, which means they are practical in real-world applications and can meet a variety of needs. Figure 5 (f) indicates that the composite material with two electroless nickel plating deposition processes has good absorption performance. Figure 5 (l) indicates that treating the carbon fiber cloth with this method for 20 minutes can give it the strongest electromagnetic shielding capability, which is mainly reflected in its ability to efficiently reflect electromagnetic waves. Figure 6 (a) through 6(e) show that the initial surface Sa value of CFC was 36.263 μm. During several rounds of electroless nickel plating, the Sa measurement value first decreased, then increased again, and finally reached 62.011 μm. Figure 6 As shown in (f), this trend is likely due to the decreasing deposition rate of nickel nanoparticles over time, causing the process to shift from uniform surface coverage to localized reaction sites. With the accumulation of more nickel, the surface of the CFC becomes increasingly covered, leading to increased surface roughness. This surface roughness becomes more pronounced after the final reaction. Figure 6(g) to 6(k) show that the contact angle gradually increases with increasing electroless nickel plating time. On rougher surfaces, water droplets tend to generate significant cavitation, which reduces the actual contact area between the droplet and the surface. Figure 6 (l) indicates that with the treatment of electroless nickel plating, the hydrophobic properties of the electromagnetic dual gradient composite material gradually increase. The hydrophobic properties of the three and four depositions are almost the same, and the trend of change is not obvious.

[0046] As the duration of electroless nickel plating increases, the amount of nickel deposited on the CFC surface also increases. This enhancement effect strengthens the micro / nano composite structure, and the contact angle gradually increases. When the number of electroless plating cycles reaches three, the CFC surface is completely covered with metallic nickel, forming an optimal micro / nano structure that endows the CFC with excellent hydrophobic properties. Conversely, further extension of the reaction time leads to a large accumulation of nickel. This accumulation of metallic nickel may cause particle agglomeration and reduce nanoscale features, thereby affecting the hydrophobic properties of the CFC.

[0047] To adapt to different application scenarios, electromagnetic dual-gradient composite materials require excellent mechanical properties. For example... Figure 7 As shown in (a) and 7(b), the tensile strength of the original carbon fiber fabric was 5.4 MPa. In contrast, after 20 minutes of electroless nickel plating, the electromagnetic dual-gradient composite with a single deposition reached a maximum tensile strength of 11.7 MPa, more than twice that of the original CFC. The superior mechanical properties of the composite compared to CFC are mainly attributed to the synergistic effect of electroless nickel plating and densification. Electroless nickel plating and densification endow the electromagnetic dual-gradient composite with excellent mechanical properties, demonstrating its application potential in fields such as construction, flexible wearable devices, and portable electronic devices. Furthermore, the electromagnetic dual-gradient composite exhibits good flexibility and shape recovery. Figure 7 As shown in (c) and 7(d), the material recovers its original shape even after multiple twisting and bending deformations. Meanwhile, the single-deposited electromagnetic dual-gradient composite material can fold and withstand a load of 1.5 L. Figure 7 (e) This directly demonstrates its excellent flexibility and high mechanical strength.

[0048] Figure 7(f) The thermal camouflage performance of the electromagnetic dual-gradient composite material was evaluated. In low-temperature tests, when attached to a bucket surface, the electromagnetic dual-gradient composite material exhibited a radiation temperature of 23.9°C, highly matching the ambient temperature (26.1°C). In medium-temperature tests, when placed on a hand and a working mobile phone, its radiation temperature was also very close to the ambient temperature. Under high-temperature test conditions, when connected to a power adapter, the thermal image showed a temperature of only 28.5°C, displaying a color similar to the environment. Overall, the area covered by the electromagnetic dual-gradient composite material achieved good environmental matching over a wide temperature range, reducing the difference in infrared radiation between military targets and their surroundings, thereby effectively reducing their exposure risk. To verify this concept, experiments were conducted using tank and aircraft models, with temperatures set at approximately 35.3°C and 33°C, respectively, simulating situations where the target temperature is higher than the ambient temperature. The results showed that the area covered by the electromagnetic dual-gradient composite material exhibited a color similar to the background, while other exposed parts could be clearly identified by infrared sensors, fully demonstrating its passive camouflage capability. This capability stems from the low infrared emissivity of the composite material, making it suitable for situations where the target temperature exceeds the background temperature, such as at night or in jungle environments. However, it should be noted that relying solely on low emissivity for infrared signature mixing has limitations and may fail when there is a large temperature difference between the target and the environment. To overcome this limitation, additional heating is required to balance the temperature difference. Therefore, the electrothermal conversion capability of electromagnetic dual-gradient composite materials offers potential for their application in active infrared camouflage.

[0049] Electromagnetic dual-gradient composite material photographs Figure 8 As shown in (a), Figure 8 (b) Figure 8 (c) and Figure 8 (d) shows the obstruction between the coil and the bulb when the switch is off, and the locations where they are separated by the electromagnetic double-gradient composite material. The electric and magnetic field values ​​of the chassis were measured using a DLY-1701 electromagnetic radiation tester, yielding electric and magnetic field values ​​of 17 V / m and 0.38 Ut, respectively. Figure 8 (f) The chassis surface was covered with the sample, and the obtained electric field value was almost 0 V / m, and the magnetic field value was 0.17 uT. Figure 8 (e)). For example Figure 8 As shown in (h), the electromagnetic dual-gradient composite material still exhibits good magnetic properties after high-temperature heat treatment for 30s, 60s, and 90s. This phenomenon indicates that the electromagnetic dual-gradient composite material possesses high-temperature usability and electromagnetic shielding performance under high-temperature conditions. All the above experiments demonstrate that the electromagnetic dual-gradient composite material can shield electromagnetic waves in practical applications. Figure 8(g) is a comparison graph showing the relationship between electromagnetic interference (EMI) shielding effectiveness and high-temperature resistance. As can be seen from the comparison, when the high-temperature resistance of the material in this application approaches 1000℃, its EMI shielding effectiveness reaches almost 70 dB, far exceeding that of other control groups.

[0050] exist Figure 8 In (i), these three images show how the sample surface exhibits a self-cleaning process. Specifically, when the liquid interacts with the surface, it can easily remove dirt and contaminants and prevent contamination. The remaining three images depict droplets of methylene blue solution just rolling off the surface without adhering, demonstrating their hydrophobic properties.

[0051] like Figure 9 As shown in (a), the temperature variation characteristics of the electromagnetic double-gradient composite material under different driving voltages (U) were systematically studied. It was found that the steady-state equilibrium temperature (Ts) is positively correlated with the applied voltage. With increasing applied voltage, the steady-state equilibrium temperature (Ts) of the system significantly increases, maintaining a high-efficiency Joule heating effect even when the voltage is less than 2V. Through analysis, a relationship between steady-state temperature and the square of the voltage (U) was established. 2 Quantitative relationship between ) Figure 9 (b) The saturation temperature is approximately linearly related to the square of the applied voltage, described by the following equation: y = 38.39 + 48.37x, with a fitting coefficient R0. 2 The value is 0.9857, which is highly consistent with the classic Joule thermodynamics theory. Step voltage loading experiment ( Figure 9 (c) further verified the controllable heating performance of the material. Cyclic stability test at a constant voltage of 1.25 V ( Figure 9 (d) indicates that NCFCCs exhibit excellent temperature response repeatability, with highly consistent temperature rise-fall curves for each cycle. Furthermore, Figure 9 The durability test results in (d) and 9(e) show that the material has stable electrothermal properties, and the electromagnetic dual-gradient composite material can maintain a steady-state operating temperature of 135.5℃ at a working voltage of 1.25 V. According to Figure 9 The data in (f) show that the surface temperature of the composite film stabilizes at 46.4°C when a voltage of 0.5 V is applied, and rises to 220.0°C at 2.0 V, fully demonstrating its excellent temperature control performance. This unique electrothermal characteristic allows the surface temperature of the film to respond rapidly to voltage regulation, thereby precisely matching the infrared radiation characteristics of different objects. Comparison of the Joule heating performance of the electromagnetic dual-gradient composite material with other reported multilayer heaters shows that the electromagnetic dual-gradient composite material has a significant advantage in achieving high temperatures at lower voltages.

[0052] Figure 10This indicates that induced electromagnetic waves cause the magnetic moment of amorphous ferroelectric perovskite crystals to oscillate periodically, resulting in magnetic resonance and converting electromagnetic energy into heat (resonance loss). Under an alternating magnetic field, the change in magnetization of the electromagnetic dual-gradient composite material exhibits a hysteresis effect, causing continuous energy dissipation (hysteresis loss) through repeated absorption-release cycles. The outer coating of these nickel nanoparticles has many protrusions and depressions, leading to uneven surface charge distribution. This promotes charge migration and redistribution, thus exacerbating polarization loss. Simultaneously, the metallic nickel particles arranged in a fibrous pattern on the carbon fibers cause electromagnetic waves to undergo scattering and reflection processes within the material, which will exacerbate polarization loss and weaken the intensity of the electromagnetic signal. The remaining electromagnetic waves will then reach the highly conductive metallic nickel layer. There is a significant difference in conductivity between these two layers. Furthermore, they form an interwoven network, resulting in numerous reflection and scattering points at the interface, further affecting wave propagation. Some electromagnetic waves are redirected to the carbon fiber layer, leading to additional hysteresis and resonance loss, effectively lengthening their propagation path. When electromagnetic waves reach the highly conductive nickel metal layer, a significant difference in conductivity (10) occurs. 3 The interlaced network structure generates strong scattering / reflection at the interface. The central partial wave is reflected back to the CF layer for secondary magnetic loss absorption. The residual wave is scattered by the irregular microstructure in the CFC layer and attenuated by conduction loss and Joule heating.

[0053] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0054] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing an electromagnetic dual-gradient composite material containing Ni and CFC, characterized in that, Includes the following steps: (1) Pretreatment: The carbon fiber cloth was cut into small pieces, and then the carbon fiber was polished with sandpaper. Next, the sample was immersed in the sensitizing solution for 15 minutes at room temperature, and then the sample was immersed in the activation solution for 90 seconds. The sensitizers used in the electroless nickel plating process include nickel sulfate hexahydrate and dilute hydrochloric acid. (2) Electroless nickel plating: Ammonia was added to adjust the pH of the electroless nickel plating solution. Electroless nickel plating was performed at 60°C, with nickel deposition occurring 1-4 times, each time for 20 minutes. The carbon fiber cloth was turned over every 3 minutes. After the reaction was completed, the solution was washed with deionized water for 2 minutes, then pressed for 48 hours, and finally dried in an oven to obtain the electromagnetic dual-gradient composite material.

2. The method for preparing a Ni- and CFC-containing electromagnetic dual-gradient composite material according to claim 1, characterized in that, The size of the small piece is 5cm × 5cm; the sandpaper is 600 grit sandpaper.

3. The method for preparing a Ni- and CFC-containing electromagnetic dual-gradient composite material according to claim 1, characterized in that, The sensitizing solution is a mixture of nickel sulfate hexahydrate and hydrochloric acid, with a concentration of 0.7-0.9 mL / g.

4. The method for preparing a Ni- and CFC-containing electromagnetic dual-gradient composite material according to claim 1, characterized in that, The activation solution is a mixture of sodium hydroxide and sodium borohydride, with a mass ratio of sodium hydroxide to sodium borohydride of (0.7-0.9):(0.9-1.1).

5. The method for preparing a Ni- and CFC-containing electromagnetic dual-gradient composite material according to claim 1, characterized in that, The electroless nickel plating solution is prepared by adding 9.9 g of nickel sulfate, 9.0 g of sodium citrate, 8.4 g of sodium hypophosphite, and 9.0 mg of thiourea to 300 mL of distilled water, and finally adding ammonia to adjust the pH of the plating solution to 9.

0.

6. The method for preparing a Ni- and CFC-containing electromagnetic dual-gradient composite material according to claim 1, characterized in that, The pressing is performed using a 2-3 kg weight; the drying temperature is 70-90℃.

7. An electromagnetic dual-gradient composite material containing Ni and CFC, characterized in that, It is prepared by the preparation method according to any one of claims 1-6.

8. The application of the Ni- and CFC-containing electromagnetic dual-gradient composite material as described in claim 7 in construction, flexible wearable devices, precision electronic instruments, aerospace technology and military instruments.

Images