Multifunctional electromagnetic material with high-frequency electromagnetic absorption and corrosion resistance and preparation method and application thereof

Abstract

The present application relates to the field of high-frequency microwave absorbing material and technology, disclose a kind of multifunctional electromagnetic material with high-frequency electromagnetic absorption and corrosion resistance characteristics and its preparation method and application, the multifunctional electromagnetic material is the core-shell structure with 10-100nm particle size, core is metal magnetic alloy component, shell layer is multilayer graphite carbon;It is obtained by carbonization treatment after dissolving and precipitating of metal salt, surfactant and organic ligand, the magnetic alloy component of core body in material and the graphite carbon matrix of shell layer form conductive network, conducive to the conduction loss caused by electron transition;Mutual hetero-interface is conducive to the interface polarization loss of electromagnetic wave.In addition, magnetic component provides strong magnetic loss, optimizes the impedance matching of wave-absorbing body, further enhances the attenuation ability to electromagnetic wave;And shell layer can effectively prevent the penetration and transmission of various corrosive media on the surface of target matrix, it is a kind of multifunctional electromagnetic material with high-frequency electromagnetic absorption and corrosion resistance characteristics.

Description

Technical Field

[0001] This invention belongs to the field of high-frequency microwave absorbing materials and technology, specifically relating to a class of multifunctional electromagnetic materials that combine high-frequency electromagnetic absorption and corrosion resistance, as well as their preparation methods and applications. Background Technology

[0002] With the development of the 5G smart era, communication technology using gigahertz electromagnetic waves has brought ultra-high information transmission efficiency to industrial automation and intelligent communication, promoting the rapid development of related intelligent devices and greatly facilitating people's production and lives. However, the electromagnetic radiation accompanying ultra-high information transmission also causes electromagnetic interference to related equipment and instruments, which has triggered an urgent demand for related electromagnetic functional composite materials. At the same time, with the widespread application of 5G smart devices in industrial equipment, communication base stations, and marine military fields, conventional electromagnetic wave absorbing materials will undergo irreversible chemical corrosion in harsh application environments such as the ocean, acid rain, or alkaline environments, thus deteriorating their electromagnetic functions. For example, in marine environments, coating peeling caused by metal corrosion on the surface of warships and submarines often leads to the failure of electromagnetic wave absorption performance. Therefore, the development of dual-functional electromagnetic wave materials with both electromagnetic absorption and corrosion resistance properties is a practical necessity.

[0003] Publication number CN112492869A discloses a Prussian blue redox-derived iron-based microwave absorbing material and its preparation method. The iron-based microwave absorbing material, with a filler content of 40 wt% and a thickness of 1-5 mm, has an effective absorption bandwidth of 0-5.44 GHz and a maximum coverage of over 90% in the Ku band.

[0004] Publication number CN114554819A discloses an electromagnetic wave absorbing agent based on iron-based metal-organic frameworks (MOFs) and its preparation method. The electromagnetic wave absorbing agent is a composite of iron nitride and porous carbon, with the iron nitride uniformly distributed within the porous carbon matrix. The resulting composite material has a specific surface area of ​​50-150 cm² / g, and the iron nitride particle diameter ranges from 0.5 to 1.5 μm. Furthermore, the presence of the porous structure not only reduces the material's density, but the high specific surface area also enhances the interfacial polarization capability, increasing the number of reflections and absorptions of electromagnetic waves within the material, thus giving the electromagnetic wave absorber excellent absorption performance. It can be seen that novel absorbing materials using MOFs as precursors have significant research value, possessing advantages such as lightweight and high-loss electromagnetic attenuation.

[0005] However, whether electromagnetic wave functional materials can maintain corrosion resistance in complex and harsh environments remains unknown or has not been explored. Given the widespread application of electromagnetic wave functional materials in industrial equipment, communication base stations, and marine military fields, there is an urgent practical need for corrosion resistance in these materials. If both electromagnetic absorption and corrosion resistance could be simultaneously achieved, it would significantly promote the expansion of the application areas of electromagnetic wave materials. Summary of the Invention

[0006] There is limited research on the corrosion resistance of electromagnetic wave materials. This invention provides a method for preparing an organic framework derivative electromagnetic functional material that combines high-frequency electromagnetic absorption and corrosion resistance. This composite magnetoelectric functional material is obtained by high-temperature carbonization of MOF precursors and exhibits both excellent electromagnetic absorption and corrosion resistance properties.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A type of multifunctional electromagnetic material that combines high-frequency electromagnetic absorption and corrosion resistance, wherein the multifunctional electromagnetic material has a core-shell structure with a particle size of 10-100 nm, the core is a transition metal magnetic alloy component, and the shell is a multilayer graphite carbon; the multifunctional electromagnetic material contains at least two transition metal elements selected from iron, cobalt, and nickel.

[0009] Preferably, the particle size of the multifunctional electromagnetic material is 20-80 nm;

[0010] This invention provides a method for preparing the multifunctional electromagnetic material that combines high-frequency electromagnetic absorption and corrosion resistance, comprising the following steps:

[0011] Step 1: Dissolve the metal salt and surfactant in water to prepare solution A, and dissolve the organic ligand in water to prepare solution B; mix solution A and solution B, stir, let stand, centrifuge, wash, and dry to obtain the metal-organic framework precursor;

[0012] Step 2: The metal-organic framework precursor is carbonized and annealed to obtain the multifunctional electromagnetic material.

[0013] This invention prepares a core-shell composite material using a co-precipitation method and a high-temperature annealing carbonization process. The core of the material is a magnetic alloy component, and the shell is a multilayered graphite carbon matrix. The magnetic alloy component in the core and the graphite carbon matrix in the shell form a conductive network, which is beneficial for conduction losses caused by electron transitions. Simultaneously, the heterogeneous interfaces between the graphite carbon and the magnetic alloy component, and between the alloy components, are beneficial for interfacial polarization losses of electromagnetic waves. Furthermore, the magnetic component can provide strong magnetic loss, optimizing the impedance matching of the absorber and further enhancing its attenuation capability for electromagnetic waves. At the same time, the multilayered graphite carbon layers outside the magnetic alloy component can also effectively prevent various corrosive media (such as H₂) from penetrating. + OH- , Cl - , O2, and H2O) penetrate and transfer on the surface of the target substrate, thereby achieving the purpose of corrosion protection and obtaining a multifunctional electromagnetic material with both high-frequency electromagnetic absorption and corrosion resistance characteristics.

[0014] Preferably, the metal elements in the metal salt include one or two of Fe, Co, and Ni; different metals can form different types of binary / ternary Prussian blue analog (PBA) precursors with different organic ligands. After further high-temperature carbonization treatment, cores with different alloy phases can be formed. Among them, the main influence is reflected in the differences in the atomic magnetic moments of different metals, where Ni < Co < Fe, resulting in differences in the saturation magnetization intensities of the alloy phases formed after different metal combinations. NiCo < NiFe < NiCoFe < CoFe, and the differences in saturation magnetization intensity may be reflected in the differences in the magnetic loss mechanism and attenuation ability. For example, NiCoFe@C compared with CoFe@C, due to the enhanced coupling effect between magnetic particles in the double magnetic alloy phase formed after carbonization, optimized impedance matching and attenuation performance are obtained.

[0015] The metal salt includes one or more of metal nitrates, sulfates, carbonates, acetates, or chlorides;

[0016] Preferably, the organic ligand includes one of potassium nickel cyanide, potassium cobalt cyanide, potassium ferrocyanide, or potassium ferricyanide.

[0017] Further preferably, the metal elements in the metal salt are not completely the same as the transition metal elements in the organic ligand; that is, the multifunctional electromagnetic material contains at least two transition metal elements, preferably three transition metal elements.

[0018] The surfactant is sodium citrate.

[0019] The molar ratio of the organic ligand to the metal salt is (0.5 - 1):1. The ratio of the metal salt to the organic matter can regulate the content of metal components in PBA, thereby further optimizing the alloy components and content after carbonization.

[0020] The molar ratio of the metal salt to the surfactant is 1:(0.5 - 1.5);

[0021] In step 1, solution A is slowly dropped into solution B at room temperature, and stirring is continued for 0.5 - 12 h, followed by standing and aging for 12 - 24 h. After separating the obtained sample, it is dried at 60 - 80 °C.

[0022] In step 2, the carbonization annealing is carried out in an inert atmosphere, including a mixed gas of Ar / N2 and H2, and the volume content of H2 is 1 - 8%.

[0023] Preferably, in step 2, the carbonization annealing temperature is specifically 200-400℃ for 0.5-1h, followed by heating to 500-900℃ and holding for 2-8h. Different carbonization temperatures affect the degree of carbonization of PBA (such as the degree of alloy reduction, the degree of graphitization of graphitic carbon, and defect concentration), thereby affecting the dielectric / magnetic parameters, and ultimately the attenuation capability. However, the effect can be either positive or negative, as changes in dielectric / magnetic parameters may lead to changes in absorption performance at different frequency bands. Furthermore, excessively low temperatures result in insufficient carbonization, while excessively high carbonization temperatures can damage the PBA structure and affect impedance matching performance, both of which affect the overall performance of the product.

[0024] The multifunctional electromagnetic material provided by this invention combines high-frequency electromagnetic absorption and corrosion resistance properties. It exhibits excellent localized high-frequency electromagnetic absorption performance and superior corrosion resistance, and can be applied to the field of high-frequency electromagnetic protection in corrosive environments.

[0025] The multifunctional electromagnetic material prepared by this invention not only has excellent wave absorption performance, but also exhibits excellent corrosion resistance in acidic, neutral, or alkaline environments, demonstrating superior lightweight broadband absorption characteristics and comprehensive corrosion resistance, as well as application potential.

[0026] Preferably, the multifunctional electromagnetic material of the present invention has a maximum reflectivity of -47.6 dB and an effective absorption bandwidth of 5.83 GHz. Even after being immersed in a 3.5 wt% NaCl solution for thirty days, it retains its magnetism. In a neutral 3.5 wt% NaCl solution environment, its self-corrosion potential and self-corrosion current density are 0.122 V and 1.4793 μA·cm, respectively. 2 This demonstrates its excellent microwave absorption and corrosion resistance properties.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) This invention prepares a multifunctional composite material with both high-frequency electromagnetic absorption and corrosion resistance by co-precipitation and high-temperature annealing carbonization. The magnetic alloy component in the core and the graphite carbon matrix in the shell work synergistically to improve the microwave absorption performance of the material. At the same time, the shell can effectively prevent the penetration and transmission of various corrosive media on the surface of the target matrix, including acidic, alkaline, neutral, oxygen or water, etc., and has excellent corrosion resistance.

[0029] (2) The preparation method of the multifunctional electromagnetic material of the present invention is simple, and the product has multiple functions, and is expected to be further expanded in the fields of aviation or marine military. Attached Figure Description

[0030] Figure 1TEM images and particle size distribution diagrams of NiCoFe@C, NiCo@C, NiFe@C and CoFe@C prepared in Examples 1-4.

[0031] Figure 2 The images show the XRD patterns of NiCoFe@C, NiCo@C, NiFe@C, and CoFe@C prepared in Examples 1-4.

[0032] Figure 3 The reflection loss curves of NiCoFe@C, NiCo@C, NiFe@C and CoFe@C prepared in Examples 1-4 are shown in the range of 2-18 GHz.

[0033] Figure 4 The diagrams are: A) Open circuit potential diagrams of NiCoFe@C, NiCo@C, NiFe@C and CoFe@CM prepared in Examples 1-4 in acidic, neutral and alkaline NaCl solutions, and B) Polarization curves of the three absorbing agents under neutral conditions.

[0034] Figure 5 TEM images of Ni / C, Co / C and Fe / C prepared in Comparative Examples 1-3.

[0035] Figure 6 The reflection loss curves of Ni / C, Co / C and Fe / C prepared for Comparative Examples 1-3 in the 2-18 GHz frequency band are shown.

[0036] Figure 7 The reflection loss curves of NiCoFe@C-600, NiCoFe@C-800, and NiCoFe@C-900 prepared in Comparative Example 4 are shown in the range of 2-18 GHz, and the comparison diagram is shown at t=2 mm. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention.

[0038] All raw materials used in the following specific implementation methods were purchased from the market.

[0039] Example 1: Preparation of NiCoFe@C

[0040] (1) At room temperature, 1.5 mmol Ni(CH3OO)2·4H2O, 4.5 mmol Co(CH3OO)2·4H2O, and 9 mmol sodium citrate dihydrate were dissolved in 200 mL of deionized water to form a homogeneous solution A. 4 mmol potassium ferricyanide (K3[Fe(CN)6]) was dissolved in 500 mL of deionized water to form a homogeneous solution B. Solution B was slowly added dropwise to solution A, stirred for 30 min, and then allowed to stand at room temperature for 24 hours. Finally, the blue-gray precipitate was collected by centrifugation, washed three times with ethanol, and dried at 60 °C to obtain the NiCoFe@C precursor.

[0041] (2) The NiCoFe@C precursor from (1) was placed in an alumina crucible and heated to 300°C at 2°C / min in a tube furnace (Ar / H2 atmosphere). After holding at this temperature for 60 min, the temperature was further increased to 700°C and held for 2 h. Finally, the NiCoFe@C composite material was obtained by naturally cooling to room temperature.

[0042] TEM of composite materials, such as Figure 1 As shown in A and A-2, the prepared NiCoFe@C exhibits a typical core-shell structure, with the magnetic alloy forming the core, and an average size of 43.6 nm (e.g., ...). Figure 1 A-1), the carbon layer is the shell.

[0043] Example 2: Preparation of NiCo@C

[0044] (1) At room temperature, 6 mmol Ni(CH3OO)2·4H2O and 9 mmol polyvinylpyrrolidone were dissolved in 200 mL of deionized water to form a homogeneous solution A. 4 mmol potassium cobalt cyanide (K3[Co(CN)6]) was dissolved in 500 mL of deionized water to form a homogeneous solution B. Solution B was slowly added dropwise to solution A, stirred for 30 min, and then allowed to stand at room temperature for 24 hours. Finally, the blue precipitate was collected by centrifugation, washed three times with ethanol, and dried at 60 °C to obtain the NiCo@C precursor.

[0045] (2) The NiCo@C precursor from (1) was placed in an alumina crucible and heated to 300°C at 5°C / min in a tube furnace (Ar / H2 atmosphere). After holding at this temperature for 60 min, the temperature was further increased to 700°C and held for 2 h. Finally, the NiCo@C composite material was obtained by natural cooling to room temperature.

[0046] TEM of composite materials, such as Figure 1 As shown in B and B-2, the prepared NiCo@C exhibits a typical core-shell structure, with the magnetic alloy forming the core, and the particle size distribution is as follows. Figure 1 B-1 has an average size of 46.13 nm and a carbon shell.

[0047] Example 3: Preparation of NiFe@C

[0048] (1) At room temperature, 6 mmol of Ni(CH3OO)2·4H2O and 9 mmol of 1,4-butynediol were dissolved in 200 mL of deionized water to form a homogeneous solution A. 4 mmol of potassium ferricyanide (K3[Fe(CN)6]) was dissolved in 500 mL of deionized water to form a homogeneous solution B. Solution B was slowly added dropwise to solution A, stirred for 30 min, and then allowed to stand at room temperature for 24 hours. Finally, the yellow precipitate was collected by centrifugation, washed three times with ethanol, and dried at 60 °C to obtain the NiFe@C precursor.

[0049] (2) The NiFe@C precursor from (1) was placed in an alumina crucible and heated to 300°C at 2°C / min in a tube furnace (Ar / H2 atmosphere). After holding at this temperature for 60 min, the temperature was further increased to 700°C and held for 2 h. Finally, the mixture was allowed to cool naturally to room temperature to obtain the NiFe@C composite material.

[0050] TEM of composite materials, such as Figure 1 As shown in C and C-2, the prepared NiFe@C exhibits a typical core-shell structure, with the magnetic alloy forming the core, and the particle size distribution is as follows. Figure 1 C-1 has an average size of 62.17 nm and a carbon shell.

[0051] Example 4: Preparation of CoFe@C

[0052] (1) At room temperature, 6 mmol of Co(CH3OO)2·4H2O and 9 mmol of polyvinyl alcohol were dissolved in 200 mL of deionized water to form a homogeneous solution A. 4 mmol of potassium ferricyanide (K3[Fe(CN)6]) was dissolved in 500 mL of deionized water to form a homogeneous solution B. Solution B was slowly added dropwise to solution A, stirred for 30 min, and then allowed to stand at room temperature for 24 hours. Finally, the brown precipitate was collected by centrifugation, washed three times with ethanol, and dried at 60 °C to obtain the CoFe@C precursor.

[0053] (2) The CoFe@C precursor from (1) was placed in an alumina crucible and heated to 300°C at 2°C / min in a tube furnace (Ar / H2 atmosphere). After holding at this temperature for 60 min, the temperature was further increased to 700°C and held for 2 h. Finally, the mixture was allowed to cool naturally to room temperature to obtain the CoFe@C composite material.

[0054] TEM of composite materials, such as Figure 1 As shown in D and D-2, the prepared CoFe@C exhibits a typical core-shell structure, with the magnetic alloy forming the core, and the particle size distribution is as follows. Figure 1 D-1 has an average size of 45.06 nm and a carbon shell.

[0055] Meanwhile, XRD tests were performed on the multifunctional electromagnetic materials prepared in Examples 1-4, and the XRD results showed that ( Figure 2 The four types of microwave absorbers have good alloy crystal phases and are typical binary or ternary alloys.

[0056] The electromagnetic materials prepared in Examples 1-4 and Comparative Examples 1-4 were tested for electromagnetic wave absorption as follows: A certain mass of the prepared sample was mixed with a certain mass fraction of paraffin (mass fraction ratio 50%:50%), and pressed into a ring-shaped sample with an outer diameter of 7.00 mm, an inner diameter of 3.04 mm, and a thickness of ~2.00 mm. The complex permittivity and complex permeability in the 2-18 GHz frequency band were measured using a vector network analyzer (VNA). Then, the maximum reflection loss (RL) of the target material was calculated using classical transmission line theory.

[0057] As can be seen from the above, the NiCoFe@C prepared in Example 1 ( Figure 3 A) Adjustable absorption performance was achieved within a thickness range of 1-5 mm, with the strongest reflectivity loss being -40 dB. Meanwhile, NiCo@C( Figure 3 B), NiFe@C ( Figure 3 C), CoFe@C( Figure 3 D) The three absorbers have the strongest reflectivity losses of -32dB, -35dB, and -40dB, respectively, exhibiting good electromagnetic wave absorption characteristics.

[0058] Regarding corrosion resistance, the testing process was as follows: At room temperature, the open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization curve of the target sample were measured using a three-electrode system on an electrochemical workstation (model CHI660E). The reference electrode was a saturated calomel electrode; the counter electrode was a Pt sheet; the working electrode was prepared by dropping a mixture of the test sample (5.00 mg) and Nafion solution into the surface of a 4 mm diameter glassy carbon electrode disk and then ultrasonically treating it for 30 minutes. Simultaneously, the corrosion resistance of the sample under three different environments was tested using acidic, neutral, and alkaline 3.5 wt% NaCl solutions. It should be noted that the open circuit potential (OCP) test required a duration of 2400 s, while the EIS test was conducted within 10 seconds. 5 -10 -2 Within the Hz frequency range, the signal disturbance is 10mV.

[0059] The results showed that all four microwave absorbers exhibited excellent corrosion resistance under acidic, alkaline, and neutral conditions. Figure 4(A) shows the changes in open circuit potential (OCP) of the four samples after stabilization in 3.5 wt% NaCl solutions in acidic (pH=1.33), neutral (pH=7.9), and alkaline (pH=13.3) conditions for 40 min.

[0060] As can be seen, under neutral conditions, the OCP values ​​are positive, at 0.0409V, 0.3062V, 0.2227V, and 0.2614V respectively. Under alkaline conditions, the OCP values ​​fluctuate between -0.1046V and -0.1051V, showing stable values. Under acidic conditions, the OCP values ​​range from -0.3V to -0.4V. This indicates that the four microwave absorbers exhibit good corrosion resistance (low corrosion tendency) under acidic, neutral, and alkaline conditions, with the best performance under neutral conditions.

[0061] Figure 4 (B) shows the Tafel curve of the sample under neutral conditions. After fitting, the self-corrosion current density of NiCoFe@C is as low as 9.741 × 10⁻⁶. -6 A / cm 2 The self-corrosion current densities of the other three absorbers are 9.695 × 10⁻⁶. -5 1.496×10 -5 and 1.61×10 -5 A / cm 2 It exhibits excellent corrosion resistance.

[0062] Comparative Example 1: Preparation of Ni / C

[0063] (1) At room temperature, 6 mmol Ni(CH3OO)2·4H2O and 9 mmol sodium dodecylbenzenesulfonate were dissolved in 200 mL of deionized water to form a homogeneous solution A. 6 mmol potassium nickel cyanide (K2[Ni(CN)4]) was dissolved in 500 mL of deionized water to form a homogeneous solution B. Solution B was slowly added dropwise to solution A, stirred for 30 min, and then allowed to stand at room temperature for 24 hours. Finally, the precipitate was collected by centrifugation, washed three times with ethanol, and dried at 60 °C to obtain the Ni / C precursor.

[0064] (2) The Ni / C precursor from (1) was placed in an alumina crucible and heated to 300°C at 2°C / min in a tube furnace (Ar / H2 atmosphere). After holding at this temperature for 60 min, the temperature was further increased to 700°C and held for 2 h. Finally, the Ni / C composite material was obtained by natural cooling to room temperature.

[0065] TEM images of Ni / C composite materials Figure 5 As can be seen from A, the prepared Ni / C exhibits poor dispersion, with a relatively low content of core-shell structured materials. At the same time, the size distribution of the metal components is relatively large, and the distribution of carbon materials is more random.

[0066] Comparative Example 2: Preparation of Co / C

[0067] (1) At room temperature, 6 mmol of Co(CH3OO)2·4H2O and 9 mmol of sodium dodecylbenzenesulfonate were dissolved in 200 mL of deionized water to form a homogeneous solution A. 4 mmol of potassium cobalt cyanide (K3[Co(CN)6]) was dissolved in 200 mL of deionized water to form a homogeneous solution B. Solution B was slowly added dropwise to solution A, and the mixture was stirred for 1 h. The suspension was then allowed to stand for 24 h. Finally, the pink precipitate was collected, washed three times with ethanol and deionized water, and dried at 60 °C to obtain the Co@C precursor.

[0068] (2) The Co@C precursor prepared in (1) was placed in an alumina crucible and heated to 300°C at 2°C / min in a tube furnace. After holding at this temperature for 60 min, the temperature was further increased to 700°C and held for 2 h. Finally, the Co@C composite material was obtained by natural cooling to room temperature.

[0069] Co@C composite TEM, such as Figure 5 B shows that the prepared Co / C also exhibits poor dispersion, low content of metal material coated in the carbon layer, and uneven coating effect.

[0070] Comparative Example 3: Preparation of Fe / C

[0071] (1) At room temperature, 4 mmol of Fe(NO3)3·9H2O and 6 mmol of sodium citrate dihydrate were dissolved in 200 mL of deionized water to form a homogeneous mixed solution A. 4 mmol of potassium ferrocyanide (K4[Fe(CN)6]·3H2O) was completely dissolved in another 200 mL of deionized water to form a homogeneous solution B. Solution B was slowly added dropwise to solution A, stirred for 1 h, and then the suspension was allowed to stand for 24 h. Finally, the precipitate was collected, washed three times with ethanol and deionized water, and dried at 60 °C to obtain the Fe / C precursor.

[0072] (2) The Fe / C precursor prepared in (1) was placed in an alumina crucible and heated to 300°C at 2°C / min in a tube furnace. After holding at this temperature for 60 min, the temperature was further increased to 700°C and held for 2 h. Finally, the Fe / C composite material was obtained by naturally cooling to room temperature.

[0073] Fe / C composite TEM such as Figure 5 As can be seen from Figure C, the content of the prepared Fe / C core-shell structured material is relatively higher than that of Ni / C and Co / C, mainly due to the higher catalytic activity of Fe compared to Ni and Co. However, compared to the binary or ternary alloy materials in Examples 1-4, the quality and quantity of its core-shell structure are still relatively low.

[0074] Based on the microstructure analysis of Ni / C, Co / C and Fe / C, the exposed metal components are more susceptible to marine corrosion in harsh marine environments, which in turn affects their wave absorption characteristics.

[0075] Figure 6 (AC) is a schematic diagram showing the comparative microwave absorption performance of the three microwave absorbers Ni / C, Co / C, and Fe / C in Examples 1-3. As can be seen, compared with the binary or ternary alloy materials in Examples 1-4, the strongest reflectivity of the three microwave absorbers Ni / C, Co / C, and Fe / C is only -22, -11, and -27 dB, respectively.

[0076] Comparative Example 4

[0077] The effect of different carbonization temperatures on the microwave absorption properties of NiCoFe@C was investigated. The preparation process was exactly the same as in Example 1, except that the carbonization temperatures were selected as 600℃, 800℃, and 900℃, and the prepared samples were named NiCoFe@C-600, NiCoFe@C-800, and NiCoFe@C-900, respectively. Figure 7 (AC) As can be seen, the three types of NiCoFe@C prepared at annealing temperatures of 600℃, 800℃, and 900℃ achieved adjustable microwave absorption performance within a thickness range of 1-5mm, with the strongest reflectivity losses being -22, -11, and -28dB, respectively, exhibiting a good wideband annealing temperature window, which is beneficial to ensuring the microwave absorption stability of the prepared electromagnetic wave absorber.

Claims

1. A multifunctional electromagnetic material possessing both high-frequency electromagnetic absorption and corrosion resistance properties, characterized in that, The multifunctional electromagnetic material has a core-shell structure with a particle size of 10-100 nm, the core being a transition metal magnetic alloy component, and the shell being a multilayer graphite carbon; the multifunctional electromagnetic material contains at least two transition metal elements selected from iron, cobalt, and nickel; The preparation method of the multifunctional electromagnetic material includes the following steps: Step 1: Dissolve the metal salt and surfactant in water to prepare solution A, and dissolve the organic ligand in water to prepare solution B; mix solution A and solution B, stir, let stand, centrifuge, wash, and dry to obtain the metal-organic framework precursor; Step 2: The metal-organic framework precursor is carbonized and annealed to obtain the multifunctional electromagnetic material; the carbonization and annealing temperature in Step 2 is specifically 200-400℃ for 0.5-1h, followed by heating to 500-900℃ and holding for 2-8h. The organic ligand includes one of potassium nickel cyanide, potassium cobalt cyanide, potassium ferrocyanide, or potassium ferrocyanide; the metal element in the metal salt is not exactly the same as the transition metal element in the organic ligand.

2. The method for preparing the multifunctional electromagnetic material with both high-frequency electromagnetic absorption and corrosion resistance properties according to claim 1, characterized in that, Including the following steps: Step 1: Dissolve the metal salt and surfactant in water to prepare solution A, and dissolve the organic ligand in water to prepare solution B; mix solutions A and B, stir, let stand, centrifuge, wash, and dry to obtain the metal-organic framework precursor; the organic ligand includes one of potassium nickel cyanide, potassium cobalt cyanide, potassium ferrocyanide, or potassium ferrocyanide; the metal element in the metal salt is not exactly the same as the transition metal element in the organic ligand; Step 2 involves carbonizing and annealing the metal-organic framework precursor to obtain the multifunctional electromagnetic material. Specifically, the carbonization and annealing temperature in Step 2 is 200-400℃ for 0.5-1h, followed by heating to 500-900℃ and holding for 2-8h.

3. The method for preparing the multifunctional electromagnetic material with both high-frequency electromagnetic absorption and corrosion resistance properties according to claim 2, characterized in that, The metal salt contains one or two of the metal elements Fe, Co, and Ni. The metal salt includes one or more of the following: metal nitrates, sulfates, carbonates, acetates, or chlorides.

4. The method for preparing the multifunctional electromagnetic material with both high-frequency electromagnetic absorption and corrosion resistance properties according to claim 2, characterized in that, The surfactant is sodium citrate.

5. The method for preparing the multifunctional electromagnetic material with both high-frequency electromagnetic absorption and corrosion resistance properties according to claim 2, characterized in that, The molar ratio of the organic ligand to the metal salt is (0.5-1):1; and / or the molar ratio of the metal salt to the surfactant is 1:(0.5-1.5).

6. The method for preparing the multifunctional electromagnetic material with both high-frequency electromagnetic absorption and corrosion resistance properties according to claim 2, characterized in that, In step 1, solution A is added dropwise to solution B at room temperature, and the mixture is stirred for 0.5-12 hours and then allowed to stand for 12-24 hours to age. After separation, the sample is dried at 60-80℃.

7. The method for preparing the multifunctional electromagnetic material with both high-frequency electromagnetic absorption and corrosion resistance properties according to claim 2, characterized in that, In step 2, the carbonization annealing is carried out under an inert atmosphere, including a mixture of Ar / N2 and H2.

8. The multifunctional electromagnetic material with both high-frequency electromagnetic absorption and corrosion resistance properties as described in claim 1 is applied to the field of high-frequency electromagnetic protection in corrosive environments.

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