Fe3C-coated C assembled nano wave-absorbing structure and preparation method thereof

Abstract

The invention discloses a Fe3C (at) C assembled nano wave-absorbing structure and a preparation method thereof, and the preparation method comprises the following steps: synthesizing Fe2O3 (at) C spheres through a hydrothermal method, carrying out carbon removal treatment on the Fe2O3 (at) C spheres by adopting an air oxidation method to obtain a Fe2O3 hollow sphere precursor, and finally carrying out chemical vapor deposition (CVD) reaction on the obtained Fe2O3 hollow sphere precursor to convert a Fe2O3 phase in the Fe2O3 hollow sphere precursor into a Fe3C phase to form Fe3C hollow spheres, thereby obtaining the Fe3C assembled nano wave-absorbing structure. And growing a C nano-particle array on the surface of the Fe3C hollow sphere in situ so as to obtain the Fe3C-C assembled nano wave-absorbing structure. The problems that an existing magnetic wave-absorbing material is large in density, poor in impedance matching, low in electromagnetic wave loss efficiency and the like are solved. According to the prepared nano wave-absorbing structure, coupling of dielectric loss and magnetic loss and optimization of impedance matching are easily achieved, the multiple scattering effect of electromagnetic waves is greatly enhanced through the C nano-particle array structure and the hollow structure on the surface of the nano wave-absorbing structure, enhancement of the interface polarization relaxation loss effect is promoted through a large number of Fe3C-C heterogeneous interfaces, and the wave-absorbing performance is improved.

Description

Technical Field

[0001] The present invention relates to, but is not limited to, the technical field of absorbing materials, and in particular to a Fe3C@C assembled nano-absorbing structure and a preparation method thereof. Background Art

[0002] With the continuous growth of the communications market, a large number of radio frequency systems have emerged, causing a large amount of electromagnetic radiation pollution. This not only seriously endangers human health but also interferes with the operation of precision instruments. Therefore, the development of high-performance absorbing materials has become urgent. Absorbing materials can provide electromagnetic protection by converting electromagnetic wave energy into heat or other forms of energy. The current difficulty in the research of absorbing materials lies in how to prepare high-performance absorbing materials that meet the multiple requirements of light weight, thin thickness, high absorption intensity, and wide absorption bandwidth in practical application scenarios.

[0003] According to the different electromagnetic wave loss mechanisms, absorbing materials can be divided into dielectric loss type and magnetic loss type. Iron-based materials are a representative type of magnetic loss absorbing materials. Due to their high magnetic permeability and high saturation magnetization, they can induce various magnetic loss modes such as eddy current loss, natural resonance and exchange resonance loss, and are therefore widely used in the field of electromagnetic wave absorption. However, existing magnetic loss absorbing materials still have the following shortcomings, which make their absorbing performance unsatisfactory: (1) The density is high, which is not conducive to meeting the requirements of lightweight absorbing materials; (2) The electromagnetic wave attenuation ability mainly comes from the magnetic loss mechanism, the dielectric loss is insufficient, and the impedance matching is poor; (3) Most of them are solid structures with high density and low electromagnetic wave loss efficiency. Summary of the Invention

[0004] The purpose of the present invention is to provide a Fe3C@C assembled nano-wave absorbing structure and a preparation method thereof to solve the problems of existing magnetic absorbing materials such as high density, poor impedance matching, and low electromagnetic wave loss efficiency.

[0005] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a Fe3C@C assembled nano-wave absorbing structure, comprising: Step 1, synthesizing Fe2O3@C spheres by hydrothermal method; Step 2: The Fe2O3@C spheres synthesized in step 1 are oxidized by air oxidation to remove the C spheres and obtain a Fe2O3 hollow sphere precursor; Step 3: Perform a chemical vapor deposition (CVD) reaction on the Fe2O3 hollow sphere precursor obtained in step 2 to transform the Fe2O3 phase in the Fe2O3 hollow sphere precursor into a Fe3C phase to form Fe3C hollow spheres, and in situ grow a C nanoparticle array on the surface of the Fe3C hollow spheres to obtain a Fe3C@C assembled nanowave absorbing structure.

[0006] Optionally, in the preparation method of the Fe3C@C assembled nano-wave absorbing structure as described above, In step 1, the synthesized Fe2O3@C sphere is a spherical core-shell structure with Fe2O3 as the shell and the internal C sphere as the core; In the step 2, the Fe2O3@C balls are subjected to oxidation treatment to remove the C balls filled in the Fe2O3 shell.

[0007] Optionally, in the method for preparing the Fe3C@C assembled nano-wave absorbing structure as described above, step 1 comprises: 2.5-15 mmol ferric nitrate nonahydrate, 1-10 mmol citric acid, 3-10 mmol glucose, and 2-8 mmol urea were dissolved in deionized water and ultrasonically treated to obtain a yellow transparent solution. The solution was transferred to a hydrothermal reactor for hydrothermal reaction. The hydrothermal product was washed three times with anhydrous ethanol and distilled water and dried in an oven at 60-90°C for 12-36 h to obtain Fe2O3@C spheres.

[0008] Optionally, in the above-mentioned method for preparing the Fe3C@C assembled nano-wave absorbing structure, the reaction process of step 1 is: On the one hand, during the high temperature and high pressure hydrothermal process, glucose decomposes to produce C atoms, which nucleate and spontaneously grow isotropically into C spheres; on the other hand, citric acid and Fe 3+ The complexed ferric citrate slowly releases Fe at high temperature 3+ , reacting with ammonia produced by the decomposition of urea to form Fe2O3 nuclei, which adhere to the surface of the C sphere and gradually deposit and thicken, forming Fe2O3@C spheres with a core-shell structure.

[0009] Optionally, in the method for preparing the Fe3C@C assembled nano-wave absorbing structure as described above, step 2 comprises: The Fe2O3@C balls synthesized in step 1 are oxidized in a muffle furnace; the reaction temperature of the oxidation treatment is 400~600℃, the oxidation time is 0.5~3h, and the muffle furnace heating rate is 3~8℃ / min.

[0010] Optionally, in the method for preparing the Fe3C@C assembled nano-wave absorbing structure as described above, step 3 comprises: An Fe2O3 hollow sphere precursor was placed in an ark, which was then transferred to a CVD furnace. The CVD furnace was heated to 300-700°C at a rate of 3-8°C / min for a CVD reaction of 0.5-3h. Argon (Ar) and anhydrous ethanol were introduced throughout the entire process of heating and CVD reaction. Anhydrous ethanol was used as a carbon source in the CVD reaction, which reacted with the Fe2O3 hollow sphere precursor to transform the Fe2O3 phase into the Fe3C phase, forming Fe3C hollow spheres. C nanoparticle arrays were in situ grown on the surface of the Fe3C hollow spheres, transforming the Fe2O3 hollow sphere precursor into a Fe3C@C assembled nano-wave absorbing structure with a protruding C nanoparticle array on the surface. Ar was used as a protective gas for the CVD reaction.

[0011] Optionally, in the above-mentioned method for preparing the Fe3C@C assembled nano-wave absorbing structure, the role of anhydrous ethanol in the CVD reaction process of step 3 is: The hydrogen H2 produced by the decomposition of anhydrous ethanol at high temperature quickly reduces Fe2O3 to Fe. The C atoms and C atomic clusters produced by the decomposition of anhydrous ethanol at high temperature dissolve in the Fe lattice and react with it to form Fe3C. After reaching saturation concentration, they precipitate on the surface of Fe3C, and grow C nanoparticles distributed in an array on the surface of Fe3C, eventually forming a Fe3C@C assembled nano-absorbing structure with a protruding C nanoparticle array on the surface, that is, a Fe3C@C hollow sphere structure with a protruding C nanoparticle array on the surface.

[0012] Optionally, the method for preparing the Fe3C@C assembled nano-wave absorbing structure as described above is characterized in that: In step 3, the method of introducing argon Ar and anhydrous ethanol is as follows: argon Ar is introduced into the anhydrous ethanol solution contained in the conical flask at a flow rate of 100-400 ml / min to form a mixed gas of anhydrous ethanol vapor and argon Ar, and the mixed gas is introduced into the CVD furnace.

[0013] In a second aspect, the present invention further provides a Fe3C@C assembled nano-wave absorbing structure, which is prepared by the method for preparing the Fe3C@C assembled nano-wave absorbing structure as described in any one of the above items; Among them, the Fe3C@C assembled nano-wave absorbing structure is a Fe3C@C assembled nano-wave absorbing hollow sphere structure with a protruding C nanoparticle array on the surface prepared by hydrothermal-oxidation treatment-CVD method; and the Fe3C@C assembled nano-wave absorbing structure is a Fe3C@C hollow sphere with a wall thickness of 200~400nm, with a large number of C nanoparticles distributed in an array attached to the surface, and the nanoparticle size is 30~70nm.

[0014] The beneficial effects of the present invention are as follows: the present invention provides a Fe3C@C assembled nano-wave absorbing structure and a preparation method thereof, which realizes the preparation of a Fe3C@C assembled nano-wave absorbing structure with a protruding C nanoparticle array on the surface through a hydrothermal-oxidation treatment-CVD method; the hollow structure with a protruding C nanoparticle array on the surface prepared by the present invention has the following advantages: (1) it can improve the multiple scattering of electromagnetic waves and extend the transmission path of electromagnetic waves; (2) the introduction of C can enhance dielectric loss, optimize impedance matching, and realize the coupling effect of dielectric loss and magnetic loss; (3) the in-situ generation of C nanoparticles constructs a large number of Fe3C-C heterogeneous interfaces, and the resulting interface polarization loss can further achieve the attenuation of electromagnetic waves. By changing the Ar flow rate during the CVD reaction, the morphology and phase composition of the Fe3C@C assembled nano-wave absorbing structure are regulated, the dielectric constant and magnetic permeability as well as the impedance matching are optimized, and finally the improvement of the electromagnetic wave absorption performance is achieved. The technical solution provided by the present invention has the following beneficial effects: First, the preparation method of the Fe3C@C assembled nano-absorbent structure provided by the present invention has good repeatability, low raw material cost, simple process and low energy consumption during the preparation process. The CVD reaction used in this preparation method integrates the transformation of the Fe2O3 phase to the Fe3C phase, the diffusion and precipitation of C atoms / C atomic clusters in the Fe3C phase, and the chemical vapor deposition of arrayed C nanoparticles. Through a one-step CVD method, the coordinated electromagnetic microstructure and phase composition regulation from the precursor to the final product are achieved. Second, the Fe3C@C assembled nano-wave absorbing structure provided by the present invention is novel, lightweight, and highly efficient. It easily optimizes the coupling of dielectric and magnetic losses and impedance matching, providing an effective approach for the design of ideal and practical composite electromagnetic absorbing materials. Furthermore, the present invention is the first to apply Fe3C / C hollow spheres with protruding C nanoparticle arrays on their surfaces to the field of wave absorption. Third, the synthesized absorbing material comprises hollow Fe3C spheres with an array of protruding C nanoparticles on their surface, which scatter electromagnetic waves at varying angles and extend their transmission path. Furthermore, the C nanoparticles are introduced via an in-situ growth method, creating a large number of Fe3C-C heterointerfaces, which enhance interfacial polarization relaxation losses. Furthermore, the coupling between the magnetic Fe3C component and the dielectric C component creates multiple electromagnetic wave absorption mechanisms, improving the material's impedance mismatch and significantly enhancing its overall absorbing performance. With a thickness of just 2.4 mm, the material exhibits an effective bandwidth of 3.57 GHz, a minimum reflection loss of -22.98 dB, and an average reflectivity of -14.80 dB in the X-band. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings are used to provide a further understanding of the technical solution of the present invention and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solution of the present invention and do not constitute a limitation on the technical solution of the present invention.

[0016] Figure 1 A flow chart of a method for preparing a Fe3C@C assembled nano-wave absorbing structure provided in an embodiment of the present invention; Figure 2 This is the XRD spectrum of the Fe3C@C assembled nano-wave absorbing structure sample in Example 1; Figure 3 This is a schematic diagram of the sample of the Fe3C@C assembled nano-wave absorbing structure in Example 1. Figure 3 Figures a and b are SEM photos. Figure 3 Figure c is a high-resolution TEM photo; Figure 4 This is a schematic diagram of the sample of the Fe3C@C assembled nano-wave absorbing structure in Example 1. Figure 4 Figure a is the reflection loss diagram. Figure 4 A three-dimensional map of the b-wave properties; Figure 5 This is a schematic diagram of the sample of the Fe3C@C assembled nano-wave absorbing structure in Example 2. Figure 5 Figure a is the reflection loss diagram. Figure 5 Three-dimensional mapping of the b-wave properties. DETAILED DESCRIPTION

[0017] To make the purpose, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, unless there is a conflict, the embodiments and features in the embodiments of the present application can be combined with each other in any manner.

[0018] The above background information explains the role and research challenges of absorbing materials. Research has shown that structural design of magnetic materials or combining magnetic loss materials with dielectric loss materials can enhance their absorbing properties. Carbon materials, as typical dielectric loss absorbing materials, have attracted widespread attention due to their low density, high conductivity, high dielectric constant, and chemical stability.

[0019] Based on the above analysis, the designers of the present invention considered that structural design of magnetic materials or compounding of magnetic materials with lightweight carbon materials are effective means to improve their absorbing performance. Based on this design concept, the present invention provides a Fe3C@C assembled nano-absorbing structure and a preparation method thereof. The Fe3C@C assembled nano-absorbing structure with a protruding C nanoparticle array on the surface is prepared by a hydrothermal-oxidation treatment-CVD method.

[0020] The present invention provides the following specific embodiments that can be combined with each other. The same or similar concepts or processes may not be described in detail in some embodiments.

[0021] Figure 1 A flow chart of a method for preparing a Fe3C@C assembled nano-wave absorbing structure provided in an embodiment of the present invention; Figure 1 As shown, the preparation method of the Fe3C@C assembled nano-wave absorbing structure provided by the embodiment of the present invention includes the following steps: Step 1, synthesizing Fe2O3@C spheres by hydrothermal method; Step 2: The Fe2O3@C spheres synthesized in step 1 are oxidized by air oxidation to remove the C spheres and obtain a Fe2O3 hollow sphere precursor; Step 3: Perform a chemical vapor deposition (CVD) reaction on the Fe2O3 hollow sphere precursor obtained in step 2 to transform the Fe2O3 phase in the Fe2O3 hollow sphere precursor into a Fe3C phase to form Fe3C hollow spheres, and in situ grow a C nanoparticle array on the surface of the Fe3C hollow spheres to obtain a Fe3C@C assembled nanowave absorbing structure.

[0022] It should be noted that the Fe2O3@C spheres synthesized in the above step 1 are spherical core-shell structures with Fe2O3 as the shell and internal C spheres as the core; correspondingly, in the above step 2, the Fe2O3@C spheres are oxidized to remove the C spheres filling the Fe2O3 shell.

[0023] In one implementation of the embodiment of the present invention, the implementation process of the above step 1 includes: dissolving 2.5-15 mmol of ferric nitrate nonahydrate, 1-10 mmol of citric acid, 3-10 mmol of glucose, and 2-8 mmol of urea in deionized water, and ultrasonically treating to obtain a yellow transparent solution; transferring the solution to a hydrothermal kettle for hydrothermal reaction, washing the formed hydrothermal product with anhydrous ethanol and distilled water three times, and drying it in an oven at 60-90°C for 12-36 hours to finally obtain Fe2O3@C balls.

[0024] In one implementation of the embodiment of the present invention, the implementation process of the above step 2 includes: The Fe2O3@C balls synthesized in step 1 are oxidized in a muffle furnace; the reaction temperature of the oxidation treatment is 400-600°C, the oxidation time is 0.5-3 h, and the muffle furnace heating rate is 3-8°C / min.

[0025] In one implementation of an embodiment of the present invention, the implementation process of the above-mentioned step 3 includes: placing an Fe2O3 hollow sphere precursor in an ark, transferring the ark to a CVD furnace, heating the CVD furnace to 300~700℃ at a temperature of 3~8℃ / min, and performing a CVD reaction, and the CVD reaction time is 0.5~3h; introducing argon Ar and anhydrous ethanol during the entire process of heating and CVD reaction; the CVD reaction uses anhydrous ethanol as a carbon source, and the carbon source reacts with the Fe2O3 hollow sphere precursor to transform the Fe2O3 phase into the Fe3C phase to form Fe3C hollow spheres, and in situ grows a C nanoparticle array on the surface of the Fe3C hollow sphere, so that the Fe2O3 hollow sphere precursor is transformed into a Fe3C@C assembled nano-wave absorbing structure with a protruding C nanoparticle array on the surface; wherein Ar is used as a protective gas for the CVD reaction.

[0026] In a specific implementation of this implementation, the method of introducing argon Ar and anhydrous ethanol in step 3 is: argon Ar is introduced into the anhydrous ethanol solution contained in the conical flask at a flow rate of 100~400 ml / min to form a mixed gas of anhydrous ethanol vapor and argon Ar, and the mixed gas is introduced into the CVD furnace.

[0027] The principle of the preparation method provided by the embodiment of the present invention is as follows: first, Fe2O3@C balls are synthesized by hydrothermal method; on the one hand, glucose decomposes to produce C atoms during the high temperature and high pressure hydrothermal process, and the C atoms nucleate and spontaneously grow isotropically into C balls; on the other hand, citric acid and Fe 3+ The complexed ferric citrate slowly releases Fe at high temperature 3+ , reacting with ammonia produced by urea decomposition to form Fe2O3 cores. These Fe2O3 cores adhere to the surface of the C spheres and gradually deposit and thicken, forming Fe2O3@C spheres with a core-shell structure. The hydrophobic C is located on the interior, while the hydrophilic Fe2O3 forms the shell, avoiding the formation of a high-energy C-H2O interface and conforming to the minimum energy principle. The chemical reactions involved in this process are as follows: C6H 12 O6→C+H2O; C6H8O7+Fe 3+ → FeC6H5O7+ H + ; FeC6H5O7+ H + → C6H8O7+Fe 3+ ; CO(NH2)2+H2O→CO2↑+NH3↑; H2O+NH3→NH4 + +OH - ; Fe 3+ + OH -→Fe(OH)3↓; Fe(OH)3→Fe2O3+H2O.

[0028] Subsequently, the Fe2O3@C balls are decarbonized by oxidation to form hollow Fe2O3 balls. Finally, the phase transformation of the Fe2O3 hollow balls and the in-situ growth of the C nanoparticle array on their surface are simultaneously achieved through a one-step chemical vapor deposition (CVD) reaction, thereby obtaining a Fe3C@C assembled nano-wave absorbing structure having a protruding C nanoparticle array on the surface. The role of anhydrous ethanol in the CVD reaction process of step 3 is as follows: the H2 produced by the decomposition of anhydrous ethanol at high temperature quickly reduces Fe2O3 to Fe, and the C atoms and C atom clusters produced by the decomposition of anhydrous ethanol at high temperature dissolve in the Fe lattice and react with it to form Fe3C, and precipitate on the Fe3C surface after reaching saturation concentration, finally forming a Fe3C@C assembled nano-wave absorbing structure having a protruding C nanoparticle array on the surface (i.e., a Fe3C@C assembled nano-wave absorbing structure having a protruding C nanoparticle array on the surface). It should be noted that the one-step CVD method used in the present invention achieves multiple goals at one stroke. The following chemical reactions mainly occur in the CVD process: C2H5OH→C + H2+O2; Fe2O3+ H2→ Fe + H2O; Fe+C→Fe3C; Fe3C→Fe+C.

[0029] Based on the preparation method of the Fe3C@C assembled nano-wave absorbing structure provided by the above embodiment of the present invention, the embodiment of the present invention also provides a Fe3C@C assembled nano-wave absorbing structure prepared by the above preparation method.

[0030] The Fe3C@C assembled nano-wave absorbing structure is a Fe3C@C assembled nano-wave absorbing hollow sphere structure with a protruding C nanoparticle array on the surface, prepared by a hydrothermal-oxidation treatment-CVD method; and the Fe3C@C assembled nano-wave absorbing structure is a Fe3C@C hollow sphere with a wall thickness of 200-400nm, with a large number of C nanoparticles distributed in an array attached to the surface, and the nanoparticle size is 30-70nm.

[0031] The present invention provides a Fe3C@C assembled nano-wave absorbing structure and a preparation method thereof. The preparation of the Fe3C@C assembled nano-wave absorbing structure with a protruding C nanoparticle array on the surface is achieved by a hydrothermal-oxidation treatment-CVD method. The hollow structure with a protruding C nanoparticle array on the surface prepared by the present invention has the following advantages: (1) it can improve the multiple scattering of electromagnetic waves and extend the transmission path of electromagnetic waves; (2) the introduction of C can enhance dielectric loss, optimize impedance matching, and realize the coupling effect of dielectric loss and magnetic loss; (3) the in-situ generation of C nanoparticles constructs a large number of Fe3C-C heterogeneous interfaces, and the resulting interface polarization loss can further achieve electromagnetic wave attenuation. By changing the Ar flow rate during the CVD reaction, the morphology and phase composition of the Fe3C@C assembled nano-wave absorbing structure are regulated, the dielectric constant and magnetic permeability as well as the impedance matching are optimized, and finally the improvement of the electromagnetic wave absorption performance is achieved. The technical solution provided by the present invention has the following beneficial effects: First, the preparation method of the Fe3C@C assembled nano-absorbent structure provided by the present invention has good repeatability, low raw material cost, simple process and low energy consumption during the preparation process. The CVD reaction used in this preparation method integrates the transformation of the Fe2O3 phase to the Fe3C phase, the diffusion and precipitation of C atoms / C atomic clusters in the Fe3C phase, and the chemical vapor deposition of arrayed C nanoparticles. Through a one-step CVD method, the coordinated electromagnetic microstructure and phase composition regulation from the precursor to the final product are achieved. Second, the novel and lightweight Fe3C@C assembled nano-wave absorbing structure provided by the present invention provides an effective approach for the design of ideal and practical composite electromagnetic absorbing materials. Furthermore, the present invention is the first to apply Fe3C / C hollow spheres with protruding C nanoparticle arrays on their surfaces to the field of wave absorption. Third, the synthesized absorbing material comprises hollow Fe3C spheres with an array of protruding C nanoparticles on their surface, which scatter electromagnetic waves at varying angles and extend their transmission path. Furthermore, the C nanoparticles are introduced via an in-situ growth method, creating numerous Fe3C-C heterointerfaces that generate interfacial polarization relaxation losses. Furthermore, the coupling between the magnetic Fe3C component and the dielectric C component creates multiple electromagnetic wave absorption mechanisms, alleviating the material's impedance mismatch and enhancing its absorbing performance. With a thickness of just 2.4 mm, the material exhibits an effective bandwidth of 3.57 GHz, a minimum reflection loss of -22.98 dB, and an average reflectivity of -14.80 dB in the X-band.

[0032] The following is a schematic illustration of the Fe3C@C assembled nano-wave absorbing structure and its preparation method provided by the present invention through some examples.

[0033] Example 1: The method for preparing the Fe3C@C assembled nano-wave absorbing structure provided in this embodiment includes the following steps: Step 1: Dissolve 5.0 mmol of ferric nitrate nonahydrate, 5.0 mmol of citric acid, 5.5 mmol of glucose, and 5.0 mmol of urea in 30 ml of deionized water and sonicate for 20 minutes to obtain a yellow, transparent solution. The solution was transferred to a hydrothermal reactor for a hydrothermal reaction at 180°C for 16 hours. The hydrothermal product was washed three times with anhydrous ethanol and distilled water and dried in an oven at 80°C for 24 hours to obtain Fe2O3@C spheres.

[0034] In step 2, the oxidation treatment of the Fe2O3@C balls was carried out in a muffle furnace at an oxidation temperature of 450 °C, an oxidation time of 2 h, and a muffle furnace heating rate of 5 °C / min.

[0035] Step 3: Transfer the Fe2O3 hollow sphere precursor to a CVD furnace, heat the CVD furnace to 480°C at a temperature of 5°C / min, and keep it warm for 1.5 hours for CVD reaction. During the entire process of heating and CVD reaction, Ar was introduced with an Ar flow rate of 150 ml / min. Ar brought anhydrous ethanol into the tube furnace through a conical flask containing anhydrous ethanol. The reaction product was cooled in an Ar atmosphere, and finally a Fe3C@C assembled nano-wave absorbing structure with a protruding C nanoparticle array on the surface was obtained. The specific preparation process is as follows: Figure 1 As shown. The Fe3C@C assembled nano-wave absorbing structure prepared in this example was uniformly mixed with paraffin wax (mass ratio of 3:7) and cut into a rectangular parallelepiped with a size of 22.86 mm × 10.16 mm × 2.5 mm. Its dielectric constant (ε=ε′ - jε′′) and magnetic permeability (μ=μ′- jμ′′) were tested by a vector network analyzer, and its reflectivity was calculated using transmission line theory. Obvious C and Fe3C characteristic peaks can be observed from the XRD spectrum of the Fe3C@C assembled nano-wave absorbing structure, as shown in Figure 2. Figure 2Figure 2 shows the XRD pattern of the Fe3C@C assembled nano-absorbing structure sample in Example 1. The diffraction peaks at 37.7°, 39.8°, 40.7°, 42.9°, 43.8°, 44.6°, 45.1°, 45.9°, 48.6°, 49.1°, and 51.8° correspond to the (121), (002), (201), (211), (102), (220), (031), (112), (131), (221), and (122) crystal planes of Fe3C (PDF #01-077-0255), respectively, while the peak at 26.5° is consistent with the (002) crystal plane of graphitic carbon (PDF #00-002-0456). Clearly, the carbon diffraction peak is broad, indicating that the carbon prepared in situ by this CVD method has low crystallinity and many defects. Under the influence of electromagnetic waves, these defect structures can induce defect dipole polarization, enhancing the overall dielectric loss of the Fe3C@C assembled nanostructure.

[0036] Figure 3 This is a schematic diagram of the sample of the Fe3C@C assembled nano-wave absorbing structure in Example 1. Figure 3 Figures a and b are SEM photos. Figure 3 Figure c is a high-resolution TEM photo. Figure 3 Figures a and b show SEM images of the Fe3C@C assembled nanostructure. The structure is spherical, hollow inside, with a large number of protruding nanoparticles distributed in an array pattern on the surface. The wall thickness of the hollow sphere ranges from 200 to 400 nm, and the diameter is less than 4 μm. High-magnification TEM observation of a single protruding nanoparticle reveals that the nanoparticle has numerous lattice defects and lacks a distinct lattice structure, which corresponds to the broad C peak in the XRD results, indicating that the nanoparticle is composed of C. Figure 3 Figure c. Combining the results of SEM, TEM and XRD, it can be seen that the Fe3C@C assembled nano-absorbing structure prepared in this scheme is a Fe3C@C hollow sphere with an array of C nanoparticles attached to the surface. The absorbing performance of the Fe3C@C assembled nano-absorbing structure is shown in Figure 4 , is a schematic diagram of a sample of the Fe3C@C assembled nano-wave absorbing structure in Example 1, Figure 4 Figure a is the reflection loss diagram. Figure 4 Figure b shows a three-dimensional mapping of the wave performance. When the thickness is 3.7 mm, its effective bandwidth is 1.34 GHz, the minimum reflectivity is -11.71 dB, and the average reflectivity in the X-band is -9.03 dB.

[0037] Example 2: The method for preparing the Fe3C@C assembled nano-wave absorbing structure provided in this embodiment includes the following steps: Step 1: Dissolve 5.0 mmol of ferric nitrate nonahydrate, 5.0 mmol of citric acid, 5.5 mmol of glucose, and 5 mmol of urea in 30 ml of deionized water and sonicate for 20 minutes to obtain a yellow, transparent solution. The solution was transferred to a hydrothermal reactor for a hydrothermal reaction at 180°C for 16 hours. The hydrothermal product was washed three times with anhydrous ethanol and distilled water and dried in an oven at 80°C for 24 hours to obtain Fe2O3@C spheres.

[0038] In step 2, the oxidation treatment of the Fe2O3@C balls was carried out in a muffle furnace at an oxidation temperature of 450 °C, an oxidation time of 2 h, and a muffle furnace heating rate of 5 °C / min.

[0039] In step 3, the Fe2O3 hollow sphere precursor was transferred to a CVD furnace. The furnace was heated to 480°C at a rate of 5°C / min and held at this temperature for 1.5 hours for the CVD reaction. Ar was introduced throughout the heating and CVD reaction at a flow rate of 300 ml / min. The argon was introduced into the tube furnace via an Erlenmeyer flask containing anhydrous ethanol. The reaction product was cooled in an Ar atmosphere, ultimately yielding an Fe3C@C assembled nano-absorber structure with a protruding C nanoparticle array on its surface. The Fe3C@C assembled nano-absorber structure prepared in this example was uniformly mixed with paraffin wax (mass ratio of 3:7) and cut into rectangular blocks measuring 22.86 mm × 10.16 mm × 2.5 mm. The dielectric constant (ε = ε′ - jε′′) and magnetic permeability (μ = μ′ - jμ′′) of the structure were measured using a vector network analyzer, and the reflectivity was calculated using transmission line theory. By changing the Ar flow rate to control the morphology and composition of the Fe3C@C assembled nano-absorbing structure, the dielectric constant and dielectric loss are enhanced, as well as the impedance matching is improved, and the absorbing performance is improved. Figure 5 The figure shows a sample schematic diagram of the Fe3C@C assembled nano-wave absorbing structure in Example 2. Figure 5 Figure a is the reflection loss diagram. Figure 5 Figure b shows a three-dimensional mapping of the wave performance. When the thickness is only 2.4 mm, the effective bandwidth is 3.57 GHz, the minimum reflection loss is -22.98 dB, and the average reflectivity in the X-band reaches -14.80 dB. The sample prepared in Example 2 can obtain good wave absorbing performance with a thickness of only 2.4 mm and a loading of only 30 wt.%, thanks to the coupling effect of the dielectric loss of the C component and the magnetic loss of the Fe3C component, the interface polarization loss generated by the large number of Fe3C-C heterogeneous interfaces formed by the in-situ growth of C particles, and the synergistic effect of various absorption mechanisms such as the special hollow structure and the array structure formed by C nanoparticles on multiple scattering of electromagnetic waves.

[0040] Example 3: The method for preparing the Fe3C@C assembled nano-wave absorbing structure provided in this embodiment includes the following steps: Step 1: Dissolve 10.0 mmol of ferric nitrate nonahydrate, 5.0 mmol of citric acid, 5.5 mmol of glucose, and 5.0 mmol of urea in 30 ml of deionized water and sonicate for 20 minutes to obtain a yellow, transparent solution. The solution was transferred to a hydrothermal reactor for a hydrothermal reaction at 180°C for 16 hours. The hydrothermal product was washed three times with anhydrous ethanol and distilled water and dried in an oven at 80°C for 24 hours to obtain Fe2O3@C spheres.

[0041] In step 2, the oxidation treatment of the Fe2O3@C balls was carried out in a muffle furnace at an oxidation temperature of 450 °C, an oxidation time of 2 h, and a muffle furnace heating rate of 5 °C / min.

[0042] Step 3: Transfer the Fe2O3 hollow sphere precursor to a CVD furnace, heat the CVD furnace to 480°C at a temperature of 5°C / min, and keep it warm for 1.5 hours to carry out the CVD reaction. During the entire process of heating and CVD reaction, Ar is introduced at a flow rate of 150 ml / min. Ar brings anhydrous ethanol into the tube furnace through a conical flask containing anhydrous ethanol. The reaction product is cooled in an Ar atmosphere, and finally a Fe3C@C assembled nano-wave absorbing structure with a protruding C nanoparticle array on the surface is obtained. The electromagnetic parameters of the Fe3C@C assembled nano-wave absorbing structure prepared in this example are tested according to the method of Example 1, and its reflection loss is calculated. When the thickness is 2.3 mm, the effective bandwidth is 3.01 GHz and the minimum reflection loss is -16.38 dB.

[0043] Example 4: The method for preparing the Fe3C@C assembled nano-wave absorbing structure provided in this embodiment includes the following steps: Step 1: Dissolve 5 mmol of ferric nitrate nonahydrate, 5 mmol of citric acid, 10 mmol of glucose, and 5.0 mmol of urea in 30 ml of deionized water and sonicate for 20 minutes to obtain a yellow, transparent solution. The solution was transferred to a hydrothermal reactor for a hydrothermal reaction at 180°C for 16 hours. The hydrothermal product was washed three times with anhydrous ethanol and distilled water and dried in an oven at 80°C for 24 hours to obtain Fe2O3@C spheres.

[0044] In step 2, the oxidation treatment of the Fe2O3@C balls was carried out in a muffle furnace at an oxidation temperature of 450 °C, an oxidation time of 2 h, and a muffle furnace heating rate of 5 °C / min.

[0045] Step 3: Transfer the Fe2O3 hollow sphere precursor to a CVD furnace, heat the CVD furnace to 480°C at a temperature of 5°C / min, and keep it warm for 1.5 hours to carry out the CVD reaction. During the entire process of heating and CVD reaction, Ar is introduced at a flow rate of 150 ml / min. Ar brings anhydrous ethanol into the tube furnace through a conical flask containing anhydrous ethanol. The reaction product is cooled in an Ar atmosphere, and finally a Fe3C@C assembled nano-wave absorbing structure with a protruding C nanoparticle array on the surface is obtained. The electromagnetic parameters of the Fe3C@C assembled nano-wave absorbing structure prepared in this embodiment are tested according to the method of Example 1, and its reflection loss is calculated. When the thickness is 1.92 mm, the effective bandwidth is 2.67 GHz and the minimum reflection loss is -19.33 dB.

[0046] Example 5: The method for preparing the Fe3C@C assembled nano-wave absorbing structure provided in this embodiment includes the following steps: Step 1: Dissolve 5.0 mmol of ferric nitrate nonahydrate, 5.0 mmol of citric acid, 5.5 mmol of glucose, and 5.0 mmol of urea in 30 ml of deionized water and sonicate for 20 minutes to obtain a yellow, transparent solution. The solution was transferred to a hydrothermal reactor for a hydrothermal reaction at 180°C for 16 hours. The hydrothermal product was washed three times with anhydrous ethanol and distilled water and dried in an oven at 80°C for 24 hours to obtain Fe2O3@C spheres.

[0047] In step 2, the oxidation treatment of the Fe2O3@C balls was carried out in a muffle furnace at an oxidation temperature of 450 °C, an oxidation time of 2 h, and a muffle furnace heating rate of 5 °C / min.

[0048] Step 3: Transfer the Fe2O3 hollow sphere precursor to a CVD furnace, heat the CVD furnace to 480°C at a temperature of 5°C / min, and keep it warm for 0.5 h to carry out the CVD reaction. During the entire process of heating and CVD reaction, Ar is introduced at a flow rate of 150 ml / min. Ar brings anhydrous ethanol into the tube furnace through a conical flask containing anhydrous ethanol. The reaction product is cooled in an Ar atmosphere, and finally a Fe3C@C assembled nano-wave absorbing structure with a protruding C nanoparticle array on the surface is obtained. The electromagnetic parameters of the Fe3C@C assembled nano-wave absorbing structure prepared in this embodiment are tested according to the method of Example 1, and its reflection loss is calculated. When the thickness is 2.1 mm, the effective bandwidth is 3.32 GHz and the minimum reflection loss is -25.75 dB.

[0049] Among the above embodiments, embodiment 2 is the best embodiment.

[0050] The Fe3C@C assembled nano-absorbing structures prepared in the above-mentioned embodiments of the present invention are characterized by lightness and high efficiency, and are easy to achieve the optimization of coupling of dielectric loss and magnetic loss and impedance matching. Their special surface C nanoparticle array structure and hollow structure greatly enhance the multiple scattering effect of electromagnetic waves. Their large number of Fe3C-C heterogeneous interfaces promote the enhancement of the interface polarization relaxation loss effect, thereby effectively improving the overall absorbing performance of the material.

[0051] Although the embodiments disclosed herein are as described above, the contents are merely provided to facilitate understanding of the present invention and are not intended to limit the present invention. Any person skilled in the art may make any modifications and variations in the form and details of the embodiments without departing from the spirit and scope of the present invention. However, the scope of patent protection of the present invention shall remain subject to the scope defined by the appended claims.

Claims

1. A method for preparing a Fe3C@C assembled nano-wave absorbing structure, characterized in that: The following steps are involved: Step 1, synthesizing Fe2O3@C spheres by hydrothermal method; Step 2: The Fe2O3@C spheres synthesized in step 1 are oxidized by air oxidation to remove the C spheres and obtain a Fe2O3 hollow sphere precursor; Step 3: Perform a chemical vapor deposition (CVD) reaction on the Fe2O3 hollow sphere precursor obtained in step 2 to transform the Fe2O3 phase in the Fe2O3 hollow sphere precursor into a Fe3C phase to form Fe3C hollow spheres, and in situ grow a C nanoparticle array on the surface of the Fe3C hollow spheres to obtain a Fe3C@C assembled nanowave absorbing structure.

2. The method for preparing the Fe3C@C assembled nano-wave absorbing structure according to claim 1, characterized in that: In step 1, the synthesized Fe2O3@C sphere is a spherical core-shell structure with Fe2O3 as the shell and the internal C sphere as the core; In the step 2, the Fe2O3@C balls are subjected to oxidation treatment to remove the C balls filled in the Fe2O3 shell.

3. The method for preparing the Fe3C@C assembled nano-wave absorbing structure according to claim 2, characterized in that: The step 1 comprises: 2.5-15 mmol ferric nitrate nonahydrate, 1-10 mmol citric acid, 3-10 mmol glucose, and 2-8 mmol urea were dissolved in deionized water and ultrasonically treated to obtain a yellow transparent solution. The solution was transferred to a hydrothermal reactor for hydrothermal reaction. The hydrothermal product was washed three times with anhydrous ethanol and distilled water and dried in an oven at 60-90°C for 12-36 h to obtain Fe2O3@C spheres.

4. The method for preparing the Fe3C@C assembled nano-wave absorbing structure according to claim 3, characterized in that: The reaction process of step 1 is: On the one hand, during the high temperature and high pressure hydrothermal process, glucose decomposes to produce C atoms, which nucleate and spontaneously grow isotropically into C spheres; on the other hand, citric acid and Fe 3+ The complexed ferric citrate slowly releases Fe at high temperature 3+ , reacting with ammonia produced by the decomposition of urea to form Fe2O3 nuclei, which adhere to the surface of the C sphere and gradually deposit and thicken, forming Fe2O3@C spheres with a core-shell structure.

5. The method for preparing the Fe3C@C assembled nano-wave absorbing structure according to claim 2, characterized in that: The step 2 includes: The Fe2O3@C balls synthesized in step 1 are oxidized in a muffle furnace; the reaction temperature of the oxidation treatment is 400~600℃, the oxidation time is 0.5~3h, and the muffle furnace heating rate is 3~8℃ / min.

6. The method for preparing a Fe3C@C assembled nano-wave absorbing structure according to any one of claims 1 to 5, characterized in that: The step 3 comprises: An Fe2O3 hollow sphere precursor was placed in an ark, which was then transferred to a CVD furnace. The CVD furnace was heated to 300-700°C at a rate of 3-8°C / min for a CVD reaction of 0.5-3h. Argon (Ar) and anhydrous ethanol were introduced throughout the entire process of heating and CVD reaction. Anhydrous ethanol was used as a carbon source in the CVD reaction, which reacted with the Fe2O3 hollow sphere precursor to transform the Fe2O3 phase into the Fe3C phase, forming Fe3C hollow spheres. C nanoparticle arrays were in situ grown on the surface of the Fe3C hollow spheres, transforming the Fe2O3 hollow sphere precursor into a Fe3C@C assembled nano-wave absorbing structure with a protruding C nanoparticle array on the surface. Ar was used as a protective gas for the CVD reaction.

7. The method for preparing the Fe3C@C assembled nano-wave absorbing structure according to claim 6, characterized in that: The role of anhydrous ethanol in the CVD reaction process of step 3 is: The hydrogen H2 produced by the decomposition of anhydrous ethanol at high temperature quickly reduces Fe2O3 to Fe. The C atoms and C atomic clusters produced by the decomposition of anhydrous ethanol at high temperature dissolve in the Fe lattice and react with it to form Fe3C. After reaching saturation concentration, they precipitate on the surface of Fe3C, and grow C nanoparticles distributed in an array on the surface of Fe3C, eventually forming a Fe3C@C assembled nano-absorbing structure with a protruding C nanoparticle array on the surface, that is, a Fe3C@C hollow sphere structure with a protruding C nanoparticle array on the surface.

8. The method for preparing the Fe3C@C assembled nano-wave absorbing structure according to claim 6, characterized in that: In step 3, the method of introducing argon Ar and anhydrous ethanol is as follows: argon Ar is introduced into the anhydrous ethanol solution contained in the conical flask at a flow rate of 100-400 ml / min to form a mixed gas of anhydrous ethanol vapor and argon Ar, and the mixed gas is introduced into the CVD furnace.

9. A Fe3C@C assembled nano-wave absorbing structure, characterized in that: The Fe3C@C assembled nano-wave absorbing structure is prepared by the preparation method of the Fe3C@C assembled nano-wave absorbing structure according to any one of claims 1 to 8; Among them, the Fe3C@C assembled nano-wave absorbing structure is a Fe3C@C assembled nano-wave absorbing hollow sphere structure with a protruding C nanoparticle array on the surface prepared by hydrothermal-oxidation treatment-CVD method; and the Fe3C@C assembled nano-wave absorbing structure is a Fe3C@C hollow sphere with a wall thickness of 200~400nm, with a large number of C nanoparticles distributed in an array attached to the surface, and the nanoparticle size is 30~70nm.

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