A preparation method of a neodymium element doped high-entropy oxide / high-entropy alloy / C double-core-shell structure microwave absorption composite material

Abstract

The application discloses a neodymium element doped high-entropy oxide / high-entropy alloy / C double nuclear shell structure microwave absorption composite material and a preparation method thereof. 0.1 A Nd-doped (CoCrFeMnNiNd)3O4 high-entropy oxide precursor is synthesized through a coprecipitation method; a coupling relationship of an epoxy resin content of 8-12 wt%, a carbonization temperature of 780-820 DEG C and a holding time of 4-7 h is controlled, in-situ carbon thermal reduction on the surface of the oxide is realized, high-entropy alloy nanoparticles and a carbon shell are synchronously generated, and a "high-entropy oxide / high-entropy alloy / C" double nuclear shell hetero-interface is successfully constructed. The obtained powder is compounded with graphene and polylactic acid to prepare 3D printing wires and components. The design optimizes intrinsic electromagnetic parameters through Nd doping, realizes multiple synergies by interface polarization introduced by the double nuclear shell structure, magnetic loss of the high-entropy alloy and dielectric loss of the high-entropy oxide, the effective absorption bandwidth can be up to 4.48 GHz or more, the minimum reflection loss is-49.86 dB, and the design has the advantages of light weight, thin layer, wide frequency, strong absorption and green environmental protection.

Description

Technical Field

[0001] This invention relates to the field of composite material technology, specifically to a lightweight broadband microwave absorbing material with a rare-earth Nd-doped "high-entropy oxide@high-entropy alloy@C" double core-shell structure and its controllable preparation method. Background Technology

[0002] With the rapid development of high-frequency and high-speed electronic technologies such as 5G and the Internet of Things, electromagnetic interference and electromagnetic radiation problems are becoming increasingly prominent, creating an urgent need for high-performance microwave absorbing materials that are "thin, light, wide, and strong." High-entropy oxides, as an emerging material, have attracted attention due to their tunable composition and excellent dielectric properties, but their magnetic loss capability is generally weak, resulting in poor impedance matching and limiting further improvement in absorption performance.

[0003] Neodymium (Nd), a rare-earth element, possesses a unique 4f electron shell structure. Introducing it into high-entropy oxides can effectively regulate intrinsic electromagnetic parameters such as conductivity, dielectric constant, and magnetic anisotropy. However, combining the advantages of Nd doping with effective magnetic loss mechanisms and significant interfacial polarization effects is key to overcoming performance bottlenecks. Constructing core-shell structures is an effective strategy for introducing interfacial polarization, but current techniques struggle to achieve controllable, in-situ interfacial engineering on the surface of Nd-doped high-entropy oxides. Insufficient reduction results in the inability to generate a sufficient magnetic phase; excessive reduction damages the high-entropy oxide matrix, leading to the loss of Nd's regulatory effect and dielectric loss.

[0004] Based on this, this invention proposes to construct a "high-entropy oxide@high-entropy alloy@C" double-core shell structure: high-entropy alloy nanoparticles are generated in situ on the oxide surface using controllable carbothermal reduction, and a C=C carbon shell is simultaneously formed, thereby introducing abundant heterogeneous interfaces. This design fully leverages the interfacial polarization effect and the synergistic effect of the bilayer magnetic properties of the high-entropy alloy and the high-entropy oxide, enabling more efficient energy conversion during microwave absorption, significantly improving microwave absorption efficiency, reducing thickness requirements, and achieving thinner designs, thus meeting the urgent need for lightweight microwave absorbing materials in modern electronic devices. Therefore, developing an effective method for preparing a Nd-added high-entropy oxide@high-entropy alloy@C double-core shell structure has significant theoretical and practical value for promoting the development of high-performance microwave absorbing materials and solving electromagnetic interference and radiation hazards, and will also provide strong support for the sustainable development of information technology. Summary of the Invention

[0005] This invention introduces a method for preparing a high-entropy oxide / high-entropy alloy / C double-core-shell structure using rare-earth element Nd. This fully utilizes the electronic structure characteristics of Nd, effectively adjusting key parameters such as conductivity, dielectric constant, and magnetic permeability, thereby significantly improving microwave absorption performance in thinner and lighter designs. This high-entropy oxide / high-entropy alloy / C double-core-shell structure design fully leverages the interface effect and the microwave absorption effect of the double-layer magnetic material of high-entropy alloy + high-entropy oxide, enabling more efficient energy conversion during microwave absorption, improving microwave absorption efficiency, reducing material thickness requirements, and achieving a thinner design that meets the demands of modern electronic devices for lightweight and thinner microwave absorbing materials. Furthermore, this invention uses biodegradable polylactic acid (PLA) as the matrix material and utilizes 3D printing technology to manufacture microwave absorbing samples, achieving a green and environmentally friendly goal. The technical solution is as follows:

[0006] A neodymium-regulated high-entropy oxide / high-entropy alloy / C double core-shell structure microwave absorbing composite material, wherein the composite material has a core-shell structure, the core is a neodymium-doped high-entropy oxide, the middle layer is high-entropy alloy nanoparticles, and the outer shell is a carbon layer; the high-entropy alloy nanoparticles are formed by in-situ carbothermal reduction of part of the high-entropy oxide and embedded in the heterogeneous interface between the high-entropy oxide and the carbon layer.

[0007] The general chemical formula of the neodymium-doped high-entropy oxide is (CoCrFeMnNiNd). 0.1 )3O4, wherein the molar ratio of each metal element in Co, Cr, Fe, Mn, Ni and Nd is 0.8~1.2:0.8~1.2:0.8~1.2:0.8~1.2:0.08~0.12.

[0008] The high-entropy alloy nanoparticles have a face-centered cubic or body-centered cubic structure and a particle size of 30-80µm.

[0009] The carbon layer is a carbon skeleton structure containing C=C double bonds, formed by carbonizing epoxy resin in an inert atmosphere at 780~820℃.

[0010] The preparation method of high-entropy oxide core-shell composite material of rare earth element Nd includes the following steps:

[0011] (1) Select the nitrates of Co, Cr, Fe, Mn and Ni and neodymium nitrate in a mass ratio of 0.8~1.2:0.8~1.2; 0.8~1.2; 0.8~1.2; 0.8~1.2; 0.08~0.12, and obtain the hydroxide precipitate by co-precipitation method.

[0012] (2) The precipitate was dried at 80-120℃ for 7-9 hours to obtain a dried hydroxide. The dried hydroxide was placed in a muffle furnace with the furnace set to a final temperature of 700-800℃, a heating time of 2-2.5 hours, and a holding time of 2-2.5 hours to allow an oxide layer to adhere to its surface, resulting in (CoCrFeMnNiNd) 0.1 3O4 high-entropy oxide powder.

[0013] (3) Prepared (CoCrFeMnNiNd) 0.1 3O4 high-entropy oxide powder was mechanically stirred with EP, GR and anhydrous ethanol at a mass ratio of 18-22:0.4-0.6:150-160, with the stirrer speed set to 400-600 r / min, until the anhydrous ethanol was completely evaporated, so that EP was completely coated with (CoCrFeMnNiNd). 0.1 3O4 particles.

[0014] (4) The coated mixture is placed in a vacuum constant temperature drying oven and dried at 40-50℃ for 10-12 hours to remove moisture and other volatile components. Then, the dried mixture is placed in a carbonization furnace and heated at a rate of 780-820℃ at a rate of 1℃ per minute under nitrogen protection. The temperature is held for 4-7 hours until the EP is completely decomposed, leaving only a carbon shell formed by a carbon skeleton containing C=C double bonds. By controlling the coupling window of carbonization temperature, holding time and EP content, high-entropy alloy nanoparticles are locally reduced on the oxide surface, ultimately forming a "high-entropy oxide / high-entropy alloy / C" double core-shell structure, rather than a single oxide or complete alloying.

[0015] (5) The prepared high-entropy oxide / high-entropy alloy / C is mixed with GR and PLA at a mass ratio of 4:0-1.4:14.6-16. The mixture is mechanically ball-milled using a planetary ball mill. The mass ratio of the ball mill beads to the mixed powder is 1:1, the operating speed of the ball mill is 50 r / min, and the ball milling time is 1-2 hours to ensure that the components are fully mixed.

[0016] The epoxy resin (EP) has a mass fraction of 8~12 wt%. By adjusting the coupling relationship between carbonization temperature, holding time and epoxy resin content, the phase ratio and interface structure of high-entropy oxide and high-entropy alloy are controlled.

[0017] The EP content was reduced to 5 wt%. EP serves a dual function as both a carbon source and a reducing agent in this process. Insufficient EP content results in an inadequate concentration of the reducing atmosphere, hindering the effective reduction reaction. The XRD pattern of the product primarily exhibits characteristic peaks of the high-entropy oxide phase, with almost no diffraction peaks observed in the high-entropy alloy phase. Due to the inability to generate high-entropy alloy nanoparticles to provide magnetic loss, impedance matching is poor, and microwave absorption performance is inadequate. Therefore, the lower limit of EP content (8 wt%) is the critical threshold for triggering an effective reduction reaction and generating the necessary magnetic phase.

[0018] When the EP content is higher than 12wt%, the concentration of reducing gases such as methane and hydrogen produced by EP pyrolysis is too high, which will reduce a large amount of high-entropy oxides into alloys, which is inconsistent with the preset target.

[0019] The coupling relationship is as follows:

[0020] When the carbonization temperature is 800≤T≤820℃, the holding time t is controlled at 4~5 hours;

[0021] When the carbonization temperature is 780 ≤ T < 800℃, the holding time t should be controlled at 6~7 hours.

[0022] When the carbonization temperature is increased to above 820℃, most of the high-entropy oxide core is reduced. The characteristic peak intensity of the high-entropy oxide phase in the XRD pattern of the product is weak, and the high-entropy alloy phase is dominant, making it difficult to form a "high-entropy oxide / high-entropy alloy / C" dual-core-shell heterostructure. Therefore, setting the upper limit of the carbonization temperature to 820℃ is crucial and not obvious for preventing excessive reduction and maintaining the dual-phase coexistence structure.

[0023] When the carbonization temperature drops below 780℃, the thermodynamic driving force of the carbonization reaction weakens significantly, making it difficult to fully activate the carbon source and suppressing the reduction reaction of high-entropy oxides, thus hindering the formation of a "high-entropy oxide / high-entropy alloy" core-shell structure. Therefore, setting the lower limit of the carbonization temperature to 780℃ is a necessary prerequisite for ensuring the appropriate progress of the reduction reaction and achieving the synergistic effect between the two-phase structure and the carbon layer.

[0024] This invention also provides a microwave absorbing composite product, which is composed of a dual-core-shell structure microwave absorbing composite material, graphene, and a polylactic acid matrix; wherein the mass ratio of the dual-core-shell structure powder, graphene, and polylactic acid is 4:(0~1.4):(14.6-16). That is, graphene can be selectively added.

[0025] The product is a 3D printed filament or a wave-absorbing component formed by 3D printing technology.

[0026] A method for preparing the microwave absorbing composite product includes the following steps:

[0027] The dual-core-shell structure powder, graphene, and polylactic acid were mixed in a certain proportion and then ball-milled.

[0028] The ball-milled mixture is processed into 3D printing filaments using a melt extrusion process.

[0029] The 3D printing filament is printed into a pre-defined shape of a wave-absorbing component using a 3D printer.

[0030] In some preferred embodiments, the process includes the following steps: extruding the ball-milled composite powder into 3D-printed composite filaments using a single-screw melt extruder. Temperature control zones: Zone 1: 150-155℃; Zone 2: 155-160℃; Zone 3: 160-165℃; Water tank temperature: 20-25℃; Screw speed: 25-30 r / min; traction variable frequency speed: 12-16 r / min; Inlet pressure: 42-47 MPa; Outlet pressure: 22-27 MPa.

[0031] The prepared 3D printing filament was used to print coaxial ring samples for testing electromagnetic parameters using an Allcct Tank 3D printer. Printing nozzle size: 0.4 - 0.6 mm; nozzle temperature: 185-195℃; substrate temperature: 60 - 75℃; printing speed: 30 - 36 mm / s; fan speed: 150 - 255 r / min; layer height: 0.1 - 0.2 mm.

[0032] The technical concept of this invention addresses the limitations of simple high-entropy oxides in microwave absorption performance, namely weak magnetic loss and poor impedance matching. It introduces the rare-earth element neodymium (Nd), leveraging its unique 4f electronic structure and rich physicochemical properties to introduce impurity energy levels into the oxide bandgap. Key electromagnetic parameters such as conductivity, dielectric constant, and magnetic anisotropy are pre-tuned. Furthermore, utilizing a ternary coupling window of "EP content-carbonization temperature-holding time," controllable carbothermic reduction is triggered in situ on the surface of the Nd-doped high-entropy oxide, locally generating high-entropy alloy nanoparticles and simultaneously forming a C=C carbon shell, constructing a "high-entropy oxide / high-entropy alloy / C" dual-core-shell structure. This structure retains the tunability of electromagnetic parameters provided by Nd while fully utilizing the synergistic effect of the strong magnetic loss of the high-entropy alloy and the polarization loss of the heterojunction. This enables more efficient energy conversion during microwave absorption, significantly improving microwave absorption efficiency and reducing matching thickness, meeting the urgent needs of modern electronic devices for thin, wide-bandwidth, and highly efficient microwave absorbing materials.

[0033] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in the following aspects:

[0034] 1. This high-entropy oxide / high-entropy alloy / C double-core shell structure design fully utilizes the interface effect and the microwave absorption effect of the double-layer magnetic material of high-entropy alloy + high-entropy oxide, enabling the material to achieve more efficient energy conversion during microwave absorption, improving microwave absorption efficiency, reducing the material thickness requirement, realizing a thin design, and meeting the needs of modern electronic devices for lightweight microwave absorbing materials.

[0035] 2. Rare-earth Nd-doped core-shell high-entropy oxides utilize the properties of Nd to adjust electromagnetic parameters and leverage the properties of high-entropy oxides to optimize the material's structure and performance. This enables the material to achieve more efficient energy conversion during microwave absorption, improve microwave absorption efficiency, reduce material thickness, and meet the demands of modern electronic devices for lightweight and thin microwave absorbing materials.

[0036] 3. Lightweight: The combination of high-entropy oxides and Nd, along with PLA, which has a lower density, results in a significant weight reduction for the same volume compared to high-entropy alloys and traditional ferrites. This makes it particularly suitable for aerospace, electronic equipment, and other fields with stringent requirements for lightweighting.

[0037] 4. Green and environmentally friendly: This invention uses biodegradable polylactic acid (PLA) as the matrix material and combines it with a pollution-free preparation process to achieve the preparation of green and environmentally friendly microwave absorbing materials, which is in line with the concept of sustainable development.

[0038] 5. Low cost: This invention uses common and inexpensive raw materials and a simple and easy preparation process, which effectively reduces the preparation cost of microwave absorbing materials and facilitates large-scale promotion and application. Attached Figure Description

[0039] Figure 1 The image shows the SEM image of the product obtained in the 7th group of Example 1.

[0040] Figure 2 The XRD pattern of the product obtained in the 7th group in Example 1 is shown.

[0041] Figure 3 The SEM image is shown for Example 2.

[0042] Figure 4 The XRD pattern is shown for Example 2.

[0043] Figure 5 The EDS is the product obtained from group 7 in Example 1.

[0044] Figure 6 The electromagnetic parameters of Example 1 are shown.

[0045] Figure 7 This is the reflection loss curve for Example 1. Detailed Implementation

[0046] The present invention will be further described in detail below through examples and comparative examples, but the scope of protection of the present invention is not limited thereto.

[0047] Example 1:

[0048] This embodiment demonstrates the preparation and properties of the material under the preferred parameters of the present invention (which conform to the coupling relationship of "800≤T≤820℃, t=4-5h").

[0049] (1) Preparation of precursor by coprecipitation: The corresponding metal nitrates were accurately weighed and dissolved in deionized water at a molar ratio of Co:Cr:Fe:Mn:Ni:Nd = 1.0:1.0:1.0:1.0:1.0:0.1. Ammonia solution was slowly added dropwise to pH=9.0 under vigorous stirring to form a hydroxide coprecipitate. The precipitate was aged, filtered, washed, and then dried at 100℃ for 8 hours.

[0050] (2) High-temperature oxidation: The dried precursor was placed in a muffle furnace and heated to 800°C at a rate of 1°C / min in air atmosphere, held for 4 hours, cooled with the furnace, and then ground to obtain (CoCrFeMnNiNd) 0.1 )3O4 high entropy oxide powder (HEOs).

[0051] (3) Epoxy resin coating: Weigh 20g of the above high entropy oxide powder, mix it with 10g of epoxy resin (EP, model E-44, i.e., EP content is 10 wt%), 0.5g of graphene (GR) and 155g of anhydrous ethanol, and mechanically stir at 500 r / min for 4 hours until the ethanol is completely evaporated.

[0052] (4) Carbonization reduction to construct a double core-shell structure: The coated mixture is heated to 800℃ (800≤T≤820℃) at a heating rate of 1℃ / min under a nitrogen atmosphere, and held at this temperature for 5 hours (t=4-5h), and then naturally cooled to room temperature to form a high-entropy oxide@high-entropy alloy@C double core-shell structure powder.

[0053] (5) Preparation of 3D printing filament: The high-entropy oxide@high-entropy alloy@C double core shell structure powder obtained in step (4) is mixed with GR and polylactic acid (PLA) at a mass ratio of 4:0-1.4:14.6-16, and then ball-milled and twin-screw extruded (temperature 155-165℃) to make 3D printing filament.

[0054] Example 1 was conducted in eight groups. The mass of the dual-core shell structure powder was kept constant at 4g, accounting for 20wt% of the total mass of 20g. The content of graphene and polylactic acid was adjusted to ensure that the total mass of 20g remained constant.

[0055] Group 0 consists of: 0g of graphene (GR), 16g of polylactic acid (PLA), and 4g of bicore-shell structure powder, which means that graphene (GR) accounts for 0wt%, polylactic acid (PLA) accounts for 80wt%, and bicore-shell structure powder accounts for 20wt%.

[0056] Group 1 consists of: 0.2g of graphene (GR), 15.8g of polylactic acid (PLA), and 4g of bicore-shell structure powder, which means that graphene (GR) accounts for 1wt%, polylactic acid (PLA) accounts for 79wt%, and bicore-shell structure powder accounts for 20wt%.

[0057] Group 2 consists of: 0.4g of graphene (GR), 15.6g of polylactic acid (PLA), and 4g of bicore-shell structure powder, which means that graphene (GR) accounts for 2wt%, polylactic acid (PLA) accounts for 78wt%, and bicore-shell structure powder accounts for 20wt%.

[0058] Group 3 consists of: 0.6g of graphene (GR), 15.4g of polylactic acid (PLA), and 4g of bicore-shell structure powder, which means that graphene (GR) accounts for 3wt%, polylactic acid (PLA) accounts for 77wt%, and bicore-shell structure powder accounts for 20wt%.

[0059] Group 4 consists of: 0.8g of graphene (GR), 15.2g of polylactic acid (PLA), and 4g of bicore-shell structure powder, which means that graphene (GR) accounts for 4wt%, polylactic acid (PLA) accounts for 76wt%, and bicore-shell structure powder accounts for 20wt%.

[0060] Group 5 consists of 1g of graphene (GR), 15g of polylactic acid (PLA), and 4g of bicore-shell structure powder, which means that graphene (GR) accounts for 5wt%, polylactic acid (PLA) accounts for 75wt%, and bicore-shell structure powder accounts for 20wt%.

[0061] Group 6 consists of: 1.2g of graphene (GR), 14.8g of polylactic acid (PLA), and 4g of bicore-shell structure powder, which means that graphene (GR) accounts for 6wt%, polylactic acid (PLA) accounts for 74wt%, and bicore-shell structure powder accounts for 20wt%.

[0062] Group 7 consists of: 1.4g of graphene (GR), 14.6g of polylactic acid (PLA), and 4g of bicore-shell structure powder, which means that graphene (GR) accounts for 7wt%, polylactic acid (PLA) accounts for 73wt%, and bicore-shell structure powder accounts for 20wt%.

[0063] Characterization and performance:

[0064] Morphology and structure: Figure 1 SEM images show that the obtained composite material consists of micron-sized irregular particles with a rough surface, exhibiting obvious coating and stacking morphology, which conforms to the characteristics of a core-shell structure. Figure 2 The XRD pattern of (Curve of Example 1) shows that the product contains clear diffraction peaks of both high-entropy oxide (spinel structure) and high-entropy alloy (face-centered cubic structure), which conclusively proves that "two phases coexist".

[0065] Figure 5 The EDS energy dispersive spectroscopy detected all expected elements, including C, O, Co, Cr, Fe, Mn, Ni, and Nd, confirming the successful doping of Nd.

[0066] Figure 6 (a), (b), (c), and (d) represent the complex permittivity, respectively. The real and imaginary parts of ) and complex permeability ( The relationship between the real and imaginary parts of the complex permittivity and frequency. Complex permittivity and complex permeability are two key parameters affecting the microwave absorption performance of composite materials. and These represent the storage capacity of electrical energy and magnetic energy, respectively. and This represents the attenuation capacity of electrical and magnetic energy. For example... Figure 6 As shown in (a, b), the real part of the dielectric constant of the composite material increases with the increase of GR content. It is significantly enhanced. However, as the frequency increases, The frequency dispersion exhibits a decreasing trend because the dielectric polarization process cannot keep up with the rapid changes in the electric field, thus displaying frequency dispersion characteristics. In the high-frequency range, and The resonance peaks further reveal the dielectric resonance phenomenon, which significantly increases the dielectric loss of the material by converting electromagnetic wave energy into heat energy. In contrast, and A smaller value indicates a weaker magnetic response, with dielectric loss playing a dominant role. In the attached figure, 0, 1, 2, 3, 4, 5, 6, and 7 represent groups 0, 1, 2, 3, 4, 5, 6, and 7, respectively. The electromagnetic parameters show that the material has high real and imaginary values ​​of the complex permittivity, indicating strong dielectric polarization and loss capabilities; the imaginary part of the complex permeability exhibits resonance peaks near 4 GHz and 12 GHz, confirming the existence of effective magnetic loss. This reveals the mechanism of dielectric-magnetic synergistic loss.

[0067] Figure 7The reflection loss curves show the relationship between reflection loss and frequency for different thicknesses in Figure (a); for Group 0, Figure (b); for Group 1, Figure (c); for Group 2, Figure (d); for Group 3, Figure (e); for Group 4, Figure (f); for Group 5, Figure (g); for Group 6, Figure (h); and for Group 7, Figure (h).

[0068] from Figure 7 As shown in Figure (a), which is group 0, when the thickness is 4.5 mm, the minimum reflection loss is −7.95 dB and the effective absorption bandwidth of the material (RL ≤ -10 dB) is 0.

[0069] from Figure 7 As shown in Figure (b), which is group 1, when the thickness is 4.5 mm, the minimum reflection loss is −7.86 dB and the effective absorption bandwidth of the material (RL ≤ -10 dB) is 0.

[0070] from Figure 7 As shown in Figure (c), which is group 2, when the thickness is 4.5 mm, the minimum reflection loss is −8.21 dB and the effective absorption bandwidth of the material (RL ≤ -10 dB) is 0.

[0071] from Figure 7 As shown in Figure (d), which is group 3, when the thickness is 2.0 mm, the minimum reflection loss is −8.93 dB and the effective absorption bandwidth of the material (RL ≤ -10 dB) is 0.

[0072] from Figure 7 As shown in Figure (e), i.e. Group 4, when the thickness is 2.0 mm, the minimum reflection loss is −11.96 dB and the effective absorption bandwidth of the material (RL ≤ -10 dB) is above 2.81 GHz.

[0073] from Figure 7 As shown in Figure (f), which is group 5, when the thickness is 1.5 mm, the minimum reflection loss is −21.8 dB and the effective absorption bandwidth of the material (RL ≤ -10 dB) is above 2.43 GHz.

[0074] from Figure 7 As can be seen from Figure (g), i.e. Group 6, when the thickness is 1.50 mm, the minimum reflection loss is −47.03 dB and the effective absorption bandwidth of the material (RL ≤ -10 dB) is above 3.84 GHz.

[0075] from Figure 7 As shown in Figure (h), which represents Group 7, when the thickness is 1.58 mm, the minimum reflection loss is −49.86 dB, and the effective absorption bandwidth (RL ≤ -10 dB) of the material is above 4.48 GHz. Considering the four aspects of “thin, wide, light, and strong”, it can be concluded that Group 7 has the best performance.

[0076] Example 2:

[0077] This embodiment is used to demonstrate that the target material can also be successfully prepared at the other end of the coupling relationship ("780≤T<800℃, t=6-7h").

[0078] Preparation process: The powder ratio of group 7 with the best performance was selected, namely, 1.4g of graphene (GR), 14.6g of polylactic acid (PLA), and 4g of bicore-shell structure powder. The preparation steps were exactly the same as in Example 1, except that the carbonization parameters in step (4) were changed: the carbonization temperature was set to 790℃ (780≤T<800℃), and the holding time was set to 6.5 hours (t=6-7h).

[0079] Characterization and performance: Figure 4 The XRD pattern of (Curve of Example 2) shows that its product also exhibits characteristic diffraction peaks of coexistence of high-entropy oxide and high-entropy alloy phases, which is highly similar to the pattern of Example 1, but the diffraction peaks of the alloy phase are slightly wider. Figure 3 The SEM images show that its morphology is similar to that of Example 1, both being rough-surfaced coating structures. The microwave absorption performance of the material obtained in this example is slightly lower than that of Example 1. Example 3:

[0080] This embodiment is used to demonstrate that a double-core shell structure cannot be achieved when T < 780℃ and t = 4-7h.

[0081] Preparation process: The powder ratio of group 7 with the best performance was selected, namely, 1.4g of graphene (GR), 14.6g of polylactic acid (PLA), and 4g of bicore-shell structure powder. The preparation steps were exactly the same as in Example 1, except that the carbonization parameters in step (4) were changed: the carbonization temperature was set to 760℃ (T < 780℃), and the holding time was set to 5.5 hours (t = 4-7h).

[0082] Characterization and performance: The carbonization temperature was set at 760℃. Due to the insufficient activity of the carbon source generated by the carbonization and decomposition of epoxy resin at this temperature, the reduction reaction of high-entropy oxide to high-entropy alloy lacked sufficient driving force, resulting in the inability to fully carry out the reduction process. Ultimately, the target "high-entropy oxide / high-entropy alloy / C" double core-shell heterostructure could not be formed, and only a high-entropy oxide@C single core-shell structure could be formed.

[0083] Example 4:

[0084] This embodiment is used to demonstrate that a double-core shell structure cannot be achieved when T>820℃ and t=4-7h.

[0085] Preparation process: The powder ratio of group 7 with the best performance was selected, namely, 1.4g of graphene (GR), 14.6g of polylactic acid (PLA), and 4g of bicore-shell structure powder. The preparation steps were exactly the same as in Example 1, except that the carbonization parameters in step (4) were changed: the carbonization temperature was set to 880℃ (T>820℃), and the holding time was set to 5.5 hours (t=4-7h).

[0086] Characterization and performance: The carbonization temperature was set at 880℃ (above the critical upper limit of 820℃). At this temperature, the thermodynamic driving force of the reduction reaction was too strong, and the high-entropy oxide core was completely reduced. The originally designed "high-entropy oxide / high-entropy alloy / C" double core-shell heterostructure was destroyed, and only a high-entropy alloy@C single core-shell structure could be formed.

Claims

1. A method for preparing a dual-core-shell structured microwave absorbing composite material, characterized in that, The composite material has a core-shell structure, with a neodymium-doped high-entropy oxide core, a high-entropy alloy nanoparticle middle layer, and a carbon layer outer shell. The high-entropy alloy nanoparticles are formed by in-situ carbothermal reduction of some high-entropy oxides and embedded in the heterogeneous interface between the high-entropy oxides and the carbon layer, including the following steps: (1) Preparation of precursors by coprecipitation: The nitrates of Co, Cr, Fe, Mn and Ni and neodymium nitrate were dissolved in deionized water and the hydroxide coprecipitates were obtained by coprecipitation. (2) High-temperature oxidation: After drying the precipitate obtained in step (1), it is calcined at 700~800℃ to obtain neodymium-doped high-entropy oxide powder; (3) Epoxy resin coating: The high entropy oxide powder obtained in step (2) is mixed with epoxy resin, graphene and solvent, and stirred to coat the surface of the high entropy oxide particles with epoxy resin. (4) Carbonization reduction to construct a double core-shell structure: The coated particles obtained in step (3) are heated to 780~820℃ at a heating rate of 0.5-1℃ / min under an inert atmosphere and kept at the temperature for 4~7 hours to carbonize the epoxy resin to form a carbon shell, and simultaneously induce some high-entropy oxides to be reduced in situ to generate high-entropy alloy nanoparticles, thereby forming a high-entropy oxide@high-entropy alloy@C double core-shell structure.

2. The preparation method according to claim 1, characterized in that, In step (4), the mass fraction of the epoxy resin is 8~12 wt%. By adjusting the coupling relationship between the carbonization temperature, the holding time and the epoxy resin content, the phase ratio and interface structure of the high-entropy oxide and the high-entropy alloy are controlled.

3. The preparation method according to claim 2, characterized in that, The coupling relationship is as follows: When the carbonization temperature is 800≤T≤820℃, the holding time t is controlled at 4~5 hours; When the carbonization temperature is 780 ≤ T < 800℃, the holding time t should be controlled at 6~7 hours.

4. The preparation method according to claim 1, characterized in that, The general chemical formula of the neodymium-doped high-entropy oxide is (CoCrFeMnNiNd). 0.1 )3O4, wherein the molar ratio of each metal element in Co, Cr, Fe, Mn, Ni and Nd is 0.8~1.2:0.8~1.2:0.8~1.2:0.8~1.2:0.08~0.

12.

5. The preparation method according to claim 1, characterized in that, The high-entropy alloy nanoparticles have a face-centered cubic or body-centered cubic structure and a particle size of 30-80µm.

6. The preparation method according to claim 1, characterized in that, The carbon layer is a carbon skeleton structure containing C=C double bonds, formed by carbonizing epoxy resin in an inert atmosphere at 780~820℃.

7. A method for preparing a microwave-absorbing composite product, characterized in that, include: (1) A dual-core-shell structured microwave absorbing composite material is prepared by the preparation method according to any one of claims 1-6; (2) The dual-core shell structure microwave absorbing composite material, graphene and polylactic acid were mixed in proportion and then ball-milled; (3) The ball-milled mixture is processed into 3D printing filaments by melt extrusion. (4) The 3D printing filament is printed into a microwave absorbing component of a preset shape by a 3D printer.

8. The method for preparing the microwave absorbing composite product according to claim 7, characterized in that, The mass ratio of the dual-core-shell structured microwave absorbing composite material, graphene, and polylactic acid is 4:(0~1.4):(14.6-16).

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