Magnetic metal powder / porous carbon composite, method for preparing the same, and use thereof

Abstract

The application provides a magnetic metal powder / porous carbon composite material, a preparation method and application thereof. The preparation method comprises the following steps: step S1, performing surface oxidation reaction on a magnetic carbonyl metal powder to form pretreated metal powder; step S2, dissolving a copolymer PS n -b-PEO m in a first solvent, adding a mixed solution of ethanol and water into the first solvent to obtain a milk emulsion; step S3, adding the pretreated metal powder, pyrrole and FeCl3 into the milk emulsion to perform in-situ polymerization reaction, so as to form a precursor and obtain a precursor solution; step S4, removing the spherical PS n -b-PEO m micelles in the precursor by a solvothermal method, and then drying to obtain a porous precursor; and step S5, calcining the porous precursor under an inert atmosphere to obtain the magnetic metal powder / porous carbon composite material. The magnetic metal powder / porous carbon composite material prepared by the application has better wave absorption performance in a low frequency band.

Description

Technical Field

[0001] This invention relates to the field of microwave absorbing materials technology, and more specifically, to a magnetic metal powder / porous carbon composite material, its preparation method and application. Background Technology

[0002] With the rapid development of electronic technology, especially the widespread use of mobile communication and computers, the harm caused by electromagnetic radiation has become increasingly serious. In recent years, microwave absorbing materials have been widely used in research on electromagnetic interference resistance. Meanwhile, to cope with the ever-evolving reconnaissance and detection methods, stealth technology has become a strategic priority for countries worldwide, and as a core component of stealth technology, the research and application of microwave absorbing materials has become a hot topic in the field of military materials. Currently, most microwave absorbing materials are designed for the X and Ku bands of fire control radar. Due to limitations in the intrinsic electromagnetic parameters of the materials, their absorption capacity for low-frequency (L-S band) radar waves is limited. As the frequency bands of radar detection gradually widen, decimeter and meter waves in the low-frequency band are playing an increasingly important role, making it increasingly urgent to improve the low-frequency absorption performance of materials. As a typical magnetic loss type microwave absorbing material, carbonyl iron has a high saturation magnetization. The sheet-like morphology obtained after ball milling can break through the Snoek limit and further improve the permeability. Although sheet-like carbonyl iron powder has great absorption potential in the low-frequency S-band, the impedance mismatch caused by the excessively high dielectric constant has always been the problem affecting its microwave absorption effect.

[0003] Surface coating of iron powder is an effective way to improve electromagnetic impedance mismatch. Commonly used surface modification methods include direct treatment with coupling agents, hydrolysis of tetraethyl orthosilicate to deposit nano-silica on the iron powder surface, phosphating of iron powder, generating oxides on the iron powder surface using hydrothermal / co-precipitation methods, and initiating polymerization reactions on the iron powder surface to generate polymers. For example, patent CN105921741A utilizes the hydrolysis and condensation of alkoxysilanes under alkaline conditions to coat the iron powder surface with a silica shell. While this method can reduce the dielectric constant by introducing insulating silica onto the iron powder surface to hinder interparticle contact, the density and thickness uniformity of the silica layer cannot be stably controlled. Patent CN111876762A prepares phosphated iron powder by soaking iron powder in a mixed solution of phosphoric acid and acetone. This method oxidizes the surface of iron powder into iron phosphate through chemical corrosion, which increases its density. However, the decrease in surface conductivity inevitably shifts the absorption peak frequency towards higher frequencies. Although the absorption bandwidth and absorption peak intensity increase, this results in a change in the operating frequency band. A key challenge is how to improve the matching of electromagnetic parameters to increase the absorption bandwidth and absorption intensity while ensuring that the operating frequency band does not shift towards higher frequencies. Summary of the Invention

[0004] The main objective of this invention is to provide a magnetic metal powder / porous carbon composite material, its preparation method and application, in order to solve the problem that in the prior art, modified magnetic metal powder, while improving absorption bandwidth and absorption intensity, shifts the absorption frequency band too much to higher frequencies.

[0005] To achieve the above objectives, according to one aspect of the present invention, a method for preparing a magnetic metal powder / porous carbon composite material is provided, comprising the following steps: Step S1, subjecting magnetic carbonyl metal powder to a surface oxidation reaction under the action of a bluing agent to form pretreated metal powder; Step S2, reacting the copolymer PS... n -b-PEO m Dissolved in a first solvent, and a mixture of ethanol and water is added to make the copolymer PS n -b-PEO m Spherical micelles are formed to obtain an emulsion; where n is 50–300 and m is 45–114; in step S3, pretreated metal powder, pyrrole, and FeCl3 are added to the emulsion, and in-situ polymerization is carried out under stirring to form polypyrrole / spherical PS coated on the surface. n -b-PEO m A carbonyl metal powder precursor for a micelle composite layer is obtained, yielding a precursor solution; in step S4, spherical PS particles in the precursor are removed by a solvothermal method. n -b-PEO m The micelles are then dried to obtain a porous precursor; in step S5, the porous precursor is calcined under an inert atmosphere to obtain a magnetic metal powder / porous carbon composite material.

[0006] Furthermore, the magnetic carbonyl metal powder is carbonyl iron powder, carbonyl nickel powder, or carbonyl alloy powder; preferably, the magnetic carbonyl metal powder is flake powder with a thickness of 0.3 to 0.8 μm.

[0007] Further, step S1 includes: dispersing magnetic carbonyl metal powder in a second solvent, then adding a bluing agent to perform a surface oxidation reaction, followed by solid-liquid separation and drying to obtain pretreated metal powder; preferably, the second solvent is ethanol; preferably, the weight ratio of magnetic carbonyl metal powder to bluing agent is 1:1 to 2; preferably, the temperature of the surface oxidation reaction process is 75 to 85°C, and the time is 40 to 80 minutes.

[0008] Further, in step S2, the first solvent is tetrahydrofuran; in the mixture of ethanol and water, the mass concentration of ethanol is 10-90%; preferably, 0.01-0.02 g of copolymer PS is dissolved in each milliliter of the first solvent. n -b-PEO m Furthermore, the volume ratio of the ethanol and water mixture to the first solvent is 2.5 to 3.5:1.

[0009] Further, in step S3, 0.02-0.1 g of pretreated metal powder, 0.002-0.005 g of pyrrole and 0.003-0.005 g of FeCl3 are added to each milliliter of emulsion, and the FeCl3 is added in the form of FeCl3·6H2O; preferably, the temperature of the in-situ polymerization reaction is 0-5℃ and the time is 5-24 h.

[0010] Further, in step S4, the precursor solution is heated to 145–155°C to remove spherical PS from the precursor by a solvothermal method. n -b-PEO m Micelles.

[0011] Furthermore, in step S5, the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0012] Furthermore, the temperature for calcining the porous precursor is 800–900℃, and the time is 2–5 hours.

[0013] According to another aspect of the present invention, a magnetic metal powder / porous carbon composite material is also provided, which is prepared by the above-described preparation method.

[0014] According to another aspect of the present invention, a microwave absorbing material is also provided, comprising the above-described magnetic metal powder / porous carbon composite material.

[0015] This invention provides a method for preparing a magnetic metal powder / porous carbon composite material, which involves copolymerizing PS... n -b-PEO m The mixture is dissolved and prepared into spherical micelles. Then, magnetic carbonyl metal powder oxidized from a bluing agent and pyrrole monomers are added. The pyrrole monomers undergo in-situ polymerization on the surface of the magnetic carbonyl metal powder under the initiation of FeCl3, forming a polypyrrole coating layer. Due to the presence of spherical micelles in the system, they can be orderly distributed within the polypyrrole coating layer, thus forming a surface coated with polypyrrole / spherical PS. n -b-PEO m Carbonyl metal powder precursor for micelle composite layers. Secondly, spherical PS in the coating layer can be obtained via a solvothermal method. n -b-PEO m After micelle removal, the resulting porous precursor is calcined to form an ordered porous carbon coating layer on the surface of the magnetic carbonyl metal powder, thus obtaining the final magnetic metal powder / porous carbon composite material.

[0016] The magnetic metal powder / porous carbon composite material prepared using the soft template method described in this invention has the advantages of a wide absorption band and high absorption intensity. More importantly, its absorption frequency band does not shift excessively to higher frequencies. In summary, the magnetic metal powder / porous carbon composite material prepared by this invention exhibits better absorption performance in the low-frequency range. Attached Figure Description

[0017] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0018] Figure 1 A schematic flowchart of a method for preparing a magnetic metal powder / porous carbon composite material according to the present invention is shown. Detailed Implementation

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0020] As described in the background section, while modified magnetic metal powders in the prior art improve the absorption bandwidth and absorption intensity, they also have the problem of shifting the absorption frequency band too much to higher frequencies.

[0021] To address the above problems, this invention provides a method for preparing magnetic metal powder / porous carbon composite materials, such as... Figure 1 As shown, it includes the following steps: Step S1, subjecting magnetic carbonyl metal powder a to a surface oxidation reaction under the action of bluing agent b to form pretreated metal powder c; Step S2, subjecting copolymer PS... n -b-PEO m Dissolved in a first solvent, and a mixture of ethanol and water is added to make the copolymer PS n -b-PEO m Spherical micelles d are formed to obtain an emulsion; where n is 50-300 and m is 45-114; in step S3, pretreated metal powder, pyrrole and FeCl3 are added to the emulsion, and in-situ polymerization is carried out under stirring to form polypyrrole / spherical PS coated on the surface. n -b-PEO m The carbonyl metal powder precursor e of the micelle composite layer is used to obtain a precursor solution; in step S4, the spherical PS in the precursor e is removed by a solvothermal method. n -b-PEO m The micelles are then dried to obtain a porous precursor f; in step S5, the porous precursor is calcined under an inert atmosphere to obtain a magnetic metal powder / porous carbon composite material g.

[0022] The preparation method involves copolymer PS n -b-PEO mThe mixture is dissolved and prepared into spherical micelles. Then, magnetic carbonyl metal powder oxidized from a bluing agent and pyrrole monomers are added. The pyrrole monomers undergo in-situ polymerization on the surface of the magnetic carbonyl metal powder under the initiation of FeCl3, forming a polypyrrole coating layer. Due to the presence of spherical micelles in the system, they can be orderly distributed within the polypyrrole coating layer, thus forming a surface coated with polypyrrole / spherical PS. n -b-PEO m Carbonyl metal powder precursor for micelle composite layers. Secondly, spherical PS in the coating layer can be obtained via a solvothermal method. n -b-PEO m After micelle removal, the resulting porous precursor is calcined to form an ordered porous carbon coating layer on the surface of the magnetic carbonyl metal powder, thus obtaining the final magnetic metal powder / porous carbon composite material.

[0023] Specifically, the present invention uses copolymer PS n -b-PEO m After dissolving in the first solvent, the block copolymer PS can be made soluble by adding a mixture of ethanol and water. n -b-PEO m Selective self-assembly into spherical micelles with a PS end as the core and a PEO end as the shell (e.g. Figure 1 (As shown). Using this spherical PS n -b-PEO m Micelles were used as pore-forming templates to coat a layer of porous polypyrrole onto the surface of magnetic carbonyl metal powder using a soft template method, followed by calcination and carbonization to ultimately form a porous carbon coating. Since the polymerization of pyrrole monomers requires Fe... 3+ Catalysis, and Fe 3+ The introduction of [a specific substance] will cause a redox reaction with the carbonyl metal powder, destroying its structure. Therefore, this invention first performs a bluing treatment on the magnetic carbonyl metal powder, using a bluing agent to convert its surface metal element (such as Fe) into a metal oxide film (such as Fe3O4) to protect the metal. PS n -b-PEO m Spherical micelles were used as pore-forming templates, polypyrrole as a carbon source, and magnetic carbonyl metal powder as a substrate. An ordered mesoporous magnetic carbonyl metal powder / polypyrrole porous precursor was prepared by the ordered self-assembly of spherical micelles on the surface of magnetic carbonyl metal powder. After carbonization in an inert atmosphere, a magnetic metal powder / porous carbon composite material was prepared.

[0024] The presence of a porous structure allows the outermost layer of the material to contain air, which not only significantly improves impedance matching but also adds a multi-scattering mechanism for electromagnetic waves through the cavity. Compared to previous insulating materials, the excellent conductivity of the coated porous carbon mitigates the decrease in dielectric constant, preventing the operating frequency from shifting too much towards higher frequencies. Furthermore, the multi-layered structure design introduces several different interfaces: metal / metal oxide, metal oxide and porous carbon, and porous carbon and air, enhancing interface polarization and improving dielectric loss.

[0025] The magnetic metal powder / porous carbon composite material prepared using the soft template method described in this invention has the advantages of a wide absorption band and high absorption intensity. More importantly, its absorption frequency band does not shift excessively to higher frequencies. In summary, the magnetic metal powder / porous carbon composite material prepared by this invention exhibits better absorption performance in the low-frequency range.

[0026] It should also be noted that Fe is involved in the catalytic synthesis of polypyrrole. 3+ Under aqueous and aerobic conditions, hydrolysis occurs to produce Fe(OH)3, which is present in the PPy film encapsulating spherical micelles. During the subsequent solvothermal removal of the spherical micelles, it is further converted to Fe2O3, which is present in the porous precursor (e.g., Figure 1 (As shown in the porous precursor f). These Fe2O3 can undergo complex reactions with the PPy organic layer during the subsequent high-temperature carbonization process, eventually producing Fe3O4 in the magnetic metal powder / porous carbon composite material g (which can be approximated as a compound composed of ferrous oxide and ferric oxide).

[0027] Bluing agents are known reagents in the prior art, and their main components are sodium nitrate, sodium nitrite, sodium hydroxide, etc., which can be purchased commercially.

[0028] copolymer PS n -b-PEO m It is a block copolymer of polystyrene and polyethylene oxide, where n represents the degree of polymerization of the polystyrene segment and m represents the degree of polymerization of the polyethylene oxide segment. This material is a known material in the prior art and is commercially available.

[0029] In a preferred embodiment, the copolymer PS n -b-PEO m In this context, n is 100 and m is 114, meaning the copolymer PS 100 -b-PEO 114 Using the spherical micelles formed by this copolymer as pore-forming templates results in a more complete spherical structure with more suitable size, leading to a more stable subsequent solvothermal removal process. This is beneficial for further improving the pore structure of the final magnetic metal powder / porous carbon composite material and is more advantageous for the material's low-frequency microwave absorption performance.

[0030] Preferably, the magnetic carbonyl metal powder is carbonyl iron powder, carbonyl nickel powder, or carbonyl alloy powder, more preferably carbonyl iron powder. Compared with other materials, carbonyl iron powder has better wave absorption performance. More preferably, the magnetic carbonyl metal powder is a flake powder with a thickness of 0.3 to 0.8 μm.

[0031] As mentioned earlier, the polymerization of pyrrole monomers requires Fe... 3+ Catalysis, and Fe 3+ The introduction of [a specific substance] will cause a redox reaction with the carbonyl metal powder, damaging its structure. Therefore, this invention first performs a bluing treatment on the magnetic carbonyl metal powder, using a bluing agent to convert the surface metal element (e.g., Fe) into a metal oxide film (e.g., Fe3O4) to protect the metal. To allow the bluing agent to work more fully and form a more complete and dense metal oxide film on the surface of the metal powder for better protection of the internal metal, in a preferred embodiment, step S1 includes: dispersing the magnetic carbonyl metal powder in a second solvent, then adding a bluing agent to perform a surface oxidation reaction, followed by solid-liquid separation and drying to obtain pretreated metal powder. Preferably, the second solvent is ethanol. Using ethanol to disperse the magnetic carbonyl metal powder has a better dispersion effect, which is more conducive to the surface oxidation reaction, and the formed protective film is more uniform, thus promoting the overall performance of the final material. Preferably, the weight ratio of magnetic carbonyl metal powder to bluing agent is 1:1 to 2; preferably, the temperature of the surface oxidation reaction process is 75 to 85°C, and the time is 40 to 80 minutes.

[0032] To achieve a more complete and uniform morphology of the spherical micelles, thereby further improving the ordered porous structure of the final material and its low-frequency absorption performance, in a preferred embodiment, in step S2 above, the first solvent is tetrahydrofuran; the mass concentration of ethanol in the mixture of ethanol and water is 10-90%, preferably 40-90%. Using the above-mentioned first solvent and the mixture of ethanol and water results in a better morphology of the formed spherical micelles, which has a better pore-forming effect as a pore-forming template. Preferably, 0.01-0.02 g of copolymer PS is dissolved in each milliliter of the first solvent. n -b-PEO m Furthermore, the volume ratio of the ethanol and water mixture to the first solvent is 2.5–3.5:1. By controlling the amounts of each component within the above range, the resulting spherical micelles have a more suitable size, which in turn leads to a more suitable carbon layer pore structure size in the final material, thus being more beneficial to the overall performance of the material.

[0033] In a preferred embodiment, in step S3, 0.02–0.1 g of pretreated metal powder, 0.002–0.005 g of pyrrole, and 0.003–0.005 g of FeCl3 are added per milliliter of emulsion, with the FeCl3 added in the form of FeCl3·6H2O. Controlling the amounts of each raw material within the above range results in a more suitable thickness of the polypyrrole layer formed after in-situ polymerization, and a more suitable thickness of the porous carbon layer in the final material. Preferably, the in-situ polymerization reaction is carried out at a temperature of 0–5°C (ice bath) for 5–24 hours. Under these conditions, the polymerization rate is more suitable, and as the polymerization reaction proceeds, the polypyrrole and spherical micelles further coat the surface of the magnetic carbonyl metal powder, forming a more complete and uniform coating layer.

[0034] After in-situ polymerization is completed, in order to ensure more thorough and stable removal of spherical micelles, in a preferred embodiment, in step S4 above, the precursor solution is heated to 145–155°C to remove the spherical PS in the precursor by a solvothermal method. n -b-PEO m Micelles.

[0035] Preferably, in step S5, the inert atmosphere is a nitrogen atmosphere or an argon atmosphere. More preferably, the calcination temperature of the porous precursor is 800–900°C, and the time is 2–5 hours. Calcination under these conditions is beneficial for more complete carbonization of polypyrrole, which has a better promoting effect on the microwave absorption performance of the final material.

[0036] In summary, this invention coats the surface of magnetic carbonyl metal powder with an ordered mesoporous carbon layer through a template method and high-temperature carbonization, improving the impedance matching of the material. At the same time, the ordered porous structure can perform multiple reflections of electromagnetic waves, and the introduction of multiple interfaces significantly increases the interfacial polarization effect. The good conductivity of the porous carbon on the surface not only keeps the absorption frequency of the material relatively unchanged, but also increases the absorption bandwidth, thus improving the overall absorption performance of the material. Furthermore, this method has a large space for adjusting the electromagnetic parameters of the absorbing agent and is highly designable.

[0037] According to another aspect of the present invention, a magnetic metal powder / porous carbon composite material is also provided, which is prepared by the above-described preparation method. The magnetic metal powder / porous carbon composite material prepared using the soft template method of the present invention has the advantages of a wider absorption band and higher absorption intensity; more importantly, its absorption frequency band does not shift excessively to higher frequencies. In summary, the magnetic metal powder / porous carbon composite material prepared by the present invention exhibits better absorption performance in the low-frequency range.

[0038] According to another aspect of the present invention, a microwave absorbing material is also provided, comprising the above-mentioned magnetic metal powder / porous carbon composite material.

[0039] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0040] All reagents used in the examples are commercially available.

[0041] Example 1

[0042] Take 16g of flake carbonyl iron powder (thickness 0.3-0.8μm) and disperse it in 50mL of anhydrous ethanol. Sonicate for 30min. Mix 80mL of deionized water and 16g of bluing agent and add it dropwise to the suspension. Stir at 250r / min at 80℃ for 60min. After standing for a while, pour off the upper transparent liquid. Wash three times with anhydrous ethanol and dry for later use.

[0043] 0.5g of block copolymer PS 100 -b-PEO 114 Spherical micelles were prepared by dissolving the powder in 50 mL of tetrahydrofuran and adding 150 mL of a 40% ethanol aqueous solution. 5 g of the treated flake-shaped carbonyl iron powder and 1 mL of pyrrole were added to the resulting PS solution. 100 -b-PEO 114 After stirring the mixed solution thoroughly, 1g of FeCl3·6H2O was added dropwise to initiate the polymerization of pyrrole monomers. The mixture was stirred in an ice bath for 24 hours, then heated to 150℃ to remove spherical micelles. After drying, flake-like iron carbonyl / polypyrrole was obtained. The flake-like iron carbonyl / polypyrrole was then held at 700℃ for 3 hours under a nitrogen atmosphere and allowed to cool naturally to room temperature to obtain a flake-like iron carbonyl powder / porous carbon composite material.

[0044] Example 2

[0045] Take 16g of flake carbonyl iron powder (thickness 0.3-0.8μm) and disperse it in 50mL of anhydrous ethanol. Sonicate for 30min. Mix 80mL of deionized water and 16g of bluing agent and add it dropwise to the suspension. Stir at 250r / min at 80℃ for 60min. After standing for a while, pour off the upper transparent liquid. Wash three times with anhydrous ethanol and dry for later use.

[0046] 0.5g of block copolymer PS 100 -b-PEO 114 Spherical micelles were prepared by dissolving the powder in 50 mL of tetrahydrofuran and adding 150 mL of a 40% ethanol aqueous solution. 5 g of the treated flake-shaped carbonyl iron powder and 0.5 mL of pyrrole were added to the resulting PS solution. 100 -b-PEO 114After stirring the mixed solution thoroughly, 1g of FeCl3·6H2O was added dropwise to initiate the polymerization of pyrrole monomers. The mixture was stirred in an ice bath for 24 hours, then heated to 150℃ to remove spherical micelles. After drying, flake-like iron carbonyl / polypyrrole was obtained. The flake-like iron carbonyl / polypyrrole was then held at 700℃ for 3 hours under a nitrogen atmosphere and allowed to cool naturally to room temperature to obtain a flake-like iron carbonyl powder / porous carbon composite material.

[0047] Example 3

[0048] Take 16g of flake carbonyl iron powder (thickness 0.3-0.8μm) and disperse it in 50mL of anhydrous ethanol. Sonicate for 30min. Mix 80mL of deionized water and 16g of bluing agent and add it dropwise to the suspension. Stir at 250r / min at 80℃ for 60min. After standing for a while, pour off the upper transparent liquid. Wash three times with anhydrous ethanol and dry for later use.

[0049] 0.5g of block copolymer PS 100 -b-PEO 114 Spherical micelles were prepared by dissolving the powder in 50 mL of tetrahydrofuran and adding 150 mL of a 40% ethanol aqueous solution. 5 g of the treated flake-shaped carbonyl iron powder and 0.5 mL of pyrrole were added to the resulting PS solution. 100 -b-PEO 114 After stirring the mixed solution thoroughly, 1g of FeCl3·6H2O was added dropwise to initiate the polymerization of pyrrole monomers. The mixture was stirred in an ice bath for 24 hours, then heated to 150℃ to remove spherical micelles. After drying, flake-like iron carbonyl / polypyrrole was obtained. The flake-like iron carbonyl / polypyrrole was then held at 800℃ for 3 hours under a nitrogen atmosphere and allowed to cool naturally to room temperature to obtain a flake-like iron carbonyl powder / porous carbon composite material.

[0050] Example 4

[0051] Take 16g of flake carbonyl iron powder (thickness 0.3-0.8μm) and disperse it in 50mL of anhydrous ethanol. Sonicate for 30min. Mix 80mL of deionized water and 16g of bluing agent and add it dropwise to the suspension. Stir at 250r / min at 80℃ for 60min. After standing for a while, pour off the upper transparent liquid. Wash three times with anhydrous ethanol and dry for later use.

[0052] 0.5g of block copolymer PS 100 -b-PEO 114 Spherical micelles were prepared by dissolving the powder in 50 mL of tetrahydrofuran and adding 150 mL of a 40% ethanol aqueous solution. 5 g of the treated flake-shaped carbonyl iron powder and 1 mL of pyrrole were added to the resulting PS solution. 100 -b-PEO 114After stirring the mixed solution thoroughly, 1g of FeCl3·6H2O was added dropwise to initiate the polymerization of pyrrole monomers. The mixture was stirred in an ice bath for 24 hours, then heated to 150℃ to remove spherical micelles. After drying, flake-like iron carbonyl / polypyrrole was obtained. The flake-like iron carbonyl / polypyrrole was then held at 800℃ for 3 hours under a nitrogen atmosphere and allowed to cool naturally to room temperature to obtain a flake-like iron carbonyl powder / porous carbon composite material.

[0053] Example 5

[0054] Take 16g of flake carbonyl iron powder (thickness 0.3-0.8μm) and disperse it in 50mL of anhydrous ethanol. Sonicate for 30min. Mix 80mL of deionized water and 16g of bluing agent and add it dropwise to the suspension. Stir at 250r / min at 80℃ for 60min. After standing for a while, pour off the upper transparent liquid. Wash three times with anhydrous ethanol and dry for later use.

[0055] 1g block copolymer PS 100 -b-PEO 114 Spherical micelles were prepared by dissolving the powder in 50 mL of tetrahydrofuran and adding 150 mL of a 40% ethanol aqueous solution. 5 g of the treated flake-shaped carbonyl iron powder and 1 mL of pyrrole were added to the resulting PS solution. 100 -b-PEO 114 After stirring the mixed solution thoroughly, 1g of FeCl3·6H2O was added dropwise to initiate the polymerization of pyrrole monomers. The mixture was stirred in an ice bath for 24 hours, then heated to 150℃ to remove spherical micelles. After drying, flake-like iron carbonyl / polypyrrole was obtained. The flake-like iron carbonyl / polypyrrole was then held at 900℃ for 3 hours under a nitrogen atmosphere and allowed to cool naturally to room temperature to obtain a flake-like iron carbonyl powder / porous carbon composite material.

[0056] Example 6

[0057] Take 16g of flake carbonyl iron powder (thickness 0.3-0.8μm) and disperse it in 50mL of anhydrous ethanol. Sonicate for 30min. Mix 80mL of deionized water and 32g of bluing agent and add it dropwise to the suspension. Stir at 250r / min at 75℃ for 80min. After standing for a while, pour off the upper transparent liquid. Wash three times with anhydrous ethanol and dry for later use.

[0058] 0.5g of block copolymer PS 100 -b-PEO 114 Spherical micelles were prepared by dissolving the powder in 50 mL of tetrahydrofuran and adding 150 mL of 90% ethanol aqueous solution. 4 g of the treated flake-shaped carbonyl iron powder and 0.4 mL of pyrrole were added to the resulting PS solution. 100 -b-PEO 114After stirring the mixed solution thoroughly, 1g of FeCl3·6H2O was added dropwise to initiate the polymerization of pyrrole monomers. The mixture was stirred in an ice bath for 24 hours, then heated to 155℃ to remove spherical micelles. After drying, flake-like iron carbonyl / polypyrrole was obtained. The flake-like iron carbonyl / polypyrrole was then held at 700℃ for 3 hours under a nitrogen atmosphere and allowed to cool naturally to room temperature to obtain a flake-like iron carbonyl powder / porous carbon composite material.

[0059] The flake carbonyl iron powder / porous carbon obtained in Examples 1 to 6 were mixed with paraffin wax at a mass ratio of 4:1 and heated in an oven at 60°C. After the paraffin wax melted, the mixture was quickly removed and stirred until homogeneous, forming a viscous solid. This solid was then filled into a coaxial ring mold (7 mm outer diameter, 3 mm inner diameter) to prepare samples with a thickness of 1-2 mm. The complex permittivity and complex permeability were measured using a network vector analyzer. Based on the electromagnetic field transmission line theory, the reflection loss curve of the test sample with a thickness of 2 mm was calculated using MATLAB simulation. For comparison, the flake carbonyl iron powder and paraffin wax were also mixed at a mass ratio of 4:1 to form a coaxial ring for testing electromagnetic parameters, and the reflection loss curve was calculated using simulation. The measurement results are shown in Table 1.

[0060] Table 1

[0061] Serial Number Frequency point location / GHz Absorption peak intensity / dB -10dB bandwidth / GHz Comparative Example 2.86 -13.26 0.62 Example 1 3.12 -16.34 0.70 Example 2 3.15 -15.87 0.72 Example 3 3.03 -14.38 0.68 Example 4 3.07 -15.04 0.72 Example 5 2.97 -17.05 0.84 Example 6 2.89 -15.65 0.74

[0062] The location of the absorption peak frequency depends on the electromagnetic parameters (dielectric constant and permeability) and thickness of the absorbing material. With a fixed thickness, the electromagnetic parameters are the key factors determining the frequency location. A higher dielectric constant results in a lower frequency bias, and due to poorer impedance matching, both peak intensity and bandwidth deteriorate. A large difference between the dielectric constant and permeability of sheet-like metal powder leads to impedance differences, resulting in unsatisfactory low-frequency performance. This patented method introduces a carbon layer and a porous structure without altering the permeability. Adjusting the carbonization process changes the degree of graphitization in the carbon layer structure, thereby controlling its conductivity. Changing the conductivity modulates the reduction in dielectric constant, improving impedance matching. Simultaneously, the porous structure and the resulting interfaces also contribute to reducing electromagnetic wave loss. Overall, the absorption frequency shifts towards higher frequencies, and the absorption intensity and bandwidth increase, but the overall operating range remains within the low-frequency range. Typically, the low-frequency range refers to 1–4 GHz.

[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a magnetic metal powder / porous carbon composite material, characterized in that, Includes the following steps: Step S1: The magnetic carbonyl metal powder is subjected to a surface oxidation reaction under the action of a bluing agent to form pretreated metal powder; Step S2, copolymer PS n -b-PEO m The copolymer PS is dissolved in a first solvent, and a mixture of ethanol and water is added thereto. n -b-PEO m Spherical micelles are formed to obtain an emulsion; where n is 50~300 and m is 45~114; Step S3: Add the pretreated metal powder, pyrrole, and FeCl3 to the emulsion, and carry out an in-situ polymerization reaction under stirring to form polypyrrole / spherical PS coated on the surface. n -b-PEO m A precursor solution was obtained from a carbonyl metal powder precursor of a micelle composite layer. Step S4: Remove the spherical PS from the precursor using a solvothermal method. n -b-PEO m Micelles were then dried to obtain a porous precursor. Step S5: Calcine the porous precursor under an inert atmosphere to obtain the magnetic metal powder / porous carbon composite material.

2. The preparation method according to claim 1, characterized in that, The magnetic carbonyl metal powder is carbonyl iron powder, carbonyl nickel powder, or carbonyl alloy powder.

3. The preparation method according to claim 1, characterized in that, The magnetic carbonyl metal powder is in the form of flakes with a thickness of 0.3~0.8μm.

4. The preparation method according to any one of claims 1 to 3, characterized in that, Step S1 includes: dispersing the magnetic carbonyl metal powder in a second solvent, then adding the bluing agent to perform the surface oxidation reaction, and then sequentially performing solid-liquid separation and drying to obtain the pretreated metal powder.

5. The preparation method according to claim 4, characterized in that, The second solvent is ethanol.

6. The preparation method according to claim 4, characterized in that, The weight ratio of the magnetic carbonyl metal powder to the bluing agent is 1:1~2.

7. The preparation method according to claim 4, characterized in that, The surface oxidation reaction process is carried out at a temperature of 75~85℃ for a time of 40~80min.

8. The preparation method according to any one of claims 1 to 3, characterized in that, In step S2, the first solvent is tetrahydrofuran; in the mixture of ethanol and water, the mass concentration of ethanol is 10-90%.

9. The preparation method according to claim 1, characterized in that, Dissolve 0.01~0.02g of the copolymer PS in each milliliter of the first solvent. n -b-PEO m The volume ratio of the ethanol and water mixture to the first solvent is 2.5 to 3.5:

1.

10. The preparation method according to any one of claims 1 to 3, characterized in that, In step S3, 0.02-0.1g of the pretreated metal powder, 0.002-0.005g of the pyrrole and 0.003-0.005g of the FeCl3 are added to each milliliter of the emulsion, and the FeCl3 is added in the form of FeCl3·6H2O.

11. The preparation method according to claim 1, characterized in that, The in-situ polymerization reaction is carried out at a temperature of 0~5℃ for 5~24h.

12. The preparation method according to any one of claims 1 to 3, characterized in that, In step S4, the precursor solution is heated to 145-155°C to remove the spherical PS from the precursor by the solvothermal method. n -b-PEO m Micelles.

13. The preparation method according to any one of claims 1 to 3, characterized in that, In step S5, the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

14. The preparation method according to claim 13, characterized in that, The porous precursor is calcined at a temperature of 800~900℃ for 2~5 hours.

15. A magnetic metal powder / porous carbon composite material, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 14.

16. A microwave absorbing material, characterized in that, Including the magnetic metal powder / porous carbon composite material as described in claim 15.

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