Composite wave-absorbing material and preparation method thereof

Abstract

The embodiment of the invention provides a composite wave-absorbing material and a preparation method thereof.In the preparation method provided by the embodiment of the invention, spherical carbonyl iron powder and polycrystalline carbonyl iron fibers are combined through plasma-assisted ball milling, a carbonyl iron core of a dual-scale structure is constructed, and the composite wave-absorbing material is obtained; the in-plane magnetic anisotropy of the spherical carbonyl iron powder can be utilized to excite high-frequency resonance so as to improve the magnetic saturation, and the long-axis magnetic anisotropy of the micron-sized polycrystalline carbonyl iron fibers can be utilized to excite low-frequency natural resonance so as to enhance the anisotropy, so that broadband absorption is realized; the surface of the core material is coated with barium titanate through plasma-assisted ball milling to form a stable core-shell structure, and the dielectric-magnetic performance of the composite material can be cooperatively regulated and controlled, so that collaborative optimization of electromagnetic parameters of the material is realized, impedance matching is improved, and the wave-absorbing performance is enhanced; therefore, the method can effectively relieve the problem that the existing carbonyl iron powder is difficult to consider high magnetic loss, impedance matching performance and broadband absorption performance at the same time.

Description

Technical Field

[0001] The present application relates to the technical field of ferromagnetic absorbing materials, and in particular to a composite absorbing material based on carbonyl iron powder and a preparation method thereof. Background Art

[0002] Spherical carbonyl iron powder has become an important candidate for high-performance absorbing materials due to its high saturation magnetization, excellent magnetic permeability and temperature stability.

[0003] However, constrained by the Snoek limit, the real part of the magnetic permeability (μ') of spherical carbonyl iron (SCI) in the 0.5 GHz frequency band is generally less than 1.5, resulting in seriously insufficient magnetic loss capacity in the low-frequency band. Secondly, although the material can be flaked to improve magnetic anisotropy through processes such as mechanical ball milling, the flaky structure easily forms a three-dimensional conductive network, causing the imaginary part of the dielectric constant (ε") to exceed 10, resulting in severe impedance mismatch.

[0004] To address the above problems, existing technologies mostly use surface coating modification technologies (such as chemical plating, sol-gel method, etc.), which often have complicated process steps and are difficult to maintain good low-frequency absorption performance while reducing the dielectric constant. Summary of the Invention

[0005] The technical problem to be solved by the present application is to provide a composite absorbing material and a preparation method thereof, so as to solve the problem that the existing carbonyl iron powder is difficult to achieve high magnetic loss, impedance matching performance and broadband absorption performance.

[0006] In order to solve the above problems, this application is implemented through the following technical solutions:

[0007] This application proposes a method for preparing a composite absorbing material, which includes:

[0008] Plasma-assisted ball milling of a carbonyl iron mixture to obtain a core material; wherein the carbonyl iron mixture comprises spherical carbonyl iron powder and polycrystalline carbonyl iron fibers;

[0009] The core material is mixed with barium titanate and then subjected to plasma-assisted ball milling to obtain a composite wave-absorbing material.

[0010] Furthermore, in the preparation method, the diameter of the polycrystalline carbonyl iron fiber is 3 to 10 μm and the aspect ratio is greater than or equal to 500; and / or the particle size of the spherical carbonyl iron powder is 6 to 8 μm; and the particle size of the barium titanate is 50 to 500 nm.

[0011] Furthermore, in the plasma-assisted ball milling, the ball-to-material ratio is 5 to 15:1, the discharge voltage is 10 to 15 kV, the current is 1.0 to 1.5 A, the frequency is 12 to 15 kHz, the protective gas is argon or nitrogen, and the processing time is 0.5 to 3 hours.

[0012] Furthermore, the preparation method further comprises, before subjecting the carbonyl iron mixture to plasma-assisted ball milling:

[0013] The spherical carbonyl iron powder is subjected to annealing treatment.

[0014] Furthermore, in the preparation method, the spherical carbonyl iron powder is subjected to annealing treatment, comprising:

[0015] Heat to 400-600℃ in a protective gas atmosphere and perform heat treatment for 1-5h.

[0016] Furthermore, in the preparation method, the carbonyl iron mixture further comprises an organic medium; and the plasma-assisted ball milling of the carbonyl iron mixture comprises:

[0017] Spherical carbonyl iron powder, polycrystalline carbonyl iron fiber and organic medium are mixed and then subjected to plasma-assisted ball milling.

[0018] Furthermore, in the preparation method, the organic medium is selected from at least one of ethanol, acetone, polyethylene glycol, and liquid paraffin.

[0019] Furthermore, in the preparation method, after mixing the spherical carbonyl iron powder, the polycrystalline carbonyl iron fiber and the organic medium, the following steps are included:

[0020] According to the mass ratio of spherical carbonyl iron powder to polycrystalline carbonyl iron fiber (4-10): 1, the organic medium accounts for 10% to 80% of the total mass of the spherical carbonyl iron powder and polycrystalline carbonyl iron fiber, and the spherical carbonyl iron powder and the carbonyl iron fiber are mixed in the organic medium.

[0021] Furthermore, in the preparation method, the core material is mixed with barium titanate, comprising:

[0022] The core material is mixed with barium titanate according to the percentage of barium titanate in the total mass of the core material being 3% to 8%.

[0023] Furthermore, after the core material and barium titanate are mixed and subjected to plasma-assisted ball milling, the preparation method further comprises:

[0024] The product after the plasma-assisted ball milling is vacuum-treated at 80 to 150° C. for 1 to 4 hours.

[0025] The present application also proposes a composite absorbing material prepared by the above method.

[0026] Furthermore, the composite absorbing material comprises:

[0027] A core, the core comprising a first flaky carbonyl iron and a second flaky carbonyl iron, wherein the first flaky carbonyl iron has a diameter of 10 to 20 μm and a thickness of 100 to 500 nm, and the second flaky carbonyl iron has a diameter of 20 to 60 μm and a thickness of 500 to 1500 nm;

[0028] A shell layer is coated on the surface of the core, and the shell layer comprises barium titanate.

[0029] Furthermore, in the composite absorbing material, the mass ratio of the first flake carbonyl iron to the second flake carbonyl iron is (4-10):1.

[0030] Furthermore, in the composite absorbing material, the mass percentage of the shell layer to the core is 3wt% to 8wt%.

[0031] Compared with the prior art, the embodiments of the present application have the following advantages:

[0032] In an embodiment of the present application, a method for preparing a composite absorbing material is provided. Spherical carbonyl iron powder and polycrystalline carbonyl iron fibers are combined through plasma-assisted ball milling to construct a carbonyl iron core with a dual-scale structure. The in-plane magnetic anisotropy of the spherical carbonyl iron powder can be used to excite high-frequency resonance to increase magnetic saturation, and the long-axis magnetic anisotropy of the micron-sized polycrystalline carbonyl iron fibers can be used to excite low-frequency natural resonance, enhancing anisotropy and thus achieving broadband absorption. Furthermore, barium titanate is coated on the surface of the core material through plasma-assisted ball milling to form a stable core-shell structure. This can synergistically regulate the dielectric and magnetic properties of the composite material, thereby achieving synergistic optimization of the material's electromagnetic parameters, improving impedance matching and enhancing absorbing performance. Therefore, this method can effectively alleviate the problem of existing carbonyl iron powders that are difficult to balance high magnetic loss, impedance matching performance, and broadband absorption performance.

[0033] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic flow chart of a method for preparing a composite absorbing material provided in an embodiment of the present application;

[0035] Figure 2 is the X-ray diffraction test pattern of each sample in Example 1 of the present application;

[0036] Figure 3is a scanning electron microscope image of each sample in Example 1 of the present application;

[0037] Figure 4 is an electromagnetic parameter diagram of each sample in Example 1 of the present application;

[0038] Figure 5 This is a reflection loss curve diagram of each sample in Example 1 of the present application. DETAILED DESCRIPTION

[0039] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0040] Applicants have discovered that traditional magnetic absorbers, such as spherical carbonyl iron (SCI), are subject to the Snoek limit, resulting in a real part of their magnetic permeability (μ') generally below 1.5 in the 0.5 GHz frequency band, leading to weak low-frequency absorption performance. While lamellar modification (such as mechanical ball milling) can enhance magnetic anisotropy, it easily forms a three-dimensional conductive network, causing the imaginary part of the dielectric constant (ε") to exceed 10, deteriorating impedance matching. Furthermore, existing modification techniques such as ball milling to prepare flaky carbonyl iron or using silica coating often involve complex process steps and make it difficult to maintain good low-frequency absorption performance while reducing the dielectric constant.

[0041] In order to solve the above problems, the present invention also provides a method for preparing a composite absorbing material. Figure 1 As shown, it includes steps 101 to 102:

[0042] Step 101: subjecting a carbonyl iron mixture to plasma-assisted ball milling to obtain a core material; wherein the carbonyl iron mixture includes spherical carbonyl iron powder and polycrystalline carbonyl iron fibers.

[0043] In the above step 101, the spherical carbonyl iron powder and the polycrystalline carbonyl iron fiber are mixed by stirring, rotating, etc., so that the polycrystalline carbonyl iron fiber can be evenly distributed around the spherical carbonyl iron powder; wherein the spherical carbonyl iron powder can provide high magnetic saturation, and the carbonyl iron fiber can enhance anisotropy.

[0044] In this step, plasma-assisted ball milling technology is used to composite spherical carbonyl iron powder and polycrystalline carbonyl iron fibers. Among them, plasma-assisted ball milling uses the cold plasma generated by dielectric barrier discharge (DBD) (such as high-energy electrons and ions excited by high frequency and high voltage under argon protection) and mechanical ball milling to synergize, using plasma high-energy bombardment to activate the particle surface, induce thermal stress micro-forging and melting, reduce the material yield strength and promote elongation into a sheet structure, and at the same time combine the shear force of ball milling to optimize dispersibility and reduce agglomeration; this plasma-assisted ball milling technology combines spherical carbonyl iron powder with polycrystalline carbonyl iron fibers to regulate the anisotropic morphology of the carbonyl iron composite material, significantly improve the matching of electromagnetic parameters, break through the Snoek limit, and ultimately achieve dual optimization of absorption performance and structural stability.

[0045] Optionally, in one embodiment, the diameter of the polycrystalline carbonyl iron fiber is 3 to 10 μm and the aspect ratio is greater than or equal to 500, which can avoid agglomeration during the preparation process and prevent poor interface bonding, thereby ensuring uniform dispersion.

[0046] In some embodiments, the diameter of the polycrystalline carbonyl iron fiber may be in the range of one or any two of 3 μm, 4 μm, 5 μm, 6 μm, 8 μm, and 10 μm, and the aspect ratio may be in the range of one or any two of 500, 510, 550, 600, 700, 800, 900, and 1000.

[0047] Optionally, in one embodiment, the spherical carbonyl iron powder is a micron-sized carbonyl iron powder with a particle size of 6 to 8 μm. This particle size range can not only ensure the uniformity of heat treatment during the preparation process and avoid sintering agglomeration, but also take into account the powder fluidity, reduce the coercive force, and increase the magnetic permeability, thereby improving the soft magnetic properties.

[0048] In some embodiments, the particle size of the spherical carbonyl iron powder may be within the range of 6 μm, 7 μm, 8 μm, or any two of them.

[0049] In the above steps, under this ratio, the composite material can obtain relatively excellent wave absorbing performance while maintaining the feasibility of the process.

[0050] Step 102: Mix the core material and barium titanate and perform plasma-assisted ball milling to obtain a composite absorbing material.

[0051] In the above step 102, the core material formed by combining spherical carbonyl iron powder and polycrystalline carbonyl iron fiber is mixed with barium titanate, and then nano-scale barium titanate is added. Then, plasma-assisted ball milling is performed to coat the barium titanate on the surface of the core material to form a shell layer, thereby synergistically regulating the dielectric-magnetic properties of the composite material, improving impedance matching and enhancing the absorption performance.

[0052] Optionally, in one embodiment, the barium titanate is nano-scale barium titanate with a particle size of 50 to 500 nm, which can effectively achieve synergistic optimization of the electromagnetic parameters of the core material through coating.

[0053] In some embodiments, the particle size of barium titanate may be within the range of one or any two of 50 nm, 60 nm, 80 nm, 100 nm, 200 nm, 300 nm, 400 nm, and 500 nm.

[0054] Optionally, in a specific embodiment, in plasma-assisted ball milling, the ball-to-material ratio is 5 to 15:1, the discharge voltage is 10 to 15 kV, the current is 1.0 to 1.5 A, the frequency is 12 to 15 kHz, the protective gas is argon or nitrogen, and the processing time is 0.5 to 3 hours.

[0055] In this specific embodiment, argon or nitrogen is used as the protective gas, the ball-to-material ratio is controlled to be 5 to 15:1, and the treatment is carried out for 0.5 to 3 hours at a discharge voltage of 10 to 15 kV, a current of 1.0 to 1.5 A, and a frequency of 12 to 15 kHz. This can not only effectively combine the spherical carbonyl iron powder and the polycrystalline carbonyl iron fiber to form a core, but also can coat the barium titanate on the surface of the core material to form a stable core-shell structure, thereby synergistically regulating the dielectric-magnetic properties of the composite material, improving impedance matching and enhancing the wave absorption performance, while taking into account the process feasibility and cost efficiency of large-scale production.

[0056] Optionally, in plasma-assisted ball milling, the ball-to-material ratio can be a range value of one of 5:1, 6:1, 8:1, 10:1, 15:1 or any two of the range values; the discharge voltage can be a range value of one of 10kV, 11kV, 12kV, 13kV, 14kV, 15kV or any two of the range values; the current can be a range value of one of 1.0A, 1.1A, 1.2A, 1.3A, 1.4A, 1.5A or any two of the range values; the frequency can be a range value of one of 12KHz, 13KHz, 14KHz, 15KHz or any two of the range values; and the processing time can be a range value of one of 0.5 hour, 0.6 hour, 1 hour, 2 hours, 3 hours or any two of the range values.

[0057] In step 102, plasma-assisted ball milling at the aforementioned ball-to-material ratio ensures uniform coating of the barium titanate nanoparticles while preventing damage to the matrix structure caused by excessive mechanical forces. The aforementioned ball milling duration ensures sufficient dispersion and coating of the titanate while preventing excessive particle size reduction due to prolonged milling. Within this parameter range, uniform coating of the surface of the barium titanate flake-like carbonyl iron core material can be achieved, forming a stable core-shell structure. This synergistically modulates the dielectric and magnetic properties of the composite material, improving impedance matching and enhancing microwave absorption performance, while also balancing process feasibility and the cost-effectiveness of large-scale production.

[0058] Optionally, plasma-assisted ball milling can be performed in a ball milling jar, and the peak-to-peak amplitude can be controlled to be 10-15 mm.

[0059] The preparation method provided in the embodiment of the present application combines spherical carbonyl iron powder and polycrystalline carbonyl iron fibers through plasma-assisted ball milling to construct a carbonyl iron core with a dual-scale structure. The in-plane magnetic anisotropy of the spherical carbonyl iron powder can be used to excite high-frequency resonance to improve magnetic saturation, and the long-axis magnetic anisotropy of the micron-sized carbonyl iron fibers can be used to excite low-frequency natural resonance to enhance anisotropy, thereby achieving broadband absorption. Furthermore, through plasma-assisted ball milling, barium titanate is coated on the surface of the core material to form a stable core-shell structure, which can synergistically regulate the dielectric-magnetic properties of the composite material, thereby achieving synergistic optimization of the material's electromagnetic parameters, improving impedance matching and enhancing absorption performance. Therefore, this method can effectively alleviate the problem that existing carbonyl iron powder is difficult to balance high magnetic loss, impedance matching performance and broadband absorption performance.

[0060] Optionally, in one embodiment, the preparation method provided in the examples of the present application, before subjecting the carbonyl mixture to plasma-assisted ball milling, further comprises:

[0061] The spherical carbonyl iron powder is subjected to annealing treatment.

[0062] In this embodiment, before mixing the spherical carbonyl iron powder and the polycrystalline carbonyl iron fiber, the spherical carbonyl iron powder is annealed separately, which can eliminate the internal stress of the raw material and optimize its microstructure, making it easier to press and adsorb the polycrystalline carbonyl iron fiber on the surface of the spherical carbonyl iron powder through plasma-assisted ball milling.

[0063] Optionally, in a specific embodiment, the spherical carbonyl iron powder is subjected to an annealing treatment, comprising:

[0064] Heat to 400-600℃ in a protective gas atmosphere and perform heat treatment for 1-5h.

[0065] In this specific embodiment, the spherical carbonyl iron powder is heat treated at a temperature of 400-600° C. for 1-5 hours in a protective gas atmosphere, which can not only effectively eliminate the internal stress of the raw material and optimize its microstructure, but also avoid affecting the overall magnetic effect of the material due to high temperature.

[0066] Optionally, in one embodiment, the carbonyl iron mixture further includes an organic medium, and the above step 101 specifically includes:

[0067] Spherical carbonyl iron powder, polycrystalline carbonyl iron fiber and organic medium are mixed and then subjected to plasma-assisted ball milling to obtain the core material.

[0068] In this embodiment, after the spherical carbonyl iron powder and polycrystalline carbonyl iron fibers are mixed by stirring, rotating, etc., an appropriate amount of organic medium is added as a process control agent, which reduces fiber entanglement through wetting and has a buffering and protective effect on the carbonyl iron powder, making it easier and more uniform for the carbonyl iron fibers and subsequent barium titanate to be combined with the surface of the spherical carbonyl iron powder.

[0069] Optionally, in a specific embodiment, the organic medium is selected from at least one of ethanol, acetone, polyethylene glycol, and liquid paraffin, which can effectively reduce fiber entanglement through wetting.

[0070] Alternatively, in one embodiment, spherical carbonyl iron powder, polycrystalline carbonyl iron fiber and an organic medium are mixed, comprising:

[0071] According to the mass ratio of spherical carbonyl iron powder to polycrystalline carbonyl iron fiber (4-10): 1, the organic medium accounts for 10% to 80% of the total mass percentage of the spherical carbonyl iron powder and polycrystalline carbonyl iron fiber, and the spherical carbonyl iron powder and the carbonyl iron fiber are mixed with the organic medium.

[0072] In this embodiment, the mass ratio of spherical carbonyl iron powder to polycrystalline carbonyl iron fiber is controlled to be (4-10):1, which can effectively inhibit the aggregation of spherical particles while avoiding the problem of polycrystalline carbonyl iron fiber breakage or entanglement, which is not conducive to uniform dispersion.

[0073] In this embodiment, the organic medium is added as a process control agent at a mass percentage of 10% to 80% of the total mass of the spherical carbonyl iron powder and the polycrystalline carbonyl iron fiber, which can avoid the problem of wall sticking or agglomeration without affecting the function of the organic medium.

[0074] Optionally, in one embodiment, after mixing the core material and barium titanate and performing plasma-assisted ball milling, the method further comprises:

[0075] The product after the plasma-assisted ball milling is vacuum-treated at 80 to 150° C. for 1 to 4 hours.

[0076] In this embodiment, the ball-milled product of the core material and barium titanate is heated to 80-150° C. and then vacuum-dried for 1-4 hours to slowly remove processing aids such as organic media. After cooling, the product is ground in a mortar to achieve efficient removal. Finally, the product is ground manually for 3-10 minutes using a mortar such as an agate to obtain a composite absorbing material with ideal morphology and performance.

[0077] Compared with the prior art, the preparation method provided in this application has the following advantages and beneficial effects:

[0078] (1) Plasma ball milling technology is used to achieve material flaking and surface coating in one step, simplifying the traditional multi-step process;

[0079] (2) The process parameters have a wide adjustable range, which is suitable for the preparation of materials with different performance requirements;

[0080] (3) The process is simple, energy consumption is low, and it is suitable for large-scale industrial production;

[0081] (4) The effective absorption bandwidth (RL < -10dB) of the prepared composite absorbing material reaches 4.0GHz, covering the main frequency bands from C to Ku bands; the maximum reflection loss value reaches -42.18dB, which is significantly improved compared with traditional materials; the optimal matching thickness is only 2.2mm, which meets the requirements of modern equipment for lightness and thinness.

[0082] The present application also proposes a composite absorbing material, wherein the composite absorbing material is obtained by processing using the above method.

[0083] Alternatively, in one embodiment, the composite absorber comprises: a core comprising a first carbonyl iron flake and a second carbonyl iron flake, wherein the first carbonyl iron flake has a diameter of 10-20 μm and a thickness of 100-500 nm, and the second carbonyl iron flake has a diameter of 20-60 μm and a thickness of 500-1500 nm; and a shell coating the surface of the core, comprising barium titanate. This successfully constructs a flake carbonyl iron matrix with a unique dual-scale structure.

[0084] In this embodiment, the first sheet-shaped carbonyl iron is formed by pressing spherical carbonyl iron powder, and the second sheet-shaped carbonyl iron is formed by pressing polycrystalline carbonyl iron fibers.

[0085] In this embodiment, a carbonyl iron core having a dual-scale structure is constructed by a first sheet of carbonyl iron pressed from spherical carbonyl iron powder and a second sheet of carbonyl iron pressed from polycrystalline carbonyl iron fibers. The carbonyl iron core can utilize the in-plane magnetic anisotropy of the spherical carbonyl iron powder to excite high-frequency resonance, and utilize the long-axis magnetic anisotropy of the micron-scale fibers to excite low-frequency natural resonance, thereby achieving broadband absorption. The core is surface-coated with barium titanate to form a stable core-shell structure, which can synergistically regulate the dielectric-magnetic properties of the composite material, thereby achieving synergistic optimization of the material's electromagnetic parameters, improving impedance matching, and enhancing wave absorption performance.

[0086] Optionally, in one embodiment, the mass ratio of the first flake carbonyl iron to the second flake carbonyl iron is (4-10):1, which can effectively inhibit the aggregation of spherical particles while avoiding the problem of polycrystalline carbonyl iron fiber breaking or entanglement, which is not conducive to uniform dispersion.

[0087] In some embodiments, the mass ratio of the first platelet-shaped carbonyl iron to the second platelet-shaped carbonyl iron may be in the range of one or any two of 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, and 10:1.

[0088] Optionally, in one embodiment, the mass percentage of the shell to the core is 3wt% to 8wt%, which can not only significantly regulate the dielectric constant of the core material, thereby effectively enhancing the electromagnetic wave absorption performance, but also avoid the particles from agglomerating due to high surface energy, thereby reducing the dispersion uniformity.

[0089] In some embodiments, the mass percentage of the shell layer to the core may be in the range of one or any two of 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, and 8 wt%.

[0090] Optionally, in one embodiment, the barium titanate is nano-scale barium titanate with a particle size of 50 to 500 nm, which can effectively achieve synergistic optimization of the electromagnetic parameters of the core material through coating.

[0091] In some embodiments, the particle size of barium titanate may be within the range of one or any two of 50 nm, 60 nm, 80 nm, 100 nm, 200 nm, 300 nm, 400 nm, and 500 nm.

[0092] The composite absorbing material provided in the examples of the present application exhibits excellent electromagnetic properties at a filling amount of 60 wt. %: in the low frequency band (0.5 GHz), the real part of the magnetic permeability reaches 2.9, which is 123% higher than that of traditional spherical carbonyl iron; in the high frequency band (12 GHz), the imaginary part of the dielectric constant is only 2.8, which is 67% lower than that of the uncoated sample, and the impedance matching coefficient is stably maintained below 1.5, significantly improving the impedance matching characteristics; at a matching thickness of 2.2 mm, the material exhibits a maximum reflection loss of -42.18 dB and has a wide-band effective absorption bandwidth of 4.0 GHz (RL <-10 dB), covering the main frequency bands from C to Ku bands.

[0093] For the above composite absorbing material embodiment, the above composite absorbing material is obtained by the above method and can achieve the same technical effect. To avoid repetition, it will not be described here. For relevant details, please refer to the partial description of the method embodiment.

[0094] The present application is described in detail below through examples.

[0095] Performance testing methods

[0096] (1) X-ray diffraction (XRD) test:

[0097] The test equipment used is Japan Rigaku Smartlab 9KW, which uses a Cu target K with a wavelength of 0.1541nm. α Rays were used as the light source, and the specific test parameters were: 45kV voltage and 40mA current, a scanning angle range of 20° to 90°, and a scanning speed of 10° / min.

[0098] The working principle of XRD testing is to use the diffraction phenomenon of X-rays between crystal planes to obtain information about microscopic crystal structure and phase composition.

[0099] (2) The scanning electron microscope used was a Supra 40 manufactured by Zeiss, Germany. Secondary electrons (SE2) were mainly used during the test to analyze the microscopic morphology of the material surface.

[0100] (3) Electromagnetic performance test:

[0101] The relative complex dielectric constant ε of carbonyl iron flakes and their composites was measured using a Keysight N5227B vector network analyzer. r and relative complex permeability μ r .

[0102] (4) Reflection loss curve:

[0103] The electromagnetic parameters of the flake carbonyl iron and its composite materials were tested by a vector network analyzer, and then their reflection loss values ​​were calculated according to the transmission line theory.

[0104] Example 1

[0105] (1) Weighing 70 g of micron-sized spherical carbonyl iron with a particle size of 6 to 8 μm, placing it in a tube furnace, and annealing it at 500° C. in an argon atmosphere for 3 hours to obtain spherical carbonyl iron S1;

[0106] (2) The annealed spherical carbonyl iron S1 was mixed with 10 g of polycrystalline carbonyl iron fibers having a diameter of 3 to 10 μm and an aspect ratio of 500 or greater, and 65 mL of liquid paraffin was added. The mixture was placed in a plasma ball mill, 7 kg of carbide grinding balls were added, and 0.05 MPa of argon gas was filled. The mixture was ball milled for 1 hour at a discharge voltage of 12 kV, a current of 1.2 A, and a frequency of 13 kHz to obtain the core material S2;

[0107] (3) 5 g of barium titanate with a particle size of 100 nm was added to the core material, and then placed in a plasma ball mill with 7 kg of carbide grinding balls, filled with 0.05 MPa of argon gas, and ball milled for 1 hour at a discharge voltage of 12 kV, a current of 1.2 A, and a frequency of 13 kHz to obtain ball-milled product S3;

[0108] (4) The ball-milled product was vacuum-treated at 100° C. for 2 hours, and then ground to obtain the final composite absorbing material.

[0109] Examples 2-3

[0110] The difference between Examples 2 and 3 and Example 1 is that the amount of spherical carbonyl iron added in step (1) is adjusted to 2.4 g and 6.4 g respectively.

[0111] Examples 4-5

[0112] The difference between Examples 4 and 5 and Example 1 is that the amount of barium titanate added in step (3) is adjusted to 11 mL and 85 mL respectively.

[0113] Examples 6-7

[0114] The difference between Examples 6 and 7 and Example 1 is that the amount of liquid paraffin added in step (2) is adjusted to 11 mL and 85 mL, respectively.

[0115] Example 8

[0116] The difference between Example 8 and Example 1 is that the liquid paraffin in the adjustment step (2) is polyethylene glycol.

[0117] Comparative Example 1

[0118] Pure spherical carbonyl iron (without any treatment) is used as the absorbing material.

[0119] Comparative Example 2

[0120] The difference between Comparative Example 2 and Example 1 is that step (3) is omitted.

[0121] The control parameters of each embodiment are shown in Table 1.

[0122] The spherical carbonyl iron S1, core material S2, and ball milling product S3 in Example 1 were subjected to XRD tests respectively. The results are as follows: Figure 2 shown.

[0123] Samples S1 and S2 exhibit distinct diffraction peaks at 2θ = 44.71°, 65.05°, and 82.33°, corresponding to the (110), (200), and (211) crystal planes of body-centered cubic Fe (PDF#96-900-8537), respectively. This confirms that the carbonyl iron powder retains its original crystal structure and does not undergo oxidation after heat treatment and ball milling. Sample S3, in addition to the aforementioned characteristic peaks of Fe, exhibits new diffraction peaks at 2θ = 22.2°, 31.55°, 38.89°, and 56.19°, which fully match those of a standard card of tetragonal BaTiO3 (PDF#96-901-4669), corresponding to its (100), (101), and (211) crystal planes, respectively, confirming that BaTiO3 nanoparticles have been successfully coated on the carbonyl iron surface. Notably, no impurities were detected in any of the samples. This is due to the inert atmosphere used throughout the preparation process (vacuum in the tube furnace and argon in the ball mill), which effectively prevented oxidation and deterioration of the materials. These characterization results confirm the successful preparation of the composite materials at the crystal structure level and provide a structural foundation for subsequent electromagnetic performance studies.

[0124] The spherical carbonyl iron S1, the core material S2, and the ball-milled product S3 in Example 1 were examined by scanning electron microscopy. The results of the spherical carbonyl iron S1 are as follows. Figure 3 As shown in (a), the core material S2 results are as follows Figure 3 As shown in (b), the ball milling product S3 results are as follows Figure 3 As shown in (c) to (d); among them, Figure 3 The magnifications of (c) and (d) are 3000x and 5000x, respectively.

[0125] The results showed that the spherical carbonyl iron S1 maintained a complete spherical morphology after annealing, with a uniform particle size of 6 to 8 μm and a smooth surface, confirming that the annealing process did not change its microstructure; after ball milling, the morphology of the core material S2 changed significantly, from a regular sphere to a flaky structure, but still maintained its surface smoothness; the composite absorbing material prepared after adding barium titanate exhibited unique surface characteristics. Although the overall flaky morphology and size range were similar to those of the sample without barium titanate addition, the surface roughness increased significantly, and nano-scale barium titanate particles were unevenly coated on the surface of the flaky carbonyl iron, with agglomeration in some areas. This morphological feature is mainly attributed to the agglomeration tendency caused by the high specific surface area and surface energy of the nano-barium titanate particles, forming a special "flaky iron matrix-nano-barium titanate coating" composite structure, which can enhance the electromagnetic wave absorption performance through interfacial polarization and multiple scattering mechanisms.

[0126] The electromagnetic properties of the spherical carbonyl iron S1, the core material S2, and the ball-milled product S3 in Example 1 were tested to obtain the relative complex dielectric constant ε r and relative complex permeability μr , the results are as follows Figure 4 shown.

[0127] Depend on Figure 4 It can be seen that in the wide frequency range of 0.5 to 18 GHz, sample S2 shows the best dielectric loss performance (ε" and tan δe The highest value is achieved in the 1.5-GHz band, which is mainly attributed to its flaky structure breaking through the Snoek limit and significantly improving the magnetic permeability (μ' increases from 1.3 to 2.9 at 0.5 GHz). The BaTiO3-coated sample S3 exhibits a dielectric loss peak in the 9.6-12.0 GHz frequency band (due to the dipole polarization effect of BaTiO3), but its overall dielectric constant decreases. This is because the non-conductive property of BaTiO3 hinders the formation of a conductive network, which in turn improves the impedance matching characteristics. The flaky core material S2 maintains the highest magnetic permeability across the entire frequency range of 0.5-18 GHz (μ" reaches 0.73 at 3.65 GHz), while the ball-milled product S3 coated with barium titanate suffers a slight decrease in magnetic properties due to the BaTiO3 coating.

[0128] Overall, S2 exhibits the strongest electromagnetic wave loss capability, while S3 has more advantages in impedance matching and broadband absorption, which provides an important reference for the design of high-performance absorbing materials: by regulating the material morphology (lamellarization) and dielectric-magnetic composite (BaTiO3 coating), the attenuation characteristics and impedance matching can be synergistically optimized.

[0129] The electromagnetic parameters of the spherical carbonyl iron S1, the core material S2, and the ball-milled product S3 in Example 1 were measured by a vector network analyzer, and then the reflection loss value (RL) was calculated according to the transmission line theory to obtain the reflection loss curve. The results are as follows: Figure 5 shown.

[0130] Depend on Figure 5 It can be seen that the spherical carbonyl iron S1 did not achieve effective absorption (RL < -10dB) in the entire test frequency band (0.5-18GHz); the core material S2 showed excellent absorption performance at a thickness of 2.4mm, with a peak loss of -42.18dB at 7.85GHz and an effective absorption bandwidth of 3.6GHz; the ball-milled product S3 coated with barium titanate achieved a peak loss of -21.04dB (10.65GHz) and a wider effective bandwidth of 4.0GHz at a thickness of 2.2mm.

[0131] The above test results show that the core material S2 is suitable for strong absorption applications in specific frequency bands, while the ball-milled product S3 exhibits better broadband absorption characteristics. This performance difference mainly stems from the structural design of the materials: the flaky structure of S2 enhances magnetic loss by breaking the Snoek limit, while the BaTiO3 coating layer of S3 expands the absorption bandwidth by optimizing impedance matching.

[0132] The absorbing materials prepared in the examples and comparative examples were mixed with paraffin wax at a ratio of 60 wt.% to prepare coaxial ring samples with an outer diameter of 7.00 mm and an inner diameter of 3.04 mm. The electromagnetic parameters were tested using a vector network analyzer. The test data are shown in Table 1.

[0133] Table 1

[0134]

[0135]

[0136] Where ε′ represents the real part of the dielectric constant, ε″ represents the imaginary part of the dielectric constant, and μ′ represents the real part of the magnetic permeability.

[0137] In summary, in this embodiment, spherical carbonyl iron powder and polycrystalline carbonyl iron fibers are combined through plasma-assisted ball milling to construct a carbonyl iron core with a dual-scale structure. The in-plane magnetic anisotropy of the spherical carbonyl iron powder can be used to excite high-frequency resonance to improve magnetic saturation, and the long-axis magnetic anisotropy of the micron-sized fiber can be used to excite low-frequency natural resonance to enhance anisotropy, thereby achieving broadband absorption. Moreover, through plasma-assisted ball milling, barium titanate is coated on the surface of the core material to form a stable core-shell structure, which can synergistically regulate the dielectric-magnetic properties of the composite material, thereby achieving synergistic optimization of the electromagnetic parameters of the material, improving impedance matching and enhancing absorption performance. Therefore, this method can effectively alleviate the problem that existing carbonyl iron powder is difficult to balance high magnetic loss, impedance matching performance and broadband absorption performance.

[0138] The composite absorbing material provided in the embodiments of this application exhibits significantly superior comprehensive performance indicators to existing technologies, demonstrating broad application prospects in areas such as military stealth, electronic countermeasures, and 5G communications. In particular, its groundbreaking broadband absorption characteristics offer a novel technical solution to current electromagnetic pollution and electromagnetic compatibility issues.

[0139] Although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they become aware of the basic inventive concepts. Therefore, the claims are intended to include the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0140] The above is a detailed introduction to a composite absorbing material and its preparation method provided by the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only intended to help understand the method and core concept of the present application. At the same time, for those skilled in the art, based on the concept of the present application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present application.

Claims

1. A method for preparing a composite absorbing material, characterized in that: include: Plasma-assisted ball milling of a carbonyl iron mixture to obtain a core material; wherein the carbonyl iron mixture comprises spherical carbonyl iron powder and polycrystalline carbonyl iron fibers; The core material is mixed with barium titanate and then subjected to plasma-assisted ball milling to obtain a composite wave-absorbing material.

2. The preparation method according to claim 1, characterized in that The polycrystalline carbonyl iron fiber has a diameter of 3 to 10 μm and an aspect ratio of greater than or equal to 500; and / or the spherical carbonyl iron powder has a particle size of 6 to 8 μm; and the barium titanate has a particle size of 50 to 500 nm.

3. The preparation method according to claim 1, characterized in that In plasma-assisted ball milling, the ball-to-material ratio is 5 to 15:1, the discharge voltage is 10 to 15 kV, the current is 1.0 to 1.5 A, the frequency is 12 to 15 kHz, the protective gas is argon or nitrogen, and the processing time is 0.5 to 3 hours.

4. The preparation method according to claim 1, characterized in that Prior to subjecting the carbonyl iron mixture to plasma-assisted ball milling, the following steps are also included: The spherical carbonyl iron powder is subjected to annealing treatment.

5. The preparation method according to claim 4, characterized in that The spherical carbonyl iron powder is subjected to an annealing treatment, comprising: Heat to 400-600℃ in a protective gas atmosphere and perform heat treatment for 1-5h.

6. The preparation method according to any one of claims 1 to 5, characterized in that The carbonyl iron mixture further includes an organic medium; and the plasma-assisted ball milling of the carbonyl iron mixture includes: Spherical carbonyl iron powder, polycrystalline carbonyl iron fiber and organic medium are mixed and then subjected to plasma-assisted ball milling.

7. The preparation method according to claim 6, characterized in that The organic medium is selected from at least one of ethanol, acetone, polyethylene glycol, and liquid paraffin.

8. The preparation method according to claim 6, characterized in that Spherical carbonyl iron powder, polycrystalline carbonyl iron fiber and organic medium are mixed, including: According to the mass ratio of spherical carbonyl iron powder to polycrystalline carbonyl iron fiber (4-10): 1, the organic medium accounts for 10% to 80% of the total mass of the spherical carbonyl iron powder and polycrystalline carbonyl iron fiber, and the spherical carbonyl iron powder and the carbonyl iron fiber are mixed in the organic medium.

9. The preparation method according to claim 1, characterized in that The core material is mixed with barium titanate, comprising: The core material is mixed with barium titanate according to the percentage of barium titanate in the total mass of the core material being 3% to 8%.

10. The preparation method according to claim 6, characterized in that After mixing the core material and barium titanate and performing plasma-assisted ball milling, the method further comprises: The product after the plasma-assisted ball milling is vacuum-treated at 80 to 150° C. for 1 to 4 hours.

11. A composite absorbing material, characterized in that: Prepared by the method according to any one of claims 1 to 10.

12. The composite absorbing material according to claim 11, characterized in that: include: A core, the core comprising a first flaky carbonyl iron and a second flaky carbonyl iron, wherein the first flaky carbonyl iron has a diameter of 10 to 20 μm and a thickness of 100 to 500 nm, and the second flaky carbonyl iron has a diameter of 20 to 60 μm and a thickness of 500 to 1500 nm; A shell layer is coated on the surface of the core, and the shell layer comprises barium titanate.

13. The composite absorbing material according to claim 12, characterized in that: The mass ratio of the first flake carbonyl iron to the second flake carbonyl iron is (4-10):

1.

14. The composite absorbing material according to claim 12 or 13, characterized in that: The mass percentage of the shell layer to the core is 3 wt% to 8 wt%.

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