W-type ferrite wave-absorbing agent as well as preparation method and application thereof

Abstract

The invention provides a W-type ferrite wave-absorbing agent as well as a preparation method and application thereof, and relates to the technical field of ferrite wave-absorbing agents. Specifically, the W-type ferrite wave-absorbing agent disclosed by the invention is of a sheet-shaped core-shell structure; the molecular formula of the core material comprises AxMe < 2 > Fe < 16 > O < 27 >; the molecular formula of the shell material comprises REmC1-m-nDn; a comprises at least one of Sr, Ba, Ca, Mg or Pb, Me comprises at least one of Zn, Co, Ni or Cu, C comprises at least one of Fe, Co or Ni, and D comprises at least one of Cu, Al, Zn, Bi, Sn or Pb. The invention provides a formula system with high universality, and the material has a good sheet-shaped structure, high impedance matching performance and good wave-absorbing performance, and has a good application prospect in preparation of wave-absorbing materials.

Description

Technical Field

[0001] The present invention relates to the technical field of ferrite wave-absorbing agents, and in particular, to a W-type ferrite wave-absorbing agent, a preparation method thereof, and an application thereof. Background Art

[0002] A wave-absorbing material is a material that regulates the intrinsic parameters, microstructure, etc. of the material, and then regulates the spatial conduction, absorption, and reflection characteristics of electromagnetic waves to achieve the purpose of reducing electromagnetic wave reflection or interference. Currently, wave-absorbing materials have important applications in stealth technology, microwave anechoic chambers, improving the electromagnetic compatibility of the whole machine, anti-metal isolation of RFID antennas, preventing electromagnetic radiation or leakage from harming the human body, etc. Therefore, the role and status of wave-absorbing materials are becoming increasingly important.

[0003] A wave-absorbing material is a structure such as a coating or a film prepared from a wave-absorbing agent, an adhesive, and various auxiliary additives, and among them, the wave-absorbing agent is the key. There are many types of wave-absorbing agents, and they can generally be divided into four categories according to the wave-absorbing mechanism: resistive wave-absorbing agents (such as carbon black, graphite, carbon fiber, carbon nanotubes, silicon carbide, etc.), dielectric wave-absorbing agents (such as barium titanate ferroelectric ceramics, silicon nitride, iron nitride, etc.), magnetic dielectric wave-absorbing agents (such as carbonyl iron powder, ferrite, ultrafine metal powder, etc.), and new wave-absorbing agents (such as conductive polymers, Schiff base wave-absorbing agents, plasma wave-absorbing agents, polycrystalline iron fibers, chiral wave-absorbing agents, nano-wave-absorbing agents, etc.). Among them, the ferrite wave-absorbing agent has both electrical loss and magnetic loss for incident electromagnetic waves, with a relatively large magnetic loss and a relatively small electrical loss; it is a wave-absorbing material with relatively strong wave-absorbing ability; in addition, the ferrite wave-absorbing agent also has advantages such as moisture and corrosion resistance, low cost, good frequency characteristics, and impedance matching; therefore, the application of ferrite wave-absorbing agents in the military and civilian fields has been showing an increasing trend year by year.

[0004] The preparation methods of ferrite wave-absorbing agents mainly include the oxide method, the chemical co-precipitation method, the sol-gel method, etc. Among them, the oxide method has the advantages of simple process, low equipment requirements, low production cost, and easy mass production, and is widely used by enterprises; the chemical co-precipitation method, the sol-gel method, etc. are favored by scientific research institutions and universities because the ferrite wave-absorbing agents prepared by these methods have more advantages in terms of morphology, particle size, and wave-absorbing performance, but they are at a disadvantage in mass production. The technical solutions of the traditional oxide method include processes such as formula design, mixing, densification treatment, sintering, and crushing in sequence; however, there are certain technical defects in each link of this set of processes, resulting in the lack of performance of the ferrite wave-absorbing agent.

[0005] (1) In formula design, taking the traditional and typical molecular formula of the W-type ferrite wave-absorbing agent as AMe 2 Fe 16 O 27For example (A is at least one of Sr and Ba; Me is at least one of divalent metal ions such as Zn, Co, and Ni), the existing formulation systems are relatively simple, which results in poor universality of ferrite wave-absorbing agents and cannot meet the absorption requirements for electromagnetic waves in different frequency bands.

[0006] (2) In terms of mixing materials, the traditional mixing method is generally wet mixing; for example, several raw material powders, grinding balls, and water are first loaded into a material tank in a specific ratio, and after wet mixing on a roller mill for a certain period of time, they are successively subjected to sedimentation, filtration, drying, and dispersion; usually, wet mixing performs well in terms of mixing uniformity, particle size consistency, and sintering reaction activity, but the operation is complex, time-consuming, and inefficient.

[0007] (3) In terms of sintering, usually, the material balls or blocks are heated to about 1200°C - 1300°C and kept warm; there are defects such as a relatively high sintering temperature and high energy consumption; in addition, it is well-known in the art that the flaky shape is the best state of the wave-absorbing agent, and it is difficult to obtain a wave-absorbing agent product with an ideal microconfiguration by conventional sintering methods.

[0008] In summary, overall, the traditional oxide method preparation process has advantages such as simplicity and high industrialization degree, but the prepared ferrite wave-absorbing agents, especially W-type ferrite wave-absorbing agents, have many problems such as poor flakiness, small electrical loss, insufficient magnetic loss, and poor impedance matching. In view of this, the present invention is specifically proposed. Summary of the Invention

[0009] The first object of the present invention is to provide a W-type ferrite wave-absorbing agent, which is mainly used to solve technical problems such as poor flakiness, small electrical loss, insufficient magnetic loss, and poor impedance matching of the W-type ferrite wave-absorbing agent.

[0010] The second object of the present invention is to provide a preparation method of the W-type ferrite wave-absorbing agent, which is based on the conventional oxide method but is significantly different from the traditional oxide method.

[0011] The third object of the present invention is to provide a wave-absorbing material.

[0012] In order to achieve the above objects of the present invention, the following technical solutions are specifically adopted:

[0013] A W-type ferrite wave-absorbing agent, the W-type ferrite wave-absorbing agent has a core-shell structure; wherein, the molecular formula of the core material includes A x Me 2 Fe 16 O 27 , A includes at least one of Sr, Ba, Ca, Mg, or Pb, Me includes at least one of Zn, Co, Ni, or Cu, and 0.7 ≤ x ≤ 1;

[0014] The molecular formula of the shell material includes RE m C 1-m-n D n , where RE includes at least one of La, Ce, Pr, Nd, Sm or Y, C includes at least one of Fe, Co or Ni, D includes at least one of Cu, Al, Zn, Bi, Sn or Pb, 0.1 ≤ m ≤ 0.3, and 0.1 ≤ n ≤ 0.3.

[0015] A preparation method of the W-type ferrite wave-absorbing agent described above includes the following steps:

[0016] (1) Weigh the raw materials according to the molecular formula of the core material, add a sintering promoter to the prepared raw materials, and then perform mixing treatment and densification treatment in sequence to obtain the material to be sintered;

[0017] (2) Sinter the material to be sintered to obtain a sintered material; among them, the temperature of the sintering treatment is 1150 °C to 1200 °C, and the heat preservation time of the sintering treatment is 0.5 h to 3 h;

[0018] (3) Perform crushing treatment, pickling treatment and dispersion treatment on the sintered material in sequence to obtain the core material;

[0019] (4) Mix the alloy powder of the shell material with the core material and then perform a second sintering treatment to obtain the W-type ferrite wave-absorbing agent; among them, the temperature of the second sintering treatment is 600 °C to 900 °C, and the heat preservation time of the second sintering treatment is 0.5 h to 3 h.

[0020] An absorbing material includes the W-type ferrite wave-absorbing agent described above.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] (1) The present invention provides a W-type ferrite wave-absorbing agent with a core-shell structure, and the molecular formulas of the core material and the shell material are respectively defined; by reasonably adjusting the element selection and ratio in the molecular formula, a formula system with high universality can be obtained; at the same time, the W-type ferrite wave-absorbing agent has a good flaky configuration, high impedance matching and good wave-absorbing performance.

[0023] (2) The present invention provides a preparation method of the W-type ferrite wave-absorbing agent. By reasonably controlling the conditions of the two sinterings, a wave-absorbing agent product with excellent flakiness can be obtained; the present invention creatively designs a pickling process to achieve low impurity phases and high main phases, greatly improving the purity of the core structure, and further through diffusion heat treatment, a wave-absorbing agent product with a good core-shell structure can be obtained without reducing the magnetic loss. Description of the Drawings

[0024] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0025] Figure 1 The SEM diagram of Example 1 of the present invention is provided;

[0026] Figure 2 The SEM diagram of Comparative Example 3 of the present invention is provided;

[0027] Figure 3 The reflection loss diagram of Example 1 of the present invention is provided;

[0028] Figure 4 The reflection loss diagram of Comparative Example 3 of the present invention is provided. Specific Embodiments

[0029] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the drawings and specific embodiments. However, those skilled in the art will understand that the following described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention. For those conditions not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase. In addition, the terms "first", "second", and "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0030] The first aspect of the present invention lies in providing a W-type ferrite wave absorber.

[0031] The ferrite wave absorber provided by the present invention first satisfies the crystal structure of the W-type ferrite wave absorber in the microscopic configuration, and realizes the sheet structure with the best absorption performance, the field effect of high magnetocrystalline anisotropy, and the natural resonance frequency through the special oxygen arrangement and metal atom stacking structure. At the same time, it satisfies the core-shell structure macroscopically, that is, the diffusion coating of the wave absorber is realized through the magnetic conductive alloy powder, and the impedance matching and wave absorption performance of the ferrite wave absorber are improved.

[0032] The ways to improve the wave absorption performance of the ferrite wave absorber include: Condition 1 is to dissipate the incident electromagnetic wave as much as possible inside the wave absorption material, and Condition 2 is that the surface impedance of the wave absorption material is numerically as close as possible to the free space impedance to achieve the condition of no reflection.

[0033] To meet Condition 1, the relative permeability in complex form (μ r = μ' - iμ") and the relative permittivity in complex form (ε r = ε' - iε") should be as large as possible. In the formula, μ' and μ" are the real part and the imaginary part of the relative permeability respectively, simply referred to as the real part and the imaginary part of the complex permeability; ε' and ε" are the real part and the imaginary part of the relative permittivity respectively, simply referred to as the real part and the imaginary part of the complex permittivity. The real parts μ' and ε' respectively represent the ability to store magnetic energy and electric energy, while the imaginary parts μ" and ε" respectively represent the ability to dissipate magnetic energy and electric energy. In addition to μ r and ε r , the magnetic loss tangent tanδ μ (tanδ μ = μ" / μ') and the dielectric loss tangent tanδ ε (tanδ ε = ε" / ε') can also be used to characterize the strength of the ability of the material to dissipate electromagnetic waves.

[0034] To meet Condition 2, theoretically, it is required that μ r and ε r of the wave-absorbing material are equal, but such a material has not been realized yet. Therefore, we can only seek a second-best solution to make μ r and ε r as close as possible; for the ferrite wave-absorbing agent, when tanδ μ is large and tanδ ε is small, then μ r and ε r differ greatly, and the impedance matching is not very good.

[0035] In the composite ferrite wave-absorbing agent with a core-shell structure of the present invention, first, a magnetic conductive alloy layer is formed on the surface of the flaky W-type ferrite wave-absorbing agent powder, so that the tanδ ε of the wave-absorbing agent increases, enhancing the dielectric loss. At the same time, the difference between μ r and ε r is reduced, improving the impedance matching of the material; second, the crystal defects and internal stresses generated by crushing in the wave-absorbing agent powder are repaired and eliminated to a certain extent, which is also beneficial to further improving the wave-absorbing performance. Through the above two methods, without reducing the magnetic loss of the wave-absorbing agent, its electric loss and impedance matching are improved.

[0036] The molecular formula of the nuclear material of the present invention includes A x Me 2 Fe 16 O 27, A includes at least one of Sr, Ba, Ca, Mg or Pb, Me includes at least one of Zn, Co, Ni or Cu, and 0.7 ≤ x ≤ 1; it is understood that the subscripts involved above correspond to the molar ratios of the atoms of each element.

[0037] A corresponds to the alkaline earth metal element necessary for the ferrite absorbent, and Me is an optional divalent metal ion. As a preferred embodiment, the core material further includes a non-essential doped rare earth element B, and B includes at least one of La, Ce, Pr, Nd, Sm or Y.

[0038] When the above preferred embodiment is satisfied, incorporating the doping element B into the core material molecular formula can obtain another molecular formula of the core material: A 1-y B y Me 2 Fe 16 O 27 , 0 < y ≤ 0.3; it is understood that A and Me in this molecular formula have the same reference or selection as those in the above molecular formula; the molecular formulas of the two core materials only refer to different situations of whether they contain doping elements.

[0039] When there are doping elements in the core material, the main technical indicators such as the effective bandwidth, minimum reflection loss, and matching thickness of the absorbent material will change significantly; further, when the types and molar ratios of the doping elements in the core material are designed appropriately, it usually exhibits a wider effective bandwidth, a smaller minimum reflection loss, and a thinner matching thickness, that is, the absorbent performance will be higher; at the same time, the doping elements also make the formulation design more flexible and can adapt to the application requirements in various different scenarios.

[0040] As an optional embodiment, the value of x includes but is not limited to any one or any numerical interval composed of any two of 0.7, 0.72, 0.74, 0.75, 0.76, 0.78, 0.8, 0.82, 0.84, 0.85, 0.86, 0.88, 0.9, 0.92, 0.94, 0.95, 0.96, 0.98, 1; the value of y includes but is not limited to any one or any numerical interval composed of any two of 0.01, 0.02, 0.05, 0.08, 0.1, 0.12, 0.14, 0.15, 0.16, 0.18, 0.2, 0.22, 0.24, 0.25, 0.26, 0.28, 0.3.

[0041] The molecular formula of the shell material of the present invention includes RE m C 1-m-n D n, RE includes at least one of La, Ce, Pr, Nd, Sm or Y, C includes at least one of Fe, Co or Ni, D includes at least one of Cu, Al, Zn, Bi, Sn or Pb, 0.1 ≤ m ≤ 0.3, 0.1 ≤ n ≤ 0.3; it can be understood that the subscripts involved above correspond to the molar ratios of the atoms of each element. The formulation system of the present invention has universality, and the element selection and ratio can be flexibly adjusted within a relatively large range to meet the absorption requirements of electromagnetic waves in different frequency bands.

[0042] RE corresponds to the rare earth element in the shell material. In the present invention, on the one hand, RE partially replaces the A atoms in the core structure, thereby achieving the effect of adjusting the electromagnetic parameters of the absorber; on the other hand, RE helps to break and pulverize the shell raw materials during the preparation process. The role of C in the present invention is to utilize the high magnetic loss characteristics of Fe, Co, and Ni to offset the decrease in magnetic loss caused by the introduction of non-magnetic elements RE and D in the diffusion material. D corresponds to a class of low-melting-point metal elements. In the present invention, the role of D is to lower the melting point of the diffusion material so that during subsequent sintering, the shell layer diffusion material can diffuse and coat the core layer at a lower temperature, while avoiding the negative impact of high temperature on the microstructure of the core layer.

[0043] As an alternative embodiment, the value of m includes, but is not limited to, any one or any numerical interval composed of any two of 0.1, 0.12, 0.14, 0.15, 0.16, 0.18, 0.2, 0.22, 0.24, 0.25, 0.26, 0.28, 0.3, and the value of n includes, but is not limited to, any one or any numerical interval composed of any two of 0.1, 0.12, 0.14, 0.15, 0.16, 0.18, 0.2, 0.22, 0.24, 0.25, 0.26, 0.28, 0.3.

[0044] As a preferred embodiment, the mass ratio of the core material to the shell material is 100:(1 - 10).

[0045] As an alternative embodiment, the mass ratio of the core material to the shell material includes, but is not limited to, any one or any ratio interval composed of any two of 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, 100:10.

[0046] As a preferred embodiment, the average particle size of the W-type ferrite absorber is 1.2 μm - 32 μm, wherein the average particle size of the core material is 1 μm - 30 μm, and the thickness of the shell material is 0.1 μm - 1 μm.

[0047] As an alternative embodiment, the average particle size of the W-type ferrite wave absorber includes, but is not limited to, any one of 1.2, 1.5, 1.8, 2, 3, 5, 10, 15, 20, 25, 30, 32 (μm) or a numerical range composed of any two of them; the average particle size of the core material includes, but is not limited to, any one of 1, 2, 3, 5, 10, 15, 20, 25, 28, 30 (μm) or a numerical range composed of any two of them, and the thickness of the shell material includes, but is not limited to, any one of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 (μm) or a numerical range composed of any two of them.

[0048] The second aspect of the present invention is to provide a preparation method of the W-type ferrite wave absorber described above.

[0049] The preparation method mainly includes the following steps: (1) According to the molecular formula of the core material, ingredients are prepared, a sintering promoter is added to the prepared raw materials, and then mixing treatment and densification treatment are carried out in sequence to obtain a material to be sintered; (2) The material to be sintered is subjected to a sintering treatment to obtain a sintered material; wherein, the temperature of the sintering treatment is 1150°C to 1200°C, and the heat preservation time of the sintering treatment is 0.5 h to 3 h; (3) The sintered material is subjected to crushing treatment, pickling treatment and dispersion treatment in sequence to obtain the core material; (4) The alloy powder of the shell material is mixed with the core material and then subjected to a second sintering treatment to obtain the W-type ferrite wave absorber; wherein, the temperature of the second sintering treatment is 600°C to 900°C, and the heat preservation time of the second sintering treatment is 0.5 h to 3 h.

[0050] As a preferred embodiment, in step (1), for the raw materials of the present invention:

[0051] Taking A x Me 2 Fe 16 O 27 as an example, the source raw materials of A include carbonates or oxides of corresponding metal elements. More preferably, carbonates are used to enhance the chemical reaction activity; that is, the source raw materials of A include at least one of strontium carbonate, barium carbonate, calcium carbonate, magnesium carbonate or lead carbonate, or the source raw materials of A include at least one of strontium oxide, barium oxide, calcium oxide, magnesium oxide or lead oxide, or the source raw materials of A are selected as a mixture of the above-listed carbonates and oxides, such as some elements are selected as corresponding carbonates and other elements are selected as corresponding oxides;

[0052] The source raw materials of Me include oxides of corresponding metal elements; that is, the source raw materials of Me include at least one of zinc oxide, cobalt oxide, nickel oxide or copper oxide;

[0053] The source raw material of Fe is iron(III) oxide (iron red, Fe 2 O 3 );

[0054] As a more preferred embodiment, when taking A 1-y B y Me 2 Fe 16 O 27 as an example, the source raw material of B includes oxides of corresponding metal elements; that is, the source raw material of B includes at least one of lanthanum oxide, cerium oxide, praseodymium oxide, neodymium oxide, samarium oxide or yttrium oxide.

[0055] As a preferred embodiment, in step (1), the sintering promoter includes at least one of calcium chloride or strontium chloride.

[0056] As a preferred embodiment, in step (1), the purity of each raw material is independently ≥99.2%, and at this time, the purity of the synthesized nuclear material can be effectively guaranteed.

[0057] As a preferred embodiment, in step (1), the particle size of each raw material is independently 0.1 μm to 10 μm; as a more preferred embodiment, the particle size of each raw material is independently 0.1 μm to 5 μm; at this time, the reaction activity during the synthesis process of the nuclear material can be effectively guaranteed.

[0058] As a preferred embodiment, in step (1), based on the formulated raw materials, the addition amount of the sintering promoter is 0.3 wt.% to 3.0 wt.%, including but not limited to any one or any numerical range composed of any two of 0.3, 0.5, 0.8, 1.0, 1.2, 1.5, 1.8, 2.0, 2.2, 2.5, 2.8, 3.0.

[0059] In step (1) of the present invention, by adding a sintering promoter, using the low melting point characteristics of SrCl 2 or CaCl 2 , the sintering temperature can be reduced and the sintering time can be shortened during the subsequent sintering process. It should be noted that the sintering promoter does not participate in the chemical reaction for synthesizing the nuclear material, and moreover, most of the sintering promoter will be dissolved and removed during the pickling process in subsequent step (3); when within the above-mentioned limited dosage, the sintering promoter is beneficial and harmless.

[0060] As a preferred embodiment, in step (1), the mixing treatment includes but is not limited to dry mixing or wet mixing, etc., as long as the uniform mixing of the raw materials can be achieved; the equipment for the mixing treatment includes but is not limited to high-speed mixers, roller mills or stirring mills, etc.

[0061] As an alternative implementation, in step (1), the mixing process includes loading the raw materials into the feed tank of a high-speed mixer according to the formulation ratio and performing dry mixing for 1 min to 10 min; or loading the raw materials, grinding balls, and water into the feed tank together and performing wet mixing on a roller mill for 1 h to 3 h, followed by sedimentation, filtration, drying, and dispersion in sequence.

[0062] It can be understood that dry mixing has the advantages of simplicity and high efficiency, but the mixing degree of the powder after mixing, the consistency of particle size, and the chemical reaction activity during the subsequent sintering process are slightly lower than those of wet mixing; on the contrary, for wet mixing, the mixing degree of the powder, the consistency of particle size, and the chemical reaction activity during the subsequent sintering process are better, but the operation is complex, time-consuming, and inefficient.

[0063] As a preferred implementation, in step (1), the densification process includes: adding water to the mixed raw materials through a pelletizer or granulator to prepare pellets or granules; or pressing the mixed raw materials into briquettes through a press. Through densification, the contact between different raw material powder particles can be made closer, which can reduce the subsequent sintering temperature and shorten the sintering time required.

[0064] As a more preferred implementation, in step (1), the densification process uses pelletizing, and the obtained pellets have a particle size of 10 mm to 20 mm and a density of 1 g / cm 3 ~3 g / cm 3 .

[0065] As an alternative implementation, in step (2), the sintering temperature includes but is not limited to any one of 1150, 1155, 1160, 1165, 1170, 1175, 1180, 1185, 1190, 1195, 1200 (°C) or any numerical range composed of any two of them, and the holding time of the sintering process includes but is not limited to any one of 0.5, 0.6, 0.7, 0.8, 1, 1.2, 1.4, 1.5, 1.6, 1.8, 2, 2.2, 2.4, 2.5, 2.6, 2.8, 3 (h) or any numerical range composed of any two of them.

[0066] It should be noted that in step (2), if the sintering temperature is lower than 1150 °C, the nuclear material of the target phase cannot be synthesized; if the sintering temperature is higher than 1200 °C, although the nuclear material of the target phase can be synthesized, the grains will grow excessively and no longer be flaky, resulting in a decrease in wave absorption performance; therefore, only when the sintering temperature is controlled within the range of 1150 °C to 1200 °C can a more ideal flaky configuration of the nuclear material be obtained.

[0067] As a preferred embodiment, in step (2), the equipment for the sintering treatment includes, but is not limited to, muffle furnaces, roller kilns, pusher kilns, etc.

[0068] As a preferred embodiment, in step (2), the furnace atmosphere in the heating stage, heat preservation stage and cooling stage of the sintering treatment is air or oxygen-rich atmosphere; at the same time, the present invention does not limit the heating and cooling rates in any way, and more preferably, a heating rate or cooling rate of 3°C / min to 15°C / min is adopted.

[0069] As a preferred embodiment, in step (3), the average particle size of the material after the crushing treatment is 1 μm to 30 μm; the determination of the average particle size can be carried out by the air permeability method and the average particle size analyzer; as a more preferred embodiment, the average particle size of the material after the crushing treatment is 3 μm to 20 μm; as a further preferred embodiment, the average particle size of the material after the crushing treatment is 5 μm to 10 μm.

[0070] As a preferred embodiment, in step (3), the equipment for the crushing treatment includes, but is not limited to, sealed sample preparation crushers, vibration mills, trapezoidal mills, etc.

[0071] As a preferred embodiment, in step (3), the acid for the pickling treatment includes at least one of hydrochloric acid, sulfuric acid or nitric acid, and the volume concentration of the acid is 0.5% to 5%; it can be understood that, taking 5% as an example, the volume concentration means that every 100 mL of the acid solution contains 5 mL of pure acid;

[0072] As a preferred embodiment, in step (3), the pickling treatment includes: pouring the material into the acid solution and soaking for 0.5 h to 12 h; optionally, mechanical stirring is carried out during the soaking process.

[0073] As a preferred embodiment, in step (3), after the pickling treatment, it further includes: washing with water 1 to 5 times until the pH of the washing liquid is 6.8 to 7.2, and then drying at 100°C to 200°C.

[0074] There are a small amount of sintering promoters, unreacted raw materials, impurities introduced due to impure raw materials, iron filings impurities introduced during the crushing process and other harmful impurity phases in the sintered material; in step (3) of the present invention, most of these impurity phases can be removed by pickling, improving the purity of the target phase nuclear material, and thus improving the wave absorption performance of the product.

[0075] As a preferred embodiment, in step (3), the material after the pickling treatment and drying will show obvious caking, so the dispersion treatment is required; optionally, it can be dispersed by equipment such as a high-speed mixer for 1 min to 5 min; in the art, the dispersion treatment generally does not further refine the particle size, but only restores the consolidated particles after pickling and drying to their original particle size. Therefore, the particle size of the nuclear material after the dispersion treatment is basically the same as that of the nuclear material after the crushing treatment.

[0076] As a preferred embodiment, in step (4), the alloy powder of the shell material can be a powdery raw material obtained by processing an alloy ingot or a rapidly solidified cast sheet corresponding to the molecular formula of the shell material, and the processing methods include but are not limited to mechanical crushing and hydrogen absorption embrittlement, etc.

[0077] As a more preferred embodiment, the alloy raw material of the shell material is first roughly crushed by a jaw crusher, and then finely ground by a ball mill in a vacuum or inert gas protection atmosphere to obtain the alloy powder; the hydrogen absorption embrittlement here utilizes the characteristic that rare earth alloys will absorb hydrogen and expand under certain conditions (for example: in a hydrogen environment of room temperature - 500 °C × 0.01 MPa to 0.1 MPa), and then many microcracks are generated and embrittled.

[0078] As an alternative embodiment, in step (4), the temperature of the second sintering treatment includes but is not limited to any one of 600, 620, 650, 680, 700, 720, 750, 780, 800, 820, 850, 880, 900 (°C) or a numerical range composed of any two of them, and the holding time of the second sintering treatment includes but is not limited to any one of 0.5, 0.6, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3 (h) or a numerical range composed of any two of them.

[0079] As a preferred embodiment, in step (4), the second sintering treatment is carried out in a vacuum atmosphere or a protective gas atmosphere, and the protective gas includes but is not limited to helium, neon, argon, etc.; the present invention does not limit the heating and cooling rates of the second sintering treatment in any way, and more preferably, a heating rate or a cooling rate of 3 °C / min to 15 °C / min is adopted.

[0080] In the second sintering treatment (or "diffusion heat treatment") of step (4) of the present invention, if the sintering temperature is lower than 600 °C, the alloy of the diffusion material has not completely melted, and the diffusion efficiency is too low to form a shell layer with sufficient thickness on the surface of the nuclear material; if the sintering temperature is higher than 900 °C, the high-temperature deoxidation problem of the nuclear material is significantly aggravated, and the molecular formula of the nuclear material will change, resulting in a decrease in magnetic loss; only when the temperature is controlled within the range of 600 °C to 900 °C can an ideal core-shell structure flaky W-type ferrite wave-absorbing agent be obtained.

[0081] As a preferred embodiment, in step (4), since the powder will be adhesively bonded to a certain extent after the diffusion heat treatment, therefore, after the second sintering treatment, it further includes: it can be dispersed by equipment such as a high-speed mixer for 1 min to 5 min; the particle size of the core-shell type wave-absorbing agent after the dispersion treatment meets the average particle size of the W-type ferrite wave-absorbing agent defined in the preferred case of the present invention.

[0082] The third aspect of the present invention lies in providing a wave-absorbing material.

[0083] The wave-absorbing material described includes the W-type ferrite wave-absorbing agent described in the first aspect of the present invention. In some optional embodiments, the preparation raw materials of the wave-absorbing material include conventional or unconventional raw material components such as wave-absorbing agents, adhesives, and various auxiliary additives, which are usually determined based on the use of the wave-absorbing material. The present invention does not impose any restrictions on the type or composition selection of the raw materials and the preparation method. It can be understood that the wave-absorbing materials prepared when including the W-type ferrite wave-absorbing agent all belong to an embodiment of the third aspect of the present invention.

[0084] Example 1

[0085] Step 1. Formula design: According to the molecular formula SrZn 0.8 Co 1.2 Fe 16 O 27 , weigh 147.6 grams of SrCO 3 , 65.1 grams of ZnO, 96.3 grams of Co 3 O 4 , 1277.5 grams of Fe 2 O 3 respectively; in addition, weigh 48 grams of CaCl 2 as a sintering aid, and its content accounts for about 3 wt.% of the total weight of the materials.

[0086] Step 2. Mixing: Load the weighed above-mentioned materials into the material tank of a high-speed mixer and mix them dry at a speed of 300 r / min for 5 minutes.

[0087] Step 3. Densification treatment: Use a pelletizing machine to prepare the mixed powder into green balls with an average particle size of about 15 mm.

[0088] Step 4. Sintering: Use a high-temperature box-type muffle furnace. In an air atmosphere, heat the green balls to 1200 °C at a heating rate of 5 °C / min and hold for 1 h. After the holding is completed, the balls are cooled with the furnace.

[0089] Step 5. Crushing: Use a sealed sample preparation pulverizer to crush the sintered clinker balls to an average particle size of 9 μm.

[0090] Step 6. Pickling: Pour the crushed powder into a 2% (by volume) hydrochloric acid aqueous solution and stir for 1 h; then, filter out the acid solution, wash the slurry 3 times with water until the pH value of the water body is 7; dry the slurry at 120 °C; use a high-speed mixer to disperse the dried powder for 1 min to obtain flaky W-type ferrite absorbent powder.

[0091] Step 7. Diffusion heat treatment: Mix the diffusion material powder La 0.3 Ni 0.4 Al 0.3 with the W-type ferrite absorbent powder in a mass ratio of 1:100; then, use a high-temperature box-type muffle furnace to heat the mixed powder to 600 °C at a heating rate of 5 °C / min and hold for 3 h in a vacuum environment.

[0092] Step 8. Use a high-speed mixer to disperse the agglomerated powder for 5 min to obtain the absorbent of this example. Perform scanning electron microscope (SEM) detection on the absorbent prepared in this example to obtain the SEM image as Figure 1 shown.

[0093] Example 2

[0094] It is basically the same as Example 1, with the only difference being that:

[0095] In the formula design of Step 1: According to the molecular formula Sr 0.9 Ba 0.1 Zn 0.8 Co 1.2 Fe 16 O 27 , weigh 132.9 g of SrCO 3 , 19.7 g of BaCO 3 , 65.1 g of ZnO, 96.3 g of Co 3 O 4 , 1277.5 g of Fe 2 O 3 ; then weigh 48 g of CaCl 2As a sintering aid, its content accounts for about 3 wt.% of the total weight of the material;

[0096] In the sintering of Step Four, heat to 1150 °C and hold for 3 h;

[0097] In the crushing of Step Five, crush to an average particle size of 7.2 μm;

[0098] In the pickling of Step Six, pour into a 5% by volume hydrochloric acid aqueous solution and stir for 0.5 h;

[0099] In the diffusion heat treatment of Step Seven, the diffusion material powder La 0.1 Ni 0.8 Cu 0.1 is mixed evenly with the W-type ferrite wave-absorbing agent powder according to a mass ratio of 10:100; then, using a high-temperature box furnace, heat the mixed powder to 900 °C at a heating rate of 5 °C / min and hold for 0.5 h in a vacuum environment.

[0100] Example 3

[0101] It is basically the same as Example 1, except that:

[0102] In the formula design of Step One: according to the molecular formula Sr 0.9 La 0.1 Zn 0.8 Co 1.2 Fe 16 O 27 , respectively weigh 132.9 g of SrCO 3 , 16.3 g of La 2 O 3 , 65.1 g of ZnO, 96.3 g of Co 3 O 4 , 1277.5 g of Fe 2 O 3 ; then weigh 16 g of CaCl 2 as a sintering aid, and its content accounts for about 1 wt.% of the total weight of the material;

[0103] In the sintering of Step Four, heat to 1175 °C and hold for 1 h;

[0104] In the crushing of Step Five, crush to an average particle size of 7.5 μm;

[0105] In the pickling of Step Six, pour into a 0.5% by volume hydrochloric acid aqueous solution and soak for 12 h;

[0106] In the diffusion heat treatment of Step Seven, the diffusion material powder La 0.1 Ce 0.1 Ni 0.6 Cu 0.1 Al 0.1Mix evenly with W-type ferrite absorbent powder in a mass ratio of 5:100; then, using a high-temperature box furnace, heat the mixed powder to 800 °C at a heating rate of 5 °C / min and keep it in a vacuum environment for 1 h.

[0107] Example 4

[0108] Basically the same as Example 1, the only difference is that:

[0109] In the formula design of Step 1: According to the molecular formula Sr 0.7 Ba 0.1 La 0.1 Ce 0.1 Zn 0.75 Co 1.2 Cu 0.05 Fe 16 O 27 , respectively weigh 103.3 grams of SrCO 3 , 19.7 grams of BaCO 3 , 16.3 grams of La 2 O 3 , 17.2 grams of CeO 2 , 61.1 grams of ZnO, 96.3 grams of Co 3 O 4 , 4.0 grams of CuO, 1277.5 grams of Fe 2 O 3 ; then weigh 16 grams of SrCl 2 as a sintering aid, and its content accounts for about 1 wt.% of the total weight of the material;

[0110] In the mixing of Step 2, first put the weighed above-mentioned material powders, grinding balls and water into a material tank, mix them wet on a roller mill for 3 h, and then successively pass through sedimentation, filtration, drying, and dispersion to obtain raw material powders;

[0111] In the densification treatment of Step 3, press the mixed powder into multiple Ф30mm×10mm blocks through a press;

[0112] In the sintering of Step 4, the holding time is 0.5 h;

[0113] In the crushing of Step 5, crush to an average particle size of 6.3 μm;

[0114] In the pickling of Step 6, pour it into a 1% volume concentration nitric acid aqueous solution;

[0115] In the diffusion heat treatment of Step 7, the diffusion material powders La 0.1 Ce 0.1 Ni 0.4 Co 0.2 Al 0.1 Zn 0.1Mix evenly with W-type ferrite absorbent powder at a mass ratio of 3:100; then, use a high-temperature box furnace to heat the mixed powder to 750 °C at a heating rate of 5 °C / min and keep it warm for 2 h in a vacuum environment.

[0116] Comparative Example 1

[0117] It is basically the same as Example 1, with the only difference being that Steps 7 to 8 are cancelled.

[0118] Comparative Example 2

[0119] It is basically the same as Example 1, with the only difference being that the addition of the sintering aid in Step 1 is cancelled.

[0120] Comparative Example 3

[0121] It is basically the same as Example 1, with the only difference being that in the sintering of Step 4, it is heated to 1300 °C and kept warm for 1 h.

[0122] In addition, the absorbent prepared in this comparative example was detected by scanning electron microscopy (SEM), and the SEM image as shown in Figure 2 was obtained.

[0123] Comparative Example 4

[0124] It is basically the same as Example 1, with the only difference being that in the crushing of Step 5, it is crushed to an average particle size of 11.0 μm.

[0125] Comparative Example 5

[0126] It is basically the same as Example 1, with the only difference being that Step 6 is cancelled.

[0127] Test Example

[0128] The average particle size, electromagnetic parameters, and reflection loss of the W-type ferrite absorbent products of the above examples and comparative examples were detected. The detection results are shown in Table 1.

[0129] Among them, the test method for the average particle size: Use the WLP-216 type average particle size analyzer of Dandong Huayu Instrument Co., Ltd. to test by the "permeability method" (also known as the "Fisher method").

[0130] Test method for electromagnetic parameters and reflection loss: After mixing the prepared W-type ferrite absorbent and paraffin evenly at a mass ratio of 3:1, press them into a ring-shaped sample with an inner diameter of 3 mm and an outer diameter of 7 mm. Use a vector network analyzer (model: Rohde&Schwarz ZNA43 of Germany), and use the standard coaxial line method to test the electromagnetic parameters (ε', ε", μ', μ") of the ring-shaped sample at room temperature and different frequencies, and then use software to simulate and calculate the reflection loss (RL) characteristics of the material at different thicknesses.

[0131] The sheet-like W-type ferrite wave-absorbing agent with a core-shell structure of the present invention is applicable to the frequency band of 8 GHz to 18 GHz. Therefore, Table 1 lists the electromagnetic parameters (ε', ε", μ', μ") and reflection loss tanδ (tanδ = tanδ ε +tanδ μ = ε" / ε'+μ" / μ', tanδ ε is the electrical loss, tanδ μ is the magnetic loss, and tanδ represents the total loss) of each example and comparative example at 8, 10, 12, 14, 16, and 18 (GHz) respectively, which are used to compare and evaluate the reflection loss ability of the material to electromagnetic waves. It can be understood that the absorption of electromagnetic waves by the material mainly depends on ε", μ", and tanδ; the larger ε", μ", and tanδ are, the better the wave-absorbing performance is.

[0132] In addition, the reflection loss characteristics of Example 1 and Comparative Example 3 are plotted into a graph, and the comparison graph as shown in Figure 3 、 Figure 4 is obtained.

[0133] Table 1

[0134]

[0135]

[0136]

[0137] It can be seen from Table 1 that:

[0138] (1) In terms of ε', ε", and tanδ ε , the examples are significantly higher than the comparative examples, which is mainly due to the new process of diffusion heat treatment (corresponding to Step 7). Furthermore, it is found that as the addition amount of the diffusion material increases, the values of ε', ε", and tanδ ε become higher and higher, indicating that the electrical loss of the material is getting larger.

[0139] (2) In terms of μ', there is little difference between the examples and the comparative examples.

[0140] (3) In terms of μ" and tanδ μ , the examples are significantly higher than the comparative examples, which is mainly due to the purification effect of pickling on the main phase of the core structure, as well as the repair and elimination of crystal defects and internal stress of the main phase by diffusion heat treatment; the higher values of μ" and tanδ μ represent that the magnetic loss of the material is larger.

[0141] (4)Regarding the total loss tangent tanδ, at any frequency from 8 GHz to 18 GHz, the examples are significantly superior to the comparative examples, which indicates that the flaky W-type ferrite microwave absorbing material with a core-shell structure of the present invention has significantly better reflection loss for incident electromagnetic waves than the traditional W-type ferrite microwave absorbing material, demonstrating excellent microwave absorption ability.

[0142] Although the present invention has been illustrated and described with reference to specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it; those of ordinary skill in the art should understand that: without departing from the spirit and scope of the present invention, the technical solutions described in the foregoing embodiments may be modified, or some or all of the technical features may be equivalently replaced; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such replacements and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A W-type ferrite absorber, characterized in that: The W-type ferrite absorber is a core-shell structure; wherein, The molecular formula of the core material includes A x Me2Fe 16 O 27 , A includes at least one of Sr, Ba, Ca, Mg or Pb, Me includes at least one of Zn, Co, Ni or Cu, 0.7≤x≤1; The molecular formula of the shell material includes RE m C 1-m-n D n , RE includes at least one of La, Ce, Pr, Nd, Sm or Y, C includes at least one of Fe, Co or Ni, D includes at least one of Cu, Al, Zn, Bi, Sn or Pb, 0.1≤m≤0.3, 0.1≤n≤0.

3.

2. The W-type ferrite absorber according to claim 1, characterized in that: The core material further includes a doping element B, and B includes at least one of La, Ce, Pr, Nd, Sm or Y; Preferably, the molecular formula of the core material is A 1-y B y Me2Fe 16 O 27 , 0<y≤0.

3.

3. The W-type ferrite absorber according to claim 1, characterized in that: The mass ratio of the core material to the shell material is 100:(1-10).

4. The W-type ferrite absorber according to claim 1, characterized in that: The particle size of the W-type ferrite absorber is 1.2 μm to 32 μm; Preferably, the particle size of the core material is 1.0 μm to 30 μm, and the thickness of the shell material is 0.1 μm to 1.0 μm.

5. The method for preparing the W-type ferrite absorber according to any one of claims 1 to 4, characterized in that: The preparation method comprises the following steps: (1) According to the molecular formula of the core material, a sintering accelerator is added to the prepared raw material, and then a mixing process and a densification process are performed in sequence to obtain a material to be sintered; (2) sintering the material to be sintered to obtain a sintered material; wherein the sintering temperature is 1150° C. to 1200° C., and the sintering time is 0.5 h to 3 h; (3) sequentially crushing, pickling and breaking up the sintered material to obtain a core material; (4) Mixing the alloy powder of the shell material with the core material and performing a second sintering treatment to obtain a W-type ferrite absorber; wherein the temperature of the second sintering treatment is 600°C to 900°C, and the insulation time of the second sintering treatment is 0.5h to 3h.

6. The method for preparing the W-type ferrite absorber according to claim 5, characterized in that: The sintering promoter includes one or both of strontium chloride and calcium chloride; Preferably, based on the prepared raw materials, the added amount of the sintering promoter is 0.3 wt.% to 3.0 wt.%.

7. The method for preparing the W-type ferrite absorber according to claim 5, characterized in that: The densification treatment includes one of balling, granulation or pressing; Preferably, the particle size of the material to be sintered after the densification treatment is 10 mm to 20 mm, and the density is 1 g / cm 3 ~3g / cm 3 .

8. The method for preparing the W-type ferrite absorber according to claim 5, characterized in that: The acid used in the pickling treatment includes at least one of hydrochloric acid, sulfuric acid or nitric acid, and the volume concentration of the acid is 0.5% to 5%.

9. The method for preparing the W-type ferrite absorber according to claim 5, characterized in that: The pickling treatment comprises: pouring the crushed sintered material into an acid solution and soaking it for 0.5h to 12h; Preferably, after the pickling treatment, the method further includes: washing the material with water for 1 to 5 times until the pH of the washing liquid is 6.8 to 7.2, and then drying the material at 100° C. to 200° C. to obtain the core material before the disintegration treatment.

10. A wave absorbing material, characterized in that: The absorbing material comprises the W-type ferrite absorbing agent as claimed in any one of claims 1 to 4.

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