Wave absorbing agent as well as preparation method and application thereof

Abstract

The invention discloses a wave-absorbing agent as well as a preparation method and application thereof. The wave-absorbing agent is a composite hollow microsphere, and the structure of the composite hollow microsphere comprises a hollow cavity, and a glass ball shell layer, a ferrite shell layer and a magnetic metal shell layer which coat the hollow cavity and are sequentially arranged from inside to outside; wherein the ferrite shell layer is composed of ferrite and metal silver doped in the ferrite, and at least part of the metal silver is located at the interface of the ferrite shell layer and the magnetic metal shell layer. Combination of electrical loss and magnetic loss is achieved through compounding of multi-component components and three layers of spherical shells in the wave absorbing agent structure, electromagnetic wave scattering and polarization loss are enhanced through high-conductivity particles and heterogeneous interfaces in the spherical shells, and the excellent electromagnetic wave absorbing effect can be obtained.

Description

Technical Field

[0001] This invention relates to the field of powder materials technology. More specifically, it relates to a microwave absorbing agent, its preparation method, and its application. Background Technology

[0002] Magnetic metals are widely used in the research and development of high-performance electromagnetic wave absorbers (wave absorbers) due to their excellent composition and structural designability, as well as their dual electromagnetic response characteristics. However, despite their superior electromagnetic functionality and performance controllability, the significantly higher density of magnetic metals compared to other wave absorber candidates is a major factor limiting their application. This is especially true given the increasing demand for lightweight materials and equipment design, where the high density of magnetic metals becomes even more pronounced. To address this issue, designing hollow or porous structures for magnetic metals, or combining them with low-density materials, are important ways to achieve lightweighting. On the other hand, in addition to lightweighting, advanced wave absorbers also need to meet stringent requirements such as thinner thickness, wider frequency response, and stronger absorption. Therefore, hollowing out the structure and composite composition of wave absorbers are possible ways to simultaneously meet these requirements, and magnetic metal wave absorbers are no exception.

[0003] Considering factors such as process feasibility, hollow structure stability, and ease of use as filler, composite magnetic metal hollow microspheres offer unique advantages in achieving lightweight and high performance. First, magnetic metals can be easily hollowed out and sphericalized through a rationally designed synthesis route or with the aid of a hollow carrier. Second, compared to other hollow structures, hollow microspheres have the smallest specific surface area and correspondingly lower surface energy, effectively preventing performance degradation caused by unintended surface chemical reactions. Third, the spherical shape facilitates stress dispersion under external forces, avoiding stress concentration and the resulting weakening of mechanical strength, thus imparting high stability to the hollow structure. Fourth, since most microwave absorbing agents are composited with a matrix to form microwave absorbing composite materials, the spherical shape facilitates high flowability and fillability. Furthermore, it is worth mentioning that compared to self-formed magnetic metal hollow microspheres, using pre-formed hollow microspheres with a large proportion of cavities as a carrier allows for the step-by-step forming and synergistic performance of the supporting and functional shells, simultaneously achieving low density, high strength, and high performance. In light of this, magnetic metal composite hollow microspheres utilizing pre-formed carriers have gained favor among researchers of advanced microwave absorbing agents.

[0004] However, currently, the metal shells of magnetic metal composite hollow microspheres prepared using preformed carriers are mostly continuous film-shaped shells formed through chemical reduction, evaporation, or sputtering. Although these shells can achieve lightweighting and performance control, they are prone to forming conductive networks when filled in large proportions, leading to severe impedance mismatch and significantly affecting the absorption capacity of the absorber and the overall absorption effect. Summary of the Invention

[0005] Based on the above problems, the purpose of this invention is to provide a microwave absorbing agent, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] On one hand, the present invention provides a microwave absorbing agent, which is a composite hollow microsphere. The structure of the composite hollow microsphere includes a hollow cavity and a glass sphere shell layer, a ferrite shell layer and a magnetic metal shell layer arranged sequentially from the inside to the outside of the hollow cavity.

[0008] The ferrite shell is composed of ferrite and metallic silver doped in the ferrite, and at least a portion of the metallic silver is located at the interface between the ferrite shell and the magnetic metal shell.

[0009] In the technical solution of this invention, the glass sphere shell layer is preferably made of silicate glass.

[0010] It is understood that in the technical solution of this invention, a portion of the metallic silver located at the interface between the ferrite shell and the magnetic metal shell is exposed on the outer surface of the ferrite shell and in contact with the magnetic metal shell. The metallic silver exposed on the outer surface of the ferrite shell at the interface can better catalyze the formation of a magnetic metal shell that is firmly bonded to the ferrite shell.

[0011] Furthermore, the diameter of the hollow cavity is 10-70 micrometers.

[0012] Furthermore, the magnetic metal shell is made of one, two, or three of the following alloys: cobalt, nickel, and iron.

[0013] Furthermore, the alloy may or may not contain phosphorus.

[0014] In this invention, the ferrite has the chemical formula M x Fe y O4, where M is one or a mixture of two of nickel, cobalt, iron, copper, zinc, and manganese; x + y = 3, and both x and y are positive numbers greater than 0. For example, x = 1, y = 2.

[0015] Furthermore, the apparent density of the composite hollow microspheres is 0.55-1.25 g / cm³. 3 .

[0016] Furthermore, by mass percentage, the composite hollow microspheres contain: 35-55% glass sphere shell, 5-20% ferrite, 3-15% metallic silver, and 20-50% magnetic metal shell.

[0017] Furthermore, the ferrite shell contains 40-85% ferrite and 15-60% metallic silver by mass percentage.

[0018] By designing and controlling the composition and content of each layer of the composite hollow microsphere, the composite hollow microsphere is endowed with a stable structure and excellent electromagnetic wave absorption effect.

[0019] The microwave absorber provided in this invention features a hollow structure due to its cavity, mechanical support due to its glass spherical shell, and functionalities due to its ferrite, silver, and magnetic metal components, including electrical, magnetic, and electromagnetic wave absorption. The combination of the multi-component components and the three-layered shell in this composite hollow microsphere achieves a balance between electrical and magnetic losses, resulting in excellent electromagnetic wave absorption.

[0020] In another aspect, the present invention provides a method for preparing the microwave absorbing agent as described above, the method comprising the following steps:

[0021] Glass hollow microspheres were dispersed in an aqueous solution containing a soluble salt of a metal that forms ferrite and a soluble silver salt. After mixing, drying, and heat treatment, intermediate A hollow microspheres were obtained.

[0022] The hollow microspheres of intermediate A were dispersed in an aqueous solution of inorganic acid and stirred to obtain hollow microspheres of intermediate B.

[0023] The hollow microspheres of intermediate B were dispersed in an aqueous solution containing a soluble salt of magnetic metal. After stirring and reacting, the mixture was filtered and dried to obtain the microwave absorbing agent.

[0024] The aforementioned hollow glass microspheres are glass microspheres containing hollow cavities, which can be obtained commercially or prepared using conventional methods in the art. For example, the density of the hollow glass microspheres is 0.3-0.6 g / cm³. 3 .

[0025] Furthermore, the soluble salt of the metal forming the ferrite is selected from nitrates or organic acid salts of the metal forming the ferrite. For example, the soluble salt of the metal forming the ferrite includes soluble salts of iron (e.g., ferric nitrate) and soluble salts of other metals selected from one or a mixture of two of nickel, cobalt, iron, copper, zinc, and manganese.

[0026] Furthermore, the soluble silver salt is selected from silver nitrate.

[0027] Furthermore, in the process of preparing intermediate A hollow microspheres, the dispersion concentration of the glass hollow microspheres in the aqueous solution is 0.1-0.4 g / mL.

[0028] Furthermore, in the preparation of intermediate A hollow microspheres, the aqueous solution also contains water-soluble organic matter selected from at least one of sucrose, starch, citric acid, chitosan, and cellulose, with a concentration of 200-400 g / L. The water-soluble organic matter can assist in the combustion and decomposition of the metal salt and help the decomposition products coat the surface of the glass hollow microspheres.

[0029] Furthermore, in the process of preparing hollow microspheres of intermediate A, the concentration of soluble silver salt in the aqueous solution is 60-120 g / L, and the concentration of soluble salt of the metal that forms ferrite is 300-500 g / L.

[0030] Furthermore, the heat treatment is carried out in an air atmosphere at a temperature of 500-700℃ for 0.5-2 hours. By controlling the heat treatment conditions, structurally stable composite hollow microspheres are obtained.

[0031] For example, the temperature of the heat treatment is 500-600℃, 600-700℃, 600℃, etc.

[0032] For example, the heat treatment time is 0.5-1h, 1-2h, 1h, etc.

[0033] Furthermore, after the heat treatment, a sieve dispersion step is also included. The preferred method of sieve dispersion is to gently grind, press, and disperse the reaction product on a 50-300 mesh standard sieve and pass it through the sieve holes.

[0034] Hollow microspheres of intermediate A were prepared by solution combustion coating method. This method is fast, convenient and suitable for mass production.

[0035] Furthermore, in the process of preparing intermediate B hollow microspheres, the dispersion concentration of intermediate A hollow microspheres in the aqueous solution of inorganic acid is 20-60 g / L.

[0036] Furthermore, in the process of preparing hollow microspheres of intermediate B, the concentration of the inorganic acid in the aqueous solution is 0.05-0.2 mol / L.

[0037] Furthermore, the inorganic acid is selected from hydrochloric acid.

[0038] Furthermore, during the preparation of intermediate B hollow microspheres, the stirring temperature is 10-60℃ and the stirring time is 10-40 min.

[0039] For example, in the process of preparing hollow microspheres of intermediate B, the stirring temperature includes, but is not limited to, 30-60℃, 30-40℃, 40-60℃, 30℃, 40℃, 60℃, etc.

[0040] Furthermore, in the process of preparing intermediate B hollow microspheres, after stirring, the steps of washing with water, filtering, and drying are also included.

[0041] By dispersing intermediate A in an aqueous solution of the aforementioned inorganic acid and stirring, and then etching it with acid, the metallic silver doped in the hollow microspheres of intermediate A is at least partially exposed on the outer surface of the resulting ferrite shell, which facilitates the subsequent directional assembly and molding of the magnetic metal sphere shell.

[0042] Furthermore, the dispersion concentration of the hollow microspheres of intermediate B in an aqueous solution containing a soluble salt of magnetic metal is 0.005-0.016 g / mL.

[0043] Furthermore, in the aqueous solution containing the soluble salt of the magnetic metal, the concentration of the soluble salt of the magnetic metal is 15-80 g / L. For example, the concentration of the soluble salt of the magnetic metal may include, but is not limited to, 15-40 g / L, 25-40 g / L, etc.

[0044] Furthermore, the soluble salt of the magnetic metal is selected from sulfates, nitrates, or chlorides of the magnetic metal. Exemplary soluble salts of magnetic metals include, but are not limited to, one or more selected from cobalt sulfate, nickel sulfate, ferrous ammonium sulfate, etc.

[0045] Furthermore, the aqueous solution containing the soluble salt of the magnetic metal also contains a stabilizer, a reducing agent, and a pH adjuster.

[0046] Furthermore, the stabilizer is selected from ammonium sulfate and / or potassium sodium tartrate, and the concentration of the stabilizer in the aqueous solution is 40-160 g / L.

[0047] Furthermore, the pH adjuster is an inorganic base, and the liquid pH adjuster preferably makes the pH of the aqueous solution 8-11.

[0048] Furthermore, the reducing agent is selected from sodium hypophosphite, and the concentration of the reducing agent in the aqueous solution is 40-80 g / L, preferably 50-60 g / L.

[0049] Furthermore, the temperature of the stirring reaction is 60-85℃, and the time is 20-60 min.

[0050] In another aspect, the present invention provides the application of the microwave absorbing agent as described above in microwave absorption or shielding.

[0051] Furthermore, as a microwave absorbing or shielding material, it can be used as one of the following: in the field of military stealth, electromagnetic radiation protection for radio and television transmitters, microwave anechoic chamber materials, and electromagnetic shielding materials in buildings or radio communication equipment.

[0052] The beneficial effects of this invention are as follows:

[0053] The multi-component and three-layer spherical shell composite structure of the microwave absorber provided in this invention achieves a combination of electrical and magnetic losses, and enhances electromagnetic wave scattering and polarization loss through highly conductive particles and heterogeneous interfaces within the spherical shell, thus facilitating the achievement of excellent electromagnetic wave absorption.

[0054] The microwave absorbing agent preparation method provided in this invention cleverly utilizes the catalytic effect of silver, which not only enables the formation of functional components but also assists in the subsequent assembly of magnetic metals, avoiding the dependence on expensive active seed nuclei in traditional magnetic technology assembly processes. Specifically, the preparation method involves the synergistic pyrolysis of ferrite and silver precursors, followed by an etching-chemical plating process. Through the linking and anchoring effect of ferrite, silver is uniformly distributed and firmly bonded within the spherical shell. The magnetic metal spherical shell formed with silver as the catalytic active site enhances electromagnetic functionality. Attached Figure Description

[0055] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0056] Figure 1 A schematic diagram of the structure of the microwave absorbing agent of the present invention is shown.

[0057] Figure 2 A schematic diagram of a preparation process for the microwave absorbing agent of the present invention is shown.

[0058] Figure 3 The image shows a scanning electron microscope (SEM) image of the absorbing agent of Embodiment 1 of the present invention. Detailed Implementation

[0059] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further explains the invention. Similar components in the drawings are indicated by the same reference numerals. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0060] Performance testing:

[0061] The electromagnetic properties of the products prepared in the following embodiments were tested. The test method was as follows: apparent density was obtained by measuring dimensions and weight;

[0062] Porosity is obtained by measuring true density;

[0063] The transmission parameters were tested using a vector network analyzer (test frequency 8-12GHz, sample thickness 2.5mm) to analyze its shielding performance.

[0064] Electromagnetic parameters were tested using a vector network analyzer (test frequency 2-18GHz) to analyze its wave absorption performance.

[0065] Example 1

[0066] A microwave absorbing agent (hollow microspheres with a glass-ferrite-silver-magnetic metal composite shell) (its structural schematic diagram is shown below) Figure 1 The preparation method shown is illustrated in the diagram below. Figure 2 As shown, the specific steps include the following:

[0067] 1) Commercial hollow glass microspheres (density 0.31 g / cm³) 3 Mix the mixture with treatment solution A containing 3g silver nitrate, 13g ferric nitrate, 4.5g cobalt nitrate, 14g citric acid and 13g water at a ratio of 0.31g / mL; then dry the mixture at 50℃; then treat it at 600℃ for 1h in air atmosphere, and disperse it through an 80-mesh sieve to obtain hollow microspheres of intermediate A.

[0068] 2) Disperse the hollow microspheres of intermediate A obtained in step 1) in treatment solution B (0.05 mol / L hydrochloric acid aqueous solution) at a ratio of 50 g / L, treat at 30℃ for 10 min, then wash with water, filter and dry to obtain hollow microspheres of intermediate B;

[0069] 3) The hollow microspheres of intermediate B obtained in step 2) were dispersed at an addition amount of 0.005 g / mL in treatment solution B containing 14 g / L cobalt sulfate, 14 g / L nickel sulfate, 50 g / L sodium hypophosphite, and 75 g / L potassium sodium tartrate, with a pH of approximately 9.2 (adjusted with ammonia). The mixture was stirred in a water bath at 70°C for 30 min, filtered, and dried to obtain hollow microspheres with a glass-ferrite-silver-magnetic metal composite shell. The scanning electron microscope image is shown below. Figure 3 As shown.

[0070] The hollow microspheres with a glass-ferrite-silver-magnetic metal composite shell obtained in this embodiment have a density of 0.75 g / cm³. 3 The diameter of the core cavity is 43 micrometers; the mass fractions of glass, magnetic metal, ferrite, and silver are 40.6%, 48.7%, 5.9%, and 4.8%, respectively.

[0071] The hollow microsphere with a glass-ferrite-silver-magnetic metal composite shell has a survival rate of 82.7% at 33 MPa; the optimized electromagnetic wave reflection loss is -67.7 dB, the effective absorption bandwidth is 5.2 GHz, and the electromagnetic shielding effectiveness is 69-82 dB.

[0072] Example 2

[0073] A method for preparing a microwave absorbing agent (hollow microspheres with a glass-ferrite-silver-magnetic metal composite shell) specifically includes the following steps:

[0074] 1) Commercial hollow glass microspheres (density 0.33 g / cm³) 3 Mix the mixture with treatment solution A containing 3g silver nitrate, 13g ferric nitrate, 4.5g nickel nitrate, 14g citric acid and 13g water at a ratio of 0.24g / mL; then dry the mixture at 50℃; then treat it at 600℃ for 1h in air atmosphere, and disperse it through an 80-mesh sieve to obtain hollow microspheres of intermediate A.

[0075] 2) Disperse the hollow microspheres of intermediate A obtained in step 1) in treatment solution B (0.08 mol / L hydrochloric acid aqueous solution) at a ratio of 50 g / L, treat at 30℃ for 15 min, then wash with water, filter and dry to obtain hollow microspheres of intermediate B;

[0076] 3) Disperse the hollow microspheres of intermediate B obtained in step 2) at an addition amount of 0.009 g / mL in treatment solution B containing 15 g / L cobalt sulfate, 14 g / L nickel sulfate, 50 g / L sodium hypophosphite and 75 g / L potassium sodium tartrate, with pH≈9.5 (adjusted with ammonia). Stir and react in a water bath at 70℃ for 30 min, filter, and dry to obtain hollow microspheres with a glass-ferrite-silver-magnetic metal composite shell.

[0077] The hollow microspheres with a glass-ferrite-silver-magnetic metal composite shell obtained in this embodiment have a density of 0.66 g / cm³. 3 The diameter of the core cavity is 42.4 micrometers; the mass fractions of glass, magnetic metal, ferrite, and silver are 48.9%, 34.2%, 9.3%, and 7.6%, respectively.

[0078] The hollow microsphere with a glass-ferrite-silver-magnetic metal composite shell has a survival rate of 83.8% at 33 MPa; the optimized electromagnetic wave reflection loss is -56.3 dB, the effective absorption bandwidth is 4.2 GHz, and the electromagnetic shielding effectiveness is 54-66 dB.

[0079] Example 3

[0080] A method for preparing a microwave absorbing agent (hollow microspheres with a glass-ferrite-silver-magnetic metal composite shell) specifically includes the following steps:

[0081] 1) Commercial hollow glass microspheres (density 0.37 g / cm³) 3 Mix the mixture with treatment solution A containing 3g silver nitrate, 13g ferric nitrate, 4.2g zinc nitrate, 14g starch and 13g water at a ratio of 0.19g / mL; then dry the mixture at 50℃; then treat it at 600℃ for 1h in air atmosphere, and disperse it through an 80-mesh sieve to obtain hollow microspheres of intermediate A.

[0082] 2) Disperse the hollow microspheres of intermediate A obtained in step 1) in treatment solution B (0.1 mol / L hydrochloric acid aqueous solution) at a ratio of 50 g / L, stir at 30°C for 25 min, then wash with water, filter and dry to obtain hollow microspheres of intermediate B;

[0083] 3) Disperse the hollow microspheres of intermediate B obtained in step 2) at an addition amount of 0.014 g / mL in treatment solution B containing 20 g / L ferrous ammonium sulfate, 16 g / L nickel sulfate, 60 g / L sodium hypophosphite and 90 g / L potassium sodium tartrate, with pH≈11 (adjusted with ammonia). Stir and react in a water bath at 70℃ for 60 min, filter, and dry to obtain hollow microspheres with a glass-ferrite-silver-magnetic metal composite shell.

[0084] The hollow microspheres with a glass-ferrite-silver-magnetic metal composite shell obtained in this embodiment have a density of 0.68 g / cm³. 3 The diameter of the core cavity is 39.6 micrometers; the mass fractions of glass, magnetic metal, ferrite, and silver are 52.9%, 23.8%, 12.8%, and 10.5%, respectively.

[0085] The hollow microsphere with a glass-ferrite-silver-magnetic metal composite shell has a survival rate of 86.3% at 33 MPa; the optimized electromagnetic wave reflection loss is -43.9 dB, the effective absorption bandwidth is 3.7 GHz, and the electromagnetic shielding effectiveness is 40-52 dB.

[0086] Example 4

[0087] A method for preparing a microwave absorbing agent (hollow microspheres with a glass-ferrite-silver-magnetic metal composite shell) specifically includes the following steps:

[0088] 1) Commercial hollow glass microspheres (density 0.46 g / cm³) 3 Mix the mixture with treatment solution A containing 3g silver nitrate, 13g ferric nitrate, 3.9g copper nitrate, 14g sucrose and 13g water at a ratio of 0.16g / mL; then dry the mixture at 50℃; then treat it at 600℃ for 1h in air atmosphere, and disperse it through an 80-mesh sieve to obtain hollow microspheres of intermediate A.

[0089] 2) Disperse the hollow microspheres of intermediate A obtained in step 1) in treatment solution B (0.12 mol / L hydrochloric acid aqueous solution) at a ratio of 50 g / L, treat at 40℃ for 20 min, then wash with water, filter and dry to obtain hollow microspheres of intermediate B;

[0090] 3) Disperse the hollow microspheres of intermediate B obtained in step 2) at an addition amount of 0.008 g / mL in treatment solution B containing 18 g / L cobalt sulfate, 11 g / L nickel sulfate, 50 g / L sodium hypophosphite and 105 g / L potassium sodium tartrate, with pH≈10.5 (adjusted with ammonia). Stir the reaction in a water bath at 70℃ for 30 min, filter, and dry to obtain hollow microspheres with a glass-ferrite-silver-magnetic metal composite shell.

[0091] The hollow microspheres with a glass-ferrite-silver-magnetic metal composite shell obtained in this embodiment have a density of 1.04 g / cm³. 3 The diameter of the core cavity is 18.2 micrometers; the mass fractions of glass, magnetic metal, ferrite, and silver are 42.5%, 35.7%, 12.0%, and 9.8%, respectively.

[0092] The hollow microsphere with a glass-ferrite-silver-magnetic metal composite shell has a survival rate of 94.2% at 33 MPa; the optimized electromagnetic wave reflection loss is -60.7 dB, the effective absorption bandwidth is 4.5 GHz, and the electromagnetic shielding effectiveness is 61-70 dB.

[0093] Example 5

[0094] A method for preparing a microwave absorbing agent (hollow microspheres with a glass-ferrite-silver-magnetic metal composite shell) specifically includes the following steps:

[0095] 1) Commercial hollow glass microspheres (density 0.51 g / cm³) 3 Mix the mixture with treatment solution A containing 3g silver nitrate, 13g ferric nitrate, 4.5g cobalt nitrate, 14g citric acid and 13g water at a ratio of 0.14g / mL; then dry the mixture at 50℃; then treat it at 600℃ for 1h in air atmosphere, and disperse it through an 80-mesh sieve to obtain hollow microspheres of intermediate A.

[0096] 2) Disperse the hollow microspheres of intermediate A obtained in step 1) in treatment solution B (0.2 mol / L hydrochloric acid aqueous solution) at a ratio of 50 g / L, treat at 60℃ for 10 min, then wash with water, filter and dry to obtain hollow microspheres of intermediate B;

[0097] 3) Disperse the hollow microspheres of intermediate B obtained in step 2) at an addition amount of 0.02 g / mL in treatment solution B containing 20 g / L cobalt sulfate, 18 g / L nickel sulfate, 60 g / L sodium hypophosphite and 120 g / L potassium sodium tartrate, with pH≈8.2 (adjusted with ammonia). Stir and react in a water bath at 80℃ for 30 min, filter, and dry to obtain hollow microspheres with a glass-ferrite-silver-magnetic metal composite shell.

[0098] The hollow microspheres with a glass-ferrite-silver-magnetic metal composite shell obtained in this embodiment have a density of 1.10 g / cm³. 3 The diameter of the core cavity is 34.8 micrometers; the mass fractions of glass, magnetic metal, ferrite, and silver are 45.0%, 27.9%, 14.9%, and 12.2%, respectively.

[0099] The hollow microsphere with a glass-ferrite-silver-magnetic metal composite shell has a survival rate of 96.1% at 33 MPa; the optimized electromagnetic wave reflection loss is -49.4 dB, the effective absorption bandwidth is 3.9 GHz, and the electromagnetic shielding effectiveness is 46-61 dB.

[0100] Example 6

[0101] A method for preparing a microwave absorbing agent (hollow microspheres with a glass-ferrite-silver-magnetic metal composite shell) specifically includes the following steps:

[0102] 1) Commercial hollow glass microspheres (density 0.42 g / cm³) 3 Mix the mixture with treatment solution A containing 3g silver nitrate, 13g ferric nitrate, 2.5g nickel nitrate, 2g cobalt nitrate, 14g citric acid and 13g water at a ratio of 0.13g / mL; then dry the mixture at 50℃; then treat it at 600℃ for 1h in air atmosphere, and disperse it through an 80-mesh sieve to obtain intermediate A hollow microspheres.

[0103] 2) Disperse the hollow microspheres of intermediate A obtained in step 1) in treatment solution B (0.15 mol / L hydrochloric acid aqueous solution) at a ratio of 50 g / L, treat at 40℃ for 40 min, then wash with water, filter and dry to obtain hollow microspheres of intermediate B;

[0104] 3) Disperse the hollow microspheres of intermediate B obtained in step 2) at an addition amount of 0.008 g / mL in treatment solution B containing 12 g / L cobalt sulfate, 15 g / L nickel sulfate, 50 g / L sodium hypophosphite and 70 g / L potassium sodium tartrate, with pH≈10.8 (adjusted with ammonia). Stir the reaction in a water bath at 60℃ for 30 min, filter, and dry to obtain hollow microspheres with a glass-ferrite-silver-magnetic metal composite shell.

[0105] The hollow microspheres with a glass-ferrite-silver-magnetic metal composite shell obtained in this embodiment have a density of 1.03 g / cm³. 3 The diameter of the core cavity is 38.1 micrometers; the mass fractions of glass, magnetic metal, ferrite, and silver are 38.8%, 35.0%, 14.4%, and 11.8%, respectively.

[0106] The hollow microsphere with a glass-ferrite-silver-magnetic metal composite shell has a survival rate of 91.4% at 33 MPa; the optimized electromagnetic wave reflection loss is -63.5 dB, the effective absorption bandwidth is 4.8 GHz, and the electromagnetic shielding effectiveness is 65-78 dB.

[0107] Comparative Example 1

[0108] A method for preparing a microwave absorbing agent, the preparation process of which is the same as in Example 1, except that the treatment solution A does not contain silver nitrate.

[0109] In this embodiment, due to the lack of silver catalysis, the assembly of magnetic metals could not be achieved, and the density of the resulting hollow microspheres with glass-ferrite metal composite shells was 0.35 g / cm³. 3 The diameter of the core cavity is 43 micrometers; the mass fractions of glass and ferrite are 88% and 12%, respectively.

[0110] The hollow microsphere with a glass-ferrite-silver-magnetic metal composite shell has a survival rate of 66.7% at 33 MPa; the optimized electromagnetic wave reflection loss is -5.3 dB, and no effective absorption bandwidth is observed; the electromagnetic shielding effectiveness is 0.8-1.2 dB.

[0111] Comparative Example 2

[0112] A method for preparing a microwave absorbing agent, the preparation process of which is the same as in Example 1, except that the treatment solution A does not contain cobalt nitrate and ferric nitrate, and the content of silver nitrate is 6.2g.

[0113] In this comparative example, the ferrite in the intermediate layer was replaced with an equal mass of metallic silver, resulting in hollow microspheres with a glass-silver-magnetic metallic composite shell with a density of 0.78 g / cm³. 3 The diameter of the core cavity is 43 micrometers; the mass fractions of glass, magnetic metal, and silver are 39.5%, 47.5%, and 13%, respectively.

[0114] The hollow microsphere with a glass-ferrite-silver-magnetic metal composite shell has a survival rate of 73.5% at 33 MPa; the optimized electromagnetic wave reflection loss is -45.3 dB, the effective absorption bandwidth is 1.9 GHz, and the electromagnetic shielding effectiveness is 60-71 dB.

[0115] Comparative Example 3

[0116] A method for preparing a microwave absorbing agent, the preparation process of which is the same as in Example 1, except that the content of silver nitrate in the treatment solution A is 1g.

[0117] In this embodiment, the ferrite in the intermediate layer is replaced with an equal mass of metallic silver, resulting in hollow microspheres with a glass-silver-magnetic metal composite shell having a density of 0.72 g / cm³. 3The diameter of the core cavity is 43 micrometers; the mass fractions of glass, magnetic metal, ferrite, and silver are 44%, 49.4%, 4.2%, and 2.4%, respectively.

[0118] The hollow microsphere with a glass-ferrite-silver-magnetic metal composite shell has a survival rate of 75.9% at 33 MPa; the optimized electromagnetic wave reflection loss is -42.7 dB, the effective absorption bandwidth is 2.6 GHz, and the electromagnetic shielding effectiveness is 56-65 dB.

[0119] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A microwave absorbing agent, characterized in that, The microwave absorber is a composite hollow microsphere. The structure of the composite hollow microsphere includes a hollow cavity and a glass sphere shell, a ferrite shell and a magnetic metal shell arranged sequentially from the inside to the outside of the hollow cavity. The ferrite shell is composed of ferrite and metallic silver doped in the ferrite, and at least a portion of the metallic silver is located at the interface between the ferrite shell and the magnetic metal shell.

2. The microwave absorbing agent according to claim 1, characterized in that, The metallic silver at the interface is exposed on the outer surface of the ferrite shell and comes into contact with the magnetic metal shell.

3. The microwave absorbing agent according to claim 1, characterized in that, The magnetic metal shell is made of an alloy of one, two, or three of the following: cobalt, nickel, and iron.

4. The microwave absorbing agent according to claim 1, characterized in that, The apparent density of the composite hollow microspheres is 0.55-1.25 g / cm³. 3 ; and / or The diameter of the hollow cavity is 10-70 micrometers; and / or The composite hollow microspheres, by mass percentage, comprise: 35-55% glass sphere shell, 5-20% ferrite, 3-15% metallic silver, and 20-50% magnetic metal shell.

5. The microwave absorbing agent according to claim 4, characterized in that, The ferrite shell contains 40-85% ferrite and 15-60% metallic silver by mass percentage.

6. The method for preparing the microwave absorbing agent according to any one of claims 1-5, characterized in that, Includes the following steps: Glass hollow microspheres were dispersed in an aqueous solution containing a soluble salt of a metal that forms ferrite and a soluble silver salt. After mixing, drying, and heat treatment, intermediate A hollow microspheres were obtained. The hollow microspheres of intermediate A were dispersed in an aqueous solution of inorganic acid and stirred to obtain hollow microspheres of intermediate B. The hollow microspheres of intermediate B were dispersed in an aqueous solution containing a soluble salt of magnetic metal. After stirring and reacting, the mixture was filtered and dried to obtain the microwave absorbing agent.

7. The preparation method according to claim 6, characterized in that, In the process of preparing hollow microspheres of intermediate A The dispersion concentration of the hollow glass microspheres in the aqueous solution is 0.1-0.4 g / mL; and / or The aqueous solution also contains water-soluble organic matter selected from at least one of sucrose, starch, citric acid, chitosan, and cellulose, with a concentration of 200-400 g / L; and / or In the aqueous solution, the concentration of the soluble silver salt is 60-120 g / L, and the concentration of the soluble salt of the metal forming the ferrite is 300-500 g / L; and / or The heat treatment is carried out in an air atmosphere at a temperature of 500-700℃ for 0.5-2 hours.

8. The preparation method according to claim 6, characterized in that, In the process of preparing intermediate B hollow microspheres The dispersion concentration of the hollow microspheres in intermediate A in an aqueous solution of inorganic acid is 20-60 g / L; and / or The concentration of the inorganic acid in the aqueous solution is 0.05-0.2 mol / L; and / or The stirring temperature is 10-60℃ and the stirring time is 10-40 min.

9. The preparation method according to claim 6, characterized in that, The dispersion concentration of the hollow microspheres in intermediate B in an aqueous solution containing a soluble salt of a magnetic metal is 0.005-0.016 g / mL; and / or In the aqueous solution containing the soluble salt of the magnetic metal, the concentration of the soluble salt of the magnetic metal is 15-80 g / L; and / or The aqueous solution containing the soluble salt of the magnetic metal also contains a stabilizer, a reducing agent, and a pH adjuster; and / or The stirring reaction is carried out at a temperature of 60-85℃ for 20-60 minutes.

10. The application of the microwave absorbing agent as described in any one of claims 1-5 in microwave absorption or shielding.

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