A core-shell structure composite microsphere microwave absorber and its preparation method and application

Abstract

The present invention discloses a core-shell structure composite microsphere microwave absorber, which comprises a core structure and a shell structure. Among them, the core structure is a silica microsphere; the shell layer is a carbon-metal composite layer coated on the surface of the silica microsphere; the carbon-metal composite layer is a heterogeneous composite structure, in which carbon is the continuous phase, the metal is dispersed in the continuous phase, and a heterogeneous interface is formed between the carbon and the metal. The nano-silica particle core in the core-shell composite microsphere has a supporting and wave-transmitting effect, while the outer magnetic material-carbon heterogeneous spherical shell has magnetic, electrical conductance and dielectric properties. The present invention also discloses a preparation method and application of the microwave absorber.

Description

Technical Field

[0001] The present invention relates to the field of functional materials. More specifically, it relates to a core-shell structured composite microsphere microwave absorber and its preparation method and application. Background Art

[0002] With the development of society and the progress of science and technology, electromagnetic waves are increasingly widely used in fields such as communication, broadcasting, detection, and radar detection. While bringing great convenience to people's production and life, this has also caused serious electromagnetic wave pollution problems. To control electromagnetic wave pollution, electromagnetic wave absorption and shielding materials are usually required. For such materials, compared with reflecting the incident electromagnetic waves to shield and protect the target, effectively dissipating the incident electromagnetic waves through appropriate absorption loss mechanisms can avoid secondary reflection wave pollution, which is a more efficient and environmentally friendly electromagnetic wave control method. To effectively achieve the dissipation of electromagnetic waves, microwave absorbers with multiple different loss mechanisms are usually compounded to effectively regulate the overall electromagnetic matching and loss capabilities of the material. The compounding of electromagnetic wave absorbers can be achieved by directly mixing different microwave absorbers or assembling micro-nano microwave absorbers into heterogeneous composite structures. Compared with the former, the latter is superior in realizing the micro-nano scale mixing of heterogeneous microwave absorbers, introducing heterogeneous interfaces, improving the mixing uniformity, and enhancing the application convenience of the composite structure, and is an important focus of current research and development work.

[0003] Constructing a core-shell structure or hetero-doping is two common methods to form a composite structure. Integrating multiple functional components within the same microstructure can endow the composite structure with more excellent physical and chemical properties that even the individual components do not possess. Taking the core-shell structured microwave absorber as an example, wrapping a core material with high conductivity and high loss ability with a magnetic material shell with low conductivity can effectively solve the problem of synergistically optimizing impedance matching and loss ability. For nano-scale active shell assembly units, the formation of the core-shell structure can also effectively avoid the agglomeration of nano-assembly units, improve their dispersibility, and the uniform distribution problem during the use as fillers. Currently, more attention has been paid to the material selection and shape of the inner core and spherical shell of the core-shell structured microwave absorber. The materials of the core and shell are mostly single-component electromagnetic functional materials, while less attention has been paid to the microscopic composite of heterogeneous components inside the spherical shell and the combination with the composite between the spherical shell and the inner core. If the core-shell structure is combined with hetero-material doping and compounding, in addition to constructing the core-shell structure, more abundant interfaces can be generated inside the spherical shell, increasing the interface scattering and interface polarization effects of the microwave absorber on electromagnetic waves and enhancing the attenuation ability. Summary of the Invention

[0004] The first object of the present invention is to provide a core-shell structure composite microsphere absorber. The nano-silicon dioxide particle core in the core-shell composite microsphere has supporting and wave-transmitting functions, while the outer magnetic material-carbon heterogeneous spherical shell has magnetic, conductive and dielectric properties. When used as electromagnetic functional fillers, the core and shell work together to have the following advantages: first, the dispersibility of the outer spherical shell component units can be improved through the supporting and dispersing effect of the core material; second, the density of the silica core is lower than that of traditional electromagnetic functional materials, which can reduce the density of the microspheres; third, the electromagnetic wave loss network can be formed through the loss effect of the spherical shell material and the overlap between the microspheres to enhance the electromagnetic wave absorption capacity.

[0005] The second object of the present invention is to provide a method for preparing a core-shell structure composite microsphere absorber.

[0006] The third object of the present invention is to provide an application of a core-shell structure composite microsphere absorber.

[0007] In order to achieve the above first object, the present invention adopts the following technical scheme:

[0008] A core-shell structure composite microsphere absorber, comprising a core structure and a shell structure, wherein the core structure is a silica microsphere; the shell layer is a carbon-metal composite layer coated on the surface of the silica microsphere;

[0009] The carbon-metal composite layer is a heterogeneous composite structure, wherein carbon is a continuous phase, metal is dispersed in the continuous phase, and a heterogeneous interface is formed between the carbon and the metal.

[0010] Further, in the carbon-metal composite layer, the molar ratio of carbon to metal is 1:10-20:1. Exemplarily, in the carbon-metal composite layer, the molar ratio of carbon to metal includes but is not limited to 1:1-20:1, 1:1-4:1, 1.8:1-20:1, 10:1-19:1, etc. Under this condition, the prepared absorber has better absorbing performance.

[0011] Furthermore, in the shell layer, the metal is converted from its corresponding water-soluble metal salt.

[0012] Furthermore, the metal includes magnetic metal.

[0013] Furthermore, the metal also includes non-magnetic metal.

[0014] Furthermore, the metal exists in the form of a single substance, an alloy or a mixture thereof. Exemplarily, the metal is selected from one or more of cobalt, iron, silver and copper.

[0015] Further, the carbon is a homogeneous carbon obtained by carbonizing water-soluble organic molecules. Exemplarily, the water-soluble organic molecules include, but are not limited to, those selected from starch, glucose, citric acid, sucrose, chitosan, cellulose, fructose, etc.

[0016] Further, the density of the composite microsphere absorbent is 1.5 - 3.5 g / cm 3 ; in the composite microsphere absorbent, the particle size of the silica microspheres is 2 - 100 μm, and the thickness of the carbon-metal composite layer is 0.05 - 2 μm, preferably 0.2 - 1.2 μm. Exemplarily, the thickness of the carbon-metal composite layer is 0.9 - 2 μm, 1.2 - 2 μm, 1.4 - 2 μm, etc.

[0017] To achieve the above second object, the present invention adopts the following technical solutions:

[0018] The preparation method of the core-shell structure composite microsphere absorbent as described above includes the following steps:

[0019] Mix silica sol, organic carbon source, and metal salt evenly to obtain a mixed solution;

[0020] Atomize and dry the mixed solution to obtain spherical intermediates;

[0021] Heat-treat the intermediates in a reducing atmosphere or an inert atmosphere to obtain the core-shell structure composite microsphere absorbent;

[0022] The organic carbon source is selected from one or more of starch, glucose, sucrose, fructose, citric acid, chitosan, dopamine, and cellulose.

[0023] Further, the solid content of the silica sol is 15 - 30 wt%, and in the silica sol, the particle size of the particles is 3 - 100 nm, preferably 10 - 50 nm.

[0024] Further, the reducing atmosphere is hydrogen or nitrogen.

[0025] Further, the mass ratio of the silica sol, organic carbon source, and metal salt is 100:(10 - 50):(6 - 50).

[0026] Further, the conditions for atomizing and drying are: the inlet temperature is 180 - 450 °C, and the drying atmosphere is air.

[0027] Further, the heat treatment temperature is 500 - 1500 °C, and the heat preservation time is 0.5 - 12 h. Exemplarily, the heat treatment temperature includes, but is not limited to, 600 - 800 °C, 650 - 800 °C, 700 - 800 °C, 600 - 750 °C, 600 - 700 °C, 650 - 700 °C, etc.

[0028] In order to achieve the third object, the present invention provides the use of the core-shell structure composite microsphere absorber as described in the first object in the preparation of an absorbing material.

[0029] The beneficial effects of the present invention are as follows:

[0030] The core-shell structure composite microsphere wave absorber provided by the present invention can ensure the stability of the structure and reduce the density through the support effect of the internal silicon dioxide core.

[0031] The core-shell structure composite microsphere absorber provided by the present invention can simultaneously realize the assembly of microscopic nanoparticles and the micronization of macroscopic size, and can prevent the agglomeration of electromagnetic functional carbon-metal composite materials through the physical dispersion and spatial barrier of the shell layer by silicon dioxide.

[0032] The preparation method of the core-shell structure composite microsphere absorber provided by the present invention is convenient and quick, and the core-shell composite structure can be directly obtained by spray drying-heat treatment; in addition, the loading amount of metal element, alloy, metal oxide or their combination, shell thickness or density and composition can be adjusted by controlling the metal salt feeding amount and the precursor calcination conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0034] Figure 1 A schematic diagram showing the process of preparing the core-shell structure composite microsphere absorber of the present invention.

[0035] Figure 2 The SEM image of the core-shell structure composite microsphere absorber prepared in Example 3 is shown.

[0036] Figure 3 The XRD patterns of the porous core-shell composite functional microspheres prepared in Comparative Example 1 (curve a) and Example 3 (curve b) are shown. DETAILED DESCRIPTION

[0037] In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with preferred embodiments and accompanying drawings. Similar components in the accompanying drawings are represented by the same reference numerals. It should be understood by those skilled in the art that the content specifically described below is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0038] Example 1

[0039] 80 g of acidic silica sol with a solid content of 20% (the particle size of the sol particles is 30 nm) was placed in a glass beaker, and 0.5 g of PVP and 9 g of starch were added successively, and magnetically stirred at room temperature until a uniform suspension was obtained. Then, 15 g of nickel nitrate and 16 g of cobalt nitrate were weighed into the suspension mixture, and magnetically stirred at room temperature until the metal salts were completely dissolved to obtain a mixed solution. The prepared mixed solution was subjected to atomization drying treatment using a pneumatic atomization drying device with an inlet temperature of 250 °C and a drying atmosphere of air to obtain spherical intermediates. Then, the obtained microsphere precursors were calcined in a nitrogen atmosphere, heated to 750 °C at a heating rate of 10 °C / min, and held for 2 h. A core-shell structure composite microsphere microwave absorber was obtained. The average particle size of the composite microspheres is 21 μm, the inner core component is SiO2, the outer shell component is carbon and cobalt-nickel alloy, and the thickness is 0.65 μm; the molar ratio of carbon to metal is 1:1.

[0040] Example 2-10

[0041] The specific implementation steps were carried out according to Example 1, and the specific different conditions are shown in Table 1:

[0042] Table 1 Variation table of preparation conditions for core-shell structure composite microsphere microwave absorbers

[0043]

[0044] Performance test:

[0045] The electromagnetic properties of the products prepared in the above examples were tested. The test method was as follows: The hollow composite microspheres (microwave absorbing materials) prepared in each example were mixed with paraffin, and the mixing mass ratio of the two was 20%-70% (exemplary mixing mass ratios include but are not limited to preferably 35%-50%, 40%-50%) to prepare coaxial rings with an inner diameter of 3 mm, an outer diameter of 7 mm, and a thickness of 2 mm. Then, the electromagnetic parameters were tested by a vector network analyzer to analyze their electromagnetic properties. The results are shown in Table 2 below.

[0046] Table 2 Comparison of electromagnetic properties of example samples under different process conditions

[0047]

[0048] Obviously, the above examples of the present invention are merely examples for clearly explaining the present invention, and are not intended to limit the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation manners here. Any obvious changes or modifications derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A core-shell structured composite microsphere microwave absorber, characterized in that It includes a core structure and a shell structure. Among them, the core structure is a silica microsphere; the shell is a carbon-metal composite layer coated on the surface of the silica microsphere; The carbon-metal composite layer is a heterogeneous composite structure. Among them, carbon is the continuous phase, the metal is dispersed in the continuous phase, and a heterogeneous interface is formed between carbon and the metal; In the carbon-metal composite layer, the molar ratio of carbon to metal is 1:10 - 20:1; The metal contains magnetic metal; The metal exists in the form of a single substance, an alloy or a mixture thereof; The carbon is a homogeneous carbon obtained by carbonizing water-soluble organic molecules.

2. The core-shell structured composite microsphere microwave absorber according to claim 1, characterized in that The density of the composite microsphere microwave absorber is 1.5 - 3.5 g / cm 3 ; in the composite microsphere microwave absorber, the particle size of the silica microspheres is 2 - 100 μm, and the thickness of the carbon-metal composite layer is 0.05 - 2 μm.

3. A preparation method of the core-shell structured composite microsphere microwave absorber according to any one of claims 1-2, characterized in that It includes the following steps: Mix silica sol, organic carbon source and metal salt evenly to obtain a mixed solution; Atomize and dry the mixed solution to obtain a spherical intermediate; Heat-treat the intermediate in a reducing atmosphere or an inert atmosphere to obtain the core-shell structure composite microsphere absorbent; The organic carbon source is selected from one or more of starch, glucose, sucrose, fructose, citric acid, chitosan, dopamine, cellulose; The mass ratio of the silica sol, organic carbon source and metal salt is 100:(10 - 50):(6 - 50); The heat treatment temperature is 500 - 1500 °C, and the holding time is 0.5 - 12 h.

4. The preparation method according to claim 3, characterized in that The solid content of the silica sol is 15 - 30 wt%, and in the silica sol, the particle size is 3 - 100 nm.

5. The preparation method according to claim 3, characterized in that In the silica sol, the particle size is 10 - 50 nm.

6. The preparation method according to claim 3, characterized in that The conditions for atomizing and drying are: the inlet temperature is 180 - 450 °C, and the drying atmosphere is air.

7. Application of the core-shell structured composite microsphere microwave absorber according to any one of claims 1-2 in the preparation of microwave absorbing materials.

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