A magnetic metal-carbon composite microsphere absorber with a hollow structure and a preparation method thereof

Abstract

The present invention discloses a magnetic metal-carbon composite microsphere absorber with a hollow structure. The absorber comprises a hollow core and a spherical shell. The hollow core is an air cavity, and the shell is composed of a continuous carbon phase and a dispersed metal-carbon composite particle structure. The internal hollow cavity reduces the absorber's density and simultaneously achieves structural control of microscopic and nanoparticles while minimizing their macroscopic size, preventing nanoparticle aggregation and facilitating the absorber's use. The present invention also discloses a method for preparing the absorber.

Description

Technical Field

[0001] The present invention relates to the field of functional particle materials, and more specifically to a magnetic metal-carbon composite microsphere absorber with a hollow structure and a preparation method thereof. Background Art

[0002] The rapid development of microwave technology has created enormous demand and opportunities for the research and application of absorbing materials. Absorbers are the core and key of absorbing materials, so their research and development have attracted considerable attention, and the design and controllable preparation of new absorbers are in full swing. To meet increasingly stringent performance requirements, researchers are increasingly focusing on heterogeneous composite absorbers with dual (or multiple) electromagnetic wave loss mechanisms. Among them, composite materials of magnetic metals and carbon have attracted increasing attention in the design of high-performance electromagnetic wave absorbers (absorbers) due to their easily tailored magnetic properties, conductive (dielectric) properties, and macrostructure. In this type of composite absorber, magnetic metals have high saturation magnetization and conductivity, and can dissipate the energy of incident electromagnetic waves through magnetic loss and leakage conduction loss. Carbon materials, on the other hand, can significantly control dielectric and electrical conductivity depending on their degree of graphitization and microstructure, making it possible to achieve optimized impedance matching and dielectric and leakage conduction losses. More importantly, the combination of magnetic metals and carbon materials at the microscopic scale can also introduce a large number of interfaces into the composite material system. These interfaces have very different electrical and dielectric properties. On the one hand, this can realize the scattering and reflection of the incident electromagnetic waves, increase the transmission path of the electromagnetic waves, and help to give full play to the loss capacity of the absorber; on the other hand, it can realize the accumulation and relaxation of space charges in the interface area in the alternating electromagnetic field, thereby losing electromagnetic wave energy through polarization relaxation.

[0003] Given the performance advantages and vast scope for structural and compositional manipulation of magnetic metal-carbon composites, researchers and developers have developed a variety of magnetic metal-carbon composite structural materials using diverse methods. The metals used for these composites are primarily iron, cobalt, nickel, and their alloys; however, the range of carbon materials available is even broader, including graphene, carbon fibers, carbon nanotubes, various types of carbon black, and porous carbon. Furthermore, composites of magnetic metals and carbon can be formed in various ways, including supported, adsorbed, core-shell, and embedded. Furthermore, to meet the requirements for lightweight absorbers, various hollow structures have been developed. However, the preparation and performance control of magnetic metal-carbon composites currently face challenges, including complex and time-consuming molding processes, low production efficiency, and difficulties in designing and manipulating the material's internal structure (e.g., localized variations in the degree of graphitization and interface morphology) and properties. These challenges hinder the mass production and application development of these absorbers. Summary of the Invention

[0004] The first object of the present invention is to provide a magnetic metal-carbon composite microsphere absorber with a hollow structure.

[0005] Another object of the present invention is to provide a method for preparing a magnetic metal-carbon composite microsphere absorber having a hollow structure.

[0006] In order to achieve the above first object, the present invention adopts the following technical solutions:

[0007] A magnetic metal-carbon composite microsphere absorber with a hollow structure consists of a hollow core and a spherical shell; wherein the hollow core is an air cavity; the structure of the spherical shell consists of carbon as a continuous phase and metal-carbon composite particles as a dispersed phase.

[0008] Furthermore, the particle size of the absorber is 10-70 μm and the density is 0.5-2.0 g / cm 3 .

[0009] Furthermore, in the absorber, the thickness of the carbon-metal composite shell is 0.2-2 μm, wherein the molar ratio of carbon to metal is 2:1-15:1.

[0010] Furthermore, the metal is selected from one or more of metal elements and alloys.

[0011] Furthermore, the metal is a magnetic metal, preferably including but not limited to iron, cobalt, nickel and alloys thereof.

[0012] Furthermore, the metal is converted from initially added magnetic metal nanoparticles, or initially added magnetic metal oxide nanoparticles through reduction.

[0013] Furthermore, the carbon in the continuous phase is obtained by carbonizing water-soluble organic molecules; and the carbon in the metal-carbon composite particles is converted by heat treatment of the phenolic coating layer.

[0014] In order to achieve the above second purpose, the present invention adopts the following technical solutions:

[0015] A method for preparing a magnetic metal-carbon composite microsphere absorber having a hollow structure comprises the following steps:

[0016] (1) dispersing magnetic metal or its oxide nanoparticles in a reaction solution, heating and stirring the solution to obtain phenolic resin-coated nanoparticles;

[0017] (2) mixing an organic carbon source, water, and the phenolic resin-coated nanoparticles obtained in step (1), and stirring the mixture to obtain a spray slurry;

[0018] (3) atomizing and drying the slurry to obtain a spherical intermediate;

[0019] (4) heat-treating the intermediate in a reducing or inert atmosphere to obtain the magnetic metal-carbon composite microsphere absorber having a hollow structure.

[0020] Furthermore, in step (1), the ratio of the magnetic metal or its oxide nanoparticles to the reaction solution is 3 g:3000 mL.

[0021] Furthermore, the mass ratio of the magnetic metal or its oxide nanoparticles to the organic carbon source and water in the slurry is 1-6:5-30:10-30.

[0022] Furthermore, the organic carbon source is selected from one or more of water-soluble glucose, sucrose, starch, citric acid, and dopamine.

[0023] Furthermore, the conditions for the atomization drying are: an inlet temperature of 180-400° C., and the drying atmosphere is air.

[0024] Furthermore, the heat treatment temperature is 700-1000° C., and the holding time is 1-20 hours.

[0025] Furthermore, the reaction solution is prepared by the following method:

[0026] Anhydrous ethanol and deionized water were uniformly mixed in a mass ratio of 4:1, and then 0.6% by mass (equivalent to the mass percentage of the mixed solution) of resorcinol, 2.5% by mass (equivalent to the mass percentage of the mixed solution) of formaldehyde solution (37 wt.%), and 4% by mass (equivalent to the mass percentage of the mixed solution) of concentrated ammonia water (25 wt.%) were added to the mixed solution, and the mixture was stirred and mixed to obtain the reaction solution.

[0027] Furthermore, the stirring and mixing is carried out at a temperature of 40° C. and for a time of 10-20 hours.

[0028] The beneficial effects of the present invention are as follows:

[0029] The hollow magnetic metal-carbon composite microsphere absorber provided by the present invention can reduce the density of the absorber through the internal hollow cavity; and the absorber can simultaneously achieve structural control of microscopic nanoparticles and micronization of macroscopic size, thereby preventing the agglomeration of nanoparticles and facilitating the use of the absorber.

[0030] In the preparation method of the absorber provided by the present invention, the hollow structure molding method is convenient and fast, and the hollow composite structure can be efficiently obtained directly through spray drying and heat treatment. In addition, the composition and performance of the hollow microsphere absorber can be adjusted by controlling the type and content of the metal particles and the different graphitization degrees of the carbon component. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0032] Figure 1 Schematic diagram showing the preparation process of heterogeneous composite hollow microsphere absorbers with hierarchical cavity structure.

[0033] Figure 2 The scanning electron microscope (SEM) image of the core-shell structure composite microsphere absorber prepared in Example 3 (Co) is shown.

[0034] Figure 3 The scanning electron microscope (SEM) image of the core-shell structure composite microsphere absorber prepared in Example 3 is shown.

[0035] Figure 4 The transmission electron microscope (TEM) image of the core-shell structure composite microsphere absorber prepared in Example 3 is shown.

[0036] Figure 5 The X-ray diffraction (XRD) pattern of the core-shell structure composite microsphere absorber prepared in Example 3 is 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 following detailed description is illustrative rather than restrictive and should not be used to limit the scope of protection of the present invention.

[0038] Example 1

[0039] 2400 mL of anhydrous ethanol and 600 mL of deionized water were mixed. 15 g of resorcinol, 62.5 g of formaldehyde solution (37 wt.%), and 100 g of concentrated ammonia (25 wt.%) were added to the mixture. After stirring, 3 g of ferroferric oxide nanoparticles (50 nm in diameter) were added and the mixture was stirred at 40°C for 12 hours to produce phenolic resin-coated nanoparticles. 8 g of soluble starch and 2 g of sucrose were added to 20 g of water and stirred thoroughly to dissolve. The phenolic resin-coated nanoparticles were then added while stirring to produce a spray slurry. The prepared slurry was atomized and dried using an airflow atomization drying apparatus with an inlet temperature of 220°C and an outlet temperature of 120°C in an air drying atmosphere to produce a spherical precursor. The resulting precursor was then heat-treated at 750°C for 3 hours in a hydrogen / argon (5% hydrogen) mixed gas atmosphere. A magnetic metal-carbon composite microsphere absorber with a hollow structure was obtained. The molar ratio of carbon to metal in the hollow microsphere absorber was 8:1, and the density was 0.93 g / cm 3 , spherical shell thickness is 950nm and average particle size is 17μm.

[0040] Example 2

[0041] 2400 mL of anhydrous ethanol and 600 mL of deionized water were mixed. 15 g of resorcinol, 62.5 g of formaldehyde solution (37 wt.%), and 100 g of concentrated ammonia (25 wt.%) were added to the mixture and stirred thoroughly. After stirring, 3 g of nickel oxide nanoparticles (90 nm in diameter) were added and the mixture was stirred at 40°C for 15 hours to produce phenolic resin-coated nanoparticles. 12 g of sucrose was added to 20 g of water and stirred thoroughly to dissolve. The phenolic resin-coated nanoparticles were then added while stirring to produce a spray slurry. The prepared slurry was then atomized and dried using an airflow atomization drying apparatus with an inlet temperature of 260°C and an outlet temperature of 130°C in an air drying atmosphere to produce a spherical precursor. The resulting precursor was then heat-treated at 850°C for 5 hours under a nitrogen atmosphere. A magnetic metal-carbon composite microsphere absorber with a hollow structure was obtained. The molar ratio of carbon to metal in the hollow microsphere absorber was 9:1, and the density was 1.03 g / cm 3 , spherical shell thickness 1120nm, average particle size 21μm.

[0042] Example 3

[0043] 2400 mL of anhydrous ethanol and 600 mL of deionized water were mixed. 15 g of resorcinol, 62.5 g of formaldehyde solution (37 wt.%), and 100 g of concentrated ammonia (25 wt.%) were added to the mixture and stirred thoroughly. After stirring, 3 g of cobalt nanoparticles (80 nm in diameter) were added and the mixture was stirred at 40°C for 15 hours to produce phenolic resin-coated nanoparticles. 5 g of sucrose and 5 g of citric acid were added to 20 g of water and stirred thoroughly to dissolve. The phenolic resin-coated nanoparticles were then added while stirring to produce a spray slurry. The prepared slurry was atomized and dried using an airflow atomization drying apparatus with an inlet temperature of 290°C and an outlet temperature of 150°C in an air drying atmosphere to produce a spherical precursor. The resulting precursor was then heat-treated at 700°C for 5 hours under an argon atmosphere. A magnetic metal-carbon composite microsphere absorber with a hollow structure was obtained. The molar ratio of carbon to metal in the hollow microsphere absorber was 5.5:1, and the density was 1.41 g / cm 3 , spherical shell thickness 1690nm, average particle size 15μm.

[0044] Example 4

[0045] 2400 mL of anhydrous ethanol and 600 mL of deionized water were mixed. 15 g of resorcinol, 62.5 g of formaldehyde solution (37 wt.%), and 100 g of concentrated ammonia (25 wt.%) were added to the mixture. After stirring, 3 g of ferric oxide nanoparticles (55 nm in diameter) were added and the mixture was stirred at 40°C for 10 h to produce phenolic resin-coated nanoparticles. 2 g of starch, 1.5 g of sucrose, and 1 g of citric acid were added to 20 g of water and thoroughly stirred to dissolve. The phenolic resin-coated nanoparticles were then added while stirring to produce a spray slurry. The prepared slurry was then atomized and dried using an airflow atomization drying apparatus with an inlet temperature of 230°C and an outlet temperature of 120°C in an air drying atmosphere to produce a spherical precursor. The resulting precursor was then heat-treated at 800°C for 8 h in a hydrogen / argon (5% hydrogen) mixed gas atmosphere. A magnetic metal-carbon composite microsphere absorber with a hollow structure was obtained. The molar ratio of carbon to metal in the hollow microsphere absorber was 3.5:1, and the density was 0.63 g / cm 3 , spherical shell thickness 380nm, average particle size 19μm.

[0046] Example 5

[0047] 2400 mL of anhydrous ethanol and 600 mL of deionized water were mixed. 15 g of resorcinol, 62.5 g of formaldehyde solution (37 wt.%), and 100 g of concentrated ammonia (25 wt.%) were added to the mixture and stirred thoroughly. Then, 3 g of cobalt ferrite nanoparticles (95 nm in diameter) were added and stirred at 40°C for 10 h to produce phenolic resin-coated nanoparticles. 3 g of starch and 10 g of sucrose were added to 20 g of water and stirred thoroughly to dissolve. The phenolic resin-coated nanoparticles were then added while stirring to produce a spray slurry. The prepared slurry was atomized and dried using an airflow atomization drying apparatus with an inlet temperature of 240°C and an outlet temperature of 125°C in an air drying atmosphere to produce a spherical precursor. The resulting precursor was then heat-treated at 900°C for 6 h under an argon atmosphere. A magnetic metal-carbon composite microsphere absorber with a hollow structure was obtained. The molar ratio of carbon to metal in the hollow microsphere absorber was 9.6:1, and the density was 1.67 g / cm 3 , spherical shell thickness 1820nm, average particle size 14μm.

[0048] Example 6

[0049] 2400mL of anhydrous ethanol and 600mL of deionized water were mixed. 15g of resorcinol, 62.5g of formaldehyde solution (37wt%), and 100g of concentrated ammonia (25wt%) were added to the mixture. After stirring, 3g of nickel ferrite nanoparticles (90nm in diameter) were added and the mixture was stirred at 40°C for 14 hours to produce phenolic resin-coated nanoparticles. 5g of starch and 11g of sucrose were added to 20g of water and stirred thoroughly to dissolve. The phenolic resin-coated nanoparticles were then added while stirring to produce a spray slurry. The prepared slurry was atomized and dried using an airflow atomization drying apparatus with an inlet temperature of 210°C and an outlet temperature of 110°C in an air drying atmosphere to produce a spherical precursor. The resulting precursor was then heat-treated at 950°C for 7 hours under a nitrogen atmosphere. A magnetic metal-carbon composite microsphere absorber with a hollow structure was obtained. The molar ratio of carbon to metal in the hollow microsphere absorber was 12.3:1, and the density was 1.82 g / cm 3 , spherical shell thickness 1950nm, average particle size 13μm.

[0050] Example 7

[0051] 2400 mL of anhydrous ethanol and 600 mL of deionized water were mixed. 15 g of resorcinol, 62.5 g of formaldehyde solution (37 wt.%), and 100 g of concentrated ammonia (25 wt.%) were added to the mixture and stirred thoroughly. After stirring, 3 g of cobalt oxide nanoparticles (85 nm in diameter) were added and the mixture was stirred at 40°C for 17 hours to produce phenolic resin-coated nanoparticles. 8 g of starch and 12 g of sucrose were added to 20 g of water and stirred thoroughly to dissolve. The phenolic resin-coated nanoparticles were then added while stirring to produce a spray slurry. The prepared slurry was then atomized and dried using an airflow atomization drying apparatus with an inlet temperature of 320°C and an outlet temperature of 170°C in an air drying atmosphere to produce a spherical precursor. The resulting precursor was then heat-treated at 900°C for 5 hours under a nitrogen atmosphere. A magnetic metal-carbon composite microsphere absorber with a hollow structure was obtained. The molar ratio of carbon to metal in the hollow microsphere absorber was 14.4:1, and the density was 1.32 g / cm 3 , spherical shell thickness 1550nm, average particle size 11μm.

[0052] Example 8

[0053] Mix 2400mL of anhydrous ethanol and 600mL of deionized water. Add 15g of resorcinol, 62.5g of formaldehyde solution (37wt.%), and 100g of concentrated ammonia (25wt.%) to the mixture. Stir and mix thoroughly, then add 3g of iron nanoparticles (particle size 45nm). Stir and react at 40°C for 17h to obtain phenolic resin-coated nanoparticles. Add 5g of starch, 5g of sucrose, and 5g of citric acid to 35g of water and stir thoroughly to dissolve. Then, add the above-mentioned phenolic resin-coated nanoparticles while stirring to obtain a spray slurry. The prepared slurry is atomized and dried using an airflow atomization drying device with an inlet temperature of 350°C and an outlet temperature of 190°C in an air drying atmosphere to obtain a spherical precursor. The obtained precursor is then heat-treated at 800°C for 1h under a nitrogen atmosphere. A magnetic metal-carbon composite microsphere absorber with a hollow structure was obtained. The molar ratio of carbon to metal in the hollow microsphere absorber was 7.9:1, and the density was 1.02 g / cm 3 , spherical shell thickness 1040nm, average particle size 10μm.

[0054] Example 9

[0055] 2400 mL of anhydrous ethanol and 600 mL of deionized water were mixed. 15 g of resorcinol, 62.5 g of formaldehyde solution (37 wt.%), and 100 g of concentrated ammonia (25 wt.%) were added to the mixture and stirred thoroughly. After stirring, 3 g of nickel nanoparticles (55 nm in diameter) were added and the mixture was stirred at 40°C for 15 hours to produce phenolic resin-coated nanoparticles. 4 g of starch, 6 g of sucrose, and 7 g of citric acid were added to 25 g of water and stirred thoroughly to dissolve. The phenolic resin-coated nanoparticles were then added while stirring to produce a spray slurry. The prepared slurry was atomized and dried using an airflow atomization drying apparatus with an inlet temperature of 250°C and an outlet temperature of 130°C in an air atmosphere to produce a spherical precursor. The resulting precursor was then heat-treated at 700°C for 1 hour under a nitrogen atmosphere. A magnetic metal-carbon composite microsphere absorber with a hollow structure was obtained. The molar ratio of carbon to metal in the hollow microsphere absorber was 8.8:1, and the density was 1.32 g / cm 3 , spherical shell thickness 1430nm, average particle size 9μm.

[0056] Performance testing:

[0057] The electromagnetic properties of the products prepared in the above examples were tested. The testing method involved mixing the hollow composite microspheres (absorbing materials) prepared in each example with paraffin wax at a mass ratio of 30% to 60% to form coaxial rings with an inner diameter of 3 mm, an outer diameter of 7 mm, and a thickness of 2 mm. The electromagnetic parameters and performance were then analyzed using a vector network analyzer. The results are shown in Table 1.

[0058] Table 1 Performance parameters of samples in various embodiments

[0059]

[0060] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A magnetic metal-carbon composite microsphere absorber with a hollow structure, characterized in that: It consists of a hollow core and a spherical shell; wherein the hollow core is an air cavity; the structure of the spherical shell is composed of a continuous phase of carbon and a dispersed phase of metal-carbon composite particles; The metal is a magnetic metal selected from iron, cobalt, nickel and alloys thereof; The particle size of the absorber is 10-70 μm and the density is 0.5-2.0 g / cm 3 ; In the absorber, the carbon-metal composite shell has a thickness of 0.2-2 μm, wherein the molar ratio of carbon to metal is 2:1-15:1; The preparation method of the wave absorbing agent comprises the following steps: (1) dispersing magnetic metal or its oxide nanoparticles in a reaction solution, heating and stirring the solution to obtain phenolic resin-coated nanoparticles; (2) mixing an organic carbon source, water, and the phenolic resin-coated nanoparticles obtained in step (1), and stirring uniformly to obtain a spray slurry, wherein the organic carbon source is selected from one or more of water-soluble glucose, sucrose, starch, citric acid, and dopamine; (3) atomizing and drying the slurry to obtain a spherical intermediate; (4) heat-treating the intermediate in a reducing or inert atmosphere to obtain the magnetic metal-carbon composite microsphere absorber having a hollow structure; The heat treatment temperature is 700-1000° C., and the heat preservation time is 1-20 hours.

2. The wave absorbing agent according to claim 1, characterized in that: The carbon in the continuous phase is obtained by carbonizing an organic carbon source; and the carbon in the metal-carbon composite particles is converted by heat treatment of the phenolic coating layer.

3. The wave absorbing agent according to claim 1, characterized in that: The mass ratio of the magnetic metal or its oxide nanoparticles to the organic carbon source and water in the slurry is 1-6:5-30:10-30.

4. The wave absorbing agent according to claim 1, characterized in that The conditions for the atomization drying are: an inlet temperature of 180-400° C., and an air drying atmosphere.

5. The wave absorbing agent according to claim 1, characterized in that: The reaction solution was prepared by the following method: Anhydrous ethanol and deionized water were mixed uniformly in a mass ratio of 4:1, and then 0.6 wt % of resorcinol, 2.5 wt % of formaldehyde solution, and 4 wt % of concentrated ammonia water were added to the mixture, and the mixture was stirred and mixed uniformly to obtain the reaction solution.

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