Ferrite-hollow glass bead composite material and preparation method thereof

Abstract

The invention relates to a ferrite-hollow glass bead composite material and a preparation method thereof, and belongs to the technical field of electromagnetic wave absorbing materials. The preparation method comprises the following steps: (1) dispersing amino-functionalized hollow glass beads, a bivalent soluble iron salt and a trivalent soluble iron salt in water, and carrying out a co-precipitation reaction under an alkaline condition; and (2) carrying out hydrothermal crystallization reaction on the reaction system after the coprecipitation reaction in the step (1) at 150-200 DEG C. Through the optimized two-step process, high-quality and complete coating of the ferrite shell layer is realized, and the product performance is remarkably improved. The preparation method disclosed by the invention does not need complex equipment, is mild in reaction condition and simple in process flow, and is suitable for industrial large-scale production.

Description

Technical Field

[0001] This invention relates to a ferrite-hollow glass microsphere composite material and its preparation method, belonging to the field of electromagnetic wave absorbing materials technology. Background Technology

[0002] With the advancement of science and technology, people's lifestyles and production methods have undergone significant changes. The use of electronic products such as mobile phones, computers, and tablets is becoming increasingly widespread, and electronic devices are indispensable in fields such as aerospace, communications, radio frequency identification, and electronic information. However, the electromagnetic radiation generated by various everyday electronic products and devices poses an increasingly serious threat to human health and environmental stability, and can also affect the normal operation of instruments and equipment and production accuracy. Therefore, developing an absorbing material capable of weakening or eliminating electromagnetic radiation is of great significance.

[0003] Microwave absorbing materials are widely used in electromagnetic interference protection fields such as communication, navigation systems, and stealth technology. To achieve effective microwave absorption performance, microwave absorbing materials must simultaneously possess good electromagnetic impedance matching capability and electromagnetic loss capability. On the other hand, considering practical applications, in addition to having a wide absorption band and frequency band and a high absorption rate, microwave absorbing materials are also required to have characteristics such as light weight, high temperature resistance, and corrosion resistance.

[0004] Currently, there are many types of microwave absorbing materials, mainly including magnetic metals, polymer-based composites, ferrites, and carbon-based materials. Ferrites, as a commonly used microwave absorbing material, have advantages such as wide bandwidth, high absorption rate, and thin matching thickness. Furthermore, due to good impedance matching, electromagnetic waves can easily enter ferrites and are rapidly attenuated through magnetic and electrical absorption, thus making ferrite materials widely used in the field of electromagnetic wave absorption. However, the high density, narrow bandwidth, and poor high-temperature resistance of ferrite materials limit their application in specific fields. Currently, the mainstream strategy is to dope them with other functional materials to address these shortcomings. Hollow glass microspheres, with their advantages of light weight, corrosion resistance, chemical stability, and good cost-effectiveness, are promising candidates, but they also suffer from low dielectric loss. Therefore, it is foreseeable that composite materials of ferrites and hollow glass microspheres will achieve excellent microwave absorption performance.

[0005] Chinese invention patent application CN101710523A, published on May 19, 2010, discloses a ferrite-coated hollow glass microsphere composite magnetic material and its preparation method. Specifically, a certain amount of hollow glass microspheres is added to an alkaline (NaOH) solution for ultrasonic cleaning. The cleaned hollow glass microspheres are then added to a reactor containing a small amount of water, heated at 25-95℃ under normal pressure with stirring, while a mixed salt solution and a mixed alkaline solution are added dropwise to the reactor. During the dropwise addition, the pH is adjusted to 9-12, and the addition is completed in 1-5 hours. After the reaction is complete, the mixture is filtered, washed with distilled water or deionized water until the pH value is near neutral, and dried at 40-80℃ to obtain a precursor. The precursor is then calcined at 700-1200℃ for 1-5 hours to obtain ferrite-coated glass microsphere composite powder.

[0006] Chinese invention patent CN113214787B, published on June 14, 2022, discloses a microwave absorbing powder material, its preparation method, and its application. The microwave absorbing powder material consists of cobalt ferrite-iron-cobalt alloy co-coated hollow glass microspheres and carbon microspheres. The preparation method includes the following steps: 1) dispersing soluble iron salt, soluble cobalt salt, hollow glass microspheres, and citric acid in water and carrying out a sol-gel reaction to obtain cobalt ferrite-coated hollow glass microspheres; 2) dispersing cobalt ferrite-coated hollow glass microspheres and glucose in water and carrying out a hydrothermal reaction to obtain a ternary composite material; 3) placing the ternary composite material in a protective atmosphere and calcining it.

[0007] Chinese invention patent CN109943018B, published on July 5, 2022, discloses microwave absorbing agents, microwave absorbing materials, and their respective preparation methods. The preparation method of the microwave absorbing agent includes: dispersing and stirring hollow glass microspheres and ferrite until a colloidal colloid is formed; drying the colloid to obtain a dried gel; heat-treating the dried gel to obtain ferrite-coated hollow glass microspheres; adding graphene oxide to the ferrite-coated hollow glass microspheres, mixing and reacting to obtain a graphene composite gel; and grinding the graphene composite gel to obtain the microwave absorbing agent.

[0008] Analysis of the existing technologies reveals that current preparation methods (such as simple physical mixing or conventional co-precipitation) are insufficient to form a complete, dense, and highly crystalline ferrite shell on the surface of hollow glass microspheres. This results in materials exhibiting poor interfacial bonding, a simplistic loss mechanism, and limited and unstable microwave absorption performance. Furthermore, existing ferrite-hollow glass microsphere composites involve complex preparation processes requiring high-temperature calcination, making them unsuitable for large-scale industrial production. Summary of the Invention

[0009] The first objective of this invention is to provide a method for preparing ferrite-hollow glass microsphere composite materials, which provides a simple method for preparing ferrite-hollow glass microsphere composite materials with strong absorption, excellent broadband absorption performance, and a wide range of microwave absorption properties.

[0010] The second objective of this invention is to provide a ferrite-hollow glass microsphere composite material, which provides a microwave absorbing material with strong absorption and excellent broadband microwave absorption performance.

[0011] To achieve the above objectives, the technical solution of the preparation method of ferrite-hollow glass microsphere composite material in this invention is as follows: A method for preparing a ferrite-hollow glass microsphere composite material includes the following steps: (1) Amino-functionalized hollow glass microspheres, divalent soluble iron salts and trivalent soluble iron salts are dispersed in water and co-precipitated under alkaline conditions; (2) The reaction system after the coprecipitation reaction in step (1) is subjected to hydrothermal crystallization reaction at 150~200℃.

[0012] The beneficial effects of the above technical solution are as follows: The preparation method of the ferrite-hollow glass microsphere composite material of the present invention is a pioneering invention. Through an optimized two-step process, the present invention achieves high-quality and complete coating of the ferrite shell, significantly improving product performance. Moreover, the preparation method of the present invention requires no complex equipment, has mild reaction conditions, and a simple process flow, making it suitable for large-scale industrial production.

[0013] As a further improvement, the molar ratio of the divalent soluble iron salt to the trivalent soluble iron salt is 1:(1.5~2.5); the mass ratio of the amino-functionalized hollow glass microspheres to the divalent soluble iron salt is 1:(0.2~0.4).

[0014] As a further improvement, the divalent soluble iron salt is FeCl2·4H2O or FeSO4·7H2O, and the trivalent soluble iron salt is FeCl3·6H2O.

[0015] As a further improvement, the temperature of the coprecipitation reaction in step (1) is 60℃~85℃, and the reaction time is 0.5h~2h.

[0016] As a further improvement, ammonia or sodium hydroxide solution is added dropwise to achieve the alkaline conditions; the pH of the alkaline conditions is 8-11.

[0017] As a further improvement, the hydrothermal crystallization reaction in step (2) takes 3 to 12 hours.

[0018] As a further improvement, the amino-functionalized hollow glass microspheres are prepared by a method mainly comprising the following steps: dispersing the hollow glass microspheres in a solvent, adding a silane coupling agent, and stirring and refluxing to react.

[0019] As a further improvement, 1.8~2.2mL of silane coupling agent is added to every 2g of the hollow glass microspheres; the silane coupling agent is γ-aminopropyltriethoxysilane.

[0020] As a further improvement, the reflux reaction temperature is 70℃~80℃, and the reaction time is 4~5h.

[0021] To achieve the above objectives, the technical solution of the ferrite-hollow glass microsphere composite material in this invention is as follows: A ferrite-hollow glass microsphere composite material is prepared by the above-described method for preparing ferrite-hollow glass microsphere composite materials.

[0022] The beneficial effects of the above technical solution are as follows: The ferrite-hollow glass microsphere composite material provided by the present invention uses hollow glass microspheres as the core, and a continuous, dense, and highly crystalline ferrite shell is chemically bonded to the surface of the microspheres. Experiments have proven that this composite material possesses excellent microwave absorption properties, including being lightweight, having strong absorption capabilities, and a wide bandwidth. Attached Figure Description

[0023] Figure 1 This is a SEM image of the ferrite-hollow glass microsphere composite material in Example 2 of the present invention. Detailed Implementation

[0024] Ferrites, as a magnetic material, can be used as permanent magnets, microwave absorbers, perpendicular recording materials, and magnetic field recording materials, and are currently widely used in radio electronics, automatic control, computers, laser modulation, magnetic field devices, and high-frequency equipment. However, ferrites have a high density, which makes it difficult to meet the increasingly important requirements of "light weight and thin thickness" in magnetic materials, thus limiting the application range of the material in related fields. Hollow glass microspheres, due to their fine particle size, hollow structure, light weight, and high temperature resistance, have been gradually applied in the field of microwave absorption in recent years, but they also have the disadvantage of low dielectric loss. Research has found that coating the surface of hollow glass microspheres with ferrite can produce composite magnetic materials with good static and electromagnetic absorption properties, light weight, high temperature resistance, and chemical stability.

[0025] However, existing preparation methods (such as simple physical mixing or conventional co-precipitation methods) are insufficient to form a complete, dense, and highly crystalline ferrite shell on the surface of hollow glass microspheres, resulting in weak interfacial bonding, a single loss mechanism, and limited and unstable microwave absorption performance. Therefore, this invention provides a method for preparing a ferrite-hollow glass microsphere composite material.

[0026] This invention employs a synergistic strategy of "surface functionalization-co-precipitation screening-hydrothermal crystallization." First, crystal nuclei are anchored through chemical bonding. Then, the high-temperature, high-pressure environment of the hydrothermal method promotes perfect crystal growth and interfacial fusion. The preparation method ensures the continuity, high crystallinity, and excellent adhesion of the ferrite shell to the substrate, effectively preventing detachment and significantly enhancing the interfacial polarization effect and dielectric loss. The highly crystalline Fe3O4 shell provides superior magnetic loss capability, which, combined with the dielectric loss contributed by the hollow glass microspheres and the interface, forms a multiple loss mechanism, synergistically improving microwave absorption performance.

[0027] Specifically, the preparation method of the ferrite-hollow glass microsphere composite material of the present invention includes the following steps: (1) Amino-functionalized hollow glass microspheres, divalent soluble iron salts and trivalent soluble iron salts are dispersed in water and co-precipitated under alkaline conditions; (2) The reaction system after the coprecipitation reaction in step (1) is subjected to hydrothermal crystallization reaction at 150~200℃.

[0028] The adsorption of Fe by amino-functionalized hollow glass microspheres is mainly achieved through "electrostatic adsorption" and "coordination," with the specific mechanisms as follows: First, the hollow glass microspheres were surface-modified using an agent such as a silane coupling agent (e.g., KH550), resulting in the grafting of abundant amino (-NH2) functional groups onto their surface. Before the co-precipitation reaction began, iron salts (Fe...)... 2+ and Fe 3+ The amino group dissolves in water, forming positively charged metal ions. Before the subsequent addition of an alkaline solution (such as ammonia) to make the system alkaline (pH 8-11), the solution may be weakly acidic or neutral, at which point the amino group may be partially protonated (-NH3). + There is a certain electrostatic interaction between the ferrite (Fe3O4) and the positively charged iron ions. More importantly, when the coprecipitation reaction occurs, the primary particles of the ferrite (such as Fe3O4) or precursors (such as Fe(OH)2 / Fe(OH)3) generated in the solution usually carry a charge on their surface, thus achieving electrostatic adsorption. At the same time, the nitrogen atom in the amino group (-NH2) has a lone pair of electrons, which can act as an electron donor, interacting with the iron ions (Fe3O4 / Fe(OH)3). 2+ and Fe 3+ The empty orbitals of the ferrite crystals form coordinate bonds. This chemical force is much stronger than simple physical adsorption, and can firmly anchor iron ions or ferrite crystal nuclei to the surface of hollow glass microspheres, thus achieving coordination.

[0029] The main purpose of the coprecipitation stage is not to make the reaction "complete," but rather to achieve "nucleation and initial growth." During the coprecipitation stage, on the surface of the amino-functionalized microbeads and in the solution, Fe... 2+ and Fe 3+ With OH - The reaction generates ferrite precursors (such as amorphous hydroxide colloids or very fine crystal nuclei), which preferentially adhere to the surface of the microspheres. The product's state: The resulting ferrite material typically has low crystallinity, small particles, and may have an incomplete structure. It is more like a uniformly distributed "seed layer" or "gel layer" covering the surface of the microspheres, rather than the dense, highly crystalline shell desired in the end.

[0030] The subsequent hydrothermal crystallization reaction specifically occurs as follows: In a high-temperature, high-pressure hydrothermal environment, the amorphous or low-crystallinity precursors generated during the co-precipitation stage partially dissolve and subsequently recrystallize into a more thermodynamically stable crystalline phase (spinel Fe3O4). This process significantly improves the crystallinity of the shell material, and high crystallinity is essential for achieving excellent magnetic loss characteristics. Small, unstable crystals or particles gradually dissolve, and the dissolved material deposits and grows on larger, more stable crystals. This process (Ostwald ripening) causes the Fe3O4 particles on the surface of the microspheres to grow and fuse, ultimately forming a continuous, dense, and smooth complete shell, rather than isolated, loose particles.

[0031] Interface strengthening and chemical bonding: High temperature and high pressure conditions enhance the interaction between Fe3O4 and the amino groups on the surface of microspheres, which may promote the strengthening of some coordination bonds or the formation of more stable chemical connections. At the same time, the newly formed Fe3O4 crystals will be "embedded" into the rough structure or chemical sites on the surface of microspheres during the growth process, thereby achieving a strong interface bond and solving the problem of easy detachment in physical mixing methods.

[0032] Phase purification and control: The hydrothermal environment helps eliminate impurities that may be generated during the co-precipitation stage, promoting the final transformation of all iron sources into a single, pure Fe3O4 spinel phase. The reaction temperature and time can control the size of the Fe3O4 grains and the density of the shell.

[0033] Unlike the calcination process in existing technologies, the hydrothermal crystallization of this invention is a process of "atomic-level refinement" of materials using water as a chemical medium and pressure carrier at a mild temperature. This process simultaneously solves four often conflicting requirements in the design of microwave absorbing materials: crystal quality, microstructure, interface engineering, and carrier protection. Calcination, on the other hand, is a "brutal" heat treatment that, while improving crystallinity, comes at the cost of sacrificing the carrier structure, introducing impurities, and deteriorating the interface.

[0034] Preferably, the molar ratio of the divalent soluble iron salt to the trivalent soluble iron salt is 1:(1.5~2.5); the mass ratio of the amino-functionalized hollow glass microspheres to the divalent soluble iron salt is 1:(0.2~0.4).

[0035] Preferably, the divalent soluble iron salt is FeCl2·4H2O or FeSO4·7H2O, and the trivalent soluble iron salt is FeCl3·6H2O.

[0036] Preferably, the temperature of the coprecipitation reaction in step (1) is 60℃~85℃, and the reaction time is 0.5h~2h. To improve the reaction rate, it is even more preferably that the temperature of the coprecipitation reaction in step (1) is 60℃~80℃.

[0037] Preferably, ammonia or sodium hydroxide solution is added dropwise to achieve the alkaline conditions; the pH of the alkaline conditions is 8-11. More preferably, the pH of the alkaline conditions is 9-11.

[0038] Preferably, the hydrothermal crystallization reaction in step (2) takes 3 to 12 hours. To balance the properties of the composite material and the cost of the reaction, it is further preferred that the hydrothermal crystallization reaction in step (2) takes 3 to 10 hours.

[0039] Preferably, the amino-functionalized hollow glass microspheres are prepared by a method mainly comprising the following steps: dispersing the hollow glass microspheres in a solvent, adding a silane coupling agent, and stirring under reflux. More preferably, the temperature of the stirring under reflux reaction is 70°C to 80°C, and the reaction time is 4 to 5 hours.

[0040] Preferably, 1.8~2.2mL of silane coupling agent is added to every 2g of the hollow glass microspheres; the silane coupling agent is γ-aminopropyltriethoxysilane.

[0041] Furthermore, this invention uses low-density hollow glass microspheres as the core, significantly reducing the overall density of the material and meeting the requirements of lightweight modern microwave absorbing coatings. Moreover, the hollow glass microspheres not only serve as a lightweight carrier, but their low dielectric properties also help optimize the impedance matching of the entire material, making it easier for electromagnetic waves to enter the material's interior. At the same time, their hollow structure can cause multiple reflections and scattering of electromagnetic waves, extending their propagation path and thus enhancing energy loss.

[0042] Experimental verification shows that the composite material prepared by this invention has a minimum reflection loss (RL) of less than -44.23dB and an optimal effective absorption bandwidth (RL<-10dB) of more than 3.74GHz in the frequency range of 2~18GHz when the matching thickness is 3.5mm~5mm, exhibiting strong absorption and wide bandwidth characteristics.

[0043] The present invention will now be further described in conjunction with specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments. The equipment and raw materials used are all commercially available or commonly used in the art. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0044] Specific embodiments of the ferrite-hollow glass microsphere composite material and its preparation method of the present invention: Example 1 The preparation method of the ferrite-hollow glass microsphere composite material in this embodiment is specifically implemented as follows: 1. Preparation of amino-functionalized hollow glass microspheres: Weigh 2.0 g of hollow glass microspheres (particle size 10-50 μm) and disperse them in 60 mL of anhydrous ethanol, then sonicate for 30 minutes. Add 2 mL of silane coupling agent KH550 to the suspension and reflux the mixture in an 80 °C water bath with mechanical stirring for 4 hours. After the reaction is complete, centrifuge the mixture, wash it three times with ethanol, and dry it in a vacuum drying oven at 60 °C for 6 hours to obtain amino-functionalized hollow glass microspheres.

[0045] 2. Ferrite loading: (1) Disperse 0.5g of amino-functionalized hollow glass microspheres in 100mL of deionized water and sonicate for 30 minutes. Add 0.20g of FeCl2·4H2O and 0.46g of FeCl3·6H2O sequentially, and mechanically stir for 30 minutes under nitrogen protection to allow the iron salts to be fully adsorbed. Raise the water bath temperature to 80℃, slowly add 1mol / L ammonia water, adjust the pH of the system to 9.5, and continue stirring at this temperature for 1.5 hours to co-precipitate and form a preliminary ferrite nucleus layer.

[0046] (2) Transfer the reaction slurry after step (1) to a 100mL polytetrafluoroethylene-lined hydrothermal reactor, place it in an oven, and perform hydrothermal crystallization reaction at 180℃ for 6 hours to allow Fe3O4 particles to grow in situ and adhere firmly to the surface of the microspheres, forming a complete and dense shell.

[0047] 3. Post-processing: After the reaction was completed, the supernatant was discarded, and the product was washed three times each with deionized water and anhydrous ethanol. Finally, it was dried in a vacuum drying oven at 60°C for 12 hours to obtain a black powder product, which is the ferrite-hollow glass microsphere composite material of this embodiment.

[0048] Example 2 The preparation method of the ferrite-hollow glass microsphere composite material in this embodiment is specifically implemented as follows: 1. Preparation of amino-functionalized hollow glass microspheres: Weigh 2.0 g of hollow glass microspheres (particle size 10-50 μm) and disperse them in 60 mL of anhydrous ethanol, then sonicate for 30 minutes. Add 2 mL of silane coupling agent KH550 to the suspension and reflux the mixture in a 70 °C water bath with mechanical stirring for 5 hours. After the reaction is complete, centrifuge the mixture, wash it three times with ethanol, and dry it in a vacuum drying oven at 60 °C for 6 hours to obtain amino-functionalized hollow glass microspheres.

[0049] 2. Ferrite loading: (1) Disperse 0.5g of amino-functionalized hollow glass microspheres in 100mL of deionized water and sonicate for 30 minutes. Add 0.20g of FeCl2·4H2O and 0.65g of FeCl3·6H2O in sequence, and mechanically stir for 30 minutes under nitrogen protection to allow the iron salt to be fully adsorbed. Raise the water bath temperature to 70℃, slowly add 1mol / L ammonia water, adjust the pH of the system to 11, and continue stirring at this temperature for 0.5 hours to form a preliminary ferrite crystal nucleus layer.

[0050] (2) Transfer the reaction slurry after step (1) to a 100mL polytetrafluoroethylene-lined hydrothermal reactor, place it in an oven, and perform hydrothermal crystallization reaction at 150℃ for 10 hours to allow Fe3O4 particles to grow in situ and adhere firmly to the surface of the microspheres, forming a complete and dense shell.

[0051] 3. Post-processing: After the reaction was complete, the supernatant was discarded, and the product was washed three times each with deionized water and anhydrous ethanol. Finally, it was dried in a vacuum drying oven at 60°C for 12 hours to obtain a black powdery product, which is the ferrite-hollow glass microsphere composite material of this embodiment. Figure 1 As shown, the surface of the microspheres is covered with a complete and dense Fe3O4 shell.

[0052] Example 3 The preparation method of the ferrite-hollow glass microsphere composite material in this embodiment is specifically implemented as follows: 1. Preparation of amino-functionalized hollow glass microspheres: Weigh 2.0 g of hollow glass microspheres (particle size 10-50 μm) and disperse them in 60 mL of anhydrous ethanol, then sonicate for 30 minutes. Add 2 mL of silane coupling agent KH550 to the suspension and reflux the mixture in an 80 °C water bath with mechanical stirring for 4 hours. After the reaction is complete, centrifuge the mixture, wash it three times with ethanol, and dry it in a vacuum drying oven at 60 °C for 6 hours to obtain amino-functionalized hollow glass microspheres.

[0053] 2. Ferrite loading: (1) Disperse 0.5g of amino-functionalized hollow glass microspheres in 100mL of deionized water and sonicate for 30 minutes. Add 0.10g of FeCl2·4H2O and 0.21g of FeCl3·6H2O sequentially, and mechanically stir for 30 minutes under nitrogen protection to allow the iron salt to be fully adsorbed. Raise the water bath temperature to 60℃, slowly add 1mol / L ammonia water, adjust the pH of the system to 10, and continue stirring at this temperature for 2 hours to form a preliminary ferrite crystal nucleus layer.

[0054] (2) Transfer the reaction slurry after step (1) to a 100mL polytetrafluoroethylene-lined hydrothermal reactor, place it in an oven, and perform hydrothermal crystallization reaction at 200℃ for 3 hours to allow Fe3O4 particles to grow in situ and adhere firmly to the surface of the microspheres, forming a complete and dense shell.

[0055] 3. Post-processing: After the reaction was completed, the supernatant was discarded, and the product was washed three times each with deionized water and anhydrous ethanol. Finally, it was dried in a vacuum drying oven at 60°C for 12 hours to obtain a black powder product, which is the ferrite-hollow glass microsphere composite material of this embodiment.

[0056] Comparative Example 1 The preparation method of this comparative ferrite-hollow glass microsphere composite material is as follows: 1. Preparation of amino-functionalized hollow glass microspheres: Weigh 2.0 g of hollow glass microspheres (particle size 10-50 μm) and disperse them in 60 mL of anhydrous ethanol, then sonicate for 30 minutes. Add 2 mL of silane coupling agent KH550 to the suspension and reflux the mixture in an 80 °C water bath with mechanical stirring for 4 hours. After the reaction is complete, centrifuge the mixture, wash it three times with ethanol, and dry it in a vacuum drying oven at 60 °C for 6 hours to obtain amino-functionalized hollow glass microspheres.

[0057] 2. Ferrite loading: 0.5 g of amino-functionalized hollow glass microspheres were dispersed in 100 mL of deionized water and sonicated for 30 minutes. Then, 0.20 g of FeCl₂·4H₂O and 0.46 g of FeCl₃·6H₂O were added sequentially, and the mixture was mechanically stirred for 30 minutes under nitrogen protection to ensure complete adsorption of the iron salts. The water bath temperature was raised to 80 °C, and 1 mol / L ammonia solution was slowly added dropwise to adjust the pH of the system to 9.5. The co-precipitation reaction was continued at this temperature with stirring for 1.5 hours.

[0058] 3. Post-processing: After the reaction was completed, the supernatant was discarded, and the product was washed three times each with deionized water and anhydrous ethanol. Finally, it was dried in a vacuum drying oven at 60°C for 12 hours to obtain a black powder product, which is the ferrite-hollow glass microsphere composite material of this comparative example.

[0059] Comparative Example 2 The preparation method of this comparative ferrite-hollow glass microsphere composite material is as follows: 1. Ferrite loading: Disperse 0.5 g of hollow glass microspheres in 100 mL of deionized water and sonicate for 30 minutes. Add 0.20 g of FeCl₂·4H₂O and 0.46 g of FeCl₃·6H₂O sequentially, and mechanically stir for 30 minutes under nitrogen protection to ensure complete adsorption of iron salts. Raise the water bath temperature to 80 °C, slowly add 1 mol / L ammonia solution, adjust the pH of the system to 9.5, and continue stirring at this temperature for 1.5 hours to allow the co-precipitation reaction to proceed.

[0060] 2. Post-processing After the reaction was completed, the supernatant was discarded, and the product was washed three times each with deionized water and anhydrous ethanol. Finally, it was dried in a vacuum drying oven at 60°C for 12 hours to obtain a black powder product, which is the ferrite-hollow glass microsphere composite material of this comparative example.

[0061] Experiment Example 1: Electromagnetic Wave Absorption Performance Test In this experiment, the ferrite-hollow glass microsphere composite materials prepared in Examples 1-3 and Comparative Examples 1 and 2 were mixed with paraffin at a mass ratio of 0.7:0.3 to form a coaxial ring (outer diameter 7.00 mm, inner diameter 3.00 mm). The electromagnetic parameters of the ring in the 2-18 GHz frequency band were tested using a vector network analyzer, and the reflection loss (RL) was simulated and calculated. The results are shown in Table 1.

[0062] Table 1. Electromagnetic wave absorption performance test results

[0063] Note: The thicknesses in Table 1 are data obtained from tests conducted using a vector network analyzer on the corresponding samples. The results were derived through simulation and optimization of the relationship between reflection loss (RL) and frequency for the material at different matching thicknesses (typically 1-5 mm). Generally, only the optimal performance value (i.e., minimum RL) achievable by all samples at that thickness and its corresponding thickness are shown.

[0064] As shown in the table, the ferrite-hollow glass microsphere composite material of Example 1 achieved a minimum reflection loss (RL) of -31.37 dB. The ferrite-hollow glass microsphere composite material of Example 2, with a thickness of 3.7 mm, achieved a minimum reflection loss (RL) of -44.23 dB and an effective absorption bandwidth (RL < -10 dB) of 1.7 GHz. The ferrite-hollow glass microsphere composite material of Example 3 also exhibited excellent performance, with an RL of -24.32 dB.

[0065] The ferrite-hollow glass microsphere composite material in Comparative Example 1 exhibits significantly poor microwave absorption performance due to uneven Fe3O4 loading, with an RL of only -17.98 dB. Specifically, the ferrite in Comparative Example 1 only undergoes initial growth within the microspheres after loading, forming some Fe3O4 particles or agglomerates on the microsphere surface. These particles cannot further grow and fuse into a continuous, dense, and fully crystalline coating layer, thus it is not an ideal ferrite-hollow glass microsphere composite material. Therefore, Comparative Example 1 yields an intermediate product with incomplete coating and an undesirable structure, whose microwave absorption performance is far inferior to that of Examples 1-3, which underwent hydrothermal crystallization.

[0066] In Comparative Example 2, the ferrite-hollow glass microsphere composite material exhibited significantly poor microwave absorption performance due to the lack of surface functionalization, uneven Fe3O4 loading, and easy detachment, with an RL of only -13.61 dB. This fully demonstrates the crucial role of surface functionalization in achieving high performance.

[0067] In summary, this invention provides a method for preparing a ferrite-hollow glass microsphere composite material, successfully producing a lightweight, efficient, and broadband ferrite-hollow glass microsphere composite material with broad application prospects in the field of electromagnetic wave absorption.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. The scope of patent protection of the present invention shall be determined by the claims. Similarly, any equivalent structural changes made based on the description and drawings of the present invention shall also be included within the scope of protection of the present invention.

Claims

1. A method for preparing a ferrite-hollow glass microsphere composite material, characterized in that: Includes the following steps: (1) Amino-functionalized hollow glass microspheres, divalent soluble iron salts and trivalent soluble iron salts are dispersed in water and co-precipitated under alkaline conditions; (2) The reaction system after the coprecipitation reaction in step (1) is subjected to hydrothermal crystallization reaction at 150~200℃.

2. The method for preparing the ferrite-hollow glass microsphere composite material according to claim 1, characterized in that: The molar ratio of the divalent soluble iron salt to the trivalent soluble iron salt is 1:(1.5~2.5); the mass ratio of the amino-functionalized hollow glass microspheres to the divalent soluble iron salt is 1:(0.2~0.4).

3. The method for preparing the ferrite-hollow glass microsphere composite material according to claim 2, characterized in that: The divalent soluble iron salt is FeCl2·4H2O or FeSO4·7H2O, and the trivalent soluble iron salt is FeCl3·6H2O.

4. The method for preparing the ferrite-hollow glass microsphere composite material according to any one of claims 1 to 3, characterized in that: The temperature of the coprecipitation reaction in step (1) is 60℃~85℃, and the reaction time is 0.5h~2h.

5. The method for preparing the ferrite-hollow glass microsphere composite material according to claim 4, characterized in that: Ammonia or sodium hydroxide solution is added dropwise to achieve the alkaline conditions; the pH of the alkaline conditions is 8-11.

6. The method for preparing the ferrite-hollow glass microsphere composite material according to any one of claims 1 to 3, characterized in that: The hydrothermal crystallization reaction in step (2) takes 3 to 12 hours.

7. The method for preparing the ferrite-hollow glass microsphere composite material according to any one of claims 1 to 3, characterized in that: The amino-functionalized hollow glass microspheres are prepared by a method mainly comprising the following steps: dispersing the hollow glass microspheres in a solvent, adding a silane coupling agent, and stirring and refluxing to react.

8. The method for preparing the ferrite-hollow glass microsphere composite material according to claim 7, characterized in that: 1.8~2.2mL of silane coupling agent is added to every 2g of the hollow glass microspheres; the silane coupling agent is γ-aminopropyltriethoxysilane.

9. The method for preparing the ferrite-hollow glass microsphere composite material according to claim 8, characterized in that: The reflux reaction is carried out at a temperature of 70℃~80℃ for 4~5 hours.

10. A ferrite-hollow glass microsphere composite material, characterized in that: It is prepared by the method for preparing ferrite-hollow glass microsphere composite material according to any one of claims 1 to 9.

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