Multi-shell hollow metal oxide / boron nitride composite material and preparation method and application thereof

Abstract

The invention provides a multi-shell hollow metal oxide / boron nitride composite material as well as a preparation method and application thereof. The multi-shell hollow metal oxide / boron nitride composite material comprises two-dimensional boron nitride sheet layers and multi-shell hollow metal oxide microspheres dispersed between the two-dimensional boron nitride sheet layers, and the multi-shell hollow metal oxide microspheres are made of nickel oxide and cobaltosic oxide. According to the multi-shell hollow metal oxide / boron nitride composite material disclosed by the invention, two-dimensional boron nitride sheet layers are used as a carrier, multi-shell hollow metal oxide microspheres are uniformly dispersed between the boron nitride sheet layers, and the two boron nitride sheet layers are combined through electrostatic self-assembly to form a composite structure with high thermal conductivity and high microwave absorption performance; the material has high heat-conducting property and high microwave absorption property, and has an application prospect in heat management and microwave interference resistance of electronic equipment. The invention also provides a preparation method and application of the composite material.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorbing materials technology, specifically relating to a multi-shell hollow metal oxide / boron nitride composite material, its preparation method, and its application. Background Technology

[0002] With the rapid development of electronic devices towards miniaturization, integration, and high frequency, a large amount of waste heat accumulates during operation. This not only reduces the performance of electronic devices but also shortens their lifespan and may even pose safety risks, placing higher demands on device thermal management. Meanwhile, electronic devices are susceptible to high-frequency electromagnetic interference in complex electromagnetic environments, leading to decreased operational stability. Therefore, materials that combine efficient thermal management with microwave interference resistance have become a key focus of industry research and development.

[0003] Boron nitride (BN) is considered a promising ceramic-based filler material for thermal management of electronic devices due to its excellent chemical stability, electrical insulation, thermal stability, and high thermal conductivity. However, BN itself is a typical microwave-transparent material with a low dielectric constant and negligible dielectric loss, making it difficult to achieve effective microwave absorption. Furthermore, its large specific surface area and high chemical inertness lead to agglomeration under van der Waals forces, which greatly hinders its recombination with microwave-absorbing materials and limits its application in the field of multifunctional materials.

[0004] Existing research indicates that multi-shell hollow metal oxides possess highly efficient microwave trapping capabilities, achieving excellent microwave absorption performance. However, due to van der Waals forces and surface hydroxyl interactions, these metal oxide microspheres are prone to agglomeration, leading to localized impedance mismatch issues. This results in significant microwave reflection at the material surface, preventing effective incident and absorption, and failing to meet the practical requirements of electronic devices for microwave absorption performance. Therefore, current technology lacks a composite material that can simultaneously address boron nitride agglomeration, impedance mismatch in multi-shell hollow metal oxides, and possess both high thermal conductivity and high microwave absorption performance; this technological gap urgently needs to be filled. Summary of the Invention

[0005] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. To this end, the present invention provides a multi-shell hollow metal oxide / boron nitride composite material that can simultaneously solve the problems of boron nitride agglomeration and impedance mismatch in multi-shell hollow metal oxides, while also possessing high thermal conductivity and high microwave absorption performance.

[0006] This invention also provides a method for preparing multi-shell hollow metal oxide / boron nitride composite materials.

[0007] The present invention also provides a microwave absorbing material.

[0008] A first aspect of the present invention provides a multi-shell hollow metal oxide / boron nitride composite material, comprising two-dimensional boron nitride sheets and multi-shell hollow metal oxide microspheres dispersed between the two-dimensional boron nitride sheets, wherein the multi-shell hollow metal oxide microspheres are made of nickel oxide and cobalt tetroxide.

[0009] One technical solution of the present invention relating to multi-shell hollow metal oxide / boron nitride composite materials has at least the following beneficial effects: The multi-shell hollow metal oxide / boron nitride composite material of this invention possesses both high thermal conductivity and high microwave absorption performance, showing promising applications in thermal management and microwave interference resistance for electronic devices. "Multi-shell" refers to three or more shell layers. Specifically: This invention selects two-dimensional boron nitride sheets as a carrier and uses the cationic polymer polydiallyldimethylammonium chloride to modify its surface, thereby obtaining a positively charged boron nitride composite material. Simultaneously, carbon spheres are used as a template. By using electrostatic force, nickel and cobalt ions in the solution are adsorbed to prepare precursor particles. Under the action of electrostatic force, the negatively charged precursor particles and the positively charged boron nitride composite material complete electrostatic self-assembly. Then, the multi-shell hollow metal oxide / boron nitride composite material is obtained by high-temperature calcination. The thermally conductive boron nitride endows the composite material with high thermal conductivity, while the multi-shell hollow metal oxide endows the composite material with high microwave absorption performance, so that the composite material has both high thermal conductivity and high microwave absorption performance.

[0010] The uniform distribution of the multi-shell hollow metal oxide in the boron nitride composite material of the present invention between the boron nitride sheets optimizes the local impedance matching, thereby further improving the microwave absorption performance of the multi-shell hollow metal oxide.

[0011] The multi-shell hollow metal oxide / boron nitride composite material of the present invention uses two-dimensional boron nitride sheets as a carrier, with multi-shell hollow metal oxide microspheres uniformly dispersed between the boron nitride sheets. The two are bonded together through electrostatic self-assembly to form a composite structure with both high thermal conductivity and high microwave absorption performance. Wherein: In terms of overall microstructure characteristics: The composite material consists of two core components: multi-shell hollow metal oxide microspheres and two-dimensional boron nitride sheets. The multi-shell hollow metal oxide microspheres are made of nickel oxide (NiO) and cobalt tetroxide (Co3O4), while the two-dimensional boron nitride sheets serve as a carrier to provide support.

[0012] Regarding the positional relationship between the multi-shell hollow metal oxide microspheres and the two-dimensional boron nitride sheets: The multi-shell hollow metal oxide microspheres are not aggregated or attached to the surface of boron nitride sheets, but are uniformly distributed between the two-dimensional boron nitride sheets, without local agglomeration. This uniform dispersion is achieved by an "electrostatic self-assembly" process. After surface modification, the boron nitride becomes positively charged, while the metal oxide precursor particles become negatively charged. The two are bound together by electrostatic attraction, preventing microsphere agglomeration.

[0013] Two-dimensional boron nitride sheets serve as a carrier, and their sheet-like structure provides a stable support space for the microspheres. At the same time, their high thermal conductivity allows the composite material to have excellent overall thermal conductivity.

[0014] Multi-shell hollow metal oxide microspheres are dispersed between layers. Their multi-shell hollow structure can optimize local impedance matching, reduce microwave reflection on the material surface, and enhance microwave incident and absorption, thereby achieving high microwave absorption performance.

[0015] Regarding structural advantages: This "layered support-microsphere dispersion" microstructure solves two key problems simultaneously: This avoids the decrease in microwave absorption efficiency caused by the agglomeration of multi-shell hollow metal oxide microspheres, and also solves the problem that boron nitride is difficult to combine with other materials due to agglomeration.

[0016] The high thermal conductivity of boron nitride and the high microwave absorption of metal oxide microspheres work synergistically, enabling the composite material to simultaneously meet the dual requirements of "thermal management" and "microwave interference resistance" for electronic devices.

[0017] According to some embodiments of the present invention, the particle size of the multi-shell hollow metal oxide / boron nitride composite material is 15~25μm.

[0018] According to some embodiments of the present invention, the particle size of the multi-shell hollow metal oxide / boron nitride composite material is any value among 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, and 25μm, such as 20μm, or any range formed by both, such as 20μm to 22μm.

[0019] According to some embodiments of the present invention, the size of the two-dimensional boron nitride sheet is 5~10 μm.

[0020] According to some embodiments of the present invention, the size of the two-dimensional boron nitride sheet is any value among 5μm, 6μm, 7μm, 8μm, 9μm, and 10μm, such as 8μm, or any range formed by both, such as 6μm to 9μm.

[0021] According to some embodiments of the present invention, the particle size of the multi-shell hollow metal oxide microspheres is 450~550 nm.

[0022] According to some embodiments of the present invention, the particle size of the multi-shell hollow metal oxide microspheres is any value among 450nm, 460nm, 470nm, 480nm, 490nm, 500nm, 510nm, 520nm, 530nm, 540nm, and 550nm, such as 500nm, or any range formed by both, such as 480nm to 520nm.

[0023] A second aspect of the present invention provides a method for preparing a multi-shell hollow metal oxide / boron nitride composite material according to the first aspect of the present invention, comprising the following steps: S1: Prepare boron nitride composite material and metal oxide precursor particles respectively; S2: The boron nitride composite material and metal oxide precursor particles are added to a solvent, and the composite material precursor particles are obtained after the reaction. S3: The precursor particles of the composite material are calcined in an aerobic environment to obtain the multi-shell hollow metal oxide / boron nitride composite material.

[0024] The method for preparing multi-shell hollow metal oxide / boron nitride composite materials according to the present invention has at least the following beneficial effects: 1. The process logic is highly adaptable, precisely matching the structural requirements of the product. The preparation method, through a process design of "stepwise preparation - composite assembly - calcination molding," is highly compatible with the microstructure of the composite material, which is "layered support - microsphere dispersion." In step S1, “preparing boron nitride composite material and metal oxide precursor particles separately” allows for independent control of the properties of the two core components: on the one hand, surface modification (such as using polydiallyldimethylammonium chloride) ensures that boron nitride forms a stable positively charged surface; on the other hand, water bath impregnation with carbon ball template and nickel / cobalt salt ensures that the metal oxide precursor particles are uniformly loaded and negatively charged, laying the foundation for charge matching for subsequent composites. The “composite reaction” in step S2 relies on the principle of electrostatic self-assembly, which allows the positively charged boron nitride composite material to combine efficiently with the negatively charged metal oxide precursor particles. This can accurately achieve uniform dispersion of metal oxide precursor particles between boron nitride sheets, avoiding the agglomeration problem that is easy to occur in traditional mixing processes. The "aerobic calcination" in step S3 can completely remove the carbon sphere template, promote the transformation of the metal oxide precursor into a multi-shell hollow structure (nickel oxide and cobalt tetroxide), and ensure the crystal stability of the boron nitride sheets, ultimately forming the target product with both "high thermal conductivity and high microwave absorption".

[0025] 2. The product performance has high controllability, ensuring the stability of core functions. The preparation method achieves precise control over the core properties of the composite material through the adjustability of key process parameters: By controlling the surface modification temperature (25~60℃) of boron nitride, the water bath immersion temperature (40~80℃) and time (1~12h) of the metal oxide precursor in step S1, the uniformity of the positively charged boron nitride layer and the metal ion loading can be ensured, thereby guaranteeing the dispersion of microspheres and the integrity of the multi-shell hollow structure after subsequent composite. By adjusting the calcination temperature (400~600℃) and heating rate (1~10℃ / min) in step S3, excessive growth of metal oxide grains or agglomeration of boron nitride can be avoided, thus ensuring the high thermal conductivity of the composite material (e.g., a thermal conductivity of 3.87 W / m in Example 1). K) and high microwave absorption performance (reflection loss as low as -63.34dB, effective absorption bandwidth up to 5.76GHz); The overall process can stably reproduce the structure of "multi-shell hollow metal oxide microspheres uniformly dispersed between boron nitride sheets", optimize local impedance matching, avoid the decrease in microwave absorption efficiency caused by microsphere agglomeration, and solve the problem of difficult boron nitride recombination, ensuring the consistency of product function.

[0026] 3. The process is simple to operate and has potential for industrial application. The preparation method is designed to balance "efficiency" and "ease of operation," without any particularly demanding conditions. The raw materials used (boron nitride, carbon source, nickel salt, cobalt salt, surface modifier, etc.) are all conventional chemical raw materials, which are widely available and cost-controllable, and do not need to rely on rare or high-cost reagents. The core processes (surface modification, hydrothermal reaction, water bath impregnation, and calcination) are all mature technologies in the field of materials preparation. They have low equipment requirements (such as conventional reaction vessels, water baths, and muffle furnaces), and the operation process is easy to standardize. They can achieve batch preparation of products through large-scale production. No toxic or harmful byproducts are generated during the reaction process. Aerobic calcination only produces CO2 (from the carbon sphere template), which conforms to the concept of green chemical industry and reduces the environmental treatment costs in industrial production.

[0027] 4. Good process compatibility, expanding the application scenarios of the product. This preparation method has a certain range of parameter adjustment, and the product properties can be adjusted according to different application requirements: The composition ratio of multi-shell hollow metal oxides can be adjusted by changing the molar ratio of nickel salt to cobalt salt in step S1, thereby optimizing the microwave absorption frequency band and absorption intensity of the composite material and adapting to the anti-microwave interference requirements of different electronic devices (such as communication equipment and precision instruments). By adjusting the ratio of boron nitride composite material to metal oxide precursor particles in step S2, a balance can be achieved between "high thermal conductivity" and "high microwave absorption" performance, meeting the personalized needs of different scenarios (such as high-power devices focusing on thermal conductivity and high-frequency communication equipment focusing on microwave absorption), and further broadening the application range of the product.

[0028] According to some embodiments of the present invention, the preparation method of the boron nitride composite material includes: dispersing boron nitride in a solvent and adding a surface modifier to carry out a reaction.

[0029] According to some embodiments of the present invention, the preparation method of the boron nitride composite material includes: dispersing boron nitride in a mixed solution of deionized water and anhydrous ethanol, adding a surface modifier to react, and then vacuum filtering, washing and drying to obtain a positively charged boron nitride composite material.

[0030] According to some embodiments of the present invention, a surface modifier is added to carry out the reaction at a temperature of 25~60°C.

[0031] According to some embodiments of the present invention, a surface modifier is added to carry out the reaction, and the reaction temperature is any value of 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, and 60°C, such as 25°C, or any range of both, such as 40~50°C.

[0032] According to some embodiments of the present invention, a surface modifier is added to carry out the reaction, and the reaction time is 10-30 min.

[0033] According to some embodiments of the present invention, a surface modifier is added to carry out a reaction, and the reaction time is any value of 10 min, 15 min, 20 min, 25 min, or 30 min, such as 15 min, or any range of both, such as 15 min to 25 min.

[0034] According to some embodiments of the present invention, the surface modifier includes at least one selected from silane coupling agent, polydiallyl dimethyl ammonium chloride, and hexadecyltrimethylammonium bromide.

[0035] According to some embodiments of the present invention, the method for preparing the metal oxide precursor particles includes the following steps: (1) Dissolve the carbon source in water and carry out a hydrothermal reaction to obtain template particles; (2) The template particles are dispersed in a solvent, and then nickel salt and cobalt salt are added and impregnated in a water bath to obtain metal oxide precursor particles.

[0036] According to some embodiments of the present invention, in step (1), the carbon source is dissolved in deionized water and subjected to a hydrothermal reaction. After centrifugation, washing and drying, a carbon ball template is obtained.

[0037] According to some embodiments of the present invention, in step (1), the carbon source includes at least one of glucose, sucrose and starch.

[0038] According to some embodiments of the present invention, in step (1), the temperature of the hydrothermal reaction is 150~200°C.

[0039] According to some embodiments of the present invention, in step (1), the temperature of the hydrothermal reaction is any value among 150°C, 160°C, 170°C, 180°C, 190°C, and 200°C, such as 180°C, or any range formed by both, such as 160°C to 190°C.

[0040] According to some embodiments of the present invention, the hydrothermal reaction time is 1 to 4 hours.

[0041] According to some embodiments of the present invention, the hydrothermal reaction time is any value among 1h, 2h, 3h, and 4h, such as 2h, or a range of any two, such as 2h to 3h.

[0042] According to some embodiments of the present invention, in step (2), the carbon ball template is dispersed in a mixed solution composed of deionized water and anhydrous ethanol, impregnated in a water bath, and then vacuum filtered, washed and dried to obtain metal oxide precursor particles.

[0043] According to some embodiments of the present invention, in step (2), the nickel salt includes at least one of nickel chloride, nickel acetate, nickel sulfate and nickel nitrate.

[0044] According to some embodiments of the present invention, in step (2), the cobalt salt includes at least one of cobalt chloride, cobalt acetate, cobalt sulfate and cobalt nitrate.

[0045] According to some embodiments of the present invention, in step (2), the molar ratio of the nickel salt and the cobalt salt is (1~2):1.

[0046] According to some embodiments of the present invention, in step (2), the molar ratio of the nickel salt and the cobalt salt is any one of 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, such as 1:1, or any range of the two, such as 1.2:1 to 1.8:1.

[0047] According to some embodiments of the present invention, in step (2), the temperature of the water bath immersion is 40~80°C.

[0048] According to some embodiments of the present invention, in step (2), the temperature of the water bath immersion is any value among 40°C, 50°C, 60°C, 70°C, and 80°C, such as 45°C, or any range formed by both, such as 50°C to 70°C.

[0049] According to some embodiments of the present invention, in step (2), the water bath immersion time is 1 to 12 hours.

[0050] According to some embodiments of the present invention, in step (2), the water bath immersion time is any value among 1h, 2h, 4h, 6h, 8h, 10h, and 12h, such as 6h, or any range formed by both, such as 4h to 8h.

[0051] According to some embodiments of the present invention, in step S2, the solvent may be a mixed solution composed of deionized water and anhydrous ethanol.

[0052] According to some embodiments of the present invention, in step S2, the boron nitride composite material and the metal oxide precursor particles are added to a solvent for reaction at a reaction temperature of 25~60°C.

[0053] According to some embodiments of the present invention, in step S2, the boron nitride composite material and the metal oxide precursor particles are added to a solvent for reaction, and the reaction temperature is any value among 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, and 60°C, such as 25°C, or any range formed by both, such as 40~50°C.

[0054] According to some embodiments of the present invention, in step S2, the boron nitride composite material and the metal oxide precursor particles are added to a solvent for reaction, and the reaction time is 1 to 6 hours.

[0055] According to some embodiments of the present invention, in step S2, the boron nitride composite material and the metal oxide precursor particles are added to a solvent to react for a reaction time of any value among 1h, 2h, 3h, 4h, 5h, and 6h, such as 3h, or any range formed by both, such as 2h to 4h.

[0056] According to some embodiments of the present invention, in step S3, the calcination method is as follows: heating to 400-600°C at a heating rate of 1-10°C / min, and holding at that temperature for 1-3 hours.

[0057] A third aspect of the present invention provides a microwave absorbing material, the raw materials of which include the multi-shell hollow metal oxide / boron nitride composite material of the first aspect of the present invention.

[0058] The microwave absorbing material provided in the third aspect of this invention, because its raw materials include the multi-shell hollow metal oxide / boron nitride composite material of the first aspect, possesses significant and unique beneficial effects: This microwave absorbing material not only inherits the optimized microstructure of the multi-shell hollow metal oxide / boron nitride composite material of "sheet support - microsphere dispersion," but also provides stable support for the multi-shell hollow metal oxide microspheres (made of nickel oxide and cobalt tetroxide) by two-dimensional boron nitride sheets, preventing their aggregation. The multi-shell hollow structure of the microspheres can effectively optimize local impedance matching and reduce microwave reflection on the material surface. Simultaneously, the high thermal conductivity of boron nitride can solve the problem of local heat accumulation due to energy conversion in traditional microwave absorbing materials during microwave absorption, which affects absorption performance and service life. This invention addresses the problem of achieving synergistic effects between "efficient microwave absorption" and "timely heat dissipation." By leveraging the controllability of material parameters (such as multi-shell hollow metal oxide microspheres with a particle size of 450-550 nm and composite material particle size of 15-25 μm), this microwave absorbing material can achieve excellent microwave absorption performance with a reflection loss as low as -63.34 dB and an effective absorption bandwidth of up to 5.76 GHz by adjusting the amount or proportion of multi-shell hollow metal oxide / boron nitride composite materials in the raw materials. Furthermore, its thermal conductivity is 921% higher than that of simple multi-shell hollow metal oxide, fully meeting the dual requirements of electronic devices for "microwave interference resistance" and "thermal management." It has outstanding application value in the fields of miniaturized, integrated, and high-frequency electronic devices. Attached Figure Description

[0059] Figure 1 This is a schematic diagram illustrating the formation process of the multi-shell hollow metal oxide / boron nitride composite material of the present invention.

[0060] Figure 2 This is a SEM image of the multi-shell hollow metal oxide / boron nitride composite material in Example 1.

[0061] Figure 3 This is a TEM image of the multi-shell hollow metal oxide / boron nitride composite material in Example 1.

[0062] Figure 4 The image shows the XRD pattern of the multi-shell hollow metal oxide / boron nitride composite material in Example 1.

[0063] Figure 5 The diagram shows the reflection loss of the multi-shell hollow metal oxide / boron nitride composite materials in Examples 1-3 and the multi-shell hollow metal oxide composite material in Comparative Example 1.

[0064] Figure 6 Impedance matching for the multi-shell hollow metal oxide / boron nitride composite materials in Examples 1-3 and the multi-shell hollow metal oxide in Comparative Example 1.

[0065] Figure 7The attenuation constants are those of the multi-shell hollow metal oxide / boron nitride composite materials in Examples 1-3 and the multi-shell hollow metal oxide in Comparative Example 1.

[0066] Figure 8 The thermal conductivity is given by the multi-shell hollow metal oxide / boron nitride composite materials in Examples 1-3 and the multi-shell hollow metal oxide in Comparative Example 1. Detailed Implementation

[0067] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0068] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0069] Unless otherwise specified, "room temperature" in this invention means 25℃±5℃.

[0070] Unless otherwise specified, "about" in this invention means that the allowable error is within ±2%.

[0071] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0072] Example 1 A multi-shell hollow metal oxide / boron nitride composite material was prepared, and the specific steps are as follows: (1) 60 mg boron nitride was dispersed in a mixed solvent consisting of 25 mL deionized water and 25 mL anhydrous ethanol, and then 20 μL of polydiallyldimethylammonium chloride was added. The mixture was magnetically stirred at 25 °C for 15 min, filtered, and the filtered solid was washed three times with deionized water and dried in an oven at 60 °C for 12 h to obtain a positively charged boron nitride composite material.

[0073] (2) Add 34.23g of sucrose to 100mL of deionized water, stir magnetically at 25℃ for 10min, transfer the above solution to a 200mL reactor, and hydrothermally react in an oven at 180℃ for 2h to obtain a carbon ball suspension. The carbon ball suspension is centrifuged in a centrifuge at 9000r / min, the separated solid is washed 3 times with deionized water, and dried in an oven at 80℃ for 12h to obtain a carbon ball template. (3) Disperse 60 mg of carbon ball template in a mixed solvent consisting of 50 mL of deionized water and 50 mL of anhydrous ethanol, then add 1.87 g of nickel acetate and 1.87 g of cobalt acetate, stir for 30 min and then sonicate for 15 min, place in a 45 °C water bath and let stand for 6 h, filter, wash the filtered solid with deionized water 3 times, and dry in an 80 °C oven for 12 h to obtain precursor particles; (4) Disperse 60 mg of positively charged boron nitride composite material and 60 mg of precursor particles in a mixed solvent consisting of 25 mL of deionized water and 25 mL of anhydrous ethanol, stir magnetically for 3 h, filter, wash the filtered solid with deionized water 3 times, and dry in an oven at 80 °C for 12 h to obtain composite material precursor particles. (5) Place the precursor particles of the composite material in an air atmosphere, heat them to 500°C at a heating rate of 1°C / min, keep them at that temperature for 1.5 hours, and then let them cool naturally to obtain the multi-shell hollow metal oxide / boron nitride composite material.

[0074] Example 2 A multi-shell hollow metal oxide / boron nitride composite material was prepared, and the specific steps are as follows: (1) 30 mg boron nitride was dispersed in a mixed solvent consisting of 25 mL deionized water and 25 mL anhydrous ethanol, and then 20 μL of polydiallyldimethylammonium chloride was added. The mixture was magnetically stirred at 25 °C for 15 min, filtered, and the filtered solid was washed three times with deionized water and dried in an oven at 60 °C for 12 h to obtain a positively charged boron nitride composite material.

[0075] (2) Add 34.23g of sucrose to 100mL of deionized water, stir magnetically at 25℃ for 10min, transfer the above solution to a 200mL reactor, and hydrothermally react in an oven at 180℃ for 2h to obtain a carbon ball suspension. The carbon ball suspension is centrifuged in a centrifuge at 9000r / min, the separated solid is washed 3 times with deionized water, and dried in an oven at 80℃ for 12h to obtain a carbon ball template. (3) Disperse 60 mg of carbon ball template in a mixed solvent consisting of 50 mL of deionized water and 50 mL of anhydrous ethanol, then add 1.87 g of nickel acetate and 1.87 g of cobalt acetate, stir for 30 min and then sonicate for 15 min, place in a 45 °C water bath and let stand for 6 h, filter, wash the filtered solid with deionized water 3 times, and dry in an 80 °C oven for 12 h to obtain precursor particles; (4) 30 mg of positively charged boron nitride composite material and 60 mg of precursor particles were dispersed in a mixed solvent consisting of 25 mL of deionized water and 25 mL of anhydrous ethanol. The mixture was magnetically stirred for 3 h, filtered, and the filtered solid was washed three times with deionized water and dried in an oven at 80 °C for 12 h to obtain the composite material precursor particles. (5) Place the precursor particles of the composite material in an air atmosphere, heat them to 500°C at a heating rate of 1°C / min, keep them at the temperature for 1.5h, and cool them naturally to obtain a multi-shell hollow metal oxide / boron nitride composite material.

[0076] Example 3 A multi-shell hollow metal oxide / boron nitride composite material was prepared, and the specific steps are as follows: (1) 90 mg boron nitride was dispersed in a mixed solvent consisting of 25 mL deionized water and 25 mL anhydrous ethanol, and then 20 μL of polydiallyldimethylammonium chloride was added. The mixture was magnetically stirred at 25 °C for 15 min, filtered, and the filtered solid was washed three times with deionized water and dried in an oven at 60 °C for 12 h to obtain a positively charged boron nitride composite material.

[0077] (2) Add 34.23g of sucrose to 100mL of deionized water, stir magnetically at 25℃ for 10min, transfer the above solution to a 200mL reactor, and hydrothermally react in an oven at 180℃ for 2h to obtain a carbon ball suspension. The carbon ball suspension is centrifuged in a centrifuge at 9000r / min, the separated solid is washed 3 times with deionized water, and dried in an oven at 80℃ for 12h to obtain a carbon ball template. (3) Disperse 60 mg of carbon ball template in a mixed solvent consisting of 50 mL of deionized water and 50 mL of anhydrous ethanol, then add 1.87 g of nickel acetate and 1.87 g of cobalt acetate, stir for 30 min and then sonicate for 15 min, place in a 45 °C water bath and let stand for 6 h, filter, wash the filtered solid with deionized water 3 times, and dry in an 80 °C oven for 12 h to obtain precursor particles; (4) 90 mg of positively charged boron nitride composite material and 60 mg of precursor particles were dispersed in a mixed solvent consisting of 25 mL of deionized water and 25 mL of anhydrous ethanol. The mixture was magnetically stirred for 3 h, filtered, and the filtered solid was washed three times with deionized water and dried in an oven at 80 °C for 12 h to obtain the composite material precursor particles. (5) Place the precursor particles of the composite material in an air atmosphere, heat them to 500°C at a heating rate of 1°C / min, keep them at the temperature for 1.5h, and cool them naturally to obtain a multi-shell hollow metal oxide / boron nitride composite material.

[0078] Comparative Example 1 A multi-shell hollow metal oxide was prepared, and the specific steps are as follows: (1) Add 34.23g of sucrose to 100mL of deionized water, stir magnetically at 25℃ for 10min, transfer the above solution to a 200mL reactor, and hydrothermally react in an oven at 180℃ for 2h to obtain a carbon ball suspension. The carbon ball suspension is centrifuged in a centrifuge at 9000r / min, the separated solid is washed 3 times with deionized water, and dried in an oven at 80℃ for 12h to obtain a carbon ball template. (2) Disperse 60 mg of carbon ball template in a mixed solvent consisting of 50 mL of deionized water and 50 mL of anhydrous ethanol, then add 1.87 g of nickel acetate and 1.87 g of cobalt acetate, stir for 30 min and then sonicate for 15 min, place in a 45 °C water bath and let stand for 6 h, filter, wash the filtered solid with deionized water 3 times, and dry in an 80 °C oven for 12 h to obtain precursor particles; (3) Place the precursor particles in an air atmosphere and heat them to 500°C at a heating rate of 1°C / min. Hold the temperature for 1.5 hours and allow them to cool naturally to obtain a multi-shell hollow metal oxide.

[0079] The following are the experimental data for the products prepared in Examples 1-3 and Comparative Example 1: like Figure 1 As shown, the preparation process of the multi-shell hollow metal oxide / boron nitride composite material in this embodiment is as follows: Polydiallyldimethylammonium chloride is compounded with boron nitride to form a positively charged boron nitride / polydiallyldimethylammonium chloride composite material. Under the action of electrostatic force, negatively charged precursor particles and positively charged boron nitride / polydiallyldimethylammonium chloride composite material electrostatically self-assemble to form a precursor / polydiallyldimethylammonium chloride / boron nitride composite material, which is then calcined in air to obtain the multi-shell hollow metal oxide / boron nitride composite material.

[0080] like Figure 2 As shown, in Example 1, multi-shell hollow metal oxides are uniformly distributed and intercalated between boron nitride sheets.

[0081] like Figure 3 As shown, in Example 1, the multi-shell hollow metal oxide has a multi-shell hollow structure, while the boron nitride sheet is very thin.

[0082] like Figure 4As shown, in Example 1, the characteristic diffraction peaks at diffraction angles of 37.3°, 43.3°, 62.8°, and 75.4° correspond to the (111), (200), (220), and (311) crystal planes of NiO, respectively (PDF#47-1049). The peaks at 31.2°, 36.8°, 38.6°, 44.8°, 55.6°, 59.4°, and 65.2° are the (220), (311), (222), (400), (422), (511), and (440) crystal planes of Co3O4 (PDF#42-1467). A sharp and strong diffraction peak appeared at 26.6°, corresponding to the (002) crystal plane of boron nitride (PDF#45-0893), while the weak diffraction peaks at 41.4°, 43.7°, 50.1°, and 55.0° belong to the (100), (101), (102), and (004) crystal planes of boron nitride, respectively. The above test results indicate that the multi-shell hollow metal oxide material includes nickel oxide and cobalt tetroxide, and that multi-shell hollow metal oxide and boron nitride were successfully combined to form a multi-shell hollow metal oxide / boron nitride composite material.

[0083] The multi-shell hollow metal oxide / boron nitride composite materials from Examples 1-3, and the multi-shell hollow metal oxide and paraffin from Comparative Example 1, were placed in a beaker at a 5:5 ratio, heated to melt, and mixed evenly. The mixture was then pressed into a coaxial ring for microwave absorption performance testing. It can be seen that: like Figure 5 As shown, Figure 5 The diagram shows the reflection loss of the multi-shell hollow metal oxide / boron nitride composite materials in Examples 1-3 and the multi-shell hollow metal oxide composite material in Comparative Example 1. Figure 5 In the diagram, 'a' represents the reflection loss diagram of Example 1. Figure 5 In the diagram, b represents the reflection loss diagram of Example 2. Figure 5 In the diagram, 'c' represents the reflection loss diagram of Example 3. Figure 5 In the diagram, d represents the reflection loss diagram of Comparative Example 1.

[0084] In Example 1, the reflection loss reaches a minimum of -63.34 dB at 2.5 mm, while the effective absorption bandwidth reaches a maximum of 5.76 GHz at 1.7 mm. In Example 2, the reflection loss reaches a minimum of -43.46 dB at 2.9 mm, while the effective absorption bandwidth reaches a maximum of 4.56 GHz at 2.0 mm. In Example 3, the reflection loss reaches a minimum of -34.31 dB at 2.1 mm, while the effective absorption bandwidth reaches a maximum of 3.76 GHz at 1.8 mm. In Comparative Example 1, the reflection loss reaches a minimum of -25.97 dB at 4.9 mm, while the effective absorption bandwidth reaches a maximum of 3.92 GHz at 1.8 mm.

[0085] like Figure 6 As shown, Figure 6 Impedance matching was performed on the multi-shell hollow metal oxide / boron nitride composite materials in Examples 1-3 and the multi-shell hollow metal oxide composite material in Comparative Example 1. Figure 6 In the diagram, 'a' represents the reflection loss diagram of Example 1. Figure 6 In the diagram, b represents the reflection loss diagram of Example 2. Figure 6 In the diagram, 'c' represents the reflection loss diagram of Example 3. Figure 6 In the diagram, d represents the reflection loss diagram of Comparative Example 1.

[0086] The closer the impedance matching value is to 1, the better the impedance matching, and the more microwaves can penetrate into the material rather than be reflected at its surface. An impedance matching value in the range of 0.8 to 1.2 is considered good. Examples 1-3 all showed good impedance matching in the X-band (8-12 GHz). Example 1, at 2.5 mm, showed an impedance matching value close to 1, indicating ideal impedance matching. Comparative Example 1 showed good impedance matching in the C-band (4-8 GHz).

[0087] like Figure 7 As shown, the larger the attenuation constant value, the stronger the microwave attenuation capability of the material. The attenuation constant values ​​of Example 1 range from 26 to 127, those of Example 2 range from 34 to 235, those of Example 3 range from 14 to 64, and those of Comparative Example 1 range from 43 to 281. Example 1 exhibits excellent microwave absorption performance under the synergistic effect of ideal impedance matching and strong microwave attenuation capability.

[0088] like Figure 8 As shown, the thermal conductivity of Example 1 is 3.87 W / m·K, that of Example 2 is 2.32 W / m·K, that of Example 3 is 4.41 W / m·K, and that of Comparative Example 1 is 0.42 W / m·K. The thermal conductivity of Examples 1-3 is much greater than that of Comparative Example 1, which is because boron nitride in the system improves the thermal conductivity of the composite material. Specifically, the thermal conductivity of Example 1 is increased by 921% compared to Example 1.

[0089] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A multi-shell hollow metal oxide / boron nitride composite material, characterized by, The multi-shell hollow metal oxide / boron nitride composite material comprises two-dimensional boron nitride sheet layers and multi-shell hollow metal oxide microspheres dispersed between the two-dimensional boron nitride sheet layers, and the material of the multi-shell hollow metal oxide microspheres comprises nickel oxide and tricobalt tetroxide.

2. The multi-shell hollow metal oxide / boron nitride composite material of claim 1, wherein, The particle size of the multi-shell hollow metal oxide / boron nitride composite material is 15-25 μm; and / or the size of the two-dimensional boron nitride sheet layer is 5-10 μm; and / or the particle size of the multi-shell hollow metal oxide microspheres is 450-550 nm.

3. A method for producing the multi-shell hollow metal oxide / boron nitride composite material according to claim 1 or 2, characterized by, The method comprises the following steps: S1: preparing boron nitride composite material and metal oxide precursor particles, respectively; S2: adding the boron nitride composite material and metal oxide precursor particles into a solvent to obtain composite material precursor particles after reaction; S3: calcining the composite material precursor particles in an oxygen environment to obtain the multi-shell hollow metal oxide / boron nitride composite material.

4. The method of claim 3, wherein, The preparation method of the boron nitride composite material comprises dispersing boron nitride in a solvent and adding a surface modifier for reaction.

5. The method of claim 4, wherein, The surface modifier comprises at least one of a silane coupling agent, polydiallyldimethylammonium chloride and cetyltrimethylammonium bromide.

6. The method of claim 3, wherein, The preparation method of the metal oxide precursor particles comprises the following steps: (1) dissolving a carbon source in water to perform hydrothermal reaction to obtain template particles; (2) dispersing the template particles in a solvent, and then adding nickel salt and cobalt salt to perform water bath immersion to obtain metal oxide precursor particles.

7. The method of claim 6, wherein, The carbon source comprises at least one of glucose, sucrose and starch; and / or the temperature of the hydrothermal reaction is 150-200 ℃; and / or the time of the hydrothermal reaction is 1-4 h.

8. The method of claim 6, wherein, The nickel salt comprises at least one of nickel chloride, nickel acetate, nickel sulfate and nickel nitrate; the cobalt salt comprises at least one of cobalt chloride, cobalt acetate, cobalt sulfate and cobalt nitrate; and / or the temperature of the water bath immersion is 40-80 ℃; and / or the time of the water bath immersion is 1-12 h.

9. The method of claim 3, wherein, In step S3, the calcination method is to raise the temperature to 400-600 ℃ at a temperature raising rate of 1-10 ℃ / min.

10. A microwave absorbing material, characterized by, The raw material comprises the multi-shell hollow metal oxide / boron nitride composite material according to claim 1 or 2.

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