Preparation method of large-size high-quality three-dimensional hexagonal boron nitride network

Abstract

The present application relates to a new material and its application field, and in particular to a preparation method of a large-size high-quality three-dimensional hexagonal boron nitride (h-BN) network. A porous metal is used as a template, a boron source is uniformly fixed on the surface of the template hole wall through pretreatment, then a chemical vapor deposition (CVD) process is used, a nitrogen-containing gas is used as a nitrogen source, the h-BN is catalytically grown on the surface of the porous metal skeleton under suitable temperature and atmosphere conditions, and after the metal substrate is removed, a high-quality three-dimensional h-BN network is obtained. By adjusting the substrate template and other reaction parameters, the pore size, morphology, layer number and other parameters of the three-dimensional h-BN network can be precisely controlled. Compared with the existing preparation process of the three-dimensional h-BN network, the present application can avoid the uneven growth of the h-BN network caused by the difficulty of the boron source to diffuse in the bulk phase during the CVD process, and the layer number, network morphology and porosity of the h-BN are adjustable, the process is simple, the production cost is low, and the production is easy to scale up. The prepared h-BN has a high crystalline quality and can be applied in many fields.

Description

TECHNICAL FIELD

[0001] The present application relates to a new material and its application field, in particular to a preparation method of a large-size high-quality three-dimensional hexagonal boron nitride network. BACKGROUND

[0002] Hexagonal boron nitride (h-BN) exhibits many excellent physical and chemical properties, such as: excellent mechanical properties, the in-plane mechanical strength can reach 500 N / m; h-BN also has excellent high-temperature resistance, the oxidation resistance temperature in air is 1000℃, and the temperature resistance in vacuum can reach 2000℃; more importantly, h-BN also has excellent thermal conductivity, the theoretical thermal conductivity can be as high as 1700-2000 W / mK, which is 5 times that of silver and copper; at the same time, h-BN has excellent insulation performance, the band gap is 5.26eV, the breakdown strength is as high as 35kV / mm, and the dielectric constant is 2.9. Therefore, h-BN is an ideal thermal conductive and insulating wave-transparent material, and the porous network structure has high porosity, low density, high specific surface area, damping and noise reduction, etc. The porous material constructed by two-dimensional h-BN can have both the porous structure and the intrinsic excellent properties of h-BN, and has great potential application advantages in the fields of thermal conduction, energy storage, catalysis, adsorption, aerospace, etc.

[0003] The preparation methods of h-BN network material mainly include self-assembly and direct growth, the self-assembly method includes ice template method, salt template method, bubble template method, etc., which relies on van der Waals force and hydrogen bond to connect h-BN sheets to construct a three-dimensional structure, so the prepared h-BN porous material is not stable and has poor mechanical properties. More importantly, since the h-BN sheets are in a lapping state, there are many micro interfaces between the h-BN sheets, and the thermal conductivity and other properties are not ideal; the direct growth method mainly uses chemical vapor deposition (CVD), which deposits boron nitride on the skeleton of metal, polymer and other porous materials. Compared with the self-assembly method, the h-BN is connected by covalent bond, which shows more excellent performance. However, the current CVD precursor is mainly ammonia borane and borazine, which is expensive and toxic, and is not suitable for large-scale preparation. At the same time, the CVD process generally uses gaseous nitrogen source and boron source to volatilize to the substrate surface for growth. However, the gaseous boron source including ammonia borane generally has large molecular weight and is difficult to diffuse uniformly in the bulk phase, so it is difficult to realize the uniform growth of large-size, especially large-thickness and dense pore bulk phase h-BN network. Therefore, it is of great significance to develop an economical and environmental friendly, simple and efficient large-size high-quality three-dimensional h-BN network scale preparation technology. SUMMARY

[0004] The application aims to provide a preparation method of large-size high-quality three-dimensional hexagonal boron nitride network.

[0005] The technical scheme of the application is:

[0006] The application provides a preparation method of large-size high-quality three-dimensional hexagonal boron nitride network, which comprises the following steps:

[0007] (1) adding solid boron source in the form of dry powder or dispersion liquid into the pores of a foam metal substrate template through shaking, oscillation, repeated lifting and pulling, ultrasonic or vacuum immersion, and then putting the foam metal loaded with the boron source into an oven for sufficient drying;

[0008] (2) heating the reaction furnace cavity to a set pretreatment temperature under a carrier gas protection atmosphere;

[0009] (3) putting the foam metal loaded with the solid boron source on the surface into the constant temperature zone of the reaction furnace cavity, introducing a pretreatment atmosphere, and pretreating for 10-120 min;

[0010] (4) taking out the pretreated foam metal in step (3) after cooling under the carrier gas protection atmosphere, and obtaining the foam metal with the boron source uniformly distributed on the surface;

[0011] (5) heating the reaction furnace cavity to a set reduction temperature under a carrier gas protection atmosphere;

[0012] (6) putting the pretreated foam metal into the constant temperature zone of the reaction furnace cavity, introducing a reduction gas, and reducing for 10-60 min;

[0013] (7) introducing a mixed atmosphere of a nitrogen source gas, a reduction gas and a carrier gas into the reaction furnace cavity, and converting the solid boron source and the nitrogen source gas into h-BN on the surface of the foam metal substrate; the flow ratio of the nitrogen source gas, the reduction gas and the carrier gas in the mixed atmosphere is 1:(0.5-80):(0-100), and the reaction time is 1-500 min;

[0014] (8) taking out the foam metal obtained in step (7) after cooling under the carrier gas protection atmosphere, and obtaining a high-quality three-dimensional h-BN network structure grown on the foam metal substrate.

[0015] According to specific application requirements, the foam metal substrate can be selected to be reserved or removed by using a metal etching liquid, the h-BN without the foam metal substrate is sufficiently washed and dried, and the high-quality three-dimensional h-BN network is obtained.

[0016] The preparation method of the large-size high-quality three-dimensional hexagonal boron nitride network, in step (1), the solid boron source includes but is not limited to one or more than two kinds of mixture of boron oxide, boron powder, boric acid.

[0017] The preparation method of the large-size high-quality three-dimensional hexagonal boron nitride network, in step (1), the foam metal substrate template is a foam metal with a three-dimensional interconnected open hole structure, and the foam metal has a certain boron solid solubility or can form an intermediate product with boron, including but not limited to one of foam nickel, foam copper, foam iron, foam cobalt or an alloy formed by two or more than two kinds of metals; the porosity of the foam metal substrate template is distributed in 50-1000 PPI, the density is 0.1-1.5 g / cm 3 , the thickness is 0.1 mm-50 mm, and the length and width are 0.5 cm-2 m.

[0018] The preparation method of the large-size high-quality three-dimensional hexagonal boron nitride network, in step (2), the pretreatment temperature is 300-1050℃, preferably 600-1000℃.

[0019] The preparation method of the large-size high-quality three-dimensional hexagonal boron nitride network, in step (3), the pretreatment atmosphere is one or a mixture of two or more than two kinds of oxygen, argon, nitrogen, helium or hydrogen, and oxygen and hydrogen cannot be used at the same time, and the flow rate is 10-5000 sccm.

[0020] The preparation method of the large-size high-quality three-dimensional hexagonal boron nitride network, in steps (2), (4), (5), (7), (8), the carrier gas is one or a mixture of two kinds of argon and helium.

[0021] The preparation method of the large-size high-quality three-dimensional hexagonal boron nitride network, in step (7), the nitrogen source gas is ammonia or nitrogen, and the flow rate is 10-2000 sccm; in steps (6) and (7), the reducing gas is hydrogen, and the flow rate of the reducing gas in step (6) is 10-5000 sccm; in steps (5), (6), (7), the temperature of the reaction furnace cavity is 900-1300℃.

[0022] The preparation method of the large-size high-quality three-dimensional hexagonal boron nitride network, by selecting different foam metal substrates and / or adjusting the temperature, boron source type, nitrogen source type, and reaction atmosphere during preparation, the morphology, porosity, and layer number of the prepared three-dimensional h-BN network can be precisely controlled.

[0023] The preparation method of the large-size high-quality three-dimensional hexagonal boron nitride network, the prepared high-quality three-dimensional h-BN network is applied in the fields of heat conduction, energy storage, catalysis, adsorption or aerospace.

[0024] The mechanism of the present application is as follows:

[0025] The present application firstly loads solid boron source particles into the pores of the foam metal template, and then uniformly distributes and fixes the boron source on the surface of the foam metal template by treating the foam metal under a specific atmosphere and temperature. The solid boron source and gaseous nitrogen source are reacted on the surface of the foam metal template to generate a high-quality boron nitride layer under the catalysis of the foam metal template at a suitable temperature by using the CVD process.

[0026] The present application has the following advantages and beneficial effects:

[0027] 1. The present application uses the CVD process, which is superior to the ice template method, the salt template method, the bubble template method and other methods that rely on the assembly and connection of micron / nanometer-scale h-BN sheets to form a network with a large number of micro interfaces. The h-BN network prepared by the CVD process has the characteristics of controllable layer number and natural long-range connectivity, thereby having more excellent thermal and mechanical properties.

[0028] 2. The present application uses a foam metal with high catalytic activity as a base template to ensure that the prepared h-BN has excellent crystalline quality.

[0029] 3. The present application preloads solid boron source particles into the pores of the foam metal base, and then uniformly distributes and fixes the boron source on the surface of the foam metal base by treating the foam metal under a specific atmosphere and temperature. This overcomes the problem that the boron source is difficult to uniformly diffuse in the bulk phase when preparing large-size and dense-pore boron nitride networks by using the CVD process, and realizes the uniform and controllable preparation of large-size, especially large-thickness, three-dimensional h-BN networks.

[0030] 4. The present application can precisely control the morphology, porosity, pore size, shape, layer number and other indexes of the prepared three-dimensional h-BN network by selecting different foam metal bases and / or adjusting the temperature, boron source type, nitrogen source type, reaction atmosphere and other parameters during the preparation process. In the present application, the technical index range of the three-dimensional h-BN network structure is as follows: the average pore size is 25-500 mu m, the porosity is 50-1000 PPI, the layer number is 1-30 layers, and the area is 0.25 cm 2 ~ 4 m 2 .

[0031] 5. The present application uses boron oxide, boron powder or boric acid as the solid boron source, which is cheaper and safer than the precursor materials such as ammonia borane and borazine commonly used in conventional CVD, and lays a foundation for more economical and environmentally friendly large-scale preparation of large-size high-quality three-dimensional h-BN networks.

[0032] 6. The process is simple, low in production cost, and easy to mass-produce. Various characterization methods show that the prepared boron nitride has high crystalline quality and can be applied in the fields of heat conduction, energy storage, catalysis, adsorption, aerospace, etc. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The scanning electron microscope photos of the boron oxide supported on the surface of the nickel foam. Among them, Figure 1 b is Figure 1 a is a local enlarged view, Figure 1 b is the boron oxide powder marked in the box.

[0034] Figure 2 The energy spectrum characterization of the boron distribution on the surface of the nickel foam. Among them, Figure 2 a is the nickel foam, Figure 2 b is the boron oxide supported on the surface of the nickel foam.

[0035] Figure 3 The macroscopic photo of the three-dimensional h-BN network.

[0036] Figure 4 The scanning electron microscope photo of the three-dimensional h-BN network.

[0037] Figure 5 The Raman spectrum analysis of the three-dimensional h-BN network. In the figure, the horizontal coordinate Raman Shift represents the Raman shift (cm -1 ), and the vertical coordinate Intensity represents the relative intensity (a.u.).

[0038] Figure 6 The X-ray diffraction (XRD) analysis of the three-dimensional h-BN network. In the figure: the horizontal coordinate 2Theta represents the diffraction angle (degree), and the vertical coordinate Intensity represents the relative intensity (a.u.).

[0039] Figure 7 The macroscopic photo of the three-dimensional h-BN network.

[0040] Figure 8 The macroscopic photo of the comparative example 1.

[0041] Figure 9 The scanning electron microscope photo of the comparative example 1.

[0042] Figure 10 The macroscopic photo of the comparative example 2. DETAILED DESCRIPTION

[0043] In the specific implementation process, the present application uses porous metal as a template, uniformly fixes boron source on the surface of the template hole wall through pretreatment, and then uses chemical vapor deposition process to catalytically grow h-BN on the surface of the porous metal skeleton under suitable temperature and atmosphere conditions with nitrogen-containing gas as the nitrogen source. After removing the metal substrate, high-quality three-dimensional h-BN network can be obtained.

[0044] The present application will be further described in detail below in combination with the drawings and examples.

[0045] Example 1

[0046] A foam nickel with a size of 5 cm x 7 cm x 2 mm (porosity of 110 PPI and density of 0.2 g / cm 3 ) is placed in a container containing 10 g of boron oxide powder, shaken and oscillated for 10 min, and then taken out to obtain foam nickel loaded with a certain amount of boron oxide Figure 1 . A CVD horizontal tube furnace is used for pretreatment (solidification and uniform diffusion of boron source). First, the central region is heated to 850 DEG C under argon protection, 500 sccm of hydrogen is introduced, and after 30 min of heat preservation, it is pushed out of the high-temperature region and cooled to room temperature. Energy spectrum analysis of the surface of the pretreated foam nickel shows that the boron source is uniformly distributed Figure 2 b) on the surface of the foam nickel substrate Figure 2 a). Then the central region is heated to 1050 DEG C under argon protection, the pretreated foam nickel is placed in the constant temperature region of the reaction furnace cavity, and 500 sccm of hydrogen is introduced. The reduction time is 20 min. 500 sccm of ammonia, 500 sccm of hydrogen and 1000 sccm of argon are continuously introduced into the reaction furnace cavity for reaction, and three-dimensional h-BN network grown on the foam nickel can be obtained after 1 h of growth. The above foam nickel is taken out after cooling to room temperature under argon protection. According to the requirements, after etching the foam nickel with hydrochloric acid etching solution, cleaning and drying, three-dimensional h-BN network can be obtained. In this embodiment, the technical indicators of the three-dimensional h-BN network structure are as follows: the average pore size is 230 μm, the porosity is 110 PPI, the average number of layers is 5 layers, and the area is 35 cm 2 .

[0047] The macroscopic state and micro-morphology of the three-dimensional h-BN network are shown in Figure 3 and Figure 4 , respectively. As can be seen from the figures, the h-BN network has uniform number of layers and natural long-range open structure. As shown in Figure 5 , it can be seen from the Raman spectrum characterization of the obtained sample that due to the high reaction temperature and the catalytic activity of the metal substrate, the h-BN characteristic peak is obvious and sharp, and no defect peak appears. As shown in Figure 6As shown, the XRD results can show that the three-dimensional h-BN network has obvious characteristic diffraction peaks, the peak position is 26.5 degrees, the half-width is 0.102 degrees, and there is no peak position shift and impurity peak. The above results all show that the h-BN prepared by the method has very high crystalline quality.

[0048] Since the boron distribution energy spectrum analysis of the foam metal surface, the three-dimensional h-BN network micro-morphology, the Raman spectrum, and the XRD results in the following examples are basically the same as those in Example 1, they will not be described again.

[0049] Example 2:

[0050] A foam nickel with a size of 2 cm x 2 cm x 5 mm was put into a container containing 10 g of boron oxide powder, shaken and oscillated for 20 min, and then taken out to obtain a foam nickel loaded with a certain amount of boron oxide (porosity 300 PPI, density 0.5 g / cm 3 ). A CVD horizontal tube furnace was used for pretreatment. First, the central zone was heated to 800°C under argon protection, 150 sccm of hydrogen was introduced, and after 1 h of heat preservation, the foam nickel was pushed out of the high-temperature zone and cooled to room temperature to obtain a foam nickel uniformly loaded with solid boron source on the surface. Then the central zone was heated to 1000°C under argon protection, the pretreated foam nickel was put into the constant temperature zone of the reaction furnace cavity, and 100 sccm of hydrogen was introduced for reduction for 30 min; 150 sccm of ammonia and 300 sccm of hydrogen were continuously introduced into the reaction furnace cavity for reaction, and after 30 min of growth, a three-dimensional h-BN network grown on the foam nickel was obtained. After cooling to room temperature under argon protection, the above foam nickel was taken out. According to the requirements, after etching the foam nickel with hydrochloric acid etching solution, cleaning and drying, a three-dimensional h-BN network Figure 7 ) was obtained. In this example, the technical indicators of the three-dimensional h-BN network structure are as follows: the average pore size is 85 μm, the porosity is 300 PPI, the average number of layers is 10 layers, and the area is 4 cm 2 .

[0051] Example 3:

[0052] 3 g of boron powder was dissolved in 30 ml of ethanol, and ultrasonic treatment was performed for 30 min to obtain a uniform dispersion of boron powder. A foam nickel with a size of 3 cm x 3 cm x 5 mm (porosity 160 PPI, density 0.3 g / cm 3) repeatedly in the boron powder dispersion liquid, and dried to obtain the foam nickel loaded with a certain amount of boron powder. A CVD horizontal tube furnace was used for pretreatment. First, the center area was heated to 900°C under helium protection, 150 sccm of mixed gas of nitrogen and argon with a volume ratio of 1:1 was introduced, and after 1 h of heat preservation, the foam nickel was pushed out of the high-temperature area and cooled to room temperature to obtain the foam nickel uniformly loaded with solid-state boron source on the surface. Then, the center area was heated to 1020°C under helium protection, the pretreated foam nickel was put into the constant temperature area of the reaction furnace cavity, 800 sccm of hydrogen was introduced, and the reduction time was 50 min; 150 sccm of ammonia and 500 sccm of hydrogen were continuously introduced into the reaction furnace cavity for reaction, and after 30 min of growth, three-dimensional h-BN network grown on the foam nickel was obtained. The above foam nickel was taken out after cooling to room temperature under argon protection. According to the needs, the foam nickel was etched with nitric acid etching solution, and after cleaning and drying, three-dimensional h-BN network was obtained. In this embodiment, the technical indexes of the three-dimensional h-BN network structure are as follows: the average pore size is 160 μm, the porosity is 160 PPI, the average layer number is 3 layers, and the area is 9 cm 2 .

[0053] Example 4

[0054] 10 g of boric acid was dissolved in 200 ml of pure water, and ultrasonic treatment was performed for 30 min to obtain a boric acid solution. Foam nickel with a size of 5 cm x 10 cm x 1 cm (porosity of 200 PPI and density of 0.35 g / cm 3 ) was repeatedly pulled and dried in the boric acid solution to obtain foam nickel loaded with a certain amount of boric acid. A CVD horizontal tube furnace was used for pretreatment. First, the center area was heated to 600°C under argon protection, 100 sccm of hydrogen was introduced for reaction, and after 1 h of heat preservation, the foam nickel was pushed out of the high-temperature area and cooled to room temperature to obtain the foam nickel uniformly loaded with solid-state boron source on the surface. Then, the center area was heated to 1050°C under argon protection, the pretreated foam nickel was put into the constant temperature area of the reaction furnace cavity, and 120 sccm of hydrogen was introduced. The reduction time was 30 min; 150 sccm of nitrogen and 300 sccm of hydrogen were continuously introduced into the reaction furnace cavity for reaction, and after 2 h of growth, three-dimensional h-BN network grown on the foam nickel was obtained. The above foam nickel was taken out after cooling to room temperature under argon protection. According to the needs, the foam nickel was etched with hydrochloric acid etching solution, and after cleaning and drying, three-dimensional h-BN network was obtained. In this embodiment, the technical indexes of the three-dimensional h-BN network structure are as follows: the average pore size is 130 μm, the porosity is 200 PPI, the average layer number is 12 layers, and the area is 50 cm 2 .

[0055] Example 5

[0056] 50g boric acid was dissolved in 2000ml pure water, and ultrasonic treatment was performed for 30min to obtain a boric acid solution. A foam nickel with a size of 20cmx40cmx1mm (porosity of 400PPI and density of 0.5g / cm 3 ) was repeatedly pulled and dried in the boric acid solution to obtain foam nickel loaded with a certain amount of boric acid. A CVD horizontal tube furnace was used for pretreatment. First, the center zone was heated to 700°C under argon protection, 2000sccm of hydrogen was introduced for reaction, and after 1h of heat preservation, the foam nickel was pushed out of the high-temperature zone and cooled to room temperature to obtain foam nickel uniformly loaded with solid-state boron source on the surface. Then, the center zone was heated to 1020°C under argon protection, the pretreated foam nickel was placed in the constant temperature zone of the reaction furnace cavity, and 2000sccm of hydrogen was introduced for reduction for 40min. Then, 1000sccm of ammonia, 3000sccm of hydrogen and 2000sccm of argon were continuously introduced into the reaction furnace cavity for reaction, and after 3h of growth, three-dimensional h-BN network grown on the foam nickel was obtained. After cooling to room temperature under argon protection, the above foam nickel was taken out. According to the requirements, after etching the foam nickel with hydrochloric acid etching solution, the three-dimensional h-BN network was obtained after cleaning and drying. In this embodiment, the technical indexes of the three-dimensional h-BN network structure are as follows: the average pore size is 64μm, the porosity is 400PPI, the average layer number is 20 layers, and the area is 800cm 2 .

[0057] Example 6

[0058] A foam copper with a size of 3cmx2cmx3mm (porosity of 90PPI and density of 0.15g / cm 3 ) was placed in a container containing 10g of boron oxide powder, shaken and oscillated for 20min, and then taken out to obtain foam copper loaded with a certain amount of boron oxide. A CVD horizontal tube furnace was used for pretreatment. First, the center zone was heated to 800°C under helium protection, 150sccm of hydrogen was introduced, and after 1h of heat preservation, the foam copper was pushed out of the high-temperature zone and cooled to room temperature to obtain foam copper uniformly loaded with solid-state boron source on the surface. Then, the center zone was heated to 1000°C under helium protection, the pretreated foam copper was placed in the constant temperature zone of the reaction furnace cavity, and 70sccm of hydrogen was introduced for reduction for 20min. Then, 100sccm of ammonia and 200sccm of hydrogen were continuously introduced into the reaction furnace cavity for reaction, and after 4h of growth, three-dimensional h-BN network grown on the foam copper was obtained. After cooling to room temperature under argon protection, the above foam copper was taken out. According to the requirements, after etching the foam copper with sulfuric acid etching solution, the three-dimensional h-BN network was obtained after cleaning and drying. In this embodiment, the technical indexes of the three-dimensional h-BN network structure are as follows: the average pore size is 282μm, the porosity is 90PPI, the average layer number is 4 layers, and the area is 6cm 2 .

[0059] Example 7:

[0060] Foamed iron with a size of 2 cm x 2 cm x 1 mm (porosity of 110 PPI, density of 0.26 g / cm 3 ) was placed in a container containing 10 g of boron oxide powder, shaken for 20 min, and then taken out to obtain foamed iron loaded with a certain amount of boron oxide. A CVD horizontal tube furnace was used for pretreatment. First, the central zone was heated to 850°C under helium protection, 150 sccm of hydrogen was introduced, and after 1 h of heat preservation, the foamed iron was pushed out of the high-temperature zone and cooled to room temperature to obtain foamed iron uniformly loaded with solid-state boron source on the surface. Then, the central zone was heated to 1150°C under helium protection, the pretreated foamed iron was placed in the constant temperature zone of the reaction furnace cavity, and 90 sccm of hydrogen was introduced. The reduction time was 20 min. Then, 150 sccm of ammonia and 300 sccm of hydrogen were continuously introduced into the reaction furnace cavity for reaction. After 30 min of growth, three-dimensional h-BN networks grown on the foamed iron were obtained. The above foamed iron was taken out after cooling to room temperature under argon protection. According to the requirements, the three-dimensional h-BN networks were obtained by etching the foamed iron with hydrochloric acid etching solution, and then washing and drying. In this embodiment, the technical indicators of the three-dimensional h-BN network structure are as follows: the average pore size is 230 μm, the porosity is 110 PPI, the average number of layers is 6 layers, and the area is 4 cm 2 .

[0061] Comparative Example 1:

[0062] Foamed nickel with a size of 2 cm x 2 cm x 5 mm (porosity of 110 PPI, density of 0.2 g / cm 3 ) was ultrasonically treated in a 10% wt BN nanosheet isopropyl alcohol dispersion for 30 min, taken out and dried on a 70°C hot table for 30 min, and then the process was repeated three times to obtain foamed nickel loaded with BN nanosheets on the surface. A CVD horizontal tube furnace was used for growth. The above foamed nickel was pushed into the central temperature zone and heated to 1050°C under argon protection. After 2 h of heat preservation, the above foamed nickel was taken out after cooling to room temperature under argon protection. The foamed nickel was etched in hydrochloric acid, and then washed and dried to obtain high-temperature sintered h-BN networks. As shown in FIGS. Figure 8 and Figure 9 , due to the dependence on only the weak intermolecular interaction force during sintering, the material is easy to break, the microstructure cannot form a complete and connected three-dimensional network structure, there is obvious collapse, the interlayer overlap is loose, and the number of layers is uncontrollable.

[0063] Comparative Example 2:

[0064] A CVD horizontal tube furnace was used for growth. First, foamed nickel with a size of 1 cm x 1 cm x 5 mm (porosity of 110 PPI, density of 0.2 g / cm 3) Put in the center temperature zone of the tube furnace, take 0.3g ammonia borane powder, put it into the quartz boat, push it into the furnace tube near the gas inlet end, heat the ammonia borane powder through the external heating table. Under the protection of inert gas, heat the center temperature zone to 800℃, pass in 200sccm hydrogen, treat for 1h, so as to remove the surface adsorbed impurities of the foamed nickel. Increase the temperature of the center temperature zone to 1050℃, at the same time, increase the temperature of the heating table to 130℃, pass in 200sccm argon as carrier gas, grow for 2h. After cooling to room temperature under the protection of argon, take out the above foamed nickel, etch the foamed nickel in hydrochloric acid, clean and dry thoroughly to obtain the boron nitride network grown by ammonia borane. Due to the steric hindrance effect of the porous metal structure on the gas flow, the volatilized macromolecular ammonia borane cannot fully and uniformly penetrate the nickel foam, resulting in that the boron nitride growth is not completed in most of the bulk phase of the foamed nickel, so that there are obvious hollows in the center of the boron nitride foam prepared finally Figure 10

[0065] In summary, compared with the existing preparation process of three-dimensional h-BN network, the present application can avoid the problems of uneven growth and size limitation caused by the difficulty of boron source diffusion in the bulk phase, and the number of layers and network morphology of h-BN are controllable, the process is simple, the production cost is low, and the production is easy to put into mass production. The prepared boron nitride has high crystalline quality and can be applied in many fields.

[0066] The above provided examples are only explanatory and should not be considered as limiting the scope of the present application, any method of equivalent replacement or change according to the technical solutions and inventive concept of the present application should be covered within the protection scope of the present application.​

Claims

1. A method for preparing a large-size, high-quality three-dimensional hexagonal boron nitride network, characterized in that, The method includes the following steps: (1) Add the solid boron source in the form of dry powder or dispersion into the pores of the foam metal substrate template by shaking, oscillation, repeated lifting, ultrasonication or vacuum impregnation, and then put the boron-loaded foam metal into an oven to dry it thoroughly. (2) Heat the reactor chamber to the set pretreatment temperature under a carrier gas protective atmosphere; (3) Place foam metal with a solid boron source loaded on the surface into the constant temperature zone of the reactor cavity, introduce a pretreatment atmosphere, and pretreatment for 10 min to 120 min. In step (3), the pretreatment atmosphere is one or more of oxygen, argon, nitrogen, helium or hydrogen, and oxygen and hydrogen cannot be used at the same time. The flow rate is 10 to 5000 sccm. (4) Under the protective atmosphere of carrier gas, the foam metal pretreated in step (3) is cooled and taken out to obtain foam metal with boron source uniformly distributed on the surface; (5) Under the protective atmosphere of carrier gas, heat the reactor chamber to the set reduction temperature; (6) Place the pretreated foam metal into the constant temperature zone of the reactor cavity and introduce reducing gas for 10 min to 60 min. (7) A mixed atmosphere of nitrogen source gas, reducing gas and carrier gas is introduced into the reaction furnace cavity, and the solid boron source and nitrogen source gas are converted into h-BN on the surface of the foam metal substrate; in the mixed atmosphere, the flow rate ratio of nitrogen source gas, reducing gas and carrier gas is 1:(0.5~80):(0~100), and the reaction time is 1 min~500 min; (8) Under the protective atmosphere of carrier gas, the foam metal obtained in step (7) is cooled and taken out to obtain a high-quality h-BN network structure that is grown on the foam metal substrate and is three-dimensionally connected.

2. The method for preparing a large-size, high-quality three-dimensional hexagonal boron nitride network according to claim 1, characterized in that, Depending on the specific application requirements, you can choose to retain the foamed metal substrate or remove the foamed metal substrate using a metal etching solution. After removing the foamed metal substrate, the h-BN is thoroughly cleaned and dried to obtain a high-quality three-dimensional h-BN network.

3. The method for preparing a large-size, high-quality three-dimensional hexagonal boron nitride network according to claim 1, characterized in that, In step (1), the solid boron source includes, but is not limited to, one or a mixture of two or more of boron oxide, boron powder, and boric acid.

4. The method for preparing a large-size, high-quality three-dimensional hexagonal boron nitride network according to claim 1, characterized in that, In step (1), the foam metal substrate template is a foam metal with a three-dimensional interconnected open-cell structure. The foam metal has a certain boron solid solubility or can form intermediate products with boron, including but not limited to alloys formed by one or more of the following metals: nickel foam, copper foam, iron foam, and cobalt foam. The porosity of the foam metal substrate template is distributed between 50 and 1000 PPI, and the density is between 0.1 and 1.5 g / cm³. 3 The thickness ranges from 0.1 mm to 50 mm, and the length and width range from 0.5 cm to 2 m.

5. The method for preparing a large-size, high-quality three-dimensional hexagonal boron nitride network according to claim 1, characterized in that, In step (2), the pretreatment temperature is 300–1050 °C.

6. The method for preparing a large-size, high-quality three-dimensional hexagonal boron nitride network according to claim 1, characterized in that, In step (2), the pretreatment temperature is 600-1000 ℃.

7. The method for preparing a large-size, high-quality three-dimensional hexagonal boron nitride network according to claim 1, characterized in that, In steps (2), (4), (5), (7), and (8), the carrier gas is one or a mixture of argon and helium.

8. The method for preparing a large-size, high-quality three-dimensional hexagonal boron nitride network according to claim 1, characterized in that, In step (7), the nitrogen source gas is ammonia or nitrogen, and the flow rate is 10-2000 sccm; in steps (6) and (7), the reducing gas is hydrogen, and the flow rate of the reducing gas in step (6) is 10-5000 sccm; in steps (5), (6) and (7), the temperature of the reaction furnace cavity is 900-1300 ℃.

9. The method for preparing a large-size, high-quality three-dimensional hexagonal boron nitride network according to claim 1, characterized in that, This method allows for precise control over the morphology, porosity, and number of layers of the prepared three-dimensional h-BN network by selecting different foam metal substrates and / or adjusting the temperature, boron source type, nitrogen source type, and reaction atmosphere during the preparation process.

10. The method for preparing a large-size, high-quality three-dimensional hexagonal boron nitride network according to claim 1, characterized in that, The high-quality three-dimensional h-BN network prepared can be applied in the fields of thermal conduction, energy storage, catalysis, adsorption, or aerospace.

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