Fiber-reinforced boron nitride-based composite material and preparation method thereof

Abstract

The invention relates to the technical field of composite material processing, in particular to a fiber-reinforced boron nitride-based composite material and a preparation method thereof. The preparation method of the fiber-reinforced boron nitride-based composite material comprises the following steps: modifying boron nitride by adopting a modifier so as to introduce an active functional group on the surface of boron nitride, thereby obtaining modified boron nitride; mixing and ball-milling the modified boron nitride, polyborazine and an organic solvent to obtain hybrid composite slurry; infiltrating fiber reinforcements in the hybrid composite slurry, and then laying the fiber reinforcements infiltrated with the hybrid composite slurry layer by layer to obtain a laminated structure body; heating and curing the laminated structural body to obtain a solid-state three-dimensional network structural body; and sequentially carrying out hot pressing treatment and high-temperature cracking on the solid-state three-dimensional network structure body to obtain the fiber-reinforced boron nitride-based composite material. According to the method, the fiber-reinforced boron nitride-based composite material with relatively high density can be prepared in a short period by adopting a one-time forming and cracking process.

Description

Technical Field

[0001] This invention relates to the technical field of composite material processing, specifically to a fiber-reinforced boron nitride-based composite material and its preparation method. Background Technology

[0002] Composite materials with excellent wave transmission properties, lightweight and high strength, good thermal stability, and good environmental adaptability are gradually becoming key materials in high-end equipment manufacturing. Among them, fiber-reinforced boron nitride-based composite materials are considered an ideal choice for high-performance wave transmission materials due to their excellent physicochemical properties, such as low dielectric constant, high temperature resistance, corrosion resistance, and good mechanical properties.

[0003] Currently, methods for preparing fiber-reinforced boron nitride-based composites, such as polymer impregnation pyrolysis (PIP), chemical vapor deposition (CVD), and hot pressing sintering, suffer from numerous drawbacks, including long preparation cycles and high sintering temperatures. Taking polymer impregnation pyrolysis as an example, each impregnation and pyrolysis cycle can only gradually fill the pores, requiring multiple cycles to achieve the required density, severely limiting the large-scale application of the material. Furthermore, the repeated high-temperature treatments in traditional processes can damage the fibers, easily generating defects such as micropores and cracks in the composite material. These defects significantly reduce the material's wave transmission properties, mechanical properties, and thermal stability. Summary of the Invention

[0004] The technical problem solved by this invention is how to simplify the preparation process while preparing fiber-reinforced boron nitride-based composite materials with excellent wave transmission properties, mechanical properties, and thermal stability.

[0005] To address the aforementioned problems, as a first aspect, the present invention provides a method for preparing fiber-reinforced boron nitride-based composite materials, comprising: Boron nitride was modified using a modifier to introduce active functional groups onto the surface of the boron nitride, thereby obtaining modified boron nitride. The modified boron nitride, polyboronazine, and organic solvent were mixed and ball-milled to obtain a hybrid composite slurry; The fiber reinforcement is impregnated in the hybrid composite slurry, and then the fiber reinforcement impregnated with the hybrid composite slurry is laid layer by layer to obtain a laminated structure. The laminated structure is heated and cured to obtain a solid three-dimensional network structure. The solid three-dimensional network structure was subjected to hot pressing and high-temperature pyrolysis in sequence to obtain the fiber-reinforced boron nitride-based composite material.

[0006] Optionally, before impregnating the fiber reinforcement with the hybrid composite slurry, the method further includes heating the fiber reinforcement to 400 to 600°C and holding it at that temperature for 1 to 2 hours.

[0007] Optionally, the boron nitride is hexagonal boron nitride; and / or, the fiber reinforcement is selected from any one or more of silicon nitride fibers, boron nitride fibers, alumina fibers, carbon fibers, and quartz fibers.

[0008] Optionally, the modifier is selected from any one or more of urea, hydrogen peroxide, polycarboxylic organic acids, and silane coupling agents.

[0009] Optionally, the mass ratio of boron nitride to urea is 1:(2 to 10), the volume ratio of hydrogen peroxide solution to boron nitride is (5 to 10):1, the volume ratio of boron nitride to the polycarboxylic organic acid is 1:(2 to 15), and the mass ratio of boron nitride to the silane coupling agent is 1:(0.1 to 1).

[0010] Optionally, the heating and curing temperature of the laminated structure is 100 to 400°C, and the heat preservation time is 1 to 10 hours.

[0011] Optionally, in the hybrid composite slurry, the mass ratio of the modified boron nitride to the polyborazine is 1:(2 to 4).

[0012] Optionally, the temperature of the hot pressing treatment of the solid three-dimensional network structure is 100 to 500 °C and the pressure is 2 to 40 MPa; and / or, the temperature of the high-temperature pyrolysis of the solid three-dimensional network structure is 800 to 1600 °C and the holding time is 1 to 3 hours.

[0013] Optionally, the laminated structure is heated and cured in an inert atmosphere, a reducing atmosphere, or a vacuum environment to obtain the solid three-dimensional network structure; and / or, the high-temperature pyrolysis of the solid three-dimensional network structure is carried out in a reducing atmosphere environment.

[0014] As a second aspect, the present invention also provides a fiber-reinforced boron nitride-based composite material, which is prepared by the method for preparing fiber-reinforced boron nitride-based composite materials as described in the first aspect.

[0015] The advantages of this invention compared to related technologies include: This invention first uses modified boron nitride as a raw material. Amino, hydroxyl, and carboxyl functional groups are introduced onto the surface of boron nitride using a modifier. These functional groups can form stronger chemical bonds with polyboronazine, thereby improving the stability, uniformity, and interfacial bonding strength of the hybrid composite slurry. Good interfacial bonding effectively improves the mechanical properties of the material, making the composite material more stable under load and reducing the possibility of interfacial separation. Then, based on the characteristic that polyboronazine softens and melts upon heating, temperature and pressure are applied to promote the directional alignment of boron nitride layers, eliminating pores within the composite material and improving its density and mechanical properties. This allows for the preparation of high-density fiber-reinforced boron nitride-based composite materials in a short cycle using a one-time molding and pyrolysis process. Single-stage molding avoids damage to the reinforcing fibers caused by repeated high-temperature treatments. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the preparation process of fiber-reinforced boron nitride-based composite material in an exemplary embodiment of the present invention; Figure 2 This is a cross-sectional micrograph of the fiber-reinforced boron nitride-based composite material prepared in Example 1 of the present invention; Figure 3 Microscopic morphology of the boron nitride matrix of the composite material prepared in Example 1 of this invention; Figure 4 The image shows the transmission (TEM) image of the boron nitride matrix of the composite material prepared in Example 1 of this invention. Figure 5 This is a curve showing the flexural strength-displacement of the composite material prepared in Example 1 of the present invention. Detailed Implementation

[0017] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0018] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in the description of this application is for the purpose of describing particular embodiments only and is not intended to limit this application. The term "comprising" and its variations as used herein are open-ended, meaning "including but not limited to"; the term "based on" means "at least partially based on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments"; and the term "optionally" means "optional embodiments". Definitions of other terms will be given in the description below. It should be noted that the concepts of "first," "second," etc., mentioned in this invention are used to distinguish different objects, not to describe a specific order or hierarchy. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0019] This invention provides a method for preparing fiber-reinforced boron nitride-based composite materials, referring to... Figure 1 As shown, it includes the following steps: Step S1: Boron nitride is modified with a modifier to introduce active functional groups on the surface of boron nitride, thereby obtaining modified boron nitride; Step S2: The modified boron nitride, polyboronazine, and organic solvent are mixed and ball-milled to obtain a hybrid composite slurry; Step S3: Impregnate the fiber reinforcement in the hybrid composite slurry, and then lay the fiber reinforcement impregnated with the hybrid composite slurry layer by layer to obtain a laminated structure; Step S4: Heat and cure the laminated structure to obtain a solid three-dimensional network structure; Step S5: The solid three-dimensional network structure is subjected to hot pressing and high-temperature pyrolysis in sequence to obtain fiber-reinforced boron nitride-based composite material.

[0020] This invention first uses modified boron nitride as a raw material. A modifier introduces functional groups such as amino, hydroxyl, and carboxyl groups onto the surface of the boron nitride. These functional groups can form stronger chemical bonds with polyboron azela, thereby improving the stability, uniformity, and interfacial bonding strength of the hybrid composite slurry. Good interfacial bonding effectively improves the mechanical properties of the material, making the composite material more stable under load and reducing the possibility of interfacial separation. Then, based on the characteristic that polyboron azela softens and melts upon heating, temperature and pressure are applied to promote the directional alignment of boron nitride layers, eliminating pores within the composite material and improving its density and mechanical properties. This allows for the preparation of a high-density fiber-reinforced boron nitride-based composite material in a short cycle using a one-time molding and pyrolysis process. Single-stage molding avoids damage to the reinforcing fibers caused by repeated high-temperature treatments.

[0021] In some optional embodiments, in step S1 above, the modifier can be selected from any one or more of urea, hydrogen peroxide solution, polycarboxylic organic acids, and silane coupling agents. For example, taking urea as an example, urea contains an amino donor, which can introduce amino functional groups onto the surface of boron nitride. When modifying boron nitride with urea, boron nitride can be mixed with urea and deionized water and ball-milled at a speed of 300 to 500 r / min for 12 to 72 hours to obtain modified boron nitride. Thus, through the synergistic effect of mechanical force and chemical reaction, the chemical bonding between amino molecules and the surface of boron nitride is promoted, and active functional groups such as amino and hydroxyl groups are introduced onto the surface of boron nitride. The resulting slurry is vacuum filtered, rinsed with deionized water, and dried to obtain modified boron nitride with interface activation and functionalization. Hydrogen peroxide can generate hydroxyl functional groups on the surface of boron nitride. Specifically, the reaction of oxidant molecules on the surface of boron nitride and interlayer embedding can be promoted by ball milling. Polycarboxylic organic acids introduce carboxyl groups into the surface of hydroxylated boron nitride through esterification. Citric acid is an example of a polycarboxylic organic acid donor. In addition, silane coupling agents further modify the surface hydroxylated boron nitride with silanization, so that the surface of boron nitride has both organic and inorganic phase characteristics, which significantly improves its interfacial compatibility and dispersion stability with organic polymers. Examples of silane coupling agents include γ-aminopropyltriethoxysilane, KH-550, etc.

[0022] Specifically, when modifying boron nitride with urea, hydrogen peroxide solution, polycarboxylic organic acids, and silane coupling agents, the mass ratio of boron nitride to urea can be 1:(2 to 10), the volume ratio of hydrogen peroxide solution to boron nitride can be (5 to 10):1, the volume ratio of boron nitride to polycarboxylic organic acids can be 1:(2 to 15), and the mass ratio of boron nitride to silane coupling agents can be 1:(0.1 to 1). By adjusting the ratio of boron nitride to the modifier, it is beneficial to ensure the efficient introduction and uniform distribution of functional groups.

[0023] In some optional embodiments, the boron nitride is hexagonal boron nitride (h-BN), specifically hexagonal boron nitride powder. The fiber reinforcement is selected from any one or more of silicon nitride fibers, boron nitride fibers, alumina fibers, carbon fibers, and quartz fibers. Hexagonal boron nitride has a lamellar structure with directional arrangement characteristics, and can be oriented under pressured liquid phase conditions, eliminating pores and facilitating the formation of a dense composite material. Furthermore, during high-temperature pyrolysis, polyborane nitride decomposes into amorphous boron nitride, which is distributed between the layers of hexagonal boron nitride, and nano-sized boron nitride crystals precipitate in situ within the amorphous boron nitride. Therefore, the directional arrangement characteristics of hexagonal boron nitride and the in-situ precipitated nanocrystals can be used simultaneously to improve the crack propagation path during the fracture process of the composite material, thereby enhancing the mechanical properties of the composite material.

[0024] In some optional embodiments, in step S2 above, the organic solvent in the hybrid composite slurry is selected from one or more of toluene, xylene, and N,N-dimethylformamide, and the mass ratio of modified boron nitride to polyborazine is 1:(2 to 4). In this step, the polyborazine, modified boron nitride powder, and organic solvent are mixed and ball-milled at a speed of 200 to 500 r / min for 2 to 20 hours under an inert atmosphere. This allows the polyborazine molecules to achieve uniform adsorption and coating on the surface of the boron nitride sheets under the synergistic effect of mechanical force and intermolecular interactions, thereby constructing a stable organic-inorganic interface coupling structure at the nanoscale. This process not only endows the modified boron nitride with excellent dispersibility and interfacial bonding ability but also forms a chemically reactive hybrid composite slurry, providing a highly efficient, uniform, and high-performance boron nitride matrix for subsequent composite materials.

[0025] In some optional embodiments, step S3 above, before impregnating the fiber reinforcement with the hybrid composite slurry, further includes: heating the fiber reinforcement to 400 to 600°C and holding it at that temperature for 1 to 2 hours. This achieves complete pyrolysis removal of the wetting agent and organic residues on the surface of the fiber reinforcement, while simultaneously forming active sites on the fiber surface to achieve interface activation treatment, thereby significantly improving the bonding efficiency of the fiber-matrix interface.

[0026] In some optional embodiments, in step S3 above, the interface-activated fiber reinforcement is fully immersed in the hybrid composite slurry for a specific immersion time of more than 20 minutes to ensure uniform coating and deep wetting of the fiber surface. Subsequently, the fibers are laid layer by layer in the mold according to the designed direction to form a laminated structure with controllable spatial orientation. This step, through the regularization of fiber orientation and the uniform penetration of the interface slurry, achieves efficient synergy between the fiber reinforcement and the boron nitride matrix in the microstructure, providing structural assurance for densification and directional reinforcement during subsequent curing and hot pressing processes.

[0027] In some optional embodiments, in step S4 above, the heating and curing temperature of the laminated structure is 100 to 400°C, and the holding time is 1 to 10 hours. Specifically, this step can be carried out in an inert atmosphere, a reducing atmosphere, or a vacuum environment. The inert atmosphere can be nitrogen or argon, and the reducing atmosphere can be ammonia, hydrogen, or a mixture of these gases with nitrogen. The purpose of this step is to remove organic solvents and promote the crosslinking reaction between polyboronazine molecules and modified boron nitride, transforming the hybrid composite slurry from a fluid dynamic state into a continuous solid three-dimensional network structure. This achieves preliminary stable bonding at the fiber-matrix interface and provides structural integrity and morphological retention for subsequent hot pressing densification and high-temperature pyrolysis.

[0028] In some optional embodiments, in step S5 above, the temperature during hot pressing of the solid three-dimensional network structure is 100 to 500 °C, and the pressure is 2 to 40 MPa. Specifically, the solid three-dimensional network structure can be placed in a mold, and overall densification can be achieved through simultaneous heating and pressurization. During the hot pressing process, polyboronazine softens and melts upon heating, thereby acting as a transient liquid phase to promote the directional alignment of hexagonal boron nitride sheets under the action of an external pressure field; at the same time, the presence of liquid-phase polyboronazine helps to effectively eliminate internal pores and facilitate matrix flow rearrangement, thereby significantly improving the density of the composite material and endowing it with the ability to form complex shapes.

[0029] In some optional embodiments, in step S5 above, the temperature during high-temperature pyrolysis of the solid-state three-dimensional network structure is 800 to 1600 °C, and the holding time is 1 to 3 hours. The high-temperature pyrolysis of the solid-state three-dimensional network structure is carried out in a reducing atmosphere, which is ammonia, hydrogen, or a mixture of these gases with nitrogen. During this process, polyborane pyrolysis is converted into amorphous boron nitride, and boron nitride nanocrystals are precipitated in situ. The amorphous boron nitride acts as a binder phase, promoting strong interfacial bonding of the hexagonal boron nitride sheets, while the precipitation of boron nitride nanocrystals endows the composite material with excellent mechanical reinforcement. This dual-phase synergistic mechanism can effectively improve the strength, toughness, and structural stability of the composite material, ensuring its reliability in high-temperature service environments.

[0030] Another embodiment of the present invention provides a fiber-reinforced boron nitride-based composite material, which is prepared by the method described above for preparing fiber-reinforced boron nitride-based composite materials.

[0031] The present invention will be described in detail below through specific embodiments: Example 1 Weigh 10g of hexagonal boron nitride powder and 60g of urea powder, add an appropriate amount of deionized water, and place them in a ball mill jar. Then, ball mill the mixture in a planetary ball mill at 500 r / min for 24 hours. Next, remove the solution by vacuum filtration, repeatedly rinse with deionized water, and dry to obtain the modified boron nitride powder.

[0032] 10g of modified boron nitride powder, 40g of polyboronazine, and an appropriate amount of xylene were added to a ball mill jar and ball-milled at 300 rpm for 8 hours under nitrogen protection to obtain a hybrid composite slurry. Alumina continuous fibers were arranged in a muffle furnace and heated to 600℃ at a heating rate of 5℃ / min under air atmosphere and held for 60 minutes. The interface-activated fiber cloth was cut into 50mm × 50mm pieces, then uniformly impregnated in the hybrid composite slurry. The multi-layered impregnated fibers were then arranged in a quartz crucible in a layered configuration to obtain a laminated structure.

[0033] The laminated structure was placed in a tube furnace and heated to 200°C at a rate of 1°C / min under an ammonia atmosphere and held for 2 hours to allow the slurry to complete cross-linking, curing and structural immobilization, resulting in a solid three-dimensional network structure.

[0034] The solid three-dimensional network structure is further transferred to a stainless steel mold and placed in a hot press for directional densification. The upper and lower plates of the hot press are simultaneously heated to 180°C and subjected to a pressure of 10 MPa. The temperature and pressure are maintained for 2 hours to achieve the softening and flow of polyborane and the preferred orientation of boron nitride sheets, effectively eliminating pores and improving the material density.

[0035] Finally, the hot-pressed solid three-dimensional network structure was placed in a 900℃ high-temperature furnace and subjected to high-temperature pyrolysis in an ammonia atmosphere for 2 hours to obtain fiber-reinforced boron nitride-based composite material.

[0036] The cross-sectional microstructure of the fiber-reinforced boron nitride-based composite material prepared in this embodiment is as follows: Figure 2 As shown, Figure 2 It can be observed that the overall structure of the composite material is dense and the porosity is extremely low, indicating that the preparation process of this embodiment can achieve one-time efficient densification molding of fiber-reinforced boron nitride-based composite materials.

[0037] The boron nitride matrix microstructure of the composite material prepared in this embodiment is as follows: Figure 3 As shown, from Figure 3 As can be clearly seen, the boron nitride sheets exhibit a distinct directional arrangement within the material matrix. Therefore, through the softening properties of polyboronazine and the hot-pressing process, the hexagonal boron nitride sheets achieve an ordered arrangement. This directional arrangement effectively eliminates pores within the material and promotes the densification of the boron nitride matrix.

[0038] Figure 4 The image shows a transmission electron microscopy (TEM) image of the boron nitride matrix of the composite material prepared in this embodiment. It can be seen that the hexagonal boron nitride exhibits a directional arrangement, and the amorphous boron nitride converted from polyboronazine is distributed between the layers of hexagonal boron nitride, serving to fill pores and act as a binder. Furthermore, [the image is derived from...]. Figure 4 In situ precipitated nanocrystals can be observed, which are beneficial to improving the mechanical properties of composite materials.

[0039] Figure 5 This is a graph showing the flexural strength-displacement curve of the composite material prepared in this embodiment. Figure 5 The horizontal axis represents flexural displacement, and the vertical axis represents flexural strength. As shown in the figure, the flexural strength of the composite material at room temperature reaches 31 MPa.

[0040] Example 2 Weigh 10g of hexagonal boron nitride powder and 80g of urea powder, add an appropriate amount of deionized water, and place them in a ball mill jar. Then, ball mill the mixture in a planetary ball mill at 400 r / min for 48 hours. The resulting slurry is then vacuum filtered to remove the solution, repeatedly rinsed with deionized water, and dried to finally obtain modified boron nitride powder.

[0041] 10g of modified boron nitride powder, 20g of polyboronazine, and an appropriate amount of toluene were added to a ball mill jar and ball-milled at 250 rpm for 8 hours under nitrogen protection to obtain a hybrid composite slurry. Alumina continuous fibers were arranged in a muffle furnace and heated to 600℃ at a heating rate of 5℃ / min under air atmosphere and held for 60 minutes. The interface-activated fiber cloth was cut into 50mm×50mm pieces, then uniformly impregnated in the hybrid composite slurry. The multi-layered impregnated fibers were then arranged in a quartz crucible in a layered configuration to obtain a laminated structure.

[0042] The laminated structure was placed in a tube furnace and heated to 200°C at a rate of 2°C / min under an ammonia atmosphere and held for 2 hours to allow the slurry to complete cross-linking, curing and structural fixation, resulting in a solid three-dimensional network structure.

[0043] The solid three-dimensional network structure is further transferred to a stainless steel mold and placed in a hot press for directional densification. The upper and lower plates of the hot press are simultaneously heated to 180°C and subjected to a pressure of 10 MPa. The constant temperature and pressure are maintained for 3 hours to achieve the softening and flow of polyborane and the preferred orientation of boron nitride sheets, effectively eliminating pores and improving the material density.

[0044] Finally, the hot-pressed solid three-dimensional network structure was placed in a 1200℃ high-temperature furnace and subjected to high-temperature pyrolysis in an ammonia atmosphere for 2 hours to obtain fiber-reinforced boron nitride-based composite material.

[0045] The boron nitride-based composite material prepared in this embodiment has a bulk density of 1.80 g·cm³. -3 The composite material not only exhibits excellent mechanical properties, but also displays typical pseudoplastic fracture characteristics, indicating that it has excellent energy dissipation and fracture resistance during loading, providing a reliable guarantee for the application of high-temperature structural ceramics.

[0046] Example 3 The difference between this embodiment and Embodiment 1 is that this embodiment modifies the hexagonal boron nitride powder in the following way: Hexagonal boron nitride powder was introduced into a high-energy ball milling system along with an appropriate amount of hydrogen peroxide solution and deionized water. The mixture was continuously ball-milled at 300 r / min for 48 hours to generate hydroxyl functional groups on the surface of the boron nitride. The volume ratio of hydrogen peroxide solution to the mass ratio of hexagonal boron nitride was 5:1. The resulting slurry was then vacuum-filtered, repeatedly washed with deionized water, and dried at 100℃ to obtain hydroxylated modified boron nitride powder.

[0047] Example 4 The difference between this embodiment and Example 1 is that this embodiment further modifies the hydroxylated boron nitride powder in Example 3 using the following method: The hydroxylated modified boron nitride powder from Example 3 was mixed with citric acid at a mass ratio of 1:5. The mixture was first preheated at 120°C for 30 minutes to melt the citric acid and fully wet the surface of the hydroxylated modified boron nitride powder. Then, the temperature was raised to 180°C and held for 12 hours. Through the synergistic effect of thermally induced dehydration condensation and mechanical stirring, the carboxyl groups in the citric acid molecules underwent an esterification reaction with the hydroxyl groups on the boron nitride surface, forming stable ester bonds. Simultaneously, some unreacted free carboxyl groups (–COOH) were retained. After the reaction, the mixture was cooled, ground, and washed repeatedly with deionized water to remove unreacted substances. Vacuum drying yielded BN-COOH powder with a carboxyl-rich surface. This modification process significantly improves the surface polarity and chemical activity of the boron nitride powder, resulting in stronger reactivity and dispersion stability in subsequent composite reactions or interfacial bonding, providing better interfacial compatibility for its application in polymer composites and functional interface construction.

[0048] Example 5 The difference between this embodiment and Embodiment 1 is that this embodiment modifies the hexagonal boron nitride powder in the following way: The hydroxylated modified boron nitride powder from Example 3 was mixed with γ-aminopropyltriethoxysilane and anhydrous ethanol to form a homogeneous suspension system under stirring. The mass ratio of the hydroxylated modified boron nitride powder to γ-aminopropyltriethoxysilane was 1:1. The homogeneous suspension system was refluxed at 80°C for 26 hours. Through silane hydrolysis and condensation reactions, the Si–O groups in the silane coupling agent molecule chemically bonded to the hydroxyl groups on the surface of boron nitride, forming BN–O–Si covalent bonds. After the reaction, the reaction mixture was vacuum filtered and washed alternately with ethanol and deionized water to remove unreacted substances. It was then dried at 80°C to obtain silanized modified boron nitride powder. This modification endows the surface of boron nitride with both organic and inorganic phase characteristics, significantly improving its interfacial compatibility and dispersion stability with organic polymers.

[0049] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A method for preparing a fiber-reinforced boron nitride-based composite material, characterized in that, include: Boron nitride was modified using a modifier to introduce active functional groups onto the surface of the boron nitride, thereby obtaining modified boron nitride. The modified boron nitride, polyboronazine, and organic solvent were mixed and ball-milled to obtain a hybrid composite slurry; The fiber reinforcement is impregnated in the hybrid composite slurry, and then the fiber reinforcement impregnated with the hybrid composite slurry is laid layer by layer to obtain a laminated structure. The laminated structure is heated and cured to obtain a solid three-dimensional network structure. The solid three-dimensional network structure was subjected to hot pressing and high-temperature pyrolysis in sequence to obtain the fiber-reinforced boron nitride-based composite material.

2. The method for preparing fiber-reinforced boron nitride-based composite materials according to claim 1, characterized in that, Before immersing the fiber reinforcement in the hybrid composite slurry, the method further includes heating the fiber reinforcement to 400 to 600°C and holding it at that temperature for 1 to 2 hours.

3. The method for preparing fiber-reinforced boron nitride-based composite materials according to claim 1, characterized in that, The boron nitride is hexagonal boron nitride; and / or, the fiber reinforcement is selected from any one or more of silicon nitride fibers, boron nitride fibers, alumina fibers, carbon fibers, and quartz fibers.

4. The method for preparing fiber-reinforced boron nitride-based composite materials according to claim 1, characterized in that, The modifier is selected from any one or more of urea, hydrogen peroxide solution, polycarboxylic organic acids and silane coupling agents.

5. The method for preparing fiber-reinforced boron nitride-based composite materials according to claim 4, characterized in that, The mass ratio of boron nitride to urea is 1:(2 to 10), the volume ratio of hydrogen peroxide solution to the mass of boron nitride is (5 to 10):1, the volume ratio of boron nitride to the polycarboxylic organic acid is 1:(2 to 15), and the mass ratio of boron nitride to the silane coupling agent is 1:(0.1 to 1).

6. The method for preparing fiber-reinforced boron nitride-based composite materials according to claim 1, characterized in that, The heating and curing temperature of the laminated structure is 100 to 400°C, and the heat preservation time is 1 to 10 hours.

7. The method for preparing fiber-reinforced boron nitride-based composite materials according to claim 1, characterized in that, In the hybrid composite slurry, the mass ratio of the modified boron nitride to the polyboronazine is 1:(2 to 4).

8. The method for preparing fiber-reinforced boron nitride-based composite material according to claim 1, characterized in that, The solid three-dimensional network structure is subjected to hot pressing at a temperature of 100 to 500 °C and a pressure of 2 to 40 MPa; and / or, the solid three-dimensional network structure is subjected to high-temperature pyrolysis at a temperature of 800 to 1600 °C and a holding time of 1 to 3 hours.

9. The method for preparing fiber-reinforced boron nitride-based composite material according to claim 1, characterized in that, The laminated structure is heated and cured in an inert atmosphere, a reducing atmosphere, or a vacuum environment to obtain the solid three-dimensional network structure; and / or, the high-temperature pyrolysis of the solid three-dimensional network structure is carried out in a reducing atmosphere environment.

10. A fiber-reinforced boron nitride-based composite material, characterized in that, The fiber-reinforced boron nitride-based composite material was prepared using the preparation method described in any one of claims 1 to 9.

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