Pyrolytic carbon armored boron nitride aerogel and preparation method thereof

Abstract

The invention discloses pyrolytic carbon armored boron nitride aerogel and a preparation method thereof, and relates to the technical field of aerogel materials. The method comprises the step of armoring pyrolytic carbon on the surface of boron nitride aerogel through a chemical vapor deposition method to obtain the pyrolytic carbon armoured boron nitride aerogel. The pyrolytic carbon armored boron nitride aerogel prepared by the invention has the characteristic of cross-magnitude customization of mechanical properties, and shows ultrahigh compression strength, elastic response conductivity and excellent flame retardant property. The preparation method is simple and efficient, the preparation period is short, large-scale production is easy, and the production cost can be remarkably reduced.

Description

Technical Field

[0001] The invention relates to the technical field of aerogel materials, and in particular to a pyrolytic carbon-armored boron nitride aerogel and a preparation method thereof. Background Art

[0002] From thermal protection of deep space probes to thermal management in extreme environments, human demand for extreme materials has shifted from single light weight and high temperature resistance to comprehensive requirements for mechanical properties and multifunctionality. Ceramic aerogels are ideal candidate materials for extreme environment applications due to their high porosity, light weight and excellent thermal stability. However, traditional ceramic aerogels are usually constructed of loosely cross-linked nanoparticles, and their fragile network structure is prone to failure under high mechanical loads. This long-standing defect significantly limits its practical application potential. Therefore, researchers continue to explore new strategies to overcome the key challenge of mechanical brittleness.

[0003] Introducing a second phase to support the network structure or changing the constituent units of ceramic aerogels can effectively solve the problem of mechanical brittleness. The prior art discloses a method for obtaining a highly elastic titanium dioxide nanowire aerogel material by a complex high-temperature hydrothermal reaction of titanate wet gel, and through acid treatment, solvent exchange, supercritical drying and heat treatment. However, the preparation method has a long cycle and high requirements for preparation conditions, which limits its practical application. At the same time, the prior art discloses a method for preparing a high-strength and low-thermal-conductivity ceramic aerogel material. After the SiO2 nanofibers and the aerogel precursor liquid are evenly dispersed, freeze-molded, freeze-dried, and sintered at high temperature, the obtained aerogel is immersed in a graphene and silica sol dispersion again and freeze-dried along the axial direction of the hole to obtain a bamboo-like structure ceramic aerogel material. This method achieves the high strength of ceramic aerogels through the coordinated structural assembly of multi-phase components, but the preparation process of this method is complex and has low universality.

[0004] Therefore, there is still an urgent need to develop a simple, efficient and scalable regulation strategy to achieve multi-scale mechanical property regulation of ceramic aerogels and give them high-temperature stability and multifunctional integration capabilities in extreme environments to meet the actual needs of aerospace, energy storage, high-temperature protection and other fields. Summary of the invention

[0005] In view of the deficiencies in the above-mentioned background technology, the present invention mainly solves the problems that the preparation process of existing ceramic aerogels is complicated and the preparation cycle is long. The present invention provides a pyrolytic carbon armored boron nitride aerogel and a preparation method thereof. The method adopts a chemical vapor deposition method to prepare pyrolytic carbon armored boron nitride aerogel, and by regulating the thickness of the pyrolytic carbon armor, an order of magnitude improvement in the mechanical properties of the aerogel is achieved. The pyrolytic carbon armored boron nitride aerogel provided by the present invention has the characteristics of cross-order customization of mechanical properties, and exhibits ultra-high compressive strength, elastic response conductivity and excellent flame retardant properties. The preparation method is simple and efficient, has a short preparation cycle, is easy to mass produce, and can significantly reduce production costs.

[0006] The first object of the present invention is to provide a method for preparing pyrolytic carbon-armored boron nitride aerogel, comprising the following steps: The surface of the boron nitride aerogel is armored with pyrolytic carbon by chemical vapor deposition to obtain pyrolytic carbon armored boron nitride aerogel.

[0007] Preferably, when pyrolytic carbon is armored on the surface of boron nitride aerogel by chemical vapor deposition, it includes: Under the protection of an inert atmosphere, the boron nitride aerogel is placed in a deposition chamber at 900-1200°C and reactant gas is introduced for deposition for 0.1-10 hours. Wherein, the reaction gas is methane or propylene.

[0008] Preferably, the reaction gas has an inlet flow rate of 50-200 mL / min.

[0009] Preferably, the boron nitride aerogel is placed in a deposition chamber and heated to 900-1200° C. at a rate of 2-10° C. / min.

[0010] Preferably, the boron nitride aerogel is prepared according to the following steps: dissolving melamine and boric acid in a solvent to obtain a melamine / boric acid supramolecular solution; The melamine / boric acid supramolecular solution is subjected to vacuum freeze drying to obtain a melamine / boric acid supramolecular aerogel; In a mixed atmosphere, the melamine / boric acid supramolecular aerogel is heat-treated at 1000-1500°C for 2-6 hours to obtain boron nitride aerogel; Wherein, the mixed atmosphere is one or more of ammonia, argon, and nitrogen; The solvent is prepared from water solvent and polar solvent.

[0011] Preferably, the molar ratio of melamine to boric acid is 1:1-6.

[0012] Preferably, the polar solvent includes one or more of methanol, ethanol, ethylene glycol, n-propanol, isopropanol, isobutanol, sec-butanol, tert-butanol, and dimethyl sulfoxide; The volume ratio of the water solvent to the polar solvent is 1:0.5-2.

[0013] Preferably, during the vacuum freeze-drying process, the temperature is -196 to -20°C and the duration is 24 to 48 hours.

[0014] The second object of the present invention is to provide a pyrolytic carbon armored boron nitride aerogel, characterized in that the volume density of the pyrolytic carbon armored boron nitride aerogel is 20-300 mg / cm 3 , the thickness of pyrolytic carbon is 10~800 nm.

[0015] The third object of the present invention is to provide an application of pyrolytic carbon armored boron nitride aerogel in thermal protection.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a pyrolytic carbon armored boron nitride aerogel and a preparation method thereof. The present invention adopts a chemical vapor deposition method to prepare a pyrolytic carbon armored boron nitride aerogel, and achieves an order of magnitude improvement in the mechanical properties of the aerogel by regulating the thickness of the pyrolytic carbon armor. Boron nitride aerogel solves the problem of the fragile mechanical properties of traditional ceramic aerogels through effective armoring with pyrolytic carbon, and can directly customize the mechanical properties of the aerogel from superelasticity to rigidity. At the same time, the material is endowed with excellent conductivity and high-temperature stability, which makes it show broad application prospects in the fields of pressure sensors, flexible electronic devices, high-temperature protection, etc., and has important research value and industrialization potential.

[0017] The main raw materials used in the present invention include melamine and boric acid, and the boron nitride aerogel is prepared by freeze drying and heat treatment process, and the pyrolytic carbon armored boron nitride aerogel is prepared by chemical vapor deposition. The preparation method is simple and efficient, suitable for large-scale production, and significantly reduces the production cost; The present invention achieves an order of magnitude improvement in the mechanical properties of aerogel by regulating the thickness of the pyrolytic carbon armor. The prepared superelastic aerogel has a compressive strength of up to 200 kPa at 60% strain, showing ultra-high compressive strength. At the same time, the material has excellent compression resilience, and there is no permanent deformation after 100 cyclic compression tests at 60% strain. The mechanical fatigue performance is significantly improved, which can meet the needs of high-load applications. In addition, changing the thickness of the pyrolytic carbon armor can achieve a qualitative change in the mechanical properties of the aerogel, which can withstand megapascal stress strength under low strain.

[0018] The pyrolytic carbon armored boron nitride aerogel prepared by the present invention has elastic responsive conductivity. When the aerogel is subjected to compressive stress, the contact points of the outer pyrolytic carbon armor increase, thereby forming a conductive three-dimensional network. This property gives the aerogel potential for application in pressure sensors and flexible electronic devices.

[0019] The pyrolytic carbon armored boron nitride aerogel prepared by the present invention has high-temperature mechanical stability and flame retardant properties. Thanks to the protection of the pyrolytic carbon armor, the aerogel still maintains good mechanical stability after high-temperature heat treatment. Under the flame of a 600°C alcohol lamp, the aerogel did not show combustion or oxidation damage, showing excellent physical and chemical stability and safety in use, greatly expanding its application possibilities in high temperature and extreme environments.

[0020] In summary, the present invention prepares pyrolytic carbon armored boron nitride aerogel with ultra-high mechanical properties, elastic conductivity and flame retardant properties through a process combining freeze drying and chemical vapor deposition. The method is simple and efficient and suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is an optical photograph of the pyrolytic carbon armored boron nitride aerogel prepared in Example 1; Figure 2 The mechanical properties of the pyrolytic carbon armored boron nitride aerogel prepared in Example 1 are shown; Figure 3 The elastic responsive conductivity of the pyrolytic carbon armored boron nitride aerogel prepared in Example 1 is demonstrated; Figure 4 The flame retardant properties of the pyrolytic carbon armored boron nitride aerogel prepared in Example 1; Figure 5 The mechanical properties of the boron nitride aerogel and the pyrolytic carbon armored boron nitride aerogel prepared in Examples 1 to 4 are adjustable across orders of magnitude. DETAILED DESCRIPTION

[0022] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention is further described below in conjunction with specific embodiments and drawings, but the embodiments are not intended to limit the present invention.

[0023] The present invention aims to achieve cross-scale mechanical property regulation of ceramic aerogels and endow them with high temperature stability and multifunctional integration capabilities in extreme environments to meet the actual needs of aerospace, energy storage, high temperature protection and other fields. A pyrolytic carbon armored boron nitride aerogel and a preparation method thereof are provided, and the pyrolytic carbon armored boron nitride aerogel is prepared by chemical vapor deposition. The preparation method is simple and efficient, suitable for large-scale production, and significantly reduces production costs.

[0024] In order to achieve the above object, the first aspect of the present invention provides a method for preparing a pyrolytic carbon armored boron nitride aerogel, comprising the following steps: The surface of the boron nitride aerogel is armored with pyrolytic carbon by chemical vapor deposition to obtain pyrolytic carbon armored boron nitride aerogel.

[0025] The present invention adopts chemical vapor deposition to prepare pyrolytic carbon armored boron nitride aerogel, and achieves an order of magnitude improvement in the mechanical properties of the aerogel by regulating the thickness of the pyrolytic carbon armor. Boron nitride aerogel solves the problem of fragile mechanical properties of traditional ceramic aerogels through effective armoring with pyrolytic carbon, and can directly customize the mechanical properties of aerogels from superelasticity to rigidity. At the same time, the material is endowed with excellent conductivity and high-temperature stability, which makes it show broad application prospects in the fields of pressure sensors, flexible electronic devices, high-temperature protection, etc., and has important research value and industrialization potential.

[0026] According to the present invention, when armoring pyrolytic carbon on the surface of boron nitride aerogel by chemical vapor deposition, it includes: placing the boron nitride aerogel in a deposition chamber under the protection of an inert atmosphere, at 900-1200° C., and introducing a reaction gas, and depositing for 0.1-10 hours; wherein the reaction gas is methane or propylene.

[0027] The flow rate of the reaction gas is 50-200 mL / min.

[0028] The present invention controls the thickness of armored pyrolytic carbon by controlling the duration of deposition. Pyrolytic carbon is chemically deposited on the surface of boron nitride aerogel. The chemical vapor deposition process specifically includes: 1) Precursor decomposition: CH4 is cracked at high temperature to generate carbon radicals (such as ·CH3, ·CH2, etc.) and hydrogen (H2); 2) Surface reaction: The cracking products are chemically adsorbed and reorganized on the surface of boron nitride to form stable CC or CB / N bonds; 3) Nucleation and growth: Carbon atoms gradually build up the pyrolytic carbon coating through covalent bonds. The whole process involves the breaking and formation of chemical bonds, which is a typical chemical deposition mechanism rather than physical adsorption.

[0029] The boron nitride aerogel is placed in a deposition chamber and heated to 900-1200°C at a rate of 2-10°C / min.

[0030] According to the present invention, the boron nitride aerogel is prepared according to the following steps: dissolving melamine and boric acid in a solvent to obtain a melamine / boric acid supramolecular solution; The melamine / boric acid supramolecular solution is subjected to vacuum freeze drying to obtain melamine / boric acid supramolecular aerogel; the vacuum freeze drying is performed to maintain the band structure of the supramolecular, and the overall structure is not changed during the solvent sublimation process, thereby forming a porous three-dimensional network.

[0031] In a mixed atmosphere, melamine / boric acid supramolecular aerogel is heat treated at 1000~1500℃ for 2~6h to obtain boron nitride aerogel; according to the thermogravimetric curve, the polymer supramolecular will completely decompose above 1000℃, so it is necessary to carry out pyrolysis and reaction at the temperature of 1000~1500℃ to finally obtain the boron nitride aerogel.

[0032] The mechanism of formation of boron nitride aerogel in the present invention includes: Supramolecular self-assembly: Melamine and boric acid assemble into an ordered M·2B supramolecular network through hydrogen bonding interactions (such as NH···O, BO···HN); the polarity of the solvent (such as a mixed solution of water and tert-butanol) is used to regulate the hydrogen bond strength and molecular arrangement to form a three-dimensional porous gel skeleton.

[0033] Heat treatment and structural evolution: First, the dehydration stage (150~200°C): H3BO3 dehydrates to form B2O3, destroying some hydrogen bonds but retaining the covalent bond network; condensation stage (200~400°C): B2O3 and melamine (C3N6H6) form a covalent bridge structure through the BON bond, and melamine itself deaminates and condenses to form an organic-inorganic hybrid network wrapped in an amorphous boron oxide matrix. Ring opening and decomposition (around 500°C): The azine ring opens to generate oxygen / nitrogen-containing intermediates (such as -NH=C=O, N≡C-NH-), and releases CO2 and HCN gases, gradually decarbonizing and forming a boron-nitrogen-rich skeleton. Nitriding stage (500~1000°C): B2O3 reacts with NH3 (or nitrogen-containing gas released in situ) to generate OBN and final NBN bonds, forming a planar hexagonal network structure of hexagonal boron nitride (h-BN).

[0034] Porous structure retention: The hydrogen bond network of the supramolecular precursor is converted into a covalent bond network at the initial stage of heat treatment to maintain the stability of the porous skeleton; the release of volatiles (H2O, NH3, CO2, etc.) further optimizes the pore structure and ultimately forms a lightweight boron nitride aerogel.

[0035] Wherein, the mixed atmosphere is one or more of ammonia, argon and nitrogen. Since the reaction is carried out at high temperature, the mixed atmosphere is selected to provide an inert environment.

[0036] The solvent is prepared by mixing a water solvent and a polar solvent.

[0037] The molar ratio of melamine to boric acid is 1:1-6.

[0038] The polar solvent includes one or more of methanol, ethanol, ethylene glycol, n-propanol, isopropanol, isobutanol, sec-butanol, tert-butanol, and dimethyl sulfoxide; The polar solvent used in the present invention is intended to promote hydrogen bond assembly and regulate assembly dynamics and morphology. Among them, promoting hydrogen bond assembly: the original molecules (melamine and boric acid) contain abundant polar groups (-NH2, -OH, BO, etc.), and the water solvent interacts with the molecules through strong hydrogen bonds, promotes supramolecular self-assembly, and regulates assembly dynamics and morphology, while the polarity (dielectric constant) of the solvent affects the strength and direction of the intermolecular forces. For example: water-tert-butyl alcohol mixed solvent: the lower polarity part of tert-butyl alcohol destroys the hydrogen bond strength, slows down the assembly rate, and leads to a flat microstructure; the difference in the volatility of the solvent will also affect the formation and distribution of gel pores.

[0039] The volume ratio of the water solvent to the polar solvent is 1:0.5-2.

[0040] During the vacuum freeze-drying process, the temperature is -196~-20°C and the duration is 24~48h.

[0041] Exemplarily, a method for preparing pyrolytic carbon-armored boron nitride aerogel comprises: Step 1: heat-treating the melamine / boric acid supramolecular aerogel to obtain boron nitride aerogel; Step 2: Using chemical vapor deposition to deposit pyrolytic carbon on boron nitride aerogel to obtain pyrolytic carbon armored boron nitride aerogel.

[0042] The preparation method of the melamine / boric acid supramolecular aerogel in step 1 comprises the following steps: Dissolving melamine and boric acid in a solvent to obtain a transparent melamine / boric acid supramolecular solution, wherein the molar ratio of melamine to boric acid is 1:6 to 1:1; The melamine / boric acid supramolecular solution is subjected to vacuum freeze drying to obtain the melamine / boric acid supramolecular aerogel, wherein the freezing temperature is -196 to -20°C and the vacuum freeze drying time is 24 to 48 hours.

[0043] The thermal treatment of the melamine / boric acid supramolecular aerogel in step 1 comprises the following steps: The melamine / boric acid supramolecular aerogel is placed in a high temperature atmosphere for heat treatment, the heat treatment temperature is 1000-1500° C., and the heat treatment time is 2-6 hours. Among them, one of ammonia, argon, and nitrogen or a mixed atmosphere of any two of them is used as the high temperature atmosphere.

[0044] The chemical vapor deposition method in step 2 for pyrolytic carbon deposition on boron nitride aerogel comprises the following steps: The boron nitride aerogel is placed in the heating zone, and the entire process is carried out in flowing argon. After heating to 900-1200°C at a rate of 2-10°C / min, the precursor is one of methane or propylene, the gas flow rate is 50-200 mL / min, and the deposition time is 0.1 to 10 hours.

[0045] The second aspect of the present invention provides a pyrolytic carbon armored boron nitride aerogel, wherein the volume density of the pyrolytic carbon armored boron nitride aerogel is 20-300 mg / cm 3 , the thickness of pyrolytic carbon is 10~800 nm.

[0046] A third aspect of the present invention provides an application of pyrolytic carbon armored boron nitride aerogel in thermal protection.

[0047] It should be noted that the experimental methods used in the present invention are all conventional methods unless otherwise specified; the reagents and materials used are all commercially available unless otherwise specified.

[0048] Example 1 A method for preparing pyrolytic carbon-armored boron nitride aerogel comprises the following steps: Step 1: First, melamine and boric acid are dissolved in a solvent consisting of water and tert-butyl alcohol in a volume ratio of 1:2 in a molar ratio of 1:2 to obtain a transparent melamine / boric acid supramolecular solution. Subsequently, the solution is freeze-dried to obtain melamine / boric acid supramolecular aerogel, wherein the freezing temperature is -60°C and the vacuum freeze-drying time is 48 hours. Finally, the melamine / boric acid supramolecular aerogel is placed in a high-temperature ammonia atmosphere for heat treatment at a temperature of 1100°C and a heat preservation time of 4 hours to obtain boron nitride aerogel.

[0049] Step 2: During the chemical vapor deposition process, the boron nitride aerogel is placed in the heating zone, and the entire process is carried out in flowing argon. After heating to 900°C at a rate of 10°C / min, the carbon source precursor methane is introduced, the gas flow rate is controlled at 50 mL / min, and the deposition time is 1 h, and finally the pyrolysis carbon armored boron nitride aerogel is obtained.

[0050] The volume density of the prepared pyrolytic carbon armored boron nitride aerogel is 20 mg / cm 3 The deposition thickness of pyrolytic carbon is 20 nm. Boron nitride aerogel armored with pyrolytic carbon has excellent compression resilience. At 60% strain, its compression strength is as high as 80kPa. After 100 cycles of compression with a strain of 60%, no permanent deformation occurs.

[0051] Example 2 A method for preparing pyrolytic carbon-armored boron nitride aerogel comprises the following steps: Step 1: First, melamine and boric acid are dissolved in a solvent consisting of water and tert-butyl alcohol in a volume ratio of 1:1 in a molar ratio of 1:1 to obtain a transparent melamine / boric acid supramolecular solution. Subsequently, the solution is freeze-dried to obtain a melamine / boric acid supramolecular aerogel, wherein the freezing temperature is -40°C and the vacuum freeze-drying time is 48 hours. Finally, the melamine / boric acid supramolecular aerogel is placed in a high-temperature nitrogen atmosphere for heat treatment at a temperature of 1300°C and a heat preservation time of 4 hours to obtain a boron nitride aerogel.

[0052] Step 2: During the chemical vapor deposition process, the boron nitride aerogel is placed in the heating zone, and the entire process is carried out in flowing argon. After heating to 1000°C at a rate of 10°C / min, the carbon source precursor methane is introduced, the gas flow rate is controlled to 60 mL / min, and the deposition time is 2h, and finally the pyrolysis carbon armored boron nitride aerogel is obtained.

[0053] The volume density of the prepared pyrolytic carbon armored boron nitride aerogel is 50 mg / cm 3 The deposition thickness of pyrolytic carbon is 50 nm. The boron nitride aerogel armored with pyrolytic carbon has excellent compression resilience. At 60% strain, its compression strength is as high as 200kPa. After 100 cycles of compression with a strain of 60%, no permanent deformation occurs.

[0054] Example 3 A pyrolytic carbon-armored boron nitride aerogel and a preparation method thereof, comprising the following steps: Step 1: First, melamine and boric acid are dissolved in a solvent consisting of water and tert-butyl alcohol in a volume ratio of 2:3 in a molar ratio of 1:2 to obtain a transparent melamine / boric acid supramolecular solution. Subsequently, the solution is freeze-dried to obtain melamine / boric acid supramolecular aerogel, wherein the freezing temperature is -196°C and the vacuum freeze-drying time is 48 hours. Finally, the melamine / boric acid supramolecular aerogel is placed in a high-temperature nitrogen atmosphere for heat treatment at a temperature of 1400°C and a heat preservation time of 4 hours to obtain boron nitride aerogel.

[0055] Step 2: During the chemical vapor deposition process, the boron nitride aerogel is placed in the heating zone, and the entire process is carried out in flowing argon. After heating to 1100°C at a rate of 10°C / min, the carbon source precursor methane is introduced, the gas flow rate is controlled to 70 mL / min, and the deposition time is 3 h, and finally the pyrolysis carbon armored boron nitride aerogel is obtained.

[0056] The volume density of the prepared pyrolytic carbon armored boron nitride aerogel is 80 mg / cm 3The deposition thickness of pyrolytic carbon is 150 nm. Boron nitride aerogel armored with pyrolytic carbon has excellent compression resilience. At 60% strain, its compression strength is as high as 500kPa. After 100 cycles of compression with a strain of 60%, no permanent deformation occurs.

[0057] Example 4 A pyrolytic carbon-armored boron nitride aerogel and a preparation method thereof, comprising the following steps: Step 1: First, melamine and boric acid are dissolved in a solvent consisting of water and tert-butyl alcohol in a volume ratio of 1:2 in a molar ratio of 1:1 to obtain a transparent melamine / boric acid supramolecular solution. Subsequently, the solution is freeze-dried to obtain a melamine / boric acid supramolecular aerogel, wherein the freezing temperature is -20°C and the vacuum freeze-drying time is 48 hours. Finally, the melamine / boric acid supramolecular aerogel is placed in a high-temperature nitrogen atmosphere for heat treatment at a temperature of 1400°C and a heat preservation time of 4 hours to obtain a boron nitride aerogel.

[0058] Step 2: During the chemical vapor deposition process, the boron nitride aerogel is placed in the heating zone, and the entire process is carried out in flowing argon. After heating to 1200°C at a rate of 10°C / min, the carbon source precursor methane is introduced, the gas flow rate is controlled to 80 mL / min, and the deposition time is 6 h, and finally the pyrolysis carbon armored boron nitride aerogel is obtained.

[0059] The volume density of the prepared pyrolytic carbon armored boron nitride aerogel is 200 mg / cm 3 The deposition thickness of pyrolytic carbon is 600 nm. The boron nitride aerogel armored with pyrolytic carbon has super rigidity, and its compressive strength is as high as 1000kPa at a low strain of 10%.

[0060] The pyrolytic carbon armored boron nitride aerogel prepared in Example 1 of the present invention has a density of only 20 mg / cm 3 ,like Figure 1 As shown in the figure, this lightweight aerogel can be stably placed on the fibers of foxtail grass. The pyrolytic carbon armor gives the aerogel excellent mechanical stability, and no permanent deformation occurs after 100 cycles of compression with a strain of 60%. Figure 2 The compression resilience of the aerogel is vividly demonstrated, and there is still no deformation loss after high strain compression. The significant improvement of its mechanical properties and the stability of mechanical fatigue are attributed to the change of the load-bearing stress unit. A layer of tough pyrolytic carbon armor is deposited on the surface of the original boron nitride nanobelt, which improves the mechanical properties of the brittle ceramic nanounit. In addition, the stress-bearing area increases, allowing the pyrolytic carbon armored boron nitride aerogel to withstand greater stress loads.

[0061] The armoring of pyrolytic carbon armor not only significantly improves the mechanical properties of aerogels, but also gives the insulating ceramic aerogels unique elastic responsive conductivity. Figure 3 As shown, when the pyrolytic carbon armored boron nitride aerogel is placed in a conductive loop and a compressive stress is applied from top to bottom, a slight deformation causes an increase in the number of conductive pyrolytic carbon contact points in the three-dimensional network, thereby forming a conductive path and lighting the light bulb. The combination of excellent compression resilience, mechanical stability and elastic responsive conductivity makes aerogels have great potential in pressure sensing, flexible electronics and other fields. In particular, pyrolytic carbon armored boron nitride aerogels also exhibit excellent flame retardant properties. Figure 4 As shown, the aerogel exhibited good physical and chemical stability under the flame of an alcohol lamp at 600°C, staying above the flame for 0s, 5s, 60s, 120s or 180s respectively without burning or other deformation damage, which greatly improved its application safety.

[0062] The present invention prepares boron nitride aerogel by freeze drying and heat treatment process, and deposits a pyrolytic carbon layer on the boron nitride aerogel by chemical vapor deposition, and successfully prepares pyrolytic carbon armored boron nitride aerogel. The preparation method is simple and efficient, with a short preparation cycle, and is suitable for large-scale production. By regulating the thickness of the pyrolytic carbon armor, cross-scale customization of the mechanical properties of the aerogel is achieved. The prepared superelastic aerogel has a compressive strength of up to 200 kPa at 60% strain, and also has excellent compression resilience and mechanical fatigue properties, with no permanent deformation after 100 cycles of compression. In particular, increasing the thickness of the pyrolytic carbon armor can significantly improve the rigidity of the aerogel, and it can withstand stress strength of megapascals at low strains. In addition, the aerogel has elastic responsive conductivity, showing a wide range of application potentials in pressure sensors and flexible electronic devices. Thanks to the protection of the pyrolytic carbon armor, the aerogel exhibits excellent high-temperature mechanical stability and flame retardant properties. It maintains physical and chemical stability under the flame of a 600°C alcohol lamp without any combustion or deformation damage, greatly expanding its application scenarios in high temperature and extreme environments.

[0063] Figure 5 The differences in mechanical properties between the original boron nitride aerogel and the pyrolytic carbon armored boron nitride aerogel in different implementation cases are specifically demonstrated. The mechanical properties of the aerogel can be customized across orders of magnitude by adjusting the thickness of the pyrolytic carbon armor. As the thickness of the pyrolytic carbon armor increases, the compressive strength of the sample increases. At the same time, with the formation of the pyrolytic carbon welding point, the mechanical behavior of the aerogel gradually changes from superelasticity to rigidity.

[0064] The present invention describes preferred embodiments and their effects. However, those skilled in the art may make additional changes and modifications to these embodiments once they are aware of the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0065] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing pyrolytic carbon-armored boron nitride aerogel, characterized in that: The following steps are involved: The surface of the boron nitride aerogel is armored with pyrolytic carbon by chemical vapor deposition to obtain pyrolytic carbon armored boron nitride aerogel.

2. The method for preparing pyrolytic carbon-armored boron nitride aerogel according to claim 1, characterized in that: When pyrolytic carbon is armored on the surface of boron nitride aerogel by chemical vapor deposition, it includes: Under the protection of an inert atmosphere, the boron nitride aerogel is placed in a deposition chamber at 900-1200°C and reactant gas is introduced for deposition for 0.1-10 hours. Wherein, the reaction gas is methane or propylene.

3. The method for preparing pyrolytic carbon armored boron nitride aerogel according to claim 2, characterized in that: The flow rate of the reaction gas is 50-200 mL / min.

4. The method for preparing pyrolytic carbon armored boron nitride aerogel according to claim 2, characterized in that: The boron nitride aerogel is placed in a deposition chamber and heated to 900-1200°C at a rate of 2-10°C / min.

5. The method for preparing pyrolytic carbon armored boron nitride aerogel according to claim 1, characterized in that: The boron nitride aerogel is prepared according to the following steps: dissolving melamine and boric acid in a solvent to obtain a melamine / boric acid supramolecular solution; The melamine / boric acid supramolecular solution is subjected to vacuum freeze drying to obtain a melamine / boric acid supramolecular aerogel; In a mixed atmosphere, the melamine / boric acid supramolecular aerogel is heat-treated at 1000-1500°C for 2-6 hours to obtain boron nitride aerogel; Wherein, the mixed atmosphere is one or more of ammonia, argon, and nitrogen; The solvent is prepared from water solvent and polar solvent.

6. The method for preparing pyrolytic carbon armored boron nitride aerogel according to claim 5, characterized in that: The molar ratio of melamine to boric acid is 1:1-6.

7. The method for preparing pyrolytic carbon armored boron nitride aerogel according to claim 5, characterized in that: The polar solvent includes one or more of methanol, ethanol, ethylene glycol, n-propanol, isopropanol, isobutanol, sec-butanol, tert-butanol, and dimethyl sulfoxide; The volume ratio of the water solvent to the polar solvent is 1:0.5-2.

8. The method for preparing pyrolytic carbon armored boron nitride aerogel according to claim 5, characterized in that: During the vacuum freeze-drying process, the temperature is -196~-20°C and the duration is 24~48h.

9. A pyrolytic carbon armored boron nitride aerogel prepared by the method according to any one of claims 1 to 8, characterized in that: The volume density of the pyrolytic carbon armored boron nitride aerogel is 20-300 mg / cm 3 , the thickness of pyrolytic carbon is 10~800 nm.

10. Use of the pyrolytic carbon armored boron nitride aerogel according to claim 9 in thermal protection.

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