Preparation method of super-high-strength micro-nano multi-level structure carbon / silicon carbide porous ceramic aerogel

Abstract

This invention provides a method for preparing ultra-high strength micro-nano multi-level carbon / silicon carbide porous ceramic aerogel, comprising: (1) mixing a single-molecule silicon source and a macromolecular cross-linked silicon source in a certain proportion to form a dual silicon source; (2) if the carbon source is liquid, mixing the carbon source and the dual silicon source to obtain a sol; or if the carbon source is solid, immersing the carbon source in the dual silicon source to obtain a carbon source filled with a dual silicon source sol; aging the sol or the carbon source gel filled with the dual silicon source sol; (3) replacing the solvent of the aged precursor and drying it; (4) sintering the dried precursor in an argon atmosphere at a temperature gradient to obtain a carbon / silicon carbide porous ceramic aerogel material. The silicon carbide porous ceramic aerogel has a micron-nano multi-level composite three-dimensional structure. Through the synergistic effect of the composite structure of "nanofiber riveting micron units", the brittleness problem is effectively solved, and stress is efficiently transferred and dispersed, thereby significantly improving the mechanical strength.

Description

Technical Field

[0001] This invention belongs to the field of advanced ceramic materials technology, and in particular relates to a method for preparing ultra-high strength micro-nano hierarchical carbon / silicon carbide porous ceramic aerogels. Background Technology

[0002] Porous ceramic aerogels, especially silicon carbide aerogels, are considered ideal next-generation high-temperature insulation materials due to their high-temperature resistance, oxidation resistance, and intrinsic nanoporous properties. However, they typically face a common challenge: the network structure composed of brittle ceramic nanoparticle nodes results in extremely poor mechanical properties, making them prone to structural collapse under mechanical loads or thermal shocks, severely limiting their engineering applications in harsh environments.

[0003] To improve mechanical properties, researchers have tried various methods, such as introducing fiber reinforcements and constructing dual-network structures. However, these methods are often complex in process, or difficult to achieve precise control of the material structure at the molecular / nanoscale, or to achieve uniform composite and strong interfacial bonding between the reinforcing phase and the matrix at the nanoscale. The improvement in strength and toughness is limited, often at the expense of excellent thermal insulation properties. Furthermore, single-scale pore structures cannot simultaneously meet the multifunctional requirements of mechanical, thermal, and electrical properties. Therefore, developing a ceramic aerogel that can be intrinsically (in-situ, self-assembled) constructed with multi-level microstructures through a simple process, achieving in-situ self-assembly and reinforcement of the material's internal structure, thereby simultaneously achieving high strength, high porosity, low thermal conductivity, and multifunctionality, has become a pressing technical challenge in this field. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a method for preparing ultra-high strength micro-nano multi-level carbon / silicon carbide porous ceramic aerogels. This method uses a multi-scale silicon source-induced strategy to generate micro-nano multi-level carbon / silicon carbide composite porous ceramic aerogels in situ through self-assembly. It aims to solve the problem that silicon carbide aerogels can simultaneously possess high porosity, low density, ultra-high mechanical strength, excellent high-temperature thermal insulation performance, and effective electromagnetic wave absorption performance.

[0005] This invention provides a method for preparing ultra-high strength micro-nano hierarchical carbon / silicon carbide porous ceramic aerogels, comprising the following steps:

[0006] (1) Mix the monomolecule silicon source and the macromolecule cross-linked silicon source in a certain proportion to form a dual silicon source;

[0007] (2) The carbon source is in liquid state. The carbon source and the dual silicon source are mixed evenly to obtain a sol.

[0008] Alternatively, the carbon source may be in a solid state, and the carbon source may be immersed in a dual silicon source to obtain a carbon source fully immersed in a dual silicon source sol.

[0009] The sol or carbon source impregnated with dual silicon source sol is gel aged to obtain the aged precursor.

[0010] (3) The aged precursor is solvent-displaced and dried to obtain the dried precursor.

[0011] (4) The dried precursor is subjected to temperature gradient sintering in an argon atmosphere to obtain a carbon / silicon carbide porous ceramic aerogel with ultra-high strength micro-nano hierarchical structure.

[0012] Preferably, the single-molecule silicon source is selected from one or more of silicon monoxide, trichloromethylsilane, methyltrimethoxysilane, dimethyldimethoxysilane, and triethoxymethylsilane;

[0013] The macromolecular crosslinking silicon source is selected from silicon dioxide, polycarbosilane, hydrolysis products of trichloromethylsilane, hydrolysis products of methyltrimethoxysilane, hydrolysis products of dimethyldimethoxysilane, and hydrolysis products of triethoxymethylsilane.

[0014] Preferably, the mass ratio of the monomolecular silicon source to the macromolecular crosslinked silicon source is (1~100):(1~100), and the stirring time is 0.5~24h.

[0015] Preferably, the carbon source is selected from one or more of trichloromethylsilane and its hydrolysis products, methyltrimethoxysilane and its hydrolysis products, dimethyldimethoxysilane and its hydrolysis products, and triethoxymethylsilane and its hydrolysis products;

[0016] The solid carbon source is selected from carbon fiber felt pads.

[0017] Preferably, the volume ratio of the carbon source to the dual silicon source is (1~20):(0.5~10).

[0018] Preferably, the gel aging temperature is 30~80℃ and the gel aging time is 1~48h.

[0019] Preferably, the solvent used for solvent replacement is selected from one or more of tert-butanol, ethanol, and water.

[0020] Preferably, the solvent replacement is performed at least 6 times;

[0021] Each solvent replacement lasts for 1 to 48 hours.

[0022] Preferably, the temperature gradient range is 200~2000℃;

[0023] The gradient range is from 10 to 1000℃;

[0024] The heating rate is 1~50℃ / min.

[0025] Preferably, the sintering time is 1 to 10 hours.

[0026] This invention provides a method for preparing a carbon / silicon carbide porous ceramic aerogel with an ultra-high strength micro-nano hierarchical structure, comprising the following steps: (1) mixing a single-molecule silicon source and a macromolecular cross-linked silicon source in a certain proportion to form a dual silicon source; (2) if the carbon source is liquid, mixing the carbon source and the dual silicon source to obtain a sol; or if the carbon source is solid, immersing the carbon source in the dual silicon source to obtain a carbon source filled with the dual silicon source sol; gel aging the sol or the carbon source filled with the dual silicon source sol to obtain an aged precursor; (3) solvent replacement and drying of the aged precursor to obtain a dried precursor; (4) temperature gradient sintering of the dried precursor in an argon atmosphere to obtain a carbon / silicon carbide porous ceramic aerogel with an ultra-high strength micro-nano hierarchical structure. The silicon carbide porous ceramic aerogel prepared by the method provided in this invention possesses a micron-nano multi-level composite three-dimensional structure. The synergistic effect of the composite structure, characterized by "nanofiber riveting micron units," effectively solves the brittleness problem, achieving efficient stress transfer and dispersion, thereby significantly improving mechanical strength; it also exhibits high-temperature resistance and thermal insulation. Experimental results show that the silicon carbide porous ceramic aerogel can achieve integrated structure and function; the multi-level structure can withstand a compressive stress of 12.7 MPa, and the material maintains high porosity (>85%) and low density (<0.5 g / cm³). 3 This combination results in excellent thermal insulation performance and superior electromagnetic wave absorption capabilities provided by the carbon component and heterogeneous interface; the thermal conductivity is as low as 0.037 W·m at room temperature. -1 ·K -1 Even at 1100℃, it is only 0.118 W·m. -1 ·K -1 . Attached Figure Description

[0027] Figure 1 Flowchart for the preparation of carbon / silicon carbide composite porous ceramic aerogel provided by the present invention;

[0028] Figure 2 This is a photograph of the precursor of the carbon / silicon carbide composite porous ceramic aerogel material prepared in Example 1.

[0029] Figure 3 This is a photograph of the carbon / silicon carbide composite porous ceramic aerogel material prepared in Example 1;

[0030] Figure 4 This is a schematic diagram of the structure of the carbon / silicon carbide composite porous ceramic aerogel material prepared in Example 1;

[0031] Figure 5 SEM image of the carbon / silicon carbide composite porous ceramic aerogel material prepared in Example 1;

[0032] Figure 6 This is a diagram illustrating the compressive strength of the carbon / silicon carbide composite porous ceramic aerogel material prepared in Example 1.

[0033] Figure 7 This is a schematic diagram of the microwave absorption performance of the carbon / silicon carbide composite porous ceramic aerogel material prepared in Example 1.

[0034] Figure 8 This is a schematic diagram of infrared thermal imaging of the back-fired side of the carbon / silicon carbide composite porous ceramic aerogel material prepared in Example 2 under butane spray gun outer flame at 1400℃.

[0035] Figure 9 This is a diagram illustrating the compressive strength of the carbon / silicon carbide composite porous ceramic aerogel material prepared in Example 3;

[0036] Figure 10 SEM image of the pure silicon carbide nanofiber aerogel material prepared in Comparative Example 1. Detailed Implementation

[0037] This invention provides a method for preparing ultra-high strength micro-nano hierarchical carbon / silicon carbide porous ceramic aerogels, comprising the following steps:

[0038] (1) Mix the monomolecule silicon source and the macromolecule cross-linked silicon source in a certain proportion to form a dual silicon source;

[0039] (2) The carbon source is in liquid state. The carbon source and the dual silicon source are mixed evenly to obtain a sol.

[0040] Alternatively, the carbon source may be in a solid state, and the carbon source may be immersed in a dual silicon source to obtain a carbon source fully immersed in a dual silicon source sol.

[0041] The sol or carbon source impregnated with dual silicon source sol is gel aged to obtain the aged precursor.

[0042] (3) The aged precursor is solvent-displaced and dried to obtain the dried precursor.

[0043] (4) The dried precursor is subjected to temperature gradient sintering in an argon atmosphere to obtain a high-temperature resistant, ultra-high-strength silicon carbide porous ceramic aerogel material with a multi-level structure of micron and nano-structure.

[0044] The silicon carbide porous ceramic aerogel prepared by the method provided in this invention has a micron-nano multi-level composite three-dimensional structure. The composite structure of "nanofiber riveting micron units" effectively solves the brittleness problem, realizes efficient stress transfer and dispersion, and thus significantly improves mechanical strength.

[0045] See Figure 1 The present invention provides a flowchart for the preparation of carbon / silicon carbide composite porous ceramic aerogels:

[0046] This invention involves uniformly mixing a monomolecular silicon source and a macromolecular cross-linked silicon source in a specific ratio to form a dual silicon source. The monomolecular silicon source is a nanoscale silicon source; the macromolecular cross-linked silicon source is a micrometer-scale silicon source. Simultaneously employing silicon sources of different scales allows for in-situ self-assembly to generate micro-nano hierarchical structures. The monomolecular silicon source is selected from one or more of silicon monoxide, trichloromethylsilane, methyltrimethoxysilane, dimethyldimethoxysilane, and triethoxymethylsilane.

[0047] The macromolecular crosslinking silicon source is selected from silicon dioxide, polycarbosilane, hydrolysis products of trichloromethylsilane, hydrolysis products of methyltrimethoxysilane, hydrolysis products of dimethyldimethoxysilane, and hydrolysis products of triethoxymethylsilane.

[0048] In this invention, the preferred mass ratio of the monomolecular silicon source to the macromolecular cross-linked silicon source is (1~100):(1~100), specifically 1:1, 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, 1:55, 1:60, 1:65, 1:70, 1:75, 1:80, 1:85, 1:90, 1:95, or 1:100. A higher proportion of monomolecular silicon source results in a higher proportion of micron- and nanofibers generated; a higher proportion of macromolecular cross-linked silicon source also results in a higher proportion of nanofibers generated. The stirring time is 0.5~24h, specifically 0.5h, 1h, 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, or 24h.

[0049] In this invention, the carbon source is in liquid form, and the carbon source and the dual silicon source are mixed evenly to obtain a sol; or the carbon source is in solid form, and the carbon source is immersed in the dual silicon source to obtain a carbon source filled with dual silicon source sol; the sol is subjected to gel aging to obtain an aged precursor.

[0050] In this invention, the carbon source is selected from one or more of trichloromethylsilane and its hydrolysis products, methyltrimethoxysilane and its hydrolysis products, dimethyldimethoxysilane and its hydrolysis products, triethoxymethylsilane and its hydrolysis products, and added organic carbon sources. The solid carbon source is selected from carbon fiber felt pads and is an added organic carbon source.

[0051] The volume ratio of the carbon source and the dual silicon source in this invention is (1~20):(0.5~10); specifically, it is 1:0.5, 1:10, 10:5, 20:5, 20:10, 10:10, 20:0.5 or 8:5.

[0052] In this invention, the gel aging temperature is 30~80℃, specifically 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, or 80℃. The gel aging time is 1~48h, specifically 1h, 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h, 26h, 28h, 30h, 32h, 34h, 36h, 38h, 40h, 42h, 44h, 46h, and 48h.

[0053] This invention involves solvent displacement and drying of the aged precursor to obtain a dried precursor. The solvent used for solvent displacement in this invention is selected from one or more of tert-butanol, ethanol, and water. The number of solvent displacements is no less than 6, specifically 6, 7, 8, 9, 10, 12, 14, or 16 times; the duration of each solvent displacement is 1 to 48 hours, specifically 1 hour, 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, 26 hours, 28 hours, 30 hours, 32 hours, 34 hours, 36 hours, 38 hours, 40 hours, 42 hours, 44 hours, 46 hours, or 48 hours.

[0054] Solvent replacement followed by drying; the drying is carried out in a vacuum oven; the drying temperature is 30~150℃, specifically 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃ or 150℃; the drying time is 2~48h, specifically 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h, 26h, 28h, 30h, 32h, 34h, 36h, 38h, 40h, 42h, 44h, 46h or 48h.

[0055] The present invention involves performing temperature gradient sintering of the dried precursor in an argon atmosphere to obtain a high-temperature resistant, ultra-high-strength silicon carbide porous ceramic aerogel material with a multi-level structure of micron and nanometer structures.

[0056] In this invention, the temperature gradient range is 200~2000℃, preferably 200~1800℃; the gradient range is every 10~1000℃, preferably every 10~500℃; specifically, the intervals can be 50℃, 100℃, 150℃, 200℃, 250℃, 300℃, 350℃, 400℃, 450℃ or 500℃.

[0057] The heating rate is 1~50℃ / min, preferably 1~30℃ / min; specifically, it can be 1℃ / min, 5℃ / min, 10℃ / min, 15℃ / min, 20℃ / min, 25℃ / min or 30℃ / min. The sintering time is 1~10h, preferably 1~5h, specifically 1h, 2h, 3h, 4h or 5h.

[0058] Compared with traditional methods for preparing porous silicon carbide ceramic aerogels, this invention has the following advantages: (1) The porous silicon carbide ceramic aerogel obtained by the method of this invention has a micron-nano multi-level composite three-dimensional structure. The composite structure of "nanofiber riveting micron units" effectively solves the brittleness problem, realizes efficient stress transfer and dispersion, and thus significantly improves mechanical strength. (2) The porous silicon carbide ceramic aerogel obtained by the method of this invention can achieve integrated structure and function. The multi-level structure can withstand a compressive stress of 12.7 MPa. The material maintains high porosity (>85%) and low density (<0.5 g / cm³). 3 This results in excellent thermal insulation performance (thermal conductivity as low as 0.037 W·m at room temperature). -1 ·K -1 Even at 1100℃, it is only 0.118 W·m. -1 ·K -1 (3) The silicon carbide porous ceramic aerogel obtained by the method of the present invention has a simple process and controllable cost. The entire preparation process does not require expensive equipment such as supercritical drying, and adopts atmospheric pressure drying, which is simple and conducive to large-scale production. (4) The microstructure of silicon carbide porous ceramic aerogel obtained by the method of the present invention is controllable. In the preparation process, by adjusting the ratio and type of dual silicon sources and the sintering regime, the micro-nano multi-level structure of the material can be precisely controlled, thereby customizing the performance requirements of different application scenarios.

[0059] To further illustrate the present invention, the following detailed description, in conjunction with embodiments, of a method for preparing an ultra-high strength micro-nano hierarchical carbon / silicon carbide porous ceramic aerogel provided by the present invention, should not be construed as limiting the scope of protection of the present invention.

[0060] Example 1

[0061] According to the preparation flowchart, the preparation process is as follows: Take 80 ml of methyltrimethoxysilane and 40 ml of H2O, mix them together, and stir for 10 min. Then add 20 g of SiO powder and 3 g of urea, stir again for 10 min, and then... 3 The Kevlar felt pad was completely immersed in the mixture, the internal air was removed by vacuum, and it was immersed again. This process was repeated 5 times. Next, the carbon felt pad soaked in the dual-silicon source sol was placed in an 80°C oven for gel aging for 6 hours, then removed. It was then immersed in an isopropanol solution, sealed, and placed in a 60°C oven for 12 hours. This process was repeated 3 times. The precursor was then removed and dried in an 80°C oven for 10 hours to obtain a preform for preparing a high-strength, multi-level structured silicon carbide. The silicon carbide porous material preform was heated to 800°C in an argon atmosphere at a heating rate of 10°C / min and held for 20 minutes to allow for complete decomposition of the siloxane and complete carbonization of the Kevlar fibers. Then, the temperature was increased to 1500°C at a rate of 30°C / min and held for 2 hours to obtain a carbon / silicon carbide composite porous ceramic aerogel with a micron-nano multi-level gradient structure. The density of the carbon / silicon carbide porous material obtained in Example 1 can be as low as 0.4 g / cm³. 3 It also has a porosity as high as 87%. Its thermal conductivity at room temperature is only 0.037 W / m². -1 K -1 . Figure 2 and Figure 3 The precursor of the silicon carbide porous material obtained in Example 1 and the product obtained after sintering are shown.

[0062] Structurally, silicon carbide nanofibers exhibit a distinct micron-nano hierarchical composite three-dimensional structure (see...). Figure 3 and Figure 4 and Figure 5 This is mainly because during sintering, SiO primarily undergoes a gas-solid reaction, while the silicon dioxide produced by the decomposition of siloxanes primarily undergoes a solid-solid reaction. These two different reaction types correspond to different reaction rates and temperatures, resulting in a core-shell structure with a micron-sized silicon carbide shell coating a carbon core and a silicon carbide nanofiber composite three-dimensional structure. Therefore, the carbon / silicon carbide porous material obtained in Example 1 can possess high compressive strength and exhibit excellent compressive performance. Figure 6 It is known that the maximum compressive strength can reach 12.7 MPa, and the loose and porous carbon core and the gaps between the fibers enhance the microwave absorption performance of the sample. Figure 7 As can be seen, the minimum reflection loss was less than 10 dB at all tested matching thicknesses, confirming its effective electromagnetic wave absorption performance. At the optimal matching thickness of 4 mm, the sample achieved a minimum reflection loss of -38.7 dB.

[0063] Example 2

[0064] The preparation process is as follows: Take 20 ml of dimethyldimethoxysilane, 80 ml of H2O, and 2 ml of ammonia water, mix them together, and stir for 10 minutes. Then add 10 ml of trichloromethylsilane and stir again until homogeneous. (The final step is to prepare a 4×4×1 cm...) 3 The carbon fiber felt pad was completely impregnated into the mixture, the internal air was removed by vacuum, and it was impregnated again. This process was repeated three times. Next, the felt pad, soaked in sol, was placed in a 40°C oven for gel aging for 6 hours. After removal, it was immersed in a tert-butanol solution, sealed, and placed back in a 40°C oven for 2 hours. This process was repeated three times. The precursor was then removed and dried in a 100°C oven for 5 hours to obtain a preform for preparing a high-strength, multi-level structured silicon carbide. The silicon carbide porous material preform was heated to 600°C in an argon atmosphere at a heating rate of 20°C / min and held for 20 minutes to allow for complete decomposition of the siloxane and complete carbonization of the Kevlar fibers. Then, the temperature was increased to 1800°C at a rate of 30°C / min and held for 2 hours to obtain a carbon / silicon carbide composite porous ceramic aerogel with a micron-nano multi-level gradient structure. The density of the carbon / silicon carbide porous material obtained in Example 2 can be as low as 0.2 g / cm³. 3 It also has a porosity as high as 94%. Its thermal conductivity at room temperature is only 0.028 W / m². -1 K -1 .

[0065] To verify the excellent thermal insulation performance of the silicon carbide porous composite insulation material prepared by this method, an infrared thermal imager was used to record the temperature distribution within the butane torch flame. Figure 8 As can be seen from the results, the 1 cm thick silicon carbide porous material obtained in Example 2 exhibits a center temperature exceeding 1200°C on the exposed surface and only around 150°C on the unexposed surface, demonstrating its excellent high-temperature insulation capabilities. Therefore, the multi-level ceramic aerogel obtained in this invention can be directly used in the field of high-temperature insulation.

[0066] Example 3

[0067] Mix 100 ml of methyltrimethoxysilane, 100 ml of H2O and 2 ml of ammonia water together and stir to obtain a macromolecular crosslinked silicon source.

[0068] Take the above-mentioned macromolecular cross-linked silicon source and 100 ml of dimethyldimethoxysilane to form a dual silicon source, then add 100 ml of dimethyldimethoxysilane as a carbon source, mix evenly to obtain a sol;

[0069] Next, the sol was gelled and aged in a 40°C oven for 6 hours, then removed and immersed in an ethanol solution. After sealing, it was placed back into a 60°C oven for 2 hours, and this process was repeated three times. The precursor was then removed and dried in a 100°C oven for 5 hours to obtain a preform for preparing a high-strength, multi-level structured silicon carbide. The preform was heated to 800°C in an argon atmosphere at a heating rate of 20°C / min and held for 30 minutes to allow for complete decomposition and carbonization of the siloxanes. Then, the temperature was increased to 1600°C at a rate of 10°C / min and held for 2 hours to obtain a carbon / silicon carbide composite porous ceramic aerogel with a micron-nano multi-level gradient structure.

[0070] The density of the carbon / silicon carbide porous material obtained in Example 3 can be as low as 0.3 g / cm³. 3 It also has a porosity as high as 90%. Its thermal conductivity at room temperature is only 0.033 W / m². -1 K -1 .

[0071] Figure 9 The compressive strength of the sample in Example 3 was demonstrated to be as high as 8.5 MPa, indicating that in the micron-nano hierarchical three-dimensional structure, nanofibers can anchor microfibers, and the microfibers serve as the overall framework of the aerogel. The synergistic effect of both achieves the excellent compressive strength of the sample. Therefore, the hierarchical ceramic aerogel obtained by this invention can be directly used in the field of aerogel materials requiring high strength and lightweight properties.

[0072] Comparative Example 1

[0073] According to the preparation flowchart, the preparation process is as follows: Take 40 ml of dimethyldimethoxysilane and 160 ml of H2O, mix them together, add 1 ml of hydrochloric acid, and then... (The sentence is incomplete and requires more context to translate accurately.) 3 The carbon fiber felt pad was completely impregnated into the mixture, the internal air was removed by vacuum, and it was impregnated again. This process was repeated three times. Next, the felt pad, soaked in sol, was placed in a 40°C oven for gel aging for 6 hours. After removal, it was immersed in a tert-butanol solution, sealed, and placed back in a 40°C oven for 2 hours. This process was repeated three times. The precursor was then removed and dried in a 100°C oven for 5 hours to obtain a preform for preparing a high-strength, multi-level structured silicon carbide. The silicon carbide porous material preform was heated to 600°C in an argon atmosphere at a heating rate of 20°C / min and held for 20 minutes to allow for complete decomposition of the siloxane and complete carbonization of the Kevlar fibers. Then, the temperature was increased to 1800°C at a rate of 30°C / min and held for 2 hours to obtain a silicon carbide porous ceramic aerogel with a pure nano-level gradient structure. The density of the silicon carbide porous material obtained in Comparative Example 1 can be as low as 0.043 g / cm³. 3 It also boasts a porosity as high as 98%. Its thermal conductivity at room temperature is only 0.023 W / m². -1 K -1.

[0074] Since no SiO powder was added during the preparation of the sample in Comparative Example 1, the structure of its sample was pure silicon carbide nanofibers, without micron-sized fiber structures, which was confirmed by the relevant SEM images. Figure 10 ).

[0075] As can be seen from the above embodiments, the present invention provides a method for preparing a carbon / silicon carbide porous ceramic aerogel with an ultra-high strength micro-nano hierarchical structure, comprising the following steps: (1) mixing a single-molecule silicon source and a macromolecular cross-linked silicon source in a certain proportion to form a dual silicon source; (2) if the carbon source is liquid, mixing the carbon source and the dual silicon source to obtain a sol; or if the carbon source is solid, immersing the carbon source in the dual silicon source to obtain a carbon source filled with the dual silicon source sol; gel aging the sol or the carbon source filled with the dual silicon source sol to obtain an aged precursor; (3) solvent replacement and drying of the aged precursor to obtain a dried precursor; (4) temperature gradient sintering of the dried precursor in an argon atmosphere to obtain a carbon / silicon carbide porous ceramic aerogel with an ultra-high strength micro-nano hierarchical structure. The silicon carbide porous ceramic aerogel prepared by the method provided in this invention has a micron-nano multi-level composite three-dimensional structure. The composite structure of "nanofiber riveting micron units" effectively solves the brittleness problem, realizes efficient stress transfer and dispersion, and thus significantly improves mechanical strength.

[0076] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an ultra-high strength micro-nano hierarchical carbon / silicon carbide porous ceramic aerogel, comprising the following steps: (1) A single-molecule silicon source and a macro-crosslinked silicon source are stirred and mixed evenly in a certain ratio to form a dual silicon source; the single-molecule silicon source is selected from one or more of silicon monoxide, trichloromethylsilane, methyltrimethoxysilane, dimethyldimethoxysilane and triethoxymethylsilane; the macro-crosslinked silicon source is selected from polycarbosilane, hydrolysis product of trichloromethylsilane, hydrolysis product of methyltrimethoxysilane, hydrolysis product of dimethyldimethoxysilane and hydrolysis product of triethoxymethylsilane; the mass ratio of the single-molecule silicon source and the macro-crosslinked silicon source is (1~100):(1~100), and the stirring time is 0.5~24h; (2) The carbon source is liquid. The carbon source and the dual silicon source are mixed evenly to obtain a sol. The liquid carbon source is selected from one or more of trichloromethylsilane and its hydrolysis products, methyltrimethoxysilane and its hydrolysis products, dimethyldimethoxysilane and its hydrolysis products, and triethoxymethylsilane and its hydrolysis products. Alternatively, the carbon source may be solid, and the carbon source may be impregnated in a dual silicon source to obtain a carbon source impregnated with a dual silicon source sol; the solid carbon source may be selected from carbon fiber felt pads. The sol was gel aged to obtain the aged precursor. (3) The aged precursor is solvent-displaced and dried to obtain the dried precursor. (4) The dried precursor is sintered at a temperature gradient in an argon atmosphere to obtain a high-temperature resistant, ultra-high-strength silicon carbide porous ceramic aerogel material with a multi-level structure of micron and nano-structure. The temperature gradient range is 200~2000℃; the gradient range is every 10~1000℃; the heating rate is 10~50℃ / min.

2. The preparation method according to claim 1, characterized in that, The volume ratio of the carbon source to the dual silicon source is (1~20):(0.5~10).

3. The preparation method according to claim 1, characterized in that, The gel aging temperature is 30~80℃, and the gel aging time is 1~48h.

4. The preparation method according to claim 1, characterized in that, The solvent used for solvent displacement is selected from one or more of tert-butanol, ethanol, and water.

5. The preparation method according to claim 1, characterized in that, The number of solvent replacements shall not be less than 6; Each solvent replacement lasts for 1 to 48 hours.

6. The preparation method according to claim 1, characterized in that, The sintering time is 1 to 10 hours.

Images