Preparation method of carbon / silicon carbide porous ceramic aerogel with ultrahigh-strength micro-nano multilevel structure

Abstract

The invention provides a preparation method of carbon / silicon carbide porous ceramic aerogel with an ultra-high-strength micro-nano multilevel structure, which comprises the following steps: (1) uniformly stirring and mixing a monomolecular silicon source and a macromolecular cross-linked silicon source according to a certain proportion to form double silicon sources; (2) uniformly mixing the carbon source with the double silicon sources in a liquid state to obtain sol; or the carbon source is in a solid state, dipping the carbon source in the double silicon sources to obtain the carbon source fully dipped with the double silicon source sol; aging the sol or the carbon source gel fully soaked with the double-silicon-source sol; (3) replacing the aged precursor solvent, and drying; and (4) carrying out temperature gradient sintering on the dried precursor in an argon atmosphere to obtain the carbon / silicon carbide porous ceramic aerogel material. The silicon carbide porous ceramic aerogel has a micron-nano multi-stage composite three-dimensional structure, the problem of brittleness is effectively solved through the synergistic effect of a composite structure that nano-fibers are riveted with micron units, efficient stress transmission and dispersion are achieved, and then the mechanical strength is remarkably improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of advanced ceramic materials, and particularly relates to a preparation method of carbon / silicon carbide porous ceramic aerogel with super-high strength and micro-nano multi-level structure. BACKGROUND

[0002] Porous ceramic aerogels, especially silicon carbide aerogels, are considered as the next generation of high-temperature thermal insulation materials due to their high-temperature resistance, oxidation resistance and intrinsic nano-porous characteristics. However, they usually face a common challenge: the network structure composed of brittle ceramic nanoparticle nodes leads to extremely poor mechanical properties, which makes them prone to structural collapse under mechanical load or thermal shock, seriously restricting their engineering application in harsh environments.

[0003] In order to improve their mechanical properties, researchers have tried various methods, such as introducing fiber reinforcement, building a double network structure, etc. However, these methods are often complex in process, or difficult to achieve precise control of material structure at the molecular / nano scale, or difficult to achieve uniform composite and strong interface bonding of the reinforcing phase and the matrix at the nano scale. The strength and toughness are limited, and often at the expense of their excellent thermal insulation performance. In addition, the single-scale pore structure also cannot meet the multifunctional requirements of mechanics, heat and electricity. Therefore, developing a ceramic aerogel that can construct a multi-level microstructure through a simple process intrinsic (in situ, self-assembly) to realize in-situ self-assembly and strengthening of the internal structure of the material, so as to realize high strength, high porosity, low thermal conductivity and multifunctionality, has become a technical problem to be solved in the field. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a preparation method of carbon / silicon carbide porous ceramic aerogel with super-high strength and micro-nano multi-level structure, which generates micro-nano multi-level structure carbon / silicon carbide composite porous ceramic aerogel through a multi-scale silicon source induction strategy, aiming to solve the problem that silicon carbide aerogel can have high porosity, low density, super-high mechanical strength, excellent high-temperature thermal insulation performance and effective electromagnetic wave absorption performance.

[0005] The present application provides a preparation method of carbon / silicon carbide porous ceramic aerogel with super-high strength and micro-nano multi-level structure, comprising the following steps:

[0006] (1) uniformly stirring and mixing monomolecular silicon source and macromolecular crosslinking silicon source in a certain proportion to form a double silicon source;

[0007] (2) mixing the carbon source and the double silicon source uniformly to obtain a sol, wherein the carbon source is in a liquid state;

[0008] or the carbon source is solid, the carbon source is impregnated in the dual silicon source to obtain a carbon source impregnated with the dual silicon source sol;

[0009] the sol or the carbon source impregnated with the dual silicon source sol is subjected to gel aging to obtain an aged precursor;

[0010] (3) the aged precursor is subjected to solvent replacement and drying to obtain a dried precursor;

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

[0012] Preferably, the monomolecular 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 and the macromolecular crosslinking 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 and 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 in the solvent replacement is selected from one or more of tert-butyl alcohol, ethanol and water.

[0020] Preferably, the number of times of solvent replacement is not less than 6 times;

[0021] Each time of solvent replacement lasts for 1-48h.

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

[0023] The gradient range is every 10-1000℃;

[0024] The temperature rising rate is 1-50℃ / min.

[0025] Preferably, the sintering time is 1-10h.

[0026] The application provides a preparation method of carbon / silicon carbide porous ceramic aerogel with super-high strength and micro-nano multi-level structure, and comprises the following steps: (1) uniformly stirring and mixing monomolecular silicon source and macromolecular cross-linked silicon source at a certain ratio to form double silicon source; (2) mixing the carbon source and the double silicon source uniformly to obtain sol, or immersing the carbon source in the double silicon source to obtain carbon source immersed with double silicon source sol; performing gel aging on the sol or the carbon source immersed with double silicon source sol to obtain a precursor after aging; (3) performing solvent replacement on the precursor after aging and drying to obtain a dried precursor; and (4) performing temperature gradient sintering on the dried precursor in an argon atmosphere to obtain the carbon / silicon carbide porous ceramic aerogel with super-high strength and micro-nano multi-level structure. The silicon carbide porous ceramic aerogel prepared by the method has a micron-nano multi-level composite three-dimensional structure, and the composite structure of 'nanofiber riveting micron unit' effectively solves the brittleness problem, realizes efficient stress transmission and dispersion, and further significantly improves the mechanical strength; and the silicon carbide porous ceramic aerogel is also high-temperature resistant and heat-insulating. Experimental results show that the silicon carbide porous ceramic aerogel can realize structure and function integration, the multi-level structure can withstand a pressure stress of 12.7 MPa, the material maintains high porosity (>85%) and low density (<0.5 g / cm 3 ), so as to have excellent heat-insulating performance and excellent electromagnetic wave absorption capacity provided by the carbon component and the heterogeneous interface; the thermal conductivity is as low as 0.037 W·m -1 ·K -1 at normal temperature, and is only 0.118 W·m -1 ·K -1 at 1100℃. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 A preparation flow chart of the carbon / silicon carbide composite porous ceramic aerogel is provided in the application;

[0028] Figure 2 A physical picture of the precursor of the carbon / silicon carbide composite porous ceramic aerogel material prepared in Example 1 is provided;

[0029] Figure 3 A physical picture of the carbon / silicon carbide composite porous ceramic aerogel material prepared in Example 1 is provided;

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

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

[0032] Figure 6 Compression performance display image of the carbon / silicon carbide composite porous ceramic aerogel material prepared for Example 1;

[0033] Figure 7 Microwave absorption performance schematic diagram of the carbon / silicon carbide composite porous ceramic aerogel material prepared for Example 1;

[0034] Figure 8 Backfire infrared thermal imaging schematic diagram of the carbon / silicon carbide composite porous ceramic aerogel material prepared for Example 2 under butane lance 1400℃ outer flame injection;

[0035] Figure 9 Compression performance display image of the carbon / silicon carbide composite porous ceramic aerogel material prepared for Example 3;

[0036] Figure 10 SEM image of the pure silicon carbide nanofiber aerogel material prepared for Comparative Example 1. DETAILED DESCRIPTION

[0037] The present application provides a preparation method of an ultra-high-strength carbon / silicon carbide porous ceramic aerogel with micro-nano multi-level structure, comprising the following steps:

[0038] (1) uniformly stirring and mixing monomolecular silicon source and macromolecular crosslinking silicon source in a certain proportion to form a double silicon source;

[0039] (2) the carbon source is liquid, the carbon source and the double silicon source are uniformly mixed to obtain a sol;

[0040] or the carbon source is solid, the carbon source is immersed in the double silicon source to obtain a carbon source soaked with double silicon source sol;

[0041] the sol or the carbon source soaked with double silicon source sol is subjected to gel aging to obtain an aged precursor;

[0042] (3) the aged precursor is subjected to solvent replacement and drying to obtain a 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 micro-nano multi-level structure.

[0044] The silicon carbide porous ceramic aerogel prepared by the method provided by the present application has a micro-nano multi-level composite three-dimensional structure, and the brittle problem is effectively solved through the synergistic effect of the composite structure of "nanofiber riveting micro unit", realizing efficient stress transmission and dispersion, and further significantly improving the mechanical strength.

[0045] Referring to Figure 1 The present application provides a carbon / silicon carbide composite porous ceramic aerogel preparation flow chart:

[0046] The present application mixes the single-molecule silicon source and the macromolecular cross-linked silicon source in a certain proportion to form a double silicon source. The single-molecule silicon source in the present application is a nano-scale silicon source; the macromolecular cross-linked silicon source is a micro-scale silicon source, and different scale silicon sources are used to generate micro-nano multi-level structures in situ; the single-molecule silicon source is selected from one or more of silicon monoxide, trichloromethylsilane, methyltrimethoxysilane, dimethyldimethoxysilane and triethoxymethylsilane.

[0047] The macromolecular cross-linked 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 the present application, the mass ratio of the single-molecule silicon source and the macromolecular cross-linked silicon source is preferably (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; in the ratio of the single-molecule silicon source and the macromolecular cross-linked silicon source, the single-molecule silicon source accounts for a larger proportion, and more micron-nanofibers are generated; the macromolecular cross-linked silicon source accounts for a larger proportion, and more nanofibers are 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 the present application, the carbon source is liquid, the carbon source and the double silicon source are mixed uniformly to obtain a sol; or the carbon source is solid, the carbon source is immersed in the double silicon source to obtain a carbon source filled with double silicon source sol; the sol is aged to obtain a precursor after aging.

[0050] In the present application, 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 an additional organic carbon source. The solid carbon source is selected from carbon fiber felt mat, which is an additional organic carbon source.

[0051] The volume ratio of the carbon source and the double silicon source in the application is (1-20):(0.5-10); specifically, 1:0.5, 1:10, 10:5, 20:5, 20:10, 10:10, 20:0.5 or 8:5.

[0052] The temperature for gel aging in the application is 30-80 DEG C, specifically 30 DEG C, 35 DEG C, 40 DEG C, 45 DEG C, 50 DEG C, 55 DEG C, 60 DEG C, 65 DEG C, 70 DEG C, 75 DEG C or 80 DEG C. The time for gel aging 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 or 48h.

[0053] The precursor after aging in the application is subjected to solvent replacement, drying, to obtain a dried precursor. The solvent used in solvent replacement in the application is selected from one or more of t-butyl alcohol, ethanol and water. The number of times of solvent replacement is not less than 6, specifically can be 6, 7, 8, 9, 10, 12, 14 or 16; the time for each solvent replacement lasts 1-48h, specifically can be 1h, 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.

[0054] After solvent replacement, drying is performed; the drying is performed in a vacuum oven; the temperature for drying is 30-150 DEG C, specifically 30 DEG C, 40 DEG C, 50 DEG C, 60 DEG C, 70 DEG C, 80 DEG C, 90 DEG C, 100 DEG C, 110 DEG C, 120 DEG C, 130 DEG C, 140 DEG C or 150 DEG C; the time for drying 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 dried precursor in the application is subjected to temperature gradient sintering in an argon atmosphere, to obtain a high-temperature-resistant ultra-high-strength porous silicon carbide aerogel material with a micro-nano structure of a multi-level structure.

[0056] In the present application, the temperature gradient ranges from 200 to 2000℃, preferably from 200 to 1800℃; the gradient range is every 10 to 1000℃, preferably every 10 to 500℃; and specifically, it can be every 50℃, 100℃, 150℃, 200℃, 250℃, 300℃, 350℃, 400℃, 450℃ or 500℃.

[0057] The heating rate is 1 to 50℃ / min, preferably 1 to 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 to 10h, preferably 1 to 5h, and specifically 1h, 2h, 3h, 4h or 5h.

[0058] Compared with the traditional preparation method of silicon carbide porous ceramic aerogel, the present application has the following advantages: (1) The silicon carbide porous ceramic aerogel obtained by the method has a micron-nanometer multi-level composite three-dimensional structure, and the composite structure of "nanofiber riveting micron unit" effectively solves the problem of brittleness, realizes efficient stress transmission and dispersion, and significantly improves the mechanical strength. (2) The silicon carbide porous ceramic aerogel obtained by the method can realize structure and function integration, and the multi-level structure can withstand a pressure stress of 12.7 MPa, and the material maintains high porosity (>85%) and low density (<0.5 g / cm 3 ), thereby having excellent thermal insulation performance (the thermal conductivity is as low as 0.037 W·m -1 ·K -1 at room temperature, and only 0.118 W·m -1 ·K -1 at 1100℃) and excellent electromagnetic wave absorption ability provided by the carbon component and heterogeneous interface. (3) The silicon carbide porous ceramic aerogel obtained by the method has simple process and controllable cost. The entire preparation process does not require expensive equipment such as supercritical drying, and adopts normal pressure drying, which is simple and beneficial to large-scale production. (4) The microstructure of the silicon carbide porous ceramic aerogel obtained by the method is controllable. In the preparation process, by adjusting the ratio, type and sintering system of the double silicon source, the micro-nano multi-level structure of the material can be precisely controlled, so as to meet the performance requirements of different application scenarios.

[0059] In order to further illustrate the present application, the preparation method of the ultra-high strength micro-nano multi-level structure carbon / silicon carbide porous ceramic aerogel provided by the present application is described in detail below in combination with examples, but they should not be understood as limiting the scope of protection of the present application.

[0060] Example 1

[0061] According to the preparation flow chart, the preparation process is as follows: take 80 ml of methyltrimethoxysilane, 40 ml of H2O, mix together, and stir for 10 min, then add 20 g of SiO powder and 3 g of urea into it, stir again for 10 min, then immerse a 4x4x1 cm 3 Kevlar felt pad into the mixture, vacuum out the internal air, and immerse again, repeat the above operation 5 times. Then put the carbon felt pad soaked with the double-silicon source sol into an oven at 80°C for 6 h of gel aging, take it out; immerse it into an isopropanol solution, seal it again, and put it into an oven at 60°C for 12 h, repeat the operation 3 times, then take out the precursor and dry it in an oven at 80°C for 10 h to obtain a preform for preparing high-strength multi-level structure silicon carbide. The silicon carbide porous material preform is heated to 800°C at a heating rate of 10°C / min in an argon atmosphere, kept for 20 min to make the siloxane fully decompose and the Kevlar fiber fully carbonize, then heated to 1500°C at a rate of 30°C / min and kept for 2 h to obtain a carbon / silicon carbide composite porous ceramic aerogel with a micron-nanometer multi-level gradient structure. The carbon / silicon carbide porous material obtained in Example 1 can have a density as low as 0.4 g / cm 3 , while the porosity is as high as 87%. The thermal conductivity at room temperature is only 0.037 Wm -1 K -1 . Figure 2 and Figure 3 show the precursor and the product obtained after sintering of the silicon carbide porous material obtained in Example 1.

[0062] From the structure, the silicon carbide nanofiber presents a clear micron-nanometer multi-level composite three-dimensional structure (see Figure 3 and Figure 4 and Figure 5 ), which is mainly because in the sintering process, SiO mainly occurs gas-solid reaction, and the silica produced by the decomposition of siloxane mainly occurs solid-solid reaction, two different forms of reactions correspond to different reaction speeds and reaction temperatures, thereby generating a core-shell structure of a micron-level silicon carbide shell layer 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 have high compressive strength and exhibit excellent compressive performance, as can be seen from Figure 6 , the maximum compressive strength can reach 12.7 MPa, while the voids between the loose porous carbon core and the fibers enhance the wave absorption performance of the sample, as can be seen from Figure 7 , the minimum value of the reflection loss is less than 10 dB under all test matching thicknesses, which confirms the effective electromagnetic wave absorption performance. Under the optimal matching thickness of 4 millimeters, the minimum reflection loss of the sample reaches -38.7 dB.

[0063] Example 2

[0064] The preparation process is as follows: 20 ml of dimethyl dimethoxy silane, 80 ml of H2O, and 2 ml of ammonia water are mixed together and stirred for 10 min, 10 ml of trichloromethyl silane is then added thereto, and the mixture is stirred again to be uniformly mixed, a 4x4x1 cm 3 carbon fiber felt mat is completely immersed in the mixture, the internal air is vacuumed out and the mat is immersed again, and the above operation is repeated 3 times. Then the sol-impregnated felt mat is taken out and placed in an oven at 40°C for gel aging for 6 h, and then taken out and immersed in a t-butyl alcohol solution, sealed and placed in an oven at 40°C again for 2 h, and the operation is repeated 3 times, and then the precursor is taken out and dried in an oven at 100°C for 5 h to obtain a precursor for preparing high-strength multi-level structure silicon carbide. The silicon carbide porous material precursor is heated to 600°C at a heating rate of 20°C / min in an argon atmosphere, and kept for 20 min to allow the siloxane to be fully decomposed and the Kevlar fiber to be fully carbonized, and then heated to 1800°C at a heating rate of 30°C / min and kept for 2 h to obtain a carbon / silicon carbide composite porous ceramic aerogel with a micro-nano multi-level gradient structure. The carbon / silicon carbide porous material obtained in Example 2 has a density as low as 0.2 g / cm 3 , and a porosity as high as 94%. The thermal conductivity at room temperature is only 0.028 Wm -1 K -1 .

[0065] In order to verify that the carbonized silicon porous material composite heat insulation material prepared by the method has excellent heat insulation performance, an infrared thermal imager is used to record the temperature distribution in the flame of a butane spray gun. It can be seen from Figure 8 that the center temperature of the 1 cm thick carbonized silicon porous material obtained in Example 2 is more than 1200°C, and the back surface temperature is only about 150°C, which indicates that it has excellent high-temperature heat insulation capacity. Therefore, the multi-level structure ceramic aerogel obtained by the method can be directly used in the field of high-temperature heat insulation.

[0066] Example 3

[0067] 100 ml of methyl trimethoxy silane, 100 ml of H2O, and 2 ml of ammonia water are mixed together and stirred to prepare a macromolecular cross-linked silicon source;

[0068] The above macromolecular cross-linked silicon source and 100 ml of dimethyl dimethoxy silane are mixed to form a double silicon source, and 100 ml of dimethyl dimethoxy silane is added as a carbon source, and the mixture is uniformly mixed to obtain a sol;

[0069] The sol was then placed in an oven at 40°C to gel and age for 6h, then removed and soaked in an ethanol solution, sealed and placed in an oven at 60°C for 2h, repeating this process 3 times, then the precursor was removed and dried in an oven at 100°C for 5h to produce a precursor for the high strength multi-scale structured silicon carbide. The precursor was heated in an argon atmosphere at a rate of 20°C / min to 800°C for 30min to fully decompose the siloxane and carbonize, then heated at a rate of 10°C / min to 1600°C for 2h to produce a carbon / silicon carbide composite porous ceramic aerogel with a micro-nano multi-scale gradient structure.

[0070] The carbon / silicon carbide porous material obtained in Example 3 can have a density as low as 0.3 g / cm 3 , and a porosity as high as 90%. The thermal conductivity at room temperature is only 0.033 Wm -1 K -1 .

[0071] Figure 9 The compressive strength of the sample obtained in Example 3 is as high as 8.5MPa, indicating that in the micro-nano multi-scale three-dimensional structure, the nanofibers can anchor the microfibers, and the microfibers act as the overall framework of the aerogel, and the two work together to achieve excellent compressive performance of the sample. Therefore, the multi-scale ceramic aerogel obtained by the present application can be directly used in the field of aerogel materials requiring high strength and light weight.

[0072] Comparative Example 1

[0073] According to the preparation flow chart, the preparation process is as follows: 40ml of dimethyl dimethoxysilane and 160ml of H2O are mixed together, 1ml of hydrochloric acid is added, and a 4x4x1cm 3 carbon fiber felt pad is completely immersed in the mixture, the internal air is vacuumed out and immersed again, and the above operation is repeated 3 times. Then the felt pad soaked with the sol is placed in an oven at 40°C to gel and age for 6h, then removed and soaked in a tert-butyl alcohol solution, sealed and placed in an oven at 40°C for 2h, repeating this process 3 times, then the precursor is removed and dried in an oven at 100°C for 5h to produce a precursor for the high strength multi-scale structured silicon carbide. The silicon carbide porous material precursor is heated in an argon atmosphere at a rate of 20°C / min to 600°C for 20min to fully decompose the siloxane and carbonize the Kevlar fibers, then heated at a rate of 30°C / min to 1800°C for 2h to produce a silicon carbide porous ceramic aerogel with a pure nano multi-scale gradient structure. The silicon carbide porous material obtained in Comparative Example 1 can have a density as low as 0.043 g / cm 3 , and a porosity as high as 98%. The thermal conductivity at room temperature is only 0.023 Wm -1 K -1.

[0074] Since Comparative Example 1 does not add SiO powder when preparing the sample, the structure of the sample is pure silicon carbide nanofiber without micron fiber structure, which is confirmed by the relevant SEM image Figure 10 )。

[0075] From the above examples, the present application provides a preparation method of ultra-high strength micro-nano multi-level structure carbon / silicon carbide porous ceramic aerogel, comprising the following steps: (1) stirring and mixing monomolecular silicon source and macromolecular crosslinking silicon source uniformly in a certain proportion to form a double silicon source; (2) the carbon source is liquid, the carbon source and the double silicon source are mixed uniformly to obtain a sol; or the carbon source is solid, the carbon source is immersed in the double silicon source to obtain a carbon source soaked with double silicon source sol; the sol or the carbon source soaked with double silicon source sol is subjected to gel aging to obtain an aged precursor; (3) the aged precursor is subjected to solvent replacement and drying to obtain a dried precursor; (4) the dried precursor is subjected to temperature gradient sintering in an argon atmosphere to obtain an ultra-high strength micro-nano multi-level structure carbon / silicon carbide porous ceramic aerogel. The silicon carbide porous ceramic aerogel prepared by the method provided by the present application has a micron-nano multi-level composite three-dimensional structure, and the brittle problem is effectively solved through the synergistic effect of the composite structure of "nanofiber riveting micron unit", realizing efficient stress transmission and dispersion, and further significantly improving the mechanical strength.

[0076] The above only describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the principles of the present application, several improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A method for preparing an ultra-high strength micro-nano hierarchical carbon / silicon carbide porous ceramic aerogel, comprising the following steps: (1) Mix the monomolecule silicon source and the macromolecule cross-linked silicon source in a certain proportion to form a dual silicon source; (2) The carbon source is in liquid state. The carbon source and the dual silicon source are mixed evenly to obtain a sol; 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. 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 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.

2. The preparation method according to claim 1, characterized in that, The single-molecule silicon source is selected from one or more of silicon monoxide, trichloromethylsilane, methyltrimethoxysilane, dimethyldimethoxysilane, and triethoxymethylsilane; 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.

3. The preparation method according to claim 1, characterized in that, The mass ratio of the monomolecular silicon source to the macromolecular cross-linked silicon is (1~100):(1~100), and the stirring time is 0.5~24h.

4. The preparation method according to claim 1, characterized in that, 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; The solid carbon source is selected from carbon fiber felt pads.

5. 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).

6. 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.

7. 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.

8. 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.

9. The preparation method according to claim 1, characterized in that, The temperature gradient range is 200~2000℃; The gradient range is from 10 to 1000℃; The heating rate is 1~50℃ / min.

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

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