SiBCN aerogel and normal pressure drying preparation method and application thereof

Abstract

The application relates to SiBCN aerogel and a normal-pressure drying preparation method and application thereof, and belongs to the technical field of functional ceramic aerogel. In order to solve the problems of high equipment requirement, high cost and large energy consumption of the existing SiBCN aerogel preparation method, the application provides a normal-pressure drying preparation method of SiBCN aerogel, and the steps include preparation of a precursor solution, hydrothermal cross-linking reaction, solvent replacement, normal-pressure drying and high-temperature ceramicization heat treatment. The application effectively reduces the damage of capillary force to the gel skeleton in the solvent evaporation process through step-by-step solvent replacement and normal-temperature and normal-pressure drying treatment, and can guarantee the integrity of the gel skeleton. The application can be implemented only by using ordinary room temperature and normal pressure, and the preparation process is simple, efficient, easy to control and the like. The preparation method has low energy consumption and low preparation cost, meets actual production requirements, is suitable for large-scale production, provides a technical basis for popularization and application of the SiBCN aerogel, and the like.

Description

Technical Field

[0001] This invention belongs to the field of advanced inorganic non-metallic materials technology, and particularly relates to the field of functional ceramic aerogel technology, specifically a SiBCN aerogel and its preparation method and application under normal pressure drying. Background Technology

[0002] Hypersonic vehicles undergo severe aerodynamic heating during service, posing a serious threat to their overall safe operation. To ensure the normal operation of internal electronic equipment and the integrity of the airframe structure, thermal protection materials are typically used to protect the vehicle. With the continuous development of hypersonic vehicle technology, their service environment is becoming increasingly demanding, placing higher requirements on the oxidation resistance, heat insulation, and temperature resistance of thermal protection materials.

[0003] Aerogels are materials with a three-dimensional nano-network structure and abundant pores, possessing advantages such as low density, high porosity, high specific surface area, and low thermal conductivity. Therefore, they have broad application prospects in catalysis, thermal insulation, sound absorption, and environmental protection. However, currently widely used oxide aerogels generally suffer from insufficient temperature resistance and are prone to phase transitions under high-temperature conditions, while carbon aerogels mainly face the problem of easy failure in high-temperature aerobic environments. SiBCN aerogel, as a ceramic aerogel, has excellent oxidation resistance and typically does not undergo phase separation at 1500℃. Its crystallization temperature in an inert atmosphere reaches as high as 1800℃. Compared to common ceramic aerogels such as SiC, SiOC, and SiCN, it has better temperature resistance and is expected to become a candidate thermal protection material for hypersonic vehicles.

[0004] Patent application CN113979753A discloses a method for preparing SiBCN aerogel, which involves obtaining a precursor gel through a hydrosilylation reaction, obtaining a polyborosilicate aerogel through freeze-drying, and then obtaining a SiBCN ceramic aerogel with a well-developed pore structure through a precursor conversion method. However, the freeze-drying ice crystal growth process usually has a certain impact on the pore structure of the material, and it typically has the problem of requiring sophisticated equipment.

[0005] Patent application CN110818431A discloses a zirconium-containing polyborosilazane precursor aerogel, a silicon boron carbon nitride / zirconium dioxide ceramic aerogel, its preparation method, and its application. It combines hydrosilylation reaction and supercritical CO2 drying with precursor conversion to synthesize SiBCN-ZrO2 ceramic aerogel. While supercritical drying can generally effectively preserve the pore structure of aerogel materials, it commonly suffers from high cost, high energy consumption, and demanding equipment requirements.

[0006] To address the limitations of the aforementioned methods, there is an urgent need to develop a more economical, simpler, and mass-producible drying method. This would better meet the practical application needs of SiBCN aerogel in fields such as hypersonic vehicles and provide a technological foundation for its large-scale application in industrial insulation, building insulation, and other fields in the future. Summary of the Invention

[0007] To address the problems of high equipment requirements, high cost, and high energy consumption in existing SiBCN aerogel preparation methods, this invention provides a SiBCN aerogel and its preparation method and application under normal pressure drying.

[0008] The technical solution of the present invention:

[0009] A method for preparing SiBCN aerogel by atmospheric pressure drying includes the following steps:

[0010] Step 1: Prepare the precursor solution:

[0011] Polyborosilazane was added to an organic solvent as a precursor and stirred until homogeneous. Then, divinylbenzene, a crosslinking agent, and a catalyst were added to the resulting mixture and stirred until homogeneous to obtain a wet gel precursor solution.

[0012] Step 2, hydrothermal crosslinking reaction:

[0013] The wet gel precursor solution obtained in step one was subjected to a hydrothermal crosslinking reaction at a certain temperature to obtain polyborosilicate wet gel.

[0014] Step 3: Solvent replacement and drying at atmospheric pressure:

[0015] Prepare a concentration gradient mixed solution of the displacement solvent and the organic solvent. Immerse the polyborosilicate wet gel obtained in step two in the concentration gradient mixed solution with the gradually increasing concentration of the displacement solvent. The organic solvent in the polyborosilicate wet gel is gradually replaced by the displacement solvent. The replaced polyborosilicate wet gel is dried at room temperature and normal pressure to obtain polyborosilicate dry gel.

[0016] Step 4: High-temperature ceramicization heat treatment:

[0017] The polyborosilicate dry gel obtained in step three was subjected to high-temperature heat treatment under a protective atmosphere to obtain SiBCN aerogel.

[0018] Furthermore, the organic solvent in step one is one of n-hexane, cyclohexane, or toluene, the catalyst is a Karstedt catalyst, and the concentration of the catalyst in the wet gel precursor solution is 20 ppm.

[0019] Furthermore, the mass ratio of the crosslinking agent divinylbenzene to polyborosilazane in the wet gel precursor solution obtained in step one is 1:0.5 to 1.5; the mass percentage of polyborosilazane in the wet gel precursor solution is 7.5 to 12.5 wt.%.

[0020] Furthermore, the temperature of the hydrothermal crosslinking reaction in step two is 120–150°C, and the reaction time is 20 h.

[0021] Furthermore, in step three, the volume concentrations of the displacement solvent in the concentration gradient mixed solution are 20%, 40%, 60%, 80%, and 100% respectively, and the displacement solvent is ethanol.

[0022] Furthermore, in step three, the soaking time of the polyborosilicate wet gel in each concentration gradient mixed solution is 24 hours.

[0023] Furthermore, the drying process at room temperature and normal pressure described in step three takes 4 days.

[0024] Furthermore, the protective atmosphere in step four is a nitrogen atmosphere, the heating rate of the high-temperature heat treatment is 2-3℃ / min, the heat treatment temperature is 800-1000℃, and the heat treatment time is 2h.

[0025] A SiBCN aerogel prepared by an atmospheric pressure drying method provided by the present invention has a density of 0.20–0.26 g / cm³. 3 .

[0026] An application of the SiBCN aerogel prepared according to the present invention in the fields of aircraft thermal protection, industrial thermal insulation or building insulation.

[0027] The beneficial effects of this invention are:

[0028] The method for preparing SiBCN aerogel by atmospheric pressure drying provided by this invention effectively reduces the destructive effect of capillary forces on the gel skeleton during solvent evaporation through stepwise solvent replacement and room temperature and atmospheric pressure drying, thus ensuring the integrity of the gel skeleton. The polyborosilicate aerogel prepared by this method does not crack and has an average drying dimensional shrinkage rate of <5%.

[0029] The SiBCN aerogel preparation method provided by this invention can be carried out under normal room temperature and pressure conditions, solving the problem of high equipment requirements in existing SiBCN aerogel preparation methods. This makes the preparation process simple, efficient, and easy to control precisely. The method of this invention has low energy consumption and low preparation cost, meeting practical production needs and suitable for large-scale production, thus providing a technical foundation for the promotion and application of SiBCN aerogels. Attached Figure Description

[0030] Figure 1 SEM image of the SiBCN aerogel prepared in Example 1;

[0031] Figure 2 TEM image of the SiBCN aerogel prepared in Example 1;

[0032] Figure 3 Photographs of the polyborosilicate dry gel prepared in Example 1 and the SiBCN aerogel obtained by high-temperature ceramic heat treatment. Detailed Implementation

[0033] The technical solution of the present invention will be further described below with reference to embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention. In the following embodiments, the process equipment or apparatus not specifically specified are all conventional equipment or apparatus in the art. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commercially available; unless otherwise specified, the technical means used in the embodiments of the present invention are all conventional means well known to those skilled in the art.

[0034] Example 1

[0035] This embodiment provides a method for preparing SiBCN aerogel by atmospheric pressure drying, including the following steps:

[0036] Step 1: Prepare the precursor solution:

[0037] Polyborosilazane was added to toluene and stirred until homogeneous. Divinylbenzene was then added to the resulting mixture at a mass ratio of 1:1 to polyborosilazane. Finally, the Karstedt catalyst was added, and the mixture was stirred until homogeneous to obtain a wet gel precursor solution. The mass percentage of polyborosilazane in the obtained wet gel precursor solution was 10 wt.%, and the concentration of the Karstedt catalyst in the wet gel precursor solution was 20 ppm.

[0038] Step 2, hydrothermal crosslinking reaction:

[0039] The wet gel precursor solution obtained in step one was added to a hydrothermal reactor lined with polytetrafluoroethylene for magnetic therapy, reacted at 120°C for 20 hours, and then removed after natural cooling to room temperature to obtain polyborosilicate wet gel.

[0040] Step 3: Solvent replacement and drying at atmospheric pressure:

[0041] Prepare a concentration gradient mixture of ethanol and toluene. The resulting polyborosilicate wet gel is first immersed in a 20% (v / v) anhydrous ethanol-toluene mixture for 24 hours; then in a 40% (v / v) anhydrous ethanol-toluene mixture for 24 hours; then in a 60% (v / v) anhydrous ethanol-toluene mixture for 24 hours; then in an 80% (v / v) anhydrous ethanol-toluene mixture for 24 hours; and finally in 100% anhydrous ethanol for 24 hours. Each time the solvent is changed, ensure the ratio of wet gel to solvent remains consistent to guarantee the gradual replacement effect.

[0042] The replaced polyborosilicate wet gel was transferred to a desiccator and dried at room temperature and normal pressure for 4 days to obtain polyborosilicate dry gel. The gel drying shrinkage rate was 4.1%.

[0043] Step 4: High-temperature ceramicization heat treatment:

[0044] The polyborosilicate dry gel obtained in step three was placed in a high-temperature tube furnace and heated to 800°C at a rate of 2°C / min under a flowing nitrogen atmosphere, and held at that temperature for 2 hours to obtain SiBCN ceramic aerogel. The density of the obtained SiBCN ceramic aerogel was 0.22 g / cm³. 3 .

[0045] Figure 1 The image shown is a scanning electron microscope (SEM) image of the SiBCN aerogel prepared in Example 1. Figure 1 It can be seen from this that, Figure 1 As can be seen, the aerogel surface exhibits a uniform porous structure with a relatively uniform pore distribution, showing good network structure characteristics.

[0046] Figure 2 This is a transmission electron microscopy (TEM) image of the SiBCN aerogel prepared in Example 1. Figure 2 As can be seen, the aerogel exhibits a fine nanoscale structure with uniformly distributed crystal particles, and the pore structure is consistent with the network structure observed in the scanning electron microscopy image.

[0047] Figure 3 These are photographs of the polyborosilazane dry gel prepared in Example 1 and the SiBCN aerogel obtained by high-temperature ceramic heat treatment. Figure 3 As can be seen, both the polyborosilicate dry gel and the SiBCN aerogel obtained by ceramic heat treatment have extremely low density and weight.

[0048] Example 2

[0049] This embodiment provides a method for preparing SiBCN aerogel by atmospheric pressure drying, including the following steps:

[0050] Step 1: Prepare the precursor solution:

[0051] Polyborosilazane was added to cyclohexane and stirred until homogeneous. Divinylbenzene was then added to the resulting mixture at a mass ratio of 1:1 to polyborosilazane. Finally, the Karstedt catalyst was added, and the mixture was stirred until homogeneous to obtain a wet gel precursor solution. The mass percentage of polyborosilazane in the obtained wet gel precursor solution was 10 wt.%, and the concentration of the Karstedt catalyst in the wet gel precursor solution was 20 ppm.

[0052] Step 2, hydrothermal crosslinking reaction:

[0053] The wet gel precursor solution obtained in step one was added to a hydrothermal reactor lined with polytetrafluoroethylene for magnetic therapy, reacted at 120°C for 20 hours, and then removed after natural cooling to room temperature to obtain polyborosilicate wet gel.

[0054] Step 3: Solvent replacement and drying at atmospheric pressure:

[0055] Prepare a concentration gradient mixture of ethanol and cyclohexane. The resulting polyborosilicate wet gel is first immersed in a 20% (v / v) anhydrous ethanol-cyclohexane mixture for 24 hours; then in a 40% (v / v) anhydrous ethanol-cyclohexane mixture for 24 hours; then in a 60% (v / v) anhydrous ethanol-cyclohexane mixture for 24 hours; then in an 80% (v / v) anhydrous ethanol-cyclohexane mixture for 24 hours; and finally in 100% anhydrous ethanol for 24 hours. Each time the solvent is changed, ensure the ratio of wet gel to solvent remains consistent to guarantee the effect of gradual replacement.

[0056] The replaced polyborosilicate wet gel was transferred to a desiccator and dried at room temperature and normal pressure for 4 days to obtain polyborosilicate dry gel. The gel drying shrinkage rate was 4.0%.

[0057] Step 4: High-temperature ceramicization heat treatment:

[0058] The polyborosilicate dry gel obtained in step three was placed in a high-temperature tube furnace and heated to 800°C at a rate of 2°C / min under a flowing nitrogen atmosphere, and held at that temperature for 2 hours to obtain SiBCN ceramic aerogel. The density of the obtained SiBCN ceramic aerogel was 0.22 g / cm³. 3 .

[0059] Example 3

[0060] This embodiment provides a method for preparing SiBCN aerogel by atmospheric pressure drying, including the following steps:

[0061] Step 1: Prepare the precursor solution:

[0062] Polyborosilazane was added to n-hexane and stirred until homogeneous. Divinylbenzene was then added to the resulting mixture at a mass ratio of 1:1 to polyborosilazane. Finally, the Karstedt catalyst was added, and the mixture was stirred until homogeneous to obtain a wet gel precursor solution. The mass percentage of polyborosilazane in the obtained wet gel precursor solution was 10 wt.%, and the concentration of the Karstedt catalyst in the wet gel precursor solution was 20 ppm.

[0063] Step 2, hydrothermal crosslinking reaction:

[0064] The wet gel precursor solution obtained in step one was added to a hydrothermal reactor lined with polytetrafluoroethylene for magnetic therapy, reacted at 120°C for 20 hours, and then removed after natural cooling to room temperature to obtain polyborosilicate wet gel.

[0065] Step 3: Solvent replacement and drying at atmospheric pressure:

[0066] Prepare a concentration gradient mixture of ethanol and n-hexane. The resulting polyborosilicate wet gel is first immersed in a 20% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; then in a 40% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; then in a 60% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; then in an 80% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; and finally in 100% anhydrous ethanol for 24 hours. Each time the solvent is changed, ensure the ratio of wet gel to solvent remains consistent to guarantee the effect of gradual replacement.

[0067] The replaced polyborosilicate wet gel was transferred to a desiccator and dried at room temperature and normal pressure for 4 days to obtain polyborosilicate dry gel. The gel drying shrinkage rate was 3.5%.

[0068] Step 4: High-temperature ceramicization heat treatment:

[0069] The polyborosilicate dry gel obtained in step three was placed in a high-temperature tube furnace and heated to 800°C at a rate of 2°C / min under a flowing nitrogen atmosphere, and held at that temperature for 2 hours to obtain SiBCN ceramic aerogel. The density of the obtained SiBCN ceramic aerogel was 0.20 g / cm³. 3 .

[0070] Example 4

[0071] This embodiment provides a method for preparing SiBCN aerogel by atmospheric pressure drying, including the following steps:

[0072] Step 1: Prepare the precursor solution:

[0073] Polyborosilazane was added to n-hexane and stirred until homogeneous. Divinylbenzene was then added to the resulting mixture at a mass ratio of 1:1 to polyborosilazane. Finally, the Karstedt catalyst was added, and the mixture was stirred until homogeneous to obtain a wet gel precursor solution. The mass percentage of polyborosilazane in the obtained wet gel precursor solution was 7.5 wt.%, and the concentration of the Karstedt catalyst in the wet gel precursor solution was 20 ppm.

[0074] Step 2, hydrothermal crosslinking reaction:

[0075] The wet gel precursor solution obtained in step one was added to a hydrothermal reactor lined with polytetrafluoroethylene for magnetic therapy, reacted at 120°C for 20 hours, and then removed after natural cooling to room temperature to obtain polyborosilicate wet gel.

[0076] Step 3: Solvent replacement and drying at atmospheric pressure:

[0077] Prepare a concentration gradient mixture of ethanol and n-hexane. The resulting polyborosilicate wet gel is first immersed in a 20% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; then in a 40% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; then in a 60% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; then in an 80% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; and finally in 100% anhydrous ethanol for 24 hours. Each time the solvent is changed, ensure the ratio of wet gel to solvent remains consistent to guarantee the effect of gradual replacement.

[0078] The replaced polyborosilicate wet gel was transferred to a desiccator and dried at room temperature and normal pressure for 4 days to obtain polyborosilicate dry gel. The gel drying shrinkage rate was 4.4%.

[0079] Step 4: High-temperature ceramicization heat treatment:

[0080] The polyborosilicate dry gel obtained in step three was placed in a high-temperature tube furnace and heated to 800°C at a rate of 2°C / min under a flowing nitrogen atmosphere, and held at that temperature for 2 hours to obtain SiBCN ceramic aerogel. The density of the obtained SiBCN ceramic aerogel was 0.26 g / cm³. 3 .

[0081] Example 5

[0082] This embodiment provides a method for preparing SiBCN aerogel by atmospheric pressure drying, including the following steps:

[0083] Step 1: Prepare the precursor solution:

[0084] Polyborosilazane was added to n-hexane and stirred until homogeneous. Divinylbenzene was then added to the resulting mixture at a mass ratio of 1:1 to polyborosilazane. Finally, the Karstedt catalyst was added, and the mixture was stirred until homogeneous to obtain a wet gel precursor solution. The mass percentage of polyborosilazane in the obtained wet gel precursor solution was 12.5 wt.%, and the concentration of the Karstedt catalyst in the wet gel precursor solution was 20 ppm.

[0085] Step 2, hydrothermal crosslinking reaction:

[0086] The wet gel precursor solution obtained in step one was added to a hydrothermal reactor lined with polytetrafluoroethylene for magnetic therapy, reacted at 120°C for 20 hours, and then removed after natural cooling to room temperature to obtain polyborosilicate wet gel.

[0087] Step 3: Solvent replacement and drying at atmospheric pressure:

[0088] Prepare a concentration gradient mixture of ethanol and n-hexane. The resulting polyborosilicate wet gel is first immersed in a 20% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; then in a 40% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; then in a 60% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; then in an 80% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; and finally in 100% anhydrous ethanol for 24 hours. Each time the solvent is changed, ensure the ratio of wet gel to solvent remains consistent to guarantee the effect of gradual replacement.

[0089] The replaced polyborosilicate wet gel was transferred to a desiccator and dried at room temperature and normal pressure for 4 days to obtain polyborosilicate dry gel. The gel drying shrinkage rate was 3.8%.

[0090] Step 4: High-temperature ceramicization heat treatment:

[0091] The polyborosilicate dry gel obtained in step three was placed in a high-temperature tube furnace and heated to 800°C at a rate of 2°C / min under a flowing nitrogen atmosphere, and held at that temperature for 2 hours to obtain SiBCN ceramic aerogel. The density of the obtained SiBCN ceramic aerogel was 0.24 g / cm³. 3 .

[0092] Example 6

[0093] This embodiment provides a method for preparing SiBCN aerogel by atmospheric pressure drying, including the following steps:

[0094] Step 1: Prepare the precursor solution:

[0095] Polyborosilazane was added to n-hexane and stirred until homogeneous. Divinylbenzene was then added to the resulting mixture at a mass ratio of divinylbenzene to polyborosilazane of 1:0.5. Finally, the Karstedt catalyst was added, and the mixture was stirred until homogeneous to obtain a wet gel precursor solution. The mass percentage of polyborosilazane in the obtained wet gel precursor solution was 10 wt.%, and the concentration of the Karstedt catalyst in the wet gel precursor solution was 20 ppm.

[0096] Step 2, hydrothermal crosslinking reaction:

[0097] The wet gel precursor solution obtained in step one was added to a hydrothermal reactor lined with polytetrafluoroethylene for magnetic therapy, reacted at 120°C for 20 hours, and then removed after natural cooling to room temperature to obtain polyborosilicate wet gel.

[0098] Step 3: Solvent replacement and drying at atmospheric pressure:

[0099] Prepare a concentration gradient mixture of ethanol and n-hexane. The resulting polyborosilicate wet gel is first immersed in a 20% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; then in a 40% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; then in a 60% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; then in an 80% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; and finally in 100% anhydrous ethanol for 24 hours. Each time the solvent is changed, ensure the ratio of wet gel to solvent remains consistent to guarantee the effect of gradual replacement.

[0100] The replaced polyborosilicate wet gel was transferred to a desiccator and dried at room temperature and normal pressure for 4 days to obtain polyborosilicate dry gel. The gel drying shrinkage rate was 3.9%.

[0101] Step 4: High-temperature ceramicization heat treatment:

[0102] The polyborosilicate dry gel obtained in step three was placed in a high-temperature tube furnace and heated to 800°C at a rate of 2°C / min under a flowing nitrogen atmosphere, and held at that temperature for 2 hours to obtain SiBCN ceramic aerogel. The density of the obtained SiBCN ceramic aerogel was 0.23 g / cm³. 3 .

[0103] Example 7

[0104] This embodiment provides a method for preparing SiBCN aerogel by atmospheric pressure drying, including the following steps:

[0105] Step 1: Prepare the precursor solution:

[0106] Polyborosilazane was added to n-hexane and stirred until homogeneous. Divinylbenzene was then added to the resulting mixture at a mass ratio of 1:1 to polyborosilazane. Finally, the Karstedt catalyst was added, and the mixture was stirred until homogeneous to obtain a wet gel precursor solution. The mass percentage of polyborosilazane in the obtained wet gel precursor solution was 10 wt.%, and the concentration of the Karstedt catalyst in the wet gel precursor solution was 20 ppm.

[0107] Step 2, hydrothermal crosslinking reaction:

[0108] The wet gel precursor solution obtained in step one was added to a hydrothermal reactor lined with polytetrafluoroethylene for magnetic therapy, reacted at 150°C for 20 hours, and then removed after natural cooling to room temperature to obtain polyborosilicate wet gel.

[0109] Step 3: Solvent replacement and drying at atmospheric pressure:

[0110] Prepare a concentration gradient mixture of ethanol and n-hexane. The resulting polyborosilicate wet gel is first immersed in a 20% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; then in a 40% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; then in a 60% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; then in an 80% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; and finally in 100% anhydrous ethanol for 24 hours. Each time the solvent is changed, ensure the ratio of wet gel to solvent remains consistent to guarantee the effect of gradual replacement.

[0111] The replaced polyborosilicate wet gel was transferred to a desiccator and dried at room temperature and normal pressure for 4 days to obtain polyborosilicate dry gel. The gel drying shrinkage rate was 4.4%.

[0112] Step 4: High-temperature ceramicization heat treatment:

[0113] The polyborosilicate dry gel obtained in step three was placed in a high-temperature tube furnace and heated to 800°C at a rate of 2°C / min under a flowing nitrogen atmosphere, and held at that temperature for 2 hours to obtain SiBCN ceramic aerogel. The density of the obtained SiBCN ceramic aerogel was 0.23 g / cm³. 3 .

[0114] Example 8

[0115] This embodiment provides a method for preparing SiBCN aerogel by atmospheric pressure drying, including the following steps:

[0116] Step 1: Prepare the precursor solution:

[0117] Polyborosilazane was added to n-hexane and stirred until homogeneous. Divinylbenzene was then added to the resulting mixture at a mass ratio of divinylbenzene to polyborosilazane of 1:1.5. Finally, the Karstedt catalyst was added, and the mixture was stirred until homogeneous to obtain a wet gel precursor solution. The mass percentage of polyborosilazane in the obtained wet gel precursor solution was 10 wt.%, and the concentration of the Karstedt catalyst in the wet gel precursor solution was 20 ppm.

[0118] Step 2, hydrothermal crosslinking reaction:

[0119] The wet gel precursor solution obtained in step one was added to a hydrothermal reactor lined with polytetrafluoroethylene for magnetic therapy, reacted at 120°C for 20 hours, and then removed after natural cooling to room temperature to obtain polyborosilicate wet gel.

[0120] Step 3: Solvent replacement and drying at atmospheric pressure:

[0121] Prepare a concentration gradient mixture of ethanol and n-hexane. The resulting polyborosilicate wet gel is first immersed in a 20% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; then in a 40% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; then in a 60% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; then in an 80% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; and finally in 100% anhydrous ethanol for 24 hours. Each time the solvent is changed, ensure the ratio of wet gel to solvent remains consistent to guarantee the effect of gradual replacement.

[0122] The replaced polyborosilicate wet gel was transferred to a desiccator and dried at room temperature and normal pressure for 4 days to obtain polyborosilicate dry gel. The gel drying shrinkage rate was 3.4%.

[0123] Step 4: High-temperature ceramicization heat treatment:

[0124] The polyborosilicate dry gel obtained in step three was placed in a high-temperature tube furnace and heated to 800°C at a rate of 2°C / min under a flowing nitrogen atmosphere, and held at that temperature for 2 hours to obtain SiBCN ceramic aerogel. The density of the obtained SiBCN ceramic aerogel was 0.24 g / cm³. 3 .

[0125] Example 9

[0126] This embodiment provides a method for preparing SiBCN aerogel by atmospheric pressure drying, including the following steps:

[0127] Step 1: Prepare the precursor solution:

[0128] Polyborosilazane was added to n-hexane and stirred until homogeneous. Divinylbenzene was then added to the resulting mixture at a mass ratio of 1:1 to polyborosilazane. Finally, the Karstedt catalyst was added, and the mixture was stirred until homogeneous to obtain a wet gel precursor solution. The mass percentage of polyborosilazane in the obtained wet gel precursor solution was 10 wt.%, and the concentration of the Karstedt catalyst in the wet gel precursor solution was 20 ppm.

[0129] Step 2, hydrothermal crosslinking reaction:

[0130] The wet gel precursor solution obtained in step one was added to a hydrothermal reactor lined with polytetrafluoroethylene for magnetic therapy, reacted at 120°C for 20 hours, and then removed after natural cooling to room temperature to obtain polyborosilicate wet gel.

[0131] Step 3: Solvent replacement and drying at atmospheric pressure:

[0132] Prepare a concentration gradient mixture of ethanol and n-hexane. The resulting polyborosilicate wet gel is first immersed in a 20% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; then in a 40% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; then in a 60% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; then in an 80% (v / v) anhydrous ethanol-n-hexane mixture for 24 hours; and finally in 100% anhydrous ethanol for 24 hours. Each time the solvent is changed, ensure the ratio of wet gel to solvent remains consistent to guarantee the effect of gradual replacement.

[0133] The replaced polyborosilicate wet gel was transferred to a desiccator and dried at room temperature and normal pressure for 4 days to obtain polyborosilicate dry gel. The gel drying shrinkage rate was 3.5%.

[0134] Step 4: High-temperature ceramicization heat treatment:

[0135] The polyborosilicate dry gel obtained in step three was placed in a high-temperature tube furnace and heated to 1000℃ at a rate of 2℃ / min under a flowing nitrogen atmosphere, and held at that temperature for 2 hours to obtain SiBCN ceramic aerogel. The density of the obtained SiBCN ceramic aerogel was 0.25 g / cm³. 3 .

Claims

1. A method for preparing a SiBCN aerogel by atmospheric pressure drying, characterized by, Comprising the following steps: Step one, preparation of precursor solution: Polyborosilazane is added into an organic solvent and stirred until uniform, a crosslinking agent divinylbenzene and a catalyst are added into the obtained mixture, and the mixture is stirred until uniform to obtain a wet gel precursor solution; Step two, hydrothermal crosslinking reaction: The wet gel precursor solution obtained in step one is subjected to hydrothermal crosslinking reaction at a certain temperature to obtain a polyborosilazane wet gel; Step three, solvent replacement and normal pressure drying: A concentration gradient mixed solution of a replacement solvent and the organic solvent is prepared, the polyborosilazane wet gel obtained in step two is sequentially immersed in the concentration gradient mixed solution with gradually increasing concentration of the replacement solvent, so that the replacement solvent gradually replaces the organic solvent in the polyborosilazane wet gel, and the replaced polyborosilazane wet gel is subjected to room temperature normal pressure drying treatment to obtain a polyborosilazane dry gel; Step four, high-temperature ceramicization heat treatment: The polyborosilazane dry gel obtained in step three is subjected to high-temperature heat treatment in a protective atmosphere to obtain a SiBCN aerogel. 2.The method according to claim 1, wherein, The organic solvent in step one is one of n-hexane, cyclohexane or toluene, the catalyst is Karstedt catalyst, and the concentration of the catalyst in the wet gel precursor solution is 20 ppm. 3.The method according to claim 1 or 2, wherein, The mass ratio of the crosslinking agent divinylbenzene to polyborosilazane in the wet gel precursor solution obtained in step one is 1:0.5-1.5, and the mass percentage content of polyborosilazane in the obtained wet gel precursor solution is 7.5-12.5 wt.%. 4.The method according to claim 3, wherein the SiBCN aerogel is dried at normal pressure. The temperature of the hydrothermal crosslinking reaction in step two is 120-150℃, and the reaction time is 20 h.

5. The method according to claim 4, wherein the SiBCN aerogel is dried at atmospheric pressure. The volume concentration of the replacement solvent in the concentration gradient mixed solution in step three is 20%, 40%, 60%, 80% and 100% in sequence, and the replacement solvent is ethanol. 6.The method according to claim 5, wherein the SiBCN aerogel is dried at atmospheric pressure. The immersion time of the polyborosilazane wet gel in each concentration gradient mixed solution in step three is 24 h. 7.The method according to claim 6, wherein the SiBCN aerogel is dried at atmospheric pressure. The time of the room temperature normal pressure drying treatment in step three is 4 days. 8.The method according to claim 7, wherein the SiBCN aerogel is dried at atmospheric pressure. The protective atmosphere in step four is nitrogen atmosphere, the heating rate of the high-temperature heat treatment is 2-3℃ / min, the heat treatment temperature is 800-1000℃, and the heat treatment time is 2 h.

9. SiBCN aerogel prepared by the method of dry preparation at atmospheric pressure according to any one of claims 1 to 8, characterized in that, The SiBCN aerogel has a density of 0.20-0.26 g / cm 3 .

10. Application of the SiBCN aerogel in claim 9 in the field of aircraft thermal protection, industrial thermal insulation or building thermal insulation.

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