Method for improving ablation performance of phenolic aerogel by physical doping

Abstract

The application discloses a method for improving ablation performance of phenolic aerogel by physical doping, and is suitable for preparation of ZrB2, ZrSi2, ZrO2, TiB2, B4C, SiC or SiO2 particle-reinforced phenolic aerogel. The preparation method provided by the application uses polyvinylpyrrolidone as a dispersant and a phase separation agent, improves dispersion stability of the filling particles in a sol solution, promotes phase separation and growth of a phenolic skeleton on the surface of the filling particles, solves the problem of poor compatibility between the filling particles and the phenolic aerogel, guarantees the integrity of the holes of the phenolic aerogel in a normal-pressure drying process, is simple in operation, is widely applicable, and can be applied to production and preparation of an aerospace vehicle ablation-type thermal protection material.

Description

Technical Field

[0001] This invention relates to a method for improving the ablation performance of phenolic aerogel through physical doping, which can be applied to the production of ablation-type thermal protection materials for aerospace vehicles. Background Technology

[0002] Phenolic aerogels possess unique properties such as low cost, lightweight, thermal insulation, and ablation resistance, meeting the thermal protection requirements of many aircraft operating in atmospheric environments. However, as aircraft speeds increase, thermal protection materials face even more severe aerodynamic heat flux challenges. Hypersonic aircraft surface temperatures can reach 2000℃, rendering the ablation performance of conventional phenolic aerogels insufficient. Therefore, improving the ablation performance of phenolic aerogels has become a key technology in the field of thermal protection materials.

[0003] Currently, there are two main methods to improve the ablation performance of phenolic aerogels: bulk modification and physical doping. Both methods involve introducing inorganic high-temperature resistant elements to enhance the high-temperature ablation performance of phenolic aerogels. Bulk modification involves introducing inorganic elements into the phenolic matrix through chemical bonding. For example, Niu et al. introduced POSS (cage-type polysilsesquioxane), which can decompose into SiO2 at high temperatures, into phenolic aerogels, effectively improving the residual weight of the aerogel and reducing the linear ablation rate (see: [link to relevant documentation]). Journal of Materials Science & Technology (2022, 141, 199-208). However, due to the stringent process control required for bulk modification, physical doping is a more commonly used method. Physical doping involves dispersing filler particles into a phenolic sol, ensuring uniform dispersion within the phenolic resin during the subsequent gelation. Commonly used filler particles are various ceramic powders, such as ZrB2, ZrSi2, ZrO2, TiB2, B4C, SiC, and SiO2. These filler particles can effectively slow down the ablation rate of phenolic resin at high temperatures. However, due to the poor compatibility between the filler particles and phenolic resin, as well as the instability of the sol dispersion, physical doping is more often used in the production of bulk phenolic resin. To realize the application of filler particles in phenolic aerogels, the filler particles must be modified or the gelation speed of phenolic resin must be improved. For example, Liu et al. successfully prepared halloysite nanotube-reinforced phenolic aerogels by modifying halloysite nanotubes with 3-aminopropyltriethoxysilane; Li et al. used trifluoroacetic acid as a catalyst to achieve gelation of phenolic sol within 30 seconds, successfully preparing TiB2–B4C-filled phenolic aerogels (see: Ceramics International 2021, 47, 6487–6495; Nanotechnology Reviews 2022, 11, 3031–3041). However, these existing methods reported have the following drawbacks:

[0004] (1) There is a lack of application examples with the prospect of mass production in the existing methods.

[0005] (2) In order to improve the compatibility between the filler particles and the phenolic aerogel body, the existing methods require precise and complicated chemical modification of the filler particles.

[0006] (3) In order to achieve uniform distribution of filling particles in phenolic aerogel, the existing method requires the phenolic sol system to gel rapidly. Summary of the Invention

[0007] To address the aforementioned technical problems, the present invention aims to provide a method for improving the ablation performance of phenolic aerogels through physical doping. This method can be used to prepare phenolic aerogels reinforced with particles such as ZrB2, ZrSi2, ZrO2, TiB2, B4C, SiC, or SiO2.

[0008] To achieve the above objectives, the specific technical solution of the present invention is as follows:

[0009] A method for improving the ablation performance of phenolic aerogel through physical doping includes the following steps:

[0010] (1) Take linear phenolic resin, dissolve it in anhydrous ethanol to obtain a phenolic resin solution;

[0011] (2) Add polyvinylpyrrolidone to the phenolic solution and stir to dissolve;

[0012] (3) Add filler particles to the phenolic solution containing polyvinylpyrrolidone and stir vigorously to obtain a uniform dispersion;

[0013] (4) Add hexamethylenetetramine curing agent to the dispersion and stir to dissolve;

[0014] (5) Place the dispersion after adding hexamethylenetetramine in a sealed container and heat to solidify to obtain phenolic wet gel;

[0015] (6) Dry the phenolic wet gel at room temperature and pressure to obtain phenolic aerogel.

[0016] In the above technical solution, the dispersion obtained by vigorous stirring will be accompanied by bubbles, which are then drained or ultrasonically treated to remove the bubbles.

[0017] In the above technical solution, polyvinylpyrrolidone is used as a dispersant, and a stable dispersion of filled particles can be obtained after vigorous stirring.

[0018] In the above technical solution, the filling particles can be at least one of inorganic particles such as ZrB2, ZrSi2, ZrO2, TiB2, B4C, SiC or SiO2, that is, the filling particles in the phenolic aerogel can be one type or several types.

[0019] In the above technical solution, the diameter of the filling particles is 5nm~10μm.

[0020] In the above technical solution, the amount of the filler particles is 0% to 40% of the mass of the linear phenolic resin.

[0021] In the above technical solution, the amount of polyvinylpyrrolidone used is 3% to 30% of the mass of the filler particles.

[0022] In the above technical solution, the amount of linear phenolic resin used is 10% to 40% of the total mass of the dispersion.

[0023] In the above technical solution, the molecular weight of the polyvinylpyrrolidone is 1000~10000.

[0024] In the above technical solution, the amount of hexamethylenetetramine curing agent is 5% to 30% of the mass of linear phenolic resin.

[0025] In the above technical solution, the curing temperature is 70℃~120℃, and the curing time is 10 hours~7 days.

[0026] The present invention also provides a phenolic aerogel prepared by the above method.

[0027] The principle of this invention is as follows: On the one hand, polyvinylpyrrolidone (PVP) can be used as a dispersant to achieve uniform and stable dispersion of filler particles in anhydrous ethanol, ensuring that no particle sedimentation or segregation occurs during the phenolic gelation process, and ultimately obtaining a uniform phenolic aerogel; on the other hand, PPVP can act as a phase separating agent to promote phase separation of phenolic sol on the surface of filler particles, thereby enhancing the compatibility between filler particles and the phenolic matrix, ensuring the integrity and uniformity of the gel skeleton to withstand atmospheric pressure drying and obtain the aerogel.

[0028] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0029] 1. This invention does not involve chemical modification of the filler particles.

[0030] 2. This invention prepares phenolic aerogel by atmospheric pressure drying.

[0031] 3. This invention is applicable to the preparation of phenolic aerogels reinforced with particles such as ZrB2, ZrSi2, ZrO2, TiB2, B4C, SiC, SiB6, or SiO2.

[0032] In summary, the preparation method of this invention uses polyvinylpyrrolidone as a dispersant and phase separating agent, which improves the dispersion stability of the filler particles in the sol solution, promotes the phase separation and growth of the phenolic skeleton on the surface of the filler particles, solves the problem of poor compatibility between the filler particles and the phenolic aerogel bulk, ensures the integrity of the pores of the phenolic aerogel during atmospheric pressure drying, is simple to operate, has wide applicability, and can be applied to the production and preparation of ablation-type thermal protection materials for aerospace vehicles. Attached Figure Description

[0033] Figure 1 This is a photograph of the SiO2-reinforced phenolic aerogel from Example 1.

[0034] Figure 2 This is a scanning electron microscope image of the SiO2-enhanced phenolic aerogel in Example 1;

[0035] Figure 3 Thermogravimetric analysis (TGA) diagram of SiO2-reinforced phenolic aerogel in air atmosphere in Example 1. Detailed Implementation

[0036] The following is in conjunction with the appendix Figures 1-3 The present invention will be further described in conjunction with the embodiments:

[0037] Example 1

[0038] A method for improving the ablation performance of phenolic aerogel by physically doping with SiO2 includes the following steps:

[0039] (1) Weigh 30g of linear phenolic resin and add it to a 200mL beaker. Add 70g of anhydrous ethanol to the beaker and stir to dissolve at room temperature.

[0040] (2) Add 0.3g of polyvinylpyrrolidone to the solution prepared in (1) and stir to dissolve at room temperature.

[0041] (3) Add 3g of SiO2 filler particles with a particle size of 50nm to the solution prepared in (2) and stir vigorously at room temperature until the SiO2 is evenly dispersed.

[0042] (4) Drain and pour the prepared dispersion from (3) to remove air bubbles.

[0043] (5) Add 6g of hexamethylenetetramine to the non-foaming dispersion obtained in (4) and stir to dissolve at room temperature.

[0044] (6) Place the dispersion obtained in (5) in a sealed reactor and solidify at 90°C for 2 days.

[0045] (7) The phenolic wet gel obtained in (6) is placed at room temperature and pressure to dry until the mass no longer changes, thus obtaining SiO2-reinforced phenolic aerogel.

[0046] The final SiO2-reinforced phenolic aerogel had a density of 0.50 g / cm³. 3 The drying shrinkage rate is 12%, and the specific surface area is 235 m². 2 / g, residual weight at 800℃ in nitrogen atmosphere: 57.68%.

[0047] Figure 1 The image shows a physical sample of the SiO2-reinforced phenolic aerogel prepared by the above method.

[0048] Figure 2 Scanning electron microscope (SEM) image of the SiO2-reinforced phenolic aerogel prepared by the above method. It can be seen that no clusters of SiO2 were observed in the phenolic aerogel; SiO2 was uniformly distributed throughout the aerogel.

[0049] Figure 3 Thermogravimetric analysis (TGA) of SiO2-reinforced phenolic aerogel prepared by the above method in air atmosphere is shown. It can be seen that the residual weight of the phenolic aerogel gradually stabilizes after reaching 58%.

[0050] Example 2

[0051] A method for improving the ablation performance of phenolic aerogel by physically doping TiB2 includes the following steps:

[0052] (1) Weigh 30g of linear phenolic resin and add it to a 200mL beaker. Add 60g of anhydrous ethanol to the beaker and stir to dissolve at room temperature.

[0053] (2) Add 0.4g of polyvinylpyrrolidone to the solution prepared in (1) and stir to dissolve at room temperature.

[0054] (3) Add 2g of TiB2 filler particles with a particle size of 5μm to the solution prepared in (2) and stir vigorously at room temperature until TiB2 is evenly dispersed.

[0055] (4) Drain and pour the prepared dispersion from (3) to remove air bubbles.

[0056] (5) Add 8g of hexamethylenetetramine to the non-foaming dispersion obtained in (4) and stir to dissolve at room temperature.

[0057] (6) Place the dispersion obtained in (5) in a sealed reactor and cure at 120°C for 1 day.

[0058] (7) The phenolic wet gel obtained in (6) is placed at room temperature and pressure to dry until the mass no longer changes, thus obtaining TiB2 reinforced phenolic aerogel.

[0059] The final TiB2-reinforced phenolic aerogel had a density of 0.52 g / cm³. 3 The drying shrinkage rate is 10%, and the specific surface area is 203 m². 2 / g, residual weight at 800℃ in nitrogen atmosphere: 62.17%.

[0060] Example 3

[0061] A method for improving the ablation performance of phenolic aerogels by physically doping SiC and SiB6 includes the following steps:

[0062] (1) Weigh 15g of linear phenolic resin and add it to a 200mL beaker. Add 85g of anhydrous ethanol to the beaker and stir to dissolve at room temperature.

[0063] (2) Add 0.2g of polyvinylpyrrolidone to the solution prepared in (1) and stir to dissolve at room temperature.

[0064] (3) Add 1.5g of SiC with a particle size of 10μm and 1.5g of SiB6 with a particle size of 10μm to the solution prepared in (2), and stir vigorously at room temperature until SiC and SiB6 are evenly dispersed.

[0065] (4) Drain and pour the prepared dispersion from (3) to remove air bubbles.

[0066] (5) Add 1.5g of hexamethylenetetramine to the non-foaming dispersion obtained in (4) and stir to dissolve at room temperature.

[0067] (6) Place the dispersion obtained in (5) in a sealed reactor and solidify at 80°C for 4 days.

[0068] (7) The phenolic wet gel obtained in (6) is dried at room temperature and pressure until its mass no longer changes, thus obtaining SiC and SiB6 reinforced phenolic aerogel.

[0069] The final SiC and SiB6 reinforced phenolic aerogel had a density of 0.22 g / cm³. 3 The drying shrinkage rate is 8%, and the specific surface area is 153 m². 2 / g, residual weight at 800℃ in nitrogen atmosphere: 66.56%.

[0070] The specific embodiments of the present invention disclosed above are intended to help understand the content of the present invention and to implement it accordingly. Those skilled in the art will understand that various substitutions, changes, and modifications are possible without departing from the spirit and scope of the present invention. The present invention should not be limited to the content disclosed in the embodiments of this specification; the scope of protection of the present invention is defined by the claims.

Claims

1. A method for improving the ablation performance of phenolic aerogel through physical doping, characterized in that, Includes the following steps: Take linear phenolic resin, dissolve it in anhydrous ethanol to obtain a phenolic resin solution; Add polyvinylpyrrolidone to the phenolic solution and stir to dissolve; Add filler particles to a phenolic solution containing polyvinylpyrrolidone and stir vigorously to obtain a uniform dispersion. Add hexamethylenetetramine curing agent to the dispersion and stir to dissolve; The dispersion after adding hexamethylenetetramine was placed in a sealed container and heated to solidify to obtain a phenolic wet gel. Phenolic wet gel was dried at room temperature and pressure to obtain phenolic aerogel; The polyvinylpyrrolidone serves as a dispersant to achieve uniform and stable dispersion of the filler particles in anhydrous ethanol. Furthermore, the polyvinylpyrrolidone acts as a phase separation agent to promote phase separation of the phenolic sol on the surface of the filler particles, enhance the compatibility between the filler particles and the phenolic bulk, and ensure the integrity and uniformity of the gel skeleton to withstand atmospheric pressure drying to obtain an aerogel. The diameter of the filler particles is 5 nm to 10 μm; the amount of filler particles used is 0% to 40% of the mass of the linear phenolic resin. The amount of polyvinylpyrrolidone used is 3% to 30% of the mass of the filler particles; The molecular weight of the polyvinylpyrrolidone is 1000~10000; The amount of the linear phenolic resin used is 10% to 40% of the total mass of the dispersion.

2. The method according to claim 1, characterized in that, The dispersion obtained by vigorous stirring is drained or ultrasonically treated to remove air bubbles.

3. The method according to claim 1, characterized in that, The filling particles are at least one of ZrB2, ZrSi2, ZrO2, TiB2, B4C, SiC, or SiO2 inorganic particles.

4. The method according to claim 1, characterized in that, The amount of hexamethylenetetramine curing agent used is 5% to 30% of the mass of the linear phenolic resin.

5. The method according to claim 1, characterized in that, The curing temperature is 70℃~120℃, and the curing time is 10 hours~7 days.

6. Phenolic aerogel prepared by the method according to any one of claims 1 to 5.

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