High-temperature-ablation-resistant heat-insulating aerogel as well as preparation method and application thereof

Abstract

According to the preparation method of the high-temperature-ablation-resistant heat-insulation aerogel, a plasticizer polyethylene glycol is introduced into a graphene and silicon dioxide dispersion liquid for composite film laying, then a solvent plasticizing foaming technology is utilized for preparing the composite aerogel, and the prepared aerogel has the ablation-resistant function and the excellent heat insulation function; and meanwhile, the material has the advantages of light weight, good compression resilience and the like, and can be repeatedly used by maintaining the original shape and performance at high temperature. The scheme has the advantages of simple process, controllable process, low reaction conditions, suitability for industrial production and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials, and in particular relates to a high temperature ablation resistant thermal insulation aerogel and a preparation method and application thereof. Background Art

[0002] With the rapid development of hypersonic aircraft and space shuttles, thermal protection materials are needed to resist high-temperature oxidation and ablation of combustion airflow while having good thermal insulation function to prevent excessive temperature rise from affecting the normal operation of aircraft electronic components. Graphene aerogel has attracted widespread attention due to its low density, high specific surface area and low thermal conductivity, as well as good processability and easy preparation of bulk materials. However, graphene-based materials are easily oxidized in oxygen-containing environments above 600°C. Secondly, when faced with the ablation impact brought by high-temperature airflow, the porous carbonized layer formed is easily oxidized, leading to oxidative corrosion and mechanical erosion, which seriously affects its service reliability and stability. Therefore, it is crucial to solve the ablation failure problem of graphene aerogel materials to adapt to harsh use environments. Summary of the invention

[0003] In order to overcome the above technical defects, the present invention proposes a high temperature ablation resistant heat insulating aerogel and a preparation method thereof. The composite aerogel is prepared by coating a graphene and silicon dioxide dispersion liquid with a plasticizer polyethylene glycol, using solvent plasticizing foaming technology, and then high temperature heat treatment to prepare a silicon carbide / carbon composite aerogel.

[0004] The present invention introduces silicon carbide into the pore wall of the aerogel as an ablation-resistant protective layer. When silicon carbide is ablated at high temperature, it will first be transformed into a dense oxide to prevent further ablation. The two-dimensional graphene carbon skeleton provides a curved surface connection for silicon carbide, and after foaming, it forms an anisotropic structure to reduce vertical heat transfer. The prepared aerogel has both ablation resistance and excellent thermal insulation functions, and has the advantages of light weight and good compression resilience, and can maintain its original shape and performance at high temperatures.

[0005] One of the technical solutions of the present invention is to provide a high-temperature ablation-resistant thermal insulation aerogel. The aerogel pore wall is a three-layer structure. The middle layer is a graphene skeleton, and the outer layer is silicon carbide grown in situ on the graphene. The silicon carbide and the graphene skeleton are tightly combined. In a high-temperature oxygen-containing environment, dense silicon dioxide can be generated to protect the internal graphene skeleton.

[0006] The second technical solution of the present invention is to provide a method for preparing a high temperature ablation resistant thermal insulation aerogel, which specifically comprises the following steps: (1) uniformly mixing polyethylene glycol, graphene oxide aqueous dispersion and silicon dioxide aqueous dispersion, coating to form a film and drying at room temperature to obtain a composite film; (2) placing the composite film in a foaming agent solution for foaming, and drying after foaming to obtain a composite aerogel; (3) The composite aerogel is heat-treated to obtain a high temperature ablation-resistant thermal insulation aerogel.

[0007] Furthermore, the molecular weight of the polyethylene glycol in step 1 is 800-10000. The mass ratio of polyethylene glycol to graphene oxide is 1:1.

[0008] Furthermore, the concentration of the graphene oxide aqueous dispersion in step 1 is 0.1-50 mg / g, the concentration of the silicon dioxide aqueous dispersion is 10 mg / g, and the solid content of silicon dioxide accounts for 50-90wt% of the total solid content of silicon dioxide and graphene oxide.

[0009] Furthermore, the foaming agent solution in step 2 is one of hydrazine hydrate solution, sodium borohydride solution, sodium bicarbonate solution and sodium carbonate solution.

[0010] Furthermore, the heat treatment in step 3 is performed at 1500-1700° C. in an argon atmosphere for 2 hours.

[0011] When PEG is applied to silica materials, it can effectively increase the surface tension of silica. This property is particularly important for resisting stress damage generated inside the material during the drying process. In the process of the material changing from a wet state to a dry state, the evaporation of water will cause tensile stress to be generated inside. If this stress is too large, it may cause cracks on the surface or inside the material. PEG can effectively alleviate the stress concentration in this process by increasing the elasticity and strength of the surface, thereby reducing or even avoiding the possibility of cracking of silica materials during the drying process. In the foaming solution, the molecular chain of PEG exhibits good plastic characteristics, which enables it to effectively drive the orderly migration of silica particles during the growth of bubbles. Through this orderly migration, the silica particles can be evenly distributed inside the bubbles, thereby forming a uniform and stable pore wall structure. This uniform pore wall not only improves the mechanical properties of the material, but also improves its thermal insulation and other physical properties to a certain extent, providing a wider range of possibilities for the application of foaming materials.

[0012] Introducing silicon dioxide into the interlayer of graphene oxide can weaken the interlayer force, causing it to quickly peel off at the silicon dioxide interface during the foaming process and form a silicon dioxide surface. Further during the heat treatment process, this silicon dioxide is carbonized to form a silicon carbide protective layer, thereby obtaining an ABA pore wall structure of silicon carbide-coated carbon, which effectively avoids the problem of ablation and oxidation.

[0013] The third technical solution of the present invention is to provide a thermal insulation application of the above-mentioned high temperature ablation resistant thermal insulation aerogel. The thermal conductivity of the aerogel prepared by the present invention can be as low as 15mW / mK in the vertical direction, and the residual weight is not less than 70% after heat treatment at 800℃ for 30 minutes, which has good thermal insulation effect and high temperature ablation resistance. In addition, the aerogel made by the present invention retains more than 90% of its deformation after being compressed by 60%.

[0014] Beneficial effects of the present invention: (1) Polyethylene glycol plasticizer is added to the silica and graphene oxide solution to improve the plasticity of the film so as to obtain a large-sized complete composite film, which is then plasticized and foamed into aerogel by solvent. The size of the film and aerogel is controllable. The solvent plasticization and foaming process is relatively simple and does not require a special drying process, so it is more conducive to industrial development.

[0015] (2) Silicon carbide is introduced into the outer layer of the graphene carbon wall, and is converted into oxide in a high-temperature oxygen atmosphere to form a protective layer, which prevents oxygen from entering the inner layer of the pore wall and effectively inhibits the thermal decomposition of the carbon skeleton, achieving the effect of ablation resistance. In addition, a large number of -Si-C bonds and -Si-O are introduced into the surface layer of the graphene skeleton, which improves the thermal stability and residual carbon rate of the aerogel. After heat treatment at 800°C for 30 minutes, the residual weight is not less than 70%.

[0016] (3) The aerogel prepared by the solvent plasticization foaming technology has an anisotropic structure, which reduces the heat transfer in the vertical direction and has a low thermal conductivity in the vertical direction. At the same time, the nano-silicon carbide particles have a large number of nanopores, which reduce the gas heat conduction. The thermal conductivity in the vertical direction can be as low as 15mW / mK.

[0017] (4) The solvent plasticization and foaming technology used supports the silica particles through two-dimensional graphene sheets to form curved pore units. The prepared aerogel block has low density, high porosity and excellent mechanical properties. It can withstand different deformations and maintain its original shape and performance at high temperatures. The deformation retention of the aerogel after compression by 60% is higher than 90%. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 SEM image of silica composite aerogel Figure 2 This is the SEM image of the high temperature ablation resistant thermal insulation aerogel of Example 1. DETAILED DESCRIPTION

[0019] The following examples are used to further illustrate the present invention, and their purpose is to illustrate the present invention and should not be construed as limiting the scope of the present invention. Unless otherwise specified, all parts by weight and weight percentages are used below.

[0020] The raw materials used in the present invention, unless otherwise specified, are conventional commercially available products; the methods used in the present invention, unless otherwise specified, are conventional methods in the art.

[0021] The embodiments of the present invention are further described below with reference to a plurality of embodiments.

[0022] It should be clear that the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0023] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0024] The molecular weight referred to in the present invention generally refers to the weight average molecular weight.

[0025] Example 1 Polyethylene glycol with a molecular weight of 800 was added to a mixed solution of 10 mg / ml aqueous graphene oxide (purchased from Hangzhou Gaoxin Technology Co., Ltd., with an average size of 20 um) dispersion and 10 mg / g nano-silica microsphere dispersion. Polyethylene glycol, graphene oxide, and silica were mixed in a solid content mass ratio of 1:1:1. The film was laid, and after the film was naturally dried, it was placed in 80% hydrazine hydrate for 4 hours, and then replaced with ethanol and n-hexane in turn and dried at normal pressure to obtain a composite aerogel, such as Figure 1 As shown in the figure, it can be seen that the silica particles are evenly dispersed on the surface of the pore wall. Subsequently, a high-temperature ablation-resistant thermal insulation aerogel was obtained by heating at 1500°C in an argon atmosphere for 2 hours. Figure 2 As shown in the figure, it can be seen that after high temperature treatment, the uniform particles of silicon dioxide are carbonized into silicon carbide, forming a dense network on the surface of the pore wall. Silicon carbide is located on the surface of the pore wall, which further enhances the high temperature stability and thermal insulation performance of the material, laying the foundation for its application in high temperature environments.

[0026] In a high-temperature thermal environment, silicon carbide will first transform into a dense oxide during high-temperature ablation, thereby preventing further ablation, while the curved pore wall provides elasticity. The thermal conductivity of the aerogel in the vertical direction is 20mW / mK, and the density is 10mg / cm3. The ablation resistance effect is tested at a high temperature of 800℃. After 30 minutes of heat treatment, the residual weight is 70%, and the deformation retention is 95% after compression of 60%.

[0027] Example 2 Polyethylene glycol with a molecular weight of 800 was added to 0.1 mg / ml aqueous graphene oxide (purchased from Hangzhou Gaoxin Technology Co., Ltd., with an average size of 20 um) dispersion and 10 mg / g nano-silica microsphere dispersion. Polyethylene glycol, graphene oxide, and silica were mixed in a solid content mass ratio of 1:1:9. The film was then placed in 80% hydrazine hydrate for foaming for 4 hours after natural drying, and then replaced with ethanol and n-hexane and dried at normal pressure to obtain a composite aerogel, such as Figure 1 As shown in the figure, it can be seen that the silica particles are evenly dispersed on the surface of the pore wall. Subsequently, a high-temperature ablation-resistant thermal insulation aerogel was obtained by heating at 1700°C in an argon atmosphere for 2 hours. The thermal conductivity of the aerogel in the vertical direction is 15mW / mK and the density is 20mg / cm 3 ,, the ablation resistance effect was tested at a high temperature of 800℃. The residual weight was 78% after 30 minutes of heat treatment, and the deformation retention was 92% after compression of 60%.

[0028] Example 3 Same as Example 1, except that the molecular weight of polyethylene glycol is replaced by 1w, the obtained high temperature ablation resistant material has a vertical thermal conductivity of 15mW / mK and a density of 20mg / cm 3 , after heat treatment at 800℃ for 30 minutes, the residual weight is 70%, and after compression by 60%, the deformation retention is 90%.

[0029] Example 4 Polyethylene glycol with a molecular weight of 10,000 was added to 50 mg / ml of aqueous graphene oxide (purchased from Hangzhou Gaoxin Technology Co., Ltd., with an average size of 20um) and 10 mg / g of nano-silica microsphere dispersion. Polyethylene glycol, graphene oxide, and silica were mixed in a solid content mass ratio of 1:1:4. The film was laid, and then the naturally dried film was placed in 80% hydrazine hydrate for foaming for 4 hours, and then replaced with ethanol and n-hexane and dried at normal pressure to obtain a composite aerogel. Subsequently, a high-temperature resistant ablation insulation aerogel was obtained by heating at 1700°C in an argon atmosphere for 2 hours. The thermal conductivity of the aerogel in the vertical direction is 15 mW / mK and the density is 17mg / cm 3 The ablation resistance effect was tested at a high temperature of 800°C. The residual weight was 77% after 30 minutes of heat treatment, and the deformation retention was 95% after compression by 60%.

[0030] Comparative Example 1 10mg / ml of aqueous graphene oxide (purchased from Hangzhou Gaoxin Technology Co., Ltd., with an average size of 20um) was compounded with 10mg / g of nano-silicon dioxide microsphere dispersion, in which the solid content of silicon dioxide was 60%, and then directly freeze-dried and then heat-treated in argon at 2000℃. The thermal conductivity of the aerogel in the vertical direction is 30mW / mK, and the density is 10mg / cm3 The ablation resistance effect was tested at a high temperature of 800°C. The residual weight was 65% after 30 minutes of heat treatment, and the deformation retention was 67% after compression of 60%.

[0031] In this embodiment, since there is no foaming to expose SIO2, ABA cannot be formed and the effect is not good.

[0032] Comparative Example 2 10 mg / ml of aqueous graphene oxide (purchased from Hangzhou Gaoxin Technology Co., Ltd., with an average size of 20 um) was compounded with 10 mg / g of nano-silica microsphere dispersion and then spread as a film. After natural drying, due to the high brittleness of the silica particles and the weak interaction between the particles, a complete composite film could not be obtained during the film drying process due to the large surface tension.

[0033] The above embodiments describe in detail the structure, features and effects of the present invention. The above are only preferred embodiments of the present invention. Any changes made in accordance with the concept of the present invention, or modifications to equivalent embodiments with equivalent changes, which do not exceed the scope covered by the specification, should be within the protection scope of the present invention.

Claims

1. A high temperature ablation resistant thermal insulation aerogel, characterized in that: The aerogel pore wall has a three-layer structure, with the middle layer being a graphene skeleton and the outer layer being silicon carbide grown in situ on the graphene.

2. A method for preparing the high temperature ablation resistant thermal insulation aerogel according to claim 1, characterized in that: The following steps are involved: (1) uniformly mixing polyethylene glycol, graphene oxide aqueous dispersion and silicon dioxide aqueous dispersion, coating to form a film and drying at room temperature to obtain a composite film; (2) placing the composite film in a foaming agent solution for foaming, and drying after foaming to obtain a composite aerogel; (3) The composite aerogel is heat-treated to obtain a high temperature ablation-resistant thermal insulation aerogel.

3. The preparation method according to claim 2, characterized in that: The molecular weight of the polyethylene glycol in step 1 is 800-10000.

4. The preparation method according to claim 2, characterized in that: In step 1, the concentration of the graphene oxide aqueous dispersion is 0.1-50 mg / g, the concentration of the silicon dioxide aqueous dispersion is 10 mg / g, and the solid content of silicon dioxide accounts for 50-90wt% of the total solid content of silicon dioxide and graphene oxide.

5. The preparation method according to claim 2, characterized in that: The mass ratio of polyethylene glycol to graphene oxide is 1:

1.

6. The preparation method according to claim 2, characterized in that: The foaming agent solution in step 2 is one of hydrazine hydrate solution, sodium borohydride solution, sodium bicarbonate solution and sodium carbonate solution.

7. The preparation method according to claim 2, characterized in that: The heat treatment in step 3 is performed at 1500-1700° C. in an argon atmosphere for 2 hours.

8. A thermal insulation application of the high temperature ablation resistant thermal insulation aerogel prepared by the preparation method as claimed in claim 2.

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