Ablation dimensional modified phenolic aerogel and preparation method thereof

Abstract

The invention discloses ablative dimensional modified phenolic aerogel and a preparation method thereof, and belongs to the field of light ablative aerogel. According to the preparation method, a mixed solution of phenolic aldehyde sol and nano mineral sol is taken as a sol reaction solution, and phenolic aldehyde can be synchronously subjected to sol-gel along with nano minerals in a gradient heating process, so that a double-framework structure with the nano minerals as a lap joint structure and the phenolic aldehyde as a coating structure can be finally formed. The double-skeleton structure can ensure that after the phenolic aldehyde is ablated and consumed, the nano mineral skeleton can maintain the integrity of the whole structure of the aerogel, so that the aerogel still has good heat insulation performance. The method has the characteristics of simplicity in operation, no need of supercritical drying, suitability for industrial production and the like, and is expected to be applied to a heat prevention and insulation integrated material in the field of light thermal protection.

Description

Technical Field

[0001] This invention relates to an ablation-modified phenolic aerogel and its preparation method, belonging to the field of lightweight ablation aerogels. Background Technology

[0002] Phenolic aerogels possess lightweight, flame-retardant, and ablation-resistant properties, making them widely used in lightweight thermal protection applications. However, traditional phenolic aerogels undergo severe ablation and pyrolysis under harsh aerodynamic and thermal environments, particularly prolonged aerobic conditions. This leads to aerogel volume shrinkage, pore collapse, and even cracking of the thermal protection layer, resulting in thermal insulation failure and aerodynamic shape damage. Therefore, improving the ablation shape retention of phenolic aerogels to achieve integrated thermal insulation is a crucial development direction in the field of lightweight thermal protection.

[0003] There are generally two methods to improve the ablation shape retention of phenolic aerogel. One is to introduce a ceramic component, so that the ceramic component can simultaneously melt and sinter during the ablation process, thereby forming a dense ceramic layer on the surface of the phenolic aerogel to isolate oxygen and slow down the ablation rate. The other is to introduce a second component skeleton with certain temperature resistance to ensure that there are still aerogel skeletons remaining after the phenolic aerogel is ablated, so as to maintain the heat insulation effect of the heat protection layer.

[0004] Patent CN114736400A discloses a method for preparing ceramizable phenolic aerogel. By introducing ceramizable fillers (such as kaolin, halloysite, and ZrB2), the method improves the residual carbon content of the phenolic aerogel at high temperatures and constructs a ceramic protective layer, thereby enhancing its high-temperature insulation and oxidation resistance. However, some shortcomings remain. This method primarily relies on the reaction between the pyrolysis gas from the phenolic resin during carbonization and the inorganic filler to generate ceramic and glassy phases. This process requires strict temperature control and oxidizing atmosphere conditions, is complex, and its final performance is significantly affected by the stability of the reaction process, easily leading to uneven ceramic phase distribution or pore collapse. Furthermore, this method mainly focuses on improving high-temperature performance after carbonization, lacking a systematic design for maintaining the stability of the skeleton and the structural support mechanism during high-temperature ablation. Once the phenolic skeleton is severely ablated, insufficient structural integrity remains a problem.

[0005] Patent CN109575510A discloses a method for preparing a three-dimensional phenolic resin aerogel material reinforced with nanofiber minerals. This method involves activating nano-clay mineral fibers, constructing a three-dimensional fiber-based composite gel, and combining this with vacuum impregnation and microwave curing of phenolic resin. This produces a three-dimensional phenolic aerogel material with a tiered porous structure, low thermal conductivity, and high strength. While this method offers advantages in improving the strength, density, and thermal insulation properties of the composite aerogel, it still has several significant drawbacks. First, the process is complex, involving multiple energy-intensive or equipment-dependent steps such as acid activation, liquid nitrogen rapid freezing, long-term freeze-drying, vacuum impregnation, and microwave curing. The overall preparation cycle is long and inefficient, hindering large-scale production. Second, although this method uses fiber reinforcement to improve structural strength, structural stability relies primarily on fiber support rather than network synergy. Therefore, it may face the risk of overall framework instability during high-temperature ablation or localized structural damage.

[0006] Patent application CN117624713A discloses a method for preparing a high-temperature ablation-resistant phenolic aerogel. By introducing alumina nanocrystals and phenolic resin to co-gel and form a dual-framework structure, the method improves the aerogel's resistance to collapse and overall strength during atmospheric pressure drying. However, it still has some significant limitations. First, alumina nanocrystals are expensive and have limited dispersibility and interfacial compatibility, easily leading to uneven gel structure and affecting the stability of the final material's properties. Second, this method mainly focuses on structural preservation during atmospheric pressure drying, lacking an effective support mechanism for the carbonization or decomposition of the phenolic matrix under high-temperature ablation conditions. Once the phenolic framework pyrolyzes, the overall structure is prone to collapse, making it difficult to meet the long-term heat insulation and protection requirements under extreme thermal environments. Furthermore, the preparation process requires a lengthy aging step, is time-consuming, and lacks interfacial binders, making it difficult to achieve efficient synergy between the inorganic reinforcing phase and the organic matrix, limiting further performance improvements and process controllability.

[0007] The aforementioned existing technologies generally suffer from the following problems: To achieve uniform dispersion of the ceramicizable components, phenolic sols typically require rapid gelation within a very short time (e.g., 10–40 seconds), resulting in a narrow process window, stringent operational requirements, and difficulty in control. Furthermore, existing methods cannot simultaneously construct a dual-framework structure of nano-minerals and phenolic resins in a single process; different components are often introduced step-by-step using freeze-drying, which is not only cumbersome and energy-intensive but also limits the feasibility of industrial-scale preparation. In addition, to achieve the dual-framework structure, reported methods often require the separate synthesis of the second component sol, further increasing process complexity and cost. In summary, existing technologies have significant shortcomings in terms of process simplicity, structural construction pathways, and industrial applicability. Summary of the Invention

[0008] The purpose of this invention is to propose an ablation-modified phenolic aerogel and its preparation method, which realizes a one-step sol-gel of phenolic resin and nano-minerals, effectively optimizes the preparation process, and can be applied to integrated heat-insulating materials in the field of lightweight thermal protection.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing ablation-modified phenolic aerogel includes the following steps:

[0011] (1) The nano-minerals, silicon esters and acids are evenly dispersed in a mixture of water and ethanol to obtain nano-mineral sol;

[0012] (2) Mix and dissolve phenol and aldehyde to obtain phenolic sol;

[0013] (3) Mix the nano-mineral sol and phenolic sol evenly, then add ammonia water and stir evenly to obtain the sol reaction solution;

[0014] (4) Put the sol reaction solution into a sealed container, and then put it into an oven for gradient temperature curing;

[0015] (5) After curing, the container is cooled, the wet gel is taken out, soaked in a mixture of water and ethanol, and then dried at room temperature and pressure until the mass does not change, finally obtaining ablation-modified phenolic aerogel.

[0016] Furthermore, the nano-minerals are selected from one or more of attapulgite, halloysite, and sepiolite.

[0017] Furthermore, the silyl ester is selected from one or more of methyltrimethoxysilane, methyltriethoxysilane, and methyl orthosilicate.

[0018] Furthermore, the mass ratio of the nano-minerals to the silicon ester is 1:0.8 to 1:1.

[0019] Furthermore, the acid is selected from one or more of hydrochloric acid, glacial acetic acid, and sulfuric acid, and the amount of acid added is selected according to the amount of nano-minerals and silicon esters added to ensure a complete reaction.

[0020] Furthermore, the phenol is selected from one or more of phenol, resorcinol, and naphthol.

[0021] Furthermore, the aldehyde is selected from one or more of formaldehyde, acetaldehyde, and furfural.

[0022] Furthermore, the molar ratio of the phenol and aldehyde is in the range of 1:2 to 2:1.

[0023] Furthermore, the mass of the phenolic sol is 10% to 40% of the mass of the nano-mineral sol.

[0024] Furthermore, the mass of the water and ethanol mixture in steps (1) and (5) can be selected as needed, and the volume ratio of water to ethanol is 1:1 to 4:1, which can be adjusted as needed.

[0025] Furthermore, the mass of the ammonia solution is 1% to 5% of the mass of the reaction sol.

[0026] Furthermore, the curing temperature range of the oven is 50–120°C.

[0027] Furthermore, the gradient temperature curing includes four stages: curing at room temperature for 12 hours, curing at 50°C for 24 hours, curing at temperature T1 for 24 hours, and curing at temperature T3 for 24 hours, wherein the 50°C curing stage... <T1<T2≤120℃。

[0028] An ablation-modified phenolic aerogel was prepared by the above method.

[0029] The principle of this invention is:

[0030] During the gradient temperature curing process, the natural nano-minerals in the sol-gel reaction solution undergo a sol-gel reaction simultaneously with the phenolic components under the synergistic effect of silicone ester as a binder, forming a dual three-dimensional network structure in situ with nano-minerals as the overlapping framework and phenolic resin as the coating framework. Even after phenolic resin ablation or carbonization, this structure can still maintain the overall continuity and structural integrity of the aerogel thanks to the nano-mineral framework, thus ensuring that the material retains good thermal insulation and mechanical support capabilities even in extreme environments.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] 1. This invention realizes a one-step synergistic sol-gel reaction between natural nano-minerals and phenolic resins, constructing an in-situ cross-linked dual-framework structure, which improves network synergy and overall material performance.

[0033] 2. The present invention uses naturally sourced nano-mineral materials (such as sepiolite, halloysite, etc.). These materials are commercially mature, do not require separate synthesis, are green and environmentally friendly, and have a cost far lower than the graphene, nanocrystals or functional materials used in the comparative patents, thus having good accessibility and sustainability.

[0034] 3. By rationally controlling the gradient heating conditions, this invention can achieve drying under normal pressure conditions, without relying on high-cost processes such as freeze drying, and has significant advantages in engineering and large-scale preparation; at the same time, the process window is large and the reaction conditions are mild, which facilitates production control.

[0035] 4. Because the present invention forms a stable dual-framework structure, the nano-mineral network still supports the aerogel framework after the phenolic components are ablated, which can significantly improve the problem of structural disintegration of existing phenolic aerogels under high temperature environment and improve the service life and thermal stability of the material.

[0036] 5. The aerogel obtained by this invention has good mechanical strength, low thermal conductivity and structural stability, and exhibits higher comprehensive performance, especially in the field of thermal protection and insulation. Attached Figure Description

[0037] Figure 1 This is a scanning electron microscope image of the attapulgite nanominerals used in Example 1;

[0038] Figure 2 This is a scanning electron microscope image of the ablated fibrous phenolic aerogel in Example 1;

[0039] Figure 3 This is a scanning electron microscope image of the halloysite nanominerals used in Example 2;

[0040] Figure 4 This is a scanning electron microscope image of the ablated phenolic aerogel in Example 2. Detailed Implementation

[0041] To make the various technical features, advantages, or effects of the present invention more apparent and understandable, the following detailed description is provided through embodiments and in conjunction with the accompanying drawings.

[0042] Example 1

[0043] A method for preparing ablation-modified phenolic aerogel includes the following steps:

[0044] (1) Disperse 10g of attapulgite nano-minerals, 10g of methyltrimethoxysilane and 1mL of concentrated hydrochloric acid evenly in a mixture of 100mL of water and ethanol (volume ratio 4:1) to obtain nano-mineral sol.

[0045] (2) Weigh 11g of resorcinol and 19g of furfural and stir to dissolve to obtain phenolic sol.

[0046] (3) Mix the sols in (1) and (2) evenly, then add 5g of ammonia water and stir evenly to obtain the sol reaction solution.

[0047] (4) The reaction solution obtained in (3) is placed in a sealed container and left at room temperature for 12 hours. Then, the container is placed in an oven and heated at 50°C for 1 day, 90°C for 1 day, and 120°C for 1 day for curing.

[0048] (5) After the container in (4) has cooled down, take out the wet gel and soak it in a mixture of 3 times the volume of water and ethanol (volume ratio 1:1) for 24 hours. Then, dry it at room temperature and pressure until the mass does not change, and finally obtain the ablation-modified phenolic aerogel.

[0049] The final ablation-modified phenolic aerogel had a density of 0.45 g / cm³. 3 The drying shrinkage rate is 9%, and the specific surface area is 138 m². 2 / g.

[0050] Figure 1 The image shows a scanning electron microscope (SEM) image of the attapulgite nanominerals used. The diameter of the attapulgite rod crystals is approximately 50 nm, and the length is approximately 600 nm.

[0051] Figure 2 This is a scanning electron microscope (SEM) image of an ablated fibrous phenolic aerogel. It can be seen that the aerogel has a rich nanoporous structure, with phenolic resin and nanoparticles uniformly distributed, and no "island" or other phase-separated structures observed.

[0052] Example 2

[0053] A method for preparing ablation-modified phenolic aerogel includes the following steps:

[0054] (1) Disperse 20g halloysite nanominerals, 20g methyltriethoxysilane and 1mL concentrated sulfuric acid evenly in a mixture of 100mL water and ethanol (volume ratio 4:1) to obtain nanomineral sol.

[0055] (2) Weigh 11g of resorcinol and 8g of formaldehyde (formalin solution), stir and dissolve to obtain phenolic sol.

[0056] (3) Mix the sols in (1) and (2) evenly, then add 7g of ammonia water and stir evenly to obtain the sol reaction solution.

[0057] (4) The reaction solution obtained in (3) is placed in a sealed container and left at room temperature for 12 hours. Then, the container is placed in an oven and heated at 50°C for 1 day, 70°C for 1 day, and 90°C for 1 day to cure.

[0058] (5) After the container in (4) has cooled down, take out the wet gel and soak it in a mixture of 3 times the volume of water and ethanol (volume ratio 1:1) for 24 hours. Then, dry it at room temperature and pressure until the mass does not change, and finally obtain the ablation-modified phenolic aerogel.

[0059] The final ablation-modified phenolic aerogel had a density of 0.52 g / cm³. 3 The drying shrinkage rate is 13%, and the specific surface area is 102 m². 2 / g.

[0060] Figure 3 The image shows a scanning electron microscope (SEM) image of the halloysite nanominerals used. The halloysite rods are approximately 50 nm in diameter and 400 nm in length.

[0061] Figure 4 This is a scanning electron microscope (SEM) image of an ablated fibrous phenolic aerogel. It can be seen that the aerogel has a rich nanoporous structure, with phenolic resin and nanoparticles uniformly distributed, and no "island" or other phase-separated structures observed.

[0062] Example 3

[0063] A method for preparing ablation-modified phenolic aerogel includes the following steps:

[0064] (1) Disperse 25g sepiolite nanominerals, 20g methyl orthosilicate and 1mL glacial acetic acid evenly in a mixture of 100mL water and ethanol (volume ratio 4:1) to obtain nanomineral sol.

[0065] (2) Weigh 18g of phenol and 8g of formaldehyde (formalin solution), stir and dissolve to obtain phenolic sol.

[0066] (3) Mix the sols in (1) and (2) evenly, then add 8g of ammonia solution and stir evenly to obtain the sol reaction solution.

[0067] (4) The reaction solution obtained in (3) is placed in a sealed container and left at room temperature for 12 hours. Then, the container is placed in an oven and heated at 50°C for 1 day, 90°C for 1 day, and 120°C for 1 day for curing.

[0068] (5) After the container in (4) has cooled down, take out the wet gel and soak it in a mixture of 3 times the volume of water and ethanol (volume ratio 1:1) for 24 hours. Then, dry it at room temperature and pressure until the mass does not change, and finally obtain the ablation-modified phenolic aerogel.

[0069] The final ablation-modified phenolic aerogel had a density of 0.61 g / cm³. 3 The drying shrinkage rate is 13%, and the specific surface area is 118 m². 2 / g.

[0070] Although the present invention has been disclosed above with reference to embodiments, it is not intended to limit the present invention. Appropriate modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention should be covered within the protection scope of the present invention, which is defined by the claims.

Claims

1. A method for preparing ablation-modified phenolic aerogel, characterized in that, Includes the following steps: (1) The nano-minerals, silicon esters and acids are evenly dispersed in a mixture of water and ethanol to obtain nano-mineral sol; (2) Mix and dissolve phenol and aldehyde to obtain phenolic sol; (3) Mix the nano-mineral sol and phenolic sol evenly, then add ammonia water and stir evenly to obtain the sol reaction solution; (4) Put the sol reaction solution into a sealed container, and then put it into an oven for gradient temperature curing; (5) After curing, the container is cooled, the wet gel is taken out, soaked in a mixture of water and ethanol, and then dried at room temperature and pressure until the mass does not change, finally obtaining ablation-modified phenolic aerogel.

2. The method as described in claim 1, characterized in that, The nano-minerals are selected from one or more of attapulgite, halloysite, and sepiolite; the silicide is selected from one or more of methyltrimethoxysilane, methyltriethoxysilane, and methyl orthosilicate; and the acid is selected from one or more of hydrochloric acid, glacial acetic acid, and sulfuric acid.

3. The method as described in claim 1 or 2, characterized in that, The mass ratio of the nano-minerals to the silicone ester is 1:0.8 to 1:

1.

4. The method as described in claim 1, characterized in that, The phenol is selected from one or more of phenol, resorcinol, and naphthol; the aldehyde is selected from one or more of formaldehyde, acetaldehyde, and furfural.

5. The method as described in claim 1 or 4, characterized in that, The molar ratio of phenol to aldehyde is in the range of 1:2 to 2:

1.

6. The method as described in claim 1, characterized in that, The mass of the phenolic sol is 10% to 40% of the mass of the nano-mineral sol.

7. The method as described in claim 1, characterized in that, The mass of the ammonia solution is 1% to 5% of the mass of the reaction sol.

8. The method as described in claim 1, characterized in that, The curing temperature range of the oven is 50–120°C.

9. The method as described in claim 8, characterized in that, The gradient temperature curing process comprises four stages: curing at room temperature for 12 hours, curing at 50°C for 24 hours, curing at temperature T1 for 24 hours, and curing at temperature T3 for 24 hours, with the 50°C stage being the most advanced stage. <T1<T2≤120℃。 10. An ablation-modified phenolic aerogel, characterized in that, Prepared by the method described in any one of claims 1-9.

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