A dual phase transition temperature gradient aerogel thermal insulation material and a preparation method and application thereof

Abstract

This invention belongs to the technical field of aerogel insulation materials, specifically relating to a dual-phase change temperature gradient aerogel insulation material, its preparation method, and its application. The material comprises a silica aerogel matrix and a dual-phase change gradient composite fiber mat loaded within it. The dual-phase change gradient composite fiber mat consists of a fiber mat and a dual-phase change core-shell material loaded within the fiber mat. The dual-phase change material includes Na2SO4@SiO2 and NaNO3@SiO2 phase change core-shell materials. The material exhibits a three-dimensional cross-linked morphology, forming a core-shell structure with fibers as the framework and silica aerogel as the matrix. The phase change material is uniformly distributed inside and on the surface of the material. It can achieve passive insulation through the aerogel structure and active insulation through the phase change heat absorption of the phase change material. It has the advantages of being lightweight, high-strength, having high insulation performance, high thermal cycling count, and high temperature resistance.

Description

Technical Field

[0001] This invention belongs to the technical field of aerogel thermal insulation materials, specifically relating to a two-phase change temperature gradient aerogel thermal insulation material, its preparation method, and its application. Background Technology

[0002] With the increasing demands for thermal protection systems in aerospace, energy, and chemical industries, there is an urgent need to develop new materials that can withstand extreme high temperatures, adapt to complex temperature variations, and possess lightweight, high strength, and long-term stable thermal insulation properties. Traditional thermal insulation materials suffer from problems such as high density, easy aging, and significant degradation of thermal insulation performance at high temperatures, making it difficult to meet the increasingly stringent operating conditions.

[0003] Aerogel materials are considered ideal candidates for high-temperature insulation due to their ultra-low density, high porosity, and extremely low thermal conductivity. Among them, inorganic oxide (such as silica) aerogel systems have been widely used due to their good chemical stability, high temperature resistance, and mature processing technology. However, traditional aerogels still have significant shortcomings in complex thermal environments: their thermal regulation capabilities are limited, their phase transition enthalpy is low, making it difficult to cope with drastic temperature fluctuations, resulting in low thermal management efficiency; at the same time, their mechanical properties are usually weak, and they are prone to structural failure under strong thermal shock.

[0004] To improve the thermal management capabilities of aerogels, researchers have attempted to combine phase change materials (PCMs) with aerogels, utilizing the latent heat absorption of the phase change process to achieve active temperature regulation. However, current aerogel / PCM composite materials still have significant shortcomings: existing systems are mostly designed based on a single phase change temperature, making it difficult to cover the thermal protection requirements of a wide temperature range and multiple temperature gradients; PCMs are prone to leakage at high temperatures, have poor compatibility with the matrix, and are prone to phase separation or aggregation, affecting structural stability and service life; most studies focus on medium- and low-temperature PCMs (such as paraffin and fatty acids), limiting their application potential in extreme environments. Summary of the Invention

[0005] The purpose of this invention is to provide a two-phase change temperature gradient aerogel thermal insulation material, its preparation method and application, thereby overcoming the shortcomings of the prior art, realizing gradient temperature control in the range of 300 ℃ to 900 ℃, improving the thermal insulation performance, thermal shock resistance and mechanical properties of the material, and expanding its application range in extreme high temperature environments.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, embodiments of the present invention provide a dual-phase change temperature gradient aerogel insulation material, comprising a silica aerogel matrix and a dual-phase change gradient composite fiber felt loaded therein; the dual-phase change gradient composite fiber felt is composed of a fiber felt and a dual-phase change core-shell material loaded inside the fiber felt; the dual-phase change material includes Na2SO4@SiO2 phase change core-shell material and NaNO3@SiO2 phase change core-shell material.

[0007] The silica aerogel in this thermal insulation material provides excellent overall thermal insulation performance, while the gradient-distributed fiber felt effectively enhances the material's mechanical strength and toughness. The two core-shell phase change materials, Na2SO4@SiO2 and NaNO3@SiO2, can efficiently absorb and regulate heat through a reversible phase change process over a wide temperature range, thereby significantly improving the material's thermal insulation stability, thermal protection efficiency, and structural reliability under high-temperature extreme environments.

[0008] Secondly, embodiments of the present invention provide a method for preparing a two-phase change temperature gradient aerogel insulation material, comprising the following steps: (1) Add Na2SO4 or NaNO3 phase change core material to the solvent and stir to mix. Then add organosilicon source and stir to react. After washing and drying, the dual-phase change core-shell material is obtained. (2) The two-phase change core-shell material is dispersed in a solvent and then added to the fiber felt. After vacuum filtration, drying and pressing, the two-phase change gradient composite fiber felt is obtained. (3) The two-phase change temperature gradient aerogel insulation material is obtained by vacuum impregnation, sol-gel, static aging, solvent replacement and supercritical drying of the two-phase change temperature gradient composite fiber felt and silica sol in sequence.

[0009] This preparation method first uses a controllable sol-gel encapsulation process to prepare Na2SO4@SiO2 and NaNO3@SiO2 phase change materials with stable core-shell structures, ensuring the encapsulation reliability and cycle stability of the phase change core material at high temperatures. Subsequently, the two phase change materials are loaded into fiber felt using vacuum filtration technology to form a gradient composite preform, achieving uniform loading and spatial distribution control of the functional phases. Finally, the fiber preform is encapsulated in a nanoporous silica aerogel matrix through sol impregnation and supercritical drying processes, achieving a firm and uniform composite of the reinforcing phase and the thermal insulation matrix in three-dimensional space.

[0010] Thirdly, embodiments of the present invention provide the application of dual-phase change temperature gradient aerogel insulation materials in aerospace and industrial manufacturing.

[0011] The Na2SO4@SiO2 and NaNO3@SiO2 dual-phase change silica aerogel composite fiber felt material provided by this invention overcomes the defects of traditional aerogel insulation materials, such as insufficient thermal regulation capability, phase change leakage, poor adaptability to multiple temperature zones, and structural collapse in high-temperature environments. It achieves gradient temperature regulation of the material from 300℃ to 900℃, improves the material's thermal insulation performance, thermal shock resistance, and mechanical properties, and expands its application range in extreme high-temperature environments.

[0012] The beneficial effects of this invention are: (1) This invention achieves “micron-fiber reinforced” by constructing a Na2SO4@SiO2 and NaNO3@SiO2 dual-phase transformation core-shell structure in situ in the fiber felt skeleton and using a silica aerogel matrix for three-dimensional encapsulation. Nanoporous thermal insulation The multi-level synergy of "high-temperature phase change temperature control" is achieved. The SiO2 rigid shell not only physically locks the molten salt core material and completely solves the problem of high-temperature liquid phase leakage, but also inhibits the agglomeration of nanoparticles by improving interfacial compatibility. This allows the material to maintain ultra-low density while increasing the compressive strength under 60% strain to over 0.50 MPa, fundamentally overcoming the structural defects of traditional aerogels such as "brittleness, dispersion, and leakage".

[0013] (2) The present invention adopts a "step-by-step coating" Gradient load The "supercritical solidification" preparation route offers a wide process window and good reproducibility. This is achieved by adjusting the sol... The gel kinetic parameters enable precise control of the core-shell wall thickness and aerogel pore size; the entire process uses water / ethanol as the medium, eliminating the need for high-temperature calcination or toxic crosslinking agents, and simultaneously completing material shaping and impurity removal during the supercritical drying stage. It also boasts advantages such as low energy consumption and zero emissions, and has significant potential for industrial scale-up.

[0014] (3) The material prepared by the present invention exhibits excellent wide-temperature-range thermal insulation and thermal stability. Under extreme conditions of burning at 1300 ℃ for 300 s, the cold surface temperature can still be controlled below 200 ℃, which is more than 300 ℃ lower than the temperature difference of traditional aerogel materials. At the same time, it still maintains structural integrity and phase change components do not decompose after heat treatment at 1000 ℃, which can meet the urgent needs of aerospace and high-end industrial manufacturing for long-term and reliable high-temperature thermal protection. Attached Figure Description

[0015] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0016] Figure 1 These are actual images of the Na2SO4@SiO2 and NaNO3@SiO2 dual-phase change silica aerogel composite mullite fiber felt material prepared in Example 1 of this invention; Figure 2These are scanning electron microscope (SEM) images of the Na2SO4@SiO2 and NaNO3@SiO2 biphase change silica aerogel composite mullite fiber felt material prepared in Example 1 of this invention. In the images, a is a SEM image of the biphase change silica aerogel composite mullite fiber felt material with a scale bar of 5 μm, b is a magnified view of a, c is a magnified view of b, d is a SEM image of the biphase change silica aerogel composite mullite fiber felt material with a scale bar of 10 μm, e is a magnified view of d, f is a magnified view of e, g is a SEM image of the biphase change silica aerogel composite mullite fiber felt material with a scale bar of 20 μm, h is a magnified view of g, and i is a magnified view of h. Figure 3 These are the N2 adsorption-desorption curves of the Na2SO4@SiO2 and NaNO3@SiO2 two-phase change silica aerogel composite mullite fiber felt materials prepared in Examples 1, 3 and Comparative Examples 1-3 of this invention. Figure 4 These are curves showing the temperature change of the cold surface over time obtained by the NaNO3@SiO2 surface thermocouple monitoring in Embodiment 3 and Comparative Examples 1-3 of the present invention. Figure 5 This is a schematic diagram of the physical preparation process of Embodiment 1 of the present invention; Figure 6 This is a drawing of the customized stainless steel pressing mold used in Embodiment 1 of the present invention; Figure 7 This is a diagram of the high-temperature thermal insulation performance testing platform constructed in Embodiment 1 of the present invention; Among them, SAP 10 The sample prepared in Example 1, SAP 15 The sample prepared in Example 3, SAP 20 SAP5 is the sample prepared in Comparative Example 1, SAP2 is the sample prepared in Comparative Example 2, and SAP3 is the sample prepared in Comparative Example 3. Detailed Implementation

[0017] Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the invention. Specific conditions not specified in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Components whose manufacturers are not specified are all commercially available conventional products.

[0018] Existing aerogel composite materials mostly focus on single phase change temperature or homogeneous structure design, lacking strategies for multi-temperature coupling control, and cannot achieve stepwise heat absorption and buffering; phase change materials are prone to leakage at high temperatures, and have poor compatibility with aerogel matrices, easily leading to phase separation or agglomeration.

[0019] This invention uses fiber felt as a three-dimensional support skeleton to improve overall mechanical properties, generates nanoporous silica aerogel in situ in its pores to achieve efficient thermal insulation, and innovatively introduces Na2SO4@SiO2 and NaNO3@SiO2 core-shell materials with different phase transition temperatures (approximately 300℃ and above 880℃). By utilizing their stepwise phase transition process, heat is actively absorbed and regulated in multiple key temperature zones, thereby significantly improving its thermal insulation capacity, structural stability and service reliability under extreme high-temperature environments while maintaining the material's lightweight characteristics.

[0020] The specific solution adopted in this invention is as follows: In a first aspect, embodiments of the present invention provide a dual-phase change temperature gradient aerogel insulation material, comprising a silica aerogel matrix and a dual-phase change gradient composite fiber felt loaded inside it; the dual-phase change gradient composite fiber felt is composed of a fiber felt and a dual-phase change core-shell material loaded inside the fiber felt. Dual-phase change materials include Na2SO4@SiO2 phase change core-shell materials and NaNO3@SiO2 phase change core-shell materials.

[0021] This invention employs a process where Na2SO4@SiO2 (hot side) and NaNO3@SiO2 (cold side) are respectively composited with fiber mats and pressed into a bilayer gradient framework. Then, silica aerogel is grown in situ within the gaps of the fiber framework using a sol-gel method. Regarding material selection, this application is not limited to specific materials such as Na2SO4, NaNO3, mullite fiber, or SiO2 aerogel. Instead, it proposes a general bilayer gradient material design concept: "high-melting-point core-shell phase change core material on the hot side + low-melting-point core-shell phase change core material on the cold side + fiber framework pressing and shaping + in-situ filling of the aerogel continuous phase." This is achieved through a process sequence of loading, pressing, and in-situ growth, along with a comprehensive preparation method designed to address interfacial stress, sol penetration, and structural compatibility. This design concept features material interchangeability (the core material can be replaced with carbonates, metal alloys, etc., the fiber can be replaced with alumina, silicon carbide, etc., and the aerogel can be replaced with alumina, zirconium oxide, etc.), providing a universal solution for the development of extreme thermal insulation materials for different temperature ranges.

[0022] In some other embodiments, the particle size of the Na2SO4@SiO2 phase change core-shell material is 1-3 μm, and the phase change temperature is 880-900 ℃; The NaNO3@SiO2 phase change core-shell material has a particle size of 1-3 μm and a phase change temperature of 300-310 ℃.

[0023] Na2SO4@SiO2 materials undergo a phase transition in the high-temperature range of 880-900℃, while NaNO3@SiO2 materials undergo a phase transition in the mid-temperature range of 300-310℃. This stepped phase transition design enables the materials to efficiently absorb and regulate heat in multiple key temperature zones. At the same time, both materials have a fine particle size of 1-3 μm, which is conducive to their uniform dispersion and full contact in the matrix, thereby ensuring the sensitivity of the phase transition response and the uniformity of thermal management, significantly enhancing the comprehensive thermal insulation and thermal protection performance of the materials in an ultra-wide temperature range from 300℃ to nearly 900℃.

[0024] In other embodiments, the fiber diameter of the fiber mat is 5-15 μm, and the loading of Na2SO4@SiO2 phase change core-shell material and NaNO3@SiO2 phase change core-shell material in the fiber mat is 250-1000 g / m. 3 The fiber felt has a three-dimensional skeleton constructed of fibers, which ensures the basic strength and toughness of the structure, while providing a uniform load space for functional materials; the load of the two core-shell phase change materials ensures the efficient performance of the phase change function in a wide temperature range without significantly increasing the weight of the material.

[0025] The silica aerogel matrix has a nanoporous structure with a pore size of 5-25 nm and a specific surface area of ​​35.35-163.55 m². 2 / g. The silica aerogel matrix has fine nanopores and a high specific surface area, which not only endows the material with excellent static thermal insulation properties, but also provides it with rich interfaces, thereby enhancing the bonding force between the material and the fiber skeleton and phase change material, and synergistically improving the overall structural integrity and thermal stability of the material at high temperatures.

[0026] In some other embodiments, the dual-phase change temperature gradient aerogel insulation material maintains structural stability after heat treatment at 1000 °C, and has a compressive strength of 0.50-0.83 MPa at 60% strain.

[0027] Secondly, embodiments of the present invention provide a method for preparing a two-phase change temperature gradient aerogel insulation material, comprising the following steps: (1) Add Na2SO4 or NaNO3 phase change core material to the solvent and stir to mix. Then add organosilicon source and stir to react. After washing and drying, the dual-phase change core-shell material is obtained. (2) The two-phase change core-shell material is dispersed in a solvent and then added to the fiber felt. After vacuum filtration, drying and pressing, the two-phase change gradient composite fiber felt is obtained. (3) The two-phase change temperature gradient aerogel insulation material is obtained by vacuum impregnation, sol-gel, static aging, solvent replacement and supercritical drying of the two-phase change temperature gradient composite fiber felt and silica sol in sequence.

[0028] The preparation method of this invention is simple and highly operable. It adopts a process that combines vacuum impregnation, pressing, sol-gel and supercritical drying, which is easy to scale up for production. Moreover, the raw materials used in the preparation process are readily available and environmentally friendly, with no harmful gases generated, which meets the requirements of green production.

[0029] In some other embodiments, in step (1), the solvent includes one or both of ethanol and water; the pH of the solvent is 12-13, and 8-20 mL of solvent is added per gram of phase change core material; the organosilicon source includes tetraethyl orthosilicate, and 2-7 g of phase change core material is added per milliliter of organosilicon source.

[0030] By controlling the composition of the solvent, pH value, and raw material ratio, a balance between process efficiency and product structural stability was achieved. Using ethanol and water as solvents and controlling the pH at an alkaline environment of 12-13 promoted the hydrolysis and polycondensation of tetraethyl orthosilicate (TEOS) while ensuring good dispersibility and controllability of the reaction system. Precise control of the feeding ratio of the phase change core material to the solvent (8-20 mL / g) and the organosilicon source (2-7 g / mL) effectively regulated the coating thickness and density of the silica shell. This prevented core material leakage while ensuring the integrity and uniformity of the shell, thereby improving the encapsulation reliability, thermal cycling stability, and interfacial compatibility with the substrate of the core-shell phase change material.

[0031] For example, the solvent is a mixture of ethanol and water in a mass ratio of (30-60):(5-15), and the pH is adjusted to 13 with an alkaline solution such as ammonia. 8, 10, 15, 17 or 20 mL of solvent are added per gram of phase change core material. Add 2, 5, or 7 g of phase change core material per milliliter of organosilicon source.

[0032] In some other embodiments, in step (1), the stirring reaction time is 10-20 h, the solvent used for washing is ethanol, and the drying is carried out at 75-85 °C for 20-30 h; the dual-phase change core-shell material includes Na2SO4@SiO2 phase change core-shell material and NaNO3@SiO2 phase change core-shell material; in the core-shell material preparation stage, controlling the stirring reaction time can ensure that the silica shell layer is fully and uniformly coated on the surface of the phase change core material; using ethanol washing and gentle drying can thoroughly remove impurities while avoiding core material deformation or shell layer cracking caused by excessive temperature, thus ensuring the integrity of the core-shell structure.

[0033] In step (2), the loading of the two-phase change core-shell material in the two-phase change gradient composite fiber felt is 250-1000 g / m. 3 The thickness of the dual-phase change gradient composite fiber mat is 1-2 cm. This design allows the phase change material to be uniformly dispersed and firmly fixed in the three-dimensional fiber skeleton, achieving a high phase change enthalpy while ensuring that the subsequent aerogel can fully penetrate and composite. For example, the stirring reaction time is 10, 12, 15, 18 or 20 h, and the drying is carried out at 75, 80 or 85 °C for 20, 24 or 30 h; in step (2), the loading of the dual-phase change core-shell material in the dual-phase change gradient composite fiber felt is 250, 500, 700 or 1000 g / m², respectively. 3 The thickness of the dual-phase gradient composite fiber felt is 1, 1.5 or 2 cm.

[0034] In some other embodiments, in step (3), the silica sol is formed by mixing solution A and solution B in a mass ratio of 1:(0.8-1.2), wherein solution A is formed by mixing organosilicon source and ethanol in a volume ratio of (45-46):(54-55); and solution B is formed by mixing anhydrous ethanol, deionized water and ammonia in a volume ratio of (44-45):(55-56):(0.3-0.4).

[0035] By mixing solution A (organosilicon source and ethanol) with solution B (ethanol, water, and ammonia) and strictly controlling the volume ratio of each component, an optimal balance in concentration, hydrolysis rate, and gelation time was achieved in the reaction system. This ensured that the generated sol had suitable viscosity and reactivity, allowing it to fully penetrate the pores of the fiber composite felt during vacuum impregnation. Ultimately, through gelation and aging, a nanoporous silica network with uniform pore size distribution, high specific surface area, and complete structure was formed, thus providing the entire composite material with excellent thermal insulation performance and stable mechanical support.

[0036] For example, the volume fraction of tetraethyl orthosilicate is 45.45%, and the volume fraction of anhydrous ethanol is 54.55%; in solution B, the volume fraction of anhydrous ethanol is 44.30%, the volume fraction of deionized water is 55.37%, and the volume fraction of concentrated ammonia is 0.33%; the mass ratio of solution A to solution B is 1:1, the dropping rate is 2-3 mL / min, the ice-water bath temperature is 0-5 ℃, and the total stirring time is 40 min.

[0037] In some other embodiments, in step (3), the mass ratio of the dual-phase change gradient composite fiber felt to the silica sol is 1:(10-15). The vacuum impregnation time is 1-3 min, the sol-gel time is 4-6 min, the standing aging time is 20-30 h, and the solvent used for solvent replacement is ethanol, which is replaced every 10-12 h. The temperature for supercritical drying is 260-280℃, the pressure is 9.5-10 MPa, and the drying time is 1-3 h.

[0038] For example, the vacuum impregnation time was 2 min, the sol-gel time was 5 min, and the aging time was 24 h. Anhydrous ethanol was replaced every 12 h until the water in the sample was completely replaced; the supercritical drying temperature was 270 °C, the pressure was 9.5 or 10 MPa, and the drying time was 2 h.

[0039] Thirdly, embodiments of the present invention provide applications of dual-phase change temperature gradient aerogel insulation materials in aerospace and industrial manufacturing. The dual-phase change temperature gradient aerogel insulation material prepared by the present invention exhibits excellent thermal insulation performance. After being burned at 1300 ℃ for 300 s, the cold surface temperature can be controlled below 200 ℃, representing a temperature difference of over 300 ℃ compared to traditional aerogel insulation materials. Simultaneously, it possesses good thermal stability; its structure remains intact after heat treatment at 1000 ℃, and the phase change material does not decompose. It can be used for extended periods in extreme high-temperature environments, demonstrating broad application prospects.

[0040] Example 1 This embodiment provides a two-phase change temperature gradient aerogel insulation material and its preparation method. A schematic diagram of the actual preparation process is shown below. Figure 5 As shown, the specific steps include: 40 mL of ethanol (EtOH) was mixed with 10 mL of deionized water and stirred for 10 min. Then, 1 mL of concentrated ammonia was added and stirring was continued for another 10 min. The pH was adjusted to around 13. 5 g of Na2SO4 was added and stirred for 30 min. Then, 1 mL of tetraethyl orthosilicate (TEOS) was added and stirring was continued for 12 h. After stirring was stopped, the mixture was washed with ethanol and filtered 5 times. The mixture was then placed in an oven at 80 °C and vacuum dried for 24 h to obtain a white Na2SO4@SiO2 core-shell phase change material.

[0041] 40 mL of EtOH was mixed with 10 mL of deionized water and stirred for 10 min. Then, 1 mL of concentrated ammonia was added and stirred for another 10 min. The pH was adjusted to around 13. 5 g of NaNO3 was added and stirred for 30 min. Then, 1 mL of TEOS was added and stirred for another 12 h. After stirring was stopped, the mixture was washed with ethanol and filtered 5 times. It was then placed in an oven at 80 °C and vacuum dried for 24 h to obtain a white NaNO3@SiO2 core-shell phase change material.

[0042] 10 g of each of the synthesized NaNO3@SiO2 and Na2SO4@SiO2 phase change core-shell materials were weighed out and dispersed separately in 300 mL of anhydrous ethanol. After rapid stirring with a magnetic stirrer for 15 min, the mixtures were poured into molds containing mullite fiber felt and placed in a vacuum drying oven for 5 min under vacuum, then dried at 80 ℃ for 12 h. After drying, two composite mullite fiber felts impregnated with the same mass of NaNO3@SiO2 and Na2SO4@SiO2 were used in a custom-made stainless steel mold. Figure 6 Pressing is performed, such as... Figure 6 As shown, the mold consists of two perforated stainless steel square plates and eight external hexagonal bolts, with the eight bolts evenly distributed at the four corners and four sides. The thickness of the two laminated composite mullite fiber felts is adjusted using the bolts and nuts, pressing them together to form a single sheet with a thickness of 37% of the original thickness. The resulting product is marked SAP. 10 .

[0043] First, two silica sol precursor solutions were prepared, including solution A and solution B. Specifically, solution A was an ethanol solution of TEOS, with a TEOS volume fraction of 45.45% and anhydrous ethanol volume fraction of 54.55%. Solution A was placed on a magnetic stirrer and stirred at 500 rpm for 20 min. Solution B consisted of anhydrous ethanol, deionized water, and ammonia. First, 44.30% anhydrous ethanol and 55.37% deionized water were added to a beaker. The mixture was then placed on a stirrer and stirred. 0.33% concentrated ammonia was added, and the beaker was sealed with plastic wrap. The mixture was stirred rapidly for 30 min. While solution A was being vigorously stirred, solution B was slowly added dropwise to solution A through a constant-pressure dropping funnel at a rate of approximately 2-3 mL / min. Simultaneously, the solution A system was placed in an ice-water bath to prevent the system from overheating and accelerating polymerization due to the vigorous reaction of solution B during the dropwise addition. At this point, solution A gradually changes from transparent to translucent and then to turbid. After the addition is complete, seal the solution with inorganic plastic wrap and continue stirring for 30 minutes. The mixed solution gradually becomes clear. After it becomes clear, continue stirring for 10 minutes to ensure that TEOS undergoes a full hydrolysis-condensation reaction under the action of an alkaline catalyst to form a stable silica sol.

[0044] After stirring, the silica sol was quickly poured into the pressed fiber felt mold and placed in a vacuum oven for vacuum impregnation for 2 minutes. After 5 minutes, the sol gel was removed, sealed with inorganic plastic wrap, and allowed to stand for 24 hours. Anhydrous ethanol was poured into the sample, and the ethanol was replaced every 12 hours until all moisture was completely replaced. The completely replaced sample was then placed in an ethanol supercritical drying autoclave for drying. The process parameters were set as follows: temperature 270 °C, pressure 9.5 MPa, and the temperature and pressure were maintained for 2 hours, resulting in a two-phase change temperature gradient aerogel insulation board.

[0045] The resulting physical images are as follows Figure 1 As shown, all samples exhibit regular geometric shapes and complete block structures with smooth surfaces, clear edges, and no obvious cracks or defects. This indicates that the pressing and sol-gel processes in the preparation process successfully constructed a composite material with a uniform structure.

[0046] Example 2 This embodiment provides a two-phase change temperature gradient aerogel thermal insulation material and its preparation method, specifically including the following steps: 30 mL of EtOH was mixed with 5 mL of deionized water and stirred for 10 min. Then, 1 mL of concentrated ammonia was added and stirred for another 10 min. The pH was adjusted to around 13. 2 g of Na2SO4 was added and stirred for 30 min. Then, 1 mL of TEOS was added and stirred for another 12 h. After stirring was stopped, the mixture was washed with ethanol, filtered 5 times, and then placed in an oven at 80 °C for vacuum drying for 24 h to obtain a white Na2SO4@SiO2 core-shell phase change material.

[0047] 30 mL of EtOH was mixed with 5 mL of deionized water and stirred for 10 min. Then, 1 mL of concentrated ammonia was added and stirred for another 10 min. The pH was adjusted to around 13. 2 g of NaNO3 was added and stirred for 30 min. Then, 1 mL of TEOS was added and stirred for another 12 h. After stirring was stopped, the mixture was washed with ethanol and filtered 5 times. It was then placed in an oven at 80 °C and vacuum dried for 24 h to obtain a white NaNO3@SiO2 core-shell phase change material.

[0048] 15 g of each of the synthesized NaNO3@SiO2 and Na2SO4@SiO2 phase change core-shell materials were weighed and dispersed in 300 mL of anhydrous ethanol. After stirring rapidly with a magnetic stirrer for 15 min, the mixtures were poured into molds containing mullite fiber felt and placed in a vacuum drying oven for 5 min under vacuum and dried at 80 ℃ for 12 h. After drying, two composite mullite fiber felts impregnated with the same mass of NaNO3@SiO2 and Na2SO4@SiO2 were pressed together using a custom stainless steel mold. The thickness of the two composite mullite fiber felts was adjusted using screws and nuts, and the two stacked mullite fiber felts were pressed together into one, with a thickness of 37% of the original thickness.

[0049] First, two silica sol precursor solutions, namely solution A and solution B, were prepared. Specifically, solution A was an ethanol solution of TEOS, with a TEOS volume fraction of 45.45% and anhydrous ethanol volume fraction of 54.55%. Solution A was stirred at 500 rpm for 20 min on a magnetic stirrer. Solution B consisted of anhydrous ethanol, deionized water, and ammonia. First, 44.30% anhydrous ethanol and 55.37% deionized water were added to a beaker. The mixture was then stirred, and 0.33% concentrated ammonia was added. The beaker was sealed with plastic wrap and stirred rapidly for 30 min. While solution A was being vigorously stirred, solution B was slowly added dropwise to solution A through a constant-pressure dropping funnel at a rate of approximately 2-3 mL / min. Simultaneously, the system of solution A was placed in an ice-water bath to prevent the system from overheating and accelerating polymerization due to the vigorous reaction during the addition of solution B. At this point, solution A gradually changes from transparent to translucent and then to turbid. After the addition is complete, seal the solution with inorganic plastic wrap and continue stirring for 30 minutes. The mixed solution gradually becomes clear. After it becomes clear, continue stirring for 10 minutes to ensure that TEOS undergoes a full hydrolysis-condensation reaction under the action of an alkaline catalyst to form a stable silica sol.

[0050] After stirring, the mixture was quickly poured into the pressed fiber felt mold and placed in a vacuum oven for vacuum impregnation for 2 minutes. After removal, the mixture underwent sol-gelation for 5 minutes, was sealed with inorganic plastic wrap, and allowed to stand for 24 hours. The sample was then poured into anhydrous ethanol, with the ethanol being replaced every 12 hours until all moisture was completely replaced. The completely replaced sample was then placed in an ethanol supercritical drying autoclave for drying. The process parameters were set as follows: temperature 270 ℃, pressure 9.5 MPa, and the temperature and pressure were maintained for 2 hours, resulting in a two-phase change temperature gradient aerogel insulation board.

[0051] Example 3 This embodiment provides a two-phase change temperature gradient aerogel thermal insulation material and its preparation method, specifically including the following steps: 60 mL of EtOH was mixed with 15 mL of deionized water and stirred for 10 min. Then, 1 mL of concentrated ammonia was added, and stirring was continued for another 10 min. The pH was adjusted to approximately 13, and 7 g of Na₂SO₄ was added. After stirring for 30 min, 1 mL of TEOS was added, and stirring was continued for 12 h. After stopping stirring, the mixture was washed with ethanol, filtered five times, and then vacuum dried in an oven at 80 °C for 24 h to obtain a white Na₂SO₄@SiO₂ core-shell phase change material.

[0052] 60 mL of EtOH was mixed with 15 mL of deionized water and stirred for 10 min. Then, 1 mL of concentrated ammonia was added, and stirring was continued for another 10 min. The pH was adjusted to approximately 13, and 7 g of NaNO3 was added. After stirring for 30 min, 1 mL of TEOS was added, and stirring was continued for 12 h. After stopping stirring, the mixture was washed with ethanol five times, filtered, and then vacuum dried in an oven at 80 °C for 24 h to obtain a white NaNO3@SiO2 core-shell phase change material.

[0053] 15 g of each of the synthesized NaNO3@SiO2 and Na2SO4@SiO2 phase change core-shell materials were weighed and dispersed separately in 300 mL of anhydrous ethanol. After rapid stirring with a magnetic stirrer for 15 min, the mixtures were poured into molds containing fiber felts and placed in a vacuum drying oven for 5 min under vacuum, then dried at 80 ℃ for 12 h. After drying, two composite mullite fiber felts impregnated with the same mass of NaNO3@SiO2 and Na2SO4@SiO2 were pressed together using a custom stainless steel mold. The thickness of the two composite mullite fiber felts was adjusted using screws and nuts, and the two stacked mullite fiber felts were pressed together into one, with a thickness of 37% of the original thickness. The resulting product was labeled SAP. 15 .

[0054] First, two silica sol precursor solutions, namely solution A and solution B, were prepared. Specifically, solution A was an ethanol solution of TEOS, with a TEOS volume fraction of 45.45% and anhydrous ethanol volume fraction of 54.55%. Solution A was placed on a magnetic stirrer and stirred at 500 rpm for 20 min. Solution B consisted of anhydrous ethanol, deionized water, and ammonia. First, 44.30% anhydrous ethanol and 55.37% deionized water were added to a beaker. The mixture was then placed on a magnetic stirrer and stirred. 0.33% concentrated ammonia was added, and the beaker was sealed with inorganic plastic wrap. The mixture was stirred rapidly for 30 min. After vigorous stirring of solution A, solution B was slowly added dropwise to solution A through a constant-pressure dropping funnel at a rate of approximately 2-3 mL / min. Simultaneously, the solution A system was placed in an ice-water bath to prevent the system from overheating and accelerating polymerization due to vigorous reaction during the addition of solution B. At this point, solution A gradually changes from transparent to translucent and then to turbid. After the addition is complete, seal the solution with inorganic plastic wrap and continue stirring for 30 minutes. The mixed solution gradually becomes clear. After it becomes clear, continue stirring for 10 minutes to ensure that TEOS undergoes a full hydrolysis-condensation reaction under the action of an alkaline catalyst to form a stable silica sol.

[0055] After stirring, the mixed solution was quickly poured into the pressed fiber felt mold and placed in a vacuum oven for vacuum impregnation for 2 minutes. After removal, sol-gel treatment was performed within 5 minutes, followed by sealing with inorganic plastic wrap and standing for 24 hours. Anhydrous ethanol was poured into the sample, and the ethanol was replaced every 12 hours until all moisture was completely replaced. The completely replaced sample was then placed in an ethanol supercritical drying autoclave for drying. The process parameters were set as follows: temperature 270℃, pressure 9.5 MPa, and the temperature and pressure were maintained for 2 hours, resulting in a two-phase change temperature gradient aerogel insulation board.

[0056] Comparative Example 1 Unlike Example 3, the amount of the two phase change core-shell materials added (both 20 g) is different; the other preparation steps are the same as in Example 1. The specific preparation process is as follows: Two 20 g samples of the synthesized NaNO3@SiO2 and Na2SO4@SiO2 phase change core-shell materials were separately weighed and dispersed in 300 mL of anhydrous ethanol. After rapid stirring with a magnetic stirrer for 15 min, the mixtures were poured into molds containing fiber felts and placed in a vacuum drying oven for 5 min under vacuum, then dried at 80 ℃ for 12 h. After drying, two composite mullite fiber felts impregnated with the same mass of NaNO3@SiO2 and Na2SO4@SiO2 were pressed together using a custom stainless steel mold. The thickness of the two composite mullite fiber felts was adjusted using screws and nuts, and the two stacked mullite fiber felts were pressed together into one, with a thickness of 37% of the original thickness. The resulting product was labeled SAP. 20 .

[0057] Comparative Example 2 Unlike Example 3, the amount of the two phase change core-shell materials added (5 g each) is different; the other preparation steps are the same as in Example 1. The specific preparation process is as follows: Five g of each of the synthesized NaNO3@SiO2 and Na2SO4@SiO2 phase change core-shell materials were separately weighed and dispersed in 300 mL of anhydrous ethanol. After rapid stirring with a magnetic stirrer for 15 min, the mixtures were poured into molds containing fiber felts and placed in a vacuum drying oven for 5 min under vacuum, then dried at 80 ℃ for 12 h. After drying, two composite mullite fiber felts impregnated with the same mass of NaNO3@SiO2 and Na2SO4@SiO2 were pressed together using a custom stainless steel mold. The thickness of the two composite mullite fiber felts was adjusted using screws and nuts, and the two stacked mullite fiber felts were pressed together into one, with a thickness of 37% of the original thickness. The resulting product was labeled SAP5.

[0058] Comparative Example 3 Unlike Example 3, no two core-shell phase change materials (0 g each) were added; the other preparation steps were the same as in Example 1. The specific preparation process is as follows: Two composite mullite fiber felts were pressed together using a custom stainless steel mold. The thickness of the two pressed mullite fiber felts was adjusted using screws and nuts. The two stacked mullite fiber felts were then pressed together into one, with the thickness of the pressed product being 37% of the original thickness. The resulting product is marked SAP0.

[0059] Comparative Example 4 Unlike Example 3, Na2SO4@SiO2 phase change core-shell material was used to replace NaNO3@SiO2 phase change core-shell material in equal amounts, while other preparation steps were the same as in Example 1.

[0060] Comparative Example 5 Unlike Example 3, Na2SO4@SiO2 phase change core-shell material was replaced with NaNO3@SiO2 phase change core-shell material in equal amounts, while other preparation steps were the same as in Example 1.

[0061] Performance testing 1. Scanning electron microscopy test: The scanning electron microscope test results of the sample prepared in Example 1 are as follows: Figure 2 As shown, in Figure 2 In a, mullite fiber skeleton can be observed, with fiber diameters ranging from 5 to 15 μm, forming the macroscopic support framework of the material; Figure 2 In sections b and c, a continuous and uniform silica aerogel matrix fills the spaces between the fibers, exhibiting a typical nanoporous structure with pore sizes mainly distributed between 20-50 nm. This open porous network provides the structural basis for reducing gas-phase heat conduction. Figure 2 Among d, e, and f, NaNO3@SiO2 phase change core-shell material can be identified as uniformly dispersed in the aerogel matrix. Its particles are regular spherical with a particle size range of 1-3 μm. The silica coating layer of the outer shell is intact and tightly bonded to the matrix, effectively preventing leakage of the phase change core material. Figure 2 g and h in the figure show the 10-30 nm pore structure of the aerogel and silica particles of about 20 nm, which are interconnected to form a strong framework. Figure 2 The image clearly shows the Na2SO4@SiO2 phase change core-shell material. The particles marked with yellow circles exhibit a typical core-shell structure. The spherical particles have smooth surfaces, intact shells, and a diameter of approximately 2 μm, successfully encapsulating the internal sodium sulfate phase change material. In summary, SEM confirms that silica aerogel was successfully coated onto the mullite fiber framework, and both phase change core-shell materials are uniformly dispersed in a three-dimensional porous network.

[0062] 2. N2 adsorption-desorption curve test: Depend on Figure 3 It can be seen that the specific surface area decreases with increasing amounts of phase change core-shell material. From 163.55 m... 2 / g decreased to 35.35 m 2 / g. Figure 3 The figures show the nitrogen adsorption-desorption isotherms and pore size distribution curves. The adsorption-desorption isotherms of the untreated sample exhibit typical Type IV curves with an H3-type hysteresis loop, indicating that the material is predominantly mesoporous with an irregular pore distribution. When the relative pressure (P / P0) approaches 0.5, the adsorption rate increases gradually, indicating a low micropore content in the material. When P / P0 approaches 1, the adsorption rate increases sharply, corresponding to the capillary condensation of nitrogen within the mesopores, reflecting a well-developed mesoporous network in the material.

[0063] 3. Thermal insulation performance test: (1) The thermal insulation performance of Examples 1 and Comparative Examples 1-3 was tested on a self-built high-temperature thermal insulation performance testing platform. The specific device of the self-built high-temperature thermal insulation performance testing platform is as follows: Figure 7 As shown, the apparatus includes a heating device, a sample, and a measuring device connected in sequence. The heating device is a butane spray gun with an outer flame temperature reaching 1300 ℃. During the experiment, the distance between the nozzle and the hot surface of the sample was strictly controlled at 10 cm to ensure stable and uniform burning of the hot surface by the outer flame. A digital thermocouple probe was attached to the cold surface of the sample to monitor the temperature change of the cold surface in real time. During the test, the sample was clamped on an iron stand, the butane spray gun was placed on one side of the hot surface of the sample, aligned with the center of the sample, and the digital thermocouple probe was attached to the center of the cold surface; the thermocouple was turned on, and then the butane spray gun was ignited for the test.

[0064] The specific testing steps are as follows: ① Sample Preparation: The sample uses fiber felt as the supporting framework and silica aerogel as the continuous matrix. Two core-shell phase change materials with different phase transition temperatures are loaded into the silica aerogel matrix: Na₂SO₄@SiO₂ and NaNO₃@SiO₂. The fiber felt consists of two layers: the upper layer loaded with Na₂SO₄@SiO₂ as the hot surface, and the lower layer loaded with NaNO₃@SiO₂ as the cold surface. The two layers are then pressed together with the silica aerogel matrix to form a dual-phase-change-temperature gradient structure. A sample measuring 10 cm × 10 cm × 1.5 cm was selected, heat-treated at 1000 ℃ for 2 h, cooled to room temperature, and then polished smooth for later use.

[0065] ② High-temperature burning test: The hot side of the sample faces the constant temperature heat source of 1300 ℃. Thermocouples are attached to the hot side, cold side and the midpoint of the sample. The sample is burned continuously for 300 s. Temperature data is recorded every 10 s. The highest temperature of the cold side is measured after 300 s. The test is repeated 3 times and the average value is taken.

[0066] ③ Thermal conductivity test: The thermal conductivity of the sample was measured at 25 ℃, 300 ℃, 500 ℃, 800 ℃ and 1000 ℃ using a thermal conductivity meter. The temperature was held at each temperature for 30 min before the test was repeated 3 times and the average value was taken.

[0067] ④ Retest after thermal shock: After the sample is heated at 1300 ℃ for 300 s and then cooled to room temperature, steps ② and ③ are repeated, and the initial test data are compared to verify the thermal insulation stability.

[0068] The heating device uses a butane spray gun, whose outer flame temperature can reach 1300 ℃. The curves of the cold surface temperature versus time of the materials prepared in Example 1 and Comparative Examples 1-3 are shown below. Figure 4 As shown. By Figure 4 It can be seen that, due to the absence of phase change material, the cold surface temperature of Comparative Example 3 rapidly increased from room temperature to nearly 200 °C within 300 s, indicating that the basic aerogel skeleton has limited thermal insulation capacity under prolonged high-temperature impact. After introducing phase change material, the temperature rise rate of Comparative Example 2 and Comparative Example 1 slowed down significantly, with the final temperatures stabilizing at approximately 145 °C and 100 °C, respectively, confirming that the phase change endothermic mechanism effectively delayed heat transfer. Example 1 exhibited the best overall thermal insulation performance, with its temperature curve lower than that of Comparative Example 1 after 200 s, and its final temperature further decreased by approximately 20 °C compared to Comparative Example 1. Because no phase change material was added, a high temperature of 1300 °C was applied to the hot surface of Comparative Example 3. After 300 s, the cold surface temperature of Comparative Example 3 decreased by 311.91 °C, and the overall temperature decreased by 193.12 °C.

[0069] The performance test results of the materials prepared in the examples and comparative examples are shown in Table 1.

[0070] Table 1 Performance Test Results

[0071] Table 1 shows the performance comparison results of the dual-phase change temperature gradient aerogels under the condition of high-temperature calcination at 1300 ℃ for 300 s. The overall performance exhibits a clear trend: the cold surface temperature of Examples 1-3 with the dual-phase change design is only 80-122 ℃, far lower than that of Comparative Example 3 (245 ℃) without phase change and Comparative Examples 4 and 5 (133 ℃, 165 ℃) with only single-phase change. This verifies that the gradient phase change endothermic reaction of Na2SO4@SiO2 (880 ℃) and NaNO3@SiO2 (300 ℃) can achieve active temperature control over a wide temperature range, with an effect far superior to the passive insulation of aerogels. Simultaneously, there is an optimal window for the phase change material loading; Example 1 with a 15 g loading exhibits better insulation performance than a low 5 g loading (Comparative Example 2, 193 ℃) and an excessive 20 g loading (Comparative Example 1, 141 ℃). Excessive particles can clog the pores of the aerogel, thus degrading the thermal insulation effect. In terms of mechanical properties, the higher the proportion of phase change core material, the stronger the compressive strength (0.83 MPa in Example 3), and all examples meet the strength requirement of ≥0.50 MPa. Although the thermal conductivity increases slightly with the phase change load, it remains at an ultra-low level of 0.0367-0.0380 W / (m·K), proving that the design achieves the optimal balance between thermal insulation, mechanical and thermal conductivity properties, and is an effective solution for extreme high temperature thermal insulation materials.

[0072] Because the core-shell structure of Na2SO4@SiO2 has a particle size of 1-3 μm, this core-shell structure will be dispersed in the mesoporous structure of the aerogel matrix after the subsequent addition of aerogel; the core-shell structure of NaNO3@SiO2 also has a particle size of 1-3 μm and will be dispersed in the mesoporous structure of the aerogel matrix after the subsequent addition of aerogel. Simply stacking Na2SO4@SiO2 and NaNO3@SiO2 together and adding them to the aerogel will cause the two core-shell structures to clog the pore structure of the aerogel, making it impossible to achieve the thermal insulation performance described in this invention. This invention does not address the simple coexistence of materials, but rather how heat is absorbed stepwise according to temperature zones, enabling SiO2 aerogel insulation boards to exceed the 1300 ℃ high-temperature resistance limit at the same thickness.

[0073] The dual-phase temperature gradient aerogel insulation material prepared in this invention, compared with other insulation materials that use fiber felt and aerogel composites, can be continuously burned at 1300 ℃ for 100 s while the cold surface temperature remains at around 50 ℃. After continuous burning for 300 s, the final cold surface temperature remains at around 80 ℃, which is an insulation capability that the latter cannot achieve.

[0074] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A two-phase change temperature gradient aerogel insulation material, characterized in that, The invention includes a silica aerogel matrix and a two-phase change gradient composite fiber mat loaded therein; the two-phase change gradient composite fiber mat is composed of a fiber mat and a two-phase change core-shell material loaded inside the fiber mat. The dual-phase change materials include Na2SO4@SiO2 phase change core-shell materials and NaNO3@SiO2 phase change core-shell materials.

2. The dual-phase change temperature gradient aerogel insulation material as described in claim 1, characterized in that, The Na2SO4@SiO2 phase change core-shell material has a particle size of 1-3 μm and a phase change temperature of 880-900 ℃. The NaNO3@SiO2 phase change core-shell material has a particle size of 1-3 μm and a phase change temperature of 300-310 ℃.

3. The dual-phase change temperature gradient aerogel insulation material as described in claim 1, characterized in that, The fiber diameter of the fiber felt is 5-15 μm, and the loading of Na2SO4@SiO2 phase change core-shell material and NaNO3@SiO2 phase change core-shell material in the fiber felt is 250-1000 g / m. 3 ; The silica aerogel matrix has a three-dimensional nanoporous structure with a pore size of 5-25 nm and a specific surface area of ​​35.35-163.55 m². 2 / g.

4. The dual-phase change temperature gradient aerogel insulation material as described in claim 1, characterized in that, The dual-phase temperature gradient aerogel insulation material maintains structural stability after heat treatment at 1000 ℃, and its compressive strength at 60% strain is 0.50-0.83 MPa.

5. A method for preparing a two-phase change temperature gradient aerogel insulation material according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Add Na2SO4 or NaNO3 phase change core material to the solvent and stir to mix. Then add organosilicon source and stir to react. After washing and drying, the dual-phase change core-shell material is obtained. (2) The two-phase change core-shell material is dispersed in a solvent and then added to the fiber felt. After vacuum filtration, drying and pressing, the two-phase change gradient composite fiber felt is obtained. (3) The two-phase change temperature gradient aerogel insulation material is obtained by vacuum impregnation, sol-gel, static aging, solvent replacement and supercritical drying of the two-phase change temperature gradient composite fiber felt and silica sol in sequence.

6. The method for preparing the dual-phase change temperature gradient aerogel insulation material as described in claim 5, characterized in that, In step (1), the solvent includes one or both of ethanol and water; the pH of the solvent is 12-13, and 8-20 mL of solvent is added per gram of phase change core material; the organosilicon source includes tetraethyl orthosilicate, and 2-7 g of phase change core material is added per milliliter of organosilicon source.

7. The method for preparing the dual-phase change temperature gradient aerogel insulation material as described in claim 5, characterized in that, In step (1), the stirring reaction time is 10-20 h, the solvent used for washing is ethanol, and the drying is carried out at 75-85℃ for 20-30 h; the dual-phase change core-shell materials include Na2SO4@SiO2 phase change core-shell materials and NaNO3@SiO2 phase change core-shell materials; In step (2), the loading of the two-phase change core-shell material in the two-phase change gradient composite fiber felt is 250-1000 g / m. 3 The thickness of the dual-phase gradient composite fiber felt is 1-2 cm.

8. The method for preparing the two-phase change temperature gradient aerogel insulation material as described in claim 5, characterized in that, In step (3), the silica sol is formed by mixing solution A and solution B in a mass ratio of 1:(0.8-1.2). Solution A is formed by mixing organosilicon source and ethanol in a volume ratio of (45-46):(54-55); solution B is formed by mixing anhydrous ethanol, deionized water and ammonia in a volume ratio of (44-45):(55-56):(0.3-0.4).

9. The method for preparing the two-phase change temperature gradient aerogel insulation material as described in claim 5, characterized in that, In step (3), the mass ratio of the dual-phase change gradient composite fiber felt to silica sol is 1:(10-15). The vacuum impregnation time is 1-3 min, the sol-gel time is 4-6 min, the static aging time is 20-30 h, and the solvent used for solvent replacement is ethanol, which is replaced every 10-12 h. The temperature for supercritical drying is 260-280℃, the pressure is 9.5-10 MPa, and the drying time is 1-3 h.

10. The application of a dual-phase change temperature gradient aerogel insulation material according to any one of claims 1-4 in aerospace and industrial manufacturing.

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