A high-efficiency high-temperature-resistant heat insulation film based on a multi-scale nanofiber composite structure and a preparation method thereof

Abstract

This invention relates to the field of heat insulation film technology, and discloses a high-efficiency high-temperature resistant heat insulation film based on a multi-scale nanofiber composite structure and its preparation method. A precursor, spinning aid, and nanofiller are mixed to prepare a spinning solution. Electrospinning technology is used to spin the spinning solution, allowing different fiber layers to be deposited layer by layer to form a fiber film with a multi-scale stacked structure. The fiber film is then subjected to step-by-step high-temperature sintering to obtain a high-efficiency high-temperature resistant heat insulation film. The multi-scale stacked structure design combined with the step-by-step high-temperature sintering process significantly improves the high-temperature stability and heat insulation performance of the heat insulation film. The resulting product has broad application prospects in aerospace, high-temperature industrial equipment, and building energy conservation.

Description

Technical Field

[0001] This invention relates to the field of heat insulation film technology, specifically to a high-efficiency high-temperature heat insulation film based on a multi-scale nanofiber composite structure and its preparation method. Background Technology

[0002] In recent years, the rapid development of aerospace, electronic devices, and new energy transportation has placed increasingly higher demands on the performance of high-efficiency, high-temperature resistant thermal insulation materials. These materials not only require extremely low thermal conductivity but also need to maintain good structural stability and mechanical properties under extreme high-temperature conditions, while also considering processability and environmental adaptability. Traditional insulation materials such as glass fiber and mineral wool have low thermal conductivity at room temperature, but they generally suffer from insufficient strength, significantly increased radiative thermal conductivity, and poor structural stability in high-temperature environments, making it difficult to meet the long-term use requirements of complex and extreme conditions. Therefore, novel thermal insulation films based on electrospun nanofibers, aerogels, and multi-component ceramics have gradually become a research hotspot.

[0003] Inorganic ceramic nanofiber systems, such as SiO2, Al2O3, mullite, and ZrO2, are often prepared through electrospinning combined with sol-gel and high-temperature calcination processes, exhibiting high porosity, low thermal conductivity, and excellent high-temperature resistance. Meanwhile, high-entropy ceramic fibers, due to their multi-component thermal stability and creep resistance, maintain good thermal insulation capabilities above 1200℃, making them an important research direction in the field of high-temperature insulation. In terms of structural design, multi-scale and multi-layered structures are becoming the trend. Nanofiber networks scatter phonons and photons, micron-sized fibers enhance toughness and load-bearing capacity, and macroscopic layered or oriented structures control heat flow paths. Layered gradient structures are particularly valued, such as introducing matting agents into the hot-end layer, constructing ultra-loose porous layers in the middle layer, and densifying the cold-end layer to enhance mechanical and wear resistance properties, thus balancing thermal insulation, strength, and durability. In terms of preparation processes, electrospinning combined with sol-gel remains the mainstream process, supplemented by freeze-drying and graded solvent replacement to maintain the pore structure. Other studies have proposed growing secondary phases in situ on the electrospun fiber skeleton to form an interpenetrating network structure, thereby improving anti-powdering properties.

[0004] However, existing high-temperature thermal insulation film technologies still have many shortcomings. Above 600℃, radiative heat flow dominates. Current research improves radiative thermal conductivity by adding matting agents such as TiO2 and SiC, but single-addition methods easily lead to increased solid-phase thermal conductivity, making it difficult to achieve the optimal balance between thermal insulation and solid-phase thermal conductivity. Traditional SiO2 or Al2O3 aerogels and fiber membranes are prone to sintering and grain growth at high temperatures, causing pore collapse, thickness shrinkage, and rapid degradation of thermal insulation performance. Moreover, single nanofiber membranes or aerogel materials are generally brittle and have low strength, easily pulverizing and shedding during use, limiting their long-term service and independent use. Some SiO2-based materials have strong hygroscopicity in humid and hot environments, leading to increased thermal conductivity and structural deterioration, while common organic hydrophobic modifications are prone to failure at high temperatures, making it difficult to maintain hydrophobic properties for a long time. Furthermore, thermal insulation performance depends on thickness; thick films easily lose flexibility, and thin films are easily torn, making it difficult to balance flexibility and thermal insulation performance.

[0005] Therefore, there is an urgent need to develop a new type of heat insulation film that combines high-efficiency heat insulation, excellent mechanical properties, high-temperature stability, and good processability to meet the application requirements under extreme working conditions.

[0006] Summary of the Invention (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a high-efficiency high-temperature resistant heat insulation film based on a multi-scale nanofiber composite structure and its preparation method, which solves the problems of high radiative thermal conductivity, poor structural stability, and insufficient mechanical properties of existing heat insulation films at high temperatures.

[0007] (II) Technical Solution To achieve the above objectives, this invention discloses a method for preparing a high-efficiency high-temperature resistant heat-insulating film based on a multi-scale nanofiber composite structure, comprising the following steps: Step 1: Mix the precursor, spinning aid, nanofiller and pure water to prepare at least two spinning solutions with different solid contents; Step 2: Using electrospinning technology, the spinning solution is spun into fibers, and different fiber layers are deposited sequentially to obtain a fiber membrane with a multi-scale stacked structure. Step 3: Perform high-temperature sintering on the fiber membrane from Step 2 to obtain a high-efficiency high-temperature heat insulation film.

[0008] Preferably, the precursor in step one includes any one of aluminum sol, silica sol, and boehmite.

[0009] Preferably, the spinning aid in step one includes any one of polyvinyl alcohol (PVA), polyethylene oxide (PEO), polyethylene glycol (PEG), and polyvinylpyrrolidone (PVP).

[0010] Preferably, the nanofiller in step one includes any one or more of nano-silicon dioxide (SiO2), nano-alumina (Al2O3), nano-zirconium oxide (ZrO2), nano-silicon carbide (SiC), nano-silicon nitride (Si3N4), and nano-titanium dioxide (TiO2).

[0011] Preferably, in step one, based on the total mass of the spinning solution, the precursor has a mass percentage of 5% to 20%, the spinning aid has a mass percentage of 2% to 10%, the nanofiller has a mass percentage of 1% to 10%, and the remainder is pure water.

[0012] Preferably, the process parameters for electrospinning technology in step two are as follows: spinning voltage of 10~30 kV, receiving distance of 10~25 cm, spinning solution propulsion rate of 0.5~5 mL / h, spinning environment temperature of 20~35 ℃, relative humidity of 30%~60%, and needle inner diameter of 0.3~1.2 mm. During the spinning process, the alternating deposition of different fiber layers is achieved by setting at least two independent liquid supply channels, each corresponding to a different spinning solution. Each liquid supply channel is switched by an independently controlled injection pump or by alternating spraying with multiple needles. According to the preset deposition sequence and deposition time of each layer, different types of spinning solutions are sequentially sprayed onto the receiving device to form a multi-scale stacked structure through alternating deposition. The deposition time of each fiber layer is 30~180 min, and the deposition interval between two adjacent layers does not exceed 1 min to achieve in-situ solvent welding between layers.

[0013] Preferably, the stacked structure consists of 3 to 7 fiber sublayers, with each fiber sublayer having a thickness of 5 to 50 μm along the thickness direction. The fiber diameters between adjacent fiber sublayers are distributed in a gradient. The different fiber layers are deposited by switching different spinning solution injection pumps or changing different spinning solution reservoirs. The adjacent fiber layers are bonded together by in-situ solvent welding or hot pressing.

[0014] Preferably, the holding time for the step-by-step high-temperature sintering in step three is 3-6 h, and the sintering time is 6-12 h. The step-by-step high-temperature sintering includes a low-temperature removal of additives stage and a high-temperature crystallization and densification stage. The temperature gradient, heating rate and holding time of the two stages are set separately to achieve complete removal of spinning additives and ceramic transformation of fiber structure.

[0015] Preferably, the stepwise high-temperature sintering adopts a staged sintering process: it is carried out in an atmosphere furnace, with the atmosphere being any one of air, nitrogen, or argon, and the gas flow rate being 1~10 L / min; a programmed temperature control method is used, first heating from room temperature to 300~500 ℃ at a heating rate of 1~10 ℃ / min, and holding at 300~500 ℃ for 1~2 h, this stage is used to remove spinning auxiliaries and organic components; then heating is continued at a heating rate of 2~8 ℃ / min to 600~1000 ℃, and holding at 600~1000 ℃ for 2~4 h, this stage is used for fiber crystallization and densification; finally cooling to room temperature at a cooling rate of 5~15 ℃ / min.

[0016] A high-efficiency, high-temperature resistant thermal insulation film based on a multi-scale nanofiber composite structure is prepared by the aforementioned method. The high-efficiency, high-temperature resistant thermal insulation film based on a multi-scale nanofiber composite structure obtained by the above method has a three-dimensional ceramic fiber network structure. This three-dimensional network is composed of interwoven ceramic fibers derived from a precursor, with inorganic nanofillers uniformly dispersed and anchored within and on the surface of the ceramic fiber network. A strong interfacial bond is formed between the nanofillers and the ceramic fibers through mechanical interlocking or partial solid solution.

[0017] (iii) Beneficial technical effects Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention constructs a multi-scale stacked structure (3-7 layers) formed by alternating deposition of fibers of different diameters using electrospinning technology. This multi-scale structure synergistically suppresses solid-state heat conduction, gas convection heat transfer, and radiative heat transfer, achieving an ultra-low thermal conductivity. Specifically: the coarser fiber layer acts as a mechanical framework, providing compressive strength and structural support; the finer fiber layer forms a high specific surface area network, effectively scattering phonons, increasing the propagation path length of heat within the solid framework, and reducing solid-state heat conduction; the submicron-level pores formed between the fibers prevent air molecules from flowing freely, suppressing gas convection heat transfer; simultaneously, the inorganic nanofillers (such as ZrO2, SiC, etc.) dispersed within and on the surface of the fibers have high infrared reflectivity and absorption characteristics, effectively scattering or absorbing infrared photons, reducing radiative heat conduction at high temperatures. The synergistic effect of the above multi-scale structure results in a low thermal conductivity of the insulation film of this invention, significantly superior to traditional single-scale insulation materials.

[0018] (2) This invention employs an aqueous spinning system combined with graded high-temperature sintering (two temperature platforms) to impart excellent high-temperature stability and structural integrity to the fiber membrane. During electrospinning, pure water is used as the solvent to mix the precursor (such as aluminum sol, silica sol, or zirconium sol), spinning aid (such as polyvinyl alcohol PVA, polyethylene oxide PEO, or polyvinylpyrrolidone PVP), and nanofiller to form a spinning solution. The precursor particles are rich in hydroxyl groups (-OH) on their surface, and the spinning aid molecular chains contain a large number of hydroxyl or carbonyl groups (such as -OH of PVA and C=O of PVP). The two can form a stable colloidal dispersion system through intermolecular hydrogen bonding, allowing the nanofiller to be uniformly suspended in it (no additional modification is required; uniform distribution can be achieved by using electrostatic repulsion and steric hindrance. In this example, ultrasonic-assisted dispersion is used to further ensure uniformity). During electrospinning, water evaporates rapidly, and the spinning aid molecular chains become entangled and form a three-dimensional polymer network, "freezing" the precursor particles and nanofiller inside and on the surface of the fiber, thus achieving uniform mixing of the components at the nanoscale. The process then involves staged high-temperature sintering: the first temperature plateau (300~500 ℃, holding for 1~2 h) allows for the slow removal of spinning aids and residual organic matter through thermal decomposition. Controlling the heating rate (1~10 ℃ / min) allows for gas diffusion channels, preventing pore collapse or cracking caused by violent decomposition. The second temperature plateau (600~1000 ℃, holding for 2~4 h) completely transforms the precursor into a stable ceramic phase (such as γ-Al2O3, α-Al2O3, ZrO2, or composite oxides), while simultaneously forming a strong interfacial bond between the nanofiller and the ceramic matrix (such as mechanical interlocking or partial solid solution). Through staged sintering, the complete removal of organic components is ensured, while also promoting appropriate growth and densification of ceramic grains, ultimately yielding a high-purity, highly crystalline ceramic fiber membrane without significant defects. This fiber membrane maintains structural integrity above 800 ℃, with a thermal weight loss rate of less than 5%, exhibiting excellent high-temperature resistance.

[0019] (3) This invention forms a reinforced laminated structure by alternately depositing fiber layers of different diameters. The coarser fiber layer acts as a load-bearing skeleton, providing tensile strength; the finer fiber layer acts as a filling network, dispersing stress and preventing crack propagation. In-situ solvent welding occurs between adjacent fiber layers due to incomplete evaporation of solvent during spinning, causing fibers in different layers to interpenetrate and entangle, thus avoiding interlayer delamination. Compared with single-scale nanofiber membranes, the multi-scale laminated structure of this invention effectively improves mechanical properties, overcomes the brittleness of traditional ceramic fiber membranes, and maintains high porosity (>80%), achieving a good balance between thermal insulation and mechanical properties.

[0020] (4) The precursors (aluminum sol, silica sol, etc.), spinning aids (PVA, PEO, etc.) and nanofillers (ZrO2, SiC, etc.) selected in this invention are all commercially available raw materials. Pure water is used as a solvent, which is non-toxic and environmentally friendly, reducing production costs and the burden of waste liquid treatment. The electrospinning process parameters (voltage 10~30 kV, receiving distance 10~25 cm, etc.) and the staged sintering procedure (two temperature platforms) have a wide window range, which is easy to achieve stable control in industrial production. The prepared heat insulation film has ultra-low thermal conductivity (0.03~0.08 W / (m·K)), high temperature resistance (>800 ℃) and good mechanical properties. It can be widely used in aerospace thermal protection systems, high-temperature industrial furnace insulation layers, new energy vehicle battery thermal insulation films, building energy-saving insulation materials and other fields, replacing traditional ceramic fiber felt, aerogel composite materials and other products, showing significant advantages in high-temperature heat insulation scenarios. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0022] Figure 1 This is a process flow diagram for the preparation of the high-efficiency high-temperature heat-insulating film in this invention; Figure 2 This is a cross-sectional scanning electron microscope image of the high-efficiency high-temperature resistant heat insulation film prepared in Example 1 of this invention; Figure 3 This is a bar chart comparing the thermal conductivity of the heat insulation films prepared in Examples 1-6 and Comparative Examples 1-4 of this invention; In the figure: 1. Beaker, 2. Stirring rod, 3. Nanofiller, 4. Precursor and pure water, 5. High voltage power supply, 6. Syringe, 7. Spinning solution, 8. Multi-scale laminated fiber membrane, 9. Receiving substrate, 10. Atmosphere furnace. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0024] Example 1 This embodiment provides a high-efficiency high-temperature resistant heat insulation film based on a multi-scale nanofiber composite structure, and its preparation method is as follows: Step 1: Preparation of spinning solution: Using boehmite (Al2O3 purity ≥ 99.9%) as a precursor, polyvinyl alcohol (PVA, Mw = 8 w) as a spinning aid, nano-silica (particle size 30-50 nm) as a nanofiller, and pure water as a solvent, two spinning solutions with different solid contents were prepared. Based on the total mass of the spinning solution, the precursor content is 6%, the spinning aid content is 2.5%, the nanofiller content is 1.5%, and the balance is 90% pure water. After mixing, the solution is stirred in a 60 ℃ water bath for 4 h to obtain a low-concentration homogeneous spinning solution with a solid content of 10%. Based on the total mass of the spinning solution, the precursor content is 14%, the spinning aid content is 6%, the nanofiller content is 5%, and the balance is 75% pure water. After mixing, the solution is stirred in a 60 ℃ water bath for 4 h to obtain a high-concentration homogeneous spinning solution with a solid content of 25%. Step 2: Electrospinning preparation of multi-scale layered fiber membranes: Electrospinning was performed using an electrospinning device. During the spinning process, the spinning voltage was 20 kV, the receiving distance was 15 cm, the spinning solution propulsion rate was 1.5 mL / h, the spinning environment temperature was 25℃, the relative humidity was 45%, and the needle inner diameter was 0.6 mm. During the spinning process, a nanofiber layer (average fiber diameter 200 nm) was first spun with a low-concentration homogeneous spinning solution with a solid content of 10% for 2 h; then, a micron fiber layer (average fiber diameter 2 μm) was directly deposited on the nanofiber layer with a high-concentration homogeneous spinning solution with a solid content of 25% for 1 h. The above alternating deposition process was repeated 3 times to obtain a total of 6 layers (3 nanofiber layers and 3 micron fiber layers arranged alternately) of multi-scale layered fiber membranes with a total thickness of 150 μm. Step 3, step-by-step high-temperature sintering: The multi-scale laminated fiber membrane obtained in Step 2 is placed in an atmosphere furnace for step-by-step high-temperature sintering. First, the temperature is raised to 500 ℃ at a heating rate of 5 ℃ / min and held for 1 h to allow the spinning aids to decompose and volatilize. Then, the temperature is raised to 1000 ℃ at a heating rate of 5 ℃ / min and held for 2 h to allow the precursor to be completely transformed into the ceramic phase. After natural cooling to room temperature, a high-efficiency high-temperature heat insulation membrane is obtained.

[0025] Example 2 Compared with Example 1, the difference in this embodiment is that the nanofiller is replaced with nano alumina (average particle size 50nm), the average fiber diameter of the nanofiber layer is 180 nm, and the average fiber diameter of the microfiber layer is 1.5 μm. Other components, dosages, and process parameters are the same as in Example 1.

[0026] Example 3 Compared with Example 1, the difference in this embodiment is that the nanofiller is replaced with nano-zirconia (average particle size 30nm), the average fiber diameter of the nanofiber layer is 220 nm, and the average fiber diameter of the microfiber layer is 2.5 μm. Other components, dosages, and process parameters are the same as in Example 1.

[0027] Example 4 Compared with Example 1, the difference in this embodiment is that the spinning aid is replaced with polyethylene oxide (PEO, Mw=30w), the average fiber diameter of the nanofiber layer is 150 nm, the average fiber diameter of the microfiber layer is 1 μm, and the other components, dosages, and process parameters are the same as in Example 1.

[0028] Example 5 Compared with Example 1, the difference in this embodiment lies in the multi-scale layered structure in step two, which consists of 5 layers (3 alternating nanofiber layers and 2 microfiber layers). The total number of layers differs. The spinning time for each nanofiber layer (average fiber diameter 200 nm) is 1.5 h, for a total of 3 layers; the spinning time for each microfiber layer (average fiber diameter 2 μm) is 1 h, for a total of 2 layers. The total thickness of the fiber membrane is approximately 120 μm (each layer is approximately 24 μm thick). Testing showed that the porosity of the fiber membrane in this embodiment is 82%, and the tensile strength is 1.8 MPa. Other process parameters are the same as in Example 1.

[0029] Example 6 Compared with Example 1, the difference in this embodiment lies in the step-by-step high-temperature sintering process in step three: first, the temperature is raised to 450 ℃ at a heating rate of 3 ℃ / min and held for 1.5 h; then, the temperature is raised to 900 ℃ at a heating rate of 5 ℃ / min and held for 2.5 h. The average fiber diameter of the nanofiber layer is 200 nm, and the average fiber diameter of the microfiber layer is 2 μm. Other process parameters are the same as in Example 1.

[0030] Example 7 This embodiment provides a high-efficiency high-temperature resistant heat insulation film based on a multi-scale nanofiber composite structure, and its preparation method is as follows: Step 1: Preparation of spinning solution: Using boehmite (Al2O3 purity ≥ 99.9%) as a precursor, polyvinyl alcohol (PVA, Mw = 8 w) as a spinning aid, nano-silica (average particle size 30 nm) as a nanofiller, and pure water as a solvent, two spinning solutions with different solid contents were prepared; the component amounts were the same as in Example 1. Step 2: Electrospinning preparation of multi-scale layered fiber membranes: Electrospinning was performed using an electrospinning device. During the spinning process, the spinning voltage was 20 kV, the receiving distance was 15 cm, the spinning solution propulsion rate was 1.5 mL / h, the spinning environment temperature was 25℃, the relative humidity was 45%, and the needle inner diameter was 0.6 mm. During the spinning process, a nanofiber layer (average fiber diameter 150 nm) was first spun with a low-concentration homogeneous spinning solution with a solid content of 10% for 1 h; then, a micron fiber layer (average fiber diameter 1 μm) was directly deposited and spun on the nanofiber layer with a high-concentration homogeneous spinning solution with a solid content of 25% for 0.5 h. The above alternating deposition process was repeated once to obtain a multi-scale layered fiber membrane with 3 layers (2 nanofiber layers and 1 micron fiber layer alternating), and the total thickness of the fiber membrane was 50 μm. Step 3, step-by-step high-temperature sintering: The fiber membrane obtained in step 2 is placed in an atmosphere furnace for step-by-step high-temperature sintering. First, the temperature is raised to 400 ℃ at a heating rate of 1 ℃ / min and held for 2 h to allow the spinning aids to decompose and volatilize. Then, the temperature is raised to 800 ℃ at a heating rate of 2 ℃ / min and held for 3 h to allow the precursor to be completely transformed into the ceramic phase. After naturally cooling to room temperature, a high-efficiency high-temperature heat insulation membrane is obtained.

[0031] Comparative Example 1 Compared with Example 1, the difference in this comparative example is that no nano-filler nano-silica was added to the spinning solution. In order to maintain the same total solid content (10%) as in Example 1, the mass percentages of the precursor and spinning aid were adjusted to 7.5% for the precursor, 2.5% for the spinning aid, and 90% for pure water. All other process parameters were the same as in Example 1.

[0032] Comparative Example 2 Compared with Example 1, this comparative example differs in that it does not use a multi-scale layered structure, but only spins a single-scale nanofiber layer without depositing a micron fiber layer. The spinning solution used is the same as the one used in step two of Example 1, with a lower concentration (10% solid content). Continuous spinning for 3 hours yields a single nanofiber layer fiber membrane with a total thickness of approximately 150 μm. Other process parameters are the same as in Example 1.

[0033] Comparative Example 3 Compared with Example 1, this comparative example differs in that it does not use stepwise high-temperature sintering, but uses one-step high-temperature sintering. The sintering process is as follows: the temperature is directly raised to 1000 ℃ at a heating rate of 5 ℃ / min and held for 3 h. Other process parameters are the same as in Example 1.

[0034] Comparative Example 4 Compared with Example 1, the difference in this comparative example is that the pure water solvent is replaced with a mixed solvent, which is obtained by mixing anhydrous ethanol and pure water in a volume ratio of 1:1. The other components, dosages, and process parameters are the same as in Example 1.

[0035] Performance testing methods The high-efficiency high-temperature resistant heat insulation films prepared in Examples 1-6 and Comparative Examples 1-4 of this invention were subjected to relevant performance tests. The specific test methods are as follows: (1) Room temperature thermal conductivity: The room temperature thermal conductivity of the insulation film was determined by heat flow meter method. The test was carried out in accordance with GB / T 10295-2008 "Determination of steady-state thermal resistance and related properties of thermal insulation materials by heat flow meter method". The sample size was 300 mm × 300 mm, the thickness was the original thickness, the test environment temperature was 25 ± 2 ℃, the relative humidity was 50% ± 5%, the cold plate temperature was 15 ℃, the hot plate temperature was 35 ℃, the temperature difference was 20 ℃, and the applied pressure was 2.5 kPa. (2) High-temperature stability (mass retention rate): The high-temperature stability of the insulation film was determined using a thermogravimetric analyzer. The insulation film sample was placed in the thermogravimetric analyzer and heated from room temperature to 800 ℃ at a heating rate of 10 ℃ / min in an air atmosphere. The sample was then held at 800 ℃ for 2 h, and the mass change was recorded. The mass retention rate was calculated using the following formula: Mass retention rate (%) = (mass of sample after heat treatment at 800 ℃ for 2 h / initial sample mass) × 100%; (3) Tensile strength test: The tensile strength of the heat insulation film was determined in accordance with GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets". The heat insulation film was cut into dumbbell-shaped specimens with a total length ≥75 mm, a gauge length of 25 mm, and a width of 4 mm. The test was conducted using an electronic universal testing machine with a tensile speed of 5 mm / min, an ambient temperature of 25±2 ℃, and a relative humidity of 50%±5%. (4) Porosity of fiber membrane: The porosity of the heat insulation membrane is determined by the density method and calculated by the following formula: Porosity (%) = (1-ρ_film / ρ_material)*100%, where ρ_film is the apparent density of the fiber membrane (calculated from the mass and geometric volume of the fiber membrane), and ρ_material is the true density of the fiber membrane material (determined by the helium specific gravity bottle method). (5) Specific surface area: The specific surface area of ​​the heat insulation film was determined by nitrogen adsorption BET method. The heat insulation film sample was vacuum degassed at 105℃ for 6 h, and then nitrogen adsorption-desorption test was carried out at liquid nitrogen temperature (-196 ℃). The relative pressure (P / P0) ranged from 0.05 to 0.30. The specific surface area was calculated using the Brunauer-Emmett-Teller (BET) model. For each group of samples tested above, three parallel samples were tested, and the arithmetic mean was taken as the final test result; the test results are shown in Table 1: Table 1 Based on the test results above, it can be seen from the comparison between Example 1 and Comparative Example 1 that the addition of nanofillers can significantly reduce the thermal conductivity of the insulation film, with the room temperature thermal conductivity decreasing from 0.060 W / (m·K) in Comparative Example 1 to 0.036 W / (m·K). At the same time, it improves high-temperature stability and mechanical properties, indicating that nanofillers play a role in enhancing the thermal insulation effect and structural stability of the fiber membrane.

[0036] A comparison between Example 1 and Comparative Example 2 shows that the multi-scale laminated structure design allows the thermal insulation film to maintain a high porosity while significantly improving its tensile strength, increasing it from 3.7 MPa in Comparative Example 2 to 13.6 MPa in Example 1, while also reducing the thermal conductivity. This indicates that the alternating composite of microfiber layers and nanofiber layers helps to construct a denser and more stable fiber network structure, improving mechanical properties while ensuring thermal insulation performance.

[0037] The comparison between Example 1 and Comparative Example 3 shows that the step-by-step high-temperature sintering process is conducive to the full decomposition of spinning auxiliaries and the uniform transformation of ceramic phase, thereby obtaining a lower thermal conductivity and better high-temperature stability. The intermediate heat preservation stage can effectively control the volatilization rate of organic components and avoid fiber structure defects caused by excessive volatilization.

[0038] A comparison of Example 1 and Comparative Example 4 shows that using pure water as a solvent is not only environmentally friendly but also beneficial for achieving lower thermal conductivity and higher high-temperature stability. The water-based system avoids the potential impact of residual organic solvents on the fiber structure, while simultaneously reducing production costs and environmental burden.

[0039] The test results of Examples 1-6 further demonstrate that the component ratio range, process parameter range, and multi-scale structural parameter range defined in this invention are reasonable and universal. Example 1 (nano-silica filler, 6-layer multi-scale stacked structure, 1000℃ stepwise sintering) exhibits the best overall performance across all indicators and can be considered a preferred embodiment. Example 7 uses the fewest stacked layers (3 layers) and a sintering temperature of 800℃, resulting in a high thermal conductivity. This is mainly attributed to the incomplete growth of ceramic grains and the lower degree of neck fusion between fibers at lower temperatures, leading to a slightly higher solid-phase thermal resistance. In summary, this invention, through the synergistic effect of a pure water-based spinning system, multi-scale stacked structure design, and stepwise high-temperature sintering process, successfully prepares a high-efficiency high-temperature resistant thermal insulation film with excellent thermal insulation performance, high-temperature stability, and good mechanical properties.

[0040] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. A method for preparing a high-efficiency high-temperature resistant heat-insulating film based on a multi-scale nanofiber composite structure, characterized in that: Includes the following steps: Step 1: Mix the precursor, spinning aid, nanofiller and pure water to prepare at least two spinning solutions with different solid contents; Step 2: Using electrospinning technology, the spinning solution is spun into fibers, and different fiber layers are deposited sequentially to obtain a fiber membrane with a multi-scale stacked structure. Step 3: Perform high-temperature sintering on the fiber membrane from Step 2 to obtain a high-efficiency high-temperature heat insulation film.

2. The method for preparing a high-efficiency high-temperature resistant heat-insulating film based on a multi-scale nanofiber composite structure according to claim 1, characterized in that: The precursor in step one includes any one of aluminum sol, silica sol, and pseudoboehmite.

3. The method for preparing a high-efficiency high-temperature resistant heat-insulating film based on a multi-scale nanofiber composite structure according to claim 1, characterized in that: The spinning aid in step one includes any one of polyvinyl alcohol, polyethylene oxide, polyethylene glycol, and polyvinylpyrrolidone.

4. The method for preparing a high-efficiency high-temperature resistant heat-insulating film based on a multi-scale nanofiber composite structure according to claim 1, characterized in that: The nanofiller in step one includes any one or more of nano-silica, nano-alumina, nano-zirconia, nano-silicon carbide, nano-silicon nitride, and nano-titanium dioxide.

5. The method for preparing a high-efficiency high-temperature resistant heat-insulating film based on a multi-scale nanofiber composite structure according to claim 1, characterized in that: In step one, based on the total mass of the spinning solution, the precursor has a mass percentage of 5% to 20%, the spinning aid has a mass percentage of 2% to 10%, the nanofiller has a mass percentage of 1% to 10%, and the remainder is pure water.

6. The method for preparing a high-efficiency high-temperature resistant heat-insulating film based on a multi-scale nanofiber composite structure according to claim 1, characterized in that: The process parameters for electrospinning technology used in step two are as follows: spinning voltage is 10–30 kV, receiving distance is 10–25 cm, spinning solution propulsion rate is 0.5–5 mL / h, spinning environment temperature is 20–35 ℃, relative humidity is 30%–60%, and needle inner diameter is 0.3–1.2 mm. During the spinning process, different fiber layers are deposited alternately layer by layer in the following way: at least two independent liquid supply channels are set up, each corresponding to a different spinning solution. Each liquid supply channel is switched by an independently controlled injection pump or by alternating spraying with multiple needles. According to the preset deposition sequence and deposition time of each layer, different types of spinning solutions are sprayed onto the receiving device in sequence, forming a multi-scale stacked structure through alternating deposition. The deposition time of each fiber layer is 30–180 min, and the deposition interval between two adjacent layers does not exceed 1 min, so as to achieve in-situ solvent welding between layers.

7. The method for preparing a high-efficiency high-temperature resistant heat-insulating film based on a multi-scale nanofiber composite structure according to claim 6, characterized in that: The stacked structure consists of 3 to 7 fiber sublayers, with each fiber sublayer having a thickness of 5 to 50 μm along the thickness direction. The fiber diameters between adjacent fiber sublayers are distributed in a gradient. The different fiber layers are deposited by switching different spinning solution injection pumps or changing different spinning solution reservoirs. The interlayer bonding between adjacent fiber layers is achieved by in-situ solvent welding or hot pressing.

8. The method for preparing a high-efficiency high-temperature resistant heat-insulating film based on a multi-scale nanofiber composite structure according to claim 1, characterized in that: In step three, the holding time for the stepwise high-temperature sintering is 3-6 h, and the sintering time is 6-12 h. The stepwise high-temperature sintering includes a low-temperature removal of additives stage and a high-temperature crystallization and densification stage. The temperature gradient, heating rate and holding time of the two stages are set separately to achieve complete removal of spinning additives and ceramic transformation of fiber structure.

9. The method for preparing a high-efficiency high-temperature resistant heat-insulating film based on a multi-scale nanofiber composite structure according to claim 8, characterized in that: The stepwise high-temperature sintering is carried out in an atmosphere furnace, with the atmosphere being any one of air, nitrogen, or argon, and the gas flow rate being 1~10 L / min. The sintering is performed using a programmed temperature control method according to the following temperature program: the temperature is increased from room temperature to 300~500 ℃ at a heating rate of 1~10 ℃ / min, held at 300~500 ℃ for 1~2 h, then increased to 600~1000 ℃ at a heating rate of 2~8 ℃ / min, held at 600~1000 ℃ for 2~4 h, and finally cooled to room temperature at a cooling rate of 5~15 ℃ / min.

10. A high-efficiency high-temperature resistant heat insulation film based on a multi-scale nanofiber composite structure, characterized in that, The high-efficiency high-temperature heat-insulating film based on a multi-scale nanofiber composite structure, as described in any one of claims 1-9, is prepared by the method for preparing such film.

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