High compression strength low thermal conductivity ceramic nanofiber aerogel and method of making same

Abstract

The application relates to a ceramic nanofiber aerogel with high compressive strength and low thermal conductivity and a preparation method thereof. The method comprises the following steps: performing air-jet spinning on a ceramic precursor spinning solution to obtain a precursor fiber membrane, then performing high-temperature calcination at 600-800 DEG C and high-temperature calcination at 1100-1500 DEG C to obtain a ceramic nanofiber membrane, wherein the ceramic precursor in the ceramic precursor spinning solution comprises a zirconium ceramic precursor; stacking the ceramic nanofiber membrane in an aluminum dihydrogen phosphate solution layer by layer, then performing ultrasonic-assisted impregnation, freeze drying and high-temperature calcination at 1100-1500 DEG C to obtain the ceramic nanofiber aerogel with high compressive strength and low thermal conductivity. The application solves the problem of low compressive strength of the existing ceramic aerogel without sacrificing the heat insulation performance and high-temperature resistance of the material, and the ceramic nanofiber aerogel prepared by the application has the characteristics of high compressive strength and low thermal conductivity, so that the strength is improved while the thermal conductivity is not increased but decreased.

Description

Technical Field

[0001] This invention belongs to the field of ceramic fiber materials technology, and particularly relates to a ceramic nanofiber aerogel with high compressive strength and low thermal conductivity and its preparation method. Background Technology

[0002] Ceramic aerogels have become important research subjects in fields such as thermal insulation, catalytic support, filtration, and energy storage due to their ultra-light weight, high specific surface area, excellent high-temperature resistance, and extremely low thermal conductivity. However, their inherent brittleness greatly limits their feasibility in practical applications. To enhance the mechanical properties of ceramic aerogels, early research mainly focused on introducing flexible one-dimensional fibers to strengthen the network structure constructed from ceramic particles. However, the interfacial bonding between fibers and particles in these composite materials is weak, leading to easy particle detachment and poor structural stability.

[0003] Recently, ceramic nanofiber sponges constructed using one-dimensional nanostructures have exhibited excellent elastic recovery properties, partially recovering their deformation even at compressive strains as high as 80%. Furthermore, highly elastic ceramic fiber aerogels can be prepared by electrospinning nanofibers, homogenizing them to form a stable dispersion, and then freeze-drying them. While these materials offer advantages in configuration, the primarily point-to-point connections between the fibers limit the effective force transmission paths, resulting in low compressive strength, often less than 10 kPa at 80% strain, making them ill-suited to withstand severe mechanical loads or high-temperature thermal shocks.

[0004] To improve its mechanical properties, some researchers have attempted to construct aerogels with a layered porous structure by impregnating and stacking ceramic fiber membranes, thereby enhancing their compressive strength. Although this structure improves the overall mechanical properties, its thermal conductivity is much higher than that of traditional silica particle aerogels.

[0005] Currently, how to significantly enhance the mechanical properties of ceramic aerogels without sacrificing their thermal insulation and high-temperature resistance remains a key challenge that urgently needs to be addressed.

[0006] In summary, there is an urgent need to develop a ceramic nanofiber aerogel with high compressive strength and low thermal conductivity, and its preparation method, so as to improve its ability to avoid damage under severe compression deformation without sacrificing the material's thermal insulation and high temperature resistance. Summary of the Invention

[0007] To address one or more technical problems existing in the prior art, this invention provides a ceramic nanofiber aerogel with high compressive strength and low thermal conductivity, and a method for preparing the same. This invention solves the problem of low compressive strength in existing ceramic nanofiber aerogels without sacrificing the material's thermal insulation and high-temperature resistance. The ceramic nanofiber aerogel prepared by this invention exhibits high compressive strength and low thermal conductivity. Compared to pre-fabricated ceramic nanofiber materials, while increasing strength, the thermal conductivity is actually reduced.

[0008] The present invention provides a method for preparing high compressive strength and low thermal conductivity ceramic nanofiber aerogel in a first aspect, the method comprising the following steps:

[0009] (1) The ceramic precursor spinning solution is subjected to air-jet spinning to obtain a precursor fiber membrane, which is then subjected to a first high-temperature calcination at 600-800℃ and a second high-temperature calcination at 1100-1500℃ to obtain a ceramic nanofiber membrane; the ceramic precursor in the ceramic precursor spinning solution includes a zirconium ceramic precursor.

[0010] (2) The ceramic nanofiber membrane was placed in aluminum dihydrogen phosphate solution and stacked layer by layer. Then, it was subjected to ultrasonic-assisted impregnation, freeze drying and third high-temperature calcination at 1100-1500℃ to obtain ceramic nanofiber aerogel with high compressive strength and low thermal conductivity.

[0011] Preferably, the diameter of the ceramic nanofibers in the ceramic nanofiber membrane is 800-900 nm; the total thickness of the ceramic nanofiber aerogel is 4-50 mm; the thickness of a single ceramic nanofiber membrane is 4-10 mm; and / or the number of layers of the ceramic nanofiber membrane stacked layer by layer is 1-10.

[0012] Preferably, the ultrasonic-assisted impregnation time is 0.5 to 6 hours, and more preferably 4 to 6 hours.

[0013] Preferably, the concentration of the aluminum dihydrogen phosphate solution is 0.5–2 wt%; the mass ratio of all ceramic nanofiber membranes stacked layer by layer to the aluminum dihydrogen phosphate solution is 1:(30–60); the freeze-drying time is 48–72 h; and / or the first high-temperature calcination, the second high-temperature calcination, and / or the third high-temperature calcination time is 1–3 h, the heating rate to the first high-temperature calcination, the second high-temperature calcination, and / or the third high-temperature calcination temperature is 1–5 °C / min, preferably, the first high-temperature calcination, the second high-temperature calcination, and / or the third high-temperature calcination are carried out in an air atmosphere or an oxygen atmosphere.

[0014] Preferably, the zirconium ceramic precursor is zirconium oxychloride octahydrate and / or zirconium oxynitrate; and / or the ceramic precursor in the ceramic precursor spinning solution further contains a phase stabilizer and / or a dopant.

[0015] Preferably, the phase stabilizer is yttrium nitrate hexahydrate; the dopant is one or more of aluminum chloride hexahydrate, aluminum nitrate nonahydrate, methyl orthosilicate, ethyl orthosilicate, or hafnium chloride; and / or the mass ratio of the zirconium ceramic precursor to the phase stabilizer or the dopant is (8-12):1.

[0016] Preferably, the ceramic precursor spinning solution is obtained by uniformly mixing a ceramic precursor, a spinning aid, and a solvent. The spinning aid is one or more of polyvinylpyrrolidone, polyvinyl alcohol, polyacrylonitrile, or polyvinyl butyral. The solvent is composed of an organic solvent and water in a volume ratio of 1:(1-3). Preferably, the organic solvent is one or more of anhydrous ethanol, N,N-dimethylformamide, N,N-dimethylacetamide, or dimethyl sulfoxide. Preferably, the ceramic precursor spinning solution contains 5-50 wt% ceramic precursor and / or 1-10 wt% spinning aid.

[0017] Preferably, the air pressure of the air jet spinning is 0.03-0.08 MPa, the injection rate of the ceramic precursor spinning solution is 1-5 mL / h, the receiving distance of the air jet spinning is 15-30 cm, the temperature of the air jet spinning is 20-30 °C, the relative humidity of the air jet spinning is 30-40%, and / or the protrusion distance between the inner needle and the outer needle of the coaxial needle head of the double needle seat in the spinning equipment used for air jet spinning is 0.1-0.5 mm.

[0018] In a second aspect, the present invention provides a ceramic nanofiber aerogel with high compressive strength and low thermal conductivity prepared by the preparation method described in the first aspect of the present invention.

[0019] Preferably, zirconium pyrophosphate is formed in the high compressive strength, low thermal conductivity ceramic nanofiber aerogel; the apparent density of the high compressive strength, low thermal conductivity ceramic nanofiber aerogel is 20–100 mg / cm³. 3 It has a reversible compressive strain of up to 90%, can be cyclically compressed at -196℃ to 1300℃, has a compressive strength of not less than 310kPa at 80% strain, a compressive strength of not less than 1100kPa at 90% strain, a thermal conductivity of not more than 0.02869W / (m·K) at 25℃, and a thermal conductivity of not more than 0.07223W / (m·K) at 800℃; and / or the thermal conductivity of the high compressive strength and low thermal conductivity ceramic nanofiber aerogel is less than the thermal conductivity of the ceramic nanofiber membrane.

[0020] Compared with the prior art, the present invention has at least the following beneficial effects:

[0021] (1) This invention introduces soluble aluminum dihydrogen phosphate as a high-temperature binder to build bonding points between fiber layers and fibers, thereby improving the overall strength of ceramic nanofiber aerogels. The compressive strength is increased by 1 to 2 orders of magnitude compared to previously reported ceramic aerogels. Compared with traditional methods for preparing ceramic fiber aerogels, the synthesis strategy of this invention combines the simplicity of the ceramic nanofiber membrane impregnation and stacking assembly process with the wide availability of air-jet spun ceramic nanofiber membranes, making the preparation of structurally editable ceramic nanofiber aerogels simple, efficient, universal, and controllable. More importantly, the ceramic nanofiber aerogels prepared by this invention not only significantly improve compressive strength but also do not sacrifice their excellent thermal insulation and high-temperature resistance properties (e.g., preferably a thermal conductivity of no more than 0.02869 W / (m·K) at 25°C and preferably no more than 0.07223 W / (m·K) at 800°C). These excellent comprehensive properties make the ceramic nanofiber aerogels of this invention more suitable for extended applications in complex environments coupled with high-frequency vibration and extreme environments.

[0022] (2) By controlling the type of ceramic precursor, the concentration of aluminum dihydrogen phosphate solution, the temperature of the third high-temperature calcination, and the use of ultrasonic-assisted impregnation, the present invention can generate a large amount of zirconium pyrophosphate in the ceramic nanofiber aerogel prepared by the present invention. Thus, while improving the strength of the ceramic nanofiber aerogel, its thermal conductivity does not increase but decreases.

[0023] (3) The ceramic nanofiber membrane prepared by air-jet spinning in this invention has relatively coarse fibers (diameter of 800-900 nm). This invention found that the ceramic nanofiber membrane formed by coarser fibers has larger pore sizes. This pore structure facilitates the penetration of aluminum dihydrogen phosphate solution, but its specific surface area is smaller than that of finer fibers, which reduces the reaction sites between aluminum dihydrogen phosphate and zirconium oxide. To overcome this problem, this invention also introduces ultrasonic-assisted impregnation, which not only improves the penetration efficiency of aluminum dihydrogen phosphate in the fiber membrane, but also increases the opportunity for contact between nanofibers, greatly increasing the probability of the formation of bonding points between fibers. This allows more aluminum dihydrogen phosphate to react with zirconium oxide to form zirconium pyrophosphate, rather than being ineffectively lost due to crystallization during freeze-drying, thus improving the utilization rate of aluminum dihydrogen phosphate. Meanwhile, this invention employs a ceramic nanofiber membrane with relatively coarse fibers and an ultrasonic-assisted impregnation process, enabling the generation of more zirconium pyrophosphate in the ceramic nanofiber aerogel. This achieves the goal of efficient in-situ generation of zirconium pyrophosphate, significantly improving the strength and thermal insulation performance of the ceramic nanofiber aerogel. More importantly, ceramic nanofiber aerogels assembled from small-diameter nanofibers typically exhibit superior mechanical properties. This is because small-diameter fibers have better flexibility and can form a denser network structure in three-dimensional space, thereby enhancing the connection strength between fibers. Furthermore, the uniform distribution and synergistic deformation ability among fine fibers also help disperse stress, improve compressive strength, and structural toughness. However, this invention, through ultrasonic-assisted impregnation, enables ceramic nanofiber aerogels assembled from large-diameter nanofibers to exhibit compressive strength comparable to or even superior to that of ceramic nanofiber aerogels assembled from small-diameter nanofibers. This broadens the application possibilities of submicron ceramic nanofibers in the field of high-compressive-strength ceramic nanofiber aerogels. In addition, the formation of more bonding points transforms the heat transfer path from continuous nanofibers to discontinuous, irregular paths, which also plays a positive role in reducing the thermal conductivity of the ceramic nanofiber aerogel. All of these factors ultimately result in an increase in the compressive strength of the ceramic nanofiber aerogel prepared by this invention, while the thermal conductivity does not increase or even decreases compared to pre-prepared ceramic nanofiber materials. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a physical image of the high compressive strength and low thermal conductivity ceramic nanofiber aerogel prepared in Example 1 of the present invention.

[0026] Figure 2 This is a low-magnification SEM image of the high compressive strength and low thermal conductivity ceramic nanofiber aerogel prepared in Example 1 of this invention.

[0027] Figure 3 This is a high-magnification SEM image of the high compressive strength and low thermal conductivity ceramic nanofiber aerogel prepared in Example 1 of this invention.

[0028] Figure 4 This is the compressive stress-strain curve of the high compressive strength and low thermal conductivity ceramic nanofiber aerogel prepared in Example 1 of the present invention.

[0029] Figure 5 These are SEM images of ceramic nanofiber aerogels obtained by treating with 0.5wt% and 1wt% aluminum dihydrogen phosphate solution in Examples 2 and 3 of the present invention, respectively.

[0030] Figure 6 These are the stress-strain curves of ceramic nanofiber aerogels obtained by treating with aluminum dihydrogen phosphate solutions of different concentrations in Examples 3-6 of this invention at 60% strain.

[0031] Figure 7 These are XRD patterns of ceramic nanofiber aerogels obtained by calcination at different temperatures in Examples 1 and 7-10 of this invention, and the ceramic nanofiber membrane prepared in Comparative Example 1. The temperatures shown in the figures are the temperatures of the third high-temperature calcination. Uncalcined corresponds to the ceramic nanofiber membrane prepared in Comparative Example 1. Cubic ZrP2O7 represents zirconium pyrophosphate with a cubic crystal structure, and Monoclinic Al2P6O3 represents the ceramic nanofiber membrane prepared in Comparative Example 1. 18 The symbols represent aluminum phosphate compounds with a monoclinic crystal system, OrthorhombicAlPO4 represents aluminum phosphate with an orthorhombic crystal system, Monoclinic ZrO2 represents zirconium oxide with a monoclinic crystal system, and Tetragonal ZrO2 represents zirconium oxide with a tetragonal crystal system. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0033] The present invention provides a method for preparing high compressive strength and low thermal conductivity ceramic nanofiber aerogel in a first aspect, the method comprising the following steps:

[0034] (1) A ceramic precursor spinning solution is subjected to air-jet spinning to obtain a precursor fiber membrane, which is then subjected to a first high-temperature calcination at 600-800℃ (e.g., 600℃, 700℃ or 800℃) and a second high-temperature calcination at 1100-1500℃ (e.g., 1100℃, 1200℃, 1300℃, 1400℃ or 1500℃), preferably 1100-1300℃ (e.g., 1100℃, 1150℃, 1200℃, 1250℃ or 1300℃) to obtain a ceramic nanofiber membrane; the ceramic precursor in the ceramic precursor spinning solution includes a zirconium ceramic precursor; in this invention, the ceramic nanofiber membrane comprises zirconium oxide.

[0035] (2) The ceramic nanofiber membrane is placed in an aluminum dihydrogen phosphate solution and stacked layer by layer. Then, it is subjected to ultrasonic-assisted impregnation, freeze drying, and a third high-temperature calcination at 1100-1500℃ (e.g., 1100℃, 1200℃, 1300℃, 1400℃ or 1500℃), preferably 1100-1300℃ (e.g., 1100℃, 1150℃, 1200℃, 1250℃ or 1300℃) to obtain a ceramic nanofiber aerogel with high compressive strength and low thermal conductivity (abbreviated as ceramic nanofiber aerogel). The ultrasonic-assisted impregnation in this invention refers to the impregnation assisted by ultrasonic vibration after the ceramic nanofiber membrane is placed in an aluminum dihydrogen phosphate solution and stacked layer by layer. The frequency of the ultrasonic vibration can be, for example, 20-40kHz.

[0036] This invention introduces soluble aluminum dihydrogen phosphate as a high-temperature binder to construct bonding points between fiber layers and fibers, thereby enhancing the overall strength of ceramic nanofiber aerogels. The compressive strength is increased by 1-2 orders of magnitude compared to previously reported ceramic aerogels. Compared to traditional methods for preparing ceramic fiber aerogels, the synthesis strategy of this invention combines the simplicity of the ceramic nanofiber membrane impregnation and stacking assembly process with the wide availability of air-jet spun ceramic nanofiber membranes, making the preparation of structurally editable ceramic nanofiber aerogels simple, efficient, versatile, and controllable. More importantly, the ceramic nanofiber aerogels prepared by this invention not only significantly improve compressive strength but also do not sacrifice their excellent thermal insulation and high-temperature resistance properties (e.g., preferably a thermal conductivity of no more than 0.02869 W / (m·K) at 25°C, and preferably no more than 0.07223 W / (m·K) at 800°C). These superior comprehensive properties make the ceramic nanofiber aerogels of this invention more suitable for extended applications in complex environments coupled with high-frequency vibration and extreme conditions.

[0037] In this invention, by controlling the type of ceramic precursor, the concentration of aluminum dihydrogen phosphate solution, the temperature of the third high-temperature calcination, and by using ultrasonic-assisted impregnation, it is beneficial to generate a large amount of zirconium pyrophosphate in the ceramic nanofiber aerogel prepared in this invention. This can improve the strength of the ceramic nanofiber aerogel while reducing its thermal conductivity instead of increasing it.

[0038] According to some preferred embodiments, the ceramic nanofibers in the ceramic nanofiber membrane have a diameter of 800-900 nm and a grain size of 20-200 nm. It should be noted that the diameter of the ceramic nanofibers in this invention is 800-900 nm, which can still be considered as nanofibers in a broad sense, but also belongs to submicron fibers. The ceramic nanofibers in this invention can also be referred to as ceramic submicron fibers.

[0039] This invention produces ceramic nanofiber membranes with relatively coarse fibers (800-900 nm in diameter) prepared by air-jet spinning. The invention reveals that the coarser fibers create ceramic nanofiber membranes with larger pore sizes. This porous structure facilitates the permeation of aluminum dihydrogen phosphate solution, but its specific surface area is smaller than that of finer fibers, which reduces the reaction sites between aluminum dihydrogen phosphate and zirconium oxide. To overcome this problem, this invention simultaneously introduces ultrasonic-assisted impregnation, which improves the permeation efficiency of aluminum dihydrogen phosphate in the fiber membrane and increases the opportunities for contact between nanofibers. This significantly increases the probability of bonding points forming between fibers, allowing more aluminum dihydrogen phosphate to react with zirconium oxide to form zirconium pyrophosphate, rather than being ineffectively lost due to crystallization during freeze-drying, thus improving the utilization rate of aluminum dihydrogen phosphate. Meanwhile, this invention employs a ceramic nanofiber membrane with relatively coarse fibers and an ultrasonic-assisted impregnation process, enabling the generation of more zirconium pyrophosphate in the ceramic nanofiber aerogel. This achieves the goal of efficient in-situ generation of zirconium pyrophosphate, significantly improving the strength and thermal insulation performance of the ceramic nanofiber aerogel. More importantly, ceramic nanofiber aerogels assembled from small-diameter nanofibers typically exhibit superior mechanical properties. This is because small-diameter fibers have better flexibility and can form a denser network structure in three-dimensional space, thereby enhancing the connection strength between fibers. Furthermore, the uniform distribution and synergistic deformation ability among fine fibers also help disperse stress, improve compressive strength, and structural toughness. However, this invention, through ultrasonic-assisted impregnation, enables ceramic nanofiber aerogels assembled from large-diameter nanofibers to exhibit compressive strength comparable to or even superior to that of ceramic nanofiber aerogels assembled from small-diameter nanofibers. This broadens the application possibilities of submicron ceramic fibers in the field of high-compressive-strength ceramic nanofiber aerogels. In addition, the formation of more bonding points transforms the heat transfer path from continuous nanofibers to discontinuous, irregular paths, which also plays a positive role in reducing the thermal conductivity of the ceramic nanofiber aerogel. All of these factors ultimately result in an increase in the compressive strength of the ceramic nanofiber aerogel prepared by this invention, while the thermal conductivity does not increase or even decreases compared to pre-prepared ceramic nanofiber materials.

[0040] According to some specific implementation methods, the ceramic nanofiber aerogel is prepared as follows:

[0041] ① Mix the ceramic precursor, spinning aid and solvent evenly to obtain the precursor spinning solution.

[0042] ② The obtained precursor spinning solution is subjected to air-jet spinning to obtain a precursor fiber membrane.

[0043] ③ The obtained precursor fiber membrane is subjected to high-temperature calcination (including first high-temperature calcination and second high-temperature calcination) to obtain a ceramic nanofiber membrane.

[0044] ④ The ceramic nanofiber membrane is immersed and stacked in aluminum dihydrogen phosphate solution, and ultrasonic impregnation is performed. Then, it is freeze-dried and calcined at high temperature (third high temperature calcination) to obtain ceramic nanofiber aerogel with high compressive strength and low thermal conductivity.

[0045] According to some preferred embodiments, the total thickness of the ceramic nanofiber aerogel is 4 to 50 mm (e.g., 4, 5, 10, 15, 20, 25, 30, 35, 40, 45 or 50 mm); the thickness of a single ceramic nanofiber membrane is 4 to 10 mm (e.g., 4, 5, 6, 7, 8, 9 or 10 mm); and / or the number of layers of the ceramic nanofiber membrane stacked layer by layer is 1 to 10 (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 layers).

[0046] According to some preferred embodiments, the ultrasonic-assisted impregnation time is 0.5 to 6 hours (e.g., 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, or 6 hours), preferably 4 to 6 hours (e.g., 4, 4.5, 5, 5.5, or 6 hours). In this invention, the ultrasonic-assisted impregnation time is preferably 4 to 6 hours. If the ultrasonic time is insufficient, the contact opportunities between nanofibers will be relatively reduced, which will limit the formation of reactive bonding points. The appropriate ultrasonic-assisted impregnation time in this invention is of great significance for improving the strength and thermal insulation performance of ceramic nanofiber aerogel materials.

[0047] According to some preferred embodiments, the concentration of the aluminum dihydrogen phosphate solution is 0.5–2 wt% (e.g., 0.5 wt%, 1 wt%, 1.5 wt%, or 2 wt%), preferably 1–2 wt%. In this invention, the aluminum dihydrogen phosphate solution is an aqueous solution of aluminum dihydrogen phosphate. This invention does not specifically limit the source of the aluminum dihydrogen phosphate solution; it can be a directly purchased product or a product prepared using existing methods. Those skilled in the art can conventionally choose a solution, as long as the concentration of aluminum dihydrogen phosphate is 0.5–2 wt%. For example, the method in Chinese Patent CN115322687B can be referenced, wherein the aluminum dihydrogen phosphate solution is prepared by a mass ratio of 100: The aerogel is prepared by adding a solution of phosphoric acid (10-30):(5-10):(1.1-6), aluminum hydroxide, sodium aluminate, and alumina, and then adding water to prepare a 0.5-2 wt% aluminum dihydrogen phosphate solution. The present invention found that if the concentration of aluminum dihydrogen phosphate does not exceed 0.5 wt%, the lower concentration will lead to a larger interlayer spacing, lower compressive strength, and even separation of ceramic nanofiber aerogel. If the concentration of aluminum dihydrogen phosphate is greater than 2 wt%, the compressive strength of ceramic nanofiber aerogel can be further improved, but the corresponding energy dissipation hysteresis loop is also larger. This means that the excessive introduction of brittle components will lead to a weakening of the recoverable deformation ability of ceramic nanofiber aerogel.

[0048] According to some preferred embodiments, the mass ratio of all ceramic nanofiber membranes stacked layer by layer to the aluminum dihydrogen phosphate solution is 1:(30-60) (e.g., 1:30, 1:35, 1:40, 1:45, 1:50, 1:55, or 1:60), that is, the total mass ratio of all layers of ceramic nanofiber membranes stacked layer by layer to the mass ratio of the aluminum dihydrogen phosphate solution is 1:(30-60); the freeze-drying time is 48-72 hours (e.g., 48, 60, or 72 hours); the present invention has a high degree of cold... The freeze-drying operation is not specifically limited, and those skilled in the art can choose conventionally; and / or the time for the first high-temperature calcination, the second high-temperature calcination, and / or the third high-temperature calcination is 1 to 3 hours (e.g., 1, 1.5, 2, 2.5, or 3 hours), and the heating rate to the temperature of the first high-temperature calcination, the second high-temperature calcination, and / or the third high-temperature calcination is 1 to 5 °C / min. Preferably, the first high-temperature calcination, the second high-temperature calcination, and / or the third high-temperature calcination are carried out in an air atmosphere or an oxygen atmosphere.

[0049] According to some preferred embodiments, the zirconium ceramic precursor is zirconium oxychloride octahydrate and / or zirconium oxynitrate; and / or the ceramic precursor in the ceramic precursor spinning solution further comprises a phase stabilizer and / or a dopant.

[0050] According to some preferred embodiments, the phase stabilizer is yttrium nitrate hexahydrate; the dopant is one or more of aluminum chloride hexahydrate, aluminum nitrate nonahydrate, methyl orthosilicate, ethyl orthosilicate, or hafnium chloride; in this invention, preferably, the main component of the ceramic nanofiber membrane includes zirconium oxide, and also includes one or more of yttrium oxide, aluminum oxide, silicon oxide, mullite, or hafnium oxide; and / or the mass ratio of the zirconium ceramic precursor to the phase stabilizer or the dopant is (8-12):1 (e.g., 8:1, 9:1, 10:1, 11:1, or 12:1), that is, in this invention, preferably, the mass ratio of the zirconium ceramic precursor to the phase stabilizer is (8-12):1, or the mass ratio of the zirconium ceramic precursor to the dopant is (8-12):1.

[0051] According to some preferred embodiments, the ceramic precursor spinning solution is obtained by uniformly mixing a ceramic precursor, a spinning aid, and a solvent. The spinning aid is one or more of polyvinylpyrrolidone, polyvinyl alcohol, polyacrylonitrile, or polyvinyl butyral. The solvent is composed of an organic solvent and water in a volume ratio of 1:(1-3) (e.g., 1:1, 1:1.5, 1:2, 1:2.5, or 1:3). Preferably, the organic solvent is one or more of anhydrous ethanol, N,N-dimethylformamide, N,N-dimethylacetamide, or dimethyl sulfoxide. Preferably, the ceramic precursor spinning solution contains 5 to 50 wt% ceramic precursor (e.g., 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, or 50 wt%), and / or the ceramic precursor spinning solution contains 1 to 10 wt% spinning aid (e.g., 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, or 10 wt%).

[0052] According to some preferred embodiments, the ceramic precursor is composed of zirconium oxychloride octahydrate and yttrium nitrate hexahydrate, preferably, the mass ratio of zirconium oxychloride octahydrate to yttrium nitrate hexahydrate is (8-12):1.

[0053] According to some preferred embodiments, the air pressure of the air-jet spinning is 0.03–0.08 MPa (e.g., 0.03, 0.04, 0.05, 0.06, 0.07, or 0.08 MPa), the injection rate of the ceramic precursor spinning solution is 1–5 mL / h (e.g., 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, or 5 mL / h), and the receiving distance of the air-jet spinning is 15–30 cm (e.g., 15, 3.5, 4, 5, 5, 6, 7, 8, 9, 10, 15, 10 ... The air-jet spinning temperature is 20–30°C (e.g., 20°C, 25°C, or 30°C), and the relative humidity of the air-jet spinning is 30–40% (e.g., 30%, 35%, or 40%); and / or the protrusion distance between the inner needle and the outer needle of the coaxial needle head of the double needle seat in the air-jet spinning equipment is 0.1–0.5 mm (e.g., 0.1, 0.2, 0.3, 0.4, or 0.5 mm).

[0054] In a second aspect, the present invention provides a high compressive strength and low thermal conductivity ceramic nanofiber aerogel (abbreviated as ceramic nanofiber aerogel) prepared by the preparation method described in the first aspect of the present invention. The ceramic nanofiber aerogel of the present invention is formed by stacking, impregnating (aluminum dihydrogen phosphate solution + ultrasonic-assisted impregnation), freeze-drying and calcining of multiple layers (e.g., 1 to 10 layers) of flexible ceramic nanofiber membranes. The high compressive strength and low thermal conductivity ceramic nanofiber aerogel prepared by the present invention has a porous and layered structure, consisting of loosely stacked ceramic nanofiber layers, interlayers connected to ceramic nanofibers, and bonding points between ceramic nanofibers.

[0055] According to some preferred embodiments, the high compressive strength and low thermal conductivity ceramic nanofiber aerogel has a porous and layered structure, consisting of loosely stacked ceramic nanofiber layers, interlayers connected to the ceramic nanofibers, and bonding points between the ceramic nanofibers.

[0056] According to some preferred embodiments, zirconium pyrophosphate is generated in the high compressive strength, low thermal conductivity ceramic nanofiber aerogel; the apparent density of the high compressive strength, low thermal conductivity ceramic nanofiber aerogel is 20–100 mg / cm³. 3 The reversible compressive strain is up to 90%, and it can be cyclically compressed at temperatures ranging from -196℃ to 1300℃. The compressive strength at 80% strain is not less than 310 kPa, and the compressive strength at 90% strain is not less than 1100 kPa. The thermal conductivity at 25℃ is not greater than 0.02891 W / (m·K), preferably not greater than 0.02869 W / (m·K), and the thermal conductivity at 800℃ is not greater than 0.07243 W / (m·K), preferably not greater than 0.07223 W / (m·K); and / or the thermal conductivity of the high compressive strength and low thermal conductivity ceramic nanofiber aerogel is less than that of the ceramic nanofiber membrane.

[0057] The present invention will be further described below by way of examples, but the scope of protection of the present invention is not limited to these embodiments. The present invention may have many other embodiments, and those skilled in the art can make various corresponding changes and modifications based on the present invention without departing from its spirit and essence; however, all such corresponding changes and modifications should fall within the scope of protection of the appended claims.

[0058] Example 1

[0059] ① Dissolve 23.4g of zirconium oxychloride octahydrate and 2.212g of yttrium nitrate hexahydrate in a solvent consisting of 30mL of deionized water and 10mL of anhydrous ethanol. Stir magnetically for 1 hour to ensure complete dissolution and obtain a mixture. Then, slowly add 3.352g of polyvinylpyrrolidone to the mixture and stir magnetically for 12 hours to obtain a ceramic precursor spinning solution.

[0060] ② The ceramic precursor spinning solution was injected into an air-jet spinning device (using a dual-seat coaxial needle with an inner needle of 14G and an outer needle of 21G, wherein the protrusion distance of the inner needle relative to the outer needle is 0.3mm; the ceramic precursor spinning solution was drawn into a 10mL syringe; the syringe was placed on the injection pump; the dual-seat coaxial needle and the syringe were connected by a rubber hose with a Luer connector, and the rotating shaft receiver was fixed) for air-jet spinning to obtain a precursor fiber membrane; during the air-jet spinning process, the gas compressor pump pressure was set to 0.05MPa, the distance between the collector and the coaxial needle was 25cm, the injection rate of the ceramic precursor spinning solution was 3.7mL / h; the air-jet spinning temperature was 25℃, and the air-jet spinning relative humidity was 30%RH.

[0061] ③ The prepared precursor fiber membrane was placed in a muffle furnace (air atmosphere) and heated to 600℃ at a heating rate of 1℃ / min. After holding at this temperature for 1 hour, the temperature was increased to 1100℃ at a heating rate of 3℃ / min and held for another hour. Then, the temperature was cooled to room temperature with the furnace to obtain a ceramic nanofiber membrane (zirconium-based ceramic nanofiber membrane). The fiber diameter in the prepared ceramic nanofiber membrane was measured to be 800-900 nm.

[0062] ④ Four zirconium-based ceramic nanofiber membranes with a thickness of 7 mm were stacked layer by layer in a 2 wt% aluminum dihydrogen phosphate solution and ultrasonically impregnated for 6 h. The total mass ratio of the four zirconium-based ceramic nanofiber membranes to the aluminum dihydrogen phosphate solution was 1:45. Subsequently, the four zirconium-based ceramic nanofiber membranes immersed in the aluminum dihydrogen phosphate solution were freeze-dried for 72 h. Finally, the freeze-dried uncrosslinked ceramic nanofiber aerogel was placed in a muffle furnace (air atmosphere) and heated to 1100 °C at a heating rate of 5 °C / min. After holding at this temperature for 1 h, it was cooled to room temperature with the furnace to obtain a ceramic nanofiber aerogel with high compressive strength and low thermal conductivity (zirconium-based ceramic nanofiber aerogel).

[0063] A physical image of the high compressive strength and low thermal conductivity ceramic nanofiber aerogel prepared in this embodiment is shown below. Figure 1 As shown; the low-magnification and high-magnification SEM images of the high compressive strength and low thermal conductivity ceramic nanofiber aerogel prepared in this embodiment are shown in the figures below. Figure 2 and Figure 3 As shown.

[0064] The compressive stress-strain curve of the high compressive strength and low thermal conductivity ceramic nanofiber aerogel prepared in this embodiment is as follows: Figure 4 As shown.

[0065] Example 2

[0066] Example 2 is basically the same as Example 1, except that:

[0067] ④ Four zirconium-based ceramic nanofiber membranes with a thickness of 7 mm were stacked layer by layer in a 0.5 wt% aluminum dihydrogen phosphate solution and ultrasonically impregnated for 6 h. The total mass ratio of the four zirconium-based ceramic nanofiber membranes to the aluminum dihydrogen phosphate solution was 1:45. Subsequently, the four zirconium-based ceramic nanofiber membranes immersed in the aluminum dihydrogen phosphate solution were freeze-dried for 72 h. Finally, the freeze-dried uncrosslinked ceramic nanofiber aerogel was placed in a muffle furnace (air atmosphere) and heated to 1300 °C at a heating rate of 5 °C / min. After holding at this temperature for 1 h, it was cooled to room temperature with the furnace to obtain a ceramic nanofiber aerogel with high compressive strength and low thermal conductivity (zirconium-based ceramic nanofiber aerogel).

[0068] Example 3

[0069] Example 3 is basically the same as Example 1, except that:

[0070] ④ Four zirconium-based ceramic nanofiber membranes with a thickness of 7 mm were stacked layer by layer in a 1 wt% aluminum dihydrogen phosphate solution and ultrasonically impregnated for 6 h. The total mass ratio of the four zirconium-based ceramic nanofiber membranes to the aluminum dihydrogen phosphate solution was 1:45. Subsequently, the four zirconium-based ceramic nanofiber membranes immersed in the aluminum dihydrogen phosphate solution were freeze-dried for 72 h. Finally, the freeze-dried uncrosslinked ceramic nanofiber aerogel was placed in a muffle furnace (air atmosphere) and heated to 1300 °C at a heating rate of 5 °C / min. After holding at this temperature for 1 h, it was cooled to room temperature with the furnace to obtain a ceramic nanofiber aerogel with high compressive strength and low thermal conductivity (zirconium-based ceramic nanofiber aerogel).

[0071] SEM images of ceramic nanofiber aerogels obtained by treatment with 0.5wt% and 1wt% aluminum dihydrogen phosphate solutions in Examples 2-3 of this invention are shown below. Figure 5 As shown; from Figure 5 The results show that if the aluminum dihydrogen phosphate concentration does not exceed 0.5 wt%, the lower concentration will lead to a larger interlayer spacing, lower compressive strength, and even separation of ceramic nanofiber aerogel.

[0072] Example 4

[0073] Example 4 is basically the same as Example 1, except that:

[0074] ④ Four zirconium-based ceramic nanofiber membranes with a thickness of 7 mm were stacked layer by layer in a 1.5 wt% aluminum dihydrogen phosphate solution and ultrasonically impregnated for 6 h. The total mass ratio of the four zirconium-based ceramic nanofiber membranes to the aluminum dihydrogen phosphate solution was 1:45. Subsequently, the four zirconium-based ceramic nanofiber membranes immersed in the aluminum dihydrogen phosphate solution were freeze-dried for 72 h. Finally, the freeze-dried uncrosslinked ceramic nanofiber aerogel was placed in a muffle furnace (air atmosphere) and heated to 1300 °C at a heating rate of 5 °C / min. After holding at this temperature for 1 h, it was cooled to room temperature with the furnace to obtain a ceramic nanofiber aerogel with high compressive strength and low thermal conductivity (zirconium-based ceramic nanofiber aerogel).

[0075] Example 5

[0076] Example 5 is basically the same as Example 1, except that:

[0077] ④ Four zirconium-based ceramic nanofiber membranes with a thickness of 7 mm were stacked layer by layer in a 2 wt% aluminum dihydrogen phosphate solution and subjected to ultrasonic-assisted impregnation for 6 h. The total mass ratio of the four zirconium-based ceramic nanofiber membranes to the aluminum dihydrogen phosphate solution was 1:45. Subsequently, the four zirconium-based ceramic nanofiber membranes immersed in the aluminum dihydrogen phosphate solution were freeze-dried as a whole for 72 h. Finally, the freeze-dried uncrosslinked ceramic nanofiber aerogel was placed in a muffle furnace (air atmosphere) and heated to 1300 °C at a heating rate of 5 °C / min. After holding at this temperature for 1 h, it was cooled to room temperature with the furnace to obtain a ceramic nanofiber aerogel with high compressive strength and low thermal conductivity (zirconium-based ceramic nanofiber aerogel).

[0078] Example 6

[0079] Example 6 is basically the same as Example 1, except that:

[0080] ④ Four zirconium-based ceramic nanofiber membranes with a thickness of 7 mm were stacked layer by layer in a 2.5 wt% aluminum dihydrogen phosphate solution and ultrasonically impregnated for 6 h. The total mass ratio of the four zirconium-based ceramic nanofiber membranes to the aluminum dihydrogen phosphate solution was 1:45. Subsequently, the four zirconium-based ceramic nanofiber membranes immersed in the aluminum dihydrogen phosphate solution were freeze-dried for 72 h. Finally, the freeze-dried uncrosslinked ceramic nanofiber aerogel was placed in a muffle furnace (air atmosphere) and heated to 1300 °C at a heating rate of 5 °C / min. After holding at this temperature for 1 h, it was cooled to room temperature with the furnace to obtain a ceramic nanofiber aerogel with high compressive strength and low thermal conductivity (zirconium-based ceramic nanofiber aerogel).

[0081] The stress-strain curves of ceramic nanofiber aerogels obtained by treating with aluminum dihydrogen phosphate solutions of different concentrations in Examples 3-6 of this invention at 60% strain are shown below. Figure 6 As shown; from Figure 6 The results show that if the aluminum dihydrogen phosphate concentration is greater than 2wt%, the compressive strength of ceramic nanofiber aerogel can be further improved, but the corresponding energy dissipation hysteresis loop is also larger. This means that the excessive introduction of brittle components will lead to a weakening of the recoverable deformation ability of ceramic nanofiber aerogel.

[0082] Example 7

[0083] Example 7 is basically the same as Example 1, except that:

[0084] ③ The prepared precursor fiber membrane was placed in a muffle furnace (air atmosphere) and heated to 600℃ at a heating rate of 1℃ / min. After holding at this temperature for 1 hour, the temperature was increased to 800℃ at a heating rate of 3℃ / min and held for another hour. Then, the temperature was cooled to room temperature with the furnace to obtain a ceramic nanofiber membrane (zirconium-based ceramic nanofiber membrane). The fiber diameter in the prepared ceramic nanofiber membrane was measured to be 800-900 nm.

[0085] ④ Four zirconium-based ceramic nanofiber membranes with a thickness of 7 mm were stacked layer by layer in a 2 wt% aluminum dihydrogen phosphate solution and ultrasonically impregnated for 6 h. The total mass ratio of the four zirconium-based ceramic nanofiber membranes to the aluminum dihydrogen phosphate solution was 1:45. Subsequently, the four zirconium-based ceramic nanofiber membranes immersed in the aluminum dihydrogen phosphate solution were freeze-dried for 72 h. Finally, the freeze-dried uncrosslinked ceramic nanofiber aerogel was placed in a muffle furnace (air atmosphere) and heated to 800 °C at a heating rate of 5 °C / min. After holding at this temperature for 1 h, it was cooled to room temperature with the furnace to obtain a ceramic nanofiber aerogel with high compressive strength and low thermal conductivity (zirconium-based ceramic nanofiber aerogel).

[0086] Example 8

[0087] Example 8 is basically the same as Example 1, except that:

[0088] ③ The prepared precursor fiber membrane was placed in a muffle furnace (air atmosphere) and heated to 600℃ at a heating rate of 1℃ / min. After holding at this temperature for 1 hour, the temperature was increased to 1000℃ at a heating rate of 3℃ / min and held for another hour. Then, the temperature was cooled to room temperature with the furnace to obtain a ceramic nanofiber membrane (zirconium-based ceramic nanofiber membrane). The fiber diameter in the prepared ceramic nanofiber membrane was measured to be 800-900 nm.

[0089] ④ Four zirconium-based ceramic nanofiber membranes with a thickness of 7 mm were stacked layer by layer in a 2 wt% aluminum dihydrogen phosphate solution and subjected to ultrasonic-assisted impregnation for 6 h. The total mass ratio of the four zirconium-based ceramic nanofiber membranes to the aluminum dihydrogen phosphate solution was 1:45. Subsequently, the four zirconium-based ceramic nanofiber membranes immersed in the aluminum dihydrogen phosphate solution were freeze-dried as a whole for 72 h. Finally, the freeze-dried uncrosslinked ceramic nanofiber aerogel was placed in a muffle furnace (air atmosphere) and heated to 1000 °C at a heating rate of 5 °C / min. After holding at this temperature for 1 h, it was cooled to room temperature with the furnace to obtain a ceramic nanofiber aerogel with high compressive strength and low thermal conductivity (zirconium-based ceramic nanofiber aerogel).

[0090] Example 9

[0091] Example 9 is basically the same as Example 1, except that:

[0092] ③ The prepared precursor fiber membrane was placed in a muffle furnace (air atmosphere) and heated to 600℃ at a heating rate of 1℃ / min. After holding at this temperature for 1 hour, the temperature was increased to 1300℃ at a heating rate of 3℃ / min and held for another hour. Then, the temperature was cooled to room temperature with the furnace to obtain a ceramic nanofiber membrane (zirconium-based ceramic nanofiber membrane). The fiber diameter in the prepared ceramic nanofiber membrane was measured to be 800-900 nm. This invention found that when the second calcination temperature is not greater than 1300℃, it has virtually no effect on the fiber diameter in the ceramic nanofiber membrane.

[0093] ④ Four zirconium-based ceramic nanofiber membranes with a thickness of 7 mm were stacked layer by layer in a 2 wt% aluminum dihydrogen phosphate solution and subjected to ultrasonic-assisted impregnation for 6 h. The total mass ratio of the four zirconium-based ceramic nanofiber membranes to the aluminum dihydrogen phosphate solution was 1:45. Subsequently, the four zirconium-based ceramic nanofiber membranes immersed in the aluminum dihydrogen phosphate solution were freeze-dried as a whole for 72 h. Finally, the freeze-dried uncrosslinked ceramic nanofiber aerogel was placed in a muffle furnace (air atmosphere) and heated to 1300 °C at a heating rate of 5 °C / min. After holding at this temperature for 1 h, it was cooled to room temperature with the furnace to obtain a ceramic nanofiber aerogel with high compressive strength and low thermal conductivity (zirconium-based ceramic nanofiber aerogel).

[0094] Example 10

[0095] Example 10 is basically the same as Example 1, except that:

[0096] ③ The prepared precursor fiber membrane was placed in a muffle furnace (air atmosphere) and heated to 600°C at a heating rate of 1°C / min. After holding at this temperature for 1 hour, the temperature was increased to 1500°C at a heating rate of 3°C / min and held for another hour. Then, the temperature was cooled to room temperature with the furnace to obtain a ceramic nanofiber membrane (zirconium-based ceramic nanofiber membrane). In this embodiment, the precursor fiber membrane was finally heated to 1500°C for calcination. The fiber diameter became coarser due to abnormal grain growth. The fiber diameter in the prepared ceramic nanofiber membrane was measured to be greater than 900 nm.

[0097] ④ Four zirconium-based ceramic nanofiber membranes with a thickness of 7 mm were stacked layer by layer in a 2 wt% aluminum dihydrogen phosphate solution and subjected to ultrasonic-assisted impregnation for 6 h. The total mass ratio of the four zirconium-based ceramic nanofiber membranes to the aluminum dihydrogen phosphate solution was 1:45. Subsequently, the four zirconium-based ceramic nanofiber membranes immersed in the aluminum dihydrogen phosphate solution were freeze-dried for 72 h. Finally, the freeze-dried uncrosslinked ceramic nanofiber aerogel was placed in a muffle furnace (air atmosphere) and heated to 1500 °C at a heating rate of 5 °C / min. After holding at this temperature for 1 h, the temperature was cooled to room temperature with the furnace to obtain ceramic nanofiber aerogel (zirconia-based ceramic nanofiber aerogel).

[0098] In this embodiment, the temperature was raised to 1500℃ for calcination. Due to the abnormal growth of the grains, the mechanical properties of the ceramic nanofiber aerogel were affected. Therefore, it was difficult to obtain ceramic nanofiber aerogel with high compressive strength, and the recoverable strain was significantly reduced.

[0099] The XRD patterns of ceramic nanofiber aerogels obtained by calcination at different temperatures in Examples 1, 7-10 of this invention are as follows: Figure 7 As shown; from Figure 7 It can be seen that the third high-temperature calcination temperature of the present invention is 1100-1500℃, which allows zirconium pyrophosphate to be generated in the ceramic nanofiber aerogel. More preferably, the third high-temperature calcination is carried out at 1100-1300℃, which is beneficial for generating more zirconium pyrophosphate. Figure 7 As can be seen, the yttrium component in this invention does not exhibit diffraction peaks because it forms a solid solution with zirconium oxide, which proves that yttrium oxide can effectively stabilize zirconium oxide.

[0100] Example 11

[0101] Example 11 is basically the same as Example 1, except that:

[0102] ④ Four zirconium-based ceramic nanofiber membranes with a thickness of 7 mm were stacked layer by layer in a 2 wt% aluminum dihydrogen phosphate solution and ultrasonically impregnated for 2 h. The total mass ratio of the four zirconium-based ceramic nanofiber membranes to the aluminum dihydrogen phosphate solution was 1:45. Subsequently, the four zirconium-based ceramic nanofiber membranes immersed in the aluminum dihydrogen phosphate solution were freeze-dried for 72 h. Finally, the freeze-dried uncrosslinked ceramic nanofiber aerogel was placed in a muffle furnace (air atmosphere) and heated to 1100 °C at a heating rate of 5 °C / min. After holding at this temperature for 1 h, it was cooled to room temperature with the furnace to obtain a ceramic nanofiber aerogel with high compressive strength and low thermal conductivity (zirconium-based ceramic nanofiber aerogel).

[0103] Comparative Example 1

[0104] ① Dissolve 23.4g of zirconium oxychloride octahydrate and 2.212g of yttrium nitrate hexahydrate in a solvent consisting of 30mL of deionized water and 10mL of anhydrous ethanol. Stir magnetically for 1 hour to ensure complete dissolution and obtain a mixture. Then, slowly add 3.352g of polyvinylpyrrolidone to the mixture and stir magnetically for 12 hours to obtain a ceramic precursor spinning solution.

[0105] ② The ceramic precursor spinning solution was injected into an air-jet spinning device (using a dual-seat coaxial needle with an inner needle of 14G and an outer needle of 21G, wherein the protrusion distance of the inner needle relative to the outer needle is 0.3mm; the ceramic precursor spinning solution was drawn into a 10mL syringe; the syringe was placed on the injection pump; the dual-seat coaxial needle and the syringe were connected by a rubber hose with a Luer connector, and the rotating shaft receiver was fixed) for air-jet spinning to obtain a precursor fiber membrane; during the air-jet spinning process, the gas compressor pump pressure was set to 0.05MPa, the distance between the collector and the coaxial needle was 25cm, the injection rate of the ceramic precursor spinning solution was 3.7mL / h; the air-jet spinning temperature was 25℃, and the air-jet spinning relative humidity was 30%RH.

[0106] ③ The prepared precursor fiber membrane was placed in a muffle furnace (air atmosphere) and heated to 600℃ at a heating rate of 1℃ / min. After holding at this temperature for 1 hour, the temperature was increased to 1100℃ at a heating rate of 3℃ / min and held for another hour. Then, the temperature was cooled to room temperature with the furnace to obtain a ceramic nanofiber membrane (zirconium-based ceramic nanofiber membrane). The fiber diameter in the prepared ceramic nanofiber membrane was measured to be 800-900 nm.

[0107] In this comparative example, without the introduction of aluminum dihydrogen phosphate solution as a binder, the compressive strength of the prepared ceramic nanofiber membrane material at 20% strain was only 0.09 kPa, at 40% strain only 0.68 kPa, at 60% strain only 2.33 kPa, and at 80% strain only 41.9 kPa. In contrast, the ceramic nanofiber aerogel obtained in Example 1 of this invention, after treatment in step ④, exhibited a high compressive strength of 58.6 kPa at 60% strain and a high compressive strength of 310 kPa at 80% strain, significantly improving the compressive strength compared to the ceramic nanofiber membrane material without aluminum dihydrogen phosphate solution treatment. Furthermore, the ceramic nanofiber aerogel obtained by step ④ of Example 1 of the present invention has thermal conductivity of 0.02869 W / (m·K) at 25℃ and 0.07223 W / (m·K) at 800℃. Compared with the thermal conductivity of the ceramic nanofiber membrane material of Comparative Example 1 without aluminum dihydrogen phosphate solution treatment (0.03023 W / (m·K), 25℃; 0.07343 W / (m·K), 800℃), it did not increase but decreased. This shows that the present invention did not impair the excellent thermal insulation performance and high temperature resistance of the ceramic nanofiber membrane material. The ceramic nanofiber aerogel prepared by the present invention improves the strength while reducing the room temperature thermal conductivity and high temperature thermal conductivity, thus improving the thermal insulation performance and temperature resistance of the material.

[0108] Comparative Example 2

[0109] Comparative Example 2 is basically the same as Example 1, except that:

[0110] ④ Four zirconium-based ceramic nanofiber membranes with a thickness of 7 mm were stacked in a 2 wt% aluminum dihydrogen phosphate solution and immersed for 6 h. The total mass ratio of the four zirconium-based ceramic nanofiber membranes to the aluminum dihydrogen phosphate solution was 1:45. Subsequently, the four zirconium-based ceramic nanofiber membranes immersed in the aluminum dihydrogen phosphate solution were freeze-dried for 72 h. Finally, the freeze-dried uncrosslinked ceramic nanofiber aerogel was placed in a muffle furnace (air atmosphere) and heated to 1100 °C at a heating rate of 5 °C / min. After holding at this temperature for 1 h, the aerogel was cooled to room temperature with the furnace to obtain ceramic nanofiber aerogel.

[0111] Comparative Example 3

[0112] ① At room temperature, 1.269 g of aluminum chloride hexahydrate AlCl3·6H2O and 2.665 g of aluminum isopropoxide AIP were dissolved in 30 g of a water / ethanol / acetic acid mixed solvent (the mass ratio of water, ethanol and acetic acid in the mixed solvent was 1:1:0.375), and the mixture was magnetically stirred for 10 h to obtain alumina sol. The alumina sol was mixed with zirconium acetate, and then polyethylene oxide (PEO) was added and magnetically stirred for 8 h to form a spinnable ZrO2-Al2O3 precursor solution. The alumina sol and zirconium acetate were mixed at a molar ratio of aluminum to zirconium of 15:100, and the amount of PEO added was 1% of the mass of the ZrO2-Al2O3 precursor solution.

[0113] ② The ZrO2-Al2O3 precursor solution was electrospun to obtain a precursor fiber membrane. The electrospinning voltage was 25kV, the distance between the nozzle and the receiver was 20cm, the inner diameter of the injection needle was 0.7mm, the injection rate was 4mL / h, the electrospinning temperature was 25℃, and the humidity was 30%.

[0114] ③ The precursor fiber membrane obtained by electrospinning was dried at 80℃ for 2 hours under vacuum and then calcined at 800℃ for 1 hour in an air atmosphere in a muffle furnace to obtain a ZrO2-Al2O3 nanofiber membrane; the fiber diameter in the ZrO2-Al2O3 nanofiber membrane was measured to be 380-740 nm.

[0115] ④ Four ZrO2-Al2O3 nanofiber membranes with a thickness of 7 mm were stacked in a 2 wt% aluminum dihydrogen phosphate solution and immersed for 30 min. The total mass ratio of the four ZrO2-Al2O3 nanofiber membranes to the aluminum dihydrogen phosphate solution was 1:45. Subsequently, the four ZrO2-Al2O3 nanofiber membranes immersed in the aluminum dihydrogen phosphate solution were freeze-dried for 30 h. Finally, the freeze-dried uncrosslinked ceramic nanofiber aerogel was annealed in a vacuum oven at 100 °C for 24 h, and then calcined in a muffle furnace (air atmosphere) at 800 °C for 1 h and then cooled to room temperature with the furnace to obtain ceramic nanofiber aerogel.

[0116] Comparative Example 4

[0117] Comparative Example 4 is basically the same as Comparative Example 3, except that:

[0118] Excluding step ④, what is obtained directly is a ZrO2-Al2O3 nanofiber membrane.

[0119] Comparative Example 5

[0120] Comparative Example 5 is basically the same as Comparative Example 3, except that:

[0121] ③ The precursor fiber membrane obtained by electrospinning was dried at 80℃ for 2 hours under vacuum and then calcined at 1100℃ for 1 hour in an air atmosphere in a muffle furnace to obtain a ZrO2-Al2O3 nanofiber membrane; the fiber diameter in the ZrO2-Al2O3 nanofiber membrane was measured to be 380-740 nm.

[0122] ④ Four ZrO2-Al2O3 nanofiber membranes with a thickness of 7 mm were stacked layer by layer in a 2 wt% aluminum dihydrogen phosphate solution and ultrasonically impregnated for 6 h. The total mass ratio of the four ZrO2-Al2O3 nanofiber membranes to the aluminum dihydrogen phosphate solution was 1:45. Subsequently, the four ZrO2-Al2O3 nanofiber membranes immersed in the aluminum dihydrogen phosphate solution were freeze-dried for 30 h. Finally, the freeze-dried uncrosslinked ceramic nanofiber aerogel was annealed in a vacuum oven at 100 °C for 24 h, and then calcined in a muffle furnace (air atmosphere) at 1100 °C for 1 h and cooled to room temperature with the furnace to obtain ceramic nanofiber aerogel.

[0123] Comparative Example 6

[0124] ① Dissolve 23.4g of zirconium oxychloride octahydrate and 2.212g of yttrium nitrate hexahydrate in a solvent consisting of 30mL of deionized water and 10mL of anhydrous ethanol. Stir magnetically for 1 hour to ensure complete dissolution and obtain a mixture. Then, slowly add 3.352g of polyvinylpyrrolidone to the mixture and stir magnetically for 12 hours to obtain a ceramic precursor spinning solution.

[0125] ② The ceramic precursor spinning solution was electrospun to obtain a precursor fiber membrane; the electrospinning voltage was 30kV, the distance between the nozzle and the receiver was 25cm, the inner diameter of the syringe used was 0.7mm, the injection rate of electrospinning was 2mL / h, the temperature of electrospinning was 25℃, and the relative humidity of electrospinning was 30%.

[0126] ③ The prepared precursor fiber membrane was placed in a muffle furnace (air atmosphere) and heated to 600℃ at a heating rate of 1℃ / min. After holding at this temperature for 1 hour, the temperature was increased to 1100℃ at a heating rate of 3℃ / min and held for another hour. Then, the temperature was cooled to room temperature with the furnace to obtain a ceramic nanofiber membrane (zirconium-based ceramic nanofiber membrane). The fiber diameter in the prepared ceramic nanofiber membrane was measured to be 500-700 nm.

[0127] ④ Four zirconium-based ceramic nanofiber membranes with a thickness of 7 mm were stacked layer by layer in a 2 wt% aluminum dihydrogen phosphate solution and subjected to ultrasonic-assisted impregnation for 6 h. The total mass ratio of the four zirconium-based ceramic nanofiber membranes to the aluminum dihydrogen phosphate solution was 1:45. Subsequently, the four zirconium-based ceramic nanofiber membranes immersed in the aluminum dihydrogen phosphate solution were freeze-dried for 72 h. Finally, the freeze-dried uncrosslinked ceramic nanofiber aerogel was placed in a muffle furnace (air atmosphere) and heated to 1100 °C at a heating rate of 5 °C / min. After holding at this temperature for 1 h, it was cooled to room temperature with the furnace to obtain a ceramic nanofiber aerogel with high compressive strength and low thermal conductivity (zirconium-based ceramic nanofiber aerogel).

[0128] Comparative Example 7

[0129] Comparative Example 7 is basically the same as Example 1, except that:

[0130] ④ Four zirconium-based ceramic nanofiber membranes with a thickness of 7 mm were stacked layer by layer in a 2 wt% silica sol aqueous solution and ultrasonically impregnated for 6 h. The total mass ratio of the four zirconium-based ceramic nanofiber membranes to the silica sol aqueous solution was 1:45. Subsequently, the four zirconium-based ceramic nanofiber membranes immersed in the silica sol aqueous solution were freeze-dried for 72 h. Finally, the freeze-dried uncrosslinked ceramic nanofiber aerogel was placed in a muffle furnace (air atmosphere) and heated to 1100°C at a heating rate of 5°C / min. After holding at this temperature for 1 h, the aerogel was cooled to room temperature with the furnace to obtain ceramic nanofiber aerogel. The 2 wt% silica sol aqueous solution was prepared by mixing silica sol binder and water. The silica sol binder was obtained by mixing tetraethyl orthosilicate, anhydrous oxalic acid, and water in a mass ratio of 100:5:800 and stirring for 8 h.

[0131] The use of silica sol in this comparative example limits the application of aerogel materials in harsh high-temperature environments and makes them difficult to withstand severe mechanical loads or high-temperature thermal shocks.

[0132] The properties of the materials finally obtained in each embodiment and each comparative example were tested, and the results are shown in Table 1.

[0133] Table 1

[0134]

[0135]

[0136] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0137] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a high compressive strength, low thermal conductivity ceramic nanofiber aerogel, characterized by, The method comprises the following steps: (1) air-jet spinning of a ceramic precursor spinning solution to obtain a precursor fiber membrane, and then first high-temperature calcination at 600-800 DEG C and second high-temperature calcination at 1100-1500 DEG C to obtain a ceramic nanofiber membrane; the ceramic precursor in the ceramic precursor spinning solution comprises a zirconium ceramic precursor; (2) layer-by-layer stacking of the ceramic nanofiber membrane in an aluminum dihydrogen phosphate solution, followed by ultrasonic-assisted impregnation, freeze-drying and third high-temperature calcination at 1100-1500 DEG C to obtain a high-compressive-strength low-thermal-conductivity ceramic nanofiber aerogel.

2. The preparation method according to claim 1, characterized in that: the diameter of the ceramic nanofiber in the ceramic nanofiber membrane is 800-900 nm; the total thickness of the ceramic nanofiber aerogel is 4-50 mm; the thickness of a single-layer ceramic nanofiber membrane is 4-10 mm; and / or the number of layers of the ceramic nanofiber membrane subjected to layer-by-layer stacking is 1-10.

3. The preparation method according to claim 1, characterized in that: the ultrasonic-assisted impregnation time is 0.5-6 h.

4. The preparation method according to claim 3, characterized in that: the ultrasonic-assisted impregnation time is 4-6 h.

5. The preparation method according to claim 1, characterized in that: the concentration of the aluminum dihydrogen phosphate solution is 0.5-2 wt%; the mass ratio of all the ceramic nanofiber membranes subjected to layer-by-layer stacking to the aluminum dihydrogen phosphate solution is 1:(30-60); the freeze-drying time is 48-72 h; and / or the first high-temperature calcination, the second high-temperature calcination and / or the third high-temperature calcination time is 1-3 h, and the temperature rising rate to the first high-temperature calcination, the second high-temperature calcination and / or the third high-temperature calcination temperature is 1-5 DEG C / min.

6. The preparation method according to claim 5, characterized in that: the first high-temperature calcination, the second high-temperature calcination and / or the third high-temperature calcination is carried out in an air atmosphere or an oxygen atmosphere.

7. The preparation method according to claim 1, characterized in that: the zirconium ceramic precursor is zirconium oxychloride octahydrate and / or zirconyl nitrate; and / or the ceramic precursor in the ceramic precursor spinning solution further comprises a phase stabilizer and / or a dopant.

8. The preparation method according to claim 7, characterized in that: the phase stabilizer is yttrium nitrate hexahydrate; the dopant is one or more of aluminum chloride hexahydrate, aluminum nitrate nonahydrate, methyl orthosilicate, ethyl orthosilicate or hafnium chloride; and / or the mass ratio of the zirconium ceramic precursor to the phase stabilizer or the dopant is (8-12):

1.

9. The preparation method according to claim 1, characterized in that: the ceramic precursor spinning solution is obtained by uniformly mixing a ceramic precursor, a spinning aid and a solvent, the spinning aid is one or more of polyvinylpyrrolidone, polyvinyl alcohol, polyacrylonitrile or polyvinyl butyral, and the solvent is composed of an organic solvent and water in a volume ratio of 1:(1-3).

10. The preparation method according to claim 9, characterized in that: The organic solvent is one or more of anhydrous ethanol, N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide.

11. The preparation method of claim 9, wherein: The mass fraction of the ceramic precursor in the ceramic precursor spinning solution is 5-50 wt%, and / or the mass fraction of the spinning aid in the ceramic precursor spinning solution is 1-10 wt%.

12. The preparation method of claim 1, wherein: The air pressure of the air jet spinning is 0.03-0.08 MPa, and the injection rate of the ceramic precursor spinning solution is 1-5 mL / h; The receiving distance of the air jet spinning is 15-30 cm, the temperature of the air jet spinning is 20-30℃, and the relative humidity of the air jet spinning is 30-40%; and / or The protruding distance of the inner needle head relative to the outer needle head of the double-needle-base coaxial needle head in the spinning equipment used for the air jet spinning is 0.1-0.5 mm.

13. High-compression-strength low-thermal-conductivity ceramic nanofiber aerogel prepared by the preparation method of any one of claims 1-12.

14. The high-compression-strength low-thermal-conductivity ceramic nanofiber aerogel of claim 13, wherein: Zirconium pyrophosphate is generated in the high-compression-strength low-thermal-conductivity ceramic nanofiber aerogel; The apparent density of the high compression strength and low thermal conductivity ceramic nanofiber aerogel is 20-100 mg / cm 3 The reversible compression strain is up to 90%, the compression can be recycled at-196 DEG C to 1300 DEG C, the compression strength at 80% strain is not less than 310 kPa, the compression strength at 90% strain is not less than 1100 kPa, the thermal conductivity at 25 DEG C is not more than 0.02869 W / (m.K), the thermal conductivity at 800 DEG C is not more than 0.07223 W / (m.K); and / or The thermal conductivity of the high-compression-strength low-thermal-conductivity ceramic nanofiber aerogel is less than the thermal conductivity of the ceramic nanofiber membrane.

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