Heat-insulating and high-temperature-resistant mullite fiber aerogel and preparation method thereof

Abstract

The invention provides heat-insulating and high-temperature-resistant mullite fiber aerogel and a preparation method thereof, the mullite fiber aerogel is composed of single-crystal mullite nanowires, and the porosity of the mullite fiber aerogel is gt; the length of the mullite nanowires in the mullite fiber aerogel is 1-50 microns, and the diameter of the mullite nanowires in the mullite fiber aerogel is 30-800 nm; and no high-temperature bonding phase exists at the overlapping points among the mullite nanowires. The mullite fiber aerogel is formed by taking an aluminum silicate fiber felt as a main template frame, carrying out surface pretreatment, completely converting aluminum silicate fibers into single crystal mullite nanowires through twice impregnation, normal-pressure drying and calcination under the action of a catalyst, and then carrying out self-assembly. The mullite nanowires are autonomously lapped, wound and pinned to form a continuous three-dimensional network structure, and no high-temperature bonding glass phase exists at the joints of the nanowires, so that the high-temperature use performance of the mullite fiber aerogel is remarkably improved, and the mullite fiber aerogel has the characteristics of high porosity, low thermal conductivity, high structural stability and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of artificial synthetic ceramic phases, in particular to a heat-insulating and high-temperature-resistant mullite fiber aerogel and a preparation method thereof. Background Art

[0002] Mullite fiber aerogels, due to their high-temperature resistance, low thermal conductivity, and excellent structural stability, are widely used in the field of high-temperature ceramic thermal insulation. They play a particularly important role in thermal protection systems (TPS) used in aerospace vehicles, hypersonic vehicles, and weaponry. However, because the mullite fibers used are mostly composed of microcrystalline, amorphous, or mullite precursor phases, these fibers often experience brittle fracture due to grain growth at temperatures above 1200°C. Even commercially available products such as 3M Nextel 720, CeraFib 75, and Sumitomo Altex suffer from the same problem. In recent years, in order to meet the high Mach number and long cruise requirements of new missiles and aircraft, the thermal insulation materials used in TPS must be able to isolate external heat from entering the aircraft body in high-temperature environments above 1500°C, while ensuring that the material does not suffer structural damage.

[0003] To address this issue, the method used to improve the high-temperature performance of mullite fiber materials is usually to add certain impurity atoms to control the grain size, thereby inhibiting grain growth in the mullite fiber. Because this method does not fundamentally change the fiber's polycrystalline or amorphous properties, when the material is subjected to continuous high energy input, the increase in grain size will still cause fiber breakage.

[0004] In view of this, it is necessary to develop a mullite fiber material with intrinsic high-temperature stability, high porosity, low thermal conductivity, and strong structural stability to fundamentally solve the problems of grain coarsening and fiber breakage caused by the polycrystalline or amorphous properties of mullite fiber. Summary of the Invention

[0005] The present application is to solve the problem of poor structural stability at high temperature, easy grain coarsening and fiber fracture of polycrystalline or amorphous mullite fiber, and proposes to prepare a high porosity fiber aerogel constructed by single crystal mullite nanowires. Unlike the traditional method of growing single crystal mullite fibers from aluminum silicate high temperature melt, the present application has high production efficiency and low energy consumption; at the same time, it does not need to go through the fiber dispersion process involved in the traditional preparation of aerogel (vacuum forming method, gel injection molding combined with freeze drying, additive manufacturing, etc.), simplifying the production process and shortening the product preparation cycle. The present application directly uses aluminum silicate fiber as the matrix frame material, utilizes the characteristic that mullite can grow along the c-axis in different directions under the action of a catalyst, and converts all micron fibers into mullite nanowires by a synergistic catalytic method. A mullite fiber aerogel and a preparation method thereof are obtained, which have high temperature resistance, light weight, high porosity, low thermal conductivity, and can be used at 1500 DEG C or above.

[0006] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0007] The present application provides a preparation method of a heat-insulating and high-temperature-resistant mullite fiber aerogel, comprising the following steps:

[0008] S1: impregnation and drying: the pretreated and activated aluminum silicate fiber felt is impregnated and dried once with modified sol A, and then impregnated and dried twice with solution B to obtain modified aluminum silicate fiber felt;

[0009] The modified sol A comprises silica sol and soluble aluminum salt; and the solution B comprises ammonium fluoride and ammonium molybdate;

[0010] The molar concentration ratio of aluminum atoms in the soluble aluminum salt, silicon atoms in the silica sol, fluorine atoms in the ammonium fluoride, and molybdenum atoms in the ammonium molybdate is 3:1:(1.2-2.5):(0.12-0.35);

[0011] S2: catalytic calcination of the modified aluminum silicate fiber felt: the modified aluminum silicate fiber felt obtained in S1 is calcined once, and the temperature of the first calcination is 900-1200 DEG C;

[0012] S3: post heat treatment step: the obtained mullite fiber aerogel is calcined twice, and the temperature of the second calcination is greater than or equal to 1250 DEG C.

[0013] As a further solution, the method for surface pretreatment and activation of the aluminum silicate fiber felt in S1 is: the aluminum silicate fiber felt is soaked in an acid solution or an alkali solution and ultrasonically treated, then the aluminum silicate fiber felt is rinsed with deionized water, and after rinsing, the aluminum silicate fiber felt is dried to obtain the pretreated aluminum silicate fiber felt.

[0014] As a further solution, the porosity of the aluminum silicate fiber felt in S1 is greater than 95%.

[0015] As a further preferred solution, the pH value of the acid solution is 2.0-4.0, and the pH value of the alkaline solution is 8.0-10.0.

[0016] As a further preferred solution, the S1 is immersed in an acid solution with a pH value of 2.0 to 4.0 for ultrasonic treatment.

[0017] As a further solution, the acid solution in S1 is one or more of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, and acetic acid solution.

[0018] As a further solution, the alkaline solution in S1 is one or more of potassium hydroxide solution or sodium hydroxide solution.

[0019] As a further solution, the ultrasonic treatment time in S1 is 10 to 30 minutes.

[0020] As a further solution, the drying temperature in the surface pretreatment activation method of the aluminum silicate fiber felt in S1 is 60-80° C., and the drying time is 18-30 hours.

[0021] As a further solution, the solvents of the modified sol A and solution B in S1 are both deionized water.

[0022] As a further solution, the soluble aluminum salt in S1 is one of aluminum chloride, aluminum sulfate, and aluminum nitrate.

[0023] As a further solution, the time for the first immersion in S1 is 30 to 60 minutes; the temperature for the first drying in S1 is controlled at 50 to 120° C., and the time for the first drying is 6 to 12 hours.

[0024] As a further solution, the secondary immersion time in S1 is 30 to 60 minutes; the temperature of the secondary drying in S1 is controlled at 50 to 120° C., and the secondary drying time is 6 to 12 hours.

[0025] As a further solution, in S2, the holding time of the first calcination is 2 to 6 hours, and the heating rate is 2 to 5°C / min.

[0026] As a further solution, in S3, the holding time of the secondary calcination is 30 to 60 minutes, and the heating rate is 1 to 3°C / min.

[0027] The present invention provides a heat-insulating and high-temperature-resistant mullite fiber aerogel. The mullite fiber aerogel is composed of single-crystal mullite nanowires. The porosity of the mullite fiber aerogel is greater than 95%. The length of the mullite nanowires in the mullite fiber aerogel is 1 to 50 μm, the diameter is 30 to 800 nm, and there is no high-temperature bonding phase at the overlapping points between the mullite nanowires. The main components of the mullite fiber aerogel are Al2O3 and SiO2.

[0028] As a further solution, the thermal conductivity of the heat-insulating and high-temperature-resistant mullite fiber aerogel at room temperature is ≥0.0424 W / (m·K).

[0029] As a further solution, the thermal conductivity of the heat-insulating and high-temperature-resistant mullite fiber aerogel at a high temperature of 1000 to 1500° C. is 0.12 to 0.20 W / (m·k).

[0030] As a further solution, the volume density of the heat-insulating and high-temperature resistant mullite fiber aerogel is 0.15 to 0.17 g / cm 3 .

[0031] As a further solution, the heat-insulating and high-temperature resistant mullite fiber aerogel has a compressive strength of ≥0.16 at 10% strain.

[0032] MPa, dimensional shrinkage before and after heat treatment at 1500-1700℃ is 0.2-1.5%, and strength retention rate is ≥90%.

[0033] The characteristics and beneficial effects of the present invention are:

[0034] The present application directly uses the aluminum silicate fiber felt with porosity greater than 95% as a matrix template material, and through the ammonium fluoride and ammonium molybdate synergistic catalysis process, the low-temperature and high-efficiency complete conversion from micron fibers to mullite nanowires is completed. On the one hand, the existing catalytic preparation method is difficult to meet the needs of low-temperature generation of large aspect ratio mullite and complete consumption of micron fibers, because the existing technology has not enough driving force to completely consume micron fibers at low temperature, and at a higher catalytic temperature, in addition to affecting the aspect ratio of the whisker, the rapid nucleation rate will also increase the internal defects of the whisker. The present application is different from the multi-process preparation process of traditional fiber aerogel, and can directly construct a three-dimensional network structure through an in-situ nanowire self-assembly process, which realizes the self-lapping, winding and pinning of nanowires. On the other hand, since there is no glass phase for "welding" at the lapping points in the nanofiber block, the material can have sufficient high-temperature use stability. This is due to the unique structure of the full single crystal nanowire, which effectively avoids the structural failure problem of traditional oxide fibers caused by grain growth at high temperature, so that the oxide fibers still have good structural stability at 1700 DEG C, breaking through the structural damage of oxide fibers caused by grain coarsening at >= 1200 DEG C, because the main way to damage the fiber at high temperature is to change the strong chemical bond between atoms rather than the traditional grain fracture of oxide fibers.

[0035] In addition, it is worth noting that the preparation method has the advantages of process simplification and molding flexibility, avoids the most difficult fiber dispersion in traditional processes such as additive manufacturing (i.e. 3D printing), mechanical processing, injection molding, etc., shortens the preparation period, and can customize the fiber felt size as a template according to the needs, and efficiently calcine the complex ceramic components. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0037] Figure 1 Figure 1 is a schematic diagram of the preparation process of mullite fiber aerogel.

[0038] Figure 1 Figure 1(a) is a schematic diagram of the aluminum silicate fiber felt;

[0039] Figure 1 Figure 1(b) is a schematic diagram of the aluminum silicate fiber felt 1 after the S1 step;

[0040] Figure 1Fig. 3 is a schematic diagram of the fiber aerogel composed of single-crystal mullite nanowires 2 after the S1-S2 steps;

[0041] Figure 1 Fig. 4 is a schematic diagram of the fiber grain growth 3 of the common alumino-silicate fiber felt after "1500°C calcination".

[0042] Figure 2 Fig. 5 is a scanning electron microscope image of the mullite fiber aerogel prepared in Example 1.

[0043] Figure 3 Fig. 6 is a transmission electron microscope image of the single-crystal mullite nanowires of Example 1.

[0044] Figure 4 Fig. 7 is an XRD pattern of the mullite fiber aerogel prepared in Example 2.

[0045] Figure 5 Fig. 8 is a stress-strain curve of the mullite fiber aerogel prepared in Example 2.

[0046] Figure 6 Fig. 9 is the thermal conductivity at room temperature of the mullite fiber aerogels prepared at different catalytic temperatures.

[0047] Figure 7 Fig. 10 is a scanning electron microscope image of the mullite fiber aerogel prepared in Examples 1-3 after different post-heat treatment temperatures.

[0048] Figure 8 Fig. 11 is the thermal conductivity at high temperature of the mullite fiber aerogel prepared in Example 3 at 1000°C, 1200°C, and 1500°C.

[0049] Figure 9 Fig. 12 is a scanning electron microscope image of the porous mullite fiber ceramic bulk prepared in Comparative Example 1;

[0050] Figure 9 Fig. 13 is a scanning electron microscope image of the porous mullite fiber ceramic bulk of Comparative Example 1 with an atomic ratio of Al:Si:F of 3:1:0.6 in the sol;

[0051] Figure 9 Fig. 14 is a scanning electron microscope image of the porous mullite fiber ceramic bulk of Comparative Example 1 with an atomic ratio of Al:Si:F of 3:1:1.2 in the sol;

[0052] Figure 9 Fig. 15 is a scanning electron microscope image of the porous mullite fiber ceramic bulk of Comparative Example 1 with an atomic ratio of Al:Si:F of 3:1:1.8 in the sol;

[0053] Figure 9(d) is a scanning electron microscope image of a porous mullite fiber ceramic block in which the atomic ratio of Al:Si:F in the sol of Comparative Example 1 is 3:1:2.5.

[0054] Figure 10 This is a scanning electron microscope image of the porous mullite fiber ceramic block prepared in Comparative Example 2;

[0055] Figure 10 (a) is a scanning electron microscope image of a porous mullite fiber ceramic block having an atomic ratio of Al:Si:F of 3:1:0.6 in the sol of Comparative Example 2;

[0056] Figure 10 (b) is a scanning electron microscope image of a porous mullite fiber ceramic block having an atomic ratio of Al:Si:F of 3:1:1.2 in the sol of Comparative Example 2;

[0057] Figure 10 (c) is a scanning electron microscope image of a porous mullite fiber ceramic block having an Al:Si:F atomic ratio of 3:1:1.8 in the sol of Comparative Example 2;

[0058] Figure 10 (d) is a scanning electron microscope image of a porous mullite fiber ceramic block in which the atomic ratio of Al:Si:F in the sol of Comparative Example 2 is 3:1:2.5.

[0059] Figure 11 This is a scanning electron microscope image of the porous mullite fiber ceramic block prepared in Comparative Example 3;

[0060] Figure 11 (a) is a scanning electron microscope image of a porous mullite fiber ceramic block having an Al:Si:Mo atomic ratio of 3:1:0.13 in the sol of Comparative Example 3;

[0061] Figure 11 (b) is a scanning electron microscope image of a porous mullite fiber ceramic block having an Al:Si:Mo atomic ratio of 3:1:0.25 in the sol of Comparative Example 3;

[0062] Figure 11 (c) is a scanning electron microscope image of a porous mullite fiber ceramic block having an Al:Si:Mo atomic ratio of 3:1:0.50 in the sol of Comparative Example 3;

[0063] Figure 11 (d) is a scanning electron microscope image of a porous mullite fiber ceramic block having an atomic ratio of Al:Si:Mo of 3:1:1.0 in the sol of Comparative Example 3.

[0064] Figure 12This is a scanning electron microscope image of the porous mullite fiber ceramic block prepared in Comparative Example 4.

[0065] Figure 13 This is a scanning electron microscope image of the porous mullite fiber ceramic block prepared in Comparative Example 5.

[0066] Figure 14 This is the formable complex and special-shaped ceramic component prepared in Example 1. DETAILED DESCRIPTION

[0067] In order to facilitate understanding of the present invention, the present invention will be described in more detail below, and embodiments of the present invention are given, but the scope of the present invention is not limited thereby.

[0068] To address the poor structural stability, grain coarsening, and fiber breakage of polycrystalline or amorphous mullite fibers at high temperatures, this invention proposes a high-porosity fiber aerogel constructed from single-crystal mullite nanowires. Unlike conventional methods for growing single-crystal mullite fibers from high-temperature aluminosilicate melts, this method offers extremely high production efficiency and low energy consumption. Furthermore, it eliminates the fiber dispersion processes typically required for aerogel production (vacuum forming, gel-casting combined with freeze-drying, additive manufacturing, etc.), streamlining the production process and shortening the product's production cycle. This invention directly utilizes aluminosilicate fibers as the matrix framework material and, leveraging the ability of mullite to grow anisotropically along the c-axis under the action of a catalyst, employs a synergistic catalytic method to convert all micronized fibers into mullite nanowires. The result is a mullite fiber aerogel that combines high temperature resistance, lightweight, high porosity, and low thermal conductivity, suitable for use above 1500°C, and its preparation method.

[0069] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0070] The present invention provides a method for preparing a heat-insulating and high-temperature-resistant mullite fiber aerogel, comprising the following steps:

[0071] S1: Impregnation and drying: The pre-treated activated aluminum silicate fiber felt is impregnated with modified sol A once and dried once; then impregnated with solution B twice and dried twice to obtain the modified aluminum silicate fiber felt;

[0072] The modified sol A includes silica sol and soluble aluminum salt; the solution B includes ammonium fluoride and ammonium molybdate;

[0073] The molar concentration ratio of the aluminum atoms in the soluble aluminum salt, the silicon atoms in the silica sol, the fluorine atoms in the ammonium fluoride, and the molybdenum atoms in the ammonium molybdate is 3:1:(1.2-2.5):(0.12-0.35);

[0074] S2: catalytic calcination of the modified aluminum silicate fiber felt: calcining the modified aluminum silicate fiber felt obtained in S1 once, wherein the temperature range of the first calcination is 900-1200° C.;

[0075] S3: Post-heat treatment step: performing secondary calcination on the obtained mullite fiber aerogel, wherein the temperature of the secondary calcination is ≥1250°C.

[0076] To address the problems of poor structural stability, grain coarsening, and fiber breakage at high temperatures in polycrystalline or amorphous mullite fibers, the present invention employs a modified sol A and solution B for two separate impregnation and drying steps. By utilizing the characteristic of mullite's ability to grow anisotropically along the c-axis under the action of a catalyst, a synergistic catalytic method is employed to convert all micronized fibers into mullite nanowires. The four atoms in the modified sol A and solution B complement each other to achieve a favorable reaction-driving effect. This achieves reasonable coordination from both temporal and spatial perspectives, effectively controlling the consumption of the aluminum silicate fiber mat while ensuring sufficient and timely formation of the target product and suppressing the formation of impurities. Furthermore, the invention drives the alignment of single-crystalline mullite nanowires along the c-axis, allowing the crystal nuclei to grow well after the aluminum silicate fiber mat is consumed. This results in a mullite fiber aerogel having high temperature resistance, light weight, high porosity, and low thermal conductivity, and the ability to maintain an extremely low thermal conductivity in ultra-high temperature environments exceeding 1500°C, with strong thermal insulation properties, and a preparation method thereof.

[0077] In the present invention, the molar concentration ratios of aluminum atoms in soluble aluminum salts, silicon atoms in silica sol, fluorine atoms in ammonium fluoride, and molybdenum atoms in ammonium molybdate are set within a specific range, which directly affects the efficiency of mullite crystal formation, the quality of nanowire directional growth, and the performance of the final product: on the one hand, the stoichiometric ratio of aluminum atoms and silicon atoms in mullite is strictly matched to ensure sufficient supply of aluminum oxide and silicon oxide units during lattice growth, thereby avoiding the formation of amorphous phase or impurity phase. At the same time, the reasonable ratio of fluorine atoms and molybdenum atoms ensures sufficient F -Erosion of the amorphous silicon-aluminum layer of the aluminum silicate fiber mat releases active SiO2 / Al2O3, promoting mullite nucleation. Below a certain molar ratio, insufficient etching of the aluminum silicate fiber mat will hinder the conversion of micronized fibers to nanowires. This also prevents excessive etching, which can lead to rapid and excessive destruction of the fiber skeleton structure and collapse of the aerogel network. Ensuring sufficient MoO3 generated by the thermal decomposition of ammonium molybdate forms a liquid and vapor transport environment, effectively lowering the mullite nucleation energy barrier and driving atomic alignment along the mullite c-axis. Setting the molar concentration ratios of aluminum atoms in the soluble aluminum salt, silicon atoms in the silica sol, fluorine atoms in ammonium fluoride, and molybdenum atoms in ammonium molybdate within a specific range guides the consumption of the aluminum silicate fiber mat while achieving the timely and directional growth of mullite nanowires on the surface, ultimately converting the micronized fibers to mullite nanowires. The concentration ratios of the four atoms provide an important reaction kinetic foundation for the directional and complete conversion of mullite nanowires. In addition, the present invention also adopts a strategy of two-stage impregnation and two-stage calcination. Under this strategy, the distribution state and reaction process of the reactants in the aluminum silicate fiber felt are finely controlled, effectively overcoming the problems of high concentration instability of multiple atomic solutions, uneven penetration of reactants, local concentration imbalance and reaction kinetic limitations in a single treatment, thereby further improving the overall conversion efficiency and uniformity, and can further improve the efficiency of converting all micron fibers into mullite nanowires.

[0078] As a further example, the surface pretreatment method of the aluminum silicate fiber felt in S1 is: immersing the aluminum silicate fiber felt in an acid solution or an alkaline solution for ultrasonic treatment, then rinsing the aluminum silicate fiber felt with deionized water, and drying after rinsing to obtain the pretreated aluminum silicate fiber felt.

[0079] The present invention can further remove loose impurities on the surface through the acid-base etching action of S1, while achieving the purpose of increasing fiber surface defects and improving reaction activity.

[0080] As a further example, the porosity of the aluminum silicate fiber felt in S1 is >95%.

[0081] As a further preferred example, the pH value of the acid solution is 2.0-4.0, and the pH value of the alkaline solution is 8.0-10.0.

[0082] As a further preferred example, the S1 is immersed in an acid solution with a pH value of 2.0 to 4.0 for ultrasonic treatment.

[0083] This may be because the impurities in the aluminum silicate fiber felt are more easily dissolved under acidic conditions, and at the same time, the defects of SiO2 and Al2O3 skeletons may be more in weak acid.

[0084] As a further example, the acid solution in S1 is one or more of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, and acetic acid solution.

[0085] As a further example, the alkaline solution in S1 is one or more of potassium hydroxide solution or sodium hydroxide solution.

[0086] As a further example, the ultrasonic treatment time in S1 is 10 to 30 minutes.

[0087] As a further example, in the surface pretreatment activation method of the aluminum silicate fiber felt in S1, the drying temperature is 60 to 80° C., and the drying time is 18 to 30 hours.

[0088] As a further example, the solvents of the modified sol A and solution B in S1 are both deionized water.

[0089] As a further example, the soluble aluminum salt in S1 is one of aluminum chloride, aluminum sulfate, and aluminum nitrate.

[0090] As a further example, the time for the first immersion in S1 is 30 to 60 minutes; the temperature for the first drying in S1 is controlled at 50 to 120° C., and the time for the first drying is 6 to 12 hours.

[0091] As a further example, the secondary immersion time in S1 is 30 to 60 minutes; the temperature of the secondary drying in S1 is controlled at 50 to 120° C., and the secondary drying time is 6 to 12 hours.

[0092] The strategy of double impregnation was adopted, and the time of the two impregnations as well as the temperature and time of drying were optimized. At this time, the modified sol A had sufficient time to preferentially build a uniform Si-Al layer on the fiber surface, forming a -Si-O-Al- network, providing a local reaction environment with a stoichiometric ratio matching for the mullite crystal nucleus. In the second impregnation solution B, ammonium fluoride was used as a crystal phase orientation inducer. - The amorphous silicon aluminum layer is corroded to release active SiO2 and Al2O3 components. The MoO3 generated by the decomposition of ammonium molybdate acts as a liquid and gas phase transport catalyst, reducing the lattice energy of mullite and promoting the preferential arrangement of atoms along the c-axis. The above strategy avoids the problem of coagulation caused by directly mixing soluble aluminum salts, silica sol, ammonium fluoride, and ammonium molybdate at a high concentration ratio, which is not conducive to better fixation or deposition of the catalyst on the fiber surface under impregnation. This scheme promotes the formation of mullite phase, stabilizes the network structure of nanowire aerogel, removes possible residual impurities, and achieves complete consumption of the original aluminum silicate fiber, further improving the growth rate of mullite nanowires and enhancing the high-temperature stability of mullite fiber aerogel.

[0093] As a further example, in S2, the holding time of the primary calcination is 2 to 6 hours, and the heating rate is 2 to 5°C / min.

[0094] As a further example, in S3, the holding time of the secondary calcination is 30 to 60 minutes, and the heating rate is 1 to 3°C / min.

[0095] The present invention also adopts a secondary calcination process, and optimizes the holding time and heating rate of the secondary calcination. In the first calcination, at a lower calcination temperature, the HF generated by the decomposition of ammonium fluoride etches the fiber surface to release active silicon and aluminum components. At the same time, the MoO3 generated by the pyrolysis of ammonium molybdate acts as a liquid and gas phase transport catalyst, reducing the nucleation energy barrier of mullite and driving the directional growth along the c-axis into single crystal nanowires; the secondary calcination adopts a higher calcination temperature to eliminate residual fluorine / molybdenum impurities, repair lattice defects, and promote surface diffusion sintering of adjacent nanowires at the nodes to form coherent grain boundary bridges, ultimately obtaining a single crystal mullite nanowire aerogel with intrinsic high temperature resistance, maintaining ultra-low thermal conductivity and high strength at high temperatures, while greatly reducing energy consumption in the preparation process. The heat-insulating and high-temperature resistant mullite fiber aerogel obtained at this time has a lower thermal conductivity of 0.12 to 0.20 W / (m·k) at high temperatures of 1000 to 1500°C, and a higher strength retention rate of ≥90%.

[0096] The present invention also provides a method for preparing a heat-insulating, high-temperature-resistant mullite fiber aerogel. The prepared heat-insulating, high-temperature-resistant mullite fiber aerogel comprises single-crystalline mullite nanowires. The porosity of the mullite fiber aerogel is greater than 95%. The mullite nanowires in the mullite fiber aerogel have a length of 1 to 50 μm and a diameter of 30 to 800 nm. There is no high-temperature bonding phase at the junctions between the mullite nanowires. The main components of the mullite fiber aerogel are Al2O3 and SiO2.

[0097] As a further example, the thermal conductivity of the heat-insulating and high-temperature-resistant mullite fiber aerogel at room temperature is ≥0.0424 W / (m·K).

[0098] As a further example, the thermal conductivity of the heat-insulating and high-temperature-resistant mullite fiber aerogel at a high temperature of 1000 to 1500° C. is 0.12 to 0.20 W / (m·k).

[0099] As a further example, the bulk density of the heat-insulating and high-temperature-resistant mullite fiber aerogel is 0.15 to 0.17 g / cm 3 .

[0100] As a further example, the heat-insulating and high-temperature-resistant mullite fiber aerogel has a compressive strength of ≥0.16 MPa at 10% strain, a dimensional shrinkage of 0.2-1.5% before and after heat treatment at 1500-1700° C., and a strength retention rate of ≥90%.

[0101] In order to facilitate understanding of the present invention, the present invention will be described in more detail below, and embodiments of the present invention are given, but the scope of the present invention is not limited thereby.

[0102] Example 1:

[0103] The preparation method of mullite fiber aerogel may include the following steps:

[0104] Step 1: Immerse the aluminum silicate fiber felt with a porosity greater than 95% in a hydrochloric acid solution with a pH of 3.0 and ultrasonically treat it for 20 minutes. Then, rinse the aluminum silicate fiber felt with deionized water and dry it at 70° C. for 24 hours.

[0105] Step 2: Prepare modified sol A and solution B. The modified sol A is a mixture of silica sol and aluminum chloride; the solution B is a mixture of ammonium fluoride and ammonium molybdate; the molar concentration ratio of aluminum atoms in the aluminum chloride, silicon atoms in the silica sol, fluorine atoms in the ammonium fluoride, and molybdenum atoms in the ammonium molybdate is 3:1:1.8:0.26.

[0106] Step 3: Fiber mat primary impregnation and atmospheric pressure drying. The aluminum silicate fiber mat obtained in step 1 is placed in a vacuum impregnation device, and the modified sol A is loaded onto the fiber surface using vacuum. The impregnation time is 45 minutes. It is then dried under atmospheric pressure at a temperature of 85°C for 9 hours.

[0107] Step 4: Secondary impregnation of fiber mat and drying at normal pressure: The aluminum silicate fiber mat obtained in step 3 was placed in a vacuum impregnation device, and the solution B was loaded onto the fiber surface using vacuum for 45 minutes; then, it was dried at normal pressure with the drying temperature controlled at 85°C for 9 hours.

[0108] Step 5: Catalytic calcination of the modified fiber felt. The modified aluminum silicate fiber felt obtained in step 4 was calcined in a muffle furnace at 900°C for 2 hours at a heating rate of 3°C / min to obtain mullite fiber aerogel.

[0109] Step 6: Post-heat treatment step: The obtained mullite fiber aerogel was subjected to secondary calcination at 1500° C., with a heating rate of 2° C. / min and a holding time of 30 min.

[0110] according to Figure 1The technical indicators of the prepared mullite fiber aerogel are: porosity 95.2%, thermal conductivity coefficient at room temperature 0.0424W / (m·k), volume density 0.15g / cm 3 The compressive strength at 10% strain was 0.163 MPa, and the dimensional shrinkage before and after heat treatment at 1500°C was 0.2-0.3%. After heat treatment, the aerogel microstructure remained stable, with a strength retention rate of 97%. The original aluminum silicate fibers were completely consumed, and the mullite nanowires ranged in length from 1 to 50 μm and in diameter from 30 to 500 nm. Figure 14 What is shown is the formable complex and special-shaped ceramic component prepared in Example 1.

[0111] Depend on Figure 2 It can be seen that the single crystal mullite nanowires in the mullite fiber aerogel prepared in Example 1 are well developed, all the micron fibers are converted into mullite nanowires, and there is no impurity phase. No "welded" glass phase is formed at the overlap points in the nanofiber blocks, ensuring that the material has sufficient high-temperature stability.

[0112] Depend on Figure 3 It can be seen that the diameter of the mullite nanowires in the mullite fiber aerogel in Example 1 is 36.5 nm, the crystal phase grows along the

[001] direction, and the spacing on the (001) crystal plane is The spacing on the (110) plane is This indicates that single-crystalline mullite nanowires are formed.

[0113] Example 2:

[0114] The preparation method of mullite fiber aerogel may include the following steps:

[0115] Step 1: Immerse the aluminum silicate fiber felt with a porosity greater than 95% in a hydrochloric acid solution with a pH of 3.0 and ultrasonically treat it for 20 minutes. Then, rinse the aluminum silicate fiber felt with deionized water and dry it at 70° C. for 24 hours.

[0116] Step 2: Prepare modified sol A and solution B. Sol A is a mixture of silica sol and aluminum sulfate; solution B is a mixture of ammonium fluoride and ammonium molybdate; the molar concentration ratio of aluminum atoms in the aluminum sulfate, silicon atoms in the silica sol, fluorine atoms in the ammonium fluoride, and molybdenum atoms in the ammonium molybdate is 3:1:2.5:0.12.

[0117] Step 3: Fiber mat primary impregnation and atmospheric pressure drying. The aluminum silicate fiber mat obtained in step 1 is placed in a vacuum impregnation device, and the sol A is loaded onto the fiber surface using vacuum. The impregnation time is 45 minutes. It is then dried under atmospheric pressure at a temperature of 85°C for 9 hours.

[0118] Step 4: Secondary impregnation of fiber mat and atmospheric pressure drying: Place the aluminum silicate fiber mat prepared in step 3 in a vacuum impregnation device and use vacuum to load the solution B onto the fiber surface for 45 minutes. Then, dry the fiber mat under atmospheric pressure at a temperature of 85°C for 9 hours.

[0119] Step 5: Catalytic calcination of the modified fiber felt: The aluminum silicate fiber felt obtained in step 4 was calcined in a muffle furnace at 1200° C. for 2 h at a heating rate of 3° C. / min to obtain mullite fiber aerogel.

[0120] Step 6: Post-heat treatment step: The obtained mullite fiber aerogel was subjected to secondary calcination at 1600° C., with a heating rate of 2° C. / min and a holding time of 30 min.

[0121] The technical indicators of the mullite fiber aerogel prepared in this embodiment are: porosity 95.1%, thermal conductivity at room temperature 0.066W / (m·k), and volume density 0.17g / cm 3 The compressive strength at 10% strain was 0.176 MPa, and the dimensional shrinkage before and after heat treatment at 1600°C was 0.4-0.5%. After heat treatment, the aerogel microstructure remained stable, with a strength retention rate of 90%. The original aluminum silicate fibers were completely consumed, and the mullite nanowires had lengths of 1-20 μm and diameters of 60-800 nm. Furthermore, the aerogel microstructure remained stable after heat treatment.

[0122] Depend on Figure 4 It can be seen from the X-ray diffraction pattern of the mullite fiber aerogel prepared in Example 2 that the mullite fiber aerogel prepared in Example 2 has the same sharp peaks as the standard card, without any other impurities, and has high phase purity. All diffraction peaks come from mullite crystals, which is consistent with the standard card JCPDS No.15-0776.

[0123] Depend on Figure 5 It can be seen from the stress-strain curve of the mullite fiber aerogel prepared in Example 2 that the compressive strength of the heat-insulating and high-temperature resistant mullite fiber aerogel at 10% strain is ≥0.16 MPa, and the material has strong compressive resistance and structural stability.

[0124] Example 3:

[0125] The preparation method of mullite fiber aerogel may include the following steps:

[0126] Step 1: Immerse the aluminum silicate fiber felt with a porosity greater than 95% in a potassium hydroxide solution with a pH of 9.0 for 20 minutes, then rinse the fiber felt with deionized water and dry it at 70° C. for 24 hours.

[0127] Step 2: Prepare modified sol A and solution B. Sol A is a mixture of silica sol and aluminum nitrate; solution B is a mixture of ammonium fluoride and ammonium molybdate; the molar concentration ratio of aluminum atoms in the aluminum nitrate, silicon atoms in the silica sol, fluorine atoms in the ammonium fluoride, and molybdenum atoms in the ammonium molybdate is 3:1:1.2:0.35.

[0128] Step 3: Fiber mat primary impregnation and atmospheric pressure drying. The aluminum silicate fiber mat obtained in step 1 is placed in a vacuum impregnation device, and the sol A is loaded onto the fiber surface using vacuum. The impregnation time is 45 minutes. It is then dried under atmospheric pressure at a temperature of 85°C for 9 hours.

[0129] Step 4: Secondary impregnation of fiber mat and atmospheric pressure drying: Place the aluminum silicate fiber mat prepared in step 3 in a vacuum impregnation device and use vacuum to load the solution B onto the fiber surface for 45 minutes. Then, dry the fiber mat under atmospheric pressure at a temperature of 85°C for 9 hours.

[0130] Step 5: Catalytic calcination of the modified fiber felt: The aluminum silicate fiber felt obtained in step 4 was calcined in a muffle furnace at 1100° C. for 2 h at a heating rate of 3° C. / min to obtain mullite fiber aerogel.

[0131] Step 6: Post-heat treatment step: The obtained mullite fiber aerogel was subjected to secondary calcination at 1700° C., with a heating rate of 2° C. / min and a holding time of 30 min.

[0132] The technical indicators of the mullite fiber aerogel prepared in this embodiment are: porosity 95.1%, thermal conductivity at room temperature 0.055W / (m·k), thermal conductivity at high temperature of 1000-1500°C as shown in FIG. Figure 8 The value is shown to be in the range of 0.12 to 0.20 W / (m·k), which shows that at higher temperatures, the present invention can achieve a lower thermal conductivity and have excellent thermal insulation performance. The volume density of the mullite fiber aerogel prepared in this embodiment is 0.16 g / cm 3 The compressive strength at 10% strain was 0.186 MPa, and the dimensional shrinkage before and after heat treatment at 1700°C was 0.9-1.2%. After heat treatment, the aerogel microstructure remained stable, with a strength retention rate of 94%. The original aluminum silicate fibers were completely consumed, and the mullite nanowires were 1-20 μm in length and 50-600 nm in diameter.

[0133] Comparative Example 1

[0134] According to the preparation method described in the Chinese patent with application number 201910848903.8, porous mullite fiber ceramic bulk was prepared using only ammonium fluoride as catalyst at a catalytic temperature of 1200℃.

[0135] The numbers of the different numbered mullite fiber ceramic bulks in this comparative example are:

[0136] Ceramic block a b c d Al:Si:F in sol (atomic ratio) 3:1:0.6 3:1:1.2 3:1:1.8 3:1:2.5

[0137] Comparative Example 2

[0138] On the basis of Comparative Example 1, the catalytic temperature was reduced to 900℃, and porous mullite fiber ceramic bulk was prepared.

[0139] The numbers of the different numbered mullite fiber ceramic bulks in this comparative example are:

[0140] Ceramic block a b c d Al:Si:F (atomic ratio) 3:1:0.6 3:1:1.2 3:1:1.8 3:1:2.5

[0141] Comparative Example 3

[0142] According to the paper [Zhehan Yi et. al. Super-insulated, flexible, and high resilient mullite fiber reinforced silica aerogel composites by interfacial modification with nanoscale mullite whisker. Composites Part B. 2021, vol. 230, p. 109549.], porous mullite fiber ceramic bulk was prepared using only ammonium molybdate as catalyst at a catalytic temperature of 900℃. The numbers of the different numbered mullite fiber ceramic bulks in this comparative example are:

[0143] Ceramic block a b c d Al:Si:Mo (atomic ratio) 3:1:0.13 3:1:0.25 3:1:0.50 3:1:1.0

[0144] Comparative Example 4

[0145] Different from example 1, only one-time impregnation and drying process was used, the one-time impregnation / one-time drying and two-time impregnation / two-time drying in step 1 were combined, the aluminum silicate fiber felt obtained in step 1 was placed in a vacuum impregnation device, the sol A and the solution B were mixed and simultaneously loaded onto the fiber surface using vacuum, the impregnation time was 45 min; then drying was carried out under normal pressure, the drying temperature was controlled at 85℃, and the drying time was 9 h; the catalytic calcination of the modified fiber felt in step 5 was directly carried out, and the porous mullite fiber ceramic bulk was prepared at a catalytic temperature of 900℃ using Al:Si:F:Mo (atomic ratio) = 3:1:1.8:0.26.

[0146] Comparative example 5

[0147] Different from example 1, the molar concentration ratio of aluminum atoms in the aluminum chloride, silicon atoms in the silica sol, fluorine atoms in the ammonium fluoride, and molybdenum atoms in the ammonium molybdate in step 2 was 3:1:0.4:0.3.

[0148] The technical indexes of the mullite fiber aerogel prepared in the comparative example 5 were as follows: porosity 95.8%, thermal conductivity at room temperature 0.045 W / (m·k), bulk density 0.14 g / cm 3 , compression strength at 10% strain 0.08 MPa, size shrinkage rate before and after heat treatment at 1500℃ 2.5-4.5%, and strength retention rate after heat treatment only 62%. Figure 13 It can be seen that the original aluminum silicate fiber was not completely consumed and a small amount of residue remained, still maintaining the original outline of the micron fiber, which may be caused by the insufficient contribution of fluorine atoms in the ammonium fluoride. At the same time, since the aspect ratio of the mullite whiskers is small, the whiskers cannot form a good bridging, interlocking, and continuous firm structure, so the strength is low.

[0149] Figure 6 The thermal conductivity at room temperature of the mullite fiber aerogel prepared at different catalytic temperatures was ≥0.0424 W / (m·k) at a catalytic temperature in the range of 900-1200℃.

[0150] From Figure 4 and Figure 7 It can be seen that in examples 1-3, the aluminum silicate fiber was completely consumed at a two-time calcination temperature of ≥1250℃, and no impurity phase and glass phase were generated, which indicates that the residual fluorine / molybdenum impurities can be eliminated and the crystal lattice defects can be repaired at a higher two-time calcination temperature.

[0151] By comparing Examples 1 to 3 with Comparative Examples 1 to 3, it can be seen that when only ammonium fluoride is used as a catalyst or only ammonium molybdate is used as a catalyst, due to the lack of fluorine atoms in ammonium fluoride or the lack of molybdenum atoms in ammonium molybdate, a reasonable combination of molar amounts is not achieved. At this time, the aluminum silicate fibers may be completely consumed and the mullite whiskers may grow short and the whiskers may be too thick. Alternatively, the aluminum silicate fibers may remain and not be completely consumed, resulting in a sticky glass phase.

[0152] Specific examples Figure 9 As shown, the SEM of the porous mullite fiber ceramic block prepared in Comparative Example 1, wherein, Figure 9 Middle (a)~ Figure 9 The concentration of the catalyst ammonium fluoride in (d) increases successively. It can be seen that low concentrations of ammonium fluoride are difficult to completely consume the aluminum silicate fibers, while high concentrations of ammonium fluoride can consume the aluminum silicate fibers, but the generated mullite whiskers have a smaller aspect ratio and shorter length than those in Example 1, and the microscopic network continuity is poor. This may be because the high catalytic temperature promotes the gas phase mass transfer process and accelerates the formation of mullite nuclei, which in turn leads to the coarsening of the mullite whiskers. In addition, Figure 9 In (c), it can be seen that some whiskers are bonded to each other by glass.

[0153] Figure 10 This is the SEM of the porous mullite fiber aerogel prepared in Comparative Example 2, wherein: Figure 10 (a) to Figure 10 The concentration of the catalyst ammonium fluoride in (d) increases sequentially. It can be seen that, regardless of whether low or high concentrations of ammonium fluoride are present, the aluminum silicate fibers cannot be completely consumed at low catalytic temperatures, and the mullite whiskers are extremely small. This is primarily because the gas-phase mass transfer and mullite nucleation are weakened at low temperatures, insufficient to drive the catalyst to completely consume the fibers and form mullite whiskers or nanowires.

[0154] Figure 11 This is the SEM of the porous mullite fiber ceramic block prepared in Comparative Example 3, wherein: Figure 11 (a) to Figure 11 In (d), the concentration of the catalyst ammonium molybdate increases. It can be seen that as the amount of ammonium molybdate increases, the aluminum silicate fibers are gradually consumed, the aspect ratio of the mullite whiskers decreases, while the main fiber skeleton remains, and the mullite columnar crystals are bonded to each other by a glassy phase. This is because it is generally believed that the ammonium molybdate catalytic process may involve a liquid medium, making it difficult to form longer and thinner mullite whiskers or nanowires.

[0155] Therefore, in combination with Comparative Examples 1 to 3, regardless of the lower or higher catalytic temperature, in the absence of any catalyst in the present invention, the mullite fiber aerogel of the present invention, which completely consumes the aluminum silicate fiber and converts it into "large aspect ratio nanowires" and has no glass phase, cannot be obtained.

[0156] By comparing Example 1 and Comparative Example 4, Figure 12 The SEM of the porous mullite fiber ceramic block prepared in Comparative Example 4 shows that under the conditions of a single impregnation process, Al:Si:F:Mo (atomic ratio) = 3:1:1.8:0.26 was used to prepare a clear and transparent mixed solution. The original aluminum silicate fibers were not completely consumed, the fiber outlines still existed, and there was a large amount of residue. This may be because the single impregnation and atmospheric pressure drying process could not well fix most of the catalyst on the fiber surface, resulting in insufficient contribution of fluorine atoms and molybdenum atoms in the catalyst. Therefore, limiting the use of a secondary impregnation process can overcome the problem of the catalyst not being fixed on the fiber surface in large quantities due to the single impregnation, and limiting the molar concentration ratio of aluminum atoms in soluble aluminum salts, silicon atoms in silica sol, fluorine atoms in ammonium fluoride, and molybdenum atoms in ammonium molybdate. This is of great significance for achieving complete consumption of the original fibers in the fiber felt and obtaining a good aspect ratio and mullite fiber aerogel without a glass phase.

[0157] In summary, to address the poor structural stability, grain coarsening, and fiber breakage of polycrystalline or amorphous mullite fibers at high temperatures, the present invention proposes the preparation of a high-porosity fiber aerogel constructed from single-crystal mullite nanowires. Unlike conventional methods for growing single-crystal mullite fibers from high-temperature aluminosilicate melts, the present preparation method offers extremely high production efficiency and low energy consumption. Furthermore, it eliminates the fiber dispersion processes typically required for aerogel preparation (vacuum forming, gel-casting combined with freeze-drying, additive manufacturing, etc.), simplifying the production process and shortening the product's production cycle. The present invention directly utilizes aluminosilicate fibers as the matrix framework material. Leveraging the ability of mullite to grow anisotropically along the c-axis under the action of a catalyst, the micronized fibers are completely converted into mullite nanowires through synergistic catalysis and a secondary impregnation process. The result is a mullite fiber aerogel that combines high-temperature resistance, lightweight, high porosity, and low thermal conductivity, suitable for use above 1500°C, and its preparation method.

[0158] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing heat-insulating and high-temperature resistant mullite fiber aerogel, characterized in that: The following steps are involved: S1: Impregnation and drying: The pre-treated activated aluminum silicate fiber felt is impregnated with modified sol A once and dried once; then impregnated with solution B twice and dried twice to obtain the modified aluminum silicate fiber felt; The modified sol A includes silica sol and soluble aluminum salt; the solution B includes ammonium fluoride and ammonium molybdate; The molar concentration ratio of the aluminum atoms in the soluble aluminum salt, the silicon atoms in the silica sol, the fluorine atoms in the ammonium fluoride, and the molybdenum atoms in the ammonium molybdate is 3:1:(1.2-2.5):(0.12-0.35); S2: catalytic calcination of the modified aluminum silicate fiber felt: calcining the modified aluminum silicate fiber felt obtained in S1 once, wherein the temperature range of the first calcination is 900-1200° C.; S3: Post-heat treatment step: performing secondary calcination on the obtained mullite fiber aerogel, wherein the temperature of the secondary calcination is ≥1250°C.

2. The preparation method according to claim 1, characterized in that The surface pretreatment activation method of the aluminum silicate fiber felt in S1 is: immersing the aluminum silicate fiber felt in an acid solution or an alkaline solution for ultrasonic treatment, then rinsing the aluminum silicate fiber felt with deionized water, and drying after rinsing to obtain the pretreated aluminum silicate fiber felt.

3. The preparation method according to claim 2, characterized in that The porosity of the aluminum silicate fiber felt in S1 is greater than 95%; The pH value of the acid solution is 2.0 to 4.0, and the pH value of the alkaline solution is 8.0 to 10.0; Preferably, the S1 is immersed in an acid solution with a pH value of 2.0 to 4.0 for ultrasonic treatment; Preferably, the acid solution in S1 is one or more of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, and acetic acid solution; Preferably, the alkaline solution in S1 is one or more of potassium hydroxide solution or sodium hydroxide solution; Preferably, the ultrasonic treatment time in S1 is 10 to 30 minutes; Preferably, the drying temperature in the surface pretreatment activation method of the aluminum silicate fiber felt in S1 is 60-80° C., and the drying time is 18-30 hours.

4. The preparation method according to claim 1, characterized in that The solvents of the modified sol A and solution B in S1 are both deionized water; Preferably, the soluble aluminum salt in S1 is one of aluminum chloride, aluminum sulfate and aluminum nitrate.

5. The preparation method according to claim 1, characterized in that The time for the first immersion in S1 is 30 to 60 minutes; the temperature for the first drying in S1 is controlled at 50 to 120° C., and the time for the first drying is 6 to 12 hours.

6. The preparation method according to claim 1, characterized in that The secondary immersion time in S1 is 30 to 60 minutes; the temperature of the secondary drying in S1 is controlled at 50 to 120° C., and the secondary drying time is 6 to 12 hours.

7. The preparation method according to claim 1, characterized in that In said S2, the holding time of the primary calcination is 2 to 6 hours, and the heating rate is 2 to 5°C / min; Preferably, in S3, the holding time of the secondary calcination is 30 to 60 minutes, and the heating rate is 1 to 3°C / min.

8. A heat-insulating and high-temperature-resistant mullite fiber aerogel prepared by the method for preparing the heat-insulating and high-temperature-resistant mullite fiber aerogel according to any one of claims 1 to 7, characterized in that: The mullite fiber aerogel is composed of single-crystal mullite nanowires; The porosity of the mullite fiber aerogel is greater than 95%; The length of the mullite nanowires in the mullite fiber aerogel is 1 to 50 μm, and the diameter is 30 to 800 nm; There is no high-temperature bonding phase at the overlapping points between the mullite nanowires.

9. The heat-insulating and high-temperature-resistant mullite fiber aerogel according to claim 8, characterized in that: The thermal conductivity of the heat-insulating and high-temperature-resistant mullite fiber aerogel at room temperature is ≥0.0424 W / (m·k); The thermal conductivity of the heat-insulating and high-temperature-resistant mullite fiber aerogel at a high temperature of 1000 to 1500° C. is 0.12 to 0.20 W / (m·k).

10. The heat-insulating and high-temperature-resistant mullite fiber aerogel according to claim 8, characterized in that: The volume density of the heat-insulating and high-temperature-resistant mullite fiber aerogel is 0.15 to 0.17 g / cm 3 ; The heat-insulating and high-temperature-resistant mullite fiber aerogel has a compressive strength of ≥0.16 MPa at 10% strain. The dimensional shrinkage rate before and after heat treatment at 1500-1700℃ is 0.2-1.5%, and the strength retention rate is ≥90%.

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