Thermoresistant alumina aerogel and method for preparing same

Abstract

Provided are a thermoresistant alumina aerogel and a method for preparing same. The method comprises: subjecting a first industrial aluminum hydroxide to a first solvothermal reaction; grinding the product of the first solvothermal reaction to give an alpha-type Al2O3•nH2O, wherein n is <1.2; subjecting a second industrial aluminum hydroxide to a first heat treatment, and subjecting the product obtained by the first heat treatment and a first acidic regulator to a second solvothermal reaction to give a functional group-containing aluminum-oxygen substance; mixing the functional group-containing aluminum-oxygen substance, the alpha-type Al2O3•nH2O, a second acidic regulator, and a solvent to give a slurry, and freezing the slurry to give a first alumina aerogel; and subjecting the first alumina aerogel to heat treatment sequentially in a non-oxidizing atmosphere and an air atmosphere to give the thermoresistant alumina aerogel.

Description

A high-temperature resistant alumina aerogel and its preparation method Cross-reference to related applications This application claims priority to Chinese patent application No. 202411677454.2, filed on November 22, 2024, the entire contents of which are incorporated herein by reference. Technical Field This disclosure relates to the field of alumina aerogel preparation technology, and in particular to a high-temperature resistant alumina aerogel and its preparation method. Background Technology Aerogels are ultra-low density porous solid materials composed of cross-linked nanoparticles or polymer molecules, and are currently known to have the lowest thermal conductivity among solid materials. The unique structure and properties of aerogels make them valuable for applications in catalysis, thermal insulation, glass, and ceramics. There are many types of aerogels, with oxide aerogels being one of them. Among the various oxide aerogels, alumina aerogels are favored due to their excellent temperature resistance and relatively low price. Alumina aerogels are typically prepared using the sol-gel method. Currently, the main raw materials used for preparing alumina aerogels are inorganic aluminum salts and organic aluminum alkoxides. However, the preparation of alumina aerogels using organic aluminum alkoxides suffers from problems such as lengthy preparation processes, severe shrinkage of intermediate products during solvent exchange and drying, and poor mechanical strength of the final product. Furthermore, organic aluminum alkoxides themselves are expensive, highly toxic, and difficult to control during hydrolysis, limiting their large-scale application. When preparing alumina aerogels using inorganic aluminum salts, the colloid particles formed during the sol-gel process are typically large, affecting the aerogel's formability and leading to the formation of fragmented alumina aerogels. Currently, most developed alumina aerogels have an amorphous structure. Under high-temperature operating conditions, the amorphous framework of alumina aerogels undergoes a crystal transformation, causing pore collapse and resulting in the loss of alumina aerogel properties. Furthermore, supercritical drying and atmospheric pressure drying are two commonly used drying methods in the preparation of alumina aerogels, but neither can meet ideal production requirements: supercritical drying has drawbacks such as long cycle time and high cost; atmospheric pressure drying, on the other hand, suffers from the drawback of failing to meet product performance standards. Therefore, there is an urgent need to develop a new process for preparing alumina aerogels. Summary of the Invention By utilizing one or more embodiments of the present disclosure, a high-temperature resistant alumina aerogel and its preparation method are provided, thus solving the problem of how to prepare high-temperature resistant alumina aerogel. In a first aspect, this disclosure provides a method for preparing high-temperature resistant alumina aerogel, comprising: subjecting a first industrial aluminum hydroxide to a first solvothermal reaction to obtain alumina hydrate; grinding the alumina hydrate to obtain alpha-type Al2O3•nH2O; wherein n<1.2; subjecting a second industrial aluminum hydroxide to a first heat treatment to cause a qualitative change in the microstructure of the second industrial aluminum hydroxide; subjecting the first heat-treated second industrial aluminum hydroxide to a second solvothermal reaction with a first acid modifier to obtain a functionalized aluminum oxide substance; mixing the functionalized aluminum oxide substance, the alpha-type Al2O3•nH2O, the second acid modifier, and a solvent to obtain a slurry; freezing the slurry to obtain a first alumina aerogel; and subjecting the first alumina aerogel to a second heat treatment in a non-oxidizing atmosphere and a third heat treatment in an air atmosphere to obtain a high-temperature resistant alumina aerogel.

[0001] In a second aspect, this disclosure provides a high-temperature resistant alumina aerogel, which is prepared by the method described in any one of the first aspects. Attached Figure Description The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. To more clearly illustrate the technical solutions in the embodiments or related technologies of this disclosure, the accompanying drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort. Figure 1 shows a schematic flowchart of a method for preparing a high-temperature resistant alumina aerogel according to some embodiments of the present disclosure; Figure 2 shows a scanning electron microscope image of a high-temperature resistant alumina aerogel provided according to Embodiment 1 of the present disclosure; Figure 3 shows a scanning electron microscope image of a high-temperature resistant alumina aerogel provided according to Embodiment 2 of this disclosure; Figure 4 shows a scanning electron microscope image of a high-temperature resistant alumina aerogel provided according to Embodiment 3 of this disclosure; Figure 5 shows a scanning electron microscope image of a high-temperature resistant alumina aerogel provided according to Embodiment 4 of this disclosure; Figure 6 shows a scanning electron microscope image of a high-temperature resistant alumina aerogel provided according to Embodiment 5 of this disclosure. Embodiments of the present invention To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure. Various embodiments of this disclosure may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this disclosure; therefore, it should be considered that the range description has specifically disclosed all possible subranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range. In this disclosure, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the orientation shown in the accompanying drawings. Furthermore, in the description of this disclosure, terms such as "comprising" and "including" mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships may exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this disclosure are available on the market or can be prepared by existing methods. In a first aspect, this disclosure provides a method for preparing a high-temperature resistant alumina aerogel. Figure 1 shows a schematic flow diagram of a method for preparing a high-temperature resistant alumina aerogel according to some embodiments of this disclosure. Referring to Figure 1, the preparation method includes: S1. The first industrial aluminum hydroxide is subjected to a first solvothermal reaction to obtain aluminum oxide hydrate; S2. Alumina hydrate is ground to obtain alpha-type Al2O3•nH2O, where n<1.2; S3. The second industrial aluminum hydroxide is subjected to a first heat treatment to cause a qualitative change in the microstructure of the second industrial aluminum hydroxide; S4. The second industrial aluminum hydroxide after the first heat treatment is reacted with the first acid regulator in a second solvothermal reaction to obtain an aluminum oxide substance containing functional groups. S5. Aluminum oxide containing functional groups, alpha-type Al2O3•nH2O, a second acid regulator and a solvent are mixed to obtain a slurry; S6. Freeze the slurry to obtain the first alumina aerogel; and S7. The first alumina aerogel is subjected to a second heat treatment in a non-oxidizing atmosphere and a third heat treatment in an air atmosphere to obtain a high-temperature resistant alumina aerogel. As can be seen from the above, by carrying out the first solvothermal reaction on the first industrial aluminum hydroxide, the first industrial aluminum hydroxide can be converted from trihydrate aluminum hydroxide into alumina hydrate, and at the same time, the microscopic characteristics such as particle size and internal structure of alumina hydrate can be controlled. In some embodiments, the process parameters for the first solvothermal reaction include: a temperature of 80°C to 300°C and a time of 3h to 10h. In some embodiments of this disclosure, the temperature of the first solvothermal reaction can be between 80°C and 300°C. Conducting the reaction within this temperature range provides sufficient energy for the first solvothermal reaction, promoting the complete conversion of the first industrial aluminum hydroxide into alumina hydrate product, while simultaneously ensuring the crystal structure, particle size, and crystallinity of the product. The duration of the first solvothermal reaction can be between 3 hours and 10 hours; sufficient time ensures the reactants are fully converted into the product, improving the yield and purity of the product. For example, the temperature of the first solvothermal reaction can be 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, etc.; the time of the first solvothermal reaction can be 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, etc. In some implementations, the particle size of alumina hydrate can be controlled to be below 10 μm. Controlling the particle size of alumina hydrate to below 10 μm can increase its specific surface area and improve its reactivity. For example, the particle size of alumina hydrate can be 10 μm, 9 μm, 8 μm, 7 μm, 6 μm, etc. In step S1, to obtain alumina hydrate with a particle size range of less than 10 μm, different processing methods are required depending on the initial particle size of the first industrial aluminum hydroxide raw material. For example, if the initial particle size of the first industrial aluminum hydroxide is already less than 10 μm, it can be directly subjected to the first solvothermal reaction. If the initial particle size of the first industrial aluminum hydroxide is greater than 10 μm, an auxiliary agent needs to be added to the first solvothermal reaction, and multiple first solvothermal reactions may be required until the particle size of the product of the first solvothermal reaction (i.e., alumina hydrate) reaches less than 10 μm (i.e., the particle size of the product of the first solvothermal reaction reaches the general standard of micron-sized powder); or, if the initial particle size of the first industrial aluminum hydroxide is greater than 10 μm, it can be pre-ground to less than 10 μm before the first solvothermal reaction. In some embodiments, the product after the first solvothermal reaction also needs to be filtered and dried, wherein the drying temperature can be 50℃~200℃ and the drying time can be 1h~20h. In some embodiments of this disclosure, grinding alumina hydrate can refine the alumina hydrate particles and make their particle size distribution more uniform. During the grinding process, due to the internal structure of the alumina hydrate and the interaction of internal water molecules, the alumina hydrate is further transformed into alpha-type Al2O3•nH2O. Alpha-type Al2O3•nH2O, also known as α-Al2O3•nH2O, is a form of alumina containing water of crystallization. In some embodiments of this disclosure, α-Al2O3•nH2O is a special crystal form of alumina with a trigonal crystal system. The presence of water of crystallization (i.e., nH2O, where n represents the molar content of water of crystallization) affects the physical and chemical properties of alpha-type Al2O3•nH2O. On the one hand, during the heating process of α-Al₂O₃•nH₂O, the water of crystallization itself gradually disappears from α-Al₂O₃•nH₂O to form α-Al₂O₃, thus altering the morphology and physicochemical properties of α-Al₂O₃•nH₂O. On the other hand, the presence of water of crystallization affects the solubility and other properties of α-Al₂O₃•nH₂O. In the crystal structure of α-Al₂O₃, aluminum ions and oxygen ions are arranged closely in a specific manner, giving α-Al₂O₃ its high hardness and high melting point. When α-Al₂O₃ combines with water of crystallization to form α-Al₂O₃•nH₂O containing water of crystallization, the presence of water of crystallization will, to some extent, alter the solubility and other properties of α-Al₂O₃•nH₂O, making it a white solid that is sparingly soluble in water. This white solid is odorless, tasteless, and extremely hard, and is hygroscopic but not deliquescent (it loses its hygroscopicity after being burned), while also possessing excellent thermal stability. Furthermore, the grinding process not only helps to adjust the position and binding mode of water molecules in the α-Al₂O₃ crystal structure, making them more stable in the alpha-type Al₂O₃•nH₂O structure, but also optimizes its performance by controlling the degree of hydration of alpha-type Al₂O₃•nH₂O (n < 1.2). A lower degree of hydration can give alpha-type Al₂O₃•nH₂O higher thermal stability and reactivity. For example, the value of the degree of hydration n can be 1.15, 1.1, 1.0, 0.9, 0.8, etc., and correspondingly, the grinding time can be more than 10 hours. In some embodiments, the process parameters for the first heat treatment include: a temperature of 900°C to 1200°C and a time of 3s to 10s. In some embodiments of this disclosure, the second industrial aluminum hydroxide is subjected to a first heat treatment, with the temperature of the first heat treatment limited to 900°C to 1200°C and the time of the first heat treatment being 3s to 10s. That is, the second industrial aluminum hydroxide can be rapidly dehydrated by instantaneous high temperature, transforming into highly active transition state alumina, causing a qualitative change (i.e., a fundamental alteration) in its internal microstructure. This qualitative change will reshape the physical and chemical properties of the second industrial aluminum hydroxide and the types of its functional groups. In some embodiments, the temperature in the first heat treatment can be 900℃~1200℃, and the time can be 3s~10s. This instantaneous high-temperature heat treatment can cause a qualitative change in the microstructure of the second industrial aluminum hydroxide, thereby obtaining the target product of the first heat treatment (i.e., modified second industrial aluminum hydroxide). For example, in this first heat treatment, the temperature can be 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃, 1200℃, etc.; and the time can be 3s, 4s, 5s, 6s, 7s, 8s, 9s, 10s, etc. In some embodiments, the process parameters for the second solvothermal reaction include: a temperature of 80°C to 250°C, a time of 3 to 10 hours, and a pH value of <7. In some embodiments of this disclosure, in the second solvothermal reaction, the temperature can be 80℃~250℃, the time can be 3h~10h, and the pH value can be <7. Within this temperature, time, and pH range, sufficient energy and time can be provided for the second solvothermal reaction to promote the chemical reaction between the qualitatively changed second industrial aluminum hydroxide and the organic functional groups in the first acidic regulator, thereby generating a highly active aluminum oxide substance containing functional groups. For example, in the second solvothermal reaction, the temperature can be 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, etc.; the time can be 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, etc.; and the pH value can be 6, 5, 4, 3, etc. In some embodiments, the first industrial aluminum hydroxide and the second industrial alumina can both be aluminum hydroxide obtained from fractional aluminum hydroxide, carbon-based aluminum hydroxide, neutralized aluminum hydroxide, or other forms. In some embodiments, the weight M1 of the functionalized aluminum oxide, the weight M2 of the alpha-type Al2O3•nH2O, the weight M3 of the second acid modifier, and the volume V of the solvent satisfy the following relationship: M1:M2:M3:V=(1.5~10):(2~15):(0.1~10):500; wherein, if the unit of weight is grams, the unit of volume is milliliters. In some embodiments of this disclosure, the ratio of M1:M2:M3:V can be (1.5~10):(2~15):(0.1~10):500. This ratio helps to ensure the density and temperature resistance of the final high-temperature resistant alumina aerogel. In some embodiments, functionalized aluminum oxides provide the framework structure, functional groups, and alumina components for the formation of high-temperature resistant alumina aerogels in subsequent processes; alpha-type Al2O3•nH2O mainly serves as the high-temperature resistant component of the alumina aerogel and provides sufficient active functional groups in subsequent processes; a second acidic regulator is used to adjust the pH of the slurry to pH < 7, and the solvent is used to fully disperse and dilute the functionalized aluminum oxides and alpha-type Al2O3•nH2O, and to create basic conditions for the formation of high-temperature resistant alumina aerogels, which is conducive to the formation of a porous framework structure in high-temperature resistant alumina aerogels. In some embodiments, the solvent can be water. For example, the ratio of M1:M2:M3:V can be 1.5:2:0.1:500, 3:10:5:500, 8:5:1:500, 10:15:10:500, etc. In some embodiments, during the mixing of the functionalized aluminum oxide substance, alpha-type Al2O3•nH2O, the second acid regulator, and the solvent, 1.5 g to 10 g of the functionalized aluminum oxide substance can be added per 500 ml of water, along with 2 g to 15 g of alpha-type Al2O3•nH2O and 0.1 g to 10 g of the second acid regulator. In some embodiments of this application, under the combined action of a second acidic regulator and freezing conditions, functionalized aluminum oxides and alpha-type Al₂O₃•nH₂O can undergo cross-linking to form a first alumina aerogel with a three-dimensional network structure. This process can preserve the porous structure formed by the first alumina aerogel and strengthen its framework. In some embodiments, freezing includes a first freezing and a second freezing. The temperature of the first freezing is -50°C to -60°C. The temperature of the second freezing is -50°C to -80°C. In some embodiments of this disclosure, both functionalized aluminum oxides and alpha-type Al₂O₃•nH₂O exhibit high activity. Therefore, under the combined action of a second acidic regulator and a first freezing condition, functionalized aluminum oxides and alpha-type Al₂O₃•nH₂O can undergo cross-linking to form a first alumina aerogel with a three-dimensional network structure. This process preserves the pore structure of the first alumina aerogel and strengthens its framework. Furthermore, the second freezing process can further strengthen the framework of the first alumina aerogel while removing moisture, simultaneously preserving and enhancing the pore structure formed by the alumina aerogel. To fully achieve the freezing effect, considering the morphology, pore size, and properties of the alumina aerogel, the first freezing temperature can be -50°C to -60°C, and the second freezing temperature can be -50°C to -80°C. For example, the first freezing temperature can be -50℃, -52℃, -54℃, -56℃, -58℃, -60℃, etc.; the second freezing temperature can be -50℃, -60℃, -70℃, -80℃, etc. The first freezing time can be 4h to 6h, and the second freezing time can be 12h to 48h. In some embodiments, the first acidity regulator and the second acidity regulator each comprise at least one of the following: an inorganic acid, an organic acid, and an aluminum salt. In some embodiments of this disclosure, the first acidity regulator and the second acidity regulator may be one or more combinations of inorganic acids, organic acids, and aluminum salts. In some embodiments, the temperature of the second heat treatment is 600°C to 750°C. In some embodiments, the temperature of the third heat treatment is 650°C to 700°C. In some embodiments of this disclosure, the first alumina aerogel undergoes a second heat treatment in a non-oxidizing atmosphere, which can retain easily oxidized functional groups (e.g., carbon and hydrogen) in the first alumina aerogel. During this process, the unoxidized functional groups in the first alumina aerogel can act as a framework, promoting the transformation of the first alumina aerogel into a more stable inorganic alumina gel and increasing the framework strength of the inorganic alumina gel. Subsequently, the inorganic alumina gel is subjected to a third heat treatment in an air atmosphere, where the easily oxidized elements are calcined away. Through the third heat treatment, the purity of the final product can be improved while retaining the original stable framework structure composed of the inorganic alumina gel, thereby preparing a high-temperature resistant alumina aerogel. To achieve the above effects, considering the performance of the alumina aerogel, production energy consumption, and cost, the temperature of the second heat treatment can be 600℃~750℃, and the temperature of the third heat treatment can be 650℃~700℃. For example, the temperature of the second heat treatment can be 600℃, 620℃, 640℃, 660℃, 680℃, 700℃, 720℃, 750℃, etc., and the temperature of the third heat treatment can be 650℃, 660℃, 670℃, 680℃, 690℃, 700℃, etc. The time for the second heat treatment and the time for the third heat treatment can be 4h to 8h, respectively. In some embodiments, the heating rate of the second heat treatment and the heating rate of the third heat treatment can both be 3°C / min to 5°C / min. In a second aspect, this disclosure provides a high-temperature resistant alumina aerogel, which is prepared by any one of the methods described in the first aspect. The high-temperature resistant alumina aerogel is prepared using the above-described preparation method. The specific steps of the preparation method can be found in the above embodiments. Since the high-temperature resistant alumina aerogel employs all the technical features of some of the above embodiments, it possesses at least all the beneficial effects brought about by some of the above embodiments, which will not be elaborated upon here. The present disclosure is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the disclosure. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed. Example 1 A method for preparing high-temperature resistant alumina aerogel includes the following steps. At room temperature, industrial-grade aluminum hydroxide is mixed with water to form a first slurry with a mass concentration of 40%. The first slurry is subjected to a first solvothermal reaction at 180°C and kept at that temperature for 5 hours to obtain a slurry containing alumina hydrate. The particle size of the alumina hydrate in the slurry containing alumina hydrate is <10μm. The slurry containing alumina hydrate is filtered and dried, and the dried product is alumina hydrate. At room temperature, the dried product (i.e., alumina hydrate) was added to a grinding equipment and ground for 12 hours to obtain alpha-type Al2O3•nH2O (n is 0.67). Take another piece of industrial aluminum hydroxide and subject it to a first heat treatment at 900°C for 10 seconds, thereby modifying the industrial aluminum hydroxide and altering its microstructure. Water was added to the second industrial aluminum hydroxide after the first heat treatment and stirred to form a second slurry. Formic acid was added to the second slurry to adjust the pH to 2. The second slurry was then subjected to a second solvothermal reaction at 130°C for 4 hours to obtain a slurry containing functionalized aluminum oxides. A slurry containing functionalized aluminum oxide is diluted with a solvent (water) at a concentration of 1.5 g of the functionalized aluminum oxide per 500 mL of diluted slurry. 5 g of alpha-type Al₂O₃•nH₂O and 1 g of aluminum chloride are added to each 500 mL of diluted slurry and mixed thoroughly to obtain the slurry. The slurry is frozen at -50°C for 4 hours and then freeze-dried at -50°C for 48 hours to obtain a freeze-dried composite (i.e., the first alumina aerogel). The freeze-dried composite is heated to 700°C at a heating rate of 5°C / min in a non-oxidizing atmosphere and held at 700°C for 5 hours for a second heat treatment. In an air atmosphere, the freeze-dried composite after the second heat treatment is heated to 650°C at a heating rate of 4°C / min and held at 650°C for 5 hours for a third heat treatment. The product obtained after the heat treatment is the high-temperature resistant alumina aerogel. The thermal conductivity of the high-temperature resistant alumina aerogel prepared in Example 1 at different temperatures is shown in Table 1: [Amended according to Rule 26, 25.12.2025] Table 1: Thermal conductivity (W / (mK) of the high-temperature resistant alumina aerogel of Example 1 at different temperatures. [Revised according to Rule 26, dated December 2025] Example 2 A method for preparing high-temperature resistant alumina aerogel includes the following steps. At room temperature, industrial-grade aluminum hydroxide is mixed with water to form a first slurry with a mass concentration of 40%. The first slurry is subjected to a first solvothermal reaction at 180°C and kept at that temperature for 5 hours to obtain a slurry containing alumina hydrate. The particle size of the alumina hydrate in the slurry containing alumina hydrate is <10μm. The slurry containing alumina hydrate is filtered and dried, and the dried product is alumina hydrate. At room temperature, the dried product (i.e., alumina hydrate) was added to a grinding equipment and ground for 12 hours to obtain alpha-type Al2O3•nH2O (n is 0.67). Take another piece of industrial aluminum hydroxide and subject it to a first heat treatment at 1100℃ for 3 seconds, thereby modifying the industrial aluminum hydroxide and altering its microstructure. Water was added to the second industrial aluminum hydroxide after the first heat treatment and stirred to form a second slurry. Formic acid was added to the second slurry to adjust the pH to 2. The second slurry was then subjected to a second solvothermal reaction at 150°C for 4 hours to obtain a slurry containing functionalized aluminum oxides. The slurry containing functionalized aluminum oxide is diluted with a solvent (water). The dilution standard is 2.5 grams of the functionalized aluminum oxide in every 500 ml of diluted slurry. 5 grams of the alpha-type Al2O3•nH2O obtained in the first step and 5 grams of aluminum chloride are added to every 500 ml of diluted slurry and mixed evenly to obtain the slurry. The slurry was frozen at -50°C for 4 hours, and then freeze-dried at -50°C for 48 hours to obtain a frozen composite (i.e., the first alumina aerogel). The frozen composite was then heated to 700°C in a non-oxidizing atmosphere at a heating rate of 5°C / min and held at 700°C for 5 hours for a second heat treatment. In an air atmosphere, the frozen composite after the second heat treatment was heated to 660°C at a heating rate of 3-5°C / min and then held at 660°C for 5 hours for a third heat treatment. The product obtained after the heat treatment is the high-temperature resistant alumina aerogel. The thermal conductivity of the high-temperature resistant alumina aerogel prepared in Example 2 at different temperatures is shown in Table 2. [Amended according to Rule 26, 25.12.2025] Table 2 Thermal conductivity (w / (mk) of the high-temperature resistant alumina aerogel of Example 2 at different temperatures [Revised according to Rule 26, dated December 2025] Example 3 A method for preparing high-temperature resistant alumina aerogel includes the following steps. At room temperature, industrial-grade aluminum hydroxide is mixed with water to form a first slurry with a mass concentration of 40%. The first slurry is subjected to a first solvothermal reaction at 200°C and kept at that temperature for 3 hours to obtain a slurry containing alumina hydrate. The particle size of the alumina hydrate in the slurry containing alumina hydrate is <10μm. The slurry containing alumina hydrate is filtered and dried, and the dried product is alumina hydrate. At room temperature, the dried product (i.e., alumina hydrate) was added to a grinding equipment and ground for 14 hours to obtain alpha-type Al2O3•nH2O (n is 0.73). Take another piece of industrial aluminum hydroxide and subject it to a first heat treatment at 1100°C for 3 seconds, thereby modifying the industrial aluminum hydroxide and altering its microstructure. Water was added to the industrial aluminum hydroxide after the first heat treatment and stirred to form a second slurry. Acetic acid was added to the second slurry to adjust the pH to 2. The second slurry was then subjected to a second solvothermal reaction at 140°C for 4 hours to obtain a slurry containing functionalized aluminum oxides. The slurry containing functionalized aluminum oxide is diluted with a solvent (water). The dilution standard is 2.5 grams of the functionalized aluminum oxide in every 500 ml of diluted slurry. 7 grams of alpha-type Al2O3•nH2O and 3 grams of aluminum chloride are added to every 500 ml of diluted slurry and mixed thoroughly to obtain the slurry. The slurry was frozen at -50°C for 4 hours, and then freeze-dried at -50°C for 48 hours to obtain a frozen composite (i.e., the first alumina aerogel). The frozen composite was then heated to 700°C in a non-oxidizing atmosphere at a heating rate of 5°C / min and held at 700°C for 5 hours for a second heat treatment. In an air atmosphere, the frozen composite after the second heat treatment was heated to 680°C at a heating rate of 4°C / min and then held at 680°C for 5 hours for a third heat treatment. The product obtained after the heat treatment is the high-temperature resistant alumina aerogel. The thermal conductivity of the high-temperature resistant alumina aerogel prepared in Example 3 at different temperatures is shown in Table 3. [Amended according to Rule 26, 25.12.2025] Table 3: Thermal conductivity (w / (mk) of the high-temperature resistant alumina aerogel of Example 3 at different temperatures. [Revised according to Rule 26, dated December 2025] Example 4 A method for preparing high-temperature resistant alumina aerogel includes the following steps. At room temperature, industrial aluminum hydroxide is mixed with water to form a first slurry with a mass concentration of 20%. 3.5 wt% of a grain control agent is added to the first slurry, and the first slurry is subjected to a first solvothermal reaction at 180°C for 3 hours to obtain a slurry containing alumina hydrate. The particle size of the alumina hydrate in the slurry is <10 μm. The slurry containing alumina hydrate is filtered and dried, and the dried product is alumina hydrate. At room temperature, the dried product (i.e., alumina hydrate) was added to a grinding equipment and ground for 13 hours to obtain alpha-type Al2O3•nH2O (n is 0.68). Take another piece of industrial aluminum hydroxide and subject it to a first heat treatment at 1100℃ for 3 seconds, thereby modifying the industrial aluminum hydroxide and altering its microstructure. Water was added to the second industrial aluminum hydroxide after the first heat treatment and stirred to form a second slurry. Formic acid and acetic acid were added to the second slurry to adjust the pH to 2. The second slurry was subjected to a second solvothermal reaction at 135°C for 4 hours to obtain a slurry containing functionalized aluminum oxides. The slurry containing functionalized aluminum oxide is diluted with a solvent (water). The dilution standard is 5 grams of the functionalized aluminum oxide in every 500 ml of diluted slurry. 10 grams of alpha-type Al2O3•nH2O and 3 grams of a mixture of aluminum chloride and aluminum nitrate are added to every 500 ml of diluted slurry and mixed thoroughly to obtain the slurry. The slurry was frozen at -50°C for 4 hours, and then freeze-dried at -50°C for 48 hours to obtain a frozen composite (i.e., the first alumina aerogel). The frozen composite was then heated to 700°C in a non-oxidizing atmosphere at a heating rate of 5°C / min and held at 700°C for 5 hours for a second heat treatment. In an air atmosphere, the frozen composite after the second heat treatment was heated to 680°C at a heating rate of 3°C / min and held at 680°C for 5 hours for a third heat treatment. The product obtained after the heat treatment is the high-temperature resistant alumina aerogel. The thermal conductivity of the high-temperature resistant alumina aerogel prepared in Example 4 at different temperatures is shown in Table 4. [Amended according to Rule 26, 25.12.2025] Table 4: Thermal conductivity (W / (mK) of the high-temperature resistant alumina aerogel of Example 4 at different temperatures. [Revised according to Rule 26, dated December 2025] Example 5 A method for preparing high-temperature resistant alumina aerogel includes the following steps. At room temperature, industrial-grade aluminum hydroxide is mixed with water to form a first slurry with a mass concentration of 20%. 3.5 wt% of a grain control agent is added to the first slurry, and the first slurry is subjected to a first solvothermal reaction at 180°C for 3 hours to obtain a slurry containing alumina hydrate. The particle size of the alumina hydrate in the slurry is <10 μm. The slurry containing alumina hydrate is filtered and dried, and the dried product is alumina hydrate. At room temperature, the dried product (i.e., alumina hydrate) was added to a grinding equipment and ground for 15 hours to obtain alpha-type Al2O3•nH2O (n is 0.76). Take another piece of industrial aluminum hydroxide and subject it to a first heat treatment at 1100℃ for 3 seconds, thereby modifying the industrial aluminum hydroxide and altering its microstructure. Water was added to the second industrial aluminum hydroxide after the first heat treatment and stirred to form a second slurry. Formic acid was added to the second slurry to adjust the pH to 2. The second slurry was then subjected to a second solvothermal reaction at 160°C for 4 hours to obtain a slurry containing functionalized aluminum oxides. A slurry containing functionalized aluminum oxide is diluted with a solvent (water) at a concentration of 2.5 g of the functionalized aluminum oxide per 500 mL of diluted slurry. 5 g of alpha-type Al₂O₃•nH₂O and 1 g of aluminum nitrate are added to each 500 mL of diluted slurry and mixed thoroughly to obtain the slurry. The slurry is frozen at -50°C for 4 hours and then freeze-dried at -50°C for 48 hours to obtain a freeze-dried composite (i.e., the first alumina aerogel). The freeze-dried composite is heated to 700°C in a non-oxidizing atmosphere at a heating rate of 5°C / min and held at 700°C for 5 hours. In an air atmosphere, the second heat-treated freeze-dried composite is heated to 700°C at a heating rate of 5°C / min and then held at 700°C for 5 hours for a third heat treatment. The product obtained after the heat treatment is the high-temperature resistant alumina aerogel. The thermal conductivity of the high-temperature resistant alumina aerogel prepared in Example 5 at different temperatures is shown in Table 5: [Amended according to Rule 26, 25.12.2025] Table 5: Thermal conductivity (w / (mk) of the high-temperature resistant alumina aerogel of Example 5 at different temperatures. [Revised according to Rule 26, dated December 2025] Comparative Example 1 A method for preparing high-temperature resistant alumina aerogel includes the following steps. At room temperature, industrial-grade aluminum hydroxide is mixed with water to form a first slurry with a mass concentration of 40%. The first slurry is subjected to a first solvothermal reaction at 180°C and kept at that temperature for 5 hours to obtain a slurry containing alumina hydrate. The particle size of the alumina hydrate in the slurry containing alumina hydrate is <10μm. The slurry containing alumina hydrate is filtered and dried, and the dried product is alumina hydrate. At room temperature, the dried product (i.e., alumina hydrate) is added to a grinding equipment and ground for 13 hours to obtain alpha-type Al2O3•nH2O (n is 1). Take a second batch of industrial aluminum hydroxide, add water and stir to form a second slurry, then add formic acid to the second slurry to adjust the pH to 2. Perform a second solvothermal reaction on the second slurry at 130°C for 4 hours to obtain an aluminum hydroxide slurry. Aluminum hydroxide slurry was diluted with a solvent (water) at a concentration of 1.5 g of aluminum hydroxide per 500 mL of diluted slurry. 5 g of alpha-type Al₂O₃•nH₂O and 1 g of aluminum chloride were added to each 500 mL diluted slurry and mixed thoroughly to obtain a slurry. The slurry was frozen at -50°C for 4 hours and then freeze-dried at -50°C for 48 hours to obtain a frozen composite (i.e., the first alumina aerogel). The frozen composite was heated to 700°C at a heating rate of 5°C / min in a non-oxidizing atmosphere and held at 700°C for 5 hours for a first heat treatment. In an air atmosphere, the frozen composite after the first heat treatment was heated to 650°C at a heating rate of 4°C / min and held at 650°C for 5 hours for a second heat treatment. The product obtained after the heat treatment was the alumina aerogel. The thermal conductivity of the alumina aerogel prepared in Comparative Example 1 at different temperatures is shown in Table 6. [Revised according to Rule 26, 25.12.2025] Table 6 Thermal conductivity (w / (mk) of alumina aerogel of Comparative Example 1 at different temperatures [Revised according to Rule 26, dated December 2025] As shown in Examples 1-5, the thermal conductivity of the high-temperature resistant alumina aerogel is no higher than 0.03 W / (mK) under conditions ranging from room temperature (25°C) to 1400°C, demonstrating excellent high-temperature resistance. Figure 2 shows a scanning electron microscope (SEM) image of a high-temperature resistant alumina aerogel provided according to Example 1 of this disclosure; Figure 3 shows a SEM image of a high-temperature resistant alumina aerogel provided according to Example 2 of this disclosure; Figure 4 shows a SEM image of a high-temperature resistant alumina aerogel provided according to Example 3 of this disclosure; Figure 5 shows a SEM image of a high-temperature resistant alumina aerogel provided according to Example 4 of this disclosure; and Figure 6 shows a SEM image of a high-temperature resistant alumina aerogel provided according to Example 5 of this disclosure. Referring to Figures 2-6 and Tables 1-5, it is evident that the high-temperature resistant alumina aerogels prepared according to the embodiments of this disclosure exhibit good uniformity, unique internal structure, and good temperature resistance. In Comparative Example 1, the industrial aluminum hydroxide was not subjected to the first heat treatment (i.e., instantaneous heat treatment) as in Examples 1 to 5. According to Table 6, the alumina aerogel obtained in Comparative Example 1 has poor temperature resistance. Compared with related technologies, the method for preparing high-temperature resistant alumina aerogel provided in this disclosure has at least the following advantages: The first solvothermal reaction of industrial aluminum hydroxide converts trihydrate aluminum hydroxide into alumina hydrate, and modulates the microstructure of the alumina hydrate. Milling the alumina hydrate refines the particles and ensures a uniform particle size distribution. Due to the internal structure of the alumina hydrate and the influence of internal water molecules, it transforms into alpha-type Al₂O₃•nH₂O, which possesses excellent thermal stability, where n is <1.2. The lower degree of hydration contributes to the higher thermal stability of alpha-type Al₂O₃•nH₂O and enhances its reactivity. The second-stage industrial aluminum hydroxide undergoes a first heat treatment. The instantaneous high temperature of the first heat treatment rapidly dehydrates the second-stage industrial aluminum hydroxide, transforming it into a highly active transition-state alumina, causing a qualitative change (fundamental alteration) in its internal microstructure. This qualitative change reshapes the physical and chemical properties and functional group types of the second-stage industrial aluminum hydroxide. The product obtained from the first heat treatment undergoes a second solvothermal reaction with a first acidic regulator to generate functionalized aluminum oxides. The generated functionalized aluminum oxides and alpha-type Al₂O₃•nH₂O both exhibit high activity. After mixing the functionalized aluminum oxides, alpha-type Al₂O₃•nH₂O, the second acidic regulator, and the solvent to obtain a slurry, under the combined action of the second acidic regulator and freezing conditions, the functionalized aluminum oxides and alpha-type Al₂O₃•nH₂O can undergo cross-linking, thereby forming a first alumina aerogel with a three-dimensional network structure. A second heat treatment of the first alumina aerogel, which has a three-dimensional network structure, in a non-oxidizing atmosphere preserves easily oxidizable elements (e.g., carbon and hydrogen). During this process, unoxidized functional groups in the first alumina aerogel act as a framework, promoting its transformation into a more stable inorganic alumina gel. Subsequently, a third heat treatment is performed on the inorganic alumina gel in air, where easily oxidizable elements are calcined away. This third heat treatment improves the purity of the final product while preserving the original stable framework structure of the inorganic alumina gel, thus enabling the preparation of a high-temperature resistant alumina aerogel. One or more technical solutions in the embodiments of this disclosure have at least the following technical effects or advantages: (1) The main raw materials used in the preparation method of high temperature resistant alumina aerogel provided in this embodiment are industrial aluminum hydroxide and industrial aluminum hydroxide, which are industrially produced aluminum hydroxide. Organic aluminum salts and inorganic aluminum salts are not used, which can greatly reduce the production cost. (2) The high-temperature resistant alumina aerogel prepared by the method provided in this embodiment has significantly improved high-temperature resistance compared with alumina aerogel prepared by other processes. (3) The method for preparing high-temperature resistant alumina aerogel provided in this disclosure, compared with the currently commonly used supercritical drying method for drying alumina aerogel, does not require a high-cost and long-cycle supercritical drying process. The preparation cycle is short and the manufacturing cost is low, which lays the foundation for large-scale industrial preparation of high-temperature resistant alumina aerogel. The above description is merely a specific embodiment of this disclosure, enabling those skilled in the art to understand or implement it. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing high-temperature resistant alumina aerogel, comprising: Aluminum hydroxide from the first industrial plant was subjected to a first solvothermal reaction to obtain aluminum oxide hydrate; The alumina hydrate was milled to obtain alpha-type Al2O3•nH2O, where n < 1.2; The second industrial aluminum hydroxide is subjected to a first heat treatment to cause a qualitative change in the microstructure of the second industrial aluminum hydroxide; The second industrial aluminum hydroxide after the first heat treatment is subjected to a second solvothermal reaction with a first acidic regulator to obtain an aluminum oxide substance containing functional groups. The functional group-containing aluminum oxide substance, the alpha-type Al2O3•nH2O, the second acid regulator, and the solvent are mixed to obtain a slurry; The slurry was frozen to obtain a first alumina aerogel; The first alumina aerogel was subjected to a second heat treatment in a non-oxidizing atmosphere and a third heat treatment in an air atmosphere to obtain a high-temperature resistant alumina aerogel.

2. The method according to claim 1, wherein, The process parameters for the first solvothermal reaction include: temperature of 80℃~300℃ and time of 3h~10h.

3. The method according to claim 1 or 2, wherein, The alumina hydrate has a particle size of less than 10 μm.

4. The method according to claim 1, wherein, The process parameters for the first heat treatment include: a temperature of 900℃~1200℃ and a time of 3s~10s.

5. The method according to claim 1, wherein, The process parameters for the second solvothermal reaction include: temperature of 80℃~250℃, time of 3h~10h, and pH value <7.

6. The method according to claim 1, wherein, The weight M1 of the functional group-containing aluminum oxide substance, the weight M2 of the alpha-type Al2O3•nH2O, the weight M3 of the second acid regulator, and the volume V of the solvent satisfy the following relationship: M1:M2:M3:V=(1.5~10):(2~15):(0.1~10):500; where the unit of weight is grams, and the unit of volume is milliliters.

7. The method according to claim 1, wherein, The freezing includes a first freezing and a second freezing; wherein the temperature of the first freezing is -50°C to -60°C, and the temperature of the second freezing is -50°C to -80°C.

8. The method according to claim 1, wherein, The first acidity regulator and the second acidity regulator each include at least one of the following: inorganic acid, organic acid and aluminum salt.

9. The method according to any one of claims 1 to 8, wherein, The temperature of the second heat treatment is 600℃~750℃; and / or, The temperature of the third heat treatment is 650℃~700℃.

10. A high-temperature resistant alumina aerogel, wherein the high-temperature resistant alumina aerogel is prepared by the method described in any one of claims 1 to 9.

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