A high temperature resistant alumina aerogel and preparation method thereof

Abstract

The present application relates to a high-temperature resistant alumina aerogel and a preparation method thereof, and relates to the technical field of alumina aerogel preparation. The method comprises: subjecting industrial aluminum hydroxide to a solvothermal reaction, then grinding the product of the solvothermal reaction to obtain α-type Al2O3·nH2O, where n is less than 1.2; subjecting the industrial aluminum hydroxide to a heat treatment, then subjecting the heat-treated product to a solvothermal reaction with an acidic modifier to obtain an alumina-containing substance; mixing the alumina-containing substance, α-type Al2O3·nH2O, an acidic modifier, and a solvent, and then freezing to obtain a first alumina aerogel; and sequentially heat-treating the first alumina aerogel in a non-oxidizing atmosphere and in an air atmosphere to obtain a high-temperature resistant alumina aerogel. The alumina aerogel provided in the present application has a thermal conductivity of no more than 0.03 W / mK under conditions of 25°C to 1400°C.

Description

Technical Field

[0001] The present application relates to the technical field of alumina aerogel preparation, and in particular to a high-temperature resistant alumina aerogel and a preparation method thereof. Background Art

[0002] Aerogel is an ultra-low-density, porous solid material composed of aggregated nanoparticles or polymer molecules. It currently boasts the lowest thermal conductivity of any solid material. Its unique structure and properties make it highly valuable for applications in catalysis, thermal insulation, glass, and ceramics. There are many types of aerogel, with oxide aerogel being one of them. Among these oxide aerogels, alumina aerogel is favored for its high temperature resistance and low price.

[0003] Alumina aerogels are primarily prepared using the sol-gel method, with inorganic aluminum salts and organic aluminum alcohol salts as the primary raw materials. However, alumina aerogels prepared using organic aluminum alcohol salts are subject to lengthy preparation processes, severe sample shrinkage during solvent exchange and drying, and poor mechanical strength. Organic aluminum alcohol salts are expensive, highly toxic, and difficult to control during hydrolysis, limiting their large-scale application. Alumina aerogels prepared using inorganic aluminum salts typically have larger alumina particles, which affects their formability and makes them more likely to form fragments. Currently, most alumina aerogels developed are amorphous. Under high-temperature conditions, the alumina undergoes crystal transformation, leading to pore collapse and loss of aerogel properties. Furthermore, supercritical drying of aerogels suffers from long cycles and high costs, while atmospheric pressure drying of aerogels can make it difficult to meet performance standards. Therefore, a new process for preparing alumina aerogels is being developed. Summary of the Invention

[0004] The present application provides a high-temperature resistant alumina aerogel and a preparation method thereof to solve the following technical problems: providing a new preparation method of alumina aerogel.

[0005] In a first aspect, the present application provides a method for preparing a high-temperature resistant alumina aerogel, the method comprising:

[0006] subjecting the first industrial aluminum hydroxide to a first solvent thermal reaction to obtain aluminum oxide hydrate;

[0007] The alumina hydrate is ground to obtain alphah-type Al2O3·nH2O, wherein n<1.2;

[0008] performing a first heat treatment on the second industrial aluminum hydroxide so as to cause a qualitative change in the microstructure of the second industrial aluminum hydroxide;

[0009] performing a second solvent thermal reaction on the second industrial aluminum hydroxide after the first heat treatment and the first acidic regulator to obtain an aluminum oxide substance containing a functional group;

[0010] Mixing the aluminum oxide material containing a functional group, the alphah-type Al2O3·nH2O, a second acidic regulator, and a solvent to obtain a slurry;

[0011] Freezing the slurry to obtain a first alumina aerogel;

[0012] The first alumina aerogel is sequentially 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.

[0013] Optionally, the process parameters of the first solvent thermal reaction include: temperature of 80°C to 300°C, and time of 3h to 10h.

[0014] Optionally, the particle size of the alumina hydrate is less than 10 μm.

[0015] Optionally, the process parameters of the first heat treatment include: temperature of 900° C. to 1200° C., and time of 3s to 10s.

[0016] Optionally, the process parameters of the second solvent thermal reaction include: temperature of 80° C. to 250° C., time of 3 h to 10 h, and pH value <7.

[0017] Optionally, the weight M1 of the aluminum oxide substance containing functional groups, the weight M2 of the alphah-type Al2O3·nH2O, the weight M3 of the second acidic regulator and the volume V of the solvent satisfy the relationship: M1:M2:M3:V=(1.5~10):(2~15):(0.1~10):500; wherein, if the unit of weight is gram, the unit of volume is milliliter.

[0018] Optionally, 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.

[0019] Optionally, the first acidic regulator and the second acidic regulator each include at least one of the following: an inorganic acid, an organic acid, and an aluminum salt.

[0020] Optionally, the temperature of the second heat treatment is 600° C. to 750° C.; and / or,

[0021] The temperature of the third heat treatment is 650°C to 700°C.

[0022] In a second aspect, the present application provides a high temperature resistant alumina aerogel, which is prepared by any one of the methods described in the first aspect.

[0023] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0024] The preparation method of the high-temperature resistant alumina aerogel provided in an embodiment of the present application comprises the following steps: subjecting a first industrial aluminum hydroxide to a first solvent thermal reaction to obtain an alumina hydrate; grinding the alumina hydrate to obtain alphah-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 second industrial aluminum hydroxide after the first heat treatment to a second solvent thermal reaction with a first acidic regulator to obtain an aluminum oxide substance containing a functional group; mixing the aluminum oxide substance containing a functional group, the alphah-type Al2O3·nH2O, a second acidic regulator, 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 in sequence to obtain a high-temperature resistant alumina aerogel. The first industrial aluminum hydroxide undergoes a first solvent thermal reaction, which can convert the trihydrate aluminum hydroxide in the industrial aluminum hydroxide into aluminum oxide hydrate and regulate the microscopic characteristics of the aluminum oxide hydrate; the aluminum oxide hydrate is ground to make the aluminum oxide hydrate refined and uniform. Due to its internal structure and internal water, the aluminum oxide hydrate will be converted into alphah-type Al2O3·nH2O, and Al2O3 is alphah-type, which has excellent thermal stability; n is <1.2, and a lower degree of hydration can make alphah-type Al2O3·nH2O have higher thermal stability and improve the reaction activity of alphah-type Al2O3·nH2O; the second industrial aluminum hydroxide undergoes a first heat treatment, which can cause the attached water, crystallization water content and internal microstructure of the second industrial aluminum hydroxide to undergo qualitative changes, and this qualitative change will reshape the physical and chemical properties and functional group types of the second industrial aluminum hydroxide. The product obtained by the first heat treatment undergoes a second solvent thermal reaction with a first acidic regulator, and the generated functional group-containing aluminum oxide substance and alphah-type Al2O3·nH2O both have high activity. Under the action of the second acidic regulator and freezing conditions, the functional group-containing aluminum oxide substance and alphah-type Al2O3·nH2O can undergo a gluing chain reaction, thereby forming a first alumina aerogel with a three-dimensional network structure; the first alumina aerogel with a three-dimensional network structure undergoes a second heat treatment in a non-oxidizing atmosphere, which can retain the elements that will oxidize in the first alumina aerogel, and the functional group elements that have not oxidized in the first alumina aerogel can provide a skeleton to form an inorganic alumina gel; when the inorganic alumina gel undergoes a third heat treatment in an air atmosphere, the elements that will oxidize will be oxidized and calcined, while retaining the original skeleton structure of the first alumina aerogel, thereby preparing a high-temperature resistant alumina aerogel. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0026] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0027] Figure 1 A schematic flow chart of a method for preparing a high-temperature resistant alumina aerogel provided in an embodiment of the present application;

[0028] Figure 2 This is a scanning electron microscope image of a high-temperature resistant alumina aerogel provided in Example 1 of the present application;

[0029] Figure 3 This is a scanning electron microscope image of a high-temperature resistant alumina aerogel provided in Example 2 of the present application;

[0030] Figure 4 This is a scanning electron microscope image of a high-temperature resistant alumina aerogel provided in Example 3 of the present application;

[0031] Figure 5 This is a scanning electron microscope image of a high-temperature resistant alumina aerogel provided in Example 4 of the present application;

[0032] Figure 6 This is a scanning electron microscope image of a high-temperature resistant alumina aerogel provided in Example 5 of the present application. DETAILED DESCRIPTION

[0033] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0034] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a hard limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numbers within the range. For example, the description of a range from 1 to 6 should be considered to have specifically disclosed sub-ranges 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., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0035] In this application, unless otherwise specified, the directional words used, such as "upper" and "lower", refer specifically to the directions of the drawings in the accompanying drawings. In addition, in the description of the present application specification, the terms "including", "comprising", etc. mean "including but not limited to". In this article, relational terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. Wherein A and B can be singular or plural. In this article, "at least one" refers to one or more, and "plurality" refers to 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, c can be single or multiple.

[0036] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0037] In a first aspect, the present application provides a method for preparing high temperature resistant alumina aerogel. Figure 1 A schematic diagram of a process for preparing a high temperature resistant alumina aerogel provided in an embodiment of the present application; see Figure 1 , the method comprising:

[0038] S1. subjecting the first industrial aluminum hydroxide to a first solvothermal reaction to obtain aluminum oxide hydrate;

[0039] In the embodiment of the present application, the first industrial aluminum hydroxide undergoes a first solvothermal reaction, which can convert the trihydrate aluminum hydroxide in the industrial aluminum hydroxide into aluminum oxide hydrate, and regulate the particle size, internal structure and other microscopic characteristics of the aluminum oxide hydrate.

[0040] In some embodiments, the process parameters of the first solvothermal reaction include: temperature of 80° C. to 300° C., and time of 3 h to 10 h.

[0041] In the embodiment of the present application, the temperature of the first solvent thermal reaction can be 80℃~300℃. Within this temperature range, it can provide sufficient energy for the first solvent thermal reaction to promote the transformation of the first industrial aluminum hydroxide to form aluminum oxide hydrate, while ensuring the crystal structure, particle size and crystallinity of the product. The time of the first solvent thermal reaction can be 3h~10h. Sufficient time can ensure that the reactants are fully converted into products and improve the yield and purity of the products. For example, the temperature 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 can be 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, etc.

[0042] In some embodiments, the particle size of the alumina hydrate is less than 10 μm.

[0043] In the embodiment of the present application, the particle size of the alumina hydrate may be less than 10 μm, thereby increasing the specific surface area of ​​the alumina hydrate and improving the reactivity of the alumina hydrate. For example, the particle size of the alumina hydrate may be 10 μm, 9 μm, 8 μm, 7 μm, 6 μm, etc.

[0044] Specifically, in step S1, if the first industrial aluminum hydroxide is less than 10 μm, the first industrial aluminum hydroxide can be directly subjected to the first solvent thermal reaction; if the first industrial aluminum hydroxide is greater than 10 μm, an auxiliary agent needs to be added to the first solvent thermal reaction, and the first solvent thermal reaction may be performed multiple times until the particle size of the product of the first solvent thermal reaction reaches less than 10 μm, similar to a micron-sized industrial aluminum hydroxide powder or a product produced by hydrothermal treatment of a micron-sized industrial aluminum hydroxide powder; or the first industrial aluminum hydroxide greater than 10 μm is ground and subjected to the first solvent thermal reaction. In addition, the product after the first solvent thermal reaction needs to be filtered and dried, and the product drying temperature is 50°C to 200°C, and the drying time is 1h to 20h.

[0045] S2. Grinding the alumina hydrate to obtain alphah-type Al2O3·nH2O, wherein n<1.2;

[0046] In the embodiments of the present application, alumina hydrate is ground to make the alumina hydrate more refined and uniform. Due to the internal structure of the alumina hydrate and the interaction of internal water, the alumina hydrate is further converted into alphah-type Al2O3·nH2O. Alphah-type Al2O3·nH2O, also known as α_Al2O3·nH2O, is a form of aluminum oxide containing crystal water. Among them, α_Al2O3·nH2O is a crystal form of aluminum oxide with a trigonal crystal structure. The presence of crystal water (nH2O, n represents the molar content of crystal water) will affect its physical and chemical properties. For example, during the heating process, crystal water will gradually be lost, thereby changing the form and properties of the substance. Alumina contains the elements aluminum and oxygen. The aluminum ions and oxygen ions in this structure are arranged according to a specific crystal structure. Under the α_Al2O3 crystal form, its atomic arrangement gives it higher hardness, melting point and other characteristics. When combined with crystal water, its solubility and other properties will change to a certain extent. It is usually a white solid that is insoluble in water. It is odorless, tasteless, extremely hard, and easy to absorb moisture without deliquescing (it is not hygroscopic after burning). α_Al2O3·nH2O has excellent thermal stability. The grinding process helps to adjust the position and binding mode of water molecules in the alumina crystal structure, making it more stable in the alphah-type Al2O3·nH2O structure; n is <1.2, and the lower degree of hydration can make alphah-type Al2O3·nH2O have higher thermal stability and improve the reactivity of alphah-type Al2O3·nH2O. Exemplary, the n can be 1.15, 1.1, 1.0, 0.9, 0.8, etc., and the grinding time can be more than 10 hours.

[0047] S3, performing a first heat treatment on the second industrial aluminum hydroxide to cause a qualitative change in the microstructure of the second industrial aluminum hydroxide;

[0048] In some embodiments, the process parameters of the first heat treatment include: a temperature of 900° C. to 1200° C., and a time of 3 seconds to 10 seconds.

[0049] In an embodiment of the present application, in an embodiment of the present application, the second industrial aluminum hydroxide undergoes a first heat treatment, which can cause the attached water, crystallization water content and internal microstructure of the second industrial aluminum hydroxide to undergo qualitative changes, and this qualitative change will reshape the physical and chemical properties and functional group types of the second industrial aluminum hydroxide. In the first heat treatment, the temperature can be 900°C to 1200°C, and the time can be 3s to 10s. This instantaneous high-temperature heat treatment can fully cause the microstructure of the second industrial aluminum hydroxide to undergo qualitative changes, and obtain the target first heat treatment product (modified second industrial aluminum hydroxide). Exemplarily, in the first heat treatment, the temperature can be 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C, 1200°C, etc.; the time can be 3s, 4s, 5s, 6s, 7s, 8s, 9s, 10s, etc.

[0050] S4, subjecting the second industrial aluminum hydroxide after the first heat treatment to a second solvent thermal reaction with the first acidic regulator to obtain an aluminum oxide substance containing a functional group;

[0051] In some embodiments, the process parameters of the second solvothermal reaction include: temperature of 80° C. to 250° C., time of 3 h to 10 h, and pH value <7.

[0052] In the embodiment of the present application, in the second solvent thermal reaction, the temperature can be 80°C to 250°C, the time can be 3h to 10h, and the pH value can be <7. Within this temperature, time and pH value range, sufficient energy and time can be provided for the first solvent thermal reaction to promote the chemical reaction of the second industrial aluminum hydroxide and the organic functional groups in the first acidic regulator, thereby generating aluminum oxide substances with higher activity containing functional groups. Exemplary, in the second solvent thermal reaction, the temperature can be 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 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. The first industrial aluminum hydroxide and the second industrial aluminum oxide can both be aluminum hydroxide obtained in the form of seed hydrogenation aluminum, carbon hydrogenation aluminum, neutralized hydrogenation aluminum or other forms.

[0053] S5, mixing the aluminum oxide material containing a functional group, the alphah-type Al2O3·nH2O, a second acidic regulator and a solvent to obtain a slurry;

[0054] In some embodiments, the weight M1 of the aluminum oxide material containing functional groups, the weight M2 of the alphah-type Al2O3·nH2O, the weight M3 of the second acidic regulator, and the volume V of the solvent satisfy the relationship: M1:M2:M3:V=(1.5~10):(2~15):(0.1~10):500; wherein, if the unit of weight is gram, the unit of volume is milliliter.

[0055] In the embodiment of the present application, M1:M2:M3:V can be = (1.5-10): (2-15): (0.1-10): 500, which can ensure the density and temperature resistance of the alumina aerogel. The aluminum oxide material containing functional groups provides a skeleton, functional groups and aluminum oxide components for the subsequent formation of inorganic alumina colloid; alphah-type Al2O3·nH2O provides the high-temperature resistant components of the alumina aerogel and provides a sufficient number of functional groups; the second acidic regulator adjusts the pH value of the slurry to <7, and the solvent fully disperses and dilutes the aluminum oxide material containing functional groups and alphah-type Al2O3·nH2O, and lays the basic conditions for the subsequent formation of alumina aerogel, facilitating the formation of a porous skeleton structure. The solvent can be water. Exemplarily, the above-mentioned 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. Therefore, 1.5 to 10 grams of alumina material containing functional groups can be added to every 500 ml of water, and 2 to 15 grams of alphah-type Al2O3·nH2O and 0.1 to 10 grams of a second acidic regulator can be added at the same time.

[0056] S6, freezing the slurry to obtain a first alumina aerogel;

[0057] In the embodiment of the present application, under the action of the second acidic regulator and freezing conditions, the functional group-containing aluminum oxide substance and alphah-type Al2O3·nH2O can undergo a glue chain reaction, thereby forming a first alumina aerogel with a three-dimensional network structure, while retaining the pore structure formed by the first alumina aerogel and strengthening the alumina aerogel skeleton.

[0058] In some embodiments, the freezing comprises 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.

[0059] In the embodiment of the present application, the functional group-containing aluminum oxide material and alphah-type Al2O3·nH2O both have high activity. Under the action of the second acidic regulator and the first freezing condition, the functional group-containing aluminum oxide material and alphah-type Al2O3·nH2O can form a glue chain reaction, thereby forming a first alumina aerogel with a three-dimensional network structure, while retaining the pore structure formed by the first alumina aerogel and strengthening the alumina aerogel skeleton; the second freezing removes moisture from the alumina aerogel while strengthening and retaining the pore structure formed by the alumina aerogel. In order to fully achieve the above-mentioned freezing effect, and taking into account the morphology, pore size and performance of the alumina aerogel, the temperature of the first freezing can be -50°C to -60°C, and the temperature of the second freezing can be -50°C to -80°C. For example, the temperature of the first freezing can be -50°C, -52°C, -54°C, -56°C, -58°C, -60°C, etc.; the temperature of the second freezing can be -50°C, -60°C, -70°C, -80°C, etc. The first freezing time can be 4 to 6 hours, and the second freezing time can be 12 to 48 hours.

[0060] In some embodiments, the first acidic regulator and the second acidic regulator each include at least one of the following: an inorganic acid, an organic acid, and an aluminum salt.

[0061] In an embodiment of the present application, the first acidic regulator and the second acidic regulator may be a combination of one or more of an inorganic acid, an organic acid, and an aluminum salt.

[0062] S7. Subjecting the first alumina aerogel to a second heat treatment in a non-oxidizing atmosphere and a third heat treatment in an air atmosphere in sequence to obtain a high-temperature resistant alumina aerogel.

[0063] In some embodiments, the temperature of the second heat treatment is 600° C. to 750° C.; and / or,

[0064] The temperature of the third heat treatment is 650°C to 700°C.

[0065] In an embodiment of the present application, the first alumina aerogel undergoes a second heat treatment in a non-oxidizing atmosphere, which can retain the elements in the first alumina aerogel that are susceptible to oxidation. The functional group elements in the first alumina aerogel that are not oxidized can provide a skeleton effect, forming an inorganic alumina gel and increasing the strength of the pore skeleton of the first alumina aerogel. When the inorganic alumina gel undergoes a third heat treatment in an air atmosphere, the elements that are susceptible to oxidation are oxidized and calcined, thereby improving the purity of the first alumina aerogel while retaining the original skeleton structure of the first alumina aerogel, thereby preparing a high-temperature resistant alumina aerogel. In order to achieve the above effects, and taking into account the performance and production energy consumption cost of the alumina aerogel, the temperature of the second heat treatment can be 600°C to 750°C, and the temperature of the third heat treatment can be 650°C to 700°C. For example, the temperature of the second heat treatment may be 600°C, 620°C, 640°C, 660°C, 680°C, 700°C, 720°C, 750°C, etc.; the temperature of the third heat treatment may be 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, etc. The duration of the second heat treatment and the duration of the third heat treatment may be 4 hours to 8 hours, respectively, and the heating rate of the second heat treatment and the third heat treatment may be 3°C / min to 5°C / min.

[0066] In a second aspect, the present application provides a high temperature resistant alumina aerogel, which is prepared by any one of the methods described in the first aspect.

[0067] The high-temperature resistant alumina aerogel is realized based on the above-mentioned preparation method of the high-temperature resistant alumina aerogel. The specific steps of the preparation method of the high-temperature resistant alumina aerogel can refer to the above-mentioned embodiment. Since the high-temperature resistant alumina aerogel adopts part or all of the technical solutions of the above-mentioned embodiment, it has at least all the beneficial effects brought about by the technical solutions of the above-mentioned embodiment, which will not be repeated here.

[0068] The present application will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present application only and are not intended to limit the scope of the present application. The experimental methods in the following examples where specific conditions are not specified are usually measured in accordance with national standards. If there are no corresponding national standards, then the methods are carried out in accordance with general international standards, conventional conditions, or according to the conditions recommended by the manufacturer.

[0069] Example 1

[0070] A method for preparing high-temperature resistant alumina aerogel specifically comprises: forming a 40% mass concentration slurry of industrial aluminum hydroxide and water at room temperature, maintaining the reaction at 180°C for 5 hours to obtain an alumina hydrate slurry, wherein the alumina hydrate has a particle size of less than 10 μm; filtering and drying the alumina hydrate slurry; and adding the dried product to a grinding device at room temperature for 12 hours to obtain alphah-type Al2O3·nH2O (n is 0.67).

[0071] Industrial aluminum hydroxide was modified at 900°C for 10 seconds, and the modified industrial aluminum hydroxide was stirred with water to form a slurry. Formic acid was added to control the pH value to 2, and the mixture was hydrothermally treated at 130°C for 4 hours to obtain a slurry of aluminum oxide containing functional groups. The slurry of aluminum oxide containing functional groups was diluted to a standard of 1.5 grams of aluminum oxide containing functional groups per 500 ml of water, and 5 grams of alphah-type Al2O3·nH2O and 1 gram of aluminum chloride were added and mixed uniformly to obtain a mixed slurry. The mixed slurry was frozen at -50°C for 4 hours and then freeze-dried at -50°C for 48 hours to obtain a frozen composite. The frozen composite was heated at 700°C in a non-oxidizing atmosphere for 5 hours at a heating rate of 5°C / min. The composite was heated to 650°C in an air atmosphere at a heating rate of 4°C / min and kept at this temperature for 5 hours to obtain a high-temperature resistant aluminum oxide aerogel. The thermal conductivity coefficients of the aluminum oxide aerogel prepared in Example 1 at different temperatures are shown in Table 1:

[0072] Table 1 Thermal conductivity of high temperature resistant alumina aerogel of Example 1 at different temperatures (w / (mk)

[0073]

[0074] Example 2

[0075] A method for preparing high-temperature resistant alumina aerogel specifically comprises: forming a 40% mass concentration slurry of industrial aluminum hydroxide and water at room temperature, maintaining the reaction at 180°C for 5 hours to obtain an alumina hydrate slurry, wherein the alumina hydrate has a particle size of less than 10 μm; filtering and drying the alumina hydrate slurry; and adding the dried product to a grinding device at room temperature for 12 hours to obtain alphah-type Al2O3·nH2O (n is 0.67).

[0076] Industrial aluminum hydroxide was modified at 1100°C for 3 seconds, and the modified industrial aluminum hydroxide was stirred with water to form a slurry. Formic acid was added to control the pH value at 2, and the mixture was hydrothermally treated at 150°C for 4 hours to obtain a slurry of aluminum oxide containing functional groups. The slurry of aluminum oxide containing functional groups was diluted to a standard of 2.5 grams of aluminum oxide containing functional groups per 500 ml of water. 5 grams of the alpha-type new aluminum oxide obtained in the first step and 5 grams of aluminum chloride were added and mixed uniformly to obtain a mixed slurry. The mixed slurry was frozen at -50°C for 4 hours and then freeze-dried at -50°C for 48 hours to obtain a frozen composite. The frozen composite was heated at 700°C in a non-oxidizing atmosphere for 5 hours at a heating rate of 5°C / min. The composite was heated to 660°C in an air atmosphere at a heating rate of 3-5°C / min and then kept warm for 5 hours to obtain a high-temperature resistant aluminum oxide aerogel. The thermal conductivity coefficients of the aluminum oxide aerogels prepared in Example 2 at different temperatures are shown in Table 2:

[0077] Table 2 Thermal conductivity of high temperature resistant alumina aerogel of Example 2 at different temperatures (w / (mk)

[0078]

[0079]

[0080] Example 3

[0081] A method for preparing high-temperature resistant alumina aerogel specifically comprises: forming a 40% mass concentration slurry of industrially produced aluminum hydroxide and water at room temperature, and then heat-retaining the mixture at 200°C for 3 hours to obtain an alumina hydrate slurry, wherein the alumina hydrate has a particle size of less than 10 μm; filtering and drying the alumina hydrate slurry, and adding the dried product to a grinding device for 14 hours to obtain alphah-type Al2O3·nH2O (n is 0.73).

[0082] Industrial aluminum hydroxide was modified at 1100°C for 3 seconds, and the modified industrial aluminum hydroxide was stirred with water to form a slurry. Acetic acid was added to control the pH value to 2, and the mixture was hydrothermally treated at 140°C for 4 hours to obtain a slurry of aluminum oxide containing functional groups. The slurry of aluminum oxide containing functional groups was diluted to a standard of 2.5 grams of aluminum oxide containing functional groups per 500 ml of water. 7 grams of alphah-type Al2O3·nH2O and 3 grams of aluminum chloride were added and mixed uniformly to obtain a mixed slurry. The mixed slurry was frozen at -50°C for 4 hours and then freeze-dried at -50°C for 48 hours to obtain a frozen composite. The frozen composite was heated at 700°C in a non-oxidizing atmosphere for 5 hours at a heating rate of 5°C / min. The composite was heated to 680°C in an air atmosphere at a heating rate of 4°C / min and then kept at this temperature for 5 hours to obtain a high-temperature resistant aluminum oxide aerogel. The thermal conductivity coefficients of the aluminum oxide aerogels prepared in Example 3 at different temperatures are shown in Table 3:

[0083] Table 3 Thermal conductivity of high temperature resistant alumina aerogel of Example 3 at different temperatures (w / (mk)

[0084]

[0085] Example 4

[0086] A method for preparing high-temperature resistant alumina aerogel specifically comprises: forming a 20% mass concentration slurry of industrial aluminum hydroxide and water at room temperature, adding 3.5% by weight of a grain control agent, and maintaining the reaction at 180°C for 3 hours to obtain an alumina hydrate slurry, wherein the alumina hydrate has a particle size of less than 10 μm; filtering and drying the alumina hydrate slurry, adding the dried product to a grinding device, and grinding it for 13 hours to obtain alphah-type Al2O3·nH2O (n is 0.68).

[0087] Industrial aluminum hydroxide is modified at 1100°C for 3 seconds, the modified industrial aluminum hydroxide is stirred with water to form a slurry, formic acid and acetic acid are added to control the pH value to 2, and the mixture is hydrothermally treated at 135°C for 4 hours to obtain a slurry of aluminum oxide containing functional groups. The slurry of aluminum oxide containing functional groups is diluted to a standard of 5 grams of aluminum oxide containing functional groups per 500 ml of water, and 10 grams of alphah-type Al2O3·nH2O and 3 grams of a mixture of aluminum chloride and aluminum nitrate are added and mixed uniformly to obtain a mixed slurry. The mixed slurry is frozen at -50°C for 4 hours and then freeze-dried at -50°C for 48 hours to obtain a frozen composite. The frozen composite is heated at 700°C in a non-oxidizing atmosphere for 5 hours at a heating rate of 5°C / min. The temperature is then increased to 680°C in an air atmosphere at a heating rate of 3°C / min and then maintained at this temperature for 5 hours to obtain a high-temperature resistant alumina aerogel. The thermal conductivity of the alumina aerogel prepared in Example 4 at different temperatures is shown in Table 4:

[0088] Table 4 Thermal conductivity of high temperature resistant alumina aerogel of Example 4 at different temperatures (w / (mk)

[0089]

[0090] Example 5

[0091] A method for preparing high-temperature resistant alumina aerogel specifically comprises: forming a 20% mass concentration slurry of industrial aluminum hydroxide and water at room temperature, adding 3.5% by weight of a grain control agent, and maintaining the reaction at 180°C for 3 hours to obtain an alumina hydrate slurry, wherein the alumina hydrate has a particle size of less than 10 μm; filtering and drying the alumina hydrate slurry, adding the dried product to a grinding device, and grinding for 15 hours to obtain alphah-type Al2O3·nH2O (n is 0.76).

[0092] Industrial aluminum hydroxide was modified at 1100°C for 3 seconds, and the modified industrial aluminum hydroxide was stirred with water to form a slurry. Formic acid was added to control the pH value to 2, and the mixture was hydrothermally treated at 160°C for 4 hours to obtain a slurry of aluminum oxide containing functional groups. The slurry of aluminum oxide containing functional groups was diluted to a standard of 2.5 grams of aluminum oxide containing functional groups per 500 ml of water. 5 grams of alphah-type Al2O3·nH2O and 1 gram of aluminum nitrate were added and mixed uniformly to obtain a mixed slurry. The mixed slurry was frozen at -50°C for 4 hours and then freeze-dried at -50°C for 48 hours to obtain a frozen composite. The frozen composite was heated at 700°C in a non-oxidizing atmosphere for 5 hours at a heating rate of 5°C / min. The composite was heated to 700°C in an air atmosphere at a heating rate of 5°C / min and then kept at this temperature for 5 hours to obtain a high-temperature resistant aluminum oxide aerogel. The thermal conductivity coefficients of the aluminum oxide aerogel prepared in Example 5 at different temperatures are shown in Table 5:

[0093] Table 5 Thermal conductivity of high temperature resistant alumina aerogel of Example 5 at different temperatures (w / (mk))

[0094]

[0095] Comparative Example 1

[0096] A method for preparing high-temperature resistant alumina aerogel specifically comprises: forming a 40% mass concentration slurry of industrial aluminum hydroxide and water at room temperature, maintaining the reaction at 180°C for 5 hours to obtain an alumina hydrate slurry, wherein the alumina hydrate has a particle size of less than 10 μm; filtering and drying the alumina hydrate slurry; and adding the dried product to a grinding device at room temperature for 13 hours to obtain alphah-type Al2O3·nH2O (n is 1).

[0097] Industrial aluminum hydroxide was stirred into a slurry by adding water, formic acid was added to control the pH value to 2, and hydrothermally treated at 130°C for 4 hours. The hydrothermally treated aluminum hydroxide slurry was diluted to a dilution standard of 1.5 grams of aluminum oxide per 500 ml of water, and 5 grams of alphah-type Al2O3·nH2O and 1 gram of aluminum chloride were added and mixed uniformly to obtain a mixed slurry. The mixed slurry was frozen at -50°C for 4 hours and then freeze-dried at -50°C for 48 hours to obtain a frozen composite. The frozen composite was heated at 700°C in a non-oxidizing atmosphere for 5 hours at a heating rate of 5°C / min. The composite was then heated to 650°C in an air atmosphere at a heating rate of 4°C / min and kept at that temperature for 5 hours to obtain a high-temperature resistant alumina aerogel. The thermal conductivity coefficients of the alumina aerogels prepared in Comparative Example 1 at different temperatures are shown in Table 6:

[0098] Table 6 Thermal conductivity of high temperature resistant alumina aerogel of Comparative Example 1 at different temperatures (w / (mk)

[0099]

[0100] It can be seen from Examples 1 to 5 that the thermal conductivity of the high-temperature resistant alumina aerogel is no more than 0.03w / (mk) under the conditions of room temperature (25°C) to 1400°C, which demonstrates excellent high-temperature resistance. Figure 2 This is a scanning electron microscope image of a high-temperature resistant alumina aerogel provided in Example 1 of the present application; Figure 3 This is a scanning electron microscope image of a high-temperature resistant alumina aerogel provided in Example 2 of the present application; Figure 4 This is a scanning electron microscope image of a high-temperature resistant alumina aerogel provided in Example 3 of the present application; Figure 5 This is a scanning electron microscope image of a high-temperature resistant alumina aerogel provided in Example 4 of the present application; Figure 6 This is a scanning electron microscope image of a high-temperature resistant alumina aerogel provided in Example 5 of this application; see Figures 2 to 6 , combined with Tables 1 to 5, it is shown that the alumina aerogel prepared in the present embodiment has good uniformity, a unique internal structure, and good heat resistance. In contrast, in Comparative Example 1, the industrial aluminum hydroxide was not subjected to transient heat treatment. Combined with Table 6, it is shown that the alumina aerogel obtained in Comparative Example 1 has poor heat resistance.

[0101] One or more technical solutions in the embodiments of the present application may have at least the following technical effects or advantages:

[0102] (1) The raw materials used in the preparation method of the high-temperature resistant alumina aerogel provided in the embodiment of the present application are all industrially produced aluminum hydroxide, and no organic aluminum salt or inorganic aluminum salt is used, which greatly reduces the production cost;

[0103] (2) The method for preparing high-temperature resistant alumina aerogel provided in the embodiment of the present application is resistant to high temperatures compared with other processes for preparing alumina aerogel; thirdly, compared with the currently commonly used supercritical drying method for preparing aerogel, this process does not require a high-cost, long-cycle supercritical drying process. The process has a short preparation cycle and low manufacturing cost, laying the foundation for large-scale industrial preparation of high-temperature resistant alumina aerogel.

[0104] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. 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 the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A method for preparing high temperature resistant alumina aerogel, characterized in that: The method comprises: subjecting the first industrial aluminum hydroxide to a first solvent thermal reaction to obtain aluminum oxide hydrate; The alumina hydrate is ground to obtain alphah-type Al2O3·nH2O, wherein n<1.2; performing a first heat treatment on the second industrial aluminum hydroxide so as to cause a qualitative change in the microstructure of the second industrial aluminum hydroxide; performing a second solvent thermal reaction on the second industrial aluminum hydroxide after the first heat treatment and the first acidic regulator to obtain an aluminum oxide substance containing a functional group; Mixing the aluminum oxide material containing a functional group, the alphah-type Al2O3·nH2O, a second acidic regulator, and a solvent to obtain a slurry; Freezing the slurry to obtain a first alumina aerogel; The first alumina aerogel is sequentially 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, characterized in that The process parameters of the first solvent thermal reaction include: temperature of 80° C. to 300° C., and time of 3 h to 10 h.

3. The method according to claim 1 or 2, characterized in that The particle size of the alumina hydrate is 10 μm or less.

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

5. The method according to claim 1, wherein The process parameters of the second solvent thermal reaction include: temperature of 80° C. to 250° C., time of 3 h to 10 h, and pH value <7.

6. The method according to claim 1, characterized in that The weight M1 of the aluminum oxide substance containing functional groups, the weight M2 of the alphah-type Al2O3·nH2O, the weight M3 of the second acidic regulator and the volume V of the solvent satisfy the relationship: M1:M2:M3:V=(1.5~10):(2~15):(0.1~10):500; wherein, if the unit of weight is gram, the unit of volume is milliliter.

7. The method according to claim 1, characterized in that 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, characterized in that The first acidic regulator and the second acidic regulator each include at least one of the following: an inorganic acid, an organic acid, and an aluminum salt.

9. The method according to claim 1, characterized in that The temperature of the second heat treatment is 600° C. to 750° C.; and / or, The temperature of the third heat treatment is 650°C to 700°C.

10. A high temperature resistant alumina aerogel, characterized in that: The alumina aerogel is prepared by the method according to any one of claims 1 to 9.

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