A method for preparing an alumina aerogel

Abstract

The application provides a preparation method of an alumina aerogel, and belongs to the field of aerogels. The method comprises the following steps: modifying industrial aluminum hydroxide to cause a crystal type transformation of the industrial aluminum hydroxide; mixing the modified industrial aluminum hydroxide with a solvent to obtain a first slurry; adjusting the pH value of the first slurry to a set pH value; performing hydrothermal treatment on the first slurry with the set pH value to obtain a second slurry; adjusting the solid content of the second slurry to a set solid content; adding an aluminum salt to the second slurry with the set solid content to obtain a third slurry; sequentially performing freezing and freeze-drying on the third slurry to obtain a frozen composite; and sequentially performing first heating in a non-oxidizing atmosphere and second heating in an oxidizing atmosphere on the frozen composite to obtain the alumina aerogel. Thus, a new preparation method of the alumina aerogel is provided.

Description

Technical Field

[0001] The present application relates to the technical field of aerogels, and in particular to a method for preparing alumina aerogels. Background Art

[0002] Aerogel is an ultra-low density porous solid material composed of nanoparticles or polymer molecules. The spatial structure can reach 95% of the total volume. The pore size is generally 1nm to 100nm and the specific surface area is 200m 2 / g~1000m 2 / g, and the density can vary by 0.03g / mL to 0.5g / mL. Compared with conventional solid materials, it has many special properties in mechanics, acoustics, thermals, optics, etc., such as extremely low apparent density, small refractive index, low Young's modulus and porosity of more than 90%. It is currently the solid material with the lowest thermal conductivity. The unique structure and properties of aerogel make it have great application value in catalysis, thermal insulation, glass and ceramics. There are many types of aerogels, and different classification standards can be used to divide them into different categories. Oxide aerogels are one of them. Among oxide aerogels, alumina aerogels are favored because of their high temperature resistance and low price.

[0003] Alumina aerogels are primarily prepared using the sol-gel method. Depending on the precursor, there are two main methods: the inorganic aluminum salt method and the organic alcohol aluminum salt method. Generally speaking, alumina aerogels prepared using organic alcohol aluminum salts have relatively good formability and relatively low density. However, due to the lengthy preparation process, severe sample shrinkage during solvent exchange and drying, poor mechanical strength, high cost, high toxicity, and difficult-to-control hydrolysis process of organic alcohol aluminum salts, their large-scale application is limited. Compared with organic alcohol aluminum salts, preparing alumina aerogels using inorganic aluminum salts as the aluminum source offers advantages such as simpler processes, easier reaction control, and lower costs. The inorganic aluminum salt method has greater economic value and development potential. However, alumina aerogels prepared using inorganic aluminum salts typically have larger alumina particles, which affects the aerogel's formability and makes it more likely to form fragments. Currently, supercritical drying is generally used to prepare various aerogels, and even aerogel production methods that have entered the industrial application stage still use supercritical drying. Although some companies use atmospheric pressure drying to produce aerogels, their product performance has rarely been recognized by market users. However, supercritical drying methods have a long preparation cycle and high costs. In line with the principles of shortening the drying cycle and reducing costs, a new process for preparing alumina aerogels is being developed. Summary of the Invention

[0004] The present application provides a method for preparing alumina aerogel to solve the following technical problems: providing a new method for preparing alumina aerogel.

[0005] In a first aspect, the present application provides a method for preparing an alumina aerogel, the method comprising:

[0006] Modifying industrial aluminum hydroxide so as to cause the industrial aluminum hydroxide to undergo a crystal transformation;

[0007] Mixing the modified industrial aluminum hydroxide with a solvent to obtain a first slurry;

[0008] adjusting the pH value of the first slurry to a set pH value;

[0009] hydrothermally treating the first slurry having a set pH value to obtain a second slurry;

[0010] adjusting the solid content of the second slurry to a set solid content;

[0011] adding aluminum salt to the second slurry having a set solid content to obtain a third slurry;

[0012] freezing and freeze-drying the third slurry in sequence to obtain a frozen composite; and

[0013] The frozen composite is sequentially subjected to a first heating in a non-oxidizing atmosphere and a second heating in an oxidizing atmosphere to obtain an alumina aerogel.

[0014] Optionally, the modification includes the following parameters: a heat treatment temperature of 900° C. to 1200° C., and a heat treatment time of 3s to 10s.

[0015] Optionally, the set pH value is <7.

[0016] Optionally, the hydrothermal treatment includes the following parameters: temperature of 80°C to 250°C, and time of 3h to 10h.

[0017] Optionally, the solid content is set to 5g / L to 30g / L.

[0018] Optionally, the mass ratio of the hydrous aluminum oxide to the aluminum salt in the third slurry is (2.5-15):1, and the aluminum salt includes at least one of the following: an organic aluminum salt and an inorganic aluminum salt.

[0019] Optionally, the freezing includes the following parameters: freezing temperature is -50°C to -20°C, and freezing time is 3h to 5h.

[0020] Optionally, the freeze-drying time is 12 hours to 48 hours.

[0021] Optionally, the first heating includes the following parameters: a heating rate of 3°C / min to 5°C / min, an end point temperature of 600°C to 750°C, and a holding time of 4h to 6h.

[0022] Optionally, the second heating includes the following parameters: a heating rate of 3°C / min to 5°C / min, an end point temperature of 650°C to 700°C, and a holding time of 4h to 6h.

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

[0024] The present application provides a method for preparing alumina aerogel, which comprises: modifying industrial aluminum hydroxide to cause the industrial aluminum hydroxide to undergo a crystal transformation; mixing the modified industrial aluminum hydroxide with a solvent to obtain a first slurry; adjusting the pH value of the first slurry to a set pH value; subjecting the first slurry with the set pH value to a hydrothermal treatment to obtain a second slurry; adjusting the solid content of the second slurry to a set solid content; adding an aluminum salt to the second slurry with the set solid content to obtain a third slurry; freezing and freeze-drying the third slurry in sequence to obtain a frozen composite; and heating the frozen composite in a non-oxidizing atmosphere for a first time and in an oxidizing atmosphere for a second time to obtain the alumina aerogel. First, by modifying the industrial aluminum hydroxide, a rapid transformation of the industrial aluminum hydroxide from a stable crystalline structure to a highly active amorphous structure is achieved; second, by adjusting the pH value of the slurry and performing a hydrothermal treatment, the desired intermediate substance is generated; and third, by freezing and freeze-drying, the material structure in the slurry is effectively fixed and the water activity is reduced. This also facilitates the formation of a primary aerogel of a certain strength and improves the internal structure of the aerogel. Finally, through the first heating in a non-oxidizing atmosphere and the second heating in an oxidizing atmosphere, a high-strength aerogel is formed that can resist damage caused by stress. At the same time, the acid ions and other oxidizable substances in the aerogel are successfully removed, forming a pure alumina aerogel. This provides a new method for preparing 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 an alumina aerogel provided in an embodiment of the present application;

[0028] Figure 2 The XRD pattern of industrial aluminum hydroxide provided in Example 1 of the present application;

[0029] Figure 3 This is the XRD pattern of the industrial aluminum hydroxide provided in Example 1 of the present application after modification;

[0030] Figure 4 This is the XRD pattern of the alumina aerogel provided in Example 1 of the present application. DETAILED DESCRIPTION

[0031] 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.

[0032] 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.

[0033] In addition, in the description of the present application, the terms "comprise", "contain" and the like mean "comprise but not limited to". In this paper, such as "first" and "second" and other relational terms are only used 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 the entities or operations. In this paper, "and / or", the association relationship between the associated objects, means that there can be three kinds of relationships, for example, A and / or B can represent: A exists alone, A and B exist together, and B exists alone. Where A, B can be singular or plural. In this paper, "at least one" means one or more, and "multiple" means two or more. "At least one", "at least one of the following" or similar expressions means any combination of these items, including any combination of single item or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can represent a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple. "Parts ratio" such as weight parts, mass parts and the like represents the proportional relationship between the components. In the proportional relationship involved in this paper, the parameters that need to be described by proportion should be understood as the front item of the proportional formula in the order of description, and the proportional number is understood as the latter item of the proportional formula, for example, the mass ratio of substance A, substance B and substance C is 1:2:3, then substance A, substance B and substance C should be one-to-one corresponding in the proportional formula with the proportional number according to the description order, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0034] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0035] Figure 1 A flowchart of a preparation method of an alumina aerogel provided in an embodiment of the present application.

[0036] As shown in Figure 1 The present application provides a preparation method of an alumina aerogel, which comprises:

[0037] S1, modifying industrial aluminum hydroxide to cause the industrial aluminum hydroxide to undergo crystal type transformation;

[0038] In some embodiments, the industrial aluminum hydroxide can be a kind of aluminum hydroxide, carbon aluminum hydroxide, neutral aluminum hydroxide or other forms of aluminum hydroxide.

[0039] Before modification, industrial aluminum hydroxide is trihydrate aluminum oxide, which has a relatively stable crystal structure. After modification, the trihydrate aluminum oxide undergoes a crystal transformation from a crystal structure to an amorphous structure. This amorphous structure is between the crystal structure and amorphous aluminum oxide, has a very high charge density, and has very good activity, which is conducive to the subsequent reaction steps.

[0040] In some embodiments, the modification includes the following parameters: a heat treatment temperature of 900° C. to 1200° C., and a heat treatment time of 3 s to 10 s.

[0041] The heat treatment temperature is limited to 900℃~1200℃, and the heat treatment time is 3s~10s, so that the formed material has the required structure and activity. If the heat treatment temperature is lower than 900℃, even if the time is very long, the material with such activity and structure cannot be obtained. Moreover, if the heat treatment time is too long at low temperature, the amorphous material will also undergo structural changes, resulting in changes in the properties of the newly formed material. The time required at high temperature is extremely short. If the heat treatment time is higher than 10s, transitional alumina with different structures will be generated at high temperature, losing the properties required by the present invention. For example, the heat treatment temperature can be 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃, 1200℃, etc., and the heat treatment time is 3s, 4s, 5s, 6s, 7s, 8s, 9s, 10s, etc.

[0042] S2, mixing the modified industrial aluminum hydroxide with a solvent to obtain a first slurry;

[0043] S3, adjusting the pH value of the first slurry to a set pH value;

[0044] In some embodiments, the set pH value is <7.

[0045] Alumina is an amphoteric substance. Different reactions will occur under alkaline or acidic conditions to produce substances with different structures. If the pH is greater than 7, it is an alkaline solution. As the pH value increases, the aluminum hydroxide trihydrate treated at high temperature becomes very active and will gradually dissolve into the aqueous solution to form sodium aluminate. If the pH value is kept below 7, it is an acidic solution. As long as the appropriate pH value is controlled, even if a very small amount of active substances dissolves into the solution in the form of colloidal particles, it is beneficial to the preparation of aerogels. Moreover, as long as the appropriate pH range is controlled for the substances treated at high temperature, most of them will not dissolve into the aqueous solution and will not affect the preparation process of aerogels. For example, the pH value can be set to 0.5, 1, 2, 3, 4, 5, 6, 6.5, etc.

[0046] S4, hydrothermally treating the first slurry having a set pH value to obtain a second slurry;

[0047] In some embodiments, the hydrothermal treatment includes the following parameters: temperature of 80° C. to 250° C., and time of 3 h to 10 h.

[0048] The purpose of hydrothermal treatment is to provide sufficient energy to generate the required intermediate substances. If the temperature of the hydrothermal treatment is higher than 250°C, under sealed conditions, the pressure will vary greatly, which is a severe test for the equipment. In addition, under acidic conditions, the temperature and pressure will accelerate the corrosion of the equipment and increase the safety risks of the equipment. If the temperature is lower than 80°C, the reaction time will be very long. If the time is too long, some substances will also undergo transformation, reducing the activity and affecting the subsequent process. For example, the temperature of the hydrothermal treatment can be 80°C, 100°C, 120°C, 150°C, 200°C, 220°C, 250°C, etc., and the time can be 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, etc.

[0049] S5. Adjusting the solid content of the second slurry to a set solid content;

[0050] In some embodiments, the set solid content is 5 g / L to 30 g / L.

[0051] Solid content refers to the ratio of the mass of solid matter in the slurry to the total volume of the slurry.

[0052] S6. Adding aluminum salt to the second slurry having a set solid content to obtain a third slurry;

[0053] In some embodiments, the mass ratio of the hydrous aluminum oxide to the aluminum salt in the third slurry is (2.5-15):1, and the aluminum salt includes at least one of the following: an organic aluminum salt and an inorganic aluminum salt.

[0054] In some embodiments, the organic aluminum salt includes aluminum isopropoxide, aluminum n-butoxide and other aluminum-based complex organic substances; the inorganic aluminum salt includes aluminum sulfate, aluminum chloride and aluminum nitrate or a mixture thereof.

[0055] The purpose of adding aluminum salt is twofold: first, it adjusts the pH value of the solution with aluminum salt, and second, it provides a certain amount of acid ions, which will play a role in subsequent experiments. For example, the solid content can be set to 5g / L, 8g / L, 10g / L, 12g / L, 15g / L, 20g / L, 22g / L, 25g / L, 28g / L, 30g / L, etc. The mass ratio of hydrous alumina to aluminum salt in the third slurry can be 2.5:1, 4:1, 5:1, 8:1, 10:1, 12:1, 15:1, etc.

[0056] S7, sequentially freezing and freeze-drying the third slurry to obtain a frozen composite; and

[0057] In some embodiments, the freezing includes the following parameters: freezing temperature is -50°C to -20°C, and freezing time is 3h to 5h.

[0058] In some embodiments, the freeze-drying time is 12 hours to 48 hours.

[0059] The purpose of freezing is to fix the material structure in the slurry and prevent deformation or damage during the subsequent drying process. Freezing also reduces the water activity in the slurry, facilitating the subsequent freeze-drying process. Freeze-drying has two purposes: first, removing moisture through freeze-drying, reducing the surface tension in the gel pores, and forming a primary aerogel of a certain strength; second, after freeze-drying, the internal structure of the primary aerogel undergoes a certain degree of rearrangement, improving the performance and strength of the subsequent aerogel. This rearrangement facilitates the formation of high-performance aerogels. For example, the freezing temperature can be -50°C, -40°C, -35°C, -30°C, -20°C, etc., the freezing time can be 3 hours, 3.2 hours, 3.5 hours, 3.8 hours, 4 hours, 4.2 hours, 4.5 hours, 4.8 hours, 5 hours, etc., and the freeze-drying time can be 12 hours, 16 hours, 20 hours, 25 hours, 30 hours, 35 hours, 40 hours, 45 hours, 48 ​​hours, etc.

[0060] S8. sequentially heating the frozen composite in a non-oxidizing atmosphere for a first time and in an oxidizing atmosphere for a second time to obtain an alumina aerogel.

[0061] It is understood that non-oxidizing atmospheres generally refer to those that can prevent or slow down the oxidation reaction of materials. Such atmospheres usually contain inert gases (such as nitrogen, argon, helium, etc.) or reducing gases (such as hydrogen, carbon monoxide, etc.). Oxidizing atmospheres refer to those that contain sufficient oxygen to support or promote the oxidation reaction of materials. This atmosphere is usually ordinary air.

[0062] In some embodiments, the first heating includes the following parameters: a heating rate of 3°C / min to 5°C / min, an end point temperature of 600°C to 750°C, and a holding time of 4h to 6h.

[0063] The primary aerogel with a certain strength contains a certain amount of acid ions inside. In a non-oxidizing atmosphere, these acid ions will not react with oxygen to generate gas, causing the internal pores of the primary aerogel to collapse and rupture. Therefore, the present application limits the heating rate of the first heating to 3°C / min to 5°C / min, the end temperature to 600°C to 750°C, and the holding time to 4h to 6h, which is conducive to the formation of an unbroken, high-quality aerogel. Exemplary, the heating rate of the first heating can be 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min, 5°C / min, etc., the end temperature can be 600°C, 620°C, 650°C, 680°C, 700°C, 720°C, 750°C, etc., and the holding time can be 4h, 4.5h, 5h, 5.5h, 6h, etc.

[0064] In some embodiments, the second heating includes the following parameters: a heating rate of 3° C. / min to 5° C. / min, an end point temperature of 650° C. to 700° C., and a holding time of 4 h to 6 h.

[0065] The aerogel formed by freeze drying in a non-oxidizing atmosphere has very good strength and can resist damage caused by stress, but still contains a certain amount of acid ions or other particles, which remain in the aerogel. Under an oxidizing atmosphere, these ions and oxidizable substances are removed by oxidation to form pure alumina aerogel. Exemplary, the heating rate of the second heating can be 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min, 5°C / min, etc., the end temperature can be 650°C, 655°C, 660°C, 665°C, 670°C, 680°C, 700°C, etc., and the holding time can be 4h, 4.5h, 5h, 5.5h, 6h, etc.

[0066] In summary, the preparation method of alumina aerogel provided in the embodiments of the present application has the following significant advantages:

[0067] (1) Low cost and wide source of raw materials: This method uses industrially produced aluminum hydroxide as raw material, which is lower in cost and more widely available than organic aluminum salts or inorganic aluminum salts, thereby greatly reducing production costs.

[0068] (2) Overcoming the shortcomings of traditional preparation methods: This method not only overcomes the problems of large alumina particles, easy formation of fragments, and difficulty in forming when preparing alumina aerogels using inorganic aluminum salts as raw materials, but also solves the shortcomings of organic alcohol aluminum salts, such as high price, high toxicity, difficult to control the hydrolysis process, and limited large-scale application. This allows this method to prepare high-quality alumina aerogels while maintaining good economic and feasibility.

[0069] (3) Simple process and short preparation cycle: Compared with the currently commonly used supercritical drying method, this method avoids the high cost and long cycle of supercritical drying. Through a series of precisely controlled steps, including modification, mixing, pH adjustment, hydrothermal treatment, solid content adjustment, addition of aluminum salt, freezing and freeze drying, and two heating treatments, alumina aerogel is quickly prepared. This process is simple and efficient, significantly shortening the preparation cycle.

[0070] (4) Low manufacturing cost and easy industrialization: Since the raw materials used in this method are low-cost and the process is simple and efficient, the manufacturing cost is relatively low. This lays a solid foundation for the large-scale industrial preparation of alumina aerogels, making this material more competitive in a wider range of applications.

[0071] (5) Excellent product performance: Although this method focuses on cost control and process simplification, the prepared alumina aerogel still has excellent performance. By precisely controlling the conditions and parameters of each step, the high strength, good stability and other required physical and chemical properties of the aerogel are ensured.

[0072] The preparation method of alumina aerogels exhibits significant advantages in terms of raw material costs, process efficiency, manufacturing costs, product performance, and industrialization potential. These advantages give this method broad application prospects and market competitiveness in the field of alumina aerogel preparation.

[0073] 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 generally measured according to industry standards. If there are no corresponding industry standards, then the methods are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0074] Example 1

[0075] Industrial aluminum hydroxide is modified at 900°C for 10 seconds, the modified industrial aluminum hydroxide is added with water and stirred into a slurry, and formic acid is added to control the pH value at 2,130 and hydrothermally treated for 4 hours; the aluminum hydroxide slurry after hydrothermal treatment is diluted, and the dilution standard is 2.5g of aluminum oxide per 500mL of water, and 1g of aluminum chloride is added at the same time; the slurry is stirred evenly, frozen at -50°C for 4 hours, and then freeze-dried for 48 hours; the frozen composite is heated at 700°C in a non-oxidizing atmosphere for 5 hours, with a heating rate of 5°C / min; in an air atmosphere, the temperature is increased to 650°C at a heating rate of 3°C / min and kept warm for 5 hours to obtain an alumina aerogel product.

[0076] Example 2

[0077] Industrial aluminum hydroxide is modified at 1100°C for 3 seconds, the modified industrial aluminum hydroxide is added with water and stirred into a slurry, formic acid is added to control the pH value at 2, and hydrothermally treated at 140°C for 4 hours; the aluminum hydroxide slurry after hydrothermal treatment is diluted, and the dilution standard is 2.5g of aluminum oxide per 500mL of water, and 1g of aluminum chloride is added at the same time; the slurry is stirred evenly, frozen at -50°C for 4 hours, and then freeze-dried for 48 hours; the frozen composite is heated at 700°C in a non-oxidizing atmosphere for 5 hours, with a heating rate of 5°C / min; in an air atmosphere, the temperature is increased to 700°C at a heating rate of 4°C / min, and then kept warm for 5 hours to obtain an alumina aerogel product.

[0078] Example 3

[0079] Industrial aluminum hydroxide is modified at 1100°C for 3 seconds, the modified industrial aluminum hydroxide is added with water and stirred into a slurry, acetic acid is added to control the pH value at 2, and hydrothermally treated at 150°C for 4 hours; the aluminum hydroxide slurry after hydrothermal treatment is diluted, and the dilution standard is 2.5g of aluminum oxide per 500mL of water, and 1g of aluminum chloride is added at the same time; the slurry is stirred evenly, frozen at -50°C for 4 hours, and then freeze-dried for 48 hours; the frozen composite is heated at 700°C in a non-oxidizing atmosphere for 5 hours, with a heating rate of 5°C / min; in an air atmosphere, the temperature is increased to 660°C at a heating rate of 5°C / min, and then kept warm for 5 hours to obtain an alumina aerogel product.

[0080] Example 4

[0081] Industrial aluminum hydroxide is modified at 1100°C for 3 seconds, the modified industrial aluminum hydroxide is added with water and stirred into a slurry, formic acid and acetic acid are added to control the pH value at 2, and hydrothermally treated at 140°C for 4 hours; the aluminum hydroxide slurry after hydrothermal treatment is diluted, and the dilution standard is 2.5g of aluminum oxide per 500mL of water, and 1g of a mixture of aluminum chloride and aluminum nitrate is added at the same time; the slurry is stirred evenly, frozen at -50°C for 4 hours, and then freeze-dried for 48 hours; the frozen composite is heated at 700°C in a non-oxidizing atmosphere for 5 hours, with a heating rate of 5°C / min; in an air atmosphere, the temperature is increased to 680°C at a heating rate of 4°C / min, and then kept warm for 5 hours to obtain an alumina aerogel product.

[0082] Example 5

[0083] Industrial aluminum hydroxide is modified at 1100°C for 3 seconds, the modified industrial aluminum hydroxide is added with water and stirred into a slurry, formic acid is added to control the pH value at 2, and hydrothermally treated at 160°C for 4 hours; the aluminum hydroxide slurry after hydrothermal treatment is diluted, the dilution standard is 2.5g of aluminum oxide per 500mL of water, and 1g of aluminum nitrate is added at the same time; they are stirred evenly, frozen at -50°C for 4 hours, and then freeze-dried for 48 hours; the frozen complex is heated at 700°C in a non-oxidizing atmosphere for 5 hours, with a heating rate of 5°C / min; in an air atmosphere, the temperature is increased to 700°C at a heating rate of 4°C / min, and then kept warm for 5 hours to obtain an alumina aerogel product.

[0084] Comparative Example 1

[0085] The difference between this comparative example and the embodiment is that industrial aluminum hydroxide is not subjected to modification treatment. Specifically, it includes:

[0086] Industrial aluminum hydroxide was added with water and stirred into 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; the aluminum hydroxide slurry after hydrothermal treatment was diluted, and the dilution standard was 2.5g of aluminum oxide per 500mL of water, and 1g of aluminum chloride was added at the same time; the slurry was stirred evenly, frozen at -50°C for 4 hours, and then freeze-dried for 48 hours; the frozen complex was heated at 700°C in a non-oxidizing atmosphere for 5 hours at a heating rate of 5°C / min; in an air atmosphere, the temperature was increased to 650°C at a heating rate of 4°C / min and kept warm for 5 hours. No aerogel was obtained, but a gamma alumina powder product was obtained.

[0087] Comparative Example 2

[0088] The difference between this comparative example and the embodiment is that the modification time of industrial aluminum hydroxide is greater than 10s. Specifically, it includes:

[0089] Industrial aluminum hydroxide was modified at 1100°C for 60 minutes, the modified industrial aluminum hydroxide was added with water and stirred into a slurry, formic acid was added to control the pH value at 2, and hydrothermally treated at 150°C for 4 hours; the aluminum hydroxide slurry after hydrothermal treatment was diluted, and the dilution standard was 2.5g of aluminum oxide per 500mL of water, and 1g of aluminum chloride was added at the same time; the slurry was stirred evenly, frozen at -50°C for 4 hours, and then freeze-dried for 48 hours; the frozen composite was heated at 700°C in a non-oxidizing atmosphere for 5 hours, with a heating rate of 5°C / min; in an air atmosphere, the temperature was raised to 700°C at a heating rate of 4°C / min, and then kept warm for 5 hours. No aerogel was obtained, but an alpha and gamma mixed alumina powder product was obtained.

[0090] Comparative Example 3

[0091] The difference between this comparative example and the embodiment is that the industrial aluminum hydroxide is not modified and the temperature is less than 900°C. Specifically, it includes:

[0092] Industrial aluminum hydroxide is modified at 500°C for 3 seconds, the modified industrial aluminum hydroxide is added with water and stirred into a slurry, acetic acid is added to control the pH value at 2, and hydrothermally treated at 130-160°C for 4 hours; the aluminum hydroxide slurry after hydrothermal treatment is diluted, the dilution standard is 2.5g of aluminum oxide per 500mL of water, and 1g of aluminum chloride is added at the same time; the slurry is stirred evenly, frozen at -50°C for 4 hours, and then freeze-dried for 48 hours; the frozen composite is heated at 700°C in a non-oxidizing atmosphere for 5 hours, with a heating rate of 5°C / min; in an air atmosphere, the temperature is increased to 680°C at a heating rate of 4°C / min, and then kept warm for 5 hours, but no alumina aerogel is obtained, and a gamma-type alumina powder product is obtained.

[0093] Comparative Example 4

[0094] The difference between this comparative example and the embodiment is that the slurry is not subjected to hydrothermal treatment. Specifically, it includes:

[0095] Industrial aluminum hydroxide is modified at 1100°C for 3 seconds, the modified industrial aluminum hydroxide is added with water and stirred into a slurry, and formic acid and acetic acid are added to control the pH value at 2; the modified industrial aluminum hydroxide is diluted with water slurry, and the dilution standard is 2.5g of aluminum oxide per 500mL of water, and 1g of aluminum chloride and aluminum nitrate mixture is added at the same time; the slurry is stirred evenly, frozen at -50°C for 4h, and then freeze-dried for 48h; the frozen composite is heated at 700°C in a non-oxidizing atmosphere for 5h, with a heating rate of 5°C / min; in an air atmosphere, the temperature is increased to 650°C at a heating rate of 4°C / min, and then kept warm for 5h, no alumina aerogel is obtained, and an alumina powder product is obtained.

[0096] Comparative Example 5

[0097] The difference between this comparative example and the embodiment is that the slurry is not frozen or freeze-dried. Specifically, it includes:

[0098] Industrial aluminum hydroxide is modified at 1100°C for 3 seconds, the modified industrial aluminum hydroxide is added with water and stirred into a slurry, formic acid and acetic acid are added to control the pH value at 2, and hydrothermally treated at 150°C for 4 hours; the modified industrial aluminum hydroxide is diluted with water slurry, the dilution standard is 2.5g of aluminum oxide per 500mL of water, and 1g of aluminum chloride and aluminum nitrate mixture is added at the same time; the slurry is dried to obtain a composite; the composite is heated at 700°C in a non-oxidizing atmosphere for 5 hours at a heating rate of 5°C / min; in an air atmosphere, the temperature is increased to 650°C at a heating rate of 4°C / min, and then kept warm for 5 hours. No alumina aerogel is obtained, but an alumina powder product is obtained.

[0099] Comparative Example 6

[0100] The difference between this comparative example and the embodiment is that the frozen composite is not heated in a non-oxidizing atmosphere. Specifically, the following steps are performed:

[0101] Industrial aluminum hydroxide is modified at 1100°C for 3 seconds, the modified industrial aluminum hydroxide is added with water and stirred into a slurry, formic acid and acetic acid are added to control the pH value at 2, and hydrothermally treated at 160°C for 4 hours; the modified industrial aluminum hydroxide is diluted with water slurry, the dilution standard is 2.5g of aluminum oxide per 500mL of water, and 1g of aluminum chloride and aluminum nitrate mixture is added at the same time; the slurry is stirred evenly, frozen at -50°C for 4 hours, and then freeze-dried for 48 hours; in an air atmosphere, the composite is heated to 650°C at a heating rate of 5°C / min, and then kept warm for 5 hours. No alumina aerogel is obtained, but an alumina powder product is obtained.

[0102] The thermal conductivity of the products obtained in Examples 1 to 5 and Comparative Examples 1 to 6 was measured at different temperatures. The results are shown in Table 1.

[0103] Table 1 Thermal conductivity of the products of Examples 1 to 5 and Comparative Examples 1 to 6

[0104]

[0105]

[0106] As shown in Table 1, the thermal conductivity of the alumina aerogel product obtained in the Examples of the present application is ≤0.015 at room temperature and ≤0.035 at 900°C. The comparative examples lack important steps or important parameters are outside the specified ranges, resulting in the inability to obtain an alumina aerogel product.

[0107] Figure 2 The XRD pattern of industrial aluminum hydroxide provided in Example 1 of the present application; Figure 3 This is the XRD pattern of the industrial aluminum hydroxide provided in Example 1 of the present application after modification; Figure 4 This is the XRD pattern of the alumina aerogel provided in Example 1 of the present application. Figures 2 to 4 It can be seen that aluminum hydroxide trihydrate becomes a highly active amorphous substance after being modified by heat treatment, and the amorphous substance is converted into alumina aerogel after being treated by the process of the present invention.

[0108] In addition, one or more technical solutions in the embodiments of the present application have at least the following technical effects or advantages:

[0109] In the embodiments of the present application, industrialized production of aluminum hydroxide is used as raw material, and organic aluminum salt and inorganic aluminum salt are not used, so that the production cost is greatly reduced. Not only can the defects of inorganic aluminum salt as raw material for preparing alumina aerogel, such as large alumina particles, easy to form broken pieces and difficult to form, be overcome, but also the defects of organic alcohol aluminum salt, such as high price, high toxicity, difficult to control the hydrolysis process and limited in large-scale application, can be solved,

[0110] Compared with the supercritical drying method commonly used at present for preparing aerogel, the process does not need to go through the high-cost and long-period supercritical drying process, the preparation period of the process is short, the production cost is low, and the process lays a foundation for large-scale industrialized preparation of alumina aerogel.

[0111] The above only describes the specific embodiments of the present application, so that those skilled in the art can understand or implement the present application. Various modifications of these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features applied herein.

Claims

1. A method for preparing an alumina aerogel, the method comprising: Modifying industrial aluminum hydroxide so as to cause the industrial aluminum hydroxide to undergo a crystal transformation; Mixing the modified industrial aluminum hydroxide with a solvent to obtain a first slurry; adjusting the pH value of the first slurry to a set pH value; hydrothermally treating the first slurry having a set pH value to obtain a second slurry; adjusting the solid content of the second slurry to a set solid content; adding aluminum salt to the second slurry having a set solid content to obtain a third slurry; freezing and freeze-drying the third slurry in sequence to obtain a frozen composite; and sequentially heating the frozen composite in a non-oxidizing atmosphere for a first time and in an oxidizing atmosphere for a second time to obtain an alumina aerogel; The modification includes the following parameters: heat treatment temperature is 900°C to 1200°C, heat treatment time is 3s to 10s; The set pH value is less than 7; The hydrothermal treatment includes the following parameters: temperature of 80°C to 250°C, time of 3h to 10h; The solid content is set to 5g / L to 30g / L; The first heating includes the following parameters: a heating rate of 3°C / min to 5°C / min, an end point temperature of 600°C to 750°C, and a holding time of 4h to 6h; The second heating includes the following parameters: a heating rate of 3°C / min to 5°C / min, an end point temperature of 650°C to 700°C, and a holding time of 4h to 6h.

2. The method according to claim 1, characterized in that The mass ratio of the hydrous aluminum oxide to the aluminum salt in the third slurry is (2.5-15):1, and the aluminum salt includes at least one of the following: an organic aluminum salt and an inorganic aluminum salt.

3. The method according to claim 1, characterized in that The freezing process includes the following parameters: a freezing temperature of -50°C to -20°C, and a freezing time of 3 hours to 5 hours.

4. The method according to claim 1, wherein The freeze-drying time is 12 hours to 48 hours.

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