Preparation method of alumina aerogel

Abstract

The invention provides a preparation method of alumina aerogel, and belongs to the field of aerogel. The method comprises the following steps: modifying industrial aluminum hydroxide, so that the industrial aluminum hydroxide is subjected to crystal form transformation; mixing the modified industrial aluminum hydroxide with a solvent to obtain first slurry; adjusting the pH value of the first slurry to a set pH value; performing hydrothermal treatment on the first slurry with a set pH value to obtain second slurry; adjusting the solid content of the second slurry to a set solid content; aluminum salt is added into the second slurry with the set solid content, and third slurry is obtained; sequentially freezing and freeze-drying the third slurry to obtain a frozen compound; the frozen compound is sequentially subjected to first heating in a non-oxidizing atmosphere and second heating in an oxidizing atmosphere, and the aluminum oxide aerogel is obtained. Therefore, the invention provides a novel preparation method of the aluminum oxide aerogel.

Description

Technical Field

[0001] The present application relates to the technical field of aerogels, and in particular to a method for preparing aluminum oxide 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, the density change can reach 0.03g / mL~0.5g / mL. Compared with conventional solid materials, it has many special properties in mechanics, acoustics, thermal, optics, etc., such as extremely small apparent density, small refractive index, low Young's modulus and porosity of more than 90%; it is the solid material with the lowest thermal conductivity at present. 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 divided into different types. Oxide aerogel is one of them. Among oxide aerogels, alumina aerogel is favored because of its high temperature resistance and low price.

[0003] Alumina aerogel is mainly prepared by sol-gel method. There are two main preparation methods, inorganic aluminum salt method and organic alcohol aluminum salt method, depending on the precursor. Generally speaking, alumina aerogel prepared by organic alcohol aluminum salt as raw material has relatively good formability and relatively low density. However, due to its lengthy preparation process, severe shrinkage of samples during solvent exchange and drying, poor mechanical strength of products, expensive price and high toxicity of organic alcohol aluminum salt, and difficult control of hydrolysis process, it is limited in large-scale application. Compared with organic alcohol aluminum salt, the preparation of alumina aerogel using inorganic aluminum salt as aluminum source has the characteristics of simple process, easy reaction control, low cost, etc. The inorganic aluminum salt method has higher economic value and development potential. However, alumina aerogel prepared by inorganic aluminum salt as raw material usually has larger alumina particles, which affects the formability of aerogel and is more likely to form alumina aerogel in the form of fragments. At present, the preparation of various aerogels basically adopts supercritical drying method, and even the aerogel production method entering the industrial application stage adopts supercritical drying. Although some companies use atmospheric pressure drying to produce aerogels, their product performance is hardly recognized by market users. However, the supercritical drying method has a long preparation cycle and high cost. Based on the principle of shortening the drying cycle and reducing costs, a new process for preparing alumina aerogels is planned to be developed. Summary of the invention

[0004] The present application provides a method for preparing an alumina aerogel to solve the following technical problems: providing a new method for preparing an 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 that the industrial aluminum hydroxide undergoes 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] The first slurry having a set pH value is subjected to hydrothermal treatment 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 subjected to a first heating in a non-oxidizing atmosphere and a second heating in an oxidizing atmosphere in sequence 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: the freezing temperature is -50°C to -20°C, and the freezing time is 3h to 5h.

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

[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 includes: modifying industrial aluminum hydroxide so that the industrial aluminum hydroxide undergoes 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 with 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 with a 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 in sequence to obtain an alumina aerogel. First, by modifying industrial aluminum hydroxide, a rapid transformation of industrial aluminum hydroxide from a stable crystal structure to a highly active non-crystalline structure is achieved; secondly, by adjusting the pH of the slurry and hydrothermally treating it, it is helpful to generate the desired intermediate substance; and again, by freezing and freeze-drying, the material structure in the slurry is effectively fixed and the water activity is reduced. At the same time, it is conducive to forming a primary aerogel with a certain strength and improving 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, which can resist damage caused by stress, and the acid ions and other oxidizable substances in the aerogel are successfully removed to form a pure alumina aerogel. Thus, a new method for preparing alumina aerogel is provided. 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 drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0027] Figure 1 A schematic diagram of a process 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 The XRD diagram of industrial aluminum hydroxide after modification provided in Example 1 of the present application;

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

[0031] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work 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 rigid 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 numerical values ​​within the range. For example, the range description 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 apply 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 specification of the present application, the terms "including", "comprising", etc. mean "including but not limited to". In this article, relational terms such as "first" and "second", etc. 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 these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: 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" means one or more, and "plurality" means two or more. "At least one", "the following at least one item (items)" or similar expressions refer to any combination of these items, including any combination of single items (items) or plural items (items). For example, "at least one of a, b, or c", or "at least one of a, b, and c", can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple. "Parts" such as parts by weight and parts by mass indicate the proportional relationship between the components. In the proportional relationship involved in this article, the parameters that need to be described by proportion should be understood as the first term of the proportional formula in the order of description, and the proportional numbers should be understood as the second term 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 correspond one-to-one with the proportional numbers in the proportional formula in the order of description, 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 this application can be purchased from the market or prepared by existing methods.

[0035] Figure 1 A schematic flow chart of a method for preparing an alumina aerogel provided in an embodiment of the present application.

[0036] like Figure 1 As shown, the present application provides a method for preparing an alumina aerogel, the method comprising:

[0037] S1. Modifying industrial aluminum hydroxide so as to cause the industrial aluminum hydroxide to undergo a crystal transformation;

[0038] In some embodiments, the industrial aluminum hydroxide may be aluminum hydroxide obtained in the form of seed hydrogenation aluminum, carbon hydrogenation aluminum, neutralized hydrogen aluminum or other forms.

[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: heat treatment temperature is 900° C. to 1200° C., and heat treatment time is 3s to 10s.

[0041] The heat treatment temperature is limited to 900°C to 1200°C, and the heat treatment time is 3s to 10s, so that the formed material has the required structure and activity. If the heat treatment temperature is lower than 900°C, 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 generated 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, and the performance required by the present invention will be lost. Exemplarily, the heat treatment temperature can be 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C, 1200°C, 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 generate 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 are dissolved 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 substances treated at high temperature, most of them will not dissolve into the aqueous solution and will not affect the preparation process of aerogels. Exemplarily, the pH value can be set to 0.5, 1, 2, 3, 4, 5, 6, 6.5, etc.

[0046] S4, subjecting the first slurry having a set pH value to hydrothermal treatment 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 enough energy to generate the required intermediate substances; if the temperature of 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, temperature and pressure will accelerate the corrosion of equipment and increase equipment safety hazards; 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 change, reducing activity and affecting subsequent processes. Exemplarily, the temperature of 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 solid content is set to be 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 with 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 composite organic substances; the inorganic aluminum salt includes aluminum sulfate, aluminum chloride and aluminum nitrate or a mixture thereof.

[0055] There are two purposes for adding aluminum salts. One is to use aluminum salts to adjust the pH value of the solution, and the other is to provide certain acid ions, which will play their due role in subsequent experiments. Exemplarily, 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 aluminum oxide 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, freezing and freeze-drying the third slurry in sequence to obtain a frozen composite; and

[0057] In some embodiments, the freezing includes the following parameters: the freezing temperature is -50°C to -20°C, and the 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 to prevent deformation or damage during the subsequent drying process. At the same time, freezing can also reduce the water activity in the slurry, which is beneficial to the subsequent freeze-drying process. There are two purposes of freeze-drying. One is to remove moisture by freeze-drying, reduce the surface tension in the gel pores, and form a primary aerogel with a certain strength; the other is that the internal structure of the primary aerogel will be rearranged to a certain extent after freeze-drying, which improves the performance of the subsequent aerogel and increases the strength of the aerogel. This arrangement is conducive to the formation of high-performance aerogels. Exemplarily, the freezing temperature can be -50°C, -40°C, -35°C, -30°C, -20°C, etc., the freezing time can be 3h, 3.2h, 3.5h, 3.8h, 4h, 4.2h, 4.5h, 4.8h, 5h, etc., and the freeze-drying time can be 12h, 16h, 20h, 25h, 30h, 35h, 40h, 45h, 48h, etc.

[0060] S8. The frozen composite is subjected to a first heating in a non-oxidizing atmosphere and a second heating in an oxidizing atmosphere in sequence to obtain an alumina aerogel.

[0061] It is understood that non-oxidizing atmospheres generally refer to those atmospheres that can prevent or slow down the oxidation reaction of materials. Such atmospheres generally contain inert gases (such as nitrogen, argon, helium, etc.) or reducing gases (such as hydrogen, carbon monoxide, etc.). Oxidizing atmospheres refer to atmospheres that contain enough oxygen to support or promote the oxidation reaction of materials. Such atmospheres are 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 defines the heating rate of the first heating as 3°C / min to 5°C / min, the terminal temperature as 600°C to 750°C, and the insulation time as 4h to 6h, which is conducive to the formation of an unbroken, high-quality aerogel. Exemplarily, 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 terminal temperature can be 600°C, 620°C, 650°C, 680°C, 700°C, 720°C, 750°C, etc., and the insulation 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 4h to 6h.

[0065] The aerogel formed by freeze drying and 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 are still retained in the aerogel. Under the oxidizing atmosphere, these ions and oxidizable substances are removed by oxidation to form pure alumina aerogel. Exemplarily, 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 terminal temperature can be 650°C, 655°C, 660°C, 665°C, 670°C, 680°C, 700°C, etc., and the insulation time can be 4h, 4.5h, 5h, 5.5h, 6h, etc.

[0066] In summary, the method for preparing 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 defects of traditional preparation methods: This method can not only overcome the problems of large alumina particles, easy formation of fragments and difficulty in forming when preparing alumina aerogel using inorganic aluminum salt as raw material, but also solve the defects of organic alcohol aluminum salt, such as high price, high toxicity, difficult control of hydrolysis process and limited large-scale application. This makes this method maintain good economy and feasibility while preparing high-quality alumina aerogel.

[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 supercritical drying process. 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, the rapid preparation of alumina aerogel is achieved. This process is simple and efficient, greatly 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 application fields.

[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 aerogel has significant advantages in terms of raw material cost, process efficiency, manufacturing cost, product performance and industrialization potential, etc. These advantages make this method have broad application prospects and market competitiveness in the preparation field of alumina aerogel.

[0073] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are usually measured according to industry standards. If there is no corresponding industry standard, then the conditions recommended by the manufacturer are followed.

[0074] Example 1

[0075] Industrial aluminum hydroxide is modified at 900°C for 10s, 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 the hydrothermal treatment is performed at 130°C for 4h; the aluminum hydroxide slurry after the 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, and 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, and the heating rate is 5°C / min; in an air atmosphere, the temperature is increased to 650°C at a heating rate of 3°C / min, and the temperature is kept for 5h to obtain an alumina aerogel product.

[0076] Example 2

[0077] Industrial aluminum hydroxide is modified at 1100℃ for 3s, the modified industrial aluminum hydroxide is added with water and stirred into slurry, formic acid is added to control the pH value at 2, and hydrothermally treated at 140℃ for 4h; 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, and frozen at -50℃ for 4h, and then freeze-dried for 48h; the frozen composite is heated at 700℃ in a non-oxidizing atmosphere for 5h, and the heating rate is 5℃ / min; in an air atmosphere, the temperature is increased to 700℃ at a heating rate of 4℃ / min, and then kept warm for 5h to obtain an alumina aerogel product.

[0078] Example 3

[0079] Industrial aluminum hydroxide is modified at 1100℃ for 3s, the modified industrial aluminum hydroxide is added with water and stirred into slurry, acetic acid is added to control the pH value at 2, and hydrothermally treated at 150℃ for 4h; 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, and frozen at -50℃ for 4h, and then freeze-dried for 48h; the frozen composite is heated at 700℃ in a non-oxidizing atmosphere for 5h, and the heating rate is 5℃ / min; in an air atmosphere, the temperature is increased to 660℃ at a heating rate of 5℃ / min, and then kept warm for 5h to obtain an alumina aerogel product.

[0080] Example 4

[0081] Industrial aluminum hydroxide is modified at 1100℃ for 3s, the modified industrial aluminum hydroxide is added with water and stirred into slurry, formic acid and acetic acid are added to control the pH value at 2, and hydrothermally treated at 140℃ for 4h; 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 and aluminum nitrate mixture is added at the same time; the slurry is stirred evenly, and frozen at -50℃ for 4h, and then freeze-dried for 48h; the frozen composite is heated at 700℃ in a non-oxidizing atmosphere for 5h, and the heating rate is 5℃ / min; in an air atmosphere, the temperature is increased to 680℃ at a heating rate of 4℃ / min, and then kept warm for 5h to obtain an alumina aerogel product.

[0082] Example 5

[0083] Industrial aluminum hydroxide is modified at 1100℃ for 3s, the modified industrial aluminum hydroxide is added with water and stirred into slurry, formic acid is added to control the pH value at 2, and hydrothermally treated at 160℃ for 4h; 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 nitrate is added at the same time; they are stirred evenly, frozen at -50℃ for 4h, and then freeze-dried for 48h; the frozen complex is heated at 700℃ in a non-oxidizing atmosphere for 5h, and the heating rate is 5℃ / min; in an air atmosphere, the temperature is increased to 700℃ at a heating rate of 4℃ / min, and then kept warm for 5h 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 is stirred into slurry by adding water, and formic acid is added to control the pH value at 2, and hydrothermally treated at 150°C for 4 hours; the aluminum hydroxide slurry after hydrothermally treated 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, and 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, and the heating rate is 5°C / min; in an air atmosphere, the temperature is increased to 650°C at a heating rate of 4°C / min, and the temperature is kept for 5 hours, and no aerogel is obtained, but a gamma alumina powder product is 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 is modified at 1100℃ for 60min, the modified industrial aluminum hydroxide is added with water and stirred into slurry, formic acid is added to control the pH value at 2, and hydrothermally treated at 150℃ for 4h; 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, and frozen at -50℃ for 4h, and then freeze-dried for 48h; the frozen composite is heated at 700℃ in a non-oxidizing atmosphere for 5h, and the heating rate is 5℃ / min; in an air atmosphere, the temperature is increased to 700℃ at a heating rate of 4℃ / min, and then kept warm for 5h, no aerogel is obtained, and an alpha and gamma type mixed alumina powder product is 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 3s, water is added to the modified industrial aluminum hydroxide and stirred into slurry, acetic acid is added to control the pH value at 2, and hydrothermally treated at 130-160°C for 4h; 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, and 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, and the heating rate is 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 5h, and no alumina aerogel is obtained, but 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 3s, the modified industrial aluminum hydroxide is stirred into slurry with water, 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, and 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, and the heating rate is 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, and no alumina aerogel is obtained, but 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 3s, water is added to the modified industrial aluminum hydroxide and stirred into a slurry, formic acid and acetic acid are added to control the pH value at 2, and hydrothermal treatment is performed at 150°C for 4h; 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 a mixture of aluminum chloride and aluminum nitrate 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 5h, and the heating rate is 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.

[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, it includes:

[0101] Industrial aluminum hydroxide is modified at 1100°C for 3s, 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 4h; 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 a mixture of aluminum chloride and aluminum nitrate is added at the same time; the slurry is stirred evenly, and frozen at -50°C for 4h, and then freeze-dried for 48h; in an air atmosphere, the composite is heated to 650°C at a heating rate of 5°C / min, and then kept warm for 5h, and 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 at different temperatures was measured, and the results are shown in Table 1.

[0103] Table 1 Thermal conductivity of 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 embodiment of the present application is ≤0.015 at room temperature and ≤0.035 at 900° C. The comparative example lacks important steps or important parameters are not within the specified range, resulting in failure 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 The XRD diagram of industrial aluminum hydroxide after modification provided in Example 1 of the present application; Figure 4 This is the XRD diagram of the alumina aerogel provided in Example 1 of the present application. Figure 2 to Figure 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 embodiment of the present application, industrial aluminum hydroxide is used as raw material, and organic aluminum salts and inorganic aluminum salts are not used, so the production cost is greatly reduced. It can not only overcome the shortcomings of large aluminum oxide particles, easy formation of fragments and difficult molding in the preparation of alumina aerogel using inorganic aluminum salts as raw materials, but also solve the defects of expensive organic alcohol aluminum salts, high toxicity, difficult control of hydrolysis process and limitations in large-scale applications.

[0110] In the embodiments of the present application, compared with the currently commonly used supercritical drying method for preparing aerogels, 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 alumina aerogels.

[0111] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to 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 the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A method for preparing an alumina aerogel, the method comprising: Modifying industrial aluminum hydroxide so that the industrial aluminum hydroxide undergoes 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; The first slurry having a set pH value is subjected to hydrothermal treatment 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; as well as The frozen composite is subjected to a first heating in a non-oxidizing atmosphere and a second heating in an oxidizing atmosphere in sequence to obtain an alumina aerogel.

2. The method according to claim 1, characterized in that The modification includes the following parameters: heat treatment temperature is 900° C. to 1200° C., and heat treatment time is 3s to 10s.

3. The method according to claim 1, characterized in that The set pH value is <7.

4. The method according to claim 1, characterized in that: The hydrothermal treatment includes the following parameters: temperature is 80° C. to 250° C., and time is 3 h to 10 h.

5. The method according to claim 1, characterized in that The solid content is set to be 5 g / L to 30 g / L.

6. 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.

7. 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 3h to 5h.

8. The method according to claim 1, characterized in that The freeze-drying time is 12h to 48h.

9. The method according to claim 1, characterized in that: 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.

10. The method according to claim 1, characterized in that 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.

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