A method for preparing a silica aerogel and a silica aerogel

Abstract

The application relates to the field of aerogels, and discloses a method for preparing a silica aerogel and the silica aerogel. The method comprises the following steps: (1) performing hydrolysis on water glass in the presence of inorganic acid and organic acid to obtain a silicic acid sol; (2) performing first mixing on the silicic acid sol and an organic co-precursor to obtain a silica hydrosol; (3) performing second mixing on the silica hydrosol, a non-polar organic solvent, an alkali catalyst and a surface modifier to obtain a silica wet gel; and (4) performing aging and drying on the silica wet gel to obtain the silica aerogel. The preparation method is simple in process, low in equipment requirement and beneficial to large-scale production.

Description

Technical Field

[0001] This invention relates to the field of aerogel technology, and more specifically to a method for preparing silica aerogel and silica aerogel. Background Technology

[0002] Aerogels, known as the "lightest solid material," have become a novel thermal insulation material of international interest due to their excellent thermal insulation properties. Silica aerogel is a nanoporous amorphous solid material with a three-dimensional spatial network structure composed of interconnected silica particles. It effectively suppresses gas convection heat transfer, reduces solid-state heat conduction, and possesses extremely low thermal conductivity—the lowest known thermal conductivity among solid materials. Due to its unique structure, silica aerogel materials exhibit a series of special properties, including low density, high specific surface area, high porosity, low thermal conductivity, low sound wave propagation velocity, and low dielectric constant.

[0003] However, due to limitations in the preparation process, silica aerogel materials are more expensive than traditional insulation materials, making them difficult to promote in many fields, especially building insulation.

[0004] Currently, the main method for preparing silica aerogels is to use organosilicon as the silicon source and employ supercritical drying technology. However, organosilicon sources are more expensive than industrial water glass, and the supercritical drying process involves high-temperature and high-pressure equipment, posing certain safety risks during production. Furthermore, the limitations of the supercritical equipment reactor make it difficult to achieve continuous large-scale production.

[0005] However, the biggest problem with using inexpensive and readily available water glass as the silicon source is that water glass contains sodium ions and small amounts of iron, aluminum, and other metal ions. The presence of these ions will affect the aerogel properties and even cause the collapse of the pore structure, making it impossible to prepare silica aerogels with a three-dimensional network structure of nanopores. Therefore, a necessary step in the preparation of silica aerogels using water glass is the removal of sodium and iron ions.

[0006] Currently, there are several methods for removing salt and impurities from water glass: 1) Low-temperature crystallization: This method requires cooling the sol, which consumes a lot of energy. Furthermore, even at low temperatures, complete salt precipitation cannot be guaranteed; even at 0°C, the solubility of sodium sulfate in water is 4.9 g / 100 g water. 2) Ion exchange: This method uses strongly acidic cation exchange resins to remove sodium ions and other metal ions from the water glass. However, due to the limited capacity of cation exchange resins (generally 5 mmol / g), high concentrations of sodium ions (7.5-12.8 wt%) in the water glass would quickly saturate the resin, making continuous production impossible. 3) Washing with deionized or distilled water: This method involves continuous dilution with water after gel formation to remove salt from the gel. While this method can be industrialized, it consumes a large amount of water and is time-consuming. 4) Electrode desalination: This method also utilizes the electrolyte properties of the salt to remove salt after gel formation. Similar to the difficulties encountered with electrode-based seawater desalination, finding large-capacity, inexpensive electrodes is challenging. 5) Ethanol crystallization method: This method utilizes the poor solubility of sulfates such as sodium sulfate and ferric sulfate in organic solvents to remove sodium. Although this method can effectively remove sodium salts, during the atmospheric pressure drying process, ethanol needs to be replaced by a large amount of solvent to a low surface tension organic solvent. Moreover, the process generates a large amount of mixed solution, and the recovery of this mixed solution is energy-intensive, increasing production costs.

[0007] US20190256363A1 discloses a method for preparing micron-sized spherical silica aerogels. This method includes adding a first organosilane compound to an acidic silica sol to prepare a surface-modified silica sol; then dispersing and mixing the surface-modified silica sol, a second organosilane compound, and the surface-modified silica sol to obtain a silica hydrogel; aging the silica hydrogel to remove sodium-containing water extracted from the spherical silica hydrogel; and finally drying to obtain the spherical silica aerogel. Although this method does not require cation exchange resins to remove sodium ions and has a simple preparation process, it uses sulfuric acid or nitric acid to hydrolyze the water glass solution. Excessive strong acid can easily cause uneven pore structure distribution, leading to structural collapse during drying at normal pressure. Summary of the Invention

[0008] The purpose of this invention is to solve the problems of complex preparation process and uneven pore structure distribution of silica aerogel in the prior art.

[0009] To achieve the above objectives, a first aspect of the present invention provides a method for preparing silica aerogel, the method comprising the following steps:

[0010] (1) In the presence of inorganic acid and organic acid, water glass is hydrolyzed to obtain silica sol; the inorganic acid is sulfuric acid and / or nitric acid; the organic acid is oxalic acid and / or acetic acid; the molar ratio of water glass (calculated as silica), inorganic acid (calculated as hydrogen ions), and organic acid (calculated as hydrogen ions) is 1:(0.2-0.6):(0.05-0.1);

[0011] (2) The silica sol is first mixed with the organic co-propellant to obtain silica hydrosol; the organic co-propellant is a combination of silane coupling agent and surfactant.

[0012] (3) The silica hydrosol is mixed with a nonpolar organic solvent, an alkaline catalyst, and a surface modifier to obtain a silica wet gel; the surface modifier is selected from at least one of hexamethyldisilazane, methyltrimethoxysilane, and dimethyldiethoxysilane;

[0013] (4) The silica wet gel is aged and dried to obtain the silica aerogel.

[0014] A second aspect of the present invention provides a silica aerogel prepared by the method described in the first aspect.

[0015] This invention uses water glass as a silicon source and, based on the molar amount of water glass (calculated as silicon dioxide), controls the molar ratio of inorganic acid to organic acid to be (0.2-0.6):(0.05-0.1) to hydrolyze the water glass. Through the dual action of non-polar organic solvent and surface modifier, gel aging, surface modification, and solvent replacement are achieved simultaneously.

[0016] The preparation method of the present invention is simple and requires less equipment, which is conducive to large-scale production. At the same time, the resulting silica aerogel has a more uniform pore structure. Attached Figure Description

[0017] Figure 1 This is a SEM image of the silica aerogel obtained in Embodiment 1 of the present invention;

[0018] Figure 2 This is a SEM image of the silica aerogel prepared in Comparative Example 3 of the present invention. Detailed Implementation

[0019] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0020] As previously described, a first aspect of the present invention provides a method for preparing silica aerogel, the method comprising the following steps:

[0021] (1) In the presence of inorganic acid and organic acid, water glass is hydrolyzed to obtain silica sol; the inorganic acid is sulfuric acid and / or nitric acid; the organic acid is oxalic acid and / or acetic acid; the molar ratio of water glass (calculated as silica), inorganic acid (calculated as hydrogen ions), and organic acid (calculated as hydrogen ions) is 1:(0.2-0.6):(0.05-0.1);

[0022] (2) The silica sol is first mixed with the organic co-propellant to obtain silica hydrosol; the organic co-propellant is a combination of silane coupling agent and surfactant.

[0023] (3) The silica hydrosol is mixed with a nonpolar organic solvent, an alkaline catalyst, and a surface modifier to obtain a silica wet gel; the surface modifier is selected from at least one of hexamethyldisilazane, methyltrimethoxysilane, and dimethyldiethoxysilane;

[0024] (4) The silica wet gel is aged and dried to obtain the silica aerogel.

[0025] Preferably, in step (1), the water glass contains silicon dioxide, sodium oxide, and iron ions.

[0026] Preferably, the silica content is 25wt%-30wt% based on the total weight of the water glass.

[0027] In a preferred embodiment, the sodium oxide content is 8.0-10.0 wt%, based on the total weight of the water glass.

[0028] To achieve a more uniform pore structure distribution in the silica aerogel, the iron ion content in the water glass is less than or equal to 0.03 wt% based on the total weight of the water glass. More preferably, the iron ion content is less than or equal to 0.02 wt% based on the total weight of the water glass. In this preferred embodiment, the inventors have found that the resulting silica aerogel has a more uniform pore structure distribution, resulting in a lower thermal conductivity.

[0029] In a preferred embodiment, the water glass is liquid water glass produced by Shandong Qianqian Chemical Technology Co., Ltd. In this preferred embodiment, the inventors discovered that the resulting silica aerogel has a more uniform pore structure distribution, resulting in a lower thermal conductivity.

[0030] In this invention, the content of silicon dioxide and sodium oxide in the water glass is obtained by modulus titration, and the iron ion is obtained by o-phenanthroline spectrophotometry.

[0031] Preferably, the molar ratio of the water glass (based on silica), the inorganic acid (based on hydrogen ions), and the organic acid (based on hydrogen ions) is 1:(0.4-0.6):(0.06-0.08). The inventors of this invention have discovered that, under this preferred condition, the resulting silica aerogel has a more uniform pore structure distribution and is less prone to structural collapse during the drying process.

[0032] Preferably, in step (1), the control conditions are such that the pH value of the obtained silica sol is less than 3. More preferably, in step (1), the control conditions are such that the pH value of the obtained silica sol is ≤1.

[0033] Preferably, in step (1), the hydrolysis of the water glass is carried out in the presence of water, and the molar ratio of the water glass to water, calculated as silica, is 1:(37.5-62).

[0034] It should be noted that the hydrolysis in this invention is carried out at room temperature with stirring. There are no special requirements for the stirring time and speed; parameters known in the art can be used. For example, water glass is stirred at 300 r / min for 30 min in the presence of inorganic and organic acids.

[0035] Preferably, in step (2), the organic co-propellant is a combination of a silane coupling agent and a surfactant, and the molar ratio of the surfactant, the silane coupling agent and the silica sol (calculated as silica) is (0.01-0.3):(0.3-0.8):1.

[0036] More preferably, in step (2), the organic co-propellant is a combination of a silane coupling agent and a surfactant, and the molar ratio of the surfactant, the silane coupling agent, and the silica sol (based on silica) is (0.01-0.3):(0.5-0.65):1. The inventors of this invention have found that, under this preferred condition, the resulting silica aerogel has a more uniform pore structure distribution.

[0037] In a preferred embodiment, in step (2), the silane coupling agent is selected from at least one of methyltrimethoxysilane, methyltriethoxysilane, and dimethyldimethoxysilane.

[0038] Preferably, the surfactant is selected from at least one of hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, and sodium dodecyl sulfate.

[0039] Preferably, in step (2), the control conditions are such that the pH value of the obtained silica hydrosol is less than 3.

[0040] According to a preferred embodiment, in step (2), the conditions for the first mixing are at least: the reaction temperature is 35-55°C, the stirring speed is 200-500 r / min, and the stirring time is 10-30 min.

[0041] In a preferred embodiment, the method further includes: in step (2), subjecting the intermediate obtained after the first mixing of the silica sol and the organic co-propellant to static hydrolysis, thereby causing the organic co-propellant and the silica sol to co-condense and form a short-chain network structure. The present invention does not impose any particular limitation on the static hydrolysis time, which can be selected by those skilled in the art as needed. For example, after the first mixing of the silica sol and the organic co-propellant, static hydrolysis is performed for 8 hours.

[0042] According to another preferred embodiment, in step (3), the conditions for the second mixing are at least: the reaction temperature is 35-55°C, the stirring speed is 200-1000 r / min, and the stirring time is 5-20 min.

[0043] Preferably, in step (3), the alkaline catalyst is ammonia and / or sodium hydroxide.

[0044] In a preferred embodiment, in step (3), the nonpolar organic solvent is selected from at least one of n-hexane, n-butanol, n-pentane, and n-heptane.

[0045] Preferably, in step (3), the molar ratio of the silica hydrosol, the alkaline catalyst, and the surface modifier, based on a dry basis and calculated as silica, is 1:(0-0.15):(0.25-0.5). More preferably, in step (3), the molar ratio of the silica hydrosol, the alkaline catalyst, and the surface modifier, based on silica, is 1:(0.1-0.15):(0.4-0.5). The inventors have found that, under this preferred condition, the obtained silica aerogel has a more uniform pore structure distribution and a lower thermal conductivity.

[0046] It should be noted that the present invention does not have any special requirements on the amount of non-polar organic solvent used in step (3), as long as it can displace most of the water in the silica hydrosol. For example, the amount of non-polar organic solvent used is 450-550 mL relative to 1 mol of water glass based on silica.

[0047] Preferably, in step (4), the aging conditions are at least: a temperature of 45-65°C and a time of 1-6 hours.

[0048] In a preferred embodiment, after the silica wet gel is aged, the aged silica wet gel is further subjected to stirring and filtration to remove most of the water and inorganic salts in the solution. The present invention does not impose any particular restrictions on the stirring and filtration methods, which can be carried out by those skilled in the art based on known techniques.

[0049] It should be noted that the present invention does not have any special requirements for the drying method described in step (4), which can be atmospheric pressure drying, vacuum drying, or microwave drying; at the same time, the present invention does not have any special restrictions on the drying temperature and time, and those skilled in the art can choose according to their needs. For example, drying is carried out at 0.06 MPa and 40-150℃ for 20-120 minutes.

[0050] As previously stated, a second aspect of the present invention provides a silica aerogel prepared by the method described in the first aspect.

[0051] The silica aerogel prepared by this invention has a specific surface area of ​​470-800 m². 2 / g, thermal conductivity is 0.018-0.025W / (m·K), density is 80-150kg / m³ 3 .

[0052] The present invention will be described in detail below through examples. Unless otherwise specified, the instruments, reagents, materials, etc. involved in the following examples are all conventional instruments, reagents, materials, etc. that are already available in the prior art and can be obtained through legitimate commercial channels.

[0053] The main materials used in the examples are all commercially available, as detailed below:

[0054] raw material:

[0055] Water glass:

[0056] Water glass I: 28wt% silica, 8.41wt% sodium oxide, 0.02wt% iron ion, liquid water glass, industrial grade, transparent, purchased from Shandong Qianqian Chemical Technology Co., Ltd.

[0057] Water glass II: 26wt% silica, 8.31wt% sodium oxide, 0.03wt% iron ion, industrial grade transparent, purchased from Jinan Qianqi Chemical Co., Ltd.

[0058] Water glass III: 28wt% silica, 8.2wt% sodium oxide, 0.05wt% iron ion, industrial grade, opaque, purchased from Tianjin Zhonghe Shengteng Chemical Co., Ltd.

[0059] Organic acids:

[0060] Oxalic acid, analytical grade, purity ≥99.5%, purchased from Jiangsu Qiangsheng Functional Chemical Co., Ltd. The concentration used in the following examples is 1 mol / L;

[0061] Acetic acid, analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd. The concentration used in the following examples is 1 mol / L;

[0062] Inorganic acids:

[0063] Sulfuric acid, analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd., is used at a concentration of 3.0 mol / L in the following examples;

[0064] Nitric acid, analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd., is used at a concentration of 1.8 mol / L in the following examples;

[0065] Silane coupling agents:

[0066] Methyltrimethoxysilane, industrial grade, purchased from Jiangxi Chenguang New Materials Co., Ltd.

[0067] Methyltriethoxysilane, industrial grade, purchased from Jiangxi Chenguang New Materials Co., Ltd.

[0068] Dimethyldimethoxysilane, industrial grade, purchased from Shandong Silicon Science New Materials Co., Ltd.

[0069] Surfactants:

[0070] Hexadecyltrimethylammonium bromide, analytical grade, purchased from Ron Reagents;

[0071] Sodium dodecyl sulfate, with a content of over 90%, was purchased from Wujiang Delong Fine Chemical Co., Ltd.

[0072] Sodium dodecylbenzenesulfonate, industrial grade, purchased from Jinan Beiyate Chemical Technology Co., Ltd.

[0073] Alkali catalyst:

[0074] Ammonia water, analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd., is used at a concentration of 5 mol / L in the following examples;

[0075] Sodium hydroxide, analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0076] Surface modifiers:

[0077] Hexamethyldisilazane, industrial grade, purchased from Xinyaqiang Silicon Chemical Jiangsu Co., Ltd.;

[0078] Methyltrimethoxysilane, industrial grade, purchased from Jiangxi Chenguang New Materials Co., Ltd.

[0079] Dimethyldiethoxysilane, industrial grade, purchased from Shandong Silicon Science New Materials Co., Ltd.

[0080] Non-polar organic solvents:

[0081] n-Hexane, analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0082] n-Pentane, analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0083] n-Heptane, analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0084] Example 1

[0085] This embodiment illustrates the preparation of silica aerogel according to the formula and process parameters in Table 1 and the method described below.

[0086] The steps for preparing silica aerogel are as follows:

[0087] (1) In the presence of inorganic acid and organic acid, 1 mol of water glass (calculated as silica) was stirred at 300 r / min for 30 min to obtain silica sol;

[0088] (2) At 50℃ and 400r / min, 1 mol of the silica sol, calculated as silica, was mixed with silane coupling agent and surfactant for 30 min (i.e., the first mixture), and allowed to stand for hydrolysis for 8 hours to obtain silica hydrosol.

[0089] (3) At 45℃ and 800r / min, 1 mol of the silica hydrosol (calculated as silica) was mixed with a non-polar organic solvent, an alkaline catalyst and a surface modifier for 15 min (i.e., the second mixing) to obtain a silica wet gel.

[0090] (4) The silica wet gel was aged at 60°C for 3.5 h, then stirred and filtered to remove water from the silica wet gel. It was then dried at 0.06 MPa at 40°C for 30 min and then at 120°C for 1 h to obtain silica aerogel.

[0091] Unless otherwise specified, the remaining examples were carried out using a similar process to Example 1, except that the amounts of each substance and the process parameters were different during the preparation of silica aerogel, as detailed in Table 1.

[0092] Comparative Example 1

[0093] This comparative example was carried out using similar steps to Example 1, except that the amount of sulfuric acid used in this comparative example was 1 mol and the amount of oxalic acid was 0.08 mol, as detailed in Table 1.

[0094] Comparative Example 2

[0095] This comparative example was carried out using similar steps to Example 1, except that the amount of sulfuric acid used in this comparative example was 0.1 mol and the amount of oxalic acid used was 0.15 mol, as detailed in Table 1.

[0096] Comparative Example 3

[0097] This comparative example was carried out using similar steps to Example 1, except that oxalic acid was not used in this comparative example, as detailed in Table 1.

[0098] Table 1

[0099]

[0100]

[0101] Continued from Table 1

[0102]

[0103] Test case

[0104] The performance testing equipment and instruments used for silica aerogels in the above examples are shown in Table 2.

[0105] Table 2

[0106] Test Project Instrument Model factory Specific surface area 3H-2000PS Best Instruments Technology Co., Ltd. thermal conductivity TC3000 Xi'an Xiaxi Electronic Technology Co., Ltd.

[0107] Test method:

[0108] The method for testing the density of aerogel powder is as follows: The volumetric tapping method is used. Specifically, the aerogel powder is placed in a 25mL graduated cylinder, weighed, and then the graduated cylinder is vibrated vertically to the table 20 times to measure the volume of the aerogel powder. The density of the aerogel powder is then calculated.

[0109] The specific surface area was tested using the static volumetric method. Specifically, N2 was used as the adsorbate. Before the test, the sample was vacuum dried and degassed at 200℃ for 1 hour. Then, N2 was adsorbed at 70K for testing.

[0110] The thermal conductivity test method uses the transient hot wire method. Specifically, the aerogel powder is placed in the test sample cell (sample cell size: 30mm*50mm*40mm), and the thin-film probe of the thermal conductivity meter is placed in the middle of the sample cell, ensuring that the aerogel powder completely covers the probe from top to bottom. The equipment is started to perform thermal equilibrium detection, and then the thermal conductivity value is measured using a 0.5V voltage.

[0111] The performance of the silica aerogel samples in the examples was tested, and the results are shown in Table 3.

[0112] Table 3

[0113]

[0114]

[0115] As can be seen from the results in Table 3, the silica aerogel prepared by the method of the present invention has a thermal conductivity of 0.018-0.025 W / (m·K) and a specific surface area of ​​470-800 m². 2 / g, density is 80-150kg / m³ 3 .

[0116] The present invention provides, by way of example, SEM images of the silica aerogel prepared in Example 1. Figure 1 Specifically, from Figure 1 It can be seen that the pore structure of silica aerogel is uniformly distributed.

[0117] The present invention also provides SEM images of the silica aerogel prepared in Comparative Example 3. Figure 2 Specifically, from Figure 2 It can be seen that the pore structure of silica aerogel is unevenly distributed and exhibits pore structure collapse.

[0118] pass Figure 1 and Figure 2 The comparison shows that the silica aerogel prepared in the presence of both inorganic and organic acids has a more uniform pore structure distribution.

[0119] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method of preparing a silica aerogel, characterized by, The method includes the following steps: (1) In the presence of an inorganic acid and an organic acid, water glass is hydrolyzed to obtain a silica sol; the inorganic acid is sulfuric acid and / or nitric acid; the organic acid is oxalic acid and / or acetic acid; the molar ratio of the water glass (calculated as silica), the inorganic acid (calculated as hydrogen ions), and the organic acid (calculated as hydrogen ions) is 1:(0.2-0.6):(0.05-0.1); (2) The silica sol is first mixed with the organic co-propellant to obtain silica hydrosol; the organic co-propellant is a combination of silane coupling agent and surfactant; the molar ratio of the surfactant, the silane coupling agent and the silica sol (based on silica) is (0.01-0.3):(0.5-0.65):1; (3) The silica hydrosol is mixed with a nonpolar organic solvent, an alkaline catalyst, and a surface modifier to obtain a silica wet gel; the surface modifier is selected from at least one of hexamethyldisilazane, methyltrimethoxysilane, and dimethyldiethoxysilane; the molar ratio of the silica hydrosol, the alkaline catalyst, and the surface modifier, based on silica, is 1:(0.1-0.15):(0.4-0.5). (4) The silica wet gel is aged and dried to obtain the silica aerogel.

2. The method according to claim 1, wherein, In step (1), the water glass contains silicon dioxide, sodium oxide, and iron ions.

3. The method according to claim 2, wherein, Based on the total weight of water glass, the content of silica is 25wt%-30wt%.

4. The method according to claim 2, wherein, Based on the total weight of water glass, the sodium oxide content is 8.0-10.0 wt%.

5. The method according to claim 2, wherein, Based on the total weight of water glass, the iron ion content is less than or equal to 0.03 wt%.

6. The method according to any one of claims 1-5, wherein, The molar ratio of the water glass (calculated as silica), the inorganic acid (calculated as hydrogen ions), and the organic acid (calculated as hydrogen ions) is 1:(0.4-0.6):(0.06-0.08).

7. The method according to any one of claims 1-5, wherein, In step (1), the control conditions are such that the pH value of the resulting silica sol is less than 3.

8. The method according to any one of claims 1-5, wherein, In step (1), the control conditions are such that the pH value of the obtained silica sol is ≤1.

9. The method according to any one of claims 1-5, wherein, In step (2), the silane coupling agent is selected from at least one of methyltrimethoxysilane, methyltriethoxysilane and dimethyldimethoxysilane.

10. The method according to any one of claims 1-5, wherein, The surfactant is selected from at least one of hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, and sodium dodecyl sulfate.

11. The method according to any one of claims 1-5, wherein, In step (2), the control conditions are such that the pH value of the obtained silica hydrosol is less than 3.

12. The method according to any one of claims 1-5, wherein, In step (2), the conditions for the first mixing must at least be: reaction temperature of 35-55℃, stirring speed of 200-500r / min, and stirring time of 10-30min.

13. The method according to any one of claims 1-5, wherein, In step (3), the conditions for the second mixing must at least be: reaction temperature of 35-55℃, stirring speed of 200-1000r / min, and stirring time of 5-20min.

14. The method according to any one of claims 1-5, wherein, The alkaline catalyst is ammonia and / or sodium hydroxide.

15. The method according to any one of claims 1-5, wherein, In step (4), the aging conditions must at least meet the following requirements: temperature of 45-65℃ and time of 1-6h.

16. Silica aerogel prepared by the method according to any one of claims 1-15.

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