Silica aerogel and preparation method and application thereof

Abstract

The application discloses silica aerogel and a preparation method and application thereof, and by using a combination of an organic silicon source and an inorganic silicon source, the preparation cost of SiO2 aerogel powder is significantly reduced; the method adopts normal pressure drying, is simple to operate, does not need complex equipment or steps, and is favorable for realizing large-scale preparation and industrial production of the aerogel powder. In addition, by accurate raw material proportioning and a preparation process, the prepared SiO2 aerogel powder retains excellent performances of aerogel prepared from the organic silicon source, such as a pore structure, a specific surface area and the like. Finally, the preparation method provided by the application can prepare silica aerogel with excellent physical and chemical performances at low cost and in large quantities, and the operation process is simple, complex processes and equipment are not needed, and the method is suitable for industrial production, and has wide application prospects in the fields of heat insulation, adsorption, catalysis and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of aerogel powder materials, and in particular to a silicon dioxide aerogel and a preparation method and application thereof. Background Art

[0002] As a lightweight, porous material, aerogel powder, with its unique three-dimensional network structure and excellent physical and chemical properties, shows broad application prospects in fields such as thermal insulation, adsorption, and catalysis. However, the high cost of preparing aerogel powder has been a key factor limiting its industrial production and large-scale application. Aerogel powder is mostly prepared using a silicon source as the raw material, with water, ethanol, and other solvents as the solvent. In the initial reaction, the silicon source is hydrolyzed to produce the active monomer silicic acid. The silicic acid then condenses to form a polymer (sol) composed mainly of silicon oxide (-Si-O-Si-), which then cross-links to form a gel skeleton with a three-dimensional network structure. After the wet gel is prepared and aged, it is hydrophobically modified to increase its hydrophobicity. The liquid solvent in the gel is then replaced with a gaseous substance through a drying process, thus producing the aerogel powder.

[0003] In the related art, the preparation of aerogel powder materials mainly relies on two types of materials: organic silicon sources or inorganic silicon sources. Although the use of organic silicon sources to prepare aerogels can produce products with relatively superior performance, the high cost of raw materials and complex preparation processes make the entire production process expensive, greatly limiting the application of aerogels in more fields. In contrast, the preparation of aerogels from inorganic silicon sources has the advantage of lower cost. Inorganic silicon sources such as water glass and silica sol are widely available and inexpensive, which can effectively reduce the preparation cost of aerogels. However, aerogels prepared from inorganic silicon sources often find it difficult to achieve the performance level of products prepared from organic silicon sources. Although some technicians have tried to use a combination of the two to reduce raw material costs, for example, Chinese patent CN115806427A discloses a low-cost method for preparing SiO2 aerogel, which uses an organic-inorganic composite silicon source to prepare aerogel. However, its subsequent drying process uses supercritical drying, which has high requirements for equipment and personnel, and the process is also relatively cumbersome and has certain safety risks. The method of preparing SiO2 aerogel by atmospheric pressure drying is simple and easy to operate, highly safe, and has low equipment requirements. However, the atmospheric pressure drying method has high requirements for the purity of the silicon source, and the performance of the prepared aerogel does not have advantages, which is not conducive to large-scale industrial production and promotion of aerogel.

[0004] Therefore, providing a silica aerogel preparation process that can produce high-performance silica aerogels at low cost and in large quantities, which is simple to operate, does not require complex processes and equipment, and is suitable for industrial production, has important practical significance and production value. Summary of the Invention

[0005] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application proposes a silica aerogel and a preparation method and application thereof, aiming to provide a method for preparing high-performance silica aerogel at low cost, solving the problems of high preparation cost using organic silicon source as raw material, insufficient performance of aerogel prepared using inorganic silicon source as raw material, and complicated process and harsh drying method in the current aerogel preparation process.

[0006] In a first aspect of the present application, a preparation method of silica aerogel is provided, comprising the steps of:

[0007] S1, a certain amount of organic silicon source, alcohol solvent A, water and catalyst are mixed uniformly and hydrolyzed for a predetermined time one, to obtain sol A, wherein the volume ratio of the organic silicon source, alcohol solvent A, water and catalyst is 10:(20-30):(4-5):(1-2);

[0008] S2, a certain amount of inorganic silicon source is added to alcohol solvent B under rapid stirring to obtain sol B, wherein the volume ratio of the inorganic silicon source and alcohol solvent B is 10:(20-30);

[0009] S3, a certain amount of sol A and sol B are mixed to form a wet gel according to the volume ratio of the organic silicon source and the inorganic silicon source (30-40):(60-70), and after aging for a predetermined time two, a gel block is obtained;

[0010] S4, the gel block is crushed, and then a modifier is added for a predetermined time three to obtain a modified gel;

[0011] S5, the modified gel is dried at normal pressure for a predetermined time four to obtain silica aerogel powder.

[0012] According to the preparation method of silica aerogel of the embodiment of the present invention, there are at least the following beneficial effects: the preparation method provided by the present invention significantly reduces the preparation cost of silica (SiO2) aerogel powder by using a composite of an organic silicon source and an inorganic silicon source, thereby improving the economic performance of the entire preparation process; not only that, the present invention also uses rapid stirring and slow dripping of the inorganic silicon source to dilute it first to increase the proportion of the inorganic silicon source in the composite silicon source, further reducing costs. The operation process is simple, and the above-mentioned preparation method adopts atmospheric drying, which maintains its easy-to-operate characteristics and does not require complex equipment or steps, which is conducive to the large-scale preparation and industrial production of aerogel powder. In addition, the present invention also uses precise raw material ratios and preparation processes to ensure that the prepared SiO2 aerogel powder retains the excellent properties of aerogels prepared from organic silicon sources, such as pore structure, specific surface area, etc.; at the same time, the precise ratio also controls the water content in the system, so that the water content is maintained within an appropriate range, avoiding the collapse of the gel network during the drying process that may be caused by excessive water, and can be dried at atmospheric pressure without the need for a dehydration step, further simplifying the process. Finally, the preparation method provided by the present invention can produce silica aerogels with excellent physical and chemical properties in large quantities at low cost. Moreover, the operation process is simple, does not require complex processes and equipment, and is suitable for industrial production. It has broad application prospects in many fields such as thermal insulation, adsorption, and catalysis.

[0013] In some embodiments of the present invention, the organic silicon source is selected from at least one of methyl orthosilicate, tetraethyl orthosilicate, or polysiloxane.

[0014] In some preferred embodiments of the present invention, the polysiloxane includes methyltrimethoxysilane, methyltriethoxysilane, etc., but is not limited thereto.

[0015] In some embodiments of the present invention, the inorganic silicon source is selected from alkaline silica sol. Alkaline silica sol is a dispersion of nanometer-sized silica particles in water or a solvent. The pH value of alkaline silica sol solution is generally between 9 and 11, which is alkaline. Alkaline silica sol has a large specific surface area and a porous structure, and has excellent adsorption capacity and high surface activity. Inorganic silicon sources are inexpensive and widely available. Using low-cost inorganic silicon sources to replace more expensive organic silicon sources does not increase the cost of the subsequent atmospheric pressure drying process, thereby improving the economic efficiency of the entire preparation process.

[0016] In some preferred embodiments of the present invention, the particle size of the alkaline silica sol is 8 to 40 nm, preferably 8 to 30 nm.

[0017] In some preferred embodiments of the present invention, the silicon dioxide content of the alkaline silica sol is 30% to 50%.

[0018] For organosilicon sources, additional alkali is typically added after hydrolysis to adjust the pH and rapidly gel the sol. This invention utilizes the alkalinity of the inorganic silicon source silica sol to effectively compound the organosilicon source with the inorganic silicon source, reducing costs while maintaining the simplicity of the aerogel synthesis process. Because alkaline silica sol has limited solubility in alcoholic solvents, this invention uses rapid stirring and slow dripping to initially dilute the silica sol, facilitating subsequent mixing with the alcoholic solution of the organosilicon source.

[0019] In some embodiments of the present invention, the alcohol solvent A is selected from one or both of methanol and ethanol, but is not limited thereto.

[0020] In some embodiments of the present invention, the alcohol solvent B is selected from one or both of methanol and ethanol, but is not limited thereto.

[0021] In some embodiments of the present invention, the catalyst is selected from one or more of hydrochloric acid, oxalic acid, and sulfuric acid, but is not limited thereto.

[0022] In some embodiments of the present invention, the modifier is selected from one of trimethylchlorosilane and hexamethyldisilazane, but is not limited thereto.

[0023] In some embodiments of the present invention, the amount of the modifier added is 3% to 8% of the total mass of the system.

[0024] In some embodiments of the present invention, in step S1, the predetermined time one is 12 to 24 hours.

[0025] In some embodiments of the present invention, in step S1, the hydrolysis step is: sealing the system and continuously stirring for 12 to 24 hours.

[0026] In some embodiments of the present invention, in step S2, a certain amount of inorganic silicon source is slowly added to the alcohol solvent B under rapid stirring conditions to obtain sol B.

[0027] In some embodiments of the present invention, in step S2, the inorganic silicon source is slowly added to the alcohol solvent B under stirring at a rotation speed of 1200 to 1500 r / min to obtain sol B.

[0028] In some embodiments of the present invention, in step S2, the inorganic silicon source is added to the alcohol solvent B under rapid stirring at a dropwise addition rate of 0.1 to 0.3 mL / s to obtain sol B.

[0029] The solubility of inorganic silicon sources in alcohol solvents is limited. Therefore, the present invention increases the amount of alcohol used during dilution by rapid stirring and slow dripping to facilitate subsequent mixing with the alcohol solution of the organic silicon source, thereby increasing the proportion of the inorganic silicon source in the composite silicon source and further reducing costs.

[0030] In some embodiments of the present invention, in step S3, the second predetermined time is 8 to 16 hours.

[0031] In some embodiments of the present invention, in step S3, the aging step is: sealing the system and placing it at room temperature for aging for 8 to 16 hours.

[0032] In some embodiments of the present invention, in step S3, the sol B is slowly added to the sol solution while stirring. Since alkaline silica sol has limited solubility in alcoholic solvents, stirring and slow dropwise addition facilitates mixing of the alcoholic solution of the inorganic silicon source and the alcoholic solution of the organic silicon source.

[0033] In some embodiments of the present invention, in step S4, the gel blocks are crushed before modification and solvent replacement, which can increase the contact area between the gel and the solvent and facilitate the modification and replacement steps.

[0034] In some embodiments of the present invention, in step S4, the predetermined time three is 6 to 8 hours.

[0035] In some embodiments of the present invention, in step S4, the modification step includes: adding the modifier and continuously stirring for 6 to 8 hours. The present invention uses the modifier to hydrophobically modify the aerogel to avoid pore collapse caused by capillary forces during atmospheric pressure drying.

[0036] In some embodiments of the present invention, after step S4, the step of replacing the solvent with n-hexane three times is further included. The three solvent replacement processes with n-hexane can remove excess modifiers and replace methanol and ethanol with n-hexane with low surface tension.

[0037] In some embodiments of the present invention, in step S5, the predetermined time period is 12 to 24 hours.

[0038] In some embodiments of the present invention, in step S5, the temperature of the normal pressure drying is 60-100°C.

[0039] The present invention utilizes the alkalinity of the inorganic silicon source silica sol to effectively compound the organic silicon source with the inorganic silicon source, reducing costs while maintaining the simplicity of the aerogel synthesis process. Due to the limited solubility of alkaline silica sol in alcoholic solvents, the silica sol is first diluted using rapid stirring and slow dripping to facilitate subsequent mixing with the alcoholic solution of the organic silicon source. Gel blocks are crushed before modification and solvent replacement to increase the contact area between the gel and the solvent, facilitating the modification and replacement steps. A modifier is used to hydrophobically modify the aerogel to avoid pore collapse caused by capillary forces during atmospheric pressure drying. This method, utilizing a composite organic silicon source with an inorganic silicon source, reduces the production cost of aerogel powder while maintaining the excellent properties of aerogels prepared from the organic silicon source. Furthermore, the method is simple to operate and is suitable for large-scale production of low-cost aerogel powder.

[0040] At present, the preparation process of silica aerogel using organic-inorganic composite silicon source still uses supercritical drying as the drying method. This is because the method of combining composite silicon source with atmospheric pressure drying technology still has certain technical barriers: since inorganic silicon sources (such as water glass, silica sol, etc.) are stored in the form of aqueous solution, the surface tension of water is relatively large, which will cause the gel network to shrink significantly or even collapse during the atmospheric pressure drying process (the effect of water content in supercritical drying is much smaller than that in atmospheric pressure drying). The dehydration process will use a large amount of organic solvents (mostly alcohols), which will increase the cost and make the drying process cumbersome. Therefore, the technical route of combining organic-inorganic composite silicon source with atmospheric pressure drying method still needs to solve the above problems. In response to the above technical problems, the present invention uses precise raw material ratios and preparation processes to enable silica aerogels prepared from organic-inorganic composite silicon sources to successfully retain the excellent properties of aerogels prepared from organic silicon sources, such as pore structure and specific surface area. Moreover, the precise ratio also controls the water content in the system, maintaining the water content within an appropriate range, avoiding the collapse of the gel network during the atmospheric pressure drying process caused by excessive water, and the atmospheric pressure drying step can be performed without the need for a water removal step. Ultimately, the present invention utilizes an organic-inorganic composite silicon source in combination with an atmospheric pressure drying method, which can reduce costs while maintaining the simplicity of the drying process, making it suitable as a low-cost method for producing high-performance aerogel powders.

[0041] In a second aspect of the present invention, a silica aerogel is provided. The silica aerogel is prepared using the above-mentioned method for preparing silica aerogel.

[0042] In some embodiments of the present invention, the specific surface area of ​​the silica aerogel is 600 to 700 m 2 / g, for example, 600 to 650 m 2 / g, 650~700m 2 / g.

[0043] In some embodiments of the present invention, the pore size of the silica aerogel is 18 to 20 nm, for example, 18 to 19 nm, or 19 to 20 nm.

[0044] In some embodiments of the present invention, the pore volume of the silica aerogel is 3 to 4 m 3 / g, for example, 3.0 to 3.1 m 3 / g, 3.1~3.2m 3 / g, 3.2~3.3m 3 / g, 3.3~3.4m 3 / g, 3.4~3.5m 3 / g, 3.5~3.6m 3 / g, 3.6~3.7m 3 / g, 3.7~3.8m 3 / g, 3.8~3.9m 3 / g, 3.9~4.0m 3 / g.

[0045] In some embodiments of the present invention, the tap density of the silica aerogel is 0.07 to 0.09 g / cm 3 , for example, it can be 0.07 to 0.08 g / cm 3 , 0.08~0.09g / cm 3 .

[0046] The silica aerogel according to the embodiments of the present invention has at least the following beneficial effects: The silica aerogel prepared by the present invention is prepared using an organic-inorganic composite silicon source. While maintaining the excellent properties of aerogels prepared from an organic silicon source (such as pore structure and specific surface area), the production cost of the aerogel powder is significantly reduced. This aerogel powder possesses excellent physical and chemical properties and is relatively low in cost. It has broad application prospects in various fields, including thermal insulation, adsorption, and catalysis, and is expected to promote the development and progress of related industries.

[0047] The silica aerogel of the present invention is based on the aforementioned preparation method. The detailed parameters and processes in the preparation method are as described above and will not be repeated here.

[0048] The third aspect of the present invention proposes the application of the above-mentioned silica aerogel or the silica aerogel prepared by the above-mentioned silica aerogel preparation method in the fields of thermal insulation, optics, electricity, catalysis and medicine.

[0049] The "volume" in the present application, if not specified, is the volume of the material in the natural state. The "natural state" refers to the case without any stress (compression or tension), one atmosphere and without heat (room temperature). BRIEF DESCRIPTION OF DRAWINGS

[0050] The present application will be further described below in conjunction with the accompanying drawings and examples, in which:

[0051] Figure 1 Schematic diagram of the aerogel powder prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0052] The concept and technical effects of the present application will be described below in conjunction with the examples, so as to fully understand the purpose, features and effects of the present application. Obviously, the described examples are only a part of the examples of the present application, but not all the examples. Based on the examples of the present application, other examples obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0053] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example" or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are contained in at least one embodiment or example of the present application. In the present specification, the exemplary description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0054] In the following examples, if the specific technology or condition is not specified, the technology or condition described in the literature in the art or according to the product instruction is used. If the manufacturer of all reagents or instruments is not specified, it is a conventional product that can be obtained by market purchase.

[0055] Example 1

[0056] (1) 10 mL of tetraethyl orthosilicate was measured into a 250 mL beaker, and then 4 mL of deionized water, 20 mL of ethanol and 1 mL of hydrochloric acid (0.1 mol / L) were sequentially added. The hydrolysis was completed at room temperature for 18 h with stirring to obtain sol A.

[0057] (2) Another beaker was taken, 40 mL of ethanol solution was measured into the beaker, and then 20 mL of basic silica sol (average particle size ~ 8 nm) was slowly added to the ethanol solution at a speed of 0.1 mL / s under the condition of stirring at 1500 r / min for dilution. After stirring uniformly, sol B was obtained.

[0058] (3) Sol B was slowly added to the beaker of Sol A while stirring. After about 50 seconds, the system gelled. After the beaker was sealed and aged for 16 hours, the obtained gel block was crushed and modified by adding 3 mL of trimethylchlorosilane as a modifier. After 6 hours, the modification was completed. Three solvent replacement processes were carried out with n-hexane to remove the residual trimethylchlorosilane. At the same time, the high surface tension ethanol was replaced with low surface tension n-hexane.

[0059] (4) Finally, the powder obtained in step (3) was placed in a dry glass watch glass and dried in an oven at 80°C for 24 hours to obtain an aerogel powder material.

[0060] Example 2

[0061] (1) 10 mL of methyl orthosilicate was placed in a 250 mL beaker, followed by the addition of 5 mL of deionized water, 20 mL of methanol, and 1 mL of sulfuric acid (0.1 mol / L). The mixture was stirred at room temperature for 12 h to complete hydrolysis, yielding Sol A.

[0062] (2) Take another beaker, measure 30 mL of methanol solution and place it in the beaker, then measure 15 mL of alkaline silica sol (average particle size ~10 nm), slowly add it to the methanol solution at a rate of 0.3 mL / s under stirring at 1200 r / min to dilute it, and after stirring evenly, obtain Sol B.

[0063] (3) Sol B was slowly added to the beaker of Sol A while stirring. After about 30 seconds, the system gelled. After the beaker was sealed and aged for 10 hours, the obtained gel was crushed and modified by adding 3 mL of hexamethyldisilazane as a modifier. After 6 hours, the modification was completed. Three solvent replacement processes were carried out with n-hexane to remove residual trimethylchlorosilane. At the same time, the high surface tension methanol was replaced with low surface tension n-hexane.

[0064] (4) Finally, the powder obtained in step (3) was placed in a dry glass watch glass and dried in an oven at 60°C for 24 hours to obtain an aerogel powder material.

[0065] Example 3

[0066] (1) 10 mL of tetraethyl orthosilicate was placed in a 250 mL beaker, followed by the addition of 4 mL of deionized water, 30 mL of ethanol, and 2 mL of oxalic acid (0.1 mol / L). The mixture was stirred at room temperature for 18 h to complete hydrolysis, yielding Sol A.

[0067] (2) Take another beaker, measure 36 mL of ethanol solution and place it in the beaker, then measure 18 mL of alkaline silica sol (average particle size ~30 nm), slowly add it to the ethanol solution at a rate of 0.2 mL / s under stirring at 1300 r / min to dilute it, and after stirring evenly, obtain Sol B.

[0068] (3) Sol B was slowly added to the beaker of Sol A while stirring. After about 60 seconds, the system gelled. After the beaker was sealed and aged for 15 hours, the obtained gel was crushed and modified by adding 3 mL of trimethylchlorosilane as a modifier. After 6 hours, the modification was completed. Three solvent replacement processes were carried out with n-hexane to remove the excess modifier. At the same time, the high surface tension ethanol was replaced with low surface tension n-hexane.

[0069] (4) Finally, the powder obtained in step (3) was placed in a dry glass watch glass and dried in an oven at 100° C. for 20 h to obtain an aerogel powder material.

[0070] Comparative Example 1

[0071] (1) 10 mL of tetraethyl orthosilicate was placed in a 250 mL beaker, followed by the addition of 4 mL of deionized water, 20 mL of ethanol, and 1 mL of hydrochloric acid (0.1 mol / L). The mixture was stirred at room temperature for 18 h to complete hydrolysis, yielding Sol A.

[0072] (2) Take another beaker, measure 80 mL of ethanol solution and place it in the beaker, then measure 40 mL of silica sol (average particle size ~8 nm), slowly add it to the ethanol solution at a rate of 0.1 mL / s while stirring at 1500 r / min to dilute it, and after stirring evenly, obtain Sol B.

[0073] (3) Sol B was slowly added to the beaker of Sol A while stirring. After about 50 seconds, the system gelled. After the beaker was sealed and aged for 16 hours, the obtained gel block was crushed and modified by adding 3 mL of trimethylchlorosilane as a modifier. After 6 hours, the modification was completed. Three solvent replacement processes were carried out with n-hexane to remove the residual trimethylchlorosilane. At the same time, the high surface tension ethanol was replaced with low surface tension n-hexane.

[0074] (4) Finally, the powder obtained in step (3) was placed in a dry glass watch glass and dried in an oven at 80°C for 24 hours to obtain an aerogel powder material.

[0075] Comparative Example 2

[0076] (1) Take 10 mL of tetraethyl orthosilicate into a 250 mL beaker, then add 4 mL of deionized water, 20 mL of ethanol and 1 mL of hydrochloric acid (0.1 mol / L) in sequence, complete hydrolysis under stirring at room temperature for 18 h to obtain sol A.

[0077] (2) Take another beaker, take 80 mL of ethanol solution into the beaker, then take 40 mL of silica sol (average particle size ~ 8 nm) and slowly add it into the ethanol solution at a speed of 0.1 mL / s under stirring at 1500 r / min to dilute, after stirring uniformly, obtain sol B.

[0078] (3) Slowly add sol B into the beaker of sol A under stirring, the system gels after about 50 s, then seal the beaker and age for 16 h, after that, crush the obtained gel block, then replace most of the water in the system with ethanol for three times;

[0079] (4) Add 3 mL of trimethylchlorosilane as a modifier to modify, complete modification after 6 h, then replace the residual trimethylchlorosilane with n-hexane for three times, and replace the ethanol with high surface tension with n-hexane with low surface tension.

[0080] (5) Finally, place the powder obtained in step (4) on a dry glass surface dish, and dry in an oven at 80°C for 24 h to obtain aerogel powder material.

[0081] Comparative Example 3

[0082] (1) Take 10 mL of tetraethyl orthosilicate into a 250 mL beaker, then add 4 mL of deionized water, 20 mL of ethanol and 1 mL of hydrochloric acid (0.1 mol / L) in sequence, complete hydrolysis under stirring at room temperature for 18 h to obtain sol A.

[0083] (2) Take another beaker, take 40 mL of ethanol solution into the beaker, then take 20 mL of silica sol (average particle size ~ 8 nm) and slowly add it into the ethanol solution at a speed of 0.1 mL / s under stirring at 1500 r / min to dilute, after stirring uniformly, obtain sol B.

[0084] (3) Slowly add sol B into the beaker of sol A under stirring, the system gels after about 50 s, then seal the beaker and age for 16 h, after that, perform supercritical drying with ethanol to obtain aerogel powder material.

[0085] Comparative Example 4

[0086] (1) 10 mL of tetraethyl orthosilicate was placed in a 250 mL beaker, followed by the addition of 4 mL of deionized water, 20 mL of ethanol, and 1 mL of hydrochloric acid (0.1 mol / L). The mixture was stirred at room temperature for 18 h to complete hydrolysis, yielding Sol A.

[0087] (2) Take another beaker, measure 40 mL of ethanol solution and place it in the beaker, then measure 20 mL of silica sol (average particle size ~8 nm), and slowly add it to the ethanol solution at a rate of 0.1 mL / s while stirring at 800 r / min to dilute it. When about half of the solution is added, the system becomes turbid and the silica sol precipitates, making it impossible to proceed to the next step of the experiment.

[0088] Comparative Example 5

[0089] (1) 10 mL of tetraethyl orthosilicate was placed in a 250 mL beaker, followed by the addition of 4 mL of deionized water, 20 mL of ethanol, and 1 mL of hydrochloric acid (0.1 mol / L). The mixture was stirred at room temperature for 18 h to complete hydrolysis, yielding Sol A.

[0090] (2) Take another beaker, measure 40 mL of ethanol solution and place it in the beaker, then measure 20 mL of silica sol (average particle size ~8 nm), and slowly add it to the ethanol solution at a rate of 1 mL / s under stirring at 1500 r / min to dilute it. When about half of the solution is added, the system becomes turbid and the silica sol precipitates from the solution, making it impossible to proceed to the next step of the experiment.

[0091] Comparative Example 6

[0092] (1) 10 mL of tetraethyl orthosilicate was placed in a 250 mL beaker, followed by the addition of 4 mL of deionized water, 20 mL of ethanol, and 1 mL of hydrochloric acid (0.1 mol / L). The mixture was stirred at room temperature for 18 h to complete hydrolysis, yielding Sol A.

[0093] (2) Then, 20 mL of alkaline silica sol (average particle size ~8 nm) was measured and slowly added to sol A at a rate of 1 mL / s under stirring at 1500 r / min. When about 10 mL of alkaline silica sol was added, the system became turbid and could not be added dropwise. The system gelled in about 10 seconds. After the system gelled, the beaker was sealed and aged for 16 hours. The gel was crushed and 3 mL of trimethylchlorosilane was added as a modifier. After 6 hours, the modification was completed. Three solvent replacement processes were carried out with n-hexane to remove residual trimethylchlorosilane. At the same time, the high surface tension ethanol was replaced with low surface tension n-hexane.

[0094] (3) Finally, the powder obtained in step (2) was placed in a dry glass watch glass and dried in an oven at 80°C for 24 hours to obtain an aerogel powder material.

[0095] Comparative Example 7

[0096] The difference from Example 1 is that a pure organic silicon source (tetraethyl orthosilicate) is selected to prepare the aerogel powder.

[0097] Comparative Example 8

[0098] The difference from Example 1 is that a pure inorganic silicon source (alkaline silica sol, average particle size of 8 nm) is selected to prepare the aerogel powder.

[0099] The schematic diagram of the aerogel powder prepared in Example 1 of the present invention is as follows Figure 1 The samples prepared in the above examples and comparative examples were tested for performance, wherein the tap density test method adopted the standard GB / T 21354 "General method for determination of tap density of powder products"; the specific surface area, pore volume, and pore diameter test methods adopted the standard GB / T 10722 "Determination of total surface area and external surface area of ​​carbon black - Nitrogen adsorption method". The obtained performance is shown in Table 1:

[0100] Table 1

[0101]

[0102] From the above performance tests, it can be seen that the aerogel powder materials prepared in the embodiments of the present invention (see Examples 1-3) have excellent performance, and all indicators meet the industry standards (JC / T 2518-2019, hydrophobic silica aerogel powder).

[0103] It can be seen from Examples 1-3 and Comparative Example 1 that when the ratio of the organic silicon source to the inorganic silicon source exceeds the range specified in the present invention, the performance of the aerogel powder decreases significantly and it is difficult to meet the standard requirements. The reasons are as follows: 1) The solubility of silica sol in alcohol solvents is limited, resulting in impaired performance; 2) When the amount of silica sol is too large, the total water content in the system increases, causing the gel network to shrink or collapse.

[0104] It can be seen from Examples 1-3 and Comparative Example 2 that the ratio of the organic silicon source to the inorganic silicon source exceeds the range specified in the present invention. The performance of the aerogel powder can be improved by adding an ethanol replacement step, but this will increase the solvent cost and the atmospheric pressure drying step. The comparative group also demonstrates the effect of water on atmospheric pressure drying, and the material performance is improved after removing the water.

[0105] As shown in Examples 1-3 and Comparative Example 3, the silicon source ratio in the preparation method of the present invention is also suitable for supercritical drying, as supercritical drying requires a lower silicon source than atmospheric pressure drying. However, due to the high requirements for equipment and personnel required for supercritical drying and the risk of explosion, the present invention emphasizes the combination of a composite silicon source and atmospheric pressure drying. It can be seen that the performance of the aerogel powder prepared by the atmospheric pressure drying method in the present invention is comparable to that of the material prepared by the supercritical method.

[0106] It can be seen from Examples 1-3 and Comparative Examples 4 and 5 that high rotation speed and slow droplet speed play an important role in diluting silica sol, which can avoid the precipitation of silica sol and facilitate the subsequent mixing with the organic silicon source.

[0107] Examples 1-3 and Comparative Example 6 show that adding undiluted silica sol directly to an alcoholic solution of an organosilicon source will limit the amount of silica sol added, thereby increasing the proportion of the organosilicon source and partially increasing the silicon source cost. This may be because undiluted silica sol is highly alkaline, and adding it to the organosilicon source system results in excessively high and alkaline silicon concentrations in local areas, causing silica sol precipitation or premature gelation, making it impossible to add further silica sol. Diluting the silica sol first can avoid this problem. Comparative Examples 4, 5, and 6 show that using a large amount of alcohol to dilute the silica sol in advance plays an important role in the preparation of aerogel powders.

[0108] Compared with Examples 1-3 and Comparative Example 7 of the organic silicon source, the cost of the silicon source material is reduced by about half, and the performance has no obvious disadvantage.

[0109] Compared with Examples 1-3 and Comparative Example 8 of the inorganic silicon source, although the silicon source has the lowest cost, its specific surface area, pore volume and density do not meet the standard requirements.

[0110] In summary, the silica aerogel prepared by the present invention significantly reduces raw material costs while maintaining the excellent performance of the aerogel powder. In addition, the present invention utilizes a normal pressure drying method, which is simple and does not require complex equipment, making it easy to promote on a large scale.

[0111] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A method for preparing silica aerogel, characterized in that: Including steps: A certain amount of organosilicon source, alcohol solvent A, water and catalyst are uniformly mixed and hydrolyzed for a predetermined time to obtain sol A, wherein the volume ratio of the organosilicon source, alcohol solvent A, water and catalyst is 10:(20-30):(4-5):(1-2); Adding a certain amount of inorganic silicon source at a dropwise rate of 0.1-0.3 mL / s to an alcohol solvent B under stirring at a rotation speed of 1200-1500 r / min to obtain a sol B, wherein the volume ratio of the inorganic silicon source to the alcohol solvent B is 10:(20-30), and the inorganic silicon source is selected from an alkaline silica sol; According to the volume ratio of the organic silicon source to the inorganic silicon source (30-40): (60-70), a certain amount of the sol A and sol B are mixed to form a wet gel, and after aging for a predetermined time, a gel block is obtained; crushing the gel block, and then adding a modifier to modify it for a predetermined time to obtain a modified gel; The modified gel is dried at normal pressure for a predetermined time to obtain silica aerogel powder.

2. The method for preparing silica aerogel according to claim 1, wherein The organic silicon source is selected from at least one of methyl orthosilicate, tetraethyl orthosilicate or polysiloxane.

3. The method for preparing silica aerogel according to claim 1, wherein: The alkaline silica sol has a particle size of 8-40 nm and a silicon dioxide content of 30%-50%.

4. The method for preparing silica aerogel according to claim 1, wherein: The alcohol solvent A is selected from one or both of methanol and ethanol; And / or, the alcohol solvent B is selected from one or both of methanol and ethanol; And / or, the catalyst is selected from one or more of hydrochloric acid, oxalic acid, and sulfuric acid; And / or, the modifier is selected from any one of trimethylchlorosilane and hexamethyldisilazane.

5. The method for preparing silica aerogel according to claim 1, wherein: The scheduled time is 12 to 24 hours; And / or, the second predetermined time is 8 to 16 hours; And / or, the predetermined time three is 6 to 8 hours; And / or, the predetermined time 24 is 12 to 24 hours; And / or, the temperature of the normal pressure drying is 60-100°C.

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