Silica aerogel, preparation method thereof and thermal insulation material

Abstract

The invention provides silicon dioxide aerogel, a preparation method thereof and a thermal insulation material. The preparation method of the silicon dioxide aerogel comprises the following steps: obtaining a water glass solution, and carrying out hydrolysis reaction and polycondensation reaction to form silicon dioxide sol; carrying out aging and solvent replacement on the silicon dioxide sol to form silicon dioxide wet gel; performing hydrophobic modification on the silicon dioxide wet gel by using a modifier, and drying; wherein the modifier comprises a trichlorosilane derivative with a substituent group containing an alkenyl group. According to the preparation method of the silicon dioxide aerogel, the water glass is used for preparing the silicon dioxide wet gel, and the silicon dioxide wet gel is modified by using the trichlorosilane derivative of which the substituent group is alkenyl as a modifier, so that the modified wet gel is endowed with a large number of carbon-carbon double bond sites. And drying to obtain the silicon dioxide aerogel with high structural strength.

Description

Technical Field

[0001] The present application relates to the field of aerogel materials, and in particular to a silica aerogel and a preparation method thereof, and a thermal insulation material. Background Art

[0002] Silica aerogel is a nanoporous material with high porosity, high specific surface area, low light refractive index, low sound propagation velocity, low thermal conductivity, non-flammability and high temperature resistance. Due to these characteristics, silica aerogel is widely used in high and low temperature insulation, space field, catalyst carrier and other fields.

[0003] However, the surface of wet silica gel usually has hydrophilic hydroxyl groups, which makes wet silica gel easy to combine with water, resulting in large drying stress in the process of preparing silica aerogel, which is easy to damage the skeleton structure of silica aerogel, making the particle connection of silica aerogel after drying relatively fragile. In some weakly connected areas, the particles are only composed of a small amount of silicon-oxygen bonds, with a small connection area and easy to break. The above structural characteristics make the strength of traditional silica aerogel poor, which seriously restricts the promotion and application of silica aerogel insulation materials. Summary of the invention

[0004] Based on this, it is necessary to provide a silica aerogel and a preparation method thereof, and a thermal insulation material to overcome the problem of low structural strength of traditional silica aerogels.

[0005] In a first aspect of the present application, a method for preparing a silica aerogel is provided.

[0006] A method for preparing a silica aerogel comprises the following steps:

[0007] Obtaining a water glass solution, and performing a hydrolysis reaction and a polycondensation reaction to form a silica sol;

[0008] Aging and solvent replacement of the silica sol to form a silica wet gel;

[0009] Using a modifier to hydrophobically modify the silicon dioxide wet gel to form a modified wet gel;

[0010] Drying the modified wet gel;

[0011] Wherein, the modifier includes a trichlorosilane derivative whose substituent is an alkenyl group.

[0012] In some embodiments, the mass percentage of sodium silicate in the water glass solution is 5% to 20%.

[0013] In some embodiments, the modifier includes one or more of vinyltrichlorosilane, 2-propenyltrichlorosilane, 2-butenyltrichlorosilane, 5-hexenyltrichlorosilane, and 7-octenyltrichlorosilane.

[0014] In some embodiments, the hydrophobic modification step includes placing the wet silica gel in a first solution containing the modifier.

[0015] In some embodiments, the hydrophobic modification satisfies one or more of the following conditions:

[0016] (1) The temperature of the hydrophobic modification is 25°C to 70°C;

[0017] (2) The hydrophobic modification time is 12h~72h;

[0018] (3) The first solution includes one or more of toluene, dichloromethane, n-hexane and n-heptane.

[0019] In some embodiments, the mass percentage of the modifier in the first solution is 5% to 40%.

[0020] In some embodiments, the aging step includes placing the silica sol in an aging solution.

[0021] In some embodiments, the aging solution includes one of water, an aqueous solution of ethyl orthosilicate, and a water glass solution.

[0022] In a second aspect of the present application, a silica aerogel is provided.

[0023] A silicon dioxide aerogel is prepared by adopting the above-mentioned method for preparing the silicon dioxide aerogel.

[0024] In a third aspect of the present application, a thermal insulation material is provided.

[0025] A thermal insulation material contains the above-mentioned silica aerogel.

[0026] The above-mentioned silica aerogel preparation method uses water glass as a silicon source, forms a preliminary cross-linked silica sol through a hydrolysis reaction and a condensation reaction, and further ages and solvent-replaces the silica sol to form a silica wet gel. On this basis, the silica wet gel is modified by using a trichlorosilane derivative with an alkenyl substituent as a modifier, giving the modified wet gel a large number of hydrophobic carbon-carbon double bond functional groups, effectively improving the hydrophobicity of the modified wet gel, and after drying, a silica aerogel that is not easy to fall off can be obtained. DETAILED DESCRIPTION

[0027] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below. In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present application, so the present application is not limited by the specific embodiments disclosed below.

[0028] In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise clearly and specifically defined. In this application, "at least one" means more than one, such as one, two and more than two. "Multiple" or "several" means at least two, such as two, three, etc.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0030] When a numerical range is disclosed herein, the above range is considered to be continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0031] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0032] In this application, "above" or "below" includes the number itself. For example, "1 below" includes 1.

[0033] The temperature parameters in this application, unless otherwise specified, are allowed to be either constant temperature treatment or to vary within a certain temperature range. It should be understood that the constant temperature treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument. Fluctuations within the range of ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are allowed.

[0034] the term

[0035] Unless otherwise specified or incompatible herewith, the terms and phrases used herein shall have the following meanings:

[0036] "Alkenyl" refers to a group containing at least one unsaturated site, i.e., a carbon-carbon sp 2 A monovalent residue formed by a hydrogen atom of a hydrocarbon having a double bond, a positive carbon atom, a secondary carbon atom, a tertiary carbon atom or a ring carbon atom. Suitable examples include, but are not limited to, vinyl (-CH=CH 2 ), allyl (-CH 2 CH=CH 2 ), cyclopentenyl (-C 5 H 7 ), 5-hexenyl (-CH 2 CH 2 CH 2 CH 2 CH=CH 2 ).

[0037] Rational use of energy and energy conservation are of great significance to the sustainable development of the economy. Using new technologies and processes to develop environmentally friendly thermal insulation materials is one of the most effective and economical measures to save energy, which can not only reduce energy consumption, but also reduce the environmental burden and promote green development.

[0038] Silica aerogel is a nanoporous material with high porosity, high specific surface area, low light refractive index, low sound propagation velocity, low thermal conductivity, non-flammability and high temperature resistance. Due to these characteristics, silica aerogel is widely used in high and low temperature insulation, space field, catalyst carrier and other fields.

[0039] However, the surface of silica wet gel has hydrophilic hydroxyl groups, which not only increases the thermal conductivity of silica aerogel after drying, but also makes it difficult for silica aerogel to have good hydrophobicity. The above shortcomings restrict the further promotion and application of silica aerogel insulation materials.

[0040] In view of the shortcomings of the conventional technology, one embodiment of the present application relates to a method for preparing a silica aerogel. The method for preparing a silica aerogel can be used to obtain a silica aerogel that is not prone to powdering.

[0041] The preparation method of silica aerogel comprises the following steps:

[0042] Obtaining a water glass solution, and performing a hydrolysis reaction and a polycondensation reaction to form a silica sol;

[0043] The silica sol is subjected to aging and solvent replacement to form a silica wet gel;

[0044] Using a modifier to hydrophobically modify the silica wet gel to form a modified wet gel;

[0045] The modified wet gel is dried to obtain silica aerogel.

[0046] The modifier includes a trichlorosilane derivative having an alkenyl group as a substituent.

[0047] In some embodiments, the sodium silicate (NaSiO 3 ) is 5% to 20% by mass. Optionally, the mass percentage of sodium silicate can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% or other values ​​within the range of 5% to 20%.

[0048] The present application adopts a trichlorosilane derivative with an alkenyl substituent as a modifier, and obtains a modified silica wet gel containing a hydrophobic functional group by condensing the alkenyl group into the network structure of the silica wet gel through a condensation reaction with the Si-OH group remaining on the surface of the silica wet gel.

[0049] In order to reduce the influence of water on the drying process of silica wet gel, the silica wet gel needs to be hydrophobically modified. However, the surface of the silica wet gel obtained after aging is mostly hydrophilic silanol, while the alkenyl group is a hydrophobic group, resulting in poor compatibility between the modifier with hydrophobic groups and the sol particles, further resulting in a prolonged tightening reaction time, poor reaction efficiency, and ultimately resulting in fewer hydrophobic groups in the modified wet gel. For this reason, the present application uses a silane coupling agent with a chlorine group to increase the reaction rate of the hydrophobic modification, so as to increase the number and efficiency of the grafted hydrophobic groups (alkenyl groups). At the same time, considering that when selecting a silane coupling agent with multiple substituent branches, the same incompatibility problem will be faced, and the presence of steric hindrance will further hinder the reaction. To this end, the present application selects trichlorosilane derivatives with multiple chlorine-substituted groups, and utilizes the characteristics of trichlorosilane derivatives with small steric hindrance and good compatibility to introduce more hydrophobic groups into the structure of silica wet gel, thereby giving the silica wet gel better hydrophobicity, which is conducive to obtaining silica aerogel with high structural strength and not easy to fall off after drying.

[0050] In some embodiments, the modifier includes one or more of vinyltrichlorosilane, 2-propenyltrichlorosilane, 2-butenyltrichlorosilane, 5-hexenyltrichlorosilane, and 7-octenyltrichlorosilane.

[0051] In some embodiments, the step of hydrolysis reaction comprises:

[0052] The pH of the water glass solution is adjusted to 2-6 by ion exchange resin to form a prepolymer solution.

[0053] Optionally, the step of hydrolysis reaction can also be:

[0054] The pH of the water glass solution is adjusted to 2-6 using an acidic regulator to form a prepolymer solution.

[0055] Optionally, the acidic regulator includes one or more of hydrochloric acid, nitric acid and sulfuric acid.

[0056] In some embodiments, the hydrolysis reaction time is 0.5h~4h. Optionally, the hydrolysis time can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h or other values ​​within the range of 0.5h~4h.

[0057] In some embodiments, the polycondensation step comprises:

[0058] The pH of the prepolymer solution is adjusted to 7-10 to form a silica sol.

[0059] In some embodiments, an alkaline regulator is used to adjust the pH of the system to 7 to 10. Optionally, the alkaline regulator includes one or both of ammonia water and sodium hydroxide.

[0060] In some embodiments, the polycondensation reaction time is 0.5 h to 4 h. Alternatively, the polycondensation reaction time can be 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h or other values ​​within the range of 0.5 h to 4 h.

[0061] After the water glass solution undergoes hydrolysis and condensation, a primary gel network will be constructed to form a silica sol. At this time, only a few silicon-oxygen bonds in the gel network will be connected together, and the structural strength is low. For this reason, the silica sol needs to be aged to form a silica wet gel with higher structural strength.

[0062] In some embodiments, the aging step includes placing the silica sol in an aging solution and allowing the solution to stand.

[0063] In some embodiments, the aging solution includes one of water, an ethanol solution of tetraethyl orthosilicate, and a water glass solution.

[0064] Optionally, the aging solution may be an ethanol solution of ethyl orthosilicate with a mass percentage of 1% to 20%.

[0065] Optionally, the aging solution may be a water glass solution with a mass percentage of 1% to 20%.

[0066] In some embodiments, during aging, the standing time is 6 hours to 72 hours. The standing aging time can be but is not limited to 6 hours, 12 hours, 18 hours, 24 hours, 30 hours, 36 hours, 42 hours, 48 ​​hours, 54 hours, 60 hours, 66 hours, 72 hours or other values ​​within the range of 6 hours to 72 hours.

[0067] In some embodiments, during aging, the static temperature is maintained at 25° C. to 70° C. The static aging temperature can be, but is not limited to, 25° C., 30° C., 35° C., 40° C., 45° C., 50° C., 55° C., 60° C., 65° C., 70° C., or other values ​​within the range of 25° C. to 70° C.

[0068] During aging, when the system temperature is low, the molecular kinetic energy in the system is relatively low, the molecular motion is relatively stable, the hydrolysis and polycondensation reactions slow down, and the degree of crosslinking of the obtained silica wet gel is low. When the temperature is too high, the hydrolysis and condensation reaction rates will be too fast, which will easily lead to the volume shrinkage of the wet gel. In the temperature range of 25℃~70℃, it is conducive to obtaining silica wet gel with high structural strength.

[0069] Optionally, the wet silica gel is washed with 1 to 4 times the volume of deionized water. The impurities introduced into the system by the water glass solution can be further removed by washing.

[0070] In some embodiments, the water washing temperature is 25°C to 60°C, the water washing time is 2h to 18h, and the water washing is repeated 0 to 10 times.

[0071] The structure of the aged silica wet gel preform contains a large amount of water. The surface tension of water is large, and the stress during drying is large, which can easily affect the skeleton structure of the silica aerogel. Therefore, it is necessary to use a solvent with low surface tension to perform solvent replacement to remove the residual water inside the gel.

[0072] In some embodiments, the step of solvent replacement comprises:

[0073] immersing the silicon dioxide wet gel preform in a replacement solvent and allowing it to stand or stir;

[0074] Repeat the above steps 0 to 6 times.

[0075] Wherein, the replacement solvent includes one or more of n-hexane, cyclohexane, n-heptane and acetone.

[0076] During the solvent replacement, the water in the wet silica gel will be exchanged with the organic solvent. It can be understood that repeating the above operation means: repeating the steps of immersing the wet silica gel in the organic solvent and letting it stand. When the number of repeated operations is 0, it means that no repeated operation is performed.

[0077] In some embodiments, during solvent replacement, the volume ratio of the wet silica gel to the organic solvent is 1:1 to 1:4. The volume ratio of the wet silica gel to the organic solvent can be, but is not limited to, 1:1, 1:2, 1:3, 1:4 or other values ​​within the range of 1:1 to 1:4.

[0078] In some embodiments, the temperature of the solvent replacement is 25° C. to 60° C. The temperature of the solvent replacement can be, but is not limited to, 25° C., 30° C., 35° C., 40° C., 45° C., 50° C., 55° C., 60° C. or other values ​​within the range of 25° C. to 60° C.

[0079] In some embodiments, the standing time of the solvent replacement is 1 h to 12 h. The standing time can be but is not limited to 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h or other values ​​within the range of 1 h to 12 h.

[0080] In some embodiments, the aged silica sol (gel) is washed with deionized water.

[0081] In some embodiments, the washing step includes: immersing the aged silica sol (gel) in deionized water and stirring the deionized water.

[0082] In some embodiments, the washing temperature is 25° C. to 60° C., the single washing time is 2 h to 18 h, and the washing is repeated 2 to 8 times.

[0083] In some embodiments, the hydrophobic modification step includes placing the wet gel in a first solution containing a modifying agent.

[0084] In some embodiments, the solvent of the first solution includes one or more of toluene, dichloromethane, n-hexane and n-heptane.

[0085] In some embodiments, the temperature of hydrophobic modification is 25° C. to 70° C. The heating temperature of hydrophobic modification can be but is not limited to 25° C., 35° C., 40° C., 45° C., 50° C., 55° C., 60° C., 65° C., 70° C. or other values ​​within the range of 25° C. to 70° C.

[0086] In some embodiments, the hydrophobic modification time is 12 hours to 72 hours. The stirring time of the hydrophobic modification can be but is not limited to 12 hours, 24 hours, 36 hours, 48 ​​hours, 60 hours, 72 hours or other values ​​within the range of 12 hours to 72 hours.

[0087] In some embodiments, in the first solution, the mass percentage of the modifier is 5% to 40%. The mass percentage of the modifier includes but is not limited to 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40% or other values ​​within the range of 5% to 40%.

[0088] In some embodiments, the first solution is continuously stirred during the hydrophobic modification process.

[0089] In some embodiments, the modified wet gel is washed with a washing solvent, which includes one or more of propanol, n-hexane, and n-heptane.

[0090] In some embodiments, the volume ratio of the cleaning solvent to the modified wet gel is 0.5: 1 to 3: 1. The soaking time for each cleaning is 2 hours to 24 hours, and the cleaning is repeated 2 to 5 times.

[0091] In some embodiments, the drying method includes atmospheric pressure drying, supercritical drying or freeze drying.

[0092] In some embodiments, the step of drying at normal pressure includes: drying the modified wet gel at 25°C to 60°C for 12h to 48h, heating to 100°C to 200°C, and continuing drying for 1h to 4h. Through the drying step, the liquid phase inside the modified wet gel can be replaced by a gas phase to obtain a silica aerogel.

[0093] In one embodiment of the present application, a silica aerogel is provided. The silica aerogel is prepared by the above-mentioned method for preparing silica aerogel.

[0094] In another embodiment of the present application, a thermal insulation material is provided. The thermal insulation material contains the above-mentioned silica aerogel. In this embodiment, the thermal insulation material has a low thermal conductivity and excellent structural strength, and is not prone to powdering during use.

[0095] The present application is further described in detail below in conjunction with specific embodiments.

[0096] In the following specific embodiments and comparative examples, the raw materials used, unless otherwise specified, are all commercially available products; the instruments used, unless otherwise specified, are all commercially available products; and the processes used, unless otherwise specified, are all routinely selected by those skilled in the art.

[0097] Example 1

[0098] This embodiment provides a silica aerogel. The preparation method of the silica aerogel is:

[0099] Obtain a water glass solution with a mass percentage of 10% sodium silicate, adjust the pH to 3 with hydrochloric acid, and hydrolyze for 4 hours. Use ammonia water to adjust the pH to 8, polycondense for 4 hours, and obtain a silica sol. Place the silica sol in an equal volume of water and age it for 48 hours. Use deionized water to wash the aged silica sol (gel) at room temperature for 4 times, each time for 2 hours. Place the aged silica sol in a n-hexane solvent and perform solvent replacement at room temperature for 4 times, each time for 12 hours, to obtain a wet silica gel.

[0100] At 30°C, the silica wet gel was placed in a 25wt% n-hexane solution of vinyltrichlorosilane for hydrophobic modification and immersed for 36 hours to obtain a modified wet gel. The modified wet gel was washed 4 times with an equal volume of n-hexane, and the immersion time for each wash was 24 hours. The silica aerogel was obtained by drying at normal pressure. The drying conditions were: drying at 60°C for 24 hours, and then drying at 120°C for 4 hours to obtain the silica aerogel.

[0101] Example 2

[0102] This embodiment provides a silicon dioxide aerogel.

[0103] The difference between the silica aerogel of this embodiment and that of embodiment 1 is that the wet silica gel is placed in a 25 wt % n-hexane solution of 2-butenyltrichlorosilane for hydrophobic modification.

[0104] Example 3

[0105] This embodiment provides a silicon dioxide aerogel.

[0106] The difference between the silica aerogel of this embodiment and that of embodiment 1 is that the wet silica gel is placed in a 5 wt % n-hexane solution of vinyltrichlorosilane for hydrophobic modification.

[0107] Example 4

[0108] This embodiment provides a silicon dioxide aerogel.

[0109] The difference between the silica aerogel of this embodiment and that of embodiment 1 is that the wet silica gel is placed in a 40 wt % n-hexane solution of vinyltrichlorosilane for hydrophobic modification.

[0110] Comparative Example 1

[0111] This comparative example provides a silica aerogel.

[0112] Silica aerogel is prepared by direct CO2 assisted generation of wet silica gel 2 The silicon dioxide wet gel is prepared by supercritical drying.

[0113] Comparative Example 2

[0114] This comparative example provides a silica aerogel.

[0115] The silica aerogel in this comparative example is different from that in Example 1 in that the modifier is trimethylchlorosilane.

[0116] Comparative Example 3

[0117] This comparative example provides a silica aerogel.

[0118] The silica aerogel in this comparative example is different from that in Example 3 in that the modifier is trimethylchlorosilane.

[0119] Test Case

[0120] The performance of the silica aerogels of the above examples and comparative examples was tested, and the test results are shown in Table 1.

[0121] Powder loss rate: The silica aerogel was placed on a vibrating shaker and vibrated for 10 minutes. The relative percentage of the mass difference before and after vibration to the mass before vibration was recorded as the powder loss rate of the silica aerogel.

[0122] Thermal conductivity: The thermal conductivity of silica aerogel was tested according to the method of GB / T34336-2017.

[0123] Table 1

[0124]

[0125] As shown in Table 1, the silica aerogels of Examples 1 to 4 have a lower powder loss rate and a lower thermal conductivity, and show a lower powder loss rate than the silica aerogel of Comparative Example 1 without hydrophobic modification, indicating that the silica aerogel has good structural strength. At the same time, comparing Examples 1 to 4 with Comparative Examples 2 to 3, it can be seen that the use of trichlorosilane derivatives as hydrophobic modifiers helps to prepare silica aerogels with lower powder loss rate and lower thermal conductivity at low modifier content.

[0126] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0127] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims, and the description may be used to interpret the contents of the claims.

Claims

1. A method for preparing a silica aerogel, characterized in that: The steps include: Obtaining a water glass solution, and performing a hydrolysis reaction and a polycondensation reaction to form a silica sol; Aging and solvent replacement of the silica sol to form a silica wet gel; Using a modifier to hydrophobically modify the silicon dioxide wet gel to form a modified wet gel; Drying the modified wet gel; Wherein, the modifier includes a trichlorosilane derivative whose substituent is an alkenyl group.

2. The method for preparing silica aerogel according to claim 1, characterized in that: The mass percentage of sodium silicate in the water glass solution is 5% to 20%.

3. The method for preparing the silica aerogel according to claim 1, characterized in that: The modifier includes one or more of vinyl trichlorosilane, 2-propylene trichlorosilane, 2-butenyl trichlorosilane, 5-hexenyl trichlorosilane and 7-octenyl trichlorosilane.

4. The method for preparing the silica aerogel according to any one of claims 1 to 3, characterized in that: The hydrophobic modification step comprises: placing the silicon dioxide wet gel into a first solution containing the modifier.

5. The method for preparing the silica aerogel according to claim 4, characterized in that: The hydrophobic modification satisfies one or more of the following conditions: (1) The temperature of the hydrophobic modification is 25°C to 70°C; (2) The hydrophobic modification time is 12h~72h; (3) The first solution includes one or more of toluene, dichloromethane, n-hexane and n-heptane.

6. The method for preparing the silica aerogel according to claim 4, characterized in that: The mass percentage of the modifier in the first solution is 5% to 40%.

7. The method for preparing a silica aerogel according to any one of claims 1 to 3, characterized in that: The aging step comprises: placing the silica sol in an aging solution.

8. The method for preparing silica aerogel according to claim 7, characterized in that: The aging solution includes one of water, an aqueous solution of ethyl orthosilicate and a water glass solution.

9. A silica aerogel, characterized in that: The silica aerogel is prepared by the preparation method of any one of claims 1 to 8.

10. A heat insulating material, characterized in that: The thermal insulation material comprises the silica aerogel according to claim 9.

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