Silicon dioxide aerogel and aging and drying method thereof
By setting an organic solvent protective layer on the surface of the wet silica gel and extending the aging time, the problem of the aerogel solid framework being destroyed during the drying process was solved, and low-density silicon dioxide with a continuous network structure was successfully prepared. Aerogel.
Patent Information
- Application Number
- CN202411941926.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-26
- Publication Date
- 2025-02-18
AI Technical Summary
In the prior art, the solid skeleton of the aerogel is easily destroyed during the drying process, and it is impossible to form an aerogel with a continuous network structure.
By providing an organic solvent protective layer on the surface of the silica wet gel and controlling the second aging time >168h, the solid skeleton is prevented from being destroyed during the drying process, forming an aerogel with a continuous network structure.
A solid framework for protecting the wet silica gel during the drying process is realized, and a low-density silica aerogel with a nano-order continuous network structure is prepared.
Smart Images
Figure CN119461393A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of new material preparation, and specifically relates to a silicon dioxide aerogel and an aging and drying method thereof. Background Art
[0002] Aerogel is a material with a nanoporous structure, and its solid phase and pore structure are both nanometer-scale. It is usually composed of colloidal particles or polymer molecules that aggregate to form a nanoporous network structure, and the pores are filled with gaseous dispersion medium. According to the skeleton components of aerogels, they can be divided into three categories: inorganic aerogels, organic aerogels, and carbon aerogels. Among them, the main types of inorganic aerogels are silicon aerogels and metal oxide aerogels; the precursors used in organic aerogels are mostly resorcinol-formaldehyde; carbon aerogels are obtained by carbonizing organic aerogels under inert atmosphere and high temperature conditions to retain only the carbon skeleton structure.
[0003] In the prior art, aerogels are usually obtained by supercritical drying wet gels. In the preparation process of sol-gel solutions, by controlling the hydrolysis and polycondensation reaction conditions of the solution, nanoclusters of different structures are formed in the solution, and the clusters adhere to each other to form a gel, and the solid skeleton of the gel is filled with liquid reagents remaining after the chemical reaction. These remaining liquid reagents have surface tension on the solid skeleton of the gel. In the subsequent drying process, the surface tension in the micropores of the solid skeleton will cause the solid skeleton of the aerogel to be destroyed, and an aerogel with a continuous network structure cannot be formed. Summary of the invention
[0004] The object of the present invention is to provide a silica aerogel and an aging and drying method thereof. The silica aerogel aging and drying method provided by the present invention will not damage the solid skeleton in the silica wet gel, and can prepare a silica aerogel with a continuous network structure.
[0005] In order to achieve the purpose of the present invention, the present invention provides the following technical solutions:
[0006] A method for aging and drying a silica aerogel comprises the following steps:
[0007] providing a silica sol-gel solution;
[0008] The silica sol-gel solution is subjected to a first aging to obtain a wet gel; the first aging time is 24 to 48 hours;
[0009] An organic solvent protective layer is provided on the surface of the wet gel, and then a second aging is performed, and the silicon dioxide aerogel is obtained after drying; the second aging time is greater than 168 hours.
[0010] Preferably, the organic solvent in the organic solvent protective layer includes ethanol or acetone.
[0011] Preferably, the thickness of the organic solvent protective layer is 5 to 15 mm higher than that of the wet gel.
[0012] Preferably, the temperature of the first aging and the second aging is set at 20-50°C.
[0013] Preferably, the drying temperature is 100-180° C. and the drying time is 3-24 hours.
[0014] Preferably, after the second aging, the aging product obtained may be subjected to hydrophobic modification and dried to obtain a hydrophobic silica aerogel.
[0015] Preferably, the reagent used for the hydrophobic modification includes trimethylchlorosilane or hexamethyldisilazane.
[0016] Preferably, the hydrophobic modification comprises immersing the obtained aged product in a hydrophobic modification agent for a modification time of 4 to 6 hours.
[0017] The present invention also provides the silicon dioxide aerogel prepared by the aging and drying method described in the above technical scheme.
[0018] The present invention provides an aging and drying method for silica aerogel, comprising the following steps: providing a silica sol-gel solution; subjecting the silica sol-gel solution to a first aging to obtain a wet gel; the first aging time is 24 to 48 hours; providing an organic solvent protective layer on the surface of the wet gel, and then performing a second aging to obtain the silica aerogel after drying; the second aging time is greater than 168 hours. The present invention can prevent the surface of the silica wet gel from drying during the subsequent aging process by providing an organic solvent protective layer on the surface of the silica wet gel, thereby causing the liquid surface tension in the micropores of the solid skeleton to destroy the solid skeleton that has not been fully strengthened; and the present invention controls the second aging time to be greater than 168 hours, and during this aging process, the solid skeleton in the silica wet gel is continuously strengthened, so that the surface tension formed by the remaining liquid reagent in the solid skeleton will not cause the solid skeleton to be destroyed during drying, and a porous, disordered, low-density silica aerogel with a nano-scale continuous network structure is obtained. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.
[0020] Figures 1-2 This is a scanning electron microscope image of the silica aerogel prepared in Example 1 at a scale of 200 nm;
[0021] Figures 3-4 This is a scanning electron microscope image of the silica aerogel prepared in Example 2 at a scale of 200 nm;
[0022] Figures 5-6 This is a scanning electron microscope image of the silica aerogel prepared in Example 3 at a scale of 200 nm;
[0023] Figure 7 This is a scanning electron microscope image of the silica aerogel prepared in Example 3 at a scale of 100 nm. DETAILED DESCRIPTION
[0024] The present invention provides an aging and drying method for a silica aerogel, comprising the following steps:
[0025] providing a silica sol-gel solution;
[0026] The silica sol-gel solution is subjected to a first aging to obtain a wet gel; the first aging time is 24 to 48 hours;
[0027] An organic solvent protective layer is provided on the surface of the wet gel, and then a second aging is performed, and the aerogel is obtained after drying; the second aging time is greater than 168 hours.
[0028] In the present invention, unless otherwise specified, all preparation raw materials are preferably commercially available products well known to those skilled in the art.
[0029] In the present invention, the method for preparing the silica sol-gel solution comprises the following steps:
[0030] The silicon precursor, the organic solvent, the acid reagent and the alkali reagent are mixed and reacted to obtain the silicon dioxide sol-gel solution.
[0031] In the present invention, the silicon precursor includes tetraethyl orthosilicate or methyl orthosilicate, and in a specific embodiment, it can be tetraethyl orthosilicate; the organic solvent includes ethanol, acetone, etc., and in a specific embodiment, it can be ethanol; the acid reagent is hydrochloric acid; the pH value of the hydrochloric acid is 2.3-5, and in a specific embodiment, it can be 3 or 4; the alkali reagent is ammonia water and ethanol; the ratio of ammonia water to ethanol is 1:40-70, and in a specific embodiment, it can be 1:50 or 1:60.
[0032] In the present invention, the ratio of the silicon precursor, the organic solvent and the acid reagent can be 1:4:4; the amount of the alkali reagent is 25-35% of the total weight of the silicon precursor, the organic solvent and the acid reagent, and can be 30% in a specific embodiment.
[0033] The present invention is carried out by mixing and stirring tetraethyl orthosilicate, anhydrous ethanol and water to hydrolyze, as shown in Formula I:
[0034]
[0035] After the above hydrolysis, an active monomer (hydroxyl-polar group) is generated, and the hydroxyl group is polymerized, as shown in Formula II:
[0036]
[0037] After the hydroxyl groups are polymerized, a sol is formed, and then a silica sol-gel solution with a certain spatial structure is generated through two-step catalysis of acid and base.
[0038] In the present invention, the silica sol-gel solution is modified; the reagent used for the modification is dimethylformamide; the modifier accounts for 0.3-0.6% of the mass of the silica sol-gel solution, and in a specific embodiment, it can be 0.5%. The present invention does not specifically limit the conditions of the modification. The present invention uses dimethylformamide to modify the silica sol-gel solution, which is beneficial to the formation of silicon chains (hydroxyl polymers) of the solid skeleton and is beneficial to the separation from the liquid in the micropores of the solid skeleton.
[0039] The present invention performs a first aging on the sol-gel solution to obtain a wet gel; the first aging time is 24 to 48 hours. In the present invention, the temperature of the first aging is 20 to 50°C, and in a specific embodiment, it can be 25°C, 35°C or 40°C; the first aging time is 24 to 48 hours, and in a specific embodiment, it can be 36 hours or 40 hours. The present invention can obtain a wet gel through the first aging so that it can be covered with an organic solvent protective layer to prevent the surface of the wet gel from drying during the second aging process.
[0040] In the present invention, the organic solvent in the organic solvent protective layer includes ethanol or acetone, and in a specific embodiment, it can be ethanol; the ethanol is anhydrous ethanol; the thickness of the organic solvent protective layer is 5 to 15 mm higher than the upper surface of the wet gel. In a specific embodiment, it can be 5 mm, 8 mm or 10 mm. The present invention can prevent the surface of the wet gel from drying during the subsequent aging process by arranging an organic solvent protective layer on the surface of the wet gel, thereby preventing the surface tension of the liquid in the micropores of the solid skeleton from destroying the solid skeleton.
[0041] In the present invention, the temperature of the second aging is 20-50°C, and in a specific embodiment, it can be 25°C, 35°C or 40°C; the time of the second aging is >168h, and can be 200-2000h, and in a specific embodiment, it can be 200h, 300h, 600h, 1000h or 2000h.
[0042] In the present invention, the drying temperature is 100-180°C, and in a specific embodiment, it can be 120°C, 150°C or 160°C; the time is 3-24h, and in a specific embodiment, it can be 5h or 12h; the drying method can be airing, drying or negative pressure microwave.
[0043] In the present invention, the product obtained after the second aging is directly dried, and the obtained aerogel is a hydrophilic silica aerogel.
[0044] In the present invention, the second aging further comprises subjecting the obtained aging product to hydrophobic modification, and obtaining the hydrophobic silica aerogel after drying.
[0045] In the present invention, the reagent used for the hydrophobic modification includes trimethylchlorosilane; the trimethylchlorosilane is used in the form of a trimethylchlorosilane solution; the solvent of the trimethylchlorosilane solution is n-hexane, and the volume ratio of the trimethylchlorosilane to n-hexane is 1:7-10, and in a specific embodiment, it can be 1:9.
[0046] In the present invention, the hydrophobic modification comprises the following steps: immersing the obtained aged product in a hydrophobic modification reagent; the hydrophobic modification reagent covers the aged product colloid by 3 to 20 mm, and in a specific embodiment, it can be 5 mm or 10 mm.
[0047] In the present invention, the temperature of the hydrophobic modification is 20-50° C., and the time is 4-12 hours. In a specific embodiment, it can be 6 hours.
[0048] The present invention also provides silicon dioxide aerogel prepared by the aging and drying method described in the above technical solution.
[0049] In order to further illustrate the present invention, the silica aerogel and the aging and drying method thereof provided by the present invention are described in detail below in conjunction with the accompanying drawings and examples, but they should not be construed as limiting the scope of protection of the present invention.
[0050] Example 1
[0051] TEOS, anhydrous ethanol and dilute hydrochloric acid with a pH value of 3 were stirred for 15 minutes in a ratio of 1:4:4, and then a mixture of ammonia water and anhydrous ethanol in a ratio of 1:50 was added as an alkali reagent, and stirring was continued for 60 minutes to obtain a silica sol-gel solution;
[0052] The silica sol-gel solution is poured into a container and covered with a lid to a thickness of 20 mm. The container is placed in an environment of 20 to 50° C. and aged for 48 hours to obtain a wet silica gel.
[0053] The lid of the container containing the above-mentioned wet silica gel is opened, anhydrous ethanol is added to the upper surface of the gel so that the anhydrous ethanol completely covers the gel and is 10 mm higher than the gel, and then the lid of the container containing the gel is closed, and the aging is continued in an environment of 20 to 50° C. for 600 hours. The lid of the container containing the aged wet silica gel is opened, and the remaining anhydrous ethanol is poured out without closing the lid again. Then, the container is placed in a high-temperature drying oven and dried at 120° C. for 3 hours to obtain a hydrophilic silica aerogel.
[0054] Example 2
[0055] TEOS, anhydrous ethanol and dilute hydrochloric acid with a pH value of 3 were stirred for 15 minutes in a ratio of 1:4:4, and then a mixture of ammonia water and anhydrous ethanol in a ratio of 1:50 was added as an alkali reagent, and stirring was continued for 60 minutes to obtain a silica sol-gel solution;
[0056] The silica sol-gel solution is poured into a container and covered with a lid to a thickness of 20 mm. The container is placed in an environment of 20 to 50° C. and aged for 48 hours to obtain a wet silica gel.
[0057] The lid of the container containing the wet silica gel is opened, anhydrous ethanol is added to the upper surface of the gel, so that the anhydrous ethanol completely covers the gel and is 10 mm higher than the gel, and then the lid of the container containing the gel is closed, and the gel is aged for 600 h in an environment of 20 to 50° C., the lid of the container containing the aged wet silica gel is opened, the remaining anhydrous ethanol is poured out, and a mixture of trimethylchlorosilane and n-hexane in a volume ratio of 1:9 is added to the container, so that the mixture covers the aged wet silica gel. 3mm of hydrophobic modified silica wet gel, then immediately cover with a lid to seal, and react for 6 hours in an environment of 20-50°C; open the lid to pour out the remaining liquid, then pour anhydrous ethanol into it and cover the hydrophobic modified silica wet gel by 3mm, and soak for 24 hours; open the lid of the container containing the hydrophobic modified silica wet gel, pour out the remaining anhydrous ethanol, no need to cover the lid again, and then place it in a high-temperature drying oven, dry it at 120°C for 3 hours to obtain hydrophobic silica aerogel.
[0058] Example 3
[0059] TEOS, anhydrous ethanol and dilute hydrochloric acid with a pH value of 3 were stirred for 15 minutes in a ratio of 1:4:4, and then a mixture of ammonia water and anhydrous ethanol in a ratio of 1:50 was added as an alkali reagent, and stirring was continued for 60 minutes to obtain a silica sol-gel solution;
[0060] The silica sol-gel solution is poured into a container and covered with a lid to a thickness of 20 mm. The container is placed in an environment of 20 to 50° C. and aged for 48 hours to obtain a wet silica gel.
[0061] The lid of the container containing the above-mentioned wet silica gel is opened, anhydrous ethanol is added to the upper surface of the gel so that the anhydrous ethanol completely covers the gel and is 10 mm higher than the gel, and then the lid of the container containing the gel is closed, and the aging is continued in an environment of 20 to 50° C. for 600 hours. The lid of the container containing the aged wet silica gel is opened, and the remaining anhydrous ethanol is poured out without covering the lid again. Then, it is placed in dry sunlight and dried at a temperature above 20° C. for 24 hours (the drying process can be interrupted in the middle) to obtain a hydrophilic silica aerogel.
[0062] Test Case
[0063] The silica aerogels prepared in Examples 1 to 3 were characterized using a 400,000x scanning electron microscope, and the results are as follows:
[0064] Figures 1-2 This is a scanning electron microscope image of the silica aerogel prepared in Example 1 at a scale of 200 nm;
[0065] Figures 3-4 This is a scanning electron microscope image of the silica aerogel prepared in Example 2 at a scale of 200 nm;
[0066] Figures 5-6 This is a scanning electron microscope image of the silica aerogel prepared in Example 3 at a scale of 200 nm;
[0067] Figure 7 This is a scanning electron microscope image of the silica aerogel prepared in Example 3 at a scale of 100 nm;
[0068] Depend on Figures 1 to 7 It can be seen that the aerogel preparation process of the present invention avoids the destruction of the network structure of the solid skeleton of the silica gel during the drying process, and prepares a low-density silica aerogel with a nano-scale continuous network structure.
[0069] The properties of the silica aerogels prepared in Examples 1 to 3 were tested, and the results are shown in Table 1 below:
[0070] Table 1 Performance test results of silica aerogels prepared in Examples 1 to 3
[0071]
[0072] It can be seen from the results in Table 1 that the silica aerogel prepared in the present invention is a porous, disordered, low-density silica aerogel with a nanoscale continuous network structure.
[0073] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.
Claims
1. A method for aging and drying a silica aerogel, characterized in that: The following steps are involved: providing a silica sol-gel solution; The silica sol-gel solution is subjected to a first aging to obtain a wet gel; the first aging time is 24 to 48 hours; An organic solvent protective layer is provided on the surface of the wet gel, and then a second aging is performed, and the silicon dioxide aerogel is obtained after drying; the second aging time is greater than 168 hours.
2. The aging and drying method according to claim 1, characterized in that: The organic solvent in the organic solvent protective layer includes ethanol or acetone.
3. The aging and drying method according to claim 1 or 2, characterized in that: The thickness of the organic solvent protective layer is 5 to 15 mm higher than that of the wet gel.
4. The aging and drying method according to claim 1, characterized in that: The temperature of the first aging and the second aging is set at 20-50°C.
5. The aging and drying method according to claim 1, characterized in that: The drying temperature is 100-180° C. and the drying time is 3-24 hours.
6. The aging and drying method according to claim 1, characterized in that: After the second aging, the aging product obtained can also be subjected to hydrophobic modification and dried to obtain a hydrophobic silica aerogel.
7. The aging and drying method according to claim 6, characterized in that: The reagent used for the hydrophobic modification includes trimethylchlorosilane or hexamethyldisilazane.
8. The aging and drying method according to claim 6 or 7, characterized in that: The hydrophobic modification comprises immersing the obtained aged product in a hydrophobic modification agent for a modification time of 4 to 6 hours.
9. The silica aerogel prepared by the aging and drying method according to any one of claims 1 to 8.