Preparation method of high-strength low-thermal-conductivity silica aerogel

Abstract

The invention relates to the technical field of aerogel, in particular to a preparation method of high-strength low-thermal-conductivity silica aerogel, which comprises the following steps: S1, preparing a sodium silicate solution, a PDMS solution and a mixed solution containing an additive; s2, at room temperature, performing sol-gel treatment on the sodium silicate solution obtained in the step S1, the PDMS solution obtained in the step S1 and the mixed solution, and aging to obtain an aged material; and S3, adding ethanol and normal hexane into the aged material obtained in the step S2, carrying out solvent exchange, and modifying to obtain the high-strength low-thermal-conductivity silica aerogel. The silica aerogel prepared by the invention has higher compressive strength and lower heat conductivity coefficient, and is wide in application range.

Description

Technical Field

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

[0002] Silica aerogel, a lightweight porous material composed of a nanoscale silicon-oxygen network filled with numerous closed or semi-closed pores, exhibits excellent thermal insulation, acoustic damping, and catalytic support properties due to its extremely low bulk density, ultra-high porosity, and unique nanoscale microstructure. It holds broad application prospects in aerospace, building energy conservation, electronic device heat dissipation, and new energy fields. Among its key performance advantages, low thermal conductivity is one of the most significant. Its thermal conductivity at room temperature and pressure can be as low as 0.012-0.020 W / (m·K), far superior to traditional insulation materials such as rock wool, glass wool, and polyurethane foam. Therefore, in scenarios with stringent thermal insulation requirements, silica aerogel has become a highly competitive candidate material.

[0003] Patent CN116495774B discloses a silica aerogel and its preparation method. The method involves mixing water glass, sodium methylsiloxane solution, and distilled water to prepare a silica gel, then adding secondary modified titanium dioxide nanorods. After gelation, the gel undergoes multiple rapid aging and solvent replacement processes, followed by the addition of a modifier for modification. After the reaction, the oil and water are separated, and the upper organic layer is dried to obtain hydrophobic silica aerogel powder. This invention uses an inexpensive silicon source to prepare silica aerogel powder, resulting in a simple and convenient process, rapid gelation, low drying requirements, and low cost, while also exhibiting good hydrophobicity. Although this invention imparts good hydrophobic properties to the silica aerogel, it does not provide further research on its compressive strength.

[0004] Patent CN109019612B discloses a solid silica aerogel that can be prepared under normal temperature and pressure conditions, has a short processing time, is suitable for industrialization, and can improve the toughness and heat resistance of silica aerogels. The solid silica aerogel is prepared by placing a rare-earth-toughened solid silica aerogel precursor in a drying autoclave and then subjecting it to microwave vacuum drying. The solid silica aerogel has an average pore size of 24-26 nm and a specific surface area of ​​558-588 m². 2 / g, loose specific gravity 0.057-0.061g / cm³, superhydrophobic, flame retardant, thermal conductivity 0.0196-0.021W / M·K, heat resistance temperature 725-920℃, compressive strength 0.118-0.125Mpa. Although the compressive strength of this patent is improved, the thermal conductivity does not decrease further, thus not affecting its application range.

[0005] Therefore, there is an urgent need in the market for a high-strength, low-thermal-conductivity silicone aerogel. Summary of the Invention

[0006] In view of the problems existing in the prior art, the purpose of this invention is to obtain a silica aerogel with high compressive strength and low thermal conductivity.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a method for preparing high-strength, low-thermal-conductivity silica aerogel, comprising the following steps: S1. Add sodium silicate to deionized water and stir at 100-200 rpm for 30-40 min to obtain a sodium silicate solution; add PDMS to ethanol and stir at 1500-2000 rpm for 15-20 min to obtain a PDMS solution; add the additive to ethanol and stir at 500-600 rpm for 15-20 min to obtain a mixed solution. S2. At room temperature, the sodium silicate solution obtained in step S1 is stirred at 1500-2000 rpm. While stirring, the PDMS solution and mixture obtained in step S1 are added, and the pH is adjusted to 4-5. Then the pH is adjusted to 7-8. After that, the mixture is stirred at 38-42℃ at 40-50 rpm for 6-8 hours to obtain the aged material. S3. Add ethanol and n-hexane to the aged material obtained in step S2 for solvent exchange, then add the modifier solution, continue stirring for 2-3 hours, and dry to obtain high-strength, low-thermal-conductivity silica aerogel.

[0008] In some embodiments, the mass ratio of sodium silicate to PDMS is 1:(0.05-0.1).

[0009] In some embodiments, the mass ratio of sodium silicate to additive is 1:(0.03-0.12). In some embodiments, the method for preparing the additive includes the following steps: Rare earth metal oxides and vinyltrimethoxysilane are added to an ethanol solution and stirred for 40-60 minutes. Then N-vinylimidazole and an initiator are added and stirred at 55-65°C for 0.5-1.5 hours. The mixture is then filtered, washed, and dried to obtain the additive.

[0010] This invention designs and synthesizes a multifunctional composite additive that combines organic-inorganic hybridization, enhanced chemical bonding, and multifunctional synergistic properties. This solves the contradiction between strength and thermal insulation performance in traditional silica aerogels. A possible reason is that rare earth metal oxides, as rigid inorganic cores, possess extremely high hardness and stability, improving the mechanical strength of the aerogel. Furthermore, N-vinylimidazolium and vinyltrimethoxysilane copolymerize on the surface of the rare earth metal oxides to form numerous flexible segments. On one hand, steric hindrance prevents the agglomeration of the rare earth metal oxides, ensuring their uniform dispersion in the aerogel matrix. On the other hand, their flexible polymer chains effectively absorb and disperse external stress, avoiding stress concentration, thereby significantly improving the material's toughness and strength and preventing brittle fracture. In addition, rare earth metal oxides are excellent mid-infrared absorption / scattering materials; their nanoparticles, uniformly dispersed in the aerogel, effectively block heat radiation transfer, thus further reducing the overall thermal conductivity of the aerogel while enhancing mechanical properties, achieving a balance between "high strength" and "low thermal conductivity."

[0011] In some embodiments, the mass ratio of the rare earth metal oxide to N-vinylimidazole is 1:(0.2-0.5).

[0012] In some embodiments, the method for preparing the modifier includes the following steps: (1) Add polyethylene glycol and hexanoic acid to chloroform, then add sulfuric acid, stir at 55-65℃ for 5-6 hours, and dry to obtain modified polyethylene glycol; (2) Add the modified polyethylene glycol, isocyanate, γ-aminopropyltriethoxysilane and dibutyltin dilaurate obtained in step (1) to acetone, react at 45-55℃ for 1-2 h, and dry to obtain the modifier.

[0013] This invention covers and modifies the surface of the entire gel network through a chemical reaction after gel aging. It can form strong Si-O-Si covalent bonds with a large number of silanol groups on the aerogel skeleton, anchoring it to the aerogel skeleton. In addition, the molecular backbone is hydrophobic, which can effectively repel water and provide superhydrophobicity. The long flexible chain segments act as "elastic bridges" between the brittle siloxane skeleton of the aerogel, which can absorb and disperse external forces, greatly improving the flexibility and impact resistance of the material, and fundamentally overcoming the brittleness of traditional silicone aerogels.

[0014] In some embodiments, the mass ratio of polyethylene glycol to hexanoic acid is 1:(0.2-0.3).

[0015] In some embodiments, the mass ratio of the modified polyethylene glycol, isocyanate and γ-aminopropyltriethoxysilane in step (2) is (0.05-0.2):(0.1-0.2):1.

[0016] In some embodiments, in step S3, the volume ratio of ethanol to n-hexane is (8-10):1.

[0017] In some embodiments, the drying temperature in step S3 is 100-150°C and the time is 8-12 hours.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention provides a method for preparing silica aerogel. The silica aerogel prepared by adding additives and surface modifiers has good mechanical properties, superhydrophobicity and low thermal conductivity.

[0019] (2) This invention uses rare earth metal oxides as rigid inorganic cores and utilizes N-vinylimidazolium and vinyltrimethoxysilane copolymerization to form a large number of flexible segments on the surface of rare earth metal oxides. A multifunctional composite additive with organic-inorganic hybridization, chemical bonding enhancement and multifunctional synergistic properties is designed and synthesized, which solves the contradiction between the strength and thermal insulation performance of traditional silicone aerogels and achieves the unity of "high strength" and "low thermal conductivity".

[0020] (3) After gel aging, the present invention covers and modifies the surface of the entire gel network through chemical reaction, which can form strong Si-O-Si covalent bonds with a large number of silanol groups on the aerogel skeleton, anchoring it to the aerogel skeleton. In addition, the long flexible chain segments act as "elastic bridges" between the brittle siloxane skeleton of the aerogel, which can absorb and disperse external forces, greatly improving the flexibility and impact resistance of the material, solving the problem of the large brittleness of traditional silicone aerogels, and at the same time having good hydrophobicity. Detailed Implementation

[0021] The present invention will be described below with reference to specific embodiments. It should be noted that the following embodiments are examples of the present invention and are used only to illustrate the invention, not to limit it. Other combinations and various modifications within the scope of the present invention can be made without departing from its spirit or scope.

[0022] In the following examples and comparative examples, the compounds and related reagents used were all commercially available, and the polyPDMS (polydimethylsiloxane) was model 500CS.

[0023] Preparation Example 1 The preparation method of additive-1 includes the following steps: Add 10g of cerium oxide and 3g of vinyltrimethoxysilane to 100ml of 80wt% ethanol solution and stir for 50min. Then add 3g of N-vinylimidazolium and 0.1g of azobisisobutyronitrile and stir at 60℃ for 1h. Filter, wash and dry to obtain additive-1.

[0024] Preparation Example 2 The preparation method of additive-2 is the same as that of preparation example 1, except that the amount of N-vinylimidazole added is 5.5g.

[0025] Preparation Example 3 The preparation method of modifier-1 includes the following steps: (1) Add 10g of polyethylene glycol-400 and 2.5g of hexanoic acid to 100ml of chloroform, then add 5ml of 85wt% sulfuric acid, stir at 60℃ for 5.5h, and dry to obtain modified polyethylene glycol; (2) Add 1g of modified polyethylene glycol, 1.5g of dicyclohexylmethane diisocyanate, 10g of γ-aminopropyltriethoxysilane and 0.05g of dibutyltin dilaurate obtained in step (1) to 100ml of acetone, react at 50℃ for 1.5h, and dry to obtain modifier-1.

[0026] Preparation Example 4 The preparation method of modifier-2 is the same as that of preparation example 3, except that octanoic acid is replaced by an equal amount of octanoic acid.

[0027] Preparation Example 5 The preparation method of modifier-3 is the same as that of preparation example 3, except that the amount of hexanoic acid added is 3.5g.

[0028] Preparation Example 6 The preparation method of modifier-4 is the same as that of preparation example 3, except that the amount of modified polyethylene glycol added is 2.5g.

[0029] Example 1 A method for preparing a high-strength, low-thermal-conductivity silica aerogel includes the following steps: S1. Add 10g of sodium silicate with a modulus of 3 to 3 times its mass of deionized water at 100℃ and stir at 150 rpm for 35 min to obtain a sodium silicate solution; add 0.8g of PDMS to 3 times its mass of anhydrous ethanol and stir at 1800 rpm for 18 min to obtain a PDMS solution; add 1g of additive-1 to 2 times its mass of anhydrous ethanol and stir at 550 rpm for 18 min to obtain a mixture. S2. At room temperature, the sodium silicate solution obtained in all steps S1 is stirred at 1800 rpm. While stirring, the PDMS solution and mixture obtained in all steps S1 are added. The pH is adjusted to 4.5 with 8 mol / L acetic acid, and then the pH is adjusted to 7.5 with sodium hydroxide. The mixture is then stirred at 45 rpm at 40°C for 7 hours. The upper liquid is removed to obtain the aged material. S3. Add equal masses of anhydrous ethanol and n-hexane (volume ratio of anhydrous ethanol to n-hexane is 9:1) to the aged material obtained in all steps S2 for solvent exchange. Replace the solvent every 8 hours for 3 times. Then add an ethanol solution of 30wt% modifier-1 with the same mass as the aged material, continue stirring for 2.5 hours, heat to 130℃ at a heating rate of 1℃ / min and dry for 10 hours to obtain high-strength, low-thermal-conductivity silica aerogel.

[0030] Example 2 A method for preparing a high-strength, low-thermal-conductivity silica aerogel includes the following steps: S1. Add 10g of sodium silicate with a modulus of 3 to 3 times its mass of deionized water at 100℃ and stir at 100 rpm for 40 min to obtain a sodium silicate solution; add 0.5g of PDMS to 3 times its mass of anhydrous ethanol and stir at 1500 rpm for 20 min to obtain a PDMS solution; add 0.3g of additive-1 to 2 times its mass of anhydrous ethanol and stir at 500 rpm for 20 min to obtain a mixture. S2. At room temperature, the sodium silicate solution obtained in all steps S1 is stirred at 1500 rpm. While stirring, the PDMS solution and mixture obtained in all steps S1 are added. The pH is adjusted to 4 with 8 mol / L acetic acid, and then the pH is adjusted to 7 with sodium hydroxide. The mixture is then stirred at 38°C at 40 rpm for 8 hours. The upper liquid is removed to obtain the aged material. S3. Add equal masses of anhydrous ethanol and n-hexane (volume ratio of anhydrous ethanol to n-hexane is 8:1) to the aged material obtained in all steps S2 for solvent exchange. Replace the solvent every 8 hours for 3 times. Then add an ethanol solution of 30wt% modifier-1 with the same mass as the aged material, continue stirring for 2 hours, heat to 100℃ at a heating rate of 1℃ / min and dry for 12 hours to obtain high-strength, low-thermal-conductivity silica aerogel.

[0031] Example 3 A method for preparing a high-strength, low-thermal-conductivity silica aerogel includes the following steps: S1. Add 10g of sodium silicate with a modulus of 3 to 3 times its mass of deionized water at 100℃ and stir at 200 rpm for 30 min to obtain a sodium silicate solution; add 1g of PDMS to 3 times its mass of anhydrous ethanol and stir at 2000 rpm for 15 min to obtain a PDMS solution; add 1.2g of additive-1 to 2 times its mass of anhydrous ethanol and stir at 600 rpm for 15 min to obtain a mixture. S2. At room temperature, the sodium silicate solution obtained in all steps S1 is stirred at 2000 rpm. While stirring, the PDMS solution and mixture obtained in all steps S1 are added. The pH is adjusted to 5 with 8 mol / L acetic acid, and then the pH is adjusted to 8 with sodium hydroxide. The mixture is then stirred at 50 rpm at 42°C for 6 hours. The upper liquid is removed to obtain the aged material. S3. Add equal masses of anhydrous ethanol and n-hexane (volume ratio of anhydrous ethanol to n-hexane is 10:1) to the aged material obtained in all steps S2 for solvent exchange. Replace the solvent every 8 hours for 3 times. Then add an equal mass of 30wt% ethanol solution of modifier-1 and continue stirring for 3 hours. Heat to 150℃ at a heating rate of 1℃ / min and dry for 8 hours to obtain high-strength, low-thermal-conductivity silica aerogel.

[0032] Example 4 A method for preparing a high-strength, low-thermal-conductivity silica aerogel is described, with the specific implementation method being the same as in Example 1, except that additive-1 is replaced with an equal amount of additive-2.

[0033] Example 5 A method for preparing a high-strength, low-thermal-conductivity silica aerogel is described, with the specific implementation method being the same as in Example 1, except that modifier-1 is replaced with an equal amount of modifier-2.

[0034] Example 6 A method for preparing a high-strength, low-thermal-conductivity silica aerogel is described, with the specific implementation method being the same as in Example 1, except that modifier-1 is replaced by modifier-3 in equal amounts.

[0035] Example 7 A method for preparing a high-strength, low-thermal-conductivity silica aerogel is described, with the specific implementation method being the same as in Example 1, except that modifier-1 is replaced with an equal amount of modifier-4.

[0036] Example 8 A method for preparing a high-strength, low-thermal-conductivity silica aerogel is described, with the specific implementation method being the same as in Example 1, except that the amount of PDMS added is 1.2g.

[0037] Example 9 A method for preparing a high-strength, low-thermal-conductivity silica aerogel is described, with the specific implementation method being the same as in Example 1, except that the amount of additive-1 added is 1.5g.

[0038] Example 10 A method for preparing a high-strength, low-thermal-conductivity silica aerogel is described, with the specific implementation method being the same as in Example 1, except that additive-1 is replaced with an equal amount of cerium oxide.

[0039] Example 11 A method for preparing a high-strength, low-thermal-conductivity silica aerogel is described, with the specific implementation method being the same as in Example 1, except that modifier-1 is replaced in equal amounts with γ-aminopropyltriethoxysilane.

[0040] Performance testing The high-strength, low-thermal-conductivity silica aerogels obtained in the above embodiments were subjected to the following tests: 1. Hydrophobicity The contact angle of silica aerogel was tested using a contact angle meter via the water droplet method.

[0041] 2. Compressive strength The silica aerogel was cut to a thickness of 10mm ± 2mm, and the compressive strain of the silica aerogel was tested using a universal testing machine at a compression speed of 2mm / min to obtain the compressive strength.

[0042] 3. Thermal conductivity The thermal conductivity of silica aerogels was tested using the transient planar heat source method according to ISO 22007-2.

[0043] The test results are shown in Table 1: Table 1 As shown in Table 1, the silica aerogels obtained in Examples 1-3 of this invention have high compressive strength, low thermal conductivity, and good hydrophobicity. A comparison between Example 4 and Example 1 shows that changing the ratio of cerium oxide to N-vinylimidazole may lead to excessive steric hindrance, affecting the compactness of the aerogel and reducing its compressive strength and hydrophobicity. A comparison between Examples 5 and 6 and Example 1 shows that replacing octanoic acid with an equal amount and changing the ratio of polyethylene glycol to octanoic acid may fill the pores of the aerogel, increasing its thermal conductivity. A comparison between Example 7 and Example 1 shows that the modified polyethylene glycol, isocyanate, and γ-aminopropyltriethoxylate... The change in the silane ratio leads to a decrease in the hydrophobicity and an increase in the thermal conductivity of the silica gel. A comparison of Example 8 and Example 1 shows that a change in the ratio of PDMS and sodium silicate may alter the effective crosslinking sites for forming a three-dimensional network, resulting in a decrease in the compressive strength of the silica gel. A comparison of Example 9 and Example 1 shows that a change in the ratio of additives to sodium silicate leads to a decrease in the compressive strength of the silica gel. A comparison of Example 10 and Example 1 shows that directly using cerium oxide as an additive decreases the compressive strength of the silica aerogel and increases its thermal conductivity. A comparison of Example 11 and Example 1 shows that using γ-aminopropyltriethoxysilane as a modifier decreases the compressive strength of the silica gel.

[0044] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing high-strength low-conductive silicon aerogel, characterized by, The method comprises the following steps: S1, stirring sodium silicate into deionized water at a speed of 100-200 rpm for 30-40 min to obtain a sodium silicate solution; stirring PDMS into ethanol at a speed of 1500-2000 rpm for 15-20 min to obtain a PDMS solution; stirring additives into ethanol at a speed of 500-600 rpm for 15-20 min to obtain a mixed solution; S2, stirring the sodium silicate solution obtained in step S1 at a speed of 1500-2000 rpm at room temperature, adding the PDMS solution and the mixed solution obtained in step S1 while stirring, adjusting the pH to 4-5, then adjusting the pH to 7-8, and then continuing to stir at a speed of 40-50 rpm at 38-42 ℃ for 6-8 h to obtain an aging material; S3, adding ethanol and n-hexane to the aging material obtained in step S2 to perform solvent exchange, then adding a modifier solution, continuing to stir for 2-3 h, and drying to obtain a high-strength low-thermal-conductivity silicon aerogel.

2. The method for preparing high-strength, low-thermal-conductivity silica aerogel according to claim 1, characterized in that, The mass ratio of the sodium silicate to the PDMS is 1:(0.05-0.1).

3. The method for preparing high-strength, low-thermal-conductivity silica aerogel according to claim 1, characterized in that, The mass ratio of the sodium silicate to the additives is 1:(0.03-0.12).

4. The method of claim 1, wherein the high-strength low thermal conductivity silica aerogel is prepared by the steps of: The preparation method of the additives comprises the following steps: adding rare earth metal oxide and vinyltrimethoxysilane into an ethanol solution, stirring for 40-60 min, then adding N-vinylimidazole and an initiator, stirring at 55-65 ℃ for 0.5-1.5 h, filtering, washing, and drying to obtain the additives.

5. The method of claim 4, wherein the high-strength, low thermal conductivity silica aerogel is prepared by the steps of: The mass ratio of the rare earth metal oxide to the N-vinylimidazole is 1:(0.2-0.5).

6. The method of claim 1, wherein the high-strength low thermal conductivity silica aerogel is prepared by the steps of: The preparation method of the modifier comprises the following steps: (1) adding polyethylene glycol and heptanoic acid into chloroform, then adding sulfuric acid, stirring at 55-65 ℃ for 5-6 h, and drying to obtain modified polyethylene glycol; (2) adding the modified polyethylene glycol obtained in step (1), isocyanate, γ-aminopropyltriethoxysilane, and dibutyltin dilaurate into acetone, reacting at 45-55 ℃ for 1-2 h, and drying to obtain the modifier.

7. The method of claim 6, wherein the high-strength, low thermal conductivity silica aerogel is prepared by the steps of: The mass ratio of the polyethylene glycol to the heptanoic acid is 1:(0.2-0.3).

8. The method of claim 6, wherein the high-strength, low thermal conductivity silica aerogel is prepared by the steps of: In step (2), the mass ratio of the modified polyethylene glycol, the isocyanate, and the γ-aminopropyltriethoxysilane is (0.05-0.2):(0.1-0.2):

1.

9. The method of claim 1, wherein the high-strength low thermal conductivity silica aerogel is prepared by the steps of: In step S3, the volume ratio of the ethanol to the n-hexane is (8-10):

1.

10. The method for preparing high-strength, low-thermal-conductivity silica aerogel according to claim 1, characterized in that, The drying temperature in step S3 is 100-150 ℃, and the drying time is 8-12 h.

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