Preparation method of silicon-based aerogel with ultralow thermal conductivity

Abstract

The invention provides a preparation method of ultra-low thermal conductivity silicon-based aerogel, and relates to the field of aerogel material preparation, and the preparation method comprises the following steps: S1, preparing a component A and a component B. The component A is prepared by fully mixing a silicon source, a modified silicon dioxide seed crystal, absolute ethyl alcohol and deionized water, then slowly adding an acid catalyst, and carrying out hydrolysis; the component B is a basic catalyst solution obtained by uniformly mixing deionized water and stronger ammonia water; step S2, gelling: fully mixing the component A and the component B to obtain wet gel, and then mixing the wet gel with a fiber felt to obtain a wet gel felt; step S3, aging; and S4, performing supercritical drying. According to the method, by introducing the modified silicon dioxide seed crystal, the thermal conductivity of a solid structure of the aerogel is effectively reduced, meanwhile, formation of macropores, communicating pores and the like is inhibited, and the performance of the aerogel is improved.

Description

Technical Field

[0001] This invention relates to the field of aerogel material preparation technology, specifically to a method for preparing ultra-low thermal conductivity silicon-based aerogel. Background Technology

[0002] Silica aerogel is a three-dimensional porous material with excellent properties such as low density, high porosity, large specific surface area, and low thermal conductivity, and is widely used in aerospace, automobile manufacturing, and construction engineering. However, silica aerogel has poor mechanical properties and is brittle, easily causing problems such as breakage, disintegration, and powdering. In addition, its surface contains a large number of Si-OH groups, which are hydrophilic. After absorbing moisture, the skeleton expands and cracks, resulting in a significant decrease in its excellent properties. Currently, traditional methods utilize silica sol as a core-shell structure, which can effectively improve the pore structure of silica aerogel and increase its specific surface area. At the same time, silica sol can fill the micropores and structural defects on the surface of silica aerogel to a certain extent, playing the role of a "support skeleton," thereby improving the mechanical properties of silica aerogel and preventing it from easily cracking, disintegrating, or shedding powder. In addition, the shell structure formed by silica sol can also act as a "moisture barrier," physically preventing water from penetrating the aerogel core and directly reducing the contact between Si-OH groups and water. This avoids problems such as skeleton expansion and structural collapse after the aerogel absorbs water (i.e., avoiding the decrease in thermal insulation performance caused by the collapse of the three-dimensional network structure of the aerogel).

[0003] However, traditional silica sol particles are not uniform in size and have defects such as micropores, mesopores, and macropores. Aerogels on their surface are prone to random nucleation, forming macropores (i.e., pores with a diameter greater than 100 nm) or interconnected pores, which seriously affects the thermal insulation performance of aerogels (i.e., gas molecules in the pores can freely collide and form convective heat transfer, leading to a sharp increase in gas heat conduction). In addition, existing silica sols cannot be uniformly dispersed in the organosilicon sol-gel system of aerogels, resulting in local structures that are too dense or too sparse, thus causing large fluctuations in the thermal insulation performance of the prepared silica aerogels. Summary of the Invention

[0004] To address the problems existing in the prior art, the present invention aims to provide a method for preparing ultra-low thermal conductivity silicon-based aerogels. This method introduces modified silica seeds to guide the directional growth of the aerogel framework, thereby forming a uniform, fine, and highly continuous nanoframework. This avoids the formation of locally coarse "thermal bridge" structures (where heat is easily transferred rapidly through a coarse framework), thus effectively reducing the thermal conductivity of the aerogel solid structure. Simultaneously, by using modified silica seeds as a core-shell template, the formation of macropores and interconnected pores is effectively suppressed, promoting the formation of smaller and more uniformly distributed closed pores. This suppresses gas molecule movement and significantly reduces gas convection and conduction heat loss.

[0005] The objective of this invention is achieved through the following technical solution: A method for preparing ultra-low thermal conductivity silicon-based aerogel, comprising: Step S1: Prepare component A and component B: Component A: After thoroughly mixing the silicon source, modified silica seed crystals, anhydrous ethanol and deionized water, an acid catalyst is slowly added to adjust the pH of the solution to 1.5-5.5, and hydrolysis is carried out to obtain component A; Component B: After uniformly mixing deionized water and concentrated ammonia, an alkaline catalyst solution is obtained; Step S2, Gel: First, mix component A and component B thoroughly to obtain a wet gel; then immediately spray the mixed wet gel into the impregnation tank, which is pre-filled with fiber mat so that the fiber mat and the sol are mixed to obtain a wet gel mat. Step S3, Aging: Immerse the wet gel felt in a sealed autoclave containing anhydrous ethanol and keep it warm for aging. Step S4, Supercritical Drying: The aged wet gel felt is subjected to supercritical drying to obtain the final product.

[0006] Based on further optimization of the above scheme, the silicon source adopts a combination of fluorine-free silicon source and fluorine-containing silicon source. The fluorine-free silicon source adopts one or more of tetraethyl orthosilicate, methyl orthosilicate, methyltriethoxysilane, methyltrimethoxysilane, and polyethyl orthosilicate. The fluorine-containing silicon source adopts one or more of trifluoropropanetrimethoxysilane, 3,3,3-trifluoropropyltriethoxysilane, perfluorodecyltriethoxysilane, and perfluorooctyltrimethoxysilane. The mass ratio of fluorine-free silicon source to fluorine-containing silicon source is 1:0.1 to 1.

[0007] Based on further optimization of the above scheme, in component A, the mass ratio of silicon source, modified silica seed crystal, anhydrous ethanol and deionized water is 1:0.025~0.1:20~40:2~4.

[0008] Based on further optimization of the above scheme, in component A, the modified silica seed crystals are multifunctional composite modified seed crystals. The specific preparation method is as follows: First, fumed silica is added to a dispersion medium composed of anhydrous ethanol and deionized water at room temperature, and after high-speed stirring and dispersion, ultrasonic dispersion is performed to obtain a uniform suspension; then, the temperature is raised to 62–68°C, and under a nitrogen atmosphere, dibutyltin dilaurate is added to the suspension. After stirring the Dilaurate catalyst until homogeneous, add isopropyl triisostearate titanate dropwise and maintain the temperature for 3.3–3.7 h. Then, cool to 48–52 °C, add glacial acetic acid (analytical grade, concentration ≥ 99.5%) to adjust the pH to 3.5–4.0, then add perfluorobutylsulfonic acid and 3-aminopropyltriethoxysilane dropwise sequentially, stirring for 2.2–2.8 h. Next, add triethylamine (analytical grade, concentration ≥ 99%) to adjust the pH to 5.0–5.5, and then add polyetheramine (such as polyetheramine M-2070) dropwise. The number-average molecular weight is approximately 2000, and the amine value is approximately 56 mg KOH / g. The mixture is kept at this temperature for 2.5–3.5 h. Then, the temperature is raised to 58–62 °C, and octa(aminophenyltrioxosilane) is added. The mixture is stirred for 3.5–4.5 h, then cooled to 42–48 °C. γ-glycidoxypropyltrimethoxysilane is added dropwise, along with monoethyl phosphate. The mixture is stirred for 1.8–2.2 h, and the pH is adjusted to 6.5–7.0 using sodium hydroxide solution. Finally, after vacuum degassing and centrifugation, modified silica seed crystals are obtained.

[0009] Based on further optimization of the above scheme, the solid-liquid ratio (i.e., mass-volume ratio) of the fumed silica to the dispersion medium is 1g:120-130mL; the mass ratio of fumed silica, dibutyltin dilaurate, isopropyl triisostearate titanate, perfluorobutylsulfonic acid, γ-aminopropyltriethoxysilane (KH550), polyetheramine, octa(aminophenyltrioxysilane), γ-glycidyl etheroxypropyltrimethoxysilane (KH560), and monoethyl phosphate is 1:0.05-0.07:0.28-0.3:0.14-0.16:0.11-0.13:0.29-0.31:0.19-0.21:0.17-0.19:0.09-0.11.

[0010] Based on further optimization of the above scheme, in the dispersion medium, the volume ratio of anhydrous ethanol to deionized water is 0.9–1.1:0.9–1.1; and the concentration of sodium hydroxide solution is 0.1–0.5 mol / L.

[0011] Based on further optimization of the above scheme, the vacuum degree of the vacuum degassing is -0.08 to -0.1 MPa, the temperature is 25 to 30°C, the stirring rate is 100 to 200 rpm, and the degassing time is 38 to 42 min; the centrifugation speed is 7500 to 8500 rpm, and the centrifugation time is 9 to 11 min.

[0012] Based on further optimization of the above scheme, the concentration of acid catalyst in component A is 0.1 to 1 mol / L, and the acid catalyst is any one of hydrochloric acid, oxalic acid, nitric acid, sulfuric acid, acetic acid, and hydrofluoric acid.

[0013] Based on further optimization of the above scheme, the hydrolysis temperature of component A is 50-80℃ and the hydrolysis time is 2-16h.

[0014] Based on further optimization of the above scheme, the concentration of the alkaline catalyst solution of component B is 0.1 to 1 mol / L.

[0015] Based on further optimization of the above scheme, in step S2, component A and component B are mixed at a volume ratio of 1:0.01 to 0.1.

[0016] Based on further optimization of the above scheme, the fiber felt is made of one or more of glass fiber, basalt fiber, ceramic fiber, alumina fiber, and zirconium oxide fiber. Before being added to the impregnation tank, the fiber felt is pretreated. The pretreatment is as follows: the fiber felt is first soaked in a 4.5% to 5.5% KH550-ethanol solution at room temperature for 28 to 32 minutes, then dried at 105 to 115°C for 1.8 to 2.2 hours, and finally cooled to room temperature to complete the pretreatment.

[0017] Based on further optimization of the above scheme, the gel after mixing the fiber felt and sol has a width of 0.5–1.5 m, a thickness of 1–10 mm, and a bulk density of 70–200 kg / m³. 3 .

[0018] Based on further optimization of the above scheme, the heat preservation aging temperature is 20-80℃ and the aging time is 12-48h.

[0019] Based on further optimization of the above scheme, the supercritical drying adopts CO2 supercritical drying or ethanol supercritical drying; CO2 supercritical drying specifically involves drying the aerogel under the protection of CO2 gas at a temperature of 30-50℃, controlling the pressure of the autoclave at 8-12MPa, and the reaction time at 12-24h; the ethanol supercritical drying process involves drying the aerogel under the protection of nitrogen gas at a temperature of 250-280℃, controlling the pressure of the autoclave at 8-15MPa, and the reaction time at 2-8h.

[0020] The following are the effects of the technical solution of the present invention: This invention utilizes a combination of fluorine-free and fluorine-containing silicon sources in the aerogel preparation process to reduce the surface energy and enhance hydrophobicity of the material, thereby specifically addressing the issue of hydrophilic hygroscopicity of Si-OH groups. Combined with a composite shell structure formed by modified silica seeds and silica sol, this effectively prevents moisture intrusion, avoiding the problems of framework expansion, cracking, and three-dimensional network structure collapse that occur after aerogels absorb moisture. Simultaneously, the directional growth guided by specific modified silica seeds forms a uniform, fine, and highly continuous nanoframework, fundamentally controlling the framework morphology and pore size distribution. This significantly improves the pore structure of the aerogel (i.e., inhibiting the formation of macropores and interconnected pores, and promoting the formation of small, uniformly distributed closed pores), and substantially increases its specific surface area and porosity.

[0021] In selecting modified silica seed crystals, a multi-functional composite modification was adopted. The composite modification of triisostearate titanate isopropyl triisostearate and octa(aminophenyltrioxysilane) not only ensures the high-temperature stability of the aerogel and avoids thermal decomposition of organic segments under high-temperature conditions (e.g., 250–300°C), but also provides rigid support through a cage-like structure, preventing pore shrinkage and filling micropores and structural defects on the aerogel surface. This prevents closed pores from transforming into interconnected pores under pressure surges such as supercritical drying. Furthermore, the combination of perfluorobutylsulfonic acid and γ-aminopropyltriethoxysilane simultaneously adapts to both fluorinated and non-fluorinated silicon sources, uniformly guiding the growth of both silicon sources and avoiding differences in affinity between a single organic modified segment and fluorinated or non-fluorinated silicon sources. Large pores can lead to uneven silicon source growth rates, thus avoiding the formation of macropore defects caused by differences in growth rates. The combination of polyetheramine and monoethyl phosphate utilizes the stable coordination bonds formed between bidentate phosphonate and silanol groups, along with the steric hindrance of the long chains formed after polyetheramine grafting, effectively preventing the aggregation of modified segments due to hydrogen bond adsorption during hydrolysis, thus improving the dispersibility of modified silica seeds. Furthermore, the combination of monoethyl phosphate and γ-glycidoxypropyltrimethoxysilane forms chemical bonds between epoxy groups and hydroxyl groups in the fiber felt, enhancing the bonding strength between the "seed-fiber-silicon source" and preventing problems such as gap thermal bridges and insufficient compressive strength caused by the aerogel layer peeling off from the fiber felt. In addition, γ-glycidoxypropyltrimethoxysilane can also form an inorganic-organic hybrid structure with isopropyl triisostearate titanate, thus balancing high-temperature stability and directional growth efficiency, further avoiding problems such as aerogel fragmentation, disintegration, and powdering caused by oxidative decomposition under high-temperature conditions.

[0022] This invention employs a sol-gel-aging-supercritical drying process to maximize the preservation of the closed pore structure, avoiding the decline in thermal insulation performance caused by pore collapse during preparation, and maintaining a high-efficiency thermal insulation effect over a long period. The aerogel developed using this invention significantly reduces the thermal conductivity of fiber materials, with typical values ​​not exceeding 0.0145 W / (m·K) at 25℃, not exceeding 0.0163 W / (m·K) at 80℃, and not exceeding 0.0189 W / (m·K) at 300℃. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the silicon-based aerogel prepared in an embodiment of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0025] Example 1: A method for preparing ultra-low thermal conductivity silicon-based aerogel, comprising: Step S1: Prepare component A and component B: Component A: After thoroughly mixing silicon source, modified silica seed crystals, anhydrous ethanol and deionized water, their mass ratio is 1:0.025:20:2; then slowly add acid catalyst with a concentration of 0.1 mol / L, adjust the pH of the solution to 5.5, and hydrolyze at 50℃ for 16 h to obtain component A; The silicon source is a combination of fluorine-free silicon source and fluorine-containing silicon source. The fluorine-free silicon source is tetraethyl orthosilicate (CAS: 78-10-4), and the fluorine-containing silicon source is trifluoropropanetrimethoxysilane (CAS: 429-60-7). The mass ratio of fluorine-free silicon source to fluorine-containing silicon source is 1:0.1.

[0026] The modified silica seed crystals are multifunctional composite modified seed crystals. The specific preparation method is as follows: First, fumed silica is added to a dispersion medium composed of anhydrous ethanol and deionized water at room temperature. The volume ratio of anhydrous ethanol to deionized water is 0.9:0.9, and the solid-liquid ratio (i.e., mass-volume ratio) of fumed silica to dispersion medium is 1g:120mL. After stirring and dispersing at 17500rpm for 9min, it is then ultrasonically dispersed at a power of 200W and a frequency of 20kHz for 16min to obtain a uniform suspension. Then, the temperature was raised to 62°C, and under a nitrogen atmosphere (the entire subsequent process was carried out under a nitrogen atmosphere), dibutyltin dilaurate (CAS: 77-58-7) catalyst was added to the suspension. After stirring evenly (stirring at 300 rpm for 32 min), isopropyl triisostearate titanate (CAS: 61417-49-0, dropping rate 0.017 g / min) was added dropwise, and the mixture was kept at this temperature for 3.7 h. Afterward, the temperature was lowered to 48°C, and glacial acetic acid (analytical grade, concentration above 99.5%) was added to adjust the pH to 3.5. Then, perfluorobutylsulfonic acid (CAS: 375-73-5, dropping rate 0.014 g / min) and 3-aminopropyltriethoxysilane (KH550, CAS: 9) were added dropwise in sequence. 19-30-2, dropping rate 0.011 g / min), stir for 2.8 h (stirring at 300 rpm); then, add triethylamine (analytical grade, concentration above 99%) to adjust pH to 5.0, and dropwise add polyetheramine (such as polyetheramine M-2070, number average molecular weight ≈2000, amine value ≈56 mg KOH / g; CAS: 83713-01-3, Huntsman (Jeffamine) model M-2070, which can be selected according to its properties at Yangzhou Chenhua New Materials Co., Ltd. Materials Co., Ltd.; Dropping rate 0.015 g / min), hold at temperature for 3.5 h; then, heat to 58 °C, add octa(aminophenyltrioxosilane) (CAS: 518359-82-5), stir for 4.5 h (stirring at 300 rpm), then cool to 42 °C, dropwise add γ-glycidoxypropyltrimethoxysilane (KH560, CAS: 5230-83-8, dropping rate 0.017 g / min), and simultaneously add monoethyl phosphate. (CAS: 1623-14-9) After stirring for 2.2 h (stirring at a rate of 300 rpm), the pH was adjusted to 6.5 using a 0.1 mol / L sodium hydroxide solution. Finally, after vacuum degassing and centrifugation, modified silica seeds were obtained. The vacuum degree of vacuum degassing was -0.08 MPa, the temperature was 25℃, the stirring rate was 100 rpm, the degassing time was 42 min, the centrifugation speed was 7500 rpm, and the centrifugation time was 11 min. The mass ratio of fumed silica, dibutyltin dilaurate, isopropyl triisostearate titanate, perfluorobutylsulfonic acid, γ-aminopropyltriethoxysilane, polyetheramine, octa(aminophenyltrioxosilane), γ-glycidyl etheroxypropyltrimethoxysilane, and monoethyl phosphate is 1:0.05:0.28:0.14:0.11:0.29:0.19:0.17:0.09.

[0027] Hydrochloric acid is used as the acid catalyst.

[0028] Component B: After uniformly mixing deionized water and concentrated ammonia, an alkaline catalyst solution with a concentration of 0.1 mol / L is obtained.

[0029] Step S2, Gel Preparation: First, thoroughly mix component A and component B at a volume ratio of 1:0.01 to obtain a wet gel. Then, immediately spray the mixed wet gel into an impregnation tank pre-filled with fiber mat, which is made of glass fiber. Before adding the fiber mat to the impregnation tank, the fiber mat is pre-treated as follows: first, immerse the fiber mat in a 4.5% KH550-ethanol solution at room temperature for 32 minutes, then dry it at 105℃ for 2.2 hours, and finally cool it to room temperature to complete the pretreatment. This allows the fiber mat to mix with the sol, obtaining a wet gel mat. The width of the gel after mixing the fiber mat and the sol is 0.5 m, the thickness is 1 mm, and the bulk density is 100 kg / m³. 3 .

[0030] Step S3, Aging: Immerse the wet gel felt in a sealed container filled with anhydrous ethanol and age it at 30°C for 48 hours.

[0031] Step S4, Supercritical Drying: The aged wet aerogel mat is subjected to supercritical drying to obtain the final product; supercritical drying is performed using CO2 supercritical drying. Specifically, the aerogel is dried at 40℃ under the protection of CO2 gas, the pressure in the autoclave is controlled at 8MPa, and the reaction time is 24h.

[0032] Example 2: A method for preparing ultra-low thermal conductivity silicon-based aerogel, comprising: Step S1: Prepare component A and component B: Component A: After thoroughly mixing silicon source, modified silica seed crystals, anhydrous ethanol and deionized water, their mass ratio is 1:0.0625:30:3; then slowly add acid catalyst with a concentration of 0.5 mol / L, adjust the pH of the solution to 3.5, and hydrolyze at 65℃ for 13 h to obtain component A; The silicon source uses a combination of fluorine-free silicon source and fluorine-containing silicon source. The fluorine-free silicon source is methyltriethoxysilane (CAS: 2031-67-6), and the fluorine-containing silicon source is 3,3,3-trifluoropropyltriethoxysilane (CAS: 86876-45-1). The mass ratio of fluorine-free silicon source to fluorine-containing silicon source is 1:0.5.

[0033] The modified silica seed crystals are multifunctional composite modified seed crystals. The specific preparation method is as follows: First, fumed silica is added to a dispersion medium composed of anhydrous ethanol and deionized water at room temperature. The volume ratio of anhydrous ethanol to deionized water is 1:1, and the solid-liquid ratio (i.e., mass-volume ratio) of fumed silica to dispersion medium is 1g:125mL. After stirring and dispersing at 18000rpm for 8min, it is then ultrasonically dispersed at a power of 250W and a frequency of 30kHz for 15min to obtain a uniform suspension. Then, the temperature was raised to 65°C, and under a nitrogen atmosphere (the entire subsequent process was carried out under a nitrogen atmosphere), dibutyltin dilaurate (CAS: 77-58-7) catalyst was added to the suspension. After stirring evenly (stirring at 450 rpm for 30 min), isopropyl triisostearate titanate (CAS: 61417-49-0, dropping rate 0.021 g / min) was added dropwise, and the mixture was kept at this temperature for 3.5 h. Afterward, the temperature was lowered to 50°C, and glacial acetic acid (analytical grade, concentration above 99.5%) was added to adjust the pH to 3.7. Then, perfluorobutylsulfonic acid (CAS: 375-73-5, dropping rate 0.015 g / min) and 3-aminopropyltriethoxysilane (KH550, CAS: 919-30-2, dropping rate 0.012 g / min), stir for 2.5 h (stirring at 450 rpm); then, add triethylamine (analytical grade, concentration ≥ 99%) to adjust pH to 5.2, and dropwise add polyetheramine (such as polyetheramine M-2070, number average molecular weight ≈ 2000, amine value ≈ 56 mg KOH / g; CAS: 83713-01-3, Huntsman (Jeffamine) model M-2070, which can be selected according to its properties in Yangzhou). Chenhua New Materials Co., Ltd.; Dropping rate 0.017 g / min), kept at this temperature for 3 hours; then, the temperature was raised to 60°C, and octa(aminophenyltrioxosilane) (CAS: 518359-82-5) was added, stirred for 4 hours (stirring at a rate of 450 rpm), then cooled to 45°C, and γ-glycidoxypropyltrimethoxysilane (KH560, CAS: 5230-83-8, dropping rate 0.018 g / min) was added dropwise, along with monoethyl phosphate. The ester (CAS: 1623-14-9) was stirred for 2 hours (at a stirring speed of 450 rpm), and the pH was adjusted to 6.7 using a 0.3 mol / L sodium hydroxide solution. Finally, after vacuum degassing and centrifugation, modified silica seed crystals were obtained. The vacuum degassing conditions were -0.09 MPa, 27℃, 150 rpm, and 40 min. The centrifugation speed was 8000 rpm, and the centrifugation time was 10 min. The mass ratio of fumed silica, dibutyltin dilaurate, isopropyl triisostearate titanate, perfluorobutylsulfonic acid, γ-aminopropyltriethoxysilane, polyetheramine, octa(aminophenyltrioxosilane), γ-glycidyl etheroxypropyltrimethoxysilane, and monoethyl phosphate was 1:0.06:0.29:0.15:0.12:0.3:0.2:0.18:0.1.

[0034] The acid catalyst used is nitric acid.

[0035] Component B: After uniformly mixing deionized water and concentrated ammonia, an alkaline catalyst solution with a concentration of 0.5 mol / L is obtained.

[0036] Step S2, Gel Preparation: First, thoroughly mix component A and component B at a volume ratio of 1:0.05 to obtain a wet gel. Then, immediately spray the mixed wet gel into an impregnation tank pre-filled with basalt fiber mat. Before adding the fiber mat to the impregnation tank, pre-treat the fiber mat by immersing it in a 5% KH550-ethanol solution at room temperature for 30 minutes, then drying it at 110℃ for 2 hours, and finally cooling it to room temperature. This completes the pre-treatment. The fiber mat is then mixed with the sol to obtain a wet gel mat. The width of the gel after mixing the fiber mat and the sol is 1 m, the thickness is 2 mm, and the bulk density is 110 kg / m³. 3 .

[0037] Step S3, Aging: Immerse the wet gel felt in a sealed container filled with anhydrous ethanol and age it at 40°C for 25 hours.

[0038] Step S4, Supercritical Drying: The aged wet gel mat is subjected to supercritical drying to obtain the product. Supercritical drying is performed using ethanol supercritical drying. Specifically, the aerogel is dried at 275℃ under the protection of nitrogen gas, the pressure of the autoclave is controlled at 11.5MPa, and the reaction time is 3h.

[0039] Example 3: A method for preparing ultra-low thermal conductivity silicon-based aerogel, comprising: Step S1: Prepare component A and component B: Component A: After thoroughly mixing silicon source, modified silica seed crystals, anhydrous ethanol and deionized water, their mass ratio is 1:0.1:40:4; then slowly add acid catalyst with a concentration of 1 mol / L, adjust the pH of the solution to 1.5, and hydrolyze at 80℃ for 10 h to obtain component A; The silicon source uses a combination of fluorine-free silicon source and fluorine-containing silicon source. The fluorine-free silicon source is polyethyl silicate (CAS: 11099-06-2), and the fluorine-containing silicon source is perfluorooctyltrimethoxysilane (CAS: 85857-16-5). The mass ratio of fluorine-free silicon source to fluorine-containing silicon source is 1:1.

[0040] The modified silica seed crystals are multifunctional composite modified seed crystals. The specific preparation method is as follows: First, fumed silica is added to a dispersion medium composed of anhydrous ethanol and deionized water at room temperature. The volume ratio of anhydrous ethanol to deionized water is 1.1:1.1, and the solid-liquid ratio (i.e., mass-volume ratio) of fumed silica to dispersion medium is 1g:130mL. After stirring and dispersing at 18500rpm for 7min, it is then ultrasonically dispersed at 300W power and 40kHz frequency for 14min to obtain a uniform suspension. Then, the temperature was raised to 68°C, and under a nitrogen atmosphere (the entire subsequent process was carried out under a nitrogen atmosphere), dibutyltin dilaurate (CAS: 77-58-7) catalyst was added to the suspension. After stirring evenly (stirring at 600 rpm for 28 min), isopropyl triisostearate titanate (CAS: 61417-49-0, dropping rate 0.025 g / min) was added dropwise, and the mixture was kept at this temperature for 3.3 h. Afterward, the temperature was lowered to 52°C, and glacial acetic acid (analytical grade, concentration above 99.5%) was added to adjust the pH to 4.0. Then, perfluorobutylsulfonic acid (CAS: 375-73-5, dropping rate 0.016 g / min) and 3-aminopropyltriethoxysilane (KH550, CAS: 9) were added dropwise in sequence. 19-30-2, dropping rate 0.013 g / min), stirring for 2.2 h (stirring at 600 rpm); then, triethylamine (analytical grade, concentration ≥ 99%) was added to adjust the pH to 5.5, and polyetheramine (such as polyetheramine M-2070, number average molecular weight ≈ 2000, amine value ≈ 56 mg KOH / g; CAS: 83713-01-3, Huntsman (Jeffamine) model M-2070, which can be used in Yangzhou Chenhua according to its properties) was added dropwise. New Materials Co., Ltd.; Dropping rate 0.02 g / min), held at this temperature for 2.5 h; then, heated to 62 °C, added octa(aminophenyltrioxosilane) (CAS: 518359-82-5), stirred for 3.5 h (stirring at 600 rpm), then cooled to 48 °C, and dropwise added γ-glycidoxypropyltrimethoxysilane (KH560, CAS: 5230-83-8, dropping rate 0.019 g / min), while simultaneously adding monoethyl phosphate. The ester (CAS: 1623-14-9) was stirred for 1.8 h (at a stirring speed of 600 rpm), and the pH was adjusted to 7.0 using a 0.5 mol / L sodium hydroxide solution. Finally, after vacuum degassing and centrifugation, modified silica seed crystals were obtained. The vacuum degassing conditions were -0.1 MPa, 30℃, 200 rpm, and 38 min. The centrifugation speed was 8500 rpm and the centrifugation time was 9 min. The mass ratio of fumed silica, dibutyltin dilaurate, isopropyl triisostearate titanate, perfluorobutylsulfonic acid, γ-aminopropyltriethoxysilane, polyetheramine, octa(aminophenyltrioxosilane), γ-glycidyl etheroxypropyltrimethoxysilane, and monoethyl phosphate was 1:0.07:0.3:0.16:0.13:0.31:0.21:0.19:0.11.

[0041] Acetic acid is used as the acid catalyst.

[0042] Component B: After uniformly mixing deionized water and concentrated ammonia, an alkaline catalyst solution with a concentration of 1 mol / L is obtained.

[0043] Step S2, Gel Preparation: First, thoroughly mix component A and component B at a volume ratio of 1:0.1 to obtain a wet gel. Then, immediately spray the mixed wet gel into an impregnation tank pre-filled with alumina fiber mat. Before adding the wet gel to the impregnation tank, the fiber mat undergoes pretreatment. Specifically, the fiber mat is immersed in a 5.5% KH550-ethanol solution at room temperature for 28 minutes, then dried at 115℃ for 1.8 hours, and finally cooled to room temperature to complete the pretreatment. This allows the fiber mat to mix with the sol, obtaining a wet gel mat. The gel after mixing the fiber mat and sol has a width of 1.5 m, a thickness of 3 mm, and a bulk density of 120 kg / m³. 3 .

[0044] Step S3, Aging: Immerse the wet gel felt in a sealed container filled with anhydrous ethanol and age it at 60°C for 12 hours.

[0045] Step S4, Supercritical Drying: The aged wet gel mat is subjected to supercritical drying to obtain the product. Supercritical drying is carried out using ethanol supercritical drying. Specifically, the aerogel is dried at 280℃ under the protection of nitrogen gas, the pressure of the autoclave is controlled at 15MPa, and the reaction time is 2h.

[0046] Example 4: A method for preparing ultra-low thermal conductivity silicon-based aerogel, comprising: Step S1: Configure component A and component B. The configuration methods for components A and B are consistent with any of the embodiments in Examples 1 to 3.

[0047] Step S2, Gel: First, mix component A and component B thoroughly at a volume ratio of 1:0.01 to 0.1 to obtain a wet gel with a pH value of 6.5 to 8. The mixing time is 10 to 30 minutes and the mixing speed is 300 to 600 rpm.

[0048] Step S3, Aging: Immerse the wet gel in a sealed container filled with anhydrous ethanol and age it at a temperature of 10-40°C for 12-48 hours.

[0049] Step S4, Supercritical Drying: The aged wet gel is subjected to supercritical drying to obtain the final product. Supercritical drying can be performed using CO2 supercritical drying or ethanol supercritical drying. Specifically, CO2 supercritical drying involves drying the aerogel under the protection of CO2 gas at a temperature of 30–50°C, controlling the pressure in the autoclave at 8–12 MPa, and the reaction time at 12–24 h. The ethanol supercritical drying process involves drying the aerogel under the protection of nitrogen gas at a temperature of 250–280°C, controlling the pressure in the autoclave at 8–15 MPa, and the reaction time at 2–8 h.

[0050] Comparative Example 1: A method for preparing a silica-based aerogel, comprising: Step S1: Prepare component A and component B: Component A: After thoroughly mixing silicon source, modified silica seed crystals, anhydrous ethanol and deionized water, their mass ratio is 1:0.0625:30:3; then slowly add acid catalyst with a concentration of 0.5 mol / L, adjust the pH of the solution to 3.5, and hydrolyze at 65℃ for 13 h to obtain component A; The silicon source uses a combination of fluorine-free silicon source and fluorine-containing silicon source. The fluorine-free silicon source is methyltriethoxysilane (CAS: 2031-67-6), and the fluorine-containing silicon source is 3,3,3-trifluoropropyltriethoxysilane (CAS: 86876-45-1). The mass ratio of fluorine-free silicon source to fluorine-containing silicon source is 1:0.5.

[0051] The modified silica seed crystals are multifunctional composite modified seed crystals, and their specific preparation method is basically the same as that in Example 2, except for the order of addition. First, dibutyltin dilaurate is added to the suspension, followed by perfluorobutylsulfonic acid and 3-aminopropyltriethoxysilane, then isopropyl triisostearate titanate, and then polyetheramine, octa(aminophenyltrioxosilane), γ-glycidyl etheroxypropyltrimethoxysilane, and monoethyl phosphate are added sequentially. Finally, the pH value is adjusted with sodium hydroxide solution, and after vacuum degassing and centrifugation, the modified silica seed crystals are obtained. The proportions of each component and the process parameters are consistent with those in Example 2.

[0052] The acid catalyst used is nitric acid.

[0053] Component B: After uniformly mixing deionized water and concentrated ammonia, an alkaline catalyst solution with a concentration of 0.5 mol / L is obtained.

[0054] Step S2, Gel: Same as step S2 in Example 2.

[0055] Step S3, Aging: Same as step S3 in Example 2.

[0056] Step S4, supercritical drying: consistent with step S4 in Example 2.

[0057] Comparative Example 2: A method for preparing a silica-based aerogel, comprising: Step S1: Prepare component A and component B: Component A: After thoroughly mixing silicon source, modified silica seed crystals, anhydrous ethanol and deionized water, their mass ratio is 1:0.0625:30:3; then slowly add acid catalyst with a concentration of 0.5 mol / L, adjust the pH of the solution to 3.5, and hydrolyze at 65℃ for 13 h to obtain component A; The silicon source uses a combination of fluorine-free silicon source and fluorine-containing silicon source. The fluorine-free silicon source is methyltriethoxysilane (CAS: 2031-67-6), and the fluorine-containing silicon source is 3,3,3-trifluoropropyltriethoxysilane (CAS: 86876-45-1). The mass ratio of fluorine-free silicon source to fluorine-containing silicon source is 1:0.5.

[0058] The modified silica seed crystals are multifunctional composite modified seed crystals. The specific preparation method is basically the same as in Example 2, except for the order of addition. First, dibutyltin dilaurate is added to the suspension, followed by isopropyl triisostearate titanate, then polyetheramine, then perfluorobutylsulfonic acid and 3-aminopropyltriethoxysilane, and then octa(aminophenyltrioxosilane), γ-glycidyl etheroxypropyltrimethoxysilane, and monoethyl phosphate are added sequentially. Finally, the pH is adjusted with sodium hydroxide solution, and after vacuum degassing and centrifugation, the modified silica seed crystals are obtained. The proportions of each component and the process parameters are consistent with those in Example 2.

[0059] The acid catalyst used is nitric acid.

[0060] Component B: After uniformly mixing deionized water and concentrated ammonia, an alkaline catalyst solution with a concentration of 0.5 mol / L is obtained.

[0061] Step S2, Gel: Same as step S2 in Example 2.

[0062] Step S3, Aging: Same as step S3 in Example 2.

[0063] Step S4, supercritical drying: consistent with step S4 in Example 2.

[0064] Comparative Example 3: A method for preparing a silica-based aerogel, comprising: Step S1: Prepare component A and component B: Component A: After thoroughly mixing silicon source, modified silica seed crystals, anhydrous ethanol and deionized water, their mass ratio is 1:0.0625:30:3; then slowly add acid catalyst with a concentration of 0.5 mol / L, adjust the pH of the solution to 3.5, and hydrolyze at 65℃ for 13 h to obtain component A; The silicon source uses a combination of fluorine-free silicon source and fluorine-containing silicon source. The fluorine-free silicon source is methyltriethoxysilane (CAS: 2031-67-6), and the fluorine-containing silicon source is 3,3,3-trifluoropropyltriethoxysilane (CAS: 86876-45-1). The mass ratio of fluorine-free silicon source to fluorine-containing silicon source is 1:0.5.

[0065] The modified silica seed crystals are multifunctional composite modified seed crystals. The specific preparation method is basically the same as in Example 2, except for the order of addition. First, dibutyltin dilaurate is added to the suspension, followed by isopropyl triisostearate titanate, then perfluorobutylsulfonic acid, then octa(aminophenyltrioxosilane), then polyetheramine and 3-aminopropyltriethoxysilane, then γ-glycidyl etheroxypropyltrimethoxysilane and monoethyl phosphate. Finally, the pH is adjusted with sodium hydroxide solution, and after vacuum degassing and centrifugation, the modified silica seed crystals are obtained. The proportions of each component and the process parameters are consistent with those in Example 2.

[0066] The acid catalyst used is nitric acid.

[0067] Component B: After uniformly mixing deionized water and concentrated ammonia, an alkaline catalyst solution with a concentration of 0.5 mol / L is obtained.

[0068] Step S2, Gel: Same as step S2 in Example 2.

[0069] Step S3, Aging: Same as step S3 in Example 2.

[0070] Step S4, supercritical drying: consistent with step S4 in Example 2.

[0071] Comparative Example 4: A method for preparing a silica-based aerogel, comprising: Step S1: Prepare component A and component B: Component A: After thoroughly mixing silicon source, modified silica seed crystals, anhydrous ethanol and deionized water, their mass ratio is 1:0.0625:30:3; then slowly add acid catalyst with a concentration of 0.5 mol / L, adjust the pH of the solution to 3.5, and hydrolyze at 65℃ for 13 h to obtain component A; The silicon source uses a combination of fluorine-free silicon source and fluorine-containing silicon source. The fluorine-free silicon source is methyltriethoxysilane (CAS: 2031-67-6), and the fluorine-containing silicon source is 3,3,3-trifluoropropyltriethoxysilane (CAS: 86876-45-1). The mass ratio of fluorine-free silicon source to fluorine-containing silicon source is 1:0.5.

[0072] The modified silica seed crystals are multifunctional composite modified seed crystals. The specific preparation method is basically the same as in Example 2, except for the order of addition. First, dibutyltin dilaurate is added to the suspension, followed by γ-glycidyl etheroxypropyltrimethoxysilane and monoethyl phosphate. Then, isopropyl triisostearate titanate, perfluorobutyl sulfonic acid, 3-aminopropyltriethoxysilane, polyetheramine, and octa(aminophenyltrioxysilane) are added sequentially. Finally, the pH is adjusted with sodium hydroxide solution, and after vacuum degassing and centrifugation, the modified silica seed crystals are obtained. The proportions of each component and the process parameters are consistent with those in Example 2.

[0073] The acid catalyst used is nitric acid.

[0074] Component B: After uniformly mixing deionized water and concentrated ammonia, an alkaline catalyst solution with a concentration of 0.5 mol / L is obtained.

[0075] Step S2, Gel: Same as step S2 in Example 2.

[0076] Step S3, Aging: Same as step S3 in Example 2.

[0077] Step S4, supercritical drying: consistent with step S4 in Example 2.

[0078] Comparative Example 5: A method for preparing a silica-based aerogel, comprising: Step S1: Prepare component A and component B: Component A: After thoroughly mixing silicon source, modified silica seed crystals, anhydrous ethanol and deionized water, their mass ratio is 1:0.0625:30:3; then slowly add acid catalyst with a concentration of 0.5 mol / L, adjust the pH of the solution to 3.5, and hydrolyze at 65℃ for 13 h to obtain component A; The silicon source uses a combination of fluorine-free silicon source and fluorine-containing silicon source. The fluorine-free silicon source is methyltriethoxysilane (CAS: 2031-67-6), and the fluorine-containing silicon source is 3,3,3-trifluoropropyltriethoxysilane (CAS: 86876-45-1). The mass ratio of fluorine-free silicon source to fluorine-containing silicon source is 1:0.5.

[0079] The modified silica seed crystals are multifunctional composite modified seed crystals, and their specific preparation method is basically the same as that in Example 2. The difference is that isopropoxy titanium tristearate (CAS: 68443-53-8) is used instead of isopropyl triisostearate titanium triisostearate (CAS: 61417-49-0), while the rest are the same.

[0080] The acid catalyst used is nitric acid.

[0081] Component B: After uniformly mixing deionized water and concentrated ammonia, an alkaline catalyst solution with a concentration of 0.5 mol / L is obtained.

[0082] Step S2, Gel: Same as step S2 in Example 2.

[0083] Step S3, Aging: Same as step S3 in Example 2.

[0084] Step S4, supercritical drying: consistent with step S4 in Example 2.

[0085] Comparative Example 6: A method for preparing a silica-based aerogel, comprising: Step S1: Prepare component A and component B: Component A: After thoroughly mixing silicon source, modified silica seed crystals, anhydrous ethanol and deionized water, their mass ratio is 1:0.0625:30:3; then slowly add acid catalyst with a concentration of 0.5 mol / L, adjust the pH of the solution to 3.5, and hydrolyze at 65℃ for 13 h to obtain component A; The silicon source uses a combination of fluorine-free silicon source and fluorine-containing silicon source. The fluorine-free silicon source is methyltriethoxysilane (CAS: 2031-67-6), and the fluorine-containing silicon source is 3,3,3-trifluoropropyltriethoxysilane (CAS: 86876-45-1). The mass ratio of fluorine-free silicon source to fluorine-containing silicon source is 1:0.5.

[0086] The modified silica seed crystals are multifunctional composite modified seed crystals, and their specific preparation method is basically the same as that in Example 2. The difference is that the γ-glycidoxypropyltrimethoxysilane (KH560, CAS: 5230-83-8) added later is replaced with 3-aminopropyltriethoxysilane (KH550, CAS: 919-30-2), and the rest are the same (i.e., KH560 is not added, and KH550 is added twice).

[0087] The acid catalyst used is nitric acid.

[0088] Component B: After uniformly mixing deionized water and concentrated ammonia, an alkaline catalyst solution with a concentration of 0.5 mol / L is obtained.

[0089] Step S2, Gel: Same as step S2 in Example 2.

[0090] Step S3, Aging: Same as step S3 in Example 2.

[0091] Step S4, supercritical drying: consistent with step S4 in Example 2.

[0092] Comparative Example 7: A method for preparing a silica-based aerogel, comprising: Step S1: Prepare component A and component B: Component A: After thoroughly mixing silicon source, modified silica seed crystals, anhydrous ethanol and deionized water, their mass ratio is 1:0.0625:30:3; then slowly add acid catalyst with a concentration of 0.5 mol / L, adjust the pH of the solution to 3.5, and hydrolyze at 65℃ for 13 h to obtain component A; The silicon source uses a combination of fluorine-free silicon source and fluorine-containing silicon source. The fluorine-free silicon source is methyltriethoxysilane (CAS: 2031-67-6), and the fluorine-containing silicon source is 3,3,3-trifluoropropyltriethoxysilane (CAS: 86876-45-1). The mass ratio of fluorine-free silicon source to fluorine-containing silicon source is 1:0.5.

[0093] The modified silica seed crystals are multifunctional composite modified seed crystals, and their specific preparation method is basically the same as that in Example 2. The difference is that the 3-aminopropyltriethoxysilane (KH550, CAS: 919-30-2) added earlier is replaced with γ-glycidoxypropyltrimethoxysilane (KH560, CAS: 5230-83-8), while the rest remains the same (i.e., KH550 is not added, and KH560 is added twice).

[0094] The acid catalyst used is nitric acid.

[0095] Component B: After uniformly mixing deionized water and concentrated ammonia, an alkaline catalyst solution with a concentration of 0.5 mol / L is obtained.

[0096] Step S2, Gel: Same as step S2 in Example 2.

[0097] Step S3, Aging: Same as step S3 in Example 2.

[0098] Step S4, supercritical drying: consistent with step S4 in Example 2.

[0099] Comparative Example 8: A method for preparing a silica-based aerogel, comprising: Step S1: Prepare component A and component B: Component A: After thoroughly mixing silicon source, modified silica seed crystals, anhydrous ethanol and deionized water, their mass ratio is 1:0.0625:30:3; then slowly add acid catalyst with a concentration of 0.5 mol / L, adjust the pH of the solution to 3.5, and hydrolyze at 65℃ for 13 h to obtain component A; The silicon source uses a combination of fluorine-free silicon source and fluorine-containing silicon source. The fluorine-free silicon source is methyltriethoxysilane (CAS: 2031-67-6), and the fluorine-containing silicon source is 3,3,3-trifluoropropyltriethoxysilane (CAS: 86876-45-1). The mass ratio of fluorine-free silicon source to fluorine-containing silicon source is 1:0.5.

[0100] The modified silica seed crystals are multifunctional composite modified seed crystals, and their specific preparation method is basically the same as that in Example 2. The difference is that diethyl phosphate (CAS: 598-02-7) is used instead of monoethyl phosphate (CAS: 1623-14-9), while the rest are the same.

[0101] The acid catalyst used is nitric acid.

[0102] Component B: After uniformly mixing deionized water and concentrated ammonia, an alkaline catalyst solution with a concentration of 0.5 mol / L is obtained.

[0103] Step S2, Gel: Same as step S2 in Example 2.

[0104] Step S3, Aging: Same as step S3 in Example 2.

[0105] Step S4, supercritical drying: consistent with step S4 in Example 2.

[0106] The aerogel samples prepared in Examples 1-3 and Comparative Examples 1-8 were subjected to N2 adsorption-desorption tests using a fully automated specific surface area analyzer under the same conditions (i.e., the same ambient temperature of 25°C, humidity, etc.). The corresponding pore parameters were calculated according to the BET model (at least 5 samples were selected for testing in each test group, and the final test results were averaged). The porosity calculation formula is as follows: ; In the formula: r b ,r s These are apparent density and skeletal density, respectively. r s The value is 2.2 g / cm³. 3 ; Meanwhile, in accordance with standard GB / T10294 The thermal conductivity of aerogel samples prepared in Examples 1-3 and Comparative Examples 1-8 was tested at 25℃, 80℃, and 300℃ according to the 2008 standard "Determination of Steady-State Thermal Resistance and Related Properties of Thermal Insulation Materials - Protective Hot Plate Method". (At least 5 samples were selected for each test group, and the final test results were averaged). The test results are shown in the table below:

[0107] As shown in the table above, the specific modifying groups and specific feeding sequence of the present invention, in preparing composite modified silica seed crystals, can effectively ensure a more uniform aerogel skeleton and smaller pore size, guarantee a more stable aerogel felt structure, reduce the porosity of carbon fibers, and thus effectively increase the specific surface area and porosity of the aerogel, reduce its thermal conductivity, and improve the thermal insulation performance of the aerogel. However, after changing the feeding sequence (i.e., Comparative Examples 1 to 4), problems such as the inability to uniformly graft functional groups, self-agglomeration, and ineffective condensation affect the actual role played by the functional groups, thereby affecting the performance of the final aerogel. At the same time, after replacing some substances (i.e., Comparative Examples 5 to 8), the loss of specific functional groups leads to a weaker synergistic effect between various functional groups, thus affecting the performance of the aerogel.

Claims

1. A method for preparing ultra-low thermal conductivity silicon-based aerogel, characterized in that: include: Step S1: Prepare component A and component B: Component A: After thoroughly mixing the silicon source, modified silica seed crystals, anhydrous ethanol and deionized water, an acid catalyst is slowly added to adjust the pH of the solution to 1.5-5.5, and hydrolysis is carried out to obtain component A; Component B: After uniformly mixing deionized water and concentrated ammonia, an alkaline catalyst solution is obtained; Step S2, Gel: First, mix component A and component B thoroughly to obtain a wet gel; then immediately spray the mixed wet gel into the impregnation tank, which is pre-filled with fiber mat so that the fiber mat and the sol are mixed to obtain a wet gel mat. Step S3, Aging: Immerse the wet gel felt in a sealed autoclave containing anhydrous ethanol and keep it warm for aging. Step S4, Supercritical Drying: The aged wet gel felt is subjected to supercritical drying to obtain the final product.

2. The method for preparing an ultra-low thermal conductivity silicon-based aerogel according to claim 1, characterized in that: The silicon source is a combination of a fluorine-free silicon source and a fluorine-containing silicon source. The fluorine-free silicon source is one or more of tetraethyl orthosilicate, methyl orthosilicate, methyltriethoxysilane, methyltrimethoxysilane, and polyethyl orthosilicate. The fluorine-containing silicon source is one or more of trifluoropropanetrimethoxysilane, 3,3,3-trifluoropropyltriethoxysilane, perfluorodecyltriethoxysilane, and perfluorooctyltrimethoxysilane. The mass ratio of the fluorine-free silicon source to the fluorine-containing silicon source is 1:0.1 to 1.

3. A method for preparing an ultra-low thermal conductivity silicon-based aerogel according to claim 1 or 2, characterized in that: In component A, the mass ratio of silicon source, modified silica seed crystal, anhydrous ethanol and deionized water is 1:0.025-0.1:20-40:2-4.

4. A method for preparing an ultra-low thermal conductivity silicon-based aerogel according to claim 1 or 3, characterized in that: In component A, the modified silica seed crystals are multifunctional composite modified seed crystals. The specific preparation method is as follows: First, fumed silica is added to a dispersion medium composed of anhydrous ethanol and deionized water at room temperature. After high-speed stirring and dispersion, ultrasonic dispersion is performed to obtain a uniform suspension. Then, the temperature is raised to 62–68°C, and under a nitrogen atmosphere, dibutyltin dilaurate catalyst is added to the suspension. After stirring evenly, isopropyl triisostearate titanate is added dropwise, and the mixture is kept at this temperature for 3.3–3.7 h. Afterward, the temperature is lowered to 48–52°C, glacial acetic acid is added to adjust the pH to 3.5–4.0, and then perfluorobutyl sulfonate is added dropwise. Acid and 3-aminopropyltriethoxysilane were stirred for 2.2–2.8 h; then, triethylamine was added (to adjust the pH to 5.0–5.5), polyetheramine was added dropwise, and the mixture was kept at this temperature for 2.5–3.5 h; then, the temperature was raised to 58–62 °C, octa(aminophenyltrioxysilane) was added, and the mixture was stirred for 3.5–4.5 h; then the temperature was lowered to 42–48 °C, γ-glycidoxypropyltrimethoxysilane was added dropwise, and monoethyl phosphate was added simultaneously. After stirring for 1.8–2.2 h, the pH was adjusted to 6.5–7.0 using sodium hydroxide solution; finally, after vacuum degassing and centrifugation, modified silica seed crystals were obtained.

5. A method for preparing an ultra-low thermal conductivity silicon-based aerogel according to claim 1 or 4, characterized in that: The solid-liquid ratio of the fumed silica to the dispersion medium is 1 g: 120-130 mL; the mass ratio of fumed silica, dibutyltin dilaurate, isopropyl triisostearate titanate, perfluorobutylsulfonic acid, γ-aminopropyltriethoxysilane, polyetheramine, octa(aminophenyltrioxosilane), γ-glycidyl etheroxypropyltrimethoxysilane, and monoethyl phosphate is 1: 0.05-0.07: 0.28-0.3: 0.14-0.16: 0.11-0.13: 0.29-0.31: 0.19-0.21: 0.17-0.19: 0.09-0.

11.

6. The method for preparing an ultra-low thermal conductivity silicon-based aerogel according to claim 1, characterized in that: The concentration of the acid catalyst in component A is 0.1–1 mol / L, and the acid catalyst is any one of hydrochloric acid, oxalic acid, nitric acid, sulfuric acid, acetic acid, and hydrofluoric acid.

7. The method for preparing an ultra-low thermal conductivity silicon-based aerogel according to claim 1, characterized in that: The hydrolysis temperature of component A is 50–80℃, and the hydrolysis time is 2–16 h.

8. The method for preparing an ultra-low thermal conductivity silicon-based aerogel according to claim 1, characterized in that: The concentration of the alkaline catalyst solution of component B is 0.1–1 mol / L.

9. The method for preparing an ultra-low thermal conductivity silicon-based aerogel according to claim 1, characterized in that: In step S2, component A and component B are mixed at a volume ratio of 1:0.01 to 0.

1.

10. The method for preparing an ultra-low thermal conductivity silicon-based aerogel according to claim 1, characterized in that: The supercritical drying process employs either CO2 supercritical drying or ethanol supercritical drying. Specifically, CO2 supercritical drying involves drying the aerogel under CO2 gas protection at a temperature of 30–50°C, controlling the pressure in the autoclave at 8–12 MPa, and conducting the reaction for 12–24 hours. The ethanol supercritical drying process involves drying the aerogel under nitrogen gas protection at a temperature of 250–280°C, controlling the pressure in the autoclave at 8–15 MPa, and conducting the reaction for 2–8 hours.

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