Modified silicon dioxide aerogel as well as preparation method and application thereof

Abstract

The invention provides a modified silicon dioxide aerogel and a preparation method and application thereof, the preparation method comprises the following steps: (1) mixing an organic silicon source, water and ethanol, adding a solution to adjust the pH to be acidic, and reacting to obtain a solution A; (2) mixing 3-glycidoxypropyltrimethoxysilane, a cross-linking agent and ethanol, so as to obtain a solution B; (3) mixing the solution A with the solution B to obtain wet gel; and (4) carrying out surface modification on the wet gel obtained in the step (3) to obtain the modified silicon dioxide aerogel. The modified silicon dioxide aerogel has low heat conductivity, low density and excellent mechanical property and hydrophobicity, meanwhile, raw materials used in the preparation process are low in toxicity and environmentally friendly, and potential safety hazards are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of silica aerogels, and in particular to a modified silica aerogel and a preparation method and application thereof. Background Art

[0002] Liquefied natural gas (LNG) is natural gas that has been compressed and cooled to its boiling point to become a liquid. Typically, LNG is stored in cryogenic storage tanks at approximately -160°C and 0.1MPa. Extremely low temperatures must be maintained during storage, transportation, and use. Therefore, storage equipment must possess excellent low-temperature resistance and cold-keeping properties, placing a high demand on thermal insulation materials with excellent cold-keeping properties.

[0003] Silica aerogel has a nanoporous structure and low thermal conductivity, and is a material with excellent cold-insulation properties. However, silica aerogel is brittle and has low strength, which seriously restricts its application in cold-insulation. Therefore, organic modification of silica aerogel to meet the requirements of LNG cold-insulation materials for light weight, thermal insulation, and high strength is an effective means to solve the above problems.

[0004] CN104341594B discloses a polyimide-reinforced SiO2 hybrid aerogel prepared by a sol-gel method using bis[3-(trimethoxysilyl)propyl]amine as a coupling agent, mixing a polyimide prepolymer solution with silica sol. This method establishes a stable covalent bond between the polyimide segments and the inorganic silicon network, forming an organic-inorganic synergistic crosslinking structure, effectively improving the strength and toughness of the aerogel skeleton.

[0005] Chandana Mandal et al. (Journal of Sol-Gel Science and Technology, 2019, 92, 84-100) reported that the aliphatic triisocyanate Desmodur N3200A was used to crosslink the silica aerogel skeleton formed by TMOS-APTES co-gel with polyurea. By constructing a core-shell organic-inorganic synergistic network, the mechanical properties of the aerogel were significantly improved. 2 / g and an average pore diameter of 29.4nm, its compressive Young's modulus reaches a maximum of 119MPa.

[0006] Zhang Junwei et al. (Journal of Sol-Gel Science and Technology, 2015, 75, 98-123) reported that they successfully prepared high-strength polymer-cross-linked template silica aerogel (CTSA) bulk materials with an ordered tubular mesoporous structure through an acid-catalyzed surfactant-templated sol-gel method combined with polyurea covalent cross-linking technology. This effectively improved the mechanical properties of the aerogel. The Young's modulus of the modified aerogel was as high as 800 MPa, but its thermal insulation performance was reduced, and the thermal conductivity was increased to 0.070-0.129 W / (m·K).

[0007] However, the above-mentioned prior art still has the following deficiencies: (1) Unable to guarantee cold-keeping performance: Due to the lack of effective regulation of the cross-linking behavior of the organic phase, the disorderly introduced organic components easily destroy the original microporous structure of the silica aerogel, resulting in increased density and thermal conductivity after drying, thereby weakening its cold-keeping performance; (2) Environmental and safety risks: Some organic modifiers and the organic solvents used in them are toxic to a certain extent, and there are environmental pollution and safety hazards in the preparation process.

[0008] Therefore, it is necessary to select low-toxic and environmentally friendly organic phase materials and rationally optimize the organic modification process to improve the mechanical properties of aerogels while maintaining their good cold-keeping properties, so as to achieve the efficient preparation of thermally and mechanically superior organically modified silica aerogels.

[0009] Therefore, developing a method for preparing silica aerogel with excellent cold-insulating performance and mechanical properties is an urgent problem to be solved in this field. Summary of the Invention

[0010] In response to the shortcomings of the existing technology, the present invention provides a modified silica aerogel, a preparation method and application thereof. The silica aerogel obtained by this preparation method has low thermal conductivity, low density, excellent mechanical properties and hydrophobicity. At the same time, the raw materials required for preparation are low in toxicity and environmentally friendly, avoiding the safety hazards caused by the toxicity of organic matter, and meeting the requirements of LNG cold insulation materials for light weight, heat insulation and high strength.

[0011] To achieve this object, the present invention adopts the following technical solutions:

[0012] In a first aspect, the present invention provides a method for preparing a modified silica aerogel, the preparation method comprising the following steps:

[0013] (1) mixing an organosilicon source, water, and ethanol, adjusting the pH to acidic, and reacting to obtain solution A;

[0014] (2) mixing 3-glycidyloxypropyltrimethoxysilane, a crosslinking agent, and ethanol to obtain a solution B;

[0015] (3) mixing solution A and solution B to obtain a wet gel;

[0016] (4) Surface modification of the wet gel obtained in step (3) to obtain modified silica aerogel.

[0017] The present invention selects 3-glycidyloxypropyltrimethoxysilane (GPTMS) as the organic phase raw material, performs preliminary cross-linking with a cross-linking agent, and then hydrolyzes it. The condensation reaction occurs with the Si-OH functional groups on the surface of the silica sol particles, and the GPTMS molecules are orderly connected to the neck region of the gel particles, thereby improving the neck strength. The surface modification of the wet gel gives the silica aerogel excellent hydrophobic properties. In addition, the GPTMS and the cross-linking agent in the present invention have low toxicity and can be dissolved in environmentally friendly solvents such as water and ethanol, thus avoiding the safety hazards caused by the toxicity of the organic phase.

[0018] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the objectives and beneficial effects of the present invention can be better achieved and realized.

[0019] Preferably, the organic silicon source comprises ethyl orthosilicate and / or methyl orthosilicate.

[0020] Preferably, in step (1), the solution for adjusting pH comprises hydrochloric acid and / or sulfuric acid.

[0021] Preferably, the pH is adjusted to 2-4, for example, 2, 3 or 4.

[0022] Preferably, in step (1), the mixing temperature is room temperature.

[0023] Preferably, in step (1), the reaction time is 1-12 h, for example, 1 h, 2 h, 4 h, 6 h, 8 h, 10 h or 12 h.

[0024] Preferably, in step (1), the concentration of silicon dioxide in the solution A is 5-12 wt%, for example, 5 wt%, 7 wt%, 9 wt%, 11 wt% or 12 wt%.

[0025] Preferably, the cross-linking agent comprises diethylenetriamine and / or ethylenediamine.

[0026] Preferably, in step (2), the molar ratio of the 3-glycidyloxypropyltrimethoxysilane to the cross-linking agent is 1:(0.2-0.4), for example, 1:0.2, 1:0.3 or 1:0.4.

[0027] Preferably, in step (2), the concentration of 3-glycidyloxypropyltrimethoxysilane in the solution B is 15-30 wt%, for example, 15 wt%, 20 wt%, 25 wt% or 30 wt%.

[0028] Preferably, in step (2), the mixing temperature is room temperature.

[0029] Preferably, in step (2), the mixing method includes stirring.

[0030] Preferably, in step (2), the mixing time is 1-6 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours.

[0031] Preferably, in step (3), the molar ratio of the organosilicon source in solution A to 3-glycidyloxypropyltrimethoxysilane in solution B is (9-4):1, for example, 9:1, 8:1, 7:1, 6:1, 5:1 or 4:1.

[0032] Preferably, in step (3), the mixing temperature is room temperature.

[0033] Preferably, in step (3), the mixing further comprises standing.

[0034] Preferably, the standing time is 5-10 hours, for example, 5 hours, 6 hours, 8 hours or 10 hours.

[0035] Preferably, step (4) further includes the steps of hydrothermal aging and solvent replacement before surface modification of the wet gel.

[0036] Preferably, the aging solution for hydrothermal aging comprises ethanol and a cross-linking agent.

[0037] Preferably, the cross-linking agent in the aging solution is the same as the cross-linking agent used in step (2). For example, if diethylenetriamine is used in step (2), then the cross-linking agent in the aging solution should also be diethylenetriamine, and the two should be kept consistent.

[0038] Preferably, the concentration of the cross-linking agent in the aging solution is 0.025-0.3 mol / L, for example, 0.025 mol / L, 0.026 mol / L, 0.027 mol / L, 0.028 mol / L, 0.029 mol / L or 0.3 mol / L.

[0039] Preferably, the hydrothermal aging step comprises: placing the wet gel obtained in step (3) in an aging solution, and hydrothermally aging the gel at 150-200° C. (for example, 150° C., 160° C., 170° C., 180° C., 190° C., or 200° C., etc.) for 12-24 h (for example, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, or 24 h, etc.).

[0040] During the hydrothermal aging process, the high temperature environment promotes the cross-linking of GPTMS and the cross-linking agent, thereby increasing the skeleton strength of the silica aerogel and improving the mechanical properties of the aerogel without affecting the cooling effect of the silica aerogel.

[0041] Preferably, the solvent replacement uses ethanol and n-hexane in sequence.

[0042] Preferably, the solvent replacement step comprises: placing the wet gel after hydrothermal aging in ethanol, replacing it once every 6-12 hours (for example, it can be 6 hours, 8 hours, 10 hours or 12 hours, etc.), replacing it 3-6 times (for example, it can be 3 times, 4 times, 5 times or 6 times), and then placing it in n-hexane, replacing it once every 6-12 hours (for example, it can be 6 hours, 8 hours, 10 hours or 12 hours, etc.), replacing it 3-6 times (for example, it can be 3 times, 4 times, 5 times or 6 times).

[0043] Preferably, the surface modification solution in step (4) comprises a hydrophobic modification substance and n-hexane.

[0044] Preferably, the hydrophobic modifying substance includes any one of trimethylchlorosilane, methyltrimethoxysilane or methyltriethoxysilane, or a combination of at least two thereof.

[0045] Preferably, the volume ratio of the hydrophobic modified substance to n-hexane is 1:(5-15), for example, 1:5, 1:7, 1:9, 1:11, 1:13 or 1:15.

[0046] Preferably, the surface modification temperature is 30-80°C, for example, 30°C, 40°C, 50°C, 60°C, 70°C or 80°C.

[0047] Preferably, the surface modification time is 18-36 hours, for example, 18 hours, 22 hours, 26 hours, 30 hours, 34 hours or 36 hours.

[0048] Preferably, step (4) further includes a drying step after surface modification of the gel.

[0049] Preferably, the drying is carried out under normal pressure.

[0050] Preferably, the drying temperature is 50-100°C, for example, 50°C, 60°C, 70°C, 80°C, 90°C or 100°C.

[0051] Preferably, the drying time is 8-24 hours, for example, 8 hours, 12 hours, 16 hours, 20 hours or 24 hours.

[0052] In a second aspect, the present invention provides a modified silica aerogel, which is prepared by the preparation method described in the first aspect.

[0053] In a third aspect, the present invention provides a use of the modified silica aerogel as described in the second aspect in a cold-insulating material.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] (1) The present invention modifies silica aerogel by cross-linking GPTMS with a cross-linking agent. On the basis of not destroying the nanoporous structure of silica aerogel, the skeleton strength of silica aerogel is effectively enhanced, and the silica aerogel has low thermal conductivity, low density and excellent mechanical properties, meeting the requirements of LNG cold insulation materials for light weight, heat insulation and high strength.

[0056] (2) In the present invention, the surface of the silica aerogel is modified so that the modified silica aerogel has excellent hydrophobic properties;

[0057] (3) The present invention uses environmentally friendly GPTMS and a cross-linking agent as organic phases to carry out organic modification of silica aerogel, thereby avoiding the safety hazards caused by the toxicity of organic matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 This is a physical photo of the modified silica aerogel of Example 1;

[0059] Figure 2 is a SEM image of the modified silica aerogel of Example 1;

[0060] Figure 3 Graphs showing nitrogen adsorption-desorption curves and pore size distribution curves of the modified silica aerogel of Example 2;

[0061] Figure 4 Schematic diagram of the contact angle of the modified silica aerogel in Example 3;

[0062] Figure 5 This is a graph showing the compressive strength of the modified silica aerogel of Example 4;

[0063] Figure 6 This is a graph showing the compressive strength of the modified silica aerogel of Example 5;

[0064] Figure 7 Schematic diagram of the contact angle of the modified silica aerogel in Example 6. DETAILED DESCRIPTION

[0065] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0066] Example 1

[0067] This embodiment provides a modified silica aerogel and a preparation method thereof, wherein the preparation method comprises the following steps:

[0068] (1) 10.4 g of TEOS, 3.6 mL of water, and 45.6 mL of ethanol were mixed at room temperature, 1 mL of 4 mol / L hydrochloric acid was added to adjust the pH to 2.5, and the mixture was reacted at room temperature for 6 h to obtain solution A (the concentration of silica in solution A was 6 wt %);

[0069] (2) 11.8 g of GPTMS, 1.0 g of DETA (molar ratio of 1:0.2), and 83.6 mL of ethanol (GPTMS concentration is 15 wt%) were mixed at room temperature for 3 h to obtain solution B;

[0070] (3) 45.0 g of solution A was mixed with 7.88 g of solution B (the molar ratio of TEOS to GPTMS was 9:1), stirred evenly at room temperature, and allowed to stand for 6 h to obtain a wet gel;

[0071] A 0.1 mol / L aging solution was prepared using 100 mL of ethanol and 1.0 g of DETA. The wet gel obtained in step (3) was placed in the aging solution and hydrothermally aged at 180° C. for 24 h.

[0072] After the hydrothermal aging, the hydrothermal aged wet gel was first subjected to solvent replacement with ethanol, replacing the ethanol every 8 hours for 3 times; then the solvent was replaced with n-hexane, replacing the n-hexane every 7 hours for 4 times;

[0073] (4) A modification solution was prepared using 5 mL of trimethylchlorosilane (TMCS) and 50 mL of n-hexane (volume ratio 1:10). The wet gel after solvent replacement was placed in the modification solution and modified at 40 °C for 24 h.

[0074] The surface-modified wet gel was dried at 60° C. under normal pressure for 12 h to obtain modified silica aerogel.

[0075] from Figure 1It can be seen that the modified silica aerogel obtained by the present invention has a complete appearance and a smooth surface; Figure 2 It can be seen that the internal microstructure of the modified silica aerogel is a porous structure formed by the accumulation of spherical nanoparticles.

[0076] Example 2

[0077] This embodiment provides a modified silica aerogel and a preparation method thereof, wherein the preparation method comprises the following steps:

[0078] (1) 8.3 g of TEOS, 2.9 mL of water, and 23.8 mL of ethanol were mixed at room temperature, 1.1 mL of 3.9 mol / L hydrochloric acid was added to adjust the pH to 2.8, and the mixture was reacted at room temperature for 5 h to obtain solution A (the concentration of silica in solution A was 8 wt %);

[0079] (2) 9.5 g of GPTMS, 0.8 g of DETA (molar ratio of 1:0.2), and 46.9 mL of ethanol were mixed at room temperature for 2 h (the concentration of GPTMS was 20 wt%) to obtain solution B;

[0080] (3) 24.0 g of solution A was mixed with 9.45 g of solution B (the molar ratio of TEOS to GPTMS was 4:1), stirred evenly at room temperature, and allowed to stand for 5 h to obtain a wet gel;

[0081] A 0.075 mol / L aging solution was prepared using 100 mL of ethanol and 0.8 g of DETA. The wet gel obtained in step (3) was placed in the aging solution and hydrothermally aged at 160° C. for 18 h.

[0082] After the hydrothermal aging, the wet gel was first subjected to solvent replacement with ethanol, with the ethanol replaced every 7 h for 4 times; then the solvent was replaced with n-hexane, with the n-hexane replaced every 8 h for 3 times;

[0083] (4) A modification solution was prepared using 6 mL of TMCS and 60 mL of n-hexane (volume ratio 1:10). The wet gel after solvent replacement was placed in the modification solution and modified at 50 °C for 30 h.

[0084] The surface-modified wet gel was dried at 70° C. under normal pressure for 18 h to obtain modified silica aerogel.

[0085] from Figure 3 It can be seen that the modified silica aerogel obtained by the present invention is an H3 type hysteresis loop in the IV type curve, and the specific surface area is 439.2m 2 / g, and the average pore volume is 1.89cm 3 / g, the average pore diameter is 8.61nm, and the most probable pore diameter is about 11nm.

[0086] Example 3

[0087] This embodiment provides a modified silica aerogel and a preparation method thereof, wherein the preparation method comprises the following steps:

[0088] (1) 12.5 g of TEOS, 4.3 mL of water, and 24.3 mL of ethanol were mixed at room temperature, 1.2 mL of 4.1 mol / L hydrochloric acid was added to adjust the pH to 3, and the mixture was reacted at room temperature for 8 h to obtain solution A (the concentration of silica in solution A was 10 wt %);

[0089] (2) 14.2 g of GPTMS, 1.2 g of DETA (molar ratio of 1:0.2), and 52.3 mL of ethanol were mixed at room temperature for 2 h (the concentration of GPTMS was 25 wt%) to obtain solution B;

[0090] (3) 32.4 g of solution A was mixed with 5.67 g of solution B (the molar ratio of TEOS to GPTMS was 9:1), stirred evenly at room temperature, and allowed to stand for 8 h to obtain a wet gel;

[0091] A 0.2 mol / L aging solution was prepared using 100 mL of ethanol and 2.1 g of DETA. The wet gel obtained in step (3) was placed in the aging solution and hydrothermally aged at 170° C. for 16 h.

[0092] After the hydrothermal aging, the wet gel was first subjected to solvent replacement with ethanol, with the ethanol replaced every 6 h for 4 times; then the solvent was replaced with n-hexane, with the n-hexane replaced every 8 h for 3 times;

[0093] (4) A modification solution was prepared using 4.5 mL of TMCS and 45 mL of n-hexane (volume ratio 1:10). The wet gel after solvent replacement was placed in the modification solution and modified at 70 °C for 20 h.

[0094] The surface-modified wet gel was dried at 90° C. under normal pressure for 16 h to obtain modified silica aerogel.

[0095] Figure 4 Schematic diagram of the contact angle of the modified silica aerogel in this embodiment, the hydrophobic angle is 133°.

[0096] Example 4

[0097] This embodiment provides a modified silica aerogel and a preparation method thereof, wherein the preparation method comprises the following steps:

[0098] (1) 10.4 g of TEOS, 3.6 mL of water, and 24.5 mL of ethanol were mixed at room temperature, 1 mL of 3.8 mol / L hydrochloric acid was added to adjust the pH to 2.6, and the mixture was reacted at room temperature for 4 h to obtain solution A (the concentration of silica in solution A was 9 wt %);

[0099] (2) 11.8 g of GPTMS, 1.0 g of DETA (molar ratio 1:0.2), and 58.6 mL of ethanol were mixed at room temperature for 2 h (the concentration of GPTMS was 20 wt%) to obtain solution B;

[0100] (3) 26.7 g of solution A was mixed with 11.82 g of solution B (the molar ratio of TEOS to GPTMS was 4:1), stirred evenly at room temperature, and allowed to stand for 7 h to obtain a wet gel;

[0101] A 0.05 mol / L aging solution was prepared using 100 mL of ethanol and 0.5 g of DETA. The wet gel obtained in step (3) was placed in the aging solution and hydrothermally aged at 160° C. for 18 h.

[0102] After the hydrothermal aging, the wet gel after hydrothermal aging was first subjected to solvent replacement with ethanol, replacing the ethanol every 7 hours for 5 times; then the solvent was replaced with n-hexane, replacing the n-hexane every 5 hours for 5 times;

[0103] (4) A modification solution was prepared using 5 mL of TMCS and 50 mL of n-hexane (volume ratio 1:10). The wet gel after solvent replacement was placed in the modification solution and modified at 60 °C for 18 h.

[0104] The surface-modified wet gel was dried at 80° C. under normal pressure for 19 h to obtain modified silica aerogel.

[0105] from Figure 5 It can be seen that the sample exhibits linear elastic behavior in the strain range below 5%, enters the plastic deformation stage in the strain range of 5%-30%, begins to fracture in the strain range of 30%-50%, and the compressive strength is 1.977 MPa (20% strain).

[0106] Example 5

[0107] This embodiment provides a modified silica aerogel and a preparation method thereof, wherein the preparation method comprises the following steps:

[0108] (1) 7.6 g of TMOS, 3.6 mL of water, and 33.3 mL of ethanol were mixed at room temperature, 1 mL of 4 mol / L hydrochloric acid was added to adjust the pH to 2.6, and the mixture was reacted at room temperature for 4 h to obtain solution A (the concentration of silica in solution A was 8 wt %);

[0109] (2) 11.8 g of GPTMS, 1.2 g of ethylenediamine (EDA) (molar ratio 1:0.4), and 58.4 mL of ethanol were mixed at room temperature for 3 h (the concentration of GPTMS was 20 wt%) to obtain solution B;

[0110] (3) 30.0 g of solution A was mixed with 11.82 g of solution B (the molar ratio of TMOS to GPTMS was 4:1), stirred evenly at room temperature, and allowed to stand for 9 h to obtain a wet gel;

[0111] A 0.05 mol / L aging solution was prepared using 100 mL of ethanol and 3.0 g of EDA. The wet gel obtained in step (3) was placed in the aging solution and hydrothermally aged at 150° C. for 20 h.

[0112] After the hydrothermal aging, the wet gel after hydrothermal aging was first subjected to solvent replacement with ethanol, replacing the ethanol every 6 hours for 3 times; then the solvent was replaced with n-hexane, replacing the n-hexane every 7 hours for 4 times;

[0113] (4) A modification solution was prepared using 5 mL of TMCS and 50 mL of n-hexane (volume ratio 1:10). The wet gel after solvent replacement was placed in the modification solution and modified at 60 °C for 18 h.

[0114] The surface-modified wet gel was dried at 70° C. under normal pressure for 22 h to obtain modified silica aerogel.

[0115] from Figure 6 It can be seen that the sample exhibits linear elastic behavior in the strain range below 5%, enters the plastic deformation stage in the strain range of 5%-30%, begins to fracture in the strain range of 30%-50%, and the compressive strength is 1.830 MPa (20% strain).

[0116] Example 6

[0117] This embodiment provides a modified silica aerogel and a preparation method thereof, wherein the preparation method comprises the following steps:

[0118] (1) 12.5 g of TEOS, 4.3 mL of water, and 35.7 mL of ethanol were mixed at room temperature, 0.8 mL of 4.1 mol / L sulfuric acid was added to adjust the pH to 2.5, and the mixture was reacted at room temperature for 3 h to obtain solution A (the concentration of silica in solution A was 8 wt %);

[0119] (2) 14.2 g of GPTMS, 1.9 g of DETA (molar ratio of 1:0.3) and 69.5 mL of ethanol were mixed at room temperature for 3 h (the concentration of GPTMS was 20 wt%) to obtain solution B;

[0120] (3) 40.5 g of solution A was mixed with 7.09 g of solution B (the molar ratio of TEOS to GPTMS was 9:1), stirred evenly at room temperature, and allowed to stand for 8 h to obtain a wet gel;

[0121] A 0.1 mol / L aging solution was prepared using 100 mL of ethanol and 1.0 g of DETA. The wet gel obtained in step (3) was placed in the aging solution and hydrothermally aged at 160° C. for 18 h.

[0122] After the hydrothermal aging, the wet gel was first subjected to solvent replacement with ethanol, with the ethanol replaced every 5 h for 3 times; then the solvent was replaced with n-hexane, with the n-hexane replaced every 6 h for 4 times;

[0123] (4) A modification solution was prepared using 5 mL of methyltrimethoxysilane (MTMS) and 45 mL of n-hexane (volume ratio 1:9). The wet gel after solvent replacement was placed in the modification solution and modified at 50 °C for 20 h.

[0124] The surface-modified wet gel was dried at 80° C. under normal pressure for 20 h to obtain modified silica aerogel.

[0125] Figure 7 Schematic diagram of the contact angle of the modified silica aerogel in this embodiment, with a hydrophobic angle of 128°.

[0126] Example 7

[0127] This embodiment provides a modified silica aerogel and a preparation method thereof. The preparation method is different from that of Example 1 only in that the hydrothermal aging at 180°C for 24 hours in step (4) is adjusted to aging at 80°C for 24 hours, and the rest is the same as that of Example 1.

[0128] Comparative Example 1

[0129] This comparative example provides a modified silica aerogel and a preparation method thereof. The preparation method differs from Example 1 only in that step (2) is omitted and step (3) is adjusted to adding 5 mL of 0.1 mol / L ammonia water to solution A, stirring uniformly at room temperature, and standing for 6 h to obtain a wet gel. The rest is the same as Example 1.

[0130] Performance testing:

[0131] (1) Density: The volume density ρ of the silica aerogel sample is calculated according to formula I:

[0132] ρ=m / VFormula I

[0133] Where m is the mass of the sample and V is the volume of the sample: for cylindrical samples, V = (πd 2h) / 4, d is the sample diameter, h is the sample height; for block samples, V=abh, a is the sample length, b is the sample width, and h is the sample height.

[0134] (2) Specific surface area: The pore structure of the samples was analyzed using a Quantachrome NOVA 43 2200e surface area analyzer (Quanta Instruments, USA). The samples were degassed at 120°C for 2 h with N2 as the loading gas. The pore type of the samples can be confirmed by analyzing the shape of the N2 adsorption-desorption curve.

[0135] The specific surface area of ​​the sample was calculated using the Brunner-Emmett-Taylor (BET) method. The BET calculation formula is shown in Formula II:

[0136]

[0137] When the relative pressure P / P0 is in the range of 0.05 to 0.35, a straight line can be obtained from Equation II. The monolayer saturated adsorption capacity V can be obtained based on the slope and intercept of the obtained straight line. m , and then the specific surface area S of the sample can be calculated using formula III, where N0 is Avogadro's constant and σ is the cross-sectional area of ​​a single adsorbed molecule.

[0138] S=V m N0σ / 22400W Formula III

[0139] In addition, the pore size distribution and pore volume of the samples were calculated using the Barrett-Joyner-Halendar (BJH) method applicable to the mesoporous columnar model, and the pore size distribution was expressed as the relationship curve between dV(r) and pore diameter r.

[0140] (3) Room temperature thermal conductivity: The thermal conductivity was measured using the TC 3000 thermal conductivity meter from Xi'an Xiaxi Electronic Technology Co., Ltd. using the hot wire method.

[0141] (4) Compressive strength: The compressive strength of the samples was tested using a universal testing machine (LD23.503, China) at a loading rate of 1.0 mm / min. The calculation formula is shown in Equation IV.

[0142] σ=F / S Formula IV

[0143] Where σ is the compressive strength (or tensile strength), in MPa; F is the load corresponding to a certain deformation, in N; S is the cross-sectional area, in mm 2 .

[0144] (5) Hydrophobic angle: The characterization was performed using an OCA15EC contact angle meter from Dataphysics, Germany. The sample was placed on a stage, and a 3 μL droplet of deionized water was gently dripped onto the sample surface using a microinjector. The camera was used to capture the image and the computer was used to analyze and calculate the contact angle between the sample and the deionized water droplet.

[0145] The modified silica aerogels provided in the above examples and comparative examples were subjected to performance tests, and the test data are shown in Table 1:

[0146] Table 1

[0147]

[0148]

[0149] As shown in Table 1, the present invention modifies the silica aerogel by cross-linking GPTMS with a cross-linking agent. On the basis of not destroying the nanoporous structure of the silica aerogel, the skeleton strength of the silica aerogel is effectively enhanced, and the silica aerogel has low thermal conductivity, which can reach 0.0228W / m·K, and low density, which can reach 0.194g / cm 3 , excellent mechanical properties, compressive strength up to 5.157MPa (20% strain) and excellent hydrophobicity (hydrophobic angle 127°~133°), meeting the requirements of LNG cold insulation materials for light weight, heat insulation and high strength.

[0150] From the comparison between Example 1 and Example 7, it can be seen that if the hydrothermal aging temperature is too low, the density of the modified silica aerogel will increase (0.3562 g / cm 3 ), the room temperature thermal conductivity increases (0.0478W / m·K).

[0151] In Comparative Example 1, the silica aerogel was not modified with GPTMS, resulting in low skeleton strength of the silica aerogel, with a compressive strength of only 0.195 MPa (20% strain), which does not meet the high strength requirement of LNG cold insulation materials.

[0152] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing modified silica aerogel, characterized in that: The preparation method comprises the following steps: (1) mixing an organosilicon source, water, and ethanol, adjusting the pH to acidic, and reacting to obtain solution A; (2) mixing 3-glycidyloxypropyltrimethoxysilane, a crosslinking agent, and ethanol to obtain a solution B; (3) mixing solution A and solution B to obtain a wet gel; (4) Surface modification of the wet gel obtained in step (3) to obtain modified silica aerogel.

2. The preparation method according to claim 1, characterized in that The organosilicon source includes ethyl orthosilicate and / or methyl orthosilicate; Preferably, in step (1), the solution for adjusting pH comprises hydrochloric acid and / or sulfuric acid; Preferably, the pH is adjusted to 2-4; Preferably, in step (1), the mixing temperature is room temperature; Preferably, in step (1), the reaction time is 1-12 hours; Preferably, in step (1), the concentration of silicon dioxide in the solution A is 5-12 wt%.

3. The preparation method according to claim 1 or 2, characterized in that The cross-linking agent includes diethylenetriamine and / or ethylenediamine; Preferably, in step (2), the molar ratio of 3-glycidyloxypropyltrimethoxysilane to the crosslinking agent is 1:(0.2-0.4); Preferably, in step (2), the concentration of 3-glycidyloxypropyltrimethoxysilane in the solution B is 15-30 wt%; Preferably, in step (2), the mixing temperature is room temperature; Preferably, in step (2), the mixing method includes stirring; Preferably, in step (2), the mixing time is 1-6 hours.

4. The preparation method according to any one of claims 1 to 3, characterized in that In step (3), the molar ratio of the organosilicon source in solution A to the 3-glycidyloxypropyltrimethoxysilane in solution B is (9-4):1; Preferably, in step (3), the mixing temperature is room temperature; Preferably, in step (3), the mixing further comprises standing; Preferably, the standing time is 5-10 hours.

5. The preparation method according to any one of claims 1 to 4, characterized in that Step (4) also includes the steps of hydrothermal aging and solvent replacement before surface modification of the wet gel; Preferably, the hydrothermal aging solution comprises ethanol and a cross-linking agent; Preferably, the cross-linking agent in the aging solution is the same as the cross-linking agent used in step (2); Preferably, the concentration of the cross-linking agent in the aging solution is 0.025-0.3 mol / L; Preferably, the hydrothermal aging step comprises: placing the wet gel obtained in step (3) in an aging solution and hydrothermally aging it at 150-200° C. for 12-24 hours.

6. The preparation method according to any one of claims 1 to 5, characterized in that The solvent replacement uses ethanol and n-hexane in sequence; Preferably, the solvent replacement step comprises: placing the wet gel after hydrothermal aging in ethanol, replacing it once every 6-12 hours, and replacing it 3-6 times; then placing it in n-hexane, replacing it once every 6-12 hours, and replacing it 3-6 times.

7. The preparation method according to any one of claims 1 to 6, characterized in that The surface modification solution in step (4) comprises a hydrophobic modification substance and n-hexane; Preferably, the hydrophobic modifying substance comprises any one or a combination of at least two of trimethylchlorosilane, methyltrimethoxysilane or methyltriethoxysilane; Preferably, the volume ratio of the hydrophobic modified substance to n-hexane is 1:(5-15); Preferably, the surface modification temperature is 30-80°C; Preferably, the surface modification time is 18-36 hours.

8. The preparation method according to any one of claims 1 to 7, characterized in that Step (4) further includes a drying step after surface modification of the gel; Preferably, the drying is carried out under normal pressure; Preferably, the drying temperature is 50-100°C; Preferably, the drying time is 8-24 hours.

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

10. Use of the modified silica aerogel according to claim 9 in cold insulation materials.

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