Atmospheric pressure dried anisotropic silicon-based aerogel composite fiber paper and its preparation method

Abstract

This invention provides a method for preparing anisotropic silica-based aerogel composite fiber paper under normal pressure drying, belonging to the field of heat-resistant materials technology. The method includes: preparing at least two hydrophobic siloxane coupling agent solvents of different concentrations; preparing an aerogel silica sol by mixing the hydrophobic siloxane coupling agent solvent with the lowest concentration, tetraethyl orthosilicate, and a first organic solvent; using the remaining hydrophobic siloxane coupling agent solvents as gradient solvents; laying aluminosilicate fiber paper and wetting the upper surface with the first organic solvent; adding the aerogel silica sol to the upper surface, and then adding gradient solvents in ascending order of concentration under reduced pressure to form a siloxane layer; and performing aging, drying, and settling treatments to obtain the composite fiber paper. This invention reduces the crosslinking degree of the aerogel, improves its flexibility, and the concentration gradient, combined with the reduced pressure method for preparing anisotropic aerogels, ensures the heat resistance temperature of the fiber paper and avoids the drawback of reduced heat transfer efficiency.

Description

Technical Field

[0001] This invention belongs to the field of heat-resistant materials technology, and particularly relates to an anisotropic silicon-based aerogel composite fiber paper dried at normal pressure and its preparation method. Background Technology

[0002] Aluminosilicate fiber paper is a special inorganic fiber material composed of aluminosilicate fibers, high-temperature binders, and additives. It possesses excellent thermal insulation properties and chemical stability. Aluminosilicate fiber paper is primarily used as a thermal insulation and fireproofing material for high-temperature equipment. Its advantages include high-temperature stability, lightweight, low density, good flexibility, and excellent thermal insulation performance. In short, aluminosilicate fiber paper is an outstanding high-temperature insulation material widely used in high-temperature equipment in industries such as steel, petrochemicals, and power.

[0003] In the ceramic manufacturing process, aluminosilicate fiber paper is used in large quantities as a consumable. However, after high-temperature baking, the mechanical properties of aluminosilicate fiber paper deteriorate, making it unusable.

[0004] In traditional methods, silica aerogel is combined with aluminum silicate fiber paper. Although this can enhance the heat resistance of the material to some extent, the aerogel is brittle. A simple composite process will increase the brittleness of the fiber paper after baking. At the same time, the introduction of aerogel can hinder heat transfer, which will have a significant impact on the overall firing process of ceramic products.

[0005] In summary, existing traditional processing methods have drawbacks, such as increasing the brittleness of the composite fiber paper and hindering heat transfer, which in turn affects the firing process of ceramic products and causes inconvenience to the preparation of ceramic products. Summary of the Invention

[0006] To address the above problems, this invention provides a method for preparing anisotropic silica-based aerogel composite fiber paper that is dried under normal pressure, comprising:

[0007] S1. Prepare at least two different concentrations of hydrophobic siloxane coupling agent solvents; take the hydrophobic siloxane coupling agent solvent with the lowest relative concentration and prepare it with tetraethyl orthosilicate and a first organic solvent to obtain an aerogel silica sol; and use the remaining concentrations of the hydrophobic siloxane coupling agent solvents as gradient solvents.

[0008] S2. Lay aluminum silicate fiber paper, and wet the upper surface of the aluminum silicate fiber paper with the first organic solvent.

[0009] S3. The aerogel silica sol is added to the wetted surface of the aluminum silicate fiber paper under normal temperature and pressure conditions, so that the aerogel silica sol grows in situ on the surface of the aluminum silicate fiber paper to form a silica sol layer.

[0010] S4. Under reduced pressure, the gradient solvents are added sequentially to the silica sol layer according to the concentration from small to large to form siloxane layers of different concentrations.

[0011] S5. Perform aging and drying treatment and static treatment to obtain the composite fiber paper.

[0012] Preferably, in step S4, where gradient solvents are added sequentially to the silica sol layer in ascending order of concentration under reduced pressure to form siloxane layers of different concentrations, the pressure condition under reduced pressure is no greater than 0.098 MPa.

[0013] Preferably, the hydrophobic siloxane coupling agent solvents of different concentrations are prepared based on the amount of tetraethyl orthosilicate.

[0014] Preferably, the molar ratio of the tetraethyl orthosilicate and the hydrophobic siloxane coupling agent is in the range of 1:(0.1-1.0).

[0015] Preferably, the aerogel silica sol is prepared by the tetraethyl orthosilicate, the hydrophobic siloxane coupling agent and the first organic solvent in a molar ratio of 1:(0.1-1.0):(10-50).

[0016] Preferably, the hydrophobic siloxane coupling agent is any one or more of methyltrimethoxysilane, methyltriethoxysilane, dimethoxydiethoxysilane, phenyltriethoxysilane, and trimethylmethoxysilane.

[0017] Preferably, the first organic solvent is any one or more of methanol, ethanol, propanol, isopropanol, n-butanol, tert-butanol, sec-butanol, pentanol and its isomers, hexanol and its isomers, and acetone.

[0018] Preferably, after the step of adding the aerogel silica sol to the wetted aluminosilicate fiber paper surface under normal temperature and pressure conditions, allowing the aerogel silica sol to grow in situ on the surface of the aluminosilicate fiber paper, a settling step is also included.

[0019] Preferably, the settling time is 0.5 hours to 3.0 hours.

[0020] Preferably, in step S4, under reduced pressure, the gradient solvents are added sequentially to the silica sol layer according to the concentration from small to large to form siloxane layers of different concentrations. After a preset interval, the next concentration of the hydrophobic siloxane coupling agent solvent is added.

[0021] Preferably, the preset interval time is 0.5 hours to 1.0 hours.

[0022] Preferably, the aging and drying process is as follows:

[0023] The second organic solvent was used as the aging solution, and aging and drying were carried out under normal pressure.

[0024] Preferably, the aging and drying process takes 12 to 60 hours.

[0025] Preferably, the aging and drying process is carried out at one atmosphere.

[0026] Preferably, the second organic solvent is one or more of methanol, ethanol, propanol and acetone.

[0027] Preferably, the settling time is 6 to 60 hours.

[0028] Preferably, the length of the aluminum silicate fiber paper is 1cm-50cm, the width of the aluminum silicate fiber paper is 1cm-10cm, and the thickness of the aluminum silicate fiber paper is 1mm-4mm.

[0029] In addition, to solve the above problems, the present invention also provides a composite fiber paper, which is prepared by the preparation method of anisotropic silicon-based aerogel composite fiber paper with normal pressure drying as described above.

[0030] This invention provides an anisotropic silica-based aerogel composite fiber paper dried under normal pressure and its preparation method. The preparation method includes: preparing at least two hydrophobic siloxane coupling agent solvents of different concentrations; preparing an aerogel silica sol by mixing the hydrophobic siloxane coupling agent solvent with the lowest concentration, tetraethyl orthosilicate, and a first organic solvent; using the remaining hydrophobic siloxane coupling agent solvents as gradient solvents; laying aluminosilicate fiber paper and wetting the upper surface with the first organic solvent; adding the aerogel silica sol to the upper surface, and sequentially adding gradient solvents according to increasing concentration under reduced pressure to form a siloxane layer; and performing aging, drying, and settling treatments to obtain the composite fiber paper. Based on aluminosilicate fiber paper, this invention utilizes in-situ growth of anisotropic silica sol layers to obtain a porous elastic interconnect network and a robust yet flexible composite structure. The addition of hydrophobic siloxane coupling agents reduces the crosslinking degree of the aerogel, thereby improving its flexibility. Simultaneously, the change in concentration gradient, combined with a decompression method to prepare anisotropic aerogels, ensures the heat resistance temperature of the fiber paper and avoids the defect of reduced heat transfer efficiency. Attached Figure Description

[0031] Figure 1 This is an electron microscope image of the microstructure of aluminosilicate fiber paper in Example 1 of the preparation method of anisotropic silica-based aerogel composite fiber paper dried at normal pressure according to the present invention.

[0032] Figure 2This is an electron microscope image of the microstructure of the composite fiber paper prepared in Example 1 of the preparation method of the anisotropic silicon-based aerogel composite fiber paper dried under normal pressure according to the present invention.

[0033] Figure 3 This is an electron microscope image of the microstructure of the composite fiber paper prepared in Comparative Example 2 of the method for preparing anisotropic silicon-based aerogel composite fiber paper under normal pressure drying according to the present invention.

[0034] Figure 4 This is a comparative graph showing the highest stability point and the dimensional shrinkage rate of the highest stability point in the transverse comparative test experiment of the preparation method of the anisotropic silicon-based aerogel composite fiber paper dried at normal pressure of the present invention.

[0035] Figure 5 This is a comparative graph showing the relationship between the changes in thermal conductivity at 300°C and the amount of aerogel silica sol prepared at different concentration gradients in the cross-sectional comparative test experiment of the preparation method of the anisotropic silica-based aerogel composite fiber paper dried at normal pressure of the present invention.

[0036] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0037] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Unless otherwise defined below, all technical and scientific terms used in the specific embodiments of this invention are intended to have the same meaning as commonly understood by those skilled in the art. While it is believed that the following terms will be well understood by those skilled in the art, the following definitions are set forth to better explain the invention.

[0039] As used in this invention, the terms “comprising,” “including,” “having,” “containing,” or “involving” are inclusive or open-ended and do not exclude other unlisted elements or method steps. The term “consisting of” is considered a preferred embodiment of the term “comprising.” If a group is defined below as comprising at least a certain number of embodiments, this should also be understood to disclose a group that preferably consists only of those embodiments.

[0040] When referring to a singular noun, the indefinite or definite article used, such as "a" or "a kind of," "the," includes the plural form of the noun.

[0041] The term "approximately" in this invention refers to an accuracy range that, as would be understood by those skilled in the art, still guarantees the technical effects of the features in question. This term typically indicates a deviation from the indicated value of ±10%, preferably ±5%.

[0042] Furthermore, the terms first, second, third, (a), (b), (c), and similar terms used in the specification and claims are for distinguishing similar elements and are not necessary for the order of description or chronological sequence. It should be understood that such terms are interchangeable in appropriate contexts, and the embodiments described in this invention can be implemented in a different order than that described or illustrated in this invention.

[0043] Unless otherwise defined or clearly indicated by the context, all technical and scientific terms used in this disclosure have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains.

[0044] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, but this does not constitute any limitation on the present invention. Any limited modifications made by any person within the scope of the claims of the present invention are still within the scope of the claims of the present invention.

[0045] This invention provides a method for preparing anisotropic silica-based aerogel composite fiber paper that is dried under normal pressure, comprising:

[0046] S1. Prepare at least two different concentrations of hydrophobic siloxane coupling agent solvents; take the hydrophobic siloxane coupling agent solvent with the lowest relative concentration and prepare it with tetraethyl orthosilicate and a first organic solvent to obtain an aerogel silica sol; and use the remaining concentrations of the hydrophobic siloxane coupling agent solvents as gradient solvents.

[0047] S2. Lay aluminum silicate fiber paper, and wet the upper surface of the aluminum silicate fiber paper with the first organic solvent.

[0048] S3. The aerogel silica sol is added to the wetted surface of the aluminum silicate fiber paper under normal temperature and pressure conditions, so that the aerogel silica sol grows in situ on the surface of the aluminum silicate fiber paper to form a silica sol layer.

[0049] S4. Under reduced pressure, the gradient solvents are added sequentially to the silica sol layer according to the concentration from small to large to form siloxane layers of different concentrations.

[0050] S5. Perform aging and drying treatment and static treatment to obtain the composite fiber paper.

[0051] As described above, in step S1, at least two different concentrations of hydrophobic siloxane coupling agent solvents need to be prepared, which can be divided into two parts according to their concentrations:

[0052] (1) The first part is the hydrophobic siloxane coupling agent solvent with the lowest concentration, which needs to be further prepared. Specifically, this part (the hydrophobic siloxane coupling agent solvent with the lowest concentration) is prepared with tetraethyl orthosilicate and the first organic solvent to obtain aerogel silica sol.

[0053] (2) Second part: one or more of the remaining concentrations of hydrophobic siloxane coupling agent solvents as gradient solvents.

[0054] For example, S1 can be implemented in the following specific steps:

[0055] (1) First step, prepare at least 4 different concentrations of hydrophobic siloxane coupling agent solvents; in order of increasing concentration, they are A, B, C, and D;

[0056] (2) In the second step, take the hydrophobic siloxane coupling agent solvent A with the lowest concentration and prepare it with tetraethyl orthosilicate and the first organic solvent to obtain aerogel silica sol.

[0057] (3) The third step is to use the remaining hydrophobic siloxane coupling agent solvents of other concentrations, namely B, C and D, three different concentrations of hydrophobic siloxane coupling agent solvents, as gradient solvents.

[0058] The second and third steps can be performed either one first or simultaneously.

[0059] The details are shown in the table below:

[0060] Table 1. Comparison of components of the pre-prepared aerogel silica sol and gradient solvent in step S1

[0061]

[0062] As described above, in step S2, after laying the aluminum silicate fiber paper, the first organic solvent is added to the upper surface of the aluminum silicate fiber paper to wet it.

[0063] Specifically, under normal pressure, filters, funnel devices, etc., such as sand core filters can be used. A vacuum flask is placed at the bottom of the sand core filter and connected to a vacuum pump. A sand core funnel is placed at the top. Aluminum silicate fiber paper is laid at the sand core position. Under normal pressure, a small amount of the first organic solvent is added to the upper surface of the aluminum silicate fiber paper, allowing the first organic solvent to gradually penetrate and wet the paper.

[0064] As described above, the aluminosilicate fiber paper is placed on a filter device and wetted with a small amount of solvent. This is done to form a uniform thin layer on the surface of the fiber paper so that the aerogel silica sol in subsequent steps can better bond with it.

[0065] As described above, in step S3, also under normal pressure, the aerogel silica sol is added to the surface of the wetted aluminum silicate fiber paper, so that the aerogel silica sol grows in situ on the surface of the aluminum silicate fiber paper to form a silica sol layer.

[0066] In step S3, the pressure condition is normal pressure. The prepared aerogel silica sol is added to the surface of the already wetted aluminosilicate fiber paper, so that the aerogel silica sol grows in situ on the fiber surface of the aluminosilicate fiber paper.

[0067] As described above, the prepared aerogel silica sol is slowly introduced into the filtration device, where it grows in situ on the bottom fiber surface of the aluminosilicate fiber paper. This means that the aerogel silica sol is precisely positioned on the surface of the fiber paper, rather than penetrating its interior or other areas. During this process, the silica sol gradually gels on the surface of the fiber paper and forms a three-dimensional network structure, thereby fixing the fiber paper together and enhancing its mechanical properties.

[0068] The above chemical reaction can be represented by the following reaction formula:

[0069] (1)Si(OEt)4+2H2O→Si(OH)4+4EtOH;

[0070] (2) Si(OH)4→SiO2+2H2O.

[0071] In step S4, under reduced pressure, a gradient solvent is introduced onto the aluminosilicate fiber paper in the filtration device, causing it to react briefly on the silica sol surface to form a multilayered hydrophobic siloxane film. This treatment improves the hydrophobicity and water resistance of the composite fiber paper. The gradient solvent is added in ascending order of concentration onto the silica sol layer.

[0072] In summary, this method utilizes the combination of aerogel silica sol and aluminosilicate fiber paper to prepare composite fiber paper, and its performance can be further improved by controlling the introduction of gradient solvents with different concentration gradients.

[0073] Furthermore, in step S4, where gradient solvents are added sequentially to the silica sol layer in ascending order of concentration under reduced pressure to form siloxane layers of different concentrations, the pressure condition under reduced pressure is no greater than 0.098 MPa.

[0074] As mentioned above, in step S4, the pressure condition under the decompression state is no greater than 0.098 MPa, which can be 0 MPa < P ≤ 0.098 MPa.

[0075] It should be noted that the pressure conditions are closely related to the key factors in forming anisotropic silica-based aerogel composite fiber paper. The decompression process is achieved by reducing the internal pressure of the system, which causes dissolved substances in the gas or liquid to be released, forming bubbles or pores. The decompression process is crucial in the preparation of anisotropic aerogel composite fiber paper because it controls the structure and morphology of the aerogel.

[0076] By limiting the pressure condition under the decompression state to no more than 0.098 MPa in step S4, a suitable decompression effect can be ensured. The principle is as follows:

[0077] (1) Controlling the pore structure of aerogel: A certain pressure can cause more gas or liquid to be released from the fiber paper, forming more pores. This can obtain more pore structure, increase the specific surface area and porosity of aerogel, and thus enhance its adsorption capacity and thermal insulation performance.

[0078] (2) Ensure the heat resistance of fiber paper: A certain pressure can reduce the degree of cross-linking of aerogel in fiber paper, maintain the flexibility and elasticity of fiber paper, and thus improve its heat resistance. Excessive pressure may lead to excessive cross-linking of aerogel, making fiber paper brittle and reducing its heat resistance.

[0079] Based on the above principles, limiting the pressure to no more than 0.098 MPa under reduced pressure conditions can ensure the formation of anisotropic silicon-based aerogel composite fiber paper with suitable pore structure and excellent heat resistance.

[0080] Furthermore, the different concentrations of hydrophobic siloxane coupling agent solvents are prepared based on the amount of tetraethyl orthosilicate.

[0081] Furthermore, the molar ratio of the tetraethyl orthosilicate to the hydrophobic siloxane coupling agent ranges from 1:(0.1-1.0). For example, it can be 1:0.1, 1:0.2, 1:0.4, 1:0.6, 1:0.8, 1:1.0, etc.

[0082] Furthermore, the aerogel silica sol is prepared by the tetraethyl orthosilicate, the hydrophobic siloxane coupling agent and the first organic solvent in a molar ratio of 1:(0.1-1.0):(10-50).

[0083] Furthermore, the hydrophobic siloxane coupling agent is any one or more of methyltrimethoxysilane, methyltriethoxysilane, dimethoxydiethoxysilane, phenyltriethoxysilane, and trimethylmethoxysilane.

[0084] Furthermore, the first organic solvent is any one or more of methanol, ethanol, propanol, isopropanol, n-butanol, tert-butanol, sec-butanol, pentanol and its isomers, hexanol and its isomers, and acetone.

[0085] Furthermore, after the step of adding the aerogel silica sol to the wetted surface of the aluminosilicate fiber paper under normal temperature and pressure conditions, so that the aerogel silica sol grows in situ on the surface of the aluminosilicate fiber paper, a settling step is also included.

[0086] The settling time can be 0.5 hours to 3.0 hours. For example, it can be 0.5 hours, 1.0 hour, 1.5 hours, 2.0 hours, 2.5 hours, 3.5 hours, etc.

[0087] Furthermore, in step S4, under reduced pressure, the gradient solvents are added sequentially to the silica sol layer according to their concentrations from small to large to form siloxane layers of different concentrations. After a preset interval, the next concentration of the hydrophobic siloxane coupling agent solvent is added.

[0088] Furthermore, the preset interval time is 0.5 hours to 1.0 hours. For example, it can be 0.5 hours, 0.6 hours, 0.7 hours, 0.8 hours, 0.9 hours, 1.0 hours, etc.

[0089] Furthermore, the aging and drying process is as follows:

[0090] The second organic solvent was used as the aging solution, and aging and drying were carried out under normal pressure.

[0091] Furthermore, the aging and drying process takes 12 to 60 hours; for example, it can be 12 hours, 16 hours, 20 hours, 24 hours, 30 hours, 36 hours, 40 hours, 48 ​​hours, 60 hours, etc.

[0092] Furthermore, the aging and drying process is carried out at one atmosphere of atmospheric pressure.

[0093] As mentioned above, one atmosphere of pressure can be 1013.25 kPa.

[0094] Furthermore, the second organic solvent is one or more of methanol, ethanol, propanol, and acetone.

[0095] Furthermore, the settling time for the settling treatment is 6 hours to 60 hours. For example, it can be 6 hours, 10 hours, 16 hours, 20 hours, 24 hours, 30 hours, 36 hours, 40 hours, 48 ​​hours, 60 hours, etc.

[0096] Furthermore, the length of the aluminosilicate fiber paper is 1cm-50cm, the width is 1cm-10cm, and the thickness is 1mm-4mm. For example, the length of the aluminosilicate fiber paper can be 1cm, 5cm, 10cm, 15cm, 20cm, 25cm, 30cm, 35cm, 40cm, 45cm, 50cm, 55cm, 60cm, etc.; the width can be 1cm, 2cm, 4cm, 6cm, 8cm, 10cm, etc.; and the thickness can be 1mm, 2mm, 3mm, 4mm, etc.

[0097] In addition, the present invention also provides a composite fiber paper, which is prepared by the method for preparing anisotropic silicon-based aerogel composite fiber paper by normal pressure drying as described above.

[0098] The present invention will be further illustrated below with specific embodiments. However, it should be understood that these embodiments are merely for the purpose of more detailed illustration and should not be construed as limiting the present invention in any way.

[0099] Example 1

[0100] Composite fiber paper is prepared using the following method:

[0101] Step 1: Take a piece of aluminosilicate fiber paper that is 50cm long, 10cm wide, and 3mm thick, and refer to... Figure 1 The image shows an electron microscope image of aluminosilicate fiber paper. The aluminosilicate fiber paper was placed in a sand core filter and wetted with a small amount of the first organic solvent.

[0102] Step 2: Based on the molar ratio range of hydrophobic siloxane coupling agent and tetraethyl orthosilicate (0.1-1.0):1, prepare four concentrations as follows:

[0103] (1) Concentration 1:0.1:1;

[0104] (2) Concentration 2:0.3:1;

[0105] (3) Concentration 3:0.6:1;

[0106] (4) Concentration 4:1:1.

[0107] The concentration of tetraethyl orthosilicate is 6 mol / mL; correspondingly, the concentrations of the hydrophobic siloxane coupling agent solvent (methyltrimethoxysilane) are 0.6 mol / mL (concentration 1), 1.8 mol / mL (concentration 2), 3.6 mol / mL (concentration 3) and 6 mol / mL (concentration 4).

[0108] Take 1 mL of 0.6 mol / mL methyltrimethoxysilane solvent (concentration 1 is the lowest concentration), 1 mL of 6 mol / mL tetraethyl orthosilicate, and 20 mol of the first organic solvent (methanol) and mix them to prepare a silicon mixture. Stir for 30 minutes and after hydrolysis, obtain aerogel silica sol.

[0109] The remaining three concentrations of hydrophobic siloxane coupling agent solvents, namely 1.8 mol / mL, 3.6 mol / mL, and 6 mol / mL, were used as gradient solvents.

[0110] Step 3: Using a vacuum pump to maintain a reduced pressure, the pressure is controlled within the range of 0MPa < P ≤ 0.098MPa. The gradient solvents (the remaining hydrophobic siloxane coupling agents of different concentrations) are introduced into the filter in order of increasing concentration. Specifically, the solvents are 0.24mL of 1.8mol / mL methyltrimethoxysilane, 0.05mL of 3.6mol / mL methyltrimethoxysilane, and 0.01mL of 6mol / mL methyltrimethoxysilane, with a preset interval of 30 minutes between each concentration.

[0111] Step 4: Let stand for 1.0 hour until the product is basically set. Gently remove it and place it flat in a petri dish. Use a suitable volatile organic solvent as the aging solution and age and dry it under normal pressure for 48 hours to finally obtain anisotropic composite fiber paper. (Reference) Figure 2 This is an electron microscope image of the composite fiber paper.

[0112] Example 2

[0113] The preparation method used in this embodiment is basically the same as that in Example 1, except that three concentrations were prepared in step 2, calculated based on the molar ratio of hydrophobic siloxane coupling agent and tetraethyl orthosilicate:

[0114] (1) Concentration 1:0.1:1;

[0115] (2) Concentration 2:0.3:1;

[0116] (3) Concentration 3:0.6:1.

[0117] Among them, concentration 1 (0.6 mol / mL) was used as the minimum concentration for preparing aerogel silica sol; the remaining concentrations 2 (1.8 mol / mL) and 3 (3.6 mol / mL) were used as gradient solvents.

[0118] Example 3

[0119] The preparation method used in this embodiment is basically the same as that in Example 1, except that the aerogel silica sol prepared in step 2 has two concentrations, calculated based on the molar ratio of hydrophobic siloxane coupling agent and tetraethyl orthosilicate:

[0120] (1) Concentration 1:0.1:1;

[0121] (2) Concentration 2:0.3:1.

[0122] Concentration 1 (0.6 mol / mL) was used as the minimum concentration for preparing aerogel silica sol; the remaining concentration 2 (1.8 mol / mL) was used as a gradient solvent.

[0123] Comparative Example 1

[0124] The preparation method used in this comparative example is basically the same as that in Example 1, except that the aerogel silica sol prepared in step 2 has a concentration of 1, calculated by the molar ratio of hydrophobic siloxane coupling agent and tetraethyl orthosilicate as 1:1, with a concentration of 6 mol / mL.

[0125] Comparative Example 2

[0126] To compare with composite fiber paper with anisotropic structure, step 3 of this comparative example does not use decompression treatment, and the rest of the preparation methods are basically the same as in Example 1.

[0127] Horizontal comparison test experiment:

[0128] The composite fiber papers prepared in Examples 1-3, Comparative Examples 1 and 2 were tested for their high-temperature resistance point, dimensional shrinkage at the highest high-temperature resistance point, and thermal conductivity at 300°C. The test results are as follows:

[0129] Table 2. Test results of heat resistance and thermal conductivity of fiber paper in the examples and comparative examples.

[0130]

[0131] Note: In the group items in the table above, "Real 1" is the abbreviation for Example 1, "Real 2" is the abbreviation for Example 2, "Real 3" is the abbreviation for Example 3, "Comparative 1" is the abbreviation for Comparative Example 1, and "Comparative 2" is the abbreviation for Comparative Example 2.

[0132] Experimental results:

[0133] (1) From Table 2 and Figure 4 and Figure 5The data comparison shows that the smaller the concentration gradient of the aerogel silica sol used in the preparation process of the composite fiber paper, the lower the maximum temperature resistance point reached. Specifically, the composite fiber papers in Examples 1-3 obtained using the method provided by this invention all have a maximum temperature resistance point exceeding 800℃, with Example 1 reaching 1020℃. Comparative Example 1, however, only reaches 750℃.

[0134] (2) The dimensional shrinkage rate at the highest temperature resistance point refers to the proportion of dimensional change of a material when it undergoes thermal expansion and contraction at high temperatures. The higher this value, the greater the dimensional change of the material at high temperatures. Experimental results show that the smaller the concentration gradient of the aerogel silica sol used, the greater the dimensional shrinkage rate at the highest temperature resistance point. Comparative Example 1 reached 24.2%.

[0135] (3) Thermal conductivity is a physical quantity that describes the thermal conductivity of a material. It represents the ability of a unit thickness of material to transfer heat under a temperature gradient per unit time. From the data in Table 2, and reference... Figure 4 As shown, it can be concluded that with the addition of silane coupling agents of different concentration gradients, the higher the thermal conductivity, the more gradients are added. Specifically, the ratio of Examples 1, 2, and 3 using the preparation method of this invention is 0.08 mW·m. -1 ·K -1 0.07mW·m -1 ·K -1 and 0.06mW·m -1 ·K -1 In contrast, Comparative Example 1, which did not employ the preparation method provided in this invention, only used a single gradient, resulting in a thermal conductivity of only 0.04 mW·m at 300°C. -1 ·K -1 This is because the fiber paper is anisotropic from top to bottom, and this structure makes heat transfer performance better and more convenient.

[0136] (4) Under the same conditions and preparation methods, in a comparative test experiment, Comparative Example 2 investigated the surface structure and morphology of the composite fiber paper prepared in step 3 without pressure reduction, i.e., under normal pressure. In Comparative Example 2, no pressure reduction was performed during the reaction between the aerogel and the fiber paper, resulting in the silane coupling agent (gradient solvent) being in a uniformly dispersed state, thus preventing the formation of functional and structural anisotropy. Reference Figure 3 The electron microscope images show that Comparative Example 2 not only lacks structural anisotropy, but its thermal conductivity is also greatly affected. Therefore, it can be determined that the fiber paper prepared in Comparative Example 2 under normal pressure has no anisotropy in structure or function.

[0137] In summary, the preparation method provided by this invention utilizes in-situ growth of anisotropic silica sol layers on the basis of aluminosilicate fiber paper to obtain a porous elastic interconnect network and a robust and flexible composite structure. Due to the addition of hydrophobic siloxane coupling agents, the cross-linking degree of aerogel is reduced, thereby improving flexibility. At the same time, the use of aerogel silica sol with multiple concentration gradients, and the preparation of anisotropic aerogel based on the change of concentration gradient combined with the decompression method, can ensure the heat resistance temperature of the fiber paper and avoid the defect of reducing the efficiency of heat transfer.

[0138] The above describes preferred embodiments and corresponding examples of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, including but not limited to adjustments in proportions, processes, and dosages. These modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing anisotropic silica-based aerogel composite fiber paper dried at ambient pressure, characterized in that, include: S1. Prepare at least two different concentrations of hydrophobic siloxane coupling agent solvents; take the hydrophobic siloxane coupling agent solvent with the lowest relative concentration, and prepare an aerogel silica sol with tetraethyl orthosilicate and a first organic solvent; and use the remaining concentrations of the hydrophobic siloxane coupling agent solvent as gradient solvents; wherein the molar ratio of the tetraethyl orthosilicate and the hydrophobic siloxane coupling agent is in the range of 1:(0.1-1.0); S2. Lay aluminum silicate fiber paper, and wet the upper surface of the aluminum silicate fiber paper with the first organic solvent. S3. The aerogel silica sol is added to the wetted surface of the aluminum silicate fiber paper under normal temperature and pressure conditions, so that the aerogel silica sol grows in situ on the surface of the aluminum silicate fiber paper to form a silica sol layer. S4. Under a reduced pressure of no more than 0.098 MPa, the gradient solvents are added sequentially to the silica sol layer according to the concentration from small to large to form siloxane layers of different concentrations; wherein, a preset interval of 0.5 hours to 1.0 hours is maintained before adding the next gradient solvent of a higher concentration. S5. Perform aging and drying treatment and static treatment to obtain the composite fiber paper.

2. The method for preparing anisotropic silica-based aerogel composite fiber paper dried at atmospheric pressure as described in claim 1, characterized in that, The different concentrations of hydrophobic siloxane coupling agent solvents were prepared based on the amount of tetraethyl orthosilicate.

3. The method for preparing anisotropic silica-based aerogel composite fiber paper dried at atmospheric pressure as described in claim 1, characterized in that, The aerogel silica sol is prepared by the tetraethyl orthosilicate, the hydrophobic siloxane coupling agent and the first organic solvent in a molar ratio of 1:(0.1-1.0):(10-50).

4. The method for preparing anisotropic silica-based aerogel composite fiber paper dried at atmospheric pressure as described in claim 1, characterized in that, The hydrophobic siloxane coupling agent is any one or more of methyltrimethoxysilane, methyltriethoxysilane, dimethoxydiethoxysilane, phenyltriethoxysilane, and trimethylmethoxysilane.

5. The method for preparing anisotropic silica-based aerogel composite fiber paper dried at atmospheric pressure as described in claim 1, characterized in that, The first organic solvent is any one or more of methanol, ethanol, propanol, isopropanol, n-butanol, tert-butanol, sec-butanol, pentanol and its isomers, hexanol and its isomers, and acetone.

6. The method for preparing anisotropic silica-based aerogel composite fiber paper dried at atmospheric pressure as described in claim 1, characterized in that, After the step of adding the aerogel silica sol to the wetted aluminosilicate fiber paper surface under normal temperature and pressure conditions, allowing the aerogel silica sol to grow in situ on the surface of the aluminosilicate fiber paper, a settling step is also included.

7. The method for preparing anisotropic silica-based aerogel composite fiber paper dried at atmospheric pressure as described in claim 6, characterized in that, The settling time is 0.5 hours to 3.0 hours.

8. The method for preparing anisotropic silica-based aerogel composite fiber paper dried at atmospheric pressure as described in claim 1, characterized in that, The aging and drying process is as follows: The second organic solvent was used as the aging solution, and aging and drying were carried out under normal pressure.

9. The method for preparing anisotropic silica-based aerogel composite fiber paper dried at atmospheric pressure as described in claim 8, characterized in that, The aging and drying process takes 12 to 60 hours.

10. The method for preparing anisotropic silica-based aerogel composite fiber paper dried at atmospheric pressure as described in claim 8, characterized in that, The aging and drying process is carried out at one atmosphere of atmospheric pressure.

11. The method for preparing anisotropic silica-based aerogel composite fiber paper dried at atmospheric pressure as described in claim 8, characterized in that, The second organic solvent is one or more of methanol, ethanol, propanol and acetone.

12. The method for preparing anisotropic silica-based aerogel composite fiber paper dried at atmospheric pressure as described in claim 1, characterized in that, The settling time for the static treatment is 6 to 60 hours.

13. The method for preparing anisotropic silica-based aerogel composite fiber paper dried at ambient pressure as described in claim 1, characterized in that, The aluminum silicate fiber paper has a length of 1cm-50cm, a width of 1cm-10cm, and a thickness of 1mm-4mm.

14. A composite fiber paper, characterized in that, It is prepared by the method for preparing anisotropic silicon-based aerogel composite fiber paper under normal pressure drying as described in any one of claims 1-3.

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