Bionic dual-network nanofiber aerogel with integrated functions of high-temperature heat insulation, low-frequency noise reduction and fire prevention and flame retardance and preparation method of bionic dual-network nanofiber aerogel

Abstract

The invention discloses bionic dual-network nanofiber aerogel with integrated functions of high-temperature heat insulation, low-frequency noise reduction and fire prevention and flame retardance and a preparation method of the nanofiber aerogel, and belongs to the technical field of fiber aerogel. The preparation method of the bionic dual-network nanofiber aerogel integrating the functions of high-temperature heat insulation, low-frequency noise reduction and fire prevention and flame retardance comprises the following steps: mixing a silane precursor, water and an acid catalyst to obtain hydrolyzed silane sol; adding Laponite powder into the hydrolyzed silane sol, so as to obtain a Laponite aqueous dispersion liquid; the preparation method comprises the following steps: preparing Laponite aqueous dispersion liquid, mixing the Laponite aqueous dispersion liquid with SiO2 nanofibers to obtain Laponite mixed SiO2 nanofiber dispersion liquid, carrying out directional freezing, and then carrying out vacuum drying and sintering to obtain the bionic double-network nanofiber aerogel (LAPSNAs) with integrated functions of high-temperature heat insulation, low-frequency noise reduction, fire prevention and flame retardance. Compared with the prior art, the material has wide-temperature-section compression resilience with constant temperature, good high-temperature heat insulation characteristic, excellent low-frequency noise reduction performance and fireproof and flame-retardant functions.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber aerogels, and particularly to a bionic double-network high-temperature heat insulation-low-frequency noise reduction-fire retardancy integrated nanofiber aerogel and a preparation method thereof. Background Art

[0002] Aerogel materials have been widely used in the fields of heat insulation, sound absorption and noise reduction, gas adsorption, etc. due to their good high porosity, high specific surface area and low density. However, its microstructure is a pearl chain structure composed of nanoparticles through an inter-neck connection method. The nanoparticles have a high surface energy and are extremely easy to sinter at high temperatures, resulting in structural collapse. At the same time, this connection method endows the aerogel with brittle characteristics, which is not conducive to coping with instantaneous impacts and large external force extrusion during actual application, and it is easy to cause structural cracks from the inside to the outside of the entire material, resulting in serious consequences. Using a silicon source containing organic groups (such as methyl, ethyl) can improve this situation and transform brittle aerogels into flexible aerogels, but they still cannot cope with extreme strains, and the plastic deformation after rebound is relatively high.

[0003] The nanofiber aerogel with one-dimensional nanofibers as the basic constituent unit changes the inter-neck connection method between the microscopic nanoparticles of the traditional aerogel into a fiber lap joint method, significantly improving the stress transmission method and efficiency. The prepared nanofiber aerogel has good resilience and is suitable for actual production applications. Generally, the interior of the nanofiber aerogel has an interpenetrating through-hole structure, and sound waves are easy to propagate outward through the holes and cannot be fully dissipated; by introducing a nanosheet structure to close these interpenetrating through-holes, constructing a complex one-dimensional nanofiber / two-dimensional nanosheet composite aerogel with a maze structure is expected to endow the nanofiber aerogel with excellent heat insulation and noise reduction properties at the same time.

[0004] In the existing technology, in order to achieve the stable and uniform preparation of materials when preparing nanofiber aerogels, a room-temperature organic binder is introduced and then removed by sintering; the removal of the organic matter will inevitably cause the shrinkage of the sample, affecting the uniformity of the material, and the process is cumbersome. At the same time, in order to achieve the functional integration of the material, researchers often use relatively complex technologies such as 3D printing to construct an aerogel material with a multi-level pore structure, increasing the time and process costs.

[0005] Patent CN202410918266.8 uses water as a solvent and mixes one or more of bacterial cellulose and its derivative nanofibers with a crosslinking agent, a crosslinking catalyst, a dispersant, and a thickening agent, and obtains a porous nanofiber aerogel through freeze-drying. However, in order to ensure the uniform stability of the material, an organic dispersant and a thickening agent are added, which not only increases the types of raw materials, increases the preparation cost and process complexity, but also the prepared material is not resistant to high temperatures. At the same time, due to the presence of organic substances, certain sample shrinkage is inevitably generated during the thermal crosslinking process, which is not conducive to maintaining the internal structure formed by its freeze-drying.

[0006] Patent CN202411467854.0 mixes ceramic particles with a binder and uses in-situ freezing technology as an aid to prepare an anisotropic ceramic aerogel by 3D printing technology. However, this technology requires strict control of the viscosity of the printing slurry and needs to be sintered at an ultra-high temperature of 2000 °C. The process is cumbersome and the synthesis cost is relatively high. Moreover, its minimum radial thermal conductivity at room temperature is close to 0.09 W·m -1 ·k -1 , which is much greater than the thermal conductivity of air (0.027 W·m -1 ·k -1 ), and is still at a relatively high level; although its noise reduction coefficient (NRC) is relatively high, the frequency range corresponding to its sound absorption peak is relatively narrow, and the sound absorption coefficient of its anisotropic material is mostly below 0.6 when it is below 2000 Hz, which is not conducive to absorbing unknown frequency noises.

[0007] Therefore, there is an urgent need to develop a functional integrated nanofiber composite aerogel with a simple method and low cost, making high-temperature heat insulation, low-frequency sound absorption, and fire retardancy under extreme conditions possible. Summary of the Invention

[0008] The purpose of the present invention is to provide a bionic double-network high-temperature heat insulation-low-frequency noise reduction-fire retardancy functional integrated nanofiber aerogel and its preparation method to solve the above problems in the background technology.

[0009] To achieve the above purpose, the present invention provides the following technical solutions:

[0010] One of the technical solutions of the present invention: provides a preparation method of a bionic double-network high-temperature heat insulation-low-frequency noise reduction-fire retardancy functional integrated nanofiber aerogel, including the following steps:

[0011] Mix a silane precursor, water, and an acid catalyst to obtain a hydrolyzed silane sol;

[0012] Add Laponite powder to the hydrolyzed silane sol to obtain a Laponite aqueous dispersion;

[0013] Mix the Laponite aqueous dispersion with SiO 2 nanofibers to obtain a Laponite mixed SiO 2 nanofiber dispersion, subject it to directional freezing, then vacuum drying and sintering to obtain the bionic double-network high-temperature heat insulation-low-frequency noise reduction-fire retardant integrated nanofiber aerogel.

[0014] Preferably, the step of mixing the silane precursor, water and acid catalyst is as follows: First, add water to a container, add the acid catalyst after stable stirring, and then add the silane precursor after stabilization. After sufficient stirring and hydrolysis, the hydrolyzed silane sol is obtained; the hydrolysis time is 0.5 - 3 h.

[0015] More preferably, during the high-speed homogenization and dispersion, use an ice-water bath to ensure that the temperature of the slurry is within the range of 20 - 40 °C to prevent gelation due to a rapid increase in the solution temperature, thereby obtaining a viscous and stable Laponite aqueous dispersion.

[0016] This process needs to ensure appropriate rotation speed and time to prevent the mixed slurry from showing shear thinning or rapid gelation phenomena.

[0017] Preferably, the silane precursor is one or more of methyltrimethoxysilane, methyltriethoxysilane, methyl orthosilicate, and tetraethyl orthosilicate; the acid catalyst is acetic acid and / or oxalic acid.

[0018] Preferably, the volume ratio of water, silane precursor and acid catalyst is 90:0.71 - 2.14:0.036.

[0019] Preferably, the mass ratio of water, SiO 2 nanofibers and Laponite powder is 90:0.3 - 0.9:0.09 - 0.9.

[0020] Preferably, the preparation method of the SiO 2 nanofibers is as follows: First, cut the SiO 2 nanofiber non-woven fabric into small pieces, and use a wall breaker for pre-cutting for 3 min to obtain a SiO 2 nanofiber suspension without obvious SiO 2 nanofiber non-woven fabric small pieces, then perform homogenizing cutting at a rotation speed of 13000 r / min for 20 min to obtain a homogeneous liquid, and then dry it at 120 °C for 24 h to obtain the SiO 2 nanofibers.

[0021] Preferably, the directional freezing is as follows: Subject the Laponite mixed SiO 2The nanofiber dispersion is placed into a mold, and then the mold is placed into an ultra-low temperature storage box with a unidirectional temperature gradient distribution for directional freezing; the bottom of the mold contacts with the copper block of the ultra-low temperature storage box, and the copper block plays a role in unidirectional freezing. The temperature of the copper block is -86°C, and the time for directional freezing is 20 - 180 min.

[0022] Preferably, the internal environment temperature of the dryer during vacuum drying is -50°C to 50°C, the temperature of the water-cooled trap is -70°C to -45°C, the time is 24 - 96 h, and the vacuum degree is 5 - 30 Pa; for sintering, it is heated to 900°C at a heating rate of 1 - 2°C / min and then held for 120 min, and the atmosphere for sintering is air atmosphere.

[0023] The second technical solution of the present invention: provides a preparation method of a bionic double-network high-temperature heat insulation - low-frequency noise reduction - fireproof and flame-retardant functional integrated gradient density nanofiber aerogel, including the following steps:

[0024] (1) Mix a silane precursor, water, and an acid catalyst to obtain a hydrolyzed silane sol; add Laponite powder to the hydrolyzed silane sol to obtain a Laponite aqueous dispersion.

[0025] (2) Mix the Laponite aqueous dispersion with SiO 2 nanofibers to obtain a first Laponite - mixed SiO 2 nanofiber dispersion.

[0026] (3) Repeat step (2) to prepare N Laponite - mixed SiO 2 nanofiber dispersions with the same or different SiO 2 nanofiber concentrations.

[0027] (4) Before the first Laponite - mixed SiO 2 nanofiber dispersion is directionally frozen until completely frozen and solidified, repeatedly add N Laponite - mixed SiO 2 nanofiber dispersions for directional freezing.

[0028] (5) Vacuum dry and sinter the product of step (4) to obtain the bionic double-network high-temperature heat insulation - low-frequency noise reduction - fireproof and flame-retardant functional integrated gradient density nanofiber aerogel.

[0029] The third technical solution of the present invention: Provide a bionic double-network high-temperature heat insulation-low-frequency noise reduction-fire retardant functional integrated nanofiber aerogel obtained according to the above preparation method. The nanofiber aerogel is composed of a bionic loofah network structure and a kagome structure network. On a large scale, it is a bionic loofah network structure in which fibers are cross-linked and fixed by a silane sol. On a small scale, it is a kagome structure network composed of nanosheets between fiber pores.

[0030] Preferably, the density of the composite aerogel is 5-40 mg / cm 3 , the porosity is 98.75-99.14%, the thermal conductivity at room temperature is 0.027-0.032 W·m -1 ·k -1 , the high-temperature thermal conductivity at 800 °C is 0.0749-0.0886 W·m -1 ·k -1 , and the noise reduction coefficient NRC value is 0.40-0.76.

[0031] The technical principle of the present invention is as follows:

[0032] Laponite is a synthetic lithium montmorillonite nanoclay that forms a card-house structure during continuous stirring to achieve thickening, so no additional binder is required. After the stirring is completed, during the directional freezing process, the Laponite nanosheets with this card-house structure will be squeezed into the fiber wall by the directionally frozen ice crystals. This disordered arrangement of Laponite nanosheet structures fills the through holes in the aerogel, which is expected to enhance the reflection and dissipation of sound waves. Moreover, during the reaction and forming process, there are various interaction forces between Laponite, silane sol, and SiO 2 nanofibers, which ensure the structural stability of LAPSNAs after forming. The hydrolyzed silane sol has abundant hydroxyl groups. The Laponite nanosheets are adsorbed and bonded in the silica sol through hydrogen bonding and the electrostatic interaction between the positively charged Na ions and the silica sol. At the same time, during the high-speed stirring process, the silica sol and Laponite nanosheets are fully mixed and approach each other continuously. The electrostatic interaction between the free Na ions in Laponite and the O atoms with lone pairs of electrons in the silica sol will prompt them to form abundant coordination bonds. In addition, the hydrogen bonds between the hydroxyl groups in SiO 2 nanofibers, hydrolyzed silica sol, and Laponite nanosheets further enhance the interaction between the components of the composite material. After high-temperature sintering, SiO 2Dehydration occurs between the nanofibers and the silane sol, as well as between the hydroxyl groups of the silane sol itself, to form a more stable Si-O-Si structure, further enhancing the structural stability of the composite material. Based on this, the prepared LAPSNAs have extremely strong structural stability, which is also the basis for ensuring their functional integration.

[0033] Natural loofah sponge has a maze structure with reticular through-holes. In this structure, heat transfer needs to proceed along complex channels, greatly extending the path of heat transfer and reducing the efficiency of heat transfer. At the same time, numerous through-holes and tortuous channels in this maze structure can effectively impede the flow of air, reducing the heat convection effect. And the inner wall of this maze structure will absorb and reflect heat radiation multiple times, reducing heat radiation. In addition, this structure also has a strong restricting effect on sound wave transmission. When sound waves enter the maze structure of the reticular through-holes, they will cause the vibration of the air inside the structure, and the vibration will cause friction between it and the wall surface, converting the sound energy into heat energy and dissipating it. At the same time, this complex maze structure contains through-holes and cavities of various sizes and shapes, and its natural frequency may match sound waves of different frequencies, resulting in resonance phenomena. Therefore, the broadband noise reduction performance of the structure may be improved in this complex network structure. To sum up, the reticular through-hole maze structure of natural loofah sponge has natural advantages in heat insulation and noise reduction, and is expected to construct an integrated heat insulation and noise reduction material. Inspired by this, in the present invention, through the method of directional freeze-drying, the extrusion effect of ice crystals on SiO 2 nanofibers is utilized, so that single fibers are gradually assembled into a fiber bundle structure. The fiber bundles are continuously connected and intertwined, gradually forming a complex reticular maze structure, and constructing a nanofiber aerogel with a biomimetic loofah sponge network structure. This aerogel is composed of a first-level large-scale biomimetic loofah sponge network structure and a second-level kagome network structure between the fiber bundles, and is a good insulator for heat and sound waves.

[0034] Based on the above principles, the present invention designs and prepares a biomimetic double-network nanofiber aerogel, aiming to improve the high-temperature heat insulation, low-frequency noise reduction and fire retardancy performance of the aerogel, and realize the characteristics of functional integration.

[0035] The beneficial technical effects of the present invention are as follows:

[0036] The present invention utilizes the kagome network structure generated by Laponite during the high-speed homogenization process and the bionic loofah-like structure formed during the directional freeze-drying process to construct a bionic double-network nanofiber aerogel with integrated functions of high-temperature heat insulation, low-frequency noise reduction, and fire retardancy. The primary loofah-like network structure affects solid-state heat conduction and radiation reflection, the secondary kagome network structure affects gaseous heat conduction and heat convection, and the tertiary nanosheet-like structure affects the diffusion of oxygen and heat, which is conducive to the formation of a physical heat insulation layer to prevent the transfer of heat, oxygen, and combustible volatiles. At the same time, Laponite has high thermal stability and can maintain the integrity of the structure at high temperatures, thereby prolonging the fire resistance time of the material. In addition, when sound waves pass through the internal pores of the nanofiber aerogel, they will generate frictional dissipation with the fiber wall surface and are reflected by the kagome network structure between the fiber bundles, extending the propagation path of the sound waves and dissipating fully within the kagome structure, further enhancing the dissipation effect of the sound waves. Therefore, the prepared bionic double-network nanofiber aerogel has the integrated characteristics of high-temperature heat insulation, low-frequency noise reduction, and fire retardancy, and is expected to be used for material coating applications under extreme conditions.

[0037] The present invention utilizes the kagome structure formed by Laponite to enhance the viscosity of the mixed slurry, which can maintain a stable and uniform suspension state for a long time and will not settle due to its own gravity during the process of being extruded by ice crystals during directional freezing. This enables the preparation of a super-low-density nanofiber aerogel with a uniform and stable structure without the need for a room-temperature binder, reducing the use of additional raw materials, greatly reducing the weight of material coating, and being efficient and environmentally friendly. This stable preparation method can easily prepare large samples of aerogel that meet industrial production requirements, and at the same time has strong expandability and customizability. For different actual industrial production needs, it can be customized into shapes such as dumbbell-shaped, triangular, tubular, square, circular, and any letter shape, etc., and the size, thickness, and dimensions can be adjusted arbitrarily, showing flexible expandability and being expected to be applied to key and complex parts of equipment.

[0038] The density of the bionic double-network high-temperature heat insulation - low-frequency noise reduction - fire retardant functional integrated nanofiber aerogel prepared by the present invention is 5 - 40 mg / cm 3 , the porosity is 98.75 - 99.14%, the room-temperature thermal conductivity is 0.027 - 0.032 W·m -1 ·k -1 , and the high-temperature thermal conductivity at 800 °C is 0.0749 - 0.0886 W·m -1 ·k -1, the noise reduction coefficient NRC value is 0.40 - 0.76, and the maximum heat resistance can reach 1000 °C. At the same time, this aerogel has superelasticity with constant temperature and can still maintain good compression and rebound performance in liquid nitrogen and the flame of a butane spray gun. In addition, in the actual high-temperature pipeline coating experiment and the noise reduction experiment of the actual noise source of this aerogel, it shows better high-temperature heat insulation performance and low-frequency sound absorption performance than commercial heat insulation and sound absorption materials respectively. The preparation method of the present invention is simple, environmentally friendly, low-cost, and has a wide range of application fields, and can meet the coating applications of various complex components in extreme environments. Brief Description of the Drawings

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0040] Figure 1 It is the bionic structure, principle and microstructural diagram of Example 1 of the bionic double-network aerogel of the present invention. Among them, (a) is the card house structure in architecture; (b) is the card house structure formed by nanosheets in the product of Example 1; (c) is the Laponite nanosheet network structure in the product of Example 1; (d) is the natural loofah structure; (e) is the enlarged view of the natural loofah structure; (f) is the bionic loofah network structure in the product of Example 1.

[0041] Figure 2 It is the physical diagram of the Laponite mixed SiO 2 nanofiber dispersion liquid and the large-sized aerogel prepared according to the method of Example 1. Among them, (a) is the physical diagram of the Laponite mixed SiO 2 nanofiber dispersion liquid; (b) is the physical diagram of the large-sized aerogel with a size of 2300 cm 3 .

[0042] Figure 3 In (a) is the physical diagram of the ultra-light aerogel prepared in Example 11, and (b) is the physical diagram of aerogels with various sizes and shapes prepared according to the method of Example 1.

[0043] Figure 4 It is the micro-morphology diagram of the products of Examples 1, 7 - 9. Among them, (a)-(d) are LAP0.1SNA; (e)-(h) are LAP0.4SNA; (i)-(l) are LAP0.7SNA; (m)-(p) are LAP1.0SNA.

[0044] Figure 5Microscopic morphology diagrams of the products of Examples 1, 4 - 6. Among them, (a)-(d) are for LAPSNA 0.5; (e)-(h) are for LAPSNA 1.0; (i)-(l) are for LAPSNA 1.5; (m)-(p) are for LAPSNA 2.0.

[0045] Figure 6 Shows the compression and resilience performance of the product of Example 4 at extreme temperatures. Among them, (a) is the resilience of the product in the butane torch flame at 1000 °C; (b) is the resilience of the product in liquid nitrogen at -196 °C.

[0046] Figure 7 Morphology and heat insulation performance of the samples of Examples 1, 7 - 9. Among them, (a) is the physical picture of the sample; (b) is the density and normal temperature thermal conductivity of the sample; (c) is the high temperature thermal conductivity of the sample.

[0047] Figure 8 Morphology and heat insulation performance of the samples of Examples 1, 4 - 6. Among them, (a) is the physical picture of the sample; (b) is the density and normal temperature thermal conductivity of the sample; (c) is the high temperature thermal conductivity of the sample.

[0048] Figure 9 Comparison diagram of high temperature resistance performance of the sample of Example 1 with carbon fiber felt, glass fiber needle punched felt, and glass fiber felt on a flat plate heater. Among them, (a) is the optical image; (b)-(d) are the infrared images after different heating times.

[0049] Figure 10 High temperature resistance performance diagram of the sample of Example 1 on an alcohol lamp flame. Among them, (a) is the optical image; (b)-(d) are the infrared images after different heating times.

[0050] Figure 11 High temperature resistance performance diagram of the sample of Example 1 in a butane torch flame. Among them, (a) is the optical image; (b)-(d) are the infrared images after different heating times.

[0051] Figure 12 Temperature difference diagram between the hot and cold surfaces of the sample of Example 1 under a butane torch.

[0052] Figure 13 Morphology and sound absorption performance diagrams of the samples of Examples 1, 11 - 13. Among them, (a) is the physical picture; (b) is the sound absorption coefficient curve; (c) is the noise reduction coefficient value (NRC).

[0053] Figure 14 Sound absorption performance diagrams of the samples of Example 1 with different thicknesses. Among them, (a) is the sound absorption coefficient curve; (b) is the noise reduction coefficient value (NRC).

[0054] Figure 15 Morphology and sound absorption performance diagrams of the samples of Example 1 and Examples 4 - 6. Among them, (a) is a physical picture; (b) is the sound absorption coefficient curve; (c) is the NRC value.

[0055] Figure 16 Morphology and sound absorption performance diagrams of the samples of Example 1 and Examples 7 - 9. Among them, (a) is a physical picture; (b) is the sound absorption coefficient curve; (c) is the NRC value.

[0056] Figure 17 Fundamental properties and air flow resistance diagrams of the samples of Example 1 and Examples 7 - 9. Among them, (a) is the porosity and density; (b) is the air flow resistance.

[0057] Figure 18 Absolute sound pressure distribution diagrams of the samples of Example 1 and Examples 7 - 9.

[0058] Figure 19 Comparison diagrams of the sound absorption performance between the sample of Example 1 and other materials. Among them, (a) is the comparison of the sound absorption coefficient curves between the sample and commercial sound - absorbing cotton; (b) is the relationship between the NRC values and the surface density of different sound - absorbing materials.

[0059] Figure 20 Morphology diagrams of the sample of Example 16. Among them, (a) is the macroscopic morphology diagram; (b) is the microscopic morphology diagram of the gradient density structure.

[0060] Figure 21 Sound absorption performance of the samples of Example 16 - 20. Among them, (a) is the sound absorption coefficient curve; (b) is the NRC value.

[0061] Figure 22 Absolute sound pressure distribution of the samples of Example 16 - 20.

[0062] Figure 23 Comparison diagram of the actual pipeline coating heat insulation performance between the sample of Example 1 and glass fiber felt. Among them, (a) is the physical picture of the semi - tubular sample; (b) is the physical picture of the sample coated on the high - temperature steam pipeline; (c) is the infrared image of the sample coated on the high - temperature steam pipeline; (d) is the physical picture of the semi - tubular glass fiber felt; (e) is the physical picture of the glass fiber felt coated on the high - temperature steam pipeline; (f) is the infrared image of the glass fiber felt coated on the high - temperature steam pipeline.

[0063] Figure 24 Actual pipeline coating simulation diagrams of the sample of Example 1 and glass fiber felt. Among them, (a) is the simulation result of the sample coated on the high - temperature pipeline; (b) is the simulation result of the glass fiber felt coated on the high - temperature pipeline.

[0064] Figure 25Comparison chart of the cladding thickness of the sample of Example 15 and the original glass wool product used in the ship pipeline when maintaining the same outer surface temperature.

[0065] Figure 26 Sound intensity cloud map results of the sample of Example 1 and commercial sound-absorbing cotton. Among them, (a) is the diagram of the sound intensity cloud map test device; (b) is the sound intensity cloud map without materials; (c) is the sound intensity cloud map when covered with commercial sound-absorbing cotton; (d) is the sound intensity cloud map when covered with the prepared material.

[0066] Figure 27 Schematic diagram of the force mechanism between components during the forming process of the samples of Examples 1-20 of the present invention. Detailed implementation manners

[0067] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention. It should be understood that the terms described in the present invention are only used to describe specific implementation manners and are not used to limit the present invention.

[0068] In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0069] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention.

[0070] Regarding the terms "comprising", "including", "having", "containing", etc. used in the present invention, they are all open-ended terms, meaning including but not limited to.

[0071] SiO used in the following examples and comparative examples of the present invention 2 The preparation method of the nanofibers is as follows: First, cut the SiO 2 nanofiber non-woven fabric into small pieces, and use a wall breaker for pre-cutting for 3 minutes to obtain SiO without obvious 2 nanofiber non-woven fabric small pieces of SiO 2 nanofiber suspension, and then use a T25 easy clean high-speed homogenizer to perform homogenization cutting at a speed of 13000 r / min for 20 minutes to obtain a homogenate, and then dry it in an oven at 120 °C for 24 hours to obtain single SiO2 Nanofibers.

[0072] In the present invention, "normal temperature" is calculated as 20 - 30°C unless otherwise specified.

[0073] In the present invention, raw materials are all of analytical purity unless otherwise specified.

[0074] All raw materials used in the following examples and comparative examples of the present invention are commercially available products.

[0075] Example 1

[0076] Preparation of nanofiber aerogel:

[0077] Add 90 g of deionized water and 0.036 ml of acetic acid into a 150 mL beaker, place it in a magnetic stirrer and stir evenly at a speed of 1200 r / min. Then add 2.14 ml of methyltrimethoxysilane solution, increase the stirring speed to 1800 r / min and continue stirring for 0.5 h to obtain a stable hydrolyzed silane sol. Subsequently, add 0.9 g of Laponite powder into the hydrolyzed silane sol, and homogenize and cut it at a speed of 10000 r / min for 10 min by a T18 easy clean high-speed homogenizer to obtain a stable Laponite aqueous dispersion. Then transfer the stable Laponite aqueous dispersion into a magnetic stirrer, continue stirring until stable and add 0.9 g of SiO 2 nanofibers, continue stirring at a speed of 1800 r / min for 0.5 h to obtain a stable Laponite mixed SiO 2 nanofiber dispersion.

[0078] Pour the stable Laponite mixed SiO 2 nanofiber dispersion into a polytetrafluoroethylene mold, then place the mold into an ultra-low temperature storage box with -86°C. The bottom of the mold is in contact with the copper block in the directional freezing device, and the copper block plays a role in directional freezing. Carry out directional freezing for 30 min when the temperature of the copper block is -86°C. During the directional freezing process, the mold needs to be covered with thick heat insulation cotton to isolate the heat transfer from all around and ensure the unidirectionality of the freezing process.

[0079] After the whole slurry is completely frozen into a block, quickly transfer it into a freeze dryer and dry it by vacuum drying for 24 h at a vacuum degree of 5.7 Pa and a supplementary water cold trap temperature of -60°C to obtain the aerogel to be sintered. Then transfer it into a muffle furnace, heat it to 900°C at a heating rate of 1°C / min in an air atmosphere, and keep it warm for 120 min to obtain the nanofiber aerogel (denoted as LAPSNA1.0 or LAP1.0SNA).

[0080] Example 2

[0081] The difference from Example 1 is only that methyltrimethoxysilane is replaced with an equal volume of methyltriethoxysilane, the stirring time in the stage of preparing the hydrolyzed silane sol is modified to 3 h, and the vacuum degree in the vacuum drying stage is modified to 10.2 Pa and the time is modified to 28 h.

[0082] Example 3

[0083] The difference from Example 1 is only that acetic acid is replaced with an equal volume of oxalic acid, methyltrimethoxysilane is replaced with an equal volume of tetraethyl orthosilicate, the vacuum degree in the vacuum drying stage is modified to 7.3 Pa and the time is modified to 36 h, and the heating rate in the sintering stage is modified to 2 °C / min.

[0084] Examples 1 - 3 are for preparing LAPSNAs using different silane precursors and acid catalysts.

[0085] Example 4

[0086] The difference from Example 1 is only that 2.14 ml of methyltrimethoxysilane solution is replaced with 1.07 ml of methyltriethoxysilane solution, and the vacuum degree in the vacuum drying stage is modified to 6.1 Pa, and the obtained product is denoted as LAPSNA0.5.

[0087] Example 5

[0088] The difference from Example 1 is only that the addition amount of methyltrimethoxysilane solution is modified to 3.20 ml, and the vacuum degree in the vacuum drying stage is modified to 5.8 Pa, and the obtained product is denoted as LAPSNA1.5.

[0089] Example 6

[0090] The difference from Example 1 is only that 2.14 ml of methyltrimethoxysilane solution is replaced with 4.27 ml of methyltriethoxysilane solution, and the vacuum degree in the vacuum drying stage is modified to 9.2 Pa, and the obtained product is denoted as LAPSNA2.0.

[0091] Examples 1, 4 - 6 are for preparing LAPSNAs with different silane sol contents.

[0092] Example 7

[0093] The difference from Example 1 is only that methyltrimethoxysilane is replaced with an equal volume of methyltriethoxysilane, the addition amount of Laponite powder is modified to 0.09 g, and the vacuum degree in the vacuum drying stage is modified to 11.3 Pa, and the obtained product is denoted as LAP0.1SNA.

[0094] Example 8

[0095] The difference from Example 1 is only that methyltrimethoxysilane is replaced with an equal volume of methyltriethoxysilane, the addition amount of Laponite powder is modified to 0.36 g, and the vacuum degree in the vacuum drying stage is modified to 14.4 Pa. The obtained product is denoted as LAP0.4SNA.

[0096] Example 9

[0097] The difference from Example 1 is only that methyltrimethoxysilane is replaced with an equal volume of methyltriethoxysilane, the addition amount of Laponite powder is modified to 0.63 g, and the vacuum degree in the vacuum drying stage is modified to 11.3 Pa. The obtained product is denoted as LAP0.7SNA.

[0098] Examples 1, 7 - 9 are for preparing LAPSNAs with different Laponite contents.

[0099] Example 10

[0100] The difference from Example 1 is only that 2.14 ml of methyltrimethoxysilane solution is replaced with 0.71 ml of methyltriethoxysilane solution, the addition amount of Laponite powder is modified to 0.30 g, the addition amount of SiO 2 nanofibers is modified to 0.30 g, and the vacuum degree in the vacuum drying stage is modified to 12.7 Pa.

[0101] Example 11

[0102] The difference from Example 1 is only that 2.14 ml of methyltrimethoxysilane solution is replaced with 1.07 ml of methyltriethoxysilane solution, the addition amount of Laponite powder is modified to 0.45 g, the addition amount of SiO 2 nanofibers is modified to 0.45 g, and the vacuum degree in the vacuum drying stage is modified to 15.1 Pa.

[0103] Example 12

[0104] The difference from Example 1 is only that 2.14 ml of methyltrimethoxysilane solution is replaced with 1.42 ml of methyltriethoxysilane solution, the addition amount of Laponite powder is modified to 0.60 g, the addition amount of SiO 2 nanofibers is modified to 0.60 g, and the vacuum degree in the vacuum drying stage is modified to 13.2 Pa.

[0105] Example 13

[0106] The difference from Example 1 is only that 2.14 ml of methyltrimethoxysilane solution is replaced by 1.78 ml of methyltriethoxysilane solution, the addition amount of Laponite powder is modified to 0.75 g, the addition amount of SiO 2 nanofibers is modified to 0.75 g, and the vacuum degree in the vacuum drying stage is modified to 13.4 Pa.

[0107] Examples 1, 10 - 13 are for preparing LAPSNAs with different densities.

[0108] Example 14 (large-scale sample)

[0109] Add 800 g of deionized water and 0.32 ml of acetic acid into a 1000 mL beaker, place it in a magnetic stirrer and stir evenly at a speed of 1200 r / min. Then add 18.99 ml of methyltriethoxysilane solution, increase the stirring speed to 1800 r / min and continue stirring for 0.5 h to obtain a stable hydrolyzed silane sol. Subsequently, add 8 g of Laponite powder into the hydrolyzed silane sol, and homogenize and cut it at a speed of 10000 r / min for 10 min by a T18 easy clean high-speed homogenizer to obtain a stable Laponite aqueous dispersion. Then transfer the stable Laponite aqueous dispersion into a magnetic stirrer, continue stirring until stable and then add 8 g of SiO 2 nanofibers, and continue stirring at a speed of 2000 r / min for 0.5 h to obtain a stable Laponite mixed SiO 2 nanofiber dispersion.

[0110] Repeat the above operations 2 more times to obtain 3 cups of the same Laponite mixed SiO 2 nanofiber dispersion. Then pour it into an extra-large polytetrafluoroethylene mold (size: 34 cm * 34 cm * 2.5 cm), and then place the mold in an ultra-low temperature storage box with -86 °C. The bottom of the mold is in contact with the copper block in the directional freezing device, and the copper block plays a role in directional freezing. Conduct directional freezing for 90 min when the temperature of the copper block is -86 °C. During the directional freezing process, the mold needs to be covered with thick heat insulation cotton to isolate the heat transfer from all around and ensure the unidirectionality of the freezing process.

[0111] After the whole slurry is completely frozen into a block, quickly transfer it into a freeze dryer, and dry it by vacuum drying for 72 h at a vacuum degree of 16.7 Pa and a supplementary water-cooled trap temperature of -60 °C to obtain the aerogel to be sintered. Then transfer it into a muffle furnace, heat it to 900 °C at a heating rate of 1 °C / min in an air atmosphere, and keep it at this temperature for 120 min to obtain the nanofiber aerogel.

[0112] Example 15 (Sample of High-temperature Insulating Pipeline Coating)

[0113] Preparation of nanofiber aerogel:

[0114] Add 270 g of deionized water and 0.108 ml of acetic acid into a 500 mL beaker. After placing it in a magnetic stirrer and stirring evenly at a speed of 1200 r / min, add 6.41 ml of methyltrimethoxysilane solution. Increase the stirring speed to 1800 r / min and continue stirring for 0.5 h to obtain a stable hydrolyzed silane sol. Subsequently, add 0.27 g of Laponite powder into the hydrolyzed silane sol, and homogenize and cut it at a speed of 10000 r / min for 10 min by a T18 easy clean high-speed homogenizer to obtain a stable Laponite aqueous dispersion. Then transfer the stable Laponite aqueous dispersion into a magnetic stirrer. After continuous stirring and stabilization, add 2.7 g of SiO 2 nanofibers, and continue stirring at a speed of 1800 r / min for 0.5 h to obtain a stable Laponite mixed SiO 2 nanofiber dispersion.

[0115] Pour the stable Laponite mixed SiO 2 nanofiber dispersion into a tubular polytetrafluoroethylene mold. Then place the mold in a cryogenic storage box with a temperature of -86°C. The bottom of the mold is in contact with the copper block in the directional freezing device, and the copper block plays a role in directional freezing. Conduct directional freezing for 180 min when the temperature of the copper block is -86°C. During the directional freezing process, the mold needs to be covered with thick heat-insulating cotton to isolate the heat transfer from all around and ensure the unidirectionality of the freezing process.

[0116] After the entire slurry is completely frozen into a block, quickly transfer it into a freeze dryer. Dry it by vacuum drying for 96 h at a vacuum degree of 10.2 Pa and a supplementary water-cooled trap temperature of -60°C to obtain the aerogel to be sintered. Then transfer it into a muffle furnace. Under an air atmosphere, heat it to 900°C at a heating rate of 1°C / min and hold for 120 min to obtain the nanofiber aerogel.

[0117] Example 16

[0118] Preparation of gradient density nanofiber aerogel:

[0119] Respectively take the Laponite mixed SiO 2 nanofiber dispersions prepared in Example 1, Example 10, and Example 12.

[0120] First, the Laponite mixed SiO 2The nanofiber dispersion was poured into a polytetrafluoroethylene mold, and then the mold was placed in an ultra-low temperature storage box at -86°C. The bottom of the mold was in contact with the copper block in the directional freezing device. Before the entire slurry was almost completely frozen into a block (only a layer of molten slurry remained on the surface, and the required directional freezing time was 10 min), the dispersion in Example 12 was poured in. Before the entire slurry was almost completely frozen into a block (only a layer of molten slurry remained on the surface, and the required directional freezing time was 12 min), the dispersion in Example 10 was poured in to continue the freezing process. After the entire slurry was completely frozen into a block (the required directional freezing time was 14 min), it was quickly transferred to a freeze dryer and dried for 32 h by gradient heating vacuum drying at a vacuum degree of 8.2 Pa and a supplementary water cold trap temperature of -60°C to obtain the aerogel to be sintered. Then it was transferred to a muffle furnace and heated to 900°C at a heating rate of 1°C / min in an air atmosphere and held for 120 min to obtain a gradient density nanofiber aerogel (denoted as LG-LAPSNA-SL).

[0121] Example 17

[0122] Preparation of gradient density nanofiber aerogel:

[0123] Respectively take the Laponite mixed SiO prepared in Example 11, Example 12 and Example 13 2 nanofiber dispersion.

[0124] First, the dispersion in Example 13 was poured into a polytetrafluoroethylene mold, and then the mold was placed in an ultra-low temperature storage box at -86°C. The bottom of the mold was in contact with the copper block in the directional freezing device. Before the entire slurry was almost completely frozen into a block (only a layer of molten slurry remained on the surface, and the required directional freezing time was 10 min), the dispersion in Example 12 was poured in. Before the entire slurry was almost completely frozen into a block (only a layer of molten slurry remained on the surface, and the required directional freezing time was 12 min), the dispersion in Example 11 was poured in to continue the freezing process. After the entire slurry was completely frozen into a block (the required directional freezing time was 14 min), it was quickly transferred to a freeze dryer and dried for 32 h by gradient heating vacuum drying at a vacuum degree of 17.1 Pa and a supplementary water cold trap temperature of -60°C to obtain the aerogel to be sintered. Then it was transferred to a muffle furnace and heated to 900°C at a heating rate of 1°C / min in an air atmosphere and held for 120 min to obtain a gradient density nanofiber aerogel (denoted as SG-LAPSNA-SL).

[0125] Example 18

[0126] Preparation of gradient density nanofiber aerogel:

[0127] Take 3 portions of the Laponite prepared in Example 12 and mix with SiO 2 nano-fiber dispersion liquid.

[0128] First, pour the dispersion liquid in the first cup of Example 12 into a polytetrafluoroethylene mold, then place the mold in an ultra-low temperature storage box at -86°C. The bottom of the mold is in contact with the copper block in the directional freezing device. Before the entire slurry is almost completely frozen into a block (only a layer of molten slurry remains on the surface, and the required directional freezing time is 10 min), pour the dispersion liquid in the second cup of Example 12. Before the entire slurry is almost completely frozen into a block (only a layer of molten slurry remains on the surface, and the required directional freezing time is 12 min), pour the dispersion liquid in the third cup of Example 12 to continue the freezing process. After the entire slurry is completely frozen into a block (the required directional freezing time is 14 min), quickly transfer it to a freeze dryer and dry it for 32 h by gradient heating vacuum drying at a vacuum degree of 10.8 Pa and a supplementary water-cooled trap temperature of -60°C to obtain the aerogel to be sintered. Then transfer it to a muffle furnace and heat it to 900°C at a heating rate of 1°C / min in an air atmosphere and hold for 120 min to obtain a gradient density nano-fiber aerogel (denoted as UG-LAPSNA).

[0129] Example 19

[0130] Preparation of gradient density nano-fiber aerogel:

[0131] Take the Laponite prepared in Example 11, Example 12, and Example 13 respectively and mix with SiO 2 nano-fiber dispersion liquid.

[0132] First, pour the dispersion liquid in Example 11 into a polytetrafluoroethylene mold, then place the mold in an ultra-low temperature storage box at -86°C. The bottom of the mold is in contact with the copper block in the directional freezing device. Before the entire slurry is almost completely frozen into a block (only a layer of molten slurry remains on the surface, and the required directional freezing time is 10 min), pour the dispersion liquid in Example 12. Before the entire slurry is almost completely frozen into a block (only a layer of molten slurry remains on the surface, and the required directional freezing time is 12 min), pour the dispersion liquid in Example 13 to continue the freezing process. After the entire slurry is completely frozen into a block (the required directional freezing time is 14 min), quickly transfer it to a freeze dryer and dry it for 32 h by gradient heating vacuum drying at a vacuum degree of 17.1 Pa and a supplementary water-cooled trap temperature of -60°C to obtain the aerogel to be sintered. Then transfer it to a muffle furnace and heat it to 900°C at a heating rate of 1°C / min in an air atmosphere and hold for 120 min to obtain a gradient density nano-fiber aerogel (denoted as SG-LAPSNA-LS).

[0133] Example 20

[0134] Preparation of gradient density nanofiber aerogel:

[0135] Take the Laponite prepared in Example 1, Example 10 and Example 12 respectively and mix it with SiO 2 nanofiber dispersion liquid.

[0136] First, pour the dispersion liquid in Example 10 into a polytetrafluoroethylene mold, then place the mold in an ultra-low temperature storage box with -86°C. The bottom of the mold is in contact with the copper block in the directional freezing device. Before the whole slurry is almost completely frozen into a block (only a layer of molten slurry remains on the surface, and the required directional freezing time is 10 min), pour the dispersion liquid in Example 12. Before the whole slurry is almost completely frozen into a block (only a layer of molten slurry remains on the surface, and the required directional freezing time is 12 min), pour the dispersion liquid in Example 1 to continue the freezing process. After the whole slurry is completely frozen into a block (the required directional freezing time is 14 min), quickly transfer it to a freeze dryer and dry it for 32 h by gradient heating vacuum drying at a vacuum degree of 18.8 Pa and a water-cooled trap temperature of -60°C to obtain the aerogel to be sintered. Then transfer it to a muffle furnace and heat it to 900°C at a heating rate of 1°C / min in an air atmosphere and keep it warm for 120 min to obtain the gradient density nanofiber aerogel (denoted as LG-LAPSNA-LS).

[0137] Examples 16 - 20 are samples with different density gradients.

[0138] Effect verification

[0139] In order to better verify the performance and cost advantages of the products of each example (collectively referred to as LAPSNAs) in actual engineering applications, the present invention carried out actual pipeline coating energy-saving calculations on LAPSNAs and the glass wool originally used for high-temperature pipelines. During the simulation calculation process, the diameter of the steam pipeline was set to 32 mm, the temperature inside the pipe was assumed to be 350°C, and the adiabatic surface temperature was 55°C. The thickness of the adiabatic layer required for a 1 m long main steam pipeline was simulated.

[0140] (1) Adiabatic layer thickness

[0141] According to GB 50264 "Code for Design of Thermal Insulation Engineering of Industrial Equipment and Piping", the calculation method of the adiabatic layer thickness is as follows:

[0142]

[0143] α s = α r + α c (5)

[0144] In the formula:

[0145] D 1 is the outer diameter of the insulation layer (m); D 0 is the outer diameter of the pipeline (m); λ is the thermal conductivity of the insulation layer (℃); T 0 is the temperature of the outer surface of the pipeline (℃); T s is the temperature of the outer surface of the insulation layer (℃); T a is the ambient temperature (℃); α r is the radiative heat transfer coefficient of the outer surface of the insulation layer (W / (m 2 ·K)); α c is the convective heat transfer coefficient of the outer surface of the insulation layer; α s is the heat transfer coefficient of the outer surface of the insulation layer; ε is the emissivity of the material on the outer surface of the insulation layer. Referring to the table of the emissivities of common materials in the standard, it can be known that the emissivity of the fiber fabric is about 0.75.

[0146] (2) Weight of the insulation layer per unit length

[0147] Calculate the weight of the insulation layer per unit length from the thickness of the insulation layer and the density of the insulation material. The calculation formula:

[0148]

[0149] where m is the weight of the insulation layer per unit length and ρ is the density of the insulation material.

[0150] (3) Heat loss of the insulation layer per unit length

[0151] Calculate the heat loss per unit length from the outer diameter of the insulation layer and the surface heat release coefficient. The calculation formula:

[0152] q = πD 1 α s (T s - T a ) (7)

[0153] where q is the heat loss of the insulation layer per unit length.

[0154] Table 1 shows the comparative analysis of different insulation materials covering situations.

[0155] Table 1 Comparison of Different Insulation Materials Covering Situations

[0156]

[0157] As can be seen from Table 1, the materials prepared by the present invention have obvious advantages compared with the original glass wool products. The thermal conductivity of the prepared materials is less than 3 / 5 of that of the original glass wool, and the density is only about 1 / 10 of that of the original glass wool. The unit length coating thickness of the glass wool is 60.7 mm, while when the outer surface is reduced to the same temperature, the prepared materials only need 37.1 mm, which is reduced by about 2 / 5, as Figure 25 shown. At the same time, the unit length coating volume and the unit length coating weight are reduced by 55.6% and 94.1% respectively, which are 0.008 m 3 and 0.145 kg respectively, greatly reducing the load-bearing. And the heat dissipation per unit length of the pipeline coated with the prepared materials is 71.2 W / m, which is 29.2% lower than 100.5 W / m of the original glass wool products, greatly reducing the heat loss. To sum up, compared with the original glass wool products, the prepared materials have reduced coating thickness, volume, weight and heat dissipation per unit length. Especially, the coating weight is reduced by about 94.1% compared with the original, greatly reducing the use of raw materials, and the energy-saving effect and economic benefit are remarkable.

[0158] Figure 1 This is the bionic structure, principle of the bionic double-network aerogel of the present invention and the microstructural diagram of Example 1. Among them, (a) is the card house structure in the building; (b) is the card house structure formed by the nanosheets in the product of Example 1; (c) is the Laponite nanosheet network structure in the product of Example 1; (d) is the natural loofah structure; (e) is the enlarged view of the natural loofah structure; (f) is the bionic loofah network structure in the product of Example 1.

[0159] In the process of preparing the bionic double-network aerogel, various shapes can be prepared by changing different molds. To verify this property, the present invention prepared a variety of samples by only adjusting the shape of the polytetrafluoroethylene mold in Example 1, and the physical diagrams are as Figure 2 and Figure 3 shown in (b).

[0160] Figure 2 This is the physical diagram of the Laponite mixed SiO 2 nanofiber dispersion liquid in Example 1 and the large aerogel sample prepared according to the method of Example 1. Among them, (a) is the physical diagram of the Laponite mixed SiO 2 nanofiber dispersion liquid; (b) is the physical diagram of the large aerogel sample with a size of 2300 cm 3 .

[0161] Figure 2 It shows that the products prepared by the method of the present invention can be used for large-scale preparation in industrial production and are expected to be used in the coating application of large equipment.

[0162] Figure 3 Figure (a) is a physical picture of the ultra-light aerogel prepared in Example 11, and figure (b) is a physical picture of aerogels with various sizes and shapes prepared according to the method of Example 1.

[0163] Figure 3 The prepared material has the characteristics of ultra-light weight and exhibits flexible scalability, and is expected to be applied to key complex parts of equipment.

[0164] Figure 4 Figure is the microscopic morphology diagram of the products of Examples 1, 7-9. Among them, (a)-(d) are LAP0.1SNA; (e)-(h) are LAP0.4SNA; (i)-(l) are LAP0.7SNA; (m)-(p) are LAP1.0SNA.

[0165] Figure 4 It shows a typical double-network structure. As the content of Laponite increases, the complexity of the kagome structure network increases, and more Laponite nanosheets will fill the pores in the kagome structure network, increasing the opportunity for sound wave reflection and dissipation.

[0166] Figure 5 Figure is the microscopic morphology diagram of the products of Examples 1, 4-6. Among them, (a)-(d) are LAPSNA0.5; (e)-(h) are LAPSNA1.0; (i)-(l) are LAPSNA1.5; (m)-(p) are LAPSNA2.0.

[0167] Figure 5 It shows that too much silane sol will wrap around the kagome structure network composed of Laponite nanosheets, affecting the original morphology of the kagome structure network, and will increase the wall thickness, affecting the pore uniformity, which is not conducive to performance improvement.

[0168] Figure 6 Figure shows the compression and resilience performance of the product of Example 4 at extreme temperatures. Among them, (a) is the resilience of the product in the butane torch flame at 1000 °C; (b) is the resilience of the product in liquid nitrogen at -196 °C.

[0169] Figure 6 It shows that the prepared material can still maintain good compression and resilience at extreme temperatures, and is expected to be used in the field of coating of equipment under complex loads at extreme temperatures.

[0170] Figure 7 Figure shows the morphology and heat insulation performance of the samples of Examples 1, 7-9. Among them, (a) is the physical picture of the sample; (b) is the density and room temperature thermal conductivity of the sample; (c) is the high temperature thermal conductivity of the sample.

[0171] Figure 7Shows the influence of the Laponite content on the thermal conductivity and density of the prepared materials. The samples exhibit low density and low thermal conductivity. With the increase of the Laponite content, the solid-phase heat conduction increases and the thermal conductivity rises. However, even at 800 °C, a relatively low thermal conductivity is maintained, only around 0.08 W·m -1 ·K -1 .

[0172] Figure 8 Are the morphologies and heat insulation performances of the samples of Example 1 and Examples 4 - 6. Among them, (a) is the physical picture of the sample; (b) is the density and room-temperature thermal conductivity of the sample; (c) is the high-temperature thermal conductivity of the sample.

[0173] Figure 8 Shows the influence of the silane sol content on the thermal conductivity and density of the prepared materials. The results show that the silane sol has an adverse effect on the increase of the thermal conductivity and density. However, the low thermal conductivity of the sample with the highest silane sol content at 800 °C is still lower than 0.09 W·m -1 ·K -1 .

[0174] Carries out a comparison of the high-temperature resistance performance between the sample of Example 1 with a thickness of 12 mm and the carbon fiber felt.

[0175] Figure 9 Is the comparison chart of the high-temperature resistance performance of the sample of Example 1, the carbon fiber felt, the glass fiber needle-punched felt, and the glass fiber felt on the flat-plate heater. Among them, (a) is the optical image; (b)-(d) are the infrared images after different heating times.

[0176] Figure 9 Indicates that, compared with the fiber felt, the glass fiber needle-punched felt, and the glass fiber felt, the material prepared by the present invention has the best heat insulation performance under the surface heat source heating of the flat-plate heater. After 600 s, the surface temperature is only 61.4 °C and remains stable.

[0177] Carries out a high-temperature resistance performance test on the sample of Example 1 with a thickness of 12 mm on the alcohol lamp flame.

[0178] Figure 10 Is the high-temperature resistance performance chart of the sample of Example 1 on the alcohol lamp flame. Among them, (a) is the optical image; (b)-(d) are the infrared images after different heating times.

[0179] Figure 10 Indicates that under the point heat source heating of the alcohol lamp, the cold surface temperature field distribution of the prepared material is also uniform, without obvious temperature concentration phenomenon, indicating that the material can diffuse the heat at its center to the entire surface of the material, further proving the uniformity of the bionic double-network structure of the material. After 10 min, the surface temperature is only 64.3 °C and remains stable, showing good heat insulation performance.

[0180] The high temperature resistance performance test of the sample of Example 1 with a thickness of 12 mm was carried out in the flame of a butane torch.

[0181] Figure 11 It is the high temperature resistance performance diagram of the sample of Example 1 in the flame of a butane torch. Among them, (a) is the optical image; (b)-(d) are the infrared images after different heating times.

[0182] Figure 11 It shows that the prepared material also has the characteristics of fire prevention and flame retardancy. Under the continuous heating of the 1000 high-temperature butane torch flame, the temperature on its back can still be stabilized at 68.2 °C.

[0183] The temperature difference test of the hot and cold surfaces of the sample of Example 1 with a thickness of 12 mm was carried out under a butane torch.

[0184] Figure 12 It is the temperature difference diagram of the hot and cold surfaces of the sample of Example 1 under a butane torch.

[0185] Figure 12 It shows that the temperature difference on the freezing surface of the prepared material is as high as 932 °C under the butane torch flame, and the 12-mm sample has a temperature gradient as high as 777 °C / cm, further demonstrating its excellent complex heat insulation network structure.

[0186] The morphology and sound absorption performance tests of the samples of Example 1 and Examples 11-13 with a thickness of 30 mm were carried out.

[0187] Figure 13 It is the morphology and sound absorption performance diagram of the samples of Example 1 and Examples 11-13. Among them, (a) is the physical picture; (b) is the sound absorption coefficient curve; (c) is the noise reduction coefficient value (NRC).

[0188] Figure 13 It shows that with the increase of density, the sound absorption performance of the sample is improved, which is due to the increase of density increasing the complex structure inside the material.

[0189] Samples with different thicknesses (10, 20, 30, 40, 50 mm) were prepared by only adjusting the shape of the polytetrafluoroethylene mold in Example 1, and the morphology and sound absorption performance were characterized. The test results are as Figure 14 shown.

[0190] Figure 14 It is the sound absorption performance diagram of the samples of Example 1 with different thicknesses. Among them, (a) is the sound absorption coefficient curve; (b) is the noise reduction coefficient value (NRC).

[0191] Figure 14It shows that with the increase of thickness, the sound absorption performance of the sample is improved. The thickness extends the path of sound wave dissipation and enhances the dissipation of sound waves.

[0192] The samples of Example 1 and Examples 4 - 6 with a thickness of 30 mm were tested for morphology and sound absorption performance.

[0193] Figure 15 It is the morphology and sound absorption performance diagram of the samples of Example 1 and Examples 4 - 6. Among them, (a) is the physical picture; (b) is the sound absorption coefficient curve; (c) is the NRC value.

[0194] Figure 15 It shows that too much or too little silane sol is not beneficial to the improvement of sound absorption performance, and LAPSNA1.0 has the best sound absorption performance.

[0195] The samples of Example 1 and Examples 7 - 9 with a thickness of 30 mm were tested for morphology and sound absorption performance.

[0196] Figure 16 It is the morphology and sound absorption performance diagram of the samples of Example 1 and Examples 7 - 9. Among them, (a) is the physical picture; (b) is the sound absorption coefficient curve; (c) is the NRC value.

[0197] Figure 16 It shows that with the increase of Laponite content, the sound absorption performance of the sample is improved. This is because the Laponite content affects the complexity of the card house network structure and improves the level of sound wave dissipation.

[0198] Figure 17 It is the basic property and air flow resistance diagram of the samples of Example 1 and Examples 7 - 9. Among them, (a) is the porosity and density; (b) is the air flow resistance.

[0199] Figure 17 It shows that the prepared material has ultra - high porosity and low density, and the air flow resistance increases with the increase of Laponite content, which is consistent with Figure 16 the results.

[0200] Figure 18 It is the absolute sound pressure distribution diagram of the samples of Example 1 and Examples 7 - 9.

[0201] Figure 18 The absolute sound pressure distribution of samples with different Laponite contents was simulated. Among them, LAP1.0SNA shows the largest sound pressure drop, transitioning from red to dark green, and has the best sound absorption performance. While the transmitted sound pressure in LAP0.1SNA still remains at a relatively high level, indicating insufficient sound absorption performance.

[0202] Figure 19Comparison chart of the sound absorption performance of the sample of Example 1 and other materials. Among them, (a) is the comparison of the sound absorption coefficient curves of the sample and commercial sound-absorbing cotton; (b) is the relationship between the NRC value and the surface density of different sound-absorbing materials.

[0203] Figure 19 Among them, in (a), the sample of Example 1 with a thickness of 30 mm and commercial sound-absorbing cotton were tested; in (b), the sample of Example 1, as well as straw fiber, glass fiber, porous ceramic, silica aerogel, yucca fiber, micro / nano fiber aerogel, sandwich foam, and polypropylene fiber mat were tested.

[0204] Figure 19 It shows that the sound absorption coefficient of the 30-mm sample is better than that of commercial sound-absorbing cotton. When compared with some commercial sound-absorbing materials and materials with excellent sound absorption performance that have been reported, it has the highest NRC value and extremely low surface density. At the same time, its NRC value is as high as 0.76, exceeding the research results of some high-level papers (DOI: 10.1038 / s41467-021-26890-9, DOI: 10.1021 / acsnano.2c06011, DOI: 10.1002 / adfm.202301870). At the same time, its ultra-high NRC value meets the requirements of corresponding broadband noise reduction for high-efficiency sound-absorbing materials (NRC≥0.56), and it belongs to the second-level sound-absorbing material (0.8>NRC≥0.6), having a very broad application prospect in industrial noise reduction.

[0205] Figure 20 Morphology diagram of the sample of Example 16. Among them, (a) is the macroscopic morphology diagram; (b) is the microscopic morphology diagram of the gradient density structure.

[0206] Figure 20 Among them, the corresponding sample thickness is 36 mm, and the thickness of each density unit is 12 mm.

[0207] From Figure 20 From the results shown, from top to bottom, the material becomes denser, the pore size decreases, and the porosity decreases. And there is no obvious transition trace at the connection of each basic density unit, further demonstrating the uniform size of the gradient density material.

[0208] Figure 21 Sound absorption performance of the samples of Examples 16 - 20. Among them, (a) is the sound absorption coefficient curve; (b) is the NRC value.

[0209] Figure 21 Among them, the corresponding sample thickness is 36 mm, and the thickness of each density unit is 12 mm.

[0210] Figure 21It shows that LG-LAPSNA-SL has the best sound absorption performance, which is due to the low-density cells on the surface allowing more sound waves to enter, and the high-density cells inside fully dissipating the sound waves, broadening the frequency range corresponding to sound absorption.

[0211] Figure 22 It is the absolute sound pressure distribution of the samples in Examples 16 - 20.

[0212] Figure 22 The absolute sound pressure results also show that the smaller the density of the first cells on the surface, the more sound waves enter (corresponding to the red area), and the larger the density of the third cells inside, the faster the color change, indicating a higher dissipation of low-frequency sound waves, which is consistent with Figure 21 It also corresponds.

[0213] A comparative test on the actual pipeline cladding heat insulation performance of the sample of Example 1 with a thickness of 25 mm and glass fiber felt was carried out.

[0214] Figure 23 It is the comparative diagram of the actual pipeline cladding heat insulation performance of the sample of Example 1 and glass fiber felt. Among them, (a) is the physical picture of the semi-tubular sample; (b) is the physical picture of the sample cladded on the high-temperature steam pipeline; (c) is the infrared image of the sample cladded on the high-temperature steam pipeline; (d) is the physical picture of the semi-tubular glass fiber felt; (e) is the physical picture of the glass fiber felt cladded on the high-temperature steam pipeline; (f) is the infrared image of the glass fiber felt cladded on the high-temperature steam pipeline.

[0215] Figure 23 It shows that in the actual pipeline cladding experiment, the prepared material has better actual high-temperature heat insulation performance than commercial glass fiber felt, and is expected to be extended to the applications of cladding other complex equipment.

[0216] Figure 24 It is the actual pipeline cladding simulation diagram of the sample of Example 1 and glass fiber felt. Among them, (a) is the simulation result of the sample cladding on the high-temperature pipeline; (b) is the simulation result of the glass fiber felt cladding on the high-temperature pipeline.

[0217] Figure 24 The simulation results of the actual pipeline cladding of the prepared material and glass fiber felt are simulated, which is consistent with Figure 23 the actual performance results. However, in the actual pipeline cladding experiment, in addition to the high-temperature transfer from the inner pipeline, the surface of the material is also affected by the radiative heat transfer from the surrounding pipelines to the surface of the material. Therefore, its surface temperature is different from the experimental data.

[0218] Figure 25 It is the comparative diagram of the cladding thickness of the sample of Example 15 and the original glass wool product of the ship pipeline when maintaining the same outer surface temperature.

[0219] Figure 25It can be visually shown that, compared with the original glass wool products, the prepared materials can significantly reduce the coating thickness, thereby reducing costs.

[0220] The sound intensity cloud map test was carried out on the sample of Example 1 with a thickness of 20 mm and commercial sound-absorbing cotton.

[0221] Figure 26 It is the sound intensity cloud map results of the sample of Example 1 and commercial sound-absorbing cotton. Among them, (a) is the diagram of the sound intensity cloud map test device; (b) is the sound intensity cloud map without materials; (c) is the sound intensity cloud map when coated with commercial sound-absorbing cotton; (d) is the sound intensity cloud map when coated with the prepared materials.

[0222] From Figure 26 it can be seen that the prepared materials have better actual noise reduction ability than commercial sound-absorbing cotton. The central sound pressure level without materials is about 74 dB, and after putting in commercial sound-absorbing cotton, the central sound pressure level is about 69 dB, which is reduced by about 5 dB. After putting in the prepared materials, the central sound pressure level is about 55 dB, which is reduced by about 19 dB. It further verifies that the prepared materials have better noise reduction ability than commercial sound-absorbing cotton in practical applications.

[0223] Figure 27 It is the schematic diagram of the force mechanism between components during the forming process of the samples of Examples 1-20 of the present invention.

[0224] The above-described embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a bionic double-network high-temperature heat insulation-low-frequency noise reduction-fire retardant integrated nanofiber aerogel, characterized in that: The following steps are involved: mixing a silane precursor, water and an acid catalyst to obtain a hydrolyzed silane sol; Adding Laponite powder to the hydrolyzed silane sol to obtain a Laponite aqueous dispersion; The Laponite aqueous dispersion is mixed with SiO2 nanofibers to obtain a Laponite mixed SiO2 nanofiber dispersion, which is directionally frozen, then vacuum dried, and sintered to obtain the bionic double-network high-temperature thermal insulation-low-frequency noise reduction-fire retardant integrated nanofiber aerogel.

2. The preparation method according to claim 1, characterized in that: The silane precursor is one or more of methyltrimethoxysilane, methyltriethoxysilane, methyl orthosilicate and ethyl orthosilicate; the acid catalyst is acetic acid and / or oxalic acid.

3. The preparation method according to claim 1, characterized in that: The volume ratio of the water, the silane precursor and the acid catalyst is 90:0.71-2.14:0.

036.

4. The preparation method according to claim 1, characterized in that: The mass ratio of the water, SiO2 nanofiber and Laponite powder is 90:0.3-0.9:0.09-0.

9.

5. The preparation method according to claim 1, characterized in that: The preparation method of the SiO2 nanofiber is as follows: first, the SiO2 nanofiber non-woven fabric is cut into small pieces, and pre-cut for 3 minutes using a wall breaking machine to obtain a SiO2 nanofiber suspension without obvious SiO2 nanofiber non-woven fabric pieces, and then homogenized and cut at a speed of 13000r / min for 20 minutes to obtain a homogenous liquid, and then dried at 120°C for 24 hours to obtain the SiO2 nanofiber.

6. The preparation method according to claim 1, characterized in that: The preparation method of the Laponite aqueous dispersion is: adding Laponite powder into the hydrolyzed silane sol, and then performing high-speed homogenization dispersion at a rotation speed of 8000-13000 r / min for 10-20 minutes.

7. The preparation method according to claim 1, characterized in that: The directional freezing is unidirectional freezing, the temperature is -196 to -70°C, and the time is 20 to 180 minutes.

8. The preparation method according to claim 1, characterized in that: The ambient temperature of the vacuum drying is -50°C to 50°C, the time is 24 to 96 hours, and the vacuum degree is 5 to 30 Pa; the sintering is performed by heating the temperature to 900°C at a heating rate of 1 to 2°C / min and then keeping the temperature for 120 minutes, and the sintering atmosphere is an air atmosphere.

9. A method for preparing a bionic double-network high-temperature thermal insulation-low-frequency noise reduction-fire retardant integrated gradient density nanofiber aerogel, characterized in that: The following steps are involved: (1) mixing a silane precursor, water and an acid catalyst to obtain a hydrolyzed silane sol; adding Laponite powder to the hydrolyzed silane sol to obtain a Laponite aqueous dispersion; (2) mixing the Laponite aqueous dispersion with SiO2 nanofibers to obtain a first Laponite-SiO2 nanofiber dispersion; (3) repeating step (2) to prepare an Nth Laponite mixed SiO2 nanofiber dispersion having the same or different SiO2 nanofiber concentrations; (4) Directional freezing the first Laponite mixed SiO2 nanofiber dispersion until it is completely frozen and solidified, and repeatedly adding N Nth Laponite mixed SiO2 nanofiber dispersions for directionally freezing; (5) vacuum drying and sintering the product of step (4) to obtain the bionic double-network high-temperature thermal insulation, low-frequency noise reduction, and fire retardant integrated gradient density nanofiber aerogel.

10. A bionic double-network nanofiber aerogel with integrated high-temperature thermal insulation, low-frequency noise reduction and fire retardant functions obtained according to the preparation method according to any one of claims 1 to 8.

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