A high-strength, high-temperature resistant ceramic fiber aerogel and its preparation method

Abstract

The application discloses a kind of high-strength high-temperature-resistant ceramic fiber aerogel and preparation method thereof, aerogel is composed of modified sunscreen agent, binder and ceramic fiber, ceramic fiber forms honeycomb hole, binder and modified sunscreen agent are uniformly attached on hole wall;Wherein modified sunscreen agent is the " double-layer ball " structure of silica wrapping titanium dioxide particle.The application is bonded by binder between fiber and fiber, and directional freeze drying is prepared anisotropic ceramic fiber aerogel, after high-temperature heat treatment, aerogel shows extremely high strength, can withstand 500KPa pressure in single orientation, can satisfy many actual needs.

Description

Technical Field

[0001] This invention belongs to the field of nanoporous materials technology, specifically relating to a high-strength, high-temperature resistant ceramic fiber aerogel and its preparation method. Background Technology

[0002] Since its invention in 1931, aerogels have been widely used in fields such as thermal insulation, electromagnetic shielding, and catalyst support due to their unique characteristics such as high porosity and high specific surface area. However, traditional aerogels, due to their "pearl chain" network structure, have limitations such as high brittleness, easy pulverization, and inconvenience in use, making it difficult to meet the requirements of compression and bending in practical applications. On the other hand, the pore structure of traditional aerogels such as silica is severely damaged as the temperature increases, resulting in a significant weakening of their intrinsic properties, especially their thermal insulation and high-temperature protection performance. To address these problems, numerous improvements have been made, and significant progress has been achieved.

[0003] Claudio Ferraroe et al. (Adv. Funct. Mater. 2016, 26, 1636-1645) prepared ceramic fiber aerogels by adding alumina as a binder to tightly connect the ceramic fibers. These aerogels exhibited excellent high-temperature resistance, but their mechanical properties still failed to meet practical requirements.

[0004] Xu et al. (Science 363, 723-727, 2019) used specialized equipment to blow boron nitride ceramic sheets into graphene aerogel, obtaining a two-dimensional ceramic sheet aerogel via a sacrificial template method. This aerogel could withstand intense thermal shock and exhibited excellent compressive strain resistance. However, the aerogel's resistance to high-temperature oxidation was limited because boron nitride has a low oxidation temperature and cannot be exposed to high-temperature air environments for extended periods. Furthermore, this aerogel was prepared using a special method on specialized equipment, making it difficult to imitate, resulting in high manufacturing costs and hindering mass production.

[0005] Zhang et al. (ACS Nano 2020, 14, 15616-15625) used electrospinning to prepare ceramic fiber aerogels to replace two-dimensional ceramic sheet aerogels. They cleverly designed the fiber microstructure through electrospinning to prepare ceramic fiber membranes, exhibiting enhanced mechanical properties, good flexibility, and excellent high-temperature resistance. However, the preparation of ceramic fiber aerogels by electrospinning is labor-intensive, time-consuming, difficult to mass-produce, and requires high pressure, posing certain risks. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing anisotropic ceramic fiber aerogels by bonding fibers together with an adhesive and then performing directional freeze-drying. After high-temperature heat treatment, the aerogels exhibit extremely high strength, capable of withstanding a pressure of 500 kPa in a single orientation, thus meeting many practical needs. A method for preparing this gel is also provided.

[0007] The objective of this invention is achieved through the following technical solution: a high-strength, high-temperature resistant ceramic fiber aerogel, composed of a modified opaque agent, a binder, and ceramic fibers. The ceramic fibers form honeycomb-like pores, and the binder and modified opaque agent are uniformly attached to the pore walls. The modified opaque agent is a "double-layer sphere" structure consisting of silica encapsulated titanium dioxide particles. After heat treatment, the binder bonds the binder and modified opaque agent together on the pore walls of the honeycomb, resulting in a tightly layered structure for the ceramic fiber aerogel.

[0008] The binder is aluminum dihydrogen phosphate. The ceramic fiber has an aspect ratio of 50 to 1000 and a diameter of 100 to 700 nm; the ceramic fiber is one or more of silicon carbide, silicon nitride, and silicon dioxide.

[0009] A method for preparing high-strength, high-temperature resistant ceramic fiber aerogel, comprising the following steps:

[0010] (1) Disperse titanium dioxide particles in a mixed solution of ethanol and water, add dispersant and ammonia to adjust the pH to 7-9, and stir to prepare titanium dioxide suspension A;

[0011] (2) Dissolve tetraethyl orthosilicate in ethanol to make the concentration of tetraethyl orthosilicate 3.6-5.8 wt%, and add it dropwise to the suspension A obtained in step (1). The volume ratio of suspension A to this tetraethyl orthosilicate ethanol solution is about 5:1. After stirring, the powdered "double-layer sphere" structure opaque agent B is obtained by vacuum filtration. The silica in the "double-layer sphere" structure opaque agent B comes from the hydrolysis-condensation process of tetraethyl orthosilicate.

[0012] (3) The light-blocking agent B and ceramic fibers were dispersed together in an acidic chitosan solution and ultrasonically dispersed evenly. Then the binder was added and stirred evenly to obtain the precursor solution C.

[0013] (4) The precursor solution C is sequentially subjected to directional freezing, freeze drying and high-temperature heat treatment. After treatment, the ceramic fibers form honeycomb-like pores, and the binder and modified opaque agent are uniformly attached to the pore walls to obtain high-strength high-temperature resistant ceramic fiber aerogel.

[0014] The titanium dioxide particles in step (1) have a diameter of 100-500 nm; the dispersant is one or more of sodium hexametaphosphate, sodium phosphate, and sodium pyrophosphate.

[0015] The acidic chitosan solution in step (3) contains chitosan, water, and a component that provides an acidic environment. The component that provides the acidic environment includes one or more of aluminum chloride, aluminum chloride trihydrate, and aluminum chloride hexahydrate. The molar ratio of the component that provides the acidic environment to the added binder is 1 to 3:1. The mass ratio of chitosan to water in the acidic chitosan solution is 1 to 3:200. The mass ratio of the light-blocking agent B, ceramic fiber, water, and binder is 1 to 3:10 to 25:1000:10 to 25.

[0016] The heat treatment time in step (4) is 20 to 30 minutes, the heat treatment temperature is 700 to 900°C, and the heating rate is 2 to 5°C / min.

[0017] The beneficial effects of this invention are as follows: By bonding fibers together with an adhesive and combining this with directional freeze-drying, an anisotropic ceramic fiber aerogel is prepared. After high-temperature heat treatment, the aerogel exhibits extremely high strength, capable of withstanding a pressure of 500 kPa in a single orientation, thus meeting many practical needs. Furthermore, due to the excellent thermal stability of ceramic fibers, the entire aerogel can maintain its original shape for an extended period at 1000°C. The addition of a "double-sphere" structure light-blocking agent provides more connection sites while effectively reducing the thermal conductivity of the aerogel under high-temperature infrared radiation above 600°C. Such excellent comprehensive performance satisfies the stability and application range of this ceramic fiber aerogel in high-temperature environments.

[0018] The simple and effective preparation method provided by this invention is within a reasonable range in terms of both ease of operation and time cost, making it feasible for practical production. Compared with preparation methods such as vapor deposition, electrospinning, and blown spinning, this invention has a greater cost advantage. Furthermore, this low-cost preparation method is of great significance for environmental protection and energy utilization. Detailed Implementation

[0019] In order to simultaneously meet the requirements of excellent mechanical properties and high temperature resistance, based on the above research, the present invention has made the following innovations to prepare high-strength, high-temperature resistant ceramic fiber aerogel.

[0020] First, a "double-layer spherical" structure of titanium dioxide coated with silica is used as a light-shielding agent, significantly reducing thermal conductivity. The structure of this light-shielding agent draws inspiration from a method for preparing a hydrophobic coating (CN110540765A) and a novel method for preparing hollow titanium dioxide nanocup catalysts (CN107335418A), but this is the first time it has been used to design a light-shielding agent to reduce thermal infrared radiation. The outer silica layer of this light-shielding agent cleverly provides lower solid thermal conductivity without affecting the infrared reflectivity of the inner titanium dioxide, thus exhibiting higher infrared reflectivity compared to conventional silicon carbide particle light-shielding agents.

[0021] Secondly, high-concentration aluminum dihydrogen phosphate is used as a binder to connect ceramic fibers, giving them extremely high strength in high-temperature air environments. Compared to low-concentration aluminum dihydrogen phosphate, high-concentration aluminum dihydrogen phosphate enables the pores formed during the directional freeze-drying process of the aerogel to exhibit a dense lamellar structure. Therefore, the resulting aerogel has higher strength and high-temperature resistance, meeting the requirements for applications in various thermal environments. Furthermore, these relatively readily available raw materials make large-scale production possible.

[0022] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0023] A high-strength, high-temperature resistant ceramic fiber aerogel is composed of a modified opacifier, a binder, and ceramic fibers. The ceramic fibers form honeycomb-like pores, and the binder and modified opacifier are uniformly adhered to the pore walls. The modified opacifier has a "double-layer spherical" structure consisting of silica encapsulating titanium dioxide particles. After heat treatment, the binder bonds the binder and modified opacifier together on the pore walls of the honeycomb, resulting in a tightly layered structure for the ceramic fiber aerogel.

[0024] The binder is aluminum dihydrogen phosphate. The aspect ratio of the ceramic fiber is 50-1000, more preferably 100-1000; the diameter is 100-700 nm, more preferably 100-600 nm; the ceramic fiber is one or more of silicon carbide, silicon nitride and silicon dioxide, preferably a mixture of silicon carbide and silicon nitride.

[0025] Example 1

[0026] A method for preparing high-strength, high-temperature resistant ceramic fiber aerogel, comprising the following steps:

[0027] (1) Disperse 1g of titanium dioxide with a diameter of 280nm in 104ml of a mixed solution of ethanol and water with a volume ratio of 25:1, add ammonia dropwise until the pH value is 8, add 0.1g of sodium hexametaphosphate as a dispersant, and stir for 5min to prepare titanium dioxide suspension A.

[0028] (2) Tetraethyl orthosilicate was dissolved in 20 mL of ethanol to make the concentration of tetraethyl orthosilicate 5.8 wt%, and then added to the prepared titanium dioxide suspension A. After magnetic stirring for 5 h, the mixture was vacuum filtered to obtain powder, which was then washed three times with ethanol to obtain a silica-coated powdered "double-layer sphere" structure opacifier B. The silica in the "double-layer sphere" structure opacifier B comes from the hydrolysis-condensation process of tetraethyl orthosilicate.

[0029] (3) Dissolve 0.06g aluminum chloride and 0.15g chitosan uniformly in 15ml deionized water to form an acidic chitosan solution. Disperse 0.03g opacifier and 0.3g silicon carbide fiber in the resulting solution, sonicate for 30min, and then stir until uniform. Then add 0.15g aluminum dihydrogen phosphate as a binder and mix evenly to obtain aerogel precursor solution C.

[0030] (4) The obtained aerogel precursor solution C was frozen solid in a liquid nitrogen directional freezing mold, and then dried in a freeze dryer for 72 hours. After treatment, the ceramic fibers formed honeycomb-like pores, and the binder and modified opacifier were uniformly attached to the pore walls, thus obtaining the aerogel. The obtained aerogel was heated to 800℃ in a muffle furnace at a heating rate of 2℃ / min and held for 25 minutes. After natural cooling, a high-strength, high-temperature resistant ceramic fiber aerogel was obtained.

[0031] In the above embodiments, the diameter of the titanium dioxide particles in step (1) is 100-500 nm, preferably 100-300 nm. In this embodiment, 280 nm is used. The particle size of titanium dioxide does not affect the key performance of the aerogel of the present invention. The dispersant can also be sodium phosphate or sodium pyrophosphate or a mixture of two or three of sodium hexametaphosphate, sodium phosphate and sodium pyrophosphate.

[0032] In step (3), one or more of aluminum chloride trihydrate and aluminum chloride hexahydrate can be used to replace aluminum chloride to provide an acidic environment for the solution. The molar ratio of the component providing the acidic environment to the added binder is 1 to 3:1. The mass ratio of chitosan to water in the acidic chitosan solution is 1:100; in this embodiment, the mass ratio of light-blocking agent B, ceramic fiber, water, and binder is 2:20:1000:10.

[0033] Example 2

[0034] A method for preparing high-strength, high-temperature resistant ceramic fiber aerogel is provided. The preparation steps are the same as in Example 1, except that the heating rate is changed from 2℃ / min to 3℃ / min.

[0035] Example 3

[0036] A method for preparing high-strength, high-temperature resistant ceramic fiber aerogel is provided. The preparation steps are the same as in Example 1, except that the heating rate is changed from 2℃ / min to 4℃ / min.

[0037] Example 4

[0038] A method for preparing high-strength, high-temperature resistant ceramic fiber aerogel is provided. The preparation steps are the same as in Example 1, except that the heat treatment temperature is changed from 800℃ to 850℃.

[0039] Example 5

[0040] A method for preparing high-strength, high-temperature resistant ceramic fiber aerogel is provided. The preparation steps are the same as in Example 1, except that the heat treatment temperature is changed from 800℃ to 900℃.

[0041] The high-strength, high-temperature resistant ceramic fiber aerogels obtained in Examples 1-5 were subjected to performance tests, and the test results are shown in Table 1 below.

[0042] Table 1. Structural parameters and performance test results of high-strength, high-temperature resistant ceramic fiber aerogels from different embodiments.

[0043]

[0044] As shown in Table 1, the high-strength, high-temperature resistant ceramic fiber aerogel obtained by this invention has high strength, with an ultimate pressure of 500–556 kPa. The high-strength, high-temperature resistant ceramic fiber aerogel obtained by this invention also has low density (0.257–0.274 g / cm³), low thermal conductivity (0.0362–0.0413 W / (m·K), and a temperature resistance range of -150–1100℃.

[0045] This invention first disperses titanium dioxide particles in a mixed solution of tetraethyl orthosilicate, ammonia, ethanol, and deionized water, and adds sodium hexametaphosphate as a dispersant. After stirring and vacuum filtration, a white powdery opacifier is obtained. Subsequently, the opacifier and ceramic fibers are dispersed together in a chitosan solution. After ultrasonic dispersion, aluminum dihydrogen phosphate is added as a binder and stirred until homogeneous. Finally, the resulting solution is subjected to directional freezing, vacuum drying, and calcination to obtain a high-strength, high-temperature resistant ceramic fiber aerogel.

[0046] The present invention also provides a method for preparing the high-strength, high-temperature resistant ceramic fiber aerogel, thereby obtaining the high-strength, high-temperature resistant ceramic fiber aerogel.

[0047] This invention uses aluminum dihydrogen phosphate as a binder to connect fibers together, combined with directional freeze-drying and the directional growth of ice crystals. After sublimation, a single-oriented porous microstructure is left, thus giving the aerogel anisotropy. In the direction parallel to the pore structure, this invention can withstand huge pressure loads. The addition of particulate light-blocking agents improves the bonding effect of the binder. In addition, the light-blocking agents can reduce the heat conduction caused by infrared radiation at high temperatures.

[0048] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A method of making high-strength, high-temperature resistant ceramic fiber aerogel, characterized by, The method comprises the following steps: (1) dispersing titanium dioxide particles in a mixed solution of ethanol and water, adding a dispersing agent and ammonia water to adjust the pH to 7-9, and stirring to prepare a titanium dioxide suspension A; (2) dissolving tetraethyl orthosilicate in ethanol to obtain a concentration of 3.6-5.8 wt%, and then adding it dropwise into the suspension A, stirring, and then vacuum filtering to obtain a powder-like "double-layered sphere" structure sunscreen B; (3) dispersing the sunscreen B and ceramic fibers in an acidic chitosan solution together and uniformly dispersing by ultrasonic, then adding a binder and uniformly stirring to obtain a precursor solution C; (4) sequentially passing the precursor solution C through directional freezing, freeze-drying and high-temperature heat treatment to obtain a high-strength high-temperature-resistant ceramic fiber aerogel.

2. The method for preparing a high-strength, high-temperature resistant ceramic fiber aerogel according to claim 1, characterized in that, In step (1), the diameter of the titanium dioxide particles is 100-500 nm; and the dispersing agent is one or more of sodium hexametaphosphate, sodium phosphate and sodium pyrophosphate.

3. The method of claim 1, wherein the ceramic fiber aerogel has a high strength and a high temperature resistance. In step (3), the acidic chitosan solution comprises chitosan, water and an acidic environment-providing component, the acidic environment-providing component comprises one or more of aluminum chloride, aluminum chloride trihydrate and aluminum chloride hexahydrate, the molar ratio of the acidic environment-providing component to the added binder is 1-3:1, the mass ratio of chitosan to water in the acidic chitosan solution is 1-3:200, and the mass ratio among the sunscreen B, the ceramic fibers, water and the binder is 1-3:10-25:1000:10-25.

4. The method for preparing a high-strength, high-temperature resistant ceramic fiber aerogel according to claim 1, characterized in that, In step (4), the heat treatment time is 20-30 min, the heat treatment temperature is 700-900℃, and the heating rate is 2-5℃ / min.

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