CN111848205A - A method for preparing high temperature resistant aerogel thermal insulation material by drying under normal pressure - Google Patents

Abstract

The invention relates to a method for preparing a high temperature resistant aerogel heat insulating material by drying under normal pressure. 4) gelation process, (5) hydrophobic modification process, (6) normal pressure drying process, (7) post-treatment process. The method uses high aspect ratio alumina nanowires for three-dimensional lap bonding, and uses silica sol as a sintering aid to achieve high-temperature stable phase formation and strengthening of nano-framework. The wet gel was modified with a hydrophobic reagent to realize the drying process at atmospheric pressure. The invention realizes the low-cost and short-period preparation of the high-temperature-resistant (above 1400° C.) heat insulating material.

Description

A method for preparing high temperature resistant aerogel thermal insulation material by drying under normal pressure

technical field

The invention relates to the technical field of aerogel preparation, in particular to a method for preparing a high temperature resistant aerogel heat insulating material by drying under normal pressure.

Background technique

Aerogel is a nanoporous material with a three-dimensional network structure. As a solid with high porosity, aerogel is filled with a large amount of gas. Its porosity is as high as 80-99.8%, the typical size of the pores is 1-100nm, the specific surface area is 200-1000m ² /g, the density can be as low as 3kg/m ³ , and the room temperature thermal conductivity can be as low as 0.012W/m·k . It is precisely because of these characteristics that aerogel materials have broad application potential in thermal, acoustics, optics, microelectronics, and particle detection. There are many preparation methods for aerogels. However, the drying process is difficult to break through in the preparation. Due to the slender skeleton structure of aerogels, during the drying process at normal pressure, the tension of the solvent causes the material to shrink and the three-dimensional network structure is destroyed. Due to the above limitations, the current drying method of aerogels is still the general method of supercritical drying, and a few kinds of aerogels can be freeze-dried or dried under normal pressure. However, whether it is supercritical drying or atmospheric drying, it will bring high cost and long cycle, which severely limits the popularization and application of aerogel materials. Therefore, developing an effective atmospheric drying method is an important issue for aerogel preparation.

In the existing research on atmospheric drying methods, the skeleton is mainly modified by introducing long-chain organic precursors, and the strong skeleton is used to resist the tension of the drying process, or the surface of the wet gel skeleton is modified with organic groups, and the surface hydrophobicity is used to avoid the drying process. shrinkage problem. However, the existing atmospheric drying methods are mainly based on silica aerogels, carbon aerogels and other oxide aerogels with lower temperature resistance grades. There is no report on the atmospheric drying method of aerogel materials resistant to higher temperature (1200°C).

In recent years, nano-ceramic fiber aerogels have attracted extensive attention of researchers due to their good temperature resistance, elasticity and lightweight properties. At present, most methods for preparing nano-ceramic fiber aerogels are to prepare nano-fibers by electrospinning, disperse the nano-fibers and freeze-dry them. The nanofibrous aerogel prepared by this method has excellent comprehensive properties. However, the preparation of aerogel materials by electrospinning has the limitation of high cost and not easy to scale up preparation.

Chinese patent document CN101254449A discloses a method for preparing oxide nanowire reinforced transparent aerogel bulk material, wherein a composite gel is formed after mixing sol and oxide nanowire, and drying after aging to obtain oxide nanowire reinforced transparent aerogel The colloidal bulk material, wherein the mass ratio of oxide nanowires to sol is 1:0.5-1000, the diameter of the nanowires is 1-100 nm, and the aspect ratio is 10-1000. However, the sol was preformed rather than in situ hydrolysis when the silicon source material was mixed with the alumina nanowires. Nanowires act as reinforcement and are less abundant. The material system is used for preparing transparent aerogel, and the material system has insufficient temperature resistance, large deformation degree during drying, and poor thermal insulation performance.

With the development of science and technology, various fields have put forward higher requirements for the temperature resistance and high temperature insulation performance of thermal insulation materials. Therefore, it is very necessary to develop a low-cost, short-cycle method to prepare high-temperature and high-temperature thermal insulation materials. Aerogel material for efficient thermal insulation at high temperatures. This patent proposes a preparation method of nanowire aerogel, and the aerogel has good temperature resistance. And through surface modification and physical self-supporting effect, atmospheric pressure drying is used to prepare high temperature resistant and high performance aerogel thermal insulation materials.

SUMMARY OF THE INVENTION

In order to solve the technical problems existing in the prior art, the present invention provides a method for preparing a high temperature resistant aerogel insulating material by normal pressure drying instead of complex processes such as supercritical drying and freeze drying.

The present invention provides, in a first aspect, a method for preparing a high temperature resistant aerogel thermal insulation material by atmospheric drying, characterized in that the method comprises the following steps:

(1) Preparation of nanowire solution: Alumina nanowire dispersion was prepared by hydrothermal method;

(2) nanowire solution dispersion: adding the nanowire dispersion prepared in step (1) into a solvent by stirring and ultrasonic treatment to obtain a uniformly mixed solution, and the solid content in the solution is controlled at 7% by weight to 20% by weight;

(3) silicon source hydrolysis process: in the dispersion liquid of step (2), add the mixture of methyl orthosilicate and ethyl orthosilicate and then stir to make the silicon ester hydrolysis; The solution is evacuated to remove air bubbles;

(4) Gel process: after removing the bubbles in step (3), add catalyst, stir and mix well, seal and stand for gelation reaction to obtain gel, and stand for 5h to 48h at 25° C. 1h to 144h at 80°C;

(5) Hydrophobic modification process: the above gel is placed in n-hexane for solvent replacement, the volume ratio of gel to solvent is 1:10, replacement is performed 1-5 times, and each replacement is performed for 1-5 days. The reagent is a mixture of trimethylchlorosilane and an organic solvent, and finally washed 1-5 times in a pure solvent, each 2h to 24h, the pure solvent is the pure solvent of the organic solvent used;

(6) Atmospheric drying process: the wet gel after solvent replacement is subjected to an atmospheric drying process to obtain an aerogel. Dry for 0.5h to 24h, and dry at 100°C to 200°C for 0.5h to 24h;

(7) Post-treatment process: the prepared aerogel is subjected to staged heat treatment, and the staged heat treatment is to treat at 500°C to 700°C for 0.1h to 20h, and at 900°C to 1100°C for 0.1h to 20h, respectively. , at 1100°C to 1300°C for 0.1h to 20h, and at 1300°C to 1500°C for 1min-200min.

In the method for preparing a high temperature resistant aerogel insulating material by atmospheric drying of the present invention, the hydrothermal method is performed at 100°C-300°C for 1-10 hours.

In the method for preparing a high temperature resistant aerogel heat insulating material by atmospheric drying of the present invention, the aspect ratio of the alumina nanowires is 10-1000.

In the method for preparing a high temperature resistant aerogel thermal insulation material by atmospheric drying of the present invention, in the mixture of methyl orthosilicate and ethyl orthosilicate, the molar ratio of methyl orthosilicate and ethyl orthosilicate is 1:1-1:10.

In the method for preparing high temperature resistant aerogel thermal insulation material by atmospheric drying of the present invention, the organic solvent in the hydrophobic reagent described in step (5) is selected from the group consisting of n-hexane, ethanol and acetone, trimethyl chloride The molar ratio of silane to the organic solvent is 1:1-1:10.

In the method for preparing a high temperature resistant aerogel heat insulating material by atmospheric drying of the present invention, the catalyst in step (4) is 1M ammonium fluoride.

In the method for preparing a high temperature resistant aerogel heat insulating material by atmospheric drying of the present invention, the solvent in step (2) is water and/or ethanol.

In the method for preparing a high temperature resistant aerogel heat insulating material by atmospheric drying of the present invention, the ultrasonic treatment conditions in step (2) are 30kHZ to 80kHZ, 250min.

In the method for preparing a high temperature resistant aerogel heat insulating material by atmospheric drying of the present invention, in step (3), the silicon ester is subjected to a hydrolysis process reaction, so that the final weight ratio of silicon:aluminum is 3:7.

In the method for preparing a high temperature resistant aerogel heat insulating material by atmospheric drying of the present invention, the staged heat treatment in step (7) is: treating at 500°C to 700°C for 0.2h to 6h, and at 900°C to 1100°C respectively. Treat at ℃ for 0.2h to 6h, treat at 1100℃ to 1300℃ for 0.2h to 6h, treat at 1300℃ to 1500℃ for 1min to 40min.

In the second aspect of the present invention, there is provided a high temperature resistant special-shaped nanocrystalline aerogel material prepared by the preparation method described in the first aspect of the present invention.

Compared with the prior art, the present invention at least has the following beneficial effects:

(1) In the present invention, nanowires with longer length are used as the main unit for the assembly process, which not only ensures low thermal conductivity, but also improves the overall temperature resistance of the material due to the self-supporting effect of the three-dimensional network structure.

(2) Nanowires with an aspect ratio of 10-1000, preferably 20-200, can realize a physical cross wet gel network structure in the dispersion, and can effectively realize the sub-support during the normal pressure drying process, avoiding the size shrinkage serious problem.

(3) The preparation method adopts the hydrophobic modification process in the gel stage, which can reduce the surface tension of solvent removal, and adopts the normal pressure drying instead of the supercritical drying process, which greatly reduces the preparation cost and shortens the preparation period.

(4) The post-treatment process of this patent adopts a graded heat treatment process, so that the hydroxyl groups on the surface of aluminum hydroxide react with the silicon-aluminum components, forming a high-temperature stable phase and strengthening the skeleton, which effectively improves the temperature resistance and mechanical properties of the material. .

(5) The nanowire aerogel prepared in this patent has a high degree of three-dimensional network overlapping structure, realizing that the pore volume accounts for more than 99% of the total volume, and realizing the preparation of ultra-low density aerogel.

(6) The silicon phase component is added in this patent, and the silicon dioxide component and the alumina component form a high temperature resistant mullite phase at high temperature, so as to realize the high temperature stability of the material.

Description of drawings

Fig. 1 is the preparation flow chart of the present invention.

FIG. 2 is a SEM image of the alumina nanowires prepared in Embodiment 1. FIG.

FIG. 3 is a macroscopic optical photograph of the alumina nanowire aerogel prepared in Embodiment 1. FIG.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It is obvious that the described embodiments are part of examples of the present invention and do not limit the scope of protection of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

The present invention provides, in a first aspect, a method for preparing a high temperature resistant special-shaped nanocrystalline aerogel material, the method comprising the following steps:

(1) Preparation of nanowire solution: Alumina nanowire dispersion was prepared by hydrothermal method;

(2) nanowire solution dispersion: adding the nanowire dispersion prepared in step (1) into a solvent by stirring and ultrasonic treatment to obtain a uniformly mixed solution, and the solid content in the solution is controlled at 7% by weight to 20% by weight;

(3) Hydrolysis process of silicon source: add the mixture of methyl orthosilicate and ethyl orthosilicate in the dispersion liquid of step (2), and then stir, such as high-speed stirring, so that the hydrolysis reaction of silicon ester occurs; After complete, the above solution is vacuumized to remove air bubbles;

(4) Gel process: after removing the bubbles in step (3), add catalyst, stir and mix well, seal and stand for gelation reaction to obtain gel, and stand for 80 hours after 5-48h at 25°C. 1-144h at ℃;

(5) Hydrophobic modification process: place the above-mentioned gel in n-hexane for solvent replacement, the volume ratio of gel to solvent is 1:10 for replacement 1-5 times, each replacement is 1-5 days, the hydrophobic reagent It is a mixture of trimethylchlorosilane and an organic solvent, and finally washed 1-5 times in pure solvent for 2-24 hours each time, and the pure solvent is the pure solvent of the organic solvent used;

(6) Atmospheric drying process: the wet gel after solvent replacement is subjected to an atmospheric drying process to obtain aerogels. The atmospheric drying process is drying at room temperature for 12-72 hours and drying at 30-60° C. 0.5-24h, drying at 100-200℃ for 0.5-24h;

(7) Post-treatment process: The prepared aerogels are heat-treated in stages, treated at 500-700 °C for 0.1-20 h, 900-1100 °C for 0.1-20 h, and 1100-1300 °C for 0.1 h. -20h, treated at 1300-1500°C for 1min-200min.

In the preparation method of the alumina nanowire aerogel thermal insulation material of the present invention, an example of the preparation of the nanowire solution in step (1) is: 1-30 g of alumina nano-powder (with a particle size of 5-50 nm) Dissolve in 10-300mL water, add 0.001-1mol/L sulfuric acid as adsorbent and react at 100-300℃ for 1-10h to obtain alumina nanowires with diameters of 10nm-300nm and lengths of 1μm-5μm.

An example of the dispersion of the nanowire solution in step (2) is: adding a certain amount of water and ethanol (volume ratio 1:1-10:1) to the nanowire dispersion in step (1) to mix the solution uniformly by stirring and ultrasonic treatment , the solid content of the solution is controlled at 7% by weight to 20% by weight.

The example of the step (3) silicon source hydrolysis process is: take 50g of the dispersion liquid of step (2), add 3-20g of a mixture of 1:1 methyl orthosilicate and ethyl orthosilicate, and perform high-speed stirring to make the silicon ester. A hydrolysis process occurs, so that the final solid content ratio of silicon and aluminum is 1:9-5:5; the obtained mixed solution is evacuated for 0.1-2h under the conditions of a temperature of 10-50°C and a vacuum degree of 0.1-0.3MPa, The obtained mixed solution of alumina nanowires/silica sol/boric acid is allowed to stand for 6-72 hours to defoaming.

An example of the gel process in step (4) is: in step (3), after methyl orthosilicate and ethyl orthosilicate are completely hydrolyzed, add 0.5-5 g of a catalyst (1M ammonium fluoride), stir and mix well, seal and stand for a while. Gelation reaction (5-48h at 25°C and 1-144h at 80°C);

An example of the hydrophobic modification process in step (5) is: the above-mentioned gel is placed in n-hexane for solvent replacement, and the volume ratio of gel to solvent is 1:10 for 1-5 replacements, each replacement for 1-5 days. Modified by soaking in a mixture of hydrophobic reagent (trimethylchlorosilane) and organic solvent (n-hexane, ethanol and/or acetone, etc.) (molar ratio of 1:1-1:10) for 1-5 days, and finally in pure solvent Wash (1-5 times, 2-24h each time).

An example of the drying process at atmospheric pressure in step (6) is: subjecting the modified wet gel to an atmospheric drying process, which is drying at room temperature for 12-72 hours, drying at 30-60° C. for 0.5-24 hours, and drying at 100°C for 12-72 hours. Dry at -200℃ for 0.5-24h.

An example of the post-treatment process of step (7) is: heat treatment of the prepared aerogel in stages, at 500-700°C for 0.2-6h, at 900-1100°C for 0.2-6h, and at 1100-1300°C Treat at ℃ for 0.2-6h, and treat at 1300-1500℃ for 1-40min. Finally, the preparation of high temperature resistant aerogel insulation material is realized.

One or more of the above examples of steps (1) to (7) may be combined together to form an example of the method of the present invention.

The alumina nanowires of the present invention are prepared by a hydrothermal method, and the temperature is 100° C.-300° C. for 1-10 hours.

The aspect ratio of the alumina nanowires of the present invention is 10-1000, preferably 20-800, 30-700, 50-500 or 100-200. If the aspect ratio is less than 10, it is difficult for the nanorods to achieve normal pressure drying through their self-lapping effect; if the aspect ratio is greater than 1000, the strength of the nanorods crosses, and serious crosslinking and agglomeration occur. For example, the linear shrinkage of the comparative example 5 alumina nanowire aerogel material prepared with alumina nanowires with an aspect ratio of 5 is too high.

The organic solvent in the hydrophobic reagent of the present invention is n-hexane, ethanol and acetone, and the molar ratio of trimethylchlorosilane to the organic solvent is 1:1-1:10. By diluting the nanowires with a suitable organic solvent, the nanowires can be freely stretched and exist in a linear form in the final system to increase the strength of the alumina nanowire aerogel material, for example, see Comparative Example 2.

Step (3) During the hydrolysis of the silicon source, relative to 50 g of the dispersion liquid, the added volume is 3-20 g of a mixture of 1:1 methyl orthosilicate and ethyl orthosilicate. If the content of silicon ester added is too small, the system cannot be gelled and hydrophobic modification cannot be performed, for example, see Comparative Example 3.

The mixed liquid obtained by mixing and hydrolyzing the dispersing liquid and the silicate in step (3) needs to be subjected to vacuum treatment to avoid the formation of pore defects in the material.

The catalyst described in the step (4) of the present invention is 1M ammonium fluoride.

The solvent described in the step (2) of the present invention is water and ethanol.

The ultrasonic treatment conditions described in the step (2) of the present invention are 30kHZ-80kHZ, 20min-50min.

In the step (3) of the present invention, the weight ratio of silicon:aluminum is 1:9-5:5, preferably 3:7. If the silicon content is too small, the overlap between the nanowires will not be fixed by enough silicon oxide, and the strength is weak; if the silicon content is too high, the silicon oxide content will reduce the temperature resistance of the material.

In the present invention, the silicon source material is mixed with the alumina nanowires, and then the silicon source material is hydrolyzed in-situ. The significance of the in-situ hydrolysis is that the silicon ester is hydrolyzed during the hydrolysis process and has adsorption and weak interaction with the nanowires. effect.

In the mixture of methyl orthosilicate and ethyl orthosilicate of the present invention, the molar ratio of methyl orthosilicate and ethyl orthosilicate is 1:1-1:20, preferably 1:1-1:10.

During the hydrolysis of the silicon source in step (3), the generated silica sol particles can be adsorbed on the surface of the nanowires through physical adsorption to form a dispersed phase, which reduces the interaction between the nanoparticles, thereby reducing the overall viscosity of the material system.

The step (6) of the present invention is to dry the modified wet gel at atmospheric pressure, and the process is to dry at room temperature for 12-72 hours, at 30-60° C. for 0.5-24 hours, and at 100-200° C. for 0.5 hours. -24h. The significance of this step-by-step drying is that the rate of water volatilization can be adapted to the water content in the wet gel, so as to avoid the rapid volatilization of water in the wet gel and the collapse of the skeleton. For example, the alumina nanowire aerogel material of Comparative Example 4 prepared by one-step drying has too small specific surface area and too high thermal shrinkage rate.

The step (7) of the present invention is to perform heat treatment on the prepared aerogel in stages, at 500-700°C for 0.2-6h, at 900-1100°C for 0.2-6h, and at 1100-1300°C for 0.2-6h. Treat for 0.2-6h, and treat at 1300-1500°C for 1-40min. Finally, the preparation of high temperature resistant aerogel insulation material is realized. The significance of staged heat treatment is that different temperature ranges lead to different dehydration or crystal transformation reactions, which will induce a certain volume shrinkage of the material. The significance of the staged heat treatment is to completely react the crystal transformation process of each temperature range, slow down the rate of volume shrinkage, and avoid the collapse of the material structure. At the same time, the staged heat treatment also provides sufficient time for the construction of the high temperature stable phase, which can also inhibit the shrinkage of the material. Through the above-mentioned staged heat treatment of the present invention, an optimal balance between dehydration and/or crystal transformation and material volume shrinkage can be achieved, thereby obtaining a high temperature stable phase. The reaction occurs between the hydroxyl groups on the surface of aluminum hydroxide and the silicon-alumina components to generate a high-temperature stable phase and strengthen the skeleton, which effectively improves the temperature resistance and mechanical properties of the material. It can be seen from Comparative Example 6 that without the step-by-step heat treatment of the present invention, the material has obvious powder drop phenomenon, weak strength, and insufficient temperature resistance.

The present invention will be further described below by way of examples, but the protection scope of the present invention is not limited to these embodiments.

Example 1

(1) Dissolve 12 g of alumina nano-powder (particle size is 15 nm) in 100 mL of water, and the solid content of the prepared solution is 10.7%. Add 0.025mol/L sulfuric acid as adsorbent and react at 230℃ for 8h to obtain alumina nanowires with two-dimensional diameter of 200nm and length of 2-4μm.

(2) Nanowire solution dispersion: Add a certain amount of water and ethanol (volume ratio 2:1) to the nanowire dispersion in step (1) to mix the solution uniformly by stirring and ultrasonic treatment, and the solid content of the solution is controlled at 10%.

(3) Hydrolysis process of silicon source: take 50 g of the dispersion liquid in step (2) and add 7 g of a mixture of 1:1 methyl orthosilicate and ethyl orthosilicate, and perform high-speed stirring to make the silicon ester undergo a hydrolysis process, so that the final The solid content ratio of silicon and aluminum is 3:7; the obtained mixed solution is evacuated for 0.5 h under the conditions of a temperature of 25 ° C and a vacuum degree of 0.1 to 0.3 MPa, and the obtained mixed solution of alumina nanowires/silica sol/boric acid , let stand for 12h to defoam;

(4) Gel process: in step (3), after methyl orthosilicate and ethyl orthosilicate are completely hydrolyzed, add 4 g of catalyst (1M ammonium fluoride), stir and mix, seal and stand for gelation reaction (25 24h at ℃ and then 48h at 80℃);

(5) Hydrophobic modification process: The above-mentioned gel was placed in n-hexane for solvent replacement, and the volume ratio of gel to solvent was 1:10 for 2 replacements, each replacement for 3 days. Modified by soaking in a mixture (molar ratio of 1:4) of hydrophobic reagent (trimethylchlorosilane) and organic solvent (n-hexane, ethanol, acetone, etc.) for 4 days, and finally washed in pure solvent (2 times, 24h each time) ).

(6) Drying process at atmospheric pressure: The modified wet gel is subjected to atmospheric drying process, which is drying at room temperature for 24 hours, drying at 45 °C for 5 hours, and drying at 120 °C for 5 hours.

(7) Post-treatment process: The prepared aerogels were heat-treated in stages at 600 °C for 1 h, 1000 °C for 1 h, 1200 °C for 1 h, and 1400 °C for 10 min. Finally, the preparation of high temperature resistant aerogel insulation material is realized.

The alumina aerogel prepared under this condition has a specific surface area of 88 m ² /g, a density of 0.18 g/cm ³ , and a linear shrinkage of 7.5% after heat treatment at 1400° C. for 1 h.

Example 2

Example 2 is basically the same as Example 1, except that the alumina nanocrystals in step 1 are 20 g, and the solid content of the prepared solution is 18%.

The thermal insulation performance test was carried out on the alumina nanowire aerogel material in Example 2, and it was found that the surface of the aerogel material did not change color, and did not fall off when it was lightly touched. Other performance indicators are shown in Table 1.

Comparative Example 1

Comparative Example 1 is basically the same as Example 1, except that the hydrophobic modification process of Step 5 is not performed.

Comparing the thermal insulation performance test of the alumina nanowire aerogel material in Comparative Example 1, it is found that the surface of the aerogel material has no discoloration, and no peeling off when lightly touched. Other performance indicators are shown in Table 1.

Comparative Example 2

Comparative Example 2 is basically the same as Example 1, except that the dilution process of ethanol and water in Step 2 is not carried out.

In Comparative Example 2, since the dilution process was not carried out, the nanowires were viscous and knotted, and finally a flat surface aerogel material could not be formed.

Comparative Example 3

Comparative Example 3 is basically the same as Example 1, except that 2 g of silicon ester is added in the preparation process.

In Comparative Example 3, the alumina nanowires added less silicon ester, so the system could not be gelled and hydrophobic modification could not be carried out.

Comparative Example 4

Comparative Example 4 is basically the same as Example 1, except that the drying process in Step 6 is 2h at 150°C.

The thermal insulation performance of the alumina nanowire aerogel material in Comparative Example 4 was tested, and it was found that the surface of the nanowire aerogel material did not discolor, and did not fall off when it was lightly touched. Other performance indicators are shown in Table 1.

Comparative Example 5

Comparative Example 5 is basically the same as Example 1, except that: in step 1, the hydrothermal reaction time of the nanowires is 2h, and a low aspect ratio nanowire with a diameter of 40 nm and a length of 200 nm is obtained.

The thermal insulation performance of the alumina nanowire aerogel material in Comparative Example 5 was tested, and it was found that the surface of the nanowire aerogel material had no discoloration and no peeling off when lightly touched. Other performance indicators are shown in Table 1.

Comparative Example 6

Comparative Example 6.1 is basically the same as Example 1, except that no post-treatment process is performed.

The thermal insulation performance of the alumina nanowire aerogel material in Comparative Example 6.1 was tested, and it was found that the material had obvious powder drop phenomenon, weak strength, and insufficient temperature resistance.

Comparative Example 6.2 is basically the same as Example 1, except that the post-treatment is performed in one step: 1000° C. for 4 h.

Comparative Example 6.3 is basically the same as Example 1, except that the post-treatment is carried out in 2 steps: 600°C for 2h, then 1000°C for 2h.

The thermal insulation performance of the alumina nanowire aerogel material in Comparative Example 6.1 was tested, and it was found that the material had obvious powder drop phenomenon, weak strength, and insufficient temperature resistance.

The thermal insulation performance of the alumina nanowire aerogel material in Comparative Example 6.2 was tested, and it was found that the silicon oxide component of the material was not completely sintered, resulting in weak material strength and insufficient temperature resistance.

The thermal insulation performance of the alumina nanowire aerogel material in Comparative Example 6.3 was tested, and it was found that the sintering process of the material did not undergo a step heating, the shrinkage was large, and the silicon oxide component was not completely sintered, resulting in weak strength and temperature resistance of the material. Sexual insufficiency.

Comparative Example 7

Comparative Example 7 is basically the same as Example 1, except that: in Step 1, spherical nanocrystals with a diameter of 13 nm are used instead of nanowire materials, and the subsequent steps are the same.

The results show that the obtained material has large drying shrinkage under normal pressure and unsatisfactory temperature resistance.

Comparative Example 8

Comparative example 8 is basically the same as embodiment 1, and the difference is: in step 3, the vacuum pumping process is not carried out;

The prepared material was tested by SEM, and it was found that there were a large number of pores inside the material, causing defects.

Comparative Example 9

①Sol preparation

Weigh 160 g of methyl orthosilicate and 160 g of acetonitrile into a 500 mL beaker, seal it with plastic wrap, and perform magnetic stirring for 1 min. After mixing evenly, add 60 g of hydrochloric acid with a concentration of 0.003 mol/L as a catalyst. This process needs to be added slowly, and magnetic stirring is performed for 5 min; And accompanied by refluxing for 30min, the first solution of siliceous sol precursor was obtained; 160g of methyl orthosilicate was added to the obtained first solution of siliceous sol precursor, and the heating and magnetic stirring were continued at 70°C for 16h. A siliceous sol (silica sol) was obtained. The siliceous sol was diluted, 300 g of the solvent contained in the siliceous sol was evaporated, and 600 g of acetonitrile was added and mixed evenly to obtain a diluted siliceous sol, and the diluted siliceous sol was refrigerated for later use.

②Spherical nanocrystal assembly process

Dissolve 3.7g of alumina spherical nanocrystalline powder in 34g of acetonitrile, stir evenly to obtain a first mixed solution, then add 8g of the above-mentioned diluted silica sol to the first mixed solution as a binder, and ultrasonically disperse After 20 min, a second mixed solution was obtained, and 2 g of ammonia water with a concentration of 0.43 mol/L was added to the second mixed solution, and the ultrasonic wave was continued for 20 min to prepare an aerogel wet gel with oxide nanocrystals as a skeleton.

③Gelling and aging

The prepared aerogel wet gel was placed in a mold, left standing for 24 hours, and then placed in an oven at 60° C. for 48 hours to complete the process of gelation and aging.

④Solvent replacement

The gel after gelation and aging was taken out and put into 10 times the volume of ethanol for solvent replacement. The solvent replacement time was 3 d, and the solvent replacement process was repeated 3 times.

⑤ supercritical drying to obtain aerogel materials.

⑥ Heat treatment process

The above aerogel material was heated to 1200°C (heat treatment temperature) in a furnace, the heating rate was 10°C/min, and the temperature was kept for 1 h (heat treatment time) and then cooled to room temperature with the furnace to obtain a high temperature resistant aerogel material.

In Comparative Example 9, the assembly process of spherical nanocrystals is used instead of nanowires or nanorods, and the solvent system used is acetonitrile, and the drying process is a supercritical drying process.

Table 1 shows the performance indexes of the high temperature resistant special-shaped nanocrystalline aerogel materials in Examples 1 to 2 and the high temperature resistant aerogel materials in Comparative Examples 1 to 9.

Comparative Example 10

Comparative Example 10 was prepared according to Example 1 disclosed in CN110282958A (ie, drying under high pressure supercritical conditions).

Specifically, the specific process of Comparative Example 10 is as follows.

S1. Preparation of special-shaped nanocrystal dispersion: using alumina nanopowder as raw material, disperse 20g of alumina nanopowder in 500mL aqueous solution, wherein the particle size of a single particle of nanopowder is in the range of 10-200nm; choose 2mol/L 15mL of hydrochloric acid was added as a catalyst (adsorbent) to the mixture of the above-mentioned alumina nanoparticles, the mixture was placed in a reaction kettle with polytetrafluoroethylene as an inner liner, sealed, and placed at 240 ° C to react for 3h to obtain special-shaped nanometer particles. crystal dispersion.

S2. Self-assembly process of special-shaped nanocrystals: fully mix 30 g of the above-prepared special-shaped nanocrystal dispersion with 20 g of silicic acid with a concentration of 4 wt%, fully stir with the magnet for 5 hours, and then ultrasonicate for 30 minutes to obtain a mixed phase of self-assembled special-shaped nanocrystals first solution.

S3, gelation reaction process: add 2g of NH ₄ F solution with a concentration of 1 mol/L/ to the above-mentioned mixed phase first solution, fully stir with a magnet for 0.5 h and then ultrasonicate for 30 min to obtain a mixed phase second solution; The second solution of the mixed phase is placed at 25° C., and the vacuum degree is 0.5 MPa, and then the solution is taken out for 0.1 h and left to stand to obtain a gelation reaction solution.

S4. Aging process: seal the above gelling reaction solution and place it at 25°C for 12h aging to make the network fully overlapped, and then place it in a water bath for 72h at 60°C for aging. At this time, the humidity in the beaker is required to be 80%. above.

S5. Drying process: the above gelation reaction solution is aged and gelled, and then undergoes a solvent replacement process with ethanol. Each replacement is performed for 3 days, and the replacement is performed 3 times to obtain a silica-alumina wet gel, and then anhydrous ethanol is used as a drying medium. supercritical drying: the silicon-alumina composite wet gel is placed in a supercritical drying equipment and the supercritical drying equipment is placed in an autoclave, anhydrous ethanol is added to the autoclave and sealed to make the pressure in the autoclave The temperature is 25MPa, the temperature is 30°C, the pressure and temperature are maintained for 24h, and then the anhydrous ethanol and the fluid produced in the drying process are discharged to prepare the special-shaped nanocrystalline aerogel material.

S6, heat treatment process (post-treatment process): the first stage of the special-shaped nanocrystalline aerogel material obtained in step S5 is treated at a low temperature of 300 ° C for 5 hours, so that the silicon-aluminum composite aerogel undergoes a dehydroxylation process, and the silicon-aluminum composite aerogel is realized. The first step of the aerogel has a strong skeleton; after the above steps are carried out, the sample is cooled to room temperature, and the second stage is heat treated at 600 ° C for 3 hours, so that the crystal form of the composite silica-alumina sol undergoes a preliminary transformation; Cool to room temperature, carry out the third stage, heat treatment at 1200 ° C for 1 h, and finally cool down to room temperature with the furnace to obtain a high temperature resistant special-shaped nanocrystalline aerogel material with a strong structural skeleton; the heating rates of the above three stages of heat treatment process are all is 3°C/min.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand: it can still be Modifications are made to the technical solutions described in the foregoing embodiments, or some technical features thereof are equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (10)

1. The method for preparing the high-temperature-resistant aerogel heat-insulating material by normal-pressure drying is characterized by comprising the following steps of:

(1) preparing a nanowire solution: preparing an aluminum oxide nanowire dispersion by a hydrothermal method;

(2) and (3) nanowire solution dispersion: adding the nanowire dispersion prepared in the step (1) into a solvent, and stirring and performing ultrasonic treatment to obtain a uniformly mixed solution, wherein the solid content in the solution is controlled to be 7-20 wt%;

(3) the hydrolysis process of the silicon source: adding a mixture of methyl orthosilicate and ethyl orthosilicate into the dispersion liquid in the step (2), and then stirring to enable silicon ester to generate hydrolysis reaction; after the hydrolysis of the silicon ester is completed, vacuumizing the solution to remove bubbles;

(4) And (3) gel process: after the bubbles are removed in the step (3), adding a catalyst, stirring uniformly, sealing and standing for gelation reaction to obtain gel, wherein the standing condition is 5h to 48h at 25 ℃, and then 1h to 144h at 80 ℃;

(5) hydrophobic modification process: and (3) placing the gel in n-hexane for solvent replacement, wherein the volume ratio of the gel to the solvent is 1: 10, replacing for 1-5 times, wherein each time of replacement is 1-5 days, the hydrophobic reagent is a mixture of trimethylchlorosilane and an organic solvent, and finally washing for 1-5 times in a pure solvent, wherein each time of 2-24 hours, and the pure solvent is the pure solvent of the used organic solvent;

(6) and (3) drying under normal pressure: carrying out normal pressure drying process on the wet gel after solvent replacement to obtain the aerogel, wherein the normal pressure drying process is respectively drying at room temperature for 12h to 72h, drying at 30 ℃ to 60 ℃ for 0.5h to 24h, and drying at 100 ℃ to 200 ℃ for 0.5h to 24 h;

(7) and (3) post-treatment process: and carrying out staged heat treatment on the prepared aerogel, wherein the staged heat treatment is respectively carried out for 0.1 to 20 hours at 500 to 700 ℃, for 0.1 to 20 hours at 900 to 1100 ℃, for 0.1 to 20 hours at 1100 to 1300 ℃ and for 1min to 200min at 1300 to 1500 ℃.

2. The process of claim 1, wherein the hydrothermal process is carried out at 100 ℃ to 300 ℃ for 1h to 10 h.

3. The method of claim 1, wherein the alumina nanowires have an aspect ratio of 10 to 1000.

4. The method of claim 1, wherein the mixture of methyl orthosilicate and ethyl orthosilicate has a molar ratio of methyl orthosilicate to ethyl orthosilicate in the range of 1:1 to 1: 20.

5. The method of claim 1, wherein in step (5) the organic solvent of the hydrophobic reagent is selected from the group consisting of n-hexane, ethanol and acetone, and the molar ratio of trimethylchlorosilane to the organic solvent is 1:1 to 1: 10.

6. the process of claim 1, wherein the catalyst in step (4) is 1M ammonium fluoride.

7. The method of claim 1, wherein the solvent in step (2) is water and/or ethanol.

8. The method of claim 1, wherein the sonication conditions in step (2) are between 30 and 80kHZ, between 2 and 50 min.

9. The method of claim 1, wherein the step (3) comprises hydrolyzing the silicon ester to form a silicon: the weight ratio of aluminum is 3: 7.

10. the method of claim 1, the staged heat treatment in step (7) being: respectively treating at 500-700 deg.C for 0.2-6 h, at 900-1100 deg.C for 0.2-6 h, at 1100-1300 deg.C for 0.2-6 h, and at 1300-1500 deg.C for 1-40 min.

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