CN111848205B - Method for preparing high-temperature-resistant aerogel heat-insulating material by normal-pressure drying - Google Patents

Abstract

The invention relates to a method for preparing a high-temperature resistant aerogel heat insulation material by normal-pressure drying, which comprises the following steps: the preparation method comprises the following steps of (1) preparing a nanowire solution, (2) dispersing the nanowire solution, (3) hydrolyzing a silicon source, (4) gelling, (5) performing hydrophobic modification, (6) drying at normal pressure, and (7) performing post-treatment. The method adopts the alumina nanowires with high length-diameter ratio to carry out three-dimensional lap joint, and adopts silica sol as a sintering aid to realize the generation of high-temperature stable phases and the strengthening of a nanometer framework. And (3) modifying the wet gel by adopting a hydrophobic reagent to realize a normal-pressure drying process. The invention realizes the low-cost and short-period preparation of the high-temperature (above 1400 ℃) resistant heat-insulating material.

Description

A method for preparing high-temperature-resistant airgel thermal insulation materials by drying under normal pressure

technical field

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

Background technique

Airgel is a nanoporous material with a three-dimensional network structure. As a solid with high porosity, airgel 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 thermal conductivity at room temperature can be as low as 0.012W/m·k . It is precisely because of these characteristics that airgel materials have broad application potential in thermal, acoustic, optical, microelectronics, and particle detection. There are many ways to prepare airgel. However, the drying process is difficult to break through in the preparation. Due to the fine skeleton structure of airgel, during the normal pressure drying process, 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 airgel drying method is still the general method of supercritical drying, and a few types of airgel can be freeze-dried or dried under normal pressure. However, whether it is supercritical drying or normal pressure drying, it will bring high cost and long cycle, which seriously limits the popularization and application of airgel materials. Therefore, developing an efficient atmospheric drying method is an important issue for airgel preparation.

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

In recent years, nano-ceramic fiber aerogels have attracted extensive attention of researchers due to their good temperature resistance, elasticity and light weight properties. At present, most of the methods for preparing nano-ceramic fiber aerogels are to prepare nano-fibers by electrospinning, disperse the nano-fibers and then freeze-dry them. The nanofiber airgel prepared by this method has excellent comprehensive properties. However, the preparation of airgel materials by electrospinning has the limitations of high cost and difficult scale-up.

Chinese patent document CN101254449A discloses a preparation method of oxide nanowire-reinforced transparent airgel bulk material, in which the sol and oxide nanowire are mixed to form a composite gel, dried after aging to obtain oxide nanowire-enhanced transparent airgel The gel bulk material, wherein the mass ratio of the oxide nanowires to the sol is 1:0.5-1000, the diameter of the nanowires is 1-100nm, and the aspect ratio is 10-1000. But the sol is pre-formed rather than formed in situ by hydrolysis when the silicon source material is mixed with the alumina nanowires. The nanowires play the role of reinforcement, and the content is less. This material system is used to prepare transparent airgel, and the material system has insufficient temperature resistance, and its deformation degree is large during the drying process, and its thermal insulation performance is poor.

With the development of science and technology, various fields have put forward higher requirements for the temperature resistance and high temperature insulation performance of insulation materials. Therefore, it is very necessary to develop a low-cost, short-cycle method to prepare high temperature resistant and Airgel materials that can effectively insulate heat at high temperatures. This patent proposes a preparation method of nanowire airgel, which has good temperature resistance. And through the surface modification and physical self-supporting effect, the airgel insulation material with high temperature resistance and high performance can be prepared by drying under normal pressure.

Contents of the invention

In order to solve the technical problems existing in the prior art, the present invention provides a method for preparing high-temperature-resistant airgel heat-insulating materials by replacing complex processes such as supercritical drying and freeze-drying with normal-pressure drying.

In the first aspect, the present invention provides a method for preparing high-temperature-resistant airgel thermal insulation materials by drying under normal pressure, characterized in that the method comprises the following steps:

(1) Preparation of nanowire solution: prepare aluminum oxide nanowire dispersion by hydrothermal method;

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

(3) Silicon source hydrolysis process: add a mixture of methyl orthosilicate and ethyl orthosilicate to the dispersion liquid in step (2) and then stir to make the silicon ester hydrolyze; after the silicon ester is hydrolyzed completely, the above The solution is vacuumized to remove air bubbles;

(4) Gelation process: after removing the air bubbles in step (3), add a catalyst and stir to mix evenly, seal and stand still for gelation reaction to obtain a gel. The standing condition is 5h to 48h at 25°C, and then 1h to 144h at 80°C;

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

(6) Atmospheric pressure drying process: The wet gel after solvent replacement is subjected to an atmospheric pressure drying process to obtain an aerogel. The atmospheric pressure drying process is to dry at room temperature for 12h to 72h, at 30°C to 60°C Drying for 0.5h to 24h, drying at 100°C to 200°C for 0.5h to 24h;

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

In the method for preparing high-temperature-resistant airgel thermal insulation materials by drying under normal pressure in the present invention, the hydrothermal method is carried out at 100° C.-300° C. for 1-10 hours.

In the method for preparing the high-temperature-resistant airgel thermal insulation material by drying under normal pressure of the present invention, the aspect ratio of the aluminum oxide nanowires is 10-1000.

In the method for preparing the high-temperature-resistant airgel thermal insulation material by normal pressure 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 airgel thermal insulation materials by normal pressure 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 high-temperature-resistant airgel thermal insulation materials by drying under normal pressure of the present invention, the catalyst in step (4) is 1M ammonium fluoride.

In the method for preparing the high-temperature-resistant airgel thermal insulation material by drying under normal pressure of the present invention, the solvent in step (2) is water and/or ethanol.

In the method for preparing high temperature-resistant airgel thermal insulation material by drying under normal pressure of the present invention, the ultrasonic treatment condition in step (2) is 30kHZ to 80kHZ, 2 to 50min.

In the method for preparing high-temperature-resistant airgel thermal insulation materials by drying under normal pressure in the present invention, in step (3), the silicon ester undergoes a hydrolysis reaction, and finally the final silicon:aluminum weight ratio is 3:7.

In the method for preparing high-temperature-resistant airgel thermal insulation materials by drying under normal pressure in the present invention, the staged heat treatment in step (7) is: 0.2h to 6h at 500°C to 700°C, 0.2h to 6h at 900°C to 1100°C 0.2h to 6h at ℃, 0.2h to 6h at 1100℃ to 1300℃, 1min to 40min at 1300℃ to 1500℃.

The second aspect of the present invention provides the high temperature resistant special-shaped nanocrystalline airgel material prepared by the preparation method described in the first aspect of the present invention.

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

(1) In the present invention, nanowires with longer lengths 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) The nanowires with an aspect ratio of 10-1000, preferably 20-200, can realize a physical cross-wet gel network structure in the dispersion liquid, and can effectively realize the sub-support function during the normal pressure drying process, avoiding size shrinkage serious problem.

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

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

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

(6) In this patent, a silicon phase component is added, and the silicon dioxide component and the alumina component form a high-temperature-resistant mullite phase at high temperature to achieve high-temperature stability of the material.

Description of drawings

Fig. 1 is the preparation flowchart of the present invention.

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

Fig. 3 is a macroscopic optical photo of the alumina nanowire airgel prepared in Embodiment 1.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some examples of the present invention and cannot limit the protection scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

In a first aspect, the present invention provides a method for preparing a high-temperature resistant special-shaped nanocrystalline airgel material, said method comprising the steps of:

(1) Preparation of nanowire solution: prepare aluminum oxide nanowire dispersion by hydrothermal method;

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

(3) Silicon source hydrolysis process: add the mixture of methyl orthosilicate and ethyl orthosilicate to the dispersion liquid of step (2), then stir, for example high-speed stirring, make silicon ester hydrolysis reaction; After completion, the above solution is vacuumed to remove air bubbles;

(4) Gelation process: After removing the air bubbles in step (3), add a catalyst and stir to mix evenly, seal and stand still for gelation reaction to obtain a gel. 1-144h at ℃;

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

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

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

In the preparation method of the aluminum oxide nanowire airgel thermal insulation material of the present invention, an example of preparing the nanowire solution in step (1) is: 1-30g of aluminum oxide nanopowder (with a particle size of 5-50nm) Dissolve in 10-300mL water, add 0.001-1mol/L sulfuric acid as an adsorbent and react at 100-300°C for 1-10h to obtain alumina nanowires with a diameter of 10nm-300nm and a length of 1μm-5μm.

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

An example of the silicon source hydrolysis process in step (3) is: take 50 g of the dispersion liquid in step (2) and add 3-20 g of a mixture of methyl orthosilicate and ethyl orthosilicate in a volume of 1:1, and stir at a high speed to make the silicon ester The hydrolysis process occurs, so that the final solid content ratio of silicon and aluminum is 1:9-5:5; the obtained mixed solution is vacuumed for 0.1-2 hours at a temperature of 10-50°C and a vacuum degree of 0.1-0.3MPa. The obtained aluminum oxide nanowire/silica sol/boric acid mixed solution was allowed to stand still for 6-72 hours to defoam.

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

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

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

An example of the post-treatment process in step (7) is: heat-treat the prepared airgel in stages, respectively at 500-700°C for 0.2-6h, at 900-1100°C for 0.2-6h, at 1100°C-1300°C 0.2-6h at ℃, 1-40min at 1300-1500℃. Finally, the preparation of high temperature resistant airgel 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 at 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 own self-lapping effect; if the aspect ratio is greater than 1000, the strength of the nanorods will cross, and serious crosslinking and agglomeration will occur. For example, the wire shrinkage rate of the comparative example 5 alumina nanowire airgel 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, acetone, and the molar ratio of trimethylchlorosilane to the organic solvent is 1:1-1:10. Diluting the nanowires with a suitable organic solvent can make the nanowires stretch freely and exist in a linear form in the final system to increase the strength of the aluminum oxide nanowire airgel material, see Comparative Example 2 for example.

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

The mixed solution obtained after the dispersion liquid and the silicate ester are mixed and hydrolyzed in step (3) needs to be vacuumized to avoid the formation of pore defects in the material.

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

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

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

In 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 have enough silicon oxide to fix, and the strength will be 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 nanowire, and then the silicon source material is hydrolyzed in situ. The significance of the in situ hydrolysis lies in the fact that the silicon ester undergoes adsorption and weak interaction with the nanowire while being hydrolyzed during the hydrolysis process. effect.

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

During the hydrolysis process 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, reduce the interaction between the nanoparticles, and then reduce the overall viscosity of the material system.

The step (6) of the present invention is to dry the wet gel under normal pressure after modification. -24h. The significance of this step-by-step drying is that the rate of moisture volatilization can be adapted to the water content in the wet gel, so as to avoid the collapse of the skeleton caused by the rapid and large volatilization of moisture in the wet gel. For example, the specific surface area of the aluminum oxide nanowire airgel material prepared by one-step drying in Comparative Example 4 is too small, and the thermal shrinkage rate is too high.

Step (7) of the present invention is to heat-treat the prepared airgel in stages, respectively at 500-700°C for 0.2-6h, at 900-1100°C for 0.2-6h, and at 1100°C-1300°C Treat for 0.2-6h, and treat at 1300-1500°C for 1-40min. Finally, the preparation of high temperature resistant airgel 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 staged heat treatment is to completely react the crystal transformation process in 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 a 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 volume shrinkage of the material can be achieved, thereby obtaining a high-temperature stable phase. The reaction between the hydroxyl group on the surface of the aluminum oxyhydroxide and the silicon-aluminum component generates a high-temperature stable phase and strengthens the skeleton, effectively improving the temperature resistance and mechanical properties of the material. It can be seen from Comparative Example 6 that, without performing the staged heat treatment of the present invention, the material has obvious powder falling phenomenon, weak strength, and insufficient temperature resistance.

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

Example 1

(1) 12g of aluminum oxide nanopowder (15nm in particle size) was dissolved in 100mL of water, and the solid content of the obtained solution was 10.7%. Add 0.025 mol/L sulfuric acid as an adsorbent and react at 230° C. for 8 hours to obtain alumina nanowires with a two-dimensional diameter of 200 nm and a length of 2-4 μm.

(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 evenly by stirring and ultrasonic treatment, and control the solid content of the solution at 10%.

(3) Silicon source hydrolysis process: Take 50 g of the dispersion liquid in step (2) and add 7 g of a mixture of methyl orthosilicate and ethyl orthosilicate in a volume of 1:1, and stir at a high speed to cause the hydrolysis process of the silicon ester to make the final The solid content ratio of silicon to aluminum is 3:7; the obtained mixed solution is evacuated for 0.5h at a temperature of 25°C and a vacuum degree of 0.1-0.3MPa, and the obtained alumina nanowire/silica sol/boric acid mixed solution , let stand for 12h to defoam;

(4) Gel process: step (3) after methyl orthosilicate and ethyl orthosilicate are completely hydrolyzed, add catalyzer (1M ammonium fluoride) 4g, stir and mix, seal and leave standstill to treat gelation reaction (25 48h at 80°C after 24h at ℃);

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

(6) Atmospheric pressure drying process: The modified wet gel was subjected to a normal pressure drying process, which was to dry at room temperature for 24 hours, at 45° C. for 5 hours, and at 120° C. for 5 hours.

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

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

Example 2

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

The thermal insulation performance test of the aluminum oxide nanowire airgel material in Example 2 shows that the surface of the airgel material has no discoloration and does not fall off when 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 in Step 5 is not carried out.

The thermal insulation performance of the alumina nanowire airgel material in Comparative Example 1 was tested, and it was found that the surface of the airgel material did not change color and did not fall 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, because the nanowires were not diluted, the nanowires were viscous and knotted, and eventually the airgel material with a smooth surface 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 during the preparation process.

Compared with the aluminum oxide nanowires in Comparative Example 3, due to the small amount of silicon ester added, the system cannot be gelled and hydrophobic modification cannot be performed.

Comparative example 4

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

The thermal insulation performance of the alumina nanowire airgel material in Comparative Example 4 was tested, and it was found that the surface of the nanowire airgel material did not change color and did not fall off when touched lightly. 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 nanowire hydrothermal reaction time is 2 hours, 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 airgel material in Comparative Example 5 was tested, and it was found that the surface of the nanowire airgel material did not change color and did not fall 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 test of the aluminum oxide nanowire airgel material in Comparative Example 6.1 revealed that the material had obvious powder dropping phenomenon, weak strength, and insufficient temperature resistance.

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

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

The thermal insulation performance test of the aluminum oxide nanowire airgel material in Comparative Example 6.1 revealed that the material had obvious powder dropping phenomenon, weak strength, and insufficient temperature resistance.

The thermal insulation performance test of the aluminum oxide nanowire airgel material in Comparative Example 6.2 revealed that the silicon oxide component of the material was not completely sintered, resulting in weak strength and insufficient temperature resistance of the material.

The thermal insulation performance test of the alumina nanowire airgel material in Comparative Example 6.3 found that the sintering process of the material did not undergo a stepwise temperature rise, and the shrinkage was relatively large, and the silicon oxide component was not completely sintered, resulting in weak strength and low temperature resistance. Insufficient sex.

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 a large drying shrinkage under normal pressure, and its temperature resistance is not ideal.

Comparative example 8

Comparative example 8 is substantially 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 found that there were a large number of pores inside the material, resulting in 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 a plastic wrap and perform magnetic stirring for 1 min. After mixing evenly, add 60g of hydrochloric acid with a concentration of 0.003mol/L as a catalyst. This process needs to be added slowly and stirred by magnetic force for 5 minutes; add the above mixed solution into a 1000mL three-necked flask, heat and magnetically stir at 70°C, And accompanied by refluxing for 30 minutes, the first solution of the siliceous sol precursor was obtained; 160 g of methyl orthosilicate was added to the obtained first solution of the siliceous sol precursor, and heating and magnetic stirring were continued at 70° C., and the reaction was carried out for 16 hours. A siliceous sol (silica sol) is obtained. Dilute the siliceous sol, distill 300 g of the solvent contained in the siliceous sol, add 600 g of acetonitrile and mix evenly to obtain the diluted siliceous sol, and refrigerate the diluted siliceous sol for future use.

②Spherical nanocrystal assembly process

Dissolve 3.7g of alumina spherical nanocrystalline powder in 34g of acetonitrile, stir evenly to obtain the 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 minutes, the second mixed solution was obtained, and then 2 g of ammonia water with a concentration of 0.43 mol/L was added to the second mixed solution, and ultrasonication was continued for 20 minutes to prepare an airgel wet gel with oxide nanocrystals as the skeleton.

③Gelation and aging

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

④Solvent replacement

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

⑤Supercritical drying to prepare airgel materials.

⑥Heat treatment process

The above airgel material was heated up to 1200°C (heat treatment temperature) with the furnace at a heating rate of 10°C/min, held for 1 hour (heat treatment time), and then cooled to room temperature with the furnace to obtain a high temperature resistant airgel material.

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

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

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 liquid: 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 Add 15mL of hydrochloric acid as a catalyst (adsorbent) to the above-mentioned mixed solution of alumina nanoparticles, put the mixed solution in a reaction kettle with polytetrafluoroethylene as a liner, seal it, and place it at 240°C for 3 hours to obtain special-shaped nano 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 magnetons 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 2 g of NH ₄ F solution with a concentration of 1 mol/L/ to the first solution of the mixed phase, fully stir it with magnets for 0.5 h, and then ultrasonicate for 30 min to obtain the second solution of the mixed phase; The second solution of the mixed phase was placed at 25° C., vacuumed at a vacuum degree of 0.5 MPa for 0.1 h, and then the solution was taken out and left to stand to obtain a gelation reaction solution.

S4. Aging process: Seal the above gelation reaction solution and place it at 25°C for 12 hours to fully overlap the network, then put it in a water bath environment at 60°C for 72 hours, and at this time, the humidity in the beaker is required to be 80%. above.

S5. Drying process: after aging the above-mentioned gelation reaction solution, the gel is subjected to a solvent replacement process with ethanol. Each replacement is 3 days, and the replacement is 3 times to obtain a silica-alumina wet gel, and then use absolute ethanol as a drying medium. Supercritical drying: put the silicon-aluminum composite wet gel in supercritical drying equipment and place the supercritical drying equipment in an autoclave, add absolute ethanol to the autoclave and seal it, so that the pressure in the autoclave The temperature is 25MPa, the temperature is 30°C, and the pressure and temperature are maintained for 24 hours, and then the absolute ethanol and the fluid generated during the drying process are discharged to prepare a special-shaped nanocrystalline airgel material.

S6. Heat treatment process (post-treatment process): the first stage of the special-shaped nanocrystalline airgel material prepared in step S5 is treated at a low temperature of 300 ° C for 5 hours, so that the dehydroxylation process of the silicon-aluminum composite airgel occurs, and the silicon-aluminum composite 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 then 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; the sample in the previous step Cool to room temperature, proceed to the third stage, heat treatment at 1200°C for 1 hour, and finally cool down to room temperature with the furnace to obtain a high-temperature-resistant special-shaped nanocrystalline airgel material with a strong structural skeleton; the heating rates of the above three stages of heat treatment are the same 3°C/min.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than 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 that: it can still be Modifications are made to the technical solutions described in the foregoing embodiments, or equivalent replacements are made to some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims (8)

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, wherein the length-diameter ratio of the aluminum oxide nanowire is 10-1000;

(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 the silicon ester to have hydrolysis reaction, and finally enabling the ratio of silicon: the weight ratio of aluminum is 3:7; 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 a gelation reaction to obtain a 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 is 1-5 days, then placing the gel into a hydrophobic reagent to be soaked for 1-5 days for modification, wherein 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 is 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 24h;

(7) And (3) post-treatment process: performing staged heat treatment on the prepared aerogel, wherein the staged heat treatment is performed for 0.1 to 20 hours at 500 to 700 ℃, 0.1 to 20 hours at 900 to 1100 ℃, 0.1 to 20 hours at 1100 to 1300 ℃ and 1min to 200min at 1300 to 1500 ℃;

wherein boric acid is added in the step (3).

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

3. The method of claim 1, wherein the molar ratio of methyl orthosilicate to ethyl orthosilicate in the mixture of methyl orthosilicate and ethyl orthosilicate is 1.

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

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

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

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

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

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