Preparation method of high-emissivity high-temperature-resistant silicate high-entropy aerogel

Abstract

The application belongs to the field of preparation process of nanoporous materials, and particularly relates to a preparation method of high-emissivity high-temperature-resistant silicate high-entropy aerogel. The application utilizes a relatively simple sol-gel method to prepare high-entropy silicate aerogel material with excellent high-temperature stability, and the material is expected to meet the needs of the fields of current aerospace, civil kiln and the like. Meanwhile, the simple preparation method of the high-entropy silicate aerogel is conducive to promoting the development of the industrialization of aerogels, and solving the problems of high preparation cost, difficulty in simultaneously achieving high-temperature resistance and high emission of the high-entropy aerogel.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of preparation of nanoporous materials, and particularly relates to a preparation method of a high-emissivity high-temperature-resistant silicate high-entropy aerogel. BACKGROUND

[0002] Aerogel material is a three-dimensional nanoporous network structure material formed by the accumulation of nanoparticles, and has the characteristics of low density, high porosity and high specific surface area, and has high application value in heat insulation, adsorption and the like.

[0003] The increase of the Mach number of a hypersonic vehicle makes the aerodynamic heating environment faced by the surface of the vehicle increasingly severe. The high-temperature airflow outside the vehicle will transfer heat to the vehicle, causing the surface temperature of the vehicle to rise, which poses a great challenge to the safe operation of the vehicle. Therefore, it is of great significance to develop new ultrahigh-temperature, lightweight and high-efficiency thermal insulation materials in view of the requirements of the thermal protection system of different parts of the hypersonic vehicle.

[0004] Due to the high-entropy effect, high-entropy ceramics have better high-temperature stability than single-component ceramics. At present, the synthesis methods of ultrahigh-temperature ceramic powders mainly include element combination method, reduction reaction method, sol-gel method, mechanical alloying method and the like. A variety of new high-entropy oxides have been prepared, including high-entropy rare earth aluminates, high-entropy rare earth zirconates, high-entropy oxides with defect fluorite structure, high-entropy rare earth silicates, high-entropy rare earth phosphates and the like. The research results show that these high-entropy ceramic materials have low thermal conductivity, slow grain growth, controllable thermal expansion coefficient and excellent high-temperature stability. Ren et al. synthesized high-entropy and found that it has higher Young's modulus and lower thermal conductivity than single-component silicate (literature "Ren X, Tian Z, Zhang J, et al. Equiatomic quaternary (Y 0.25 Ho 0.25 Er 0.25 Yb 0.25 )2SiO5silicate: Aperspective multifunctional thermal and environmental barrier coating material[J]. Scripta Materialia, 2019, 168." ). Liu et al. synthesized high-entropy ceramics (Sm 0.2 Eu 0.2 Tb 0.2 Dy 0.2 Lu 0.2)Zr2O7 aerogel powder, and high-entropy ceramic bulk is synthesized by subsequent processes such as pressing and sintering (literature "A novel high-entropy (Sm 0.2 Eu 0.2 Tb 0.2 Dy 0.2 Lu 0.2 )Zr2O7 ceramic aerogel with ultralow thermal conductivity[J].Ceramics International,2021,47,29960-29968.”). However, the high-entropy ceramic synthesized by the above method has a low porosity, a small specific surface area, a low emissivity, and a complex actual operation, and cannot be directly formed into a bulk after high-temperature heat treatment, which is limited in practical application.

[0005] In summary, the high-entropy silicate aerogel material with low thermal conductivity and excellent high-temperature stability is prepared by a simple sol-gel method, which is expected to meet the needs of the fields of aerospace, civil kiln and the like. At the same time, the simple preparation method of the high-entropy silicate aerogel is conducive to promoting the industrialization development of the aerogel, and solving the problems of high preparation cost, high emissivity and high-temperature resistance of the high-entropy aerogel. SUMMARY

[0006] The purpose of the present application is to overcome the problems of the above-mentioned existing ceramic aerogel technology, and to provide a simple operation of a bulk high-entropy silicate aerogel preparation method, to solve the complex preparation process of the high-entropy silicate aerogel, to provide an ultralow thermal conductivity material, to solve the technical problem of insufficient temperature resistance of the high-entropy ceramic aerogel, and most importantly, to have a high emissivity, to solve the "stealth" effect required in the actual use process of the super-speed aircraft, and to expand the application and conversion of the aerogel material.

[0007] The technical scheme of the present application is as follows: a preparation method of a high-emissivity high-temperature-resistant silicate high-entropy aerogel, comprising the following specific steps:

[0008] Five kinds of inorganic metal salts are weighed and added to a mixed solution of a certain proportion of anhydrous ethanol and deionized water until completely dissolved to obtain a mixed salt solution; then a long-chain dispersant is added, and after sufficient stirring, a silicon source is added, and the stirring is continued for a period of time to obtain a silicate precursor solution; the obtained silicate precursor solution is added with a coagulant, stirred and poured into a mold, and after gelation, aging and solvent replacement, supercritical drying is performed, and finally calcination is performed under air atmosphere to obtain a high-entropy silicate aerogel bulk.

[0009] Preferably, the inorganic metal salt is a nitrate and / or halide salt of five different rare earth elements in equimolar ratio, and the silica aerogel has a chemical formula of RE2Si2O7, wherein RE is Mo, Y, W, Ta and Yb.

[0010] Preferably, the molar ratio of the components is 1: (10-60): (10-60): (1-2): (5-10) for the inorganic metal salt: deionized water: anhydrous ethanol: long-chain dispersant: coagulant.

[0011] Preferably, the molar ratio of the inorganic metal salt to the silicon source is 1: (0.75-1.25).

[0012] Preferably, the silicon source is one of tetraethyl orthosilicate, methyl orthosilicate, tetrabutyl orthosilicate, methyltrimethoxysilane, methyltriethoxysilane or hexamethyldisilazane; and the stirring time after adding the silicon source is 20-120 min.

[0013] Preferably, the long-chain dispersant is one of polyacrylic acid, phenolic resin or citric acid; and the stirring time after adding the long-chain dispersant is 30-120 min.

[0014] Preferably, the coagulant is propylene oxide; and the stirring time after adding the coagulant is 1-10 min. Preferably, the gel temperature is 25-60 ℃.

[0015] Preferably, the solvent replacement and aging time is 1-4 d, and the aging liquid (solvent) is replaced every 6-12 h, and the aging liquid (solvent) is anhydrous ethanol.

[0016] Preferably, the supercritical drying is one of ethanol supercritical drying and CO2 supercritical drying; the calcination time is 1-4 h, the calcination temperature is 1050-1600 ℃, and the heating rate is 1-8 ℃ / min. Advantages

[0017] (1) Compared with the preparation of high-entropy silicate materials reported in the literature, the present application is an aerogel material with high porosity (≥95%), and does not require high-energy ball milling technology, and the preparation process is simple and easy to operate;

[0018] (2) Compared with other high-entropy ceramic materials, the silicate aerogel material prepared by the present application has high specific surface area, high emissivity and low thermal conductivity, and has excellent heat insulation and wave absorption performance, with RL=-12 dB (4-18 GHz band) at 700 ℃.

[0019] (3) The series of high-entropy oxides of the present application are all high-entropy silicate aerogels, which have excellent high-temperature stability and a thermal conductivity as low as 0.051 W / (m·K) at 700℃. Meanwhile, the prepared high-entropy silicate aerogels are in the form of blocks. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 macroscopic sample image of the (Mo 0.2 Y 0.2 W 0.2 Ta 0.2 Yb 0.2 )2Si2O7 aerogel prepared in Example 1;

[0021] Figure 2 pore size distribution graph of the (Mo 0.2 Y 0.2 W 0.2 Ta 0.2 Yb 0.2 )2Si2O7 aerogel prepared in Example 2;

[0022] Figure 3 scanning electron microscope graph of the (Mo 0.2 Y 0.2 W 0.2 Ta 0.2 Yb 0.2 )2Si2O7 aerogel prepared in Example 3. DETAILED DESCRIPTION

[0023] The present application will be further described below in conjunction with examples, but the scope of protection is not limited thereto.

[0024] Example 1

[0025] Take 0.5 mol of inorganic metal salt (0.1 mol of MoCl5, YCl3, WCl4, TaCl5 and YbCl3, respectively) and add it to 10 mol of anhydrous ethanol and 20 mol of deionized water, stir until completely dissolved to obtain a mixed salt solution, then add 0.5 mol of polyacrylic acid, stir for 60 min, then add 0.5 mol of tetraethyl orthosilicate, continue to stir for 20 min to obtain a silicate precursor solution. Add 5 mol of propylene oxide to the obtained silicate precursor composite solution, stir for 2 min, then pour into a mold, gel at 25℃, then perform solvent replacement with anhydrous ethanol and aging for 2 days to obtain a silicate precursor gel (replace the aging liquid every 8 h).

[0026] Through CO2 supercritical drying, a silicate aerogel is obtained, which is then calcined at 1400℃ under an air atmosphere at a temperature rising rate of 2 ℃ / min for 3 h to finally obtain a high-entropy silicate aerogel.

[0027] The prepared high-entropy silicate aerogel sample is shown in FIG. 1 as a complete block, which is convenient for practical application. The porosity is 95%, and the three-dimensional nanometer network structure has a thermal conductivity as low as 0.044 W / (m·K) at 600°C, and RL=-10 dB (4~18GHz band) at 600°C. Figure 1

[0028] Example 2

[0029] Take 0.5 mol of inorganic metal salt (0.1 mol of MoCl5, Y(NO3)3, WCl4, TaCl5, Yb(NO3)3, respectively) and add it to 30 mol of anhydrous ethanol and 30 mol of deionized water, stir until completely dissolved to obtain a mixed salt solution, then add 0.7 mol of phenolic resin, stir for 30 min, then add 0.6 mol of tetra-n-butyl orthosilicate, continue to stir for 90 min to obtain a silicate precursor solution. Add 3.5 mol of propylene oxide to the obtained silicate precursor composite solution, stir for 1 min, then pour into a mold at 55°C to gel, then use anhydrous ethanol for solvent replacement and aging for 2 days to obtain a silicate precursor gel (replace the aging liquid every 9 h).

[0030] The silicate aerogel is obtained by CO2 supercritical drying, then calcined at 1200°C under air atmosphere at a temperature rising rate of 1°C / min for 4h, and finally a high-entropy silicate aerogel is obtained.

[0031] The prepared high-entropy silicate aerogel has a three-dimensional nanometer network structure, and the pore size distribution is shown in FIG. 2, which is mainly distributed in the range of 9~70 nm, and the thermal conductivity is as low as 0.051 W / (m·K) at 700°C, and RL=-12 dB (4~18GHz band) at 700°C. Figure 2

[0032] Example 3

[0033] Take 0.5 mol of inorganic metal salt (0.1 mol of MoCl5, YCl3, WCl4, TaCl5, Yb(NO3)3, respectively) and add it to 5 mol of anhydrous ethanol and 20 mol of deionized water, stir until completely dissolved to obtain a mixed salt solution, then add 1 mol of citric acid, stir for 120 min, then add 0.375 mol of methyltrimethoxysilane, continue to stir for 100 min to obtain a silicate precursor solution. Add 4 mol of propylene oxide to the obtained silicate precursor composite solution, stir for 7 min, then pour into a mold, gel at 35°C, then use anhydrous ethanol for solvent replacement and aging for 3 days to obtain a silicate precursor gel (replace the aging liquid every 6 h).

[0034] ​​The silicate aerogel is obtained by CO2 supercritical drying, and then is calcined at 1050 ℃ under an air atmosphere at a temperature rising rate of 6 ℃ / min for 2 h, and finally the high-entropy silicate aerogel is obtained.

[0035] The SEM image of the prepared high-entropy silicate aerogel is shown in Figure 3 It can be clearly seen that a three-dimensional nanometer network structure is presented, the porosity is 96%, the thermal conductivity at 650 ℃ is 0.05 W / (m·K), and RL=-9.5 dB (4~18GHz band) under the condition of 650 ℃.

[0036] Example 4

[0037] 0.5 mol of inorganic metal salt (0.1 mol of MoCl5, Y(NO3)3, WCl4, TaCl5, Yb(NO3)3 respectively) is added into 30 mol of anhydrous ethanol and 20 mol of deionized water, and stirred until completely dissolved to obtain a mixed salt solution, then 0.5 mol of citric acid is added, and after fully stirring for 40 min, 0.5 mol of methyl orthosilicate is added, and the stirring is continued for 50 min, and finally a silicate precursor solution is obtained. 2.5 mol of propylene oxide is added to the obtained silicate precursor composite solution, and after stirring for 10 min, it is poured into a mold, and then gelled at 30 ℃, and then solvent replacement and aging are performed with anhydrous ethanol for 2 days to obtain a silicate precursor gel (the aging liquid is replaced every 10 h).

[0038] The silicate aerogel is obtained by CO2 supercritical drying, and then is calcined at 1550 ℃ under an air atmosphere at a temperature rising rate of 5 ℃ / min for 1 h, and finally the high-entropy silicate aerogel is obtained.

[0039] The prepared high-entropy silicate aerogel presents a three-dimensional nanometer network structure, the porosity is 96.7%, the thermal conductivity at 600 ℃ is 0.043 W / (m·K), and RL=-10.2 dB (4~18GHz band) under the condition of 600 ℃.

[0040] Example 5

[0041] Take 0.5 mol of inorganic metal salt (0.1 mol of MoCl5, Y(NO3)3, WCl4, TaCl5, YbCl3 respectively) into 30 mol of anhydrous ethanol and 5 mol of deionized water, stir until completely dissolved to obtain a mixed salt solution, then add 0.8 mol of polyacrylic acid, stir for 50 min, then add 0.625 mol of methyl triethoxysilane, continue to stir for 60 min to obtain a silicate precursor solution. Add 3 mol of propylene oxide to the obtained silicate precursor composite solution, stir for 1 min, then pour into a mold and gel at 60°C, then perform solvent replacement with anhydrous ethanol and aging for 1 day to obtain a silicate precursor gel (replace the aging liquid every 6 h).

[0042] Through CO2 supercritical drying, a silicate aerogel is obtained, which is then calcined at 1350°C under an air atmosphere at a heating rate of 4°C / min for 2.5h to finally obtain a high-entropy silicate aerogel.

[0043] The prepared high-entropy silicate aerogel has a three-dimensional nanometer network structure, a porosity of 97.1%, a thermal conductivity of 0.046 W / (m·K) at 600°C, and an RL of -10.5 dB (4-18 GHz band) at 600°C.

[0044] Example 6

[0045] Take 0.5 mol of inorganic metal salt (0.1 mol of MoCl5, YCl3, WCl4, TaCl5, Yb(NO3)3 respectively) into 10 mol of anhydrous ethanol and 20 mol of deionized water, stir until completely dissolved to obtain a mixed salt solution, then add 0.5 mol of phenolic resin, stir for 100 min, then add 0.45 mol of hexamethyldisilazane, continue to stir for 120 min to obtain a silicate precursor solution. Add 4 mol of propylene oxide to the obtained silicate precursor composite solution, stir for 5 min, then pour into a mold and gel at 40°C, then perform solvent replacement with anhydrous ethanol and aging for 3 days to obtain a silicate precursor gel (replace the aging liquid every 12 h).

[0046] Through CO2 supercritical drying, a silicate aerogel is obtained, which is then calcined at 1600°C under an air atmosphere at a heating rate of 8°C / min for 2h to finally obtain a high-entropy silicate aerogel.

[0047] The prepared high-entropy silicate aerogel has a three-dimensional nanometer network structure, a porosity of 95.9%, a thermal conductivity of 0.049 W / (m·K) at 600°C, and an RL of -9.6 dB (4-18 GHz band) at 700°C.

Claims

1. A method for preparing a high-emissivity, high-temperature resistant silicate high-entropy aerogel, characterized in that, The specific steps are as follows: Five inorganic metal salts were weighed and added to a mixed solution of anhydrous ethanol and deionized water in a certain proportion until completely dissolved to obtain a mixed salt solution. Then, a long molecular chain dispersant was added, and after thorough stirring, a silicon source was added. After stirring for a period of time, a silicate precursor solution was obtained. A coagulating accelerator was added to the obtained silicate precursor solution, and after stirring, it was poured into a mold. After gelation, aging, and solvent replacement, it was subjected to supercritical drying. Finally, it was calcined in an air atmosphere to obtain a high-entropy silicate aerogel block. The inorganic metal salt is composed of nitrates or halides of Mo, Y, W, Ta and Yb in equimolar ratios. The chemical formula of the silicate aerogel is RE2Si2O7, where RE is Mo, Y, W, Ta and Yb.

2. The preparation method according to claim 1, characterized in that, The molar ratio of each component is: five inorganic metal salts: deionized water: anhydrous ethanol: long molecular chain dispersant: coagulant = 1: (10-60): (10-60): (1-2): (5-10).

3. The preparation method according to claim 1, characterized in that, The molar ratio of the inorganic metal salt to the silicon source is 1:(0.75~1.25).

4. The preparation method according to claim 1, characterized in that, The silicon source is one of tetraethyl orthosilicate, methyl orthosilicate, tetrabutyl orthosilicate, methyltrimethoxysilane, methyltriethoxysilane, or hexamethyldisilazane; the stirring time after adding the silicon source is 20-120 min.

5. The preparation method according to claim 1, characterized in that, The long molecular chain dispersant is one of polyacrylic acid, phenolic resin or citric acid; the stirring time after adding the long molecular chain dispersant is 30 to 120 minutes.

6. The preparation method according to claim 1, characterized in that, The coagulant is propylene oxide; the stirring time after adding the coagulant is 1 to 10 minutes.

7. The preparation method according to claim 1, characterized in that, The gel temperature is 25–60°C.

8. The preparation method according to claim 1, characterized in that, The aging and solvent replacement time is 1 to 4 days; the aging solution is replaced every 6 to 12 hours, and the aging solution is anhydrous ethanol.

9. The preparation method according to claim 1, characterized in that, The supercritical drying is one of ethanol supercritical drying and CO2 supercritical drying; the calcination time is 1-4 h, the calcination temperature is 1050-1600 ℃, and the heating rate is 1-8 ℃ / min.

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