A method for preparing a high emissivity silicide ceramic aerogel

Abstract

The application belongs to the field of preparation process of nanoporous materials, and particularly relates to a preparation method of high-emissivity silicide ceramic aerogel. The application utilizes a simple sol-gel method to prepare high-emissivity silicide ceramic aerogel material with excellent high-temperature stability, and the material is expected to meet the needs of the fields of aviation and spaceflight at present. Meanwhile, the simple preparation method of the high-emissivity silicide ceramic aerogel is conducive to promoting the development of the industrialization of aerogel and solving the problems of high preparation cost of high-emissivity silicide ceramic at present.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of preparation process of nanoporous materials, and particularly relates to a preparation method of high-emissivity silicide ceramic aerogel. BACKGROUND

[0002] The increase of the Mach number of a hypersonic vehicle makes the aerodynamic heating environment faced by the surface of the vehicle increasingly severe. Compared with conventional high-temperature structural materials, ultra-high-temperature ceramics have the characteristics of ultra-high temperature resistance, ablation resistance, high strength, thermal shock resistance and chemical stability, and can withstand extreme environments such as hypersonic long-time flight, trans-atmospheric flight and atmospheric re-entry, and are mostly used in key hot end parts or components of hypersonic vehicles such as wing leading edges.

[0003] Refractory metal silicides have the advantages of high melting point and moderate density, and from the structure, due to the combination of metal and silicon atoms, the silicides have many excellent properties of metal bonds and covalent bonds. The silicides with pseudo-forbidden band "semi-metal" properties have high emissivity in the ultraviolet-visible light region due to the transition of electrons from the valence band to the conduction band. Therefore, refractory metal silicides play an important role in high-emissivity component design.

[0004] In the prior art (CN 110002881 A), expensive molybdenum powder is used to synthesize molybdenum silicide, and the preparation steps are complex; the use of molybdenum silicide, thallium silicide and tungsten silicide in high-temperature resistant coatings is costly; therefore, a simple one-step sol-gel method is used to prepare low-thermal-conductivity high-emissivity silicide ceramic aerogel material, which is expected to meet the needs of the current aviation field. SUMMARY

[0005] The purpose of the present application is to overcome the problems of the existing silicide ceramic aerogel technology, and a preparation method of high-emissivity silicide ceramic aerogel is proposed to solve the problems of complex and tedious preparation process, and to prepare low-thermal-conductivity high-emissivity silicide ceramic aerogel material (the lowest can reach 0.015 W / (m·K) and high-emissivity (600 ℃, 2.31-18 GHz band).

[0006] The technical scheme of the present application is as follows: a preparation method of high-emissivity silicide ceramic aerogel, the specific steps are as follows:

[0007] (1) The inorganic metal salt is weighed and added to a mixed solution of anhydrous ethanol and deionized water, and stirred until completely dissolved; then a dispersing agent is added and stirred for a period of time, and then a silicon source is added and stirred to obtain a silicide precursor solution;

[0008] (2) The silicide precursor solution obtained in step (1) is stirred after adding a coagulant, poured into a mold, subjected to gelation, solvent replacement and aging, and then supercritical drying is performed, and finally calcination is performed in an air atmosphere to obtain bulk silicide ceramic aerogel.

[0009] Preferably, the molar ratio of the components in step (1) is inorganic metal salt: anhydrous ethanol: deionized water: dispersant: silicon source = 1: (15-65): (10-65): (0.5-2): (0.7-1.3).

[0010] Preferably, the inorganic metal salt in step (1) is one of nitrate or chloride of Mo, Ta or W.

[0011] Preferably, the dispersant in step (1) is one of polyacrylic acid, phenolic resin, citric acid or formamide; the stirring time after adding the dispersant is 20-150 min.

[0012] Preferably, the silicon source in step (1) is one of tetraethyl orthosilicate, methyl orthosilicate, tetrabutyl orthosilicate, methyltrimethoxysilane, methyltriethoxysilane or hexamethyldisilazane; the stirring time after adding the silicon source is 30-160 min.

[0013] Preferably, the coagulant in step (2) is methyl oxirane; the molar ratio of inorganic metal salt to coagulant is 1: (4-10); the stirring time after adding the coagulant is 0.5-20 min. Preferably, the gelation temperature in step (2) is 20-60 ℃.

[0014] Preferably, the solvent replacement and aging time in step (2) is 1-5 d; the aging liquid is replaced every 6-12 h; the aging liquid is anhydrous ethanol.

[0015] Preferably, the supercritical drying in step (2) is one of ethanol supercritical drying or CO2 supercritical drying.

[0016] Preferably, the calcination time in step (2) is 1-5 h, the calcination temperature is 1550-2100 ℃, and the heating rate is 1-8 ℃ / min. Advantages

[0017] (1) Compared with existing silicide preparation technology, the silicide aerogel material prepared by the sol-gel method using low-cost inorganic metal salt has lower cost, simple preparation process and easy operation, and avoids the complicated preparation process of traditional silicides, which is expected to realize industrialization.

[0018] (2) Compared with other silicide ceramic materials, the silicide aerogel material prepared in the application has the characteristics of high emissivity, low thermal conductivity, oxidation resistance and the like, which cannot be achieved by other silicide ceramic materials;

[0019] (3) The silicide ceramic aerogel in the application is in a block shape, breaking the situation that the existing silicide material only exists in a powder state, expanding the application field thereof, and the material prepared in the application has a uniform microstructure, and has potential application prospects in the heat insulation field and the high-temperature-resistant field. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 A macroscopic sample diagram of the silicide aerogel prepared in Example 1;

[0021] Figure 2 A pore size distribution diagram of the silicide aerogel prepared in Example 2;

[0022] Figure 3 A scanning electron microscope diagram of the silicide aerogel prepared in Example 3. DETAILED DESCRIPTION

[0023] The application will be further described below in combination with examples, but the protection scope is not limited thereto. Example 1

[0024] (1) 0.1 mol of MoCl5 was weighed and added to a mixed solution of 2 mol of anhydrous ethanol and 5 mol of deionized water, and stirred until completely dissolved. Then 0.1 mol of phenol formaldehyde resin was added, stirred for 40 min, and then 0.12 mol of methyltrimethoxysilane was added and stirred for 30 min to obtain a silicide precursor solution;

[0025] (2) 0.6 mol of methyl epoxide was added to the obtained silicide precursor solution and stirred for 3 min, then poured into a mold, gelled at 25℃, and then solvent exchanged with anhydrous ethanol and aged for 2 d to obtain a silicide precursor gel (the aging liquid was replaced every 8 h). The silicide aerogel precursor gel was obtained by supercritical drying of ethanol, and then calcined at 1600℃ under air atmosphere, with a temperature rising rate of 2 ℃ / min, for 3 h, to finally obtain a silicide aerogel.

[0026] The prepared silicide aerogel presents a three-dimensional nano network structure, and a sample diagram is as shown in Figure 1 The silicide aerogel is in an integrated block shape, which is convenient for practical application, has a porosity of 90%, better heat insulation performance of 550℃, a thermal conductivity of 0.051 W / (m·K), and L=-12 dB (4~14.16GHz wave band). Example 2

[0027] (1) 0.1 mol TaCl5 was weighed and added to a mixed solution of 3 mol anhydrous ethanol and 6.5 mol deionized water, and stirred until completely dissolved. Then 0.1 mol polyacrylic acid was added, stirred for 90 min, and then 0.09 mol tetraethyl orthosilicate was added, and stirred for 50 min to obtain a silicide precursor solution;

[0028] (2) 1 mol methyl oxirane was added to the obtained silicide precursor solution, stirred for 0.5 min, and then poured into a mold, gelled at 20°C, and then solvent exchanged with anhydrous ethanol and aged for 4 d to obtain a silicide precursor gel (the aging liquid was replaced every 6 h). The silicide precursor aerogel was obtained by CO2 supercritical drying, and then calcined at 2100°C under an air atmosphere at a temperature rising rate of 4 ℃ / min for 1 h to finally obtain a silicide aerogel.

[0029] The pore size distribution graph of the prepared silicide aerogel is shown in Figure 2 The pore size mainly distributes in the range of 9-100 nm, the porosity is 80%, the thermal conductivity is 0.056 W / (m·K) at 600°C, and the RL is -9 dB (4-14.16 GHz band). Example 3

[0030] (1) 0.1 mol WCl6 was weighed and added to a mixed solution of 1.5 mol anhydrous ethanol and 4 mol deionized water, and stirred until completely dissolved. Then 0.15 mol citric acid was added, stirred for 80 min, and then 0.12 mol methyl orthosilicate was added, and stirred for 160 min to obtain a silicide precursor solution;

[0031] (2) 0.4 mol methyl oxirane was added to the obtained silicide precursor solution, stirred for 20 min, and then poured into a mold, gelled at 35°C, and then solvent exchanged with anhydrous ethanol and aged for 3 d to obtain a silicide precursor gel (the aging liquid was replaced every 12 h). The silicide precursor aerogel was obtained by ethanol supercritical drying, and then calcined at 1550°C under an air atmosphere at a temperature rising rate of 1 ℃ / min for 5 h to finally obtain a silicide aerogel.

[0032] The SEM graph of the prepared silicide aerogel is shown in Figure 3 It can be clearly seen that the aerogel presents a three-dimensional nanometer network structure, the porosity is 85%, the thermal conductivity is 0.051 W / (m·K) at 500°C, and the RL is -12 dB (4-14.16 GHz band). Example 4

[0033] (1) 0.1 mol Mo(NO3)2 was weighed and added to a mixed solution of 5 mol anhydrous ethanol and 1 mol deionized water, and stirred until completely dissolved. Then 0.2 mol formamide was added, and after stirring for 150 min, 0.1 mol hexamethyldisilazane was added, and stirring was continued for 30 min to obtain a silicide precursor solution;

[0034] (2) 0.6 mol methyl epoxide was added to the obtained silicide precursor solution, and stirred for 7 min, then poured into a mold, gelled at 60°C, and then solvent exchanged with anhydrous ethanol and aged for 1 d to obtain a silicide precursor gel (the aging liquid was replaced every 6 h). The silicide precursor aerogel was obtained by CO2 supercritical drying, and then calcined at 1600°C under air atmosphere at a heating rate of 5 ℃ / min for 5 h to finally obtain a silicide aerogel.

[0035] The prepared silicide aerogel has a three-dimensional nanometer network structure, a porosity of 88%, a thermal conductivity of 0.055 W / (m·K) at 550°C, and RL=-10 dB (4-14.16 GHz band). Example 5

[0036] (1) 0.1 mol Mo(NO3)2 was weighed and added to a mixed solution of 4 mol anhydrous ethanol and 5 mol deionized water, and stirred until completely dissolved. Then 0.12 mol citric acid was added, and after stirring for 20 min, 0.13 mol methyltrimethoxysilane was added, and stirring was continued for 70 min to obtain a silicide precursor solution;

[0037] (2) 0.5 mol methyl epoxide was added to the obtained silicide precursor solution, and stirred for 15 min, then poured into a mold, gelled at 25°C, and then solvent exchanged with anhydrous ethanol and aged for 2 d to obtain a silicide precursor gel (the aging liquid was replaced every 9 h). The silicide precursor aerogel was obtained by ethanol supercritical drying, and then calcined at 1800°C under air atmosphere at a heating rate of 8 ℃ / min for 4 h to finally obtain a silicide aerogel.

[0038] The prepared silicide aerogel has a three-dimensional nanometer network structure, a porosity of 80%, a thermal conductivity of 0.042 W / (m·K) at 450°C, and RL=-15 dB (4-14.16 GHz band). Example 6

[0039] (1) 0.1 mol TaCl5 was added into a mixed solution of 6.5 mol anhydrous ethanol and 2 mol deionized water, and stirred until completely dissolved. Then 0.05 mol polyacrylic acid was added, and stirred for 50 min. Then 0.07 mol tetra-n-butyl orthosilicate was added, and stirred for 80 min to obtain a silicide precursor solution;

[0040] (2) 0.8 mol methyl epoxide was added into the obtained silicide precursor solution, and stirred for 2 min. Then the solution was poured into a mold, and gelled at 50°C. Then solvent replacement and aging were performed with anhydrous ethanol for 5 d (the aging solution was replaced every 10 h). A silicide precursor aerogel was obtained by CO2 supercritical drying. Then the silicide precursor aerogel was calcined at 1750°C under an air atmosphere at a temperature rising rate of 6 ℃ / min for 3 h, to obtain a silicide aerogel.

[0041] The prepared silicide aerogel has a three-dimensional nano network structure, a porosity of 83%, a thermal conductivity of 0.041 W / (m·K) at 450°C, and RL=-18 dB (4-14.16 GHz wave band).

Claims

1. A method for preparing a high emissivity silicide ceramic aerogel, characterized in that, The specific steps are as follows: (1) The inorganic metal salt is weighed and added to a mixed solution of anhydrous ethanol and deionized water, and stirred until completely dissolved; then a dispersing agent is added and stirred for a period of time, and then a silicon source is added for continuous stirring to obtain a silicide precursor solution; wherein the inorganic metal salt is one of nitrate or chloride of Mo, Ta or W; (2) The silicide precursor solution obtained in step (1) is added with a coagulant and stirred, then poured into a mold, and after gelation, solvent replacement and aging, supercritical drying is performed, and finally calcined under air atmosphere to obtain bulk silicide ceramic aerogel.

2. The production method according to claim 1, characterized by, The molar ratio of the components in step (1) is inorganic metal salt: anhydrous ethanol: deionized water: dispersing agent: silicon source = 1: (15-65): (10-65): (0.5-2): (0.7-1.3).

3. The preparation method according to claim 1, characterized in that, The dispersing agent in step (1) is one of polyacrylic acid, phenolic resin, citric acid or formamide; the stirring time after adding the dispersing agent is 20-150 min.

4. The production method according to claim 1, characterized by, The silicon source in step (1) is one of tetraethyl orthosilicate, methyl orthosilicate, tetrabutyl orthosilicate, methyltrimethoxysilane, methyltriethoxysilane or hexamethyldisilazane; the continuous stirring time after adding the silicon source is 30-160 min.

5. The preparation method according to claim 1, characterized in that, The coagulant in step (2) is methyl oxirane; the molar ratio of inorganic metal salt to coagulant is 1: (4-10); the stirring time after adding the coagulant is 0.5-20 min.

6. The method of claim 1, wherein, The gelation temperature in step (2) is 20-60℃.

7. The preparation method according to claim 1, characterized in that, The solvent replacement and aging time in step (2) is 1-5d; the aging liquid is replaced every 6-12h; the aging liquid is anhydrous ethanol.

8. The method of claim 1, wherein, The supercritical drying in step (2) is one of ethanol supercritical drying or CO2 supercritical drying.

9. The method of claim 1, wherein, The calcination time in step (2) is 1-5h, the calcination temperature is 1550-2100℃, and the heating rate is 1-8℃ / min.

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