Preparation method of high-temperature-resistant amorphous SiC coated mullite aerogel

Abstract

The invention belongs to the field of preparation processes of nano-porous materials, and particularly relates to a preparation method of high-temperature-resistant amorphous SiC coated mullite aerogel. The aerogel precursor is prepared by using a simple self-assembly method, the amorphous SiC coated mullite aerogel is obtained through high-temperature calcination, and the material is expected to meet the thermal protection requirements in the fields of metallurgy, energy, aerospace and the like at present. Meanwhile, the temperature resistance of the amorphous SiC coated framework mullite aerogel in the air is improved to 1500 DEG C, and the application of a thermal protection material on the surface of an aircraft in an extreme environment is expected to be realized.

Description

Technical Field

[0001] The invention belongs to the field of preparation technology of nano porous composite materials, and particularly relates to a preparation method of high-temperature resistant amorphous SiC-coated mullite aerogel. Background Art

[0002] Ceramic aerogels, with their low density, low thermal conductivity, excellent thermal stability, and heat resistance, play an important role in high-temperature thermal insulation in the presence of oxygen. However, the pearl-chain-like skeleton structure of traditional aerogels results in weak connections between the necks of the particles. Furthermore, the high surface energy of nanoparticles increases sintering activity, leading to particle agglomeration at high temperatures and destruction of the mesoporous structure during sintering. Consequently, the application of traditional ceramic aerogels in aerobic environments is limited, with operating temperatures rarely exceeding 1300°C.

[0003] Mullite is the only stable phase in the Al2O3-SiO2 system. Due to its excellent thermal stability and high-temperature creep resistance, it has become the preferred material in the field of high-temperature thermal insulation. In addition, before reaching the decomposition temperature, mullite generally exhibits a stable crystal structure without any crystal phase transition, avoiding the collapse of pores and skeleton structure caused by crystal transformation. The one-dimensional skeleton not only avoids the high surface energy of the nano-skeleton, but also eliminates the weak connection between the pearl chain skeleton, further improving the high-temperature structural stability of the aerogel. The amorphous SiC-coated mullite skeleton can effectively protect the internal structure and slow down decomposition. Therefore, amorphous SiC-coated mullite aerogel not only has the inherent advantages of mullite, but also has a unique gas-solid interface and high porosity, which can give full play to the advantages of its composition and structure, making it a strong candidate for thermal insulation materials in extreme environments.

[0004] Existing technologies, such as ZL115974539B, disclose a bulk, high-temperature-resistant mullite aerogel. However, the highly sintered nanoparticle skeleton and the large amount of carbon in its structure limit its maximum operating temperature in an aerobic environment to only 1300°C. ZL114132940B discloses an ultra-light, high-temperature-resistant bulk mullite aerogel. However, its preparation process is complex, using a two-dimensional porous, crystalline metal covalent organic framework containing aluminum as the aluminum source, resulting in high costs. Summary of the Invention

[0005] To overcome the problems of the existing mullite aerogel technology, the present invention aims to provide a method for preparing high-temperature resistant amorphous SiC-coated mullite aerogel. By constructing an amorphous SiC-coated mullite skeleton, the present invention solves the problems of poor temperature resistance, complex process, and high cost of current mullite aerogels. The present invention prepares an aerogel precursor by self-assembly of Al2O3 nanorods and SiO2 sol, and prepares the amorphous SiC-coated mullite aerogel through a heat treatment process. The mullite aerogel has low raw material cost, simple process, and controllable microstructure. It exhibits ultrahigh thermal stability and heat resistance in an aerobic environment, and has great application value in fields such as metallurgy, energy, and aerospace.

[0006] The technical solution of the present invention is: a method for preparing high-temperature resistant amorphous SiC-coated mullite aerogel, the specific steps of which are as follows:

[0007] (1) adding acid to deionized water, stirring and dissolving an aluminum source to obtain an aluminum solution; placing the aluminum solution in a hydrothermal reactor for hydrothermal reaction to obtain an Al2O3 nanorod solution;

[0008] (2) adding a silicon source to the Al2O3 nanorod solution prepared in step (1), stirring and hydrolyzing, adding a coagulant and stirring, adjusting the pH to 7-8 to obtain an Al2O3 nanorod / SiO2 sol, adding a solvent for replacement and aging, and then drying to obtain an Al2O3 nanorod / SiO2 aerogel precursor;

[0009] (3) The Al2O3 nanorod / SiO2 aerogel precursor prepared in step (2) is placed in an atmosphere furnace for high-temperature calcination to obtain a high-temperature resistant amorphous SiC-coated mullite aerogel.

[0010] Preferably, the molar ratio of deionized water, acid, and aluminum source in step (1) is 1:(0.004-0.30):(0.03-0.2); the acid is one of sulfuric acid, nitric acid, hydrochloric acid, or acetic acid; and the aluminum source is one of aluminum chloride hexahydrate, aluminum chloride nonahydrate, aluminum nitrate nonahydrate, aluminum isopropoxide, or aluminum sec-butoxide.

[0011] Preferably, the temperature of the hydrothermal reaction in step (1) is 150-200° C., and the time of the hydrothermal reaction is 4-12 h.

[0012] Preferably, the molar ratio of the aluminum source described in step (1) to the silicon source described in step (2) is 1:(0.5-4); the silicon source is one of tetraethyl orthosilicate, methyl orthosilicate, methyltrimethoxysilane, dimethyldimethoxysilane or 3-aminopropyltrimethoxysilane; and the stirring hydrolysis time is 0.5-2h.

[0013] Preferably, the coagulant in step (2) is one of ammonia water, sodium carbonate or sodium hydroxide; and the stirring time after adding the coagulant is 0.2 to 1 hour.

[0014] Preferably, the gel temperature in step (2) is room temperature, the aging and solvent replacement time is 1 to 4 days, and the solvent is replaced every 4 to 12 hours; the solvent is one of methanol, ethanol, acetone or n-hexane.

[0015] Preferably, the drying method in step (2) is CO2 supercritical drying, ethanol supercritical drying or atmospheric pressure drying. The drying temperature of CO2 supercritical drying is 48-52°C, the drying pressure is 9-10 MPa, and the drying time is 5-8 hours; the drying temperature of ethanol supercritical drying is 240-280°C, the drying pressure is 9-10 MPa, and the drying time is 4-8 hours; the drying temperature of atmospheric pressure drying is 60-120°C, and the drying time is 4-8 hours.

[0016] Preferably, the atmosphere in step (3) is argon, nitrogen or helium.

[0017] Preferably, the calcination temperature in step (3) is 1300-1600° C., the calcination time is 1-3 h, and the heating rate is 2-10° C. / min.

[0018] Beneficial effects:

[0019] (1) Compared with the existing mullite preparation technology, the present invention prepares Al2O3 nanorod / SiO2 precursor aerogel by self-assembly method, avoids the introduction of high molecular polymer, and generates amorphous SiC-coated mullite aerogel by high-temperature calcination without the need for secondary air calcination, which has a simple process and low cost;

[0020] (2) The present invention generates an amorphous SiC-coated mullite skeleton in situ at high temperature, which fully utilizes the stability of mullite and avoids the weak connection of the neck of the nano-pearl chain. It has good high-temperature thermal stability and structural stability and can withstand high temperatures of 1500°C.

[0021] (3) The high-temperature resistant amorphous SiC-coated mullite aerogel described in the present invention is in a complete block shape and can be designed according to the shape and size of the outer surface of the aircraft. Its good temperature resistance makes it have potential application prospects in the field of extreme thermal protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a macroscopic sample picture of the high-temperature resistant amorphous SiC-coated mullite aerogel prepared in Example 1;

[0023] Figure 2 This is an SEM image of the high-temperature resistant amorphous SiC-coated mullite aerogel prepared in Example 2;

[0024] Figure 3 This is an SEM image of the surface of the high-temperature resistant amorphous SiC-coated mullite aerogel prepared in Example 2 after ablation under a butane flame;

[0025] Figure 4 This is the XRD pattern of the high-temperature resistant amorphous SiC-coated mullite aerogel prepared in Example 4. DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to examples, but the scope of protection is not limited thereto.

[0027] Example 1

[0028] (1) Weighing 0.008 mol of nitric acid and adding it to 2 mol of deionized water, stirring evenly, then adding 0.1 mol of aluminum chloride hexahydrate and stirring until completely dissolved to obtain an aluminum solution; placing the aluminum solution in a hydrothermal reactor and performing a hydrothermal reaction at 160° C. for 8 h to obtain an Al 2 O 3 nanorod solution;

[0029] (2) Add 0.05 mol of 3-aminopropyltrimethoxysilane to the Al2O3 nanorod solution and stir for 1 hour until it is completely hydrolyzed; add sodium carbonate to adjust the pH to 7, stir for 1 hour and then let it stand; after gelation at room temperature, use acetone to age and solvent exchange for 2 days, and replace the solvent every 6 hours, and then dry at normal pressure (dry at 60°C for 8 hours) to obtain Al2O3 nanorod / SiO2 aerogel precursor;

[0030] (3) The Al2O3 nanorods / SiO2 aerogel precursor was calcined at 1600℃ and a heating rate of 2℃ / min for 2h in a nitrogen atmosphere to finally obtain amorphous SiC-coated mullite aerogel.

[0031] The prepared amorphous SiC-coated mullite aerogel is a complete block, which is convenient for practical application. The macroscopic sample is shown in the figure. Figure 1 As shown, the density is 0.15g / cm 3 , thermal conductivity is 0.034W / (m·K), and compressive strength is 0.26MPa. After heat treatment in air at 1500℃ for 0.5h, the sample has only a linear shrinkage of 2.4%, and still has a complete structure, with excellent heat resistance and structural stability.

[0032] Example 2

[0033] (1) Weighing 0.3 mol of acetic acid and adding it to 1 mol of deionized water, stirring evenly, then adding 0.03 mol of aluminum isopropoxide and stirring until completely dissolved to obtain an aluminum solution; placing the aluminum solution in a hydrothermal reactor and performing a hydrothermal reaction at 180° C. for 6 h to obtain an Al 2 O 3 nanorod solution;

[0034] (2) 0.1 mol of methyltrimethoxysilane was added to the Al2O3 nanorod solution and stirred for 0.5 h until it was completely hydrolyzed; ammonia water was added to adjust the pH to 7.5, stirred for 0.5 h and then allowed to stand; after gelation at room temperature, the solution was aged and solvent replaced with ethanol for 4 days, and the solvent was replaced every 12 h. The Al2O3 nanorod / SiO2 aerogel precursor was then obtained by supercritical drying with ethanol (drying at 250°C for 8 h under a pressure of 10 MPa);

[0035] (3) The Al2O3 nanorods / SiO2 aerogel precursor was calcined at 1500℃ and a heating rate of 4℃ / min for 3h in an argon atmosphere to finally obtain amorphous SiC-coated mullite aerogel.

[0036] The density of the prepared amorphous SiC-coated mullite aerogel is 0.17 g / cm 3 , thermal conductivity is 0.037W / (m·K), and compressive strength is 0.35MPa. The microstructure of aerogel is as follows Figure 2 As shown, it has a clear one-dimensional skeleton structure. After heat treatment in air at 1500℃ for 1h, the sample has only 1.3% linear shrinkage and still has a complete structure, with excellent heat resistance and structural stability. When the sample is exposed to a butane torch at 1300℃, a large number of SiC nanowires can be observed growing on the surface of the mullite skeleton, inhibiting the diffusion of airflow into the interior, as shown in Figure 2. Figure 3 shown.

[0037] Example 3

[0038] (1) Weigh 0.008 mol of sulfuric acid and add it to 0.8 mol of deionized water, stir evenly, then add 0.16 mol of aluminum sec-butoxide and stir until completely dissolved to obtain an aluminum solution; place the aluminum solution in a hydrothermal reactor and perform a hydrothermal reaction at 200°C for 4 h to obtain an Al2O3 nanorod solution;

[0039] (2) Add 0.32 mol of tetraethyl orthosilicate to the Al2O3 nanorod solution and stir for 2 h until it is completely hydrolyzed; add sodium hydroxide to adjust the pH to 8, stir for 0.2 h and then let it stand; after gelation at room temperature, use n-hexane for aging and solvent replacement for 1 day, and replace the solvent every 4 h. Then, dry at normal pressure (120 ° C for 4 h) to obtain Al2O3 nanorod / SiO2 aerogel precursor;

[0040] (3) The Al2O3 nanorods / SiO2 aerogel precursor was calcined at 1300℃ and a heating rate of 10℃ / min for 1h in a nitrogen atmosphere to finally obtain amorphous SiC-coated mullite aerogel.

[0041] The density of the prepared amorphous SiC-coated mullite aerogel is 0.22 g / cm 3, thermal conductivity is 0.046W / (m·K), and compressive strength is 0.52MPa. After heat treatment in air at 1400℃ for 1h, the sample has only a linear shrinkage of 0.9% and still has a complete structure, showing excellent heat resistance and structural stability.

[0042] Example 4

[0043] (1) Weighing 0.01 mol of hydrochloric acid and adding it to 1 mol of deionized water, stirring evenly, then adding 0.08 mol of aluminum chloride nonahydrate and stirring until completely dissolved to obtain an aluminum solution; placing the aluminum solution in a hydrothermal reactor and performing a hydrothermal reaction at 150° C. for 12 h to obtain an Al 2 O 3 nanorod solution;

[0044] (2) 0.32 mol of methyl orthosilicate was added to the Al2O3 nanorod solution and stirred for 2 h until it was completely hydrolyzed; sodium carbonate was added to adjust the pH to 8, stirred for 0.5 h and then allowed to stand; after gelation at room temperature, the solution was aged and solvent replaced with ethanol for 3 days, with the solvent replaced every 8 h, and then dried by CO2 supercritical drying (drying at 50 °C for 8 h under a pressure of 10 MPa) to obtain an Al2O3 nanorod / SiO2 aerogel precursor;

[0045] (3) The Al2O3 nanorods / SiO2 aerogel precursor was calcined at 1400℃ and a heating rate of 3℃ / min for 3h in an argon atmosphere to finally obtain amorphous SiC-coated mullite aerogel.

[0046] The density of the prepared amorphous SiC-coated mullite aerogel is 0.18 g / cm 3 , thermal conductivity is 0.039W / (m·K), and compressive strength is 0.19MPa. After heat treatment in air at 1500℃ for 1h, the sample has only a linear shrinkage of 2.7% and still has a complete structure, showing excellent heat resistance and structural stability. Figure 4 This is the XRD pattern of amorphous SiC-coated mullite aerogel. All peaks are characteristic peaks of mullite, proving that the sample is a single-phase mullite aerogel.

[0047] Example 5

[0048] (1) Weighing 0.2 mol of acetic acid and adding it to 1 mol of deionized water, stirring evenly, then adding 0.08 mol of aluminum nitrate nonahydrate and stirring until completely dissolved to obtain an aluminum solution; placing the aluminum solution in a hydrothermal reactor and performing a hydrothermal reaction at 170° C. for 10 h to obtain an Al 2 O 3 nanorod solution;

[0049] (2) 0.08 mol of dimethyldimethoxysilane was added to the Al2O3 nanorod solution and stirred for 1.5 h until it was completely hydrolyzed; ammonia water was added to adjust the pH to 7, stirred for 0.5 h and then allowed to stand; after gelation at room temperature, it was aged and solvent replaced with methanol for 2 days, and the solvent was replaced every 6 h, and then the Al2O3 nanorod / SiO2 aerogel precursor was obtained by supercritical drying with ethanol (drying at 280°C for 4 h under 9 MPa pressure);

[0050] (3) The Al2O3 nanorods / SiO2 aerogel precursor was calcined at 1500℃ and a heating rate of 4℃ / min for 1h in a nitrogen atmosphere to finally obtain amorphous SiC-coated mullite aerogel.

[0051] The density of the prepared amorphous SiC-coated mullite aerogel is 0.14 g / cm 3 , thermal conductivity is 0.033W / (m·K), and compressive strength is 0.21MPa. After heat treatment in air at 1500℃ for 1h, the sample has only 5.1% linear shrinkage and still has a complete structure, showing excellent heat resistance and structural stability.

[0052] Example 6

[0053] (1) Weighing 0.01 mol of nitric acid and adding it to 1 mol of deionized water, stirring evenly, then adding 0.12 mol of aluminum isopropoxide and stirring until completely dissolved to obtain an aluminum solution; placing the aluminum solution in a hydrothermal reactor and performing a hydrothermal reaction at 190° C. for 5 h to obtain an Al 2 O 3 nanorod solution;

[0054] (2) 0.072 mol of methyltrimethoxysilane was added to the Al2O3 nanorod solution and stirred for 2 h until it was completely hydrolyzed; sodium hydroxide was added to adjust the pH to 7, stirred for 1 h and then allowed to stand; after gelation at room temperature, the solution was aged and solvent replaced with ethanol for 4 days, with the solvent replaced every 6 h, and then dried by CO2 supercritical drying (at 9 MPa pressure, 48 ° C for 5 h) to obtain Al2O3 nanorod / SiO2 aerogel precursor;

[0055] (3) The Al2O3 nanorods / SiO2 aerogel precursor was calcined at 1400℃ and a heating rate of 6℃ / min for 3h in a helium atmosphere to finally obtain amorphous SiC-coated mullite aerogel.

[0056] The density of the prepared amorphous SiC-coated mullite aerogel is 0.21 g / cm 3 , thermal conductivity is 0.039W / (m·K), and compressive strength is 0.29MPa. After heat treatment in air at 1500℃ for 0.5h, the sample has only 1.4% linear shrinkage and still has a complete structure, showing excellent heat resistance and structural stability.

Claims

1. A method for preparing high-temperature resistant amorphous SiC-coated mullite aerogel, the specific steps of which are as follows: (1) adding acid to deionized water, stirring and dissolving an aluminum source to obtain an aluminum solution; placing the aluminum solution in a hydrothermal reactor for hydrothermal reaction to obtain an Al2O3 nanorod solution; (2) adding a silicon source to the Al2O3 nanorod solution prepared in step (1), stirring and hydrolyzing, adding a coagulant and stirring, adjusting the pH to 7-8 to obtain an Al2O3 nanorod / SiO2 sol, adding a solvent for replacement and aging, and then drying to obtain an Al2O3 nanorod / SiO2 aerogel precursor; (3) The Al2O3 nanorod / SiO2 aerogel precursor prepared in step (2) is placed in an atmosphere furnace for high-temperature calcination to obtain a high-temperature resistant amorphous SiC-coated mullite aerogel.

2. The preparation method according to claim 1, wherein The molar ratio of deionized water, acid and aluminum source in step (1) is 1:(0.004-0.30):(0.03-0.2); the acid is one of sulfuric acid, nitric acid, hydrochloric acid or acetic acid; and the aluminum source is one of aluminum chloride hexahydrate, aluminum chloride nonahydrate, aluminum nitrate nonahydrate, aluminum isopropoxide or aluminum sec-butoxide.

3. The preparation method according to claim 1, wherein The temperature of the hydrothermal reaction in step (1) is 150-200° C., and the time of the hydrothermal reaction is 4-12 hours.

4. The preparation method according to claim 1, characterized in that The molar ratio of the aluminum source described in step (1) to the silicon source described in step (2) is 1:(0.5-4); the silicon source is one of tetraethyl orthosilicate, methyl orthosilicate, methyltrimethoxysilane, dimethyldimethoxysilane or 3-aminopropyltrimethoxysilane; and the stirring hydrolysis time is 0.5-2h.

5. The preparation method according to claim 1, characterized in that The coagulant in step (2) is one of ammonia water, sodium carbonate or sodium hydroxide; the stirring time after adding the coagulant is 0.2 to 1 hour.

6. The preparation method according to claim 1, characterized in that The aging and solvent replacement time in step (2) is 1 to 4 days, and the solvent is replaced every 4 to 12 hours; the solvent is one of methanol, ethanol, acetone or n-hexane.

7. The preparation method according to claim 1, characterized in that The drying method in step (2) is CO2 supercritical drying, ethanol supercritical drying or atmospheric pressure drying.

8. The preparation method according to claim 1, characterized in that The drying temperature of CO2 supercritical drying is 48-52°C, the drying pressure is 9-10MPa, and the drying time is 5-8h; the supercritical drying temperature of ethanol is 240-280°C, the drying pressure is 9-10MPa, and the drying time is 4-8h; the temperature of atmospheric pressure drying is 60-120°C, and the drying time is 4-8h.

9. The preparation method according to claim 1, characterized in that The atmosphere in step (3) is argon, nitrogen or helium.

10. The preparation method according to claim 1, characterized in that The calcination temperature in step (3) is 1300-1600° C., the calcination time is 1-3 hours, and the heating rate is 2-10° C. / min.

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