Self-growing nanowire-reinforced silicon carbide aerogel material and preparation method thereof

Abstract

The present application discloses a self-growing nanowire-reinforced silicon carbide aerogel material and a preparation method thereof. The invention comprises the following steps: uniformly mixing ethanol, terephthalaldehyde, siloxane, aminosiloxane, deionized water and acid, and fully reacting to obtain a sol; heating the sol to obtain gel A; subjecting gel A to multiple organic solvent replacements and then drying to obtain aerogel A; impregnating aerogel A into the sol obtained in the first step to obtain a mixture; heating the mixture to obtain gel B; subjecting gel B to organic solvent replacement and then drying to obtain aerogel B; repeating the impregnation, heating, replacement and drying, and finally subjecting the aerogel to high-temperature heat treatment to obtain a self-growing nanowire-reinforced silicon carbide aerogel.

Description

Technical Field

[0001] The present invention relates to the technical field of aerogel materials, and in particular to a self-growing nanowire reinforced silicon carbide aerogel material and a preparation method thereof. Background Art

[0002] Aerogel originated in the 1930s and, after more than 90 years of development, has gradually achieved commercialization. The continuous three-dimensional network structure of aerogels gives them low density, high specific surface area, high porosity, and low thermal conductivity, making them important in a wide range of fields, including energy conservation and storage, thermal insulation, catalytic filtration, and more. Silicon carbide aerogel, due to its low density, excellent high-temperature oxidation resistance, and chemical stability, is suitable for a variety of high-temperature and highly corrosive environments, especially in high-temperature thermal insulation, where it holds broad potential applications.

[0003] Currently, silicon carbide aerogels are typically prepared using a sol-gel method to prepare a wet gel, which is then dried and heat-treated at high temperatures to convert it into silicon carbide aerogel. For example, Chinese invention patent CN 102897764 B discloses a block silicon carbide aerogel material and a preparation method thereof. This method uses a one-pot process to prepare RF-SiO2 composite aerogel through sol-gel, aging, and atmospheric pressure drying. This aerogel is then subjected to a carbon thermal reduction reaction under an argon atmosphere and then calcined in air to obtain silicon carbide aerogel. Chinese invention patent CN 112537964A discloses a preparation method for silicon carbide aerogel. This method uses polycarbosilane as a precursor, undergoes a hydrosilylation reaction under the catalysis of platinum to obtain a precursor gel, and then undergoes high-temperature cracking under an inert atmosphere to obtain silicon carbide aerogel.

[0004] The silicon carbide aerogel obtained by the above-mentioned preparation method generally has the following three problems: First, the presence of nanopores inside the obtained silicon carbide aerogel inevitably introduces a large number of macropores with pore sizes on the micron scale. On the one hand, the presence of these macropores greatly reduces the strength of the material, seriously affecting its practical application. On the other hand, because the pore size is much larger than the mean free path of gas molecules, it affects the thermal insulation performance of the material. Second, the silicon carbide aerogel obtained using the above-mentioned method is composed of a stack of zero-dimensional silicon carbide nanoparticles. Stress concentration is prone to occur at the neck-shaped joints between the particles, and the toughness of the material is poor. Third, the preparation process usually involves a hydrothermal reactor, a precious metal catalyst, and supercritical drying, and the process is cumbersome. Summary of the Invention

[0005] Technical problem to be solved: This application mainly proposes a self-growing nanowire reinforced silicon carbide aerogel material and its preparation method to overcome the problems of low strength, high brittleness and complex preparation process of silicon carbide aerogel in the existing technology, and alleviate the contradiction between the thermal insulation performance and mechanical properties of silicon carbide aerogel.

[0006] Technical solution:

[0007] A method for preparing a self-grown nanowire reinforced silicon carbide aerogel material, the method comprising the following steps:

[0008] Step 1: Mix ethanol, terephthalaldehyde, siloxane, aminosilicone, deionized water and acid for 10-60 minutes to obtain a sol;

[0009] Step 2: The sol obtained in the first step is heated to obtain gel A;

[0010] Step 3: The gel A prepared in the second step is subjected to 3-8 replacements of the organic solvent and then dried to obtain aerogel A, wherein the amount of the organic solvent used is 3-10 times the volume of the gel A;

[0011] Step 4: impregnating the aerogel A obtained in the third step into the sol obtained in the first step to obtain a mixture, wherein the volume ratio of the sol to the aerogel A is 1:1-3;

[0012] Step 5: heating the mixture obtained in step 4 to obtain gel B;

[0013] Step 6: The gel B obtained in the fifth step is subjected to 3-8 replacements of the organic solvent and then dried to obtain aerogel B, wherein the amount of the organic solvent used is 3-10 times the volume of the gel B;

[0014] Step 7: Repeat steps 4 to 6 1-5 times using aerogel B;

[0015] Step 8: The aerogel obtained in the seventh step is subjected to high-temperature heat treatment to obtain a self-grown nanowire-reinforced silicon carbide aerogel.

[0016] As a preferred technical solution of the present invention: in the first step, the molar ratio of ethanol, terephthalaldehyde, siloxane, aminosilicone, deionized water and acid is 1:(0.005-0.05):(0.01-0.1):(0.01-0.1):(0.5-0.1):(0.01-0.1).

[0017] As a preferred technical solution of the present invention: in the first step, the siloxane is methyltrimethoxysilane; the aminosiloxane is 3-aminopropyltriethoxysilane and / or 3-aminopropyltrimethoxysilane; and the acid is acetic acid and / or hydrochloric acid.

[0018] As a preferred technical solution of the present invention: the heating conditions in the second and fifth steps are 40-70° C. and maintained for 6-24 hours.

[0019] As a preferred technical solution of the present invention: the temperature of the organic solvent replacement in the third and sixth steps is 40-70°C, the replacement time is 8-24 hours, and the organic solvent is one or more of ethanol, methanol, n-hexane, and isopropanol.

[0020] As a preferred technical solution of the present invention: the drying process in the third and sixth steps is drying at 40-80° C. under normal pressure for 36-48 hours or vacuum drying at 60-80° C. for 12-24 hours.

[0021] As a preferred technical solution of the present invention, the impregnation process in the fourth step is performed under a vacuum environment. As a preferred technical solution of the present invention, the high-temperature heat treatment temperature in the eighth step is 1400-1700°C, the holding time is 2-6 hours, and the heating rate is 3-5°C / min. After natural cooling, the self-grown nanowire-reinforced silicon carbide aerogel is obtained.

[0022] The present application also discloses a self-growing nanowire-reinforced silicon carbide aerogel material, which is a blue or gray-green block with a density of ≤0.2g / cm 3 , thermal conductivity ≤ 0.05W / mK, strength ≥ 0.25MPa.

[0023] Beneficial effects: The self-grown nanowire-reinforced silicon carbide aerogel material and its preparation method described in this application adopt the above technical solution and have the following technical effects compared with the existing technology:

[0024] 1. The cyclic impregnation process greatly reduces the macropores in silicon carbide aerogel, increasing its strength while hardly affecting its thermal insulation performance.

[0025] 2. Silicon carbide aerogel is reinforced by nanowires, which enhances the toughness of ceramic aerogel.

[0026] 3. The preparation process is simple by adopting one-step sol-gel method, vacuum / normal pressure drying and one-step heat treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a scanning electron microscope image of the self-grown nanowire-reinforced silicon carbide aerogel material prepared in Example 1 of the present application;

[0028] Figure 2 This is a scanning electron microscope image of the self-grown nanowire-reinforced silicon carbide aerogel material prepared in Example 2 of the present application;

[0029] Figure 3 This is a photo of the self-grown nanowire-reinforced silicon carbide aerogel material prepared in Example 3 of the present application. DETAILED DESCRIPTION

[0030] The present invention will be further described in detail below with reference to specific implementation cases. It should be noted that the purpose of the examples is to more clearly illustrate the practical application process of the present invention, and is not intended to limit the scope of protection of the present invention.

[0031] Example 1:

[0032] A method for preparing a self-grown nanowire reinforced silicon carbide aerogel material, the method comprising the following steps:

[0033] Step 1: 15ml ethanol, 4mmol terephthalaldehyde, 5mmol methyltrimethoxysilane, 4mmol

[0034] 3-Aminopropyltriethoxysilane, 3 ml of deionized water, and 0.3 ml of acetic acid were stirred with a magnetic stirrer for 20 minutes to obtain a sol;

[0035] Step 2: The sol obtained in the first step was placed in a 50°C environment for 12 hours to gel and age to obtain gel A;

[0036] Step 3: The gel A obtained in the second step was replaced with n-hexane at 50°C for 4 times, each time for 12 hours, with an amount of n-hexane of 80 ml. After replacement, it was dried at 60°C for 48 hours to obtain aerogel A;

[0037] Step 4: The aerogel A prepared in the third step was immersed in a mixed solution of 20 ml of ethanol, 4 mmol of terephthalaldehyde, 5 mmol of methyltrimethoxysilane, 4 mmol of 3-aminopropyltriethoxysilane, 3 ml of deionized water, and 0.3 ml of acetic acid to obtain a mixture;

[0038] Step 5: placing the mixture obtained in step 4 in an environment at 50°C for 12 hours to obtain gel B;

[0039] Step 6: The gel B obtained in the fifth step was replaced with n-hexane at 50°C for 4 times, each time for 12 hours, with an amount of n-hexane of 80 ml. After the replacement, it was dried at 60°C for 48 hours to obtain aerogel B;

[0040] Step 7: The aerogel B obtained in step 6 was heated to 1500°C at a heating rate of 2°C / min. After heat treatment at 1500°C for 3 hours, it was naturally cooled to obtain a self-grown nanowire-reinforced silicon carbide aerogel with a density of 0.14 g / cm 3 , thermal conductivity is 0.04W / mK, strength is 0.50MPa, scanning electron microscope pictures are as follows Figure 1 shown.

[0041] Example 2:

[0042] A method for preparing a self-grown nanowire reinforced silicon carbide aerogel material, the method comprising the following steps:

[0043] Step 1: 20ml ethanol, 4mmol terephthalaldehyde, 8mmol methyltrimethoxysilane, 4mmol

[0044] 3-Aminopropyltriethoxysilane, 4 ml of deionized water and 0.4 ml of acetic acid were mixed evenly and stirred in an ultrasonic cleaner for 15 minutes to allow for thorough mixing and reaction to obtain a sol;

[0045] Step 2: The sol obtained in the first step was placed in a 65°C environment for 12 hours to gel and age to obtain gel A;

[0046] Step 3: The gel A prepared in the second step was replaced with ethanol at 65°C for 4 times, each time for 12 hours, with an ethanol dosage of 100 ml. After replacement, it was dried at 80°C for 12 hours to obtain aerogel A;

[0047] Step 4: The aerogel A prepared in the third step was immersed in a mixed solution of 20 ml of ethanol, 4 mmol of terephthalaldehyde, 8 mmol of methyltrimethoxysilane, 4 mmol of 3-aminopropyltriethoxysilane, 4 ml of deionized water, and 0.4 ml of acetic acid to obtain a mixture;

[0048] Step 5: placing the mixture obtained in step 4 in an environment at 65°C for 12 hours to obtain gel B;

[0049] Step 6: The gel B obtained in the fifth step was replaced with ethanol at 65°C for 4 times, each time for 12 hours, with an ethanol dosage of 100 ml. After replacement, it was dried at 80°C for 12 hours to obtain aerogel B;

[0050] Step 7: The aerogel B obtained in step 6 was heated to 1500°C at a heating rate of 3°C / min. After heat treatment at 1500°C for 5 hours, it was naturally cooled to obtain a self-grown nanowire-reinforced silicon carbide aerogel with a density of 0.12 g / cm 3 , thermal conductivity is 0.04W / mK, strength is 0.40MPa, scanning electron microscope pictures are as follows Figure 2 shown.

[0051] Example 3:

[0052] A method for preparing a self-grown nanowire reinforced silicon carbide aerogel material, the method comprising the following steps:

[0053] Step 1: 30ml ethanol, 4mmol terephthalaldehyde, 5mmol methyltrimethoxysilane, 4mmol

[0054] 3-Aminopropyltriethoxysilane, 4 ml of deionized water, and 0.1 ml of hydrochloric acid were mixed evenly, and stirred in an ultrasonic cleaner for 15 minutes to allow for thorough mixing and reaction to obtain a sol;

[0055] Step 2: The sol obtained in the first step was placed in a 60°C environment for 12 hours to gel and age to obtain gel A;

[0056] Step 3: The gel A prepared in the second step was replaced with isopropanol 4 times at 60°C for 12 hours each time, with an amount of isopropanol of 120 ml. After replacement, the gel was dried at 80°C under vacuum for 12 hours to obtain aerogel A.

[0057] Step 4: The aerogel A prepared in the third step was immersed in a mixed solution of 40 ml of ethanol, 4 mmol of terephthalaldehyde, 8 mmol of methyltrimethoxysilane, 4 mmol of 3-aminopropyltriethoxysilane, 4 ml of deionized water, and 0.1 ml of hydrochloric acid to obtain a mixture A;

[0058] Step 5: Place the mixture A obtained in step 4 in an environment at 60°C for 12 hours to obtain gel B;

[0059] Step 6: The gel B obtained in the fifth step was replaced with ethanol at 60°C for 4 times, each time for 12 hours, with an ethanol dosage of 120 ml. After replacement, the gel was dried at 80°C for 12 hours to obtain aerogel B.

[0060] Step 7: The aerogel B obtained in the sixth step was immersed in a mixed solution of 40 ml of ethanol, 4 mmol of terephthalaldehyde, 8 mmol of methyltrimethoxysilane, 4 mmol of 3-aminopropyltriethoxysilane, 4 ml of deionized water, and 0.1 ml of hydrochloric acid to obtain a mixture B; the obtained mixture B was placed in an environment at 60°C for 12 hours to obtain gel C; gel C was replaced with ethanol at 60°C four times, each time for 12 hours, with an amount of ethanol used being 120 ml, and then dried at 80°C for 12 hours to obtain aerogel C;

[0061] Step 8: Aerogel C was heated to 1600°C at a heating rate of 3°C / min. After heat treatment at 1600°C for 2 hours, it was naturally cooled to obtain self-grown nanowire-reinforced silicon carbide aerogel with a density of 0.15 g / cm 3 , thermal conductivity is 0.03W / mK, strength is 0.45MPa, as shown in the photo Figure 3 shown.

[0062] The foregoing description of the specific embodiments of the present invention is for purposes of illustration and description. These descriptions are not intended to limit the invention to the precise forms disclosed, and many modifications and variations are possible in light of the above teachings. The exemplary embodiments have been selected and described to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to make and utilize various exemplary embodiments of the invention without departing from the scope of the invention. The true scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for preparing a self-grown nanowire reinforced silicon carbide aerogel material, characterized in that: The method comprises the following steps: The first step is to mix ethanol, terephthalaldehyde, siloxane, aminosilicone, deionized water and acid for 10-60 minutes and mix them evenly to obtain a sol; the molar ratio of ethanol, terephthalaldehyde, siloxane, aminosilicone, deionized water and acid in the first step is 1:(0.005-0.05):(0.01-0.1):(0.01-0.1):(0.5-0.1):(0.01-0.1); Step 2: The sol obtained in the first step is heated to obtain gel A; Step 3: The gel A prepared in the second step is subjected to 3-8 replacements of the organic solvent and then dried to obtain aerogel A, wherein the amount of the organic solvent used is 3-10 times the volume of the gel A; Step 4: impregnating the aerogel A obtained in the third step into the sol obtained in the first step to obtain a mixture, wherein the volume ratio of the sol to the aerogel A is 1:1-3; the impregnation process in the fourth step is performed under a vacuum environment; Step 5: heating the mixture obtained in step 4 to obtain gel B; Step 6: The gel B obtained in the fifth step is subjected to 3-8 replacements of the organic solvent and then dried to obtain aerogel B, wherein the amount of the organic solvent used is 3-10 times the volume of the gel B; Step 7: Repeat steps 4 to 6 1-5 times using aerogel B; Step 8: performing high-temperature heat treatment on the aerogel obtained in the seventh step to obtain a self-grown nanowire-reinforced silicon carbide aerogel; the high-temperature heat treatment temperature in the eighth step is 1400-1700° C., the holding time is 2-6 hours, the heating rate is 3-5° C. / min, and after natural cooling, the self-grown nanowire-reinforced silicon carbide aerogel is obtained; In the first step, the siloxane is methyltrimethoxysilane; the aminosiloxane is 3-aminopropyltriethoxysilane and / or 3-aminopropyltrimethoxysilane; and the acid is acetic acid and / or hydrochloric acid; The temperature for organic solvent replacement in the third and sixth steps is 40-70° C., the replacement time is 8-24 hours, and the organic solvent is one or more of ethanol, methanol, n-hexane, and isopropanol.

2. The method for preparing the self-grown nanowire reinforced silicon carbide aerogel material according to claim 1, characterized in that: The heating conditions in the second and fifth steps are 40-70° C. and maintained for 6-24 hours.

3. The method for preparing the self-grown nanowire reinforced silicon carbide aerogel material according to claim 1, characterized in that: The drying process in the third and sixth steps is to dry at 40-80° C. under normal pressure for 36-48 hours or to dry in vacuum at 60-80° C. for 12-24 hours.

4. A self-grown nanowire reinforced silicon carbide aerogel material prepared by the preparation method according to any one of claims 1 to 3, characterized in that: The self-grown nanowire-reinforced silicon carbide aerogel material is a blue or gray-green block with a density of ≤0.2 g / cm 3 , thermal conductivity ≤ 0.05 W / mK, strength ≥ 0.25MPa.

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