CN111807368A - Preparation method of high-temperature-resistant ultralow-density silicon carbide nanotube aerogel - Google Patents

Preparation method of high-temperature-resistant ultralow-density silicon carbide nanotube aerogel Download PDF

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CN111807368A
CN111807368A CN202010502072.1A CN202010502072A CN111807368A CN 111807368 A CN111807368 A CN 111807368A CN 202010502072 A CN202010502072 A CN 202010502072A CN 111807368 A CN111807368 A CN 111807368A
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aerogel
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silicon carbide
polyalkylsiloxane
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云山
郭探
李彦兴
李爱平
徐海青
洪坤
陈静
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Huaiyin Institute of Technology
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Abstract

The invention discloses a preparation method of a high-temperature-resistant ultralow-density silicon carbide nanotube aerogel, which comprises the following specific steps of: (1) dissolving alkyltrialkoxysilane, dialkyldialkoxysilane and hexadecyltrimethylammonium bromide in deionized water to obtain a transparent solution, wherein the molar ratio of the alkyltrialkoxysilane to the dialkyldialkoxysilane to the hexadecyltrimethylammonium bromide to the deionized water is 1: 0.1-0.5: 40-80. According to the invention, the polyalkylsiloxane gel with a macroporous structure is obtained by utilizing the phase separation of the alkyl siloxane in the sol-gel process in a water system, the macroporous structure can greatly reduce the capillary force in the normal pressure process, and the low-density aerogel block can be obtained under the normal pressure drying, so that the preparation method is simpler.

Description

Preparation method of high-temperature-resistant ultralow-density silicon carbide nanotube aerogel
Technical Field
The invention belongs to the field of preparation of porous materials, and particularly relates to a preparation method of high-temperature-resistant ultralow-density silicon carbide aerogel.
Background
The aerogel is a new material with a three-dimensional nano porous structure, has the properties of low density (0.003-0.8 g.cm < -3 >), high porosity (80-99.8%), high specific surface area (200-1000 m 2. g < -1 >), low thermal conductivity (0.02 W.m < -1 > K < -1 >) and the like, and has very wide prospects in the application fields of aerospace, chemical engineering, energy-saving buildings, military affairs, communication, electronics, metallurgy and the like. However, the conventional silica aerogel has a sintering phenomenon at a high temperature of more than 650 ℃, which causes the collapse of a nano-pore structure and the performance reduction, and is difficult to apply to the high-temperature field.
Silicon carbide aerogels have received attention because of their ability to withstand temperatures above 1200 c. Currently, there are two main methods for preparing silicon carbide aerogel, one is to prepare an aerogel co-precursor containing a carbon source and a silicon source, and perform high-temperature reduction, for example, chinese patent (publication No. CN 102897764A) discloses that hydroquinone, formaldehyde and a silicon source are used as raw materials, and are subjected to sol-gel, aging and normal-pressure drying to obtain RF-SiO2 composite aerogel, the RF-SiO2 composite aerogel is subjected to carbothermic reduction reaction under the protection of argon gas, and then is calcined in the air to obtain a massive silicon carbide aerogel material, and the density of the silicon carbide aerogel prepared by the method is relatively high (0.2-0.3 g/cm 3); chinese patent (publication No. CN 103864076A) takes supercritical dried silicon dioxide aerogel as a template, carbon sources are infiltrated into the template, and then the silicon carbide aerogel is prepared by high-temperature reaction, but the method adopts expensive supercritical equipment; the other preparation method is to prepare the silicon carbide precursor aerogel by adopting a silicon carbide precursor and a polyvinyl compound and then carrying out high-temperature reaction. For example, Chinese patent (publication No. CN 105600785A) discloses that polycarbosilane and vinyl compound are dissolved in an organic solvent, and the reaction is catalyzed by a karstedt catalyst for 4-8 hours at 70-90 ℃ to obtain polycarbosilane gel; drying the polycarbosilane gel to obtain polycarbosilane aerogel; and (3) carrying out heat treatment on the polycarbosilane aerogel and calcining for 1-5 h at 500-700 ℃ under an aerobic condition to obtain the silicon carbide aerogel. The polyvinyl compounds employed in this process are readily self-polymerizing and require expensive Pt-containing catalysts.
Therefore, there is still a need for a simple and efficient production method for preparing SiC aerogel with low density.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a preparation method of high-temperature-resistant ultralow-density silicon carbide aerogel, which can effectively solve the defects of high density of the prepared gel and utilization of expensive catalysts in the background art, and is simple.
The invention is realized by the following technical scheme:
a preparation method of high-temperature-resistant ultralow-density silicon carbide nanotube aerogel comprises the following specific steps:
(1) dissolving alkyltrialkoxysilane, dialkyldialkoxysilane and hexadecyltrimethylammonium bromide in deionized water to obtain a transparent solution, wherein the molar ratio of the alkyltrialkoxysilane to the dialkyldialkoxysilane to the hexadecyltrimethylammonium bromide to the deionized water is 1: 0.1-0.5: 40-80;
(2) adding ammonia water into the solution to adjust the pH value of the solution to 9.0-12.0 to form gel, and soaking the gel for 3-5 times by using absolute ethyl alcohol, wherein each time is 8-12 hours; directly placing the soaked gel into a drying oven to carry out drying under normal pressure, wherein the drying temperature is 80-180 ℃, and the drying time is 24-48 h to obtain polyalkylsiloxane aerogel;
(3) immersing the polyalkylsiloxane aerogel in the step (2) into a dimethylbenzene solution containing polycarbosilane until the gel is completely wetted by the solution, and carrying out vacuum drying on the wetted polyalkylsiloxane aerogel to obtain polyalkylsiloxane aerogel with the surface adsorbing the polycarbosilane;
(4) and (3) placing the polyalkylsiloxane aerogel adsorbing polycarbosilane in the step (3) in a tubular furnace, introducing Ar, then heating to 1400-1500 ℃ in a gradient manner for cracking for 2-4h, naturally cooling, then etching the cracked product for 2-5 h by using a concentrated sodium hydroxide solution, cleaning by using deionized water, and drying to obtain the high-temperature-resistant ultralow-density silicon carbide nanotube aerogel.
Further, the alkyltrialkoxysilane described in step (1) is any one of methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, hexadecyltrimethoxysilane, hexadecyltriethoxysilane, dodecyltrimethoxysilane, dodecyltriethoxysilane, octadecyltrimethoxysilane and octadecyltriethoxysilane.
Further, the dialkyldialkoxysilane in the step (1) is any one of dimethyldimethoxysilane, dimethyldiethoxysilane, methylvinyldimethoxysilane, methylvinyldiethoxysilane, methylphenyldimethoxysilane, methylphenyldiethoxysilane, diisobutyldimethoxysilane, diisobutyldiethoxysilane, octylmethyldimethoxysilane, octylmethyldiethoxysilane, cyclohexylmethyldimethoxysilane and cyclohexylmethyldiethoxysilane.
Further, the concentration of the ammonia water in the step (2) is 2-4 mol/L.
Further, the mass concentration of the polycarbosilane in the xylene solution of the polycarbosilane in the step (3) is 1-5%.
Further, the mass concentration of the concentrated sodium hydroxide solution in the step (4) is 40-70%.
Preferably, the gradient heating rate of the step (4) is 2-5 ℃/min, and the flow rate of introducing Ar is 0.5-2 mL/min.
The high-temperature-resistant ultralow-density silicon carbide nanotube aerogel is characterized in that: the aerogel can be applied to the field of high-temperature heat insulation.
The invention has the beneficial effects that:
firstly, the invention utilizes the alkyl siloxane to carry out phase separation in the sol-gel process in a water system to obtain the polyalkylsiloxane gel with a macroporous structure, the macroporous structure can greatly reduce the capillary force in the normal pressure process, and the low-density aerogel block can be obtained under the normal pressure drying, and the preparation method is simpler.
Secondly, the prepared polyalkylsiloxane aerogel has a macroporous structure, the average pore diameter is 420-2200 nm, the density of the silicon carbide nanotube aerogel is 0.015-0.08 g/cm3, the macroporous structure of the polyalkylsiloxane aerogel is beneficial to the polycarbosilane solution to diffuse in the aerogel to form a uniform polycarbosilane adsorption layer, the formation of the silicon carbide nanotube is facilitated in the final etching process, and meanwhile, an unreacted silicon dioxide template is removed.
Thirdly, the polyalkylsiloxane aerogel contains a large amount of methyl, so that the proportion of oxygen atoms in a material system is effectively reduced, and the damage of SiCxOy intercrystalline relative aerogel structures generated in the cracking process can be reduced.
Drawings
FIG. 1 is a schematic representation of a silicon carbide nanotube aerogel prepared in example 1.
FIG. 2 is a microscopic topography of the polyalkylsiloxane aerogel prepared in example 1
Fig. 3 is an X-ray diffraction pattern of the SiC aerogel prepared in example 2.
Detailed Description
The technical solutions of the present invention will be described in detail below with reference to specific examples, which are provided only for illustrating the present invention in detail and are not intended to limit the embodiments of the present invention. It will be apparent to those skilled in the art that many more modifications and variations are possible in light of the above teaching, without necessarily requiring all of the described embodiments to be included herein.
Example 1
Dissolving methyltrimethoxysilane, dimethyldimethoxysilane and hexadecyltrimethylammonium bromide in deionized water to obtain a transparent solution, wherein the molar ratio of the methyltrimethoxysilane to the dimethyldimethoxysilane to the hexadecyltrimethylammonium bromide to the deionized water is 1:0.1: 0.1: 80; adding 2 mol/L ammonia water into the solution to adjust the pH value of the solution to 9.0 to form gel, and soaking the gel with absolute ethyl alcohol for three times, wherein each time lasts for 12 hours; and directly putting the soaked gel into an oven to dry at the normal pressure, wherein the drying temperature is 80 ℃, and drying for 48 hours to obtain the polyalkylsiloxane aerogel. The average pore diameter of the prepared polyalkylsiloxane aerogel was 2200 nm.
Immersing polyalkylsiloxane aerogel into a dimethylbenzene solution containing 1% polycarbosilane until the solution completely wets the gel, carrying out vacuum drying (the vacuum degree is less than 20Pa and the drying temperature is 30 ℃) on the wetted polyalkylsiloxane aerogel to obtain the polyalkylsiloxane aerogel with the surface adsorbing polycarbosilane, carrying out gas condensation on the polyalkylsiloxane with the adsorbed polycarbosilane in a tubular furnace, introducing Ar at the speed of 0.5 mL/min, heating to 1450 ℃ at the speed of 3 ℃/min for cracking for 4h, naturally cooling, etching the cracking product for 2 h at the temperature of 60 ℃ by using 40% concentrated sodium hydroxide solution, cleaning by using deionized water, and drying to obtain the high-temperature-resistant ultra-low-density silicon carbide nanotube aerogel.
The density of the prepared high-temperature-resistant ultra-low density silicon carbide nanotube aerogel is 0.015 g/cm3The thermal conductivity was 0.024W/(mK).
Example 2
Dissolving methyltrimethoxysilane, dimethyldimethoxysilane and hexadecyltrimethylammonium bromide in deionized water to obtain a transparent solution, wherein the molar ratio of the methyltrimethoxysilane to the dimethyldimethoxysilane to the hexadecyltrimethylammonium bromide to the deionized water is 1:0.2: 0.2: 60; adding 3 mol/L ammonia water into the solution to adjust the pH value of the solution to 10.0 to form gel, and soaking the gel with absolute ethyl alcohol for three times, wherein each time lasts for 12 hours; and directly putting the soaked gel into an oven to dry at normal pressure, wherein the drying temperature is 100 ℃, and drying for 48 hours to obtain the polyalkylsiloxane aerogel. The average pore diameter of the prepared polyalkylsiloxane aerogel was 1200 nm.
Immersing polyalkylsiloxane aerogel into a dimethylbenzene solution containing 2% polycarbosilane until the solution completely wets the gel, carrying out vacuum drying (the vacuum degree is less than 20Pa and the drying temperature is 40 ℃) on the wetted polyalkylsiloxane aerogel to obtain the polyalkylsiloxane aerogel with the surface adsorbing polycarbosilane, carrying out gas condensation on the polyalkylsiloxane with the adsorbed polycarbosilane in a tubular furnace, introducing Ar at the speed of 0.5 mL/min, heating to 1400 ℃ at the speed of 2 ℃/min for cracking for 4h, naturally cooling, etching the cracking product for 4h at the temperature of 45 ℃ by using 40% concentrated sodium hydroxide solution, cleaning by using deionized water, and drying to obtain the high-temperature-resistant ultra-low-density silicon carbide nanotube aerogel.
The density of the prepared high-temperature-resistant ultra-low density silicon carbide nanotube aerogel is 0.032 g/cm3The thermal conductivity was 0.027W/(mK).
Example 3
Dissolving ethyl trimethoxy silane, dimethyl diethoxy silane and hexadecyl trimethyl ammonium bromide in deionized water to obtain a transparent solution, wherein the molar ratio of the ethyl trimethoxy silane to the dimethyl diethoxy silane to the hexadecyl trimethyl ammonium bromide to the deionized water is 1:0.5: 0.3: 60; adding 3 mol/L ammonia water into the solution to adjust the pH value of the solution to 11.0 to form gel, and soaking the gel with absolute ethyl alcohol for three times, wherein each time lasts for 12 hours; and directly putting the soaked gel into an oven to dry at normal pressure, wherein the drying temperature is 120 ℃, and drying for 30 hours to obtain the polyalkylsiloxane aerogel. The average pore diameter of the prepared polyalkylsiloxane aerogel was 820 nm.
Immersing polyalkylsiloxane aerogel into a dimethylbenzene solution containing 3% polycarbosilane until the solution completely wets the gel, carrying out vacuum drying (the vacuum degree is less than 20Pa, the drying temperature is 50 ℃) on the wetted polyalkylsiloxane aerogel to obtain the polyalkylsiloxane aerogel with the surface adsorbing polycarbosilane, carrying out gas condensation on the polyalkylsiloxane with the adsorbed polycarbosilane in a tubular furnace, introducing Ar at the speed of 1 mL/min, heating to 1450 ℃ at the speed of 2 ℃/min for cracking for 3 h, naturally cooling, etching the cracked product for 2 h at the temperature of 40 ℃ by using 60% concentrated sodium hydroxide solution, cleaning by using deionized water, and drying to obtain the high-temperature-resistant ultralow-density silicon carbide nanotube aerogel.
The density of the prepared high-temperature-resistant ultra-low density silicon carbide nanotube aerogel is 0.048 g/cm3The thermal conductivity was 0.028W/(mK).
Example 4
Dissolving vinyl triethoxysilane, methyl vinyl dimethoxysilane and hexadecyl trimethyl ammonium bromide in deionized water to obtain a transparent solution, wherein the molar ratio of the vinyl triethoxysilane to the methyl vinyl dimethoxysilane to the hexadecyl trimethyl ammonium bromide to the deionized water is 1:0.8: 0.4: 50; adding 4mol/L ammonia water into the solution to adjust the pH value of the solution to 11.0 to form gel, and soaking the gel in absolute ethyl alcohol for five times, wherein each time is 8 hours; and directly putting the soaked gel into an oven to dry at the normal pressure, wherein the drying temperature is 150 ℃, and drying for 26 hours to obtain the polyalkylsiloxane aerogel. The average pore diameter of the prepared polyalkylsiloxane aerogel was 640 nm.
Immersing polyalkylsiloxane aerogel into a dimethylbenzene solution containing 4% polycarbosilane until the solution completely wets the gel, carrying out vacuum drying (the vacuum degree is less than 20Pa, the drying temperature is 30 ℃) on the wetted polyalkylsiloxane aerogel to obtain the polyalkylsiloxane aerogel with the surface adsorbing polycarbosilane, carrying out gas condensation on the polyalkylsiloxane with the adsorbed polycarbosilane in a tubular furnace, introducing Ar at the speed of 2 mL/min, heating to 1500 ℃ at the speed of 5 ℃/min for cracking for 2 h, naturally cooling, etching the cracked product for 5h at the temperature of 40 ℃ by using 40% concentrated sodium hydroxide solution, cleaning by using deionized water, and drying to obtain the high-temperature-resistant ultralow-density silicon carbide nanotube aerogel.
The density of the prepared high-temperature-resistant ultra-low density silicon carbide nano tube aerogel is 0.066 g/cm3The thermal conductivity was 0.031W/(mK).
Example 5
Dissolving methyltrimethoxysilane, dimethyldimethoxysilane and hexadecyltrimethylammonium bromide in deionized water to obtain a transparent solution, wherein the molar ratio of the methyltrimethoxysilane to the dimethyldimethoxysilane to the hexadecyltrimethylammonium bromide to the deionized water is 1:0.1: 0.5: 40; adding 4mol/L ammonia water into the solution to adjust the pH value of the solution to 12.0 to form gel, and soaking the gel with absolute ethyl alcohol for three times, wherein each time lasts for 12 hours; and directly putting the soaked gel into an oven to dry at the normal pressure, wherein the drying temperature is 180 ℃, and drying for 24 hours to obtain the polyalkylsiloxane aerogel. The average pore diameter of the prepared polyalkylsiloxane aerogel was 420 nm.
Immersing polyalkylsiloxane aerogel into a dimethylbenzene solution containing 5% polycarbosilane until the solution completely wets the gel, carrying out vacuum drying (the vacuum degree is less than 20Pa and the drying temperature is 40 ℃) on the wetted polyalkylsiloxane aerogel to obtain the polyalkylsiloxane aerogel with the surface adsorbing polycarbosilane, carrying out gas condensation on the polyalkylsiloxane with the adsorbed polycarbosilane in a tubular furnace, introducing Ar at the speed of 1 mL/min, heating to 1500 ℃ at the speed of 5 ℃/min for cracking for 2 h, naturally cooling, etching the cracked product for 2 h at the temperature of 30 ℃ by using 70% concentrated sodium hydroxide solution, cleaning by using deionized water, and drying to obtain the high-temperature-resistant ultralow-density silicon carbide nanotube aerogel.
The density of the prepared high-temperature-resistant ultra-low density silicon carbide nanotube aerogel is 0.08 g/cm3The thermal conductivity was 0.033W/(mK).
The above references to aerogel testing were made using a laser thermal conductivity meter.
The foregoing shows and describes the general principles and broad features of the present invention and advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims (8)

1. A preparation method of high-temperature-resistant ultralow-density silicon carbide nanotube aerogel is characterized by comprising the following steps of: the preparation method of the aerogel comprises the following specific steps:
(1) dissolving alkyltrialkoxysilane, dialkyldialkoxysilane and hexadecyltrimethylammonium bromide in deionized water to obtain a transparent solution, wherein the molar ratio of the alkyltrialkoxysilane to the dialkyldialkoxysilane to the hexadecyltrimethylammonium bromide to the deionized water is 1: 0.1-0.5: 40-80;
(2) adding ammonia water into the solution to adjust the pH value of the solution to 9.0-12.0 to form gel, and soaking the gel for 3-5 times by using absolute ethyl alcohol, wherein each time is 8-12 hours; directly placing the soaked gel into a drying oven to carry out drying under normal pressure, wherein the drying temperature is 80-180 ℃, and the drying time is 24-48 h to obtain polyalkylsiloxane aerogel;
(3) immersing the polyalkylsiloxane aerogel in the step (2) into a dimethylbenzene solution containing polycarbosilane until the gel is completely wetted by the solution, and carrying out vacuum drying on the wetted polyalkylsiloxane aerogel to obtain polyalkylsiloxane aerogel with the surface adsorbing the polycarbosilane;
(4) and (3) placing the polyalkylsiloxane aerogel adsorbing polycarbosilane in the step (3) in a tubular furnace, introducing Ar, then heating to 1400-1500 ℃ in a gradient manner for cracking for 2-4h, naturally cooling, then etching the cracked product for 2-5 h by using a concentrated sodium hydroxide solution, cleaning by using deionized water, and drying to obtain the high-temperature-resistant ultralow-density silicon carbide nanotube aerogel.
2. The preparation method of the high temperature resistant ultra-low density silicon carbide nanotube aerogel according to claim 1, wherein the preparation method comprises the following steps: the alkyltrialkoxysilane in the step (1) is any one of methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, hexadecyltrimethoxysilane, hexadecyltriethoxysilane, dodecyltrimethoxysilane, dodecyltriethoxysilane, octadecyltrimethoxysilane and octadecyltriethoxysilane.
3. The preparation method of the high temperature resistant ultra-low density silicon carbide nanotube aerogel according to claim 1, wherein the preparation method comprises the following steps: the dialkyldialkoxysilane in the step (1) is any one of dimethyldimethoxysilane, dimethyldiethoxysilane, methylvinyldimethoxysilane, methylvinyldiethoxysilane, methylphenyldimethoxysilane, methylphenyldiethoxysilane, diisobutyldimethoxysilane, diisobutyldiethoxysilane, octylmethyldimethoxysilane, octylmethyldiethoxysilane, cyclohexylmethyldimethoxysilane and cyclohexylmethyldiethoxysilane.
4. The method of claim 1, wherein: the concentration of the ammonia water in the step (2) is 2-4 mol/L.
5. The preparation method of the high temperature resistant ultra-low density silicon carbide nanotube aerogel according to claim 1, wherein the preparation method comprises the following steps: and (3) the mass concentration of the polycarbosilane in the xylene solution of the polycarbosilane is 1-5%.
6. The preparation method of the high temperature resistant ultra-low density silicon carbide nanotube aerogel according to claim 1, wherein the preparation method comprises the following steps: the mass concentration of the concentrated sodium hydroxide solution in the step (4) is 40-70%.
7. The preparation method of the high temperature resistant ultra-low density silicon carbide nanotube aerogel according to claim 1, wherein the preparation method comprises the following steps: the gradient heating rate of the step (4) is 2-5 ℃/min, and the flow of Ar introduced is 0.5-2 mL/min.
8. The high-temperature-resistant ultralow-density silicon carbide nanotube aerogel is characterized in that: the aerogel can be applied to the field of high-temperature heat insulation.
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CN114452950A (en) * 2021-12-15 2022-05-10 淮阴工学院 Preparation method and application of high-strength double-crosslinked-network rubidium/cesium special-effect adsorbent
CN114452950B (en) * 2021-12-15 2023-10-20 淮阴工学院 Preparation method and application of high-strength double-crosslinked network rubidium/cesium specific adsorbent
CN114715896A (en) * 2022-04-14 2022-07-08 中国科学技术大学先进技术研究院 Preparation method of silicon carbide nanotube aerogel
CN116814005A (en) * 2023-07-03 2023-09-29 无菌时代复合新材料(苏州)有限公司 High-temperature-resistant silicon carbide aerogel master batch and preparation method thereof
CN116814005B (en) * 2023-07-03 2024-01-30 无菌时代复合新材料(苏州)有限公司 High-temperature-resistant silicon carbide aerogel master batch and preparation method thereof

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