CN111807368A - A kind of preparation method of high temperature resistant ultra-low density silicon carbide nanotube aerogel - Google Patents

Abstract

The invention discloses a preparation method of a high temperature resistant ultra-low density silicon carbide nanotube aerogel. The preparation method of the aerogel comprises the following specific steps: (1) Alkyltrialkoxysilane, dialkyldialkylene Alkoxysilane and cetyltrimethylammonium bromide are dissolved in deionized water to obtain a transparent solution, wherein alkyltrialkoxysilane, dialkyldialkoxysilane, cetyltrimethyl bromide The molar ratio of ammonium chloride and deionized water is 1:0.1~1:0.1~0.5:40~80. In the present invention, the polyalkylsiloxane gel with macroporous structure is obtained by utilizing the phase separation of the alkyl siloxane in the sol-gel process in the water system, and the macroporous structure can greatly reduce the capillary force in the normal pressure process. , a low-density aerogel block can be obtained under normal pressure drying, and the preparation method is simpler.

Description

A kind of preparation method of high temperature resistant ultra-low density silicon carbide nanotube aerogel

technical field

The invention belongs to the field of porous material preparation, and in particular relates to a preparation method of high temperature resistant ultra-low density silicon carbide aerogel.

Background technique

Aerogel is a new material with a three-dimensional nanoporous structure, with low density (0.003~0.8 g·cm-3), high porosity (80~99.8%), and high specific surface area (200~1000 m2·g- 1), low thermal conductivity (~0.02 W·m-1K-1) and other properties, it has a very broad prospect in aerospace, chemical industry, energy-saving buildings, military, communications, electronics, metallurgy and other application fields. However, the sintering phenomenon of traditional silica aerogels occurs at high temperatures over 650 °C, resulting in collapse of the nanoporous structure and performance degradation, making it difficult to apply in high temperature fields.

Silicon carbide aerogels have attracted attention due to their ability to withstand high temperatures above 1200 °C. At present, there are two main methods for preparing silicon carbide aerogels. One is to prepare an aerogel co-precursor containing a carbon source and a silicon source, and then perform high-temperature reduction. , formaldehyde, silicon source as raw materials, through sol-gel, aging and atmospheric drying to obtain RF-SiO2 composite aerogel, RF-SiO2 composite aerogel is subjected to carbothermic reduction reaction under argon protection, and then calcined in air That is, the bulk silicon carbide aerogel material is obtained, and the density of the silicon carbide aerogel obtained by this method is high (0.2~0.3g/cm3); Chinese patent (publication number CN103864076A) uses supercritically dried silica aerogel to condense The glue is used as a template, and the carbon source is infiltrated into the template to perform a high-temperature reaction to prepare silicon carbide aerogel, but this method uses expensive supercritical equipment; another preparation method is to use silicon carbide precursors and polyvinyl compounds to prepare Silicon carbide precursor aerogel is prepared by high temperature reaction. For example, a Chinese patent (publication number CN105600785A) discloses that polycarbosilane and vinyl compounds are dissolved in an organic solvent, and the karstedt catalyst catalyzes the reaction for 4 to 8 hours at 70°C to 90°C to obtain polycarbosilane gel; polycarbosilane is condensed After the glue is dried, polycarbosilane aerogel is obtained; the polycarbosilane aerogel is subjected to heat treatment and calcined at 500° C. to 700° C. for 1 to 5 hours under aerobic conditions to obtain silicon carbide aerogel. The polyvinyl compounds used in this method are easy to self-polymerize and require expensive Pt-containing catalysts.

Therefore, there is still a need for a simple and efficient production method to prepare low-density SiC aerogels.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the deficiencies of the prior art, and to provide a method for preparing a high temperature resistant ultra-low density silicon carbide aerogel, which can effectively solve the problems of the high density of the prepared gel and the use of Insufficient expensive catalyst, the preparation method of this method is simple.

The present invention is achieved through the following technical solutions:

A preparation method of high temperature resistant ultra-low density silicon carbide nanotube aerogel, the preparation method of the aerogel comprises the following specific steps:

(1) Dissolve alkyltrialkoxysilane, dialkyldialkoxysilane and cetyltrimethylammonium bromide in deionized water to obtain a transparent solution, wherein alkyltrialkoxysilane, The molar ratio of alkyldialkoxysilane, cetyltrimethylammonium bromide and deionized water is 1:0.1~1:0.1~0.5:40~80;

(2) Add ammonia water to the above solution to adjust the pH value of the solution to 9.0~12.0 to form a gel, soak the gel with absolute ethanol for 3-5 times, soaking for 8-12 hours each time; then put the soaked gel directly Put it into an oven for atmospheric drying, the drying temperature is 80-180 °C, and the drying time is 24-48 h to obtain a polyalkylsiloxane aerogel;

(3) Immerse the polyalkylsiloxane aerogel in step (2) into the xylene solution containing polycarbosilane until the solution wets the gel completely, and aerosol the wetted polyalkylsiloxane The glue is vacuum-dried to obtain polyalkylsiloxane aerogels with surface adsorption of polycarbosilane;

(4) The polyalkylsiloxane gas that adsorbed polycarbosilane in step (3) was placed in a tube furnace, and after passing Ar, the temperature was gradually heated to 1400-1500 ° C for 2-4 hours, and the cracking was carried out after natural cooling. The product was etched with concentrated sodium hydroxide solution for 2-5 h, washed with deionized water, and dried to obtain a high temperature resistant ultra-low density silicon carbide nanotube aerogel.

Further, the alkyltrialkoxysilane described in step (1) is methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, propyl group Trimethoxysilane, propyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, hexadecyltrimethoxysilane triethoxysilane, hexadecyltriethoxysilane, dodecyltrimethoxysilane, dodecyltriethoxysilane, octadecyltrimethoxysilane, octadecyltriethoxysilane any of the.

Further, the dialkyldialkoxysilane described in step (1) is dimethyldimethoxysilane, dimethyldiethoxysilane, methylvinyldimethoxysilane, methylethylene Diethoxysilane, methylphenyldimethoxysilane, methylphenyldiethoxysilane, diisobutyldimethoxysilane, diisobutyldiethoxysilane, octylmethyl Any of oxydimethoxysilane, octylmethyldiethoxysilane, cyclohexylmethyldimethoxysilane, and cyclohexylmethyldiethoxysilane.

Further, the ammonia concentration described in step (2) is 2-4 mol/L.

Further, the mass concentration of polycarbosilane in the xylene solution of polycarbosilane described in step (3) is 1-5%.

Further, the mass concentration of the concentrated sodium hydroxide solution described in step (4) is 40～70%.

Preferably, in step (4), the gradient heating rate is 2-5°C/min, and the flow rate of Ar introduced is 0.5-2 mL/min.

A high-temperature-resistant and ultra-low-density silicon carbide nanotube aerogel is characterized in that the aerogel can be used in the field of high-temperature heat insulation.

The beneficial effects of the present invention are:

1. The present invention obtains a polyalkylsiloxane gel with a macroporous structure by utilizing alkyl siloxane in a sol-gel process in an aqueous system to undergo phase separation, and the macroporous structure can greatly reduce the pressure in the normal pressure process. Capillary force, low-density aerogel blocks can be obtained under normal pressure drying, and the preparation method is simpler.

2. The polyalkylsiloxane aerogel prepared by the present invention has a macroporous structure, the average pore diameter is 420~2200nm, the density of the silicon carbide nanotube aerogel is 0.015~0.08 g/cm3, and the polyalkylsiloxane The macroporous structure of the alkane aerogel is conducive to the diffusion of the polycarbosilane solution in the aerogel to form a uniform polycarbosilane adsorption layer, which is conducive to the formation of silicon carbide nanotubes in the final etching process, while removing unreacted Silica template.

3. The polyalkylsiloxane aerogel of the present invention contains a large amount of methyl groups, which effectively reduces the proportion of oxygen atoms in the material system, and can reduce the destruction of the relative aerogel structure between SiCxOy crystals during the cracking process.

Description of drawings

1 is a schematic diagram of the silicon carbide nanotube aerogel prepared in Example 1.

Fig. 2 is the microscopic topography of the polyalkylsiloxane aerogel prepared in Example 1

3 is an X-ray diffraction pattern of the SiC aerogel prepared in Example 2.

Detailed ways

The technical solutions of the present invention are described in detail below through specific examples. The following examples are only examples for illustrating the present invention in detail, and are not intended to limit the embodiments of the present invention. For those skilled in the art, changes in other forms can be made on the basis of the description of the content of the present invention, and it is not necessary to list all the embodiments here.

Example 1

Dissolve methyltrimethoxysilane, dimethyldimethoxysilane and hexadecyltrimethylammonium bromide in deionized water to obtain a transparent solution, wherein methyltrimethoxysilane, dimethyldimethoxysilane The molar ratio of base silane, cetyltrimethylammonium bromide and deionized water is 1:0.1:0.1:80; adding 2 mol/L ammonia water to the above-mentioned solution to adjust the pH value of the solution to be 9.0 to form a gel. The gel was soaked three times with absolute ethanol for 12 h each time; the soaked gel was directly put into an oven for drying under normal pressure, and the drying temperature was 80 °C for 48 h to obtain a polyalkylsiloxane aerogel. The average pore size of the prepared polyalkylsiloxane aerogel is 2200 nm.

Immerse the polyalkylsiloxane aerogel in a xylene solution containing 1% polycarbosilane until the solution fully wets the gel, and vacuum dry the wetted polyalkylsiloxane aerogel ( The vacuum degree is less than 20Pa, and the drying temperature is 30℃) to obtain the polyalkylsiloxane aerogel with adsorption of polycarbosilane on the surface. Ar was introduced at a speed of 3 °C/min and then heated to 1450 °C for 4 h at a rate of 3 °C/min. After natural cooling, the cracked product was etched with 40% concentrated sodium hydroxide solution at 60 °C for 2 h, and then used After cleaning with ionized water, drying is performed to obtain a high temperature resistant ultra-low density silicon carbide nanotube aerogel.

The prepared high temperature resistant ultra-low density silicon carbide nanotube aerogel has a density of 0.015 g/cm ³ and a thermal conductivity of 0.024 W/(mK).

Example 2

Dissolve methyltrimethoxysilane, dimethyldimethoxysilane and hexadecyltrimethylammonium bromide in deionized water to obtain a transparent solution, wherein methyltrimethoxysilane, dimethyldimethoxysilane The molar ratio of base silane, cetyltrimethylammonium bromide and deionized water is 1:0.2:0.2:60; in the above solution, adding 3 mol/L ammonia water to adjust the pH value of the solution to form a gel is 10.0, and the The gel was soaked three times with absolute ethanol for 12 h each time; the soaked gel was directly put into an oven for drying under normal pressure, the drying temperature was 100 °C, and the polyalkylsiloxane aerogel was obtained by drying for 48 h. The average pore size of the prepared polyalkylsiloxane aerogel is 1200 nm.

Immerse the polyalkylsiloxane aerogel in a xylene solution containing 2% polycarbosilane until the solution wets the gel completely, and vacuum dry the wetted polyalkylsiloxane aerogel ( The vacuum degree is less than 20Pa, and the drying temperature is 40℃) to obtain the polyalkylsiloxane aerogel with adsorption of polycarbosilane on the surface. Ar was introduced at a rate of 2°C/min and then heated to 1400°C for 4 h at a rate of 2°C/min. After natural cooling, the cracked product was etched with 40% concentrated sodium hydroxide solution at 45°C for 4 h, and then used After cleaning with ionized water, drying is performed to obtain a high temperature resistant ultra-low density silicon carbide nanotube aerogel.

The prepared high temperature resistant ultra-low density silicon carbide nanotube aerogel has a density of 0.032 g/cm ³ and a thermal conductivity of 0.027 W/(mK).

Example 3

Dissolve ethyltrimethoxysilane, dimethyldiethoxysilane and cetyltrimethylammonium bromide in deionized water to obtain a transparent solution, wherein ethyltrimethoxysilane, dimethyldiethoxysilane The molar ratio of base silane, hexadecyltrimethylammonium bromide and deionized water is 1:0.5:0.3:60; adding 3 mol/L ammonia water to the above solution to adjust the pH value of the solution to be 11.0 to form a gel, The gel was soaked three times with absolute ethanol for 12 h each time; the soaked gel was directly put into an oven for drying under normal pressure, the drying temperature was 120 °C, and the polyalkylsiloxane aerogel was obtained by drying for 30 h. The average pore size of the prepared polyalkylsiloxane aerogel is 820 nm.

Immerse the polyalkylsiloxane aerogel in a xylene solution containing 3% polycarbosilane until the solution fully wets the gel, and vacuum dry the wetted polyalkylsiloxane aerogel ( The vacuum degree is less than 20Pa, and the drying temperature is 50℃) to obtain the polyalkylsiloxane aerogel with adsorption of polycarbosilane on the surface, and the polyalkylsiloxane with adsorption of polycarbosilane is placed in a tube furnace, 1 mL Ar was introduced at a rate of 2°C/min and then heated to 1450°C for 3 h at a rate of 2°C/min. After natural cooling, the cracked product was etched with 60% concentrated sodium hydroxide solution at 40°C for 2 h, and then used After cleaning with ionized water, drying is performed to obtain a high temperature resistant ultra-low density silicon carbide nanotube aerogel.

The prepared high temperature resistant ultra-low density silicon carbide nanotube aerogel has a density of 0.048 g/cm ³ and a thermal conductivity of 0.028 W/(mK).

Example 4

Dissolve vinyltriethoxysilane, methylvinyldimethoxysilane and cetyltrimethylammonium bromide in deionized water to obtain a transparent solution, wherein vinyltriethoxysilane, methylethylene The molar ratio of dimethoxysilane, hexadecyltrimethylammonium bromide and deionized water is 1:0.8:0.4:50; in the above solution, adding 4 mol/L ammonia water to adjust the pH value of the solution is 11.0 to form The gel was soaked in absolute ethanol for five times, 8 h each time; the soaked gel was directly put into an oven for drying under normal pressure, the drying temperature was 150 °C, and the polyalkylsiloxane was dried for 26 h. Aerogel. The average pore size of the prepared polyalkylsiloxane aerogel is 640 nm.

Immerse the polyalkylsiloxane aerogel in a xylene solution containing 4% polycarbosilane until the solution fully wets the gel, and vacuum dry the wetted polyalkylsiloxane aerogel ( The vacuum degree is less than 20Pa, and the drying temperature is 30℃) to obtain the polyalkylsiloxane aerogel with adsorption of polycarbosilane on the surface. Ar was introduced at a rate of 5°C/min and then heated to 1500°C for 2 h at a rate of 5°C/min. After natural cooling, the cracked product was etched with 40% concentrated sodium hydroxide solution at 40°C for 5 h, and then used After cleaning with ionized water, drying is performed to obtain a high temperature resistant ultra-low density silicon carbide nanotube aerogel.

The prepared high temperature resistant ultra-low density silicon carbide nanotube aerogel has a density of 0.066 g/cm ³ and a thermal conductivity of 0.031 W/(mK).

Example 5

Dissolve methyltrimethoxysilane, dimethyldimethoxysilane and hexadecyltrimethylammonium bromide in deionized water to obtain a transparent solution, wherein methyltrimethoxysilane, dimethyldimethoxysilane The molar ratio of base silane, cetyltrimethylammonium bromide and deionized water is 1:0.1:0.5:40; in the above solution, adding 4 mol/L ammonia water to adjust the pH value of the solution to be 12.0 to form a gel, the The gel was soaked three times with absolute ethanol for 12 h each time; the soaked gel was directly placed in an oven for drying under normal pressure, the drying temperature was 180 °C, and the polyalkylsiloxane aerogel was obtained by drying for 24 h. The average pore size of the prepared polyalkylsiloxane aerogel is 420 nm.

Immerse the polyalkylsiloxane aerogel in a xylene solution containing 5% polycarbosilane until the solution fully wets the gel, and vacuum dry the wetted polyalkylsiloxane aerogel ( The vacuum degree is less than 20Pa, and the drying temperature is 40℃) to obtain the polyalkylsiloxane aerogel adsorbing polycarbosilane on the surface, and placing the polyalkylsiloxane adsorbing polycarbosilane in a tube furnace, 1 mL Ar was introduced at a speed of 5°C/min and then heated to 1500°C for 2 h at a rate of 5°C/min. After natural cooling, the cracked product was etched with 70% concentrated sodium hydroxide solution at 30°C for 2 h, and then used After cleaning with ionized water, drying is performed to obtain a high temperature resistant ultra-low density silicon carbide nanotube aerogel.

The prepared high temperature resistant ultra-low density silicon carbide nanotube aerogel has a density of 0.08 g/cm ³ and a thermal conductivity of 0.033 W/(mK).

The above-mentioned aerogel detection is detected with a laser thermal conductivity meter.

The basic principles and main features of the present invention and the advantages of the present invention have been shown and described above. Those skilled in the art should understand that the present invention is not limited by the above-mentioned embodiments. The above-mentioned embodiments and descriptions only illustrate the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will also have Various changes and modifications fall within the scope of the claimed invention. The claimed scope of the present invention is defined by the appended claims and their equivalents.

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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