CN110668446B - Preparation method of high-temperature-resistant SiC aerogel - Google Patents
Preparation method of high-temperature-resistant SiC aerogel Download PDFInfo
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Abstract
A preparation method of high temperature resistant SiC aerogel relates to a preparation method of aerogel. The invention aims to solve the technical problems that the existing method for preparing the SiC aerogel is low in yield and the microstructure of the aerogel is easy to damage. The method comprises the following steps: firstly, preparing solution A and solution B, and mixing the solution A and the solution B to obtain hydrolysate; secondly, preparing wet gel; thirdly, preparing aerogel; and fourthly, reacting the aerogel with magnesium powder, cleaning and drying to obtain the SiC aerogel. The invention adopts magnesiothermic reduction to reduce the aerogel precursor into SiC aerogel under the protection of inert gas. Successfully avoid R1SiO1.5SiO gas is generated in the reduction process, and the shape and the integrity of the product are kept to the maximum extent. And preparing the organic silicon aerogel with uniform pore structure and complete shape by supercritical drying. The invention belongs to the field of aerogel preparation.
Description
Technical Field
The invention relates to a preparation method of aerogel.
Background
As a high-porosity three-dimensional porous material, the aerogel has the characteristics of low density, high specific surface area, low thermal conductivity, high acoustic resistance and the like, and is widely applied to the fields of heat insulation, sound insulation, adsorption, catalysis and the like. Currently, the aerogel reported is based on Silicon (SiO)2Aerogel), carbon-based (carbon aerogel, graphene aerogel, cellulose aerogel) and metal oxide-based (Al)2O3Aerogel) is predominant. However, such materials can be more or less problematic:
for SiO2Although the aerogel has a good thermal insulation coefficient, the high-temperature resistance of the aerogel is poor, and the three-dimensional porous framework is easy to collapse and loses the thermal insulation capability after the temperature is higher than 600 ℃; for carbon aerogel, the oxidation resistance is poor, and the carbon aerogel is easily oxidized and decomposed at a high temperature; for Al2O3The aerogel has good high temperature resistance, but the acid and alkali resistance of the aerogel is relatively general, and particularly, the aerogel is easy to generate double decomposition reaction under an acidic condition and loses due performance.
Compared with the materials, the SiC has stable chemical property, excellent wear resistance and high temperature resistance, and is an ideal refractory material. Currently, SiC is mainly prepared by a carbothermic reduction reaction of a silicon source and a carbon source at a high temperature, and for example, chinese patent publication No. CN102897764A discloses a preparation method of SiC aerogel, which uses benzenediol-formaldehyde as a carbon source, 3-aminopropyltriethoxysilane-tetraethoxysilane as a mixed silicon source, and obtains a SiC aerogel material by carbothermic reduction at a high temperature of 1500-. However, the method is very easy to generate SiO gas intermediate phase in the synthesis process, the microstructure of the aerogel is damaged, and the yield of the bulk SiC aerogel is greatly reduced. Compared with a carbothermic reduction method, the reaction temperature of the magnesiothermic reduction method is lower (less than 800 ℃), the generation of SiO intermediate phase can be greatly avoided in the synthesis process of the SiC aerogel, so that the appearance integrity of the precursor can be kept, and the method is suitable for preparing various special-shaped parts. For example, journal of atomic energy science and technology discloses a method for preparing SiC aerogel through magnesiothermic reduction, wherein the SiC aerogel can be prepared at 700 ℃ by using resorcinol-formaldehyde as a carbon source and tetraethoxysilane as a silicon source. However, no matter magnesium thermal reduction or carbon thermal reduction, proper silicon source and carbon source need to be selected, the process is complicated, the product components are complex, and the yield is relatively low.
Disclosure of Invention
The invention aims to solve the technical problems that the existing method for preparing SiC aerogel is low in yield and the microstructure of the aerogel is easy to damage, and provides a method for preparing high-temperature resistant SiC aerogel.
The preparation method of the high-temperature resistant SiC aerogel comprises the following steps:
weighing 9.9g R1Si(OR2)37.6g of methyl orthosilicate, and magnetically stirring for 5min to obtain a mixed solution A;
weighing 46g of ethanol, 1.8g of deionized water and 0.25g of span-20, and mixing to obtain a mixed solution B;
thirdly, mixing the mixed solution A and the mixed solution B, and dripping 0.5mL of 1mol/L hydrochloric acid into the mixed solution to perform magnetic stirring for 2 hours at normal temperature to obtain hydrolysate;
fourthly, taking 25mL of hydrolysate, dripping 0.5mL of ammonia water with the concentration of 1mol/L into the hydrolysate, transferring the hydrolysate to a closed container, and placing the hydrolysate in a 50 ℃ oven for 0.5 to 10 hours to obtain wet gel;
aging the wet gel with 25mL of methanol at 50 ℃ for 24h, exchanging with 25mL of ethanol for 2 times, exchanging with 25mL of n-hexane for 3 times, and exchanging at normal pressureGradient drying to obtain phenyl hybrid SiO2An aerogel;
sixthly, 2.0g of phenyl hybridized SiO2Placing aerogel and 2.5g of magnesium powder with the particle size of 10-100 mu m in a stainless steel reactor, then placing the stainless steel reactor in a tubular furnace, firstly purging the furnace body for 0.5h by adopting argon with the flow rate of 100mL/min, raising the temperature to 650 ℃ at the speed of 5 ℃/min under the protection of argon, keeping the temperature for 5h, and then naturally cooling to room temperature to obtain a crude product;
and seventhly, cleaning the crude product for 3 hours by respectively adopting hydrofluoric acid with the mass concentration of 5%, hydrochloric acid with the concentration of 6mol/L and hydrochloric acid with the concentration of 1mol/L, washing the crude product with deionized water until the washing liquid is neutral, and then drying the washed product in vacuum at 90 ℃ to obtain the SiC aerogel.
In step one, R is1Si(OR2)3Wherein R is2＝CH3Or CH2CH3，R1Aromatic hydrocarbon or alkane with carbon number more than or equal to 6.
The preparation method of the high-temperature resistant SiC aerogel comprises the following steps:
firstly, weighing 23g to 46g of ethanol, 0.9g to 1.8g of deionized water and 0.125g to 0.25g of span-20, mixing, magnetically stirring for 5min, and then dropwise adding 14.5g to 19.8g R1Si(OR2)30.5mL of hydrochloric acid with the concentration of 0.1mol/L, and stirring for 2 hours in an oil bath at the temperature of 50-80 ℃ to obtain hydrolysate;
secondly, taking 25mL of hydrolysate, dripping 0.5-1 mL of ammonia water with the concentration of 6-12 mol/L into the hydrolysate, transferring the hydrolysate into a closed container, and placing the container in a 50 ℃ oven for 0.5-10 h to obtain wet gel;
aging the wet gel with 25mL of methanol at 50 ℃ for 24h, exchanging with 25mL of ethanol for 2 times, exchanging with 25mL of n-hexane for 3 times, and then performing supercritical drying at 8MPa and 30 ℃ for 4h to obtain aerogel;
fourthly, placing 1.8g to 2.3g of aerogel and 2.3g to 2.8g of magnesium powder with the grain diameter of 10 to 100 mu m into a stainless steel reactor, then placing the stainless steel reactor into a tubular furnace, firstly purging the furnace body for 0.5h by adopting argon with the flow rate of 100mL/min, heating to 650 ℃ at the speed of 5 ℃/min under the protection of the argon, keeping the temperature for 5h, and then naturally cooling to the room temperature to obtain a crude product;
and fifthly, cleaning the crude product for 3 hours by respectively adopting hydrofluoric acid with the mass concentration of 5%, hydrochloric acid with the concentration of 6mol/L and hydrochloric acid with the concentration of 1mol/L, washing the crude product with deionized water until the washing liquid is neutral, then carrying out vacuum drying at 90 ℃, transferring the washed product into a muffle furnace, and then calcining the dried product for 2 hours at 550 ℃ to obtain the SiC aerogel.
In step one, R is1Si(OR2)3Wherein R is2＝CH3Or CH2CH3，R1Aromatic hydrocarbon or alkane with carbon number more than or equal to 6.
The preparation method of the high-temperature resistant SiC aerogel comprises the following steps:
firstly, weighing 10.3g of propyl triethoxysilane and 10.4g of ethyl orthosilicate, and magnetically stirring for 5min to obtain a mixed solution A;
weighing 40.8g of ethanol, 4.0g of deionized water and 0.25g of hexadecyl trimethyl ammonium bromide, and mixing to obtain a mixed solution B;
mixing the mixed solution A and the mixed solution B, dripping 1mL of hydrochloric acid with the concentration of 1mol/L, and magnetically stirring for 4 hours at the temperature of 50 ℃ to obtain hydrolysate;
fourthly, taking 25mL of hydrolysate, dripping 0.5mL of ammonia water with the concentration of 1mol/L into the hydrolysate, transferring the hydrolysate to a closed container, and placing the hydrolysate in a 50 ℃ oven for 0.5 to 10 hours to obtain wet gel;
fifthly, aging the wet gel for 24h at 50 ℃ by 25mL of methanol, exchanging for 2 times by 25mL of ethanol and exchanging for 3 times by 25mL of n-hexane, and drying in a gradient manner under normal pressure to obtain the phenyl hybridized SiO2An aerogel;
sixthly, 2.0g of phenyl hybridized SiO2Placing aerogel and 2.5g of magnesium powder with the particle size of 10-100 mu m in a stainless steel reactor, then placing the stainless steel reactor in a tubular furnace, firstly purging the furnace body for 0.5h by adopting argon with the flow rate of 100mL/min, then raising the temperature to 650 ℃ at the speed of 5 ℃/min under the protection of argon, keeping the temperature for 5h, and then naturally cooling to room temperature to obtain a crude product;
and seventhly, cleaning the crude product for 3 hours by respectively adopting hydrofluoric acid with the mass concentration of 5%, hydrochloric acid with the concentration of 6mol/L and hydrochloric acid with the concentration of 1mol/L, washing the crude product with deionized water until the washing liquid is neutral, and then drying the washed product in vacuum at 90 ℃ to obtain the SiC aerogel.
In the first stepThe R is1Si(OR2)3Wherein R is2＝CH3Or CH2CH3，R1Aromatic hydrocarbon or alkane with carbon number more than or equal to 6.
The invention has the following advantages:
1. starting from the source, raw material components are simplified, and organic silicon only containing C, Si and O elements is used as a single precursor. The general structural formula can be written as R1Si(OR2)3Wherein R is2＝CH3Or CH2CH3，R1The aromatic hydrocarbon or alkane with the carbon number being more than or equal to 6 comprises but not limited to one or more of phenyl, hexyl, heptyl and octyl.
2. Adopts a sol-gel method and is subjected to supercritical drying to prepare the organic silicon aerogel with uniform pore channel structure and complete shape, and the structural general formula can be written as R1SiO1.5Wherein R is1The aromatic hydrocarbon or alkane with the carbon number being more than or equal to 6 comprises but not limited to one or more of phenyl, hexyl, heptyl and octyl.
3. And reducing the aerogel precursor into SiC aerogel by adopting magnesiothermic reduction under the protection of inert gas. The method successfully avoids R1SiO1.5SiO gas is generated in the reduction process, and the shape and the integrity of the product are kept to the maximum extent.
Drawings
FIG. 1 is a schematic view of a magnesiothermic stainless steel reactor;
FIG. 2 is a schematic diagram of hydrolytic polymerization in experiment one;
FIG. 3 is a schematic diagram of hydrolytic polymerization in experiment two;
FIG. 4 is an XRD pattern of the SiC aerogel obtained in experiment one;
fig. 5 is an SEM image of the SiC aerogel obtained in experiment one;
fig. 6 is a BET image of the SiC aerogel obtained in experiment one;
fig. 7 is a pore size distribution diagram of the SiC aerogel obtained in experiment one;
fig. 8 is a thermogravimetric plot of the SiC aerogel obtained in experiment one.
Detailed Description
The technical solution of the present invention is not limited to the following specific embodiments, but includes any combination of the specific embodiments.
The first embodiment is as follows: the preparation method of the high-temperature resistant SiC aerogel provided by the embodiment comprises the following steps:
weighing 9.9g R1Si(OR2)37.6g of methyl orthosilicate, and magnetically stirring for 5min to obtain a mixed solution A;
weighing 46g of ethanol, 1.8g of deionized water and 0.25g of span-20, and mixing to obtain a mixed solution B;
thirdly, mixing the mixed solution A and the mixed solution B, and dripping 0.5mL of 1mol/L hydrochloric acid into the mixed solution to perform magnetic stirring for 2 hours at normal temperature to obtain hydrolysate;
fourthly, taking 25mL of hydrolysate, dripping 0.5mL of ammonia water with the concentration of 1mol/L into the hydrolysate, transferring the hydrolysate to a closed container, and placing the hydrolysate in a 50 ℃ oven for 0.5 to 10 hours to obtain wet gel;
fifthly, aging the wet gel for 24h at 50 ℃ by 25mL of methanol, exchanging for 2 times by 25mL of ethanol and exchanging for 3 times by 25mL of n-hexane, and drying in a gradient manner under normal pressure to obtain the phenyl hybridized SiO2An aerogel;
sixthly, 2.0g of phenyl hybridized SiO2Placing aerogel and 2.5g of magnesium powder with the particle size of 10-100 mu m in a stainless steel reactor, then placing the stainless steel reactor in a tubular furnace, firstly purging the furnace body for 0.5h by adopting argon with the flow rate of 100mL/min, raising the temperature to 650 ℃ at the speed of 5 ℃/min under the protection of argon, keeping the temperature for 5h, and then naturally cooling to room temperature to obtain a crude product;
and seventhly, cleaning the crude product for 3 hours by respectively adopting hydrofluoric acid with the mass concentration of 5%, hydrochloric acid with the concentration of 6mol/L and hydrochloric acid with the concentration of 1mol/L, washing the crude product with deionized water until the washing liquid is neutral, and then drying the washed product in vacuum at 90 ℃ to obtain the SiC aerogel.
The second embodiment is as follows: the difference between the first embodiment and the second embodiment is that R is described in the first embodiment1Si(OR2)3Wherein R is2＝CH3Or CH2CH3，R1Aromatic hydrocarbon or alkane with carbon number more than or equal to 6. The rest is the same as the first embodiment.
The third concrete implementation mode: this embodiment is different from the first or second embodiment in that R is the same as R in the first step1Si(OR2)3Is phenyl trimethoxy silane. The others are the same as in the first or second embodiment.
The fourth concrete implementation mode: the preparation method of the high-temperature resistant SiC aerogel provided by the embodiment comprises the following steps:
firstly, weighing 23g to 46g of ethanol, 0.9g to 1.8g of deionized water and 0.125g to 0.25g of span-20, mixing, magnetically stirring for 5min, and then dropwise adding 14.5g to 19.8g R1Si(OR2)30.5mL of hydrochloric acid with the concentration of 0.1mol/L, and stirring for 2 hours in an oil bath at the temperature of 50-80 ℃ to obtain hydrolysate;
secondly, taking 25mL of hydrolysate, dripping 0.5-1 mL of ammonia water with the concentration of 6-12 mol/L into the hydrolysate, transferring the hydrolysate into a closed container, and placing the container in a 50 ℃ oven for 0.5-10 h to obtain wet gel;
aging the wet gel with 25mL of methanol at 50 ℃ for 24h, exchanging with 25mL of ethanol for 2 times, exchanging with 25mL of n-hexane for 3 times, and then performing supercritical drying at 8MPa and 30 ℃ for 4h to obtain aerogel;
fourthly, placing 1.8g to 2.3g of aerogel and 2.3g to 2.8g of magnesium powder with the grain diameter of 10 to 100 mu m into a stainless steel reactor, then placing the stainless steel reactor into a tubular furnace, firstly purging the furnace body for 0.5h by adopting argon with the flow rate of 100mL/min, heating to 650 ℃ at the speed of 5 ℃/min under the protection of the argon, keeping the temperature for 5h, and then naturally cooling to the room temperature to obtain a crude product;
and fifthly, cleaning the crude product for 3 hours by respectively adopting hydrofluoric acid with the mass concentration of 5%, hydrochloric acid with the concentration of 6mol/L and hydrochloric acid with the concentration of 1mol/L, washing the crude product with deionized water until the washing liquid is neutral, then carrying out vacuum drying at 90 ℃, transferring the washed product into a muffle furnace, and then calcining the dried product for 2 hours at 550 ℃ to obtain the SiC aerogel.
The fifth concrete implementation mode: the fourth difference between this embodiment and the embodiment is that R is described in step one1Si(OR2)3Wherein R is2＝CH3Or CH2CH3，R1Aromatic hydrocarbon or alkane with carbon number more than or equal to 6. The rest is the same as the fourth embodiment.
The sixth specific implementation mode: the fourth or fifth difference between the present embodiment and the present embodiment is that R is described in step one1Si(OR2)3Is phenyl trimethoxy silane or dodecyl trimethoxy silane. The others are the same as the fourth or fifth embodiments.
The seventh embodiment: the preparation method of the high-temperature resistant SiC aerogel provided by the embodiment comprises the following steps:
firstly, weighing 10.3g of propyl triethoxysilane and 10.4g of ethyl orthosilicate, and magnetically stirring for 5min to obtain a mixed solution A;
weighing 40.8g of ethanol, 4.0g of deionized water and 0.25g of hexadecyl trimethyl ammonium bromide, and mixing to obtain a mixed solution B;
mixing the mixed solution A and the mixed solution B, dripping 1mL of hydrochloric acid with the concentration of 1mol/L, and magnetically stirring for 4 hours at the temperature of 50 ℃ to obtain hydrolysate;
fourthly, taking 25mL of hydrolysate, dripping 0.5mL of ammonia water with the concentration of 1mol/L into the hydrolysate, transferring the hydrolysate to a closed container, and placing the hydrolysate in a 50 ℃ oven for 0.5 to 10 hours to obtain wet gel;
fifthly, aging the wet gel for 24h at 50 ℃ by 25mL of methanol, exchanging for 2 times by 25mL of ethanol and exchanging for 3 times by 25mL of n-hexane, and drying in a gradient manner under normal pressure to obtain the phenyl hybridized SiO2An aerogel;
sixthly, 2.0g of phenyl hybridized SiO2Placing aerogel and 2.5g of magnesium powder with the particle size of 10-100 mu m in a stainless steel reactor, then placing the stainless steel reactor in a tubular furnace, firstly purging the furnace body for 0.5h by adopting argon with the flow rate of 100mL/min, then raising the temperature to 650 ℃ at the speed of 5 ℃/min under the protection of argon, keeping the temperature for 5h, and then naturally cooling to room temperature to obtain a crude product;
and seventhly, cleaning the crude product for 3 hours by respectively adopting hydrofluoric acid with the mass concentration of 5%, hydrochloric acid with the concentration of 6mol/L and hydrochloric acid with the concentration of 1mol/L, washing the crude product with deionized water until the washing liquid is neutral, and then drying the washed product in vacuum at 90 ℃ to obtain the SiC aerogel.
The specific implementation mode is eight: the seventh embodiment is different from the seventh embodiment in that R is described in the first step1Si(OR2)3Wherein R is2＝CH3Or CH2CH3，R1Aromatic hydrocarbon or alkane with carbon number more than or equal to 6. The rest is the same as the seventh embodiment.
The specific implementation method nine: the seventh embodiment is different from the seventh embodiment in that R is described in the first step1Si(OR2)3Is propyltriethoxysilane. The rest is the same as the seventh embodiment.
The following experiments are adopted to verify the effect of the invention:
experiment one:
the preparation method of the high-temperature resistant SiC aerogel comprises the following steps:
firstly, weighing 9.9g of phenyltrimethoxysilane and 7.6g of methyl orthosilicate, and magnetically stirring for 5min to obtain a mixed solution A;
secondly, 46g of ethanol, 1.8g of deionized water and 0.25g of span-20 are weighed and mixed to obtain mixed liquid B.
And thirdly, mixing the mixed solution A and the mixed solution B, and dripping 0.5mL of 1mol/L hydrochloric acid into the mixed solution A to magnetically stir the mixed solution at normal temperature for 2 hours to hydrolyze the methoxyl in the mixed solution A to obtain hydrolysate.
And fourthly, taking 25mL of hydrolysate, slowly dripping 0.5mL of ammonia water with the concentration of 1mol/L into the hydrolysate, transferring the hydrolysate into a closed glass container, and then placing the hydrolysate into an oven at 50 ℃ for 0.5h to realize the polymerization crosslinking of the hydrolysate (as shown in figure 2) to obtain the wet gel.
Fifthly, aging the wet gel for 24h by 25mL of methanol at 50 ℃, exchanging for 2 times by 25mL of ethanol, exchanging for 3 times by 25mL of n-hexane, and drying at normal pressure in a gradient manner to obtain the phenyl hybridized SiO2An aerogel.
Sixthly, placing 2.0g of aerogel and 2.5g of magnesium powder with the particle size of 10-100 mu m into a stainless steel reactor (the device diagram is shown in figure 1), then placing the stainless steel reactor into a tubular furnace, firstly purging the furnace body for 0.5h by adopting argon with the flow rate of 100mL/min, heating to 650 ℃ at the speed of 5 ℃/min under the protection of argon, keeping the temperature for 5h, and then naturally cooling to the room temperature to obtain a crude product.
And seventhly, cleaning the crude product for 3 hours by respectively adopting hydrofluoric acid with the mass concentration of 5%, hydrochloric acid with the concentration of 6mol/L and hydrochloric acid with the concentration of 1mol/L, washing the crude product with deionized water until the washing liquid is neutral, and then drying the washed product in vacuum at 90 ℃ to obtain the SiC aerogel.
The obtained SiC aerogel has the porosity of 80 percent and the specific surface area of 150m2(iv) g, density of 0.19g/cm3, and can withstand a high temperature of 800 ℃ in air without significant mass change.
Experiment two:
the preparation method of the high-temperature resistant SiC aerogel comprises the following steps:
firstly, 46g of ethanol, 1.8g of deionized water and 0.25g of span-20 are weighed and mixed, then the mixture is magnetically stirred for 5min, 19.8g of phenyltrimethoxysilane and 0.5mL of hydrochloric acid with the concentration of 0.1mol/L are dropwise added into the mixture, and the mixture is stirred for 2h in an oil bath at the temperature of 50 ℃, so that methoxyl in the phenyltrimethoxysilane is hydrolyzed to obtain hydrolysate.
And secondly, taking 25mL of hydrolysate, slowly dripping 0.5mL of ammonia water with the concentration of 6mol/L into the hydrolysate, transferring the hydrolysate into a closed glass container, and placing the hydrolysate in an oven at 50 ℃ for 1h to realize the polymerization crosslinking of the hydrolysate (as shown in figure 3) to obtain the wet gel.
And thirdly, aging the wet gel for 24 hours by 25mL of methanol at 50 ℃, exchanging for 2 times by 25mL of ethanol and exchanging for 3 times by 25mL of n-hexane, and then performing supercritical drying for 4 hours at the temperature of 30 ℃ under the pressure of 8MPa to obtain the phenyl polysilsesquioxane (PhSQ) aerogel.
Fourthly, placing 2.3g of aerogel and 2.8g of magnesium powder with the particle size of 10-100 mu m into a stainless steel reactor, then placing the stainless steel reactor into a tubular furnace, firstly purging the furnace body for 0.5h by adopting argon with the flow rate of 100mL/min, heating to 650 ℃ at the speed of 5 ℃/min under the protection of argon, keeping the temperature for 5h, and then naturally cooling to room temperature to obtain a crude product.
And fifthly, washing the crude product for 3 hours by using hydrofluoric acid with the mass concentration of 5%, hydrochloric acid with the concentration of 6mol/L and hydrochloric acid with the concentration of 1mol/L respectively, removing unreacted magnesium, magnesium oxide and magnesium silicide byproducts, finally washing the C/SiC crude product by using deionized water until the washing liquid is neutral, and carrying out vacuum drying at 90 ℃ to obtain the C/SiC aerogel. And transferring the C/SiC aerogel into a muffle furnace, and calcining for 2 hours at 550 ℃ in the air to obtain the SiC aerogel.
The porosity of the obtained SiC aerogel is 85 percent, and the specific surface area is 280m2G, density 0.18g/cm3Can endure the high temperature of 800 ℃ in the airWithout significant quality variation.
Experiment three:
the preparation method of the high-temperature resistant SiC aerogel comprises the following steps:
firstly, weighing 23g of ethanol, 0.9g of deionized water and 0.125g of span-20, mixing, magnetically stirring for 5min, and then dropwise adding 14.5g of dodecyl trimethoxy silane and 0.5mL of 5mol/L hydrochloric acid under the condition of an oil bath at 80 ℃ for stirring for 2h to hydrolyze methoxy in dodecyl trimethoxy silane, thereby obtaining a hydrolysate.
And secondly, taking 25mL of hydrolysate, slowly dripping 1mL of ammonia water with the concentration of 12mol/L into the hydrolysate, transferring the hydrolysate to a closed glass container, and placing the hydrolysate in a 50 ℃ oven for 9 hours to realize the polymerization crosslinking of the hydrolysate to obtain the wet gel.
And thirdly, aging the wet gel for 24 hours by 25mL of methanol at 50 ℃, exchanging for 2 times by 25mL of ethanol and exchanging for 3 times by 25mL of n-hexane, and then performing supercritical drying for 4 hours at the temperature of 30 ℃ under the pressure of 8MPa to obtain the dodecyl polysilsesquioxane (DSQ) aerogel.
Fourthly, placing 1.8g of aerogel and 2.3g of magnesium powder with the particle size of 10-100 mu m into a stainless steel reactor, then placing the stainless steel reactor into a tubular furnace, firstly purging the furnace body for 0.5h by adopting argon with the flow rate of 100mL/min, heating to 650 ℃ at the speed of 5 ℃/min under the protection of argon, keeping the temperature for 5h, and then naturally cooling to room temperature to obtain a crude product.
Fifthly, cleaning the crude product for 3 hours by respectively adopting hydrofluoric acid with the mass concentration of 5%, hydrochloric acid with the concentration of 6mol/L and hydrochloric acid with the concentration of 1mol/L, and removing unreacted magnesium, magnesium oxide and magnesium silicide byproducts. And finally, washing the C/SiC crude product with deionized water until the washing liquid is neutral, and carrying out vacuum drying at 90 ℃ to obtain the C/SiC aerogel. And transferring the C/SiC aerogel into a muffle furnace, and calcining for 2 hours at 550 ℃ in the air to obtain the SiC aerogel.
The obtained SiC aerogel has a porosity of 80% and a specific surface area of 100m2G, density 0.25g/cm3Can endure high temperature of 800 ℃ in air without obvious quality change.
Experiment four:
the preparation method of the high-temperature resistant SiC aerogel comprises the following steps:
firstly, weighing 10.3g of propyl triethoxysilane and 10.4g of ethyl orthosilicate, and magnetically stirring for 5min to obtain a mixed solution A;
weighing 40.8g of ethanol, 4.0g of deionized water and 0.25g of hexadecyl trimethyl ammonium bromide, and mixing to obtain a mixed solution B.
And thirdly, mixing the mixed solution A and the mixed solution B, dripping 1mL of hydrochloric acid with the concentration of 1mol/L, and then magnetically stirring for 4 hours at the temperature of 50 ℃ to hydrolyze the ethoxy in the mixed solution A to obtain a hydrolysate.
And fourthly, taking 25mL of hydrolysate, slowly dripping 0.5mL of ammonia water with the concentration of 1mol/L into the hydrolysate, transferring the hydrolysate into a closed glass container, and putting the hydrolysate into an oven at 50 ℃ for 8 hours to realize polymerization crosslinking of the hydrolysate (as shown in figure 2) to obtain the wet gel.
Fifthly, aging the wet gel for 24h at 50 ℃ by 25mL of methanol, exchanging for 2 times by 25mL of ethanol and exchanging for 3 times by 25mL of n-hexane, and drying in a gradient manner under normal pressure to obtain the phenyl hybridized SiO2An aerogel.
Sixthly, placing 2.0g of aerogel and 2.5g of magnesium powder with the particle size of 10-100 mu m into a stainless steel reactor (the device diagram is shown in figure 1), then placing the stainless steel reactor into a tubular furnace, firstly purging the furnace body for 0.5h by adopting argon with the flow rate of 100mL/min, then heating to 650 ℃ at the speed of 5 ℃/min under the protection of argon, keeping the temperature for 5h, and then naturally cooling to room temperature to obtain a crude product.
And seventhly, cleaning the crude product for 3 hours by respectively adopting hydrofluoric acid with the mass concentration of 5%, hydrochloric acid with the concentration of 6mol/L and hydrochloric acid with the concentration of 1mol/L, and removing unreacted magnesium, magnesium oxide and magnesium silicide byproducts. And finally, washing the SiC crude product with deionized water until the washing liquid is neutral, and carrying out vacuum drying at 90 ℃ to obtain the SiC aerogel.
The obtained SiC aerogel has the porosity of 82 percent and the specific surface area of 300m2G, density 0.16g/cm3Can endure high temperature of 800 ℃ in air without obvious quality change.
Claims (7)
1. The preparation method of the high-temperature resistant SiC aerogel is characterized by comprising the following steps:
weighing9.9 g R1Si(OR2)37.6g of methyl orthosilicate, and magnetically stirring for 5min to obtain a mixed solution A;
weighing 46g of ethanol, 1.8g of deionized water and 0.25g of span-20, and mixing to obtain a mixed solution B;
thirdly, mixing the mixed solution A and the mixed solution B, and dripping 0.5mL of 1mol/L hydrochloric acid into the mixed solution to perform magnetic stirring for 2 hours at normal temperature to obtain hydrolysate;
fourthly, taking 25mL of hydrolysate, dripping 0.5mL of ammonia water with the concentration of 1mol/L into the hydrolysate, transferring the hydrolysate to a closed container, and placing the hydrolysate in a 50 ℃ oven for 0.5 to 10 hours to obtain wet gel;
fifthly, aging the wet gel for 24h at 50 ℃ by 25mL of methanol, exchanging for 2 times by 25mL of ethanol and exchanging for 3 times by 25mL of n-hexane, and drying in a gradient manner under normal pressure to obtain the phenyl hybridized SiO2An aerogel;
sixthly, 2.0g of phenyl hybridized SiO2Placing aerogel and 2.5g of magnesium powder with the particle size of 10-100 mu m in a stainless steel reactor, then placing the stainless steel reactor in a tubular furnace, firstly purging the furnace body for 0.5h by adopting argon with the flow rate of 100mL/min, raising the temperature to 650 ℃ at the speed of 5 ℃/min under the protection of argon, keeping the temperature for 5h, and then naturally cooling to room temperature to obtain a crude product;
and seventhly, cleaning the crude product for 3 hours by respectively adopting hydrofluoric acid with the mass concentration of 5%, hydrochloric acid with the concentration of 6mol/L and hydrochloric acid with the concentration of 1mol/L, washing the crude product with deionized water until the washing liquid is neutral, and then drying the washed product in vacuum at 90 ℃ to obtain the SiC aerogel.
2. The method for preparing the high-temperature resistant SiC aerogel according to claim 1, wherein R in the step one is1Si(OR2)3Wherein R is2=CH3Or CH2CH3，R1An aromatic hydrocarbon or an alkane having not less than 6 carbon atoms.
3. The method for preparing the high-temperature resistant SiC aerogel according to claim 1, wherein R in the step one is1Si(OR2)3Is phenyl trimethoxy silane.
4. The preparation method of the high-temperature resistant SiC aerogel is characterized by comprising the following steps:
firstly, weighing 23g to 46g of ethanol, 0.9g to 1.8g of deionized water and 0.125g to 0.25g of span-20, mixing, magnetically stirring for 5min, and then dropwise adding 14.5g to 19.8g R1Si(OR2)30.5mL of hydrochloric acid with the concentration of 0.1mol/L, and stirring for 2 hours in an oil bath at the temperature of 50-80 ℃ to obtain hydrolysate;
secondly, taking 25mL of hydrolysate, dripping 0.5-1 mL of ammonia water with the concentration of 6-12 mol/L into the hydrolysate, transferring the hydrolysate into a closed container, and placing the container in a 50 ℃ oven for 0.5-10 h to obtain wet gel;
aging the wet gel with 25mL of methanol at 50 ℃ for 24h, exchanging with 25mL of ethanol for 2 times, exchanging with 25mL of n-hexane for 3 times, and then performing supercritical drying at 8MPa and 30 ℃ for 4h to obtain aerogel;
fourthly, placing 1.8g to 2.3g of aerogel and 2.3g to 2.8g of magnesium powder with the grain diameter of 10 to 100 mu m into a stainless steel reactor, then placing the stainless steel reactor into a tubular furnace, firstly purging the furnace body for 0.5h by adopting argon with the flow rate of 100mL/min, heating to 650 ℃ at the speed of 5 ℃/min under the protection of the argon, keeping the temperature for 5h, and then naturally cooling to the room temperature to obtain a crude product;
and fifthly, cleaning the crude product for 3 hours by respectively adopting hydrofluoric acid with the mass concentration of 5%, hydrochloric acid with the concentration of 6mol/L and hydrochloric acid with the concentration of 1mol/L, washing the crude product with deionized water until the washing liquid is neutral, then carrying out vacuum drying at 90 ℃, transferring the washed product into a muffle furnace, and then calcining the dried product for 2 hours at 550 ℃ to obtain the SiC aerogel.
5. The method for preparing the high-temperature SiC aerogel according to claim 4, wherein R is the same as R in the first step1Si(OR2)3Wherein R is2=CH3Or CH2CH3，R1An aromatic hydrocarbon or an alkane having not less than 6 carbon atoms.
6. The method for preparing the high-temperature SiC aerogel according to claim 4, wherein R is the same as R in the first step1Si(OR2)3Is phenyl trimethoxy silane or dodecyl trimethoxy silane.
7. The preparation method of the high-temperature resistant SiC aerogel is characterized by comprising the following steps:
firstly, weighing 10.3g of propyl triethoxysilane and 10.4g of ethyl orthosilicate, and magnetically stirring for 5min to obtain a mixed solution A;
weighing 40.8g of ethanol, 4.0g of deionized water and 0.25g of hexadecyl trimethyl ammonium bromide, and mixing to obtain a mixed solution B;
mixing the mixed solution A and the mixed solution B, dripping 1mL of hydrochloric acid with the concentration of 1mol/L, and magnetically stirring for 4 hours at the temperature of 50 ℃ to obtain hydrolysate;
fourthly, taking 25mL of hydrolysate, dripping 0.5mL of ammonia water with the concentration of 1mol/L into the hydrolysate, transferring the hydrolysate to a closed container, and placing the hydrolysate in a 50 ℃ oven for 0.5 to 10 hours to obtain wet gel;
fifthly, aging the wet gel for 24h at 50 ℃ by 25mL of methanol, exchanging for 2 times by 25mL of ethanol and exchanging for 3 times by 25mL of n-hexane, and drying in a gradient manner under normal pressure to obtain the phenyl hybridized SiO2An aerogel;
sixthly, 2.0g of phenyl hybridized SiO2Placing aerogel and 2.5g of magnesium powder with the particle size of 10-100 mu m in a stainless steel reactor, then placing the stainless steel reactor in a tubular furnace, firstly purging the furnace body for 0.5h by adopting argon with the flow rate of 100mL/min, then raising the temperature to 650 ℃ at the speed of 5 ℃/min under the protection of argon, keeping the temperature for 5h, and then naturally cooling to room temperature to obtain a crude product;
and seventhly, cleaning the crude product for 3 hours by respectively adopting hydrofluoric acid with the mass concentration of 5%, hydrochloric acid with the concentration of 6mol/L and hydrochloric acid with the concentration of 1mol/L, washing the crude product with deionized water until the washing liquid is neutral, and then drying the washed product in vacuum at 90 ℃ to obtain the SiC aerogel.
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