CN115724436A - Preparation method of hydrophobic silica gradient aerogel with adjustable structure - Google Patents
Preparation method of hydrophobic silica gradient aerogel with adjustable structure Download PDFInfo
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- CN115724436A CN115724436A CN202211631132.5A CN202211631132A CN115724436A CN 115724436 A CN115724436 A CN 115724436A CN 202211631132 A CN202211631132 A CN 202211631132A CN 115724436 A CN115724436 A CN 115724436A
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- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 title claims abstract description 108
- 239000004964 aerogel Substances 0.000 title claims abstract description 66
- 239000000377 silicon dioxide Substances 0.000 title claims abstract description 48
- 230000002209 hydrophobic effect Effects 0.000 title claims abstract description 31
- 238000002360 preparation method Methods 0.000 title claims abstract description 13
- 238000000034 method Methods 0.000 claims abstract description 24
- 239000000725 suspension Substances 0.000 claims abstract description 22
- 238000001035 drying Methods 0.000 claims abstract description 17
- 239000003054 catalyst Substances 0.000 claims abstract description 14
- 239000000499 gel Substances 0.000 claims abstract description 14
- 239000002105 nanoparticle Substances 0.000 claims abstract description 14
- 239000011240 wet gel Substances 0.000 claims abstract description 14
- 229910044991 metal oxide Inorganic materials 0.000 claims abstract description 13
- 150000004706 metal oxides Chemical class 0.000 claims abstract description 13
- 238000010438 heat treatment Methods 0.000 claims abstract description 11
- 239000002245 particle Substances 0.000 claims abstract description 7
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims abstract 4
- 239000001569 carbon dioxide Substances 0.000 claims abstract 2
- 229910002092 carbon dioxide Inorganic materials 0.000 claims abstract 2
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 claims description 24
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 12
- NKSJNEHGWDZZQF-UHFFFAOYSA-N ethenyl(trimethoxy)silane Chemical compound CO[Si](OC)(OC)C=C NKSJNEHGWDZZQF-UHFFFAOYSA-N 0.000 claims description 11
- 238000002210 supercritical carbon dioxide drying Methods 0.000 claims description 11
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 10
- 230000004048 modification Effects 0.000 claims description 10
- 238000012986 modification Methods 0.000 claims description 10
- 239000002904 solvent Substances 0.000 claims description 10
- 239000008367 deionised water Substances 0.000 claims description 7
- 229910021641 deionized water Inorganic materials 0.000 claims description 7
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 7
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 claims description 6
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 6
- 230000007062 hydrolysis Effects 0.000 claims description 6
- 238000006460 hydrolysis reaction Methods 0.000 claims description 6
- 239000003607 modifier Substances 0.000 claims description 6
- 229910052710 silicon Inorganic materials 0.000 claims description 6
- 239000010703 silicon Substances 0.000 claims description 6
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 claims description 5
- 235000011114 ammonium hydroxide Nutrition 0.000 claims description 5
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 4
- LFQCEHFDDXELDD-UHFFFAOYSA-N tetramethyl orthosilicate Chemical compound CO[Si](OC)(OC)OC LFQCEHFDDXELDD-UHFFFAOYSA-N 0.000 claims description 4
- WGTYBPLFGIVFAS-UHFFFAOYSA-M tetramethylammonium hydroxide Chemical compound [OH-].C[N+](C)(C)C WGTYBPLFGIVFAS-UHFFFAOYSA-M 0.000 claims description 4
- BOTDANWDWHJENH-UHFFFAOYSA-N Tetraethyl orthosilicate Chemical compound CCO[Si](OCC)(OCC)OCC BOTDANWDWHJENH-UHFFFAOYSA-N 0.000 claims description 3
- 238000007796 conventional method Methods 0.000 claims description 3
- 229910018072 Al 2 O 3 Inorganic materials 0.000 claims description 2
- YYLGKUPAFFKGRQ-UHFFFAOYSA-N dimethyldiethoxysilane Chemical compound CCO[Si](C)(C)OCC YYLGKUPAFFKGRQ-UHFFFAOYSA-N 0.000 claims description 2
- RSIHJDGMBDPTIM-UHFFFAOYSA-N ethoxy(trimethyl)silane Chemical compound CCO[Si](C)(C)C RSIHJDGMBDPTIM-UHFFFAOYSA-N 0.000 claims description 2
- 125000002496 methyl group Chemical group [H]C([H])([H])* 0.000 claims description 2
- WVDDGKGOMKODPV-ZQBYOMGUSA-N phenyl(114C)methanol Chemical compound O[14CH2]C1=CC=CC=C1 WVDDGKGOMKODPV-ZQBYOMGUSA-N 0.000 claims description 2
- 239000007788 liquid Substances 0.000 claims 1
- 235000012239 silicon dioxide Nutrition 0.000 abstract description 4
- RMAQACBXLXPBSY-UHFFFAOYSA-N silicic acid Chemical compound O[Si](O)(O)O RMAQACBXLXPBSY-UHFFFAOYSA-N 0.000 abstract description 2
- 239000011521 glass Substances 0.000 description 14
- 239000000463 material Substances 0.000 description 8
- 239000004965 Silica aerogel Substances 0.000 description 5
- 238000009413 insulation Methods 0.000 description 4
- 230000008859 change Effects 0.000 description 3
- 238000007865 diluting Methods 0.000 description 3
- 238000002156 mixing Methods 0.000 description 3
- 230000008569 process Effects 0.000 description 3
- 238000003756 stirring Methods 0.000 description 3
- 238000002834 transmittance Methods 0.000 description 3
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 239000002131 composite material Substances 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 description 2
- 229910010271 silicon carbide Inorganic materials 0.000 description 2
- 238000003786 synthesis reaction Methods 0.000 description 2
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000006555 catalytic reaction Methods 0.000 description 1
- 238000007334 copolymerization reaction Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 238000004146 energy storage Methods 0.000 description 1
- 238000009776 industrial production Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000005543 nano-size silicon particle Substances 0.000 description 1
- ISWSIDIOOBJBQZ-UHFFFAOYSA-N phenol group Chemical group C1(=CC=CC=C1)O ISWSIDIOOBJBQZ-UHFFFAOYSA-N 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 230000003014 reinforcing effect Effects 0.000 description 1
- 238000001878 scanning electron micrograph Methods 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 230000035939 shock Effects 0.000 description 1
- 238000003980 solgel method Methods 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 238000005303 weighing Methods 0.000 description 1
Images
Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/50—Improvements relating to the production of bulk chemicals
- Y02P20/54—Improvements relating to the production of bulk chemicals using solvents, e.g. supercritical solvents or ionic liquids
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- Silicon Compounds (AREA)
Abstract
The invention discloses a preparation method of a hydrophobic silica gradient aerogel with an adjustable structure, which comprises the following steps: (1) preparing a silica wet gel; (2) Adding metal oxide nano particles into the silicon dioxide wet gel, and uniformly dispersing the metal oxide nano particles in a silicon dioxide wet gel solution to form a suspension by using ultrasonic vibration and heating; (3) Placing the suspension in a centrifuge, and adding a gel catalyst to carry out centrifugal layering gel; (4) And (4) modifying the aerogel obtained in the step (3), and drying by using supercritical carbon dioxide. According to the invention, nano metal oxide particles are uniformly dispersed in silica sol by using ultrasonic waves to form a suspension, the state of the suspension is changed again by a centrifugal-gel method to obtain the hydrophobic silica gradient aerogel, the density, the temperature resistance range and the transparency of different areas of the gradient aerogel show gradient changes, and the use requirements of the aerogel in different environments can be met.
Description
Technical Field
The invention belongs to the technical field of composite materials, and particularly relates to a preparation method of a hydrophobic silica gradient aerogel with an adjustable structure.
Background
The nano silicon dioxide aerogel is a porous material with high porosity, high specific surface area, low thermal conductivity and low density, has excellent functions of heat insulation and sound insulation, adsorption, catalysis, energy storage and the like, has wide application prospect in the fields of light, electricity, heat, sound and the like, and arouses the interest of wide researchers. However, silica aerogel use temperatures in excess of 700 ℃ can lead to "thermal failure" problems, limiting the practical range of silica aerogel applications. In recent years, although research on high-temperature resistant aerogel materials such as alumina, zirconia, and silicon carbide has achieved certain effects, certain unilateral properties (such as thermal conductivity and specific surface area) of the high-temperature resistant aerogel materials are lower than those of silica aerogel, and the application of the high-temperature resistant aerogel materials in special fields is limited.
The physical properties of aerogel materials have a correlation with their corresponding densities. Therefore, the preparation of the silica aerogel into the composite aerogel material with a controllable structure and a gradient change in a certain direction has wider application fields. The preparation method of the gradient aerogel comprises the following steps: temperature gradient synthesis, high-speed centrifugal synthesis, a layered adhesion method, a layer-by-layer gel method and a gradient sol-gel method. For example, gradient phenolic aerogel is prepared by controlling the dropping speed of the catalyst, and density gradient silica aerogel is prepared by a density gradient forming device and a sol copolymerization method, and the gradient aerogels are used in the fields of researching the state of low temperature and high pressure of plasma, shock wave delay and the like. Therefore, the research on the excellent heat insulation performance of the gradient aerogel material in extreme environments is one of the development directions of multifunctional gradient aerogels, and has important significance for the development of new materials in China and the fields of aerospace, military use and civil use.
Disclosure of Invention
In order to solve the problems, the invention aims to provide a preparation method of a hydrophobic silica gradient aerogel with a tunable structure.
A preparation method of a hydrophobic silica gradient aerogel with an adjustable structure comprises the following steps:
(1) And preparing the silicon dioxide wet gel from a silicon source, a solvent, a hydrolysis catalyst and deionized water by a conventional method.
(2) Adding metal oxide nanoparticles as a high-temperature-resistant reinforcing phase into silica wet gel, and uniformly dispersing the metal oxide nanoparticles in a silica wet gel solution to form a suspension by using ultrasonic vibration and heating, wherein the volume ratio of a silicon source, a solvent, deionized water, a hydrolysis catalyst to the metal oxide nanoparticles is 1: (7-12): (0.05-0.1): (0.01-0.025): (0.06-0.24); the silicon source comprises one or two of methyl orthosilicate, ethyl orthosilicate and methyl polysilicate; the solvent comprises one of benzyl alcohol, methanol and ethanol; the hydrolysis catalyst comprises one of hydrochloric acid and sulfuric acid; the metal oxide nano particles are Al 2 O 3 、ZrO 2 One or two of SiC with the particle size of 50nm-500nm; the ultrasonic vibration frequency is 35KHz-60KHz, the heating temperature is 40 ℃ to 70 ℃, and the ultrasonic vibration time is 24h-72h.
(3) Placing the suspension in the step (2) into a watch glass which is cylindrical, the diameter of the bottom of the watch glass is 2.5cm-10cm, the height of the watch glass is 5cm-20cm, the top of the watch glass is a sealing cover, the cover is covered after the gel catalyst is added, and then placing the watch glass into a centrifuge for centrifugal layering of gel, wherein the volume ratio of the suspension to the gel catalyst is 1: (0.01-0.06), the gel catalyst comprises one of tetramethylammonium hydroxide, ammonia water and potassium hydroxide; the rotating speed of the centrifuge is 30r/min-500r/min, the centrifugal inclination angle is 0.5-15 degrees,
(4) Adding a hydrophobic modifier diluted by a solvent into the aerogel obtained in the step (3) for modification, wherein the volume ratio of the solvent to the hydrophobic modifier is 1: (0.05-0.2), the hydrophobic modifier comprises one of vinyltrimethoxysilane, trimethylethoxysilane and dimethyldiethoxysilane, the modification time is 8-48 h, and the modification temperature is 50-80 ℃; and (3) putting the modified silica gradient aerogel into a supercritical carbon dioxide drying kettle for supercritical carbon dioxide drying to obtain the hydrophobic silica gradient aerogel with a controllable structure, wherein the pressure in the drying kettle is 12-15 MPa, the drying temperature is 50-60 ℃, and the drying time is 2-7 h.
Compared with the prior art, the preparation method of the hydrophobic silica gradient aerogel with the adjustable structure has the beneficial effects that: 1. according to the invention, nano metal oxide particles are uniformly dispersed in silica sol by using ultrasonic waves to form a suspension, the state of the suspension is changed again by a centrifugation-gel method by means of the density difference of the suspension and the control of the centrifugal rotating speed and the centrifugal inclination angle to obtain the hydrophobic silica gradient aerogel, the density, the temperature resistance range and the transparency of different areas of the gradient aerogel present gradient changes, and meanwhile, the normal-temperature heat conductivity coefficient of the silica gradient aerogel material shows gradient increase along with the change of the centrifugal inclination angle, so that the use requirements of the aerogel under different environments can be met; 2. the aerogel prepared by the invention has the transparency and the heat insulation property of the aerogel, also has the high temperature resistance of the metal oxide nanoparticle aerogel, meets the use requirements of the same aerogel in different special environments, has simple preparation process and high production efficiency, and is convenient for industrial production.
Drawings
The present invention will be described in further detail with reference to the accompanying drawings.
FIG. 1 is a flow diagram of the centrifuge-gel process of the present invention;
FIG. 2 is an SEM image of the microstructure of the silica gradient aerogel prepared in example 1 of the present invention;
FIG. 3 is a graph of a silica gradient aerogel sample prepared in example 2 of the present invention;
FIG. 4 is a graph showing the transparency of a silica gradient aerogel sample prepared in example 3 of the present invention;
FIG. 5 is a graph of thermal conductivity (K) and centrifugal inclination angle (θ) of silica gradient aerogels prepared in examples 1-3 of the present invention at different temperatures;
FIG. 6 is a graph of the variation of thermal conductivity (Δ K) and the gradient off-center tilt angle (Δ θ) of the silica gradient aerogels prepared in examples 1 to 3 of the present invention at different temperatures.
Detailed Description
The following description of the embodiments of the present invention is provided for illustrative purposes, and other advantages and effects of the present invention will become apparent to those skilled in the art from the present disclosure.
It should be understood that the structures, proportions, and dimensions shown in the drawings and described in the specification are for illustrative purposes only and are not intended to limit the scope of the present invention, which is defined by the claims. In addition, the terms such as "upper", "lower", "left" and "right" used in the present specification are for convenience of description only, and are not intended to limit the scope of the present invention, and changes or modifications of the relative relationship thereof may be made without substantial changes in the technical content.
In the description of the present invention, it is to be noted that, unless otherwise explicitly specified or limited, the terms "connected" and "connected" are to be interpreted broadly, e.g., as being fixed or detachable or integrally connected; can be mechanically or electrically connected; may be directly connected or indirectly connected through an intermediate. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
It should be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
Example 1
As shown in fig. 1, a method for preparing a hydrophobic silica gradient aerogel with a tunable structure comprises the following steps:
(1) The silica wet gel is prepared by mixing ethyl orthosilicate, ethanol, deionized water and hydrochloric acid according to the volume ratio of 1.
(2) 0.15g of ZrO was weighed 2 Adding the nano particles into the silica wet gel, using ultrasonic vibration and heating to dissolve and disperse the star-shaped particles into suspension, wherein the ultrasonic vibration frequency is 60KHz, the heating temperature is 55 ℃, and the ultrasonic vibration time is 48h.
(3) Measuring 50mL of suspension, placing the suspension in a self-made watch glass, setting the rotating speed of a centrifuge to be 120r/min and the centrifugal inclination angle to be 8 degrees, adding 1mL of ammonia water, uniformly stirring, fastening a watch glass cover, placing the watch glass cover in the centrifuge, centrifuging, layering and gelling, and finishing gelling after 13 min.
(4) Diluting 3mL of vinyl trimethoxy silane with ethanol, and adding the diluted vinyl trimethoxy silane into the aerogel obtained in the step (3) for modification, wherein the volume ratio of ethanol to vinyl trimethoxy silane is 1; and (3) putting the modified silica gradient aerogel into a supercritical carbon dioxide drying kettle for supercritical carbon dioxide drying to obtain the hydrophobic silica gradient aerogel with a controllable structure, wherein the pressure in the drying kettle is 14.5MPa, the drying temperature is 55 ℃, and the drying time is 5h.
The microstructure of the silica gradient aerogel prepared in this example is shown in fig. 2. The tested thermal conductivity coefficient is 0.023W/(m.K) at 25 ℃, 0.028W/(m.K) at 500 ℃, 0.036W/(m.K) at 1000 ℃, the visible light transmittance range is 7-60 percent, and the density range is 0.18g/cm 3 -0.29 g/cm 3 。
Example 2
As shown in fig. 1, a method for preparing a hydrophobic silica gradient aerogel with a tunable structure comprises the following steps:
(1) Using a conventional preparation method, mixing methyl orthosilicate, methanol, deionized water and hydrochloric acid according to a volume ratio of 1.
(2) 0.1g of Al is weighed 2 O 3 Adding the nano particles into the silica wet gel, and using ultrasonic vibration and heating to dissolve and disperse the star-shaped particles into suspension, wherein the ultrasonic vibration frequency is 50KHz, the heating temperature is 45 ℃, and the ultrasonic vibration time is 48h.
(3) Measuring 50mL of suspension, placing the suspension in a self-made watch glass, setting the rotating speed of a centrifuge to be 180r/min and the centrifugal inclination angle to be 5 degrees, adding 1.5mL of ammonia water, uniformly stirring, fastening a watch glass cover, placing the watch glass into the centrifuge, centrifuging, layering and gelling, and finishing gelling after 9 min.
(4) Diluting 5mL of vinyl trimethoxy silane with methanol, and adding the diluted vinyl trimethoxy silane into the aerogel obtained in the step (3) for modification, wherein the volume ratio of the methanol to the vinyl trimethoxy silane is 1; and (3) putting the modified silica gradient aerogel into a supercritical carbon dioxide drying kettle for supercritical carbon dioxide drying to obtain the hydrophobic silica gradient aerogel with a controllable structure, wherein the pressure in the drying kettle is 14.5MPa, the drying temperature is 55 ℃, and the drying time is 5h.
The silica gradient aerogel sample prepared in this example is shown in fig. 3. The tested thermal conductivity coefficient is 0.021W/(m.K) at 25 ℃, 0.031W/(m.K) at 500 ℃, 0.045W/(m.K) at 1000 ℃, the visible light transmittance range is 9-65%, and the density range is 0.16g/cm 3 -0.25 g/cm 3 。
Example 3
As shown in fig. 1, a method for preparing a hydrophobic silica gradient aerogel with a tunable structure comprises the following steps:
(1) Using a conventional preparation method, mixing methyl orthosilicate, methanol, deionized water and hydrochloric acid according to a volume ratio of 1.
(2) 0.1g of Al is weighed 2 O 3 、0.1g ZrO 2 Adding the nano particles into the silica wet gel, using ultrasonic vibration and heating to dissolve and disperse the star-shaped particles into suspension, wherein the ultrasonic vibration frequency is 60KHz, the heating temperature is 45 ℃, and the ultrasonic vibration time is 48h.
(3) Weighing 50mL of suspension, placing the suspension in a self-made watch glass, setting the rotating speed of a centrifuge to be 120r/min and the centrifugal inclination angle to be 3 degrees, adding 1.5mL of ammonia water, uniformly stirring, fastening a watch glass cover, placing the watch glass into the centrifuge, centrifuging, layering and gelling, and finishing gelling after 10 min.
(4) Diluting 8mL of vinyl trimethoxy silane with methanol, adding the diluted vinyl trimethoxy silane into the aerogel obtained in the step (3) for modification, wherein the volume ratio of the methanol to the vinyl trimethoxy silane is 1; and (3) putting the modified silica gradient aerogel into a supercritical carbon dioxide drying kettle for supercritical carbon dioxide drying to obtain the hydrophobic silica gradient aerogel with a controllable structure, wherein the pressure in the drying kettle is 14.5MPa, the drying temperature is 55 ℃, and the drying time is 5h.
The transparency of the silica gradient aerogel sample prepared in this example is shown in fig. 4. The tested thermal conductivity coefficient is 0.019W/(m.K) at 25 ℃, 0.027W/(m.K) at 500 ℃, 0.036W/(m.K) at 1000 ℃, the visible light transmittance range is 4-54%, and the density range is 0.2g/cm 3 -0.27 g/cm 3 。
As shown in fig. 5 and 6, the gradient aerogel prepared by the method has a gradient mode of temperature resistance change in density and gap distribution, and the overall low-temperature thermal conductivity coefficient and the centrifugal inclination angle are in positive correlation and the high-temperature thermal conductivity coefficient and the centrifugal inclination angle are in negative correlation.
Other parts of the invention not described in detail are conventional techniques known to the person skilled in the art.
The scope of the present invention is not limited to the technical solutions disclosed in the embodiments, and any modifications, equivalent substitutions, improvements, etc. made to the above embodiments according to the technical spirit of the present invention fall within the scope of the present invention.
Claims (9)
1. A preparation method of hydrophobic silica gradient aerogel with an adjustable structure is characterized by comprising the following steps: the method comprises the following steps:
(1) Preparing a silica wet gel;
(2) Adding metal oxide nano particles into the silica wet gel, and uniformly dispersing the metal oxide nano particles into the silica wet gel solution to form a suspension by using ultrasonic vibration and heating;
(3) Placing the suspension liquid in the step (2) in a centrifuge, and adding a gel catalyst to carry out centrifugal layering gel;
(4) And (4) modifying the aerogel obtained in the step (3), and drying by using supercritical carbon dioxide.
2. The method for preparing the hydrophobic silica gradient aerogel with tunable structure according to claim 1, wherein: the silica wet gel is prepared from a silicon source, a solvent, a hydrolysis catalyst and deionized water by adopting a conventional method.
3. The method for preparing the hydrophobic silica gradient aerogel with adjustable structure according to claim 2, wherein: the volume ratio of the silicon source, the solvent, the deionized water, the hydrolysis catalyst and the metal oxide nanoparticles is 1: (7-12): (0.05-0.1): (0.01-0.025): (0.06-0.24), wherein the volume ratio of the suspension to the gel catalyst is 1: (0.01-0.06).
4. The method for preparing the hydrophobic silica gradient aerogel with tunable structure as claimed in claim 2 or 3, characterized in that: the silicon source comprises one or two of methyl orthosilicate, ethyl orthosilicate and methyl polysilicate; the solvent comprises one of benzyl alcohol, methanol and ethanol; the hydrolysis catalyst comprises one of hydrochloric acid and sulfuric acid; the gel catalyst comprises one of tetramethylammonium hydroxide, ammonia water and potassium hydroxide.
5. The method for preparing the hydrophobic silica gradient aerogel with tunable structure according to claim 4, wherein: the metal oxide nano particles are Al 2 O 3 、ZrO 2 One or two of SiC with a particle size of 50nm-500nm。
6. The method for preparing the hydrophobic silica gradient aerogel with adjustable structure according to claim 5, wherein the method comprises the following steps: in the step (2), the ultrasonic vibration frequency is 35KHz-60KHz, the heating temperature is 40 ℃ to 70 ℃, and the ultrasonic vibration time is 24h-72h.
7. The method for preparing the hydrophobic silica gradient aerogel with tunable structure of claim 6, wherein: in the step (3), the rotating speed of the centrifuge is 30r/min-500r/min, and the centrifugal inclination angle is 0.5-15 degrees.
8. The method for preparing the hydrophobic silica gradient aerogel with tunable structure according to claim 7, wherein: and (3) adding a hydrophobic modifier diluted by a solvent into the aerogel obtained in the step (3), wherein the volume ratio of the solvent to the hydrophobic modifier is 1: (0.05-0.2), the hydrophobic modifier comprises one of vinyltrimethoxysilane, trimethylethoxysilane and dimethyldiethoxysilane, the modification time is 8-48 h, and the modification temperature is 50-80 ℃.
9. The method for preparing the hydrophobic silica gradient aerogel with tunable structure according to claim 8, wherein: the supercritical carbon dioxide drying is to place the modified silicon dioxide gradient aerogel into a supercritical carbon dioxide drying kettle for supercritical carbon dioxide drying, wherein the pressure in the drying kettle is 12MPa-15MPa, the drying temperature is 50 ℃ to 60 ℃, and the drying time is 2h-7h.
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