CN114394612A - High-temperature-resistant low-density alumina nanorod aerogel and preparation method thereof - Google Patents
High-temperature-resistant low-density alumina nanorod aerogel and preparation method thereof Download PDFInfo
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- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 title claims abstract description 116
- 239000004964 aerogel Substances 0.000 title claims abstract description 91
- 239000002073 nanorod Substances 0.000 title claims abstract description 82
- 238000002360 preparation method Methods 0.000 title claims abstract description 26
- DGXAGETVRDOQFP-UHFFFAOYSA-N 2,6-dihydroxybenzaldehyde Chemical compound OC1=CC=CC(O)=C1C=O DGXAGETVRDOQFP-UHFFFAOYSA-N 0.000 claims abstract description 43
- 238000010438 heat treatment Methods 0.000 claims abstract description 34
- 238000000034 method Methods 0.000 claims abstract description 26
- 238000006243 chemical reaction Methods 0.000 claims abstract description 11
- 238000009413 insulation Methods 0.000 claims abstract description 8
- 238000000352 supercritical drying Methods 0.000 claims abstract description 7
- 230000032683 aging Effects 0.000 claims abstract description 6
- 238000004321 preservation Methods 0.000 claims abstract description 6
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims description 26
- 239000002131 composite material Substances 0.000 claims description 21
- 238000003756 stirring Methods 0.000 claims description 21
- 238000005336 cracking Methods 0.000 claims description 20
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 claims description 18
- GHMLBKRAJCXXBS-UHFFFAOYSA-N resorcinol Chemical compound OC1=CC=CC(O)=C1 GHMLBKRAJCXXBS-UHFFFAOYSA-N 0.000 claims description 18
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 claims description 16
- 239000008367 deionised water Substances 0.000 claims description 15
- 229910021641 deionized water Inorganic materials 0.000 claims description 15
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 15
- WSFSSNUMVMOOMR-UHFFFAOYSA-N Formaldehyde Chemical compound O=C WSFSSNUMVMOOMR-UHFFFAOYSA-N 0.000 claims description 13
- 239000001569 carbon dioxide Substances 0.000 claims description 13
- 229910002092 carbon dioxide Inorganic materials 0.000 claims description 13
- 238000002156 mixing Methods 0.000 claims description 13
- SMZOGRDCAXLAAR-UHFFFAOYSA-N aluminium isopropoxide Chemical compound [Al+3].CC(C)[O-].CC(C)[O-].CC(C)[O-] SMZOGRDCAXLAAR-UHFFFAOYSA-N 0.000 claims description 10
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 claims description 9
- 239000008098 formaldehyde solution Substances 0.000 claims description 9
- 239000002253 acid Substances 0.000 claims description 8
- 238000001035 drying Methods 0.000 claims description 8
- 229910000029 sodium carbonate Inorganic materials 0.000 claims description 8
- 239000000126 substance Substances 0.000 claims description 7
- 238000001027 hydrothermal synthesis Methods 0.000 claims description 6
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 5
- 239000007788 liquid Substances 0.000 claims description 5
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 4
- 238000001816 cooling Methods 0.000 claims description 4
- 239000002904 solvent Substances 0.000 claims description 4
- WSFSSNUMVMOOMR-NJFSPNSNSA-N methanone Chemical compound O=[14CH2] WSFSSNUMVMOOMR-NJFSPNSNSA-N 0.000 claims description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 2
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 2
- 229910017604 nitric acid Inorganic materials 0.000 claims description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 abstract description 35
- 229910052799 carbon Inorganic materials 0.000 abstract description 34
- 239000013078 crystal Substances 0.000 abstract description 11
- 239000010410 layer Substances 0.000 abstract description 8
- 230000008569 process Effects 0.000 abstract description 8
- 230000009467 reduction Effects 0.000 abstract description 4
- 238000005245 sintering Methods 0.000 abstract description 4
- 238000000197 pyrolysis Methods 0.000 abstract description 3
- 239000012792 core layer Substances 0.000 abstract description 2
- 230000008707 rearrangement Effects 0.000 abstract description 2
- 239000000243 solution Substances 0.000 description 14
- 230000000052 comparative effect Effects 0.000 description 10
- 230000008859 change Effects 0.000 description 6
- 239000006185 dispersion Substances 0.000 description 6
- 230000014759 maintenance of location Effects 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 description 4
- 230000009286 beneficial effect Effects 0.000 description 4
- 239000002609 medium Substances 0.000 description 4
- 229910001593 boehmite Inorganic materials 0.000 description 3
- FAHBNUUHRFUEAI-UHFFFAOYSA-M hydroxidooxidoaluminium Chemical compound O[Al]=O FAHBNUUHRFUEAI-UHFFFAOYSA-M 0.000 description 3
- 239000004966 Carbon aerogel Substances 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000006555 catalytic reaction Methods 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
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- 230000003287 optical effect Effects 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 238000001179 sorption measurement Methods 0.000 description 2
- 230000009466 transformation Effects 0.000 description 2
- 239000003054 catalyst Substances 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000008094 contradictory effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000018044 dehydration Effects 0.000 description 1
- 238000006297 dehydration reaction Methods 0.000 description 1
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- 239000000413 hydrolysate Substances 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F7/00—Compounds of aluminium
- C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
- C01F7/021—After-treatment of oxides or hydroxides
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F7/00—Compounds of aluminium
- C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
- C01F7/021—After-treatment of oxides or hydroxides
- C01F7/025—Granulation or agglomeration
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2002/00—Crystal-structural characteristics
- C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
- C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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- C01P2004/01—Particle morphology depicted by an image
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- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/01—Particle morphology depicted by an image
- C01P2004/03—Particle morphology depicted by an image obtained by SEM
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- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/10—Solid density
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- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/12—Surface area
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/12—Surface area
- C01P2006/13—Surface area thermal stability thereof at high temperatures
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/32—Thermal properties
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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
Abstract
The invention discloses a high-temperature-resistant low-density alumina nanorod aerogel and a preparation method thereof. Gelling, aging and supercritical drying; after pyrolysis, the resorcinol-formaldehyde is converted to a carbon shell layer in the pyrolysis, and the shrinkage force generated in the conversion process effectively inhibits the crystal phase conversion and the crystal lattice rearrangement of the core layer alumina to the alpha phase at high temperature, thereby avoiding the sintering and the great reduction of the specific surface area caused by the rapid growth of the alpha phase crystal grains. And finally, removing the carbon template through heating treatment to obtain the alumina nanorod aerogel with the three-dimensional network structure. The alumina nanorod aerogel prepared by the invention has good high-temperature resistance, and can be applied to the fields of heat insulation and preservation such as aerospace, petrochemical industry and industrial kilns.
Description
Technical Field
The invention relates to the technical field of aerogel preparation, in particular to high-temperature-resistant low-density alumina nanorod aerogel and a preparation method thereof.
Background
The aerogel is a novel nano material which takes a solid as a framework and gas as a dispersion medium and has a three-dimensional porous network structure, and shows excellent performances such as high specific surface area, high porosity, low density and the like, so that the aerogel has a great application prospect in the fields of adsorption, catalysis, sensing, heat insulation and the like. SiO 22Aerogel is a mature aerogel thermal insulation material which is researched at present, but at a high temperature of more than 800 ℃, crystal grains can grow rapidly, and structural collapse and performance reduction are shown. The carbon aerogel has good high temperature resistance, can bear the high temperature of more than 1800 ℃ in an oxygen-free environment, but has insufficient oxidation resistance, which seriously limits the application field of the carbon aerogel.
In contrast, the alumina aerogel has more excellent temperature resistance and oxidation resistance, does not undergo significant sintering even under the aerobic condition of 1000 ℃, can keep higher specific surface area, is a good high-temperature-resistant light heat-insulating material, and is expected to be applied to the field of high-temperature heat insulation.
In the existing preparation method of alumina aerogel, fibrous boehmite is used as a raw material to prepare transparent alumina aerogel, boehmite fibers prepared by a hydrothermal method are used as a raw material, and ultra-light Al with optical transparency is prepared by carbon dioxide supercritical2O3Fibrous aerogels (rho ═ 1.2mg/cm3). The aerogel material can resist the high temperature of 1000 ℃, but after heat treatment at 1300 ℃, the volume of the aerogel is greatly shrunk, the density is increased by 150 times, and the specific surface area is from 382m2The g is reduced to 4m2The specific surface area retention was only 1.05% per gram, and the microstructure rolled from a fibrous shape into a sphere, with the optical transparency also disappearing. This is because boehmite phase is unstable at high temperature, dehydration and crystal transformation to alpha-phase alumina occur with temperature rise, and the rapid growth of alpha-phase alumina crystal grains leads to great reduction of the specific surface area and volume shrinkage of the alumina fiber aerogel. Therefore, the temperature resistance of the existing pure alumina aerogel still needs to be further improved.
Disclosure of Invention
The invention provides an alumina nanorod aerogel, and a preparation method and application thereof, which are used for overcoming the defects of insufficient temperature resistance and the like of pure alumina aerogel in the prior art.
In order to achieve the purpose, the invention provides a preparation method of an alumina nanorod aerogel, which comprises the following steps:
s1: mixing aluminum isopropoxide and deionized water under a stirring condition, heating to 50-80 ℃, preserving heat for 0.5-3 h at 50-80 ℃, then heating to 85-100 ℃ from 50-80 ℃, preserving heat for 0.5-2 h at 85-100 ℃, adding an acid substance, carrying out hydrothermal reaction, and cooling to room temperature to obtain an aluminum oxide nanorod;
s2: mixing resorcinol and deionized water under stirring, dropwise adding a sodium carbonate solution, stirring for 5-60 min, adding formaldehyde, uniformly mixing, and standing to obtain a resorcinol-formaldehyde solution; adding the aluminum oxide nano-rods into the resorcinol-formaldehyde solution, heating and stirring to obtain an aluminum oxide/resorcinol-formaldehyde reaction solution;
s3: heating the alumina/resorcinol-formaldehyde reaction solution to 50-90 ℃ under normal pressure, preserving heat for 2-5 hours at 50-90 ℃, aging, carrying out alcohol solvent replacement, and carrying out supercritical drying by taking carbon dioxide as a drying medium to obtain the alumina/resorcinol-formaldehyde composite aerogel;
s4: and cracking the aluminum oxide/resorcinol-formaldehyde composite aerogel in an inert atmosphere, and then heating in an air atmosphere to obtain the aluminum oxide nanorod aerogel.
In order to achieve the purpose, the invention also provides an alumina nanorod aerogel prepared by the preparation method.
In order to achieve the purpose, the invention also provides an application of the alumina nanorod aerogel, and the alumina nanorod aerogel prepared by the preparation method or the alumina nanorod aerogel is applied to the fields of heat insulation and preservation of aerospace, petrochemical industry and industrial kilns.
Compared with the prior art, the invention has the beneficial effects that:
1. the preparation method of the alumina nanorod aerogel adopts a carbon template method, firstly prepares the alumina nanorod,the one-dimensional alumina nano-rod with higher length-diameter ratio is adopted as a basic construction unit, compared with the traditional spherical nano-particle, the one-dimensional rod-shaped lap joint is more beneficial to the formation of a three-dimensional network structure, so that the original framework structure can be inherited even after a carbon shell layer is removed, the self-support of the alumina nano-rod is realized, and the unique porous structure also endows the alumina nano-rod aerogel with the ultra-light characteristic (rho is less than 0.1 g/cm)3). Using resorcinol-formaldehyde as a carbon source, and completely coating the aluminum oxide nano-rods by the carbon source through gelation, aging and supercritical drying; and then, the resorcinol-formaldehyde is converted to the carbon shell layer in the high-temperature cracking process through the high-temperature cracking, and the shrinkage force generated in the conversion process effectively inhibits the crystal phase conversion and the crystal lattice rearrangement of the core-layer alumina to the alpha phase at high temperature, so that the sintering and the great reduction of the specific surface area caused by the rapid growth of the alpha phase crystal grains are avoided, and the temperature resistance of the alumina nanorod is improved. And finally, removing the carbon template through heating treatment to obtain the alumina nanorod aerogel with the three-dimensional network structure. The preparation method provided by the invention has the advantages of simple and controllable process, short period of the whole process flow and suitability for batch preparation.
2. The alumina nanorod aerogel prepared by the invention has good high-temperature resistance. After the aerogel is subjected to high-temperature treatment, the aerogel still has high specific surface area retention rate and a mesoporous structure. After being treated at 1300 ℃ and 1400 ℃ for 30min respectively, the specific surface area retention rates can reach 81.3 percent and 36.4 percent respectively. According to the invention, resorcinol-formaldehyde with a higher carbon residue rate is used as a carbon source, and the adsorption effect between rich hydrophilic groups on resorcinol-formaldehyde molecules and the alumina nanorods is utilized to realize the full coating of the alumina nanorods, so that the alumina nanorods can be effectively isolated by carbon subjected to high-temperature cracking in an inert atmosphere, the fusion and sintering of contact points at high temperature are avoided, the prepared aerogel material can still maintain a complete mesoporous three-dimensional network structure even at the high temperature of 1400 ℃, and the high-efficiency heat insulation at the high temperature is favorably realized. The alumina nanorod aerogel prepared by the invention can be applied to the fields of heat insulation and preservation such as aerospace, petrochemical industry and industrial kilns.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the structures shown in the drawings without creative efforts.
FIG. 1 is a flow chart of a method for preparing an alumina nanorod aerogel provided by the present invention;
FIG. 2a is an SEM picture of an alumina/carbon composite aerogel prepared in example 1;
FIG. 2b is a photomicrograph of the alumina/carbon composite aerogel prepared in example 1;
FIG. 3 is an SEM picture of the alumina nanorod aerogel prepared in example 1;
fig. 4 is an XRD spectrum of the alumina nanorod aerogel prepared in example 1.
The implementation, functional features and advantages of the objects of the present invention will be further explained with reference to the accompanying drawings.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In addition, the technical solutions in the embodiments of the present invention may be combined with each other, but it must be based on the realization of those skilled in the art, and when the technical solutions are contradictory or cannot be realized, such a combination of technical solutions should not be considered to exist, and is not within the protection scope of the present invention.
The drugs/reagents used are all commercially available without specific mention.
The invention provides a preparation method of an alumina nanorod aerogel, which comprises the following steps as shown in figure 1:
s1: aluminum isopropoxide (Al (OCHCH)3CH3)3) Mixing the aluminum oxide nano rod with deionized water under a stirring condition, heating to 50-80 ℃, preserving heat for 0.5-3 h at 50-80 ℃, then heating to 85-100 ℃ from 50-80 ℃, preserving heat for 0.5-2 h at 85-100 ℃, adding an acid substance as a morphology regulator, carrying out hydrothermal reaction, and cooling to room temperature to obtain the aluminum oxide nano rod.
And preserving the heat for 0.5-3 hours at 50-80 ℃ to obtain the fully hydrolyzed alumina solution.
And preserving the temperature for 0.5-2 hours at 85-100 ℃ to evaporate the isopropanol generated by hydrolysis.
Preferably, the molar ratio of the aluminum isopropoxide to the deionized water is (10-50): 1; the molar ratio of the acid substance to the aluminum isopropoxide is 4-18: 1.
Preferably, the acid substance is one of dilute hydrochloric acid, dilute sulfuric acid and dilute nitric acid and acetic acid.
Preferably, the hydrothermal reaction is carried out at 160-220 ℃ for 4-24 h.
Controlling the mole ratio of aluminum isopropoxide to deionized water, the mole ratio of acid substances to aluminum isopropoxide and hydrothermal conditions to obtain rod-shaped alumina, otherwise, obtaining the lamellar or feather-shaped alumina under normal conditions.
S2: mixing resorcinol and deionized water under stirring, dropwise adding a sodium carbonate solution as a catalyst, stirring for 5-60 min, adding formaldehyde, uniformly mixing, and standing to obtain a resorcinol-formaldehyde solution; adding the aluminum oxide nano-rods into the resorcinol-formaldehyde solution, heating and stirring to obtain an aluminum oxide/resorcinol-formaldehyde reaction solution.
Preferably, the molar ratio of the resorcinol to the formaldehyde to the sodium carbonate to the deionized water is 1:2:0.002 (4-64), and the resorcinol and the formaldehyde form resorcinol-formaldehyde under the catalysis of the sodium carbonate; the mass ratio of the resorcinol-formaldehyde solution to the alumina nano-rods is (0.05-2): 1, the ratio is controlled to control the carbon content, too much carbon is not beneficial to forming after carbon removal, too little carbon is not fully wrapped by alumina, and the temperature resistance is not beneficial to improvement.
Preferably, the heating and stirring temperature is 30-60 ℃ so as to fully and uniformly mix the resorcinol-formaldehyde and the aluminum oxide; the heating and stirring process further comprises vacuumizing, wherein vacuumizing is carried out for 10-60 min under the conditions that the temperature is 15-25 ℃ and the vacuum degree is 0.1-0.5 MPa, so that bubbles are prevented from being generated, and the preparation of the aerogel with the high specific surface area is not favorable.
S3: heating the alumina/resorcinol-formaldehyde reaction solution to 50-90 ℃ under normal pressure, preserving heat for 2-5 hours at 50-90 ℃, aging, carrying out alcohol solvent replacement, and carrying out supercritical drying by taking carbon dioxide as a drying medium to obtain the alumina/resorcinol-formaldehyde composite aerogel.
Aging, and keeping the temperature at 50-90 ℃ for 2-5 days.
Preferably, the supercritical drying is specifically:
the method comprises the steps of pre-charging 5-7 MPa liquid carbon dioxide by taking carbon dioxide as a drying medium, heating at the speed of 1-2 ℃/min to enable the temperature (30-60 ℃) and the pressure (8-15 MPa) to reach above the supercritical point of the carbon dioxide, and releasing the pressure at the speed of 30-60 kPa/min after heat preservation for 2-8 h. This drying mode facilitates the formation of nanoporous aerogels, and the pore structure is collapsed by surface tension generated by solvent evaporation during atmospheric drying.
S4: and cracking the aluminum oxide/resorcinol-formaldehyde composite aerogel in an inert atmosphere, and then heating in an air atmosphere to obtain the aluminum oxide nanorod aerogel.
Cracking to carbonize resorcinol-formaldehyde, and forming a carbon layer on the surface of the alumina nano rod.
And (4) heating to remove the carbon layer on the surface of the alumina nano rod.
Preferably, the cracking temperature is 1000-1500 ℃, and the time is 1-10 h; the temperature of the heating treatment is 500-1000 ℃, and the time is 1-10 h.
The invention also provides an alumina nanorod aerogel prepared by the preparation method.
The invention also provides application of the alumina nanorod aerogel prepared by the preparation method or the alumina nanorod aerogel prepared by the preparation method to the heat insulation field of aerospace, petrochemical industry and industrial kilns.
Example 1
The embodiment provides a preparation method of an alumina nanorod aerogel, which comprises the following steps:
s1: aluminum isopropoxide (Al (OCHCH)3CH3)3) With deionized water (H)2O) mixing under stirring, heating to 70 ℃, and keeping the temperature for 5 hours to obtain fully hydrolyzed alumina hydrolysate; further raising the temperature to 90 ℃ and preserving the temperature for 0.5h, and evaporating isopropanol generated by hydrolysis to obtain alumina sol; mixing alumina sol and acetic acid according to the weight ratio of 10: 1, placing the mixture in a hydrothermal kettle, heating to 160 ℃, preserving heat for 10 hours, and cooling to room temperature to obtain the alumina nanorod dispersion liquid.
S2: fully mixing resorcinol and deionized water under stirring, dropwise adding a sodium carbonate solution into the solution after the resorcinol and the deionized water are fully dissolved, stirring for 30min, adding a certain amount of formaldehyde into the mixed solution, stirring for a period of time, and standing for 1h to obtain a resorcinol-formaldehyde solution, wherein the molar ratio of resorcinol to formaldehyde to sodium carbonate to deionized water is 1:2:0.002: 32. And (2) mixing resorcinol-formaldehyde with the alumina nanorod dispersion liquid obtained in the step one according to the mass ratio of 0.8:1, stirring for 1h at 25 ℃, and vacuumizing to obtain the alumina/resorcinol-formaldehyde sol.
S3: heating the alumina/resorcinol-formaldehyde sol to 50 ℃ under normal pressure, preserving the temperature for 5h to form alumina/resorcinol-formaldehyde composite gel, keeping the temperature at 50 ℃ for aging for 3 days, and performing ethanol solvent replacement to obtain the replaced alumina/resorcinol-formaldehyde composite gel. And (3) placing the replaced composite gel in an autoclave, adopting carbon dioxide (the mass fraction is more than or equal to 99.5%) as a drying medium, pre-charging 7MPa liquid carbon dioxide, heating to 50 ℃ at the speed of 1-2 ℃/min, enabling the temperature and the pressure (12MPa) to reach above the supercritical point of the carbon dioxide, keeping the temperature for 6h, and slowly releasing the pressure at the speed of 30 kPa/min to finally obtain the alumina/resorcinol-formaldehyde composite aerogel.
S4: cracking the alumina/resorcinol-formaldehyde composite aerogel obtained in the step S3 for 2 hours under the conditions of inert atmosphere and 1400 ℃ to obtain alumina/carbon composite aerogel (shown in a figure 2 b); further, the alumina/carbon composite aerogel is placed in an air atmosphere and subjected to heat treatment at the temperature of 600 ℃ for 5 hours to obtain the high-temperature-resistant low-density alumina nanorod aerogel.
The specific surface area of the alumina nanorod aerogel prepared in the example (after carbon removal) is 107m2(ii)/g, the specific surface area and retention after heat treatment at 1300 ℃ are respectively 87m2(81.3%) and a specific surface area and a retention rate after heat treatment at 1400 ℃ of 29m2G and 36.4%. Fig. 2a shows the microscopic morphology of the alumina/carbon composite aerogel captured by a scanning electron microscope, in which it can be seen that the rod-shaped alumina is sufficiently wrapped by the rough carbon shell layer, and the wrapping is relatively uniform. FIG. 3 shows the microscopic morphology of the high temperature resistant alumina nanorod aerogel, which is photographed by a scanning electron microscope, and it is found that the nanorods can be sufficiently lapped and form a three-dimensional network structure after the carbon is removed. Fig. 4 is an XRD spectrogram of the high temperature resistant alumina nanorod aerogel, which shows that after pyrolysis, alumina is not converted into an alpha phase, but a theta phase with smaller grains is formed, indicating that the carbon shell layer effectively inhibits the crystal phase conversion of alumina, thereby improving the temperature resistance of alumina.
Example 2
In this embodiment, compared with embodiment 1, in step S4, the alumina/carbon composite aerogel material is placed in an air atmosphere and heat-treated at 800 ℃ for 5 hours, so as to obtain the high-temperature-resistant and low-density alumina nanorod aerogel. The other procedures were the same as in example 1.
The high temperature resistant alumina nanorod aerogel prepared in the embodiment is subjected to temperature resistance examination, and the specific surface area of a sample subjected to 1300 ℃ thermal examination (air atmosphere) for 30min is 72m2G, no apparent surface of the sampleChanged and no cracking and structural collapse occurred; the specific surface area of the sample after being subjected to 1400 ℃ thermal examination (air atmosphere) for 30min is 26m2The samples have no obvious change on the surface and no cracking or structural collapse, which indicates that the samples can resist the high temperature of 1400 ℃, and other performance parameters are shown in the table 1.
Example 3
In this embodiment, compared with example 1, in step S2, the resorcinol-formaldehyde and the alumina nanorod dispersion are mixed according to a mass ratio of 0.8:1, and then the alumina/resorcinol-formaldehyde sol is directly obtained without vacuum pumping. The other procedures were the same as in example 1.
The high temperature resistant alumina nanorod aerogel prepared in the embodiment is subjected to temperature resistance examination, and the specific surface area of a sample subjected to 1300 ℃ thermal examination (air atmosphere) for 30min is found to be 62m2(iv) g, no significant change in the sample surface and no cracking and structural collapse; the specific surface area of the sample after being subjected to 1400 ℃ thermal examination (air atmosphere) for 30min is 20m2The samples have no obvious change on the surface and no cracking or structural collapse, which indicates that the samples can resist the high temperature of 1400 ℃, and other performance parameters are shown in the table 1.
Example 4
This example provides a preparation method of an alumina nanorod aerogel, compared to example 1, in step S4, the alumina/resorcinol-formaldehyde composite aerogel is cracked for 1h under an inert atmosphere and at a temperature of 1400 ℃, so as to obtain an alumina/carbon composite aerogel material. The other procedures were the same as in example 1.
The high-temperature resistant alumina nanorod aerogel prepared in the embodiment is subjected to temperature resistance examination, and the surface of a sample is not obviously changed and cracking and structural collapse are not generated after the sample is subjected to 1300 ℃ thermal examination (air atmosphere) for 30 min; after the sample is subjected to 1400 ℃ thermal examination (air atmosphere) for 30min, the surface of the sample has no obvious change and no cracking and structural collapse occur, which shows that the sample can resist 1400 ℃ high temperature, and other performance parameters are shown in table 1.
Example 5
This example provides a method for preparing an alumina nanorod aerogel, wherein, compared to example 1, in step S2, resorcinol-formaldehyde and an alumina nanorod dispersion are mixed in a mass ratio of 0.3: 1. The other procedures were the same as in example 1.
The high-temperature resistant alumina nanorod aerogel prepared in the embodiment is subjected to temperature resistance examination, and the surface of a sample is not obviously changed and cracking and structural collapse are not generated after the sample is subjected to 1300 ℃ thermal examination (air atmosphere) for 30 min; after the sample is subjected to 1400 ℃ thermal examination (air atmosphere) for 30min, the surface of the sample has no obvious change and no cracking and structural collapse occur, which shows that the sample can resist 1400 ℃ high temperature, and other performance parameters are shown in table 1.
Comparative example 6
Compared with the preparation method of the alumina nanorod aerogel, in the step S4, the alumina/resorcinol-formaldehyde composite aerogel is cracked for 2 hours under the conditions of inert atmosphere and 1300 ℃ to obtain the alumina/carbon composite aerogel material. The other procedures were the same as in example 1.
The high-temperature resistant alumina nanorod aerogel prepared in the comparative example is subjected to temperature resistance examination, and the specific surface area of a sample subjected to 1300 ℃ thermal examination (air atmosphere) for 30min is found to be 24m2(iv) g, no significant change in the sample surface and no cracking and structural collapse; the specific surface area of the sample is less than 10m after being subjected to 1400 ℃ thermal examination (air atmosphere) for 30min2And g, the sample is obviously shrunk and cracks appear on the surface, which indicates that the sample cannot resist the high temperature of 1400 ℃, and other performance parameters are shown in the table 1.
Comparative example 1
This comparative example provides a method for preparing an alumina nanorod aerogel, in which, compared to example 1, resorcinol-formaldehyde and an alumina nanorod dispersion are mixed in a mass ratio of 3:1 in step S2. The other procedures were the same as in example 1.
In the process of performing temperature resistance examination on the high-temperature-resistant alumina nanorod aerogel prepared in the comparative example, the fact that the strength of a sample is extremely low after carbon removal, the sample is crushed after slight vibration, and further temperature resistance test cannot be performed is found, because the carbon content is too high, an excessive isolation effect is generated on the alumina nanorod, the alumina nanorod after the carbon shell layer is removed cannot be effectively lapped and self-supported, the strength of the sample is greatly reduced, and other performance parameters are shown in table 1.
Comparative example 2
This comparative example provides a method for preparing an alumina nanorod aerogel, in which, in comparison with example 1, resorcinol-formaldehyde and an alumina nanorod dispersion are mixed in a mass ratio of 0.02:1 in step S2. The other procedures were the same as in example 1.
The temperature resistance of the high-temperature-resistant alumina nanorod aerogel prepared in the comparative example is examined, and the fact that after the high-temperature-resistant alumina nanorod aerogel is subjected to 1300 ℃ thermal examination (air atmosphere) for 30min, the sample is obviously shrunk and cracks appear on the surface of the sample indicates that the sample cannot bear the high temperature of 1300 ℃, because the carbon content is too low, the alumina nanorods cannot be fully coated, the carbon template does not play a role in fully isolating and inhibiting the crystal form transformation of alumina, the sample is sintered in the high-temperature examination process, and other performance parameters are shown in table 1.
Table 1 is a comparison table of performance parameters of the high temperature resistant alumina nanorod aerogels prepared in examples 1 to 5 and comparative examples 1 to 3, and it can be known from table 1 that the main parameters affecting the performance of the aerogel in the present invention are the molar ratio of the carbon source precursor to alumina, the cracking temperature and the time.
TABLE 1 Performance parameters of the high temperature resistant alumina nanorod aerogels prepared in examples 1-5 and comparative examples 1-3
The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention, and all modifications and equivalents of the present invention, which are made by the contents of the present specification and the accompanying drawings, or directly/indirectly applied to other related technical fields, are included in the scope of the present invention.
Claims (10)
1. A preparation method of high-temperature-resistant low-density alumina nanorod aerogel is characterized by comprising the following steps:
s1: mixing aluminum isopropoxide and deionized water under a stirring condition, heating to 50-80 ℃, preserving heat for 0.5-3 h at 50-80 ℃, then heating to 85-100 ℃ from 50-80 ℃, preserving heat for 0.5-2 h at 85-100 ℃, adding an acid substance, carrying out hydrothermal reaction, and cooling to room temperature to obtain an aluminum oxide nanorod;
s2: mixing resorcinol and deionized water under stirring, dropwise adding a sodium carbonate solution, stirring for 5-60 min, adding formaldehyde, uniformly mixing, and standing to obtain a resorcinol-formaldehyde solution; adding the aluminum oxide nano-rods into the resorcinol-formaldehyde solution, heating and stirring to obtain an aluminum oxide/resorcinol-formaldehyde reaction solution;
s3: heating the alumina/resorcinol-formaldehyde reaction solution to 50-90 ℃ under normal pressure, preserving heat for 2-5 hours at 50-90 ℃, aging, carrying out alcohol solvent replacement, and carrying out supercritical drying by taking carbon dioxide as a drying medium to obtain the alumina/resorcinol-formaldehyde composite aerogel;
s4: and cracking the aluminum oxide/resorcinol-formaldehyde composite aerogel in an inert atmosphere, and then heating in an air atmosphere to obtain the aluminum oxide nanorod aerogel.
2. The preparation method according to claim 1, wherein in step S1, the molar ratio of aluminum isopropoxide to deionized water is (10-50): 1; the molar ratio of the acid substance to the aluminum isopropoxide is 4-18: 1.
3. The method according to claim 1 or 2, wherein the acid is one of dilute hydrochloric acid, dilute sulfuric acid, and dilute nitric acid and acetic acid.
4. The method according to claim 1, wherein in step S1, the hydrothermal reaction is carried out at 160-220 ℃ for 4-24 hours.
5. The preparation method according to claim 1, wherein in step S2, the molar ratio of the resorcinol to the formaldehyde to the sodium carbonate to the deionized water is 1:2:0.002 (4-64); the mass ratio of the resorcinol-formaldehyde solution to the alumina nano-rods is (0.05-2): 1.
6. The method according to claim 1 or 5, wherein in step S2, the temperature of the heating and stirring is 30 to 60 ℃; and vacuumizing for 10-60 min under the conditions that the temperature is 15-25 ℃ and the vacuum degree is 0.1-0.5 MPa after the heating and stirring.
7. The method according to claim 1, wherein in step S3, the supercritical drying is specifically:
pre-charging 5-7 MPa liquid carbon dioxide by taking carbon dioxide as a drying medium, heating at the speed of 1-2 ℃/min to enable the temperature and the pressure to reach above the supercritical point of the carbon dioxide, and releasing the pressure at the speed of 30-60 kPa/min after heat preservation for 2-8 h; the temperature is 30-60 ℃, and the pressure is 8-15 MPa.
8. The method of claim 1, wherein in step S4, the temperature of the cracking is 1000-1500 ℃, and the time is 1-10 h; the temperature of the heating treatment is 500-1000 ℃, and the time is 1-10 h.
9. A high-temperature-resistant low-density alumina nanorod aerogel is characterized by being prepared by the preparation method of any one of claims 1-8.
10. An application of the high-temperature-resistant and low-density alumina nanorod aerogel is characterized in that the alumina nanorod aerogel prepared by the preparation method of any one of claims 1 to 8 or the alumina nanorod aerogel of claim 9 is applied to the fields of heat insulation and preservation of aerospace, petrochemical industry and industrial kilns.
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