CN115432710B - Preparation method of ultralow-density silica aerogel block - Google Patents
Preparation method of ultralow-density silica aerogel block Download PDFInfo
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- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 title claims abstract description 112
- 239000004965 Silica aerogel Substances 0.000 title claims abstract description 84
- 238000002360 preparation method Methods 0.000 title claims abstract description 44
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 claims abstract description 92
- ZHNUHDYFZUAESO-UHFFFAOYSA-N Formamide Chemical compound NC=O ZHNUHDYFZUAESO-UHFFFAOYSA-N 0.000 claims abstract description 68
- 239000011240 wet gel Substances 0.000 claims abstract description 66
- NTHWMYGWWRZVTN-UHFFFAOYSA-N sodium silicate Chemical compound [Na+].[Na+].[O-][Si]([O-])=O NTHWMYGWWRZVTN-UHFFFAOYSA-N 0.000 claims abstract description 45
- 239000002904 solvent Substances 0.000 claims abstract description 43
- 238000001035 drying Methods 0.000 claims abstract description 39
- 239000002243 precursor Substances 0.000 claims abstract description 33
- 239000003607 modifier Substances 0.000 claims abstract description 29
- 239000004115 Sodium Silicate Substances 0.000 claims abstract description 25
- 229910052911 sodium silicate Inorganic materials 0.000 claims abstract description 25
- RMAQACBXLXPBSY-UHFFFAOYSA-N silicic acid Chemical compound O[Si](O)(O)O RMAQACBXLXPBSY-UHFFFAOYSA-N 0.000 claims abstract description 22
- 230000002209 hydrophobic effect Effects 0.000 claims abstract description 16
- 238000012986 modification Methods 0.000 claims abstract description 14
- 230000004048 modification Effects 0.000 claims abstract description 14
- 238000006068 polycondensation reaction Methods 0.000 claims abstract description 14
- 239000003960 organic solvent Substances 0.000 claims abstract description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 33
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 28
- 238000000034 method Methods 0.000 claims description 26
- VLKZOEOYAKHREP-UHFFFAOYSA-N n-Hexane Chemical compound CCCCCC VLKZOEOYAKHREP-UHFFFAOYSA-N 0.000 claims description 22
- 229910052681 coesite Inorganic materials 0.000 claims description 21
- 229910052906 cristobalite Inorganic materials 0.000 claims description 21
- 229910052682 stishovite Inorganic materials 0.000 claims description 21
- 229910052905 tridymite Inorganic materials 0.000 claims description 21
- 235000019353 potassium silicate Nutrition 0.000 claims description 20
- IMNFDUFMRHMDMM-UHFFFAOYSA-N N-Heptane Chemical compound CCCCCCC IMNFDUFMRHMDMM-UHFFFAOYSA-N 0.000 claims description 18
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 claims description 14
- IJOOHPMOJXWVHK-UHFFFAOYSA-N chlorotrimethylsilane Chemical compound C[Si](C)(C)Cl IJOOHPMOJXWVHK-UHFFFAOYSA-N 0.000 claims description 14
- 239000008235 industrial water Substances 0.000 claims description 13
- 238000006460 hydrolysis reaction Methods 0.000 claims description 11
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 claims description 9
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 claims description 9
- PEDCQBHIVMGVHV-UHFFFAOYSA-N Glycerine Chemical compound OCC(O)CO PEDCQBHIVMGVHV-UHFFFAOYSA-N 0.000 claims description 8
- OFBQJSOFQDEBGM-UHFFFAOYSA-N Pentane Chemical compound CCCCC OFBQJSOFQDEBGM-UHFFFAOYSA-N 0.000 claims description 8
- FFUAGWLWBBFQJT-UHFFFAOYSA-N hexamethyldisilazane Chemical compound C[Si](C)(C)N[Si](C)(C)C FFUAGWLWBBFQJT-UHFFFAOYSA-N 0.000 claims description 8
- 239000007810 chemical reaction solvent Substances 0.000 claims description 7
- 239000005051 trimethylchlorosilane Substances 0.000 claims description 7
- DKGAVHZHDRPRBM-UHFFFAOYSA-N Tert-Butanol Chemical compound CC(C)(C)O DKGAVHZHDRPRBM-UHFFFAOYSA-N 0.000 claims description 5
- 235000011187 glycerol Nutrition 0.000 claims description 4
- UQEAIHBTYFGYIE-UHFFFAOYSA-N hexamethyldisiloxane Chemical compound C[Si](C)(C)O[Si](C)(C)C UQEAIHBTYFGYIE-UHFFFAOYSA-N 0.000 claims description 4
- BFXIKLCIZHOAAZ-UHFFFAOYSA-N methyltrimethoxysilane Chemical compound CO[Si](C)(OC)OC BFXIKLCIZHOAAZ-UHFFFAOYSA-N 0.000 claims description 3
- 238000006467 substitution reaction Methods 0.000 claims description 2
- 239000004964 aerogel Substances 0.000 abstract description 18
- 230000000704 physical effect Effects 0.000 abstract description 5
- 239000000499 gel Substances 0.000 description 17
- 230000000052 comparative effect Effects 0.000 description 11
- 102100024239 Sphingosine-1-phosphate lyase 1 Human genes 0.000 description 9
- 101710122496 Sphingosine-1-phosphate lyase 1 Proteins 0.000 description 9
- 238000001000 micrograph Methods 0.000 description 8
- 230000008569 process Effects 0.000 description 8
- 239000008367 deionised water Substances 0.000 description 7
- 229910021641 deionized water Inorganic materials 0.000 description 7
- 239000000377 silicon dioxide Substances 0.000 description 7
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 6
- 238000010586 diagram Methods 0.000 description 6
- 229910052710 silicon Inorganic materials 0.000 description 6
- 239000010703 silicon Substances 0.000 description 6
- 239000011734 sodium Substances 0.000 description 6
- 239000000126 substance Substances 0.000 description 6
- 101150042817 NFS1 gene Proteins 0.000 description 5
- 101100126298 Rickettsia conorii (strain ATCC VR-613 / Malish 7) iscS gene Proteins 0.000 description 5
- 101150114492 SPL1 gene Proteins 0.000 description 5
- 230000009286 beneficial effect Effects 0.000 description 5
- 239000003054 catalyst Substances 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- NWUYHJFMYQTDRP-UHFFFAOYSA-N 1,2-bis(ethenyl)benzene;1-ethenyl-2-ethylbenzene;styrene Chemical compound C=CC1=CC=CC=C1.CCC1=CC=CC=C1C=C.C=CC1=CC=CC=C1C=C NWUYHJFMYQTDRP-UHFFFAOYSA-N 0.000 description 4
- 101150056353 SPL2 gene Proteins 0.000 description 4
- 101150090744 SPL3 gene Proteins 0.000 description 4
- 101150031993 SPL4 gene Proteins 0.000 description 4
- 238000011031 large-scale manufacturing process Methods 0.000 description 4
- 238000001179 sorption measurement Methods 0.000 description 4
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 239000003513 alkali Substances 0.000 description 3
- 150000001768 cations Chemical class 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 230000006835 compression Effects 0.000 description 3
- 238000007906 compression Methods 0.000 description 3
- 238000009413 insulation Methods 0.000 description 3
- 239000003456 ion exchange resin Substances 0.000 description 3
- 229920003303 ion-exchange polymer Polymers 0.000 description 3
- 239000000843 powder Substances 0.000 description 3
- 229910001415 sodium ion Inorganic materials 0.000 description 3
- 238000000352 supercritical drying Methods 0.000 description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- PPBRXRYQALVLMV-UHFFFAOYSA-N Styrene Chemical compound C=CC1=CC=CC=C1 PPBRXRYQALVLMV-UHFFFAOYSA-N 0.000 description 2
- 239000002253 acid Substances 0.000 description 2
- 238000007171 acid catalysis Methods 0.000 description 2
- 238000006555 catalytic reaction Methods 0.000 description 2
- 239000000919 ceramic Substances 0.000 description 2
- 229910010293 ceramic material Inorganic materials 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 239000003795 chemical substances by application Substances 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 239000000835 fiber Substances 0.000 description 2
- 230000007062 hydrolysis Effects 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 238000004321 preservation Methods 0.000 description 2
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonium chloride Substances [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 description 1
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 1
- MKYBYDHXWVHEJW-UHFFFAOYSA-N N-[1-oxo-1-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)propan-2-yl]-2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidine-5-carboxamide Chemical class O=C(C(C)NC(=O)C=1C=NC(=NC=1)NCC1=CC(=CC=C1)OC(F)(F)F)N1CC2=C(CC1)NN=N2 MKYBYDHXWVHEJW-UHFFFAOYSA-N 0.000 description 1
- 229910004298 SiO 2 Inorganic materials 0.000 description 1
- BOTDANWDWHJENH-UHFFFAOYSA-N Tetraethyl orthosilicate Chemical compound CCO[Si](OCC)(OCC)OCC BOTDANWDWHJENH-UHFFFAOYSA-N 0.000 description 1
- 239000003377 acid catalyst Substances 0.000 description 1
- QGZKDVFQNNGYKY-UHFFFAOYSA-N ammonia Natural products N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 1
- 235000011114 ammonium hydroxide Nutrition 0.000 description 1
- 239000002585 base Substances 0.000 description 1
- 239000003729 cation exchange resin Substances 0.000 description 1
- 125000002091 cationic group Chemical group 0.000 description 1
- 238000012512 characterization method Methods 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 239000003085 diluting agent Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- WGCNASOHLSPBMP-UHFFFAOYSA-N hydroxyacetaldehyde Natural products OCC=O WGCNASOHLSPBMP-UHFFFAOYSA-N 0.000 description 1
- 238000009776 industrial production Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000007783 nanoporous material Substances 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 150000001282 organosilanes Chemical class 0.000 description 1
- 230000036314 physical performance Effects 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 230000036632 reaction speed Effects 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 235000012239 silicon dioxide Nutrition 0.000 description 1
- 238000003980 solgel method Methods 0.000 description 1
- LFQCEHFDDXELDD-UHFFFAOYSA-N tetramethyl orthosilicate Chemical compound CO[Si](OC)(OC)OC LFQCEHFDDXELDD-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/113—Silicon oxides; Hydrates thereof
- C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
- C01B33/14—Colloidal silica, e.g. dispersions, gels, sols
- C01B33/157—After-treatment of gels
- C01B33/158—Purification; Drying; Dehydrating
- C01B33/1585—Dehydration into aerogels
Landscapes
- Chemical & Material Sciences (AREA)
- Dispersion Chemistry (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Silicon Compounds (AREA)
Abstract
The application discloses a preparation method of an ultralow-density silica aerogel block, and belongs to the technical field of silica aerogel. The preparation method of the application comprises the following steps: preparing a precursor solution containing sodium silicate, and adding formamide and ethylene glycol into the precursor solution to react to obtain silica sol; performing polycondensation reaction on the silica sol to obtain wet gel; immersing the wet gel into an organic solvent for solvent replacement, and then adding the wet gel into a mixed modifier for surface modification to obtain a modified wet gel; and (3) drying the modified wet gel step by step under the normal pressure condition to obtain the ultra-low density silica aerogel block. The preparation method of the application not only can simplify the preparation process and reduce the cost, but also can improve the forming property and physical property of the aerogel to obtain regular cylinder or cube aerogel blocks with the density less than 0.20g/cm 3, the hydrophobic angle more than 139 degrees and the diameter size of 3-5 cm.
Description
Technical Field
The application belongs to the technical field of silica aerogel, and particularly relates to a preparation method of an ultralow-density silica aerogel block.
Background
The silica aerogel is a low-density, transparent and structurally controllable nano porous material, and has excellent adsorption and heat preservation and heat insulation characteristics due to a unique structure, and is widely applied to the fields of adsorption of automobile tail gas/marine floating oil, heat preservation and heat insulation of buildings and the like. However, the traditional silica aerogel is prepared by mainly taking organosilane such as ethyl orthosilicate, methyl orthosilicate and the like as raw materials, preparing wet gel by adopting a sol-gel method, and then performing supercritical drying, so that the organosilicon source is high in price and high in supercritical drying equipment requirement, and the preparation cost is high, and the large-scale production is greatly limited.
In order to solve the problem of high preparation cost of the silica aerogel, liu Guangwu et al propose a one-step method for rapidly preparing the composite reinforced SiO 2 aerogel, which uses water glass as a silicon source to prepare wet gel, carries out solvent replacement and surface modification on the wet gel, and then dries the wet gel at normal pressure to finally obtain a silica aerogel block, thereby reducing the preparation cost of the silica aerogel.
However, when the wet gel is prepared by taking water glass as a silicon source, the preparation method needs to pass the water glass precursor diluent through an exchange column filled with strong acid styrene cation exchange resin to remove sodium ions and other cations in the water glass, and add sodium hydroxide solution after treatment to perform catalytic reaction to form the wet gel, so that the preparation process is complex, the material consumption is serious, the cost is high, and the large-scale production is difficult.
Disclosure of Invention
The application aims to provide a preparation method of an ultralow-density silica aerogel block, which effectively solves the technical problems of complex process, serious material consumption, high cost and difficult mass production of the existing preparation method of the silica aerogel block.
In order to achieve the above object, the technical solution of the embodiment of the present application is:
According to a first aspect of the embodiment of the application, a preparation method of an ultralow-density silica aerogel block is provided, and comprises the following steps:
s101: preparing a precursor solution containing sodium silicate;
S102: adding formamide and ethylene glycol into the precursor solution for hydrolysis reaction to obtain silica sol;
s103: carrying out polycondensation reaction on the silica sol at the temperature of 35-65 ℃ to obtain wet gel;
S104: immersing the wet gel into an organic solvent for solvent replacement, and adding the wet gel into a mixed modifier for surface modification treatment after the solvent replacement is completed to obtain a modified wet gel;
S105: and (3) drying the modified wet gel step by step under the normal pressure condition to obtain the ultra-low density silica aerogel block.
In a preferred implementation of the first aspect of the embodiment of the present application, the method for preparing a precursor solution containing sodium silicate includes:
Mixing industrial water glass with water according to the volume ratio of 1:1-7 to obtain a precursor solution, wherein the concentration of the industrial water glass is 30-50%, and the modulus is 1.5-3.5.
In a preferred implementation manner of the first aspect of the embodiment of the present application, when the formamide and the ethylene glycol are added, a molar ratio of sodium silicate to formamide to ethylene glycol is 1:1-6:0.5-3.
In a preferred implementation of the first aspect of the embodiment of the present application, the temperature at which the polycondensation is performed is between 35 and 90 ℃ for 15 to 120 minutes.
In a preferred implementation manner of the first aspect of the embodiment of the present application, the solvent for performing the solvent replacement is any one of n-hexane, ethanol, isopropanol, and methanol.
In a preferred implementation of the first aspect of the embodiment of the present application, the temperature at which the solvent replacement is performed is 45-65 ℃ for 24-72 hours.
In a preferred implementation manner of the first aspect of the embodiment of the present application, the mixed modifier is formed by mixing a hydrophobic modifier, a reaction solvent and a low surface tension solvent according to a volume ratio of 1-3:0.5-1.5:7-10.
In a preferred implementation manner of the first aspect of the embodiment of the present application, the hydrophobic modifier is any one of trimethylchlorosilane, hexamethyldisilazane, hexamethyldisiloxane, methyltrimethoxysilane;
and the reaction solvent is any one of n-hexane, n-pentane, acetone and ethanol;
And the low surface tension solvent is any one of n-heptane, isopropanol, tertiary butanol and glycerin.
According to a second aspect of the embodiment of the application, the ultra-low density silica aerogel block prepared by the preparation method according to the first aspect has a density of less than 0.20g/cm 3, a hydrophobic angle of more than 139 degrees and a compression strength of 80-200KPa.
Compared with the prior art, the embodiment of the application has the advantages or beneficial effects that at least the advantages or beneficial effects comprise:
According to the preparation method of the ultralow-density silica aerogel block, formamide and ethylene glycol are added into a precursor solution containing sodium silicate to react to obtain silica sol, the silica sol is subjected to polycondensation reaction to form wet gel, and the wet gel is subjected to solvent replacement and surface modification and then is dried at normal pressure, so that the ultralow-density silica aerogel block can be prepared. In view of the above, the preparation method of the application does not need to remove sodium ions and other cations in the precursor solution through ion exchange resin, simplifies the preparation process, reduces the preparation cost and is more beneficial to large-scale production; on the other hand, no alkali catalyst is needed to be added, and a large amount of ceramic fiber reinforced aerogel structures are not needed, so that the material consumption is effectively saved, the preparation process is further simplified, and the preparation cost is further reduced; the third aspect is that the preparation method of the application can effectively improve the forming property and physical property of the silica aerogel block, thereby reducing the density to below 0.20g/cm 3 and improving the water contact angle to above 139 degrees.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required to be used in the description of the embodiments will be briefly described below. It is obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained from these drawings without inventive effort for a person of ordinary skill in the art.
FIG. 1 is a physical view of an ultra-low density silica aerogel monolith SPL1 prepared in example 1;
FIG. 2 is a scanning electron microscope image of an ultra-low density silica aerogel monolith SPL1 prepared in example 1;
FIG. 3 is a compression-strain diagram of an ultra-low density silica aerogel monolith SPL1 prepared in example 2;
FIG. 4 is a physical view of an ultra-low density silica aerogel monolith SPL2 prepared in example 2;
FIG. 5 is a scanning electron microscope image of an ultra-low density silica aerogel monolith SPL2 prepared in example 2;
FIG. 6 is a physical view of an ultra-low density silica aerogel monolith SPL3 prepared in example 3;
FIG. 7 is a scanning electron microscope image of an ultra-low density silica aerogel monolith SPL3 prepared in example 3;
FIG. 8 is a physical view of an ultra-low density silica aerogel monolith SPL4 prepared in example 4;
FIG. 9 is a scanning electron microscope image of an ultra-low density silica aerogel monolith SPL4 prepared in example 4;
FIG. 10 is a physical diagram of silica aerogel CSPL1 prepared in comparative example 1;
FIG. 11 is a physical diagram of silica aerogel CSPL2 prepared by comparative example 2.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. It will be apparent that the described embodiments are some, but not all, embodiments of the application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
In the following description of the present embodiment, the term "and/or" is used to describe an association relationship of association objects, which means that three relationships may exist, for example, a and/or B may mean: a alone, B alone and both a and B. Wherein A, B may be singular or plural. The character "/" generally indicates that the context-dependent object is an "or" relationship.
In the following description of the present embodiments, the term "at least one" means one or more, and "a plurality" means two or more. "at least one of" or the like means any combination of these items, including any combination of single item(s) or plural items(s). For example, "at least one (individual) of a, b, or c," or "at least one (individual) of a, b, and c" may each represent: a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, wherein a, b, c may be single or multiple, respectively.
It should be understood by those skilled in the art that, in the following description of the present embodiment, the sequence number does not mean that the execution sequence is sequential, and some or all of the steps may be executed in parallel or sequentially, and the execution sequence of each process should be determined by its functions and inherent logic, and should not constitute any limitation on the implementation process of the embodiment of the present application.
The terminology used in the embodiments of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this application and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
In a first aspect, embodiments of the present application provide a method for preparing an ultra-low density silica aerogel block, the method comprising the following steps S101 to S104.
S101: preparing a precursor solution containing sodium silicate;
S102: adding formamide and ethylene glycol into the precursor solution for hydrolysis reaction to obtain silica sol;
s103: carrying out polycondensation reaction on the silica sol at the temperature of 35-65 ℃ to obtain wet gel;
S104: immersing the wet gel into an organic solvent for solvent replacement, and adding the wet gel into a mixed modifier for surface modification treatment after the solvent replacement is completed to obtain a modified wet gel;
S105: and (3) drying the modified wet gel step by step under the normal pressure condition to obtain the ultra-low density silica aerogel block.
On one hand, the preparation method of the embodiment of the application does not need to remove sodium ions and other cations in the precursor solution through ion exchange resin, simplifies the preparation process, reduces the preparation cost and is more beneficial to large-scale production; on the other hand, no alkali catalyst is needed to be added, and a large amount of ceramic fiber reinforced aerogel structures are not needed, so that the material consumption is effectively saved, the preparation process is further simplified, and the preparation cost is further reduced; the third aspect is that the preparation method of the application can effectively improve the physical properties of the silica aerogel block, thereby reducing the density to 0.05-0.2g/cm 3 and increasing the water contact angle to 145-165 degrees.
The embodiment of the application also provides a preparation method of the precursor solution containing sodium silicate, which specifically comprises the following steps: mixing industrial water glass with water according to the volume ratio of 1:1-7 to obtain a precursor solution, wherein the concentration of the industrial water glass is 30-50%, and the modulus is 1.5-3.5.
The embodiment of the application takes the cheap industrial water glass as a silicon source, so that the preparation cost is greatly reduced, and the industrial production and the market application of the silicon dioxide aerogel are facilitated; meanwhile, in order to avoid introducing other cationic impurities, the solvent in the precursor solution is preferably deionized water.
In the embodiment of the application, when the formamide and the ethylene glycol are added, the molar ratio of the sodium silicate to the formamide to the ethylene glycol is 1:1-6:0.5-3.
In the embodiment of the application, formamide is used as a catalyst and is mainly used for regulating the pH value of a precursor solution; ethylene glycol is used as a drying control agent, and is mainly used for reducing capillary force and increasing pore diameter, so that the structure of the gel is kept complete when the gel is dried. Meanwhile, the molar ratio of sodium silicate to formamide to glycol is controlled to be 1:1-6:0.5-3, so that the pH of the solution is controlled to be 10-10.8, the gel is facilitated, the mixing of impurities in the gel process is reduced, and the purity effect of the gel is improved.
In the embodiment of the application, the temperature for carrying out the polycondensation reaction is preferably 35-90 ℃, and the time is preferably 15-120min.
The embodiment of the application controls the temperature of the polycondensation reaction to be 35-90 ℃, can properly accelerate and keep the hydrolysis speed of the formamide stable, and prevents rapid pH change of the solution caused by too fast hydrolysis of the formamide, thereby playing a role in ensuring uniform gel structure.
In the embodiment of the present application, the solvent for performing the solvent replacement is preferably any one of n-hexane, ethanol, isopropanol, and methanol.
It should be noted that the main function of the solvent replacement in the embodiment of the application is to replace the solvent water with larger surface tension in the wet gel skeleton with the organic solvent with smaller surface tension, thereby ensuring that the gel skeleton will not collapse and the integrity of the gel structure is maintained during the subsequent normal pressure drying.
In the embodiment of the application, the temperature for carrying out solvent replacement is preferably 45-65 ℃ and the time is preferably 24-72h.
It should be noted that, the solvent replacement is performed at the temperature of 45-65 ℃, which is helpful for promoting the solvent replacement reaction, and can prevent the solvent volatilization from influencing the replacement effect due to the overhigh temperature, and can stabilize the replacement reaction and prevent the gel structure from being damaged due to strong replacement; in addition, the replacement time is controlled to be 24-72h, so that the water in the gel gaps can be completely replaced.
In the embodiment of the application, the mixed modifier is formed by mixing a hydrophobic modifier, a reaction solvent and a low surface tension solvent according to the volume ratio of 1-3:0.5-1.5:7-10.
The main function of the hydrophobic modifier is to replace hydrophilic group-hydroxyl group on the surface of wet gel with hydrophobic group-methyl, so that the wet gel has hydrophobic property; the main function of the reaction solvent is to convey the hydrophobic modifier into the wet gel; the main function of the low surface tension solvent is to slow down the reaction speed of the hydrophobic modifier and prevent the severe reaction of the hydrophobic modifier from damaging the gel structure.
In the embodiment of the application, the hydrophobic modifier is any one of trimethylchlorosilane, hexamethyldisilazane, hexamethyldisiloxane and methyltrimethoxysilane; the reaction solvent is any one of n-hexane, n-pentane, acetone and ethanol; the low surface tension solvent is any one of n-heptane, isopropanol, tertiary butanol and glycerin.
In the embodiment of the application, the step-by-step drying is divided into four stages, and the four stages are as follows:
the first stage is drying at 30-50deg.C for 1-3 hr;
The second stage is drying at 60-90deg.C for 1-3h;
the third stage is drying at 100-130deg.C for 1-3h;
the fourth stage is drying at 150-190 deg.C for 1-3h.
In the embodiment of the application, the modified wet gel is dried step by step under the normal pressure condition, so that the liquid in the holes of the modified wet gel is completely volatilized, the drying is ensured to be sufficient, collapse caused by severe shrinkage of the framework in the drying process is reduced, and the formability of the aerogel block is ensured, so that the aerogel block with the diameter size of 3-5cm and the shape of a regular cylinder or cube is obtained.
In summary, the preparation method of the ultralow-density silica aerogel block provided in the first aspect of the embodiment of the present application at least includes:
1) When water glass is used as a silicon source to prepare wet gel, the application firstly provides a technical thought of using formamide as a catalyst and a drying control agent, on one hand, the process of ion exchange resin and acid/alkali catalysis which are necessary when the conventional water glass is used as the silicon source to prepare aerogel is omitted, the rapid preparation of sol-gel is realized by a one-step method, the process is greatly simplified, the preparation cost is reduced, and the method is more environment-friendly; on the other hand, the regular silica aerogel block is directly prepared, which is beneficial to the market application of the aerogel.
2) According to the preparation method provided by the embodiment of the application, the cheap water glass can be used as a silicon source, sol-gel is completed by a one-step method to prepare wet gel, and after organic solvent replacement and surface group modification, the ultra-low density silica aerogel block can be prepared by normal pressure drying, so that the preparation process is simplified, the material cost is reduced, the use of supercritical drying equipment is avoided, the preparation cost is further reduced, and the industrialized production and market application of the aerogel are facilitated.
In a second aspect, the embodiment of the application provides the ultra-low density silica aerogel block prepared by the preparation method, and the preparation method can effectively improve the forming performance and physical performance of the silica aerogel block, so that the density of the silica aerogel block is less than 0.20g/cm 3, the water contact angle is more than 139 degrees, and the compression strength is controlled at 80-200KPa; meanwhile, the diameter of the silica aerogel block is stable (3-5 cm), and the silica aerogel block is a regular cylinder or cube block, and is easier to directly apply to the fields of heat insulation, adsorption and the like than aerogel powder.
The technical scheme of the application will be further described in connection with specific embodiments.
Example 1
This example 1 provides a method for preparing an ultra-low density silica aerogel monolith SPL1, specifically comprising the following steps S101 to S105.
S101: mixing industrial water glass (with the concentration of 42%, the mass ratio of solution substances of n (Na 2O):n(SiO2) =1:2.31) and deionized water according to the volume ratio of 1:4, and uniformly mixing to obtain a precursor solution containing sodium silicate.
S102: and (3) adding formamide and ethylene glycol into the precursor solution prepared in the step (S101), and performing hydrolysis reaction at room temperature to obtain silica sol. Wherein, the addition amount of the formamide and the ethylene glycol is metered by the molar ratio of sodium silicate to the formamide and the ethylene glycol being 1:3:1.
S103: and (3) placing the silica sol prepared in the step (S102) in a constant-temperature water bath, and performing polycondensation reaction at the temperature of 45 ℃ for 90min to obtain wet gel.
S104: immersing the wet gel prepared in the step S103 into ethanol, and performing solvent replacement in a constant-temperature water bath kettle at 45 ℃ for 48 hours; after the solvent replacement is completed, the wet gel is soaked in the mixed modifier, and the surface modification treatment is carried out in a constant-temperature water bath kettle at 45 ℃ for 12 hours, so as to obtain the modified wet gel. Wherein the mixed modifier is formed by mixing trimethylchlorosilane, n-hexane and n-heptane according to the volume ratio of 1:1:9.
S105: and (3) drying the modified wet gel prepared in the step (S104) step by step under normal pressure to obtain the ultra-low density silica aerogel block SPL1. The four stages of gradual drying are at 40 ℃, 70 ℃,120 ℃ and 180 ℃ in sequence, and the drying time of each stage is 2 hours.
Example 2
This example 2 provides a method for preparing ultra-low density silica aerogel monolith SPL2, specifically comprising the following steps S101 to S105.
S101: mixing industrial water glass (with the concentration of 42%, the mass ratio of solution substances of n (Na 2O):n(SiO2) =1:2.31) and deionized water according to the volume ratio of 1:4, and uniformly mixing to obtain a precursor solution containing sodium silicate.
S102: and (3) adding formamide and ethylene glycol into the precursor solution prepared in the step (S101), and performing hydrolysis reaction at room temperature to obtain silica sol. Wherein, the addition amount of the formamide and the ethylene glycol is metered by the molar ratio of sodium silicate to the formamide and the ethylene glycol being 1:2:1.
S103: and (3) placing the silica sol prepared in the step (S102) in a constant-temperature water bath, and performing polycondensation reaction at the temperature of 65 ℃ for 50min to obtain wet gel.
S104: immersing the wet gel prepared in the step S103 into isopropanol, and performing solvent replacement in a constant-temperature water bath kettle at 45 ℃ for 48 hours; after the solvent replacement is completed, the wet gel is soaked in the mixed modifier, and the surface modification treatment is carried out in a constant-temperature water bath kettle at 45 ℃ for 12 hours, so as to obtain the modified wet gel. Wherein, the mixed modifier is formed by mixing hexamethyldisiloxane, n-pentane and tertiary butanol according to the volume ratio of 1:2:8.
S105: and (3) drying the modified wet gel prepared in the step (S104) step by step under normal pressure to obtain the ultra-low density silica aerogel block SPL2. The four stages of gradual drying are at 40 ℃, 60 ℃, 100 ℃ and 150 ℃ in sequence, and the drying time of each stage is 2 hours.
Example 3
This example 3 provides a method for preparing ultra-low density silica aerogel monolith SPL3, specifically comprising the following steps S101 to S105.
S101: mixing industrial water glass (with the concentration of 42%, the mass ratio of solution substances of n (Na 2O):n(SiO2) =1:2.31) and deionized water according to the volume ratio of 1:3, and uniformly mixing to obtain a precursor solution containing sodium silicate.
S102: and (3) adding formamide and ethylene glycol into the precursor solution prepared in the step (S101), and performing hydrolysis reaction at room temperature to obtain silica sol. Wherein, the addition amount of the formamide and the ethylene glycol is metered by the molar ratio of sodium silicate to the formamide and the ethylene glycol being 1:3:1.
S103: and (3) placing the silica sol prepared in the step (S102) in a constant-temperature water bath, and performing polycondensation reaction at the temperature of 55 ℃ for 70min to obtain wet gel.
S104: immersing the wet gel prepared in the step S103 into n-hexane, and performing solvent replacement in a constant-temperature water bath kettle at 55 ℃ for 48 hours; after the solvent replacement is completed, the wet gel is soaked in the mixed modifier, and the surface modification treatment is carried out in a constant-temperature water bath kettle at 50 ℃ for 12 hours, so as to obtain the modified wet gel. Wherein the mixed modifier is formed by mixing trimethylchlorosilane, n-hexane and glycerin according to a volume ratio of 2:1:8.
S105: and (3) drying the modified wet gel prepared in the step (S104) step by step under normal pressure to obtain the ultra-low density silica aerogel block SPL3. The four stages of gradual drying are at 40 ℃, 60 ℃,120 ℃ and 180 ℃ in sequence, and the drying time of each stage is 2 hours.
Example 4
The present embodiment 4 provides a method for preparing an ultra-low density silica aerogel block SPL4, specifically comprising the following steps S101 to S105.
S101: mixing industrial water glass (with the concentration of 42%, the mass ratio of solution substances of n (Na 2O):n(SiO2) =1:2.31) and deionized water according to the volume ratio of 1:5, and uniformly mixing to obtain a precursor solution containing sodium silicate.
S102: and (3) adding formamide and ethylene glycol into the precursor solution prepared in the step (S101), and performing hydrolysis reaction at room temperature to obtain silica sol. Wherein, the addition amount of the formamide and the ethylene glycol is metered by the molar ratio of sodium silicate to the formamide and the ethylene glycol being 1:3:1.
S103: and (3) placing the silica sol prepared in the step (S102) in a constant-temperature water bath, and performing polycondensation reaction at the temperature of 35 ℃ for 120min to obtain wet gel.
S104: immersing the wet gel prepared in the step S103 into ethanol, and performing solvent replacement in a constant-temperature water bath kettle at 55 ℃ for 48 hours; after the solvent replacement is completed, the wet gel is soaked in the mixed modifier, and the surface modification treatment is carried out in a constant-temperature water bath kettle at 45 ℃ for 12 hours, so as to obtain the modified wet gel. Wherein, the mixed modifier is formed by mixing hexamethyldisilazane, ethanol and tertiary butanol according to the volume ratio of 1:1:9.
S105: and (3) drying the modified wet gel prepared in the step (S104) step by step under normal pressure to obtain the ultra-low density silica aerogel block SPL4. The four stages of gradual drying are sequentially carried out at 60 ℃, 80 ℃,120 ℃ and 180 ℃ and the drying time of each stage is 3 hours.
The ultra-low density silica aerogel blocks SPL1-SPL4 prepared in this example 1-4 were characterized for physical properties and the results are shown in table 1 below.
TABLE 1 physical Properties of ultra Low Density silica aerogel blocks
As can be seen from Table 1, the silica aerogel blocks prepared by the preparation method of the embodiment of the application have extremely low density which is less than or equal to 0.12g/cm 3; the volume shrinkage is not obvious in the heat treatment process, and the volume shrinkage rate is 7.2-9.0%; the porous ceramic material has larger porosity with the porosity of 94-96%, and provides a foundation for the application of the porous ceramic material in the adsorption field; has excellent hydrophobic performance, and the contact angle is more than 139 degrees; and good formability (diameter 3.7-4.1 cm).
Meanwhile, the ultra-low density silica aerogel blocks SPL1-SPL4 were characterized, and the results are shown in fig. 1 to 9. FIG. 1 is a pictorial view of an ultra low density silica aerogel monolith SPL 1; FIG. 2 is a scanning electron microscope image of an ultra-low density silica aerogel monolith SPL 1; FIG. 3 is a compression-strain diagram of an ultra-low density silica aerogel monolith SPL 1; FIG. 4 is a pictorial view of an ultra low density silica aerogel monolith SPL 2; FIG. 5 is a scanning electron microscope image of an ultra-low density silica aerogel monolith SPL 2; FIG. 6 is a pictorial view of an ultra low density silica aerogel monolith SPL 3; FIG. 7 is a scanning electron microscope image of an ultra-low density silica aerogel monolith SPL 3; FIG. 8 is a pictorial view of an ultra low density silica aerogel monolith SPL 4; FIG. 9 is a scanning electron microscope image of an ultra-low density silica aerogel monolith SPL 4.
As can be seen from fig. 1, 4, 6 and 8: the silica aerogel block is a cylinder with a regular shape, and the surface of the silica aerogel block has no crack, which indicates that the preparation method of the application can improve the forming performance of the silica aerogel block.
As can be seen from fig. 2, 5, 7 and 9: the silica aerogel block prepared by the method has a classical three-dimensional network structure of the aerogel, and accords with microscopic characteristics of the aerogel.
As can be seen from fig. 3: the aerogel block prepared by the method has the critical strain of 25%, the ultimate stress of 80KPa and good compression resistance.
In addition, comparative example 1 and comparative example 2 are also provided in this example. Wherein, comparative example 1 adds an acid catalyst to the finished sol-gel; comparative example 2a base catalyst was added to the finished sol-gel, and the other steps and process parameters were the same as in example 1, specifically as follows:
Comparative example 1
Comparative example 1 provides a method for preparing silica aerogel cscl 1, specifically comprising the following steps S101 to S105.
S101: mixing industrial water glass (with the concentration of 42%, the mass ratio of solution substances of n (Na 2O):n(SiO2) =1:2.31) and deionized water according to the volume ratio of 1:4, and uniformly mixing to obtain a precursor solution containing sodium silicate.
S102: and (3) adding formamide and ethylene glycol into the precursor solution prepared in the step (S101), and performing hydrolysis reaction at room temperature to obtain silica sol. Wherein, the addition amount of the formamide and the ethylene glycol is metered by the molar ratio of sodium silicate to the formamide and the ethylene glycol being 1:3:1.
S103: to the silica sol prepared in step S102, a hydrochloric acid solution of 3mol·l -1 was added dropwise thereto to adjust ph=10.8, followed by placing in a thermostatic water bath, and polycondensation reaction at 45 ℃ for 90min, to obtain a wet gel.
S104: immersing the wet gel prepared in the step S103 into ethanol, and performing solvent replacement in a constant-temperature water bath kettle at 45 ℃ for 48 hours; after the solvent replacement is completed, the wet gel is soaked in the mixed modifier, and the surface modification treatment is carried out in a constant-temperature water bath kettle at 45 ℃ for 12 hours, so as to obtain the modified wet gel. Wherein the mixed modifier is formed by mixing trimethylchlorosilane, n-hexane and n-heptane according to the volume ratio of 1:1:9.
S105: and (3) drying the modified wet gel prepared in the step (S104) step by step under normal pressure to obtain the silica aerogel CSPL1. The four stages of gradual drying are at 40 ℃, 70 ℃, 120 ℃ and 180 ℃ in sequence, and the drying time of each stage is 2 hours.
Comparative example 2
Comparative example 2 provides a method for preparing silica aerogel cscl 2, specifically comprising the following steps S101 to S105.
S101: mixing industrial water glass (with the concentration of 42%, the mass ratio of solution substances of n (Na 2O):n(SiO2) =1:2.31) and deionized water according to the volume ratio of 1:4, and uniformly mixing to obtain a precursor solution containing sodium silicate.
S102: and (3) adding formamide and ethylene glycol into the precursor solution prepared in the step (S101), and performing hydrolysis reaction at room temperature to obtain silica sol. Wherein, the addition amount of the formamide and the ethylene glycol is metered by the molar ratio of sodium silicate to the formamide and the ethylene glycol being 1:3:1.
S103: to the silica sol prepared in step S102, an aqueous ammonia solution of 1mol·l -1 was added dropwise thereto to adjust ph=6.5, followed by placing in a thermostatic water bath, and polycondensation reaction at 45 ℃ for 90min, to obtain a wet gel.
S104: immersing the wet gel prepared in the step S103 into ethanol, and performing solvent replacement in a constant-temperature water bath kettle at 45 ℃ for 48 hours; after the solvent replacement is completed, the wet gel is soaked in the mixed modifier, and the surface modification treatment is carried out in a constant-temperature water bath kettle at 45 ℃ for 12 hours, so as to obtain the modified wet gel. Wherein the mixed modifier is formed by mixing trimethylchlorosilane, n-hexane and n-heptane according to the volume ratio of 1:1:9.
S105: and (3) drying the modified wet gel prepared in the step (S104) step by step under normal pressure to obtain a silica aerogel block CSPL2. The four stages of gradual drying are at 40 ℃, 70 ℃,120 ℃ and 180 ℃ in sequence, and the drying time of each stage is 2 hours.
The silica aerogels cscl 1, cscl 2 prepared in comparative examples 1and2 were subjected to performance characterization, and the results are shown in fig. 10 to 11. Wherein, fig. 10 is a physical diagram of silica aerogel CSPL 1; fig. 11 is a physical diagram of silica aerogel CSPL 2.
As can be seen from fig. 10: the silica aerogel CSPL1 is powder, so that the application of the silica aerogel CSPL1 is greatly limited, and the silica aerogel powder is obtained by carrying out acid catalysis in the finished sol-gel to change the aerogel structure;
As can be seen from fig. 11: the silica aerogel CSPL2 is a disintegrated block, cannot form a regular geometric block, greatly limits the application of the silica aerogel CSPL2, and indicates that the aerogel cannot maintain the integral structure due to the fact that the aerogel is subjected to acid catalysis in the finished sol-gel, and disintegrates after the drying is finished.
Various embodiments in this specification are described in an incremental manner, and identical or similar parts of the various embodiments are referred to each other, with each embodiment focusing on differences from the other embodiments.
The above embodiments are only for illustrating the technical solution of the present application, and not for limiting the present application; although the application has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced with equivalents; such modifications and substitutions do not depart from the spirit of the application.
Claims (6)
1. The preparation method of the ultra-low density silica aerogel block is characterized by comprising the following steps of:
s101: preparing a precursor solution containing sodium silicate;
S102: adding formamide and ethylene glycol into the precursor solution for hydrolysis reaction to obtain silica sol, wherein the addition of the formamide and the ethylene glycol is metered by the molar ratio of sodium silicate to the formamide to the ethylene glycol being 1:3:1;
S103: carrying out polycondensation reaction on the silica sol at the temperature of 35-65 ℃ for 50-120min to obtain wet gel;
S104: immersing the wet gel into an organic solvent for solvent replacement, and adding the wet gel into a mixed modifier for surface modification treatment after the solvent replacement is finished to obtain a modified wet gel, wherein the temperature for solvent replacement is 45-65 ℃ and the time is 24-72h;
S105: step-by-step drying the modified wet gel under normal pressure to obtain an ultralow-density silica aerogel block, wherein the compressive strength of the ultralow-density silica aerogel block is 80-200KPa;
The step-by-step drying is divided into four stages, and the four stages are as follows:
the first stage is drying at 30-50deg.C for 1-3h;
the second stage is drying at 60-90deg.C for 1-3h;
The third stage is drying at 100-130deg.C for 1-3h;
The fourth stage is drying at 150-190 ℃ for 1-3h.
2. The method of preparing a precursor solution comprising sodium silicate according to claim 1, wherein the method of preparing a precursor solution comprising sodium silicate comprises:
Mixing industrial water glass with water according to the volume ratio of 1:1-7 to obtain a precursor solution, wherein the concentration of the industrial water glass is 30-50%, and the modulus is 1.5-3.5.
3. The method according to claim 1, wherein the solvent used for the solvent substitution is any one of n-hexane, ethanol, isopropanol, and methanol.
4. The preparation method according to claim 1, wherein the mixed modifier is formed by mixing a hydrophobic modifier, a reaction solvent and a low surface tension solvent in a volume ratio of 1-3:0.5-1.5:7-10.
5. The preparation method according to claim 4, wherein the hydrophobic modifier is any one of trimethylchlorosilane, hexamethyldisilazane, hexamethyldisiloxane, methyltrimethoxysilane;
and the reaction solvent is any one of n-hexane, n-pentane, acetone and ethanol;
And the low surface tension solvent is any one of n-heptane, isopropanol, tertiary butanol and glycerin.
6. An ultra-low density silica aerogel block prepared according to any one of claims 1-5, wherein the ultra-low density silica aerogel block has a density of < 0.20g/cm 3 and a hydrophobic angle of > 139 °.
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