CN117487255B - Heat-insulating flame-retardant boron nitride-based aerogel and preparation method thereof - Google Patents
Heat-insulating flame-retardant boron nitride-based aerogel and preparation method thereof Download PDFInfo
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- PZNSFCLAULLKQX-UHFFFAOYSA-N Boron nitride Chemical compound N#B PZNSFCLAULLKQX-UHFFFAOYSA-N 0.000 title claims abstract description 206
- 229910052582 BN Inorganic materials 0.000 title claims abstract description 167
- 239000004964 aerogel Substances 0.000 title claims abstract description 117
- RNFJDJUURJAICM-UHFFFAOYSA-N 2,2,4,4,6,6-hexaphenoxy-1,3,5-triaza-2$l^{5},4$l^{5},6$l^{5}-triphosphacyclohexa-1,3,5-triene Chemical compound N=1P(OC=2C=CC=CC=2)(OC=2C=CC=CC=2)=NP(OC=2C=CC=CC=2)(OC=2C=CC=CC=2)=NP=1(OC=1C=CC=CC=1)OC1=CC=CC=C1 RNFJDJUURJAICM-UHFFFAOYSA-N 0.000 title claims abstract description 90
- 239000003063 flame retardant Substances 0.000 title claims abstract description 90
- 238000002360 preparation method Methods 0.000 title claims abstract description 42
- 239000000945 filler Substances 0.000 claims abstract description 96
- 238000009413 insulation Methods 0.000 claims abstract description 83
- 239000012670 alkaline solution Substances 0.000 claims abstract description 29
- 239000012266 salt solution Substances 0.000 claims abstract description 29
- 239000000843 powder Substances 0.000 claims abstract description 28
- 239000002121 nanofiber Substances 0.000 claims abstract description 24
- 238000002156 mixing Methods 0.000 claims abstract description 23
- 238000003756 stirring Methods 0.000 claims abstract description 23
- 238000001027 hydrothermal synthesis Methods 0.000 claims abstract description 22
- 238000000034 method Methods 0.000 claims abstract description 18
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 14
- -1 aluminum ions Chemical class 0.000 claims abstract description 14
- 238000004108 freeze drying Methods 0.000 claims abstract description 14
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 48
- 229920001661 Chitosan Polymers 0.000 claims description 45
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 claims description 42
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 claims description 29
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 29
- 239000003054 catalyst Substances 0.000 claims description 27
- 229910052796 boron Inorganic materials 0.000 claims description 24
- 229910052757 nitrogen Inorganic materials 0.000 claims description 24
- 239000000243 solution Substances 0.000 claims description 24
- 238000006243 chemical reaction Methods 0.000 claims description 23
- WNROFYMDJYEPJX-UHFFFAOYSA-K aluminium hydroxide Chemical compound [OH-].[OH-].[OH-].[Al+3] WNROFYMDJYEPJX-UHFFFAOYSA-K 0.000 claims description 22
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 18
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 18
- 229910052760 oxygen Inorganic materials 0.000 claims description 18
- 239000001301 oxygen Substances 0.000 claims description 18
- NWZSZGALRFJKBT-KNIFDHDWSA-N (2s)-2,6-diaminohexanoic acid;(2s)-2-hydroxybutanedioic acid Chemical compound OC(=O)[C@@H](O)CC(O)=O.NCCCC[C@H](N)C(O)=O NWZSZGALRFJKBT-KNIFDHDWSA-N 0.000 claims description 15
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 claims description 15
- IKDUDTNKRLTJSI-UHFFFAOYSA-N hydrazine monohydrate Substances O.NN IKDUDTNKRLTJSI-UHFFFAOYSA-N 0.000 claims description 15
- 239000002904 solvent Substances 0.000 claims description 15
- 239000003431 cross linking reagent Substances 0.000 claims description 14
- 239000008367 deionised water Substances 0.000 claims description 14
- 229910021641 deionized water Inorganic materials 0.000 claims description 14
- 238000001035 drying Methods 0.000 claims description 14
- 150000004767 nitrides Chemical class 0.000 claims description 14
- 238000005406 washing Methods 0.000 claims description 14
- 238000001816 cooling Methods 0.000 claims description 13
- VSCWAEJMTAWNJL-UHFFFAOYSA-K aluminium trichloride Chemical compound Cl[Al](Cl)Cl VSCWAEJMTAWNJL-UHFFFAOYSA-K 0.000 claims description 12
- 239000002994 raw material Substances 0.000 claims description 10
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonia chloride Chemical compound [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 claims description 8
- 238000010438 heat treatment Methods 0.000 claims description 8
- 239000012535 impurity Substances 0.000 claims description 8
- 229910001220 stainless steel Inorganic materials 0.000 claims description 8
- 239000010935 stainless steel Substances 0.000 claims description 8
- SXRSQZLOMIGNAQ-UHFFFAOYSA-N Glutaraldehyde Chemical compound O=CCCCC=O SXRSQZLOMIGNAQ-UHFFFAOYSA-N 0.000 claims description 7
- BFNBIHQBYMNNAN-UHFFFAOYSA-N ammonium sulfate Chemical compound N.N.OS(O)(=O)=O BFNBIHQBYMNNAN-UHFFFAOYSA-N 0.000 claims description 7
- 229910052921 ammonium sulfate Inorganic materials 0.000 claims description 7
- 235000011130 ammonium sulphate Nutrition 0.000 claims description 7
- 238000003760 magnetic stirring Methods 0.000 claims description 7
- BNGXYYYYKUGPPF-UHFFFAOYSA-M (3-methylphenyl)methyl-triphenylphosphanium;chloride Chemical compound [Cl-].CC1=CC=CC(C[P+](C=2C=CC=CC=2)(C=2C=CC=CC=2)C=2C=CC=CC=2)=C1 BNGXYYYYKUGPPF-UHFFFAOYSA-M 0.000 claims description 5
- DIZPMCHEQGEION-UHFFFAOYSA-H aluminium sulfate (anhydrous) Chemical compound [Al+3].[Al+3].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O DIZPMCHEQGEION-UHFFFAOYSA-H 0.000 claims description 4
- 235000019270 ammonium chloride Nutrition 0.000 claims description 4
- 239000004327 boric acid Substances 0.000 claims description 4
- 229910052810 boron oxide Inorganic materials 0.000 claims description 4
- ILZSSCVGGYJLOG-UHFFFAOYSA-N cobaltocene Chemical compound [Co+2].C=1C=C[CH-]C=1.C=1C=C[CH-]C=1 ILZSSCVGGYJLOG-UHFFFAOYSA-N 0.000 claims description 4
- JKWMSGQKBLHBQQ-UHFFFAOYSA-N diboron trioxide Chemical compound O=BOB=O JKWMSGQKBLHBQQ-UHFFFAOYSA-N 0.000 claims description 4
- KTWOOEGAPBSYNW-UHFFFAOYSA-N ferrocene Chemical compound [Fe+2].C=1C=C[CH-]C=1.C=1C=C[CH-]C=1 KTWOOEGAPBSYNW-UHFFFAOYSA-N 0.000 claims description 4
- KGBXLFKZBHKPEV-UHFFFAOYSA-N boric acid Chemical compound OB(O)O KGBXLFKZBHKPEV-UHFFFAOYSA-N 0.000 claims description 3
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims description 2
- 229910052759 nickel Inorganic materials 0.000 claims description 2
- 239000000463 material Substances 0.000 abstract description 15
- 239000002070 nanowire Substances 0.000 abstract description 5
- 230000000052 comparative effect Effects 0.000 description 9
- 230000008901 benefit Effects 0.000 description 8
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- 239000000126 substance Substances 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- 239000004005 microsphere Substances 0.000 description 3
- 239000002127 nanobelt Substances 0.000 description 3
- 239000011148 porous material Substances 0.000 description 3
- 230000035484 reaction time Effects 0.000 description 3
- 230000009286 beneficial effect Effects 0.000 description 2
- 238000002485 combustion reaction Methods 0.000 description 2
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- 206010000369 Accident Diseases 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 230000000903 blocking effect Effects 0.000 description 1
- 125000005619 boric acid group Chemical group 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 229910010293 ceramic material Inorganic materials 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 230000001010 compromised effect Effects 0.000 description 1
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- 230000009977 dual effect Effects 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 230000017525 heat dissipation Effects 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 229910010272 inorganic material Inorganic materials 0.000 description 1
- 239000011147 inorganic material Substances 0.000 description 1
- 239000011810 insulating material Substances 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 229920005615 natural polymer Polymers 0.000 description 1
- QMMRZOWCJAIUJA-UHFFFAOYSA-L nickel dichloride Chemical compound Cl[Ni]Cl QMMRZOWCJAIUJA-UHFFFAOYSA-L 0.000 description 1
- 238000005121 nitriding Methods 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 238000004321 preservation Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- 238000002210 supercritical carbon dioxide drying Methods 0.000 description 1
- 238000005979 thermal decomposition reaction Methods 0.000 description 1
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Abstract
The invention belongs to the technical field of heat-insulating flame-retardant materials, and discloses a heat-insulating flame-retardant boron nitride-based aerogel and a preparation method thereof, wherein the boron nitride heat-insulating filler comprises nanofibers and hollow spheres, the diameters of the nanofibers are respectively 40-90 nm, and the lengths of the nanowires are 40-90 mu m; the diameter of the hollow sphere is also 40-90 nm, and the porosity of the aerogel is 75-90%. The method for preparing the boron nitride based aerogel comprises the following steps: firstly preparing nano boron nitride heat insulation filler by adopting a hydrothermal method, stirring and mixing the nano boron nitride heat insulation filler with an alkaline solution, stirring and mixing the nano boron nitride heat insulation filler with a salt solution containing aluminum ions to obtain boron nitride heat insulation filler-aluminum hydroxide flame retardant powder, and finally preparing the boron nitride-based aerogel by adopting a freeze drying method. The boron nitride-based aerogel has good heat insulation, flame retardance and mechanical properties, and the preparation method is simple to operate and high in efficiency, and has a wide application prospect.
Description
Technical Field
The invention relates to the field of heat-insulating flame-retardant materials, in particular to heat-insulating flame-retardant boron nitride-based aerogel and a preparation method thereof.
Background
Fire safety has been a focus of attention in modern society. In fire accidents, heat-insulating flame-retardant materials are one of the important factors for protecting the life and property safety of personnel. The heat-insulating flame-retardant material can effectively slow down the spread of fire and reduce the hazard degree of fire. Therefore, developing materials with excellent heat insulation and flame retardance has important significance for improving the performance and application range of fire-fighting equipment.
The heat-insulating flame-retardant material has the advantages of light weight, high strength, low heat conductivity coefficient and the like, and can keep good stability at high temperature. With the increasing importance of people on safety performance, the demand of heat-insulating flame-retardant materials is also increasing. Aerogel is a heat insulating flame retardant material of great interest in recent years. Aerogel is a gel with a three-dimensional network structure, has abundant internal holes and has very high specific surface area and porosity. Because of its unique structure and excellent properties, aerogels exhibit excellent properties in the fields of thermal insulation, heat preservation, flame retardance, and the like.
Boron nitride is a compound of the formula BN and has a number of unique characteristics that make it an important fire fighting material. Firstly, boron nitride has extremely high thermal stability, so that the boron nitride has good thermal stability in a high-temperature environment. In addition, boron nitride has excellent chemical stability and corrosion resistance, and can be used in many corrosive environments. These features have led to widespread use of boron nitride in many fields, such as fire protection, ceramic materials, cutting tools, electronics, and the like. Boron nitride based aerogel is a material made of boron nitride with a highly porous structure. It has extremely low density and excellent heat insulating performance, and is one excellent heat insulating material. The pore structure of the aerogel can effectively reduce heat conduction and heat radiation, thereby reducing heat transfer. In addition, the boron nitride-based aerogel has excellent flame retardant property, can inhibit flame spread and provides good flame retardant effect. However, the boron nitride based aerogel has the following problems: 1. the heat insulation and flame retardance of the boron nitride-based aerogel need to be further improved, for example, chinese patent publication No. CN110104619A discloses a boron nitride-based aerogel prepared by a template method and a supercritical CO 2 drying method, and the aerogel has high temperature resistance and high specific surface area, but no flame retardant is added, so that the flame retardance has certain limitation. 2. The mechanical properties of boron nitride based aerogels need to be improved. For example, chinese patent publication No. CN116715204a discloses a hollow microsphere aerogel of boron nitride, which is formed by mutually overlapping and assembling hollow microspheres of boron nitride to form a three-dimensional porous network structure, but only by mutually overlapping hollow microspheres, so that the mechanical properties including flexibility still need to be further improved. 3. The flame retardant performance of boron nitride needs to be further improved, for example, chinese patent publication No. CN109704296B discloses a flexible boron nitride nanobelt aerogel and a preparation method thereof, the aerogel flexible boron nitride nanobelt aerogel has a communicated three-dimensional porous network structure, and the blocking effect of the crossed aerogel nanobelts on oxygen and heat needs to be still enhanced. Therefore, the thermal insulation, flame retardance and mechanical properties of the boron nitride-based aerogel still need to be further improved at present so as to meet the thermal insulation and flame retardance requirements of more severe environments.
Disclosure of Invention
The invention aims to provide a heat-insulating flame-retardant boron nitride-based aerogel and a preparation method thereof, which solve the problem that the existing heat-insulating flame-retardant material has defects in heat insulation performance, flame retardance and mechanical property.
In order to achieve the above object, the present invention provides the following technical solutions:
The boron nitride aerogel is prepared from three components of boron nitride heat insulation filler, aluminum hydroxide flame retardant and chitosan gel, wherein the boron nitride heat insulation filler is characterized in that one or more of nanofibers and hollow spheres are mixed, the diameter of the nanofibers is 40-90 nm, the length of the nanofibers is 40-90 mu m, the diameter of the hollow spheres is 40-90 nm, the boron nitride is prepared from a boron source, a nitrogen source and a catalyst serving as raw materials through a hydrothermal reaction method, and the mass fractions of the boron nitride heat insulation filler, the aluminum hydroxide flame retardant and the chitosan gel are respectively (70-85%): (10-20 percent): (5-10%) and the aerogel has a porosity of 75-90%.
The preparation method of the aerogel comprises the following steps:
S1: preparing a nano boron nitride heat insulation filler: uniformly mixing a boron source, a nitrogen source and a catalyst as raw materials, using hydrazine hydrate as a solvent, obtaining nano boron nitride heat insulation filler through a hydrothermal method, and removing impurities through deionized water to obtain clean nano nitride heat insulation filler; the technological parameters of the hydrothermal method are as follows: taking a stainless steel reaction kettle as a container, wherein the preparation temperature is 350-550 ℃, the heating rate is 1-10 ℃/min, the reaction time is 5-24 h, the reaction pressure is 5-10 MPa, the mass fraction of the solvent hydrazine hydrate is 40-60%, and cooling along with a furnace after the reaction is completed;
S2: preparation of boron nitride heat insulation filler-aluminum hydroxide flame retardant powder: uniformly mixing the nano-nitride heat-insulating filler obtained in the step S1 and an alkaline solution through magnetic stirring, magnetically stirring for 1-3 hours in a water bath at 60-90 ℃, cooling to room temperature, washing and drying by deionized water to obtain the alkaline nano-boron nitride heat-insulating filler, magnetically stirring the alkaline nano-boron nitride heat-insulating filler and a salt solution containing aluminum ions for 1-3 hours in the water bath at room temperature, and washing and drying to finally obtain boron nitride heat-insulating filler-aluminum hydroxide flame retardant powder;
S3: preparation of boron nitride based aerogel: and (3) obtaining the boron nitride-based aerogel by a freeze drying method through the boron nitride heat insulation filler-aluminum hydroxide flame retardant powder obtained in the step (2).
Further, in the step S1, the boron source is one or more of amorphous boron powder, boron oxide and boric acid.
Further, in the step S1, the nitrogen source is one or more of ammonium chloride and ammonium sulfate.
Further, the catalyst in the step S1 is one or more of ferrocene, cobaltocene and nickel dichloride.
In addition, the molar ratio of the boron source to the nitrogen source to the catalyst in the step S1 is 1:1 (0-0.1).
Further, the preparation method of the heat-insulating flame-retardant boron nitride-based aerogel comprises the following technological parameters of a hydrothermal method in the step S1: the stainless steel reaction kettle is taken as a container, the preparation temperature is 350-550 ℃, the heating rate is 1-10 ℃/min, the reaction time is 5-24 h, the reaction pressure is 5-10 MPa, the mass fraction of the solvent hydrazine hydrate is 40-60%, and the reaction is cooled along with the furnace after the completion of the reaction.
In some embodiments, the boron nitride thermal insulation filler is characterized by a blend of one or more of nanofibers and hollow spheres, wherein the nanofibers have a diameter of 40-90 nm, a length of 40-90 μm, and the hollow spheres have a diameter of 40-90 nm.
In addition, the alkaline solution in the step S2 is one or more of sodium hydroxide and potassium hydroxide, the mass concentration of the alkaline solution is 1-10%, and the mass ratio of the nano nitride heat insulation filler to the alkaline solution is 1: (10-100).
In addition, the salt solution of aluminum ions in the step S2 is one or more of aluminum chloride, aluminum nitrate or aluminum sulfate, the concentration of the salt solution is 5-15%, and the mass ratio of the alkaline nano boron nitride thermal insulation layer filler to the salt solution is 1: (10-100).
Further, a preparation method of the heat-insulating flame-retardant boron nitride-based aerogel is provided, wherein the preparation method of the boron nitride-based aerogel in the step S3 comprises the following steps: firstly, uniformly mixing chitosan and 4% acetic acid to obtain a chitosan solution, wherein the mass ratio of the chitosan to the acetic acid is 1: (12-20), adding the boron nitride heat insulation filler-aluminum hydroxide flame retardant powder obtained in the step S2 into chitosan solution, and taking glutaraldehyde with the mass fraction of 2% as a cross-linking agent, wherein the mass ratio of the cross-linking agent to the chitosan solution is 1: (20-60), magnetically stirring for 1h at room temperature, and then freeze-drying for 24-72 h at-30 to-50 ℃ to obtain the boron nitride aerogel.
In some embodiments, the mass fractions of the boron nitride heat insulation filler, the aluminum hydroxide flame retardant and the chitosan gel are respectively (70-85%): (10-20 percent): (5-10%) and the aerogel has a porosity of 75-90%.
In some embodiments, the boron nitride based aerogel prepared in the step S3 has a thermal conductivity of 0.02-0.06W/(mK) at room temperature, a limiting oxygen index of 42-53.5%, and a compressive stress at 20% strain of 70-120 kPa.
The heat-insulating flame-retardant boron nitride-based aerogel disclosed by the invention has the main advantages that the design purpose of adopting boron nitride as a heat-insulating filler is that the nano boron nitride hollow sphere has low density, high strength, high specific surface area, thermal stability and excellent heat-insulating property, the density of the aerogel can be effectively reduced, the strength, the heat-insulating property and the stability of the aerogel are improved, and the adsorption and storage properties are enhanced. The nano nitriding tube has high specific surface area, high mechanical strength, high temperature resistance and flame retardance, and can increase the adsorption capacity, heat insulation, mechanical strength and safety of aerogel. The combination of the two can comprehensively improve the performance of the aerogel, form a multi-layer pore structure, form a multi-channel heat insulation path and provide better heat insulation performance and stability.
The heat-insulating flame-retardant boron nitride-based aerogel is also particularly limited to 70-85% by mass of the boron nitride heat-insulating filler, for example, 70%, 72%, 74%, 76%, 78%, 80%, 82% and 85% by mass of the heat-insulating filler, and when the mass fraction of the heat-insulating filler is too low, the performance and the effect of the aerogel can be influenced. First, the insulation performance is reduced because the content of boron nitride is reduced, thereby reducing the insulation ability of the aerogel. Second, strength and stability can also be affected because the reduction of the insulating filler can result in the aerogel being susceptible to damage or deformation from external forces. In addition, the high temperature resistance is also impaired because the content of boron nitride is insufficient to provide sufficient high temperature resistance. Finally, the fire resistance of the aerogel may be compromised and the fire resistance of the aerogel may be reduced, thereby increasing the risk of fire. Therefore, to ensure the performance and effect of the aerogel, the mass fraction of the insulating filler should be controlled between 70 and 85% to ensure that the aerogel contains sufficient boron nitride filler. Of course, appropriate adjustments and optimizations may also be made, depending on the particular requirements and application environment.
The heat-insulating flame-retardant boron nitride-based aerogel disclosed by the invention adopts aluminum hydroxide as a flame retardant, and has the following main advantages in design purposes: firstly, aluminum hydroxide has good flame retardant properties. Because aluminum hydroxide has a high melting point and a high thermal decomposition temperature, when the aerogel is exposed to a fire source, the aluminum hydroxide is decomposed to generate steam, so that the spread and combustion of flame are effectively inhibited. And secondly, the aluminum hydroxide has good thermal stability, and can exist stably in a room temperature environment without decomposing to lose flame retardant property. In addition, aluminum hydroxide has good physical and chemical properties, and is not easy to react with other components or generate harmful substances. By combining aluminum hydroxide with boron nitride aerogel, the advantages of the aluminum hydroxide and the boron nitride aerogel can be fully exerted, and the dual effects of flame retardance and heat insulation are realized. Finally, because aluminum hydroxide is an inorganic material widely applied, the heat-insulating flame-retardant boron nitride-based aerogel has the advantages of lower cost and easy acquisition, and has good application prospect and economic benefit. In conclusion, the heat-insulating flame-retardant boron nitride-based aerogel disclosed by the invention adopts aluminum hydroxide as a flame retardant, has the advantages of excellent flame retardant property, good thermal stability, good physical and chemical properties, low cost and the like, and is suitable for various flame-retardant heat-insulating application scenes.
The invention has at least the following beneficial effects:
1. Excellent heat insulation performance: the boron nitride-based aerogel adopts mixed filler of nano fiber and hollow sphere, has larger specific surface area and pore structure, can effectively block heat conduction and heat radiation, can obviously reduce heat transmission, and provides excellent heat insulation performance, thereby effectively saving energy and reducing energy consumption.
2. Better flame retardant capability: aluminum hydroxide is used as a flame retardant, and can effectively inhibit flame propagation and combustion. When contacting the high-temperature flame, the aluminum hydroxide can decompose to generate water vapor, thereby playing a role in extinguishing the flame and reducing the risk and hazard of fire. Therefore, the boron nitride-based aerogel adopting aluminum hydroxide as the flame retardant has excellent flame retardant property and can protect the substrate from being damaged by fire.
3. Better stability: the nano fiber and hollow sphere in the boron nitride heat insulation filler have different structural and performance characteristics. The nanofiber has higher specific surface area and length-diameter ratio, and can enhance the mechanical property and heat insulation property of the material; the hollow sphere has lower density and higher heat insulation performance, and the mixed structure enables the aerogel to have more excellent mechanical property and stability. In addition, the chitosan gel in the boron nitride-based aerogel can enhance the structural stability of the material and improve the compression resistance and deformation resistance of the material.
4. Green environmental protection characteristics: the use of boron nitride as the primary filler can reduce negative environmental impact. In addition, the chitosan gel used in the boron nitride-based aerogel is a natural polymer which can be biodegraded, and does not pollute the environment. The aerogel has good sustainable development and environmental protection characteristics, and meets the requirements of the modern society on low-carbon and environmental protection materials.
Drawings
FIG. 1 is a schematic flow chart of a preparation method of the heat-insulating flame-retardant boron nitride-based aerogel;
FIG. 2 is an SEM photograph of a hollow boron nitride filler prepared in example 1 of the present invention.
FIG. 3 is an XRD phase analysis result of the hollow boron nitride filler prepared in example 1 of the present invention.
FIG. 4 is an SEM photograph of a hollow boron nitride filler prepared in example 2 of the present invention.
FIG. 5 is an SEM photograph of a boron nitride nanowire filler prepared in example 4 of the present invention
Detailed Description
The invention is further illustrated by the following embodiments, it being understood that the following is only intended to limit the invention.
The invention provides a heat-insulating flame-retardant boron nitride-based aerogel, which consists of three components of boron nitride heat-insulating filler, aluminum hydroxide flame retardant and chitosan gel, wherein the morphology of the boron nitride heat-insulating filler is characterized in that one or more of nanofibers and hollow spheres are mixed, the diameter of the nanofibers is 40-90 nm, the length of the nanofibers is 40-90 mu m, the diameter of the hollow spheres is 40-90 nm, the boron nitride is prepared by a hydrothermal reaction method by taking a boron source, a nitrogen source and a catalyst as raw materials, and the mass fractions of the boron nitride heat-insulating filler, the aluminum hydroxide flame retardant and the chitosan gel are respectively (70-85%): (10-20 percent): (5-10%) and the aerogel has a porosity of 75-90%.
The invention also provides a preparation method of the heat-insulating flame-retardant boron nitride-based aerogel, which comprises the following steps:
S1: preparing a nano boron nitride heat insulation filler: uniformly mixing a boron source, a nitrogen source and a catalyst as raw materials, using hydrazine hydrate as a solvent, obtaining nano boron nitride heat insulation filler through a hydrothermal method, and removing impurities through deionized water to obtain clean nano nitride heat insulation filler; wherein the boron source is one or more of amorphous boron powder, boron oxide and boric acid, the nitrogen source is one or more of ammonium chloride and ammonium sulfate, the catalyst is one or more of ferrocene, cobaltocene and nickel dicyclopentadienyl, the molar ratio of the boron source to the nitrogen source to the catalyst is 1:1 (0-0.1), and the technological parameters of the hydrothermal method are as follows: the stainless steel reaction kettle is taken as a container, the preparation temperature is 350-550 ℃, the heating rate is 1-10 ℃/min, the reaction time is 5-24 h, the reaction pressure is 5-10 MPa, the mass fraction of the solvent hydrazine hydrate is 40-60%, and the reaction is cooled along with the furnace after the completion of the reaction.
In some embodiments, the boron nitride thermal insulation filler is characterized by a blend of one or more of nanofibers and hollow spheres, wherein the nanofibers have a diameter of 40-90 nm, a length of 40-90 μm, and the hollow spheres have a diameter of 40-90 nm.
S2: preparation of boron nitride heat insulation filler-aluminum hydroxide flame retardant powder: uniformly mixing the nano-nitride heat-insulating filler obtained in the step S1 and an alkaline solution through magnetic stirring, magnetically stirring for 1-3 hours in a water bath at 60-90 ℃, cooling to room temperature, washing and drying by deionized water to obtain the alkaline nano-boron nitride heat-insulating filler, magnetically stirring the alkaline nano-boron nitride heat-insulating filler and a salt solution containing aluminum ions in the water bath at room temperature for 1-3 hours, and washing and drying to finally obtain boron nitride heat-insulating filler-aluminum hydroxide flame retardant powder; wherein the alkaline solution is one or more of sodium hydroxide and potassium hydroxide, the mass concentration of the alkaline solution is 1-10%, and the mass ratio of the nano nitride heat insulation filler to the alkaline solution is 1: (10-100). The salt solution of aluminum ions is one or more of aluminum chloride, aluminum nitrate or aluminum sulfate, the concentration of the salt solution is 5-15%, and the mass ratio of the alkaline nano boron nitride heat insulation layer filler to the salt solution is 1: (10-100).
S3: preparation of boron nitride based aerogel: and (3) obtaining the boron nitride-based aerogel by a freeze drying method through the boron nitride heat insulation filler-aluminum hydroxide flame retardant powder obtained in the step (2). The method comprises the following specific steps: firstly, uniformly mixing chitosan and 4% acetic acid to obtain a chitosan solution, wherein the mass ratio of the chitosan to the acetic acid is 1: (12-20), adding the boron nitride heat insulation filler-aluminum hydroxide flame retardant powder obtained in the step S2 into chitosan solution, and taking glutaraldehyde with the mass fraction of 2% as a cross-linking agent, wherein the mass ratio of the cross-linking agent to the chitosan solution is 1: (20-60), magnetically stirring for 1h at room temperature, and then freeze-drying for 24-72 h at-30 to-50 ℃ to obtain the boron nitride aerogel. The thermal conductivity of the prepared boron nitride-based aerogel at room temperature is 0.02-0.06W/(mK), the limiting oxygen index is 42-53.5%, and the compressive stress at 20% strain is 70-120 kPa.
In some embodiments, the mass fractions of the boron nitride heat insulation filler, the aluminum hydroxide flame retardant and the chitosan gel are respectively (70-85%): (10-20 percent): (5-10%) and the aerogel has a porosity of 75-90%.
In some embodiments, the thermal conductivity of the boron nitride based aerogel prepared in the step S3 is 0.02-0.06W/(mK) at room temperature, and the limiting oxygen index is 42-53.5%.
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.
Example 1
The preparation method of the heat-insulating flame-retardant boron nitride-based aerogel comprises the following steps:
S1: preparing a nano boron nitride heat insulation filler: uniformly mixing a boron source, a nitrogen source and a catalyst as raw materials, using hydrazine hydrate as a solvent, obtaining nano boron nitride heat insulation filler through a hydrothermal method, and removing impurities through deionized water to obtain clean nano nitride heat insulation filler; wherein the boron source is amorphous boron powder, the nitrogen source is ammonium sulfate, the molar ratio of the mixed boron source to the nitrogen source to the catalyst is 1:1:0, i.e. no catalyst is used, and the technological parameters of the hydrothermal method are as follows: taking a stainless steel reaction kettle as a container, preparing at 400 ℃, heating at 2 ℃/min, reacting for 12 hours at 5MPa, and cooling with a furnace after the reaction is completed to obtain the boron nitride hollow sphere with the diameter of 80nm, wherein the mass fraction of the solvent hydrazine hydrate is 45%.
S2: preparation of boron nitride heat insulation filler-aluminum hydroxide flame retardant powder: uniformly mixing the nano-nitride heat-insulating filler obtained in the step S1 and an alkaline solution through magnetic stirring, magnetically stirring for 1-3 hours in a water bath at 60 ℃, cooling to room temperature, washing and drying by deionized water to obtain the alkaline nano-boron nitride heat-insulating filler, magnetically stirring the alkaline nano-boron nitride heat-insulating filler and a salt solution containing aluminum ions in the water bath at room temperature for 1 hour, washing and drying to obtain boron nitride heat-insulating filler-aluminum hydroxide flame retardant powder; wherein the alkaline solution is sodium hydroxide, the mass concentration of the alkaline solution is 3%, and the mass ratio of the nano nitride heat insulation filler to the alkaline solution is 1:20. the salt solution of aluminum ions is aluminum chloride, the mass concentration of the salt solution is 5%, and the mass ratio of the alkaline nano boron nitride heat insulation layer filler to the salt solution is 1:20.
S3: preparation of boron nitride based aerogel: and (3) obtaining the boron nitride-based aerogel by a freeze drying method through the boron nitride heat insulation filler-aluminum hydroxide flame retardant powder obtained in the step (2). The method comprises the following specific steps: firstly, uniformly mixing chitosan and 4% acetic acid to obtain a chitosan solution, wherein the mass ratio of the chitosan to the acetic acid is 1:12, adding the boron nitride heat insulation filler-aluminum hydroxide flame retardant powder obtained in the step S2 into a chitosan solution, wherein glutaraldehyde with the mass fraction of 2% is used as a cross-linking agent, and the mass ratio of the cross-linking agent to the chitosan solution is 1:20, then magnetically stirring for 1h at room temperature, and then freeze-drying for 30h at-40 ℃ to obtain the boron nitride-based aerogel. The thermal conductivity of the prepared boron nitride-based aerogel at room temperature is 0.06W/(mK), the limiting oxygen index is 52%, and the compressive stress at 20% strain is 70kPa.
The thermal conductivity, limiting oxygen index and compressive stress parameters of the prepared boron nitride-based aerogel are shown in table 1.
Example 2
The preparation method of the heat-insulating flame-retardant boron nitride-based aerogel comprises the following steps:
S1: preparing a nano boron nitride heat insulation filler: uniformly mixing a boron source, a nitrogen source and a catalyst as raw materials, using hydrazine hydrate as a solvent, obtaining nano boron nitride heat insulation filler through a hydrothermal method, and removing impurities through deionized water to obtain clean nano nitride heat insulation filler; wherein the boron source is amorphous boron powder, the nitrogen source is ammonium sulfate, the molar ratio of the mixed boron source to the nitrogen source to the catalyst is 1:1:0, i.e. no catalyst is used, and the technological parameters of the hydrothermal method are as follows: taking a stainless steel reaction kettle as a container, preparing at 550 ℃, heating at 8 ℃/min, reacting for 16 hours at 8MPa, and cooling with a furnace after the reaction is completed to obtain the boron nitride hollow sphere with the diameter of 50nm, wherein the mass fraction of the solvent hydrazine hydrate is 50%.
S2: preparation of boron nitride heat insulation filler-aluminum hydroxide flame retardant powder: uniformly mixing the nano-nitride heat-insulating filler obtained in the step S1 and an alkaline solution through magnetic stirring, magnetically stirring for 1-3 hours in a water bath at 60 ℃, cooling to room temperature, washing and drying by deionized water to obtain the alkaline nano-boron nitride heat-insulating filler, magnetically stirring the alkaline nano-boron nitride heat-insulating filler and a salt solution containing aluminum ions in the water bath at room temperature for 1 hour, washing and drying to obtain boron nitride heat-insulating filler-aluminum hydroxide flame retardant powder; wherein the alkaline solution is potassium hydroxide, the mass concentration of the alkaline solution is 4%, and the mass ratio of the nano nitride heat insulation filler to the alkaline solution is 1:50. the salt solution of aluminum ions is aluminum nitrate, the concentration of the salt solution is 8%, and the mass ratio of the alkaline nano boron nitride heat insulation layer filler to the salt solution is 1:30.
S3: preparation of boron nitride based aerogel: and (3) obtaining the boron nitride-based aerogel by a freeze drying method through the boron nitride heat insulation filler-aluminum hydroxide flame retardant powder obtained in the step (2). The method comprises the following specific steps: firstly, uniformly mixing chitosan and 4% acetic acid to obtain a chitosan solution, wherein the mass ratio of the chitosan to the acetic acid is 1:12, adding the boron nitride heat insulation filler-aluminum hydroxide flame retardant powder obtained in the step S2 into a chitosan solution, wherein glutaraldehyde with the mass fraction of 2% is used as a cross-linking agent, and the mass ratio of the cross-linking agent to the chitosan solution is 1: and (3) magnetically stirring for 1h at room temperature, and then freeze-drying for 40h at-45 ℃ to obtain the boron nitride-based aerogel. The thermal conductivity of the prepared boron nitride-based aerogel at room temperature is 0.02W/(mK), the limiting oxygen index is 50%, and the compressive stress at 20% strain is 75kPa.
The thermal conductivity, limiting oxygen index and compressive stress parameters of the prepared boron nitride-based aerogel are shown in table 1.
Example 3
The preparation method of the heat-insulating flame-retardant boron nitride-based aerogel comprises the following steps:
S1: preparing a nano boron nitride heat insulation filler: uniformly mixing a boron source, a nitrogen source and a catalyst as raw materials, using hydrazine hydrate as a solvent, obtaining nano boron nitride heat insulation filler through a hydrothermal method, and removing impurities through deionized water to obtain clean nano nitride heat insulation filler; wherein the boron source is boron oxide, the nitrogen source is ammonium sulfate, the catalyst is cobaltocene, the molar ratio of the boron source to the nitrogen source to the catalyst is 1:1:0.02, and the technological parameters of the hydrothermal method are as follows: the preparation method comprises the steps of taking a stainless steel reaction kettle as a container, preparing at 500 ℃, heating at 8 ℃/min, reacting for 12 hours, reacting at 8MPa, and cooling with a furnace after the reaction is completed, wherein the mass fraction of solvent hydrazine hydrate is 60%.
S2: preparation of boron nitride heat insulation filler-aluminum hydroxide flame retardant powder: uniformly mixing the nano-nitride heat-insulating filler obtained in the step S1 and an alkaline solution through magnetic stirring, magnetically stirring for 1-3 hours in a water bath at 79 ℃, cooling to room temperature, washing and drying by deionized water to obtain the alkaline nano-boron nitride heat-insulating filler, magnetically stirring the alkaline nano-boron nitride heat-insulating filler and a salt solution containing aluminum ions in the water bath at room temperature for 2 hours, washing and drying to obtain boron nitride heat-insulating filler-aluminum hydroxide flame retardant powder; wherein the alkaline solution is sodium hydroxide, the mass concentration of the alkaline solution is 6%, and the mass ratio of the nano nitride heat insulation filler to the alkaline solution is 1:60. the salt solution of aluminum ions is aluminum chloride, the concentration of the salt solution is 10%, and the mass ratio of the alkaline nano boron nitride heat insulation layer filler to the salt solution is 1:80.
S3: preparation of boron nitride based aerogel: and (3) obtaining the boron nitride-based aerogel by a freeze drying method through the boron nitride heat insulation filler-aluminum hydroxide flame retardant powder obtained in the step (2). The method comprises the following specific steps: firstly, uniformly mixing chitosan and 4% acetic acid to obtain a chitosan solution, wherein the mass ratio of the chitosan to the acetic acid is 1:16, adding the boron nitride heat insulation filler-aluminum hydroxide flame retardant powder obtained in the step S2 into a chitosan solution, wherein glutaraldehyde with the mass fraction of 2% is used as a cross-linking agent, and the mass ratio of the cross-linking agent to the chitosan solution is 1:40, then magnetically stirring for 1h at room temperature, and then freeze-drying for 60h at-50 ℃ to obtain the boron nitride-based aerogel. The thermal conductivity of the prepared boron nitride-based aerogel at room temperature is 0.05W/(mK), the limiting oxygen index is 56%, and the compressive stress at 20% strain is 70-120 kPa.
The thermal conductivity, limiting oxygen index and compressive stress parameters of the prepared boron nitride-based aerogel are shown in table 1.
Example 4
The preparation method of the heat-insulating flame-retardant boron nitride-based aerogel comprises the following steps:
s1: preparing a nano boron nitride heat insulation filler: uniformly mixing a boron source, a nitrogen source and a catalyst as raw materials, using hydrazine hydrate as a solvent, obtaining nano boron nitride heat insulation filler through a hydrothermal method, and removing impurities through deionized water to obtain clean nano nitride heat insulation filler; wherein the boron source is boric acid, the nitrogen source is mixed with ammonium chloride and ammonium sulfate, the catalyst is ferrocene, the molar ratio of the boron source to the nitrogen source to the catalyst is 1:1:0.8, and the technological parameters of the hydrothermal method are as follows: the preparation method comprises the steps of taking a stainless steel reaction kettle as a container, preparing at 550 ℃, heating at a rate of 4 ℃/min, reacting for 24 hours, reacting at 9MPa, and cooling with a furnace after the reaction is completed, wherein the mass fraction of the solvent hydrazine hydrate is 65%.
S2: preparation of boron nitride heat insulation filler-aluminum hydroxide flame retardant powder: uniformly mixing the nano-nitride heat-insulating filler obtained in the step S1 and an alkaline solution through magnetic stirring, magnetically stirring for 1-3 hours in a water bath at 85 ℃, cooling to room temperature, washing and drying by deionized water to obtain the alkaline nano-boron nitride heat-insulating filler, magnetically stirring the alkaline nano-boron nitride heat-insulating filler and a salt solution containing aluminum ions for 3 hours in the water bath at room temperature, washing and drying to obtain boron nitride heat-insulating filler-aluminum hydroxide flame retardant powder; wherein the alkaline solution is one or more of sodium hydroxide and potassium hydroxide, the mass concentration of the alkaline solution is 7%, and the mass ratio of the nano nitride heat insulation filler to the alkaline solution is 1:27. the salt solution of aluminum ions is one or more of aluminum chloride, aluminum nitrate or aluminum sulfate, the concentration of the salt solution is 12 percent, and the mass ratio of the alkaline nano boron nitride heat insulation layer filler to the salt solution is 1:60.
S3: preparation of boron nitride based aerogel: and (3) obtaining the boron nitride-based aerogel by a freeze drying method through the boron nitride heat insulation filler-aluminum hydroxide flame retardant powder obtained in the step (2). The method comprises the following specific steps: firstly, uniformly mixing chitosan and 4% acetic acid to obtain a chitosan solution, wherein the mass ratio of the chitosan to the acetic acid is 1:14, adding the boron nitride heat insulation filler-aluminum hydroxide flame retardant powder obtained in the step S2 into a chitosan solution, wherein glutaraldehyde with the mass fraction of 2% is used as a cross-linking agent, and the mass ratio of the cross-linking agent to the chitosan solution is 1:30, then magnetically stirring for 1h at room temperature, and then freeze-drying for 72h at-50 ℃ to obtain the boron nitride-based aerogel. The thermal conductivity of the prepared boron nitride-based aerogel at room temperature is 0.05W/(mK), the limiting oxygen index is 42%, and the compressive stress at 20% strain is 120kPa.
The thermal conductivity, limiting oxygen index and compressive stress parameters of the prepared boron nitride-based aerogel are shown in table 1.
Comparative example 1
The preparation method of the heat-insulating flame-retardant boron nitride-based aerogel has the steps basically same as those of the embodiment 1, and is different in that the hydrothermal reaction temperature and the hydrothermal reaction pressure in the step S1 are too low, so that solid boron nitride is generated.
Comparative example 2
A preparation method of heat-insulating flame-retardant boron nitride-based aerogel has the same steps as in example 1, except that step S2 is omitted and no flame retardant is added.
The boron nitride-based aerogels prepared in examples 1 to 4 and comparative examples 1 to 2 were subjected to thermal conductivity, compressive stress test and limiting oxygen index, and the aerogel thermal conductivity test was referred to the GB/T10294 standard; compressive stress test the test was carried out on an aerogel by applying a 1000g weight, limiting oxygen index reference GB2406-80, the parameters of the examples and comparative examples are listed in table 1 below:
TABLE 1
Compared with example 1, the main difference is that the preparation temperature in the step S1 is increased from 400 ℃ to 550 ℃, the reaction pressure is increased from 5MPa to 10MPa, the diameter of the obtained boron nitride hollow sphere is reduced from 80nm to 50nm, the specific surface area of the boron nitride heat insulation filler is increased, and the heat dissipation is favorably increased, so that the heat conductivity coefficient of the prepared final aerogel is reduced from 0.06W/mK to 0.02W/mK, and the other properties are not quite different.
Example 3 is mainly different from example 1 in that the catalyst is added to the boron nitride prepared in step S1, so that the morphology of the prepared boron nitride is that the nanofibers and the hollow spheres are mixed, and the high aspect ratio of the nanofibers and the hollow spheres are mixed to be beneficial to increasing the mechanical properties of the aerogel, so that the compressive stress of the aerogel is increased from 70KPa to 100KPa in example 1, and the other properties are not very different.
Example 4 is mainly distinguished from example 1 in that the preparation of boron nitride in step S1 adds more catalyst, so that the resulting boron nitride filler is entirely nanofibers, a large number of high aspect ratio nanofibers increase the compressive stress of the aerogel from 70KPa to 120KPa in example 1, and the limiting oxygen index of the pure nanofibers decreases from 53% to 42% in example 1.
Example 3 compared with examples 2 and 4, the boron nitride filler composed of hollow spheres and nanofibers has superior combination properties in terms of thermal conductivity, compressive stress and limiting oxygen index.
Comparative example 1 is mainly different from example 1 in that the hydrothermal reaction and reaction pressure in step S1 are too low, resulting in the boron nitride filler being solid boron nitride, which has a thermal conductivity far higher than that of hollow boron nitride, and thus the thermal conductivity increases from 0.06W/mK of example 1 to 6W/mK of comparative example 1, and thus the heat removal performance is poor.
Comparative example 2 is mainly different from example 1 in that comparative example 2 is free from the addition of flame retardant, and thus limiting oxygen index is reduced from 52% of example 1 to 14% of comparative example 2, and thus flame retardant effect is further reduced without the addition of aluminum hydroxide flame retardant.
FIG. 1 is a schematic flow chart of a preparation method of the heat-insulating flame-retardant boron nitride-based aerogel;
FIG. 2 shows the hollow boron nitride filler prepared in example 1 of the present invention, and it can be seen that the hollow structure is remarkable, and the diameter of the boron nitride filler is uniform, and the average diameter is 80nm.
Fig. 3 shows the phase analysis result of the hollow boron nitride filler prepared in example 1 of the present invention, and the non-phase analysis result shows that the prepared pure boron nitride is free from other impurities.
FIG. 4 shows the hollow boron nitride filler prepared in example 2 of the present invention, and shows that the diameter of the boron nitride filler is uniform, and the average diameter of the boron nitride is 50nm, which proves that the size of the hollow sphere can be regulated.
Fig. 5 shows the nanowire fiber prepared in example 4 of the present invention, which shows that the nanowire fiber has a very long length-diameter ratio and a uniform nanowire diameter, and the addition of the catalyst can realize the regulation of the morphology of boron nitride.
Finally, it should be noted that: the above embodiments are only for illustrating the technical aspects of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the above embodiments, it should be understood by those of ordinary skill in the art that: all changes in the structure and details of the invention which may be made in the invention are encompassed by the scope of the invention as defined by the claims.
Claims (6)
1. The heat-insulating flame-retardant boron nitride-based aerogel is characterized by comprising three components of boron nitride heat-insulating filler, aluminum hydroxide flame retardant and chitosan gel, wherein the boron nitride heat-insulating filler is characterized in that one or more of nanofibers and hollow spheres are mixed, the diameter of the nanofibers is 40-90 nm, the length of the nanofibers is 40-90 mu m, the diameter of the hollow spheres is 40-90 nm, the boron nitride is prepared by a hydrothermal reaction method by taking a boron source, a nitrogen source and a catalyst as raw materials, and the mass fractions of the boron nitride heat-insulating filler, the aluminum hydroxide flame retardant and the chitosan gel are respectively (70-85%), (10-20%), (5-10%), and the porosity of the aerogel is 75-90%;
The preparation method of the aerogel comprises the following steps:
s1: preparing a nano boron nitride heat insulation filler: uniformly mixing a boron source, a nitrogen source and a catalyst as raw materials, using hydrazine hydrate as a solvent, obtaining nano boron nitride heat insulation filler through a hydrothermal method, and removing impurities through deionized water to obtain clean nano nitride heat insulation filler; the technological parameters of the hydrothermal method are as follows: taking a stainless steel reaction kettle as a container, preparing at 350-550 o ℃, heating at 1-10 o C/min, reacting for 5-24 h at 5-10 MPa, and cooling with a furnace after the reaction is completed, wherein the mass fraction of the solvent hydrazine hydrate is 40-60%;
S2: preparation of boron nitride heat insulation filler-aluminum hydroxide flame retardant powder: uniformly mixing the nano-nitride heat-insulating filler obtained in the step S1 and an alkaline solution through magnetic stirring, magnetically stirring for 1-3 hours in a water bath with the temperature of 60-90 o ℃, cooling to room temperature, washing and drying by deionized water to obtain the alkaline nano-boron nitride heat-insulating filler, magnetically stirring the alkaline nano-boron nitride heat-insulating filler and a salt solution containing aluminum ions in the water bath with the temperature of room temperature for 1-3 hours, and washing and drying to finally obtain boron nitride heat-insulating filler-aluminum hydroxide flame retardant powder;
S3: preparation of boron nitride based aerogel: firstly, uniformly mixing chitosan and 4% acetic acid to obtain a chitosan solution, wherein the mass ratio of the chitosan to the acetic acid is 1: (12-20), adding the boron nitride heat insulation filler-aluminum hydroxide flame retardant powder obtained in the step S2 into a chitosan solution, and taking glutaraldehyde with the mass fraction of 2% as a cross-linking agent, wherein the mass ratio of the cross-linking agent to the chitosan solution is 1: (20-60), magnetically stirring for 1h at room temperature, and freeze-drying for 24-72 h at-30 to-50 ℃ to obtain the boron nitride-based aerogel.
2. The thermally insulating and flame retardant boron nitride based aerogel of claim 1, wherein the boron source in step S1 is one or more of amorphous boron powder, boron oxide and boric acid, the nitrogen source is one or more of ammonium chloride and ammonium sulfate, and the catalyst is one or more of ferrocene, cobaltocene and nickel dicyclopentadienyl.
3. The heat-insulating flame-retardant boron nitride-based aerogel according to claim 1, wherein the molar ratio of the boron source to the nitrogen source to the catalyst in the step S1 is 1:1 (0-0.1).
4. The heat-insulating flame-retardant boron nitride-based aerogel according to claim 1, wherein in the step S2, the alkaline solution is one or more of sodium hydroxide and potassium hydroxide, the mass concentration of the alkaline solution is 1-10%, and the mass ratio of the nano nitride heat-insulating filler to the alkaline solution is 1: (10-100).
5. The heat-insulating flame-retardant boron nitride-based aerogel according to claim 1, wherein in the step S2, the salt solution is one or more of aluminum chloride, aluminum nitrate or aluminum sulfate, the concentration of the salt solution is 5-15%, and the mass ratio of the alkaline nano boron nitride heat-insulating layer filler to the salt solution is 1: (10-100).
6. The heat-insulating flame-retardant boron nitride-based aerogel according to claim 1, wherein the boron nitride-based aerogel prepared in the step S3 has a thermal conductivity of 0.02-0.06W/(mK) at room temperature, a limiting oxygen index of 42-53.5%, and a compressive stress at 20% strain of 70-120 kPa.
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