CN111252789A - High-temperature-resistant alumina nanocrystalline aerogel material and preparation method thereof - Google Patents
High-temperature-resistant alumina nanocrystalline aerogel material and preparation method thereof Download PDFInfo
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- CN111252789A CN111252789A CN202010056049.4A CN202010056049A CN111252789A CN 111252789 A CN111252789 A CN 111252789A CN 202010056049 A CN202010056049 A CN 202010056049A CN 111252789 A CN111252789 A CN 111252789A
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Abstract
The invention relates to a high-temperature-resistant alumina nanocrystalline aerogel material and a preparation method thereof. The method comprises the following steps: uniformly mixing the alumina nanocrystals with the chitosan solution to obtain a mixed solution, adding glacial acetic acid to dissolve chitosan, and heating at 60-100 ℃ for 4-8 h to obtain a chitosan dispersion solution of the alumina nanocrystals; performing vacuum pumping on the dispersion liquid to obtain an alumina nanocrystal/chitosan reaction liquid; freezing and freeze-drying the reaction solution, and then carrying out pyrolysis to obtain the alumina/carbon composite aerogel; and (3) carrying out heat treatment on the alumina/carbon composite aerogel in an air atmosphere to prepare the high-temperature-resistant alumina nanocrystalline aerogel material. According to the invention, the alumina/carbon composite aerogel is obtained through pyrolysis, and the carbon coating layer can fix the nano particles and play a certain isolation role, so that the sintering effect of the material is prevented, the material is transited to a stable crystal form under the condition of no sintering, and the preparation of the high-temperature resistant alumina aerogel is realized.
Description
Technical Field
The invention relates to the technical field of aerogel preparation, in particular to a high-temperature-resistant alumina nanocrystalline aerogel material and a preparation method thereof.
Background
The aerogel material is a gel material with a gas as a dispersion medium, and is a nano porous solid material with a network structure formed by mutually accumulating colloidal particles or high polymer molecules, and the size of pores in the material is in the order of nanometers. The porosity of the porous ceramic is as high as 80-99.8%, the typical size of the pores is 1-100 nm, and the specific surface area is 200-1000 m2A density of as low as 3kg/m3The room temperature thermal conductivity can be as low as 0.012W/m.k. Due to the characteristics, the aerogel material has wide application potential in the aspects of thermal, acoustic, optical, microelectronic and particle detection. Currently, the widest field of application of aerogels is still the field of thermal insulation, since the unique nanostructure of aerogels can effectively reduce convection conduction, solid phase conduction and thermal radiation. In the prior art, aerogel has proved to be an effective heat insulation material, but the maximum temperature resistance limit of the high-temperature resistant aerogel material which is reported at present does not exceed 1100 ℃ under long-term use (more than 30 min).
The existing high-temperature resistant aerogel mainly comprises carbon aerogel, ceramic aerogel, silica aerogel, alumina aerogel, zirconia aerogel and the like. Carbon aerogel and ceramic aerogel have good high temperature resistance, but the application of the carbon aerogel and the ceramic aerogel has certain limitation, namely the carbon aerogel and the ceramic aerogel can realize heat insulation application at the temperature of more than 1400 ℃ only in an oxygen-free environment, and the oxidation resistance of the carbon aerogel and the ceramic aerogel is not overcome by an effective method. Oxide aerogels such as silicon dioxide, aluminum oxide, zirconium oxide and the like can have serious crystal form transformation and sintering at high temperature to cause structure collapse, so that nano particles grow up and holes are reduced, the specific surface area of the aerogel is sharply reduced, the heat insulation performance of the aerogel is greatly weakened, and the heat insulation failure is realized. For the limitation of oxide aerogel, there are related researches on modification processes such as rare earth metal oxide or multi-component doping, but the effect is limited.
Chinese patent application CN201810068117.1 discloses preparation of high-temperature-resistant aerogel materialThe aerogel prepared by the method has good high-temperature resistance, the heat resistance temperature is more than 1000 ℃, even can resist the high temperature of more than 1300 ℃, but the aerogel material still generates a series of phase changes at the high temperature of more than 1200 ℃, so that the specific surface area of the aerogel material after high-temperature heat treatment at 1400 ℃ is smaller and is not more than 10m2And/g, the high temperature insulation performance of the aerogel material is not very good.
With the development of science and technology, various fields have higher requirements on the temperature resistance and high-temperature heat insulation performance of heat insulation materials, so that an effective method for preparing aerogel materials with high temperature resistance and high-efficiency heat insulation performance at high temperature is very needed to be developed.
Disclosure of Invention
In order to solve the technical problems in the prior art, the invention provides a novel high-temperature-resistant alumina nanocrystal aerogel material (high-temperature-resistant alumina aerogel material) which is simple in preparation process, good in high-temperature resistance of the material and capable of efficiently insulating heat at high temperature and a preparation method thereof.
The invention provides a preparation method of a high-temperature-resistant alumina nanocrystalline aerogel material in a first aspect, which comprises the following steps:
(1) uniformly mixing the alumina nanocrystal dispersion liquid and a chitosan solution to obtain a mixed solution;
(2) adding glacial acetic acid into the mixed solution obtained in the step (1) to dissolve chitosan contained in the mixed solution to obtain a chitosan alumina nanocrystalline mixed solution, and then heating the chitosan alumina nanocrystalline mixed solution at 60-100 ℃ for 4-8 h to obtain a chitosan dispersion liquid of alumina nanocrystals;
(3) vacuumizing the chitosan dispersion liquid of the alumina nanocrystals obtained in the step (2) for 0.1-1 h at the temperature of 25 ℃ and the vacuum degree of 0.1-0.5 MPa to obtain an alumina nanocrystal/chitosan reaction liquid;
(4) sequentially freezing and freeze-drying the alumina nanocrystal/chitosan reaction solution obtained in the step (3) to obtain an alumina/chitosan composite aerogel material;
(5) cracking the alumina/chitosan composite aerogel material obtained in the step (4) for 0.5-12 h under the conditions of inert atmosphere and temperature of 1200-1500 ℃ to obtain an alumina/carbon composite aerogel material; and
(6) and (3) carrying out heat treatment on the alumina/carbon composite aerogel material obtained in the step (5) for 1-12 h in an air atmosphere at the temperature of 500-1400 ℃ to obtain the high-temperature-resistant alumina nanocrystalline aerogel material.
Preferably, the mass ratio of the used amount of the alumina nanocrystal dispersion liquid to the used amount of the chitosan solution to the used amount of the glacial acetic acid is (10-20): 20: (0.3-0.6).
Preferably, the mass concentration of the chitosan solution is 1.5-3%.
Preferably, the diameter of the alumina nanocrystal contained in the alumina nanocrystal dispersion is 100-200nm, and the length is 1-3 μm.
Preferably, in step (4), the freezing is performed under liquid nitrogen for 2 h.
Preferably, in the step (4), the freeze drying is performed under the condition of a temperature of-70 ℃ for 12-144 h.
Preferably, in the step (2), the chitosan-alumina nanocrystal mixed solution is heated at 80 ℃ for 6h to obtain a chitosan dispersion of alumina nanocrystals.
Preferably, in the step (5), the alumina/chitosan composite aerogel material obtained in the step (4) is cracked for 1.5-3 hours under the condition of inert atmosphere and temperature of 1200-1500 ℃.
Preferably, in the step (6), the alumina/carbon composite aerogel material obtained in the step (5) is subjected to heat treatment for 2-5 hours in an air atmosphere at the temperature of 500-700 ℃.
In a second aspect, the present invention provides a refractory alumina nanocrystalline aerogel material prepared by the preparation method of the first aspect of the present invention.
Compared with the prior art, the invention at least has the following beneficial effects:
(1) different from other methods for preparing high-temperature resistant aerogel thermal insulation materials by doping modification, the chitosan surface has a hydrophilic group and can perform a good adsorption effect with the alumina nanocrystals, so that the surface of the alumina nanocrystals is completely coated, the cracked carbon has good temperature resistance in an inert atmosphere, and the alumina/carbon composite aerogel material with the carbon skeleton coated with the alumina nanocrystals is obtained after cracking; under the coating and isolating action of the carbon skeleton, the sintering process of the alumina aerogel material under high-temperature cracking is avoided, the coating process is sufficient, the nanocrystalline particles can be fully isolated, the sintering of the nanocrystalline particles is avoided, and the nano-sized aerogel material is formed, so that the high-temperature resistant alumina nanocrystalline aerogel material prepared by the invention can still keep a nano structure and a small shrinkage rate even at 1400 ℃, and the improvement method is more feasible.
(2) The invention adopts carbon to coat the surface of the alumina nanocrystalline, and the alumina is transited to α phase under the support of the carbon skeleton to form stable α phase, and meanwhile, the process is not sintered due to the isolation effect of the carbon skeleton, so that the problem that the nano α phase powder cannot be obtained due to the growth of the powder in the preparation process of α phase powder in the traditional method can be avoided.
(3) The alumina nano-crystal adopted in some preferred embodiments of the invention is a nanorod (with the diameter of 100-200nm and the length of 1-3 μm) with high length-diameter ratio, the nanorod has a lapping effect relative to spherical nano-particles, a three-dimensional network alternating framework structure can be remained after a carbon layer is removed, pulverization does not occur, and a network alumina aerogel is formed, and the network alumina aerogel has ultra-light weight characteristics.
(4) The invention can adopt water as a reaction dispersion phase, and avoids environmental pollution and waste caused by using an organic solvent in the preparation process.
(5) The prepared alumina aerogel is α phase, the crystal form is the most stable crystal form of alumina, and the α phase alumina aerogel still has stable performance at 1400 ℃, so that the traditional temperature resistance limit is broken through.
(6) The invention adopts the freeze drying process to dry the aerogel, avoids the solvent replacement and supercritical drying process, simplifies the flow and shortens the period.
Drawings
FIG. 1 is a flow chart of the preparation of the present invention.
FIG. 2 is an SEM image of an alumina/chitosan composite aerogel prepared in example 1 of the present invention without pyrolysis and without heat treatment.
FIG. 3 is an SEM image of a high temperature resistant alumina aerogel after pyrolysis and heat treatment prepared in example 1 of the present invention.
FIG. 4 is an XRD spectrum of the refractory alumina aerogel prepared in example 1 of the present invention. In fig. 4, the abscissa 2 θ represents twice the diffraction angle in degrees (°), and the ordinate represents the intensity (a.u).
FIG. 5 is an analysis of the XRD spectrum of FIG. 4, corresponding to α phase alumina 10-0173 card.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
The invention provides a preparation method of a high-temperature-resistant alumina nanocrystalline aerogel material in a first aspect, which comprises the following steps:
(1) uniformly mixing the alumina nanocrystal dispersion liquid and a chitosan solution to obtain a mixed solution; in the present invention, for example, the alumina nanocrystal dispersion and the chitosan solution are uniformly mixed by stirring and ultrasonic treatment to obtain the mixed solution; in the present invention, the alumina nanocrystal dispersion is prepared by dissolving alumina nanocrystals in water, and the mass fraction (mass concentration) of the alumina nanocrystals contained in the alumina nanocrystal dispersion may be, for example, 8 to 12%, preferably 10%; in the present invention, the chitosan solution may be, for example, an aqueous chitosan solution.
(2) Adding glacial acetic acid into the mixed solution obtained in the step (1) to dissolve chitosan contained in the mixed solution to obtain a chitosan alumina nanocrystal mixed solution, and then heating the chitosan alumina nanocrystal mixed solution at 60-100 ℃ (for example, 60 ℃, 65 ℃, 70 ℃, 75 ℃, 80 ℃, 85 ℃, 90 ℃, 95 ℃ or 100 ℃) for 4-8 h (for example, 4, 5, 6, 7 or 8h) to obtain a chitosan dispersion liquid of alumina nanocrystals, so as to complete the coating process of the chitosan solution on the alumina nanocrystals; in the invention, for example, a certain amount of glacial acetic acid is added into the mixed solution obtained in the step (1), chitosan is dispersed and fully dissolved under an acidic condition through stirring and/or ultrasonic treatment to form a chitosan-alumina nanocrystal mixed solution, and then the mixed solution is heated at 80 ℃ for 6 hours to obtain a chitosan dispersed solution of alumina nanocrystals; in the invention, the chitosan-alumina nanocrystalline mixed solution is heated for 4-8 hours, preferably 6 hours, at 60-100 ℃, preferably 80 ℃, so that the chitosan is dissolved more fully, the heating viscosity is reduced, and the bubble removal is facilitated.
(3) Vacuumizing the chitosan dispersion liquid of the alumina nanocrystals obtained in the step (2) for 0.1-1 h (for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1h) at the temperature of 25 ℃ and under the vacuum degree of 0.1-0.5 MPa (for example, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 or 0.5MPa), so as to obtain an alumina nanocrystal/chitosan reaction liquid; in the invention, the alumina nanocrystal chitosan dispersion liquid obtained in the step (2) is subjected to a vacuum air extraction process to remove bubbles formed in a stirring process, so that a bubble-free viscous reaction liquid (bubble-free alumina nanocrystal/chitosan reaction liquid) can be obtained, and the fact that the subsequently prepared aerogel has no macroporous structure is ensured.
(4) Sequentially freezing and freeze-drying the alumina nanocrystal/chitosan reaction solution obtained in the step (3) to obtain an alumina/chitosan composite aerogel material (also called as alumina/chitosan composite aerogel or alumina nanocrystal/chitosan composite aerogel); in the invention, the obtained alumina/chitosan composite aerogel is porous alumina/chitosan composite aerogel; in the invention, for example, the alumina nanocrystal/chitosan reaction solution obtained in step (3) is frozen under liquid nitrogen, and then is subjected to freeze drying to obtain the porous alumina/chitosan composite aerogel.
(5) Cracking (pyrolyzing) the alumina/chitosan composite aerogel material obtained in the step (4) in an inert atmosphere (such as an argon atmosphere) at 1200-1500 ℃ (such as 1200 ℃, 1300 ℃, 1400 ℃ or 1500 ℃) for 0.5-12 h (such as 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12h) to obtain an alumina/carbon composite aerogel material (also referred to as alumina/carbon composite aerogel or alumina nanocrystal/carbon composite aerogel);
in the invention, the alumina/chitosan composite aerogel material obtained in the step (4) is subjected to pyrolysis to form a carbon layer (carbon coating layer), so as to obtain the alumina/carbon composite aerogel material with the carbon skeleton coated with alumina nanocrystals; in the invention, the cracking temperature can determine the heat-resistant temperature of the material, and the material can generate corresponding crystal form transformation at the cracking temperature and is suitable for the use temperature of the material.
(6) And (3) carrying out heat treatment on the alumina/carbon composite aerogel material obtained in the step (5) for 1-12 h (for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12h) in an air atmosphere at the temperature of 500-1400 ℃ (for example, 500 ℃, 600 ℃, 700 ℃, 900 ℃, 1000 ℃, 1100 ℃, 1200 ℃, 1300 ℃ or 1400 ℃) to remove the carbon layer, thus obtaining a high-temperature-resistant alumina nanocrystalline aerogel material (also called as high-temperature-resistant alumina aerogel or high-temperature-resistant alumina nanocrystalline aerogel).
The alumina nano-crystal is coated by chitosan, the alumina/chitosan composite aerogel is prepared by taking chitosan as a framework, then the alumina nano-crystal coated by a carbon framework is obtained after high-temperature cracking, the alumina nano-crystal is subjected to crystal form transformation under the support and fixation of a carbon coating layer to form a stable α phase, the effective isolation action of the carbon framework reduces or even avoids the sintering action of the nano-crystal particles, the alumina nano-crystal is converted to the stable crystal form under the condition of no sintering, the high-temperature resistant aerogel material with the nano-size high-temperature resistant gel α phase is formed, the alumina aerogel material with the high-temperature resistant pore structure can be prepared even if the alumina aerogel material with the high-temperature resistant pore structure and the high-temperature resistant aerogel material with the high-temperature resistant pore structure are relatively small, and the high-temperature resistant aerogel material with the high-temperature resistant pore structure and the high-temperature resistant heat-insulating property of the alumina nano-gel is relatively high in favor of preparing the high-temperature resistant aerogel material with the high-temperature resistant heat-insulating property of high-temperature resistant nano-alumina nano-crystal, high-temperature resistant aerogel material and high-temperature resistant pore structure, even if the alumina nano-gel material with the high-temperature resistant heat-insulating property of 1400 ℃ is relatively small, the high-temperature resistant nano-temperature resistant aerogel material with the high-temperature resistant alumina nano-temperature resistant aerogel material with the high-temperature resistant heat-temperature resistant nano-resistant heat-resistant aerogel material with the high-resistant heat-resistant nano-temperature resistant nano-resistant aerogel.
The method adopts a freeze drying process for preparation, the preparation cost and the preparation period are far lower than those of the existing method for preparing the high-temperature-resistant alumina aerogel, water can be used as a reaction dispersion phase, and environmental pollution and waste caused by using an organic solvent are avoided in the preparation process.
According to the invention, under the combined action of the steps (1) to (6), the high-temperature resistant α -phase alumina nanocrystalline aerogel material which has good high-temperature resistance, a stable structure at high temperature and high-efficiency heat insulation can be prepared, and the high-temperature resistant alumina nanocrystalline aerogel material can not be prepared by the deletion of any step.
According to some preferred embodiments, the mass ratio of the amounts of the alumina nanocrystal dispersion, the chitosan solution and the glacial acetic acid is (10-20): 20: (0.3-0.6) (e.g., 10:20:0.3, 10:20:0.4, 10:20:0.5, 10:20:0.6, 15:20:0.3, 15:20:0.4, 15:20:0.5, 15:20:0.6, 20:20:0.3, 20:20:0.4, 20:20:0.5, or 20:20: 0.6).
According to some preferred embodiments, the chitosan solution has a mass concentration of 1.5-3% (e.g., 1.5%, 2%, 2.5%, or 3%) preferably 2%; that is, in the present invention, the mass fraction of chitosan contained in the chitosan solution is preferably 1.5 to 3%.
According to some preferred embodiments, the alumina nanocrystals contained in the alumina nanocrystal dispersion have a diameter of 100 to 200nm and a length of 1 to 3 μm, i.e., in the present invention, the alumina nanocrystals used are nanorods with a high aspect ratio, and the alumina nanocrystals contained in the alumina nanocrystal dispersion are nanorods with a high aspect ratio, a diameter of 100 to 200nm and a length of 1 to 3 μm; in the invention, preferably, the alumina nanocrystals contained in the alumina nanocrystal dispersion are alumina nanorods with a high aspect ratio and a diameter of 100-200nm and a length of 1-3 μm, namely, the alumina nanocrystal dispersion is preferably prepared by the alumina nanorods with a high aspect ratio and a diameter of 100-200nm and a length of 1-3 μm, and the nanorods have a lapping effect relative to spherical nanoparticles, can retain a three-dimensional network alternate framework structure after a carbon layer is removed, ensure the strength of the prepared aerogel, do not generate pulverization, form a network alumina aerogel, and enable the prepared aerogel to have the property of ultra-light weight.
According to some preferred embodiments, in step (4), the freezing is performed under conditions of liquid nitrogen for 2 h. In the invention, compared with the long-time freezing at the temperature of-75 ℃ to-45 ℃, the high-temperature resistant alumina nanocrystalline aerogel material is preferably frozen for 2 hours under liquid nitrogen, so that the high-temperature resistant alumina nanocrystalline aerogel material with smaller pore size and lower corresponding thermal conductivity (thermal conductivity) can be obtained more favorably.
According to some preferred embodiments, in step (4), the freeze-drying is performed under conditions of a temperature of-70 ℃ for 12 to 144h (e.g., 12, 24, 36, 48, 60, 72, 84, 96, 108, 120, 132, or 144 h).
According to some preferred embodiments, in the step (2), the chitosan-alumina nanocrystal mixed solution is heated at 80 ℃ for 6h to obtain a chitosan dispersion liquid of alumina nanocrystals.
According to some preferred embodiments, in the step (5), the alumina/chitosan composite aerogel material obtained in the step (4) is cracked for 1.5 to 3 hours (e.g., 1.5, 2, 2.5 or 3 hours) under the condition of inert atmosphere and temperature of 1200 to 1500 ℃ (e.g., 1200 ℃, 1300 ℃, 1400 ℃ or 1500 ℃).
According to some preferred embodiments, in the step (6), the alumina/carbon composite aerogel material obtained in the step (5) is subjected to heat treatment for 2 to 5 hours (e.g., 2, 2.5, 3, 3.5, 4, 4.5, or 5 hours) in an air atmosphere at a temperature of 500 to 700 ℃ (e.g., 500 ℃, 550 ℃, 600 ℃, 650 ℃, or 700 ℃).
According to some specific embodiments, the preparation process of the high temperature resistant alumina nanocrystal aerogel material of the present invention is as follows:
s1, mixing 10g of the alumina nanocrystal dispersion liquid with 20g of 2% chitosan solution, fully stirring, and performing ultrasonic treatment for 1 hour to obtain a mixed solution; wherein the alumina nano-crystal dispersion liquid is prepared by alumina nano-rods with the diameter of 100-200nm and the length of 1-3 mu m.
S2, adding a certain amount (with the purity of 99%) of glacial acetic acid (0.4g) into the mixed solution obtained in the step S1, fully stirring to dissolve chitosan to form chitosan-alumina nanocrystalline mixed solution, and heating at 80 ℃ for 6 hours to obtain the alumina nanocrystalline chitosan dispersion solution.
S3, vacuumizing the chitosan dispersion liquid of the alumina nanocrystals obtained in the step S2 for 0.1-1 h at the temperature of 25 ℃ and the vacuum degree of 0.1-0.5 MPa to obtain the alumina nanocrystal/chitosan reaction liquid.
And S4, freezing the alumina nanocrystal/chitosan reaction solution obtained in the step S3 under liquid nitrogen for 2 hours, and then carrying out freeze drying at-70 ℃ for 12-144 hours to obtain the alumina/chitosan composite aerogel.
S5, cracking the alumina/chitosan composite aerogel obtained in the step S4 at 1200-1500 ℃ for 0.5-12 h under the protection of argon gas to obtain the alumina/carbon composite aerogel.
And S6, carrying out heat treatment on the alumina/carbon composite aerogel obtained in the step S5 in an air atmosphere, and carrying out heat treatment at 500-1400 ℃ for 1-12 h to obtain the high-temperature-resistant alumina nanocrystalline aerogel.
In a second aspect, the present invention provides a refractory alumina nanocrystalline aerogel material prepared by the preparation method of the first aspect of the present invention.
The invention will be further illustrated by way of example, but the scope of protection is not limited to these examples.
Example 1
S1, mixing 10g of 10 mass percent alumina nanocrystal dispersion liquid with 20g of 2 mass percent chitosan solution, fully stirring, and performing ultrasonic treatment for 1 hour to obtain a mixed solution; wherein, the alumina nano-crystal dispersion liquid is prepared by alumina nano-rods with the diameter of 120nm and the length of 2 mu m.
S2, adding a certain amount (with the purity of 99%) of glacial acetic acid (0.4g) into the mixed solution obtained in the step S1, fully stirring to dissolve chitosan to form chitosan-alumina nanocrystalline mixed solution, and heating at 80 ℃ for 6 hours to obtain the alumina nanocrystalline chitosan dispersion solution.
S3, vacuumizing the chitosan dispersion liquid of the alumina nanocrystals obtained in the step S2 for 0.5h under the conditions that the temperature is 25 ℃ and the vacuum degree is 0.25MPa, and obtaining the alumina nanocrystal/chitosan reaction liquid.
And S4, freezing the alumina nanocrystal/chitosan reaction solution obtained in the step S3 under liquid nitrogen for 2 hours, and then carrying out freeze drying at-70 ℃ for 72 hours to obtain the alumina/chitosan composite aerogel.
S5, cracking the alumina/chitosan composite aerogel obtained in the step S4 at 1400 ℃ for 2h under the protection of argon gas to obtain the alumina/carbon composite aerogel.
And S6, carrying out heat treatment on the alumina/carbon composite aerogel obtained in the step S5 in an air atmosphere, and carrying out heat treatment at 600 ℃ for 5h to obtain the high-temperature-resistant alumina nanocrystalline aerogel.
The heat insulation performance test of the high temperature resistant alumina nanocrystal aerogel material in this example shows that the surface of the high temperature resistant alumina nanocrystal aerogel material has no light loss, no discoloration, and no shedding, and other performance indexes are shown in table 1.
The specific surface area of the high-temperature-resistant alumina nanocrystalline aerogel material prepared by the embodiment is 49m2The density is 0.1g/cm (i.e. the specific surface area after being subjected to 1400 ℃ pyrolysis for 2h under the protection of argon and 600 heat treatment for 5h under the atmosphere of air) in the embodiment3(ii) a The linear shrinkage rate of the high-temperature-resistant alumina nanocrystalline aerogel material prepared by the embodiment after heat treatment at 1400 ℃ for 1 hour in the air atmosphere is 4.5%, which shows that the high-temperature-resistant alumina nanocrystalline aerogel material prepared by the embodiment has the heat resistance temperature of 1400 ℃ and can efficiently insulate heat at high temperature. In the invention, after the prepared high-temperature-resistant alumina nanocrystalline aerogel material is subjected to heat treatment at a high heat treatment temperature (for example, 1200-1400 ℃) in an air atmosphere, the linear shrinkage of the aerogel material is more than 10%, which means that the heat-resistant temperature of the aerogel material is less than the heat treatment temperature.
Example 2
Example 2 is essentially the same as example 1, except that: the amount of the alumina nanocrystal dispersion used in step S1 was 20 g.
The heat insulation performance test of the high temperature resistant alumina nanocrystal aerogel material in example 2 shows that the surface of the high temperature resistant alumina nanocrystal aerogel material has no light loss, no color change and no shedding, and other performance indexes are shown in table 1.
The linear shrinkage rate of the high-temperature-resistant alumina nanocrystalline aerogel material prepared in the embodiment after heat treatment at 1400 ℃ for 1 hour in air atmosphere is 5.3%.
Example 3
Example 3 is essentially the same as example 1, except that: in step S4, the freezing condition is-45 deg.C freezing for 72h, and the freeze-drying condition is-70 deg.C drying for 72 h.
The heat insulation performance test of the high-temperature resistant alumina aerogel material in example 3 shows that the surface of the high-temperature resistant special-shaped nanocrystalline aerogel material has no light loss, no color change and no shedding, and other performance indexes are shown in table 1.
The linear shrinkage of the high-temperature-resistant alumina nanocrystalline aerogel material prepared in the embodiment after heat treatment at 1400 ℃ for 1 hour is 8.6%.
Example 4
Example 4 is essentially the same as example 1, except that: in step S4, the freezing condition is-75 deg.C freezing for 72h, and the freeze-drying condition is-70 deg.C drying for 72 h.
The heat insulation performance of the high-temperature resistant alumina aerogel material in example 4 is tested, and it is found that the surface of the high-temperature resistant special-shaped nanocrystalline aerogel material has no light loss, no color change and no shedding, and other performance indexes are shown in table 1.
The linear shrinkage of the high-temperature-resistant alumina nanocrystalline aerogel material prepared in the embodiment after heat treatment at 1400 ℃ for 1 hour is 7.9%.
Example 5
Example 5 is essentially the same as example 1, except that: in step S4, the freezing condition is-60 deg.C freezing for 72h, and the freeze-drying condition is-70 deg.C drying for 72 h.
The heat insulation performance of the high-temperature resistant alumina aerogel material in example 5 is tested, and the surface of the high-temperature resistant special-shaped nanocrystalline aerogel material is found to have no light loss, no color change and no shedding, and other performance indexes are shown in table 1.
The linear shrinkage of the high-temperature-resistant alumina nanocrystalline aerogel material prepared in the embodiment after heat treatment at 1400 ℃ for 1 hour is 8.3%.
Example 6
Example 6 is substantially the same as example 1 except that in step S5, the pyrolysis temperature is 1300 ℃ for 2 h.
The heat insulation performance test of the high-temperature resistant special-shaped nanocrystalline aerogel material in example 6 shows that the surface of the high-temperature resistant special-shaped nanocrystalline aerogel material has no light loss, no color change and no shedding, and other performance indexes are shown in table 1.
The linear shrinkage rate of the high-temperature-resistant alumina nanocrystalline aerogel material prepared in the embodiment after heat treatment at 1300 ℃ for 1h in air atmosphere is 3.5%.
The linear shrinkage rate of the high-temperature-resistant alumina nanocrystalline aerogel material prepared by the embodiment after heat treatment at 1400 ℃ for 1h in air atmosphere is more than 10%, and the high temperature of 1400 ℃ cannot be resisted.
Example 7
Example 7 is essentially the same as example 1, except that: in step S1, the alumina nanocrystal dispersion is prepared from alumina nanorods with a diameter of 100nm and a length of 1.5 μm.
The heat insulation performance test of the high temperature resistant alumina aerogel material in example 7 shows that the surface of the high temperature resistant special-shaped nanocrystalline aerogel material has no light loss, no color change and no shedding, and other performance indexes are shown in table 1.
The linear shrinkage of the high-temperature-resistant alumina nanocrystalline aerogel material prepared in the embodiment after heat treatment at 1400 ℃ for 1 hour is 5.3%.
Comparative example 1
Comparative example 1 is substantially the same as example 1 except that: in step S1, the alumina nanocrystal dispersion is prepared using spherical nanocrystals with a diameter of 13 nm.
The heat insulation performance test of the high-temperature resistant aerogel material prepared by the comparative example shows that the material has lower strength and is pulverized when being touched, and other performance results are shown in table 1.
Comparative example 2
Comparative example 2 is substantially the same as example 1 except that: not including step S3, directly using the alumina nanocrystalline chitosan dispersion obtained in step S2 as a reaction solution; the reaction solution was then sequentially subjected to freezing, freeze-drying, pyrolysis at 1400 ℃ under argon protection for 2 hours, and heat treatment at 600 ℃ under an air atmosphere for 5 hours in the same manner as in steps S4, S5, and S6 in example 1.
SEM test of the high temperature resistant aerogel material prepared by the comparative example shows that a large amount of pores exist in the material, and other performance indexes are shown in Table 1.
The heat conductivity coefficient of the high-temperature-resistant aerogel material prepared by the comparative example is very high and reaches 0.038W/mK, and the heat insulation performance is poor because bubbles are not completely removed.
Comparative example 3
① Sol preparation
160g of methyl orthosilicate and 160g of acetonitrile were weighed into a 500mL beaker, sealed with a preservative film and magnetically stirred for 1 min. After mixing evenly, 60g of hydrochloric acid with the concentration of 0.003mol/L is added as a catalyst, the process needs to be slowly added, and the mixture is stirred for 5min by magnetic force; adding the mixed solution into a 1000mL three-necked bottle, heating at 70 ℃, magnetically stirring, and refluxing for 30min to obtain a first solution of a silica sol precursor; 160g of methyl orthosilicate is added into the obtained first solution of the silica sol precursor, and the mixture is heated and magnetically stirred under the condition of 70 ℃ to react for 16h, so that silica sol (silicon dioxide sol) is obtained. Diluting the silica sol, evaporating out 300g of solvent contained in the silica sol, adding 600g of acetonitrile, uniformly mixing to obtain diluted silica sol, and refrigerating the diluted silica sol for later use.
② nanocrystal assembly process
Dissolving 3.7g of alumina nano powder in 34g of acetonitrile, uniformly stirring to obtain a first mixed solution, adding 8g of diluted silica sol serving as an adhesive into the first mixed solution, performing ultrasonic dispersion for 20min to obtain a second mixed solution, adding 2g of ammonia water with the concentration of 0.43mol/L into the second mixed solution, and continuing performing ultrasonic treatment for 20min to obtain the aerogel wet gel taking oxide nanocrystals as a framework.
③ gelling and aging
And (3) placing the prepared aerogel wet gel in a mold, standing for 24h, and then placing in an oven at 60 ℃ for 48h to finish the gelling and aging processes.
④ solvent displacement
And taking out the gel after the completion of the gelation and the aging, putting the gel into ethanol with the volume being 10 times of that of the gel for solvent replacement, wherein the solvent replacement time is 3d, and the solvent replacement process is repeated for 3 times.
⑤ and carrying out supercritical drying to obtain the aerogel material.
⑥ Heat treatment process under air atmosphere
And (3) heating the aerogel material to 1200 ℃ along with the furnace (the heat treatment temperature), wherein the heating rate is 10 ℃/min, keeping the temperature for 1h (the heat treatment time), and then cooling along with the furnace to room temperature to obtain the high-temperature-resistant aerogel material.
The performance of the high temperature resistant aerogel materials of this comparative example was tested and the results are shown in table 1.
The specific surface area of the high-temperature-resistant aerogel material prepared by the comparative example is 99m2(specific surface area after heat treatment at 1200 ℃ for 1 hour), the linear shrinkage rate of the high temperature resistant aerogel material prepared by the comparative example is 1%, and the heat resistant temperature is 1200 ℃ compared with the aerogel material which is not subjected to heat treatment at 1200 ℃ for 1 hour.
Comparative example 4
① A preparation method of the irregular nanocrystalline dispersion liquid comprises the steps of taking alumina nano powder as a raw material, dispersing 20g of the alumina nano powder in 500mL of aqueous solution, selecting 2mol/L hydrochloric acid solution 15mL as a catalyst (adsorbent) to be added into the mixed liquid of the alumina nano particles, putting the mixed liquid into a reaction kettle with polytetrafluoroethylene as an inner container, sealing, and reacting at 240 ℃ for 3 hours to obtain the irregular nanocrystalline dispersion liquid.
② self-assembly process of the special-shaped nanocrystalline, namely, fully mixing 30g of the prepared special-shaped nanocrystalline dispersion liquid with 20g of silicic acid with solid content of 4%, fully stirring magnetons for 5h, and then carrying out ultrasonic treatment for 30min to obtain a mixed phase first solution for self-assembly of the special-shaped nanocrystalline.
③ gelation reaction, adding 2g NH with concentration of 1 mol/L/into the mixed phase first solution4Fully stirring the solution F and magnetons for 0.5h, and then carrying out ultrasonic treatment for 30min to obtain a mixed phase second solution; then, the mixed phase second solution is placed at 25 ℃ and vacuumized for 0.1h under the vacuum degree of 0.5MPa, and then the solution is taken out and is kept stillStanding to obtain a gelation reaction solution.
④ aging process, which comprises sealing the gelation reaction liquid, aging at 25 deg.C for 12h to fully lap the network, aging in water bath at 60 deg.C for 72h to make the humidity in the beaker above 80%.
⑤ drying, namely aging the gelation reaction liquid, performing solvent replacement for 3 days each time by ethanol for 3 times to obtain silicon-aluminum wet gel, then performing supercritical drying by taking absolute ethanol as a drying medium, namely loading the silicon-aluminum composite wet gel into supercritical drying equipment, placing the supercritical drying equipment into a high-pressure kettle, adding absolute ethanol into the high-pressure kettle, sealing, keeping the pressure and the temperature in the high-pressure kettle at 30 ℃ for 24 hours, and then discharging the absolute ethanol and fluid generated in the drying process to obtain the special-shaped nanocrystalline aerogel material.
⑥ Process of heat treatment in air atmosphere (post-treatment process) comprises treating ⑤ of the shaped nanocrystalline aerogel material at 300 deg.C for 5h to dehydroxylate the Si-Al composite aerogel and strengthen the first skeleton of the Si-Al composite aerogel, cooling the sample to room temperature after the above steps, performing heat treatment at 600 deg.C for 3h to primarily transform the crystal form of the composite Si-Al sol, cooling the sample to room temperature in the above steps, performing heat treatment at 1200 deg.C for 1h, and cooling to room temperature with a furnace to obtain the high temperature resistant shaped nanocrystalline aerogel material with strong structural skeleton, wherein the heating rate of the heat treatment process in the above three stages is 3 deg.C/min.
The heat insulation performance test of the high-temperature resistant special-shaped nanocrystalline aerogel material in the comparative example shows that the surface of the high-temperature resistant special-shaped nanocrystalline aerogel material has no light loss, no color change and no shedding, and other performance indexes are shown in table 1.
The density of the high-temperature resistant special-shaped nanocrystalline aerogel material prepared by the comparative example is 0.15g/cm3The porosity is 92%, the pore size is 100-130 nm, the particle size of gel particles is 100-130 nm, and the specific surface area is 328m2The heat resistance temperature was 1200 ℃ and the thermal conductivity was 0.024W/m.K.
In this comparative example, the linear shrinkage rate of the high temperature resistant shaped nanocrystalline aerogel material prepared by this comparative example was 0.65% and the heat resistant temperature was 1200 ℃, compared to the shaped nanocrystalline aerogel material prepared by ⑤ without being heat treated in the above three stages of this comparative example.
Comparative example 5
Comparative example 5 is substantially the same as comparative example 3, except that, in the heat treatment in the air atmosphere of step ⑥, the aerogel material prepared in step ⑤ was heated in the air atmosphere to 1400 ℃ in the furnace at a heating rate of 10 ℃/min, and after 1 hour of heat treatment, the aerogel material was cooled in the furnace to room temperature to prepare a high temperature resistant aerogel material.
The high-temperature resistant aerogel material prepared by the comparative example has a small specific surface area of not more than 10m after high-temperature heat treatment at 1400 ℃ in air atmosphere2(ii)/g; compared with the aerogel material which is not subjected to 1400 ℃ heat treatment for 1 hour, the linear shrinkage rate of the high-temperature-resistant aerogel material prepared by the comparative example is more than 30% after the high-temperature-resistant aerogel material is subjected to 1400 ℃ heat treatment, and the high-temperature-resistant aerogel material prepared by the comparative example cannot resist the high temperature of 1400 ℃.
Comparative example 6
Comparative example 6 is substantially the same as comparative example 4, except that in the step ⑥ of performing a heat treatment process (post-treatment process) in an air atmosphere, the first stage of the special-shaped nanocrystalline aerogel material prepared in the step ⑤ is subjected to low-temperature treatment at 300 ℃ for 5 hours to enable the silicon-aluminum composite aerogel to undergo a dehydroxylation process, so that the first-stage framework of the silicon-aluminum composite aerogel is strong, after the steps are performed, the sample is cooled to room temperature, the second stage of the sample is subjected to heat treatment at 600 ℃ for 3 hours to enable the crystal form of the composite silicon-aluminum sol to undergo preliminary transformation, after the sample is cooled to room temperature in the step, the third stage of the sample is subjected to heat treatment at 1400 ℃ for 1 hour, and finally the temperature is reduced to room temperature along with a furnace, so that the special-shaped high-temperature resistant nanocrystalline aerogel material with a strong structural framework is obtained.
Compared with the special-shaped nanocrystalline aerogel material prepared in the step ⑤ without being subjected to the heat treatment in the three stages, the linear shrinkage rate of the high-temperature-resistant special-shaped nanocrystalline aerogel material prepared in the comparative example after being subjected to the heat treatment in the third stage at 1400 ℃ for 1 hour is more than 10%, and the high temperature of 1400 ℃ cannot be resisted.
The performance indexes of the high-temperature-resistant alumina nanocrystalline aerogel materials prepared in the embodiments 1 to 7 and the high-temperature-resistant aerogel materials prepared in the comparative examples 1 to 4 are shown in table 1.
The symbol "-" in Table 1 indicates that no corresponding performance index was measured.
Specifically, the following are mentioned: in the present invention, the pore size refers to the average pore size of the microstructure within the aerogel material as a whole, and the gel particle diameter refers to the size of the nanoparticles within the aerogel particles.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention 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 solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. A preparation method of a high-temperature-resistant alumina nanocrystalline aerogel material is characterized by comprising the following steps:
(1) uniformly mixing the alumina nanocrystal dispersion liquid and a chitosan solution to obtain a mixed solution;
(2) adding glacial acetic acid into the mixed solution obtained in the step (1) to dissolve chitosan contained in the mixed solution to obtain a chitosan alumina nanocrystalline mixed solution, and then heating the chitosan alumina nanocrystalline mixed solution at 60-100 ℃ for 4-8 h to obtain a chitosan dispersion liquid of alumina nanocrystals;
(3) vacuumizing the chitosan dispersion liquid of the alumina nanocrystals obtained in the step (2) for 0.1-1 h at the temperature of 25 ℃ and the vacuum degree of 0.1-0.5 MPa to obtain an alumina nanocrystal/chitosan reaction liquid;
(4) sequentially freezing and freeze-drying the alumina nanocrystal/chitosan reaction solution obtained in the step (3) to obtain an alumina/chitosan composite aerogel material;
(5) cracking the alumina/chitosan composite aerogel material obtained in the step (4) for 0.5-12 h under the conditions of inert atmosphere and temperature of 1200-1500 ℃ to obtain an alumina/carbon composite aerogel material; and
(6) and (3) carrying out heat treatment on the alumina/carbon composite aerogel material obtained in the step (5) for 1-12 h in an air atmosphere at the temperature of 500-1400 ℃ to obtain the high-temperature-resistant alumina nanocrystalline aerogel material.
2. The method of claim 1, wherein:
the mass ratio of the dosage of the alumina nanocrystal dispersion liquid to the dosage of the chitosan solution to the dosage of the glacial acetic acid is (10-20): 20: (0.3-0.6).
3. The method of claim 1, wherein:
the mass concentration of the chitosan solution is 1.5-3%.
4. The method of claim 1, wherein:
the diameter of the alumina nanocrystal contained in the alumina nanocrystal dispersion liquid is 100-200nm, and the length of the alumina nanocrystal is 1-3 μm.
5. The method of claim 1, wherein:
in the step (4), the freezing condition is that the freezing is carried out for 2 hours under liquid nitrogen.
6. The method of claim 1, wherein:
in the step (4), the freeze drying is carried out for 12-144 h under the condition that the temperature is-70 ℃.
7. The production method according to any one of claims 1 to 6, characterized in that:
in the step (2), the chitosan alumina nanocrystalline mixed solution is heated for 6 hours at 80 ℃ to obtain the chitosan dispersion liquid of alumina nanocrystals.
8. The production method according to any one of claims 1 to 6, characterized in that:
in the step (5), the alumina/chitosan composite aerogel material obtained in the step (4) is cracked for 1.5-3 hours under the condition of inert atmosphere and the temperature of 1200-1500 ℃.
9. The production method according to any one of claims 1 to 6, characterized in that:
in the step (6), the alumina/carbon composite aerogel material obtained in the step (5) is subjected to heat treatment for 2-5 hours in an air atmosphere at the temperature of 500-700 ℃.
10. A high temperature resistant alumina nanocrystalline aerogel material prepared by the preparation method of any one of claims 1 to 9.
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