CN114804199B - Titanium dioxide-alumina aerogel material and preparation method thereof - Google Patents

Titanium dioxide-alumina aerogel material and preparation method thereof Download PDF

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CN114804199B
CN114804199B CN202210563027.6A CN202210563027A CN114804199B CN 114804199 B CN114804199 B CN 114804199B CN 202210563027 A CN202210563027 A CN 202210563027A CN 114804199 B CN114804199 B CN 114804199B
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boron nitride
titanium dioxide
nano powder
alumina
aerogel material
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张恩爽
李文静
张昊
雷朝帅
刘圆圆
张凡
黄红岩
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Aerospace Research Institute of Materials and Processing Technology
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Abstract

The invention relates to a titanium dioxide-alumina aerogel material and a preparation method thereof, wherein the method comprises the following steps: uniformly mixing alumina nano powder, boron nitride nanosheets, titanium dioxide nano powder and sulfuric acid solution by using water to obtain a mixed solution, and then placing the mixed solution at the temperature of 150-300 ℃ for hydrothermal reaction for 12-18h to obtain gel; the mass fraction of the alumina nano powder contained in the mixed solution is 5-20%, and the mass fraction of the boron nitride nano sheet contained in the mixed solution is 1-5%; and sequentially carrying out aging, solvent replacement and supercritical drying on the obtained gel to obtain the titanium dioxide-alumina aerogel material. The invention obtains the titanium dioxide-alumina aerogel material with strong structure, low density and high-efficiency heat insulation.

Description

Titanium dioxide-alumina aerogel material and preparation method thereof
Technical Field
The invention relates to the technical field of aerogel preparation, in particular to a titanium dioxide-alumina aerogel material and a preparation method thereof.
Background
The nano porous aerogel (short for 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 material reaches 80-99.8%, the typical size of the pores is 1-100 nm, and the specific surface area is 200-1000 m 2 A density of as low as 3kg/m 3 And the 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.
The aerogel exhibits excellent low-temperature heat insulation properties by virtue of high porosity and fine skeleton, however, strong infrared radiation at high temperature reduces the heat insulation efficiency of the material at high temperature. Therefore, how to improve the radiation resistance becomes an important breakthrough point for improving the high-temperature insulation material. At the present stage, the infrared radiation performance of the material is mainly improved through two modes, firstly, the radiation resistance is reduced layer by layer through the design of the radiation-resistant screen, and finally, the heat-insulating performance is improved. The method has high requirements on the technological properties of the heat-insulating material and has limited application scenes. The other mode is to dope an anti-radiation agent, wherein the anti-radiation agent comprises powder, whisker, fiber and the like, and the types comprise carbon black, titanium dioxide, iron oxide and the like. The doping mode mainly needs to solve the problem of sedimentation of the anti-radiation agent.
In addition, most of the traditional aerogel materials are pearl necklace-shaped structures formed by accumulating nano particles, the aerogel materials with the structures are brittle, and fiber reinforcement is needed in practical application to realize structure reinforcement. However, the fiber reinforcement process will result in increased density, increased solid phase thermal conductivity and increased process complexity. In addition, some methods for strengthening the skeleton to prepare pure-phase aerogel materials have good structural strength, however, the method usually requires a high-temperature sintering process to increase the size of the skeleton to improve the strength of the materials, so that new problems of high thermal conductivity, high brittleness and the like are brought. The nano-cellulose can prepare nano-cellulose aerogel with a tough structure to a certain degree, but the organic components determine that the nano-cellulose aerogel has poor temperature resistance and is not suitable for heat insulation application. Therefore, developing a nano aerogel material with good structure toughness has important significance.
With the development of science and technology, various fields put higher demands on the toughness, temperature resistance, light weight and heat insulation performance of heat insulation materials, so that an effective method for preparing a titanium dioxide-alumina aerogel material with good structural toughness and high-efficiency heat insulation is needed to be developed.
Disclosure of Invention
In order to solve one or more technical problems in the prior art, the invention provides a titanium dioxide-alumina aerogel material and a preparation method thereof.
The present invention provides in a first aspect a process for the preparation of a titania-alumina aerogel material, the process comprising the steps of:
(1) Uniformly mixing alumina nano powder, boron nitride nanosheets, titanium dioxide nano powder and sulfuric acid solution by using water to obtain a mixed solution, and then placing the mixed solution at the temperature of 150-300 ℃ for hydrothermal reaction for 12-18h to obtain gel; the mass fraction of the alumina nano powder contained in the mixed solution is 5-20%, and the mass fraction of the boron nitride nano sheet contained in the mixed solution is 1-5%;
(2) And (2) sequentially carrying out aging, solvent replacement and supercritical drying on the gel obtained in the step (1) to obtain the titanium dioxide-alumina aerogel material.
Preferably, the particle size of the boron nitride nanosheet is 500nm-10 μm, and the thickness of the boron nitride nanosheet is 50-300 nm.
Preferably, the particle size of the boron nitride nanosheet is 1-2 μm.
Preferably, the particle size of the alumina nano powder is 10-100 nm; and/or the particle size of the titanium dioxide nano powder is 20-200 nm.
Preferably, the amount of the titanium dioxide nanopowder is 1-50%, preferably 10-25%, of the mass of the alumina nanopowder.
Preferably, the amount of the sulfuric acid solution is 0.8 to 7% of the total mass of the mixed solution.
Preferably, the concentration of the sulfuric acid solution is 0.1-30 mmol/L.
Preferably, the aging is: aging for 0.5-10h at 20-90 ℃.
Preferably, the supercritical drying is supercritical carbon dioxide drying, and preferably, the temperature of the supercritical drying is 20-60 ℃ and the pressure is 10-16MPa.
The present invention provides, in a second aspect, a titania-alumina aerogel material produced by the production method according to the first aspect of the present invention.
Compared with the prior art, the invention at least has the following beneficial effects:
(1) Compared with the traditional pearl necklace aerogel material, the nano aerogel material has better mechanical strength, the nano aerogel material is constructed into a 'brick sand' structure, the microstructure of the titanium dioxide-alumina aerogel material in the invention takes a network formed by mutually winding nano wires as sand, and boron nitride nano sheets as bricks are embedded in the network formed by the nano wires, so that the structural strength of the aerogel material is greatly improved, and the pure-phase aerogel material still has good toughness without a relatively high-temperature sintering process.
(2) According to the invention, the solution system adopts a sulfuric acid solution as an adsorbent, so that strong hydrogen bond action exists among nano particles, the action shows that the solution has a macroscopic performance of larger solution viscosity, the nano particles are weakly interacted to form a large network, the large network cannot settle, the added titanium dioxide nano powder does not settle at all, and the uniformly dispersed titanium dioxide nano powder doped aerogel material can be prepared; compared with the traditional method, the system effectively solves the problem of titanium dioxide nano powder sedimentation; the invention realizes the in-situ doping of the titanium dioxide nano powder, the titanium dioxide nano powder in the invention is in-situ doped in a network formed by mutually winding the alumina nanowires, and the formed hierarchical titanium dioxide-alumina aerogel material greatly improves the heat insulation efficiency of the material.
(3) The gel process in the preparation method of the aerogel is a hydrothermal process, is different from the traditional RTM (resin transfer molding) pressing glue injection process, is not limited by the shape and size of the reinforcement, and can be used for preparing aerogel materials with any shape and thickness.
(4) The invention provides a nanowire self-supporting mode for preparing the stable-structure aerogel material for high-temperature-resistant and high-efficiency heat insulation application, the improvement method is feasible, and the nanowire aerogel material with good temperature resistance, toughness and low density can be obtained without a graded heat treatment process, so that the nanowire aerogel material has the advantages of simple preparation process, short preparation period and the like.
(5) The invention can adopt water phase as reaction medium, and avoids environmental pollution and waste caused by using organic solvent in the preparation process.
(6) The density of the graded titanium dioxide-alumina aerogel material prepared by the invention can be as low as 0.12g/cm 3 Compared with other low-density aerogel materials with the same strength, the aerogel material has the characteristic of ultralow density; the aerogel material prepared by the method has excellent high temperature resistance on the premise of keeping low thermal conductivity (as low as 0.024W/m.K), and can realize long-term 900 ℃ heat insulation application.
(7) The porosity of the nanowire aerogel material prepared by the method is about 95%, the diameter of a nanowire unit contained in the nanowire aerogel material prepared by the method is 20-50 nm, the length of the nanowire unit is 5-30 mu m, the specific surface area is large, and the heat-resistant temperature is more than 900 ℃.
Drawings
FIG. 1 is a flow chart of the preparation of the present invention.
FIG. 2 is a schematic view of the "brick sand structure" structure of the titania-alumina aerogel material of the present invention.
FIG. 3 is an optical photograph of the titania-alumina aerogel material prepared in example 1 of the present invention.
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 present invention provides in a first aspect a process for the preparation of a titania-alumina aerogel material, the process comprising the steps of:
(1) Uniformly mixing alumina nano powder, boron nitride nanosheets, titanium dioxide nano powder and a sulfuric acid solution by using water to obtain a mixed solution, and then putting the mixed solution at the temperature of 150-300 ℃ for hydrothermal reaction for 12-18h (such as 12, 13, 14, 15, 16, 17 or 18 h) to obtain gel; the mixed solution contains 5 to 20% by mass of alumina nano-powder (e.g., 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%), and 1 to 5% by mass of boron nitride nano-sheet (e.g., 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%); in the present invention, the gel is a semi-solid gel; the sources of the aluminum oxide nano powder, the boron nitride nano sheet and the titanium dioxide nano powder are not particularly limited, and the products which can be directly purchased in the market are adopted; in the invention, for example, the alumina nano powder, the boron nitride nanosheet, the titanium dioxide nano powder and the sulfuric acid solution are uniformly mixed with water by means of stirring (such as magnetic stirring) and/or ultrasound, and the invention has no special requirement on the stirring and ultrasound conditions, so that the alumina nano powder, the boron nitride nanosheet, the titanium dioxide nano powder and the sulfuric acid solution are uniformly mixed in water; specifically, for example, after magnetic stirring for 1 to 24 hours, ultrasound for 1 to 4 hours, and in the ultrasound process, for example, stopping for 5 minutes every 10 minutes of ultrasound, and then continuing ultrasound; in some specific embodiments, for example, magnetic stirring for 4h followed by sonication for 2h; in the invention, the mixed solution is put into a closed container to carry out hydrothermal reaction for 12 to 18 hours at a temperature of between 150 and 300 ℃ to obtain semi-solid gel; in the present invention, the hydrothermal reaction is required to be carried out under a closed condition, and the material of the closed container is required to be a material which does not react with the system.
(2) Sequentially carrying out aging, solvent replacement and supercritical drying on the gel obtained in the step (1) to obtain a titanium dioxide-alumina aerogel material; in the present invention, it is preferable that the aging is: aging the gel block in an oven at 20-90 ℃ for 0.5-10h, specifically, aging the gel block in a container in an air non-sealed environment at 20-90 ℃ for 0.5-10h, so that the gel block can slightly and slowly shrink in the air atmosphere, the strength of the gel block can be improved, and demolding is facilitated; the solvent substitution may employ, for example, ethanol as a solvent; the supercritical drying may be, for example, supercritical carbon dioxide drying.
In the invention, when the gel is prepared, a sulfuric acid solution is used as a catalyst, so that the finally obtained alumina nanowire aerogel can be ensured; in the invention, titanium dioxide nano powder is added into the raw materials for preparing the gel, so that the titanium dioxide nano powder can be doped in a network formed by the alumina nanowires in situ; according to the invention, the boron nitride nanosheets are added into the raw materials for preparing the gel, and the addition of the boron nitride nanosheets enables the nano aerogel material to be constructed into a brick sand structure (which can also be called as a shell-like structure), the brick sand structure takes the boron nitride nanosheets as bricks, and a network constructed by alumina nanowires as sand, and the special microstructure enables the aerogel in the invention to show a high-strength structural characteristic in a macroscopic view, so that compared with the traditional pearl necklace-shaped aerogel material, the nano aerogel has better mechanical strength, and even pure-phase aerogel does not need a relatively high-temperature sintering process and still has good toughness; for example, chinese patent application CN111943704A discloses a method for preparing a reusable high-temperature resistant nanocrystalline aerogel material, which effectively improves the structural strength of the high-temperature resistant nanocrystalline aerogel, but it needs to perform graded high-temperature heat treatment at 500-700 ℃, 1100-1300 ℃ and a relatively high temperature of 1200-1600 ℃ in sequence to achieve the microscopic strengthening and toughening of the aerogel material, so that the structural strength of the aerogel material is significantly improved.
The invention discloses a preparation method of a gel, which is characterized in that boron nitride nanosheets instead of boron nitride nanopowders are added into the raw materials for preparing the gel, and the boron nitride nanosheets have a certain lamellar area and can be used as a reinforcement material to have a certain structural supporting force so as to increase the mechanical strength of the material; in addition, in the present invention, the mass fraction of the boron nitride nanosheets contained in the mixed solution needs to be controlled within a proper range, that is, the mass fraction of the boron nitride nanosheets contained in the mixed solution is controlled to be 1 to 5%, and the present invention finds that if the content of the boron nitride nanosheets is too small, the effect of improving the structural strength of the aerogel material is not significant, and if the content of the boron nitride nanosheets is too large, the thermal conductivity of the aerogel material is increased, and meanwhile, due to the fact that the content of the boron nitride nanosheets is too large, nanowires contained in the formed nanowire aerogel are separated by the boron nitride nanosheets and become discontinuous, which is also not beneficial to improving the strength of the aerogel material.
According to some preferred embodiments, the boron nitride nanoplates have a particle size (also referred to as a plate size) of 500nm to 10 μm, preferably 1 to 2 μm, and a thickness of 50 to 300nm; in the invention, the thickness of the boron nitride nanosheet is in the nanometer level, so the boron nitride nanosheet is marked as the boron nitride nanosheet; in the invention, the particle size of the boron nitride nanosheet is preferably 500nm-10 μm, and the invention finds that if the particle size of the boron nitride nanosheet is too small, the morphology of the boron nitride nanosheet is close to that of boron nitride nanopowder, and the boron nitride nanosheet cannot well play a role in enhancing the structure of the aerogel material, and if the particle size of the boron nitride nanosheet is too large, the boron nitride is easily lapped and connected with each other in the aerogel to form a heat conduction passage, so that the heat insulation performance of the aerogel material is obviously adversely affected; in the invention, the thickness of the boron nitride nanosheet is preferably 50-300 nm, and it is found that if the thickness of the boron nitride nanosheet is too small, the boron nitride nanosheet is too thin, so that the boron nitride nanosheet is in a folded sheet shape, the strength of the boron nitride nanosheet is small, and the improvement of the strength of the aerogel material is not facilitated, and if the thickness of the boron nitride nanosheet is too large, the dimensions of the boron nitride nanosheet in the X, Y and Z directions are large, and the dimensions are equivalent to a boron nitride solid block, so that on one hand, the heat insulation performance of the aerogel material is reduced, on the other hand, the density of the material is also improved, and the characteristics of the aerogel material, such as high-efficiency heat insulation and light weight, are not facilitated.
According to some preferred embodiments, the boron nitride nanosheets in step (1) are modified boron nitride nanosheets prepared by: placing the boron nitride nanosheet in 45-50 wt% sodium hydroxide solution, performing ultrasonic treatment at 80-100 ℃, then repeatedly washing and filtering with deionized water, and drying to obtain a modified boron nitride nanosheet; preferably, the sonication time is between 20 and 40min (e.g. 20, 25, 30, 35 or 40 min); in the invention, the deionized water is used for repeatedly washing and filtering, which means that the step of repeatedly washing and filtering is carried out by the deionized water until the washed water is neutral; in the invention, the boron nitride nanosheet is preferably the modified boron nitride nanosheet, and the invention finds that the surface of the boron nitride nanosheet treated by the sodium hydroxide solution contains more hydroxyl groups, so that the boron nitride nanosheet has better compatibility in a mixed solution for preparing gel, the boron nitride nanosheet can be well dispersed in an aqueous solution, and the hydroxyl groups on the surface of the boron nitride can form hydrogen bonds with the alumina nanowire, so that the boron nitride nanosheet is not easy to settle, and finally the strength and the heat insulation performance of the aerogel material can be improved more favorably.
According to some preferred embodiments, the alumina nano powder has a particle size of 10 to 100nm; and/or the particle size of the titanium dioxide nano powder is 20-200 nm.
According to some preferred embodiments, the titanium dioxide nanopowder is used in an amount of 1 to 50% (e.g., 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%) and preferably 10 to 25% (e.g., 10%, 12%, 15%, 18%, 20%, 22%, or 25%) of the mass of the alumina nanopowder.
According to some preferred embodiments, the sulfuric acid solution is used in an amount of 0.8 to 7% (e.g., 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, or 7%) of the total mass of the mixed solution; in the present invention, it is preferable that the amount of the sulfuric acid solution is 0.8 to 7% of the total mass of the mixed solution, and if the amount of the sulfuric acid solution is too large, the nanowires become short and thick, which is not favorable for the assembly process, may cause severe pulverization and shrinkage of the material, may also cause weak strength of the material, and may increase the thermal conductivity.
According to some preferred embodiments, the concentration of the sulfuric acid solution is 0.1 to 30mmol/L (e.g., 0.1, 0.5, 1, 3, 5, 8, 10, 15, 20, 25, or 30 mmol/L); in the invention, the concentration of the sulfuric acid solution is preferably 0.1-30 mmol/L, and the invention finds that by adopting the sulfuric acid solution with the preferred concentration, compared with the sulfuric acid solution with high concentration, the nanowire with longer length-diameter ratio can be ensured, the formation of a gel block with stronger strength is facilitated, and the aerogel can be stronger after being dried.
According to some preferred embodiments, the aging is: aging for 0.5-10h at 20-90 ℃.
According to some preferred embodiments, the supercritical drying is supercritical carbon dioxide drying, preferably the supercritical drying is at a temperature of 20 to 60 ℃ and a pressure of 10 to 16MPa.
According to some specific embodiments, the preparation of the titania-alumina aerogel material comprises the steps of:
(1) mixing alumina nano powder with the particle size range of 10-100nm, boron nitride nano sheet with the particle size of 500-10 mu m and the thickness of 50-300 nm, titanium dioxide nano powder with the particle size of 20-200 nm and sulfuric acid solution with the concentration of 0.1-30 mmol/L into deionized water, firstly magnetically stirring for 1-24 h, and then carrying out ultrasonic treatment for 1-4 h (stopping for 5min every 10min of ultrasonic treatment, continuing the ultrasonic treatment), thus obtaining uniformly mixed liquid; in the mixed solution, the mass percent of the alumina nano powder is 5-20%, the mass percent of the boron nitride nano sheet is 1-5%, the dosage of the sulfuric acid solution accounts for 1% of the total weight of the mixed solution, and the dosage of the titanium dioxide nano powder is 1-50% of the dosage of the alumina nano powder.
(2) Placing the mixed solution in a closed container, and performing hydrothermal reaction at 150-300 deg.C for 12-18h to obtain semisolid gel.
(3) Aging the gel in an oven at 20-90 ℃ for 0.5-10 h; the method specifically comprises the following steps: and (3) placing the gel blocks in a container, and aging in air in a non-sealed environment at the temperature of 20-90 ℃ for 0.5-10h.
(4) Carrying out a solvent replacement process and a supercritical drying step on the treated gel block obtained in the step (3) to prepare a titanium dioxide-alumina aerogel material; the method comprises the following specific steps: the solvent replacement adopts ethanol as solvent, and the gel block is replaced for 3 times according to 10 times of the volume of the gel block, and then the supercritical carbon dioxide drying process is carried out, wherein the temperature of the supercritical drying is 20-60 ℃, and the pressure is 10-16MPa.
The present invention provides, in a second aspect, a titania-alumina aerogel material produced by the production method according to 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
(1) Mixing aluminum oxide nano powder with the particle size range of 10-15nm, boron nitride nano sheet with the particle size range of 1-2 mu m and the thickness range of 60-120 nm, titanium dioxide nano powder with the particle size of 20-30 nm and sulfuric acid solution with the concentration of 10mmol/L in deionized water, firstly magnetically stirring for 4 hours, and then carrying out ultrasonic treatment for 2 hours (in the ultrasonic treatment, stopping for 5 minutes every 10 minutes of ultrasonic treatment, and then continuing the ultrasonic treatment), so as to obtain uniformly mixed solution; in the mixed solution, the mass percent of the aluminum oxide nano powder is 8%, the mass percent of the boron nitride nano sheet is 2%, the dosage of the sulfuric acid solution accounts for 1% of the total weight of the mixed solution, and the dosage of the titanium dioxide nano powder is 15% of the mass of the aluminum oxide nano powder.
(2) The mixed solution is put into a closed container to carry out hydrothermal reaction for 12 hours at 230 ℃ to obtain semisolid gel.
(3) The gel is placed in a container and aged for 2h in an oven at 65 ℃ under the air-non-airtight condition.
(4) Carrying out a solvent replacement process and a supercritical drying step on the treated gel block obtained in the step (3) to prepare a titanium dioxide-alumina aerogel material; the method comprises the following specific steps: the solvent replacement adopts ethanol as solvent, and the gel block is replaced for 3 times according to 10 times of the volume of the gel block, and then the supercritical carbon dioxide drying process is carried out, wherein the temperature of the supercritical drying is 50 ℃, and the pressure is 14MPa.
The titanium dioxide-alumina aerogel material (also referred to as titanium dioxide-alumina nanowire aerogel material) prepared in this example has good structural strength, and when a heat insulation performance test is performed, it is found that the surface of the aerogel material has no light loss, no color change, and no falling off.
The diameter of the nanowire unit contained in the prepared titanium dioxide-alumina aerogel material is 20-50 nm, and the length of the nanowire unit is 5-30 μm; the aerogel material prepared in this example had a heat resistance temperature of 900 ℃. Wherein the heat-resistant temperature test is as follows: carrying out heat treatment (in a nitrogen atmosphere) on the aerogel material finally prepared in each embodiment at a certain high temperature for 30min, wherein the linear shrinkage rate of the aerogel material is not more than 5%, which indicates that the aerogel material can tolerate the high temperature; for this example, the aerogel material prepared in this example was heat treated at 900 deg.C (nitrogen atmosphere) for 30min, and the linear shrinkage of the aerogel material was not greater than 5%, and the heat resistance temperature was 900 deg.C.
The compressive strength of the titanium dioxide-alumina aerogel material prepared in the embodiment at 10% compression is 0.82MPa, and the test standard adopted in the compressive strength test of the invention is GB/T134802014 'determination of compressive property of heat insulation products for buildings'.
Example 2
Example 2 is essentially the same as example 1, except that:
in the step (1), the particle size of the boron nitride nanosheet is in the range of 6-10 μm, and the thickness is in the range of 150-250 nm.
The titanium dioxide-alumina aerogel material prepared by the embodiment has good structural strength, and no light loss, no color change and no shedding are found on the surface of the aerogel material when a heat insulation performance test is carried out.
Example 3
Example 3 is essentially the same as example 1, except that:
in the step (1), the particle size of the boron nitride nanosheet ranges from 1 to 2 μm, and the thickness ranges from 15 to 30nm.
Example 4
Example 4 is essentially the same as example 1, except that:
in the step (1), the particle size of the boron nitride nanosheet ranges from 1 to 2 microns, and the thickness ranges from 350 to 400nm.
Example 5
Example 5 is essentially the same as example 1, except that:
in the step (1), the particle size of the boron nitride nanosheet is in the range of 12-15 μm, and the thickness of the boron nitride nanosheet is in the range of 350-400 nm.
Example 6
Example 6 is essentially the same as example 1, except that:
in the step (1), in the mixed solution, the mass percentage of the alumina nano powder is 8%, and the mass percentage of the boron nitride nanosheet is 5.5%.
Example 7
Example 7 is essentially the same as example 1, except that:
in the step (1), the concentration of the sulfuric acid solution used is 2mol/L.
Example 8
Example 8 is essentially the same as example 1, except that:
the step (1) is as follows: mixing alumina nano powder with the particle size range of 10-15nm, a modified boron nitride nanosheet, titanium dioxide nano powder with the particle size of 20-30 nm and a sulfuric acid solution with the concentration of 10mmol/L into deionized water, firstly magnetically stirring for 4h, and then carrying out ultrasound for 2h (stopping for 5min every 10min in the ultrasound process, and then continuing to carry out ultrasound), so as to obtain a uniformly mixed solution; in the mixed solution, the mass percent of the aluminum oxide nano powder is 8%, the mass percent of the modified boron nitride nano sheet is 2%, the use amount of the sulfuric acid solution accounts for 1% of the total weight of the mixed solution, and the use amount of the titanium dioxide nano powder is 15% of the mass of the aluminum oxide nano powder; wherein the preparation of the modified boron nitride nanosheet comprises the following steps: placing the boron nitride nanosheet with the particle size range of 1-2 mu m and the thickness range of 60-120 nm in a sodium hydroxide solution with the concentration of 48wt% for ultrasonic treatment at 80 ℃ for 30min, then repeatedly washing and filtering the boron nitride nanosheet by using deionized water until the washing liquid is neutral after filtering, and drying the boron nitride nanosheet to obtain the modified boron nitride nanosheet.
Example 9
Example 9 is essentially the same as example 1, except that:
the step (1) is as follows: mixing alumina nano powder with the particle size range of 10-15nm, titanium dioxide nano powder with the particle size range of 20-30 nm and a sulfuric acid solution with the concentration of 10mmol/L into deionized water, firstly magnetically stirring for 4 hours, and then carrying out ultrasound for 2 hours (in the ultrasound process, stopping for 5 minutes every 10 minutes, and continuing to carry out ultrasound), so as to obtain a uniformly mixed solution; in the mixed solution, the mass percentage of the aluminum oxide nano powder is 8%, the dosage of the sulfuric acid solution accounts for 1% of the total weight of the mixed solution, and the dosage of the titanium dioxide nano powder accounts for 15% of the mass of the aluminum oxide nano powder.
The strength of the aerogel material prepared in this example is weaker than that of example 1, but the aerogel material can also form a complete block, and other performance indexes are shown in table 1.
Example 10
Example 10 is essentially the same as example 1, except that:
in step (1), an experiment was conducted using an acetic acid solution having a concentration of 10mmol/L instead of the sulfuric acid solution.
The aerogel material prepared by the embodiment has weak strength, the titanium dioxide nano powder is unevenly distributed, and a relatively complete block is not formed.
Example 11
Example 11 is essentially the same as example 1, except that:
in the step (1), the dosage of the sulfuric acid solution accounts for 0.5% of the total weight of the mixed solution.
The aerogel material that this embodiment made is weak in intensity, has the pulverization phenomenon, can't obtain the compressive strength under 10% compression to and can't obtain coefficient of thermal conductivity data.
Example 12
Example 12 is essentially the same as example 1, except that:
in the step (1), the amount of the sulfuric acid solution is 20% of the total weight of the mixed solution.
The aerogel material that this embodiment made is relatively weak in strength, has the pulverization phenomenon.
Example 13
Example 13 is essentially the same as example 1, except that:
the step (1) is as follows: mixing alumina nano powder with the particle size range of 10-15nm, boron nitride nanosheet with the particle size range of 1-2 microns and the thickness range of 60-120 nm and sulfuric acid solution with the concentration of 10mmol/L into deionized water, magnetically stirring for 4 hours, and then carrying out ultrasound for 2 hours (in the ultrasound process, stopping for 5 minutes every 10 minutes of ultrasound, and then continuing to carry out ultrasound), so as to obtain uniformly mixed liquid; in the mixed solution, the mass percent of the aluminum oxide nano powder is 8%, the mass percent of the boron nitride nano sheet is 2%, and the dosage of the sulfuric acid solution accounts for 1% of the total weight of the mixed solution.
The aerogel material in this embodiment has a tough structure and is free from powder falling and falling.
Example 14
Example 14 is essentially the same as example 1, except that:
in the step (1), the amount of the titanium dioxide nanopowder is 50% by mass of the alumina nanopowder.
The aerogel thermal insulation material prepared by the embodiment has weak strength and has the powder falling phenomenon.
Example 15
Example 15 is essentially the same as example 1, except that:
(4) directly performing a supercritical carbon dioxide drying step on the treated gel block obtained in the step (3) without solvent replacement to prepare a titanium dioxide-alumina aerogel material; the supercritical carbon dioxide drying temperature is 50 deg.C, and the pressure is 14MPa.
The aerogel material prepared in the example has serious pulverization and is difficult to form.
Example 16
Example 16 is essentially the same as example 1, except that:
in the step (4), normal pressure drying is adopted to replace the supercritical carbon dioxide drying process.
The aerogel material prepared by the embodiment has larger shrinkage and larger density.
Example 17
Referring to example 1 of chinese patent application CN111943704A, a high temperature resistant nanocrystalline aerogel material was prepared, and the performance index thereof is shown in table 1.
The aerogel materials finally prepared in the embodiments are subjected to performance tests, and the performance indexes are shown in table 1.
Figure BDA0003657376290000141
Figure BDA0003657376290000151
In Table 1, the symbol "-" indicates that the performance index was not tested.
The invention has not been described in detail and is in part known to those of skill in the art.
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 should 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 (9)

1. A method for preparing a titania-alumina aerogel material, comprising the steps of:
(1) Uniformly mixing alumina nano powder, boron nitride nano sheets, titanium dioxide nano powder and a sulfuric acid solution by using water to obtain a mixed solution, and then carrying out hydrothermal reaction on the mixed solution at the temperature of 150 to 300 ℃ for 12 to 18h to obtain gel; the mass fraction of the alumina nano powder contained in the mixed solution is 5-20%, and the mass fraction of the boron nitride nano sheet contained in the mixed solution is 1-5%; the particle size of the boron nitride nanosheet is 500nm to 10 mu m, and the thickness of the boron nitride nanosheet is 50 to 300nm; the dosage of the sulfuric acid solution accounts for 0.8 to 7 percent of the total mass of the mixed solution; the concentration of the sulfuric acid solution is 0.1 to 30mmol/L;
(2) And (2) sequentially carrying out aging, solvent replacement and supercritical drying on the gel obtained in the step (1) to obtain the titanium dioxide-alumina aerogel material.
2. The method of claim 1, wherein:
the particle size of the boron nitride nanosheet is 1-2 μm.
3. The production method according to claim 1 or 2, characterized in that:
the particle size of the alumina nano powder is 10 to 100nm; and/or
The particle size of the titanium dioxide nano powder is 20 to 200nm.
4. The production method according to claim 1 or 2, characterized in that:
the dosage of the titanium dioxide nano powder is 1 to 50 percent of the mass of the aluminum oxide nano powder.
5. The method of manufacturing according to claim 4, characterized in that:
the dosage of the titanium dioxide nano powder is 10 to 25 percent of the mass of the aluminum oxide nano powder.
6. The production method according to claim 1 or 2, characterized in that:
the aging is as follows: aging at 20-90 ℃ for 0.5-10h.
7. The production method according to claim 1 or 2, characterized in that:
the supercritical drying is supercritical carbon dioxide drying.
8. The method for producing according to claim 7, characterized in that:
the temperature of the supercritical drying is 20 to 60 ℃, and the pressure is 10 to 169MPa.
9. The titania-alumina aerogel material produced by the production method according to any one of claims 1 to 8.
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