CN117263657A

CN117263657A - Efficient heat-insulation-thermoelectric conversion integrated carbon-doped ceramic nanowire aerogel material and preparation method thereof

Info

Publication number: CN117263657A
Application number: CN202311157179.7A
Authority: CN
Inventors: 程飘; 张恩爽; 李文静; 周彤辉; 廖亚龙; 刘韬; 黄红岩; 赵英民; 张昊
Original assignee: Aerospace Research Institute of Materials and Processing Technology
Current assignee: Aerospace Research Institute of Materials and Processing Technology
Priority date: 2023-09-08
Filing date: 2023-09-08
Publication date: 2023-12-22

Abstract

The invention relates to a high-efficiency heat-insulation-thermoelectric conversion integrated carbon-doped ceramic nanowire aerogel material and a preparation method thereof, wherein the method comprises the following steps: mixing alumina nano powder, an acidic solution and a carbon nano tube dispersion liquid in deionized water, and obtaining a mixed liquid through stirring and ultrasonic treatment; placing the mixed solution in a closed container for hydrothermal reaction to obtain semisolid gel blocks, namely wet gel blocks; sequentially performing aging, solvent replacement and supercritical drying steps on the wet gel block to obtain a carbon nanotube doped nanowire aerogel material; and carrying out heat treatment on the carbon nanotube doped nanowire aerogel material. The preparation method can obtain the carbon-doped ceramic nanowire aerogel material integrating high-efficiency heat insulation and thermoelectric conversion.

Description

Efficient heat-insulation-thermoelectric conversion integrated carbon-doped ceramic nanowire aerogel material and preparation method thereof

Technical Field

The invention relates to the technical field of aerogel preparation, in particular to a carbon-doped ceramic nanowire aerogel material integrating efficient heat insulation and thermoelectric conversion and a preparation method thereof.

Background

Deep space detectors face the problem of power supply due to too little solar radiation and the problem of not obtaining sufficient power in permanently shaded areas. Thermoelectric materials are functional materials that can be converted into electrical energy using a large temperature difference between a high temperature surface and a low temperature surface. However, the existing inorganic thermoelectric materials have the problems of high price, brittleness, poor processability, heavy weight and small power factor. Good thermoelectric materials tend to have higher electrical conductivity and lower thermal conductivity. The aerogel material is a gel material with a dispersion medium as gas, the porosity is up to 80-99.8%, and the density can be as low as 3kg/m ³ The composite material has low density and low heat conductivity, can realize larger temperature difference between the back surface temperature and the front surface temperature, meets the favorable condition of thermoelectric conversion, and has great potential in the aspect of being used as a matrix material of the thermoelectric composite material.

Aerogel materials commonly used for thermoelectric conversion at present are graphene aerogel materials with higher electrical conductivity and thermal conductivity, but due to the limitation of carbon materials, the aerogel materials are easy to oxidize and have lower temperature resistance (450 ℃), so that the aerogel materials are unfavorable for improving output voltage and output current. The traditional ceramic aerogel material has good temperature resistance and is not easy to oxidize, but the pearl necklace-shaped structure formed by stacking most of nano particles often shows brittleness, and serious strength decay and structural collapse occur under larger mechanical stress or thermal shock. In practical applications, fiber reinforcement is required to achieve structural reinforcement. In practical application, the nanowire aerogel has the characteristics of high efficiency, heat insulation and high mechanical strength, but the traditional nanofiber aerogel material is prepared by adopting a nanofiber membrane prepared by electrostatic spinning, dispersing again and then drying in a cold way, and the length-diameter ratio of the fiber is reduced after redispersing again, so that the strength is weak. Therefore, the nanofiber material tends to have larger holes and weaker strength, and is easy to cause short circuit in thermoelectric conversion application, and the problem of current and voltage output cannot be realized. In addition, the conductivity of the ceramic nanowire aerogel material is low, which is unfavorable for the rising of output voltage and current. Therefore, it is important to develop a ceramic nanowire aerogel material with certain strength, high temperature resistance and higher thermal conductivity, ensure that the aerogel material is light and high temperature resistance temperature is not sacrificed, and realize high-efficiency thermoelectric conversion by utilizing the driving of the great temperature difference of the cold surface and the hot surface of the aerogel material.

Disclosure of Invention

In order to solve the technical problems in the prior art, the invention provides the carbon-doped ceramic nanowire aerogel material with simple preparation process, good high-temperature resistance of the material, light weight, high efficiency and integration of heat insulation and thermoelectric conversion and the preparation method thereof.

The invention provides a preparation method of a carbon-doped ceramic nanowire aerogel material integrating efficient heat insulation and thermoelectric conversion, which comprises the following steps:

(1) Mixing alumina nano powder, an acidic solution and a carbon nano tube dispersion liquid in deionized water, and obtaining a mixed liquid through stirring and ultrasonic treatment;

(2) Placing the mixed solution in a closed container for hydrothermal reaction to obtain semisolid gel blocks, namely wet gel blocks;

(3) Sequentially performing aging, a solvent replacement process and a supercritical drying step on the wet gel block obtained in the step (2) to obtain a carbon nanotube doped nanowire aerogel material;

(4) And (3) performing heat treatment on the carbon nanotube doped nanowire aerogel material obtained in the step (3).

Further, the specific steps of the step (1) are as follows: dissolving alumina nano powder with the diameter of 10-100nm in water, adding sulfuric acid solution with the mass of 0.1-30mmol/L of the total solution, then adding single-wall carbon nano tube dispersion liquid with the diameter of 2-3nm and the length of 1 mu m, wherein the alumina nano powder accounts for 5-10% of the mass fraction of the mixed solution, and the single-wall carbon nano tube accounts for 8-15% of the mass fraction of the mixed solution. Stirring in a homogenizing and dispersing machine for 60-90 min after mixing.

And (2) placing the mixed solution in a closed container for hydrothermal reaction at 150-300 ℃ for 5-48h to obtain a semisolid gel block.

Further, step (2) includes: pouring the mixed solution into a polytetrafluoroethylene container, filling the container into a reaction kettle, placing the container into an oven at 150-300 ℃ for heat preservation for 5-48h, and obtaining the carbon nanotube doped hydrated alumina nanowire wet gel after heat preservation is finished. The reaction needs to be carried out under the fully-closed condition, and the material of the container needs to be polymer material which does not react with the system.

Further, the aging temperature in the step (3) is 50-90 ℃ and the aging time is 12-24 hours; the solvent replacement adopts ethanol as a solvent, and the supercritical carbon dioxide drying process is carried out after 3 times of replacement is carried out according to 10 times of the volume of the gel block.

Further, the temperature of the supercritical drying is 20-60 ℃ and the pressure is 10-16Mpa.

Further, the treatment atmosphere of the heat treatment is air atmosphere, the treatment temperature is 600-1200 ℃, and the treatment time is 0.5-2h.

The present invention provides in a second aspect a highly efficient thermally insulating-thermoelectric conversion-integrated carbon-doped ceramic nanowire aerogel material made by the method of the present invention described in the first aspect.

Compared with the prior art, the invention has at least the following beneficial effects:

(1) Compared with the traditional pearl necklace-like aerogel material, the invention has better mechanical strength, the microstructure is formed by mutually winding the nano wires, and even pure aerogel still has good toughness.

(2) The gel process in the preparation method of the aerogel is a hydrothermal process, is different from the traditional RTM (resin transfer molding) pressurizing and injecting process, is not limited by the shape and the size of the reinforcement body, and can be used for preparing aerogel materials with any shape and thickness.

(3) The aerogel material obtained from the gel and post-treatment process to supercritical drying in the preparation process has no size shrinkage, can realize the net size molding of the product, and avoids the problems of cost and cycle increase caused by the machining process.

(4) The carbon nanotube doped alumina nanowire aerogel material prepared by the invention has the functions of heat insulation and thermoelectric, and can be used for preparing functional aerogel materials.

(5) The basic structure of the aerogel material prepared by the method is a nanowire structure, has a self-supporting effect, and has higher temperature resistance level than the aerogel material prepared by the traditional solution-gel method.

(6) Compared with the nanofiber prepared by electrostatic spinning or melt spinning, the nanofiber prepared by the method has a smaller diameter and more excellent heat insulation performance.

(8) The invention can adopt water phase as reaction medium, and avoid environmental pollution and waste caused by using organic solvent in the preparation process.

(10) The aerogel material prepared by the method has excellent high temperature resistance on the premise of keeping low thermal conductivity of less than 0.026W/m.K, and can realize heat insulation application at 1200 ℃ for a long time.

(11) The porosity of the nano-wire aerogel material prepared by the method is above 95%, the pore size is 5-500 nm, the diameter of the nano-wire of the aerogel is 30-200 nm, and the specific surface area at high temperature is 100-600 m ² And/g, the heat-resistant temperature is above 1200 ℃.

Drawings

FIG. 1 is a flow chart of the preparation of the carbon doped ceramic nanowire aerogel material of the present invention.

Fig. 2 is an SEM image of the carbon-doped ceramic nanowire aerogel prepared in example 1 of the present invention.

FIG. 3 is a compressive stress strain graph of the carbon doped ceramic nanowire aerogel prepared in example 1 of the present invention.

FIG. 4 is a graph of output voltage versus time for a carbon doped ceramic nanowire aerogel material prepared in accordance with 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 in connection with the embodiments of the present invention. It will be apparent that the described embodiments are some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

The invention provides a preparation method of a carbon-doped ceramic nanowire aerogel material integrating efficient heat insulation and thermoelectric conversion, which is shown in a figure 1, and comprises the following steps:

(1) Mixing the alumina nano powder, the acid solution and the carbon nano tube dispersion liquid in deionized water, and obtaining a mixed liquid through stirring and ultrasonic treatment.

The method comprises the following specific steps: dissolving alumina nano powder with the diameter of 10-100nm in water, adding sulfuric acid solution with the mass of 0.1-30mmol/L of the total solution, then adding single-wall carbon nano tube dispersion liquid with the diameter of 2-3nm and the length of 1 mu m, wherein the nano powder accounts for 5-10% of the mass of the mixed solution, and the single-wall carbon nano tube accounts for 8-15% of the mass of the mixed solution. Mixing, and stirring in a homogenizing and dispersing machine for 30min.

(2) Placing the mixed solution into a closed container for hydrothermal reaction at 150-300 ℃ for 5-48h to obtain semisolid gel blocks.

The method comprises the following specific steps: pouring the mixed solution into a polytetrafluoroethylene container, filling the container into a reaction kettle, placing the container into an oven at 150-300 ℃ for heat preservation for 5-48h, and obtaining the carbon nanotube doped hydrated alumina nanowire wet gel after heat preservation is finished. The method comprises the following specific steps: the reaction needs to be carried out under the fully-closed condition, and the material of the container needs to be polymer material which does not react with the system.

(3) And (3) sequentially performing aging, a solvent replacement process and a supercritical drying step on the wet gel block obtained in the step (2) to obtain the carbon nanotube doped nanowire aerogel material.

The method comprises the following specific steps: aging at 50-90 ℃ for 12-24h, replacing the solvent with ethanol as the solvent, replacing for 3 times according to 10 times of the volume of the gel block, and performing carbon dioxide supercritical drying. The supercritical drying temperature is 20-60deg.C, and pressure is 10-16Mpa.

(4) And (3) carrying out heat treatment on the aerogel, wherein the treatment system is that the treatment temperature is 600-1000 ℃ and the treatment time is 0.5-2h under the air atmosphere.

The carbon-doped ceramic nanowire aerogel material integrating high-efficiency heat insulation and thermoelectric conversion is realized through the steps.

The invention will be further illustrated by way of example, but the scope of the invention is not limited to these examples.

Example 1

The method comprises the following specific steps: dissolving alumina nano powder with the diameter of 10-100nm in water, adding sulfuric acid solution with the mass of 0.1-30mmol/L, which is 1% of the total solution, then adding single-wall carbon nano tube dispersion liquid with the diameter of 2-3nm and the length of 1 mu m, wherein the nano powder accounts for 8% of the mass of the mixed solution, and the single-wall carbon nano tube accounts for 12% of the mass of the mixed solution. Mixing, and stirring in a homogenizing and dispersing machine for 30min.

(2) The mixed solution is put into a closed container to carry out hydrothermal reaction for 12 hours at 220 ℃ to obtain semisolid gel blocks.

The method comprises the following specific steps: pouring the mixed solution into a polytetrafluoroethylene container, loading the container into a reaction kettle, and placing the container into a baking oven at 220 ℃ for heat preservation for 12 hours to obtain the potassium titanate nanowire wet gel after heat preservation. The method comprises the following specific steps: the reaction needs to be carried out under the fully-closed condition, and the material of the container needs to be polymer material which does not react with the system.

The method comprises the following specific steps: and performing a carbon dioxide supercritical drying process. The temperature of supercritical drying is 50deg.C, and the pressure is 14Mpa.

(4) And carrying out heat treatment on the aerogel, wherein the treatment condition is that the treatment temperature is 600 ℃ and the treatment time is 0.5h under the air atmosphere. The heat treatment has the following functions: on one hand, boehmite crystal phase is converted into alumina, and on the other hand, the stability of the framework structure of the aerogel material is enhanced, so that the problem of heat preservation performance reduction caused by structural damage is not easy to occur at a higher temperature.

The aerogel material prepared in example 1 has good structural strength, and the mechanical property, the thermoelectric property output voltage and the heat insulation property of the high-temperature-resistant high-strength nanowire aerogel in example 1 are tested, as shown in fig. 2, 3 and 4, and the surface of the nanowire aerogel material is free from light loss, discoloration and falling, and other performance indexes are shown in table 1.

As can be seen from fig. 2, the morphology of the carbon-doped ceramic nanowire aerogel material constructs nanowires with one-dimensional basic units, and the nanowires are constructed into a porous network structure, and the carbon nanotubes are uniformly distributed in the network structure. As can be seen from fig. 3, the carbon-doped ceramic nanowire aerogel material has a compressive strength of 1.2MPa at 30% strain, and has the advantage of obvious mechanical strength in the aerogel with the same density. As can be seen from fig. 4, the carbon-doped ceramic nanowire aerogel material has good thermoelectric conversion performance, and an output voltage exists as long as a temperature difference is provided. And the output voltage gradually increases as the temperature difference increases.

Example 2

Example 2 is substantially the same as example 1 except that: in the preparation process of the dispersion liquid in the step 1, the single-walled carbon nanotube dispersion liquid is not added.

The nano aerogel material prepared in example 2 was tested for output voltage, and found to have an output voltage of 0, and other performance indexes are shown in table 1.

Example 3

Example 3 is substantially the same as example 1 except that: in the preparation process of the dispersion liquid in the step 1, only single-wall carbon nano tube dispersion liquid accounting for 5% of the total mass of the solution is added, and alumina nano powder and acid solution are not added.

The output voltage of the nano aerogel material in example 3 was so weak that the nano aerogel material was unstable, and the output voltage data could not be obtained, and other performance indexes are shown in table 1.

Example 4

Example 4 is substantially the same as example 1 except that: in the preparation process of the nano dispersion liquid in the step 1, the multi-wall carbon nano tube with the mass fraction of 15% in the mixed solution is added.

The output voltage for the nano-aerogel of example 4 was lower than that of example 1, and other performance metrics are shown in Table 1

Example 5

Example 5 is substantially the same as example 1 except that: in the preparation process of the nano dispersion liquid in the step 1, the nano powder accounts for 12% by mass.

The nano aerogel in example 5 has weak strength and has chalking phenomenon, and other performance indexes are shown in table 1.

Example 6

Example 6 is substantially the same as example 1 except that: and 2, preparing the nano aerogel material at the temperature of 200 ℃ in the hydrothermal reaction in the step 2.

The nano aerogel material in example 5 has weak strength and has chalking phenomenon, and other performance indexes are shown in table 1.

Example 7

Example 7 is substantially the same as example 1 except that: and 2, carrying out hydrothermal reaction for 10 hours to obtain the nano aerogel material.

The nano aerogel material in example 7 was tested for heat insulation performance, and the aerogel material was found to be weak in strength and to have chalking phenomenon, and other performance indexes are shown in table 1.

Example 8

Example 8 is substantially the same as example 1 except that: and (3) not performing the supercritical drying process in the step (4) and performing normal-pressure drying instead to obtain the nanowire aerogel material.

The aerogel material of the nano aerogel material in example 8 has larger shrinkage and large density, and other performance indexes are shown in table 1.

Example 9

Example 9 is substantially the same as example 1 except that: the nanowire aerogel material is prepared without a heat treatment process.

The aerogel material of the nano aerogel material in example 9 has no pulverization, no shrinkage and good formability, and other performance indexes are shown in table 1.

Example 10

Example 10 is substantially the same as example 1 except that: and 5, the heat treatment process is 1000 ℃, and the nanowire aerogel material is prepared.

The aerogel material of the nano aerogel material in example 10 has no pulverization, no shrinkage and good formability, and other performance indexes are shown in table 1.

Table 1: performance index of carbon-doped ceramic nanowire aerogel materials prepared in examples 1 to 10 and aerogel materials of comparative examples

As can be seen from table 1, carbon nanotubes play an important role in thermoelectric conversion under conditions where aerogels provide low thermal conductivity and high porosity. As the amount of carbon nanotubes added increases, the output voltage increases, but the more the carbon nanotubes are, the better the interface thermal conductivity is, the more the 12% added amount is optimal, and the more the 8% added amount, the lower the output voltage is. The optimal solution of the addition amount of the nano powder is 8%, the addition amount is higher than 8%, the strength is weaker, and the pulverization phenomenon exists; the reaction temperature and the reaction time have influence on the compression strength and the heat conductivity of the carbon-doped ceramic nanowire aerogel material and output voltage, and the temperature and the time are insufficient to ensure that the nanowire aerogel material is weak in strength and has pulverization phenomenon, a continuous network structure cannot be formed and the voltage cannot be output.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; although the 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 scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. The preparation method of the carbon-doped ceramic nanowire aerogel material integrating high-efficiency heat insulation and thermoelectric conversion is characterized by comprising the following steps of:

mixing alumina nano powder, an acidic solution and a carbon nano tube dispersion liquid in deionized water, and obtaining a mixed liquid through stirring and ultrasonic treatment;

placing the mixed solution in a closed container for hydrothermal reaction to obtain semisolid gel blocks, namely wet gel blocks;

sequentially carrying out aging, solvent replacement and supercritical drying on the wet gel block to obtain a carbon nanotube doped nanowire aerogel material;

and carrying out heat treatment on the carbon nanotube doped nanowire aerogel material.

2. The method of claim 1, wherein mixing the alumina nano-powder, the acidic solution, and the carbon nanotube dispersion in deionized water comprises: dissolving alumina nano powder with the diameter of 10-100nm in water, adding sulfuric acid solution with the mass of 0.1-30mmol/L, which is 1% of the total solution mass, and then adding single-wall carbon nano tube dispersion liquid with the diameter of 2-3nm and the length of 1 mu m.

3. The method of claim 1, wherein the alumina nano powder comprises 5-10% of the mixed solution by mass, and the single-walled carbon nano tube comprises 8-15% of the mixed solution by mass.

4. The method according to claim 1, wherein the hydrothermal reaction of the mixed solution is carried out in a closed container by placing the mixed solution in a closed container and performing the hydrothermal reaction at 150-300 ℃ for 5-48 hours.

5. The method according to claim 4, wherein the hydrothermal reaction is carried out by pouring the mixed solution into a polytetrafluoroethylene container, loading the container into a reaction kettle, and placing the container into an oven at 150-300 ℃ for heat preservation for 5-48h to obtain the carbon nanotube doped hydrated alumina nanowire wet gel after heat preservation.

6. The method of claim 1, wherein the aging is at a temperature of 50-90 ℃ for a time of 12-24 hours.

7. The method of claim 1, wherein the solvent displacement is performed 3 times at 10 times the gel block volume using ethanol as the solvent.

8. The method according to claim 1, wherein the supercritical drying is performed at a temperature of 20-60 ℃ and a pressure of 10-16Mpa.

9. The method according to claim 1, wherein the heat treatment atmosphere is an air atmosphere, the treatment temperature is 600-1200 ℃, and the treatment time is 0.5-2h.

10. The carbon-doped ceramic nanowire aerogel material integrated with high-efficiency heat insulation and thermoelectric conversion prepared by the method according to any one of claims 1 to 9.