CN109553395B

CN109553395B - Low-cost preparation method of ceramic aerogel

Info

Publication number: CN109553395B
Application number: CN201811620414.9A
Authority: CN
Inventors: 王红洁; 苏磊; 卢德; 牛敏; 彭康
Original assignee: Xian Jiaotong University
Current assignee: Xian Jiaotong University
Priority date: 2018-12-28
Filing date: 2018-12-28
Publication date: 2021-11-19
Anticipated expiration: 2038-12-28
Also published as: CN109553395A

Abstract

The invention discloses a low-cost preparation method of ceramic aerogel, belonging to the technical field of aerogel preparation. The method comprises the following steps: 1) preparing slurry: preparing a ceramic precursor sol, and uniformly dispersing the chopped carbon fibers in the precursor sol; 2) molding: shaping the short carbon fibers to construct a porous three-dimensional block material formed by overlapping sol bonded carbon fibers; 3) curing and cracking: heating the porous three-dimensional block material to a precursor curing temperature, carrying out heat preservation treatment, then heating to a precursor cracking temperature, carrying out heat preservation for a certain time, and cooling along with a furnace; 4) carbon removal: and heating the obtained material to 400-1000 ℃, and preserving heat to obtain the ceramic aerogel. The method is suitable for preparing various ceramic aerogels, does not need high-cost drying equipment or long-time-consuming drying process, has the characteristics of low cost and high efficiency, can prepare the ceramic aerogels with various shapes and sizes, and is suitable for large-scale production of the aerogels.

Description

Low-cost preparation method of ceramic aerogel

Technical Field

The invention belongs to the technical field of aerogel preparation, and relates to a low-cost preparation method of ceramic aerogel.

Background

The aerogel is a solid material consisting of gas with the volume of more than 90% and solid with the volume of less than 10%, has the characteristics of low density, high specific surface area and the like, has stable chemical properties, unique acoustic, optical, thermal, mechanical and electrical properties, and has great application value in the fields of heat insulation, heat preservation, catalytic filtration, energy storage, energy conservation, intelligent sensing and the like. The ceramic aerogel has the advantages of high temperature resistance, oxidation resistance, flame retardance and the like, and is an ideal high-temperature heat-insulating material.

The mainstream preparation technique of ceramic aerogels at present is a drying method, aiming at obtaining high porosity by removing the solvent in the gel. The method comprises three modes of supercritical drying, freeze drying and normal pressure drying: 1) supercritical drying is the earliest and most mature process researched in the current aerogel preparation technology. The method mainly comprises the steps of controlling pressure and temperature to enable a solvent to be in a gas-liquid equilibrium state in the drying process, enabling the density of liquid to be the same as the density of saturated steam of the solvent, enabling a gas-liquid interface to disappear, enabling capillary force to disappear, replacing the solvent in gel with a drying medium, and then slowly reducing the pressure to release fluid to obtain the aerogel with the porous network structure. Supercritical drying needs the use of an autoclave, the requirement on the tightness of the autoclave is high, the process operation is complex, the cost is high, the solvent consumption is high, and the problems of safety and explosion prevention exist, so that the large-scale production of the aerogel is limited to a certain extent; 2) the freeze drying is to freeze and form the mixture of target grains or fibers and sol at low temperature, during the process, a great amount of columnar ice crystals grow, the target grains or fibers are gathered among the ice crystals to form a three-dimensional network structure, and then the temperature and the pressure are raised to sublimate the solvent, so that the aerogel with high porosity is left. However, when the gel is frozen, the solvent undergoes phase change, usually resulting in volume change, and stress is generated in the three-dimensional network structure formed by the target particles and fibers, which damages the pore structure of the gel, thus reducing the reliability of the freeze-drying technology and being not suitable for preparing large-size aerogels. In addition, the freeze-drying process has long time for preparing the aerogel and low production efficiency, so that the cost is high and the freeze-drying process is difficult to be used for industrial mass production of the aerogel; 3) the normal pressure drying refers to drying the solvent under the normal pressure environment, the process condition is simple, and the harsh process conditions of supercritical drying at high temperature and high pressure are avoided. However, due to the capillary forces, the drying process at atmospheric pressure tends to cause gel shrinkage cracking, requiring modification of the gel to reduce gel shrinkage. And the problem of long time consumption of solvent replacement exists in the normal pressure drying process, and the required low surface tension solvent is usually toxic, the solvent consumption is large, so that the application of the normal pressure drying preparation technology is limited.

The three methods have the common characteristics of high cost, complex process, long period and low efficiency, and seriously limit the preparation and application of the ceramic aerogel.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide a low-cost preparation method of ceramic aerogel, which has the advantages of simple process, low requirement on equipment, high preparation efficiency and easy realization of industrial large-scale production.

In order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:

the invention discloses a low-cost preparation method of ceramic aerogel, which comprises the following steps:

1) sol preparation: preparing corresponding precursor sol according to the components of the target aerogel;

2) preparing slurry: mixing a certain amount of chopped carbon fibers with the precursor sol to uniformly disperse the chopped carbon fibers in the precursor sol;

3) molding: shaping the short carbon fibers to construct a porous three-dimensional block material formed by overlapping sol bonded carbon fibers;

4) curing and cracking: heating the porous three-dimensional block material to a precursor curing temperature, preserving heat, then heating to a precursor cracking temperature, preserving heat, generating a one-dimensional nano material through chemical reaction between cracking gases, and finally cooling to room temperature along with a furnace to obtain a one-dimensional nano ceramic/carbon fiber composite block material;

5) carbon removal: and (3) placing the one-dimensional nano ceramic/carbon fiber composite block material in an air furnace, heating to 400-1000 ℃, and preserving heat to obtain the ceramic aerogel.

Preferably, in step 1), different kinds of ceramic aerogels can be prepared by selecting the components of the precursor sol.

Preferably, in the step 2), the density and strength of the ceramic aerogel can be adjusted by adjusting the amount of the sol on the surface of the chopped carbon fibers.

Preferably, the density and porosity of the ceramic aerogel can be adjusted by adjusting the length of the chopped carbon fibers and the skeleton density of the chopped carbon fibers.

Preferably, in step 4), different kinds of ceramic aerogels are prepared by adjusting the cracking temperature and atmosphere.

Preferably, the ceramic aerogel prepared by the method has a network-shaped microstructure formed by lapping fibers.

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

according to the preparation method of the ceramic aerogel disclosed by the invention, when the slurry is prepared, the chopped carbon fibers are mixed with the precursor sol, the precursor gel of the target aerogel material exists only on the surfaces and nodes of the chopped carbon fiber templates, and the gaps formed among the chopped carbon fibers do not contain or contain a very small amount of the precursor gel, so that the whole chopped carbon fiber framework still has high porosity, and a maximized space is provided for the generation of the target material. Meanwhile, the precursor gel of the target material in the chopped carbon fiber framework is correspondingly in a porous framework structure, so that the precursor gel can be converted into the target material to the maximum extent, and the obtained aerogel is high in purity and very few in impurities or free of impurities. The whole preparation process is simple, the high porosity is realized by removing the chopped carbon fibers through oxidation, expensive special drying equipment and a drying process which is long in time consumption and severe in process conditions are not needed, the requirement on the equipment is low, and the ceramic aerogel with various shapes and sizes, which is difficult to prepare by the mainstream technology, can be prepared. The method does not need to consume a large amount of solvent, and the used solvent is nontoxic and can be recycled, and the method has the characteristics of high preparation efficiency, high efficiency and low cost. Therefore, the method of the invention is suitable for SiC and Si₃N₄、SiO₂And preparing various ceramic aerogels. Simultaneously, the ceramic aerogel prepared all has the network-like microstructure that the mutual overlap joint of fibre formed for ceramic aerogel possesses excellent flexibility when keeping stable mechanical properties, has overcome the fragility problem that the ceramic aerogel that mainstream technology prepared has, makes ceramic aerogel's reliability obtain showing and improves, makes the application scene of aerogel abundanter.

Drawings

FIG. 1 is a process route diagram of a low-cost preparation method of ceramic aerogel disclosed in the present invention;

FIG. 2-1 is a photomicrograph of the SiC aerogel prepared in example 1;

fig. 2-2 is an XRD pattern of the SiC aerogel prepared in example 1;

FIGS. 2-3 are SEM images of SiC aerogels prepared in example 1;

FIG. 3-1 shows Si prepared in example 2₃N₄A macroscopic photograph of the aerogel;

FIG. 3-2 shows Si prepared in example 2₃N₄XRD pattern of aerogel;

FIGS. 3 to 3 are Si prepared in example 2₃N₄SEM images of aerogels;

FIG. 4-1 is SiO preparation of example 3₂A macroscopic photograph of the aerogel;

FIG. 4-2 is SiO prepared in example 3₂XRD pattern of aerogel;

FIGS. 4-3 are SiO preparations from example 3₂SEM image of aerogel.

Detailed Description

In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

The invention is described in further detail below with reference to the accompanying drawings:

referring to fig. 1, the method for preparing ceramic aerogel with low cost according to the present invention comprises the following steps:

1) preparing slurry: preparing ceramic precursor sol with a certain concentration, and uniformly dispersing a certain amount of chopped carbon fibers in the precursor solution;

2) molding: shaping the short carbon fibers to construct a porous three-dimensional block material formed by overlapping sol bonded carbon fibers;

3) curing and cracking: heating the porous three-dimensional block material to a precursor curing temperature, preserving heat for a certain time, then heating to a precursor cracking temperature, preserving heat for a certain time, and cooling along with a furnace;

4) carbon removal: heating the obtained material to 400-1000 ℃, and preserving heat for a certain time to obtain the ceramic aerogel.

Example 1

The embodiment prepares the SiC aerogel, and the specific steps are as follows:

1) and preparing a precursor solution. Preparing a silica sol by taking polysiloxane sol (with the mass fraction of 50 wt.%) as a raw material and absolute ethyl alcohol as a solvent (with the mass fraction of 50 wt.%);

2) dispersing chopped carbon fibers (with the length of 1mm and the mass fraction of 1 wt.%) in silica sol, and mechanically stirring to uniformly disperse the chopped carbon fibers in the silica sol;

3) removing redundant silica sol by adopting a vacuum filtration method, and enabling carbon fibers dispersed in the sol to be mutually overlapped to form a block body with a layered structure;

4) heating to 100 ℃, carrying out heat preservation treatment for 4 hours to solidify the SiC nanowire, then heating to 1500 ℃, carrying out heat preservation treatment for 4 hours by using argon, carrying out gel cracking to generate SiC nanowire, and cooling to room temperature along with a furnace to form an intermediate structure of the SiC nanowire/carbon fiber framework;

5) and heating the intermediate structure to 700 ℃ again, and carrying out heat preservation treatment for 2h to obtain the SiC aerogel.

The macroscopic photograph of the SiC aerogel prepared in this example is shown in fig. 2-1, and it can be seen from the figure that the SiC aerogel stands on the tips of the veins of the asparagus fern, and the veins of the asparagus fern are not bent and deformed, indicating that the SiC aerogel prepared in this example has an ultra-low density.

The XRD pattern of the SiC aerogel prepared in this example is shown in fig. 2-2, and it can be seen from the XRD pattern that the SiC aerogel prepared in this example is 3C — SiC and exhibits a small peak around 33.7 °, which is caused by the stacking faults in the silicon carbide nanowires. The nano-wires in the silicon carbide aerogel prepared by the method have more faults, and the thermal conductivity of the silicon carbide is reduced.

Referring to fig. 2 to 3, SEM photographs of the SiC aerogel prepared in this example show that the SiC aerogel has a three-dimensional network structure formed by a large number of SiC nanowires intertwined with each other. The length of the silicon carbide nanowire is 50-300 mu m, and the diameter of the silicon carbide nanowire is 30-200 nm.

Example 2

This example prepares Si₃N₄The aerogel comprises the following specific steps:

1) and preparing a precursor solution. Preparing a silica sol by taking polysiloxane sol (with the mass fraction of 60 wt.%) as a raw material and absolute ethyl alcohol as a solvent (with the mass fraction of 40 wt.%);

2) dispersing 10g of chopped carbon fibers (the average length is about 1mm) in 1000ml of silica sol, and carrying out ultrasonic and mechanical stirring to uniformly disperse the chopped carbon fibers in the silica sol;

3) removing redundant silica sol by adopting a filter pressing method, and enabling carbon fibers to be mutually overlapped to form a block body with a layered structure;

4) heating to 70 deg.C, maintaining for 8 hr to solidify sol, heating to 1550 deg.C, maintaining with nitrogen for 2 hr to crack gel, and reacting to obtain Si₃N₄Nanobelt, furnace cooling to form Si₃N₄A nanobelt/carbon fiber skeleton intermediate structure;

5) the intermediate structure was placed in an air oven and warmed to 10 deg.fKeeping the temperature at 00 ℃ for 0.5h, oxidizing and removing carbon fibers to obtain Si₃N₄An aerogel.

Si obtained in this example₃N₄The macroscopic photograph of the aerogel is shown in FIG. 3-1, from which it can be seen that the Si is present₃N₄The aerogel is white macroscopically, and the surface of the aerogel contains millimeter-sized ultra-long silicon nitride nanobelts.

The XRD pattern of the SiC aerogel prepared in this example is shown in FIG. 3-2, and from the XRD pattern, it can be seen that Si prepared in this example₃N₄The characteristic peak of the aerogel belongs to typical alpha-Si 3N4, and no other impurity peak indicates that the Si prepared by the method₃N₄The purity of the aerogel is high.

Si obtained in this example₃N₄SEM photographs of aerogels referring to FIGS. 3-3, it can be seen that Si₃N₄The aerogel microcosmic structure is a network structure formed by numerous silicon nitride nanobelts intertwined with each other. The network structure with high porosity ensures that the silicon nitride aerogel has excellent heat insulation performance.

Example 3

This example prepares SiO₂The aerogel comprises the following specific steps:

1) preparing silica sol by taking tetraethoxysilane (with the mass fraction of 40 wt.%) as a raw material and absolute ethyl alcohol (with the mass fraction of 60 wt.%) as a solvent;

2) dispersing 2g of chopped carbon fibers in 300ml of silica sol, and mechanically stirring for 10min to uniformly disperse the chopped carbon fibers in the silica sol;

3) adopting a vacuum filtration method to enable the carbon fibers to be mutually overlapped into a block body with a layered structure;

4) heating to 150 deg.C, holding for 3 hr to solidify sol, heating to 800 deg.C under the protection of argon gas, holding for 2 hr, and cracking to obtain SiO₂Cooling to room temperature along with the furnace to obtain SiO₂A carbon fiber intermediate structure;

5) placing the intermediate structure in an air furnace, heating to 400 ℃, carrying out heat preservation treatment for 10 hours, and oxidizing to remove carbon fibers to obtain SiO₂An aerogel.

SiO produced in this example₂The macroscopic photograph of the aerogel is shown in FIG. 4-1, from which it can be seen that the SiO is₂The aerogel is macroscopically white.

SiO produced in this example₂The XRD pattern of the aerogel is shown in FIG. 4-2, and from the XRD pattern, the SiO prepared in this example₂The aerogel belongs to amorphous silicon oxide. Compared with crystalline silica aerogel, amorphous silica aerogel has lower thermal conductivity and is more suitable for thermal insulation applications.

SiO produced in this example₂SEM photograph of aerogel referring to FIGS. 4-3, it can be seen that SiO₂The aerogel microstructure is a network structure consisting of countless hollow silicon oxide microtubes, and the diameter of the microtubes is about 2 mu m.

The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.

Claims

1. A low-cost preparation method of ceramic aerogel is characterized by comprising the following steps:

1) sol preparation: preparing corresponding precursor sol according to the components of the target aerogel; the target aerogel comprises SiC aerogel and Si₃N₄Aerogel and SiO₂An aerogel;

2) preparing slurry: mixing a certain amount of chopped carbon fibers with the precursor sol to uniformly disperse the chopped carbon fibers in the precursor sol; the precursor gel of the target aerogel exists only on the surfaces and joints of the chopped carbon fiber templates; the average length of the chopped carbon fibers is 1 mm;

3) molding: shaping the chopped carbon fibers to construct a porous three-dimensional block material which is formed by overlapping sol bonded carbon fibers and has a layered structure, wherein a target aerogel precursor in a chopped carbon fiber framework is correspondingly in a porous framework structure;

2. The method for preparing a ceramic aerogel at low cost according to claim 1, wherein the density and strength of the ceramic aerogel can be adjusted by adjusting the amount of the sol on the surface of the chopped carbon fibers in step 2).

3. The method for preparing a ceramic aerogel at low cost according to claim 1, wherein the density and porosity of the ceramic aerogel can be adjusted by adjusting the length of the chopped carbon fibers and the skeleton density of the chopped carbon fibers.

4. The method for preparing ceramic aerogel with low cost according to claim 1, wherein in step 4), different kinds of ceramic aerogel are prepared by adjusting cracking temperature and atmosphere.

5. The low-cost preparation method of the ceramic aerogel according to any one of claims 1 to 4, wherein the prepared ceramic aerogel has a network-like microstructure formed by mutually lapping fibers.