CN115368119A - Flexible aerogel made of sub-crystalline alumina nano fibers and preparation method thereof - Google Patents
Flexible aerogel made of sub-crystalline alumina nano fibers and preparation method thereof Download PDFInfo
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Abstract
The invention relates to a sub-crystalline alumina nanofiber flexible aerogel and a preparation method thereof. The preparation method comprises the following steps: mixing the aluminum sol and the binder to obtain spinning solution; performing electrostatic spinning on the spinning solution to obtain an alumina nanofiber precursor, and drying; folding the alumina nanofiber precursor into a fiber bundle for multiple times, and performing compression molding to obtain an alumina nanofiber aerogel precursor; keeping the temperature of the alumina nanofiber aerogel precursor at 400-600 ℃ for 0.8-1.2 h, and cooling to room temperature for degumming; heating the mixture to 700-1000 ℃, preserving the heat for 10-60 min, and cooling the mixture to room temperature to obtain the sub-crystalline alumina nano-fiber flexible aerogel material. The technical problem to be solved is how to prepare the sub-crystalline alumina sodiumThe rice fiber flexible aerogel has better comprehensive performance and lower density (less than or equal to 0.03 g/cm) 3 ) The heat-insulating material also has the advantages of heat conductivity coefficient (less than or equal to 0.02W/m.K), good heat-insulating effect and better mechanical property (the proportion of 100 times of compression and rebound is more than or equal to 96.5%).
Description
Technical Field
The invention belongs to the technical field of aerogel material preparation, and particularly relates to a crystalline alumina nanofiber flexible aerogel and a preparation method thereof.
Background
The aerogel is a novel nano material with a three-dimensional porous network structure and taking solid as a framework and gas as a dispersion medium, the pore diameter of the aerogel reaches hundreds of nanometers, the porosity exceeds 95 percent, and the dispersed phase is porous solid of air. Due to the characteristics, the aerogel material has wide application potential in the aspects of thermal, acoustic, optical, microelectronic and particle detection.
The most widespread field of application of aerogels remains the field of thermal insulation. Due to the unique nanostructure of the aerogel, convective conduction, solid phase conduction and thermal radiation can be effectively reduced. Prior work has demonstrated that aerogel is an effective insulation material.
At present, the common aerogel materials are mainly prepared by preparing sol, aging the sol into wet gel, and drying the wet gel to obtain an aerogel product. But the aerogel product prepared by the method has the advantages of high density, high material brittleness, low strength, no flexibility and elasticity and poor high temperature resistance; the aerogel product prepared by the method can generate serious crystal form transformation and sintering under the high-temperature condition, collapse of an aerogel structure is caused, nano particles grow up, holes are reduced, the specific surface area of the oxide aerogel is sharply reduced, the heat insulation performance of the oxide aerogel is greatly weakened, and heat insulation failure is caused.
Compared with silica aerogel, the alumina aerogel has relatively better high temperature resistance and thermal stability because the microstructure comprises amorphous and various crystal forms, but because the periphery of Si in the silica aerogel is a four-bond and the periphery of Al in the alumina aerogel is a three-bond, the mutual linkage of the alumina aerogel is not tight, and the network structure is looser, so that the alumina aerogel has higher brittleness and poorer strength, the density of the alumina aerogel is high, and the thermal insulation is poor, thereby influencing the popularization and application of the alumina aerogel material.
Disclosure of Invention
The invention mainly aims to provide a flexible ethylene oxide nanofiber aerogel and a preparation method thereof, and aims to solve the technical problem that how to prepare the flexible ethylene oxide nanofiber aerogel can enable the flexible ethylene oxide nanofiber aerogel to have better comprehensive performance and lower density (less than or equal to 0.03 g/cm) 3 ) The heat-insulating material has the advantages of heat conductivity coefficient (less than or equal to 0.02W/m.K), good heat-insulating effect, good mechanical property (the ratio of 100 times of compression and rebound is more than or equal to 96.5%), simple preparation process and more practicability.
The purpose of the invention and the technical problem to be solved are realized by adopting the following technical scheme. The invention provides a preparation method of a flexible aerogel material made of sub-crystalline alumina nano fibers, which comprises the following steps:
1) Mixing the aluminum sol and the binder to obtain spinning solution;
2) Performing electrostatic spinning on the spinning solution to obtain an alumina nanofiber precursor, and drying;
3) Folding the dried alumina nanofiber precursor into a fiber bundle for multiple times, and performing compression molding to obtain an alumina nanofiber aerogel precursor;
4) Keeping the temperature of the alumina nanofiber aerogel precursor at 400-600 ℃ for 0.8-1.2 h, and cooling to room temperature for degumming;
5) And heating the precursor of the alumina nanofiber aerogel after the binder removal to 700-1000 ℃, preserving the heat for 10-60 min, and cooling to room temperature to obtain the sub-crystalline alumina nanofiber flexible aerogel material.
The purpose of the invention and the technical problem to be solved can be further realized by adopting the following technical measures.
Preferably, in the preparation method, the preparation steps of the aluminum sol are as follows:
i) Adding aluminum nitrate into deionized water, and stirring for 0.5-1 h;
II) adding aluminum isopropoxide and ethyl orthosilicate into the solution obtained in the step I), and stirring for 1-3 h;
III) distilling the solution obtained in the step II) at 80 +/-2 ℃ under reduced pressure to obtain the aluminum sol.
Preferably, in the preparation method, the mass ratio of the raw materials aluminum nitrate, aluminum isopropoxide, ethyl orthosilicate and deionized water in the aluminum sol is 1:2 to 3:0.15 to 0.25:75 to 85.
Preferably, in the preparation method, the binder is an absolute ethyl alcohol solution of polyvinylpyrrolidone, and the mass concentration of the binder is 5% to 50%.
Preferably, in the preparation method, the mass ratio of the aluminum sol to the binder is 1:0.5 to 1.
Preferably, in the preparation method, the electrostatic spinning in step 2) is to suck the spinning solution into a syringe of an electrostatic spinning device to inject and discharge filaments; wherein the voltage of electrostatic spinning is-8 KV-7 KV, the injection speed of the spinning solution is 0.35 ml/h-0.37 ml/h, and the distance between the needle point and the fiber collecting plate is 13.5 cm-14.5 cm; the drying is carried out for 18 to 24 hours at the temperature of between 50 and 100 ℃.
Preferably, in the preparation method, in the step 3), the dried alumina nanofiber precursor is folded for multiple times, starting from one end of the alumina nanofiber precursor, and the alumina nanofiber precursor is sequentially folded in a reversing manner according to a set length until the alumina nanofiber precursor is folded into a fiber bundle.
Preferably, in the above preparation method, the press forming in step 3) is to mechanically press a plurality of the fiber bundles to form a block.
The invention aims to solve the technical problem by adopting the following technical schemeIn (1). According to the flexible aerogel material of the sub-crystalline alumina nano-fiber, the density is less than or equal to 0.03g/cm 3 The heat conductivity coefficient is less than or equal to 0.02W/m.K, and the ratio of 100 times of compression resilience is more than or equal to 96.5 percent.
The purpose of the invention and the technical problem to be solved can be further realized by adopting the following technical measures. Preferably, the above-mentioned sub-crystalline alumina nanofiber flexible aerogel material is prepared according to the preparation method of the above-mentioned sub-crystalline alumina nanofiber flexible aerogel material.
By means of the technical scheme, the sub-crystalline alumina nanofiber flexible aerogel and the preparation method provided by the invention at least have the following advantages:
firstly, preparing aluminum nitrate, aluminum isopropoxide, ethyl orthosilicate and deionized water into aluminum sol, and then mixing the aluminum sol and an absolute ethyl alcohol solution of polyvinylpyrrolidone to prepare a specific spinning solution; then carrying out electrostatic spinning on the prepared spinning solution to prepare an alumina nanofiber precursor; then folding and pressing the dried alumina nanofiber precursor for multiple times to form, and carrying out two-stage heat treatment to obtain a sub-crystalline alumina nanofiber flexible aerogel material; namely, the invention prepares a spinning solution with a specific composition by adding a certain adhesive into the alumina sol; because the organic binder is introduced into the spinning solution, the fiber prepared by the spinning solution through electrostatic spinning overcomes the defects that the alumina sol fiber yarn is high in brittleness and difficult to fold or is easy to fold and break through the modification of the organic binder, so that the fiber yarn can be folded for multiple times in the subsequent process; meanwhile, the organic binder is introduced into the fiber yarns, so that the fiber yarns have certain cohesiveness, and the folded fiber bundle can be pressed and formed into a block by mechanical pressurization with small strength to obtain an alumina nanofiber aerogel precursor; then, carrying out two-stage heat treatment on the aerogel precursor to obtain an aerogel final product with excellent comprehensive performance; the two-stage heat treatment process includes maintaining the temperature below the crystallization temperature for some time to avoid crystallization of alumina; in the heat-preserving process, on the one hand, the gas is removedThe organic binder in the gel precursor enables the gel precursor to be removed, so that certain porosity can be increased; on the other hand, a certain amount of carbon residue can still be remained in the aerogel precursor by controlling the temperature and time of the section of heat preservation, so that the carbon residue can act on the sintering procedure of the second-section heat preservation in the subsequent process; the second-stage heat preservation is sintering at a crystallizable temperature, on one hand, the residual carbon remained in the first-stage heat preservation can prevent the crystallization of the second-stage heat preservation from being too fast, so that the structure of the second-stage heat preservation is mainly sub-crystalline grains, on the other hand, by controlling the sintering temperature and the heat preservation time of the second-stage heat preservation, the structure of the fiber yarn can be the noncrystalline alumina on the surface layer, and the crystalline sub-crystalline grains are arranged inside the fiber yarn, so that the noncrystalline coated nano-crystalline grain nano-fiber structure is formed, the high flexibility of a single alumina nano-fiber yarn is realized, and the breaking resistance of the alumina nano-fiber aerogel can be improved; furthermore, the flexible aerogel containing the sub-crystalline alumina nanofibers is prepared by reasonably designing the folding process of the alumina nanofiber precursor and then carrying out two-stage heat treatment process, so that the flexibility of the alumina aerogel material is further improved; the alumina aerogel material prepared by the technical scheme has low density (less than or equal to 0.03 g/cm) 3 ) The composite material has the characteristics of low thermal conductivity (less than or equal to 0.02W/m.K), high elasticity and high flexibility (the rebound ratio is more than or equal to 96.5 percent after 100 times of repeated compression), has excellent heat insulation effect and mechanical property, overcomes the brittleness of alumina aerogel, can deal with more working scenes, and has good application prospect in the field of aerospace.
The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical solutions of the present invention more clearly understood and to make the technical solutions of the present invention practical in accordance with the contents of the specification, the following detailed description is given of preferred embodiments of the present invention with reference to the accompanying drawings.
Drawings
FIG. 1 is an SEM image of a sub-crystalline alumina nanofiber flexible aerogel material prepared in example 1 of the present invention;
fig. 2 is a schematic diagram of the effect of multiple folding of the alumina nanofiber precursor in the embodiment of the present invention.
Detailed Description
To further illustrate the technical means and effects of the present invention adopted to achieve the predetermined objects, the following detailed description will be given to the detailed description of the flexible aerogel made of sub-crystalline alumina nanofibers and the preparation method, the structure, the features and the effects thereof according to the present invention with reference to the accompanying drawings and the preferred embodiments.
The invention provides a flexible aerogel of sub-crystalline alumina nano-fiber and a preparation method thereof, which comprises the steps of firstly mixing alumina sol and a binder to prepare a spinning solution; then carrying out electrostatic spinning on the spinning solution to obtain an alumina nanofiber precursor, and drying; then folding the dried alumina nano fiber precursor into a fiber bundle for multiple times, and performing compression molding to obtain an alumina nano fiber aerogel precursor; and finally, preserving the heat of the alumina nanofiber aerogel precursor at 400-600 ℃ for 0.8-1.2 h, cooling to room temperature for degumming, heating the alumina nanofiber aerogel precursor after degumming to 700-1000 ℃, preserving the heat for 10-60 min, and cooling to room temperature to obtain the sub-crystalline alumina nanofiber flexible aerogel material with excellent comprehensive performance.
In the above technical scheme, the preparation of the spinning solution is a very critical technology. The preferred technical scheme is that firstly, aluminum sol and a binder are prepared; specifically, the preparation steps of the aluminum sol are as follows: adding aluminum nitrate into deionized water, and stirring for 0.5-1 h to fully dissolve the aluminum nitrate to obtain an aluminum nitrate solution; adding aluminum isopropoxide and tetraethoxysilane into the aluminum nitrate solution, and stirring for 1-3 h, wherein the aluminum isopropoxide and tetraethoxysilane are fully dissolved, and the aluminum isopropoxide, tetraethoxysilane and aluminum nitrate are subjected to hydrolysis reaction and crosslinking reaction to generate a crosslinked network structure; then, carrying out reduced pressure distillation on the mixed solution after the reaction under the vacuum condition (the vacuum degree is below 0.8 KPa) of 80 +/-2 ℃, removing water in the solution and micromolecule products generated by the reaction, and obtaining the aluminum sol. A large number of tests show that the mass ratio of the preferred raw materials of aluminum nitrate, aluminum isopropoxide, ethyl orthosilicate and deionized water in the aluminum sol is 1-2.15-0.25; further, the method comprisesThe mass ratio of the raw materials of aluminum nitrate, aluminum isopropoxide, ethyl orthosilicate and deionized water is 1. However, the alumina sol prepared by the above method has poor spinning property when used for spinning, is easily broken, and is difficult to fold. Therefore, the bonding agent is mixed into the aluminum sol according to a certain proportion, on one hand, the filamentation of the aluminum sol is improved so as to facilitate spinning, the flexibility of the fiber after spinning is increased, the fiber is not easy to break, and the subsequent process is easy to carry out after folding; on the other hand, the binding agent can also enable the spun fiber to have certain binding property, and the regularly folded fiber can be pressed and formed through mechanical pressurization with low strength. The binder is an absolute ethyl alcohol solution of polyvinylpyrrolidone, and the mass concentration of the binder is 5-50%; the adhesive is prepared by adding polyvinylpyrrolidone into absolute ethyl alcohol, and the mass concentration of the polyvinylpyrrolidone is controlled to be 5-50% by controlling the addition proportion; preferably, the mass concentration of the polyvinylpyrrolidone is 10-15%; more preferably, the mass concentration of polyvinylpyrrolidone is 12%. The mass ratio of the aluminum sol to the binder is 1:0.5 to 1. That is, the amount of the binder added is 50% to 100% based on the mass of the alumina sol. The addition ratio of the binder in this step has a very important influence on the performance of the final sub-crystalline alumina nanofiber flexible aerogel product. When the binder addition amount was 50%, the density of the final product was 0.05g/cm as shown in example 1 3 The thermal conductivity coefficient is 0.04W/(m.K), the rebound ratio after 100 times of compression is 98.5 percent, the density is small, the thermal conductivity coefficient is low, the heat insulation effect is good, and the elasticity and the flexibility are excellent. As the amount of the binder added to the spinning dope was increased, as shown in example 3, when the amount of the binder added was 100%, the density of the final product was further decreased to 0.03g/cm 3 The product is further light; the thermal conductivity coefficient is further reduced to 0.02W/(m.K), and the heat insulation effect is better; presumably, the reason for this is that the binder is decomposed and burned off in the subsequent two-stage heat treatment process, so that more pores appear in the final product, thereby further reducing the density and further improving the heat insulation effect; while as the amount of the binder added to the spinning dope increases, 1The 00-compression rebound ratio was also reduced to 96.5%, at which time it exhibited a tendency to deteriorate in elasticity and flexibility, although it still had excellent elasticity and flexibility; presumably, the reason for this is probably that as the addition ratio of the binder increases, the filament diameter thereof at the time of spinning becomes larger. Therefore, in order to ensure that the final product of the flexible aerogel containing the sub-crystalline alumina nano-fibers has excellent comprehensive performance, the mass ratio of the alumina sol to the binder in the spinning solution is preferably 1:0.5 to 1.
In the technical scheme, the spinning solution is subjected to electrostatic spinning to obtain an alumina nanofiber precursor, and then the drying step can adopt a mature spinning process in the prior art to carry out spinning and drying; according to the performance of the self-prepared spinning solution, the spinning solution is preferably drawn into an injector of electrostatic spinning equipment for injection spinning; wherein the voltage of electrostatic spinning is-8 KV-7 KV, the injection speed of the spinning solution is 0.35 ml/h-0.37 ml/h, and the distance between the needle point and the fiber collecting plate is 13.5 cm-14.5 cm; in the subsequent embodiment of the invention, the electrostatic spinning is carried out by taking the electrostatic spinning voltage as-7.5 KV, the injection speed of the spinning solution as 0.36ml/h and the distance between the needle point and the fiber collecting plate as 14cm as an example for explanation; the drying is carried out by keeping the temperature at 50-100 ℃ for 18-24 h to fully dry; in the subsequent examples of the present invention, the drying manner is illustrated only by way of example of drying at 60 ℃ for 24h in a forced air drying oven.
In the technical scheme, the process of folding the dried alumina nanofiber precursor into a fiber bundle for multiple times, pressing and forming to obtain the alumina nanofiber aerogel precursor and then carrying out two-stage heat treatment is a very key technology. The preferred technical scheme is that the dried alumina nanofiber precursor is folded for multiple times, wherein the multiple folding is to sequentially fold the alumina nanofiber precursor in a reversing manner from one end of the alumina nanofiber precursor according to a set length until the alumina nanofiber is folded into a fiber bundle; the specific folding mode can be seen in figure 2; the compression molding is to mechanically press a plurality of fiber bundles to form a block; according to the process for preparing the block aerogel precursor by performing pressure forming on the spinning solution after multiple times of folding, on one hand, proper irregular gaps can be reserved among fiber yarns, so that the fiber yarns can achieve low density and low heat conductivity coefficient of a final product due to proper porosity, and on the other hand, the fiber bundles after being folded can be formed into the block aerogel precursor with a regular shape only by mechanical pressure with small force due to the existence of the binder, so that the subsequent heat treatment and other processing are facilitated; meanwhile, the binder is decomposed and burnt in the later heat treatment process, so that more pores are reserved in the final product to ensure the low density and low heat conductivity of the final product.
And finally, carrying out two-stage heat treatment on the block aerogel precursor. Firstly, the alumina nanofiber aerogel precursor is subjected to heat preservation for 0.8 h-1.2 h at the temperature of 400-600 ℃, cooled to room temperature for degumming, then the alumina nanofiber aerogel precursor subjected to degumming is heated to the temperature of 700-1000 ℃ for heat preservation for 10-60 min, and cooled to room temperature, and the sub-crystal alumina nanofiber flexible aerogel material with excellent comprehensive performance is obtained. The two-stage heat treatment is carried out by keeping the temperature for a certain time at the temperature lower than the crystallization temperature, namely 400-600 ℃ so that the alumina is not crystallized completely; under the condition of the heat preservation, the method mainly aims at removing the organic binder in the block aerogel precursor, namely binder removal, so that on one hand, the purity of a final product is ensured, and on the other hand, the porosity of the product can be increased; meanwhile, a certain amount of carbon residue can be reserved in the block aerogel precursor by strictly controlling the temperature and time of the section of heat preservation, so that the carbon residue can act on the sintering procedure of the second-section heat preservation in the subsequent process to control the crystallization speed and the grain size of the crystal grains during the second-section heat preservation; the optimal heat preservation temperature of the section of heat preservation condition is 450-550 ℃; further preferably, the incubation temperature is 500 ℃ and the incubation time at the incubation temperature is 1 hour. The second-stage heat preservation is to preserve heat for a certain time at a crystallizable temperature condition, namely 700 ℃ to 1000 ℃ for sintering, on one hand, the residual carbon remained in the first-stage heat preservation can prevent the crystallization of the second-stage heat preservation from being too fast, so that the structure of the second-stage heat preservation is mainly sub-crystalline grains, on the other hand, the fiber wire structure can present an amorphous alumina-coated nano-crystalline grain nanofiber structure by controlling the sintering temperature and the heat preservation time of the second-stage heat preservation, so that the amorphous alumina-coated nano-crystalline grain nanofiber structure is formed, the high flexibility of the single alumina nano-fiber wire is realized, and the fracture resistance of the alumina nano-fiber aerogel can be improved; the temperature of the second-stage heat preservation is not too low, and if the sintering temperature is lower than 700 ℃, carbon residue may remain in the final product, so that the heat conductivity of the final product is influenced, and the heat insulation effect of the final product is poor; however, the temperature of the second-stage heat preservation is not too high, and if the sintering temperature is higher than 1000 ℃, pores of a final product can be closed due to welding, so that the performance of the final product is affected; the preferable heat preservation temperature of the section of heat preservation condition is 750-850 ℃; further preferably, the holding temperature is 800 ℃ and the holding time at the holding temperature is preferably 10 to 60min. Furthermore, the invention prepares the sub-crystal alumina nanofiber flexible aerogel by reasonably designing the folding process of the alumina nanofiber precursor and then by two-stage heat treatment process, thus further improving the flexibility of the alumina aerogel material.
The alumina aerogel material prepared by the technical scheme has low density (less than or equal to 0.03 g/cm) 3 ) Low thermal conductivity (less than or equal to 0.02W/m.K), high elasticity and high flexibility (the rebound ratio is more than or equal to 96.5 percent after 100 times of repeated compression), has excellent heat insulation effect and mechanical property, and overcomes the original brittleness of the alumina aerogel.
The present invention will be further described with reference to the following examples, which should not be construed as limiting the scope of the invention, but rather as providing those skilled in the art with the necessary understanding that certain insubstantial modifications and variations of the invention can be made without departing from the spirit and scope of the invention as defined above.
Unless otherwise specified, the following materials, reagents and the like are commercially available products well known to those skilled in the art; unless otherwise specified, all methods are well known in the art. Unless defined otherwise, technical or scientific terms used herein shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention belongs.
Example 1
The preparation method of the sub-crystalline alumina nanofiber flexible aerogel comprises the following specific steps:
1. adding 1.4 parts by mass of aluminum nitrate into 112 parts by mass of deionized water, and stirring for 0.5 hour to obtain an aluminum nitrate solution; then, respectively adding 3.5 parts of aluminum isopropoxide and 0.28 part of ethyl orthosilicate into the aluminum nitrate solution, and continuously stirring for 1 hour to obtain a mixed solution; finally, distilling the mixed solution at 80 ℃ to obtain alumina sol; adding 5 parts of polyvinylpyrrolidone into 50 parts of absolute ethyl alcohol, and uniformly stirring to obtain a binder; and adding 50 parts of binder into 100 parts of alumina sol, and uniformly stirring to obtain the spinning solution.
2. Sucking the spinning solution into an injector of electrostatic spinning equipment, and setting parameters of electrostatic spinning, wherein the voltage of the electrostatic spinning is-7.5 KV, the injection speed of the spinning solution is 0.36ml/h, and the distance between the needle point of the injector and a fiber collecting plate is 14cm; and (3) carrying out electrostatic spinning on the spinning solution according to set process parameters to obtain the alumina nanofiber precursor.
3. Drying the alumina nanofiber precursor in a forced air drying oven at 60 ℃ for 24h; then, the dried alumina nano fiber precursor is folded into a fiber bundle for multiple times according to the folding mode shown in the attached figure 2; then, preserving the heat of the fiber bundle in a resistance furnace at 500 ℃ for 1h, cooling to room temperature, and removing the colloid in PVP; and putting the material after the glue discharging into a resistance furnace again for rapid heating, keeping the temperature at 800 ℃ for 30min, and cooling to room temperature to obtain the sub-crystalline alumina nano-fiber flexible aerogel material.
An SEM photograph of the sub-crystalline alumina nanofiber flexible aerogel prepared in this example is shown in fig. 1. Through inspection, the density of the flexible aerogel made of the sub-crystalline alumina nano-fibers in the embodiment is 0.05g/cm 3 The 100-time compression rebound ratio is 98.5%, and the thermal conductivity is 0.04W/(m.K).
Example 2
The preparation method of the sub-crystalline alumina nanofiber flexible aerogel comprises the following specific steps:
1. adding 1.3 parts by mass of aluminum nitrate into 98 parts by mass of deionized water, and stirring for 1 hour to obtain an aluminum nitrate solution; then, respectively adding 2.6 parts of aluminum isopropoxide and 0.32 part of ethyl orthosilicate into the aluminum nitrate solution, and continuously stirring for 3 hours to obtain a mixed solution; finally, distilling the mixed solution at 80 ℃ to obtain alumina sol; adding 7.5 parts of polyvinylpyrrolidone into 75 parts of absolute ethyl alcohol, and uniformly stirring to obtain a binder; and adding 75 parts of binder into 100 parts of alumina sol, and uniformly stirring to obtain the spinning solution.
2. Sucking the spinning solution into an injector of electrostatic spinning equipment, and setting electrostatic spinning parameters, wherein the voltage of electrostatic spinning is set to be-7.5 KV, the injection speed of the spinning solution is 0.36ml/h, and the distance between the needle point of the injector and a fiber collecting plate is 14cm; and (3) carrying out electrostatic spinning on the spinning solution according to set process parameters to obtain the alumina nanofiber precursor.
3. Drying the alumina nanofiber precursor in a forced air drying oven at 60 ℃ for 24h; then, the dried alumina nano fiber precursor is folded into a fiber bundle for multiple times according to the folding mode shown in the attached figure 2; then, preserving the heat of the fiber bundle in a resistance furnace at 400 ℃ for 1.2h, cooling to room temperature, and removing the colloid in PVP; and putting the material after the glue discharge into a resistance furnace again for rapid heating, keeping the temperature at 700 ℃ for 60min, and cooling to room temperature to obtain the sub-crystalline alumina nano-fiber flexible aerogel material.
Through inspection, the density of the flexible aerogel made of the sub-crystalline alumina nano-fibers in the embodiment is 0.04g/cm 3 The rebound ratio after 100 times of compression is 97.5%, and the thermal conductivity is 0.03W/(m.K).
Example 3
The preparation method of the sub-crystalline alumina nanofiber flexible aerogel comprises the following specific steps:
1. adding 1.2 parts by mass of aluminum nitrate into 102 parts by mass of deionized water, and stirring for 1 hour to obtain an aluminum nitrate solution; then, respectively adding 3.6 parts of aluminum isopropoxide and 0.18 part of ethyl orthosilicate into the aluminum nitrate solution, and continuously stirring for 2 hours to obtain a mixed solution; finally, distilling the mixed solution at 80 ℃ to obtain aluminum sol; adding 15 parts of polyvinylpyrrolidone into 100 parts of absolute ethyl alcohol, and uniformly stirring to obtain a binder; and adding 100 parts of binder into 100 parts of alumina sol, and uniformly stirring to obtain the spinning solution.
2. Sucking the spinning solution into an injector of electrostatic spinning equipment, and setting parameters of electrostatic spinning, wherein the voltage of the electrostatic spinning is-7.5 KV, the injection speed of the spinning solution is 0.36ml/h, and the distance between the needle point of the injector and a fiber collecting plate is 14cm; and (3) carrying out electrostatic spinning on the spinning solution according to set process parameters to obtain the alumina nanofiber precursor.
3. Drying the alumina nanofiber precursor in a forced air drying oven at 60 ℃ for 24h; then, folding the dried alumina nano fiber precursor into a fiber bundle for multiple times according to the folding mode shown in the attached figure 2; then, preserving the heat of the fiber bundle in a resistance furnace at 600 ℃ for 0.8h, cooling to room temperature, and removing the colloid in PVP; and putting the material after the glue discharge into a resistance furnace again for rapid heating, preserving the heat at 1000 ℃ for 10min, and cooling to room temperature to obtain the sub-crystalline alumina nano-fiber flexible aerogel material.
Through inspection, the density of the flexible aerogel containing the sub-crystalline alumina nano fibers prepared by the embodiment is 0.03g/cm 3 The 100-time compression rebound ratio is 96.5%, and the thermal conductivity is 0.02W/(m.K).
Comparative example 1
The comparative example prepares an alumina aerogel, and the specific steps are as follows:
1. preparing an aluminum sol by the same method as example 1;
2. aging the aluminum sol at room temperature for 72 hours;
3. and (3) placing the blank body after the gelation in absolute ethyl alcohol for solvent replacement, carrying out freeze drying after the replacement is finished, and obtaining the alumina aerogel after the drying is finished.
The alumina aerogel prepared in this comparative example was examined to have a density of 0.2g/cm 3 The material has high brittleness, no compression resilience and thermal conductivity of 0.06W/(m.K).
The features of the invention claimed and/or described in the specification may be combined, and are not limited to the combinations set forth in the claims by the recitations therein. The technical solutions obtained by combining the technical features in the claims and/or the specification also belong to the scope of the present invention.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, and any simple modification, equivalent change and modification made to the above embodiment according to the technical spirit of the present invention are still within the scope of the technical solution of the present invention.
Claims (10)
1. A preparation method of a sub-crystalline alumina nanofiber flexible aerogel material is characterized by comprising the following steps:
1) Mixing the aluminum sol and the binder to obtain spinning solution;
2) Performing electrostatic spinning on the spinning solution to obtain an alumina nanofiber precursor, and drying;
3) Folding the dried alumina nanofiber precursor into a fiber bundle for multiple times, and performing compression molding to obtain an alumina nanofiber aerogel precursor;
4) Keeping the temperature of the alumina nanofiber aerogel precursor at 400-600 ℃ for 0.8-1.2 h, and cooling to room temperature for degumming;
5) And heating the precursor of the alumina nanofiber aerogel after the binder removal to 700-1000 ℃, preserving the heat for 10-60 min, and cooling to room temperature to obtain the sub-crystalline alumina nanofiber flexible aerogel material.
2. The method according to claim 1, wherein the aluminum sol is prepared by the steps of:
i) Adding aluminum nitrate into deionized water, and stirring for 0.5-1 h;
II) adding aluminum isopropoxide and ethyl orthosilicate into the solution obtained in the step I), and stirring for 1-3 h;
III) distilling the solution obtained in the step II) at 80 +/-2 ℃ under reduced pressure to obtain the aluminum sol.
3. The preparation method according to claim 1, wherein the mass ratio of the raw materials of aluminum nitrate, aluminum isopropoxide, ethyl orthosilicate and deionized water in the aluminum sol is 1:2 to 3:0.15 to 0.25:75 to 85.
4. The method according to claim 1, wherein the binder is an absolute ethyl alcohol solution of polyvinylpyrrolidone, and the mass concentration of the binder is 5 to 50%.
5. The production method according to claim 1, wherein the mass ratio of the aluminum sol to the binder when mixed is 1:0.5 to 1.
6. The preparation method according to claim 1, wherein the electrospinning in step 2) is performed by sucking the spinning solution into a syringe of an electrospinning device and injecting and discharging the spinning solution; wherein the voltage of electrostatic spinning is-8 KV-7 KV, the injection speed of the spinning solution is 0.35 ml/h-0.37 ml/h, and the distance between the needle point and the fiber collecting plate is 13.5 cm-14.5 cm; the drying is carried out for 18 to 24 hours at the temperature of between 50 and 100 ℃.
7. The preparation method according to claim 1, wherein the step 3) of folding the dried alumina nanofiber precursor for multiple times is to fold the alumina nanofiber precursor for a set length in a reverse direction from one end of the alumina nanofiber precursor until the alumina nanofiber precursor is folded into a fiber bundle.
8. The method according to claim 1, wherein the step 3) of press-forming is to mechanically press the plurality of fiber bundles to form a block.
9. The flexible aerogel material of the sub-crystalline alumina nano-fiber is characterized in that the density is less than or equal to 0.03g/cm 3 The heat conductivity coefficient is less than or equal to 0.02W/m.K, and the proportion of 100 times of compression resilience is more than or equal to 96.5 percent.
10. The sub-crystalline alumina nanofiber flexible aerogel material according to claim 9, characterized in that it is prepared according to the preparation method of the sub-crystalline alumina nanofiber flexible aerogel material according to any of claims 1 to 8.
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