阅读说明：本技术 一种耐高温块状氧化铝气凝胶制备方法 (Preparation method of high-temperature-resistant massive alumina aerogel ) 是由 冯坚 彭飞 姜勇刚 冯军宗 李良军 于 2021-09-14 设计创作，主要内容包括：本发明提供了一种耐高温块状氧化铝气凝胶制备方法,包括以下步骤：S1、制备氧化铝溶胶：将铝源加入去离子水中,进行反应,然后自然冷却得到水解液；在水解液中加入酸搅拌均匀,将混合液倒入高压釜中,开启搅拌,加热并保温,然后自然冷却,最后加入促凝剂充分搅拌溶解,得到氧化铝溶胶；S2、凝胶老化与置换：将氧化铝溶胶进行凝胶和老化；然后在室温下,将凝胶浸泡在质量分数≥99.5％的无水乙醇中,每隔12h用新的无水乙醇对凝胶浸泡液进行置换,得到凝胶；S3、超临界干燥：将凝胶置于超临界干燥釜中,进行临界干燥,得到耐高温块状氧化铝气凝胶。(The invention provides a preparation method of high-temperature resistant massive alumina aerogel, which comprises the following steps: s1, preparing alumina sol: adding an aluminum source into deionized water, reacting, and naturally cooling to obtain a hydrolysate; adding acid into the hydrolysate, stirring uniformly, pouring the mixed solution into a high-pressure kettle, starting stirring, heating, preserving heat, naturally cooling, and finally adding a coagulant, stirring fully and dissolving to obtain alumina sol; s2, gel aging and replacement: gelling and aging the alumina sol; then, soaking the gel in absolute ethyl alcohol with the mass fraction of more than or equal to 99.5% at room temperature, and replacing the gel soaking solution with new absolute ethyl alcohol every 12 hours to obtain gel; s3, supercritical drying: and (3) placing the gel in a supercritical drying kettle, and carrying out critical drying to obtain the high-temperature resistant massive alumina aerogel.)

1. A preparation method of high-temperature resistant massive alumina aerogel is characterized by comprising the following steps:

s1, preparing alumina sol: adding an aluminum source into deionized water, reacting, and naturally cooling to obtain a hydrolysate; adding acid into the hydrolysate, uniformly stirring, pouring the mixed solution into a high-pressure kettle, starting stirring, heating, preserving heat, naturally cooling, adding a coagulant, stirring and dissolving to obtain alumina sol;

s2, gel aging and replacement: gelling and aging the alumina sol; then, soaking the gel in absolute ethyl alcohol with the mass fraction of more than or equal to 99.5% at room temperature, and replacing the gel soaking solution with new absolute ethyl alcohol every preset time for several times to obtain gel;

s3, supercritical drying: and (3) placing the gel in a supercritical drying kettle, and carrying out critical drying to obtain the high-temperature resistant massive alumina aerogel.

2. The method for preparing a refractory bulk alumina aerogel according to claim 1, wherein in step S1: the aluminum source is any one or a combination of more of aluminum isopropoxide, aluminum sec-butoxide and aluminum n-butoxide; the molar ratio of the deionized water to the aluminum source is (20-80): 1.

3. the method for preparing a refractory bulk alumina aerogel according to claim 1, wherein in step S1: and adding the aluminum source into deionized water at the temperature of 50-95 ℃, and keeping the temperature of 50-95 ℃ for reaction for 1 hour.

4. The method for preparing a refractory bulk alumina aerogel according to claim 1, wherein in step S1: the acid is any one of nitric acid, hydrochloric acid and acetic acid, and the molar ratio of the acid to the aluminum source is (0.05-0.3): 1.

5. the method for preparing the high temperature resistant bulk alumina aerogel according to claim 1, wherein in step S1, the temperature of the mixed solution heated and maintained in the autoclave is 120 to 180 ℃, the temperature maintaining time is 0.5 to 24 hours, and the pressure in the autoclave is 0.1 to 1 MPa.

6. The method for preparing high temperature resistant bulk alumina aerogel according to claim 1, wherein in step S1, the coagulant is any one of urea and hexamethylenetetramine; the molar ratio of the coagulant to the aluminum source is (0.08-0.3): 1.

7. the method for preparing refractory block alumina aerogel according to claim 1, wherein the alumina sol is gelled and aged in step S2 by: and standing the alumina sol for 24-72 hours at the temperature of 80-160 ℃.

8. The method for preparing a refractory block alumina aerogel according to claim 1, wherein in step S2, every predetermined time is every 12 hours; the gel soaking solution is replaced by new anhydrous ethanol for 3-5 times.

9. The method for preparing a refractory bulk alumina aerogel according to claim 1, wherein in step S3, the supercritical drying method comprises: absolute ethyl alcohol with the mass fraction of more than or equal to 99.5% is used as a drying medium, 0.5-2 MPa nitrogen is pre-filled in an autoclave, the autoclave is heated to a temperature above the supercritical point of the ethanol at a speed of 0.5-2 ℃/min, the pressure is slowly released at a speed of 30-100 kPa/min after the autoclave is kept warm for 2-8 h, and finally nitrogen is used for flushing for 15-60 min to obtain the high-temperature resistant massive alumina aerogel.

Technical Field

The invention belongs to the technical field of aerogel material preparation, and particularly relates to a preparation method of high-temperature resistant massive alumina aerogel.

Background

The aerogel is a nano porous material with low density, high porosity and high specific surface area, and has wide application prospects in the fields of heat insulation, catalysis, adsorption and the like. Among them, silica aerogel is the most well studied and has been used as a high-performance heat insulating material. Silica aerogels begin to sinter significantly above 650 c, and their short-term service temperatures typically do not exceed 800 c.

Compared with silica aerogel, the alumina aerogel has more excellent temperature resistance and has great application potential in the fields of heat insulation, catalysis and the like at higher temperature. However, as the temperature increases, the alumina aerogel first dehydrates to transition phase alumina and then to alpha phase alumina. In this process, there are accompanying reductions in specific surface area, volume shrinkage, and collapse of the pore structure.

Baumann et al (Baumann, T.F., et al, Synthesis of high-surface-area alumina precursors with out of the use of alumina precursors. chemistry of materials,2005.17: p.395-401) prepared alumina aerogel using an inorganic aluminum source as a precursor and propylene oxide as a coagulant. The initial specific surface area of the aerogel was high, but at 800 ℃ it decreased significantly, with linear shrinkage reaching 45%.

Zu et al (Guoqing, Z., et al, Synthesis and Thermal beer of High-Surface-area Monolithic Alumina. Rare Metal Materials and Engineering,2016.45(S1): p.522-529) by adding a small amount of chelating agent to Alumina sol and subjecting the mixture to ethanol supercritical drying to obtain a product with an initial specific Surface area of 400-500 m²The specific surface area of the blocky alumina aerogel is reduced to 183m after the blocky alumina aerogel is treated for 2 hours at the temperature of 1000 DEG C²/g。

Chinese patent CN201310403362.0 adopts alcohol dehydration method to control hydrolysis and polycondensation process of aluminum alkoxide, prepares massive alumina aerogel through gelation, aging, solvent replacement and ethanol supercritical drying, and treats aerogel at 1000 deg.CArea of 304m²/g。

Poco et al (Poco, J.F., J.H.S.Jr., and L.W.Hrubesh, Synthesis of hoprosity, monogenic aluminum aerogels. journal of Non-Crystalline Solids,2001.285: p.57-63) proposed hydrolysis of aluminum sec-butoxide with less than stoichiometric water to give an alumina sol, which was catalyzed by addition of acetic acid to gel, and bulk alumina aerogel was prepared by ethanol supercritical drying. The aerogel does not sinter below 950 ℃ and the dimensional shrinkage is 2% at 1050 ℃.

Chinese patent CN201811094188.5 proposes that after aluminum sec-butoxide is dissolved in a mixed solution of water and ethanol, concentrated nitric acid is added to adjust the pH value, methanol, acetone and a catalyst are mixed and then added to generate gel, and the gel is subjected to ethanol displacement and supercritical drying to obtain alumina aerogel. The volume shrinkage of the prepared aerogel after being treated at 900 ℃ and 1100 ℃ for 2 hours is respectively 2 percent and 30 percent. The method needs methanol, aniline and other substances as raw materials, and has high toxicity.

Gaoqingfu et al (Gaoqingfu, et al, preparation of low density, bulk alumina aerogel. inorganic chemistry journal, 2008.24(9): p.1456-1460) prepare bulk alumina aerogel by adding a chelating agent to alumina sol to control the hydrolysis and polycondensation rates of the aluminum alkoxide. After the aerogel is treated for 2 hours at 1200 ℃, the specific surface area is 73m²/g。

Kim et al (Kim, S. -W., S.Iwamoto, and M.Inoue, Surface and core structure of aluminum derivative from Materials,2010.17: p.377-385) used aluminum isopropoxide as a raw material and subjected to solvent heat treatment (heat preservation at 300 ℃ for 2 hours) using ethanol as a medium to prepare the alumina aerogel particles. Initial specific surface area of 177m²Per g, the specific surface area is 66m after being treated for 0.5h at 1200 DEG C²A small amount of alpha phase alumina is produced,/g.

Keysar et al (Keysar, S., et al, Heat treatment of alumina aerogels, chemistry of materials,1997.9: p.2464-2467) prepared alumina aerogel using aluminum sec-butoxide and nitric acid as main raw materials and studied the thermal stability of alumina aerogel. After being treated for 1h at 1200 ℃, the specific surface area of the aerogel is less than 100m²The crystal phase is theta phase; after 1300 ℃ treatment for 1h, the specific surface area of the aerogel is reduced to 50m²Less than/g, the conversion is mainly alpha-phase alumina.

It can be seen that the alumina aerogel, although having a high thermal stability, still undergoes a significant shrinkage and a reduction in specific surface area above 1000 ℃, and finally converts to dense alpha-phase alumina. Meanwhile, some alumina aerogels require the use of more toxic raw materials for their preparation. How to prepare the high-temperature resistant massive alumina aerogel material by a simple process and environment-friendly raw materials is still a difficult problem.

Disclosure of Invention

The invention aims to provide a preparation method of high-temperature-resistant massive alumina aerogel, the preparation method has simple process and almost non-toxic raw materials, and the prepared alumina aerogel has the characteristics of high temperature resistance, good blocking property and the like and has wide application prospect in the fields of high-temperature heat insulation, catalysis, adsorption and the like.

The technical scheme of the invention is that the preparation method of the high-temperature resistant massive alumina aerogel comprises the following steps:

s1, preparing alumina sol: adding an aluminum source into deionized water, reacting, and naturally cooling to obtain a hydrolysate; adding acid into the hydrolysate, stirring uniformly, pouring the mixed solution into a high-pressure kettle, starting stirring, heating, preserving heat, naturally cooling, and finally adding a coagulant, stirring fully and dissolving to obtain alumina sol;

s2, gel aging and replacement: gelling and aging the alumina sol; then soaking the gel in absolute ethyl alcohol at room temperature, replacing the gel soaking solution with new absolute ethyl alcohol every predetermined time for several times to obtain gel;

s3, supercritical drying: and (3) placing the gel in a supercritical drying kettle, and carrying out critical drying to obtain the high-temperature resistant massive alumina aerogel.

According to the method, the aluminum source is fully hydrolyzed by using excessive water, so that the crystallinity of a hydrolysate product is improved, and the content of organic groups in the prepared aerogel is greatly reduced; the alumina sol is prepared by high-temperature closed treatment, the size and the shape of the alumina sol particles are regulated and controlled, the crystallinity is improved, the skeleton particles forming the aerogel are in an anisotropic rod-like shape, the contact among aerogel particles is reduced, and the surface activity of crystal particles is reduced. The two measures make the aerogel not easy to sinter and change phase at high temperature and still have very high specific surface area above 1300 ℃. The thermal stability of the alumina aerogel of the present invention is significantly higher than that reported previously.

Further, in step S1, the method includes: the aluminum source is any one or a combination of more of aluminum isopropoxide, aluminum sec-butoxide and aluminum n-butoxide; the molar ratio of the deionized water to the aluminum source is (20-80): 1.

Further, in step S1, the method includes: and adding the aluminum source into deionized water at the temperature of 50-95 ℃, and keeping the temperature of 50-95 ℃ for reaction for 1 hour.

Further, in step S1, the method includes: the acid is any one of nitric acid, hydrochloric acid and acetic acid, and the molar ratio of the acid to the aluminum source is (0.05-0.3): 1.

further, in the step S1, the temperature of the mixed solution after being heated in the autoclave is 120-180 ℃, the time of heat preservation is 0.5-24 h, and the pressure in the autoclave is 0.1-1 MPa.

And (3) in natural air, placing the hydrolysate in an autoclave, sealing, heating to 120-180 ℃, keeping the temperature for 0.5-24 h, keeping the pressure in the autoclave at 0.1-1 MPa, and increasing the aggregation and growth of sol particles at high temperature, so that the crystallinity is improved, the size of crystal grains is increased, and the temperature and the time are important for controlling the growth of the crystal grains.

Further, in step S1, the coagulant is any one of urea and hexamethylenetetramine; the molar ratio of the coagulant to the aluminum source is (0.08-0.3): 1.

Further, in step S2, the method for gelling and aging the alumina sol includes: and standing the alumina sol for 24-72 hours at the temperature of 80-160 ℃.

Further, in the above step S2, every predetermined time means every 12 hours; the gel soaking solution is replaced by new anhydrous ethanol for 3-5 times.

Further, in step S3, the supercritical drying method includes: absolute ethyl alcohol with the mass fraction of more than or equal to 99.5% is used as a drying medium, 0.5-2 MPa of nitrogen is pre-filled in an autoclave, the autoclave is heated to the supercritical point (243.1 ℃ and 6.38MPa) of the ethanol at the speed of 0.5-2 ℃/min, the pressure is slowly released at the speed of 30-100 kPa/min after the temperature is kept for 2-8 h, and finally nitrogen is used for flushing for 15-60 min to obtain the high-temperature resistant massive alumina aerogel.

Drying is carried out in a supercritical mode, so that the surface tension of ethanol in gel pores is zero, and the blocking property and the nano porous structure of the aerogel are ensured.

The invention can achieve the following beneficial effects:

(1) the raw materials adopted by the method have low toxicity, the preparation process is simple and easy to implement, and batch preparation can be realized.

(2) The alumina aerogel obtained by the method has good high-temperature resistance: the initial specific surface area of the aerogel was 250m²More than g, still has very high specific surface area after being treated for 2 hours at 1200, 1300 and 1400 ℃, and is respectively 160, 95 and 28m²/g。

(3) The aerogel obtained by the method still keeps smaller particle size and a porous network structure at 1300 ℃, takes transition phase alumina (theta phase) as a main component, and only has a small amount of alpha phase alumina; theta phase alumina remains at 1400 ℃. Thus, the alumina aerogel of the present invention can maintain its properties at high temperatures without significant degradation.

(4) The alumina aerogel obtained by the method has good blocking property.

According to the method, an excessive deionized water is used for fully hydrolyzing an aluminum source, alumina sol is prepared through high-temperature sealing treatment, and alumina aerogel is obtained through ethanol supercritical drying, so that the raw materials are easily obtained and almost non-toxic, and the preparation process is simple; according to the invention, an aluminum source is fully hydrolyzed by excessive water, so that the crystallinity of a hydrolysate product is improved, and the content of organic groups in the prepared aerogel is greatly reduced; the high-temperature closed treatment of the autoclave realizes the regulation and control of the size and the morphology of alumina sol particles and the increase of the size of crystal grains, so that the skeleton particles forming the aerogel are in an anisotropic rod-like morphology, the contact among the particles is reduced, the surface activity of the crystal grains is reduced, the aerogel is not easy to sinter and change phase, and the aerogel still has a very high specific surface area at the temperature of more than 1300 ℃. The thermal stability of the alumina aerogel of the present invention is significantly higher than that reported previously.

Drawings

These and/or other aspects and advantages of the present invention will become more apparent and more readily appreciated from the following detailed description of the embodiments of the invention, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a flow chart of a process for preparing a high temperature resistant bulk alumina aerogel in an embodiment of the present invention;

FIG. 2 is a transmission electron micrograph of an alumina aerogel prepared in an example of the present invention after drying (300 ℃ C.);

FIG. 3 is a transmission electron microscope image of the alumina aerogel prepared in the example of the present invention after heat treatment at 1300 ℃;

FIG. 4 is a graph showing changes in specific surface area values of alumina aerogels prepared in examples of the present invention after heat treatment at different temperatures.

Detailed Description

In order that those skilled in the art will better understand the present invention, the following detailed description of the invention is provided in conjunction with the accompanying drawings and the detailed description of the invention.

Example 1

A preparation method of high-temperature resistant massive alumina aerogel is shown in a flow chart of a preparation process of the high-temperature resistant massive alumina aerogel as shown in figure 1, and comprises the following steps:

the first step is as follows: uniformly adding aluminum isopropoxide into deionized water at 80 ℃, keeping the temperature of 80 ℃ for reaction for 1h, and naturally cooling to obtain hydrolysate. Adding nitric acid into the hydrolysate, stirring uniformly, pouring the mixed solution into a high-pressure kettle, starting stirring, heating to 140 ℃, preserving heat for 1h, naturally cooling, adding urea, and stirring uniformly to obtain the alumina sol. The molar ratio of deionized water, nitric acid, urea and aluminum isopropoxide is 40:0.1:0.15: 1.

The second step is that: keeping the alumina sol at 90 ℃ for 72h, and gelling and aging the alumina sol; soaking the gel in anhydrous ethanol at room temperature, and replacing the anhydrous ethanol every 12h for 3 times.

And thirdly, placing the gel in a supercritical drying kettle, adopting absolute ethyl alcohol (the mass fraction is more than or equal to 99.5%) as a drying medium, pre-charging 2MPa nitrogen, heating to the temperature above the supercritical point of the ethyl alcohol at the speed of 1 ℃/minute, keeping the temperature for 8 hours, and slowly releasing the pressure at the speed of 50 kPa/minute to obtain the massive alumina-silica aerogel.

The alumina aerogel prepared in example 1 is in a block shape, the microscopic morphology of the alumina aerogel is shown in a transmission electron microscope image shown in fig. 2, the shape of the particles is rod-shaped, the length and width directions of the particles are about 30nm, the thickness of the particles is about 4nm, and the anisotropic structure can reduce contact points among the particles so as to inhibit the tendency of the particles to sinter and grow at high temperature. As shown in the transmission electron micrograph of FIG. 3, the alumina aerogel prepared in example 1 had a compositional particle size of less than 50nm after heat treatment at 1300 deg.C, indicating that no significant sintering and growth occurred. As shown in FIG. 4, the initial specific surface area was 250m²The specific surface areas of the particles are 160, 95 and 28m after being treated for 2 hours at 1200, 1300 and 1400 DEG C²Per g, has good temperature resistance.

Example 2

The first step is as follows: and uniformly adding aluminum sec-butoxide into deionized water at 85 ℃, reacting for 1h at 85 ℃, and naturally cooling to obtain hydrolysate. Adding nitric acid into the hydrolysate, stirring uniformly, pouring the mixed solution into a high-pressure kettle, starting stirring, heating to 140 ℃, preserving heat for 1h, naturally cooling, adding urea, and stirring uniformly to obtain the alumina sol. The molar ratio of deionized water, nitric acid, urea and aluminum sec-butoxide is 40:0.1:0.15: 1.

The second step is that: keeping the alumina sol at 90 ℃ for 72h, and gelling and aging the alumina sol; soaking the gel in anhydrous ethanol at room temperature, and replacing the anhydrous ethanol every 12h for 3 times.

And thirdly, placing the gel in a supercritical drying kettle, adopting absolute ethyl alcohol (the mass fraction is more than or equal to 99.5%) as a drying medium, pre-charging 2MPa nitrogen, heating to the temperature above the supercritical point of the ethyl alcohol at the speed of 1 ℃/minute, keeping the temperature for 8 hours, and slowly releasing the pressure at the speed of 50 kPa/minute to obtain the blocky alumina aerogel.

The alumina aerogel prepared in example 2 was in the form of a block, and the shape of the particles constituting the aerogel was rod-like. The initial specific surface area of the aerogel was 224m²The specific surface areas of the particles are 125, 83 and 26m after being treated for 2 hours at 1200, 1300 and 1400 DEG C²/g。

Example 3

A preparation method of high-temperature resistant massive alumina aerogel is shown in a flow chart of a preparation process of the high-temperature resistant massive alumina aerogel as shown in figure 1, and comprises the following steps:

the first step is as follows: uniformly adding aluminum isopropoxide into deionized water at 80 ℃, keeping the temperature of 80 ℃ for reaction for 1h, and naturally cooling to obtain hydrolysate. Adding nitric acid into the hydrolysate, stirring uniformly, pouring the mixed solution into a high-pressure kettle, starting stirring, heating to 140 ℃, preserving heat for 1h, naturally cooling, adding urea, and stirring uniformly to obtain the alumina sol. The molar ratio of deionized water, nitric acid, urea and aluminum isopropoxide is 20:0.1:0.15: 1.

The second step is that: keeping the alumina sol at 90 ℃ for 72h, and gelling and aging the alumina sol; soaking the gel in anhydrous ethanol at room temperature, and replacing the anhydrous ethanol every 12h for 3 times.

And thirdly, placing the gel in a supercritical drying kettle, adopting absolute ethyl alcohol (the mass fraction is more than or equal to 99.5%) as a drying medium, pre-charging 2MPa nitrogen, heating to the temperature above the supercritical point of the ethyl alcohol at the speed of 1 ℃/minute, keeping the temperature for 8 hours, and slowly releasing the pressure at the speed of 50 kPa/minute to obtain the massive alumina-silica aerogel.

The alumina aerogel prepared in example 3 had an initial specific surface area of 246m²The specific surface areas of the particles are respectively 141, 65 and 16m after being treated for 2 hours at 1200, 1300 and 1400 DEG C²/g。

Example 4

A preparation method of high-temperature resistant massive alumina aerogel is shown in a flow chart of a preparation process of the high-temperature resistant massive alumina aerogel as shown in figure 1, and comprises the following steps:

the first step is as follows: uniformly adding aluminum isopropoxide into deionized water at 80 ℃, keeping the temperature of 80 ℃ for reaction for 1h, and naturally cooling to obtain hydrolysate. Adding nitric acid into the hydrolysate, stirring uniformly, pouring the mixed solution into a high-pressure kettle, starting stirring, heating to 140 ℃, preserving heat for 1h, naturally cooling, adding urea, and stirring uniformly to obtain the alumina sol. The molar ratio of deionized water, nitric acid, urea and aluminum isopropoxide is 80:0.1:0.15: 1.

The second step is that: keeping the alumina sol at 90 ℃ for 72h, and gelling and aging the alumina sol; soaking the gel in anhydrous ethanol at room temperature, and replacing the anhydrous ethanol every 12h for 3 times.

And thirdly, placing the gel in a supercritical drying kettle, adopting absolute ethyl alcohol (the mass fraction is more than or equal to 99.5%) as a drying medium, pre-charging 2MPa nitrogen, heating to the temperature above the supercritical point of the ethyl alcohol at the speed of 1 ℃/minute, keeping the temperature for 8 hours, and slowly releasing the pressure at the speed of 80 kPa/minute to obtain the massive alumina-silica aerogel.

The alumina aerogel prepared in example 4 had an initial specific surface area of 261m²(g) the specific surface areas of the particles after being treated at 1200, 1300 and 1400 ℃ for 2 hours are 157, 89 and 24m respectively²/g。

Example 5

A preparation method of high-temperature resistant massive alumina aerogel is shown in a flow chart of a preparation process of the high-temperature resistant massive alumina aerogel as shown in figure 1, and comprises the following steps:

the first step is as follows: uniformly adding aluminum isopropoxide into deionized water at 80 ℃, keeping the temperature of 80 ℃ for reaction for 1h, and naturally cooling to obtain hydrolysate. Adding nitric acid into the hydrolysate, stirring uniformly, pouring the mixed solution into a high-pressure kettle, starting stirring, heating to 120 ℃, preserving heat for 0.5h, naturally cooling, adding urea, and stirring uniformly to obtain the alumina sol. The molar ratio of deionized water, nitric acid, urea and aluminum isopropoxide is 40:0.1:0.15: 1.

The second step is that: keeping the alumina sol at 90 ℃ for 72h, and gelling and aging the alumina sol; soaking the gel in anhydrous ethanol at room temperature, and replacing the anhydrous ethanol every 12h for 3 times.

And thirdly, placing the gel in a supercritical drying kettle, adopting absolute ethyl alcohol (the mass fraction is more than or equal to 99.5%) as a drying medium, pre-charging 2MPa nitrogen, heating to the temperature above the supercritical point of the ethyl alcohol at the speed of 1 ℃/minute, keeping the temperature for 8 hours, and slowly releasing the pressure at the speed of 50 kPa/minute to obtain the massive alumina-silica aerogel.

The alumina aerogel prepared in example 5 had an initial specific surface area of 268m²The specific surface areas of the particles are 123, 35 and 14m after being treated for 2 hours at 1200, 1300 and 1400 DEG C²/g。

Example 6

A preparation method of high-temperature resistant massive alumina aerogel is shown in a flow chart of a preparation process of the high-temperature resistant massive alumina aerogel as shown in figure 1, and comprises the following steps:

the first step is as follows: uniformly adding aluminum isopropoxide into deionized water at 80 ℃, keeping the temperature of 80 ℃ for reaction for 1h, and naturally cooling to obtain hydrolysate. Adding nitric acid into the hydrolysate, stirring uniformly, pouring the mixed solution into a high-pressure kettle, starting stirring, heating to 180 ℃, preserving heat for 24 hours, naturally cooling, adding urea, and stirring uniformly to obtain the alumina sol. The molar ratio of deionized water, nitric acid, urea and aluminum isopropoxide is 40:0.1:0.15: 1.

The second step is that: keeping the alumina sol at 90 ℃ for 72h, and gelling and aging the alumina sol; soaking the gel in anhydrous ethanol at room temperature, and replacing the anhydrous ethanol every 12h for 3 times.

And thirdly, placing the gel in a supercritical drying kettle, adopting absolute ethyl alcohol (the mass fraction is more than or equal to 99.5%) as a drying medium, pre-charging 2MPa nitrogen, heating to the temperature above the supercritical point of the ethyl alcohol at the speed of 1 ℃/minute, keeping the temperature for 8 hours, and slowly releasing the pressure at the speed of 50 kPa/minute to obtain the massive alumina-silica aerogel.

The alumina aerogel prepared in example 6 had an initial specific surface area of 197m²The specific surface areas of the particles are 124, 33 and 14m after being treated for 2 hours at 1200, 1300 and 1400 DEG C²/g。

Example 7

The first step is as follows: uniformly adding aluminum isopropoxide into deionized water at 80 ℃, keeping the temperature of 80 ℃ for reaction for 1h, and naturally cooling to obtain hydrolysate. Adding hydrochloric acid into the hydrolysate, stirring uniformly, pouring the mixed solution into a high-pressure kettle, starting stirring, heating to 140 ℃, preserving heat for 24 hours, naturally cooling, adding urea, and stirring uniformly to obtain the alumina sol. The molar ratio of deionized water, hydrochloric acid, urea and aluminum isopropoxide is 25:0.1:0.15: 1.

The second step is that: keeping the alumina sol at 90 ℃ for 72h, and gelling and aging the alumina sol; soaking the gel in anhydrous ethanol at room temperature, and replacing the anhydrous ethanol every 12h for 3 times.

And thirdly, placing the gel in a supercritical drying kettle, adopting absolute ethyl alcohol (the mass fraction is more than or equal to 99.5%) as a drying medium, pre-charging 2MPa nitrogen, heating to the temperature above the supercritical point of the ethyl alcohol at the speed of 1 ℃/minute, keeping the temperature for 4 hours, and slowly releasing the pressure at the speed of 50 kPa/minute to obtain the blocky alumina aerogel.

The alumina aerogel prepared in example 3 had an initial specific surface area of 253m²The specific surface areas of the particles are 135 m, 71 m and 26m respectively after being treated for 2 hours at 1200 ℃, 1300 ℃ and 1400 DEG C²/g。

Example 8

The first step is as follows: uniformly adding aluminum isopropoxide into deionized water at 80 ℃, keeping the temperature of 80 ℃ for reaction for 1h, and naturally cooling to obtain hydrolysate. Adding nitric acid into the hydrolysate, stirring uniformly, pouring the mixed solution into a high-pressure kettle, starting stirring, heating to 140 ℃, preserving heat for 1h, naturally cooling, adding urea, and stirring uniformly to obtain the alumina sol. The molar ratio of deionized water, nitric acid, urea and aluminum isopropoxide is 40:0.06:0.15: 1.

The second step is that: keeping the alumina sol at 90 ℃ for 72h, and gelling and aging the alumina sol; soaking the gel in anhydrous ethanol at room temperature, and replacing the anhydrous ethanol every 12h for 3 times.

And thirdly, placing the gel in a supercritical drying kettle, adopting absolute ethyl alcohol (the mass fraction is more than or equal to 99.5%) as a drying medium, pre-charging 2MPa nitrogen, heating to the temperature above the supercritical point of the ethyl alcohol at the speed of 1 ℃/minute, keeping the temperature for 4 hours, and slowly releasing the pressure at the speed of 50 kPa/minute to obtain the blocky alumina aerogel.

The alumina aerogel prepared in example 4 was in the form of a block having an initial specific surface area of 237m²Per g at 1200, 1300, 1400 deg.CThe specific surface areas after 2h are respectively 134, 53 and 18m²/g。

Example 9

The first step is as follows: uniformly adding aluminum isopropoxide into deionized water at 80 ℃, keeping the temperature of 80 ℃ for reaction for 1h, and naturally cooling to obtain hydrolysate. Adding hydrochloric acid into the hydrolysate, stirring uniformly, pouring the mixed solution into a high-pressure kettle, starting stirring, heating to 140 ℃, preserving heat for 1h, naturally cooling, adding urea, and stirring uniformly to obtain the alumina sol. The molar ratio of deionized water, hydrochloric acid, urea and aluminum isopropoxide is 40:0.1:0.15: 1.

The second step is that: keeping the alumina sol at 90 ℃ for 72h, and gelling and aging the alumina sol; soaking the gel in anhydrous ethanol at room temperature, and replacing the anhydrous ethanol every 12h for 3 times.

And thirdly, placing the gel in a supercritical drying kettle, adopting absolute ethyl alcohol (the mass fraction is more than or equal to 99.5%) as a drying medium, pre-charging 2MPa nitrogen, heating to the temperature above the supercritical point of the ethyl alcohol at the speed of 1 ℃/minute, keeping the temperature for 4 hours, and slowly releasing the pressure at the speed of 50 kPa/minute to obtain the blocky alumina aerogel.

The alumina aerogel prepared in example 5 was in the form of a block, and the particles constituting the aerogel were in the form of rods. The initial specific surface area of the aerogel was 238m²The specific surface areas of the particles are respectively 142, 58 and 23m after being treated for 2 hours at 1200, 1300 and 1400 DEG C²/g。

Example 10

The first step is as follows: uniformly adding aluminum isopropoxide into deionized water at 80 ℃, keeping the temperature of 80 ℃ for reaction for 1h, and naturally cooling to obtain hydrolysate. Adding nitric acid into the hydrolysate, stirring uniformly, pouring the mixed solution into a high-pressure kettle, starting stirring, heating to 120 ℃, preserving heat for 1h, naturally cooling, adding hexamethylenetetramine, and stirring uniformly to obtain the alumina sol. The molar ratio of deionized water, hexamethylenetetramine, urea and aluminum isopropoxide is 40:0.1:0.15: 1.

The second step is that: keeping the alumina sol at 90 ℃ for 72h, and gelling and aging the alumina sol; soaking the gel in anhydrous ethanol at room temperature, and replacing the anhydrous ethanol every 12h for 3 times.

And thirdly, placing the gel in a supercritical drying kettle, adopting absolute ethyl alcohol (the mass fraction is more than or equal to 99.5%) as a drying medium, pre-charging 2MPa nitrogen, heating to the temperature above the supercritical point of the ethyl alcohol at the speed of 1 ℃/minute, keeping the temperature for 4 hours, and slowly releasing the pressure at the speed of 50 kPa/minute to obtain the blocky alumina aerogel.

The alumina aerogel prepared in example 6 was in the form of a block, and the shape of the particles constituting the aerogel was a rod. The initial specific surface area of the aerogel was 245m²The specific surface areas of the particles are respectively 148, 52 and 21m after being treated for 2 hours at 1200, 1300 and 1400 DEG C²/g。

Having described embodiments of the present invention, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.