A method for synthesizing Al2O3-SiO2 aerogel with organic aluminum alcoholate and trialkoxysilane

Abstract

The application provides a preparation method of Al2O3-SiO2 aerogel synthesized by using an organic aluminum alcoholate and a trialkoxysilane. The application uses an organic trialkoxysilane as a silicon source and an organic aluminum alcoholate as an aluminum source, and obtains a translucent block-shaped Al2O3-SiO2 aerogel with low thermal conductivity and high mechanical strength through a sol-gel method, aging, solvent replacement and supercritical fluid drying. 3 The room temperature thermal conductivity and the apparent density of the obtained aerogel are 0.0252 W / (m*K) and 0.207 g / cm 2 , respectively, the specific surface area after initial and 1200 DEG C heat treatment is 639.68 m 2 / g and 90.67 m 2 / g, respectively, and the compressive Young's modulus is 55.33 MPa. The technology helps to promote the application of the Al2O3-SiO2 aerogel in high-efficiency thermal insulation materials.

Description

Technical Field

[0001] This invention relates to a method for preparing Al2O3-SiO2 aerogel using organoaluminum alkoxides and trialkoxysilanes, belonging to the field of aerogel preparation. Background Technology

[0002] In the fields of thermal insulation such as petrochemicals, industrial kilns, and aerospace, in order to improve space utilization, reduce energy consumption, and adapt to harsh environments while ensuring thermal insulation performance, it is necessary to use lightweight, high-temperature resistant, and low-thermal-conductivity high-efficiency thermal insulation materials.

[0003] Aerogels are highly dispersed solid materials composed of nanoscale colloidal particles aggregated to form a nanoporous network structure, with gaseous dispersion media filling the pores. The nanoparticle framework structure and nanoscale pore size distribution of aerogels result in low thermal conductivity, low density, high porosity (up to 99% or more), and high specific surface area (up to 1000 m²). 2 With advantages such as high thermal insulation properties (above / g), it is currently the best solid-state material in terms of thermal insulation performance and is also known as a "super thermal insulation material". Inorganic aerogels have high heat resistance, among which Al2O3-SiO2 aerogel has even better heat resistance and low high-temperature thermal conductivity. The room temperature thermal conductivity of existing alumina-based aerogels is generally 0.029 W / (m·K). By increasing the amount of solvent, the porosity and microstructure of the aerogel can be controlled to reduce the solid-phase thermal conductivity, but this will lead to a decrease in mechanical properties. How to reduce thermal conductivity while improving mechanical properties is particularly important. The chloride ions of inorganic aluminum salt aluminum chloride can corrode metal equipment and cause equipment damage. The removal of chloride ions increases the process flow and cost, which is not conducive to industrial production. At the same time, the alumina-based aerogel prepared by organoaluminum alkoxides has better heat resistance than that of inorganic aluminum salts. Therefore, using organoaluminum alkoxides as the aluminum source and through innovative material processes and ratios to simultaneously improve the thermal insulation and mechanical properties of Al2O3-SiO2 aerogel is of great significance for promoting the engineering application of Al2O3-SiO2 aerogel. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing Al2O3-SiO2 aerogel using organoaluminum alkoxides and trialkoxysilanes. This method uses organoaluminum alkoxides as the silicon source and organoaluminum alkoxides as the aluminum source, and obtains a semi-transparent, blocky Al2O3-SiO2 aerogel with low thermal conductivity and high mechanical strength through sol-gel method, aging, solvent replacement, and supercritical fluid drying. The obtained aerogel has a room temperature thermal conductivity of 0.0252 W / (m·K) and an apparent density of 0.207 g / cm³. 3 The specific surface areas after initial heat treatment at 1200℃ are 639.68 and 90.67 m², respectively. 2 / g, with a compressive Young's modulus of 55.33MPa. This technology helps promote the application of Al2O3-SiO2 aerogel in high-efficiency thermal insulation materials.

[0005] The objective of this invention is achieved through the following technical solution.

[0006] A method for preparing Al2O3-SiO2 aerogel using organoaluminate alkoxides and trialkoxysilanes includes the following steps:

[0007] Step 1: Stir the organoaluminum alkoxide, ethanol, and deionized water uniformly at 40-70℃ for 20-100 min. After it becomes clear, let it stand and cool to obtain an alumina sol. Add acid, acetone, aniline, and organotrialkoxysilane, stir for 5-30 minutes to mix evenly, seal and let it stand for about 0.5-5 h to form a gel, thus obtaining an Al2O3-SiO2 gel. The molar ratio of organoaluminum alkoxide, ethanol, deionized water, acid catalyst, acetone, aniline, and organotrialkoxysilane is 1:(0.5-30):(0.3-3):(0.001-0.1):(0.5-4):(0.4-3.8):(0-1).

[0008] Step 2: Cover the Al2O3-SiO2 wet gel obtained in Step 1 with ethanol and age it for 1-5 days, then replace it with ethanol for 1-5 days, replacing the ethanol every 12-24 hours.

[0009] Step 3: Place the Al2O3-SiO2 wet gel obtained in Step 2 into a supercritical drying vessel and perform supercritical drying to obtain Al2O3-SiO2 aerogel.

[0010] This invention uses organoaluminum alkoxides as the aluminum source and organotrialkoxysilanes with non-hydrolyzable hydrophobic groups to replace tetraethyl orthosilicate as the silicon source to prepare Al2O3-SiO2 aerogels. Tetraethyl orthosilicate is a common silicon source for Al2O3-SiO2 aerogels. Organoaluminum alkoxides can avoid the problem of anion removal from inorganic aluminum salts, and the prepared aerogels have better heat resistance. Compared with tetraethyl orthosilicate as the silicon source, organotrialkoxysilanes can reduce the shrinkage rate and increase the mesopore size during the Al2O3-SiO2 aerogel preparation process, thereby controlling the microstructure of Al2O3-SiO2 aerogels and preparing Al2O3-SiO2 aerogels with low thermal conductivity.

[0011] Furthermore, the organoaluminum alkoxide mentioned in step one is any one of aluminum isopropoxide, aluminum n-propoxide, aluminum sec-butoxide, and aluminum n-butoxide.

[0012] Furthermore, the acid mentioned in step one is any one of hydrochloric acid, nitric acid, sulfuric acid, acetic acid, and oxalic acid.

[0013] Furthermore, the organic trialkoxysilane mentioned in step one is any one of methyltriethoxysilane, ethyltriethoxysilane, propyltriethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, 3-aminopropyltriethoxysilane, and phenyltriethoxysilane.

[0014] Furthermore, the drying medium used in the supercritical drying method described in step one is either ethanol or carbon dioxide.

[0015] Beneficial effects:

[0016] (1) A method for preparing Al2O3-SiO2 aerogel using organoaluminum alkoxide and organotrialkoxysilane according to the present invention, wherein the aerogel is prepared by using organoaluminum alkoxide and organotrialkoxysilane as raw materials, and the room temperature thermal conductivity of the aerogel is 0.0252 W / (m·K), which is lower than the thermal conductivity of 0.0313 W / (mk) using tetraethyl orthosilicate as silicon source.

[0017] (2) A method for preparing Al2O3-SiO2 aerogel using organoaluminum alkoxides and trialkoxysilanes according to the present invention, wherein the obtained Al2O3-SiO2 aerogel has a high specific surface area and good heat resistance: the initial specific surface area is 639.68 m². 2 / g, the specific surface areas after heat treatment at 800, 1000, and 1200℃ are 535.76, 337.28, and 90.67 m², respectively. 2 / g.

[0018] (3) The present invention provides a method for preparing Al2O3-SiO2 aerogel using organoaluminum alkoxides and trialkoxysilanes. The resulting Al2O3-SiO2 aerogel is a translucent, crack-free block with good mechanical properties, exhibiting a compressive Young's modulus of 55.33 MPa. In summary, the method of the present invention prepares an Al2O3-SiO2 aerogel synthesized using organoaluminum alkoxides and trialkoxysilanes, which possesses excellent thermal insulation, mechanical properties, and heat resistance, thus contributing to the application of Al2O3-SiO2 aerogel as a highly efficient thermal insulation material. Attached Figure Description

[0019] Figure 1 A photograph of the Al2O3-SiO2 aerogel prepared in Example 1;

[0020] Figure 2 These are scanning electron microscope (SEM) images of the Al2O3-SiO2 aerogel prepared in Example 1 before and after heat treatment at 1200℃ for 2 hours; wherein, Figure 2 a is the SEM image before heat treatment; Figure 2b is the SEM image after heat treatment at 1200℃;

[0021] Figure 3 The nitrogen adsorption and desorption curves of the Al2O3-SiO2 aerogel prepared in Example 1 are shown in the initial and heat-treated curves at different temperatures.

[0022] Figure 4 The image shows the compressive stress-strain curve of the Al2O3-SiO2 aerogel prepared in Example 1. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Example 1

[0025] A method for preparing Al2O3-SiO2 aerogel using organoaluminum alkoxides and trialkoxysilanes involves stirring aluminum sec-butoxide, ethanol, and water at 60°C for 1 hour, clarifying, and then cooling and allowing to stand to obtain an alumina sol. Nitric acid, acetone, aniline, and methyltriethoxysilane are added to the alumina sol, and the mixture is stirred for 10 minutes to obtain Al2O3-SiO2 sol. The molar ratio of aluminum sec-butoxide, ethanol, water, nitric acid, acetone, aniline, and methyltriethoxysilane is 1:2:1:0.050:2.1:1.9:0.125. The Al2O3-SiO2 sol is sealed and allowed to stand, gelling in approximately 2 hours. After aging, the sol is replaced with ethanol solvent for 3 days, with the ethanol being replaced every 12 hours. Low thermal conductivity Al2O3-SiO2 aerogel is obtained by supercritical fluid drying with ethanol (260°C, 12 MPa). Figure 1 The image shows a macroscopic photograph of the obtained aerogel, revealing it to be a translucent, crack-free block. From... Figure 2 a and b are scanning electron microscope images of the aerogel before and after heat treatment at 1200℃. Figure 2 As can be seen from a, the aerogel before heat treatment exhibits a three-dimensional network structure resembling pearl chains, with no obvious agglomeration. This structure helps to reduce the thermal conductivity of the aerogel; from Figure 2 b shows that there was no severe sintering after 1200℃, and the resulting Al2O3-SiO2 aerogel has good heat resistance. Figure 3 The nitrogen adsorption-desorption curves of the aerogel after heat treatment at different temperatures are shown. All curves are typical type IV curves. When the relative pressure approaches 1, the adsorption amount increases sharply, indicating that the aerogel is a mesoporous material with uniform pore size and high specific surface area before and after heat treatment. Figure 4 The compressive stress-strain curve of the aerogel shows that it has a Young's modulus of 55.33 MPa and exhibits no obvious brittle fracture, indicating that the obtained aerogel possesses excellent mechanical properties. Characterization revealed that the apparent density and room temperature thermal conductivity of the obtained aerogel are 0.207 g / cm³. 3With a flux of 0.0252 W / (m·K), the initial specific surface area is 639.68 m². 2 / g, the specific surface areas after heat treatment at 800, 1000, and 1200℃ are 535.76, 337.28, and 90.67 m², respectively. 2 / g.

[0026] Example 2

[0027] A method for preparing Al2O3-SiO2 aerogel using organoaluminum alkoxides and trialkoxysilanes involves stirring aluminum isopropoxide, ethanol, and water at 65°C for 40 min, clarifying, and then cooling and allowing to stand to obtain an alumina sol. Hydrochloric acid, acetone, aniline, and methyltrimethoxysilane are added to the aluminum sol, and the mixture is stirred for 10 min to obtain Al2O3-SiO2 sol. The molar ratio of aluminum isopropoxide, ethanol, water, hydrochloric acid, acetone, aniline, and methyltrimethoxysilane is 1:8:0.9:0.005:2:1.8:0.2. The Al2O3-SiO2 sol is sealed and allowed to stand, gelling in approximately 2 hours. After aging, the sol is replaced with ethanol solvent for 5 days, with the ethanol being replaced every 24 hours. Al2O3-SiO2 aerogel is obtained by supercritical carbon dioxide drying (55°C, 13 MPa). Characterization shows that the apparent density and room temperature thermal conductivity of the obtained aerogel are 0.169 g / cm³. 3 With a heat capacity of 0.0238 W / (m·K), the initial specific surface area is 584.68 m². 2 / g, after heat treatment at 1200℃, the specific surface area is 125.10m². 2 / g.

[0028] Example 3

[0029] A method for preparing Al2O3-SiO2 aerogel using organoaluminum alkoxides and trialkoxysilanes involves stirring aluminum butoxide, ethanol, and water at 70°C for 35 min, clarifying the solution, and allowing it to cool and stand to obtain an alumina sol. Acetic acid, acetone, aniline, and vinyltriethoxysilane are then added to the alumina sol, and the mixture is stirred for 10 min to obtain Al2O3-SiO2 sol. The molar ratio of aluminum butoxide, ethanol, water, acetic acid, acetone, aniline, and vinyltriethoxysilane is 1:5.5:1:0.040:2.1:1.9:0.2. The Al2O3-SiO2 sol is sealed and allowed to stand, gelling in approximately 2 hours. After aging, the sol is replaced with ethanol solvent for 3 days, with the ethanol being replaced every 12 hours. The Al2O3-SiO2 aerogel is then obtained by supercritical fluid drying with ethanol (260°C, 12 MPa). After characterization, the apparent density and room temperature thermal conductivity of the obtained aerogel were 0.168 g / cm³. 3 With a strength of 0.0212 W / (m·K), the initial specific surface area is 618.04 m². 2 / g, after heat treatment at 1200℃, the specific surface area is 127.29m². 2 / g.

[0030] Example 4

[0031] A method for preparing Al2O3-SiO2 aerogel using organoaluminate alkoxides and trialkoxysilanes is disclosed. Aluminum propoxide, ethanol, and water are stirred at 55°C for 70 min, clarified, and then cooled and allowed to stand to obtain an alumina sol. Sulfuric acid, acetone, aniline, and ethyltriethoxysilane are added to the alumina sol, and the mixture is stirred for 10 min to obtain Al2O3-SiO2 sol. The molar ratio of aluminum propoxide, ethanol, water, sulfuric acid, acetone, aniline, and ethyltriethoxysilane is 1:10.5:0.7:0.002:2.2:2.0:0.125. The Al2O3-SiO2 sol is sealed and allowed to stand, gelling in approximately 2 hours. After aging, the sol is replaced with ethanol solvent for 3 days, with the ethanol being replaced every 12 hours. Al2O3-SiO2 aerogel is obtained by supercritical fluid drying with ethanol (260°C, 12 MPa). Characterization shows that the apparent density of the obtained aerogel is 0.104 g / cm³. 3 The initial specific surface area is 529.01 m². 2 / g, after heat treatment at 1200℃, the specific surface area is 126.81m². 2 / g.

[0032] Example 5

[0033] A method for preparing Al2O3-SiO2 aerogel using organoaluminum alkoxides and trialkoxysilanes involves stirring aluminum sec-butoxide, ethanol, and water at 60°C for 60 min, clarifying, and then cooling and allowing to stand to obtain an alumina sol. Oxalic acid, acetone, aniline, and ethyltrimethoxysilane are added to the alumina sol, and the mixture is stirred for 10 min to obtain Al2O3-SiO2 sol. The molar ratio of aluminum sec-butoxide, ethanol, water, oxalic acid, acetone, aniline, and ethyltrimethoxysilane is 1:3:0.6:0.020:1.8:1.6:0.33. The Al2O3-SiO2 sol is sealed and allowed to stand, gelling in approximately 2 hours. After aging, the sol is replaced with ethanol solvent for 3 days, with the ethanol being replaced every 12 hours. The Al2O3-SiO2 aerogel is then obtained by supercritical fluid drying with ethanol (260°C, 12 MPa). After characterization, the apparent density and room temperature thermal conductivity of the obtained aerogel were 0.265 g / cm³. 3 With a flux of 0.0265 W / (m·K), the initial specific surface area is 409.83 m². 2 / g, after heat treatment at 1200℃, the specific surface area is 110.82m². 2 / g.

[0034] Example 6

[0035] A method for preparing Al2O3-SiO2 aerogel using organoaluminum alkoxides and trialkoxysilanes involves stirring aluminum sec-butoxide, ethanol, and water at 60°C for 60 min, clarifying the solution, and then cooling and allowing it to stand to obtain an alumina sol. Nitric acid, acetone, aniline, and propyltriethoxysilane are added to the alumina sol, and the mixture is stirred for 10 min to obtain Al2O3-SiO2 sol. The molar ratio of aluminum sec-butoxide, ethanol, water, nitric acid, acetone, aniline, and propyltriethoxysilane is 1:3:0.5:0.08:1.8:1.6:0.25. The Al2O3-SiO2 sol is sealed and allowed to stand, gelling in approximately 2 hours. After aging, the sol is replaced with ethanol solvent for 3 days, with the ethanol being replaced every 12 hours. The Al2O3-SiO2 aerogel is then obtained by supercritical fluid drying with ethanol (260°C, 12 MPa). After characterization, the apparent density and room temperature thermal conductivity of the obtained aerogel were 0.277 g / cm³. 3 With a strength of 0.031 W / (m·K), the initial specific surface area was 609.19 m². 2 / g, after heat treatment at 1200℃, the specific surface area is 65.29m². 2 / g.

[0036] Comparative Example 1 (using tetraethyl orthosilicate as the silicon source)

[0037] Aluminum sec-butoxide, ethanol, and water were stirred at 60°C for 1 hour, clarified, and then cooled and allowed to stand to obtain an alumina sol. Nitric acid, acetone, aniline, and tetraethyl orthosilicate were added to the alumina sol, and the mixture was stirred for 10 minutes to obtain an Al₂O₃-SiO₂ sol. The molar ratio of aluminum sec-butoxide, ethanol, water, nitric acid, acetone, aniline, and tetraethyl orthosilicate was 1:2:1:0.050:2.1:1.9:0.125. The Al₂O₃-SiO₂ sol was sealed and allowed to stand, gelling in approximately 2 hours. After aging, the sol was replaced with ethanol solvent for 3 days, with the ethanol being replaced every 12 hours. Al₂O₃-SiO₂ aerogel with tetraethyl orthosilicate as the silicon source was obtained by supercritical fluid drying with ethanol (260°C, 12 MPa). The apparent density and room temperature thermal conductivity of the obtained aerogel were 0.259 g / cm³. 3 And 0.0313 W / (m·K).

[0038] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing Al2O3-SiO2 aerogel using organoaluminate alkoxides and trialkoxysilanes, characterized in that, Includes the following steps: (1) Preparation of Al2O3-SiO2 gel: Organoaluminate, ethanol and deionized water are stirred evenly at 40-70℃. After the mixture is clear, it is allowed to stand and cool to obtain alumina sol. Add acid catalyst, acetone, aniline and organotrialkoxysilane, stir evenly, seal and stand until Al2O3-SiO2 wet gel is obtained. The molar ratio of organoaluminate, ethanol, deionized water, acid catalyst, acetone, aniline and organotrialkoxysilane is 1:(0.5-30):(0.3-3):(0.001-0.1):(0.5-4):(0.4-3.8):(0-1). (2) Aging and solvent replacement: The Al2O3-SiO2 wet gel was covered with ethanol for 1-5 days and then replaced with ethanol for 1-5 days. The ethanol was replaced every 12-24 hours. (3) Supercritical drying: The aged and solvent-replaced Al2O3-SiO2 wet gel is placed in a supercritical drying vessel and subjected to supercritical drying to obtain Al2O3-SiO2 aerogel.

2. The method as described in claim 1, characterized in that: The organoaluminum alkoxide mentioned in step (1) is any one of aluminum isopropoxide, aluminum n-propoxide, aluminum sec-butoxide, and aluminum n-butoxide.

3. The method as described in claim 1, characterized in that: The acid catalyst mentioned in step (1) is any one of hydrochloric acid, nitric acid, sulfuric acid, acetic acid, and oxalic acid.

4. The method as described in claim 1, characterized in that: The organic trialkoxysilane mentioned in step (1) is any one of methyltriethoxysilane, ethyltriethoxysilane, propyltriethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, 3-aminopropyltriethoxysilane, and phenyltriethoxysilane.

5. The method as described in claim 1, characterized in that: The drying medium used in the supercritical drying in step (3) is either ethanol or carbon dioxide.

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