A method for rapidly preparing high-thermal-stability silicon-zirconium binary aerogels under normal pressure drying conditions

Abstract

The application provides a method for rapidly preparing high-thermal-stability silicon-zirconium binary aerogel under normal pressure and dry conditions, and belongs to the technical field of aerogel.The silicon source, organic silane modifier and ethanol are mixed, and then water and acid catalyst are added to carry out hydrolysis, so as to obtain solution A; the zirconium source, water and ethanol are mixed to carry out hydrolysis, so as to obtain solution B; the solution A and the solution B are mixed to obtain modified silicon-zirconium precursor sol; then, the base catalyst is added to carry out gel skeleton roughening, and then, after standing until the gel reaction is completed, drying is carried out, so as to obtain high-thermal-stability silicon-zirconium binary aerogel.The application initiatively combines the aerogel normal pressure drying preparation new process of the modification of the co-precursor method and the enhancement of the skeleton strength by the base catalyst, so that the effect of reducing the capillary force and the structure morphology not being damaged during rapid drying is achieved.The method discards the tedious solvent exchange and the aging stage of hydrophobic modification, and greatly shortens the preparation time of the conventional normal pressure drying, and the fastest time is only 8.5 hours.

Description

Technical Field

[0001] This invention belongs to the field of aerogel technology, specifically relating to a method for rapidly preparing highly thermally stable silicon-zirconium binary aerogels under normal pressure drying conditions. Background Technology

[0002] The preparation process of aerogels mainly consists of three steps: the first step is to form a porous gel through a sol-gel process involving hydrolysis and condensation; the second step is to coarsen the gel's framework structure through an aging process; and the third step is to replace the liquid substances within the gel with gaseous substances through a specific drying method, thus obtaining the aerogel. During drying, due to the nanostructured pores on the gel surface, the removal of the solvent generates significant capillary forces, ultimately leading to the shrinkage or even collapse of the gel structure. Currently, the most commonly used drying method for aerogels is supercritical drying, which can reduce the surface tension of the gel to zero, preventing shrinkage and collapse. However, the reaction conditions are quite harsh; high pressure (5-15 MPa) and high temperature (250-270℃) make the supercritical drying process dangerous and difficult. Due to the high risk and cost, it is difficult to implement in large-scale production. Traditional freeze-drying methods suffer from problems such as damage to the aerogel structure, excessively long drying time, and generally only yielding aerogel powder or granules.

[0003] Atmospheric pressure drying can overcome the various problems faced by supercritical drying and freeze drying methods. For example, CN201110100550.7 discloses a low-cost method for preparing silica-based aerogels with different contact angles by atmospheric pressure drying. After the gel is formed by the sol-gel method, it is aged for 2-6 days and then soaked and washed in a water bath at 35-60℃ for 24 hours. The wet gel is then immersed in a modifying solution and surface modified at 50℃ for 24 hours. A certain amount of n-hexane is added to exchange the unreacted modifier twice within 24 hours. The gel is then dried in stages at atmospheric pressure and finally cooled to room temperature to obtain silica-based aerogels prepared by atmospheric pressure drying.

[0004] However, current atmospheric pressure drying methods typically involve multiple solvent exchange and surface modification processes. While these methods significantly reduce complexity and improve safety compared to supercritical drying, they still suffer from problems such as long preparation cycles, cumbersome steps, and the consumption of large amounts of organic solvents and modifiers. For example, the atmospheric pressure drying method disclosed in CN201110100550.7 requires a lengthy and complex preparation process of 5-9 days, consuming large amounts of n-hexane solvent and modification liquid, which ultimately increases both time and raw material costs. Summary of the Invention

[0005] In view of this, the present invention aims to provide a method for rapidly preparing highly thermally stable silicon-zirconium binary aerogels under ambient pressure drying conditions. By combining precursor modification with alkaline catalyst enhancement to strengthen the framework, the capillary forces generated during drying are reduced, and the gel framework strength is enhanced. This method eliminates the cumbersome solvent exchange and hydrophobic modification aging stages, significantly shortening the preparation time of conventional ambient pressure drying, and eliminating the need for large amounts of reagent modifiers and organic solvents. It is low-cost, highly efficient, and has great application potential in the large-scale industrial production of aerogels.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for rapidly preparing highly thermally stable silicon-zirconium binary aerogels under normal pressure drying conditions, comprising the following steps:

[0008] 1) Mix the silicon source, organosilane modifier and ethanol, then add water and acid catalyst for hydrolysis to obtain solution A;

[0009] 2) Solution B is obtained by hydrolyzing a mixture of zirconium source, water, and ethanol.

[0010] 3) Mix solution A and solution B to obtain a modified silicon-zirconium precursor sol;

[0011] 4) Add excess alkaline catalyst to the modified silicon-zirconium precursor sol to roughen the gel skeleton and obtain a modified silicon-zirconium composite wet gel with a roughened skeleton.

[0012] 5) The modified silicon-zirconium composite wet gel with roughened skeleton is allowed to stand until the gelation reaction is complete, and then dried to obtain a silicon-zirconium binary aerogel with high thermal stability.

[0013] Preferably, in step 1), the molar ratio of silicon source, organosilane modifier, water, ethanol and acid catalyst is 1:0.5~3:3~9:3~15:0.001~0.01.

[0014] Preferably, the silicon source in step 1) is any one or more of tetraethyl orthosilicate, methyl orthosilicate, and silicon tetrachloride.

[0015] Preferably, the organosilane modifier in step 1) is one or more of methyltriethoxysilane, dimethyldiethoxysilane, trimethylethoxysilane, or tetramethylsilane.

[0016] Through the above technical solutions, the present invention uses organosilane modifiers in the preparation process to make the silicon-zirconium binary aerogel have excellent hydrophobic properties and greatly reduce the number of highly active hydroxyl groups on the surface, thereby improving its stability.

[0017] Preferably, the acid catalyst in step 1) is hydrochloric acid, nitric acid, oxalic acid, or acetic acid.

[0018] Preferably, the hydrolysis time in step 1) is 1-3 hours.

[0019] Preferably, the molar ratio of zirconium source, water and ethanol in step 2) is 1:0 to 8:6 to 15.

[0020] Preferably, the zirconium source in step 2) is any one or more of zirconium oxychloride and zirconium oxynitrate.

[0021] Preferably, the hydrolysis time in step 2) is 1-3 hours.

[0022] In this invention, steps 1) and 2) can be hydrolyzed simultaneously, saving preparation time.

[0023] Preferably, in step 3), the molar ratio of silicon source, organosilane modifier and zirconium source in the modified silicon-zirconium precursor sol is 1:0.5-3:0.5-4.

[0024] Preferably, the mixing time of solution A and solution B in step 3) is 0.5-6 hours.

[0025] Preferably, in step 4), the molar ratio of the alkaline catalyst to the silicon source in the modified silicon-zirconium precursor sol is 0.50 to 2.5:1.

[0026] Preferably, the alkaline catalyst in step 4) is ammonia.

[0027] Through the above technical solutions, a large amount of alkaline catalyst makes the gelation reaction more intense, the gelation reaction is completed more quickly, and the strength of the gel skeleton is increased, making the gel strong enough to resist the reduced capillary force and have excellent compressive strength. The compressive strength is tested to reach 0.6Mpa-1.5Mpa.

[0028] Preferably, in step 5), the gelation reaction time is 1-6 hours; the drying temperature is 50℃-80℃, and the drying time is 6-24 hours. The gelation reaction time varies depending on the amount of alkaline catalyst used.

[0029] It contains at least the following beneficial technical effects:

[0030] 1. In the sol-gel stage, this invention introduces methylsilane-containing compounds through co-precursor modification, enabling the gel to possess excellent hydrophobic properties without requiring extensive modification during the aging stage, thus reducing capillary forces generated during drying. Furthermore, the increased content of the alkaline catalyst during gelation makes the gelation reaction more vigorous. Therefore, the gelation reaction is completed more rapidly, increasing the strength of the gel skeleton, making the gel sufficient to resist the reduced capillary forces. This achieves the effect of maintaining the gel skeleton structure during rapid drying, significantly shortening the preparation time under normal pressure, to as little as 8.5 hours.

[0031] 2. The aerogel prepared by this invention has a contact angle greater than 140°, exhibiting excellent hydrophobic properties. This effectively alleviates the corrosion failure problem of thermal insulation materials caused by immersion in water and moisture, significantly extending their service life. Simultaneously, the modification with methyl groups greatly reduces the number of highly active hydroxyl groups on the surface. After calcination at 1000℃, compared to unmodified silicon-zirconium binary aerogel, the crystallinity and crystal facet types are significantly reduced, exhibiting excellent high-temperature thermal stability. It can be used in harsh humid and high-temperature environments.

[0032] 3. The preparation method of this invention does not require the use of large amounts of modifiers and organic solvents. It is low-cost and highly efficient, and has great application prospects in the large-scale industrial production of aerogels. Attached Figure Description

[0033] Figure 1 The image shows the optical image of the high thermal stability silicon-zirconium binary aerogel obtained in Example 1 after cutting.

[0034] Figure 2 This is a schematic diagram of the contact angle of the high thermal stability silicon-zirconium binary aerogel prepared in Example 1.

[0035] Figure 3 The images show the XRD patterns of the high thermal stability silicon-zirconium binary aerogel prepared in Example 1 and the unmodified silicon-zirconium binary aerogel after heat treatment at 1000℃.

[0036] Figure 4 This is a microstructure diagram of the highly thermally stable silicon-zirconium binary aerogel prepared in Example 1.

[0037] Figure 5 This is a microstructure diagram of the highly thermally stable silicon-zirconium binary aerogel prepared in Example 2.

[0038] Figure 6 This is a microstructure diagram of the high thermal stability silicon-zirconium binary aerogel prepared in Example 3. Detailed Implementation

[0039] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0040] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0041] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention, and no reference numerals in the claims should be construed as limiting the scope of the claims.

[0042] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. These other embodiments are also covered within the scope of protection of this invention.

[0043] It should also be understood that the specific embodiments described above are only used to explain the present invention, and the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or changes made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

[0044] Example 1

[0045] This embodiment provides a method for rapidly preparing highly thermally stable silicon-zirconium binary aerogels under normal pressure drying conditions, the steps of which are as follows:

[0046] 1) Mix tetraethyl orthosilicate, dimethyldiethoxysilane and ethanol, then add water and hydrochloric acid and hydrolyze for 1 hour to obtain solution A;

[0047] The molar ratio of tetraethyl orthosilicate, dimethyldiethoxysilane, water, ethanol and hydrochloric acid is 1:1.5:6:6:0.002.

[0048] 2) While hydrolyzing in step 1), zirconium oxychloride, water and ethanol are mixed and hydrolyzed for 1 hour to obtain solution B;

[0049] The molar ratio of zirconium oxychloride, water, and ethanol is 1:8:8.

[0050] 3) Stir and mix the solutions A and B for 0.5 h to obtain the modified silicon-zirconium precursor sol;

[0051] During mixing, the amounts of solution A and solution B are controlled so that the molar ratio of tetraethyl orthosilicate, dimethyldiethoxysilane and zirconium oxychloride in the modified silicon-zirconium precursor sol is 1:1.5:1.

[0052] 4) Add ammonia to the prepared modified silicon-zirconium precursor sol to roughen the gel skeleton, and obtain a modified silicon-zirconium composite wet gel with a roughened skeleton.

[0053] The ratio of ammonia water to tetraethyl orthosilicate in the modified silicon-zirconium precursor sol is 1.5:1.

[0054] 5) After the modified silicon-zirconium composite wet gel with roughened skeleton was allowed to stand for 1 hour until the gelation reaction was complete, it was dried at 65℃ for 6 hours to obtain a silicon-zirconium binary aerogel with high thermal stability.

[0055] The density of the prepared aerogel was measured to be 0.253 g / cm³. 3 Thermal conductivity 0.035 W / m -1 K -1 .

[0056] Figure 4 This is a microstructure diagram of the silicon-zirconium binary aerogel prepared in this embodiment.

[0057] Example 2

[0058] This embodiment provides a method for rapidly preparing highly thermally stable silicon-zirconium binary aerogels under normal pressure drying conditions, the steps of which are as follows:

[0059] 1) Tetramethyl orthosilicate, methyltriethoxysilane and ethanol are mixed and then water and nitric acid are added for hydrolysis for 2 hours to obtain solution A;

[0060] The molar ratio of tetramethyl orthosilicate, methyltriethoxysilane, water, ethanol and nitric acid is 1:0.5:8:10:0.005.

[0061] 2) After mixing zirconium oxynitrate, water, and ethanol, hydrolyze for 2 hours to obtain solution B;

[0062] The molar ratio of zirconium oxynitrate, water, and ethanol is 1:5:6.

[0063] 3) Stir and mix the solutions A and B for 3 hours to obtain the modified silicon-zirconium precursor sol;

[0064] During mixing, the amounts of solution A and solution B are controlled so that the molar ratio of tetramethyl orthosilicate, methyltriethoxysilane and zirconium oxynitrate in the modified zirconium silicate precursor sol is 1:0.5:0.5.

[0065] 4) Add ammonia to the prepared modified silicon-zirconium precursor sol to roughen the gel skeleton, and obtain a modified silicon-zirconium composite wet gel with a roughened skeleton.

[0066] The ratio of ammonia water to tetramethyl orthosilicate in the modified silicon zirconium precursor sol is 1:1.

[0067] 5) After the modified silicon-zirconium composite wet gel with roughened skeleton was allowed to stand for 3 hours until the gelation reaction was complete, it was dried at 50℃ for 10 hours to obtain a silicon-zirconium binary aerogel with high thermal stability.

[0068] Testing revealed that the density of the prepared aerogel at room temperature was 0.298 g / cm³. 3 Thermal conductivity 0.038 W / m -1 K -1 .

[0069] Figure 5 This is a microstructure diagram of the silicon-zirconium binary aerogel prepared in this embodiment.

[0070] Example 3

[0071] This embodiment provides a method for rapidly preparing highly thermally stable silicon-zirconium binary aerogels under normal pressure drying conditions, the steps of which are as follows:

[0072] 1) Mix silicon tetrachloride, trimethylethoxysilane and ethanol, then add water and oxalic acid and hydrolyze for 3 hours to obtain solution A;

[0073] The molar ratio of silicon tetrachloride, trimethylethoxysilane, water, ethanol and oxalic acid is 1:3:9:15:0.01.

[0074] 2) After mixing zirconium oxychloride, water, and ethanol, hydrolyze for 3 hours to obtain solution B;

[0075] The molar ratio of zirconium oxychloride, water, and ethanol is 1:8:15.

[0076] 3) Stir and mix the solutions A and B for 6 hours to obtain the modified silicon-zirconium precursor sol;

[0077] During mixing, the amounts of solution A and solution B are controlled so that the molar ratio of silicon tetrachloride, trimethylethoxysilane and zirconium oxychloride in the modified silicon zirconium precursor sol is 1:2:2.

[0078] 4) Add ammonia to the prepared modified silicon-zirconium precursor sol to roughen the gel skeleton, and obtain a modified silicon-zirconium composite wet gel with a roughened skeleton.

[0079] The ratio of ammonia water to tetraethyl orthosilicate in the modified silicon-zirconium precursor sol is 0.75:1.

[0080] 5) After the modified silicon-zirconium composite wet gel with roughened skeleton was allowed to stand for 12 hours to complete the gelation reaction, it was dried at 50°C for 24 hours to obtain a silicon-zirconium binary aerogel with high thermal stability.

[0081] The density of the prepared aerogel was measured to be 0.371 g / cm³. 3 Thermal conductivity 0.048 W / m -1 K -1 .

[0082] Figure 6 This is a microstructure diagram of the silicon-zirconium binary aerogel prepared in this embodiment.

[0083] Example 4

[0084] The preparation method of this embodiment is the same as that of Example 1, except that the molar ratio of ammonia water to tetraethyl orthosilicate in the modified silicon zirconium precursor sol is 0.5:1 in step 4).

[0085] The density of the prepared aerogel was measured to be 0.378 g / cm³. 3 Thermal conductivity 0.045 W / m -1 K -1 .

[0086] Example 5

[0087] The preparation method of this embodiment is the same as that of Example 1, except that in step 1), the silicon source is a combination of tetraethyl orthosilicate and methyl orthosilicate in a molar ratio of 1:1.

[0088] The density of the prepared aerogel was measured to be 0.286 g / cm³. 3 Thermal conductivity 0.040 W / m -1 K -1 .

[0089] Example 6

[0090] The preparation method of this embodiment is the same as that of Example 1, except that in step 1), the organosilane modifier is a combination of methyltriethoxysilane and dimethyldiethoxysilane in a molar ratio of 1:1.

[0091] The density of the prepared aerogel was measured to be 0.267 g / cm³. 3 Thermal conductivity 0.043 W / m -1 K -1 .

[0092] Example 7

[0093] The preparation method of this embodiment is the same as that of Example 1, except that in step 1), the zirconium source is a combination of zirconium oxychloride and zirconium oxynitrate in a molar ratio of 1:1.

[0094] The density of the prepared aerogel was measured to be 0.288 g / cm³. 3 Thermal conductivity 0.047 W / m -1 K -1 .

[0095] Comparative Example 1

[0096] The preparation method of this comparative example is the same as that of Example 1, except that step 1) does not contain methyltriethoxysilane;

[0097] In step 5), after drying for 72 hours, the particles agglomerate into small glassy particles, indicating that the drying process under normal pressure has failed.

[0098] Comparative Example 2

[0099] The comparative example is prepared in the same way as Example 1, except that the molar ratio of the amount of alkaline catalyst to the amount of tetraethyl orthosilicate in the modified silicon zirconium precursor sol in step 4) is 0.25:1.

[0100] In step 5), after drying for 72 hours, the gel skeleton structure could not resist capillary forces, resulting in significant shrinkage. All indicators decreased drastically, with a density of 0.667 g / cm³. 3 Thermal conductivity 0.078 W / m -1 K -1 .

[0101] Experimental Example 1

[0102] The hydrophobic properties of the high thermal stability silicon-zirconium binary aerogel prepared in Example 1 were tested.

[0103] The detection method is as follows: the contact angle of the sample is measured using a contact angle / surface tension meter.

[0104] like Figure 2 As shown, Figure 2 As shown, the obtained high thermal stability silicon-zirconium binary aerogel has a contact angle greater than 140° and excellent hydrophobic properties to reduce capillary forces generated during drying. At the same time, it can effectively alleviate the corrosion failure problem of thermal insulation materials caused by water immersion and moisture, thus greatly extending the service life.

[0105] Experiment Example 2

[0106] The mechanical properties of the high thermal stability silicon-zirconium binary aerogel prepared in Example 1 were tested.

[0107] The testing method is as follows: the stress-strain curve of the sample is tested using an electronic universal testing machine.

[0108] The high thermal stability silicon-zirconium binary aerogel prepared in Example 1 was tested and found to have a compressive strength of 0.83 MPa, and fractured at 12% deformation. Due to its suitable compressive strength and plasticity, the prepared aerogel exhibits excellent processability. It can be cut into various shapes. Figure 1 This will increase the number of applications for aerogels.

[0109] This invention improves the strength of the gel skeleton by using an excessive amount of alkaline catalyst. In Comparative Examples 1 and 2, the skeleton strength was insufficient during the drying process, and the capillary force caused the aerogel to shrink severely, resulting in the failure of drying at normal pressure.

[0110] Experimental Example 3

[0111] The thermal stability of the high thermal stability silicon-zirconium binary aerogel prepared in Example 1 and the unmodified silicon-zirconium binary aerogel prepared in Comparative Example 1 were tested.

[0112] The detection method was as follows: the prepared aerogel was placed in a muffle furnace at 1000℃ for 0.5h heat treatment, and the crystallinity of the aerogel was analyzed by X-ray diffraction.

[0113] like Figure 3 As shown, the modification with methyl groups gives the silicon-zirconium binary aerogel excellent hydrophobic properties, while significantly reducing the number of abundant and highly active hydroxyl groups on its surface. After calcination at 1000℃, the crystallinity and crystal facet types are significantly reduced compared to the unmodified silicon-zirconium binary aerogel, exhibiting excellent high-temperature thermal stability.

[0114] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for rapidly preparing highly thermally stable silicon-zirconium binary aerogel under normal pressure drying conditions, characterized in that, Includes the following steps: 1) Mix the silicon source, organosilane modifier and ethanol, then add water and acid catalyst for hydrolysis to obtain solution A; 2) Solution B is obtained by hydrolyzing a mixture of zirconium source, water, and ethanol. 3) Mix solution A and solution B to obtain a modified silicon-zirconium precursor sol; 4) Add excess alkaline catalyst to the modified silicon-zirconium precursor sol to roughen the gel skeleton and obtain a modified silicon-zirconium composite wet gel with a roughened skeleton. 5) The modified silicon-zirconium composite wet gel with roughened skeleton was allowed to stand until the gelation reaction was complete, and then dried to obtain a silicon-zirconium binary aerogel with high thermal stability. In step 1), the molar ratio of silicon source, organosilane modifier, water, ethanol and acid catalyst is 1:0.5~3:3~9:3~15:0.001~0.01; In step 1), the silicon source is any one or more of tetraethyl orthosilicate, methyl orthosilicate, and silicon tetrachloride; the organosilane modifier is one or more of methyltriethoxysilane, dimethyldiethoxysilane, trimethylethoxysilane, or tetramethylsilane; and the acid catalyst is hydrochloric acid, nitric acid, oxalic acid, or acetic acid. In step 2), the molar ratio of zirconium source, water, and ethanol is 1:0 to 8:6 to 15. In step 3), the molar ratio of silicon source, organosilane modifier and zirconium source in the modified silicon-zirconium precursor sol is 1:0.5-3:0.5-4. In step 4), the molar ratio of the alkaline catalyst to the silicon source in the modified silicon-zirconium precursor sol is 0.5-2.5:

1. In step 4), the alkaline catalyst is ammonia.

2. The method according to claim 1, characterized in that, In step 2), the zirconium source is any one or more of zirconium oxychloride and zirconium oxynitrate.

3. The method according to claim 1, characterized in that, In step 3), the mixing time of solution A and solution B is 0.5-6 hours.

4. The method according to claim 1, characterized in that, In step 5), the gelation reaction time is 1-6 hours; the drying temperature is 50℃-80℃, and the drying time is 6-24 hours.

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