Preparation method of silicon dioxide aerogel heat insulation composite material

Abstract

The invention provides a low-cost normal-pressure drying method, a super-hydrophobic aerogel composite material is prepared, a fiber aerogel composite material is obtained through a sol impregnation method and normal-pressure drying modification, and the preparation method specifically comprises the following steps: preparing silicon dioxide sol by taking aluminum silicate fibers as a skeleton structure, and preparing the fiber aerogel composite material; uniformly impregnating the fiber felt with the silica sol to obtain a fiber / sol mixture; and aging the gel, and drying at normal pressure. The preparation process is simple, the cost is low, supercritical drying equipment is not needed, complicated surface modification and solvent replacement processes are omitted, the raw material price is low, the equipment is simple, the requirement for the environment is low, the whole technological process is short in time consumption, the preparation method is suitable for industrial production, the use temperature of the material is high and can reach 1300 DEG C, the hydrophobicity is good, and the density is small. Meanwhile, the mechanical property of the nano thermal insulation material is enhanced, and the machining property of the nano thermal insulation material is improved.

Description

Technical Field

[0001] The present invention relates to the field of thermal insulation materials, and particularly to a preparation method of a silica aerogel thermal insulation composite material. Background Art

[0002] The preparation of aerogels by supercritical technology and freeze-drying technology has certain safety risks, and is also characterized by low efficiency, expensive equipment, high cost, complex process, and inability to produce continuously. The atmospheric pressure preparation technology, due to its simple preparation process, can solve the disadvantages of non-atmospheric pressure drying to a certain extent, and has always been a hot topic pursued by researchers. Replacing supercritical drying technology with atmospheric pressure drying technology undoubtedly increases the possibility of reducing the preparation cost of aerogels, shortening the cycle, and realizing industrial production. On the basis of realizing the industrial production of aerogels, the cost should be reduced as much as possible, and further attention should be paid to and utilization of the special properties of aerogels to prepare advanced aerogel materials integrating structure and function to improve their performance in practical applications. However, pure aerogels often have weak mechanical strength and poor toughness, which limits their operability and applicability. Currently, the effective compounding of aerogels and fibers is helpful for improving structural stability and is more effective for improving mechanical properties, thus expanding the application aspects of aerogels.

[0003] Previously, the main technologies for preparing fiber aerogel composites included the sol impregnation method and the fiber / sol hybrid gel method. The sol impregnation method is simple and direct. It is a method for preparing fiber-reinforced nanoparticle aerogels by injecting an aerogel precursor sol into a fiber body and then undergoing processes such as gelation, aging, and drying. The other method is to use a high-performance framework material as the skeleton and deposit silica nanoparticles on the skeleton subsequently to form a composite aerogel material. These two methods each have their own characteristics. Especially the sol impregnation method, due to its simple operation, can immerse a fiber felt in a sol and then gel, which has great potential for large-scale production. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of a silica aerogel thermal insulation composite material to solve the deficiencies of the existing supercritical technology for preparing aerogel materials, such as complex process and low efficiency.

[0005] The present invention is achieved through the following technical solutions:

[0006] A preparation method of a silica aerogel thermal insulation composite material includes the following steps:

[0007] (1) Mix and stir tetraethyl orthosilicate, ethanol, and deionized water, add an acidic solution dropwise until acidic for hydrolysis, then add a basic solution dropwise until basic, and let it stand to obtain a sol;

[0008] (2) Using fibers as the skeleton structure, the sol impregnation method is adopted to combine the sol in step (1) with the fibers, and then hydrophobic modification is carried out, followed by drying at atmospheric pressure to obtain the composite material.

[0009] The method of the present invention prepares a superhydrophobic aerogel composite material. Through the sol impregnation method, a fiber composite aerogel is obtained after modification by drying at atmospheric pressure. During the preparation process of the aluminosilicate fiber reinforced aerogel composite material, it is found that the aerogel structure can uniformly fill the pores between the fibers and tightly wrap around the fiber surface, significantly reducing the lapping phenomenon between the fibers. This fiber reinforcement phase plays a significant strengthening and toughening function in the material, thereby improving the overall performance of the composite material. Therefore, the selection of fiber types has a great influence on the temperature resistance and high-temperature thermal conductivity of the material. By reasonably selecting fiber types, the temperature resistance performance of the composite material can be effectively improved, enabling it to have more stable performance in high-temperature environments.

[0010] In the present invention, by precisely controlling the pH value, tetraethyl orthosilicate (TEOS) is fully hydrolyzed. TEOS, absolute ethanol, and deionized water are mixed according to a certain ratio, and then reacted with ammonia water to raise the pH of the hydrolysis solution to a fixed value, and continuous stirring is carried out to form a stable sol.

[0011] In the present invention, the volume ratio of tetraethyl orthosilicate, ethanol, and deionized water in step (1) is 10:7 - 10:3 - 5.

[0012] In the present invention, the pH range of acidic hydrolysis in step (1) is 1 - 3; the alkaline pH range is 7 - 9.

[0013] In the present invention, the acidic solution in step (1) is hydrochloric acid solution, and the alkaline solution is ammonia water.

[0014] Furthermore, the hydrolysis time with the addition of the acidic solution is 1 - 2 hours.

[0015] In the present invention, the fiber in step (2) is aluminosilicate fiber.

[0016] In the present invention, the hydrophobic modification in step (2) is to soak the gel in a trimethylchlorosilane / n - hexane mixed solution for surface modification, and then carry out solvent replacement.

[0017] Furthermore, the solvent replacement in step (2) is to soak the gel in n - hexane for treatment, replacing the ethanol and water in the gel pores with n - hexane.

[0018] In the present invention, the drying in step (2) adopts gradient drying, which is divided into three stages. The first stage is dried at 60 - 80 °C for 10 - 12 hours; the temperature is raised to 100 - 120 °C in the second stage and dried for 8 - 10 hours; the third stage is high-temperature dried at 140 - 160 °C for 2 - 4 hours.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The material prepared by the present invention has a high BET specific surface area, superhydrophobicity, low density, low thermal conductivity, and also has good thermal stability.

[0021] (2) The material prepared by the present invention has good compressive capacity. Most importantly, the silica composite aerogel material synthesized by this method has a simple method and low cost, and is suitable for large-scale production. This method can greatly reduce the amount of low-surface-tension solvent used in the preparation process, providing various types of methods for the industrial production of silica aerogel, and has high potential value. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is the XRD pattern of the silica aerogel thermal insulation composite material obtained in Example 1 of the present invention.

[0023] Figure 2 It is the SEM pattern of the silica aerogel thermal insulation composite material obtained in Example 1 of the present invention.

[0024] Figure 3 It is the infrared spectrum of the silica aerogel thermal insulation composite material obtained in Example 1 of the present invention.

[0025] Figure 4 It is the hydrophilic-hydrophobic diagram of the silica aerogel thermal insulation composite material obtained in Example 1 of the present invention.

[0026] Figure 5 It is the thermal conductivity curve of the silica aerogel thermal insulation composite material obtained in Example 1 of the present invention.

[0027] Figure 6 It is the combustion experiment diagram of the silica aerogel thermal insulation composite material obtained in Example 1 of the present invention.

[0028] Figure 7 It is the mechanical property diagram of the silica aerogel thermal insulation composite material obtained in Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] The following further describes the present invention in conjunction with specific embodiments, so that those skilled in the art can better understand and implement the technical solutions of the present invention.

[0030] The preparation method of the silica aerogel thermal insulation composite material of the present invention prepares a superhydrophobic aerogel composite material. Through the sol impregnation method, after being modified by atmospheric drying, a fiber aerogel composite material is obtained. This method can not only reduce the manufacturing cost, but also shorten the production time, and can be mass-produced to achieve industrialization. In the present invention, specific precursors, solvents, and acid-base two-step catalysts are used. First, tetraethyl orthosilicate (TEOS) is selected as the core precursor, and ethanol and deionized water are combined as solvents. Subsequently, hydrochloric acid and ammonia water are selected as the acid-base two-step catalysts respectively, and each link is precisely controlled. From aging to drying, each step is carried out, and finally a silica aerogel composite material is obtained. A formulation with excellent mechanical properties is selected, and a large number of repetitive experiments are carried out. The process conditions are precisely and strictly controlled, and a large number of repetitions are carried out to obtain an aerogel composite material with good mechanical properties.

[0031] Example 1

[0032] A preparation method of a silica aerogel thermal insulation composite material includes the following steps:

[0033] (1) Mix and stir tetraethyl orthosilicate, ethanol, and deionized water, add an acidic solution dropwise until acidic for hydrolysis, then add a basic solution dropwise until basic, and let it stand to obtain a sol.

[0034] The specific process is as follows: Take 20 ml of tetraethyl orthosilicate, 15.7 ml of ethanol, and 6.4 ml of deionized water and mix and stir. Slowly add hydrochloric acid solution dropwise to adjust the solution to an acidic pH of 3, hydrolyze for 1 hour, then add ammonia water solution dropwise to adjust to a basic pH of 7, and let the sol stand for later use.

[0035] (2) Using the fiber as the skeleton structure, adopt the sol impregnation method, combine the sol in step (1) with the fiber, then carry out hydrophobic modification, and dry at atmospheric pressure to obtain a composite material.

[0036] The specific process is as follows:

[0037] Mold loading: Put the treated aluminosilicate fiber into the mold and lay it flat, cover it with a hollow lid, use glass balls to expel the air in the fiber and compact it, squeeze out the internal air, and pour a fixed mass of silicon sol into it after pressing it flat, and uniformly impregnate the silicon sol in the fiber felt.

[0038] Soaking and aging: Pour the ethanol solution into the mold for soaking, and use an oven to accelerate the aging process of the alcohol gel. The aging time is 12 hours.

[0039] Demolding: Soak and age in ethanol to demold the gel.

[0040] Hydrophobic modification: To endow the material with better hydrophobic properties, it was demolded by soaking and aging in ethanol, and the wet gel was soaked in a mixed solution of n-hexane and trimethylchlorosilane, followed by soaking in n-hexane. Specifically, the gel was soaked in a 7% (volume fraction) trimethylchlorosilane / n-hexane mixed solution and surface-modified twice, each time for 12 hours. Solvent replacement: The gel was soaked in n-hexane to replace ethanol and water in the pores with n-hexane, and the n-hexane was changed every 12 hours.

[0041] Graded drying: It was dried in three stages. In the first stage, it was dried at 60 °C for 12 hours; in the second stage, the temperature was raised to 100 °C and dried for 8 hours; in the third stage, it was dried at a high temperature of 150 °C for 2 hours. After drying, an aerogel composite material was obtained.

[0042] Example 2

[0043] A preparation method of a silica aerogel thermal insulation composite material includes the following steps:

[0044] (1) Tetraethyl orthosilicate, ethanol, and deionized water were mixed and stirred, and an acidic solution was added dropwise until acidic for hydrolysis, and then an alkaline solution was added dropwise until alkaline, and then left standing to obtain a sol.

[0045] The specific process is as follows: 20 ml of tetraethyl orthosilicate, 15 ml of ethanol, and 10 ml of deionized water were taken and mixed and stirred. Hydrochloric acid solution was slowly added dropwise to adjust the solution to an acidic pH of 2 for hydrolysis for 1 hour, and then ammonia water solution was added dropwise to adjust to an alkaline pH of 8, and the sol was left standing for later use.

[0046] (2) Using fibers as the skeleton structure, by the sol impregnation method, the sol in step (1) was combined with the fibers, and then hydrophobic modification was carried out, and the composite material was obtained by atmospheric drying.

[0047] The specific process is as follows:

[0048] Molding: The treated aluminosilicate fibers were loaded into the mold and laid flat, covered with a hollow lid, and glass balls were used to expel the air in the fibers and compact them, extruding the internal air. After pressing to be flat, a fixed mass of silicon sol was poured into it, and the silicon sol was evenly impregnated in the fiber felt.

[0049] Soaking and aging: Ethanol solution was poured into the mold for soaking, and an oven was used to accelerate the aging process of the alcogel, and the aging time was 12 hours.

[0050] Demolding: Soaking and aging in ethanol to demold the gel.

[0051] Hydrophobic modification: To endow the material with better hydrophobic properties, it was demolded by soaking in ethanol for aging, and the wet gel was immersed in a mixed solution of n-hexane and trimethylchlorosilane, followed by soaking in n-hexane. Specifically, the gel was immersed in a 7% (volume fraction) trimethylchlorosilane / n-hexane mixed solution and surface-modified twice, each time for 12 hours. Solvent replacement: The gel was immersed in n-hexane to replace ethanol and water in the pores with n-hexane, and the n-hexane was changed every 12 hours.

[0052] Graded drying: It was dried in three stages. In the first stage, it was dried at 70 °C for 10 hours; in the second stage, the temperature was raised to 110 °C and dried for 8 hours; in the third stage, it was dried at a high temperature of 140 °C for 3 hours. After drying, an aerogel composite material was obtained.

[0053] Example 3

[0054] A preparation method of a silica aerogel thermal insulation composite material includes the following steps:

[0055] (1) Tetraethyl orthosilicate, ethanol, and deionized water were mixed and stirred, and an acidic solution was added dropwise until acidic for hydrolysis, and then an alkaline solution was added dropwise until alkaline, and it was left standing to obtain a sol.

[0056] The specific process is as follows: 20 ml of tetraethyl orthosilicate, 20 ml of ethanol, and 10 ml of deionized water were taken and mixed and stirred. Hydrochloric acid solution was slowly added dropwise to adjust the solution to an acidic pH of 2.5 for hydrolysis for 1 hour, and then ammonia water solution was added dropwise to adjust to an alkaline pH of 9, and the sol was left standing for later use.

[0057] (2) Using fibers as the skeleton structure, by the sol impregnation method, the sol in step (1) was combined with the fibers, and then hydrophobic modification was carried out, and it was dried at atmospheric pressure to obtain a composite material.

[0058] The specific process is as follows:

[0059] Molding: The treated aluminosilicate fibers were loaded into the mold and laid flat, covered with a hollow lid, and glass balls were used to expel the air in the fibers and compact them, extruding the internal air. After pressing to be flat, a fixed mass of silicon sol was poured into it, and the silicon sol was evenly impregnated in the fiber felt.

[0060] Soaking and aging: Ethanol solution was poured into the mold for soaking, and an oven was used to accelerate the aging process of the alcohol gel, and the aging time was 12 hours.

[0061] Demolding: Soaking and aging in ethanol to demold the gel.

[0062] Hydrophobic modification: To endow the material with better hydrophobic properties, it was demolded by soaking and aging in ethanol, and the wet gel was immersed in a mixed solution of n - hexane and trimethylchlorosilane, followed by soaking in n - hexane. Specifically, the gel was immersed in a 7% (volume fraction) trimethylchlorosilane / n - hexane mixed solution and surface - modified twice, 12 hours each time. Solvent replacement: The gel was immersed in n - hexane to replace ethanol and water in the pores with n - hexane, and the n - hexane was changed every 12 hours.

[0063] Graded drying: It was dried in three stages. In the first stage, it was dried at 60 °C for 12 hours; in the second stage, the temperature was raised to 100 °C and dried for 8 hours; in the third stage, it was dried at 150 °C for 2 hours. After drying, an aerogel composite material was obtained.

[0064] Performance testing

[0065] As Figure 1 shown, it is the XRD pattern of the silica aerogel thermal insulation composite material obtained in Example 1 of the present invention. It was observed that both the pure aerogel and the fiber - based silica aerogel composite material showed a typical broad diffraction peak of silica at about 2θ = 22°, and this obvious characteristic peak revealed that the material had an amorphous structure. By comparing the peak patterns of the two, it was not difficult to find that there was no crystal structure formation during the transformation from the polymer - adhered silica nanofiber membrane to the pure silica nanofiber membrane.

[0066] As Figure 2 shown, it is the SEM pattern of the silica aerogel thermal insulation composite material obtained in Example 1 of the present invention. The fibers were tightly combined with the aerogel block, and the aerogel effectively filled the gaps between the fibers. This special microstructure endows the material with a low thermal conductivity. Due to the existence of the network structure, the heat transfer path becomes diversified, increasing heat loss, thus significantly reducing the thermal conductivity of the composite material. It is worth noting that the outer surface of the fiber was uniformly coated with aerogel, and this coating not only enhanced the binding force between the fiber and the aerogel but also endows the material with a certain strength. This structure plays an important role in supporting the framework and provides strong support for the application of the fiber - based silica aerogel composite material.

[0067] As Figure 3 shown, it is the infrared spectrum of the silica aerogel thermal insulation composite material obtained in Example 1 of the present invention. By analyzing the molecular structure characteristics of the fiber - based aerogel composite material through infrared spectroscopy, the chemical groups therein can be determined. The samples were dried at different temperatures and named samples 1 to 4 respectively. It was found that there was almost no difference. The peak at about 3400 cm -1 corresponded to the stretching vibration of the - OH group, which confirmed the presence of - OH in the aerogel. And the peak appearing at the wavenumber of 2800 cm -1 corresponded to - CH 3Symmetric and asymmetric stretching vibration peaks of C-H in the group. It is worth noting that this peak shows a splitting phenomenon, which is attributed to the existence of both individual -CH 3 in silica aerogel, and also -OCH 2 CH 3 -CH 3 . This splitting phenomenon further supports the hydrolysis process of tetraethyl orthosilicate. In addition, the peak at a wavenumber of 1300 cm -1 corresponds to the vibration of the Si-O-Si bond in the main chain of the silica aerogel molecule. Since the Si-O-Si bond is the most abundant in the material, this peak is particularly sharp. The peak observed at a wavenumber of 840 cm -1 is caused by the vibration of the Si-C bond, indicating that the addition of the hydrophobic agent has an impact on the material structure. The main components of the composite material are the silica skeleton, a small amount of water (including adsorbed water), and possibly existing silica. There may also be a small amount of ethanol, modifiers such as n-hexane and trimethylchlorosilane.

[0068] Such as Figure 4 shown, is the hydrophilic-hydrophobic diagram of the silica aerogel thermal insulation composite material obtained in Example 1 of the present invention. It can be found that the silica aerogel composite material has good hydrophobicity to solutions, and the contact angles are all above 150°.

[0069] Such as Figure 5 shown, is the thermal conductivity curve diagram of the silica aerogel thermal insulation composite material obtained in Example 1 of the present invention. The steady-state heat flux and heat transfer characteristics are measured by the heat flow meter method to detect the thermal conductivity of the material at a set temperature. The aerogel is prepared into a 10 cm * 10 cm sample and placed in a thermal conductivity tester for testing. The temperature is raised to 800 degrees under normal pressure environment, and the instrument obtains data every five minutes. The results show that as the test time increases, the thermal conductivity shows a tendency to stabilize. At the moment of reaching the set temperature, 15 relatively stable points are taken to calculate the average thermal conductivity of the aerogel. The lowest value of its thermal conductivity reaches 0.033 Wm -1 K -1 , and the highest value is 0.041 Wm -1 K -1 . Thus, it can be seen that under normal pressure drying conditions, the thermal conductivity of the silica aerogel prepared in this experiment is similar to that of air, showing its remarkable characteristic of low heat conduction.

[0070] Such as Figure 6As shown, it is the combustion test diagram of the silica aerogel thermal insulation composite material obtained in Example 1 of the present invention. The aerogel composite material was subjected to a combustion test to test its fireproof and heat insulation performance. When continuously contacting with a flame at up to 1300 degrees for up to 30 seconds or even longer, as shown, most areas of the surface showed no obvious change, the surface morphology remained unchanged, and only a small part was carbonized, showing significant non-combustible characteristics. When placed on the outer flame of an alcohol lamp, the flame could not pass through the material. When the composite material was removed from above the flame, as Figure 6 shown in e, the side in contact with the flame was carbonized, while the other side not in contact with the flame was hardly affected. Therefore, the composite material showed excellent flame retardant and heat insulation performance.

[0071] As Figure 7 shown, it is the mechanical property diagram of the silica aerogel thermal insulation composite material obtained in Example 1 of the present invention. The compression performance of the material was tested, and the results showed that the silica composite aerogel had good compressive ability and still had good compressive performance under a strain pressure of 80%, and the maximum compressive stress reached 23.1 MPa.

[0072] The above embodiments have elaborated in detail the implementation process of the present invention. However, the implementation manners of the present invention are not limited thereto. Those of ordinary skill in the art can achieve the purpose of the present invention based on the content disclosed in the present invention. Any improvements and deformations made based on the concept of the present invention fall within the protection scope of the present invention. The specific protection scope shall be subject to what is recorded in the claims.

Claims

1. A method for preparing a silica aerogel thermal insulation composite material, characterized in that: The following steps are involved: (1) mixing tetraethyl orthosilicate, ethanol and deionized water, adding an acidic solution dropwise until the mixture becomes acidic for hydrolysis, then adding an alkaline solution dropwise until the mixture becomes alkaline, and allowing the mixture to stand to obtain a sol; (2) Using the fiber as the skeleton structure, the sol in step (1) is combined with the fiber by a sol impregnation method, and then hydrophobic modification is performed and the composite material is obtained by drying at normal pressure.

2. The method for preparing the silica aerogel thermal insulation composite material according to claim 1, characterized in that: In step (1), the volume ratio of ethyl orthosilicate, ethanol and deionized water is 10:7-10:3-5.

3. The method for preparing nano thermal insulation material at normal pressure according to claim 1 or 2, characterized in that: The pH range of the acidic hydrolysis in step (1) is 1-3; the pH range of the alkaline hydrolysis is 7-9.

4. The method for preparing the silica aerogel thermal insulation composite material according to claim 3, characterized in that: In step (1), the acidic solution is a hydrochloric acid solution, and the alkaline solution is aqueous ammonia; The time for hydrolysis by adding acidic solution is 1-2 hours.

5. The method for preparing the silica aerogel thermal insulation composite material according to claim 3, characterized in that: The fiber in step (2) is aluminum silicate fiber.

6. The method for preparing the silica aerogel thermal insulation composite material according to claim 3, characterized in that: The hydrophobic modification in step (2) is to immerse the gel in a trimethylchlorosilane / n-hexane mixed solution for surface modification, and then perform solvent replacement.

7. The method for preparing the silica aerogel thermal insulation composite material according to claim 6, characterized in that: In step (2), the solvent replacement is performed by immersing the gel in n-hexane to replace the ethanol and water in the gel cavities with n-hexane.

8. The method for preparing the silica aerogel thermal insulation composite material according to claim 3, characterized in that: In step (2), drying is performed by graded drying, which is divided into three stages: the first stage is drying at 60-80°C for 10-12 hours; the second stage is drying at 100-120°C for 8-10 hours; and the third stage is drying at a high temperature of 140-160°C for 2-4 hours.

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