CN101671029B - Method for preparing SiO2 airgel by drying under normal pressure - Google Patents

Abstract

The invention discloses a method for preparing _SiO2 airgel by drying under normal pressure, which relates to a preparation method of _SiO2 airgel. The invention overcomes the disadvantages of complex equipment, high production cost and high risk in the method for preparing _SiO2 airgel by supercritical drying, and the disadvantage that it is difficult to obtain a complete _SiO2 airgel block in the existing normal pressure drying process. The preparation method of the SiO ₂ airgel of the present invention is as follows: the SiO ₂ airgel is obtained after sol-gel, aging, solvent replacement, surface modification, cleaning and drying. The method has the characteristics of low cost, low requirement on equipment and good safety. The _SiO2 airgel block prepared by the method of the invention has uniform texture, good integrity, porosity of 90% to 95%, water repellency and low thermal conductivity.

Description

Method for preparing SiO2 airgel by drying under normal pressure

technical field

The invention relates to a preparation method of _SiO2 airgel.

Background technique

SiO ₂ aerogels were first prepared by supercritical drying in the early 1930s, used as liquid fuel storage materials in the 1960s, and used in large deep space probes in the early 1980s, and have received extensive attention since then. It has a series of special properties such as low density, high specific surface area, high porosity, low thermal conductivity, low acoustic wave propagation velocity and low dielectric constant, and is displayed in acoustics, mechanics, heat, optics, electricity and catalysis. It has unique value, such as dielectric materials used in Cherenkov detectors, substrate materials for large-scale integrated circuits with high-speed computing, catalyst carriers, gas filters, acoustic impedance coupling materials, and it is currently the best thermal insulation performance of solid material.

The conventional method of SiO ₂ airgel is to adopt supercritical drying method to prepare. The airgel prepared by the supercritical method has relatively good performance, but the equipment system is complex and expensive, and it needs to work under high temperature and pressure, which is highly dangerous. However, due to the shrinkage of the gel during the drying process in the existing atmospheric pressure drying method, it is easy to break or crack, and it is still difficult to obtain a complete SiO ₂ airgel block at present.

Contents of the invention

The invention provides a method for preparing _SiO2 airgel by normal pressure drying; to overcome the shortcomings of complex equipment, high production cost and high risk in the preparation of _SiO2 airgel by supercritical drying, and the existing normal pressure drying The disadvantage that the process is not easy to obtain a complete SiO ₂ airgel block.

Normal pressure drying of the present invention prepares _SiO The method for aerogel is carried out according to the following steps:

1. Mix ethyl orthosilicate (TEOS), absolute ethanol, oxalic acid and water and carry out hydrolysis reaction for 48-60 hours, wherein the molar ratio between ethyl orthosilicate and water is 1:1, ethyl orthosilicate and The molar ratio of absolute ethanol is 1:7, and the molar ratio of ethyl orthosilicate and oxalic acid is 1:9×10 ^-4 ;

2. Then add water, N, N-dimethylformamide and ammonia water, and let it stand for 24-48 hours to obtain a gel;

3. Place the gel prepared in step 2 in a drying oven at 20-60°C for 2-6 hours, then place it in an aqueous solution with a volume concentration of 80% ethanol, and perform aging treatment at 40-60°C for 12-24 hours, and then Put it in a mixture of tetraethyl orthosilicate and ethanol with a volume ratio of 1:5, and age at 40-60°C for 12-24 hours;

4. Put the aging-treated gel into isopropanol for solvent replacement for 4-8 hours, and then put it into a mixture of isopropanol and n-hexane with a volume ratio of 1-4:5 for solvent replacement for 1-5 times , each time for 4-8 hours, then put into n-hexane for solvent replacement for 4-8 hours, and then use a mixture of trimethylchlorosilane and n-hexane with a volume ratio of 1:1-50 to modify the surface until it is completely transparent, and then use volume Wash with a mixture of isopropanol and n-hexane at a ratio of 1:1-50 for 4-8 hours, and then wash with n-hexane for 4-8 hours;

5. Dry the gel treated in step 4 at 40-80°C for 6-10 hours to obtain an airgel; wherein the molar ratio of the water described in step 2 and the tetraethyl orthosilicate described in step 1 is 3:1, the molar ratio of the N,N-dimethylformamide described in step two and the tetraethyl orthosilicate described in step one is 0.8:1, the ammonia water described in step two and the orthosilicate described in step one The molar ratio of ethyl silicate is 4×10 ^-3 :1.

The method of the invention is carried out under normal pressure, and the reaction temperature does not exceed 100 DEG C, and the reaction conditions are mild. Therefore, the method of the invention has low requirements on equipment, reduces production costs, and improves safety.

The _SiO2 airgel block prepared by the method of the invention has uniform texture, good integrity, no cracks or cracks, good transparency, porosity of 90% to 95%, water repellency and low thermal conductivity. The above-mentioned aerogels have broad application prospects in thermal insulation fields such as spacecraft wave-transmissive thermal insulation windows.

Description of drawings

Fig. 1 is the topographical figure of _SiO2 airgel blocks prepared by Embodiment 11; Fig. 2 is the morphology showing the transparent characteristics of _SiO2 Airgel blocks prepared by Embodiment 11; Fig. 3 is a water droplet Dropped on the prepared SiO ₂ airgel block material surface non-wetting figure; Fig. 4 is the figure of a coin floating on the water of the prepared SiO ₂ airgel block weight of the specific embodiment eleven; Fig. 5 It is a figure showing low thermal conductivity by holding a SiO ₂ airgel block prepared in Embodiment 11 and burning it on an alcohol torch.

Detailed ways

The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any combination of the specific embodiments. .

Specific embodiment one: present embodiment normal pressure drying prepares _SiO The method for aerogel is carried out according to the following steps: one, carry out hydrolysis reaction 48h after mixing ethyl orthosilicate, dehydrated alcohol, oxalic acid and water, Wherein the mol ratio of ethyl orthosilicate and water is 1: 1, the mol ratio of ethyl orthosilicate and dehydrated alcohol is 1: 7, the mol ratio of ethyl orthosilicate and oxalic acid is 1: 9 * 10 ^{- 4} ; two, add water, N,N-dimethylformamide and ammonia water again, stand for 36h to obtain a gel; three, place the gel prepared in step 2 in a drying oven at 20～60°C for 2～6h, Then place it in an aqueous solution with a volume concentration of 80% ethanol, and perform aging treatment at 40-60°C for 12-24 hours, and then place it in a mixed solution of tetraethyl orthosilicate and ethanol with a volume ratio of 1:5. Aging treatment at ℃ for 12 to 24 hours; 4. Put the aged gel in isopropanol for solvent replacement for 6 hours, and then put it in a mixture of isopropanol and n-hexane with a volume ratio of 1 to 4:5 Carry out solvent replacement 1 to 5 times, each time for 5h (replacement time), then put it into n-hexane for solvent replacement for 5h, and then use a mixture of trimethylchlorosilane and n-hexane with a volume ratio of 1:1~50 for surface Modify until completely transparent, then wash with a mixture of isopropanol and n-hexane with a volume ratio of 1:1-50 for 5 hours, and then wash with n-hexane for 5 hours; 5. Put the gel treated in step 4 at 40-80°C Dry for 8h to obtain an airgel; wherein the molar ratio of the water described in step two and the tetraethyl orthosilicate described in step one is 3:1, the N,N-dimethylformamide described in step two and the The molar ratio of ethyl orthosilicate described in step 1 is 0.8:1, and the molar ratio of ammonia water described in step 2 and ethyl orthosilicate described in step 1 is 4×10 ⁻³ :1.

The airgel prepared in this embodiment has a good block-forming property, and the color is white with light blue, and the color is uniform, and the porosity is 90%-95%.

Embodiment 2: The difference between this embodiment and Embodiment 1 is that the drying temperature in Step 3 is 30-50°C. Other steps and parameters are the same as those in Embodiment 1.

Embodiment 3: The difference between this embodiment and Embodiment 1 is that the drying temperature in step 3 is 40°C. Other steps and parameters are the same as those in Embodiment 1.

Embodiment 4: This embodiment is different from Embodiments 1 to 3 in that: in step 3, the aging temperature in the aqueous solution of ethanol is 45-55°C. Other steps and parameters are the same as those in Embodiments 1 to 3.

Embodiment 5: This embodiment differs from Embodiments 1 to 3 in that: in step 3, the aging temperature in an aqueous solution of ethanol is 50° C. Other steps and parameters are the same as those in Embodiments 1 to 3.

Embodiment 6: This embodiment differs from Embodiments 1 to 5 in that: in step 3, the aging temperature in the mixed solution of ethyl orthosilicate and ethanol is 45-55°C. Other steps and parameters are the same as those in Embodiments 1 to 5.

Embodiment 7: This embodiment differs from Embodiments 1 to 5 in that: in step 3, the aging temperature in the mixed solution of ethyl orthosilicate and ethanol is 50°C. Other steps and parameters are the same as those in Embodiments 1 to 5.

Embodiment 8: This embodiment is different from Embodiments 1 to 7 in that: the drying temperature in step 5 is 50-70°C. Other steps and parameters are the same as those in Embodiments 1 to 7.

Embodiment 9: This embodiment differs from Embodiments 1 to 7 in that: the drying temperature in step 5 is 55-65°C. Other steps and parameters are the same as those in Embodiments 1 to 7.

Embodiment 10: This embodiment is different from Embodiments 1 to 7 in that: the drying temperature in step 5 is 55-65°C. Other steps and parameters are the same as those in Embodiments 1 to 7.

Embodiment 11: The method for preparing SiO _airgel by normal pressure drying in this embodiment is carried out according to the following steps: 1. After mixing ethyl orthosilicate, dehydrated alcohol, oxalic acid and water, carry out hydrolysis reaction for 48h , wherein the molar ratio of ethyl orthosilicate to water is 1:1, the molar ratio of ethyl orthosilicate to absolute ethanol is 1:7, and the molar ratio of ethyl orthosilicate to oxalic acid is 1:9×10 ^-4 ; Two, add water, N, N-dimethylformamide and ammonia water again, and leave it for 24 hours to obtain a gel; Three, place the gel prepared in step 2 in a drying oven at 40°C for 6 hours, and then place Aging treatment at 60°C for 24 hours in an aqueous solution with a volume concentration of 80% ethanol, and then placed in a mixed solution of tetraethyl orthosilicate and ethanol at a volume ratio of 1:5, and aging treatment at 60°C for 24 hours; 4. Put the aged gel in isopropanol for solvent replacement for 6 hours, then put it in a mixture of isopropanol and n-hexane with a volume ratio of 3.75:5 for solvent replacement for 5 hours, and then put it into a mixture of isopropanol and n-hexane with a volume ratio of 2.5: 5 isopropanol and n-hexane mixed solution for solvent replacement for 5 hours, then put into isopropanol and n-hexane mixed solution with a volume ratio of 1.25:5 for solvent replacement for 5 hours, then put into n-hexane for solvent replacement for 5 hours, and then Use a mixture of trimethylchlorosilane and n-hexane with a volume ratio of 1:10 to modify the surface until it is completely transparent, then wash with a mixture of isopropanol and n-hexane with a volume ratio of 1:10 for 5 hours, and then wash with n-hexane for 5 hours; , drying the gel treated in step 4 at 65°C for 8h to obtain SiO ₂ airgel; wherein the molar ratio of the water described in step 2 and the tetraethyl orthosilicate described in step 1 is 3:1 , the molar ratio of the N,N-dimethylformamide described in step two and the ethyl orthosilicate described in step one is 0.8:1, the ammonia water described in step two and the ethyl orthosilicate described in step one The molar ratio of ester is 4×10 ^-3 :1.

The airgel prepared by this embodiment has good block characteristics (as shown in Figure 1), the color is white with light blue, and the color is uniform, the transparency is good (as shown in Figure 2), the porosity At 94.5%.

At present, it is difficult to obtain an aerogel with a diameter greater than 50 mm in the existing normal pressure drying process; however, the diameter of the aerogel prepared in this embodiment is equal to 55 mm.

When water is dropped on the airgel prepared in this embodiment, the water is in the shape of an ellipsoid on the surface of the airgel, and the airgel is not wetted (as shown in FIG. 3 ). Put the airgel prepared in this embodiment into water, put a one-yuan coin on the airgel, and the airgel floats in the water (as shown in FIG. 4 ). The above experiments prove that the airgel prepared in this embodiment is non-wetting and non-absorbent.

A hand-held airgel was burnt with an alcohol torch for 45 seconds. The result is shown in FIG. 5 . It can be seen from FIG. 5 that the aerogel prepared in this embodiment has good heat insulation and heat resistance properties.

Claims (9)

1. normal pressure drying prepares SiO The method for aerogel is characterized in that normal pressure drying prepares _SiO The method for aerogel is carried out as follows _: one, tetraethyl orthosilicate, dehydrated alcohol, oxalic acid After mixing with water, carry out the hydrolysis reaction for 48-60 hours, wherein the molar ratio of ethyl orthosilicate to water is 1:1, the molar ratio of ethyl orthosilicate to absolute ethanol is 1:7, ethyl orthosilicate and The molar ratio of oxalic acid is 1:9×10 ^-4 ; 2. add water, N,N-dimethylformamide and ammonia water, and let it stand for 24-48 hours to obtain a gel; 3. put the gel prepared in step 2 in Place it in a drying oven at 20-60°C for 2-6 hours, then place it in an aqueous solution with a volume concentration of 80% ethanol, perform aging treatment at 40-60°C for 12-24 hours, and then place it in a normal solution with a volume ratio of 1:5. In the mixture of ethyl silicate and ethanol, aging treatment at 40-60°C for 12-24 hours; 4. Put the aged gel in isopropanol for solvent replacement for 4-8 hours, and then put it into the volume Solvent replacement in the mixture of isopropanol and n-hexane with a ratio of 1 to 4:5 for 1 to 5 times, each time for 4 to 8 hours, then put into n-hexane for solvent replacement for 4 to 8 hours, and then use a volume ratio of 1: 1-50 mixed solution of trimethylchlorosilane and n-hexane to modify the surface until completely transparent, then wash with a mixed solution of isopropanol and n-hexane with a volume ratio of 1:1-50 for 4-8 hours, and then wash with n-hexane for 4-8 hours 5. Dry the gel treated in step 4 at 40-80°C for 6-10 hours to obtain an airgel; wherein the molar ratio of the water described in step 2 to the tetraethyl orthosilicate described in step 1 is 3:1, the molar ratio of N,N-dimethylformamide described in step two and tetraethyl orthosilicate described in step one is 0.8:1, the ammoniacal liquor described in step two and the The molar ratio of ethyl orthosilicate is 4×10 ^-3 :1. 2. The method for preparing SiO ₂ airgel by drying under normal pressure according to claim 1, characterized in that the drying temperature in step 3 is 30-50°C. 3. The method for preparing SiO ₂ airgel by drying under normal pressure according to claim 1, characterized in that the drying temperature in step 3 is 40°C. 4. The method for preparing SiO ₂ airgel by drying under normal pressure according to claim 1, 2 or 3, characterized in that in step 3, the aging temperature in the aqueous ethanol solution is 45-55°C. 5. The method for preparing SiO ₂ airgel by drying under normal pressure according to claim 1, 2 or 3, characterized in that in step 3, the aging temperature in the aqueous ethanol solution is 50°C. 6 . The method for preparing SiO ₂ airgel by drying under normal pressure according to claim 4 , characterized in that in step 3, the aging temperature in the mixed solution of ethyl orthosilicate and ethanol is 45-55° C. 7 . 7. The method for preparing _SiO2 airgel by drying under normal pressure according to claim 4, characterized in that in step 3, the aging temperature in the mixed solution of ethyl orthosilicate and ethanol is 50°C. 8. The method according to claim 1, 2, 3, 6 or ₇ , characterized in that the drying temperature in step 5 is 50-70°C. 9. The method according to claim 1, 2, 3, 6 or ₇ , characterized in that the drying temperature in step 5 is 55-65°C.

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