Silicon dioxide aerogel and preparation method thereof

Abstract

The invention relates to the field of silicon dioxide aerogel, in particular to silicon dioxide aerogel and a preparation method thereof. According to the preparation method provided by the invention, the application of a hydrothermally controlled dynamic slow-release technology on the metamaterial aerogel is realized, a silicon dioxide aerogel skeleton is fully modified on the basis of soaking reaction activation of hydrothermal slow release, and through more excellent pore protection and homogenized silicon methyl modification, the performance of the aerogel is greatly improved. And more excellent optical and mechanical properties are realized. A gradient normal-pressure drying technology is used for assisting and replacing a traditional supercritical drying technology, so that the whole aerogel can be directly prepared. The silicon dioxide aerogel obtained by the preparation method provided by the invention has more excellent mechanical properties and also has the excellent characteristic of high light transmittance. The silicon dioxide aerogel is excellent in thermal insulation property and compressive strength and high in visible optical transmittance, so far, the silicon dioxide aerogel is the best aerogel which is prepared through a normal-pressure drying technology and has excellent light transmittance.

Description

Technical Field

[0001] The present invention relates to the field of silicon dioxide aerogels, in particular to a silicon dioxide aerogel and a preparation method thereof. Background Art

[0002] Silica aerogel is a three-dimensional metamaterial composed of stacked nano-microscopic silicon oxide particles. Its three-dimensional structure is filled with more than 95% air medium, so the material has a low density (usually <0.3g / cm 3 ), large specific surface area, low thermal conductivity (<0.028W m -1 ·K -1 ) and other excellent properties, and has broad application prospects in industrial insulation, battery protection, new energy power generation and other fields.

[0003] Silica aerogel has a history of nearly a hundred years since its discovery. Due to its excellent performance, as early as 1997, the United States has applied it as a thermal insulation material in aerospace and other fields. However, silica aerogel still faces many challenges. First, its mechanical strength is poor, and it is difficult to preserve it in a larger size. It mostly exists in the form of powder or fragments. Secondly, the preparation process is complicated and costly. It usually requires a sol-gel method combined with high-energy consumption processes such as supercritical drying or freeze-drying, which makes it difficult to achieve large-scale low-cost production. In addition, due to the difficulty in controlling the pores of silica aerogel, it is difficult to achieve a high transparency of the aerogel, which limits its application in optics. These problems have restricted its further development and application.

[0004] Therefore, if the three-dimensional improvement of cost reduction, transparency and enhancement can be achieved, while improving the strength and performance of aerogel materials to adapt to a wider range of applications, atmospheric pressure drying can be used to replace traditional supercritical drying or freeze-drying processes, which will help expand the application of aerogels. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a silica aerogel and a preparation method thereof. The preparation method provided by the present invention can prepare large pieces of transparent silica aerogel with uniform hydrophobic modification and excellent mechanical properties.

[0006] The present invention provides a method for preparing a silica aerogel, comprising the following steps:

[0007] The solid acid, hexamethyldisiloxane silane and aged silica hydrogel are subjected to hydrothermal reaction, followed by drying under normal pressure to obtain silica aerogel;

[0008] The temperature of the hydrothermal reaction is 80°C to 150°C, and the time of the hydrothermal reaction is 30 minutes to 120 minutes. Preferably, the temperature of the hydrothermal reaction of the present invention is 90°C to 150°C, and the time of the hydrothermal reaction is 90 minutes to 120 minutes.

[0009] The present invention firstly subjects solid acid, hexamethyldisiloxane silane and aged silica hydrogel to a hydrothermal reaction. Specifically, firstly, subject solid acid, hexamethyldisiloxane silane solution and aged silica hydrogel to a hydrothermal reaction. In certain embodiments of the present invention, the aged silica hydrogel is placed in a hexamethyldisiloxane silane solution, and then solid acid is added thereto to conduct a hydrothermal reaction. The amount of solid acid used in the present invention is 4% to 6% of the mass of the aged silica hydrogel, preferably 5%; the amount of hexamethyldisiloxane used is 40-100% of the mass of the aged silica hydrogel, preferably 60%.

[0010] The hexamethyldisiloxane silane solution of the present invention is specifically a mixed solution of hexamethyldisiloxane silane and alcohol. The alcohol of the present invention is selected from one or more of ethanol, isopropyl alcohol, acetone, etc. The volume ratio of hexamethyldisiloxane silane to alcohol in the mixed solution of hexamethyldisiloxane silane and alcohol of the present invention is (0.35-0.45): (0.55-0.65). In certain embodiments of the present invention, the hexamethyldisiloxane silane solution of the present invention is a mixed solution of hexamethyldisiloxane silane and ethanol, wherein the volume ratio of hexamethyldisiloxane silane to ethanol is 0.4:0.6.

[0011] The solid acid of the present invention is a sustained-release acid with abundant active sites on its surface. It can have efficient acid catalytic activity without significantly increasing the pH of the solution, and can achieve uniform modification of the hydrogel as a whole by promoting high-temperature hydrothermal heating. And due to the unique characteristics of the solid acid, the damage of the acid to the hydrogel network skeleton is avoided, which also improves the performance of the product aerogel. Preferably, the solid acid is selected from ion exchange resin type solid acid. More preferably, the solid acid is selected from polystyrene sulfonic acid type solid acid. In certain embodiments of the present invention, the solid acid is selected from one or more of Hnd-580, 732 strong acid cation exchange resin and Amberlyst-15.

[0012] The aged silica hydrogel of the present invention is obtained by aging silica hydrogel, the aging temperature is 50° C. to 70° C., preferably 60° C., and the aging time is 20 h to 30 h, preferably 24 h; that is, the skeleton is strengthened through Oswald ripening.

[0013] The aged silica hydrogel of the present invention is prepared by the following steps:

[0014] S1) acid-catalyzing and hydrolyzing silane in sequence to obtain a polysiloxane precursor;

[0015] S2) gelling the polysiloxane precursor in the presence of a weak base to obtain a silica hydrogel.

[0016] The present invention first acid-catalyzes and hydrolyzes silane to produce a polysiloxane precursor. Specifically, the silane is acid-catalyzed in an acid, and the acid-catalyzed material is then hydrolyzed in water to produce a silica hydrogel. In certain embodiments of the present invention, an acid catalyst is added to the silane, and then water is added to the silane for hydrolysis to produce the polysiloxane precursor.

[0017] The silane described in the present invention is selected from tetraethyl orthosilicate. The silane described in the present invention is specifically a silane solution. In certain embodiments of the present invention, the silane described in the present invention is a 98wt% tetraethyl orthosilicate solution. The acid used in the acid catalysis described in the present invention is selected from one or more of hydrochloric acid, polystyrene sulfonic acid type solid acid (such as HND-580, 732, Amberlyst-15). The acid used in the acid catalysis described in the present invention is an alcohol solution of the acid, and its concentration is 0.5mol / L to 1.0mol / L. In certain embodiments of the present invention, the acid used in the acid catalysis described in the present invention is an ethanol solution of hydrochloric acid, and its concentration is 0.626mol / L. The amount of acid added in the acid catalysis described in the present invention is 25% to 35% of the mass fraction of the silane, preferably 30%; the amount of water added in the hydrolysis described in the present invention is 10% to 15% of the mass fraction of the silane, preferably 14%.

[0018] The acid catalysis of the present invention can be carried out at room temperature. Room temperature refers to the temperature under standard atmospheric pressure without artificial heating or cooling treatment, generally 15°C to 35°C. The hydrolysis of the present invention is also called pre-catalysis or prepolymerization. The hydrolysis of the present invention can also be carried out at room temperature. There is no special limitation on the time of the acid catalysis and the hydrolysis of the present invention. The acid used for the acid catalysis and the water used for the hydrolysis are added dropwise at a dropping rate of 10mL / h to 30mL / h. In certain embodiments of the present invention, a constant pressure dropping funnel is used for control during the acid catalysis and hydrolysis process.

[0019] After obtaining the polysiloxane precursor, the present invention gels the polysiloxane precursor under a weak base to obtain a silica hydrogel. The gelation of the present invention can be carried out at room temperature. The gelation time of the present invention is not particularly limited, and it can be observed that the gelation is complete, which is generally 1 minute to 5 minutes. The weak base of the present invention is selected from one or more of ammonia water, sodium bicarbonate, sodium acetate, and solid base, preferably selected from ammonia water. The present invention specifically gels the polysiloxane precursor under a weak base solution, and the solvent of the weak base solution is an alcohol, preferably one or more of ethanol, cyclohexane, n-hexane or methanol. The concentration of the weak base of the present invention is 0.5 mol / L to 1 mol / L, and the amount of the weak base added is 8% to 12% of the mass fraction of the polysiloxane precursor, preferably 10%.

[0020] After the hydrothermal reaction, the present invention performs atmospheric drying to obtain silica aerogel. The atmospheric drying of the present invention is preferably gradient atmospheric drying, wherein the gradient atmospheric drying is specifically drying at 55°C to 65°C for 6 hours to 12 hours, heating to 110°C to 130°C and drying for 15 minutes to 30 minutes; preferably, the gradient atmospheric drying is specifically drying at 60°C for 6 hours to 12 hours, heating to 120°C and drying for 15 minutes to 30 minutes. The present invention uses gradient atmospheric drying technology to replace traditional supercritical drying technology, thereby directly preparing a whole piece of aerogel.

[0021] After the hydrothermal reaction, the present invention further comprises: performing solvent replacement at 55°C to 75°C for 12 hours to 24 hours to remove the hexamethyldisiloxane silane, preferably at 60°C; performing solvent replacement at 55°C to 75°C for 12 hours to 24 hours to remove the solid acid, preferably at 60°C. The solvent replacement of the present invention specifically involves placing the gel after the hydrothermal reaction in a solvent and allowing it to stand. The present invention places the gel after the hydrothermal reaction in one or more of ethanol, n-hexane or acetone for solvent replacement to remove the hexamethyldisiloxane silane; the present invention places the gel after the hydrothermal reaction in n-hexane for solvent replacement to remove the solid acid.

[0022] The preparation method of silica aerogel provided by the present invention is based on the "hydrothermal sustained release" technology. Through the precise control of heat and reaction diffusion dynamics, the three-dimensional silica pearl string skeleton is fully modified. In the modification reaction process, high-temperature heat is used to drive the activation of the solid acid catalyst carrier, thereby modifying uniform silyl functional groups in the gel network. The aerogel material has better hydrophobic properties and better internal pore uniformity, thereby greatly improving mechanics, transparency, etc., and because the gel skeleton network is strong enough, the aerogel can be directly obtained by drying at normal pressure.

[0023] The present invention provides a silica aerogel and a preparation method thereof. The preparation method provided by the present invention realizes the application of hydrothermally controlled kinetic sustained release technology to aerogel, a metamaterial. Based on the homogenization reaction activation of "hydrothermal sustained release", the silica aerogel skeleton is fully modified, and through better pore protection and homogenized silicon methyl modification, more excellent optical and mechanical properties are achieved. In addition, with the assistance of gradient atmospheric pressure drying technology, the traditional supercritical drying technology is replaced, so that the whole aerogel can be directly prepared. The silica aerogel obtained by the preparation method provided by the present invention has more excellent mechanical properties and also has the excellent characteristic of high light transmittance. The thermal conductivity of the silica aerogel reaches from room temperature (0.028W m -1 ·K -1 ~0.046W m -1 ·K -1 , 323K, air conditions) to medium temperature (0.047W m -1 ·K -1 ~0.0054W m -1 ·K -1 The silica aerogel prepared by atmospheric drying technology has excellent thermal insulation performance (at 473K, air conditions), compressive strength (23% compression 240kPa), and visible optical transmittance >90%, making it the best aerogel with excellent light transmittance produced to date using atmospheric drying technology. The silica aerogel prepared by atmospheric drying in this invention opens up new avenues for the aerogel new materials industry to further expand its application in multiple fields and reduce costs and increase efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A comparison of the microscopic morphologies of the silica aerogel prepared by the method of the present invention and conventional commercial silica aerogel;

[0025] Figure 2 This is a comparison chart of the thermal conductivity of the silica aerogel prepared by the method of the present invention and traditional commercial silica aerogel;

[0026] Figure 3 This is a comparison chart of the mechanical compressive strength of the silica aerogel prepared by the method of the present invention and traditional commercial silica aerogel;

[0027] Figure 4 This is a comparison chart of the optical transmittance and hydrophobic angle of the silica aerogel prepared by the method of the present invention and traditional commercial silica aerogel;

[0028] Figure 5 This is a comparison of the appearance of the silica aerogel prepared by the method of the present invention and traditional commercial silica aerogel;

[0029] Figure 6Schematic diagram of the model for preparing aerogel by thermally stimulated two-phase interface diffusion of the present invention and the traditional single-phase mixing method;

[0030] Figure 7 This is a comparison of the appearance of the aerogel prepared in Example 1 of the present invention and the aerogel prepared in Comparative Example 1 by a conventional single-phase mixing reaction;

[0031] Figure 8 This is a comparison of infrared spectroscopy microscopy images of the aerogel prepared in Example 1 of the present invention and the aerogel prepared in Comparative Example 1 by conventional single-phase mixing reaction;

[0032] Figure 9 This is a graph showing the change in the residual ratio of HMDSO converted to TMCS during the surface hydrophobization process of 0 to 120 minutes for the aerogel prepared in Example 1 of the present invention and the aerogel prepared by traditional single-phase mixing reaction in Comparative Example 1. DETAILED DESCRIPTION

[0033] The present invention discloses a silica aerogel and a method for preparing the same. Those skilled in the art may refer to the contents herein and appropriately modify the process parameters to achieve the desired results. It should be noted that all similar substitutions and modifications obvious to those skilled in the art are considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately alter and combine the methods and applications herein to implement and apply the technology of the present invention without departing from the content, spirit, and scope of the present invention.

[0034] The present invention will be further described below with reference to the embodiments:

[0035] Example 1

[0036] Preparation of polysiloxane precursor solution: Add 197 g of tetraethyl silicate to a round-bottom flask. Dissolve 71.5 g of hydrochloric acid (0.628 mol / L) dispersed in ethanol in a constant pressure dropping funnel at a rate of 10 mL / h. After 8 hours, add 30.58 g of deionized water at a rate of 10 mL / h. After the addition is complete, place the solution in an oven and evaporate to 250 g to obtain a polysiloxane precursor solution.

[0037] Preparation and modification of hydrogel: 2.5mL of polysiloxane precursor liquid was added to a polytetrafluoroethylene mold, 0.2mL of 0.5mol / L ammonia solution (ethanol dispersion) was added, and the gel was allowed to gel for 5 minutes. The sample was then aged in an oven for 24 hours. After aging, the mold was removed and the silica hydrogel sample was placed in a 60mL hydrothermal autoclave. 20mL of ethanol and 10mL of hexamethyldisiloxane were added. 0.45g of Hnd-580 strong acid solid acid was added and the sample was hydrothermally treated at 120°C for 120 minutes. The pH was approximately 7 at the beginning of thermal stimulation. Afterwards, the solid acid was slowly released to maintain the pH of the system between 4 and 5. The modified hydrogel was obtained after hydrothermal treatment.

[0038] Aerogel preparation: The hydrogel was placed in ethanol and oven-displaced at 60°C for 12 hours. After the displacement, the ethanol was replaced with n-hexane and oven-displaced for another 12 hours. After the displacement was complete, the gel was dried at room temperature for one day to obtain a xerogel. The xerogel was then placed in an oven-drying position at 120°C for 30 minutes. The xerogel rebounded, resulting in a transparent aerogel.

[0039] The thermal conductivity of the transparent aerogel block obtained in this example at 323K is 0.035 W·m -1 K -1 The thermal conductivity at 573K is 0.047W·m -1 K -1 , the compressive strength is 806kPa at 34% compression.

[0040] We compared the parameters of this aerogel with those of aerogel prepared by traditional technology that can achieve a transparency of nearly 80°C. Figure 1 The microscopic morphology comparison diagram of the silica aerogel prepared by the method of the present invention and the traditional commercial silica aerogel (purchased from Jiazhiqi New Materials) is shown in FIG. Figure 1 (a) shows the microscopic morphology of the silica aerogel prepared by the method of the present invention. Figure 1 (b) in the figure shows a traditional commercial silica aerogel. The results show that the silica aerogel prepared by the method of the present invention has a more uniform pore structure inside, which is maintained at 2nm to 50nm, while the traditional commercial aerogel has many uneven macropores inside due to the effects of acid and non-uniform heating.

[0041] like Figure 2 As shown, Figure 2 The thermal conductivity comparison chart of the silica aerogel prepared by the method of the present invention and the traditional commercial silica aerogel is shown in FIG. Figure 2 The results show that solid acid hydrothermal modification can make the material have better thermal insulation performance. Under the same modification and test conditions, the thermal conductivity of the aerogel prepared by solid acid hydrothermal method at 50℃ is close to 0.03W m -1 ·K -1As a control, the samples treated with traditional technology had low modification efficiency and structural damage in the same time, with thermal conductivity as high as 0.064W m -1 ·K -1 .

[0042] like Figure 3 As shown, Figure 3 The figure is a comparison of the mechanical compressive strength of the silica aerogel prepared by the method of the present invention and the traditional commercial silica aerogel. Figure 3 It shows that the compressive strength of aerogels prepared by solid acid hydrothermal method and hydrochloric acid hydrothermal method can reach 806KPa under 33% strain, which is about five times that of aerogels prepared by hydrochloric acid hydrothermal method. This shows that we can achieve dual enhancement of mechanical and compressive strength through solid acid hydrothermal method.

[0043] like Figure 4 As shown, Figure 4 The figure shows the comparison of the optical transmittance and hydrophobic angle of the silica aerogel prepared by the method of the present invention and the traditional commercial silica aerogel. Figure 4 It shows that the samples prepared by the solid acid sustained-release method have better optical transmittance and hydrophobicity than traditional aerogel products. In the wavelength range of 400-800nm, the optical transmittance of solid acid hydrothermal aerogel can reach more than 90%.

[0044] like Figure 5 As shown, Figure 5 This is a comparison of the appearance of the silica aerogel prepared by the method of the present invention and traditional commercial silica aerogel. Figure 5 The left picture shows the appearance of the silica aerogel prepared by the method of the present invention, and the right picture shows the appearance of conventional commercial silica aerogel. Figure 5 It can be intuitively found that the aerogel prepared by hydrothermal sustained-release technology has high transparency and excellent size characteristics, while the aerogel products prepared by traditional technology are easy to break and lack transparency.

[0045] Example 2

[0046] Preparation of polysiloxane precursor solution: Add 197 g of tetraethyl silicate to a round-bottom flask. Dissolve 71.5 g of hydrochloric acid (0.628 mol / L) dispersed in ethanol in a constant pressure dropping funnel at a rate of 10 ml / h. After 8 hours, add 30.58 g of deionized water at a rate of 10 mL / h. After the addition is complete, place the solution in an oven and evaporate to 250 g to obtain a polysiloxane precursor solution.

[0047] Preparation and modification of the hydrogel: 2.5 mL of the polysiloxane precursor solution was added to a polytetrafluoroethylene mold. 0.2 mL of a 0.5 mol / L ammonia solution (dispersed in ethanol) was added, and the mixture was allowed to gel for 5 minutes. The sample was then aged in an oven for 24 hours. After aging, the mold was removed and the silica hydrogel sample was placed in a 60 mL hydrothermal autoclave. 20 mL of ethanol and 10 mL of hexamethyldisiloxane were added, along with 0.6 g of 732 strong acid cation exchange resin. The sample was hydrothermally treated at 120°C for 120 minutes. The pH was initially around 7 upon thermal stimulation, but the solid acid was slowly released to maintain the pH of the system between 4 and 5. The modified hydrogel was obtained after hydrothermal treatment.

[0048] Aerogel preparation: The hydrogel was placed in ethanol and oven-displaced at 60°C for 12 hours. After the displacement, the ethanol was replaced with n-hexane and oven-displaced for another 12 hours. After the displacement was complete, the gel was dried at room temperature for one day to obtain a xerogel. The xerogel was then placed in an oven-drying position at 120°C for 30 minutes. The xerogel rebounded, resulting in a transparent aerogel.

[0049] Example 3

[0050] Preparation of polysiloxane precursor solution: Add 197 g of tetraethyl silicate to a round-bottom flask. Dissolve 71.5 g of hydrochloric acid (0.628 mol / L) dispersed in ethanol in a constant pressure dropping funnel at a rate of 10 mL / h. After 8 hours, add 30.58 g of deionized water at a rate of 10 mL / h. After the addition is complete, place the solution in an oven and evaporate to 250 g to obtain a polysiloxane precursor solution.

[0051] Preparation and modification of hydrogels: 2.5 mL of polysiloxane precursor solution was added to a polytetrafluoroethylene mold. 0.2 mL of 0.5 mol / L ammonia solution (ethanol dispersion) was added, and the mixture was allowed to gel for 5 minutes. The sample was then aged in an oven for 24 hours. After aging, the mold was removed and the silica hydrogel sample was placed in a 60 mL hydrothermal autoclave. 20 mL of ethanol and 10 mL of hexamethyldisiloxane were added, along with 0.4 g of Amberlyst-15 strong acid cation exchange resin. The sample was hydrothermally treated at 120°C for 120 minutes. The pH was initially around 7 upon thermal stimulation. After this, the solid acid was slowly released, maintaining the pH of the system between 4 and 5. The modified hydrogel was obtained after hydrothermal treatment.

[0052] Aerogel preparation: The hydrogel was placed in ethanol and oven-displaced at 60°C for 12 hours. After the displacement, the ethanol was replaced with n-hexane and oven-displaced for another 12 hours. After the displacement was complete, the gel was dried at room temperature for one day to obtain a xerogel. The xerogel was then placed in an oven-drying position at 120°C for 30 minutes. The xerogel rebounded, resulting in a transparent aerogel.

[0053] The performance parameters of the aerogels of Examples 1 to 3 are listed in Table 1:

[0054] Table 1

[0055] Catalytic acid model Thermal conductivity (W / m·K) Compression resistance (KPa) Visible light transmittance (%) Hnd-580 0.035 806 90～95 732 0.046 784 85～90 Amberlyst-15 0.0039 501 85～90

[0056] Comparative Example 1

[0057] Preparation of polysiloxane precursor solution: Add 197 g of tetraethyl silicate to a round-bottom flask. Dissolve 71.5 g of hydrochloric acid (0.628 mol / L) dispersed in ethanol in a constant pressure dropping funnel at a rate of 10 mL / h. After 8 hours, add 30.58 g of deionized water at a rate of 10 mL / h. After the addition is complete, place the solution in an oven and evaporate to 250 g to obtain a polysiloxane precursor solution.

[0058] Preparation and modification of hydrogels: 2.5 mL of polysiloxane precursor solution was added to a polytetrafluoroethylene mold. 0.2 mL of 0.5 mol / L ammonia solution (dispersed in ethanol) was added, and the mixture was allowed to gel for 5 minutes. The sample was then aged in an oven for 24 hours. After aging, the mold was removed and the silica hydrogel sample was placed in a 60 mL hydrothermal autoclave. 20 mL of ethanol and 10 mL of hexamethyldisiloxane were added, along with 1 mL of 1 mol / L dilute hydrochloric acid. The sample was hydrothermally treated at 120°C for 120 minutes, maintaining a pH between 1 and 2 during the reaction.

[0059] Aerogel Preparation: The hydrogel was placed in ethanol and oven-displaced at 60°C for 12 hours. After the displacement, the ethanol was replaced with n-hexane and oven-displaced for another 12 hours. After the displacement was complete, the gel was dried at room temperature for one day to obtain a xerogel. The xerogel was then dried in an oven at 120°C for 30 minutes. The xerogel rebounded to obtain a transparent aerogel. Specifically, the process for preparing the transparent aerogel in this comparative example is the same as the process for preparing the aerogel using the hydrochloric acid hydrothermal method described above.

[0060] like Figure 6 As shown, Figure 6 This is a schematic diagram of the model of aerogel preparation by thermally stimulated two-phase interface diffusion in the present invention and aerogel preparation by traditional single-phase mixing method. The aerogel preparation by thermally stimulated two-phase interface diffusion can produce large aerogels, while the traditional single-phase mixing method can only produce small white aerogels. The actual appearance of the aerogel prepared in Example 1 of the present invention and the aerogel prepared in the traditional single-phase mixing reaction in Comparative Example 1 are compared. Figure 7 As shown, Figure 7The left figure shows the appearance of the aerogel prepared in Example 1 of the present invention, and the right figure shows the appearance of the aerogel prepared in the traditional single-phase mixing reaction in Comparative Example 1. It can be seen that the method of the present invention can produce large pieces of transparent aerogel, while the traditional single-phase mixing reaction can only produce small pieces of whitish aerogel.

[0061] The aerogel prepared in Example 1 and the aerogel prepared in Comparative Example 1 were subjected to infrared spectroscopy microscopy testing. The results are as follows: Figure 8 As shown, Figure 8 This is a comparison of infrared spectroscopy microscopy images of the aerogel prepared in Example 1 of the present invention and the aerogel prepared in the conventional single-phase mixing reaction in Comparative Example 1. The upper figure shows the infrared spectroscopy microscopy image of the aerogel prepared in Example 1 of the present invention, and the lower figure shows the infrared spectroscopy microscopy image of the aerogel prepared in the conventional single-phase mixing reaction in Comparative Example 1. The left side of the upper and lower figures shows the modification of Si-O-Si in the aerogel, and the right side of the upper and lower figures shows the modification of Si-CH3 in the aerogel. Figure 8 It can be seen that the Si-CH3 modification on the surface of the aerogel obtained by the solid acid interface thermal excitation diffusion method of the present invention is more uniform, so the obtained aerogel is more transparent and integral; in contrast, the silicon methyl modification on the surface of the aerogel obtained by mixing is uneven, so it is smaller and whiter.

[0062] The conversion of HMDSO to TMCS and its participation in the gelation reaction is related to time, temperature, and conversion amount. The remaining ratio of HMDSO converted to TMCS under the conditions of preparing aerogels in Example 1 and Comparative Example 1 was studied respectively. Figure 9 As shown, Figure 9 The graph shows the change in the residual ratio of HMDSO converted to TMCS during the surface hydrophobization process of the aerogel prepared in Example 1 of the present invention and the aerogel prepared by the traditional single-phase mixing reaction in Comparative Example 1 during the 0-120 min surface hydrophobization process. Figure 9 It can be seen that the traditional method of hydrophobic modification of the present invention by forming a two-phase interface between a solid acid or ion exchange resin and the gel through thermally stimulated two-phase interface diffusion is compared with the method of mixing the gel and a solution and then immersing it in a hydrophobic modifier for hydrophobic modification. When the hydrophobic groups such as HMDSO are converted to TMCS and the surface hydrophobicization reaction is carried out, the traditional method directly reacts completely within 30 minutes, while the method of the present invention has a slower reaction rate. Based on thermal excitation at 80°C to 150°C and pH 4 to 5, the amount of HMDSO converted to TMCS is a steadily decreasing process, and the overall time is in the range of 30 to 120 minutes. The aerogel obtained in this way will be more transparent as a whole.

[0063] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing silica aerogel, characterized in that: The following steps are involved: The solid acid, hexamethyldisiloxane silane and aged silica hydrogel are subjected to hydrothermal reaction, followed by drying under normal pressure to obtain silica aerogel; The temperature of the hydrothermal reaction is 80° C. to 150° C., and the time of the hydrothermal reaction is 30 min to 120 min.

2. The preparation method according to claim 1, characterized in that The solid acid is selected from ion exchange resin type solid acid.

3. The preparation method according to claim 1, characterized in that The solid acid is selected from one or more of Hnd-580, 732 strong acid cation exchange resin and Amberlyst-15.

4. The preparation method according to claim 1, characterized in that The amount of the solid acid is 4% to 6% of the mass of the aged silica hydrogel, and the amount of the hexamethyldisiloxane is 40 to 100% of the mass of the aged silica hydrogel.

5. The preparation method according to claim 1, characterized in that The aged silica hydrogel is obtained by aging silica hydrogel, the aging temperature is 50° C. to 70° C., and the aging time is 4 hours to 30 hours.

6. The preparation method according to claim 1, characterized in that After the hydrothermal reaction, the method further comprises: Performing solvent replacement at 55° C. to 75° C. for 12 to 24 hours to remove the hexamethyldisiloxane silane; Solvent replacement is performed at 55° C. to 75° C. for 12 to 24 hours to remove the solid acid.

7. The preparation method according to claim 1, characterized in that The aged silica hydrogel is prepared by the following steps: S1) acid-catalyzing and hydrolyzing silane in sequence to obtain a polysiloxane precursor; S2) gelling the polysiloxane precursor in the presence of a weak base to obtain a silica hydrogel.

8. The preparation method according to claim 7, characterized in that In step S1), the silane is selected from ethyl orthosilicate; In step S1), the acid used for acid catalysis is selected from one or more of hydrochloric acid and polystyrene sulfonic acid type solid acid; In step S2), the weak base is selected from one or more of ammonia water, sodium bicarbonate, sodium acetate, and solid base.

9. The preparation method according to claim 7, characterized in that In step S1), the amount of acid used in the acid catalysis is 25% to 35% of the mass fraction of the silane; In step S1), the amount of water added for the hydrolysis is 10% to 15% of the mass fraction of the silane; In step S2), the concentration of the weak base is 0.5 mol / L to 1 mol / L, and the amount of the weak base added is 8% to 12% of the mass fraction of the polysiloxane precursor.

10. Silica aerogel obtained by the preparation method according to any one of claims 1 to 9.

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