Transparent aerogel as well as preparation method and application thereof

Abstract

The invention relates to the technical field of aerogel preparation, and discloses transparent aerogel as well as a preparation method and application thereof. The method comprises the following steps: in the presence of a solvent and a catalyst I, contacting silica sol with a silicon source for a first reaction to obtain a mixture I; in the presence of a solvent and a catalyst II, carrying out second reaction on the mixture I and a modifier to obtain wet gel; and sequentially carrying out solvent replacement and normal-pressure drying on the wet gel to obtain the transparent aerogel. The transparent aerogel prepared by the method provided by the invention is fine in skeleton and uniform in pore distribution.

Description

Technical Field

[0001] The present invention relates to the technical field of aerogel preparation, and specifically, to a transparent aerogel, a preparation method thereof, and an application thereof. Background Art

[0002] Silica (SiO2) aerogel is a lightweight nano-porous amorphous solid material with a spatial network structure formed by the cross-linking of colloidal particles or polymer molecules. Its pore size and skeleton size are respectively between 1 - 100 nm and 1 - 50 nm. Silica aerogel has many unique properties, such as high specific surface area, high porosity, high thermal insulation, low density, etc. The excellent properties of silica aerogel make it have broad and huge application prospects in the fields of optics, thermal insulation, acoustics, catalyst carriers, microelectronics, chemical engineering, aerospace, etc.

[0003] Currently, the preparation of silica aerogel generally includes two steps: preparing a wet gel by the sol-gel method and drying the wet gel to obtain an aerogel. In the existing acid-base two-step method, the nucleation rate and nucleus growth rate are difficult to control, the particle size and pore size in the aerogel skeleton obtained are too large, and the distribution is not concentrated, resulting in the dried aerogel showing blue or milky white, thus limiting the application of aerogel in the optical field.

[0004] In CN105110340A, CN113247912A, and CN115180629A, a supercritical drying process is used to prepare a transparent aerogel, which has a high equipment cost investment, resulting in a low input-output ratio and a low production capacity ceiling; while in CN106629750A, although an atmospheric pressure drying process is used to prepare a transparent aerogel, its preparation process is cumbersome and the repeatability is poor.

[0005] Therefore, there is an urgent need to provide a method for preparing a high-transparency aerogel with low cost and good repeatability. Summary of the Invention

[0006] The purpose of the present invention is to provide a preparation method for preparing an aerogel with high transparency, slender skeleton, and uniform pore distribution.

[0007] To achieve the above purpose, the first aspect of the present invention provides a method for preparing a transparent aerogel, the method comprising:

[0008] (1) In the presence of a solvent and a catalyst I, contacting a silica sol with a silicon source to carry out a first reaction to obtain a mixture I; the silica sol does not contain a hydrophobic group, and the linear average particle size of the solids in the silica sol is 6 - 10 nm; the weight ratio of the silica sol to the silicon source is 1:0.3 - 1.3;

[0009] The conditions for the first reaction include: carried out under stirring conditions, with the stirring speed being 50 - 300 rpm, the temperature being 5 - 35 °C, and the time being 0.5 - 4 h;

[0010] (2) In the presence of a solvent and catalyst II, contacting the mixture I with a modifier to carry out a second reaction to obtain a wet gel; the weight ratio of the mixture I to the catalyst II is 100:0.1 - 1;

[0011] (3) Subjecting the wet gel to solvent replacement and atmospheric drying in sequence to obtain the transparent aerogel.

[0012] The second aspect of the present invention provides a transparent aerogel prepared by the method described in the first aspect above.

[0013] The third aspect of the present invention provides an application of the transparent aerogel described in the second aspect above in optical materials and heat insulation materials.

[0014] In the present invention, a sol reaction is carried out between a silica sol without a hydrophobic group and a silicon source, and at the same time, by controlling the reaction conditions to control the nucleation and the nuclear growth rate, a target sol is obtained; then in the presence of a catalyst and a modifier, while the surface of the clusters of the target sol is hydrophobized, the nuclear growth reaction continues to form a wet gel, and after solvent replacement, the solvent in the wet gel is removed by atmospheric drying to form a transparent aerogel with slender skeletons and uniformly distributed pores. Description of the Drawings

[0015] Figure 1 is a macroscopic view of the transparent aerogel J1 prepared in Example 1 of the present invention;

[0016] Figure 2 is an SEM image of the transparent aerogel J1 prepared in Example 1 of the present invention;

[0017] Figure 3 is a particle size distribution diagram of the transparent aerogel J1 prepared in Example 1 of the present invention;

[0018] Figure 4 is a pore size distribution diagram of the transparent aerogel J1 prepared in Example 1 of the present invention;

[0019] Figure 5 is a macroscopic view of the transparent aerogel DJ1 prepared in Comparative Example 1 of the present invention;

[0020] Figure 6 is an SEM image of the transparent aerogel DJ1 prepared in Comparative Example 1 of the present invention;

[0021] Figure 7It is the particle size distribution diagram of the transparent aerogel DJ1 prepared in Comparative Example 1 of the present invention;

[0022] Figure 8 It is the pore size distribution diagram of the transparent aerogel DJ1 prepared in Comparative Example 1 of the present invention. Specific embodiments

[0023] The endpoints and any values in the ranges disclosed herein are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0024] In the present invention, the linear average particle size of the solids in the silica sol is measured by transmission electron microscopy (TEM).

[0025] As described above, the first aspect of the present invention provides a method for preparing a transparent aerogel, the method comprising:

[0026] (1) In the presence of a solvent and a catalyst I, contacting the silica sol with a silicon source to carry out a first reaction to obtain a mixture I; the silica sol does not contain a hydrophobic group, and the linear average particle size of the solids in the silica sol is 6-10 nm; the weight ratio of the silica sol to the silicon source is 1:0.3-1.3;

[0027] The conditions of the first reaction include: carried out under stirring conditions, and the stirring speed is 50-300 rpm, the temperature is 5-35 °C, and the time is 0.5-4 h;

[0028] (2) In the presence of a solvent and a catalyst II, contacting the mixture I with a modifier to carry out a second reaction to obtain a wet gel; the weight ratio of the mixture I to the catalyst II is 100:0.1-1;

[0029] (3) Subjecting the wet gel to solvent replacement and atmospheric drying in sequence to obtain the transparent aerogel.

[0030] The present invention finds that if a silica sol containing a hydrophobic group is continuously contacted with a silicon source to carry out a sol reaction, the pore size distribution of the gel will be significantly increased and the visible light transmittance will be greatly reduced. The present invention also finds that when the linear average particle size of the solids in the silica sol is greater than 10 nm, the visible light transmittance will be reduced, resulting in the aerogel showing a blue light on the macroscopic scale; when the linear average particle size of the solids in the silica sol is less than 6 nm, the mechanical properties of the aerogel skeleton will be greatly reduced, and the gel skeleton is extremely prone to collapse during atmospheric drying.

[0031] It should be noted that the hydrophobic group in the present invention is a hydrophobic group known to those skilled in the art.

[0032] It should be noted that the present invention has no particular limitation on the source of the silica sol. A commercially available silica sol can be used, or a silica source precursor can be used for preparation; as long as it does not contain a hydrophobic group and the linear average particle size of the solid matter therein is within the foregoing range.

[0033] According to a preferred embodiment, in step (1), the method for preparing the silica sol includes: hydrolyzing a silica source precursor in the presence of a solvent and a catalyst III.

[0034] Preferably, in step (1), the conditions for the hydrolysis reaction include: being carried out under stirring conditions, and the stirring speed is 50 - 300 rpm, the temperature is 5 - 45 °C, and the time is 0.5 - 4 h.

[0035] Preferably, in step (1), the silica source precursor is selected from at least one of methyl orthosilicate, ethyl orthosilicate, butyl orthosilicate, isopropyl orthosilicate, sodium silicate, and potassium silicate.

[0036] Preferably, in step (1), the weight ratio of the amount of the silica source precursor to the amount of the catalyst III is 100:0.1 - 1.

[0037] Preferably, in step (1), the catalyst I and the catalyst III are each independently selected from at least one of hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, acetic acid, phosphoric acid, boric acid, formic acid, and citric acid.

[0038] Preferably, in step (1), the weight ratio of the amount of the silica source to the amount of the catalyst I is 100:0.1 - 2.

[0039] According to another preferred embodiment, in step (1), the silica source is selected from at least one of methyl orthosilicate, ethyl orthosilicate, butyl orthosilicate, isopropyl orthosilicate, sodium silicate, potassium silicate, methyltrimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, dimethyldimethoxysilane, vinyltriethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, sodium methylsilicate, and potassium methylsilicate.

[0040] The present invention discovers that when a silica source containing a hydrophobic group is reacted with a silica sol, it can significantly reduce the amount of the modifier while shortening the reaction time of the second reaction, and the hydrophobicity and high-temperature stability of the obtained aerogel are greatly improved.

[0041] Further preferably, in step (1), the silica source is selected from at least one of methyl orthosilicate and ethyl orthosilicate.

[0042] Preferably, in step (2), before the mixture I contacts with the modifier, the mixture I is contacted with the nano-functional agent. The present invention finds that the aerogel obtained in this preferred case has a higher infrared barrier rate.

[0043] Further preferably, in step (2), the weight ratio of the amount of the mixture I to the nano-functional agent is 100:0.5 - 3.

[0044] More preferably, in step (2), the nano-functional agent is selected from at least one of indium tin compound (ITO), rare earth compound, cesium tungsten oxide (CTO), antimony-doped tin oxide (ATO), vanadium dioxide, and nano-silver.

[0045] Preferably, in step (2), the rare earth compound is selected from at least one of cerium oxide and praseodymium oxide.

[0046] Particularly preferably, in step (2), the linear average particle size of the nano-functional agent is 10 - 100 nm.

[0047] Preferably, in step (2), the catalyst II is selected from at least one of ammonia water, sodium hydroxide, potassium hydroxide, ammonium fluoride, ethanolamine, diethanolamine, triethanolamine, methylamine, dimethylamine, ethylamine, diethylamine, propylamine, dipropylamine, isopropanolamine, aniline, o-phenylenediamine, m-phenylenediamine, and p-phenylenediamine.

[0048] According to a preferred specific embodiment, in step (2), the conditions of the second reaction include: being carried out under stirring conditions, with the stirring speed being 50 - 300 rpm, the temperature being 5 - 35 °C, and the time being 0.5 - 4 h.

[0049] Preferably, in step (2), the modifier is selected from at least one of trimethylchlorosilane, dimethyldichlorosilane, hexamethyldisilazane, and hexamethyldisiloxane. More preferably, the modifier is selected from at least one of hexamethyldisilazane and hexamethyldisiloxane. In this preferred case, the obtained transparent aerogel has better visible light transmittance.

[0050] Preferably, in step (2), the weight ratio of the amount of the mixture I to the modifier is 100:3 - 7.

[0051] Preferably, in step (2), the weight ratio of the amount of the mixture I to the catalyst II is 100:0.1 - 1.

[0052] Preferably, in step (3), the solvent replacement conditions include: using an organic solvent, and the number of replacements is 2-4, the interval time is 3-5h, and the temperature is 40-60° C. More preferably, in step (3), the organic solvent is anhydrous ethanol.

[0053] According to another preferred embodiment, in step (3), the conditions for drying at normal pressure include: a temperature of 70-90°C.

[0054] It should be noted that when the wet gel in the present invention is dried at normal pressure, there is no particular requirement for the method of providing the above temperature, as long as the drying temperature can reach 70-90° C. For example, air blast heating, infrared heating or microwave heating can be used.

[0055] According to another particularly preferred embodiment, the solvent is deionized water.

[0056] As mentioned above, the second aspect of the present invention provides a transparent aerogel prepared by the method described in the first aspect.

[0057] Preferably, the transparent aerogel has a skeleton size of 13nm-23nm and a pore size of 16nm-32nm.

[0058] As mentioned above, the third aspect of the present invention provides a use of the transparent aerogel described in the second aspect in optical materials and thermal insulation materials.

[0059] The transparent aerogel in the present invention can be made into lighting glass, aerogel coating, or aerogel film as an optical material or heat insulation material.

[0060] The present invention will be described in detail below by way of examples.

[0061] In the following examples, unless otherwise specified, all raw materials used were commercially available.

[0062] Preparation Example 1: Preparation of Silica Sol I

[0063] In the presence of deionized water (solvent) and phosphoric acid (catalyst III), tetraethyl orthosilicate (silicon source precursor) is subjected to a hydrolysis reaction; the weight ratio of the silicon source precursor to the catalyst III is 100:0.15;

[0064] The conditions of the hydrolysis reaction include: carrying out the reaction under stirring conditions, with a stirring speed of 50 rpm, a temperature of 45° C., and a time of 4 h;

[0065] Silica sol I was prepared, wherein the linear average particle size of the solid matter in the silica sol I was 6 nm.

[0066] Silica sol II: HDK® H15 hydrophobic silica sol, with a linear average particle size of the solid content of 12 nm, purchased from Wacker Chemie AG, Germany.

[0067] Example 1

[0068] (1) In the presence of deionized water (solvent) and phosphoric acid (catalyst I), silica sol I was contacted with methyl orthosilicate (silicon source) to carry out the first reaction to obtain mixture I; the weight ratio of the amount of silica sol to the silicon source was 1:0.3; the weight ratio of the amount of the silicon source to catalyst I was 100:0.1;

[0069] The conditions for the first reaction were: carried out under stirring conditions, and the stirring speed was 300 rpm, the temperature was 35 °C, and the time was 0.5 h;

[0070] (2) In the presence of deionized water (solvent) and ammonia water (catalyst II), mixture I was reacted with hexamethyldisilazane (modifier) to carry out the second reaction to obtain a wet gel; the weight ratio of the amounts of mixture I, modifier, and catalyst II was 100:3:0.5;

[0071] The conditions for the second reaction were: carried out under stirring conditions, and the stirring speed was 50 rpm, the temperature was 35 °C, and the time was 4 h;

[0072] (3) The wet gel was successively subjected to solvent replacement and atmospheric drying. The conditions for solvent replacement were: carried out with absolute ethanol, and the number of replacements was 2, the interval time was 4 h, and the temperature was 50 °C;

[0073] The conditions for atmospheric drying were: the temperature was 80 °C;

[0074] Transparent aerogel J1 was prepared.

[0075] Example 2

[0076] (1) In the presence of deionized water (solvent) and oxalic acid (catalyst I), silica sol I was contacted with tetraethyl orthosilicate (silicon source) to carry out the first reaction to obtain mixture I; the weight ratio of the amount of silica sol to the silicon source was 1:1.3; the weight ratio of the amount of the silicon source to catalyst I was 100:2;

[0077] The conditions for the first reaction were: carried out under stirring conditions, and the stirring speed was 50 rpm, the temperature was 5 °C, and the time was 4 h;

[0078] (2) In the presence of deionized water (solvent) and sodium hydroxide (catalyst II), mixture I was reacted with hexamethyldisiloxane (modifier) to carry out the second reaction to obtain a wet gel; the weight ratio of the amounts of mixture I, modifier, and catalyst II was 100:7:0.5;

[0079] The conditions for the second reaction are as follows: it is carried out under stirring conditions, the stirring speed is 300 rpm, the temperature is 5 °C, and the time is 0.5 h;

[0080] (3) The wet gel is successively subjected to solvent replacement and atmospheric drying. The conditions for solvent replacement are as follows: anhydrous ethanol is used, the number of replacements is 2, the interval time is 4 h, and the temperature is 60 °C;

[0081] The conditions for drying are: the temperature is 80 °C;

[0082] Transparent aerogel J2 is prepared.

[0083] Example 3

[0084] This example is carried out in a similar method to Example 1, the difference is:

[0085] In step (2), the modifier is adjusted to an equal weight of dimethyldichlorosilane, and at the same time, the dosage of ammonia water is adjusted so that the weight ratio of the amount of mixture I to catalyst II is 100:1. The other conditions are the same as those in Example 1, and transparent aerogel J3 is prepared.

[0086] Example 4

[0087] This example is carried out in a similar method to Example 1, the difference is:

[0088] In step (2), before the mixture I contacts with the modifier, the mixture I is contacted with indium tin compound (nano-functional agent), and the weight ratio of the amount of mixture I to the nano-functional agent is 100:0.5. The other conditions are the same as those in Example 1, and transparent aerogel J4 is prepared.

[0089] Comparative Example 1

[0090] Tetraethyl orthosilicate, water, ethanol, and hydrochloric acid are mixed in proportion to carry out a sol reaction to obtain a sol; the weight ratio of the amounts of tetraethyl orthosilicate, water, ethanol, and hydrochloric acid is 100:40:90:0.8;

[0091] The conditions for the sol reaction are as follows: it is carried out under stirring conditions, the stirring speed is 50 rpm, the temperature is 30 °C, and the time is 3 h;

[0092] Subsequently, ammonia water is added to the above reaction system to carry out a gel reaction to obtain a wet gel; the weight ratio of the amount of tetraethyl orthosilicate to ammonia water is 100:0.16;

[0093] The conditions for the gel reaction are as follows: it is carried out under stirring conditions, the stirring speed is 50 rpm, and the temperature is 30 °C;

[0094] The above wet gel was hydrophobically modified with hexamethyldisilazane and then subjected to solvent replacement with absolute ethanol and atmospheric drying. Among them, the number of replacements was 2, the interval time was 4 h, and the temperature was 60 °C; the temperature of atmospheric drying was 80 °C, and the transparent aerogel DJ1 was prepared.

[0095] Comparative Example 2

[0096] This comparative example was carried out in a similar manner to Example 1, except that:

[0097] In step (1), silica sol I was replaced with an equal weight of silica sol II, and the other conditions were the same as those in Example 1, and the transparent aerogel DJ2 was obtained.

[0098] Comparative Example 3

[0099] This comparative example was carried out in a similar manner to Example 1, except that:

[0100] In step (1), the dosage of the silicon source was adjusted so that the weight ratio of silica sol to the silicon source was 1:2, and the other conditions were the same as those in Example 1, and the transparent aerogel DJ3 was obtained.

[0101] Test Example

[0102] The transparent aerogels prepared in the examples and comparative examples were tested according to the following method. Specifically, the test results are shown in Table 1:

[0103] Skeleton size and pore size: The crystal microstructure of the aerogel sample was photographed by a scanning electron microscope, and the data analysis of the photo was obtained by Nano Measure software.

[0104] Table 1

[0105] Skeleton size (nm) Pore size (nm) Example 1 18.31 26.57 Example 2 20.08 30.17 Example 3 17.69 21.97 Example 4 17.94 24.43 Comparative Example 1 25.05 32.81 Comparative Example 2 29.75 37.02 Comparative Example 3 31.31 36.29

[0106] It can be seen from the results in Table 1 that the transparent aerogel prepared by the method provided by the present invention has a slender skeleton and basically the same pore size.

[0107] The macroscopic images, SEM images, particle size distribution images, and pore size distribution images of the transparent aerogels prepared in the other examples of the present invention are similar to those of the transparent aerogel JI prepared in Example 1. The macroscopic image of the transparent aerogel JI is exemplarily provided in the present invention ( Figure 1 ), SEM image ( Figure 2 ), particle size distribution image ( Figure 3 ), pore size distribution image ( Figure 4 ).

[0108] Such as Figure 1As shown, the transparent aerogel J1 prepared by the method provided by the present invention has high transparency, while the aerogel DJ1 prepared by the method in Comparative Example 1 significantly shows a blue light (as Figure 5 shown), indicating that the light transmittance of the aerogel DJ1 is significantly lower than that of the transparent aerogel J1.

[0109] From Figure 2 , Figure 3 and Figure 4 , it can be seen that the transparent aerogel J1 prepared by the method provided by the present invention has uniform and small particle sizes and basically consistent pore sizes. While from Figure 6 , Figure 7 and Figure 8 , it can be seen that the particle sizes of the aerogel DJ1 prepared by the method in Comparative Example 1 are not as uniform and small as those of the transparent aerogel J1, and the pore size consistency is also inferior.

[0110] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the technical concept scope of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for preparing a transparent aerogel, characterized in that, The method comprises: (1) contacting silica sol with a silicon source in the presence of a solvent and a catalyst I to carry out a first reaction to obtain a mixture I; the silica sol does not contain a hydrophobic group, and the linear average particle size of the solid content in the silica sol is 6-10 nm; the weight ratio of the silica sol to the silicon source is 1:0.3-1.3; The conditions of the first reaction include: carried out under stirring conditions, and the stirring speed is 50-300 rpm, the temperature is 5-35 °C, and the time is 0.5-4 h; (2) contacting the mixture I with a modifier in the presence of a solvent and a catalyst II to carry out a second reaction to obtain a wet gel; the weight ratio of the mixture I to the catalyst II is 100:0.1-1; (3) subjecting the wet gel to solvent replacement and atmospheric drying in sequence to obtain the transparent aerogel.

2. The method according to claim 1, wherein In step (1), the method for preparing the silica sol includes: carrying out a hydrolysis reaction on a silicon source precursor in the presence of a solvent and a catalyst III; and / or, In step (1), the conditions of the hydrolysis reaction include: carried out under stirring conditions, and the stirring speed is 50-300 rpm, the temperature is 5-45 °C, and the time is 0.5-4 h; and / or, In step (1), the silicon source precursor is selected from at least one of methyl orthosilicate, ethyl orthosilicate, butyl orthosilicate, isopropyl orthosilicate, sodium silicate, and potassium silicate.

3. The method according to claim 2, wherein In step (1), the catalyst I and the catalyst III are each independently selected from at least one of hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, acetic acid, phosphoric acid, boric acid, formic acid, and citric acid; and / or, In step (1), the silicon source is selected from at least one of methyl orthosilicate, ethyl orthosilicate, butyl orthosilicate, isopropyl orthosilicate, sodium silicate, potassium silicate, methyltrimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, dimethyldimethoxysilane, vinyltriethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, sodium methylsilicate, and potassium methylsilicate.

4. The method according to any one of claims 1 to 3, wherein, In step (2), before the mixture I is contacted with the modifier, the mixture I is contacted with a nano-functional agent; and / or, In step (2), the weight ratio of the mixture I to the nano-functional agent is 100:0.5-3; and / or, In step (2), the nano-functional agent is selected from at least one of indium tin compounds, rare earth compounds, cesium tungsten oxide, antimony-doped tin oxide, vanadium dioxide, and nano-silver; and / or, In step (2), the linear average particle size of the nano-functional agent is 10-100 nm.

5. The method according to any one of claims 1-3, wherein, In step (2), the catalyst II is selected from at least one of ammonia water, sodium hydroxide, potassium hydroxide, ammonium fluoride, ethanolamine, diethanolamine, triethanolamine, methylamine, dimethylamine, ethylamine, diethylamine, propylamine, dipropylamine, isopropanolamine, aniline, o-phenylenediamine, m-phenylenediamine, and p-phenylenediamine; and / or, In step (2), the conditions of the second reaction include: carried out under stirring conditions, and the stirring speed is 50-300 rpm, the temperature is 5-35 °C, and the time is 0.5-4 h.

6. The method according to any one of claims 1-3, wherein, In step (2), the modifier is selected from at least one of trimethylchlorosilane, dimethyldichlorosilane, hexamethyldisilazane, and hexamethyldisiloxane; and / or, In step (2), the weight ratio of the amount of mixture I to the modifier is 100:3 - 7.

7. According to the method according to any one of claims 1 to 3, wherein In step (3), the conditions for solvent replacement include: carried out with an organic solvent, the number of replacements is 2 - 4, the interval time is 3 - 5 h, and the temperature is 40 - 60 °C; and / or, In step (3), the conditions for atmospheric drying include: the temperature is 70 - 90 °C.

8. A transparent aerogel prepared by the method according to any one of claims 1 - 7.

9. The transparent aerogel according to claim 8, wherein The skeleton size of the transparent aerogel is 13 nm - 23 nm, and the pore size is 16 nm - 32 nm.

10. Use of the transparent aerogel according to claim 8 or 9 in optical materials and heat insulation materials.

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