KR100823072B1 - A method for preparation of aerogel having high transparency and an aerogel prepared therefrom - Google Patents

Abstract

A method for preparation of a silica aerogel having high transparency at a low cost by a simplified preparation process is provided, and a silica aerogel having high transparency prepared by the method is provided. A method for preparation of a silica aerogel having high transparency comprises: a first step of injecting a silica sol into a sealed polypropylene container and gelling the silica sol to form a wet gel; a second step of adding 2-propanol into the polypropylene container to age the wet gel; a third step of solvent-exchanging alcohol presenting in the aged wet gel into xylene; a fourth step of modifying a surface of the solvent-exchanged wet gel with HMDSZ(hexamethyldisilazane); a fifth step of cleaning the surface-modified wet gel with xylene, and drying the cleaned wet gel; and a sixth step of heat-treating the dried wet gel.

Description

A method of manufacturing a high-transparency airgel and the airgel produced thereby {A METHOD FOR PREPARATION OF AEROGEL HAVING HIGH TRANSPARENCY AND AN AEROGEL PREPARED THEREFROM}

1 is a schematic diagram of a method for producing an atmospheric pressure dried silica airgel using the HMDSZ of the present invention,

2 is a view showing the results of the FT-IR structure analysis of various modifiers for the dried gel obtained by surface modification of the silica airgel according to the present invention and dried at room temperature,

3 is a photograph and a microstructure photograph of a silica airgel according to the present invention.

The present invention relates to a method for preparing silica airgel having high transparency and to a high transparency silica airgel prepared therefrom.

Silica aerogel has the highest porosity (~ 90%), low density (3 ~ 120 mg / cm ³ ), low refractive index (~ 1.01) and low sound speed (100m) among the existing materials with three-dimensional network structure. / s), high specific surface area (≥700 m ² / g), low dielectric constant (~ 1.1) and very low thermal conductivity (~ 0.01W / K Has Aerogels having such physical properties are materials having unlimited application potential in energy, environment, and electrical and electronic fields, such as transparent insulation (TIM), solar heating systems, catalyst carriers, and insulating films. To date, most of the research in the field of monolithic silica airgels is insulators, which is expected to be the fastest commercially viable one. Nano-porous airgel can be used as a chemical / bio sensor based on molecular recognition function through selective separation / adsorption of measurement molecules only, which can be applied to chemical process control, environmental pollution measurement, and biochemical reaction detection. In addition, for the functional application, the shape of the material is not a powder, but the shape of the nano-pore structure is required, and a film forming technique and a patterning technique for application to the device is also required.

In addition, the manufacture of aerogels has been manufactured using an autoclave equipment for a supercritical drying method to prevent destruction of micropores during drying, but such a supercritical drying method has a high pressure and a high temperature. This is followed by the risk of explosion. In addition, the autoclave, which is a supercritical drying equipment, has the disadvantage of not only continuous processing but also high manufacturing cost.

Silica airgel is generally manufactured through super critical drying using colloidal based silica powder and tetramethylorthosilicate (TMOS) as starting materials. This is a burdensome part. This requires a manufacturing method through atmospheric pressure drying of the airgel. However, due to the hydrogen bond between the OH group on the surface of the airgel and the moisture in the air during atmospheric pressure drying, moisture in the air is adsorbed on the airgel, thereby significantly deteriorating physical properties of the airgel.

Accordingly, in order to solve the problems described above, the present inventors have made hydrophobic by replacing an OH group on the surface of an airgel with an alkyl group or an aryl group at atmospheric pressure in order to use an atmospheric pressure drying method instead of a conventional supercritical drying method. By changing, the method of inventing the physical property of an airgel does not fall. Therefore, the method of the present invention not only simplifies the process but also lowers the manufacturing cost, thereby facilitating the commercialization of the light-transmissive silica airgel, and using the same for various applications using aerogels and silica airgel for thermal insulation of windows and doors such as smart glazing. Can be used.

It is an object of the present invention to provide a method for preparing silica airgel having high transparency with low cost and a high transparency silica airgel prepared therefrom.

In order to achieve the above object, the present invention provides a method for producing a silica aerosol having the following high transparency:

A first step of gelling silica sol in a closed polypropylene container to form a wet gel; A second step of ripening the wet gel by adding 2-propanol to the polypropylene container; Solvent-substituting the alcohol present in the matured wet gel with xylene; A fourth step of performing surface modification of the solvent-substituted wet gel with hexa methyl di silazane (HMDSZ); A fifth step of washing and drying the modified wet gel with xylene; A sixth step of heat-treating the dried wet gel.

In the first step, the wet gel is prepared by gelling the silica sol in a sealed polypropylene container at 40-60 ° C., preferably at 50 ° C. for 1-3 hours, preferably 2 hours. The aging of the second step is carried out at 40-60 ° C., preferably at 50 ° C., for 12-36 hours, preferably for 24 hours.

In addition, the solvent replacement process of the third step is to prevent the occurrence of minute cracks due to rapid evaporation. In the fourth step of surface modification, the solvent-substituted wet gel of the third step is sealed in a polypropylene container to which a mixed solution of hexamethyldisylzan (HMDSZ) and xylene is added, and sealed at 40-60 ° C., preferably Preferably, surface modification is carried out at 50 ° C. for 2-4 days, preferably 3 days, so that the hydrogel surface of the wet gel is modified with a hydrophobic surface. The amount of HMDSZ is also mixed at 5-10 vol%, preferably 6 vol% of xylene.

In addition, the washing step of the fifth step is to remove the unreacted substances present in the inside of the wet gel in which the surface modification is completed in the fourth step and to prevent the breakage during drying, preferably at 40-60 ° C., preferably 50 1-10 times, preferably 3-6 times, more preferably 4 times washing with xylene for 12-36 hours at room temperature, preferably 24 hours, and when the washing is complete In an atmosphere of 2-4 days, preferably 3 days, and then at 40-60 ° C., preferably at 50 ° C. again for 2-4 days, preferably 3 days. The dried wet gel is heated at a temperature of 0.1-10 ° C./min at room temperature, preferably at a temperature increase rate of 5 ° C./min to 100-300 ° C., preferably at 270 ° C., and then at 100-300 ° C. Heat treatment is preferably performed at 270 ° C. for 1-3 hours, preferably for 2 hours.

The present invention also provides a high transparency silica airgel prepared by the above method.

Hereinafter, the present invention will be described in detail.

A commercially available silica sol used in the present invention may be purchased and used, and TMOS (tetramethoxysilane, Si (OCH ₃ ) ₄ ) or TEOS (tetraethoxysilane, Si (OCH ₂ CH ₃ ) ₄ ) Using as a starting material can be used to directly prepare a silica sol using the sol-gel method.

The sol-gel process is a chemical process in which a substance that is a mixed oxide is produced from a suitable sol mixture, starting from a solution of organic and inorganic compounds of the metal and then converting the solution into fine particles of the metal oxide by hydrolysis and polymerization of the compound in the solution. After making a dissolved sol and further reacting and gelling, an alkoxide hydrolyzes a compound of the formula M (OR) n (M: metal or metalloid element, R: alkyl group), and two alkoxides react with OH-OR. By forming a dimer to form a gel having a SiO ₂ network structure.

The silica sol prepared by the sol-gel method is gelled in a polypropylene container at 40-60 ° C., preferably at 50 ° C. for 1-3 hours, preferably 2 hours, to prepare a wet gel. In this case, the siloxane particles may be formed to solidify by gradually increasing the viscosity of the solution and decreasing the volume, thereby obtaining a transparent wet gel.

2-propanol is added to the obtained polypropylene container containing the wet gel and aged at 40-60 ° C., preferably at 50 ° C. for 12-36 hours, preferably 24 hours. In the state of gelation by hydrolysis and polymerization reaction, the bond to siloxane particles is not very strong in point contact. In order to change this into a strong bond, the contact part of the round particles is necked by aging while maintaining the wet gel state to form a -Si-O-Si- bond.

A mesh structure is formed in the gel formed as described above, and alcohol is present in the structure. Such alcohols must be replaced with a suitable solvent that is not reactive with the modifier because it causes a chemical reaction with the modifier in the reforming step and substantially reduces the reaction with hydroxyl groups in the network structure. In the selection of the solvent, a non-polar solvent which is not reactive with a modifier should be selected. A solvent having a low vapor pressure that can prevent the formation of invisible fine cracks due to rapid evaporation at the manufacturing stage is preferable. Preferred examples thereof include xylene. This xylene is used to substitute the isopropyl alcohol (IPA) solvent contained in the gel. When xylene is used to replace the solvent, not only the reactivity with the modifier is suppressed, but also the rapid reaction with the hydroxyl group on the surface of the colloid particle composed of the modifier and the network structure is suppressed. Suppresses the occurrence of fine cracks.

In general, the physical properties of aerogels having a high specific surface area are greatly influenced not only by the structural characteristics but also by the chemical bonding state of the surface, and the surface is composed of many hydroxyl groups (OH). Hydroxyl groups present on the surface induce physical adsorption of polar molecules such as water molecules, which may cause contraction of the skeletal structure of the wet gel, resulting in structural change or cracking or destruction. For this reason, the surface modification process is essential in order to prevent the destruction of the wet gel during the atmospheric pressure drying process. Currently known surface modification method is to convert the hydroxyl group on the surface of the silica gel with an alkyl group (CH ₃ ) using TMCS (Tri methyl chloro silane). However, when Chloro of TMCS reacts with hydrogen of silica gel, hydrochloric acid (HCl), which is a reaction product, is generated. This hydrochloric acid is dangerous as a hazardous substance. That is, in the case of TMCS, three methyl groups and one chloro are bonded to one silane, and HCl is generated by reacting with H of the OH group on the surface of the aerogel during surface modification. Trimethylsilane (TriMethylSilane, (CH ₃ ) ₃ Si) is bonded to be modified (see Equation (1) below).

(CH ₃ ) ₃ SiCl + OH-Si≡ → ≡Si-O-Si (CH ₃ ) ₃ + HCl (1)

Therefore, in the present invention, in order to overcome the above problems and to improve the physical properties and to prevent deformation and breakage during drying, HMDSZ (hexamethyldisylzan) is used instead of the conventional TMCS used for the surface modification process. Perform a surface modification process. In other words, the HMDSZ used in the present invention binds trimethylsilane (CH ₃ ) ₃ Si) to both sides of NH, and when H is modified, two H and NH are bonded to each other. Trimethylsilane is occupied one by one in the place where it is bound, and is reformed to actually generate HCl and NH ₃ after the modification (see Equation (2) below).

(CH ₃ ) ₃ Si ₂ NH + 2 (OH-Si≡) → (≡Si-O-Si (CH ₃ ) ₃ ) ₂ + NH ₃ (2)

Therefore, in the present invention, the wet gel in which the solvent is substituted is placed in a polypropylene container containing HMDSZ (hexamethyldisylzane) and a solution in which xylene, which is a solvent used at the time of solvent replacement, is added and sealed, and then sealed at 40-60 ° C. In a surface modification process, preferably at 50 ° C. for 2-4 days, preferably for 3 days. The wet gel, which has undergone a surface modification, is converted from hydroxyl groups to methyl groups on the colloidal surface. The amount of HMDSZ in the above is mixed at 5-10 vol%, preferably 6 vol% of xylene.

Unreacted materials that may be present inside the surface modified wet gel are removed by performing four washes with xylene at 40-60 ° C., preferably at 50 ° C. for 12-36 hours, preferably 24 hours, This washing process can also prevent breakage of the drying process of the wet gel. The amount of xylene used in the washing may be used in a volume ratio of 5-20 times, preferably 10 times, each time of the wet gel.

The washed wet gel is dried under the atmosphere of an atmospheric pressure drying process rather than an expensive supercritical drying method, and the wet gel is dried in an atmosphere of xylene for 2-4 days, preferably 3 days. The drying is then carried out again at 40-60 ° C., preferably at 50 ° C. for 2-4 days, preferably for 3 days. When drying is complete, the temperature is raised to 100-300 ° C., preferably 270 ° C. at a rate of 0.1-10 ° C./min, preferably 5 ° C./min at room temperature, and preferably at 100-300 ° C., preferably Silica airgel having high transparency can be prepared by heat treatment at 270 ° C. for 1-3 hours, preferably 2 hours.

Hereinafter, the present invention will be described in more detail with reference to the following Examples and Experimental Examples. However, the following Examples and Experimental Examples are only examples of the present invention, and the scope of the present invention is not limited thereto.

Example  One. High transparency  Preparation of Silica Airgel

Using tetraethoxysilane (TEOS) as a starting material, a hydrophobic airgel modified with HMDSZ was prepared, and the method is as follows.

The starting solution was prepared by adding HCl as an alcohol solution as water and a catalyst required for hydrolysis of TEOS to the IPA solution, and finally adding ammonia water (NH ₄ OH) solution to complete the polymerization reaction to prepare a final silica sol. It was. In this case, the addition of the acidic catalyst or the basic catalyst may be omitted to control the pore size of the silica airgel formed in the subsequent process.

The prepared silica sol was placed in a sealed polypropylene container to form a gel at 50 ° C. for 2 hours. Thereafter, 2-propanol was charged into a polypropylene container containing silica gel, and aged at 50 ° C. for 24 hours. After aging, the wet gel was subjected to solvent replacement with isopropyl alcohol (IPA) in the gel using xylene. For surface modification of the solvent-substituted wet gel with xylene, a solution of HMDSZ and xylene (the amount of HMDSZ is 6 vol% of xylene) is placed in a polypropylene container, and the wet gel is immersed and sealed. It was left for 3 days at a temperature of 50 ° C. to induce rapid modification.

To remove the unreacted substances present in the inside of the wet gel in which the surface modification was completed and to prevent breakage during drying, four washes were performed with xylene solvent at a temperature of 50 ° C. for 24 hours. The amount of solvent at this time was 10 times the volume of the gel each time.

Atmospheric drying was performed to dry the wet gel in which the washing was completed. The most important part of atmospheric drying is to prevent rapid solvent evaporation to prevent gel breakage. Therefore, after the washing gel was added to the chalet and sealed with a wrap, and dried at room temperature for 3 days, and then dried at 50 ℃ for 3 days to suppress the rapid evaporation of the solvent. Thereafter, in order to increase the porosity of the dried silica gel under normal pressure, a heat treatment is performed as a final step of the preparation to evaporate the solvent remaining in the gel pores, at which time the heat treatment is performed from room temperature to 270 ° C. at a rate of 5 ° C./min. The temperature was raised, and the final silica air gel was prepared by performing heat treatment at 270 ° C. for 2 hours.

Experimental Example  1. Measurement of physical properties of silica airgel of the present invention

The physical properties such as density, porosity, surface area, average pore volume and diameter of the silica airgel prepared by Example 1 were measured, and the results are shown in Table 1 below.

Surface modifier Density (g / cm ³ ) Porosity (%) Surface area (m ² / g) Average pore volume (cm ³ / g) Average pore diameter (nm) HMDSZ 0.39 82.2 838 1.2 5.4

In addition, as shown in Figure 3, the silica airgel prepared in Example 1, it was confirmed that the transparency is very high. In addition, the microstructure of the silica airgel was confirmed that the nano-sized pores.

Experimental Example  2. By reformer  FT- IR  Structural analysis experiment

The silica airgel prepared in Example 1 was dried on a room temperature after the surface modification of HMDSZ with a modifier and dried gel at room temperature, as a comparative example using only the modifier TMCS, MTES or MTMS and the preparation method is The surface modification level to hydrophobicity of the dried gels obtained by surface modification of the silica airgel and drying at room temperature in the same manner was confirmed by FR-IR structure analysis.

As a result of the experiment, as shown in FIG. 2, in the airgel modified with trimethlychlorosilane (TMCS) and HMDSZ (hexamethyldisilazane) in the silica airgel structure, the CH group (2965 cm-1) appeared, but methyl or ethyl group (C _{2 5} H - modifying agents (methlytriethoxylsilane of) one or more oxygen attached to methoxy (CH ₃ O-), ethoxy groups and (C ₂ H ₅ O-) in: MTES and methlytrimethoxysilane: the MTMS) CH (2965 cm-1 ) peak Did not occur, and it was confirmed that the use of HMDSZ according to the present invention had a stable hydrophobic structure that did not adsorb water on the surface of the silica airgel.

As described above, the present invention relates to a method for producing a high-transparency embodiment car aerogel, the method of the present invention to simplify the process and lower the manufacturing cost by using an atmospheric pressure drying process, and also to perform the atmospheric pressure drying process The hydrophobic surface modification is performed using HMDSZ as a modifier in order to prevent changes in the structure of the wet gel or cracks or fractures that may occur at the time.

Therefore, by using the method of the present invention can overcome the existing high cost and the difficulty of manufacturing a large amount of airgel and contribute to the practical use of the bulk and powder of the airgel, the application fields of various airgel (energy saving, environmental protection, electrical and electronic fields, etc.) Based on the application in) has the effect of providing a cheaper and more practical airgel.

Claims (8)

A first step of gelling silica sol in a closed polypropylene container to form a wet gel; A second step of ripening the wet gel by adding 2-propanol to the polypropylene container; Solvent-substituting the alcohol present in the matured wet gel with xylene; A fourth step of performing surface modification of the solvent-substituted wet gel with hexa methyl di silazane (HMDSZ); A fifth step of washing the modified wet gel with xylene and then drying; Method of manufacturing a silica airgel having a high transparency consisting of a sixth step of heat-treating the dried wet gel. The method of claim 1, wherein the first step is to place the silica sol in a closed polypropylene container gelled at 40-60 ℃ for 1-3 hours. The method of claim 1, wherein the aging of the second step is carried out at 40-60 ° C for 12-36 hours. The method of claim 1, wherein the surface modification process of the fourth step is performed by sealing the solvent-substituted wet gel of the third step in a polypropylene container to which a mixed solution of hexamethyldisilzan (HMDSZ) and xylene is added. Method for producing a silica airgel is to perform a surface modification for 2-4 days at -60 ℃. The method of claim 1, wherein the fifth step of washing is performed 1-10 times with xylene at 40-60 ° C. for 12-36 hours. The silica airgel of claim 1, wherein the drying process of the fifth step is to dry the washed wet gel in an atmosphere of xylene for 2-4 days and then to dry at 40-60 ° C. for 2-4 days. Manufacturing method. The silica airgel of claim 1, wherein the heat treatment of the sixth step is performed by increasing the temperature from 100 ° C. to 300 ° C. at a rate of 0.1 ° C. to 10 ° C./min from 100 ° C. to 300 ° C. for 1-3 hours. Manufacturing method. delete

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