KR101227065B1 - Aerogel and Preparation Method Thereof - Google Patents

Abstract

One embodiment of the present invention is an aerogel using a metal alkoxide or water glass having a hydroxyl group on the surface is substituted with a modifier and alkoxy (Si-C bond 5 to 9, CO bond 18 to 25 relative to the total bond 100 as a precursor and its preparation It is about a method. The method for preparing an airgel according to the present invention comprises the steps of: (a) mixing a metal alkoxide or water glass with an acid and a base to prepare a hydrogel by a sol-gel method;

(b) a hydrogel obtained from step (a) and methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol and octanol alone or mixtures thereof with alcohol and 5 to 15 carbon atoms Preparing a ternary azeotropic mixture by mixing an organic solvent at 60 ° C. to 200 ° C .;

(c) firstly organicizing the hydroxyl groups present in the gel by mixing and heating a ternary azeotropic mixture with an acid;

(d) mixing the primary organicized gel obtained from the step (c) with a modifier to secondary organicize the remaining hydroxyl groups present in the gel; And

(e) drying the gel obtained from step (d).

Porous Powder, Acid, Organic Halide

Description

Aerogel and Preparation Method {Aerogel and Preparation Method Thereof}

The present invention relates to an airgel in which a hydroxyl group on the surface is substituted with a modifier and an alkoxy group (OR) and a method for producing the same.

Airgel is a transparent ultra-low density material with a porosity of more than 90% and a specific surface area of several hundred to 1000 m ² / g. Therefore, the airgel having such a nanoporous structure can be applied to the fields of ultra low dielectric, catalyst, electrode material, soundproofing material, etc. In particular, the silica airgel is a silicon dioxide (SiO ₂ ) nano nanofibers in the form of a yarn with a thickness of 10,000 hairs. Although the structure is intertwined like a nonwoven fabric, the space occupying 98% of the total volume between the yarn is filled with air, which has a high specific surface area (600m ² / with a porosity of about 80 to 99% and a pore size in the range of 1 to 50 nm. BET specific surface area (g) or more, and is the lightest, most excellent ultra-insulation and low-dielectric property among the solid materials developed by mankind.

The manufacturing of such an airgel is the core technology of drying without shrinkage while maintaining the pore structure of the intermediate hydrogel (wet gel).

Until recently, supercritical drying processes have been known as the standard drying method for airgel production. However, this requires special equipment, requires a lot of energy and risks due to high / high pressure process conditions, and it is difficult to use due to the disadvantage that the continuous process is impossible.

Therefore, in order to replace the supercritical drying method, a method of drying the wet gel at normal pressure has been studied. However, when the airgel is manufactured by atmospheric pressure drying, there is a problem in that the physical properties of the airgel are significantly lowered as a result of capillary contraction caused by solvent evaporation between nanopores. Therefore, a process of modifying the -OH group on the surface of the hydrogel, which causes a condensation reaction upon drying, with a non-reactive chemical species is being made. However, the conventional process is expensive because a modifier such as TMCS is commercially expensive and takes a long time to manufacture. There is this.

Therefore, the present invention is a hydroxyl group of the surface modifier And an aerogel substituted with an alkoxy group (OR) and a method for efficiently preparing the same.

One embodiment of the present invention is a hydroxyl group of the surface modifier And an aerogel substituted with alkoxy and using metal alkoxide or water glass having Si-C bonds 5 to 9 and CO bonds 18 to 25 relative to the total bonds 100 as precursors.

In addition, an embodiment of the present invention comprises the steps of (a) preparing a hydrogel by the sol-gel (sol-gel) method by mixing the metal alkoxide or water glass and acid and base;
(b) a hydrogel obtained from step (a) and methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol and octanol alone or mixtures thereof with alcohol and 5 to 15 carbon atoms Preparing a ternary azeotropic mixture by mixing an organic solvent at 60 ° C. to 200 ° C .;
(c) firstly organicizing the hydroxyl groups present in the gel by mixing and heating a ternary azeotropic mixture with an acid;
(d) mixing the primary organicized gel obtained from the step (c) with a modifier to secondary organicize the remaining hydroxyl groups present in the gel; And
(e) It provides a method for producing an airgel comprising a drying step of drying the gel obtained from the step (d).

delete

delete

delete

delete

According to one embodiment of the present invention, unlike the conventional method of drying the hydrogel in a supercritical method, it is possible to dry the atmospheric pressure, it is possible to manufacture the airgel in a short manufacturing process and low cost.

One embodiment of the present invention is a hydroxyl group of the surface modifier And an aerogel substituted with alkoxy and using metal alkoxide or water glass having Si-C bonds 5 to 9 and CO bonds 18 to 25 relative to the total bonds 100 as precursors.

The whole bond is a concept including all bonds between internal metal oxides other than the surface, Si-C bond is a bond formed by the substitution of a hydroxyl group by a modifier, and C-O bond is a bond formed by the substitution of a hydroxyl group by an alkoxy group. The schematic diagram in the case of using TMCS as a modifier is shown in Scheme 1.

According to one embodiment of the present invention, unlike the conventional method of only replacing the hydroxyl group on the surface of the hydrogel with a non-reactive substance, the substitution with an alkoxy group is also performed, thereby reducing the use of expensive modifiers.

As the metal alkoxide, each alkyl group having 1 to 6 carbon atoms and 1 to 4 carbon atoms may be used. Examples of the metal alkoxide include, but are not limited to, tetraethoxysilane (TEOS), tetramethoxysilane (TEMS), and tetra n-propoxysilane, aluminum isopropoxide, aluminum sec-butoxide, cerium isopropoxide, hafnium tert-butoxide, magnesium aluminum isopropoxide, yttrium isopropoxide, titanium isopropoxide, At least one or more selected from the group consisting of rubidium isopropoxide and zirconium isopropoxide may be used, and preferably tetraethoxysilane (TEOS), tetramethoxysilane (TEMS) is used. The chemical formula of tetramethoxysilane (TMOS) is Si (OCH ₃ ) ₄ , the chemical formula of tetraethoxysilane (TEOS) is Si (OCH ₂ CH ₃ ) ₄ , and the water glass has a ratio of an alkali salt and silica 1: 2-. It is suitable to be 3 ranges.

One embodiment of the invention also

Preparing a hydrogel by sol-gel by mixing a metal alkoxide or water glass with an acid and a base;

Preparing a ternary azeotropic mixture by mixing the hydrogel obtained from the step with an alcohol and an organic solvent;

Firstly organicizing the hydroxyl group present in the gel by mixing and heating a ternary azeotropic mixture with at least one of an acid or an organic halide;

Mixing the primary organicized gel obtained from the step with a modifier to secondary organically retain the remaining hydroxyl groups present in the gel; And

It provides a method for producing an airgel comprising a drying step of drying the gel obtained from the above step.

Each step is described in more detail below (see FIG. 1).

The sol-gel reaction has gained considerable appreciation in the glass and ceramics field over the years. The sol-gel method is a process of making a colloidal floating state (sol: sol) and converting it into a liquid network (gel: gel) through the gelation process of the sol to form an inorganic network. The sol-gel process occurs in three steps:

1.Polymerization of monomers to form particles

2. Growth of particles

3. Linking of particles into chains, then networks that extend throughout the liquid medium, thickening into a gel.

More specifically,

First, prepare metal alkoxide or water glass as starting material. As the metal alkoxide, those having 1 to 6 carbon atoms and 1 to 4 carbon atoms in each alkyl group may be used. Examples of the metal alkoxide include, but are not limited to, tetraethoxysilane (TEOS), tetramethoxysilane (TEMS), and tetra- n-propoxysilane, aluminum isopropoxide, aluminum sec-butoxide, cerium isopropoxide, hafnium tert-butoxide, magnesium aluminum isopropoxide, yttrium isopropoxide, titanium isopropoxide, rubidium At least one or more selected from the group consisting of isopropoxide and zirconium isopropoxide can be used, preferably tetraethoxysilane (TEOS), tetramethoxysilane (TEMS). The chemical formula of tetramethoxysilane (TMOS) is Si (OCH ₃ ) ₄ , the chemical formula of tetraethoxysilane (TEOS) is Si (OCH ₂ CH ₃ ) ₄ , and the water glass has a ratio of an alkali salt and silica 1: 2-. It is suitable to be 3 ranges. If water glass is used as the precursor, a pretreatment step in the acid is required to remove the salt, which is common.

Thereafter, acid is added to hydrolyze and then a base is added to condense to form a gel. When water glass is used as a precursor, the same effect can be achieved by using a strong acidic ion exchange resin without adding an acid. Examples of acids include, but are not limited to, sulfuric acid, hydrochloric acid, phosphoric acid, acetic acid, nitric acid, and the like, preferably hydrochloric acid (HCl). Examples of the base include, but are not limited to, sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonia water, and the like, and preferably ammonia water (NH ₄ OH) is used. The gelled network is aged at 50-70 ° C. for 18-32 hours to strengthen the network structure. Or aged from 55 ° C. to 65 ° C. for 20 to 28 hours. At this time, the pore size of the airgel formed in the subsequent process can be controlled by adjusting the amount of acid or base.

In the first organic phase of the gel, the hydrogel is mixed with alcohol and an organic solvent to dehydrate the gel by ternary azeotropic mixing. At least one of an acid or an organic halide may be mixed and heated to remove moisture by a ternary azeotropic mixing method, and an organic reaction may be performed. The weight ratio of each component is suitably a ratio of at least one of hydrogel: alcohol: organic solvent: acid or organic compound = 200: 30 ~ 150: 50 ~ 150: 10 ~ 100.

In order for the dehydration condensation reaction between the hydroxyl group and the alcohol present on the surface of the hydrogel to occur, the azeotropic azeotropic mixing method should remove the water molecules generated during the dehydration reaction with water present in the gel. This is because the acid-catalyzed dehydration condensation reaction of the hydroxyl group and the alcohol is a reversible reaction. Each component is mixed, heated to reflux by reflux, and when water is removed by a water separator, the dehydration reaction of the hydroxyl groups and alcohol on the surface of the hydrogel proceeds to organicize the hydrogel. The boiling point varies depending on the composition of the mixture, but the heating is usually performed for 2 to 3 hours in the range of 60 ° C to 130 ° C, 70 ° C to 90 ° C, or 70 ° C to 80 ° C. This reaction produces 18-25 C-O bonds relative to 100 total bonds.

As an example, when silica is used and an acid is used as an additive of the ternary azeotrope, the reaction is shown in Scheme 2.

When organic halides are used, the product, halogen acid, acts as an acid catalyst. Thereafter, the reaction proceeds as using an alcohol and an acid catalyst, and the same as in Scheme 3.

The organic solvent may have 5 to 15 carbon atoms, and a boiling point of 60 ° C. to 200 ° C., preferably 90 ° C. to 150 ° C., may be used. Examples include, but are not limited to, octane, cyclohexane, methylcyclohexane, benzene, toluene, xylene, ethyl benzene, Organic solvents such as diethyl benzene and isopropyl benzene, and mixtures thereof. For example, xylene may be used.

Herein, the alcohols are those having 1 to 10 carbon atoms and may be used alone or in combination thereof. Preferably, the alcohols are added from the lower boiling alcohols using 2 to 4 kinds of alcohols. The amount is suitably 15 to 75 parts by weight relative to 100 parts by weight of hydrogel. Examples include, but are not limited to, 1,2, tertiary alcohols of methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol. Preferably ethanol, propanol, butanol is used.

Examples of the acid here include, but are not limited to, acids such as hydrochloric acid, sulfuric acid, nitric acid, acetic acid, phosphoric acid, oxalic acid, hydrofluoric acid, formic acid, and mixtures thereof, preferably hydrochloric acid is used. The amount of acid is suitably 5 to 50 parts by weight or 15 to 30 parts by weight relative to 100 parts by weight of hydrogel.

Organic halides here have from 2 to 9 carbon atoms and are suitable compounds in which bromine or chlorine atoms are composed alone or in combination. Examples include, but are not limited to, chloro ethane, tri-chloro ethane, tetra-chloro ethane, penta-chloro ethane, tri-chloro propane, tetra-chloro ethylene, tri-chloro ethylene, tri-chloro propane, di-chloro propane chlorobutane, amyl chloride, hexyl chloride, ethyl hexyl chloride, bromo ethylene, tetra-bromo ethane, bromo chloro ethane, chloro benzene, di-chloro benzene, chloro toluene, bromo benzene. Preferably butyl chloride, amyl chloride, octyl chloride can be used. The amount of the organic halide is preferably 5 parts by weight to 50 parts by weight or 15 parts by weight to 30 parts by weight relative to 100 parts by weight of the hydrogel.

Acids and organic halides may be used alone or in combination.

The first organicized gel is washed with a solvent that is not reactive with modifiers such as n-hexane, iso-hexane, heptane, octane and iso-octane. This is to remove the alcohol that is reactive with the modifier to prevent unnecessary consumption of the modifier. Thereafter, a modifier is added to proceed with the secondary organicization of residual hydroxyl groups present in the gel. This reaction yields 5 to 9 Si-C bonds relative to 100 total bonds.

Examples of modifiers include, but are not limited to, trimethylchlorosilane (TMCS), hexamethyldisilazane (HMDSZ), dimethyldichlorosilane (DMDCS), phenyltrimethoxysilane (PTMS), phenyltriethoxysilane (PTES) And at least one selected from the group consisting of methyltriethoxysilane (MTES) and methyltrimethoxysilane (MTMS), and when such a modifier is used, the remaining hydroxyl groups present in the gel are substituted with unreactive alkyl groups. When trimethylchlorosilane (TMCS) is used, the scheme of the reforming reaction is shown in Scheme 4.

In this case, the amount of the modifying agent is appropriately 0.2 to 10 parts by weight or 2 to 3 parts by weight relative to 100 parts by weight of the hydrogel, and when the amount of the modifying agent is less than 0.2 parts by weight, the organicization is not completely performed due to solvent evaporation between the nanopores. Shrinkage due to capillary action cannot occur to obtain an aerogel of a desired density, and when it is 10 parts by weight or more, it may be consumed more than necessary. However, because the excess modifiers and solvents can be reused, no upper limit is necessary.

The organic gel having the porous nanopores with the rough surface organicated to the second organic phase is separated from the solvent and subjected to 30 to 90 minutes at 60 ° C. to 200 ° C., 60 ° C. to 150 ° C., or 60 ° C. to 120 ° C. under atmospheric pressure. Dry in a fluid bed drier for 30 to 60 minutes, or 40 to 60 minutes.

The resulting airgel can be used in the form of powder, thin film, cluster or the like.

Hereinafter, examples will be described in detail to help understand the present invention. However, the following examples are merely to illustrate the content of the present invention is not limited to the scope of the present invention. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

< Example  1> Preparation of Porous Nano Silica Powder

(1) silica hydration Gel  Produce

To prepare silica hydrogel, a 10% solution of water glass was passed through a strong acidic ion exchange resin to prepare a silicic acid solution having a pH of 2.5. Thereafter, the pH of the solution was adjusted to 5 to 6 with 0.15 mol of ammonia water (NH ₄ OH) to form a gel. The hydrogel was prepared by aging at 60 ° C. for 24 hours to strengthen the network structure.

(2) Hydrogel  Mixing alcohol and organic solvent Organicization  Steps to

 The solidified hydrogel was pulverized and filtered through a mesh sieve 150. Then, 200 g of hydrogel was added to a three-necked flask, and 100 ml of isopropyl alcohol (isoprophyl alcohol), 50 ml of butanol, 100 ml of 0.1 mol HCl, and 100 ml of octane were mixed. The mixture was allowed to react until no water was separated from the oil / water separator, and after the water was removed, the temperature was gradually raised to separate the organicated gel at 120 ° C.

(3) secondary Organicization  Steps to

The separated partially organicated gel was washed with n-hexane, and then 4 ml of 10% TMCS solution was added and reacted at 60 ° C. for 1 hour.

(4) drying step

After the reaction, the solvent was discharged and dried for 30 minutes at 150 ℃ at atmospheric pressure.

The airgel prepared through the above step showed a density of 0.1 and a thermal conductivity of 0.016 W / m · k.

< Example  2> organic halide addition

(1) silica hydration Gel  Produce

To prepare silica hydrogel, TEOS was dissolved in isopropyl alcohol, and hydrolyzed by adding 0.1 mol of HCl. Thereafter, 0.15 mol of ammonia water (NH ₄ OH) was added to adjust the pH of the solution to 5 to 6 to form a gel. The hydrogel was prepared by aging at 60 ° C. for 24 hours to strengthen the network structure.

(2) Hydrogel  Mixing alcohol and organic solvent Organicization  Steps to

The solidified hydrogel was pulverized and filtered through a mesh sieve 150. Then, 200 g of hydrogel was added to a three-necked flask and mixed with 100 ml of isopropyl alcohol (isoprophyl alcohol), 50 ml of butyl chloride, 50 ml of butanol, and 100 ml of ethyl benzene. The mixture was allowed to react until no water was separated from the oil / water separator, and after the water was removed, the temperature was gradually raised to separate the organicated gel at 120 ° C.

(3) secondary Organicization  Steps to

The separated partially organicated gel was washed with n-hexane, and then 5 ml of 10% TMCS solution was added and reacted at 60 ° C. for 30 minutes.

(4) drying step

After the reaction, the solvent was discharged and dried for 30 minutes at 150 ℃ at atmospheric pressure.

The airgel prepared in this manner had a density of 0.09 and a thermal conductivity of 0.014 W / m · k.

< Comparative example  1>

After preparing a hydrogel in the same manner as in Example 1, 200 g of hydrogel was added to 500 ml of ethanol, and aged for 24 hours, and repeated three times for 24 hours to prepare alcohol gels in which water and alcohol were substituted for a total of 72 hours. Then, 200 g of alcohol gel, 200 ml of isopropyl alcohol (isoprophyl alcohol), 300 ml of n-hexane, and 100 ml of 10% TMCS solution were added to carry out a surface modification reaction. Drying produced an airgel.

The specific gravity of the thus prepared airgel showed a density of 0.08 and a thermal conductivity of 0.015 W / m · k.

[Table 1] Comparison of Properties of Porous Nano Silica Powders

Precursor Hydrogel TMCS Reaction time importance Thermal conductivity (W / m · k) Example 1 water glass 200g 4ml 24 hours 0.1 0.016 Example 2 TEOS 200g 5ml 24 hours 0.09 0.014 Comparative Example 1 water glass 200g 100 ml More than 72 hours 0.08 0.015

According to the table, the physical properties of the airgel of the present invention can be seen to show a similar function without much difference compared to the comparative example, but the comparative example uses a significantly larger amount of expensive modifiers compared to the example and takes a long time do.

< Comparative example  2>

EMP-SAP (EM-Power. Co, Korea) was used.

< Experimental Example  1> gas chromatography

Pyrolyzer-GC / MS was used for the qualitative analysis of the airgel of Example 2, Comparative Example 2 and the results are shown in FIG.

In the case of the aerogels produced through Example 2, isobutylene and propylene were detected, which appears to be derived from the alkoxy groups on the surface.

The airgel of Comparative Example 2 did not show this result.

< Experimental Example  2> XPS  Quantitative analysis

Company: PHI 5800 ESCA System

background pressure: 2x10 -10 torr

Xray Source: Monochromator AL Ka (1486.6 eV) Anode (250W, 10kV, 27mA)

Calibrating: C1s peak (284.6 eV)

Spot size: 400㎛ x 400㎛

Under the above conditions, the airgels of Example 2 and Comparative Example 2 were quantitatively analyzed, and the results of Si-C bonds are shown in FIG. 4, and the results of C-O bonds are shown in FIG. 5.

The Si—C bond of Example 2 was found to be 527 relative to the total bond of 7600 (527 + 7073), which corresponds to 6.9%. The C-O bond was found to be 1344 relative to the total bonds of 5992 (1344 + 4648), corresponding to 22.4%.

The Si—C bond of Comparative Example 2 was found to be 1244 relative to the total bond of 6954 (1244 + 5710), which corresponds to 17.9%. The C-O bonds were 410 compared to the total bonds 5892 (410 + 5482), corresponding to 6.96%.

The results are summarized in a table as follows.

[Table 2] XPS analysis results and physical property comparison

Example 2 Comparative Example 2 Si-C bond (organic silane) 6.9% 17.9% C-O bond (alcohol) 22.4% 6.96% Density (g / cm ³⁾ 0.9 0.05 ~ 0.1 Thermal conductivity (W / m · k) 0.014 0.02 Specific surface area (m ² / g) 600-650 700-800

As shown in the above table, it can be seen that the surface bonding ratio of the two materials is significantly different. This is related to the amount of the modifier used, it can be seen that the use of the organosilane-based modifier of the present invention is significantly less. Nevertheless, it can be seen that the physical properties of both materials are similar, so that the present invention has the same effect at low cost.

1 is a flow chart for sequentially explaining a method of manufacturing an airgel according to the present invention;

Figure 2 is a photograph of the microstructure of the airgel according to the present invention.

3 is a graph of the results of gas chromatography. (a) is by Example 2, (b) is by Comparative Example 2.

4 is a graph of the results of XPS for Si-C bonds. (a) is by Example 2, (b) is by Comparative Example 2.

5 is a graph of the results of XPS for C-O bonds. (a) is by Example 2, (b) is by Comparative Example 2.

Claims (12)

delete delete (a) preparing a hydrogel by sol-gel by mixing a metal alkoxide or water glass with an acid and a base; (b) a hydrogel obtained from step (a) and methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol and octanol alone or mixtures thereof with alcohol and 5 to 15 carbon atoms Preparing a ternary azeotropic mixture by mixing an organic solvent at 60 ° C. to 200 ° C .; (c) firstly organicizing the hydroxyl groups present in the gel by mixing and heating a ternary azeotropic mixture with an acid; (d) mixing the primary organicized gel obtained from the step (c) with a modifier to secondary organicize the remaining hydroxyl groups present in the gel; And (e) a method of producing an airgel comprising a drying step of drying the gel obtained from step (d). The method of claim 3, The metal alkoxide includes tetraethoxysilane (TEOS), tetramethoxysilane (TEMS), tetra-n-propoxysilane, aluminum isopropoxide, aluminum sec-butoxide, cerium isopropoxide, hafnium tert-butoxide A method for producing an aerogel, which is at least one or more selected from the group consisting of side, magnesium aluminum isopropoxide, yttrium isopropoxide, titanium isopropoxide, rubidium isopropoxide and zirconium isopropoxide. delete The method of claim 3, Alcohol used in the ternary azeotropic mixture manufacturing step is 15 to 75 parts by weight compared to 100 parts by weight of the hydrogel gel airgel manufacturing method. The method of claim 3, wherein the acid used in the first organication step is at least one selected from the group consisting of hydrochloric acid, sulfuric acid, acetic acid, nitric acid, phosphoric acid, oxalic acid, hydrofluoric acid, and formic acid. delete The method of claim 3, The amount of acid in the first organic phase is 5 to 50 parts by weight based on 100 parts by weight of the hydrogel gel of the airgel production method. The method of claim 3, The modifiers of the second organication step are trimethylchlorosilane (TMCS), hexamethyldisilazane (HMDSZ), dimethyldichlorosilane (DMDCS), phenyltrimethoxysilane (PTMS), phenyltriethoxysilane (PTES), methyl Method of producing an airgel is at least one selected from the group consisting of triethoxysilane (MTES) and methyltrimethoxysilane (MTMS). The method of claim 3, The amount of the modifier in the second organic step is 0.2 to 10 parts by weight of the preparation of the airgel compared to 100 parts by weight of the hydrogel. The method of claim 3, The drying step is a method for producing an airgel is dried for 30 to 90 minutes at 60 ℃ to 200 ℃ at atmospheric pressure.

Images