KR100896790B1 - Fabrication method for silica aerogel and silica aerogel fabricated therefrom - Google Patents

Abstract

The present invention relates to a method for producing a silica airgel and to a silica airgel produced thereby. The method for preparing silica airgel according to the present invention comprises the steps of preparing a wet gel by a sol-gel method; Substituting a solvent of the wet gel using a ternary azeotropic mixing method and surface modifying the wet gel in which the solvent is substituted; It characterized in that it comprises an atmospheric pressure drying step of drying the surface-modified wet gel at normal pressure. Thereby, a method for producing a silica airgel having both high strength and high transparency and a silica airgel produced thereby are provided.

Description

Method for manufacturing silica airgel and silica airgel manufactured thereby

The present invention relates to a method for preparing silica airgel and an airgel prepared therefrom, and more particularly, to a method for preparing silica airgel having both high strength and high transparency and a high strength and high transparency silica airgel prepared therefrom.

Silica aerogel has been spotlighted as a super lightweight new material with excellent physical properties. Specifically, silica airgel has the highest porosity (~ 90%), low density (3 ~ 120 mg / cm ³ ), low refractive index (~ 1.01), low sound velocity among the existing materials having a three-dimensional network structure. (100m / s), high specific surface area (= 700 m ² / g), low dielectric constant (~ 1.1) and very small thermal conductivity (~ 0.01W / K · m). These physical properties of silica aerosols are exhibited by the mesh nanopore structure.

These physical silica airgels are used for transparent insulation materials (TIM), skylights in indoor gymnasiums, complex complexes, offices and kitchens, solar dust permeable windows and solar heating systems, safety cover coatings for halogen lamps, LNG Super insulation material for transport ship, insulation material for space probe equipment, medical equipment such as long-term storage and transportation of body organs, catalyst carrier, electric insulation film with low dielectric constant, etc. It is a super lightweight new material with the potential.

To date, most of the research in the field of monolithic silica airgels is in the field of super insulation, which is expected to have the fastest commercial potential in the field. In addition, nano-porous and highly porous aerogels can be used as chemical / biosensors based on molecular recognition through selective separation / adsorption reactions of measurement molecules, resulting in chemical process control, environmental pollution measurement, and biochemical reaction detection. The application of is possible. Therefore, not only the form of the powder, granules and bulk in the form of the material for this functional application, but also a patterning technique for the formation of the thick film / thin film and application to electronic devices.

In order to obtain the above physical properties, the micropores of the airgel should not be destroyed, and the micropores of the airgel may be destroyed during the drying process of the airgel manufacturing process. In order to prevent destruction of the micropores of the airgel, silica airgel is manufactured by using an autoclave equipment for a supercritical drying method. However, such a supercritical drying method requires a high pressure and a high temperature, thereby resulting in a risk of safety accident. In addition, autoclave, a supercritical drying equipment, has the disadvantage of high manufacturing cost as well as difficulty in continuous process due to the limitation of the container size.

Therefore, in order to replace such a supercritical drying method, a method of drying silica airgel at normal pressure has been studied. However, when the airgel is manufactured by atmospheric pressure drying, the adsorption of water by hydrogen bonding between the -OH group on the inner surface of the airgel and the moisture in the air results in a significant decrease in the physical properties of the airgel and a decrease in transparency. There is a problem.

In order to solve this problem, the silica airgel should have a surface structure of hydrophobic airgel after atmospheric pressure drying. Specifically, the airgel must be changed from hydrophilic to hydrophobic by changing the -OH group on the surface of the airgel to an alkyl group or an aryl group.

However, even if the surface of the airgel is changed to hydrophobic by the above method, the mechanical strength is very low due to the high porosity of the airgel manufactured by the above method has a problem that special care must be taken in use and handling. . That is, in this case, the temperature of heat treatment for surface modification was 200 ~ 230 ° C, and after modification, airgel's structural porosity is very easily broken due to its very small impact, which requires special attention to handling. have. In addition, there is a problem that the transparency of the airgel thus prepared is also relatively poor.

Accordingly, it is an object of the present invention to provide a method for producing silica airgel having both high strength and high transparency.

Another object of the present invention is to provide a high strength and high transparency silica airgel.

According to the present invention, there is provided a method for producing a silica airgel, comprising: preparing a wet gel by a sol-gel method; Substituting a solvent of the wet gel using a ternary azeotropic mixing method and surface modifying the wet gel in which the solvent is substituted; It is achieved by a method for producing a silica airgel, characterized in that it comprises an atmospheric pressure drying step of drying the surface-modified wet gel at normal pressure.

Here, the preparing of the wet gel may include mixing any one of tetramethoxysilane (TMOS), tetraethoxysilane (TEOS) and water glass from which Na is removed in an isopropyl alcohol (IPA) solution; Hydrolysis by addition of hydrochloric acid (HCL); And ammonia water (NH ₄ OH) may be added to condense the condensation reaction.

After the condensation reaction, the method may further include aging the wet gel prepared in isopropyl (IPA) solution at 40 ° C. to 80 ° C. for 10 to 48 hours.

Herein, the solvent of the wet gel is an isopropyl alcohol (IPA) solution, and the step of replacing the solvent of the wet gel and surface modifying the wet gel in which the solvent is substituted is not reactive with the modifier added for surface modification of the wet gel. A first solvent substitution step of replacing the isopropyl alcohol (IPA) solution with a substitution solvent; It may include a surface modification step of replacing the hydroxyl group of the wet gel with an unreactive species by adding a modifier to the solvent- substituted wet gel.

In addition, the substitution solvent includes n-buthanol, the modifier includes trimethylchlorosilane (TMCS), and the hydroxyl group may be substituted with an alkyl group.

In addition, the second solvent substituted step of replacing the normal-butanol (n-buthanol) substituted in the first solvent substitution step to the normal-butanol (n-buthanol) to remove the unreacted product of the wet gel; The second solvent replacement step may further include a third solvent replacement step of replacing the normal-butanol (n-buthanol) substituted with any one of octane, heptane (heptane) and hexane (hexane).

In addition, the first solvent replacement step to the third solvent replacement step may be performed by leaving the wet gel in the solvent to be substituted for 10 hours to 48 hours at 40 ℃ to 80 ℃.

In addition, the volume of the solvent substituted in the first to third solvent replacement step may be 6 to 15 times the volume of the wet gel.

Here, the atmospheric drying step may be dried for 24 to 48 hours at 70 ℃ to 151 ℃ at a temperature increase rate of 1 ℃ / min.

Another object of the invention is achieved according to the invention by a silica airgel, which is produced according to any one of claims 1 to 9.

Hereinafter, as a means for solving the problem of the present invention will be described with respect to the silica airgel manufacturing method and the silica airgel produced thereby.

According to the present invention, the method for preparing silica airgel at low temperature forms a wet gel based on the sol-gel method, and the hydroxyl group inside the wet gel is a n-butanol solvent and a modifier ( Substituting an alkyl group using a silylation agent). As a result, the condensation reaction of the hydroxyl group is suppressed, and irreversible shrinkage due to the condensation reaction during the drying of the wet gel is minimized, thereby maintaining the pores of the wet gel. Accordingly, it is possible to manufacture a silica airgel using a simplified atmospheric drying method at a low temperature in a three step process by a ternary azeotropic mixing method at low temperature compared with the conventional method.

The sol-gel process is a chemical process in which a substance which is a mixed oxide is produced from a mixture of suitable sol. Specifically, the sol-gel method starts with a solution of organic and inorganic compounds of a metal, and the solution is sol in which the fine particles of the metal oxide are dissolved through the hydrolysis and condensation reaction of the compound in the solution. Make Thereafter, the reaction was further carried out, and after gelation, alkoxide hydrolyzed the compound of the formula M (OR) n (M is a metal or metalloid element and R represents an alkyl group). The alkoxide undergoes OH-OR polymerization to form a dimmer to produce a wet gel.

The wet gel thus formed has alcohol in the inner network structure (net structure). These alcohols react chemically with the modifiers in the reforming step and actually reduce the reaction with hydroxyl groups in the network structure (net-like), so that the solvent replacement step of changing the solvent of the wet gel with an appropriate solvent which is not reactive with the modifier. 1 solvent replacement step) is required.

The conventional solvent replacement method using normal-heptane (n-Heptane) takes a lot of time to perform surface modification with trimethylchlorosilane (TMCS) after solvent replacement, and has a lot of trouble to change the solvent several times. It was not suitable. In addition, there are many disadvantages in terms of efficiency and convenience of the process.

In order to improve this disadvantage, the present invention simplifies the solvent replacement process by carrying out the solvent replacement process by the Ternary azeotropic mixing method.

That is, since the solvent-substituted wet gel is composed of a solvent that is not reactive with the modifier in the network structure, the substituted solvent is not reactive with the modifier, and the hydroxyl group on the surface of the colloidal particle composed of the modifier and the network structure (net structure). Do not react suddenly with. Accordingly, cracks due to the reaction of hydroxyl groups are minimized and prevented. Under these conditions, the surface modification step proceeds. In the surface-modified wet gel, a hydroxyl group is substituted with a methyl group (-CH ₃ ) on the colloidal surface.

Due to this reaction, unreacted substances generated in the surface modification reaction are removed in the washing step (second solvent replacement step). Subsequently, the solvent of the wet gel is substituted with any one of octane, heptane, and hexane in a third step by a tertiary azeotropic mixing method (third solvent replacement step). Another reason for replacing the solvent in the three-stage solvent replacement process by the ternary azeotropic mixing method is to effectively minimize and prevent cracking of the silica airgel due to rapid solvent change. Subsequently, the silica airgel with improved light transmittance and mechanical strength is prepared by drying at a low temperature of 70 to 151? In the air by an atmospheric pressure drying process, rather than an expensive supercritical drying method.

As described above, according to the present invention, unlike the conventional method of drying silica airgel by a supercritical method, atmospheric pressure drying using a ternary azeotropic mixing method is possible, thereby simplifying the manufacturing process and economically inexpensive. It is possible to prepare a silica airgel transparent and enhanced strength. Therefore, it is possible to use and apply the bulk and powder which overcome the weak difficulties in manufacturing and handling the existing high cost and large amount of silica airgel and maintaining and improving the physical properties of the silica airgel.

It is easy to manufacture cheaper and more practical airgel based on the application of various airgel application fields (energy saving, environmental protection, electric and electronic field) using this technology.

Hereinafter, with reference to the drawings will be described a specific embodiment for practicing the present invention.

1 is a flow chart for sequentially explaining a method for producing a silica airgel according to the present invention.

First, any one of tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), and Na-free water glass is prepared as a starting material for the sol-gel process for preparing silica airgel. The chemical formula of tetramethoxysilane (TMOS) is Si (OCH ₃ ) ₄ , and the chemical formula of tetraethoxysilane (TEOS) is Si (OCH ₂ CH ₃ ) ₄ . In the embodiment of the present invention, as shown in Figure 1, tetraethoxysilane (TEOS) was prepared as a starting material.

In the sol-gel method used in the embodiment of the present invention, silica sol was first prepared through the following two-step process. In the first step, the prepared tetraethoxysilane (TEOS) is first mixed with isopropyl alcohol (IPA) solution (S10). Thereafter, hydrochloric acid solution (HCl) is added to the mixed solution for catalysis. The molar ratio of the added component is TEOS: H ₂ O: HCl molar ratio of = 1: 1: 1.80 × 10 - ^3. At this time, the manufacturing temperature of the sole was maintained at about 25 ℃ for the production of stable and uniformly dispersed silica sol. As a second step, a solution of aqueous ammonia (NH ₄ OH) is added slowly to cause condensation. The molar ratio of the added component is TEOS: H ₂ O: 1 molar ratio of _{NH 4 OH: 3: 8.12 ×} 10 - ^3. A silica sol is manufactured through the process as described above (S20).

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.

All the above process was given a sufficient time by simple stirring using a magnetic stirrer in the beaker to complete the reaction. The prepared silica sol was measured for viscosity using an R / S Rheometer (Brookfieldield). When the viscosity of the silica sol is 18cP to 20cP, the silica sol is sealed in a container and then gelled by standing in an isopropyl alcohol solution at room temperature for 1 hour (S30). Thereafter, the mixture was aged at about 50 ° C. for 10 hours to 48 hours in an isopropyl alcohol (IPA) solution (S40). At this time, the siloxane particles are produced, the viscosity of the solution gradually increases, the volume decreases and solidifies, and a transparent gel (wet gel) is obtained. On the other hand, according to the change of the process conditions and environment changes to produce the wet gel, the temperature conditions in the aging step can be appropriately adjusted in the temperature range of 40 ℃ to 80 ℃, the aging time is also a little from 10 hours to 48 hours It may go away.

However, when the silica gel (wet gel) is aged, in the state in which gelation is formed by hydrolysis and condensation, the bonding in the state of continuing to the siloxane particles is not so strong in point contact.

In order to change this into strong bonds (reinforcement of the net), the process of necking the contact part of the round particles by aging while maintaining the wet gel state to make -Si-O-Si- bond is performed. need.

Next, in order to prepare a strong silica airgel of the network structure (net structure) and to proceed with atmospheric pressure drying, three steps of solvent replacement step and surface modification step are required.

First, the solvent of the wet gel should be replaced with a solvent (substitution solvent) suitable for surface modification, which is a subsequent process (first solvent substitution step, S50). In selecting a substitution solvent, it should be considered as a nonpolar solvent which is not reactive with the modifier, and the surface tension is relatively high to prevent the invisible microcracks caused by the rapid evaporation at the manufacturing stage and to enhance the strength of the gel. It should be a low solvent. Suitable substitution solvents for this are suitably n-buthanol having a surface tension of about 24. 6 dyne / cm.

Therefore, in the embodiment of the present invention, the solvent isopropyl alcohol (IPA) solution of the wet gel is solvent-substituted with a normal butanol (n-buthanol) solution (first solvent replacement step, S50).

Thereafter, the surface modification step of the wet gel is performed (S60).

The surface reforming step is a reforming process of the surface bonding reactor to convert the hydroxyl group (-OH), which causes a condensation reaction at atmospheric pressure, to an inactive species and to secure hydrogel surface hydrophobicity. The physical properties of aerogels with a high specific surface area are greatly influenced not only by the structural features but also by the chemical bonding state of the surface. The surface is composed of many hydroxyl groups (OH). Hydroxyl groups present on the surface serve to induce physical adsorption of polar molecules such as water molecules, resulting in contraction of the skeletal structure of the wet gel, resulting in structural change, cracking or destruction. Therefore, it can be said that surface modification is an essential process in order to eliminate cracks in the atmospheric drying process. In the surface modification method according to the present invention, trimethyl chlorosilane (TMCS) is used to convert the hydroxyl group (OH) on the surface of the wet gel into an alkyl group (CH ₃ ). In the case of trimethylchlorosilane (TMCS), three methyl groups and one chlorine are bonded to one silane. As shown in the following chemical reaction formula (1), H and H of the surface portion of the airgel OH group are modified. HCl is formed by the reaction, and (CH ₃ ) ₃ Si trimethylchlorosilane (TriMethylSilane) is attached to the H-site which is broken with Cl, thereby reforming.

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

In summary, in the present invention, the silica wet gel matured in isopropyl alcohol (IPA) solution is placed in a container filled with a normal butanol solution, and left at about 50 ° C. for about 24 hours, so that the first solvent replacement is performed. 1 solvent replacement step). Thereafter, the wet gel was maintained at about 50 ° C. for about 24 hours in a solution in which a predetermined amount of trimethylchlorosilane (TMCS) and normal-butanol were synthesized for surface modification of the silica wet gel (surface modification step). .

Next, to wash the unreacted material inside the wet gel, solvent replacement is once again performed at about 50 ° C. for about 24 hours once more (second solvent replacement step, S70). Subsequently, n-buthanol is replaced with octane, hexane, or heptane in three steps by a ternary azeotropic mixing method (third solvent replacement step). , S80). The reason for substituting solvent by ternary azeotropic mixing method is to effectively prevent cracks caused by drastic solvent environment change and to simplify the manufacturing process by adopting lower drying temperature. At this time, the amount of the substituted solvent is an amount of 6 to 15 times the volume of the wet gel each time, preferably about 10 times the volume. On the other hand, depending on the change in the solvent replacement and surface modification process conditions, the temperature conditions of the first solvent replacement step to the third solvent replacement step can be appropriately adjusted in the temperature range of 40 ℃ to 80 ℃, time is also somewhat 24 hours It can also go away.

Then, as shown in Table 1 below, the surface modification and the solvent replacement is completed, the gel is slowly dried for 24 to 48 hours at 70 ~ 151 ℃ at a temperature increase rate of 1 ° / min (atmospheric drying step, S90). The atmospheric pressure drying step of the present invention is a manufacturing process time significantly compared to the method of drying at room temperature for 3 days and then drying at least 50 days again for 3 days at room temperature to prevent rapid solvent evaporation during conventional atmospheric pressure drying to prevent cracking of the gel It is shortened. In addition, the atmospheric pressure drying method according to the present invention can omit the conventional heat treatment process can reduce the manufacturing cost. Specifically, conventionally, in order to increase the porosity of silica gel dried at atmospheric pressure, heat treatment was performed at about 270 ° C. for 2 hours as a final process to evaporate the solvent remaining in the pores inside the gel. However, in the present invention, it is possible to produce a silica airgel of the same or improved form as the conventional one, even if the heat treatment step is omitted.

By this process, silica airgel having both high strength and high transparency is produced.

Table 1. Physical Properties and Drying Conditions of Wet Gel of Azeotroic Mixtures

Mix. No. Major components Azeotrope composition (mol%) Boiling point of azeotrope (℃) Boiling point of hydrocarbon (℃) 1st step (heating rate; holding time) 2nd step (heating rate; holding time) One H ₂ O / n-butanol / hexane 19.2 / 2.9 / 77.9 61.5 68.7 v = 1 ° / min to 62 ° C; t = 24h v = 0.1 ° / min to 70 ° C; t = 24h 2 H ₂ O / n-butanol / heptane 41.4 / 7.6 / 51.0 78.1 98.45 v = 1 ° / min to 78 ° C .; t = 24h v = 0.1 ° / min to 100 ° C .; t = 24h 3 H ₂ O / n-butanol / octane 60.0 / 14.5 / 25.5 86.1 125.75 v = 1 ° / min to 86 ° C .; t = 24h v = 0.1 ° / min to 130 ° C .; t = 24h 4 H ₂ O / n-butanol / nonane 69.9 / 18.3 / 11.8 90 151 v = 1 ° / min to 90 ° C .; t = 24h v = 0.1 ° / min to 151 ° C .; t = 24h

Hereinafter, the physical properties of the silica airgel prepared by the above-described method was measured.

Table 2 shows the physical properties of the crack-free silica airgel prepared by the manufacturing process of FIG. 1 under the conditions using the azeotropic composition of Table 1.

Table 2. Properties of the prepared high transparency, high strength aerogels

Sample code Azeotropic composition used Drying temp. regime 2step / (℃) Bulk density (g / cm ³ ) Specific surface area (m ² / g) Pore volume (cm ³ / g) Average pore diameter (Å) Porosity (%) 1 (N5) 1 in Table 1 62 + 70 0.52 880 1.18 43.6 80.6 2 Table 1 2 78 + 100 0.52 872 1.04 33.4 80.3 3 (C1) Table 1 3 86 + 130 0.47 938 1.34 57.0 84.3 4 (F1) Table 1 3 86 + 130 0.40 938 1.29 55.7 85.0 5 Table 1 3 86 + 130 0.42 995 1.55 55.1 87.3 6 Table 1 3 86 + 130 +180 0.48 928 1.39 50.6 81.9 7 Table 1 3 86 + 250 crack 1012 1.39 49.8 crack 8 Table 1 3 62 + 70 0.75 855 0.93 39.8 cloudy 9 (P5) Table 1 4 90 + 151 0.54 979 1.12 41.2 79.8

Based on the measurement results of the physical properties shown in Table 2, the volume of the internal pores of the silica airgel corresponding to the sample code number 1 (N5), 3 (C1), 4 (F1) and 9 (P5), respectively, is shown in FIG. It was. It can be seen that the silica airgel prepared from FIG. 2 maintains porosity.

And, FT-IR structure analysis results of the silica airgel is shown in FIG. For samples heat-treated at 100 ° C. normal-butanol and samples heat-treated at 130 ° C. octane, these peaks were surface-modified from OH to CH (Si—CH ₃ bonds). However, in the case of Sample 7 heat-treated in octane at 250 ° C., the hydrophilicity was lost due to the disappearance of CH bonds due to the high heat treatment temperature.

Transmittance of the airgel thus prepared (sample 4) is shown in Figure 4, and TEM image of the translucent enhancement airgel heat-treated at 130 ℃ is shown in Figure 5. It can be seen that the prepared silica airgel shows high light transmittance, and rearrangement of particles occurs at high temperatures during the drying process of the airgel to form closed pores.

As described above, in the embodiment of the present invention, a hydrophobic airgel modified with trimethylchlorosilane (TMCS) was prepared using tetraethoxysilane as a starting material. The prototype of the sol-gel method starts from a solution and gels to form a desired shape such as bulk or thin / thick film, and then SiO ₂ by a typical sol-gel method. A mesh structure was prepared. Thereafter, silica aerogels having high strength and high transparency were prepared through the above three steps of solvent replacement step, surface modification step and atmospheric pressure drying step. Such a manufacturing method has the advantage of reducing the manufacturing time while being cheaper than the conventional method.

1 is a flow chart for sequentially explaining a method for producing a silica airgel according to the present invention;

Figure 2 is a graph showing the measurement results for the internal pore volume of the silica airgel according to the present invention,

Figure 3 is a graph showing the results of the FT-IR structure analysis of silica airgel according to the present invention,

Figure 4 is a graph showing the transmittance of the silica airgel according to the present invention,

Figure 5 is a photograph of the microstructure of the silica airgel prepared according to the production method of the present invention.

Claims (10)

In the method for producing a silica airgel, (a) preparing a wet gel by a sol-gel method, (b) a first solvent substitution step of replacing the solvent of the wet gel with a substitution solvent which is not reactive with a modifier, (c) adding a modifier to the wet gel obtained from step (b) to replace the hydroxyl group of the wet gel with an inactive chemical species, and (d) a second solvent substitution step of removing the unreacted substance in the wet gel by substituting the solvent of the surface-modified wet gel obtained in step (c) with the substitution solvent; (e) the solvent of the wet gel obtained from the step (d) water; Normal-butanol; And 1 solvent selected from the group consisting of hexane, heptane, octane and nonane A third solvent substitution step of substituting with a solvent consisting of a ternary azeotropic mixture mixed with a azeotropic composition; (f) an atmospheric pressure drying step of drying the wet gel obtained from the above step (e) at normal pressure Method for producing a silica airgel comprising a. According to claim 1, wherein the step (a) of preparing the wet gel, (Iii) mixing any one of tetramethoxysilane (TMOS), tetraethoxysilane (TEOS) and Na-free water glass into an isopropyl alcohol (IPA) solution, (Ii) hydrolysis by addition of hydrochloric acid (HCl), (Iii) condensation reaction by addition of aqueous ammonia (NH ₄ OH) Method for producing a silica airgel comprising a. According to claim 2, wherein the step (a) of preparing the wet gel, after the step (iii), the step of putting the prepared wet gel in isopropyl alcohol and aged for 10 to 48 hours at 40 ℃ to 80 ℃ Method for producing a silica airgel, characterized in that it further comprises. The method of claim 1, wherein the solvent used in step (a) of preparing the wet gel is isopropyl alcohol. The method of claim 1, wherein the substitution solvent of steps (b) and (d) is normal-butanol. The method of claim 1, wherein the modifier of step (c) is trimethylchlorosilane, and the non-reactive species of step (c) is an alkyl group. The method of claim 1, wherein the first to third solvent substitution steps are performed by leaving the wet gel in the substitution solvent at 40 ° C. to 80 ° C. for 10 to 48 hours. Way. The method of claim 1, wherein the volume of the substituted solvent in the first to third solvent substitution steps is 6 to 15 times the volume of the wet gel. The method of claim 1, wherein the atmospheric drying step is a method for producing silica airgel, characterized in that the drying for 24 to 48 hours at 70 ℃ to 151 ℃ at a temperature increase rate of 1 ℃ / min. Silica airgel prepared by any one of claims 1 to 9.

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