WO2008038935A1

WO2008038935A1 - Method of fabricating superhydrophobic silica chain powders

Info

Publication number: WO2008038935A1
Application number: PCT/KR2007/004548
Authority: WO
Inventors: Kwangyoon Park; Sharad D. Bhagat
Original assignee: Il Shin Chemical Co., Ltd.
Priority date: 2006-09-26
Filing date: 2007-09-19
Publication date: 2008-04-03
Also published as: KR100796253B1

Abstract

Disclosed is a method of manufacturing superhydrophobic silica-based powder, including adding a water glass solution, subjected to ion exchange, with an inorganic acid and an organosilane compound having an alkaline pH to thus subject the water glass solution to gelation and surface modification at the same time, thereby producing silylated hydrogel; immersing the silylated hydrogel in a nonpolar solvent to thus subject the silylated hydrogel to solvent exchange; and drying the silylated hydrogel, subjected to solvent exchange, at ambient pressure, thereby manufacturing aerogel powder. This invention has a very simple process and realizes economic benefits. Thus, this invention is very important from an industrial point of view.

Description

METHOD OF FABRICATING SUPERHYDROPHOBIC SILICA

CHAIN POWDERS

Technical Field

[1] The present invention relates to a method of manufacturing superhydrophobic silica-based powder, and more particularly, to a method of simply and economically manufacturing superhydrophobic silica-based (silica aerogel/xerogel) powder from water glass using a drying process at ambient pressure in an air atmosphere (atmospheric condition). Background Art

[2] Silica aerogel powder is a well-known competitive heat-insulating component because it has a low tapping density, and thus exhibits very low solid heat-conductivity, and also has nanoporous properties so as to be able to greatly inhibit gas heat-conductivity. Further, silica aerogel powder is advantageously easy to load into a container having a complicated shape, thanks to its superior free flowability to fiber or foamed products. Furthermore, silica aerogel powder, having a high specific surface area, has been used as a catalyst support to date. Moreover, superhydrophobic aerogel powder, which is on a micro scale/nano scale, may be used to effectively transport liquids.

[3] Conventionally, some attempts to synthesize aerogel powder have been made, and research into the thermal properties thereof has been conducted. However, conventional aerogel powder production requires the use of an expensive precursor, such as tetraethoxysilane (TEOS), and the employment of a supercritical fluid extraction technique for drying gel, which is a factor that makes mass production difficult. Meanwhile, in the synthesis of aerogel from water glass via ambient pressure drying (APD), chemical surface modification (which is essential to maintain the high porosity of the gel during APD) of hydrogel using an organosilane reagent is conducted.

[4] Generally, the surface modification of the hydrogel is conducted through a surface derivatization process. The surface derivatization process essentially accompanies a reaction for the displacement of pore water with an organic solvent. However, because the chemical reaction in the surface derivatization process is dominated by the dispersion of a reactant in a gel body, the process time is lengthened (about 6 days), and, as well, the consumption of the chemical material necessary for the reaction is increased.

Disclosure of Invention Technical Problem [5] Accordingly, the present invention has been devised keeping in mind the above problems occurring in the related art, and provides a method of simply and economically manufacturing superhydrophobic silica-based (silica aerogel/xerogel) powder. Technical Solution

[6] The present inventors have developed a novel method including rapidly synthesizing aerogel powder from an inexpensive precursor such as water glass (sodium silicate) and drying the aerogel at ambient pressure in an air atmosphere (atmospheric condition). The present inventors have overcome conventional problems, such as the time-consuming surface modification and solvent exchange in the synthesis of aerogel from water glass via APD, by reducing the total treatment time of aerogel/xerogel powder to 5 hours by means of a co-precursor method using HNO / hexamethyldisilazane (HMDS) for the rapid surface modification of hydrogel. The method of manufacturing the aerogel/xerogel powder is considered very important from the points of view of mass production and commercial availability thereof.

[7] According to a first aspect of the present invention, there is provided a method of manufacturing superhydrophobic silica-based powder, including adding a water glass solution, subjected to ion exchange, with an inorganic acid and an organosilane compound having an alkaline pH to thus subject the water glass solution to gelation and surface modification at the same time, thereby producing silylated hydrogel; immersing the silylated hydrogel in a nonpolar solvent to thus subject the silylated hydrogel to solvent exchange; and drying the silylated hydrogel, subjected to solvent exchange, at ambient pressure, thereby manufacturing aerogel powder.

[8] According to a second aspect of the present invention, there is provided a method of manufacturing superhydrophobic silica-based powder, including adding a water glass solution, subjected to ion exchange, with an inorganic acid and an organosilane compound having an alkaline pH to thus subject the water glass solution to gelation and surface modification at the same time, thereby producing silylated hydrogel; and drying the silylated hydrogel at ambient pressure, thereby manufacturing xerogel powder.

[9] The water glass solution may be an inorganic precursor of silica (29 wt%), and may be used with a silica content in a range of 4-8 wt% by diluting the precursor with deionized water.

[10] The ion exchange may be conducted for 5-10 min using a cation exchange resin

(Amberlite IR 120 H⁺). The water glass solution may be mixed with the cation exchange resin (Amberlite IR 120 H⁺) at a volume ratio of 1:0.5-1:1.

[11] The inorganic acid may be acetic acid or hydrochloric acid, and the organosilane compound may be hexamethyldisilazane (HMDS). Further, the nonpolar solvent may be hexane or heptane. [12] The drying may be conducted at an ambient pressure of 1 atm at a temperature ranging from 175⁰C to 200⁰C for 30 min, and the solvent exchange may be completed within 3 hours. Further, the nonpolar solvent may be recovered through vapor condensation at the time of drying.

Advantageous Effects

[13] According to the present invention, a method of manufacturing silica-based (silica aerogel/xerogel) powder has a very simple process and generates economic benefits. Thus, this invention is considered significant from an industrial point of view. Brief Description of the Drawings

[14] FIG. 1 is a flowchart illustrating the process of manufacturing superhydrophobic silica-based powder, according to the present invention. Best Mode for Carrying Out the Invention

[15] Hereinafter, a detailed description will be given of a method of manufacturing superhydrophobic silica aerogel/xerogel powder according to a preferred embodiment of the present invention, with reference to the appended drawings.

[16] FIG. 1 is a flowchart illustrating the process of manufacturing superhydrophobic silica-based (silica aerogel/xerogel) powder according to the present invention. As illustrated in FIG. 1, silylated hydrogel may be directly manufactured using a co- precursor method (S 130). Specifically, in the present invention, a water glass solution is subjected to ion exchange (Sl 10, S 120), after which the water glass solution, subjected to ion exchange, is added with an inorganic acid (acetic acid or hydrochloric acid) and an organosilane compound. The organosilane compound, having an alkaline pH, is responsible for surface modification and gelation. Gelation and surface modification are typically conducted at room temperature (27⁰C). Thus, the present invention completely obviates the use of an alkaline catalyst, which is otherwise necessary for gelation. Further, as is apparent from the results of surface modification by the organosilane compound, pore water is drained out of the hydrogel, and, in order to produce the silica aerogel powder, according to the present invention, the hydrogel is immersed in an n-hexane solution, which is a nonpolar solvent immiscible with water. Then, water is drained out of the network of the gel and hexane infiltrates the pores via solvent exchange (S 140). Alternatively, in the case where the silica xerogel powder is produced according to the present invention, the hydrogel may be dried immediately after the surface modification, with omission of immersion in the n- hexane/heptane.

[17] After water drainage and solvent exchange (which is conducted when the aerogel powder is synthesized), the gel is not subjected to aging but is dried at an ambient pressure in an air atmosphere (atmospheric condition) (S 150). The drying is conducted in a furnace. In this case, the temperature of the furnace is increased to 170~200°C, after which the gel is loaded in the furnace to dry it. Thereby, the gel is completely dried within 30 min. During the drying process, the nonpolar solvent may be recovered through vapor condensation. The silica aerogel powder thus produced has very low density and exhibits good insulating properties. Further, the aerogel/xerogel powder is superhydrophobic.

[18] Accordingly, the aerogel/xerogel powder may be applied to various fields, thanks to its superhydrophobic properties. Further, the powder is maintained in a superhydrophobic state to a maximum temperature of 500⁰C, above which the powder becomes hydrophilic. In this way, the method of manufacturing the aerogel/xerogel powder according to the present invention has a very simple process and generates economic benefits. Therefore, the method of the present invention is considered to be a very important technique from an industrial point of view. Mode for the Invention

[19] 50 ml of a 5.2 wt% water glass (WG) solution was mixed with the same volume of a cation exchange resin, for example, Amberlite IR 120 H⁺, so that the Na⁺ of the water glass solution was subjected to ion exchange with H⁺. Specifically, the mixture of water glass (WG) solution and Amberlite IR 120 H⁺ was stirred for 5-10 min, after which the water glass solution, subjected to ion exchange, was collected in a separate beaker (250 ml). As such, the water glass solution is composed of an inorganic precursor of silica (29 wt%), and may be used with a silica content in the range of 4-8 wt% by diluting the precursor with deionized water. The water glass solution and the Amberlite IR 120 H⁺ may be mixed at a volume ratio of 1:0.5-1:1.

[20] Thereafter, the water glass solution, subjected to ion exchange, was added with acetic acid (1.5 ml) and hexamethyldisilazane (5.0 ml) for about 5 min under predetermined stirring conditions, thus obtaining uniform sol, which was then gelated within 5 min.

[21] Thereafter, the hydrogel was allowed to stand in an n-hexane solution (60 ml) for about 3 hours to subject it to solvent exchange, so that pore water was completely drained out of the hydrogel and the n-hexane solvent infiltrated the pores of the hydrogel.

[22] After the solvent exchange, the hydrogel was removed from the beaker and was then dried at ambient pressure. The drying process was conducted at 170~200°C.

[23] The silica aerogel powder thus obtained had a low tapping density (-0.115 g/cm ) and was superhydrophobic. The silica aerogel powder floats on the water surface. The hydrophobicity of the silica aerogel powder is stably maintained to a maximum temperature of 500⁰C.

[24] Below, the properties of the silica aerogel powder, manufactured according to the present invention, are evaluated. [25] The silica aerogel powder was prepared as above, and the effect of the wt% of water glass (WG) was investigated. The data results of the tapping density of the silica aerogel powder depending on the wt% of water glass are summarized in Table 1 below.

[26] Table 1

[27] Further, using X-ray photoelectron spectroscopy (XPS), elements of the silica aerogel powder were analyzed, and, at two different HNO AVG volume ratios, bonding energy (BE) and atom% (At%) were determined. The results are given in Tables 2 and 3 below.

[28] Table 2 HNO AVG volume ratio = 2 x 10^~2

[29]

[30] In addition, silica xerogel powder was manufactured as above, with the exception that the immersion of the hydrogel in the n-hexane solution was not conducted. Specifically, the solvent exchange was omitted, and the silylated hydrogel was directly dried in a furnace at ambient pressure. The tapping density of the silica xerogel powder thus obtained depending on the change in the HMDSAVG volume ratio was determined. The results are shown in Table 4 below.

[31] Table 4

[32] The silica aerogel/xerogel powder, manufactured according to the present invention, has a sufficiently low tapping density, as can be seen from the above properties. [33] As described hereinbefore, the preferred embodiment of the present invention in regard to the method of manufacturing superhydrophobic silica-based (silica aerogel/ xerogel) powder with reference to the appended drawings is set forth to illustrate, but is not to be construed as the limit of, the present invention.

[34] Further, those skilled in the art will appreciate that various modifications, additions and substitutions are possible without departing from the scope and technical spirit of the invention, as disclosed in the accompanying claims. Industrial Applicability

[35] The present invention may be variously applied to the energy field, environmental field, electrical/electronic field, and other fields. Specifically, the silica-based powder according to the present invention may be used in the energy field, including transparent/semi-transparent insulators, polyurethane substitutes, interior/exterior construction materials, etc., the environmental field, including gas/liquid separating filters, VOC/NOx removing catalyst systems, etc., the electrical/electronic field, including interlay er insulating films for semiconductors, microwave circuit materials, etc., and other fields, including sound-absorbing paint, sound-absorbing panels, other sound- absorbing materials, and luminescent materials.

Claims

[I] A method of manufacturing superhydrophobic silica-based powder, comprising: adding a water glass solution, subjected to ion exchange, with an inorganic acid and an organosilane compound having an alkaline pH to thus subject the water glass solution to gelation and surface modification simultaneously, thereby producing a silylated hydrogel; immersing the silylated hydrogel in a nonpolar solvent to thus subject the silylated hydrogel to solvent exchange; and drying the silylated hydrogel, subjected to solvent exchange, at an ambient pressure, thereby manufacturing an aerogel powder. [2] A method of manufacturing superhydrophobic silica-based powder, comprising: adding a water glass solution, subjected to ion exchange, with an inorganic acid and an organosilane compound having an alkaline pH to thus subject the water glass solution to gelation and surface modification simultaneously, thereby producing a silylated hydrogel; and drying the silylated hydrogel at an ambient pressure, thereby manufacturing a xerogel powder. [3] The method according to claim 1 or 2, wherein the water glass solution is an inorganic precursor of silica (29 wt%), and is used with a silica content in a range of 4-8 wt% by diluting the precursor with deionized water. [4] The method according to claim 1 or 2, wherein the ion exchange is conducted for

5-10 min using a cation exchange resin. [5] The method according to claim 4, wherein the water glass solution is mixed with the cation exchange resin at a volume ratio of 1:0.5-1:1. [6] The method according to claim 1 or 2, wherein the inorganic acid is acetic acid or hydrochloric acid. [7] The method according to claim 1 or 2, wherein the organosilane compound is hexamethyldisilazane (HMDS). [8] The method according to claim 1, wherein the nonpolar solvent is hexane or heptane. [9] The method according to claim 1 or 2, wherein the drying is conducted at an ambient pressure of 1 atm at a temperature ranging from 175⁰C to 200⁰C for 30 min. [10] The method according to claim 1, wherein the solvent exchange is completed within 3 hours.

[I I] The method according to claim 1, wherein the nonpolar solvent is recovered through vapor condensation during the drying.