• 한국세라믹학회지
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• 제33권12호
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• pp.1319-1324
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• 1996

Silica aerogels were synthesis by the sol-gel-supercritical drying process using isopropanol as a solvent. Effets of the heat-treatment and the surface modification through propoxylation on the structural reinforcement as well as the surface hydrophobic/hydrophilic characteristics of aerogels were investigated. Silica aerogels synthesized by supercritical drying were hydrophobic but aerogels heat-treated above 20$0^{\circ}C$ were transformed to be hydrophilic. In particular it was found that the skeletal structure of aerogels heat-treated at 50$0^{\circ}C$ was strong enough not to crack after adsorbing a large amount of water vapor. Hydrophilic aerogels modified by propoxylation at 28$0^{\circ}C$ for 20 h were reversed to the hydrophobic form. Transition between hydrophobicity and hydrophilicity was reversible. The hydrophobicvity and the hydrophilicity of silica aerogels were attributed to the Si-Oh bond and the nonpolar C-H bond groups of orgainc species respectively.

• 펄프종이기술
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• 제33권4호
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• pp.1-6
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• 2001

Today's paper industry tries to use greater amount of high yield pulp and recycled fiber and to close mill water system, which results in higher fines content and buildup of organic and inorganic contaminants in white water system. Researches are being focused to develop chemical additives that provide good retention and drainage in a closed papermaking system. A microparticle retention system consisted of cationic guar gum and anionic colloidal silica so has been developed to meet the requirements for improving machine speed and product quality. The objective of this investigation was to determine the effects of the degree of cationic guar gums, charge density and structure of anionic colloidal silica sols, and the degree of system closure on the performances of this microparticle retention system. Cationic guar gums and anionic colloidal silica sols with higher charge densities showed better retention performance. Particularly, wider maximum in retention was obtained when structure colloidal silica was used suggesting as mechanism of microparticle bridging is functioning in this system.

• Bulletin of the Korean Chemical Society
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• 제30권4호
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• pp.869-872
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• 2009

Double-doped magnetic particles that incorporated magnetites into both the surface and inside the silica cores were fabricated via the sol-gel reaction of citrate-stabilized magnetites with silicon alkoxide. Double-doped magnetic particles were easily fabricated and exhibited an higher magnetism in comparison to the singledoped magnetic particles that were prepared by the erosion of surface-deposited magneties from double-doped magentic particles. Thin gold layer was formed over magnetic silica nanospheres via nanoseed-mediated growth of gold clusters. The plasmon-derived absorption bands of double-doped magnetic silica-gold nanoshells were more broadened and shifted down by ca. 20 nm as compared to those of single-doped magnetic silicagold nanoshells, which were attributed to not only the surface scattering of incident light due to relatively rough surafce morphology, but also heterogeneous permittivity of dielectric cores due to surface-deposited magnetites.

• 한국세라믹학회지
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• 제34권9호
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• pp.969-978
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• 1997

The properties of microstructure, hydrophobicity/hydrophilicity, mechanical strength, and thermal conduction of pure/opacified silica aerogels synthesized by the sol-gel supercritical drying technique were investigated. The hydrophobic surface of opacified silica aerogels doped with carbon (0.13 g/cm3 density, 94% porosity, 580 m2/g specific surface area) transformed to hydrophilic surface after heat-treated above 30$0^{\circ}C$. The values of compressive modulus (1.85 MPa) and strength (0.5 MPa) of opacfied silica aerogels were about 20 times higher than those of pure silica aerogels. The mechanical properties of pure silica aerogels heat-treated at $700^{\circ}C$ were also considerably improved without changing their porosity and density. Particularly, compressive modulus and compressive strength of pure silica aerogels GPSed under 100$0^{\circ}C$ and 80 bar were improved 140 and 37 times, respectively. Thermal conductivities of pure/opacified silica aerogels measured at room temperature and 227$^{\circ}C$ were about 0.013 and 0.019 W/m.K, respectively, and were to be found very low value of 0.004 W/m.K below 10 torr pressure at room temperature.

• 한국세라믹학회지
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• 제30권10호
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• pp.838-844
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• 1993

To control the pore size of silcia gel, formamide (FA), N,N-dimethyl formamide (DMF), polyethylene glycol (PEG) and polyacrylic acid (PAA) were added in the sol-gel process from starting solution with tetramethyl orthosilicate (TMOS). The gels were characterized using porosimeter, TG-DTA and SEM. As a result, the more contents of FA and PAA was increased the more gelation time was decreased, also the more contents of DMF and PEG was increased the more gelling time was increased. The mean pore size of gels was larger in the order of PAA, DMF, FA and PEG. And the mean pore size of porous silica glass was 59.0$\AA$, 31.5$\AA$, 29.9$\AA$ and 29.0$\AA$, respectively, heated at 75$0^{\circ}C$/100$0^{\circ}C$.

• 한국막학회:학술대회논문집
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• 한국막학회 1996년도 추계 총회 및 학술발표회
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• pp.55-57
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• 1996

다공성 무기막은 높은투과도와 뛰어난 내열.내화학성, 그리고 경제성 때문에 기존의 PSA공정이나 증류와 같은 고에너지 분리공정을 대체하는 공정으로 각광을 받고 있다. 무기재료막의 제조하는 방법으로 주로 알콕사이드를 사용하는 솔-젤법(1)과 금속(2) 또는 기상반응(3)을 이용하는 화학증착법이 사용된다. 또한 고온에서 수소를 연속적으로 분리하여 화학평형에 기인한 한계를 극복하여 높은 수율을 얻고자하는 막반응기에 관한 연구가 활발히 진행되고 있다. 본 연구에서는 $\alpha$-알루미나 지지체의 미세한 다공성 구조 내부에서 TEOS(Tetraethylorthosilicate)와 산성의 알코올-물 혼합물을 확산시켜 실리카 솔을 생성시킴과 동시에 젤화시켜 기공의 크기를 감소시켜 막을 제조하였다. 이렇게 제조된 막은 높은 투과도와 낮은 수소선택도(selectivity=3-4)를 보였고, 두번째 단계로 silica sol을 제조하여 진공 하에서 dip-coating을 행하였다. 이렇게 2단계로 기공 구조를 개선시킨 실리카 막은 저압에서 상대적으로 높은 수소의 분리도(selectivity=5-7)를 보였으며 여전히 높은 투과도를 갖는다.

• 대한화학회지
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• 제52권4호
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• pp.387-393
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• 2008

• 센서학회지
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• 제13권3호
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• pp.169-174
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• 2004

A fiber optic pH sensor has been fabricated using nile blue entrapped in an ammonia catalyzed silica sol-gel film coated on glass substrate by dip-coating. The sensor was fixed on the end of an optical fiber. The sensor showed pH sensitivity when dipped into liquids at different pHs. Linear and reproducible responses were obtained in standard buffer solutions in the pH range $6.0{\sim}8.5$, which encompasses the clinically-relevant range. The effects of interferences on the determination of pH were also investigated. The sensors were successfully applied to the determination of pH in different commercial ionic drinks.

• 한국응용과학기술학회지
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• 제16권4호
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• pp.317-322
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• 1999

Transparent films were prepared using the sol-gel process by mixing TEOS with PVA solution that was solved in EtOH and distilled water homogeneously. HCl, $CH_3COOH$ and $NH_4OH$ were used as catalysts of the sol-gel process, and for improving the flexibility of films glycerol was used as plasticizer. In case of each catalyst, transparency and tensile strength were increased, and glass transition temperature (Tg) was shifted to higher temperature with increasing TEOS ratio. Also, in case of adding the plasticizer, the flexibility of films was increased. On the contrary, transparency, thermal stability and tensile strength were decreased with increasing HCl and $NH_4OH$ ratio. Also, the range of being made of film type was expanded when $CH_3COOH$ was used than HCl and $NH_4OH$.

• Advances in nano research
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• 제14권4호
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• pp.355-362
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• 2023

Physical exercise, especially intense exercise and high intensity interval training (HIIT) by trampoline, can lead to muscle injuries. These effects can be reduced with intelligent products made of nanocomposite materials. Most of these nanocomposites are polymers reinforced with silicon dioxide, alumina, and titanium dioxide nanoparticles. This study presents a polymer nanocomposite reinforced with silica. As a result of the rapid reaction between tetraethyl orthosilicate and ammonia in the presence of citric acid and other agents, silica nanostructures were synthesized. By substituting bis (4-amino phenoxy) phenyl-triptycene in N, N-dimethylformamide with potassium carbonate, followed by catalytic reduction with hydrazine and Pd/C, the diamine monomer bis (4-amino phenoxy) phenyl-triptycene is prepared. We synthesized a new polyaromatic (imide) with triptycene unit by sol-gel method from aromatic diamines and dianhydride using pyridine as a condensation reagent in NMP. PI readily dissolves in solvents and forms robust and tough polymer films in situ. The FTIR and NMR techniques were used to determine the effects of SiO₂ on the sol-gel process and the structure of the synthesized nanocomposites. By using a simultaneous thermal analysis (DTA-TG) method, the appropriate thermal operation temperature was also determined. Through SEM analysis, the structure, shape, size, and specific surface area of pores were determined. Analysis of XRD results is used to determine how SiO₂ affects the crystallization of phases and the activation energy of crystallization.