• Applied Chemistry for Engineering
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• v.22 no.2
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• pp.209-213
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• 2011

Hydrophobic silica aerogel beads with low thermal conductivity and high porosity were prepared using a cost-effective sodium silicate as a silica source via an ambient-pressure drying process. Monolithic wet gels were first prepared by adjusting pH (~5) of a diluted sodium silicate solution. The silica aerogel beads (0.5~20 mm) were manufactured by breaking the wet gel monoliths under a simultaneous solvent exchange/surface modification process and an ambient-pressure drying process without using co-precursors or templates. Dried silica aerogel beads exhibit a comparable porosity ($593m^2/g$ of surface area, 34.9 nm of pore size, and $4.4cm^3/g$ of pore volume) to that of the aerogel powder prepared in the same conditions. Thermal conductivity of the silica aerogel beads (19.8 mW/mK at $20^{\circ}C$) is also identical to the aerogel powder.

• New Physics: Sae Mulli
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• v.68 no.11
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• pp.1203-1207
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• 2018

In this study, silica nanowires were formed using silicon oxide films with different oxygen contents, and their microstructure and physical properties were compared with those of silica nanowires formed using Si wafers. The silicon oxide films were fabricated by using a plasma-enhanced chemical vapor deposition method. Silica nanowires were formed by thermally annealing silicon oxide films coated with nickel films as a catalyst. In the case of silicon oxide films having an oxygen content of approximately 50 at.% or less, the formation mechanism, microstructure, and physical properties of the nanowires were not substantially different from those of the silicon wafer. In particular, the uniformity of the thickness showed better behavior in the silicon oxide films. These results imply that silicon oxide films can be used as an alternative for fabricating high-quality silica nanowires at low cost.

• Journal of Sensor Science and Technology
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• v.15 no.5
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• pp.371-377
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• 2006

Nano porous, transparent silica aerogels monoliths were prepared under ambient drying (1 atm, $270^{\circ}C$) condition by the combination of sol-gel process and surface modification with subsequent heat treatment. Three kinds of solvent, n-hexane, n-heptane and xylene, were selected in the point view of low surface tension and vapor pressure in order to restrain a formation of cracks during drying. Crack-free silica aerogels with over 93 % of porosity and below $0.14g/cm^3$ of density were obtained by solvent exchange and surface modification under atmosphere condition. Optimum solvent was confirmed n-heptane among these solvents through estimation of FT-IR, TGA, BET and SEM. Modified silica aerogel exhibited a higher porosity and pore size compare to unmodified aerogels. Hydrophobicity was also controled by C-H and H-OH bonding state in the gel structure and heat treatment over $400^{\circ}C$ effects to the hydrophobicity due to oxidation of C-H radicals.

• Korean Journal of Materials Research
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• v.30 no.4
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• pp.155-159
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• 2020

Nanoporous silica aerogel insulation material is both lightweight and efficient; it has important value in the fields of aerospace, petrochemicals, electric metallurgy, shipbuilding, precision instruments, and so on. A theoretical calculation model and experimental measurement of equivalent thermal conductivity for nanoporous silica aerogel insulation material are introduced in this paper. The heat transfer characteristics and thermal insulation principle of aerogel nano are analyzed. The methods of SiO₂ aerogel production are compared. The pressure range of SiO₂ aerogel is 1Pa-atmospheric pressure; the temperature range is room temperature-900K. The pore diameter range of particle SiO₂ aerogel is about 5 to 100 nm, and the average pore diameter range of about 20 ~ 40 nm. These results show that experimental measurements are in good agreement with theoretical calculation values. For nanoporous silica aerogel insulation material, the heat transfer calculation method suitable for nanotechnology can precisely calculate the equivalent thermal conductivity of aerogel nano insulation materials. The network structure is the reason why the thermal conductivity of the aerogel is very low. Heat transfer of materials is mainly realized by convection, radiation, and heat transfer. Therefore, the thermal conductivity of the heat transfer path in aerogel can be reduced by nanotechnology.

• Journal of Powder Materials
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• v.21 no.6
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• pp.441-446
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• 2014

In this study, we synthesize silica-core gold-satellite nanoparticles (SGNPs) for the surface-enhanced Raman scattering (SERS) based sensing applications. They consist of gold satellite nanoparticles (AuNPs) fixed on the silica core nanoparticles, which sizes of AuNPs can be tunned by varying the amount of reactants (growth solution and reducing agent). Their surface plasmon resonance (SPR) properties were characterized by using UV-vis spectroscopy, showing that the growth of AuNPs on silica cores leads to the light absorption in the longer wavelength region. Furthermore, the size increase of AuNPs exhibited the dramatic change in SERS activity due to the formation of hot spots. The optimized SGNPs showing enhancement factor ${\sim}3.8{\times}10^6$ exhibited a detection limit of rhodamine 6G (R6G) as low as $10^{-8}M$. These findings suggest the importance of size control of SGNPs and their SPR properties to develop highly efficient SERS sensors.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.157-158
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• 2006

A novel nanofabrication process has been developed using two-photon crosslinking (TPC) for the fabrication of three-dimensional (3D) SiCN ceramic microstructures applicable to high functional 3D devices, which can be used in harsh working environments requiring a high temperature, a resistance to chemical corrosion, as well as tribological properties. After sequential processes: TPC and pyrolysis, 3D ceramic microstructures are obtained. However, large shrinkage due to low-ceramic yield during the pyrolysis is a serious problem to be solved in the precise fabrication of 3D ceramic microstructures. In this work, silica nanoparticles were employed as a filler to reduce the amount of shrinkage. In particular, the ceramic microstructures containing 40 wt% silica nanoparticles exhibited relatively isotropic shrinkage owing to its sliding free from the substrate during pyrolysis.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.179-187
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• 2009

Bentonite-based grouting has been popularly used to seal a borehole installed for a closed-loop vertical ground heat exchanger in a geothermal heat pump system (GHP) because of its high swelling potential and low hydraulic conductivity. The bentonite-based grout, however, has relatively lower thermal conductivity than that of ground formation. Accordingly, it is common to add some additives such as silica sand to the bentonite-based grout for enhancing thermal performance. In this study, graphite is adapted to substitute silica sand as an addictive because graphite has very high thermal conductivity. The effect of graphite on the thermal conductivity of bentonite-based grouts has been quantitatively evaluated for seven bentonite grouts from different product sources. In addition, comparisons of viscosity between applications of graphite and silica sand as additives has been carried out. In conclusion, using graphite has thermal conductivity about three times higher than that of silica sand.

• Journal of Sensor Science and Technology
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• v.16 no.6
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• pp.395-400
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• 2007

Ambient drying sol-gel processing was used for monolithic silica ambigels in the temperature range of $130-250^{\circ}C$. A new method of mesopore ambigels, which mean the aerogels prepared by ambient pressure drying process synthesis, is suggested at first. This method includes two important approaches. The first point is that $SiO_{2}$ surface modification of wet gel was performed by trimethylchlorosilane in n-butanol solution. This procedure is provided the silica gel mesopore structure formation. The second point is a creation of the ternary azeotropic mixture water/n-butanol/octane as porous liquid, which is effectively provided removing of water such a low temperature by 2 step drying condition under ambient pressure. The silica aerogels, which were prepared by ambient pressure drying from azeotropic mixture of water/n-butanol/octane, are transparent, crack-free and mesoporous (pore size ${\sim}$ 5.6 nm) with surface area of ${\sim}$ $923{\;}m^2/g$, bulk density of $0.4{\;}g/cm^3$ and porosity of 85 %.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.275-276
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• 2008

통신기기가 고주파수화 함에 따라서 저유전 저손실 재료의 필요성이 증대되고 있으며, 세라믹/폴리머 복합재료를 고주파 회로 기판 소재로 이용하려는 관심이 증폭되고 있다. 본 연구에서는 저손실, 저유전율 특성을 구현하기 위해 $SiO_2$를 세라믹 필러로 복합물을 제작하였다. 평균 입자 크기가 16nm, $2.3{\mu}m$의 fumed 실리카와 평균 입자 크기 $1{\mu}m$, $4{\mu}m$의 fused 실리카를 사용하였다. 이 4종류 실리카를 사용하여 slurry를 제작하고 이를 활용하여 tape을 제작하였다. 제작된 복합체 tape을 적층하여 기판을 제작해 기판의 유전특성을 측정하였다. fumed 실리카의 경우 $SiO_2$ 10vol%이상에서는 균일한 tape성형이 어려워졌으며, 유전 손실이 fused 실리카와 비교하였을 때 큰 폭으로 증가하였다. fumed silica, fused silica 두 종류 모두 입도가 증가하면 유전손실이 증가하였다.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.11a
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• pp.68-71
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• 2013

Reactive Powder Concrete (RPC) is an ultra high strength and high ductility cement-based composite material and has shown some promise as a new generation concrete in construction field. It is characterized by a silica fume-cement mixture with very low water-binder (w/b) ratio and very dense microstructure, which is formed using various powders such as cement, silica fume and very fine quartz sand (0.15~0.4mm) instead of ordinary coarse aggregate. However, the unit weight of cement in RPC is as high as 900~1,000 kg/㎥ due to the use of very fine sand instead of coarse aggregate, and a large volume of relatively expensive silica fume as a high reactivity pozzolan is also used, which is not produced in Korea and thus must be imported. Since the density of RPC has a heavy weight at 2.5~3.0 g/㎤. In this study, the modified RPC was made by the combination of ternary pozzolanic materials such as blast furnace slag and fly ash, silica fume in order to economically and practically feasible for Korea's situation. The fire resistance and structural behavior of the modified RPC exposed to high temperature were investigated.