• Economic and Environmental Geology
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• v.28 no.4
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• pp.315-326
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• 1995

The layer charge characteristics of smectites from the Tertiary basins in the Pohang area have been studied in detail using the alkyl-ammonium method. On the basis of layer charges, the smectite in the Pobang area can be classed as normal and high-charge (hc) smectite. The layer charge of the normal smectite averages 0.3, and ranges from 0.25 to 0.38/half unit cell. The hc-smectite collapses on K-saturation to become illite-like material and shows $10{\AA}$-series reflections on X-ray diffraction. The layer charge of the he-smectite ranges from 0.5 to 1. The layer cbarges of the Pohang smectite are in general heterogeneous. The layer charges distribute between 0.21 and 0.45, and the most frequent layer charge is 0.30~0.32. The layer charge and the layer charge distribution do not appear to be related to stratification or basins of occurrence. Thus, the layer charge may not have developed as a result of burial. Rather, it may have developed due to heat and hydrothermal solutions associated with volcanic activities. Volcanic sills and dykes are ubiquitous in the region.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.318.1-318.1
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• 2014

Metal nano-crystals have been received much attentions owing to their excellent catalytic property and surface plasmon effect. In the last decade, many studies on synthesizing well-dispersive nanoparticles and on understanding their distinct physical properties have been performed. There were tremendous reports revealing the electrochemical activities and enhancement of surface plasmonic effect were dependent mainly on the size, shape, and composition. So far, most fabrication methods have been based on vacuum based deposition techniques, such as chemical vapor deposition and electron-beam evaporation, and then annealed them to transform into the nanoparticles. Recently, there were several reports regarding to the photoinduced nano-crystal synthesis as an effective way to produce the metal nanoparticles. In this study, we report synchrotron x-ray mediated synthesis of Au nanoparticles on ZnO nanowires. ZnO nanowires were fabricated by hydrothermal method, and then they were dip into a solution having Au clusters. Detailed structural evolution of Au nanoparticles was investigated using scanning electron microscopy and photoluminescence measurements. The results on formation of well-dispersive Au nanoparticles on ZnO nanowires will be presented.

• Korean Journal of Materials Research
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• v.11 no.10
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• pp.846-850
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• 2001

In the present study, nano-size powders of ternary ferrites, $Ni_{0.5}Zn_{0.5}Fe_2O_4$, as the potential catalysts of $CO_2$decomposition, were prepared by the wet processing of hydrothermal synthesis and coprecipitation method, and the catalyzing effects of impregnation of the noble metals, Pt and Pd, onto $Ni_{0.5}Zn_{0.5}Fe_2O_4$for the $CO_2$decomposition were investigated. XRD results of the synthesized ferrites showed a typical spinel structure of ferrite and the particle size was very small as about 6~10 nm. BET surface area of the ternary ferrites was not affected by the impregnation of Pt and Pd. The reactivity of the $CO_2$decomposition to carbon was improved by the impregnation of the noble metals of Pd and Pt. The effect of Pd-impregnation on the $CO_2$decomposition rate was higher than Pt-impregnation.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.200-200
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• 2011

Hierarchical mesoporous ZSM-5 with enhanced mesoporosity was synthesized by microwave through the rapid assembly via ionic interaction between sulfonic acid functionalized ZSM-5 nano particles and cationic surfactant. The catalytic performance of enhanced accessibility due to mesoporosity and acidity were investigated in the alkylation of mesitylene with benzyl alcohol as alkylating agent. The effect of mole ratio of aromatic with benzyl alcohol, reaction time and alkylation agent were also studied. The enhanced mesoporosity and acidity of sulfonic acid functionalized mesoporous ZSM-5 induced activity enhancement compared with non-functionalized mesoporous ZSM-5, sulfonic functionalized mesoporous ZSM-5 synthesized by hydrothermal method and conventional microporous ZSM-5. The sulfonic acid functionalized mesoporous ZSM-5 showed much higher chemoselectivity of benzylated mesitylene than others, whereas the others mainly show dibenzyl ether as product. This significant difference in catalytic selectivity was resulted from the existence of mesopores, which definitely allowed the benzylation in mesopores.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.450-450
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• 2011

This study reports the hydrogen sulfide gas sensing properties of ZnO nanorods bundle and the investigation of gas sensing mechanism. Also the improvement of sensing properties was also studied through the application of ZnO heterstructured nanorods. The 1-Dimensional ZnO nano-structure was synthesized by hydrothermal method and ZnO nano-heterostructures were prepared by sonochemical reaction. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) spectra confirmed a well-crystalline ZnO of hexagonal structure. The gas response of ZnO nanorods bundle sensor increased with increasing temperature, which is thought to be due to chemical reaction of nanorods with gas molecules. Through analysis of X-ray photoelectron spectroscopy (XPS), the sensing mechanism of ZnO nanorods bundle sensor was explained by well-known surface reaction between ZnO surface atoms and hydrogen sulfide. However at high sensing temperature, chemical conversion of ZnO nanorods becomes a dominant sensing mechanism in current system. In order to improve the gas sensing properties, simple type of gas sensor was fabricated with ZnO nano-heterostructures, which were prepared by deposition of CuO, Au on the ZnO nanorods bundle. These heteronanostructures show higher gas response and higher current level than ZnO nanorods bundle. The gas sensing mechanism of the heteronanostructure can be explained by the chemical conversion of sensing material through the reaction with target gas.

• Applied Chemistry for Engineering
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• v.27 no.6
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• pp.669-671
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• 2016

Hydroxyapatite (HAP) was prepared by a hydrothermal synthesis method and also silver was introduced on the surface of HAP through an ion exchange reaction. The crystal phase and morphology of HAP were then evaluated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). In addition, the absorption property of HAP was characterized by diffuse reflectance UV-Vis spectroscopy. The presence of silver nanoparticles on the surface of HAP was also verified by XRD and TEM analysis. Particularly, the silver doped HAP showed an enhanced absorption property in UV-Vis region compared to that of the pristine HAP.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.11a
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• pp.127-128
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• 2012

ZnO nanostructures were grown by the hydrothermal method on ZnO seed layers post-heated in the range $350-500^{\circ}C$. The effects of the post-heated ZnO seed layers on the structural and optical properties of the ZnO nanostructures were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) spectroscopy, and photoluminescence (PL) spectroscopy. The average grain sizes in the ZnO seed layers increased with increasing post-heating temperature, and nano-fibrous structures were observed on the surface of the ZnO seed layers post-heated at $450^{\circ}C$. The ZnO seed layers post-heated in the range $350-500^{\circ}C$ affected the residual stress, lattice distortion in the ZnO nanostructures and the intensity, positions, and full widths at half maximum of the 2-theta and PL peaks in the XRD and PL spectra for the ZnO nanostructures.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.51-51
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• 2012

There is a growing interest in innovative chemical synthesis in microreactors owing to high efficiency, selectivity, and yield. In microfluidic systems, the low-volume spatial and temporal control of reactants and products offers a novel method for chemical manipulation and product generation. Glass, silicon, poly(dimethylsiloxane) (PDMS), and plastics have been used for the fabrication of miniaturized devices. However, these materials are not the best due to either of low chemical durability or expensive fabrication costs. In our group, we have recently addressed the demand for economical resistant materials that can be used for easy fabrication of microfluidic systems with reliable durability. We have suggested the use of various specialty polymers such as silicon-based inorganic polymers and fluoropolymer, flexible polyimide (PI) films that have not been used for microfluidic devices, although they have been used for other areas. And inexpensive lithography techniques were used to fabricate Lab-on-a-Chip type of microreactors with differently devised microchannel design. These microreactors were demonstrated for various synthetic reactions: liquid, liquid-gas organic chemical reactions in heterogeneous catalytic processes, syntheses of polymer and non-trivial inorganic materials. The microreactors were inert, and withstand even harsh conditions, including hydrothermal reaction. In addition, various built-in microstructures inside the microchannels, for example Pd decorated peptide nanowires, definitely enhance the uniqueness and performance of microreactors. These user-friendly Lab-on-a-Chip devices are useful alternatives for chemist and chemical engineer to conventional chemical tools such as glass.

• Bulletin of the Korean Chemical Society
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• v.34 no.10
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• pp.3005-3012
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• 2013

The effect of Mn-promotion on high surface area Al-pillared montmorillonite (AlMMT) supported Co nanoparticles prepared by hydrothermal method have been investigated. A series of different weight% Mn-promoted Co nanoparticles were prepared and characterized by XRD, TPR, TGA, BET and SEM techniques. An increase in the surface area of MMT is observed with Al-pillaring. Fischer-Tropsch catalytic activity of the as prepared catalysts was studied in a fixed bed micro reactor at $225^{\circ}C$, $H_2/CO$ = 2 and at 1 atm pressure. The data showed that by the addition of Mn the selectivity of $C_1$ dropped drastically while that of $C_2-C_{12}$ hydrocarbons increased significantly over all the Mn-promoted Co/AlMMT catalysts. The $C_{13}-C_{20}$ hydrocarbons remained almost same for all the catalysts while the selectivity of $C_{21+}$ long chain hydrocarbons decreased considerably with the addition of Mn. The catalyst with 3.5%Mn showed lowest $C_{21+}$ and highest $C_2-C_{12}$ hydrocarbons selectivity due to cracking of long chain hydrocarbons over acidic sites of MMT.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2002.11a
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• pp.181-184
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• 2002

본 연구에서는 아이솔레이터(Isolator)의 핵심소재로 사용되는 YIG-ferrites를 수열합성법에 의해 초미세 분말로 합성하고, 합성된 분말을 원료로 사용하여 제조 공정된 YIG-ferrites 소결체의 미세구조와 전자기적 특성에 관하여 고찰하였다. 수열합성법(Hydrothermal synthesis method)으로 YIG［ $Y_3$F $e_{5}$ $O_{12}$］분말을 먼저 합성하고 Ca, V, In, Al 등을 첨가시킴으로서 $Y_{2.1}$C $a_{0.9}$ $Y_{4.4}$ $V_{0.5}$I $n_{0.05}$ $O_{12}$의 조성을 지닌 시편을 제조하였다. 초기열처리는 30$0^{\circ}C$에서 90$0^{\circ}C$의 온도 범위에서 15$0^{\circ}C$간격으로 진행하였다.. 그 결과 75$0^{\circ}C$로 초기열처리 하였을 경우 단일 YIG peak가 나타남을 알 수 있었다. 수열합성법으로 제조된 YIG 소결시편의 전자기적 특성은 일반 시약급원료를 사용하여 제조된 소결시편과 비교하여 마이크로파 특성을 평가하였다. 그밖에 YIG-ferrites의 결정성, 미세구조, 자기적 특성, 마이크로파 특성을 XRD, SEM, VSM, Network Analyzer를 이용하여 고찰하였다.여 고찰하였다.다.다.다.다.