• 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.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.190-190
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• 2010

Zinc oxide is the most attractive material due to the large direct band gap (3.37 eV), excellent chemical and thermal stability, and large exciton binding energy (60 meV). Recently, ZnO nanorods were used as the high efficient antireflection coating layer of solar cells based on silicon (Si). In this reports, we studied the effects of rapid thermal annealing (RTA) treatment on optical properties of ZnO nanorods. For fabrication of ZnO nanorods, there are many methods such as hydrothermal method, sol-gel method, and metal organic chemical vapor deposition method. Among of them, we used the conventional wet chemical method which is simple and low temperature growth. In order to synthesize the ZnO nanorods, the ZnO films were deposited on Si substrate by RF magnetron sputtering at room temperature and the samples were dipped to aqua solution containing the zinc nitrate and hexamethylentetramines (HMT). The synthesis process was achieved in keeping with temperature of $90-95^{\circ}C$ and under constant stirring. The morphology of ZnO nanorods on glass and Si was characterized by scanning electron microscopy. For the analysis of antireflection performance, the reflectance and transmittance were measured by spectrophotometer. And for analyzing the effects of RTA treatment on ZnO nanorods, crystalline properties were investigated by X-ray diffraction measurements and optical properties was estimated by photoluminescence spectra.

• Korean Journal of Materials Research
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• v.31 no.2
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• pp.92-96
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• 2021

We report the growth and enhanced photoelectrochemcial (PEC) water-splitting reactivity of few-layer MoS2 nanosheets on TiO2 nanowires. TiO2 nanowires with lengths of ~1.5 ~ 2.0 ㎛ and widths of ~50~300 nm are synthesized on fluorine-doped tin oxide substrates at 180 ℃ using hydrothermal methods with Ti(C4H9O)4. Few-layer MoS2 nanosheets with heights of ~250 ~ 300 nm are vertically grown on TiO2 nanowires at a moderate growth temperature of 300 ℃ using metalorganic chemical vapor deposition. The MoS2 nanosheets on TiO2 nanowires exhibit typical Raman and ultraviolet-visible light absorption spectra corresponding to few-layer thick MoS2. The PEC performance of the MoS2 nanosheet/TiO2 nanowire heterostructure is superior to that of bare TiO2 nanowires. MoS2/TiO2 heterostructure shows three times higher photocurrent than that of bare TiO2 nanowires at 0.6 V. The enhanced PEC photocurrent is attributed to improved light absorption of MoS2 nanosheets and efficient charge separation through the heterojunction. The photoelectrode of the MoS2/TiO2 heterostructure is stably sustained during on-off switching PEC cycle.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.4
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• pp.413-418
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• 2021

Nano-materials with high effective surface areas have been applied to functional materials, such as high sensitive gas sensors and biosensors and high-efficiency catalytic materials. In this study, titanate sheets with a 3D nano-wall-like structure, high effective surface area, were synthesized vertically to the substrate by a chemical bath deposition (CBD) process using a Ti sheet and urea. The synthesis temperature and synthesis duration time were controlled to the optimal conditions of a 3D nano-wall-like structure in the CBD process. The synthesized ammonium titanate sheets with a 3D nano-wall-like structure were annealed in air to transform to TiO2 with a 3D nano-wall-like structure for various applications. As a result, the optimal temperature in the CBD process for the synthesis of a uniform ammonium titanate sheet with a 3D nano-wall-like structure was 90 ℃. TiO2 with a 3D nano-wall-like structure was obtained from the ammonium titanate sheet with a 3D nano-wall-like structure by annealing above 550 ℃ for three hours. In particular, TiO2 with a 3D nano-wall-like structure with a dominant rutile phase was obtained by post-annealing at 700 ℃. On the other hand, damage to the 3D nano-wall edge was observed after 700 ℃ post-annealing.

• Economic and Environmental Geology
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• v.36 no.2
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• pp.75-87
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• 2003

The Haman-Gunbuk mineralized area is located within the Cretaceous Gyeongsang Basin along the southeastern part of the Korean peninsula. Major ore minerals, magnetite, scheelite, molybdenite and chalcopyrite, together with base-metal sulfides and minor sulfosalts, occur in fissure-filling tourmaline, quartz and carbonates veins contained within Cretaceous sedimentary and volcanic rocks anu/or granodiorite (118{\pm}$3.0 Ma). The ore and gangue mineral paragenesis can be divided into three distinct stages: Stage 1, tourmaline+quartz+Fe-Cu ore mineralization; Stage II, quartz+sulfides+sulfosalts+carbonates; Stage 111, barren calcite. Earliest fluids are recorded in stage I and early por-tions of stage II veins as hypersaline (35~70 equiv. wt.% NaCl+KCl) and vapor-rich inclusions which homogenize from ~30$0^{\circ}C$ to $\geq$50$0^{\circ}C$. The high-salinity fluids are complex chloride brines with significant concentrations of sodium, potassium, iron, copper, and sulfur, though sulfide minerals are not associated with the early mineral assemblage produced by this fluid. Later solutions circulated through newly formed fractures and reopened veins, and are recorded as lower-salinity(less than ~20 equiv. wt.% NaCl) fluid inclusions which homogenize primarily from ~200 to 40$0^{\circ}C$. The oxygen and hydrogen isotopic compositions of fluid in the Haman-Gunbuk hydrothermal system represents a progressive shift from magmatic-hydrothermal dominance during early mineralization stage toward meteoric-hydrothermal dominance during late mineralization stage. The earliest hydrothermal fiuids to circu-late within the granodiorite stock localiring the ore body at Haman-Gunbuk could have exsolved from the crystal-lizing magma and unmixed into hypersaline liquid and $H_2O$-NaCl vapor. As these magmatic fluids moved throughfractures, tourmaline and early Fe, W, Mo, Cu ore mineralization occurred without concomitant deposition of othersulfides and sulfosalts. Later solutions of dominantly meteoric origin progressively formed hypogene copper and base-metal sulfides, and sulfosalt mineralization.

• Clean Technology
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• v.20 no.3
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• pp.306-313
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• 2014

Nanoporous $TiO_2$ films are commonly used as working electrodes in dye-sensitized solar cells (DSSCs). So far, there have been attempts to synthesize films with various $TiO_2$ nanostructures to increase the power-conversion efficiency. In this work, vertically aligned rutile $TiO_2$ nanorods were grown on fluorinated tin oxide (FTO) glass by hydrothermal synthesis, followed by deposition of an anatase $TiO_2$ film. This new method of anatase $TiO_2$ growth avoided the use of a seed layer that is usually required in hydrothermal synthesis of $TiO_2$ electrodes. The dense anatase $TiO_2$ layer was designed to behave as the electron-generating layer, while the less dense rutile nanorods acted as electron-transfer pathwaysto the FTO glass. In order to facilitate the electron transfer, the rutile phase nanorods were treated with a $TiCl_4$ solution so that the nanorods were coated with the anatase $TiO_2$ film after heat treatment. Compared to the electrode consisting of only rutile $TiO_2$, the power-conversion efficiency of the rutile-anatase hybrid $TiO_2$ electrode was found to be much higher. The total thickness of the rutile-anatase hybrid $TiO_2$ structures were around $4.5-5.0{\mu}m$, and the highest power efficiency of the cell assembled with the structured $TiO_2$ electrode was around 3.94%.

• Economic and Environmental Geology
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• v.43 no.5
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• pp.443-453
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• 2010

The Samsung gold-silver deposit consists of quartz veins that fill along the fault zone within Cretaceous shale and sandstone. Mineralization is occurred within fault-breccia zones and can be divided into two stages. Stage I is main ore mineralization and stage II is barren. Stage I is associated with wall-rock alteration minerals(sericite, pyrite, chlorite, quartz), rutile, base-metal sulfides(pyrrhotite, pyrite, sphalerite, chalcopyrite, galena), and electrum. Stage II occur quartz, calcite and pyrite. Fluid inclusion data indicate that homogenization temperatures and salinities of stage I range from 145 to $309^{\circ}C$ and from 0.4 to 12.4 wt.% NaCl, respectively. It suggests that hydrothermal fluids were cooled and diluted with the mixing of meteoric water. The main deposition of base-metal sulfides and electrum occurred as a result of cooling and dilution at temperature between $200^{\circ}C$ and $300^{\circ}C$. Sulfur(9.3~10.8‰) isotope composition indicates that ore sulfur was mainly derived from a magmatic source as well as the host rocks. The calculated oxygen[-2.3~0.9‰(quartz: 0.3‰, 0.9‰, calcite: -2.3‰)] and hydrogen[-86~-76‰(quartz: -86‰, -82‰, calcite: -76‰)] isotope compositions indicate that hydrothermal fluids may be meteoric origin with some degree of mixing of another meteoric water for paragenetic time.

• Economic and Environmental Geology
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• v.25 no.2
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• pp.115-131
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• 1992

Late Cretaceous (90.5 Ma), epithermal gold-silver vein mineralization of the Weolseong and Samchang mines in the Sulcheon area, 60 km southeast of Taejeon, can be separated into two distinct stages (I and II) during which fault-related fissures in Precambrian gneiss and Cretaceous (102 Ma) porphyritic granite were filled. Fluid inclusion and mineralogical data suggest that quartz-sulfide-electrum-argentite-forming stage I evolved from initial high temperatures $({\approx}340^{\circ}C})$ to later lower temperatures $({\approx}140^{\circ}C})$ at shallow depths of about 400 to 700 m. Ore fluid salinities were in the range between 0.2 and 6.6 wt. % eq. NaCl. A simple statistic model for fluid-fluid mixing indicates that the mixing ratio (the volumetric ratio between deep hydrothermal fluids and meteoric water) systematically decreased with time. Gold-silver deposition occurred at temperatures of $230{\pm}40^{\circ}C$ mainly as a result of progressive cooling of ore-forming fluids through mixing with less-evolved meteoric waters. Measured and calculated hydrogen and oxygen isotope values of hydrothermal fluids indicate meteoric water dominance, approaching unexchanged meteoric water values. The geologic, mineralogic, and geochemical data from the Weolseong and Samchang mines are similar to those from other Korean epithermal gold-silver vein deposits.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.17 no.1
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• pp.75-94
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• 2019

As the present single-layer repository concept requires too large an area for the site of the repository, a multi-layer repository concept has been suggested to improve the disposal density. The effects of the excavation damaged zone around the multi-layer repository constructed in the deep host rock on the temperature distribution in the repository were analyzed. For the thermal analysis of the multi-layer repository, the hydrothermal model was used to consider the resaturation process occurring in the buffer, backfill and rock. The existence of an excavation damaged zone has a significant effect on the temperature distribution in the repository, and the maximum peak temperatures of double-layer and triple-layer repositories can rise to $7^{\circ}C$ and $12^{\circ}C$, respectively depending on the size of the excavation damaged zone and the degree of decrease of the thermal conductivity. The dominant factor affecting the peak temperature in the multi-layer repository is the decrease of thermal conductivity in the excavation damaged zone, and the excavation damaged zone formed around the deposition hole has more significant effects on the peak temperature than does the excavation damaged zone formed around the disposal tunnel.

• Economic and Environmental Geology
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• v.3 no.2
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• pp.55-73
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• 1970

The district investigated covers the central and southern portions of the Uiryong Quadrangle amounting to $40km^2$ in area and is bounded approximately by geographical coordinates of $128^{\circ}$ 28' $40^{{\prime}{\prime}}{\sim}128^{\circ}$ 24' 25"E in longitude and $35^{\circ}10{\prime}{\sim}35^{\circ}14^{\prime}06^{{\prime}{\prime}}N$ in latitude. The purpose of this investigation was to provide basic information in drawing up a comprehensive development plan of the copper ore deposits known to exist in the HamanKumbuk district with special emphasis given to the ascertainment of geological and paragenetic characteristics. The area consists chiefly of shale, sandy shale and chert, all belong to Kyongsang System of Cretaceous age. Intruded into these rocks are andesite, granodiorite, basic dikes, and acidic dikes. The mineralization which took place in the area, consists of mostly fissure-filling vein deposits, numbering several tens, with varying magnitudes. The fissures and shear zones created in rocks, such as chert and granodiorite, hosted the deposition of mineralizing vapors and/or hydrothermal solutions along their openings. The strike lengths of these veins vary from 50 to 600 meters in extension and 0.1 to 3 meters in width. Although the degree of fluctuation in width is great, it averages 0.3m. The stuctural patterns, which apparently affected the deposition of veins, are fissure patterns, trend NS to $N30^{\circ}W$, and steep-pitching tension fractures as well as normal fault pattern. Ore minerals associated with vein matters are primarily chalcopyrite and small amounts of scheelite, cobaltiferous arsenopyrite, and gold and silver intimately associated with sulphide minerals. Associated with these ore mineral are pyrite, pyrrhotite, magnetite, specularite and arsenopyrite. Gangue minerals noted are quartz, calcite, chlorite, tourmaline and hornblende. In terms of the compositions of associated minerals, the vein deposits in the district could be grouped under the following four categories: 1. Pyrrhoitite, Arsenopyrite, Gold and Silver Bearing Copper Vein (Type I) 2. Calcite-Scheelite-Copper Vein (Type II) 3. Magnetite-Pyrite-Copper Vein (Type III) 4. Tourmaline Copper Vein (Type IV) Of the four types, the first and the fourth are presently yielding relatively higher grades: of copper ores and concentrates. The estimated ore reserves total some 222,000 metric tons with the following breakdown in terms of metal contents: Name of Mines Au(g/t) Ag(g/t) Cu(%) Reserves(M/T) Kunbuk 15.92 78.69 6,074 60.498 Cheil Kunbuk - - 1.040 60,847 Haman - - 2.688 101,204 222,549 As rehabilitation of old workings and/or exploration of veins at depth proceed, additional estimation of ore reserves may become apparent and necessary. With regard to the problem of beneficiation and upgrading of low-grade ores in the district, it would be advisable to make decisions on location, treating capacity and mill flowsheet after sufficient amount of exploration is completed as suggested in the report.