• Journal of the Korean Chemical Society
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• 제47권3호
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• pp.213-219
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• 2003

The photochemical transformation of carbon monoxide in aqueous solution has been investigated at $25{\pm}0.1^{\circ}C$using ZnO as a photocatalyst. After irradiation of 253.7 nm UV light in the solution, carboxylation and carbonylation processes were carried out, and the formation of formic acid, oxalic acid, glyoxylic acid, formaldehyde and glyoxal was observed. The formation of the products depended on the pH values in the solution. The yield of formaldehyde and glyoxal increased in acidic solution whereas it decreased in basic solution. When the pH values in the solution increased above 11.5, the yield of formic acid increased rapidly. The initial quantum yields of the products were determined and the probable mechanisms for the reactions were presented on the basis of the products analysis.

• Economic and Environmental Geology
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• 제25권3호
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• pp.233-243
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• 1992

Ore mineralization of the Hwanghak copper deposit in the Ogsan area occurred in three stages of quartz (stage I and II) and calcite (stage III) veining along fissures in Early Cretaceous sedimentary rocks. Ore minerals are pyrite, pyrrhotite, chalcopyrite (dominant), sphalerite, hematite, galena, and Ag-, Pb-, and Bi-sulfosalts. These were deposited during the first stage at temperatures between $370^{\circ}C$ and < $200^{\circ}C$ from fluids with salinities between 0.5 and 7.6 equiv. wt. % NaCl. There is evidence of boiling and this suggests pressures of less than 180 bars during the first stage. Equilibrium thermodynamic interpretation accompanying with mineral paragenesis and fluid inclusion data indicates that copper precipitation in the hydrothermal system occurred due to cooling and changing in chemical conditions ($fs_2$, $fo_2$, pH). Gradual temperature decrease from $350^{\circ}$ to $250^{\circ}C$ of ore fluids by boiling and mixing with less-evolved meteoric waters mainly led to copper deposition through destabilization of copper chloride complexes. Sulfur isotope values of sulfide minerals decrease systematically with paragenetic time from calculated ${\delta}^{34}S_{H_2S}$ values of 8.2 to 4.7‰. These values, together with the observed change from sulfide-only to sulfide-hematite assemblages and fluid inclusion data, suggest progressively more oxidizing conditions, with a corresponding increase of the $sulfate/H_2S$ ratio of hydrothermal fluids. Measured and calculated hydrogen and oxygen isotope valutls of ore-forming fluids suggest meteoric water dominance, approaching unexchanged meteoric water values.

• Journal of the Korean Vacuum Society
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• 제20권4호
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• pp.300-306
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• 2011

We report the surface distribution of metal (Ag, Au) nanoparticles grown on polarity-patterned ferroelectric substrates by photochemical reaction. Single crystal periodically polarity-patterned $LiNbO_3$(PPLN) was used as a ferroelectric substrate. The nanoparticles were grown by ultra-violet (UV) light exposure of the PPLN in the aqueous solutions including metas. The surface distribution of the grown nanoparticles were measured by atomic force microscopy and identification of the orientation of the polarity of the ferroelectric surface was performed by piezoelectric force microscopy. The Ag- and Au-nanoparticles grown on +z polarity regions are larger and denser than that on -z polarity regions. In particlur, the largest and denser Ag-nanoparticles were grwon on the polarity boundary regions of the PPLN while Au-nanoparticles were not specifically grown on the boundary regions. Thus, we found that the size and position of metal nanoparticles grown on ferroelectric surfaces can be controlled by UV-exposure time and polarity pattern structures. Also, we discuss the difference of the surface distribution of the metal nano-particles depending on the polarity of the ferroelectric surfaces in terms of surface band structures, reduced work fucntion, and inhomogeneous electric field distribution.

• Economic and Environmental Geology
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• 제25권2호
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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.

• Economic and Environmental Geology
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• 제32권5호
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• pp.435-444
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• 1999

The antimony deposits of the Hyundong mine, located in the northeastern part of the Sobaegsan massif, occur as hydrothermal quartz+carbonate veins and stockworks which fill the fault fractures developed in Precambrian metamOlphic rocks (mainly, granitic gneiss). Hydrothermal alteration occurs commonly in the vicinity of mineralized veins and is characterized by sericitization and silicification. A K-Ar age of alteration sericite is 139.2$\pm$ 4.4 Ma, implying the early Cretaceous age of mineralization, possibly in association with intrusion of nearby acidic dikes (mainly, quartz porphyry). The hydrothermal mineralization occurred in five mineralization stages. These are: (I) stage I, characterized by deposition of chalcedonic quartz; (2) stage II, deposition of quartz with base-metal sulfides and stibnite; (3) stage III, deposition of quartz and carbonates (calcite, dolomite, ankerite, rhodochrosite) with various antimony-bearing minerals such as stibnite, polybasite, berthierite, native antimony, gudmundite and ullmannite; (4) stage IV, deposition of calcite with stibnite; and (5) stage V, deposition of barren calcite. Antimony occurs mostly as stibnite within stages II to IV veins, which has various habits including disseminated, veinlets and euhedral coarse crystals. Fluid inclusion studies indicate that hydrothermal mineralization at Hyundong occurred from the fluids with temperature and salinity of $330^{\circ}$C to 120 and 5.3 wI. % equiv. NaCI. The temperature and salinity of ore fluids systematically decreased with elapsed time in the course of mineralization, possibly due to the influx of larger amounts of meteoric groundwater. The deposition of antimony-bearing minerals occurred at low temperatures «$250^{\circ}$C), mainly due to the cooling and dilution of fluids. Based on the evidence of fluid boiling during the early stage II mineralization, the mineralization occurred under low pressure conditions (about 80 bars, corresponding to depths of about 350 m under hydrostatic pressure regime). Thermodynamic considerations of ore . mineral assemblages indicate that antimony deposition also occurred as the results of decreases in temperature and sulfur fugacity of hydrothermal fluids. Calculated sulfur isotope composition of ore fluids ($\delta^{34}S_{\Sigma s}$=5.4 to 7.8$\textperthousand$) indicates an igneous source of sulfur.

• Journal of the korean academy of Pediatric Dentistry
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• 제44권2호
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• pp.138-146
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• 2017

The aim of this study was to estimate time of biomineralization in developmental stages of rat lower incisors. Eruption length was measured. Four stages of incisor development were identified on histologic and microscopic computerized tomography (micro-CT) sections: (1) preodontoblast, (2) dentin matrix secretion, (3) enamel matrix secretion, and (4) enamel calcification. The overall eruption rate of the rat lower incisor was $600{\pm}70{\mu}m/day$ ($mean{\pm}SD$; n = 12). The length of the enamel secretion was $4.59{\pm}0.75mm$ in histologic section, was $3.64{\pm}0.63mm$ in radiographic section, which converts to $180.4{\pm}30.0hours$, $145{\pm}25hours$ respectively (n = 24). These findings suggested that the four biomineralizing developmental stages of the rat incisor took only several days. The significance of this animal study was to provide understanding for the rapid biomineralization process of developing rat tooth germ by analysis of tooth forming period.

• Economic and Environmental Geology
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• 제52권5호
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• pp.323-336
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• 2019

The Mesozoic activity on the Korean Peninsula is mainly represented by the Triassic post-collisional, Jurassic orogenic, and Cretaceous post-orogenic igneous activities. The diversity of mineralization by each geological period came from various geothermal systems derived from the geochemical characteristics of magma with different emplacement depth. The Cretaceous metallic mineralization has been carried out over a wide range of time periods from ca. 115 to 45 Ma (main stage; ca. 100 to 60 Ma) related to post-orogenic igneous activity, and spatial distribution patterns of most metal deposits are concentrated along small granitic stocks. The late Cretaceous metal deposits in the Gyeonggi and Yeongnam massifs are generally distributed along the boundary among the Gongju-Eumseong fault system and the Yeongdong-Gwangju fault system and the Gyeongsang Basin, most of them are in the form of a distal epithermal~mesothermal Au-Ag vein or a transitional mesothermal Zn-Pb-Cu vein. On the other hand, diverse metal commodities in the Taebaeg Basin, the Okcheon metamorphic belt and the Gyeongsang Basin are produced from various deposit types such as skarn, carbonate-replacement, vein, porphyry, breccia pipe, and Carlin type. In the late Cretaceous metallic mineralization, various mineral deposits and commodities were induced not only by the pathway of the hydrothermal solution, but also by the diversity of precipitation environment in the proximity difference of the granitic rocks. The diversity of these types of Cretaceous deposits is fundamentally dependent on the geochemical characteristics such as degree of differentiation and oxidation state of related igneous rocks, and ore-forming fluids generally exhibit the evolutionary characteristics of intermediate- to low-sulfur hydrothermal fluids.

• Journal of Korean Society of Environmental Engineers
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• 제28권4호
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• pp.429-437
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• 2006

To establish the efficient treatment technology of chemical cleaning wastewater from power plant, several AOPs($UV/H_2O_2,\;UV/TiO_2/H_2O_2$, Photo-Fenton oxidation) were investigated. Treatment efficiencies and the electrical energy requirements based on the EE/O parameter(the electrical energy, required per order of pollutant removal in $1m^3$ wastewater) were evaluated. TOC removal efficiencies of $UV/H_2O_2,\;UV/TiO_2/H_2O_2$, Photo-Fenton oxidation at the optimum conditions were 95.5%, 92.3%, 91.5%, respectively. The electrical energy requirements of $UV/H_2O_2,\;UV/TiO_2/H_2O_2$, Photo-Fenton oxidation were $11.26kWh/m^3,\;3.85kWh/m^3,\;0.799kWh/m^3$, respectively. From these results, it could be concluded that all of the three oxidation processes were effective for the degradation of citric acid. Considering the treatment efficiency and economical aspect, photo-Fenton oxidation was the most efficient treatment process among the three processes tested.

• Korean Journal of Environmental Biology
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• 제17권2호
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• pp.199-204
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• 1999

The effects of temperature stress and paraquat on the superoxide dismutase (SOD) activity and the photochemical efficiency of photosystem II were studied in the leaves of Araliaceae plants. The SOD activity of Acanthopanax koreanum leaf discs increased at 4$^{\circ}C$ and 28$^{\circ}C$, and increased significantly at 4$^{\circ}C$ ,28$^{\circ}C$ and 35$^{\circ}C$ in the presence of paraquat. However, the SOD activity of Dendropanax morbifera leaf discs decreased at 4$^{\circ}C$, 28$^{\circ}C$ and 35$^{\circ}C$ regardless of paraquat treatment. The photochemical efficiency of photosystem II, Fv/Fm, of leaf discs of A. koreanum and D. morbifera fell remarkably at 35$^{\circ}C$. In the presence of paraquat, the Ev/Fm values fell slightly at 4$^{\circ}C$ in A. koreanum leaf discs and at 35$^{\circ}C$, in D. morbifera leaf discs. These results indicate that A. koreanum plants are more resistant to temperature stress or oxidative stress than D. morbifera plants although their photochemical efficiency falls slightly at 4$^{\circ}C$ in the presence of paraquat.

• Korean Chemical Engineering Research
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• 제61권2호
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• pp.240-246
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• 2023

This study was performed to convert NO_x in atmosphere by photochemical reaction utilizing the eco-friendly solar energy. The mortar specimen coated with photocatalyst was fabricated and the photochemical conversion efficiency of NO_x was analyzed. The photocatalyst coated concrete was fabricated by first adding TiO₂ photocatalyst on the bottom of mold first and next adding cement mortar and, then, curing the concrete mortar. The grease was sprayed on the bottom of mold in advance so that the concrete can be demolded easily after curing. The conversion efficiencies of NO_x by photochemical reactions were investigated systematically by changing the process variable conditions of amount of TiO₂ coating, UV-A light intensity, total gas flow rate, relative humidity and initial NO_x concentration. It was confirmed that the photocatalyst coated concrete fabricated in this study could convert NO_x successfully for various process conditions in atmosphere. In future, we believe this research result can be utilized as basic data to design the infrastructure of building, tunnel and road for controlling efficiently the air pollutants such as NO_x, SO_x, and VOCs.