• Economic and Environmental Geology
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• v.21 no.3
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• pp.223-234
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• 1988

A large number of gold and/or silver-bearing quartz veins occur in or near Mesozoic granite batholith elongated in a NE-SW direction within the Chungcheong Province. Precambrian schists and gneisses, and Jurassic and Cretaceous granitic rocks serve as hosts for gold and/or silver deposits. On the basis of Ag/Au total production and ore grade ratio, 15 mines may be divided into three major groups: gold-dominant deposits, gold-silver deposits, and silver-dominant deposits. The chemical composition of electrum from skarn deposit (Geodo mine), alaskite-type deposit (Geumjeong mine) and 15 vein deposits was summarized. It was found that the Au content of electrum for vein deposits ranging from 5.2 to 86.5 is lower than that for skarn and alaskite deposits. Among 15 vein deposits, the composition of electrum associated with pyrrhotite is relatively high and has a narrow range of 40.8 to 86.5 atomic % Au, but the Au content of electrum with pyrite is in range of 5.2 to 82.8 atomic %, and is clearly lower than that with pyrrhotite. The grouping of ages for these mines indicates that gold and/or silver mineralizations occurred during two periods in the Mesozoic. Daebo igneous activities are restricted to gold mineralization in the range of 158 to 133 Ma, whereas Bulgugsa igneous activities are related to gold and/or silver mineralization ranging from 108 to 71 Ma. Generally speaking, Jurassic gold-dominant veins have many common characteristics; notably prominent association with pegmatites, simply massive vein morphology, high fineness in the ore concentrates, rarity of silver minerals, and a distinctively simple mineralogy, including sphalerite, galena, chalcopyrite, pyrrhotite and/or pyrite. Although individual deposits exhibit widely differing diversity, Cretaceous gold-silver and silver-dominant veins are characterized by features such as complex vein, low to medium fineness in the ore concentrates and abundance of silver minerals including Ag sulfosalts, Ag sulfides, Ag tellurides and native silver.

• Journal of Sensor Science and Technology
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• v.25 no.2
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• pp.143-147
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• 2016

Characteristics of the conventional gold (Au) surface plasmon resonance (SPR) chip, bi-metallic(Au/silver (Ag)) SPR chip, and tri-metallic(Au/Ag/Au) SPR chip were investigated and compared in the intensity measurement mode for the enhancement of SPR image sensor reactivity. Reflectance curves of the Au, bi- and tri-metallic SPR chips were acquired in phosphate-buffered saline (PBS) solution and were compared. The line width of the reflectance curve of the bi-metallic chip was the narrowest among the three different types of the chips. Also, the tangential slope of the bi-metallic chip was steeper than those of the other chips. Various concentrations of bovine serum albumin (BSA) were utilized in the SPR experiment. As a result, among the above three chips reflectance variation value of the bi-metallic chip was the largest.

• Korean Journal of Dental Materials
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• v.42 no.2
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• pp.95-106
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• 2015

Hardening mechanism associated with post-firing heat treatment of softening heat treated and then firing simulated Pd-Ag-Au alloy for bonding porcelain was examined by observing the change in hardness, crystal structure and microstructure. By post-firing heat treatment of as-cast, solution treated and pre-firing heat treated specimens at $650^{\circ}C$ after casting, the hardness value increased within 10 minutes. Then, hardness consistently increased until 30 minutes, and gap of hardness value among the specimens was reduced. The increase in hardness after post-firing heat treatment was caused by grain interior precipitation in the matrix. The softening heat treatment did not affect the increase in hardness by post-firing heat treatment. The precipitated phase from the parent Pd-Ag-Au-rich ${\alpha}$ phase with face-centered cubic structure by post-firing heat treatment was $Pd_3$(Sn, In) phase with face-centered tetragonal structure, which has lattice parameters of $a_{200}=4.0907{\AA}$, $c_{002}=3.745{\AA}$. From above results, appropriate post-firing heat treatment in order to support the hardness of Pd-Ag-Au metal substructure was expected to bring positive effects to durability of the prosthesis.

• Korean Journal of Dental Materials
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• v.44 no.3
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• pp.197-206
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• 2017

The hardening effect by ice-quenching after oxidation of a Pd-Ag-Sn-Au metal-ceramic alloy during porcelain firing simulation was investigated by means of hardness test, field emission scanning electron microscopic observations, and X-ray diffraction analysis. The hardness decreased by ice-quenching after oxidation, which was induced by the homogenization of the ice-quenched specimen. The decreased hardness by ice-quenching after oxidation was recovered from the wash stage which was the first stage of the remaining firing process for bonding porcelain. After wash stage, the hardness of the ice-quenched specimens decreased during the subsequent porcelain firing process. But the final hardness of the ice-quenched specimens after oxidation was higher than that of the specimens cooled at stage 0 after oxidation. The increase in hardness of the specimens during the first firing process was caused by the lattice strains generated at the interface between the face-centered cubic Pd-Ag-rich matrix and the face-centered tetragonal Pd3(Sn, Ga, In) precipitate. The decrease in hardness of the specimens during the remaining firing process was caused by the microstructural coarsening.

• Journal of the Korean Magnetics Society
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• v.12 no.3
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• pp.94-98
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• 2002

Sputtering conditions and various underlayer such as Al, Cu, Ni, Cr, Ag, Mg, Fe, Co, Pd, Au, Pt, Mo and Hf were investigated for coercivity enhancement of 20 nm Ti/CoCrPt thin films in order to increase the coercivity of the films thinner than 20 nm. Among them, Ag and Mg were effective to increase the coercivity. Particularly 2 nm Ag was very effective to increase the coercivity and nucleation field as well as to reduce ${\alpha}$ value in CoCrPt thin film such that the coercivity of 2 nm Ag/18 nm Ti/10 nm CoCrPt film was 2200 Oe. However, it seemed that other coercivity enhancement mechanism operated in CoCrPt films because Ti (002) preferred texture was not developed with Ag underlayer contrary to a general expectation. And the coercivity and nucleation field were decreased when glass substrate with rougher surface was used.

• Journal of Technologic Dentistry
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• v.31 no.4
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• pp.9-15
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• 2009

The purpose of this study was to observe the change of mechanical property and microstructure in porcelain fused to gold alloy by heat treatment. PFG alloys are composed with Au-Pd-Ag alloy of the additional elements with indium, tin and copper. Specimens were tested in hardness using vicker,s micro-hardness tester and the surface micro structural changes were analysed by SEM and EDS. The results were as fellows: 1. The vickers hardness showed highest in Au-Pd-Ag alloy of the additional element with tin. 2. By hardening-oxiding result, the vicker,s hardness increased in additional element with tin but there was no significant difference in additional elements with indium and copper. 3. The surface oxide layer of Au-Pd-Ag alloy with added indium and tin increased but there was small change in additional element with copper. 4. The elements of indium and tin increased with increasing heat treatment in the surface alloy.

• Economic and Environmental Geology
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• v.27 no.6
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• pp.549-556
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• 1994

Geochemical studies on gold-bearing quartz veins and wallrocks from the Okgye mine were carried out in order to investigate the primary dispersion patterns of gold and associated elements and to quantify the dispersion width of elements with distance from the gold-bearing quartz veins. Gold-bearing quartz veins occur in basaltic trachyandesite of unknown age. Enrichment of $k_2O$, MnO, Au, As, Rb, Sb, Pb, Zn, Cu, Ag and Cd, and depletion of $Na_2O$ and Sr are found in altered wallrocks. The ratio of $k_2O(k_2O+Na_2O)$, alteration index for trace elements, and Rb/Sr in altered wallrocks are increased, whereas Sr/CaO ratio is decreased with approach to the gold-bearing quartz veins. The widths of primary dispersion range from 17 cm to 155 cm. The relative dispersion width increases in order Au=Cu=Zn=Ag=Cd$k_2O$=Rb and Ba< $Na_2O$ $Na_2O$, As, Sb, Sr, Pb, Au, Cu, Zn, Ag and Cd, and a quadratic function for $k_2O$, MnO, Rb and Ba.

• Economic and Environmental Geology
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• v.27 no.6
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• pp.537-548
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• 1994

The Weolyu gold-silver deposits at Hwanggan, Chungcheongbukdo, is of a late Cretaceous $(74.24{\pm}1.63Ma)$ epithermal vein-type, and is hosted in the quartz porphyry of late Cretaceous age. Based on mineral paragenetic sequence interpreted from vein structure and mineral assemblages, three stages mineralization were distinguished. A variety of ore minerals occurs including pyrite, sphalerite, chalcopyrite, galena with small amount of electrum, native silver, argentite, pearceite, sb-pearceite, argyrotite. The gangue minerals are quartz, rutile, calcite, apatite, fluorite and rhodochrocite. Wall-rock alteration such as pyritization, chloritization, sericitization, silicification is observed near the quartz veins. Au-Ag minerals were crystallized at middle and late stage of the two mineralization sequences. Results from the analysis of fluid inclusion and thermodynamic calculation indicate that Au-Ag mineral deposits were formed primarily by cooling and dilution of hydrothermal fluids($165{\sim}313^{\circ}C$, 0.4~2.4wt.% equivalent NaCl) with some degree mixing of meteoric water.

• Journal of Environmental Science International
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• v.29 no.12
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• pp.1171-1184
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• 2020

The green synthesis of inorganic nanoparticles (NPs) using biomaterials has garnered considerable attention in recent years because of its eco-friendly, non-toxic, simple, and low-cost nature. In this study, we synthesized NPs of noble metals, such as Ag and Au using an aqueous extract of a marine seaweed, Ecklonia cava. The formation of AgNPs and AuNPs was confirmed by the presence of surface plasmon resonance peaks in UV-Vis absorption spectra at approximately 430 and 530 nm, respectively. Various properties of the NPs were evaluated using characterization techniques, such as dynamic light scattering, transmission electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction analysis. Phytochemicals in the seaweed extract, such as phlorotannins, acted as both reducing and stabilizing agents for the growth of the NPs. The green-synthesized AgNPs and AuNPs were found to exhibit high catalytic activity for the decomposition of organic dyes, including azo dyes, methylene blue, rhodamine B, and methyl orange.

• Journal of Technologic Dentistry
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• v.45 no.3
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• pp.55-60
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• 2023

Purpose: This study aimed to evaluate the effects of a special heat treatment on Pd-Au-Ag metal-ceramic alloy after degassing treatment and on changes in the hardness of the alloy during the firing process. Methods: Specimen alloys were cast and subjected to degassing at 900℃ for 10 minutes. These specimens were then subjected to a special heat treatment at 600℃ for 15 minutes in a dental porcelain furnace. Further, the specimens were subjected to simulated firing in the porcelain furnace. The resulting specimens were then tested for hardness, and changes in the microstructure were observed. Results: There was a decrease in the hardness of the alloy during the simulated firing of the cast alloy due to the coarsening of the particles. Meanwhile, additional heat treatment after degassing was found to play a crucial role in preventing a decrease in hardness. This treatment effectively suppressed the coarsening of the precipitates during repeated firing at high temperatures. Conclusion: Specific heat treatment of the Pd-Au-Ag metal-ceramic alloy prevented a decrease in its hardness and extended the lifespan of the metal-ceramic prosthesis.