• Journal of the Mineralogical Society of Korea
• /
• v.27 no.3
• /
• pp.115-124
• /
• 2014

In order to leach Au and Ag from gold-silver bearing sulfide concentrate, the sulfide concentrate was ground in a ball mill for a dry pre-treatment and a wet pre-treatment process. Mineralogical studies and thiourea leaching experiments were carried out with the pre-treated sulfide concentrate. The results of the pre-treatment with the concentrate samples showed the mean particle size and iso-electrical potential was smaller in the dry pre-treatment sample than in the concentrate sample, and the contents was lower in the wet pre-treatment sample than in the dry pre-treatment sample. In XRD analysis, amorphous properties were only shown in the wet pretreatment sample. The results of the concentrate sample leaching experiments showed that the best Au, Ag leaching parameters were when the addition of thiourea was at a 1.0 g concentration, ferric sulfate was 1.0 M, sulfuric acid was 2.0 M and the leaching temperature was at $60^{\circ}C$. The Au, Ag leaching rate was always much greater and faster with the wet pre-treatment samples than with the dry pre-treatment samples. Accordingly, it is expected that more Au, Ag can be leached in an eco-friendly methodology using wet pre-treatment. The pre-treatment could be improved with an optimized grinding additive reagent and through researching grinding time in future non-cyanide processes.

• Journal of the Korean Vacuum Society
• /
• v.17 no.1
• /
• pp.51-57
• /
• 2008

we have demonstrated structural evolution and optical properties of Si-nanowires (NWs) synthesized on Si (111) substrates with nanoscale Au-Si islands by rapid thermal chemical vapor deposition (RTCVD). The Au-Si nano-islands (10-50nm in diameter) were employed as a liquid-droplet catalysis to grow Si-NWs via vapor-liquid-solid mechanism. The Si-NWs were grown by a mixture gas of SiH4 and H2 at a pressure of 1.0 Torr and temperatures of $500{\sim}600^{\circ}C$. Scanning electron microscopy measurements showed that the Si-NWs are uniformly sized and vertically well-aligned along <111> direction on Si (111) surfaces. The resulting NWs are ${\sim}60nm$ in average diameter and ${\sim}5um$ in average length. High resolution transmission microscopy measurements indicated that the NWs are single crystals covered with amorphous SiOx layers of ${\sim}3nm$ thickness. In addition, the optical properties of the NWs were investigated by micro-Raman spectroscopy. The downshift and asymmetric broadening of the Si main optical phonon peak were observed in Raman spectra of Si-NWs, which indicates a minute stress effects on Raman spectra due to a slight lattice distortion led by lattice expansion of Si-NW structures.

• Journal of the Mineralogical Society of Korea
• /
• v.32 no.3
• /
• pp.185-200
• /
• 2019

This study aimed to liberate gold from invisible gold concentrate (Au = 1,840.00 g/t) through microwave nitric acid leaching experiments. For the purpose, this study conducted microwave-nitric acid leaching experiments and examined nitric acid concentration effect, microwave leaching time effect and sample addition effect. The results of the experiments were as follows: Au (gold) contents were not detected in all of the microwave leaching conditions. In the insoluble-residue, weight loss rate tended to decrease as the nitric acid concentration, microwave leaching time and sample addition increased. In an XRD analysis with solid-residue, it was suggested that gypsum and anglesite were formed due to dissolution of calcite and galena by nitric acid solution. When a fire assay was carried out with insoluble-residue, it was discovered that gold contents of the solid-residue were 1.3 (Au = 2,464.70 g/t) and 28.8 (52,952.80 g/t) times more than those of concentrate. But in the gold contents recovered, a severe gold nugget effect appeared. It is expected that the gold nugget effect will decrease if a sampling method of concentrate is improved in the microwave-nitric acid leaching experiments and filtering paper with smaller pore size is used for leaching solution and burned filter paper is used for sampling in lead-fire assay.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.588-588
• /
• 2013

Nanoscale noble-metals have attracted enormous attention from researchers in various fields of study because of their unusual optical properties as well as novel chemical properties. They have possible uses in diverse applications such as devices, transistors, optoelectronics, information storages, and energy converters. It is well-known that nanoparticles of noble-metals such as silver and gold show strong absorption bands in the visible region due to their surface-plasmon oscillation modes of conductive electrons. Silver nanocubes stand out from various types of Silver nanostructures (e.g., spheres, rods, bars, belts, and wires) due to their superior performance in a range of applications involvinglocalized surface plasmon resonance, surface-enhanced Raman scattering, and biosensing. In addition, extensive efforts have been devoted to the investigation of Gold-based nanocomposites to achieve high catalytic performances and utilization efficiencies. Furthermore, as the catalytic reactivity of Silver nanostructures depends highly on their morphology, hollow Gold nanoparticles having void interiors may offer additional catalytic advantages due to their increased surface areas. Especially, hollow nanospheres possess structurally tunable features such as shell thickness, interior cavity size, and chemical composition, leading to relatively high surface areas, low densities, and reduced costs compared with their solid counterparts. Thus, hollow-structured noblemetal nanoparticles can be applied to nanometer-sized chemical reactors, efficient catalysts, energy-storage media, and small containers to encapsulate multi-functional active materials. Silver nanocubes dispersed in water have been transformed into Ag@Au nanoboxes, which show highly enhanced catalytic properties, by adding $HAuCl_4$. By using this concept, $SiO_2$-coated Ag@Au nanoboxes have been synthesized via galvanic replacement of $SiO_2$-coated Ag nanocubes. They have lower catalytic ability but more stability than Ag@Au nanoboxes do. Thus, they could be recycled. $SiO_2$-coated Ag@Au nanoboxes have been found to catalyze the degradation of 4-nitrophenol efficiently in the presence of $NaBH_4$. By changing the amount of the added noble metal salt to control the molar ratio Au to Ag, we could tune the catalytic properties of the nanostructures in the reduction of the dyes. The catalytic ability of $SiO_2$-coated Ag@Au nanoboxes has been found to be much more efficient than $SiO_2$-coated Ag nanocubes. Catalytic performances were affected noteworthily by the metals, sizes, and shapes of noble-metal nanostructures.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.60 no.12
• /
• pp.2265-2269
• /
• 2011

1 kV high-voltage GaN Schottky diode is realized using GaN-on-Si template by oxidizing Ni-Schottky contact. The Auger electron spectroscopy (AES) analysis revealed the formation of $NiO_x$ at the top of Schottky contact. The Schottky contact was changed to from Ni/Au to Ni/Ni-Au alloy/Au/$NiO_x$ by oxidation. Ni diffusion into AlGaN improves the Schottky interface and the trap-assisted tunneling current. In addition, the reverse leakage current and the isolation-leakage current are efficiently suppressed by oxidation. The isolation-leakage current was reduced about 3 orders of magnitudes. The reverse leakage current was also decreased from 2.44 A/$cm^2$ to 8.90 mA/$cm^2$ under -100 V-biased condition. The formed group-III oxides ($AlO_x$ and $GaO_x$) during the oxidation is thought to suppress the surface leakage current by passivating surface dangling bonds, N-vacancies and process damages.

• Proceedings of the Korean Society of Applied Pharmacology
• /
• 2005.04a
• /
• pp.5-14
• /
• 2005

Recently, data from several groups have raised the concept of 'checkpoint' in transcription. As capping of nascent RNA transcript is tightly coupled to RNA polymerase II transcription, we seek to obtain direct evidence that transcripiton checkpoint via capping enzyme functions in this early regulatory step. One of temperature sensitive (ts) alleles of ceg1, a guanylyltransferase subunit of the Saccharomyces cerevisiaecapping enzyme, showed 6-azauracil (6AU) sensitivity at the permissive growth temperature, which is a phenotype that is correlated with a transcription elongational defect. This ts allele, ceg1-63 also has an impaired ability to induce PUR5 in response to a 6AU treatment. However, this cellular and molecular defect is not due to the preferential degradation of the transcript attributed from a lack of guanylyltransferase activity. On the contrary, the data suggests that the guanylyltransferase subunit of the capping enzyme plays a role in transcription elongation. First, in addition to the 6AU sensitivity, ceg1-63is synthetically lethal with elongation defective mutations of the largest subunit of RNA polymerase II. Secondly, it exhibited a lower GAL1 mRNA turn-over after glucoseshut off. Third, it decreased the transcription read through a tandem array of promoter proximal pause sites in an orientation dependent manner. Interestingly, this mutant also showed lower pass through a pause site located further downstream of the promoter. Taken together, these results suggest that the capping enzyme plays the role of an early transcription checkpoint possibly in the step of the reversion of repression by stimulating polymerase to escape from the promoter proximal arrest once RNA becomes appropriately capped.

• The Journal of Korean Academy of Prosthodontics
• /
• v.21 no.1
• /
• pp.9-26
• /
• 1983

In order to investigate the biocompatibility of silver-palladium alloys, gingival fibroblast was obtained from a healthy human gingival and cultured in MEM medium with the addition of silverpalladium alloys. Four different mixture of silver-palladium alloys comprising of Ag-Pd-Au, Ag-Pd-In and Ag-Sn were tested. Results were assessed by calculating the cell multiplication rate per millimeter of medium and morphological changes in cells were also observed and noted.The obtained results were as follows; 1. Ag-Pd-Au alloy was indicated to be most biocompatible with gingival fibroblast. Also there was a decrease in cytotoxicity of the alloy as the concentration of gold increased. 2. Ag-Pd alloy showed a decrease in cell multiplication rate as compared to Ag-Pd~Au alloy. 3. Silver-palladium alloy supplemented with Indium increased the cell multiplication rate. 4. Among the alloys tested, Ag-Sn alloy was indicated to be the most cytotoxic and the least biocompatible with human gingival fibroblast.

• The Bulletin of The Korean Astronomical Society
• /
• v.38 no.1
• /
• pp.62.2-62.2
• /
• 2013

It is considered that comets near the ecliptic plane have been injected into inner solar system from Kuiper-belt. Some of them are still active while others are dormant with no detectable tails and comae. These dormant comets have eccentric and/or inclined orbits, which are parameterized by Tisserand parameter TJ<3. In addition, dormant comets can be differentiated from asteroids based on the albedo, because they have low albedo (the geometrical albedos pv<0.1). The conditions of TJ<3 and pv<0.1 have been used as a criteria to discriminate dormant comets from asteroids. However, we must be more careful because there are 'contaminations' from the outer region, i.e. Jovian Trojans (5.05

• Journal of Korean Society of Environmental Engineers
• /
• v.30 no.10
• /
• pp.984-991
• /
• 2008

This paper reports experimental results, demonstrating the feasibility of horseradish peroxidase(HRP) and H$_2$O$_2$ to reduce phenol transport in saturated porous media. A laboratory-scale packed column reactor(ID: 4.1 cm, sand-bed height 12 cm) column was utilized to simulate injection of HRP and H$_2$O$_2$ into an aquifer contaminated with phenol. Effluent concentrations of phenol and polymerization products were monitored before and after enzyme addition under various experimental conditions(enzyme dose: 0$\sim$2 AU/mL, [ionic strength]: 5$\sim$100 mM, pH: 5$\sim$9). The concentration of phenol in the column effluent was found to decrease by nearly 90% in the presence of HRP(2 AU/mL) and H$_2$O$_2$ in the continuous flow system at pH 7 and ionic strength 20 mM. The influent phenol was converted in the system to insoluble precipitate, which deposited in pore spaces. The remains were discharged as soluble oligomers. About 8% of total pore volume in column system was decreased by deposition of polymer produced.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.28 no.4
• /
• pp.435-442
• /
• 2004

This paper presents a hermetic MEMS on-chip package bonded by a closed-loop AuSn solder-line. We design three different package specimens, including a substrate heated specimen without interconnection-line (SHX), a substrate heated specimen with interconnection-line (SHI) and a locally heated specimen with interconnection-line (LHI). Pressurized helium leak test has been carried out for hermetic seal evaluation in addition to the critical pressure test for bonding strength measurement. Substrate heating method (SHX, SHI) requires the bonding time of 40min. at 400min, while local heating method (LHI) requires 4 min. at the heating power of 6.76W. In the hermetic seal test. SHX, SHI and LHI show the leak rates of 5.4$\pm$6.7${\times}$$^{-10}$ mbar-l/s, 13.5$\pm$9.8${\times}$$^{-10}$ mbar-l/s and 18.5$\pm$9.9${\times}$$^{-10}$ mbar-l/s, respectively, for an identical package chamber volume of 6.89$\pm$0.2${\times}$$^{-10}$. In the critical pressure test, no fracture is found in the bonded specimens up to the applied pressure of 1$\pm$0.1MPa, resulting in the minimum bonding strength of 3.53$\pm$0.07MPa. We find that the present on-chip packaging using a closed AuSn solder-line shows strong potential for hermetic MEMS packaging with interconnection-line due to the hermetic seal performance and the shorter bonding time for mass production.