• Resources Recycling
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• v.20 no.4
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• pp.58-64
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• 2011

Recovery of novel metals such as Au, Ag and Ni from wastes PCB was investigated by slag treatments. The CaO-$Al_2O_3$(-$SiO_2$) and CaO-$SiO_2$-$CaF_2$ slags were employed in the present study. The PCB/Cu ratio is recommended to be lower than unity. The use of CaO-$SiO_2$-$CaF_2$ slag provided the more higher yield of Au, Ag and Ni than the CaO-$Al_2O_3$(-$SiO_2$) slag did, which was mainly due to the lower melting point and the viscosity of $CaF_2$-containing slag. The terminal descending velocity of metal droplets in the slag phase increased with decreasing slag viscosity.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.515-517
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• 2003

In order to assess the risk of adverse health effects on human exposure to arsenic and heavy metals influenced by past mining activities, environmental geochemical surveys were undertaken in the abandoned metal mine areas (Dongil Au-Ag-Cu-Zn, Okdong Cu-Pb-Zn, Songcheon Au-Ag, Dongjung Au-Ag-Pb-Zn, Dokok Au-Ag-Cu and Hwacheon Au-Ag-Pb-Zn mines). Arsenic and other heavy metals were highly elevated in the tailings from the Dongil, the Songcheon and the Dongjung mines. High concentrations of heavy metals except As were also found in tailings from the Okdong, the Dokok and the Hwacheon mines. These significant concentrations can impact on soils and waters around the tailing dumps. Risk compounds deriving from mine sites either constitute a toxic risk or a carcinogenic risk. The hazard index (H.I.) of As in the Dongil, the Okdong, the Songcheon and the Hwacheon mine areas was higher value more than 1.0. In the Okdong and the Songcheon mine areas, H.I. value of Cd exceeded 1.0. These values of As and Cd were the highest in the Songcheon mine area. Therefore, toxic risks for As and Cd exist via exposure (ingestion) of contaminated soil, groundwater and rice grain in these mine areas. The cancer risk for As in stream or ground water used for drinking water from the Songcheon, the Dongil, the Okdong, the Dongjung and the Hwacheon mine areas was 3E-3, 8E-4, 7E-4, 2E-4 and 1E-4, respectively.

• Journal of Technologic Dentistry
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• v.34 no.4
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• pp.345-352
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• 2012

Purpose: The age-hardening mechanism of an Au-Ag-Cu-Pt-Zn alloy for crown and bridge fabrication was investigated by means of hardness test, X-ray diffraction study and field emission scanning electron microscopic observation. Methods: Before hardness testing, the specimens were solution treated and then were rapidly quenched into ice brine, and were subsequently aged isothermally at $400-450^{\circ}C$ for various periods of time in a molten salt bath and then quenched into ice brain. Hardness measurements were made using a Vickers microhardness tester. The specimens were examined at 15 kV using a field emission scanning electron microscope. Results: By the isothermal aging of the solution-treated specimen at $450^{\circ}C$, the hardness increased rapidly in the early stage of aging process and reached a maximum hardness value. After that, the hardness decreased slowly with prolonged aging. However, the relatively high hardness value was obtained even with 20,000 min aging. By aging the solution-treated specimen, the f.c.c. Au-Ag-rich ${\alpha}_0$ phase was transformed into the Au-Ag-rich ${\alpha}_1$ phase and the AuCu I ordered phase. Conclusion: The hardness increase in the early stage of aging process was attributed to the formation of lattice strains by the precipitation of the Cu-rich phase and then subsequent ordering into the AuCu I-type phase. The decrease in hardness in the later stage of aging process was due to the release of coherency strains by the coarsening of tweed structure in the grain interior and by the growth and coarsening of the lamellar structure in the grain boundary. The increase of inter-lamellar space contributed slightly to the softening compared to the growth of lamellar structure toward the grain interior.

• Resources Recycling
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• v.10 no.5
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• pp.29-35
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• 2001

This study was carried out to recover gold, silver and valuable metals from the printed circuit boards (PCBs) of waste computers. PCBs samples were crushed under 1 mm by a shredder and separated into 30% conducting and loft nonconducting materials by an electrostatic separator. The conducting materials contained valuable metals which were then used as feed materials for magnetic separation. 42% of magnetic materials from the conducting materials was removed by magnetic separation as nonvaluable materials and the others, 58% of non magnetic materials, was used as leaching samples containing 0.227 mg/g Au and 0.697 mg/g Ag. Using the materials of leaching from magnetic separation, more than 95% of copper, iron, zinc, nickel and aluminium was dissolved in 2.0M sulfuric acid solution, added with 0.2M hydrogen peroxide at $85^{\circ}C$. Au and Ag were not extracted in this solution. On the other hand, more than 95% of gold and 100% of silver were leached by the selective leaching with a mixed solvent (0.2M($NH_4$)$_2$$S_2$$O_3$,0.02M $CuSO_4$,0.4M $NH_4$OH). Finally, the residues were reacted with a NaCl solution to leach Pb whereas sulfuric acid was used to leach Sn. Recoveries reached 95% and 98% in solution, respectively.

• Journal of the Microelectronics and Packaging Society
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• v.22 no.3
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• pp.39-44
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• 2015

We investigated the effect of CNT-Ag composite pad on the contact resistance of flip-chip joints, which were formed by flip-chip bonding of Cu/Au chip bumps to Cu substrate metallization using anisotropic conductive adhesive. Lower contact resistances were obtained for the flip-chip joints which contained the CNT-Ag composite pad than the joints without the CNT-Ag composite pad. While the flip-chip joints with the CNT-Ag composite pad exhibited average contact resistances of $164m{\Omega}$, $141m{\Omega}$, and $132m{\Omega}$ at bonding pressures of 25 MPa, 50 MPa, and 100 MPa, the flip-chip joints without the CNT-Ag composite pad had an average contact resistance of $200m{\Omega}$, $150m{\Omega}$, and $140m{\Omega}$ at each bonding pressure.

• Proceedings of the Korean Magnestics Society Conference
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• 2004.12a
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• pp.56-57
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• 2004

• Journal of the Microelectronics and Packaging Society
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• v.20 no.2
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• pp.59-64
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• 2013

In-situ annealing tests of Cu/Ni/Au/Sn-Ag/Cu micro-bump for 3D IC package were performed in an scanning electron microscope chamber at $135-170^{\circ}C$ in order to investigate the growth kinetics of intermetallic compound (IMC). The IMC growth behaviors of both $Cu_3Sn$ and $(Cu,Ni,Au)_6Sn_5$ follow linear relationship with the square root of the annealing time, which could be understood by the dominant diffusion mechanism. Two IMC phases with slightly different compositions, that is, $(Cu,Au^a)_6Sn_5$ and $(Cu,Au^b)_6Sn_5$ formed at Cu/solder interface after bonding and grew with increased annealing time. By the way, $Cu_3Sn$ and $(Cu,Au^b)_6Sn_5$ phases formed at the interfaces between $(Cu,Ni,Au)_6Sn_5$ and Ni/Sn, respectively, and both grew with increased annealing time. The activation energies for $Cu_3Sn$ and $(Cu,Ni,Au)_6Sn_5$ IMC growths during annealing were 0.69 and 0.84 eV, respectively, where Ni layer seems to serve as diffusion barrier for extensive Cu-Sn IMC formation which is expected to contribute to the improvement of electrical reliability of micro-bump.

• Journal of the Korean Chemical Society
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• v.53 no.4
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• pp.399-406
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• 2009

The fluorescence study was performed to see whether the adsorption orientation of 4-biphenyl acetonitrile(BPAN) on metal colloids can be changed by forming an inclusion complex with $\alpha$-cyclodextrin($\alpha$-CD). The fluorescence quenching was observed with increasing temperature to confirm the direct adsorption of BPAN to the Au and Ag colloidal surfaces. BPAN adsorbed on the metal colloids formed inclusion complex with $\alpha$-CD regardless of the kinds of metal colloids. The formation constants, 32 $M^{-1}$ and 13 $M^{-1}$ for Au and Ag colloids respectively, were obtained with Benesi-Hildebrand plot. The molecules adsorbed on both the Au and Ag colloidal surfaces behaved similarly to each other, leading to the conclusion that the orientation of BPAN adsorbed on the metal colloids can be modified with $\alpha$-CD.

• The Journal of Advanced Prosthodontics
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• v.7 no.5
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• pp.392-399
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• 2015

PURPOSE. The aim of this study was to evaluate the effect of metal primers on the bonding of dental alloys and veneer resin. Polyvinylpyrrolidone solution's tarnish effect on bonding strength was also investigated. MATERIALS AND METHODS. Disk-shape metal specimens (diameter 8 mm, thickness 1.5 mm) were made from 3 kinds of alloy (Co-Cr, Ti and Au-Ag-Pd alloy) and divided into 4 groups per each alloy. Half specimens (n=12 per group) in tarnished group were immersed into polyvinylpyrrolidone solution for 24 hours. In Co-Cr and Ti-alloy, Alloy Primer (MDP + VBATDT) and MAC-Bond II (MAC-10) were applied, while Alloy Primer and V-Primer (VBATDT) were applied to Au-Ag-Pd alloys. After surface treatment, veneering composite resin were applied and shear bond strength test were conducted. RESULTS. Alloy Primer showed higher shear bond strength than MAC-Bond II in Co-Cr alloys and Au-Ag-Pd alloy (P<.05). However, in Ti alloy, there was no significant difference between Alloy Primer and MAC-Bond II. Tarnished Co-Cr and Au-Ag-Pd alloy surfaces presented significantly decreased shear bond strength. CONCLUSION. Combined use of MDP and VBATDT were effective in bonding of the resin to Co-Cr and Au-Ag-Pd alloy. Tarnish using polyvinylpyrrolidone solution negatively affected on the bonding of veneer resin to Co-Cr and Au-Ag-Pd alloys.

• Journal of the Korean Association of Geographic Information Studies
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• v.13 no.3
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• pp.1-13
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• 2010

The aim of this study is to analyze gold-silver mineral potential in the Taebaeksan mineralized district, Korea using a Geographic Information System(GIS) and an artificial neural network(ANN) model. A spatial database considering Au and Ag deposit, geology, fault structure and geochemical data of As, Cu, Mo, Ni, Pb and Zn was constructed for the study area using the GIS. The 46 Au and Ag mineral deposits were randomly divided into a training set to analyze mineral potential using ANN and a test set to verify mineral potential map. In the ANN model, training sets for areas with mineral deposits and without them were selected randomly from the lower 10% areas of the mineral potential index derived from existing mineral deposits using likelihood ratio. To support the reliability of the Au-Ag mineral potential map, some of rock samples were selected in the upper 5% areas of the mineral potential index without known deposits and analyzed for Au, Ag, As, Cu, Pb and Zn. As the result, No. 4 of sample exhibited more enrichments of all elements than the others.