• Proceedings of the IEEK Conference
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• 2001.10a
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• pp.427-431
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• 2001

In this research, porous materials were made from mine's waste slime. As a temperature changes, a phase changes, a porosity, and a mechanical strength of porous materials were observed and measured. The process of pore-formation was observed by SEM according to the change of heat-treatment temperature and time. It fumed out that the foaming reaction of mine's waste slime was resulted from liquid phase by decomposition of the sanidine and the muscovite-3T. When heat- treated at over 120$0^{\circ}C$, it appeared high porosity. And, to activate the foaming reaction, an alkaline oxide concerned with liquid formation was added and its effects were examined.

• Economic and Environmental Geology
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• v.53 no.2
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• pp.159-166
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• 2020

In this research, we investigate the effect of microwave pretreatment on the recovery of gold from the gold concentrates by thiourea leaching. The changes in mineral phases by decomposition of pyrites in the gold concentrates using microwave were observed, and the result of microwave irradiation showed that the temperature of the irradiated sample increases with increasing irradiation time. With the reaction of temperature increases, Sulfur (S) in pyrites was converted to sulfur dioxide (SO₂), and then the content of S in the sample was reduced. The analytical results of XRD and SEM-EDS showed that pyrites are converted to magnetite and hematite, and its surfaces are changed to a porous shape where micro-cracks are developed. The Au leaching efficiency from the irradiated gold concentrates using thiourea-mixed solvent increased with the increases of irradiation time and solvent concentration. The experimental results considering leaching parameters indicate that the mechanism of microwave irradiation increases the maximum leaching efficiency and leaching rate of the gold concentrates, and the solvent does a role for the increasing of leaching rate constant.

• Geomechanics and Engineering
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• v.5 no.6
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• pp.595-611
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• 2013

This paper presents a three-dimensional (3D) integrated numerical model where the wave-induced pore pressures in a porous seabed around breakwater heads were investigated. Unlike previous research, the Navier-Stokes equation is solved with internal wave generation for the flow model, while Biot's dynamic seabed behaviour is considered in the seabed model. With the present model, a parametric study was conducted to examine the effects of wave and soil characteristics and breakwater configuration on the wave-induced pore pressure around breakwater heads. Based on numerical examples, it was found that the wave-induced pore pressures at breakwater heads are greater than that beneath a breakwater. The wave-induced seabed response around breakwater heads become more important with: (i) a longer wave period; (ii) a seabed with higher permeability and degree of saturation; and (iii) larger angle between the incident waves and breakwater. Furthermore, the relative difference of wave-induced pore pressure between fully-dynamic and quasi-static solutions are larger at breakwater heads than that beneath a breakwater.

• Korean Journal of Materials Research
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• v.5 no.6
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• pp.673-681
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• 1995

Surface morphology and preferred orientation of 20${\mu}{\textrm}{m}$ gold electrodeposit formed from aqueous solution of the sodium gold sulfite were studied in terms of current density, plating temperature and Au concentration. As the current density changed from 13.0mA/$\textrm{cm}^2$ to 4.6mA/$\textrm{cm}^2$, the solution temperature from 3$0^{\circ}C$ to 6$0^{\circ}C$, pH from 12.0 to 9.0, agitation speed from 0 rpm to 3200rpm and Au concentration from 10g/1 to 14 g/1, local Au concentration near the cathodic surface increased. With increasing the Au concentration, the surface morphology chanced from porous structure to fine-grained structure. Furthermore, it was observed that the preferred orentation of the Au layer changed from (111) to (220) upon the same variation In the Au concentration. The surface morphology and the preferred orientation of the Au layer were found to be closely related to each other.

• Journal of the Korean institute of surface engineering
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• v.54 no.1
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• pp.1-11
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• 2021

Porous dendrite structure AuCu alloy was formed using a hydrogen bubble template (HBT) technique by electroplating to improve the catalytic performance of gold, known as an excellent oxygen reduction reaction (ORR) catalyst in alkaline medium. The rich Au surface was maximized by selectively electrochemical etching Cu on the AuCu dendrite surface well formed in a leaf shape. The catalytic activity is mainly due to the synergistic effect of Au and Cu existing on the surface and inside of the particle. Au helps desorption of OH- and Cu contributes to the activation of O2 molecule. Therefore, the porous AuCu dendrite alloy catalyst showed markedly improved catalytic activity compared to the monometallic system. The porous structure AuCu formed by the hydrogen bubble template was able to control the size of the pores according to the formation time and applied current. In addition, the Au-rich surface area increased by selectively removing Cu through electrochemical etching was measured using an electrochemical calculation method (ECSA). The results of this study suggest that the alloying of porous AuCu dendrites and selective Cu dissolution treatment induces an internal alloying effect and a large specific surface area to improve catalyst performance.

• Analytical Science and Technology
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• v.33 no.3
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• pp.159-166
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• 2020

Vacuum metal deposition (VMD) is effective to develop latent fingerprints on non-porous and semi-porous surfaces. VMD can be used in cases when fingerprints that can not be developed by generalized techniques or deposited on difficult surfaces. The recommended surfaces for VMD techniques include vinyl, polymer bills, magnetic coated tickets, etc. In this study, the minimum amount of gold input was explored for developing fingerprints from at least 12 hours to up to 28 days after deposit fingerprint on the pink high density polyethylene envelope (HDPE) and low density polyethylene envelope (LDPE), which are mainly used as delivery envelopes. And the results were compared with the effects of black powder and fluorescent powder. In addition, delivery envelopes used for delivery were collected, then classified as HDPE and LDPE and pseudo-operation test was performed. As a result, VMD method developed good quality of fingerprints.

• Journal of the Microelectronics and Packaging Society
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• v.11 no.2 s.31
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• pp.11-16
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• 2004

Electronic devices are getting smaller due to integration of electronic chip, and heat generated in electronic devices can cause loss of performance and/or reliability of the devices. In this research, metals such as gold, nickel and copper are plated onto a porous membrane by electroless plating method to make an efficient micro-heatsinks. Electroless plating includes sensitization and activation steps in pre-treatment steps. A polycarbonate(PC) membrane was sensitizied, activated and deposited in each metal solution for plating. Among manufactured microfibrils, heat transfer and radiation properties of Ni-microfibril with high surface area were more effective than those of $Au^-$ and Cu-microfibril.

• Composites Research
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• v.32 no.2
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• pp.85-89
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• 2019

The size, morphology and composition of nanoparticles are regarded as the most important factors to the efficiency of catalytic reduction of various chemical compounds. In order to make a systematic comparison, gold, platinum and palladium nanoplates with 100 nm diameter with rough surface morphology were manufactured through the galvanic replacement reaction, and the reaction kinetics of the catalytic reduction of 4-nitrophenol and 4-nitroaniline was systematically analyzed by spectroscopic measurement. According to the observation, the catalytic reduction efficiency was significantly different against the constitutional elements in order of Pd > Au > Pt, and it was additionally influenced by the type of substrate.

• Journal of the Korean Electrochemical Society
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• v.3 no.1
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• pp.49-56
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• 2000

In the present we.k, temperature dependence of oxygen diffusivity in the polyvinyl chloride (PVC) film $D_f$ formed on gold electrode was investigated using steady-state rotating disk electrode (RDE) technique and modulated electrohydrodynamic (EHD) impedance technique. Both the diffusion rate defined as the ratio of oxygen diffusivity in the PVC film to the film thickness $D_f/\delta_f$ and the time constant $\delta_f^2/D_f$ for oxygen diffusion through the PVC film were obtained from plot of the limiting current versus disk rotation speed and from filing the EHD impedance spectra experimentally measured to those theoretically calculated on the basis of the diffusion equation for mass transport through the non-conductive and porous film, respectively. By combining measured $D_f/\delta_f$ with $\delta_f^2/D_f$, we determined $\delta_f\;and\;D_f$ at room temperature separately. As temperature increased, it appeared that the $D_f$ value measured for the PVC film-covered gold RDE was enhanced more rapidly than that $D_s$ value in the solution measured for the PVC film-free gold RDE. This means that the pores glowing with increasing temperature act as effective diffusion paths within the film. The present in-situ steady-state and modulated EHD measurements prove to be effective for determining $\delta_f\;and\;D_f$, separately and at the same time the porosity of the PVC film at temperatures below glass temperature $T_g$ of the film.

• Analytical Science and Technology
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• v.7 no.3
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• pp.371-378
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• 1994

The detection range of this galvanic oxygen sensor for oxygen concentration was 0.0% to 20.0%. By using gold or silver as cathode, reproducible response time and sensitivity to change of oxygen concentration were observed. The anode was Pb-Sn-Ca alloy. Oxygen selective permeable membrane was hydrophobic and porous Teflon film. The effect of the membranes varying in thickness have been studied on the temperature($10{\sim}50^{\circ}C$) and relative humidity(R. H 0~99%). Lead acetate buffer solution as the electrolyte has shown a high output voltage and longer life.