• Korean Journal of Metals and Materials
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• v.50 no.11
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• pp.823-828
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• 2012

Direct reduction of $Ta_2O_5$ using liquid calcium was investigated. The experiment was conducted in a closed stainless steel chamber in an Ar atmosphere for 5-120 minutes. Most of $Ta_2O_5$ was reduced to ${\alpha}-Ta$ in 30 minutes above 1173 K and at a molar ratio of Ca and $Ta_2O_5$ above 10. The particles size increased with the reaction temperature, but it did not change much above 1223 K. The oxygen content of metal Ta was about 1 wt%.

• Journal of Magnetics
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• v.18 no.3
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• pp.365-369
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• 2013

Coal ash is known to contain a noticeable amount of valuable elements, including transition metals and lanthanides. Therefore it is quite actual problem to extract them for metallurgy and other applications. This paper presents the results of high gradient magnetic and mechanical separation, microscopy, element analyses and optical spectroscopy of brown coal ash taken from the combustion camera and chimney-stalk of Angren thermal power station. The separated magnetic fraction was 3.4 wt.%, where the content of Fe in ferrospheres increased to 58 wt.%. The highest contents of Fe and rare earth elements were found in the fine fractions of $50-100{\mu}m$. Optical absorption spectroscopy of water solutions of the magnetic fractions revealed $Fe^{2+}$ and $Fe^{3+}$ ions in the ratio of ~1:1. The separated coal ash could be used for cleaning of technological liquid waste by means of the high gradient magnetic field.

• Korean Journal of Metals and Materials
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• v.46 no.2
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• pp.97-104
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• 2008

Black interlayer was introduced into between ITO and Bus electrodes to enhance a bright room contrast ratio of a plasma display panel. To measure the electrical resistance of the black interlayer, we designed two test patterns, type I and type II, of which type II pattern was successful. Using type II test pattern, the electrical resistance of the black interlayer was measured to be $300{\Omega}$ for $2{\mu}m$ thickness case and infinitely high for 4, $6{\mu}m$ thickness. This result shows that electrical resistance of the black interlayer in the ITO/black interlayer/Bus electrodes structure is a critical parameter which determines the electrical characteristics of the PDP.

• Korean Journal of Metals and Materials
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• v.49 no.3
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• pp.256-263
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• 2011

We have synthesized Al-Co/AlN-Co multilayer films with different layer thicknesses by using a Two-Facing Target Type dc Sputtering (TFTS) system. The deposited films were annealed isothermally at different temperatures and their microstructure, magnetic properties and resistivity were investigated. The magnetization of the as-deposited films was found to be very small, irrespective of layer thickness. It was found that the annealing conditions and layer thickness ratio of Al-Co to AlN-Co (LTR) were able to control the microstructure, as well as the physical properties of the prepared films. The resistivity and magnetization increased and the coercivity decreased with a decreasing LTR. A high resistivity of 2500 ${\mu}{\Omega}-cm$, a magnetization of 360 $emu/cm^3$, and a coercivity of 5 Oe were obtained for the films with LTR=0.175.

• Korean Journal of Metals and Materials
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• v.47 no.5
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• pp.290-296
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• 2009

We report on the effects of mixing of powders with various particle sizes on fracture toughness and wear resistance of thermally sprayed WC-10Co-4Cr coating layers fabricated by HVOF (high-velocity oxygen fuel) process. The size and the mixing ratio of powders were changed in order to get high fracture toughness and wear resistance. The mixing of small amount of coarse powders with fine powders resulted in the highest fracture toughness and wear resistance due to the lowest porosity in coating layers.

• Bulletin of the Society of Naval Architects of Korea
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• v.21 no.4
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• pp.1-9
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• 1984

This study is concerned with the economic aspects of $125,000m^3$ class LNG carriers with different propulsion plant such as conventional steam turbine and slow speed diesel engine with reliquefaction plant. The ship's speed and L/B ratio were optimized with criterion of required freight rate(RFR) by using the PROCAL computer program package. In order to investigate the effect of fuel oil price, round trip distance and boil-off rate on the RFR and the optimum speed, sensitivity analysis were also performed.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.187-188
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• 2002

Rubber has large differences in elastic characteristics from the other solid materials such as metals. Firstly, the rubber exhibits considerably large elastic compliance. Second is highly non-linear elasticity in which the compliance decreases with increase in strain. The main objective in this research is to reveal the dependence of rubber friction upon these elastic characteristics of the rubber in detail. A super elastic FEM analysis is carried out with using an elastic property of practical rubber. From the calculated result, it is cleared that the rubber makes large real contacting area easier than the metals.

• Journal of Soil and Groundwater Environment
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• v.18 no.1
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• pp.102-111
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• 2013

A novel MgO-based binder was developed and applied to treat the anoxic sediment that was collected from Seonakdong river, Korea and was contaminated with heavy metals. The treated sediment was evaluated by measuring compressive strength, expansion, leaching of heavy metals and storage characteristics for $CO_2$. Initially, an optimal blending ratio of lime (L)/fly ash (FA)/blast furnace slag (BFS) that was to be mixed with MgO was screened to be $L_{0.3}-FA_{0.1}-BFS_{0.6}$. Long-term strengths of the sediments that were treated by various mixtures of MgO and $L_{0.3}-FA_{0.1}-BFS_{0.6}$ were then evaluated and the blending ratios between 4 : 6 and 6 : 4 were found optimal, which yielded a compressive strength of 4.09 MPa. On this basis, the optimal MgO-based binder was selected to be a 5 : 5 mixture of MgO and $L_{0.3}-FA_{0.1}-BFS_{0.6}$. The good performance of the MgO-based binder was believed to be due to the formation of Mg $(OH)_2$, which filled the micropores and also increased the density of the solidified matrices. The MgO-based binder exhibited an average stabilizing capacities for heavy metals of 92.9%, which was similar to or higher than that of Portland cement. It was found that 69.1 kg of carbon dioxide could be sequestrated after 365 days of curing when treating a ton of anoxic sediments.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.2
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• pp.105-118
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• 2008

The newly developed analysis method for nanoindentation load-displacement curves are focused on not only obtaining elastic modulus and hardness values but also other mechanical properties, such as yield strength and strain hardening properties. Dao et al. developed a forward and reverse algorithm to extract the elasto-plastic properties of materials from the load-displacement curves obtained in nanoindentation test. These algorithms were only applicable for engineering metals (Poisson#s ratio 0.3) using the equivalent conical indenter of the Berkovich. However, the applicable metals are substantially limited because range of used in the finite element analysis is narrow. This study is designed to expand range of the applicable metals in the reverse algorithms established by Dao et al. and to improve the accuracy of that for extracting the elasto-plastic properties of materials. In this study, a representative strain was assumed to vary according to specific range of $E^*/{\sigma}_r$ and was defined as function of $E^*/{\sigma}_r$. Also, an initial unloading slope in reverse algorithms improved in this study was not considered as independent parameters of the load-displacement curves. The mechanical properties of materials for finite element analysis were modeled with the elastic modulus, E, the yield strength, ${\sigma}_y$, and the strain hardening exponents, n. We showed that the representative strain (0.033) suggested by Dao et al. was no longer applicable above the $E^*/{\sigma}_r$ of 400 and depended on values of $E^*/{\sigma}_r$. From these results, we constructed the dimensionless functions, in where the initial unloading slope was not included, for engineering metals up to $E^*/{\sigma}_r$ of 1500. These functions allow us to determine the mechanical properties with greater accuracy than Dao#s study.

• Economic and Environmental Geology
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• v.37 no.3
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• pp.311-324
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• 2004

We investigated the contamination and behavior of heavy metals in stream sediments within the watershed of Juam Reservoir. Many abandoned mines within the reservoir can act as a potential contaminant source for water quality. Heavy metal concentrations (Cr, Cu, Ni, Pb and Zn) in stream sediments from watershed are very low, indicating that content of heavy metals in the sediments probably do not affect the water quality in Juam Reservoir. However Pb concentration in the stream sediments increases downward streams, suggesting the possible diffusion of Pb contamination. According to the leaching ratio for stream sediments at a strong acidic condition in the abandoned mine areas, the relative mobility for metals decreases in the order of Pb＞Zn=Cu＞Ni＞Cr, indicating that Pb can have a bad effect upon the water quality in Jum Reservoir. Moreover, if contaminated sediment is placed in the bottom of reservoir (i.e., reducing condition), the relative mobility of Pb is the highest, indicating that Pb in the bottom sediments can be leached to water at interface between water and sediment with changing in physicochemical conditions.