• Transactions of the Korean hydrogen and new energy society
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• v.24 no.5
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• pp.367-372
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• 2013

Hydrogen storage as a metal hydride is the most promising alternative because of its relatively large hydrogen storage capacities near room temperature. TiMn2-based C14 Laves phases alloys are one of the promising hydrogen storage materials with easy activation, good hydriding-dehydriding kinetics, high hydrogen storage capacity and relatively low cost. In this work, multi-component, hyper-stoichiometric $Ti_{0.85}Zr_{0.13}(Fe_x-V)_{0.56}Mn_{1.47}Ni_{0.05}$ C14 Laves phase alloys were prepared by a vacuum induction melting for a hydrogen storage tank. Since pure vanadium (V) is quite expensive, the substitution of the V element in these alloys has been tried and some interesting results were achieved by replacing V by commercial ferrovanadium (FeV) raw material. In addition, the melt-spinning process, which was applied to the manufacturing of some of these alloys, could make the plateau slopes much flatter, which resulted in the increase of reversible hydrogen storage capacity. The improvement of sloping properties of melt-spun $Ti_{0.85}Zr_{0.13}(Fe_x-V)_{0.56}Mn_{1.47}Ni_{0.05}$ alloys was mainly attributed to the homogeneity of chemical composition.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.10
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• pp.665-670
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• 2016

Prevailing dissemination of machine tools and cutting technology have caused drastic developments of high speed dry machining with work materials of high hardness, and demands on the high-hardness-materials with high efficiency have become increasingly important in terms of productivity, cost reduction, as well as environment-friendly issue. Addition of Si to TiAlN has been known to form nano-composite coating with higher hardness of over 30 GPa and oxidation temperature over $1,000^{\circ}C$. However, it is not easy to add Si to TiAlN by using conventional PVD technologies. Therefore, Ti-Al-Si-N have been prepared by hybrid process of PVD with multiple target sources or PVD combined with PECVD of Si source gas. In this study, a single composite target of Ti-Al-Si was prepared by powder metallurgy of MA (mechanical alloying) and SPS (spark plasma sintering). Properties of he resulting alloying targets were examined. They revealed a microstructure with micro-sized grain of about $1{\sim}5{\mu}m$, and all the elements were distributed homogeneously in the alloying target. Hardness of the Ti-Al-Si-N target was about 1,127 Hv. Thin films of Ti-Al-Si-N were prepared by unbalanced magnetron sputtering method by using the home-made Ti-Al-Si alloying target. Composition of the resulting thin film of Ti-Al-Si-N was almost the same with that of the target. The thin film of Ti-Al-Si-N showed a hardness of 35 GPa and friction coefficient of 0.66.

• The Journal of Advanced Prosthodontics
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• v.6 no.4
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• pp.266-271
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• 2014

PURPOSE. The purpose of this study was to compare the fracture strength of the metal and the bond strength in metal-ceramic restorations produced by selective laser sintering (SLS) and by conventional casting (CAST). MATERIALS AND METHODS. Non-precious alloy (StarLoy C, DeguDent, Hanau, Germany) was used in CAST group and metal powder (SP2, EOS GmbH, Munich, Germany) in SLS group. Metal specimens in the form of sheets ($25.0{\times}3.0{\times}0.5mm$) were produced in accordance with ISO 9693:1999 standards (n=30). To measure the bond strength, ceramic was fired on a metal specimen and then three-point bending test was performed. In addition, the metal fracture strength was measured by continuing the application of the load. The values were statistically analyzed by performing independent t-tests (${\alpha}=.05$). RESULTS. The mean bond strength of the SLS group (50.60 MPa) was higher than that of the CAST group (46.29 MPa), but there was no statistically significant difference. The metal fracture strength of the SLS group (1087.2 MPa) was lower than that of the CAST group (2399.1 MPa), and this difference was statistically significant. CONCLUSION. In conclusion the balling phenomenon and the gap formation of the SLS process may increase the metal-ceramic bond strength.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.2
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• pp.95-101
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• 2003

In this paper, partial discharges(PDs), lift off and breakdown voltage were measured when metal particles existed in a model GIS coated with epoxy resin on its bottom electrode, and the measured results were analyzed after comparing with the model DIS not coated. In order to presume the various fault case in GIS, we measured the experimental values with changing some experimental factors, such as the mixture ratio of SF$\_$6//N$_2$, the pressure of the gases, the kinds and diameter of the metal particles, and the coating thickness of the epoxy resin. As a result, the PDIV increased with the thickness of the epoxy resin, while the magnitude of PDs decreased at the same condition. The lift off voltages of steel alloy particles were higher than that of copper particles, and increased wit diameter of particles. Futhermore, the lift off voltages in the case of the electrode coated with epoxy resin were higher than that in the case of the uncoated one. In addition, the thicker the thickness of the epoxy resin was, the higher the breakdown voltage were. Thus, it was confirmed that the GIS coated with epoxy resin on its inner surface could be improved in insulation performance.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.9
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• pp.1159-1168
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• 2013

In pressurized water nuclear reactors (PWRs), the reactor pressure vessel (RPV) upper head contains penetration nozzles that use a control rod drive mechanism (CRDM). The penetration nozzle uses J-groove weld geometry. Recently, the occurrence of cracking in alloy 600 CRDM penetration nozzle has increased. This is attributable to primary water stress corrosion cracking (PWSCC). PWSCC is known to be susceptible to the welding residual stress and operational stress. Generally, the tensile residual stress is the main factor contributing to crack growth. Therefore, this study investigates the effect on weld residual stress through different analysis methods for normal operating conditions using finite element analysis. In addition, this study also considers the effect of repeated normal operating condition cycles on the weld residual stress. Based on the analysis result, this paper presents a normal operating condition analysis method.

• Journal of Oral Medicine and Pain
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• v.39 no.3
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• pp.90-95
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• 2014

Purpose: To investigate viscosity and wettability of hyaluronic acid (HA) solutions according to supplementation of lysozyme and/or peroxidase, and different ionic strength and pH conditions. Methods: Solutions containing HA were prepared using distilled deionized water (DDW) and simulated salivary buffer (SSB) in different conditions. Different concentrations of hen egg-white lysozyme and bovine lactoperoxidase was added into HA solutions. HA solutions with antimicrobials in different ionic strength and pH conditions were prepared. Viscosity was measured using cone-and-plate digital viscometer at six different shear rates and wettability on acrylic resin and Co-Cr alloy was determined by contact angle. Results: The viscosity values of HA dissolved in DDW were decreased in order of HA, HA containing lysozyme, HA containing peroxidase, and HA containing lysozyme and peroxidase. The viscosity values for HA in DDW were decreased as the concentration of lysozyme and/or peroxidase increased. However, the viscosity values for HA in SSB showed no significant changes according to the concentration of lysozyme and/or peroxidase. The viscosity values of HA solutions were inversely proportional to ionic strength and pH. The contact angle of HA solutions showed no significant differences according to tested surface materials, addition of lysozyme and/or peroxidase, and different ionic strength and pH conditions. Contact angles on acrylic resin by HA solutions in all tested conditions were much higher than those by human saliva. Conclusions: The rheological properties of HA supplemented with lysozyme and/or peroxidase in different ionic strength and pH conditions were objectively confirmed, indicating the possibility of HA with lysozyme and/or peroxidase as main components in the development of effective saliva substitutes.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.155-155
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• 2017

Surface modifications are commonly utilized to adjust the properties of the titanium and its alloy surface to the specific needs of the medical applications, but there are disadvantages such as poor osteoconductive properties and low adhesion of bone cell to implant surface. In order to improve these disadvantages, changes in surface properties have an important effect on osseointegration during implantation. In this paper we applied new technological method for improving a unique surface modification using the characteristic of an electrolytic Solution. Thus, in the electrolyte containing NaF in Na2SO4, TiO2 nanoporous was uniformly formed, and HAp nanoparticles were electrodeposited around the TiO2 nanopores, but in the electrolyte containing NH4F in (NH4)H2PO4, the coarse protrusions including HAp nano particles were regularly deposited onto the TiO2 barrier layer. The surface characteristics and the distributed elements and have been investigated by EDS analysis, and ultra-fine structure of surface are carried out using FE-SEM. To investigate the behavior of the anion, the analysis of chemical states was performed by XPS, and the narrow spectrums for Ti2P, Ca 2p, and P 2p seems to be almost similar depending on the characteristics of the electrolyte solution respectively. In addition, Ca 2p spectrum could be resolved into two peaks for Ca 2p3/2 and 2p1/2 at 347.4 and 351.3 eV, which are related to hydroxyapatite. And, the P peak can also be deconvoluted into two peaks for P1/2 and P3/2 levels with binding energy 134.2 and 133.4 eV, respectively. From the result of soaking test, the apatite morphologys were well-formed onto the modified surface according to the different conditions.

• Progress in Superconductivity
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• v.1 no.1
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• pp.61-67
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• 1999

We evaluated the effect of alloying element additions to Ag sheath on mechanical, electrical and thermal properties of Bi-2223. Additions of Au, Pd and Mg to Ag sheath increased hardness and strength, while reduced elongation and electrical and thermal conductivity. In addition, microstructural investigation showed that the grain size of Ag significantly decreased with increasing content of alloying elements. The improvements in strength and hardness are believed to be due to the presence of alloying elements that lead to strengthen materials by combined effects of solid-solution, dispersion hardening and grain size hardening. Thermal conductivity of Ag and Ag alloys was evaluated in the temperature range from 77 K to 300 K, and com-pared to calculated value obtained by Wiedermann-Franz law. It was observed that the thermal conductivity decreased with increasing the content of alloying elements. Specifically, the thermal conductivity of $Ag_{0.92}Pd_{0.06}Mg_{0.02}$ alloy was measured to be $48.2W/(m{\cdot}K)$ at 77 K, which is about 6 times lower than that of $Ag(302.6W/(m{\cdot}K))$.

• Journal of the Korean Vacuum Society
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• v.9 no.4
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• pp.436-441
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• 2000

Plasma nitrocarburising is a thermochemical heat treatment, and can be used for plain carbon steels and low alloy steels to improve wear, corrosion and fatigue resistance. The process is performed on automotive parts, machinery parts and engineering tools. However, it is still facing problems in obtaining a mono $\varepsilon$ phased compound layer. Therefore, the aim of this research is to investigate the possibility of forming a mono $\varepsilon$ phased compound layer using a gas mixture of nitrogen and methane. It was found that high nitrogen contents were essential for the production of $\varepsilon$ phase compound layer and with increasing methane content in the gas mixture, $\varepsilon$ phase compound layer was favoured. In addition, when the methane content was further increased, cementite was observed in the compound layer. $\gamma$' phase was produced after 10 minutes treatment time and cementite was formed in the compound layer resulting in decreasing the thickness of the compound layer.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.3
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• pp.297-304
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• 2016

A numerical simulation has been performed for the penetration of a long-rod penetrator into a metal block (ceramic-tile-inserted 4340-steel plate). The impact velocity is 1.5km/s at a normal incidence angle. The first two validations are conducted for a semi-infinite block measuring the depth of penetration (DOP). The material model of ceramic is the JH-2 (Johnson-Holmquist) model. The predicted DOP values are in close agreement with the experimental data. Then, the primary simulation is performed by varying the position of the confined ceramic tile for three types of thickness of ceramic tile. The residual velocity, residual mass and residual kinetic energy of the long-rod are obtained from the simulation. Based on these predicted values, the trend of the ballistic performance of the protective structure is estimated. In addition, the mass efficiency is calculated in order to determine the performance of the ceramic-tile-inserted metal block. Finally, the optimum protective structure is identified.