• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.171-171
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• 1999

We studied the charge redistribution in the Pt-M (M=Cu, Co) alloys by X-ray Absorption Near Edge Spectroscopy(XANES) and X-ray Photoelectron Spectroscopy(XPS). These analysis tools provide us information about the charge transfer in the valence band of intermetallic bonding. The samples were prepared by arc-melting method. After annealing this samples in vacuum for several hours, we cold get the ordered samples, which were confirmed with XRD analysis. the core and valence level energy shift in these system were investigated by Mg $K\alpha$(1253.6eV) x-ray source for Pt-Co alloys and monochromatized Al $K\alpha$ (1486.6eV) for Pt-Cu alloys. Pt L2, L3-edge, and Cu, Co K-edge XANES spectra were measured with the total electron-yield mode detector at the 3Cl beam line of the PLS (Pohang light source0. from the changes of White line (WL) area and the core level shifts of the each metal sites, we can obtain the information about the electrons participating in the intermetallic bonding of the Pt-Cu and Pt-Co alloys.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.8
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• pp.1371-1379
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• 2003

RP&M (Rapid Prototyping and Manufacturing) is the most appropriate technology for the small-lot production system, because the production cycle is getting shorter owing to various needs of the consumer. In this paper, rapid tooling technology is applied to the casting process. The casting process has the ability to reflect complicated shapes in one process. But it has not been widely used to make a die and mold because of the poor surface quality caused by air bubbles on the surface of the casting product. In this study, the porous casting mold is fabricated from a mixture of plaster and water-soluble binder. The porous casting mold can improve the characteristics of casting products with the help of the vacuum sealed casting process. The vacuum sealed casting process is an advanced technology that removes the air bubbles between the porous casting mould and the liquid metal, thus making the surface of the casting product finer. The purpose of this paper is to develop a high quality shoe mold using porous casting mold and to apply the RP&M technology to the shoe industry.

• Korean Journal of Materials Research
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• v.17 no.3
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• pp.179-183
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• 2007

A plate heat exchanger (PHE) normally uses vacuum brazing technology for connecting plates and fins. However, the reliability of high temperature brazing, especially with nickel-based filler metals containing boron the formation of brittle intermetallic compounds (IMCs) in brazed joints is of major concern. since they considerably degrade the mechanical properties. This research was examined the vacuum brazing of commercially SUS304 stainless steel with BNi-2 (Ni-Cr-B-Si) filler metal, and discussed to determine the influence of brazing temperatures on the microstructure and mechanical strength of brazed joints. In the metallographic analysis it is observed that considerable large area of Cr-B intermetallic compound phases at the brazing layer and the brazing tensile strength is related to removal of this brittle phase greatly. The mechanical properties of brazing layer could be stabilized through increasing the brazing temperature over $100^{\circ}C$ more than melting temperature of filler metals, and diffusing enough the brittle intermetallic compound formed in the brazing layer to the base metal.

• Journal of Welding and Joining
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• v.25 no.4
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• pp.42-48
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• 2007

An inert gas atomized NiTiZrSiSn bulk metallic glass feedstock was sprayed onto the copper plate using vacuum plasma spraying process. In order to change the in-flight particle energy, that is, thermal energy, the hydrogen gas flow rate in plasma gas mixture was increased at the constant flow rate of argon gas. Coating and single pass spraying bead were produced with the least feeding rate. Regardless of the plasma gas composition, fully melted through unmelted particle could be observed on the overlay coating. However, the frequency of the unmelted particle number density was increased with the decrease of the hydrogen gas flow rate. The amorphous phase fraction within coating was also affected by the number density of the unmelted particle.

• Korean Journal of Materials Research
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• v.16 no.5
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• pp.277-284
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• 2006

The alloys were prepared by a non-consumable vacuum arc melting and homogenized at $1050^{\circ}C$ for 24 hrs. Two kind of surface modifications were performed alkali treatment in 5.0M NaOH solution subsequent and heat treatment in vacuum furnace at $600^{\circ}C$, and were oxidizing treatment at the temperature range of 550 to $750^{\circ}C$ for 30 minutes. After surface modification, these samples were soaked in SBF which consists of nearly the same ion concentration as human blood plasma. Cytotoxicity tests were performed in MTT assay treated L929 fibroblast cell culture, using indirect methods. A porous and thin activated layer was formed on Titanium and Ti-8Ta-3Nb alloy by the alkali treatment. A bone-like hydroxyapatite was nucleated on the activated porous surfaces during the in vitro test. However, Ti-8Ta-3Nb alloys showed better bioactive properties than Titanium. According to XRD results, oxide layers composed of mostly $TiO_2$(rutile) phases. Cytotoxicity test also revealed that moderate oxidation treatment lowers cell toxicity and Ti-8Ta-3Nb alloy showed better results compared with Titanium.

• 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.

• Korean Journal of Materials Research
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• v.15 no.10
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• pp.667-670
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• 2005

Binary skutterudite $CoSb_3$ compounds were prepared by the arc melting and hot pressing processes and their thermoelectric properties were investigated in the range from 300 to 600 K. Annealing effect was correlated to phase transformation and homogenization. Thermoelectric properties of the arc-melted and hot-pressed $CoSb_3$ were discussed and compared. Undoped intrinsic $CoSb_3$ prepared by the arc melting showed p-type conduction, while it showed metallic behavior with increasing measuring temperature. However, hot pressed specimens showed n-type conduction, possibly due to Sb evaporation. Thermoelectric properties were remarkably improved by annealing In vacuum and they were closely related to phase transformation.

• Journal of the Korea Furniture Society
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• v.22 no.1
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• pp.54-62
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• 2011

The metalized wood composites with natural grain of imported Juglans nigra, which was impregnated with low melting alloy were manufactured and evaluated in this study. And the proper manufacturing conditions was also investigated in this study. The low melting alloy with bismuth (Bi) and tin (Sn) which are harmless to humans, was applied to this new composites. The composites showed not only no defects of discoloration, delamination, swelling, and cracking, because of high dimensional stability and low thickness swelling, but also much improved performance such as high bending strength, high hardness, abrasion resistance, high thermal conductivity as floor materials. This study also suggested the proper impregnating condition, such as 10 minutes of the preliminary vacuum time, $186^{\circ}C$ of the heating temperature and 10 minutes of the maintaining pressure time at the pressure of $30kgf/cm^2$. This metalized wood composites showed 7 times higher density than control, great increase in bending strength from $131.8N/mm^2$ to $192.3N/mm^2$, and great increase in hardness from $18.2N/mm^2$ to $90.4N/mm^2$. The composites demonstrated not only high emissivity of 91%, high shilding effectiveness of 92.59∼99.99%, high fire resistance but also great decrease in abrasion depth, water absorption and thickness swelling.

• Korean Journal of Materials Research
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• v.15 no.2
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• pp.89-92
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• 2005

The induction melting was employed to prepare Nb-doped $CoSb_3$ skutterudites and their thermoelectric properties were investigated. Single phase $\delta-CoSb_3$ was successfully obtained by induction melting and subsequent annealing at $400^{\circ}C$ for 2 hrs in vacuum. The positive signs of Seebeck coefficients for all the specimens revealed that Nb atoms acted as p-type dopants by substituting Co atoms. Electrical conductivity decreased and then increased with increasing temperature, indicating mixed conduction behavior. Electrical conductivity increased by Nb doping, and it was saturated at high temperature. Maximum value of the thermoelectric power factor was shifted to higher temperature with increasing the amount of Nb doping, mainly originated from the high Seebeck coefficient around mixed conduction temperature and high electrical conductivity.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.3
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• pp.126-130
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• 2013

In this study, a shape-stabilized phase change material (SSPCM) was prepared by octadecane and exfoliated graphite nanoplate (xGnP) in a vacuum, to improve thermal storage performance. The octadecane as an organic phase change material (PCM) is very stable against phase separation of PCM, and has the proper temperature range for thermal comfort in the building; and the xGnP is a porous carbon nano-material. Scanning electron microscope (SEM) and Fourier transformation infrared spectrophotometer (FT-IR) were used to confirm the chemical and physical stability of the Ocatadecane/xGnP SSPCM. In addition, thermal properties were determined by Deferential scanning calorimeter (DSC), and Thermogravimetric analysis (TGA). The specific heat of Octadecane/xGnP SSPCM was $14.1J/g{\cdot}K$ at $31.3^{\circ}C$. The melting temperature ranges of melting and freezing were found to be $26{\sim}35^{\circ}C$ and $26{\sim}19^{\circ}C$, respectively. At this time, the latent heats of melting and freezing were 110.9 J/g and 104.5 J/g, respectively. The Octadecane was impregnated into xGnP by as much as about 56.0% of the Octadecane/xGnP SSPCM's mass fraction.