• Journal of the Korean Society for Heat Treatment
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• v.28 no.1
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• pp.17-23
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• 2015

Hydroxyapatite coatings were fabricated by a room temperature spray method on zirconia substrates and the influence of heat-treatment on their microstructure was also investigated. Phase composition of coated hydroxyapatite films was similar to the starting powder, but the grain size of hydroxyapatite particles was reduced to the size of nano-scale about 100 nm. Grain size, particle compactness, and adhesiveness to zirconia of hydroxyapatite coatings were increased with heat-treatment temperature, but some of cracks by heat-treatment above $1100^{\circ}C$ were initiated between hydroxyapatite coatings and zirconia substrate. Heat-treated hydroxyapatite layers show the dissolution in SBF solution for 5 days. Hydroxyapatite-coated specimen heat-treated at $1100^{\circ}C$ for 1 h has a good biocompatibility, which specimen induced the nanocrystalline hydroxyapatite precipitates on the coating surface by the immersion in SBF solution for 5 days.

• Korean Journal of Materials Research
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• v.28 no.4
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• pp.221-226
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• 2018

The property changes of 18, 14, and 8K green gold alloys for jewelry are observed by adding 0.0, 3.0, and 5.0 wt% of indium (In), respectively. To check the composition of the alloys, an energy dispersive spectroscopy (EDS) analysis is conducted. Color and microstructure analysis is executed through bare-eye, macro camera, UV-VIS-NIR-colormeter, and optical microscope. The melting point, wetting angle, and hardness are measured using TGA-DTA, a wetting angle tester, and a Vickers hardness tester. The EDS analysis result demonstrates that each of the green gold alloys was manufactured with purposed contents. The color analysis result shows that the color of the alloys is similar to the color of the conventional 4 wt%-Cd 18K green gold, and the green color improves as the In content increases. The micro structure analysis result demonstrates that grain refinement improves as the amount of In increases. Enhancements in the melting point, wettability, and Vickers hardness changes appear as the In content increases and Au content decreases. The hardness is up to 260, which implies good durability. Therefore, the results suggest that the proposed 18, 14, and 8K In-added green gold alloys enhance the properties of jewelry products with regard to the green color, castability, and durability.

• Korean Journal of Materials Research
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• v.28 no.4
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• pp.227-234
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• 2018

We investigate the effect of the modification of cellulose acetate propionate as an organic vehicle for silver paste on solar cell efficiency. For the modification of cellulose acetate propionate, poly(ethylene glycol) is introduced to the hydroxyl groups of a cellulose acetate propionate backbone via esterification reaction. The chemical structure and composition of poly(ethylene glycol) functionalized cellulose acetate propionate is characterized by Attenuated total reflectance Fourier transform infrared, $^1H$ nuclear magnetic resonance, differential scanning calorimetry and thermogravimetric analysis. Due to the effect of structural change for poly(ethylene glycol) functionalized cellulose acetate propionate on the viscosity of silver paste, the solar cell efficiency increases from 18.524 % to 18.652 %. In addition, when ethylene carbonate, which has a structure similar to poly(ethylene glycol), is introduced to cellulose acetate propionate via ring opening polymerization, we find that the efficiency of the solar cell increases from 18.524 % to 18.622 %.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.161-161
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• 2013

Two-dimensional electron gas (2DEG) has been investigated at the heterointerface between two insulating dielectric perovskite oxides, $LaAlO_3$ (LAO)/$SrTiO_3$ (STO). Properties of the 2DEG have attracted an enormous interest in condensed matter physics due to multifunctional properties such as the coexistence of ferromagnetism and superconductivity, as well as the high electron mobility. Here, we have grown $Ta_2O_5$ thin films using pulsed laser deposition on $SrTiO_3$ substrate to investigate the electric properties of the $Ta_2O_5$/STO heterointerface. Our research reveal that the non-polar $Ta_2O_5$/$TiO_2$ heterointerface favors the formation of 2DEG similar to that at the LAO/STO heterointerface. The metallic behavior was found in this heterointerface with the current about $10{\sim}100{\mu}A$ at 5 V by using conventional I-V measurements, when the $Ta_20_5$ film thickness reaches over critical thickness, $d_c{\simeq}2uc$. The finding that electrons was localized at $Ta_2O_5$/STO heterointerface have attracted to be strong and new candidate for nanoscale oxide device applications.

• Transactions of Materials Processing
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• v.27 no.4
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• pp.222-226
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• 2018

Severe plastic deformation (SPD) is a promising method for drastically enhancing the mechanical properties of the materials by grain refinement of metallic materials. However, inhomogeneous deformation during the SPD process results in the inhomogeneous microstructure of the SPD-processed material. We manufactured cylindrical copper specimens of 42 mm in diameter with ultrafine grains (UFG) using an equal channel angular pressing (ECAP) to figure out the relationship between homogeneous microstructure and the number of the processing passes. Two specimens, which are ECAP-processed 4 times (4pass) and 6 times (6pass) each with Route Bc, are prepared for comparison of mechanical properties and microstructure. The results show that the mechanical properties of the two specimens (4pass and 6pass) are similar. Moreover, both the specimens show highly enhanced mechanical properties. The 4pass specimen, however, shows inhomogeneity in hardness distribution, while the 6pass specimen shows a homogeneous distribution. Microstructure analysis reveals that the 4pass specimen has an inhomogeneous microstructure with incompletely refined grain structure. This inhomogeneity of the 4pass specimen could be explained by the circumferential rotation during ECAP process.

• Bulletin of the Korean Chemical Society
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• v.34 no.3
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• pp.851-855
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• 2013

This paper describes an environmentally friendly process for the recovery of $LiFePO_4$ cathode materials from scrap electrodes by a simple thermal treatment method. The active materials were easily separated from the aluminum substrate foil and polymeric binders were also decomposed at different temperatures ($400^{\circ}C$, $500^{\circ}C$, $600^{\circ}C$) for 30 min under nitrogen gas flow. The samples were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), Raman spectroscopy, Thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The electrochemical properties of the recycled $LiFePO_4$ cathode were evaluated by galvanostatic charge and discharge modes. The specific charge/discharge capacities of the recycled $LiFePO_4$ cathode were similar to those of the original $LiFePO_4$ cathode. The $LiFePO_4$ cathode material recovered at $500^{\circ}C$ exhibits a somewhat higher capacity than those of other recovered materials at high current rates. The recycled $LiFePO_4$ cathode also showed a good cycling performance.

• Progress in Medical Physics
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• v.30 no.4
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• pp.155-159
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• 2019

Radiological properties of newly introduced and existing 3-dimensional (3D) printing materials were evaluated by measuring their Hounsfield units (HUs) at varying infill densities. The six materials for 3D printing which consisted of acrylonitrile butadiene styrene (ABS), a unique ABS plastic blend manufactured by Zortrax (ULTRAT), high impact polystyrene (HIPS), polyethylene terephthalate glycol (PETG), polylactic acid (PLA), and a thermoplastic polyester elastomer manufactured by Zortrax (FLEX) were used. We used computed tomography (CT) imaging to determine the HU values of each material, and thus assess its suitability for various applications in radiation oncology. We found that several material and infill density combinations resembled the HU values of fat, soft tissues, and lungs; however, none of the tested materials exhibited HU values similar to that of bone. These results will help researchers and clinicians develop more appropriate instruments for improving the quality of radiation therapy. Using optimized infill densities will help improve the quality of radiation therapy by producing customized instruments for each field of radiation therapy.

• Journal of the Korean Ceramic Society
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• v.43 no.3 s.286
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• pp.148-151
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• 2006

In order to examine the process parameters for the vitrification of Low and Intermediate Level radioactive Waste (LILW) generated from nuclear power plants, measurements of several melt properties was performed for four selected glasses containing simulated waste. Electrical conductivity and viscosity were determined at temperatures ranging from 1123 to $1673^{\circ}C$. The temperature dependences of both properties in the molten state showed a similar behavior in which their values decrease as the temperature increases. The values of the electrical conductivity and viscosity at a temperature of 1423K adopted in an induction cold crucible melter process were $0.27{\sim}0.42$ S/cm and $9.8{\sim}42$ dPas, respectively.

• Journal of Electrochemical Science and Technology
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• v.5 no.2
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• pp.58-64
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• 2014

The surface of an ordered mesoporous silica (OMS) was functionalized using 1H,1H,2H,2H-perfluorooctyltrimethoxysilane at $20^{\circ}C$ and $60^{\circ}C$. It was shown that only elevated temperature allows lyophobic properties on the walls of OMS, eventually preventing pore flooding with nonaqueous electrolytes. The functionalized OMSs (OMS-F) were characterized with various techniques: wettability test, $N_2$ sorption measurement, high-resolution transmission electron microscopy (HR-TEM). Cathodes of $10mg/cm^2$ loading were prepared with a commercial Pt/C catalyst and polyvinylidene fluoride (PVDF, 2.5 wt.%) binder using a typical doctor blade method on a commercial gas diffusion layer (GDL) in the presence or in the absence of OMS-F additives. Subsequent discharge-charge curves were taken in a 1M LiTFSI-TEGDME electrolyte at 60oC in pure oxygen atmosphere. It was found that the discharge capacity was significantly affected by OMS-F: 5 wt.% of additive extended discharge capacity by a factor 1.5. On the other hand, a similar OMS material but synthesized at $20^{\circ}C$ did not show lyophobic properties and deteriorated cathode capacity.

• Fashion & Textile Research Journal
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• v.10 no.1
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• pp.68-75
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• 2008

Demands and attempts to express Korean traditional beauty are increasing. Some schools choose the uniform in designs expressing the image of Hanbok, but recently there is a few increment of wearing the uniforms. For the improvement of the uniforms, first of all, the shape and the clothing materials of the uniforms should be considered. We have compared and analyzed the shape and the clothing materials of the uniforms reflecting the image of Hanbok, according to seasons and clothing items. The uniforms reflecting the image of Hanbok were worn in eight schools and all of them are Saenghwal Hanbok style. The shape of Saenghwal Hanbok school uniforms showed both Korean style and western style characteristics. Korean style characteristics were expressed through the appearance-related parts while western style characteristics showed through the performance-related parts such as open/closure method, armhole pattern and straight sleeve line. It was shown that girls' uniforms are more diverse and similar to the western style uniforms than boys' uniforms. It was found that most of the clothing material were synthetic fiber or mixture of natural/synthetic fiber, and polyester was shown to be used most.