• Journal of the Korean Ceramic Society
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• v.40 no.2
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• pp.118-122
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• 2003

The performance evaluation on Pt loading in the self-humidifying polymer electrolyte membrane for Polymer Electrolyte Mem-Brane Fuel Cell(PEMFC) was investigated by using single cell test and measurement of membrane resistance. The self-humidifying membrane comprised two membranes made of perfluorosulfonylfluroride copolymer resin and fine Pt particles tying between them, coated by sputtering. From the results of performance characteristics of self-humidifying membrane cell with different Pt loading, a single cell using self-humidifying membrane with 0.15 mg/$\textrm{cm}^2$ Pt loading showed better performance than that with the others over entire current density. Also, a single cell with 0.15 mg/$\textrm{cm}^2$ Pt loading had a lower resistance value than the other cells under externally nonhumidifying condition. It is indicated that the water produced in the membrane cell with 0.15 mg/$\textrm{cm}^2$ Pt loading showed a higher provision to maintain ionic conductivity of the membrane than the other cells. The optimum amount of Pt particles embedded in the membrane for self-humidifying PEMFC was determined to be about 0.15 mg/$\textrm{cm}^2$.

• Journal of the Korean Society of Visualization
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• v.10 no.3
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• pp.16-20
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• 2012

In the past decades, extensive studies on convection heat transfer on internal flow have been conducted by using high specific surface area, by increasing heat transfer coefficient and swirl flow, and by improving the transport properties. In this study, we applied a tangential slot swirl generator to improve heat transfer in a horizontal circular copper tube. The Al-Mg particles (approximately $100{\mu}m$ to $130{\mu}m$) were employed for this experimental work. The copper tube was heated uniformly by winding a heating coil with a resistance of 9ohm per meter for heat transfer. Using Al-Mg particles, experiments were performed in the Reynolds number range of 5,000 to 13,130, with and without swirl. Experimental data transfers or comparisons between Nusselt numbers with and without swirl along the test tube and Reynolds numbers are presented. The Nusselt number is improved by increasing Reynolds numbers or swirl intensities along the test tube.

• Bulletin of the Korean Chemical Society
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• v.34 no.5
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• pp.1345-1348
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• 2013

We investigated the tribochemical and wear properties of Polytetrafluoroethylene (PTFE) based polymer matrix composites with nanoceramic (NC) ${\beta}$-sialon, and $Al_2O_3$ particles for the mechanical seal applications at low temperature. SEM showed that NC particles were homogeneously distributed in the polymer matrix and initiated the formation of the supramolecular spherulites around NC. From the temperature stimulated depolarization (TSD) current results, it was analyzed that the surface charge on nanoceramic affected the formation of the spherulites structure. 2 wt % $Al_2O_3$ NC did not degrade the mechanical properties of PTFE so that composites showed the similar values of tensile strength, elongation at the rupture and friction coefficient as those of neat PTFE. However, the composite with 2 wt % $Al_2O_3$ NC revealed the improved wear resistance, wear rate of 0.4-1.2 mg/h at room temperature and 0.28 mg/h at $-40^{\circ}C$, respectively, while the neat PTFE the 70-75 mg/h at room temperature and 70.3 mg/h at $-40^{\circ}C$.

• Journal of Dairy Science and Biotechnology
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• v.25 no.1
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• pp.55-60
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• 2007

Contents of scorched particles in infant formula were studied to provide a scientific evidence for standardization of Food Regulation in Korea. The specification of scorched particles in infant formula in Korea was satisfied with CODEX, USDA and so on. But food regulations for scorched particles in baby food are not mentioned in Korea. Nowadays social interests of scorched particles in infant formula are being increased in the respect of safety for baby food. The composition and contents of scorched particles were analyzed with Scanning Electron Microscope-Energy Dispersive X-ray Spectrometer(SEM-EDS) and Inductively Coupled Plasma Mass Spectrometer(ICP-MS). The results indicate that the scorched particles consist Ca, Na, Fe, Mg and trace elements derived from the ingredient of infant formula. Infant formula are composed of milk, skimmed milk, whey, mixed vegetable oils, minerals and vitamins. These results also show that the contents of scorched particles of infant formula in Korea are little or similar level to those reported in other countries. In general, heavy metals derived from scorched particle are originally used as a source of minerals in infant formula. And it has been thought that they doesn't effect on Provisional Tolerable Weekly Intake set by FAO/WHO for contents and composition of scorched particles.

• Progress in Superconductivity and Cryogenics
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• v.19 no.1
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• pp.36-41
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• 2017

The effects of $MgB_4$ addition on the superconducting properties and the microstructure of in situ processed $MgB_2$ bulk superconductors were studied. $MgB_4$ powder of 1-20 wt.% was mixed with (Mg + 2B) powder and then pressed into pellets. The pellets of (Mg + 2B + $xMgB_4$) were heat-treated at $650^{\circ}C$ for 1 h in flowing argon. The powder X-ray diffraction (XRD) analysis for the heat-treated samples showed that the major formed phase in all samples was $MgB_2$ and the minor phases were $MgB_4$ and MgO. The full width at half maximum (FWHM) values showed that the grain size of $MgB_2$ decreased as the amount of $MgB_4$ addition increased. $MgB_4$ particles included in a $MgB_2$ matrix is considered to suppress the grain growth of $MgB_2$. The onset temperatures ($T_{c,onset}$) of $MgB_2$ with $MgB_4$ addition (0-10 wt.%) was between 37-38 K. The 20 wt.% $MgB_4$ addition slightly reduced the $T_{c,onset}$ of $MgB_2$ to 36.5 K. This result indicates that $MgB_4$ addition did not influence the superconducting transition temperature ($T_c$) of $MgB_2$ significantly. On the other hand, the small additions of 1-5 wt.% $MgB_4$ increased the critical current density ($J_c$) of $MgB_2$. The $J_c$ enhancement by $MgB_4$ addition is attributed not only to the grain size refinement but also to the possible flux pinning of $MgB_4$ particles dispersed in a $MgB_2$ matrix.

• Journal of the Korean Society for Heat Treatment
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• v.23 no.5
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• pp.239-244
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• 2010

Influence of Zr addition on grain stability at elevated temperatures has been investigated for extruded pure Mg and Mg-0.25%Zr alloy. The grain size of pure Mg increases rapidly with increasing annealing temperature when isochronally annealed for 60 min from 573 to 773 K, whereas the grains are stable up to 723 K for the Zr-containing alloy. The activation energies for grain growth ($E_g$) at this temperature range were determined as 75.3 and 105.9 kJ/mole for the pure Mg and Mg-0.25%Zr alloy, respectively. TEM observations on the annealed Mg-Zr samples revealed that higher thermal stability and higher activation energy for grain growth resulting from Zr addition in Mg may well be associated with the restriction of grain growth by nano-sized Zr particles distributed in the microstructure.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.5
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• pp.1349-1353
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• 2008

Size-segregated mass and ion concentrations of atmospheric aerosols in Cheonan City were measured using a high volume air sampler equipped with a 5-stage cascade impactor and a ion chromatography between March 2006 and April 2007. The mean values of 24-hr average concentrations of TSP, PM10, PM2.5, and PM1 were 61.7, 55.2, 43.7, $33.2{\mu}g/m^3$, respectively. Mass size distributions of atmospheric aerosols were bimodal distributions with a saddle point in $1.5\;{\sim}\;3.0{\mu}m$ range in diameter separating coarse and fine particle modes. Fine particles, PM2.5 were 70.8% of the total mass of aerosols. Major ion components in aerosols were ${NH_{4}}^+$, $Na^+$, $K^+$, $Ca^{2+}$, $Mg^{2+}$ for cations, and ${SO_{4}}^{2-}$, ${NO_{3}}^-$, $Cl^-$ for anions. ion components occupied 37.4% of coarse particles and 46.2% of fine particles in mass.

• Korean Journal of Materials Research
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• v.20 no.12
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• pp.691-698
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• 2010

Magnesium hydroxide-melamine core-shell particles were prepared through the coating of melamine monomer on the surface of magnesium hydroxide in the presence of phosphoric acid. The melamine monomer was dissolved in hot water but recrystallized on the surface of magnesium hydroxide by quenching to room temperature in the presence of phosphoric acid. The core-shell particle was applied to low-density polyethylene/ ethylene vinyl acetate (LDPE/EVA) resin by melt-compounding at $180^{\circ}C$ as flame retardant. The effect of magnesium hydroxide and melamine content has been studied on the flame retardancy of the core-shell particles in LDPE/EVA resin according to the preparation process and purity of magnesium hydroxide. Magnesium hydroxide prepared with sodium hydroxide rather than with ammonia solution revealed higher flame retardancy in core-shell particles with LDPE/EVA resin. At 50 wt% loading of flame retardant, core-shell particles revealed higher flame retardancy compared to that of the exclusive magnesium hydroxide in LDPE/EVA composite, and it was possible to satisfy the V0 grade in the UL-94 vertical test. The synergistic flame retardant effect of magnesium hydroxide and melamine core-shell particles was explained as being due to the endothermic decomposition of magnesium hydroxide and melamine, which was followed by the evolution of water from the magnesium hydroxide and porous char formation due to reactive nitrogen compounds, and carbon dioxide generated from melamine.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1998.09a
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• pp.117-121
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• 1998

The Rapid Expansion of supercritical fluid Solutions (RESS) process was applied to particles coating. Experiments were conducted in a fluidized bed with an internal nozzle in the center of the reaction tube. Microcapsules (mean particle size : 49$\mu\textrm{m}$) prepared by spray drying method were used as the core particles. Supercritical CO2 solutions of paraffin were expanded through the nozzle in to the bed that was fluidized by air. Surface morphology prepared particles was observed by SEM. For the inspection of particle size change, particle size distributions were measured before and after coating. The releasing behavior of Mg2+ ions inspected by AA.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05b
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• pp.80-85
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• 1997

Studies on particles formed in the laser melted zone (LMZ) of sensitized Ni base Alloy 600 have been carried out using microscopic equipments. Most of them were identified as TiN type and MgS type particles were also found in the cell boundaries. All of the particles were located in the cellular solidification region, but no particle was formed in the plane front solidification regions of the LMZ. Cr carbides which had formed during sensitization treatment were completely melted during laser surface melting and hardly re-precipitated during the matrix solidification.