• 한국수소및신에너지학회논문집
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• 제28권5호
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• pp.521-530
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• 2017

Improving the microstructure of NiO/YSZ is one of several approaches used to enhance the electrical and mechanical properties of an anode support in Solid Oxide Fuel Cells (SOFCs). The aim of the work reported in this paper was to predict the relationship between these microstructural changes and the resulting properties. To this end, modification of the anode microstructure was carried out using different sizes of Poly (Methyl Methacrylate) (PMMA) beads as a pore former. The electrical conductivity and mechanical strength of these samples were measured using four-probe DC, and three-point bend-test methods, respectively. Thermal etching followed by high resolution SEM imaging was performed for sintered samples to distinguish between the three phases (NiO, YSZ, and pores). Recently developed image analysis techniques were modified and used to calculate the porosity and the contiguity of different phases of the anode support. Image analysis results were verified by comparison with the porosity values determined from mercury porosimetry measurements. Contiguity of the three phases was then compared with data from electrical and mechanical measurements. A linear relationship was obtained between the contiguity data determined from image analysis, and the electrical and mechanical properties found experimentally. Based upon these relationships we can predict the electrical and mechanical properties of SOFC support from the SEM images.

• 한국수소및신에너지학회논문집
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• 제22권5호
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• pp.569-578
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• 2011

The $SiO_2$ membranes for polymer electrolyte membrane fuel cell (PEMFC) are preapared by electrospinning method. It leads to high porosity and surface area of membrane to accommodate the proton conducting materials. The composite membrane was prepared by impregnating of Nafion ionomer into the pores of electrospun $SiO_2$ membranes. The $SiO_2$:heteropolyacid (HPA) nano-particles as a inorganic proton conductor were prepared by microemulsion process and the particles are added to the Nafion ionomer. The characterization of the membranes was confirmed by field emission scanning electron microscope (FE-SEM), thermogravimetry analysis (TGA), and single cell performance test for PEMFC. The Nafion impregnated electrospun $SiO_2$ membrane showed good thermal stability, satisfactory mechanical properties and high proton conductivity. The addition of the $SiO_2$:HPA nano-particle improved proton conductivity of the composite membrane, which allow further extension for operation temperature in low humidity environments. The composite membrane exhibited a promising properties for the application in high temperature PEMFC.

• 한국분말재료학회지
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• 제28권4호
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• pp.331-335
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• 2021

The effects of drying temperature on the microstructure of porous W fabricated by the freeze-casting process of tert-butyl alcohol slurry with WO₃ powder was investigated. Green bodies were hydrogen-reduced at 800℃ for 1 h and sintered at 1000℃ for 6 h. X-ray diffraction analysis revealed that WO₃ powders were completely converted to W without any reaction phases by hydrogen reduction. The sintered body showed pores aligned in the direction of tert-butyl alcohol growth, and the porosity and pore size decreased as the amount of WO₃ increased from 5 to 10vol%. As the drying temperature of the frozen body increased from -25℃ to -10℃, the pore size and thickness of the struts increased. The change in microstructural characteristics based on the amount of powder added and the drying temperature was explained by the growth behavior of the freezing agent and the degree of rearrangement of the solid powder during the solidification of the slurry.

• 아시안잔디학회지
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• 제3권2호
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• pp.89-94
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• 1989

Research was conducted to obtain t he optimum treatment Of sodium hypochlorite(NaOC I) at various temperatures in t he seed scarification for stimulating germination of zoysiagrass (Zocysia Japonica Steud ) seed. Morphological changes of seed coat were also examined by scanning electron micros cop(SEM). l. Differences in temperature of scarification with 2 .4% NaOCI showed little influence on promoting germination of seeds but seeds treated with 1% solution at l5˚C germinated less than that of higher temperatures. The promotion effect of 4% solution on germination was diminished when seeds were treated for 8 hours of more. The most favorable seed scarification unaffected hy temperature for enhancing germination was 4-6hours treatment at 4% solution in fresh seeds. 2. $GA_3$, treatment did not enhance germination of water-pretreated control seeds hut germination of seeds pretreated with NaOCI l was increased additional 10% or more hy$ GA_3$, Water pretreated control seeds treated with 50 mM hydrogen peroxide(H'O )germinated about 44%. In NaOCI treated seeds. $H_2$$O_2$ treatment increased germination additional l 0% or more. 3. NaOCI l and KOH treatment softened the seed coat and formed the pores hy removing the scab-like thikenings attached to the seed surface. These results suggest that the modes of action of NaOCl in the promotion of seed germination reside in it increase of the permeability of the seed coat, and in the provision of additional oxygen to the seed.

• 한국분말재료학회지
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• 제27권3호
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• pp.198-202
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• 2020

The effect of sublimable vehicles on the pore structure of Cu fabricated by freeze drying is investigated. The 5 vol% CuO-dispersed slurries with camphene and various camphor-naphthalene compositions are frozen in a Teflon mold at -25℃, followed by sublimation at room temperature. After hydrogen reduction at 300℃ and sintering at 600 ℃, the green bodies of CuO are completely converted to Cu with various pore structures. The sintered samples prepared using CuO/camphene slurries show large pores that are aligned parallel to the sublimable vehicle growth direction. In addition, a dense microstructure is observed in the bottom section of the specimen where the solidification heat was released, owing to the difference in the solidification behavior of the camphene crystals. The porous Cu shows different pore structures, such as dendritic, rod-like, and plate shaped, depending on the composition of the camphornaphthalene system. The change in pore structure is explained by the crystal growth behavior of primary camphor and eutectic and primary naphthalene.

• Nuclear Engineering and Technology
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• 제40권3호
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• pp.233-238
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• 2008

This study investigates the surface modification of a Hastelloy X plate and diffusion bonding in the assembly of surface modified plates. These types of plates are involved in the key processes in the fabrication of a process heat exchanger (PHE) for a $SO_3$ decomposer. Strong adhesion of a SiC film deposited onto Hastelloy X can be achieved by a thin SiC film deposition and a subsequent N ion beam bombardment followed by an additional deposition of a thicker film that prevents the Hastelloy X surface from becoming exposed to a corrosive environment through the pores. This process not only produces higher corrosion resistance as proved by electrolytic etching but also exhibits higher endurance against thermal stress above 9$900^{\circ}C$. A process for a good bonding between Hastelloy X sheets, which is essential for a good heat exchanger, was developed by diffusion bonding. The diffusion bonding was done by mechanically clamping the sheets under a heat treatment at $900^{\circ}C$. When the clamping jig consisted of materials with a thermal expansion coefficient that was equal to or less than that of the Hastelloy X, sound bonding was achieved.

• 한국세라믹학회지
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• 제31권4호
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• pp.375-380
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• 1994

Matrices retaining electrolyte in phosphoric acid fuel cell were prepared with SiC to SiC whisker mixing ratios of 1:0.5, 1:1, 1:1.5, 1:2, 1:3 by tape casting method. When viscosity of the slurry was 5.9 poise and the SiC to SiC whisker mixing ratios were 1:1, 1:1.5, 1:2, the ranges of porosity, acid absorbency and bubble pressure were 80~90%, 2.5~6 and 700~2200 mmH2O, respectively. Those ranges are acceptable for a practical electrolyte-retaining matrix. With increasing the mixing ratio of SiC whisker to SiC, the porosity and the vol.% of large pores in the main pore size distribution which is between 1 and 10 ${\mu}{\textrm}{m}$, increased rapidly. Impedance spectroscopy was measured to know characteristics of matrix inside and contact region of matrix to catalyst layer. When the SiC to SiC whisker mixing ratio was 1:2, hydrogen ions were transported in the matrix most effectively because of high ionic conductivity and low activation energy due to high acid absorbency in spite of high interfacial resistance. The cell current density of the cell made using the matrix was 220 mA/$\textrm{cm}^2$ at 0.7 V.

• Corrosion Science and Technology
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• 제20권4호
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• pp.175-182
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• 2021

Magnesium alloy is limited in the industrial field because its standard electrode potential is -2.363 V vs. NHE (Normal Hydrogen Electrode) at 25 ℃. This high electrochemical activity causes magnesium to quickly corrode with oxygen in air; chemical conversion coating prevents corrosion but causes surface defects like cracks and pores. We have examined the anti-corrosion effect of sol-gel coating sealed on the defected conversion coating layer. Sol-gel coatings produced higher voltage current and smaller pore than the chemical conversion coating layer. The conversion coating on magnesium alloy AZ31 was prepared using phosphate-permanganate solution. The sol-gel coating was designed using trimethoxymethylsilane (MTMS) and (3-Glycidyloxypropyl) trimethoxysilane (GPTMS) as precursors, and aluminum acetylacetonate as a ring-opening agent. The thermal shock resistance was tested by exposing specimens at 140 ℃ in a convection oven; the results showed changes in the magnesium alloy AZ31 surface, such as oxidization and cracking. Scanning electron microscope (FE-SEM) analysis confirmed a sealed sol-gel coating layer on magnesium alloy AZ31. Electrochemical impedance spectroscopy (EIS) measured the differences in corrosion protection properties by sol-gel and conversion coatings in 0.35 wt% NaCl solution, and the potentiodynamic polarization test and confirmed conversion coating with the sol-gel coating show significantly improved resistance by crack sealing.

• 융합정보논문지
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• 제11권3호
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• pp.220-228
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• 2021

본 연구에서는 2020년 10월12일부터 2020년 11월15까지 35~55세의 중년여성 20여명을 대상으로 연구하였다. 실험군에는 진여수클린미스트를 사용하도록 하였고, 대조군 10명의 여성들에게는 평소 사용하는 이온수 성분을 함유하지 않은 미스트제품을 사용하도록 설계하였다. 실험에 사용된 Janus 안면진단기(주. 피에스아이)로 피부에 조사하여 광원의 차이에 따라 관찰 되는 모공, 주름, 탄력, UV색소침착, 색소침착, 피부톤을 측정하였다. 실험전 클렌징을 하고 10분간 안정한 뒤 안면진단기로 촬영을 하였고, 진여수클린미스트 사용 후 7일에 1회씩 총 4회 촬영이 진행되었다. 통계처리는 SPSS 통계프로그램 21.0을 활용하여 실험에 참여한 두 집단 간 실험 전 데이터와 실험 후 데이터의 평균을 비교하기 위해 대응표본 t-test를 사용하였다. 야누스III의 데이터 분석자료에서 분석수치는 평균연령의 데이터를 기본값으로 하였으며 0(zoro)에서 숫자가 증가할수록 나이에 비해 개선이 요구된다. 분석결과, 진여수이클린미스트 제품을 사용한 집단에서 모공(t=3.280, p<.01), 주름((t=4.353, p<.01), 탄력(t=3.003, p<.05), 피부톤(t=3.280, p<.01)에서 통계적 유의수준 하에서 차이가 있는 것으로 나타났다. 반면 색소침착과 UV색소침착과 피부톤은 통계적으로 유의하지 않은 것으로 분석되었다.

• 한국재료학회지
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• 제26권6호
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• pp.337-341
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• 2016

Cu-30 vol% SiC composites with relatively densified microstructure and a sound interface between the Cu and SiC phases were obtained by pressureless sintering of PCS-coated SiC and Cu powders. The coated SiC powders were prepared by thermal curing and pyrolysis of PCS. Thermal curing at $200^{\circ}C$ was performed to fabricate infusible materials prior to pyrolysis. The cured powders were heated treated up to $1600^{\circ}C$ for the pyrolysis process and for the formation of SiC crystals on the surface of the SiC powders. XRD analysis revealed that the main peaks corresponded to the ${\alpha}$-SiC phase; peaks for ${\beta}$-SiC were newly appeared. The formation of ${\beta}$-SiC is explained by the transformation of thermally-cured PCS on the surface of the initial ${\alpha}$-SiC powders. Using powder mixtures of coated SiC powder, hydrogen-reduced Cu-nitrate, and elemental Cu powders, Cu-SiC composites were fabricated by pressureless sintering at $1000^{\circ}C$. Microstructural observation for the sintered composites showed that the powder mixture of PCS-coated SiC and Cu exhibited a relatively dense and homogeneous microstructure. Conversely, large pores and separated interfaces between Cu and SiC were observed in the sintered composite using uncoated SiC powders. These results suggest that Cu-SiC composites with sound microstructure can be prepared using a PCS coated SiC powder mixture.