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        검색결과 393

        161.
        2009.08 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Disk type porous nickel membrane was fabricated by in-situ reduction/sintering process using compacted NiO/PMMA (PMMA; Polymethyl methacrylate) mixture at 800℃ in hydrogen atmosphere. The porosity (4958%) of these membrane was investigated as an amount of PMMA additive. The thermal decomposition and reduction behavior of NiO/PMMA were analyzed by TG/DTA in hydrogen atmosphere and the activation energy for the hydrogen reduction of NiO and thermal degradation of PMMA was calculated as 61.1 kJ/mol, evaluated by Kissinger method. Finally, the filtering performance and pressure drop were measured by particle counting system.
        4,000원
        162.
        2009.07 KCI 등재 SCOPUS 구독 인증기관 무료, 개인회원 유료
        Niobium(Nb) and Tantalum(Ta) are rarely found apart in nature and never in the free state. The element niobium amounts to 3% of the crustal abundance. On the whole, the niobium capacitor showed somewhat more unstable characteristics than the commercial tantalum capacitors, but is nonetheless considered applicable as a future substitute for tantalum capacitors. In this study, niobium powder was made from potassium heptafluoroniobite(K2NbF7) by using sodium(Na) as a reductant and KCl and KF as diluents based on the hunter sodiothermic reduction method.,In order to obtain a high surface area niobium powder via the sodiothermic reduction method, a certain amount of diluent, such as alkali metal halides selected from NaCl, KCl, KF and NaF, was added in the raw materials to be reduced. However, if a higher surface area of powder is required, more diluents need to be used in the said method in order to produce niobium powder. But when more diluents are used, the niobium powder will be contaminated with more impurities and the yield will also decreased.
        4,000원
        168.
        2009.04 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Niobium powder was made from potassium heptafluoroniobite () as the raw material using sodium (Na) as a reducing agent based on the hunter process. The apparatus for the experiment was designed and built specifically for the present study. The niobium particle size greatly increased as the reduction temperature increased from to . The particle size was fairly uniform, varying from to depending on the reduction temperatures. The niobium powder morphology and particle size are very sensitive to a reaction temperature in the metallothermic reduction process. The yield of niobium powder increased from 55% to 80% with a increasing a reaction temperature.
        4,000원
        169.
        2009.04 KCI 등재 구독 인증기관 무료, 개인회원 유료
        The ultrafine titanium carbonitride particles () below 100nm in mean size were successfully synthesized by Mg-thermal reduction process. The nanostructured sub-stoichiometric titanium carbide () particles were produced by the magnesium reduction at 1123K of gaseous and the heat treatments in vacuum were performed for five hours to remove residual magnesium and magnesium chloride mixed with . And final phase was obtained by nitrification under normal gas at 1373K for 2 hrs. The purity of produced particles was above 99.3% and the oxygen contents below 0.2 wt%. We investigated in particular the effects of the temperatures in vacuum treatment on the particle refinement of final product.
        4,000원
        170.
        2009.03 KCI 등재 구독 인증기관 무료, 개인회원 유료
        In this study, the emission characteristics of reduced sulfur compounds (RSC) were investigated under decaying conditions using 3 food types with strong odor properties: (1) Kimchi (KC), (2) Fresh fish (FF), and (3) Salted fish (SF). The concentrations of RSC from food decaying samples were measured 5 times during the full study period over 15 days. All the analysis of RSC were made by gas chromatography/pulsed flame photometric detector (GC/PFPD) combined with air server/thermal desorber (AS/TD). According to our analysis, CH₃SH recorded the highest mean concentration (53.8 ppb) out of all RSCs investigated concurrently. Comparison between 3 food types showed that KC had the highest odor strength in primary stage, although it showed a notable decrease through time. On the other hand, FF and SF maintained generally low RSC concentrations in the beginning stage, but they showed large increases in emission concentrations with time. Thus, the results indicate that the relative pattern of RSC emissions tends to vary greatly with food types rather than RSC type.
        4,000원
        171.
        2008.12 KCI 등재 SCOPUS 구독 인증기관 무료, 개인회원 유료
        Ni-GDC (gadolinia-doped ceria) composite powders, the anode material for the application of solid oxide fuel cells, were prepared by a solution reduction method using hydrazine. The distribution of Ni particles in the composite powders was homogeneous. The Ni-GDC powders were sintered at 1400˚C for 2 h and then reduced at 800˚C for 24 h in 3% H2. The percolation limit of Ni of the sintered composite was 20 vol%, which was significantly lower than these values in the literature (30-35 vol%). The marked decrease of percolation limit is attributed to the small size of the Ni particles and the high degree of dispersion. The hydrazine method suggests a facile chemical route to prepare well-dispersed Ni-GDC composite powders.
        3,000원
        175.
        2008.09 KCI 등재 구독 인증기관 무료, 개인회원 유료
        To analyze trace-level, reduced sulfur compounds (RSC) in ambient air, gas chromatography (GC) is used as the commonest method. The GC-based analysis is generally conducted by transferring samples via direct injection into GC or by the combined treatment of cryofocusing (CF) and thermal desorption (TD). In this study, experimental bias involved in GC analysis is examined by evaluating the calibration properties of each transfer approach. To this end, the detection properties of RSCs were evaluated with respect to the two major variables of sample concentration and sample volume. The recovery rate of TD application was also discussed based on the most recent findings in which its recovery rate is compared against the results derived by the direct injection method. The overall results suggest that the TD-based analysis of RSCs can be optimized by unifying the experimental conditions between sample and standard gases.
        4,000원
        176.
        2008.09 KCI 등재 SCOPUS 구독 인증기관 무료, 개인회원 유료
        30 % TBP/NDD-2 M HNO3 (0.005 M K2Cr2O7 함유) 계에 의해 산화 추출된 Np의 유기상을 대상으로 n-butyraldehyde (NBA)에 의한 Np의 환원 역추출을 고찰하였다. Np의 역추출은 NBA의 농도 증가에 따라, 역추출 수용상 내 질산농도 감소에 따라, 그리고 반응 온도 감소에 따라 증가하였으며, 이때 겉보기 환원 역추출 속도식은 -d [Np]Org./dt =1,524 exp(-2,906/T) [NBA]0.91[H+]-0.92 [Np]Org. 이었다. 1.04M NBA 및 2M HNO3에서 Np 및 U의 역추출률은 각각 70.1 % 및 7.1 % 이며 이때 분리계수((DU/DNp)는 30.4 정도로, TBP-HNO3 계에 의해 공추출된 Np과 U은 NBA에 의해 효과적으로 상호 분리할 수 있음을 알 수 있었다.
        4,000원
        177.
        2008.08 KCI 등재 SCOPUS 구독 인증기관 무료, 개인회원 유료
        SnO nanosheets were prepared at room temperature through a reaction between an aqueous solution of SnCl2, N2F4, and NaOH and were converted into SnO2 nanosheets without a morphological change. The SnO nanosheets were formed through a dissolution-recrystallization mechanism. Uniform and well-dispersed SnO nanosheets with the round-shape morphology were attained when the solution was treated by ultrasonic sound immediately after the addition of NaOH. The SnO2 nanosheets prepared by means of solution reduction under the ultrasonic treatment, and subsequent oxidation at 600˚C showed a high level of gas sensitivity to C2H5OH and CH3COCH3.
        4,000원
        178.
        2008.07 KCI 등재 SCOPUS 구독 인증기관 무료, 개인회원 유료
        Hydrogen production via high high-temperature steam electrolysis consumes less electrical energy than compared to conventional low low-temperature water electrolysis, mainly due to the improved thermodynamics and kinetics at elevated temperaturetemperatures. The elementalElemental powders of Cu, Ni, and YSZ are were used to synthesize high high-temperature electrolysis cathodecathodes, of Ni/YSZ and Cu/YSZ composites, by mechanical alloying. The metallic particles of the composites were uniformly covered with finer YSZ particles. Sub-micron sized pores are were homogeneously dispersed in the Ni/YSZ and Cu/YSZ composites. In this study, The cathode materials were synthesized and their Characterizations properties were evaluated in this study: It was found that the better electric conductivity of the Cu/YSZ composite was measured improved compared tothan that of the Ni/YSZ composite. Slight A slight increase in the resistance can be produced for in a Cu/YSZ cathode by oxidation, but it this is compensated offset for by a favorable thermal expansion coefficient. Therefore, Cu/YSZ cermet can be adequately used as a suitable cathode material of in high high-temperature electrolysis.
        4,000원
        179.
        2008.06 KCI 등재 구독 인증기관 무료, 개인회원 유료
        This study is focused on the antimicrobial activity of cyanobacteria Microcystis aeruginosa by the reduction and oxidation reaction of copper and zinc alloy metal fiber filter. Cu/Zn ion is easily makes radicals with molecular hydroperoxide. Especially, hydroperoxide radical shows strong toxicity to the strains. Plasma membrane causes conformational change when hydroperoxide radical binds to plasma membrane. Elution of copper ion from copper and zinc alloy metal fiber is detected in the cyanobacteria solution as 0.5 ppm, and that of zinc ion is 0 ppm respectively. Zinc ion is figured to form a hydroxide in the cyanobacteria solution and precipitated to form a sludge. The concentration of chlorophyll-a in the cyanobacteria solution was proved to be the index of antimicrobial level of Microcystis aeruginosa.
        4,000원