• Title/Summary/Keyword: Reaction Disk

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Electrocatalytic Reduction of Dioxygen at Glassy Carbon Electrodes with Irreversible Self-assembly of N-hexadecyl-N'-methyl Viologen

  • Lee, Chi-Woo;Jang, Jai-Man
    • Bulletin of the Korean Chemical Society
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    • v.15 no.7
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    • pp.563-567
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    • 1994
  • The electroreduction of dioxygen at glassy carbon electrodes with irreversible self-assembly of N-hexadecyl-N'-methyl viologen $(C_{16}VC_1)$ proceeds at potentials more positive than those where the reduction occurs at bare electrodes. The electrocatalyzed reduction takes place at potentials well ahead of those where the catalyst is reduced in the absence of dioxygen and the limiting currents observed at rotating disk electrodes did not deviate from the thoretical Levich line up to 6400 rpm, indicating that the electrocatalysis is extremely rapid. The rate constant for the heterogeneous reaction between $C_{16}V^+C_1$ immobilized on the electrode surface and $O_2$ in solution was estimated to be ca. $10^8\;M^{-1}s^{-1}$. The half-wave potential of dioxygen reduction was independent of solution pH.

Pulsed DB/AB T-Burner Test for Measurement of Combustion Response Function of Solid Propellants

  • Lim, Jih-Wan;Yoon, Woong-Sup;Yoo, Ji-Chang
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2008.03a
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    • pp.431-436
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    • 2008
  • T-burner tests of an Al/HTPB propellant in conjunction with a Pulsed DB/AB Method were conducted to find an acoustic amplification factor. Aluminum-free and aluminum-heavy propellants were examined. Instant surface ignition was successfully made by the use of a supplementary propellant of fractionally higher reaction rate. With the presence of higher aluminum concentration in the propellants, the pressure perturbations were promptly damped down and the pressure fluctuations were no longer dispersive. Addition of aluminum particles into the propellant was advantageous for stabilizing pressure-coupled unstable waves.

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A Study on Plasma Etching Reaction of Cobalt for Metallic Surface Decontamination (금속 표면 제염을 위한 코발트의 플라즈마 식각 반응 연구)

  • Jeon, Sang-Hwan;Kim, Yong-Soo
    • Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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    • v.6 no.1
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    • pp.17-23
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    • 2008
  • In this study, plasma processing of metal surface is experimentally investigated to enhance the surface decontamination efficiency and to find out the reaction mechanism. Cobalt, the major contaminant in the nuclear facilities, and three fluorine-containing gases, $CF_4/O_2$, $SF_6/O_2$, and $NF_3$ are chosen for the investigation. Thin metallic disk specimens are prepared and their surface etching reactions with the three plasma gases are examined. Results show that the maximum etching rate of $17.2\;{\mu}m/min.$ is obtained with NF3 gas at $420^{\circ}C$, while with $CF_4/O_2$, $SF_6/O_2$ gas plasmas those of $2.56\;{\mu}m/min.$ and $1.14\;{\mu}m/min.$ are obtained, respectively. Along with etching experiments, constituent elements of the reaction products are identified to be cobalt, oxygen, and fluorine by AES (Auger Electron Spectroscopy) analysis. It turns out that the oxygen atoms are physically adsorbed ones to the surface from the ambient not participation ones during the analysis after reaction, which supports that the surface reaction of cobalt is mainly to be a fluorination reaction.

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Composition Survey and Analysis of Non-Pt Oxygen Reduction Catalysts for Proton Exchange Membrane Fuel Cells (고체 고분자 연료전지용 비백금계 산소환원촉매 조성 조사 및 분석)

  • Kwon, Kyung-Jung
    • Journal of the Korean Electrochemical Society
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    • v.15 no.1
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    • pp.12-18
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    • 2012
  • The prohibitively high cost of Pt catalyst might be the biggest barrier for the commercialization of proton exchange membrane fuel cells (PEMFC) of which wide application is expected. Worldwide research efforts for the development of alternative to Pt oxygen reduction reaction (ORR) catalyst are made recently. One of the important considerations in the catalyst development is durability issue as well as economic aspect. From this point of view, platinum group metals (PGM) except Pt can be a candidate for replacing Pt catalyst because the material properties and the catalytic activity of PGM are expected to be similar to Pt. In contrast to Ir, Rh and Os to which not so much attention has been paid as an ORR catalyst, Pd that is most similar to Pt in terms of material properties and catalytic activity and Ru that is in the form of chalcogenide have been studied intensively. Activity comparison between non-Pt and Pt oxygen reduction catalysts by half cell test using RDE (rotating disk electrode) or PEMFC MEA (membrane electrode assembly) operation indicates that Pd-based catalysts show the most similar activity to Pt. In this paper we analyze the composition of PGM ORR catalyst in literature to promote the development of non-Pt ORR catalyst.

Electrochemical Behavior of Dissolved Hydrogen and Hydrogen Peroxide in Boric Acid Solution at the Elevated Temperature (붕산수용액 매질에서 용존수소와 과산화수소의 고온 전기화학 거동연구)

  • Yeon Jei-Won;Woo Seung-Kyun;Choi Young-Ku;Jung Yongju;Kim Won-Ho
    • Journal of the Korean Electrochemical Society
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    • v.7 no.1
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    • pp.21-25
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    • 2004
  • The electrochemical behaviors of dissolved hydrogen and hydrogen peroxide at a platinum disk electrode were investigated in boric acid solution by potentiostatic polarization method at the temperature of 25 and $200^{\circ}C$. The oxidation of dissolved hydrogen at $25^{\circ}C$ was kinetically controlled reaction, the rate of which depends upon the electron transfer on the electrode surface. As temperature was raised, however, the electrochemical characteristics of dissolved hydrogen were changed from a kinetically controlled reaction to a diffusion controlled one. One notable feature, with dissolved hydrogen at high temperature, is that an abnormal potential range was observed, where the oxidation rate of dissolved hydrogen rapidly decreased just before starting potential of water oxidation. We think it is caused by the deactivation of the electrode that results from the adsorption of hydroxyl ion on the surface of the platinum disk. On the contrary, a definite change with temperature was not identified in the case of the hydrogen peroxide except for the increase in current density that was due to the increasing diffusion coefcient with an increase of temperature.

Reaction Characteristics of Combined Steam and Carbon Dioxide Reforming of Methane Reaction Using Pd-Ni-YSZ Catalyst (Pd-Ni-YSZ 촉매를 이용한 수증기-이산화탄소 복합개질 반응 특성)

  • Kim, Sung Su
    • Applied Chemistry for Engineering
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    • v.29 no.4
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    • pp.382-387
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    • 2018
  • In this study, the reaction characteristics of combined steam and carbon dioxide reforming of methane (CSCRM) reaction using Pd-Ni-YSZ catalyst were investigated according to types of catalysts and gas compositions. Catalysts were prepared in the form of powder and porous disk. The injected gases were supplied at different ratios of $CH_4/CO_2/H_2O$. As a result, the conversion of $CH_4$ and $CO_2$ was improved as a result of using the porous disc type catalyst as compared with that of the powder type catalyst. When the $CH_4/CO_2/H_2O$ ratio of the feed gas was 1 : 0.5 : 0.5, the $H_2/CO$ ratio was adjusted close to 2. However, after 6 hours of the reaction, $CH_4$ conversion was partially reduced by the carbon deposition and the pressure drop increased from 0.1 to 0.8. This issue was then solved by optimizing the water content. As a result, it was confirmed that the durability was secured by preventing the carbon deposition when the gas was supplied at a $CH_4/CO_2/H_2O$ ratio of 1 : 0.5 : 1, and the conversion rate was maintained at a relatively high level.

A study of the synthesis and the properties on microwave dielectric material of $BaO-Sm_2O_3-TiO_2$ system ($BaO-Sm_2O3-TiO_2$계 마이크로파 유전체의 합성 및 그 특성에 관한 연구)

  • 이용석;김준수;이병하
    • Electrical & Electronic Materials
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    • v.10 no.3
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    • pp.274-283
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    • 1997
  • These days, according to surprising development of communication enterprises, every soft of devices is getting smaller and cheaper. Among these Devices, microwave dielectric ceramics are studied and progressed briskly as the materials of dielectric resonator. Dielectric properties of BaO-S $M_{2}$ $O_{3}$-Ti $O_{2}$, one of the BaO Lnsub 2/ $O_{3}$-Ti $O_{2}$ (Ln=La, Sm, Nd, Pr…) system, synthesized by solid-reaction and coprecipitation method were investigated. Disk-type samples were sintered at 1250-1400.deg. C for 2hrs. As a result, single phase was not synthesized in both method. First created the second phase of S $M_{2}$ $Ti_{2}$ $O_{7}$, and then the last phase of $Ba_{3.75}$S $m_{9.5}$ $Ti_{18}$ $O_{54}$, Ti $O_{2}$, and $Ba_{2}$ $Ti_{9}$ $O_{20}$. When the sample was sintered at 1280.deg. C (in solid reaction method) and at 1310.deg. C (in coprecipitation method), it obtained highest dielectric constant (72.96 and 71.70, respectively) and high Q value. Above that temperature, dielectric constant and Q value decreased because of lattice defect according to oxygen vacancies........

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Patterns of Antimicrobial Resistance and Genotyping of Extended Spectrum $\beta$-Lactamase (ESBL) Producing Clinical Isolates in Korea

  • Lee, Gyu-Sang;Kim, Jong-Bae
    • Biomedical Science Letters
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    • v.13 no.4
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    • pp.293-304
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    • 2007
  • The emergence of extended spectrum $\beta$-lactamase (ESBL) producing bacteria is worldwide concern. Until recently, the most frequently identified strains in the Republic of Korea were E. coli and Klebsiella spp. The incidence of resistance to extended spectrum $\beta$-lactam antibiotics is increasing in Wonju city, Korea. Total 57 strains of ESBL producing E. coli and Klebsiella species were isolated from Wonju Christian Hospital during a 9 month-period from April to December, 2003. To determine the prevalence and genotypes of the ESBL producing clinical isolates, antibiotic susceptibility and ESBL activity test by VITEK system and double disk synergy (DDS) test, and PCR based genotyping were performed. Fourteen (82%) isolates of 17 ESBL producing E. coli were found to have $bla_{TEM}$ gene and 5 (29%) isolates were found to have $bla_{CTX-M}$ gene by polymerase chain reaction (PCR). Thirty (75%) isolates of 40 ESBL producing Klebsiella species with $bla_{TEM}$ gene, 38 (95%) isolates with $bla_{SHV}$ gene, and 7 (20%) isolates with $bla_{CTX-M}$ type gene were also identified. Enterobacterial repetitive intergenic consensus (ERIC) PCR and similarity index by dendrogram for genetical similarity to band pattern of each clinical isolates were examined. ESBL producing E. coli were grouped into 6 clusters up to 84% of similarity index and Klebsiella species were grouped into 12 clusters up to 76% of similarity index. In conclusion, ESBL producing clinical isolates were characterized with the results from antimicrobial resistance pattern and genetical similarity using ERiC PCR.

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A Study of a Changing of Physical and Chemical Intra-structure on Si-DLC Film during Tribological Test (실리콘 함유 DLC 박막의 마찰마모 시험에 의한 물리적 특성 및 화학적 결합 구조 변화 고찰)

  • Kim, Sang-Gweon;Lee, Jae-Hoon;Kim, Sung-Wan
    • Journal of the Korean Society for Heat Treatment
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    • v.24 no.3
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    • pp.127-132
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    • 2011
  • The silicon-containing Diamond-like Carbon (Si-DLC) film as an low friction coefficient coating has especially treated a different silicon content by plasma-enhanced chemical vapor deposition (PECVD) process at $500^{\circ}C$ on nitrided-STD 11 mold steel with (TMS) gas flow rate. The effects of variable silicon content on the Si-DLC films were tested with relative humidity of 5, 30 and 85% using a ball-on-disk tribometer. The wear-tested and original surface of Si-DLC films were analysed for an understanding of physical and chemical characterization, including a changing structure, via Raman spectra and nano hardness test. The results of Raman spectra have inferred a changing intra-structure from dangling bonds. And high silicon containing DLC films have shown increasing carbon peak ratio ($I_D/I_G$) values and G-peak values. In particular, the tribological tested surface of Si-DLC was shown the increasing hardness value in proportional to TMS gas flow rate. Therefore, at same time, the structure of the Si-DLC film was changed to a different intra-structure and increased hardness film with mechanical shear force and chemical reaction.

Development of Mixed Conducting Ceramic Membrane for High Purity Hydrogen and Carbon Production from Methane Direct Cracking (복합전도성 세라믹 분리막의 탄화수소 직접분해에 의한 고순도 수소와 탄소 제조)

  • Kim, Ji-Ho;Choi, Duck-Kyun;Kim, Jin-Ho;Cho, Woo-Seok;Hwang, Kwang-Taek
    • Transactions of the Korean hydrogen and new energy society
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    • v.22 no.5
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    • pp.649-655
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    • 2011
  • Methane direct cracking can be utilized to produce $CO_x$ and $NO_x$-free hydrogen for PEM fuel cells, oil refineries, ammonia and methanol production. We present the results of a systematic study of methane direct cracking using a mixed conducting oxide, Y-doped $BaZrO_3$ ($BaZr_{0.85}Y_{0.15}O_3$), membrane. In this paper, dense $BaZr_{0.85}Y_{0.15}O_3$ membrane with disk shape was successfully sintered at $1400^{\circ}C$ with a relative density of more 93% via addition of 1 wt% ZnO. The ($BaZr_{0.85}Y_{0.15}O_3$) membrane is covered with Pd as catalyst for methane decomposition with an DC magnetron sputtering method. Reaction temperature was $800^{\circ}C$ and high purity methane as reactant was employed to membrane side with 1.5 bar pressure. The $H_2$ produced by the reaction was transported through mixed conducting oxide membrane to the outer side. In addition, it was observed that the carbon, by-product, after methane direct cracking was deposited on the Pd/ZnO-$BaZr_{0.85}Y_{0.15}O_3$ membrane. The produced carbon has a shape of sphere and nanosheet, and a particle size of 80 to 100 nm.