• Title/Summary/Keyword: Gas diffusion layer

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A study on the Effect for Process Parameters on the Micro-pulse Plasma Nitriding of Ductile Cast Iron (구상흑연주철의 마이크로 펄스 플라즈마 질화에 미치는 공정변수의 영향에 관한 연구)

  • 김무길;이철민;권성겸;정병호;이재식;유용주;김기준
    • Journal of Advanced Marine Engineering and Technology
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    • v.24 no.3
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    • pp.43-51
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    • 2000
  • The effect of time, temperature and gas composition on the case hardened thickness, hardness and nitride formation in the surface of ductile cast iron(GCD400) have been studied by micro-pulse plasma technique. Typically, external compound layer and internal diffusion layer which is much thicker than compound layer was observed in the nitride hardening of ductile cast iron. The relative amount kind of phases formed in the nitrided hardening changed with the change of nitriding conditions. Generally, only nitride phases such as $\gamma^'$($Fe_4N$), or $\varepsilon$($Fe_{2-3}N$) phases were detected in compound layer by XRD analysis. The thickness of compound layer increased with the increase of nitrogen content in the gas composition. The optimum nitriding temperature was obtained at $520^{\circ}C$. The nitrided hardening thickness parabolically with nitriding time(t) and thus, the case hardened layer(d) fits well with the typical parabolic equation ; d=kt. The material constant k for GCD400 nitrided at $520^{\circ}C$ was $0.04919\times10^3{\mu}m.hr^{-1/2}$.

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Effect of Post-Metallization Anneal (PMA) on Interface Trap Density of Si-$SiO_2$ (금속후 어닐링 방법이 Si-$SiO_2$ 계면 전하 농도에 미치는 영향)

  • Jung, Jong-Wan
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2007.11a
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    • pp.157-158
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    • 2007
  • Effects of post-metallization anneal (PMA) on interface trap characteristics of Si-$SiO_2$ are studied. The conventional PMA method utilizes forming gas anneal, where 10% hydrogen in nitrogen atmosphere is used. A new PMA method utilizes hydrogen rich PECVD- silicon nitride $(SiN_x)$ film as a hydrogen diffusion source and a out-diffusion blocking layer. It can be shown through charge pumping current measurement that the new PMA is indeed effective to decrease Si-$SiO_2$ interface trap density.

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Generation of Microcellular Foams in Viscoelastic Polymer Solutions (점탄성 폴리머 용액에서의 초미세 폼의 생성)

  • Kang, Sung- Lin;Kim, Ki-Young;Kwak, Ho-Young
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.6
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    • pp.726-733
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    • 2004
  • The growth of the critical size bubble by diffusion process in viscoelastic medium was treated by an integral method for the concentration boundary layer adjacent to the bubble wall. In this study, we obtained a set of the first order time dependent equations to obtain bubble radius and gas pressure inside the bubble simultaneously. The calculated final cell sizes depending on the initial saturation pressure are in close agreement with the observed ones. The governing equations developed in this study may be used in polymer processing of microcellular foams.

Performance Analysis of Fuel Cell by Controlling Active Layer Thickness of Catalyst (촉매 활성층 두께 제어를 통한 연료전지 성능 해석)

  • Kim, H.G.
    • Transactions of the Korean Society of Machine Tool Engineers
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    • v.16 no.3
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    • pp.133-140
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    • 2007
  • A 2-D model of fluid flow, mass transport and electrochemistry is analysed to examine the effect of current density at the current collector depending on active layer thickness of catlyst in polymer elecrolyte fuel cells. The finite element method is used to solve the continuity, potential and Maxwell-Stefan equations in the flow channel and gas diffusion electrode regions. For the material behavior of electrode reactions in the active catalyst layers, the agglomerate model is implemented to solve the diffusion-reaction problem. The calculated model results are described and compared with the different thickness of active catalyst layers. The significance of the results is discussed in the viewpoint of the current collecting capabilities as well as mass transportation phenomena, which is inferred that the mass transport of reactants dictates the efficiency of the electrode in the present analysis.

Electrodeposition of Zr on AISI 304 Stainless Steel in Molten Chlorides. (염화물계 혼합염욕중에서 AISI 304 Srainless Steel의 Zr 전해피복에 관한연구)

  • 반장호;백영현
    • Journal of the Korean institute of surface engineering
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    • v.30 no.3
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    • pp.159-166
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    • 1997
  • The metalliding technique was adopted to obtain the diffusion coating of zirconium on AISI 304 Stainless Steel in molten mixed chlorides (32.9wt.%LICl-34.8wt.%NaCl-32.3wt.%). Experiments were carried out in argon gas atmosphere. The electrolytic cell was consisted of a AISI 304 Stainless steel cathode and a consumable zirconium anode. The quality of deposit was analysed by SEM, Optical Microscope, EDS, and also examined by the Micro-Vickers hardness and corrosion tests. Interface of deposit layer was identified as zirconium-iron alloy layer caused by diffusion process at elevated temperatures. The optimum condition for the metalliding was found to be the bath temperature of $550^{\circ}C$, the concentration of $K_2ZrF_6$ ,5wt.%, cathodic current derrent density of 7.0 to 10.0mA/$\textrm{cm}^2$ , and anodic current density of 2.0mA/$\textrm{cm}^2$.

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Generation of Microcellular Foams in Viscoelastic Polymer Solutions (점탄성 폴리머 용액에서의 초미세 폼의 생성)

  • Kang, Sung-Lin;Kim, Ki-Young;Kwak, Ho-Young
    • Proceedings of the KSME Conference
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    • 2004.04a
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    • pp.174-179
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    • 2004
  • The growth of the critical size bubble by diffusion process in viscoelastic medium was treated by an integral method for the concentration boundary layer adjacent to the bubble wall. In this study, we obtained a set of the first order time dependent equations to obtain bubble radius and gas pressure inside the bubble simultaneously. The calculated final cell sizes depending on the initial saturation pressure are in close agreement with the observed ones. The governing equations developed in this study may be used in polymer processing of microcellular foams.

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Concentration Interaction of Premixed and Triple-layer Flames in Lean Burn with Methane Fuel (희박연소에서 발생하는 메탄의 농도 상호작용과 삼중화염에 대한 연구)

  • Oh, Tae-Kyun;Chung, Suk-Ho
    • Transactions of the Korean Society of Automotive Engineers
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    • v.14 no.6
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    • pp.171-178
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    • 2006
  • The performance in the practical combustion system including reciprocating engines and gas turbine combustors is being much governed by turbulent reacting flow that is often analyzed by both a laminar flamelets concept and flame interaction. The characteristics of laminar flame interaction have been investigated numerically to provide basic understanding of wrinkled turbulent flames under concentration interaction resulting from inhomogeneity in fuel-air mixing, especially focused on the transition of flame characteristics such as diffusion flame, partially premixed diffusion flame, and triple-layer flame by the variation in the degree of premixedness. The extinction stretch rates to the premixedness have also been obtained in this paper. The boundary defining the regime of the existence of triple-layer flames as functions of both stretch rate and premixedness has been determined which agrees well with previously reported experiment measuring OH radical concentration peaks based on PLIF.

A Numerical Study of Cathode Block and Air Flow Rate Effect on PEMFC Performance (고분자전해질 연료전지의 환원극 블록과 공기 유량 영향에 대한 전산 해석 연구)

  • Jo, Seonghun;Kim, Junbom
    • Applied Chemistry for Engineering
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    • v.33 no.1
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    • pp.96-102
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    • 2022
  • Reactants of PEMFC are hydrogen and oxygen in gas phases and fuel cell overpotential could be reduced when reactants are smoothly transported. Numerous studies to modify cathode flow field design have been conducted because oxygen mass transfer in high current density region is dominant voltage loss factor. Among those cathode flow field designs, a block in flow field is used to forced supply reactant gas to porous gas diffusion layer. In this study, the block was installed on a simple fuel cell model. Using computational fluid dynamics (CFD), effects of forced convection due to blocks on a polarization curve and local current density contour were studied when different air flow rates were supplied. The high current density could be achieved even with low air supply rate due to forced convection to a gas diffusion layer and also with multiple blocks in series compared to a single block due to an increase of forced convection effect.

Effects of Nitrogen Contents on the Nitriding Characteristics of the Micro-Pulse Plasma and Post Oxidation Treated SCM440 Steel (SCM440강의 마이크로 펄스 플라즈마 질화 및 후산화처리시 질소농도에 따른 특성변화)

  • Lee, S.K.;Chung, I.S.;Lee, J.S.
    • Journal of the Korean Society for Heat Treatment
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    • v.12 no.2
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    • pp.117-128
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    • 1999
  • This study was carried out to investigate the surface characteristics of SCM440 steel nitrided with various nitrogen contents for 7 hours at $520^{\circ}C$ by using micro-pulse plasma nitriding apparatus of hot wall type. The effects of oxidation treatment was also investigated on plasma nitrided in 30% nitrogen and post oxidized SCM440 steel at $500^{\circ}C$ in $H_2O$ atmosphere. The ${\gamma}^{\prime}-Fe_4N$ and ${\varepsilon}-Fe_{2-3}N$ phases were detected in compound layer of the nitrided steel. As the content of nitrogen in plasma gas increased with 30, 50, 70% on the micro-pulse plasma nitriding for SCM440 steel, the thickness of compound, diffusion layer and the surface hardness were increased. From the wear test results, the best wear resistance was appeared in the condition of ductile ${\gamma}^{\prime}-Fe_4N$ phase formed specimen at 30% nitrogen, whereas that of the treated with 50% and 70% nitrogen decreased owing to the exfoliation of brittle ${\varepsilon}-Fe_{2-3}N$ phase in the compound layer. On the nitrided and subsequently oxidized SCM440 steel, the surface layer consisted of $Fe_3O_4$, ${\gamma}^{\prime}-Fe_4N$, and ${\varepsilon}-Fe_{2-3}N$ phases. In these treatments, the dissolution of nitrides affect hardness and hardening depth in compound and diffusion layers. For the nitrided in 30% nitrogen and post oxidized specimen at $500^{\circ}C$ for 1 hour, the wear resistance was lower than that of the only nitrided one in 30% nitrogen but higher than those of the nitrided ones in 50 and 70% nitrogen.

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An Experimental Study on Flame Structure and Combustion Characteristics of Turbulent Diffusion Flame(I) (난류확산화염의 화염구조와 연소특성에 관한 실험적 연구)

  • Choe, Byeong-Ryun;Jang, In-Gap;Choe, Gyeong-Min
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.3
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    • pp.1028-1039
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    • 1996
  • This study was focused on the examination of the flame structure and the combustion characteristics of diffusion flame which was formed the turbulent shear flow of a double coaxial air jet system. The shear flow was formed by the difference velocity of surrounding air jet(U$\_$s/) and center air jet (U$\_$c/). So experimental condition was divided S-type flame (.lambda. > 1) and C-type flame (.lambda. < 1) by velocity ratio .lambda. (=U$\_$s//U$\_$c/). For examination of the flame structure and the combustion characteristics in diffusion flame, coherent structure was observed in flame by schlieren photograph method. We measured fluctuating temperature and ion current simultaneously and accomplished the statistical analysis of its. According to schlieren photograph, the flame was stabilized in the rim of the direction of lower velocity air jet, coherent eddy was produced and developed by higher velocity air jet. The statistical data of fluctuating temperature and ion current was indicated that reaction was dominated by higher velocity air jet. The mixing state of burnt gas and non-burnt gas was distributed the wide area at Z = 100 mm of C-type flame.