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Kwak, Jinsung,Kwon, Tae-Yang,Chu, Jae Hwan,Choi, Jae-Kyung,Lee, Mi-Sun,Kim, Sung Youb,Shin, Hyung-Joon,Park, Kibog,Park, Jang-Ung,Kwon, Soon-Yong The Royal Society of Chemistry 2013 Physical chemistry chemical physics Vol.15 No.25
<P>A single-layer graphene has been uniformly grown on a Cu surface at elevated temperatures by thermal processing of a poly(methyl methacrylate) (PMMA) film in a rapid thermal annealing (RTA) system under vacuum. The detailed chemistry of the transition from solid-state carbon to graphene on the catalytic Cu surface was investigated by performing <I>in situ</I> residual gas analysis while PMMA/Cu-foil samples were being heated, in conjunction with interrupted growth studies to reconstruct <I>ex situ</I> the heating process. The data clearly show that the formation of graphene occurs by vaporizing hydrocarbon molecules from PMMA, such as methane and/or methyl radicals, which act as precursors, rather than by the direct graphitization of solid-state carbon. We also found that the temperature for vaporizing hydrocarbon molecules from PMMA and the length of time the gaseous hydrocarbon atmosphere is maintained, which are dependent on both the heating temperature profile and the amount of a solid carbon feedstock, are the dominant factors that determine the crystalline quality of the resulting graphene film. Under optimal growth conditions, the PMMA-derived graphene was found to have a carrier (hole) mobility as high as ∼2700 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> at room temperature, which is superior to common graphene converted from solid carbon.</P> <P>Graphic Abstract</P><P>Single-layer graphene films can be uniformly prepared on Cu by vaporizing hydrocarbon molecules from PMMA. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3cp50959a'> </P>
곽진성(Kwak Jinsung),오진호(Oh Jinho),이종민(Lee Jong-min) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12
In this paper, hydraulic mass is estimated by numerical method which simulates experiments in which the fluid dynamic forces acting on perforated plates vibrating in water. In the experiments, natural frequency of rigid plates with regularly aligned holes in air was compared to that of the same plates in water. From the results, hydraulic mass was estimated and formulated in dimensionless form. But the frequency was solved from simple harmonic oscillation, the result was limited to apply to solve problems related to plates flexibility. In this paper, hydraulic mass expressed in terms of added mass is estimated in the same way of the test and it is expanded to flexible plate which has a variety of hole shapes. Acoustic element is used to reflect the effect of water. The results are validated by comparing natural frequencies between with the added mass and with the acoustic element.
다중 압력 스펙트럼 밀도를 이용한 감쇠 탱크 구조 건전성 평가
곽진성(Kwak Jinsung),정민규(Jung Min-kyu),오진호(Oh Jinho),이종민(Lee Jong-min) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12
The main purpose of PCS(Primary Cooling System) is to remove heat generated from the reactor core through the heat exchangers. The coolant passing through the reactor core contains a variety of radionuclides. N-16 governs the coolant radioactivities at the core exit, but it has a very short decay time. The main function of decay tank is to decay the readionuclides, especially N-16 by providing enough transient time to ensure that N-16 activity decreases in the decay tank. The decay tank has three internal perforated plates which spread the coolant into the whole section of the decay tank to increase transit time. The perforated plate is affected by various loadings such as seismic load, thermal load, flow induced vibration and etc. Specially, the pressure induced by flow gives the main effect to the structure integrity of the perforated plate. In this paper, structure integrity of decay tank including fatigue is evaluated through the pressure power spectral density functions that are derived from turbulent flow.
Sim, Yeoseon,Kwak, Jinsung,Kim, Se-Yang,Jo, Yongsu,Kim, Seunghyun,Kim, Sung Youb,Kim, Ji Hyun,Lee, Chi-Seung,Jo, Jang Ho,Kwon, Soon-Yong The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.4
<P>Improving the lifetime and the operational stability of polymer electrolyte membrane fuel cells (PEMFCs) is critical for realizing their implementation as a practical and highly-efficient energy conversion system. However, the corrosion of metal bipolar plates, which are a key component in PEMFCs, leads to decreased efficiency and durability. Here, we prepared poly(methyl methacrylate)-derived multilayer graphene (Gr) coatings with high crystallinity and a continuous three-dimensional (3D) structure using a rapid thermal annealing (RTA) system for short periods (≤5 min). The resulting 3D Gr-coated Ni foam is demonstrated to act as a bipolar plate with long-term operating stability. Electrochemical analysis revealed that the synthesized graphene on Ni foam outperforms bare Ni foam and amorphous-carbon-coated Ni foam by providing a two-order-of-magnitude lower corrosion rate in the operating environment for a PEMFC. In addition, after stability tests in a destructive environment, the 3D Gr-coated Ni foam maintained its outstanding interfacial contact resistance of 9.3 mΩ cm<SUP>2</SUP>at 10.1 kgf cm<SUP>−2</SUP>. A H2/air PEMFC fabricated using the Gr-coated Ni foam embedded within the groove of a graphite-based bipolar plate exhibited a substantially enhanced power density of ∼967 mW cm<SUP>−2</SUP>at a cell potential of 0.5 V with further advantages of weight reduction and no additional machinery process for the gas flow channel. This facile coating approach addresses one of the key limitations of current metal bipolar plates in PEMFCs, and paves the way to further enhance energy conversion systems through interface engineering.</P>