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Kim Yong Hyeon,Park Sungyu,Kwon Chang Il,Kim So Young,Watanabe Kenji,Taniguchi Takashi,Kim Jun Sung 한국물리학회 2023 Current Applied Physics Vol.46 No.-
We investigated the electrical transport properties of optimally Li+-intercalated FeSe nanoflakes. Using solid electrolyte gating, we obtained high and uniform electron doping up to ~0.55 electrons per Fe sites in the FeSe nanoflakes, which exhibit a sharp superconducting transition at Tc ~45.0 K. The temperature and magnetic-field dependent current-voltage characteristics clearly revealed the two-dimensional nature of the superconductivity in the intercalated FeSe nanoflakes. From the self-field critical current measurements, we found two distinct isotropic superconducting gaps with different gap ratios. These findings suggest that the highly electron-doped FeSe hosts two interband pairing channels between the hybridized electron pockets, in contrast to the case of pristine FeSe with electron and hole pockets.
Hojin Kim,Jinju Kim,Sungyu Park,Je Hyun Bae The Korean Electrochemical Society 2024 Journal of electrochemical science and technology Vol.15 No.2
To date, methods used to assess the interfacial transition zone (ITZ), which represents the boundary between the aggregate and paste inside concretes, have primarily relied on destructive tests, and non-destructive tests has received little attention until recently. This study assessed the interfaces of concretes with lightweight aggregates based on electrochemical impedance spectroscopy (EIS) for high-strength concretes and examined the possibility of estimating the compressive strength of concretes through non-destructive testing using EIS. The experimental results revealed that the impedance of the hardened cement increased with increasing compressive strength and aggregate density. In particular, when the results of impedance measurement were displayed as a Nyquist plot, the intercept of the x-axis depicting the effective conductivity was proportional to the compressive strength. Furthermore, an equivalent circuit was selected to interpret the correlation between cement aggregates and impedance. Consequently, the compressive strength was found to increase with the value of the resistances of the electrolyte filled in continuous pores in the cement aggregate. And, the pores formed in the ITZ affect this value. The resistance at the ITZ for different aggregates was also obtained, and it was found that the resistance was consistent with the results predicted by SEM images of the ITZ and correlated with the strength of the concretes. The proposed method can be used as a way to easily determine the strength of cement according to differences in aggregate.
대기 부식에 의해 생성된 Al1050 및 Al7075 알루미늄 합금 산화막에 대한 투과전자현미경 분석
김선규(Sungyu Kim),이찬형(Chanhyeong Lee),반치범(Chi Bum Bahn) 한국표면공학회 2017 한국표면공학회지 Vol.50 No.6
Al1050 and Al7075 alloy specimens were exposed to atmospheric conditions for maximum 12 months and analyzed by Transmission Electron Microscopy (TEM) to characterize the early-stage corrosion behavior and thin surface oxide layers. By comparing of oxide films between Al1050 and Al7075 alloys, it is concluded that Al7075 has a relatively thicker surface oxide film than Al1050 but Al1050 has relatively more significant oxygen penetration through grain boundaries. The oxygen penetration through grain boundaries appeared to be influenced by intermetallic particles at the grain boundary. In the case of aluminum alloys, localized corrosion like pitting or intergranular corrosion should be considered as well as uniform corrosion when estimating the atmospheric corrosion rate.
Initial oxidation behavior of Fe-Cr-Si alloys in 1200 °C steam
Moon, Joonho,Kim, Sungyu,Park, Won Dong,Kim, Tae Yong,McAlpine, Samuel Westcott,Short, Michael P.,Kim, Ji Hyun,Bahn, Chi Bum ELSEVIER 2019 JOURNAL OF NUCLEAR MATERIALS Vol.513 No.-
<P><B>Abstract</B></P> <P>Accident-tolerant fuel (ATF) cladding with high oxidation resistance during severe accidents is of critical importance to light water reactor safety and sustainability. One newly proposed ATF cladding concept, a multi-metallic layered composite (MMLC), hinges upon the oxidation resistance of an outer Fe-Cr-Si layer on top of a Zr-based alloy, separated by barrier layers to avoid Fe-Zr eutectic formation. The initial oxidation resistance of three potential Fe-Cr-Si alloys was evaluated by exposing them to 1200 °C oxidizing steam for up to one hundred seconds, along with a Zr–Nb–Sn alloy as a reference. The oxidation resistance of Fe12Cr2Si and Fe16Cr2Si was poor, exhibiting a porous, incomplete multilayer oxide composed mainly of mixed Fe/Cr/Si spinels. However, Fe20Cr2Si showed excellent oxidation resistance due to a continuous amorphous SiO<SUB>2</SUB> layer formed at the metal–oxide interface, followed by almost fully dense Cr<SUB>2</SUB>O<SUB>3</SUB>. This motivates the consideration of Fe-Cr-Si alloys as an additional ATF design choice, similar to FeCrAl alloys in performance and oxidation resistance mechanism.</P>