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High-pressure growth of fluorine-free SmFeAsO<sub>1−<i>x</i></sub> superconducting single crystals
Lee, H-S,Park, J-H,Lee, J-Y,Kim, J-Y,Sung, N-H,Koo, T-Y,Cho, B K,Jung, C-U,Saini, S,Kim, S-J,Lee, H-J IOP Publishing Ltd 2009 Superconductor science & technology Vol.22 No.7
<P>Fluorine-free SmFeAsO<SUB>1−<I>x</I></SUB> single crystals of a nominal composition with <I>x</I> = 0.15 were grown under the pressure of 3.3 GPa and at 1350–1450 °C by using the self-flux method. Plate-shaped crystals of a few–200 µm in lateral size were obtained. The resistively determined superconducting transition of a single crystal was at about 53.5 K, with a narrow resistive transition width of 0.5 K. The detailed crystal structure was analyzed by using synchrotron-irradiated x-ray diffractometry and high-resolution scanning transmission electron microscopy. A sharp transition, a low residual resistivity, and a large residual resistivity ratio indicate the high quality of our single crystals. The temperature and magnetic field dependences of the magnetization also confirmed the absence of extrinsic impurity phases.</P>
이충길,이우붕,여환진,이광필,배준웅,이무상,여수동,정원우 慶北大學校 師範大學 科學敎育硏究所 1998 科學敎育硏究誌 Vol.22 No.-
The purpose of this study was to develop the PC program of learning aids by using three dimension molecular model for high school chemistry class. Specifically, this study developed instructional materials of molecular structure and crystall model using Virtual Reality modeling Language The developed program would be expected to be helpful for constructing image of molecular and crystal structure in high school students. Also, it may be useful for chemistry teachers who want to introduce molecular and crystal model into their classes.
Selective silver ion adsorption onto mesoporous graphitic carbon nitride
Lee, S.U.,Jun, Y.S.,Lee, E.Z.,Heo, N.S.,Hong, W.H.,Huh, Y.S.,Chang, Y.K. Pergamon Press ; Elsevier Science Ltd 2015 Carbon Vol.95 No.-
A 3D cubic structure of mesoporous graphitic carbon nitride (3D-g-CN) was fabricated by nano casting using the mesoporous silica hard template KIT-6. The abundant intrinsic amine functionalities of 3D-g-CN were applied as a selective adsorbent for silver ions using the unique affinity of silver and amine functionalities. The large surface area of 3D-g-CN resulted in increased amine functionalities at the surface and enabled it to form complexes with silver ions. As a result, almost 400 mg/g of silver ion could be removed from 100 mM of initial solution at 293.15 K. The isotherm of silver ion adsorption onto 3D-g-CN was described by the Freundlich and Sips models and indicated heterogeneity of the adsorbent surface. Thermodynamic parameters determined from temperature dependent isotherms were verified by the endothermic silver ion adsorption process of 3D-g-CN. The adsorption capacity of silver ion on 3D-g-CN was maintained during several reuses without a significant decrease in capacity. Overall, the results indicate that 3D-g-CN has intrinsic amine functional groups with a large surface area and could therefore be utilized as an efficient selective adsorbent of silver ions for water purification.
Lee, S. h.,Koo, K. Y.,Jung, U. H.,Shul, Y. G.,Yoon, W. L. Springer Science + Business Media 2016 Research on chemical intermediates Vol.42 No.5
<P>We investigated the pre-reforming of n-tetradecane (C14H30) over the K-promoted 50 wt% Ni/MgO-Al2O3 catalyst and also analysed the coke resistance. The 50 wt% Ni/MgO-Al2O3 catalysts were prepared by the deposition-precipitation method and 1-5 wt% of potassium was added to the catalyst using the impregnation method. The catalysts were characterized by ICP, XRD, H-2-chemisorption, H-2-TPR, and BET. The pre-reforming of n-tetradecane was performed under the reaction conditions of S/C = 4.0, GHSV = 3000 h(-1), and 400-450 A degrees C. The Ni crystallite size increased, whereas the Ni dispersion and surface area of catalysts decreased with increasing amounts of K. The 50 wt% Ni/MgO-Al2O3 showed large amounts of coke deposition compared to the K-promoted catalysts. It was found that the K addition over 50 wt% Ni/MgO-Al2O3 catalyst was beneficial for coke removal by promoting the coke gasification. A 1 wt%K/50 wt% Ni/MgO-Al2O3 catalyst showed stable activity during pre-reforming at S/C = 4.0, GHSV = 3000 h(-1), and 400 A degrees C. Furthermore, it had the lowest amount of surface coke, as observed by SEM, TEM, and TG analysis.</P>