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Now showing items 81 - 84 of 84

  • Metal halide doped metal borohydrides for hydrogen storage: The case of Ca(BH(4))(2)-CaX(2) (X = F, Cl) mixture RID C-3834-2012

    Lee, Ji Youn   Lee, Young-Su   Suh, Jin-Yoo   Shim, Jae-Hyeok   Cho, Young Whan  

    We have explored metal halide doping in metal borohydrides in order to modify hydrogen desorption/absorption properties of such high-capacity solid-state hydrogen storage materials. The specific application here is 10 mol% addition of CaX(2) (X = F, Cl) to Ca(BH(4))(2). The materials are analyzed using insitu X-ray diffraction, differential scanning calorimetry, thermogravimetry, and IR spectroscopy, and the experimental results are compared against theoretical predictions from first-principles. Interestingly, in a fully hydrogenated state, CaCl(2) dissolves into Ca(BH(4))(2) whereas CaF(2) exists as a separate phase. During the course of dehydrogenation, CaH(2)-CaF(2) solid solution, CaHCl, and a new Ca-H-Cl compound are observed. In-situ X-ray diffraction study reveals that CaX(2) interacts with Ca(BH(4))(2) in the early stage of decomposition, which could facilitate a direct decomposition of Ca(BH(4))(2) into CaH(2) and CaB(6) without forming intermediate phases such as CaB(2)H(x) which seem to be thermodynamically in close competition with the formation of CaH(2) and CaB(6). Our first-principles calculation estimates that the decrease in the decomposition temperature due to the CaH(2)-CaX(2) interaction would be less than 10 degrees C, and therefore the major contribution of CaX(2) is to change the dehydrogenation pathway rather than the overall thermodynamics. (c) 2010 Elsevier B.V. All rights reserved.
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  • Stability for the Mixed Type of Quartic and Quadratic Functional Equations

    Lee, Young-Su   Kim, Soomin   Kim, Chaewon  

    We establish the general solutions of the following mixed type of quartic and quadratic functional equation: f(2x + y) + f(2x - y) = 4f(x + y) + 4f(x - y) + 2f(2x) - 8f(x) - 6f(y). Moreover we prove the Hyers-Ulam-Rassias stability of this equation under the approximately quartic and the approximately quadratic conditions.
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  • Effect of Hydrogen Back Pressure on Dehydrogenation Behavior of LiBH(4)-Based Reactive Hydride Composites

    Shim, Jae-Hyeok   Lim, Jae-Hag   Rather, Sami-ullah   Lee, Young-Su   Reed, Daniel   Kim, Yoonyoung   Book, David   Cho, Young Whan  

    Hydrogen back pressure remarkably promotes the formation of metal boride during, the dehydrogenation of 4LiBH(4) + YH(3), 6LiBH(4) + CeH(2) and 6LiBH(4) + CaH(2) composites, which seems to be a general phenomenon in LiBH(4)-based reactive, hydride composites that enables mutual destabilization,between LiBH(4) and metal,hydride. The formation of metal boride plays a crucial role in the reversible hydrogen storage properties of these composites. The dependence of the dehydrogenation behavior on hydrogen back pressure might be associated with the microstructural evolution of the dehydrogenation products formed by a solid liquid reaction.
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  • Numerical simulation of long-term precipitate evolution in austenitic heat-resistant steels RID D-1605-2011 RID C-3834-2012

    Shim, Jae-Hyeok   Kozeschnik, Ernst   Jung, Woo-Sang   Lee, Seung-Cheol   Kim, Dong-Ik   Suh, Jin-Yoo   Lee, Young-Su   Cho, Young Whan  

    Numerical simulation of the long-term precipitate evolution in five different austenitic heat-resistant steels - NE709, Super304H, Sanicro25, CE8C-PLUS and HTUPS - has been carried out. MX and M(23)C(6) are predicted to remain as major precipitates during long-term aging in these steels. While the average size of MX is maintained below several ten nanometers during the aging, that of M23C6 exceeds 100 urn after 100,000 h of aging at 700 degrees C. The addition of 3 wt% Cu produces very fine Cu-rich precipitates during aging in Super304H and Sanicro25. It is found that the amount of Z phase starts to increase remarkably between 1000 and 10,000 h of aging at the expense of MX precipitates in the steels containing a high nitrogen content. However, the growth rate of Z phase is relatively slow and its average size reaches at most a few ten nanometers after 100,000 h of aging at 700 degrees C, compared with 9%-12% Cr ferritic heat-resistant steels. The simulated precipitation sequence and precipitate size during aging are in general agreement with experimental observations. (C) 2010 Elsevier Ltd. All rights reserved.
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