460981 Phase Transition of Acid Clathrate Hydrate Related to the Proton Conduction: Structural Analysis of Perchloric Acid Hydrate

Monday, November 14, 2016
Grand Ballroom B (Hilton San Francisco Union Square)
Kyuchul Shin, School of Applied Chemical Engineering, Kyungpook National University, Daegu, South Korea, Minjun Cha, Dep. of Energy and Resources Eng., Kangwon National University, Chuncheon-si, South Korea, Wonhee Lee, Climate Change Research Division, Korea Institute of Energy Research, Daejeon, South Korea and Huen Lee, Korea Advanced Institute of Science and Technology (KAIST), Department of Chemical and Biomolecular Engineering, Daejeon, South Korea

Clathrate hydrates are nonstoichiometic crystalline compounds which are stabilized by van der Waals interaction between the hydrophobic guest molecules and the hydrogen-bonded water host framework. Unlike classical clathrate hydrates, ionic clathrate hydrates additionally show an ionic interaction between cationic or anionic guest species and counterion-doped host network. A few strong acids form clathrate structures in which anions are encaged into the protonated water cavities. There are two types of protonated host framework. One is hydrogen fluoride-contained host framework such as hexahydrates of HPF6, HAsF6, or HSbF6 and another is hydrogen fluoride-free host framework such as hydrates of HBF4 or HClO4. The latter is believed to contain several vacancy sites in the hydrogen bonding lattice for protonation of the host framework. In this work, the neutron powder diffraction patterns of a DClO4·5.5D2O clathrate were obtained at various temperatures and refined by Rietveld analysis with the direct space method. A position change of vacancy sites was predicted at about 180 K, and this phenomenon is expected to induce a phase transition related to the proton conduction behavior of the perchlorate acid clathrate. The present work provides a better understanding of the proton dynamics of the hydrogen fluoride-free acid clathrate hydrates.

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