Nihon Kessho Gakkaishi
Online ISSN : 1884-5576
Print ISSN : 0369-4585
Part 2. Crystal Structure and Physical Properties of Minerals in the Earth's and Planetary Interior
Changes in Phases and Physical Properties of Gas Hydrates Under Low to High Temperatures and High Pressures and their Implications of Interiors of Icy Bodies
Hisako HIRAIHirokazu KADOBAYASHI
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2018 Volume 60 Issue 1 Pages 54-61

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Abstract

Gas hydrates, clathrate compounds, consist of hydrogen-bonded water molecules forming cages and of guest species included in the host cages. A wide variety of gas hydrate exhibits phase changes depending on pressure and guest size, and finally transforms to filled ice structures. Upon phase transition between cage structures, e.g. sⅠ to sH of methane hydrate, a characteristic “cage recombination mechanism” using an analogy from genetic recombination was observed, while upon sH to filled ice structure, typical reconstructive mechanism was observed. At low temperatures and high pressures phase changes induced orientational ordering of guest molecules occurs for methane hydrate and hydrogen hydrate. At high temperatures and high pressures, methane hydrate decomposes to solid methane and ice Ⅶ. The stability region and decomposition curve was obtained.

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© 2018 The Crystallographic Society of Japan
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