High-pressure phase transition of methane hydrate in water-methane-ammonia system

Hirokazu Kadobayashi, Hisako Hirai, Kenji MacHita, Hiroaki Ohfuji, Michihiro Muraoka, Suguru Yoshida, Yoshitaka Yamamoto

Research output: Contribution to journalConference articlepeer-review

1 Citation (Scopus)

Abstract

The phase transition of methane hydrate in water-methane-ammonia system was investigated under pressures up to 20 GPa using synchrotron X-ray powder diffraction (XRD) combined with diamond anvil cells. The XRD experiments revealed that the sI cage structure (MH-I) of methane hydrate transforms into an sH cage structure (MH-II) at approximately 1 GPa, further transforms into a filled-ice Ih structure (MH-III) at approximately 2 GPa, and remains in this structure under pressures up to at least 20 GPa. Ammonia was observed as ammonia hemihydrate phase-II above 3.8 GPa. It is therefore considered that methane hydrate can coexist with aqueous ammonia below 3.8 GPa and coexist with ammonia hemihydrate phase-II above 3.8 GPa. The transition pressures of methane hydrate in the investigated system were consistent with those in water-methane system. These results indicate that, although ammonia is thought to inhibit methane hydrate formation, methane hydrate can be stable in water-methane-ammonia system up to at least 20 GPa and at room temperature. The pressure range in this study covered the pressure conditions inside icy moons, indicating that methane hydrate has a potential to be the main constituent of them.

Original languageEnglish
Article number012006
JournalJournal of Physics: Conference Series
Volume1609
Issue number1
DOIs
Publication statusPublished - 2020 Aug 17
Externally publishedYes
Event27th AIRAPT International Conference on High Pressure Science and Technology - Rio de Janeiro, Brazil
Duration: 2019 Aug 42019 Aug 9

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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