Effect of ammonia on methane hydrate stability under high-pressure and high-temperature conditions

Hirokazu Kadobayashi, Hisako Hirai, Hiroaki Ohfuji, Hideaki Kawamura, Michihiro Muraoka, Suguru Yoshida, Yoshitaka Yamamoto

Research output: Contribution to journalArticlepeer-review

Abstract

High-pressure experiments were conducted to investigate the stability and phase transition of methane hydrate (MH) in the water-methane-ammonia system at room-to-high temperatures employing Raman spectroscopy and synchrotron X-ray powder diffraction, in combination with an externally heated diamond anvil cell. The results revealed that, at room temperature, MH undergoes phase transitions from MH-I to MH-II at ∼1.0 GPa and from MH-II to MH-III at ∼2.0 GPa. These transition behaviors are consistent with those in the water-methane system, which indicates that ammonia has a negligible effect on a series of phase transitions of MH. Contrarily, a sequential in situ Raman spectroscopy revealed that ammonia affects the stability of MH-III under high pressure and high temperature: the dissociation temperature of MH-III was more than 10 K lower in the water-methane-ammonia system than in the water-methane system. These findings aid in improving the internal structural models of icy bodies and estimating the origin of their atmospheric methane.

Original languageEnglish
Pages (from-to)10890-10896
Number of pages7
JournalJournal of Physical Chemistry A
Volume124
Issue number51
DOIs
Publication statusPublished - 2020 Dec 24
Externally publishedYes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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