TY - JOUR
T1 - High-pressure phase transition of methane hydrate in water-methane-ammonia system
AU - Kadobayashi, Hirokazu
AU - Hirai, Hisako
AU - MacHita, Kenji
AU - Ohfuji, Hiroaki
AU - Muraoka, Michihiro
AU - Yoshida, Suguru
AU - Yamamoto, Yoshitaka
N1 - Funding Information:
This research was partly supported by the JSPS Kakenhi programs (to H.K.; number 19J01467 and 19K14815). This research was also supported by the Joint Usage/Research Center PRIUS, Ehime University, Japan.
Publisher Copyright:
© Published under licence by IOP Publishing Ltd.
PY - 2020/8/17
Y1 - 2020/8/17
N2 - 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.
AB - 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.
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U2 - 10.1088/1742-6596/1609/1/012006
DO - 10.1088/1742-6596/1609/1/012006
M3 - Conference article
AN - SCOPUS:85093365773
VL - 1609
JO - Journal of Physics: Conference Series
JF - Journal of Physics: Conference Series
SN - 1742-6588
IS - 1
M1 - 012006
T2 - 27th AIRAPT International Conference on High Pressure Science and Technology
Y2 - 4 August 2019 through 9 August 2019
ER -