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Updated: Nov 25, 2025

Methane Hydrate Crystallization on Sessile Water Droplets
Published on: May 26, 2021
Effect of Ammonia on Methane Hydrate Stability under High-Pressure and High-Temperature Conditions
Hirokazu Kadobayashi1, Hisako Hirai2, Hiroaki Ohfuji3
1National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan.
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.
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