title: Texture change of ice on anomalously preserved methane clathrate hydrate.
abstract: We used a confocal scanning microscope to observe growth and texture change of ice due to the dissociation of methane gas clathrate hydrate (CH(4) hydrate). The experiments were done under CH(4) gas atmospheric pressure and isothermal conditions between 170 and 268 K. Above 193 K, the dissociation of CH(4) hydrate resulted in many small ice particles that covered the hydrate surface. These ice particles had roughly the same shape and density between 193 and 210 K. In contrast, above 230 K the ice particles developed into a sheet of ice that covered the hydrate surface. Moreover, the measured release of CH(4) gas decreased when the sheet of ice formed at the surface of the hydrate. These findings can explain the anomalous preservation behavior of CH(4) hydrate; that is, the known increase of storage stability of CH(4) hydrate above 240 K is likely related to the formation of the ice that we observed in the experiments.
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), Tsukisamu-Higashi, Sapporo 062-8517, Japan.
authors.forename: Wataru
authors.initials: W
authors.lastname: Shimada
authors.forename: Satoshi
authors.initials: S
authors.lastname: Takeya
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Kamata
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Uchida
authors.forename: Jiro
authors.initials: J
authors.lastname: Nagao
authors.forename: Takao
authors.initials: T
authors.lastname: Ebinuma
authors.forename: Hideo
authors.initials: H
authors.lastname: Narita