title: Experimental study on the effect of ammonia on the phase behavior of tetrahydrofuran clathrates.
abstract: Clathrate hydrates, ice-like crystalline compounds in which small guest molecules are enclosed inside cages formed by tetrahedrally hydrogen-bonded water molecules, are naturally abundant on Earth and are generally expected to exist on icy celestial bodies. A prototypical example is Saturn's moon Titan, where dissociation of methane clathrates, a major crustal component, could contribute significantly to the replenishment of atmospheric methane. Ammonia is an important clathrate inhibiting agent that may be present (potentially at high concentrations) in Titan's interior. In this study, low-temperature Raman experiments are conducted to examine the dissociation point of tetrahydrofuran clathrates, an ambient-pressure analogue of methane clathrates, over a wide range of ammonia concentrations from 0 to 25 wt %. A phase diagram for the H2O-THF-NH3 system is generated, showing two main results: (i) ammonia lowers the dissociation point of clathrate hydrates to a similar extent compared to the melting of water ice and (ii) THF clathrate exhibits a "liquidus-like" behavior in the presence of ammonia, with a eutectic temperature of about 203.6 K. As temperatures higher than this estimated eutectic are anticipated within Titan's icy crust, these results imply that partial dissociation of clathrates can occur readily and may contribute to outgassing from the interior.
authors.affiliation: NASA Jet Propulsion Laboratory, California Institute of Technology , 4800 Oak Grove Drive, Pasadena, California 91109, United States.
authors.forename: Tuan Hoang
authors.initials: TH
authors.lastname: Vu
authors.forename: Elodie
authors.initials: E
authors.lastname: Gloesener
authors.forename: Mathieu
authors.initials: M
authors.lastname: Choukroun
authors.forename: Anaïs
authors.initials: A
authors.lastname: Ibourichene
authors.forename: Robert
authors.initials: R
authors.lastname: Hodyss