Other
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993jgr....9813109y&link_type=abstract
Journal of Geophysical Research (ISSN 0148-0227), vol. 98, no. E7, p. 13,109-13,117.
Other
16
Ammonia, Comets, Eutectics, Icy Satellites, Planetary Composition, Water, Ammonium Compounds, Calorimeters, Cooling, Enthalpy, Glass Transition Temperature, Volcanoes, Planets, Outer Planets, Ammonia, Water, Laboratory Studies, Freezing, Calorimetry, Procedure, Heating, Temperature, Water Ice, Chronology, Ammonia Dihydrate, Partial Melting, Thermal Effects, Stability, Data, Equilibrium, Satellites, Icy Bodies, Phases, Cooling, Experiments, Analysis, Calculations, Comets, Gas Planets
Scientific paper
A series of heating experiments was performed on the condensed ammonia-water system using a differential scanning calorimeter (DSC). The water-rich samples were cooled quickly to below 130 K, then heated at a variety of rates. Rather than a single peritectic melt at 176 K, expected for the equilibrium system of water ice and ammonia dihydrate, four enthalpic transitions were repeatedly seen in the temperature range 150-176 K. These transitions are generally consistent with the earlier calorimetric results of Van Kasteren (1973), who interpreted the lowest temperature exotherm as crystallization of an amorphous ammonia-water compound formed during cooling. We propose that both sets of experiments are seeing the crystallization of ammonia monohydrate, which is metastable relative to the dihydrate, followed by partial remelting and crystallization of dihydrate upon further heating. The apparent stability of the monohydrate in the dihydrate equilibrium field implies a potentially complex behavior of ammonia-water ices in satellites. Possible self-heating of the mixture by several tens of degrees up to the 170 K eutectic could make mobilization of ammonia-water liquids in icy satellite interiors energetically easier than previously thought.
Burke Martin
Lunine Jonathan I.
Yarger J.
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