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Calorimetric studies of the ammonia-water system with application to the outer solar systemA 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.
Document ID
19930069766
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Yarger, Jeffery
(NASA Headquarters Washington, DC United States)
Lunine, Jonathan I.
(NASA Headquarters Washington, DC United States)
Burke, Michael
(Arizona Univ. Tucson, United States)
Date Acquired
August 16, 2013
Publication Date
July 25, 1993
Publication Information
Publication: Journal of Geophysical Research
Volume: 98
Issue: E7
ISSN: 0148-0227
Subject Category
Lunar And Planetary Exploration
Accession Number
93A53763
Distribution Limits
Public
Copyright
Other

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