Melt-Grown Grain Textures of Eutectic Mixtures of Water Ice with Magnesium- and Sodium-Sulfate Hydrates and Sulfuric-Acid Hydrate Using Cryogenic SEM (CSEM)

Details Melt-Grown Grain Textures of Eutectic Mixtures of Water Ice with Magnesium- and Sodium-Sulfate Hydrates and Sulfuric-Acid Hydrate Using Cryogenic SEM (CSEM) Melt-Grown Grain Textures of Eutectic Mixtures of Water Ice with Magnesium- and Sodium-Sulfate Hydrates and Sulfuric-Acid Hydrate Using Cryogenic SEM (CSEM)

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.t42a0275m&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #T42A-0275

Mathematics

Logic

5470 Surface Materials And Properties, 5494 Instruments And Techniques, 6020 Ice, 8147 Planetary Interiors (5430, 5724)

Scientific paper

Tectonic processes on Europa are influenced by the rheology of ice and icy compounds. The rheology of water ice alloyed with one or more hydrates at planetary conditions is not well known. We investigate grain size effects on ice rheology in Europan eutectic systems. Although much is known about the rheology of pure ice, the addition of other phases can potentially affect the grain textures and rheologies of polyphase mixtures. We make such alloys by cooling and crystallizing aqueous binaries of water with sodium-sulfate hydrate, magnesium-sulfate hydrate or sulfuric acid hydrate. Using a precision cryobath and seeded growth, we can make eutectic mixtures of ice with these hydrates by precisely controlled freezing of these solutions. This method of controlled growth with only small undercooling of the eutectics avoids the problem of rapid, uncontrolled growth that occurs when no seed material is used. A field-emission SEM fitted with a cryogenic prepping station and observation stage permits detailed SEM microscopy on fractured surfaces of these specimens without decomposition under the electron beam. We also use energy dispersive x-ray spectra to distinguish between the ice and sulfate-hydrate phases. We see reproducible eutectic grain textures developed using these methods and observe two types of grain morphologies made evident by differences in surface relief: (1) Large ice grains; (2) Fine eutectoid intergrowths associated with simultaneous growth of ice and hydrate. Grain sizes of the eutectic intergrowths range from approximately 5 to 50 microns, far smaller than developed during free growth of ice from the melt and apparently stable at temperatures near eutectic. We plan deformation tests on such samples to investigate the effects of these fine grain sizes on sample strengths compared to the strenths of cold-pressed mixtures of these same phases. This ongoing work is a first look at these important grain textures in chemical systems that are probably volumetrically important in Europa. Understanding the effects of these complex and intriguing intergrowths on rheology may enable prediction of the behavior of such material under stress and better explain morphological features on Europa's surface.

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