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|A study of hexagonal and cubic ice at low temperatures
Ice crystal formation
Ice crystal structure
Ice crystal orientation
|Cold Regions Research and Engineering Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
|Research report (Cold Regions Research and Engineering Laboratory (U.S.)) ; 231.
Abstract: The formation of hexagonal and cubic forms of ice was studied by the use of a cold stage in an electron microscope within the temperature range of -190 to 170°C. Ice crystal specimens were made on cold substrates, i. e. , a collodion film, gold foil, or copper grid on the specimen holder of the cold stage. The structural forms of the ice were detected with the electron microscope using the selected area electron diffraction method. The hexagonal form of ice formed on the cold substrates at temperatures from -90 to -100°C. At -100 to -130°C, both hexagonal and cubic forms of ice were detected. From -130 to -160°C only cubic ice was found. At temperatures below -170°C, minute crystals of cubic ice were detected. No transformation of the structural form of ice from hexagonal to cubic or from cubic to hexagonal occurred when the temperature of the specimens was varied in the range of -90 to -160°C. The minute crystals of cubic ice formed below -160°C were transformed into larger cubic ice crystals by heating them to a tem perature between -130 and -150°C. The lattice constants of hexagonal and cubic ice, and the coefficient of thermal expansion of ice were calculated from the experimental results.
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