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|Effect of growth parameters on substructure spacing in NaCl ice crystals
|Dartmouth College. Department of Earth Sciences
Lofgren, Gary E.
Weeks, W. F.
Ice crystal structure
Ice crystal growth
Ice crystal formation
|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.)) ; 195.
Abstract: The effect of growth velocity 𝗏 and solute concentration 𝖢 on the cellular substructure that develops in NaCl ice is studied in the range 3 x 10^-3 to 10^-5 cm/sec and 1 to 100 ‰ respectively. The substructure is the result of the formation of a constitutionally supercooled zone in the liquid ahead of the advancing interface. Unidirectional freezing runs were made by placing a cold plate in contact with the top of the solution and using cold-plate temperatures of -20 and -70°C. The growth velocities were determined from a least-squares fit of the growth data to a power series. The average spacings between neighboring substructures a 0 were measured from photomicrographs of precisely located thin sections. Log-log plots of a𝗈 vs 𝗏 show that the slope 𝗇 gradually changes as a function of 𝗏. In the run where no convection occurs, 𝗇 changes from 1/2 to 1 as 𝗏 decreases in agreement with the prediction of Bolling and Tiller. The results of Rohatgi and Adams are also shown to be in good agreement with this prediction. On the other hand, when convection occurs, 𝗇 changes from 1/2 to approximately 0 as 𝗏 decreases. This is caused by convection reducing the effective value of 𝖢 at the growing interface. The variation of a𝗈 with 𝖢 is quite complex and shows a minimum in the composition range 9 to 25 ‰ NaCl.
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