EFFECT OF GROWTH PARAMETERS ON SUBSTRUCTURE SPACING IN NaCl ICE CRYSTALS.
COLD REGIONS RESEARCH AND ENGINEERING LAB HANOVER N H
Pagination or Media Count:
The effect of growth velocity v and solute concentration C on the cellular substructure that develops in NaCl ice is studied in the range 0.003 to 0.00001 cmsec and 1 to 100 ooo 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 -70C. The growth velocities were determined from a least-squares fit of the growth data to a power series. The average spacings between neighboring substructures and o were measured from photomicrographs of precisely located thin sections. Log-log plots of a sub o vs v show that the slope n gradually changes as a function of v. In the run where no convection occurs, n changes from 12 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 12 to approximately 0 as v decreases. This is caused by convection reducing the effective value of C at the growing interface. The variation of a sub o with C is quite complex and shows a minimum in the composition range 9 to 25 ooo NaCl. Author
- Physical and Dynamic Oceanography
- Snow, Ice and Permafrost