Co-Authors:
Tanny, J., Center for Technological Education Holon, P.O.B. 305, Holon, 58102, Israel
Abstract:
Crystallization of a uniform binary liquid at the cooled vertical boundary of an enclosure can generate compositional stratification in the melt. During its evolution the induced stratified region is separated from the uniform melt by a sharp density interface which migrates with time. This phenomenon is studied experimentally in an axisymmetric geometry, by cooling and crystallizing a uniform aqueous solution of sodium carbonate (Na2CO3) by means of a vertical circular pipe through which coolant is circulated. The investigation is focused on the effect of the applied undercooling on the structure of the crystal and on the growth rates of the stratified layer depth and the typical crystal diameter. It is shown that, at low undercooling, the dendrites at the mush-liquid interface are packed, the stratified layer depth grows as t1.1 and the typical crystal diameter grows like t0.45 (where t is the time from initiation of cooling). At larger undercooling, the dendrites are spiky and the stratified layer depth and the typical crystal diameter grow like t1.5 and t0.7, respectively. © 1995.
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