In solidification process of aqueous solution, mushy region appears between the pure solid part and liquid part, which contains pure dendritic ice crystals and liquid solution. In this report, the effects of supercooling degree and initial concentration on microscopic structure are experimentally examined. Dendritic structure is observed when the supercooling degree is large and the concentration is low, while cellular structure is observed in opposite conditions. Three stages are observed; non-equilibrium stage, stagnation stage and equilibrium stage. The relation between crystal growth velocity and supercooling degree is obtained. The crystal growth velocity in the first stage shows the nonequilibrium process in the equilibrium chart.
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