Effects of phase separation on crystallization behavior

The effects of phase separation on the kinetics of crystal growth have been investigated for three compositions in the Na₂OSiO₂ system, containing about 1.5, 10 and 15 mol% Na₂O. In the two cases for which reliable data could be obtained over the full range of temperature (10 and 15% Na₂O), the measured growth rates are independent of time, for crystallization temperatures within as well as outside the miscibility gap. In both cases, the growth rate versus temperature relations are continuous through the region of the immiscible boundary. These results are related to previous data on the effects of phase separation on viscosity in the Na₂OSiO₂ system and on nucleation and crystallization in the Li₂OSiO₂ system. It is suggested that transport at the crystal-liquid interface in a phase-separating system involves different types of atomic rearrangements than those involved in viscous flow.