Nucleation velocity of NaPO3 melts

The time τ for visible crystallization of NaPO₃ melts is measured in the whole range of undercoolings from the melting temperature T_m to the temperature of vitrification T_g. It is shown that the time τ, needed for the appearance of a visible crystallization at high supersaturations is determined by the linear growth rate, whereas the rate of heterogeneous nucleation is the main factor, determining the experimentally measured time τ at low supersaturations. The specific surface energy σ at the melt-crystal interface is calculated from the data on nucleation velocity in the vicinity of T_m and the temperature dependences of both heterogeneous and homogeneous nucleation velocity for NaPO₃ melts are constructed. It is concluded that at normal cooling rates only nucleation, initiated by active crystallized cores could be observed for NaPO₃.