Interface Behavior under First Phase Transition: A Qualitative Analysis

A qualitative analysis of the stability of the stationary regime of directed crystallization is considered. Non-equilibrium boundary conditions are taken at the interface, i.e., it is taken into account that interface temperature is not equal to the equilibrium temperature of a phase transition. In this case, the stability of the interface is affected by both a change of the equilibrium temperature of a phase transition during crystallization and a change of the interface temperature. The present work does not consider the spatial distribution of temperature over the phases. The description of stability is reduced to the analysis of a system with distributed parameters, the relationship between them being described by the linear oscillator equation. It is shown that there is a variety of conditions under which the stationary movement of the flat interface can be unstable. An important result is that even in such a schematic description, interface instability in an asymptotic case of quasi-equilibrium problem formulation qualitatively differs from interface instability in the case of non-equilibrium problem formulation.