Interfacial stability of migrating brine inclusions in alkali halide single crystals supporting a temperature gradient

Abstract

Application of a temperature gradient to a solid containing inclusions exerts a driving force which sets the inclusions in motion towards higher temperatures. Since the inclusions are essentially negative crystals, they retain definite shape with the inclusion walls being low index crystallographic planes of the host solid matrix. The migration speed of these inclusions is known to depend on the kinetics of interfacial crystallization/dissolution, which favors layer-by-layer growth/dissolution. Despite these effects, which tend to keep the inclusion walls stable and straight, interfacial instabilities are occasionally observed in the migrating inclusions. A perturbation method is used to analyze such instabilities at a planar interface growing from solution. The model is applied to the interfaces of the temperature gradient driven brine inclusions in alkali halide single crystals, and the resulting stability criteria are checked against limited available experimental data.