Migration of Small Pores in Potassium Chloride Due to a Temperature Gradient

Pore migration in KCl crystals subjected to a temperature gradient occurs by a vaporization-condensation mechanism. The behavior of small (<100 μm) pores was observed using hot-stage microscopy. A size-dependent probability of pore motion was noted in which the fraction of mobile pores in a given size range steadily increased with size. Pores larger than =50 μm were always mobile. These observations are explained in terms of the probabilities of pore-dislocation intersections. Screw-type dislocations are found to be essential for providing molecular height surface ledges needed for vaporization and pore motion. The observation that some small pores moved and then stopped is explained by the fact that the vaporization rate becomes very low when the pore-dislocation intersection occurs at the edge of a faceted pore.