Void migration in sodium chloride crystal under temperature gradient

A simulation experiment on columnar grain formation in UO₂ was performed using NaCl single crystals, to examine the progress of void formation and migration. When two single crystals of NaCl were held together under a temperature gradient, plate-like or lenticular voids were observed to generate and migrate towards the hot side, forming columnar grains in the NaCl crystal. The crystallographic orientation of the colder crystal was found to affect the void shapes observed in the hotter crystal. This void behavior is explained by calculations concerning the evaporation and condensation of the NaCl molecule. (author)