The relationship between local plastic deformation and precipitation morphology in ionic crystals

Abstract

The non‐equilibrium precipitation morphology is considered. A new mechanism is suggested whereby rod‐like precipitates are formed as a result of the local plastic deformation of the matrix due to the volume change during precipitation. The mechanism includes three elements: (i) the generation of a set of prismatic dislocation loops and their movement along the slip vector, (ii) the secondary nucleation on the loops, and (iii) the subsequent coagulation of the microprecipitates giving rise to rods with fixed orientations parallel to the operative slip direction. Microscopic evidence indicates that the proposed mechanism does operate when NiCl2 particles are precipitated in NaCl crystals at a relatively high supersaturation.

Precipitation of Nickel Dihalide in Thermally Pretreated NaCl:Ni2+Crystals

“…In terms of the considered precipitation models [11,12], they should be rods oriented along (110) direction. Ιn fact, this shape was confirmed experimentally by some microscopic observations [13,14].…”