The growth of phase IV ammonium nitrate crystals and their transformation to the phase III structure

Abstract

Previous studies of the IV III transition in ammonium nitrate have indicated a wide variation in transition temperature between samples and highlighted the catalytic role played by water. In the current work an examination of the relationship between the transformation behaviour of phase IV single crystals and their single-crystal growth history is made. A very clear correlation exists between the probability of transformation and the morphology of solution-grown phase IV crystals. This experimental morphology is found to agree well with theoretical predictions for crystals grown at low supersaturations. For high supersaturations the crystal habit becomes dominated by kinetic factors which favour growth along the a axis and inclusion of trapped solution.