Crystal Morphology Prediction of Hexahydro-1,3,5-trinitro-1,3,5-triazine by the Spiral Growth Model

The crystal morphology of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) was predicted by the advanced Burton–Cabrera–Frank (BCF) model with consideration of non-centrosymmetric growth units. The present modeling showed that the advanced BCF model provides reliable results and understanding of the growth habit of RDX crystals grown from acetone and γ-butyrolactone, in which the {210} and {111} faces are dominantly developed. In the present work, the kink rate, which is the net flux input and output from kink sites along the edge, is found to be a critical factor for the crystal growth of RDX, where the energy required for detaching the growth unit from a kink site determines the existence probability of a growth unit. The {210} and {111} faces were found to show slow kink rates originated from the kink sites with a low existence probability and consequently became morphologically important faces. Moreover, the effect of solvent on the crystal growth habit of RDX, the difference in morphology of RDX grown from acetone and γ-butyrolactone, was confirmed by utilizing local concentration contained in the kink rate term.