The influence of solution chemistry on the morphology of ammonium dinitramide crystals

The influence of solutions on ammonium dinitramide (ADN) crystal morphology was investigated using a combined experimental and molecular dynamics simulation approach. Scanning electron microscopy showed that ADN recrystallized from acetone, propanol, dimethyl sulfoxide (DMSO), and ethanol exhibited a lamellar structure, in contrast to the polyhedron structure obtained with isopropanol/NaF. X-ray diffraction analysis revealed that ADN crystals are mainly composed of six crystal faces (010, 011, 110, 100, 121, 031), and acetone, propanol, DMSO, and ethanol result in crystals in which growth at face (100) dominated. Molecular dynamics simulations indicated that the accessible surfaces and lattice energy (E_latt) vary with the crystal faces. The interaction energy between solutions and crystal faces (E_int) was dependent on both crystal faces and solution components, as was the attachment energy (E_att). The relative standard deviation R_dev^′ of the growth rate of the crystal faces was ordered as follows: acetone (0.117) > propanol (0.098) > DMSO (0.094) > ethanol (0.087) > isopropanol (0.078) > isopropanol/NaF (0.073). A larger R_dev^′ resulted in a lamellar structure, while a smaller R_dev^′ gave more homogeneous growth rates that resulted in polyhedron crystals.