Kinetics of direct and reverse polymorphic transformations in molecular crystals of energetic compounds

The β → γ polymorphic transformation (PT) in polycrystalline 1,1-diamino-2,2-dinitroethylene (DADNE) was studied by isothermal calorimetry. The kinetics of the β → γ PT, like that of the α → β process studied earlier, follows the first-order autocatalytic equation. The rate constants and activation energy of the process were determined. The kinetics of the reverse β → α and γ → α PTs in DADNE was studied by IR spectroscopy. The rates of the β → α and γ → α PTs follow first-order kinetics with the rate constants that depend on morphological features of the crystals. The general features of the kinetics of direct and reverse polymorphic transformations in molecular crystals of energetic compounds are discussed.