Prediction of Phase Transition and Ignition Sensitivity of Ammonium Periodate

The ammonium periodate (NH4IO4, API) was theoretically investigated to understand the influence of the crystalline structure on mechanical ignition sensitivity. Density functional theory (DFT) calculations predicted polymorphism of API, showing a phase change from tetragonal (API(T)) to monoclinic (API(M)) starting at an external pressure of similar to 3 GPa. During this transformation, isolated IO4- ions are linked to form a chain structure. Theoretically predicted optimal phase change temperature is similar to 450 K, where calculated enthalpy of phase transition Delta H-phase reaches a minimum of 4.6 kJ/mol. The API(M) has properties correlated with ignition sensitivity, including low resistance to shear, with Young's modulus of 16.27 GPa compared with 25.99 GPa of API(T), and smaller electronic band gap, 3.51 eV compared with 4.46 eV of API(T). The Delta H-phase is reduced from 7.3 kJ/mol at 0 K to 4.62 kJ/mol at 450 K, indicating that heat should facilitate the phase transition. The calculated enthalpy of decomposition (Delta H-dec) of -12 and -17 kJ/mol for API(T) and API(M) indicates a relatively small difference, suggesting that phase transition does not affect combustion performance. Therefore, the polymorphism induced by shear and facilitated by higher temperatures may be a powerful mechanism of ignition for API.