Kinetics and Mechanism of AP Combustion Initiation: A Complete Quantum Chemical Prediction for Reactions in Three Phases

Abstract

In an extensive series of studies on the initiation process of ammonium perchlorate (AP) combustion employing high-level quantum chemical techniques, we have investigated 85 reactions occurring in the gas phase, in solution and on AP crystal surface. Gas-phase reactions including the unimolecular decomposition of HOClO₃ and numerous bimolecular processes such as OH + ClO₃, NH_x + ClO_y (x = 2, 3; y = 0 - 4), HOCl + H/O/HO/HO₂ , HOCl + ClO_x (x = 1- 4) and HOCl + HNO_x (x = 1, 3), Cl/ClO/OH + HClO₃, ClO + NO_x/HO_x (x = 1 - 2), among others, have been studied by molecular orbital and quantum-statistical theory calculations. Several examples of these processes will be discussed. For the reactions occurring on the AP surface and in water solution, we have employed the periodic boundary and continuum solvent models (PCM) to study the effects of water on the sublimation and decomposition of AP. The results of these calculations agree quantitatively with available experimental kinetic data. The activation energies for redox processes in water solution were computed to be very high and no reactions leading to the production of NO_x, ClO₂ and HOCl species as proposed in the literature could be identified.