Mechanism and Kinetics for Ammonium Perchlorate Sublimation: A First-principles Study

Abstract

We have studied for the first time the kinetics and mechanism for the sublimation/decomposition of NH4ClO4 by first-principles calculations, using a generalized gradient approximation with the plane-wave density functional theory. Supercells containing 4, 8, and 16 NH4ClO4 units were used; the predicted enthalpic change for solid NH4ClO4 to gaseous NH3 and HClO4 is 45.0 ± 1.5 kcal/mol. The calculated desorption activation energies for NH3, HClO4, and H3N···HOClO3 molecular complexes, individually, from the relaxed surface are 45.3, 43.5, and 28.1 kcal/mol, respectively. The rate constant for the dominant sublimation process desorbing H3N···HOClO3 as a pair can be presented by ksub.= 6.53 × 1012 exp (−28.8 kcal/mol/RT) s−1, which is in reasonable agreement with available experimental data. Expectably, the decomposition of H3N···HOClO3 (g) to NH3 (g) and HOClO3 (g) is considerably faster, about 1 × 107 times greater than that for the sublimation process in the same temperature range. The rate constant for t...