Thermal decomposition of ammonium perchlorate

Abstract

The thermal decomposition of ammonium perchlorate has been studied by measuring either the loss in weight, or the pressure increase in a closed system, as functions of time. Analysis of the former measurements is complicated by concurrent sublimation of the salt. Measurements of the sublimation rate have therefore been made over a wide temperature range and kinetic parameters both for sublimation and for thermal decomposition have been established. The activation energy for the low temperature thermal decomposition is 26.63 ± 0.87 kcal/mole from Avrami-Erofeev rate constants and 30.08 ± 1.98 kcal/mole from induction periods. The activation energy for sublimation is 28.04 ± 0.43 kcal/mole from contracting volume rate constants. It is uncertain whether the activation energy for decomposition changes at the transition point : least mean squares values are 33.91 ± 1.64 kcal/mole below the transition point and 26.97 ± 2.36 kcal/mole above the transition point. The catalytic effects of ammonia (negative) and of perchloric acid(positive) have led to the formulation of a unified mechanism for sublimation and decomposition which involves proton transfer from NH⁺₄ to ClO^–₄ ions as the basic step.