Effect of ammonia on the thermal decomposition of orthorhombic and cubic ammonium perchlorate

The inhibiting effect of ammonia vapours on the kinetics of the thermal decomposition of ammonium perchlorate(AP) in the temperature range 215–270°C has been investigated. An initial ammonia pressure of about 200 Torr is necessary for the practically full suppression of the decomposition of the orthorhombic crystals at temperatures close to the point of AP polymorphic transformation (240°C). With the cubic crystals, 0.5 Torr is the corresponding pressure required. In the case of complete inhibition of the decomposition in the presence of ammonia, AP crystals become yellowish. The activation energy of decomposition of the orthorhombic modification is 29 ± 0.6 kcal mole^?1 in the absence of ammonia, and 38 ± 1.1 kcal mole^?1 under ammonia vapour pressure of 6.5 Torr. A kinetic analysis of the traditional proton model of AP decomposition has been made showing that the increase of the activation energy in the presence of ammonia may be derived from this model.