Kinetics of thermal decomposition of cubic ammonium perchlorate

The methods of thermogravimetric analysis (TGA) and differential scanning c alorimettry (DSC) have been used to study the thermal decomposition of ammo nium perchlorate (AP). TGA curves obtained under both isothermal and noniso thermal conditions show a characteristic slowdown at the extents of convers ion, alpha = 0.30-0.35. DSC demonstrates that in this region the process ch anges from an exothermic to an endothermic regime. The latter is ascribed t o dissociative sublimation of AP. A new computational technique (advanced i soconversional method) has been used to determine the dependence of the eff ective activation energy (E-alpha) on alpha for isothermal and nonisotherma l TGA data. At alpha > 0.1, the E-alpha dependencies obtained from isotherm al and nonisothermal data are similar. By the completion of decomposition ( alpha --> 1) the activation energy for the isothermal and nonisothermal dec omposition respectively rises to similar to 110 and similar to 130 kJ mol(- 1), which are assigned to the activation energy of sublimation. The initial decomposition (alpha --> 0) shows the activation energy of 90 kJ mol(-1) f or the isothermal decomposition and 130 kJ mol(-1) for the nonisothermal de composition. The difference is explained by different rate-limiting steps, which are nucleation and nuclei growth for isothermal and nonisothermal dec ompositions, respectively.