Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and high pressure DSC (HP-DSC) have been used to study the thermal decomposition of ammonium perchlorate samples in the form of 2-mm, monocrystals, 265- and 3-mu m powders, and pellets pressed at 4 and 7 tons. HP-DSC runs have been performed to determine the effect of pressure on decomposition. TGA and DSC techniques have been employed to examine the effect of sample type on the kinetics of the process. The effects have been evaluated as changes in the temperature, reaction heat, and rate of decomposition. Isoconversional kinetic analysis has been carried out to detect changes in the effective activation energy of the process. These measurements and calculations show sublimation and decomposition for ammonium perchlorate to be highly dependent on sample preparation and applied pressure. This calculation finds that the activation energy for the early stages of sublimation/decomposition for all samples starts at similar to 120 kJ mol(-1), which is followed by a dramatic drop to similar to 60 kJ mol(-1) at 20% mass loss. The activation energy for the later stages of sublimation/decomposition varies with sample type ranging from similar to 95 to 145 kJ mol(-1) (c) 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.