The kinetic of thermal decomposition of PETN, Pentastite and Pentolite by TG/DTA non-isothermal methods

The non-isothermal TG/DTA technique has been used to study the thermal decomposition of PETN, Pentastite (93:7 of PETN:wax) and Pentolite (50:50 of TNT:PETN). The DTA curves were showed an exothermic peak for decomposition of PETN and Pentastite and the exothermic double peaks for decomposition of Pentolite over the range of 150-270 A degrees C at heating rates of 4, 6, 8 and 10 K min(-1) under argon atmosphere. The double peaks in decomposition of Pentolite were related to PETN and TNT, respectively. The overlapped peaks were resolved by peak fitting procedure. Then, the activation energy (E (a)) of thermal decomposition of PETN, Pentastite and Pentolite was calculated by model-free methods of KAS, OFW and Friedman for different conversion fraction (alpha) values in the range 0.1-0.9. The pre-exponential factor and the best kinetic model for decomposition of explosives were determined by means of the compensation effect, and the selected model was confirmed by the nonlinear model-fitting method. The activation energy was 135.1-136.9, 143.6-149.2, 123.0-125.0 and 59.9-75.2 kJ mol(-1) for PETN, Pentastite and first peak of Pentolite (PETN) and second peak of Pentolite (TNT), respectively. The higher activation energy and thermal stability of Pentastite versus PETN is related to the additive paraffin wax. While, the synergic effect between two explosives in Pentolite is due to decrease of the E (a) of its components. The mechanism function of Avrami-Erofeev A (3/2), A (5/4), A (2) and A (3) was the most probable models for description of thermal decomposition reactions of PETN, Pentastite, PETN (first peak) in Pentolite and TNT (second peak) in Pentolite, respectively.