Autocatalytic thermal decomposition kinetics of TNT

Thermal analysis has been employed to determine the kinetics and the energetics of the slow cook-off chemistry of 2,4,6-trinitrotoluene (TNT) by isothermal differential scanning calorimetry (DSC) in high-pressure crucibles sealed under air. Model-free isoconversional analysis of the DSC kinetic traces has been used to determine activation energies (Eα) and the functional form of the reaction model (dependence of reaction rate on the extent of conversion, α). While the variation in Eα with α is in qualitative agreement with the literature it is nevertheless constant within the 95% confidence limits at 140±10 kJ mol−1. Hence, no systematic variation in Eα occurs over the course of the reaction. Rather, the reaction model exhibits a large increase in the range 0.1<α<0.25 and a decrease for 0.25<α<0.43. Thus, the observed acceleratory period is caused by an increase in the reaction model, not by a decrease in activation energy, as might be expected for autocatalysis. This kinetic behavior is ascribed to nucleation and growth of reaction centers in liquid state TNT. In addition, a heat of reaction, Q=(4.9±1.5)×102 kJ mol−1 during the thermal decomposition of TNT has been shown to be independent of the heating rate and sample size.