Autocatalytic thermal decomposition kinetics of TNT

Abstract

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 ( E α ) and the functional form of the reaction model (dependence of reaction rate on the extent of conversion, α). While the variation in E α 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 E α 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)×10 2 kJ mol −1 during the thermal decomposition of TNT has been shown to be independent of the heating rate and sample size.