Thermal decomposition of hexanitrostilbene at low temperatures

Abstract

The thermal decomposition of hexanitrostilbene (HNS), a well known heat resistant explosive, has been investigated by simultaneous TGA/DTA at heating rates between 0.05 and 40°C min −1. Depending on the temperature/time history, the reaction takes place either in the solid phase or in the liquid phase after melting of the sample. In order to observe the solid phase reaction, experiments with constant heating rates well below 2.5°C min −1 have to be performed. Therefore, it is impossible to judge the thermal stability of solid HNS using kinetic models derived from DSC experiments at heating rates of 10–20°C min −1, as is the standard procedure. In this work, a formal kinetic model has been developed for the thermal decomposition of high bulk density HNS in its solid phase. The model consists of three consecutive reaction steps (1) a three dimensional phase boundary reaction, dominantly a sublimation, (2) an autocatalytic decomposition reaction, and (3) a slow reaction of fractal order, supposedly a high temperature pyrolysis of primary solid products. The model was used to simulate the stability of HNS under isothermal conditions at temperatures below 300°C.