Comparative investigation of thermal decomposition of various modifications of hexanitrohexaazaisowurtzitane (CL-20)

The thermal decomposition kinetics of different polymorphs of CL-20 (alpha, gamma and epsilon) has been investigated by thermogravimetry, IR spectrosc opy and optical and electronic microscopy. The reactions proceed with self- acceleration and can be described by a kinetic law of first order with auto catalysis. Already at the earliest stages of decomposition (less than or eq ual to1%) phase transitions take place from alpha --> gamma and from epsilo n --> gamma. For this reason the observed decomposition is related to the d ecomposition of gamma -CL-20. On the other hand, the kinetics of decomposit ion depends on the initial polymorphic state, so that the thermal decomposi tion increases in the series: alpha < <gamma> < <epsilon>. Experiments with different samples of alpha -CL-20 demonstrate that different rates of deco mposition are observed for the same polymorph depending on the mean size an d the size distribution of the crystals and their morphological features. I n some cases the thermal stability of alpha -CL-20 can be increased by prev ious annealing. It is concluded that the thermal decomposition of CL-20 is purely a solid-state process. Microscopical and spectroscopical analysis of the condensed CL-20 decomposition product (formed after prolonged heating at high temperature) show that it has a network structure and consists main ly of carbon and nitrogen.