Relating polymorphism and decomposition of RDX under static and dynamic compression

Knowledge of the reactive behavior of energetic crystals at static high pressures and high temperatures (HP-HT) is an important step toward understanding the shock wave initiation of these crystals. Vibrational spectroscopy in a diamond anvil cell was used to examine the behavior of RDX crystals at the pressures and temperatures relevant to shock wave initiation. Phase boundaries between three RDX polymorphs ($\alpha $, $\gamma $, and $\varepsilon )$ were determined up to 12 GPa and 600 K. Decomposition kinetics for the $\varepsilon $- and $\gamma $-phases were examined at various pressures and temperatures, and were found to have positive volumes of activation. CO$_{2}$, N$_{2}$O and H$_{2}$O were identified as the main decomposition species. Static HP-HT results were used to identify and understand the following processes in shocked RDX: $\alpha -\gamma $ phase transition, identification of the crystal phase at decomposition, and the role of pressure and temperature in accelerating the RDX decomposition under shock compression. This work demonstrated that static HP-HT results provide an important complementary route to elucidate the physical and chemical processes in shocked RDX crystals.