The phase diagram of rdx (hexahydro-1,3,5-trinitro-s-triazine) under hydrostatic pressure

Raman spectroscopy has been used to determine the phase diagram and phase behavior of RDX (hexahydro-1,3,5-trinitro-s-triazhe) up to 16 GPa at temperatures ranging from 150 K to over 450 K. Two new stable solid polymorphs have been identified: a high pressure/low temperature form that converts reversibly to α-RDX (the form stable at ambient conditions) at 3.8 GPa, independent of temperature from 150 to 375 K. We also find a high pressure/high temperature form of RDX that is highly metastable, shows a very large hysteresis, and is probably the polymorph known as β-RDX.