Phase transitions and isothermal equations of state of epsilon hexanitrohexaazaisowurtzitane (CL-20)

The phase stability of epsilon hexanitrohexaazaisowurtzitane at high pressure and temperature was investigated using synchrotron angle-dispersive x-ray diffraction experiments. The samples were compressed at room temperature using a Merrill-Bassett diamond anvil cell. For high-temperature compression experiments a hydrothermal diamond anvil cell developed by Bassett was used. Pressures and temperatures of around 5 GPa and 175 degrees C, respectively, were achieved. The epsilon phase was determined to be stable under ambient pressure to a temperature of 120 degrees C. A phase transition to the gamma phase was seen at 125 degrees C and the gamma phase remained stable until thermal decomposition above 150 degrees C. Pressure-volume data for the epsilon phase at ambient and 75 degrees C were fitted to the Birch-Murnaghan formalism to obtain isothermal equations of state.