Isothermal equations of state of beta octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine at high temperatures

Isothermal pressure-volume equations of state of beta HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) at temperatures of 30, 100, and 140 degrees C under both hydrostatic and nonhydrostatic compressions have been obtained using synchrotron angle-dispersive x-ray diffraction experiments. The samples were heated to the isotherm temperature and compressed up to 5.8 GPa. At all temperatures HMX remained in the beta phase up to 5.8 GPa. However, at 140 degrees C upon decompression to ambient from nonhydrostatic pressures above 4 GPa, HMX underwent a phase transition to the delta phase. The same transition was seen upon decompression to ambient from hydrostatic compression; however, parts of the sample remain in the beta phase, resulting in a mixed-phase sample. The diffraction data were analyzed to yield unit-cell dimensions at each pressure, and further analyzed to yield thermal expansion, bulk modulus, and the pressure derivative of the bulk modulus. (C) 2005 American Institute of Physics.