Phase transition of HMX and their significance for the sensitivity of explosives.

Alphy- and Gamma-HMX were prepared. Gamma-HMX still contained small amounts of Beta-HMX. Alpha-, Beta- und Gamma-HMX were heated to 240 degreeC at the x-ray diffractometer. The phase transitions Alpha to Delta, Beta to Delta and Gamma to Delta were observed. However, no transition Beta to Alpha was found. On cooling the reversion from Delta-HMX was delayed considerably. A nonlinear change of the lattice distances was observed on heating Gamma-HMX. In reversion experiments Alpha- and Beta-HMX were heated to temperatures from 190 to 230 degreeC and stored at room temperature. With increasing temperatures the decomposition of HMX favorizes the reversion Delta to Alpha and with still higher temperatures Delta-HMX is stabilized. The decomposition of HMX was investigated with a thermobalance. The kinetic parameters were determined. Friction and impact sensitivity tests were performed with the 4 HMX-phases. Friction sensitivity is slightly increased with Alphaand Delta-HMX. Unusually low impa ct energies were obtained with Delta-HMX the larger crystals being more sensitive than the ground ones.