Nature of the Enhanced Self-Heating Ability of Imperfect Energetic Crystals Relative to Perfect Ones

It is extensively deemed that the increased self-heating ability of defects relative to perfect crystals increases the sensitivity, or reduces the safety, of energetic materials. Nevertheless, the nature of such increased self-heating ability remains unclear. The present work provides insight into the origin of such ability by ReaxFF reactive molecular dynamics simulations on the thermal decay of perfect and twinned beta-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) under three typical heating conditions constant-temperature, programmed, and adiabatic that represent various rates of heat exchange between the HMX crystal and environment. As a result, it is found that the enhanced self-heating ability stemmed from the high internal energy of the molecules around the defects, and such ability is remarkably exhibited with low heat-exchange rates between the energetic materials EMs and environment. Adiabatic heating is an extreme to exhibit the most remarkable such ability, as the superiority of the high internal energy of the molecules around the defects cannot be lowered without heat exchange. Thereby, the twin-induced shock sensitivity enhancement of HMX and a small difference in differential scanning calorimetric measurement values between perfect and twinned HMX can well be understood by means of the insight.