Phase Retransformation and Void Evolution of Previously Heated HMX-Based Plastic-Bonded Explosive in Wet Air

Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine-based plastic-bonded explosive (HMX-based PBX) is one of the most important solid energetic materials. The properties of HMX-based PBX are significantly affected by defects, which were reported recently to be generated during the postheating storage. However, the related mechanism is not well understood. In the study, with the in situ X-ray diffraction and small-angle neutron scattering, we explored the phase retransform and void evolution of previously heated HMX particles and HMX-based PBX as a function of time in controlled environments. Compared to a “dry atmosphere”, the relative humidity of 60% accelerated the phase transition of metastable δ-HMX to stable β-HMX and increased the void volume fraction over about a 2 h period.