4D Imaging in Thermally Damaged Polymer-bonded Explosives

PBXs are composites in which explosive crystallites are bound by compliant polymers. There are safety benefits derived from compliant binders; e.g. they mitigate some effects of mechanical insult. However, during elevated thermal insult, degradation of binder and HE crystallites can modify the morphology in ways that can reduce safety margins by increasing post-ignition reaction violence. The response of thermally damaged PBXs, before and following self-ignition has safety implications and it is desirable to understand the fundamental physics controlling the rate of pre-ignition thermal runaway and the post-ignition flame propagation in thermal accident scenarios. Coupled with this there is an ongoing effort to make in situ, time-resolved, measurements of the size, nature and extent of micro-porosity in PBX 9501 during thermal decomposition. We report on PBX heating experiments conducted at the Diamond synchrotron with both PBX 9501 and an inert mock. During heating, CT radiography was conducted in order to observe void production and interconnectivity of gas flow pathways, as well as to monitor phase changes within the crystals. We explore the variation of behavior as a function of heating rate, soak temperature, soak time and confinement.