Changes in pore size distribution upon thermal cycling of TATB-based explosives measured by ultra-small angle X-ray scattering

Hot-spot models of initiation and detonation show that voids or porosity ranging from nanometer to micrometer in size within highly insensitive energetic materials affect initiability and detonation properties. Thus, the knowledge of the void size distribution, and how it changes with the volume expansion seen with temperature cycling, are important to understanding the properties of the insensitive explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB). In this paper, void size distributions in the 2 nm to 2 mu m regime, obtained from small-angle X-ray scattering measurements, are presented for LX-17-1, PBX-9502, and ultrafine TATB formulations, both as processed and after thermal cycling. Two peaks were observed in the void size distribution: a narrow peak between 7-10 nm and a broad peak between 20 nm and about 1 mm. The first peak was attributed to porosity intrinsic to the TATB crystallites. The larger pores were believed to be intercrystalline, a result of incomplete consolidation during processing and pressing. After thermal cycling, these specimens showed an increase in both the number and size of these larger pores. These results illuminate the nature of the void distributions in these TATB-based explosives from 2 nm to 2 mu m and provide empirical experimental input for computational models of initiation and detonation.