Changes in Pore Size Distribution upon Thermal Cycling of TATB‐based Explosives Measured by Ultra‐Small Angle X‐Ray Scattering

Abstract

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 μm regime, obtained from small‐angle X‐ray scattering measurements, are presented for LX‐17‐1, PBX‐9502, and ultra‐fine 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 μm and provide empirical experimental input for computational models of initiation and detonation.

The effects of PBX 9502 ratchet growth on detonation failure as determined via the lanl failure cone test

“…Pore size distributions were determined for each material via micro X-ray computed tomography image analysis and ultra-small-angle neutron scattering data analysis. Similar microstructure studies of TATB-based explosives are detailed in the work by Willey et al [2]. Both studies present data that reveals how ratchet growth affects these distributions.…”

“…Through continued thermal cycling phases, its volume progressively ratchets towards an eventual limit in diminishing fashion. This ratchet effect has been observed and studied for over 30 years [1,2,3,4].…”

Analyses on the effect of hot spot density on material consumption rate

“…Even though more porosity means more initiation sites, it also means that as the porosity increases (and the pressure evolves to increase) the initial pore size leading to a critical hot spot can also be smaller. Since the initial pore size leading to a critical hot spot size decreases, there are many more of them since it seems the frequency distribution of pore size is an exponential [10].…”

Effects of crystal quality and preferred orientation on the irreversible growth of compact TATB cylindrical explosives

“…Willey et al 13,14 found that the cavity quantity and size of multi-crystal TATB-based PBX cylinder increased after thermal cycling. Willey 13,14 and Sun 15 thought that additional interstices between TATB powders originated from the thermal cycling should be responsible for the irreversible growth of TATB-based PBX. TATB crystal quality should have much effect on additional interstice production, and further affect the irreversible growth of TATB-based PBX.…”