The Microstructure of TATB-Based Explosive Formulations During Temperature Cycling Using Ultra-Small-Angle X-Ray Scattering

TATB (1,3,5 triamino-2,4,6-trinitrobenzene), an extremely insensitive explosive, is used both in polymer-bound explosives (PBXs) and as an ultra-fine pressed powder (UFTATB). Many TATB-based explosives, including LX-17, a mixture of TATB and Kel-F 800 binder, experience an irreversible expansion with temperature cycling known as ratchet growth. Additional voids, with sizes hundreds of nanometers to a few micrometers, account for much of the volume expansion. Measuring these voids is important feedback for hot-spot theory and for determining the relationship between void size distributions and detonation properties. Also, understanding mechanisms for ratchet growth allows future choice of explosive/binder mixtures to minimize these types of changes, further extending PBX shelf life. This paper presents the void size distributions of LX-17, UFTATB, and PBXs using commercially available Cytop M, Cytop A, and Hyflon AD60 binders during temperature cycling between -55 and 70 degrees C. These void size distributions are derived from ultrasmall-angle X-ray scattering (USAXS), a technique sensitive to structures from about 2 nm to about 2 mu m. Structures with these sizes do not appreciably change in UFTATB. Compared to TATB/ Kel-F 800, Cytop M and Cytop A show relatively small increases in void Volume from 0.9 to 1.3% and 0.6 to 1.1%, respectively, while Hyflon fails to prevent irreversible volume expansion (1.2-4.6%). Computational mesoscale models combined with experimental results indicate both high glass transition temperature as well as TATB binder adhesion and wetting are important to minimize ratchet growth.