Microstructure of Pre-Pressed PBX Prills Explored by X-ray Computed Tomography

PBX (plastic bonded explosive) prills are spongy nuggets a few millimeters in diameter, comprising a nonuniform distribution of HE crystals and binder. When pressed—especially at elevated temperatures at which the binder has softened or melted—one hopes that it will flow to uniformly coat the HE crystals. In reality it does so imperfectly, such that X-ray tomographic scans often look like a collection of prills mashed together. Lore is that the larger the prill, the more heterogeneous the binder distribution. Even if that were not so, the larger the prill the farther binder must flow in order to homogenize. Thus, the degree to which it homogenizes depends in part on prill size. The degree to which binder flows during pressing in turn affects the void distribution within pressed charges, which one suspects will affect shock sensitivity and material strength. In this paper we will use X-ray CT to measure and compare the pre-pressed prill structure for three PBX 9502 formulation batches using the same TATB powder lot, and three PBX 9501 lots.