Effect of Prill Size on PBX 9502 Corner Turning Performance Measured by the Los Alamos ECOT Test

PBX 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 nonuniform is 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 binder homogenizes depends in part on the molding-powder prill size. The degree to which it 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 explore, for three PBX 9502 formulation batches using the same TATB powder lot, how prill size correlates with ECOT-test corner-turning distance.