Abstract and subjects
PBX prills are spongy nuggets a few millimeters in diameter, comprising a nonuniform distribution of high explosive (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. The degree that 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 explore, via micro computed tomography (CT) for several PBX explosives, the residual prill structure within 12.7 x 12.7 mm cylindrical pellets. The PBX explosives under study were 9407, 9501, 9502, and 9701. In the case of PBX 9501 we also imaged wedges pressed to different densities, as well as discs that had been thermally treated. We showed that micro-CT is an excellent tool for understanding HE prill structure and defects. While HE grayscale can give some hint as to the distribution of HE and binder, as well as overall part density, determination of density or prill composition based on CT grayscale alone is quite challenging. We also observed that despite all being made with a wet slurry process, each HE appeared to have a unique structure, and the distribution of voids was influenced by the prill scale. This was especially obvious in the parts that had been heated or pressed to lower density.