Three-dimensional microstructural characterization of HMX-based propellant via synchrotron X-ray tomography

Although octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) plays a critical role in high-performance weapon systems, its microstructural behavior within the grains of solid propellants and PBXs has not been fully explored. This challenge arises from the difficulty of distinguishing HMX from other components during structural characterization. In this study, synchrotron X-ray tomography (SR-μCT) coupled with advanced image processing was employed to non-destructively characterize a cylindrical propellant grain composed of HMX, ammonium perchlorate (AP), aluminum (Al), and hydroxyl-terminated polybutadiene (HTPB) binder. The morphology, size, and distribution uniformity of HMX particles within the grain were successfully characterized. The calculated values from the 3D reconstruction closely matched the experimental results, confirming the accuracy of the proposed reconstruction methodology. The results also revealed that AP particles were more concentrated at the bottom of the propellant grain, likely due to gravitational settling during curing, while HMX and Al exhibited uniform distributions. However, at a finer scale, these particles were found to be unevenly distributed. This work pioneers the quantitative 3D characterization of HMX particulates within propellant grains, contributing to a better understanding of the microstructural behavior of solid particles within the grain.