Mechanism of compaction-induced microstructure evolution and its impact on thermal aging and shock output in ultrafine HNS

The microstructural characteristics of polymer-bonded explosives are crucial to their safety and performance. Ultrafine hexanitrostilbene (HNS)-based PBXs hold potential for micro-detonation systems. However, the structural changes during compaction and thermal aging, as well as their effects on shock response, remain incompletely understood. This study employs advanced characterization techniques to investigate microstructural evolution in ultrafine HNS and its molding powder during die compaction, and to correlate initial microstructure with thermal aging and shock output. The densification of ultrafine HNS is achieved via strong plastic deformation and pore filling, resulting in a 9.4% reduction in R g1 . During the molding process, the powder densifies as particles rearrange and large pores collapse, leading to a 3.6% reduction in R g1 and a more concentrated distribution of smaller pores. The initial microstructure governs the rate and extent of aging, while material composition defines the aging pathway. Ultrafine HNS (UD) follows the Ostwald ripening mechanism. Higher initial free energy intensifies pore evolution, with compact density > 1.5 g/cm 3 yielding > 40% specific surface area (SSA) attenuation after one year of room-temperature storage. HNS molding powder (PD) undergoes interfacial reconstruction and pore coalescence above the softening temperature ( T m ≈ 50 °C). Density and porosity alone do not determine the shock-wave velocity; SSA plays a critical role in regulating Us. This work links processing, microstructure, and performance, providing a basis for the design and evaluation of ultrafine explosive microcharges. • Established quantitative links between compaction conditions, multiscale pore metrics, and shock response with microsecond resolution using USAXS/SAXS, SEM, and LASEM. • Ultrafine HNS (UD) ages via Ostwald ripening, whereas molding powder (PD) compacts age via pore coalescence driven by binder softening, with rates determined by the initial microstructure. • Specific surface area derived from SAXS is the strongest predictor of shock-wave velocity Us, outperforming bulk density and nanoscale porosity across die-pressed discs.