Solid-phase ripening of hexanitrostilbene (HNS) nanoparticles: Effects of temperature and solvent vapour

The solid-phase ripening of nano explosives leads to the performance degradation of explosives with time, and it has been a long-standing challenge to understand the solid-phase ripening kinetics of small-molecule nanomaterials. Using an in situ atomic force microscope (AFM) and small angle X-ray scattering (SAXS), this study captured the variations in the morphology and specific surface area (SSA), respectively of hexanitrostilbene (HNS) nanoparticles, which have been applied as an advanced brisant explosive, during their ripening. The solid-phase ripening mechanisms and kinetics were discussed. Both Ostwald ripening (OR) and Smoluchowski ripening (SR) of HNS nanoparticles were observed at 60oC. This study established an empirical model to describe the decrease in SSA in 30 days, which yielded the predicted results with root mean square errors (RMSEs) lower than 5%. Moreover, it demonstrated the significant acceleration effects of dimethyl formamide (DMF) vapour on the ripening rate of HNS nanoparticles. Overall, this study may lay the foundation for scientifically predicting the long-term stability and substantially reducing the ripening rate of HNS nanoparticles and provide a methodology for the study of the solid-phase ripening of small-molecule nanomaterials.