Resolving Detonation Nanodiamond Size Evolution and Morphology at Sub-Microsecond Timescales during High-Explosive Detonations

Characterization of the initial morphology of detonation nanodiamond (DND) has been the focus of many research studies that aim to develop a fundamental under-standing of carbon condensation under extreme conditions. Identifying the pathways of DND formation has the potential for significant impact on many of the controlled synthesis of nanoscale carbon with a tailored functionality; currently, a wide range of possible (and conflicting) mechanisms of nucleation and growth have been proposed, and further research is essential. Building a comprehensive understanding of DND formation is challenging because it requires in situ characterization on the sub-microsecond (sub-mu s) timescale during a high-explosive detonation. In this study, time-resolved small-angle X-ray scattering (TR-SAXS) is used to reveal the early-stage DND morphology from <0.1 to 6 mu s after the detonation front passes through the X-ray beam path. We address the ambiguity of models previously reported for the analysis of small-angle scattering from DND by comparing (i) in situ, TR-SAXS recorded during early-stage particulate formation and (ii) ex situ SAXS and transmission electron microscopy (TEM) measurements of products recovered from detonation of the same high explosive within a carefully designed ice chamber. The SAXS from both late-time (>1 mu s) in situ and recovered DND exhibits consistent features in the I(q) curve. Such a close similarity allows a high-fidelity SAXS model derived from the ex situ SAXS and TEM measurements to be applied to the in situ data, which yields new insight into the early-stage (<1 mu s) morphology of DND. Our analysis indicates that the size distribution of DND particles is observed within 0.1 /is postdetonation, which indicates that carbon is condensed within the reaction zone. Between 0.1 and 0.3 mu s, the mean size of the diamond particles increases slightly toward 4 nm, and evidence of surface texture is observed. Based on TEM imaging, this surface texture consists of hemispherical protrusions that extend similar to 1 nm from the surface. Beyond 0.3 mu s, neither the mean size of the diamond core nor the surface texture changes significantly for several microseconds after the detonation. Combined with thermochemical simulations, these results indicate that during detonation of composition B, carbon is condensed into nanoscale diamond much faster than that previously reported in other studies. Furthermore, the surface texture of the DND is shown to arise during condensation rather than via subsequent graphitization.