High explosive crystals
Researchers using the ChemMatCARS Sector 15 beamline at the APS have determined the high-pressure structure of an insensitive high explosive (HE) crystal for the first time. The ε-FOX-7 structure could be of significant interest to researchers involved in HE research.
High-performance resulting from chemical energy release and low sensitivity to initiation are the desired characteristics of high explosive (HE) crystals and provide the motivation for continuing research efforts to develop safer HE crystals.
A good understanding of the molecular and crystalline attributes that govern the insensitivity of known insensitive HE (IHE) crystals is needed to tailor and develop IHE crystals that provide specific functionality and have a high threshold for initiation.
Understanding the insensitivity/stability of insensitive high explosive crystals requires detailed structural information at high pressures and high temperatures of interest. Synchrotron single crystal x-ray diffraction experiments were used to determine the high-pressure structures of 1,1-diamino-2,2-dinitroethene (FOX-7), a prototypical insensitive high explosive.
The phase transition around 4.5 GPa was investigated and the structures were determined at 4.27 GPa (α’-phase) and 5.9 GPa (ε-phase). The α’-phase (monoclinic, P21/n), structurally indistinguishable from the ambient α-phase, transforms to the new ε-phase (triclinic, P1). The most notable features of the ε-phase, compared to the α’-phase, are: formation of planar layers and flattening of molecules. Density functional theory (DFT-D2) calculations complemented the experimental results. The results presented here are important for understanding the molecular and crystalline attributes governing the high-pressure insensitivity/stability of insensitive high explosive crystals.
Zbigniew A Dreger, Adam I Stash, Zhi-Gang Yu, Yu-Sheng Chen, Yuchuan Tao and Yogendra M. Gupta, “High Pressure Crystal Structures of an Insensitive Energetic Crystal – 1,1-Diamino-2,2-Dinitroethene (FOX-7),” The Journal of Physical Chemistry C, Just Accepted Manuscript, DOI: 10.1021/acs.jpcc.5b10644, Published Online December 3, 2015.