Phase-transition-mediated impact desensitization of FOX-7 at elevated temperatures

The reduction of mechanical sensitivity in energetic materials is a critical safety concern. This research demonstrates that the temperature-induced polymorphic transition in 1,1-diamino-2,2-dinitroethene (FOX-7) is an effective method for desensitization. By employing <i>in-situ</i> X-ray diffraction and elevated-temperature impact tests, we reveal that the β-phase of FOX-7, which is attained at temperatures exceeding 116 °C, shows significantly diminished impact sensitivity. The characteristic drop height (<i>H</i>₅₀) of unmodified FOX-7 increases substantially following the α to β transition, with a 57% enhancement noted at 126 °C compared to the baseline at ambient temperature. This improvement in safety is attributed to structural reorganization and alterations in hydrogen-bonding configurations that facilitate more efficient energy dissipation pathways. Additionally, the application of a polydopamine (PDA) coating combined with a fluoropolymer (F2314) binder further elevates the <i>H</i>₅₀ value to 111.6 cm at 126 °C, thereby enhancing safety while maintaining energetic performance. A finite-element thermo-mechanical model was developed to accurately predict the kinetics of phase transition and stress evolution, providing a computational framework for the optimization of formulations. These findings highlight the potential of phase-transition engineering as a promising strategy for the development of intrinsically safer high-energy materials.