Initial reaction pathways of anhydrous hydrazine deflagration: insights from Ab initio molecular dynamics and coupled stimuli experiments

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Understanding the microscopic mechanisms of anhydrous hydrazine (N 2 H 4 ) is critical for preventing cascading accidents. In order to elucidate the thermal decomposition behavior and deflagration hazards, we carried out slow cook-off tests on gram-scale samples, impact sensitivity evaluations at varying temperatures, and ab initio molecular dynamics (AIMD) simulations. Results indicate that a distinct evaporation plateau (∼1.4 h at 117.1 o C) occurs in glass containers. Conversely, no plateau is detected in stainless steel, suggesting that high thermal conductivity masks pre-runaway evaporation. The dominant impact hazard mechanism is identified not as intrinsic decomposition, but as an impact-induced, temperature-sensitized N 2 H4-O 2 deflagration. High-speed imaging supports this pathway, which is driven by aerodynamic dispersion and fuel-air mixing. Furthermore, AIMD simulations reveal the atomic-level signature of deflagration: an ultrafast (<20 ps) runaway reaction mediated by a complex radical pool (NH x , NO x , HO x ). This provides direct molecular-level evidence for a non-detonative, impact-induced explosive pathway. This study elucidates the complex deflagration mechanisms of anhydrous hydrazine by bridging macroscopic experiments with microscopic simulations. We reveal that the thermal runaway signature is heavily masked by the thermal conductivity of confinement materials. Crucially, mechanical impact triggers an oxidative deflagration driven by aerodynamic dispersion and adiabatic compression, which is significantly sensitized by temperature coupling. Furthermore, ab initio molecular dynamics simulations uncover the atomic-level kinetics, identifying a hyper-fast reaction network mediated by a specific radical pool. These insights provide a comprehensive understanding of hydrazine safety characteristics under coupled stimuli. • High thermal conductivity of confinement masks the critical pre-runaway evaporation signature of anhydrous hydrazine. • Mechanical impact triggers a temperature-sensitized oxidative deflagration driven by aerodynamic dispersion rather than intrinsic decomposition. • Ab initio molecular dynamics reveal a hyper-fast (<20 ps) runaway reaction pathway mediated by a complex radical pool.

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