15N substitution enhances the detonation performances of energetic materials: A case study of ammonium nitrate

While isotope substitution has been extensively used to probe reaction mechanisms in energetic materials (EMs), its potential for modulating detonation performance remains largely unexplored. This work demonstrates, through an integrated theoretical and experimental study of ammonium nitrate (AN) and its fully 15N-substituted analog (15NH₄15NO₃), that heavy nitrogen isotope substitution can significantly enhance detonation performances. The Chapman-Jouguet (CJ) parameters were evaluated using the quantum mechanics molecular dynamics (QM-MD) simulations and thermodynamic code EXPLO5. Compared with NH₄NO₃, 15NH₄15NO₃ exhibits markedly superior performance: QM-MD predicts an increase of 8.28% in detonation velocity (ΔD%) and 22.96% in detonation pressure (ΔP%), while EXPLO5 yields relatively lower increases of ΔD% (3.34%) and ΔP% (9.13%). Experimental validation via viscous-state explosive detonation and laser-induced micro-detonation techniques confirms the performance enhancement, showing a higher initial shock-wave velocity for the 15NH₄15NO₃. QM-MD results reveal an increased quantity of N₂, NO₂, and NO, along with a reduced amount of NO₃ at the CJ state. DFT calculations further indicate a reverse kinetic isotope effect that lowers the energy barrier for the key steps to NO₂ and NO formation. Collectively, these findings suggest that 15N-substitution elevates the decomposition pressure, thereby shifting the kinetic pathways of detonation toward a faster and more exothermic pathway, which in turn creates a positive feedback loop for further pressure increase. This work establishes 15N-substitution as an effective and feasible atomic-level strategy for enhancing the detonation performance of EMs.