Molecular Dynamics and Energetic Performance of PBX Explosives Containing Al-Li Alloys via Binder and Content Regulation

Abstract

Context To clarify the molecular-scale synergistic mechanism of the dual-layer wax-binder coating interface governing the safety and energy characteristics of Al-Li alloy modified HMX-based composite explosives, systematic molecular dynamics (MD) simulations are performed within MATERIALS STUDIO 2023. Three series of sandwich-structured models, including HMX/Wax/Binder, AP/Wax/Binder, and Al-Li alloy/Wax/binder systems with gradient lithium concentrations, are constructed sequentially. Miscibility between microcrystalline wax and four typical energetic binders, binding energy ( E bind ), and cohesive energy density (CED) are quantitatively evaluated. EXPLO-5 software is adopted to compute the theoretical detonation performance metrics of corresponding explosive formulations at varying lithium doping ratios. The results demonstrate that F 2604 emerges as the optimal binder as the optimal adhesive, exhibits good compatibility with wax. It possesses both a high interfacial E bind of 13261 kJ·mol − 1 , a CED of 6.03×10 8 kJ·cm − 3 and shortening HMX average N-NO 2 trigger bond length by 4.23%, while the system with 3% lithium doping exhibits the highest molecular packing density and balanced comprehensive performance. Following formulation optimisation, HMX/AP/Al-3Li composite explosive, as Al-to-oxygen ratio ( R Al/O ) rises, more AP-supplied reactive oxygen improves metal fuel reaction efficiency, forming a trend of decreasing heat of detonation, increasing detonation velocity, and both the explosion temperature and detonation pressure peak at R Al/O is 0.34 with the total generation of detonation gases at its minimum, which provides solid theoretical support for the molecular-level formulation design of high-energy low-sensitivity PBXs containing Al-Li alloys. Methods The all model, with all calculations carried out under the COMPASS III [26] force field. Geometry optimization was performed with a 50,000-iteration maximum, where the system was constrained at 10 − 4 GPa external pressure. The optimized systems underwent 500 ps low-temperature NVT relaxation at 100 K using the Berendsen thermostat with a 0.1 fs time step, with Gaussian-distributed random initial velocities to eliminate high-energy disturbances to the energetic crystal framework. The relaxed models were subsequently transferred to 298 K, 10 − 4 GPa NPT ensemble for 1 ns equilibrium production with Berendsen thermostat-barostat dual control, which preserves skeleton and interface integrity and ensures rapid convergence to experiment-consistent equilibrated configurations. Electrostatic interactions were computed via Ewald summation, while van der Waals interactions adopted the Atom-based scheme with a unified 12.5 Å cutoff radius.

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