Surface-Accelerated Decomposition of δ-HMX

Area of Science:

• Energetic Materials Science
• Computational Chemistry
• Chemical Physics

Background:

• Understanding HMX (octogen) explosive decomposition is crucial for safety and performance.
• The δ-phase of HMX is more reactive than the stable β-phase, transforming under heat/pressure.
• Complex parallel processes, including phase transitions, complicate HMX initiation studies.

Purpose of the Study:

• To investigate the precursor reactions of HMX decomposition using first principles modeling.
• To elucidate the factors contributing to the high sensitivity of the δ-HMX phase.
• To understand the interplay between different decomposition pathways in HMX.

Main Methods:

• First principles modeling of gas-phase, ideal crystal, and (100) surface of δ-HMX.
• Exploration of homolytic NO2 loss and HONO elimination reactions.
• Analysis of surface interactions and molecular dipole moment effects.

Main Results:

• Calculations identified surface interactions and molecular dipoles as key factors in δ-HMX sensitivity.
• Both NO2 loss and HONO elimination pathways were found to coexist.
• Exothermic HONO-isomer formation was shown to catalyze N-NO2 homolysis.

Conclusions:

• The high reactivity of δ-HMX is significantly influenced by its surface properties and internal molecular structure.
• A synergistic effect between HONO elimination and NO2 homolysis accelerates the decomposition of HMX.
• This research provides fundamental insights into the initiation mechanisms of energetic materials like HMX.