Monitoring high-temperature solid-solid phase transitions of HMX with atomic force microscopy

Area of Science:

• Materials Science
• Chemical Engineering
• Solid-State Chemistry

Background:

• Octahydro-1,3,5,7,-tetrazocine (HMX) is a high-energy material with significant applications.
• Understanding its phase transitions is crucial for predicting its behavior and ensuring safety.
• Previous studies have explored HMX polymorphism, but real-time observation of solid-solid transitions at high temperatures remained limited.

Purpose of the Study:

• To investigate the real-time solid-solid phase transition of HMX using high-temperature atomic force microscopy.
• To characterize the surface morphological changes during the phase transition.
• To correlate observed microstructural changes with the material's reaction sensitivity.

Main Methods:

• High-temperature atomic force microscopy (HT-AFM) was employed to monitor HMX surface evolution.
• In-situ temperature control allowed for observation of phase transitions as they occurred.
• Surface topography and roughness were quantitatively analyzed before, during, and after the transition.

Main Results:

• Massive surface reconstruction was observed during the first-order solid-solid phase transition of HMX.
• Temperature-induced increases in void space and surface roughness were quantified in the delta polymorph.
• These morphological changes directly impact the growth rate and volume of shock-initiated hot spots.

Conclusions:

• The study provides the first real-time visualization of HMX solid-solid phase transitions.
• Surface morphology changes significantly influence the energetic properties of HMX.
• Increased surface roughness and void space enhance hot spot formation, thereby increasing reaction sensitivity.