1,1-Diamino-2,2-dinitroethylene under high pressure-temperature

Area of Science:

• Materials Science
• Chemistry
• Physics

Background:

• 1,1-diamino-2,2-dinitroethylene (FOX-7) is an energetic material.
• Understanding its structural phase stability under extreme conditions is crucial for safety and performance.

Purpose of the Study:

• To investigate the structural phase stability of FOX-7 under isothermal compression up to 10 GPa at 100 °C and 200 °C.
• To identify pressure-induced structural transformations and assess thermal decomposition limits.

Main Methods:

• Synchrotron mid- and far-infrared spectroscopy were employed.
• Isothermal compression experiments were conducted at controlled temperatures (100 °C and 200 °C).
• Vibrational spectra were analyzed to detect structural changes.

Main Results:

• Structural distortions and potential phase transformations (α, α', α") were observed at specific pressures (e.g., 2.2 GPa, 6.1 GPa at 100 °C; 2.1 GPa, 5.3 GPa at 200 °C).
• These pressure-induced changes were found to be nearly isobaric and partially reversible upon decompression.
• No sample decomposition was observed up to 10 GPa and 200 °C, but decomposition onset was detected at 360 °C under isobaric heating at 1.07 GPa.

Conclusions:

• FOX-7 exhibits significant structural changes under high pressure and moderate temperature, suggesting phase transitions.
• The material remains stable against decomposition up to 200 °C at 10 GPa.
• Further diffraction studies are needed to fully elucidate the observed high-pressure structural modifications.