All ETDs from UAB

Advisory Committee Chair

Yogesh K Vohra

Advisory Committee Members

Tracy P Hamilton

Aaron L Lucius

Nenad Velisavljevic

Sergey Vyazovkin

Document Type

Dissertation

Date of Award

2016

Degree Name by School

Doctor of Philosophy (PhD) College of Arts and Sciences

Abstract

The high pressure-temperature (P-T) phase diagram of 1,1-diamino-2,2-dinitroethylene (FOX-7) was determined by in situ synchrotron infrared radiation spectroscopy and resistively heated diamond anvil cell (DAC) techniques. The stability of the high P-T FOX-7 polymorphs is established from ambient pressure up to 10 GPa and temperatures until decomposition. The phase diagram indicates two near isobaric phase boundaries at ~2 GPa (  I) and ~ 5 GPa ( I  ) that persists from 25oC until the onset of decomposition at ~300oC. In addition, the ambient pressure, high-temperature    phase transition (~111oC) lies along a steep boundary (~100oC/GPa) with an ( +  +  triple point at ~1 GPa and 300oC. A 0.9 GPa isobaric temperature ramping measurement indicated a limited stability range for the -phase between 0.5 – 0.9 GPa and 180 – 260oC, terminating in a ( +  +  triple point. With increasing pressure, the-phase exhibited a small negative dT/dP slope (up to ~0.2 GPa) before turning over to a positive 70oC/GPa slope, at higher pressures; until ~ 2 GPa, where it appears to terminate in an ( +  + Phase-I) triple point. The decomposition boundary then exhibits an anomalous change of slope at an (a + Phase I + decomposition) triple point with a negative slope of ~180oC/GPa; which may indicate a structural modification to a higher symmetry than the -phase (P21/n) or evidence of a potential ‘island’ phase. The high pressure -phase has a moderate positive decomposition boundary slope of ~29oC/GPa up to 10 GPa. Additionally, the high P-T phase diagram of 2,4,6-triamino-1,3,5-trinitrobenzene (TATB) was determined from ambient pressure up to 10 GPa and decomposition. TATB appeared to remain triclinic (P1) and has a very moderate ~4oC/GPa decomposition boundary slope up to 10 GPa. The similarities between the decomposition boundaries of the -phase of FOX-7 and TATB are remarkable: both phases have triclinic symmetry and planar molecular/layering structures with moderate positive slopes extending over a broad range of pressure. These results provide the first recorded evidence of high P-T stability of two similar high explosives and the potential mechanisms behind sensitivity and performance.

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