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Probing the Dynamics of Ultra-Fast Condensed State Reactions in Energetic Materials
Piekiel, Nicholas William
Zachariah, Michael R
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Energetic materials (EMs) are substances with a high amount of stored energy and the ability to release that energy at a rapid rate. Nanothermites and green organic energetics are two classes of EMs which have gained significant interest as they each have desirable properties over traditional explosives. These systems also possess downfalls, which could potentially be overcome if more were understood about the nature of their reactions. However, ultra-fast reactions are prominent during ignition and combustion, and increase the difficulty in probing the initial and intermediate reaction steps. The goal of this study is to probe the early phases of reaction in nanothermites and green EMs, and to do so we have developed a Temperature-Jump/Time-of-Flight Mass Spectrometer (T-Jump/TOFMS) capable of rapid sampling and heating rates. Various nanothermites have been investigated with this system, and analysis has shown that nanothermite ignition is dependent on the decomposition of the metal oxide, and in certain systems there is distinct evidence of condensed phase initiation. Carbon/metal oxide mixtures, which have application to chemical looping combustion, were also investigated and further demonstrate condensed phase reaction. Aside from mass spectrometry, complementary high heating rate SEM/TEM, pressure cell, and optical experiments were also performed. Many organic energetics including a variety of tetrazole containing ionic salts have also been examined. To investigate the breakdown of the tetrazole ring, a common substructure in green organic energetics, several tetrazole containing salts with minor variations in either functional group or anion composition were studied. Two main tetrazole decomposition pathways were identified and are affected by the placement of functional groups along the tetrazole ring. Many differences were also observed in comparison to previous works at slow heating rates due to either different reaction processes or the presence of secondary reactions in the previous studies. A μ-DSC experiment showed a decrease in activation energy for tetrazole containing materials under high heating rates, further suggesting different mechanistic processes are at play.