Initiation and Decomposition of Tetrazole Containing Green Energetic Materials
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Initiation and Decomposition of Tetrazole Containing Green Energetic Materials Nicholas W. Piekiel1, Richard E. Cavicchi2, and Michael R. Zachariah1,2 Department of Mechanical Engineering, University of Maryland, College Park, MD 20742, U.S.A. 2 Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, MD, 20899
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ABSTRACT A T-Jump/Time-of-Flight Mass Spectrometer (T-Jump/TOFMS) is used to probe the decomposition of several aminotetrazole containing energetic materials under very high heating rates of 105-106 K/s. Subtle differences between materials in functional group placement and anion composition allow for further understanding of the decomposition pathway of the tetrazole structure and various anions. Two decomposition pathways for the tetrazole ring are observed, which result in the primary formation of HN3 or N2. Further analysis is performed using a rapidheating µ-DSC device, which revealed lower activation energies than previously reported. INTRODUCTION There have been several experimental and theoretical studies to help understand the thermal decomposition of aminotetrazole containing materials.[1-9] However, these experiments are traditionally performed under low heating rates (10-100 K/min). Under rapid-heating conditions closer to that of a real-time combustion event, it is highly likely that different chemical processes are dominant. A recent rapid heating study of tetrazole containing energetics has shown that the position of functional groups on the tetrazole ring play a significant role on the thermal stability and decomposition pathway of the tetrazole structure.[4] Despite some rapid heating rate studies on tetrazole containing materials, to our knowledge none exist for the materials of this study. Slow heating rate DSC studies, mass spectrometry, and IR spectroscopy have been performed by Fischer and co-workers for MeDAT_DN and MeDAT_N3.[9] Their decomposition analysis for these materials will be used for comparison and breakdown of the reaction products in this investigation. EXPERIMENT The primary experimental device is a Temperature-Jump/Time-Of-Flight Mass Spectrometer (T-Jump/TOFMS), which has been described in detail elsewhere.[10] The core of this instrument is a fine platinum filament of ~76 µm in diameter and 1-2 cm in length. This filament can be heated at very high rates up to 106 K/s using a tunable current pulse. Samples are received in a solution of ethanol or methanol, and 1-10 µg samples are placed onto the sample probe by manually applying a drop of the solution to the platinum wire. Heating of the samples is performed under high vacuum conditions (10-7 torr). This allows for the probing of condensed phase decomposition reactions, as any gas phase reaction products will be ejected into
the vacuum region. All samples used in this experiment with the exception of 5-aminotetrazole (Sigma Aldrich[11]) are provided by T.M. Klapötke of Ludwig-Maximilians University in Munich, Germany, and consist of 5-amino-1-methyl-1H-tetrazolium di
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