Date of Award
Doctor of Philosophy in Chemistry
Jimmie C. Oxley
Chemical, biological, radiological, nuclear, and explosives (CBRNE) terrorist threats put law enforcement and soldiers at risk both at home and abroad. Law enforcement and soldiers must be provided with tools and knowledge to stay ahead of the capabilities of terrorists. Hexamethylene Triperoxide Diamine (HMTD) is a homemade explosive easily synthesized from hexamine, citric acid, and hydrogen peroxide. Although HMTD is very sensitive and prone to stability problems, it has a history of terrorists use, such as in the London bombing of 2005. Because law enforcement personnel must handle this material with no guarantee of purity nor indication of additives, for the sake of safety, knowledge of the stability and reactivity of HMTD was expanded in order to make handling safer. Differential scanning calorimetry was utilized to screen the compatibility of HMTD with various additives. It was found that water and weak acids, such as citric acid, destabilize HMTD. Gas chromatography / mass spectrometry (GC/MS) was employed to characterize both headspace gases (e.g. trimethylamine and dimethylformamide) and condensed phase decomposition products. Monitoring the decomposition of HMTD at room temperature and with gentle heating (60 ⁰C) under various levels of humidity proved that humidity plays a major role in the kinetics of HMTD decomposition. Liquid chromatography / mass spectrometry was helpful for identification of condensed phase decomposition products and monitoring isotopic labeling studies. Through a labeling study with equimolar 15N and 14N hexamine during the synthesis of HMTD, it was found that hexamine dissociates before the formation of HMTD.
There is currently a need for specialized pyrotechnic materials to combat the threat of biological weapons. Materials have been characterized and will be chosen based on their potential to produce heat and iodine to kill spore-forming bacteria (e.g. anthrax). One formulation, already proven to kill anthrax simulants, is diiodine pentoxide with aluminum; however, it suffers from poor stability and storage problems. The heat and iodine output from this mixture and candidate replacement mixtures were measured with bomb calorimetry and extraction and analysis of iodine by UV-Vis spectroscopy. Of the mixtures analyzed, calcium iodate and aluminum was found to be the highest producer of iodine gas. The heat output of this mixture and others can be increased by adding more fuel, with the cost of some iodine produced. Products of combustion were analyzed by thermal analysis, XPS, XRD, and LC/MS. Evidence was collected supporting the formation of metal iodides and metal oxides. One key reaction explaining the loss of iodine with increase in aluminum content is the reaction between aluminum and iodine, which forms aluminum triiodide.
As seen in multiple cases, including the Boston Marathon bombing, improvised explosives may be as simple as a fuel/oxidizer (FOX) mixture initiated by a hot wire. The knowledge of which materials or compositions are explosive is incomplete, and tests for explosivity are currently conducted at specific scales. For example, ammonium nitrate is classified as an oxidizer because it does not explode at the pound scale, but can become explosive at a larger scale or with a fuel added. Herein, a bomb calorimeter with a pressure transducer has been studied for its use as a small scale metric (2 g) for predicting whether fuel/oxidizer mixtures will be explosive at larger scales. These results have been compared with calculated and measured detonation velocities, and measured air blast pressures. A positive correlation was observed between heat of burning and detonation velocity, and between heat of burning and air blast TNT equivalence.
Porter, Matthew Michael, "Tools to Fight the Terrorist Threat" (2017). Open Access Dissertations. Paper 563.
Available for download on Wednesday, April 17, 2019