EXPLORING THE RELATIONSHIPS BETWEEN FUEL AND OXIDIZER REACTION OF BIOCIDAL ENERGETIC MATERIALS
Zachariah, Michael R.
MetadataShow full item record
Energetic materials are defined as a class of material with extremely high amount of stored chemical energy that can be released when ignited, along with intensive light emission and shock generation. Developing new energetic materials with high efficiency neutralization of biological warfare agents has gained increased attention due to the increased threat of bioterrorism. The objective of this dissertation is to develop new energetic materials with biocidal capabilities and apply them in various nanothermite systems to explore the relationships between fuel and oxidizer reactions. Aerosol techniques offer a convenient route and potentially direct route for preparation of small particles with high purity, and is a method proven to be amenable and economical to scale-up. Here I demonstrate the synthesis of various iodine oxides/iodic acids microparticles by a direct one-step aerosol method from iodic acid. A previously misidentified phase of I4O9 hydrate is in fact a new polymorph of HIO3 which crystalizes in the orthorhombic space group P212121. Various iodine oxides/iodic acids, including I2O5, HI3O8 and HIO3, were employed as oxidizers in thermite systems. Their decomposition behaviors were studied using a home-made time resolved temperature-jump/time-of-flight mass spectrometer (T-Jump/TOFMS). In addition, nano-aluminum (nAl), nano-tantalum and carbon black were adopted as the fuel or additive in order to fully understand how iodine containing oxidizers react with the fuel during ignition. The ignition and reaction process of those thermites were characterized with T-Jump/TOFMS. Carbon black was found to be able to lower both initiation and iodine release temperatures compared to those of Al/iodine oxides and Ta/iodine oxides thermites. Their combustion properties were evaluated in a constant-volume combustion cell and results show that nAl/a-HI3O8 has the highest pressurization rate and peak pressure and shortest burn time. However, an ignition delay was always present in their pressure profiles while combusting. To shorten or eliminate this ignition delay, a secondary oxidizer CuO is incorporated into Al/I2O5 system and four different Al/I2O5/CuO thermites by varying the mass ratio between two oxidizers are prepared and studied in a constant volume combustion cell. Significant enhancement is observed for all four thermites and their peak pressures and pressurization rates are much higher than that of Al/I2O5 or Al/CuO. Two other oxidizers also demonstrate similar effects as to CuO on promoting the combustion performance of Al/I2O5. A novel oxidizer AgFeO2 particles was prepared via a wet-chemistry method and evaluated as an oxidizer in aluminum-based thermite system. Its structure, morphologies and thermal behavior were investigated using X-ray diffraction, scanning electron microscopy, TGA/DSC, and T-Jump/TOFMS. The results indicate the decomposition pathways of AgFeO2 vary with heating rates from a two-step at low heating rate to a single step at high heating rate. Ignition of Al/AgFeO2 at a temperature just above the oxygen release temperature and is very similar to Al/CuO. However, with a pressurization rate three times of Al/CuO, Al/AgFeO2 yields a comparable result to Al/hollow-CuO or Al/KClO4/CuO, with a simpler preparation method. T-Jump/TOFMS was used to study the ignition and decomposition of boron-based thermites. The ignition behaviors of bare boron nanopowders and boron-based nanothermites at various gaseous oxygen pressure were investigated using the T-Jump method. High-heating rate transmission electron microscopy studies were performed on both B/CuO and B/Bi2O3 nanothermites to evaluate the ignition process. I propose a co-sintering effect between B2O3 and the oxidizer play an important role in the ignition process of boron-based nanothermites.