Chemistry & Biochemistry Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2752
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Item RAPID HEATING AND CHEMICAL SPECIATION CHARACTERIZATION FOR COMBUSTION PERFORMANCE ANALYSIS OF METALLIZED, NANOSCALE THERMITES AND PVDF BOUND SOLID PROPELLANT COMPOSITIONS(2021) Rehwoldt, Miles Christian; Rodriguez, Efrain; Zachariah, Michael R; Chemical Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Energetic materials research focuses on performance analysis of cost-effective solid materials which safely, precisely, and efficiently transitions stored chemical potential energy to kinetic energy at a rate throttled through chemical or architectural means. Heterogenous compositions of metal fuels and solid materials with a high storage capacity of condensed oxidizing elements, such as oxygen and/or fluorine, is a class of energetic material of interest given its relatively high reaction enthalpies and adiabatic flame temperatures. In the wake of the earliest instances of metal fuels being used as a high energy additive during World War II, characterizing the reaction mechanisms of micron and nanoparticle aluminum fuels with various oxidizer sources has been a primary subject of research within the solid energetics community. The advent of nanotechnologies within the past two decades brought with it the promise of a prospective revolution within the energetics community to expand the utility and characterization of metallized energetic materials in solid propellants and pyrotechnics. Significant prior research has mapped reactivity advantages, as well as the many short comings of aluminum-based nanoscale energetic formulations. Examples of short comings include difficulties of materials processing, relative increase in native oxide shell thickness, and particle aggregate sintering before primary reaction. The less than flaw-less promises of nanoscale aluminum fuels have thus become the impetus for the development of novel architectural solutions and material formulations to eliminate drawbacks of nanomaterial energetics while maintaining and improving the benefits. This dissertation focuses on further understanding reaction mechanisms and overall combustion behavior of nanoscale solid energetic composite materials and their potential future applications. My research branches out from the heavy research involved in binary, aluminum centric systems by developing generalized intuition of reaction and combustion behaviors through modeling efforts and coupling time-of-flight mass spectrometry to rapid heating techniques and novel modes of product sampling. The studies emphasize reaction mechanisms and microwave sensitivities of under-utilized compositions using metal fuels such as titanium, generalize the understanding of the interaction of fluoropolymer binders with metal fuels and oxidizer particles, and characterize how multi-scale architectural structure-function relations of materials effect ignition properties and energy release rates.Item Understanding the Relationships Between Architecture, Chemistry, and Energy Release of Energetic Nanocomposites(2017) DeLisio, Jeffery Brandon; Zachariah, Michael R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Energetic nanocomposites are a class of reactive material that incorporate nanosized materials or features in order to enhance reaction kinetics and energy densities. Typically, these systems employ metal nanoparticles as the fuel source and have demonstrated reactivities orders of magnitude larger than more traditionally used micron-sized metal fuels. One drawback of using nanosized metals is that the nascent oxide shell comprises a significant weight percent as the particle size decreases. This shell also complicates the understanding of oxidation mechanisms of nanosized metal fuels. In this dissertation, I apply a two-fold approach to understanding the relationships between architecture, chemistry, and energy release of energetic nanocomposites by 1) investigating alternative metal fuels to develop a deeper understanding of the reaction mechanisms of energetic nanocomposites and 2) creating unique microstructures to tailor macroscopic properties allowing for customizability of energetic performance. In order to accurately study these systems, new analytical techniques capable of high heating rate analysis were developed. The oxidation mechanisms of tantalum nanoparticles was first probed using high heating rate TEM and Temperature-Jump Time-of-Flight Mass Spectrometry (T-Jump TOFMS) and shell crystallization was found to plan an important role in the mechanism. An air-sensitive sample holder was developed and employed to analyze the decomposition and oxidation of molecular aluminum compounds, which theoretically can achieve similar energy release rates to monomolecular explosives in addition to much higher energy densities. In order to obtain simultaneous thermal and speciation data at high heating rates, a nanocalorimeter was integrated into the TOFMS system and measurements were performed on Al/CuO nanolaminates to probe the effect of bilayer thickness on energy release. An electrospray based approach to creating energetic nanocomposites with tunable architectures is also described. An in depth study on the electrospray synthesized nAl/PVDF thin film reaction mechanism was performed using T-Jump TOFMS. The nAl/PVDF system was also studied using a Molecular Beam Sampling Time-of-Flight Mass Spectrometer designed and built primarily to investigate the reaction mechanisms of energetic nanocomposites at 1 atm in both aerobic and anaerobic environments.Item Understanding and Tuning Nanostructured Materials for Chemical Energy Conversion(2014) Jian, Guoqiang; Zachariah, Michael R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The conversion of energy that employs chemical reaction is termed chemical energy conversion. In my dissertation, I have focused on chemical energy conversion systems involving energetic materials and lithium ion batteries, where performance is strongly dependent on the properties of materials and their architecture. The objective of this study is to enhance our understanding and tuning of nanostructured materials that might find application toward energetic materials and electrode materials in lithium ion batteries. Rapid heating diagnostics tools, i.e. temperature-jump techniques, have been used to study the ignition of aluminum nanoparticles, nanothermite reaction mechanism and metal oxides nanoparticles decomposition under rapid heating conditions (~105-106 K/s). Time-resolved mass spectra results support the hypothesis that Al containing species diffuse outwards through the oxide shell. Low effective activation energies were found for metal oxides nanoparticles decomposition at high heating rates, implying the mass transfer control at high heating rates. The role of oxygen release from oxidizer in nanothermite reactions have been examined for several different systems, including some using microsized oxidizer (i.e., nano-Al/micro-I2O5). In particular, for periodate based nanothermites, direct evidence from high heating rate SEM and mass spectrometry results support that direct gas phase oxygen release from oxidizer decomposition is critical in its ignition and combustion. Efforts have also been made to synthesize nanostructured materials for nanoenergetic materials and lithium ion batteries applications. Hollow CuO spheres were synthesized by aerosol spray pyrolysis, employing a gas blowing mechanism for the formation of hollow structure during aerosol synthesis. The materials synthesized as oxidizers in nanothermite demonstrated superior performance, and of particular note, periodate salts based nanothermite demonstrated the best gas generating performance for nanothermite materials. Energetic composite nanofibrous mats (NC/Al-CuO, NC/Al-Fe2O3, and NC/Al-Bi2O3) were also prepared by an electrospinning method and evaluated for their combustion performance. Aerosol spray pyrolysis was employed to produce carbon coated CuO hollow spheres, Mn3O4 hollow spheres, and Fe2O3 mesoporous spheres. These hollow/mesoporous spheres demonstrated superior electrochemical performance when used as anode materials in lithium ion batteries. The effects of the amorphous and crystal structures on the electrochemical performance and the structure evolution during electrochemical tests were also investigated.