Spectroscopic Measurements of the Combustion of Aluminum and Aluminum-Based Energetic Material Particles Using a Heterogeneous Shock Tube
Bazyn, Timothy A.
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https://hdl.handle.net/2142/83843
Description
Title
Spectroscopic Measurements of the Combustion of Aluminum and Aluminum-Based Energetic Material Particles Using a Heterogeneous Shock Tube
Author(s)
Bazyn, Timothy A.
Issue Date
2006
Doctoral Committee Chair(s)
Nick Glumac
Department of Study
Mechanical Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Mechanical
Language
eng
Abstract
Aluminum is a desirable component of propellants, explosives, and energetic materials due to the high energy release associated with its oxidation. Considerable research has been done on aluminum combustion, but questions remain about the behavior of aluminum particles, particularly at small particle sizes where the traditional optical imaging techniques can no longer be employed. This study looks at the behavior of small (10 mum and smaller) aluminum and aluminum-based particles, including aluminum hydride and aluminum/metal oxide nanocomposites, using a heterogeneous shock tube. A dispersed cloud of individually burning particles is examined by analyzing the spectral emission and absorption of the burning cloud, through techniques including pyrometry, photometry, and emission and absorption spectroscopy. These measurements have led to the determination that aluminum particles below 10 mum do not burn with the gas-phase diffusion flame observed in larger (>20 mum) sizes, but rather with reactions occurring very close to the particle surface. These particles thus have lower combustion temperatures and longer burn times than would be expected under correlations developed based on large particle combustion. This size regime of particles is currently used in rocket propellants, and as compared to larger sizes, these particles burn with significantly different properties, such as a significant pressure dependence on burn rate and lower combustion temperatures. As size is decreased further to the nano-particle regime (∼10-500 nm), the particles were observed to burn with lower combustion temperatures, smaller diameter dependence, and Arrhenius-style burn rates. This behavior is consistent with a shrinking-core flame structure, where the oxide coating remains around the particle while condensed phase diffusion controls the oxidation process. The same diagnostic tools have also been applied to aluminum hydride to determine its combustion characteristics, as well as aluminum/metal oxide nanocomposites to measure the ignition characteristics and the degree of participation of the ambient environment in its combustion process. These measurements have significant implications for the use of aluminum-based particles in practical energetic material applications, and these implications will also be discussed.
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