Structure Property Relationships and Energy Release in Thermite Reactive Nanolaminates
Open Access
- Author:
- Skidmore, Chloe
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- July 01, 2024
- Committee Members:
- Darren Pagan, Major Field Member
Jon-Paul Maria, Chair & Dissertation Advisor
Ismaila Dabo, Major Field Member
Richard Yetter, Outside Unit & Field Member
John Mauro, Program Head/Chair - Keywords:
- energetic materials
thermite
nanocomposites
physical vapor deposition
reactive nanolaminates - Abstract:
- Research into cost-effective energetic materials with highly tunable ignition and actuation have important applications in military and commercial sectors.1,2 Organic explosives are known for their rapid reaction speeds and high power densities, while inorganic energetics exhibiting low rates of energy release have been historically overlooked for potential applications outside of welding, incendiary devices, and low concentration additives. However, organic materials are thermodynamically limited by the formation energies of common organic (CHNO) bonds and the theoretical energy density of inorganic energetics easily surpasses that of common organic explosives, suggesting potential for greater material tunability.3,4 Therefore, there is incentive to create inorganic energetics with increased power densities. A possible solution is designing inorganic material systems that allow for the fastest avenues of diffusion by decreasing the overall travel distance between reactants. Significant progress in nanotechnology and synthesis techniques means that the fuel and oxidizer of inorganic energetic materials can now be combined on the nanoscale. Consequently, the field of nanoenergetics has grown and implementation of methods such as sol-gel synthesis, arrested reactive milling, nano powder mixing and thin film deposition has resulted in energetic materials with enhanced surface area and intimately mixed chemical constituents.3 These new nanoenergetics show promise as stand-alone explosives with great reliability, heat release, and combustion efficiency.1,3 However, nanoenergetic composites are more heterogeneous than their organic counterparts and experimental reaction speed improvements do not align with the predictions of current conceptual models.4,5 If the high energy release and improved tunability provided by the diverse chemistries of inorganic energetics is to be utilized a fundamental understanding of the initiation and propagation processes in new nanoenergetic materials is necessary. Thermite has been identified as a versatile inorganic energetic of interest due to the highly exothermic redox reaction that occurs between metal and oxide constituents, resulting in self-sustaining heat production.6 This project proposes synthesis and characterization of multilayer thermite thin films via magnetron sputtering to better elucidate mechanisms of mechanical, chemical and thermal energy transfer across reactive nanolaminate interfaces. More specifically, this work discusses the fabrication of Mg/CuO multilayers to explore how material characteristics and sample processing parameters influence thermite reaction properties. Moreover, due to a shift in the author’s personal goals, this thesis includes recent results from the field of wurtzite ferroelectrics. Please note that while an in-depth introduction and literature review of ferroelectric materials is not presented, relevant chapters have been formatted to properly orient the reader. In Chapter 1 we will classify and define energetic materials with respect to thermite, discuss nanomaterial fabrication methods, and review our current understanding of initiation and propagation mechanisms in reactive multilayers. Chapter 2 will familiarize the reader with the experimental synthesis and characterization techniques used throughout this work. Chapter 3 presents an analysis of the reaction mechanisms and oxygen exchange processes that occur in magnetron sputtered Mg/CuO nanolaminates. Chapter 4 examines how reactant layering sequence and substrate orientation impacts Mg/CuO multilayer film characteristics and energy release. In Chapter 5 we shift to ferroelectric systems and discuss the fabrication of ferroelectric, epitaxial Al1-x-yBxScyN /n-GaN heterostructures with high crystallinity and smooth microstructures. Chapter 6 introduces the proximity ferroelectricity model through detailed analyses of heterostructures consisting of ferroelectric layer(s) (Al1-xBxN, Al1-xScxN and Zn1-xMgxO) and non-ferroelectric layer(s) (AlN or ZnO). Concluding remarks and the progress of current work will be outlined in Chapter 7.