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Investigation on Reaction Mechanisms of Nano-Energetic Materials and Application in Joining Investigation on Reaction Mechanisms of Nano-energetic Materials and Application in Joining by Hongtao Sui A thesis presented to the University of Waterloo in fulfilment of the thesis requirement for the degree of Doctor of Philosophy in Mechanical and Mechatronics Engineering Waterloo, Ontario, Canada, 2019 © Hongtao Sui 2019 Examining Committee Membership External Examiner NAME Catalin Florin Petre Title Defense Scientist Supervisor(s) NAME John Z. Wen Title Associate professor Internal Member NAME Zhongchao Tan Title Professor Internal Member NAME Adrian Gerlich Title Associate Professor Internal-external Member NAME Luis Ricardez Sandoval Title Associate Professor ii Author’s Declaration I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I understand that my thesis may be made electronically available to the public. iii Abstract Nano-energetic materials, also known as metastable intermetallic composites (MICs), have shown promise in applications such as propellants, pyrotechnics, and explosives. The work in this thesis pursues a deep understanding of the reaction mechanisms of typical nano- thermite composites and the functions of CNTs in nano-thermite reactions. The thesis begins with the development of nano-thermite composites with layered structure using Al and Fe2O3 nanoparticles via the Electrophoretic Deposition (EPD) process. The nano-thermite composites show a consistency in onset temperature even with different ratios of Al and Fe2O3, which suggests uniform interfacial formation, where the nano-thermite reactions are initiated. This work investigates the reaction mechanisms of typical nano-thermite composites: Al/CuO and Al/NiO. The results show that the Al/CuO nano-thermite system exhibits a gas-solid reaction mechanism, whereas the Al/NiO system exhibits a condensed- phase reaction mechanism. Furthermore, the functions of CNTs in nano-thermite reactions are investigated. The mass transfer mechanisms and thermal conductivities affect the energy release and reaction rate. Improvements in thermal conductivity and mass transfer are able to enhance the reactivity of nano-thermite composites. Measurements indicate that CNTs possess extremely high thermal conductivity compared with Al and metal oxidizers. Meanwhile, the NiO nanoparticles and CNTs react to release CO or CO2 at the initial stage of the thermite reaction. The CO or CO2 carry the oxygen atoms to the Al layers, followed by the reaction between Al and CO2. Overall, the function of CNTs in nano-thermite reactions using the Al/NiO nano-thermite composite is to change the reaction from a solid-solid iv mechanism to a condensed-phase mechanism. Finally, silicon wafers are welded using nano- thermite composites in order to achieve the application attempt. It has been shown that increasing energy release and decreasing apparent activation energy can provide an enhanced amount of energy to the interfacial area, which produces better mechanical strength in the welded zone. v Acknowledgements I would first like to thank my advisor, Dr. John Z. Wen. He has taught me much more than how to conduct experiments. He has taught me how to obtain deep understanding from initial experimental data, and has supported me in every step along the way. I would like to appreciate my committee members, Dr. Catalin Florin Petre, Dr. Zhongchao Tan, Dr. Adrian Gerlich, and Dr. Luis Ricardez Sandoval, who evaluate the thesis and attend the thesis defense in their extremely busy schedule. I would like to acknowledge my colleagues, Mr. Florin Saceleanu, Ms. Lauren Lesergent, Ms. Boyu Li, and Ms. Yiqi Zhang, who discuss the experiments with me to help obtain more understandings on the results. My thanks are also extended to my wife, parents, and friends, who encourage me during the four years. I also acknowledge support from the Natural Sciences and Engineering Research Council of Canada (NSERC) through the Discovery and Discovery Accelerator Supplements grants. vi Table of Content Examining Committee Membership ................................................................................... ii Author’s Declaration ........................................................................................................... iii Abstract ................................................................................................................................. iv Acknowledgements .............................................................................................................. vi List of Figures ..................................................................................................................... xiv List of Tables ........................................................................................................................ xx Chapter 1: Introduction ....................................................................................................... 1 1.1 Energetic materials ................................................................................................. 1 1.2 Thermite composites and applications .................................................................. 3 1.3 Drawbacks of traditional thermite composites .................................................... 5 1.4 Nano-thermite composites ...................................................................................... 7 1.5 Motivation .............................................................................................................. 11 1.6 Objectives .............................................................................................................. 13 1.7 Thesis organization ............................................................................................... 15 Chapter 2: Literature review ............................................................................................. 17 2.1 Background ........................................................................................................... 17 2.2 Comparison of micro- and nano-thermite composites ...................................... 18 2.2.1 Energetic properties................................................................................... 18 2.2.2 Reaction kinetics ........................................................................................ 21 2.3 Definition of nano-thermite composites .............................................................. 22 vii 2.4 Design principle of nano-thermite composites ................................................... 22 2.4.1 Thermal conductivity and adiabatic temperature .................................. 24 2.4.2 Heat of reaction for different nEMs ......................................................... 25 2.5 Methodology of preparation of nano-thermite composites ............................... 27 2.5.1 Types of nEM structures ........................................................................... 28 2.5.2 Physical mixing .......................................................................................... 30 2.5.3 Sol-gel .......................................................................................................... 31 2.5.4 Self-assembly .............................................................................................. 32 2.5.5 Arrested reactive milling ........................................................................... 34 2.5.6 Thermite nanocomposites with layered structures ................................. 35 2.5.7 Fabrication methods .................................................................................. 39 2.5.7.1 Electrophoretic deposition (EPD) .................................................. 40 2.5.7.2 Vacuum filtration (VF) ................................................................... 41 2.5.8 Summary ..................................................................................................... 42 2.6 Characterization of nanocomposites ................................................................... 43 2.6.1 Aluminum nanoparticles ........................................................................... 43 2.6.1.1 Particle size and active content of Al nanoparticles .................... 43 2.6.1.2 Ignition of Al nanoparticles ........................................................... 47 2.6.2 Nano-thermite composites ......................................................................... 50 2.6.2.1 Reaction of nanocomposites ........................................................... 50 2.6.2.2 Combustion properties of nanocomposites ................................... 53 viii 2.6.2.3 Thermal analysis ............................................................................. 55 2.6.3 Characterization methods ......................................................................... 56 2.6.3.1 X-Ray Diffraction (XRD) ............................................................... 56 2.6.3.2 Thermogravimetric Analysis (TGA) ............................................. 57 2.6.3.3 Differential Scanning Calorimetry (DSC) .................................... 58 2.6.3.4 Scanning Electron Microscopy (SEM) .......................................... 59 2.6.3.5 Energy Dispersive X-Ray Spectroscopy (EDS) ............................ 60 2.6.3.6 Microhardness ................................................................................. 62 2.6.4 Reaction kinetics .......................................................................................
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