Investigation on Reaction Mechanisms of Nano-energetic Materials and Application in Joining

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 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.