Development of nanoenergetic arrays based on core/shell nanothermites


Student thesis: Doctoral Thesis

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  • Daguo XU


Awarding Institution
Award date15 Jul 2015


Energetic materials (EMs) including propellants, explosives and pyrotechnics have found various applications in defense and civil industries such as airbag igniters, mining, de-construction, fuses, joining, soldering, brazing, etc. In recent years, many applications of EMs in microenergetic field have been explored, including micro initiators, micro thrusters, gases produced for actuation or chemical reaction, and other energy demanding situations. However, the compatibility of EMs with microelectromechanical systems (MEMS) is not fully achieved. It is desirable to develop novel EMs with faster combustion velocity and higher energy density for microscale applications. Compared to conventional EMs, nanoenergetic materials (nEMs) exhibit improved performance, including faster energy release, lower ignition temperature, and higher reaction temperature, which result from the intimate contact between the oxidizer and the fuel. As a class of nEMs, nanothermites, or called metastable intermolecular composites (MIC), were extensively studied due to the fast reaction rate and the highly exothermic reaction. The thermite reaction involves a metal as the fuel with a metallic or nonmetallic oxide as the oxidizer. It is promising to study the integration of nanothermites on silicon substrate which is straight forward to realize functional devices. In this work, Co3O4, CuO, and MoO3 are chosen as the oxidizers, and Al is chosen as the fuel. The thesis work mainly focus on developing synthesis approaches for different core/shell nanoenergetic arrays on silicon substrate and carrying out morphology characterizations and thermal analysis on the nanoenergetic arrays. This thesis is composed of six parts. In the first part, single-crystal Co3O4 nanowalls and nanowires are synthesized onto silicon substrates by low-temperature thermal oxidation of sputtered Co thin films in static air. Unlike the pure nanostructure arrays, the mechanical adhesion between the Co3O4 nanowalls, nanowires, the film and the silicon substrate is observed to be very strong, which is beneficial for many practical applications. Based on the experimental observations, the detailed growth mechanisms of the nanowalls and nanowires are presented. Lastly, the Co3O4 nanowalls and nanowires are integrated with Al forming core/shell structure and the resulting nEMs are investigated by thermal analysis (DSC and DTA). In the second part, Co3O4/Al core/shell nanoenergetic arrays are obtained by integrating nano-Al with Co3O4 nanorods that are synthesized through a chemical route. The Co3O4 nanorod arrays are confirmed to consist of pure nanostructure and vertically grow along the Si substrate surface. The thermite reaction between the Co3O4 and Al is characterized by differential thermogravimetric analysis (DTA), and differential scanning calorimetry (DSC). The heat of reaction, especially the exothermic reaction before Al melting, is greatly increased by using Co3O4 pure nanostructures. In the third part, CuOx/Al based nanoenergetic arrays are synthesized by the thermal oxidation of Cu thin films deposited onto silicon substrates followed by Al integration through thermal evaporation. By comparing the thermite reactions and ignition properties of Al with micro-CuO and Al with nano-CuO, it is experimentally proven that one-dimensional nanostructures (CuO nanowires) and nano-Al affect greatly the exothermic behaviors and ignition properties of the CuO/Al based EMs. The higher surface energy associated with the CuO nanowires and the deposited nano-Al is believed to be a possible factor contributing to the enhanced exothermic reactions that occur below the melting point of Al and the smaller ignition delay and lower ignition energy. In the fourth part, CuO/Al/Cu2O core/double-shell nanoenergetic arrays on silicon substrate are developed. For studying the oxidation of Al in long-term storage, an additional layer of Cu2O is deposited onto the CuO/Al arrays to prevent the Al from oxidation in dry air. The storage stability of CuO/Al/Cu2O core/double-shell arrays is tested by observing the changes in heat release after period of storage in dry air condition, and it is proved that the Cu2O acting as the protective shell can prevent the Al shell from oxidation in dry air and thus significantly extend the shelf-life. In the fifth part, aligned MoO3 belt arrays have been synthesized onto silicon substrates by a flame synthesis technique. The as-synthesized nanoplates and tree-like arrays are confirmed to be single-crystal orthorhombic α-MoO3. The MoO3/Al core/shell nanoenergetic arrays, obtaining by integrating nano-Al with the MoO3 nanobelt arrays, are characterized in DSC and DTA. In the sixth part, preliminary results on the CuO/MoO3/Al hybrid core/shell nanoenergetic arrays are presented. The synthesis of MoO3 nanostructure on CuO nanowires is experimentally studied. The effect of the MoO3 on tuning reactivity of the CuO/MoO3/Al hybrid core/shell nanoenergetic arrays is investigated.

    Research areas

  • Power resources, Nanostructured materials