Melt-Dispersion Mechanism for Energetic Reactions of Aluminum Nanoparticles

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CBET-0755236LevitasAluminum particles are becoming integrated into energetic formulations and considered for overlapping technologies such as materials synthesis and thermites for ordnance applications. Recently, a new mechanochemical mechanism has been introduced that shows potential for understanding extremely fast Al nanoparticle reactions. This theory applies during fast heating of Al nanoparticles, where the volume change due to melting of the Al core encased in an alumina shell induces extreme pressures of 1-2 GPa, resulting in a spallation of the oxide shell. The unbalanced pressure between the Al core and exposed surface creates an unloading wave with high tensile pressures, resulting in dispersion of small liquid Al clusters that fly at high velocity. Thus, nanoparticle reactions are not limited by diffusion. The proposed melt-dispersion mechanism is the only existing explanation that resolves a number of basic puzzles in nano-Al combustion. The goal of this project is to define the main conditions and controlling physical parameters for operation of the melt-dispersion mechanism for reactions of Al nanoparticles; to extend this mechanism for micron-scale particles; and to utilize obtained fundamental knowledge for the improvement of Al-based formulations. The following tasks will be considered: (a) develop comprehensive theories for physical processes participating in the melt-dispersion mechanism, (b) synthesize Al particles based on theoretical predictions and new particle design concepts, (c) study implications of the melt-dispersion mechanism experimentally, (d) expand the melt-dispersion mechanism to micron-scale particles, and (e) predict and experimentally confirm methods that will improve the reactivity of Al particles in various formulations. Beyond the potential for technological impact, a mentoring program will be developed where undergrads work with grad students in a research environment. In addition, nanoparticle combustion will be integrated into the combustion curriculum and a continuing-education program in energetic materials. The investigators also plan to organize special symposia devoted to "mechanochemical" processes at various international conferences.