Mechanism and Model-based Improvement of Energetic Aluminum Nanoparticles

The current proposal addresses the need for development of an accurate and complete mechanism for the reaction of nanoparticles (using Al as a test case), formulation of mathematical models describing all the chemical, mechanical, and physical processes, predictions for the improvement of Al nanoparticle reactivity, and development of diagnostic approaches and experiments that can critically assess the validity of the reaction mechanisms and suggested improvements. The work will include (1)critical comparison of the existing reaction mechanisms for Al nanoparticles, including analyses of the main consequences and the accuracy of current predictions, (2) extension of the melt-dispersion mechanism with conceptual models to capture more detailed features than previously achieved. An initial multiphysics finite element model will serve as a platform for incorporating these advanced features, (3) formulation of the means to compare theoretical predictions with experiments that would allow determination of the actual reaction mechanism and controlling parameters, and (4) review and feasibility testing of diagnostic approaches that will enable multiscale model validation, including critical analysis of both microscopic and macroscopic performance parameters. BENEFIT: The uniqueness of the proposed research program lies in the development of a new model that can capture realistic reaction rates that have previously eluded conventional diffusive models. This work expands upon pioneering theoretical work and will include a more sophisticated and detailed physical description of the mechano-chemical processes that contribute to the melt dispersion mechanism. This work will include the effects of premelting and kinetics of melting on transformational expansion of the core and shell as a function of heating rate, surface energy between the core and shell, thermo-mechanical properties, and geometrical parameters. A finite element model, to be developed starting in Phase I, will be used to capture the interplay of these phenomena as well as three-dimensional features of non-spherical geometry and shell fracture. This approach has already shown great promise in predicting anomalous size-dependent nanoparticle behavior, and when coupled with advanced experimental techniques offers a unique opportunity for a critical breakthrough in understanding and predicting nanoenergetic particle performance. The proposed research will pave the way for detailed coupling of experimental, theoretical and numerical studies leading to the mechanism- and model-based improvement of the reactivity of Al and other nanoparticles. This has tremendous implications for improvement of propulsion systems, including rockets as well as gas-turbine engines with additized fuels.