Reaction Kinetics and Thermodynamics of Nanothermite Propellants
Anand Prakash, University of Maryland, Graduate Research Assistant, 2121 Glenn L. Martin Hall, College Park, MD 20742, Michael R. Zachariah, Mechanical Engineering, Professor, 2121 Glenn Martin Hall, College Park, MD 20742, and Alon V. McCormick, University of Minnesota, Professor, 421 washington Ave SE, Minneapolis, MN 55455.
Nanocomposite energetic materials composed of thermite materials are attractive because of their high exothermicity and extremely fast reactivity. While the possible combinations of fuel and oxidizer are nearly infinite, remarkably few combinations of nano-based thermites have been investigated. The most studied combinations are nano-Aluminum combined with Fe2O3, CuO and MoO3. These Al-oxidizer combinations are also termed as MIC (Metastable Intermolecular Composite). In this article, we present the synthesis of KMnO4 nanoparticles as a new high intensity oxidizer. We present a comparison of reactivity of the new MIC formulation (Al/KMnO4) with other traditional formulations. Reaction kinetics of MIC ignition was measured under confined combustion in terms of pressurization rate of a constant volume pressure vessel. The observed pressurization rate for the Al/KMnO4 (290 psi/Ás) nanocomposite was about two orders of magnitude higher than that for Al/CuO and Al/MoO3 (~8 psi/Ás) and several orders of magnitude higher than Al/Fe2O3 (0.01 psi/Ás). We have attempted to explain our experimental observations with thermodynamic calculations of equilibrium species composition, which suggests that, at adiabatic flame temperatures of combustion, the pressurization rates are very strongly correlated to the fraction of nascent oxygen present in the reaction product.