(644b) Comparison of Different Nano-Energetic Powder Mixtures for Pressure Impulse Generation

During the two last decades, major progresses have been made in developing highly-exothermic reactive mixtures. Mixtures of metallic and oxide powders have been used to release temperature and pressure waves and new compounds through exothermic reactions. Downscaling powders size and varying the oxidizer nature make it possible to tune the performance of these materials and multiply the range of possible applications. For applications as impact primers, it is required to generate high pressure peaks with the highest possible pressurization rates. In this paper, we investigate the burning rate performances and over-pressure generation of different kinds of nanothermite mixtures prepared using aluminum nanoparticles mixed with different nano-sized metallic-oxide oxidizers (CuO, Al/Bi2O3 and MoO3) and micron-sized PTFE. The unconfined burning rate spans from 60 to a few hundreds of m/s, depending on the powder mixture: the highest velocity is obtained for Al/Bi₂O₃,and slowest for Al/PTFE.  The Al/Bi₂O₃ mixture exhibits the maximum pressurization rate (~ 5762 kPa/µs) as well as the shortest time needed to reach maximal pressure (225 µs). So the fastest reaction seems to result in a reduced ignition delay. The maximum pressure is a function of Theoretical Maximum Density (TMD) percentage and is greatly impacted by the degree of completion of the reaction. The gas is generated by the decomposition and vaporization of the oxide particles. In the case of Al/CuO, this corresponds to the conversion of CuO into Cu₂O with the release of oxygen at low temperatures and then the vaporization of Al and Cu if temperature exceeds 2790 K. For Al/Bi₂O₃, gaseous species is thought to be Bi, and Bi₂O₃ and over 2160 K, O₂ and Bi₂.  For Al/MoO_3, gaseous species at high temperature are only MoO₃. Although the exact chemistry and physics of nanothermite reactions would require further research, we propose to analyze the pressure results from basic thermodynamic equilibrium calculations.