The influence of gas generation on flame propagation for nano-Al based energetic materials

This study examines the reactions of two nanocomposite thermites, aluminum (Al) with copper oxide (CuO) and aluminum with nickel oxide (NiO). These oxidizers were selected based on their predicted properties: similar adiabatic flame temperatures but significantly opposing gas generation properties. Thermal equilibrium calculations predicted that the Al+CuO would have a high gas output and the Al+NiO would produce little to no gas. Flame propagation rates and peak pressure measurements were taken for both composites at various equivalence ratios using an instrumented flame tube apparatus. Results show that over the range of equivalence ratios studied, Al+CuO had an average propagation rate of 582.9 ± 87.6 m/s, while Al+NiO had an average velocity of 193.7 ± 72.2 m/s. The average peak pressures observed for the reactions were 3.75 ± 0.85 MPa for Al+CuO and 1.68 ± 0.88 MPa for Al+NiO. A DSC/TGA was also used to determine the properties of the composites and reactants under low heating rates. These low heating rate tests indicate that the gas production properties of the composites are highly dependent on heating rate, with both composites experiencing almost no mass loss under slow heating. The results suggest that the melt-dispersion mechanism, which is only engaged at high heating rates, leads to a dispersion of high velocity molten Al clusters that promotes a pressure build-up by inducing a bulk movement of fluid. This mechanism may promote convection without the need for additional gas generation.