Enhanced Convective Heat Transfer in Nongas Generating Nanoparticle Thermites

Abstract

Flame propagation and peak pressure measurements were taken of two nanoscaled thermites using aluminum (Al) fuel and copper oxide (CuO) or nickel oxide (NiO) oxidizers in a confined flame tube apparatus. Thermal equilibrium simulations predict that the Al+CuO reaction exhibits high gas generation and, thus, high convective flame propagation rates while the Al+NiO reaction produces little to no gas and, therefore, should exhibit much lower flame propagation rates. Results show flame propagation rates ranged between 200 m/s and 600 m/s and peak pressures ranged between 1.7 MPa and 3.7 MPa for both composites. These results were significantly higher than expected for the Al+NiO, which generates virtually no gas. For nanometric Al particles, oxidation has recently been described by a melt-dispersion oxidation mechanism that involves a dispersion of high velocity alumina shell fragments and molten Al droplets that promote a pressure build-up by inducing a bulk movement of fluid. This mechanism unique to nanoparticle reaction may promote convection without the need for additional gas generation.