Thermal initiation of consolidated nanocomposite thermites

Reactive nanocomposite powder with bulk composition of 8AI.MoO3 was prepared by arrested reactive milling and cold-pressed into 0.635 cm diameter cylindrical pellets. The material was consolidated to densities up to 99% of theoretical maximum density, or 3.217 g/cm(3), while maintaining high reactivity. Pellets were ignited by a CO2 laser beam and the ignition delays increased at lower laser powers and greater pellet densities. A simple numerical model was developed to describe the heating and thermal initiation of the reactive pellets. The model described adequately the observed effects of both laser power and pellet density on the measured ignition delays. The exothermic reaction governing thermal initiation of the prepared consolidated samples is described by the same Arrhenius term as that used to describe ignition of thin layers of respective unconsolidated nanocomposite powders coated on an electrically heated filament. An exothermic reaction with the same activation energy is also detected by earlier thermo-analytical studies with Al-MoO3 nanocomposite thermites and is suggested to be rate-limited by the reduction of MoO3. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.