Thermite Initiation Processes and Thresholds

The objectives of this work are to characterize thermite initiation processes and thresholds, and to develop thermite reactive trains, where a sensitive nanothermite ignites an insensitive micron thermite, which produces little gas. Nanothermites, including Al/AgIO3, Al/Bi2O3, Al/MoO3, Al/Fe3O4, and Ti/AgIO3, were characterized for their ignition behavior by spark and resistive heating. Energies for spark and thermal initiation were as low as 9 and 140 µJ, respectively. Thermal initiation results were consistent with local temperature as the main controlling factor. The propagation rate of the Al/Fe3O4 nanothermite was about 100X slower than that of the other nanothermites. This low reactivity is attributed to the high volatilization temperature and high melting point of the oxidizer. Mixing of 90% Al/Fe3O4 nanothermite with 10% of a more sensitive, high-gas-producing nanothermite gave materials with the same sensitivity as the sensitive nanothermite. Thus, the mixture provides a safer sensitive nanothermite. Thermites with micron-scale ingredients were pressed into pellets and ignited with small amounts of nanothermite. Gas production of micron thermite compositions was reduced by adding the intermetallic composite, Ti/2B, or excess iron. In both cases, a single hot mass was produced, while the pure micron Al/Fe2O3 produced a dispersion of particles.