(564e) Ignition and Combustion Mechanisms of Mg-Ca(IO3)2 Reactive Nanocomposites

Iodine is extensively explored as a potent biocidal additive in bio-agent defeat energetic formulations. Release of iodine into surrounding areas needs to accompany explosion and combustion of energetic charge. In one approach, elemental iodine is added to metal powders serving as high energy density fuels; its release thus occurs during combustion of such iodine-doped aerosolized metal particles. To increase the iodine concentration in the energetic charge and accelerate combustion, a compound containing oxidized iodine can also be added as part of an oxidizer, combined into composite metal-oxidizer reactive material particles. In this work, combustion of one such composite reactive material is explored with Mg used as a fuel and Ca(IO₃)₂ as an oxidizer. Recently, a metal rich composite was prepared mechanochemically with four moles of Mg per mole of Ca(IO₃)₂, 4Mg·Ca(IO₃)₂. Thermo-gravimetric experiments showed that the material lost 17.5% of its weight when heated to 450 °C, which is about one-half of its theoretical I₂ content. When coated on an electrically heated filament, this material was observed to ignite in two distinct stages, occurring at ca. 400 and 875 °C for the heating rate of 1900 K/s. Powder particles injected into an air-acetylene flame burned producing optical emission pulses with distinct double peaks. The first, sharp and short peak occurred upon ignition. It was followed by a broader peak, somewhat similar to that observed for combustion of similarly sized pure Mg powder particles. When the same composite 4Mg·Ca(IO₃)₂ particles were ignited in air by passing through a CO₂ laser beam, they burned much faster than in the air-acetylene flame and only showed one sharp emission peak. Here, combustion processes leading to the observed unusual emission profiles are explored experimentally. Combustion environments and flow conditions are varied in the laser ignition tests and their effects on the combustion stage durations and temperatures are characterized optically.