Nanocomposite Thermites with Calcium Iodate Oxidizer

Iodine bearing reactive materials and fuel additives are being developed to inactivate harmful aerosolized spores and bacteria by combined thermal and chemical effects. Nanocomposite thermites with aluminum and boron serving as fuels and calcium iodate as an oxidizer were prepared by arrested reactive milling. Both materials contained 80 wt % of calcium iodate. Morphology and particle sizes of the prepared materials were characterized using scanning electron microscopy (SEM). Both powders comprised particles finer than ca. 10 μm with fuel and oxidizer mixed on the submicrometer scale. Powders were exposed to room air to assess their stability. They were ignited as a thin coating on an electrically heated filament. Powders were injected in an air-acetylene flame to observe combustion of individual particles. Pressed pellets for both prepared materials were prepared and ignited using a CO2 beam. Al ⋅ Ca(IO3)2 oxidizes rapidly in room air, whereas no aging was detected for B ⋅ Ca(IO3)2. Ignition of Al ⋅ Ca(IO3)2 occurs around 1150 K, after both aluminum and calcium iodate melt. Ignition is accompanied by ejection of sintered particles undergoing microexplosions while they are combusting. Ignition of B ⋅ Ca(IO3)2 occurs between 600 and 700 K, before either of the components melt. Combustion is accompanied by the formation of a luminous halo above the material, suggesting a vapor-phase reaction involving boron suboxides. Longer ignition delays are observed for the pellets of Al ⋅ Ca(IO3)2 heated by the CO2 laser beam compared to similar pellets of B ⋅ Ca(IO3)2. Burn rates of B ⋅ Ca(IO3)2 pellets are nearly twice as fast as those of Al ⋅ Ca(IO3)2, primarily due to the lower ignition temperature for the boron-based thermite. The flame temperatures obtained from the time-integrated optical spectra are close to 2140 and 2060 K for Al ⋅ Ca(IO3)2 and B ⋅ Ca(IO3)2, respectively. Individual particles of B ⋅ Ca(IO3)2 injected into an air-acetylene flame burn slower than similar Al ⋅ Ca(IO3)2 particles. Based on their better stability, lower ignition temperatures, shorter ignition delays, and longer burn times leading to a more gradual release of iodine, B ⋅ Ca(IO3)2 composites are suggested to be better suited as components of energetic formulations aimed to defeat stockpiles of biological weapons.