Arrested reactive milling is used to prepare a composite thermite powder combining magnesium metal with calcium iodate, Ca(IO3)(2). Upon ignition, this material generates iodine, a biocidal species capable of effective inactivation of aerosolized microorganisms. The prepared material is metal-rich with a fuel/oxidizer ratio of 4. It contains 29 wt% of iodine. The material is a micron-sized powder with each particle having a magnesium matrix and nanosized inclusions of calcium oxide. A similar composite with a stoichiometric ratio of fuel to oxidizer is found to be unstable in air. The prepared metal-rich composite was characterized using thermo-gravimetric analysis, ignition experiments using an electrically heated filament, and particle combustion experiments in both air and the combustion products of an air-acetylene flame. The powder was found to readily release iodine upon heating. It ignited in two distinct stages, with the first, low-temperature ignition prompted by iodine release, and second stage ignition caused by reaction of any remaining magnesium. In an air-acetylene flame, the powder particles burned in two distinct stages, unlike other similar materials. In air, only one combustion stage was distinguished. Combustion of the prepared powders in air occurs much faster than in the products of the air-acetylene flame; burn rates of the prepared composite powders in both air and products of air-acetylene flame are slightly lower than those of pure magnesium burning in the same environments.