Effect of environment on iodine oxidation state and reactivity with aluminum

Abstract

Iodine oxide is a highly reactive solid oxidizer and with its abundant generation of iodine gas during reaction, this oxidizer also shows great potential as a biocidal agent. A problem with using I₂O₅ in an energetic mixture is its highly variable reactive behavior. This study isolates the variable reactivity associated with I₂O₅ as a function of its chemical reaction in various environments. Specifically, aluminum fuel and iodine oxide powder are combined using a carrier fluid to aid intermixing. The carrier fluid is shown to significantly affect the oxidation state of iodine oxide, thereby affecting the reactivity of the mixture. Four carrier fluids were investigated ranging in polarity and water miscibility in increasing order from hexane < acetone < isopropanol < water as well as untreated, dry-mixed reactants. Oxidation state and reactivity were examined with experimental techniques including X-ray photoelectric spectroscopy (XPS) and differential scanning calorimetry (DSC). Results are compared with thermal equilibrium simulations. Flame speeds increased with polarity of the fluid used to intermix the powder and ranged from 180 to 1202 m s⁻¹. The I₂O₅ processed in the polar fluids formed hydrated states of iodine oxide: HIO₃ and HI₃O₈; and, the nonpolar and dry-mixed samples formed: I₂O₄ and I₄O₉. During combustion, the hydrated iodine oxides rapidly dehydrated from HIO₃ to HI₃O₈ and from HI₃O₈ to I₂O₅. Both steps release 25% of their mass as vapor during combustion. Increased gas generation enhances convective energy transport and accounts for the increase in reactivity seen in the mixtures processed in polar fluids. These results explain the chemical mechanisms underlying the variable reactivity of I₂O₅ that are a function of the oxide's highly reactive nature with its surrounding environment. These results will significantly impact the selection of carrier fluid in the synthesis approach for iodine containing reactive mixtures.