Exothermic surface reactions in alumina-aluminum shell-core nanoparticles with iodine oxide decomposition fragments

A pre-ignition reaction (PIR) once thought to be unique to aluminum (Al) and fluorine-based oxidizer reactions is observed for aluminum and an iodine-containing oxidizer. This PIR is exothermic and precedes the main exothermic reaction corresponding to aluminum combustion. For the aluminum and iodine oxide system, exothermic surface chemistry was recently predicted for I-O fragments forming bridge bonds with the alumina passivation shell using first principle calculations, but now has been observed experimentally. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) were used to assess aluminum and iodine pentoxide (I2O5) powder mixtures. Various equivalence ratios were examined and found to affect the PIR onset temperature. Prior to this work, the PIR was attributed solely to surface reactions of the halogen with the Al2O3 surface, but, results shown here indicate that both the alumina surface and aluminum core contribute to a PIR and a minimum activation energy is necessary for PIR production.