Effect of composition on properties of reactive Al·B·I2 powders prepared by mechanical milling

• Stable ternary Al·B·I2 powders prepared at room temperature via mechanical alloying.
• A stage wise iodine release observed for all prepared materials.
• AlB2 formation between 400–500 °C causes a significant iodine release.
• Boron retains iodine up to about 900 °C.
• Iodine is released from ternary Al·B·I2 powders at temperatures substantially exceeding its boiling point.

Metal-based fuels producing halogen-containing combustion products are being developed to enable rapid inactivation of harmful aerosolized spores and bacteria. Ternary reactive materials containing aluminum, boron, and iodine were prepared by mechanical milling with systematically varied Al:B ratio. The aluminum mass fraction varied from 0% to 70%, and most materials included 20 wt% of iodine. Prepared powders were inspected by electron microscopy; particle size distributions were measured using low angle laser light scattering. Stability of materials was studied using thermo-gravimetry and differential scanning calorimetry. As-prepared as well as pre-heated and quenched samples were analyzed using x-ray diffraction. Iodine was released upon heating in several stages. Low-temperature iodine release was relatively small. It overlapped with decomposition of B(OH)3 releasing water. The most significant amounts of iodine were released when the samples were heated to 400–500 °C, when AlB2 formed. Both AlB2 formation and iodine release were further accelerated by melting of aluminum. For the boron-rich samples, in which boron remained after all aluminum was used to form AlB2, an additional, high-temperature iodine release stage was observed near 900 °C. The results show that both boron and aluminum are capable of stabilizing substantial quantities of iodine in the metal matrix. The iodine is released at temperatures much greater than its boiling point. The mechanism by which iodine is retained in boron and aluminum remains unclear.