Mechanically alloyed magnesium–boron–iodine composite powders

Abstract

Iodine-bearing reactive materials are of interest for munitions aimed to defeat biological weapons because of strong biocidal properties of iodine-containing gas species. Ternary Mg·B·I2 composite powders with 20 wt% of iodine were prepared by two-stage mechanical milling. A binary B·I2 powder was prepared, chilled at dry ice temperature, and mixed with magnesium prior to the second milling stage. Materials with systematically varied Mg/B ratios were prepared. Resulting composite particles were near 30 µm in diameter. Iodine release and oxidation of the prepared powders were studied using thermogravimetric analysis in both inert and oxidizing environments. The most stable material was obtained with 33 wt% of Mg and 47 wt% of B. Up to 450 °C (723 K), it showed only about 1 % mass loss. Iodine is lost in steps: the first step, around 100 °C, is associated with release of unattached iodine. The second step, between 300 and 400 °C, is associated with formation of MgB2. The majority of the iodine is lost above 600 °C. The material did not age when stored in an inert gas; however, it became markedly less stable after storage in ambient air. Stepwise oxidation behavior was observed when the material was heated in an oxidizing gas. Oxidation started at a higher temperature than the initial weight loss caused by iodine release. Apparent activation energies, determined by model free processing for both iodine loss and oxidation, were near 100 kJ/mol for low-temperature iodine loss, and around 400–500 kJ/mol for high-temperature oxidation.