(655b) Ternary Mg∙B∙I2 Reactive Composite Materials with Biocidal Combustion Products

Ternary Mg∙B∙I₂ reactive composite materials with biocidal combustion products

S. Wang, A. Abraham, M. Schoenitz, E.L. Dreizin

New Jersey Institute of Technology, Newark, NJ 07102

Abstract

Recent research demonstrated that ternary aluminum-boron-iodine (Al·B·I₂) materials prepared by mechanical milling are effective in generating biocidal combustion products. Such reactive materials are of interest for the munitions aimed to defeat stockpiles of biological weapons. Additional reactive materials generating biocidal combustion products are of interests.  The materials should be stable at low temperatures, enabling their handling and storage.  At the same time, they should be sufficiently reactive to warrant their use as components of energetic formulations.

In this research, ternary Mg∙B∙I₂ composites were synthesized using two-stage mechanical milling of elemental powders of magnesium, boron, and iodine. In the first stage, a binary B∙I₂ powder was prepared by mechanical milling using a shaker mill.  The milling time was set to one hour. In the second stage, magnesium was added and the ternary material was prepared using additional 3-hour milling.  Prior to adding magnesium, boron-iodine composite prepared in the first milling stage was chilled to 0ºC for 30 min.  Prepared ternary composites were removed from the milling vials in the argon-filled glove box.  

For all the prepared materials, the concentration of iodine was fixed at 20 wt%. The mass ratios of Mg/B were selected as 15/65, 20/60, 25/55, 33/47, 50/30, and 70/10. Stability of the prepared materials was assessed by their heating in argon at a constant rate using Thermo Gravimetric Analysis (TGA) and observing weight loss due to iodine vaporization.  To minimize the effect of magnesium evaporation, the maximum temperature was limited to 450 ºC.  Ternary Mg∙B∙I₂ composite powders prepared by two-stage milling were more stable than any of the previously prepared iodine-bearing materials with the same concentration of iodine. Among different prepared samples, materials containing 33 and 50 wt% Mg retained more iodine upon heating. These two materials were selected for further oxidation, ignition and combustion studies.

Oxidation of the prepared powders was also studied by TGA.  Particle size distributions were measured using low-angle laser light scattering. Powders were ignited using in an air-acetylene flame and in a constant volume explosion apparatus.  Particle burn times and temperatures were measured optically.  Substantially longer burn times and lower combustion temperatures were observed for the prepared materials compared to the reference pure Mg powder. In aerosol combustion texts, the pressure produced by the ternary composites was inversely proportional to the concentration of boron in the material.