Combustion of Composites of Boron with Bismuth and Cobalt Fluorides in Different Environments

Composite powders of boron and 50 wt-% of either bismuth or cobalt fluoride were prepared by arrested reactive milling. Particle combustion was studied in air, and in the products of air-hydrogen and air-acetylene flames, respectively. Combustion times, determined from 700 to 800 nm emission pulses, were correlated with particle sizes. Combustion temperatures were determined for select cases. In air, the composite particles burned faster than elemental boron with comparable combustion temperatures. However, the composite particles burned in one stage unlike the two-stage combustion pattern known for boron. In flame combustion products, the composite powders burned more slowly than elemental boron, but also in a single stage. Light emission was reduced compared to combustion in air, suggesting lower temperatures. Across all conditions, the B·BiF₃ composites had shorter burn times compared to B·CoF₂. Washing boron in acetonitrile prior to composite preparation to remove surface oxide/hydroxide had no significant effect on the combustion of the resulting composites.