Experimental effective metal oxides to enhance boron combustion

Abstract

Thermite reactions between metal fuels and oxide oxidizers are highly exothermic and self-sustaining, so they find wide applications in the explosion, pyrotechnics, thermal batteries, micro-actuator, and material synthesis and process. Compared to the well-studied aluminum (Al)-based thermites, boron (B)-based thermites are thermodynamically attractive due to boron's higher volumetric and gravimetric energy densities and they received limited attention. Previous studies have compared the effect of metal oxide on the reaction onset temperature of B-based thermites and identified that B/Bi2O3 and B/CuO thermites have lower reaction onset temperatures than other B/metal oxides. Nevertheless, there is no systematic study on the effect of metal oxide on both ignition and combustion of B-based thermite. In addition, no study has investigated the effect of binary metal oxide mixtures for B-based thermite. Herein, we experimentally tested five common metal oxides (CuO, Bi2O3, MoO3, Co3O4, and Fe2O3) on the ignition and combustion characteristics of sub-micron sized B particles using Xenon flash ignition, constant-volume pressure vessel and bomb calorimeter experiments. We observed that Bi2O3 and CuO are the most effective oxidizer for ignition and combustion of boron, respectively. We further identified that the binary oxide mixture (75 wt% B–CuO + 25 wt% B–Bi2O3) is more effective than all the single metal oxide for the ignition and combustion of boron particles. The results suggest that mixed oxides are potentially beneficial for ignition and combustion of other metal fuels as well.