Probing boron thermite energy release at rapid heating rates

Boron (B) is a promising fuel for energetic materials due to its high gravimetric and volumetric energy density. The enhanced ignition and combustion of B in a thermite with CuO and Bi₂O₃ and their mixtures compared to single metal oxides was recently demonstrated. In this study, we compared the early-time reaction B-thermite mixtures using the laser-induced air shock from energetic materials (LASEM) technique, bomb calorimetry, and differential scanning calorimetry (DSC). The application of LASEM to B/metal oxide samples has enabled the quantification of their microsecond-timescale energy release and excitation temperatures under extremely high heating rates, and the elucidation of their chemistry differences on both the microsecond and millisecond timescales. The time to peak combustion determined by LASEM follows the trend B/CuO/Bi₂O₃ < B/Bi₂O₃ < B/CuO. The energy release measured by LASEM on both the microsecond- (laser-induced shock velocities) and millisecond- (combustion reactions) timescales was the highest for B/CuO/Bi₂O₃. These relative measurements are in agreement with the heat of reaction as measured by the bomb calorimetry and onset of DSC traces, which follow similar ordering and suggests that enhanced ignition of these composites is contributing to the early-time energy release. Finally, our morphology characterization revealed that CuO has a strong affinity for both B and Bi₂O₃; we suggest the CuO pulls the Bi₂O₃ into closer contact with the B particles in the binary metal oxide mixture, resulting in a synergetic enhancement effect compared to the single metal oxide.