Initiation and Reaction in Al/Bi₂O₃ Nanothermites: Evidence for the Predominance of Condensed Phase Chemistry

Abstract

This study explores the reaction between Al and Bi₂O₃ nanoparticles under high heating rate conditions with temperature-jump/time of flight mass spectrometry (T-Jump/TOFMS), high speed imaging, and rapid sample heating within a scanning electron microscope (SEM). Comparison of rapid heating of Al/Bi₂O₃ thermite and neat Bi₂O₃ shows that initiation of the Al/Bi₂O₃ reaction occurs at a much lower temperature than the point where oxygen is released from the neat Bi₂O₃ powder. Thus, without the presence of a gas phase oxidizer, it can be concluded that a condensed phase initiation mechanism must be at play in the Al/Bi₂O₃ nanothermite. C/Bi₂O₃ heating experiments were used for a mechanistic comparison between two different fuel types since the carbon represents a nonvolatile fuel in contrast to the aluminum. This formulation showed a similar condensed phase initiation as was seen with the aluminum nanothermite. Qualitative comparison of high speed imaging for Al/Bi₂O₃ and Al/CuO indicates that the initiation reaction in Al/Bi₂O₃ is about twice as fast as a comparable copper oxide system, which has not been apparent from bulk thermite combustion studies. Bi₂O₃ is known to possess unique ion transport properties, which combined with the presence of oxygen and aluminum ions within the nanothermite system may play a significant role in the speed of the nanothermite reaction.

Keywords:

• Bismuth oxide
• Condensed phase reaction
• Mass spectrometry
• Nanothermite
• Rapid heating