INITIATION AND REACTION IN Al/Bi2O3 NANOTHERMITES: EVIDENCE FOR THE PREDOMINANCE OF CONDENSED PHASE CHEMISTRY

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.