Transient ion ejection during nanocomposite thermite reactions

Abstract

We observe an intense ion pulse from nanocomposite thermite reactions, which we temporally probe using a recently developed temperature jump/time of flight mass spectrometer. These ion pulses are observed to be much shorter in duration than the overall thermite reaction time. Ion ejection appears in stages as positive ions are ejected prior to nanocomposite thermite ignition, and ignition of the thermite mixtures leads to a second ionization step which is primarily dominated by negative species. The positive species are identified from mass spectrometric measurements and the results show that the positive ion species are comprised of Na ions with minor species of Al and K ions. This observation can be explained by a diffusion based ion-current mechanism, in which strong Al ion diffusion flux formed through the oxide shell, and the surface Na and K ions from salt contaminations are ejected by the strong electrostatic repulsion. The fact that the negative ionization step occurs during the ignition event suggests a strong relation between the nanocomposite thermite reaction and the negative ionization process.

Time-Resolved Mass Spectrometry of the Exothermic Reaction between Nanoaluminum and Metal Oxides: The Role of Oxygen Release

“…Recently, we reported the finding of intense ejection of ionized species coincident to or in some cases just before visible reaction . The current pulse caused a catastrophic malfunction of the high voltage bias on the ion extraction optics and resulted in a loss of mass spectrum signal.…”

“…Recently, we reported the finding of intense ejection of ionized species coincident to or in some cases just before visible reaction. 24 The current pulse caused a catastrophic malfunction of the high voltage bias on the ion extraction optics and resulted in a loss of mass spectrum signal. As a result, it was necessary to modify the ion optics configuration to minimize the effect of electric impulse and enable the collection of spectra.…”

Ignition of Nanocomposite Thermites by Electric Spark and Shock Wave

“…A model describing exothermic reactions for the thermally initiated, fully dense nano-thermite particles has been proposed quantifying individual reaction steps and predicting a thermal runaway to occur in vicinity of the experimental ignition temperature [19]. However, additional processes, including the release of oxygen prior to ignition [17,18,[20][21][22] and a burst of ions produced by the rapidly heated nano-thermites [23], possibly associated with the oxygen release, have been reported but have not been well understood. Such processes can affect ignition and ensuing combustion of reactive nanomaterials; the effect may depend on the rate of heating and respective ignition delay.…”

Reaction kinetics study of Al-Fe2O3 nanoenergetics

“…This effect will allows earlier diffusion of Al ions through the oxide layer cracks compared to micron size Al and subsequently react with the surrounding oxidisers. This observation is consistent with the results reported by Zachariah [123,128]. Difference in reaction paths taken by nano and micronthermites were observed using XRD at different temperature intervals.…”