Transient ion ejection during nanocomposite thermite reactions

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. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3225907]