Chemical Dynamics of Aluminum Nanoparticles in Ammonium Nitrate and Ammonium Perchlorate Matrices: Enhanced Reactivity of Organically Capped Aluminum

Aluminum nanoparticles have been a subject of active investigation in recent years because of their potential to enhance the energy content of energetic materials. The associated kinetics of the chemical reaction and energy release are, in many cases, governed by the properties of the passivation layer protecting the particle rather than those of the underlying metal core. The passivation layer of Al particles is typically an oxide shell several nanometers thick, but other possibilities are now available. We have previously developed synthesis routes to produce air-stable Al nanoparticles that are capped by oleic acid. In the present study, we examine the chemical dynamics of these materials in ammonium nitrate and ammonium perchlorate matrices. For comparison, the analogous experiments were also performed on samples using traditional oxide-protected particles. Reactions are initiated by a 20 mu s IR laser pulse and then probed via time-of-flight mass spectrometry of the evolved gases and by emission spectroscopy of the flame. In both ammonium nitrate and ammonium perchlorate matrices, the organically passivated nanoparticles are found to be significantly more reactive and are able to access some reaction pathways unavailable to oxide-protected particles.