Influence of Aluminum Passivation on the Reaction Mechanism: Flame Propagation Studies

Currently, two main known mechanisms of aluminum (Al) nanoparticle reaction are discussed in the literature, namely those based on diffusion through an oxide shell and melt-dispersion. The two mechanisms lead to opposite predictions in nanoparticle design. The diffusion mechanism suggests that the reduction or complete elimination of the oxide shell will increase Al reactivity, whereas the meltdispersionmechanismsuggestsanincreaseininitialoxidethicknessuptoanoptimalvalue.Thegoalofthis study is to perform critical experiments in a confined flame tube apparatus to compare these two predictions. Specifically, the flame propagation rates of perfluoroalkyl carboxylic acid (C13F27COOH)treatedAlnanoparticleswithandwithoutanaluminashellweremeasured.Resultsshowthatwhenthereis no alumina passivation shell encasing the Al core, the flame rate decreases by a factor of 22-95 and peak pressure deceases by 3 orders of magnitude, in comparison with the Al particles with an oxide shell. These results imply that the melt-dispersion reaction mechanism is responsible for high flame propagation rates observed in these confined tube experiments.