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 these based on diffusion through an oxide shell melt dispersion. The two mechanisms lead to opposite predictions in nanoparticle design. This diffusion mechanism suggests that the reduction or complete elimination of the oxide shell will increase Al reactivity, whereas the melt-dispersion mechanism suggests an increase in initial oxide thickness up to an optimal value. The goal of this 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). treated Al nanoparticles with and without an alumina shell were measured. Results show that when there is no alumina passivation shell encasing the Al core, the flame rate decreases by a factor of 22-95 and peak pressure decease by 3 orders of manitude, in comparision with the A1 particles with an oxide shell. These results imply that the melt-dispersion reaction mechanism is responisble for high flame propagation rates observed in these confined tube experiments.