The influence of aluminum passivation on the reaction mechanism: Flame propagation studies

In this study, two types of nano-Al/metal oxide composites are examined. The first Al sample is passivated with Al₂O₃ and treated with perfluoroalkyl carboxylic acid (C₁₃F₂₇COOH). The second Al sample is devoid of an alumina shell and instead passivated with perfluoroalkyl carboxylic acid (C₁₃F₂₇COOH). The goal of this study is to understand the role of the passivation shell and associated reaction mechanism on flame propagation. Results show that when there is no alumina passivation shell encasing the Al core the flame propagation rates are reduced by two orders of magnitude. All flame propagation experiments were performed in a confined flame tube apparatus which may not be ideal for characterizing materials with significantly different ignition sensitivities. Results indicate that flame speeds measured with this apparatus are dependent on the ignition sensitivity of the mixture. Acid treated Al particles are shown to be roughly five times less ignition sensitive than the Al particles with no acid treatment; however, both particles produce roughly the same heat of combustion in thermal equilibrium measurements.