Combustion of nanoscale Al/MoO₃ thermite in microchannels

Microscale combustion is of interest in small-volume energy-demanding systems, such as power supplies, actuation, Ignition, and propulsion. Energetic materials can have high burning rates that make these materials advantageous, especially for microscale applications in which the rate of energy release is important or in which air is not available as an oxidizer. In this study we examine the combustion of mixtures of nanoscale aluminum with molybdenum trioxide in microscale channels. Nanoscale composites can have very high burning rates that are much higher than typical materials. Quartz and acrylic tubes are used. Rectangular steel microchannels are also considered. We find that the optimum mixture ratio for the maximum propagation rate is aluminum rich. We use equilibrium calculations to argue that the propagation rate is dominated by a convective process where hot liquids and gases are propelled forward heating the reactants. This is the first study to report the dependence of the propagation rate with a tube diameter for this class of materials. We find that the propagation rate decreases linearly with 1/d. The propagation rate remains high in tubes or channels with dimensions down to the scale of 100 μm, which makes these materials applicable to microcombustion applications.