Microstructure Effect on the Ignition Behavior of Nanoaluminum/PVDF Energetic Composites*

The inclusion of metallic micro- and nanoparticles in energetic composites is known to have significant effects on reactions. However, the physical response of materials containing nanoparticles during ignition can vary widely. To understand and predict responses, we develop a microstructure-explicit model that accounts for the thermodynamics, chemical reaction, and mass transport. The material considered consists of aluminum nanoparticles in a PVDF (polyvinylidene fluoride) matrix. The particles are 25 nm to 35 nm in radius with 70 wt.% active aluminum. The initial heating is caused by optical lasers at wavelengths of 532 and 1064 nm. An Arrhenius model is used to capture the dominant exothermic reaction, the fluorination of aluminum. The analysis focuses on the ignition process, conditions for self-sustained reaction, and the reaction front propagation speed. The effect of aluminum fractions between 10 wt.% and 40 wt.% on the reaction behavior is quantified. It is found that the optimal Al loading level is ~20% in terms of the minimum energy input for self-sustained reaction or ignition. The predicted propagation velocity or burn rate and the underlying trend are in agreement with experimental observations.