Reaction dynamics of aluminum-viton^®-acetone droplets

The fluoroelastomer Viton (C₅H_3.5F_6.5) is a binder used in energetic material composites that can be dissolved in acetone and mixed with solid metal fuel particles, such as aluminum. The slurry can be molded into any configuration and the acetone is evaporated off leaving a solid homogeneous reactant mixture. Fundamentally understanding the reaction dynamics of acetone, Viton, and aluminum is useful for not only consolidating reactants, but also for the potential to use nanometric aluminum particles in liquid combustion applications. The objective of this study is to examine acetone-Viton droplet burning as a function of aluminum particle size and concentration. A diagnostic was developed that suspends the multiphase 3 mm droplet on a fiber and enables droplet surface regression rates to be monitored with a high-speed video camera. Results show that acetone combined with Viton (5%) and either 2.5% micron aluminum (10-14 μm) or nanometric aluminum (80 nm) burned with two distinct stages. However, acetone combined with Viton and more than 5% nanometric aluminum burned with a distinct three-stage behavior. The three stages are described as evaporation, combustion, and burning of carbon residue. Addition of micron aluminum to Viton and acetone droplets decrease the droplet regression rate 82% when compared with Viton and acetone droplets with nanometric aluminum particles. These results suggest that the presence of nanometric aluminum particles generates localized hot spots that consume the carbon present from Viton decomposition, thereby eliminating the third stage.