The effects of fuel particle size on the thermal degradation of AI/Teflon mixtures

Reactive mixtures of aluminum (AI) and Teflon have applications in propellants, explosives, and pyrotechnics. This study examines the thermal degradation behavior of Teflon and nanometer scale AI particles compared with micron-scale AI particles. Differential scanning calorimetry and thermo-gravimetric analyses were performed in an argon environment on both nanometer and micron scale mixtures revealing lower onset temperatures and larger exothermic activity for the nanometer scale AI mixture. A pre-ignition reaction (PIR) unique to the nano-AI mixture is found. Experiments show the mechanism of the PIR to be the adsorption of fluoride ions from the Teflon polymer onto the aluminum oxide shell of the AI particles. The decreased alumina surface area inherent in larger AI particles lowers the exothermic effect of the PIR. The PIR may be the mechanism of ignition for nano-composite samples heated in air. Experimental results are discussed along with reviewed literature to explain the thermal degradation process of the mixtures. These results are helpful in the fundamental understanding of AI/Teflon degradation and particle size effects on the reactivity of AI/Teflon composites.