The effects of fuel particle size on the reaction of Al/Teflon mixtures

Reactive mixtures of aluminum (Al) and Teflon have applications in propellants, explosives, and pyrotechnics. This study examines the thermal degradation behavior of Teflon and nanometer scale Al particles compared with micron-scale Al 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 Al mixture. A pre-ignition reaction (PIR) unique to the nano-Al 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 Al particles. The decreased alumina surface area inherent in larger Al 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 Al/Teflon degradation and particle size effects on the reactivity of Al/Teflon composites.

The effects of Teflon particles on the sensitivity of thermite composites are also studied experimentally using a drop-weight apparatus. It was found that the addition of Teflon to an Al/MoO3 thermite composite increases its sensitivity to impact.