User:Cs32en/911/Sources/Osbourne/2006/content

"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."

"[...] Teflon is an ingredient that differs fundamentally from traditional oxidizers due to the fluorine content of the material. Teflon has been studied as an energetic component in micron-scale heterogeneous composites for some time; however, recent advances in technology have enabled the availability of nano-scale Al and Teflon particles, allowing for the study of such components in energetic applications. [...]

However, recent studies by Levitas et al. (2005) have revealed an alternate mechanism involved with nano-particle Al oxidation based on the tremendous mechanical stresses on the oxide shell unique to nano-particle Al. The stresses are brought about from the difference in thermal expansion between Al and Al2O3, and the enormous pressure of the interior molten Al. [...]

Poehlein et al. (2001) found that replacing various amounts of Mg in the Mg/Teflon/Viton (MTV) mixture with Alex (a nano-Al powder produced by the wire explosion process) resulted in higher burn rates and found that the total fuel loading of MTV may be reduced while maintaining burn rates similar to conventional fuel rich compositions without Alex. [...] A Department of Defense newsletter (Miziolek, 2002) recently identified nano-particle Al/Teflon as a metastable intermolecular composite (MIC) that has received considerable attention and defined MIC as, “mixtures of nanoscale powders of reactants that exhibit thermite (high exothermicity) behavior.” [...]

Al/Teflon produces a higher heat of combustion than the conventional solid propellant mixture AP-HTPB-Al (ammonium perchlorate oxidizer, hydroxy terminated polybutadiene binder, and Al fuel), determined by Tachibana and Kimura (1988) to be 8420 J/g and 5870 J/g, respectively. Also, Al/Teflon exhaust has a very low molecular weight, consisting of primarily AlF3 (84 amu) and carbon. Koch (2002) stated that metal/fluorocarbon propellant systems have products (metal-fluorides) in the vapor phase at combustion temperatures in contrast to metal oxides in conventional propellants, and this adds to the specific impulse of the fuel. [...]

With 13 out of 15 of the thermite/Teflon pellets having a successful ignition event, it is established that a thermite pellet can ignite under drop weight conditions."