Activating Aluminum Reactivity with Fluoropolymer Coatings for Improved Energetic Composite Combustion

Abstract

Aluminum (Al) particles are passivated by an aluminum oxide (Al2O3) shell. Energetic blends of nanometer-sized Al particles with liquid perfluorocarbon-based oxidizers such as perfluoropolyethers (PFPE) excite surface exothermic reaction between fluorine and the Al2O3 shell. The surface reaction promotes Al particle reactivity. Many Al-fueled composites use solid oxidizers that induce no Al2O3 surface exothermicity, such as molybdenum trioxide (MoO3) or copper oxide (CuO). This study investigates a perfluorinated polymer additive, PFPE, incorporated to activate Al reactivity in Al-CuO and Al-MoO3. Flame speeds, differential scanning calorimetry (DSC), and quadrupole mass spectrometry (QMS) were performed for varying percentages of PFPE blended with Al/MoO3 or Al/CuO to examine reaction kinetics and combustion performance. X-ray photoelectron spectroscopy (XPS) was performed to identify product species. Results show that the performance of the thermite-PFPE blends is highly dependent on the bond dissociation energy of the metal oxide. Fluorine-Al-based surface reaction with MoO3 produces an increase in reactivity, whereas the blends with CuO show a decline when the PFPE concentration is increased. These results provide new evidence that optimizing Al combustion can be achieved through activating exothermic Al surface reactions.

Extrudable Gassy Pyrotechnic Time Delay Compositions

“…The measured burning rate results, listed in Table 1, were comparable to results obtained in other studies [12,16]. Filaments extruded for 3D printable compositions based on PVDF, with 20 wt.% aluminium as fuel, exhibited burning rates of up to 18.7 ±1.3 mm•s −1 [12].…”

“…Filaments extruded for 3D printable compositions based on PVDF, with 20 wt.% aluminium as fuel, exhibited burning rates of up to 18.7 ±1.3 mm•s −1 [12]. Potgieter et al [16] measured the burning rates of energetic films based on Viton B fluoropolymer as oxidant with 50 wt.% metal fuel.…”

“…The variance for the burn rate doubled with the increased LFC-1 content. The variability of the burn rate provides an indication of the quality of the extruded filaments [12]. The burn rate increases can be explained by the increase in the reaction temperature.…”

Improved Energetic-Behaviors of Spontaneously Surface-Mediated Al Particles

“…Fluoro-polymers such as polytetrafluoroethylene (PTFE) and perfluoropolyether (PFPE) have even been shown to be capable of improving the oxidation efficiency of Al particles because fluorine atoms decompose the alumina shell surrounding the Al particles into AlF 3 products 21–24 . Once the internal Al material is continuously exposed as fluorine-compounds are formed and evaporated, the oxidation reaction proceeds efficiently compared to that with pure Al particles with a dense surface oxide that inhibits continuous combustion 25, 26 .…”

Boron Carbide Based Biocide Compositions: A Study of Iodate Particle Size on Combustion and Iodine Output

“…Shaw et al. also has shown that a B 4 C/NaIO 4 system with the addition of a fluoropolymer binder, polytetrafluoroethylene (PTFE), can result in halogenated fumigants . The versatility of B 4 C as a fuel has also been shown by Shaw et al.…”