Activating Aluminum Reactivity with Fluoropolymer Coatings for Improved Energetic Composite Combustion.
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.
Department of Mechanical Engineering, Texas Tech University , Lubbock, Texas 79409, United States.
Jena
J
McCollum
Department of Mechanical Engineering, Texas Tech University , Lubbock, Texas 79409, United States.
Michelle L
ML
Pantoya
Department of Chemistry and Chemistry Research Center, United States Air Force Academy , 2355 Fairchild Drive, Suite 2N225, Colorado Springs, Colorado 80840, United States.
Scott T
ST
Iacono
aluminum fluoride; aluminum powder; combustion; energetic materials; exothermic surface chemistry; fluorine; oligomers; preignition reaction