Synergistically Enhanced Long-Term Effectiveness and Combustion Performance of Aluminum Nanoparticles by Partially Fluorinating External Alumina Shell

Aluminum (Al) particles, especially nanosized Al (n-Al), are extremely liable to deteriorate when exposed to air during the preparation and storage process, which seriously threatens their inherent energy density and limits their combustion behavior. Until now, it is really challenging and urgent to improve the combustion performance without sacrificing the original high energy density. Here, in situ direct fluorination by utilizing F2/N2 mixed gas as a fluorinating agent was first applied to modify n-Al particles, and the nonenergetic Al2O3 shell with a high melting point was converted into a partially fluorinated metal oxide (aluminum oxyfluoride, AlOxFy) shell. The results indicated that surficial direct fluorination equipped n-Al particles with a much better corrosion resistance to oxygen and moisture. Especially, regarding the problem of aqueous corrosion, the corrosion rate of fluorinated samples surprisingly decreased up to 4.46 mil/year from 68.69 mil/year of raw samples. More importantly, AlOxFy was readily decomposed by being heated and the produced AlF3 easily vaporized due to its lower boiling point in comparison with Al2O3, which effectively promoted the oxidation behavior of fluorinated n-Al particles. Furtherly, the improved energy release in ignition experiments confirmed the synergistically enhanced long-term effectiveness and combustion performance of the fluorinated n-Al samples. Therefore, a feasible strategy was demonstrated to enhance ultimate energy release performance of n-Al particles, and its advantages of high efficiency and solvent-free procedure highlight its great potential in practical applications.