Chainlike products from the reaction of aluminum nanoparticles in HF atmosphere: an atomic insight

The fluorination of aluminum nanoparticles (ANPs) has been widely used in energetic formulations and nanomaterials preparation, with various aluminum fluoride nanostructures generated. However, the structural evolution of ANPs in fluorination with atomic-level understanding still remains unrevealed and unclear. In this work, we perform reactive molecular dynamics simulations to reveal the structural evolutions of ANPs and Al@Al2O3 in HF atmosphere. For the first time, the growth of chainlike aluminum fluoride products is revealed on the atomic-scale, including two stages of the HF etching of ANPs (Al@Al2O3) to numerous active clusters and the self-assembly of clusters into chainlike structures. The effects of F/Al molar ratio (1-8), temperature (500-2500 K), particle size (5.0-10.0 nm) and oxide shell thickness (0.2-1.0 nm) on the growth were examined atomically. The chainlike structures show unique peaks in Al-F-Al (76 degrees) and F-Al-F (67 degrees or 100 degrees) bond-angle distribution functions, in Al-F (4.2 or 6.6 angstrom) and Al-Al (5.3 angstrom) pair distribution functions, and specific coordination configurations of Al/F atoms. More importantly, four types of individual chains (straight, curve, branched and cyclic chains) and stacking of chains are observed after annealed, consistent with the AlF3 nanorods and wires in experiments. Our simulated results facilitate to guide the practical fluorination process and nanomaterials preparation. [GRAPHICS] .