The role of reducing agents in the nucleation and growth of Al metalloid clusters: Ab initio molecular dynamics study

Abstract

Abstract. Ab initio simulations are used to study the growth of metalloid aluminum clusters from their monohalide (AlCl) precursors. Larger metalloid clusters have recently been considered as a novel energetic material with fast metal oxidation kinetics, but the growth of these systems in solution is not understood. Molecular dynamics (MD) simulations are used to study the role of lithium-aluminum hydride (LiAlH 4 , LAH) and sodium borohydride (NaBH 4 , NaB) reducing agents in the nucleation and growth of these clusters. MD simulations of AlCl liquid with LAH show spontaneous metalloid cluster nucleation by rapid formation of Al-Al bonds. The growth process is initiated by Li detachment from LAH followed by hydrogen transfer from the hydride to a nearby Al. This process aids in the formation of trivalent impurities (AlH 3 ) in the solution. Growth towards larger metalloid clusters then proceeds via repeated insertion of AlCl into Al-Cl bonds. The transferred hydrogen plays a significant role in reducing monohalide species from the liquid. The energy barrier associated with the Al-Cl bond is dropped from 7.8 eV to ≈ 4.0 eV as a consequence of this transfer between Al centers. However, this process is hindered in the case of NaB due to strong ionic bonding between Na and B centers, and consequently no cluster growth is observed.