Computational Modeling of Dehydration Energetics of Aluminum (Oxy) hydroxides

Modifying the surface chemistry of metal fuels is an effective strategy to promote greater power generation. Aluminum, a common fuel used in energy generation technologies. is a good candidate to study surface modification. Most pyrophoric metals are passivated by their nascent oxide, and for aluminum core particles, this shell is formed by aluminum oxide phases. In this study, we investigate the initial phase transformation of aluminum oxide into aluminum hydroxide. The hydrated surface modification represents the first step toward further derivatization, leading to a more oxygen rich and stable surface passivation. Among the materials involved in these surface transformations, α-Al(OH)3 has proved to be the most promising. We employ density functional theory (DFT) calculations to analyze the dehydration process of aluminum oxide surfaces, particularly γ-AlO(OH) (boehmite), α-Al(OH)3 (bayerite), and γ-Al2O3 (alumina). Specifically, we computed hydroxyl-removal (OH-vacancy formation) energy and the energy associated with removing a neighboring proton in both vacuum and polar environments, thereby characterizing the removal of water. The results show that, in a polar environment, boehmite can match-or, in some configurations, outperform the bayerite polymorph. However, this comparable dehydration/dehydroxylation energies are believed to act in conjunction with the overarching transformation mechanism, which converts boehmite into a meta-stable form of alumina. This study addresses a key gap in understanding aluminum-based nanoscale coatings: although γ-AlO(OH) and Al(OH)₃ have both been employed to passivate and functionalize core particles, their relative efficacy has not been fully explained. By highlighting the structural and chemical distinctions between these shells, we aim to inform the design of improved passivation layers for metal particles requiring both stability and chemical tunability.