Effect of Al₂O₃ polymorphs on the combustion behavior of Aluminum: A Molecular-Level study

This study employs reactive molecular dynamics simulations, supplemented by experimental validation, to systematically investigate the effect of α-Al₂O₃, θ-Al₂O₃, and γ-Al₂O₃ shell structures on the combustion behavior of aluminum particles. Simulation results reveal that the crystalline structure of Al₂O₃ significantly alters oxygen diffusion, interfacial reactivity, and energy release during combustion. Among the three polymorphs, γ-Al₂O₃ exhibits the most favorable combustion performance, characterized by shorter ignition delay, higher intermediate species diversity, lower activation energy, and enhanced combustion completeness, which are attributed to its high porosity, abundant surface defects, and superior oxygen permeability. In contrast, α-Al₂O₃ forms a dense and thermodynamically stable shell that restricts oxygen transport and delays combustion onset. Experimental results, including high-speed imaging, spectral analysis, and transmission electron microscopy, corroborate the simulation findings and confirm that γ-Al₂O₃ coatings accelerate ignition and shorten combustion duration. The enhanced combustion efficiency associated with γ-Al₂O₃ is attributed to its loose microstructure and elevated interfacial reactivity, which promote rapid mass and heat transfer. This integrated study elucidates molecular-level mechanisms underlying crystal-phase-dependent regulation of aluminum combustion and provides a theoretical basis for understanding and regulating aluminum combustion behavior.