Reaction Mechanism of the Aluminum Nanoparticle: Physicochemical Reaction and Heat/Mass Transfer

A lack of clarity in the reaction mechanism of the aluminum nanoparticle (ANP) severely restricts its effective applications. By describing the physicochemical evolution of ANP burning in typical oxidizers (CO₂, H₂O, and O₂) at the nanoscale, three principal reaction modes including physical adsorption, chemical adsorption, and reactive diffusion were captured during the reaction. Initially, oxidizer molecules are physically and chemically adsorbed on the ANP surface until ignition in which reaction heat plays a more important role in contrast to heat transfer. Subsequently, partial oxidizer atoms adsorbed by surface diffuse across the shell to react with the Al core, presenting the dominant mode of reactive diffusion. It is assumed that the binding energy between Al and oxidizer atoms is in an inverse relation to atomic diffusivity but is positively correlated to reaction heat, resulting in various ANP structures and heat release rates. Our findings provide design guidelines to control various oxidizer supplies with respect to the reaction stages to balance the energy release and the residence time of ANP.