Atomic insight into the agglomeration evolution mechanism of aluminum nanoparticles with core-shell structure

Abstract

Aluminum nanoparticles present excellent combustion characteristics, but such advantage is weakened due to particle agglomeration. This work focuses on this crucial behavior of aluminum nanoparticles in propellant and explore its underlying evolution mechanism from an atomic view. Molecular dynamic simulation method is used to simulate the agglomeration behavior under typical temperature of aluminum-based propellant. A two-staged accumulation-aggregation behavior is observed under low temperature due to atom movement driven by surface diffusion and grain boundary diffusion. A third stage of agglomeration dominated by viscous flow mechanism is achieved when the particle temperature is above 1500 K. The transition from aggregation to agglomeration is initiated by the solid-liquid phase transformation of the oxide shell, which happens under temperature lower than the melting point of alumina due to the formation of aluminum suboxide with low melting point. Decreasing the oxide layer thickness and integrity as well as particle size could accelerate the agglomeration and thus weakening the size advantage of aluminum nanoparticles.