Observing coalescence of aluminum nanoparticles during burning using aluminum/ammonia perchlorate sandwiched films

Abstract

To observe the agglomeration, an important parasitic process in metal composite combustion, sandwiched structures with laminates of aluminum (Al) and ammonia perchlorate (AP) layers are prepared and characterized by high-speed macro and microscopic imaging systems with pyrometry. The bilayer structure prepared by electrospraying was confirmed by Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS) and the composition was confirmed by thermogravimetric analysis/differential thermal calorimetry (TGA/DSC). We found that the burn rate of the Al/AP sandwich films increases with the decrease of bilayer thickness of Al and AP, owing to the shorter diffusion distance between fuel and oxidizer. More importantly, the complete process of the agglomeration/sintering of Al nanoparticles (NPs) is observed in-situ, which demonstrates the different stages of agglomeration process of Al NPs. Temperature measurement from pyrometry reveals the temperature of agglomerates during combustion, consistent with the agglomerate size and burn rate observation. Simple calculations based on “pocket-theory” support the observed changes in agglomeration size with bilayer thickness.