A comparison study of the agglomeration mechanism of nano- and micrometer aluminum particles

The agglomeration mechanism of micro- and nanosize aluminum particles with a primary mean particle diameter of 4.5 μm and 75 nm, respectively, was comparatively investigated under an incident shock wave. The morphology, particle size, and agglomeration process of micro- and nanometer alumina particles were comprehensibly compared by X-ray diffraction, transmission electron microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. Images of X-ray diffraction reveal that a varied of phases of alumina (γ-, δ-, ε-, and α-Al2O3) were simultaneously found in the nanosize alumina products, which may give some detail information of the wide variety of reacting temperature of aluminum nanoparticles, while Al4C3 was detected in micrometer alumina products, which also gives some dynamic information of aluminum to alumina, i.e., aluminas have actually reacted with the free active carbon atoms to produce their intermediates. The microstructure of aluminas induced by the incident shock waves was detected and analyzed by using transmission electron microscopy combined with X-ray photoelectron spectroscopy spectrum. These results are an additive evidence to support that the initial stage sintering of the alumina nanosize powders is dominated by grain boundary diffusion, while the volume diffusion is the main character for the initial stage sintering of the micrometer alumina powders.