Nanostructural approach to the thickening behavior and oxidation of calcium-stabilized aluminum foams

The influences of calcium content on thickening stage, dynamic oxidation and subsequent formation of cell walls in closed-cell aluminum foams were investigated by both precise thermodynamic and experimental studies. A novel technique was also used for the sample preparation, and the compendious characterization by transmission electron microscopy. Based on nanostructural investigations, the results indicated that in low calcium amounts (0.5 wt.%), the formation of complex oxide nanoparticles plays a key role in cell wall formation and bubble stabilization, when ignoring the effect of foaming agents. The higher calcium contents (1.5 wt.%) result in different thickening mechanism in which, relatively thick and brittle complex oxide layers are formed. Breaking of these oxide layers due to mechanical stirring causes the entrapment of several fragments in the interface of bubbles and consequently lead to cell wall stabilization. Due discussions were carried out about the effects of different thickening mechanism on the mechanical behavior of cell walls.