Morphological Analysis of Slip-Cast Emulsion-Templated Alumina Foams by Microfocus Computer Tomography

Bulk alumina foams were generated by slip casting of suspensions combined with particle-stabilized emulsion droplets as pore templates. Because of the volatile nature of the template, the green foams could be consolidated by sintering without a debinding step. The porous structure of the consolidated foams was analyzed nondestructively using image analysis of microfocus computer tomography (micro-CT) data. The fraction of open and closed pores, as well as the pore sizes and pore size distributions, were calculated from the generated 3D micro-CT datasets and correlated to the applied processing parameters. The anisotropy in the produced structures was assessed and elucidated by a detailed analysis of segmented tomography data. The results indicate that the width of the pore size distribution and the average macropore size, ranging from 225 to 136 μm, depend on the slip rheology. Any anisotropy caused in the structure was linked to the template preparation but is only present in a narrow zone near the bottom of the foams. Although the macroporosity (≥20 μm) was only 24%–31%, tomographic analysis showed that over 90% of these macropores were interconnected through ≥20-μm-diameter windows.