Preparation of cellular alumina ceramics via biological foaming with yeast and its microstructural characterization via stereological relations

Abstract

The preparation of highly porous (cellular) alumina ceramics via biological foaming with yeast is described and its microstructure is characterized via image analysis using stereological relations. The ceramics prepared usually have total porosities in the range 78–84% and the porosities related to large pores (volume fraction of foam bubbles) are usually in the range 58–75%. The mean chord length and Jeffries size, i.e. pore size measures related to the interface density and the mean curvature integral density, respectively, are rather close to each other (usually 0.8–1.4 and 0.8–1.2 mm) with a ratio close to unity (0.9–1.4), and the mean surface-to-surface distance gives a realistic picture of the average wall thickness (usually 0.46–0.69 mm). Using a special processing variant (excess ethanol addition) it is possible to obtain microstructures with lower porosity (total porosity 68–70%, foam bubble volume fractions 50–56%) and smaller pore size (approx. 0.5 mm).