Layered Alumina Ceramics with Porosity Steps

Abstract

This work deals with the preparation and characterization of macroporous alumina ceramics and permeable laminates with a stepwise (layerwise) porosity gradient in the range of approx. 20–50 %. Layered structures are made by sequential casting and draining of ceramic suspensions containing corn starch (median size approx. 14 micrometers), using both traditional slip casting (TSC) and starch consolidation casting (SCC). In both techniques starch acts as a poreformer, which is eliminated during firing. The influence of the alumina concentration and starch content in the suspension on the porosity, pore size and pore connectivity in the individual layers is studied. It is shown that differential shrinkage of the layers in the case of SCC, caused by the different starch content, may be avoided by controlling the alumina content. The distribution of pore throat diameters (cell window sizes) is determined by mercury porosimetry, whereas the distribution of pore cavity diameters (cell sizes) is measured by microscopic image analysis.