Starch as a Pore‐forming and Body‐forming Agent in Ceramic Technology

Abstract

AbstractWheat and corn starch can be used for the preparation of porous alumina ceramics via the SCC (starch consolidation casting) process, resulting in porosities ranging from > 20% to approx. 50% (using nominal starch contents of 10 – 50%, v/v), with open porosity dominating (closed porosity < 6.5%). The character of porosity and the shape of the pores corresponds to the starch granules used, but the pore size is determined by a complex interplay between starch swelling (during the body‐forming step) and pore shrinkage (during sintering of the ceramic). Typically, for low starch contents (e.g. nominal starch contents of around 10%, v/v) starch swelling is a significant effect, and the pores after sintering are larger than the size of the starch granules. For higher starch contents swelling is constrained (by limited space and/ or water availability), and the matrix shrinkage during sintering overcompensates the swelling effect, so that the final pores in the ceramic can be significantly smaller than the original starch granule size. In this paper it is shown how porosity is related to pore size. In particular, it is demonstrated that the porosity indirectly determined from image analysis (via the median pore size) is closely related to the porosity directly measured via the Archimedes method. On the other hand, mercury porosimetry measures the distribution of pore throat sizes. With increasing starch content in the suspension, the pore throat size in the as‐fired ceramic materials increases, resulting in a more open microstructure.