Factors affecting the microstructure of a fine ceramic foam

Sintered cellular ceramics with varying degrees of reticulation were prepared using coarse and fine alumina powders and a 70/30 mixture thereof. The ceramic foams had fine cell size (about 150 mum diameter) in each case. The method of preparation involved the free expansion of suspensions of these powders at 20 vol.% in a polyurethane foaming system. In order to modify the microstructure, the expansion was opposed using a die, and this reduced the void fraction and window size. In addition, directional rising was achieved by expanding the foam in a long cylindrical Vessel and this modified the cell shape of the final foam. These foams have potential use in a range of applications including catalysis, but the main aim of the present work was to prepare preforms for metal matrix composites. (C) 2000 Elsevier Science Ltd and Techna S.r.l. All rights reserved.