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 μm 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.