Effect of forming process on the integrity of pore-gradient Al2O3 ceramic foams by gelcasting

Pore-gradient Al2O3 foams were produced by gelcasting using the epispastic polystyrene (EPS) sphere template. This approach allows the design of porous ceramics with degree of pore connectivity and height of gradient layers via appropriate selection of the sizes and numbers of spheres. The fabrication processing of open-cell porous ceramics limited by polymeric sponge template, sharp cracks at the strut edges and closed pores can be resolved by this approach. To achieve the optimal manufacturing conditions of maintaining integrity of the network, the effects of solid loads, height of the slurry and the pre-removal of the polymeric foam template on the struts of the ceramic foams were studied. The results revealed that 55 vol.% Al2O3 slurries with 0.5 wt.% ammonium polyacrylate kept good fluidity for casting and avoided the inner inordinate shrinkage. Different shrinkage behavior of the top and bottom of the sample was effectively reduced due to approximately same water vapor diffusion areas on the top and bottom. The integrity of dendritic solidification structure maintained perfectly through template pre-removed in dichloromethane compared with direct heating.