Synergy of polysaccharide mixtures in gelcasting of alumina

The synergetic effect of mixtures of agar and galactomannan on their gelling ability was exploited to consolidate concentrated aqueous alumina suspensions by gelcasting. Aqueous polysaccharide solutions were prepared at 60 degrees C and added to stabilised and highly concentrated alumina suspensions maintained at the same temperature. These ceramic/polymer slurries were then poured into non-porous moulds, and direct consolidation was accomplished by cooling. Rheological characterisation was used to study the influence of alumina particles on gel network and to determine the optimal processing conditions for gelcasting. Relatively low amounts of polymers (approximate to 1 wt%) were sufficient for consolidation, thereby avoiding the binder burnout step. High green density was achieved by this method due to the bimodal character of the starling alumina powder. However, the presence of relatively coarse particles in the starting powder exerted a deleterious effect on densification and requires the use of an external driving force to full densify the samples. (C) 2000 Elsevier Science Ltd. All rights reserved.