THE CHARACTERIZATION OF CAKE STRUCTURE AND RHEOLOGY VIA PRESSURELESS SLIP CASTING

For an aqueous alumina slip having an average particle size of 0.5 mum , the cake structure and rheology were investigated. Tetrasodium pyrop hosphate (TSPP) was chosen as a dispersant. Results showed that a part ially flocculated slip (adding 0.28 wt% TSPP based on solids) had high er viscosity but faster casting rate in comparison to a deflocculated slip (adding 0.42 wt% TSPP). The resultant cake from the partially flo cculated slip had an average green density of 2.24 g cm-3, which was v ery close to the 2.30 g cm-3 for the cake cast from the deflocculated slip. However, the former had a more uniform pore-size distribution ac ross the cake thickness than the latter. Cake rheology was characteriz ed in situ using a parallel-plate rheometer. When the drying time (aft er casting) was less than 30 min, the cake from the partially floccula ted slip resulted in higher elastic moduli and yield stresses compared to the deflocculated slip. However, at a drying time of 60 min, cakes grown from the flocculated slips exhibited lower elastic moduli and y ield stresses. For all cakes studied, the critical elastic deformation before plastic flow was approximately equal to the average alumina po wder diameter (i.e. approximately 0.5 mum). Finally, the rheological b ehaviour of alumina slip with larger particle size (i.e. approximately 1.2 mum) and broader size distribution was compared to that of the fi ne alumina. Results showed that these alumina cakes exhibited signific antly greater plastic flow, in contrast to the 0.5 mum alumina cakes. This is believed to be an effect of the broader particle-size distribu tion.