I. Tsao et Ra. Haber, THE CHARACTERIZATION OF CAKE STRUCTURE AND RHEOLOGY VIA PRESSURELESS SLIP CASTING, Journal of Materials Science, 28(12), 1993, pp. 3214-3220
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.