Influence of solid loading on drying-shrinkage behaviour of slip cast bodies

Drying-shrinkage behaviour, described by Bigot's curves, was used to characterise slip cast bodies prepared from suspensions at different solid loading and dispel sed with polyelectrolyte type surface active agents. Various ceramic materials (alumina, silicon carbide and calcium carbonate) were examined in order to establish a general relationship among solid lending of the starting suspension, particle packing in green state and drying behaviour. The Bigot's curves indicated that the shrinkage decreases with increasing solids' concentration, whereas the critical moisture content (CMC) shows an initial decrease followed by a trend towards a constant value at higher solid lending. The slope of the straight lines corresponding to the first stage of drying first increases with augmenting solid concentration, but decreases again for high solid loading. For all materials tested, good relationships were found between the CMC and slip cast density (correlation coefficients higher than 0.98) as well as between the shrinkage during the first stage of the drying process and solid loading (correlation coefficients higher than 0.99). Finally, Bigot's curves revealed to be a very simple yet effective tool to characterise the porous microstructure of slip cast bodies. In contrast, evaluation of the pore size distribution in relative dense slip cast bodies by Hg-porosimetry was found to be a less reliable method. (C) 1998 Elsevier Science Limited. All rights reserved.