Influence of the stabilising mechanism and solid loading on slip casting of alumina

Two commercial surface active agents that act through different stabilisation mechanisms, were used to disperse aqueous alumina suspensions. Electrophoretic measurements were performed to determine the zeta potential curves of the bare and surface change modified alumina particles and, hence, to determine the stabilising performance of the dispersants. Drying-shrinkage behaviour (Bigot's curves) and Ng porosimetry were used to characterise the slip cast bodies prepared from the suspensions at different solid loading. The rheological behaviour of the starting alumina suspensions was also determined in order to relate the flow properties with the superficial nature of the suspended particles and the wet body microstructure. Rheological measurements have showed that the slips containing the dispersant that confers the highest zeta potential values to the alumina particles were more viscous than when using the less capable dispersant in terms of surface charge modifier. These findings were explained by a larger interaction size of the particles dispersed through a pure electrostatic mechanism which resulted in a higher effective volume solid fraction of these suspensions. For both dispersants used, the Bigot's curves indicated that the shrinkage and the slopes of the straight lines corresponding to the first stage of the drying decrease with increasing solids concentration. The variations in the slope derive from a broadening pore size distribution as a result of the increasing difficulties in stabilising the concentrated alumina suspensions, in agreement with the rheological measurements. Good correlations were found between the green microstructure, the rheology of the suspensions and the particle interaction forces. (C) 1998 Elsevier Science Limited. All rights reserved.