INFLUENCE OF THE STABILIZING MECHANISM AND SOLID LOADING ON SLIP CASTING OF ALUMINA

Two commercial surface active agents that act through different stabil isation mechanisms, were used to disperse aqueous alumina suspensions. Electrophoretic measurements were performed to determine the zeta pot ential curves of the bare and surface change modified alumina particle s and, hence, to determine the stabilising performance of the dispersa nts. Drying-shrinkage behaviour (Bigot's curves) and Ng porosimetry we re used to characterise the slip cast bodies prepared from the suspens ions at different solid loading. The rheological behaviour of the star ting alumina suspensions was also determined in order to relate the fl ow properties with the superficial nature of the suspended particles a nd the wet body microstructure. Rheological measurements have showed t hat 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 par ticles 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 shrinkag e and the slopes of the straight lines corresponding to the first stag e of the drying decrease with increasing solids concentration. The var iations in the slope derive from a broadening pore size distribution a s a result of the increasing difficulties in stabilising the concentra ted alumina suspensions, in agreement with the rheological measurement s. Good correlations were found between the green microstructure, the rheology of the suspensions and the particle interaction forces. (C) 1 998 Elsevier Science Limited. All rights reserved.