Preventing ageing on Al2O3 casting slips dispersed with polyelectrolytes

Slip casting process needs a highly stabilized and well-characterized suspension, which involves not only the traditional rheological measurements, but an estimation of the colloidal stability in terms of interaction potentials between particles. For electrosterically stabilized ceramic suspensions the calculation of the steric contribution is not well described in the available theories because they are developed for ideal conditions where many variables affecting the stability of concentrated suspensions are neglected. In this work, alumina suspensions were prepared at 75 wt% solids and characterized considering the potential energy curves and the rheological behaviour. The main objective is to select the proper dispersing conditions in order to prevent ageing of the slips, which is an important problem in any manufacturing cycle. For the polyacrylate dispersant used it was shown that a concentration of 0.8 wt% provided the lowest viscosity, allowed ageing prevention and resulted in higher green and sintered densities. (C) 2000 Kluwer Academic Publishers.