Colloidal stability and sintering of yttria-silica and yttria-silica-alumina aqueous suspensions

The aim of this work was to produce dense yttrium silicate materials by sli p casting, with more than 90% of Y2SiO5 phase. The rheological behaviour of concentrated aqueous slips was studied considering the effect of the dispe rsing additives, solids content and pH. The densification kinetics was exam ined as a function of temperature and rime, and the reactions It,ere analys ed in the light of the equilibrium phase diagrams. Deflocculation of the sl ips was achieved by either an electrostatic mechanism using tetraethylammon ium hydroxide, thus requiring a high concentration of base, and by a polyel ectrolyte through an electrosteric mechanism, which provided more reliable results. In the binary system Y2O3-SiO2, a very low grade of sintering, was obtained at 1600 degrees C. The use of alumina allows sintering through a liquid phase, reaching 90% theoretical density. (C) 1999 Elsevier Science L imited. All rights reserved.