EFFECT OF SOLID-SOLUTION ADDITIVES ON THE SINTERING OF ULTRA-FINE CEO2 POWDERS

Ultra-fine CeO2 powders (particle size approximate to 10-15 nm) contai ning up to 20 at% of various divalent and trivalent cations (Mg2+, Ca2 +, SC3+, Y3+ and Nd3+) were prepared by chemical precipitation under h ydrothermal conditions. The effects of the cation concentration size a nd valency on the densification and grain growth of the compacted powd ers were examined during sintering at a constant heating rate of 10 de grees C/min. Compared to undoped CeO2, all of the additive cations cau sed a shift in the densification curve to higher temperatures. However , the density and grain size achieved after sintering depended signifi cantly on the elemental composition of the additive. When the radii of the additive cations were larger than that of the host Ce4+ cation, ( i.e. Ca2+, Y3+ and Nd-3), nearly full density and ultrafine grain size were achieved. Under identical sintering conditions lower density (ap proximate to 93-95% of the theoretical) and larger grain size were ach ieved when the radii of the additive cations were smaller than that of the host, (i.e. Mg2+ and SC3+). Powders doped simultaneously with two cations, (e.g. Ca2+ and Mg2+) showed sintering and grain growth chara cteristics which were intermediate between those for the powders doped with single cations at the equivalent concentration.