Reactive Cerium(IV) Oxide Powders by the Homogeneous Precipitation Method

CeO₂ powders have been prepared by aging a cerium(III) nitrate solution in the presence of hexamethylenetetramine. Oxidation of Ce³⁺ occurs in the precipitate and the wet precipitate is identified as crystallized CeO₂ before any heat treatment. The cold-pressed powders can be sintered to full density at temperatures as low as 1250°C in just 6 min. Moreover, the sinterability of the powders is insensitive to the calcination temperatures, particle size, or green density. The powders calcined at 850°C with a crystallite size of 600 Å have a sinterability as good as the powders calcined at 450°C with a crystallite size of 145 Å. The mechanisms for direct CeO₂ precipitation and its relation to the excellent sinterability are discussed.