Abstract
Fine particles of monodispersed yttria are desirable for preparing transparent and/or high-performance, -functional ceramics. Various shape of yttria precursors was observed in the precipitates synthesized through homogeneous precipitation from aqueous solution by reacting with each other of thermal decomposition products of urea at 115 °C. Three types precipitates of particle morphologies such as hallow spheres with rough and smooth suefaces, and rodlike shape were synthesized in an aqueous solution containing urea with sulfate ion. All of them crystallized to monophase yttria above 1,100 °C. The calcined particles were hollow basketlike, porous-spherical and rodlike with rough surface. The basketlike hollow spheres were obtained from solution of low [urea]/[yttrium ions] ratio in a short reaction time, and rodlike ones were obtained from solution of high [urea]/[yttrium ions] ratio in a long reaction time. Spherical, rodlike and platelet precipitates were synthesized in an aqueous solution of urea coexisting with nitrate ions, and a monophase of yttria was obtained above 800 °C. These facts indicate that the shape of yttria precursor obtained in the solution coexisting with sulfate or nitrate ions were controlled by the [urea]/[yttrium ions] ratio and reaction time.
