Abstract

Monodispersed cerium(IV) oxide (CeO₂) particles composed of an agglomeration of primary nanocrystalline particles with a cubic fluorite structure could be synthesized from relatively concentrated cerium(IV) sulfate solutions up to 0.5 mol dm⁻³ by thermal hydrolysis at 120 to 240 °C. The influences of the presence of urea and its concentration on their crystallite size and morphology were investigated. Upon the addition of urea and increasing its concentration, the morphology gradually changed from monodispersed particles to dispersed ultra-fine particles that had no definite shape and tight agglomeration. The mechanisms for the growth and agglomeration of the particles formed by thermal hydrolysis were discussed. The existence of a dopant such as Gd was effective for suppressing the grain growth of the ceria particles during the calcining and sintering.