NONAQUEOUS THERMAL-DECOMPOSITION ROUTE TO COLLOIDAL INORGANIC OXIDES

Ceria, zirconia and zinc oxide have been successfully prepared by the thermal decomposition of the respective soluble cerium, zirconium and zinc salts in decan-1-ol, undecan-1-ol and ethane-1,2-diol. Only those metal salts whose (solid phase) decomposition temperature was less than or equal to the reflux temperature of the solvent were found to be effective. The growth rate of the oxides was found to be governed by the metal salt:solvent molar ratio and by the volume of solvent used in the preparation. This allowed the morphology of the primary oxide particles to be controlled: low molar ratios (ca. 0.01-0.02) and large volumes of solvent (allowing precise temperature control) afforded almost spherical, relatively monodisperse, colloidal particles- high molar ratios (ca 0.2), however, led to the formation of ill defined products reminiscent of oxides formed by aqueous phase precipitation, in accord with the principles of solution nucleation and particle growth. It was further observed that in the case of ceria, the precipitation rate governed the colour of the produced solids, indicating, it is suggested, that the molar ratio of cerium : oxygen varies according to the rate at which the oxide is formed.