Thermal decomposition and crystallization of aqueous sol-gel derived zirconium acetate gels: Effects of the additive anions

Zirconia powders were prepared by forming gels by desiccation of aqueous pr ecursor solutions of zirconium acetate containing nitric or sulfuric acid a t pH 2.4 and 1.4 and pyrolyzing the gels to temperatures up to 825 degrees C. The structure development in the gels and solid pyrolysis products was i nvestigated. The crystalline zirconia structures produced monoclinic (m), m etastable cubic (c) and tetragonal (t) polymorphs. The structure transition temperatures were strongly dependent on the pH, the anions and the stoichi ometry of the zirconium complex in the precursor solution. The monoclinic p olymorph fraction in the zirconia formed by pyrolyzing the gel formed from the precursor solution containing sulfuric acid at pH 2.4 to 750 degrees C approaches zero while this ratio in the zirconia formed by pyrolyzing the g el formed from the precursor solution containing nitric acid at pH 1.4 to 8 25 degrees C is 0.7.