Low-temperature hydrothermal synthesis of yttrium-doped zirconia powders

The feasibility of low-temperature synthesis of yttrium-doped zirconia (Y-ZrO2) crystalline powders in aqueous solutions at less than or equal to 100 degrees C has been evaluated, and the hydrothermal crystallization mechanism for Y-ZrO2 powders also has been investigated. Coprecipitated (Y,Zr) hydroxide gel, mechanical mixtures of Y(OH)(3) and Zr(OH)(4) gel, and Y(OH)(3) gel have been reacted in boiling alkaline solutions. Coprecipitated (Y,Zr) hydroxide gel crystallized to cubic or tetragonal Y-ZrO2 at pH 13.9. The yttrium content in the powder synthesized from coprecipitated (Y,Zr) hydroxide is consistent with the initial precursor solution composition, as expected from the similarity in solubility of Zr(OH)(5)(-) and Y(OH)(4)(-). A diffusionless mechanism for the transformation of the (Y,Zr) hydroxide gel to Y-ZrO2 is proposed, and the phase stability in aqueous solution is discussed in terms of an in situ crystallization model. It is also demonstrated through thermodynamic arguments with experimental verification that the stable form of the Y-ZrO2 at 25 degrees C is the anhydrous phase, not the metal hydroxide as previously thought.