Low‐Temperature Hydrothermal Synthesis of Yttrium‐Doped Zirconia Powders

Abstract

The feasibility of low‐temperature synthesis of yttrium‐doped zirconia (Y‐ZrO 2 ) crystalline powders in aqueous solutions at lessthan equal to100°C has been evaluated, and the hydrothermal crystallization mechanism for Y‐ZrO 2 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‐ZrO 2 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‐ZrO 2 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‐ZrO 2 at 25°C is the anhydrous phase, not the metal hydroxide as previously thought.