Physicochemical Properties of Nanocrystalline Zirconia Hydrothermally Synthesized from Zirconyl Chloride and Zirconyl Nitrate Aqueous Solutions

摘要

Nanocrystalline ZrO_2 powders with diameters d = 4-10 nm are hydrothermally synthesized from 0.25 M zirconyl salt (ZrOCl_2, ZrO(NO_3)_2) aqueous solutions depending on the temperature (423-523 K) and processing duration tau (from 10 min to 24 h). The phase compositions and physicochemical characteristics of the powders are compared. For all of the T and tau used, only m-ZrO_2, the thermodynamically stable monoclinic zirconia phase, is prepared from zirconyl chloride or nitrate aqueous solutions. ZrOCl_2 in 0.25 M solutions is irreversibly hydrolyzed far more slowly than ZrO(NO_3)_2. For the samples prepared from ZrOl_2 and ZrO(NO_3)_2 solutions, the specific surface area S_(sp) at 423 and 523 K changes differently with increasing tau: S_(sp) decreases at 523 K and increases at 423 K, despite a rise in the coherence length observed at both temperatures. Based on scanning electron microscopy data, we propose different mechanisms to explain the nucleation of a new phase in the zirconyl solutions at 423 and 523 K and its subsequent deposition on the surface of m-ZrO_2 crystallites. With increasing pressure, the fraction of f-ZrO2 (the metastable tetragonal zirconia polymorph) in the powders synthesized by ZrO(NO_3)_2 high-temperature hydrolysis in 0.25 M solution (523 K, 30 min) increases from 5 pencent (at 3.0 GPa) to 40 pencent (at 4.0 GPa).