Physicochemical properties of nanocrystalline zirconia hydrothermally synthesized from zirconyl chloride and zirconyl nitrate aqueous solutionsстатья
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Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Аннотация:Nanocryitalline ZrO2 powders with diameters d = 4-10 nm are hydrothermally synthesized from 0.25 M zirconyl salt (ZrOCl2, ZrO(NO3)(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-ZrO2, the thermodynamically stable monoclinic zirconia phase, is prepared from zirconyl chloride or nitrate aqueous solutions. ZrOCI2 in 0.25 M solutions is irreversibly hydrolyzed far more slowly than ZrO(NO3)(2). For the samples prepared from ZrOCI2 and ZrO(NO3)(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-ZrO2 crystallites. With increasing pressure, the fraction of t-ZrO2 (the metastable tetragonal zirconia polymorph) in the powders synthesized by ZrO(NO3) high-temperature hydrolysis in 0.25 M solution (523 K, 30 min) increases from 5% (at 3.0 GPa) to 40% (at 4.0 GPa).