Hydrated surface structure and its impacts on the stabilization of t-ZrO2

摘要

We first optimized the preparation conditions to 3.6-6.0 nm ZrO2 in a Pure tetragonal structure (t-phase). All samples were characterized by X-ray diffraction, high-resolution transmission electron microscope, thermal analysis, Raman spectra, and infrared spectra. It is found that the surfaces of t-ZrO2 nanostructures were terminated by an amorphous hydration layer co-existing with small amounts of carbonate molecules. With the removal of hydrated Surface layers under hydrothermal conditions at T > 150 degrees C. t-ZrO2 nanostructures became thermodynamically unstable, which partially transformed into monoclinic ZrO2 (m-phase). Such a transformation occurs initially at Surface regions and then develops into the bulk. High-temperature annealing in air could also remove the hydrated surface lavers. which is however followed by a gradual transformation of t-ZrO2 into m-ZrO2 in both bulk and surface regions. These observations are explained in terms of the difference in surface free energies of m-ZrO2 and t-ZrO2 upon H2O adsorption. (C) 2007 Elsevier Inc. All rights reserved.