Calorimetric Measurement of Surface and Interface Enthalpies of Yttria-Stabilized Zirconia (YSZ)

Abstract

The surface and interface enthalpies of cubic stabilized zirconia solid solutions containing 8, 10, and 12 mol % Y2O3 were determined by a combination of calorimetric, morphological, and structural analyses techniques. Nanocrystalline samples with several surface areas and degrees of agglomeration were synthesized by simultaneous precipitation and annealing at temperatures of 470−900 °C. Samples were characterized by X-ray diffraction and Raman spectroscopy. Surface areas were measured by N2 adsorption, and interface areas were estimated by comparing surface areas from N2 adsorption to those derived from an analysis of the crystallite sizes refined from X-ray diffraction data. Calorimetric measurements of heat of solution in a sodium molybdate melt, as a function of surface and interface areas, enabled us to experimentally derive trends in the surface and interface enthalpies of hydroxylated surfaces. Accounting for heats of water adsorption measured by microcalorimetry allowed us to obtain the surface enthalpies (energies) of the anhydrous surfaces at each composition. Average surface enthalpies were determined to increase with yttria content, from 0.85 ± 0.07 J/m2 (for 8 mol % yttria) to 1.27 ± 0.08 J/m2 (for 12 mol % yttria) for the hydrous surface and from 1.16 ± 0.08 J/m2 to 1.80 ± 0.10 J/m2 for the anhydrous surface. Interface enthalpies were determined to be in the range of 0.9 ± 0.5 J/m2 for all studied compositions. Comparisons with measured surface energies for pure ZrO2, and Y2O3 nanopowders and grain-boundary energies for YSZ dense nanoceramics are presented.