Role of O2–, OH– and anion vacancies in the degradation of Y-TZP in moist environments

Abstract

X-Ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) have been used to study the changes in surface chemistry and crystallography of yttria–tetragonal zirconia polycrystal during exposure to either a moist air stream (200 °C) or an autoclave environment (120 or 170 °C). XPS measurements indicate that there is a significant increase in the O^2– and %Zr³⁺ levels during the transformation of the surface tetragonal phase to the monoclinic phase. No significant levels of zirconium hydroxide species were detected during exposure to moist air or autoclave treatment. Yttrium hydroxide was detected only after severe autoclave treatment at 170 °C. A model is proposed whereby destabilisation of the tetragonal phase is caused by annealing of anion vacancies by O^2–.