MOISTURE SENSITIVE DEGRADATION IN TIO2-Y2O3ZRO2

Sintered discs (1450 degrees C) of yttria-stabilised tetragonal zircon ia (3 mol% Y2O3) with additions of 1, 10 and 20 mol% TiO2, were treate d in distilled water in an autoclave at 170 degrees C for times up to 144 h. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (X PS) were used to monitor changes which occurred at the surface of the discs during autoclave treatment. The addition of TiO2 retarded the tr ansformation of the tetragonal (t)-phase to monoclinic (m)-phase as de termined by XRD. During autoclave treatment an increase in the Ti/Zr r atio, decrease in the Y/Zr ratio and a peak in the percentage Zr3+ wer e observed using XPS. Furthermore, at long autoclave treatment times t here was a surface oxygen enrichment in excess of that expected from t he stoichiometry. The data have been interpreted in terms of vacancy a nnealing and the rate of transformation to m-ZrO2 appears to be relate d to the presence of Zr3+, adsorbed water and substitutional cations s uch as Ti4+ in modifying adsorption sites at the surface.