MOISTURE SENSITIVE DEGRADATION IN TIO2-Y2O3ZRO2

Sintered discs (1450 degrees C) of yttria-stabilised tetragonal zirconia (3 mol% Y2O3) with additions of 1, 10 and 20 mol% TiO2, were treated 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 (XPS) were used to monitor changes which occurred at the surface of the discs during autoclave treatment. The addition of TiO2 retarded the transformation of the tetragonal (t)-phase to monoclinic (m)-phase as determined by XRD. During autoclave treatment an increase in the Ti/Zr ratio, decrease in the Y/Zr ratio and a peak in the percentage Zr3+ were observed using XPS. Furthermore, at long autoclave treatment times there was a surface oxygen enrichment in excess of that expected from the stoichiometry. The data have been interpreted in terms of vacancy annealing and the rate of transformation to m-ZrO2 appears to be related to the presence of Zr3+, adsorbed water and substitutional cations such as Ti4+ in modifying adsorption sites at the surface.