SURFACE ANALYTICAL STUDY OF HYDROTHERMALLY TREATED ZIRCONIA CERAMICS

The hydrothermal instability of yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) imposes serious problems on their range of applic ations as ceramic materials. It is well known that a generally uniform distribution of yttrium cations prevents the transformation of the me tastable tetragonal into the monoclinic crystallographic modification. The induced crack propagation is widely considered to be a major sour ce of mechanical failure in zirconia ceramics. The segregation was inv estigated of yttrium and other cations on the surface of hydrothermall y treated ceramic samples with angle resolved XPS (X-ray photoelectron spectroscopy). The combination of this method with the high lateral r esolution of SAM (scanning Auger microprobe) yields three dimensional distribution profiles of Y3+, Al3+ and Si4+. The relative content of t he two crystallographic modifications of zirconia at the surface has b een determined with XRD (X-ray diffraction). Additional Raman spectros copic measurements partially confirm these results but suffer from qua ntification problems. A possible mechanism for the enrichment of yttri um in the surface layer and its promotive function for the phase trans formation of zirconia is proposed. Preliminary results from experiment s with temperature variable XPS measurements also indicate the formati on of either yttrium- or zirconium hydroxide which are both suspected to contribute to crack propagation along the grain boundaries.