Surface analytical study of hydrothermally treated zirconia ceramics

Summary

The hydrothermal instability of yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) imposes serious problems on their range of applications as ceramic materials. It is well known that a generally uniform distribution of yttrium cations prevents the transformation of the metastable tetragonal into the monoclinic crystallographic modification. The induced crack propagation is widely considered to be a major source of mechanical failure in zirconia ceramics. The segregation was investigated of yttrium and other cations on the surface of hydrothermally treated ceramic samples with angle resolved XPS (X-ray photoelectron spectroscopy). The combination of this method with the high lateral resolution of SAM (scanning Auger microprobe) yields three dimensional distribution profiles of Y³⁺, Al³⁺ and Si⁴⁺. The relative content of the two crystallographic modifications of zirconia at the surface has been determined with XRD (X-ray diffraction). Additional Raman spectroscopic measurements partially confirm these results but suffer from quantification problems. A possible mechanism for the enrichment of yttrium in the surface layer and its promotive function for the phase transformation of zirconia is proposed. Preliminary results from experiments with temperature variable XPS measurements also indicate the formation of either yttrium- or zirconium hydroxide which are both suspected to contribute to crack propagation along the grain boundaries.