SURFACE SEGREGATION IN YTTRIA-STABILIZED ZIRCONIA (YSZ)

Abstract

The present PhD thesis aims to study the effect of segregation of selected lattice components on surface and near surface chemical composition of polycrystalline yttria–stabilized zirconia (YSZ) (10 mol% Y2O3), at elevated temperatures in the gas phase of controlled oxygen activity. The aim of the present work is to determine the effects of oxygen activity and temperature on segregation–induced concentration gradients of the key lattice component (yttrium) as well as several impurities, including silicon, calcium, aluminum and sodium. The experimental part of this PhD thesis determines the segregation–induced concentration profiles of these elements within the ranges of temperatures (1073 K – 1673 K) and oxygen activities (10-10 Pa < p(O2) < 75 kPa). The key analytical tool applied in surface analysis in present work is the secondary ion mass spectrometry (SIMS). This work determined the optimal conditions required to obtain enhanced concentration of specific elements by the manipulation of the annealing temperature and oxygen activity. The obtained experimental data indicate that increase of oxygen activity resulted in a substantially enhanced segregation – induced enrichment of yttrium, silicon, sodium, calcium and aluminium. The following significant conclusions stem from this study: 1. At high oxygen partial pressure activity, p(O2) the concentration enrichment of impurities at surface including yttrium, silicon, sodium, calcium and aluminium is higher rather than the one in low p(O2) condition. 2. Segregation of impurities contributes to the bi-dimensional layer on the surface with different crystal size to the bulk. The obtained experimental data may be applied for the modification of surface and near-surface composition of YSZ in a controlled manner. In other words, the phenomenon of segregation may be used as the technique for engineering the surface and near surface chemistry of YSZ, and the other related properties.