Dissolution and diffusion kinetics of yttria-stabilized zirconia into molten silicates

Abstract

The degradation of thermal barrier coatings (TBCs) by molten silicates (CMAS) represents a fundamental barrier to progress in gas turbine technology, requiring a mechanistic understanding of the problem to guide the development of improved coatings. This article investigates the dissolution of yttria-stabilized zirconia (7YSZ and 20YSZ) into two model silicate melts at 1300–1400 °C. The approach involves the 1D dissolution of YSZ into a semi-infinite melt, characterizing the dissolution rates of YSZ and the diffusion rates of Zr4+ and Y3+ therein. The assessed kinetics of YSZ dissolution and diffusion were then applied to modeling the same phenomena on TBC-relevant length scales. These findings provide fundamental insight into (i) the dissolution mechanism of YSZ, (ii) the subsequent reprecipitation upon saturation, (iii) the quantitative effects of temperature and melt composition on the dissolution and diffusion kinetics, and (iv) how the measured kinetics manifests on the scale of flow channels present in TBCs.