Thermodynamic capacity and kinetic fragility govern the degradation of 8YSZ in silicate melts

The degradation of yttria-stabilized zirconia (YSZ) by silicate melts is a first order challenge to aviation. Yet the respective roles of dissolution thermodynamics and kinetics remain insufficiently distinguished. Here, in an effort to decouple these effects, three naturally-occurring (sand, dust, and volcanic ash) and five synthetic silicate melts were reacted with 8YSZ for up to 100 h. Corrosion depths were determined from the yttrium-depleted, mechanically softened, zone and quenched interfaces which largely preserve the high-temperature reaction state, were mapped. The naturally-occurring melts exhibited a complex behavior whereby ash melt penetrated rapidly at early stages but was arrested at 29 μm, whereas sand melt exhibited sustained penetration to 49 μm. The yttrium solubility index, calculated with the aid of compositional correlation models, exhibits a higher correlation with the terminal degradation depth than other, more conventional composition-based descriptors. The kinetic fragility index captures the transitions between continuous dissolution, crystallization-induced passivation, and penetration arrest. A two-parameter map based on these two parameters (thermodynamic capacity and kinetic fragility) can be used to illustrate and rationalize the degradation trajectories of silicate melts against 8YSZ. This approach provides a potential basis for screening corrosive deposits based on their composition-projected thermodynamic capacity and kinetic fragility for the customized regional design of more resistant ceramic systems.