Molten salt attack on t′ yttria-stabilised zirconia by dissolution and precipitation

Degradation due to molten salt attack is one of the failure mechanisms of thermal barrier coatings. Thermochemical attack of the salt mixture Na2SO4–30 mol% NaVO3 on ZrO2–8 mol% YO1.5 (8YSZ) at 950 °C was studied by two types of experiments. Sintered compacts were exposed to 25 mg cm−2 salt dosage for up to 96 h. In the other set of experiments, 10–35 wt.% 8YSZ powder was mixed with the salts to study the dissolution of 8YSZ in the molten salt. The role of volatile losses was also examined. The results show that more than 25 wt.% 8YSZ dissolves in the sulphate-vanadate melt at 950 °C, followed by slow reactions to form YVO4 and NaYV2O7 at 950 °C. The unreacted Y2O3 and monoclinic ZrO2 precipitate out separately during rapid cooling (∼300 °C/min). Slow cooling at ∼3 °C/min leads to the formation of ZrOS apart from ZrO2 and Y2O3.