In Situ Raman Spectroscopic Study of Yttria-Stabilized Zirconia Attack by Molten Sodium Vanadate

Raman spectroscopy has been used to study the molten salt attack of ceramics used as thermal barrier coatings. Zirconia stabilized with 8 wt% yttria was immersed in sodium metavanadate melts and in sodium metavanadate/sodium sulfate melts. In situ Raman measurements allowed simultaneous observation of the ceramic phases and salt chemistry during the attack process. The ceramic was seen to transform from the cubic/tetragonal to the monoclinic phase, concurrent with chemical changes in the molten salt layer in contact with the ceramic. These in situ measurements were complemented by conventional postexposure examination and by postexposure Raman measurements. The rate of attack was found to be quite sensitive to the mole fraction of vanadate in the molten salt solution.