Destabilization of Yttria‐Stabilized Zirconia Induced by Molten Sodium Vanadate‐Sodium Sulfate Melts

Abstract

The extent of surface destabilization of weight percent ceramic disks was determined after exposure to molten salt mixtures of sodium sulfate containing up to 15 mole percent sodium metavanadate at 1173 K. The ceramic surface was observed to transform from the cubic/tetragonal to the monoclinic phase, concurrent with chemical changes in the molten salt layer in contact with the ceramic. Significant attack rates were observed in both sodium sulfate and sodium metavanadate‐sulfate melts in the presence of sulfur trioxide. The rate of attack was found to be quite sensitive to the mole fraction of vanadate in the molten salt solution and the partial pressure of sulfur trioxide in equilibrium with the salt melt. The observed approximately parabolic rate of attack was interpreted to be caused by a reaction controlled by diffusion in the salt that penetrated into the porous layer formed by the destabilization. The parabolic rate constant in mixed sodium metavanadate‐sodium sulfate melts was found to be proportional to the partial pressure and the square of the metavanadate concentration.