Stability of yttria stabilized zirconia membrane in molten CaCl2-CaO melt

Yttria stabilized zirconia (YSZ), as an excellent oxygen ion conductor, is increasingly used as an oxygen ion membrane for the anode in the FFC Cambridge process. However, using a membrane implies that it exhibits long term stability in the bath. It has been reported that YSZ is stable chemically, but fails electrochemically in molten CaCl2-CaO. In this work, we report, as opposed to previous reports, that YSZ is chemically not stable in molten CaCl2-CaO melts. Electromigration only accelerates the instability. The degradation is seen to occur by leaching of yttria in solution leading to the formation of monoclinic zirconia which, being porous, reacts with the molten electrolyte to form calcium zirconate. We will also highlight possible countermeasures.status: publishe